The plant polyphenol quercetin was shown to induce a significant CI- secret
ion in intestinal epithelium. In order to elucidate the structural requirem
ents of quercetin and related flavonoids for this activity, we tested the a
bility of further flavonols and other flavonoids found in edible plants to
induce CI- secretion which was measured as an increase in short-circuit cur
rent (I-sc) in rat colon. Whereas several flavonols and the flavon luteolin
increased I-sc, other flavonoids such as flavanones, flavans, flavanols, a
nd anthocyanidins failed to do so. Two glycosides of quercetin, spiraeosid,
and isoquercitrin, as well as two methoxylated quercetin metabolites, isor
hamnetin and tamarixetin, were also able to increase I-sc. We conclude that
a 2,3-double bond in conjunction with the 4-oxo group in the C ring and a
hydroxylated B ring are necessary for the secretory activity of flavonoids.
This activity requires different structural features than those mandatory
for the antioxidative properties of flavonoids. Glucosidation and methoxyla
tion of several hydroxyl groups does not necessarily abolish the secretory
potential. (C) 2001 Elsevier Science Inc. All rights reserved.