Interaction of quercetin glucosides with the intestinal sodium/glucose co-transporter (SGLT-1).

Recently it has been postulated that flavonoid glucosides may be absorbed by the small intestine via the SGLT-1. Therefore, we applied an in vitro mucosal uptake method to investigate mucosal uptake of the non-metabolisable glucose analogue methyl-alpha-D-glucopyranoside (MDG) as influenced by quercetin-3-glucoside (isoquercitrin) and quercetin-4'-glucoside (spiraeosid). We found that both glucosides significantly inhibited SGLT-1-mediated MDG uptake whereas the aglycon quercetin or the quercetin-3-rhamnoglucoside (rutin) were ineffective. Calculated apparent kinetic parameters (Km, Vmax) of initial Na+-dependent MDG uptake by the jejunal mucosa indicate a competitive type of inhibition.