| OBJECTIVETo explore the mechanism of Doxycycline in the treatment of acute lung injury (ALI) in rats induced by Lipopolysaccharide by studying changes of expression of matrix metalloproteinase (MMPs) in lung tissue , PaO2, wet/dry weight (W/D) and The histopathology of the lung tissue,try to afford the evidence of prervention the endotoxin induced ALI in clinical praetice.METHODSSeventy two male SD rats were randomly divided into 3 groups: normal control group, ALI model group and treatment group. All rats, except normal control group, were administered with LPS by intratracheal injection to induce acute lung injury. The rats in treatment group were treated by Doxycycline (20 mg.kg-1, iv). Each rat in normal control group and ALI model group received injection of 1ml normal saline. The rats in the 3 groups were killed 1, 2, 4 and 8 h after operation, and then blood gas was monitored and the lung tissue wet/dry weight (W/D) was detected. The histopathology of the lung tissue was observed by light microscope. The expression of matrix metalloproteinase-2 (MMP-2) and matrix metalloproteinase-9 (MMP-9) proteins in the lung tissues was detected by immunohistochemistry and western blotting.RESULTS1.Arterial partial pressure of oxygen(PaO2) in the ALI model group and the treatment group decreased rapidly after the rats were administered with LPS by intratracheal injection.PaO2 in the ALI model group is lower than the treatment group (P<0.05). the blood pressure of the treatment group increased was still significantly lower than that of the control group(P<0.05～0.01).2. W/D value of ALI model group and the treatment group was significantly higher (P<0. 05). W/D value of ALI model group increased over time. The degree of pulmonary edema gradually increased. W/D value of the treatment group was lower than ALI model group, and there was a statistical difference(P<0.05～0.01).3. Pathological observation of lung tissue could see the organizational structure of the control group was basically normal and alveolar structure was clear; ALI model group showed diffuse lung injury congestive edema, a large number of efflusion in the alveoli pulmonis,alveolar septal widening, a large number of interstitial lung polymorphonuclear leukocyte infiltration and hyaline membrane formation; There was minor structural damage to alveolar of the treatment group. pulmonary edema and alveolar fluid was decreased, the extent of neutrophil infiltration was lighter than ALI model group4.Immunohistochemical examination showed MMP-2 mainly localized in alveolar epithelial cells, bronchial epithelial cells, bronchial smooth muscle cells, glands, pulmonary vascular endothelial cells, and neutrophils; The distributions of MMP-9 and MMP-2 are basically the same. MMP-2 expression was weakly positive in normal lung tissue; In ALI model group, the expression of MMP-2 and MMP-9 was strongly positive. The expression of MMP-9 and MMP-2 in the treatment group was significantly weakened than that in the ALI model group(P<0.01).5.Western Blot Detection of lung tissue showed that The expression of MMP-2 and MMP-9 was increased rapidly in the lung of ALI model group and treatment group. The expression of MMP-2 and MMP-9 in treatment group were lower than in ALI model group at various time points (P<0.05～0.01). They reached the highest value after 4h.CONCLUSION1. The ALI model could be made by intratracheal injection with LPS successfully.2. The severity of ALI was closely related with the expression of MMP-2 and MMP-9. the more concentration of the MMP-2 and MMP-9, the more damage to lung functions.3. Doxycycline has protective effects on endotoxin-induced acute lung injury in rats, which may be related with the decrease in the MMP-2 and MMP-9 level. |
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