Induction of catalase, alpha, and microsomal glutathione S-transferase in CYP2E1 overexpressing HepG2 cells and protection against short-term oxidative stress

Induction of cytochrome P450 2E1 (CYP2E1) and the formation of reactive oxy gen species (ROS) appear to be one of the mechanisms by which ethanol is he patotoxic. Glutathione peroxidase and catalase detoxify H2O2 Glutathione S- transferases (GST) provide protection from membrane lipid peroxidation, hav e GSH peroxidase activity, and reduce lipid hydroperoxides. Previous studie s showed an up-regulation of GSH synthesis in CYP2E1 expressing HepG2 cells ; this finding prompted an evaluation of the levels of other antioxidant ex zymes. In CYP2E1 expressing cells, the alpha and microsomal GST messenger R NA (mRNA) are increased by 4- and 2-fold, respectively, and catalase protei n and mRNA is increased by 2-fold. The increase in alpha and microsomal GST mRNA correlates with increased total enzymatic activity and is caused by i ncreased transcription as evidenced by run-on transcription assays. In HepG 2 cells transfected to express a different cytochrome P450, CYP3A4, there w as an increase in alpha GST. However, in contrast to the CYP2E1 expressing cells, neither microsomal GST nor catalase were induced, suggesting some sp ecificity for CYP2E1. In agreement with an increased antioxidant defense sy stem, the sensitivity to added prooxidants such as menadione, antimycin A, H2O2, and 4-hydroxynonenal was lower in the CYP2E1 expressing cells as comp ared with control cells. In conclusion, overexpression of CYP2E1 in HepG2 c ells, besides elevating total GSH levels, also induces expression of catala se and alpha and microsomal GST. This induction confers resistance to the c ells against several prooxidants and is suggested to reflect an adaptive re sponse by the cells against CYP2E1-mediated oxidative stress.