Investigation of an Interaction of Flavonoids on the Antioxidant Activity of Alpha Tocopherol

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Title: Investigation of an Interaction of Flavonoids on the Antioxidant Activity of Alpha Tocopherol
Author: Willcox, Joye Kay
Advisors: George L. Catignani, Committee Chair
Abstract: The hypothesis was: dietary flavonoids interact with alpha-tocopherol (a-TOH) to improve its antioxidant capacity in a living system. This project began with an in vitro study of the flavonoid quercetin and a-TOH in a tocopherol stripped corn oil (TSCO) using the Oxidative Stability Instrument (OSI). Quercetin was a more effective antioxidant than a-tocopherol in this system at all concentrations (5-20 mM). However, when both quercetin and a-TOH were present, the antioxidant effect was less than additive. The twelve week preliminary study involved feeding twenty-four male Sprague Dawley rats one of four AIN93-G treatment diets adding: no antioxidant, 5 g quercetin, 75 IU alpha tocopherol, or both antioxidants in the same concentrations per kg of diet, to determine differences in antioxidant effectiveness. The results indicated that tocopherol is a more effective antioxidant than quercetin, and that quercetin may have a mild positive effect on the antioxidant capacity of tocopherol at the levels fed. The major study involved feeding seventy-two male SD rats tocopherol sufficient or deficient AIN93-G diets alone or supplemented with one of five treatment compounds: 5 g. quercetin, 5 g. catechin, 5 g. epicatechin, 10 g. cocoa powder, or 10 g. lignin per kg of diet. In tocopherol sufficient groups, all test compounds significantly increased liver tocopherol compared to the control. The same effect was seen in plasma with the exception of epicatechin. However, adipose tocopherol was significantly increased in animals supplemented with quercetin, catechin, and epicatechin. In the tocopherol deficient groups, tocopherol levels were significantly increased by all test compounds and only in adipose tissue. Plasma and heart F2-isoprostanes were significantly increased in plasma and heart of tocopherol deficient animals compared to controls but none of the treatment compounds significantly decreased F2-isoprostanes beyond the significant protection displayed by a-tocopherol (sufficient vs. deficient). We conclude that these antioxidant compounds at the levels fed were sufficient to spare tocopherol in these various tissues, but insufficient to alter lipid peroxidation as measured under these experimental conditions.
Date: 2003-11-25
Degree: PhD
Discipline: Nutrition

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