Oxidation of eugenol to form DNA adducts and 8-hydroxy-2'-deoxyguanosine: role of quinone methide derivative in DNA adduct formation.

We have investigated the activation of eugenol to form DNA adducts and oxidative base damage. Treatment of myeloperoxidase containing HL-60 cells with eugenol, produced a dose-dependent formation of three DNA adducts as detected with P1-enhanced 32P-post-labeling. Incubation of HL-60 cells with the combination of 100 microM eugenol and 100 microM H2O2 potentiated the levels of DNA adduct in HL-60 cells by 14-fold, which suggests peroxidase activation in adduct formation. In vitro activation of eugenol with either horseradish peroxidase or myeloperoxidase and H2O2 produced three DNA adducts that were inhibited by the addition of either ascorbic acid or glutathione, by 66 and 90%, respectively. The DNA adducts formed in HL-60 cells treated with eugenol were the same as those formed by in vitro peroxidase activation. In addition to adduct formation, peroxidase activation of eugenol produced a 2- to 3-fold increase in the level of oxidative base damage. Eugenol quinone methide was prepared by Ag(I)oxide oxidation of eugenol. Peroxidase activation of eugenol gave a product that had the same UV spectrum as eugenol quinone methide, which suggests that it was one of the products. Reaction of eugenol quinone methide with either DNA or deoxyguanosine-3'-phosphate produced two principal adducts (2 and 4). When DNA adduct 2 formed by incubation of eugenol quinone methide with deoxyguanosine-3'-phosphate was compared with DNA 2 adduct formed in HL-60 cells treated with eugenol results demonstrated that they were the same. This suggests that eugenol quinone methide is one of the reactive intermediates leading to DNA adduct formation in cells. Activation of eugenol with 10 microM copper sulfate resulted in the production of one principal (2) and several minor adducts. DNA adduct 2 formed by activation of eugenol with copper sulfate was the same as DNA adduct 2 formed by either peroxidase activation of eugenol or by reactions with eugenol quinone methide, which indicates that the reactive intermediates generated by these activation systems were similar. Copper sulfate produced a 95-fold increase in the level of oxidative base damage, which was significantly inhibited by the addition of either bathocuproinedisulphonic acid or catalase. The formation of oxidative base damage was consistent with a Fenton reaction mechanism. Our results demonstrate that eugenol can be activated to form both DNA adducts and oxidative base damage. We propose that the formation of this DNA damage may contribute to the observed toxic properties of eugenol.