Oxidation of vitamin E: evidence for competing autoxidation and peroxyl radical trapping reactions of the tocopheroxyl radical

Liebler, D.C.; Baker, P. F.; Kaysen, Kathryn L.

doi:10.1021/ja00175a037

Cited by 131 publications

(148 citation statements)

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“…This indicates that the reaction between the carboncentered radicals of methyl linoleate and a-tocopheroxyl radical occurs under air-insufficient conditions (Yamauchi et al, 1993). The other product-forming pathway yields compound 5, but the fornration mechanism of this compound is unclear (Liebler et al, 1990;Liebler & Burr, 1995).…”

Section: A-tocopherol As the Free Radical Scavengermentioning

confidence: 99%

“…Each molecule of o!-tocopherol consumes thus two lipid free radicals and terminates the free-radical chain reaction. To elucidate the free-radical scavenging mechanism of tocopherols, the reaction products of tocopherols with lipid free radicals have been investigated (Winterle et al, 1984;Ham & Liebler, 1995, 1997Liebler et al, 1990Liebler et al, , 1991Liebler & Burr, 1992;Matsuo et a/, 1989;Yamauchi et al, 1989Yamauchi et al, , 1990aYamauchi et al, , 1990bYamauchi et al, , 1990cYamauchi et al, , 1993Yamauchi et al, , 1994Yamauchi et al, , 1995a). …”

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Vitamin E: Mechanism of Its Antioxidant Activity.

Yamauchi

1997

FSTI

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The antioxidant activity of vitamin E (a-tocopherol) during the peroxidation of unsaturated lipids has been reviewed based on its reaction products. Free-radical scavenging reactions of a-tocopherol take place via the a-tocopheroxyl radical as an intermediate. If a suitable free radical is present, a non-radical product can be formed from the coupling of the free radical with the a-tocopheroxyl radical. The reaction products of a-tocopherol with lipid-peroxyl radicals are 8a-(lipid-dioxy)-a-tocopherones which are hydrolyzed to a-tocopherylquinone. If the supply of oxygen is insufficient, a-tocopherol can trap the carbon-centered radicals of lipids to form 6-0-(lipidalkyl)-a-tocopherols. On the other hand, the dimer and trimer of a-tocopherol is formed by the bimolecular self-reaction of the a-tocopheroxyl radical in a reaction mixture containing a large amount of a-tocopherol. The other product-forming pathway yields isomeric epoxy-a-tocopherylquinones and their precursors, epoxyhydroperoxy-a-tocopherones, but the mechanism of this pathway remains unknown. The reaction products of other vitamin E compounds (7-and 6-tocopherols) during lipid peroxidation are almost the same as those formed from the a-tocopherol. The tocopheroxyl radicals of 7-and 6-tocopherols prefer to react with each other to form dimeric products that are still effective as antioxidants.

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Section: A-tocopherol As the Free Radical Scavengermentioning

confidence: 99%

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confidence: 99%

Vitamin E: Mechanism of Its Antioxidant Activity.

Yamauchi

1997

FSTI

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“…Electrochemical detection also offers a Vitamin E (a-tocopherol, TH) 2 is the principal lipid-TMCS, trimethylchlorosilane; TMS, trimethylsilyl; TQ, a-tocopherolsoluble biological antioxidant and an important celluquinone; TQE1, 5,6-epoxy-a-tocopherolquinone; TQE2, 2,3-epoxya-tocopherolquinone; d 6 3 -methyl]-a-tocopherolhydroquinone; Tris-HCl, tris(hydroxymethyl)aminomethane-HCl; raphy-mass spectrometry; T…”

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Gas Chromatography–Mass Spectrometry Analysis of Vitamin E and Its Oxidation Products

Liebler

Burr

Philips

et al. 1996

Analytical Biochemistry

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149

105

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“…Since vitamin E is an excellent antioxidant (3-7) and radical inhibitor (8)(9)(10)(11), these properties have been used, in general fashion, to interpret its physiological activity and its possible role in living systems (3)(4)(5)(6)(7)(8)(9)(10)(11)(12).…”

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On the mechanism of the anticlotting action of vitamin E quinone.

Dowd

Zheng

1995

Proc. Natl. Acad. Sci. U.S.A.

114

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Vitamin E in the reduced, a-tocopherol form shows very modest anticlotting activity. By contrast, vitamin E quinone is a potent anticoagulant. This observation may have significance for field trials in which vitamin E is observed to exhibit beneficial effects on ischemic heart disease and stroke. Vitamin E quinone is a potent inhibitor of the vitamin K-dependent carboxylase that controls blood clotting. A newly discovered mechanism for the inhibition requires attachment of the active site thiol groups of the carboxylase to one or more methyl groups on vitamin E quinone. The results from a series of model reactions support this interpretation of the anticlotting activity associated with vitamin E.With the success of recent field trials of vitamin E, and the attendant promise of forestalling the onset of heart attack and stroke (1, 2), it becomes important to understand the molecular mechanistic basis of this beneficent physiological activity. Since vitamin E is an excellent antioxidant (3-7) and radical inhibitor (8-11), these properties have been used, in general fashion, to interpret its physiological activity and its possible role in living systems (3)(4)(5)(6)(7)(8)(9)(10)(11)(12).It is known that vitamin E has anticoagulant properties (13-18), but this attribute has not been applied to understanding its physiological action. The recent Finnish study of male heavy smokers (19) found little efficacy of vitamin E and 13-carotene in preventing the occurrence of cancer, but the study did show the positive potential of vitamin E in cardiovascular therapy. There were clear benefits among the participants for ischemic heart disease and ischemic stroke, but, significantly, vitamin E acted to the detriment of those prone to hemorrhagic stroke (19). Accordingly, we suggest that the anticoagulant properties of vitamin E be included when evaluating the results of such trials.What are the anticoagulant properties of vitamin E, and why have they not been used in interpreting its physiologic role? For one, there has been some confusion about which oxidation states of vitamin E are effective anticoagulants, or, alternatively, which derivatives of vitamin E interdict the vitamin K-dependent clotting cycle and how effectively (20)(21)(22)(23). In response to the second part of the question, no mechanistic underpinning for the anticlotting properties of vitamin E has been developed, nor has there been any speculation regarding molecular mechanisms by which vitamin E might act as an inhibitor of the vitamin K-dependent carboxylase that is required to activate the enzymes of the blood clotting cascade. This paper will address both issues. ResultsThe vitamin K-dependent carboxylase and the other enzymes of the vitamin K cycle were obtained from rat liver microsomes (24,25). The uptake of 14C02 by the synthetic pentapeptide substrate FLEEI, as a function of inhibitor concentration, was used as a measure of carboxylase activity and its inhibition. The Vitamin E quinone 2 production of vitamin K oxide was conveniently monitor...

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Oxidation of vitamin E: evidence for competing autoxidation and peroxyl radical trapping reactions of the tocopheroxyl radical

Cited by 131 publications

References 0 publications

Vitamin E: Mechanism of Its Antioxidant Activity.

Vitamin E: Mechanism of Its Antioxidant Activity.

Gas Chromatography–Mass Spectrometry Analysis of Vitamin E and Its Oxidation Products

On the mechanism of the anticlotting action of vitamin E quinone.

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