- 學位論文
多酚類化合物保護氧化型低密度脂蛋白所誘發內皮細胞損傷之作用機制探討
Protective effects of polyphenolic compounds on oxidized LDL-induced endothelial dysfunction
摘要
動脈粥狀硬化（atherogenesis）的特徵為脂質沈積、慢性發炎及慢性傷口癒合的過程。細胞凋亡（apoptosis）在內皮細胞損傷、壞死的核心形成及血管斑塊斷裂扮演重要角色。動脈粥狀硬化形成初期主要是經由氧化型低密度脂蛋白（oxidized low-density lipoproteins；oxLDLs）在內皮細胞（endothelial cells）的累積並活化內皮細胞及增加與單核球（monocytes）間之黏著作用。廣泛存在天然植物、蔬果及傳統中草藥中之各種不同化學結構的多酚類化合物，經由日常飲食而攝入人體內，許多的研究皆顯示這些多酚類化合物所具有的生物活性對心血管疾病、抗癌、抗病毒、抗過敏有好處。多酚類化合物可經由清除自由基、與過渡金屬螯合而抑制低密度脂蛋白的氧化作用而具抗動脈硬化之作用。本論文主要的研究目的是探討天然物所含之多酚類如白藜蘆醇（resveratrol）、鞣花酸（ellagic acid）、綠茶多酚（epigallocatechin-3-gallate; EGCG) 及中草藥如丁香酚（eugenol）、和厚朴酚（honokiol）、厚朴酚（magnolol）及銀杏（gingko）等，其抑制低密度脂蛋白所誘發之內皮細胞功能失調及細胞毒性之作用，並進一步探討其抗氧化、抗發炎之訊息傳遞路徑與分子機轉。研究結果顯示多酚類化合物減少非毒性劑量（100 ug/ml）氧化型低密度脂蛋白對一氧化氮合成酶的抑制作用、減少細胞表面黏著分子表現及與單核球細胞之黏著，此外多酚類化合物減少毒性劑量（200 ug/ml）氧化型低密度脂蛋白所誘發氧自由基產生、細胞內鈣離子增加、粒線體膜電位改變及caspase 3活化所導致的細胞凋亡。本論文所建立的分子細胞模式可快速、有效率評估多酚類化合物的抗動脈硬化效果，並進一步探討細胞內訊息傳遞路徑，這些研究結果將有助於提升多酚類化合物應用於預防及治療動脈硬化的臨床價值。
並列摘要
Atherogenesis is characterized by lipid deposition, a chronic inflammatory response, and chronic wound healing processes. Apoptosis may play a role in endothelial cell lining defects, necrotic core formation, or plaque erosion and rupture. Among the variety of proapoptotic factors present in atherosclerotic plaques, oxidized low-density lipoproteins (oxLDLs) are thought to play a crucial role by concomitantly inducing lipid storage, local inflammation, and toxic events. Polyphenolic compounds with different chemical structures are widely distributed in plant foods, vegetables, fruits and chinese herbs and, therefore, are ingested regularly with human diet. A large number of biological actions of polyphenolic compounds have been described to be beneficial for cardiovascular system, as well as anticancer, antiviral and antiallergic properties. Polyphenolic compounds can reduce LDL lipid peroxidation by scavenging ROS, chelating transition metal ions and sparing of LDL-associated antioxidants. In this study, we explored the effects of polyphenolic compounds, including resveratrol, ellagic acid, epigallocatechin-3-gallate (EGCG), eugenol, honokiol, magnolol and ginkgo, on human umbilical vein endothealial cells (HUVECs) dysfunction mediated by oxLDL. Our results showed that the suppression of endothelial nitric oxide synthase (eNOS) expression, enhancement of adhesion molecules (ICAM, VCAM, and E-selectin) expression, and adherence of monocytic THP1 cells caused by a non- cytotoxic concentration (100 ug/ml ) of oxLDL were ameliorated following a pretreatment of polyphenolic compounds in HUVECs. Furthermore, polyphenolic compounds also inhibited the ROS generation , elevation of intracellular calcium, and the subsequent mitochondrial membrane potential collapse, cytochome c release and caspase 3 activation induced by oxLDL. The cytotoxicity and apoptotic features induced by a cytotoxic concentration (200 ug/ml) of oxLDL was also attenuated by polyphenolic compounds. The present studies demonstrated that it is possible to establish an evaluation system for polyphenolic compounds, it will help us to further explore the mechanisms of pharmalogical modulatory bio-activities. Results from our findings shed some light on the potential implications of phenolic compounds in the prevention of the atherosclerotic process.