Extracellular glutathione inhibits oxygen-induced permeability changes in alveolar epithelial monolayers

Exposure to high fractional inspired oxygen for 24 h increases permeability of the alveolar epithelium, contributing to the clinical manifestations of oxygen toxicity. Utilizing a model of the alveolar epithelium in which isolated rat type II cells form polarized monolayers on polycarbonate filters [transepithelial resistance (R-t) > 1 k Omega .cm(2) by day 4], we evaluated the ability of reduced glutathione (GSH) to ameliorate these changes. On day 4, apical fluid was replaced with culture medium containing 1) no additives, 2) GSH (500 muM), or 3) GSH (500 muM) + glutathione reductase (0.5 U/ml) + nicotinamide adenine dinucleotide phosphate (250 muM). Monolayers were exposed (for 24 h) to room air (control) or 95% O-2, each containing 5% CO2. After 24 h of hyperoxia, R-t for condition 1 decreased by 45% compared with control (P < 0.001). In conditions 2 and 3, R-t did not decrease significantly (P = not significant). Hyperoxia-induced decreases in active ion transport were observed for conditions 1 and 2 (P < 0.05), but not for condition 3 (P = not significant). These findings indicate that extracellular GSH may protect the alveolar epithelium against hyperoxia-induced injury. Addition of glutathione reductase and nicotinamide adenine dinucleotide phosphate may further augment these protective effects of GSH.