Submitted on July 5, 2006
Revised on August 31, 2006
Accepted on September 1, 2006
Dietary flavonoids with a catechol structure increase 
-tocopherol in rats and protect the vitamin from oxidation in vitro
Jan Frank, Alicja Budek, Torbjörn Lundh, Robert S. Parker, Joy E. Swanson, Cátia F. Lourenço, Bruno Gago, João Laranjinha, Bengt Vessby, and Afaf Kamal-Eldin
Institute of Human Nutrition and Food Science, Christian-Albrechts-University, Kiel 24118
Corresponding Author: 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 either 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 elevation 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 radical by the flavonoids.
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