Liposome-mediated augmentation of antioxidant defenses in fetal rat pneumocytes

Cultured pneumocytes, prepared from fetal rat lung, are growth inhibited and have increased lactate dehydrogenase release and prostaglandin synthesis in response to 50 and 95% O2 exposure. The uptake of cationic liposomes by these fetal cells is more rapid and extensive than is the case with cultured adult pneumocytes. Protection of fetal pneumocytes against the cytotoxic effects of 50 or 95% O2 by liposome-entrapped antioxidant enzymes requires a liposome phospholipid concentration of only 1 nmol/cm2, compared with 45 nmol/cm2 for adult cells, which is a cytotoxic phospholipid concentration for the fetal cells. Despite this capacity of low concentrations of liposomes containing superoxide dismutase and catalase to increase endogenous antioxidant enzyme content, and to protect against cell death, such treatment does not attenuate O2-mediated alterations of cell growth or prostaglandin release. Inhibition of pneumocyte DNA synthesis, by elevated O2 concentrations, cannot be attributed to an autocrine effect of enhanced prostaglandin synthesis, because the addition of 50 microM ibuprofen to inhibit prostaglandin synthesis does not prevent O2-mediated effects on DNA synthesis.