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Natural Vitamin C (Ascorbic, Ascorbate)
Vitamin C (Ascorbic, Ascorbate) is an essential micronutrient involved in many biologic and biochemical functions. Humans cannot synthesize vitamin C because they lack the last enzyme in biosynthetic pathway.
Known functions of vitamin C are accounted for by its action as an electron donor or reducing agent. Vitamin C is a specific electron donor for 8 enzymes (81,82). Three of them are enzymes that participate in collagen hydroxylation (important step for keeping a healthy skin.
Vitamin C also has non-enzymatic-reductive functions in chemical reactions. Based on its free radical intermediate, vitamin C is a chemical reducing agent (antioxidant) in many intracellular and extracellular reactions. Vitamin c could also decrease oxidative damage in vascular walls (83,84).
Environmental exposure to ultraviolet light B (UVB, wave lengths 290-320
nm) of the solar spectrum causes major damage, including an inflammatory response, in skin. Studies using the human keratinocyte cell line, showed that stable derivative of ascorbic acid, are able to reduce UVB damage. These data suggest that ascorbic acid shows a photoprotective effect against
UVB-induced inflammation and damage in human epithelial cells (85). Topical application of ascorbic acid suppresses the cutaneous inflammation induce by ultraviolet irradiation in human and animals. Studies suggested that it prevents the acute inflammation partly through scavenging reactive oxygen species and potentiating the antioxidative activity of
alpha-tocopherol (86). Experimental studies showed that ascorbic acid inhibited
UVA-induced lipid peroxidation in cultured human keratinocytes in a concentration-dependent manner.
It has also been found that ascorbic acid was able to down regulate the proinflammatory cytokines IL-alpha and IL-6. These findings indicate a major cell-protective effect of ascorbic acid on
UVA-induced lipid peroxidation and the secretion of pro-inflammatory cytokines by UVA irradiated human keratinocytes (87).
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