Prostaglandin H synthase-mediated oxidation and binding to DNA of a detoxication metabolite of carcinogenic Sudan I, 1-(phenylazo)-2,6-dihydroxynaphthalene

The metabolite of the carcinogenic azo dye Sudan I, 1-(phenylazo)-2,6-dihydroxynaphthalene (6-OH-Sudan I), which is considered to be the detoxification product of this dye is metabolized by prostaglandin H synthase (PHS) in the presence of arachidonic acid or H2O2 in vitro. The apparent Michaelis constant value for 6-OH-Sudan I as a substrate is 98.9 μM. 1-(Phenylazo)-2,6-naphthoquinone is a principal product of the 6-OH-Sudan I oxidation. This oxidation is inhibited by radical scavengers nitrosobenzene, ascorbate, glutathione and NADH. This indicates that PHS metabolizes 6-OH-Sudan I through a one-electron oxidation mechanism, giving rise to free radicals. During the PHS-mediated reaction, 6-OH-Sudan I is activated to metabolites binding to protein and DNA. The 32P-postlabeling analysis of DNA modified by activated 6-OH-Sudan I provides evidence that covalent binding to DNA is the principal type of DNA modification. The PHS-mediated binding of 6-OH-Sudan I to DNA presumably proceeds through formation of 1-(phenylazo)-2,6-naphthoquinone. The results suggest strongly that the C-hydroxylated derivative of Sudan I (6-OH-Sudan I) should be evaluated as a proximate carcinogenic metabolite, which may participate in the initiation of Sudan I-carcinogenesis in the urinary bladder.