title: Inhibition of the efflux of glutathione S-conjugates by plant polyphenols.
abstract: The formation of dinitrophenylglutathione (DNP-SG) in human colon adenocarcinoma cells was identified and quantified by an HPLC-UV method, following exposure to 1-chloro-2,4-dinitrobenzene (CDNB) at 10 degrees for 40 min. The rate of efflux of DNP-SG at 37 degrees likewise, was measured by monitoring the DNP-SG content in the extracellular medium. Among the polyphenols examined for their action on DNP-SG export, butein was the most potent inhibitor with an IC50 value of 15 microM. The others, in order of decreasing potencies, were quercetin, tannic acid, 2'-hydroxychalcone, 2-hydroxychalcone anIIC50 values in the micromolar range. These polyphenols did not affect the ATP or the glutathione content of the cells. Mg(2+)-ATPase extracted from the plasma membrane of the cells was activated by DNP-SG in a concentration-dependent manner, and the reaction showed saturation kinetics with K(m) and Vmax values of 110 microM and 12.3 nmol/min/mg protein, respectively. However, the six polyphenols mentioned above had negligible effects on the Mg(2+)-ATPase activity, suggesting that this was probably not the target of their inhibitory action. Probenecid, p-trifluoromethoxy-phenylhydrazone (FCCP) and chlorambucil also showed varying degrees of inhibition of the export of DNP-SG.
authors.affiliation: Department of Biochemistry, Faculty of Medicine, National University of Singapore, Singapore.
authors.forename: K
authors.initials: K
authors.lastname: Zhang
authors.forename: K P
authors.initials: KP
authors.lastname: Wong
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000378:metabolism; D001693:Biological Transport, Active / Q000187:drug effects; D017301:Ca(2+) Mg(2+)-ATPase / Q000378:metabolism; D002462:Cell Membrane / Q000187:drug effects / Q000201:enzymology; D002599:Chalcone / Q000031:analogs & derivatives / Q000494:pharmacology; D047188:Chalcones; D005419:Flavonoids / Q000494:pharmacology; D005978:Glutathione / Q000031:analogs & derivatives* / Q000378:metabolism*; D005982:Glutathione Transferase / Q000378:metabolism; D006801:Humans; D047348:Hydrolyzable Tannins / Q000494:pharmacology; D007700:Kinetics; D010636:Phenols / Q000494:pharmacology*; D010944:Plants; D011108:Polymers / Q000494:pharmacology*; D011794:Quercetin / Q000494:pharmacology; D014407:Tumor Cells, Cultured; D047309:Flavones
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D000255:Adenosine Triphosphate; D017301:Ca(2+) Mg(2+)-ATPase; D002599:Chalcone; D047188:Chalcones; D005419:Flavonoids; D005978:Glutathione; D005982:Glutathione Transferase; D047348:Hydrolyzable Tannins; D010636:Phenols; D011108:Polymers; D011794:Quercetin; C030190:S-(2,4-dinitrophenyl)glutathione; C040918:butein; C008548:morin; D047309:Flavones; C013031:2'-hydroxychalcone