The Role Of LXA4 And Its Receptor In Fat Embolism Syndrome Rat Model

Objective: Establish the fat embolism(FES)rat model.To detect the changes of cytokines,inflammatory cells,endogenous lipoxin A4(LXA4),lipoxin A4 receptor(ALX/FPR2)and to investigate the effects of LXA4 and its receptor agonist BML-111,antagonist BOC-2 in rats with FES.Methods: Healthy adult male Sprague-Dawley(SD)rats were randomly assigned into control group,FES 1h,6h,12 h and 24 h group.Rats in the FES group were injected with allogeneic perirenal fat of the half lethal dose(LD50)through the tail vein,and the same dose of sterile saline was injected into the control group.(1)Lung tissue was extracted for oil red O staining and HE staining to observe the pathological changes.Then detected the changes of Wet/Dry(SD)ratio in lung tissue and total protein concentration in bronchoalveolar lavage fluid(BALF).(2)Number of leukocytes and neutrophils,the activity of myeloperoxidase(MPO),level of plasma TNF-? and IL-1? were tested to observe the inflammatory response in FES.(3)The expression of endogenous LXA4,ALX/FPR2 and ALX/FPR2 m RNA in the model were determined using ELISA kits,Immunohistochemistry and Real-time PCR,respectively.(2)According to the random number table,SD rats were divided into control group,FES 24 h group,BML-111 + FES24 h group and BOC-2 + BML-111 + FES 24 h group.Fat-induced inflammatory response and pulmonary injury were determined after the treatment of BML-111 or BOC-2.Compared the severity of lung injury using microscopy,detected the changes of inflammatory reaction and edema fluid removal in FES rats after the treatment of BML-111 and BOC-2.Results:(1)Lipid droplets were observed in alveolar space and pulmonary interstitium in FES rats.Lung injury in FES group was more serious than control group.The W/D ratio of lung tissue was significantly increased(p<0.05)and the total protein concentration of BALF was also obviously increased(p<0.05)compared with the control group.(2)After the injection of fat,plasma TNF-? and IL-1? levels,MPO activity,leukocyte and neutrophil counts were significantly elevated compared with those in control group(p<0.05).(3)In FES 24 h group,LXA4 concentration of BALF and ALX/FPR2 expression in lung tissue were markedly higher than those in other groups(p<0.05).(2)BML-111 pretreatment reduced the damage of lung tissue caused by fat injection,decreased the levels of plasma TNF-? and IL-1?,inhibited the aggregation and release of neutrophils,and the MPO activity was also significantly reduced compared with control group(p<0.05);Compared with FES group,the above mentioned indicators had no obvious statistical significance in BOC-2 + BML-111 +FES 24 h group(p>0.05).Conclusion: Inflammation plays an important role in the development and progression of FES.LXA4 can reduce fat-induced lung injury by promoting the resolution of inflammatory response.These may be realized by blinding with its special receptor ALX/FPR2.