Benzo[ a]pyrene metabolism and DNA adduct formation mediated by english sole liver enzymes

Abstract

Tritiated benzo[ a]pyrene (BaP) and (±)-7,8-dihydroxy-7,8-dihydroBaP (BaP 7,8-dihydrodiol) were incubated with English sole liver microsomes in the presence of salmon testes DNA. The modified deoxynucleosides were isolated by Sephadex LH-20 column chromatography and analyzed by reverse-phase high-pressure liquid chromatography (HPLC). A single, major adduct (60–68% of the total modified deoxynucleosides) was formed when either BaP or BaP 7,8-dihydrodiol was incubated with sole liver microsomes and DNA. Although other minor BaP-DNA adducts were formed, none represented greater than 3% of the total adducts. The major adduct had a retention time on HPLC identical to that of the N 2-[10 β(7 β,8 α,9 α-trihydroxy-7,8,9,10-tetrahydrobenzo[a]pyrene)yl]-deoxyguanosine (7R- anti-BPDE/ trans-dG) adduct formed when anti-BPDE, the ultimate carcinogen of BaP in mammals, was incubated with DNA. Analysis of the Bay region tetrols showed that only the 7α,8β,9β,10α-tetrahydroxy-7,8,9,10-tetrahydroBaP, a hydrolysis product of the anti-BPDE, was formed when BaP was incubated with sole liver microsomes. When BaP 7,8-dihydrodiol was used as the substrate, the 7α, 8β,9β,10α-, 7α,8β,9α,10β-, and 7α,8β,9α,10α-tetrahydroxy-7,8,9,10-tetrahydroBaP's were formed, indicating the formation of both anti- and syn-BPDE. The ratio of tetrols of anti-BPDE/ syn-BPDE was 2; however, the ratio of adducts of anti-BPDE/ syn-BPDE was 20. Thus, the findings show that hepatic microsomes of English sole, a fish species having a high incidence of liver neoplasia in chemically contaminated estuaries, metabolized BaP and BaP 7,8-dihydrodiol stereoselectively to form predominantly the JR- anti-BPDE/ trans-dG adduct.