Untersuchungen zur Bioverfügbarkeit und intestinalen Absorption von Quercetin und Quercetinglykosiden
Recent investigations indicate a higher bioavailability of quercetin derived from quercetin monoglucosides compared with the free aglycon or the glucorhamnoside. As a possible explanation an involvement of the intestinal Na+-dependent glucose cotranspoter (SGLT1) in the absorption of quercetin glucosides has been discussed. Therefore, the present in vivo study compared the relative bioavailability of quercetin in pigs after oral application of 165,4 and 33,1 µmol/kg body weight of quercetin aglykon,quercetin-3-glucoside (Q-3-Glc) and quercetin-3-glucorhamnoside, respectively. Furthermore the influence of Q-3-Glc on D-glucose uptake into brush border membranevesicles (BBMV) from pig jejunum was studied. After application of the higher dose the relative systemic availability of quercetin from the glucoside was higher than from the aglycon or glucorhamnoside. At the lower dose, however, there was no difference in the bioavalabilities. Irrespective of the source of quercetin the main metabolite found in blood samples of both the jugular and portal vein was conjugated quercetin. In addition to quercetin, the conjugated 3’- and 4’-methylethers of quercetin were identified. The bioavailability of quercetin depended on dietary factors as well. The plasma concentration and the systemic availability of quercetin were significantly higher when the test meal consisted of a small meat ball compared with the regular starch rich pig diet. In the BBMV experiments Q-3-Glc significantly inhibited the SGLT1 mediated D-glucose uptake, whereas the uptake of L-leucin into the BBMV was not influenced. Determinations of the kinetic parameters in absence or presence of Q-3-Glc indicated a competitive type of inhibition of the glucose uptake via the SGLT1. Under initial conditions (5 sec incubation time) a trans-stimulation of the glucose uptake by the Q-3-Glc was shown. Taken together, the present results indicate that the bioavailability of quercetin from different quercetin glycosides depends on the sugar moiety. The metabolites found in plasma after application of the different quercetin glycosides do not differ. A higher bioavailability of quercetin derived from the Q-3-Glc compared to the aglycon appears only after a relatively high dose. The specific interaction between Q-3-Glc and the SGLT1 together with the observed trans-stimulation points to a transport of Q-3-Glc via the SGLT1 and in turn could explain the higher bioavailability of the Q-3-Glc.