ANTIOXIDANT ENZYME REGULATION AND RESISTANCE TO OXIDANTS OF HUMAN BRONCHIAL EPITHELIAL-CELLS CULTURED UNDER HYPEROXIC CONDITIONS

Bronchial epithelial cells are the first cells to encounter high conce ntrations of inspired oxygen, and their damage is a typical feature in many airway diseases. The direct effect of oxygen on the expression o f the main antioxidant enzymes (AOEs) in human bronchial epithelial ce lls is unknown. We investigated the messenger RNA (mRNA) levels of man ganese superoxide dismutase (MnSOD), copper-zinc superoxide dismutase (CuZnSOD), catalase (CAT), and glutathione peroxidase (GPx), as well a s the specific activities of MnSOD, CuZnSOD, CAT, GPx, and glutathione reductase, in BEAS-2B bronchial epithelial cells exposed to hyperoxia (95% O2, 5% CO2) for 16 to 48 h. We also assessed the resistance of c ells preexposed to hyperoxia to subsequent oxidant stress. Significant cell injury was observed after 72 h exposure to hyperoxia; release of lactate dehydrogenase (LDH) from control cells and cells exposed to h yperoxia for 72 h was 7.0 +/- 1.0% and 22.0 +/- 1.0%, respectively. Hy peroxia for 16 h, 24 h, or 48 h had no effect on the mRNA levels or sp ecific activities of any of these enzymes. Despite their unchanged AOE levels, cells exposed to hyperoxia for 48 h showed increased resistan ce to H2O2 and menadione. Total glutathione content of the cells incre ased by 55% and 58% after 24 h and 38 h, respectively, compared with n ormoxic controls. However, glutathione depletion with buthionine sulfo ximine (BSO) did not diminish the oxidant resistance of hyperoxia-expo sed cells. We conclude that AOEs in human bronchial epithelial cells a re not directly upregulated by high oxygen tension, and that increases in AOE-specific activities or glutathione are not necessary for the d evelopment of increased oxidant resistance in these cells.