INVIVO GENOTOXICITY OF SODIUM ORTHO-PHENYLPHENOL - PHENYLBENZOQUINONE IS ONE OF THE DNA-BINDING METABOLITE(S) OF SODIUM ORTHO-PHENYLPHENOL

We have previously demonstrated microsomal cytochromes P450-dependent redox cycling of o-phenylphenol and in vitro genotoxicity of o-phenylphenol. In the present work, we have investigated in vivo covalent modification in skin DNA by Na-o-phenylphenol using the P-32-postlabeling method in an attempt to understand the biochemical mechanism of promotion of chemical-induced skin carcinogenesis by Na-o-phenylphenol. Topical application of Na-o-phenylphenol or phenylhydroquinone, a hydroxylated metabolite of o-phenylphenol, to female CD-1 mice skin produced 4 distinct major and several minor adducts in skin DNA. The total covalent bindings in skin DNA produced by treatment of mice with 10 mg and 20 mg Na-o-phenylphenol (doses shown to be effective for tumor promotion) were 0.31 fmoles/mug DNA and 0.62 fmoles/mug DNA, respectively. The adducts were not observed in untreated animal skin DNA. Pretreatment of mice with alpha-naphthylisothiocyanate, an inhibitor of cytochromes P450, or indomethacin, an inhibitor of prostaglandin synthase, resulted in lower levels of DNA adducts produced by Na-OPP. The in vitro incubation of DNA with o-phenylphenol or phenylhydroquinone in the presence of cytochromes P450 activation or prostaglandin synthase activation system produced 4 major adducts. The adduct pattern observed in the presence of in vitro enzymatic activation systems appears to be similar in chromatographic mobility to the in vivo adduct pattern. The chemical reaction of DNA or deoxyguanosine monophosphate with pure phenylbenzoquinone, an electrophilic metabolite of o-phenylphenol, also produced 4 major and several minor adducts. The 4 major adducts obtained in chemical reaction of phenylbenzoquinone with deoxyguanosine monophosphate are identical in chromatographic mobility to those of in vivo or in vitro DNA adducts. The results of this study demonstrated that o-phenylphenol or phenylhydroquinone, a hydroxylated metabolite of o-phenylphenol, is able to covalently bind to DNA. DNA binding can be inhibited by the inhibitor of cytochromes, P450 alpha-naphthylisothiocyanate or prostaglandin synthase, indomethacin. One of the DNA-binding metabolite(s) of o-phenylphenol both in vivo and in vitro may be phenylbenzoquinone. We conclude that Na-OPP is genotoxic. Genotoxicity caused by Na-o-phenylphenol treatment in CD-1 mice may play a role in the promotion of dimethylbenz[a]anthracene-induced skin neoplasm.