Absorption and excretion of conjugated flavonols, including quercetin-4'-O-beta-glucoside and isorhamnetin-4'-O-beta-glucoside by human volunteers after the consumption of onions.

Flavonols are polyphenols found ubiquitously in plants and plant-products. Flavonols, particularly quercetin, are potent antioxidants in vitro and their intake has been associated inversely with the incidence of coronary heart disease. The aim of this study was to investigate the accumulation in plasma and excretion in urine of flavonol glucosides following ingestion of lightly fried onions. Five healthy volunteers followed a low-flavonoid diet for 3 days. On day 4, after an overnight fast, subjects were given 300 g of lightly fried yellow onions which contain conjugates of quercetin and isorhamnetin, including quercetin-3,4 '-diO-beta-glucoside, isorhamnetin-4'-O-beta-glucoside and quercetin-4'-O-beta-glucoside. Blood collection was carried out at 0 min, 0.5, 1.0, 1.5, 2, 3, 4, 5 and 24h after the supplement. In addition, subjects collected all their urine for 24h following the onion supplement. Isorhamnetin-4'-O-beta-glucoside and quercetin-4 '-O-beta-glucoside accumulated in plasma with maximum levels, defined as proportion of intake, of 10.7+/-2.6% and 0.13+/-0.03% respectively. The time of the quercetin-4'glucoside peak plasma concentration was 1.3+/-0.2 h after the ingestion of onions while a value of 1.8+/-0.7 h was obtained for isorhamnetin-4'-glucoside. Excretion in urine, as a proportion of intake, was 17.4+/-8.3% for isorhamnetin-4'-O-beta-glucoside and 0.2+/-0.1% for quercetin-4'-O-beta-glucoside. Possible reasons for the accumulation and excretion of isorhamnetin-4'-glucoside in proportionally much higher amounts than quercetin-4'-glucoside are discussed. It is concluded that flavonols are absorbed into the bloodstream as glucosides and minor structural differences affect markedly both the level of accumulation and the extent to which the conjugates are excreted.

[1]  S. Awazu,et al.  The beta-anomeric and glucose preferences of glucose transport carrier for intestinal active absorption of monosaccharide conjugates. , 1994, Biochimica et biophysica acta.

[2]  P. Hollman,et al.  Bioavailability of the dietary antioxidant flavonol quercetin in man. , 1997, Cancer letters.

[3]  J. Kuhnau.  The flavonoids. A class of semi-essential food components: their role in human nutrition. , 1976 .

[4]  K. Herrmann.  Flavonols and flavones in food plants: a review† , 1976 .

[5]  P. Hollman,et al.  Fluorescence detection of flavonols in HPLC by postcolumn chelation with aluminum. , 1996, Analytical chemistry.

[6]  P. Hollman,et al.  Absorption and disposition kinetics of the dietary antioxidant quercetin in man. , 1996, Free radical biology & medicine.

[7]  D Kromhout,et al.  Flavonoid intake and long-term risk of coronary heart disease and cancer in the seven countries study. , 1995, Archives of internal medicine.

[8]  J. Vinson,et al.  Plant Polyphenols Exhibit Lipoprotein-Bound Antioxidant Activity Using an in Vitro Oxidation Model for Heart Disease , 1995 .

[9]  P. Hollman,et al.  Absorption of dietary quercetin glycosides and quercetin in healthy ileostomy volunteers. , 1995, The American journal of clinical nutrition.

[10]  C. Rice-Evans,et al.  Structure-antioxidant activity relationships of flavonoids and phenolic acids. , 1996, Free radical biology & medicine.

[11]  Alan Crozier,et al.  Quantitative analysis of the flavonoid content of commercial tomatoes , 1997 .

[12]  P. Hollman.  Determinants of the absorption of the dietary flavonoid quercetin in man , 1997 .

[13]  M. Lean,et al.  Quantitative analysis of flavonoids by reversed-phase high-performance liquid chromatography , 1997 .

[14]  T. Tsushida,et al.  Flavonoid in Fruits and Vegetables Part I. Isolation of Flavonoid-Glycosides in Onion and Identification by Chemical Synthesis of the Glycosides , 1995 .

[15]  Leon Shargel,et al.  Applied biopharmaceutics and pharmacokinetics , 1980 .

[16]  Mcdonald,et al.  Survey of the Free and Conjugated Myricetin and Quercetin Content of Red Wines of Different Geographical Origins. , 1998, Journal of agricultural and food chemistry.

[17]  J. B. Harborne,et al.  Plant polyphenols—XIV. , 1965 .

[18]  Peter C. H. Hollman,et al.  Optimization of a quantitative HPLC determination of potentially anticarcinogenic flavonoids in vegetables and fruits , 1992 .

[19]  E. Feskens,et al.  Dietary antioxidant flavonoids and risk of coronary heart disease: the Zutphen Elderly Study , 1993, The Lancet.

[20]  O. Texier,et al.  Dietary quercetin is recovered in rat plasma as conjugated derivatives of isorhamnetin and quercetin , 1996 .

[21]  C. Rice-Evans,et al.  The identification of flavonoids as glycosides in human plasma , 1997, FEBS letters.

[22]  C. Rice-Evans,et al.  Polyphenolic flavanols as scavengers of aqueous phase radicals and as chain-breaking antioxidants. , 1995, Archives of biochemistry and biophysics.

[23]  W. Regelson,et al.  Review of the biology of Quercetin and related bioflavonoids. , 1995, Food and chemical toxicology : an international journal published for the British Industrial Biological Research Association.

[24]  K. Herrmann.  On the occurrence of flavonol and flavone glycosides in vegetables , 1988 .

[25]  S. Rankin,et al.  Flavonoids inhibit the oxidative modification of low density lipoproteins by macrophages. , 1990, Biochemical pharmacology.