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      Uric Acid Lowering and Biomarkers of Kidney Damage in CKD Stage 3: A Post Hoc Analysis of a Randomized Clinical Trial

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          Abstract

          Rationale & Objective

          Hyperuricemia is associated with chronic kidney disease (CKD) progression. We evaluated whether lowering serum uric acid levels improves levels of biomarkers of kidney damage.

          Study Design

          Post hoc analysis of clinical trial participants.

          Setting & Participants

          A double-blind randomized placebo-controlled study designed to lower serum uric acid levels. 80 patients with stage 3 CKD and asymptomatic hyperuricemia were randomly assigned to allopurinol treatment or placebo (300 mg/d) for 12 weeks.

          Exposure/Predictor

          Allopurinol treatment versus placebo.

          Outcomes & Measures

          We evaluated the change from baseline for the following urinary biomarkers of kidney damage: albumin-creatinine ratio (ACR), neutrophil gelatinase-associated lipocalin (NGAL), kidney injury molecule 1 (KIM-1), and transforming growth factor β1 (TGF-β1). Additionally, we evaluated CKD Epidemiology Collaboration (CKD-EPI)-estimated glomerular filtration rate (eGFR) and cystatin C eGFR.

          Analytical Approach

          Generalized linear mixed modeling was used.

          Results

          After 12 weeks, allopurinol (compared to placebo) significantly lowered serum uric acid levels with an estimate of −3.3 mg/dL (95% CI, −4.1 to −2.5 mg/dL; P < 0.001). Estimates for the change for allopurinol versus placebo over time were 1.09 (95% CI, 0.77-1.54) for ACR, 0.77 (95% CI, 0.36-1.63) for NGAL, and 2.36 (95% CI, 0.97-5.70) for TGF-β1. The model did not converge for KIM-1, but Wilcoxon signed rank test showed no significant difference in change from baseline between study groups. There was no significant change observed in CKD-EPI eGFR or cystatin C eGFR.

          Limitations

          Post hoc analysis and short duration of the study.

          Conclusions

          Uric acid–lowering with allopurinol is not associated with improvement in levels of biomarkers of kidney damage in patients with asymptomatic hyperuricemia and stage 3 CKD.

          Funding

          The study was funded by the National Institutes of Health through a career development award, K23DK088833, and the Clinical and Translational Science Award UL1TR002537.

          Trial Registration

          NCT01228903.

          Graphical abstract

          Related collections

          Most cited references 27

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          A role for uric acid in the progression of renal disease.

          Hyperuricemia is associated with renal disease, but it is usually considered a marker of renal dysfunction rather than a risk factor for progression. Recent studies have reported that mild hyperuricemia in normal rats induced by the uricase inhibitor, oxonic acid (OA), results in hypertension, intrarenal vascular disease, and renal injury. This led to the hypothesis that uric acid may contribute to progressive renal disease. To examine the effect of hyperuricemia on renal disease progression, rats were fed 2% OA for 6 wk after 5/6 remnant kidney (RK) surgery with or without the xanthine oxidase inhibitor, allopurinol, or the uricosuric agent, benziodarone. Renal function and histologic studies were performed at 6 wk. Given observations that uric acid induces vascular disease, the effect of uric acid on vascular smooth muscle cells in culture was also examined. RK rats developed transient hyperuricemia (2.7 mg/dl at week 2), but then levels returned to baseline by week 6 (1.4 mg/dl). In contrast, RK+OA rats developed higher and more persistent hyperuricemia (6 wk, 3.2 mg/dl). Hyperuricemic rats demonstrated higher BP, greater proteinuria, and higher serum creatinine than RK rats. Hyperuricemic RK rats had more renal hypertrophy and greater glomerulosclerosis (24.2 +/- 2.5 versus 17.5 +/- 3.4%; P < 0.05) and interstitial fibrosis (1.89 +/- 0.45 versus 1.52 +/- 0.47; P < 0.05). Hyperuricemic rats developed vascular disease consisting of thickening of the preglomerular arteries with smooth muscle cell proliferation; these changes were significantly more severe than a historical RK group with similar BP. Allopurinol significantly reduced uric acid levels and blocked the renal functional and histologic changes. Benziodarone reduced uric acid levels less effectively and only partially improved BP and renal function, with minimal effect on the vascular changes. To better understand the mechanism for the vascular disease, the expression of COX-2 and renin were examined. Hyperuricemic rats showed increased renal renin and COX-2 expression, the latter especially in preglomerular arterial vessels. In in vitro studies, cultured vascular smooth muscle cells incubated with uric acid also generated COX-2 with time-dependent proliferation, which was prevented by either a COX-2 or TXA-2 receptor inhibitor. Hyperuricemia accelerates renal progression in the RK model via a mechanism linked to high systemic BP and COX-2-mediated, thromboxane-induced vascular disease. These studies provide direct evidence that uric acid may be a true mediator of renal disease and progression.
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            Use of allopurinol in slowing the progression of renal disease through its ability to lower serum uric acid level.

            Hyperuricemia is associated strongly with the development of hypertension, renal disease, and progression. Allopurinol decreases serum uric acid levels by inhibiting the enzyme xanthine oxidase. We hypothesized that administrating allopurinol to decrease serum uric acid levels to the normal range in hyperuricemic patients with chronic kidney disease may be of benefit in decreasing blood pressure and slowing the rate of renal disease progression in these patients. We conducted a prospective, randomized, controlled trial of 54 hyperuricemic patients with chronic kidney disease. Patients were randomly assigned to treatment with allopurinol, 100 to 300 mg/d, or to continue the usual therapy for 12 months. Clinical, hematologic, and biochemical parameters were measured at baseline and 3, 6, and 12 months of treatment. We define our study end points as: (1) stable kidney function with less than 40% increase in serum creatinine level, (2) impaired renal function with creatinine level increase greater than 40% of baseline value, (3) initiation of dialysis therapy, and (4) death. One patient in the treatment group dropped out because of skin allergy to allopurinol. Serum uric acid levels were significantly decreased in subjects treated with allopurinol, from 9.75 +/- 1.18 mg/dL (0.58 +/- 0.07 mmol/L) to 5.88 +/- 1.01 mg/dL (0.35 +/- 0.06 mmol/L; P < 0.001). There were no significant differences in systolic or diastolic blood pressure at the end of the study comparing the 2 groups. There was a trend toward a lower serum creatinine level in the treatment group compared with controls after 12 months of therapy, although it did not reach statistical significance (P = 0.08). Overall, 4 of 25 patients (16%) in the allopurinol group reached the combined end points of significant deterioration in renal function and dialysis dependence compared with 12 of 26 patients (46.1%) in the control group (P = 0.015). Allopurinol therapy significantly decreases serum uric acid levels in hyperuricemic patients with mild to moderate chronic kidney disease. Its use is safe and helps preserve kidney function during 12 months of therapy compared with controls. Results of this study need to be confirmed with an additional prospective trial involving a larger cohort of patients to determine the long-term efficacy of allopurinol therapy and in specific chronic kidney disease subpopulations.
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              Neutrophil gelatinase-associated lipocalin (NGAL) and progression of chronic kidney disease.

              Chronic kidney disease (CKD) has recently assumed epidemic proportion, becoming a troubling emerging cause of morbidity, especially if it progresses to terminal stage (ESRD). The authors aimed to evaluate whether neutrophil gelatinase-associated lipocalin (NGAL), a novel specific biomarker of acute kidney injury, could predict the progression of CKD. Serum and urinary NGAL levels, together with a series of putative progression factors, were evaluated in a cohort of 96 patients (mean age: 57 +/- 16 years) affected by nonterminal CKD (eGFR > or =15 ml/min/1.73 m(2)) of various etiology. Progression of CKD, assessed as doubling of baseline serum creatinine and/or onset of ESRD, was evaluated during follow-up. At baseline, both serum and urinary NGAL were inversely, independently, and closely related to eGFR. After a median follow-up of 18.5 mo (range 1.01 to 20), 31 patients (32%) reached the composite endpoint. At baseline, these patients were significantly older and showed increased serum creatinine, calcium-phosphate product, C-reactive protein, fibrinogen, daily proteinuria, and NGAL levels, whereas eGFR values were significantly lower. Univariate followed by multivariate Cox proportional hazard regression analysis showed that urinary NGAL and sNGAL predicted CKD progression independently of other potential confounders, including eGFR and age. In patients with CKD, NGAL closely reflects the entity of renal impairment and represents a strong and independent risk marker for progression of CKD.
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                Author and article information

                Contributors
                Journal
                Kidney Med
                Kidney Med
                Kidney Medicine
                Elsevier
                2590-0595
                26 February 2020
                Mar-Apr 2020
                26 February 2020
                : 2
                : 2
                : 155-161
                Affiliations
                [1 ]Division of Renal Diseases and Hypertension, Department of Medicine, University of Colorado Anschutz Medical Campus, Aurora, CO
                [2 ]Division of Nephrology, Department of Internal Medicine, Carver College of Medicine, Iowa City, IA
                [3 ]Institute for Clinical and Translational Science, University of Iowa, Iowa City, IA
                [4 ]Division of Pediatric Nephrology, Dialysis and Transplantation, Stead Family Department of Pediatrics, University of Iowa, Iowa City, IA
                Author notes
                [] Address for Correspondence: Diana Jalal, MD, Carver College of Medicine, Division of Nephrology, 200 Hawkins Dr, E300C GH, Iowa City, IA 52242. diana-jalal@ 123456uiowa.edu
                Article
                S2590-0595(20)30024-8
                10.1016/j.xkme.2019.11.007
                7487946
                © 2020 The Authors

                This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

                Categories
                Original Research

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