Identification of mutagenic metabolites of benzo [a] pyrene in mammalian cells

Abstract

The mutagenicity of benzo[a]pyrene and 15 of its derivatives, which included phenols, the benzo[a]pyrene 4,5 epoxide (the K region epoxide), dihydrodiols, two isomeric 7,8 diol 9,10 epoxides, a 6 methyl derivative, and a 6 hydroxymethyl derivative, were tested with Chinese hamster V79 cells in order to identify the mutagenic metabolites of benzo[a]pyrene. Mutations were characterized by resistance to ouabain or 8 azaguanine. Since V79 cells do not metabolize polycyclic hydrocarbons, mutagenesis was tested both in the presence and absence of benzo[a]pyrene metabolizing normal golden hamster cells. All the tested phenols, 4,5 diols, trans 9,10 diol, 6 methyl, and 6 hydroxymethyl derivatives of benzo[a]pyrene showed little or no mutagenicity for both genetic markers. The (±)7α,8β dihydroxy 9α,10α epoxy 7,8,9,10 tetrahydrobenzo[a]pyrene and K region 4,5 epoxide exhibited similar and moderate mutagenicity in the absence of benzo[a]pyrene metabolizing cells, but the (±)7α,8β dihydroxy 9β,10β 10w6=pressure epoxy 7,8,9,10 tetrahydrobenzo[a] pyrene showed a 2000 and 270 fold higher mutation frequency for ouabain and 8 azaguanine resistance, respectively, than did the K region 4,5 epoxide. The trans 7,8 diol which was not mutagenic in the absence of benzo[a]pyrene metabolizing cells was more mutagenic than benzo[a]pyrene after metabolism and mutagenesis by trans 7,8 diol in these cells was inhibited by 7,8 benzoflavone, an inhibitor of mixed function oxidases. Metabolically formed trans 7,8 diol was isolated and incubated with rat liver microsomes in the presence of co factors. High presure liquid chromatography analysis indicated that the major metabolite of trans 7,8 diol is 7α,8β dihydroxy 9β,10β epoxy 7,8,9,10 tetrahydrobenzo[a]pyrene. The results indicate that the latter compound is metabolically formed and the major mutagenic intermediate of benzo[a]pyrene metabolism.