Study On Endotoxin-induced Acute Lung Injury And The Antagonizing Effects Of Meloxicam In Rabbits

OBJECTIVE: Acute lung injury (ALI) is one of complications which can be early seen after severe trauma and infection, with high morbidity and mortality. Among various stimuli, endotoxin plays a major part in both the development and the outcome of ALI. So, animal ALI models were replicated with E.coli endotoxin (ET) injected intravascularly at a time in flap-eared white rabbits in this study. By observing or measuring correlative marks of physiology, biochemistry and pathology within those ET-induced ALI models, pathophysiologic changes were further researched, and the possible mechanisms of a few factors resulting in pulmonary injury, such as Cycloxygenase-2 (COX-2), matrix metalloproteinases-2 (MMP-2 ) , peroxisome proliferators-activated receptor-γ (PPAR-γ), interleukin-19 (IL-19), heart-fatty acid-binding protein (H-FABP), oxidative stress, microvascular disorder, were also further studied. Meanwhile, this study explored the effects of Meloxicam, in order to further develop the clinical therapeutic method of ALI.METHODS: 24 flap-eared white rabbits were randomly assigned to three groups: control group (group A), injury group (group B) and meloxicam-treated group (group C). There were eight animals in each group. Group A recevied saline(2ml/kg). Group B were intravenously injected ET (700μg/kg).Group C were identical to Group B but received Meloxicam (2.5mg/kg) 10 min prior to endotoxin. In the process of our experiment, respiratory rates, heart rates, blood pressures,blood gas were measured at 0h,0.5h,1h,2h,4h respectively. After 4 hours , the rabbits were killed by exsanguinations.The expression of COX-2mRNA,MMP-2mRNA, PPAR-γmRNA and PPAR-γ protein were detected in rabbits lung tissues. The activity of superoxide dismutase(SOD), the levels of malondialdehyde (MDA) and the levels of IL-19 in lung homogenate of rabbits were measured respectively. The concentration of thromboxane B₂ (TXB₂), 6-keto-prostaglandin F_1α (6-keto-PGF_1α) , endothelins-1 (ET-1) in lung homogenate and the concentration of TXB₂, 6-keto-PGF_1α) FABP in heart homogenate were detected. Then, pathologic changesof lung tissues and heart tissues were observed.RESULTS: Compared with group A, animals of group B showed typical characters of ALI at 0.5h after ET injected, including the increase of respiratory rates and heart rates,the decrease of blood pressures and arterial blood oxygen pressures (p<0.01).The pulmonary expression of COX-2 mRNA and MMP-2mRNA in group B were significantly higher than those in group A(p<0.01). The pulmonary expression of COX-2 mRNA and MMP-2mRNA in group C were significantly lower than those in group B(p<0.01), but, significantly higher than those in group A (p<0.01) . The pulmonary expression of PPAR-γ mRNA and PPAR-γ protein in group B were significantly lower than those in group A (p<0.01). The pulmonary expression of PPAR-γ mRNA and PPAR-γ protein in group C were significantly higher than those in group B (p<0.01), but, significantly lower than those in group A (p<0.01). The pulmonary levels of MDA increased significantly in group B compared to the group A and group C(respectively P<0.01,P<0.05). The activity of SOD in group B obviously decreased, compared to the group A and group C (respectively P<0.05 ,P<0.01). There was no statistical difference of the MDA levels and SOD activity between the group A and group C (P>0.05). The levels of IL-19 increased significantly in group B compared to the group A. In group C ,the levels of IL-19 were significantly lower than those in group B (p<0.01), but, significantly higher than those in group A (p<0.01).In group B, plumonary TXB₂/6-keto-PGF_1α ratio and the levels of ET-1 were significantly higher than those in group A(p<0.01). In group C, pulmonary TXB₂/6-keto-PGF_1α ratio, the levels of ET-1 were significantly lower than those in group B(p<0.01). In group B, myocardial TXB₂/6-keto-PGF_1α ratio was significantly higher than that in group A (p<0.05),the levels of myocardial H-FABP were significantly lower than those in group A(p<0.01). In group C, myocardial TXB₂/6-keto-PGF_1α ratio was between group A and group B. The levels of myocardial H-FABP in group C were significantly higher than those in group B(p<0.05). Typically pathological changes could be easily seen in group B. Pulmonary tissues of group C showed less injuries and were similar to those of group A . Focal cadiocytes swelling and small amounts of inflammatory cell infiltrationinto myocardium were observed in group B. Pathological injuries of heart in group C were alleviated.CONCLUSION: (1)ALI animal models of flap-eared white rabbits can be replicated with ET injected intravascularly at a time. (2)COX-2 is the key enzyme of prostanoid synthesis by arachidonic acid. The increased activity and expression of COX-2 play crucial roles in the pathogenesis of ALI. (3)MMP-2, one of MMPs , could degrade the main component of basal membrane- type IV collagen. That may play a important role in increasing capillary permeability, forming pulmonary edema and the infiltration of inflammatory cells. (4)PPAR-γ which is a member of type II nuclear hormone receptor superfamily of ligand-activated transcription factors, can regulate the expression of many intranuclear gene on the transcription level. The anti-inflammatory properties of PPAR-γ may control inflammation in ALI.(5)The oxidative stress reactions and oxidative injury are important in the pathogenesis of ET-induced ALI too.(6)IL-19 may play an important role in inflammatory reaction of ALI.(7)Microcirculation disorders of pulmonary tissues are significant factor to aggravate ALI. (8)H-FABP is a early marker of myocardial damage. The myocardial levels of H-FABP decreases significantly in endotoxin-induced ALI, which could indicate the myocardial damage in ALI. (9)Meloxicam can enhance the resistances of body to ET-injuries, and protect flap-eared white rabbits from ET-induced ALI to a certain extent by down-regulating the pulmonary expression of COX-2mRNA, MMP-2mRNA , by up-regulating the pulmonary expression of PPAR-γmRNA, PPAR-γprotein, by decreasing the levels of IL-19,by enhancing the activities of SOD, down-regulating the ratio of TXB₂/6-keto-PGF_1α in lung tissues , reducing the levels of ET-1 and MDA in lung tissue ,by down-regulating TXB₂/6-keto-PGF_1α ratio and increasing the myocardial levels of H-FABP ,which may posses some protective effects on ALI induced by ET in rabbits.