Formation of DNA adducts by microsomal and peroxidase activation of p-cresol: role of quinone methide in DNA adduct formation

We have investigated the activation of p-cresol to form DNA adducts using h orseradish peroxidase, rat liver microsomes and MnO2, In vitro activation o f p-cresol with horseradish peroxidase produced six DNA adducts with a rela tive adduct level of 8.03 +/- 0.43 x 10(-7). The formation of DNA adducts b y oxidation of p-cresol with horseradish peroxidase was inhibited 65 and 95 % by the addition of either 250 or 500 muM ascorbic acid to the incubation, Activation of p-cresol with phenobarbital-induced rat liver microsomes wit h NADPH as the cofactor; resulted in the formation of a single DNA adduct w ith a relative adduct level of 0.28 +/- 0.08 x 10(-7). Similar incubations of p-cresol with microsomes and cumene hydroperoxide yielded three DNA addu cts with a relative adduct level of 0.35 +/- 0.03 x 10(-7). p-Cresol was ox idized with MnO2 to a quinone methide. Reaction of p-cresol (QM) with DNA p roduced five major adducts and a relative adduct level of 20.38 +/- 1.16 x 10(-7). DNA adducts 1, 2 and 3 formed by activation of p-cresol with either horseradish peroxidase or microsomes, are the same as that produced by p-c resol (QM). This observation suggests that p-cresol is activated to a quino ne methide intermediate by these activation systems. Incubation of deoxygua nosine-3 ' -phosphate with p-cresol (QM) resulted in a adduct pattern simil ar to that observed with DNA; suggesting that guanine is the principal site for modification. Taken together these results demonstrate that oxidation of P-cresol to the quinone methide intermediate results in the formation of DNA adducts. We propose that the DNA adducts formed by p-cresol may be use d as molecular biomarkers of occupational exposure to toluene. (C) 2001 Els evier Science Ireland Ltd. All rights reserved.