探討苦瓜三萜類化合物對UVB刺激人類皮膚角質細胞的保護作用

Abstract

人體皮膚是保護身體抵抗外來傷害的第一道屏障，紫外線(UV) B（波長280-315 nm）能穿透皮膚表皮層(epidermis)，提高皮膚的氧化壓力與DNA損傷，誘導人類皮膚角質細胞(keratinocytes)產生發炎反應，導致皮膚光損傷(photodamage)及光老化(photoaging)。過度UVB曝露引起皮膚角質細胞大量凋亡而形成曬傷細胞(sunburn cells)可能導致皮膚癌。 山苦瓜(Momordica charantia L. var abbreviata Ser.)具有抗糖尿病、抗發炎、抗氧化、抗腫瘤、抗癌等藥理活性。本研究室先前研究發現山苦瓜葉甲醇粗萃物具有抑制酪胺酸酶活性、降低UVB誘導的活性氧物質等作用，因此本研究欲以細胞模式(cell-based assay)探討山苦瓜葉中三萜類化合物(triterpenoids)對於UVB刺激人類皮膚角質細胞（HaCaT細胞株）之保護作用。 本研究製備山苦瓜葉乙醇萃取物並取得5個區分物(fractions)，其中fraction 5對於UVB誘導HaCaT傷害具有良好的保護作用。自fraction 5純化得兩種葫蘆烷型(cucurbitane)三萜類化合物，分別為Kuguacin R和3, 7, 25-trihydroxycucurbita-5, 23-dien-19-al (TCD)。實驗結果證實Kuguacin R和TCD顯著提升UVB (20及30 mJ/cm2)照射後HaCaT細胞之存活率。兩種三萜類化合物都能顯著降低UVB誘導之細胞激素IL-1、IL-6、IL-8的生成，抑制MAPK蛋白質磷酸化與NF-κB活化，降低COX-2蛋白質含量並抑制PGE2生成，降低c-Jun蛋白質表現量，而TCD具顯著抑制c-Fos的能力，綜合以上結果，本研究顯示Kuguacin R和TCD具有抑制UVB誘導之發炎反應的功效。此外Kuguacin R和TCD具有抑制caspase-3活化及改善DNA斷裂的現象。另外in vitro經皮輸藥試驗確認Kuguacin R和TCD局部經皮吸收的能力。綜合上述結果，本研究推論Kuguacin R及TCD能減緩UVB造成的皮膚傷害，且有開發應用的潛力。Ultraviolet B (UVB) radiation plays a vital role in skin photodamage and photoaging. It causes serious inflammation and DNA damage of epidermis, which is the outermost viable layer of the skin and provides skin barrier function. In our previous study, methanolic leaf extract of wild bitter melon (WBM, Momordica charantia L. var abbreviata Seringe) shows anti-tyrosinase activity and significantly reduced UVB-induced reactive oxygen species (ROS) production in vitro. In this study, we investigated the protective effects of bitter melon triterpenoids on UVB-irradiated HaCaT cells. Two cucurbitane triterpenoids, Kuguacin R and 3, 7, 25-trihydroxycucurbita-5, 23-dien-19-al (TCD) were isolated from ethanolic leaf extract of WBM. HaCaT cells were pretreated for 24h with Kuguacin R or TCD prior to UVB irradiation (20-30 mJ/cm2), except for DNA fragmentation test (100 mJ/cm2). Our results showed that Kuguacin R and TCD inhibited UVB-induced cytotoxicity, and also diminished the productions of interleukin (IL)-1β, IL-6, and IL-8. Furthermore, both compounds significantly reduced phosphorylation of MAPKs, NF-κB activation, c-Jun, clyclooxygenase-2 protein levels, and the prostaglandin E2 production. In addition, both compounds inhibited caspase-3 activation and DNA fragmentation. Besides, Kuguacin R and TCD showed potential effects on percutaneous absorption in vitro. Our findings suggested that WBM triterpenoids, Kuguacin R and TCD may be beneficial for UVB-induced damage of keratinocytes and suggested its potential use in skin UV protection.