Mechanical ventilation modulates TLR4 and IRAK-3 in a non-infectious, ventilator-induced lung injury model

Progress in the relationship between mechanical ventilation parameters and ventilator-related complications during perioperative anesthesia

BACKGROUND

Mechanical ventilation, as an important respiratory support, plays an important role in general anesthesia and it is the cornerstone of intraoperative management of surgical patients. Different from spontaneous respiration, intraoperative mechanical ventilation can lead to postoperative lung injury, and its impact on surgical mortality cannot be ignored. Postoperative lung injury increases hospital stay and is related to preoperative conditions, anesthesia time, and intraoperative ventilation settings.

METHOD

Through reading literature and research reports, the relationship between perioperative input parameters and output parameters related to mechanical ventilation and ventilator-related complications was reviewed, providing reference for the subsequent setting of input parameters of mechanical ventilation and new ventilation strategies.

RESULTS

The parameters of inspiratory pressure rise time and inspiratory time can change the gas distribution, gas flow rate and airway pressure into the lungs, but there are few clinical studies on them. It can be used as a prospective intervention to study the effect of specific protective ventilation strategies on pulmonary complications after perioperative anesthesia.

CONCLUSION

There are many factors affecting lung function after perioperative mechanical ventilation. Due to the difference of human body, the ventilation parameters suitable for each patient are different, and the deviation of each ventilation parameter can lead to postoperative pulmonary complications. Inspiratory pressure rise time and inspiratory time will be used as the new ventilation strategy.

Preventive effects of hesperidin in an experimental model ofs acute lung inflammation

In this study, we hypothesized that long-term administration of hesperidin can modulate the inflammatory response and oxidative stress in animals submitted to mechanical ventilation (MV). Twenty-five C57BL/6 male mice were divided into 5 groups: control, MV, animals receiving hesperidin in three doses 10, 25 and 50 mg/kg. The animals received the doses of hesperidin for 30 days via orogastric gavage, and at the end of the period the animals were submitted to MV. In animals submitted to MV, increased lymphocyte, neutrophil and monocyte/macrophage cell counts were observed in the blood and airways. Associated to this, MV promoted an increase in inflammatory cytokine levels such as CCL2, IL-12 and TNFα. The daily administration of hesperidin in the three doses prevented the effects caused by MV, which was observed by a lower influx of inflammatory cells into the airways, a reduction in inflammatory markers and less oxidative damage.

Systemic cytokines inhibition with Imp7 siRNA nanoparticle ameliorates gut injury in a mouse model of ventilator-induced lung injury

Mechanical ventilation (MV) may negatively affect the lungs and cause the release of inflammatory mediators, resulting in extra-pulmonary organ dysfunction. Studies have revealed systemically elevated levels of proinflammatory cytokines in animal models of ventilator-induced lung injury (VILI); however, whether these cytokines have an effect on gut injury and the mechanisms involved remain unknown. In this study, VILI was generated in mice with high tidal volume mechanical ventilation (20 ml/kg). Tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), and IL-6 concentrations in serum and gut measured by ELISA showed significant elevation in the VILI mice. Significant increases in gut injury and PANoptosis were observed in the VILI mice, which were positively correlated with the serum levels of TNF-α, IL-1β, and IL-6. The VILI mice displayed intestinal barrier defects, decreased expressions of occludin and zonula occludin-1 (ZO-1), and increased expression of claudin-2 and the activation of myosin light chain (MLC). Importantly, intratracheal administration of Imp7 siRNA nanoparticle effectively inhibited cytokines production and protected mice from VILI-induced gut injury. These data provide evidence of systemic cytokines contributing to gut injury following VILI and highlight the possibility of targeting cytokines inhibition via Imp7 siRNA nanoparticle as a potential therapeutic intervention for alleviating gut injury following VILI.

Mining the key genes for ventilator-induced lung injury using co-expression network analysis

Mechanical ventilation is extensively adopted in general anesthesia and respiratory failure management, but it can also induce ventilator-induced lung injury (VILI). Therefore, it is of great urgency to explore the mechanisms involved in the VILI pathogenesis, which might contribute to its future prevention and treatment. Four microarray datasets from the GEO database were selected in our investigation, and were subjected to the Weighted Gene Co-Expression Network Analysis (WGCNA) to identify the VILI-correlated gene modules. The limma package in R software was used to identify the differentially expressed genes (DEGs) between the VILI and control groups. WGCNA was constructed by merging the GSE9314, GSE9368, GSE11434 and GSE11662 datasets. A total of 49 co-expression network modules were determined as associated with VILI. The intersected genes between hub genes screened from DEGs for VILI and those identified using WGCNA were as follows: Tlr2, Hmox1, Serpine1, Mmp9, Il6, Il1b, Ptgs2, Fos and Atf3, which were determined to be key genes for VILI. Those key genes were validated by GSE86229 and quantitative PCR (qPCR) experiment to have significantly statistical difference in their expression between the VILI and control groups. In a nutshell, nine key genes with expression differences in VILI were screened by WGCNA by integrating multiple datasets.

Roles of phosphatidyl inositol 3 kinase gamma (PI3Kγ) in respiratory diseases

Phosphatidyl inositol 3 kinase gamma (PI3Kγ) is expressed in all the cell types that are involved in airway inflammation and disease, including not only leukocytes, but also structural cells, where it is expressed at very low levels under physiological conditions, while is significantly upregulated after stress. In the airways, PI3Kγ behaves as a trigger or a controller, depending on the pathological context. In this review, the contribution of PI3Kγ in a plethora of respiratory diseases, spanning from acute lung injury, pulmonary fibrosis, asthma, cystic fibrosis and response to both bacterial and viral pathogens, will be commented.

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.

Dexmedetomidine reduces ventilator-induced lung injury (VILI) by inhibiting Toll-like receptor 4 (TLR4)/nuclear factor (NF)-κB signaling pathway

Mechanical ventilation (MV) may lead to ventilator-induced lung injury (VILI). Previous research has shown that dexmedetomidine attenuates pulmonary inflammation caused by MV, but the underlying mechanisms remain unclear. Our study aims to test whether dexmedetomidine has a protective effect against VILI and to explore the possible molecular mechanisms using the rat model. Thirty adult male Wistar rats weighing 200-250 g were randomly assigned to 5 groups (n = 6): control, low tidal volume MV (LMV), high tidal volume (HVT) MV (HMV), HVT MV + dexmedetomidine (DEX), HVT MV + dexmedetomidine + yohimbine (DEX+Y). Rats were euthanized after being ventilated for 4 hours. Pathological changes, lung wet/dry (W/D) weight ratio, lung myeloperoxidase (MPO) activity, levels of inflammatory cytokines (i.e., interleukin [IL]-1β, tumor necrosis factor alpha [TNF-α], and IL-6) in the bronchoalveolar lavage fluid (BALF) and lung tissues, expression of Toll-like receptor 4 (TLR4) and nuclear factor (NF)-κB, and activation of NF-κB in lung tissues were measured. Compared with HMV, DEX group showed fewer pathological changes, lower W/D ratios and decreased MPO activity of the lung tissues and lower concentrations of the inflammatory cytokines in the BALF and lung tissues. Dexmedetomidine significantly inhibited the expression of TLR4 and NF-κB and activation of NF-κB. Yohimbine partly alleviated the effects of dexmedetomidine. Dexmedetomidine reduced the inflammatory response to HVT-MV and had a protective effect against VILI, with the inhibition of the TLR4/NF-κB signaling pathway, at least partly via α2-adrenoceptors.

Protective effects of ghrelin in ventilator-induced lung injury in rats

Ghrelin has exhibited potent anti-inflammatory effects on various inflammatory diseases. The aim of this study was to investigate the potential effects of ghrelin on a model of ventilator-induced lung injury (VILI) established in rats. Male Sprague-Dawley rats were randomly divided into three groups: low volume ventilation (LV, Vt=8ml/kg) group, a VILI group (Vt=30ml/kg), and a VILI group pretreated with ghrelin (GH+VILI). For the LV group, for the VILI and GH+VILI groups, the same parameters were applied except the tidal volume was increased to 40ml/kg. After 4h of MV, blood gas, lung elastance, and levels of inflammatory mediators, including tumor necrosis factor (TNF)-α, interleukin (IL)-6, IL-1β, and (MIP)-2 and total protein in bronchoalveolar lavage fluid (BALF) were analyzed. Myeloperoxidase (MPO), (TLR)-4, and NF-κB, were detected in lung tissues. Water content (wet-to-dry ratio) and lung morphology were also evaluated. The VILI group had a higher acute lung injury (ALI) score, wet weight to dry ratio, MPO activity, and concentrations of inflammatory mediators (TNF-α, IL-6, IL-1β, and MIP-2) in BALF, as well as higher levels of TLR4 and NF-κB expression than the LV group (P<0.05). All histopathologic ALI, the inflammatory profile, and pulmonary dynamics have been improved by ghrelin pretreatment (P<0.05). Ghrelin pretreatment also decreased TLR4 expression and NF-κB activity compared with the VILI group (P<0.05). Ghrelin pretreatment attenuated VILI in rats by reducing MV-induced pulmonary inflammation and might represent a novel therapeutic candidate for protection against VILI.

Selective Role of Vinculin in Contractile Mechanisms of Endothelial Permeability

Increased vascular endothelial cell (EC) permeability is a result of intercellular gap formation that may be induced by contraction-dependent and contraction-independent mechanisms. This study investigated a role of the adaptor protein vinculin in EC permeability induced by contractile (thrombin) and noncontractile (IL-6) agonists. Although thrombin and IL-6 caused a similar permeability increase in human pulmonary ECs and disrupted the association between vinculin and vascular endothelial-cadherin, they induced different patterns of focal adhesion (FA) arrangement. Thrombin, but not IL-6, caused formation of large, vinculin-positive FAs, phosphorylation of FA proteins, FA kinase and Crk-associated substrate, and increased vinculin-talin association. Thrombin-induced formation of talin-positive FA and intercellular gaps were suppressed in ECs with small interfering RNA-induced vinculin knockdown. Vinculin knockdown and inhibitors of Rho kinase and myosin-II motor activity also attenuated thrombin-induced EC permeability. Importantly, ectopic expression of the vinculin mutant lacking the F-actin-binding domain decreased thrombin-induced Rho pathway activation and EC permeability. In contrast, IL-6-induced EC permeability did not involve RhoA- or myosin-dependent mechanisms but engaged Janus kinase/signal transducer and activator of transcription-mediated phosphorylation and internalization of vascular endothelial-cadherin. This process was vinculin independent but Janus kinase/tyrosine kinase Src-dependent. These data suggest that vinculin participates in a contractile-dependent mechanism of permeability by integrating FA with stress fibers, leading to maximal RhoA activation and EC permeability response. Vinculin inhibition does not affect contractile-independent mechanisms of EC barrier failure. This study provides, for the first time, a comparative analysis of two alternative mechanisms of vascular endothelial barrier dysfunction and defines a specific role for vinculin in the contractile type of permeability response.

Context Specific and Differential Gene Co-expression Networks via Bayesian Biclustering

Identifying latent structure in high-dimensional genomic data is essential for exploring biological processes. Here, we consider recovering gene co-expression networks from gene expression data, where each network encodes relationships between genes that are co-regulated by shared biological mechanisms. To do this, we develop a Bayesian statistical model for biclustering to infer subsets of co-regulated genes that covary in all of the samples or in only a subset of the samples. Our biclustering method, BicMix, allows overcomplete representations of the data, computational tractability, and joint modeling of unknown confounders and biological signals. Compared with related biclustering methods, BicMix recovers latent structure with higher precision across diverse simulation scenarios as compared to state-of-the-art biclustering methods. Further, we develop a principled method to recover context specific gene co-expression networks from the estimated sparse biclustering matrices. We apply BicMix to breast cancer gene expression data and to gene expression data from a cardiovascular study cohort, and we recover gene co-expression networks that are differential across ER+ and ER- samples and across male and female samples. We apply BicMix to the Genotype-Tissue Expression (GTEx) pilot data, and we find tissue specific gene networks. We validate these findings by using our tissue specific networks to identify trans-eQTLs specific to one of four primary tissues.

Altered Profile of Circulating Endothelial-Derived Microparticles in Ventilator-Induced Lung Injury

OBJECTIVES

Pulmonary endothelial cell injury is central to the pathophysiology of acute lung injury. Mechanical ventilation can cause endothelial disruption and injury, even in the absence of preexisting inflammation. Platelet-endothelial cell adhesion molecule-1 is a transmembrane protein connecting adjacent endothelial cells. We hypothesized that injurious mechanical ventilation will increase circulating lung endothelial-derived microparticles, defined as microparticles positive for platelet-endothelial cell adhesion molecule-1, which could serve as potential biomarkers and mediators of ventilator-induced lung injury.

DESIGN

Prospective randomized, controlled, animal investigation.

SETTING

A hospital preclinical animal laboratory.

SUBJECTS

Forty-eight Sprague-Dawley rats.

INTERVENTIONS

Animals were randomly allocated to one of the three following ventilatory protocols for 4 hours: spontaneous breathing (control group), mechanical ventilation with low tidal volume (6 mL/kg), and mechanical ventilation with high tidal volume (20 mL/kg). In both mechanical ventilation groups, positive end-expiratory pressure of 2 cm H2O was applied.

MEASUREMENTS AND MAIN RESULTS

We analyzed histologic lung damage, gas exchange, wet-to-dry lung weight ratio, serum cytokines levels, circulating endothelial-derived microparticles, platelet-endothelial cell adhesion molecule-1 lung protein content, and immunohistochemistry. When compared with low-tidal volume mechanical ventilation, high-tidal volume ventilation increased lung edema score and caused gas-exchange deterioration. These changes were associated with a marked increased of circulating endothelial-derived microparticles and a reduction of platelet-endothelial cell adhesion molecule-1 protein levels in the high-tidal volume lungs (p < 0.0001).

CONCLUSIONS

There is an endothelial-derived microparticle profile associated with disease-specific features of ventilator-induced lung injury. This profile could serve both as a biomarker of acute lung injury and, potentially, as a mediator of systemic propagation of pulmonary inflammatory response.

Lung Transcriptomics during Protective Ventilatory Support in Sepsis-Induced Acute Lung Injury

Acute lung injury (ALI) is a severe inflammatory process of the lung. The only proven life-saving support is mechanical ventilation (MV) using low tidal volumes (LVT) plus moderate to high levels of positive end-expiratory pressure (PEEP). However, it is currently unknown how they exert the protective effects. To identify the molecular mechanisms modulated by protective MV, this study reports transcriptomic analyses based on microarray and microRNA sequencing in lung tissues from a clinically relevant animal model of sepsis-induced ALI. Sepsis was induced by cecal ligation and puncture (CLP) in male Sprague-Dawley rats. At 24 hours post-CLP, septic animals were randomized to three ventilatory strategies: spontaneous breathing, LVT (6 ml/kg) plus 10 cmH2O PEEP and high tidal volume (HVT, 20 ml/kg) plus 2 cmH2O PEEP. Healthy, non-septic, non-ventilated animals served as controls. After 4 hours of ventilation, lung samples were obtained for histological examination and gene expression analysis using microarray and microRNA sequencing. Validations were assessed using parallel analyses on existing publicly available genome-wide association study findings and transcriptomic human data. The catalogue of deregulated processes differed among experimental groups. The 'response to microorganisms' was the most prominent biological process in septic, non-ventilated and in HVT animals. Unexpectedly, the 'neuron projection morphogenesis' process was one of the most significantly deregulated in LVT. Further support for the key role of the latter process was obtained by microRNA studies, as four species targeting many of its genes (Mir-27a, Mir-103, Mir-17-5p and Mir-130a) were found deregulated. Additional analyses revealed 'VEGF signaling' as a central underlying response mechanism to all the septic groups (spontaneously breathing or mechanically ventilated). Based on this data, we conclude that a co-deregulation of 'VEGF signaling' along with 'neuron projection morphogenesis', which have been never anticipated in ALI pathogenesis, promotes lung-protective effects of LVT with high levels of PEEP.

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

OBJECTIVE

To investigate the role of Toll-like receptor 2 (TLR2), TLR4, TLR9 and myeloid differentiation factor 88 (MyD88) on alveolar macrophages in ventilator-induced lung injury (VILI).

METHODS

Male, adult pathogen-free Sprague-Dawley rats weighing 300-350 g were used in this study. Animals were tracheotomized and allowed to breathe spontaneously for 4 h or mechanically ventilated for 4 h with low or high tidal volume (7 or 40 mL/kg). TLR2, TLR4, and TLR9, MyD-88 and NF-κΒ of alveolar macrophages' expression under the different ventilation conditions were detected. Pulmonary permeability, lung inflammatory, IL-6 and IL-1β were assessed as well.

RESULTS

Rats subjected to high tidal volume showed significantly greater pulmonary permeability and lung inflammatory than the control rats. Alveolar macrophages from rats subjected to high tidal volume also showed significantly higher protein expression of TLR2 (0.59±0.049 vs. 0.35±0.036 and 0.36±0.031, both P<0.001), TLR4 (0.845±0.0395 vs. 0.401±0.026 and 0.403±0.020, both P<0.001), TLR9 (0.727±0.074 vs. 0.383±0.039 and 0.367±0.043, both P<0.001), MyD-88 (1.01±0.060 vs. 0.485±0.045 and 0.507±0.046, both P<0.001) and NF-κΒ (0.776±0.067 vs. 0.448±0.043 and 0.481±0.047, both P<0.001), as well as significantly higher concentrations of IL-6 (7.32±0.24 vs. 2.42±0.13 and 2.44±0.32, both P<0.001) and IL-1β (139.95±9.37 vs. 53.63±5.26 and 53.55±6.63, both P<0.001) than the control and low tidal volume group.

CONCLUSIONS

The overexpression of TLR2, TLR4, and TLR9 on alveolar macrophages and release of pro-inflammatory cytokines play a role in VILI.

[Ventilation as a trigger for organ dysfunction and sepsis]

Both in the intensive care setting and during surgery, mechanical ventilation plays an important role in the treatment of critically ill patients with lung injury, but also in lung healthy patients. Mechanical ventilation is noncurative and is accompanied by various severe side effects. It is hypothesized that multiorgan failure can be induced by mechanical ventilation. Furthermore, there is evidence to suggest cross-talk between lungs and other organs. In particular, the activation of specific cells and cell programs in peripheral organs is an important step on the way to multiorgan failure. In addition to bidirectional connection between the lung and brain, nonprotective ventilation leads to cell apoptosis in the kidney and intestine and leads to an increase of biomarkers for organ dysfunction. It is believed that both inflammation mediators and pro-apoptotic factors are responsible for organ dysfunction.

Evaluating the effects of protective ventilation on organ-specific cytokine production in porcine experimental postoperative sepsis

Background

Protective ventilation with lower tidal volume (V_T) and higher positive end-expiratory pressure (PEEP) reduces the negative additive effects of mechanical ventilation during systemic inflammatory response syndrome. We hypothesised that protective ventilation during surgery would affect the organ-specific immune response in an experimental animal model of endotoxin-induced sepsis-like syndrome.

Methods

30 pigs were laparotomised for 2 hours (h), after which a continuous endotoxin infusion was started at 0.25 micrograms × kg⁻¹ × h⁻¹ for 5 h. Catheters were placed in the carotid artery, hepatic vein, portal vein and jugular bulb. Animals were randomised to two protective ventilation groups (n = 10 each): one group was ventilated with V_T 6 mL × kg⁻¹ during the whole experiment while the other group was ventilated during the surgical phase with V_T of 10 mL × kg⁻¹. In both groups PEEP was 5 cmH₂O during surgery and increased to 10 cmH₂O at the start of endotoxin infusion. A control group (n = 10) was ventilated with V_T of 10 mL × kg⁻¹ and PEEP 5 cm H₂0 throughout the experiment. In four sample locations we a) simultaneously compared cytokine levels, b) studied the effect of protective ventilation initiated before and during endotoxemia and c) evaluated protective ventilation on organ-specific cytokine levels.

Results

TNF-alpha levels were highest in the hepatic vein, IL-6 levels highest in the artery and jugular bulb and IL-10 levels lowest in the artery. Protective ventilation initiated before and during endotoxemia did not differ in organ-specific cytokine levels. Protective ventilation led to lower levels of TNF-alpha in the hepatic vein compared with the control group, whereas no significant differences were seen in the artery, portal vein or jugular bulb.

Conclusions

Variation between organs in cytokine output was observed during experimental sepsis. We see no implication from cytokine levels for initiating protective ventilation before endotoxemia. However, during endotoxemia protective ventilation attenuates hepatic inflammatory cytokine output contributing to a reduced total inflammatory burden.

Ventilator-induced lung injury. Similarity and differences between children and adults

It is well established that mechanical ventilation can injure the lung, producing an entity known as ventilator-induced lung injury (VILI). There are various forms of VILI, including volutrauma (i.e., injury caused by overdistending the lung), atelectrauma (injury due to repeated opening/closing of lung units), and biotrauma (release of mediators that can induce lung injury or aggravate pre-existing injury, potentially leading to multiple organ failure). Experimental data in the pediatric context are in accord with the importance of VILI, and appear to show age-related susceptibility to VILI, although a conclusive link between use of large Vts and mortality has not been demonstrated in this population. The relevance of VILI in the pediatric intensive care unit population is thus unclear. Given the physiological and biological differences in the respiratory systems of infants, children, and adults, it is difficult to directly extrapolate clinical practice from adults to children. This Critical Care Perspective analyzes the relevance of VILI to the pediatric population, and addresses why pediatric patients might be less susceptible than adults to VILI.

The receptor for advanced glycation end products in ventilator-induced lung injury

Background

Mechanical ventilation (MV) can cause ventilator-induced lung injury (VILI). The innate immune response mediates this iatrogenic inflammatory condition. The receptor for advanced glycation end products (RAGE) is a multiligand receptor that can amplify immune and inflammatory responses. We hypothesized that RAGE signaling contributes to the pro-inflammatory state induced by MV.

Methods

RAGE expression was analyzed in lung brush and lavage cells obtained from ventilated patients and lung tissue of ventilated mice. Healthy wild-type (WT) and RAGE knockout (KO) mice were ventilated with relatively low (approximately 7.5 ml/kg) or high (approximately 15 ml/kg) tidal volume. Positive end-expiratory pressure was set at 2 cm H₂O during both MV strategies. Also, WT and RAGE KO mice with lipopolysaccharide (LPS)-induced lung injury were ventilated with the above described ventilation strategies. In separate experiments, the contribution of soluble RAGE, a RAGE isoform that may function as a decoy receptor, in ventilated RAGE KO mice was investigated. Lung wet-to-dry ratio, cell and neutrophil influx, cytokine and chemokine concentrations, total protein levels, soluble RAGE, and high-mobility group box 1 (HMGB1) presence in lung lavage fluid were analyzed.

Results

MV was associated with increased RAGE mRNA levels in both human lung brush samples and lung tissue of healthy mice. In healthy high tidal volume-ventilated mice, RAGE deficiency limited inflammatory cell influx. Other VILI parameters were not affected. In our second set of experiments where we compared RAGE KO and WT mice in a 2-hit model, we observed higher pulmonary cytokine and chemokine levels in RAGE KO mice undergoing LPS/high tidal volume MV as compared to WT mice. Third, in WT mice undergoing the LPS/high tidal volume MV, we observed HMGB1 presence in lung lavage fluid. Moreover, MV increased levels of soluble RAGE in lung lavage fluid, with the highest levels found in LPS/high tidal volume-ventilated mice. Administration of soluble RAGE to LPS/high tidal volume-ventilated RAGE KO mice attenuated the production of inflammatory mediators.

Conclusions

RAGE was not a crucial contributor to the pro-inflammatory state induced by MV. However, the presence of sRAGE limited the production of pro-inflammatory mediators in our 2-hit model of LPS and high tidal volume MV.

Electronic supplementary material

The online version of this article (doi:10.1186/s40635-014-0022-1) contains supplementary material, which is available to authorized users.

Soluble platelet-endothelial cell adhesion molecule-1, a biomarker of ventilator-induced lung injury

Introduction

Endothelial cell injury is an important component of acute lung injury. Platelet-endothelial cell adhesion molecule-1 (PECAM1) is a transmembrane protein that connects endothelial cells to one another and can be detected as a soluble, truncated protein (sPECAM1) in serum. We hypothesized that injurious mechanical ventilation (MV) leads to shedding of PECAM1 from lung endothelial cells resulting in increasing sPECAM1 levels in the systemic circulation.

Methods

We studied 36 Sprague–Dawley rats in two prospective, randomized, controlled studies (healthy and septic) using established animal models of ventilator-induced lung injury. Animals (n = 6 in each group) were randomized to spontaneous breathing or two MV strategies: low tidal volume (V_T) (6 ml/kg) and high-V_T (20 ml/kg) on 2 cmH₂O of positive end-expiratory pressure (PEEP). In low-V_T septic animals, 10 cmH₂O of PEEP was applied. We performed pulmonary histological and physiological evaluation and measured lung PECAM1 protein content and serum sPECAM1 levels after four hours ventilation period.

Results

High-V_T MV caused severe lung injury in healthy and septic animals, and decreased lung PECAM1 protein content (P < 0.001). Animals on high-V_T had a four- to six-fold increase of mean sPECAM1 serum levels than the unventilated counterpart (35.4 ± 10.4 versus 5.6 ± 1.7 ng/ml in healthy rats; 156.8 ± 47.6 versus 35.6 ± 12.6 ng/ml in septic rats) (P < 0.0001). Low-V_T MV prevented these changes. Levels of sPECAM1 in healthy animals on high-V_T MV paralleled the sPECAM1 levels of non-ventilated septic animals.

Conclusions

Our findings suggest that circulating sPECAM1 may represent a promising biomarker for the detection and monitoring of ventilator-induced lung injury.

IL-1β processing in mechanical ventilation-induced inflammation is dependent on neutrophil factors rather than caspase-1

PURPOSE

Mechanical ventilation can cause ventilator-induced lung injury, characterized by a sterile inflammatory response in the lungs resulting in tissue damage and respiratory failure. The cytokine interleukin-1β (IL-1β) is thought to play an important role in the pathogenesis of ventilator-induced lung injury. Cleavage of the inactive precursor pro-IL-1β to form bioactive IL-1β is mediated by several types of proteases, of which caspase-1, activated within the inflammasome, is the most important. Herein, we studied the roles of IL-1β, caspase-1 and neutrophil factors in the mechanical ventilation-induced inflammatory response in mice.

METHODS

Untreated wild-type mice, IL-1αβ knockout and caspase-1 knockout mice, pralnacasan (a selective caspase-1 inhibitor)-treated mice, anti-keratinocyte-derived chemokine (KC)-treated mice and cyclophosphamide-treated neutrophil-depleted wild-type mice were ventilated using clinically relevant ventilator settings (tidal volume 8 ml/kg). The lungs and plasma were collected to determine blood gas values, cytokine profiles and neutrophil influx.

RESULTS

Mechanical ventilation resulted in increased pulmonary concentrations of IL-1β and KC and increased pulmonary neutrophil influx compared with non-ventilated mice. Ventilated IL-1αβ knockout mice did not demonstrate this increase in cytokines. No significant differences were observed between wild-type and caspase-1-deficient or pralnacasan-treated mice. In contrast, in anti-KC antibody-treated mice and neutropenic mice, inflammatory parameters decreased in comparison with ventilated non-treated mice.

CONCLUSIONS

Our results illustrate that IL-1 is indeed an important cytokine in the inflammatory cascade induced by mechanical ventilation. However, the inflammasome/caspase-1 appears not to be involved in IL-1β processing in this type of inflammatory response. The attenuated inflammatory response observed in ventilated anti-KC-treated and neutropenic mice suggests that IL-1β processing in mechanical ventilation-induced inflammation is mainly mediated by neutrophil factors.

Dexmedetomidine regulates inflammatory molecules contributing to ventilator-induced lung injury in dogs

BACKGROUND

Dexmedetomidine reduced mortality and inhibited the inflammatory response during endotoxemia in rats. The aim of this study was to clarify the effect of dexmedetomidine-regulating inflammation on a noninfectious, ventilator-induced lung injury (VILI) in dogs.

METHODS

Thirty healthy Beagles weighing between 8 and 12 kg were randomly divided into five groups: control group (group C, n = 6), mechanical ventilation (group MV, n = 6), and three different doses of dexmedetomidine group (group DEX1-3, n = 6). VILI was induced by high-tidal volume ventilation (tidal volume 20 mL/kg; respiratory rate 15 breaths/min; FiO2 0.5). Group DEX received intravenous Dex 20 min before endotracheal intubation (0.5, 1.0, and 2.0 μg/kg Dex was infused within 20 min and then a maintenance dose of 0.5, 1.0, and 2.0 μg/kg/h Dex was infused intravenously). Arterial blood samples were obtained from femoral artery at base state, MV1h, MV2h, and MV4h for blood gas analysis. After being mechanically ventilated for 4 h, dogs were killed and the levels of pulmonary inflammatory response and polymorphonuclear neutrophils (PMNs) count in bronchoalveolar lavage fluid were evaluated.

RESULTS

Histologic findings of the MV, DEX1, DEX2, and DEX3 groups revealed severe, moderate, mild, and normal to minimal inflammation, respectively. Myeloperoxidase level, PMNs/alveoli ratio, nuclear factor-κB messenger RNA (mRNA), tumor necrosis factor-alpha mRNA, and inducible nitric oxide synthase mRNA expression in lung tissues of the DEX2 and DEX3 were significantly lower than those of the MV group. Partial pressures of oxygen was decreased significantly at MV4h as compared with the baseline. There was no statistical significance in partial pressures of oxygen between MV and DEX2 group as well as between group MV and group DEX3.

CONCLUSIONS

Dexmedetomidine could mitigate pulmonary inflammatory response induced by VILI in dogs.

Aggravation of myocardial dysfunction by injurious mechanical ventilation in LPS-induced pneumonia in rats

BACKGROUND

Mechanical ventilation (MV) may cause ventilator-induced lung injury (VILI) and may thereby contribute to fatal multiple organ failure. We tested the hypothesis that injurious MV of lipopolysaccharide (LPS) pre-injured lungs induces myocardial inflammation and further dysfunction ex vivo, through calcium (Ca2+)-dependent mechanism.

MATERIALS AND METHODS

N = 35 male anesthetized and paralyzed male Wistar rats were randomized to intratracheal instillation of 2 mg/kg LPS or nothing and subsequent MV with lung-protective settings (low tidal volume (Vt) of 6 mL/kg and 5 cmH2O positive end-expiratory pressure (PEEP)) or injurious ventilation (high Vt of 19 mL/kg and 1 cmH2O PEEP) for 4 hours. Myocardial function ex vivo was evaluated in a Langendorff setup and Ca2+ exposure. Key mediators were determined in lung and heart at the mRNA level.

RESULTS

Instillation of LPS and high Vt MV impaired gas exchange and, particularly when combined, increased pulmonary wet/dry ratio; heat shock protein (HSP)70 mRNA expression also increased by the interaction between LPS and high Vt MV. For the heart, C-X-C motif ligand (CXCL)1 and Toll-like receptor (TLR)2 mRNA expression increased, and ventricular (LV) systolic pressure, LV developed pressure, LV +dP/dtmax and contractile responses to increasing Ca2+ exposure ex vivo decreased by LPS. High Vt ventilation aggravated the effects of LPS on myocardial inflammation and dysfunction but not on Ca2+ responses.

CONCLUSIONS

Injurious MV by high Vt aggravates the effects of intratracheal instillation of LPS on myocardial dysfunction, possibly through enhancing myocardial inflammation via pulmonary release of HSP70 stimulating cardiac TLR2, not involving Ca2+ handling and sensitivity.

High levels of S100A8/A9 proteins aggravate ventilator-induced lung injury via TLR4 signaling

Background

Bacterial products add to mechanical ventilation in enhancing lung injury. The role of endogenous triggers of innate immunity herein is less well understood. S100A8/A9 proteins are released by phagocytes during inflammation. The present study investigates the role of S100A8/A9 proteins in ventilator-induced lung injury.

Methods

Pulmonary S100A8/A9 levels were measured in samples obtained from patients with and without lung injury. Furthermore, wild-type and S100A9 knock-out mice, naive and with lipopolysaccharide-induced injured lungs, were randomized to 5 hours of spontaneously breathing or mechanical ventilation with low or high tidal volume (V_T). In addition, healthy spontaneously breathing and high V_T ventilated mice received S100A8/A9, S100A8 or vehicle intratracheal. Furthermore, the role of Toll-like receptor 4 herein was investigated.

Results

S100A8/A9 protein levels were elevated in patients and mice with lung injury. S100A8/A9 levels synergistically increased upon the lipopolysaccharide/high V_T MV double hit. Markers of alveolar barrier dysfunction, cytokine and chemokine levels, and histology scores were attenuated in S100A9 knockout mice undergoing the double-hit. Exogenous S100A8/A9 and S100A8 induced neutrophil influx in spontaneously breathing mice. In ventilated mice, these proteins clearly amplified inflammation: neutrophil influx, cytokine, and chemokine levels were increased compared to ventilated vehicle-treated mice. In contrast, administration of S100A8/A9 to ventilated Toll-like receptor 4 mutant mice did not augment inflammation.

Conclusion

S100A8/A9 proteins increase during lung injury and contribute to inflammation induced by HV_T MV combined with lipopolysaccharide. In the absence of lipopolysaccharide, high levels of extracellular S100A8/A9 still amplify ventilator-induced lung injury via Toll-like receptor 4.

Inhaled aerosolized insulin ameliorates hyperglycemia-induced inflammatory responses in the lungs in an experimental model of acute lung injury

Introduction

Previous studies have shown that patients with diabetes mellitus appear to have a lower prevalence of acute lung injury. We assumed that insulin prescribed to patients with diabetes has an anti-inflammatory property and pulmonary administration of insulin might exert beneficial effects much more than intravenous administration.

Methods

Twenty-eight mechanically ventilated rabbits underwent lung injury by saline lavage, and then the animals were allocated into a normoglycemia group (NG), a hyperglycemia group (HG), an HG treated with intravenous insulin (HG-VI) group or an HG treated with aerosolized insulin (HG-AI) group with continuous infusion of different fluid solutions and treatments: normal saline, 50% glucose, 50% glucose with intravenous insulin, or 50% glucose with inhaled aerosolized insulin, respectively. After four hours of treatment, the lungs and heart were excised en bloc, and then high-mobility group B1 concentration in bronchoalveolar lavage fluid, interleukin-8 and toll-like receptor 4 mRNA expression in bronchoalveolar lavage fluid cells, and lung myeloperoxidase activity were measured.

Results

Treatment with both aerosolized insulin and intravenous insulin attenuated toll-like receptor 4 mRNA expressions in the bronchoalveolar lavage fluid cells. Interleukin-8 and toll-like receptor 4 mRNA expression was significantly lower in the HG-AI group than in the HG-IV group. The lung myeloperoxidase activity in the normal healthy group showed significantly lower levels compared to the NG group but not different compared to those of the HG, HG-VI and HG-AI groups.

Conclusions

The results suggest that insulin attenuates inflammatory responses in the lungs augmented by hyperglycemia in acute lung injury and the insulin's efficacy may be better when administered by aerosol.

Novel approaches to minimize ventilator-induced lung injury

Despite over 40 years of research, there is no specific lung-directed therapy for the acute respiratory distress syndrome (ARDS). Although much has evolved in our understanding of its pathogenesis and factors affecting patient outcome, supportive care with mechanical ventilation remains the cornerstone of treatment. Perhaps the most important advance in ARDS research has been the recognition that mechanical ventilation, although necessary to preserve life, can itself aggravate or cause lung damage through a variety of mechanisms collectively referred to as ventilator-induced lung injury (VILI). This improved understanding of ARDS and VILI has been important in designing lung-protective ventilatory strategies aimed at attenuating VILI and improving outcomes. Considerable effort has been made to enhance our mechanistic understanding of VILI and to develop new ventilatory strategies and therapeutic interventions to prevent and ameliorate VILI with the goal of improving outcomes in patients with ARDS. In this review, we will review the pathophysiology of VILI, discuss a number of novel physiological approaches for minimizing VILI, therapies to counteract biotrauma, and highlight a number of experimental studies to support these concepts.

Innate Immune Responses in Ventilator-Associated Pneumonia

Ventilator-associated pneumonia (VAP) is a common complication of mechanical ventilation, resulting in substantial morbidity, mortality, and health care cost. Early upper airway colonization by pathogenic bacteria and microaspiration are the primary pathogenic events leading to VAP. Patients at risk for VAP have defects in structural/mechanical defenses of the respiratory tract. In addition, critical illness, including sepsis, trauma, and postoperative states, is associated with profound defects in both innate and acquired antibacterial immunity, influencing antimicrobial effector functions of both leukocytes and structural/parenchymal cells. Factors present within the lung microenvironment, including alveolar stretch, cyclical atelectasis, changes in oxygen tension, and respiratory tract microbiota, substantially impact antibacterial host responses. Mechanisms accounting for dysregulated immune homeostasis are incompletely understood, but likely involve: (1) alterations in the balance of pro- and anti-inflammatory cytokines; (2) changes in pathogen recognition receptor and G-protein coupled receptor expression and downstream signaling cascades; and (3) dysregulated cell death responses. Antibiotics and preventive strategies are the mainstay of therapy in patients with VAP. However, novel approaches are needed to reverse immunological reprogramming that occurs during critical illness and/or mechanical ventilation, and to identify patients who are most likely to benefit from immunomodulatory therapy.

[Lung-brain interaction in the mechanically ventilated patient]

Patients with acute lung injury or acute respiratory distress syndrome (ARDS) admitted to the ICU present neuropsychological alterations, which in most cases extend beyond the acute phase and have an important adverse effect upon quality of life. The aim of this review is to deepen in the analysis of the complex interaction between lung and brain in critically ill patients subjected to mechanical ventilation. This update first describes the neuropsychological alterations occurring both during the acute phase of ICU stay and at discharge, followed by an analysis of lung-brain interactions during mechanical ventilation, and finally explores the etiology and mechanisms leading to the neurological disorders observed in these patients. The management of critical patients requires an integral approach focused on minimizing the deleterious effects over the short, middle or long term.

[Lung-brain interaction in the mechanically ventilated patient]

Patients with acute lung injury or acute respiratory distress syndrome (ARDS) admitted to the ICU present neuropsychological alterations, which in most cases extend beyond the acute phase and have an important adverse effect upon quality of life. The aim of this review is to deepen in the analysis of the complex interaction between lung and brain in critically ill patients subjected to mechanical ventilation. This update first describes the neuropsychological alterations occurring both during the acute phase of ICU stay and at discharge, followed by an analysis of lung-brain interactions during mechanical ventilation, and finally explores the etiology and mechanisms leading to the neurological disorders observed in these patients. The management of critical patients requires an integral approach focused on minimizing the deleterious effects over the short, middle or long term.

Pre-treatment with allopurinol or uricase attenuates barrier dysfunction but not inflammation during murine ventilator-induced lung injury

Introduction

Uric acid released from injured tissue is considered a major endogenous danger signal and local instillation of uric acid crystals induces acute lung inflammation via activation of the NLRP3 inflammasome. Ventilator-induced lung injury (VILI) is mediated by the NLRP3 inflammasome and increased uric acid levels in lung lavage fluid are reported. We studied levels in human lung injury and the contribution of uric acid in experimental VILI.

Methods

Uric acid levels in lung lavage fluid of patients with acute lung injury (ALI) were determined. In a different cohort of cardiac surgery patients, uric acid levels were correlated with pulmonary leakage index. In a mouse model of VILI the effect of allopurinol (inhibits uric acid synthesis) and uricase (degrades uric acid) pre-treatment on neutrophil influx, up-regulation of adhesion molecules, pulmonary and systemic cytokine levels, lung pathology, and regulation of receptors involved in the recognition of uric acid was studied. In addition, total protein and immunoglobulin M in lung lavage fluid and pulmonary wet/dry ratios were measured as markers of alveolar barrier dysfunction.

Results

Uric acid levels increased in ALI patients. In cardiac surgery patients, elevated levels correlated significantly with the pulmonary leakage index. Allopurinol or uricase treatment did not reduce ventilator-induced inflammation, IκB-α degradation, or up-regulation of NLRP3, Toll-like receptor 2, and Toll-like receptor 4 gene expression in mice. Alveolar barrier dysfunction was attenuated which was most pronounced in mice pre-treated with allopurinol: both treatment strategies reduced wet/dry ratio, allopurinol also lowered total protein and immunoglobulin M levels.

Conclusions

Local uric acid levels increase in patients with ALI. In mice, allopurinol and uricase attenuate ventilator-induced alveolar barrier dysfunction.

Anti-inflammatory activity of a novel family of aryl ureas compounds in an endotoxin-induced airway epithelial cell injury model

Background

Despite our increased understanding of the mechanisms involved in acute lung injury (ALI) and the acute respiratory distress syndrome (ARDS), there is no specific pharmacological treatment of proven benefit. We used a novel screening methodology to examine potential anti-inflammatory effects of a small structure-focused library of synthetic carbamate and urea derivatives in a well established cell model of lipopolysaccharide (LPS)-induced ALI/ARDS.

Methodology/Principal Findings

After a pilot study to develop an in vitro LPS-induced airway epithelial cell injury model, a library of synthetic carbamate and urea derivates was screened against representative panels of human solid tumor cell lines and bacterial and fungal strains. Molecules that were non-cytotoxic and were inactive in terms of antiproliferative and antimicrobial activities were selected to study the effects on LPS-induced inflammatory response in an in vitro cell culture model using A549 human alveolar and BEAS-2B human bronchial cells. These cells were exposed for 18 h to LPS obtained from Escherichia coli, either alone or in combination with the test compounds. The LPS antagonists rhein and emodin were used as reference compounds. The most active compound (CKT0103) was selected as the lead compound and the impact of CKT0103 on pro-inflammatory IL-6 and IL-8 cytokine levels, expression of toll-like receptor-4 (TLR4) and nuclear factor kappa B inhibitor alpha (IκBα) was measured. CKT0103 significantly inhibited the synthesis and release of IL-6 and IL-8 induced by LPS. This suppression was associated with inhibition of TLR4 up-regulation and IκBα down-regulation. Immunocytochemical staining for TLR4 and IκBα supported these findings.

Conclusions/Significance

Using a novel screening methodology, we identified a compound – CKT0103 – with potent anti-inflammatory effects. These findings suggest that CKT0103 is a potential target for the treatment of the acute phase of sepsis and sepsis-induced ALI/ARDS.

TLR signaling prevents hyperoxia-induced lung injury by protecting the alveolar epithelium from oxidant-mediated death

Mechanical ventilation using high oxygen tensions is often necessary to treat patients with respiratory failure. Recently, TLRs were identified as regulators of noninfectious oxidative lung injury. IRAK-M is an inhibitor of MyD88-dependent TLR signaling. Exposure of mice deficient in IRAK-M (IRAK-M(-/-)) to 95% oxygen resulted in reduced mortality compared with wild-type mice and occurred in association with decreased alveolar permeability and cell death. Using a bone marrow chimera model, we determined that IRAK-M's effects were mediated by structural cells rather than bone marrow-derived cells. We confirmed the expression of IRAK-M in alveolar epithelial cells (AECs) and showed that hyperoxia can induce the expression of this protein. In addition, IRAK-M(-/-) AECs exposed to hyperoxia experienced a decrease in cell death. IRAK-M may potentiate hyperoxic injury by suppression of key antioxidant pathways, because lungs and AECs isolated from IRAK-M(-/-) mice have increased expression/activity of heme oxygenase-1, a phase II antioxidant, and NF (erythroid-derived)-related factor-2, a transcription factor that initiates antioxidant generation. Treatment of IRAK-M(-/-) mice in vivo and IRAK-M(-/-) AECs in vitro with the heme oxygenase-1 inhibitor, tin protoporphyrin, substantially decreased survival and significantly reduced the number of live cells after hyperoxia exposure. Collectively, our data suggest that IRAK-M inhibits the induction of antioxidants essential for protecting the lungs against cell death, resulting in enhanced susceptibility to hyperoxic lung injury.

Organ crosstalk during acute lung injury, acute respiratory distress syndrome, and mechanical ventilation

PURPOSE OF REVIEW

Multiple organ failure is the main cause of morbidity and mortality in acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) patients. Moreover, survivors of both ALI and ARDS often show significant neurocognitive decline at discharge. These data suggest a deleterious organ crosstalk between lungs and distal organs. This article reviews the recent literature concerning the role of this organ crosstalk during ALI, ARDS, and mechanical ventilation, especially focusing on brain-lung communication.

RECENT FINDINGS

Numerous pulmonary and extrapulmonary disorders could predispose critically ill patients to ALI and ARDS. Mechanical ventilation, although a lifesaving intervention, could contribute by modulating the mechanisms involved in the pathophysiology of lung damage and their impact on remote organs. Emerging clinical and experimental evidence supports the hypothesis of a multidirectional organ crosstalk between lungs and distal organs.

SUMMARY

Organ crosstalk is an emerging area of research in lung disease in critically ill patients. The findings of these studies are clinically relevant and show the importance of an integrative approach in the management of critical patients. However, further studies are necessary to understand the complex interactions concurring in these pathologies.

Stimulation of Rho signaling by pathologic mechanical stretch is a "second hit" to Rho-independent lung injury induced by IL-6

Most patients with acute lung injury (ALI) and acute respiratory distress syndrome of septic and nonseptic nature require assisted ventilation with positive pressure, which at suboptimal range may further exacerbate lung dysfunction. Previous studies described enhancement of agonist-induced Rho GTPase signaling and endothelial cell (EC) permeability in EC cultures exposed to pathologically relevant cyclic stretch (CS) magnitudes. This study examined a role of pathologic CS in modulation of pulmonary EC permeability caused by IL-6, a cytokine increased in sepsis and acting in a Rho-independent manner. IL-6 increased EC permeability, which was associated with activation of Jak/signal transducers and activators of transcription, p38 MAP kinase, and NF-κB signaling and was augmented by EC exposure to 18% CS. Rho kinase inhibitor Y-27632 suppressed the synergistic effect of 18% CS on IL-6-induced EC monolayer disruption but did not alter the IL-6 effects on static EC culture. 18% CS also increased IL-6-induced ICAM-1 expression by pulmonary EC and neutrophil adhesion, which was attenuated by Y-27632. Intratracheal IL-6 administration in C57BL/6J mice increased protein content and cell count in bronchoalveolar lavage fluid. These changes were augmented by high tidal volume mechanical ventilation (HTV; 30 ml/kg, 4 h). Intravenous injection of Y-27632 suppressed IL6/HTV-induced lung injury. In conclusion, this study proposes a novel mechanism contributing to two-hit model of ALI: in addition to synergistic effects on Rho-dependent endothelial hyper-permeability triggered by thrombin, TNFα, LPS, or other agonists, ventilator-induced lung injury-relevant CS may also exacerbate Rho-independent mechanisms of EC permeability induced by other inflammatory mediators such as IL-6 via mechanisms involving Rho activity.

Bench-to-bedside review: Damage-associated molecular patterns in the onset of ventilator-induced lung injury

Mechanical ventilation (MV) has the potential to worsen pre-existing lung injury or even to initiate lung injury. Moreover, it is thought that injurious MV contributes to the overwhelming inflammatory response seen in patients with acute lung injury or acute respiratory distress syndrome. Ventilator-induced lung injury (VILI) is characterized by increased endothelial and epithelial permeability and pulmonary inflammation, in which the innate immune system plays a key role. A growing body of evidence indicates that endogenous danger molecules, also termed damage-associated molecular patterns (DAMPs), are released upon tissue injury and modulate the inflammatory response. DAMPs activate pattern recognition receptors, may induce the release of proinflammatory cytokines and chemokines, and have been shown to initiate or propagate inflammation in non-infectious conditions. Experimental and clinical studies demonstrate the presence of DAMPs in bronchoalveolar lavage fluid in patients with VILI and the upregulation of pattern recognition receptors in lung tissue by MV. The objective of the present article is to review research in the area of DAMPs, their recognition by the innate immune system, their role in VILI, and the potential utility of blocking DAMP signaling pathways to reduce VILI in the critically ill.

Activation of the Wnt/β-catenin signaling pathway by mechanical ventilation is associated with ventilator-induced pulmonary fibrosis in healthy lungs

BACKGROUND

Mechanical ventilation (MV) with high tidal volumes (V(T)) can cause or aggravate lung damage, so-called ventilator induced lung injury (VILI). The relationship between specific mechanical events in the lung and the cellular responses that result in VILI remains incomplete. Since activation of Wnt/β-catenin signaling has been suggested to be central to mechanisms of lung healing and fibrosis, we hypothesized that the Wnt/β-catenin signaling plays a role during VILI.

METHODOLOGY/PRINCIPAL FINDINGS

Prospective, randomized, controlled animal study using adult, healthy, male Sprague-Dawley rats. Animals (n = 6/group) were randomized to spontaneous breathing or two strategies of MV for 4 hours: low tidal volume (V(T)) (6 mL/kg) or high V(T) (20 mL/kg). Histological evaluation of lung tissue, measurements of WNT5A, total β-catenin, non-phospho (Ser33/37/Thr41) β-catenin, matrix metalloproteinase-7 (MMP-7), cyclin D1, vascular endothelial growth factor (VEGF), and axis inhibition protein 2 (AXIN2) protein levels by Western blot, and WNT5A, non-phospho (Ser33/37/Thr41) β-catenin, MMP-7, and AXIN2 immunohistochemical localization in the lungs were analyzed. High-V(T) MV caused lung inflammation and perivascular edema with cellular infiltrates and collagen deposition. Protein levels of WNT5A, non-phospho (Ser33/37/Thr41) β-catenin, MMP-7, cyclin D1, VEGF, and AXIN2 in the lungs were increased in all ventilated animals although high-V(T) MV was associated with significantly higher levels of WNT5A, non-phospho (Ser33/37/Thr41) β-catenin, MMP-7, cyclin D1, VEGF, and AXIN2 levels.

CONCLUSIONS/SIGNIFICANCE

Our findings demonstrate that the Wnt/β-catenin signaling pathway is modulated very early by MV in lungs without preexistent lung disease, suggesting that activation of this pathway could play an important role in both VILI and lung repair. Modulation of this pathway might represent a therapeutic option for prevention and/or management of VILI.

WNT/β-catenin signaling is modulated by mechanical ventilation in an experimental model of acute lung injury

PURPOSE

The mechanisms involved in lung injury progression during acute lung injury (ALI) are still poorly understood. Because WNT/β-catenin signaling has been shown to be involved in epithelial cell injury and hyperplasia during inflammation and sepsis, we hypothesized that it would be modulated by mechanical ventilation (MV) in an experimental model of sepsis-induced ALI.

METHODS

This study was a prospective, randomized, controlled animal study performed using adult male Sprague-Dawley rats. Sepsis was induced by cecal ligation and perforation. At 18 h, surviving animals were randomized to spontaneous breathing or two strategies of MV for 4 h: low tidal volume (V (T)) (6 ml/kg) plus 10 cmH2O of positive end-expiratory pressure (PEEP) versus high (20 ml/kg) tidal volume (V (T)) with zero PEEP. Histological evaluation, measurements of WNT5A, total β-catenin, and matrix metalloproteinase-7 (MMP7) protein levels by Western blot, and their immunohistochemical localization in the lungs were analyzed.

RESULTS

Sepsis and high-V (T) MV caused lung inflammation and perivascular edema with cellular infiltrates and collagen deposition. Protein levels of WNT5A, β-catenin, and MMP7 in the lungs were increased in animals with sepsis-induced ALI. High-V (T) MV was associated with higher levels of WNT5A, β-catenin, and MMP7 protein levels (p < 0.001), compared to healthy control animals. By contrast, low-V (T) MV markedly reduced WNT5A, β-catenin, and MMP7 protein levels (p < 0.001).

CONCLUSIONS

Our findings demonstrate that the WNT/β-catenin signaling pathway is modulated early during sepsis and ventilator-induced lung injury, suggesting that activation of this pathway could play an important role in both lung injury progression and repair.

A toll-like receptor-4-interacting surfactant protein-A-derived peptide suppresses tumor necrosis factor-α release from mouse JAWS II dendritic cells

Surfactant protein-A (SP-A) and Toll-like receptor-4 (TLR4) proteins are recognized as pathogen-recognition receptors. An exaggerated activation of TLR4 induces inflammatory response, whereas SP-A protein down-regulates inflammation. We hypothesized that SP-A-TLR4 interaction may lead to inhibition of inflammation. In this study, we investigated interaction between native baboon lung SP-A and baboon and human TLR4-MD2 proteins by coimmunoprecipitation/immunoblotting and microwell-based methods. The interaction between SP-A and TLR4-MD2 proteins was then analyzed using a bioinformatics approach. In the in silico model of SP-A-TLR4-MD2 complex, we identified potential binding regions and amino acids at the interface of SP-A-TLR4. Using this information, we synthesized a library of human SP-A-derived peptides that contained interacting amino acids. Next, we tested whether the TLR4-interacting SP-A peptides would suppress inflammatory cytokines. The peptides were screened for any changes in the tumor necrosis factor-α (TNF-α) response against lipopolysaccharide (LPS) stimuli in the mouse JAWS II dendritic cell line. Different approaches used in this study suggested binding between SP-A and TLR4-MD2 proteins. In cells pretreated with peptides, three of seven peptides increased TNF-α production against LPS. However, two of these peptides (SPA4: GDFRYSDGTPVNYTNWYRGE and SPA5: YVGLTEGPSPGDFRYSDFTP) decreased the TNF-α production in LPS-challenged JAWS II dendritic cells; SPA4 peptide showed more pronounced inhibitory effect than SPA5 peptide. In conclusion, we identify a human SP-A-derived peptide (SPA4 peptide) that interacts with TLR4-MD2 protein and inhibits the LPS-stimulated release of TNF-α in JAWS II dendritic cells.

Mechanical ventilation modulates Toll-like receptor-3-induced lung inflammation via a MyD88-dependent, TLR4-independent pathway: a controlled animal study

BACKGROUND

Mechanical ventilation augments lung inflammation resulting from exposure to microbial products. The objective of this study was to test the hypothesis that ventilator-associated immune modulation requires MyD88-dependent signaling. Because MyD88 is a critical adapter protein utilized for pro-inflammatory signaling by all Toll-like receptors (TLRs), with the exception of TLR3, as well as by the IL-1 and IL-18 receptors, MyD88 dependence would implicate generation of an endogenous soluble ligand recognized by one or more of these receptors during mechanical ventilation and would provide an opportunity for a potential future therapeutic intervention.

METHODS

We compared the effect of mechanical ventilation on lung inflammation and permeability between poly(I:C) exposed mice with or without expression of MyD88. Poly(I:C) is a synthetic ligand for TLR3, the only MyD88-independent TLR, allowing isolation of the effect of MyD88 deletion on ventilator-augmentation of lung inflammation. Lung inflammation was assessed by cytokine concentration in lung tissue homogenate and polymorphonuclear cell (PMN) number in bronchoalveolar lavage fluid (BALF). Lung permeability was assessed by total protein, IgM, and intravenously injected FITC-dextran concentrations in BALF.

RESULTS

We found that MyD88 was required for mechanical ventilation augmentation of TLR3-induced lung inflammation and permeability. Because TLR4 is the most commonly reported receptor for endogenous ligands generated during tissue injury, we performed a second experiment comparing wildtype and TLR4-/- mice. We found that mechanical ventilation increased TLR3-mediated inflammation and permeability independent of TLR4.

CONCLUSION

These data support the hypothesis that mechanical ventilation with moderate tidal volumes generates an endogenous ligand(s) recognized by MyD88-dependent receptor(s) other than TLR4, and that this mechanism can contribute to the development of ventilator-associated lung inflammation and injury. Identification of these ligands and/or receptors could lead to new pharmacological treatments for ARDS.