Contribution of neutrophils to acute lung injury

Streptococcal M1 protein triggers chemokine formation, neutrophil infiltration, and lung injury in an NFAT-dependent manner

Streptococcus pyogenes of the M1 serotype can cause STSS, which is associated with significant morbidity and mortality. The purpose of the present study was to examine the role of NFAT signaling in M1 protein-induced lung injury. NFAT-luc mice were treated with the NFAT inhibitor A-285222 before administration of the M1 protein. Neutrophil infiltration, edema, and CXC chemokines were quantified in the lung, 4 h after challenge with the M1 protein. Flow cytometry was used to determine Mac-1 expression. Challenge with the M1 protein increased NFAT-dependent transcriptional activity in the lung, spleen, and liver in NFAT-luc mice. Administration of the NFAT inhibitor A-285222 abolished M1 protein-evoked NFAT activation in the lung, spleen, and liver. M1 protein challenge induced neutrophil recruitment, edema, and CXC chemokine production in the lung, as well as up-regulation of Mac-1 on circulating neutrophils. Inhibition of NFAT activity attenuated M1 protein-induced neutrophil infiltration by 77% and edema formation by 50% in the lung. Moreover, administration of A-285222 reduced M1 protein-evoked pulmonary formation of CXC chemokine >80%. In addition, NFAT inhibition decreased M1 protein-triggered Mac-1 up-regulation on neutrophils. These findings indicate that NFAT signaling controls pulmonary infiltration of neutrophils in response to streptococcal M1 protein via formation of CXC chemokines and neutrophil expression of Mac-1. Thus, the targeting of NFAT activity might be a useful way to ameliorate lung injury in streptococcal infections.

Advances in understanding of the pathogenesis of acute respiratory distress syndrome

The clinical syndrome of acute lung injury (ALI) occurs as a result of an initial acute systemic inflammatory response. This can be consequent to a plethora of insults, either direct to the lung or indirect. The insult results in increased epithelial permeability, leading to alveolar flooding with a protein-rich oedema fluid. The resulting loss of gas exchange leads to acute respiratory failure and typically catastrophic illness, termed acute respiratory distress syndrome (ARDS), requiring ventilatory and critical care support. There remains a significant disease burden, with some estimates showing 200,000 cases each year in the USA with a mortality approaching 50%. In addition, there is a significant burden of morbidity in survivors. There are currently no disease-modifying therapies available, and the most effective advances in caring for these patients have been in changes to ventilator strategy as a result of the ARDS network studies nearly 15 years ago. Here, we will give an overview of more recent advances in the understanding of the cellular biology of ALI and highlight areas that may prove fertile for future disease-modifying therapies.

A method for generating pulmonary neutrophilia using aerosolized lipopolysaccharide

Acute lung injury (ALI) is a severe disease characterized by alveolar neutrophilia, with limited treatment options and high mortality. Experimental models of ALI are key in enhancing our understanding of disease pathogenesis. Lipopolysaccharide (LPS) derived from gram positive bacteria induces neutrophilic inflammation in the airways and lung parenchyma of mice. Efficient pulmonary delivery of compounds such as LPS is, however, difficult to achieve. In the approach described here, pulmonary delivery in mice is achieved by challenge to aerosolized Pseudomonas aeruginosa LPS. Dissolved LPS was aerosolized by a nebulizer connected to compressed air. Mice were exposed to a continuous flow of LPS aerosol in a Plexiglas box for 10 min, followed by 2 min conditioning after the aerosol was discontinued. Tracheal intubation and subsequent bronchoalveolar lavage, followed by formalin perfusion was next performed, which allows for characterization of the sterile pulmonary inflammation. Aerosolized LPS generates a pulmonary inflammation characterized by alveolar neutrophilia, detected in bronchoalveolar lavage and by histological assessment. This technique can be set up at a small cost with few appliances, and requires minimal training and expertise. The exposure system can thus be routinely performed at any laboratory, with the potential to enhance our understanding of lung pathology.

The P2X1 receptor is required for neutrophil extravasation during lipopolysaccharide-induced lethal endotoxemia in mice

Extracellular ATP is becoming increasingly recognized as an important regulator of inflammation. However, the known repertoire of P2 receptor subtypes responsible for the proinflammatory effects of ATP is sparse. We looked at whether the P2X1 receptor, an ATP-gated cation channel present on platelets, neutrophils, and macrophages, participates in the acute systemic inflammation provoked by LPS. Compared with wild-type (WT) mice, P2X1(-/-) mice displayed strongly diminished pathological responses, with dampened neutrophil accumulation in the lungs, less tissue damage, reduced activation of coagulation, and resistance to LPS-induced death. P2X1 receptor deficiency also was associated with a marked reduction in plasma levels of the main proinflammatory cytokines and chemokines induced by LPS. Interestingly, macrophages and neutrophils isolated from WT and P2X1(-/-) mice produced similar levels of proinflammatory cytokines when stimulated with LPS in vitro. Intravital microscopy revealed a defect in LPS-induced neutrophil emigration from cremaster venules into the tissues of P2X1(-/-) mice. Using adoptive transfer of immunofluorescently labeled neutrophils from WT and P2X1(-/-) mice into WT mice, we demonstrate that the absence of the P2X1 receptor on neutrophils was responsible for this defect. This study reveals a major role for the P2X1 receptor in LPS-induced lethal endotoxemia through its critical involvement in neutrophil emigration from venules.

Anti-inflammatory effects of secondary metabolites of marine Pseudomonas sp. in human neutrophils are through inhibiting P38 MAPK, JNK, and calcium pathways

Activated neutrophils play a significant role in the pathogenesis of many inflammatory diseases. The metabolites of marine microorganisms are increasingly employed as sources for developing new drugs; however, very few marine drugs have been studied in human neutrophils. Herein, we showed that secondary metabolites of marine Pseudomonas sp. (N11) significantly inhibited superoxide anion generation and elastase release in formyl-L-methionyl-L-leucyl-L-phenylalanine (FMLP)-activated human neutrophils, with IC50 values of 0.67±0.38 µg/ml and 0.84±0.12 µg/ml, respectively. In cell-free systems, neither superoxide anion-scavenging effect nor inhibition of elastase activity was associated with the suppressive effects of N11. N11 inhibited the phosphorylation of p38 MAP kinase and JNK, but not Erk and Akt, in FMLP-induced human neutrophils. Also, N11 dose-dependently attenuated the transient elevation of intracellular calcium concentration in activated neutrophils. In contrast, N11 failed to alter phorbol myristate acetate-induced superoxide anion generation, and the inhibitory effects of N11 were not reversed by protein kinase A inhibitor. In conclusion, the anti-inflammatory effects of N11 on superoxide anion generation and elastase release in activated human neutrophils are through inhibiting p38 MAP kinase, JNK, and calcium pathways. Our results suggest that N11 has the potential to be developed to treat neutrophil-mediated inflammatory diseases.

Chitinase-like proteins promote IL-17-mediated neutrophilia in a tradeoff between nematode killing and host damage

Enzymatically inactive chitinase-like proteins (CLPs) such as BRP-39, Ym1 and Ym2 are established markers of immune activation and pathology, yet their functions are essentially unknown. We found that Ym1 and Ym2 induced the accumulation of neutrophils through the expansion of γδ T cell populations that produced interleukin 17 (IL-17). While BRP-39 did not influence neutrophilia, it was required for IL-17 production in γδ T cells, which suggested that regulation of IL-17 is an inherent feature of mouse CLPs. Analysis of a nematode infection model, in which the parasite migrates through the lungs, revealed that the IL-17 and neutrophilic inflammation induced by Ym1 limited parasite survival but at the cost of enhanced lung injury. Our studies describe effector functions of CLPs consistent with innate host defense traits of the chitinase family.

Exogenous normal lymph alleviates lipopolysaccharide-induced acute lung injury through lessening the adhesion molecules

PURPOSE

To evaluate the role of exogenous normal lymph (ENL) on lipopolysaccharide (LPS)-induced acute lung injury (ALI) in rats.

METHODS

ALI was induced by the jugular vein injection of LPS (iv, 15 mg/kg) in rats of the LPS and LPS+ENL groups within 15 min, then, ENL without cell components (5 ml/kg) was infused at the speed of 0.5 ml per minute in the LPS+ENL group, the same amount of saline was administered in the LPS group. The rats in the sham group received the same surgical procedure and saline. The histomorphology and the levels of P-selectin, intercellular adhesion molecule-1 (ICAM-1), myeloperoxidase (MPO) in pulmonary tissue were assessed.

RESULTS

LPS induced pulmonary injury as well as increased the wet/dry weight ratio (W/D) and the levels of P-selectin, ICAM-1, and MPO in pulmonary tissues. These deleterious effects of LPS were significantly ameliorated by ENL treatment.

CONCLUSION

Exogenous normal lymph could markedly alleviate the acute lung injury induced by lipopolysaccharide, and its effects might be related to lessening the adhesion molecules.

Wogonin prevents lipopolysaccharide-induced acute lung injury and inflammation in mice via peroxisome proliferator-activated receptor gamma-mediated attenuation of the nuclear factor-kappaB pathway

Acute lung injury (ALI) from a variety of clinical disorders, characterized by diffuse inflammation, is a cause of acute respiratory failure that develops in patients of all ages. Previous studies reported that wogonin, a flavonoid-like chemical compound which was found in Scutellaria baicalensis, has anti-inflammatory effects in several inflammation models, but not in ALI. Here, the in vivo protective effect of wogonin in the amelioration of lipopolysaccharide (LPS) -induced lung injury and inflammation was assessed. In addition, the in vitro effects and mechanisms of wogonin were studied in the mouse macrophage cell lines Ana-1 and RAW264.7. In vivo results indicated that wogonin attenuated LPS-induced histological alterations. Peripheral blood leucocytes decreased in the LPS-induced group, which was ameliorated by wogonin. In addition, wogonin inhibited the production of several inflammatory cytokines, including tumour necrosis factor-α, interleukin-1β (IL-1β) and IL-6, in the bronchoalveolar lavage fluid and lung tissues after LPS challenge, while the peroxisome proliferator-activated receptor γ (PPARγ) inhibitor GW9662 reversed these effects. In vitro results indicated that wogonin significantly decreased the secretion of IL-6, IL-1β and tumour necrosis factor-α in Ana-1 and RAW264.7 cells, which was suppressed by transfection of PPARγ small interfering RNA and GW9662 treatment. Moreover, wogonin activated PPARγ, induced PPARγ-mediated attenuation of the nuclear translocation and the DNA-binding activity of nuclear factor-κB in vivo and in vitro. In conclusion, all of these results showed that wogonin may serve as a promising agent for the attenuation of ALI-associated inflammation and pathology by regulating the PPARγ-involved nuclear factor-κB pathway.

In vivo depletion of CD206+ M2 macrophages exaggerates lung injury in endotoxemic mice

Although phenotypically polarized macrophages are now generally classified into two major subtypes termed proinflammatory M1 and anti-inflammatory M2 macrophages, a contributory role of lung M2 macrophages in the pathophysiological features of acute lung injury is not fully understood. Herein, we show in an endotoxemic murine model that M2 macrophages serve as key anti-inflammatory cells that play a regulatory role in the severity of lung injury. To study whether M2 macrophages can modify inflammation, we depleted M2 macrophages from lungs of CD206-diphtheria toxin (DT) receptor transgenic (Tg) mice during challenge with lipopolysaccharide. The i.p. administration of DT depleted CD206-positive cells in bronchoalveolar lavage fluid. The use of M2 macrophage markers Ym1 and arginase-1 identified pulmonary CD206-positive cells as M2 macrophages. A striking increase in neutrophils in bronchoalveolar lavage fluid cell contents was found in DT-treated CD206-DT receptor Tg mice. In CD206-DT receptor Tg mice given DT, endotoxin challenge exaggerated lung inflammation, including up-regulation of proinflammatory cytokines and increased histological lung damage, but the endotoxemia-induced increase in NF-κB activity was significantly reduced, suggesting that M2 phenotype-dependent counteraction of inflammatory insult cannot be attributed to the inhibition of the NF-κB pathway. Our results indicate a critical role of CD206-positive pulmonary macrophages in triggering inflammatory cascade during endotoxemic lung inflammation.

Myeloid ZFP36L1 does not regulate inflammation or host defense in mouse models of acute bacterial infection

Zinc finger protein 36, C3H type-like 1 (ZFP36L1) is one of several Zinc Finger Protein 36 (Zfp36) family members, which bind AU rich elements within 3' untranslated regions (UTRs) to negatively regulate the post-transcriptional expression of targeted mRNAs. The prototypical member of the family, Tristetraprolin (TTP or ZFP36), has been well-studied in the context of inflammation and plays an important role in repressing pro-inflammatory transcripts such as TNF-α. Much less is known about the other family members, and none have been studied in the context of infection. Using macrophage cell lines and primary alveolar macrophages we demonstrated that, like ZFP36, ZFP36L1 is prominently induced by infection. To test our hypothesis that macrophage production of ZFP36L1 is necessary for regulation of the inflammatory response of the lung during pneumonia, we generated mice with a myeloid-specific deficiency of ZFP36L1. Surprisingly, we found that myeloid deficiency of ZFP36L1 did not result in alteration of lung cytokine production after infection, altered clearance of bacteria, or increased inflammatory lung injury. Although alveolar macrophages are critical components of the innate defense against respiratory pathogens, we concluded that myeloid ZFP36L1 is not essential for appropriate responses to bacteria in the lungs. Based on studies conducted with myeloid-deficient ZFP36 mice, our data indicate that, of the Zfp36 family, ZFP36 is the predominant negative regulator of cytokine expression in macrophages. In conclusion, these results imply that myeloid ZFP36 may fully compensate for loss of ZFP36L1 or that Zfp36l1-dependent mRNA expression does not play an integral role in the host defense against bacterial pneumonia.

Proinflammatory role of neutrophil extracellular traps in abdominal sepsis

Excessive neutrophil activation is a major component in septic lung injury. Neutrophil-derived DNA may form extracellular traps in response to bacterial invasions. The aim of the present study was to investigate the potential role of neutrophil extracellular traps (NETs) in septic lung injury. Male C57BL/6 mice were treated with recombinant human (rh)DNAse (5 mg/kg) after cecal ligation and puncture (CLP). Extracellular DNA was stained by Sytox green, and NET formation was quantified by confocal microscopy and cell-free DNA in plasma, peritoneal cavity, and lung. Blood, peritoneal fluid, and lung tissue were harvested for analysis of neutrophil infiltration, NET levels, tissue injury, as well as CXC chemokine and cytokine formation. We observed that CLP caused increased formation of NETs in plasma, peritoneal cavity, and lung. Administration of rhDNAse not only eliminated NET formation in plasma, peritoneal cavity, and bronchoalveolar space but also reduced lung edema and tissue damage 24 h after CLP induction. Moreover, treatment with rhDNAse decreased CLP-induced formation of CXC chemokines, IL-6, and high-mobility group box 1 (HMGB1) in plasma, as well as CXC chemokines and IL-6 in the lung. In vitro, we found that neutrophil-derived NETs had the capacity to stimulate secretion of CXCL2, TNF-α, and HMGB1 from alveolar macrophages. Taken together, our findings show that NETs regulate pulmonary infiltration of neutrophils and tissue injury via formation of proinflammatory compounds in abdominal sepsis. Thus we conclude that NETs exert a proinflammatory role in septic lung injury.

Tissue-protective effects of NKG2A in immune-mediated clearance of virus infection

Virus infection triggers a CD8⁺ T cell response that aids in virus clearance, but also expresses effector functions that may result in tissue injury. CD8⁺ T cells express a variety of activating and inhibiting ligands, though regulation of the expression of inhibitory receptors is not well understood. The ligand for the inhibitory receptor, NKG2A, is the non-classical MHC-I molecule Qa1^b, which may also serve as a putative restricting element for the T cell receptors of purported regulatory CD8⁺ T cells. We have previously shown that Qa1^b-null mice suffer considerably enhanced immunopathologic lung injury in the context of CD8⁺ T cell-mediated clearance of influenza infection, as well as evidence in a non-viral system that failure to ligate NKG2A on CD8⁺ effector T cells may represent an important component of this process. In this report, we examine the requirements for induction of NKG2A expression, and show that NKG2A expression by CD8⁺ T cells occurs as a result of migration from the MLN to the inflammatory lung environment, irrespective of peripheral antigen recognition. Further, we confirmed that NKG2A is a mediator in limiting immunopathology in virus infection using mice with a targeted deletion of NKG2A, and infecting the mutants with two different viruses, influenza and adenovirus. In neither infection is virus clearance altered. In influenza infection, the enhanced lung injury was associated with increased chemoattractant production, increased infiltration of inflammatory cells, and significantly enhanced alveolar hemorrhage. The primary mechanism of enhanced injury was the loss of negative regulation of CD8⁺ T cell effector function. A similar effect was observed in the livers of mutant mice infected intravenously with adenovirus. These results demonstrate the immunoregulatory role of CD8⁺ NKG2A expression in virus infection, which negatively regulates T cell effector functions and contributes to protection of tissue integrity during virus clearance.

Ulinastatin prevents acute lung injury led by liver transplantation

BACKGROUND

Little is known regarding the effect of ulinastatin (UTI) on acute lung injury (ALI) induced by orthotopic liver transplantation. This study aims to investigate the protective effect of UTI on ALI induced by orthotopic autologous liver transplantation (OALT) in a rat model and to explore the potential underlying mechanism.

MATERIALS AND METHODS

Rats were randomly allocated into the following four groups (n = 8 each): (i) sham control group (group sham); (ii) model group (underwent OALT) (group model); (iii) low-dose UTI-treated group (group u1), with UTI (50 U/g) administered intravenously both before the portal vein was occluded and after liver reperfusion started; and (iv) high-dose UTI-treated group (group uh), with UTI (100 U/g) given in the same way as group ul. The lung pathologic parameters, lung water content, and levels of tumor necrosis factor (TNF)-α, interleukin (IL)-1β, IL-6, malondialdehyde (MDA), superoxide dismutase (SOD) activity, RanBP-type and C3HC4-type zinc finger-containing protein 1 (RBCK1), and peroxiredoxin-2 (Prx-2) were assessed 8 h after OALT was performed.

RESULTS

According to histology, there was severe damage in the lung of group model accompanied by increases in the TNF-α, IL-1β, IL-6, and MDA levels and decreases in SOD activity and the expression of RBCK1 and Prx-2. UTI treatment significantly reduced the pathologic scores, lung water content, and TNF-α, IL-1β, IL-6, and MDA levels while restoring the SOD activity and expression of RBCK1 and Prx-2. Furthermore, compared with group u1, treatment with a high dose of UTI resulted in a better protective effect on the lung when assessed by the TNF-α, IL-1β, IL-6, and MDA levels and SOD activity.

CONCLUSIONS

UTI dose-dependently attenuates ALI that is induced by OALT in this rat model, which is mainly due to the suppression of the inflammatory response and oxidant stress, which may, in turn, be mediated by the upregulation of RBCK1 and Prx-2 expression.

Xuebijing injection improves the respiratory function in rabbits with oleic acid-induced acute lung injury by inhibiting IL-6 expression and promoting IL-10 expression at the protein and mRNA levels

Xuebijing injection is a complex herbal medicine, and clinical and experimental studies have shown that it has a significant effect on acute respiratory distress syndrome and multiple organ dysfunction syndrome. However, the majority of studies regarding Xuebijing injection have focused on serum inflammatory factors, and few studies have been carried out from the perspective of the protein and mRNA expression of inflammatory cytokines. In this study, 60 healthy rabbits of mixed gender were randomly assigned to a normal control group (CG), oleic acid group (model group; MG) and oleic acid + Xuebijing injection group (treatment group; TG). Rabbits of the CG were treated with normal saline through the ear vein, rabbits of the MG were injected with oleic acid (0.4 ml/kg) and rabbits of the TG received 0.4 ml/kg oleic acid + 10 ml/kg Xuebijing injection. Blood samples were collected from the common carotid artery of all rabbits of all groups 1 h after the ear vein was injected with the corresponding reagent, and was used to measure the arterial partial pressure of oxygen (PaO₂) and of carbon dioxide (PaCO₂). The activity of myeloperoxidase (MPO) was tested, and the protein and mRNA expression levels of interleukin (IL)-6 and IL-10 were determined. Rabbits of the MG exhibited evident respiratory dysfunction (PaO₂ and PaCO₂ were low), histopathological lung damage and overactive inflammatory responses (the expression of the proinflammatory cytokine IL-6 and the anti-inflammatory cytokine IL-10 was increased at the protein and mRNA levels). Following the administration of the Xuebijing injection, the inflammatory response of the rabbits was significantly reduced. Xuebijing injection raised PaO₂ and PaCO₂, weakened the activity of MPO in the lung tissue, downregulated the expression of the proinflammatory cytokine IL-6 and further increased the expression of the anti-inflammatory cytokine IL-10. These results demonstrated that Xuebijing injection improved the respiratory function of rabbits with acute oleic acid-induced lung injury by inhibiting IL-6 expression and promoting IL-10 expression.

Neutrophil elastase causes tissue damage that decreases host tolerance to lung infection with burkholderia species

Two distinct defense strategies can protect the host from infection: resistance is the ability to destroy the infectious agent, and tolerance is the ability to withstand infection by minimizing the negative impact it has on the host's health without directly affecting pathogen burden. Burkholderia pseudomallei is a Gram-negative bacterium that infects macrophages and causes melioidosis. We have recently shown that inflammasome-triggered pyroptosis and IL-18 are equally important for resistance to B. pseudomallei, whereas IL-1β is deleterious. Here we show that the detrimental role of IL-1β during infection with B. pseudomallei (and closely related B. thailandensis) is due to excessive recruitment of neutrophils to the lung and consequent tissue damage. Mice deficient in the potentially damaging enzyme neutrophil elastase were less susceptible than the wild type C57BL/6J mice to infection, although the bacterial burdens in organs and the extent of inflammation were comparable between C57BL/6J and elastase-deficient mice. In contrast, lung tissue damage and vascular leakage were drastically reduced in elastase-deficient mice compared to controls. Bradykinin levels were higher in C57BL/6 than in elastase-deficient mice; administration of a bradykinin antagonist protected mice from infection, suggesting that increased vascular permeability mediated by bradykinin is one of the mechanisms through which elastase decreases host tolerance to melioidosis. Collectively, these results demonstrate that absence of neutrophil elastase increases host tolerance, rather than resistance, to infection by minimizing host tissue damage.

Analysis of leucocyte antibodies, cytokines, lysophospholipids and cell microparticles in blood components implicated in post-transfusion reactions with dyspnoea

BACKGROUND AND OBJECTIVES

Post-transfusion reactions with dyspnoea (PTR) are major causes of morbidity and death after blood transfusion. Transfusion-related acute lung injury (TRALI) and transfusion-associated circulatory overload (TACO) are most dangerous, while transfusion-associated dyspnoea (TAD) is a milder respiratory distress. We investigated blood components for immune and non-immune factors implicated in PTR.

MATERIAL AND METHODS

We analysed 464 blood components (RBCs, PLTs, L-PLTs, FFP) transfused to 271 patients with PTR. Blood components were evaluated for 1/antileucocyte antibodies, 2/cytokines: IL-1β, IL-6, IL-8, TNF-α, sCD40L, 3/lysophosphatidylcholines (LysoPCs), 4/microparticles (MPs) shed from plateletes (PMPs), erythrocytes (EMPs) and leucocytes (LMPs).

RESULTS

Anti-HLA class I/II antibodies or granulocyte-reactive anti-HLA antibodies were detected in 18.2% of blood components (RBC and FFP) transfused to TRALI and in 0.5% of FFP transfused to TAD cases. Cytokines and LysoPCs concentrations in blood components transfused to PTR patients did not exceed those in blood components transfused to patients with no PTR. Only EMPs percentage in RBCs transfused to patients with TRALI was significantly higher (P < 0.05) than in RBCs transfused to patients with no PTR.

CONCLUSION

Immune character of PTR was confirmed mainly in 1/5 TRALI cases. Among non-immune factors, only MPs released from stored RBCs are suggested as potential mediators of TRALI. Our results require further observations in a more numerous and better defined group of patients.

Mechanical ventilation-associated lung fibrosis in acute respiratory distress syndrome: a significant contributor to poor outcome

One of the most challenging problems in critical care medicine is the management of patients with the acute respiratory distress syndrome. Increasing evidence from experimental and clinical studies suggests that mechanical ventilation, which is necessary for life support in patients with acute respiratory distress syndrome, can cause lung fibrosis, which may significantly contribute to morbidity and mortality. The role of mechanical stress as an inciting factor for lung fibrosis versus its role in lung homeostasis and the restoration of normal pulmonary parenchymal architecture is poorly understood. In this review, the authors explore recent advances in the field of pulmonary fibrosis in the context of acute respiratory distress syndrome, concentrating on its relevance to the practice of mechanical ventilation, as commonly applied by anesthetists and intensivists. The authors focus the discussion on the thesis that mechanical ventilation-or more specifically, that ventilator-induced lung injury-may be a major contributor to lung fibrosis. The authors critically appraise possible mechanisms underlying the mechanical stress-induced lung fibrosis and highlight potential therapeutic strategies to mitigate this fibrosis.

The small GTPase Rap1b negatively regulates neutrophil chemotaxis and transcellular diapedesis by inhibiting Akt activation

Mice lacking the small GTPase Rap1b exhibit enhanced neutrophil recruitment to inflamed lungs and susceptibility to endotoxin shock via enhance PI3K-Akt activation.

Neutrophils are the first line of cellular defense in response to infections and inflammatory injuries. However, neutrophil activation and accumulation into tissues trigger tissue damage due to release of a plethora of toxic oxidants and proteases, a cause of acute lung injury (ALI). Despite its clinical importance, the molecular regulation of neutrophil migration is poorly understood. The small GTPase Rap1b is generally viewed as a positive regulator of immune cell functions by controlling bidirectional integrin signaling. However, we found that Rap1b-deficient mice exhibited enhanced neutrophil recruitment to inflamed lungs and enhanced susceptibility to endotoxin shock. Unexpectedly, Rap1b deficiency promoted the transcellular route of diapedesis through endothelial cell. Increased transcellular migration of Rap1b-deficient neutrophils in vitro was selectively mediated by enhanced PI3K-Akt activation and invadopodia-like protrusions. Akt inhibition in vivo suppressed excessive Rap1b-deficient neutrophil migration and associated endotoxin shock. The inhibitory action of Rap1b on PI3K signaling may be mediated by activation of phosphatase SHP-1. Thus, this study reveals an unexpected role for Rap1b as a key suppressor of neutrophil migration and lung inflammation.

An epithelial circadian clock controls pulmonary inflammation and glucocorticoid action

The circadian system is an important regulator of immune function. Human inflammatory lung diseases frequently show time-of-day variation in symptom severity and lung function, but the mechanisms and cell types underlying these effects remain unclear. We show that pulmonary antibacterial responses are modulated by a circadian clock within epithelial club (Clara) cells. These drive circadian neutrophil recruitment to the lung via the chemokine CXCL5. Genetic ablation of the clock gene Bmal1 (also called Arntl or MOP3) in bronchiolar cells disrupts rhythmic Cxcl5 expression, resulting in exaggerated inflammatory responses to lipopolysaccharide and an impaired host response to Streptococcus pneumoniae infection. Adrenalectomy blocks rhythmic inflammatory responses and the circadian regulation of CXCL5, suggesting a key role for the adrenal axis in driving CXCL5 expression and pulmonary neutrophil recruitment. Glucocorticoid receptor occupancy at the Cxcl5 locus shows circadian oscillations, but this is disrupted in mice with bronchiole-specific ablation of Bmal1, leading to enhanced CXCL5 expression despite normal corticosteroid secretion. The therapeutic effects of the synthetic glucocorticoid dexamethasone depend on intact clock function in the airway. We now define a regulatory mechanism that links the circadian clock and glucocorticoid hormones to control both time-of-day variation and the magnitude of pulmonary inflammation and responses to bacterial infection.

Silencing Bruton's tyrosine kinase in alveolar neutrophils protects mice from LPS/immune complex-induced acute lung injury

Previous observations made by our laboratory indicate that Bruton's tyrosine kinase (Btk) may play an important role in the pathophysiology of local inflammation in acute lung injury (ALI)/acute respiratory distress syndrome (ARDS). We have shown that there is cross talk between FcγRIIa and TLR4 in alveolar neutrophils from patients with ALI/ARDS and that Btk mediates the molecular cooperation between these two receptors. To study the function of Btk in vivo we have developed a unique two-hit model of ALI: LPS/immune complex (IC)-induced ALI. Furthermore, we conjugated F(ab)2 fragments of anti-neutrophil antibodies (Ly6G1A8) with specific siRNA for Btk to silence Btk specifically in alveolar neutrophils. It should be stressed that we are the first group to perform noninvasive transfections of neutrophils, both in vitro and in vivo. Importantly, our present findings indicate that silencing Btk in alveolar neutrophils has a dramatic protective effect in mice with LPS/IC-induced ALI, and that Btk regulates neutrophil survival and clearance of apoptotic neutrophils in this model. In conclusion, we put forward a hypothesis that Btk-targeted neutrophil specific therapy is a valid goal of research geared toward restoring homeostasis in lungs of patients with ALI/ARDS.

Active players in resolution of shock/sepsis induced indirect lung injury: immunomodulatory effects of Tregs and PD-1

The immunomodulatory effects of PD-1 and CD4(+)CD25(+) Tregs in the resolution of ALI are still poorly understood. Accordingly, 1 million Tregs were isolated from spleens of WT C57BL/6 or PD-1(-/-) mice (magnetical bead purification and subsequent labeling with/without Vybrant dye) and then AT into mice subjected to Hem shock during their resuscitation period, which were subsequently subjected to CLP/septic challenge (24 h post-Hem) to induce iALI. Initially, we demonstrated that Vybrant-labeled AT Tregs appear in the lungs of iALI mice. Subsequently, we found that AT of WT Tregs induced a significant repression of the indices of lung injury: a reduction of neutrophil influx to the lung tissue and a decrease of lung apoptosis compared with vehicle-treated iALI mice. In addition, these mice had substantially higher concentrations of BALF and lung-tissue IL-10 but significantly decreased levels of lung KC. However, these beneficial effects of the AT of Tregs were lost with the administration of PD-1(-/-) mouse Tregs to the recipient WT mice. ALI was exacerbated in these recipient mice receiving AT PD-1(-/-) Tregs to the same extent as iALI mice that did not receive Tregs. These data imply that Tregs can act directly to modify the innate immune response induced by experimental iALI, and this is mediated, in part, by PD-1. Hence, the manipulation of Tregs may represent a plausible target for treating iALI.

MicroRNA and mRNA expression profiling in rat acute respiratory distress syndrome

Background

Acute respiratory distress syndrome (ARDS) is characterized by pulmonary epithelial injury and extensive inflammation of the pulmonary parenchyma. Systematic analyses of microRNA (miRNA) and mRNA expression profiling in ARDS provide insights into understanding of molecular mechanisms of the pathogenesis of ARDS. The objective of this study was to identify miRNA and mRNA interactions in a rat model of ARDS by combining miRNA and mRNA microarray analyses.

Methods

Rat model of ARDS was induced by saline lavage and mechanical ventilation. The expression profiles of both mRNAs and miRNAs in rat ARDS model were performed by microarray analyses. Microarray data were further verified by quantitative RT-PCR. Functional annotation on dys-regulated mRNAs and miRNAs was carried out by bioinformatics analysis.

Results

The expression of 27 miRNAs and 37 mRNAs were found to be significantly changed. The selected miRNAs and genes were further verified by quantitative real-time PCR. The down-regulated miRNAs included miR-24, miR-26a, miR-126, and Let-7a, b, c, f. The up-regulated miRNAs were composed of miR-344, miR-346, miR-99a, miR-127, miR-128b, miR-135b, and miR-30a/b. Gene ontology and functional annotation analyses indicated that up-regulated mRNAs, such as Apc, Timp1, and Sod2, were involved in the regulation of apoptosis. Bioinformatics analysis showed the inverse correlation of altered miRNAs with the expression of their predicted target mRNAs. While Sod2 was inversely correlated with Let-7a, b, c, f., Ebf1 and Apc were inversely correlated with miR-24 and miR-26a, respectively. miR-26a, miR-346, miR-135b, miR-30a/b, miR-344, and miR-18a targeted multiple altered mRNAs. Gabrb1, Sod2, Eif2ak1, Fbln5, and Tspan8 were targeted by multiple altered miRNAs.

Conclusion

The expressions of miRNAs and mRNAs were altered in a rat model of ARDS. The identified miRNA-mRNA pairs may play critical roles in the pathogenesis of ARDS.

Protective effect of Ginkgo biloba leaves extract, EGb761, on endotoxin-induced acute lung injury via a JNK- and Akt-dependent NFκB pathway

Acute lung injury (ALI) is a clinical syndrome mainly caused by Gram-negative bacteria which is still in need of an effective therapeutic medicine. EGb761, an extract of Ginkgo biloba leaves, has several bioeffects including anti-inflammation, cardioprotection, neuroprotection, and free radical scavenging. Preadministration of EGb761 inhibited lipopolysaccharide (LPS)-induced histopathological changes and exchange of arterial blood gas. In addition, LPS-induced expression of proinflammatory mediators, such as tumor necrosis factor (TNF)-α, interleukin (IL)-6, macrophage inflammatory protein (MIP)-2, inducible nitric oxide synthase (iNOS), and cyclooxygenase-2 (COX-2), were suppressed by EGb761. The activation of nuclear factor (NF)κB, a transcription factor of proinflammatory mediators, and phosphorylation of IκB, an inhibitor of NFκB, were also reduced by EGb761. Furthermore, we found the inhibitory concentration of EGb761 on phosphorylation of JNK and Akt was less than those of ERK and p38 MAPK. In conclusion, EGb761 is a potential protective agent for ALI, possibly via downregulating the JNK- and Akt-dependent NFκB activation pathway.

Transmigrated neutrophils in the intestinal lumen engage ICAM-1 to regulate the epithelial barrier and neutrophil recruitment

Neutrophil (PMN) transepithelial migration (TEM) and accumulation in luminal spaces is a hallmark of mucosal inflammation. TEM has been extensively modeled; however, the functional consequences and molecular basis of PMN interactions with luminal epithelial ligands are not clear. Here we report that cytokine-induced expression of a PMN ligand, intercellular adhesion molecule-1 (ICAM-1), exclusively on the luminal (apical) membrane of the intestinal epithelium results in accumulation and enhanced motility of transmigrated PMN on the apical epithelial surface. Using complementary in-vitro and in-vivo approaches, we demonstrate that ligation of epithelial ICAM-1 by PMN or with specific antibodies results in myosin light-chain kinase-dependent increases in epithelial permeability that are associated with enhanced PMN TEM. Effects of ICAM-1 ligation on epithelial permeability and PMN migration in vivo were blocked after intraluminal addition of peptides derived from the cytoplasmic domain of ICAM-1. These findings provide new evidence for functional interactions between PMN and epithelial cells after migration into the intestinal lumen. Although such interactions may aid in clearance of invading microorganisms by promoting PMN recruitment, engagement of ICAM-1 under pathologic conditions would increase accumulation of epithelial-associated PMN, thus contributing to mucosal injury as observed in conditions, including ulcerative colitis.

Expression of retinoid receptors in lungs of cattle, dogs, and pigs

Retinoids play an important role in lung development and immune response. The effects of retinoids are mediated through 2 families of retinoid receptors: retinoic acid receptors (RARs) and retinoid X receptors (RXRs), with alpha (α), beta (β), and gamma (γ) subtypes in each family. To date, no data exist on the expression pattern of retinoid receptors in lungs of cattle, dogs, and pigs. Because of the biomedical importance of retinoid receptors in inflammation and immune responses, Western blot, immunohistology, and immunoelectron microscopy were used to determine the expression of retinoid receptors in normal lungs of cattle, dogs, and pigs (n = 2 for each species). Western blot showed expression of all 6 retinoid receptor subtypes in pig lungs. Immunohistology data indicated differential expression of retinoid receptors in airway epithelium, vascular endothelium, alveolar/septal macrophages, and alveolar septum in all 3 species. Electron microscopy showed nuclear localization of retinoid receptors in neutrophils and pulmonary intravascular macrophages. Retinoic acid receptors (RAR) α subtype were localized in cytoplasmic vacuoles of pig monocytes. These data indicate constitutive expression of retinoid receptors in the lungs of cattle, dogs, and pigs.

Effect of Aronia melanocarpa fruit juice on amiodarone-induced pneumotoxicity in rats

Background:

The fruits of Aronia melanocarpa (Michx.) Elliot is extremely rich in biologically active polyphenols.

Objective:

We studied the protective effect of A. melanocarpa fruit juice (AMFJ) in a model of amiodarone (AD)-induced pneumotoxicity in rats.

Materials and Methods:

AD was instilled intratracheally on days 0 and 2 (6.25 mg/kg). AMFJ (5 mL/kg and 10 mL/kg) was given orally from day 1 to days 2, 4, 9, and 10 to rats, which were sacrificed respectively on days 3, 5, 10, and 28 when biochemical, cytological, and immunological assays were performed.

Results:

AMFJ antagonized AD-induced increase of the lung weight coefficient. In bronchoalveolar lavage fluid, AD increased significantly the protein content, total cell count, polymorphonuclear cells, lymphocytes and the activity of lactate dehydrogenase, acid phosphatase and alkaline phosphatase on days 3 and 5. In AMFJ-treated rats these indices of direct toxic damage did not differ significantly from the control values. In lung tissue, AD induced oxidative stress measured by malondialdehyde content and fibrosis assessed by the hydroxyproline level. AMFJ prevented these effects of AD. In rat serum, AD caused a significant elevation of interleukin IL-6 on days 3 and 5, and a decrease of IL-10 on day 3. In AMFJ-treated rats, these indices of inflammation had values that did not differ significantly from the control ones.

Conclusion:

AMFJ could have a protective effect against AD-induced pulmonary toxicity as evidenced by the reduced signs of AD-induced direct toxic damage, oxidative stress, inflammation, and fibrosis.

Protective effect of quercetin on lipopolysaccharide-induced acute lung injury in mice by inhibiting inflammatory cell influx

Sepsis may result in lung injury through a complex cascade of events including interstitium infiltration of inflammatory cells. Quercetin, the most abundant dietary flavonoid found in various plants and food products, possesses potent anti-inflammatory and antioxidative properties. The purpose of this study was to investigate whether preventive administration of quercetin could exert beneficial effects on experimental septic acute lung injury induced by lipopolysaccharide (LPS). C57/BL6 mice were challenged with LPS and survival time was monitored from 0–96 h after LPS treatment. Quercetin markedly rescued lethality, improved survival time, and inhibited serum necrosis factor α, interleukin 1β, and interleukin 6, and nitric oxide (NO), and increased IL-10 secretion. Moreover, quercetin decreased lung pathological changes, myeloperoxidase activity, and malondialdehyde levels. Quercetin also reduced the lung permeability changes and neutrophil and macrophage recruitment to the bronchoalveolar lavage fluid compared to the vehicle. Additionally, quercetin significantly reduced COX-2, HMGB1, iNOS expression, and NF-κB p65 phosphorylation. These results suggest that treatment with quercetin in septic mice improved survival time and lung injury. Quercetin may be a promising potential therapeutic reagent for LPS-induced acute lung injury.

Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) prevents lipopolysaccharide (LPS)-induced, sepsis-related severe acute lung injury in mice

Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) is an energy metabolism-related enzyme in the glycolytic pathway. Recently, it has been reported that GAPDH has other physiological functions, such as apoptosis, DNA repair and autophagy. Some in vitro studies have indicated immunological aspects of GAPDH function, although there is no definite study discussing the advantage of GAPDH as a therapeutic target. Here, we show that GAPDH has an anti-inflammatory function by using a lipopolysaccharide (LPS)-induced, sepsis-related severe acute lung injury (ALI) mouse model, which is referred to as acute respiratory distress syndrome (ARDS) in humans. GAPDH pre-injected mice were protected from septic death, and their serum levels of proinflammatory cytokines were significantly suppressed. In lung tissue, LPS-induced acute injury and neutrophil accumulation were strongly inhibited by GAPDH pre-injection. Pulmonary, proinflammatory cytokine gene expression and serum chemokine expression in GAPDH pre-injected mice were also reduced. These data suggest the therapeutic potential of GAPDH for sepsis-related ALI/ARDS.

Growth arrest-specific protein 6 attenuates neutrophil migration and acute lung injury in sepsis

Sepsis is an acute inflammatory condition that can result in multiple organ failure and acute lung injury. Growth arrest-specific protein 6 (Gas6) is a broad regulator of the innate immune response involved with the nuclear factor κB signaling pathway. We hypothesized that Gas6 could have a protective role in attenuating the severity of acute lung injury and sepsis. Male mice were subjected to sepsis by cecal ligation and puncture (CLP) after which recombinant murine Gas6 (rmGas6; 5 μg/mouse) or normal saline (vehicle) was administered intravenously. Blood and lung tissues were collected at 20 h after CLP for various measurements. Treatment with rmGas6 significantly reduced serum levels of the injury markers aspartate aminotransferase, alanine aminotransferase, and lactate dehydrogenase, as well as proinflammatory cytokines interleukin 6 (IL-6) and IL-17, compared with the vehicle group (P < 0.05). The parenchyma of the lungs damaged by CLP was attenuated by rmGas6 treatment. Lung mRNA levels of tumor necrosis factor α, IL-1β, IL-6, IL-17, and macrophage inflammatory protein 2 (MIP-2) were decreased by 60%, 86%, 82%, 93%, and 82%, respectively, with rmGas6 treatment as determined by real-time reverse transcriptase-polymerase chain reaction (P < 0.05). The degradation of IκB-α induced by CLP in the lungs was inhibited by rmGas6 treatment. The number of neutrophils and myeloperoxidase activity in the lungs were significantly reduced in the rmGas6 group. Moreover, rmGas6 reduced the in vitro migration of differentiated human promyelocytic HL60 cells by 64%. Finally, the 10-day survival rate of mice subjected to CLP was increased from 31% in the vehicle group to 67% in the rmGas6 group (P < 0.05). Thus, Gas6 has potential to be developed as a novel therapeutic agent to treat patients with sepsis and acute lung injury.

Siglec-E promotes β2-integrin-dependent NADPH oxidase activation to suppress neutrophil recruitment to the lung

Siglec-E is a sialic acid-binding Ig-like lectin expressed on murine myeloid cells. It has recently been shown to function as a negative regulator of β2-integrin-dependent neutrophil recruitment to the lung following exposure to lipopolysaccharide (LPS). Here, we demonstrate that siglec-E promoted neutrophil production of reactive oxygen species (ROS) following CD11b β2-integrin ligation with fibrinogen in a sialic acid-dependent manner, but it had no effect on ROS triggered by a variety of other stimulants. Siglec-E promotion of ROS was likely mediated via Akt activation, because siglec-E-deficient neutrophils plated on fibrinogen exhibited reduced phosphorylation of Akt, and the Akt inhibitor, MK2206, blocked fibrinogen-induced ROS. In vivo imaging showed that siglec-E also promoted ROS in acutely inflamed lungs following exposure of mice to LPS. Importantly, siglec-E-promoted ROS were required for its inhibitory function, as the NADPH oxidase inhibitor, apocynin, reversed the siglec-E-mediated suppression of neutrophil recruitment and blocked neutrophil ROS production in vitro. Taken together, these results demonstrate that siglec-E functions as an inhibitory receptor of neutrophils via positive regulation of NADPH oxidase activation and ROS production. Our findings have implications for the inhibitory role of siglec-9 on human neutrophils in sepsis and acute lung injury.

Prevention of lung injury in cardiac surgery: a review

Inflammatory lung injury is an inevitable consequence of cardiac surgery with cardiopulmonary bypass. The lungs are particularly susceptible to the effects of the systemic inflammatory response to cardiopulmonary bypass. This insult is further exacerbated by a pulmonary ischemia-reperfusion injury after termination of bypass. Older patients and those with pre-existing lung disease will clearly be less tolerant of any lung injury and more likely to develop respiratory failure in the postoperative period. A requirement for prolonged ventilation has implications for morbidity, mortality, and cost of treatment. This review contains a summary of recent interventions and changes of practice that may reduce inflammatory lung injury after cardiac surgery. The review also focuses on a number of general aspects of perioperative management, which may exacerbate such injury, if performed poorly.

Reduced levels of interleukin‑1 receptor antagonist act as a marker for pneumonia in the elderly

Pneumonia is a disease causing serious inflammation and infection of the lungs and accounts for >50,000 mortalities annually. The elderly are at an increased risk of developing pneumonia. Pneumonia is more serious in the elderly than in any other age group due to the increased inflammation and risk of community‑acquired pneumonia associated with aging. Interleukin‑1 receptor antagonist (IL‑1RA) is an anti‑inflammatory protein that counteracts the destructive effects of inflammatory proteins. Therefore, the possible association between pneumonia in elderly individuals and reduced levels of IL‑1RA was investigated in the present study. The number of lymphocytes was counted in all subjects and the relative protein expression levels of IL‑1RA were determined using western blot analysis. In addition, the immunological activities of IL‑1RA were measured using ELISA. The results demonstrated that the numbers of lymphocytes in the serum and bronchoalveolar lavage fluid (BALF) were significantly higher in elderly patients than those in young patients. Furthermore, the serum and BALF levels of IL‑1RA in elderly patients were significantly lower than those in young patients (P<0.05 and P<0.01, respectively). Therefore, reduced levels of IL‑1RA in BALF may act as a marker for pneumonia in the elderly and may be a potential adjuvant for the diagnosis of pneumonia in elderly individuals. The results also showed that smoking was associated with significant reductions in the levels of IL‑1RA in the BALF of elderly patients. The association between smokers and non‑smokers found in this study provides support for the hypothesis that smoking may contribute to the pathogenesis of pneumonia by further reducing IL‑IRA levels in certain elderly patients.

Regulatory mechanism of pyrrolidine dithiocarbamate is mediated by nuclear factor-κB and inhibits neutrophil accumulation in ARDS mice

The aim of the present study was to investigate the regulatory mechanism of nuclear factor (NF)-κB on polymorphonuclear neutrophil (PMN) accumulation and the inflammatory response in lung tissues with acute respiratory distress syndrome (ARDS), as well as the therapeutic effect of pyrrolidine dithiocarbamate (PDTC). Mouse models of ARDS were established by intraperitoneal injection of lipopolysaccharide (LPS). BALB/c mice were divided into control, LPS and PDTC + LPS groups. The expression of PMN adhesion molecules, CD11b/CD18 and intercellular adhesion molecule-1 (ICAM-1), were detected by immunohistochemistry, while the protein expression levels of NF-κB p65 in the lung tissue were analyzed by western blot analysis. In addition, flow cytometry was used to investigate the apoptosis rate of PMNs in the bronchoalveolar fluid, and the expression levels of interleukin (IL)-1β, IL-8 and tumor necrosis factor (TNF)-α and myeloperoxidase (MPO) activity were also determined. Following an intraperitoneal injection of LPS, alveolar septum rupture, pulmonary interstitial hyperemia and PMN infiltration in the alveolar was observed. The protein expression of p65 in the pulmonary cytoplasm decreased, while the expression of p65 in the nucleus increased. The levels of IL-8, IL-1β and TNF-α increased and the high expression status was maintained for 24 h. As the time increased, CD11b/CD18 and ICAM-1 expression increased, as well as MPO activity, while the apoptosis of PMNs was delayed. Compared with the LPS group, the expression of p65 in the pulmonary cytoplasm and the PMN apoptosis rate increased following PDTC intervention, while the expression of p65 in the nucleus decreased, as well as the expression levels of the cytokines and MPO activity. Therefore, PDTC reduced the production of inflammatory cytokines via the NF-κB pathway, which reduced the activation of PMNs in the lung tissue and promoted PMN apoptosis.

Neutrophil extracellular traps promote differentiation and function of fibroblasts

Neutrophil activation by inflammatory stimuli and the release of extracellular chromatin structures (neutrophil extracellular traps - NETs) have been implicated in inflammatory disorders. Herein, we demonstrate that NETs released by neutrophils treated either with fibrosis-related agents, such as cigarette smoke, magnesium silicate, bleomycin, or with generic NET inducers, such as phorbol 12-myristate 13-acetate, induced activation of lung fibroblasts (LFs) and differentiation into myofibroblast (MF) phenotype. Interestingly, the aforementioned agents or IL-17 (a primary initiator of inflammation/fibrosis) had no direct effect on LF activation and differentiation. MFs treated with NETs demonstrated increased connective tissue growth factor expression, collagen production, and proliferation/migration. These fibrotic effects were significantly decreased after degradation of NETs with DNase1, heparin or myeloperoxidase inhibitor, indicating the key role of NET-derived components in LF differentiation and function. Furthermore, IL-17 was expressed in NETs and promoted the fibrotic activity of differentiated LFs but not their differentiation, suggesting that priming by DNA and histones is essential for IL-17-driven fibrosis. Additionally, autophagy was identified as the orchestrator of NET formation, as shown by inhibition studies using bafilomycin A1 or wortmannin. The above findings were further supported by the detection of NETs in close proximity to alpha-smooth muscle actin (α-SMA)-expressing fibroblasts in biopsies from patients with fibrotic interstitial lung disease or from skin scar tissue. Together, these data suggest that both autophagy and NETs are involved not only in inflammation but also in the ensuing fibrosis and thus may represent potential therapeutic targets in human fibrotic diseases.

TRPV4 inhibition counteracts edema and inflammation and improves pulmonary function and oxygen saturation in chemically induced acute lung injury

The treatment of acute lung injury caused by exposure to reactive chemicals remains challenging because of the lack of mechanism-based therapeutic approaches. Recent studies have shown that transient receptor potential vanilloid 4 (TRPV4), an ion channel expressed in pulmonary tissues, is a crucial mediator of pressure-induced damage associated with ventilator-induced lung injury, heart failure, and infarction. Here, we examined the effects of two novel TRPV4 inhibitors in mice exposed to hydrochloric acid, mimicking acid exposure and acid aspiration injury, and to chlorine gas, a severe chemical threat with frequent exposures in domestic and occupational environments and in transportation accidents. Postexposure treatment with a TRPV4 inhibitor suppressed acid-induced pulmonary inflammation by diminishing neutrophils, macrophages, and associated chemokines and cytokines, while improving tissue pathology. These effects were recapitulated in TRPV4-deficient mice. TRPV4 inhibitors had similar anti-inflammatory effects in chlorine-exposed mice and inhibited vascular leakage, airway hyperreactivity, and increase in elastance, while improving blood oxygen saturation. In both models of lung injury we detected increased concentrations of N-acylamides, a class of endogenous TRP channel agonists. Taken together, we demonstrate that TRPV4 inhibitors are potent and efficacious countermeasures against severe chemical exposures, acting against exaggerated inflammatory responses, and protecting tissue barriers and cardiovascular function.

Serum MMP-8 and TIMP-1 in critically ill patients with acute respiratory failure: TIMP-1 is associated with increased 90-day mortality

BACKGROUND

Matrix metalloproteinases (MMPs) likely have an important role in the pathophysiology of acute lung injury. In a recent study, high matrix metalloproteinases (MMP-8) levels in tracheal aspirates of pediatric acute respiratory distress syndrome (ARDS) patients were associated with worse outcome. In patients with sepsis, an imbalance between MMPs and their tissue inhibitors (TIMPs) has been associated with impaired survival. We hypothesized that the elevated systemic MMP-8 and TIMP-1 are associated with worse outcome in acute respiratory failure.

METHODS

This was a substudy of the observational FINNALI study conducted in 25 Finnish intensive care units over an 8-week period. All patients older than 16 years requiring mechanical ventilation for >6 hours were included. MMP-8 and TIMP-1 levels were analyzed from blood samples taken on enrollment in the study and 48 hours later. Laboratory analyses were performed by using immunofluorometric assay for MMP-8 and ELISA for TIMP-1. MMP-8 and TIMP-1 levels were compared between 90-day survivors and nonsurvivors. Survival was compared in quartiles based on TIMP-1 levels, and ROC analysis was performed to calculate areas under the curves. The relationship between MMP-8 and TIMP-1 levels and degree of hypoxemia was examined.

RESULTS

The final analyses included 563 patients. Admission TIMP-1 levels were higher in nonsurvivors, median 367 ng/mL (interquartile range 199-562), than survivors, median 240 ng/mL (interquartile range 142-412), WMWodds 1.68 (95% confidence interval [CI], 1.43-2.08). MMP-8 levels may have differed between survivors and nonsurvivors, WMWodds 1.20 (95% CI, 1.01-1.43), but no difference was found in the MMP-8/TIMP-1 molar ratio, WMWodds 0.83 (95% CI, 0.67-1.04). Difference in survival between quartiles based on TIMP-1 was significant (log-rank, P < 0.001). ROC analysis produced an area under the curve 0.63 (95% CI, 0.58-0.69) for TIMP-1. TIMP-1 was associated with severity of hypoxemia. TIMP-1 levels were higher in an ARDS subgroup than in the whole cohort, WMWodds 1.65 (95% CI, 1.15-2.44).

CONCLUSIONS

MMP-8 levels were possibly higher in 90-day nonsurvivors but performed poorly in predicting outcome. Increased systemic levels of TIMP-1 were associated with more severe hypoxemia and worse outcome in a large cohort of mechanically ventilated critically ill patients and in a subgroup of ARDS patients.

Combined effects of sivelestat and resveratrol on severe acute pancreatitis-associated lung injury in rats

Despite extensive research and clinical efforts made in the management of acute pancre-atitis during the past few decades, to date no effective cure is available and the mortality from severe acute pancre-atitis remains high. Given that lung is the primary cause of early death in acute pancreatitis patients, novel therapeutic approaches aiming to prevent lung injury have become a subject of intensive investigation. In a previous study, we demonstrated that sivelestat, a specific inhibitor of neutrophil elastase, is effective in protecting against lung failure in rats with taurocholate-induced acute pancreatitis. As part of the analyses extended from that study, the present study aimed to evaluate the role of sivelestat and/or resveratrol in the protection against acute pancreatitis-associated lung injury. The extended analyses demonstrated the following: (1) sodium taurocholate induced apparent lung injury and dysfunction manifested by histological anomalies, including vacuolization and apoptosis of the cells in the lung, as well as biochemical aberrations in the blood (an increase in amylase concentration and a decrease in partial arterial oxygen pressure) and increases in activities of reactive oxygen species, interleukin 6, myeloperoxidase, neutrophil elastase, lung edema, bronchotracho alveolar lavage protein concentration, and bronchotracho alveolar lavage cell infiltration in the lung; and (2) in lung tissues, either sivelestat or resveratrol treatment effectively attenuated the taurocholate-induced abnormalities in all parameters analyzed except for serum amylase concentration. In addition, combined treatment with both sivelestat and resveratrol demonstrated additive protective effects on pancreatitis-associated lung injury compared with single treatment.

Severe acute respiratory syndrome coronavirus envelope protein ion channel activity promotes virus fitness and pathogenesis

Deletion of Severe Acute Respiratory Syndrome Coronavirus (SARS-CoV) envelope (E) gene attenuates the virus. E gene encodes a small multifunctional protein that possesses ion channel (IC) activity, an important function in virus-host interaction. To test the contribution of E protein IC activity in virus pathogenesis, two recombinant mouse-adapted SARS-CoVs, each containing one single amino acid mutation that suppressed ion conductivity, were engineered. After serial infections, mutant viruses, in general, incorporated compensatory mutations within E gene that rendered active ion channels. Furthermore, IC activity conferred better fitness in competition assays, suggesting that ion conductivity represents an advantage for the virus. Interestingly, mice infected with viruses displaying E protein IC activity, either with the wild-type E protein sequence or with the revertants that restored ion transport, rapidly lost weight and died. In contrast, mice infected with mutants lacking IC activity, which did not incorporate mutations within E gene during the experiment, recovered from disease and most survived. Knocking down E protein IC activity did not significantly affect virus growth in infected mice but decreased edema accumulation, the major determinant of acute respiratory distress syndrome (ARDS) leading to death. Reduced edema correlated with lung epithelia integrity and proper localization of Na⁺/K⁺ ATPase, which participates in edema resolution. Levels of inflammasome-activated IL-1β were reduced in the lung airways of the animals infected with viruses lacking E protein IC activity, indicating that E protein IC function is required for inflammasome activation. Reduction of IL-1β was accompanied by diminished amounts of TNF and IL-6 in the absence of E protein ion conductivity. All these key cytokines promote the progression of lung damage and ARDS pathology. In conclusion, E protein IC activity represents a new determinant for SARS-CoV virulence.

Several highly pathogenic viruses encode small transmembrane proteins with ion-conduction properties named viroporins. Viroporins are generally involved in virus production and maturation processes, which many times are achieved by altering the ion homeostasis of cell organelles. Cells have evolved mechanisms to sense these imbalances in ion concentrations as a danger signal, and consequently trigger the innate immune system. Recently, it has been demonstrated that viroporins are inducers of cytosolic macromolecular complexes named inflammasomes that trigger the activation of key inflammatory cytokines such as IL-1β. The repercussions of this system in viral pathogenesis or disease outcome are currently being explored. SARS-CoV infection induces an uncontrolled inflammatory response leading to pulmonary damage, edema accumulation, severe hypoxemia and eventually death. In this study, we report that SARS-CoV E protein ion channel activity is a determinant of virulence, as the elimination of this function attenuated the virus, reducing the harmful inflammatory cytokine burst produced after infection, in which inflammasome activation plays a critical role. This led to less pulmonary damage and to disease resolution. These novel findings may be of relevance for other viral infections and can possibly be translated in order to find therapies for their associated diseases.

The NLRP3 inflammasome is required for the development of hypoxemia in LPS/mechanical ventilation acute lung injury

IL-1β is a potent proinflammatory cytokine that is implicated in the pathogenesis of acute respiratory distress syndrome. We hypothesized that LPS and mechanical ventilation (MV) together could lead to IL-1β secretion and the development of acute lung injury (ALI), and that this process would be dependent on caspase-1 and the nucleotide binding domain and leucine-rich repeat (NLR) pyrin domain containing 3 (NLRP3) inflammasome activation. The objectives of this study were to determine the specific role of IL-1β, caspase-1, and the NLRP3 inflammasome in a two-hit model of ALI due to LPS plus MV. We used a two-hit murine model of ALI in which both inhaled LPS and MV were required for the development of hypoxemia, pulmonary neutrophil infiltration, and alveolar leakage. Nlrp3-deficent and Casp1-deficient mice had significantly diminished IL-1β levels in bronchoalveolar lavage fluid, and were specifically protected from hypoxemia, despite similar alveolar neutrophil infiltration and leakage. The IL-1 receptor antagonist, Anakinra, significantly improved the specific development of hypoxemia without significant effects on neutrophil infiltration or alveolar leakage. MV resulted in increased bronchoalveolar lavage extracellular ATP and alveolar macrophage apoptosis as triggers of NLRP3 inflammasome activation. NLRP3 inflammasome activation and IL-1β production play a key role in ALI caused by the combination of LPS and MV, particularly in the hypoxemia associated with acute respiratory distress syndrome. Blocking IL-1 signaling in this model specifically ameliorates hypoxemia, without affecting neutrophil infiltration and alveolar leakage, disassociating these readouts of ALI. MV causes alveolar macrophage apoptosis, a key step in the activation of NLRP3 inflammasome and production of IL-1β.

Proteinase-activated receptor-1, CCL2, and CCL7 regulate acute neutrophilic lung inflammation

PAR1 plays a central role in mediating the interplay between coagulation and inflammation, but its role in regulating acute neutrophilic inflammation is unknown. We report that antagonism of PAR1 was highly effective at reducing acute neutrophil accumulation in a mouse model of LPS-induced lung inflammation. PAR1 antagonism also reduced alveolar-capillary barrier disruption in these mice. This protection was associated with a reduction in the expression of the chemokines, CCL2 and CCL7, but not the proinflammatory cytokines, TNF and IL-6, or the classic neutrophil chemoattractants, CXCL1 and CXCL2. Antibody neutralization of CCL2 and CCL7 significantly reduced LPS-induced total leukocyte and neutrophil accumulation, recovered from the bronchoalveolar lavage fluid of challenged mice. Immunohistochemical analysis revealed that CCL2 predominantly localized to alveolar macrophages and pulmonary epithelial cells, whereas CCL7 was restricted to the pulmonary epithelium. In keeping with these observations, the intranasal administration of recombinant CCL2 (rCCL2) and rCCL7 led to the accumulation of neutrophils within the lung airspaces of naive mice in the absence of any underlying inflammation. Flow cytometry analysis further demonstrated an increase in Ly6G(hi) neutrophils expressing the chemokine receptors, CCR1 and CCR2, isolated from mouse lungs compared with circulating neutrophils. Conversely, the expression of CXCR2 decreased on neutrophils isolated from the lung compared with circulating neutrophils. Furthermore, this switch in chemokine receptor expression was accentuated after acute LPS-induced lung inflammation. Collectively, these findings reveal a novel role for PAR1 and the chemokines, CCL2 and CCL7, during the early events of acute neutrophilic inflammation.