Promutagenic etheno-DNA adducts in multistage mouse skin carcinogenesis: Correlation with lipoxygenase-catalyzed arachidonic acid metabolism

Formation of the lipoxygenase-catalyzed metabolites of arachidonic acid, 8- hydroxyeicosatetraenoic acid (8-HETE) and 12-hydroxyeicosatetraenoic acid ( 12-HETE), and of the exocyclic DNA adducts 1,N-6-ethenodeoxyadenosine (epsi lon dA) and 3,N-4-ethenodeoxycytidine (epsilon dC) was investigated in NMRI mouse skin carcinogenesis induced by 7,12-dimethylbenz[a]anthracene (DMBA) and promoted by 12-O-tetradecanoylphorbol-13-acetate (TPA). In reversible papillomas obtained after 20 weeks of TPA treatment, 15- and 68-fold higher contents of 8-HETE and 12-HETE, respectively, were observed, which were pa ralleled by 12- and 9-fold increased amounts of epsilon dA and epsilon dC, respectively. When compared to the level in vehicle-treated control skin, t hese elevations were statistically significant. In irreversible papillomas harvested 20 weeks after the last TPA treatment, the levels of HETEs and et heno-DNA adducts were found to be slightly reduced, as compared to those in reversible papillomas, but were still increased over control levels in age -matched mice. Comparison of mean group values by simple regression analysi s showed a close positive correlation between HETE and etheno-DNA adduct le vels. Consistent with the miscoding properties of epsilon dA. causing mainl y A --> T transversions, its increased formation in papillomas could thus c ontribute to this type of mutation in codon 61 of cHa-ras, shown to be a ha llmark of DMBA-initiated and TPA-promoted mouse skin carcinogenesis. Althou gh direct evidence that etheno adducts are derived from lipoxygenase-cataly zed metabolites of arachidonic acid is missing, our results implicate DNA d amage by oxidative stress and lipid peroxidation as a cause of genetic inst ability observed at late stages of tumor promotion in mouse skin carcinogen esis.