MO622IMPAIRED PROTEIN-BOUND UREMIC TOXIN EXCRETION SUGGESTS TUBULAR DYSFUNCTION IN DIABETIC NEPHROPATHY

Abstract

Abstract Background and Aims Kidney tubular damage is an important prognostic determinant in diabetic nephropathy (DN) (1). Proximal tubular secretion is a vital homeostatic function that is responsible for excretion of waste, such as protein bound uremic toxins (PBUTs) that are minimally eliminated via glomerular filtration. PBUTs are potentially harmful waste products of endogenous metabolism that are efficiently excreted by tubular secretion via organic anion transporters (OATs). Currently available diagnostic methods cannot accurately detect tubular dysfunction. We hypothesize that renal PBUT clearance may be a sensitive tubular function marker. Here, we measured PBUTs in long-term streptozotocin (STZ)-induced murine diabetic nephropathy (DN), which was characterized by severe tubular atrophy and interstitial fibrosis (2). Method Diabetes mellitus was induced in C57Bl/6 mice by a single intraperitoneal injection of 200 mg/kg STZ which resulted in substantial kidney damage after 6 months evaluated by histopathology and conventional markers (2). Indoxyl sulfate (IS), hippuric acid (HA), kynurenic acid (KA), kynurenine (Kyn), p-cresol glucuronide (pCG), p-cresol sulfate (pCS) and indole acetic acid (IAA) were measured in plasma and urine after 6 and 8 months by LC-MS/MS. Results Among the PBUTs with the highest OAT affinity, viz. IS, HA and KA, plasma concentrations were 2.2-, 2.3- and 1.5-fold higher (p=0.005, 0.0006, 0.03; Fig 1A-C) after 6 months and 1.9-, 2.1- and 2-fold higher (p=0.008, 0.0005, 0.001; Fig 2A-C) after 8 in DN, and urinary excretions (normalized for plasma concentrations) were 3.3-, 2.3- and 3.0-fold lower (p=0.012, 0.16, 0.03; Fig 1G-I) after 6 months and 2.5-, 1.6-, 2.3-fold lower (p=0.028, 0.046, 0.0005; Fig 2G-I) after 8 months in DN. Other PBUTS, viz. IAA, Kyn, pCS and pCG, were not significantly affected. Conclusion Our findings suggest that OAT function is compromised in murine long-term DN. Renal clearance of IS, HA and KA may be a marker of tubular function in DN. Future studies should focus on correlations with histology and validation in other species.