Effect of butylated hydroxyanisole on the metabolism of benzo[a]-pyrene and the binding of metabolites to DNA, in vitro and in vivo, in the forestomach, lung, and liver of mice

The effects of butyldted hydroxyanisole (BHA) administrationon the amounts of benzo[a]pyrene (BP) metabolite-DNA adductsformed in vivo in the forestomach of A/HeJ mice were investigated48 h after oral administration of BP. BP was administered tomice in amounts known to result in BPInduced neoplasia in certaintissues. Analysis of deoxyribonudeosides by h.p.l.c. showedthat several BP metabolite-DNA adducts were formed in this tissue.The major identified adduct was the (±)-7ß,8-dihydroxy-9, 10-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene (BPDEI) deoxyguanosine adduct. Addition of BHA to the diet inhibitedBPDE I-DNA adduct formation in the forestomach. The inhibitionof BPDE I-DNA adduct formation by BHA occurred under the sameexperimental conditions as does inhibition of tumor formationby this compound. These results in forestomach and previousresults in lung and forestomach demonstrated that inhibitionof the formation of the BPDE I-DNA adduct in the target tissueis a possible mechanism by which BHA inhibits BP-induced neoplasia.BP metabolism and DNA binding were also studied under in vitroconditions using microsomes prepared from forestomach, lung,and liver of A/HeJ mice. The amount of BPDE-DNA adduct formedin vitro is either equal to or lower than the amount of BP phenol-oxide-DNAadduct formed. BPDE I-DNA adduct formation was not significantlydifferent in incubations containing microsomes prepared fromBHA-treated or untreated mice. These results suggest that alterationsof the microsomal monooxygenases induced by BHA feeding arenot sufficient to account for the observed decreases in BPDE-DNAadduct formation in vivo. The monooxygenases were apparentlyaltered by BHA feeding as indicated by the substantial changesin the metabolic profile of BP and the decrease in the formationof the BP phenol-oxide-DNA adducts in the forestomach. The exclusionof glutathione transferases from the in vitro incubations couldaccount for the lack of effect of BHA treatment on BPDE-DNAadduct formation. BHA enhancement of ghitathione transferaseactivity has been postulated to play a role in the anticarcinogenicaction of BHA.