Human intestinal Caco-2 cells display active transport of benzo[a]pyrene metabolites.
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.
Buesen
Roland
R
Department of Food Toxicology, School for Veterinary Medicine of Hannover, Bischofsholer Damm 15, D-30173 Hannover, Germany.
Mock
Melissa
M
Nau
Heinz
H
Seidel
Albrecht
A
Jacob
Juergen
J
Lampen
Alfonso
A
D018528:ATP-Binding Cassette Transporters / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000378:metabolism; D001189:Aryl Hydrocarbon Hydroxylases / Q000037:antagonists & inhibitors / Q000235:genetics; D001564:Benzo(a)pyrene / Q000378:metabolism* / Q000493:pharmacokinetics* / Q000633:toxicity; D001571:Benzoflavones / Q000494:pharmacology; D001693:Biological Transport, Active / Q000187:drug effects; D018938:Caco-2 Cells; D016764:Cell Polarity; D016572:Cyclosporine / Q000494:pharmacology; D019363:Cytochrome P-450 CYP1A1 / Q000037:antagonists & inhibitors / Q000235:genetics; D065633:Cytochrome P-450 CYP1B1; D020895:Enterocytes / Q000187:drug effects / Q000378:metabolism*; D015870:Gene Expression / Q000187:drug effects; D006801:Humans; D008954:Models, Biological; D011339:Probenecid / Q000494:pharmacology; D011422:Propionates / Q000494:pharmacology; D011804:Quinolines / Q000494:pharmacology; D014700:Verapamil / Q000494:pharmacology; D014747:Vinblastine / Q000494:pharmacology
D018528:ATP-Binding Cassette Transporters; D001571:Benzoflavones; D011422:Propionates; D011804:Quinolines; D001564:Benzo(a)pyrene; C059141:verlukast; D014747:Vinblastine; C011512:alpha-naphthoflavone; D016572:Cyclosporine; D000255:Adenosine Triphosphate; D014700:Verapamil; D001189:Aryl Hydrocarbon Hydroxylases; C585496:CYP1B1 protein, human; D019363:Cytochrome P-450 CYP1A1; D065633:Cytochrome P-450 CYP1B1; D011339:Probenecid