Uric acid: is it a risk factor for cardiovascular disease?

Assessing brain microstructural changes in chronic kidney disease: a diffusion imaging study using multiple models

Objectives

To explore the effectiveness of diffusion quantitative parameters derived from advanced diffusion models in detecting brain microstructural changes in patients with chronic kidney disease (CKD).

Methods

The study comprised 44 CKD patients (eGFR<59 mL/min/1.73 m2) and 35 age-and sex-matched healthy controls. All patients underwent diffusion spectrum imaging (DSI) and conventional magnetic resonance imaging. Reconstructed to obtain diffusion MRI models, including diffusion tensor imaging (DTI), neurite orientation dispersion and density imaging (NODDI) and Mean Apparent Propagator (MAP)-MRI, were processed to obtain multi-parameter maps. The Tract-Based Spatial Statistics (TBSS) analysis was utilized for detecting microstructural differences and Pearson correlation analysis assessed the relationship between renal metabolism markers and diffusion parameters in the brain regions of CKD patients. Receiver operating characteristic (ROC) curve analysis assessed the diagnostic performance of diffusion models, with AUC comparisons made using DeLong's method.

Results

Significant differences were noted in DTI, NODDI, and MAP-MRI parameters between CKD patients and controls (p < 0.05). DTI indicated a decrease in Fractional Anisotropy(FA) and an increase in Mean and Radial Diffusivity (MD and RD) in CKD patients. NODDI indicated decreased Intracellular and increased Extracellular Volume Fractions (ICVF and ECVF). MAP-MRI identified extensive microstructural changes, with elevated Mean Squared Displacement (MSD) and Q-space Inverse Variance (QIV) values, and reduced Non-Gaussianity (NG), Axial Non-Gaussianity (NGAx), Radial Non-Gaussianity (NGRad), Return-to-Origin Probability (RTOP), Return-to-Axis Probability (RTAP), and Return-to-Plane Probability (RTPP). There was a moderate correlation between serum uric acid (SUA) and diffusion parameters in six brain regions (p < 0.05). ROC analysis showed the AUC values of DTI_FA ranged from 0.70 to 0.793. MAP_NGAx in the Retrolenticular part of the internal capsule R reported a high AUC value of 0.843 (p < 0.05), which was not significantly different from other diffusion parameters (p > 0.05).

Conclusion

The advanced diffusion models (DTI, NODDI, and MAP-MRI) are promising for detecting brain microstructural changes in CKD patients, offering significant insights into CKD-affected brain areas.

Serum Uric Acid and Diabetes: From Pathophysiology to Cardiovascular Disease

Hyperuricemia, has been traditionally related to nephrolithiasis and gout. However, it has also been associated with the development of type 2 diabetes mellitus (T2DM) and cardiometabolic and cardiovascular diseases. Pathophysiologically, elevated serum uric acid (SUA) levels may be associated with abnormal lipid and glucose metabolism. In this narrative review, we consider the associations between hyperuricemia, hyperglycemia, atherosclerosis and thrombosis. Furthermore, we comment on the available evidence linking elevated SUA levels with the incidence and outcomes of coronary heart disease, stroke, peripheral artery disease and non-alcoholic fatty liver in subjects with T2DM. The effects of antidiabetic drugs (e.g. metformin, pioglitazone, sulfonylureas, dipeptidyl peptidase 4 inhibitors, glucagon-like peptide-1 receptor agonists, sodium-glucose cotransporter 2 inhibitors and insulin) on SUA concentrations are also reviewed.

Association between serum uric acid levels and cardiovascular events in hospitalized patients with type 2 diabetes

AIMS

This study aimed to determine the association between serum uric acid (UA) levels and cardiovascular events in hospitalized patients with type 2 diabetes mellitus (T2DM).

METHODS

A retrospective cohort study was conducted in 2227 hospitalized patients with T2DM. Cox proportional hazards regression was used to assess the association between serum UA and cardiovascular events, including cardiovascular death, non-fatal myocardial infarction, non-fatal stroke, heart failure, unstable angina, and arrhythmias requiring hospitalization.

RESULTS

Among 1314 men, 143 (10.9%) experienced cardiovascular events. Serum UA level was not associated with the risk of cardiovascular events (hazard ratio [HR] per 100 μmol/L increase in serum UA: 1.12, 95% confidence interval [CI]: 0.90-1.40). Among 913 women, 96 (10.5%) experienced cardiovascular events. For every 100 μmol/L increase in serum UA level, the risk of experiencing a cardiovascular event increased by 27% (HR: 1.27, 95% CI: 1.02-1.57).

CONCLUSIONS

In hospitalized patients with T2DM, baseline serum UA levels were positively associated with cardiovascular events in women, but not in men. Serum UA levels may be a significant independent risk factor for cardiovascular events in women with T2DM.

Independent association of serum uric acid levels with arterial stiffness in the absence of established cardiovascular disorders

BACKGROUND

The impact of serum uric acid (SUA) on atherosclerosis has been suspected to be epiphenomenal owing to its close relationship with metabolic abnormalities. The aim of the present study was to evaluate the association between SUA levels and arterial stiffness in the absence of established cardiovascular (CV) disorders.

METHODS

The relationship between SUA levels and brachial-ankle pulse wave velocity (baPWV) was examined in 353 asymptomatic adults (57 ± 8 years, 11.9% men) without established CV disorders defined as systolic blood pressure (BP) ≥140 mmHg or diastolic BP ≥ 90 mmHg; total cholesterol ≥240 mg/dL; low-density lipoprotein cholesterol ≥160 mg/dL; high-density lipoprotein cholesterol <40 mg/dL; fasting glucose ≥126 mg/dL; body mass index ≥25.0 kg/m² ; current smoking; and history of medication for hypertension, diabetes, and dyslipidemia. Subjects were stratified into four groups based on the quartiles of their SUA levels.

RESULTS

Mean baPWV was significantly different in all groups: group I, 1320 ± 195 cm/s; group II, 1336 ± 195 cm/s; group III, 1404 ± 199 cm/s; and group IV, 1483 ± 248 cm/s (P < .001). SUA levels were significantly correlated with baPWV (r = .364) (P < .001). Multivariate linear regression analysis showed that SUA (β: 32.93; 95% confidence interval [CI]: 18.99-54.87), together with age (β: 11.44; 95% CI: 9.36-13.53) and systolic BP (β: 8.98; 95% CI: 6.80-11.16), was significantly associated with baPWV (P < .001).

CONCLUSIONS

High SUA levels have an independent association with increased arterial stiffness even in subjects without established CV disorders.

Serum uric acid in asymptomatic adults is weakly associated with carotid artery FDG uptake but not intima-media thickness

BACKGROUND

This study investigated the association of serum uric acid (UA) with carotid fluoro-2-deoxyglucose (FDG) uptake as a marker of inflammatory atherosclerosis.

METHODS AND RESULTS

In this cross-sectional retrospective study of 970 otherwise healthy adults, subjects in the greater serum UA quartiles had higher triglyceride (P < .001), lower high-density lipoprotein cholesterol (P < .05), and lower estimated GFR (P < .001). Mean and maximum Target-to-background ratios (TBRs) of carotid FDG uptake measured by positron emission tomography were significantly increased across greater serum UA quartiles (1.35 and 1.57 for Q1, 1.38 and 1.60 for Q2, 1.39 and 1.62 for Q3, and 1.39 and 1.61 for Q4; P = .001 and < .001). Carotid intima-media thickness was not different. Serum UA showed weak but significant correlations with estimated GFR (P < .001), and with mean (P < .001) and maximum carotid TBR (P = .004). Serum UA correlated with mean TBR in male (P = .008) and female subjects (P = .011), in high (≥ 70; P = .015) and low estimated GFR (< 70; P = .035), and in normotensive (P = .001) but not in hypertensive subjects.

CONCLUSIONS

Elevated serum UA in asymptomatic adults is associated with increased carotid FDG uptake, which suggests a potential role of UA in carotid inflammatory atherosclerosis.

A facile fluorescence assay for rapid and sensitive detection of uric acid based on carbon dots and MnO2nanosheets

A sensitive turn-on fluorescence method for uric acid detection is proposed based on FRET between carbon dots and MnO₂nanosheets.

Lower serum uric acid level strongly predict short-term poor functional outcome in acute stroke with normoglycaemia: a cohort study in China

BACKGROUND

Conflicting results on the correlation between hyperuricemia and the prognosis of stroke had been reported and the close association between serum uric acid (SUA) and abnormal glycomatabolism might further complicate the assessment of the correlation. We aimed to investigate SUA in predicting the prognosis of acute stroke in different glycometabolism status.

METHODS

A total of 2907 patients aged from 18 to 85 (1220 diabetes mellitus (DM), 777 prediabetes and 910 normoglycemia) were selected from the Abnormal Glucose Regulation in Patients with Acute Stroke across China (ACROSS-China) study. The patients were divided into groups according to the SUA quartile as well as decile. The correlations between SUA and the poor outcome (mRS > 2) at discharge were assessed stratified by glucose metabolism status. Multivariate logistic regression was used to analyze the potential risk factors of poor in-hospital outcome of stroke and the risk-adjustment of the correlation between SUA and the prognosis of stroke. P < 0.05 was considered statistically significant.

RESULTS

SUA were divided first as Quartile1 to 4 (Quartile1 < 221 μmol L-1; Quartile2 (221-286) μmol L-1; Quartile3 (286-352) μmol L-1 and Quartile4 > 352 μmol L-1), then as decile1 to 10. In normoglycaemia, SUA quartiles, deciles and continuous SUA concentration were independently significantly associated with poor outcome. Q1 was independently associated with the higher possibility of poor functional outcome (compared to Q4, odds ratios (ORs) with 95% confidential interval (CI) was 3.79 (1.23-8.67) in Q1); Lower level of SUA in DM was also associated with poor functional outcome at discharge compared to the highest level of SUA(Q4)(OR with 95% CI, 2.07 (1.05-4.08)), however, lower SUA level was also related to severer stroke at admission in DM as well as in prediabetes (P < 0.001 in DM and 0.023 in prediabetes) and severer stroke resulted in worse functional outcome at discharge (OR with 95% CI, 12.15 (8.08-18.21) in DM and 11.58 (7.50-23.25) in prediabetes). But in normoglycamic stroke, SUA levels did not differ in stroke severity at admission (P = 0.066).

CONCLUSIONS

Low SUA level (<221 μmol L-1) independently and strongly predicts the short-term poor functional outcome in acute stroke with normoglycaemia other than diabetes or prediabetes.

Risk of acute gout among active smokers: data from nationwide inpatient sample

Smoking has been found to be negatively correlated with serum uric acid levels by virtue of reduced production and increased consumption of endogenous antioxidant uric acid among smokers and has been reported to decrease incidence of gout. To shed further light on the question of association between active smoking and acute gout by examining this association using a large inpatient US database, using the Nationwide Inpatient Sample data from 2009 to 2011, we identified current smokers based on the International Classification of Diseases, Ninth Revision (ICD-9) code 305.1 and were assumed to have ceased smoking during hospital stay. Patients who developed acute gout inhospital were identified based on ICD-9 code 274.01 at secondary diagnosis position. Univariate and multivariate logistic regressions were used to derive odds ratio for measures of association. Statistical analysis was done using STATA version 13.0 (College Station, TX). A total of 17,847,045 discharge records were used which included 13,932 (0.08 %) inhospital acute gouty arthritis and 2,615,944 (14.66 %) active smokers. Both univariate (OR 0.59, CI 0.54-0.63, p < 0.0001) and multivariate (OR 0.64, CI 0.59-0.68, p < 0.0001) regressions showed statistically significant reduction of acute gout among hospitalized patients who were current smokers but were assumed to have ceased smoking during hospital stay. Active tobacco use was associated with a lower risk of acute inpatient gouty arthritis, even when controlling for conventional risk factors. More study is needed to correlate this finding with uric acid levels, and a better understanding of the mechanisms that explain this finding are necessary.

Serum uric acid levels are associated with hypertension and metabolic syndrome but not atherosclerosis in Chinese inpatients with type 2 diabetes

Objective:

Serum uric acid (SUA) is associated with many cardiovascular risk factors such as hypertension (HTN) and metabolic syndrome (MetS). However, the association of SUA with atherosclerosis remains controversial. Our aim was to investigate the relationships of SUA with HTN, MetS and atherosclerosis in Chinese inpatients with type 2 diabetes.

Methods:

This cross-sectional study was performed with a sample of 2388 hospitalized Chinese patients with type 2 diabetes. Both carotid and lower limb atherosclerotic lesions were assessed for intima–media thickness, plaque and stenosis by Doppler ultrasound. Atherosclerotic plaque and stenosis were defined as the presence of either carotid or lower limb plaques and stenoses, respectively.

Results:

There were significant increases in the prevalence of both HTN and MetS across the SUA quartiles (HTN: 43.4, 49.6, 56.1 and 66.3% for the first, second, third and fourth quartiles, respectively, P < 0.001; MetS: 59.9, 68.8, 74.7 and 84.9% for the first, second, third and fourth quartiles, respectively, P < 0.001). A fully adjusted multiple logistic regression analysis revealed that SUA quartile was independently associated with the presence of HTN (P = 0.001) and MetS (P = 0.006). The prevalence of atherosclerotic plaque and stenosis was obviously higher in the patients with either HTN or MetS than in those without HTN or MetS. However, there was no significant association of SUA quartile with the presence of atherosclerotic lesions.

Conclusions:

SUA levels were closely associated with HTN and MetS, but not with atherosclerosis in type 2 diabetes. Our findings strongly suggest that, in select populations such as those with type 2 diabetes, the role of uric acid in atherosclerosis might be attributable to other cardiovascular risk factors, such as HTN and MetS.

Decreased urine uric acid excretion is an independent risk factor for chronic kidney disease but not for carotid atherosclerosis in hospital-based patients with type 2 diabetes: a cross-sectional study

Background

The associations between urine uric acid excretion (UUAE) and chronic kidney disease (CKD)/atherosclerosis have not been investigated. Our aims were to investigate the relationships between UUAE and CKD and carotid atherosclerotic lesions in hospitalized Chinese patients with type 2 diabetes.

Methods

This was a cross-sectional study that was conducted with 2627 Chinese inpatients with type 2 diabetes. UUAE was determined enzymatically using a single 24-h urine collection. The subjects were stratified into quartiles according to their UUAE levels. Carotid atherosclerotic lesions, including carotid intima-media thickness (CIMT), plaque and stenosis, were assessed by Doppler ultrasound. Both CKD and carotid atherosclerotic lesions were compared between the UUAE quartile groups.

Results

After adjustment for confounding factors, there was a significant decrease in the prevalence of CKD in the patients with type 2 diabetes across the UUAE quartiles (16.9%, 8.5%, 5.9%, and 4.9%; p < 0.001). Multiple logistic regression analyses revealed that the UUAE quartiles were significantly and inversely associated with the presence of CKD (p < 0.001). Compared with the diabetics in the highest UUAE quartile, those in the lowest quartile exhibited a nearly 4.2-fold increase in the risk of CKD (95% CI: 2.272-7.568; p < 0.001). The CIMT value (0.91 ± 0.22 mm for the diabetics with CKD and 0.82 ± 0.20 mm for the diabetics without CKD, p = 0.001) and the prevalence of carotid plaques (62.1% for the diabetics with CKD and 41.8% for the diabetics without CKD, p = 0.025) were significantly higher in the diabetics with CKD than in those without CKD. However, there was no obvious difference in carotid atherosclerotic lesions across the UUAE quartiles after controlling for the confounding factors.

Conclusions

Decreased UUAE was closely associated with the presence of CKD but not with carotid atherosclerotic lesions in hospitalized Chinese patients with type 2 diabetes. Our results suggest that UUAE is an independent risk factor for CKD in type 2 diabetes. In selected populations, such as patient with type 2 diabetes, the role of uric acid in atherosclerosis might be the result of other concomitant atherosclerotic risk factors, such as CKD.

Hyperuricemia is associated with progression of IgA nephropathy

BACKGROUND AND AIM

IgA nephropathy (IgAN) is one of the world's most common glomerular diseases. Hyperuricemia was recently defined as risk factor for chronic kidney disease. We aimed to investigate the impact of baseline serum uric acid levels on progression of IgAN.

MATERIALS AND METHODS

A total of 93 patients with IgAN were screened. Demographic information and biochemical data were recorded. eGFR (using the CKD-EPI = Chronic Kidney Disease Epidemiology Collaboration formula) was used as renal function marker. Baseline and sixth month eGFR values were calculated. Progression of renal disease was defined as the difference between baseline eGFR and sixth month eGFR (delta eGFR).

RESULTS

Mean age of the patients was 40 ± 11 years (60% were males). Baseline mean eGFR was 77.9 ± 30.2 mL/min, and baseline mean serum uric acid was 5.65 ± 1.68 mg/dL. Importantly, baseline serum uric acid levels were found to be associated with the change in eGFR (r = 0.252, p = 0.01). In multivariate analysis (adjusted R(2) = 0.171, p = 0.031), adjusting for age, gender, baseline eGFR, blood pressure, baseline albumin concentration and ACEI and/or ARB use revealed that the baseline serum uric acid levels significantly predicted the change in eGFR.

CONCLUSION

Baseline serum uric acid concentration is directly proportional to the rate of decline in renal functions in patients with IgAN. Uric acid-lowering treatments may be beneficial for the prevention of progression of IgAN. However, randomized controlled studies are needed for this purpose.

Hyperuricemia is an independent risk factor for mortality only if chronic kidney disease is present

BACKGROUND/AIMS

Hyperuricemia has been considered a risk factor for renal disease and cardiovascular disease. However, the potential contribution of hyperuricemia to mortality remains uncertain, and the results in the available literature vary according to kidney function. The aim of this study was to determine the association between hyperuricemia and mortality in patients undergoing percutaneous coronary intervention (PCI) across the interaction of kidney function.

METHOD

We retrospectively reviewed patients who underwent PCI from 2003 to 2009. Propensity scores for hyperuricemia (>7 mg/dl for males and >6 mg/dl for females) were used to assemble a matched cohort of 693 pairs of patients with and without hyperuricemia for analysis from the 3,201 patients who fulfilled the inclusion criteria among the 4,842 patients who underwent PCI.

RESULTS

Of the 3,201 patients who underwent PCI and for whom data were available regarding their baseline serum uric acid level, 763 (23.8%) had hyperuricemia. The hyperuricemia-associated hazard ratios (HRs) [95% confidence intervals (CIs)] for all-cause mortality were 1.780 (1.270-2.495) in the unmatched cohort and 1.655 (1.109-2.468) in the matched cohort. The HRs (95% CI) for all-cause mortality among those with and without chronic kidney disease (CKD) were 2.080 (1.318-3.283) and 1.592 (0.778-3.256), respectively (p for interaction, 0.001).

CONCLUSIONS

Hyperuricemia is an independent risk factor for all-cause mortality in those patients with CKD but not in those without CKD.

Riboflavin supplementation and biomarkers of cardiovascular disease in the elderly

BACKGROUND

High levels of total plasma homocysteine are potentially harmful in the elderly.

OBJECTIVE

To investigated the effects of oral riboflavin supplementation on plasma total homocysteine, ferritin, uric acid and C-reactive protein concentration in elderly people with a low riboflavin status. We performed a four-week randomized, placebo-controlled, double-blind trial of riboflavin supplementation in seven Portuguese day social centers.

DESIGN

Eighty-eight individuals (66.7% female), aged between 60 and 94 years, volunteered to participate in the study following interview. Forty-two subjects, with an erythrocyte glutathione reductase activation coefficient (EGRAC) >or= 1.2, were included in the intervention trial. All subjects gave informed consent. Study subjects were administered 10 mg riboflavin (n=21) or placebo (n=21) each day for 28 days.

RESULTS

Riboflavin supplementation significantly decreased plasma tHcy (P=0.005) and EGRAC (P=0.014), but not plasma ferritin, uric acid or C-reactive protein.

CONCLUSIONS

In this elderly group, we found that 10 mg/day oral riboflavin supplementation lowered plasma homocysteine concentrations in subjects with low riboflavin status.

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.

Relation of Serum Uric Acid Levels With the Presence and Severity of Angiographic Coronary Artery Disease

The aim of this study is to investigate the association between uric acid level and severity of coronary artery disease. Consecutive 495 patients with coronary artery disease and 356 individuals with normal coronary angiograms were included in the study. Severity of coronary artery disease was evaluated using the Gensini score index. For both groups, conventional risk factors, the levels of uric acid, and other biochemical markers were assessed. The mean uric acid levels of the patient group were significantly higher than those of the control group ( P = .002). Mean uric acid levels were higher in men than in women ( P < .001). In the coronary artery disease group, there was no significant correlation between uric acid levels and Gensini score in both sexes. Thus, it can be concluded that uric acid level is associated with the presence but not with the severity of coronary artery disease.

Independent association of high serum uric acid concentration with angiographically defined coronary artery disease

Epidemiological studies have shown that a high serum uric acid concentration is a risk factor for coronary artery disease (CAD). However, the issue of whether it is an independent cardiovascular risk factor or simply a marker of co-existing conditions is a matter of controversy. In the present case-controlled study, we explored the association between serum uric acid and angiographically defined CAD in middle-aged subjects (356 CAD patients and 350 healthy individuals). Serum uric acid in CAD patients was significantly higher than that in healthy individuals (359 +/- 88.7 and 289 +/- 79.3 micromol/l, respectively, p < 0.01) and remained significantly higher after adjusting for confounding factors (F = 79.77, p < 0.01). The association between uric acid and CAD was not limited to the hyperuricemic range of values, but was also found in the high-normal range (p < 0.01). An unadjusted odds ratio (OR) of 5.0 was obtained in both genders (p < 0.01). Female patients with > 50% stenosis (clinically significant CAD), regardless of the number of diseased vessels, had higher uric acid concentrations than those with < 50% stenosis even after adjusting for confounders (F = 3.79, p = 0.01). In conclusion, we have demonstrated that high serum uric acid is independently associated with CAD and that uric acid determination could be useful as one of the markers of clinically significant CAD.

Serum uric acid and risk of ischemic stroke: The ARIC Study

AIMS

Since serum uric acid (UA) is strongly associated with cardiovascular risk factors, it has been debated whether serum UA is a stroke risk factor or whether UA may be simply "marking" subjects with other, causal risk factors. We therefore investigated the relation between UA and ischemic stroke in the Atherosclerosis Risk in Communities (ARIC) Study.

METHODS AND RESULTS

Of 15,792 ARIC participants, 13,413 who were free of recognized stroke or coronary heart disease (CHD) at baseline and had a baseline UA measurement were included in the analysis. We followed the participants for ischemic stroke incidence (N=381) over 12.6 years. Although serum UA was independently and positively related to ischemic stroke incidence when we adjusted for age, sex, race, and education, the positive relation was weakened when additionally adjusted for possible confounding variables. The positive multivariate-adjusted association between serum UA and ischemic stroke was observed among subjects not using diuretics (adjusted relative hazard in the highest quartile versus the lowest: relative hazard (RH)=1.49; 95% confidence interval (CI): 1.00-2.23) (P for trend: 0.02), but not among diuretic users (P for interaction: 0.08).

CONCLUSION

Our findings suggest that UA is an independent predictor of ischemic stroke among subjects not using diuretics, but that elevated UA itself may not cause ischemic stroke.

Hyperuricemia and Associated Diseases

After introduction of urate-lowering therapy, asympotomatic hyperuricemia was treated with allopurinol or uricosuric agents in the belief that hyperuricemia and/or gout caused chronic kidney disease. Epidemiologic studies in the 1970s, however, failed to confirm the view that hyperuricemia and gout were independent risk factors for chronic kidney disease. As a result, urate-lowering pharmacotherapy is generally not recommended at the present time in the management of asymptomatic hyperuricemia even though recent epidemiological, experimental, and clinical studies have prompted reexamination of a causal role for hyperuricemia (with or without gout) in chronic kidney disease as well as other important disorders including cardiovascular disease, hypertension, and metabolic syndrome. The issue of such a role remains unresolved and this article reviews the current status of the relationship between hyperuricemia and associated disorders.

Uric acid and the vasculature

Hyperuricemia is a frequent finding in diseases in which the clinical manifestations are thought to be secondary to a state of generalized vascular endothelial dysfunction and related to the cardiovascular disease present in conditions associated with the metabolic syndrome, such as hypertension or diabetes. Traditionally, uric acid has not been given an active role in the pathologic process underlying these conditions. However, there is now a growing body of experimental and clinical evidence that points to a mechanistic role for uric acid in cardiovascular disease. The mechanisms that are most often thought to link uric acid and endothelial dysfunction involve inflammation and generation of oxidative stress in the vasculature. These observations allowed new clinical applications and formulations of therapies, such as the introduction of xanthine oxidase inhibitors in the management of congestive heart failure.

Diagnosis and management of gout: a rational approach

Gout is one of the best understood among the rheumatological disorders and one of the most satisfying to treat. Even non-specialists should be able to diagnose and treat most patients provided some important principles are appreciated. Management of a minority of patients, including those with renal impairment is difficult and often unsatisfactory, because of restricted treatment options. In this paper, the basic principles underlying the diagnosis and management of gout are discussed first, followed by practical approaches.

Elevated serum urate concentration independently predicts poor outcome following stroke in patients with diabetes

BACKGROUND

Type 2 diabetes is a risk factor for stroke and confers increased risk of poor outcome and further vascular events following stroke. Hyperuricaemia occurs commonly in patients with type 2 diabetes, but its significance as a predictor of outcome following stroke is uncertain. We sought to investigate the prognostic significance of elevated serum urate concentration in diabetic subjects following stroke.

METHODS

We studied a cohort of type 2 diabetes patients presenting to our unit with computed tomography-confirmed acute stroke. Fasting blood samples were drawn within 24 h of admission for urate concentration and standard battery of biochemistry and hematological tests. Information on age, stroke type, prior hypertension, smoking status, resolution time of symptoms and National Institutes of Health Stroke Score was collated. The main outcome event was time to myocardial infarction, recurrent stroke or vascular death, as defined in the CAPRIE trial. Stepwise proportional hazards regression was used to estimate the effect of the above variables on event-free survival following stroke.

RESULTS

One hundred and forty patients were studied. Median follow-up duration was 974 days (IQR 163 to 1830 days). Sixty-four patients suffered an outcome event. Urate levels of greater than 0.42 mmol/L (p < 0.001) and an increasing NIHSS score (p < 0.001) independently predicted increased likelihood of suffering an event.

CONCLUSION

Elevated urate concentration is significantly and independently associated with increased risk of future vascular events in diabetic stroke patients. Further studies to elucidate the mechanism of this observation are required.

Cyanotic congenital heart disease and coronary artery atherogenesis

Hypoxemic erythrocytotic residents of high altitudes lack coronary atherosclerosis and have low cholesterol levels. It was postulated that hypoxemic erythrocytotic adults with cyanotic congenital heart disease (CCHD) might be analogous. The incidence of coronary atherosclerosis in this patient population has not been established, and hypocholesterolemia has not previously been recognized. Accordingly, 279 patients were divided into 4 groups: group A: 143 cyanotic patients not operated on (54 men and 89 women, aged 18 to 69 years); group B: 47 cyanotic patients (28 men and 19 women rendered acyanotic by operation at age 22 to 69 years); group C: 41 acyanotic patients not operated on (22 men and 19 women, aged 22 to 75 years); and group D: 48 patients acyanotic before and after operation (24 men and 24 women, aged 21 to 70 years). Coronary arteries were studied angiographically in 59 patients and at necropsy in 5 subjects aged 37 to 56 years. Total cholesterol was <160 mg/dl in 58% of group A, 52% of group B, 10% of group C, and 12% of group D (p <0.000001, chi-square analysis). Angiograms disclosed dilated coronary arteries without obstruction. Necropsy disclosed ectatic coronary arteries with structural abnormalities of the media. In conclusion, this study provides the first quantitative and qualitative data on antiatherogenic changes in lipoproteins in adults with CCHD. The coronary arteries are atheroma free because hypocholesterolemia acts in concert with the antiatherogenic properties of upregulated nitric oxide, hyperbilirubinemia, hypoxemia, and low platelet counts. The persistence of hypocholesterolemia after the surgical elimination of cyanosis suggests a genetic determinant.

Serum uric acid and coronary heart disease in 9,458 incident cases and 155,084 controls: prospective study and meta-analysis

BACKGROUND

It has been suggested throughout the past fifty years that serum uric acid concentrations can help predict the future risk of coronary heart disease (CHD), but the epidemiological evidence is uncertain.

METHODS AND FINDINGS

We report a "nested" case-control comparison within a prospective study in Reykjavik, Iceland, using baseline values of serum uric acid in 2,456 incident CHD cases and in 3,962 age- and sex-matched controls, plus paired serum uric acid measurements taken at baseline and, on average, 12 y later in 379 participants. In addition, we conducted a meta-analysis of 15 other prospective studies in eight countries conducted in essentially general populations. Compared with individuals in the bottom third of baseline measurements of serum uric acid in the Reykjavik study, those in the top third had an age- and sex-adjusted odds ratio for CHD of 1.39 (95% confidence interval [CI], 1.23-1.58) which fell to 1.12 (CI, 0.97-1.30) after adjustment for smoking and other established risk factors. Overall, in a combined analysis of 9,458 cases and 155,084 controls in all 16 relevant prospective studies, the odds ratio was 1.13 (CI, 1.07-1.20), but it was only 1.02 (CI, 0.91-1.14) in the eight studies with more complete adjustment for possible confounders.

CONCLUSIONS

Measurement of serum uric acid levels is unlikely to enhance usefully the prediction of CHD, and this factor is unlikely to be a major determinant of the disease in general populations.

Prevention and treatment of the metabolic syndrome

The prevalence of the metabolic syndrome is increasing owing to lifestyle changes leading to obesity. This syndrome is a complex association of several interrelated abnormalities that increase the risk for cardiovascular disease and progression to diabetes mellitus (DM). Insulin resistance is the key factor for the clustering of risk factors characterizing the metabolic syndrome. The National Cholesterol Education Program (NCEP) Adult Treatment Panel (ATP) III defined the criteria for the diagnosis of the metabolic syndrome and established the basic principles for its management. According to these guidelines, treatment involves the improvement of the underlying insulin resistance through lifestyle modification (eg, weight reduction and increased physical activity) and possibly by drugs. The coexistent risk factors (mainly dyslipidemia and hypertension) should also be addressed. Since the main goal of lipid-lowering treatment is to achieve the NCEP low-density lipoprotein cholesterol (LDL-C) target, statins are a good option. However, fibrates (as monotherapy or in combination with statins) are useful for the treatment of the metabolic syndrome that is commonly associated with hypertriglyceridemia and decreased high-density lipoprotein cholesterol (HDL-C) levels. The blood pressure target is < 140/90 mm Hg. The effect on carbohydrate homeostasis should possibly be taken into account in selecting an antihypertensive drug. Patients with the metabolic syndrome commonly have other less well-defined metabolic abnormalities (eg, hyperuricemia and raised C-reactive protein levels) that may also be associated with an increased cardiovascular risk. It seems appropriate to manage these abnormalities. Drugs that beneficially affect carbohydrate metabolism and delay or even prevent the onset of DM (eg, thiazolidinediones or acarbose) could be useful in patients with the metabolic syndrome. Furthermore, among the more speculative benefits of treatment are improved liver function in nonalcoholic fatty liver disease and a reduction in the risk of acute gout.

Hypothesis: obesity and the insulin resistance syndrome play a major role in end-stage renal failure attributed to hypertension and labelled 'hypertensive nephrosclerosis'

About a third of new cases of renal failure in USA are attributed to hypertension despite controversy about the frequency and pathology of so called hypertensive nephrosclerosis. In spite of good documentation that obesity causes renal failure and in spite of the global epidemic of obesity this diagnosis does not feature on most renal failure registries. New documentation that progressive renal failure in hypertension is linked to insulin resistance and analysis of NHANES III data which shows a strong positive significant dose-response relationship between insulin resistance and chronic kidney disease strengthen the view that so called hypertensive nephrosclerosis may be linked more closely to obesity and insulin resistance than to blood pressure. The pathology of the kidney in hypertension has changed. Studies 50 years ago did not show segmental glomerulosclerosis, which has recently been shown to be the key lesion in hypertensive nephrosclerosis. Recent documentation that this is a major mechanism of progression in hypertension together with the fact that similar segmental glomerulosclerosis is the key lesion in obesity and the metabolic syndrome suggests that these factors are more important than hypertension in renal failure attributed to hypertensive nephrosclerosis.

Uric acid and chronic renal disease: Possible implication of hyperuricemia on progression of renal disease

Although hyperuricemia has long been associated with renal disease, uric acid has not been considered as a true mediator of progression of renal disease. The observation that hyperuricemia commonly is associated with other risk factors of cardiovascular and renal disease, especially hypertension, has made it difficult to dissect the effect of uric acid itself. However, recent epidemiologic evidence suggests a significant and independent association between the level of serum uric acid and renal disease progression with beneficial effect of decreasing uric acid levels. Furthermore, our experimental data using hyperuricemic animals and cultured cells have provided robust evidence regarding the role of uric acid on progression of renal disease. Hyperuricemia increased systemic blood pressure, proteinuria, renal dysfunction, vascular disease, and progressive renal scarring in rats. Recent data also suggest hyperuricemia may be one of the key and previously unknown mechanisms for the activation of the renin-angiotensin and cyclooxygenase-2 (COX-2) systems in progressive renal disease. Although we must be cautious in the interpretation of animal models to human disease, these studies provide a mechanism to explain epidemiologic data that show uric acid is an independent risk factor for renal progression. Although there is no concrete evidence yet that uric acid bears a causal or reversible relationship to progressive renal disease in humans, it is time to reevaluate the implication of hyperuricemia as an important player for progression of renal disease and to try to find safe and reasonable therapeutic modalities in individual patients based on their clinical data, medication history, and the presence of cardiovascular complications.

Uric acid correlates with the severity of histopathological parameters in IgA nephropathy

BACKGROUND

Immunoglobulin-A nephropathy (IgAN) is the most common chronic glomerulonephritis worldwide. Many clinical and histopathological risk factors for progression have been found previously. Recently, metabolic risk factors, such as hyperuricaemia and hypertriglyceridaemia, also have been associated with the progression of IgAN.

METHODS

In the present study we correlated clinical and metabolic risk factors with histopathological parameters in 202 patients with IgAN. Morphological changes in glomerular, tubulointerstitial and vascular tissue were semiquantitatively graded into three classes. Mesangial proliferation activity and the amount of inflammatory cells were also evaluated by immunohistochemical staining of Ki-67 (MIB-1), CD45 (LCA) and CD68 stainings. Serum uric acid, triglycerides and cholesterol, urine protein excretion (UPE), blood pressure and body mass index (BMI) were measured. Smoking habits and occurrence of diabetes mellitus also were evaluated. The independent role of serum uric acid in the development of renal morphological changes was evaluated in multivariate analysis.

RESULTS

Serum uric acid and UPE level correlated with several histological parameters. Uric acid level showed the strongest correlation with tubulointerstitial changes and UPE with glomerulosclerosis. The level of serum triglycerides correlated with interstitial fibrosis and hyaline arteriolosclerosis. Blood pressure correlated with hyaline arteriolosclerosis, glomerulosclerosis and tubulointerstitial changes. BMI and diabetes mellitus correlated with both tubulointerstitial and vascular changes. We found no significant correlations between histopathological parameters and smoking habits or serum cholesterol level. Serum uric acid had independent associations with the presence of tubular atrophy and interstitial fibrosis and inflammation.

CONCLUSIONS

We conclude that many metabolic factors are univariately associated with renal morphological findings in IgAN. These same factors are central in the metabolic or insulin resistance syndrome and may have a pathogenetic role in the progression of IgAN. Serum uric acid may have an independent role in development of tubulointerstitial lesions as well as being associated with inflammation in renal tissue of patients with IgAN.

Primary prevention in rheumatology: the importance of hyperuricemia

Hyperuricemia (HU) is present in 5-30% of the general population, although the prevalence is higher among some ethnic groups and seems to be increasing worldwide. Classically, chronic HU has been considered a risk factor for gout or lithiasis and is associated with alcoholism, obesity, hypertension, dyslipidemia, hyperglycemia/diabetes mellitus, renal failure and intake of certain drugs. HU is also associated with cardiovascular diseases such as hypertension, vascular disease, pre-eclampsia, pulmonary arterial hypertension, stroke, heart failure, ischemic heart disease and also metabolic syndrome, renal disease and increased mortality. It is uncertain if these associations are dependent or not, especially cardiovascular and renal diseases. Patients with chronic HU and also those with gout require both medical investigation for associated diseases or drugs as well as nutritional counseling and life-style changes. HU should alert physicians to possible complications.

Serum uric acid in traditional Pacific Islanders and in Swedes

BACKGROUND

In some western populations, increased serum uric acid has been positively associated with cardiovascular disease, possibly because hyperuricaemia could be an untoward part of the insulin-resistant metabolic syndrome. However, there is evidence that uric acid is a free radical scavenger capable of inhibiting LDL oxidation. Amongst the traditional horticulturalists of Kitava, Trobriand Islands, Papua New Guinea, cardiovascular disease, hypertension, hyperinsulinaemia and abdominal obesity are absent or rare. In contrast, serum triglycerides are similar to Swedish levels.

OBJECTIVE

To compare serum uric acid between nonwesternized and westernized populations.

METHODS

Fasting levels of serum uric acid were measured cross-sectionally in 171 Kitavans aged 20-86 years and in 244 randomly selected Swedish subjects aged 20-80 years.

RESULTS

There were small differences in serum uric acid between the two populations, although a slight increase with age was found only in Swedish males (r = 0.20; P = 0.03) and females (r = 0.36; P < 0.0001). Above 40 years of age, uric acid was approximately 10% lower in Kitavans, a difference which was statistically significant only in males, possibly because of the limited number of females. Regarding hyperuricaemia, two Kitavan males had uric acid above 450 micromol L-1 whilst none of the females was above 340 micromol L-1. Amongst the Swedish subjects, five of 117 males and 19 of 127 females had hyperuricaemia according to these definitions.

CONCLUSION

The rather similar uric acid levels between Kitava and Sweden imply that uric acid is of minor importance to explain the apparent absence of cardiovascular disease in Kitava.

Insulin sensitivity in Chinese ovo-lactovegetarians compared with omnivores

AIM

To compare the insulin sensitivity indices between Chinese vegetarians and omnivores.

METHODS

The study included 36 healthy volunteers (vegetarian, n=19; omnivore, n=17) who had normal fasting plasma glucose levels. Each participant completed an insulin suppression test. We compared steady-state plasma glucose (SSPG), fasting insulin, the homeostasis model assessment for insulin sensitivity (HOMA-IR and HOMA %S) and beta-cell function (HOMA %beta) between the groups. We also tested the correlation of SSPG with years on a vegetarian diet.

RESULTS

The omnivore subjects were younger than the vegetarians (55.7+/-3.7 vs 58.6+/-3.6 year of age, P=0.022). There was no difference between the two groups in sex, blood pressure, renal function tests and lipid profiles. The omnivores had higher serum uric acid levels than vegetarians (5.25+/-0.84 vs 4.54+/-0.75 mg/dl, P=0.011). The results of the indices were different between omnivores and vegetarians (SSPG (mean+/-s.d.) 105.4+/-10.2 vs 80.3+/-11.3 mg/dl, P<0.001; fasting insulin, 4.06+/-0.77 vs 3.02+/-1.19 microU/ml, P=0.004; HOMA-IR, 6.75+/-1.31 vs 4.78+/-2.07, P=0.002; HOMA %S, 159.2+/-31.7 vs 264.3+/-171.7%, P=0.018) except insulin secretion index, HOMA %beta (65.6+/-18.0 vs 58.6+/-14.8%, P=0.208). We found a clear linear relation between years on a vegetarian diet and SSPG (r=-0.541, P=0.017).

CONCLUSIONS

The vegetarians were more insulin sensitive than the omnivore counterparts. The degree of insulin sensitivity appeared to be correlated with years on a vegetarian diet.

Association of a 27-bp repeat polymorphism in intron 4 of endothelial constitutive nitric oxide synthase gene with serum uric acid levels in Chinese subjects with type 2 diabetes

Nitric oxide (NO) was found to modulate uric acid production through its influence on xanthine oxidase activity, and a close circadian relationship of serum uric acid (SUA) and NO was reported. Studies also revealed that serum NO activity could be determined by endothelial constitutive nitric oxide synthase gene (ecNOS) polymorphism. This study was designed to investigate whether SUA could be influenced by a 27-bp repeat polymorphism in intron 4 of ecNOS gene. A total of 398 nondiabetic subjects and 800 patients with type 2 diabetes were studied. The ecNOS gene intron 4 polymorphism was determined by polymerase chain reaction (PCR). The mean SUA level of patients having type 2 diabetes was significantly lower than that of control subjects (6.1 +/- 1.8 mg/dL v 6.6 +/- 1.8 mg/dL, P<.001); and the mean SUA level of diabetic patients with ecNOS ab/aa genotypes was lower than that of patients with bb genotype (5.7 +/- 1.6 mg/dL v 6.2 +/- 1.8 mg/dL, P=.008). When subgrouped by gender, the SUA of female diabetic subjects was found to be significantly associated with ecNOS genotype. Using Pearson's correlation analysis and multiple linear regression analysis, ecNOS genotype was noticed to be an independent factor in contributing to SUA variability in female diabetic patients. Our results suggest that SUA levels may be associated with NO activity and can be genetically predetermined.

Hyperuricemia induces a primary renal arteriolopathy in rats by a blood pressure-independent mechanism

Hyperuricemia is associated with hypertension and vascular disease, but whether this represents a causal relationship or an epiphenomenon remains unknown. We recently reported a model of mild hyperuricemia in rats that results in increased blood pressure and mild renal fibrosis. In this study, we examined the effect of hyperuricemia on the renal vasculature. Rats fed 2% oxonic acid and a low-salt diet for 7 wk developed mild hyperuricemia (1.8 vs. 1.4 mg/dl, P < 0.05), hypertension [147 vs. 127 mmHg systolic blood pressure (SBP), P < 0.05], and afferent arteriolar thickening, with a 35% increase in medial area (P < 0.05). Allopurinol or benziodarone prevented the hyperuricemia, hypertension, and arteriolopathy. Hydrochlorothiazide treatment did not prevent the hyperuricemia or arteriolopathy despite controlling blood pressure. In contrast, the arteriolopathy and hypertension were prevented by both enalapril and losartan. Uric acid also directly stimulated vascular smooth muscle cell proliferation in vitro, and this was partially inhibited by losartan. Thus hyperuricemia induces a renal arteriolopathy in rats that is blood pressure independent and involves the renin-angiotensin system.

Portable electrochemical blood uric acid meter

We describe a new portable uric acid (UA) meter, called the UASure (Apex Biotechnology Corp., Hsinchu, Taiwan). The UASure is an electrochemical blood UA meter designed for fast monitoring of UA concentrations in one drop of capillary blood using an electrochemical test strip. We compared the UASure with the standard method, the Hitachi 7600 modular system (Hitachi, Tokyo, Japan), in 146 volunteers (average age 62.5 +/- 12.8 years). Of these, 65 were known hyperuricemic subjects, 17 of whom received medical therapy. The patients donated their capillary and venous blood samples in random order. Capillary blood and one drop of venous blood were tested immediately by the UASure. The venous blood in the test tube was sent to the central laboratory for serum UA measurement by the Hitachi 7600. The intra-assay coefficients of variation (CVs) of the UASure were 4.79%, 5.77%, and 3.08% at UA levels of 5.8, 7.1, and 13.5 mg/dl, respectively. The UA concentrations tested by the UASure correlated well with those by the Hitachi 7600 (r = 0.87 in venous sampling and r = 0.78 in capillary sampling, P < 0.001). The intraclass correlation was good for venous samples by the UASure (rI = 0.84, 95% CI 0.82-0.90), somewhat below the meaningful criterion for capillary samples by the UASure (rI = 0.77, 95% CI 0.69-0.83). UASure with venous sampling is interchangeable with the standard method for UA measurement.

Serum uric acid is not an independent risk factor for coronary heart disease

Many large epidemiologic studies have confirmed a positive association between raised serum uric acid and risk of coronary heart disease or cardiovascular disease, both in the general population and among hypertensive patients. There is much controversy concerning the role of uric acid as an independent risk factor in the development of coronary heart disease because serum uric acid is related to many of the established etiologic risk factors for cardiovascular disease that could confound the observed association. This review finds little support for an independent causal role for serum uric acid in the development of coronary heart disease.