1,2-Dihydro-1,2-dihydroxy-5-methylchrysene, a Major Activated Metabolite of the Environmental Carcinogen 5-Methylchrysene

The metabolic activation of the environmental carcinogen 5-methylchrysene was studied by combining high-pressure liquid chromatographic analysis of metabolites formed in vitro with assays of these metabolites for mutagenic activity toward Salmonella typhimurlum. Metabolites were formed by incubation of 5-methylchrysene with the 9000 x g supernatant from Aroclor-treated rat livers. With the use of reverse-phase columns, the metabolites were resolved into nine peaks, A to I. Each peak was collected and tested for mutagenicity with activation. Significant mutagenic activity was observed primarily in Peak E and to a lesser extent in Peak D. None of the other metabolites showed significant mutagenic activity. The major mutagenic metabolite (Peak E) was identified as 1,2-dihydro-1,2-dihydroxy-5-methylchrysene (7.0% from 5-methylchrysene); Peak D was 7,8-dihydro-7,8-dihydroxy-5-methylchrysene (2.6% from 5-methylchrysene). Other metabolites included 9,10-dihydro-9,10-dihydroxy-5-methylchrysene, 9-hydroxy-5-methylchrysene, 7-hydroxy-5-methylchrysene, 1-hydroxy-5-methylchrysene, and 5-hy-droxymethylchrysene. These results indicate that 1,2-dihydro-1,2-dihydroxy-5-methylchrysene is a major proximate mutagen of 5-methylchrysene.