Protective Effect Of Oxytocin On LPS-induced Acute Lung Injury In Mice

BackgroundAcute lung injury(ALI),and its severe phase characterized by acute respiratory distress syndrome(ARDS),which are characterized by refractory hypoxemia and progressive dyspnea,are the main causes of acute lung failure in patients with a high mortality rate in the clinically.The main pathological change was the diffuse lung tissue injury,and the main pathogenesis was the activation of inflammasome and the release of inflammatory mediators.Although there has been made some progress in the study of its pathogenesis and treatment methods,few drugs are actually used in the clinical practice.Oxytocin(OT),a neurohypophyseal hormone synthesized in the supraoptic nuclei and paraventricular of the hypothalamus,is released into blood circulation by the hypothalamic nerve endings.And oxytocin is mainly used in the uterine smooth muscle contraction during parturition to promote delivery and prevent postpartum hemorrhage.Recently,with the further study of the mechanism of oxytocin,its anti-inflammatory and anti-oxidant properties have drawn more and more attention.Previous studies showed that oxytocin has anti-oxidant and regulation cardiovascular function to delay the progression of atherosclerosis,and oxytocin also could alleviate inflammation of imacrophages and small glial cells caused by LPS.This study aimed to evaluate the protection effects of oxytocin to LPS-induced ALI in the mice.In order to further prove the mechanism of oxytocin on the ALI,oxytocin receptor blocker L-368,899 was used.Materials and MethodsThe LPS-induced ALI model in the mice was used in this study.All mice were divided into four groups randomly(n=9 per group):Control group and three test groups:(Control,LPS,LPS+OT,LPS+OT+L-368,899),and all drugs were injected intraperitoneally(ip).Two hours after LPS treatment,the mice were anesthetized us:ing sodium pentobarbital by ip and were treated with tracheal intubation.Then,the bronchoalveolar lavage fluid(BALF)were collected to measured inflammatory mediators and myeloperoxidase(MPO)activity in order to assess the degree of injury in the lung tissues.Lung tissues were collected for hematoxylin and eosin(HE)staining and the wet and dry ratio(W/D)to observe the severity of pulmonary tissue edema and exudation,western blot(W-B)and qPCR was used to measure the expression of inflammatory proteins and the secretion of inflammatory mediators.Immunohistochemistry(IHC)and Immunofluorescence(IF)was used to further verify the expression of inflammatory proteins.The level of OT in the lung tissue and circulating was measured using OT ELISA kits to assess whether the main anti-inflammatory effects were exogenous OT or endogenous OT.ResultsIn this study,the results of MPO activity of BALF,HE staining and W/D ratio of lung tissues showed that oxytocin could significantly reduce inflammatory cell infiltration,lung histopathological injury and lung tissues edema caused by LPS-induced ALI,while oxytocin receptor blocker L-368,899 significantly weakens the protective effects of oxytocin.ELISA and qPCR showed that oxytocin could significantly reduce the levels of interleulin(IL)-1?,IL-6 and IL-18 and increase the levels of IL?4 and IL-10.In addition,as Western Blot analysis,immunohistochemistry(IHC)and immunofluorescence(IF)shown,oxytocin could significantly reduce the expression of TLR4,NF-?B,NLRP3 and Caspase-1,However,L-368,899 significantly weakens the effects of oxytocin.In addition,the expression of oxytocin receptor in lung tissue increased by LPS and L-368,899 signifcantly increased the expression of inflammatory proteins in ALI caused by LPS.The level of OT in the lung tissue and circulating was measured using OT ELISA kits.The results in the lung tissue shown that LPS signifcantly deceased OT level compared with Control group,However,pretreatment with L-368,899 signifcantly increased OT level compared with the LPS group and the LPS + OT group.But there is no obvious change in the circulating.These results suggest that oxytocin has protective effect on LPS-induced ALI,and exogenous oxytocin has mainly anti-inflammatory effects,while its receptor blocker L-368,899 significantly inhibits the protective effect of oxytocin.ConclusionsIn conclusion,the findings suggested that1.Exogenous oxytocin has protective effects on LPS-induced ALI in mice.2.Oxytocin has protective effects on LPS-induced ALI in mice by combining with oxytocin receptor(OTR)to inhibit NLRP3 inflammatory activation and TLR4 signaling pathway.