Novel Biomarkers for Early Prediction of Nephrotoxicant-induced Renal Injury

Abstract

The kidney is one of the main targets for toxicity induced by xenobiotics. Sensitive detection of early impairment is critical to assess chemical-associated renal toxicity. The aim of this study was to identify potential nephrotoxic biomarkers in rat kidney tissues after exposure to mercury (Hg), a representative nephro-toxicant, and to evaluate these new biomarkers employing in vivo and in vitro systems. Mercuric chloride was administered orally to Sprague-Dawley rats for two weeks. Proteomic analysis revealed that aldo-keto reductase (AKR7A1) and glutathione S-transferase pi (GSTP1) were significantly elevated in kidney after mercury exposure. While the levels of conventional nephrotoxic clinical markers including blood urea nitrogen and serum creatinine were not elevated, the mRNA and protein levels of AKR7A1 and GSTP1 were increased in mercury dose-dependent manner. The increase of AKR7A1 and GSTP1 were also observed in rat kidneys after an extended exposure for six weeks to low-dose mercury. In addition, several extra proteins increased in same condition were observed. In particular, ATP5 and Ef2 showed significantly different of mRNA expression levels compared to the control group and showed another possibility as a novel biomarker for long-term exposure to low-dose mercury. In order to evaluate the potential of the candidates as a diagnostic marker, urine from cisplatin-exposed rats was collected, and excreted level of protein was confirmed by Western blotting. Unfortunately, AKR7A1 was not detected in urine, and excretion level for GSTP1 shown irregularly. On the other hand, excretion of aconitase 2 (ACO2) and vimentin (VIM), identified protein in our proteomics analysis, was elevated by cisplatin in a time-dependent manner. In in vitro rat kidney proximal tubular cells, changes in AKR7A1 and GSTP1 levels correlated well with the extent of cytotoxicity induced by mercury, cadmium or cisplatin. In summary, AKR7A1 and GSTP1 were identified as new candidates for mercury-induced nephrotoxicity, suggesting that these biomarkers have potential for evaluating or predicting nephrotoxicity. In addition, ACO2 and VIM, released into the urine by cisplatin exposure, are considered to be have potential as an early diagnostic biomarker for nephrotoxicity induced by xenobiotic.