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Natural Vitamin E (Alpha Tocopherol)
The stratum corneum, the outermost barrier of the body is frequently and directly exposed to a pro-oxidative environment, including ultraviolet solar radiation. Depletion of vitamin E, being the major lipophilic antioxidant is an early and sensitive in vivo marker of UV induced photo-oxidation (60). UV radiation causes acute adverse effects like sunburn, photosensitivity reactions, or immunologic suppression, as well as long-term sequelae like photoaging or malignant skin tumors. Combined vitamins C and E reduce the sunburn reaction, which might indicate a consequent reduced risk of later sequelae (61).
Studies showed that alpha-tocopherol inhibits
UVR- induced epidermal lipid peroxidation, suggesting that this may be one mechanism by which
alpha-tocopherol prevents UVR-induced local
Immunosuppression.
Scavenging of UVR- generated lipid peroxides and reactive oxygen may inhibit loss of cell membrane integrity preventing depletion of lymphocyte numbers, thus protecting from local Immunosuppression (62).
However, application of alpha-tocopherol rich oil before exposure to UVR results in preservation of vitamin E (63). Animal experimental studies showed that topical application of
alpha-tocopherol, the most prominent naturally occurring form of vitamin E, inhibits ultraviolet induced photocarcinogenesis and DNA
photodamage. The topical application of alpha tocopherol at least 2 hours before exposure to sun is important to allow enough time for cellular uptake of alpha
-tocopherol as this is necessary for their optimal photoprotection (64). Clinical studies showed that
alpha-tochopherol act synergistically with Ascorbic acid and protect the skin against solar stimulated radiation induced skin inflammation and so suppress the sunburn reaction in healthy volunteers (65).
The presence of ozone (O (3)) in photochemical smog is considered another important health concern. The stratum corneum (SC), the outermost skin layer and the permeability barrier of the skin, represents a sensitive target for O (3)-induced oxidative stress and depletion of vitamin E. Remarkably, repeated low-level O (3) exposures resulted in cumulative oxidative effects in the stratum corneum (66). It has been found that damage of the cutaneous lipids caused by ozone exposure, is an effect that can be attenuated by vitamin E application (67).
Studies showed that vitamin E increased the stratum corneum hydration statistically significantly. There was also evidence of an enhanced water-binding capacity after treatment with vitamin E. For the hydrating effect of vitamin E its concentration is of importance. The optimum concentration turned out to be 5% (68).
Alpha-tocopherol has been found to negatively regulate proliferation of human skin fibroblasts and reduce the signs of aging, as cell proliferation is an important event in the aging process. . When
alpha-tocopherol was added to the growth medium at a physiological concentration of 50
microM, cell proliferation was inhibited by 40% in
72 h. Both the duration and concentration of the
alpha-tocopherol are important parameters of controlling the proliferation process (69).
The alpha-tocopherol topical treatment increased alpha- tocopherol levels both in the epidermis (62-fold) and the dermis (22-fold), further more it reduces the formation of epidermal lipid hydroperoxides after UV irradiation. Studies showed that topical
alpha-tocopherol application enhance the level of epidermal and dermal antioxidants and prevent ultra violet oxidative damage of cutaneous tissue. The underlying mechanism of this effect involves the up-regulation of a network of enzymatic and non -enzymatic antioxidants (70). After topical application of
alpha-tocopherol the stratum corneum was found to contain the highest concentration of vitamin E per micro m. thickness. The largest fraction of skin vitamin E following topical application was found in the deeper subcutaneous layer-the lowest layer, the papillary dermis and the dermis contained the major portion of the of the applied vitamin E. Although the papillary epidermis only represents about 16% of the total skin thickness, it contains sebaceous glands, lipid secretory organs and thus may account for the vitamin E affinity of this layer. Hence applied vitamin E penetrates rapidly through the skin but the highest concentrations are found in the uppermost 5 microns (71).
Studies showed that glycolic acid could strongly potentiate the antioxidant action of vitamin E. This suggests the advantage of combining alpha-glycolic acid with these antioxidants in skin-designed preparations, both to improve penetration and availability of antioxidants to epidermal layers and to enhance their protective potential (72).
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