Induction of phase-1 metabolizing enzymes by oltipraz, flavone and indole-3-carbinol enhance the formation and transport of benzo[a]pyrene sulfate conjugates in intestinal Caco-2 cells

The small intestine is well equipped with various phase-1 and phase-2 xenobiotic metabolizing enzymes (XME), which contribute to the detoxification process of the body. Many XME are regulated via aryl hydrocarbon receptor (AhR)-dependent pathways, and numerous naturally occurring AhR agonists (e.g. flavonoids, dietary indoles) have been identified to date. In the present study we show that pretreatment of Caco-2 cells with food-associated compounds (flavone and indole-3-carbinol) and with the anticancer chemopreventive agent oltipraz enhances the formation of the major metabolites of the procarcinogen benzo[a]pyrene (BP) formed by intestinal Caco-2 cells, namely BP-1-sulfate and BP-3-sulfate, and their transport to the apical compartment of a Transwell™ chamber. Oltipraz treatment was most effective in this regard followed by flavone and indole-3-carbinol. The effect observed here after pretreatment with oltipraz, flavone and I3C was the result of the induction of both CYP1A1 and CYP1B1, as was confirmed by analysis of CYP1A1 (protein and mRNA) and CYP1B1 (mRNA) expression. In summary, our study shows that the induction of both CYP1A1 and CYP1B1 resulted in an accelerated metabolism and an enhanced clearance of the potent procarcinogen BP, indicating that flavone, indole-3-carbinol and oltipraz have an impact on the biochemical barrier against BP in intestinal cells.