Mutagenic effects of TPA-induced clastogenic factor in Chinese hamster cells

Previous work in our laboratory has shown that the clastogenic and SCE-inducing effects of 12-O-tetradecanoylphorbol 12-acetate (TPA) are mediated by secondary products formed by the cell in response to the tumor promoter. A low-molecular-weight clastogenic factor (CF) was isolated from the medium of TPA-treated human leukocytes and caused chromosome aberrations and sister-chromatid exchanges (SCE) in fresh cultures not exposed to TPA itself. In the present study, we show that Chinese hamster fibroblasts (V79 cells) also produce CF when exposed to TPA. CF from V79 cells induced SCE not only in hamster cells, but also in human lymphocytes. Vice versa, CF from human leukocyte cultures induced SCE in hamster cells. It also increased the frequency of 6-thioguanine-resistant mutants in this cell system. All cyto- and geno-toxic effects of TPA-induced CF were prevented if the cells were treated with superoxide dismutase before exposure. The lipophilic CF seems to be derived from arachidonic acid of cell membranes released as a consequence of oxidative damage and subsequently degraded to genotoxic aldehydes in an autoxidative process. CF is formed only under culture conditions with low antioxidant content in culture media and sera. This may explain the discordant results obtained by different laboratories with regard to the genotoxic effects of TPA.