Influence of bay-region methyl group on formation of 5-methylchrysene dihydrodiol epoxide:DNA adducts in mouse skin.

The binding of tritium-labeled 5-methylchrysene to DNA of CD-1 mouse skin 24 hr after treatment has been studied. DNA was isolated from the treated skin areas of mice and hydrolyzed enzymatically to deoxyribonucleosides, and the hydrolysate was chromatographed on a Sephadex LH-20 column using a methanol:water gradient. The major adducts eluted between 70 and 100 ml (Peak 1), 470 and 590 ml (Peaks 2A to C), and 750 and 850 ml (peak 3). For identification of these products, markers were prepared from 5-methylchrysene bay-region dihydrodiol epoxides. [5-14C]1,2-dihydroxy-3,4-epoxy-1,2,3,4-tetrahydro-5-methylchrysene and [5-14C]7,8-dihydroxy-9,10-epoxy-7,8,9,10-tetrahydro-5-methylchrysene were synthesized by reacting the corresponding metabolically formed [5-14C]1,2-dihydro-1,2-dihydroxy-5-methylchrysene and [5-14C]7,8-dihydro-7,8-dihydroxy-5-methylchrysene with m-chloroperoxybenzoic acid. The structures of the dihydrodiol epoxides were established by their mass spectra and by hydrolysis to tetrols. Peak 2B was chromatographically indistinguishable, both on Sephadex LH-20 and reverse-phase high-pressure liquid chromatography, from the adduct formed when [5-14C]1,2-dihydroxy-3,4-epoxy-1,2,3,4-tetrahydro-5-methylchrysene was reacted with salmon sperm DNA in solution. Similarly, Peak 2A was chromatographically inseparable from the [5-14C]7,8-dihydroxy-9,10-epoxy-7,8,9,10-tetrahydro-5-methylchrysene:DNA adduct. Adduct 2B was formed to a greater extent than adduct 2A by the ratio of 2.7 to 1. These data indicate that 5-methylchrysene preferentially forms DNA adducts from the bay-region dihydrodiol epoxide adjacent to the methyl group.