Expression Of E-selectin In Lung Tissue Of Lipopolysaccharide-induced Acute Lung Injury In Neonatal Rats: The Effect Of Dexamethasone

Objective:Acute lung injury(ALI) is a common fetal disease in neonatal intensive care unit (NICU),is characterized by polymorphonuclear leukocyte (PMN) accumulation in the pulmonary microcirculation and alveolar spaces.ALI's severe stage is Acute respiratory distress syndrome(ARDS). And it'pathogenic mechanism has been completely unknown yet. Recently study were paid to inflammatory response. Bacterial lipopolysaccharide(LPS)could induce acute lung injury.LPS is a major constituent of endotoxin gram-negtive bacteria.It is often be used to make animal model. Infection is one of common reasons that cause ALI. Pro-inflammatory cytokines (IL-1β, TNF-αand IL-6) play a significant role in stimulate endothelial cells to express receptors.These pro-inflammatory cytokines up-regulate expression of adhesion molecules on endothelial cells.These changes include increases in the membrane expression of selectin family (L, E, andP). E-selectin (CD62E)is the main part that we study in ALI.And at the same time to investigate the effects of dexamethasone(DEX)on expression of E-selectin in neonatal rat models of ALI.So we established acute Lung injury models in neonatal rats via lipopolysaccharide intraperitoneal injection to imitate clinical neonate acute lung injury. The lung tissue pathological changes were observed under microscopy. To explore the effect of E-selectin on acute lung injury of neonatal rats and anti-inflammatory mechanism of dexamethasone.And to explain the pathogenesis mechanism of acute lung injury.Methods: 54 neonatal Sprague-Dawley rats were separated into 3 groups randomly: 1)LPS experimental group,LPS was injected intraperitoneally (4mg/kg).2) normal saline(NS)control group,equal amount of NS was injected intraperitoneally.3)Treatment group,LPS+DEX(1mg/kg) injected intraperi- toneally. After injected,rats were killed at the time points of 1h,6h and 24h,respectively.The left lung tissue of every group was fixed into 4% Polyformaldehyde solution.And then the sample was dehydrated embedded in wax,sectioned, stained with HE staining method.The immunohistochemical expression of E-selectin was detected in paraffin sections using the ABC technique and the expression was scored semiquantitatively by evaluating the intensity and incidence of positively stained endothelium of the pulmonary microvasculature.The fresh right lung tissue was weighted first,then put in 70℃incubator for 48 hours,the dryed lung tissue was weighted again.The wet to dye weight ratio was calculated.After anaesthesia ,the rats trachea was exposed and cut open,then inserted a suitable plastic tube.The lung was lavaged three times and the lavage fluid was collected and centrifuged.Measurement of total protein (TP) and malondialdehyde (MDA).Result:1. The pathological findings show inflammatory responses in the lung tissue following LPS injection.2. E-selectin was strongly expressed in all cases of the LPS experimental group.And was not very stronger expressed in LPS+DEX treatment group. E-selectin was not expressed in NS comparison group.3. The lung W/D ratio of LPS experimental group rats is higher in comparison to DEX treatment group and NS control group(P<0.05).There is no difference between DEX treatment group and NS control group.4. The TP and MDA in BALF of LPS experimental group rats is significantly higher than other two groups(P<0.05).Our findings suggest that the intraperitoneal treatment of LPS at dosage of 4mg/kg may lead to ALI in the neonatal rats.Immunohistochemical detection of an intense expression of E-selectin in lung tissue may prove to be a valuable diagnostic tool in early ALI.Dexamethasone reduce pulmonary edema of ALI in neonatal rats,and inhibit the expression of E-selectin on lung vascular endothelium cell.Conclusion:The neonatal rat of acute lung injury characterized by the rapid onset of dyspnea, hypoxemia, cyanosis. E-selectin expression is up-regulated by LPS. E-selectin participates in inflammatory response of ALI.It plays a important role in physiological and pathological progress of ALI. Dexamethasone can alleviate the pulmonary inflammatory injury caused by LPS.