Evaluation of mutagenic effects of hyperbaric oxygen (HBO) in vitro

Hyperbaric oxygen (HBO) treatment as used therapeutically (i.e., exposure to 100% oxygen at a pressure of 1.5 bar for a total of 60 min) has been shown to induce DNA damage in the alkaline comet assay with leukocytes from test subjects. Under these conditions, HBO did not lead to an induction of gene- and chromosome mutations. Due to known toxic effects, exposure of humans to HBO is limited and possible genetic consequences of HBO could not be completely evaluated in vivo. We thus established an in vitro HBO model, where human blood cells or V79 cells were exposed to hyperbaric oxygen (98% O(2) and 2% CO(2) at a pressure of either 1.5 or 3 bar) for up to 3 hr in a temperature-controlled hyperbaric chamber. Using the comet assay, we found exposure-related genotoxic effects in V79 cells, whole blood, and isolated lymphocytes. V79 cells showed the highest sensitivity toward HBO-induced DNA damage, and the exposure conditions applied to blood in vitro, to induce DNA migration, had to be higher than those used in vivo. We could also show that prolonged HBO treatment clearly increased the frequency of micronuclei in V79 cells, whereas it exerted only a marginal effect on the frequency of hprt mutations. These results demonstrate that HBO treatment of cell cultures is a well-suited model for investigating the biological significance of oxidative stress. The relationship between oxygen-induced DNA lesions and the formation of gene- and chromosome mutations is discussed.