title: Antioxidant capacity of albumin-bound quercetin metabolites after onion consumption in humans.
abstract: Quercetin is a major dietary flavonoid found in onions and other vegetables. It is known that dietary quercetin is metabolized in the intestinal mucosa and the liver and is present as its glucuronide/sulfate conjugates with or without methylation. Although quercetin is known to possess strong antioxidant activity, there are only limited reports on the antioxidant activity of its metabolites. In this study, the antioxidant capacity of quercetin metabolites under physiological conditions was investigated. After consumption of cooked onion, more than 80% of quercetin metabolites were localized in the human plasma fraction containing concentrated serum albumin. Other lipoprotein fractions contained only small amounts of quercetin metabolites. Addition of quercetin 3-O-beta-glucuronide to the lipoprotein-eliminated plasma fraction generated antioxidant activity against LDL oxidation in a dose-dependent manner. However, onion consumption failed to enhance the antioxidant activity of the lipoprotein-eliminated plasma fraction against LDL oxidation, probably because the amount of quercetin metabolites bound to albumin was less than the effective level in an ex vivo study. The physiological role of plasma albumin in retaining quercetin metabolites needs to be further clarified.
authors: Department of Food Science, Graduate School of Nutrition and Bioscience, The University of Tokushima, Tokushima, Japan.
authors: Kaeko
authors: K
authors: Murota
authors: Azusa
authors: A
authors: Hotta
authors: Hikaru
authors: H
authors: Ido
authors: Yoshichika
authors: Y
authors: Kawai
authors: Jae-Hak
authors: JH
authors: Moon
authors: Keiko
authors: K
authors: Sekido
authors: Hiroki
authors: H
authors: Hayashi
authors: Takahiro
authors: T
authors: Inakuma
authors: Junji
authors: J
authors: Terao
mesh_terms: D000328:Adult; D000975:Antioxidants / Q000008:administration & dosage / Q000378:metabolism*; D006801:Humans; D066298:In Vitro Techniques; D008077:Lipoproteins, LDL / Q000378:metabolism; D008297:Male; D008875:Middle Aged; D019697:Onions / Q000737:chemistry*; D010084:Oxidation-Reduction; D011794:Quercetin / Q000008:administration & dosage / Q000097:blood / Q000378:metabolism*; D012709:Serum Albumin / Q000378:metabolism
chemical_list: D000975:Antioxidants; D008077:Lipoproteins, LDL; D012709:Serum Albumin; D011794:Quercetin