Increased transport of resveratrol across monolayers of the human intestinal Caco-2 cells is mediated by inhibition and saturation of metabolites

Purpose. The study's aim was to investigate the dose-dependent effect of sulfation and glucuronidation on intestinal absorption of resveratrol, a dietary constituent found in grapes and various medical plants. Materials and Methods. The intestinal epithelial membrane transport kinetics and metabolism of resveratrol (10-200 mu M) was studied using Caco-2 monolayers cultured in Transwells. Results. Along with resveratrol it was possible to identify three metabolites, namely, resveratrol-4'-O-glucuronide (M1), resveratrol 3-O-gucuronide (M2), and resveratrol-3-O-sulfate (M3) by LC/MS and NMR. Efflux of the glucuronides M1 and M2 followed Michaelis-Menten kinetics significantly favouring basolateral efflux. The predominant metabolite was the monosulfate M3, however, its formation was strongly inhibited at higher resveratrol concentrations. As biotransformation was either inhibited or saturated, total amount of resveratrol transported across the Caco-2 monolayers increased as much as 3.5-fold at 200 mu M resveratrol. This value might be even higher when taking into account the high intracellular concentration of resveratrol, which accounted for up to 61% of the applied dose. Conclusions. Our data demonstrate a concentration-dependent biotransformation of resveratrol in Caco-2 cells, which may also apply to human enterocytes affecting oral bioavailability.