急性肺損傷(ALI)及急性呼吸窘迫症候群(ARDS)在加護病房以及嚴重手術之後是最常見的致死因素。急性肺損傷的基礎致病機轉主要是由發炎反應所引發的肺泡-微血管通透性增加。肺部血管內皮的活化與損傷是另一個急性肺損傷的標誌。有一些內皮標的性的療法已經過臨床實驗測試，但是都無法有效的回復肺部血管的內皮功能。越來越多的證據顯示，周邊血當中含有來自骨髓的前驅細胞。這些循環的前驅細胞有部份能夠分化成成熟的血管內皮細胞，而這些細胞被稱做內皮前驅細胞(EPCs)。最近的研究顯示，內皮前驅細胞對於心血管疾病的病人在血管的再內皮化(reendothelialization)及血管新生具有治療效果。在我們先前的研究中指出，在油酸(oleic acid)引發的急性肺損傷模式中，自體移植內皮前驅細胞能使內皮細胞功能缺失的情形減弱，也能降低肺部組織的受損程度。因此，本篇研究使用更貼近臨床狀況的氣管直接給予LPS的肺損傷模式，來探討EPCs對肺部血管再內皮化的影響。我們使用標準淋巴細胞梯度離心法從兔子周邊動脈血中分離出單核球。在培養的第七天，我們將貼附的細胞定義為早期的EPCs，這些細胞將被收下做為移植備用。麻醉後的兔子從氣管注入LPS，隨後經由耳靜脈自體移植EPCs。兔子在48小時後犧牲，組織將取下做分析。與控制組相比，EPC治療的動物動脈血中的氧氣分壓以及飽和度都明顯提升，表示肺部氣體交換功能受到較好的保護。接受EPCs移植的兔子，肺動脈的內皮依賴性舒張反應也有明顯的恢復。接下來我們使用肺部組織中Evans blue染劑的含量來測量肺部肺泡-微血管膜洩漏的程度，結果在EPCs治療的動物組別明顯的下降。肺部水含量和肺出血程度評估是利用肺部濕乾重比和組織血紅蛋白含量測定，都在EPC治療組中較減少。經過EPCs的移植，骨髓過氧化酶的活性顯著降低，顯示EPCs的移植能減緩肺部組織嗜中性白血球活化和聚集的情況。總結來說，我們的結果顯示了自體移植EPCs能藉由回復肺泡微血管及肺部內皮的功能來減緩由LPS所引發的ALI的程度。給予自體移植EPCs可能是一個新的細胞性的，針對肺部血管內皮的ALI/ARDS治療策略。

Acute lung injury (ALI) and the acute respiratory distress syndrome (ARDS) are the most common causes of death in intensive care units and after major operation. The fundamental pathogenesis of ALI is increased alveolocapillary permeability largely due to inflammatory response in the pulmonary endothelium and alveoli. Activation and damage of pulmonary endothelium is another hallmark of ALI/ARDS. A number of endothelium-targeting therapies have been tested in clinical settings, but none of these restores pulmonary endothelial function during ALI/ARDS. Accumulating evidence suggests that peripheral blood contains bone marrow-derived progenitor cells. A portion of these circulating precursor cells can differentiate into mature endothelial cells and are referred to as endothelial progenitor cells (EPCs). Recent studies have demonstrated the therapeutic effects of EPCs on reendothelialization and neovascularization in patients with cardiovascular diseases. Previous report showed that autologous transplantation of EPCs attenuates pulmonary endothelial dysfunction and lung tissue damage in rabbits with oleic acid-induced ALI. Accordingly, this project examines the effect of EPCs on pulmonary reendothelialization in a more clinically relevant rabbit model of ALI induced by direct intratracheal instillation of lipopolysaccharide (LPS). Mononuclear cells were isolated from the peripheral blood of rabbits using the standard Ficoll gradient centrifugation. At day 7 of culture, the adherent cells, termed as early EPCs, were harvested for transplantation. Anesthetized rabbits received LPS (500 g/kg) via intratracheal instillation, and followed by autologous transplantation of EPCs through the ear vein. Rabbits were sacrificed 48 hours later and tissues were obtained for analysis. Compared with control, arterial oxygen content and saturation were higher in the EPC-treat animals, indicating that function of pulmonary alveolocapillary gas exchange was better preserved following transplantation of EPC. Endothelium-dependent relaxation response of pulmonary artery was significantly restored in rabbits received EPC transplantation. The degree of alveolar-capillary barrier leakage was measured by tissue Evans blue content, and was significantly reduced in EPC-treated group. Lung water content and degree of lung hemorrhage assessed by the lung wet-to-dry ratio and tissue hemoglobin were reduced in the EPC-treated group, respectively. Myeloperoxidase (MPO) activity was also reduced following transplantation of EPCs, indicating that activation and accumulation of neutrophils was attenuated in EPC-treated group. Collectively, our data underscore that autologous transplantation of EPCs attenuates LPS-induced ALI by restoring alveolocapillary and pulmonary endothelial function. Administration of EPCs can be a novel cell-based, pulmonary endothelium-targeted therapeutic strategy for ALI/ARDS.

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