Use of allopurinol in slowing the progression of renal disease through its ability to lower serum uric acid level

Prevalence and risk factors associated with chronic kidney disease in an adult population from southern China

BACKGROUND

Population-based studies evaluating the prevalence of kidney damage in different communities have been limited in developing countries. We conducted a population-based screening study in the southern Chinese city of Guangzhou that aimed to identify the prevalence and associated risk factors of chronic kidney disease (CKD) in southern Chinese populations.

METHODS

We interviewed 6311 residents (>20 years) from six districts of Guangzhou from July 2006 to June 2007 and tested for haematuria, albuminuria and reduced renal function. Associations between age, gender, smoking, diabetes mellitus, hypertension, hyperuricaemia and kidney damage were examined.

RESULTS

There were 6311 subjects enrolled in this study. After adjustment for age and gender, the prevalence of albuminuria, haematuria and reduced estimated glomerular filtration rate (eGFR) was 6.6% [95% confidence interval (CI): 5.5-7.6%], 3.8% (95% CI: 3.4%, 4.3%) and 3.2% (95% CI: 2.4%, 3.3%), respectively. Approximately 12.1% (95% CI: 11.3%, 12.9%) of the sample population had at least one indicator of kidney damage. Age, diabetes mellitus, hypertension, central obesity, hyperlipidaemia and use of nephrotoxic medications were independently associated with albuminuria; hyperuricaemia, age, gender, hypertension and use of nephrotoxic medications were independently associated with reduced eGFR, and female gender was independently associated with haematuria.

CONCLUSIONS

In the general adult population from southern China, 12.1% has either proteinuria, haematuria and/or reduced eGFR, indicating the presence of kidney damage, with an awareness of only 9.6%. The high prevalence and low awareness of CKD in this population suggest an urgent need for CKD prevention programmes in China.

Hyperuricemia is associated with the development of the composite outcomes of new cardiovascular events and chronic allograft nephropathy

BACKGROUND

To investigate the prevalence and the predictors for the development of hyperuricemia at 6 months after kidney transplantation, and its association with clinical outcomes including patient and graft survival, the development of new cardiovascular events and chronic allograft nephropathy (CAN).

MATERIALS AND METHODS

Adult patients who underwent kidney transplantation at Mount Sinai Medical Center between January 1, 2001 and December 30, 2004 were included in the study. New cardiovascular events and biopsy-proven CAN were investigated.

RESULTS

Of the 307 patients, 163 patients (53%) had normal uric acid levels and 144 patients (47%) had hyperuricemia. After adjustment for age, race, and sex, receiving a cadaveric kidney, having an estimated glomerular filtration rate (eGFR) less than 50 mL/min, and taking diuretics or cyclosporine were associated with hyperuricemia at 6 months after transplantation. Over a mean 4.3 years of follow-up, 83 patients had one, or more, of the events, 4 died, 20 had graft failure, 40 had new cardiovascular events, and 41 developed CAN. Kaplan-Meier survival curves showed that these events occurred more frequently in patients with hyperuricemia (P<0.001). Among transplant recipients with an eGFR less than 50 mL/min, 45% of hyperuricemic and 21% of normouricemic patients had an event (P=0.038). For patients with an eGFR more than 50 mL/min, event rates were similar for patients with and without hyperuricemia, 25.0% vs. 19.4%, respectively.

CONCLUSIONS

These results suggest an important association between hyperuricemia at 6 months after kidney transplantation and new cardiovascular events and CAN in patients with decreased allograft function.

Elevated uric acid increases the risk for kidney disease

Recent epidemiologic studies suggest that uric acid predicts the development of new-onset kidney disease, but it is unclear whether uric acid is an independent risk factor. In this study, data from 21,475 healthy volunteers who were followed prospectively for a median of 7 yr were analyzed to examine the association between uric acid level and incident kidney disease (estimated GFR [eGFR] <60 ml/min per 1.73 m(2)). After adjustment for baseline eGFR, a slightly elevated uric acid level (7.0 to 8.9 mg/dl) was associated with a nearly doubled risk for incident kidney disease (odds ratio 1.74; 95% confidence interval 1.45 to 2.09), and an elevated uric acid (> or =9.0 mg/dl) was associated with a tripled risk (odds ratio 3.12; 95% confidence interval 2.29 to 4.25). These increases in risk remained significant even after adjustment for baseline eGFR, gender, age, antihypertensive drugs, and components of the metabolic syndrome (waist circumference, HDL cholesterol, blood glucose, triglycerides, and BP). In a fully adjusted spline model, the risk for incident kidney disease increased roughly linearly with uric acid level to a level of approximately 6 to 7 mg/dl in women and 7 to 8 mg/dl in men; above these levels, the associated risk increased rapidly. In conclusion, elevated levels of uric acid independently increase the risk for new-onset kidney disease.

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.

Hyperuricaemia--where nephrology meets rheumatology

Rheumatologists care for patients with gouty arthritis, a condition caused by chronic and uncontrolled hyperuricaemia. Hyperuricaemia, gout and renal dysfunction are often bedfellows, raising the possibility of the former causing the latter. We sought the answer to the question 'Among patients with normal measures of glomerular filtration, does hyperuricaemia predict future renal disease'? We identified prospective cohort studies evaluating the relationship between serum uric acid and chronic kidney function from the past 20 yrs, through MEDLINE, Cochrane Library and EMBASE searches and bibliography cross-referencing. Nine cohort studies that met the selection criteria were found. Because of the extreme heterogeneity, a statistical meta-analysis was not performed. Most (eight out of nine) studies found an independent risk factor for deterioration of kidney function. Nearly all published prospective studies support the role of hyperuricaemia as an independent risk factor for renal dysfunction. In the absence of large randomized controlled trials of uric acid reduction, it remains uncertain if this relation is causal or merely an epiphenomenon. Regardless, our review suggests that hyperuricaemia is a useful, inexpensively measured, widely available and useful early marker for chronic kidney disease.

High-normal serum uric acid is associated with impaired glomerular filtration rate in nonproteinuric patients with type 1 diabetes

BACKGROUND AND OBJECTIVES

Early renal function decline begins before the onset of proteinuria in patients with type 1 diabetes. The association of elevated serum uric acid with advanced impaired renal function prompts an examination of its role in early renal function decline in patients before proteinuria develops.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Patients with type 1 diabetes and normoalbuminuria or microalbuminuria were recruited to the Second Joslin Kidney Study. A medical history and measurements of BP, hemoglobin A1c, albumin excretion rate, and serum concentrations of uric acid and cystatin C were obtained. Estimated glomerular filtration rate was measured by a cystatin C-based formula.

RESULTS

We studied 364 patients with normoalbuminuria and 311 patients with microalbuminuria. Mean glomerular filtration rate in these groups was 119 and 99 ml/min, respectively. Mildly or moderately impaired renal function (<90 ml/min) was present in 10% of those with normoalbuminuria and 36% of those with microalbuminuria. In univariate and multivariate analyses, lower glomerular filtration rate was strongly and independently associated with higher serum uric acid and higher urinary albumin excretion rate, older age, and antihypertensive treatment.

CONCLUSIONS

Serum uric acid concentration in the high-normal range is associated with impaired renal function in patients with type 1 diabetes. Follow-up studies are needed to confirm that this level of serum uric acid is a risk factor for early renal function decline in type 1 diabetes and to determine whether its reduction would prevent the decline.

NADPH oxidases, reactive oxygen species, and hypertension: clinical implications and therapeutic possibilities

Reactive oxygen species (ROS) influence many physiological processes including host defense, hormone biosynthesis, fertilization, and cellular signaling. Increased ROS production (termed "oxidative stress") has been implicated in various pathologies, including hypertension, atherosclerosis, diabetes, and chronic kidney disease. A major source for vascular and renal ROS is a family of nonphagocytic NAD(P)H oxidases, including the prototypic Nox2 homolog-based NAD(P)H oxidase, as well as other NAD(P)H oxidases, such as Nox1 and Nox4. Other possible sources include mitochondrial electron transport enzymes, xanthine oxidase, cyclooxygenase, lipoxygenase, and uncoupled nitric oxide synthase. NAD(P)H oxidase-derived ROS plays a physiological role in the regulation of endothelial function and vascular tone and a pathophysiological role in endothelial dysfunction, inflammation, hypertrophy, apoptosis, migration, fibrosis, angiogenesis, and rarefaction, important processes underlying cardiovascular and renal remodeling in hypertension and diabetes. These findings have evoked considerable interest because of the possibilities that therapies against nonphagocytic NAD(P)H oxidase to decrease ROS generation and/or strategies to increase nitric oxide (NO) availability and antioxidants may be useful in minimizing vascular injury and renal dysfunction and thereby prevent or regress target organ damage associated with hypertension and diabetes. Here we highlight current developments in the field of reactive oxygen species and cardiovascular disease, focusing specifically on the recently identified novel Nox family of NAD(P)H oxidases in hypertension. We also discuss the potential role of targeting ROS as a therapeutic possibility in the management of hypertension and cardiovascular disease.

Uric acid as a risk factor for progression of non-diabetic chronic kidney disease? The Mild to Moderate Kidney Disease (MMKD) Study

The kidney is one of the organs most prominently affected by aging. This can be seen by a loss of renal mass which is caused by a decrease in the number of nephrons resulting in hyperfiltration, hypertrophy and elevations in glomerular pressure. The factors influencing aging of the kidney are not fully elucidated. Epidemiological, experimental and interventional studies resulted in inconsistent results and have not firmly established whether uric acid levels affect progression of Chronic Kidney Disease (CKD). Therefore, we analyzed whether uric acid levels predict the progression of CKD in the Mild to Moderate Kidney Disease Study comprising at baseline 227 Caucasian patients aged 18-65 years with primary non-diabetic CKD of various degrees of renal impairment. Of them, 177 completed a prospective follow-up of 7 years. Primary endpoint was progression of CKD defined as doubling of baseline serum creatinine and/or terminal renal failure. Patients who reached a progression endpoint (n =6 5) were significantly older, had higher baseline serum creatinine and protein excretion rates as well as lower Glomerular Filtration Rate (GFR). Uric acid levels were only higher in patients with progression of disease when patients with uric acid-lowering drugs were excluded from the analysis. Cox regression analysis revealed that increasing uric acid levels predict disease progression only when the analysis was not adjusted for baseline kidney function parameters. As soon as we adjusted the analysis for GFR and proteinuria this association completely vanished. In summary, our prospective 7 year follow-up study in patients with non-diabetic primary CKD did not support uric acid as an independent predictor for CKD progression.

Effects of febuxostat on metabolic and renal alterations in rats with fructose-induced metabolic syndrome

Increased fructose consumption is associated with hyperuricemia, metabolic syndrome, and renal damage. This study evaluated whether febuxostat (Fx), an investigational nonpurine, and selective xanthine oxidase inhibitor, could alleviate the features of metabolic syndrome as well as the renal hemodynamic alterations and afferent arteriolopathy induced by a high-fructose diet in rats. Two groups of rats were fed a high-fructose diet (60% fructose) for 8 wk, and two groups received a normal diet. For each diet, one group was treated with Fx (5-6 mg.kg(-1).day(-1) in the drinking water) during the last 4 wk (i.e., after the onset of metabolic syndrome), and the other received no treatment (placebo; P). Body weight was measured daily. Systolic blood pressure and fasting plasma uric acid (UA), insulin, and triglycerides were measured at baseline and at 4 and 8 wk. Renal hemodynamics and histomorphology were evaluated at the end of the study. A high-fructose diet was associated with hyperuricemia, hypertension, as well as increased plasma triglycerides and insulin. Compared with fructose+P, fructose+Fx rats showed significantly lowered blood pressure, UA, triglycerides, and insulin (P < 0.05 for all comparisons). Moreover, fructose+Fx rats had significantly reduced glomerular pressure, renal vasoconstriction, and afferent arteriolar area relative to fructose+P rats. Fx treatment in rats on a normal diet had no significant effects. In conclusion, normalization of plasma UA with Fx in rats with metabolic syndrome alleviated both metabolic and glomerular hemodynamic and morphological alterations. These results provide further evidence for a pathogenic role of hyperuricemia in fructose-mediated metabolic syndrome.

Allopurinol dosing in renal impairment: walking the tightrope between adequate urate lowering and adverse events

Allopurinol is the mainstay of urate-lowering therapy for patients with gout and impaired renal function. Although rare, a life-threatening hypersensitivity syndrome may occur with this drug. The risk of this allopurinol hypersensitivity syndrome (AHS) is increased in renal impairment. The recognition that AHS may be because of delayed-type hypersensitivity to oxypurinol, the main metabolite of allopurinol, and that oxypurinol concentrations are frequently elevated in patients with renal impairment prescribed standard doses of allopurinol has led to the widespread adoption of allopurinol-dosing guidelines. These guidelines advocate allopurinol dose reduction according to creatinine clearance in patients with renal impairment. However, recent studies have challenged the role of these guidelines, suggesting that AHS may occur even at low doses of allopurinol, and that these guidelines lead to under-treatment of hyperuricemia, a key therapeutic target in gout. Based on current data, we advocate gradual introduction of allopurinol according to current treatment guidelines, with close monitoring of serum uric acid concentrations. In patients with severe disease and persistent hyperuricemia, allopurinol dose escalation above those recommended by the guidelines should be considered, with careful evaluation of the benefits and risks of therapy. Further work is needed to clarify the safety and efficacy of allopurinol dose escalation, particularly in patients with renal impairment.

Is the fructose index more relevant with regards to cardiovascular disease than the glycemic index?

The glycemic index (G.I.) is a means for categorizing carbohydrates based on their ability to raise blood glucose, subsequently this index has been popularized as a way for selecting foods to reduce the risk for obesity, diabetes, and cardiovascular disease. We suggest that the G.I. is better aimed at identifying foods that stimulate insulin secretion rather than foods that stimulate insulin resistance. In this regard, fructose has a low G.I. but may be causally linked with the obesity and cardiovascular disease epidemic. The reported association of high G.I. with cardiovascular disease may be due to the association of sugar intake which contains fructose, but which has a high G.I. due to its glucose content. We propose the use of a fructose index to categorize foods and propose studies to determine the effect of low fructose diets as a means to prevent obesity, diabetes, and cardiovascular disease in the population.

Relationship of uric acid with progression of kidney disease

BACKGROUND

Uric acid levels are increased in patients with kidney dysfunction. We tested the hypothesis that uric acid may be associated with kidney disease progression.

STUDY DESIGN

Cohort study.

SETTING & PARTICIPANTS

5,808 participants of the Cardiovascular Health Study.

PREDICTOR

Uric acid levels.

OUTCOMES & MEASUREMENTS

Kidney disease progression was defined as a decrease in estimated glomerular filtration rate (GFR) of 3 mL/min/1.73 m(2) per year or greater (>or=0.05 mL/s) and as incident chronic kidney disease (CKD). Measures of kidney function were estimated GFR using the Modification of Diet in Renal Disease Study equation.

RESULTS

Higher quintiles of uric acid levels were associated with greater prevalences of estimated GFR less than 60 mL/min/1.73 m(2) (<1.00 mL/s) of 7%, 14%, 12%, 25%, and 42% for quintiles 1 (<or=4.41 mg/dL [<or=262 micromol/L]), 2 (4.41 to 5.20 mg/dL [262 to 309 micromol/L]), 3 (5.21 to 5.90 mg/dL [310 to 351 micromol/L]), 4 (5.91 to 6.90 mg/dL [352 to 410 micromol/L]), and 5 (>6.90 mg/dL [>410 micromol/L]), respectively. In comparison, there was only a modest, but significant, association between quintiles of uric acid levels and progression of kidney function decrease, with adjusted odds ratios of 1.0, 0.88 (95% confidence interval [CI], 0.64 to 1.21), 1.23 (95% CI, 0.87 to 1.75), 1.47 (95% CI, 1.04 to 2.07), and 1.49 (95% CI, 1.00 to 2.22) for quintiles 1 through 5, respectively. No significant association was found between uric acid level and incident CKD (adjusted odds ratio, 1.00; 95% CI, 0.89 to 1.14).

LIMITATIONS

Measurements of albuminuria were not available.

CONCLUSIONS

Uric acid levels are associated strongly with prevalent CKD. In comparison, greater uric acid levels had a significant, but much weaker, association with progression of kidney disease.

Lead, at low levels, accelerates arteriolopathy and tubulointerstitial injury in chronic kidney disease

Chronic lead exposure has been epidemiologically linked with hypertension and renal disease. Clinical studies suggest that low lead levels may contribute to renal progression. However, experimental studies have not examined whether low levels of lead accelerate progression in experimental chronic renal disease. Sprague-Dawley rats were administered lead (L; 150 ppm in drinking water, n = 16) for 4 wk, followed by remnant kidney (RK) surgery with continuation of lead for an additional 12 wk; control rats (n = 9) were treated similarly but did not receive lead. Lead treatment was well tolerated and resulted in modest elevations in whole blood lead levels (26.4 +/- 4.5 vs. 1 +/- 0 mug/dl, week 16, P < 0.001). Lead treatment was associated with higher systolic blood pressure (P < 0.05) and worse renal function (creatinine clearance 1.4 +/- 0.4 vs. 1.8 +/- 0.5 ml/min, RK+L vs. RK, P < 0.05), and with a tendency for greater proteinuria (6.6 +/- 6.1 vs. 3.6 +/- 1.5 mg protein/mg creatinine, RK+L vs. RK, P = 0.08). While glomerulosclerosis tended to be worse in lead-treated rats (37.6 +/- 11 vs. 28.8 +/- 2.3%, RK+L vs. RK, P = 0.06), the most striking finding was the development of worse arteriolar disease (P < 0.05), peritubular capillary loss (P < 0.05), tubulointerstitial damage, and macrophage infiltration (P < 0.05) in association with significantly increased renal expression of monocyte chemoattractant protein-1 mRNA. In conclusion, lead accelerates chronic renal disease, primarily by raising blood pressure and accelerating microvascular and tubulointerstitial injury.

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.

Clinical Study of Uric Acid Urolithiasis

Uric acid urolithiasis develops from various causes. To investigate the clinical and biochemical presentation of patients with uric acid urolithiasis, a retrospective study was designed. A total of 46 cases were enrolled between January 2004 and December 2005. The compositions of the stones were analyzed by infrared spectrophotometry. There were 39 males (84.8%) and seven females (15.2%), with a mean age of 61.5 +/- 10.6 years and mean body mass index (BMI) of 26.7 +/- 3.1 kg/m2. The stone location was kidney in 10 (21.7%), ureter in 22 (41.8%), and bladder in 14 (30.5%). Multiple stones were diagnosed in 36 patients (78.3%). Pre-existing comorbidities included diabetes mellitus in 11 patients (23.9%), hypertension in 23 (50%), gout in 13 (28.2%), and benign prostatic hyperplasia in 14 (30.4%). Mean serum creatinine and uric acid was 1.6 +/- 0.6 mg/dL and 7.6 +/- 1.8 mg/dL, respectively. There were 27 patients (58%) with creatinine > 1.4 mg/dL. The mean urinary pH was 5.42 +/- 0.46. Patients with uric acid urolithiasis were predominantly male, older, with higher BMI, multiple stone presentation, with lower urinary pH, and hyperuricemia. Exacerbation of the renal function should also be of concern because of the high proportion of patients with renal insufficiency diagnosed in this study.

Emerging therapies in the long-term management of hyperuricaemia and gout

Gout is a common chronic arthritis that can lead to significant disability. Gout is one of the few rheumatological conditions that can be diagnosed with certainty, has a known cause and can be cured with appropriate therapy. Hypouricaemic agents reduce uric acid concentrations through inhibiting uric acid production (allopurinol) or enhancing uric acid excretion (probenecid, benzbromarone). Allopurinol is the most commonly used hypouricaemic agent but at recommended doses often fails to reduce adequately uric acid concentrations and prevent acute attacks of gout. The use of probenecid is limited by lack of efficacy in renal impairment. In the last few years, new agents in the management of hyperuricaemia and gout have become available. Febuxostat, a new xanthine oxidase inhibitor, is an effective hypouricaemic agent although further data are required for patients with renal impairment and other significant medical conditions. Rasburicase, a recombinant uricase (which catalyses the conversion of uric acid to the more readily excreted allantoin) is available for prevention of tumour lysis syndrome. However, its repeated use, as would be required in chronic gout, is limited by antigenicity. A less antigenic PEGylated uricase can rapidly reduce serum uric acid concentrations and promote resorption of tophi. However, further information with regard to the long-term risks and benefits of these agents is required. These agents may ultimately be used in the short term to rapidly deplete urate stores (induction therapy) followed by long-term therapy with an alternative hypouricaemic agent to prevent subsequent accumulation of uric acid (maintenance therapy).

Therapeutic advances in gout

PURPOSE OF REVIEW

The purpose of this review is to highlight the recent developments in the management of gout.

RECENT FINDINGS

Guidelines for the diagnosis and management of gout from EULAR, quality of care indicators, and outcome measures for clinical trials have been published. The standards of gout diagnosis and management are very low. Allopurinol remains the mainstay for serum uric acid lowering therapy. In an important percentage of patients receiving allopurinol, serum uric acid levels are insufficient to promote crystal dissolution. Febuxostat, a new serum uric acid lowering drug, has shown good results. Information on uricase continues to appear. For treatment of gouty inflammation, etoricoxib (a new cyclooxygenase 2 inhibitor) has been shown to be as effective as indomethacin. Finally, the association of gout with the metabolic syndrome and its comorbidities, and the newly described association of gout with myocardial infarction, bring lifestyle and dietary modifications to the front in the management of gout.

SUMMARY

Proper gout management requires changes to the physician's attitude towards the disease; essentially: (1) an unequivocal diagnosis based in urate crystal identification, (2) a clearly settled aim of the treatment: crystal elimination from the joints and elsewhere, and (3) proper use of the available therapeutic alternatives. Promoting a proper lifestyle appears to be especially important.

Uric acid, the metabolic syndrome, and renal disease

Metabolic syndrome, characterized by truncal obesity, hypertriglyceridemia, elevated BP, and insulin resistance, is recognized increasingly as a major risk factor for kidney disease and also is a common feature of patients who are on dialysis. One feature that is common to patients with metabolic syndrome is an elevated uric acid. Although often considered to be secondary to hyperinsulinemia, recent evidence supports a primary role for uric acid in mediating this syndrome. Specifically, fructose, which rapidly can cause metabolic syndrome in rats, also raises uric acid, and lowering uric acid in fructose-fed rats prevents features of the metabolic syndrome. Uric acid also can accelerate renal disease in experimental animals and epidemiologically is associated with progressive renal disease in humans. It is proposed that fructose- and purine-rich foods that have in common the raising of uric acid may have a role in the epidemic of metabolic syndrome and renal disease that is occurring throughout the world.

J-shaped mortality relationship for uric acid in CKD

BACKGROUND

Hyperuricemia is a common feature in patients with chronic kidney disease (CKD). Hyperuricemia has been associated with increased cardiovascular mortality in the general population, but less is known about this association in patients with CKD.

METHODS

To explore possible associations of serum uric acid with all-cause mortality and comorbidity in patients with CKD, we studied 294 incident patients with CKD stage 5 (185 men; age, 53 +/- 12 years) starting renal replacement therapy with a median glomerular filtration rate of 6.4 mL/min/1.73 m(2) (0.11 mL/s/1.73 m(2); range, 0.8 to 14.3 mL/min/1.73 m(2) [0.01 to 0.24 mL/s/1.73 m(2)]). Survival was determined from the day of examination and during a mean follow-up period of 27 months (range, 3 to 72 months); 94 patients died. Patients were divided into 3 groups based on serum uric acid levels (low quintile, 3 middle quintiles, and high quintile).

RESULTS

In a nonadjusted analysis, patients in the high quintile, followed by patients in the low quintile, had greater all-cause mortality compared with patients in the 3 middle quintiles (log-rank test chi-square, 6.8; P = 0.03). After adjusting for age, sex, glomerular filtration rate, cholesterol level, phosphate level, C-reactive protein level, cardiovascular disease, diabetes mellitus, diuretics, and allopurinol treatment, the association showed a "J-shaped" association with hazard ratios of 1.96 (confidence interval, 1.10 to 3.48; P = 0.02) for the high quintile and 1.42 (confidence interval, 0.76 to 2.66; P = not significant) for the low quintile. Moreover, uric acid levels correlated positively with levels of triglycerides, phosphate, C-reactive protein, and intracellular adhesion molecule 1 and negatively with levels of calcium, high-density lipoprotein cholesterol, and apolipoprotein A.

CONCLUSION

Serum uric acid levels showed a J-shaped association with all-cause mortality, with the lowest risk in the 3 middle quintiles. Moreover, uric acid level was associated with calcium/phosphate metabolism, dyslipidemia, and inflammation.

Uric acid and the development of hypertension: the normative aging study

Experimental evidence supports a causative role for uric acid in the pathogenesis of hypertension. Prospective studies have variably adjusted for relevant confounders and have been of relatively limited duration. We prospectively examined the relationship between uric acid level and the development of hypertension in the Normative Aging Study, a longitudinal cohort of healthy adult men. Of the 2280 initial men in the Normative Aging Study, 2062 had available information for inclusion in the analysis. Cox proportional hazards model was used to examine the relationship between baseline serum uric acid level and the development of hypertension adjusting for age, body mass index, abdominal circumference, smoking, alcohol, plasma triglycerides, total cholesterol, and plasma glucose. A total of 892 men developed hypertension over a mean of 21.5 years of follow-up. Serum uric acid level independently predicted the development of hypertension in age-adjusted (relative risk [RR]: 1.10; 95% CI: 1.06 to 1.15: P<0.001) and multivariable (RR: 1.05; 95% CI: 1.01 to 1.10; P=0.02) models. Among 1277 men at risk for the development of hypertension at the time of their first serum creatinine measurement, 508 (39.8%) developed hypertension over a mean of 10.3+/-5.5 years of follow-up. Additionally adjusting for calculated glomerular filtration rate in this subset, serum uric acid remained associated with the development of hypertension (RR: 1.06; 95% CI: 1.01 to 1.12; P=0.03). The baseline serum uric acid level is a durable marker of risk for the development of hypertension. The association is independent of elements of the metabolic syndrome, alcohol intake, and renal function.

Predicting initiation and progression of chronic kidney disease: Developing renal risk scores

Epidemiological studies have raised awareness of the problem of undiagnosed chronic kidney disease (CKD) and suggest that early identification and treatment will reduce the global burden of patients requiring dialysis. This has highlighted the twin problems of how to identify subjects for screening and target intervention to those with CKD most likely to progress to end-stage renal disease. Prospective studies have identified risk factors for CKD in the general population as well as risk factors for progression in patients with established CKD. Risk factors may thus be divided into initiating factors and perpetuating factors, with some overlap between the groups. In this paper, we review current data regarding CKD risk factors and illustrate how each may impact upon the mechanisms underlying CKD progression to accelerate loss of renal function. We propose that these risk factors should be used as a basis for developing a renal risk score, analogous to the Framingham risk score for ischemic heart disease, which will allow accurate determination of renal risk in the general population and among CKD patients.

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.