Mechanical ventilation modulates Toll-like receptors 2, 4, and 9 on alveolar macrophages in a ventilator-induced lung injury model

Acute Lung Injury and the NLRP3 Inflammasome

Acute lung injury (ALI) manifests through harm to the capillary endothelium and alveolar epithelial cells, arising from a multitude of factors, leading to scattered interstitial alterations, pulmonary edema, and subsequent acute hypoxic respiratory insufficiency. Acute lung injury (ALI), along with its more serious counterpart, acute respiratory distress syndrome (ARDS), carry a fatality rate that hovers around 30-40%. Its principal pathological characteristic lies in the unchecked inflammatory reaction. Currently, the main strategies for treating ALI are alleviation of inflammation and prevention of respiratory failure. Concerning the etiology of ALI, NLRP3 Inflammasome is essential to the body's innate immune response. The composition of this inflammasome complex includes NLRP3, the pyroptosis mediator ASC, and pro-caspase-1. Recent research has reported that the inflammatory response centered on NLRP3 inflammasomes plays a key part in inflammation in ALI, and may hence be a prospective candidate for therapeutic intervention. In the review, we present an overview of the ailment characteristics of acute lung injury along with the constitution and operation of the NLRP3 inflammasome within this framework. We also explore therapeutic strategies targeting the NLRP3 inflammasome to combat acute lung injury.

Preterm lung and brain responses to mechanical ventilation and corticosteroids

Mechanical ventilation is necessary to maintain oxygenation and ventilation in many preterm infants. Unfortunately, even short periods of mechanical ventilation can cause lung and airway injury, and initiate the lung inflammation that contributes to the development of bronchopulmonary dysplasia (BPD). The mechanical stretch leads to airway cell differentiation and simplification of the alveoli, and releases cytokines that cause systemic response in other organs. Mechanical ventilation also leads to brain injury (IVH, white and gray matter) and neuronal inflammation that can affect the neurodevelopment of preterm infants. In efforts to decrease BPD, corticosteroids have been used for both prevention and treatment of lung inflammation. Corticosteroids have also been demonstrated to cause neuronal injury, so the clinician must balance the negative effects of both mechanical ventilation and steroids on the brain and lungs. Predictive models for BPD can help assess the infants who will benefit most from corticosteroid exposure. This review describes the lung and brain injury from mechanical ventilation in the delivery room and chronic mechanical ventilation in animal models. It provides updates on the current guidelines for use of postnatal corticosteroids (dexamethasone, hydrocortisone, budesonide, budesonide with surfactant) for the prevention and treatment of BPD, and the effects the timing of each steroid regimen has on neurodevelopment.

C/EBPβ Promotes LPS-Induced IL-1β Transcription and Secretion in Alveolar Macrophages via NOD2 Signaling

Objective

C/EBPβ, a crucial transcription factor, regulates innate immunity and inflammatory responses. However, the role played by C/EBPβ in alveolar macrophage (AM) inflammatory responses remains unknown. This study aimed to investigate the role and mechanism of C/EBPβ in alveolar macrophages (AMs) from the transcriptional level and to search for natural compounds targeting C/EBPβ.

Methods

Rat AMs were infected with Lv-sh-C/EBPβ and treated with LPS, and the expression levels of iNOS, TNF-α, IL-6, and IL-1β were measured by RT-qPCR, Western blotting, and ELISA. Mechanistically, transcriptome sequencing (RNA-seq) revealed changes in gene expression patterns in AMs after LPS stimulation and C/EBPβ knockdown. Functional enrichment analyses and rescue experiments identified and validated inflammation-associated cell signaling pathways regulated by C/EBPβ. Furthermore, virtual screening was used to search for natural compounds that inhibit C/EBPβ with the structure of helenalin as a reference.

Results

Following stimulation with LPS, AMs exhibited an increased expression of C/EBPβ. C/EBPβ knockdown significantly decreased the expression levels of inflammatory mediators. A total of 374 differentially expressed genes (DEGs) were identified between LPS-stimulated C/EBPβ knockdown and negative control cells. The NOD-like receptor signaling may be a key target for C/EBPβ, according to functional enrichment analyses of the DEGs. Further experiments showed that the muramyl dipeptide (MDP, NOD2 agonist) reversed the downregulation of inflammatory mediators and the NF-κB pathway caused by the C/EBPβ knockdown. The virtual screening revealed that N-caffeoyltryptophan, orilotimod, and petasiphenone have comparable pharmacological properties to helenalin (a known C/EBPβ inhibitor) and demonstrate a great binding capacity to C/EBPβ.

Conclusion

Ablation of C/EBPβ may attenuate LPS-induced inflammatory damage in AMs by inhibiting the NOD2 receptor signaling pathway. Three natural compounds, N-caffeoyltryptophan, orilotimod, and petasiphenone, may be potential C/EBPβ inhibitors.

Neutrophil-Derived IL-17 Promotes Ventilator-Induced Lung Injury via p38 MAPK/MCP-1 Pathway Activation

Ventilator-induced lung injury (VILI) is one of the most common complications of mechanical ventilation and can severely affect health. VILI appears to involve excessive inflammatory responses, but its pathogenesis has not yet been clarified. Since interleukin-17 (IL-17) plays a critical role in the immune system and the development of infectious and inflammatory diseases, we investigated here whether it plays a role in VILI. In a mouse model of VILI, mechanical ventilation with high tidal volume promoted the accumulation of lung neutrophils, leading to increased IL-17 levels in the lung, which in turn upregulated macrophage chemoattractant protein-1 via p38 mitogen-activated protein kinase. Depletion of neutrophils decreases the production IL-17 in mice and inhibition of IL-17 significantly reduced HTV-induced lung injury and inflammatory response. These results were confirmed in vitro using RAW264.7 macrophage cultures. Our results suggest that IL-17 plays a pro-inflammatory role in VILI and could serve as a new target for its treatment.

Inhibition of IP3R/Ca2+ Dysregulation Protects Mice From Ventilator-Induced Lung Injury via Endoplasmic Reticulum and Mitochondrial Pathways

Rationale

Disruption of intracellular calcium (Ca2+) homeostasis is implicated in inflammatory responses. Here we investigated endoplasmic reticulum (ER) Ca2+ efflux through the Inositol 1,4,5-trisphosphate receptor (IP3R) as a potential mechanism of inflammatory pathophysiology in a ventilator-induced lung injury (VILI) mouse model.

Methods

C57BL/6 mice were exposed to mechanical ventilation using high tidal volume (HTV). Mice were pretreated with the IP3R agonist carbachol, IP3R inhibitor 2-aminoethoxydiphenyl borate (2-APB) or the Ca2+ chelator BAPTA-AM. Lung tissues and bronchoalveolar lavage fluid (BALF) were collected to measure Ca2+ concentrations, inflammatory responses and mRNA/protein expression associated with ER stress, NLRP3 inflammasome activation and inflammation. Analyses were conducted in concert with cultured murine lung cell lines.

Results

Lungs from mice subjected to HTV displayed upregulated IP3R expression in ER and mitochondrial-associated-membranes (MAMs), with enhanced formation of MAMs. Moreover, HTV disrupted Ca2+ homeostasis, with increased flux from the ER to the cytoplasm and mitochondria. Administration of carbachol aggravated HTV-induced lung injury and inflammation while pretreatment with 2-APB or BAPTA-AM largely prevented these effects. HTV activated the IRE1α and PERK arms of the ER stress signaling response and induced mitochondrial dysfunction-NLRP3 inflammasome activation in an IP3R-dependent manner. Similarly, disruption of IP3R/Ca2+ in MLE12 and RAW264.7 cells using carbachol lead to inflammatory responses, and stimulated ER stress and mitochondrial dysfunction.

Conclusion

Increase in IP3R-mediated Ca2+ release is involved in the inflammatory pathophysiology of VILI via ER stress and mitochondrial dysfunction. Antagonizing IP3R/Ca2+ and/or maintaining Ca2+ homeostasis in lung tissue represents a prospective treatment approach for VILI.

A role for bronchial epithelial autotaxin in ventilator-induced lung injury

Background

The pathophysiology of acute respiratory distress syndrome (ARDS) may eventually result in heterogeneous lung collapse and edema-flooded airways, predisposing the lung to progressive tissue damage known as ventilator-induced lung injury (VILI). Autotaxin (ATX; ENPP2), the enzyme largely responsible for extracellular lysophosphatidic acid (LPA) production, has been suggested to play a pathogenic role in, among others, pulmonary inflammation and fibrosis.

Methods

C57BL/6 mice were subjected to low and high tidal volume mechanical ventilation using a small animal ventilator: respiratory mechanics were evaluated, and plasma and bronchoalveolar lavage fluid (BALF) samples were obtained. Total protein concentration was determined, and lung histopathology was further performed

Results

Injurious ventilation resulted in increased BALF levels of ATX. Genetic deletion of ATX from bronchial epithelial cells attenuated VILI-induced pulmonary edema.

Conclusion

ATX participates in VILI pathogenesis.

WISP1 and TLR4 on Macrophages Contribute to Ventilator-Induced Lung Injury

Injurious mechanical ventilation has been shown to directly affect pulmonary and systemic immune responses. How these responses propagate or attenuate remains unknown. The goal of this study was to further determine whether toll-like receptor (TLR) 4 and WNT1-inducible signaling pathway protein 1 (WISP1) could contribute to injurious mechanical ventilation, especially focusing on the role of macrophages during experimental ventilator-induced lung injury. A prospective, randomized, and controlled animal study was designed, and male, wild-type (WT) C57BL/6 mice, TLR4 knockout (TLR4^-/-), and lyzTLR4 knockout (lyzTLR4^-/-) mice aging 8~12 weeks were used. Animals were anesthetized and randomized to spontaneous breathing (SB) group or to high tidal volume (VT, 20 ml/kg) mechanical ventilation (HTV) group. Histological evaluation, alveolar-capillary permeability of Evan's blue albumin (EBA), WISP1 protein levels, macrophage inflammatory protein-2 (MIP-2), and interleukin-6 (IL-6) in plasma and bronchoalveolar lavage fluid (BALF) concentrations were analyzed. HTV group was associated with a significant increase of WISP1 and EBA ratio in C57BL/6 mice, a significant decrease of WISP1 protein levels, and a significant decrease of IL-6, MIP-2 in plasma, and BALF concentrations of pro-inflammatory cytokines in TLR4^-/- and lyzTLR4^-/- knockout mice. In TLR4^-/- mice and lyzTLR4^-/- mice, there were also significant differences between SB group and HTV group in terms of H&E score and EBA ratio and level of pro-inflammation cytokines. The entire TLR4-targeted mice could further improve various inflammatory changes and damages when compared with lyzTLR4-targeted mice. What is more, TLR4^-/- mice and lyzTLR4^-/- mice reacted differently to rWISP1 and/or BMMC treated. TLR4^-/- mice had no response to rWISP1, while lyzTLR4^-/- mice still showed drastic response to both treatments. TLR4 and WISP1, especially the former one, on macrophages could contribute to releasing of pro-inflammatory cytokines during ventilator-induced lung injury. Injurious mechanical ventilation may result in an immune response which is similar to that of infection.

Inhibition of p38 MAPK Mitigates Lung Ischemia Reperfusion Injury by Reducing Blood-Air Barrier Hyperpermeability

Background: Lung ischemia reperfusion injury (LIRI) is a complex pathophysiological process activated by lung transplantation and acute lung injury. The p38 mitogen-activated protein kinase (MAPK) is involved in breakdown of the endothelial barrier during LIRI, but the mechanism is still unclear. Therefore, we investigated the function of p38 MAPK in LIRI in vivo and in vitro.

Methods: Sprague–Dawley rats were subjected to ischemia reperfusion with or without pretreatment with a p38 MAPK inhibitor. Lung injury was assessed using hematoxylin and eosin staining, and pulmonary blood–air barrier permeability was evaluated using Evans blue staining. A rat pulmonary microvascular endothelial cell line was infected with lentiviral expressing short hairpin (sh)RNA targeting p38 MAPK and then cells were subjected to oxygen/glucose deprivation and reoxygenation (OGD/R). Markers of endothelial destruction were measured by western blot and immunofluorescence.

Results:In vivo LIRI models showed structural changes indicative of lung injury and hyperpermeability of the blood–air barrier. Inhibiting p38 MAPK mitigated these effects. Oxygen/glucose deprivation and reoxygenation promoted hyperpermeability of the endothelial barrier in vitro, but knockdown of p38 MAPK attenuated cell injury; maintained endothelial barrier integrity; and partially reversed injury-induced downregulation of permeability protein AQP1, endothelial protective protein eNOS, and junction proteins ZO-1 and VE-cadherin while downregulating ICAM-1, a protein involved in destroying the endothelial barrier, and ET-1, a protein involved in endothelial dysfunction.

Conclusion: Inhibition of p38 MAPK alleviates LIRI by decreasing blood–air hyperpermeability. Blocking p38 MAPK may be an effective treatment against acute lung injury.

Mitophagy-Mediated mtDNA Release Aggravates Stretching-Induced Inflammation and Lung Epithelial Cell Injury via the TLR9/MyD88/NF-κB Pathway

Background

In animal models of ventilation-induced lung injury, mitophagy triggers mitochondria damage and the release of mitochondrial (mt) DNA, which activates inflammation. However, the mechanism of this process is unclear.

Methods

A model of cyclic stretching (CS)-induced lung epithelial cell injury was established. The genetic intervention of phosphatase and tensin homolog-induced kinase 1 (PINK1) expression via lentivirus transfection was used to identify the relationship between PINK1-mediated mitophagy and mtDNA release in stretching-induced inflammatory response and injury. Pharmacological inhabitation of Toll-like receptor 9 (TLR9) and myeloid differentiation factor 88 (MyD88) expression was performed via their related inhibitors, while pre-treatment of exogenous mtDNA was used to verify the role of mtDNA in stretching-induced inflammatory response and injury.

Results

Using a cell culture model of CS, we found that knocking down PINK1 in lung epithelial cells reduced mitophagy activation and mtDNA release, leading to milder inflammatory response and injury; conversely, up-regulating PINK1 exacerbated stretching-induced inflammation and injury, and similar effects were observed by upregulating TLR9 to induce expression of MyD88 and nuclear factor-κB (NF-κB)/p65. Down-regulating MyD88 protected lung epithelial cells from stretching injury and decreased NF-κB/p65 expression.

Conclusion

These findings suggest that PINK1-dependent mitophagy and associated TLR9 activation is indeed a major factor in stretch-induced cell injury via a mechanism in which released mtDNA activates TLR9 and thereby the MyD88/NF-κB pathway. Inhibiting this process may be a therapeutic approach to prevent inflammation and cell injury in patients on mechanical ventilation.

Preconditioning with rHMGB1 ameliorates lung ischemia-reperfusion injury by inhibiting alveolar macrophage pyroptosis via the Keap1/Nrf2/HO-1 signaling pathway

BACKGROUND

Lung ischemia-reperfusion injury (LIRI) is a complex pathophysiological process that can lead to poor patient outcomes. Inflammasome-dependent macrophage pyroptosis contributes to organ damage caused by ischemia/reperfusion injury. Oxidative stress and antioxidant enzymes also play an important role in LIRI. In this study, we conducted experiments to investigate whether and how preconditioning with rHMGB1 could ameliorate LIRI in a mouse model.

METHODS

Adult male BALB/c mice were anesthetized, the left hilus pulmonis was clamped, and reperfusion was performed. rHMGB1 was administered via intraperitoneal injection before anesthesia, and brusatol was given intraperitoneally every other day before surgery. We measured pathohistological lung tissue damage, wet/dry mass ratios of pulmonary tissue, and levels of inflammatory mediators to assess the extent of lung injury. Alveolar macrophage pyroptosis was evaluated by measuring release of lactate dehydrogenase, caspase-1 expression was assessed using flow cytometry, and gasdermin-D expression was analyzed using immunofluorescent staining. Levels of oxidative stress markers and antioxidant enzymes were also analyzed.

RESULTS

Preconditioning with rHMGB1 significantly ameliorated lung injury induced by ischemia-reperfusion, based on measurements of morphology, wet/dry mass ratios, as well as expression of IL-1β, IL-6, NF-κB, and HMGB1 in lung tissues. It also alleviated alveolar macrophage pyroptosis, reduced oxidative stress and restored the activity of antioxidant enzymes. These beneficial effects were mediated at least in part by the Keap1/Nrf2/HO-1 pathway, since they were reversed by the pathway inhibitor brusatol.

CONCLUSIONS

Preconditioning with rHMGB1 may protect against LIRI by suppressing alveolar macrophage pyroptosis. This appears to involve reduction of oxidative stress and promotion of antioxidant enzyme activity via the Keap1/Nrf2/HO-1 pathway.

Marrow-derived mesenchymal stem cells regulate the inflammatory response and repair alveolar type II epithelial cells in acute lung injury of rats

Objective

We investigated the effect of untransplantable bone marrow-derived mesenchymal stem cells (BMSCs) in acute lung injury (ALI) and whether BMSCs attenuate damage of lipopolysaccharide (LPS) to alveolar type II epithelial cells (AECIIs).

Methods

ALI models were prepared by nebulizing LPS and then BMSCs were infused 1 hour later. We observed histopathological changes of lung tissue and evaluated inflammatory exudation by the wet/dry weight ratio, bronchiolar lavage fluid cell count, and protein concentration determination. Inflammatory and vascular factors were detected by immunohistochemistry and western blotting. For in vitro experiments, AECIIs were stimulated with 10 μg/mL LPS for 4 hours and then BMSCs were seeded in transit inserts to co-culture for 24 hours. The activity of AECIIs was detected.

Results

In the LPS + BMSCs group, histopathological examination showed that the degree of lung injury was significantly reduced compared with the LPS group. Protein expression of inflammatory and vascular factors was significantly lower with treatment. Optical density values and cell viability of the LPS + BMSCs group were significantly higher than those of the LPS group.

Conclusions

Untransplanted-BMSCs can inhibit the inflammatory response in ALI and promote repair of AECIIs. This might be due to substances secreted by BMSCs and interaction between these substances.

Autophagy Protects Against Developing Increased Lung Permeability and Hypoxemia by Down Regulating Inflammasome Activity and IL-1β in LPS Plus Mechanical Ventilation-Induced Acute Lung Injury

Targeting inflammasome activation to modulate interleukin (IL)-1β is a promising treatment strategy against acute respiratory distress syndrome and ventilator-induced lung injury (VILI). Autophagy is a key regulator of inflammasome activation in macrophages. Here, we investigated the role of autophagy in the development of acute lung injury (ALI) induced by lipopolysaccharide (LPS) and mechanical ventilation (MV). Two hours before starting MV, 0.2 mg/kg LPS was administered to mice intratracheally. Mice were then placed on high-volume MV (30 ml/kg with 3 cmH₂O positive end-expiratory pressure for 2.5 h without additional oxygen application). Mice with myeloid-specific deletion of the autophagic protein ATG16L1 (Atg16l1^fl/flLysM^Cre) suffered severe hypoxemia (adjusted p < 0.05) and increased lung permeability (p < 0.05, albumin level in bronchoalveolar lavage fluid) with significantly higher IL-1β release into alveolar space (p < 0.05). Induction of autophagy by fasting-induced starvation led to improved arterial oxygenation (adjusted p < 0.0001) and lung permeability (p < 0.05), as well as significantly suppressed IL-1β production (p < 0.01). Intratracheal treatment with anti-mouse IL-1β monoclonal antibody (mAb; 2.5 mg/kg) significantly improved arterial oxygenation (adjusted p < 0.01) as well as lung permeability (p < 0.05). On the other hand, deletion of IL-1α gene or use of anti-mouse IL-1α mAb (2.5 mg/kg) provided no significant protection, suggesting that the LPS and MV-induced ALI is primarily dependent on IL-1β, but independent of IL-1α. These observations suggest that autophagy has a protective role in controlling inflammasome activation and production of IL-1β, which plays a critical role in developing hypoxemia and increased lung permeability in LPS plus MV-induced acute lung injury.

PP2ACα of Alveolar Macrophages Is a Novel Protective Factor for LPS-Induced Acute Respiratory Distress Syndrome

Protein phosphatase 2A (PP2A) is one main serine/threonine phosphatase in eukaryotes, and its activation changes have been linked to modulation of numerous pathological processes, such as cancer, inflammation, fibrosis, and neurodegenerative diseases. Acute respiratory distress syndrome (ARDS), the major cause of respiratory failure, remains with limited therapies available up to now. Alveolar macrophages (AMs) are essential to innate immunity and host defense, participating in the pathogenesis of ARDS. As a result, AMs are considered as a potential therapeutic target for ARDS. In our study, we firstly found that PP2A activity was significantly decreased in the lipopolysaccharide (LPS)-stimulated AMs. Furthermore, adoptive transfer of AMs with enhanced PP2A enzyme activity that was improved by C2-ceramide prior to LPS exposure alleviated acute lung inflammation. Conversely, AM-specific ablation of PP2ACα exacerbated inflammatory responses to LPS. Mechanistically, PP2ACα negatively regulates LPS-induced cytokine secretion of AMs by NF-κB and MAPK pathways. Together, these findings provide the evidence to guide the development of novel therapeutic options targeting PP2ACα for ARDS/acute lung injury.

Targeting Notch-activated M1 macrophages attenuate lung tissue damage in a rat model of ventilator induced lung injury

Ventilator induced lung injury (VILI) may be involved in the activation of alveolar macrophages. The purpose of this study was to investigate the relationship between the Notch signaling pathway and macrophage polarization in VILI. The VILI model was established using rats. Hematoxylineosin staining was used to test the lung tissue morphology. Bicinchoninic acid assay and ELISA were performed to detect protein and tumor necrosis factor (TNF)-α, interleukin (IL)-6, IL-10 levels in bronchoalveolar lavage fluids (BALF), respectively. The ratio of alveolar M1 and M2 macrophages was detected by flow cytometry. The mRNA and protein expression levels of Notch pathway-related proteins were determined using reverse transcription-quantitative PCR and western blotting. The present study found that high-frequency mechanical ventilation could cause pulmonary edema and increase the levels of protein, TNF-α and IL-6 in BALF while decreasing the level of IL-10 in BALF. High-frequency mechanical ventilation also induced polarization of alveolar macrophages to M1. The results also showed a significant increase in the levels of Notch pathway-related proteins including notch intracellular domain, Hes1, Hes5 and Hey1. Injection of N-[N-(3,5-difluorophenylacetyl)-1-alanyl] phenylglycine t-butyl ester could inhibit the Notch pathway and such an inhibition protected lung tissue and reduced lung inflammation caused by mechanical ventilation. After the Notch pathway was inhibited, the level of M1 polarization of macrophages caused by high-frequency mechanical ventilation was reduced. VILI caused pulmonary inflammation and macrophages to polarize to M1 and upregulated the expression levels of Notch pathway-related proteins. The inhibition of Notch pathway also reduced the proportion of M1 macrophages and inflammatory responses.

Deferoxamine preconditioning ameliorates mechanical ventilation-induced lung injury in rat model via ROS in alveolar macrophages: a randomized controlled study

Background

Mechanical ventilation (MV) can provide effective breathing support; however, ventilatior-induced lung injury (VILI) has also been widely recognized in clinical practice, including in the healthy lung. Unfortunately, the morbidity and mortality of VILI remain unacceptably high, and no satisfactory therapeutic effect can be achieved. The current study aimed to examine the effects of iron chelator preconditioning on the mitochondrial reactive oxygen species (ROS) in alveolar macrophages and pathological lung injury in VILI.

Methods

Twenty four healthy male Sprague–Dawley (SD) rats (250–300 g in weight) were randomly divided into 3 groups, including the control group (NC group, n = 8), the high-volume mechanical ventilation group (HV group, n = 8), and the deferoxamine treatment group (HV + DFO group, n = 8). Rats in the HV and HV + DFO groups were subjected to high-volume MV at a dose of 40 ml/kg. DFO was administered at a dose of 200 mg/kg 15 min prior to over-ventilation. Spontaneously breathing anesthetized rats were used as the controls. The animals were sacrificed after 4 h of high-volume ventilation or under control conditions, the animals were sacrificed. Purified alveolar macrophages from bronchoalveolar lavage fluid (BALF) and lung tissue were collected for further analysis through light microscopy and flow cytometry.

Results

Compared with the controls, the high-volume-ventilated rats had exhibited typical lung edema and histological lung injury, and ROS were markedly increased in alveolar macrophages and mitochondria. Moreover, all indices of VILI were remarkably different in rats treated with DFO preconditioning. DFO could ameliorate lung injury in the mechanically ventilated SD rat model.

Conclusions

DFO preconditioning contributes to mitigating the histological lung damage while reducing ROS levels in alveolar macrophages and mitochondria, suggesting that iron metabolism in alveolar macrophages may participate in VILI.

Cobra Venom Factor-induced complement depletion protects against lung ischemia reperfusion injury through alleviating blood-air barrier damage

The purpose of this study was to study whether complement depletion induced by pretreatment with Cobra Venom Factor (CVF) could protect against lung ischemia reperfusion injury (LIRI) in a rat model and explore its molecular mechanisms. Adult Sprague-Dawley rats were randomly assigned to five groups (n = 6): Control group, Sham-operated group, I/R group, CVF group, I/R + CVF group. CVF (50 μg/kg) was injected through the tail vein 24 h before anesthesia. Lung ischemia reperfusion (I/R) was induced by clamping the left hilus pulmonis for 60 minutes followed by 4 hours of reperfusion. Measurement of complement activity, pathohistological lung injury score, inflammatory mediators, pulmonary permeability, pulmonary edema, integrity of tight junction and blood-air barrier were performed. The results showed that pretreatment with CVF significantly reduced complement activity in plasma and BALF. Evaluation in histomorphology showed that complement depletion induced by CVF significantly alleviated the damage of lung tissues and inhibited inflammatory response in lung tissues and BALF. Furthermore, CVF pretreatment had the function of ameliorating pulmonary permeability and preserving integrity of tight junctions in IR condition. In conclusion, our results indicated that complement depletion induced by CVF could inhibit I/R-induced inflammatory response and alleviate lung I/R injury. The mechanisms of its protective effects might be ameliorated blood-air barrier damage.

High Tidal Volume Induces Mitochondria Damage and Releases Mitochondrial DNA to Aggravate the Ventilator-Induced Lung Injury

Objective

This study aimed to determine whether high tidal volume (HTV) induce mitochondria damage and mitophagy, contributing to the release of mitochondrial DNA (mtDNA). Another aim of the present study was to investigate the role and mechanism of mtDNA in ventilator-induced lung injury (VILI) in rats.

Methods

Rats were tracheotomized and allowed to breathe spontaneously or mechanically ventilated for 4 h. After that, lung injury was assessed. Inhibition of toll-like receptor 9 (TLR9), named ODN2088, was used to determine the involvement of TLR9/myeloid differentiation factor 88 (MyD88)/nuclear factor-κB (NF-κB) signaling pathway in VILI. The mitochondrial damage and release of mtDNA were assessed. Pharmacological inhibition of mtDNA (chloroquine) was used to determine whether mtDNA trigger inflammation via TLR9 in VILI. EDU-labeled mtDNA deriving from mitophagy was assessed by immunofluorescence. The role of mitophagy in VILI was shown by administration of antimycin A and cyclosporine A.

Main results

Rats subjected to HTV showed more severe pulmonary edema and inflammation than the other rats. The decreased expression of TLR9, MyD88, and NF-κB were observed following the use of ODN2088. Mechanical ventilation (MV) with HTV damaged mitochondria which resulted in dysfunctional ATP synthesis, accumulation of reactive oxygen species, and loss of mitochondrial membrane potential. Moreover, the results of distribution of fluorescence in rats upon HTV stimulation indicated that mtDNA cleavage was associated with mitophagy. The expression levels of mitophagy related genes (LC3B-II/LC3B-I, PINK1, Parkin, and mitofusin 1) in animals ventilated with HTV were significantly upregulated. Administration of antimycin A aggregated the histological changes and inflammation after MV, but these effects were attenuated when administered in the presence of cyclosporine A.

Conclusion

MV with HTV induces mitochondrial damage and mitophagy, contributing to the release of mtDNA, which may be induced VILI in rat via TLR9/MyD88/NF-κB signaling pathway.

The triggering receptor expressed by myeloid cells-1 activates TLR4-MyD88-NF-κB-dependent signaling to aggravate ventilation-induced lung inflammation and injury in mice

The triggering receptor expressed by myeloid cells-1 (TREM-1) plays an important role in infectious and autoimmune diseases but how it contributes to ventilation-induced lung injury (VILI) and inflammation is unclear. Here, we examine the possibility that TREM-1 activates signaling dependent on Toll-like receptor 4 (TLR4), myeloid differentiation factor 88 (Myd88) and nuclear factor (NF)-κB, which leads in turn to VILI. In a mouse model of VILI, which we validated based on lung edema and histopathology as well as cytokine levels, we examine mRNA and protein levels of TREM-1, TLR4, MyD88, NF-κB and its inhibitory protein I-κB in animals subjected to ventilation at normal or high tidal volume. The extent of lung edema, injury and inflammation were higher in the high tidal volume animals, as were the expression levels of all proteins examined. Treatment with TREM-1 agonist aggravated these effects, whereas treatment with TREM-1 antagonist attenuated them. Our results suggest that aggravation of VILI by TREM-1 in mice may be associated with TLR4-MyD88-NF-κB-dependent signaling.

Activation of Porcine Alveolar Macrophages by Actinobacillus pleuropneumoniae Lipopolysaccharide via the Toll-Like Receptor 4/NF-κB-Mediated Pathway

Actinobacillus pleuropneumoniae is the causative agent of porcine contagious pleuropneumonia. Overproduction of proinflammatory cytokines, like interleukin-1β (IL-1β), IL-6, tumor necrosis factor alpha, and resistin, in the lung is an important feature of A. pleuropneumoniae infection. These proinflammatory cytokines enhance inflammatory and immunological responses. However, the mechanism that leads to cytokine production remains unclear. As a major virulence factor of A. pleuropneumoniae, lipopolysaccharide (LPS) may act as a potent stimulator of Toll-like receptor 4 (TLR4), triggering a number of intracellular signaling pathways that lead to the synthesis of proinflammatory cytokines. Porcine alveolar macrophages (PAMs) are the first line of defense against pathogenic microbes during pathogen invasion. The results of the present study demonstrate that A. pleuropneumoniae LPS induces PAMs to produce inflammatory cytokines in time- and dose-dependent manners. Moreover, PAMs were activated by A. pleuropneumoniae LPS, resulting in upregulation of signaling molecules, including TLR4, MyD88, TRIF-related adaptor molecule, and NF-κB. In contrast, the activation effects of A. pleuropneumoniae LPS on PAMs could be suppressed by specific inhibitors, like small interfering RNA and Bay11-7082. Taken together, our data indicate that A. pleuropneumoniae LPS can induce PAMs to produce proinflammatory cytokines via the TLR4/NF-κB-mediated pathway. These findings partially reveal the mechanism of the overproduction of proinflammatory cytokines in the lungs of swine with A. pleuropneumoniae infection and may provide targets for the prevention of A. pleuropneumoniae-induced pneumonia. All the data could be used as a reference for the pathogenesis of respiratory infection.

Effect of TLR4/MyD88 signaling pathway on sepsis-associated acute respiratory distress syndrome in rats, via regulation of macrophage activation and inflammatory response

The present study aimed to investigate the effects of the Toll-like receptor (TLR)4/myeloid differentiation primary response (MyD)88 signaling pathway on sepsis-associated acute respiratory distress syndrome (ARDS) in rats, and the involvement of macrophage activation and the inflammatory response. A total of 36 specific pathogen-free male Sprague-Dawley rats were selected to establish the rat model of sepsis-associated ARDS using cecal ligation and puncture (CLP). Rats were assigned into the Ab (anti-TLR4 monoclonal antibody)-CLP, CLP and Sham groups. Arterial partial pressure of oxygen (P_aO₂) was detected using blood gas analysis. Bronchoalveolar lavage fluid (BALF) and alveolar macrophages were collected. The pathological structure of lung tissue was observed following hematoxylin-eosin staining. The ultrastructural alterations of alveolar epithelial cells were observed under transmission electron microscope. The ratios of wet/dry weight of lung tissue and total protein content in BALF were measured. The concentration of tumor necrosis factor (TNF)-α and interleukin (IL)-1β in BALF and peripheral blood was determined by enzyme-linked immunosorbent assay. The TLR4, TLR9, MyD88 and nuclear factor (NF)-κΒ mRNA and protein expression levels in alveolar macrophages were measured by reverse transcription-quantitative polymerase chain reaction and western blotting. Compared with the Sham group, the rats in the CLP group demonstrated significantly increased respiratory frequency, lung permeability, lung edema, inflammatory infiltration, TNF-α and IL-1β expression levels in BALF and peripheral blood and TLR4, TLR9, MyD88 and NF-κΒ expression levels in macrophages, however decreased arterial P_aO₂. Following pretreatment with anti-TLR4 monoclonal antibody, rats exhibited decreased lung injury, inflammatory infiltration, lung edema, TNF-α and IL-1β expressions in BALF and peripheral blood, and TLR4, TLR9, MyD88 and NF-κΒ expression levels in macrophages, with increased arterial P_aO₂. These results suggested that the inhibition of TLR4/MyD88 signaling pathway may relieve sepsis-associated ARDS in rats through regulating macrophage activation and the inflammatory response.

Glycyrrhizin Ameliorate Ischemia Reperfusion Lung Injury through Downregulate TLR2 Signaling Cascade in Alveolar Macrophages

This experiment was conducted to study whether pretreatment with Glycyrrhizin (GL) could ameliorate ischemia-reperfusion (I/R) lung injury and investigate the mechanisms of its protective effects in a mice model. Six-eight weeks male BALB/C mice were randomly assigned to four groups (n = 6): Control, Glycyrrhizin, I/R and I/R+Glycyrrhizin. Lung I/R was achieved by clamping the left hilus pulmonis. GL (200 mg/kg) was injected intraperitoneally 30 min before anesthesia. Measurement of pathohistological lung injury score, pulmonary permeability, isolated alveolar macrophages, inflammatory mediators, TLR2 and its downstream factors (MyD88, NF-κB) were performed. The results were as anticipated. Pathohistological evaluation indicated that GL significantly ameliorated I/R-induced lung injury, pulmonary permeability and edema. Pretreatment with GL significantly inhibited I/R-induced inflammation in lung tissues and BALF. In addition, GL significantly decreased I/R-induced isolated alveolar macrophages and suppressed I/R-induced expression of TLR2 and its downstream factors in lung tissues and alveolar macrophages. Collectively, our data indicated that pretreatment with GL could ameliorate I/R lung injury. The mechanisms of its protective effects might be inhibit I/R-induced inflammatory response through downregulate TLR2 signaling cascade in alveolar macrophages.

Evaluation of self-perception of mechanical ventilation knowledge among Brazilian final-year medical students, residents and emergency physicians

OBJECTIVE:

To present self-assessments of knowledge about mechanical ventilation made by final-year medical students, residents, and physicians taking qualifying courses at the Brazilian Society of Internal Medicine who work in urgent and emergency settings.

METHODS:

A 34-item questionnaire comprising different areas of knowledge and training in mechanical ventilation was given to 806 medical students, residents, and participants in qualifying courses at 11 medical schools in Brazil. The questionnaire's self-assessment items for knowledge were transformed into scores.

RESULTS:

The average score among all participants was 21% (0-100%). Of the total, 85% respondents felt they did not receive sufficient information about mechanical ventilation during medical training. Additionally, 77% of the group reported that they would not know when to start noninvasive ventilation in a patient, and 81%, 81%, and 89% would not know how to start volume control, pressure control and pressure support ventilation modes, respectively. Furthermore, 86.4% and 94% of the participants believed they would not identify the basic principles of mechanical ventilation in patients with obstructive pulmonary disease and acute respiratory distress syndrome, respectively, and would feel insecure beginning ventilation. Finally, 77% said they would fear for the safety of a patient requiring invasive mechanical ventilation under their care.

CONCLUSION:

Self-assessment of knowledge and self-perception of safety for managing mechanical ventilation were deficient among residents, students and emergency physicians from a sample in Brazil.

Suppressive oligonucleotides inhibit inflammation in a murine model of mechanical ventilator induced lung injury

BACKGROUND

Mechanical ventilation (MV) is commonly used to improve blood oxygenation in critically ill patients and for general anesthesia. Yet the cyclic mechanical stress induced at even moderate ventilation volume settings [tidal volume (Vt) <10 mL/kg] can injure the lungs and induce an inflammatory response. This work explores the effect of treatment with suppressive oligonucleotides (Sup ODN) in a mouse model of ventilator-induced lung injury (VILI).

METHODS

Balb/cJ mice were mechanically ventilated for 4 h using clinically relevant Vt and a positive end-expiratory pressure of 3 cmH₂O under 2-3% isoflurane anesthesia. Lung tissue and bronchoalveolar lavage fluid were collected to assess lung inflammation and lung function was monitored using a FlexiVent^®.

RESULTS

MV induced significant pulmonary inflammation characterized by the influx and activation of CD11c⁺/F4/80⁺ macrophages and CD11b⁺/Ly6G⁺ polymorphonuclear cells into the lung and bronchoalveolar lavage fluid. The concurrent administration of Sup ODN attenuated pulmonary inflammation as evidenced by reduced cellular influx and production of inflammatory cytokines. Oligonucleotide treatment did not worsen lung function as measured by static compliance or resistance.

CONCLUSIONS

Treatment with Sup ODN reduces the lung injury induced by MV in mice.