Hyperuricemia after renal transplantation

Hyperuricemia: An Intriguing Connection to Metabolic Syndrome, Diabetes, Kidney Disease, and Hypertension

PURPOSE OF THE REVIEW

Our review explores the epidemiology, physiology, and clinical data surrounding the connection between hyperuricemia and metabolic syndrome, chronic kidney disease, and hypertension.

RECENT FINDINGS

Compelling physiologic mechanisms have been proposed to explain a causal relationship between hyperuricemia and metabolic syndrome, chronic kidney disease, and hypertension but clinical studies have given mixed results in terms of whether intervening with hyperuricemia using urate-lowering therapy has any beneficial effects for patients with these conditions. Despite the large amount of research already put into this topic, more randomized placebo-controlled trials are needed to more firmly establish whether a cause-effect relationship exists and whether lowering uric acid levels in patients with these conditions is beneficial.

Risk factors and management of hyperuricemia after renal transplantation

Hyperuricemia (HUA) is a common complication after renal transplantation. Currently, there is no uniform consensus on factors which increase the risk for and treatment of HUA in renal transplant recipients. The purpose of this review is to summarize current and proposed risk factors and strategies to manage HUA after renal transplantation in order to assist renal function protection and prolong graft survival time.

Hyperuricemia—a serious complication among patients with chronic kidney disease: a systematic review and meta-analysis

Aim: Hyperuricemia as a putative risk factor for chronic kidney disease (CKD) progression remains controversial and debatable. This systematic review aims to explore the prevalence of hyperuricemia among CKD patients worldwide. Methods: This study was conducted in accordance with the Meta-analysis Of Observational Studies in Epidemiology (MOOSE) guidelines by using the existing literature from online databases such as MEDLINE/PubMed, ScienceDirect, Google Scholar, Cochrane library and grey literature. The effect size with corresponding 95% confidence interval (CI) was calculated to assess the pooled prevalence of hyperuricemia in chronic kidney patients. The subgroup analysis based on gender and geography was also carried out by utilizing comprehensive meta-analysis, version 2.0. Results: Twenty-three studies containing 212,740 participants were eligible for quantitative synthesis. The pooled prevalence of 43.6% (35.2–52.4%) hyperuricemia was reported in patients with CKD globally. In India, 38.4% of prevalence was observed. The gender specific prevalence (9 studies) was reported as 67.4% (60.9–73.3%) in case of male patients and 32.6% (26.7–39.1%) in female patients with 95% CI. Conclusions: The prevalence of hyperuricemia was reported to be reasonably high among CKD patients worldwide. During the management of CKD, this high prevalence demands more prudent attention for this clinical complication which possibly can lead to positive renal outcomes.

Predictors of Hyperuricemia after Kidney Transplantation: Association with Graft Function

Background and objectives: In kidney transplant recipients (KTR), hyperuricemia (HU) is a commonly-observed phenomenon, due to calcineurin inhibitors and reduced kidney graft function. Factors predicting HU, and its association with graft function, remains equivocal. Materials and Methods: We conducted a retrospective longitudinal study to assess factors associated with HU in KTR, and to determine risk factors associated with graft function, measured as glomerular filtration rate (GFR). Moreover, GFR > 60 mL/min/1.73 m² was considered normal. HU was defined as a serum uric acid level of > 416 μmol/L (4.70 mg/dL) in men and >357 μmol/L (4.04 mg/dL) in women, or xanthine-oxidase inhibitor use. We built multiple logistic regression models to assess predictors of HU in KTR, as well as the association of demographic, clinical, and biochemical parameters of patients with normal GFR after a three-year follow-up. We investigated the effect modification of this association with HU. Results: There were 144 patients (mean age 46.6 ± 13.9), with 42.4% of them having HU. Predictors of HU in KTR were the presence of cystic diseases (OR = 9.68 (3.13; 29.9)), the use of diuretics (OR = 4.23 (1.51; 11.9)), and the male gender (OR = 2.45 (1.07; 5.56)). Being a younger age, of female gender, with a normal BMI, and the absence of diuretic medications increased the possibility of normal GFR. HU was the effect modifier of the association between demographic, clinical, and biochemical factors and a normal GFR. Conclusions: Factors associated with HU in KTR: Presence of cystic diseases, diuretic use, and male gender. HU was the effect modifier of the association of demographic, clinical, and biochemical factors to GFR.

Cyclophilin D knockout protects the mouse kidney against cyclosporin A-induced oxidative stress

Mitochondrial dysfunction and oxidative stress have been implicated in cyclosporin A (CsA)-induced nephrotoxicity. CsA interacts with cyclophilin D (CypD), an essential component of the mitochondrial permeability transition pore and regulator of cell death processes. Controversial reports have suggested that CypD deletion may or may not protect cells against oxidative stress-induced cell death. In the present study, we treated wild-type (WT) mice and mice lacking CypD [peptidylprolyl isomerase F knockout (Ppif-/-) mice] with CsA to test the role and contribution of CypD to the widely described CsA-induced renal toxicity and oxidative stress. Our results showed an increase in the levels of several known uremic toxins as well as the oxidative stress markers PGF2α and 8-isoprostane in CsA-treated WT animals but not in Ppif-/- animals. Similarly, a decline in S-adenosylmethionine and the resulting methylation potential indicative of DNA hypomethylation were observed only in CsA-treated WT mice. This confirms previous reports of the protective effects of CypD deletion on the mouse kidney mediated through a stronger resistance of these animals to oxidative stress and DNA methylation damage. However, a negative effect of CsA on the glycolysis and overall energy metabolism in Ppif-/- mice also indicated that additional, CypD-parallel pathways are involved in the toxic effects of CsA on the kidney. In summary, CsA-mediated induction of oxidative stress is associated with CypD, with CypD deletion providing a protective effect, whereas the reduction of energy production observed upon CsA exposure did not depend on the animals' CypD status.

Switching from allopurinol to febuxostat: efficacy and safety in the treatment of hyperuricemia in renal transplant recipients

The aim of this study was to evaluate the efficacy and tolerability of febuxostat in renal transplant recipients who were previously treated with allopurinol (the daily oral dose is 100 mg). A 6-month cohort study was conducted with 46 renal transplant recipients who had hyperuricemia. In 22 patients, treatment was changed from allopurinol to febuxostat (febuxostat was given at an oral dose of 20 mg once a day), and the other 24 patients continued the allopurinol treatment (the daily oral dose is 100 mg). The serum levels of uric acid (UA), creatinine, other biochemical parameters, estimated glomerular filtration rate (eGFR), and adverse events were measured at baseline as well as at 1, 3, and 6 months after the switch to febuxostat. Serum UA levels significantly decreased from 470.82 ± 34.37 to 378.77 ± 51.97 μmol/L in the febuxostat group, and decreased from 469.46 ± 33.47 to 428.21 ± 23.37 μmol/L in the allopurinol group. The eGFR increased from 75.55 to 85.23 mL/min in the febuxostat group, and decreased from 78.79 to 70.31 mL/min in the allopurinol group. In renal transplant recipients, febuxostat reduced the serum UA levels resulting in minor short-term improvement of renal function with no changes in the other biochemical parameters.

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.

Pretransplant uric acid levels may be predictive for prognosis of renal transplant donors

BACKGROUND

The living kidney donor counseling prior to the operation may be helpful to learn how to properly care for the remaining single kidney for the rest of their lives. Worsening kidney function is associated with elevated serum uric acid (UA) levels. In this study, we compared the baseline laboratory findings of renal transplant donors with their follow-up laboratory values.

METHODS

The study consisted of 173 adult donors including 91 females and 82 males with a mean age of 46.82 ± 11.31 years. The follow-up clinical and laboratory examinations were performed on the third day at the end of the first and the sixth months of the surgery. According to donor's creatinine levels we constituted two groups: high creatinine and normal creatinine.

RESULTS

Patients within the high creatinine group had significantly higher mean serum UA levels when compared with the normal creatinine group. In multivariate analysis, among the other effective variables, UA level alone was found to be the most effective parameter predicting the post-transplant creatinine levels (p = 0.004, odds ratio: 12.4, 95% CI: 2.3-68.3) at sixth month post-transplantation. In the ROC analysis for the effects of UA, the following cutoff values were found: >6 mg/dL in men (sensitivity 81.3%, specificity 76.9%, positive predictive value 89.7%, negative predictive value 62.5%, accuracy 80%) and ≥5 mg/dL in women (sensitivity 72.2, specificity 74.4%, positive predictive value 89.7%, negative predictive value 62.5%, accuracy: 73.7%).

CONCLUSION

Pretransplant serum UA levels can give important clues regarding the renal functions of the donors during the postoperative period.

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.

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.

Uric acid is highly associated with kidney allograft survival in a time-varying analysis

BACKGROUND

Hyperuricemia may be associated with the development of new cardiovascular events and graft loss in renal transplant recipients. This study was conducted to clarify whether hyperuricemia is a persistently independent predictor of long-term graft survival and patient outcome.

METHODS

Renal allograft recipients (n = 880) who underwent transplantation from December 1999 to March 2013 were included. Participants were divided into 2 groups: a hyperuricemic group (n = 389) and a normouricemic group (n = 491). 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 in the primary endpoint of graft failure by using time-varying analysis and Kaplan-Meier plots. All-cause mortality in renal transplant recipients was also surveyed.

RESULTS

During a mean follow-up of 43.3 ± 26.3 months, the major predisposing factors in the 389 patients with hyperuricemia were male predominance (62.98%), high entry serum UA (7.70; range 6.70-8.80 mg/dL), more hypertension (92.29%), previous hemodialysis mode (29.56%), hepatitis C infection (24.42%), more frequent use of UA-lowering agents (43.44%), and use of more drugs for inducing high serum UA (17.74%). After 12 months, the hyperuricemic group had persistently high serum UA (7.66 ± 2.00 vs 6.17 ± 1.60 mg/dL, P < .001) and poor renal function (serum creatinine 2.96 ± 3.20 vs 1.61 ± 1.96 mg/dL, P < .001) compared with the normouricemic group. Survival analysis showed the hyperuricemic group had poorer graft survival (60.47%) than the normouricemic group (75.82%, P = .0069) after 13-year follow-up. However, there was no difference in all-cause mortality between the 2 groups.

CONCLUSION

Persistently high serum UA seems to be implicated in elevation of serum creatinine, which could increase the risk for allograft dysfunction.

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.

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.

Hyperuricemia beyond 1 year after kidney transplantation in pediatric patients: Prevalence and risk factors

Hyperuricemia is frequent among adult renal transplant recipients; however, data among pediatric kidney recipients are scarce. This study is designed to estimate the prevalence and risk factors of late post-transplant hyperuricemia in pediatric recipients. A retrospective observational multicenter study on 179 pediatric renal recipients (5–18 years) was conducted between April 2008 and January 2011 from five kidney transplant centers of Tehran, Iran. All recipients were followed up for more than 1 year (5.9 ±3.3 years) after transplantation. A total of 17686 blood samples were obtained for serum uric acid (SUA). The normal range of SUA was defined as SUA 1.86–5.93 mg/dl for children between 2 and 15 years in both genders; 2.40–5.70 mg/dl for girls aged >15 years; 3.40–7.0 mg/dl for boys aged >15 and more than 6 and 7 mg/dl in boys and girls older than 15 years old. The median age of the children was 13 years. Male recipients were more popular than female (male/female 59/41%). Hyperuricemia was detected in 50.2% of patients. Mean SUA concentration was 5.9±1.7 mg/dl and mean SUA concentration in hyperuricemic patients was 7.7±1.2 mg/dl. While at multivariate logistic regression elevated serum creatinine concentration (P<0.001) and the time span after renal transplantation (P=0.02) had impact on late post-transplant hyperuricemia. High cyclosporine level (C0 and C2) was not risk factor for huperuricemia. Late post-transplant hyperuricemia was found in about half of pediatric renal recipients, and was associated with impaired renal allograft function.

The effects of mammalian target of rapamycin inhibitors on serum uric acid levels in renal transplant patients

BACKGROUNDS/AIMS

Elevated uric acid (UA) levels are frequently observed after renal transplantation. We investigated the consequences of shifting from calcineurin inhibitors (CNI) to mammalian target of rapamycin inhibitors (mTORi) on UA levels and graft functions.

METHODS

Ninety-six patients were enrolled. Main points of interest were changes in UA and glomerular filtration rate (GFR).

RESULTS

Mean age of the whole population was 39 ± 11 years (18-73), and 64.2 % were male. Patients were stratified into two groups according to their CNI type prior to the switch as cyclosporin A (CsA) or tacrolimus (Tac). Patients that were switched from CsA had a mean GFR of 49 ± 18 ml/min and serum UA level of 7.4 ± 1.8 mg/dl at the pre-switch period. Mean GFR increased to 53 ± 22 ml/min (p = 0.03), and UA levels decreased to 6.2 ± 1.6 mg/dl at the final visit (p < 0.001). In the Tac group, pre-switch mean GFR was 59 ± 28 ml/min and serum UA level 6.6 ± 2.6 mg/dl. In this group, mean GFR increased to 63 ± 28 ml/min (p = 0.03) and UA levels decreased to 6.2 ± 2.1 at the last visit (p < 0.001).

CONCLUSION

Switch from CNI to mTORi-based regimen provides better control of UA levels and improves renal functions.