Antioxidant Synergy and Regeneration Effect of Quercetin, (−)-Epicatechin, and (+)-Catechin on α-Tocopherol in Homogeneous Solutions of Peroxidating Methyl Linoleate

Abstract

Antioxidant interactions between flavonoids and alpha-tocopherol have been demonstrated by oximetry (oxygen concentration measured by ESR signal line width). In tert-butyl alcohol, a solvent in which flavonoids are weak retarders of peroxidation of methyl linoleate when initiated by alpha,alpha'-azoisobutyronitrile, quercetin and (-)-epicatechin were found to act synergistically with the chain-breaking antioxidant alpha-tocopherol. In chlorobenzene, a solvent in which flavonoids are chain-breaking antioxidants, quercetin and (+)-catechin each regenerated alpha-tocopherol, resulting in a co-antioxidant effect. The stoichiometric factor of the flavonoids as chain-breaking antioxidants in 1:1 mixtures with alpha-tocopherol was measured to be close to 1 for quercetin and slightly smaller for the catechins. The apparent inhibition rate constant, k(inh), for the mixture quercetin/alpha-tocopherol was measured to be 4.1 x 10(5) and 2.6 x 10(6) M(-1) s(-1) in tert-butyl alcohol and chlorobenzene, respectively, at 50 degrees C. A k(inh) of 4.4 x 10(5) M(-1) s(-1) was measured for (+)-catechin alone in chlorobenzene at 50 degrees C.

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

“…Furthermore, previous studies support the notion of a regeneration of a-T from its a-tocopheroxyl radical (a-T˙) at water-lipid interfaces by dietary phenols (18) in a way reminiscent of that of vitamin C (19). Accordingly, Q, EC, and C have been shown to reduce chemically generated a-T˙in SDS micelles and organic solutions (20,21). In agreement with ex vivo findings that C preserves a-T in human plasma (22), we previously reported that it increases a-T levels in rats (23).…”

Phenolic Molecules in Virgin Olive Oils: a Survey of Their Sensory Properties, Health Effects, Antioxidant Activity and Analytical Methods. An Overview of the Last Decade Alessandra

“…Such cooperative activity seems to explain the antioxidant synergism observed when α-tocopherol and ascorbic acid or ubiquinol are used in combination. Recent investigations have also demonstrated an antioxidant synergism between α-tocopherol and some phenolics (green tea catechins and quercetin) [105][106]. Bendini et al [104] hypothesized that phenols having an ortho-dihydroxyl structure, and in particular an isomer of 3,4-DHPEA-EDA, were able to reduce the oxidized forms of tocopherols (tocopheryl radicals and quinones).…”

Suppression of human monocyte tissue factor induction by red wine phenolics and synthetic derivatives of resveratrol

“…This plus poor absorption of these compounds in vivo [40][41][42] raise valid doubts about the importance of the individual polyphenolic constituents of red wine in providing the cardioprotective effect. However, earlier studies suggested that synergism could exist between wine phenolics in inhibiting platelet function [47] and in promoting antioxidation [48]. These data and the inability of individual wine phenolics to effectively modulate various cellular activities raise the possibility that overall cardiovascular protection afforded by a moderate consumption of red wine could perhaps come from combined and synergistic effects of various polyphenolic constituents of red wine or metabolic modification of polyphenols in digestive system to make them more potent in modulating cellular activities.…”