Genotoxicities of nitropyrenes and their modulation by apigenin, tannic acid, ellagic acid and indole-3-carbinol in the Salmonella and CHO systems

Four naturally occurring compounds, indole-3-carbinol (I3C), apigenin (Api), ellagic acid (EA) and tannic acid (TA), were tested for their inhibitory effects against 1-nitropyrene- (1-NP) or 1,6-dinitropyrene (1,6-DNP)-induced genotoxicity in Salmonella tester strains and Chinese hamster ovary (CHO) cells. Api and TA strongly inhibited the bacterial mutagenesis induced by nitropyrenes, while 13C and EA had little or no effect. For example, in TA98, 0.2 μmole Api resulted in 48% and 56% inhibition of the mutagenicity induced by 4 nmole 1-NP and 0.035 nmole 1,6-DNP, respectively. With an equal dose, expected, a good correlation was observed between the antimutagenicity of nitropyrenes and their inhibitory effect on nitroreductase activity. This indicated that one of the possible antimutagenic mechanisms of Api or TA was to inactivate the metabolism of nitropyrenes. Two biological end-points, cytotoxicity and sister-chromatid exchange (SCEs), were used to screen the antigenotoxic effects of these compounds in CHO cells. At the sub-cytotoxic dose, 13C, Api and TA all protected against the cytotoxicity induced by 1-NP and 1,6-DNP, but only TA and Api gave a significant reduction of the frequency of SCEs. Moreover, this reduction was found to be highly dose-dependent.