Comparative impacts of glutathione peroxidase-1 gene knockout on oxidative stress induced by reactive oxygen and nitrogen species in mouse hepatocytes

Abstract

Selenium-dependent glutathione peroxidase-1 (GPX1) protects against reactive-oxygen-species (ROS)-induced oxidative stress in vivo, but its role in coping with reactive nitrogen species (RNS) is unclear. Our objective was to compare the protection of GPX1 against cytotoxicity of superoxide generator diquat (DQ), NO donor S-nitroso-N-acetyl-penicillamine (SNAP) and peroxynitrite generator 3-morpholinosydnonimine (SIN-1). Primary hepatocytes were isolated from GPX1-knockout (KO) and wild-type (WT) mice and cultured in complete Williams's medium E with various levels of these agents alone or in combination for up to 12h. While the KO cells were more susceptible to cell death, DNA fragmentation and protein carbonyl formation induced by 0.25–1mM DQ, these cells were as tolerant as the WT cells to cytotoxicity of 0.1–1mM SNAP or 0.5–2mM SIN-1. Treating cells with SNAP (0.1 or 0.25mM) in addition to DQ produced synergistic cytotoxicity that minimized differences in apoptotic cell death and oxidative injuries between the KO and WT cells. Less protein nitrotyrosine was induced by 0.05–0.5mM DQ+0.25mM SNAP in the KO than in the WT cells. Total GPX activity in the WT cells was reduced by 65 and 25% by 0.5mM DQ+0.1mM SNAP and 0.5mM DQ, respectively. Decreases in Cu,Zn-superoxide dismutase (SOD) activity and increases in Mn-SOD activity in response to DQ or DQ+SNAP were greater in the KO cells than in the WT cells. In conclusion, GPX1 was more effective in protecting hepatocytes against oxidative injuries mediated by ROS alone than by ROS and RNS together. Knockout of GPX1 did not enhance cell susceptibility to RNS-associated cytotoxicity. Instead, it attenuated protein nitration induced by DQ+SNAP.