Intestinal transport of quercetin glycosides in rats involves both deglycosylation and interaction with the hexose transport pathway

flavonoids are polyphenolic plant secondary metabolites with antioxidant: a nd other biological activities potentially beneficial to health. Food-borne flavonoids occur mainly as glycosides, some of which can be absorbed in th e human small intestine; however, the mechanism of uptake is uncertain. We used isolated preparations of rat small intestine to compare the uptake of the quercetin aglycone with that of some quercetin glucosides commonly foun d in foods, and investigated interactions between quercetin-3-glucoside and the intestinal hexose transport pathway. The nature of any metabolism of q uercetin and its glucosides during small intestinal transport in vitro was determined by HPLC. The presence of quercetin-3-glucoside in the mucosal me dium suppressed the uptake of labeled galactose by competitive inhibition a nd stimulated the efflux of preloaded galactose. Quercetin-3-glucoside and quercetin-4'-glucoside, but not quercetin-3,4'-diglucoside, were transporte d into everted sacs significantly more quickly than quercetin aglycone. Int act quercetin glucosides were not detected in mucosal tissue or within the serosal compartment, but both free quercetin and its metabolites were prese nt, mainly as quercetin-3-glucuronide and quercetin-7-glucuronide. Evidentl y, quercetin derived from quercetin-3-glucoside passes across the small int estinal epithelium more rapidly than free quercetin aglycone. Monoglucoside s of quercetin interact with the sodium-dependent glucose transporter. Duri ng passage across the epithelium, quercetin-3-glucoside is rapidly deglycos ylated and then glucuronidated.