How does ascorbic acid prevent endothelial dysfunction?
Human coronary and peripheral arteries show endothelial dysfunction in a variety of conditions, including atherosclerosis, hypercholesterolemia, smoking, and hypertension. This dysfunction manifests as a loss of endothelium-dependent vasodilation to acetylcholine infusion or sheer stress, and is typically associated with decreased generation of nitric oxide (NO) by the endothelium. Vitamin C, or ascorbic acid, when acutely infused or chronically ingested, improves the defective endothelium-dependent vasodilation present in these clinical conditions. The mechanism of the ascorbic acid effect is unknown, although it has been attributed to an antioxidant function of the vitamin to enhance the synthesis or prevent the breakdown of NO. In this review, multiple mechanisms are considered that might account for the ability of ascorbate to preserve NO. These include ascorbate-induced decreases in low-density lipoprotein (LDL) oxidation, scavenging of intracellular superoxide, release of NO from circulating or tissue S-nitrosothiols, direct reduction of nitrite to NO, and activation of either endothelial NO synthase or smooth muscle guanylate cyclase. The ability of ascorbic acid supplements to enhance defective endothelial function in human diseases provides a rationale for use of such supplements in these conditions. However, it is first necessary to determine which of the many plausible mechanisms account for the effect, and to ensure that undesirable toxic effects are not present.
Department of Medicine, Vanderbilt University School of Medicine, Nashville, TN 37232-6303, USA. james.may@mcmail.vanderbilt.edu
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D000818:Animals; D000975:Antioxidants / Q000494:pharmacology* / Q000627:therapeutic use; D001161:Arteriosclerosis / Q000188:drug therapy / Q000378:metabolism / Q000517:prevention & control; D001205:Ascorbic Acid / Q000494:pharmacology / Q000502:physiology* / Q000627:therapeutic use; D003331:Coronary Vessels / Q000187:drug effects / Q000378:metabolism; D004730:Endothelium, Vascular / Q000187:drug effects / Q000503:physiopathology*; D004789:Enzyme Activation / Q000187:drug effects; D006162:Guanylate Cyclase / Q000378:metabolism; D006801:Humans; D008077:Lipoproteins, LDL / Q000378:metabolism; D008623:Mercaptoethanol; D009569:Nitric Oxide / Q000096:biosynthesis / Q000097:blood; D019001:Nitric Oxide Synthase / Q000378:metabolism; D052250:Nitric Oxide Synthase Type III; D009573:Nitrites / Q000378:metabolism; D009603:Nitroso Compounds / Q000097:blood; D010084:Oxidation-Reduction; D018384:Oxidative Stress; D011817:Rabbits; D026403:S-Nitrosothiols; D013438:Sulfhydryl Compounds / Q000502:physiology; D013481:Superoxides / Q000378:metabolism; D014664:Vasodilation / Q000187:drug effects / Q000502:physiology
D000975:Antioxidants; D008077:Lipoproteins, LDL; D009573:Nitrites; D009603:Nitroso Compounds; D026403:S-Nitrosothiols; D013438:Sulfhydryl Compounds; C099252:oxidized low density lipoprotein; D013481:Superoxides; D009569:Nitric Oxide; D008623:Mercaptoethanol; C032635:S-nitrosomercaptoethanol; C496314:NOS3 protein, human; D019001:Nitric Oxide Synthase; D052250:Nitric Oxide Synthase Type III; D006162:Guanylate Cyclase; D001205:Ascorbic Acid