Hypoxia increases the susceptibility of pulmonary artery endothelial cells to hydrogen peroxide injury

Abstract

The effect of hypoxia on subsequent susceptibility of porcine pulmonary artery endothelial cells (PAEC) to hydrogen peroxide (H₂O₂) injury was studied. Preexposure of PAEC to hypoxia for 3 or more h significantly increased susceptibility to subsequent H₂O₂ challenge. Analysis of the activities of antioxidant enzymes and xanthine oxidase/dehydrogenase suggested that changes in these enzymes in hypoxic PAEC were not responsible for the increased susceptibility. However, hypoxia resulted in significant time-dependent decreases in total glutathione at 12 h or more. The rate of glutathione regeneration in diethylmaleate-treated PAEC and the rate of uptake of cystine and glycine were significantly lower during hypoxia. Hypoxia also caused depletion of ATP and NADPH levels in PAEC, but these did not occur until well after hypoxia-enhanced susceptibility to H₂O₂ injury was demonstrable. Alterations in glutathione levels and enhanced susceptibility were reversible when hypoxic PAEC were returned to normoxia. These results indicate that hypoxia increased the susceptibility to H₂O₂ injury by decreasing the ability of PAEC to maintain and regenerate cellular glutathione content in response to H₂O₂ challenge.