Genotoxic effects of a complex mixture adsorbed onto ambient air particles on human cells in vitro; the effects of Vitamins E and C.

Genotoxicity of complex mixtures of organic compounds adsorbed onto ambient air particles (extractable organic matter, EOM) collected in Teplice (Czech Republic) as well as genotoxicity of the indirectly acting carcinogens benzo[a]pyrene (B[a]P) and 5,9-dimethyl-7H-dibenzo[c,g]carbazole (5,9-diMeDBC) was studied in human HepG2 and Caco-2 cells cultured in vitro. The level of DNA breaks was detected by conventional single-cell gel electrophoresis (alkaline comet assay). The level of DNA breaks+oxidative DNA lesions was assessed by modified single-cell gel electrophoresis. The indirectly acting chemical carcinogens studied were able to induce DNA breaks as well as oxidative DNA damage in both cell lines, but stronger DNA-damaging effects were observed in HepG2 cells, which contain a higher level of metabolic enzymes. Treatment of cells with the complex mixtures showed a dose-dependent increase of DNA breaks in HepG2 cells as well as in Caco-2 cells, with seasonal differences. Winter samples of EOM from Teplice (TP-W) were more effective in inducing DNA damage than summer samples (TP-S). Both mixtures caused significant oxidative DNA damage in HepG2 cells. The effect was less evident in cells treated with higher concentrations of TP-W, since the comet assay is limited by saturation at a higher level of DNA damage. Possible reduction of B[a]P-, 5,9-diMeDBC- or EOM-induced DNA damage by Vitamins E and C was evaluated in HepG2 cells only. Pre-treatment of these cells with either one of the vitamins considerably reduced the levels of both DNA breaks and oxidative DNA lesions induced by all compounds investigated.