Expiratory flow-limitation in mechanically ventilated patients: A risk for ventilator-induced lung injury?

Expiratory flow limitation(EFL), that is the inability of expiratory flow to increase in spite of an increase of the driving pressure, is a common and unrecognized occurrence during mechanical ventilation in a variety of intensive care unit conditions. Recent evidence suggests that the presence of EFL is associated with an increase in mortality, at least in acute respiratory distress syndrome(ARDS) patients, and in pulmonary complications in patients undergoing surgery. EFL is a major cause of intrinsic positive end-expiratory pressure(PEEPi), which in ARDS patients is heterogeneously distributed, with a consequent increase of ventilation/perfusion mismatch and reduction of arterial oxygenation. Airway collapse is frequently concomitant to the presence of EFL.When airways close and reopen during tidal ventilation, abnormally high stresses are generated that can damage the bronchiolar epithelium and uncouple small airways from the alveolar septa, possibly generating the small airways abnormalities detected at autopsy in ARDS. Finally, the high stresses and airway distortion generated downstream the choke points may contribute to parenchymal injury, but this possibility is still unproven. PEEP application can abolish EFL, decrease PEEPi heterogeneity, and limit recruitment/derecruitment.Whether increasing PEEP up to EFL disappearance is a useful criterion for PEEP titration can only be determined by future studies.

Molecular Mechanisms of Ventilator-Induced Lung Injury

Objective：Mechanical ventilation （MV） has long been used as a life-sustaining approach for several decades.However,researchers realized that MV not only brings benefits to patients but also cause lung injury if used improperly,which is termed as ventilator-induced lung injury （VILI）.This review aimed to discuss the pathogenesis of VILI and the underlying molecular mechanisms.Data Sources：This review was based on articles in the PubMed database up to December 2017 using the following keywords：＂ventilator-induced lung injury＂,＂pathogenesis＂,＂mechanism＂,and ＂biotrauma＂.Study Selection：Original articles and reviews pertaining to mechanisms of VILI were included and reviewed.Results：The pathogenesis of VILI was defined gradually,from traditional pathological mechanisms （barotrauma,volutrauma,and atelectrauma） to biotrauma.High airway pressure and transpulmonary pressure or cyclic opening and collapse of alveoli were thought to be the mechanisms of barotraumas,volutrauma,and atelectrauma.In the past two decades,accumulating evidence have addressed the importance of biotrauma during VILI,the molecular mechanism underlying biotrauma included but not limited to proinflammatory cytokines release,reactive oxygen species production,complement activation as well as mechanotransduction.Conclusions：Barotrauma,volutrauma,atelectrauma,and biotrauma contribute to VILI,and the molecular mechanisms are being clarified gradually.More studies are warranted to figure out how to minimize lung injury induced by MV.

Serum and lung endothelin-1 increased in a canine model of ventilator-induced lung injury

Background Nitric oxide （NO） plays an important role in acute lung injury （ALl）, acute respiratory distress syndrome （ARDS）, and in ventilator-induced lung injury （VILI）. A change in the balance of endothelin-1 （ET-1） and NO in the ALI/ARDS can also add to these problems. However, the profile of ET-1 and the balance of ET-1 and NO are still unknown in a VILI model. Methods Models of oleic acid induced ALl were established in dogs; these models were then randomized into three groups undergone different tidal volume （VT） mechanical ventilation, which included a VT6 group （VT equaled to 6 ml/kg body weight, positive end expiratory pressure （PEEP） equaled to 10 cmH20, n=-6）, a VT10 group （VT equaled to 10 ml/kg body weight, PEEP equaled to 10 cmH20, n=-4） and a VT20 group （VT equaled to 20 ml/kg body weight, PEEP equaled to 10 cmH20, n=-6） for 6-hour ventilation. The levels of ET-1 and NO in serum and tissue homogenates of lung were observed throughout the trial. Results PaO2 was increased after mechanical ventilation, but hypercapnia occurred in the VT6 group. The magnitudes of lung injury in the VT20 group were more severe than those in the VT6 group and the VT10 group. Serum levels of ET-1 and NO increased after ALl models were established and slightly decreased after a 6-hour ventilation in both the VT6 group and the VT20 group. The serum ET-1 level in the VT20 group was higher than that in the VT6 group and the VT10 group after the 6-hour ventilation （P 〈0.05） while the serum NO levels were similar in the three groups （all P 〉0.05）. There was no significant difference in serum ratio of ET-1/NO between any two out of three groups （P 〉0.05）, although there was a significant positive relationship between serum ET-1 and serum NO （r=0.80, P 〈0.01）. The levels of ET-1 and NO in the lung were increased after ventilation. The lung ET-1 level in the VT20 group was significantly higher than that in the VT6 group and VT10 group （both P 〈0.05） while there was no significant difference in lung NO levels between two groups （P〉0.05）. In the lung tissue, the ratio of ET-1/NO was significantly higher in the VT20 group than in the VT6 group and VT10 group after the 6-hour ventilation （P 〈0.05） as there was a significant positive relationship between ET-1 and NO in the lung （r=0.54, P 〈0.05）. Conclusions The production of ET-1 and NO was increased in serum and lung tissue in a VILI model. But the ET-1 levels increased much more than the NO levels in the lung, though there was a significant positive relationship between levels of ET-1 and NO. These results showed that there was an interaction between ET-1 and NO in a VILI model and changing the balance of ET-1 and NO levels might contribute to the pathophysiologic process of VILI.

Mesenchymal Stem Cell Attenuates Neutrophil-predominant Inflammation and Acute Lung Injury in an In Vivo Rat Model of Ventilator-induced Lung Injury

Background： Subsequent neutrophil （polymorphonuclear neutrophil [PMN]）-predominant inflammatory response is a predominant feature of ventilator-induced lung injury （VILI）, and mesenchymal stem cell （MSC） can improve mice survival model of endotoxin-induced acute lung injury, reduce lung impairs, and enhance the repair inflammatory in the VILI is still unknown. This study aimed to inflammatory in the mechanical VILI. of VILI. However, whether MSC could attenuate PMN-predominant test whether MSC intervention could attenuate the PMN-predominate Methods： Sprague-Dawley rats were ventilated for 2 hours with large tidal volume （20 mL/kg）. MSCs were given before or after ventilation. The inflammatory chemokines and gas exchange were observed and compared dynamically until 4 hours after ventilation, and pulmonary pathological change and activation of PMN were observed and compared 4 hours after ventilation. Results： Mechanical ventilation （MV） caused significant lung injury reflected by increasing in PMN pulmonary sequestration, inflammatory chemokines （tumor necrosis factor-alpha, interleukin-6 and macrophage inflammatory protein 2） in the bronchoalveolar lavage fluid, and injury score of the lung tissue. These changes were accompanied with excessive PMN activation which reflected by increases in PMN elastase activity, production of radical oxygen series. MSC intervention especially pretreatment attenuated subsequent lung injury, systemic inflammation response and PMN pulmonary sequestration and excessive PMN activation initiated by injurious ventilation. Conclusions： MV causes profound lung injury and PMN-predominate inflammatory responses. The protection effect of MSC in the VILI rat model is related to the suppression of the PMN activation.

Impact of interleukin 6 levels on acute lung injury risk and disease severity in critically ill sepsis patients

BACKGROUND Sepsis is a life-threatening condition characterized by a dysregulation of the host response to infection that can lead to acute lung injury(ALI)and multiple organ dysfunction syndrome(MODS).Interleukin 6(IL-6)is a pro-inflammatory cytokine that plays a crucial role in the pathogenesis of sepsis and its complications.AIM To investigate the relationship among plasma IL-6 levels,risk of ALI,and disease severity in critically ill patients with sepsis.METHODS This prospective and observational study was conducted in the intensive care unit of a tertiary care hospital between January 2021 and December 2022.A total of 83 septic patients were enrolled.Plasma IL-6 levels were measured upon admission using an enzyme-linked immunosorbent assay.The development of ALI and MODS was monitored during hospitalization.Disease severity was evaluated by Acute Physiology and Chronic Health Evaluation II(APACHE II)and Sequential Organ Failure Assessment(SOFA)scores.RESULTS Among the 83 patients with sepsis,38(45.8%)developed ALI and 29(34.9%)developed MODS.Plasma IL-6 levels were significantly higher in patients who developed ALI than in those without ALI(median:125.6 pg/mL vs 48.3 pg/mL;P<0.001).Similarly,patients with MODS had higher IL-6 levels than those without MODS(median:142.9 pg/mL vs 58.7 pg/mL;P<0.001).Plasma IL-6 levels were strongly and positively correlated with APACHE II(r=0.72;P<0.001)and SOFA scores(r=0.68;P<0.001).CONCLUSIONElevated plasma IL-6 levels in critically ill patients with sepsis were associated with an increased risk of ALI andMODS.Higher IL-6 levels were correlated with greater disease severity,as reflected by higher APACHE II andSOFA scores.These findings suggest that IL-6 may serve as a biomarker for predicting the development of ALI anddisease severity in patients with sepsis.

MicroRNA-451 from Human Umbilical Cord-Derived Mesenchymal Stem Cell Exosomes Inhibits Alveolar Macrophage Autophagy via Tuberous Sclerosis Complex 1/Mammalian Target of Rapamycin Pathway to Attenuate Burn-Induced Acute Lung Injury in Rats

Objective Our previous studies established that microRNA(miR)-451 from human umbilical cord mesenchymal stem cell-derived exosomes(hUC-MSC-Exos)alleviates acute lung injury(ALI).This study aims to elucidate the mechanisms by which miR-451 in hUC-MSC-Exos reduces ALI by modulating macrophage autophagy.Methods Exosomes were isolated from hUC-MSCs.Severe burn-induced ALI rat models were treated with hUC-MSC-Exos carrying the miR-451 inhibitor.Hematoxylin-eosin staining evaluated inflammatory injury.Enzyme-linked immunosorbnent assay measured lipopolysaccharide(LPS),tumor necrosis factor-α,and interleukin-1βlevels.qRT-PCR detected miR-451 and tuberous sclerosis complex 1(TSC1)expressions.The regulatory role of miR-451 on TSC1 was determined using a dual-luciferase reporter system.Western blotting determined TSC1 and proteins related to the mammalian target of rapamycin(mTOR)pathway and autophagy.Immunofluorescence analysis was conducted to examine exosomes phagocytosis in alveolar macrophages and autophagy level.Results hUC-MSC-Exos with miR-451 inhibitor reduced burn-induced ALI and promoted macrophage autophagy.MiR-451 could be transferred from hUC-MSCs to alveolar macrophages via exosomes and directly targeted TSC1.Inhibiting miR-451 in hUC-MSC-Exos elevated TSC1 expression and inactivated the mTOR pathway in alveolar macrophages.Silencing TSC1 activated mTOR signaling and inhibited autophagy,while TSC1 knockdown reversed the autophagy from the miR-451 inhibitor-induced.Conclusion miR-451 from hUC-MSC exosomes improves ALI by suppressing alveolar macrophage autophagy through modulation of the TSC1/mTOR pathway,providing a potential therapeutic strategy for ALI.

Mogroside IIE,an in vivo metabolite of sweet agent,alleviates acute lung injury via Pla2g2a-EGFR inhibition

In the face of increasingly serious environmental pollution,the health of human lung tissues is also facing serious threats.Mogroside IIE(M2E)is the main metabolite of sweetening agents mogrosides from the anti-tussive Chinese herbal Siraitia grosvenori.The study elucidated the anti-inflammatory action and molecular mechanism of M2E against acute lung injury(ALI).A lipopolysaccharide(LPS)-induced ALI model was established in mice and MH-S cells were employed to explore the protective mechanism of M2E through the western blotting,co-immunoprecipitation,and quantitative real time-PCR analysis.The results indicated that M2E alleviated LPS-induced lung injury through restraining the activation of secreted phospholipase A2 type IIA(Pla2g2a)-epidermal growth factor receptor(EGFR).The interaction of Pla2g2a and EGFR was identified by co-immunoprecipitation.In addition,M2E protected ALI induced with LPS against inflammatory and damage which were significantly dependent upon the downregulation of AKT and m TOR via the inhibition of Pla2g2a-EGFR.Pla2g2a may represent a potential target for M2E in the improvement of LPS-induced lung injury,which may represent a promising strategy to treat ALI.

Research Progress on the Pathogenesis of Acute Lung Injury(ALI)

In this review,the databases searched were PubMed and Web of Science.It is believed that the main causes of acute lung injury(ALI)and acute respiratory distress syndrome(ARDS)are inflammatory response disorders,excessive oxidative stress,cell death,endoplasmic reticulum stress,coagulation dysfunction,and weakened aquaporin function.

Research Progress on the Prevention of Premature Infant Lung Injury and Neonatal Respiratory Support

In the past 40 years,advances in neonatal intensive care unit(NICU)technology have enabled premature infants with lower birth weight and younger gestational age to survive.But with it comes an increase in the incidence of long-term respiratory dysfunction,mainly in the form of bronchopulmonary dysplasia(BPD).Preventing lung injury is crucial for preventing BPD and improving the long-term prognosis of premature infants.Therefore,how to avoid ventilator-associated lung injury has become a focus of clinical and scientific research in premature infants in recent years.This article will elaborate on the susceptibility and pathophysiology of premature infant lung injury,ventilation strategies for preventing lung injury,and new advances in neonatal respiratory support.

Modulating the crosstalk between macrophage and Th17: potential mechanism of natural products on acute lung injury

Sepsis is a life-threatening multiple organ dysfunction syndrome caused by the imbalance of the immune response to infection,featuring complex and variable conditions,and is one of the leading causes of mortality in ICU patients.Lung injury is a common organ damage observed in sepsis patients.Macrophages and Th17 cells,as crucial components of innate and adaptive immunity,play pivotal roles in the development of sepsis-induced acute lung injury(ALI).This review summarizes the alterations and mechanisms of macrophages and Th17 cells in sepsis-induced ALI.By focusing on the“cross-talk”between macrophages and Th17 cells,this review aims to provide a solid theoretical foundation for further exploring the therapeutic targets of traditional Chinese medicine formulas in the treatment of sepsis complicated with ALI,thereby offering insights and guidance for the clinical application of traditional Chinese medicine in managing sepsis-associated ALI.

Effects of minimal lipopolysaccharide-instilled lungs on ventilator-induced lung injury in rats

Mechanical ventilation （MV） may aggravate lung injury induced by a variety of injuries, including intratracheal hydrochloric acid instillation, intratracheal lipopolysaccharide （LPS） instillation with or without concurrent saline lavage, intravenous LPS, or intravenous oleic acid. However, the mechanism for this detrimental effect of MV is unclear. The purpose of the present study was to determine the effect of MV on lung injury induced by minimal LPS-instillation and on the LPS receptor CD14 in the lung.

Periplaneta Americana Extract Ameliorates LPS-induced Acute Lung Injury Via Reducing Inflammation and Oxidative Stress

Objective Acute lung injury(ALI)is an acute clinical syndrome characterized by uncontrolled inflammation response,which causes high mortality and poor prognosis.The present study determined the protective effect and underlying mechanism of Periplaneta americana extract(PAE)against lipopolysaccharide(LPS)-induced ALI.Methods The viability of MH-S cells was measured by MTT.ALI was induced in BALB/c mice by intranasal administration of LPS(5 mg/kg),and the pathological changes,oxidative stress,myeloperoxidase activity,lactate dehydrogenase activity,inflammatory cytokine expression,edema formation,and signal pathway activation in lung tissues and bronchoalveolar lavage fluid(BALF)were examined by H&E staining,MDA,SOD and CAT assays,MPO assay,ELISA,wet/dry analysis,immunofluorescence staining and Western blotting,respectively.Results The results revealed that PAE obviously inhibited the release of proinflammatory TNF-α,IL-6 and IL-1βby suppressing the activation of MAPK/Akt/NF-κB signaling pathways in LPS-treated MH-S cells.Furthermore,PAE suppressed the neutrophil infiltration,permeability increase,pathological changes,cellular damage and death,pro-inflammatory cytokines expression,and oxidative stress upregulation,which was associated with its blockage of the MAPK/Akt/NF-κB pathway in lung tissues of ALI mice.Conclusion PAE may serve as a potential agent for ALI treatment due to its anti-inflammatory and anti-oxidative properties,which correlate to the blockage of the MAPK/NF-κB and AKT signaling pathways.

Glycolysis and acute lung injury:A review

Acute lung injury is featured as diffuse pulmonary edema and persistent hypoxemia caused by lung or systemic injury.It is believed that these pathological changes are associated with damage to the alveolar epithelium and vascular endothelium,recruitment of inflammatory cells,and inflammatory factor storms.In recent years,the metabolic reprogramming of lung parenchymal cells and immune cells,particularly alterations in glycolysis,has been found to occur in acute lung injury.Inhibition of glycolysis can reduce the severity of acute lung injury.Thus,this review focuses on the interconnection between acute lung injury and glycolysis and the mechanisms of interaction,which may bring hope for the treatment of acute lung injury.

Biomarkers Associated with Radiation-Induced Lung Injury in Cancer Patients

Radiotherapy (RT) is a common and effective non-surgical treatment for thoracic solid tumors, and radiation-induced lung injury (RILI) is the most common side effect of radiotherapy. Even if RT is effective in the treatment of cancer patients, severe radiation pneumonitis (RP) or pulmonary fibrosis (PF) can reduce the quality of life of patients and may even lead to serious consequences of death. Therefore, how to overcome the problem of accurate prediction and early diagnosis of RT for pulmonary toxicity is very important. This review summarizes the related factors of RILI and the related biomarkers for early prediction of RILI.

The therapeutic mechanism of dexamethasone in lung injury induced by hydrogen sulfide

The lung is one of the primary target organs of hydrogen sulfide(H2S),as exposure to H2S can cause acute lung injury(ALI)and pulmonary edema.Dexamethasone(Dex)exerts a protective effect on ALI caused by exposure to toxic gases and is commonly used in the clinic;however,the underlying mechanisms remain elusive,and the dose is unclear.Methods:In vivo experiments:divided C57BL6 mice into 6 groups at random,12 in each group.The mice were exposed to H2S for 3 h and 5 or 50 mg/kg Dex pretreated before exposure,sacrificed 12 h later.The morphological changes of HE staining and the ultrastructural changes of lungs under transmission electron microscopy were evaluated.The wet/dry ratio of lung tissue was measured.Bronchial alveolar lavage fluid(BALF)protein content and lung permeability index were detected.The expression of AQP5 protein was measured by immunohistochemistry and Western Blot(WB).In vitro experiments:divided human lung adenocarcinoma cell line A549 into 4 groups.1μmol/L dexamethasone was added to pre-incubation.The WB analyzed the protein of p-ERK1/2,p-JNK,and p-p38 in MAPK pathway after 1 h of NaHS exposure;six hours after NaHS exposure,the AQP5 protein was measured by WB.Results:Dex treatment could significantly attenuate the H2S-induced destruction to the alveolar wall,increase the wet-to-dry weight ratio and decrease pulmonary permeability index,with high-dose dexamethasone seemingly functioning better.Additionally,our previous studies showed that aquaporin 5(AQP 5),a critical protein that regulates water flux,decreased both in a mouse and cell model following the exposure to H2S.This study indicates that tThe decrease in AQP 5 can be alleviated by Dex treatment.Additionally,the mitogen activated protein kinase(MAPK)pathway may be involved in the protective effects of Dex in ALI caused by exposure to H2S since H2Sinduced MAPK activation could be inhibited by Dex.Conclusion:The present results indicate that AQP 5 may be considered a therapeutic target for Dex in H2S or other hazardous gases-induced ALI.

Study of the anti-inflammatory effect of the Traditional Mongolian Medicine Hohgardi-9 in acute lung injury

Background:Hohgardi-9 is a well-known traditional Mongolian drug that relieves cough and removes phlegm.Although it is widely used to treat lung diseases clinically,Hohgardi-9’s bioactive constituents and mechanism of action are unknown.In this study,we explored the bioactive compounds in Hohgardi-9 and the mechanism underlying its therapeutic effect against acute lung injury(ALI).Methods:We obtained the main components of Hohgardi-9 and analyzed the targets related to ALI by searching the traditional Chinese medicine systems pharmacology database and existing literature.Then,we constructed the compound-target network using Cytoscape 3.8.0 software to obtain the bioactive compounds in Hohgardi-9 against ALI.We used a string database to investigate the interaction between the possible protein targets of Hohgardi-9.We also performed Gene Ontology function annotation and Kyoto Encyclopedia of Genes and Genomes pathway enrichment analysis to predict its anti-ALI mechanism.Further,to verify the therapeutical effects of Hohgardi-9,we used an ALI rat model and analyzed the components of Hohgardi-9 found in the rat plasma using ultra-high-performance liquid chromatography coupled with Q-Exactive mass spectrometry.Results:The network pharmacology and plasma component analysis showed that Hohgardi-9 contained 31 potentially bioactive components,including quercetin,herbacetin,izoteolin,and columbinetin acetate,which affected the NF-κB,TLR,and TNF signaling pathways via key targets,such as RELA(p65)and TLR4.The in vivo experiments using hematoxylin and eosin staining revealed that Hohgardi-9 significantly improved lung tissue injury and pulmonary edema in ALI rats.Simultaneously,Hohgardi-9 significantly reduced the expression levels of genes encoding inflammatory factors,such as TRL4,TNF-α,IL-1β,and ICAM1,in the lungs of ALI rats.Conclusion:Hohgardi-9 alleviated ALI by inhibiting inflammation-related gene expression through its active ingredients,such as quercetin and herbacetin.

Network pharmacology and molecular docking to explore Polygoni Cuspidati Rhizoma et Radix treatment for acute lung injury

BACKGROUND Polygoni Cuspidati Rhizoma et Radix(PCRR),a well-known traditional Chinese medicine(TCM),inhibits inflammation associated with various human diseases.However,the anti-inflammatory effects of PCRR in acute lung injury(ALI)and the underlying mechanisms of action remain unclear.AIM To determine the ingredients related to PCRR for treatment of ALI using multiple databases to obtain potential targets for fishing.METHODS Recognized and candidate active compounds for PCRR were obtained from Traditional Chinese Medicine Systems Pharmacology,STITCH,and PubMed databases.Target ALI databases were built using the Therapeutic Target,DrugBank,DisGeNET,Online Mendelian Inheritance in Man,and Genetic Association databases.Network pharmacology includes network construction,target prediction,topological feature analysis,and enrichment analysis.Bioinformatics resources from the Database for Annotation,Visualization and Integrated Discovery were utilized for gene ontology biological process and Kyoto Encyclopedia of Genes and Genomes network pathway enrichment analysis,and molecular docking techniques were adopted to verify the combination of major active ingredients and core targets.RESULTS Thirteen bioactive compounds corresponding to the 433 PCRR targets were identified.In addition,128 genes were closely associated with ALI,60 of which overlapped with PCRR targets and were considered therapeutically relevant.Functional enrichment analysis suggested that PCRR exerted its pharmacological effects in ALI by modulating multiple pathways,including the cell cycle,cell apoptosis,drug metabolism,inflammation,and immune modulation.Molecular docking results revealed a strong associative relationship between the active ingredient and core target.CONCLUSION PCRR alleviates ALI symptoms via molecular mechanisms predicted by network pharmacology.This study proposes a strategy to elucidate the mechanisms of TCM at the network pharmacology level.

Extracellular vesicles in the pathogenesis and treatment of acute lung injury

Acute lung injury(ALI)and acute respiratory distress syndrome(ARDS)are common life-threatening lung diseases associated with acute and severe inflammation.Both have high mortality rates,and despite decades of research on clinical ALI/ARDS,there are no effective therapeutic strategies.Disruption of alveolar-capillary barrier integrity or activation of inflammatory responses leads to lung inflammation and injury.Recently,studies on the role of extracellular vesicles(EVs)in regulating normal and pathophysiologic cell activities,including inflammation and injury responses,have attracted attention.Injured and dysfunctional cells often secrete EVs into serum or bronchoalveolar lavage fluid with altered cargoes,which can be used to diagnose and predict the development of ALI/ARDS.EVs secreted by mesenchymal stem cells can also attenuate inflammatory reactions associated with cell dysfunction and injury to preserve or restore cell function,and thereby promote cell proliferation and tissue regeneration.This review focuses on the roles of EVs in the pathogenesis of pulmonary inflammation,particularly ALI/ARDS.

Multiomics reveal human umbilical cord mesenchymal stem cells improving acute lung injury via the lung-gut axis

BACKGROUND Acute lung injury(ALI)and its final severe stage,acute respiratory distress syndrome,are associated with high morbidity and mortality rates in patients due to the lack of effective specific treatments.Gut microbiota homeostasis,including that in ALI,is important for human health.Evidence suggests that the gut microbiota improves lung injury through the lung-gut axis.Human umbilical cord mesenchymal cells(HUC-MSCs)have attractive prospects for ALI treatment.This study hypothesized that HUC-MSCs improve ALI via the lung-gut microflora.AIM To explore the effects of HUC-MSCs on lipopolysaccharide(LPS)-induced ALI in mice and the involvement of the lung-gut axis in this process.METHODS C57BL/6 mice were randomly divided into four groups(18 rats per group):Sham,sham+HUC-MSCs,LPS,and LPS+HUC-MSCs.ALI was induced in mice by intraperitoneal injections of LPS(10 mg/kg).After 6 h,mice were intervened with 0.5 mL phosphate buffered saline(PBS)containing 1×10^(6) HUC-MSCs by intraperitoneal injections.For the negative control,100 mL 0.9%NaCl and 0.5 mL PBS were used.Bronchoalveolar lavage fluid(BALF)was obtained from anesthetized mice,and their blood,lungs,ileum,and feces were obtained by an aseptic technique following CO_(2) euthanasia.Wright’s staining,enzyme-linked immunosorbent assay,hematoxylin-eosin staining,Evans blue dye leakage assay,immunohistochemistry,fluorescence in situ hybridization,western blot,16S rDNA sequencing,and non-targeted metabolomics were used to observe the effect of HUC-MSCs on ALI mice,and the involvement of the lung-gut axis in this process was explored.One-way analysis of variance with post-hoc Tukey’s test,independent-sample Student’s t-test,Wilcoxon rank-sum test,and Pearson correlation analysis were used for statistical analyses.RESULTS HUC-MSCs were observed to improve pulmonary edema and lung and ileal injury,and decrease mononuclear cell and neutrophil counts,protein concentrations in BALF and inflammatory cytokine levels in the serum,lung,and ileum of ALI mice.Especially,HUC-MSCs decreased Evans blue concentration and Toll-like receptor 4,myeloid differentiation factor 88,p-nuclear factor kappa-B(NF-κB)/NF-κB,and p-inhibitorαof NF-κB(p-IκBα)/IκBαexpression levels in the lung,and raised the pulmonary vascular endothelial-cadherin,zonula occludens-1(ZO-1),and occludin levels and ileal ZO-1,claudin-1,and occludin expression levels.HUC-MSCs improved gut and BALF microbial homeostases.The number of pathogenic bacteria decreased in the BALF of ALI mice treated with HUCMSCs.Concurrently,the abundances of Oscillospira and Coprococcus in the feces of HUS-MSC-treated ALI mice were significantly increased.In addition,Lactobacillus,Bacteroides,and unidentified_Rikenellaceae genera appeared in both feces and BALF.Moreover,this study performed metabolomic analysis on the lung tissue and identified five upregulated metabolites and 11 downregulated metabolites in the LPS+MSC group compared to the LPS group,which were related to the purine metabolism and the taste transduction signaling pathways.Therefore,an intrinsic link between lung metabolite levels and BALF flora homeostasis was established.CONCLUSION This study suggests that HUM-MSCs attenuate ALI by redefining the gut and lung microbiota.