title: Plasma quercetin metabolites: structure-antioxidant activity relationships.
abstract: We studied quercetin metabolism in rats to determine the nature and conjugation positions on the resulting metabolites and to evaluate their contribution to the antioxidant activity of plasma. HPLC analysis showed that quercetin is primarily metabolized to glucuronides and sulfoglucuronides and, to a minor extent, to sulfates. ESI-MS/MS studies confirmed these results and indicate that the most plausible positions for glucuronidation and sulfation are the hydroxyl groups located at positions 5 and 7, excluding the 3'-OH and 4'-OH groups. Plasma antioxidant status was significantly higher in animals to which quercetin was administrated, suggesting that quercetin metabolites can retain some antioxidant activity when the o-catechol group does not undergo conjugation reactions. It was also shown that plasma quercetin metabolites could compete in vivo with other molecules for peroxynitrite. These results enabled the establishment of quercetin metabolite structure-antioxidant activity relationships and, hence, to understand their contribution for the antioxidant potential of plasma.
authors.affiliation: Departamento de Química e Bioquímica, Faculdade de Ciências, Universidade de Lisboa, 1749-016 Lisboa, Portugal.
authors.forename: Gonçalo C
authors.initials: GC
authors.lastname: Justino
authors.forename: Marta R
authors.initials: MR
authors.lastname: Santos
authors.forename: Sónia
authors.initials: S
authors.lastname: Canário
authors.forename: Carlos
authors.initials: C
authors.lastname: Borges
authors.forename: M Helena
authors.initials: MH
authors.lastname: Florêncio
authors.forename: Lurdes
authors.initials: L
authors.lastname: Mira
mesh_terms: D000818:Animals; D000975:Antioxidants / Q000737:chemistry*; D002474:Cell-Free System; D002851:Chromatography, High Pressure Liquid; D044948:Flavonols / Q000737:chemistry; D006868:Hydrolysis; D008297:Male; D013058:Mass Spectrometry; D008956:Models, Chemical; D030421:Peroxynitrous Acid / Q000737:chemistry; D011794:Quercetin / Q000097:blood* / Q000737:chemistry* / Q000502:physiology / Q000031:analogs & derivatives; D051381:Rats; D017207:Rats, Sprague-Dawley; D012235:Rhodamines / Q000737:chemistry; D021241:Spectrometry, Mass, Electrospray Ionization; D013329:Structure-Activity Relationship; D013431:Sulfates / Q000737:chemistry; D013997:Time Factors
chemical_list: D000975:Antioxidants; D044948:Flavonols; D012235:Rhodamines; D013431:Sulfates; C047368:3-methylquercetin; C058319:dihydrorhodamine 123; D030421:Peroxynitrous Acid; D011794:Quercetin