HEME OXYGENASE-MEDIATED RESISTANCE TO OXYGEN-TOXICITY IN HAMSTER FIBROBLASTS

The role of heme oxygenase (HO)-1 was evaluated in the oxygen-resistan t hamster fibroblast cell line, O(2)R95, which moderately overexpress HO when compared with the parental cell line, HA-1. To suppress HO-1 e xpression, O(2)R95 were transfected with HO-1 antisense oligonucleotid e or treated with tin-mesoporphyrin (SnMP), To increase HO-1 expressio n, 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 (h yperoxia). When HO activity was suppressed, O(2)R95 cells had signific antly decreased Cell viability, increased susceptibility to lipid pero xidation, and increased protein oxidation in hyperoxia. In contrast, f urther overexpression of HO-1 did not improve resistance to oxygen tox icity. Antisense-transfected cells and SnMP-treated cells with lowered HO activity showed increased levels of cellular heme compared with co ntrols, In the HO-1 cDNA-transfected O(2)R95 cells, cellular heme was lowered compared with controls; however, cellular redox active iron le vels were increased, We conclude that HO mediates cytoprotection to ox ygen toxicity within a narrow range of expression, We speculate that t his protective effect may be mediated in part through increased metabo lism of the pro-oxidant heme but that higher levels of HO activity obv iate protection by increased redox active iron release.