Uric acid and transplantation

Hyperuricemia and its related diseases: mechanisms and advances in therapy

Hyperuricemia, characterized by elevated levels of serum uric acid (SUA), is linked to a spectrum of commodities such as gout, cardiovascular diseases, renal disorders, metabolic syndrome, and diabetes, etc. Significantly impairing the quality of life for those affected, the prevalence of hyperuricemia is an upward trend globally, especially in most developed countries. UA possesses a multifaceted role, such as antioxidant, pro-oxidative, pro-inflammatory, nitric oxide modulating, anti-aging, and immune effects, which are significant in both physiological and pathological contexts. The equilibrium of circulating urate levels hinges on the interplay between production and excretion, a delicate balance orchestrated by urate transporter functions across various epithelial tissues and cell types. While existing research has identified hyperuricemia involvement in numerous biological processes and signaling pathways, the precise mechanisms connecting elevated UA levels to disease etiology remain to be fully elucidated. In addition, the influence of genetic susceptibilities and environmental determinants on hyperuricemia calls for a detailed and nuanced examination. This review compiles data from global epidemiological studies and clinical practices, exploring the physiological processes and the genetic foundations of urate transporters in depth. Furthermore, we uncover the complex mechanisms by which the UA induced inflammation influences metabolic processes in individuals with hyperuricemia and the association with its relative disease, offering a foundation for innovative therapeutic approaches and advanced pharmacological strategies.

Serum uric acid levels in kidney transplant recipients: A cause for concern? A review of recent literature

The impact of elevated serum uric acid levels i.e., hyperuricemia, on native and transplant chronic kidney disease progression has been debated. This literature review presents an analysis of multiple studies exploring the relationship between serum uric acid levels and kidney transplant outcomes. The review includes a summary of the pathophysiology of hyperuricemia and gout, a review of urate-lowering therapies, and an appraisal of multiple studies examining the association or lack thereof between serum uric acid level and kidney transplant outcomes. Based on these studies, elevated serum uric acid levels may contribute to CKD progression in kidney transplant recipients. In this review, we also summarize current literature to highlight risk factors associated with hyperuricemia as well as the need for further investigation to monitor and manage hyperuricemia in kidney transplant recipients.

Prevalence of Musculoskeletal Manifestations in Adult Kidney Transplant's Recipients: A Systematic Review

Background and Objectives: The musculoskeletal (MSK) manifestations in the kidney transplant recipient (KTxR) could lead to decreased quality of life and increased morbidity and mortality. However, the prevalence of these MSK manifestations is still not well-recognized. This review aimed to investigate the prevalence and outcomes of MSK manifestations in KTxR in the last two decades. Materials and Methods: Research was performed in EBSCO, EMBASE, CINAHL, PubMed/MEDLINE, Cochrane, Google Scholar, PsycINFO, Scopus, Science Direct, and Web of Science electronic databases were searched during the years 2000–2020. Results: The PRISMA flow diagram revealed the search procedure and that 502 articles were retrieved from the initial search and a total of 26 articles were included for the final report in this review. Twelve studies reported bone loss, seven studies reported a bone pain syndrome (BPS) or cyclosporine-induced pain syndrome (CIPS), and seven studies reported hyperuricemia (HU) and gout. The prevalence of MSK manifestations in this review reported as follow: BPS/CIPS ranged from 0.82% to 20.7%, while bone loss ranged from 14% to 88%, and the prevalence of gout reported in three studies as 7.6%, 8.0%, and 22.37%, while HU ranged from 38% to 44.2%. Conclusions: The post-transplantation period is associated with profound MSK abnormalities of mineral metabolism and bone loss mainly caused by corticosteroid therapy, which confer an increased fracture risk. Cyclosporine (CyA) and tacrolimus were responsible for CIPS, while HU or gout was attributable to CyA. Late diagnosis or treatment of post-transplant bone disease is associated with lower quality of life among recipients

Serum uric acid is associated with increased risk of posttransplantation diabetes in kidney transplant recipients: a prospective cohort study

BACKGROUND

Serum uric acid (SUA) is associated with fasting glucose in healthy subjects, and prospective epidemological studies have shown that elevated SUA is associated with increased risk of type 2 diabetes. Whether SUA is independently associated with higher risk of posttransplantation diabetes mellitus (PTDM) in kidney transplant recipients (KTR) remains unknown.

METHODS

We performed a longitudinal cohort study of 524 adult KTR with a functioning graft ≥1-year, recruited at a university setting (2008-2011). Multivariable-adjusted Cox proportional-hazards regression analyses were performed to assess the association between time-updated SUA and risk of PTDM (defined according the American Diabetes Association's diagnostic criteria).

RESULTS

Mean (SD) SUA was 0.43 (0.11) mmol/L at baseline. During 5.3 (IQR, 4.1-6.0) years of follow-up, 52 (10%) KTR developed PTDM. In univariate prospective analyses, SUA was associated with increased risk of PTDM (HR 1.75, 95% CI 1.36-2.26 per 1-SD increment; P < 0.001). This finding remained materially unchanged after adjustment for components of the metabolic syndrome, lifestyle, estimated glomerular filtration rate, immunosuppressive therapy, cytomegalovirus and hepatitis C virus infection (HR 1.89, 95% CI 1.32-2.70; P = 0.001). These findings were consistent in categorical analyses, and robust in sensitivity analyses without outliers.

CONCLUSIONS

In KTR, higher SUA levels are strongly and independently associated with increased risk of PTDM. Our findings are in agreement with accumulating evidence supporting SUA as novel independent risk marker for type 2 diabetes, and extend the evidence, for the first time, to the clinical setting of outpatient KTR.

Serum Uric Acid Is Positively Associated with Muscle Mass and Strength, but Not with Functional Capacity, in Kidney Transplant Patients

Background: Our aim was to associate serum uric acid (UA) with muscle mass, strength and functional capacity in kidney transplant patients (KTPs). Methods: A cross-sectional study was performed on 113 KTPs. The fat-free mass and total and appendicular muscle mass were estimated by performing a bioelectrical impedance analysis. The strength was evaluated using the handgrip strength test (HGS) and the five times sit to stand test (5STS). The functional capacity was evaluated using the 4 m walk test and the short physical performance battery (SPPB). Results: Linear regression showed that the UA levels were positively associated with the muscle mass, fat-free mass, appendicular muscle mass, muscle mass index and appendicular muscle mass index. The 5STS results (seconds) were inversely associated with the UA levels, showing that individuals with higher UA were more likely to have more strength. However, UA was not associated with the HGS, 4 m walk test and SPPB results. Conclusion: UA levels were positively associated with muscle mass and strength, but not with functional capacity, in KTPs.

Prevalence of Gout in the Surviving United States Solid Organ Transplantation Population

PURPOSE

Although incidence and survival are frequent topics within the solid organ transplantation (SOT) literature, the size of the surviving SOT population is not well known. Existing studies of gout in patients with SOT have focused on the incident SOT population. This analysis was performed to characterize the prevalent SOT population and the prevalence of gout within it.

METHODS

This study includes the 2017 United States (US) population size of recipients of kidney, heart, liver, and lung transplants that was estimated by combining primary transplant recipient cohort sizes (1988-2017) with previously published survival rates for each annual cohort's time since transplantation (0-29 years). Gout among prevalent patients with SOT was assessed using Medicare and commercial claims.

RESULTS

A total of 637,231 US patients received a primary kidney (393,953), liver (142,186), heart (66,637), or lung (34,455) transplant between 1988 and 2017. An estimated 356,000 (55.8%) recipients were alive in 2017 (233,000 kidney; 78,700 liver; 29,300 heart; 14,700 lung). Gout was identified in 11% of prevalent patients with SOT in 2016. Higher rates of gout were seen in recipients of kidney (13.1%) and heart (12.7%) compared to recipients of liver (6.7%) and lung (5.6%) (P < .0001 in both datasets). Active diagnosed gout prevalence in the US population without a SOT history was 1.1% in 2016.

CONCLUSIONS

Hundreds of thousands of US patients are living with a transplanted organ today and these numbers are likely to increase. In patients with SOT, gout is a frequent comorbidity of which physicians should be aware. This study suggests a markedly higher rate of gout among transplant recipients compared to the general US population.

Gout Severity in Recipients of Kidney Transplant

PURPOSE

This retrospective analysis of medical chart data was performed to compare severity and treatment of gout in patients with or without a history of kidney transplantation (KT).

METHODS

Via an online survey, a panel of board-certified US nephrologists (N = 104) provided the following deidentified chart data for their 3 most recent patients with gout: age, sex, serum uric acid, numbers of swollen or tender joints, visible tophi, gout flare events (prior 12 months), gout drug treatment history, and KT history. The presence of "severe, uncontrolled gout" was defined as: serum uric acid ≥ 7.0 mg/dL, ≥1 tophi and ≥2 flares in the last 12 months, and history of xanthine oxidase inhibitor treatment.

RESULTS

Twenty-five out of 312 (8.0%) gout patients had a history of KT. Univariate analysis found that patients with gout and history of kidney transplants had: greater prevalence of severe uncontrolled gout (27% vs 8%, P = .007) and tophi (36% vs 17%, P = .030), and higher rates of failure or physician perceived contraindication to allopurinol (44% vs 23%, P = .028).

CONCLUSION

This study provides preliminary evidence that gout in patients with history of KT is more severe and poses greater challenges to pharmacologic management. Although gout has been linked to worse outcomes among kidney recipients in the literature, there are presently no publications on gout severity among patients with KT in comparison to other patients with gout. Further investigation of disease severity and appropriate, effective treatment options in recipients of kidney transplant with a diagnosis of gout, especially prior to the transplant, is warranted.

Comparison of efficacy and safety between febuxostat and allopurinol in early post-renal transplant recipients with new onset of hyperuricemia

What is known and objective

Febuxostat and allopurinol are xanthine oxidase inhibitors for urate‐lowering therapy. The efficacy and safety of febuxostat and allopurinol have been mostly reported in hyperuricemia patients with normal renal function. Here, we aimed to compare the effects of these two drugs in early post‐renal transplant recipients, focusing on evaluating the urate‐lowering effect and recovery of allograft renal function.

Methods

A retrospective cohort study was performed in early post‐renal transplant recipients with new onset of hyperuricemia receiving febuxostat or allopurinol therapy. Serum uric acid (UA) and estimated glomerular filtration rate (eGFR) were detected on days 3, 7 and 15 and months 1, 3 and 6 after therapy initiation. Liver and blood functions were monitored and other adverse events were recorded.

Results and discussion

A total of 48 and 33 patients were enrolled in the febuxostat and allopurinol groups, respectively. Significant UA‐lowering effects were observed on day 3 in both groups. Febuxostat caused a more rapid UA decline, starting on day 3 and lasting for 1 month. The most apparent contrast was found in UA level (267.25 ± 93.66 vs 334.18 ± 96.56 μmol/L, P = 0.003) on day 7; 62.5% and 30.3% of patients achieved target UA level in febuxostat and allopurinol groups respectively on day 3 (P = 0.004), but there was no significant difference between two groups from days 15 to months 6. The median times to achieve target UA level were 3 and 5 days in febuxostat and allopurinol groups respectively (P = 0.002). The eGFR levels and recovering rates were gradually upregulated but no significant differences were found between two groups. No abnormities related to febuxostat or allopurinol were observed.

What is new and conclusion

This is the first comprehensive evaluation of UA‐lowering effects of febuxostat and allopurinol in early post‐renal transplant recipients. Febuxostat caused a marginally quicker serum UA‐lowering effect than allopurinol, but there was no advantage for long‐term use of febuxostat. The drugs had no significant differences in impacting renal allograft function recovery, and both were well tolerated.

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.

Drug-induced hyperuricaemia and gout

Hyperuricaemia is a common clinical condition that can be defined as a serum uric acid level >6.8 mg/dl (404 µmol/l). Gout, a recognized complication of hyperuricaemia, is the most common inflammatory arthritis in adults. Drug-induced hyperuricaemia and gout present an emergent and increasingly prevalent problem in clinical practice. Diuretics are one of the most important causes of secondary hyperuricaemia. Drugs raise serum uric acid level by an increase of uric acid reabsorption and/or decrease in uric acid secretion. Several drugs may also increase uric acid production. In this review, drugs leading to hyperuricaemia are summarized with regard to their mechanism of action and clinical significance. Increased awareness of drugs that can induce hyperuricaemia and gout, and monitoring and prevention are key elements for reducing the morbidity related to drug-induced hyperuricaemia and gout.

Hyperuricemia, the kidneys, and the spectrum of associated diseases: a narrative review

Hyperuricemia (elevated serum uric acid) is prevalent, and an important mediator of gout, an increasingly common condition. In addition, hyperuricemia is associated with metabolic syndrome, diabetes, hypertension, and kidney and cardiovascular diseases. Although it remains controversial whether hyperuricemia is a causal factor for kidney disease, the kidneys play a major role in the regulation of serum uric acid levels. Approximately two-thirds of the uric acid produced in humans is excreted by the kidneys. The handling of urate in the renal proximal tubule is extensive, as uric acid undergoes filtration, reabsorption, and secretion. Variations in renal urate handling have been shown to influence the risk of gout. In observational studies, hyperuricemia has been shown to predict kidney disease onset and progression, with a variety of mechanisms implicated. Because of this close association between hyperuricemia and kidney disease, and due to limited studies on the topic, it is important to conduct future studies on the treatment of hyperuricemia to slow kidney disease progression and improve cardiovascular survival in patients with chronic kidney disease. Furthermore, it is important to monitor for gout in patients with kidney disease and to follow the guidelines for treatment of hyperuricemia in this group of patients. This narrative review provides an in-depth discussion of the link between serum uric acid levels, renal handling of uric acid, and diseases associated with dysfunction in uric acid homeostasis.

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.

Hyperuricemia in systemic lupus erythematosus: is it associated with the neuropsychiatric manifestations of the disease?

OBJECTIVES

To assess the association between hyperuricemia and different neuropsychiatric manifestations and stroke risk factors in systematic lupus erythematosus (SLE) patients.

METHODS

This study was conducted on 204 SLE patients who were admitted to a tertiary referral center. A standardized questionnaire was completed for all the participants and the medical records were reviewed regarding the occurrence of arterial or venous thrombotic events, stroke, seizure, depression, headache, psychosis, and peripheral neuropathy. In addition blood samples were drawn to obtain serum uric acid, triglyceride (TG), high-density lipoprotein (HDL) cholesterol, low-density lipoprotein (LDL) cholesterol, and total cholesterol levels.

RESULTS

Hyperuricemia (serum uric acid ≥6mg/dl for women and ≥7mg/dl for men) was detected in 16.1% of SLE patients and was significantly associated with the occurrence of stroke (OR, 2.38; 95%CI, 1.2-7.24), and peripheral neuropathy (OR, 3.49; 95% CI, 1.52-12.23), independent of hypertension and hyperlipidemia. Hyperuricemia was also significantly associated with hypertension (OR, 7.76; 95% CI, 2.72-15.76), hyperlipidemia (OR, 5.05; 95% CI, 1.59-11.32), and history of arterial thrombosis (OR, 4.95; 95% CI, 1.98-15.34), independent of age and body mass index.

CONCLUSIONS

Hyperuricemia in SLE patients is independently associated with the occurrence of stroke and peripheral neuropathy. It is also independently associated with hypertension, hyperlipidemia, and history of arterial thrombosis, which are the major stroke and myocardial infarction risk factors in SLE patients.

[Hyperuricemia in systemic lupus erythematosus: is it associated with the neuropsychiatric manifestations of the disease?]

OBJECTIVES

To assess the association between hyperuricemia and different neuropsychiatric manifestations and stroke risk factors in systematic lupus erythematosus (SLE) patients.

METHODS

This study was conducted on 204 SLE patients who were admitted to a tertiary referral center. A standardized questionnaire was completed for all the participants and the medical records were reviewed regarding the occurrence of arterial or venous thrombotic events, stroke, seizure, depression, headache, psychosis, and peripheral neuropathy. In addition blood samples were drawn to obtain serum uric acid, triglyceride (TG), high-density lipoprotein (HDL) cholesterol, low-density lipoprotein (LDL) cholesterol, and total cholesterol levels.

RESULTS

Hyperuricemia (serum uric acid ≥ 6mg/dl for women and ≥ 7mg/dl for men) was detected in 16.1% of SLE patients and was significantly associated with the occurrence of stroke (OR, 2.38; 95%CI, 1.2-7.24), and peripheral neuropathy (OR, 3.49; 95% CI, 1.52-12.23), independent of hypertension and hyperlipidemia. Hyperuricemia was also significantly associated with hypertension (OR, 7.76; 95% CI, 2.72-15.76), hyperlipidemia (OR, 5.05; 95% CI, 1.59-11.32), and history of arterial thrombosis (OR, 4.95; 95% CI, 1.98-15.34), independent of age and body mass index.

CONCLUSIONS

Hyperuricemia in SLE patients is independently associated with the occurrence of stroke and peripheral neuropathy. It is also independently associated with hypertension, hyperlipidemia, and history of arterial thrombosis, which are the major stroke and myocardial infarction risk factors in SLE patients.

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.

Prognostic Value of Serum Uric Acid in Patients on the Waiting List before and after Renal Transplantation

Background. High serum uric acid (UA) is associated with increased cardiovascular (CV) risk in the general population. The impact of UA on CV events and mortality in CKD is unclear. Objective. To assess the relationship between UA and prognosis in hemodialysis (HD) patients before and after renal transplantation (TX). Methods. 1020 HD patients assessed for CV risk and followed from the time of inception until CV event, death, or TX (HD) or date of TX, CV event, death, or return to dialysis (TX). Results. 821 patients remained on HD while 199 underwent TX. High UA (≥428 mmol/L) was not associated with either composite CV events or mortality in HD patients. In TX patients high UA predicted an increased risk of events (P = 0.03, HR 1.6, and 95% CI 1.03–2.54) but not with death. In the Cox proportional model UA was no longer significantly associated with CV events. Instead, a reduced GFR (<50 mL/min) emerged as the independent risk factor for events (P = 0.02, HR 1.79, and % CI 1.07–3.21). Conclusion. In recipients of TX an increased posttransplant UA is related to higher probability of major CV events but this association probably caused concurrent reduction in GFR.

Efficacy and safety of febuxostat, a novel nonpurine selective inhibitor of xanthine oxidase for the treatment of hyperuricemia in kidney transplant recipients

BACKGROUND

Febuxostat, a novel nonpurine selective inhibitor of xanthine oxidase, is a potential alternative to allopurinol for patients with hyperuricemia. In this study, we evaluated the efficacy and safety of febuxostat for the management of hyperuricemia in renal transplant recipients.

PATIENTS AND METHODS

Between June 2012 and January 2013, a total of 22 renal transplant recipients (56 ± 10 years old) with hyperuricemia were enrolled in this study. All patients underwent de novo kidney transplantation, except for 1 patient, who received a second kidney transplant. Ten patients receiving allopurinol and 3 patients receiving benzbromarone were converted to febuxostat at doses of 10-20 mg/d. In the remaining 9 patients, who did not have a history of other urate-lowering medications, febuxostat was initiated at a dose of 10 mg/d.

RESULTS

Uric acid levels after initiation of febuxostat were significantly lower than before treatment (5.7 ± 0.7 mg/mL vs 8.0 ± 0.8 mg/mL; P < .001). At last follow-up visit, 16 of the 22 patients (73%) achieved uric acid levels of ≤ 6.0 mg/dL, despite the low dosage of febuxostat. All patients were maintained on febuxostat without serious adverse events, except for 1 patient, who discontinued febuxostat because of numbness in the arms.

CONCLUSIONS

Low-dose febuxostat is a promising alternative to allopurinol or benzbromarone for the treatment of hyperuricemia in kidney transplant recipients. The long-term urate-lowering efficacy and safety of febuxostat with regard to renal function in kidney transplant recipients with hyperuricemia requires further investigation.

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 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.

Effect of cyclosporine on the pharmacokinetics of colchicine in healthy subjects

OBJECTIVE

Colchicine and cyclosporine are often administered together, particularly in patients who have undergone solid-organ transplantation. However, the potential for drug-drug interactions between these agents resulting in colchicine toxicity is high.

METHODS

This study sought to determine the effect of cyclosporine (100-mg capsule) on the pharmacokinetics of the US Food and Drug Administration-approved formulation of colchicine (0.6-mg tablet) after single oral-dose administration in 24 healthy subjects under fasted conditions in a phase 1, single-sequence, 2-period drug-drug interaction trial.

RESULTS

Coadministration of cyclosporine increased colchicine maximum observed plasma concentration, area under the plasma concentration-time curve to the last measurable time point, and area under the plasma concentration-time curve to time infinity on average by 224%, 216%, and 215% (ie, almost doubled), respectively, and decreased colchicine oral clearance on average by 72% (from 48.24 to 13.42 L/h), indicating substantially higher colchicine exposures when combined with cyclosporine, compared with colchicine alone.

CONCLUSION

The dose of colchicine should be reduced by ≥ 50% when colchicine and cyclosporine are administered concurrently for treatment and prophylaxis of gout flares or treatment of patients with familial Mediterranean fever. Health care professionals should be vigilant for potential adverse events during colchicine/cyclosporine coadministration, notably in patients who have undergone solid-organ transplantation.

TRIAL REGISTRATION

www.ClinicalTrials.gov identifier NCT00983931 (http://clinicaltrials.gov/ct2/show/NCT00983931).

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.

Use of uric acid-lowering agents limits experimental cyclosporine nephropathy

BACKGROUND

Hyperuricemia frequently complicates cyclosporine (CsA) therapy. Previous studies have shown that hyperuricemia exacerbates interstitial and vascular lesions in the cyclosporine model. We tested the hypothesis that normalization of uric acid could prevent the development of cyclosporine toxicity.

METHODS

CsA nephropathy was induced by administering CsA (15 mg/kg/day) for 7 weeks to rats on a low salt diet (CsA group). The effect of preventing hyperuricemia was determined by concomitant treatment with a xanthine oxidase inhibitor, allopurinol (CsAALP), or with a uricosuric, benzbromarone (CsABENZ), in drinking water. Control groups included vehicle-treated rats.

RESULTS

CsA-treated rats developed mild hyperuricemia with arteriolar hyalinosis, tubular atrophy, striped interstitial fibrosis, increased cell proliferation and decreased VEGF expression. Treatment with allopurinol or benzbromarone limited renal disease, with reduced interstitial fibrosis, cell proliferation, macrophage infiltration, osteopontin expression and arteriolar hyalinosis, in association with restoration of VEGF expression. Both drugs provided comparable protection.

CONCLUSIONS

An increase in uric acid exacerbates CsA nephropathy in the rat. Concomitant treatment with allopurinol or benzbromarone reduced the severity of renal disease. The similar protection observed with both drugs suggests that the effect is associated more with lowering uric acid levels than the antioxidant effect of allopurinol.

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.

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.

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.

Hyperuricemia is a mediator of endothelial dysfunction and inflammation in renal allograft recipients

BACKGROUND

Hyperuricemia is common in renal transplant recipients treated with calcineurin inhibitors. Uric acid induces glomerular hypertension, microvascular disease, and renal interstitial fibrosis and is an independent risk factor for cardiovascular complications. The mechanisms by which uric acid injures renal allografts and the cardiovascular system remain unclear.

OBJECTIVE

To assess the influence of uric acid on biomarkers of endothelial dysfunction and inflammation in renal allograft recipients.

PATIENTS AND METHODS

The study included 78 allograft recipients with normal allograft function. Exclusion criteria were abnormal renal function, proteinuria, diabetes mellitus, obesity, and inflammation. Participants were divided into 2 groups: 48 patients with hyperuricemia (mean [SD] uric acid concentration, 7.72 [1.33] mg/dL) and 30 patients with normouricemia (5.48 [0.92] mg/dL; control group). Concentrations of plasma resistin, CD146, and soluble vascular cell adhesion molecule-1 (sVCAM-1), which are markers of endothelial dysfunction and inflammation, were assessed in both groups. No significant differences were noted for patient demographic data including age, sex, cause of renal failure, number of HLA mismatches, delayed graft function, and number of acute rejection episodes.

RESULTS

Concentrations of the examined biomarkers were increased in the group with hyperuricemia compared with the control group: plasma resistin, 7.15 (2.42) ng/mL vs 6.29 (2.76) ng/mL; CD146, 389.7 (150.0) microg/mL vs 330 (117) microg/mL; and sVCAM-1, 1126 (371) ng/mL vs 955 (269) ng/mL (P < .03). In addition, resistin correlated significantly with sVCAM-1 (P < .01).

CONCLUSIONS

Hyperuricemia mediates endothelial dysfunction and inflammation and via this pathway, possibly contributes to chronic allograft injury and cardiovascular events in renal allograft recipients.

KDIGO clinical practice guideline for the care of kidney transplant recipients

The 2009 Kidney Disease: Improving Global Outcomes (KDIGO) clinical practice guideline on the monitoring, management, and treatment of kidney transplant recipients is intended to assist the practitioner caring for adults and children after kidney transplantation. The guideline development process followed an evidence-based approach, and management recommendations are based on systematic reviews of relevant treatment trials. Critical appraisal of the quality of the evidence and the strength of recommendations followed the Grades of Recommendation Assessment, Development, and Evaluation (GRADE) approach. The guideline makes recommendations for immunosuppression, graft monitoring, as well as prevention and treatment of infection, cardiovascular disease, malignancy, and other complications that are common in kidney transplant recipients, including hematological and bone disorders. Limitations of the evidence, especially on the lack of definitive clinical outcome trials, are discussed and suggestions are provided for future research.

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.

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

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

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

BACKGROUND

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

MATERIALS AND METHODS

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

RESULTS

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

CONCLUSIONS

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

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

Hyperuricemia is a common complication in renal transplant recipients, and uric acid (UA) may play a role in renal dysfunction. The aim of this study was to evaluate the effects of UA on chronic allograft nephropathy (CAN) in renal transplant recipients. The 133 study subjects included 34 women and 99 men of overall mean age of 34.7 +/- 9.9 years. They underwent renal transplantation between 1998 and 2000. Serum UA levels were measured in the first month after transplantation and then at yearly intervals throughout a 3-year follow-up. In the first month after transplantation, 55.3% of recipients had hyperuricemia (UA >7 mg/dL in men; UA >6 mg/dL in women), but, 3 years after transplantation, 84.6% of the subjects had that disorder (P<.001). CAN was diagnosed in 31.5% of the patients at a mean onset of 31.8 +/- 14.3 months after transplantation. Fifty-two percent of these individuals experienced graft failure within 43.3 +/- 20.8 months after transplantation. UA levels were recorded before the development of CAN. There was no association between UA levels and CAN according to a Cox regression analysis (P>.05; relative risk, 1.082; 95% confidence interval [CI] 0.9-1.3). We concluded that the prevalence of hyperuricemia was higher among recipients than in healthy individuals, but that the UA level did not affect the development of CAN during first 3 years after transplantation.

Frequency of hyperuricemia and effect of calcineurin inhibitors on serum uric acid levels in liver transplanted children

Hyperuricemia is common after renal and cardiac transplantations, but it is rarely reported after liver transplantations. The aim of this study is to determine the frequency of hyperuricemia in children following orthotopic liver transplantation and the effects of calcineurin inhibitors tacrolimus and cyclosporine) on blood uric acid levels. Between September 1997 to January 2004, 76 liver transplantations were performed in 70 children (male/female; 39/31) at Ege University, Organ Transplantation Center (37 deceased donation and 39 live donors). Patients who had been transplanted within the last three months and patients who died within six months after liver transplantation were excluded from the study. Finally 59 patients were included in this study. Uric acid levels were measured before transplantation and after transplantation within six months intervals for two yr. In these series 17 cases had increased uric acid levels after liver transplantation (28.8%). Serum uric acid levels in both groups (tacrolimus or cyclosporine) were detected to be significantly higher than initial values at 12th months (p < 0.05). Hyperuricemia developed in eight patients receiving cyclosporine (eight of 11; 72%) whereas nine patients receiving tacrolimus developed hyperuricemia (nine of 48; 18%). However, the rate of having high uric acid levels was significantly higher in cyclosporine group compared tacrolimus group (p = 0.001, OR: 11.5, CI 95% 2.5-52.4). Uric acid levels were also significantly higher in cyclosporine group in 12th and 18th months (respectively, p = 0.003 and p = 0.003). Serum creatinine levels at 12th, 18th and 24th months were significantly higher in cyclosporine group than tacrolimus group (respectively, p = 0.009, p = 0.04 and p = 0.02). Hyperuricemia is a common complication after liver transplantation in children. Cyclosporine may cause hyperuricemia more often in respect to tacrolimus and this may be related to the impairment of renal functions. Complications developing because of hyperuricemia such as gout disease or renal calculi are quite rare in children.