verlukast and alpha-naphthoflavone

Epithelial cells of the gastrointestinal tract are challenged by exposure to many potentially toxic agents including the well-known food contaminant benzo[a]pyrene (B[a]P). They are equipped with a variety of Phase 1- and Phase 2-enzymes that are able to metabolize B[a]P. Furthermore, transmembranous ABC-transport proteins are expressed at the apical pole of these cells. The aim of this study was to investigate whether [14C]B[a]P or products of the metabolism are transported by intestinal cells back into the gut lumen. The intestinal Caco-2 cell line was used as a metabolism and transport model. Experiments with Caco-2 monolayers in the Transwell-system revealed that radiolabeled substance is transported towards the apical (luminal) region. This transport was characterized as active and increased after induction of cytochromes P450 1A1 and 1B1 by beta-naphthoflavone. On the other hand, transport was decreased with the concomitant inhibition of Phase 1-metabolism. TLC-analysis revealed that the primary metabolites of B[a]P found in the supernatant were very polar; other metabolites of less polarity could only be detected in trace amounts. These results indicate that B[a]P is metabolized by Caco-2 cells to highly polar metabolites resulting from biphasic metabolism and that these polar metabolites are subject to an apically directed transport. Chemical inhibition studies showed that P-glycoprotein and MRP1 or 2 were not involved in this polarized B[a]P-metabolite secretion.

Topics: Adenosine Triphosphate; Aryl Hydrocarbon Hydroxylases; ATP-Binding Cassette Transporters; Benzo(a)pyrene; Benzoflavones; Biological Transport, Active; Caco-2 Cells; Cell Polarity; Cyclosporine; Cytochrome P-450 CYP1A1; Cytochrome P-450 CYP1B1; Enterocytes; Gene Expression; Humans; Models, Biological; Probenecid; Propionates; Quinolines; Verapamil; Vinblastine