BIOCONVERSION OF TOCOPHERYL ACETATE TO TOCOPHEROL IN HUMAN SKIN ORGAN CULTURE MODELS.
There is substantial interest in delivering the antioxidant benefits of vitamin E (tocopherol) to the skin. Since free tocopherol is inherently unstable, it is usually delivered to the skin in the form of tocopheryl acetate. The premise behind this approach is that the skin’s enzymes (esterases/lipases) would bioconvert the pro-vitamin E to the active vitamin. However, recent clinical studies by Alberts, et al. (Nutr. Cancer, 1996, 26: 193) suggest that human skin lacks the enzyme(s) necessary for this bioconversion. Thus, the objective of this study was to use human skin explants to examine the bioconversion of tocopheryl acetate to tocopherol. For comparison, two organotypic models, Living Skin Equivalent (LSE, Skin2™ ZK1300, Advanced Tissue Sciences, CA) and the EpiDerm™ Skin Model (EPI-100, MatTek Corp., MA) were also used in these studies. Samples of viable human skin obtained from breast reduction surgery were sliced into 0.5 cm2 pieces and maintained at the air-liquid interface in RPM1 medium supplemented with 5% fetal bovine serum. The organotypic models were used according to manufacturer’s recommendation. All organ cultures were treated topically (4 mg/cm2) with a lotion (oil in water emulsion) + 1% tocopheryl acetate and incubated at 37°C in a 5% CO2 environment. Skin samples were extracted with ethanol at various time points to recover tocopheryl acetate and tocopherol, which were then quantified by HPLC. Bioconversion of tocopheryl acetate to tocopherol was observed by the appearance of a new peak in the HPLC chromatogram. This bioconversion reached maximum levels at 6 hr in LSE and 10 hr in the skin explants. Additionally, in the EpiDerm model, pre-treatment with tocopheryl acetate reduced the peroxide-induced cell damage as determined by MTT assay. The results of these studies show that 1) human skin and LSE possess the enzymes necessary to bioconvert tocopheryl acetate to the active tocopherol from topical formulation and 2) the skin explant can serve as a useful model for studying the skin’s metabolic activity.
Antioxidants, Cosmetic Personal Care Products, Endpoints, MTT, Epi-100, EpiDerm, MTT, MTT ET-50 tissue viability assay, MTT assay, Skin models, cultured, Tocopherol, Tocopheryl acetate
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