動脈粥狀硬化 (atherosclerosis) 是一種包含血管內皮細胞功能損傷、發炎，以及脂肪堆積等過程的血管慢性疾病，其所產生的併發症是全球主要死亡原因。血液紊流 (disturbed flow) 好發於血管分岔和彎曲的地方，血液呈現多方向性較慢的流動，造成血管壁承受剪切力變小而亂，而內皮細胞 (endothelial cell) 位於血管的最內層，直接受到血液紊流的刺激而轉變成促進動脈粥狀硬化模式，在血液紊流之下的內皮細胞會過度表達內皮素-1 (endothelin-1)，以及分泌促炎性細胞因子。當內皮素-1與其內皮素A型受體結合之後會使血管平滑肌細胞收縮、增生、遷移。研究顯示，內皮素A型受體在病理以及發炎的條件之下會受到誘導而表達於內皮細胞，而正常的條件下，內皮素A型受體大多表達在平滑肌細胞。因此我們假設，血液紊流誘導內皮細胞表達內皮素A型受體，與內皮素-1結合後使內皮細胞失能造成動脈粥狀硬化。首先為了觀察內皮素A型受體在血液紊流之下是否會受到誘導表現於內皮細胞，在動物模式中，我們利用結紮左側總頸動脈手術造成區域血液紊流，並以口服給予小鼠內皮素A型受體拮抗劑Zibotentan，四個星期後發現，阻斷內皮素-1與內皮素A型受體的結合，可防止血液紊流刺激血管內膜新生 (neointima formation)及內皮素A型受體在內皮細胞的表達。而為了近一步觀察動脈粥狀硬化的發展過程，我們使用高血脂背景的ApoE- knockout (KO) 小鼠，施予部分頸動脈結紮手術，三個星期後血管內有明顯粥狀斑塊(plaque)形成，並每天口服給予內皮素A型受體拮抗劑Zibotentan，發現粥狀斑塊大小顯著減小。而血液紊流會誘導內皮素A型受體在內皮細胞表達，藉由阻斷內皮素-1與內皮素A型受體的結合，顯著抑制內皮素A型受體在內皮細胞的表達，也使發炎反應得到緩解，同時也減少了脂肪堆積。因此我們的實驗結果證實，內皮素A型受體會受紊流誘導在內皮細胞表達刺激動脈病變，阻斷內皮素-1與內皮素A型受體的結合可以有效地防止動脈粥狀硬化。
關鍵詞: 內皮素-1，內皮素受體A，動脈粥狀硬化，血液紊流。

Atherosclerosis is a chronic vascular disease involving endothelial dysfunction, inflammation, and lipid accumulation. The complication of atherosclerosis is the leading cause of death in the world. Disturbed flow imposes low and irregular distribution of vessel wall shear stress at arterial bifurcations and curvatures. Endothelial cells (ECs) chronically activated by disturbed flow acquire atheroprone phenotypes. Atheroprone ECs overexpress endothin-1 (ET-1) and secrete proinflammatory cytokines. ET-1 binding with its receptor ETA leads to smooth muscle cell contraction, proliferation and migration. ETA is critical in the development of diseases such as pulmonary hypertension, atherosclerosis and myocardial ischemia. ETA expression is largely found in vascular smooth muscle cells and barely detectable in ECs. We hypothesized that ETA is induced by disturbed flow in ECs to mediate ET-1-associated atherosclerosis. We used the complete-carotid-artery-ligation mouse model to generate local blood flow turbulence to induce neointima in wild-type (WT) C57BL/6 mice. The left common carotid artery (LCA) was ligated close to the bifurcation. The unligated right common carotid artery (RCA) was used as a sham control. Neointima was induced in WT mice 4 weeks after ligation. Remarkably, daily treatment of the ETA-specific antagonist Zibotentan given orally at 10 mg/kg/day using a gavage needle starting immediately after ligation effectively inhibited ligation-induced neointimal hyperplasia. Additionally, we performed partial carotid artery ligation to induce plaque formation in ApoE- knockout (KO) mice by ligating the downstream branches of LCA, including external carotid artery; internal carotid artery; occipital artery, leaving the superior thyroid artery (STA) open. We found that oral Zibotentan at 10 mg/kg/day inhibited plaque formation in ApoE-KO mice 3 weeks after ligation. The levels of ETA in the endothelium were elevated by ligation measured by immunofluorescence, which supports the use of Zibotentan to block ET-1 action in ECs. The proinflammatory cytokine monocyte chemoattractant protein-1 (MCP-1) and vascular cell adhesion molecular-1 (VECAM-1) expressions were induced by ligation. The induction of ETA, MCP-1and VCAM-1 expression in ECs was abrogated by oral Zibotentan. In conclusion, endothelial ETA expression is induced by disturbed flow. Blocking ET-1/ETA binding inhibits atherogenesis.

Key words: Endothelin-1, ETA, atherosclerosis, disturbed flow

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