Effects of citrus flavonoids on the mutagenicity of heterocyclic amines and on cytochrome P450 1A2 activity

Heterocyclic amines (HCA's) are promutagens produced by high temperature cooking of meat products and are activated by cytochrome P450 (CYP) lA2. Using Aroclor 1254 induced rat liver S9 we tested four citrus flavonoids diosmin, naringenin, naringin and rutin for their effects on the mutagenicity of HCA's MeIQx, Glu-P-1*, IQ and PhIP in Salmonella typhimurium TA98. The effects of the citrus flavonoids on CYPlA2 activity was determined by measuring demethylation of methoxyresorufin (MROD). MeIQx induced mutagenesis in S. typhimurium was significantly inhibited by all four flavonoids in a concentration dependent manner at 0.25, 0.5 and 1.0 mumole. Glu-P-1 induced mutagenesis was inhibited by rutin and naringenin. IQ induced mutagenesis was significantly inhibited by each flavonoid except diosmin at all three doses. With the exception of diosmin and naringin at 0.25 mumole all four flavonoids at all three doses significantly inhibited PhlP induced mutagenesis. The inhibition of MROD activity by the citrus flavonoids correlated best with the inhibition of MeIQx induced mutagenesis but also correlated with the inhibition of IQ induced mutagenesis except for diosmin and with the inhibition of PhlP induced mutagenesis except for the 0.25 mumole dose of diosmin and naringin. Our data suggest a chemopreventive potential for diosmin, naringin, naringenin and rutin towards CYPlA2 mediated mutagenesis of HCA's.

Effects of citrus phytochemicals on liver and lung cytochrome P450 activity and on the in vitro metabolism of the tobacco-specific nitrosamine NNK

NNK is a potent environmental carcinogen to which both smokers and nonsmokers are exposed. The response to NNK may be affected by factors including nutrition. We investigated the effects of five citrus phytochemicals on the in vitro metabolism of the tobacco-specific nitrosamine NNK and on the dealkylation of methoxyresorufin (MROD) and pentoxyresorufin (PROD) in liver and lung microsomes of the Syrian golden hamster. In the NNK metabolism experiments in vitro incubations contained 3 microCi [5-H3] NNK, 0.5 mg microsomal protein and 0.5 mumole of the citrus phytochemical diosmin, naringin, naringenin, quercetin or rutin. In the dealkylation studies incubations contained 0.5 microM methoxyresorufin or pentoxyresorufin, 0.5 mg microsomal protein and 0.5 mumole of citrus phytochemical. The major NNK metabolism pathway in hamster liver microsomes was NNK-reduction while in lung microsomes it was alpha-hydroxylation. The alpha-hydroxylation pathway produces metabolic products that methylate and pyridyloxobutylate DNA. Naringenin, a metabolite of naringin, and quercetin were the most potent inhibitors of alpha-hydroxylation of NNK in both liver and lung microsomes. This inhibition correlated with a potent inhibition of MROD and PROD activity in liver but not in lung microsomes. The metabolic activation of NNK is associated with cytochrome P450 isoforms 1A1, 1A2, 2B1, 2D6 and 2E1. Our results suggest that naringenin and quercetin from citrus fruits inhibit the activity of cytochrome P450 (CYP) isoforms that activate NNK and may afford protection against NNK-induced carcinogenesis.