Effect of vitamin C on the availability of tetrahydrobiopterin in human endothelial cells.
Vitamin C has long been known for its beneficial vascular effects, but its mechanism of action remains unclear. Recent reports suggest that vitamin C may prevent endothelial dysfunction by scavenging free radicals and increasing the bioavailability of nitric oxide. To investigate this area further, we studied the effect of vitamin C (10(-4) M) and Mn(III) tetrakis (4-benzoic acid) porphyrin chloride (MnTBAP; 10(-5) M), a scavenger of superoxide, hydrogen peroxide, and peroxynitrite, on endothelial nitric oxide synthase (eNOS) enzymatic activity in cultured human umbilical vein endothelial cells. L-Citrulline formation (a measure of eNOS enzymatic activity) was significantly increased in cells treated for 24 h with vitamin C. No effect was observed after MnTBAP treatment. Chronic administration of vitamin C also had no effect on eNOS protein expression. Treatment with vitamin C for 24 h significantly increased levels of the eNOS co-factor tetrahydrobiopterin (BH4), whereas MnTBAP did not affect its levels. Sepiapterin (10(-4) M), a precursor of BH4, significantly increased eNOS activity, whereas addition of vitamin C to cells treated with sepiapterin did not cause any further increase in eNOS activity. Our results suggest that the beneficial effect of vitamin C on endothelial function is best explained by increased intracellular BH4 content and subsequent enhancement of eNOS activity. This effect appears to be independent of the ability of vitamin C to scavenge superoxide anions.
Department of Anesthesiology, Mayo Clinic and Foundation, Rochester, Minnesota 55905, USA.
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Baker
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Milstien
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Katusic
D001205:Ascorbic Acid / Q000494:pharmacology*; D001708:Biopterins / Q000031:analogs & derivatives* / Q000378:metabolism*; D002478:Cells, Cultured; D004730:Endothelium, Vascular / Q000378:metabolism*; D006136:GTP Cyclohydrolase / Q000378:metabolism; D006801:Humans; D015151:Immunoblotting; D008665:Metalloporphyrins / Q000494:pharmacology; D019001:Nitric Oxide Synthase / Q000378:metabolism; D052250:Nitric Oxide Synthase Type III
D008665:Metalloporphyrins; C097284:manganese(III)-tetrakis(4-benzoic acid)porphyrin; D001708:Biopterins; C496314:NOS3 protein, human; D019001:Nitric Oxide Synthase; D052250:Nitric Oxide Synthase Type III; D006136:GTP Cyclohydrolase; C003402:sapropterin; D001205:Ascorbic Acid