Inhibitory effect(s) of polymeric black tea polyphenol fractions on the formation of [(3)H]-B(a)P-derived DNA adducts

Five polymeric black tea polyphenol fractions (PBP-1-5) were isolated from a popular brand of black tea. The effect of these PBPs and epigallocatechin gallate (EGCG), a major green tea polyphenol, was studied on the formation of (3)H]-B(a)P-derived DNA adducts in vitro, employing rat liver microsomes. PBP-1-3 inhibited microsome-catalyzed (3)H]-B(a)P-derived DNA adduct formation in vitro in a dose-dependent manner. This inhibition was further enhanced on preincubation of microsomes with each of the PBPs. PBP-4 was not effective per se and required preincubation with microsomes to exhibit its inhibitory effect, whereas PBP-5 remained ineffective with or without preincubation with microsomes. Further investigations revealed that the observed decrease in (3)H]-B(a)P-DNA adduct formation was due to inhibition of isozymes of CYP450s by PBPs. Overall, results suggest that polymeric black tea polyphenol fractions retain one of the chemopreventive effects exhibited by the monomeric green tea polyphenol EGCG in vitro.