| 摘要: | 黑色素是存在於動物皮膚的天然色素分子，是由分布在表皮與真皮間的黑色素細胞產生。黑色素的形成，由三種酪胺酸酶基因家族參與，包括tyrosinase， TRP1 和 TRP2。這三種酵素中，又以酪胺酸酶扮演關鍵作用，對黑色素合成最為重要。換句話說，在黑色素形成過程中，酪胺酸酶的過度活化，會造成色素性皮膚疾病，例如雀斑，黃褐斑，老年斑，和曬斑。黑色素形成的抑制可以藉由避免紫外線照射，抑制酪胺酸酶活性，以及降低黑素細胞的新陳代謝等方式。因此，除了避免紫外線照射，酪胺酸酶抑制劑的使用可能是一個簡單有效的辦法，以防止黑色素形成和皮膚色素性疾病。因此，許多研究著重於開發酪胺酸酶的抑制劑。此外，microphthalmia-associated transcription factor（MITF）是細胞中參與調控酪胺酸酶表達的主要轉錄因子。許多信號通路已被證實可以在黑色素細胞誘導黑色素合成。其中，PKA，PKC 與氧化壓力都是調節MITF 作用的關鍵因子，進而影響黑色素的形成。然而，報告也指出天然活性成分可以活化nuclear factor-E2-related factor (Nrf2) 訊號路徑可以增加抗氧化酵素的表現和保護色素細胞對抗氧化壓力。在我們先前的測試中，絡石(Trachelospermum jasminoides)表現出抗色素生成活性（如抗自由基，抗酪胺酸酶和抗黑色素合成）。這些數據表明，絡石可能可以用於預防黑色素不正常合成和色素性皮膚病。因此，在本研究第一年中，將探討絡石在 a-MSH 或 H2O2 對黑色素細胞B16 誘導的氧化壓力及黑色素合成反應，所扮演的保護作用。這項研究也將進一步確定絡石保護作用的分子機制，例如是藉由抑制MITF 或是活化Nrf2。在本研究第二年中，則將進一步確認絡石活性成分及其在酪胺酸酶的抑制作用確認。因此，本研究結果將可以確認絡石應用於抑制色素沉著的重要性。
Melanin, the natural pigment presented in animal skin, is produced by melanocytes and distribute in the basal layer between the dermis and epidermis. With regard to melanin formation, three major enzymes of the tyrosinase gene family are involved, including tyrosinase, tyrosinase-related protein 1, and tyrosinase-related protein 2. Among the three enzymes, tyrosinase is known to be the most important enzyme for melanin biosynthesis. In other words, the melanin formation because of tyrosinase activation causes dermatological disorders associated with freckles, melasma, age spots, and senile lentigines. Many reports suggested that melanin formation can be inhibited by avoiding ultraviolet exposure, by inhibiting tyrosinase activity, as well as by decreasing melanocyte metabolism. Thus, the use of tyrosinase inhibitors may be a simple and effective way to prevent melanin formation and dermatological disorders except for avoiding ultraviolet exposure. Therefore, investigations on tyrosinase inhibitors have received much attention. In addition, the microphthalmia-associated transcription factor (MITF) is the major transcription factor involved in the regulation of tyrosinase gene expression in melanocytes. Thus far, many important signaling pathways have been found to induce melanogenesis in melanocytes. Among these, the PKA-mediated pathway, the PKC-mediated pathway and oxidative stress exhibit critical roles to regulate MITF activation and melanin formation. However, many reports indicated the natural products-activated nuclear factor-E2-related factor (Nrf2) signaling can increase antioxidant enzyme expression and protect melanocytes against oxidative stress. In our previous test, a water extract of Trachelospermum jasminoides (WET) exhibited significant anti-melanogenic activities (e.g. anti-radical, anti-tyrosinase and antimelanogenesis). These data implied that WET might show beneficial effects in preventing disorders of melanogenesis and dermatology. Thus, in the first year of this study, the protective effects of WET were investigated in a-MSH or H2O2 induced oxidative stress and melanogenesis reaction in B16 cells. This study will further define the molecular mechanism (e.g. MITF inhibition and Nrf2 activation) by which WET mediates its effects on tyrosinase expression and melanogenesis. In the second year of this study, the bioactive constitutes of WET and their inhibitory effect in tyrosinase is determined. Therefore, this study attempted to assess the possibility that WET may be a possible inhibitor of hyperpigmentation. |
