Oxidative damage induced by carcinogenic polycyclic aromatic hydrocarbons and organic extracts from urban air particulate matter

We investigated the role of oxidative damage in the mechanism of action of selected individual carcinogenic PAHs (c-PAHs: benzo[a]pyrene, B[a]P; dibenzo[a,l]pyrene, DB[a,l]P), an artificial mixture of c-PAHs (c-PAHs mix) and extractable organic matter (EOM) from urban air particulate matter (PM). Two cell lines (human hepatoma cells, HepG2; human diploid lung fibroblasts, HEL) were treated for 24 and 48 h with various concentrations of compounds and mixtures. A panel of oxidative stress markers included 8-oxodeoxyguanosine (8-oxodG), 15-F2t-isoprostane (15-F2t-IsoP) and protein carbonyl groups. The response of the cell lines to the test compounds was substantially different. In HepG2 cells, oxidative damage to DNA was generally not induced by individual c-PAHs and the c-PAHs mix, but EOM increased 8-oxodG levels in these cells. In HEL cells, none of the compounds induced oxidative DNA damage. Lipid peroxidation, measured as the level of 15-F2t-IsoP, was induced by c-PAHs in HepG2 cells only after 48 h of incubation, while the effect of EOM was detected already after 24 h. In HEL cells, individual c-PAHs and the c-PAH mix generally decreased 15-F2t-IsoP levels. This effect was even stronger for EOM treatment. Protein oxidation, assessed as carbonyl levels in cell lysates, was not induced after 24 h of treatment with any compound in either cell line. Individual c-PAHs and the c-PAH mix generally induced protein oxidation in both cell lines after 48 h treatment, with the exception of DB[a,l]P in HepG2 cells. Oxidative damage to proteins caused by EOM was generally increased in HepG2 cells after 48 h of incubation, while in HEL cells the effect was observed for only one dose of EOM. In summary, our results demonstrate the ability of EOM to induce oxidative damage to DNA and lipids after 24 h of treatment, and to proteins after 48 h, in HepG2 cells, while the effect of c-PAHs was substantially less. The induction of oxidative stress by c-PAHs and EOM in HEL cells was weak.