Interaction of positional isomers of quercetin glucuronides with the transporter ABCC2 (cMOAT, MRP2)

The exporter ABCC2 (cMOAT, MRP2) is a membrane-bound protein on the apical side of enterocytes and hepatic biliary vessels that transports leukotriene C(4), glutathione, some conjugated bile salts, drugs, xenobiotics, and phytonutrients. The latter class includes quercetin, a bioactive flavonoid found in foods such as onions, apples, tea, and wine. There is no available three-dimensional (3D) structure of ABCC2. We have predicted the 3D structure by in silico modeling, showing that 3-[[3-[2-(7-chloroquinolin-2-yl)vinyl]phenyl]-(2-dimethylcarbamoylethylsulfanyl)methylsulfanyl] propionic acid (MK571) binds most tightly to the putative binding site, and then tested the computational prediction experimentally by measuring interaction with all quercetin monoglucuronides occurring in vivo (quercetin substituted with glucuronic acid at the 3-, 3'-, 4'-, and 7-hydroxyl groups). The 4'-O-beta-D-glucuronide is predicted in silico to interact most strongly and the 3-O-beta-D-glucuronide most weakly, and this prediction is supported experimentally using binding and competition assays on ABCC2-overexpressing baculovirus-infected Sf9 cells. To test the transport in situ, we examined the effect of two ABCC2 inhibitors, MK571 and cyclosporin A, on the transport into the media of quercetin glucuronides produced intracellularly by Caco2 cells. The inhibitors reduced the amount of all quercetin glucuronides in the media. The results show that the molecular model of ABCC2 agrees well with experimentally determined ABCC2-ligand interactions and, importantly, that the interaction of ABCC2 with quercetin glucuronides is dependent on the position and nature of substitution.