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Journal of Lipid Research, Vol. 47, 2718-2725, December 2006
Copyright © 2006 by American Society for Biochemistry and Molecular Biology

Dietary flavonoids with a catechol structure increase -tocopherol in rats and protect the vitamin from oxidation in vitro

Jan Frank^1,*, Alicja Budek^*, Torbjörn Lundh, Robert S. Parker, Joy E. Swanson, Cátia F. Lourenço^**, Bruno Gago^**, João Laranjinha^**, Bengt Vessby and Afaf Kamal-Eldin^*

^* Department of Food Science, Swedish University of Agricultural Sciences, Uppsala, Sweden
Department of Animal Nutrition and Management, Swedish University of Agricultural Sciences, Uppsala, Sweden
Division of Nutritional Sciences, Cornell University, Ithaca, NY
^** Faculty of Pharmacy and Center for Neurosciences, University of Coimbra, Coimbra, Portugal
Department of Public Health and Caring Sciences/Geriatrics, University of Uppsala, Uppsala, Sweden

Published, JLR Papers in Press, September 1, 2006.

¹ To whom correspondence should be addressed. e-mail: frank{at}foodsci.uni-kiel.de

To identify dietary phenolic compounds capable of improving vitamin E status, male Sprague-Dawley rats were fed for 4 weeks either a basal diet (control) with 2 g/kg cholesterol and an adequate content of vitamin E or the basal diet fortified with quercetin (Q), (–)-epicatechin (EC), or (+)-catechin (C) at concentrations of 2 g/kg. All three catechol derivatives substantially increased concentrations of -tocopherol (-T) in blood plasma and liver. To study potential mechanisms underlying the observed increase of -T, the capacities of the flavonoids to i) protect -T from oxidation in LDL exposed to peroxyl radicals, ii) reduce -tocopheroxyl radicals (-T ^· ) in SDS micelles, and iii) inhibit the metabolism of tocopherols in HepG2 cells were determined. All flavonoids protected -T from oxidation in human LDL ex vivo and dose-dependently reduced the concentrations of -T ^· . None of the test compounds affected vitamin E metabolism in the hepatocyte cultures. In conclusion, fortification of the diet of Sprague-Dawley rats with Q, EC, or C considerably improved their vitamin E status. The underlying mechanism does not appear to involve vitamin E metabolism but may involve direct quenching of free radicals or reduction of the -T ^· by the flavonoids.

Supplementary key words (+)-catechin • cytochrome P₄₅₀ • (–)-epicatechin • hepatocytes • HepG2 • quercetin • tocopherol--hydroxylase • tocopheroxyl radical

Abbreviations: C, (+)-catechin; CYP, cytochrome P₄₅₀; EC, (–)-epicatechin; Q, quercetin; -T, -tocopherol; -T ^· , -tocopheroxyl radical; UV, ultraviolet

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