Vitamin E-sparing and vitamin E-independent antioxidative effects of the flavonol quercetin in growing pigs

The aim was to investigate in vivo the antioxidative effects of the flavonol quercetin with special emphasis on interactions with vitamin E (alpha TOC) in growing pigs. It was assumed that any effects of quercetin on the antioxidant status would be more pronounced at low alpha TOC intake and that feeding diets with the addition of fish oil would induce an oxidative stress under these conditions. After a 5 week depletion period, in which all pigs (n = 26) were fed a low alpha TOC (7 mg/kg) diet, animals were assigned to one of 4 dietary groups (n = 6 or 7) according to a 2 x 2 factorial completely randomized design for four additional weeks. Factors consisted of (1) dietary supplementation of quercetin (0 or 10 mg quercetin/kg body weight/d) and (2) supplementation of fish oil (0 or 50 g/kg diet). The alpha TOC and flavonol concentrations in plasma and tissue as well as plasma thiobarbituric acid reactive substances (TBARS) and 8-iso-prostaglandin-F-2 alpha (8-iso-PGF(2 alpha)) in plasma were measured. At low vitamin E intake, supplementation of quercetin tended to elevate plasma (0.42 vs. 0.54 mu g/mL; P=0.063) and liver (0.16 vs. 0.24 mu g/g; P=0.06) alpha TOC concentrations with no influence on the concentrations of markers of lipid peroxidation (TBARS, 8-iso-PGF(2 alpha)), indicating a alpha TOC-sparing effect of quercetin. An additional alpha TOC-independent antioxidative effect of quercetin was not obvious under these conditions. However, further challenging the antioxidative mechanisms by the addition of fish oil at low alpha TOC intake resulted in a further reduction (P<0.05) of alpha TOC concentration in plasma (0.65 vs. 0.31 mu g/mL) which could not be prevented by quercetin at least at the dose fed. However, the concomittant increase in lipid peroxidation indicated by elevated (P<0.05) concentrations of TBARS and 8-iso-PGF(2 alpha) was ameliorated (P<0.05) by quercetin, suggesting a alpha TOC-independent antioxidative effect. Taken together, depending on the alpha TOC status, quercetin revealed a alpha TOC-sparing as well as alpha TOC-independent antioxidative effect at low alpha TOC intake. (C) 2011 Elsevier B.V. All rights reserved.