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C preparations are exposed to UV rays or to air, the molecule rapidly adds two electrons and converts to DHAA, which contains an aromatic ring If further oxidized, the ring irreversibly opens and the vitamin C solution becomes permanently inactive VITAMIN C AS AN ANTIOXIDANT Vitamin C has become a popular addition to aftersun products because it has been shown to interfere with the UV-induced generation of ROS by reacting with the superoxide anion117 or the hydroxyl radical118 In fact, vitamin C is known to delay the incidence of UV-induced neoplasms in mice119 Topical vitamin C was studied as a photoprotectant first using a porcine skin model26 In this study, histologic examination revealed that animals treated with topical ascorbic acid exhibited fewer sunburn cells than those treated with vehicle alone when exposed to both UVA and UVB irradiation (Sunburn cells are basal keratinocytes undergoing programmed cell death because of irreparable DNA damage and represent a method of quantifying the damaging effects of UV irradiation) Researchers also observed a significant decrease in erythema in areas treated with vitamin C and decreases in the amount of vitamin C left on the skin after UV irradiation In a subsequent study, Darr and colleagues discovered that topical vitamin C combined with either a UVA or UVB sunscreen improved sun protection as compared to the sunscreen alone120 Vitamins C and E, in combination, also provided notable protection from UVB insult, though the bulk of protection was attributable to vitamin E There are multiple studies that demonstrate that mice treated with topical vitamin C have less erythema, fewer sunburn cells, and decreased tumor formation seen in treated skin after UV exposure3 Vitamin C, a strong antioxidant itself, also reduces (and therefore recycles) oxidized vitamin E back into its active form so the antioxidant capabilities of vitamin E are amplified or regenerated in this way40 THE EFFECTS OF VITAMIN C ON COLLAGEN AND ELASTIN SYNTHESIS Ascorbate is a cofactor for the enzymatic activity of prolyl hydroxylase, an enzyme that hydroxylates prolyl residues in procollagen, elastin, and other proteins with collagenous domains prior to triple helix formation, and thus is required for collagen synthesis121 Consequently, deficiency of ascorbic acid leads to impaired
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CHAPTER 34 ANTIOXIDANTS
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WATER-SOLUBLE ANTIOXIDANTS
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These are found in hydrophobic areas of the cell and the serum and include vitamin C and glutathione
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Glutathione
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Glutathione is the most abundant antioxidant in the network It is produced from the amino acids glutamic acid, cysteine, and glycine Oral glutathione is not well absorbed into the body, so supplementation is difficult it is not even available in cosmetic products There are no studies evaluating the efficacy of glutathione as an antioxidant Significantly, though, lipoic acid can recycle glutathione
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Vitamin C
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Vitamin C is historically known for its role in the prevention of scurvy By the 18th century, sailors knew that eating citrus fruits prevented this condition associated with dental abnormalities, bleeding disorders, characteristic purpuric skin lesions, and mental deterioration In the 1930s, researchers confirmed that vitamin C is the key ingredient in citrus fruit that prevents scurvy109 In contrast to some animals, humans obtain vitamin C solely from food, such
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FIGURE 34-4 Ascorbic acid
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collagen production resulting in scurvy Elastin also contains hydroxyproline; however, prolyl hydroxylation is not required for the biosynthesis and secretion of elastin,122 and the role of vitamin C in elastin production is unclear The addition of ascorbic acid to fibroblast cultures has been reported to increase collagen production by increasing the transcription rate of procollagen genes and by elevating procollagen mRNA levels123 Although the increase of type I collagen production in cells cultured in the presence of ascorbic acid is well known, the effects of ascorbate on other extracellular matrix molecules are still poorly understood124 In fact, studies have suggested that concentrations of ascorbic acid that maximally stimulate collagen biosynthesis act as an antagonist to elastin accumulation125 In a series of studies, Bergethon et al126 elaborated on these observations by showing that elastin accumulation was sharply diminished in cell cultures treated with vitamin C124 In other words, we know that the addition of ascorbic acid to fibroblast cultures increases production of collagen but may decrease production of elastin by an unknown mechanism Clinically the relevance of these effects on collagen and elastin are limited There is one study in the literature that examines the effects of topically applied vitamin C on wrinkles127 In this study, Cellex-C was shown to decrease wrinkles when applied topically for a period of 3 months The patients were evaluated using photography assessments and optical profilometry Unfortunately, this cannot be considered a blinded study because a large proportion of the patients experienced stinging on the side treated with vitamin C However, there was a significant difference in the wrinkles on the treated side versus the untreated side The mechanism of action of this difference is not understood It might be explained by increased collagen synthesis or by inflammation and irritation induced by the product Humbert et al evaluated the effects of topical vitamin C in healthy photoaged female volunteers in a double-blind, randomized trial They topically applied cream containing 5% vitamin C over a 6-month period, comparing the action of the vitamin C cream versus excipient on photoaged skin Clinically, a statistically significant improvement in hydration, wrinkles, glare, and brown spots was noted A highly significant increase in the density of skin microrelief and a
decrease of the deep furrows were also demonstrated Ultrastructural evidence of the elastic tissue repair was documented Tissue levels of the inhibitor of MMP-1 were increased, reducing UVinduced collagen breakdown The mRNA levels of elastin and fibrillin remained unchanged The topical application of 5% vitamin C cream was well tolerated128 However, more clinical trials are necessary to unravel all of the effects of vitamin C on skin and aging VITAMIN C AS ANTI-INFLAMMATORY AGENT Vitamin C has also been shown to possess anti-inflammatory activities In various cell lines loaded with vitamin C by incubating them with DHA, Carcamo et al were able to show a significant decrease in TNF- -induced nuclear translocation of NF- B, NF- B-dependent reporter transcription, and I B phosphorylation, suggesting that intracellular vitamin C can influence inflammatory, neoplastic, and apoptotic processes via inhibition of NF- B activation The decrease of inflammation can lead to a reduction of postinflammatory hyperpigmentation TOPICAL VITAMIN C Most of the data available on the effects of vitamin C are derived from studies examining the effects of oral vitamin C or vitamin C applied to tissue cultures Unfortunately, there are no studies that demonstrate that ingestion of oral vitamin C increases the levels of vitamin C in the skin Consequently, topical vitamin C preparations have become popular Ascorbic acid can be formulated into water- or lipid-soluble forms129 Topical ascorbyl palmitate, a lipid form, is nonirritating and reportedly photoprotective and anti-inflammatory130 Unfortunately, many of the currently available topical preparations are unable to penetrate the stratum corneum and are, consequently, useless Some manufacturers claim that their products are nonionic and less lipophobic, enhancing the opportunity for percutaneous absorption6,131 The aim of these topical products is to deliver higher amounts of vitamin C to a specific local area of the skin Comparison of the absorption rate of various topical formulations has not yet been performed using human subjects Another problem with topically applied ascorbic acid is its lack of stability as described above in the chemistry section Because few preparations of topical vitamin C are packaged in airtight containers that are protected from
UV radiation, most preparations become inactive within hours of opening the bottle OTHER COSMETIC APPLICATIONS Melasma As vitamin C inhibits the enzyme tyrosinase, it can be used as a depigmenting agent132 (see 33) In the mid-1990s, Kameyama et al found that a stable derivative of ascorbic acid produced a significant lightening effect in 19 of 34 patients treated for melasma and senile lentigos114 Among patients with normal skin, however, there was no significant lightening Postlaser erythema In a study of 10 patients who underwent skin resurfacing with a CO2 laser, vitamin C topically applied 2 or more weeks after surgery decreased the duration and degree of erythema116 Stretch marks In the late 1990s, Ash et al compared topical vitamin C in combination with glycolic acid to tretinoin and glycolic acid for the treatment of striae alba115 Blinded and unblinded observers determined that both regimens produced an objective improvement in the striae Although both regimens increased the epidermal thickness, only the tretinoin/glycolic combination augmented the elastin content of the striae SIDE EFFECTS The administration of vitamin C, in either oral or topical form, appears to be safe for human use In the studies reviewed, a small number of patients experienced minimal discomfort (stinging and mild irritation) from the topically applied formulations The major disadvantages of the various formulations include high cost, questionable efficacy, and the possibility of an adverse effect on elastin production, the clinical significance of which is currently unclear Ascorbic acid is a great addition to skin care particularly when patients insist on sun exposure, cigarette smoking, or other behavior that contributes to free radical production The practitioner should advise patients, though, to take the oral form so that they will experience the same antioxidant benefits in the arteries, liver, and other amenable organs If it really works, why limit its effects to the skin SUMMARY Vitamin C preparations are useful in preventing or lessening the harmful effects of UV radiation and ameliorating disorders of hyperpigmentation, striae, and postlaser erythema
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