Effect of tannic acid on rat liver S9 mediated mutagenesis, metabolism and DNA binding of benzo[a]pyrene.

Tannic acid, a naturally occurring plant phenol, inhibited rat liver S9 mediated mutagenesis of benzo[a]pyrene in Salmonella typhimurium by 32-77% at concentrations of 5-50 micrograms/mutagenesis plate. Tannic acid (10-40 microM) had no affect on the formation of organosoluble metabolites of benzo[a]pyrene or of its water-soluble conjugates. It did, however, inhibit benzo[a]pyrene (B[a]P) metabolite binding to calf thymus DNA by 40% at a concentration of 40 microM and inhibited benzo[a]pyrene 7,8-dihydrodiol-9,10-epoxide (BPDE): deoxyguanosine adduct formation in calf thymus DNA by 12-54% at concentrations of 10-40 microM. These results suggest that the antimutagenic effect of tannic acid and inhibition of B[a]P metabolite binding to DNA is by a previously described scavenging mechanism and/or by a DNA-affinity binding mechanism that prevents BPDE interaction with DNA as previously described for ellagic acid.