Heme oxygenase-mediated resistance to oxygen toxicity in hamster fibroblasts

The role of heme oxygenase (HO)-1 was evaluated in the oxygen-resistant hamster fibroblast cell line, O(2)R95, which moderately overexpress HO when compared with the parental cell line, HA-1. To suppress HO-1 expression, O(2)R95 were transfected with HO-1 antisense oligonucleotide or treated with tin-mesoporphyrin (SnMP), To increase HO-1 expression, cells were transfected with HO-1 cDNA in a pRC/cytomegalovirus (CMV) vector, All cells were challenged with a 48-h exposure to 95% O-2 (hyperoxia). When HO activity was suppressed, O(2)R95 cells had significantly decreased Cell viability, increased susceptibility to lipid peroxidation, and increased protein oxidation in hyperoxia. In contrast, further overexpression of HO-1 did not improve resistance to oxygen toxicity. Antisense-transfected cells and SnMP-treated cells with lowered HO activity showed increased levels of cellular heme compared with controls, In the HO-1 cDNA-transfected O(2)R95 cells, cellular heme was lowered compared with controls; however, cellular redox active iron levels were increased, We conclude that HO mediates cytoprotection to oxygen toxicity within a narrow range of expression, We speculate that this protective effect may be mediated in part through increased metabolism of the pro-oxidant heme but that higher levels of HO activity obviate protection by increased redox active iron release.