Multidrug resistance-associated proteins are involved in the transport of the glutathione conjugates of the ultimate carcinogen of benzo[a]pyrene in human Caco-2 cells.
A wide variety of contaminants are ingested through food, among them the pro-carcinogenic polycyclic aromatic hydrocarbon benzo[a]pyrene (BP) that is resorbed and partially metabolized in the enterocytes of the small intestine. Previous in vitro studies have revealed that BP phenols are excreted as Phase II metabolites including glucuronides and sulfates. This export is mediated by the breast cancer resistance protein (ABCG2). The ultimate carcinogenic Phase I BP metabolite anti-BP-7,8-dihydrodiol-9,10-epoxide (BPDE) can be detoxified by glutathione conjugate formation catalyzed by glutathione S-transferases. In the present study, differentiated human intestinal Caco-2 cells were used as a model for the human small intestine to investigate the detoxification of BPDE and excretion of stereoisomeric glutathione conjugates in the presence of an inhibitor of the glutathione-cleaving enzyme γ-glutamyl transpeptidase at the cell surface. The results indicate that the glutathione conjugates of BPDE are formed and excreted mainly to the apical and to a minor extent to the basolateral side of polarized Caco-2 monolayers. Inhibition studies revealed that the multidrug resistance-associated proteins (ABCCs) are involved in the transport of BPDE glutathione conjugates. Stable ABCC1, ABCC2 and ABCC3 knockdown cell lines were generated, thus making it possible to demonstrate that ABCC1 mediates the basolateral and ABCC2 the apical excretion of BPDE glutathione conjugates. In conclusion, the ultimate carcinogen BPDE is detoxified via glutathione conjugation and subsequently excreted by Caco-2 cells in both apical and basolateral directions. This finding is equivalent to a transport into feces as well as blood system in the in vivo situation.
Department of Food Safety, Federal Institute for Risk Assessment, Max-Dohrn-Strasse 8-10, 10589 Berlin, Germany. stefanie.hessel@bfr.bund.de
Stefanie
S
Hessel
Andrea
A
John
Albrecht
A
Seidel
Alfonso
A
Lampen
D015123:7,8-Dihydro-7,8-dihydroxybenzo(a)pyrene 9,10-oxide / Q000378:metabolism / Q000633:toxicity*; D001692:Biological Transport / Q000187:drug effects; D018938:Caco-2 Cells / Q000187:drug effects* / Q000378:metabolism; D002273:Carcinogens / Q000378:metabolism / Q000633:toxicity*; D018432:Drug Resistance, Multiple / Q000502:physiology*; D015870:Gene Expression; D055785:Gene Knockdown Techniques; D005978:Glutathione / Q000378:metabolism*; D005982:Glutathione Transferase / Q000378:metabolism; D006801:Humans; D000089762:Multidrug Resistance-Associated Protein 2; D027425:ATP-Binding Cassette, Sub-Family C Proteins / Q000235:genetics / Q000378:metabolism*; D013997:Time Factors
D015123:7,8-Dihydro-7,8-dihydroxybenzo(a)pyrene 9,10-oxide; D002273:Carcinogens; D005978:Glutathione; D005982:Glutathione Transferase; D000089762:Multidrug Resistance-Associated Protein 2; D027425:ATP-Binding Cassette, Sub-Family C Proteins; C000715087:ABCC2 protein, human; C114462:multidrug resistance-associated protein 3; C421109:multidrug resistance-associated protein 1