Reappraisal of the pathogenesis and consequences of hyperuricemia in hypertension, cardiovascular disease, and renal disease

Ankle-arm index is a useful test for clinical practice in outpatients with suspected coronary artery disease

BACKGROUND

Although a low ankle-arm index (AAI) has been reported to be associated with increased risk of cardiovascular mortality in several populations, no data exist concerning the impact of AAI for outpatients with suspected coronary artery disease (CAD) in the clinical setting.

METHODS AND RESULTS

The present study enrolled 840 outpatients (age range 35-87 years, mean age 63.9+/-10.2) with suspected CAD. All patients underwent AAI measurements and coronary angiography, and based on the AAI values, they were divided into group A (AAI <0.9; n=191; CAD positive, 181) and group B (AAI >or=0.9; n=649; CAD positive, 509). Metabolic syndrome (MS), obesity, and level of the inflammatory biomarker high sensitive C-reactive protein (hsCRP) were compared between the 2 groups. The sensitivity, specificity, positive and negative predictive values in predicting CAD with an AAI value <0.9 in all patients were 26.2%, 93.3%, 94.8% and 21.6%, respectively. The patients in group A was significantly older and there was a higher female-to-male ratio than in group B. The presence of hypertension and diabetes mellitus, current smoking status, and levels of low density lipoprotein (LDL)-cholesterol level, uric acid and hsCRP differed significantly between the 2 groups. Group A had a higher percentage of high LDL-cholesterol level, high waist-to-hip ratio and more positive cases of MS than group B. Multivariate logistical regression analysis showed that AAI was related to MS, high levels of hsCRP (>3 mg/L) and uric acid (>7 mg/dl) with odds ratios of 1.769, 3.907 and 2.580, respectively.

CONCLUSIONS

The AAI test is an effective tool in predicting CAD in outpatients in clinical practise.

Unearthing uric acid: An ancient factor with recently found significance in renal and cardiovascular disease

Uric acid is strongly associated with cardiovascular and renal disease, but is usually not considered to have a causal role. However, recent experimental, epidemiological, and clinical studies provocatively suggest that uric acid may contribute to the development of hypertension, metabolic syndrome, and kidney disease in some patients. Clinical studies are urgently needed to examine this important possibility.

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 inflammatory markers

AIMS

The role of uric acid (UA) in the process of atherosclerosis and atherotrombosis is controversial. Epidemiological studies have recently shown that UA may be a risk factor for cardiovascular diseases and a negative prognostic marker for mortality in subjects with pre-existing heart failure.

METHODS AND RESULTS

We evaluate a relationship between UA levels and several inflammatory markers in 957 subjects, free of severe renal failure, from a representative Italian cohort of persons aged 65-95. Plasma levels of UA and white blood cell (WBC) and neutrophil count, C-reactive protein, interleukin-1 receptor antagonist (IL-1ra), interleukin-6 (IL-6), soluble IL-6 receptor (sIL-6r), interleukin-18 (IL-18), and tumor necrosis factor-alpha (TNF-alpha) were measured. Complete information on potential confounders was collected using standard methods. WBC (P=0.0001), neutrophils (P<0.0001), C-reactive protein (P<0.0001), IL-1ra (P<0.0001), IL-6 (P=0.0004), sIL-6r (P=0.002), IL-18 (P<0.0001), TNF-alpha (P=0.0008), and the percentage of subjects with abnormally high levels of C-reactive protein (P=0.004) and IL-6 (P=<0.0001) were significantly higher across UA quintiles. After adjustment for age, sex, behaviour- and disease-related confounders, results were virtually unchanged. In subjects with UA within the normal range, UA was significantly and independently associated with neutrophils count, C-reactive protein, IL-6, IL-1ra, IL-18, and TNF-alpha, whereas non-significant trends were observed for WBC (P=0.1) and sIL-6r (P=0.2).

CONCLUSION

A positive and significant association between UA and several inflammatory markers was found in a large population-based sample of older persons and in a sub-sample of participants with normal UA. Accordingly, the prevalence of abnormally high levels of C-reactive protein and IL-6 increased significantly across UA quintiles.

Changing electrolyte and acido-basic profile in HIV-infected patients in the HAART era

BACKGROUND

HIV-infected patients may develop a variety of underreported metabolic abnormalities that may be classified into HIVAN, specific HIV abnormalities, coincidental renal disorders and anti-retroviral-treatment-induced side effects.

METHODS

Our descriptive cross-sectional study evaluates the prevalence of electrolyte and acid base disorders in HIV patients in the HAART era in a tertiary care teaching hospital. All consecutive HIV-infected patients (n = 1,232) presenting at our Department of Infectious Disease over 3 months were included.

MEASUREMENTS

All available biochemical data obtained at admission or on the day of the visit were analyzed. We identified risk factors for electrolyte and acid base disorders with univariate regression analysis and multivariate stepwise regression analysis. Variables tested for significance included age, sex, absolute CD4 and CD8 counts, hepatitis B and C antibodies, and use and type of anti-retroviral medication.

RESULTS

Most frequent and clinically relevant abnormalities were hyperuricemia in 41.3%, hypophosphatemia in 17.2% and low bicarbonate level in 13.6% of HIV-tested patients. Plasma magnesium was out of the normal range in 38.9% and blood glucose in 25.3% of the tested patients. When CD4 count was below 200/mm3, 9.2% of tested patients experienced low serum calcium (vs. 0.5% if CD4 count >200/mm3, p < 0.002), 11.4% increased creatinine plasma level (vs. 2.3% if CD4 count >200/mm3, p < 0.0001) and 24.5% low serum bicarbonate (vs. 13.7% if CD4 count >200/mm3, p < 0.0001). Protease inhibitor treatment was a significant risk factor of hyperuricemia (p < 0.003). Non-nucleoside reverse transcriptase inhibitor therapy was significantly associated with less hyperuricemia (OR = 0.6, 95% CI 0.38-0.96) and with hypophosphatemia (OR = 2.0, 95% CI 1.1-3.4).

CONCLUSIONS

The profile of biochemical abnormalities in HIV-infected patients has changed, hyperuricemia and hypophosphatemia being the most prevalent. Causes are poorly understood. Interpretation of drug-induced side effects in the HIV patient is only meaningful if performed versus a control group of patients.

Serum uric acid is associated with microalbuminuria in prehypertension

Serum uric acid is associated with cardiovascular disease. However, the independent role of uric acid in the development of cardiovascular disease is uncertain. This study examined the cross-sectional association of serum uric acid level with microalbuminuria among 6771 subjects without diabetes or hypertension. Blood pressure was categorized as prehypertension (systolic blood pressure, 120 to 140 mm Hg or diastolic blood pressure, 80 to 90 mm Hg) and normotension (systolic blood pressure, <120 mm Hg and diastolic blood pressure, <80 mm Hg). Microalbuminuria was found in 4.0% of normotensive subjects (n=4819) and in 7.9% of prehypertensive subjects (n=1952). Prehypertensive subjects with microalbuminuria had higher uric acid level than those with normoalbuminuria (men, 387 [68] mmol/L versus 371 [69] mmol/L; P=0.017; women 286 [56] mmol/L versus 262 [54] mmol/L; P=0.006). However, the difference in serum uric acid level according to the presence or absence of microalbuminuria was not found in the normotensive group. Multiple logistic regression models showed that, in the prehypertensive group, after adjustment for other cardiovascular risk factors, the highest uric acid quartile entailed >2 times greater risk for microalbuminuria than the lowest quartile in both men (odds ratio, 2.12; 95% CI, 1.16 to 3.87) and women (odds ratio, 3.36; 95% CI, 1.17 to 9.69). In the normotensive group, serum uric acid quartile did not show the independent association with microalbuminuria. In conclusion, serum uric acid level was strongly associated with microalbuminuria in prehypertensive subjects.

Concentraciones séricas de uratos y excreción urinaria de ácido úrico en individuos con síndrome metabólico

BACKGROUND AND OBJECTIVES

Hyperuricemia is considered a feature of the metabolic syndrome (MS) despite serum uric acid (SUA) is not considered a diagnostic criterion. The main physiopathological disturbance leading to the increased SUA is not completely understood.

PATIENTS AND METHOD

Descriptive study without drug intervention including 141 subjects (NCEP-ATPIII: 105 with MS and 36 without MS). Serum UA levels were compared in subjects with and without MS. The mechanism of the rise in SUA levels was assessed (overproduction or decreased renal excretion). The relation of SUA levels to the HOMA index was also evaluated.

RESULTS

Subjects with MS showed significantly higher SUA levels (5.6 [1.6] vs 4.6 [1.7] mg/dl, p = 0.002), and lower urinary UA excretion than subjects without MS (UA clearance 3.60 [2.41] vs 4.65 [3.04] ml/min/m2, p = 0.049; excreted fraction of filtered UA 7.15 [4.72] vs 9.81 [6.78%], p = 0.045). Sex (male 6.1 [1.6] vs female 4.9 [1.6] mg/dl, p < 0.001), alcohol intake (drinkers 6.1 [1.8] vs non-drinkers 5.2 [1.6] mg/dl, p < 0.01), and MS (present 5.6 [1.6] absent 4.6 [1.7] mg/dl, p < 0.002), were significantly associated with SUA. In the multiple regression analysis, sex and MS were independently associated with SUA.

CONCLUSIONS

This study demonstrates significantly higher SUA levels in subjects with MS. A decreased urinary UA excretion, instead of urate overproduction, was the leading mechanism to explain high SUA. Serum UA levels were not associated with the HOMA index.

Uric acid: Its relationship to renal hemodynamics and the renal renin-angiotensin system

Reports relating hyperuricemia and hypertension have been filed for many decades. Nevertheless, controversy remains concerning serum uric acid concentration as an independent risk factor underlying coronary heart disease (CHD) and essential hypertension or as an indirect marker of renovascular involvement. Earlier studies in normotensive subjects and hypertensive patients demonstrated that serum uric acid concentration was closely related to intrarenal hemodynamic alterations, suggesting that it is an excellent marker of vascular involvement. Our data from clinical studies and in an animal model of severe hypertensive nephrosclerosis have strengthened this concept. Conversely, other reports have suggested that uric acid may be a pathogenetic factor. Supporting arguments for this theory maintain that experimental hyperuricemia induces hypertension and renal damage. Epidemiologically, hyperuricemia is associated with hypertension, CHD, renal disease, toxemia of pregnancy, and other outcomes, although mechanisms remain unclear. Additionally, there are no available data on the effects of lowering uric acid on pressure control and organ protection.

Lead blood concentrations and renal function evaluation: study in an exposed Mexican population

The relation of blood Pb concentrations and renal dysfunction has been reported in association with interstitial fibrosis, tubular atrophy, and decreased glomerular filtration. In this report information about blood Pb concentrations and renal function tests in a population from Oaxaca, Mexico is analyzed. The main changes found were that males had higher blood Pb concentrations than females (P<0.0012); the leading variables associated with this were occupation (glazed pottery workers, P=0.0001) and the use of glazed pottery for preparing meals (P=0.0000). Variables that better explain uric acid variability were blood Pb concentrations, sex, weight, and height (r2=0.23). Hyperuricemia was associated with blood Pb concentrations above 40 microg/dL (OR=1.74, 95% CI, 1.12-2.61). SCr was associated with sex, age, and blood Pb, with coefficient r2=0.12. Our findings might be related to inadequate control of oven emissions, a situation that will require further analysis and the implementation of preventive measurements for the nonoccupational exposed population.

Uric acid concentrations in early pregnancy among preeclamptic women with gestational hyperuricemia at delivery

OBJECTIVE

We investigated changes in serum uric acid across pregnancy in women with gestational hyperuricemia at delivery, with and without preeclampsia, compared with normal pregnant and women with preeclampsia without gestational hyperuricemia.

STUDY DESIGN

This was a nested case-control study of 116 controls, 27 women with preeclampsia with predelivery hyperuricemia, 37 women with preeclampsia without predelivery hyperuricemia, and 35 women with gestational hypertension with hyperuricemia at delivery but without proteinuria. Serum uric acid and creatinine was measured across pregnancy.

RESULTS

Women with predelivery hyperuricemia, with and without preeclampsia, had increased uric acid concentrations across pregnancy compared with controls, after 25 weeks' gestation compared with women with preeclampsia without predelivery hyperuricemia. Adjusting for differences in glomerular filtration by serum creatinine accounted for part but not all of the increase in serum uric acid among women with preeclampsia and predelivery hyperuricemia.

CONCLUSIONS

Among women with hyperuricemia at delivery, elevations in uric acid occur early. Multiple mechanisms may contribute to increased uric acid including changes in renal function.

Hormonal and cytokine effects of uric acid

PURPOSE OF REVIEW

Current evidence supports the role of soluble uric acid as a true mediator of injury, exerting its effects through the induction of growth factors, cytokines, hormones and autacoids. In the present review, we summarize recent studies on the mechanisms involved in the uric acid deleterious effects.

RECENT FINDINGS

Although uric acid is considered an antioxidant in plasma, recent clinical and epidemiological studies have found that hyperuricemia is associated with mortality and development of hypertension, cardiovascular and chronic renal diseases. Experimental studies suggest that uric acid induce its detrimental effects at the cellular level entering to vascular smooth muscle cells (VSMC) via an organic anion transport system, and followed by the activation of specific MAP kinases, nuclear transcription factors, with stimulation of COX-2, PDGF A and C chain, PDGF alpha receptor, and various inflammatory mediators, including C-reactive protein and monocyte chemoattractant protein-1. Physiologically, these effects translate into a rise of arterial pressure, VSMC hypertrophy, tubulointerstitial infiltration and glomerular hypertension in the setting of renal vasoconstriction. Uric acid also promotes endothelial dysfunction through inactivation of NO and arresting the proliferation of endothelial cells. Thus, arteriosclerosis induced by hyperuricemia may be a novel mechanism for the development of essential hypertension.

SUMMARY

Soluble uric acid has important biologic roles. While it acts as an antioxidant, there is also evidence that uric acid has pro-inflammatory and proliferative effects on VSMC, and causes dysfunction of endothelial cells. These cellular mechanisms may translate into why uric acid is associated with renal and cardiovascular disease.

Urate oxidation during percutaneous transluminal coronary angioplasty and thrombolysis in patients with coronary artery disease

Thrombolysis and percutaneous transluminal coronary angioplasty (PTCA) are kinds of procedures that can be used to restore the blood flow of previously ischemic myocardium that can be the result of excessive production of reactive oxygen and nitrogen species, such as superoxide and hydroxyl radical, hypochlorous acid and peroxynitrite. Reaction of urate with some of these potent oxidants results in allantoin production. In this study, we measured the serum allantoin levels, an oxidation product of urate, and "in vivo" marker of free radical generation in reperfusion of ischemic myocardium. After an overnight fasting state, blood samples were collected from 35 patients with coronary occlusive diseases (7 women and 28 men) and 31 healthy subjects (8 women and 23 men). Serum allantoin and urate levels were measured by a GC-MS method. Serum allantoin levels of patients on PTCA therapy (mean+/-SD, 27.4 +/- 15.2 micromol/l) and thrombolytic therapy (24.6 +/- 8.6 micromol/l) were significantly higher than those of the patients without therapy (15.8 +/- 6.2 micromol/l, p < 0.05 with PTCA and p < 0.006 with thrombolysis) and healthy controls (12.6 +/- 6.3 micromol/l, p < 0.002 with PTCA and p < 0.0001 with thrombolysis). Although serum urate levels in PTCA (380.1 +/- 72.6 micromol/l) and thrombolysis (359.5 +/- 60.0 micromol/l) were higher than those in the non-therapy patients (336.6 +/- 53.8 micromol/l) and controls (318.3 +/- 81.0 micromol/l), there were no significant differences among groups (p > 0.05). The results of the study are consistent with others which have demonstrated, higher urate levels are associated with coronary occlusive diseases. Our data support the hypothesis that generation of ROS occurs during myocardial reperfusion. Increased allantoin levels may be used as an index of increased oxidative stress during reperfusion.

Correlation of uric acid and urinary albumin excretion rate in patients with type 2 diabetes mellitus in Taiwan

BACKGROUND

Uric acid is detrimental to the kidneys in animal models. However, its role in human diabetic nephropathy has not been extensively studied. This study evaluated the association between serum uric acid and urinary albumin-to-creatinine ratio (ACR) among patients with type 2 diabetes mellitus in Taiwan.

METHODS

A total of 343 patients (144 men and 199 women), aged 62.8 +/- 10.8 years and not using uric acid-lowering agents, diuretics, or alcohol, were recruited. Serum uric acid and urinary ACR were determined. Normoalbuminuria, microalbuminuria, and macroalbuminuria were defined as ACR <30.0, 30.0 to 299.9, and > or =300.0 microg/mg, respectively.

RESULTS

The respective uric acid levels for normoalbuminuria (N= 166), microalbuminuria (N= 130), and macroalbuminuria (N= 47) were 5.2 +/- 1.6 mg/dL, 5.6 +/- 1.9 mg/dL, and 6.7 +/- 2.1 mg/dL (P < 0.001). The mean +/- SD (minimum-maximum) values of uric acid for the first to the fourth quartile were 3.4 +/- 0.6 (1.7-4.2), 4.9 +/- 0.4 (4.3-5.4), 6.0 +/- 0.3 (5.5-6.5), and 8.1 +/- 1.2 (6.6-12.2), respectively. Prevalence of abnormal albuminuria (microalbuminuria plus macroalbuminuria) for the respective quartiles were 38.4%, 51.2%, 50.6%, and 66.3% (P trend <0.01). In men, uric acid correlated positively with triglycerides and natural logarithmic [ln (ACR)] (gamma= 0.168, P < 0.05). In women, uric acid correlated positively with triglycerides, ln (ACR) (gamma= 0.277, P < 0.01) and body mass index (borderline significant P < 0.1), but negatively with calculated creatinine clearance. The standardized regression coefficient for ln (ACR) and the odds ratio for abnormal albuminuria for every 1 mg/dL increment of uric acid after adjusting for calculated creatinine clearance and other confounders were 0.138 (P < 0.05) and 1.183 (1.025-1.364), respectively. The results after excluding 127 cases with a history of hypertension were similar.

CONCLUSION

Serum uric acid is an independent correlate of urinary ACR in Taiwanese patients with type 2 diabetes mellitus.

High-protein diets: potential effects on the kidney in renal health and disease

High-protein (HP) weight-loss diets have existed in the United States for decades, although their popularity has recently surged as obesity has become more common. Despite their widespread use, valid concerns exist that HP diets may induce clinically important alterations in renal function and health. HP consumption has been found, under various conditions, to lead to glomerular hyperfiltration and hyperemia; acceleration of chronic kidney disease (CKD); increased proteinuria; diuresis, natriuresis, and kaliuresis with associated blood pressure changes; increased risk for nephrolithiasis; and various metabolic alterations. Unfortunately, a comprehensive understanding of the implications of HP diets is limited by the lack of a universally accepted definition for HP intake, a paucity of rigorous long-term human interventional studies that necessitate relying on short-term or fairly circumstantial evidence, and sparse data on the effects of HP consumption in obese individuals. In addition, matters are further complicated because the renal impact HP diets for limited periods is most likely different than that for more chronic consumption. Nevertheless, although there are no clear renal-related contraindications to HP diets in individuals with healthy kidney function, the theoretical risks should be reviewed carefully with the patient. In contrast, HP diets have the potential for significant harm in individuals with CKD and should be avoided if possible. Because CKD is often a silent disease, all individuals should undergo a screening serum creatinine measurement and urinary dipstick test for proteinuria before the initiation of such a diet.

Uric acid and the state of the intrarenal renin-angiotensin system in humans

BACKGROUND

Experimental hyperuricemia is marked by an activated intrarenal renin-angiotensin system (RAS). The renal vascular response to exogenous angiotensin II (Ang II) provides an indirect measure of intrarenal RAS activity. We tested the hypothesis that the serum uric acid concentration predicts the renal vascular response to Ang II.

METHODS

A total of 249 subjects in high sodium balance had the renal plasma flow (RPF) response to Ang II measured. Para-aminohippuric acid (PAH) clearance was used to estimate RPF. Multivariable regression analysis determined if the serum uric acid concentration independently predicts the RPF response to Ang II. Variables considered included age, gender, race, body mass index (BMI), hypertension status, blood pressure, basal RPF, creatinine clearance, serum insulin, serum glucose, serum high-density lipoprotein (HDL), serum triglycerides, and plasma renin activity (PRA).

RESULTS

Uric acid concentration negatively correlated with the RPF response to Ang II (r=-0.37, P < 0.001). In univariate analysis, age, BMI, hypertension, triglycerides, and blood pressure were negatively associated, and basal RPF, HDL, and female gender were positively associated with the RPF response to Ang II. In multivariable analysis, serum uric acid concentration independently predicted the RPF response to Ang II (beta=-5.3, P < 0.001).

CONCLUSION

Serum uric acid independently predicted blunted renal vascular responsiveness to Ang II, consistent with results from experimental hyperuricemia showing an activated intrarenal RAS. This could be due to a direct effect of uric acid or reflect a more fundamental renal process. These data may have relevance to the association of uric acid with risk for hypertension and nephropathy.

Chronic kidney disease: the global challenge

The worldwide rise in the number of patients with chronic kidney disease (CKD) and consequent end-stage renal failure necessitating renal replacement therapy is threatening to reach epidemic proportions over the next decade, and only a small number of countries have robust economies able to meet the challenges posed. A change in global approach to CKD from treatment of end-stage renal disease (ESRD) to much more aggressive primary and secondary prevention is therefore imperative. In this Seminar, we examine the epidemiology of CKD worldwide, with emphasis on early detection and prevention, and the feasibility of methods for detection and primary prevention of CKD. We also review the risk factors and markers of progressive CKD. We explore current understanding of the mechanisms underlying renal scarring leading to ESRD to inform on current and future interventions as well as evidence relating to interventions to slow the progression of CKD. Finally, we make strategic recommendations based on future research to stem the worldwide growth of CKD. Consideration is given to health economics. A global and concerted approach to CKD must be adopted in both more and less developed countries to avoid a major catastrophe.

Uric acid and transplantation

Hyperuricemia is a common complication in organ transplant recipients, and frequently is associated with chronic cyclosporine immunosuppressive therapy. Kidney and heart transplant recipients are prone to develop posttransplant hyperuricemia. Risk factors for hyperuricemia include decreased glomerular filtration rate (GFR), diuretic use, and preexistent history of hyperuricemia. The influence of hyperuricemia in patient and graft survival is unclear because uric acid is not usually considered a common risk factor for cardiovascular disease that affects graft and patient survival. However, there have been small studies that have suggested that control of uric acid levels contributes to recovery of renal function (in heart and liver transplant recipients) and in an improvement in GFR in renal transplant recipients. Despite controversies in the need for hyperuricemia treatment in transplant patients, strategies to decrease uric acid levels includes a decrease or avoidance of cyclosporine treatment, adequacy of antihypertension treatment, avoidance of diuretics, nutritional management, and use of uric acid-decreasing agents. In this article we review the incidence and risk factors for the development of posttransplant hyperuricemia, discuss the influence of different immunosuppressive agents on uric acid metabolism, and suggest some alternative treatments for posttransplant hyperuricemia. We also consider that uric acid should be considered as a potential risk factor for renal allograft nephropathy or for renal dysfunction in nonrenal transplant recipients, as well as a comorbid factor for a decrease in patient and graft survival.

Clinical evidence for the influence of uric acid on hypertension, cardiovascular disease, and kidney disease: A statistical modeling perspective

This article critically evaluates the clinical evidence regarding the influence of uric acid on hypertension, cardiovascular disease, and kidney disease. Data on these relationships are largely observational and exceedingly complex. The complexity is owing to indirect and direct relations, and bidirectional influences, simultaneously operating on multiple outcomes. Limitations of previous analyses include inadequate statistical methods using only bivariate correlations or poorly specified multiple regression models. As a result, great controversy developed as to whether uric acid is an independent predictor of important outcomes. An example of such analytic limitations is including hypertension as an independent variable, together with uric acid, in a multivariate model for predicting cardiovascular disease. Hypertension may predict significant variance in cardiovascular disease, but the contribution of uric acid may not be recognized if uric acid exerts its influence indirectly through hypertension. Path analysis, which can model direct and indirect influences on outcomes simultaneously, would address this substantive question. Studies of uric acid in relation to hypertension, cardiovascular disease, and kidney disease using a path-analytic approach would help specify such conditions as well as optimize design of clinical trials to determine if decreasing uric acid levels improves outcomes.

Prevalence of Comorbid Conditions and Prescription Medication Use Among Patients With Gout and Hyperuricemia in a Managed Care Setting

BACKGROUND

: Comorbid disorders and multiple prescription drug use are common among patients with gout and/or hyperuricemia and may influence the clinical course and outcome of gout.

OBJECTIVE

: We wanted to document the conditions and associated medications in a large group of patients with gout in a managed care setting.

METHODS

: This study was a 2-year, retrospective, administrative claims analysis examining comorbid conditions and medication use among managed care enrollees with gout/hyperuricemia across the United States.

RESULTS

: Of the 9482 study subjects (82.1% men, mean age 52 years), 57.9% had hypertension, 45.3% had a lipid disorder, 32.5% had both conditions, and 19.9% had diabetes mellitus. During the 24-month follow-up period, subjects had 5 +/- 3.14 (mean +/- standard deviation) different comorbid conditions and filled prescriptions for of 11.0 +/- 7.90 different medications. The most commonly filled prescriptions included antihypertensive drugs, 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase inhibitors (statins), and nonsteroidal antiinflammatory drugs (NSAIDs).

CONCLUSIONS

: The study indicates a high prevalence of both comorbid conditions and multiple medication use among managed care enrollees with gout and/or hyperuricemia. Heightened awareness of these associated disorders is important because they may warrant treatment of their own accord and often some modification of gout management. Drugs, particularly diuretics and prophylactic aspirin, could potentially contribute to the development of hyperuricemia and gout.

Galectin 9 is the sugar-regulated urate transporter/channel UAT

UAT, also designated galectin 9, is a multifunctional protein that can function as a urate channel/transporter, a regulator of thymocyte-epithelial cell interactions, a tumor antigen, an eosinophil chemotactic factor, and a mediator of apoptosis. We review the evidence that UAT is a transmembrane protein that transports urate, describe our molecular model for this protein, and discuss the evidence from epitope tag and lipid bilayer studies that support this model of the transporter. The properties of recombinant UAT are compared with those of urate transport into membrane vesicles derived from proximal tubule cells in rat kidney cortex. In addition, we review channel functions predicted by our molecular model that resulted in the novel finding that the urate channel activity is regulated by sugars and adenosine. Finally, the presence and possible functions of at least 4 isoforms of UAT and a closely related gene hUAT2 are discussed.

Analysis of the cardiovascular risk profile in stable kidney transplant recipients after 50% cyclosporine reduction

BACKGROUND

Long-term use of cyclosporine (CsA) contributes to post-transplant cardiovascular disease (CVD). Hence, a reduction in CsA dosage in kidney transplant recipients (KTR) may improve long-term outcomes. We analyzed the effects of 50% CsA dose reduction on the CVD risk profile in stable KTR.

METHOD

Thirty-one KTR on a regimen of CsA, prednisone and mycophenolate mofetil (MMF) were studied. Patients were randomized to either a) continue their previously determined CsA dose (control group, n = 15) or b) lower their CsA dose by 50% (CsA reduction group, n = 16). Renal function, blood pressure, lipid profile, plasma homocysteine (HCY), C-reactive protein (CRP), fibrinogen, and uric acid were compared at baseline and at 6 months.

RESULTS

At 6 months, there was a significant improvement in allograft function, systolic blood pressure, number of anti-hypertensive medications and serum uric acid levels in the CsA reduction group. No significant decrease in plasma HCY, CRP, fibrinogen or improvement in lipid profile was found. In contrast, in the Control group, there was a significant increase in HCY, uric acid, and triglycerides. No acute rejection occurred in either group.

CONCLUSIONS

A greater reduction in CsA dose could further improve CVD risk profiles, although this may increase the risk of acute or subclinical rejection.

A functional immature model of chronic partial ureteral obstruction

BACKGROUND

The most common nonlethal congenital anomaly of the urinary tract is ureteral obstruction without dysplasia. Although rarely progressive, the morbidity associated with metabolic and surgical management is considerable. Our study was designed to measure local and systemic pathophysiologic mechanisms in an immature model of chronic partial unilateral ureteral obstruction (UUO) after completion of glomerulogenesis.

METHODS

A partial UUO was created by the method of "psoas wrap" in young male weanling rats. Control animals were sham operated. Three groups were divided as follows: sham (N= 15), UUO (N= 18), and UUO + angiotensin-converting enzyme (ACE) (N= 16) inhibitor, enalapril. Renal glomerular and tubular functions were determined by creatinine and uric acid clearances. Diuresis was assessed by urine volume, osmolality, and fractional solute excretions from samples above and below the obstruction. Proteinuria was determined by the urine protein/creatinine ratio (Up/c).

RESULTS

Proteinuria was attenuated in UUO + ACE-treated animals. The hyperuricemia of the immature UUO animals was avoided by an increase in the clearance of uric acid in the UUO + ACE-treated group. Fractional solute excretions suggested a diversion of diuresis to the contralateral unobstructed kidney.

CONCLUSION

Angiotensin blockade during chronic UUO in young rats affords protection by attenuating proteinuria, promoting uricosuria, and diverting solute diuresis. These data suggest a complex interaction of local and systemic mechanisms unique to the maturing kidney.

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.

Prevalence of hyperuricemia and relation of serum uric acid with cardiovascular risk factors in a developing country

BACKGROUND

The prevalence of hyperuricemia has rarely been investigated in developing countries. The purpose of the present study was to investigate the prevalence of hyperuricemia and the association between uric acid levels and the various cardiovascular risk factors in a developing country with high average blood pressures (the Seychelles, Indian Ocean, population mainly of African origin).

METHODS

This cross-sectional health examination survey was based on a population random sample from the Seychelles. It included 1011 subjects aged 25 to 64 years. Blood pressure (BP), body mass index (BMI), waist circumference, waist-to-hip ratio, total and HDL cholesterol, serum triglycerides and serum uric acid were measured. Data were analyzed using scatterplot smoothing techniques and gender-specific linear regression models.

RESULTS

The prevalence of a serum uric acid level >420 micromol/L in men was 35.2% and the prevalence of a serum uric acid level >360 micromol/L was 8.7% in women. Serum uric acid was strongly related to serum triglycerides in men as well as in women (r = 0.73 in men and r = 0.59 in women, p < 0.001). Uric acid levels were also significantly associated but to a lesser degree with age, BMI, blood pressure, alcohol and the use of antihypertensive therapy. In a regression model, triglycerides, age, BMI, antihypertensive therapy and alcohol consumption accounted for about 50% (R2) of the serum uric acid variations in men as well as in women.

CONCLUSIONS

This study shows that the prevalence of hyperuricemia can be high in a developing country such as the Seychelles. Besides alcohol consumption and the use of antihypertensive therapy, mainly diuretics, serum uric acid is markedly associated with parameters of the metabolic syndrome, in particular serum triglycerides. Considering the growing incidence of obesity and metabolic syndrome worldwide and the potential link between hyperuricemia and cardiovascular complications, more emphasis should be put on the evolving prevalence of hyperuricemia in developing countries.

Correlation Studies of Plasma Paraoxonase Activity and Uric Acid Concentration with AAPH-Induced Erythrocyte Hemolysis in Hemodialysis Patients

Uric acid possesses antioxidant properties and is an important determinant of total plasma antioxidant capacity. Uric acid concentrations tend to be elevated in patients with renal failure requiring maintenance hemodialysis but are abruptly reduced by the dialysis procedure itself. Paraoxonase (PON1), an enzyme which circulates in association with high density lipoprotein (HDL), confers protection against free radicals by limiting the oxidation of phospholipids. The relationship between pre- and postdialysis uric acid concentration, PON1 activity, and high density lipoprotein cholesterol (HDL-C) level and the resistance of erythrocytes from hemodialysis patients to hemolysis induced by the free radical generator 2,2'-azobis(2-amidinopropane) dihydrochloride (AAPH) was studied. Red cells were washed free of plasma prior to the assay, and no plasma was added to the hemolysis assay tubes. Postdialysis erythrocytes were found to be more susceptible to hemolysis compared to blood samples obtained at the initiation of the session (784 +/- 713 vs. 256 +/- 256 micro mol/L hemoglobin released after 60 min incubation and 1530 +/- 696 vs. 1354 +/- 757 micro mol/L at 90 min). Hemolysis correlated negatively with the concentration of uric acid and positively with PON1 arylesterase activity but not with HDL-C level in the corresponding plasma samples. There was a strong negative correlation between uric acid and PON1 in predialysis blood samples (r2 = 0.4, P < 0.001). The conclusion is that the reciprocal relationship between uric acid and PON1 may reflect a mechanism that protects erythrocytes from subsequent oxidative stress.

Is there a pathogenetic role for uric acid in hypertension and cardiovascular and renal disease?

Hyperuricemia is associated with hypertension, vascular disease, renal disease, and cardiovascular events. In this report, we review the epidemiologic evidence and potential mechanisms for this association. We also summarize experimental studies that demonstrate that uric acid is not inert but may have both beneficial functions (acting as an antioxidant) as well as detrimental actions (to stimulate vascular smooth muscle cell proliferation and induce endothelial dysfunction). A recently developed experimental model of mild hyperuricemia also provides the first provocative evidence that uric acid may have a pathogenic role in the development of hypertension, vascular disease, and renal disease. Thus, it is time to reevaluate the role of uric acid as a risk factor for cardiovascular disease and hypertension and to design human studies to address this controversy.

Mild hyperuricemia induces glomerular hypertension in normal rats

Mildly hyperuricemic rats develop renin-dependent hypertension and interstitial renal disease. Hyperuricemia might also induce changes in glomerular hemodynamics. Micropuncture experiments under deep anesthesia were performed in Sprague-Dawley rats fed a low-salt diet (LS group), fed a low-salt diet and treated with oxonic acid (OA/LS group), and fed a low-salt diet and treated with oxonic acid + allopurinol (OA/LS/AP group) for 5 wk. The OA/LS group developed hyperuricemia and hypertension compared with the LS group: 3.1 +/- 0.2 vs. 1.1 +/- 0.2 mg/dl (P < 0.01) and 143 +/- 4 vs. 126 +/- 2 mmHg (P < 0.01). Hyperuricemic rats developed increased glomerular capillary pressure compared with the LS rats: 56.7 +/- 1.2 vs. 51.9 +/- 1.4 mmHg (P < 0.05). Pre- and postglomerular resistances were not increased. Histology showed afferent arteriolar thickening with increased alpha-smooth muscle actin staining of the media. Allopurinol prevented hyperuricemia (1.14 +/- 0.2 mg/dl), systemic (121.8 +/- 2.8 mmHg) and glomerular hypertension (50.1 +/- 0.8 mmHg), and arteriolopathy in oxonic acid-treated rats. Linear regression analysis showed that glomerular capillary pressure and arteriolar thickening correlated positively with serum uric acid and systolic blood pressure. Glomerular hypertension may be partially mediated by an abnormal vascular response to systemic hypertension due to arteriolopathy of the afferent arteriole.

Environmental lead exposure and urate excretion in the general population

PURPOSE

Chronic occupational exposure to lead is related to low urate excretion and a high incidence of gout in lead workers. However, whether chronic low-level environmental lead exposure influences urate excretion in the general population remains unknown.

SUBJECTS AND METHODS

We studied 111 healthy subjects with normal renal function (serum creatinine level < or =1.4 mg/dL) and no previous lead exposure or systemic diseases. All subjects had their blood lead levels measured, received ethylenediaminetetraacetic acid mobilization tests to assess their body lead burdens, and were investigated for renal function and urate excretion to assess the relation between lead and urate excretion. We studied urate excretion before and after lead chelation therapy in 24 subjects with high-normal body lead burden (>78 mg and <600 mg).

RESULTS

Healthy subjects with gout (n = 27) manifested a higher body lead burden (84 +/- 42 mg vs. 45 +/- 30 mg, P <0.0001) and lower urate clearance (3.7 +/- 1.2 mL/min/1.73 m(2) vs. 6.0 +/- 2.8 mL/min/1.73 m(2), P <0.0001) than did those without gout (n = 84). Blood lead levels and body lead burden of all subjects were within the safe range. In analyses that adjusted for age, sex, body mass index, protein intake, and creatinine clearance, blood lead level was significantly related to serum urate level (beta coefficient [+/- SE] = 0.23 +/- 0.11, P = 0.03), and body lead burdens were related to all indices of urate excretion (serum urate: beta coefficient = 0.023 +/- 0.005, P <0.0001; daily urate excretion: beta coefficient = -1.55 +/- 0.40, P = 0.0002; urate clearance: beta coefficient = -0.030 +/- 0.006, P <0.0001; fractional urate excretion: beta coefficient= -0.034 +/- 0.006, P <0.0001). Following lead chelation therapy, urate clearance increased after body lead burden was reduced (3.4 +/- 1.2 mL/min/1.73 m(2) vs. 4.9 +/- 1.4 mL/min/1.73 m(2), P <0.005).

CONCLUSION

Chronic low-level environmental lead exposure may inhibit urate excretion in the general population, and lead chelation therapy reduces this inhibition. These findings support efforts to reduce sources of environmental lead exposure and suggest alternative approaches to hyperuricemia and gout in the general population.

Uric acid, hominoid evolution, and the pathogenesis of salt-sensitivity

Humans have elevated serum uric acid as a result of a mutation in the urate oxidase (uricase) gene that occurred during the Miocene. We hypothesize that the mutation provided a survival advantage because of the ability of hyperuricemia to maintain blood pressure under low-salt dietary conditions, such as prevailed during that period. Mild hyperuricemia in rats acutely increases blood pressure by a renin-dependent mechanism that is most manifest under low-salt dietary conditions. Chronic hyperuricemia also causes salt sensitivity, in part by inducing preglomerular vascular disease. The vascular disease is mediated in part by uric acid-induced smooth muscle cell proliferation with activation of mitogen-activated protein kinases and stimulation of cyclooxygenase-2 and platelet-derived growth factor. Although it provided a survival advantage to early hominoids, hyperuricemia may have a major role in the current cardiovascular disease epidemic.

Pathogenesis of hyperuricemia: recent advances

The literature on the pathogenesis of hyperuricemia have been limited to the discussion of metabolic syndromes associated with risk factors for atherosclerosis and hyperuricemia and the genetics of the juvenile form of hyperuricemic nephropathies. A few new mutations in the hypoxanthine-guanine phosphoribosyltransferase gene, which result in Lesch-Nyhan syndrome, have been described. In addition, some new insight has been gained in the renal handling of uric acid by the human kidney.

Hyperuricemia, hypertension, and proteinuria associated with high-altitude polycythemia

Chronic exposure to high altitude is associated with the development of erythrocytosis, proteinuria, and, in some cases, hyperuricemia. We examined the relationship between high-altitude polycythemia and proteinuria and hyperuricemia in Cerro de Pasco, Peru (altitude, 4,300 m). We studied 25 adult men with hematocrits less than 65% and 27 subjects with excessive erythrocytosis (EE; hematocrit > 65%) living in Cerro de Pasco, Peru and compared them with 28 control subjects living in Lima, Peru (at sea level) and after 48 hours of exposure to high altitude. Serum urate levels were significantly elevated in patients with EE at altitude, and gout occurred in 4 of 27 of these subjects. Urate level strongly correlated with hematocrit (r = 0.71; P < 0.0001). Urate production (24-hour urine urate excretion and urine urate-creatinine ratio) was increased in this group compared with those at sea level. Fractional urate excretion was not increased, and fractional lithium excretion was reduced, in keeping with increased proximal reabsorption of filtrate. Significantly higher blood pressures and decreased renin levels in the EE group were in keeping with increased proximal sodium reabsorption. Serum urate levels correlated with mean blood pressure (r = 0.50; P < 0.0001). Significant proteinuria was more prevalent in the EE group despite normal renal function. Hyperuricemia is common in subjects living at high altitude and associated with EE, hypertension, and proteinuria. The increase in uric acid levels appears to be caused by increased urate generation secondary to systemic hypoxia, although a relative impairment in renal excretion also may contribute.

Molecular identification of a renal urate anion exchanger that regulates blood urate levels

Urate, a naturally occurring product of purine metabolism, is a scavenger of biological oxidants implicated in numerous disease processes, as demonstrated by its capacity of neuroprotection. It is present at higher levels in human blood (200 500 microM) than in other mammals, because humans have an effective renal urate reabsorption system, despite their evolutionary loss of hepatic uricase by mutational silencing. The molecular basis for urate handling in the human kidney remains unclear because of difficulties in understanding diverse urate transport systems and species differences. Here we identify the long-hypothesized urate transporter in the human kidney (URAT1, encoded by SLC22A12), a urate anion exchanger regulating blood urate levels and targeted by uricosuric and antiuricosuric agents (which affect excretion of uric acid). Moreover, we provide evidence that patients with idiopathic renal hypouricaemia (lack of blood uric acid) have defects in SLC22A12. Identification of URAT1 should provide insights into the nature of urate homeostasis, as well as lead to the development of better agents against hyperuricaemia, a disadvantage concomitant with human evolution.

High urinary excretion of uric acid combined with high excretion of calcium links kidney stone disease to familial hypertension

BACKGROUND

Past studies identified an association between kidney stone disease (KSD) and hypertension. We recently reported a high occurrence of hypertension in families of patients with hyperuricosuric KSD. As hypercalciura frequently coexists with hyperuricosuria and high urinary excretion of calcium is found in patients with hypertension, we hypothesized that hyperuricosuria that is accompanied by hypercalciuria better describes the familial association between KSD and hypertension.

METHODS

Four hundred and eighty-six KSD patients, aged 18-50 years, attending a lithotripsy unit collected a 24-h urine sample for metabolic analysis and provided information on family history of hypertension. The familial occurrence of hypertension was compared among four groups of patients: those who had combined elevation of both urinary calcium and uric acid excretions ("combined" abnormality, n=56), those who had hyperuricosuria without concomitant hypercalciuria ("pure" hyperuricosuria, n=67), those who had hypercalciuria without concomitant hyperuricosuira ("pure" hypercalciuria, n=52), and a control KSD patient group ("other" abnormality, n=311). The prevalence of treated hypertension in patients from the four groups was 16%, 12%, 2%, 10%, respectively.

RESULTS

Thirty-four per cent of the patients with the "combined" abnormality had a positive family history of hypertension, defined as two or more first-degree relatives with treated hypertension, that was significantly higher than in patients with either "pure" hyperuricosuira (15%, P<0.02), "pure" hypercalciuria (8%, P<0.001), or patients with "other" abnormality (10%, P<0.001). The adjusted OR for positive family history of hypertension in the "combined" abnormality group compared to the control KSD patient group was 5.6 (2.39-13.30). The prevalence of hypertension in siblings of patients with the "combined" abnormality (13%) was significantly higher than in siblings of patients with either "pure" hyperuricosuria (3%, P<0.001), "pure" hypercalciuria (1%, P<0.001), or siblings of control patients with "other" abnormality (4%, P<0.001). The adjusted OR for hypertension in siblings of a patient with "combined" abnormality compared to a control KSD patient was 3.4 (1.97-5.91). Patients in the "combined" abnormality group were also characterized by significantly elevated urinary sodium, phosphorus, citrate and potassium excretions.

CONCLUSIONS

Our data suggest that there is a strong, independent association between familial occurrence of hypertension and the phenotype characterized by combined elevation of both urinary uric acid and calcium excretions. The association is not present in those with "pure" hyperuricosuria or "pure" hypercalciuria. Ascertainment of patients based on this phenotype may identify more homogeneous populations for genetic analysis of hypertension.

Oxidant stress in nephrotic syndrome: comparison of F(2)-isoprostanes and plasma antioxidant potential

BACKGROUND

The nephrotic syndrome (NS) is associated with an increased risk of coronary heart disease. Increased oxidant stress may contribute to this by means of hyperlipidaemia and/or hypoalbuminaemia. In this study we assessed the contributory role of oxidant stress, as measured by F(2)-isoprostanes and plasma oxygen radical absorbance capacity (ORAC), in subjects with NS.

METHODS

We studied 14 subjects with NS and 17 age- and sex-matched healthy non-proteinuric controls. Measurement of plasma and urinary F(2)-isoprostanes was carried out using a combination of silica and reverse-phase cartridges, high-performance liquid chromatography, and gas chromatography mass spectrometry using electron-capture negative ionization. The plasma ORAC assay measured the decrease in fluorescence of phycoerythrin added to plasma in the presence of a free-radical generator. The ORAC value (microM) was calculated as the ratio of the area under the fluorescence decay curve for plasma to the area under the fluorescence decay curve for a Trolox standard.

RESULTS

Plasma ORAC was significantly lower in NS patients compared with controls: mean (standard error) NS patients 3306 microM (286); controls 4882 microM (496), P=0.011. In univariate linear regression analysis, plasma albumin was significantly positively correlated with plasma ORAC (r=0.40, P=0.03). Plasma and urinary F(2)-isoprostanes did not differ significantly between NS and control groups.

CONCLUSIONS

This study demonstrates that in the NS there is decreased free-radical trapping capacity of plasma that is inversely correlated with hypoalbuminaemia, but no increase in plasma and urinary F(2)-isoprostanes. Decreased total plasma antioxidant potential in combination with hyperlipidaemia may contribute to the increased risk of cardiovascular disease seen in NS.

Renal regulation of plasma total antioxidant capacity

Hyperuricemia has been labeled both a risk factor and marker for cardiovascular pathology in addition to being associated with gout and kidney disease. Uric acid in vitro acts as a potent antioxidant capable of scavenging hydroxy radicals and peroxynitrite and reacting with nitric oxide. Some clinical studies have provided evidence that, in vivo, uric acid is oxidized under conditions associated with high oxidant stress and may spare other antioxidants such as ascorbic acid. The plasma level of uric acid is controlled by the rates of production and excretion or degradation of uric acid. Under most circumstances, it is the renal clearance of uric acid which primarily determines the plasma concentration. Many factors of exogenous and endogenous origin can influence renal tubular absorption and secretion of uric acid. We suggest that renal urate clearance is not haphazard but regulated by an unknown signal that is issued in response to the level of oxidative stress. Since much cardiovascular pathology is now believed to have an inflammatory component and is associated with enhanced production of free radicals, the accompanying hyperuricemia may be viewed as a compensatory response of potential benefit.

Urate and arteriosclerosis in primary hyperparathyroidism

OBJECTIVE

An increased mortality due to cardiovascular disease has been reported in patients with primary hyperparathyroidism (pHPT). An association between urate and cardiovascular disease has been suggested. Metabolic abnormalities in pHPT may include urate. We therefore evaluated the metabolic arteriosclerotic risk profile in pHPT with special focus on the role of urate.

DESIGN

Retrospective analysis of data before and 1 year after surgery for pHPT.

PATIENTS

130 consecutive patients, over the age of 44 years, who underwent surgery for pHPT.

MEASUREMENTS

Biochemical variables known to reflect risk of arteriosclerotic disease (AD) and renal function tests including measurement of glomerular filtration rate (GFR) were investigated before and 1 year after surgery.

RESULTS

pHPT patients with AD (n = 40) were older and had higher serum levels of urate and triglyceride, and more impaired renal function in comparison with patients without AD. PTH and calcium values did not differ. Multiple logistic regression analysis indicated that urate was an independent risk factor for AD in pHPT (P < 0.01). Three variables were shown to be positively associated with urate; male gender (P < 0.01), fasting blood glucose (P < 0.05) and serum level of triglyceride (P < 0.05).

CONCLUSIONS

Urate was found to be an independent risk factor for arteriosclerotic disease in primary hyperparathyroidism. Serum level of urate could (in addition to gender) be associated with a metabolic disorder comprising increased glucose and triglyceride levels.

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.

Hyperuricemia exacerbates chronic cyclosporine nephropathy

BACKGROUND

Hyperuricemia frequently complicates cyclosporine (CSA) therapy. The observation that longstanding hyperuricemia is associated with chronic tubulointerstitial disease and intrarenal vasoconstriction raised the hypothesis that hyperuricemia might contribute to chronic CSA nephropathy.

METHODS

CSA nephropathy was induced by the administration of CSA (15 mg/kg/day) for 5 and 7 weeks to rats on a low salt diet (CSA group). The effect of hyperuricemia on CSA nephropathy was determined by blocking the hepatic enzyme uricase with oxonic acid (CSA-OA). Control groups included rats treated with vehicle (VEH) and oxonic acid alone (OA). Histological and functional studies were determined at sacrifice.

RESULTS

CSA treated rats developed mild hyperuricemia with arteriolar hyalinosis, tubular injury and striped interstitial fibrosis. CSA-OA treated rats had higher uric acid levels in association with more severe arteriolar hyalinosis and tubulointerstitial damage. Intrarenal urate crystal deposition was absent in all groups. Both CSA and CSA-OA treated rats had increased renin and decreased NOS1 and NOS3 in their kidneys, and these changes are more evident in CSA-OA treated rats.

CONCLUSION

An increase in uric acid exacerbates CSA nephropathy in the rat. The mechanism does not involve intrarenal uric acid crystal deposition and appears to involve activation of the renin angiotensin system and inhibition of intrarenal nitric oxide production.

Functional reconstitution, membrane targeting, genomic structure, and chromosomal localization of a human urate transporter

Elevated serum levels of uric acid have been associated with an increased risk for gout, hypertension, cardiovascular disease, and renal failure. The molecular mechanisms for the diminished excretion of urate in these disorders, however, remain poorly understood. Human galectin 9, which is highly homologous to the rat urate transporter rUAT, has been reported to be a secreted or cytosolic protein. We provide data that galectin 9 is hUAT, the first identified human urate transporter. hUAT is a highly selective urate ion channel when inserted in lipid bilayers. When expressed in renal epithelial cells it is an integral plasma membrane protein with at least two transmembrane domains. The gene for hUAT consists of 11 exons and is mapped to chromosome 17; a highly homologous gene, hUAT2, maps to a nearby region of chromosome 17 and is also likely to be a urate transporter. hUAT is expressed in a wide variety of tissues and is present in at least three isoforms; hUAT2 is less widely expressed at severalfold lower levels than hUAT. Further knowledge about the functions of hUAT, its isoforms, and hUAT2, as well as mutational analysis of hUAT1 and hUAT2 in individuals or families with hyperuricemia, should significantly improve our understanding of the molecular mechanisms of urate homeostasis.

Uric acid and cardiovascular disease: a renal-cardiac relationship?

Elevated serum uric acid is a frequent finding in patients with kidney disease and cardiovascular disease. Intrarenal ischaemia, induced by hypertension, increased sympathetic nervous system activity, and hyperinsulinaemia have all been implicated in reduced renal clearance of urate. This frequently results in elevated serum uric acid levels. The association of hyperuricaemia with cardiovascular disease remains controversial. Current evidence suggests that serum uric acid may provide additional prognostic information in patients with essential hypertension. However, there has been no test of the hypothesis that a reduction in serum uric acid would prevent cardiovascular disease. Furthermore, a critical review of the current literature does not support a causal role of serum uric acid in the development of cardiovascular disease. Serum uric acid probably reflects and integrates different risk factors and their possible interactions.

Prognostic significance of serum creatinine and uric acid in older Chinese patients with isolated systolic hypertension

We examined the relation of serum creatinine and uric acid to mortality and cardiovascular disease in older (aged >/=60 years) Chinese patients with isolated systolic hypertension (systolic/diastolic blood pressure >/=160/<95 mm Hg). We used Cox regression to correlate outcome with baseline serum creatinine and uric acid measured in 1880 and 1873, respectively, of the 2394 patients enrolled in the placebo-controlled Systolic Hypertension in China (Syst-China)

TRIAL

Median follow-up was 3 years. In multiple Cox regression analysis with adjustment for gender, age, active treatment, and other significant covariates, serum creatinine was significantly associated with a worse prognosis. The relative hazard rates (95% CIs) associated with a 20-micromol/L increase in serum creatinine for all-cause, cardiovascular, and stroke mortality were 1.16 (1.05 to 1.27, P=0.003), 1.15 (1.01 to 1.31, P=0.03), and 1.37 (1.13 to 1.65, P=0.001), respectively. In a similar analysis, which also accounted for serum creatinine, serum uric acid was also significantly and independently associated with excess mortality of cardiovascular disease and stroke. The relative hazard rates associated with a 50-micromol/L increase of serum uric acid were 1.14 (1.02 to 1.27, P=0.02) for cardiovascular mortality and 1.34 (1.14 to 1.57, P<0.001) for fatal stroke. In conclusion, in older Chinese patients with isolated systolic hypertension, serum creatinine and serum uric acid were predictors of mortality.

Total urine antioxidant capacity

Total antioxidant capacity has been determined for several body fluids and provides a convenient means to compare antioxidant defenses among patients with acute or chronic inflammatory illnesses. We have studied urine specimens from a control group and a variety of patients with hypertension and acute and chronic renal diseases using an ABTS antioxidant assay as described for blood. Other urine assays included fluorescence markers for advanced glycosylation end products (AGE) and di-tyrosine (di-tyr), protein, uric acid, and creatinine concentrations. Urine antioxidant activity was standardized against ascorbic acid. We found that both the lag time and the area under the curve (AUC) in the ABTS assay were highly correlated with one another and correlated with the protein and uric acid concentrations, except for those specimens collected from patients with acute renal failure (ARF). The lack of correlation in the ARF group was not associated with significant differences in lag time or AUC. Correlations were seen also between antioxidant parameters and fluorescence for AGE and di-tyr. The results indicate that the predominant antioxidants in the urine of patients with acute renal failure differ from those found in the urine of individuals with hypertension and chronic nephropathies. The ABTS assay provides a convenient marker for the antioxidant content of urine.