The Mechanism Of Methionine Restriction Alleviates Sepsis-induced Lung Injury In Mice

Background and Objective: Acute lung injury(ALI)is an acute,progressive hypoxic respiratory failure caused by a variety of intrapulmonary and non-cardiogenic extrapulmonary factors.The main performance of ALI is uncontrolled inflammation accompany with pulmonary microvascular endothelium and epithelium damage induced by various inflammatory cells in the lungs,of which mainly is attributed of neutrophil activation,adhesion,infiltration,leading to diffuse pulmonary interstitial and alveolar edema.The clinical features of ALI include progressive dyspnea and hypoxemia and which is difficult to correct.In recent years,with the deepening of the research on the pathophysiological mechanism of ALI and the clinical application of various therapeutic measures,the mortality rate of ALI has decreased,but still up to 40%.Therefore,search for effective measures to treat ALI is still one of the important problems in critical care medicine.Recent studies have found that methionine restriction(MR)could significantly reduced ischemia reperfusion injury in mice,and the mechanism is closely related to the increase of endogenous hydrogen sulfide production by MR.In mammals,MR benefits actually require a combined limitation of methionine and cysteine,so it is more accurately known as the sulphur amino acids limited(SAAR).Our previous studies have found that exogenous hydrogen sulfide could significantly alleviated lipopolysaccharide(LPS)caused lung injury,otherwise,metabolic enzyme inhibitor contained sulfur amino acid metabolism could inhibited the generation of endogenous hydrogen sulfide,thus aggravating lung injury caused by LPS.These results demonstrated that hydrogen sulfide play an important regulating role in LPS-induced lung injury.However,there is no hydrogen sulfide donor for clinical use,and it is not clear that whether MR can reduce the LPS-induced lung injury or offer lung protection through regulating endogenous hydrogen sulfide production.Therefore,this study aims to clarify the protective effect and the possible mechanism of MR on LPS-induced lung injury in mice.Methods: 1.Construct a mouse ALI model using non-exposed cold light source tracheal instillation method.2.The content of total protein and inflammatory factors IL-1β,IL-6 and TNF-α in mouse alveolar lavage fluid were detected by ELISA.3.QPCR was used to detect changes in COX-2,ICAM-1 and MIP2 and CSE m RNA levels in mouse lung tissues.Results:1.Successfully established the ALI model: 3 days after tracheal instillation of LPS,focal-like injury observed in lung tissue,,with alveolar epithelial hyperplasia,diffuse dilated capillaries in the alveolar septum,meanwhile,alveolar cavity is filled with a large amount of red blood cells,inflammatory cells and cellulose;7 days after LPS administration,the inflammatory cells in the alveolar space has reduced,the pulmonary interstitial edema lightened,and the alveolar epithelium was proliferated.2.SAAR pretreatment could reduced the content of total protein,IL-1β,IL-6 and TNF-α in alveolar lavage fluid 3 and 7 days after LPS injection.3.SAAR pretreatment could significantly reduced the levels of COX-2,ICAM-1 and MIP2 m RNA in lung tissue 3 days after LPS injection,and effectively reversed the decrease of lung CSE m RNA level induced by LPS.Conclusion: 1.Instilling LPS by non-exposed cold light source tracheal instillation is a simple,stable and reliable method to lead to ALI in mice,which could provide stable animal models for our next research on ALI related pathophysiological changes and treatment measures.2.SAAR could alleviated pulmonary inflammatory cells infiltration caused by LPS,reduced pulmonary interstitial edema and pulmonary hemorrhage,as well as lung damage.3.SAAR inhibited the expression of COX-2,ICAM-1 and MIP-2,increased the expression of CSE,reduced the inflammatory responses and oxidative stress induced by LPS,finally alleviated LPS-induced lung injury.