Hyperuricemia and chronic kidney disease: an enigma yet to be solved

Hyperuricaemia-associated all-cause mortality risk effect is increased by non-impaired kidney function - Is renal hyperuricaemia less dangerous?

BACKGROUND

Both hyperuricaemia and chronic kidney disease are known mortality risk factors. This study examined the modifying effect of renal function on hyperuricaemia-associated mortality risk, which is an issue that has not been studied before.

METHODS

Data on levels of serum uric acid (SUA), creatinine, cystatin C and other variables of persons aged 52-76 years were collected. Persons with SUA >410 μmol/L (75th percentile) were classified as clearly hyperuricaemic and persons with eGFR of ≤67 ml/min (25th percentile) as having reduced kidney function.

RESULTS

Reduced kidney function was associated with higher mortality in both SUA groups. When compared to individuals with SUA ≤410 μmol/L and eGFR >67 ml/min the hazard ratio (HR) for all-cause mortality was 1.53 (95 % CI: 1.26-1.84) in clearly hyperuricaemic persons with reduced kidney function, 1.26 (95 % CI: 1.02-1.55) in clearly hyperuricaemic persons with eGFR of >67 ml/min and 1.15 (95 % CI: 0.96-1.39) in persons with SUA ≤410 μmol/L and reduced kidney function. The HR for hyperuricaemia-related premature death was lowest in individuals with reduced eGFR, and it rose strikingly as the eGFR increased above 90 ml/min.

CONCLUSIONS

Reduced kidney function is a risk factor for mortality both in individuals with normal and elevated SUA. The hyperuricaemia-associated mortality risk is remarkably higher in individuals with normal kidney function than in individuals with reduced kidney function. Presumably overproduction of uric acid (metabolic hyperuricaemia) is a separate and more deleterious entity than hyperuricaemia resulting from reduced renal excretion of uric acid (renal hyperuricaemia).

Nonlinearity association between hyperuricemia and all-cause mortality in patients with chronic kidney disease

Controversy surrounds the role of serum uric acid and whether treatment intervention is favorable in retarding the progression of chronic kidney disease (CKD). The association of serum uric acid levels and CKD patient mortality risk needs to be further determined by large sample cohort studies. The National Health and Nutrition Examination Survey participants with CKD from 1998 to 2017 were enrolled in the study. Multivariable Cox regression models were used to reveal the association of serum uric acid concentrations and CKD mortality risks. A total of 9891 CKD patients were enrolled in the study, and 3698 individuals died during the follow-up. Increasing serum uric acid levels are independently relevant to higher mortality risks of CKD patients (HR per SD increase). A restricted cubic spline curve showed a nonlinear association between serum uric acid and CKD mortality risks (p for nonlinearity = 0.046). CKD patients with higher levels of serum uric acid (≥ 5.900 mg/dL) show a significant increase in mortality risks (HR = 1.102, 95% CI 1.043-1.165). Sensitivity analysis demonstrated that the results were stable and robust. High serum uric acid levels (≥ 5.900 mg/dL) may be associated with increased mortality risks in CKD patients.

Uric Acid, Ferritin, Albumin, Parathyroid Hormone and Gamma-Glutamyl Transferase Concentrations are Associated with Uremic Cardiomyopathy Characteristics in Non-Dialysis and Dialysis Chronic Kidney Disease Patients

Introduction

Circulating uric acid, ferritin, albumin, intact parathyroid hormone and gamma-glutamyl transferase each participate in biochemical reactions that reduce or/and enhance oxidative stress, which is considered the final common pathway through which pathophysiological mechanisms cause uremic cardiomyopathy. We hypothesized that the respective biomarkers may be involved in the development of uremic cardiomyopathy characteristics and can be useful in their identification among chronic kidney disease patients.

Methods

We assessed traditional and non-traditional cardiovascular risk factors including biomarker concentrations and determined central systolic blood pressure using SphygmoCor software and cardiac structure and function by echocardiography in 109 (64 non-dialysis and 45 dialysis) patients. Associations were evaluated in multivariate regression models and receiver operator characteristic (ROC) curve analysis.

Results

Each biomarker concentration was associated with left ventricular mass beyond stroke work and/or inappropriate left ventricular mass in all, non-dialysis and/or dialysis patients. Ferritin, albumin and gamma-glutamyl transferase levels were additionally associated with E/e' in all, non-dialysis and/or dialysis patients. Dialysis status influenced the relationship of uric acid concentrations with inappropriate left ventricular mass and those of gamma-glutamyl transferase levels with left ventricular mass and inappropriate left ventricular mass. In stratified analysis, low uric acid levels were related to inappropriate left ventricular mass in dialysis but not non-dialysis patients (interaction p=0.001) whereas gamma-glutamyl transferase concentrations were associated with left ventricular mass and inappropriate left ventricular mass in non-dialysis but not dialysis patients (interaction p=0.020 to 0.036). In ROC curve analysis, uric acid (area under the curve (AUC)=0.877), ferritin (AUC=0.703) and albumin (AUC=0.728) concentrations effectively discriminated between dialysis patients with and without inappropriate left ventricular hypertrophy, left ventricular hypertrophy, and increased E/e,' respectively.

Conclusion

Uric acid, ferritin, albumin, parathyroid hormone and gamma-glutamyl transferase were associated with uremic cardiomyopathy characteristics and could be useful in their identification. Our findings merit validation in future longitudinal studies.

Urate-lowering therapy for patients with gout on hemodialysis

OBJECTIVE

Gout is the most common form of inflammatory arthritis and is caused by deposition of monosodium urate crystals resulting from a high burden of uric acid (UA). High UA burden also has been associated with increased morbidity and mortality in the general population and progression to chronic kidney disease. In persons with gout and end-stage renal disease (ESRD), prior studies suggest that UA levels decrease after initiation of hemodialysis (HD). We evaluated UA level and the use of urate-lowering therapies (ULTs) in patients with gout and ESRD on HD.

METHODS

We performed a retrospective review of patients with gout and ESRD seen at a large urban public hospital (The MetroHealth System). We extracted data from the medical record (Epic) for patients diagnosed with gout and ESRD on HD. The main outcomes were the UA level and the use of ULTs before and after HD initiation.

RESULTS

We identified 131 patients with gout on HD. Of these, 21 patients had crystal proven gout diagnosis, 10 of whom had data on UA level pre-HD and post-HD and were included in the analysis. For the total sample (N = 21), the mean age was 65 years, 7 were female and 20 were African American. Mean pre-HD and post-HD UA levels were 8.4 and 3.98 mg/dL respectively. Twenty-one patients were receiving ULT pre-HD, 11 discontinued post-HD.

CONCLUSION

Among patients with gout and ESRD, we observed a decrease in UA level associated with initiation of HD. For this group, discontinuation of ULTs may be appropriate.

High Serum Uric Acid and High-Sensitivity C Reactive Protein Concentrations Predict Three-Year Cardiovascular Mortality in Patients Treated With Continuous Ambulatory Peritoneal Dialysis

AIMS

This study aims to access the predicting value of serum uric acid (UA) and high-sensitivity C reactive protein (hs-CRP) concentration on three-year cardiovascular-related mortality in patients performing continuous ambulatory peritoneal dialysis (CAPD).

METHODS

A total of267 CAPD patients [150 male (56.2%); mean age 48.93 ± 13.58 years] were included in our study. All patients had measured serum UA and hs-CRP concentration. A high-sensitivity particle-enhanced immunoturbidimetric assay determined serum hs-CRP; serum UA levels were determined using an enzymatic colorimetric assay. All patients were followed for three years to detect cardiovascular-related mortality by cardiologists and stroke specialists.

RESULTS

Mean serum UA level was 415.16 ± 84.28 µmol/L, 58.4% of patients had increased serum UA level. Median serum hs-CRP level was 2 (1-4) mg/L, 12.4% of patients had increased serum hs-CRP level. During 36 months of follow-up, 41 patients (15.4%) had cardiovascular-related mortality. The results of Cox proportional hazards regression showed that hypertension, diabetes, high serum UA and hs-CRP were risk factors that related to cardiovascular-related mortality (p<0.05). The receiver operating characteristic (ROC) curve and Kaplan-Meier analysis results showed that UA and hs-CRP level had predictive value for three-year cardiovascular-related mortality in CAPD patients [uric acid: area under the curve (AUC)=0.822; hs-CRP: AUC=0.834, p < 0.001].

CONCLUSION

High serum UA and hs-CRP levels were predictive factors of cardiovascular-related mortality in CAPD patients.

Anti-hyperuricemic potential of stevia (Stevia rebaudiana Bertoni) residue extract in hyperuricemic mice

Hyperuricemia (HUA) is considered a potent risk factor for the development of gout, renal failure, and cardiovascular disease. The current project was designed to use stevia (Stevia rebaudiana Bertoni) byproduct, named stevia residue extract (STVRE), for the treatment of HUA. Male Kunming mice were divided into six groups: normal control, model control, positive control (allopurinol, 5 mg per kg body weight [bw]), STVRE-1 (75 mg per kg bw), STVRE-2 (150 mg per kg bw), and STVRE-3 (300 mg per kg bw). HUA was induced by the administration of potassium oxonate (100 mg per kg bw), fructose (10% w/v), and yeast extract (100 mg per kg bw) for 8 weeks. STVRE significantly (p < 0.05) decreased uric acid (UA) production and ameliorated UA excretion by interacting with urate transporters. The STVRE remarkably attenuated oxidative stress mediated by UA and downregulated inflammatory-related response markers such as COX-2, NF-κB, PGE2, IL-1β, and TNF-α. Furthermore, STVRE also reversed HUA-induced abnormalities in kidneys compared with the MC group. The results of our study suggest that STVRE has potential to attenuate hyperuricemia and renal protective effects, and may be used as a natural supplement for the possible treatment of UA-related disorders.

Sex Differences in Time-Series Changes in Pseudo-R2 Values Regarding Hyperuricemia in Relation to the Kidney Prognosis

Studies on sex differences in time-series changes in pseudo-R² values regarding hyperuricemia (HU) in relation to the kidney prognosis among patients with chronic kidney disease (CKD) are scant. The kidney prognosis was evaluated in 200 patients with CKD (median follow-up, 12.3 years). Survival analyses and logistic regression analyses were conducted, generating time-series pseudo-R² values. We used four definitions of HU according to serum uric acid (SUA) levels (HU6, SUA ≥ 6.0 mg/dL; HU7, SUA ≥ 7.0 mg/dL; HU8, SUA ≥ 8.0 mg/dL) and antihyperuricemic agent use to calculate the mean and percentage of the change in pseudo-R² values from the 6th year until the end of the study (6Y–End Mean and 6Y–End Change, respectively). The multivariable Cox regression analysis showed that HU7 was significantly associated with kidney outcomes. When stratified by sex, the 6Y–End Mean was clearly higher in women than in men for all HU definitions, with the highest value (0.1755) obtained for HU7 in women. The pseudo-R² values for HU6 in women showed an increasing pattern, with a 6Y–End Change of 11.4%/year. Thus, it may be clinically meaningful to consider sex differences in the time-series pseudo-R² values regarding HU and kidney outcomes.

Assessment of the efficacy of hemodialysis on uric acid clearance in a sub-Saharan African population at the end stage kidney disease

Background

Uricemia dramatically rises with the stage of chronic kidney disease (CKD) and correlates with its mortality. Hemodialysis (HD) being the most used treatment at the end stage in sub-Saharan Africa, we sought to evaluate its efficacy on the clearance of uric acid (UAc) when used alone and twice per week.

Methods

A cross-sectional study of all consenting patients with CKD stage 5 recruited at random during HD sessions in a reference Centre in Cameroon from January to April 2017. We collected socio-demographic data, relevant clinical information, HD related variables, and measured serum uric acid (SUA) levels before and after the dialysis to assess the uric acid clearance. A clearance between 65 and 80% and above 80% was considered as low and good efficacy of HD respectively. Statistical analysis was performed using SPSS version 21.0. Factors associated with HD efficacy were assessed using Fisher’s exact test and are presented with their odds ratios (OR) and 95% confidence levels.

Results

One hundred four patients (53 females) were included. The mean age was 49.9 ± 13.3 years. Hypertension (25%) and chronic glomerulonephritis (16%) were the main suspected etiologies of CKD. The median time on renal replacement therapy by HD was 3 years [1; 6]. The prevalence of hyperuricemia was 81.9%. The means of SUA levels were 78.8 ± 13.8 mg/L and 26.4 ± 6.6 mg/L respectively before and after dialysis. Mean SUA clearance was 66% ± 10%. The efficacy of HD on UAc was moderate in 92 (63.9%) and good in 2 (1.4%) patients. Excess weight (OR 0.4 [0.2; 0.9]) and Kt/Vurea < 1.2 (OR 0.1 [0.04; 0.2]) significantly reduces the efficacy of HD.

Conclusion

HD used alone for 2 sessions per week has a moderate efficacy on uric acid clearance in CKD. Therefore, we should improve the Kt/V (> 1.2), and combine HD to uric acid lowering drugs and diet modifications to increase its efficacy.

Renal Contributions in the Pathophysiology and Neuropathological Substrates Shared by Chronic Kidney Disease and Alzheimer's Disease

Chronic kidney disease and Alzheimer's disease are chronic conditions highly prevalent in elderly communities and societies, and a diagnosis of them is devastating and life changing. Demanding therapies and changes, such as non-compliance, cognitive impairment, and non-cognitive anomalies, may lead to supplementary symptoms and subsequent worsening of well-being and quality of life, impacting the socio-economic status of both patient and family. In recent decades, additional hypotheses have attempted to clarify the connection between these two diseases, multifactorial in their nature, but even so, the mechanisms behind this link are still elusive. In this paper, we sought to highlight the current understanding of the mechanisms for cognitive decline in patients with these concurrent pathologies and provide insight into the relationship between markers related to these disease entities and whether the potential biomarkers for renal function may be used for the diagnosis of Alzheimer's disease. Exploring detailed knowledge of etiologies, heterogeneity of risk factors, and neuropathological processes associated with these conditions opens opportunities for the development of new therapies and biomarkers to delay or slow their progression and validation of whether the setting of chronic kidney disease could be a potential determinant for cognitive damage in Alzheimer's disease.

Serum Uric Acid and Mortality Risk Among Hemodialysis Patients

INTRODUCTION

Although high serum uric acid (SUA) has been consistently associated with an increased risk of death in the general population and in persons with nondialysis chronic kidney disease (CKD), studies in patients undergoing dialysis are conflicting. It has been postulated that low SUA simply reflects poor nutritional status in dialysis patients. We here characterize the association between SUA and the risk of death in a large dialysis cohort and explore effect modification by underlying nutritional status as reflected by body composition.

METHODS

In this retrospective cohort study, we included 16,057 hemodialysis (HD) patients treated during 2007 to 2016 in NephroCare centers as recorded in the European Clinical Database (EuCliD). The association between SUA, all-cause, and cardiovascular (CV)-related mortality was evaluated with competing risk models and characterized with splines. Effect modification was explored by lean tissue index (LTI) and fat tissue index (FTI).

RESULTS

During a mean of 1.8 years of follow-up, 2791 patients (17.4%) died. We found a multivariable-adjusted U-shaped pattern between SUA and all-cause mortality. Patients with SUA levels of 6.5 mg/dl (387 μmol/l) were at the lowest risk of death (subdistribution hazard ratio = 0.94 [confidence interval {CI} 0.91; 0.96]). The form of association was not meaningfully affected by underlying LTI and FTI.

CONCLUSION

We found a U-shaped pattern between SUA levels and all-cause mortality among HD patients, which was independent of the patients' body composition.

Roles of peritoneal clearance and residual kidney removal in control of uric acid in patients on peritoneal dialysis

BACKGROUND

There have been few systematic studies regarding clearance of uric acid (UA) in patients undergoing peritoneal dialysis (PD). This study investigated peritoneal UA removal and its influencing factors in patients undergoing PD.

METHODS

This cross-sectional study enrolled patients who underwent peritoneal equilibration test and assessment of Kt/V from April 1, 2018 to August 31, 2019. Demographic data and clinical and laboratory parameters were collected, including UA levels in dialysate, blood, and urine.

RESULTS

In total, 180 prevalent patients undergoing PD (52.8% men) were included. Compared with the normal serum UA (SUA) group, the hyperuricemia group showed significantly lower peritoneal UA clearance (39.1 ± 6.2 vs. 42.0 ± 8.0 L/week/1.73m²; P = 0.008). Furthermore, higher transporters (high or high-average) exhibited greater peritoneal UA clearance, compared with lower transporters (low or low-average) (42.0 ± 7.0 vs. 36.4 ± 5.6 L/week/1.73 m²; P < 0.001). Among widely used solute removal indicators, peritoneal creatinine clearance showed the best performance for prediction of higher peritoneal UA clearance in receiver operating characteristic curve analysis [area under curve (AUC) 0.96; 95% confidence interval [CI], 0.93-0.99]. Peritoneal UA clearance was independently associated with continuous SUA [standardized coefficient (β), - 0.32; 95% CI, - 6.42 to - 0.75] and hyperuricemia [odds ratio (OR), 0.86; 95% CI, 0.76-0.98] status, only in patients with lower (≤2.74 mL/min/1.73 m²) measured glomerular filtration rate (mGFR). In those patients with lower mGFR, lower albumin level (β - 0.24; 95%CI - 7.26 to - 0.99), lower body mass index (β - 0.29; 95%CI - 0.98 to - 0.24), higher transporter status (β 0.24; 95%CI 0.72-5.88) and greater dialysis dose (β 0.24; 95%CI 0.26-3.12) were independently associated with continuous peritoneal UA clearance. Furthermore, each 1 kg/m² decrease in body mass index (OR 0.79; 95% CI 0.63-0.99), each 1 g/dL decrease in albumin level (OR 0.08; 95%CI 0.01-0.47), and each 0.1% increase in average glucose concentration in dialysate (OR 1.56; 95%CI 1.11-2.19) were associated with greater peritoneal UA clearance (> 39.8 L/week/1.73m²).

CONCLUSIONS

For patients undergoing PD who exhibited worse residual kidney function, peritoneal clearance dominated in SUA balance. Increasing dialysis dose or average glucose concentration may aid in controlling hyperuricemia in lower transporters.

Complications of Renal Transplantation That Influence the Presence of Hyperuricemia in Its First Year of Evolution

INTRODUCTION

Renal transplantation (RT) has evolved to improve its functionality. Some factors have been little studied, one of which is hyperuricemia and its impact on renal graft function. The objective of this study is to determine the prevalence of complications of renal transplantation and its influence on hyperuricemia values in the first year of evolution.

MATERIAL AND METHODS

The authors completed a retrospective, observational study of 2 RT units in Mexico from January 2013 to December 2017. In total, 1009 files met the inclusion criteria; the levels of uric acid (UA) and creatinine (Cr) were determined before transplantation and in months 1, 3, 6, 9, and 12 after transplantation. Descriptive analysis was performed with measures of central tendency, measures of dispersion, difference of means with Student t test, and SPSS version 25 (IBM, Armonk, NY, United States).

RESULTS

The mean pretransplant UA was 6.24 mg/dL (standard deviation [SD] 1.97); per month was 4.73 mg/dL (SD 1.49). There is a difference in means between categorized groups of UA in the 5 post-RT moments (1, 3, 6, 9, and 12 months). A positive correlation of 0.41 to 0.47 was found with Spearman's test. The delayed function of the graft influenced in the first month after transplant in presenting hyperuricemia and acute dysfunction in month 6 showed that the rejection had no significance at any time.

CONCLUSIONS

The relationship between the values of UA and Cr in the RT represents a moderate positive correlation; delayed graft function in the first month impacts the presence of hyperuricemia, as well as acute dysfunction at month 6 after transplantation.

Rate of kidney function decline and factors predicting progression of kidney disease in type 2 diabetes mellitus patients with reduced kidney function: A nationwide retrospective cohort study

Currently, the data on independent risk factors for the progression of kidney disease in type 2 diabetes mellitus (T2DM) patients with CKD are limited. This study aimed to investigate CKD progression in T2DM patients who have reduced kidney function with baseline estimated glomerular filtration rate (eGFRs) between 15 and 59 mL/min/1.73 m² . This study was composed of a nationwide retrospective cohort of adult T2DM patients from 831 public hospitals in Thailand during the year 2015. T2DM patients with CKD stages 3 and 4 were followed up, until development of CKD stage 5, requirement of chronic dialysis, loss to follow-up, death, or 31 May 2018, whichever came first. Cox proportional hazard regression was utilized for analysis. A total of 8464 participants were included; 30.4% were male. The mean age was 69 ± 10 years. The mean eGFR was 45 ± 11 mL/min/1.73 m² . The incidence of CKD stage 5 or the need for chronic dialysis was 16.4 per 1000 person-years. The annual rate of eGFR decline during a mean follow-up of 29 months was -2.3 mL/min/1.73 m² ; 14.4% had a rapid decline in eGFR. The risk factors associated with progression to CKD stage 5 or the need for chronic dialysis were diabetes duration, systolic blood pressure, serum uric acid, albuminuria, and baseline eGFR. Conversely, older age and the use of renin-angiotensin aldosterone system blockade were associated with decreased risks for rapid CKD progression and incidence CKD stage 5 or dialysis. This study identifies multiple predictive risk factors that support a multifaceted approach to prevent progression of advanced CKD.

The Importance of Tubular Function in Chronic Kidney Disease

Glomerular filtration rate (GFR) and proteinuria-albuminuria are the renal functional parameters currently used to evaluate chronic kidney disease (CKD) severity. However, tubular secretion is another important renal functional parameter to be taken into account since proximal tubule (PT) secretion, in particular, is a crucial renal mechanism for endogenous organic cations, anions and drug elimination. The residual diuresis is a relevant survival predictor in patients on dialysis, since their urine is produced by the glomerular and tubular functions. It has been hypothesized that drugs which up-regulate some renal tubular transporters could contribute to uremic toxin excretion, and nephroprevention. However, if tubular transporters' down-regulation observed in CKD patients and experimental models is a PT adaptation to avoid intracellular accumulation and damage from uremic toxins, consequently the increase of toxin removal by inducing tubular transporters' up-regulation could be deleterious to the kidney. Therefore, a deeper understanding of this phenomenon is currently needed. In conclusion, tubular function has an important role for endogenous organic cations, anions and drug excretion in CKD patients, and a deeper understanding of its multiple mechanisms could provide new therapeutic alternatives in this population.

Uric acid predicts adverse outcomes in chronic kidney disease: a novel insight from trajectory analyses

Background

Very little is known about longitudinal trajectories of serum uric acid (SUA) over the course of chronic kidney disease (CKD). We aimed to determine whether longitudinal SUA trajectories are associated with the risk of end-stage renal disease (ESRD) and all-cause mortality among CKD patients.

Methods

We conducted a prospective cohort study from a 13-year multidisciplinary pre-ESRD care registry. The final study population consisted of 5090 CKD patients aged 20-90 years between 2003 and 2015. An individual's SUA trajectory was defined by group-based trajectory modeling in four distinct patterns: high, moderate-high, moderate and low. Time to ESRD and death was analyzed by multiple Cox regression.

Results

A total of 948 ESRD events and 472 deaths occurred with incidence rates of 57.9 and 28.7 per 1000 person-years, respectively. Compared with those with a low SUA trajectory, the adjusted hazard ratio of patients for incident ESRD was in a dose-response manner as follows: moderate, 1.89 [95% confidence interval (CI), 1.37-2.60]; moderate-high, 2.49 (1.75-3.55); and high, 2.84 (1.81-4.47); after considering the competing risk of death. For all-cause mortality, the corresponding risk estimate of the same SUA trajectory was 1.38 (95% CI, 0.89-2.12), 1.95 (1.22-3.10) and 4.52 (2.48-8.26), respectively. The unfavorable effect of elevated SUA trajectories on progression to ESRD was differentially higher among CKD patients without using urate-lowering agents at baseline (P for interaction = 0.018).

Conclusions

Elevated SUA trajectories are associated with accelerated kidney failure and all-cause mortality in CKD patients. Adequate experimental evidence is urgently needed to inform when and how to optimize SUA in this population.

Chronic kidney disease as a cardiovascular risk factor: lessons from kidney donors

Chronic kidney disease (CKD) is a major risk factor for cardiovascular disease but is often associated with other risks such as diabetes and hypertension and can be both a cause and an effect of cardiovascular disease. Although epidemiologic data of an independent association of reduced glomerular filtration rate with cardiovascular risk are strong, causative mechanisms are unclear.

Living kidney donors provide a useful model for assessing the “pure” effects of reduced kidney function on the cardiovascular system. After nephrectomy, the glomerular filtration rate ultimately falls by about one-third so many can be classified as having chronic kidney disease stages 2 or 3. This prompts concern based on the data showing an elevated cardiovascular risk with these stages of chronic kidney disease. However, initial data suggested no increase in adverse cardiovascular effects compared with control populations. Recent reports have shown a possible late increase in cardiovascular event rates and an early increase in left ventricular mass and markers of risk such as urate and albuminuria. The long-term significance of these small changes is unknown. More detailed and long-term research is needed to determine the natural history of these changes and their clinical significance.

•

Subjects with chronic kidney disease (CKD) have an elevated risk of cardiovascular disease.

•

Kidney donors have a reduced glomerular filtration rate and biochemical changes similar to CKD subjects.

•

Most studies of donors have not shown an elevated risk of death or cardiac disease.

•

Donors have structural and functional cardiovascular changes similar to early CKD.

•

The clinical significance of these changes is currently unknown.

Baicalein decreases uric acid and prevents hyperuricemic nephropathy in mice

Baicalein, a natural flavonoid, is structurally advantageous for binding to xanthine oxidoreductase. In our study, molecular docking analysis and Surface Plasmon Resonance revealed a direct interaction between baicalein and xanthine oxidoreductase. Moreover, 50 mg/kg/d baicalein treatment significantly suppressed the viability of xanthine oxidoreductase in hyperuricemia mouse model. The data showed that baicalein remarkably prevented renal dysfunction, ameliorated kidney fibrosis, alleviated epithelial-mesenchymal transition and oxidative stress in hyperuricemia mice. Thus, we concluded that baicalein executed a kidney-protection action in hyperuricemia and therefore may be used as a therapeutic alternative for hyperuricemic nephropathy.

Kidney Diseases in Agricultural Communities: A Case Against Heat-Stress Nephropathy

The beginning of the 21st century has seen the emergence of a new chronic tubulo-interstitial kidney disease of uncertain cause among agricultural communities in Central America and Sri Lanka. Despite many similarities in demography, presentation, clinical features, and renal histopathology in affected individuals in these regions, a toxic etiology has been considered mainly in Sri Lanka, whereas the predominant hypothesis in Central America has been that recurrent acute kidney injury (AKI) caused by heat stress leads to chronic kidney disease (CKD). This is termed the heat stress/dehydration hypothesis. This review attempts to demonstrate that there is sparse evidence for the occurrence of significant AKI among manual workers who are at high risk, and that there is little substantial evidence that an elevation of serum creatinine < 0.3 mg/dl in previously healthy people will lead to CKD even with recurrent episodes. It is also proposed that the extent of global warming over the last half-century was not sufficient to have caused a drastic change in the effects of heat stress on renal function in manual workers. Comparable chronic tubulo-interstitial kidney disease is not seen in workers exposed to heat in most tropical regions, although the disease is seen in individuals not exposed to heat stress in the affected regions. The proposed pathogenic mechanisms of heat stress causing CKD have not yet been proved in humans or demonstrated in workers at risk. It is believed that claims of a global warming nephropathy in relation to this disease may be premature and without convincing evidence.

Asymptomatic hyperuricemia and chronic kidney disease: Narrative review of a treatment controversial

Today there is plausible evidence both on experimental and epidemiological basis, that hyperuricemia represents a risk factor for the development and progression of chronic kidney disease (CKD). Nevertheless, the role of serum uric acid lowering treatment in CKD is still a matter of serious controversy. Review of randomised controlled trials, suggests that there may be an improvement of renal function with allopurinol treatment in CKD stage 3-5. However, these studies have included a relatively limited number of participants and provide insufficient information on adverse events and on the incidence of the end stage renal disease. Therefore, before adequately powered randomised, placebo-controlled trials are completed we cannot recommend treating asymptomatic hyperuricemia in patients with CKD.

Relationship between uric acid levels and risk of chronic kidney disease in a retrospective cohort of Brazilian workers

Uric acid (UA) levels are increased in patients with kidney dysfunction. We analyzed the association between asymptomatic hyperuricemia and new-onset chronic kidney disease (CKD). A retrospective cohort study was designed to collect data from employees of an energy generation and distribution company in the city of Rio de Janeiro, Brazil, who had undergone the company's annual medical checkup from 2008 to 2014. People with ≤2 years of follow-up, with baseline estimated glomerular filtration rate (eGFR) <60 mL·min-1·(1.73 m2)-1 or with incomplete data were excluded. The endpoint was defined as eGFR <60 mL·min-1·(1.73 m2)-1 estimated through the chronic kidney disease epidemiology collaboration equation (CKD-EPI). The study included 1094 participants. The mean follow-up period was 5.05±1.05 years and 44 participants exhibited new-onset CKD. The prevalence of hyperuricemia was 4.2%. There was a significant inverse correlation between baseline serum levels of UA and baseline eGFR (R=-0.21, P<0.001). Female gender (OR=4.00; 95%CI=1.92-8.29, P<0.001) and age (OR=1.06; 95%CI=1.02-1.11, P=0.004) but not UA levels (OR=1.12; 95%CI=0.83-1.50; P=0.465) were associated with new-onset CKD. Diabetes mellitus and body mass index were independent factors for fast progression (OR=2.17; 95%CI=1.24-3.80, P=0.007 and OR=1.04; 95%CI=1.01-1.07; P=0.020). These results did not support UA as an independent predictor for CKD progression in the studied population.

Febuxostat Attenuates Renal Damage besides Exerting Hypouricemic Effect in Streptozotocin-Induced Diabetic Rats

Aim. In this study, we aimed to investigate the effects of febuxostat, a novel inhibitor of xanthine oxidase (XO), on renal damage in streptozotocin- (STZ-) induced diabetic rats. Methods. Diabetes was induced by the intraperitoneal injection of STZ in male Sprague-Dawley rats. Sham-injected rats served as controls. The control and diabetic rats were treated with and without febuxostat for 8 weeks, respectively. Fasting blood and 24-h urine samples were collected every 4 weeks. Rat livers were extracted for detecting gene expression, content, and bioactivity of XO. Results. Diabetic rats showed significantly increased serum uric acid (SUA), serum creatinine (SCr), and urea nitrogen (BUN) levels. Daily urinary albumin (UAE), uric acid (UUA), and creatinine (UCr) excretion were also significantly increased in these rats. In diabetic rats, at week 8, febuxostat decreased SUA by 18.9%, while UAA was increased by 52.0%. However, UCr and urinary urea nitrogen (UUN) levels remained unchanged, while SCr and BUN levels decreased by >30% in these rats. Although hepatic gene expression, content, and activity of XO increased significantly in diabetic rats, febuxostat only slightly decreased its content. Conclusions. Febuxostat significantly attenuated renal damage in STZ-induced diabetic rats in addition to exerting hypouricemic effect.

Efficacy and safety of febuxostat in 73 gouty patients with stage 4/5 chronic kidney disease: A retrospective study of 10 centers

OBJECTIVES

The allopurinol dose is limited in chronic kidney disease, particularly stage 4/5 chronic kidney disease. Febuxostat has a hepatic metabolism and has been approved without dose adaptation in gouty patients with stage 1-3 chronic kidney disease. We aimed to study the safety and efficacy of febuxostat for stage 4/5 chronic kidney disease.

METHODS

In this retrospective study, we included patients with (1) a diagnosis of gout, (2) febuxostat treatment, (3) estimated glomerular filtration rate≤30mL/min/1.73m² (Modification of Diet in Renal Disease formula) at febuxostat initiation and (4) follow-up for at least 3 months after febuxostat initiation. Efficacy, safety and variation in estimated glomerular filtration rate were analyzed.

RESULTS

We included 73 patients (mean age 70.2±11.8, 61 men, 31 with vascular chronic kidney disease and 18 renal transplantation) with gout (baseline serum uric acid level=9.86±2.85mg/dL, mean gout duration 6.2±7.0 years) from 10 academic centers. Comorbidities included cardiac failure (17.8%), hypertension (98.6%), diabetes mellitus (30.1%), dyslipidemia (64.8%) and history of cardiovascular events (38.4%). At the last visit (mean follow-up 68.5±64.8 weeks), the daily dose of febuxostat was 40mg for 7 patients (10.5%), 80mg for 50 (74.6%) and 120mg for 10 (14.9%). Serum uric acid level was<6mg/dL for 49 patients (67%). Renal function improved for 18 patients, was unchanged for 24 and worsened for 31; 19 patients experienced flares and 1 patient, limb edema.

CONCLUSION

Febuxostat seemed efficient in gouty patients with stage 4/5 chronic kidney disease. However, safety data were not clear regarding renal function. Larger studies are needed to assess safety.

Serum uric acid and mortality in chronic kidney disease: A systematic review and meta-analysis

BACKGROUND

Studies have shown inconsistent results about the association between serum uric acid levels and mortality in patients with chronic kidney disease (CKD).

METHODS

A systematic literature search in MEDLINE, Web of Science and bibliographies of retrieved articles was performed to identify studies investigating the association between serum uric acid and mortality in patients with CKD. Pooled hazard ratios (HR) and corresponding 95% confidence intervals (CIs) were calculated using random-effects models.

RESULTS

A total of 24 studies with 25,453 patients with CKD were included. By meta-analysis, patients with the highest serum uric acid level were associated with a significantly higher risk for mortality (14 studies; HR, 1.52; 95% CI, 1.33-1.73) compared with patients with the lowest serum uric acid level. For dose-response analysis, a linear relationship (8 studies; Pfor non-linearity=0.14) between serum uric acid levels and risk of mortality was found. Overall, an increase of 1mg/dl in serum uric acid level was associated with an 8% increased risk of mortality (21 studies; HR, 1.08; 95% CI, 1.04-1.11).

CONCLUSIONS

Elevated serum uric acid levels are significantly associated with risk of mortality in patients with CKD. Further randomized controlled trials should attempt to determine whether it improves survival to target serum uric acid in patients with CKD.

Role of NADPH Oxidase in Metabolic Disease-Related Renal Injury: An Update

Metabolic syndrome has been linked to an increased risk of chronic kidney disease. The underlying pathogenesis of metabolic disease-related renal injury remains obscure. Accumulating evidence has shown that NADPH oxidase is a major source of intrarenal oxidative stress and is upregulated by metabolic factors leading to overproduction of ROS in podocytes, endothelial cells, and mesangial cells in glomeruli, which is closely associated with the initiation and progression of glomerular diseases. This review focuses on the role of NADPH oxidase-induced oxidative stress in the pathogenesis of metabolic disease-related renal injury. Understanding of the mechanism may help find potential therapeutic strategies.

Renal Damage Frequency in Patients with Solitary Kidney and Factors That Affect Progression

Background. The aim of this study is to assess renal damage incidence in patients with solitary kidney and to detect factors associated with progression. Methods. Medical records of 75 patients with solitary kidney were investigated retrospectively and divided into two groups: unilateral nephrectomy (group 1) and unilateral renal agenesis/dysplasia (group 2). According to the presence of kidney damage, each group was divided into two subgroups: group 1a/b and group 2a/b. Results. Patients in group 1 were older than those in group 2 (p = 0.001). 34 patients who comprise group 1a had smaller kidney size (p = 0.002) and higher uric acid levels (p = 0.028) than those in group 1b at presentation. Uric acid levels at first and last visit were associated with renal damage progression (p = 0.004, 0.019). 18 patients who comprise group 2a were compared with those in group 2b in terms of presence of DM (p = 0.038), HT (p = 0.003), baseline proteinuria (p = 0.014), and uric acid (p = 0.032) levels and group 2a showed higher rates for each. Progression was more common in patients with DM (p = 0.039), HT (p = 0.003), higher initial and final visit proteinuria (p = 0.014, for both), and higher baseline uric acid levels (p = 0.047). Conclusions. The majority of patients with solitary kidney showed renal damage at presentation. Increased uric acid level is a risk factor for renal damage and progression. For early diagnosis of renal damage and reducing the risk of progression, patients should be referred to a nephrologist as early as possible.

Targeting Uric Acid and the Inhibition of Progression to End-Stage Renal Disease--A Propensity Score Analysis

Background

The role of uric acid (UA) in the progression of chronic kidney disease (CKD) remains controversial due to the unavoidable cause and result relationship. This study was aimed to clarify the independent impact of UA on the subsequent risk of end-stage renal disease (ESRD) by a propensity score analysis.

Methods

A retrospective CKD cohort was used (n = 803). Baseline 23 covariates were subjected to a multivariate binary logistic regression with the targeted time-averaged UA of 6.0, 6.5 or 7.0 mg/dL. The participants trimmed 2.5 percentile from the extreme ends of the cohort underwent propensity score analyses consisting of matching, stratification on quintile and covariate adjustment. Covariate balances after 1:1 matching without replacement were tested for by paired analysis and standardized differences. A stratified Cox regression and a Cox regression adjusted for logit of propensity scores were examined.

Results

After propensity score matching, the higher UA showed elevated hazard ratios (HRs) by Kaplan-Meier analysis (≥6.0 mg/dL, HR 4.53, 95%CI 1.79–11.43; ≥6.5 mg/dL, HR 3.39, 95%CI 1.55–7.42; ≥7.0 mg/dL, HR 2.19, 95%CI 1.28–3.75). The number needed to treat was 8 to 9 over 5 years. A stratified Cox regression likewise showed significant crude HRs (≥6.0 mg/dL, HR 3.63, 95%CI 1.25–10.58; ≥6.5 mg/dL, HR 3.46, 95%CI 1.56–7.68; ≥7.0 mg/dL, HR 2.05, 95%CI 1.21–3.48). Adjusted HR lost its significance at 6.0 mg/dL. The adjustment for the logit of the propensity scores showed the similar results but with worse model fittings than the stratification method. Upon further adjustment for other covariates the significance was attained at 6.5 mg/dL.

Conclusions

Three different methods of the propensity score analysis showed consistent results that the higher UA accelerates the progression to the subsequent ESRD. A stratified Cox regression outperforms other methods in generalizability and adjusting for residual bias. Serum UA should be targeted less than 6.5 mg/dL.

Gout after living kidney donation: correlations with demographic traits and renal complications

BACKGROUND

The demographic and clinical correlates of gout after living kidney donation are not well described.

METHODS

Using a unique database that integrates national registry identifiers of U.S. living kidney donors (1987-2007) with billing claims from a private health insurer (2000-2007), we identified post-donation gout based on medical diagnosis codes or pharmacy fills for gout therapies. The frequencies and demographic correlates of gout after donation were estimated by Cox regression with left- and right-censoring. We also compared the rates of renal diagnoses among donors with and without gout, matched in the ratio 1:3 by age, sex, and race.

RESULTS

The study sample of 4,650 donors included 13.1% African Americans. By seven years, African Americans were almost twice as likely to develop gout as Caucasian donors (4.4 vs. 2.4%; adjusted hazard ratio, aHR, 1.8; 95% confidence interval (CI) 1.0-3.2). Post-donation gout risk also increased with older age at donation (aHR per year 1.05) and was higher in men (aHR 2.80). Gout rates were similar in donors and age- and sex-matched general non-donors (rate ratio 0.86; 95% CI 0.66-1.13). Compared to matched donors without gout, donors with gout had more frequent renal diagnoses, reaching significance for acute kidney failure (rate ratio 12.5; 95% CI 1.5-107.0), chronic kidney disease (rate ratio 5.0; 95% CI 2.1-11.7), and other disorders of the kidney (rate ratio 2.2; 95% CI 1.2-4.2).

CONCLUSION

Donor subgroups at increased risk of gout include African Americans, older donors, and men. Donors with gout have a higher burden of renal complications after demographic adjustment.