HEME OXYGENASE EXPRESSION IN SWISS 3T3 CELLS FOLLOWING EXPOSURE TO AQUEOUS CIGARETTE-SMOKE FRACTIONS

A dose-dependent and transiently elevated expression of a cytoplasmic 32 kDa protein was observed in Swiss albino 3T3 fibroblasts exposed to mainstream cigarette smoke (CS) trapped in phosphate-buffered saline solutions (smoke-bubbled PBS). The protein was identified as heme oxygenase (HO) (heme, hydrogen donor:oxygen oxidoreductase, EC 1.14.99.3) by Western blotting using an anti-rodent HO-specific antibody. Kinetic investigations revealed that HO protein and its mRNA were detectable in smoke-bubbled PBS-treated cells between 1 and 24 h after exposure to 0.03 puffs (similar to 1 cm(3)) CS per ml medium. As a result of transcriptional activation, a nearly 50-fold increase in the amount of HO mRNA was determined after 8 h exposure compared to control levels. Since literature data indicate that there is a link between glutathione depletion and HO expression, the same was assumed for cells exposed to smoke-bubbled PBS, as a decrease of more than 60% in glutathione levels was observed after the exposure. This was further supported by the observation that no elevated amounts of HO mRNA appeared in smoke-bubbled PBS-treated cells when cysteine was exogenously added. However, although these effects may be attributable to the formation of hydroxyl radicals (which have been shown to induce HO and to deplete glutathione levels and which appear in aqueous smoke-containing solutions via the iron-catalysed Fenton reaction) neither catalase nor the iron cation chelating agent o-phenanthroline were able to suppress or even to reduce HO expression in smoke-bubbled PBS-treated cells. On the contrary, at comparable concentrations both compounds were found to be potent inhibitors of smoke-dependent DNA strand breaks. Hence, reactive species other than Fenton reaction-derived hydroxyl radicals are responsible for the effects observed in the present study.