Identification of trans-1,2-dihydro-1,2-dihydroxy-6-nitrochrysene as a major mutagenic metabolite of 6-nitrochrysene

Abstract

Liver 9000 X g supernatant from rats was used to study the metabolism of [6- 14C]nitrochrysene under aerobic conditions. The major ethyl acetate-soluble metabolite (1.06 nmol/mg of protein in 30 min) was identified as 1,2-dihydro-1,2-dihydroxy-6-nitrochrysene, based on its mass, UV, and proton magnetic resonance spectra. Under aerobic conditions, 6-aminochrysene was not detected as a metabolite. However, when incubations were carried out in an atmosphere of 4% O2 in N2, both 1,2-dihydro-1,2-dihydroxy-6-nitrochrysene (0.04 nmol/mg of protein) and 6-aminochrysene (0.05 nmol/mg of protein) were detected. Further metabolism of the 14C-labeled 1,2-dihydro-1,2-dihydroxy-6-nitrochrysene by rat liver 9000 X g supernatant under aerobic conditions gave a major metabolite which was identified tentatively as 1,2-dihydroxy-6-nitrochrysene. The mutagenic activities of 6-nitrochrysene, trans-1,2-dihydro-1,2-dihydroxy-6-nitrochrysene and 6-aminochrysene were assessed in Salmonella typhimurium strains TA100 and TA98. In the absence of rat liver 9000 X g supernatant, trans-1,2-dihydro-1,2-dihydroxy-6-nitrochrysene was the more potent mutagen in TA100 but, in TA98, it was less active than was 6-nitrochrysene. In the presence of rat liver 9000 X g supernatant, both trans-1,2-dihydro-1,2-dihydroxy-6-nitrochrysene and 6-nitrochrysene were more mutagenic in TA100 than in the assays performed without an activating system, and the dihydrodiol metabolite was more mutagenic than was 6-nitrochrysene. In TA98 with activation, trans-1,2-dihydro-1,2-dihydroxy-6-nitrochrysene, 6-aminochrysene, and 6-nitrochrysene were all mutagenic. The results of this study indicate that trans-1,2-dihydro-1,2-dihydroxy-6-nitrochrysene is a major proximate mutagen of 6-nitrochrysene in S. typhimurium TA100.