title: Formation of DNA adducts by microsomal and peroxidase activation of p-cresol: role of quinone methide in DNA adduct formation.
abstract: We have investigated the activation of p-cresol to form DNA adducts using horseradish peroxidase, rat liver microsomes and MnO(2). In vitro activation of p-cresol with horseradish peroxidase produced six DNA adducts with a relative adduct level of 8.03+/-0.43 x 10(-7). The formation of DNA adducts by oxidation of p-cresol with horseradish peroxidase was inhibited 65 and 95% by the addition of either 250 or 500 microM ascorbic acid to the incubation. Activation of p-cresol with phenobarbital-induced rat liver microsomes with NADPH as the cofactor; resulted in the formation of a single DNA adduct with 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 adducts with a relative adduct level of 0.35+/-0.03 x 10(-7). p-Cresol was oxidized with MnO(2) to a quinone methide. Reaction of p-cresol (QM) with DNA produced 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-cresol (QM). This observation suggests that p-cresol is activated to a quinone methide intermediate by these activation systems. Incubation of deoxyguanosine-3'-phosphate with p-cresol (QM) resulted in a adduct pattern similar 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 used as molecular biomarkers of occupational exposure to toluene.
authors.affiliation: Department of Neurological Surgery, Brain Tumor Research Center, Box-0555, University of California, San Francisco, CA 94143-0555, USA.
authors.forename: N W
authors.initials: NW
authors.lastname: Gaikwad
authors.forename: W J
authors.initials: WJ
authors.lastname: Bodell
mesh_terms: D000818:Animals; D001205:Ascorbic Acid / Q000378:metabolism / Q000494:pharmacology; D001345:Autoradiography; D015415:Biomarkers / Q000032:analysis; D002417:Cattle; D002846:Chromatography, Affinity; D003408:Cresols / Q000378:metabolism* / Q000494:pharmacology; D004247:DNA / Q000187:drug effects; D018736:DNA Adducts / Q000032:analysis / Q000096:biosynthesis*; D004249:DNA Damage; D004781:Environmental Exposure / Q000032:analysis; D004790:Enzyme Induction; D006735:Horseradish Peroxidase / Q000378:metabolism*; D066298:In Vitro Techniques; D045563:Indolequinones; D007211:Indoles / Q000378:metabolism*; D017895:Manganese Compounds / Q000378:metabolism / Q000494:pharmacology; D008862:Microsomes, Liver / Q000187:drug effects / Q000201:enzymology*; D010084:Oxidation-Reduction; D010087:Oxides / Q000378:metabolism / Q000494:pharmacology; D010634:Phenobarbital / Q000494:pharmacology; D010761:Phosphorus Radioisotopes; D011809:Quinones / Q000378:metabolism*
chemical_list: D015415:Biomarkers; D003408:Cresols; D018736:DNA Adducts; D045563:Indolequinones; D007211:Indoles; D017895:Manganese Compounds; D010087:Oxides; D010761:Phosphorus Radioisotopes; D011809:Quinones; C068040:quinone methide; C032538:4-cresol; D004247:DNA; D006735:Horseradish Peroxidase; D001205:Ascorbic Acid; C016552:manganese dioxide; D010634:Phenobarbital