Uric acid restores endothelial function in patients with type 1 diabetes and regular smokers

Uric acid as a mediator of diabetic nephropathy

Despite advances in the management of patients with diabetes, diabetic nephropathy (DN) remains the most common cause of end-stage renal disease in the United States and worldwide. Inflammation and endothelial dysfunction appear to play a central role in the onset and the progression of DN. Recent evidence has emerged in the past decade to suggest uric acid is an inflammatory factor and may play a role in endothelial dysfunction. This has lead our group and others to explore the role of uric acid in the onset and progression of DN. In this review, we highlight some of the animal and human studies that implicate uric acid in DN. Based on the evidence we review, we conclude the need for properly planned randomized controlled studies to decrease uric acid levels and assess the impact of such therapy on diabetic kidney disease.

Uric acid: a danger signal from the RNA world that may have a role in the epidemic of obesity, metabolic syndrome, and cardiorenal disease: evolutionary considerations

All human beings are uricase knockouts; we lost the uricase gene as a result of a mutation that occurred in the mid-Miocene epoch approximately 15 million years ago. The consequence of being a uricase knockout is that we have higher serum uric acid levels that are less regulatable and can be readily influenced by diet. This increases our risk for gout and kidney stones, but there is also increasing evidence that uric acid increases our risk for hypertension, kidney disease, obesity, and diabetes. This raises the question of why this mutation occurred. In this article we review current hypotheses. We suggest that uric acid is a danger and survival signal carried over from the RNA world. The mutation of uricase that occurred during the food shortage and global cooling that occurred in the Miocene epoch resulted in a survival advantage for early primates, particularly in Europe. Today, the loss of uricase functions as a thrifty gene, increasing our risk for obesity and cardiorenal disease.

Allopurinol does not decrease blood pressure or prevent the development of hypertension in the deoxycorticosterone acetate-salt rat model

Reactive oxygen species play an important role in the pathogenesis of hypertension, disease in which reactive oxygen species levels and markers of oxidative stress are increased. Xanthine oxidase (XO) is a reactive oxygen species-producing enzyme the activity of which may increase during hypertension. Studies on XO inhibition effects on blood pressure have yielded controversial results. We hypothesized that XO inhibition would decrease blood pressure or attenuate the development of deoxycorticosterone acetate (DOCA)-salt hypertension. We administered the XO inhibitor, allopurinol (50 mg/kg per day, orally) or its vehicle to rats during the established or development stages of DOCA-salt hypertension. We validated XO inhibition by high-performance liquid chromatography measurements of XO metabolites in urine, serum, and tissues demonstrating a decrease in products, increase in substrates, and detection of the active metabolite of allopurinol, oxypurinol. We monitored blood pressure continuously through radiotelemetry and performed gross evaluations of target organs of hypertension. Allopurinol treatment did not impact the course of DOCA-salt hypertension regardless of the timing of administration. Aside from a significant decrease in pulse pressure in allopurinol-treated rats, no positive differences were observed between the allopurinol and the vehicle-treated rats. We conclude that XO does not play an important role in the development or maintenance of hypertension in the rat DOCA-salt hypertension model.

Uric acid levels are associated with microvascular endothelial dysfunction in patients with Type 1 diabetes

AIMS

Recent data identified uric acid as an independent risk factor for cardiovascular disease. The aim of the present study was to assess the association between uric acid and endothelial dysfunction in 57 patients with Type 1 diabetes and 53 healthy control subjects.

METHODS

Microvascular endothelial function was evaluated using laser Doppler perfusion monitoring coupled with pharmacological (iontophoretic administration of acetylcholine and sodium nitroprusside) and physiological (post-occlusive reactive hyperaemia and thermal hyperaemia) stimuli.

RESULTS

Uric acid was higher in subjects without diabetes than in those with diabetes (P = 0.03). Microvascular vasodilator response to acetylcholine was significantly reduced in Type 1 diabetes (P = 0.002) and was correlated to disease duration (r = -0.3, P = 0.01), triglyceride (r = -0.37, P = 0.005), insulin dose (r = -0.28, P = 0.03), fasting plasma glucose levels (r = -0.3, P = 0.02), HbA(1c) (r = -0.34, P = 0.001) and uric acid (r = -0.3, P = 0.005). On stepwise multivariate analysis, age, HbA(1c) and uric acid were the most important independent variables that were associated with the endothelium-dependent response in Type 1 diabetes (P = 0.02).

CONCLUSIONS

Glycaemic control and uric acid in the normal range were the most important contributing factors to the decreasing endothelium-dependent responses associated with Type 1 diabetes. Consequently, uric acid could be a new potential marker of microvascular endothelial dysfunction in these patients. Further studies are required to explore the clinical relevance of the relationship between uric acid levels, oxidative stress and endothelial dysfunction in patients with Type 1 diabetes, as well as whether treatment with uric acid-lowering drugs for slight elevations in uric acid would benefit these patients.

Serum uric acid is a GFR-independent long-term predictor of acute and chronic renal insufficiency: the Jerusalem Lipid Research Clinic cohort study

BACKGROUND

Kidney disease is commonly accompanied by hyperuricemia. However, the contribution of serum uric acid (SUA) to kidney injury is debated. Our objective was to assess the long-term prediction of renal failure by SUA.

METHODS

Visit 2 participants in the Jerusalem Lipid Research Clinic cohort with normal baseline kidney function were followed for 24-28 years. SUA levels were assessed for associations with acute renal failure (ARF) and chronic renal failure (CRF) as defined by hospital discharge records, and mortality, ascertained through linkage with the national population registry.

RESULTS

Among 2449 eligible participants (1470 men, 979 women aged 35-78 years in 1976-79), SUA was positively linked with male sex, serum creatinine and components of the metabolic syndrome but was lower in smokers and in diabetic subjects. The 22- to 25-year incidence of hospital-diagnosed kidney failure (145 first events, 67% CRF) and the 24- to 28-year mortality (587 events) were higher in subject with hyperuricemia (>6.5 mg/dL in men and >5.3 mg/dL in women, reflecting the upper quintiles), independent of baseline kidney function and covariates. Hyperuricemia conferred adjusted hazard ratios of 1.36 (P = 0.003), 2.14 (P < 0.001) and 2.87 (P = 0.003) for mortality, CRF and ARF, respectively.

CONCLUSIONS

SUA predicts renal failure incidence and all-cause mortality independently of demographic and clinical covariates. These results lend support to the undertaking of clinical trials to examine the effect of uric acid-lowering strategies on kidney outcomes.

Serum uric acid level and endothelial dysfunction in patients with nondiabetic chronic kidney disease

BACKGROUND

An elevated serum uric acid level is strongly associated with endothelial dysfunction and inflammation, both of which are common in chronic kidney disease (CKD). We hypothesized that endothelial dysfunction in subjects with CKD would correlate with uric acid levels.

MATERIALS AND METHODS

We evaluated the association between serum uric acid level and ultrasonographic flow-mediated dilatation (FMD) in 263 of 486 patients with recently diagnosed CKD (stage 3-5) (48% male, age 52 ± 12 years). To minimize confounding, 233 patients were excluded because they were diabetic, had established cardiovascular complications or were taking drugs (renin-angiotensin system blockers, statins) interfering with vascular function.

RESULTS

Serum uric acid level was significantly increased in all stages of CKD and strongly correlated with estimated glomerular filtration rate (eGFR-MDRD); FMD was inversely associated with serum uric acid (r = -0.49, p < 0.001). The association of serum uric acid with FMD remained after adjustment for age, gender, smoking, LDL cholesterol, eGFR, high-sensitivity C-reactive protein, systolic blood pressure, proteinuria, and homeostatic model assessment index (β = -0.27, p < 0.001).

CONCLUSION

Increased serum uric acid is an independent predictor of endothelial dysfunction in subjects with CKD.

Effect of cigarette smoking on plasma uric acid concentrations

OBJECTIVES

The purpose of this study was to examine the effect of cigarette smoking on plasma uric acid concentration and to determine the correlation between this parameter and the biological tobacco markers, plasma thiocyanate and urinary cotinine.

METHODS

The initial study was conducted on 300 subjects; 138 of them were nonsmokers (62 men and 76 women) aged 14-72 years and 162 were current smokers (145 men and 17 women) aged 16-85 years. Uric acid, creatinine, and urinary cotinine were determined by the enzymatic colorimetric method and plasma thiocyanate by selective electrode.

RESULTS

Plasma uric acid concentration was significantly lower in smokers than in nonsmokers. A statistically significant negative correlation was noted between the smoking status parameters, including both the number of cigarettes smoked/day (F (3-161) = 12.063; r = -0.9968; p = 0.0001) and the duration of smoking (F (3-161) = 1.305; r = -0.9406; p = 0.0274), and the plasma uric acid. Among smokers, we noted a negative correlation between uric acid and both plasma thiocyanates (r = -0.437; p < 0.05) and urinary cotinine (r = -0.580; p < 0.05).

CONCLUSION

After excluding the other factors affecting the uric acid levels, the significant low plasma uric acid in smokers was attributed to a reduction of the endogenous production as a result of the chronic exposure to cigarette smoke that is a significant source of oxidative stress. Therefore, it is recommended to stop or reduce smoking and to introduce plasma uric acid estimation as a routine test, since it is cheap and simple to reflect the antioxidant level.

Effect of serum insulin on the association between hyperuricemia and incident heart failure

Increased serum uric acid (UA) is associated with incident heart failure (HF). However, whether it is a direct effect of UA or an effect of increased xanthine oxidase (XO) is unknown. Because hyperuricemia in hyperinsulinemia is primarily due to impaired renal UA excretion, its association with incident HF would suggest a direct UA effect. In contrast, hyperuricemia in normoinsulinemia is likely due to increased UA production and thus its association with incident HF would suggest an XO effect. To clarify this, we examined the association of hyperuricemia with centrally adjudicated incident HF in Cardiovascular Health Study participants with and without hyperinsulinemia. Of the 5,411 participants ≥ 65 years of age without baseline HF, 1,491 (28%) had hyperuricemia (serum UA ≥ 6 mg/dl for women and ≥ 7 mg/dl for men). Propensity scores for hyperuricemia were estimated using 63 baseline characteristics. Mean serum UA levels were 6.0 and 5.3 mg/dl in those with (n = 2,731) and those without (n = 2,680) hyperinsulinemia (median serum insulin ≥ 13 mU/L), respectively (p < 0.001). Propensity-adjusted hazard ratios (95% confidence intervals) for hyperuricemia-associated incident HF during 8 years of median follow-up were 0.99 (0.83 to 1.18, p = 0.886) and 1.32 (1.04 to 1.67, p = 0.021) for those with and without hyperinsulinemia respectively (p for interaction = 0.014). In conclusion, the absence of an association of hyperuricemia with incident HF in those with hyperinsulinemia (despite a significantly higher mean serum UA) and a significant association in normoinsulinemia suggest that UA has no intrinsic association with incident HF and that it may predict incident HF when it is a marker of increased of XO activity.

Oxidative stress with an activation of the renin-angiotensin system in human vascular endothelial cells as a novel mechanism of uric acid-induced endothelial dysfunction

AIMS

Oxidative stress is known to be a major mechanism of endothelial dysfunction, which plays a key role in the development of cardiovascular disease. Although uric acid is one of the most important antioxidants, recent studies have suggested that uric acid may have a causal role in endothelial dysfunction. In order to understand the paradoxical association of uric acid with oxidative stress and vascular disease, we investigated whether uric acid induced oxidative stress in human vascular endothelial cells. We also examined whether uric acid-induced changes in redox status were related to aging and death of endothelial cells or an activation of local renin-angiotensin system, another mediator of endothelial dysfunction.

METHODS

Endothelial senescence and apoptosis were evaluated by senescence-associated beta-galactosidase staining and annexin V-propidium iodide staining in primary isolated human umbilical vein endothelial cells (HUVECs). Production of reactive oxygen species was assessed by dichlorofluorescein diacetate staining. mRNA expression of angiotensinogen, angiotensin-converting enzyme and the receptors of angiotensin II was evaluated by real-time PCR, and angiotensin II levels were measured in uric acid-stimulated HUVECs.

RESULTS

Uric acid-induced senescence and apoptosis in HUVECs at concentrations more than 6 and 9 mg/dl, respectively. Uric acid-induced alterations in cell proliferation, senescence and apoptosis were blocked by probenecid, enalaprilat or telmisartan. Uric acid significantly increased production of reactive oxygen species beginning at 5 min, and uric acid-induced senescence and apoptosis of HUVECs were ameliorated by N-acetylcysteine or tempol. Uric acid also upregulated the expression of angiotensinogen, angiotensin-converting enzyme and angiotensin II receptors and increased angiotensin II levels, which was ameliorated with tempol.

CONCLUSION

Uric acid-induced aging and death of human endothelial cells are medicated by local activation of oxidative stress and the renin-angiotensin system, which provides a novel mechanism of uric acid-induced endothelial dysfunction. Therapies targeting uric acid maybe beneficial in cardiovascular disease.

High levels of serum uric acid are associated with silent brain infarction

BACKGROUND

Uric acid has been known to exert neuroprotective effects by acting as a free radical scavenger; however, several observational studies indicated that high levels of serum uric acid increased the risk of cardiovascular events or stroke. We sought to determine whether increased levels of uric acid are associated with the presence of silent brain infarction (SBI).

METHODS

We recruited a consecutive series of non-stroke individuals who visited the Healthcare System in our hospital and underwent brain MRI (n=1577). We conducted intensive interviews and laboratory examinations, including serum uric acid. We examined associations between SBI and vascular risk factors including uric acid by controlling possible confounders.

RESULTS

Of the 1577 subjects recruited, 921 were men and 656 were women, and the uric acid level was much higher in the men (6.3±1.3) than in the women (4.7±1.0). There was a strong dose-response relationship between the quartiles of uric acid and the presence of SBI in women (p=0.001), but not in men. Multivariable analysis showed that the highest quartile of uric acid level was an independent risk factor for the presence of SBI in total patients (adjusted OR, 1.79; 95% CI, 1.11-2.91). However, this association remained significant in women (adjusted OR, 2.64; 95% CI, 1.17-5.91), but not in men.

CONCLUSIONS

Our results suggest that an increased level of uric acid may be a risk factor for the presence of SBI. Serum uric acid level might be a good serum marker of underlying SBI or future stroke, especially in women.

Uric acid and hypertension: cause or effect?

Uric acid was first associated with primary hypertension in 1874, yet its role in this condition remains unclear. Historically, uric acid was thought to be a secondary response to hypertension or its associated conditions. However, more recent experimental and clinical studies suggest that uric acid could have a contributory role in the pathogenesis of elevated blood pressure. More studies are needed to help dissect the potential mechanisms by which uric acid could initiate this response. It remains possible that uric acid is a marker for xanthine oxidase-associated oxidants and that the latter could be driving the hypertensive response. However, the weight of the evidence suggests that uric acid is a true modifying and possibly causal factor for human primary hypertension. Hence, early management of hyperuricemia might delay the development of essential hypertension.

Association between endothelial dysfunction and hyperuricaemia

OBJECTIVE

We used high-resolution peripheral vascular ultrasound imaging to assess endothelial function in hyperuricaemic patients.

METHODS

Hyperuricaemia was defined as a serum uric acid concentration of > 7.7 mg/dl in men or > 6.6 mg/dl in women. Measurements of endothelium-dependent flow-mediated vasodilation (FMD) and endothelium-independent nitroglycerin-mediated vasodilation were performed in 46 hyperuricaemic patients and an equal number of healthy age- and gender-matched normal controls by high-resolution two-dimensional ultrasonographic imaging of the brachial artery. The serum levels of glucose, creatinine, alanine aminotransferase (ALT), lipid profiles and high-sensitivity CRP were measured for both the study groups.

RESULTS

The serum uric acid levels averaged 9.24 (1.16) and 6.18 (0.99)  mg/dl in the hyperuricaemic and control groups, respectively. Body weight and BMI were significantly higher in the hyperuricaemic group than in the control group. The serum levels of creatinine, ALT, triglyceride and high-sensitivity CRP were significantly different between the two groups. The FMD values were significantly lower in the hyperuricaemic patients than in the controls [4.45% (3.13%) vs 7.10% (2.48%); P < 0.001]. The FMD values were negatively associated with serum uric acid levels (r = -0.273; P = 0.009). Multivariate regression analysis showed that the presence of hyperuricaemia (β = -0.384; P < 0.001) and body weight (β = 0.215; P = 0.017) were independent determinants of low FMD values.

CONCLUSION

Hyperuricaemia is associated with endothelial dysfunction. Decreased nitric oxide bioavailability may be the main reason.

Uric acid and antioxidant effects of wine

The aim of this article is to review the role of uric acid in the context of antioxidant effects of wine and its potential implication to human health. We described and discussed the mechanisms of increase in plasma antioxidant capacity after consumption of moderate amounts of wine. Because this effect is largely contributed by acute elevation in plasma uric acid, we paid special attention to wine constituents and metabolic processes that are likely to be involved in uric acid elevation.

Could uric acid be a modifiable risk factor in subjects with pulmonary hypertension?

A high serum uric acid is common in subjects with pulmonary hypertension. The increase in serum uric acid may be a consequence of the local tissue ischemia and/or hypoxia, and it may also result from other factors independent of ischemia or hypoxia that occur in various forms of pulmonary hypertension. While classically viewed as a secondary phenomenon, recent studies suggest that hyperuricemia may also have a role in mediating the local vasoconstriction and vascular remodeling in the pulmonary vasculature. If uric acid does have a contributory role in pulmonary hypertension, we may see an increasing prevalence of pulmonary hypertension as hyperuricemia is common in subjects with obesity and metabolic syndrome. We propose studies to investigate the role of uric acid in pulmonary hypertension and to determine if lowering serum uric acid may have clinical benefit in this condition.

Bayesian methods for instrumental variable analysis with genetic instruments ('Mendelian randomization'): example with urate transporter SLC2A9 as an instrumental variable for effect of urate levels on metabolic syndrome

The ‘Mendelian randomization’ approach uses genotype as an instrumental variable to distinguish between causal and non-causal explanations of biomarker–disease associations. Classical methods for instrumental variable analysis are limited to linear or probit models without latent variables or missing data, rely on asymptotic approximations that are not valid for weak instruments and focus on estimation rather than hypothesis testing. We describe a Bayesian approach that overcomes these limitations, using the JAGS program to compute the log-likelihood ratio (lod score) between causal and non-causal explanations of a biomarker–disease association. To demonstrate the approach, we examined the relationship of plasma urate levels to metabolic syndrome in the ORCADES study of a Scottish population isolate, using genotype at six single-nucleotide polymorphisms in the urate transporter gene SLC2A9 as an instrumental variable. In models that allow for intra-individual variability in urate levels, the lod score favouring a non-causal over a causal explanation was 2.34. In models that do not allow for intra-individual variability, the weight of evidence against a causal explanation was weaker (lod score 1.38). We demonstrate the ability to test one of the key assumptions of instrumental variable analysis—that the effects of the instrument on outcome are mediated only through the intermediate variable—by constructing a test for residual effects of genotype on outcome, similar to the tests of ‘overidentifying restrictions’ developed for classical instrumental variable analysis. The Bayesian approach described here is flexible enough to deal with any instrumental variable problem, and does not rely on asymptotic approximations that may not be valid for weak instruments. The approach can easily be extended to combine information from different study designs. Statistical power calculations show that instrumental variable analysis with genetic instruments will typically require combining information from moderately large cohort and cross-sectional studies of biomarkers with information from very large genetic case–control studies.

Uric acid does not affect the acetylcholine-induced relaxation of aorta from normotensive and deoxycorticosterone acetate-salt hypertensive rats

Uric acid (UA) results from xanthine oxidase (XO) catabolism of xanthine and is the final product of purine catabolism in humans. In this species, hyperuricemia is associated with gout, nephropathy, and increased cardiovascular disease risk. Although the effects of hyperuricemia in vascular biology are overall controversial, UA has been described as an antioxidant and as potentially improving endothelial function. Hypertension is associated with endothelial dysfunction. We hypothesized that UA improves the endothelial function of aorta from deoxycorticosterone acetate (DOCA)-salt hypertensive rats. UA (100 microM) in the presence of the uricase inhibitor oxonic acid (10 microM) did not modify relaxation to acetylcholine (ACh) (1 nM-10 microM) in the aorta from nontreated, sham normotensive, and DOCA-salt hypertensive rats [response to 10 microM ACh for UA versus vehicle, respectively: nontreated = 37 +/- 7 versus 48 +/- 7%, sham = 53 +/- 15 versus 57 +/- 20%, DOCA = 81 +/- 4 versus 85 +/- 2% from 20 microM prostaglandin 2alpha (PGF(2alpha))-induced contraction]. Allopurinol (100 microM), a XO inhibitor, did not significantly alter the ACh-induced relaxation of sham and DOCA aortic rings (response to 10 microM ACh for allopurinol versus vehicle, respectively: sham = 61 +/- 5 versus 68 +/- 9%, DOCA = 87 +/- 6 versus 88 +/- 3% from 20 microM PGF(2alpha)-induced contraction). Uricemia, ranging from unmeasurable to 547 microM in sham and to 506 microM in DOCA rats, was not significantly different between these two groups. The expression and activity of XO, as well as the expression of uricase, were not different between sham and DOCA rat aorta. We conclude that, at least in vitro, UA does not affect the ACh-induced relaxation of normotensive and DOCA-salt hypertensive rats.

Effect of uric acid on nephrotoxicity induced by mercuric chloride in rats

Oxidative stress is an important mechanism in mercury poisoning. We studied the effect of uric acid, a natural and potent reactive oxygen species and peroxynitrite scavenger, in HgCl( 2)-induced nephrotoxicity. Rats were injected with a unique dose of HgCl(2) (2.5 mg/kg body weight, subcutaneously) and then vehicle (for 3 days, twice daily) or HgCl(2) (unique dose) and intraperitoneal uric acid suspension (250 mg/kg body weight, twice daily, for 3 days), and then killed at 24, 48 and 72 hours after HgCl(2) administration (n = 5 for each group). At the end of the experimental study, kidneys and blood samples were taken. Tissues were prepared and examined under light microscopy. Uric acid significantly prevented the increase in plasma levels of creatinine and blood urea nitrogen (BUN); it helped maintain systemic nitrate/nitrite concentration and total antioxidant capacity. Uric acid attenuated the increase of renal lipid peroxidation and it markedly diminished nitrotyrosine signal and histopathological changes as early as 24 hours after HgCl(2) administration. Uric acid did not prevent a decrease in beta-actin signal caused by mercuric chloride, but it promoted a faster recovery when compared to the HgCl(2) alone group. Our results indicate that UA could play a beneficial role against HgCl(2) toxicity by preventing systemic and renal oxidative stress and tissue damage.

Serum uric acid levels predict the development of albuminuria over 6 years in patients with type 1 diabetes: findings from the Coronary Artery Calcification in Type 1 Diabetes study

BACKGROUND

Recent studies suggest that uric acid is a mediator of diabetic nephropathy. We hypothesized that elevated serum uric acid levels are a strong predictor of albuminuria in patients with type 1 diabetes.

METHODS

We analyzed data from the Coronary Artery Calcification in Type 1 Diabetes study, a prospective observational study. A stepwise logistic regression model was applied to predict the development of micro- or macroalbuminuria after 6 years of follow-up in 324 participants who had no evidence of micro- or macroalbuminuria at baseline. A P-value <0.1 was used as the criteria for entry into and removal from the model.

RESULTS

The following factors were selected in the stepwise multivariate model as predictors of micro- or macroalbuminuria at the 6-year follow-up visit: baseline serum uric acid levels, HbA(1c) and pre-albuminuria. For every 1-mg/dl increase in serum uric acid levels at baseline, there was an 80% increased risk of developing micro- or macroalbuminuria at 6 years (odds ratio 1.8; 95% confidence interval 1.2, 2.8; P = 0.005). Additional covariates considered in the stepwise model were sex, age, duration of diabetes, angiotensin-converting enzyme inhibitor or angiotensin II receptor blocker treatment, waist circumference, waist/hip ratio, body mass index, systolic and diastolic blood pressure, smoking, serum creatinine, cystatin C, high-density lipoprotein cholesterol and triglycerides.

CONCLUSION

Elevated serum uric acid levels are a strong predictor of the development of albuminuria in patients with type 1 diabetes.

Homozygous SLC2A9 mutations cause severe renal hypouricemia

Hereditary hypouricemia may result from mutations in the renal tubular uric acid transporter URAT1. Whether mutation of other uric acid transporters produces a similar phenotype is unknown. We studied two families who had severe hereditary hypouricemia and did not have a URAT1 defect. We performed a genome-wide homozygosity screen and linkage analysis and identified the candidate gene SLC2A9, which encodes the glucose transporter 9 (GLUT9). Both families had homozygous SLC2A9 mutations: A missense mutation (L75R) in six affected members of one family and a 36-kb deletion, resulting in a truncated protein, in the other. In vitro, the L75R mutation dramatically impaired transport of uric acid. The mean concentration of serum uric acid of seven homozygous individuals was 0.17 +/- 0.2 mg/dl, and all had a fractional excretion of uric acid >150%. Three individuals had nephrolithiasis, and three had a history of exercise-induced acute renal failure. In conclusion, homozygous loss-of-function mutations of GLUT9 cause a total defect of uric acid absorption, leading to severe renal hypouricemia complicated by nephrolithiasis and exercise-induced acute renal failure. In addition to clarifying renal handling of uric acid, our findings may provide a better understanding of the pathophysiology of acute renal failure, nephrolithiasis, hyperuricemia, and gout.

The role of urate and xanthine oxidase in vascular oxidative stress: future directions

Vascular oxidative stress has been shown to be a potent factor in the pathophysiology of endothelial dysfunction. Despite current optimal evidence-based therapy, mortality from various cardiovascular disorders remains high. The search for newer, novel ways of attenuating endothelial dysfunction has yielded several new and exciting possibilities, one of which is the manipulation of urate levels using xanthine oxidase inhibitors. Agents such as allopurinol have shown marked improvements in vascular endothelial function in various cohorts at risk of cardiovascular events. Most of the evidence so far comes from smaller mechanistic studies. The few large randomized controlled trials have failed to show any significant mortality benefit using these agents. This article highlights the potential avenues of further research such as dose-response, and the potential for these agents to regress left ventricular hypertrophy. The role of newer agents such as febuxostat and oxypurinol are discussed as well as potential reasons why some of the current newer agents have failed to live up to the promising early-phase data. It is crucial that these remaining questions surrounding urate, xanthine oxidase and the role of various agents that affect this important oxidative stress-generating system are answered, and therefore these promising agents should not be discarded prematurely.

Hyperuricemia, oxidative stress, and carotid artery tone in experimental renal insufficiency

BACKGROUND

Hyperuricemia may play a role in the pathogenesis of cardiovascular disease, but uric acid is also a significant antioxidant. We investigated the effects of oxonic acid-induced hyperuricemia on carotid artery tone in experimental renal insufficiency.

METHODS

Three weeks after 5/6 nephrectomy (NX) or Sham operation, male Sprague-Dawley rats were allocated to 2.0% oxonic acid or control diet for 9 weeks. Blood pressure was monitored using tail cuff, isolated arterial rings were examined using myographs, and blood and urine samples were taken, as appropriate. Oxidative stress and antioxidant status were evaluated by measuring urinary 8-isoprostaglandin F(2 alpha) (8-iso-PGF(2 alpha)) excretion and plasma total peroxyl radical-trapping capacity (TRAP), respectively.

RESULTS

Plasma creatinine was elevated twofold in NX rats, but neither NX nor oxonic acid diet influenced blood pressure. Urinary 8-iso-PGF(2 alpha) excretion was increased over 2.5-fold in NX rats on control diet. Oxonic acid diet increased plasma uric acid 2-3-fold, TRAP 1.5-fold, and reduced urinary 8-iso-PGF(2 alpha) excretion by 60-90%. Carotid vasorelaxation to acetylcholine in vitro, which could be abolished by nitric oxide (NO) synthase inhibition, was reduced following NX, whereas maximal response to acetylcholine was augmented in hyperuricemic NX rats. Vasorelaxation to nitroprusside was impaired in NX rats, whereas oxonic acid diet increased sensitivity also to nitroprusside in NX rats.

CONCLUSIONS

Oxonic acid-induced hyperuricemia reduced oxidative stress in vivo, as evaluated using urinary 8-iso-PGF(2 alpha) excretion, increased plasma TRAP, and improved NO-mediated vasorelaxation in the carotid artery in experimental renal insufficiency.

Fructose ingestion: dose-dependent responses in health research

Many hypotheses of disease risk and prevention depend on inferences about the metabolic effects of fructose; however, there is inadequate attention to dose dependency. Fructose is proving to have bidirectional effects. At moderate or high doses, an effect on any one marker may be absent or even the opposite of that observed at very high or excessive doses; examples include fasting plasma triglyceride, insulin sensitivity, and the putative marker uric acid. Among markers, changes can be beneficial for some (e.g., glycated hemoglobin at moderate to high fructose intake) but adverse for others (e.g., plasma triglycerides at very high or excessive fructose intake). Evidence on body weight indicates no effect of moderate to high fructose intakes, but information is scarce for high or excessive intakes. The overall balance of such beneficial and adverse effects of fructose is difficult to assess but has important implications for the strength and direction of hypotheses about public health, the relevance of some animal studies, and the interpretation of both interventional and epidemiological studies. By focusing on the adverse effects of very high and excessive doses, we risk not noticing the potential benefits of moderate to higher doses, which might moderate the advent and progress of type-2 diabetes, cardiovascular disease, and might even contribute to longevity. A salutary rather than hyperbolic examination of the evidence base needs to be undertaken.

Gender-dependent impacts of body mass index and moderate alcohol consumption on serum uric acid--an index of oxidant stress status?

Uric acid seems to be causally involved in a variety of medical disorders involving oxidative stress. Although alcohol abuse and obesity are known to increase serum uric acid, the interactions between moderate drinking, adiposity, and uric acid metabolism have remained poorly understood. We examined serum uric acid concentrations from 2062 apparently healthy volunteers (970 men, 1092 women) reporting either no alcohol (abstainers) or <40 g of ethanol consumption per day (moderate drinkers). The study population was further classified according to BMI as follows: <19 (underweight), 19-25 (normal weight), 25-30 (overweight), and >30 (obese). Serum uric acid concentrations in male moderate drinkers were significantly higher, and in females they were lower, than in the corresponding groups of abstainers. In the BMI-based subgroups, the highest concentrations were found in those who were overweight or obese. Significant two-factor interactions occurred between gender and drinking status (p<0.001) and between gender and BMI (p<0.02). Serum uric acid also correlated with indices of hepatocellular health (GGT, ALT, AST). The data indicate distinct gender-dependent impacts of alcohol consumption and BMI on serum uric acid. These findings should be applicable to the assessment of oxidative stress status and associated morbidity in alcohol consumers and individuals with excess body weight.

Mudanças no estilo de vida e fatores de risco para doenças crônicas não transmissíveis e sistema imune de mulheres sedentárias

OBJETIVO: Observar os efeitos de dois meses de um programa de reeducação de hábitos sobre variáveis do sistema imunológico e de risco para doenças crônicas não transmissíveis e as associações destas entre si e com a composição corporal. MÉTODOS: Cinqüenta mulheres sedentárias, com idade de 36 anos (DP=10), e índice de massa corporal de 31kg/m² (DP=12) participaram do estudo. Foram avaliados a composição corporal (antropometria e bioimpedância), o hemograma, o perfil lipídico, as concentrações plasmáticas das vitaminas A, C, betacaroteno, do zinco, do ácido úrico e da glicemia. O treinamento consistia de circuito de peso ou caminhada por 1h, três vezes por semana no primeiro mês e 1h, quatro vezes por semana no segundo mês, mais reeducação alimentar. RESULTADOS: A gordura corporal, as concentrações plasmáticas do ácido úrico, do colesterol total e da lipoproteína de alta densidade foram significativamente reduzidas. Os triglicérides, a lipoproteína de baixa densidade e as variáveis do sistema imunológico não foram alterados. O zinco não foi associado a qualquer variável. Os glóbulos brancos, os linfócitos, as plaquetas e a vitamina C foram positivamente associados à gordura corporal e negativamente, quando divididos pela massa corporal (kg). O colesterol total e a lipoproteína de baixa densidade divididos pela concentração de vitamina A e do betacaroteno foram negativamente correlacionados à gordura corporal. A vitamina C teve a maior correlação com outros fatores bioquímicos de risco. CONCLUSÃO: Houve redução dos fatores de risco para doenças crônicas não transmissíveis, mas não nos marcadores do sistema imunológico. O aumento da gordura corporal foi associado negativamente aos marcadores do sistema imunológico e das vitaminas.

Uric acid and insulin sensitivity and risk of incident hypertension

BACKGROUND

Uric acid, insulin sensitivity, and endothelial dysfunction may be important in the development of hypertension. Corresponding circulating biomarkers are associated with risk of hypertension, but because these factors may be interrelated, whether they independently affect risk is unknown.

METHODS

In 1496 women aged 32 to 52 years without hypertension at baseline, we prospectively analyzed the associations between fasting plasma levels of uric acid, insulin, triglycerides, the insulin sensitivity index, and 2 biomarkers associated with endothelial dysfunction (homocysteine and soluble intercellular adhesion molecule-1) and the odds of incident hypertension. Odds ratios were adjusted for standard risk factors and then for all biomarkers plus estimated glomerular filtration rate and total cholesterol level. Population-attributable risk was estimated for biomarkers significantly associated with hypertension.

RESULTS

All the biomarkers were associated with incident hypertension after adjustment for standard hypertension risk factors. However, after simultaneously controlling for all the biomarkers, estimated glomerular filtration rate, and total cholesterol level, only uric acid and insulin levels were independently associated with incident hypertension. Comparing the highest and lowest quartiles of uric acid levels, the odds ratio was 1.89 (95% confidence interval, 1.26-2.82). A similar comparison yielded an odds ratio of 2.03 (95% confidence interval, 1.35-3.05) for insulin levels. Using an estimated basal incidence rate of 14.6 per 1000 annually, 30.8% of all hypertension occurring in young women annually is associated with uric acid levels of 3.4 mg/dL or greater (to convert to micromoles per liter, multiply by 59.485). For insulin levels of 2.9 microIU/mL or greater (to convert to picomoles per liter, multiply by 6.945), this proportion is 24.2%.

CONCLUSIONS

Differences in uric acid and insulin levels robustly and substantially affect the risk of hypertension in young women. Measuring these biomarkers in clinical practice may identify higher-risk individuals.

Association between hyperuricemia and incident heart failure among older adults: a propensity-matched study

BACKGROUND

The association between hyperuricemia and incident heart failure (HF) is relatively unknown.

METHODS

Of the 5461 community-dwelling older adults, >or=65 years, in the Cardiovascular Health Study without HF at baseline, 1505 had hyperuricemia (baseline serum uric acid >or=6 mg/dL for women and >or=7 mg/dL for men). Using propensity scores for hyperuricemia, estimated for each participant using 64 baseline covariates, we were able to match 1181 pairs of participants with and without hyperuricemia.

RESULTS

Incident HF occurred in 21% and 18% of participants respectively with and without hyperuricemia during 8.1 years of mean follow-up (hazard ratio {HR} for hyperuricemia versus no hyperuricemia, 1.30; 95% confidence interval {CI}, 1.05-1.60; P=0.015). The association between hyperuricemia and incident HF was significant only in subgroups with normal kidney function (HR, 1.23; 95% CI, 1.02-1.49; P=0.031), without hypertension (HR, 1.31; 95% CI, 1.03-1.66; P=0.030), not receiving thiazide diuretics (HR, 1.20; 95% CI, 1.01-1.42; P=0.044), and without hyperinsulinemia (HR, 1.35; 95% CI, 1.06-1.72; P=0.013). Used as a continuous variable, each 1 mg/dL increase in serum uric acid was associated with a 12% increase in incident HF (HR, 1.12; 95% CI, 1.03-1.22; P=0.006). Hyperuricemia had no association with acute myocardial infarction or all-cause mortality.

CONCLUSIONS

Hyperuricemia is associated with incident HF in community-dwelling older adults. Cumulative data from our subgroup analyses suggest that this association is only significant when hyperuricemia is a marker of increased xanthine oxidase activity but not when hyperuricemia is caused by impaired renal elimination of uric acid.

Hypothesis: could excessive fructose intake and uric acid cause type 2 diabetes?

We propose that excessive fructose intake (>50 g/d) may be one of the underlying etiologies of metabolic syndrome and type 2 diabetes. The primary sources of fructose are sugar (sucrose) and high fructose corn syrup. First, fructose intake correlates closely with the rate of diabetes worldwide. Second, unlike other sugars, the ingestion of excessive fructose induces features of metabolic syndrome in both laboratory animals and humans. Third, fructose appears to mediate the metabolic syndrome in part by raising uric acid, and there are now extensive experimental and clinical data supporting uric acid in the pathogenesis of metabolic syndrome. Fourth, environmental and genetic considerations provide a potential explanation of why certain groups might be more susceptible to developing diabetes. Finally, we discuss the counterarguments associated with the hypothesis and a potential explanation for these findings. If diabetes might result from excessive intake of fructose, then simple public health measures could have a major impact on improving the overall health of our populace.

Fructose and vitamin C intake do not influence risk for developing hypertension

Higher uric acid levels are associated with an increased risk for developing hypertension. Higher intake of fructose increases plasma uric acid levels and higher intake of vitamin C reduces uric acid levels, but whether these nutrients are independently associated with the risk for developing hypertension is unknown. We studied this question by analyzing data from participants of three large and independent prospective cohorts: Nurses' Health Study 1 (n = 88,540), Nurses' Health Study 2 (n = 97,315), and the Health Professionals Follow-up Study (n = 37,375). Relative risks and 95% confidence intervals for incident hypertension were computed according to quintiles of fructose intake and categories of vitamin C intake using multivariable Cox proportional hazards regression. Fructose intake was not associated with the risk for developing hypertension; the multivariable relative risks (95% confidence intervals) for the highest compared with the lowest quintile of fructose intake were 1.02 (0.99 to 1.06) in Nurses' Health Study 1, 1.03 (0.98 to 1.08) in Nurses' Health Study 2, and 0.99 (0.93 to 1.05) in Heath Professionals Follow-up Study. Regarding vitamin C, the relative risks for individuals who consumed > or =1500 mg/d compared with those who consumed <250 mg/d were 0.89 (0.83 to 0.96) in Nurses' Health Study 1, 1.02 (0.91 to 1.14) in Nurses' Health Study 2, and 1.06 (0.97 to 1.15) in Health Professionals Follow-up Study. In conclusion, fructose and vitamin C intake do not substantially influence the risk for developing hypertension.

The conundrum of hyperuricemia, metabolic syndrome, and renal disease

The level of serum uric acid in human has been increasing over the last decades, and correlates with an increase prevalence of renal disease and metabolic syndrome. Understanding the role of uric acid in these conditions may provide clues for preventing the current epidemic of renal disease. Controversy still remains if hyperuricemia is simply a consequence or a cause of renal disease although epidemiological studies have attempted to resolve this issue. In this review, we discuss the clinical and experimental evidence for a causal role of hyperuricemia in renal diseases and potential relationships of hyperuricemia with metabolic syndrome.

Serum uric Acid in smokers

OBJECTIVES

To demonstrate the possible effect of smoking on serum uric acid.

METHODS

Subjects enrolled in study were divided into two groups; nonsmokers and smokers, each with 60 male volunteers of the same social class and dietary habit without history of alcohol consumption, diabetes mellitus, hyperuricemia and gout, renal, joint, lung or heart diseases. Fasting blood and random urine samples were obtained from both groups for measurement of uric acid and creatinine. Calculation of both urine uric acid/urine creatinine ratio and fraction excretion of uric acid were done. The results were statistically evaluated by standard statistical methods.

RESULTS

No significant differences in the age, serum creatinine, spot urine uric acid/urine creatinine ratio and fraction excretion of uric acid between the two groups, serum uric acid was significantly lower in smokers. In smokers there was significant negative correlation of smoking status (average number of cigarette smoked/day, duration of smoking and cumulative amount of smoking) with serum uric acid.

CONCLUSION

After exclusion of other factors affecting uric acid level, the significant low serum uric acid level in smokers was attributed to reduce endogenous production as a result of chronic exposure to cigarette smoke that is a significant source of oxidative stress. As this reduction is proportionate with smoking status and predisposes to cardiovascular disease, it is, therefore, recommended for smokers to stop or reduce smoking and introduce serum uric acid estimation as routine test since its cheap and simple to reflect their antioxidant level.

KEYWORDS

Smokers; Uric acid; CVD.

Higher circulating levels of uric acid are prospectively associated with better muscle function in older persons

BACKGROUND

Previous studies have shown that oxidative protein damage is independently associated with low grip strength and that dietary intake and circulating levels of antioxidant vitamins are positive predictors of muscle strength among older persons. Since uric acid (UA), has strong antioxidant properties, we tested the hypothesis that UA levels is cross-sectionaly associated with muscle strength and protective against the decline of strength over the aging process.

SUBJECTS AND METHODS

789 InCHIANTI Study participants underwent baseline serum UA, handgrip and knee extension torque measurements. Of these, 497 participants (226 men and 271 women, mean age 76.0+/-5.4 years) also had follow-up strength measures. Lifestyle, comorbidities, nutritional profile, inflammatory markers and other laboratory measures were considered as potential confounders.

RESULTS

Follow-up strength measures significantly increased across baseline UA tertiles. After adjusting for potential confounders and analogous baseline strength measures, higher baseline UA levels still remained significantly associated with higher follow-up strength measures.

CONCLUSIONS

Our findings suggest that higher levels of UA might represent a protective reaction aimed at counteracting the excessive production of free radicals that cause muscle protein damage and eventually contribute to the decline of muscle mass and strength.

A comparison of reactive oxygen species metabolism in the rat aorta and vena cava: focus on xanthine oxidase

Reactive oxygen species (ROS) are important mediators in vascular biology. Venous function, although relevant to cardiovascular disease, is still understudied. We compared aspects of ROS metabolism between a major artery (the aorta) and a major vein (the vena cava, VC) of the rat, with the hypothesis that venous ROS metabolism would be overall increased compared with its arterial counterpart. Superoxide and hydrogen peroxide (H2O2) release in basal conditions was higher in VC compared with aorta. The antioxidant capacity for H2O2 was also higher in VC than in aorta. Exogenous superoxide induced a higher contraction in VC compared with aorta. Protein expression of three major ROS metabolizing enzymes, xanthine oxidase (XO), CuZn-SOD, and catalase, was higher in VC compared with aorta. Because XO seemed a likely source of the higher VC ROS levels, we examined it further and found higher mRNA expression and activity of XO in VC compared with aorta. We also investigated the impact of XO inhibition by allopurinol on aorta and VC functional responses to norepinephrine, ANG II, ET-1, and ACh. Maximal ET-1-mediated contraction was decreased by allopurinol in VC but not in the aorta. Our results suggest that there are overall differences in ROS metabolism between aorta and VC, with the latter operating normally at a higher set point, releasing but also being able to handle, higher ROS levels. We propose XO to be an important source for these differences. The result of this particular comparison may be reflective of a general arteriovenous contrast.

Serum uric acid correlates with extracellular superoxide dismutase activity in patients with chronic heart failure

Increased serum uric acid has been identified as an independent risk factor for cardiovascular disease. However, because of its antioxidant capacity, uric acid may play a beneficial role in endothelial function. This paradoxical relationship between uric acid and endothelial function in chronic heart failure patients remains poorly understood. Thirty-eight chronic heart failure patients (New York Heart Association functional class II-III, mean age 58+/-10 years and mean left ventricular ejection fraction 25+/-8%) and twelve age-and-sex-matched healthy controls were studied. Chronic heart failure patients showed higher uric acid levels (7.3+/-2.3 mg/dL vs. 6.1+/-0.2 mg/dL, p<0.05) and lower extracellular superoxide dismutase activity (136+/-36 U ml(-1) min(-1) vs. 203+/-61 U ml(-1) min(-1), p<0.01) and endothelium-dependent vasodilatation (4.0+/-1.6% v. 9.1+/-3.0%, p<0.01) when compared with control subjects. In chronic heart failure patients, correlations between both uric acid levels and extracellular superoxide dismutase activity (r=0.45; p<0.01), and uric acid and endothelium-dependent vasodilatation (r=0.35; p=0.03) were detected. These correlations were not observed in healthy individuals, suggesting a positive effect of uric acid on endothelial function partially mediated by modulation of extracellular superoxide dismutase activity in chronic heart failure.

The role of urate and xanthine oxidase inhibitors in cardiovascular disease

Many studies have shown a strong correlation between urate levels and cardiovascular disease. The formation of urate is complex as the same enzyme that produces urate, xanthine oxidase (XO) also catalyzes the formation of reactive oxygen species (ROS). There is some evidence that the urate molecule has free radical scavenging properties in vitro and acute infusions of urate improve endothelial function in at-risk populations. High levels of ROS are clearly linked to worse outcome in a variety of conditions. Allopurinol has been the archetypal XO inhibitor for over 40 years. Small studies have demonstrated its beneficial effects, mainly in heart failure but also in a variety of other cohorts of patients with cardiovascular risk. It is a safe agent, provided suitable patients are chosen and monitored carefully. Newer promising agents like oxypurinol have not shown the expected benefits in larger multicentered studies. This review looks at the biology of urate, its role in cardiovascular disease, the possible mechanisms by which XO inhibitors exert their beneficial effect on endothelial dysfunction, and examines the possible causes for the failure of newer agents to live up to expectations.

Hypouricemia linked to an overproduction of nitric oxide is an early marker of oxidative stress in female subjects with type 1 diabetes

OBJECTIVE

The aim of this study is to verify whether, early in the course of type 1 diabetes and assuming hyperglycemia as the only risk factor, women demonstrate a change in oxidative status due to an interaction between nitric oxide (NO) and uric acid production.

METHODS

Thirty-eight women with type 1 diabetes of less than 10 years' duration and with no diabetic complications were compared with 25 matched healthy female controls. Insulin, C-peptide, NO, HbA(1c) and oxidative stress metabolites were determined from venous blood samples taken from all patients after a 12 h overnight fast. Urine samples were used for urinary uric acid determination.

RESULTS

Most oxidative stress metabolites were significantly increased (p < 0.0001), while plasmatic and urinary uric acid levels were significantly lower (p < 0.0001) in patients with type 1 diabetes compared with controls. Mean NO levels were inversely related to uricemia. Bivariate regression analysis showed a significant correlation between plasmatic uric acid and NO (p = 0.004), ascorbic acid (p = 0.042), triglycerides (p = 0.014) and HbA(1c) (p < 0.0001). Linear multivariate regression analysis showed a significant relationship between HbA(1c) and plasmatic uric acid (beta = - 0.465, p = 0.0004).

CONCLUSIONS

Oxidative stress is already present in the early stages of type 1 diabetes. We conclude that the initial increase in oxidative stress could be linked to a reduction in plasmatic levels of uric acid, which is probably directly caused by an overproduction of NO.

Uric acid administration in patients with acute stroke: a novel approach to neuroprotection

Uric acid (UA) is the end product of purine catabolism in humans and is a powerful antioxidant whose generation is increased under ischemic conditions. However, both clinical and experimental studies reveal a gradual exhaustion of the antioxidant capacity after transient cerebral ischemia, and the magnitude of this consumption seems to be correlated with the extent of brain tissue injury, growth of the infarction, severity of neurological impairment in the acute phase, and long-term functional outcome. Growing evidence supports the neuroprotective effect of UA administration after brain ischemia. In experimental conditions, the administration of UA is neuroprotective both in mechanical models of brain ischemia (transient or permanent intraluminal occlusion of the middle cerebral artery) and in thromboembolic models of autologous clot injection. The administration of UA is feasible and safe in healthy volunteers. In acute stroke patients treated with recombinant tissue plasminogen activator (rt-PA), co-administration of UA has proven to reduce lipid peroxidation and to prevent the fall in UA blood levels that occur very early after stroke onset. Currently, a multicentric Phase III clinical trial is testing whether the administration of UA increases the clinical benefits of rt-PA, which represents the only approved therapy in patients with acute ischemic stroke. This review summarizes the available information justifying such a novel therapeutic approach in this devastating clinical condition.