We compared the inhibitory effect of various cyclodextrins (CyDs) on P-glycoprotein (P-gp) and multidrug resistance-associated protein 2 (MRP2) function and examined the contribution of cholesterol to the inhibitory effect of 2,6-di-O-methyl-β-cyclodextrin (DM-β-CyD) on the efflux activity of the function in Caco-2 cell monolayers. Of various CyDs, DM-β-CyD significantly impaired the efflux activity of P-gp and MRP2. DM-β-CyD released P-gp and MRP2 from the monolayers in the apical side's transport buffer and decreased the extent of cholesterol as well as P-gp and MRP2 in caveolae of Caco-2 cell monolayers, but not caveolin and flotillin-1. On the other hand, DM-β-CyD did not change MDR1 and MRP2 mRNA levels. Therefore, these results suggest that the inhibitory effect of DM-β-CyD on P-gp and MRP2 function, at least in part, could be attributed to the release of these transporters from the apical membranes into the medium as secondary effects through cholesterol-depletion in caveolae after treatment of Caco-2 cell monolayers with DM-β-CyD.
