C. Morand et al., Quercetin 3-O-beta-glucoside is better absorbed than other quercetin formsand is not present in rat plasma, FREE RAD RE, 33(5), 2000, pp. 667
The effect of the nature of the sugar moiety on quercetin absorption has be
en investigated in rats. Four groups of rats received an experimental meal
containing 20 mg of quercetin equivalents, supplied as quercetin, quercetin
3-O-beta -glucoside, quercetin 3-O-beta -rhamnoside or rutin. Four hours a
fter the meal, the metabolites identified in hydrolysed plasma were identic
al in all groups (3'- and 4'-methylquercetin). However, the total concentra
tion of metabolites was markedly different: 11.2+/-1.8, 2.5+/-2.0 and 33.2/-3.5 muM for the quercetin, rutin, and quercetin 3-glucoside meals respect
ively. After quercetin 3-rhamnoside consumption, we failed to detect any me
tabolites in the plasma. These data suggest that the 3-O-glucosylation impr
oves the absorption of quercetin in the small intestine, whereas the bindin
g of a rhamnose to the aglycone markedly depresses it. Additional experimen
ts have shown that the higher plasma levels measured after quercetin 3-gluc
oside meal compared to the quercetin meal were maintained throughout the 24
-hour period following the meal. Using a multi-electrode coulometric detect
ion, together with suitable chromatographic conditions, we were able to dis
tinguish between the conjugated and the glycosylated forms. Thus, we clearl
y showed the absence of quercetin 3-O-beta -glucoside in the plasma from ra
ts fed a diet containing this glucoside. This result suggests that querceti
n 3-O-beta -glucoside is hydrolysed before or during its intestinal absorpt
ion.