Evaluation of mutagenic effects of hyperbaric oxygen (HBO) in vitro II. Induction of oxidative DNA damage and mutations in the mouse lymphoma assay

We recently showed that treatment of V79 cells with hyperbaric oxygen (HBO) efficiently induced DNA effects in the comet assay and chromosomal damage in the micronucleus test (MNT), but did not lead to gene mutations at the h prt locus. Using the comet assay in conjunction with bacterial formamidopyr imidine DNA glycosylase (FPG protein), we now provide indirect evidence tha t the same treatment leads to the induction of 8-oxoguanine, a premutagenic oxidative DNA base modification in V79 and mouse lymphoma (L5178Y) cells. We also demonstrate that HBO efficiently induces mutations in the mouse lym phoma assay (MLA). Exposure of L5178Y cells to HBO (98% O-2; 3 bar) for 2h caused a clear mutagenic effect in the MLA, which was further enhanced afte r a 3h exposure. As this mutagenic effect was solely due to the strong incr ease of small colony (SC) mutants, we suggest that HBO causes mutations by induction of chromosomal alterations. Molecular characterization of induced SC mutants by loss of heterozygosity (LOH) analysis showed an extensive lo ss of functional tk sequences similar to the pattern found in spontaneous S C mutants. This finding confirmed that the majority of HBO-induced mutants is actually produced by a clastogenic mechanism. The induction of point mut ations as a consequence of induced oxidative DNA base damage seems to be of minor importance. (C) 2000 Elsevier Science B.V. All rights reserved.