The Early Acute Lung Injury Induced By Endotoxin And Protective Effects Of Chloroquine In Rabbits

OBJECTIVE: Endotoxemia caused by Gram-negative bacteria is a common reason of acute lung injury (ALI) . This study was focused on the pathogenesis of early ALI of rabbits induced by intravascular injection of E.coli endotoxin (ET). The unbalance between proinflammatory factors and anti-inflammatory factors were studied during the early stage of ALI, as well as the roles phospholipase AaCPLAi) activation and oxidative stress. More over, the protective effects of some cytokines were observed, including interleukin-13 (IL-13), superoxide dismutase (SOD) and prostacyclin (PGh). The benefits of chloroquine in ALI therapy was discussed as an inhibitor of PLA2.METHODS: 24 rabbits were randomly assigned to three groups (n=8): control group (group A), ET injected group (group B), and ET+chloroquine therapy group (group C). ALI was induced by intravascular injection of ET (500 g/Kg). The respiratory rate and blood pressure were recorded before and after the ET injection in three groups. The arterial gas analyses were measured, as well as the activity of PLAa both in serum and pulmonary tissue. Interleukin-13 (IL-13), lipid peroxide (LPO), SOD, thromboxane B2(TXB2) and 6-keto-prostaglandin Fin(6-keto-PGFia) in lung tissue were analyzed at the 6th hour of the experiment. The changes of pulmonary tissue were observed with the help of light microscope and transmission electron microscope.RESULTS: Rabbits injected with ET showed the early injuries of ALI compared with the parameters before ET injection, such as the increase of respiratory rate, the decrease of blood pressure and PaO2, as well as metabolic acidosis and the sequestration of leucocytes and platelets in lung tissue. In chloroquine treated group, Pa02 didn't change significantly compared with control group. Metabolic acidosis was alleviated, so was the decrease of leucocyte counts. PLA2 activities both inserum and pulmonary tissue were increased in ET group and chloroquine group, compared with group A and the activity before ET injection. In chloroquine group, PLA2 activities in serum and pulmonary tissue were lower than ET group (P<0.05, P<0.05). Compared with saline control group, the increase of LPO concentration (PO.05), decrease of SOD activity (P<0.05) and 6-keto-PGF1/ TXB2 ratio (P<0.05) in lung tissue were observed in ET group. In chloroquine group, LPO and SOD were elevated, but LPO was less than ET group (PO.05), while SOD was much higher than ET group (PO.01). 6-keto-PGFio/ TXB2 ratio in chloroquine group was similar to group A. The severe histopathological injuries were presented in ET group, such as pulmonary edema, endothelial injury, pulmonary hemorrhage, the infiltration of numerous inflammatory cells in alveolar and interstitial space, the construction of hyaline membrane, partial non-expanded lung and emphysema. Ultrastructural changes showed the edema of epithelial cells and endothelial cells, both type I and type II cell injuries. In chloroquine group, pathological examination proved the injuries were alleviated compared with ET group.CONCLUSIONS: (1) Intravascular injection of ET could induce early ALI in rabbits; (2) PLA2 played a crucial role in the pathogenesis of ALI; (3) Oxidative stress was an important reason that caused histopathological injuries; (4) Chloroquine could inhibit the activation of PLA2, thus alleviate lipid peroxidation and oxidative stress, and increase the protective factors such as SOD, IL-13, and PGI2; (5) Using chloroquine to inhibite the activity of PLA2, as well as maintaining the balance between proinflammatory and anti-inflammatory factors in vivo may provide new methods in early ALI treatment.