Antioxidant Enzyme Regulation and Resistance to Oxidants of Human Bronchial Epithelial Cells Cultured under Hyperoxic Conditions

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Abstract
Bronchial epithelial cells are the first cells to encounter high concentrations of inspired oxygen, and their damage is a typical feature in many airway diseases. The direct effect of oxygen on the expression of the main antioxidant enzymes (AOEs) in human bronchial epithelial cells is unknown. We investigated the messenger RNA (mRNA) levels of manganese superoxide dismutase (MnSOD), copper-zinc superoxide dismutase (CuZnSOD), catalase (CAT), and glutathione peroxidase (GPx), as well as 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 cells 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 hyperoxia for 72 h was 7.0 +/- 1.0% and 22.0 +/- 1.0%, respectively. Hyperoxia for 16 h, 24 h, or 48 h had no effect on the mRNA levels or specific activities of any of these enzymes. Despite their unchanged AOE levels, cells exposed to hyperoxia for 48 h showed increased resistance to H2O2 and menadione. Total glutathione content of the cells increased by 55% and 58% after 24 h and 48 h, respectively, compared with normoxic controls. However, glutathione depletion with buthionine sulfoximine (BSO) did not diminish the oxidant resistance of hyperoxia-exposed cells. We conclude that AOEs in human bronchial epithelial cells are not directly upregulated by high oxygen tension, and that increases in AOE-specific activities or glutathione are not necessary for the development of increased oxidant resistance in these cells.

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