PULMONARY LEVELS OF HIGH-MOBILITY GROUP BOX 1 DURING MECHANICAL VENTILATION AND VENTILATOR-ASSOCIATED PNEUMONIA

Regulated cell death and DAMPs as biomarkers and therapeutic targets in normothermic perfusion of transplant organs. Part 2: implementation strategies

This Part 2 of a bipartite review commences with the delineation of a conceptual model outlining the fundamental role of injury-induced regulated cell death (RCD) in the release of DAMPs that drive innate immune responses involved in early inflammation-related allograft dysfunction and alloimmune-mediated allograft rejection. In relation to this topic, the focus is on the divergent role of donor and recipient dendritic cells (DCs), which become immunogenic in the presence of DAMPs to regulate alloimmunity, but in the absence of DAMPs acquire tolerogenic properties to promote allotolerance. With respect to this scenario, proposals are then made for leveraging RCD and DAMPs as biomarkers during normothermic regional perfusion (NRP) and normothermic machine perfusion (NMP) of transplant organs from DCD donors, a strategy poised to significantly enhance current policies for assessing donor organ quality. The focus is then on the ambitious goal to target RCD and DAMPs therapeutically during NRP and NMP, aiming to profoundly suppress subsequently early allograft inflammation and alloimmunity in the recipient. This strategic approach seeks to prevent the activation of intragraft innate immune cells including DCs during donor organ reperfusion in the recipient, which is driven by ischemia/reperfusion injury-induced DAMPs. In this context, available inhibitors of various types of RCD, as well as scavengers and inhibitors of DAMPs are highlighted for their promising therapeutic potential in NRP and NMP settings, building on their proven efficacy in other experimental disease models. If successful, this kind of therapeutic intervention should also be considered for application to organs from DBD donors. Finally, drawing on current global insights into the critical role of RCD and DAMPs in driving innate inflammatory and (allo)immune responses, targeting their inhibition and/or prevention during normothermic perfusion of transplant organs from DCD donors - and potentially DBD donors - holds the transformative potential to not only alleviate transplant dysfunction and suppress allograft rejection but also foster allograft tolerance.

ROLE OF CASPASE-1/CASPASE-11-HMGB1-RAGE/TLR4 SIGNALING IN THE EXACERBATION OF EXTRAPULMONARY SEPSIS-INDUCED LUNG INJURY BY MECHANICAL VENTILATION

ABSTRACT

Background: Mechanical ventilation (MV) is a clinically important measure for respiratory support in critically ill patients. Although moderate tidal volume MV does not cause lung injury, it can further exacerbate lung injury in a pathological state such as sepsis. This pathological process is known as the "two-hit" theory, whereby an initial lung injury (e.g., infection, trauma, or sepsis) triggers an inflammatory response that activates immune cells, presenting the lung tissue in a fragile state and rendering it more susceptible to subsequent injury. The second hit occurs when MV is applied to lung tissue in a fragile state, and it is noteworthy that this MV is harmless to healthy lung tissue, further aggravating preexisting lung injury through unknown mechanisms. This interaction between initial injury and subsequent MV develops a malignant cycle significantly exacerbating lung injury and severely hampering patient prognosis. The two-hit theory is critical to understanding the complicated mechanisms of ventilator-associated lung injury and facilitates the subsequent development of targeted therapeutic strategies. Methods and Results: The cecum ligation and perforation mice model was used to mimic clinical sepsis patients. After 12 h, the mice were mechanically ventilated for 2 to 6 h. MV by itself did not lead to HMGB1 release, but significantly strengthened HMGB1 in plasma and cytoplasm of lung tissue in septic mice. Plasma and lung tissue activation of cytokines and chemokines, mitogen-activated protein kinase signaling pathway, neutrophil recruitment, and acute lung injury were progressively decreased in LysM HMGB1 -/- (Hmgb1 deletion in myeloid cells) and iHMGB1 -/- mice (inducible HMGB1 -/- mouse strain where the Hmgb1 gene was globally deleted after tamoxifen treatment). Compared with C57BL/6 mice, although EC-HMGB1 -/- (Hmgb1 deletion in endothelial cells) mice did not have lower levels of inflammation, neutrophil recruitment and lung injury were reduced. Compared with LysM HMGB1 -/- mice, EC-HMGB1 -/- mice had higher levels of inflammation but significantly lower neutrophil recruitment and lung injury. Overall, iHMGB1 -/- mice had the lowest levels of all the above indicators. The level of inflammation, neutrophil recruitment, and the degree of lung injury were decreased in RAGE -/- mice, and even the above indices were further decreased in TLR4/RAGE -/- mice. Levels of inflammation and neutrophil recruitment were decreased in caspase-11 -/- and caspase-1/11 -/- mice, but there was no statistical difference between these two gene knockout mice. Conclusions: These data show for the first time that the caspase-1/caspase-11-HMGB1-TLR4/RAGE signaling pathway plays a key role in mice model of sepsis-induced lung injury exacerbated by MV. Different species of HMGB1 knockout mice have different lung-protective mechanisms in the two-hit model, and location is the key to function. Specifically, LysM HMGB1 -/- mice due to the deletion of HMGB1 in myeloid cells resulted in a pulmonary-protective mechanism that was associated with a downregulation of the inflammatory response. EC-HMGB1 -/- mice are deficient in HMGB1 owing to endothelial cells, resulting in a distinct pulmonary-protective mechanism independent of the inflammatory response and more relevant to the improvement of alveolar-capillary permeability. iHMGB1 -/- mice, which are systemically HMGB1-deficient, share both of these lung-protective mechanisms.

Mechanisms of mechanical stimulation in the development of respiratory system diseases

During respiration, mechanical stress can initiate biological responses that impact the respiratory system. Mechanical stress plays a crucial role in the development of the respiratory system. However, pathological mechanical stress can impact the onset and progression of respiratory diseases by influencing the extracellular matrix and cell transduction processes. In this article, we explore the mechanisms by which mechanical forces communicate with and influence cells. We outline the basic knowledge of respiratory mechanics, elucidating the important role of mechanical stimulation in influencing respiratory system development and differentiation from a microscopic perspective. We also explore the potential mechanisms of mechanical transduction in the pathogenesis and development of respiratory diseases such as asthma, lung injury, pulmonary fibrosis, and lung cancer. Finally, we look forward to new research directions in cellular mechanotransduction, aiming to provide fresh insights for future therapeutic research on respiratory diseases.

Geniposide ameliorates acute kidney injury via enhancing the phagocytic ability of macrophages towards neutrophil extracellular traps

Acute kidney injury (AKI) is a clinically serious disorder associated with high mortality rates and an increased risk of progression to end-stage renal disease. As an essential supportive treatment for patients with respiratory failure, mechanical ventilation not only save many critically ill patients, but also affect glomerular filtration function by changing renal hemodynamics, neurohumoral and positive end-expiratory pressure, eventually leading to AKI. AMP-activated protein kinase (AMPK), a crucial energy homeostasis regulator, could enhance macrophage phagocytic ability and inhibit inflammation, but whether it can engulf neutrophil extracellular traps (NETs) and alleviate mechanical ventilation-associated AKI is still unclear. In this study, we found that geniposide significantly ameliorated histopathological damage, reduced serum Cre and BUN levels. Besides, geniposide can also induce AMPK activation and enhance macrophage phagocytic ability toward NETs. Moreover, geniposide can markedly reduce the levels of high mobility group box 1 (HMGB1), and these effects were dependent on AMPK-PI3K/Akt signaling. Altogether, these results indicated that geniposide promoted macrophage efferocytosis by inducing AMPK-PI3K/Akt signaling activation, clearing NETs and ameliorating AKI.

GAT107-mediated α7 nicotinic acetylcholine receptor signaling attenuates inflammatory lung injury and mortality in a mouse model of ventilator-associated pneumonia by alleviating macrophage mitochondrial oxidative stress via reducing MnSOD-S-glutathionylation

Supraphysiological concentrations of oxygen (hyperoxia) can compromise host defense and increase susceptibility to bacterial and viral infections, causing ventilator-associated pneumonia (VAP). Compromised host defense and inflammatory lung injury are mediated, in part, by high extracellular concentrations of HMGB1, which can be decreased by GTS-21, a partial agonist of α7 nicotinic acetylcholine receptor (α7nAChR). Here, we report that a novel α7nAChR agonistic positive allosteric modulator (ago-PAM), GAT107, at 3.3 mg/kg, i.p., significantly decreased animal mortality and markers of inflammatory injury in mice exposed to hyperoxia and subsequently infected with Pseudomonas aeruginosa. The incubation of macrophages with 3.3 μM of GAT107 significantly decreased hyperoxia-induced extracellular HMGB1 accumulation and HMGB1-induced macrophage phagocytic dysfunction. Hyperoxia-compromised macrophage function was correlated with impaired mitochondrial membrane integrity, increased superoxide levels, and decreased manganese superoxide dismutase (MnSOD) activity. This compromised MnSOD activity is due to a significant increase in its level of glutathionylation. The incubation of hyperoxic macrophages with 3.3 μM of GAT107 significantly decreases the levels of glutathionylated MnSOD, and restores MnSOD activity and mitochondrial membrane integrity. Thus, GAT107 restored hyperoxia-compromised phagocytic functions by decreasing HMGB1 release, most likely via a mitochondrial-directed pathway. Overall, our results suggest that GAT107 may be a potential treatment to decrease acute inflammatory lung injury by increasing host defense in patients with VAP.

Glycyrrhizin through liquorice intake modulates ACE2 and HMGB1 levels-A pilot study in healthy individuals with implications for COVID-19 and ARDS

Background

Glycyrrhizin, an active component of liquorice root extract, exhibits antiviral and immunomodulatory properties by direct inhibition of the pro-inflammatory alarmin HMGB1 (High-mobility group box 1).

Objective

The aim of this study was to explore the role of liquorice intake on the viral entry receptor ACE2 (angiotensin-converting enzyme 2) and the immunoregulatory HMGB1 in healthy individuals and to explore HMGB1 expression in coronavirus disease 2019 (COVID-19) or non-COVID-19 in ARDS (acute respiratory distress syndrome patients).

Material and methods

This study enrolled 43 individuals, including hospitalised patients with i) acute respiratory distress syndrome (ARDS) due to COVID-19 (n = 7) or other underlying causes (n = 12), ii) mild COVID-19 (n = 4) and iii) healthy volunteers (n = 20). Healthy individuals took 50 g of liquorice (containing 3% liquorice root extract) daily for 7 days, while blood samples were collected at baseline and on day 3 and 7. Changes in ACE2 and HMGB1 levels were determined by Western blot analysis and enzyme-linked immunosorbent assay, respectively. Additionally, HMGB1 levels were measured in hospitalised COVID-19 patients with mild disease or COVID-19 associated acute respiratory distress syndrome (ARDS) and compared with a non-COVID-19-ARDS group.

Results

Liquorice intake significantly reduced after 7 days both cellular membranous ACE2 expression (-51% compared to baseline levels, p = 0.008) and plasma HMGB1 levels (-17% compared to baseline levels, p<0.001) in healthy individuals. Half of the individuals had a reduction in ACE2 levels of at least 30%. HMGB1 levels in patients with mild COVID-19 and ARDS patients with and without COVID-19 were significantly higher compared with those of healthy individuals (+317%, p = 0.002), but they were not different between COVID-19 and non-COVID-19 ARDS.

Conclusions

Liquorice intake modulates ACE2 and HMGB1 levels in healthy individuals. HMGB1 is enhanced in mild COVID-19 and in ARDS with and without COVID-19, warranting evaluation of HMGB1 as a potential treatment target and glycyrrhizin, which is an active component of liquorice root extract, as a potential treatment in COVID-19 and non-COVID-19 respiratory disease.

Association of the RAGE/RAGE-ligand axis with interstitial lung disease and its acute exacerbation

The receptor for advanced glycation end product (RAGE) is a transmembrane receptor highly expressed in type 1 pneumocytes of healthy lungs. RAGE is considered to play a homeostatic role in the lung, as RAGE knockout mice develop lung fibrosis as they age. In contrast, RAGE can bind numerous ligands, including high-mobility group box 1 (HMGB1). These interactions initiate pro-inflammatory signaling associated with the pathogenesis of lung injury and interstitial lung disease (ILD), including idiopathic pulmonary fibrosis (IPF). ILD is a broad category of diffuse parenchymal lung disease characterized by various extents of lung fibrosis and inflammation, and IPF is a common and progressive ILD of unknown cause. The prognosis of patients with IPF is poor, and acute exacerbation of IPF (AE-IPF) is one of the main causes of death. Recent reports indicate that acute exacerbations can occur in other ILDs (AE-ILD). Notably, ILD is frequently observed in patients with lung cancer, and AE-ILD after surgical procedures or the initiation of chemotherapy for concomitant lung cancer are clinically important due to their association with increased mortality. In this review, we summarize the associations of RAGE/soluble RAGE (sRAGE)/RAGE ligands with the pathogenesis and clinical course of ILD, including IPF and AE-IPF. Additionally, the potential use of sRAGE and RAGE ligands as predictive markers of AE-IPF and cancer treatment-triggered AE-ILD is also discussed.

Predictive role of circulatory HMGB1 in postoperative acute exacerbation of interstitial lung disease in lung cancer patients

Postoperative acute exacerbation of interstitial lung disease (AE-ILD) can be fatal in patients with lung cancer concomitant with ILD. We aimed to elucidate the predictive potential of high-mobility group box 1 (HMGB1), which is associated with the development and severity of lung injury, for evaluating the risk of this complication. We included 152 patients with lung cancer and ILD who underwent radical surgery between January 2011 and August 2019. We evaluated the preoperative levels of serum HMGB1 and its predictive potential for postoperative AE-ILD. Postoperative AE-ILD developed in 17 patients. Serum levels of HMGB1 were significantly higher in patients with postoperative AE-ILD than in those without (median [interquartile range]: 5.39 [3.29–11.70] ng/mL vs. 3.55 [2.07–5.62] ng/mL). Univariate and multivariate logistic regression analyses revealed that higher HMGB1 levels were significantly associated with the development of postoperative AE-ILD in entire studied patients (n = 152). In the subgroup analysis, higher HMGB1 levels were associated with a significantly increased risk of this complication in patients who underwent lobectomy (n = 77) than in those who underwent sublobar resection (n = 75). Serum HMGB1 could be a promising marker for evaluating the risk of postoperative AE-ILD, specifically in patients who underwent lobectomy.

Attenuation of ventilator-induced lung injury through suppressing the pro-inflammatory signaling pathways: A review on preclinical studies

Mechanical ventilation (MV) is a relatively common medical intervention in ICU patients. The main side effect of MV is the so-called "ventilator-induced lung injury" (VILI). The pathogenesis of VILI is not completely understood; however, it has been reported that MV might be associated with up-regulation of various inflammatory mediators within the lung tissue and that these mediators might act as pathogenic factors in lung tissue injury. One potential mechanism for the generation of inflammatory mediators is through the release of endogenous molecules known as damage associated molecular patterns (DAMPs). These molecules are released from injured tissues and can bind to pattern recognition receptors (PRRs). PRR activation generally leads to the production and release of inflammation-related molecules including innate immune cytokines and chemokines. It has been suggested that blocking DAMP/PRR signaling pathways might diminish the progression of VILI. Herein, we review the latest findings with regard to the effects of DAMP/PRRs and their blockade, as well as the potential therapeutic targets and future research directions in VILI. Results of studies performed on human samples, animal models of disease, as well as relevant in vitro systems will be discussed.

Concentrations of HMGB1 and Hsp70 of healthy subjects in upper and lower airway: Literature Review and Meta-analysis

Although high-mobility group box 1 and heat-shock protein 70 are implicated in airway diseases and suggested as relevant diagnostic biomarkers, their control concentrations in the airways have not yet been determined. This study aimed to evaluate concentration of healthy subjects for both these proteins in the upper and lower airways via meta-analysis. We searched MEDLINE, EMBASE, and Google Scholar for articles describing concentration of healthy subjects for these proteins. Data from healthy populations were combined using a random-effects model, and subgroup and sensitivity analyses were performed to determine between-study heterogeneity. We analyzed 22 studies involving 485 patients. Concentration of healthy subjects of high-mobility group box 1 and heat-shock protein 70 varied from "not detected" to 326.13 ng/mL and from 0.20 pg/mL to 9240.00 pg/mL, respectively, with the values showing significant heterogeneity. Subgroup analysis for high-mobility group box 1 revealed 13.63 ng/mL (95% CI 12.13-15.14), 100.31 ng/mL (95% CI -31.28-231.91), 9.54 ng/mL (95% CI 8.91-10.17), and 65.82 ng/mL (95% CI 55.51-76.14) for the lower airway, upper airway, pediatric populations, and adults, respectively, whereas that for heat-shock protein 70 revealed 20.58 pg/mL (95% CI 7.87-33.29) for the lower airway and 9240.00 ±11820 pg/mL for the upper airway. Although concentrations of healthy subjects of these proteins varied in the upper and lower airways, the levels of both these proteins were higher in the upper airway than in the lower airway, and these concentrations differed according to the age and sampling procedure. Our findings support the further evaluation of these proteins as biomarkers for airway-related diseases.

The α7 nicotinic acetylcholine receptor agonist GTS-21 improves bacterial clearance in mice by restoring hyperoxia-compromised macrophage function

BACKGROUND

Mechanical ventilation, in combination with supraphysiological concentrations of oxygen (i.e., hyperoxia), is routinely used to treat patients with respiratory distress, such as COVID-19. However, prolonged exposure to hyperoxia compromises the clearance of invading pathogens by impairing macrophage phagocytosis. Previously, we have shown that the exposure of mice to hyperoxia induces the release of the nuclear protein high mobility group box-1 (HMGB1) into the pulmonary airways. Furthermore, extracellular HMGB1 impairs macrophage phagocytosis and increases the mortality of mice infected with Pseudomonas aeruginosa (PA). The aim of this study was to determine whether GTS-21 (3-(2,4-dimethoxybenzylidene) anabaseine), an α7 nicotinic acetylcholine receptor (α7nAChR) agonist, could (1) inhibit hyperoxia-induced HMGB1 release into the airways; (2) enhance macrophage phagocytosis and (3) increase bacterial clearance from the lungs in a mouse model of ventilator-associated pneumonia.

METHOD

GTS-21 (0.04, 0.4, and 4 mg/kg) or saline were administered by intraperitoneal injection to mice that were exposed to hyperoxia (≥ 99% O₂) and subsequently challenged with PA.

RESULTS

The systemic administration of 4 mg/kg i.p. of GTS-21 significantly increased bacterial clearance, decreased acute lung injury and decreased accumulation of airway HMGB1 compared to the saline control. To determine the mechanism of action of GTS-21, RAW 264.7 cells, a macrophage-like cell line, were incubated with different concentrations of GTS-21 in the presence of 95% O₂. The phagocytic activity of macrophages was significantly increased by GTS-21 in a dose-dependent manner. In addition, GTS-21 significantly inhibited the cytoplasmic translocation and release of HMGB1 from RAW 264.7 cells and attenuated hyperoxia-induced NF-κB activation in macrophages and mouse lungs exposed to hyperoxia and infected with PA.

CONCLUSIONS

Our results indicate that GTS-21 is efficacious in improving bacterial clearance and reducing acute lung injury via enhancing macrophage function by inhibiting the release of nuclear HMGB1. Therefore, the α7nAChR represents a possible pharmacological target to improve the clinical outcome of patients on ventilators by augmenting host defense against bacterial infections.

Damage-associated molecular patterns in trauma

In 1994, the "danger model" argued that adaptive immune responses are driven rather by molecules released upon tissue damage than by the recognition of "strange" molecules. Thus, an alternative to the "self versus non-self recognition model" has been provided. The model, which suggests that the immune system discriminates dangerous from safe molecules, has established the basis for the future designation of damage-associated molecular patterns (DAMPs), a term that was coined by Walter G. Land, Seong, and Matzinger. The pathological importance of DAMPs is barely somewhere else evident as in the posttraumatic or post-surgical inflammation and regeneration. Since DAMPs have been identified to trigger specific immune responses and inflammation, which is not necessarily detrimental but also regenerative, it still remains difficult to describe their "friend or foe" role in the posttraumatic immunogenicity and healing process. DAMPs can be used as biomarkers to indicate and/or to monitor a disease or injury severity, but they also may serve as clinically applicable parameters for optimized indication of the timing for, i.e., secondary surgeries. While experimental studies allow the detection of these biomarkers on different levels including cellular, tissue, and circulatory milieu, this is not always easily transferable to the human situation. Thus, in this review, we focus on the recent literature dealing with the pathophysiological importance of DAMPs after traumatic injury. Since dysregulated inflammation in traumatized patients always implies disturbed resolution of inflammation, so-called model of suppressing/inhibiting inducible DAMPs (SAMPs) will be very briefly introduced. Thus, an update on this topic in the field of trauma will be provided.

The α7 nicotinic acetylcholine receptor agonist, GTS-21, attenuates hyperoxia-induced acute inflammatory lung injury by alleviating the accumulation of HMGB1 in the airways and the circulation

BACKGROUND

Oxygen therapy, using supraphysiological concentrations of oxygen (hyperoxia), is routinely administered to patients who require respiratory support including mechanical ventilation (MV). However, prolonged exposure to hyperoxia results in acute lung injury (ALI) and accumulation of high mobility group box 1 (HMGB1) in the airways. We previously showed that airway HMGB1 mediates hyperoxia-induced lung injury in a mouse model of ALI. Cholinergic signaling through the α7 nicotinic acetylcholine receptor (α7nAChR) attenuates several inflammatory conditions. The aim of this study was to determine whether 3-(2,4 dimethoxy-benzylidene)-anabaseine dihydrochloride, GTS-21, an α7nAChR partial agonist, inhibits hyperoxia-induced HMGB1 accumulation in the airways and circulation, and consequently attenuates inflammatory lung injury.

METHODS

Mice were exposed to hyperoxia (≥99% O2) for 3 days and treated concurrently with GTS-21 (0.04, 0.4 and 4 mg/kg, i.p.) or the control vehicle, saline.

RESULTS

The systemic administration of GTS-21 (4 mg/kg) significantly decreased levels of HMGB1 in the airways and the serum. Moreover, GTS-21 (4 mg/kg) significantly reduced hyperoxia-induced acute inflammatory lung injury, as indicated by the decreased total protein content in the airways, reduced infiltration of inflammatory monocytes/macrophages and neutrophils into the lung tissue and airways, and improved lung injury histopathology.

CONCLUSIONS

Our results indicate that GTS-21 can attenuate hyperoxia-induced ALI by inhibiting extracellular HMGB1-mediated inflammatory responses. This suggests that the α7nAChR represents a potential pharmacological target for the treatment regimen of oxidative inflammatory lung injury in patients receiving oxygen therapy.

Extracellular HMGB1: a therapeutic target in severe pulmonary inflammation including COVID-19?

BACKGROUND

The 2019 novel coronavirus disease (COVID-19) causes for unresolved reasons acute respiratory distress syndrome in vulnerable individuals. There is a need to identify key pathogenic molecules in COVID-19-associated inflammation attainable to target with existing therapeutic compounds. The endogenous damage-associated molecular pattern (DAMP) molecule HMGB1 initiates inflammation via two separate pathways. Disulfide-HMGB1 triggers TLR4 receptors generating pro-inflammatory cytokine release. Extracellular HMGB1, released from dying cells or secreted by activated innate immunity cells, forms complexes with extracellular DNA, RNA and other DAMP or pathogen-associated molecular (DAMP) molecules released after lytic cell death. These complexes are endocytosed via RAGE, constitutively expressed at high levels in the lungs only, and transported to the endolysosomal system, which is disrupted by HMGB1 at high concentrations. Danger molecules thus get access to cytosolic proinflammatory receptors instigating inflammasome activation. It is conceivable that extracellular SARS-CoV-2 RNA may reach the cellular cytosol via HMGB1-assisted transfer combined with lysosome leakage. Extracellular HMGB1 generally exists in vivo bound to other molecules, including PAMPs and DAMPs. It is plausible that these complexes are specifically removed in the lungs revealed by a 40% reduction of HMGB1 plasma levels in arterial versus venous blood. Abundant pulmonary RAGE expression enables endocytosis of danger molecules to be destroyed in the lysosomes at physiological HMGB1 levels, but causing detrimental inflammasome activation at high levels. Stress induces apoptosis in pulmonary endothelial cells from females but necrosis in cells from males.

CONCLUSION

Based on these observations we propose extracellular HMGB1 to be considered as a therapeutic target for COVID-19.

Dietary Antioxidants Significantly Attenuate Hyperoxia-Induced Acute Inflammatory Lung Injury by Enhancing Macrophage Function via Reducing the Accumulation of Airway HMGB1

Mechanical ventilation with hyperoxia is the major supportive measure to treat patients with acute lung injury and acute respiratory distress syndrome (ARDS). However, prolonged exposure to hyperoxia can induce oxidative inflammatory lung injury. Previously, we have shown that high levels of airway high-mobility group box 1 protein (HMGB1) mediate hyperoxia-induced acute lung injury (HALI). Using both ascorbic acid (AA, also known as vitamin C) and sulforaphane (SFN), an inducer of nuclear factor (erythroid-derived 2)-like 2 (Nrf2), we tested the hypothesis that dietary antioxidants can mitigate HALI by ameliorating HMGB1-compromised macrophage function in phagocytosis by attenuating hyperoxia-induced extracellular HMGB1 accumulation. Our results indicated that SFN, which has been shown to attenute HALI in mice exposed to hyperoxia, dose-dependently restored hyperoxia-compromised macrophage function in phagocytosis (75.9 ± 3.5% in 0.33 µM SFN versus 50.7 ± 1.8% in dimethyl sulfoxide (DMSO) control, p < 0.05) by reducing oxidative stress and HMGB1 release from cultured macrophages (47.7 ± 14.7% in 0.33 µM SFN versus 93.1 ± 14.6% in DMSO control, p < 0.05). Previously, we have shown that AA enhances hyperoxic macrophage functions by reducing hyperoxia-induced HMGB1 release. Using a mouse model of HALI, we determined the effects of AA on hyperoxia-induced inflammatory lung injury. The i.p. administration of 50 mg/kg of AA to mice exposed to 72 h of ≥98% O₂ significantly decreased hyperoxia-induced oxidative and nitrosative stress in mouse lungs. There was a significant decrease in the levels of airway HMGB1 (43.3 ± 12.2% in 50 mg/kg AA versus 96.7 ± 9.39% in hyperoxic control, p < 0.05), leukocyte infiltration (60.39 ± 4.137% leukocytes numbers in 50 mg/kg AA versus 100 ± 5.82% in hyperoxic control, p < 0.05) and improved lung integrity in mice treated with AA. Our study is the first to report that the dietary antioxidants, ascorbic acid and sulforaphane, ameliorate HALI and attenuate hyperoxia-induced macrophage dysfunction through an HMGB1-mediated pathway. Thus, dietary antioxidants could be used as potential treatments for oxidative-stress-induced acute inflammatory lung injury in patients receiving mechanical ventilation.

JAK2/STAT1-mediated HMGB1 translocation increases inflammation and cell death in a ventilator-induced lung injury model

Janus kinase 2/signal transducer and activators of transcription 1 (JAK2/STAT1) signaling is a common pathway that contributes to numerous inflammatory disorders, including different forms of acute lung injury (ALI). However, the role of JAK2/STAT1 in ventilator-induced lung injury (VILI) and its underlying mechanism remain unclear. In this study, using lipopolysaccharide (LPS) inhalation plus mechanical ventilation as VILI mouse model, we found that the administration of JAK2 inhibitor AZD1480 markedly attenuated lung destruction, diminished protein leakage, and inhibited cytokine release. In addition, when mouse macrophage-like RAW 264.7 cells were exposed to LPS and cyclic stretch (CS), AZD1480 prevented cell autophagy, reduced apoptosis, and suppressed lactate dehydrogenase release by downregulating JAK2/STAT1 phosphorylation levels and inducing HMGB1 translocation from the nucleus to the cytoplasm. Furthermore, HMGB1 and STAT1 knockdown attenuated LPS+CS-induced autophagy and apoptosis in RAW 264.7 cells. In conclusion, these findings reveal the connection between the JAK2/STAT1 pathway and HMGB1 translocation in mediating lung inflammation and cell death in VILI, suggesting that these molecules may serve as novel therapeutic targets for VILI.

The Role of HMGB1, a Nuclear Damage-Associated Molecular Pattern Molecule, in the Pathogenesis of Lung Diseases

Significance: High-mobility group protein box 1 (HMGB1), a ubiquitous nuclear protein, regulates chromatin structure and modulates the expression of many genes involved in the pathogenesis of lung cancer and many other lung diseases, including those that regulate cell cycle control, cell death, and DNA replication and repair. Extracellular HMGB1, whether passively released or actively secreted, is a danger signal that elicits proinflammatory responses, impairs macrophage phagocytosis and efferocytosis, and alters vascular remodeling. This can result in excessive pulmonary inflammation and compromised host defense against lung infections, causing a deleterious feedback cycle. Recent Advances: HMGB1 has been identified as a biomarker and mediator of the pathogenesis of numerous lung disorders. In addition, post-translational modifications of HMGB1, including acetylation, phosphorylation, and oxidation, have been postulated to affect its localization and physiological and pathophysiological effects, such as the initiation and progression of lung diseases. Critical Issues: The molecular mechanisms underlying how HMGB1 drives the pathogenesis of different lung diseases and novel therapeutic approaches targeting HMGB1 remain to be elucidated. Future Directions: Additional research is needed to identify the roles and functions of modified HMGB1 produced by different post-translational modifications and their significance in the pathogenesis of lung diseases. Such studies will provide information for novel approaches targeting HMGB1 as a treatment for lung diseases.

Ethyl pyruvate attenuates ventilation-induced diaphragm dysfunction through high-mobility group box-1 in a murine endotoxaemia model

Mechanical ventilation (MV) can save the lives of patients with sepsis. However, MV in both animal and human studies has resulted in ventilator-induced diaphragm dysfunction (VIDD). Sepsis may promote skeletal muscle atrophy in critically ill patients. Elevated high-mobility group box-1 (HMGB1) levels are associated with patients requiring long-term MV. Ethyl pyruvate (EP) has been demonstrated to lengthen survival in patients with severe sepsis. We hypothesized that the administration of HMGB1 inhibitor EP or anti-HMGB1 antibody could attenuate sepsis-exacerbated VIDD by repressing HMGB1 signalling. Male C57BL/6 mice with or without endotoxaemia were exposed to MV (10 mL/kg) for 8 hours after administrating either 100 mg/kg of EP or 100 mg/kg of anti-HMGB1 antibody. Mice exposed to MV with endotoxaemia experienced augmented VIDD, as indicated by elevated proteolytic, apoptotic and autophagic parameters. Additionally, disarrayed myofibrils and disrupted mitochondrial ultrastructures, as well as increased HMGB1 mRNA and protein expression, and plasminogen activator inhibitor-1 protein, oxidative stress, autophagosomes and myonuclear apoptosis were also observed. However, MV suppressed mitochondrial cytochrome C and diaphragm contractility in mice with endotoxaemia (P < 0.05). These deleterious effects were alleviated by pharmacologic inhibition with EP or anti-HMGB1 antibody (P < 0.05). Our data suggest that EP attenuates endotoxin-enhanced VIDD by inhibiting HMGB1 signalling pathway.

Trauma-Induced Damage-Associated Molecular Patterns-Mediated Remote Organ Injury and Immunosuppression in the Acutely Ill Patient

Trauma is one of the leading causes of death and disability in the world. Multiple trauma or isolated traumatic brain injury are both indicative of human tissue damage. In the early phase after trauma, damage-associated molecular patterns (DAMPs) are released and give rise to sterile systemic inflammatory response syndrome (SIRS) and organ failure. Later, protracted inflammation following sepsis will favor hospital-acquired infection and will worsen patient’s outcome through immunosuppression. Throughout medical care or surgical procedures, severe trauma patients will be subjected to endogenous or exogenous DAMPs. In this review, we summarize the current knowledge regarding DAMP-mediated SIRS or immunosuppression and the clinical consequences in terms of organ failure and infections.

Danger signals in trauma

This review summarizes a short list of currently discussed trauma-induced danger-associated molecular patterns (DAMP). Due to the bivalent character and often pleiotropic effects of a DAMP, it is difficult to describe its "friend or foe" role in post-traumatic inflammation and regeneration, both systemically as well locally in tissues. DAMP can be used as biomarkers to indicate or monitor disease or injury severity, but also may serve as clinically applicable parameters for better indication and timing of surgery. Due to the inflammatory processes at the local tissue level or the systemic level, the precise role of DAMP is not always clear to define. While in vitro and experimental studies allow for the detection of these biomarkers at the different levels of an organism-cellular, tissue, circulation-this is not always easily transferable to the human setting. Increased knowledge exploring the dual role of DAMP after trauma, and concentrating on their nuclear functions, transcriptional targets, release mechanisms, cellular sources, multiple functions, their interactions and potential therapeutic targeting is warranted.

Protective effect of SIRT3 on acute lung injury by increasing manganese superoxide dismutase-mediated antioxidation

Prolonged exposure to hyperoxia results in acute lung injury (ALI). Pulmonary damage caused by oxygen toxicity occurs due to the generation of reactive oxygen species and subsequent formation of more potent oxidants. The present study demonstrated that sirtuin 3 (SIRT3) may attenuate hyperoxia‑induced ALI due to its potential antioxidative effect. In the present study, a hyperoxia‑induced acute lung injury mouse model, reverse transcription‑quantitative polymerase chain reaction, western blotting, retroviral mediated gene over‑expression and knockdown assays revealed that the expression of SIRT3 in the lung tissue of mice with hyperoxia‑induced ALI was decreased and overexpression of SIRT3 may significantly reduce hyperoxia‑induced ALI, as reflected by decreases in protein concentration, infiltrated neutrophils in bronchoalveolar lavage (BAL) fluid and wet/dry ratio of lung tissues. Furthermore, overexpression of SIRT3 increased the protein levels and enzymatic activity of manganese superoxide dismutase (MnSOD), and inhibited oxidative stress in the lungs of ALI mice. Additionally, the current study demonstrated that SIRT3 promoted the expression of MnSOD, and this regulation was crucial for the protective effect of SIRT3 on hyperoxia‑induced ALI. In summary, the results of the current study indicated that SIRT3 overexpression may effectively ameliorate hyperoxia‑induced ALI in mice, which indicates a potential application for SIRT3‑based gene therapy to treat clinical adult respiratory distress syndrome.

High mobility group box 1 protein in bronchoalveolar lavage fluid and correlation with other inflammatory markers in pulmonary diseases

Objectives: Analysis of new markers in bronchoalveolar lavage fluid (BALF) provides new insights into the immunopathogenesis and may be helpful in differential diagnosis of lung diseases. High mobility group box 1 protein (HMGB1) is a non-histone nuclear protein and its release into the extracellular environment may be associated with the inflammatory response. The aim of the study is the analysis of HMGB1 in BALF, correlations with other markers of inflammation and differences in extracellular HMGB1 levels in various lung diagnoses. Methods: The concentration of HMGB1 was tested by an Elisa test. We calculated correlations with other inflammatory markers (leukocytes, total protein, albumin, IgG, IgA, IgM, C3 complement component, alpha-2macroglobuline, CD3, CD4, CD8, TREM-1 and TREM-2) and specified HMGB1 level in various diagnoses. Results: A positive correlation was found between the level of HMGB1 and total protein levels (p=0.0001), albumin (p=0.0058), IgA (p=0.011), IgM (0.0439) and TREM-2 (p=0.0188). Conversely, a negative correlation was revealed between HMGB1 and TREM-1 (p=0.0009). HMGB1 level varied in different diagnoses: the highest level was detected in QuantiFERON TB-positive subjects (median: 30.2) and hypersensitivity pneumonitis (median: 33.2), followed by pulmonary sarcoidosis (median: 16.8) and idiopathic pulmonary fibrosis (median: 8.8). Conclusion: HMGB1 correlates with other inflammatory markers tested in BALF. Its level varies in different lung diagnoses. (Sarcoidosis Vasc Diffuse Lung Dis 2018; 35: 268-275).

High-mobility group box 1 protein is involved in the protective effect of Saquinavir on ventilation-induced lung injury in mice

Saquinavir (SQV) is the first FDA approved HIV protease inhibitor. Previous studies showed that SQV can limit Toll-like receptor-4 (TLR4)-mediated inflammatory pathway and nuclear factor-κB (NF-κB) activation, thereby playing a protective role in many kinds of diseases. High-mobility group box 1 (HMGB1) has been identified as an inflammatory mediator and it might express its toxicity in a short period of time in ventilator-induced lung injury (VILI). In this study, C57BL/6 mice were randomly divided into four groups (n = 10): control group and control with SQV group (Con + SQV) were spontaneous breath. HTV group (HTV) received high tidal volume ventilation (HTV) for 4 h. HTV with SQV group (HTV + SQV) were pretreated with 5 mg/kg of SQV for 7 days before HTV. Mice were sacrificed after 4 h of HTV. Lung wet/dry weight (W/D) ratio, alveolar-capillary permeability to Evans blue albumin (EBA), cell counts, total proteins in bronchoalveolar lavage fluid (BALF), tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6) level in BALF and lung tissue, and lung histopathology were examined. Our results showed that HTV caused significant lung injury and NF-κB activation, which was correlated with the increase of TNF-α and IL-6 levels in BALF and plasma. SQV pretreatment significantly attenuated pulmonary inflammatory injury, as well as NF-κB activation. These findings indicate that the protective effect of SQV may be associated with the inhibition of NF-κB activation and HMGB1 expression in mice.

DANGER IN THE INTENSIVE CARE UNIT: DAMPS IN CRITICALLY ILL PATIENTS

Danger-associated molecular patterns (DAMPs) that are released by injured, threatened, or dead cells, or that originate from the extracellular matrix, influence the immune system. This is of great relevance in critically ill patients, in whom trauma or surgery-related cell damage, hypoxia, ischemia, and infections can result in extensive release of DAMPs. As many patients at the intensive care unit suffer from immune system-related complications, DAMPs could serve as markers for the prognosis of these patients and represent possible therapeutic targets. In the present review, we provide an overview of several well known DAMPs (high-mobility group box 1, heat-shock proteins, s100 proteins, nucleic acids, and hyaluronan) and their effects on the immune system. Furthermore, we discuss the role of DAMPs as markers or therapeutic targets in several conditions frequently encountered in critically ill patients, such as sepsis, trauma, ventilator-induced lung injury, and cardiac arrest.

Ascorbic Acid Attenuates Hyperoxia-Compromised Host Defense against Pulmonary Bacterial Infection

Supraphysiological concentrations of oxygen (hyperoxia) can compromise host defense and increase susceptibility to bacterial infections, causing ventilator-associated pneumonia. The phagocytic activity of macrophages is impaired by hyperoxia-induced increases in the levels of reactive oxygen species (ROS) and extracellular high-mobility group box protein B1 (HMGB1). Ascorbic acid (AA), an essential nutrient and antioxidant, has been shown to be beneficial in various animal models of ROS-mediated diseases. The aim of this study was to determine whether AA could attenuate hyperoxia-compromised host defense and improve macrophage functions against bacterial infections. C57BL/6 male mice were exposed to hyperoxia (≥98% O₂, 48 h), followed by intratracheal inoculation with Pseudomonas aeruginosa, and simultaneous intraperitoneal administration of AA. AA (50 mg/kg) significantly improved bacterial clearance in the lungs and airways, and significantly reduced HMGB1 accumulation in the airways. The incubation of RAW 264.7 cells (a macrophage-like cell line) with AA (0-1,000 μM) before hyperoxic exposure (95% O₂) stabilized the phagocytic activity of macrophages in a concentration-dependent manner. The AA-enhanced macrophage function was associated with significantly decreased production of intracellular ROS and accumulation of extracellular HMGB1. These data suggest that AA supplementation can prevent or attenuate the development of ventilator-associated pneumonia in patients receiving oxygen support.

Receptor for Advanced Glycation End Products (RAGE) Serves a Protective Role during Klebsiella pneumoniae - Induced Pneumonia

Klebsiella species is the second most commonly isolated gram-negative organism in sepsis and a frequent causative pathogen in pneumonia. The receptor for advanced glycation end products (RAGE) is expressed on different cell types and plays a key role in diverse inflammatory responses. We here aimed to investigate the role of RAGE in the host response to Klebsiella (K.) pneumoniae pneumonia and intransally inoculated rage gene deficient (RAGE^-/-) and normal wild-type (Wt) mice with K. pneumoniae. Klebsiella pneumonia resulted in an increased pulmonary expression of RAGE. Furthermore, the high-affinity RAGE ligand high mobility group box-1 was upregulated during K. pneumoniae pneumonia. RAGE deficiency impaired host defense as reflected by a worsened survival, increased bacterial outgrowth and dissemination in RAGE^-/- mice. RAGE^-/- neutrophils showed a diminished phagocytosing capacity of live K. pneumoniae in vitro. Relative to Wt mice, RAGE^-/- mice demonstrated similar lung inflammation, and slightly elevated—if any—cytokine and chemokine levels and unchanged hepatocellular injury. In addition, RAGE^-/- mice displayed an unaltered response to intranasally instilled Klebsiella lipopolysaccharide (LPS) with respect to pulmonary cell recruitment and local release of cytokines and chemokines. These data suggest that (endogenous) RAGE protects against K. pneumoniae pneumonia. Also, they demonstrate that RAGE contributes to an effective antibacterial defense during K. pneumoniae pneumonia, at least partly via its participation in the phagocytic properties of professional granulocytes. Additionally, our results indicate that RAGE is not essential for the induction of a local and systemic inflammatory response to either intact Klebsiella or Klebsiella LPS.

Preoperative chemoradiation therapy for esophageal cancer is a risk factor for the elevation of high mobility group box-1, leading to an increase in postoperative severe pulmonary complications

We herein clarified the time course of changes in the serum high mobility group box chromosomal protein-1 (HMGB-1) concentrations in esophageal cancer patients after esophagectomy, and investigated whether the perioperative serum HMGB-1 levels correlate with the administration of neoadjuvant chemoradiation therapy (NACRT) and the postoperative clinical course, especially the occurrence of pulmonary complications, in such patients. Sixty patients who underwent right transthoracic esophagectomy for esophageal cancer were enrolled in this study. The relationship between the perioperative serum HMGB-1 levels and NACRT, and the postoperative severe pulmonary complications were evaluated. Patients with severe pulmonary complications (n = 44) tended to have undergone NACRT more often than those without severe pulmonary complications (n = 16). The preoperative and postoperative day 7 serum HMGB-1 concentrations were significantly higher in patients with severe pulmonary complications than those in patients without severe pulmonary complications. In the univariate and multivariate analyses, the use of NACRT and the preoperative elevations in the serum HMGB-1 levels (>4.2 ng/mL) were found to be significantly associated with pulmonary dysfunction. Furthermore, the response to NACRT was found to be significantly associated with the preoperative serum HMGB-1 levels. The use of NACRT contributes to preoperative serum HMGB-1 elevation, and these were risk factors for the occurrence of severe postoperative pulmonary complications in patients with esophageal cancer after thoracic esophagectomy.

Lung endothelial barrier protection by resveratrol involves inhibition of HMGB1 release and HMGB1-induced mitochondrial oxidative damage via an Nrf2-dependent mechanism

High-mobility group box 1 (HMGB1) contributes to lung vascular hyperpermeability during ventilator-induced lung injury. We aimed to determine whether the natural antioxidant resveratrol protected against HMGB1-induced endothelial hyperpermeability both in vitro and in vivo. We found that HMGB1 decreased vascular endothelial (VE)-cadherin expression and increased endothelial permeability, leading to mitochondrial oxidative damage in primary cultured mouse lung vascular endothelial cells (MLVECs). Both the mitochondrial superoxide dismutase 2 mimetic MnTBAP and resveratrol blocked HMGB1-induced mitochondrial oxidative damage, VE-cadherin downregulation, and endothelial hyperpermeability. In in vivo studies, anesthetized male ICR mice were ventilated for 4h using low tidal volume (6 ml/kg) or high tidal volume (HVT; 30 ml/kg) ventilation. The mice were injected intraperitoneally with resveratrol immediately before the onset of ventilation. We found that resveratrol attenuated HVT-associated lung vascular hyperpermeability and HMGB1 production. HVT caused a significant increase in nuclear factor-erythroid 2-related factor 2 (Nrf2) nuclear translocation and Nrf2 target gene expression in lung tissues, which was further enhanced by resveratrol treatment. HMGB1 had no effect on Nrf2 activation, whereas resveratrol treatment activated the Nrf2 signaling pathway in HMGB1-treated MLVECs. Moreover, Nrf2 knockdown reversed the inhibitory effects of resveratrol on HMGB1-induced mitochondrial oxidative damage and endothelial hyperpermeability. The inhibitory effect of resveratrol on cyclic stretch-induced HMGB1 mRNA expression in primary cultured MLVECs was also abolished by Nrf2 knockdown. In summary, this study demonstrates that resveratrol protects against lung endothelial barrier dysfunction initiated by HVT. Lung endothelial barrier protection by resveratrol involves inhibition of mechanical stretch-induced HMGB1 release and HMGB1-induced mitochondrial oxidative damage. These protective effects of resveratrol might be mediated through an Nrf2-dependent mechanism.

Sputum high mobility group box-1 in asthmatic children: a noninvasive sensitive biomarker reflecting disease status

BACKGROUND

The monitoring of asthma is based mainly on clinical history, physical examination, and lung function test evaluation. To improve knowledge of the disease, new biomarkers of airway inflammation, including high mobility group box-1 (HMGB1), are being developed.

OBJECTIVE

To evaluate sputum HMGB1 levels in children with stable, off-therapy, allergic asthma and to evaluate the relation between HMGB1 levels and lung function parameters.

METHODS

Fifty children with asthma (28 boys and 22 girls, median age 11.56 ± 1.41 years) and 44 healthy children (22 boys and 22 girls, median age 11.07 ± 2.12 years) were enrolled. Sputum HMGB1 was assessed in the cohort study. Lung function (predicted percentage of forced expiratory volume in 1 second [FEV1%] and forced expiratory flow between 25% and 75% [FEF25%-75%]), serum total IgE levels, and asthma severity by validated Global Initiative for Asthma criteria were recorded.

RESULTS

Sputum HMGB1 levels were higher in children with asthma than in healthy controls (100.68 ± 10.03 vs 9.60 ± 3.76 ng/mL, P < .0001). Sputum HMGB1 levels also were positively related to total IgE levels in children with asthma (r = 0.6567, P < .0001). An inverse and strict correlation between sputum HMGB1 levels and pulmonary function indices also were observed in children with mild (FEV1%, r = -0.86544, P < .0001; FEF25%-75%, r = -0.53948, P < .05), moderate (FEV1%, r = -0.99548, P < .0001; FEF25%-75%, r = -0.48668, P < .05), and severe (FEV1%, r = -0.90191, P < .0001; FEF25%-75%, r = -0.66777, P < .05) asthma.

CONCLUSION

The present study provides evidence that sputum HMGB1 is a sensitive biomarker of allergic asthma in children because it was increased and correlated directly with asthma severity and inversely with lung function indices.

Mechanical ventilation induces neutrophil extracellular trap formation

BACKGROUND

Mechanical ventilation can injure the lung and induce a proinflammatory state; such ventilator-induced lung injury (VILI) is associated with neutrophil influx. Neutrophils release DNA and granular proteins as cytotoxic neutrophil extracellular traps (NETs). The authors hypothesized that NETs were produced in a VILI model and may contribute to injury.

METHODS

In a two-hit lipopolysaccharide/VILI mouse model with and without intratracheal deoxyribonuclease (DNase) treatment or blockade of known inducers of NET formation (NETosis), the authors assessed compliance, bronchoalveolar lavage fluid protein, markers of NETs (citrullinated histone-3 and DNA), and markers of inflammation.

RESULTS

Although lipopolysaccharide recruited neutrophils to airways, the addition of high tidal mechanical ventilation was required for significant induction of NETs markers (e.g., bronchoalveolar lavage fluid DNA: 0.4 ± 0.07 µg/ml [mean ± SEM], P < 0.05 vs. all others, n = 10 per group). High tidal volume mechanical ventilation increased airway high-mobility group box 1 protein (0.91 ± 0.138 vs. 0.60 ± 0.095) and interleukin-1β in lipopolysaccharide-treated mice (22.4 ± 0.87 vs. 17.0 ± 0.50 pg/ml, P < 0.001) and tended to increase monocyte chemoattractant protein-1 and interleukin-6. Intratracheal DNase treatment reduced NET markers (bronchoalveolar lavage fluid DNA: 0.23 ± 0.038 vs. 0.88 ± 0.135 µg/ml, P < 0.001; citrullinated histone-3: 443 ± 170 vs. 1,824 ± 403, P < 0.01, n = 8 to 10) and attenuated the loss of static compliance (0.9 ± 0.14 vs. 1.58 ± 0.17 ml/mmHg, P < 0.01, n = 19 to 20) without significantly impacting other measures of injury. Blockade of high-mobility group box 1 (with glycyrrhizin) or interleukin-1β (with anakinra) did not prevent NETosis or protect against injury.

CONCLUSIONS

NETosis was induced in VILI, and DNase treatment eliminated NETs. In contrast to experimental transfusion-related acute lung injury, NETs do not play a major pathogenic role in the current model of VILI.

HMGB1 in health and disease

Complex genetic and physiological variations as well as environmental factors that drive emergence of chromosomal instability, development of unscheduled cell death, skewed differentiation, and altered metabolism are central to the pathogenesis of human diseases and disorders. Understanding the molecular bases for these processes is important for the development of new diagnostic biomarkers, and for identifying new therapeutic targets. In 1973, a group of non-histone nuclear proteins with high electrophoretic mobility was discovered and termed high-mobility group (HMG) proteins. The HMG proteins include three superfamilies termed HMGB, HMGN, and HMGA. High-mobility group box 1 (HMGB1), the most abundant and well-studied HMG protein, senses and coordinates the cellular stress response and plays a critical role not only inside of the cell as a DNA chaperone, chromosome guardian, autophagy sustainer, and protector from apoptotic cell death, but also outside the cell as the prototypic damage associated molecular pattern molecule (DAMP). This DAMP, in conjunction with other factors, thus has cytokine, chemokine, and growth factor activity, orchestrating the inflammatory and immune response. All of these characteristics make HMGB1 a critical molecular target in multiple human diseases including infectious diseases, ischemia, immune disorders, neurodegenerative diseases, metabolic disorders, and cancer. Indeed, a number of emergent strategies have been used to inhibit HMGB1 expression, release, and activity in vitro and in vivo. These include antibodies, peptide inhibitors, RNAi, anti-coagulants, endogenous hormones, various chemical compounds, HMGB1-receptor and signaling pathway inhibition, artificial DNAs, physical strategies including vagus nerve stimulation and other surgical approaches. Future work further investigating the details of HMGB1 localization, structure, post-translational modification, and identification of additional partners will undoubtedly uncover additional secrets regarding HMGB1's multiple functions.

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.

Extracellular HMGB1 regulates multi-walled carbon nanotube-induced inflammation in vivo

Endotoxin is often used to activate NF-κB in vitro when assessing NLRP3 inflammasome activation by various exogenous particles including nanoparticles. However, the endogenous source of this signal 1 is unknown. High-mobility group box 1 (HMGB1) is known to play a critical role in acute lung injury, however the potential contribution of the alarmin HMGB1 to NLRP3 Inflammasome activation has not been determined in response to nanoparticles in vivo. In this study, the ability of multi-walled carbon nanotubes (MWCNT) to cause release of HMGB1 in vitro and in vivo, as well as the potential of HMGB1 to function as signal 1 in vitro and in vivo, was determined. HMGB1 activity in vivo was assessed by administration of HMGB1 neutralization antibodies following MWCNT exposure. Caspase-1(-/-) mice were utilized to elucidate the dependence of HMGB1 secretion on NLRP3 inflammasome activity. MWCNT exposure increased extracellular HMGB1 levels in primary alveolar macrophages from C57Bl/6 mice and C10 mouse epithelial cell culture supernatants, and in C57Bl/6 mouse lung lavage fluid. MWCNT-induced HMGB1 secretion was dependent upon caspase-1. HMGB1 increased MWCNT-induced IL-1β release from macrophages in vitro, and neutralization of extracellular HMGB1 reduced MWCNT-induced IL-1β secretion in vivo. HMGB1 neutralization was accompanied with overall decreased inflammation. In summary, this study suggests extracellular HMGB1 participates in NLRP3 inflammasome activity and regulates IL-1β associated sterile inflammation induced by MWCNT.

The α7 nicotinic acetylcholine receptor agonist GTS-21 improves bacterial clearance in mice by restoring hyperoxia-compromised macrophage function

Mechanical ventilation with supraphysiological concentrations of oxygen (hyperoxia) is routinely used to treat patients with respiratory distress. However, prolonged exposure to hyperoxia compromises the ability of the macrophage to phagocytose and clear bacteria. Previously, we showed that the exposure of mice to hyperoxia elicits the release of the nuclear protein high mobility group box-1 (HMGB1) into the airways. Extracellular HMGB1 impairs macrophage phagocytosis and increases the mortality of mice infected with Pseudomonas aeruginosa (PA). The aim of this study was to determine whether GTS-21 [3-(2,4 dimethoxybenzylidene)-anabaseine dihydrochloride], an α7 nicotinic acetylcholine receptor (α7nAChR) agonist, could inhibit hyperoxia-induced HMGB1 release into the airways, enhance macrophage function and improve bacterial clearance from the lungs in a mouse model of ventilator-associated pneumonia. GTS-21 (0.04, 0.4 and 4 mg/kg) or saline was systemically administered via intraperitoneal injection to mice that were exposed to hyperoxia (≥99% O2) and subsequently challenged with PA. We found that systemic administration of 4 mg/kg GTS-21 significantly increased bacterial clearance, decreased acute lung injury and decreased accumulation of airway HMGB1. To investigate the cellular mechanism of these observations, RAW 264.7 cells, a macrophagelike cell line, were incubated with different concentrations of GTS-21 in the presence of 95% O2. The phagocytic activity of macrophages was significantly increased by GTS-21 in a dose-dependent manner. In addition, hyperoxia-induced hyperacetylation of HMGB1 was significantly reduced in macrophages incubated with GTS-21. Furthermore, GTS-21 significantly inhibited the cytoplasmic translocation and release of HMGB1 from these macrophages. Our results indicate that GTS-21 is effective in improving bacterial clearance and reducing acute lung injury by enhancing macrophage function via inhibiting the release of nuclear HMGB1. Therefore, the α7nAChR represents a possible pharmacological target to improve the clinical outcome of patients on ventilators by augmenting host defense against bacterial infections.

Excessive mechanical stress increases HMGB1 expression in human lung microvascular endothelial cells via STAT3

Ventilator-induced lung injury (VILI) occurs when the lung parenchyma and vasculature are exposed to repetitive and excessive mechanical stress via mechanical ventilation utilized as supportive care for the adult respiratory distress syndrome (ARDS). VILI induces gene expression and systemic release of inflammatory mediators that contribute to the multi-organ dysfunction and morbidity and mortality of ARDS. HMGB1, an intracellular transcription factor with cytokine properties, is a late mediator in sepsis and ARDS pathobiology, however, the role of HMGB1 in VILI remains poorly described. We now report HMGB1 expression in human lung microvessel endothelial cells (ECs) exposed to excessive, equibiaxial mechanical stress, an in vitro correlate of VILI. We determined that high amplitude cyclic stretch (18% CS) increased HMGB1 expression (2-4-fold) via a signaling pathway with critical involvement of the transcription factor, STAT3. Concomitant exposure to 18% CS and oxidative stress (H₂O₂) augmented HMGB1 expression (~13 fold increase) whereas lipopolysaccharide (LPS) challenge increased HMGB1 expression in static EC, but not in 18% CS-challenged EC. In contrast, physiologic, low amplitude cyclic stretch (5% CS) attenuated both oxidative H₂O₂- and LPS-induced increases in HMGB1 expression, suggesting that physiologic mechanical stress is protective. These results indicate that HMGB1 gene expression is markedly responsive to VILI-mediated mechanical stress, an effect that is augmented by oxidative stress. We speculate that VILI-induced HMGB1 expression acts locally to increase vascular permeability and alveolar flooding, thereby exacerbating systemic inflammatory responses and increasing the likelihood of multi-organ dysfunction.

Inhibition of extracellular HMGB1 attenuates hyperoxia-induced inflammatory acute lung injury

Prolonged exposure to hyperoxia results in acute lung injury (ALI), accompanied by a significant elevation in the levels of proinflammatory cytokines and leukocyte infiltration in the lungs. However, the mechanisms underlying hyperoxia-induced proinflammatory ALI remain to be elucidated. In this study, we investigated the role of the proinflammatory cytokine high mobility group box protein 1 (HMGB1) in hyperoxic inflammatory lung injury, using an adult mouse model. The exposure of C57BL/6 mice to ≥99% O₂ (hyperoxia) significantly increased the accumulation of HMGB1 in the bronchoalveolar lavage fluids (BALF) prior to the onset of severe inflammatory lung injury. In the airways of hyperoxic mice, HMGB1 was hyperacetylated and existed in various redox forms. Intratracheal administration of recombinant HMGB1 (rHMGB1) caused a significant increase in leukocyte infiltration into the lungs compared to animal treated with a non-specific peptide. Neutralizing anti-HMGB1 antibodies, administrated before hyperoxia significantly attenuated pulmonary edema and inflammatory responses, as indicated by decreased total protein content, wet/dry weight ratio, and numbers of leukocytes in the airways. This protection was also observed when HMGB1 inhibitors were administered after the onset of the hyperoxic exposure. The aliphatic antioxidant, ethyl pyruvate (EP), inhibited HMGB1 secretion from hyperoxic macrophages and attenuated hyperoxic lung injury. Overall, our data suggest that HMGB1 plays a critical role in mediating hyperoxic ALI through the recruitment of leukocytes into the lungs. If these results can be translated to humans, they suggest that HMGB1 inhibitors provide treatment regimens for oxidative inflammatory lung injury in patients receiving hyperoxia through mechanical ventilation.

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Exposure to hyperoxia results in accumulation of high levels of airway HMGB1 that precede inflammatory acute lung injury (ALI).

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Airway HMGB1 is critical in mediating hyperoxia-induced inflammatory ALI via recruiting leukocytes including neutrophils.

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Extracellular HMGB1-accumulated upon prolonged exposure to hyperoxia is hyperacetylated, existing in different redox states.

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Small molecule EP, administrated even after the onset of hyperoxic exposure, can mitigate hyperoxia-induced inflammatory ALI by inhibiting HMGB1 release into the extracellular milieu.

Contribution of damage-associated molecular patterns to transfusion-related acute lung injury in cardiac surgery

BACKGROUND

The incidence of transfusion-related acute lung injury (TRALI) in cardiac surgery patients is high and this condition contributes to an adverse outcome. Damage-associated molecular pattern (DAMP) molecules, HMGB1 and S100A12, are thought to mediate inflammatory changes in acute respiratory distress syndrome. We aimed to determine whether DAMP are involved in the pathogenesis of TRALI in cardiac surgery patients.

MATERIALS AND METHODS

This was a secondary analysis of a prospective observational trial in cardiac surgery patients admitted to the Intensive Care Unit of a university hospital in the Netherlands. Fourteen TRALI cases were randomly matched with 32 transfused and non-transfused controls. Pulmonary levels of HMGB1, S100A12 and inflammatory cytokines (interleukins-1β, -6, and -8 and tumour necrosis factor-α) were determined when TRALI evolved. In addition, systemic and pulmonary levels of soluble receptor for advanced glycation end products (sRAGE) were determined.

RESULTS

HMGB1 expression and levels of sRAGE in TRALI patients did not differ from those in controls. There was a trend towards higher S100A12 levels in TRALI patients compared to the controls. Furthermore, S100A12 levels were associated with increased levels of markers of pulmonary inflammation, prolonged cardiopulmonary bypass, hypoxemia and duration of mechanical ventilation.

CONCLUSION

No evidence was found that HMGB1 and sRAGE contribute to the development of TRALI. S100A12 is associated with duration of cardiopulmonary bypass, pulmonary inflammation, hypoxia and prolonged mechanical ventilation and may contribute to acute lung injury in cardiac surgery patients.

Assessment of phagocytic activity of cultured macrophages using fluorescence microscopy and flow cytometry

Phagocytosis is the process by which phagocytes, including macrophages, neutrophils and monocytes, engulf and kill invading pathogens, remove foreign particles, and clear cell debris. Phagocytes and their ability to phagocytose are an important part of the innate immune system and are critical for homeostasis of the host. Impairment in phagocytosis has been associated with numerous diseases and disorders. Different cytokines have been shown to affect the phagocytic process. Cytokines including TNFα, IL-1β, GM-CSF, and TGF-β1 were found to promote phagocytosis, whereas high mobility group box-1 (HMGB1) inhibited the phagocytic function of macrophages. Here, we describe two commonly used methods to assess the phagocytic function of cultured macrophages, which can easily be applied to other phagocytes. Each method is based on the extent of engulfment of FITC-labeled latex minibeads by macrophages under different conditions. Phagocytic activity can be assessed either by counting individual cells using a fluorescence microscope or measuring fluorescence intensity using a flow cytometer.

Ventilation-induced lung injury

Mechanical ventilation (MV) is, by definition, the application of external forces to the lungs. Depending on their magnitude, these forces can cause a continuum of pathophysiological alterations ranging from the stimulation of inflammation to the disruption of cell-cell contacts and cell membranes. These side effects of MV are particularly relevant for patients with inhomogeneously injured lungs such as in acute lung injury (ALI). These patients require supraphysiological ventilation pressures to guarantee even the most modest gas exchange. In this situation, ventilation causes additional strain by overdistension of the yet non-injured region, and additional stress that forms because of the interdependence between intact and atelectatic areas. Cells are equipped with elaborate mechanotransduction machineries that respond to strain and stress by the activation of inflammation and repair mechanisms. Inflammation is the fundamental response of the host to external assaults, be they of mechanical or of microbial origin and can, if excessive, injure the parenchymal tissue leading to ALI. Here, we will discuss the forces generated by MV and how they may injure the lungs mechanically and through inflammation. We will give an overview of the mechanotransduction and how it leads to inflammation and review studies demonstrating that ventilator-induced lung injury can be prevented by blocking pathways of mechanotransduction or inflammation.

Potential of the angiotensin receptor blockers (ARBs) telmisartan, irbesartan, and candesartan for inhibiting the HMGB1/RAGE axis in prevention and acute treatment of stroke

Stroke is a major cause of mortality and disability worldwide. The main cause of stroke is atherosclerosis, and the most common risk factor for atherosclerosis is hypertension. Therefore, antihypertensive treatments are recommended for the prevention of stroke. Three angiotensin receptor blockers (ARBs), telmisartan, irbesartan and candesartan, inhibit the expression of the receptor for advanced glycation end-products (RAGE), which is one of the pleiotropic effects of these drugs. High mobility group box 1 (HMGB1) is the ligand of RAGE, and has been recently identified as a lethal mediator of severe sepsis. HMGB1 is an intracellular protein, which acts as an inflammatory cytokine when released into the extracellular milieu. Extracellular HMGB1 causes multiple organ failure and contributes to the pathogenesis of hypertension, hyperlipidemia, diabetes mellitus, atherosclerosis, thrombosis, and stroke. This is the first review of the literature evaluating the potential of three ARBs for the HMGB1-RAGE axis on stroke therapy, including prevention and acute treatment. This review covers clinical and experimental studies conducted between 1976 and 2013. We propose that ARBs, which inhibit the HMGB1/RAGE axis, may offer a novel option for prevention and acute treatment of stroke. However, additional clinical studies are necessary to verify the efficacy of ARBs.

Mechanical ventilation enhances HMGB1 expression in an LPS-induced lung injury model

Background

Mechanical ventilation (MV) can augment inflammatory response in lipopolysaccharide (LPS) challenged lungs. High mobility group box 1 protein (HMGB1) is a pro-inflammatory mediator in ventilator-induced lung injury, but its mechanisms are not well defined. This study investigated the role of HMGB1 in lung inflammation in response to the combination of MV and LPS treatment.

Methods

Forty-eight male Sprague-Dawley rats were randomized to one of four groups: sham control; LPS treatment; mechanical ventilation; mechanical ventilation with LPS treatment. Mechanically ventilated animals received 10 ml/kg tidal volumes at a rate of 40 breaths/min for 4 h. In the HMGB1-blockade study, sixteen rats were randomly assigned to HMGB1 antibody group or control antibody group and animals were subjected to MV+LPS as described above. A549 cells were pre-incubated with different signal inhibitors before subjected to 4 h of cyclic stretch. Lung wet/dry weight (W/D) ratio, total protein and IgG concentration, number of neutrophils in bronchoalveolar lavage fluid (BALF), and lung histological changes were examined. The levels of interleukin-1β (IL-1β), IL-6, tumor necrosis factor-α (TNF-α), macrophage inflammatory protein-2 (MIP-2) and HMGB1 in BALF were measured using ELISA. Real-time quantitative PCR and Western blot were used to analyze mRNA and protein expression of HMGB1. Western blot were employed to analyze the activation of IκB-α, NF-κB, JNK, ERK, and p38.

Results

MV significantly augmented LPS-induced lung injury and HMGB1 expression, which was correlated with the increase in IL-1β, IL-6 and MIP-2 levels in BALF. In vivo, intratracheally administration of HMGB1 antibody significantly attenuated pulmonary inflammatory injury. In vitro experiments showed cyclic stretch induced HMGB1 expression through signaling pathways including p38 and NF-κB.

Conclusions

The findings indicated that moderate tidal volume MV augmented LPS induced lung injury by up-regulating HMGB1. The mechanism of HMGB1-mediated lung injury is likely to be signaling through p38 and NF-κB pathways.

Cyclin-dependent kinase inhibition reduces lung damage in a mouse model of ventilator-induced lung injury

Mechanical ventilation (MV) has the potential to induce lung damage in healthy lungs or aggravate existing lung injury. Polymorphonuclear neutrophil (PMN) recruitment plays an important role in driving the inflammatory response in ventilator-induced lung injury (VILI). The cyclin-dependent kinase inhibitor r-roscovitine has been shown to induce apoptosis in PMNs. In this study, we investigated the potential of r-roscovitine treatment in reducing lung damage in a mouse model of VILI. Mice were tracheotomized and subjected to lung-protective MV with lower (∼7.5 mL/kg) or lung-injurious MV with higher (∼15 mL/kg) tidal volume (VT). R-roscovitine treatment enhanced apoptosis in PMNs in vitro. Ventilator-induced lung injury was associated with pulmonary PMN influx in low and high VT MV. During lung-injurious MV, r-roscovitine treatment reduced the number of PMNs and lowered levels of the lung damage markers RAGE (receptor for advanced glycation end products) and total immunoglobulin M in bronchoalveolar lavage fluid. R-roscovitine did not affect cytokine or chemokine levels in the bronchoalveolar space, neither during lung-protective nor lung-injurious MV. Thus, r-roscovitine treatment reduces lung damage in VILI, possibly dependent on increased apoptosis of PMNs.

Transfusion-Related Acute Lung Injury: The Work of DAMPs

Current notions in immunology hold that not only pathogen-mediated tissue injury but any injury activates the innate immune system. In principle, this evolutionarily highly conserved, rapid first-line defense system responds to pathogen-induced injury with the creation of infectious inflammation, and non-pathogen-induced tissue injury with 'sterile' tissue inflammation. In this review, evidence has been collected in support of the notion that the transfusion-related acute lung injury induces a 'sterile' inflammation in the lung of transfused patients in terms of an acute innate inflammatory disease. The inflammatory response is mediated by the patient's innate immune cells including lung-passing neutrophils and pulmonary endothelial cells, which are equipped with pattern recognition receptors. These receptors are able to sense injury-induced, damage-associated molecular patterns (DAMPs) generated during collection, processing, and storage of blood/blood components. The recognition process leads to activation of these innate cells. A critical role for a protein complex known as the NLRP3 inflammasome has been suggested to be at the center of such a scenario. This complex undergoes an initial 'priming' step mediated by 1 class of DAMPs and then an 'activating' step mediated by another class of DAMPs to activate interleukin-1beta and interleukin-18. These 2 cytokines then promote, via transactivation, the formation of lung inflammation.

The receptor for advanced glycation end products and acute lung injury/acute respiratory distress syndrome

The receptor for advanced glycation end products (RAGE) is a pattern-recognition receptor and evolutionary member of the immunoglobulin superfamily that is involved in the host response to infection, injury, and inflammation. It exists in two forms: membrane-bound and soluble forms (sRAGE). RAGE recognizes a variety of ligands and, via a receptor-driven signaling cascade, activates the transcription factor NF-κB, leading to the expression of proinflammatory cytokines. The soluble form, sRAGE, is a decoy receptor and competitively inhibits membrane RAGE activation. RAGE is constitutively expressed abundantly in the lung under basal conditions. This expression is enhanced during inflammatory states such as with acute lung injury (ALI) and acute respiratory distress syndrome (ARDS). This review summarizes the characteristics of RAGE, RAGE isoforms, RAGE ligands, and signaling pathways in the pathogenesis of ALI and ARDS. Additionally, the review explores the potential of RAGE as an important therapeutic target in ALI/ARDS.

Temporal and spatial expression of high-mobility group box 1 in surgically injured rat vocal folds

OBJECTIVES/HYPOTHESIS

High-mobility group box 1 (HMGB1) protein has been identified as a principal instigator of injury-induced inflammation in many organ systems. Physiologically, HMGB1 binds to chromatin in cell nucleus. Upon injury, cells release HMGB1 to extracellular milieu, triggering a destructive inflammatory response. Neutralizing or removing HMGB1 has been shown to control inflammation. Unfortunately, the role of HMGB1 in laryngeal inflammation and healing has yet to be defined. The purpose of this study was to determine spatial and temporal patterns of HMGB1 expression in surgically injured rat vocal folds up to 2 weeks after injury.

STUDY DESIGN

Prospective animal study.

METHODS

Bilateral vocal fold injury was performed on 70 Sprague-Dawley rats. An additional 14 rats served as uninjured controls. Animals were sacrificed at 1 day, 3 days, 5 days, 1 week, and 2 weeks following surgery. Immunohistochemistry staining and enzyme-linked immunosorbent assay (ELISA) were performed to determine the spatial distribution and temporal expression, respectively, of HMGB1 in vocal fold tissue. Hematoxylin-and-eosin staining for cell counting was performed to evaluate cell infiltration.

RESULTS

Cell number peaked significantly 5 days after injury. HMGB1 was positively stained in the nuclear, cytoplasmic, and extracellular compartments from days 1 to 7 after injury, whereas a strict nuclear staining was observed in uninjured controls and week 2 animals. Staining results were corroborated by ELISA.

CONCLUSIONS

Spatial and temporal changes of HMGB1 expression were shown in injured vocal fold tissue, indicating this protein may be one of the principal drivers of inflammation and healing response to surgical injury in the larynx.

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.