Dietary flavonoids with a catechol structure increase alpha-tocopherol in rats and protect the vitamin from oxidation in vitro.
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 alpha-tocopherol (alpha-T) in blood plasma and liver. To study potential mechanisms underlying the observed increase of alpha-T, the capacities of the flavonoids to i) protect alpha-T from oxidation in LDL exposed to peroxyl radicals, ii) reduce alpha-tocopheroxyl radicals (alpha-T (.) ) in SDS micelles, and iii) inhibit the metabolism of tocopherols in HepG2 cells were determined. All flavonoids protected alpha-T from oxidation in human LDL ex vivo and dose-dependently reduced the concentrations of alpha-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 alpha-T (.) by the flavonoids.
Frank
Jan
J
Department of Food Science, Swedish University of Agricultural Sciences, Uppsala, Sweden. frank@foodsci.uni-kiel.de
Budek
Alicja
A
Lundh
Torbjörn
T
Parker
Robert S
RS
Swanson
Joy E
JE
Lourenço
Cátia F
CF
Gago
Bruno
B
Laranjinha
João
J
Vessby
Bengt
B
Kamal-Eldin
Afaf
A
D000818:Animals; D002396:Catechols / Q000737:chemistry; D004032:Diet; D005419:Flavonoids / Q000737:chemistry* / Q000494:pharmacology*; D006801:Humans; D066298:In Vitro Techniques; D008077:Lipoproteins, LDL / Q000737:chemistry / Q000187:drug effects / Q000378:metabolism; D008099:Liver / Q000187:drug effects / Q000378:metabolism; D008297:Male; D015394:Molecular Structure; D010084:Oxidation-Reduction; D051381:Rats; D017207:Rats, Sprague-Dawley; D024502:alpha-Tocopherol / Q000097:blood / Q000737:chemistry / Q000378:metabolism*
D002396:Catechols; D005419:Flavonoids; D008077:Lipoproteins, LDL; D024502:alpha-Tocopherol; C034221:catechol