title: No role of DT-diaphorase (NQO1) in the protection against oxidized quercetin.
abstract: Quercetin is one of the most studied alimentary antioxidants. During its antioxidant activity, quercetin becomes oxidized into its ortho-quinone/quinone methide, denoted as QQ. QQ is toxic since it is highly reactive towards thiols. DT-diaphorase (NQO1) might protect against QQ toxicity by reducing QQ to quercetin. However, conflicting data have been reported. The aim of the present study is to elucidate the role of DT-diaphorase in the protection against QQ-mediated thiol reactivity. It was found that QQ is indeed a substrate for DT-diaphorase. However, QQ reacted much faster with glutathione or protein thiols than with DT-diaphorase in experiments with isolated compounds as well as with human liver cytosol or blood plasma. This indicates that DT-diaphorase has no role in the protection against QQ.
authors.affiliation: Department of Pharmacology and Toxicology, Faculty of Medicine, University of Maastricht, P.O. Box 616, 6200 MD Maastricht, The Netherlands. a.boots@farmaco.unimaas.nl
authors.forename: Agnes W
authors.initials: AW
authors.lastname: Boots
authors.forename: Aalt
authors.initials: A
authors.lastname: Bast
authors.forename: Guido R M M
authors.initials: GR
authors.lastname: Haenen
mesh_terms: D002851:Chromatography, High Pressure Liquid; D003600:Cytosol / Q000201:enzymology / Q000378:metabolism; D005978:Glutathione / Q000097:blood / Q000378:metabolism; D006801:Humans; D008099:Liver / Q000201:enzymology / Q000378:metabolism; D016660:NAD(P)H Dehydrogenase (Quinone) / Q000378:metabolism*; D010084:Oxidation-Reduction; D011794:Quercetin / Q000378:metabolism* / Q000633:toxicity; D013379:Substrate Specificity
chemical_list: D011794:Quercetin; D016660:NAD(P)H Dehydrogenase (Quinone); D005978:Glutathione