Efficacy of topically applied tocopherols and tocotrienols in protection of murine skin from oxidative damage induced by UV-irradiation

To assess the efficacy of various forms of vitamin E in protection of skin from UV-light-induced oxidative stress, vitamin E (tocotrienol-rich fraction of palm oil, TRF) was applied to mouse skin and the contents of antioxidants before and after exposure to UV-light were measured. Four polypropylene plastic rings (1 cm2) were glued Ohio the animals' backs, and 20 μl 5% TRF in polyethylene glycol-400 (PEG) was applied to the skin circumscribed by two rings and 20 μl PEG to the other two rings. After 2 h, the skin was washed and half of the sites were exposed to UV-irradiation (2.8 mW/cm2 for 29 mi: 3 MED). TRF treatment (n = 19 mice) increased mouse skin α-tocopherol 28 ± 16-fold, α-tocotrienol 80 ± 50-fold. γ-tocopherol 130 ± 108-fold, and γ-tocotrienol 51 ± 36-fold. A significantly higher percentage of α-tocopherol was present in the skin as compared with that in the applied TRF. After UV-irradiation, all vitamin E forms decreased significantly (p < .01), while a larger proportion of the vitamin E remained in PEG-treated (≃80%) compared with TRF-treated (≃40%) skin. Nonetheless, vitamin E concentrations in irradiated TRF-treated skin were significantly higher than in the nonirradiated PEG-treated (control) skin (p < .01). Thus, UV-irradiation of skin destroys its antioxidants; however, prior application of TRF to mouse skin results in preservation of vitamin E

Penetration and distribution of α-tocopherol, α- or γ-tocotrienols applied individually onto murine skin

To evaluate skin penetration of various vitamin E homologs, a 5% solution of either α-tocopherol, α-tocotrienol, or γ-tocotrienol in polyethylene glycol was topically applied to SKH-1 hairless mice. After 0.5, 1, 2, or 4 h (n = four per time point and four per vitamin E homolog), the skin was washed, the animals killed, the skin rapidly removed, frozen on dry ice, and a biopsy taken and sectioned: stratum corneum (two uppermost, 5-μm sections-SC1 and SC2), epidermis (next two 10-μm sections-E1 and E2), papillary dermis (next 100 μm, PD), dermis (next 400 μm, D), and subcutaneous fat (next 100 μm, SF). SC1 contained the highest vitamin E concentrations per μ thickness. To compare the distribution of the various vitamin E forms into the skin layers, the percentage of each form was expressed per its respective total. Most surprising was that the largest fraction of skin vitamin E following topical application was found in the deeper subcutaneous layers-the lowest layers, PD (40 ± 15%) and D (36 ± 15%), contained the major portion of the applied vitamin E forms. Although PD 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 for this layer. Hence, applied vitamin E penetrates rapidly through the skin, but the highest concentrations are found in the uppermost 5 microns