Inhibition of Benzo(a)pyrene and Benzo(a)pyrene-trans-7,8-diol Metabolism and DNA Binding in Mouse Lung Explants by Ellagic Acid

Abstract

The effect of ellagic acid, a naturally occurring plant phenol, on the binding to DNA and metabolism of benzo(a)pyrene (BP) and trans-7,8-dihydro-7,8-dihydroxybenzo(a)pyrene (BP 7,8-DHD) in cultured explants of strain A mouse lung was investigated. The explants were cultured in a rocking organ culture chamber for 16 h in the presence or absence of 10, 25, 50, and 100 µm ellagic acid. These concentrations of ellagic acid were nontoxic as determined by biochemical and histological methods. The ellagic acid was then removed from the cultures, and the explants were incubated with either 1 µm [³H]BP or [³H]BP 7,8-DHD for 24 h. Explant DNA was isolated using hydroxylapatite chromatography, and the BP metabolites in the medium were analyzed by high-pressure liquid chromatography. Ellagic acid (50 µm) inhibited the binding of BP and BP 7,8-DHD to lung DNA by 46 to 50% and 60 to 70%, respectively. High-pressure liquid chromatography analysis showed that ellagic acid (100 µm) inhibited the metabolism of BP by 20 to 40% and of BP 7,8-DHD by 20%, as indicated by the increased amounts of unmetabolized substrates and decreased amounts of metabolites in the medium. The major BP:DNA adduct in the explants was 7R-N²-{10β-[7β,8β,9α-trihydroxy-7,8,9,10-tetrahydrobenzo(a)pyrene]yl}:deoxyguanosine, and its formation was reduced by 60 to 65% in the presence of 100 µm ellagic acid. These data suggest that the reduction of BP and BP 7,8-DHD metabolite binding to DNA by ellagic acid may have been due to inhibition of the formation and/or removal of BP 7,8-diol-9,10-epoxide prior to its binding to DNA.