Is uric acid a predictive factor for graft dysfunction in renal transplant recipients?

Association between post-transplant serum uric acid levels and kidney transplantation outcomes

Background

Serum uric acid (UA) level has been reported to be associated with chronic allograft nephropathy and graft failure in patients who undergo kidney transplantation (KT). However, the role of serum UA level in renal graft survival remains controversial.

Objective

This study aimed to investigate the effect of mean serum UA level during two different post-KT periods on long-term renal graft outcomes in a large population cohort in which living donor KT prevails.

Material and methods

A retrospective cohort study was performed using KT data prospectively collected at a single institution. Patients (n = 2,993) were divided into low-, normal-, and high-UA groups according to the mean serum UA level within the first year (1-YR) and 1–5 years (5-YR) after transplantation.

Results

In the 1-YR Cox proportional hazards analysis, the low- and high-UA groups had a significantly decreased and increased risk, respectively, for overall graft failure (OGF), death-censored graft failure (DCGF), and composite event (return to dialysis, retransplantation, death from graft dysfunction, and 40% decline in estimated glomerular filtration rate) compared with the normal-UA group. Similarly, in the 5-YR analysis, the low-UA group had a significantly reduced risk of DCGF compared with the normal-UA group, whereas the high-UA group had a significantly increased risk of all three graft outcomes. In a marginal structural model, hyperuricemia had a significant causal effect on worsening graft outcomes, with consideration of all confounding variables (OGF: hazard ratio [HR] 2.27, 95% confidence interval [CI] 1.33–3.78; DCGF: HR 2.38, 95% CI 1.09–4.9; composite event: HR 3.05, 95% CI 1.64–5.49).

Conclusions

A low-to-normal serum UA level within the first year and 1–5 years after KT is an independent factor for better renal allograft outcomes in the long-term follow-up period rather than high serum UA level.

Efficacy and Safety of Febuxostat in Kidney Transplant Patients

OBJECTIVES

Febuxostat, a nonpurine xanthine oxidase, is known to be effective and safe, even in patients with chronic kidney disease. However, there are insufficient data about the efficacy and safety of febuxostat in kidney transplant patients.

MATERIALS AND METHODS

We reviewed medical records of all kidney transplant patients who were prescribed febuxostat between August 2012 and May 2015 at Asan Medical Center in Seoul, Korea. The efficacy and safety results of febuxostat in transplant patients were evaluated. To compare the efficacy of febuxostat, results of kidney transplant patients who were prescribed benzbromarone or allopurinol for more than 1 year during the same period were also reviewed.

RESULTS

Thirty-one patients were included in this study. The initial serum uric acid level of 481.83 ± 143.36 μmol/L decreased to 302.18 ± 150.50 μmol/L after 1 month of febuxostat use. Only 1 patient had altered sense of taste after taking febuxostat, but this symptom quickly improved and he continued treatment. No other adverse events were reported. In addition, at 12 months, mean serum uric acid levels were 280.77 ± 78.52 μmol/L in the febuxostat, 332.52 ± 72.57 μmol/L in the benzbromarone, and 363.45 ± 60.08 μmol/L in the allopurinol group. However, we found no apparent effect on estimated glomerular filtration rate (P = .344). The mean doses of febuxostat, benzbromarone, and allopurinol were 52.31 ± 5.33 mg/day, 42.19 ± 1.69 mg/day, and 146.67 ± 16.52 mg/day.

CONCLUSIONS

Febuxostat reduced serum uric acid levels effectively in kidney transplant patients without severe adverse events.

Early onset hyperuricemia is a prognostic marker for kidney graft failure: Propensity score matching analysis in a Korean multicenter cohort

It remains inconclusive whether hyperuricemia is a true risk factor for kidney graft failure. In the current study, we investigated the association of hyperuricemia and graft outcome. We performed a multi-center cohort study that included 2620 kidney transplant recipients. The patients were classified as either normouricemic or hyperuricemic at 3 months after transplantation. Hyperuricemia was defined as a serum uric acid level ≥ 7.0 mg/dL in males or ≥ 6.0 mg/dL in females or based on the use of urate-lowering medications. The two groups were compared before and after propensity score matching. A total of 657 (25.1%) patients were classified as hyperuricemic. The proportion of hyperuricemic patients increased over time, reaching 44.2% of the total cohort at 5 years after transplantation. Estimated glomerular filtration rate and donor type were independently associated with hyperuricemia. Hyperuricemia was associated with graft loss according to multiple Cox regression analysis before propensity score matching (hazard ratio [HR] = 1.56, 95% confidence interval [CI] = 1.14-2.13, P = 0.005) as well as after matching (HR = 1.65, 95% CI = 1.13-2.42, p = 0.010). Cox regression models using time-varying hyperuricemia or marginal structural models adjusted with time-varying eGFR also demonstrated significant hazards of hyperuricemia for graft loss. Cardiovascular events and recipient survival were not associated with hyperuricemia. Overall, hyperuricemia, especially early onset after transplantation, showed an increased risk for graft failure. Further studies are warranted to determine whether lowering serum uric acid levels would be beneficial to graft survival.

Post-transplant Hyperuricemıa as a Cardıovascular Risk Factor

PURPOSE

Uric acid is known to impair endothelial cell function and to stimulate the development of renal interstitial fibrosis. The aim of this study was to evaluate the association between first-year hyperuricemia with graft dysfunction and the development of cardiovascular risk disorders in renal transplant recipients.

METHODS

One hundred kidney transplant recipients (31 female, 45.9 ± 9.6 post-transplantation months) with normal graft functions were enrolled. The clinical biochemical parameters in the first post-transplantation year were retrospectively recorded and searched for the predictive value in yearly determined graft function and association with cross-sectionally analyzed cardiovascular parameters, including body composition analyses, ambulatory blood pressure monitoring data, and pulse wave velocity. Hyperuricemia was defined as an uric acid level of ≥ 6.5 mg/dL that persisted for at least 2 consecutive tests.

RESULTS

One year after transplantation, 37% of subjects had hyperuricemia. According to cross-sectional data, sagittal abdominal diameter (P = .002) and hip circumferences (P = .013) were significantly higher in hyperuricemic patients than in normouricemic ones. Hyperuricemic patients had higher fat (P = .014) and muscle mass (P = .016) than normouremic patients. Hyperuricemic patients had significantly higher mean systolic BP (P = .044) than normouremic patients. Hyperuricemic patients had significantly higher pulse wave velocity levels (P = .0001) and left ventricular mass index (P = .044) than normouremic patients. The yearly decline in estimated glomerular filtration rate levels was significantly higher in hyperuricemic patients (P = .0001) than in normouricemic ones.

CONCLUSION

Post-transplantation hyperuricemia is associated with hypertension, arterial stiffness, and dyslipidemia; it should be accepted not only as a marker for renal allograft dysfunction but also as a cardiovascular risk factor in renal transplant recipients.

Serum Uric Acid and Renal Transplantation Outcomes: At Least 3-Year Post-transplant Retrospective Multivariate Analysis

Since the association of serum uric acid and kidney transplant graft outcome remains disputable, we sought to evaluate the predictive value of uric acid level for graft survival/function and the factors could affect uric acid as time varies. A consecutive cohort of five hundred and seventy three recipients transplanted during January 2008 to December 2011 were recruited. Data and laboratory values of our interest were collected at 1, 3, 6, 12, 24 and 36 months post-transplant for analysis. Cox proportional hazard model, and multiple regression equation were built to adjust for the possible confounding variables and meet our goals as appropriate. The current cohort study lasts for 41.86 ± 15.49 months. Uric acid level is proven to be negatively associated with eGFR at different time point after adjustment for age, body mass index and male gender (standardized β ranges from -0.15 to -0.30 with all P<0.001).Males with low eGFR but high level of TG were on CSA, diuretics and RAS inhibitors and experienced at least one episode of acute rejection and diabetic issue were associated with a higher mean uric acid level. Hyperuricemia was significantly an independent predictor of pure graft failure (hazard ratio=4.01, 95% CI: 1.25-12.91, P=0.02) after adjustment. But it was no longer an independent risk factor for graft loss after adjustment. Interestingly, higher triglyceride level can make incidence of graft loss (hazard ratio=1.442, for each unit increase millimoles per liter 95% CI: 1.008-2.061, P=0.045) and death (hazard ratio=1.717, 95% CI: 1.105-2.665, P=0.016) more likely. The results of our study suggest that post-transplant elevated serum uric acid level is an independent predictor of long-term graft survival and graft function. Together with the high TG level impact on poor outcomes, further investigations for therapeutic effect are needed.

Asymptomatic hyperuricemia following renal transplantation

Evidence is accumulating indicating a role for uric acid in the genesis and progression of kidney disease, and a few studies are beginning to show a possible beneficial effect of urate-lowering therapy. Whether this holds true for renal allograft recipients is not clear. In this short review evidence from epidemiological as well as intervention studies is summarized and discussed, with some practical considerations presented at the end.

Increased urine transforming growth factor β1 (TGF-β1) and serum uric acid are associated with an early decline of glomerular filtration rate in kidney transplant recipients

BACKGROUND

The renin-angiotensin system (RAS) and transforming growth factor β1 (TGF-β1) may play a role in the pathogenesis of fibrosis in kidney allografts. Experimental hyperuricemia shows activation of intrarenal RAS. However, the association between uric acid (UA), RAS, and TGF-β1 in allograft recipients has not been demonstrated. Therefore we investigated the association between serum UA levels, RAS, and TGF-β1 in kidney transplant recipients during the 1st year after transplantation.

METHODS

Sixty-two transplant recipients were included in the study. Serum UA level, plasma renin activity (PRA), and urine TGF-β1 concentration were studied at 3, 6, and 12 months after transplantation. Statistical correlation was demonstrated with the use of Spearman rank correlation coefficient. Receiver operating characteristic curve analysis and area under the curve were performed to assess the diagnostic performance to discriminate between estimated glomerular filtration rate (eGFR) <60 and ≥ 60 mL/min/1.73 m(2).

RESULTS

For all 62 patients, urine TGF-β1 and serum UA had a tendency to increase during the 1-year follow-up period, despite no statistically significant change in eGFR. We found that increased urine TGF-β1 was correlated with rising serum UA levels and a decrease of the eGFR (r = 0.27 [P = .01]; r = -0.38 [P = .0003]). In contrast, there was no significant change in PRA and it was not correlated with eGFR or TGF-β1 (r = -0.01; P = .93).

CONCLUSIONS

Increased urine TGF-β1 and serum UA level during the 1st year after transplantation correlated with a decline in eGFR. The evaluation of these parameters in the early post-transplantation period may identify patients at risk of allograft dysfunction.

Uric acid and the risk of graft failure in kidney transplant recipients: a re-assessment

The association of hyperuricemia with kidney allograft outcomes remains controversial. We studied this problem in 1170 kidney transplants from January 2000 to December 2010. The primary endpoint was total graft failure (i.e. graft loss or death). Conventional, time-dependent and marginal structural Cox proportional hazards models were fitted, the latter accounting for kidney function as a time-varying confounder affected by prior uric acid levels. Uric acid level was associated with an increased risk of total graft failure in time-fixed and time-varying models (HR 1.02 [95% CI: 1.003-1.04] and HR 1.02 [95% CI: 1.01-1.03], respectively, for every 10 µmol/L increase in uric acid). In contrast, the marginal structural model showed a modestly protective effect (HR 0.90 [95% CI: 0.85-0.94] for every 10 µmol/L increase in uric acid). Similar results were observed for death-censored graft failure and death with graft function. In summary, the absence of a deleterious association between elevated uric acid and graft outcome after accounting for graft function as a time-varying confounder suggests that uric acid is not an independent risk factor for graft failure. The modestly protective effect of uric acid may be an indicator of nutritional status but further study is warranted.

Hyperuricemia predicts kidney disease progression after acute allograft dysfunction

BACKGROUND

Hyperuricemia is associated with the development of new cardiovascular events and chronic allograft nephropathy in patients with decreased allograft function. This study investigates whether hyperuricemia in kidney transplant recipients should be considered as an independent predictor of kidney disease progression after acute allograft dysfunction.

METHODS

Between September 1, 2010, and December 31, 2012, 124 patients who underwent kidney graft biopsy for acute allograft dysfunction were enrolled. Participants were divided into 2 groups: A hyperuricemic group (n = 57) and a normouricemic group (n = 67). The mean serum uric acid (UA) level was obtained by averaging all measurements, once per month for 3 months, before the study began. Clinical and laboratory data were collected. We investigated the role of hyperuricemia on the composite end point (CEP) of doubling of serum creatinine and graft failure by using Cox regression and Kaplan-Meier plots.

RESULTS

Over a mean follow-up of 14.27 months, the hyperuricemic group had a poor cumulative survival and easily reached the CEP of doubling of serum creatinine and graft failure (P = .025) with a first-year cumulative incidence of 29.84% and a second-year cumulative incidence of 35.09%. Cox regression models revealed that age at biopsy (unadjusted hazard ratio [HR], 1.03; 95% CI, 1.00-1.06), hyperuricemia (HR, 2.24; 95% CI, 1.13-4.46), and interstitial fibrosis and tubular atrophy (IF/TA), including <25% of parenchyma affected (HR, 3.71; 95% CI, 1.34-10.31) and ≥ 25% of parenchyma affected (HR, 5.10; 95% CI, 1.83-14.19), were highly associated with poor outcome. After adjusting different variables, hyperuricemia and IF/TA were still significant.

CONCLUSION

Persistently high serum UA and IF/TA both contribute to the risk of kidney disease progression after acute allograft dysfunction.

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

The role of uric acid (UA) on the pathogenesis and progression of chronic kidney disease (CKD) remains controversial. Experimental and clinical studies indicate that UA is associated with several risk factors of CKD including diabetes, hypertension, oxidative stress, and inflammation and hyperuricemia could be considered as a common dominator linking CKD and cardiovascular disease. Notably, the impact of serum UA levels on the survival of CKD, dialysis patients, and renal transplant recipients is also a matter of debate, as there are conflicting results from clinical studies. At present, there is no definite data whether UA is causal, compensatory, coincidental or it is only an epiphenomenon in these patients. In this article, we attempt to review and elucidate the dark side of this old molecule in CKD and renal transplantation.

Metabolic risk factors and long-term graft function after paediatric renal transplantation

The aim of this study was to evaluate metabolic risk factors and their impact on long-term allograft function in paediatric renal transplant (RTx) patients. We reviewed the medical records of 210 RTx patients who underwent transplantation at a median age of 4.5 years (range 0.7-18.2) and a median follow-up of 7.0 years (range 1.5-18.0). Data on lipid and glucose metabolism, uric acid levels, weight and blood pressure were collected up to 13 years post-RTx, and the findings were correlated with the measured glomerular filtration rate (GFR). Beyond the first year, GFR showed gradual deterioration with a mean decline of 2.4 ml/min/1.73 m(2)/year. Metabolic syndrome, overweight, hypertension and type 2 diabetes were diagnosed in 14-19%, 20-23%, 62-87% and 3-5% of the patients, respectively. These entities showed only mild association with the concomitant or long-term GFR values. Dyslipidaemia was common and hypertriglyceridaemia associated with a lower GFR at 1.5 and 5 years post-RTx (P = 0.008 and P = 0.017, respectively). Similarly, hyperuricaemia was frequent and associated significantly with GFR (P < 0.001). Except for hyperuricaemia and hypertriglyceridaemia, metabolic risk factors beyond the first postoperative year associated modestly with the long-term kidney graft function in paediatric RTx patients.

The association between serum uric acid levels at 3 months after renal transplantation and the graft outcome in living donor renal transplantation

BACKGROUND

Hyperuricemia is a common complication in renal transplant recipients in the era of cyclosporine-based immunosuppression. The evidence regarding the impact of hyperuricemia on allograft survival is controversial. The aim of this study was to investigate the association between serum uric acid levels and renal allograft outcomes.

MATERIALS AND METHODS

Between April 1991 and May 2011, adult renal transplants recipients were assessed retrospectively comparing serum creatinine levels at 3, 12, and 36 months, acute rejection rates, and long-term allograft survivals among normouricemic versus hyperuricemic (>7 mg/dL) patients at 3 months after renal transplantation.

RESULTS

Of 378 patients, 152 (40.21%) showed hyperuricemia and 226 (59.79%) showed normouricemia. Mean serum creatinine levels were 1.48 ± 0.38, 1.72 ± 2.68 and 1.64 ± 1.24 mg/dL at 3, 12, and 36 months after renal transplantation, respectively. Serum uric acid levels correlated negatively with serum creatinine levels at 12 months (P = .028). Graft survival rates at 10 years after renal transplantation were 88.6% among the normouricemic versus 78.8% among the hyperuricemic patients (P = .040).

CONCLUSIONS

High serum uric acid levels measured at 3 months after renal transplantation were associated with poorer long-term graft function.

Prevalence and risk factors of hyperuricemia among kidney transplant recipients

Hyperuricemia is common in renal transplant patients (RTRs), especially those on cyclosporine (CsA)-based therapy. We conducted a retrospective study to determine the prevalence of hyperuricemia and its risk factors among RTRs. A total of 17,686 blood samples were obtained from 4,217 RTRs between April 2008 and January 2011. Hyperuricemia was defined as an uric acid level of ≥7.0 mg/dl in men and of ≥6 mg/dl in women that persisted for at least two consecutive tests. Majority (68.2%) of RTRs were normouricemic. Hyperuricemia was more frequent in younger and female RTRs. On multivariate logistic regression, we found high trough level of cyclosporine to be a risk factor for hyperuricemia. In addition, female gender, impaired renal function, and dyslipidemia (hypercholesterolemia, hypertriglyceridemia, and elevated LDL) were also associated with higher probability of hyperuricemia. Hyperuricemia is a common complication after renal transplantation. Risk factors implicated in post-transplant hyperuricemia include high trough level of cyclosporine, female gender, renal allograft dysfunction, and dyslipidemia.

Uric acid and chronic kidney disease: A time to act?

A role for uric acid in the pathogenesis and progression of renal disease had been proposed almost a century ago, but, too hastily dismissed in the early eighties. A body of evidence, mostly accumulated during the last decade, has led to a reappraisal of the influence of uric acid on hypertension, cardiovascular, and renal disease. The focus of this review will be solely on the relationship between serum uric acid and renal function and disease. We will review experimental evidence derived from animal and human studies, evidence gathered from a number of epidemiological studies, and from the few (up to now) studies of uric-acid-lowering therapy. Some space will be also devoted to the effects of uric acid in special populations, such as diabetics and recipients of kidney allografts. Finally we will briefly discuss the challenges of a trial of uric-acid-lowering treatment, and the recent suggestions on how to conduct such a trial.

Hyperuricemia in adult renal allograft recipients: prevalence and predictors

BACKGROUND

Hyperuricemia is a common complication after kidney transplantation that may adversely affect graft survival.

OBJECTIVE

Our aim was to determine the prevalence of hyperuricemia in a sample of adult kidney graft recipients and to investigate its predictors.

METHODS

A total of 302 patients were included in the study. We used univariate analyses to compare clinical characteristics between the hyper-and normouricemic groups. We used multivariate adjusted logistic regression to detect independent predictors of hyperuricemia. Hyperuricemia was defined as serum uric acid ≥6.5 mg/dL in women and ≥7.0 mg/dL in men or allopurinol use.

RESULTS

The patients had a mean age of 49.6 ± 13.4 years, a median posttransplantation time of 7.6 years, and a mean estimated glomerular filtration rate (eGFR) of 51.9 ± 18.46 mL/min. The prevalence of hyperuricemia was 42.1% (n = 127). Hyperuricemic patients were predominately male (P = .004), older (P = .038), and with lower eGFR (P < .001). They also had a higher prevalence of hypertension (P = .001), dyslipidemia (P = .004) and proteinuria (P = .001). Multivariate adjusted regression model showed as significant predictors of hyperuricemia: male gender (odds ratio [OR], 2.46; P = .002); impaired renal function (OR 1.33 for every 10 mL/min reduction in eGFR; P < .001), higher body weight (OR 1.09 for every 1 kg/m(2) increase of body mass index; P = .044), prednisolone use (OR 2.12; P = .035), and cyclosporine versus tacrolimus use (OR 2.44; P = .039).

CONCLUSIONS

The prevalence of posttransplant hyperuricemia was high, particularly in patients with classical cardiovascular risk factors and lower eGFR. However, our findings suggest that modifiable immunosuppression options could play a role in its management.

Uric acid as a target of therapy in CKD

The prevalence of chronic kidney disease (CKD) has increased and will continue to increase in the United States and worldwide. This is alarming considering that CKD is an irreversible condition and patients who progress to chronic kidney failure have reduced quality of life and high mortality rates. As such, it is imperative to identify modifiable risk factors to develop strategies to slow CKD progression. One such factor is hyperuricemia. Recent observational studies have associated hyperuricemia with kidney disease. In addition, hyperuricemia is largely prevalent in patients with CKD. Data from experimental studies have shown several potential mechanisms by which hyperuricemia may contribute to the development and progression of CKD. In this article, we offer a critical review of the experimental evidence linking hyperuricemia to CKD, highlight gaps in our knowledge on the topic as it stands today, and review the observational and interventional studies that have examined the potential nephroprotective effect of decreasing uric acid levels in patients with CKD. Although uric acid also may be linked to cardiovascular disease and mortality in patients with CKD, this review focuses only on uric acid as a potential therapeutic target to prevent kidney disease onset and progression.

Effects of hyperuricemia on renal function of renal transplant recipients: a systematic review and meta-analysis of cohort studies

Background

Hyperuricemia is an independent risk factor of nephropathy, but its role in renal transplant recipients (RTRs) is controversial.

Methods

Based on the methods of Cochrane systematic reviews, we searched MEDLINE (1948–2011.6), EMBASE (1956–2011.6), CBM (Chinese Biomedicine Database) (1978–2011.6) to identify cohort studies assessing the association between uric acid level and kidney allograft. Two authors independently screened the studies, assessed the risk of bias of included studies and extracted data. Unadjusted odds ratio(OR), mean difference (MD), adjusted hazard ratio (aHR) and their corresponding 95%CI were pooled to assess the effects of hyperuricemia on kidney allograft.

Results

Twelve cohort studies were included and the quality was moderate to high based on the NEWCASTLE-OTTAWA quality assessment scale. RTRs with hyperuricemia had lower eGFR (P<0.0001, 95%CI−16.34∼6.14) and higher SCr (P<0.00001, 95%CI 0.17∼0.31) than those with normal uric acid level. Meta-analysis showed that hyperuricemia was a risk factor of chronic allograft nephropathy (Unadjusted OR = 2.85, 95%CI 1.84∼4.38, adjusted HR = 1.65, 95%CI 1.02∼2.65) and graft loss (Unadjusted OR = 2.29, 95%CI 1.55∼3.39; adjusted HR = 2.01, 95%CI 1.39∼2.94).

Conclusions

Current evidence suggests that hyperuricemia may be an independent risk factor of allograft dysfunction. Hyperuricemia may modestly increase the risk of poor outcomes of RTRs. Future research is needed to verify whether lowering uric acid level could improve the kidney function and prognosis of RTRs with hyperuricemia.

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?

Association of serum uric acid with graft survival after kidney transplantation: a time-varying analysis

The association of serum uric acid (UA) with kidney transplant outcomes is uncertain. We examined the predictive value of UA during the first year posttransplant as a time-varying factor for graft survival after adjustment for time-dependent and independent confounding factors. Four hundred and eighty-eight renal allograft recipients transplanted from January 2004 to June 2006 and followed for 41.1 ± 17.7 months were included. Data on UA, estimated glomerular filtration rate (eGFR), tacrolimus level, mycophenolate mofetil (MMF) and prednisone doses, use of allopurinol, angiotensin-converting enzyme-inhibitor/angiotensin-receptor-blocker (ACEi/ARB) and diuretics at 1, 3, 6, 9 and 12 months were collected. Primary endpoint of the study was graft loss, defined as graft failure and death. Cox proportional hazard models and generalized estimating equations were used for analysis. UA level was associated with eGFR, gender, retransplantation, decease-donor organ, delayed graft function, diuretics, ACEi/ARB and MMF dose. After adjustment for these confounders, UA was independently associated with increased risk of graft loss (HR: 1.15, p = 0.003; 95% CI: 1.05-1.27). Interestingly, UA interacted with eGFR (HR: 0.996, p < 0.05; 95% CI: 0.993-0.999 for interaction term). Here, we report a significant association between serum UA during first year posttransplant and graft loss, after adjustment for corresponding values of time-varying variables including eGFR, immunosuppressive drug regimen and other confounding factors. Its negative impact seems to be worse with lower eGFR.

The effect of hyperuricemia on endothelial biomarkers and renal function in kidney allograft recipients

BACKGROUND

Uric acid may play a pathogenic role in hypertension, cardiovascular morbidity, and kidney disease. The aim of this study was to assess the effect of serum uric acid on biomarkers of endothelial activation and renal function in kidney allograft recipients during 30 months of follow-up.

METHODS

The study included 100 allograft recipients with stable renal function (estimated glomerular filtration rate (eGFR) >60 mL/min). The study was performed 34 ± 12 months after transplantation. The patients were followed prospectively for 30 months. Seventy patients displayed hyperuricemia (uric acid 7.5 ± 1.0 mg/dL) and 30 normouricemia (5.5 ± 0.9 mg/dL). Concentrations of plasma resistin, soluble vascular cell adhesion molecule 1 (sVCAM-1), soluble CD146, and high-sensitivity C-reactive protein (hs-CRP) were assessed in patients at the beginning and after 30 months of follow-up. Clinical outcomes and biomarker values were analyzed in these groups and compared to a control group of 26 healthy volunteers.

RESULTS

Concentrations of resistin and CD146 were increased among the hyperuricemia versus the normouricemic group (P < .05). Serum uric acid level correlated with sVCAM-1, hs-CRP, resistin, and sCD146 concentration in both groups of kidney recipients (P < .01). Serum creatinine concentrations correlated with sVCAM-1, resistin, and sCD146 concentrations (P < .01). There were significant direct correlations between uric acid and the number of antihypertensive agents (P < .001) and inverse correlations between eGFR (P < .001) and high-density lipoprotein cholesterol (P < .04). Pulse pressure increased in hyperuricemic patients during follow-up (P < .05). The decrease in eGFR during the 30-month follow-up was similar in both groups. No subject progressed to kidney allograft failure. Patient and graft survivals were 98% among hyperuricemic and 96.7% among normouricemic individuals.

CONCLUSIONS

Hyperuricemia may injure endothelial function via resistin-dependent mechanisms. It represents a risk factor for arterial stiffness. The elevated serum uric acid may not have a causal role in the progression of renal transplant injury over 30 months of follow-up.

Hyperuricemia in kidney transplant recipients with intact graft function

OBJECTIVES

The aim of this study was to investigate the prevalence of hyperuricemia and factors predicting its occurrence, and to establish the relationship over time between serial changes in estimated glomerular filtration rate (eGFR) and uric acid (UR) concentration in kidney transplant (KT) recipients with eGFR >60 mL/min/1.73 m(2).

METHODS

Adult patients who underwent KT at the Asan Medical Center between 1990 and 2008 and maintained eGFR >60 mL/min/1.73 m(2) were retrospectively assessed. Clinical and laboratory data were obtained from inpatient and outpatient charts and from the hospital electronic database.

RESULTS

Of 356 patients, 301 (84.55%) had normal UR levels and 55 (15.45%) had hyperuricemia. After multivariate adjustment, transplant duration, male gender, eGFR, diabetes mellitus (DM), and calcium level were associated with higher mean UR levels. Mean UR level increased significantly and mean eGFR decreased significantly during the first year after transplantation, but there were no significant differences over the next 4 years. Serial UR and eGFR levels changed almost simultaneously.

CONCLUSIONS

Transplantation duration, male gender, eGFR level, DM, and serum calcium level were risk factors for hyperuricemia in kidney recipients with intact graft function. Increased uric acid after KT did not significantly affect graft function.

Hyperuricaemia, chronic kidney disease, and outcomes in heart failure: potential mechanistic insights from epidemiological data

AIM

To determine if the association between hyperuricaemia and poor outcomes in heart failure (HF) varies by chronic kidney disease (CKD).

METHODS AND RESULTS

Of the 2645 systolic HF patients in the Beta-Blocker Evaluation of Survival Trial with data on baseline serum uric acid, 1422 had hyperuricaemia (uric acid ≥6 mg/dL for women and ≥8 mg/dL for men). Propensity scores for hyperuricaemia, estimated for each patient, were used to assemble a matched cohort of 630 pairs of patients with and without hyperuricaemia who were balanced on 75 baseline characteristics. Associations of hyperuricaemia with outcomes during 25 months of median follow-up were examined in all patients and in those with and without CKD (estimated glomerular filtration rate of <60 mL/min/1.73 m(2)). Hyperuricaemia-associated hazard ratios (HRs) and 95% confidence intervals (CI) for all-cause mortality and HF hospitalization were 1.44 (1.12-1.85, P = 0.005) and 1.27 (1.02-1.58, P = 0.031), respectively. Hazard ratios (95% CIs) for all-cause mortality among those with and without CKD were 0.96 (0.70-1.31, P = 0.792) and 1.40 (1.08-1.82, P = 0.011), respectively (P for interaction, 0.071), and those for HF hospitalization among those with and without CKD were 0.99 (0.74-1.33, P = 0.942) and 1.49 (1.19-1.86, P = 0.001), respectively (P for interaction, 0.033).

CONCLUSION

Hyperuricaemia has a significant association with poor outcomes in HF patients without CKD but not in those with CKD, suggesting that hyperuricaemia may predict poor outcomes when it is primarily a marker of increased xanthine oxidase activity, but not when it is primarily due to impaired renal excretion of uric acid.

The independent association between serum uric acid and graft outcomes after kidney transplantation

BACKGROUND

Improving long-term outcomes of kidney transplantation depends on identifying novel risk factors that lead to poor outcomes. We sought to evaluate the predictive value of mean uric acid (UA) level during the first 6 months posttransplant for graft survival and function.

METHODS

Two hundred twelve recipients of living donor kidneys transplanted during January 2000 to December 2001 were included. The study outcome included graft and patient survival and graft function at 1 year posttransplant. Regression models were used to adjust for the confounding variables including graft function during first 6 months.

RESULTS

During 68.3 + or - 27.2 months follow-up, UA level (mg/dL) and hyperuricemia (n=45) were associated with graft loss (hazard ratio [HR]=1.26, P=0.026, 95% confidence interval [CI]=1.03-1.53, and HR=1.92, P=0.029, 95% CI=1.1-3.4, respectively) independent of graft function and other confounders. UA also seemed to be associated with risk of death with borderline significance (HR=1.2, P=0.096, 95% CI=0.97-1.46). Examining the predictive value for graft function, UA level and hyperuricemia were independent predictors of 1-year serum creatinine (beta=0.10, P=0.013, 95% CI=0.02-0.18, and beta=0.25, P<0.04, 95% CI=0.01-0.49, respectively). Similarly, both were associated with 1-year estimated glomerular filtration rate (beta=-3.9, P<0.001, 95% CI=-5.7 to -1.5 for UA, and beta=-7.6, P<0.02, 95% CI=-13.6 to -1.5 for hyperuricemia). Notably, these associations were all independent of renal function during first 6 months.

CONCLUSION

The results of this study suggest that mean UA level during the first 6 months posttransplant is an independent predictor of long-term graft survival and short-term graft function. Further investigations are needed to evaluate its causal association with chronic allograft injury and cardiovascular disease.

Uric acid levels have no significant effect on renal function in adult renal transplant recipients: evidence from the symphony study

BACKGROUND AND OBJECTIVES

Uric acid (UA) has been linked to renal damage in experimental models of kidney failure. In humans, no definitive link between UA and renal function has been established, but several epidemiologic studies have suggested that higher UA levels are associated with accelerated loss of renal function, higher incidence of dialysis, and death. Many of the associations have been limited by the colinearity between UA levels and renal function. Renal transplantation is no exception, and limited information is available concerning the independent role of UA on progression of renal function in transplant recipients.

DESIGN, SETTING, PARTICIPANTS, AND MEASUREMENTS

We investigated the association between UA and renal function progression during the first 3 yr after transplantation, adjusted for baseline renal function, in 1645 patients who were enrolled in the Symphony study.

RESULTS

When corrected for baseline renal function, UA levels 1 mo after transplantation were not associated with 3-yr renal function (P = 0.62). There was a strong colinearity between calculated renal function and UA levels 1 mo after transplantation. In fact, when not corrected for baseline renal function, there was a significant association between UA and renal function at 3 yr (P = 0.005).

CONCLUSIONS

Low renal function is associated with higher UA levels, but higher UA levels are not independently associated with progression of renal dysfunction after kidney transplantation.

Moderate-to-severe early-onset hyperuricaemia: a prognostic marker of long-term kidney transplant outcome

BACKGROUND

Hyperuricaemia commonly occurs in renal transplant recipients (RTRs), but the effects of post-transplant hyperuricaemia on kidney transplant outcome have not been clearly established. This work was designed to explore the impact of hyperuricaemia on renal transplant outcome.

METHODS

The authors examined this issue by analysing the clinical outcome of 281 RTRs. Hyperuricaemia (defined as UA > 7.0 mg/dl in men and >6.0 mg/dl in women for at least two consecutive tests, n = 121) was classified as early onset (within 1 year of transplant, n = 90) or late onset (n = 31). Graft function was estimated using the MDRD Study Equation 7 (eGFR(MDRD)).

RESULTS

As late-onset hyperuricaemia was found to be induced by a progressive decline in the graft function (P < 0.01), data from early-onset hyperuricaemic recipients were used. Early-onset moderate-to-severe hyperuricaemia (defined as UA >or= 8.0 mg/dl) was found to be a significant risk factor for chronic allograft nephropathy (P = 0.035) and a poorer graft survival (P = 0.026) by multivariate analysis, whereas mild hyperuricaemia was not. The impact of moderate-to-severe hyperuricaemia on renal transplant survival was dependent on the duration of exposure. Likewise, the detrimental effect of early-onset hyperuricaemia on the graft function was dependent on UA levels and exposure time. After control of the baseline graft function by analysis of only recipients with a good graft function at 1 year post-transplantation (eGFR(MDRD) > 60 ml/min), moderate-to-severe early-onset hyperuricaemia was also found to be a marker of long-term graft dysfunction and failure.

CONCLUSION

Moderate-to-severe early-onset hyperuri- caemia may be a prognostic marker of the long-term graft outcome in RTRs, which needs further investigation.

Association of uric acid with inflammation, progressive renal allograft dysfunction and post-transplant cardiovascular risk

Hyperuricemia is common after kidney transplantation. Although its risk factors are well established, its relation to inflammation, progressive renal dysfunction, and cardiovascular events is unknown. In this study, 405 stable renal transplant recipients with > or = 3 uric acid (UA) and C-reactive protein measurements from January 2005 to April 2008 were identified to determine the relations between UA and C-reactive protein and between UA and the rate of decrease in the estimated glomerular filtration rate (eGFR; using the Modification of Diet in Renal Disease equation) and cardiovascular events. Hyperuricemia was defined as UA >7.1 mg/dl (420 micromol/L) in men and >6.1 mg/dl (360 micromol/L) in women. The prevalence of hyperuricemia was 44% (180 of 405). Hyperuricemia was negatively associated with eGFR (p <0.0001) and positively associated with diuretic use (p = 0.013), time since transplantation (p = 0.014), and triglycerides (p = 0.04). Although UA was correlated with C-reactive protein (p = 0.003), adjustment for eGFR rendered this relation nonsignificant (p = 0.225). The slope of eGFR was +0.144 +/- 0.85 ml/min/1.73 m(2)/month (95% confidence interval 0.032 to 0.257) in those with normal UA levels and -0.091 +/- 0.93 ml/min/1.73 m(2)/month (95% confidence interval -0.235 to +0.054) in patients with hyperuricemia (p = 0.003). There were 17 cardiovascular events in the patients with hyperuricemia and 4 in those with normal UA levels (p = 0.001). In conclusion, hyperuricemia is associated with a decrease in renal allograft function and may be an independent cardiovascular risk factor in transplant recipients. Further studies are needed to establish its role in post-transplantation cardiovascular disease.

Determination and modelling of clinical laboratory data of healthy individuals and patients with end-stage renal failure

The analyses of 18 biochemical parameters (alanine aminotransferase, albumin, aspartate aminotransferase, calcium, cholesterol, chloride, creatinine, iron, glucose, γ- glutamyl transferase, alkaline phosphatase, phosphorus, potassium, sodium, total protein, triglycerides, uric acid, and urea nitrogen) were performed for 166 healthy individuals and 108 patients with end-stage renal failure (ESRF). The application of cluster analysis proved that there were points of similarity among all 18 biochemical parameters that formed major groups; these groups corresponded to the authors’ assumption of the existence of several overall patterns of biochemical parameters that may be termed “enzyme-specific”; “general health indicator”; “major component excretion”; “blood-specific indicator”; and “protein-specific”. These patterns also appear in the subsets of males and females that were obtained by separation of the general dataset. In addition, the performance of factor analysis similarly proved the validity of this assumption. This projection and modelling method indicated the existence of seven latent factors, which explained 70.05% of the total variance in the system for healthy individuals and more than 72% of the total variance in the system for patients with ESRF. All these results support the probability that a general health indicator could be constructed by taking into account the existing classification groups in the list of biochemical parameters.