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

Nephrolithiasis as a Risk Factor for CKD: The Atherosclerosis Risk in Communities Study

BACKGROUND AND OBJECTIVES

Previous studies demonstrated a higher risk of CKD in persons with a history of kidney stones, but these studies examined mostly white populations and did not evaluate important potential interactions such as race and plasma uric acid.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

In 10,678 Atherosclerosis Risk in Communities (ARIC) study participants free of CKD at baseline (ARIC visit 4 in 1996-1998), we assessed the association between a history of nephrolithiasis (a time-varying variable, defined by a combination of self-report and diagnostic codes) and incident CKD (defined by diagnostic codes from linkage to hospitalizations and US Centers for Medicare and Medicaid Services' records).

RESULTS

At baseline, 856 participants had a history of nephrolithiasis; 322 developed nephrolithiasis during follow-up. Over a mean follow-up of 12 years, there were 1037 incident CKD events. Nephrolithiasis history was associated with a 29% (hazard ratio [HR], 1.29; 95% confidence interval [95% CI], 1.07 to 1.54) higher risk of CKD in demographic-adjusted analyses, but the association was no longer statistically significant after multivariable adjustment (HR, 1.09; 95% CI, 0.90 to 1.32). The multivariable-adjusted association was stronger among participants with plasma uric acid levels ≤6 mg/dl (HR, 1.34; 95% CI, 1.05 to 1.72) compared with those with levels >6 mg/dl (HR, 0.94; 95% CI, 0.70 to 1.28; P(interaction) = 0.05). There was no interaction of stone disease and race with incident CKD.

CONCLUSIONS

In this community-based cohort, nephrolithiasis was not an independent risk factor for incident CKD overall. However, risk of CKD was unexpectedly elevated in participants with stone disease and lower plasma uric acid levels.

The cross-sectional association between uric acid and atherosclerosis and the role of low-grade inflammation: the CODAM study

OBJECTIVES

The aims of this study were to investigate (i) associations between uric acid and prevalent cardiovascular disease (CVD), ankle-arm blood pressure index (AAIx) and carotid intima-media thickness (CIMT) in the total population and in predefined subgroups according to glucose metabolism status and (ii) the extent to which these associations are explained by low-grade inflammation.

METHODS

Cross-sectional analyses were conducted among 530 individuals [60.6% men, mean age 58.9 years (s.d. 6.9), 52.6% normal glucose metabolism (NGM)] at increased risk of CVD from the Cohort of Diabetes and Atherosclerosis Maastricht study. A low-grade inflammation score was computed by averaging the z-scores of eight inflammation markers [CRP, TNF-α, IL-6, IL-8, serum amyloid A, intercellular adhesion molecule 1 (ICAM-1), ceruloplasmin and haptoglobin].

RESULTS

After adjustment for traditional CVD risk factors, plasma uric acid (per s.d. of 81 μmol/l) was associated with CVD in individuals with NGM [odds ratio (OR) = 1.66, 95% CI 1.06, 2.58] but not with disturbed glucose metabolism (DGM) (OR = 0.81, 95% CI 0.55, 1.19, P interaction = 0.165). Uric acid was associated with CIMT in the total population (β = 0.024, 95% CI 0.007, 0.042) and slightly more strongly in individuals with NGM (β = 0.030, 95% CI 0.006, 0.054) than DGM (β = 0.018, 95% CI -0.009, 0.044, P interaction = 0.443). There was no association between uric acid and AAIx in any group (P interaction = 0.058). Uric acid was associated with low-grade inflammation in the total population (β = 0.074, 95% CI 0.013, 0.134, P interaction = 0.737). Adding low-grade inflammation to the models did not attenuate any of the associations.

CONCLUSION

The associations for uric acid with CIMT, and with CVD in NGM only, were not explained by low-grade inflammation. A difference in the strength of the associations between individuals with NGM and DGM was suggested.

The role of uric acid in kidney fibrosis: experimental evidences for the causal relationship

Hyperuricemia is a common finding in chronic kidney disease due to decreased uric acid clearance. The role of uric acid as a risk factor for chronic kidney disease has been largely debated, and recent studies suggested a role of uric acid in the causation and progression of kidney fibrosis, a final common pathway in chronic kidney disease. Uric acid and xanthine oxidase may contribute to kidney fibrosis mainly by inducing inflammation, endothelial dysfunction, oxidative stress, and activation of the renin-angiotensin system. Besides, hyperuricemia induces alterations in renal hemodynamics via afferent arteriolopathy and contributes to the onset and progression of kidney fibrosis. Xanthine oxidase inhibitors may prevent kidney damage via lowering uric acid and/or inhibiting xanthine oxidase. However, there is still no sufficient evidence from interventional clinical researches supporting the causal relationship between uric acid and kidney fibrosis. The effect and role of xanthine oxidase inhibitors in preventing kidney fibrosis and chronic kidney disease progression must be further explored by performing future large scale clinical trials.

Acute kidney injury in the cancer patient

Acute kidney injury (AKI) is a frequent and significant complication of cancer and cancer therapy. Cancer patients frequently encounter risk factors for AKI including older age, CKD, prerenal conditions, sepsis, exposure to nephrotoxins, and obstructive physiology. AKI can also be secondary to paraneoplastic conditions, including glomerulonephritis and microangiopathic processes. This complication can have significant consequences, including effects on patients' ability to continue to receive therapy for their malignancy. This review will serve to summarize potential etiologies of AKI that present in patients with cancer as well as to highlight specific patient populations, such as the critically ill cancer patient.

Hyperuricemia predicts future metabolic syndrome: a 4-year follow-up study of a large screened cohort in Okinawa, Japan

The aim of this study was to determine whether hyperuricemia could predict future metabolic syndrome (MetS) in a large screened cohort of Japanese male and female subjects. We evaluated 5936 subjects (3144 male subjects, 2792 female subjects; mean age 48.7 years) who underwent health checkup programs in 2006 and 2010, who were MetS free in 2006. At baseline, hyperuricemia was detected in 927 male subjects (29.5%) and 276 female subjects (9.9%). Subjects with baseline hyperuricemia had significantly higher MetS prevalence in 2010 than those without (male subjects: 34.8 vs. 20.6%, P<0.0001; female subjects: 15.6 vs. 4.8%, P<0.0001). Compared with subjects in the first quintile of uric acid levels at baseline, the age-adjusted odds ratios (ORs) for MetS cumulative incidence among subjects in the third, fourth and fifth quintiles were, 1.8 (95% confidence interval (CI): 1.4-2.4: P<0.0001), 2.1 (95% CI: 1.6-2.8: P<0.0001) and 3.2 (95% CI: 2.4-4.1: P<0.0001), respectively, for male subjects and 2.4 (95% CI: 1.3-4.7: P=0.0075), 3.0 (95% CI: 1.6-5.7: P=0.0010) and 4.8 (95% CI: 2.6-8.8: P<0.0001), respectively for female subjects. Multivariable logistic analysis revealed that hyperuricemia was significantly associated with MetS cumulative incidence in male subjects (OR 1.5: 95% CI: 1.3-1.8, P<0.0001) and female (OR 2.0, 95% CI: 1.3-3.0, P<0.0001). In conclusion, hyperuricemia is a significant and independent predictor of MetS in Japanese male and female subjects. For both genders, MetS risk increases with increased serum uric acid levels.

Uric acid and chronic kidney disease: which is chasing which?

Serum uric acid is commonly elevated in subjects with chronic kidney disease (CKD), but was historically viewed as an issue of limited interest. Recently, uric acid has been resurrected as a potential contributory risk factor in the development and progression of CKD. Most studies documented that an elevated serum uric acid level independently predicts the development of CKD. Raising the uric acid level in rats can induce glomerular hypertension and renal disease as noted by the development of arteriolosclerosis, glomerular injury and tubulointerstitial fibrosis. Pilot studies suggest that lowering plasma uric acid concentrations may slow the progression of renal disease in subjects with CKD. While further clinical trials are necessary, uric acid is emerging as a potentially modifiable risk factor for CKD. Gout was considered a cause of CKD in the mid-nineteenth century, and, prior to the availability of therapies to lower the uric acid level, the development of end-stage renal disease was common in gouty patients. In their large series of gouty subjects Talbott and Terplan found that nearly 100% had variable degrees of CKD at autopsy (arteriolosclerosis, glomerulosclerosis and interstitial fibrosis). Additional studies showed that during life impaired renal function occurred in half of these subjects. As many of these subjects had urate crystals in their tubules and interstitium, especially in the outer renal medulla, the disease became known as gouty nephropathy. The identity of this condition fell in question as the presence of these crystals may occur in subjects without renal disease; furthermore, the focal location of the crystals could not explain the diffuse renal scarring present. In addition, many subjects with gout also had coexistent conditions such as hypertension and vascular disease, leading some experts to suggest that the renal injury in gout was secondary to these latter conditions rather than to uric acid per se. Indeed, gout was removed from the textbooks as a cause of CKD, and the common association of hyperuricemia with CKD was solely attributed to the retention of serum uric acid that is known to occur as the glomerular filtration rate falls. Renewed interest in uric acid as a cause of CKD occurred when it was realized that invalid assumptions had been made in the arguments to dismiss uric acid as a risk factor for CKD. The greatest assumption was that the mechanism by which uric acid would cause kidney disease would be via the precipitation as crystals in the kidney, similar to the way it causes gout. However, when laboratory animals with CKD were made hyperuricemic, the renal disease progressed rapidly despite an absence of crystals in the kidney. Since this seminal study, there has been a renewed interest in the potential role uric acid may have in both acute and CKD. We briefly review some of the major advances that have occurred in this field in the last 15 years.

Direct and indirect effects of obesity on the kidney

Over the last few decades, much of the world has experienced an epidemic of obesity. In the year 2008, 1.4 billion people worldwide were overweight, and 500 million were obese. Even more alarming is a fact that in the year 2010, 40 million children under the age of 5 years were overweight or obese. In the same time period, the incidence of CKD has also increased worldwide. Obesity has been recognized as a driving force of another global epidemic-diabetes, the leading cause of ESRD. Recent studies are confirming that in addition to risk associated with diabetes per se, increased body mass index is independently linked to increased risk for various kidney disorders, prominently CKD, but also renal cell carcinoma and nephrolithiasis. The purpose of this article is to review current knowledge regarding adverse effects of obesity on the kidney.

Reducing serum uric acid attenuates TGF-β1-induced profibrogenic progression in type 2 diabetic nephropathy

BACKGROUND

The pivotal role of transforming growth factor-β1 (TGF-β1)-induced tubulointerstitial fibrosis in the progression of chronic kidney disease is an active topic of research. Recent evidence indicates that hyperuricemia is associated with increased TGF-β1 and progressive tubulointerstitial injury. We examined the hypothesis that lowering serum uric acid attenuates TGF-β1-induced profibrogenic tubular change in type 2 diabetic nephropathy.

METHODS

KK-A(y)/Ta mice, an animal model of type 2 diabetes, were provided access to either regular drinking water or drinking water containing 10 mg/dl of allopurinol. Normal rat kidney epithelial cells were cultured and stimulated with 5 mM uric acid with or without allopurinol.

RESULTS

Type 2 diabetic mice that received allopurinol exhibited smaller increases in urinary albumin:creatinine ratio than diabetic control mice, as well as attenuated TGF-β1 and Smad pathway-induced profibrogenic tubular changes in diabetic kidneys. Allopurinol attenuated TGF-β1-induced Smad pathway activation in tubular cells. These findings were related to increases in E-cadherin, and decreases in vimentin and α-smooth muscle actin. Uric acid-induced upregulation of TGF-β1 depends on mitogen-activated protein kinase signaling.

CONCLUSIONS

This is the first study to demonstrate that reducing serum uric acid has preventive effects against to profibrogenic progression in type 2 diabetic kidney disease. These findings suggest that lowering serum uric acid may be an effective therapeutic intervention to prevent the progression of type 2 diabetic kidney disease.

Hyperuricemia as a marker for progression of immunoglobulin A nephropathy

BACKGROUND

The variable clinical and histopathological manifestations of immunoglobulin A nephropathy (IgAN) make it difficult to predict disease progression. A recent study showed that hyperuricemia, a condition common in hypertension and vascular disease, may contribute to renal dysfunction and histological changes including renal arteriosclerosis, tubular atrophy, and interstitial fibrosis. Herein, we investigated the clinical significance of uric acid level at the time of biopsy, as a marker of IgAN progression.

METHODS

We included 193 patients with biopsy-proven IgAN. Renal disease progression was defined as serum creatinine elevation above 1.2 mg/dL or over 20% elevation from baseline. Hyperuricemia was defined as a serum uric acid level ≥7.3 mg/dL in men and ≥5.3 mg/dL in women, which were 1 standard deviation above the mean value in the normal subjects.

RESULTS

The hyperuricemia group (n=50) had higher blood pressure, body mass index, and serum creatinine, and a greater amount of proteinuria and a lower glomerular filtration rate than the nonhyperuricemia group (n=143). Hyperuricemia increased the risk of IgAN progression (odds ratio, 4.53; 95% confidence interval, 1.31-15.66). The disease progression group (n=26) had a greater frequency of hyperuricemia, hypertension, and nephrotic range proteinuria than the nonprogression group (n=119). The renal survival analysis showed that the hyperuricemia group had a higher rate of IgAN disease progression.

CONCLUSION

Hyperuricemia at the time of diagnosis is an important marker for IgAN progression.

Uric acid and transplantation

Hyperuricemia is a common complication in organ transplant recipients, with a higher incidence in kidney and heart recipients. Risk factors for post-transplant hyperuricemia include reduced glomerular filtration rate, diuretic use, cyclosporine therapy, increasing age at transplant, obesity, and metabolic syndrome, as well as the presence of pretransplant hyperuricemia. The impact of hyperuricemia in patient and graft survival is unclear because uric acid only recently has been considered a risk factor for cardiovascular disease and graft survival. The effect of uric acid on graft function remains controversial, with studies suggesting that uric acid is an independent risk factor for chronic allograft dysfunction, contrasting with other studies suggesting that hyperuricemia is only a marker of reduced glomerular filtration rate. Strategies to reduce uric acid levels include reduction or avoidance of cyclosporine treatment, adequacy of antihypertension treatment, avoidance of diuretics, nutritional management, and use of uric acid-lowering agents. In this article, we review the incidence and risk factors for the development of post-transplant hyperuricemia, the effect of different immunosuppressive regimens in uric acid handling, and recent results from studies comparing uric acid levels and renal function in organ transplant recipients that try to identify which comes first: hyperuricemia or chronic allograft dysfunction?

The long-term renal and cardiovascular consequences of prematurity

Infants born prematurely at <37 weeks' gestation account for over 80% of infants weighing <2,500 g at birth-low birth weight (LBW) infants. This designation remains the surrogate marker for developmental origins of adult disease. Landmark studies spanning four decades have shown that individuals born with a LBW are more likely to develop cardiovascular and renal disease in later life, which is believed to be related to 'developmental programming' of such adult disease during vulnerable periods of growth in utero and in the early postnatal period. There has long been ambiguity regarding the distinction between infants with intrauterine growth restriction and preterm infants since both show a low nephron endowment that is associated with subsequent hypertension and chronic kidney disease. Knowledge is growing specific to the preterm infant and the developmental associations of being born preterm with the interruption of normal organogenesis relative to the vascular tree and kidney. Both systems develop by branching morphogenesis and interruptions lead to considerable deficits in their structure and function. These developmental aberrations can lead to endothelial dysfunction, hypertension, proteinuria and metabolic abnormalities that persist throughout life. This Review will examine the effect of preterm birth on the development of cardiovascular and kidney disease in later life and will also discuss potential early interventions to alter the progression of disease.

New insights into uric acid effects on the progression and prognosis of chronic kidney disease

Hyperuricemia is particularly common in patients with arterial hypertension, metabolic syndrome, or kidney disease. Its role, however, as a risk factor for both renal and cardiovascular outcomes and in the context of the well-established interrelationship between cardiovascular disease and chronic kidney disease (CKD) is debated. For decades high serum uric acid levels were mainly considered the result of renal dysfunction and not a true mediator of renal disease development and progression. However, recent epidemiological studies suggest an independent association between asymptomatic hyperuricemia and increased risk of arterial hypertension, CKD, cardiovascular events, and mortality. Furthermore, data from experimental models of hyperuricemia have provided robust evidence in this direction. Hyperuricemia causes increased arterial pressure, proteinuria, renal dysfunction, and progressive renal and vascular disease in rats. The main pathophysiological mechanisms of these deleterious effects caused by uric acid are endothelial dysfunction, activation of local renin-angiotensin system, increased oxidative stress, and proinflammatory and proliferative actions. A small number of short-term, single-center clinical studies support the beneficial influence of pharmaceutical reduction of serum uric acid on total cardiovascular risk, as well as on renal disease development and progression. Hyperuricemia is probably related to the incidence of primary hypertension in children and adolescents, as serum uric acid lowering by allopurinol has an antihypertensive action in this group of patients. Finally, it is clear that adequately powered randomized controlled trials are urgently required to elucidate the role of uric acid in cardiovascular events and outcomes, as well as in the development and progression of CKD.

Genotype-based changes in serum uric acid affect blood pressure

Elevated serum levels of uric acid consistently correlate with hypertension, but the directionality of the association remains debated. To help define this relationship, we used a controlled setting within a homogeneous Amish community and the Mendelian randomization of a nonsynonymous coding single-nucleotide polymorphism, rs16890979 (Val253Ile), in the SLC2A9 gene. This gene expresses the GLUT9 transporter that also transports uric acid and is associated with lower serum uric acid levels. We studied the unconfounded association between genotype and blood pressure in 516 Amish adults, each placed for 6 days on standardized diets, first with high sodium, followed by low sodium, with an intervening washout period. Blood pressure, measured using 24-h ambulatory monitoring, during both diet periods was used as the primary outcome. All participants were free of diuretic or other antihypertensive medications and the relationships between GLUT9 genotype and both serum uric acid and blood pressure were assessed. Each copy of the GLUT9 minor Ile allele was found to confer a significant 0.44 mg/dl reduction in serum uric acid and was associated with a significant mean decrease in the systolic blood pressure of 2.2 and 1.5 mm Hg on the high- and low-sodium diet, respectively. Thus, a Mendelian randomization analysis using variants in the GLUT9 gene indicates that a decrease in serum uric acid has a causal effect of lowering blood pressure.

Losartan therapy and hyperuricemia correction in patients with metabolic syndrome and arterial hypertension

Aim. To assess the potential of the angiotensin II receptor antagonist losartan for the correction of hyperuricemia (HU) in patients with arterial hypertension (AH) and metabolic syndrome (MS). Material and methods. This open, randomised, controlled comparative study in parallel groups included 60 AH patients with MS and HU. The patients received losartan or standard therapy for 12 weeks. Results. Throughout the follow-up period, no significant difference in antihypertensive effect was observed between the losartan and standard therapy groups. Losartan group patients demonstrated a more pronounced decrease in uric acid levels (-34,7 % vs. -7,8 % in the standard therapy group; p<0,05). In addition, losartan therapy, compared to the standard treatment, was associated with improved vascular elasticity, as manifested by the pulse wave velocity decrease (-27,8 % vs. -8,1 % for carotid-femoral index, and -30,2 % vs. -12,6 % for carotidradial index, respectively; both p<0,05).

Is there anything good in uric acid?

High uric acid (UA) levels can cause gout, urolithiasis and acute and chronic nephropathy, all of which are due to the deposit of urate crystals. There is also increasing evidence of relationships of hyperuricemia with other important disorders, including hypertension, chronic renal disease, metabolic syndrome and cardiovascular disease, as well as an increased mortality, although a causal relationship between these conditions has not been clearly established. On the other hand, low UA levels are not known to cause any disorder or disease. However, in the last few years a higher prevalence and progression of some neurological diseases have been associated with a low UA, and it is possible that they may predispose to some other disorders, mainly due to the decrease in its antioxidant activity. In this article, the known negative effects of UA are reviewed, as well as the much less-known possible positive actions, and their therapeutic implications.

Challenges associated with tyrosine kinase inhibitor therapy for metastatic thyroid cancer

Tyrosine kinase inhibitors (TKIs) which target angiogenesis are promising treatments for patients with metastatic medullary and differentiated thyroid cancers. Sorafenib, sunitinib, and pazopanib are commercially available drugs which have been studied in these diseases. Vandetanib is the first drug approved in the United States for treatment of medullary thyroid cancer. These TKIs are used as chronic therapies, and therefore it is imperative to understand the adverse event profile in order to avoid excessive toxicity and maintain patients on therapy as long as it proves beneficial. Here we review common toxicities, management of these, and other challenging situations that arise when using TKIs in patients with thyroid cancer.

Chronic kidney disease in kidney stone formers

Recent population studies have found symptomatic kidney stone formers to be at increased risk for chronic kidney disease (CKD). Although kidney stones are not commonly identified as the primary cause of ESRD, they still may be important contributing factors. Paradoxically, CKD can be protective against forming kidney stones because of the substantial reduction in urine calcium excretion. Among stone formers, those with rare hereditary diseases (cystinuria, primary hyperoxaluria, Dent disease, and 2,8 dihydroxyadenine stones), recurrent urinary tract infections, struvite stones, hypertension, and diabetes seem to be at highest risk for CKD. The primary mechanism for CKD from kidney stones is usually attributed to an obstructive uropathy or pyelonephritis, but crystal plugs at the ducts of Bellini and parenchymal injury from shockwave lithotripsy may also contribute. The historical shift to less invasive surgical management of kidney stones has likely had a beneficial impact on the risk for CKD. Among potential kidney donors, past symptomatic kidney stones but not radiographic stones found on computed tomography scans were associated with albuminuria. Kidney stones detected by ultrasound screening have also been associated with CKD in the general population. Further studies that better classify CKD, better characterize stone formers, more thoroughly address potential confounding by comorbidities, and have active instead of passive follow-up to avoid detection bias are needed.

Association of uric acid with change in kidney function in healthy normotensive individuals

BACKGROUND

Despite recent evidence, the role of uric acid as a causal factor in the pathogenesis and progression of kidney disease remains controversial, partly because of the inclusion in epidemiologic studies of patients with hypertension, diabetes, and/or proteinuria.

STUDY DESIGN

Prospective observational cohort.

SETTING & PARTICIPANTS

900 healthy normotensive adult blood donors (153 women, 747 men) evaluated at baseline and after 5 years.

PREDICTOR

Serum uric acid level.

OUTCOMES

Decrease in estimated glomerular filtration rate (eGFR) >10 mL/min/1.73 m(2), computed using the Modification of Diet in Renal Disease (MDRD) Study equation, with secondary analyses examining similar decreases using the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) and Cockcroft-Gault equations.

RESULTS

During a median follow-up of 59 months, eGFR decreased from 97 +/- 16 to 88 +/- 14 mL/min/1.73 m(2). Higher serum uric acid levels were associated with a greater likelihood of eGFR decrease in both women and men (HR, 1.13 [95% CI, 1.04-1.39] per each 1-mg/dL increase in uric acid level); in multivariable analyses adjusting for age, sex, body mass index, blood glucose level, total cholesterol level, mean blood pressure, urine albumin-creatinine ratio, and serum triglyceride level, the association remained highly significant (HR, 1.28 [95% CI, 1.12-1.48]). Results were similar using different estimating equations and when the association was examined in sex-specific subgroups.

LIMITATIONS

Analyses were based on a single baseline uric acid measurement. Women are underrepresented.

CONCLUSIONS

In healthy normotensive individuals, serum uric acid level is an independent risk factor for decreased kidney function.

Hyperuricemia associated with rapid renal function decline in elderly Taiwanese subjects

BACKGROUND/PURPOSE

Hyperuricemia is encountered frequently in patients with chronic kidney disease (CKD). We tested the hypothesis that uric acid influences glomerular filtration rate (GFR) and is associated with renal function decline in elderly Taiwanese subjects.

METHODS

We enrolled 800 elderly Taiwanese subjects for a health checkup. Estimated GFR (eGFR) was measured using the Modification of Diet in Renal Disease Study equation. eGFR < 60 mL/min/1.73 m2 was used to analyze the prevalence and incidence of CKD. Significant renal function decline was defined as a decrease in eGFR of > or = 3 mL/min/1.73 m2 per year.

RESULTS

The prevalence of CKD was 18.0% in the elderly subjects. Mean serum uric acid level was 6.6 mg/dL in male and 5.6 mg/dL in female subjects, and eGFR was 71.7 mL/min/1.73 m2. Uric acid levels were associated independently and negatively with eGFR after adjusting for conventional factors of renal function decline. One hundred and sixty-two individuals (31.2%) had a significant decline in renal function. As uric acid level increased by 1 mg/dL, the odds of a significant eGFR decline increased by 1.208.

CONCLUSION

Serum uric acid level was associated with eGFR and decline in renal function in elderly Taiwanese subjects. Whether hypouricemic therapy could retard the progression of CKD deserves further in-depth study.

Rasburicase improves hyperuricemia in infants with acute kidney injury

Recent data suggest that elevated levels of uric acid (UA) might contribute to the progression of renal disease. Rasburicase, recombinant urate oxidase, is a highly safe and efficacious hypo-uricosuric agent for treatment of elevated UA levels from tumor lysis. We adopted the use of rasburicase for management of hyperuricemia in infants with acute kidney injury (AKI) and, herein, report our experience. We conducted a retrospective chart review of infants with hyperuricemia (UA > 8 mg/dl) secondary to AKI (serum creatinine > 1.5 mg/dl) treated with rasburicase. Seven infants (mean age 34 +/- 55 days, six male), with a mean weight of 3.2 +/- 1.2 kg, were identified. Rasburicase was administered intravenously as a single, onetime, bolus of 0.17 +/- 0.04 mg/kg body weight. Within 24 h, serum UA had decreased from 13.6 +/- 4.5 mg/dl to 0.9 +/- 0.6 mg/dl (P < 0.05), creatinine had decreased from 3.2 +/- 2.0 mg/dl to 2.0 +/- 1.2 mg/dl (P < 0.05), and urinary output had increased from 2.4 +/- 1.2 ml/kg per hour to 5.9 +/- 1.8 ml/kg per hour (P < 0.05). Continued improvements in UA, creatinine, and urinary output were observed in the week following administration of rasburicase, without rebound of the UA. We observed no treatment-related side effects. All patients demonstrated a normalization of uric acid level without need of renal replacement therapy. In conclusion, a single intravenously administered bolus of rasburicase appears to be a novel treatment for hyperuricemia in infants with AKI.

Serum uric acid, hyperuricemia and body mass index in children and adolescents with intellectual disabilities

The aims of the preset study were to describe the profile of serum uric acid, the prevalence of hyperuricemia and its risk factors among children and adolescents with intellectual disabilities. We conducted a cross-sectional study of 941 children and adolescents with intellectual disabilities (aged 4-18 years) who participated in annual health examinations in three special schools in Taiwan. This study indicated 30.6% boys and 17.9% girls with intellectual disabilities were with hyperuricemia in Taiwan. The factors of gender, age and BMI were variables that can significantly predict the hyperuricemia occurrence in this vulnerable population. Those children and adolescents with intellectual disabilities were boys (OR=2.93, 95% CI=2.02-4.26) and older age (OR=6.49, 95% CI=2.19-19.21) were more likely to be hyperuricemia. With regard to BMI to hyperuricemia occurrence, those children and adolescents with intellectual disabilities were overweight (OR=1.16-3.21, 95% CI=1.16-3.21) and being obese (OR=4.95-11.58, 95% CI=4.95-11.58) was more likely to have a hyperuricemia than the normal weight group. This study provides the general profile of serum uric acid, hyperuricemia and its risk factors of children and adolescents with intellectual disabilities. Medical professionals should be highly alert to the possible consequences of hyperuricemia and provide useful information about the clinical manifestation of this condition for caregivers of children and adolescents with intellectual disabilities.

Role of ankle-brachial pressure index as a predictor of coronary artery disease severity in patients with diabetes mellitus

BACKGROUND

Previous studies have reported a close correlation between low ankle-brachial pressure index (ABPI) and various cardiovascular risk factors. However, despite the well-established potential hazards of consequent coronary artery disease (CAD), no data exist on the relationship between ABPI and the severity of CAD, particularly in patients with diabetes mellitus (DM).

METHODS

A total of 840 patients ranging from 35 to 87 years of age (mean [+/- SD] 63.9+/-10.2 years) with suspected CAD in a clinical practice were enrolled. All patients underwent ABPI measurements and coronary angiography. Patients were divided into four groups according to the results of ABPI measurements and the presence or absence of DM: group A had an ABPI value of at least 0.9 but no DM (A-/D-); group B had an ABPI value of at least 0.9 and DM (A-/D+); group C had an ABPI of less than 0.9 but no DM (A+/D-); and group D had an ABPI value of less than 0.9 and DM (A+/D+).

RESULTS

Age was significantly higher in the A+ (groups C and D) than the A- patients (groups A and B). Moreover, men predominated in all four groups. Comparisons of sex distribution among the four groups revealed that group D had the highest percentage of women, while group A had the lowest. Total cholesterol level did not differ among the four groups, although group D tended to have the highest result. Patients in group D had the highest percentages of hypertension, hypercholesterol, hypertriglyceride, low high-density lipoprotein cholesterol and high low-density lipoprotein cholesterol among the four groups. Group D exhibited the highest triglyceride and uric acid levels, the lowest high-density lipoprotein cholesterol level, and the highest metabolic syndrome criteria number and percentage of metabolic syndrome. Furthermore, group D had the highest mean lesion numbers, mean numbers of target vessel involvement, stenoses with type C classification and complex morphology lesions (chronic total occlusion, diffuse or calcified lesions) among the four groups. There were still significant differences in lesion numbers (P<0.001) and numbers of target vessel involvement (P<0.001) for ABPI predicting CAD severity after controlling for the effects of DM and age. The sensitivity, specificity, positive predictive value and negative predictive value of using an ABPI of less than 0.9 to predict CAD differed significantly between patients with and without DM.

CONCLUSIONS

ABPI is a useful noninvasive tool for predicting CAD severity, even in patients with DM.

Hyperuricemia after liver transplantation in children

Uric acid may be involved in the development and progression of kidney diseases. Hyperuricemia is a common feature in adult liver transplant recipients but there is limited information in children. In order to estimate the incidence, predictors of hyperuricemia in pediatric liver transplant recipients, and to assess whether hyperuricemia may impact long-term renal function determined by measured GFR, we reviewed data of 70 children who received a first liver transplant between 1991 and 2005 (median follow-up 7.1 yr). Renal function tests performed annually included uric acid concentration, inulin and uric acid clearances. The cumulative incidence of hyperuricemia was 32% at 10-yr post-transplantation, mainly because of decreased urate excretion. The only factor significantly associated with an increased risk of hyperuricemia was older age. After adjustment for donor and recipient age, gender, primary liver disease, immunosuppression, and post-operative acute renal failure, hyperuricemia as time dependent variable tended to predict (p = 0.05) subsequent CRI. The control of serum urate concentration in eight of the 21 hyperuricemic patients either by nutritional management or by allopurinol was not followed by a significant GFR improvement. Hyperuricemia after liver transplantation in children is a frequent problem which needs further investigation.

Uric acid: bystander or culprit in hypertension and progressive renal disease?

In humans, uric acid is the main urinary metabolite of purines. Serum levels are higher compared with other mammalians. Uric acid is an antioxidant and perhaps helps to control blood pressure during a low Na+ diet through stimulation of the renin-angiotensin system. Serum uric acid is also considered a marker of tubular reabsorption and 'effective' circulating blood volume. Moreover, hyperuricemia seems to be a cofactor in Na+ -sensitive hypertension, a marker and possibly itself responsible for microvascular damage through stimulation of the renin-angiotensin system, inhibition of endothelial nitric oxide, and proliferative effects on vascular smooth muscle. As fructose-rich diets increase uric acid levels, hyperuricemia may also play a role in the metabolic syndrome, triggering insulin resistance and hypertension.A number of studies on rats rendered hyperuricemic by administration of uricase inhibitors have recently confirmed induction of arterial hypertension and microvascular injury, particularly in the remnant kidney or in cyclosporine-induced renal fibrosis.

Gout Induced by Intoxication of Sodium Bicarbonate in Korean Native Broilers

Gout is a metabolic disorder that results in hyperuricemia and the deposition of positively birefringent monosodium urate crystals in various parts of the body. Intoxication of sodium bicarbonate (SBC) for 35 days in Korean native broilers was investigated. Sixty birds, aged 2 weeks, divided into 5 groups were exposed to excess SBC: 2 g/L (group A), 7.5 g/L (group B), 20 g/L (group C), 40 g/L (group D). Toxicopathological examination of all exposed birds revealed the manifestation of visceral and articular gout in group C, while birds of group D showed acute kidney damage with manifestation of excessive visceral gout. Interestingly, few birds in group D also showed signs of rare condition of acute articular gout. Dose-dependent increments in erythrocytic count, hematocrit values, and hemoglobin levels of the exposed birds were observed. Hypernatremia, hyperuricemia, hypokalemia, and hypochloremia were common findings among exposed birds. Microscopic examination of birds that manifested visceral gout revealed significant urate deposit, tubular necrosis, and tophi formation in renal interstitium. These findings provide a pathophysiological link that SBC intoxication may support hyperuricemia, which is an independent risk factor for gout and other renal dysfunctions. Further study is required to delineate the effect of lowering uric acid on progression of gout and other renal diseases.

Serum uric acid is associated with microalbuminuria and subclinical atherosclerosis in men with type 2 diabetes mellitus

Hyperuricemia has been reported to be associated with increased risk of renal insufficiency as well as cardiovascular events. The aim of this study was to evaluate the relationships between serum uric acid concentration and degree of urinary albumin excretion as well as markers of subclinical atherosclerosis in men with type 2 diabetes mellitus. Serum uric acid concentrations were measured in 343 men with type 2 diabetes mellitus. We then evaluated relationships of serum uric acid concentrations to degree of urinary albumin excretion as well as to major cardiovascular risk factors, including age, blood pressure, serum lipid concentration, and glycemic control (hemoglobin A1c). The relationships between serum uric acid concentration and pulse wave velocity or ankle-brachial index (n=236) and between serum uric acid concentration and carotid intima-media thickness or plaque score (n=125) were investigated additionally in a subgroup of patients. Serum uric acid concentration correlated positively with logarithm of urinary albumin excretion (r=0.302, P<.0001). Positive correlation was found between serum uric acid concentration and intima-media thickness (r=0.233, P=.0087), whereas inverse correlation was found between serum uric acid concentration and ankle-brachial index (r=-0.150, P=.0207). Multiple regression analysis demonstrated that serum uric acid concentration (beta=.281, P<.0001), duration of diabetes (beta=.253, P<.0001), hemoglobin A1c (beta=.166, P=.0034), serum triglyceride concentration (beta=.125, P=.0472), and systolic blood pressure (beta=.275, P=.0013) were independent determinants of logarithm of urinary albumin excretion. In conclusion, serum uric acid concentration is associated with microalbuminuria and subclinical atherosclerosis in men with type 2 diabetes mellitus.

PEG-uricase in the management of treatment-resistant gout and hyperuricemia

Hyperuricemia results from an imbalance between the rates of production and excretion of uric acid. Longstanding hyperuricemia can lead to gout, which is characterized by the deposition of monosodium urate monohydrate crystals in the joints and periarticular structures. Because such deposits are resolved very slowly by lowering plasma urate with available drugs or other measures, the symptoms of gout may become chronic. Persistent hyperuricemia may also increase the risk of renal and cardiovascular diseases. Unlike most mammals, humans lack the enzyme uricase (urate oxidase) that catalyzes the oxidation of uric acid to a more soluble product. This review describes the development of a poly(ethylene glycol) (PEG) conjugate of recombinant porcine-like uricase with which a substantial and persistent reduction of plasma urate concentrations has been demonstrated in a Phase 2 clinical trial. Two ongoing Phase 3 clinical trials include systematic assessments of gout symptoms, tophus resolution and quality of life, in addition to the primary endpoint of reduced plasma urate concentration.

Effect of treatment of hyperuricemia with allopurinol on blood pressure, creatinine clearence, and proteinuria in patients with normal renal functions

BACKGROUND

Hyperuricemia has been associated with the development of hypertension, cardiovascular, and renal disease. However, there is no data about the effect of lowering uric acid level on hypertension, renal function, and proteinuria in patients with glomerular filtration rate (GFR) >60 ml/min. We therefore conducted a prospective study to investigate the benefits of allopurinol treatment in hyperuricemic patients with normal renal function.

MATERIALS AND METHODS

Forty-eight hyperuricemic and 21 normouricemic patients were included in the study. Hyperuricemic patients received 300 mg/day allopurinol for three months. All patients' serum creatinine level, 24-h urine protein level, glomerular filtration rate, and blood pressure levels were measured at baseline and after three months of treatment.

RESULTS

A total of 59 patients completed the three-month follow-up period of observation. In the allopurinol group, serum uric acid levels, GFR, systolic and diastolic blood pressure, and C-reactive protein (CRP) levels significantly improved (P < 0.05). However, urine protein excretion remained unchanged (P > 0.05). No correlation was observed between changes in GFR and changes in CRP, or blood pressure in the allopurinol group. No significant changes were observed in the control group (P > 0.05).

CONCLUSION

We bring indirect evidence that hyperuricemia increases blood pressure, and decreases GFR. Hence, management of hyperuricemia may prevent the progression of renal disease, even in patients with normal renal function, suggesting that early treatment with allopurinol should be an important part of the management of chronic kidney disease (CKD) patients. Long-term follow-up studies are warranted to identify the benefits of uric acid management on renal function and hypertension.

Serum uric acid and leptin levels in metabolic syndrome: a quandary over the role of uric acid

This study investigates the impact of uric acid (UA) on the risk factors associated with metabolic syndrome. In addition, this study explores the relationship between UA and insulin resistance and serum leptin levels in metabolic syndrome. A total of 470 subjects (252 women and 218 men) were recruited from the Department of Health Management at Chang Gung Medical Center (Linkou, Taiwan). Metabolic syndrome was defined using a modified Adult Treatment Panel III (ATP III) definition. The formula for the homeostasis model assessment of insulin resistance (HOMA-IR) is as follows: fasting serum insulin (microU/mL) x fasting plasma glucose (mmol/L)/22.5. Diabetes mellitus was diagnosed in 45 subjects (9.6%); 82 subjects (17.4%) had hypertension. Hyperuricemia was diagnosed in 144 subjects (30.6%). Of these subjects, 115 (63 females and 52 males) (24.5%) were diagnosed as having metabolic syndrome. Patients with hyperuricemia had increased body mass index, waist-to-hip ratio, and triglyceride (Tg) level. The subjects also had lower high-density lipoprotein and greater hypertension. Hormone assays showed an elevation of leptin, immunoreactive insulin (IRI), and HOMA-IR in the hyperuricemia group. Uric acid appeared to be better correlated with Tg, blood pressure (both systolic and diastolic), obesity, immunoreactive insulin, and HOMA-IR. Uric acid did not correlate with leptin or blood glucose levels. Metabolic syndrome and Tg/high-density lipoprotein ratio showed a statistically significant difference in HOMA-IR using 3.8 as a cutoff value. Otherwise, there was no difference in leptin value. In conclusion, serum UA is significantly related to risk factors of metabolic syndrome except for blood glucose. Waist-to-hip ratio and HOMA-IR were statistically different in subjects with and without metabolic syndrome.

Uric acid level and its association with carotid intima-media thickness in patients with hypertension

OBJECTIVE

Carotid intima-media thickness (C-IMT) measured noninvasively by ultrasonography is now widely used as a surrogate marker for atherosclerotic disease and directly associated with increased risk of cardiovascular disease. Hyperuricemia (HU) is a well recognized risk factor for cardiovascular diseases. The independence of this association from other confounding factors has remained controversial. But the possible contributory effect of HU to carotid intima-media thickness (C-IMT) produced by hypertension (HT) has not been clarified yet. The study was designed to assess the C-IMT in patients with hypertension (HT) with or without HU.

METHODS

The study participants consisted of 30 patients (men 60%, mean age+/-S.D.: 49+/-11 years) with HT without HU, and 25 patients with HT and HU (men 52%, mean age+/-S.D.: 52+/-12 years), and 25 age-matched healthy control subjects (men 56%, mean age+/-S.D.: 50+/-13 years). All study groups were examined by B-mode ultrasound to measure the C-IMT at the far wall of the common carotid artery.

RESULTS

C-IMT were significantly higher in the patient groups (HT without HU and HT with HU) compared to the control cases (0.70+/-0.14, 0.83+/-0.16 versus 0.57+/-0.16, mm, respectively, p<0.001). In the patients groups, patients with HU had significantly higher carotid IMT compared to the patients without HU. In stepwise linear regression analysis, we found that serum uric acid (SUA) levels independently but modestly associated with C-IMT (beta=0.42, p=0.002).

CONCLUSION

We have shown that higher SUA levels are associated with atherogenesis independent from hypertension. Prospective studies will be necessary to confirm and extend these findings including early screening for hyperuricemia and lowering of SUA level looking at potential benefits in slowing progression of C-IMT in hypertensive patients.

Uric Acid and renal disease

The interrelationship between uric acid and renal disease is reviewed in a historical context. Four phases can be distinguished--the descriptions of uric acid stones and gravel in the eighteenth century, of chronically scarred kidneys containing urate crystals in the nineteenth, the appearance of the syndrome of acute urate nephropathy following tumour lysis in the mid twentieth century, and finally the realization that soluble urate affects both systemic and glomerular blood vessels, and may play a role in both hypertension and chronic renal damage.

Hyperuricaemia and long-term outcome after hospital discharge in acute heart failure patients

BACKGROUND

Uric acid (UA) may be involved in chronic heart failure (HF) pathogenesis, entailing a worse outcome. The purpose of this study was to examine the role of hyperuricaemia as a prognostic marker after hospital discharge in acute HF patients.

METHODS

We studied 212 patients consecutively discharged after an episode of acute HF with LVEF<40%. Blood samples for UA measurement were extracted in the morning prior to discharge. The evaluated endpoints were death and new HF hospitalization.

RESULTS

Mean UA levels were 7.4+/-2.4 mg/dl (range 1.6 to 16 mg/dl), with 127 (60%) of patients being within the range of hyperuricaemia. Hyperuricaemia was associated with a higher risk of death (n=48) (HR 2.0, 95% CI 1.1-3.9, p=0.028), new HF readmission (n=67) (HR 1.8, 95% CI 1.1-3.1, p=0.023) and the combined event (n=100) (HR 1.9, 95% CI 1.2-2.9, p=0.004). At 24 months, cumulative event-free survival was lower in the two higher UA quartiles (36.9% and 40.7% vs. 63.5% and 59.5%, log rank=0.006). After adjustment for potential confounders, hyperuricaemia remains an independent risk factor for adverse outcomes (HR 1.6, 95% CI 1.1-2.6, p=0.02).

CONCLUSIONS

In hospitalized patients with acute HF and LV systolic dysfunction, hyperuricaemia is a long-term prognostic marker for death and/or new HF readmission.

Gout in renal transplant recipients

AIMS

The aims of the present audit were to determine the prevalence of gout in renal transplant recipients in Canterbury, New Zealand, to identify risk factors for gout, and to assess the range of treatments used, their efficacy and complications. In addition, the authors wished to assess the impact of post-renal transplant gout on the patient.

METHODS

Patients with post-transplantation gout were identified from the Christchurch Hospital Nephrology database. For each patient with gout a post-renal transplantation recipient without gout post transplant was found matched for age, sex and date of transplant. Case notes were audited and patients interviewed.

RESULTS

In total, 47/202 (23%) living renal transplant recipients had gout post transplant. Those patients with gout were more likely to be taking a loop diuretic (68%vs 34%, P < 0.001), to have a higher serum urate and impaired renal function and to have had gout prior to the transplant. Of those patients who developed gout post transplant 70% had an attack at least every 3 months. Of those who returned to work post transplant 48% required time off work because of gout.

CONCLUSION

out is an important problem in the post-transplant population causing significant morbidity and time off work. Diuretics, impaired renal function, gout prior to transplantation and hyperuricaemia are important risk factors. The need for diuretic therapy should be kept under review in these patients. Hypouricaemic therapy should be considered early in those who develop gout post renal transplantation. Further studies are required to determine whether treatment for asymptomatic hyperuricaemia is justified.