Protection of HLE B-3 cells against hydrogen peroxide- and naphthalene-induced lipid peroxidation and apoptosis by transfection with hGSTA1 and hGSTA2

PURPOSE. To investigate the physiological role of two major α-class glutathione S-transferases (GSTs), hGSTAI-1 and hGSTA2-2 in protection against oxidative stress and lipid peroxidation (LPO) in human lens epithelial (HLE B-3) cells. METHODS. Total GSTs were purified from HLE B-3 cells by glutathione (GSH)-affinity chromatography and characterized by Western blot analysis, isoelectric focusing, and kinetic studies. The relative contributions of the α-class GSTs and the Se-dependent glutathione peroxidase (GPx)-1 in GSH-dependent reduction of phospholipid hydroperoxide (PL-OOH) were quantitated through immunoprecipitation studies using separately the specific polyclonal antibodies against human α-class GSTs and GPx-1. HLE B-3 cell membranes were prepared, peroxidized, and used to examine whether hGSTAI-1 and hGSTA2-2 catalyzes the reduction of membrane PL-OOH in situ using the microiodometric and spectrophotometric assays. The protective effects of the α-class GSTs against H₂O₂- and naphthalene-induced LPO and apoptosis were examined by transfecting HLE B-3 cells with cDNAs of hGSTA1 and hGSTA2. RESULTS. HLE B-3 cells expressed only the α and π class GSTs. The Michaelis-Menten constant (k_m) and turnover number (k_cat) of purified total GSTs toward phosphatidylcholine hydroperoxide (PC-OOH) were found to be 30 ± 4 μM and 1.95 ± 0.26 seconds, respectively. The α-class GSTs accounted for approximately 65% of the total GPx activity of HLE B-3 cells toward PC-OOH. Our results demonstrate for the first time that hGSTAI-1 and hGSTA2-2 effectively catalyzed GSH-dependent reduction of membrane PL-OOH in situ in HLE B-3 cells. Transfection with hGSTA1 or hGSTA2 protected these cells from H₂O₂- and naphthalene-induced LPO and attenuated H₂O₂- and naphthalene-induced apoptosis through inhibiting caspase 3 activation. CONCLUSIONS. These results demonstrate that the α-class GSTs hGSTAI-1 and hGSTA2-2 play a major role as antioxidant enzymes and are the main determinants of the levels of LPO caused by oxidative stress in human lens epithelial cells.