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

The role of CD146 in renal disease: from experimental nephropathy to clinics

Vascular endothelial dysfunction is a major risk factor in the development of renal diseases. Recent studies pointed out a major interest for the inter-endothelial junction protein CD146, as its expression is modulated during renal injury. Indeed, some complex mechanisms involving this adhesion molecule and its multiple ligands are observed in a large number of renal diseases in fundamental or clinical research. The purpose of this review is to summarize the most recent literature on the role of CD146 in renal pathophysiology, from experimental nephropathy to clinical trials.

Asymptomatic hyperuricemia following renal transplantation

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

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Hyperuricemia predicts kidney disease progression after acute allograft dysfunction

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSION

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

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

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

Uric acid and allograft loss from interstitial fibrosis/tubular atrophy: post hoc analysis from the angiotensin II blockade in chronic allograft nephropathy trial

BACKGROUND

Uric acid has been linked to the progression of native kidney disease. Studies evaluating its contribution to allograft function in kidney transplant recipients, among whom hyperuricemia is common, have yielded mixed results.

METHODS

We evaluated the association between baseline uric acid and the primary composite outcome of doubling of interstitium or ESRD from interstitial fibrosis and tubular atrophy (IF/TA) in the Angiotensin II Blockade for Chronic Allograft Nephropathy (ABCAN) Trial participants. Subjects underwent uric acid, iothalamte GFR, and urine albumin to creatinine (ACR) measurements annually for 5 years in addition to an allograft biopsy at baseline and 5 years.

RESULTS

Baseline uric acid was 5.57±1.48 mg/dL; male sex, higher BMI, diuretic use, and lower GFR were associated with higher uric acid, whereas older age, less than 3 HLA matches and having a female donor were associated with lower levels. In multivariate analysis adjusting for baseline GFR, uric acid was associated with doubling of interstitium or ESRD from IF/TA (OR 1.83, 95% CI, 1.06-3.17, P=0.03). Over time, a 1 mg/dL increase in time-varying uric acid was associated with a 2.39 mL/min lower final GFR (P<0.001) but not with the secondary outcome of creatinine doubling, ESRD, or death.

CONCLUSIONS

These data suggest that uric acid is associated with IF/TA and thus may be a viable target for intervention.

Uric acid has a J-shaped association with cardiovascular and all-cause mortality in kidney transplant recipients

The association between serum uric acid and kidney graft and recipient survival is uncertain. During 2000-2011, we measured serum uric acid at week 10 after transplantation. Of 2748 transplanted patients, 2200 (80.1%) attended this visit. After a median follow-up of 7.4 yr, 378 patients had died, 143 from a cardiovascular cause, and 185 patients lost their graft. The third quintile of uric acid levels (357-405 μM) had the lowest mortality risk and was used as reference group. In Cox proportional hazard models adjusting for graft and patient characteristics, the fifth quintile of uric acid levels (>474 μM) was independently associated with cardiovascular mortality (hazard ratio [HR] = 2.87 [1.55-5.32], p = 0.001) and all-cause mortality (HR = 1.57 [1.09-2.25], p = 0.02). Also, the lowest quintile of uric acid levels (<309 μM) showed a trend toward increased risk of cardiovascular mortality (HR = 1.79 [0.90-3.58], p = 0.10) and all-cause mortality (HR = 1.31 [0.89-1.93], p = 0.18). The increased risk at low uric acid levels was confined to diabetic recipients. Uric acid was not associated with death-censored graft loss. In conclusion, uric acid has a J-shaped association with cardiovascular and all-cause mortality in kidney transplant recipients.

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

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

Uric acid as a target of therapy in CKD

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