Antioxidant Enzyme Activity in Alveolar Type II Cells after Exposure of Rats to Hyperoxia

Abstract

The activity of antioxidant enzymes were measured in alveolar type II cells isolated from control and 85% oxygen-exposed rats to determine if type II cells, an oxygen resistant lung cell type had constitutively high enzyme activities and to measure the effect of hyperoxia on these antioxidant enzymes. Type II cells were isolated from lungs of control rats and rats exposed to 85% O₂ for 7 days. In -whole lungs of rats exposed to 85% oxygen there is an increase in activity (per lung or per mg lung DNA) in the antioxidant enzymes CuZn superoxide dismutase, Mn super-oxide dismutase, catalase, glutathione peroxidase and glucose-6-phosphate dehy-drogenase. Oxygen exposure significantly increased (p < 0.05) all type II cell antioxidant enzyme activities when expressed per mg DNA. The protein content of oxygen exposed type II cells increased 25% from (63.9 ± 4.8 μg/10⁶ cells to 79.6 ± 4.2 μg/10⁶ cells, p < 0.05). When type II cell enzyme activities were expressed in U/mg cell protein, only CuZn superoxide dismutase and Mn superoxide dismutase increased in activity following oxygen exposure (by 43% and 28% relative to air exposed lung type II cells, respectively, p < 0.05). This suggested that most lung cell antioxidant enzymes increased in activity following oxidant stress in proportion to increased cell mass. CuZn and Mn superoxide dismutase increased activity to an extent greater than the increase in type II cell protein content after oxygen exposure. Alveolar macrophages lavaged from control and oxygen-exposed rats were also evaluated, and they had no significant change in CuZn and Mn superoxide dismutase activities. Type II cells accounted for 10% and 17% of alveolar cells in control and oxygen treated rats. By knowing the antioxidant enzyme activities in type II cells, the total enzyme activity of whole lung and the number of type II cells in control and oxygen exposed rats from morphometric data, we calculated the percent of whole lung of type II cells and intact lung and biochemical analyses of lung homogenates and isolated cells permit the calculation of the contribution of type II cells to the antioxidant defenses of whole lung, which is composed of many different cell types.