Biological significance of DNA damage induced by hyperbaric oxygen

Hyperbaric oxygen (HBO) treatment as used therapeutically has been shown to induce DNA damage in the alkaline comet assay with leukocytes from test subjects. Using formamidopyrimidine-DNA glycosylase, a DNA repair enzyme which specifically nicks DNA at sites of 8-oxoguanines and formamidopyrimidines, we have detected enhanced DNA migration, indicating significant oxidative base damage, after HBO treatment. Increased DNA damage was seen immediately at the end of treatment, while 24 h later no effect was found. We now show that HBO-induced DNA strand breaks and oxidative base modifications are rapidly repaired, leading to a reduction in induced DNA effects of > 50% during the first hour. A similar decrease was found in blood taken immediately after exposure and post-incubated for 2 h at 37 degrees C in vitro and in blood taken and analysed 2 h after exposure, suggesting similar repair activities in vitro and in vivo. When the same blood samples showing increased DNA damage after HBO in the comet assay were analysed in the micronucleus test, no indications of induced chromosomal breakage in cultivated leukocytes could be obtained. The results suggest that the HBO-induced DNA effects observed with the comet assay are efficiently repaired and are not manifested as detectable chromosome damage.