title: Vitamins C and E: beneficial effects from a mechanistic perspective.
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.
authors.affiliation: Linus Pauling Institute, Oregon State University, Corvallis, OR 97331, USA. maret.traber@oregonstate.edu
authors.forename: Maret G
authors.initials: MG
authors.lastname: Traber
authors.forename: Jan F
authors.initials: JF
authors.lastname: Stevens
mesh_terms: D000818:Animals; D000975:Antioxidants / Q000378:metabolism* / Q000627:therapeutic use; D001205:Ascorbic Acid / Q000378:metabolism* / Q000627:therapeutic use; D019610:Cytoprotection / Q000187:drug effects; D004734:Energy Metabolism / Q000187:drug effects; D005609:Free Radicals / Q000378:metabolism; D006801:Humans; D051793:Hypoxia-Inducible Factor 1 / Q000378:metabolism; D007249:Inflammation / Q000188:drug therapy* / Q000378:metabolism; D009369:Neoplasms / Q000188:drug therapy* / Q000378:metabolism; D016032:Randomized Controlled Trials as Topic; D014810:Vitamin E / Q000378:metabolism* / Q000627:therapeutic use
chemical_list: D000975:Antioxidants; D005609:Free Radicals; D051793:Hypoxia-Inducible Factor 1; D014810:Vitamin E; D001205:Ascorbic Acid