兔内毒素性急性肺损伤中磷脂酶A_2致伤机制及氯喹保护作用的研究

The role of phospholipase A_2 in the pathogenesis of endotoxin-induced acute lung injury and the protective effects of chloroquine in rabbits

目的 研究大肠杆菌内毒素 (ET)致兔急性肺损伤 (ALI)过程中磷脂酶A2 (PLA2 )激活和氧化应激的致伤机制以及氯喹的保护作用。方法 2 4只大耳白兔随机均分为对照组、ET致伤组、ET致伤 +氯喹治疗组。静脉注射ET(5 0 0 μg/kg)致兔ALI,观测动脉血气、血清和肺组织中PLA2 的活性、肺组织脂质过氧化物(LPO)和超氧化物歧化酶 (SOD)含量的变化 ,并观察氯喹对ALI病理生理过程的影响。结果 静注ET后 ,兔出现动脉血氧分压下降、肺内白细胞扣押等ALI病理改变。ET组肺组织LPO增高 (P <0 0 5 ) ,SOD明显降低 (P <0 0 5 ) ,PLA2 活性增高 (P <0 0 1) ;病理检查见肺水肿 ,部分肺组织片状出血 ,伴局灶性肺不张和肺气肿 ;超微病理改变表现为Ⅰ型、Ⅱ型肺泡上皮细胞损伤。氯喹处理组动脉血氧分压未见下降 ,肺组织PLA2 活性低于ET组 ,LPO降低 ,SOD增高 ;病理检查见轻度肺水肿 ,炎细胞浸润较ET组少 ;肺组织超微病理检查显示损伤轻于ET组。结论 静脉注射ET可复制兔ALI动物模型 ,PLA2 激活及氧化应激在此病理生理过程中起重要作用 ;氯喹对ET所致的兔ALI具有一定的保护作用。

Objective To study the roles of phospholipase A 2 (PLA 2) and oxidative stress in the pathogenesis of acute lung injury(ALI) of rabbits induced by intravascular injection of endotoxin (ET), as well as the protective effects of chloroquine. Methods Rabbits were randomly assigned to three groups: control group, ET group, and ET+chloroquine group(n=8). Acute lung injury was induced by intravascular injection of ET (500μg/kg). The arterial blood gas analysis and serum PLA 2 activity were measured before and after the ET challenge. At the end of the experiment, PLA 2 activity, content of malodialdchyde (MDA), and superoxide dismutase (SOD) in lung tissue were assayed. Electron microscope and light microscope were used to observe the pathological injuries in the pulmonary tissue. Results Compared with saline controls, rabbits treated with ET manifested signs of ALI, such as the decrease of PaO 2(P<0.05) and leukocyte sequestration in the lung tissue. The PLA 2 activity was significantly increased in ET group compared with control group and chloroquine group both in serum and pulmonary tissue. The concentration of MDA was increased in lung tissue, while the concentration of SOD decreased. Severe histopathological injuries were present in ET group, such as pulmonary edema, endothelial injury, pulmonary hemorrhage, infiltration of numerous inflammatory cells in alveolar and interstitial spaces, the formation of hyaline membrane in alveoli, focal atelectasis and emphysema. Ultrastructural changes included edema of epithelial cells and endothelial cells, and injury to both type Ⅰ cell and type Ⅱ cell. In chloroquine group, PaO 2 was not decreased, PLA 2 activities in serum and pulmonary tissue were lower than that of ET group, the activity of SOD in lung tissue was increased significantly, while MDA content was decreased. Pathological examination proved that the lung injuries were alleviated by chloroquine. Conclusion Intravascular injection of ET induced ALI in rabbits. PLA 2 activation and oxidative stress played important roles in the pathogenesis of ALI. Chloroquine, as an inhibitor of PLA 2, can reduce MDA content and increase SOD activity in lung tissue in ALI, resulting in alleviation of the lung injury induced by endotoxin challenge.