Reactive oxygen species (ROS) are implicated as agents of cellular damage in pulmonary
oxygen toxicity.
Glutathione (GSH) and GSH-dependent
antioxidant enzymes protect against damage by ROS, and recycling of
glutathione disulfide (
GSSG) to GSH by
glutathione reductase (GR) is essential for the optimum functioning of this system. Exposure to
hyperoxia inhibits lung development in newborn animals and humans, and attenuates cell growth in proliferating cell cultures. Considerable evidence supports a role for ROS as growth-altering molecules. Previously, we have observed that gene transfer of GR to mitochondria in H441 cells, using a vector containing a mitochondrial leader sequence (LGR), protected these cells against t-BuOOH-induced cytotoxicity. The present studies tested the hypothesis that gene transfer of LGR would attenuate the
cytostatic effects of
hyperoxia exposure in H441 cells. H441 cells (0.9 x 10(6) cells/plate) transfected with adenovirus containing LGR or the
complementary DNA (
cDNA) for
manganese superoxide dismutase in reverse orientation (DOS) as a control construct, and untransfected cells (CON) were maintained in 21%
oxygen (normoxia) or 95%
oxygen (
hyperoxia) for 48 h, and cell growth was assessed by cell counts and by reduction of the tetrazolium
dye 3-(4,5 dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium
bromide (MTT) to
formazan. Cells maintained in normoxia achieved normal growth (CON, 1.98; DOS, 1.91; LGR, 2.0 x 10(6) cells/plate).
Hyperoxia inhibited cell growth and the reduction of MTT; however, cells transfected with LGR had greater mitochondrial GR activities (CON, 16+/-2; DOS, 19+/-3; LGR, 322+/-18 mU/mg of
protein), sustained more normal growth patterns (CON, 1.25+/-0.12; DOS, 1.24 +/-0.21, LGR, 1.8+/-0.25 x 10(6) cells/plate), and had less inhibition of MTT reduction (CON, 29; DOS, 27; LGR, 16% inhibition, P<0.01) after exposure to
hyperoxia for 48 h than was observed in cells transfected with DOS or in control cells not infected with virus. In addition, resistant cells had higher mitochondrial GSH levels and maintained mitochondrial GSH/
GSSG ratios in
hyperoxia, suggesting that maintaining mitochondrial GSH homeostasis determined critical aspects of cell division in these studies. The mechanisms for sustaining cell growth during
hyperoxia in H441 cells with enhanced mitochondrial GR activities are unknown, but similar effects in infants exposed to supplemental
oxygen could be highly beneficial.