Abstract

We investigated the effect of resveratrol, a constituent of the human diet that has been shown to inhibit aryl hydrocarbon-induced carcinogenesis in animals, on the carcinogen activation pathway regulated by the aryl hydrocarbon receptor. Resveratrol inhibited the metabolism of the environmental aryl hydrocarbon benzo[a]pyrene (B[a]P) catalyzed by microsomes isolated from B[a]P-treated human hepatoma HepG2 cells. Resveratrol competitively inhibited, in a concentration-dependent manner, the activity of the carcinogen activating enzymes cytochrome P-450 (CYP)1A1/CYP1A2 in microsomes and intact HepG2 cells. Resveratrol inhibited the B[a]P-induced expression of the CYP1A1 gene, as measured at the mRNA and transcriptional levels. Resveratrol abolished the binding of B[a]P-activated nuclear aryl hydrocarbon receptor to the xenobiotic-responsive element of the CYP1A1 promoter but did not itself bind to the receptor. Resveratrol was also effective in inhibiting CYP1A1 transcription induced by the aryl hydrocarbon dimethylbenz[a]anthracene in human mammary carcinoma MCF-7 cells. These data demonstrate that resveratrol inhibits aryl hydrocarbon-induced CYP1A activity in vitro by directly inhibiting CYP1A1/1A2 enzyme activity and by inhibiting the signal transduction pathway that up-regulates the expression of carcinogen activating enzymes. These activities may be an important part of the chemopreventive activity of resveratrol in vivo.