Metabolism

•Chemical transformaion of xenobiotics

•Occurs in mostly in liver (enzymatic prosesses)

•Convertion into more hydrophil. subst. - excretion urine

•May convert pro-carciogenics into cytotox., muthagenic compounds

•Different persons may have differences in methabolism (genetic diff., physiol. factors)

•Methabolism of one xenobiotic may influence metab. of amother

Xenobiotics•Drugs•Other foreign non-essential compounds

Metabolism in non-hepatic tissue•Intestine mucosa•Kidney•Lung•Bacteria in GI-tract

First-pass metabolism:Xenobiotic metabolized before reachinggeneral circulation

Pathways of metabolism

Phase 1: Biotransformation

Attachment of new functional groups, transformation of exist. funct. groups

oxidation, reduction, hydroxylation, hydrolysis etc.

Phase 2: Conjugation.

Masking of an exist. funct. group by for instance

acetylation, glycosylation, attachment amino acid etc

More hydrophilic drug

Renal excretion

O OHHO

NCH3

Morphine

Demethylation

Phase 1 O OHHO

NH

Conjugationglucuronic acid

Phase 2 O OHO

NH

O OHCO2H

OHHO

Phase 1 react. not involving CYP450

microsome: Artefactual spherical particle, not present in the living cell, derived from pieces of the endoplasmic reticulum present in homogenates of tissues or cells: microsomes sediment from such homogenates when centrifuged at 100 000 g and higher: the microsomal fraction obtained in this way is often used as a source of mono-oxygenase enzymes.

Other microsomal enzymesAzoreductase

Nitroreductase

Flavinmonooxygenase-FMO (N and S-ox.)

Peroxidases

NN NH2

SO

OH2N

H2NNH2S

O

OH2N

Prontocil Sulfanilamide

R NO2 R NH2

Flavinmonooxygenase-FMOCont. FAD

N

N

N

NHH3C

H3C

O

O

H OHOHOHH

H

OPO3 2-

Flavin mononucleotide

FMN

N

HN

NH

NHH3C

H3C

O

O

H OHOHOHH

H

OPO3 2-

FMNH2

N

N

N

NHH3C

H3C

O

O

H OHOHOHH

H

O P OO

OH

O

OHO O

HO OH

N

N

N

N

NH2

FAD

N

HN

N

NHH3C

H3C

O

ORFADH2

Flavin adenine dinucleotide

N

N

N

NHH3C

H3C

O

O

H OHOHOHH

H

OH

Riboflavin(Vit B2)

N

N N

N

NH2

O

ORHO

OP

O

O

OH

P

OO

OHHO

N

O

HO

O

NH2

N

N N

N

NH2

O

ORHO

OP

O

O

OH

P

OO

OHHO

N

O

HO

O

NH2

NADH

H H

Nicotinamid adenine dinucleotide

NADR=H

R=Phosphate: NADP+, NADPH

N

N N

N

NH2

O

OHHO

HO

Adenine(Vit. B4)

N

CO2H

Nicotinic acid / Niacin(Vit. B3)

Flavinmonooxygenase-FMO

N

N

N

NHH3C

H3C

O

OR

H2O

N

HN

N

NHH3C

H3C

O

OR

OH

N

HN

N

NHH3C

H3C

O

OR

OOH

FAD

Substrate Substrate-O

N

HN

NH

NHH3C

H3C

O

OR

FADH2

O2

NADPH

NADP+

RO

OH

NuPeroxidePeracid

O Nu

N-oxideSulfoxide

+ ROH

•Amine: ox. to N-oxide / hydroxylamine

•Sulfide: ox to sulfoxide , furter to sulfone

•Thiol:

Ox of soft Nu

R-SH R-S-S-R R-S-S-R

O

Non-microsomal enzymes•Enzymes in mitokondria•Enzymes in soubile tissue fractions

R-OH

prim or sec.

Alchohol dehydrogenase(NAD cont.)

aldehyde / ketoneR

O

H

Aldehyde dehydrogenaseR

O

OH

Alcohol dehydrogenase Aldehyde dehydrogenaseCH3OH HCO2HCH2O

SlowEtOH cometitive substr.

rel. fast

Tox. effects:AcidosisBlindness

HN

NH

NH

HN

O

O

NH

Tetrahydrofolate

NH

O CO2H

CO2H

HN

NH

NH

HN

O

O

N

NH

O CO2H

CO2H

OH

HCO2H

Dietary folic acid

10-Formyl-THF dehydrogenase

CO2

Non-microsomal enzymes (Phase 1)

Molybdenum Hydroxylases•Aldehyde oxidase•Xantine oxidase•Xantine dehydrogenase

Xanthine oxidaseElectron transfer: FAD - Fe2S2ˇI - Fe2S2ˇII - Moco - Substrate

Active form

Cont. Mo in cat. siteCont FAD and 2 Fe/s clustersUse H2O not O2

•Aldehyde oxidase

R H

O

R OH

O

N

Aza heterocycle

N OH NH

O

N

N N

N

H2N

AcO

AcO

FamciclovirAntiviral (Herpes etc)Pro-drug

Aldehyde oxidaseEsterase / hydrolysis HN

N N

N

H2N

HO

HO

O

Penciclovir

•Xantine oxidase•Xantine dehydrogenase

(requires NAD+)

xanthine oxidoreductase

HN

N

O

NH

N

Hypoxanthine

HN

NH

O

NH

N

Xanthine

O

HN

NH

O

NH

HN

Uric acid

OO

HN

N

O

NH

N

Allopurinol

HN

NH

O

NH

N

AlloxanthineInhib. enzyme

O

Treatment of gout (podagra)

Non-microsomal enzymes (Phase 1)

Oxidative deamination of amines•Monoamine oxidase (MAO)•Diamine oxidase (DAO)

R-CH2-NH2 + O2 [R-CH=NH] R-CHO + NH4+

NH

NH2

HO

Serotonin5-Hydroksotryptamin (5-HT)

MAO

NH

O

HO

Serotonine: •Neurotransmittor; temp. control, mood•Depresion: Low serotonine activity•MAO Inhibitors - Older antidepresants(low selectivity)

N NH

O O

Cl

MoklobemidAurorix® Moklobemid®

Other MAO substrates:

HN

OH

HO

HOH

Noradrenaline

NH2HO

HODopamine

Not MAO substrates (subst at α-C):

NH2

(S)-amfetaminLow dopamine conc. ≈ Parkinston

Active transport re-uptake transmittor(not Acetylcholine)

Non-selective monoamine re-uptake inhib.Tricyclic antidepressants

SSRI (selective serotonine re-uptake inhib.)“Lykkepiller” Prozac etc (Fontex)

NH2HO

HO

NH2HO

HO

OH

DA NE

HO

NH

NH2

5-HTα

β

β-Arylaminer

Y

X

RZ

N

αβ

β-Arylam

≈ β-Arylamin

Stor gruppe / sterisk hindingHindrer reopptak

O

F3C

NHH2N

Non-microsomal enzymes (Phase 1)

Oxidative deamination of amines•Monoamine oxidase (MAO)•Diamine oxidase (DAO)

Oxidize diamines, histamine NH2

HN

N

MAO like enzymes in plants

N

N NH

N

HN

BAPCYtokinin (Plant growth hormone)

N

N NH

N

NH2

O

+N

N NH

N N

N NH

N N

N NH

N

CK analogs, Anders Bråthe

Non-microsomal enzymes (Phase 1)

Miscellaneous react.

ReductionsS S RR R-SH

R-SO-R R-S-R (i.e.DMSO)

R-CO-R R-CHOH-R

R-NO-R R-NH-R

R-CH=CH-R R-CH2-CH2-R

R-OH R-H

Ar-OH Ar-H

β-Oxidation

R-CH2-CH2-CO2H R-CH2-CH2-CO-S-CoA R-CO2H

+

CHa-CO-S-CoA

Acetyl-CoA

R-CO-S-CoA

N

N N

N

NH2

O

OHPO3

OP

OP

O

HN

O OO OOH

O

HN

S

O

O

Acetyl-CoA

Nu

Hydrolysis - Esterases

O

ORR'

O

NRR'

R''

O

OHR

Esters as pro-drugs

Pathways of metabolism

Phase 1: Biotransformation

Attachment of new functional groups, transformation of exist. funct. groups

oxidation, reduction, hydroxylation, hydrolysis etc.

Phase 2: Conjugation.

Masking of an exist. funct. group by for instance

acetylation, glycosylation, attachment amino acid etc

More hydrophilic drug

Renal excretion

O OHHO

NCH3

Morphine

Demethylation

Phase 1 O OHHO

NH

Conjugationglucuronic acid

Phase 2 O OHO

NH

O OHCO2H

OHHO

Phase 2: Conjugation

Most comp. excreted as cojugates, ionic, hydrophilic groups added,

most common glucuronation

•Glucuronic acid conjugation•Sulfate conjugation•Conjugation with amino acids•Acetylation•Glutathione conjugation•Methylation

Phase 2: Conjugation

•Glucuronic acid conjugation

Substrates:

•Alchohols

•Phenols

•Amines

•Sulfides

•Carboxylic acids

•1,3-Dicarbonyls

O

HO

OHOHOH

OH

Glucose

O

CO2H

OHOOH

OH

UDP-Glucuronate

P P O

HO OH

N

N

O

O

RXH

O

CO2H

OHOH

OH

XR

RXH: Xenobiotic / Phase 1 metabolite

O

CO2H

OHOH

OH

XR

Kidney Urive excretion

Bile (galle)

RXH

O

CO2H

OHOH

OH

XR

IntestineRXH

Poor reabsorb.

O

CO2H

OHOH

OH

XR

Reabsorb

Entro-hepatic recyclingImportant for many hormones etc

O

CO2H

OHOOH

OH

UDP-Glucuronate

P P Uridine

OH

O

CO2H

OHOH

OH

OR

O

R

O

Relatively labile

Hydrolysis

OH R

O

HNu Macromolecule

Nu MacromoleculeR

O

Altered protein (hapten)Unwanted immune responce / allergic react.

Acyl migr.

ex. NSAIDs

Ar-NH2

Phase 1Ar-NH-OH Ar-NH-OH-Glu

UrinepH<7

Ar-NH-OH

H2O

Ar-N

Nitrene(c.f. carbene)

Bladder cancer

Phase 2: Conjugation

•Sulfate conjugation: Phenols, (alcohols, N-compounds)

ATPO NPO

O

OH

S

O

O

O

HO3P OH

PAPS

N

N

N

NH2HO

OS

O

O

O

•Conjugation with amino acids (Most ofthen Gly): Carboxylic acids

R-CO2H

O

R SCoA

H2N CO2H O

R NH

CO2H

No tox. conjugates known

Phase 2: Conjugation •Acetylation: N-compounds

O

H3C SCoANH N

O

•Glutathione conjugation: Electrophilic species

HS NH

HN

O CO2H

O

NH2

CO2HR-X + S NH

HN

O CO2H

O

NH2

CO2H

R

Glutathione conjugate

S OH

HN

O

O

R

Mercapturic acid der.

•Alkylhalides•Epoxides•Michael acceptors etc

may otherwisealkylate biomolecules

Br

BrRSH

Br

S

S R

Nu(i.e. DNA)

HN

O

OH

Paracetamol

Phase 1CYP450

H2O

N

O

O

HS-R

O

HN

O

SRH

HN

O

OH

SR

H2N Liver Protein

Liver dammage

Phase 2: Conjugation •Methylation (O and N- compd)

Prod. may be more lipophilic

React. mainly aimed at converting endogenic compouds

O.Metylation by COMT (catecol O-methyl transferase)

ATPO N

HO OH

N

N

N

NH2HO

OH3C

SAM (S-adenocyl methionine)

SH3C

CO2HH2N

HO

HO

SAM may also methylate N-comp.

HO

HO

OH

NH2

Noradrenaline(Norepinephrine)

MAO

HO

HO

OH

CHOAldehyde Dehydrogenase

HO

HO

OH

CO2H

COMT

HO

H3CO

OH

NH2

COMT

HO

H3CO

OH

CO2HMAO Aldehyde

Dehydrogenase

OH

NH2

EphedrineAdrenerg agonist

Conjugation react, in plant metabolism

N

N NH

N

HN

t-ZeatinCytokinin (Plant growth hormone)

N

N NH

N

NH2

OH

MAO likeenzynme

Not reversible, permanent inactivation

N

N NH

N

HN

OGlu

N

N N

N

HN

OH

Inactive storage forms

(Glu = Glucose)

N

N N

N

HN

OH

NH2

CO2H

alanine