Modulation of cytochrome P4501-mediated bioactivation of benzo[a]pyrene by volatile allyl sulfides in human hepatoma cells

Allyl sulfides such as diallyl sulfide (DAS), diallyl disulfide (DADS), and diallyl trisulfide (DATS), typical flavor components of Allium vegetables, have been shown to inhibit benzo[a]pyrene (B[a]P)-induced carcinogenesis in animal models. As a possible mechanism of this inhibition, the effect of these volatile substances on cytochrome P450 (CYP)1 (CYP1A1, 1A2 and 1B1)-mediated bioactivation of B[a]P was investigated using a human hepatoma cell model (HepG2). DADS and DATS inhibited the B[a]P-induced ethoxyresorufin O-deethylase (EROD) activity, a marker enzyme for CYP1, by 30-90% and 70-95% at 100-1,000 microM concentration, respectively. The cell viability, an indicator of the capacity to inhibit B[a]P bioactivation, was increased by treatments of 100-1,000 microM DADS and 10-100 microM DATS. Immunoblot results indicated that the B[a]P inducible CYP1A2 protein was suppressed by 100-1,000 microM of DADS and 10-100 microM of DATS, but CYP1A1 and 1B1 were not detectable in any microsomes. Analysis of B[a]P metabolites revealed that the level of 7,8-diol formed was significantly reduced in the DADS and DATS treated microsomes as compared to the control. The level of 9,10-diol and 4,5-diol formed was also lowered by the allyl sulfide treatments. These results suggest that the protective mechanism of allyl sulfides on B[a]P-induced carcinogenesis is possibly related with the modulation of CYP1-mediated bioactivation of B[a]P.