QUERCETIN GLUCOSIDES INTERACT WITH THE INTESTINAL GLUCOSE-TRANSPORT PATHWAY

Flavonols are efficient antioxidants with the potential to protect bio logical macromolecules from oxidative damage in vivo, and if absorbed into the circulation they may protect against cardiovascular disease. Although flavonol aglycones are present in foods at low concentrations , their glycosides are abundant in onions, apples, beans and tea, and are thought to be stable under the conditions of the human stomach and small bowel. There is, however, recent evidence to suggest that intac t glycosides of quercetin may be absorbed from the small intestine by a mechanism involving the glucose transport pathway. In the present st udy we tested this hypothesis by measuring the effect of quercetin gly cosides on the rate of efflux of galactose from the jejunal mucosa. Ev erted sacs of ratjejunum preloaded with C-14-galactose were exposed to quercetin glycosides isolated from onions. Quercetin mono- and digluc osides were shown to accelerate the carrier-mediated efflux of galacto se via a sodium-dependent pathway. HPLC analysis confirmed the stabili ty of the glycosides under conditions simulating those in the upper al imentary tract. These studies suggest that purified quercetin glucosid es are capable of interacting with the sodium dependent glucose transp ort receptors in the mucosal epithelium and may therefore be absorbed by the small intestine in vivo. (C) 1998 Elsevier Science Inc.