Quercetin Glucosides Are Completely Hydrolyzed in Ileostomy Patients before Absorption

Abstract

Flavonoids, dietary components in vegetables, fruits and beverages, may protect against coronary heart disease, stroke and cancer. However, the bioavailability of these compounds is questionable. A previous study in ileostomy patients of the most abundant flavonoid, quercetin, suggested a 52% absorption of its major dietary forms, monoglucoside (QMG) and diglucoside (QDG), from an onion meal. However, this was based on indirect measurements after acid hydrolysis. Because human intestinal Caco-2 cell monolayers showed minimal absorption of the glucosides, we repeated the study in ileostomy patients, using molecularly specific analytical methodology for the intact glucosides and quercetin. The onion meal had high concentrations of both QMG and QDG with only trace amounts of quercetin. The intake of QMG and QDG in four patients ranged from 10.9 to 51.6 mg. No QMG or QDG was detected in the ileostomy fluid. In contrast, the amounts of the aglycone quercetin were substantial, 2.9-11.3 mg. This corresponded to 19.5-35.2% of total quercetin glucosides ingested, implying absorption of 64.5-80.7%. These findings suggest a different interpretation than that from the previous study, i.e., that both QMG and QDG are efficiently hydrolyzed in the small intestine by beta-glucosidases to quercetin, most of which is then absorbed.

Protective Effects of Quercetin and Its Metabolites on H2O2-Induced Chromosomal Damage to WIL2-NS Cells

“…23) The question regarding the route of the flavonoid when are absorbed remains unsettled. Walle et al (2000) 24) found that both major glucosides of quercetin in the onion, quercetin-monoglucoside and quercetin-diglucoside, are hydrolyzed in the human small intestine to the aglycon quercetin, 65-81% of which is then presumably absorbed. Many other researchers have confirmed that after eating foods containing quercetin glycoside or quercetin aglycon, quercetin presented as the glucuronide or sulfate form or further as methylated forms, these were conjugated to glucuronide or sulfate in plasma.…”

Berry Fruits as a Source of Biologically Active Compounds: The Case of Lonicera Caerulea

“…38 ). Some fl avonoid glycosides could be hydrolyzed in the small intestine 39 . If the fl avonoid glycosides are able to enter the intestinal epithelial cells (enterocytes), which may include shredded cells, they may be hydrolyzed by broadspecifi c β-glucosidase (BSβG) (ref.…”

Enhancing Effect of Lipids and Emulsifiers on the Accumulation of Quercetin Metabolites in Blood Plasma after the Short-term Ingestion of Onion by Rats

“…Although the intestinal absorption and metabolism of ingested quercetin glycosides has been uncertain, substantial previous evidence has suggested that the main pathway is their conversion to conjugate metabolites through aglycone by deglycosylation activity and subsequent conjugation activity. [16][17][18][19][20][21][22][23][24][25][26][27] Moreover, conjugated metabolites of quercetin have recently been found to exhibit antioxidative properties toward lipid peroxidation in vivo and in vitro. 18,19,22,24,26,28) It has been shown that the e‹ciency of intestinal absorption of quercetin is aŠected by its solubility in the vehicle used for administration.…”