Affiliations: Unit\'e des Maladies M\'etaboliques et des
Micronutriments, INRA Theix, 63122 Ceyrat, France
Note: [] Unit\'e des Maladies M\'etaboliques et Micronutriments, INRA
Theix, 63122 Ceyrat, France. Tel.: +33 4 73 62 46 81; Fax: +33 4 73 62 46 38;
E-mail: [email protected]
Abstract: A large number of flavonoids, mostly O-glycosides, are found in
foods of plant origin. The bound sugar moiety is known to influence their
bioavailability. We examined here the effect of the nature of the sugar on the
absorption of the glycosides. Four groups of rats (n=6)
received a meal containing 20 mg of quercetin equivalents supplied as aglycone,
quercetin 3-glucoside, quercetin 3-rhamnoside or rutin. Plasma were hydrolysed
by a \beta-glucuronidase/sulfatase and analyzed by HPLC
coupled to UV detection at 370 nm. Four hours after the beginning of the meal,
the quercetin metabolites present in plasma were identical in all groups but
their total concentrations were quite different. With pure quercetin the
circulating levels were 11.7\pm 1.8 \muM,
but this level was three fold higher when quercetin was supplied as quercetin
3-glucoside (33.2\pm 3.5 \muM). By
contrast, the plasma concentrations of quercetin metabolites was quite low with
the rutin meal (about 3 \muM) and undetectable after the
quercetin 3-rhamnoside meal. These data suggest that the 3-O-glucosylation
improves the absorption of quercetin in the small intestine, whereas the
binding of a rhamnose or of a glucose-rhamnose moiety to the aglycone markedly
depressed its absorption. Additionnal experiments have shown that the higher
plasma levels measured after the meal containing quercetin 3-glucoside compared
to quercetin were maintained throughout a 24 hour period following the meal.
In conclusion, the nature of the glycosylation markedly influences
the efficiency of quercetin absorption in rats. Quercetin 3-glucose can be
absorbed in the small intestine and is better absorbed than quercetin itself.
By contrast, glycosides containing a rhamnose moiety could not be absorbed in
the small intestine.
