Glutathione deficiency alters the vitamin D-metabolizing enzymes CYP27B1 and CYP24A1 in human renal proximal tubule epithelial cells and kidney of HFD-fed mice

Chronic kidney disease (CKD) is a worldwide public health problem with an estimated prevalence of 8.2%. This study reports glutathione deficiency, excess oxidative stress, and altered vitamin D metabolism in the kidney of mice fed a high-fat diet (HFD). The levels of GCLC and GCLM gene expression were significantly downregulated and the protein carbonylation level, a hallmark of oxidative damage, was significantly increased in the kidney of HFD-fed mice. While the levels of VD-regulatory genes 1-alpha-hydroxylase (CYP27B1), VDR, and RXR alpha were significantly downregulated in the kidney of mice fed a HFD, those of 24-hydroxylase (CYP24A1) were significantly elevated. In vitro, GSH deficiency per se causes excess oxidative damage (protein carbonylation), and significantly decreases the levels of VD-regulatory genes (CYP27B1, VDR, and RXR alpha), but increases levels of CYP24A1 in human renal proximal tubule epithelial cells (RPTEC), similar to findings in the kidney of HFD-fed diabetic mice. L-cysteine supplementation restores GSH and prevents oxidative damage in RPTEC. These studies suggest a potential role of GSH precursor in reducing excess oxidative stress and renal injury that commonly accompanies obesity/diabetes.