Effect of Hyperoxia on Antioxidants in Neonatal Rat Type II Cells in Vitro and in Vivo

Abstract

ABSTRACT. Relative resistance to oxygen toxicity in newborn animals (compared to adults) has been associated with increased antioxidant enzymes and glutathione in lung homogenate. The cell type(s) involved in this increase is unknown. We investigated the effect of hyperoxia in vitro and in vivo on the following antioxidants (superoxide dismutase, catalase, glutathione peroxidase, glutathione reductase, glucose-6-phosphate dehydrogenase, and glutathione) in alveolar type I1 cells from neonatal rats. Type I1 cells were exposed to 95% oxygen or air for 48 h in vitro. When expressed per pg DNA, all the antioxidants except catalase increased during in vitro incubation; only glucose-6-phosphate dehydrogenase and glutathione increased when expressed per mg protein. None of the antioxidants was higher in oxygen-exposed cells than in airexposed cells. Neonatal rats were exposed to 100% oxygen or air in vivo for 4 d before determination of antioxidants in lung homogenate supernatant and alveolar type I1 cells. Catalase, glutathione peroxidase, and glutathione reductase were higher but glucose-6-phosphate dehydrogenase and glutathione were lower in type I1 cells than in lung homogenate from control animals. Alveolar type I1 cell gluco~e-6-phosphate dehydrogenase and glutathione were increased but catalase and glutathione reductase were decreased by exposure to hyieroxia. We conclude that the oxygen-induced increase in whole lung antioxidants is not explained by alveolar type I1 cell hypertrophy or increased antioxidants within type I1 cells during hyperoxia. Oxygen-induced lung injury is thought to result from toxic effects of partially reduced species of molecular oxygen (I), commonly referred to as oxygen free radicals. Production of oxygen free radicals is increased during exposure to hyperoxia, and antioxidant enzymes are believed to protect against cellular Received February 10, 1989; accepted June 14, 1989 damage by free radicals. Neonatal animals of some species (rats, rabbits, and mice) are relatively resistant to toxic effects of hyperoxia when compared to adult animals of the same species (2). This relative resistance is manifested by longer survival in 100% oxygen and is associated with increased activity of lung antioxidant enzymes (2). This natural protection from oxygeninduced lung injury has been attributed to increased antioxidant enzyme activities despite the fact that the increases are modest (20-40%) and result in lower enzyme activity per g of lung tissue than the basal activities of the more susceptible adult animals (3). Protection of adult rats from pulmonary oxygen toxicity can be induced by prior exposure to nonlethal hyperoxia (4) or endotoxin (5). These forms of protection have also been associated with increased antioxidant enzyme activity in lung tissue. Although newborn lambs are similarly protected by endotoxin administration, this protection is not associated with increased antioxidants in lung tissue (6). Thus it remains unclear that increased antioxidants mediate enhanced protection from o...

The Effect of Hyperoxic Exposure on Antioxidant Enzyme Activities of Alveolar Type II Cells in Neonatal and Adult Rats

“…In neonatal type I1 cells, our findings of a marked increase in SOD in neonatal type I1 cells after hyperoxic exposure differ from those of Kennedy et al (8), who reported decreases in CAT and no changes in SOD and GPX activities in neonatal type I1 cells after 4 d of exposure to >95% 02. Methodologic differences that could account for these results include oxygen concentration, duration of exposure, and method of type I1 cell isolation (trypsin versus elastase).…”

“…However, this has not been reported to occur with elastase in regard to the antioxidant enzymes (6). The decrease in cell yield from oxygen-exposed animals noted in the present study has been previously reported (6)(7)(8) and attributed to difficulties of protease digestion of edematous lung. However, isolation of a selected cell population after hyperoxic exposure cannot be totally excluded.…”

“…In the neonate, our findings of no marked differences in antioxidant enzyme (8). These data suggest that the neonatal type I1 cell does not offer protection to the lung from hyperoxia because of intrinsically high baseline antioxidant enzyme activities.…”

“…Previous investigations of adult type I1 cells have produced conflicting data on whether antioxidant enzyme activities are higher in type I1 cells than in whole lung and whether antioxidant enzyme activities in type I1 cells increase after hyperoxia (6,7). One previous investigation of neonatal type I1 cells has suggested that antioxidant enzyme activities do not increase in this cell type after hyperoxia (8). However, because the type I1 cell is relatively resistant to oxygen damage compared with other cell types and appears to be important for proliferation and repair of the pulmonary epithelial lining after damage (5, 9), we hypothesized that this cell might play a role in neonatal tolerance.…”

Substrate Utilization for Phosphatidylcholine Synthesis by Type II Pneumocytes of Neonatal Rats

“…The modified procedure yielded 1-2 x lo6 cells per pup with a purity of 83-87% compared with a range of 1-3 x 1 O6 cells per pup and purity of 85-95 % previously reported by others for 1-wk-old rats (2 1, 22). The reasons for the slightly lower purity observed in the present study are not clear but may be related to a number of factors such as the original number of cells plated, available surface area of culture flask, adhesive properties of the flask, age of animals, concentrations of trypsin used for cell isolation, and identification of type I1 cells on the basis of the appearance of lamellar body, which is dependent on the maturity of the cells (22)(23)(24). Nevertheless, using the modified procedure it was possible to process four to eight rat pups in a single isolation to provide sufficient numbers of cells for subsequent metabolic studies.…”