e39 Anti-melanogenic properties of vitamin E Comparable down-regulation of TYR, TYRP1 and TYRP2 genes and inhibition of melanogenesis by tyrostat, tocotrienol-rich fraction and tocopherol in human skin melanocytes improves skin pigmentation S. Makpol 1 , F.A. Jam 1 , N.A. Rahim 1 , S.C. Khor 1 , Z. Ismail 2 , Y.A.M. Yusof 1 , W.Z.Wan Ngah 1 1 Department of Biochemistry, Faculty of Medicine, Universiti Kebangsaan Malaysia, Jalan Raja Muda Abdul Aziz, 50300 Kuala Lumpur, Malaysia, and 2 R&D Plantation and Agri-Business Division, Sime Darby Research Sdn Bhd, 42960 Carey Island, Selangor, Malaysia Original article Clin Ter 2014; 165 (1):e39-45. doi: 10.7471/CT.2014.1670 Correspondence: Professor Dr. Suzana Makpol. Department of Biochemistry, Faculty of Medicine, Universiti Kebangsaan Malaysia, Jalan Raja Muda Abdul Aziz, 50300 Kuala Lumpur, Malaysia. Tel.: 603-92897525, 603-92897222; Fax: 603-26938037. E-mail: suzanamakpol@yahoo.com Copyright © Società Editrice Universo (SEU) ISSN 1972-6007 Introduction Skin plays an extremely important role in providing physical barrier against mechanical, chemical and microbial attacks that may affect the physiological status of the body. Skin aging is characterized histologically by the presence Abstract Background and Objective. Antioxidant has been recognized to inhibit UV-induced melanogenesis. This study aimed to elucidate the molecular mechanism of tyrostat, tocopherol and tocotrienol-rich fraction in inhibiting melanogenesis in human skin melanocytes. Materials and Methods. Primary culture of melanocytes was exposed to repeated doses of 0.6 J/cm 2 UVA for 6 days and treated with tyrostat, tocotrienol-rich fraction or tocopherol alone or in com- bination. Results. UVA irradiation increased melanin content and tyrosinase activity and up-regulated TYR, TYRP1 and TYRP2 genes. Treatment with tyrostat, tocotrienol-rich fraction or tocopherol decreased mela- nin content and down-regulated TYR, TYRP1 and TYRP2 genes with decreased tyrosinase activity. Combined treatment exerted better effects as compared to treatment with single compound in decreasing the melanin content and down-regulating TYR, TYRP1 and TYRP2 genes. These findings indicated that tyrostat, tocotrienol-rich fraction and tocopherol inhibit melanogenesis by modulating the expression of genes involved in the regulation of melanin synthesis and inhibiting tyrosinase activity. Conclusion. Tyrostat, tocopherol and tocotrienol-rich fraction possessed anti-melanogenic properties and might be useful in im- proving skin pigmentation caused by UVA exposure. Clin Ter 2014; 165(1):e39-45. doi: 10.7417/CT.2014.1670 Key words: tyrostat, tocotrienol-rich fraction and tocopherol, melanin content, tyrosinase, tyrosinase-related proteins, human skin melanocytes of irregular dispersed melanocytes, elastosis, reduction and alteration of collagen synthesis and accumulation of a variety of lipid-derived pigments such as chromolipoids and lipofuscins. Melanogenesis or skin pigmentation is a complex pathway that occurs in highly specialized cells called me- lanocytes. It produces melanin pigment and is increased during skin aging (1). Melanocytes are dendritic cells which synthesise melanin in melanosomes. Melanosomes form su- pranuclear caps that protect epidermal cells from damage by limiting the penetration of ultraviolet radiation through the epidermal layers of the skin and scavenging reactive oxygen species (ROS) that are generated by ultraviolet radiation. In this regard, melanocytes are considered as the ‘guardian of the skin’. In vitro human melanocytes respond directly to UV-light which results in increased melanogenesis (2) and has been used as a model for skin lightening study. Melanogenesis is controlled by an enzymatic cascade which is regulated by tyrosinase, tyrosinase-related protein-1 and tyrosinase-related protein-2 (TYRP1 and TYRP2) (3). The modulation of tyrosinase activity therefore represents a key-process for the regulation of skin pigmentation (4). Va- rious factors including endocrine and environmental factors affect melanogenesis (5). The predominant environmental factor that accelerates human skin aging is ultraviolet (UV) irradiation from the sun which results in photoaging. Photo- aging is a cumulative process that depends primarily on the degree of sun exposure and skin phenotype. Ultraviolet A (UVA) induces the formation of ROS that readily react with membrane lipids and amino acids (6). The most important mechanisms of skin protection from UV rays are stratum corneum thickening and melanin synthesis by melanocytes (7). UV rays induce the activity of melanocytic tyrosinase, branching of the melanocyte dendritic portions, increase the number and size of melanosomes and melanin granules in the cells and accelerate the transfer of melanin into keratinocytes.