Abstract
The mechanistic properties of two dietary antioxidants that are required by humans, vitamins C and E, are discussed relative to their biological effects. Vitamin C (ascorbic acid) is an essential cofactor for α-ketoglutarate-dependent dioxygenases. Examples are prolyl hydroxylases, which play a role in the biosynthesis of collagen and in down-regulation of hypoxia-inducible factor (HIF)-1, a transcription factor that regulates many genes responsible for tumor growth, energy metabolism, and neutrophil function and apoptosis. Vitamin C-dependent inhibition of the HIF pathway may provide alternative or additional approaches for controlling tumor progression, infections, and inflammation. Vitamin E (α-tocopherol) functions as an essential lipid-soluble antioxidant, scavenging hydroperoxyl radicals in a lipid milieu. Human symptoms of vitamin E deficiency suggest that its antioxidant properties play a major role in protecting erythrocyte membranes and nervous tissues. As an antioxidant, vitamin C provides protection against oxidative stress-induced cellular damage by scavenging of reactive oxygen species, by vitamin E-dependent neutralization of lipid hydroperoxyl radicals, and by protecting proteins from alkylation by electrophilic lipid peroxidation products. These bioactivities bear relevance to inflammatory disorders. Vitamin C also plays a role in the function of endothelial nitric oxide synthase (eNOS) by recycling the eNOS cofactor, tetrahydrobiopterin, which is relevant to arterial elasticity and blood pressure regulation. Evidence from plants supports a role for vitamin C in the formation of covalent adducts with electrophilic secondary metabolites. Mechanism-based effects of vitamin C and E supplementation on biomarkers and on clinical outcomes from randomized, placebo-controlled trials are emphasized in this review.
Copyright © 2011 Elsevier Inc. All rights reserved.
Publication types
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Research Support, N.I.H., Extramural
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Research Support, U.S. Gov't, Non-P.H.S.
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Review
MeSH terms
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Animals
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Antioxidants / metabolism*
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Antioxidants / therapeutic use
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Ascorbic Acid / metabolism*
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Ascorbic Acid / therapeutic use
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Cytoprotection / drug effects
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Energy Metabolism / drug effects
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Free Radicals / metabolism
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Humans
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Hypoxia-Inducible Factor 1 / metabolism
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Inflammation / drug therapy*
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Inflammation / metabolism
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Neoplasms / drug therapy*
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Neoplasms / metabolism
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Randomized Controlled Trials as Topic
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Vitamin E / metabolism*
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Vitamin E / therapeutic use
Substances
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Antioxidants
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Free Radicals
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Hypoxia-Inducible Factor 1
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Vitamin E
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Ascorbic Acid