Metabolism of amino acids, purine and pyrimidine bases Pavla Balínová.
CYPs, mostly FQs with/CYP1A2; Purines and Purine Metabolism · and Purine Metabolism FQ’s inhibit...
Transcript of CYPs, mostly FQs with/CYP1A2; Purines and Purine Metabolism · and Purine Metabolism FQ’s inhibit...
References 16 website: JMR, http://fluoroquinolonethyroid.com
References 16
Links, Abstracts, Articles, etc. These links should work as of 2016; sometimes you have to click on them
several times; if they don’t work, then Google/search the titles
CYPs, mostly FQs with/CYP1A2; Purines
and Purine Metabolism
FQ’s inhibit demethylases and hydroxylases. This is most evident with theophylline.
Theophylline demethylate 3-methylxanthine + 1-methylxanthine. Note: Cipro selectively
blocks these two demethylations.
Theophylline hydroxylate 1,3-dimethyluric acid. Note: Cipro selectively blocked this
hydroxylation only at high concentrations.
https://en.wikipedia.org/wiki/Demethylation Demethylation is the chemical process resulting in the
removal of a methyl group (CH3) from a molecule.[1][2] A common way of demethylation is the
replacement of a methyl group by a hydrogen atom, resulting in a net loss of one carbon and two
hydrogen atoms. The counterpart of demethylation is methylation. In biochemical systems, the
process of demethylation is catalyzed by demethylases. These enzymes oxidize N-methyl groups, which
occur in histones and some forms of DNA. (My note: note that JMHD and TET1 are demethylases).
R2N-CH3 + O → R2N-H + CH2O
One such oxidative enzyme family is the cytochrome P450[3] Alpha-ketoglutarate-dependent nonheme
enzymes are active for demethylation of DNA, operating by similar pathway.
https://en.wikipedia.org/wiki/Hydroxylation Hydroxylation is a chemical process that introduces a
hydroxyl group (-OH) into an organic compound. In biochemistry, hydroxylation reactions are often
facilitated by enzymes called hydroxylases. Hydroxylation is the first step in the oxidative degradation of
organic compounds in air. It is extremely important in detoxification since hydroxylation converts
lipophilic compounds into water-soluble (hydrophilic) products that are more readily removed by the
kidneys or liver and excreted. Some drugs (for example, steroids) are activated or deactivated by
hydroxylation. The principal hydroxylation agent in nature is cytochrome P-450, hundreds of variations
References 16 website: JMR, http://fluoroquinolonethyroid.com
of which are known. Other hydroxylating agents include flavins.[1] The principal residue to be
hydroxylated in proteins is proline. The hydroxylation occurs at the γ-C atom, forming hydroxyproline
(Hyp), an essential element of collagen, in turn a necessary element of connective tissue. Proline
hydroxylation is also a vital component of hypoxia response via hypoxia inducible factors. In some cases,
proline may be hydroxylated instead on its β-C atom. Lysine may also be hydroxylated on its δ-C atom,
forming hydroxylysine (Hyl).
These three reactions are catalyzed by very large, multi-subunit enzymes prolyl 4-hydroxylase, prolyl 3-
hydroxylase and lysyl 5-hydroxylase, respectively. These reactions require iron (as well as molecular
oxygen and α-ketoglutarate) to carry out the oxidation, and use ascorbic acid (vitamin C) to return the
iron to its oxidized state. Deprivation of ascorbate leads to deficiencies in proline hydroxylation, which
leads to less stable collagen, which can manifest itself as the disease scurvy
https://en.wikipedia.org/wiki/Dehydrogenase Dehydrogenases are a subclass of the class of enzymes
labeled “oxidoreductases.” Oxidoreductases, in general, catalyze oxidation and reduction reactions. Any
enzyme that transfers an electron from one molecule to another is considered an oxidoreductase. These
enzymes fall into six categories: oxygenases, reductases, peroxidases, oxidases, hydroxylases, and
dehydrogenases. Most oxidoreductase enzymes are dehydrogenases, although reductases are also
common. Accepted nomenclature for dehydrogenases is "donor dehydrogenase," where the donor is
the molecule giving up an electron.[1]
Oxidation-reduction reactions are essential to growth and survival of organisms, as the oxidation of
carbons produces energy. Energy-producing reactions can drive forward the synthesis of important
energy molecules, such as ATP in glycolysis. For this reason, dehydrogenases have pivotal roles in
metabolism.[2]
http://attic.volgmed.ru/depts/biochem/sources/e-enzyme1.pdf Quick review of enzymes.
http://www.saferpills.org/wp-content/uploads/2012/08/FQ-Feb-2011-Survey-Visualization-3.pdf
From 2011 FQ survey of 131 people: 46/131 = 35% answered “I do not tolerate caffeine”.
http://www.sciencedirect.com/science/article/pii/S0163725813000065 Cytochrome P450 enzymes in
drug metabolism: Regulation of gene expression, enzyme activities, and impact of genetic variation
(2013). “Cytochromes P450 (CYP) are a major source of variability in drug pharmacokinetics and
response. Of 57 putatively functional human CYPs only about a dozen enzymes, belonging to the CYP1, 2,
and 3 families, are responsible for the biotransformation of most foreign substances including 70–80% of
all drugs in clinical use. The highest expressed forms in liver are CYPs 3A4, 2C9, 2C8, 2E1, and 1A2, while
2A6, 2D6, 2B6, 2C19 and 3A5 are less abundant and CYPs 2J2, 1A1, and 1B1 are mainly expressed
extrahepatically. Expression of each CYP is influenced by a unique combination of mechanisms and
References 16 website: JMR, http://fluoroquinolonethyroid.com
factors including genetic polymorphisms, induction by xenobiotics, regulation by cytokines, hormones
and during disease states, as well as sex, age, and others. Multiallelic genetic polymorphisms, which
strongly depend on ethnicity, play a major role for the function of CYPs 2D6, 2C19, 2C9, 2B6, 3A5 and
2A6, and lead to distinct pharmacogenetic phenotypes termed as poor, intermediate, extensive, and
ultrarapid metabolizers. For these CYPs, the evidence for clinical significance regarding adverse drug
reactions (ADRs), drug efficacy and dose requirement is rapidly growing. Polymorphisms in CYPs 1A1,
1A2, 2C8, 2E1, 2J2, and 3A4 are generally less predictive, but new data on CYP3A4 show that predictive
variants exist and that additional variants in regulatory genes or in NADPH:cytochrome P450
oxidoreductase (POR) can have an influence. Here we review the recent progress on drug metabolism
activity profiles, interindividual variability and regulation of expression, and the functional and clinical
impact of genetic variation in drug metabolizing P450s.”
http://www.tandfonline.com/doi/full/10.3109/03602530903286476?scroll=top&needAccess=true
Structure, function, regulation and polymorphism and the clinical significance of human cytochrome
P450 1A2. “Human CYP1A2 is one of the major CYPs in human liver and metabolizes a number of clinical
drugs (e.g., clozapine, tacrine, tizanidine, and theophylline; n > 110), a number of procarcinogens (e.g.,
benzo[a]pyrene and aromatic amines), and several important endogenous compounds (e.g., steroids).
CYP1A2 is subject to reversible and/or irreversible inhibition by a number of drugs, natural substances,
and other compounds. The CYP1A gene cluster has been mapped on to chromosome 15q24.1, with close
link between CYP1A1 and 1A2 sharing a common 5′-flanking region. The human CYP1A2 gene spans
almost 7.8 kb comprising seven exons and six introns and codes a 515-residue protein with a molecular
mass of 58,294 Da. The recently resolved CYP1A2 structure has a relatively compact, planar active site
cavity that is highly adapted for the size and shape of its substrates. The architecture of the active site of
1A2 is characterized by multiple residues on helices F and I that constitutes two parallel substrate
binding platforms on either side of the cavity. A large interindividual variability in the expression and
activity of CYP1A2 has been observed, which is largely caused by genetic, epigenetic and environmental
factors (e.g., smoking). CYP1A2 is primarily regulated by the aromatic hydrocarbon receptor (AhR) and
CYP1A2 is induced through AhR-mediated transactivation following ligand binding and nuclear
translocation. Induction or inhibition of CYP1A2 may provide partial explanation for some clinical drug
interactions. To date, more than 15 variant alleles and a series of subvariants of the CYP1A2 gene have
been identified and some of them have been associated with altered drug clearance and response and
disease susceptibility. Further studies are warranted to explore the clinical and toxicological significance
of altered CYP1A2 expression and activity caused by genetic, epigenetic, and environmental factors.”
https://www.pharmgkb.org/pathway/PA165884757# PharmGKB Caffeine Pathway, Pharmacokinetics
(Note: Good picture of Caffeine Metabolism). “Conversely the CC genotype for ADORA2A rs5751876 is
associated with increased likelihood of being sensitive to caffeine and increased likelihood of insomnia
when exposed to caffeine. [Article:17329997]. See https://www.ncbi.nlm.nih.gov/pubmed/17329997
A genetic variation in the adenosine A2A receptor gene (ADORA2A) contributes to individual
sensitivity to caffeine effects on sleep. “Caffeine is the most widely used stimulant in Western
countries. Some people voluntarily reduce caffeine consumption because it impairs the quality of their
sleep. Studies in mice revealed that the disruption of sleep after caffeine is mediated by blockade of
References 16 website: JMR, http://fluoroquinolonethyroid.com
adenosine A2A receptors. Here we show in humans that (1) habitual caffeine consumption is associated
with reduced sleep quality in self-rated caffeine-sensitive individuals, but not in caffeine-insensitive
individuals; (2) the distribution of distinct c.1083T>C genotypes of the adenosine A2A receptor gene
(ADORA2A) differs between caffeine-sensitive and -insensitive adults; and (3) the ADORA2A c.1083T>C
genotype determines how closely the caffeine-induced changes in brain electrical activity during sleep
resemble the alterations observed in patients with insomnia. These data demonstrate a role of adenosine
A2A receptors for sleep in humans, and suggest that a common variation in ADORA2A contributes to
subjective and objective responses to caffeine on sleep.”
https://www.ncbi.nlm.nih.gov/pubmed/19274061 Allele-specific expression and gene methylation in
the control of CYP1A2 mRNA level in human livers. “The basis for interindividual variation in the
CYP1A2 gene expression is not fully understood and the known genetic polymorphisms in the gene
provide no explanation. We investigated whether the CYP1A2 gene expression is regulated by DNA
methylation and displays allele-specific expression (ASE) using 65 human livers. Forty-eight percent of the
livers displayed ASE not associated to the CYP1A2 mRNA levels. The extent of DNA methylation of a CpG
island including 17 CpG sites, close to the translation start site, inversely correlated with hepatic CYP1A2
mRNA levels (P=0.018). The methylation of two separate core CpG sites was strongly associated with the
CYP1A2 mRNA levels (P=0.005) and ASE phenotype (P=0.01), respectively. The CYP1A2 expression in
hepatoma B16A2 cells was strongly induced by treatment with 5-aza-2'-deoxycytidine. In conclusion, the
CYP1A2 gene expression is influenced by the extent of DNA methylation and displays ASE, mechanisms
contributing to the large interindividual differences in CYP1A2 gene expression.”
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1365008/ The effect of ciprofloxacin on
theophylline pharmacokinetics in healthy subjects (1995).
https://www.ncbi.nlm.nih.gov/pubmed/1312320 An evaluation of the quinolone-theophylline
interaction using the Food and Drug Administration spontaneous reporting system (1992). “A review
of the Food and Drug Administration's spontaneous reporting system identified 48 reports of adverse
events in patients who received concomitant therapy with ciprofloxacin (n = 39) or norfloxacin (n = 9) and
theophylline. The mean (SD) age of these cases was 68.4 (18.5) years; 25 patients (52%) were female.
The mean percent change in theophylline concentrations was 114%, with a range of 32% to 308%
following the addition of a quinolone to the patient's theophylline regimen. Fourteen (36%) of the 39
patients receiving ciprofloxacin and three (33%) of the nine patients receiving norfloxacin experienced a
seizure. The accumulated evidence suggests that extreme caution should be used when quinolones are
prescribed in conjunction with theophylline, particularly in elderly patients. Further research is required
to identify risk factors that will more specifically predict the magnitude of the interaction.”
https://www.ncbi.nlm.nih.gov/pubmed/1580270 The effects of quinolones on xanthine
pharmacokinetics (1992). “Caffeine, theobromine, and theophylline are among the most widely
consumed compounds in beverages and in pharmaceutical preparations. These methylxanthine alkaloids
are metabolized by similar pathways involving demethylation and hydroxylation that are predominantly
cytochrome P-450 mediated. In vivo and in vitro evidence suggests that the cytochrome P-450 isozymes
involved in the demethylation pathways are distinct from the cytochrome P-450 isozymes involved in the
References 16 website: JMR, http://fluoroquinolonethyroid.com
hydroxylation pathways. Although distinctions can be made between demethylation and hydroxylation
pathways, the evidence suggests that these different cytochrome P-450 isozymes are under common
regulatory control. Any drug inhibiting the family of cytochrome P-450 isozymes involved in the
metabolism of the methylxanthines would, therefore, be expected to have a similar effect on
theophylline, theobromine, and caffeine. A number of quinolones, including enoxacin, pipemidic acid,
ciprofloxacin, norfloxacin, and pefloxacin, have been shown to reduce the clearance of theophylline,
while lomefloxacin has no effect on theophylline or caffeine clearance. It has been hypothesized that only
fluoroquinolones that form a 4-oxo-metabolite inhibit theophylline clearance. Lomefloxacin, which does
not form a 4-oxo-metabolite, would therefore not be expected to inhibit the clearance of theophylline or
caffeine. In contrast, ciprofloxacin, which does form a 4-oxo-metabolite, has been shown to reduce
theophylline and caffeine clearances by about one third. Another hypothesis for the differences among
quinolones suggests that quinolones that have a greater impact on theophylline clearances are more
stereochemically similar to theophylline. Substitutions at position 8 on the quinolone nucleus (as in
lomefloxacin) would result in stearic hindrance and decrease the structural similarity to theophylline.”
http://journal.publications.chestnet.org/data/Journals/CHEST/21568/663.pdf New synthetic
quinolone antibacterial agents and serum concentration of theophylline (1987). “The effect of
pipemidic acid and five new synthetic antibacterial agents--norfloxacin, enoxacin, ofloxacin,
ciprofloxacin, and pefloxacin--on the serum level of theophylline was studied in healthy male adult
volunteers after concomitant oral administration of these agents with a slow release preparation of
theophylline. The results indicated that enoxacin, ciprofloxacin, and pipemidic acid might decrease the
clearance of theophylline in the liver, and the attention should be paid in clinical use when enoxacin or
pipemidic acid is coadministered with theophylline. . . . We have already reported on a study using ENX
at a dose level of 300 mg/day, half the usual dose, in combination with theophylline, 400 mg,’7 in which
a slight increase in the plasma theophylline concentration without any side effects was shown. This fact
suggests that the effect ofENX is dose dependent. . . . However, the concomitant use of a slow release
theophylline, 400 mg, and ENX, 600 mg (daily dose, respectively), is a standard regimen for COPD and
lower respiratory tract infections in Japan.34 Such concomitant use may cause a high incidence of side
effects, and this will be a problem in clinical use. . . . in spite of the fact that the drugs used in this study
belong to the same quinolone derivatives group, their effects on the theophylline level vary greatly.
However, we have no results that will explain these differences, nor are there any earlier reports that can
explain them.”
https://www.ncbi.nlm.nih.gov/pubmed/2344166 In vitro effect of fluoroquinolones on theophylline
metabolism in human liver microsomes (1990). “Some quinolone antibiotics cause increases in levels of
theophylline in plasma that lead to serious adverse effects. We investigated the mechanism of this
interaction by developing an in vitro system of human liver microsomes. Theophylline (1,3-
dimethylxanthine) was incubated with human liver microsomes in the presence of enoxacin,
ciprofloxacin, norfloxacin, or ofloxacin. Theophylline, its demethylated metabolites (3-methylxanthine
and 1-methylxanthine), and its hydroxylated metabolite (1,3-dimethyluric acid) were measured by high-
pressure liquid chromatography, and Km and Vmax values were estimated. Enoxacin and ciprofloxacin
selectively blocked the two N demethylations; they significantly inhibited the hydroxylation only at high
References 16 website: JMR, http://fluoroquinolonethyroid.com
concentrations. Norfloxacin and ofloxacin caused little or no inhibition of the three metabolites at
comparable concentrations. The extent of inhibition was reproducible in five different human livers.
Inhibition enzyme kinetics revealed that enoxacin caused competitive and mixed competitive types of
inhibition. The oxo metabolite of enoxacin caused little inhibition of theophylline metabolism and was
much less potent than the parent compound. Nonspecific inhibition of cytochrome P-450 was ruled out
since erythromycin N demethylation (cytochrome P-450 mediated) was unaffected in the presence of
enoxacin. These in vitro data correlate with the clinical interaction described for these quinolones and
theophylline. We conclude that some quinolones are potent and selective inhibitors of specific isozymes
of human cytochrome P-450 that are responsible for theophylline metabolism. This in vitro system may
be useful as a model to screen similar compounds for early identification of potential drug interactions. . .
. However, theophylline plasma levels become elevated in patients treated simultaneously with certain
quinolones, such as enoxacin or ciprofloxacin (1, 7, 14, 24, 25), and these elevated levels may result in
complaints of nausea, vomiting, tachycardia, or agitation . . . Theophylline is almost entirely (90%)
metabolized in the liver by the hepatic mixed-function oxidase system (13) to 3-methylxanthine (3-MX),
1-methylxanthine (1-MX), and 1,3-dimethyluric acid (1,3-DMU) (Fig. 1). Studies in humans indicate that
certain quinolones cause a dose-dependent inhibition of theophylline metabolism, resulting in decreased
urinary excretion of its metabolites and increased excretion of the parent compound (1, 17). Evidence for
this mechanism is further supported by investigations showing that neither protein binding nor renal
clearance of theophylline are influenced by coadministration of enoxacin (26). Wijnands et al. suggested
(27) that the oxo metabolite of enoxacin, oxo-enoxacin, might be responsible for this inhibition. However,
subsequent in vitro studies with rat hepatocytes indicate that only the parent compound inhibits
theophylline metabolism (9). . . . Studies of humans receiving quinolones which inhibit theophylline
metabolism demonstrate decreased excretion of the two demethylated metabolites of theophylline, little
change in the hydroxylated metabolite, and increased excretion of the parent compound (1, 17).
Enoxacin is the most potent inhibitor of theophylline metabolism in vivo, followed by ciprofloxacin.
Ofloxacin and norfloxacin cause only slight inhibition (12, 23). We investigated an in vitro system of
human microsomes, the results of which correlate well with that observed for in vivo interactions of
quinolones with theophylline. . . . vitro human liver microsomal system, we found that the extent of
inhibition can be graded as enoxacin > ciprofloxacin > norfloxacin. Sano et al. (18) found that the mean
cumulative urine recoveries of 3-MX, 1-MU, and 1,3-DMU in humans were decreased from that of control
by 64, 63, and 28%, respectively, after administration of enoxacin. These results correlate well with those
from our human liver microsomal system (Table 1). We found that enoxacin inhibits 3-MX, 1-MX, and
1,3-DMU formation from control by 76, 68, and 31%, respectively. . . The ratios of theophylline and the
quinolone concentrations in this model are quite similar to those observed in a clinical situation. . .
Immunoinhibition studies in our laboratory have shown that the polycyclic aromatic-hydrocarbon-
inducible cytochrome P-450 is mainly involved in the formation of the two N-demethylated metabolites.
Since enoxacin and ciprofloxacin profoundly inhibited the N demethylations and not the hydroxylation,
one can conclude that quinolones selectively inhibit only certain isozymes in this system. . . . On the basis
of our enzyme kinetics data, we speculate that an inhibitory complex is being formed between certain
quinolones and the enzymes involved in theophylline metabolism. This complexation appears to be
reversible, at least for enoxacin, since the type of inhibition was found to be mixed competitive. Since
these quinolones cause a more potent inhibition to the two N demethylations of theophylline than of the
References 16 website: JMR, http://fluoroquinolonethyroid.com
8-hydroxylation, these data suggest that a similar isozyme may be mediating the theophylline N
demethylation and the metabolism of quinolones.”
https://www.ncbi.nlm.nih.gov/pubmed/3348614 Impact of ciprofloxacin on theophylline clearance
and steadystate concentrations in serum (1988). “The effect of a multiple-dose regimen of oral
ciprofloxacin (750 mg every 12 h for 11 doses) on the clearance and steady-state concentrations of
theophylline in trough (predose) serum was evaluated in nine healthy male subjects, each serving as his
own control. Theophylline was taken as a sustained release tablet per os in a dose of 200 mg every 12 h
for 19 doses. Theophylline concentrations in serum were measured immediately before each theophylline
dose. Ciprofloxacin was administered on study day 4 through the first dose of study day 8. Theophylline
concentrations in serum were also measured on study days 3, 6, 8, and 10 at the following times after
the first dose of each day: 0, 0.25, 0.50, 1, 2, 4, 6, 8, 10, and 12 h. Steady-state theophylline
concentrations in trough serum were significantly higher during ciprofloxacin treatment (day 8) than
before (day 3) or after (day 10) ciprofloxacin administration (P less than 0.01). Likewise, theophylline
clearance was significantly slower (P less than 0.01) during ciprofloxacin treatment (day 8) than before it
(day 3) or after it (day 10). The magnitude of ciprofloxacin-induced changes was approximately 30%.
These results suggest that a multidose regimen of ciprofloxacin significantly slows the clearance of
theophylline and elevates theophylline concentrations in serum. . . . When compared with theophylline
steady-state clearances either before (study day 3) or after ciprofloxacin treatment (study day 10), the
steady-state clearance of theophylline during ciprofloxacin treatment decreased by 31 to 33%. This
decrease is virtually identical to the 30.4% decrease in theophylline clearance reported by Wijnands. . .
On the basis of our data and the data of others, it seems likely that ciprofloxacin prolongs the elimination
of theophylline from serum. Whether an automatic dosage reduction for theophylline would be
warranted is not so certain, since the magnitude of clearance slowing is approximately 30%. It would
clearly be prudent to monitor theophylline concentrations more intensely among patients receiving
ciprofloxacin and to lower theophylline doses by 25 to 33% for those patients who might actually
warrant a dose reduction. Alerting patients to symptoms of theophylline toxicity may be a sufficient
precaution in patients with steady-state theophylline levels that are less than 15 mg/liter.”
https://www.ncbi.nlm.nih.gov/pubmed/2760258 Effect of quinolone antimicrobials on theophylline
pharmacokinetics (1989). “The purpose of the research was to ascertain the comparative differences of
quinolone antibiotics on theophylline pharmacokinetics. Eight healthy male volunteers were randomly
assigned to four treatments. Each was administered norfloxacin (NOR) 800 mg/d, ciprofloxacin (C) 1 g/d,
nalidixic acid (NAL) 2 g/d and placebo (P) for 7 days. On the seventh day of each treatment, theophylline
(5 mg/kg) iv was administered. The elimination half-life (T 1/2), total body clearance (CL) and volume of
distribution at steady state (Vss) of theophylline were calculated using model-independent methods.
ANOVA for repeated measures was used for data comparisons. The mean (SD) theophylline results were:
CL l/kg/h--NOR .038 (.006), C .033 (.006), NAL .045 (.008), P .044 (.007); T 1/2 h--NOR 9.2 (1.8), C 10.6
(1.8), NAL 8.3 (1.8), P 7.5 (1.4). Theophylline Vss differences by treatment were not significant. NOR and
C significantly decreased theophylline's clearance and the clearance change can be of clinical
significance.”
References 16 website: JMR, http://fluoroquinolonethyroid.com
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1401213/ The influence of quinolone derivatives
on theophylline clearance (1986). “Enoxacin decreases the metabolic clearance of the bronchodilator
theophylline not only in severely ill patients, but also in patients with stable chronic obstructive airways
disease. In this comparative study, significantly increased plasma theophylline concentrations were
measured during co-administration of enoxacin (110.9%) and, to a lesser degree, also during co-
administration of pefloxacin (19.6%) and ciprofloxacin (22.8%). Total body clearance of theophylline was
significantly decreased by enoxacin (63.6%), ciprofloxacin (30.4%) and pefloxacin (29.4%). The
pharmacokinetic parameters of theophylline did not change during co-administration of ofloxacin and
nalidixic acid. There is growing evidence that the observed interaction is caused not by the parent drugs,
but by the 4-oxo metabolite of enoxacin, pefloxacin and ciprofloxacin.”
https://www.ncbi.nlm.nih.gov/pubmed/2328197 Comparative effects of ciprofloxacin and
lomefloxacin on the oxidative metabolism of theophylline (1990). “Nine healthy male volunteers were
studied to assess the interaction between theophylline and ciprofloxacin and to assess whether a similar
interaction occurred with lomefloxacin, using a randomised, crossover design. Subjects received
theophylline 125 mg 8 hourly with and without lomefloxacin 400 mg 12 hourly or ciprofloxacin 500 mg
12 hourly for 7 days. Ciprofloxacin treatment lowered total theophylline clearance by 27%, owing to a
decreased clearance via 1-, 3-demethylation and 8-hydroxylation. Lomefloxacin treatment did not alter
theophylline clearance. Ciprofloxacin, at usual clinical doses, could cause a clinically significant
interaction when co-administered with theophylline. . . . Theophylline is metabolised by three major
pathways, 1-demethylation, 3-demethylation and 8-hydroxylation (Birkett et al., 1985) and the effects of
the fluoroquinolones on each of these metabolic pathways has not been established. This study was
designed to identify which metabolic pathways are inhibited by ciprofloxacin and to test the hypothesis
that lomefloxacin, a newer fluoroquinolone without a 4-oxo metabolite, does not inhibit theophylline
metabolism. . . . Ciprofloxacin treatment lowered mean plasma theophylline clearance by 27%,
consistent with the 30% reduction in theophylline clearance reported previously (Wijnands et al., 1986;
Bachmann et al., 1988). Clearance by all three metabolic pathways was lowered, although the decrease
via the 8-hydroxylation pathway (24%) was less than the decrease via the 1-demethylation (37%) and 3-
demethylation (42%) pathways. . . . However, the inhibitory effect of ciprofloxacin pretreatment on the
disposition of theophylline was consistent with previously published in vitro data (Robson et al., 1987,
1988b) and in vivo data (Robson et al., 1988a) suggesting that two isozymes of cytochrome P450 are
involved in the metabolism of theophylline, one isozyme predominantly performing the demethylations
and the other performing the 8-hydroxylation. Lomefloxacin treatment had no effect on theophylline
metabolism consistent with the hypothesis that it is the 4-oxo metabolites of the fluoroquinolones which
inhibit theophylline metabolism (Wijnands et al., 1986). Lomefloxacin, unlike ciprofloxacin, does not form
a 4-oxo metabolite.
https://www.ncbi.nlm.nih.gov/pubmed/1606331 Effect of the addition of ciprofloxacin on
theophylline pharmacokinetics in subjects inhibited by cimetidine (1992). “Although the effect of
individual enzyme inhibitors on hepatic microsomal enzyme activity has been studied extensively, little
data exist on the effects of combinations of inhibiting agents. The purpose of this study was to
investigate the effect of the addition of a second hepatic oxidative enzyme inhibitor on the inhibition of
References 16 website: JMR, http://fluoroquinolonethyroid.com
metabolism in subjects already maximally inhibited by cimetidine. Ciprofloxacin was used as the second
inhibitor. In a randomized crossover sequence, subjects received theophylline 5 mg/kg on day 6 of
therapy with cimetidine 2400 mg/d, ciprofloxacin 1 g/d, both drugs, or while drug-free. Eight normal
volunteers (6 men, 2 women; mean age 25.2 y). Theophylline pharmacokinetic parameters after each
treatment were determined by model independent pharmacokinetic analysis. Statistical analysis of the
data for differences between treatments was assessed by ANOVA for repeated measures. When
administered alone, ciprofloxacin and cimetidine caused a significant increase in theophylline elimination
half-life and a decrease in clearance. Theophylline elimination half-life was significantly longer during
combined therapy compared with either drug alone. Theophylline clearance was lower during combined
treatment, although this relationship did not reach statistical significance. The addition of a second
enzyme inhibitor in subjects receiving maximally inhibiting doses of cimetidine can produce a further
decrease in the hepatic metabolism of drugs that are metabolized by the cytochrome P-450 microsomal
enzyme system. As cimetidine and ciprofloxacin are frequently used together for a variety of common
clinical indications, clinicians should be aware of this drug interaction and should consider that a similar
effect may occur when other enzyme inhibitors are used concomitantly. (My note from Wiki: Cimetidine,
sold under the brand name Tagamet among others, is a histamine H2 receptor antagonist that inhibits
stomach acid production.[2][3][4] It is available over-the-counter and is mainly used in the treatment of
heartburn and peptic ulcers.[2][4][5]. . . . Cimetidine is a potent cytochrome P450 (CYP450) enzyme
inhibitor.[17] It is not a universal inhibitor of the CYP450 oxidative system,[29] but it inhibits a broad
array of CYP450 isoforms, including CYP1A2, CYP2C9, CYP2C19, CYP2D6, CYP2E1, and
CYP3A4.[17][29][30] The drug is said to be most potent in inhibiting CYP1A2, CYP2D6, and CYP3A4,[31] of
which it is described as a moderate inhibitor,[1] and this is notable as these three isoenzymes are
involved in the majority of CYP450-mediated drug biotransformations;[32] also, CYP1A2, CYP2C9,
CYP2C19, CYP2D6, CYP2E1, and CYP3A4 have been identified as involved in the oxidative metabolism of
most commonly used drugs.[33] As such, cimetidine has the potential for a large number of drug
interactions.[17][29][30] Cimetidine is reported to be a competitive, reversible inhibitor of the CYP450
enzymes similarly to certain other inhibitors like azole antifungals and quinidine,[29][24][34][16]
although mechanism-based (suicide), irreversible inhibition has also been identified for at least
CYP2D6.[23] It reversibly inhibits CYP450 enzymes by binding directly with the complexed heme-iron of
the active site via one of its imidazole ring nitrogen atoms, thereby blocking the oxidation of other drugs.
. . . Cimetidine has been found to possess clinically significant albeit weak antiandrogen activity at high
doses.[27][36][37][38] It has been found to directly and competitively displace testosterone and
dihydrotestosterone (DHT) and antagonize the androgen receptor (AR) in animals.[39][40] In addition,
cimetidine has been found to inhibit 2-hydroxylation of estradiol (via inhibition of CYP450 enzymes,
which are involved in the metabolic inactivation of estradiol), resulting in increased levels of
estrogen.[41][42][43][44][45][46]).
https://www.ncbi.nlm.nih.gov/pubmed/9114903 Individual and combined effects of cimetidine and
ciprofloxacin on theophylline metabolism in male nonsmokers (1993). “1. The individual and
combined effects of cimetidine and ciprofloxacin on theophylline metabolism were examined in six young
male nonsmokers. 2. Treatment sequence consisted of 7 days each of cimetidine 400 mg p.o. every 12 h.
ciprofloxacin 500 mg p.o. every 12 h, and the combination of cimetidine and ciprofloxacin. 3. Studies of
References 16 website: JMR, http://fluoroquinolonethyroid.com
theophylline pharmacokinetics were performed at baseline and on the fifth day of each regimen. 4.
Individually, cimetidine and ciprofloxacin decreased the clearance of theophylline by 25% and 32%,
respectively. Therapy with the combined regimen resulted in a 41% reduction in theophylline clearance,
which was greater than that achieved with each drug alone (P < 0.01). 5. Ciprofloxacin, in contrast to
cimetidine, inhibited N-demethylations of theophylline to a significantly greater extent than the
hydroxylation pathway. Combined treatment produced a further decline in formation of 1,3-dimethyluric
acid than each drug alone. 6. These data suggest that coadministration of cimetidine and ciprofloxacin
exerts a greater impairment of theophylline biotransformation than each inhibitor alone. The enhanced
inhibitory effect from the two inhibitors will occur only when sub-maximal doses of each individual agent
are used. . . . We have also shown that cimetidine and ciprofloxacin impair both the demethylation and
the hydroxylation of theophylline (Table 2). This finding is consistent with that reported by Vestal et al.
[17] and provides further evidence that cimetidine is a nonselective inhibitor of theophylline metabolism.
In contrast, the observation that ciprofloxacin has a preferential inhibitory effect on the formation of 3-
methylxanthine and 1-methyluric acid is in keeping with the results of other in vivo and in vitro studies
[18, 19]. The proportionate lowering of theophylline clearance was greater during the combined
treatment phase than with either cimetidine or ciprofloxacin alone (Figure 2). In contrast, Davis et al. [7]
found that ciprofloxacin (500 mg twice daily) and a maximally inhibiting dose of cimetidine (2400 mg
day-') decreased theophylline clearance more than when ciprofloxacin was given alone but not when
cimetidine was given alone. This difference may be attributed to the differences in the daily dose of
cimetidine employed in these studies indicating that when a maximally inhibitory dose of one drug is
used, addition of a second inhibitor may have no further affect on the metabolism of theophylline. The
finding that the combined regimen produced a further decline in the formation of 1,3-dimethyluric acid
when compared with each individual agent suggests that the partially additive inhibitory effects of the
combined regimen on theophylline metabolism can be attributed, at least in part, to an enhanced
inhibition of the hydroxylation pathway. With regard to demethylation, the combined treatment caused
a slight increase in inhibition of the formation of 3-methylxanthine and 1-methyluric acid compared with
ciprofloxacin alone. These data indicate that the inhibitory effects of the combined treatment on
theophylline metabolism is qualitatively similar to that exerted by ciprofloxacin alone (Figure 3). In
conclusion, this study demonstrated that cimetidine and ciprofloxacin, at standard therapeutic doses, are
inhibitors of theophylline elimination. Their combined administration caused a proportionately greater
decrease in theophylline clearance than that achieved with each agent alone. This less than fully additive
effect can be attributed largely to an enhanced inhibition of the formation of 1,3-dimethyluric acid. In
patients receiving theophylline together with several inhibitors, appropriate adjustment of theophylline
dosage should be instituted based on the expected change in theophylline clearance as a result of the
drug interaction and on plasma theophylline concentration measurements.
https://www.ncbi.nlm.nih.gov/pubmed/3481317 Steady-state kinetics of the quinolone derivatives
ofloxacin, enoxacin, ciprofloxacin and pefloxacin during maintenance treatment with theophylline
(1987). “Some of the new quinolone derivatives may be of value in the treatment of respiratory tract
infections. It has been demonstrated that enoxacin, pefloxacin and ciprofloxacin, but not ofloxacin,
decreased the metabolic clearance of the bronchodilator theophylline. This resulted in elevated plasma
theophylline concentrations and, in some of the patients, theophylline toxicity. When the
References 16 website: JMR, http://fluoroquinolonethyroid.com
pharmacokinetic parameters of enoxacin, pefloxacin, ciprofloxacin and ofloxacin obtained in the present
study were compared with those obtained from other studies in healthy volunteers not given
theophylline, there was no evidence of theophylline influencing the clearance of the investigated
quinolones.” (?)
https://www.ncbi.nlm.nih.gov/pubmed/3578320 Ciprofloxacin increases serum levels of theophylline
(1987). “During a clinical trial of orally administered ciprofloxacin in respiratory tract infections,
changes in serum theophylline levels were evaluated in 33 hospitalized patients who also required
theophylline therapy. Patients received intravenous theophylline in standard titrated doses and 750 mg
of oral ciprofloxacin twice daily. Serum theophylline levels in all patients were measured before and
during ciprofloxacin therapy. The mean serum pretreatment theophylline level was 7.8 +/- 4.6
micrograms/ml; during ciprofloxacin therapy, the level increased to 14.6 +/- 7.4 micrograms/ml. Twenty
of the 33 (61 percent) patients evaluated had increases in serum theophylline levels by a mean value of
10.5 micrograms/ml. In 30 percent of patients who experienced increases, theophylline concentrations
were in the toxic range. This occurred more frequently in elderly patients with chronic obstructive
pulmonary disease. In light of the frequency and potential severity of this interaction, careful monitoring
of serum theophylline levels in patients receiving theophylline and ciprofloxacin is recommended.”
https://www.ncbi.nlm.nih.gov/pubmed/3571046 Effect of multiple dose oral ciprofloxacin on the
pharmacokinetics of theophylline and indocyanine green (1987). “Interaction between ciprofloxacin
and theophylline was studied in eight male volunteers, who were randomly divided into two groups. All
subjects were given intravenous theophylline and indocyanine green (ICG) on study days 0, 7 and 14.
Group I subjects received ciprofloxacin 750 mg orally every 12 h on days 1-7. Group II subjects received
ciprofloxacin 750 mg every 12 h on days 6-14. No significant changes in ICG clearance or half-life were
noted. A significant increase in theophylline half-life and volume of distribution was observed (P less than
0.05); however, clearance was not significantly decreased (P = 0.1). A potentially clinically significant
interaction was detected in three subjects whose theophylline clearance decreased by 42-113%. Until
further clinical experience is gained, we advise caution when these agents are coadministered. Some
adjustment in theophylline dosage may be required; therefore, these patients should have serum
theophylline concentration measurements and careful clinical assessment for theophylline toxicity.”
https://www.ncbi.nlm.nih.gov/pubmed/3443151 A clinically significant interaction between
ciprofloxacin and theophylline (1987). “We report a case of theophylline toxicity following the co-
administration of ciprofloxacin. Total theophylline clearance fell from 2.3 l.h-1 to 0.8 l.h-1 when
ciprofloxacin was added to the treatment regimen and returned to 2.1 l.h-1 after ciprofloxacin was
discontinued.”
https://www.ncbi.nlm.nih.gov/pubmed/3678060 Increased theophylline concentrations secondary to
ciprofloxacin (1987). “An 82-year-old man with a history of myasthenia gravis and heart failure was
admitted to the hospital with respiratory failure. Aminophylline and eventually theophylline therapy
were initiated to improve respiratory status. During the hospital stay, the patient developed a resistant
pseudomonal pneumonia. After failure with conventional antibiotics, ciprofloxacin was initiated because
of favorable sensitivity and the planned avoidance of aminoglycoside therapy. Seventy-two hours after
References 16 website: JMR, http://fluoroquinolonethyroid.com
initiation of ciprofloxacin, the patient's theophylline level rose from a steady-state baseline of 9.8
micrograms/ml to 34.7 micrograms/ml. After the theophylline dose was reduced by approximately 67
percent, the patient's theophylline serum concentration returned to baseline (10 micrograms/ml). Until
more data concerning the interaction of theophylline and ciprofloxacin are available, we recommend
close monitoring of theophylline serum concentrations in patients receiving concomitant ciprofloxacin.”
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2545536/ Drug point: Danger of interaction
between ciprofloxacin and theophylline (1988). “Drs J L BEM and R D MANN (Committee on Safety
ofMedicines, London SW8 5NQ) write: Ciprofloxacin (Ciproxin, Bayer), a new fluoroquinolone antibiotic,
was introduced in 1987 for the treatment of systemic infections. Quinolone antibiotics, including
ciprofloxacin, inhibit theophylline metabolism and both prolong and raise plasma theophylline
concentrations.' A warning about this is included in the ciprofloxacin datasheet. A potentially dangerous
situation occurs when a patient already being treated with theophylline is prescribed ciprofloxacin for a
respiratory tract infection. The early signs of theophylline overdose, nausea and vomiting, may easily be
overlooked or attributed to the side effects of ciprofloxacin. The Committee on Safety of Medicines has
received eight reports of clinically important interaction between ciprofloxacin and theoplylline (table). In
most cases the dose of both drugs was well within the recommended range. The signs and symptoms of
drug interaction appeared rapidly, usually two to three days after the start of ciprofloxacin. One elderly
woman treated with moderate doses of theophylline died with a toxic plasma concentration after a
coadministered short course of ciprofloxacin. Thomson et al observed twofold to threefold increases in
the concentration and 64% reduction in clearance of theophylline in elderly patients who had received
ciprofloxacin 500 mg twice daily for a few days.2 An interaction between ciprofloxacin and theophylline
is not inevitable3 and we have four reports of patients given both drugs who developed adverse
reactions due to other causes. Thus it is difficult to predict which patients are at risk of this interaction,
and we suggest that ciprofloxacin should not normally be used in patients treated with theophylline.
Patients should also be warned against self medication as some cough-cold medicines contain
theophylline. In cases in which ciprofloxacin and theophylline need to be given together plasma
theophylline concentrations should be monitored.”
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1834921/ Probable fatal interaction between
ciprofloxacin and theophylline (1988). “Dr R HOLDEN (Edinburgh) writes: Thomson et al recently
reported theophylline toxicity in an elderly patient concurrently taking ciprofloxacin.' The Committee on
Safety of Medicines has been notified of several other cases (R D Mann, personal communication). We
report a further probable interaction with a fatal outcome.”
https://www.ncbi.nlm.nih.gov/pubmed/2313005 Theophylline toxicity associated with the
administration of ciprofloxacin in a nursing home patient (1990).
https://www.ncbi.nlm.nih.gov/pubmed/2360338 Seizure with ciprofloxacin and theophylline
combined therapy (1990). “Ciprofloxacin has been reported to cause theophylline toxicity by inhibiting
theophylline metabolism. A 93-year-old woman without a known seizure history, while on ciprofloxacin
and theophylline combined therapy, experienced a grand mal seizure. Her serum theophylline
concentration at the time was 20 micrograms/mL. On previous occasion of theophylline toxicity, she had
References 16 website: JMR, http://fluoroquinolonethyroid.com
a serum theophylline concentration of 27 micrograms/ml but the patient did not experience any seizure.
Several reports suggest that the combination of theophylline and ciprofloxacin has an additive inhibitory
effect on gamma-aminobutyric acid (GABA) sites. Inhibition of the binding of GABA to its receptor sites
has been related to the convulsant effects of other drugs. The seizure in our patient may have been
caused by altered pharmacokinetics and pharmacodynamics brought about by combined therapy of
theophylline and ciprofloxacin.”
https://www.ncbi.nlm.nih.gov/pubmed/1928889 Theophylline toxicity secondary to ciprofloxacin
administration (1991). “We report the case of a 79-year-old woman who presented from a skilled
nursing facility to the emergency department with signs and symptoms of theophylline toxicity and a
serum theophylline concentration of 53.7 mg/L. The patient had been on a regular regimen of
aminophylline for two months, with the addition of ciprofloxacin three days before arrival as the only
identifiable potential cause of theophylline intoxication. She was monitored and treated conservatively
with serial doses of activated charcoal, which resulted in a reduction of her serum theophylline level to a
therapeutic concentration in 15 hours without adverse sequelae. The number of cases of theophylline
intoxication secondary to concurrent ciprofloxacin administration is likely to increase, especially in
nursing home populations, and it should be suspected when these patients present to the ED with the
appropriate signs and symptoms. Management of theophylline intoxication should be based on clinical
presentation as well as concentrations of the drug.”
https://www.ncbi.nlm.nih.gov/pubmed/1541177 Role of ciprofloxacin in fatal seizures (1992).
https://www.ncbi.nlm.nih.gov/pubmed/2867879 Comparison of theophylline and theobromine
metabolism in man (1985). “The total plasma and partial metabolic and renal clearances of
theobromine and theophylline were determined in 13 healthy volunteers. Total plasma clearance for
theobromine was 46% greater than that for theophylline, but the unbound clearances were almost
identical. Theobromine renal clearance was 67% greater than that for theophylline but most of the
difference was due to the lower protein binding of theobromine (free fraction = 0.86 compared to 0.58
for theophylline). Clearance by N-demethylation at the 3-position was 3.7-fold higher (unbound
clearance 2.5-fold higher) for theobromine than for theophylline, showing that the position of the other
methyl substituent (positions 1 or 7) is a major determinant of metabolic rate. There was a high degree
of correlation between theophylline and theobromine plasma clearances (r = 0.86) and also between
partial metabolic clearances both within drugs and across drugs (r = 0.65-0.99). The renal clearances of
theophylline and theobromine were also correlated (r = 0.71). The results support the view that
theophylline and theobromine are metabolized by a common group of cytochromes P-450 under similar
regulatory control. Theobromine is a good model compound for assessing the activity of these enzymes
in man as it has low pharmacological activity and low protein binding, its total and partial metabolic
clearances correlate closely with those of theophylline, and close to 100% of the dose can be recovered
as known metabolites.
https://www.ncbi.nlm.nih.gov/pubmed/1981505 Quinolone inhibition of cytochrome P-450-
dependent caffeine metabolism in human liver microsomes (1990). “Inhibitory effects of the
quinolone antibiotics ofloxacin, lomefloxacin, pipemidic acid, ciprofloxacin, and enoxacin on caffeine
References 16 website: JMR, http://fluoroquinolonethyroid.com
metabolism were examined in vitro with human liver microsomes of four donors. All drugs competitively
inhibited the activity of 3-demethylation, the major pathway of caffeine metabolism. Enoxacin,
ciprofloxacin, and pipemidic acid were strong inhibitors exhibiting Ki values between 0.1 and 0.2 mM.
Lomefloxacin and ofloxacin had moderate effects with Ki values of 1.2 and 3.6 mM, respectively. The rate
of caffeine 7-demethylation (which amounted to about 25% of that for 3-demethylation) was only
slightly affected by the quinolones. Minor, but inconsistent, effects were found on 8-oxidation to 1,3,7-
trimethyluric acid. The results indicate that the reduction of caffeine clearance by concomitant quinolone
application observed in vivo is primarily due to a competitive interaction of the inhibiting quinolones with
the cytochrome P-450 isoenzyme(s) mediating caffeine demethylation.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC298137/pdf/pnas00287-0044.pdf Evidence for the
involvement of several cytochromes P-450 in the first steps of caffeine metabolism by human liver
microsomes (1991). “Caffeine biotransformation and four monooxygenase activities involving
cytochrome P-450IA2, namely ethoxy- and methoxyresorufin O-dealkylases, phenacetin O-deethylase,
and acetanilide 4-hydroxylation were studied in 25 human liver microsomes. All these activities were
highly significantly intercorrelated (r greater than 0.72, p less than 0.001) and correlated with the level of
immunoreactive P-450IA2 content (r greater than 0.65; p less than 0.001). P-450IA content was
measured by immunoblotting with anti-rat P-450 beta-naphthoflavone-B, an antibody that detects only
a single band corresponding to P-450IA2. The formation rate of two caffeine metabolites, namely
paraxathine and theobromine, was correlated with the four monooxygenase activities measured and P-
450IA2-specific content (r greater than 0.75). However, inhibition studies of caffeine metabolism by
phenacetin, a specific substrate of P-450IA2, clearly indicated that only the N-3 demethylation of caffeine
was supported by this enzyme. These in vitro data demonstrate that P-450IA2 is predominantly
responsible for the major metabolic pathway of caffeine and that the formation of other demethylated
metabolites is mediated, at least partly, by other P-450 enzymes.
https://www.ncbi.nlm.nih.gov/pubmed/2813353 Human cytochrome P-450PA (P-450IA2), the
phenacetin O-deethylase, is primarily responsible for the hepatic 3-demethylation of caffeine and N-
oxidation of carcinogenic arylamines (1989). “Aromatic amines are well known as occupational
carcinogens and are found in cooked foods, tobacco smoke, synthetic fuels, and agricultural chemicals.
For the primary arylamines, metabolic N-oxidation by hepatic cytochromes P-450 is generally regarded
as an initial activation step leading to carcinogenesis. The metabolic activation of 4-aminobiphenyl, 2-
naphthylamine, and several heterocyclic amines has been shown recently to be catalyzed by rat
cytochrome P-450ISF-G and by its human ortholog, cytochrome P-450PA. We now report that human
hepatic microsomal caffeine 3-demethylation, the initial major step in caffeine biotransformation in
humans, is selectively catalyzed by cytochrome P-450PA. Caffeine 3-demethylation was highly correlated
with 4-aminobiphenyl N-oxidation (r = 0.99; P less than 0.0005) in hepatic microsomal preparations
obtained from 22 human organ donors, and both activities were similarly decreased by the selective
inhibitor, 7,8-benzoflavone. The rates of microsomal caffeine 3-demethylation, 4-aminobiphenyl N-
oxidation, and phenacetin O-deethylation were also significantly correlated with each other and with the
levels of immunoreactive human cytochrome P-450PA. Moreover, a rabbit polyclonal antibody raised to
human cytochrome P-450PA was shown to inhibit strongly all three of these activities and to inhibit the
References 16 website: JMR, http://fluoroquinolonethyroid.com
N-oxidation of the carcinogen 2-naphthylamine and the heterocyclic amines, 2-amino-6-methyldipyrido-
[1,2-a:3',2'-d]imidazole and 2-amino-3-methylimidazo[4,5-f]-quinoline. Human liver cytochrome P-450PA
was also shown to catalyze caffeine 3-demethylation, 4-aminobiphenyl N-oxidation, and phenacetin O-
deethylation. Thus, estimation of caffeine 3-demethylation activity in humans may be useful in the
characterization of arylamine N-oxidation phenotypes and in the assessment of whether or not the
hepatic levels of cytochrome P-450PA, as affected by environmental or genetic factors, contribute to
interindividual differences in susceptibility to arylamine-induced cancers.”
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC188773/ Inhibitory potency of quinolone
antibacterial agents against cytochrome P450IA2 activity in vivo and in vitro (1992). “Inhibition of
cytochrome P450IA2 activity is an important adverse effect of quinolone antibacterial agents. It results in
a prolonged half-life for some drugs that are coadministered with quinolones, such as theophylline. The
objective of the study described here was to define the parameters for quantifying the inhibitory
potencies of quinolones against cytochrome P450IA2 in vivo and in vitro and to investigate the
relationship between the results of both approaches. Cytochrome P450IA2 activity in vitro was measured
by using the 3-demethylation rate of caffeine (500 microM) in human liver microsomes. The inhibitory
potency of a quinolone in vitro was determined by calculating the decrease in the activity of cytochrome
P450IA2 caused by addition of the quinolone (500 microM) into the incubation medium. The mean values
(percent reduction of activity without quinolone) were as follows: enoxacin, 74.9%; ciprofloxacin, 70.4%;
nalidixic acid, 66.6%; pipemidic acid, 59.3%; norfloxacin, 55.7%; lomefloxacin, 23.4%; pefloxacin, 22.0%;
amifloxacin, 21.4%; difloxacin, 21.3%; ofloxacin, 11.8%; temafloxacin, 10.0%; fleroxacin, no effect. The
inhibitory potency of a quinolone in vivo was defined by a dose- and bioavailability-normalized
parameter calculated from changes of the elimination half-life of theophylline and/or caffeine reported
in previously published studies. Taking the pharmacokinetics of the quinolones into account, it was
possible to differentiate between substances with and without clinically relevant inhibitory effects by
using results of in vitro investigations. The in vitro test described here may help to qualitatively predict
the relevant drug interactions between quinolones and methylxanthines that occur during therapy.. . .
Another important biological effect of this drug class concerns the metabolism of several unrelated
pharmaceutical agents, resulting in occasional adverse reactions. It has been reported that some of the
quinolone antibacterial agents cause a reduced velocity of caffeine and theophylline degradation in vivo
(see below) (for a review, see reference 10) and in vitro (14, 40). Furthermore, reductions in the
antipyrine metabolism rate and the R-warfarin oxidation rate were observed in humans when quinolones
were coadministered with these drugs (23, 24, 46). . . . In investigations with human liver microsomes,
the mechanism of this interaction was determined for ofloxacin, ciprofloxacin, enoxacin, lomefloxacin,
and pipemidic acid. A competitive-type inhibition of P450LA2 activity by all of these compounds was
found (14). This cytochrome P450 isoform is primarily responsible for the first steps of both caffeine and
theophylline metabolism in the liver, as shown in investigations with specific antibodies (5, 37) and
genetically engineered cells that express single cytochrome P450 isoforms (13). The main metabolic
pathway of caffeine in all systems tested, i.e., 3-demethylation, is mediated almost exclusively by
cytochrome P450IA2 (5) and, therefore, may be used as a specific probe for P450LA2 activity. Serious
incidents (theophylline intoxication), including death, have occurred because of this drug interaction (3,
25). Thus, the objective of the present study was to define the parameters for quantifying the inhibitory
References 16 website: JMR, http://fluoroquinolonethyroid.com
potencies of quinolones against cytochrome P450IA2 in vivo and in vitro and to investigate the
relationship between in vitro and in vivo effects. This is of considerable interest in light of the abundance
of new quinolones. The probability of encountering these adverse drug reactions should be considered
when comparing the therapeutic values of otherwise similar quinolones. . . . All quinolones tested (with
the exception of fleroxacin) showed an inhibitory effect on caffeine 3-demethylation under the in vitro
conditions used in this study. This effect was most pronounced for enoxacin and ciprofloxacin. A possible
modification of the in vitro effects because of degradation of the quinolones has been tested for
ciprofloxacin (12). Reduction in the concentration of intact ciprofloxacin was not detectable as a result of
incubation. The concentration of the Ml metabolite (cleavage of piperazinyl substituent) of ciprofloxacin
was less than 0.3% of the ciprofloxacin concentration, and other metabolites were below the limit of
detection. It has been reported that some quinolones (i.e., enoxacin, ciprofloxacin, ofloxacin,
lomefloxacin, and pipemidic acid [14, 29]) exert a competitive type of inhibition on caffeine 3-
demethylation. The structures of the substances tested previously (14, 29) cover the range of structures
of those of the compounds included in the present investigation. Therefore, it is safe to conclude that all
congeners used in this study exerted their inhibitory effects by binding to the active site of the enzyme,
resulting in a competitive type of inhibition. . . . The low standard deviation between donors provides
further evidence that P450 isozymes other than P450IA2 (or isoforms coordinately regulated with
P450IA2) that are not susceptible to inhibition do not take part in caffeine metabolism (5). . .
.Cytochrome P450IA2 has been reported to be responsible for caffeine 3-demethylation, which is the
major caffeine degradation step in humans (5). There is evidence that this isozyme also takes part in 1-
and 7-demethylation of caffeine and mediates the main portions of the theophylline demethylation and
hydroxylation pathways (although other cytochrome P450 isoforms may also play a minor part in
primary theophylline metabolism [37]). Additionally, similar Km values for all primary metabolic steps of
theophylline and caffeine have been reported (6, 14, 15, 21). Thus, it is not surprising that inhibition of
P450IA2 activity by the concomitant application of quinolones results in a similar degree of half-life
prolongation and/or clearance reduction for both caffeine and theophylline (10). This enables the pooling
of in vivo inhibition data for both methylxanthines. The association between the increasing half-lives of
the methylxanthines with higher doses of the inhibitory quinolones (16, 38) may readily be explained by
the competitive type of inhibition that has been observed in vitro. . . . . The inhibitory effects of
quinolones on methylxanthine metabolism in vivo are postulated to be the result of a mutually exclusive
concurrence at the cytochrome P450IA2 binding site. The extent of inhibition depends not only on the
affinity of a quinolone to the site but also on the concentrations of this drug and possible active
metabolites at the cytochrome binding site. This may account for the lack of a complete correlation
between in vivo and in vitro data.”
https://www.ncbi.nlm.nih.gov/pubmed/8429824 Quinolone antibacterial agents: relationship
between structure and in vitro inhibition of the human cytochrome P450 isoform CYP1A2 (1993).
“The inhibitory effect of 44 quinolone antibacterials and derivatives (common structure, 4-oxoquinoline-
3-carboxylic acid) on cytochrome P450 isoform CYP1A2 activity was tested using human liver microsomes
and caffeine 3-demethylation as a specific test system for this enzyme. By direct comparison of molecules
differing structurally in only one position, the following structure-activity relationships were found. 3'-
Oxo derivatives had a reduced or similar activity and M1 metabolites (cleavage of piperazinyl
References 16 website: JMR, http://fluoroquinolonethyroid.com
substituent) had a greater inhibitory activity, compared with the parent molecule. Alkylation of the 7-
piperazinyl substituent resulted in a reduced inhibitory potency. Naphthyridines with an unsubstituted
piperazinyl group at position 7 displayed a greater inhibitory potency than did corresponding quinoline
derivatives. Derivatives with a fluorine substitution at position 8 had only a minor effect. Molecular
modeling studies with inhibitors and caffeine showed that it is possible to explain the potency of the
quinolones to inhibit CYP1A2 on a molecular level. The keto group, the carboxylate group, and the core
nitrogen at position 1 are likely to be the most important groups for binding to the active site of CYP1A2,
because the molecular electrostatic potential of all inhibitors is very similar to that of caffeine in these
regions. The presence of a piperazinyl substituent, however, seems to be no prerequisite for inhibitory
potency. Finally, an equation to estimate the potency to inhibit CYP1A2 was developed by quantitative
structure-activity relationship analysis.
https://www.ncbi.nlm.nih.gov/pubmed/3663445 Characterisation of theophylline metabolism in
human liver microsomes (1987). “1. A radiometric high performance liquid chromatographic method is
described for the assay of theophylline metabolism in vitro by the microsomal fraction of human liver. 2.
Formation of the three metabolites of theophylline (3-methylxanthine, 1-methylxanthine and 1,3-
dimethyluric acid) were linear with protein concentrations to 4 mg ml-1 and with incubation times up to
180 min. 3. The coefficients of variation for the formation of 3-methylxanthine, 1-methylxanthine and
1,3-dimethyluric acid were 1.2%, 1% and 1.6%, respectively. 4. Theophylline is metabolised by
microsomal enzymes with a requirement for NADPH. 5. The mean (n = 7) Km values for 1-demethylation,
3-demethylation and 8-hydroxylation were 545, 630 and 788 microM, respectively, and the mean Vmax
values were 2.65, 2.84 and 11.23 pmol min-1 mg-1, respectively. 6. There was a high correlation between
the Km and Vmax values for the two demethylation pathways suggesting that the demethylations are
performed by the same enzyme. 7. Overall the in vitro studies are consistent with the in vivo results
which suggest the involvement of two cytochrome P-450 isozymes in the metabolism of theophylline. . .
The metabolic pathways for theophylline in man have been confirmed in a number of studies (Grygiel &
Birkett, 1981; Grygiel et al., 1984; Ogilvie, 1978). The major route is the 8-hydroxylation to 1,3-
dimethyluric acid (DMU) which accounts for 45-55% of the total theophylline clearance. The other
metabolic products are 3- methylxanthine (3MX) and 1-methyluric acid (1MU) which represent 13-16%
and 20-25% of theophylline clearance, respectively. Subsequently it has been shown that 1MU is formed
from 1-methylxanthine (1MX) by a reaction mediated by xanthine oxidase (Birkett et al., 1983). Although
the metabolic pathways involved in theophylline metabolism have been identified and quantified,
relatively little information exists about the enzymes involved. In 1976 Lohman & Miech reported that
theophylline was metabolized to DMU and 1MU by rat liver slices and that this activity was blocked by
classical cytochrome P-450 inhibitors and stimulated by pretreatment with P-450 inducing agents.
Further, the subcellular localisation of this enzymatic activity supported the involvement of the
cytochrome P-450 system as theophylline metabolism was located in the microsomal fraction but not in
the mitochondrial or cytosolic fractions. No 3MX was formed in the rat liver slice preparation and this is
consistent with the hypothesis that unlike man and rabbits, rats cannot demethylate theophylline in the
1 position.. . . In man, the enzymes involved in theophylline metabolism have been investigated by in vivo
studies using known inducers and inhibitors of the P-450 system (Grygiel & Birkett, 1981; Grygiel et al.,
1984; Robson et al., 1984; Miners et al., 1985; Grygiel et al., 1979). These studies provide inferential
References 16 website: JMR, http://fluoroquinolonethyroid.com
evidence that cytochrome P-450 system is the enzyme involved in the metabolism of theophylline in man
and are consistent with the more direct evidence in rat liver slices and rat microsomes (Lohman & Miech,
1976). We have postulated on the basis of data from in vivo studies (Birkett et al., 1985) that there are at
least two isozymes of cytochrome P-450 involved in the metabolism of theophylline, one isozyme
predominantly involved in the 1- and 3-demethylations and another isozyme predominantly performing
the 8-hydroxylation. Although the involvement of two isozymes of cytochrome P-450 in these pathways
can to some extent be differentiated, particularly by inhibitors, their regulation must be closely linked as
there is a high degree of correlation between all three pathways in healthy control subjects (Birkett et al.,
1985). To gain further information on the metabolism of theophylline in man, an in vitro assay has been
developed and used to study thekinetics of theophylline metabolism in human liver microsomes. . . .
Although the in vitro metabolism of theophylline has been demonstrated in rat liver microsomes
(Lohman & Miech, 1976) this is the first report of the in vitro metabolism of theophylline by human liver
microsomes. In the absence of a NADPH generating system no products were formed. (My note: In vivo,
the cytosolic pentose pathway primarily supplies P450 enzymes with NADPH for oxidative
transformation. In vitro microsomal assays, which are devoid of the cytosolic fraction, are routinely
supplied NADPH by either direct addition of NADPH or use of an NADPH-regenerating system (NRS),
consisting of β-NADP+, glucose-6-phosphaste (G6P), and G6P dehydrogenase (G6PDH). This is
consistent with the in vitro animal data (Lohman & Miech, 1976) and the in vivo human data supporting
the involvement of the cytochrome P-450 enzyme system in the metabolism of theophylline to 3MX, 1MX
and DMU. The metabolic profile in vitro is similar to that in vivo where 50-60% is metabolised by 8-
hydroxylation, 15-20% by 3-demethylation and 20-25% by 1-demethylation. No 1-methyluric acid (1MU)
was detected which is consistent with the proposal that, in vivo, 1MU is formed from 1MX by xanthine
oxidase which is not located in the microsomal fraction used in these in vitro studies. . . . the 1- and 3-
demethylation are predominantly performed by the same P-450 isozyme and that the 8-hydroxylation is
performed by a different P-450 isozyme. . . . The data presented are consistent with the involvement of
two isozymes of cytochrome P-450 in the metabolism of theophylline, but definitive evidence awaits the
isolation and characterisation of these cytochrome P-450 isozymes.”
https://www.ncbi.nlm.nih.gov/pubmed/8236273 Biotransformation of methylxanthines in
mammalian cell lines genetically engineered for expression of single cytochrome P450 isoforms.
Allocation of metabolic pathways to isoforms and inhibitory effects of quinolones. (1993). “V79
Chinese hamster cells genetically engineered for stable expression of single forms of rat cytochromes
P450IA1, P450IA2, P450IIB1, human P450IA2, and rat liver epithelial cells expressing murine P450IA2
were used to allocate metabolic pathways of methylxanthines to specific isoforms and to test the
suitability of such cell lines for investigations on drug interactions occurring at the cytochrome expressed.
The cell lines were exposed to caffeine and/or theophylline and concentrations of metabolites formed in
the medium were determined by HPLC. Caffeine was metabolized by human, rat and murine P450IA2,
resulting in the formation of four primary demethylated and hydroxylated metabolites. However, there
were differences in the relative amounts of the metabolites. The human and the mouse P450IA2 isoforms
predominantly mediated 3-demethylation of caffeine. The rat cytochrome P450IA2 mediated both 3-
demethylation and 1-demethylation of caffeine to a similar extent. The results support the hypothesis
that caffeine plasma clearance is a specific in vivo probe for determining human P450IA2 activity.
References 16 website: JMR, http://fluoroquinolonethyroid.com
Addition of the quinolone antibiotic agents pipemidic acid or pefloxacin, both known to inhibit caffeine
metabolism in vivo and in human liver microsomes, reduced formation rates of all metabolites of caffeine
in cells expressing rat and human P450IA2. Theophylline was mainly metabolized via 8-hydroxylation. All
cell lines tested were able to carry out this reaction, with highest activities in cell lines expressing rat or
human P450IA2, or rat P450IA1.”
https://www.ncbi.nlm.nih.gov/pubmed/8966447 Clinico-pharmacological case (4). Epileptic seizure as
an unwanted drug effect on theophylline poisoning. (1994) “In spite of the better understanding of the
pharmacokinetics and optimized galenics of oral theophylline formulations, therapy with this
bronchodilator still bears risks because of its narrow therapeutic window combined with substantial
inter- and intra-individual variability of theophylline metabolism. In particular, the comedication with a
variety of drugs inhibiting theophylline metabolism requires consideration as a potential source of
toxicity. Besides mild, self-limited adverse effects, potentially life-threatening toxic manifestations such
as ventricular tachyarrhythmias, shock, and seizures can occur especially with high plasma
concentrations. We report the case of a 72-year-old patient with chronic obstructive pulmonary disease
who was admitted for surgical treatment of an ulcer of the foot. During combined therapy with
theophylline and ciprofloxacin he developed signs of theophylline toxicity with a single episode of partial
seizures. These symptoms rapidly improved with repetitive application of activated charcoal and sorbitol.
Clinically relevant drug-drug interactions with theophylline and the role and mechanism of action of
activated charcoal in intoxicated patients are discussed.”
https://www.ncbi.nlm.nih.gov/pubmed/8963004 A patient with theophylline-quinolone interaction.
Not all quinolones are equal. 1996. “
https://www.ncbi.nlm.nih.gov/pubmed/8843297 Structure-related inhibitory effect of antimicrobial
enoxacin and derivatives on theophylline metabolism by rat liver microsomes. (1996). “Enoxacin, an
antimicrobial fluoroquinolone with a 7-piperazinyl-1, 8-naphthyridine skeleton, is a potent inhibitor of
cytochrome P-450-mediated theophylline metabolism. The present study was designed to clarify, using
seven enoxacin derivatives, the molecular characteristics of the fluoroquinolone responsible for the
inhibition. Three derivatives with methyl-substituted 7-piperazine rings inhibited rat liver microsomal
theophylline metabolism to 1,3-dimethyluric acid to an extent similar to that of enoxacin (50% inhibitory
concentrations [IC50s] = 0.39 to 0.48 mM). 7-Piperazinyl-quinoline derivatives, 8-hydroenoxacin (8-Hy)
and 1-cyclopropyl-8-fluoroenoxacin (8-F1), which have a hydrogen and a fluorine at position 8,
respectively, more weakly inhibited metabolite formation (IC50s = 0.88 and 1.29 mM, respectively). Little
inhibition (IC50 > 2 mM) was observed in those with 3'-carbonyl and 4'-N-acetyl groups on the piperazine
rings. The substrate-induced difference spectra demonstrated that the affinities of enoxacin, 8-Hy, and 8-
F1 to cytochrome P-450 were parallel with their inhibitory activities. The substituent at position 8 was
found to determine the molecular conformations of the fluoroquinolones, and the planarity in molecular
shape decreased in the same order as the inhibitory activity (enoxacin > 8-Hy > 8-F1). Moreover, the 3'-
carbonyl and 4'-N-acetyl groups decreased the basicity of their vicinal 4'-nitrogen atoms when judged
from their electrostatic potentials, which showed a remarkably broadened negative charge around the
nitrogens. As a result, the planarity of the whole molecule and the basicity of the 4'-nitrogen atom of
References 16 website: JMR, http://fluoroquinolonethyroid.com
enoxacin are likely to be dominant factors in the inhibition of theophylline metabolism by cytochrome P-
450.”
https://www.ncbi.nlm.nih.gov/pubmed/8737124 Pharmacokinetic interactions related to the
chemical structures of fluoroquinolones. (1996). “Fluoroquinolone derivatives interact with
methylxanthines (theophylline, caffeine) and metallic ion-containing drugs to different degrees. The rat
appears to be a suitable model for predicting such interactions in man. It has been possible to determine
the relationship between the chemical structure of the fluoroquinolone and the magnitude of the
interaction. Fluoroquinolones with a bulky substituent at the position 8, such as sparfloxacin,
lomefloxacin and fieroxacin, are less prone to interact with theophylline than those without an 8-
substituent, such as enoxacin. This substituent determines the planarity of the whole fluoroquinolone
molecule and the interaction tends to be more significant for planar fluoroquinolones. Furthermore, a 4'-
nitrogen atom in the 7-piperazinyl group is essential for the interaction to occur. The nitrogen atom is
possibly the site that binds cytochrome P-450, which catalyses theophylline metabolism. The reduction in
bioavailability of fluoroquinolones by concurrent administration of aluminium hydroxide is more striking
for derivatives with fewer substituents on the essential structure and on the piperazinyl group, such as
norfloxacin, ciprofloxacin and enoxacin. Substitution at the 5-position diminishes the interaction, which
suggests that the 5-substituent may affect the formation and/or stability of unabsorbable chelate
complex which is the probable cause of the interaction. These findings are potentially useful in designing
fluoroquinolones less prone to drug interactions.”
https://www.ncbi.nlm.nih.gov/pubmed/9364414 Interaction between pefloxacin and aminophylline
in genetically epilepsy-prone rats. (1997). “The effects of a chronic treatment with pefloxacin on
aminophylline-induced seizures in genetically epilepsy-prone rat have been investigated. Two series of
experiments were performed. In the first, animals received pefloxacin orally twice a day for five days,
then were administered aminophylline intraperitoneally and the occurrence of seizures was evaluated. In
the second series of experiments, theophylline serum concentration was evaluated in rats subject to the
same experimental protocol. Pefloxacin significantly, and in a dose-dependent manner, increased the
occurrence of seizure phases induced by aminophylline, but did not influence theophylline serum levels
measured at different times after the injection of aminophylline. We suggest that additive neurotoxic
effects of both pefloxacin and aminophylline might contribute to the increased severity of seizure score.
The possible role of GABA-benzodiazepine, excitatory amino acid and purinergic mechanism, and the role
of pharmacokinetic factors are discussed.”
https://www.ncbi.nlm.nih.gov/pubmed/9378847 Absence of a pharmacokinetic interaction between
intravenous theophylline and orally administered levofloxacin. (1997). “A randomized, placebo-
controlled, two-way crossover study in 16 healthy men was performed to determine the effect of orally
administered levofloxacin at steady-state conditions, given at 500 mg every 12 hours, on the
pharmacokinetics of theophylline given as a single 4.5-mg/kg intravenous infusion. Participants were
assigned randomly to receive theophylline with levofloxacin in one study period and theophylline with
placebo in the other period. Fourteen individuals completed the study. Mean (+/-SD) values for
theophylline pharmacokinetic parameters for the levofloxacin and placebo treatments, respectively,
were peak plasma concentrations (Cmax) of 11.4 (1.8) micrograms/mL and 10.7 (1.3) micrograms/mL;
References 16 website: JMR, http://fluoroquinolonethyroid.com
areas under the concentration time curve from time 0 extrapolated to infinity (AUCzero-infinity) of 124
(32) micrograms.hr/mL and 126 (30) micrograms.hr/mL; volumes of distribution at steady state (Vdss)
31.7 (3.5) L and 32.0 (3.9) L; clearances (Cl) of 48.6 (11.6) mL/min and 47.4 (10.3) mL/min; and half-lives
(t1/2) of 8.1 (1.9) hours and 8.2 (1.8) hours. There were no statistically significant differences between
treatments for any of these parameters. There was no pharmacokinetic interaction between levofloxacin
administered orally at steady-state conditions and intravenously administered theophylline.”
https://www.ncbi.nlm.nih.gov/pubmed/9222075 Effect of trovafloxacin, a new fluoroquinolone
antibiotic, on the steady-state pharmacokinetics of theophylline in healthy volunteers. (1997).
“Some fluoroquinolone antibiotics interfere with theophylline clearance, thereby raising concentrations
of circulating theophylline and increasing the potential for toxicity. The effect of steady-state serum
concentrations of the new fluoroquinolone trovafloxacin on the steady-state pharmacokinetics of
theophylline was examined in 12 healthy male volunteers. For 7 days, the subjects received morning and
evening theophylline doses adjusted to achieve steady-state plasma concentrations of 8-15 mg/L, the
lower end of the therapeutic range. From day 8 to day 15, six volunteers received, in addition to
theophylline, 200 mg of trovafloxacin in the morning and placebo in the evening (group A) and six
received placebo twice daily (group B). Serial plasma samples obtained over 12 h and 60 h after the
morning theophylline dose on days 7 and 14, respectively, were analysed for theophylline by HPLC with
UV detection. There were no significant differences in mean Cmax or AUC(0-12) between the two groups
on day 7 or on day 14, nor were there significant within-group differences on the two days. On day 14,
mean Cmax, AUC(0-12) and T(1/2) (measured on day 14 only) in group A were 10.15 mg/L, 107.32 mg x
h/L and 9.0 h, respectively. In group B, the values were 10.81 mg/L, 113.73 mg x h/L and 8.3 h,
respectively. The study drugs were well tolerated, and no clinically significant changes in vital signs or
laboratory test values were noted. We conclude that steady-state concentrations of trovafloxacin have
no clinically significant effect on the steady-state concentrations of theophylline within the therapeutic
range in healthy subjects..”
https://www.ncbi.nlm.nih.gov/pubmed/9089427 Phase I pilot study of the effects of trovafloxacin
(CP-99,219) on the pharmacokinetics of theophylline in healthy men. (1997). “This study examined
the effect of trovafloxacin (CP-99,219) on the pharmacokinetics and pharmacodynamics of a single dose
of theophylline, when administered to steady-state concentrations. Twelve healthy, nonsmoking male
volunteers participated. A 450-mg dose of theophylline was administered at 7:00 AM on day 1. On day 4,
volunteers received 300 mg of trovafloxacin (CP-99,219) daily in the morning for 7 days. The 450-mg
dose of theophylline was repeated on day 8 at 7:00 AM concomitantly with 300 mg of trovafloxacin.
Theophylline concentrations in plasma and trovafloxacin in serum were determined using reverse-phase
high-performance liquid chromatography. There was no significant difference between the geometric
mean values for Cmax of theophylline, 6.42 micrograms/mL and 6.00 micrograms mL on days 1 and 8,
respectively. A change (P = 0.032) in the geometric mean of the area under the concentration-time curve
extrapolated to infinity (AUC0-infinity) for theophylline was noted for trovafloxacin was administered.
Mean terminal phase elimination rate constants (Kes) were reduced (P = 0.001) by 13% after
administration of trovafloxacin from day 1 to day 8. In general, changes in theophylline clearance of less
than 20% are unlikely to be of clinical significance. In this study, oral administration of trovafloxacin in
References 16 website: JMR, http://fluoroquinolonethyroid.com
300 mg doses to achieve steady-state concentration resulted in an 8.4% increase in the extent of
systemic exposure (AUC0-infinity) to theophylline. Assuming that this AUC change is based on oral
clearance and not absorption, one would not expect to see clinically significant changes in the
pharmacokinetics of theophylline. No pharmacodynamic changes resulted from the pharmacokinetic
changes of theophylline.”
https://www.ncbi.nlm.nih.gov/pubmed/9023273 Aging and drug interactions. III. Individual and
combined effects of cimetidine and cimetidine and ciprofloxacin on theophylline metabolism in
healthy male and female nonsmokers. (1997). “The individual and combined effects of cimetidine and
ciprofloxacin on theophylline metabolism were examined in healthy young and elderly male and female
nonsmokers. Single-dose studies of theophylline pharmacokinetics were performed at base line and on
the fifth day of each of three treatment regimens consisting of 400 mg cimetidine every 12 hr, 500 mg
ciprofloxacin every 12 hr and the combination of cimetidine and ciprofloxacin. Base-line theophylline
plasma clearance and formation clearance of theophylline metabolites decreased with age in both
gender groups to a similar extent (20% less in elderly men than in young men; 24% less in elderly women
than in young women). Individually, cimetidine and ciprofloxacin produced proportionate declines in
plasma theophylline clearance that were similar among the four groups (range, 23.4-32.7% decrease).
The combined regimen yielded further impairment in theophylline elimination compared with each agent
alone (range, 35.9-42.6% decrease). Cimetidine was a nonselective inhibitor of theophylline metabolic
pathways in young men, but it exerted a greater inhibitory effect on N-demethylation pathways in the
other groups. Ciprofloxacin inhibited N-demethylations of theophylline to a greater extent than the
hydroxylation pathway. Coadministration of these two inhibitors further reduced the formation of
theophylline metabolites. The proportionate reduction in formation clearance of theophylline
metabolites was similar among the four groups. Thus, the response to inhibition of theophylline
metabolism by cimetidine and ciprofloxacin is not influenced by age or gender.”
https://www.ncbi.nlm.nih.gov/pubmed/9433655 Theophylline and warfarin interaction studies with
grepafloxacin. (1997). “Two phase I trials, each involving 16 healthy adult volunteers, were performed
to investigate possible interactions between grepafloxacin and theophylline or warfarin. In the
theophylline study, grepafloxacin 600 mg was administered once daily for 10 days to 12 volunteers who
were receiving a maintenance dose of theophylline. This dose of theophylline was designed to produce
mean serum theophylline concentrations of 7.5 mg/L; 4 volunteers received theophylline plus placebo.
Pharmacokinetic parameters of theophylline were determined before grepafloxacin treatment and on
day 10 of grepafloxacin or placebo administration. Peak theophylline concentrations and the area under
the concentration-time curve increased significantly during grepafloxacin treatment, and apparent total
clearance of theophylline was reduced by approximately 50%. No changes were observed in the placebo
group and theophylline appeared to have no effect on the pharmacokinetics of grepafloxacin. In the
warfarin study, grepafloxacin 600 mg was given once daily for 14 days to volunteers receiving a
maintenance dose of warfarin. Warfarin was discontinued during the last 4 days of grepafloxacin
administration. The pharmacodynamics of warfarin did not change after administration of grepafloxacin.
Similarly, warfarin had no significant effect on the pharmacokinetics of grepafloxacin. We conclude that
during treatment with grepafloxacin maintenance, doses of theophylline should be reduced by 50%, and
References 16 website: JMR, http://fluoroquinolonethyroid.com
we recommend that serum concentrations of theophylline be monitored during treatment with
grepafloxacin. However, no dose adjustment is necessary for grepafloxacin when it is coadministered
with theophylline, and dose adjustment does not seem to be required in concomitant treatment with
grepafloxacin and warfarin.”
https://www.ncbi.nlm.nih.gov/pubmed/9736563 Absence of effect of rufloxacin on theophylline
pharmacokinetics in steady state. (1997). “Several quinolone antibacterial agents are known to inhibit
the metabolism of theophylline, with the potential to cause adverse events due to raised theophylline
concentrations during coadministration. A randomized crossover study was therefore conducted with 12
healthy male volunteers (ages, 23 to 34 years; body weight, 64 to 101 kg) to evaluate a possible
interaction between rufloxacin and theophylline. Both drugs were administered at steady state. . . . In
conclusion, rufloxacin did not affect theophylline pharmacokinetics at steady state. Therefore,
therapeutic coadministration of rufloxacin and theophylline is not expected to cause an increased
incidence of theophylline-related adverse events.”
https://www.ncbi.nlm.nih.gov/pubmed/9688062 Development of a new quantitative approach for
the isobolographic assessment of the convulsant interaction between pefloxacin and theophylline in
rats. (1997). “A new mathematical approach was developed to quantify convulsant interaction
between pefloxacin and theophylline in rats.”
https://www.ncbi.nlm.nih.gov/pubmed/9661016 Effects of DU-6859a, a new quinolone antimicrobial,
on theophylline metabolism in in vitro and in vivo studies. (1998). “In vitro and in vivo studies were
conducted to investigate the drug interaction between a new quinolone antimicrobial, DU-6859a, and
theophylline (TP). The effect of DU-6859a on TP metabolism was evaluated in vitro by measuring the rate
of TP metabolite formation by using human liver microsomes. DU-6859a inhibited the metabolism of TP,
especially the formation of 1-methylxanthine, in vitro, but to a lesser extent than other drugs that are
known to interact with TP. TP was administered alone (200 mg twice a day [b.i.d.] for 9 days) or in
combination with DU-6859a (50 or 100 mg b.i.d. for 5 days) to six healthy subjects. DU-6859a
administered at a dose of 50 mg resulted in no changes in serum TP concentrations, and slight increases
in serum TP concentrations were observed at a dose of 100 mg. Moreover, the administration of 100 mg
of DU-6859a resulted in decreases in all urinary TP metabolites, with significant differences. It appears
that although DU-6859a has a weak inhibitory effect on TP metabolism in vitro, its concomitant use with
TP at clinical dosage levels does not cause any adverse effects, showing only a slight increase in blood TP
concentrations and a decrease in urinary metabolites.”
http://ndt.oxfordjournals.org/content/13/4/1006.long Interactions with ciprofloxacin and
erythromycin leading to aminophylline toxicity. (1998). “A number of commonly prescribed drugs are
known to interact with the metabolism of aminophylline, many to increase plasma levels to within the
toxic range. Two cases of serious aminophylline toxicity are described, one fatal, which were precipitated
by the co-prescription of antibiotics. The management of aminophylline overdose is discussed, with
particular respect to the input from the renal and intensive care units.”
References 16 website: JMR, http://fluoroquinolonethyroid.com
https://www.ncbi.nlm.nih.gov/pubmed/12212302 Effect of enoxacin on pharmacokinetics of
theophylline in rats. (1999). “In order to obtain an experimental evidence for Enoxacin(ENX) to be
correctly used in clinical treatment, we studied the effect of ENX on the pharmacokinetic parameters of
theophylline(TP). A single oral dose of TP 20 mg/kg was given to rats and ENX(300 mg/kg, 450 mg/kg)
was co-administered orally three times to those rats. The plasma concentrations of TP were determined
by HPLC after TP was administered 1, 2, 3, 5, 7, 12 and 24 hrs. The results showed that TP was eliminated
by one compartment model. TP plasma concentrations and AUC were significantly increased. T1/2 beta
of TP was prolonged. The total clearance of TP was decreased when compared with the control. This
interaction was dose-dependent. It was concluded that the interaction between ENX and TP existed.
Concomitant use of ENX with TP should be avoided.”
https://www.ncbi.nlm.nih.gov/pubmed/10567778 Lack of effect of gemifloxacin on the steady-state
pharmacokinetics of theophylline in healthy volunteers. (1999). “In conclusion, theophylline and
gemifloxacin may be co-administered without any adjustment in theophylline dose.”
https://www.ncbi.nlm.nih.gov/pubmed/10382036 Pharmacokinetic interactions between
fluoroquinolones and methylxanthines. (1999).
https://www.ncbi.nlm.nih.gov/pubmed/10348779 Effect of HSR-903, a new fluoroquinolone, on the
concentration of theophylline in serum. (1999). “It has been reported that some quinolones, such as
enoxacin, lead to a marked increase in the concentration of theophylline in serum when they are
coadministered with theophylline, resulting in an increased risk of serious side effects (2, 8). It is,
therefore, clinically important to evaluate whether a quinolone increases the theophylline concentrations
in serum when it is administered concomitantly. Accordingly, we studied the effect of HSR-903 on the
concentrations of theophylline in serum in healthy male adult volunteers. . . . In conclusion, HSR-903
proved to slightly increase the theophylline concentrations in serum and was classified as a class II
quinolone, indicating that the theophylline concentration in serum should be monitored and the
theophylline dose should be adjusted if concomitant administration of theophylline and HSR-903 is
necessary.”
https://www.ncbi.nlm.nih.gov/pubmed/10096258 Interaction of pefloxacin and enoxacin with the
human cytochrome P450 enzyme CYP1A2. (1999). “Pefloxacin is reported to cause clinically relevant
inhibition of theophylline metabolism in vivo, but in vitro pefloxacin was only a weak inhibitor of the
cytochrome P450 CYP1A2, mediating main theophylline biotransformation. We therefore further
characterized the interaction between pefloxacin and CYP1A2. . . . Enoxacin and to a lesser extent
pefloxacin may cause clinically relevant interactions with further CYP1A2 substrates. The data suggest
that the pefloxacin interaction is partly mediated by its major metabolite norfloxacin.”
https://www.ncbi.nlm.nih.gov/pubmed/11806624 Safety and effectiveness of lomefloxacin in
patients with acute exacerbation of chronic bronchitis (AECB) chronically treated with oral
theophyllines. (2001). “Theophylline plasma levels determined in 103 patients at baseline, during and
at the end of the lomefloxacin treatment did not significantly change. We conclude that orally
administered lomefloxacin at standard recommended dosage is well tolerated and effective in elderly
References 16 website: JMR, http://fluoroquinolonethyroid.com
patients with AECB. No dose adjustment is required even when it is co-administered with
methylxanthines.”
https://www.ncbi.nlm.nih.gov/pubmed/11502527 Drug interactions with clinafloxacin. (2001).
“Concomitant administration of 200 or 400 mg of clinafloxacin reduces mean theophylline clearance by
approximately 50 and 70%, respectively, and reduces mean caffeine clearance by 84%.”
https://www.ncbi.nlm.nih.gov/pubmed/11408986 Effect of levofloxacin on theophylline clearance
during theophylline and clarithromycin combination therapy. (2001). “To report a case of decreased
theophylline clearance by the addition of levofloxacin in a patient receiving theophylline and
clarithromycin. A 59-year-old Japanese man who was receiving theophylline for emphysema
experienced stimulation, insomnia, and tachycardia due to theophylline toxicity after clarithromycin and
levofloxacin were added to the regimen. The combination of these agents resulted in a decrease in
theophylline clearance to approximately 60% of the initial value obtained while the patient was receiving
theophylline alone. The adverse effects disappeared after the dosage was reduced and the theophylline
serum concentration decreased; however, there was no change in theophylline clearance. After
discontinuation of levofloxacin, the theophylline serum concentration decreased, and theophylline
clearance returned to the initial level even though clarithromycin was continued. Levofloxacin is believed
not to influence the clearance of theophylline, although some new fluoroquinolones have been reported
to do so. This case indicates that levofloxacin and clarithromycin inhibited theophylline metabolic
pathways catalyzed by both CYP1A2 and CYP3A4 and resulted in the decrease in theophylline clearance.
The clearance of theophylline, therefore, is not influenced by clarithromycin alone. Careful monitoring is
required when levofloxacin is prescribed for patients who are taking clarithromycin with theophylline.”
https://www.ncbi.nlm.nih.gov/pubmed/11352444 Lack of pharmacokinetic interaction between
moxifloxacin, a novel 8-methoxyfluoroquinolone, and theophylline. (2001). “To investigate the
plasma and urinary pharmacokinetics, safety and tolerability of theophylline and moxifloxacin after
single and repeated doses of either compound administered alone or concomitantly with the other . . .
Moxifloxacin - in contrast to some older quinolones - does not interact pharmacokinetically with
theophylline, confirming preclinical results on the absence of cytochrome P450-mediated metabolism.”
https://www.ncbi.nlm.nih.gov/pubmed/11249829 Profile of moxifloxacin drug interactions.(2001).
“We report a brief description of the interaction profile of moxifloxacin. After oral administration, the
absorption of moxifloxacin was unaffected by ranitidine or by food consumption. Drugs containing
multivalent cations (e.g., Mg(++), Al(+++), and Fe(++), but not Ca(++)) impaired absorption. No clinically
relevant effect of moxifloxacin was seen on the pharmacokinetics of digoxin under combination steady
state conditions. Also, moxifloxacin did not affect the pharmacokinetics of theophylline or vice versa. This
result, plus further data proving lack of interaction with glyburide, warfarin, and oral contraceptives,
confirms the absence of metabolic interactions involving the cytochrome P-450 system, as previously
reported. Concomitant administration of probenecid did not affect the elimination of moxifloxacin.
Moxifloxacin thus has a unique drug interaction profile that is advantageous for its safe use.”
References 16 website: JMR, http://fluoroquinolonethyroid.com
https://www.ncbi.nlm.nih.gov/pubmed/11172695 Adverse reactions to fluoroquinolones. an
overview on mechanistic aspects. (2001). “This review focuses on the most recent research findings on
adverse reactions caused by quinolone antibiotics. Reactions of the gastrointestinal tract, the central
nervous system (CNS) and the skin are the most often observed adverse effects. Occasionally major
events such as phototoxicity, cardiotoxicity, arthropathy and tendinitis occur, leading to significant
tolerability problems. Over the years, several structure-activity and side-effect relationships have been
developed, in an effort to improve overall antimicrobial efficacy while reducing undesirable side-effects.
In this article we review the toxicity of fluoroquinolones, including the newer derivatives such
levofloxacin, sparfloxacin, graepafloxacin and the 7-azabicyclo derivatives, trovafloxacin and
moxifloxacin. A special attention is given to new data on mechanistic aspects, particularly those
regarding CNS effects. In recent years extensive in vivo and in vitro experiments have been performed in
an attempt to explain the neurotoxic effects of quinolones sometimes observed under therapeutic
conditions. However, the molecular target or receptor for such effects is still not exactly known. Several
mechanisms are thought to be responsible. The involvement of gamma-aminobutyric acid (GABA) and
excitatory amino acid (EAA) neurotransmission and the kinetics of quinolones distribution in brain tissue
are discussed. In addition, quinolones may interact with other drugs--theophylline and nonsteroidal
antiflammatory drugs (NSAID(s))--in producing CNS effects This article provides information about the
different mechanisms responsible of quinolones interaction with NSAID(s), methylxanthines, warfarin
and antiacids.”
https://www.ncbi.nlm.nih.gov/pubmed/11957117 Effect of pazufloxacin mesilate on the serum
concentration of theophylline. (2002). “We studied the effect of pazufloxacin mesilate (T-3762), a new
fluoroquinolone for intravenous administration, on the serum concentration of theophylline. Evaluation
consisted of comparisons of serum levels of theophylline (when it was given alone, as a control), with
serum levels of theophylline when T-3762 was given concomitantly. We measured the serum
concentrations and the urinary excretion rates of theophylline in healthy adult male volunteers who were
given theophylline for 5 days, followed by an i.v. infusion of T-3762. Blood and urine samples were
investigated on the third and fifth days after the concomitant dosing with T-3762, to compare the serum
levels and urinary concentrations of theophylline with the control values. We found that the serum
concentration and the urinary excretion rates of theophylline on the fifth day after concomitant dosing
with T-3762 were significantly increased compared with the levels when the volunteers had been given
theophylline alone.”
https://www.ncbi.nlm.nih.gov/pubmed/11883649 Ignoring pharmacokinetics may lead to isoboles
misinterpretation: illustration with the norfloxacin-theophylline convulsant interaction in rats. (2002).
“To investigate the norfloxacin-theophylline convulsant interaction in vivo, with an experimental
approach distinguishing between pharmacodynamics and pharmacokinetics contributions to the
observed effect. Male Sprague Dawley rats (n = 38) were infused each compound separately or in
different combination ratios. Infusion was maintained until the onset of maximal seizures. Cerebrospinal
fluid and plasma samples were collected for high performance liquid chromatography drug
determination. The nature and intensity of the pharmacodynamics interaction between drugs was
quantified with an isobolographic approach. Isobolograms suggested a relatively marked antagonism
References 16 website: JMR, http://fluoroquinolonethyroid.com
between norfloxacin and theophylline at the cerebrospinal fluid (previously shown to be part of the
biophase) and dose levels, but not at the plasma (free and total concentrations) levels. These apparent
discrepancies could be explained by nonlinear distribution or/and distribution desequilibrium
phenomenon. These findings showed that the quantitative isobolographic approach is appropriate to
assess the nature and intensity of the pharmacodynamic interaction between two drugs when data are
collected within the biophase, but that data interpretation outside the biophase can be risky due to
further pharmacokinetic complexities, in particular slow or/and nonlinear diffusion into the biophase.”
https://www.ncbi.nlm.nih.gov/pubmed/14567511 The effect of orally administered marbofloxacin on
the pharmacokinetics of theophylline. (2003). “As certain quinolones can interfere with the
metabolism of theophylline by competitive inhibition of the hepatic microsomal cytochrome P450
system, concomitant use of these drugs with theophylline could result in theophylline toxicity. This study
investigated the effect of orally administered marbofloxacin (2 and 5 mg/kg each once daily) on steady-
state plasma pharmacokinetics of theophylline after concomitant oral administration of a sustained
release theophylline preparation in dogs. Marbofloxacin caused some alteration in theophylline
metabolism. A 2 mg/kg dose of marbofloxacin did not clearly result in an increased area under the
concentration--time curve (AUC) or decreased clearance of theophylline, but at a dose of 5 mg/kg, a
statistically significant increase in AUC and a decrease in the total clearance of theophylline was found.
The 26% reduction in theophylline clearance is probably not clinically significant in healthy dogs, but for
dogs with renal impairment, there might be a chance of theophylline accumulation when dosed
concomitantly with marbofloxacin.”
https://www.ncbi.nlm.nih.gov/pubmed/?term=fluoroquinolones+caffeine+2003 Influence of sex on
the pharmacokinetic interaction of fleroxacin and ciprofloxacin with caffeine. (2003). “Previous
pharmacokinetic studies have shown that a number of the quinolones inhibit the metabolism of caffeine.
To evaluate the effect of sex on the interaction between two quinolones and caffeine. Multiple-dose,
double-blind, randomised, three-period crossover study. Twelve male and twelve female healthy
volunteers. Subjects received by mouth either fleroxacin 400 mg once daily and caffeine 100 mg three
times daily, ciprofloxacin 500 mg twice daily and caffeine 100 mg three times daily, or caffeine alone, for
3 days. Subjects received each of the other regimens after 12-day washout periods. Plasma and urine
concentrations were determined by validated high-performance liquid chromatography procedures and
the data were analysed by noncompartmental linear pharmacokinetic methods. Analysis of the
interaction by sex revealed that females showed a significant difference in caffeine pharmacokinetics in
the presence of ciprofloxacin (area under the concentration-time curve [AUC], peak plasma
concentration [C(max)], time to C(max) [t(max)] and apparent total body clearance [CL/F]) and fleroxacin
(AUC and CL/F) when compared with males. Significant differences between sexes were also observed in
the pharmacokinetics of ciprofloxacin (AUC, elimination rate constant [beta] and CL/F) and fleroxacin
(C(max) and beta) in the presence of caffeine. However, these significant differences disappeared when
AUC and C(max) were normalised to 70 kg bodyweight and CL/F was expressed as per kg bodyweight.
The effect of quinolones on the pharmacokinetics of caffeine, and the reciprocal effect, are different
between the sexes, due in part to different bodyweights.”
References 16 website: JMR, http://fluoroquinolonethyroid.com
https://www.ncbi.nlm.nih.gov/pubmed/18315779 Prevalence and predictors of potential drug-drug
interactions in Regione Emilia-Romagna, Italy. (2004). “Drug-drug interactions (DDIs) are preventable
medication errors associated with potentially serious adverse events and death . . . The most commonly
identified potentially interacting medication pairs were . . . theophylline/aminophylline and
ciprofloxacin/fluvoxamine. . . . Awareness of the most prevalent potential DDIs can help practitioners
prevent concomitant use of these dangerous medication combinations.”
https://www.ncbi.nlm.nih.gov/pubmed/15120718 A new respiratory fluoroquinolone, oral
gemifloxacin: a safety profile in context. (2004). “Adverse experiences (AEs) were observed in 44.7% of
gemifloxacin-treated patients and 47.5% of those who received comparator drugs.”
https://www.ncbi.nlm.nih.gov/pubmed/16455179 Complexation of norfloxacin with DNA in the
presence of caffeine. (2006). “1)H NMR spectroscopy (500 MHz) has been used to quantify the
complexation of the antibacterial antibiotic Norfloxacin (NOR) with DNA in the presence of Caffeine
(CAF). Separate studies have been made for the self-association of NOR, its hetero-association with CAF
and complexation with a model self-complementary DNA tetramer, 5'-d(TpGpCpA), in order to determine
the equilibrium parameters (induced chemical shifts, association constants, enthalpy and entropy) of the
two-component mixtures to aid the analysis of the three-component systems. Investigations of the self-
association of NOR and its hetero-association with CAF show that the aggregation of NOR molecules and
association with CAF in solution are driven by the stacking of aromatic chromophores. The complexation
of NOR with d(TGCA) has been analysed in terms of intercalation with the double-stranded form and
non-intercalative binding with the single-stranded form of DNA. Investigations of the competitive binding
of NOR and CAF with DNA show that at physiological concentrations of NOR (muM) and CAF (mM) the
dominant mechanism influencing the affinity of NOR with DNA is the displacement of bound NOR
molecules from DNA due to CAF-DNA complexation (i.e. the protector action of Caffeine).”
https://www.ncbi.nlm.nih.gov/pubmed/11592692 Hetero-association of caffeine and aromatic drugs
and their competitive binding with a DNA oligomer. (2001).
https://www.ncbi.nlm.nih.gov/pubmed/12084457 Self-association and unique DNA binding
properties of the anti-cancer agent TAS-103, a dual inhibitor of topoisomerases I and II. (2003).
https://www.ncbi.nlm.nih.gov/pubmed/16958785 Effect of ofloxacin on theophylline
pharmacokinetics at clinical dosage in dogs. (2006). “We examined the effects of ofloxacin (OFX) and
norfloxacin (NFX) on theophylline (TP) pharmacokinetics in dogs. OFX, as a noncompetitive and
mechanism-based inhibitor, and NFX, as a noncompetitive inhibitor, were orally administered (5 mg/kg)
for a single dose or multiple doses (12 hourly for 3 days). TP (5 mg/kg, i.v) was injected at 2 h after the
final dose of the fluoroquinolones (FQs). The same dose of TP was injected (i.v) 3 weeks before the start
of FQs treatment for control. Multiple doses of OFX significantly reduced the total body clearance (Cl(B))
of TP from 0.117 to 0.085 L/h/kg, although a single dose did not change it. Neither a single dose nor
multiple doses of NFX changed the TP pharmacokinetics. Plasma NFX concentrations increased after
multiple doses. Those of OFX also increased but were still two orders of magnitude below the K(i) for
noncompetitive inhibition of CYP1A in dogs. Time-dependent reduction in Cl(B) of TP suggests that
References 16 website: JMR, http://fluoroquinolonethyroid.com
mechanism-based inhibition of OFX was the major mode to decrease Cl(B) of TP. The mechanism-based
inhibition may result in substantial inhibition of CYP1A activities in clinical conditions.”
https://www.ncbi.nlm.nih.gov/pubmed/17516267 Visual hallucinations secondary to ciprofloxacin
treatment. (2007). “We describe a case of a 74-year-old woman who experienced visual hallucinations
after ciprofloxacin administration, when she was also taking theophylline, which resolved on cessation of
the ciprofloxacin. Although uncommon, all ophthalmologists should be aware of this potential problem
and be familiar with the adverse visual effects which may occur in patients simultaneously administered
quinolones and theophylline.”
https://www.ncbi.nlm.nih.gov/pubmed/17499154 The effect of chronic cadmium exposure on the
pharmacokinetics of theophylline and ciprofloxacin in rats. (2007). “Cadmium has been associated
with a number of adverse health effects but the impact of those effects on the pharmacokinetics of
different drugs has not been investigated. Therefore, the pharmacokinetics of theophylline and
ciprofloxacin were studied in cadmium-exposed and control rats (72 rats) following i.p. (6.5mg/kg) and
p.o. (10mg/kg) administration, respectively. The third-generation offsprings of rats exposed to 100
microg/mL of cadmium chloride in drinking water were used in this study . . . The current investigation
showed that chronic exposure to cadmium could have a very significant impact on altering the
pharmacokinetic parameters of various drugs. Therefore, in cadmium-polluted areas, dose adjustments
and drug monitoring, especially for drugs with a narrow therapeutic window, should be carried out.”
https://www.ncbi.nlm.nih.gov/pubmed/18543578 The influence of a newly developed quinolone:
antofloxacin, on CYP activity in rats. (2008). “To investigate a newly developed quinolone antibiotics,
the effect of antofloxacin hydrochloride on cytochrome P450 isoforms in rats was examined. A cocktail
approach was adopted. Theophylline (CYP1A2), midazolam (CYP3A), chlorzoxazone (CYP2E1),
dextromethorphan (CYP2D6), omeprazole (CYP2C19) and diclofenac (CYP2C9) were used as probes in the
study, and own control was adopted. In Protocol 1, probes were given to rats simultaneously by co-
administration with antofloxacin. The blood samples were obtained at designated time, and plasma
concentrations of the six probes were determined by LC-MS. The pharmacokinetic parameters were
calculated and compared in experimental groups in the absence and presence of antofloxacin. The result
showed that the presence of antofloxacin resulted in a significant increase in theophylline values of
AUC0-T and t1/2 (PAUC0-T = 0.0004 vs control Pt1/2 = 0.005 vs control), indicating that antofloxacin
delayed the clearance of theophylline. In Protocol 2, the probes' pharmacokinetic parameters were
compared in rats that received six probes before and after 14.5 days of consecutive administration of
antofloxacin (15 mg x kg(-1), given orally, twice daily). The results suggested that the AUC0-T of
chlorzoxazone was significantly decreased (P = 0.024), while that of dextromethorphan was significantly
increased (P = 0.027). In conclusion, these results indicated that antofloxacin may inhibit the activity of
CYP1A2, thus delaying the clearance of its substrates, and may have a slight inhibitory effect on CYP2D6
as well as an inductive effect on CYP2E1 following chronic administration.”
https://www.ncbi.nlm.nih.gov/pubmed/19707748 Seizures associated with levofloxacin: case
presentation and literature review. (2009). “Clinicians are exhorted to pay close attention when
References 16 website: JMR, http://fluoroquinolonethyroid.com
initiating levofloxacin therapy in patients taking medications with epileptogenic properties that are
CYP1A2 substrates.”
https://www.ncbi.nlm.nih.gov/pubmed/21234553 Ciprofloxacin-induced theophylline toxicity: a
population-based study. (2011). “Ciprofloxacin can inhibit the cytochrome P450-mediated metabolism
of theophylline, but the clinical relevance of this drug interaction is uncertain. We studied the risk of
theophylline toxicity associated with the co-prescription of ciprofloxacin and theophylline. . . . Treatment
with ciprofloxacin is associated with a significant increase in the risk of theophylline toxicity. When
clinically appropriate, alternate antibiotics should be considered for elderly patients receiving
theophylline.”
https://www.ncbi.nlm.nih.gov/pubmed/20580800 Effects of fluoroquinolones on CYP4501A and 3A in
male broilers. (2011). “The inhibitory effects of fluoroquinolones on the enzyme activity, protein levels
and mRNA expression of liver cytochrome P450 (CYP) 1A and 3A were investigated in male broiler chicks.
Enrofloxacin (20 mg/kg), sarafloxacin (8 mg/kg) and marbofloxacin (5.5 mg/kg) were administrated in
drinking water for 7 consecutive days. A cocktail of the probe drugs caffeine and dapsone was used to
determine CYP1A and 3A activity. Western blot analysis and real-time PCR were used to determine the
effects on protein levels of CYP1A and 3A, and on CYP1A4, 1A5, 3A37 mRNA levels. Enrofloxacin
increased the half-life of elimination for both caffeine and dapsone, and decreased expression of CYP1A
and 3A protein. Marbofloxacin decreased the metabolism of caffeine and expression of CYP1A protein.
However, no change in mRNA expression was observed for any treatment group. This suggested that
high doses of enrofloxacin and marbofloxacin, but not sarafloxacin, inhibit CYP in chick liver raising the
possibility of drug-drug interaction when using these compounds.”
https://www.ncbi.nlm.nih.gov/pubmed/?term=fluoroquinolone+theophylline+2010 Comparative use
of isolated hepatocytes and hepatic microsomes for cytochrome P450 inhibition studies: transporter-
enzyme interplay. (2010). “Accurate assignment of the concentration of victim drug/inhibitor available
at the enzyme active site, both in vivo and within an in vitro incubation, is an essential requirement in
rationalizing and predicting drug-drug interactions. Inhibitor accumulation within the liver, whether as a
result of active transport processes or intracellular binding, may best be accounted for using hepatocytes
rather than hepatic microsomes to estimate in vitro inhibitory potency. The aims of this study were to
compare K(i) values determined in rat liver microsomes and freshly isolated rat hepatocytes of four
cytochrome P450 (P450) inhibitors (clarithromycin, enoxacin, nelfinavir, and saquinavir) with known
hepatic transporter involvement and a range of uptake (cell/medium concentration ratios 20-3000) and
clearance (10-1200 μl/min/10(6) cells) properties. Inhibition studies were performed using two well
established P450 probe substrates (theophylline and midazolam). Comparison of unbound K(i) values
showed marked differences between the two in vitro systems for inhibition of metabolism. In two cases
(clarithromycin and enoxacin, both low-clearance drugs), inhibitory potency in hepatocytes markedly
exceeded that in microsomes (10- to 20-fold), and this result was consistent with their high cell/medium
concentration ratios. For nelfinavir and saquinavir (high-clearance, extensively metabolized drugs), the
opposite trend was seen in the K(i) values: despite very high cell/medium concentration ratios, stronger
inhibition was evident within microsomal preparations. Hence, the consequences of hepatic
accumulation resulting from uptake transporters vary according to the clearance of the inhibitor. This
References 16 website: JMR, http://fluoroquinolonethyroid.com
study demonstrates that transporter-enzyme interplay can result in differences in inhibitory potency
between microsomes and hepatocytes and hence drug-drug interaction predictions that are not always
intuitive.”
https://www.ncbi.nlm.nih.gov/pubmed/21978534 Simultaneous analysis of fluoroquinolones and
xanthine derivatives in serum by molecularly imprinted matrix solid-phase dispersion coupled with
liquid chromatography. (2011).
https://www.ncbi.nlm.nih.gov/pubmed/21882652 Effect of caffeine, norfloxacin and nimesulide on
heartbeat and VEGF expression of zebrafish larvae. (2011). “The use of pharmaceuticals during
pregnancy may causes abnormalities to the embryo. Sometime the drug also effect to the new born if the
drug transferred through lactation. We have used zebrafish model to see the effect of some
pharmaceuticals on embryos and larvae. Three drugs, caffeine, norfloxacin and nimesulide, were used for
this study to see the effect mainly the hatching rate of eggs, heart beat rate and the vascular endothelial
growth factor (VEGF) expression of the larvae. VEGF is an important signaling protein that involved
generating the new blood vessels during embryonic development. We have used 10, 20, 50, 100 microg
ml(-1) concentrations of all the drugs to see the effect. No significant mortality or malformations were
observed in zebrafish embryos. Hatching was stared from 60 hr. In control group, 91% hatching rate was
observed. Lowest hatching rate was observed using highest concentration of norfloxacin (100 microg
ml(-1)) and nimesulide (100 microg ml(-1)) i.e. 55 and 56% respectively. In control group, 110 to 115
heart beat rate was counted per minute. Significantly higher heart beat was observed in caffeine treated
group which is 125 to 140 min(-1) Lower heart beat was noted in nimesulide treated group which is 100
min(-1). We have tried to observe the possible effect of VEGF of the larvae by these three drugs.
Expression of VEGF was very low in caffeine treated group. Almost no VGF expression was observe in 100
microg ml(-1) caffeine treated group. These studies suggest that there is a possibility that high dosage of
caffeine can harm the unborn baby or new born babies, if the mothers use caffeine.”
https://www.ncbi.nlm.nih.gov/pubmed/20662110 A simple chromatographic method for
determining norfloxacin and enoxacin in pharmacokinetic study assessing CYP1A2 inhibition. (2011).
https://www.ncbi.nlm.nih.gov/pubmed/21892200 Modulation of pharmacokinetics of theophylline
by antofloxacin, a novel 8-amino-fluoroquinolone, in humans. (2011). “The 5-day treatment with
antofloxacin significantly increased the area of the plasma concentration-time curve and peak plasma
concentration of theophylline, accompanied by a decrease in the excretion of theophylline metabolites.
On the contrary, theophylline did not affect the pharmacokinetics of antofloxacin. In vitro studies using
pooled human hepatic microsomes demonstrated that antofloxacin was a weak reversible and
mechanism-based inhibitor of CYP1A2. The clinical interaction between theophylline and antofloxacin
was further validated by the in vitro results. The results showed that antofloxacin increases the plasma
theophylline concentration, partly by acting as a mechanism-based inhibitor of CYP1A2. . . . In 1984,
Wijnands et al first reported severe clinical adverse effects with the concomitant use of TP and enoxacin,
and they found that co-administration of enoxacin markedly increased plasma TP concentrations11.
Consequently, a series of fluoroquinolones, including ciprofloxacin, tosufloxacin, clinafloxacin,
grepafloxacin, and pefloxacin, have been reported to interfere with TP metabolism by inhibiting CYP1A2
References 16 website: JMR, http://fluoroquinolonethyroid.com
activity. Therefore, it is important to evaluate the interaction between ATFX and TP to understand the
pharmacokinetics and safety of these drugs. . . . A recent report has demonstrated that treatment with
ciprofloxacin is associated with a significant increase in the risk of TP toxicity in elderly patients. Our
study confirmed the idea that the co-administration of ATFX increases the plasma levels of TP in young
populations. These results indicate that ATFX probably decreases TP clearance and increases the risk of
TP toxicity in elderly patients. Further studies are required to investigate the pharmacokinetic
interactions between ATFX and TP in elderly populations. Based on the results of our study, it was
concluded that ATFX appears to be a clinical mechanism-based inhibitor of CYP1A2. Co-administration of
ATFX may increase TP concentrations in plasma, which would raise the risk of TP toxicity in patients. We
suggest that when patients receiving TP require treatment with antibiotics, avoidance of ATFX may be
clinically appropriate. Alternatively, close monitoring for TP concentrations and toxicity is warranted in
cases where the use of ATFX is required.”
https://www.ncbi.nlm.nih.gov/pubmed/21512260 A physiologically based pharmacokinetic model
characterizing mechanism-based inhibition of CYP1A2 for predicting theophylline/antofloxacin
interaction in both rats and humans. (2011). “Clinical studies have revealed that some
fluoroquinolones may cause severe adverse effects when co-administered with substrates of CYP1A2.
Our previous study showed antofloxacin (ATFX) was responsible for mechanism-based inhibition (MBI) of
the metabolism of phenacetin in rats. In the clinical setting, ATFX is likely to be administrated with
theophylline (TP), which is mainly metabolized by CYP1A2. The aim of the present study was to
investigate the possible mechanism of TP/ATFX interaction. In vitro studies showed that the inhibitory
effect of ATFX on the formation of three TP metabolites depended on NADPH, the pre-inhibition time,
and ATFX concentration, i.e., factors which characterize MBI. In vivo studies demonstrated that single-
dose ATFX (20 mg/kg) did not affect the pharmacokinetic behavior of TP, but multidose ATFX (20 mg/kg
b.i.d. for 7.5 days) significantly increased the AUC of TP, decreased the amount of three TP metabolites in
urine, and suppressed hepatic microsomal activity. A physiologically based pharmacokinetic (PBPK)
model characterizing MBI of the three TP metabolites was developed for predicting TP/ATFX interaction
in rats; this model was further extrapolated to humans. The predicted results were in good agreement
with observed data. All the results indicated that ATFX was responsible for MBI of the metabolism of TP,
and the PBPK model characterizing MBI may give good prediction of TP/ATFX interaction.”
https://www.ncbi.nlm.nih.gov/pubmed/22868963 Fluoroquinolones and theophylline can also lower
the seizure threshold. (2012).
https://www.ncbi.nlm.nih.gov/pubmed/26933518 Application of a Physiologically Based
Pharmacokinetic Model to Study Theophylline Metabolism and Its Interactions With Ciprofloxacin and
Caffeine. (2016). “Theophylline is a commonly used bronchodilator. However, due to its narrow
therapeutic range, moderate elevation of serum concentration can result in adverse drug reactions
(ADRs). ADRs occur because of interhuman pharmacokinetic variability and interactions with
coprescribed medicines. We developed a physiologically based pharmacokinetic (PBPK) model of
theophylline, caffeine, and ciprofloxacin metabolisms to: examine theophylline pharmacokinetic
variability, and predict population-level outcomes of drug-drug interactions (DDIs). A simulation-based
equation for personalized dosing of theophylline was derived. Simulations of DDI show that calculated
References 16 website: JMR, http://fluoroquinolonethyroid.com
personalized doses are safe even after cotreatment with large doses of strong inhibitors. Simulations of
adult populations indicate that the elderly are most susceptible to ADRs stemming from theophylline-
ciprofloxacin and theophylline-caffeine interactions. Females, especially Asians, due to their smaller
average size, are more susceptible to DDI-induced ADRs following typical dosing practices. Our
simulations also show that the higher adipose and lower muscle fractions in females significantly alter
the pharmacokinetics of theophylline or ciprofloxacin.”
https://www.ncbi.nlm.nih.gov/pubmed/26838075 Chronic administration of caderofloxacin, a new
fluoroquinolone, increases hepatic CYP2E1 expression and activity in rats. (2016). “Caderofloxacin is a
new fluoroquinolone that is under phase III clinical trials in China. Here we examined the effects of
caderofloxacin on rat hepatic cytochrome P450 (CYP450) isoforms as well as the potential of
caderofloxacin interacting with co-administered drugs . . . Fourteen-day administration of caderofloxacin
can induce the expression and activity of hepatic CYP2E1 in rats. When caderofloxacin is administered, a
potential drug-drug interaction mediated by CYP2E1 induction should be considered.”
https://www.ncbi.nlm.nih.gov/pubmed/25893329 Effects of norfloxacin on hepatic genes expression
of P450 isoforms (CYP1A and CYP3A), GST and P-glycoprotein (P-gp) in Swordtail fish (Xiphophorus
Helleri) (2015). “The presence of antibiotics including norfloxacin in the aquatic environment may cause
adverse effects in non-target organisms. But the toxic mechanisms of fluoroquinolone to fish species are
still not completely elucidated. Thus, it is essential to investigate the response of fish to the exposure of
fluoroquinolone at molecular or cellular level for better and earlier prediction of these environmental
pollutants toxicity. The sub-chronic toxic effects of norfloxacin (NOR) on swordtail fish (Xiphophoru s
helleri) were investigated by measuring mRNA expression of cytochrome P450 1A (CYP1A), cytochrome
P450 3A (CYP3A), glutathione S-transferase (GST) and P-glycoprotein (P-gp) and their corresponding
enzyme activities (including ethoxyresorufin O-deethylase, erythromycin N-demethylase and GST. Results
showed that NOR significantly affected the expression of CYP1A, CYP3A, GST and P-gp genes in
swordtails. The gene expressions were more responsive to NOR exposure than their corresponding
enzyme activities. Moreover, sexual differences were found in gene expression and enzyme activities of
swordtails exposed to NOR. Females displayed more dramatic changes than males. The study further
demonstrated that the combined biochemical and molecular parameters were considered as useful
biomarkers to improve our understanding of potential ecotoxicological risks of NOR exposure to aquatic
organisms.”
http://journal.waocp.org/article_31092_ed2aea50b610e26b2ea3a3d446d98584.pdf High Efficacy of
Levofloxacin-Dexlansoprazole-Based Quadruple Therapy as a First Line Treatment for Helicobacter
pylori Eradication in Thailand (2015). “During the endoscopy, 4 biopsy samples from gastric antrum
were obtained for rapid urease test, H. pylori culture and Epsilometer test (E-test) or
GenoType®HelicoDR, histological examination and CYP2C19 genotype. The results of CYP2C19 genotype
testing were expressed as: rapid metabolizer (RM), intermediate metabolizer (IM) or poor metabolizer
(PM). . . . The CYP2C19 genotype tests revealed 54.1% RM, 34.7% IM and 11.2% PM . . . Our study
supported this idea and also demonstrated high eradication rate (grade A) of H. pylori infection from 14-
day levofloxacin-dexlansoprazole quadruple therapy as a first line treatment regardless of CYP2C19
genotype PM.”
References 16 website: JMR, http://fluoroquinolonethyroid.com
https://www.ncbi.nlm.nih.gov/pubmed/24580816 A multi-biomarker assessment of single and
combined effects of norfloxacin and sulfamethoxazole on male goldfish (Carassius auratus)(2014). “In
the present study, the sublethal effects of norfloxacin alone and in combination with sulfamethoxazole in
goldfish (Carassius auratus) were investigated, the biomarkers including acetylcholinesterase (AChE) in
brain, 7-ethoxyresorufin O-deethylase (EROD), glutathione S-transferase (GST), and superoxides
dismutase (SOD) activities in liver, vitellogenin (Vtg) in serum and DNA damage in gonad were
determined after 1, 2, 4 and 7 days of exposure. Brain AChE activity was significantly inhibited by
norfloxacin (≥0.4 mg/L) after 4 and 7 days and the mixtures with sulfamethoxazole (≥0.24 mg/L) after 4
days of exposure, and significant concentration-response relationships were obtained. Liver EROD, GST
and SOD activities were significantly increased by the individual and mixed pharmaceuticals in most
cases and exhibited analogously bell-shaped concentration-response curves. Serum Vtg was increased by
the highest concentration of norfloxacin and two higher concentrations of the mixtures. Higher
concentrations of the test antibiotics induced significant DNA damage in a concentration- and time-
dependent manner. The results indicated that selected antibiotics possesses cytotoxic and genotoxic
potential against the non-target organism C. auratus.”
https://www.ncbi.nlm.nih.gov/pubmed/24717959 Evaluation of the best method to assess antibiotic
potentiation by phytochemicals against Staphylococcus aureus (2014). “The increasing occurrence of
bacterial resistance to antibiotics has now reached a critical level. Finding antibiotic coadjuvants capable
to inhibit the bacterial resistance mechanisms would be a valuable mid-term solution, until new classes
of antibiotics are discovered. Selected plant alkaloids were combined with 5 antibiotics against 10
Staphylococcus aureus strains, including strains expressing distinct efflux pumps and methicillin-resistant
S. aureus strains. The efficacy of each combination was assessed using the microdilution checkerboard,
time-kill, Etest, and disc diffusion methods. The cytotoxicity of the alkaloids was evaluated in a mouse
fibroblast cell line. Potentiation was obtained in 6% of all 190 combinations, especially with the
combination of: ciprofloxacin with reserpine (RES), pyrrolidine (PYR), and quinine (QUIN); tetracycline
with RES; and erythromycin with PYR. The highest cytotoxicity values were found for QUIN (half maximal
inhibitory concentration [IC50] = 25 ± 2.2 mg/L) and theophylline (IC50 = 100 ± 4.7 mg/L).” (My note:
From Wiki “Alkaloid”: theophylline is a purine-like alkaloid, a pseudoalkaloid – alkaloid-like compounds
that do not originate from amino acids ).
https://www.ncbi.nlm.nih.gov/pubmed/24555232 In vivo evaluation of the metabolic ratio of CYP2C9
and CYP1A2 drug markers after administration of afobazole in comparison to standard inducers and
inhibitors of cytochromes (2013). “The effect of subchronic peroral administration in effective doses of
afobazole (5 mg/kg), and cytochrome P450 inductors (rifampicin, 13.4 mg/kg; phenytoin, 10.4 mg/kg)
and inhibitors (fluconazole, 35.7 mg/kg; ciprofloxacin, 44.0 mg/kg) on the metabolic ratio (MR) of drugs-
markers of CYP2C9 and CYP1A2 activity was studied in rats. Afobazole did not change the MR of
compounds metabolized by the P450 isoforms studied. After peroral administration of standard P450
inductors and inhibitors, statistically significant bidirectional effects were identified, which demonstrated
the expedience of administering a complex of selected compounds, markers, and CYP2C9 and CYP1A2
activity modificators for comparative evaluation of the effects of new drugs in rats. It is recommended to
References 16 website: JMR, http://fluoroquinolonethyroid.com
evaluate the activity of CYP1A2 by determining the MR for one of two caffeine metabolites, paraxanthine
or theobromine, and the activity of CYP2C9 by determining the MR of metabolite Exp-3174 to losartan.”
https://www.ncbi.nlm.nih.gov/pubmed/23587793 Detection of norfloxacin and monitoring its effect
on caffeine catabolism in urine samples (2013). “A multi-walled carbon nano tube (MWCNT) modified
pyrolytic graphite (MPG) electrode is prepared and applied to detect norfloxacin (NFX) based on its
electrochemical reduction. The experimental parameters affecting the NFX determination were
optimized in terms of MWCNT amount, pH, reaction time, and square wave frequency. The dynamic
range for the NFX analysis ranged between 1.2 and 1000µM with a detection limit of 40.6±3.3nM. The
effect of NFX on the catabolism of caffeine has been studied by determining its concentration in the urine
samples after the prolonged administration of NFX using the MPG electrode. The results show that the
catabolism of caffeine is inhibited by ~65% after five days of NFX administration, consequently the
caffeine concentration in the urine sample is increased, which is reflected in terms of ~2.5 times increase
in the peak current of caffeine. The determinations of NFX and caffeine were selective and the method
was successfully applied in biological fluids and pharmaceutical tablets for the test compound analysis. In
future this method can be useful for the selective determination of NFX and studying its effect on caffeine
catabolism.”
https://www.ncbi.nlm.nih.gov/pubmed/24399735 Pharmacokinetics of sunitinib in combination with
fluoroquinolones in rabbit model (2013). “Fluoroquinolones are widely prescribed antibiotics.
Ciprofloxacin is a well-known inhibitor of cytochrome P450 CYP3A4 and causes numerous drug
interactions that are not found for levofloxacin and moxifloxacin. CYP3A4 is involved in the metabolism
of the new oral multikinase inhibitor sunitinib which is indicated for the treatment of gastrointestinal
stromal tumor (GIST) and advanced renal cell carcinoma (RCC). This study investigated the effects of
single intravenous dose of ciprofloxacin, levofloxacin or moxifloxacin on the pharmacokinetics of
sunitinib. . . . The study proved a significant effect of the coadministration of ciprofloxacin and
levofloxacin on the pharmacokinetics of sunitinib in rabbits. The influence of moxifloxacin on the
pharmacokinetics of sunitinib was insignificant. Therefore, this fluoroquinolone seems to be the most
appropriate in combination with this tyrosine kinase inhibitor.”
https://www.ncbi.nlm.nih.gov/pubmed/23356842 Effect of ciprofloxacin and grapefruit juice on oral
pharmacokinetics of riluzole in Wistar rats (2013). “The objective of this study was to explore potential
drug-drug/food interactions of ciprofloxacin and grapefruit juice, known hepatic cytochrome P450 (CYP)
1A2 inhibitors, on single-dose oral pharmacokinetics of riluzole, a substrate of CYP 1A2 enzymes.
Pharmacokinetic parameters of riluzole were determined in Wistar rats after single-dose co-
administration with ciprofloxacin and grapefruit juice. In-vitro metabolic inhibition studies using rat and
human liver microsomes and intestinal absorption studies of riluzole in a rat everted gut-sac model were
conducted to elucidate the mechanism of interaction. A validated HPLC method was employed to
quantify riluzole in the samples obtained in various studies. Co-administration of ciprofloxacin with
riluzole caused significant increase in systemic exposure of riluzole (area under the curve, maximum
plasma concentration and mean residence time were found to increase). Co-administration of grapefruit
juice with riluzole did not cause any significant difference in the pharmacokinetic parameters of riluzole.
In-vitro metabolism studies demonstrated significant inhibition of riluzole metabolism when it was co-
References 16 website: JMR, http://fluoroquinolonethyroid.com
incubated with ciprofloxacin or grapefruit juice. No significant change was observed in apparent
permeability of riluzole. Co-administration of ciprofloxacin with riluzole increases the systemic levels of
riluzole and thereby the oral pharmacokinetic properties of riluzole while co-administration of grapefruit
juice with riluzole has no significant effect.”
https://www.ncbi.nlm.nih.gov/pubmed/23073666 Effect of the fluoroquinolone antibacterial agent
DX-619 on the apparent formation and renal clearances of 6β-hydroxycortisol, an endogenous probe
for CYP3A4 inhibition, in healthy subjects (2013). “To examine the effect of the fluoroquinolone DX-
619 on CYP3A4 and urinary excretion of 6β-hydroxycortisol, an endogenous probe of hepatic CYP3A4
activity, in healthy subjects. The effect of DX-619 on CYP3A4 was examined in human liver microsomes.
The apparent formation and renal clearance of 6β-hydroxycortisol (CL(6β-OHF) and CL(renal,6β-OHF),
respectively) were determined in placebo- and DX-619-treated subjects. 6β-hydroxycortisol uptake was
determined in HEK293 cells expressing OAT1, OAT3, OCT2, MATE1, and MATE2-K. DX-619 was a
mechanism-based inhibitor of CYP3A4, with K(I) and k(inact) of 67.9 ± 7.3 μmol/l and 0.0730 ± 0.0033
min(-1), respectively. Pharmacokinetic simulation suggested in vivo relevance of CYP3A4 inhibition by
DX-619. CL(6β-OHF) and CL(renal,6β-OHF) were decreased 72% and 70%, respectively, on day 15 in DX-
619-treated group compared with placebo (P < 0.05). 6β-hydroxycortisol was a substrate of OAT3
(K(m) = 183 ± 25 μmol/l), OCT2, MATE1, and MATE2-K. Maximum unbound concentration of DX-619
(9.1 ± 0.4 μmol/l) was above K(i) of DX-619 for MATE1 (4.32 ± 0.79 μmol/l). DX-619 caused a moderate
inhibition of hepatic CYP3A4-mediated formation and significant inhibition of MATE-mediated efflux of
6β-hydroxycortisol into urine. Caution is needed in applying CL(6β-OHF) as an index of hepatic CYP3A4
activity without evaluating CL(renal,6β-OHF).”
Ibuprofen:
https://www.ncbi.nlm.nih.gov/pubmed/15289789 Interindividual variability in ibuprofen
pharmacokinetics is related to interaction of cytochrome P450 2C8 and 2C9 amino acid
polymorphisms. “Low ibuprofen clearance occurs in a substantial proportion of healthy subjects, is not
enantiospecific, and is strongly linked to CYP2C8 and CYP2C9 polymorphisms.”
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2778050/ Cytochrome P450 2C8 pharmacogenetics:
a review of clinical studies.
https://en.wikipedia.org/wiki/CYP2C9 Wiki: “CYP2C9 is an important cytochrome P450 enzyme with a
major role in the oxidation of both xenobiotic and endogenous compounds. CYP2C9 makes up about 18%
of the cytochrome P450 protein in liver microsomes (data only for antifungal). Some 100 therapeutic
drugs are metabolized by CYP2C9, including drugs with a narrow therapeutic index such as warfarin and
phenytoin and other routinely prescribed drugs such as acenocoumarol, tolbutamide, losartan, glipizide,
and some nonsteroidal anti-inflammatory drugs. By contrast, the known extrahepatic CYP2C9 often
metabolizes important endogenous compound such as 5-hydroxytryptamine and, owing to its
epoxygenase activity, various polyunsaturated fatty acids, converting these fatty acids to a wide range of
References 16 website: JMR, http://fluoroquinolonethyroid.com
biological active products.[5][6] In particular, CYP2C9 metabolizes arachidonic acid to the following
eicosatrienoic acid epoxide (termed EETs).”
Chlorpheniramine: CYP2D6
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1874352/ The roles of CYP2D6 and stereoselectivity in
the clinical pharmacokinetics of chlorpheniramine. “Stereoselective elimination of chlorpheniramine
occurs in humans, with the most pharmacologically active (S)-(+)-enantiomer cleared more slowly than
the (R)-(−)-enantiomer. CYP2D6 plays a role in the metabolism of chlorpheniramine in humans.”
http://www.tandfonline.com/doi/abs/10.3109/00498259109039454 Metabolism of chlorpheniramine
in rat and human by use of stable isotopes (1991). “1. The metabolism of chlorpheniramine (I) was
examined in vivo in rats and a human volunteer; in the rats a stable isotope was used. 2. In addition to
the unchanged drug (I) and the N-demethylated metabolites (II and III), nine further metabolites were
identified in rat urine, four of which were also found in human urine. Chlorpheniramine N-oxide (IV), 3-(p-
chlorophenyl)-3-(2-pyridyl)propanol (V), 3-(p-chlorophenyl)-3-(2-pyridyl)-N-acetylaminopropane (VII) and
3-(p-chlorophenyl)-3-(2-pyridyl)-propionic acid (XIII) were identified in rat and human urine. 3. The
hydroxylated metabolites of the pyridyl ring of the unchanged drug, II, V and VII, and the glucuronide of
XIII were identified only in rat urine. XIII was found in rat urine as long as 6 days after the last dose.”
https://www.ncbi.nlm.nih.gov/pubmed/9231341 Stereoselective N-demethylation of
chlorpheniramine by rat-liver microsomes and the involvement of cytochrome P450 isozymes (1997).
“Previous studies have suggested that degradation of the two stereoisomers of chlorpheniramine in the
liver might be catalysed by different types of cytochrome P450. Stereoselective N-demethylation of
chlorpheniramine and the involvement of cytochrome P450 (CYP) isozymes have, therefore, been
investigated in the liver microsomes of eight-week-old male rats . . . The difference between the intrinsic
clearance of the two enantiomers by N-demethylation was because of differences in affinity for the
catalysing enzyme. This is indicative of stereoselective involvement of the main enzyme concerned in the
N-demethylation of the enantiomers, considered to be CYP 2C11. Anti-CYP 2C11 also partially inhibited
the N-demethylation of racemic chlorpheniramine in rat-liver microsomes exposed to phenobarbitone
and 3-methylcholanthrene. That CYP 2B1 was involved in the N-demethylation of both enantiomers was
also supported by results from an experiment using phenobarbitone-inducible rat-liver microsomes.
CYP1A1 did not, however, catalyse the N-demethylation of either enantiomer. These results indicate that
N-demethylation of the S-(+)-enantiomer of chlorpheniramine occurs preferentially in the microsomes,
demonstrating the stereoselective contribution of CYP2C11. Immunoinhibition studies suggest,
moreover, that the N-demethylation of both chlorpheniramine enantiomers is catalysed by CYP2B1, but
not by CYP1A1.”
https://www.ncbi.nlm.nih.gov/pubmed/9616188 In vitro characterization of cytochrome P450 2D6
inhibition by classic histamine H1 receptor antagonists (1998). “Classic antihistamines, namely
References 16 website: JMR, http://fluoroquinolonethyroid.com
diphenhydramine, chlorpheniramine, clemastine, perphenazine, hydroxyzine, and tripelennamine, share
structural features with substrates and inhibitors of the polymorphic cytochrome P450 (CYP) isozyme
CYP2D6. Therefore, the current study was undertaken to characterize the in vitro inhibition of CYP2D6 by
these commonly used, histamine H1 receptor antagonists. . . . These data demonstrate that classic
histamine H1 receptor antagonists, available in over-the-counter preparations, inhibit CYP2D6 in vitro.
Furthermore, the CYP2D6-inhibitory concentrations of these antihistamines are in the range of their
expected hepatic blood concentrations, suggesting that, under specific circumstances, clinically relevant
interactions between classic antihistamines and CYP2D6 substrates might occur.”
Pseudoephedrine
http://en.cnki.com.cn/Article_en/CJFDTOTAL-BXYY201108045.htm Effect of pseudoephedrine and
ephedrine on the activities of cytochrome P450 enzymes in rat liver microsomes. (2011). “Objective:
To study the effect of ephedrine and pseudoephedrine on the activities of cytochrome P450
enzymes(CYP450s) in rat liver microsomes. Method: The probe substrate of CYP450 enzymes: diclofenac
for CYP2C6,omeprazole for CYP2C,phenacetin for CYPlA2,chlorzoxazone for CYP2E1,testosterone for
CYP3A,was individually co-incubated with different concentration of ephedrine and pseudoephedrine in
rat liver microsomes. Then the relative metabolic clearance rate(RMCR) of each probe substrate was
determined by HPLC method. Results: The IC50 values of pseudoephedrine for the activities of CYP1A1/2
and CYP2E1 were 54.0 and 206.7μmol/L respectively. Whereas at concentration up to 400μmol/L,
ephedrine promoted the RMCR of phenacetin and diclofenac up to 2.3-fold and 1.6-fold respectively.
Conclusion: Pseudoephedrine has inhibitory action on the activities of CYP1A1/2 and CYP2E1,whereas
ephedrine has induction on the activities o f CYP2C and CYP1A1/2 in some extent.”
Purines and Purine Metabolism
http://molecularautism.biomedcentral.com/articles/10.1186/s13229-016-0109-5 Urinary
metabolomics of young Italian autistic children supports abnormal tryptophan and purine
metabolism. “Urinary metabolites displaying the largest differences between young ASD and control
children belonged to the tryptophan and purine metabolic pathways. Also, vitamin B6, riboflavin,
phenylalanine-tyrosine-tryptophan biosynthesis, pantothenate and CoA, and pyrimidine metabolism
differed significantly. ASD children preferentially transform tryptophan into xanthurenic acid and
quinolinic acid (two catabolites of the kynurenine pathway), at the expense of kynurenic acid and
especially of melatonin. Also, the gut microbiome contributes to altered tryptophan metabolism, yielding
increased levels of indolyl 3-acetic acid and indolyl lactate.”
https://en.wikipedia.org/wiki/Xanthurenic_acid
https://en.wikipedia.org/wiki/Hypoxanthine
References 16 website: JMR, http://fluoroquinolonethyroid.com
https://en.wikipedia.org/wiki/Xanthosine
https://en.wikipedia.org/wiki/Inosine
https://en.wikipedia.org/wiki/Purinergic_receptor
https://en.wikipedia.org/wiki/Nucleotide_salvage A salvage pathway is a pathway in which nucleotides
(purine and pyrimidine) are synthesized from intermediates in the degradative pathway for nucleotides.
Salvage pathways are used to recover bases and nucleosides that are formed during degradation of RNA
and DNA. This is important in some organs because some tissues cannot undergo de novo synthesis.
The salvaged bases and nucleosides can then be converted back into nucleotides.
Phosphoribosyltransferases add activated ribose-5-phosphate (Phosphoribosyl pyrophosphate, PRPP) to
bases, creating nucleoside monophosphates. There are two types of phosphoribosyltransferases:
adenine phosphoribosyltransferase (APRT) and hypoxanthine-guanine phosphoribosyltransferase
(HGPRT). It is an important enzyme in Purine pathway metabolism.[1] It is also involved in Lesch-Nyhan
syndrome associated with a deficiency of HGPRT
https://en.wikipedia.org/wiki/Lesch%E2%80%93Nyhan_syndrome Lesch–Nyhan syndrome.
https://en.wikipedia.org/wiki/Hypoxanthine-guanine_phosphoribosyltransferase HPRT expression on
the mRNA and protein level is induced by hypoxia inducible factor 1 (HIF1A). HIF-1 is a transcription
factor that directs an array of cellular responses that are used for adaptation during oxygen deprivation.
This finding implies that HPRT is a critical pathway that helps preserve the cell's purine nucleotide
resources under hypoxic conditions as found in pathology such as myocardial ischemia.[9]
References 16 website: JMR, http://fluoroquinolonethyroid.com
https://wp.nyu.edu/biochemistry_2/wp-content/uploads/sites/1136/2015/04/Purine-Metabolism-de-
novo-synthesis-and-salvage-pathway-2015.pdf Purine Metabolism Info. Major site of purine synthesis
in liver. Protozoa: no de novo synthesis, must get purines from host.
http://onlinelibrary.wiley.com/doi/10.1111/j.1471-4159.2008.05275.x/full HIF-1 alpha is an essential
effector for purine nucleoside-mediated neuroprotection against hypoxia in PC12 cells and primary
cerebellar granule neurons. “Hypoxia-inducible factor-1 alpha (HIF-1α) and purine nucleosides
adenosine and inosine are critical mediators of physiological responses to acute and chronic hypoxia. The
specific aim of this paper was to evaluate the potential role of HIF-1α in purine-mediated
neuroprotection. We show that adenosine and inosine efficiently rescued clonal rat pheochromocytoma
(PC12) cells (up to 43.6%) as well as primary cerebellar granule neurons (up to 25.1%) from hypoxic
insult, and furthermore, that HIF-1α is critical for purine-mediated neuroprotection. Next, we studied
hypoxia or purine nucleoside increased nuclear accumulation of HIF-1α in PC12 cells. As a possible result
of increased protein stabilization or synthesis an up to 2.5-fold induction of HIF-1α accumulation was
detected. In cerebellar granule neurons, purine nucleosides induced an up to 3.1-fold HIF-1α
accumulation in cell lysates. Concomitant with these results, small interfering RNA-mediated reduction of
HIF-1α completely abolished adenosine- and inosine-mediated protection in PC12 cells and severely
hampered purine nucleoside-mediated protection in primary neurons (up to 94.2%). Data presented in
this paper thus clearly demonstrate that HIF-1α is a key regulator of purine nucleoside-mediated rescue
of hypoxic neuronal cells. . . . Adenosine is the final metabolite in the stepwise dephosphorylation of ATP
and it is produced and released in response to ischemia and hypoxia in the CNS. It acts as a powerful
endogenous neuroprotectant during ischemia-induced energy failure by decreasing neuronal
metabolism, increasing cerebral blood flow, and by playing a variety of different roles as an intercellular
messenger. These effects are mediated through the interaction of adenosine with specific receptors
(Rudolphi et al. 1992; Sweeney 1997; Kobayashi et al. 1998; von Lubitz 1999), and this stimulation was
hypothesized to result in an effective treatment for stroke (Dunwiddie and Masino 2001; review).
Likewise, the adenosine derivative inosine was shown to have protective effects against insults related to
ischemia and reperfusion (Shen et al. 2005), to induce neurite outgrowth (Benowitz et al. 1998), and to
stimulate the extension of new neuronal projections into denervated areas in adult rats with unilateral
cortical infarcts (Chen et al. 2002). Our own data showed that purine nucleosides protected neuronal
cells from rotenone-induced cell death (Bocklinger et al. 2004; Heftberger et al. 2005). The discovery that
purine nucleosides play a role in endogenous neuroprotection has given rise to extensive efforts towards
developing future ischemia/reperfusion drug therapies. To achieve such a goal, however, a complete
understanding of the intracellular signaling mechanisms involved in purine-mediated neuroprotection is
required. Hypoxia-inducible factor-1α (HIF-1α) is a transcription factor that plays an essential role in
cellular and systemic homeostatic responses to hypoxia (Semenza 2000). Under hypoxia, the HIF-1α
protein is stabilized and translocation into the nucleus is increased. In the nucleus, HIF-1α associates with
HIF-1β to form the active transcription factor complex. The target genes of the HIF-1 complex are
involved in energy metabolism and cell viability. The HIF-dependent hypoxic response pathway plays a
prominent role in mediating the consequences of many disease states, including cerebral ischemia (for
review, see Semenza 2000). Along these lines, it was recently demonstrated (Baranova et al. 2007) that
HIF-1-mediated responses have an overall beneficial role in the ischemic brain. . . . The aim of this study
References 16 website: JMR, http://fluoroquinolonethyroid.com
was to determine (i) whether adenosine and its derivative inosine might regulate the cellular response to
hypoxia in neuronal cells and (ii) whether HIF-1α might contribute to adenosine-mediated
neuroprotectionAs a consequence of acute reduction in oxygen tension we observed increased cell death
of PC12 cells and primary cerebellar granule neurons. To determine whether purine nucleosides may
attenuate hypoxic cell death, cells were exposed to hypoxia in the presence of adenosine and inosine. In
agreement with results by others (Huffaker et al. 1984; Braumann et al. 1986; Gysbers and Rathbone
1996; Kobayashi and Millhorn 1999; Muroi et al. 2004; Ribeiro 2005; Tomaselli et al. 2005b), the data
presented here demonstrate that adenosine and inosine efficiently rescue the viability of hypoxic PC12
cells and primary cerebellar granule neurons. Earlier data suggested that the effects of adenosine were
apparently the result of its conversion to inosine by adenosine deaminase (Haun et al. 1996). In contrast,
a more recent study (Benowitz et al. 1998) showed that the addition of adenosine induced goldfish
retinal ganglion cells to extend lengthy neurites and that these effects were highly specific and did not
reflect conversion of the nucleosides to their derivatives. The same authors also showed that the action
of inosine was not due to its hydrolysis to hypoxanthine, as hypoxanthine was inactive in retinal ganglion
cells. Along these lines, our previous results in primary neurons showed that the activity of adenosine is
not blocked by erythro-9-(2-hydroxy-3-nonyl)adenine (EHNA), an inhibitor of adenosine deaminase,
suggesting an independent effect of adenosine (Heftberger et al. 2005). Although adenosine is a full
agonist of all four human adenosine receptors, inosine may activate A1 but is apparently ineffective on
the two A2R (Fredholm et al. 2001a). This may explain the observation that inosine was less effective
than adenosine in this study at least in PC12 cells. On the other hand, Jin et al. (1997) showed that
inosine is able to bind and activate adenosine A3R, and Haskóet al. (2000) found that A1R- and A2R-
antagonists partially blocked the suppressive effect of inosine on proinflammatory cytokine production.
In addition to adenosine receptors, neurons have nucleoside transport systems that play an important
role in regulating the concentrations and effects of purine nucleosides (Benowitz et al. 1998; Heftberger
et al. 2005; and for a review, see: Rathbone et al. 1999). Along these lines other authors reported that
exogenously applied inosine acted directly on an intracellular target, which may coincide with a serine-
threonine kinase, protein kinase N (Greene and Tischler 1976; Volontéet al. 1989; Batistatou et al. 1992),
and is linked to the response elements of genes associated with axon growth, including growth
associated protein (GAP)-43, L1, and alpha-1 tubulin (Benowitz et al. 1998; Petrausch et al. 2000). There
is a strong link between adenosine and hypoxia-related signaling. The expression levels of adenosine and
adenosine receptors are regulated in conditions of cellular stress, and signal transduction increases via
one or more of the adenosine receptors. Hypoxia apparently induces a program that shifts the tissue
phenotype toward an increase in extracellular adenosine. In turn, adenosine receptor activation tends to
limit the potential damage incurred by hypoxia (for review, see Fredholm 2007). . . . Apart from
adenosine receptor-mediated signaling, a number of metabolic pathways have been identified that
regulate gene expression during hypoxia (Bickler and Donohoe 2002; Seta et al. 2002). Among these, the
activation of HIF-1 transcription factors is the best characterized. HIF-1 is considered one of the master
regulators that orchestrate physiological responses to acute and chronic hypoxia (Semenza 2000;
Baranova et al. 2007). Therefore, we studied HIF-1α modulation in hypoxia in PC12 cells as well as in
cerebellar granule cells. As a consequence of cellular exposure to reduced oxygen, we observed an
increased stability of HIF-1α protein in cellular extracts of PC12 cells as well as in primary cerebellar
granule neurons. In addition, our results suggested that hypoxia led to an increased nuclear
References 16 website: JMR, http://fluoroquinolonethyroid.com
accumulation of HIF-1α as result of possible increased stabilization or synthesis and an increased
transcriptional activity. Our data are consistent with results reported by others (Masuda et al. 1994;
Krieg et al. 1998; Ruscher et al. 1998) that showed hypoxia stimulated an increase in HIF-1 binding
activity in purified neurons and altered the regulation of HIF-1 transcriptional targets in neuronal cell
lines and glial cultures. We also tested the potential effect of purine nucleosides. Our results showed that
hypoxia-induced HIF-1α was significantly enhanced by purine nucleosides. Our data are consistent with
previous findings (De Ponti et al. 2007) that demonstrated that the activation of the A2AR by adenosine
treatment induced HIF-1 DNA-binding activity, nuclear accumulation, and transactivation capacity in
J774A.1 mouse macrophages. To further study the non-redundant role of HIF-1α in the rescue of hypoxic
PC12 cells and cerebellar granule neurons we employed a siRNA approach to specifically knockdown HIF-
1α expression. Following partial siRNA-mediated knockdown of the HIF-1α transcription factor, we
observed a significant increase in the hypoxia-induced cell death of PC12 cells and cerebellar granule
neurons. Compared with cultured PC12 cells, primary cerebellar granule neurons showed a higher
spontaneous loss of viability. Consequently, we observed that hypoxic insult led only to a further 1.5-fold
increase in neuronal cell death compared with the 3.3-fold increase in PC12 cell death. This fact may be
one of the reasons for the observation that the HIF siRNA knockdown had less striking effects on the cell
viability of primary neurons compared with PC12 cells. We found even more exciting the observation that
purine nucleoside-mediated rescue was completely abrogated upon siRNA-mediated knockdown of HIF-
1α. . . . The future challenge will be to link molecular/genetic events with physiological mechanisms.
Various authors have already published work along these lines. One group (De Ponti et al. 2007),
reported that HIF-1α activation induced by the A2A receptor-specific agonist CGS21680 required the
phosphoinositide-3 kinase and protein kinase C pathways, but was not mediated by changes in iron
levels. Another study (Sodhi et al. 2001) provided evidence that MAPK and phosphoinositide-3 kinase-Akt
pathways may interact synergistically in the activation of HIF-1α. A large literature exists on the role of
the HIF-1 transcription factor in the expression of genes, including erythropoietin, that enhance oxygen
delivery to tissues (Kallio et al. 1998; Semenza 1999). Hypoxia also increases the expression of genes
whose products facilitate alterations in metabolism that optimize cell function during hypoxia (for
review, see Bickler and Donohoe 2002). For example, hypoxic pre-conditioning, a treatment known to
protect the newborn rat brain against hypoxic–ischemic injury, markedly increased HIF-1α (Bergeron et
al. 1999). The unique feature of HIF-1α is the regulation of its concentration. During normoxia, HIF-1α is
rapidly degraded by the ubiquitin proteasome system, and exposure to hypoxic conditions prevents its
degradation (Semenza 2000). The amino-terminal half of each subunit contains basic helix-loop-helix and
Per-Arnt-Sim (PAS) motifs that are required for dimerization and DNA binding. The carboxyl-terminal half
of HIF-1α contains domains that mediate hypoxia-inducible nuclear localization, protein stabilization,
and transactivation (for review, see Semenza 2000). Among the potential mechanisms that might
regulate transactivation, phosphorylation seems to play an important role. Indeed, several studies
showed that phosphorylation via the MAPK is necessary for activation of HIF-1α transcriptional activity
but not for its stabilization in hypoxic conditions (Salceda and Caro 1997; Minet et al. 2000; Hur et al.
2001). Other studies (Conrad et al. 1999), suggested that hypoxia caused specific regulation of the stress
activated protein kinase (SAPK) and p38 MAPK or the p42/44 MAPK signaling pathways, depending on
the cell type. Despite these differences, HIF-1 is activated by hypoxia in all cell types (reviewed by Mottet
et al. 2003). . . . In conclusion, the data presented here showed that (i) adenosine and inosine, which
References 16 website: JMR, http://fluoroquinolonethyroid.com
have increasingly been recognized as powerful endogenous neuroprotectants, efficiently rescued hypoxic
PC12 cells and cerebellar granule neurons and (ii) HIF-1α plays a non-redundant role as a key regulator in
the purine nucleoside-mediated rescue of hypoxic neuronal cells.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4289108/ Genetic Variation in Melatonin Pathway
Enzymes in Children with Autism Spectrum Disorder and Comorbid Sleep Onset Delay. “ Sleep
disruption is common in individuals with autism spectrum disorder (ASD). Genes whose products regulate
endogenous melatonin modify sleep patterns and have been implicated in ASD. Genetic factors likely
contribute to comorbid expression of sleep disorders in ASD. We studied a clinically unique ASD
subgroup, consisting solely of children with comorbid expression of sleep onset delay. We evaluated
variation in two melatonin pathway genes, acetylserotonin O-methyltransferase (ASMT) and cytochrome
P450 1A2 (CYP1A2). We observed higher frequencies than currently reported (p < 0.04) for variants
evidenced to decrease ASMT expression and related to decreased CYP1A2 enzyme activity (p ≤ 0.0007).
We detected a relationship between genotypes in ASMT and CYP1A2 (r2 = 0.63). Our results indicate that
expression of sleep onset delay relates to melatonin pathway genes.” (Check out the genes again against
my data).
CYP1A2 polymorphisms in slow melatonin metabolisers: a possible relationship with autism spectrum
disorder? (Need to google link). There are wide interindividual differences (10- to 200-fold) in CYP1A2
activity (Gunes & Dahl 2008). Several reports indicate that single nucleotide polymorphisms (SNPs) in the
CYP1A2 gene are associated with increased inducibility, decreased activity or inducibility or even loss of
activity of the CYP1A2 enzyme as compared with the wild-type CYP1A2*1A (Nakajima et al. 1999; Sachse
et al. 1999; Chevalier et al. 2001; Zhou et al. 2009a,b, 2010).The (sub) variant alleles associated with
decreased or absent activity of CYP1A2 are *1C, *1K, *3, *4, *5, *6 and *7.The proportion of individuals
with the slow phenotype narrowly ranges from 12% to 14% (Butler et al. 1992; Nakajima et al. 1994), but
varies among ethnic populations (Zhou et al. 2010).The *1F variant was found in 31.8% of 495 healthy
Caucasian volunteers (Skarke et al. 2005). Caffeine clearance is considered as the gold standard for
assessment of CYP1A2 activity, because more than 90% of the primary metabolism of caffeine depends
on CYP1A2 (Härtter et al. 2006). However, as melatonin is metabolised more exclusively by CYP1A2,
melatonin has been proposed as an alternative probe drug to assess CYP1A2 activity (Härtter et al.
2001).
http://biorxiv.org/content/early/2016/04/02/046722 Low parental melatonin levels increases autism
spectrum disorder risk in children. “Background: Low melatonin levels are a frequent finding in autism
spectrum disorder (ASD) patients. Melatonin is also important for normal neurodevelopment and
embryonic growth. As a free radical scavenger and antioxidant melatonin is highly effective in protecting
DNA from oxidative damage. Melatonin deficiency, possibly due to low CYP1A2 activity, could be a major
factor, and well a common heritable variation. ASD is already present at birth. As the fetus does not
References 16 website: JMR, http://fluoroquinolonethyroid.com
produce melatonin, low maternal melatonin levels should be involved. Methods: We measured 6-
sulfatoxymelatonin in urine of mothers of a child with ASD that attended our sleep clinic for people with
an intellectual disability (ID), and asked for parental coffee consumption habits, as these are known to be
related to CYP1A2 activity. Results: 6-Sulfatoxymelatonin levels were significantly lower in mothers than
in controls (p = 0.005), as well as evening coffee consumption (p = 0.034). In mothers with a second child
with ASD and/or ID, 6-sulfatoxymelatonin levels were lower compared to mothers with one child with
ASD (p = 0.084), Conclusions: Low parental melatonin levels, likely caused by low CYP1A2 activity, seem
to be a major contributor to ASD and possibly ID etiology.”
http://phoenixrising.me/research-2/glutathione-depletionmethylation-blockades-in-chronic-fatigue-
syndrome/why-is-the-prevalence-of-chronic-fatigue-syndrome-higher-in-women-than-in-men
Plausible hypothesis involving CYP1A2.
http://molpharm.aspetjournals.org/content/79/3/549.full Organization of NADPH-Cytochrome P450
Reductase and CYP1A2 in the Endoplasmic Reticulum—Microdomain Localization Affects
Monooxygenase Function. http://www.medschool.lsuhsc.edu/pharmacology/reed.aspx “Cytochromes
P450 (P450) constitute a family of heme-containing enzymes that are important in oxidative metabolism
of a multitude of endogenous and exogenous compounds (Nelson, 2003). P450s catalyze these reactions
by interacting with their redox partner, NADPH-cytochrome P450 reductase (CPR) in a 1:1 molar ratio
(Miwa et al., 1979). During substrate metabolism, electrons are transferred from NADPH to CPR, which
can then transfer electrons to the P450 (Gigon et al., 1969). Although a 1:1 molar complex between CPR
and P450 is needed for metabolism, the concentration of P450 enzymes greatly outnumber the level of
CPR, approximately 20:1 in liver microsomes (Peterson et al., 1976). The subsaturating levels of CPR
create a situation in which a single CPR molecule must supply electrons to a number of P450 enzymes,
rendering metabolically silent those P450s that are unable to complex with CPR. Such a system must be
highly organized to maintain efficient substrate metabolism, and one potential means of organization is
through the lipid bilayer. The P450s, along with their redox partners, are embedded in the endoplasmic
reticulum (ER) membrane (Peterson et al., 1976), and it has been well established that phospholipid is a
required component of an active P450 system (Strobel et al., 1970). Most in vitro studies for the
reconstitution of P450 activities use dilauroylphosphatidylcholine as the lipid milieu, but other lipids have
been used for these systems, including phosphatidylcholine (PC), phosphatidylethanolamine,
phosphatidylserine, and phosphatidic acid (Ingelman-Sundberg et al., 1981; Kim et al., 2003; Cho et al.,
2008; Reed et al., 2008). The alteration of phospholipid components of reconstituted systems (RCS) can
lead to variations in the rate of substrate metabolism, P450 incorporation into the membrane, and
stability of the enzyme (Blanck et al., 1984; Ingelman-Sundberg et al., 1996; Reed et al., 2006; Jang et al.,
2010). Such differences attributable to lipid composition prompt questions as to how the P450 system is
organized in the ER lipid bilayer. Members of our laboratory have initiated studies to analyze and
characterize the lipid environment of ER and to determine whether the P450 system resides in discrete
lipid microdomains, which may influence CPR-P450 and P450-P450 interactions. Early structural
perceptions of the of lipid bilayer were established by the fluid mosaic model (Singer and Nicolson, 1972),
which described the bulk of the phospholipids as being organized discontinuously, a small fraction of the
lipid specifically interacting with integral proteins. Studies with the plasma and Golgi membranes have
References 16 website: JMR, http://fluoroquinolonethyroid.com
greatly enhanced our views on the organization of the lipid membrane, which has been proven to play a
fundamental role in protein-protein and protein-lipid interactions (Brown and London, 1998).
Sphingolipids and sterols create a liquid-ordered phase of the membrane as a result of their high melting
temperatures, and these domains are involved in the sorting, transmembrane signaling, and
transporting of lipids and proteins (Brown and London, 1998). These ordered lipid phases prevent the
domains from being solubilized by nonionic detergents (Brown and London, 1998), imparting the term
detergent-resistant membranes (DRMs). Such domains were initially characterized by their low density
and insolubility in ice-cold 1% Triton X-100 (Brown and London, 2000), but more recently, a number of
other nonionic detergents have been used including Brij 98. Relative to the plasma membrane, the roles
of lipid microdomains in the structure of the ER membrane and the function of ER-resident proteins has
not been fully investigated. This is probably because there are relatively low levels of sphingolipids and
cholesterol at the ER membrane (Glaumann and Dallner, 1968). These lipids are two components of the
classic DRM located in the plasma membrane (Pike, 2004). Lipid microdomains in the ER that are
analogous to those in the plasma membrane have been described (Bae et al., 2004; Pielsticker et al.,
2005; Browman et al., 2006; Hayashi and Fujimoto, 2010). Given the specificity of lipid effects on P450
activity (discussed above), it is possible that the function of these enzymes may be affected by lipid
microdomain formation in the ER (Bösterling et al., 1979). In this article, we demonstrate the existence of
lipid microdomains in the ER and the presence of the P450 system within these regions. . . . Lipid vesicles
were prepared using purified lipids to approximate the lipid composition found in the ER and DRM. CPR
and CYP1A2 were incorporated into these vesicles to assess the effect of lipid composition on substrate
metabolism and CPR-CYP1A2 binding affinity . . . Recent studies have characterized “lipid raft-like”
domains at the ER membrane (Pielsticker et al., 2005; Browman et al., 2006; Hayashi and Fujimoto,
2010), and a number of researchers have suggested that specific ER lipids may form organized domains
affecting P450 function (Stier and Sackmann, 1973; Kim et al., 2007; Jang et al., 2010). These studies
raise the following questions: 1) do the enzymes of the P450 system reside in organized raft-like
domains? and 2) does P450 localization in these membrane regions affect P450 function? To address
these questions, we attempted to isolate these organized domains from microsomal samples and
determine whether the components of the P450 system were localized to these regions. Highly organized
lipid domains display different solubility characteristics from disordered domains when treated with
nonionic detergents . . . Densitometric analysis of the blots showed that approximately 73% of CYP1A2
(Fig. 1C) and 68% of CPR (Fig. 1D) were found to reside in the DRM fractions. In contrast, only 33% of the
total protein was located in the buoyant DRM fractions. . . . Having demonstrated the presence of
CYP1A2 and CPR in DRM fractions using a typical Brij 98 treatment protocol, the next step was to
determine whether the lipid composition of these fractions possessed classic detergent-resistant
membrane characteristics. As mentioned previously, the classic detergent-resistant membranes found
within the plasma membrane and other intracellular organelles are enriched in cholesterol and
sphingolipids. Upon analysis of each fraction, cholesterol was found to be enriched in the DRM fractions
(Fig. 2). The lipid composition of the total microsomal membrane, DRM, and non-DRM fractions was then
analyzed by thin-layer chromatography. Analysis of the DRM fractions illustrated a significant
enrichment of sphingomyelin (Fig. 3), which made up approximately 12% of the lipid of these fractions, in
contrast to 4% in the total microsomal membrane and less than 1% in the non-DRM fractions. There
were significantly lower levels of phosphatidylcholine and phosphatidylinositol in the DRM fractions
References 16 website: JMR, http://fluoroquinolonethyroid.com
compared with the total microsomal membrane. Cholesterol accounted for approximately 23% of the
DRM fraction lipids. The level of this component is high in contrast to the 5 and 2% composition in the
total and non-DRM fractions, respectively. The lipid-to-protein ratio was roughly 3.7 times higher in the
DRM fraction compared with the non-DRM fractions (data not shown). It is noteworthy that this specific
lipid composition is similar to that of the DRMs found in the plasma membrane and other intracellular
organelles (Brown and London, 2000; Pike, 2004; Hayashi and Fujimoto, 2010). It should be noted that
although cholesterol content is highest in fraction 3 of the sucrose gradient (Fig. 2), the highest amounts
of CYP1A2 and CPR are present in fraction 4 (Fig. 1). These results demonstrate the heterogeneity in DRM
fractions and that not all cholesterol-containing DRMs contain CYP1A2 and CPR. Nonetheless, there are
significant quantities of cholesterol in the fractions exhibiting enrichment of CPR and CYP1A2 . . . There
was a significant shift of CYP1A2 and CPR into the more dense regions of the gradient after treatment
with MβC. Whereas intact DRM fractions contained more than 73% of microsomal CYP1A2 and 68% of
CPR, only 6% of CYP1A2 and 2.5% of CPR was detected in DRM fractions after MβC treatment and
detergent solubilization . . . It is noteworthy that when the cholesterol-depleted microsomes were
reconstituted with cholesterol by treatment with the MβC-cholesterol complex, both CYP1A2 and CPR
migrated back into the DRM fractions of the sucrose gradient. Cholesterol repletion also allowed for
partial recovery of activity in the microsomes for both substrates tested. Collectively, these results
demonstrate that cholesterol is an important structural component of the DRM and affects the catalytic
efficiency of microsomal substrate metabolism . . . To determine whether lipid composition affected
substrate binding, spectral substrate binding was examined in three different vesicle systems . . . These
results suggest that there is a differential sensitivity of CPR binding to CYP1A2 depending on the
substrate present. These results clearly demonstrate that the lipid components found in detergent-
resistant membranes stimulate CYP1A2 activities, primarily by increasing the efficiency of the CPR-
CYP1A2 complex . . . The study corroborates previous findings indicating that DRMs exist in the ER
membrane (Pielsticker et al., 2005; Browman et al., 2006; Hayashi and Fujimoto, 2010) and
demonstrates that CYP1A2 and CPR reside primarily in these domains. We then tested the effects of lipid
composition on CYP1A2 function by comparing its activity in lipid vesicles that were representative of the
total ER and ordered (detergent-resistant) lipid domains to that in standard phosphatidylcholine vesicles.
This is the first investigation to examine the effects of these specific lipid compositions on P450 activity
and its interaction with CPR with lipids at physiologically relevant concentrations. . . Plasma membrane
DRMs have been described as heterogeneous domains typically enriched in sterols and sphingomyelin
(Brown and London, 1998; Pike, 2004). In agreement with other reports, the current study illustrated that
the overall ER lipid composition was low in cholesterol and sphingomyelin (Glaumann and Dallner, 1968),
which may explain the small number of investigations attempting to characterize ER-DRMs. However, by
using a standard technique to isolate these domains from rabbit liver microsomes with Brij 98 at 37°C
(Drevot et al., 2002), detergent-resistant regions were found to be enriched in cholesterol and
sphingomyelin. There were major differences in the lipid composition of the total ER membrane
compared with the lipid composition in the DRM fractions. These results demonstrate lipid domain
formation within the ER bilayer. Lipid analysis demonstrated that ER microdomains could be isolated at
physiological temperatures and had a composition similar to DRMs found in the plasma membrane and
other intracellular organelles. CYP1A2 and CPR were found to be enriched in the DRM fractions after Brij
98 solubilization, in contrast to the total microsomal protein. Our data are consistent with a previous
References 16 website: JMR, http://fluoroquinolonethyroid.com
large proteomic study identifying 39 proteins including CYP1A2 and CPR in ER microdomains (Bae et al.,
2004). It is noteworthy that our results are in contrast to those found by Hayashi and Fujimoto (2010),
who reported that CPR did not reside in DRMs. This discrepancy can be explained by the difference in the
tissue source. Their experiments were done using Chinese hamster ovary cells. The ER of these cells has
different lipid and protein compositions, which could significantly affect the localization of individual
proteins. Our study further investigated the nature of the CYP1A2- and CPR-containing DRMs by
demonstrating that the domains were cholesterol-dependent. Cholesterol sequestration by MβC
rendered the DRMs sensitive to detergent treatment, which led to the solubilization of CYP1A2 and CPR.
Analogous to the plasma membrane, the cholesterol component seems necessary for the structural
integrity of these domains. These results are similar to those of other studies in which MβC-mediated
cholesterol depletion led to solubilization of proteins residing in ER-DRMs (Browman et al., 2006; Hayashi
and Fujimoto, 2010). It is noteworthy that when MβC-depleted microsomes were reconstituted with
cholesterol, both CYP1A2 and CPR migrated to the DRM fractions, and catalytic activities were restored .
. . Several conclusions can be drawn from the current study. First, detergent-resistant lipid microdomains
can be found in the endoplasmic reticulum and, similar to that found in the plasma membrane, the ER
DRMs are enriched with both sphingomyelin and cholesterol. Second, CYP1A2 and CPR are found to
preferentially localize to these resistant membranes, and the removal of cholesterol by treatment with
methyl-β-cyclodextrin leads to a significant shift of CYP1A2 and CPR out of the DRM fractions to more
dense regions of the gradient. Furthermore, the DRM phospholipids seem to modulate P450 function.
Reconstituted systems having phospholipid content similar to that found in the ER membrane cause
alterations in CYP1A2 metabolic activities. Although the Vmax values obtained from the CPR titration
curves were not significantly changed, there was a substantial decrease in the Kmapp for CPR compared
with phosphatidylcholine alone. It is noteworthy that elevation of sphingomyelin and cholesterol to levels
seen in detergent-resistant microdomains caused a further decrease in the Kmapp for CPR. All told, the
Kmapp for CPR in reconstituted systems having phospholipid content similar to that found in DRMs is
between 21 and 29 times smaller than that found in PC vesicles, suggesting that the unique lipid content
of these vesicles substantially increases CYP1A2-dependent metabolism by increasing the efficiency of
CPR-CYP1A2 interactions. These results demonstrate that lipid microdomains can have a significant
influence on the localization of proteins of the P450 electron transport chain and that residence in these
DRMs can have a significant influence on P450 function.”
https://en.wikipedia.org/wiki/Cytochrome_P450_reductase Cytochrome P450 reductase [3] (EC
1.6.2.4; also known as NADPH:ferrihemoprotein oxidoreductase, NADPH:hemoprotein oxidoreductase,
NADPH:P450 oxidoreductase, P450 reductase, POR, CPR, CYPOR) is a membrane-bound enzyme
required for electron transfer from NADPH to cytochrome P450 in the endoplasmic reticulum[4] of the
eukaryotic cell. Since all microsomal P450 enzymes require POR for catalysis, it is expected that
disruption of POR would have devastating consequences. The reduction of cytochrome P450 is not the
only physiological function of POR. The final step of heme oxidation by mammalian heme oxygenase
requires POR and O2.
http://www.jnsci.org/files/html/e125.htm Melatonin in Children with Autism Spectrum Disorders:
How Does the Evidence Fit Together? “In reference to defects in melatonin degradation, there are
References 16 website: JMR, http://fluoroquinolonethyroid.com
numerous polymorphisms located either within the CYP1A2 gene, or in intronic regions, that are reported
to influence subsequent enzymatic activity.[47-53] A potential relationship has also been implicated
between presence of predicted slow-metabolizing alleles in CYP1A2 and susceptibility to ASD with
comorbid sleep problem.[35, 36] Interestingly, all of the individuals included in the Braam et al., 2013
study (n=11) were diagnosed as slow melatonin metabolizers and it was observed for these children that
the efficacy of supplemental melatonin exhibited disappearing effectiveness over the course of 4-8
weeks. We also evaluated slow-metabolizing alleles in CYP1A2 and the relationship to expression of
sleep onset insomnia in a small population of children with ASD and comorbid sleep onset insomnia
(n=15).[40] While we were only able to evaluate a small sample of children, we observed increased
frequencies for variants in the CYP1A2 gene related to decreased enzyme activity (p≤0.0007). Some
patients evaluated in our genetic study were also included in the study of overnight endogenous and
pharmacokinetic melatonin profiles. There was no evidence indicating individuals with slow-metabolizing
alleles in the CYP1A2 gene were actually slow melatonin metabolizers (T1/2 > 2 hours).[30] We also did
not observe disappearing effectiveness of melatonin treatment in our patients over the course of 17
weeks. However, we observed that expression of insomnia in ASD, and response to supplemental
melatonin treatment, was potentially related to dysfunctional variation in both the ASMT and CYP1A2
melatonin pathway genes. A relationship was observed between genotypes at SNP rs6644635 in the 5’-
untranslated region of ASMT and genotypes at SNP rs2069514 (my note: not in 23andme data) in the
promoter region of CYP1A2 (r2=0.63). This implicates a potential mechanism connecting lower levels of
ASMT transcript production with reduced CYP1A2 metabolic activity in some children with ASD and
comorbid sleep onset insomnia;[40] the net result may be normal nocturnal blood melatonin levels in
these children. The Braam et al. study did not assess effects related to polymorphisms in the ASMT gene.
Therefore, it is possible the patients with a slow melatonin metabolism only had dysfunctional alleles in
CYP1A2 and not in ASMT. However, to fully understand this underlying relationship to the etiology of ASD
with comorbid sleep onset insomnia, it will be necessary to evaluate larger ASD datasets focusing on
children with comorbid sleep onset insomnia and incorporating assessment of melatonin
pharmacokinetic data.
http://www.popline.org/node/202892 The effect of oral contraceptives on the pharmacokinetics of
melatonin in healthy subjects with CYP1A2 g.-163C>A polymorphism. “The effect of oral contraceptives
(OCs) on melatonin metabolism was studied in 29 subjects genotyped for CYP1A2 SNP g.-163C>A
polymorphism. Plasma melatonin and 6-OH-melatonin concentrations were measured after a 6-mg dose
of melatonin using a validated liquid chromatography/mass spectrometry method. The mean melatonin
AUC and C(max) values were 4- to 5-fold higher in OC users than in non-OC users (P < .0001), whereas
the weight-adjusted clearance was significantly lower in OC users (P < .0001). No significant difference in
melatonin pharmacokinetics between the genotypes and no additional effect by the genotype on the OC-
induced increase in melatonin exposure were evident. Melatonin exposure had no significant effect on
the subjects' state of alertness. In conclusion, a significant inhibitory effect of OCs on the CYP1A2-
catalyzed melatonin metabolism was seen; thereby, OC use can alter CYP1A2-phenotyping results.”
http://www.ebmconsult.com/articles/pharmacogenetics-cyp1a2-genetic-polymorphisms-table Table of
CYP1A2 polymorphisms
References 16 website: JMR, http://fluoroquinolonethyroid.com
http://www.mayomedicallaboratories.com/test-catalog/Clinical+and+Interpretive/89401 Mayo Clinic
CYP1A2 Table for polymorphisms
http://molpharm.aspetjournals.org/content/64/3/659 Genetic Polymorphism of CYP1A2 in Ethiopians
Affecting Induction and Expression: Characterization of Novel Haplotypes with Single-Nucleotide
Polymorphisms in Intron 1. “We developed SNP-specific polymerase chain reaction-restriction
fragment length polymorphism genotyping and molecular haplotyping methods for the intron 1 SNPs,
and four different haplotypes were identified: CYP1A2*1A (wild-type for all SNPs), CYP1A2*1F (–164A),
CYP1A2*1J (–740G and –164A), and CYP1A2*1K (–730T, –740G, and –164A), having frequencies of 39.9,
49.6, 7.5, and 3.0%, respectively. The frequency of CYP1A2*1J and CYP1A2*1K among Saudi Arabians (n
= 136) was 5.9% and 3.6%, and among Spaniards (n = 117) 1.3% and 0.5%, respectively. Functional
significance of the different intron 1 haplotypes was analyzed. Subjects with CYP1A2*1K had significantly
decreased CYP1A2 activity in vivo, and reporter constructs with this haplotype had significantly less
inducibility with 2,3,7,8-tetrachlorodibenzo-p-dioxin in human B16A2 hepatoma cells. Electrophoretic
mobility shift assay using nuclear extracts from B16A2 cells revealed a specific DNA binding protein
complex to an Ets element. Efficient competition was obtained using oligonucleotide probes carrying the
wt sequence and Ets consensus probe, whereas competition was abolished using probes with the –
730C>T SNP alone or in combination with –740T>G (CYP1A2*1K). The results indicate a novel
polymorphism in intron 1 of importance for Ets-dependent CYP1A2 expression in vivo and inducibility of
the enzyme, which might be of critical importance for determination of interindividual differences in
drug metabolism and sensitivity to carcinogens activated by CYP1A2. CYP1A2, a hepatic enzyme
inducible by smoking, metabolizes various chemical procarcinogens, such as food-derived heterocyclic
and aromatic mutagens, N-heterocyclics found in tobacco smoke, and difuranocoumarins, to reactive
carcinogens (McManus et al., 1990). It is also involved in the metabolism of several drugs such as
paracetamol, theophylline, caffeine, and clozapine (Bertilsson et al., 1994). Endogenous substrates of
CYP1A2 include estradiol and uroporphyrinogen. The enzyme has a significant role in chemical
carcinogenesis (Eaton et al., 1995) and is induced by its substrates, and a polymorphism in its capacity to
activate procarcinogens has been indicated . . . . Several studies have indicated the presence of wide
interindividual and ethnic differences in CYP1A2 activity when caffeine has been used as a probe drug.
Striking differences (greater than 15-fold) in levels of CYP1A2 mRNA expression from human liver (Ikeya
et al., 1989) and polymorphic metabolism of procarcinogens by human liver microsomes have been
reported (Minchin et al., 1985). Unlike other drug-metabolizing cytochromes P450, such as CYP2D6 and
CYP2C19, no nucleotide differences that could clearly explain the phenotypic variability in CYP1A2 gene
expression or inducibility have been identified . . . In the present investigation we have evaluated
interindividual variability in CYP1A2 activity in an African population and compared the activity between
Ethiopians living in Sweden and Ethiopia to investigate any environmental influence. We have found
new CYP1A2 haplotypes with SNPs in intron 1, which affect binding of nuclear proteins and inducibility
in reporter gene systems, and correlate to the CYP1A2 activity monitored in vivo using caffeine as a
probe drug. . . . The only additional SNP in CYP1A2*1K, as compared with the others, is –730C>T, and,
thus, the presence of this SNP is apparently critical for a decreased CYP1A2 activity in vivo . . . However,
there was 40% less induction of cells transfected with CYP1A2*1K, and this difference was significant
compared with cells treated with CYP1A2*1A, *1F,or *1J (p < 0.01 using independent t test), indicating
References 16 website: JMR, http://fluoroquinolonethyroid.com
that the CYP1A2*1K haplotype is less inducible . . . The results indicate that polymorphism in intron 1 of
the CYP1A2 gene might be critical for CYP1A2 inducibility and that transcriptional factors of the Ets
family are of importance in this respect. By contrast, the data do not provide evidence for an important
influence of environmental factors different between Sweden and Ethiopia for the control of CYP1A2
expression, in contrast to what has been seen for CYP2D6. Three different SNPs were found in intron 1,
and we identified four haplotypes present in Ethiopians, of which two are novel, CYP1A2*1J and
CYP1A2*1K. Subjects with the CYP1A2*1K allele had significantly reduced CYP1A2 activity as compared
with those carrying CYP1A2*1A, CYP1A2*1F,or CYP1A2*1J. Thus, the –164C>A alone (CYP1A2*1F) or in
combination with –740T>G (CYP1A2*1J) has apparently no influence on CYP1A2 activity in vivo, in
accordance with other studies showing no significance of the –164 SNP on CYP1A2 activity . . . Thus, we
assume that environmental factors such as dietary habits have small effects on CYP1A2 activity and
cannot primarily explain interethnic differences in activity. This is in accordance with a recent study on
twins, which indicated that the CYP1A2 activity is mainly governed by genetic factors . . . Although
CYP1A2 is only involved in the metabolism of about 5% of commonly prescribed drugs, it apparently
participates in the metabolism of 75% of drugs associated with adverse drug reactions metabolized by
enzymes having variant alleles (Phillips et al., 2001). Interindividual differences in its activity might thus
be of substantial importance for the determination of the outcome of drug treatment, and knowledge
about the basis for such interindividual differences, both genetic and environmental, might be useful to
avoid adverse drug reactions. In combination with the well established role of CYP1A2 for the metabolic
activation of procarcinogens, the polymorphism here described in intron 1 might, thus, also be of critical
importance for determination of the individual's susceptibility to liver cancer risk following long-term
exposure to several dietary procarcinogens.”
https://www.ncbi.nlm.nih.gov/pubmed/16609368 Search for an association between the human
CYP1A2 genotype and CYP1A2 metabolic phenotype (2006) By same author above. “The genotype
responsible for more than 60-fold interindividual differences in human hepatic CYP1A2 constitutive
expression is not understood. Resequencing the human CYP1A1_CYP1A2 locus (39.6 kb) in five major
geographically isolated subgroups recently led to the identification of 85 single nucleotide
polymorphisms (SNPs), 57 of which were double-hit SNPs. Here, we attempted to correlate the CYP1A2
genotype with a metabolic phenotype. We chose 16 SNPs (all having a minor allele frequency > or =0.05
in Caucasians) to genotype 32 DNA samples (26 Caucasians, six Ethiopians) in which CYP1A2 metabolism
had previously been determined. From 280 subjects (five locations worldwide) that had been CYP1A2-
phenotyped, we genotyped the 10 highest, 14 lowest and eight intermediate DNA samples. Although no
SNP was significant (P<0.05), possibly due to the small sample size, we found a trend for several of the
six SNPs across the CYP1A2 linkage disequilibrium block associated with the trait. Five CYP1A2
haplotypes were inferred, two of which had not previously been reported; haplotype 1A2H10 showed the
greatest association with CYP1A2 activity. Regulatory sequences responsible for the large interindividual
differences in hepatic CYP1A2 gene basal expression might reside, in part, with some of these CYP1A2
SNPS but, in large part, might be located either cis (in nearby sequences not yet haplotyped) or trans in
that they are not linked to the gene. We conclude that no SNP or haplotype in the CYP1A2 gene has yet
been identified that can unequivocally be used to predict the metabolic phenotype in any individual
patient.”
References 16 website: JMR, http://fluoroquinolonethyroid.com
http://smpdb.ca/view/SMP00017 Vitamin B6 pathways, note important in aromatic and sphingolipid
https://www.ncbi.nlm.nih.gov/pubmed/15646820 Metabolism of 2-phenylethylamine to phenylacetic
acid, via the intermediate phenylacetaldehyde, by freshly prepared and cryopreserved guinea pig liver
slices. “BACKGROUND: 2-Phenylethylamine is an endogenous amine, which acts as a neuromodulator
of dopaminergic responses. Exogenous 2-phenylethylamine is found in certain foodstuffs and may cause
toxic side-effects in susceptible individuals. MATERIALS AND METHODS: The present investigation
examined the metabolism of 2-phenylethylamine to phenylacetic acid, via phenylacetaldehyde, in
freshly prepared and cryopreserved liver slices. Additionally, it compared the relative contribution of
aldehyde oxidase, xanthine oxidase and aldehyde dehydrogenase by using specific inhibitors for each
oxidizing enzyme. RESULTS: In freshly prepared and cryopreserved liver slices, phenylacetic acid was
the main metabolite of 2-phenylethalamine. In freshly prepared liver slices, phenylacetic acid was
completely inhibited by disulfiram (inhibitor of aldehyde dehydrogenase), whereas isovanillin (inhibitor
of aldehyde oxidase) inhibited acid formation to a lesser extent and allopurinol (inhibitor of xanthine
oxidase) had no effect. In cryopreserved liver slices, isovanillin inhibited phenylacetic acid by 85%,
whereas disulfiram inhibited acid formation to a lesser extent and allopurinol had no effect.
CONCLUSION: In liver slices, 2-phenylethylamine is rapidly oxidized to phenylacetic acid, via
phenylacetaldehyde, by aldehyde dehydrogenase and aldehyde oxidase with no contribution from
xanthine oxidase.
https://www.ncbi.nlm.nih.gov/pubmed/25776752 Molecular dissection of a Borrelia burgdorferi in
vivo essential purine transport system. “The Lyme disease spirochete Borrelia burgdorferi is dependent
on purine salvage from the host environment for survival. The genes bbb22 and bbb23 encode purine
permeases that are essential for B. burgdorferi mouse infectivity. We now demonstrate the unique
contributions of each of these genes to purine transport and murine infection. The affinities of
spirochetes carrying bbb22 alone for hypoxanthine and adenine were similar to those of spirochetes
carrying both genes. Spirochetes carrying bbb22 alone were able to achieve wild-type levels of adenine
saturation but not hypoxanthine saturation, suggesting that maximal hypoxanthine uptake requires the
presence of bbb23. Moreover, the purine transport activity conferred by bbb22 was dependent on an
additional distal transcriptional start site located within the bbb23 open reading frame. The initial rates
of uptake of hypoxanthine and adenine by spirochetes carrying bbb23 alone were below the level of
detection. However, these spirochetes demonstrated a measurable increase in hypoxanthine uptake over
a 30-min time course. Our findings indicate that bbb22-dependent adenine transport is essential for B.
burgdorferi survival in mice. The bbb23 gene was dispensable for B. burgdorferi mouse infectivity, yet its
presence was required along with that of bbb22 for B. burgdorferi to achieve maximal spirochete loads in
infected mouse tissues. These data demonstrate that both genes, bbb22 and bbb23, are critical for B.
burgdorferi to achieve wild-type infection of mice and that the differences in the capabilities of the two
transporters may reflect distinct purine salvage needs that the spirochete encounters throughout its
natural infectious cycle.”
References 16 website: JMR, http://fluoroquinolonethyroid.com
https://www.ncbi.nlm.nih.gov/pubmed/22710875 Borrelia burgdorferi harbors a transport system
essential for purine salvage and mammalian infection. “Borrelia burgdorferi is the tick-borne
bacterium that causes the multistage inflammatory disease Lyme disease. B. burgdorferi has a reduced
genome and lacks the enzymes required for de novo synthesis of purines for synthesis of RNA and DNA.
Therefore, this obligate pathogen is dependent upon the tick vector and mammalian host environments
for salvage of purine bases for nucleic acid biosynthesis. This pathway is vital for B. burgdorferi survival
throughout its infectious cycle, as key enzymes in the purine salvage pathway are essential for the ability
of the spirochete to infect mice and critical for spirochete replication in the tick. The transport of
preformed purines into the spirochete is the first step in the purine salvage pathway and may represent a
novel therapeutic target and/or means to deliver antispirochete molecules to the pathogen. However,
the transport systems critical for purine salvage by B. burgdorferi have yet to be identified. Herein, we
demonstrate that the genes bbb22 and bbb23, present on B. burgdorferi's essential plasmid circular
plasmid 26 (cp26), encode key purine transport proteins. BBB22 and/or BBB23 is essential for
hypoxanthine transport and contributes to the transport of adenine and guanine. Furthermore, B.
burgdorferi lacking bbb22-23 was noninfectious in mice up to a dose of 1 × 10(7) spirochetes. Together,
our data establish that bbb22-23 encode purine permeases critical for B. burgdorferi mammalian
infectivity, suggesting that this transport system may serve as a novel antimicrobial target for the
treatment of Lyme disease.”
https://www.ncbi.nlm.nih.gov/pubmed/19666713 GuaA and GuaB are essential for Borrelia
burgdorferi survival in the tick-mouse infection cycle. “Pathogens lacking the enzymatic pathways for
de novo purine biosynthesis are required to salvage purines and pyrimidines from the host environment
for synthesis of DNA and RNA. Two key enzymes in purine salvage pathways are IMP dehydrogenase
(GuaB) and GMP synthase (GuaA), encoded by the guaB and guaA genes, respectively. While these genes
are typically found on the chromosome in most bacterial pathogens, the guaAB operon of Borrelia
burgdorferi is present on plasmid cp26, which also harbors a number of genes critical for B. burgdorferi
viability. Using molecular genetics and an experimental model of the tick-mouse infection cycle, we
demonstrate that the enzymatic activities encoded by the guaAB operon are essential for B. burgdorferi
mouse infectivity and provide a growth advantage to spirochetes in the tick. These data indicate that the
GuaA and GuaB proteins are critical for the survival of B. burgdorferi in the infection cycle and highlight a
potential difference in the requirements for purine salvage in the disparate mammalian and tick
environments.”
https://www.ncbi.nlm.nih.gov/pubmed/25424653 Purine import into malaria parasites as a target for
antimalarial drug development. “Infection with Plasmodium species parasites causes malaria.
Plasmodium parasites are purine auxotrophs. In all life cycle stages, they require purines for RNA and
DNA synthesis and other cellular metabolic processes. Purines are imported from the host erythrocyte by
equilibrative nucleoside transporters (ENTs). They are processed via purine salvage pathway enzymes to
form the required purine nucleotides. The Plasmodium falciparum genome encodes four putative ENTs
(PfENT1-4). Genetic, biochemical, and physiologic evidence suggest that PfENT1 is the primary purine
transporter supplying the purine salvage pathway. Protein mass spectrometry shows that PfENT1 is
expressed in all parasite stages. PfENT1 knockout parasites are not viable in culture at purine
References 16 website: JMR, http://fluoroquinolonethyroid.com
concentrations found in human blood (<10 μM). Thus, PfENT1 is a potential target for novel antimalarial
drugs, but no PfENT1 inhibitors have been identified to test the hypothesis. Identifying inhibitors of
PfENT1 is an essential step to validate PfENT1 as a potential antimalarial drug target.”
http://jb.asm.org/content/195/19/4387.full Helicobacter pylori Salvages Purines from Extracellular
Host Cell DNA Utilizing the Outer Membrane-Associated Nuclease NucT. “Helicobacter pylori is a
bacterial pathogen that establishes life-long infections in humans, and its presence in the gastric
epithelium is strongly associated with gastritis, peptic ulcer disease, and gastric cancer. Having evolved
in this specific gastric niche for hundreds of thousands of years, this microbe has become dependent on
its human host. Bioinformatic analysis reveals that H. pylori has lost several genes involved in the de
novo synthesis of purine nucleotides, and without this pathway present, H. pylori must salvage purines
from its environment in order to grow. While the presence and abundance of free purines in various
mammalian tissues has been loosely quantified, the concentration of purines present within the gastric
mucosa remains unknown. There is evidence, however, that a significant amount of extracellular DNA is
present in the human gastric mucosal layer as a result of epithelial cell turnover, and this DNA has the
potential to serve as an adequate purine source for gastric purine auxotrophs
https://www.ncbi.nlm.nih.gov/pubmed/12735109 Intrinsic hepatic phenotype associated with the
Cyp1a2 gene as shown by cDNA expression microarray analysis of the knockout mouse. “Several
forms of cytochrome P450 (CYP) appear to metabolize principally pharmaceutical agents, as well as
other dietary and plant chemicals. Other CYP forms have major roles in steroid, sterol, and bile acid
metabolism. CYP1A2 expression is constitutively high in mouse liver and is well known for metabolizing
several drugs and many procarcinogens to reactive intermediates that can cause toxicity or cancer.
CYP1A2 is also known to carry out several endogenous functions such as uroporphyrinogen and
melatonin oxidation and the 2- and 4-hydroxylations of estradiol. We have used cDNA microarray
analysis of the untreated Cyp1a2(-/-) knockout mouse to search for changes in gene expression that
might indicate important intrinsic roles for this enzyme. For 15 of the up- or downregulated genes, these
increases or decreases were corroborated by reverse-transcription real-time polymerase chain reaction.
Other than upregulation of the Hprt gene (used in the selection procedure for disrupting the Cyp1a2
gene), we found several genes upregulated that are associated with cell-cycle regulation and lipid
metabolism. Besides Cyp1a2, the gene exhibiting the greatest downregulation was Igfbp1 (insulin-like
growth factor binding protein-1), showing only 12% expression of that in the Cyp1a2(+/+) wild-type liver.
Recurrent themes between both up- and downregulated genes include cell-cycle control, insulin action,
lipogenesis, and fatty acid and cholesterol biosynthetic pathways. Histologically, the Cyp1a2(-/-) mouse
exhibited an approximately 50% decrease in lipid stored in hepatocytes, and 50% increase in lipid present
in interstitial fat-storing cells compared with that in the Cyp1a2(+/+) wild-type. These data suggest that
the CYP1A2 enzyme might perform additional hepatic endogenous functions heretofore not
appreciated.”
https://www.ncbi.nlm.nih.gov/pubmed/12464254 Study of P450 function using gene knockout and
transgenic mice. “The xenobiotic-metabolizing P450s have been extensively studied for their ability to
metabolize endogenous and exogenous chemicals. The latter include drugs and dietary and
environmentally derived toxicants and carcinogens. These enzymes also metabolize endogenous steroids
References 16 website: JMR, http://fluoroquinolonethyroid.com
and fatty acids. P450s are thought to be required for efficient removal of most xenobiotics from the body
and to be responsible for the hazardous effects of toxicants and carcinogens based on their ability to
convert chemicals to electrophilic metabolites that can cause cellular damage and gene mutations. P450
catalytic activities have been extensively studied in vitro and in cell culture, yielding considerable
information on their mechanisms of catalysis, substrate specificities, and metabolic products. Targeted
gene disruption has been used to determine the roles of P450s in intact animals and their contributions
to the mechanisms of toxicity and carcinogenesis. The P450s chosen for study, CYP1A1, CYP1B1, CYP1A2,
and CYP2E1, are conserved in mammals and are known to metabolize most toxicants and chemical
carcinogens. Mice lacking expression of these enzymes do not differ from wild-type mice, indicating that
these P450s are not required for development and physiological homeostasis. However, the P450 null
mice have altered responses to the toxic and carcinogenic effects of chemicals as compared with wild-
type mice. These studies establish that P450s mediate the adverse effects of drugs and dietary,
environmental, and industrial chemicals and serve to validate molecular epidemiology studies that seek
to determine links between P450 polymorphisms and susceptibility to chemically associated diseases.
More recently, P450 humanized mice have been produced.”
https://www.ncbi.nlm.nih.gov/pubmed/15970798 Theophylline pharmacokinetics: comparison of
Cyp1a1(-/-) and Cyp1a2(-/-) knockout mice, humanized hCYP1A1_1A2 knock-in mice lacking either the
mouse Cyp1a1 or Cyp1a2 gene, and Cyp1(+/+) wild-type mice. “OBJECTIVES: Pharmacokinetics of
theophylline was investigated in Cyp1(+/+) wild-type mice, Cyp1a1(-/-) and Cyp1a2(-/-) knockout mice,
and humanized hCYP1A1_1A2 mice lacking either the mouse Cyp1a1 or Cyp1a2 gene. METHODS AND
RESULTS: Animals received a single dose of theophylline (8 mg/kg i.p.), either alone or pretreated with
2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD; 10 microg/kg i.p.) 24 h prior to theophylline. We found that
mouse or human CYP1A2 is the predominant enzyme for theophylline metabolism, the contribution of
mouse or human CYP1A1 to theophylline metabolism is negligible, and another TCDD-inducible enzyme
plays a minor role in 1-methyluric acid and 1,3-dimethyluric acid formation as well as enhanced
theophylline clearance from the body. The half-life of elimination from plasma was more than four times
longer in Cyp1a2(-/-) than Cyp1(+/+) mice and more than 10 times different after TCDD pretreatment. In
humanized hCYP1A1_1A2 mice lacking the mouse Cyp1a2 gene, the half-life of elimination from plasma
was two to three times longer than that in Cyp1(+/+) mice and four to five times different after TCDD
pretreatment. CONCLUSION: Replacement of mouse Cyp1a2 with a functional human CYP1A2 gene
restored the ability to metabolize theophylline, and the metabolism changed to a humanized profile (i.e.
3-methylxanthine formation, not seen in the wild-type mouse). TCDD-pretreated hCYP1A1_1A2 Cyp1a2(-
/-) mice exhibited enhanced theophylline metabolism and clearance, due to induction of the human
CYP1A2 enzyme. Comparing the hCYP1A1_1A2 Cyp1a2(-/-) and wild-type mice with published clinical
studies, we found theophylline clearance to be about 5 times and 12 times, respectively, greater than
that reported in humans.”
https://getd.libs.uga.edu/pdfs/miller_erica_f_201308_phd.pdf PURINE SALVAGE IN HELICOBACTER
PYLORI. “To fill this gap in knowledge, we asked whether H. pylori can carry out de novo purine
biosynthesis, and whether its purine salvage network is complete. Based on genomic data from the fully
sequenced H. pylori genomes, we combined mutant analysis with physiological studies to determine that
References 16 website: JMR, http://fluoroquinolonethyroid.com
H. pylori, by necessity, must acquire purines from its human host. Furthermore, we found the purine
salvage network to be complete, allowing this organism to use any single purine nucleobase or
nucleoside for growth.”
http://journal.frontiersin.org/article/10.3389/fpls.2014.00153/full Transport proteins of parasitic
protists and their role in nutrient salvage. “The loss of key biosynthetic pathways is a common feature
of important parasitic protists, making them heavily dependent on scavenging nutrients from their hosts.
This is often mediated by specialized transporter proteins that ensure the nutritional requirements of the
parasite are met. Over the past decade, the completion of several parasite genome projects has
facilitated the identification of parasite transporter proteins. This has been complemented by functional
characterization of individual transporters along with investigations into their importance for parasite
survival. In this review, we summarize the current knowledge on transporters from parasitic protists and
highlight commonalities and differences in the transporter repertoires of different parasitic species, with
particular focus on characterized transporters that act at the host-pathogen interface.”
https://repositorio-aberto.up.pt/bitstream/10216/69104/2/92437.pdf Macrophage nutriprive
antimicrobial mechanisms. “In addition to oxidative and antibiotic mechanisms of antimicrobial
activity, macrophages are able to deprive intracellular pathogens of required nutrients. Thus, microbial
killing may not rely only in the toxic environment the microbe reaches but also may result from the
scarcity of nutrients in the cellular compartment it occupies. Here, we analyze evidence for such
nutriprive (from the latin privare, to deprive of nutrients), antimicrobial mechanisms.”
http://erj.ersjournals.com/content/31/5/949 Extracellular purines are biomarkers of neutrophilic
airway inflammation.