A Critical Role for Thiol, But Not ATP, Depletion in 95% O2-Mediated Injury of Preterm Pneumocytes in Vitro

Abstract

Prolonged exposure to elevated partial pressures of oxygen results in lung cell toxicity, both in vivo and in vitro, due to the excess production and target molecule reactions of reactive oxygen species. Events primarily responsible for cell death vary with the type of oxidant injury and with cell type. Because of the susceptibility of the premature lung to oxygen toxicity, and the critical barrier function of the epithelium, we have investigated the role of two potentially lethal consequences of O2 exposure in premature distal lung epithelial cells in vitro. A 48-h exposure of distal fetal rat lung epithelial cells to 95% O2 caused cytotoxicity, which was associated with DNA injury and depletion of both cellular protein and nonprotein reduced sulfhydryls. The observed DNA injury preceded other markers of cell injury and was not sufficient to either activate the chromosomal enzyme poly(ADP-ribose) polymerase or cause secondary ATP depletion. Buthionine sulfoxamine-induced depletion of nonprotein reduced sulfhydryls increased the sensitivity of cells to subsequent O2-mediated cytotoxicity. Addition of the glutathione precursor N-acetylcysteine to the culture medium maintained cellular protein and nonprotein reduced sulfhydryl concentrations and prevented O2-mediated cytotoxicity. We conclude that loss of protein and nonprotein reduced sulfhydryls, but not DNA injury, is causally related to the toxic effects of elevated O2 on premature distal lung epithelial cells.