Multidrug resistance-associated proteins (MRPs) are involved in the detoxification of benzo[ a ]pyrene in the intestinal barrier
2010
Hessel,S. | John,A. | Seidel,A. | Lampen,A.
allemand. The human gastrointestinal tract represents the main portal for the entry of xenobiotics. The epithelium of the small intestine plays an important role in the detoxification of xenobiotics due to the expression of a number of phase I and phase II xenobiotic-metabolizing enzymes (XMEs) as well as several transport proteins of the ATP-binding cassette (ABC) superfamily.In the present study, differentiated human intestinal Caco-2 cells were used as a model for the human small intestine to investigate the metabolism and transport of the pro-carcinogenic food-contaminant benzo[ a ]pyrene (B[ a ]P). Previous studies revealed that B[ a ]P phenols are excreted as phase II metabolites such as B[ a ]P-glucuronides and B[ a ]P-sulfates. Excretion of these metabolites is mediated by breast cancer resistance protein (BCRP) (Ebert et al. , 2005). In contrast, detoxification of the ultimate carcinogenic phase I B[ a ]P metabolite anti -B[ a ]P-7,8-diol-9,10-epoxide (BPDE) occurs as glutathione conjugates formed by glutathione- S -transferases.This study demonstrates that these BPDE glutathione conjugates are excreted overall to the basolateral side of a polarized Caco-2 monolayer. Furthermore, it was shown by induction and inhibition studies that the multidrug resistance-associated proteins (MRPs), but not BCRP, are involved in the transport of the BPDE glutathione conjugates. The unspecific MRP inhibitor MK571 completely blocked transport of BPDE glutathione conjugates. For the identification of the specific MRP proteins mediating the apical and basolateral efflux of BPDE glutathione conjugates, respectively, stable MRP1, MRP2 and MRP3 knock down clones were generated by using siRNA technique. The treatment of the knock down clones supported the hypothesis that MRP1 mediates the basolateral and MRP2 the apical excretion in the Caco-2 cell line. Finally it was shown that the transport rates are increased by pre-treatment of the cells with the flavonoid quercetin, which stimulates expression of various phase I and transport proteins
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