Journal Report Fructose Induced Hyperurecemia.converted

8/6/2019 Journal Report Fructose Induced Hyperurecemia.converted

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A causal role for uric acid in fructose-

induced metabolic syndrome

Takahiko Nakagawa,1 Hanbo Hu,1 Sergey Zharikov,1

Katherine R. Tuttle,

2

Robert A. Short,

2,3

OlenaGlushakova,1Xiaosen Ouyang,1 Daniel I. Feig,4

Edward R. Block,1Jaime Herrera-Acosta,5,JawaharlalM. Patel,1 and Richard J. Johnson1


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Objective:

y To be able to determine the effects of fructose indeveloping hypermetabolic syndrome.

y To be able to determine the treatments on how toreduce uric acid in fructose induced hypermetabolismand its effects.


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The worldwide epidemic of metabolic syndrome

correlates withan elevation in serum uric acid as wellas a marked increase in total fructose intake.

Fructose raises uric acid, and the latter inhibits

nitric oxide bioavailability. Because insulin requiresnitricoxide to stimulate glucose uptake.


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ME

TABOLIC SYNDROME

CONSISTS of a clusterof cardiovascular disease risk factors that includeobesity, glucose intolerance, hyperinsulinemia,dyslipidemia, and hypertension.

The epidemic correlates with pronouncedchangesin the environment, behavior, and lifestyle and isconsidered one of the main threats to human health

worldwide. Metabolicsyndrome confers a greater thanthreefold increased risk forcardiovascular mortality


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Definition of Terms:

Dyslipidemia: it is the elevation of plasma cholesterol,triglycerides (TGs), or both, or a low high densitylipoprotein level that contributes to the development

of atherosclerosis. Diagnosis is by measuring plasmalevels of total cholesterol, TGs, and individuallipoproteins. Dyslipidemias were traditionally classified by patterns of elevation in lipids andlipoproteins.

Glucose Intolerance: is a pre-diabetic state of dysglycemia, that is associated with insulin resistanceand increased risk of cardiovascular pathology.


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H

yperinsulinemia: is a condition in which there areexcess levels of circulating insulin in the blood.

Hypertension: is a chronic medical condition in whichthe systemic arterial blood pressure is elevated. It isthe opposite ofhypotension.

Allopurinol: is a drug used primarily to treathyperuricemia (excess uric acid in blood plasma) andits complications, Allopurinol is rapidly metabolizedby its target, xanthine oxidase, to its active metaboliteoxypurinol, which is also an inhibitor of xanthineoxidase.


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Benzobromarone: is a uricosuric agent used in thetreatment ofgout, especially when allopurinol, a first-line treatment, fails or produces intolerable adverseeffects. It is structurally related to the antiarrhythmicamiodarone.

Hyperuricemia: is a level ofuric acid in the blood thatis abnormally high. In humans, the upper end of thenormal range is 360 mol/L (6 mg/dL) for women and

400 mol/L (6.8 mg/dL) for men.[1]


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Oral Glucose Tolerance Test: The oral glucosetolerance test (OGTT) measures the body's abilityto use a type of sugar, called glucose, that is thebody's main source of energy. An OGTT can beused to diagnose prediabetes and diabetes. AnOGTT is most commonly done to check fordiabetes that occurs with pregnancy (gestationaldiabetes).


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Dextrose: The term dextrose is derived fromdextrorotatory glucose. Glucose is derived fromhexanal, a chain of six carbon atoms terminating withan aldehyde group. The other five carbon atoms eachbear alcohol groups. Glucose is called an aldohexose.

Fructose: Fructose, or fruit sugar, is a simplemonosaccharide found in many foods. It is one of thethree important dietary monosaccharides along withglucose and galactose. Fructose is a component of sucrose.


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Four sets of experiments were performed. First,

pair-feeding studies showed that fructose, and notdextrose, induced features (hyperinsulinemia,hypertriglyceridemia, and hyperuricemia) of metabolicsyndrome. Second, in rats receiving a high-fructosediet,

the lowering of uric acid with either allopurinol (axanthine oxidase inhibitor) or benzbromarone (auricosuric agent) wasable to prevent or reverse featuresof metabolic syndrome


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Uric acid dose dependently inhibited endothelialfunction as manifested by a reduced vasodilatoryresponse of aortic artery rings to acetylcholine. These

data provide the first evidence that uric acid may be acause of metabolic syndrome, possibly due to its abilityto inhibit endothelial function. Fructose may have amajor role in the epidemic of metabolic syndrome andobesity due to its ability to raise uricacid.


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One distinction between fructose and glucose isthat fructose raises serum uric acid. Elevated serumuric acid predicts the development of obesity andhypertension. This raised the possibility that uric acid

may have a pathogenetic role in metabolic syndrome.In the current study, we show that fructose-inducedmetabolic syndrome is partially prevented by loweringserumuric acid in the rat. The reduction of endothelial

nitric oxide (NO) bioavailability by uric acid may be amechanism for insulinresistance and hypertension.

y

.


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Methods:

Experiment I: treatment of fructose-induced hyperuricemia with allopurinol. Male Sprague-Dawley rats(150200 g) were housed in standard conditions and fed acontrol (n = 7) or 60% fructose diet (Harlan,Madison, WI,n = 14) for 10 wk. The control diet contained 46%

carbohydrate, which is mainly composed of starch, whereasthe fructose diet contained 60% fructose as thecarbohydrate. Thecaloric content of these diets are 3.1 and3.6 kcal/g, respectively. At 4 wk, blood samples wereobtained at 11 A M after 4 h of fasting. One-half of the

fructose-fed rats were administered allopurinol (150 mg/l inthe drinking water, Sigma, St. Louis, MO) for anadditional6 wk to lower serum uric acid. Fresh drinking watercontaining allopurinol was replaced every 2 days.


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Rats were divided into three groups: control,fructose, and fructose+allopurinol. At 10 wk, an oralglucose tolerance test (OGTT) was performed, in

which rats were fasted overnight (16 h) and thenadministered 1.5 g/kg of a 50% glucose solution by

gavage. Blood was sampled at 0, 30, 60, and 120 min forblood glucose and serum insulin measurement. Therats were then killed.


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Experiment II: prevention of fructose-inducedhyperuricemia with allopurinol. To assess the effect ofpreventing hyperuricemia during theperiod of thestudy, allopurinol was initiated on the day whenthefructose diet was given (from week 0 to week 8). Three

groups(control, fructose, and fructose+allopurinol; n= 8 each) weredesigned for this prevention study. Body

weight was measuredevery 2 wk. Food consumptionwas measured for 3 days at 8 wk.


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Experiment III: effect of lowering of uric acid by eitherallopurinol or benzbromarone on body weight and foodconsumption. In this experiment, the effect ofbenzbromarone, a uricosuricagent (150 mg/l in thedrinking water, Sigma), was also examinedto confirm

the effect of lowering of uric acid on body weightandfood intake. Fresh drinking water containingbenzbromaronewas replaced every 2 days. Threegroups (control, allopurinol, and benzbromarone; n =

8 each) were studied. All groups werefed with thecontrol diet for 8 wk. Body weight and theconsumptionof food were measured weekly for 8 wk.


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y Measurements. Systolic blood pressure was assessed asthe mean value of threeconsecutive measurementsobtained in the morning using a tail-cuffsphygmomanometer (Visitech BP2000, Visitech

Systems, Apex, NC). All animals were preconditionedfor blood pressure measurements1 wk before eachexperiment. Serum uric acid was measured bytheuricase method. Blood glucose was measured with the

ONETOUCH system (Johnson&Johnson,Milpitas,CA). Rat insulinwas measured byELISA (CrystalChem, Chicago, IL).


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The insulinsensitivity index was calculated usingthe formula ofMatsuda and DeFronzo [10,000/squareroot of (fasting glucose x fasting insulin) x (meanglucose x mean insulin during OGTT)], whichis highlycorrelated (r= 0.73, P< 0.0001) with the rateof whole

body glucose disposal during the euglycemic insulinclamp. Serum lipids were measured with anautoanalyzer (VETAce, Alfa Wassermann, WestCaldwell, NJ) or a Triglyceride-SLassay kit (Diagnostic

Chemicals, Charlottetown, PE, Canada).


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Experiment IV: comparison between 60% dextrose and 60%

fructose in development of metabolic syndrome and effect oflowering uric acid with benzbromarone. Rats were pair-fedwith a 60% dextrose diet or a 60% fructose diet for 4 wk,both of which are isocaloric. Because experimentIIshowed

that each rat normally eats 2530 g/day, weadministered 25g of the diet to each rat every day. At 4 wk, total food intakeper animal was calculated from the food left over. Totalfood intake is the subtraction of the leftover food from thetotal food administered (1,425 grat128 days1). In addition

to the above two groups, a thirdgroup of fructose-fed ratswas administered benzbromarone. Theirbody weight wasmeasured weekly. At 4 wk, after 5 h of fasting, insulin,triglyceride, and uric acid were measured.


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Result:Serum uric acid levels, systolic blood pressure, and fasting

insulin levels were elevated in fructose-fed rats compared withrats fed a control diet at 4 wk (Table 1). In addition, the body

weight of fructose-fed rats tended to increase comparedwith ratsfed a normal diet (Table 1). These data demonstrate that fructosefeeding induces early features of metabolic syndromein rats.

To examine the role of uric acid in this model, one-half of

the fructose-fed rats were treated with allopurinol (a xanthineoxidase inhibitor) for 6 additional wk. This treatment waseffectiveat lowering uric acid, whereas the fructose-fed rats thatdid not receive treatment continued to be hyperuricemic (Fig.1A). In addition, we examined the urinary excretion of uric acidin these animals to clarify the mechanisms of hyperuricemia infructose-fed rats. As shown in Fig. 1B, fructose-fed rats had alower urinary excretion of uric acid. Interestingly, allopurinolprevented the reduced excretion of uric acid in fructose-fedrats.


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Table 1. Experiment I: general characteristics of control and fructose

groups at 4 wkControl (n = 7) Fructose (n = 14)

y Initial body weight, g 19012 1880.1 NSy Body weight at 4 wk, g 35715 37522 P=0.05y Systolic BP at 4 wk, mmHg 1273 14815 P


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Fig. 1. Effects of allopurinol (AP)

treatment for hyperuricemia onmetabolic parameters in fructose-fed(Fr) rats. A: Fr rats are hyperuricemicat 9 wk, and this is prevented by AP(150 mg/l). *P < 0.01 vs. control. UA,uric acid. #P< 0.05 vs. Fr. B: Fr reduced

urinary excretion ofUA at 9 wk, andthis is prevented by AP. *P< 0.01 vs. Fr.#P < 0.05 vs. control. C: hypertensiondevelops in Fr rats, which issignificantly reduced by AP. Values are

means SD.*P< 0.01 vs. control.#

P


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y Fructose Fed Rats (after 4 weeks)

y Elevated serum uric acid levelsy Elevated systolic blood pressure

y Elevated fasting insulin

y Increased body weight

Generalization: fructose feeding induces early features ofmetabolic syndrome in rats.


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Fructose-fed rats treated with allopurinol showed animprovement in metabolic syndrome. Allopurinol significantly

reduced systolic blood pressure in fructose-fed rats (Fig. 1C),although pressures remained higher than that observed in controlrats. Fructose-fed rats also developed marked hypertriglyceridemiathat was abolished by allopurinol treatment (Fig. 1D). The reductionin serum uric acid correlated directly with the decrease in

triglyceride levels (Fig. 1E). Fructose-fed rats also showed anincrease in body weight compared with controls. Allopurinolprevented the increase in body weight, although this did not reachsignificance (522 57 g in fructose vs. 470 28 g in control and 474 37 g in fructose+allopurinol, P= not significant).

While no groups developed fasting or postprandialhyperglycemia (Fig. 2A), fructose-fed rats developed fastinghyperinsulinemia that was reversed with allopurinol (Fig. 2B).Postprandial hyperinsulinemia also occurred in fructose-fed ratsadministered an OGTT, and this was partially but significantly lower

in allopurinol-treated rats (Fig. 2B

), resulting in improved insulinsensitivity (Fig.2C).


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y fructose fed rats fructose fed rats controlwith alopurinol

insulin levels insulin levels ---------

decreased

prevented weight gain ----------

Hypertriglyceridemia


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We also examined the effectiveness of allopurinol inpreventingthe development of metabolic syndrome, as opposedto treating rats to inhibit its progression. Allopurinol was givensimultaneously with the fructose diet from the starting point toavoid fructose-induced hyperuricemia. As shown in Fig. 3A, theelevation of uric acid with the fructose diet was prevented over

the 6-wk period infructose-fed rats. Allopurinol-treated rats hadsignificantly lower fasting insulin levels compared with fructose-fed rats (Fig. 3B), and the development of hypertriglyceridemia

was completely prevented (Fig. 3D). In addition, while fructose-fed rats gained weight compared with control rats (456 24 vs.414 24 g, final weights in fructose vs. control, P < 0.01),

allopurinol-treated rats had lower weight gain (final weight 426 26 g, P< 0.05 vs. fructose-fed rats). At 8 wk, the total food intakeover 3 days in fructose-fed rats was slightly higher (92 2 g)compared with that of the fructose+allopurinol group (88 4 g),although this did not reach statistical significance


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Fructose Fed Rat with Allopurinol Treatment:y Fructose increases BP

yAllopurinol treatment decrease BP

y Fructose increases triglyceride level

y

Allopurinol treatment decreases triglyceride level inthe blood

y Fructose increases body weight

yAllopurinol treatment prevents increase in weight butnot significant

yAllopurinol treatment decreases uric acid level in theblood same with triglyceride level

yAllopurinol traetment improves insulin sensitivity.


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Fig. 3. Blocking of

hyperuricemia in Fr rats withAP prevents features ofmetabolic syndrome. A: AP(150 mg/l) prevented the riseinUA in Fr rats. P< 0.05 vs.control and Fr+AP. B: AP

treatment was associatedwith significantly lowerfasting insulin levelscompared with Fr rats at 8wk. C: AP also prevented theincrease in body weight

induced with fructose.Statistical analysis among 3groups was by ANOVA withBonferroni correction


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The observation that administration of allopurinol to

fructose-fed rats prevented obesity led to additional studies toensure that allopurinol did not have specific effects on food intakeor body weight. To address this possibility, allopurinol orbenzbromarone (a uricosuric agent) was administered to rats oncontrol diets for 8 wk. A third group received the control diet alone.

Total food consumption at 8 wk and final body weight were notdifferentamong the three groups (Table 2).

Finally, we compared the effects of the 60% dextrose and 60%fructose diets on the development of metabolic syndrome. In thisexperiment, food intake was controlled so that each groupreceived

the same intake of calories and had the same weight gain.Nevertheless, only the fructose-fed rats developed hyperuricemia,hypertriglyceridemia, and hyperinsulinemia (Table 3). Importantly,these effects observed in fructose-fed rats were significantlyimproved by lowering uric acid levels with benzbromarone, theuricosuric agent (Table 3).


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Table 2. Experiment III: effect of lowering uric acid on body

weight and food consumption for 8 wk

Control (n = 8) Allopurinol (n=8) Benzbromarone(n=8)

Initial body weight, g 1627 1643 1608Final body weight at 8 wk, g 46969 50437 46843

Total food intake for 8 wk, g 145268 1562118 149490

Uric acid at 8 wk, mg/dl 1.50.5 0.50.4 1.10.3

Values are means SD. n, No. of rats.


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In Vitro Studies

Endothelial dysfunction is common in metabolicsyndrome. It is known that impaired NO response toinsulin may be a mechanism for the development of

insulin resistance (36). Previously, uric acid has beenshown to potently reduce NO levels in cultured bovineendothelial cells (18). To further examine thisrelationship, we examined the acute effect of uric acid

on acetylcholine-inducedvasodilation of rat AA rings.As shown in Fig. 4, uric aciddose dependently blockedthe vasorelaxation of AA rings in response toacetylcholine.


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Vasorelaxation in Rat Aortic Artery

SegmentRat aortic artery (AA) segments (1- to 0.5-mm diameter x 3-to 4-mm length) were isolated from 2- to 3-mo-old rats andsuspended in individual organ chambers (Radnoti Four-UnitTissue Bath System) with 5 ml in Earl's solution, oxygenated with95% O2-5%CO2 at 37C. After 1-h equilibration of resting force of

1.5g, the vascular smooth muscle cell or endothelium integrityofthis AA segment was confirmed by monitoring 0.5 MU-46619(a thromboxae A2 mimetic, Sigma)-mediated AA contraction oracetylcholine (5 M)-mediated vasodilation, respectively. Afterbeing washed several times, the segments were incubated with

various concentrations of uric acid (015 mg/dl) in an organ bath

chamber for 30 min. Stable construction was induced by 0.5 M

U-46619 for 10 min before acetylcholine-induced vasorelaxation.The vascular tensions were continuously monitored with anisometric force transducer (Harvard Apparatus, Holliston,MA).To standardize the data, the U-46619-induced stable increase in

vascular tone was set as 100%.


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y Values are means SD. n, No. of rats.y Table 3. Experiment IV: effect of pair-feeding with 60% dextrose and 60%

fructose diets at 4 wk on development of metabolic syndrome and of

lowering uric acid with benzbromaroneDext 60% Fruc 60% Fruc 60% +Benzbromarone

y Initial body weight, g 1447 1445 1447y Final body weight at 4 wk, g 35314 36417 36020y Total food intake for 4 wk, g 70010 7096 69815y Uric acid at 4 wk, mg/dl 1.40.3 2.10.9* 1.10.4y Triglyceride at 4 wk, mg/dl 11228 4196 29386y Insulin at 4 wk, pmol/l 11243 20462 14742

Values are means SD. n, No. of rats.y * P< 0.05 vs. dextrose.y P< 0.01 vs. fructose.y P< 0.01 vs. dextrose.y P< 0.05 vs. fructose.


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Fig. 4. UA inhibits ACh-

mediated vasodilation inrat aortic artery segments.

ACh (5 M)-inducedvasorelaxation was

assessed in the presence ofvarious concentrations ofUA for 10 min after stableconstruction by U-46619

(0.5 M

); n = 4. *P < 0.01vs. control. #P< 0.05 vs. 0.7mg/dl UA. ##P< 0.01 vs. 0.7mg/dlUA.


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CONCLUSION


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In this study, metabolic syndrome is usually developedby the increase uric acid levels in the blood. Fructoserelatively increase uric acid levels in the blood.Hyperuricemia, can inhibit Nitric Oxide production thatcan developed hyperinsulinemia and glucose intolerance. It

is because into the cell therefore it will develophyperinsulinemia and hyperglycemia. Hyperinsulinemiacan also increase uric acid reabsorption. Glucoseintolerance can develop dyslipidemia by increasing lipidlevel by the flux of free fatty acid from adipocyte.

Dyslipidemia can increase systolic blood pressure byincreasing blood viscosity, thereby increasing PVRresulting in increase in BP. And furtherby can developcomplication in the heart or heart disease.


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There are medications that lowers uric acid levelsin the blood such as allopurinol or benzbromarone.Both of this drug can lower serum uric acid therebycan also prevent hyperglycemia, hyperinsulinemia,

dyslipidemia, hypertension and obesity. Thereforecorrecting the disease of hypermetabolic syndrome.


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FRUCTOSE

Hyperinsulinemia

Inhibits NO2

Hyperglycemia Glucose intolerance

IncreasesURICACID


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FFA flux fromadipocyte

Increase lipid inblood

ObesityChronic

(atherosclerosis)

Acute (increases

blood viscosity)


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Increase PVR

Increases BP

Hypertension

CardiacComplications


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Journal Report Fructose Induced Hyperurecemia.converted

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