Influence of cyclosporine and tacrolimus on serum uric acid levels in stable kidney transplant recipients

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.

Lowering and Raising Serum Urate Levels: Off-Label Effects of Commonly Used Medications

Drug-induced hyperuricemia and gout present an increasingly prevalent problem in clinical practice. Herein, we review the urate-lowering or urate-raising effects of commonly used agents. We performed a PubMed search using the terms gout, urate, and medication, along with the specific agents/classes described herein. Reports were reviewed until 2022, and original studies were considered if they primarily or secondarily reported the effects of 1 or more drugs on serum urate level. Previous reviews were assessed for references to additional studies that described urate-altering effects of medications. Urate-changing drugs are summarized regarding their magnitude of effect, mechanism of action, and clinical significance. Potentially urate-lowering drugs include angiotensin II receptor blockers, calcium channel blockers, high-dose aspirin and salicylates, some nonsalicylate nonsteroidal anti-inflammatory drugs, angiotensin-converting enzyme inhibitors, sodium-glucose cotransporter 2 inhibitors, statins, and fenofibrate. Potentially urate-increasing drugs discussed include diuretics, β-blockers, insulin, pyrazinamide, ethambutol, calcineurin inhibitors, low-dose aspirin, testosterone, and lactate. In patients who have or are at risk for hyperuricemia or gout, an increased awareness of drugs that affect serum urate level may allow for prescribing that effectively treats the indicated problem while minimizing adverse effects on hyperuricemia and gout.

A Prediction Model for Tacrolimus Daily Dose in Kidney Transplant Recipients With Machine Learning and Deep Learning Techniques

Tacrolimus is a major immunosuppressor against post-transplant rejection in kidney transplant recipients. However, the narrow therapeutic index of tacrolimus and considerable variability among individuals are challenges for therapeutic outcomes. The aim of this study was to compare different machine learning and deep learning algorithms and establish individualized dose prediction models by using the best performing algorithm. Therefore, among the 10 commonly used algorithms we compared, the TabNet algorithm outperformed other algorithms with the highest R² (0.824), the lowest prediction error [mean absolute error (MAE) 0.468, mean square error (MSE) 0.558, and root mean square error (RMSE) 0.745], and good performance of overestimated (5.29%) or underestimated dose percentage (8.52%). In the final prediction model, the last tacrolimus daily dose, the last tacrolimus therapeutic drug monitoring value, time after transplantation, hematocrit, serum creatinine, aspartate aminotransferase, weight, CYP3A5, body mass index, and uric acid were the most influential variables on tacrolimus daily dose. Our study provides a reference for the application of deep learning technique in tacrolimus dose estimation, and the TabNet model with desirable predictive performance is expected to be expanded and applied in future clinical practice.

Prevalence and potential relevance of hyperuricemia in pediatric kidney transplant recipients-a CERTAIN registry analysis

BACKGROUND

Asymptomatic hyperuricemia is frequently observed in pediatric kidney transplant recipients; symptomatic hyperuricemia, however, is a rare complication. Only few data are available in this patient population. We, therefore, investigated the prevalence of hyperuricemia and its association with kidney transplant function and blood pressure in a multicenter cohort of pediatric kidney transplant recipients.

METHODS

This is a retrospective, observational multicenter registry study. All pediatric kidney transplant recipients in the CERTAIN database with at least one documented serum uric acid level and a follow-up of 5 years posttransplant were eligible. We identified 151 patients with 395 measurements of serum uric acid. We calculated the prevalence of hyperuricemia, analyzed potential risk factors and clinical consequences such as elevated blood pressure and reduced estimated glomerular filtration rate (eGFR). Statistical analysis was performed using IBM SPSS Statistics 26.

RESULTS

One hundred and ten of 395 (27.8%) serum uric acid levels were above 416 µmol/L (7.0 mg/dL), defined as the upper limit of normal. Univariate analysis showed a significant (p = .026) inverse association of serum uric acid with eGFR overtime. There was no significant association of serum uric acid concentrations with body mass index (z-score), blood pressure (z-score), or sex. No episodes of gout were documented.

CONCLUSION

This study shows that hyperuricemia is present in a considerable number of patients sometime after pediatric kidney transplantation and is associated with lower eGFR. Whether hyperuricemia contributes to faster decline of graft function or to the overall cardiovascular risk of these patients remains to be elucidated.

The Use of Machine Learning Algorithms and the Mass Spectrometry Lipidomic Profile of Serum for the Evaluation of Tacrolimus Exposure and Toxicity in Kidney Transplant Recipients

Tacrolimus has a narrow therapeutic window; a whole-blood trough target concentration of between 5 and 8 ng/mL is considered a safe level for stable kidney transplant recipients. Tacrolimus serum levels must be closely monitored to obtain a balance between maximizing efficacy and minimizing dose-related toxic effects. Currently, there is no specific tacrolimus toxicity biomarker except a graft biopsy. Our study aimed to identify specific serum metabolites correlated with tacrolinemia levels using serum high-precision liquid chromatography–mass spectrometry and standard laboratory evaluation. Three machine learning algorithms were used (Naïve Bayes, logistic regression, and Random Forest) in 19 patients with high tacrolinemia (8 ng/mL) and 23 patients with low tacrolinemia (5 ng/mL). Using a selected panel of five lipid metabolites (phosphatidylserine, phosphatidylglycerol, phosphatidylethanolamine, arachidyl palmitoleate, and ceramide), Mg2+, and uric acid, all three machine learning algorithms yielded excellent classification accuracies between the two groups. The highest classification accuracy was obtained by Naïve Bayes, with an area under the curve of 0.799 and a classification accuracy of 0.756. Our results show that using our identified five lipid metabolites combined with Mg2+ and uric acid serum levels may provide a novel tool for diagnosing tacrolimus toxicity in kidney transplant recipients. Further validation with targeted MS and biopsy-proven TAC toxicity is needed.

Impact of the ACE2 activator xanthenone on tacrolimus nephrotoxicity: Modulation of uric acid/ERK/p38 MAPK and Nrf2/SOD3/GCLC signaling pathways

AIMS

The calcineurin inhibitor tacrolimus is an effective and widely used immunosuppressant after organ transplantation to reduce graft rejection. However, its nephrotoxic effect could compel the patients to treatment discontinuation. The beneficial effects of angiotensin-converting enzyme 2 (ACE2) on the kidney and other organs have been investigated in several studies, but its role in tacrolimus nephrotoxicity still needs to be elucidated. Our study was designed to investigate effects of the ACE2 activator xanthenone on tacrolimus-induced renal injury.

MATERIALS AND METHODS

Male Wistar rats were administered xanthenone (2 mg/kg) concurrently with tacrolimus (1 mg/kg) for 3 weeks, then blood and kidney tissue samples were collected for biochemical and molecular investigations.

KEY FINDINGS

Co-administration of xanthenone significantly improved renal functions in tacrolimus-treated rats, where serum creatinine, urea, and uric acid levels were close to those of the normal control. Besides, xanthenone reduced renal angiotensin (ANG) II content, while elevated ANG (1-7). Relative protein expressions of p-ERK/ERK and p-p38 MAPK/p38 MAPK inflammatory signals were downregulated upon xanthenone administration with tacrolimus. In addition, xanthenone reinforced antioxidant defense against tacrolimus by enhancing protein expression of the transcription factor Nrf2 with subsequently increased mRNA expressions of the antioxidants SOD3 and GCLC.

SIGNIFICANCE

These protective effects of xanthenone could be attributed to ANG II degradation to ANG (1-7) by ACE2 activation resulting in regulated inflammatory and oxidative responses in the kidney. Therefore, administration of xanthenone along with tacrolimus could be a promising therapeutic strategy to reduce the adverse effects and increase the tolerability to tacrolimus immunosuppressive therapy.

Sodium-glucose cotransporter 2 inhibitors for diabetes mellitus control after kidney transplantation: Review of the current evidence

Sodium-glucose cotransporter type 2 inhibitors (SGLT2i) are promising drugs to treat chronic kidney disease patients with or without diabetes mellitus (DM). Besides improving glycemic control, SGLT2i are cardioprotective and kidney protective and decrease bodyweight, serum uric acid, blood pressure, albuminuria and glomerular hyperfiltration. These effects may benefit graft function and survival in kidney transplant (KT) patients. In this review, we evaluate data on the efficacy and safety of SGLT2i for KT patients with DM. Eleven studies with 214 diabetic KT patients treated with SGLT2i have been reported. SGLT2i lowered haemoglobin A1c and bodyweight. While glomerular filtration rate may be reduced in the short-term, it remained similar to baseline after 3-12 months. In two studies, blood pressure decreased and remained unchanged in the others. There were no significant changes in urine protein to creatinine ratio. Regarding safety, 23 patients had urinary tract infections, 2 patients had a genital yeast infection, one had acute kidney injury, and one had mild hypoglycaemia. No cases of ketoacidosis or acute rejection were reported. In conclusion, the limited experience so far suggests that SGLT2i are safe in KT patients with DM, decrease bodyweight and improve glycemic control. However, some of the benefits observed in larger studies in the non-KT population have yet to be demonstrated in KT recipients, including preservation of kidney function, reduction in blood pressure and decreased proteinuria.

New-Onset Gout as an Independent Risk Factor for Returning to Dialysis After Kidney Transplantation

Background.

The causal relationship between gout and renal transplant outcomes is difficult to assess due to multiple interacting covariates. This study sought to estimate the independent effect of new-onset gout on renal transplant outcomes using a methodology that accounted for these interactions.

Methods.

This study analyzed data on patients in the US Renal Data System (USRDS) who received a primary kidney transplant between 2008 and 2015. The exposure was new-onset gout, and the primary endpoint was returning to dialysis >12 months postindex date (transplant date). A marginal structural model (MSM) was fitted to determine the relative risk of new-onset gout on return to dialysis.

Results.

18 525 kidney transplant recipients in the USRDS met study eligibility. One thousand three hundred ninety-nine (7.6%) patients developed new-onset gout, and 1420 (7.7%) returned to dialysis >12 months postindex. Adjusting for baseline and time-varying confounders via the MSM showed new-onset gout was associated with a 51% increased risk of return to (RR, 1.51; 95% CI, 1.03-2.20).

Conclusions.

This finding suggests that new onset gout after kidney transplantation could be a harbinger for poor renal outcomes, and to our knowledge is the first study of kidney transplant outcomes using a technique that accounted for the dynamic relationship between renal dysfunction and gout.

Expert consensus on management of metabolic disease in Chinese liver transplant recipients

Metabolic disease, including diabetes mellitus, hypertension, dyslipidemia, obesity, and hyperuricemia, is a common complication after liver transplantation and a risk factor for cardiovascular disease and death. The development of metabolic disease is closely related to the side effects of immunosuppressants. Therefore, optimization of the immunosuppressive regimen is very important for the prevention and treatment of metabolic disease. The Chinese Society of Organ Transplantation has developed an expert consensus on the management of metabolic diseases in Chinese liver transplant recipients based on recent studies. Emphasis is placed on the risk factors of metabolic diseases, the effect of immunosuppressants on metabolic disease, and the prevention and treatment of metabolic diseases.

Treatment of recurrent renal transplant lithiasis: analysis of our experience and review of the relevant literature

BACKGROUND

Renal transplant lithiasis is a rather unusual disease, and the recurrence of lithiasis presents a challenging situation.

METHODS

We retrospectively analyzed the medical history of one patient who suffered renal transplant lithiasis twice, reviewed the relevant literature, and summarized the characteristics of this disease.

RESULTS

We retrieved 29 relevant studies with an incidence of 0.34 to 3.26% for renal transplant lithiasis. The summarized incidence was 0.52%, and the recurrence rate was 0.082%. The mean interval after transplantation was 33.43 ± 56.70 mo. Most of the patients (28.90%) were asymptomatic. The management included percutaneous nephrolithotripsy (PCNL, 22.10%), ureteroscope (URS, 22.65%), extracorporeal shockwave lithotripsy (ESWL, 18.60%) and conservative treatment (17.13%). In our case, the patient suffered from renal transplant lithiasis at 6 years posttransplantation, and the lithiasis recurred 16 months later. He presented oliguria, infection or acute renal failure (ARF) during the two attacks but without pain. PCNL along with URS and holmium laser lithotripsy were performed. The patient recovered well after surgery, except for a 3 mm residual stone in the calyx after the second surgery. He had normal renal function without any symptoms and was discharged with oral anticalculus drugs and strict follow-up at the clinic. Fortunately, the calculus passed spontaneously about 1 month later.

CONCLUSIONS

Due to the lack of specific symptoms in the early stage, patients with renal transplant lithiasis may have delayed diagnosis and present ARF. Minimally invasive treatment is optimal, and the combined usage of two or more procedures is beneficial for patients. After surgery, taking anticalculus drugs, correcting metabolic disorders and avoiding UIT are key measures to prevent the recurrence of lithiasis.

Immunosuppressant Use and Gout in the Prevalent Solid Organ Transplantation Population

INTRODUCTION

Gout is a common comorbidity among solid organ transplantation patients and is usually attributed to the use of cyclosporine. This study aims to evaluate the prevalence of gout among solid organ transplantation patients to determine the prevalence in the tacrolimus era.

RESEARCH QUESTIONS

To what degree is cyclosporine still used among prevalent solid organ transplantation patients? How prevalent is gout in the solid organ transplantation population not being treated by cyclosporine?

METHODS

Immunosuppressant regimens and gout prevalence among prevalent solid organ transplantation patients were assessed using retrospective claims data for a representative sample of commercially insured patients. For comparison to the prevalent solid organ transplantation population, immunosuppressant use at time of transplantation was compiled from published reports.

RESULTS

Between 2012 and 2016, the use of cyclosporine declined while use of tacrolimus increased, with greater cyclosporine use among prevalent versus incident solid organ transplantation patients. The prevalence of gout was 18.3%, 9.3%, and 9.1% for solid organ transplantation patients on cyclosporine, tacrolimus, and neither, respectively. Among all solid organ transplantation patients with gout, 66.6% and 21.5% were on tacrolimus versus cyclosporine. The prevalence of gout among noncyclosporine solid organ transplantation patients was significantly higher than in the general population without solid organ transplantation.

DISCUSSION

Despite declining cyclosporine use, gout prevalence remains high, with the majority of patients with gout receiving tacrolimus rather than cyclosporine. In summary, gout remains a frequent comorbidity of solid organ transplantation.

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.

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.

Identification of Febuxostat as a New Strong ABCG2 Inhibitor: Potential Applications and Risks in Clinical Situations

ATP-binding cassette transporter G2 (ABCG2) is a plasma membrane protein that regulates the pharmacokinetics of a variety of drugs and serum uric acid (SUA) levels in humans. Despite the pharmacological and physiological importance of this transporter, there is no clinically available drug that modulates ABCG2 function. Therefore, to identify such drugs, we investigated the effect of drugs that affect SUA levels on ABCG2 function. This strategy was based on the hypothesis that the changes of SUA levels might caused by interaction with ABCG2 since it is a physiologically important urate transporter. The results of the in vitro screening showed that 10 of 25 drugs investigated strongly inhibited the urate transport activity of ABCG2. Moreover, febuxostat was revealed to be the most promising candidate of all the potential ABCG2 inhibitors based on its potent inhibition at clinical concentrations; the half-maximal inhibitory concentration of febuxostat was lower than its maximum plasma unbound concentrations reported. Indeed, our in vivo study demonstrated that orally administered febuxostat inhibited the intestinal Abcg2 and, thereby, increased the intestinal absorption of an ABCG2 substrate sulfasalazine in wild-type mice, but not in Abcg2 knockout mice. These results suggest that febuxostat might inhibit human ABCG2 at a clinical dose. Furthermore, the results of this study lead to a proposed new application of febuxostat for enhancing the bioavailability of ABCG2 substrate drugs, named febuxostat-boosted therapy, and also imply the potential risk of adverse effects by drug-drug interactions that could occur between febuxostat and ABCG2 substrate drugs.

Tacrolimus Monotherapy after Intravenous Methylprednisolone in Adults with Minimal Change Nephrotic Syndrome

Glucocorticoid treatment is the first choice therapy for adults with minimal change nephrotic syndrome; however, this therapy associates with many adverse effects. Tacrolimus may be an alternative to conventional glucocorticoid therapy. To investigate this possibility, we conducted a prospective, randomized, controlled trial (WHO International Clinical Trials Registry Platform: ChiCTR-TRC-11001454) in eight renal units across China. We randomized enrolled patients with adult-onset minimal change nephrotic syndrome (n=119) to receive glucocorticoid therapy or tacrolimus after intravenous methylprednisolone (0.8 mg/kg per day) for 10 days. Patients received a conventional glucocorticoid regimen or tacrolimus monotherapy, starting with 0.05 mg/kg per day (target trough whole-blood level of 4-8 ng/ml) for 16-20 weeks and subsequently tapering over approximately 18 weeks. Remission occurred in 51 of 53 (96.2%; all complete remission) glucocorticoid-treated patients and 55 of 56 (98.3%; 52 complete and three partial remission) tacrolimus-treated patients (P=0.61 for remission; P=0.68 for complete remission). The groups had similar mean time to remission (P=0.55). Relapse occurred in 49.0% and 45.5% of the glucocorticoid- and tacrolimus-treated patients, respectively (P=0.71), with similar time to relapse (P=0.86). Seven (13.7%) glucocorticoid-treated and four (7.3%) tacrolimus-treated patients suffered frequent relapse (P=0.28); five glucocorticoid-treated and two tacrolimus-treated patients became drug dependent (P=0.26). Adverse events occurred more frequently in the glucocorticoid group (128 versus 81 in the tacrolimus group). Seven adverse events in the glucocorticoid group and two adverse events in the tacrolimus group were serious. Consequently, tacrolimus monotherapy after short-term intravenous methylprednisolone is noninferior to conventional glucocorticoid treatment for adult-onset minimal change nephrotic syndrome in this cohort.

Associations Between Hyperuricemia and Chronic Kidney Disease: A Review

CONTEXT

In human beings, uric acid is the poorly soluble circulating end product of the purine nucleotide metabolism. A reduction in the glomerular filtration rate (GFR) contributes to hyperuricemia, which is frequently observed in patients with chronic kidney disease (CKD).

EVIDENCE ACQUISITION

Hyperuricemia is defined as a serum uric acid level > 7.0 mg/dL in males and > 6.0 mg/dL in females, while CKD is defined as kidney damage or a GFR < 60 mL/min/1.73 m(2) for 3 months or more, irrespective of the cause. Hyperuricemia is common in CKD and may occur because of decreased excretion, increased production, or a combination of both mechanisms.

RESULTS

The causes for hyperuricemia in overproducers may be either exogenous or endogenous. CKD has become a global public health problem because of its high prevalence and the accompanying increase in the risk of end-stage renal disease, cardiovascular disease, and premature death. The most common risk factors for CKD are obesity and the metabolic syndrome, which is strongly associated with hyperuricemia probably as a consequence of insulin resistance and the effects of insulin to reduce the urinary urate excretion. For recurring bouts of hyperuricemia or gout, patients should have a blood test and joint fluid test to determine whether the medication taken is effective. Interventional studies are a useful clinical research tool in clarifying the role of hyperuricemia in CKD.

CONCLUSIONS

Although many evidence-based studies have suggested that uric acid itself may harm patients with CKD by increasing inflammation and CKD progression, the issue is still a matter of controversy. Special attention should be paid to specific contraindications to certain drugs and the possibility of infectious arthritis.

Dermal tophus: a complication of gout in a kidney transplant recipient

Gout is a chronic metabolic disease caused by disturbance of purine metabolism that leads to hyperuricemia. Hyperuricemia prevalence after renal transplant is reported as 19% to 84% in different studies. Tophaceous gout in renal transplant recipients is a consequence of increased hyperuricemia. Although tophus formation in skin and soft tissues is an indicator of chronic gout (also referred to as tophaceous gout), tophi may be the first sign of gout. In this study, we report a case of a 62-year-old male renal transplant recipient who had tophi as the first clinical sign of gout. After confirming gout diagnosis, cyclosporine was changed to sirolimus, and allopurinol was added to therapy to decrease uric acid levels. In conclusion, hyperuricemia is a common complication in renal transplant recipients. Presentation might be atypical, and diagnosis can be challenging.

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.

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.

Association between serum uric acid and inflammation in rheumatoid arthritis: perspective on lowering serum uric acid of leflunomide

BACKGROUND

The association between serum uric acid concentrations and inflammation in patients with rheumatoid arthritis (RA) has been still controversial.

METHODS

A total of 172 patients with RA who added leflunomide to methotrexate (MTX) in their treatment regimens were enrolled in this study. Twenty-seven RA patients taking MTX without leflunomide were also recruited in order to assess the fractional excretion of uric acid (FEUA).

RESULTS

After leflunomide therapy for an average of 4.6months, serum uric acid concentrations had significantly decreased compared to baseline concentrations (p<0.001). Patients treated with a combination of MTX and leflunomide (n=23) showed higher FEUA than those treated with only MTX (n=27) (p=0.007). Differences in serum uric acid concentrations after leflunomide therapy were significantly associated with those in serum creatinine concentrations (B coefficient=3.081, p<0.001), but not with those in acute phase reactants including ESR and CRP.

CONCLUSION

This study determined that leflunomide reduced serum uric acid concentrations through increased urinary excretion of uric acid, which might not reflect changes in disease activity status in RA. This implies that uric acid may not influence systemic inflammation in RA.

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.

Changes in oxidative stress in renal graft patients receiving calcineurin inhibitors: cyclosporine versus tacrolimus

OBJECTIVES

The effects of calcineurin inhibitors on oxidative stress after renal transplant are obscure. This study sought to investigate the changes in plasma oxidative stress and lipid levels in patients receiving cyclosporine or tacrolimus before and after renal transplant for 6 months.

MATERIALS AND METHODS

Twenty-one patients and 15 healthy controls were involved in our study. Twelve of the patients were treated with cyclosporine and 9 were treated with tacrolimus. Plasma malondialdehyde, nitrite/nitrate, vitamin C, vitamin E, and plasma glutathione levels, as well as total cholesterol and triglyceride levels, were evaluated before and after transplant for 6 months.

RESULTS

Before the transplant, patients had higher malondialdehyde and plasma glutathione levels than did healthy controls (3.76 ± 0.79 nmol/mL vs 3.21 ± 0.57 nmol/mL; P < .05, and 66.6 ± 23.2 μmol/L vs 43.3 ± 26.9 μmol/L; P < .05). In the overall group of patients, a significant increase in malondialdehyde levels was detected 3 and 6 months after transplant (3.76 ± 0.79 nmol/mL vs 4.38 ± 0.87 nmol/mL in the third month; P = .02; and 3.76 ± 0.79 nmol/mL vs 4.28 ± 0.69 nmol/mL in the sixth month; P = .04). A significant reduction in plasma glutathione levels 1 month after transplant and nitrite/nitrate levels 6 months after transplant was found. No changes in vitamin C and vitamin E levels were detected before and after transplant. After 3 and 6 months of transplant, cyclosporine-treated patients had higher levels of total cholesterol and triglycerides when compared with tacrolimus-treated patients.

CONCLUSIONS

An enhancement in plasma malondialdehyde levels was found after transplant at 6-month follow-up. However, no significant change in vitamin C, vitamin E, nitrite/nitrate levels between patients and controls was recorded. Although both calcineurin inhibitors showed similar effects on oxidative stress, cyclosporine-treated patients had higher levels of total cholesterol and triglycerides.

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.

Biomarkers of immunosuppressant organ toxicity after transplantation: status, concepts and misconceptions

INTRODUCTION

A major challenge in transplantation is improving long-term organ transplant and patient survival. Immunosuppressants protect the transplant organ from alloimmune reactions, but sometimes also exhibit limiting side effects. The key to improving long-term outcome following transplantation is the selection of the correct immunosuppressive regimen for an individual patient for minimizing toxicity while maintaining immunosuppressive efficacy.

AREAS COVERED

Proteomics and metabolomics have the potential to develop sensitive and specific diagnostic tools for monitoring early changes in cell signal transduction, regulation and biochemical pathways. Here, we review the steps required for the development of molecular markers from discovery, mechanistic and clinical qualification to regulatory approval, and present a critical discussion of the current status of molecular marker development as relevant for the management and individualization of immunosuppressive drug regimens.

EXPERT OPINION

Although metabolomics and proteomics-based studies have yielded several candidate molecular markers, most published studies are poorly designed, statistically underpowered and/or often have not gone beyond the discovery stage. Most molecular marker candidates are still at an early stage. Due to the high complexity of and the resources required for diagnostic marker development, initiatives and consortia organized and supported by funding agencies and regulatory agencies will be critical.

Predictive factors for ciclosporin-associated nephrotoxicity in children with minimal change nephrotic syndrome

Aims

To identify the predictive factors for ciclosporin A (CyA)-associated nephrotoxicity (CAN) in children with minimal change nephrotic syndrome (MCNS).

Methods

The clinical and laboratory findings of 58 children (median age 3.2 years, range 1.1–13.1 years, male:female 48:10) with MCNS who were treated with CyA from 1992 to 2002 were analysed retrospectively. Forty-eight (83%) of them were steroid dependent and 10 (17%) were steroid resistant. The starting dose of CyA was 5 mg/kg per day, and the desired drug level was kept at 100–200 ng/ml. Serial renal biopsies were performed before and after CyA therapy.

Results

Twenty-two patients (38%) had CAN (group I) and 36 (62%) did not (group II). There were no differences in the age at onset, sex, initial response to steroids, duration of CyA therapy and relapse rates. However, the median CyA trough levels were significantly higher in group I than in group II (218.0±15.2 vs 171.8±6.7 ng/ml, p=0.01). Changes in creatinine clearance were more decreased in group I than in group II (−39.4±8.2 vs 2.7±4.3 ml/min per 1.73 m2, p<0.0001). Multiple logistic regression analysis also revealed the median CyA trough level was an independent risk factor for the development of CAN (OR 1.025, 95% CI 1.007 to 1.044, p=0.007).

Conclusions

The median CyA trough level was an independent and significant risk factor for the development of CAN in children with MCNS receiving moderate-dose CyA.

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.

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.

Effect of oral fructose load on serum uric acid and lipids in kidney transplant recipients treated with cyclosporine or tacrolimus

Hyperuricemia, frequently observed following kidney transplantation, may adversely affect graft survival. Although hyperuricemia is a well-known adverse effect of cyclosporine (CsA), a similar effect of tacrolimus (Tac) remains debatable. Hyperuricemia is also seen after oral fructose intake in beverages and processed foods. This sugar is blamed for the epidemic of obesity and metabolic syndrome. The aim of our study was to compare the effects of CsA and Tac on an acute oral fructose load in terms of plasma uric acid, serum lipids, and blood pressure in kidney transplant patients. Thirty-two kidney transplant recipients treated with CsA- or Tac-based triple (calcineurin inhibitor + mycophenolate mofetil + prednisone) immunosuppressive therapy displaying stable allograft function (mean glomerular filtration rate = 53 mL/min/1.73m(2)) received an oral challenge with 70 g of fructose. Serum uric acid, lipids, and blood pressure were measured before as well as 60, 120, 180, and 240 minutes after fructose administration. A significant increase in serum uric acid was observed in both groups after oral fructose administration (P < .001). A peak increase in serum uric acid was recorded at 120 minutes after fructose intake. Serum total, LDL, and HDL cholesterol also significantly decreased and serum triglycerides increased to a similar extent in both CsA and Tac groups. No significant changes in blood pressure were observed after fructose consumption. Oral fructose intake induced an acute rise in serum uric acid and triglycerides and decrease in serum cholesterol among kidney transplant recipients. Those changes were similar among patients treated with CsA or Tac.

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.

Applications of metabolomics in drug discovery and development

Metabolomics is a relatively new field of 'omics' technology that is primarily concerned with the global or system-wide characterization of small molecule metabolites using technologies such as nuclear magnetic resonance, liquid chromatography and/or mass spectrometry. Its unique focus on small molecules and the physiological effects of small molecules aligns the field of metabolomics very closely with the aims and interests of many researchers in the pharmaceutical industry. Because of its conceptual and technical overlap with many aspects of pharmaceutical research, metabolomics is now finding applications that span almost the full length of the drug discovery and development pipeline, from lead compound discovery to post-approval drug surveillance. This review explores some of the most interesting or significant applications of metabolomics as they relate to pharmaceutical research and development. Specific examples are given that show how metabolomics can be used to facilitate lead compound discovery, to improve biomarker identification (for monitoring disease status and drug efficacy) and to monitor drug metabolism and toxicity. Other applications are also discussed, including the use of metabolomics to facilitate clinical trial testing and to improve post-approval drug monitoring. These examples show that metabolomics potentially offer drug researchers and drug regulators an effective, inexpensive route to addressing many of the riskier or more expensive issues associated with the discovery, development and monitoring of drug products.

Metabolomics in monitoring kidney transplants

PURPOSE OF REVIEW

The success of any given kidney transplant is closely tied to the ability to monitor patients and responsively change their medications. Transplant monitoring is still, however, dependent on relatively old technologies: serum creatinine levels, urine output, blood pressure, blood glucose and histopathology of biopsy samples. These older technologies do not offer sufficient specificity, sensitivity, or accuracy to allow appropriate and timely interventions. Using the tools of genomics, proteomics and metabolomics new biomarkers are being found that may greatly improve transplant monitoring and significantly enhance graft survival. This review describes the basic principles of metabolomics and summarizes a number of recent developments in the use of metabolite biomarkers and metabolomics to monitor kidney transplants.

RECENT FINDINGS

Changes in the concentration profiles of a number of small molecule metabolites found in either blood or urine can be used to localize organ damage, identify organs at risk of rejection, assess organs suffering from ischemia-repurfusion injury or identify organs that have been damaged by immunosuppressive drugs.

SUMMARY

The application of metabolomics to kidney transplant monitoring is still very much in its infancy. Nevertheless, there are a number of easily measured metabolites in both urine and serum that can provide reliable indications of organ function, organ injury, and immunosuppressive drug toxicity. As the field matures, metabolomics may eventually lead to the development of rapid, inexpensive and noninvasive approaches to assist clinicians in monitoring kidney transplants.

Hyperuricemia and gout following pediatric renal transplantation

Hyperuricemia and gout are common complications in adult renal transplant recipients. In pediatric recipients, however, hyperuricemia seems to be rare, but data are scarce. Thirty-two children (21 males, 11 females) were investigated for a median time of 4.8 years (range: 0.4-11.2 years) following renal transplantation. The median age of this pediatric study group was 13.9 years (range: 5.7-20.3 years), and the calculated glomerular filtration rate (GFR) was 61 ml/min per 1.73 m(2) (range:12-88 ml/min per 1.73 m(2)). All patients were given calcineurin inhibitors, with 22 and ten children receiving cyclosporine A (CSA) and tacrolimus (TAC), respectively. The median plasma uric acid was 385 micromol/l (range: 62-929 micromol/l); 15 children (47%) were above the age-related normal range. Only one patient experienced gouty arthritis. There was a significant correlation between plasma uric acid concentration and both time span after transplantation and plasma creatinine, and an inverse correlation to GFR (p<0.05). No significant correlation was found between plasma uric acid and body mass index (BMI). Plasma uric acid concentrations were neither different among CSA- and TAC-treated children, nor did they correlate with drug exposure or blood trough levels of CSA or TAC. Plasma uric acid concentration was not different when compared to children with chronic renal failure (CRF) of a similar degree in native kidneys. We conclude that hyperuricemia is common among pediatric renal transplant recipients and rather a consequence of chronic renal transplant dysfunction than the use of calcineurin inhibitors. Gout, however, is rare.