Increased interleukin-8 concentrations in the pulmonary edema fluid of patients with acute respiratory distress syndrome from sepsis

Interleukins in the pathogenesis of influenza and other acute respiratory viral infections

Influenza and other acute respiratory viral infections (ARVIs) are among the most common human diseases. In recent decades, the discovery of cytokines and their significance in the pathogenesis of diseases has led to extensive research on these compounds in various pathologies including ARVIs. The aim of the research was to study the cytokine profile in patients with ARVIs. The cases of 30 patients were investigated. Etiological diagnosis was performed by polymerase chain reaction. Different classes of cytokines in the serum were defined by the enzyme-linked immunosorbent assay (ELISA). The level of cytokines depended on the number of pathogens. The highest levels of pro-inflammatory interleukins and the lowest levels of anti-inflammatory IL-4 were observed in patients with a combination of five or more viruses compared to those with a monoinfection. Analysis of the data showed that in the acute phase, the levels of all studied pro-inflammatory cytokines - IL-2, IL-6, and TNF-α - increased by 8, 39, and 9 times, respectively, compared to those in healthy individuals. In the acute phase of ARVI, the levels of pro-inflammatory cytokines were significantly higher and depended on the severity of the disease. The imbalance of cytokines in the serum has been established in cases of ARVIs, depending on the severity of the disease.

Mechanical power of ventilation and driving pressure: two undervalued parameters for pre extracorporeal membrane oxygenation ventilation and during daily management?

The current ARDS guidelines highly recommend lung protective ventilation which include plateau pressure (P_plat < 30 cm H₂O), positive end expiratory pressure (PEEP > 5 cm H₂O) and tidal volume (V_t of 6 ml/kg) of predicted body weight. In contrast, the ELSO guidelines suggest the evaluation of an indication of veno-venous extracorporeal membrane oxygenation (ECMO) due to hypoxemic or hypercapnic respiratory failure or as bridge to lung transplantation. Finally, these recommendations remain a wide range of scope of interpretation. However, particularly patients with moderate-severe to severe ARDS might benefit from strict adherence to lung protective ventilation strategies. Subsequently, we discuss whether extended physiological ventilation parameter analysis might be relevant for indication of ECMO support and can be implemented during the daily routine evaluation of ARDS patients. Particularly, this viewpoint focus on driving pressure and mechanical power.

FAK mediates LPS-induced inflammatory lung injury through interacting TAK1 and activating TAK1-NFκB pathway

Acute lung injury (ALI), characterized by inflammatory damage, is a major clinical challenge. Developing specific treatment options for ALI requires the identification of novel targetable signaling pathways. Recent studies reported that endotoxin lipopolysaccharide (LPS) induced a TLR4-dependent activation of focal adhesion kinase (FAK) in colorectal adenocarcinoma cells, suggesting that FAK may be involved in LPS-induced inflammatory responses. Here, we investigated the involvement and mechanism of FAK in mediating LPS-induced inflammation and ALI. We show that LPS phosphorylates FAK in macrophages. Either FAK inhibitor, site-directly mutation, or siRNA knockdown of FAK significantly suppresses LPS-induced inflammatory cytokine production in macrophages. FAK inhibition also blocked LPS-induced activation of MAPKs and NFκB. Mechanistically, we demonstrate that activated FAK directly interacts with transforming growth factor-β-activated kinase-1 (TAK1), an upstream kinase of MAPKs and NFκB, and then phosphorylates TAK1 at Ser412. In a mouse model of LPS-induced ALI, pharmacological inhibition of FAK suppressed FAK/TAK activation and inflammatory response in lung tissues. These activities resulted in the preservation of lung tissues in LPS-challenged mice and increased survival during LPS-induced septic shock. Collectively, our results illustrate a novel FAK-TAK1-NFκB signaling axis in LPS-induced inflammation and ALI, and support FAK as a potential target for the treatment of ALI.

COVID-19, what could sepsis, severe acute pancreatitis, gender differences, and aging teach us?

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) causes a potentially life-threatening disease, defined as Coronavirus Disease 19 (COVID-19). The most common signs and symptoms of this pathological condition include cough, fever, shortness of breath, and sudden onset of anosmia, ageusia, or dysgeusia. The course of COVID-19 is mild or moderate in more than 80% of cases, but it is severe or critical in about 14% and 5% of infected subjects respectively, with a significant risk of mortality. SARS-CoV-2 related infection is characterized by some pathogenetic events, resembling those detectable in other pathological conditions, such as sepsis and severe acute pancreatitis. All these syndromes are characterized by some similar features, including the coexistence of an exuberant inflammatory- as well as an anti-inflammatory-response with immune depression. Based on current knowledge concerning the onset and the development of acute pancreatitis and sepsis, we have considered these syndromes as a very interesting paradigm for improving our understanding of pathogenetic events detectable in patients with COVID-19. The aim of our review is: 1)to examine the pathogenetic mechanisms acting during the emergence of inflammatory and anti-inflammatory processes in human pathology; 2)to examine inflammatory and anti-inflammatory events in sepsis, acute pancreatitis, and SARS-CoV-2 infection and clinical manifestations detectable in patients suffering from these syndromes also according to the age and gender of these individuals; as well as to analyze the possible common and different features among these pathological conditions; 3)to obtain insights into our knowledge concerning COVID-19 pathogenesis. This approach may improve the management of patients suffering from this disease and it may suggest more effective diagnostic approaches and schedules of therapy, depending on the different phases and/or on the severity of SARS-CoV-2 infection.

Neutrophil-Dependent Immunity During Pulmonary Infections and Inflammations

Rapid recruitment of neutrophils to an inflamed site is one of the hallmarks of an effective host defense mechanism. The main pathway through which this happens is by the innate immune response. Neutrophils, which play an important part in innate immune defense, migrate into lungs through the modulation actions of chemokines to execute a variety of pro-inflammatory functions. Despite the importance of chemokines in host immunity, little has been discussed on their roles in host immunity. A holistic understanding of neutrophil recruitment, pattern recognition pathways, the roles of chemokines and the pathophysiological roles of neutrophils in host immunity may allow for new approaches in the treatment of infectious and inflammatory disease of the lung. Herein, this review aims at highlighting some of the developments in lung neutrophil-immunity by focusing on the functions and roles of CXC/CC chemokines and pattern recognition receptors in neutrophil immunity during pulmonary inflammations. The pathophysiological roles of neutrophils in COVID-19 and thromboembolism have also been summarized. We finally summarized various neutrophil biomarkers that can be utilized as prognostic molecules in pulmonary inflammations and discussed various neutrophil-targeted therapies for neutrophil-driven pulmonary inflammatory diseases.

Interleukin 8 Elicits Rapid Physiological Changes in Neutrophils That Are Altered by Inflammatory Conditions

A sufficient response of neutrophil granulocytes stimulated by interleukin (IL)-8 is vital during systemic inflammation, for example, in sepsis or severe trauma. Moreover, IL-8 is clinically used as biomarker of inflammatory processes. However, the effects of IL-8 on cellular key regulators of neutrophil properties such as the intracellular pH (pHi) in dependence of ion transport proteins and during inflammation remain to be elucidated. Therefore, we investigated in detail the fundamental changes in pHi, cellular shape, and chemotactic activity elicited by IL-8. Using flow cytometric methods, we determined that the IL-8-induced cellular activity was largely dependent on specific ion channels and transporters, such as the sodium-proton exchanger 1 (NHE1) and non-NHE1-dependent sodium flux. Exposing neutrophils in vitro to a proinflammatory micromilieu with N-formyl-Met-Leu-Phe, LPS, or IL-8 resulted in a diminished response regarding the increase in cellular size and pH. The detailed kinetics of the reduced reactivity of the neutrophil granulocytes could be illustrated in a near-real-time flow cytometric measurement. Last, the LPS-mediated impairment of the IL-8-induced response in neutrophils was confirmed in a translational, animal-free human whole blood model. Overall, we provide novel mechanistic insights for the interaction of IL-8 with neutrophil granulocytes and report in detail about its alteration during systemic inflammation.

COVID-19 and islet transplantation: Different twins

For those who work in the field of islet transplantation, the microvascular coronavirus disease 2019 (COVID-19) lung vessels obstructive thrombo-inflammatory syndrome (recently referred to as MicroCLOTS) is familiar, as one cannot fail to recognize the presence of similarities with the instant blood mediated inflammatory reaction (IBMIR) occurring in the liver hours and days after islet infusion. Evidence in both MicroCLOTS and IBMIR suggests the involvement of the coagulation cascade and complement system activation and proinflammatory chemokines/cytokines release. Identification and targeting of pathway(s) playing a role as "master regulator(s)" in the post-islet transplant detrimental inflammatory events could be potentially useful to suggest innovative COVID-19 treatments and vice versa. Scientific organizations across the world are fighting the COVID-19 pandemic. Islet transplantation, and more generally the transplantation scientific community, could contribute by suggesting strategies for innovative approaches. At the same time, in the near future, clinical trials in COVID-19 patients will produce an enormous quantity of clinical and translational data on the control of inflammation and complement/microthrombosis activation. These data will represent a legacy to be transformed into innovation in the transplant field. It will be our contribution to change a dramatic event into advancement for the transplant field and ultimately for our patients.

Pulmonary Edema: A Pictorial Review of Imaging Manifestations and Current Understanding of Mechanisms of Disease

Pulmonary edema is a common clinical entity caused by the extravascular movement of fluid into the pulmonary interstitium and alveoli. The four physiologic categories of edema include hydrostatic pressure edema, permeability edema with and without diffuse alveolar damage (DAD), and mixed edema where there is both an increase in hydrostatic pressure and membrane permeability. As radiographic manifestations and etiologies are varied, an appreciation for both the common and uncommon manifestations and causes of pulmonary edema is essential for accurate diagnosis.

Tristetraprolin Overexpression in Non-hematopoietic Cells Protects Against Acute Lung Injury in Mice

Tristetraprolin (TTP) is a mRNA binding protein that binds to adenylate-uridylate-rich elements within the 3′ untranslated regions of certain transcripts, such as tumor necrosis factor (Tnf) mRNA, and increases their rate of decay. Modulation of TTP expression is implicated in inflammation; however, its role in acute lung inflammation remains unknown. Accordingly, we tested the role of TTP in lipopolysaccharide (LPS)-induced acute lung injury (ALI) in mice. LPS-challenged TTP-knockout (TTP^KO) mice, as well as myeloid cell-specific TTP-deficient (TTP^myeKO) mice, exhibited significant increases in lung injury, although these responses were more robust in the TTP^KO. Mice with systemic overexpression of TTP (TTP^ΔARE) were protected from ALI, as indicated by significantly reduced neutrophilic infiltration, reduced levels of neutrophil chemoattractants, and histological parameters of ALI. Interestingly, while irradiated wild-type (WT) mice reconstituted with TTP^KO hematopoietic progenitor cells (HPCs) showed exaggerated ALI, their reconstitution with the TTP^ΔARE HPCs mitigated ALI. The reconstitution of irradiated TTP^ΔARE mice with HPCs from either WT or TTP^ΔARE donors conferred significant protection against ALI. In contrast, irradiated TTP^ΔARE mice reconstituted with TTP^KO HPCs had exaggerated ALI, but the response was milder as compared to WT recipients that received TTP^KO HPCs. Finally, the reconstitution of irradiated TTP^KO recipient mice with TTP^ΔARE HPCs did not confer any protection to the TTP^KO mice. These data together suggest that non-HPCs-specific overexpression of TTP within the lungs protects against ALI via downregulation of neutrophil chemoattractants and reduction in neutrophilic infiltration.

Metabolic Imaging and Biological Assessment: Platforms to Evaluate Acute Lung Injury and Inflammation

Pulmonary inflammation is a hallmark of several pulmonary disorders including acute lung injury and acute respiratory distress syndrome. Moreover, it has been shown that patients with hyperinflammatory phenotype have a significantly higher mortality rate. Despite this, current therapeutic approaches focus on managing the injury rather than subsiding the inflammatory burden of the lung. This is because of the lack of appropriate non-invasive biomarkers that can be used clinically to assess pulmonary inflammation. In this review, we discuss two metabolic imaging tools that can be used to non-invasively assess lung inflammation. The first method, Positron Emission Tomography (PET), is widely used in clinical oncology and quantifies flux in metabolic pathways by measuring uptake of a radiolabeled molecule into the cells. The second method, hyperpolarized ¹³C MRI, is an emerging tool that interrogates the branching points of the metabolic pathways to quantify the fate of metabolites. We discuss the differences and similarities between these techniques and discuss their clinical applications.

Nordihydroguaiaretic acid reduces secondary organ injury in septic rats after cecal ligation and puncture

BACKGROUND

Nordihydroguaiaretic acid (NDGA) is a plant extract that has been shown to act as a free radical scavenger and pluripotent inhibitor of pro-inflammatory cytokines, two major cellular processes involved in the pathophysiology of sepsis. We investigated whether NDGA would improve markers of organ injury as well as survival in a rodent model of sepsis.

METHODS

Abdominal sepsis was induced by cecal ligation and double puncture (CLP) in male Sprague-Dawley rats. NDGA was administered either at the time of injury (pre-) or 6 hours later (post-treatment). A sham surgery group and a vehicle only group were also followed as controls. Blood and lung tissue were collected 24 h after CLP. Lung tissue was used for histopathologic analysis and to measure pulmonary edema. Arterial oxygenation was measured directly to generate PaO2/FiO2, and markers of renal injury (blood urea nitrogen), liver injury (alanine aminotransferase), and tissue hypoxia (lactate) were measured. In a separate set of animals consisting of the same treatment groups, animals were followed for up to 36 hours for survival.

RESULTS

NDGA pre-treatment resulted in improved oxygenation, less lung edema, lower lactate, lower BUN, and reduced histologic lung injury. NDGA post-treatment resulted in less lung edema, lower lactate, lower BUN, and less histologic lung injury, but did not significantly change oxygenation. None of the NDGA treatment groups statistically affected ALT or creatinine. NDGA pre-treatment showed improved survival compared with control CLP animals at 36 hours, while post-treatment did not.

CONCLUSIONS

NDGA represents a novel pleiotropic anti-inflammatory agent with potential clinical utility for modulation of organ injury secondary to sepsis.

Tobacco, but Not Nicotine and Flavor-Less Electronic Cigarettes, Induces ACE2 and Immune Dysregulation

The COVID-19 pandemic caused by the SARS-CoV-2 virus, overlaps with the ongoing epidemics of cigarette smoking and electronic cigarette (e-cig) vaping. However, there is scarce data relating COVID-19 risks and outcome with cigarette or e-cig use. In this study, we mined three independent RNA expression datasets from smokers and vapers to understand the potential relationship between vaping/smoking and the dysregulation of key genes and pathways related to COVID-19. We found that smoking, but not vaping, upregulates ACE2, the cellular receptor that SARS-CoV-2 requires for infection. Both smoking and use of nicotine and flavor-containing e-cigs led to upregulation of pro-inflammatory cytokines and inflammasome-related genes. Specifically, chemokines including CCL20 and CXCL8 are upregulated in smokers, and CCL5 and CCR1 are upregulated in flavor/nicotine-containing e-cig users. We also found genes implicated in inflammasomes, such as CXCL1, CXCL2, NOD2, and ASC, to be upregulated in smokers and these e-cig users. Vaping flavor and nicotine-less e-cigs, however, did not lead to significant cytokine dysregulation and inflammasome activation. Release of inflammasome products, such as IL-1B, and cytokine storms are hallmarks of COVID-19 infection, especially in severe cases. Therefore, our findings demonstrated that smoking or vaping may critically exacerbate COVID-19-related inflammation or increase susceptibility to COVID-19.

Phenotypes in acute respiratory distress syndrome: moving towards precision medicine

PURPOSE OF REVIEW

To provide an overview of the current research in identifying homogeneous subgroups and phenotypes in ARDS.

RECENT FINDINGS

In recent years, investigations have used either physiology, clinical data, biomarkers or a combination of these to stratify patients with ARDS into distinct subgroups with divergent clinical outcomes. In some studies, there has also been evidence of differential treatment response within subgroups. Physiologic approaches include stratification based on P/F ratio and ventilatory parameters; stratification based on P/F ratio is already being employed in clinical trials. Clinical approaches include stratification based on ARDS risk factor or direct vs. indirect ARDS. Combined clinical and biological data has been used to identify two phenotypes across five cohorts of ARDS, termed hyperinflammatory and hypoinflammatory. These phenotypes have widely divergent clinical outcomes and differential response to mechanical ventilation, fluid therapy, and simvastatin in secondary analysis of completed trials. Next steps in the field include prospective validation of inflammatory phenotypes and integration of high-dimensional 'omics' data into our understanding of ARDS heterogeneity.

SUMMARY

Identification of distinct subgroups or phenotypes in ARDS may impact future conduct of clinical trials and can enhance our understanding of the disorder, with potential future clinical implications.

Acute Respiratory Distress Syndrome Phenotypes

The acute respiratory distress syndrome (ARDS) phenotype was first described over 50 years ago and since that time significant progress has been made in understanding the biologic processes underlying the syndrome. Despite this improved understanding, no pharmacologic therapies aimed at the underlying biology have been proven effective in ARDS. Increasingly, ARDS has been recognized as a heterogeneous syndrome characterized by subphenotypes with distinct clinical, radiographic, and biologic differences, distinct outcomes, and potentially distinct responses to therapy. The Berlin Definition of ARDS specifies three severity classifications: mild, moderate, and severe based on the PaO₂ to FiO₂ ratio. Two randomized controlled trials have demonstrated a potential benefit to prone positioning and neuromuscular blockade in moderate to severe phenotypes of ARDS only. Precipitating risk factor, direct versus indirect lung injury, and timing of ARDS onset can determine other clinical phenotypes of ARDS after admission. Radiographic phenotypes of ARDS have been described based on a diffuse versus focal pattern of infiltrates on chest imaging. Finally and most promisingly, biologic subphenotypes or endotypes have increasingly been identified using plasma biomarkers, genetics, and unbiased approaches such as latent class analysis. The potential of precision medicine lies in identifying novel therapeutics aimed at ARDS biology and the subpopulation within ARDS most likely to respond. In this review, we discuss the challenges and approaches to subphenotype ARDS into clinical, radiologic, severity, and biologic phenotypes with an eye toward the future of precision medicine in critical care.

Kaempferol reduces K63-linked polyubiquitination to inhibit nuclear factor-κB and inflammatory responses in acute lung injury in mice

Acute lung injury (ALI) and its severe form, acute respiratory distress syndrome (ARDS), pose a major clinical challenge. The major driving force in this syndrome is pulmonary inflammation. Recent studies have shown that the naturally occurring flavonoid kaempferol (KPF) reduces endotoxin-induced inflammatory responses in mice. However, the mechanisms of these anti-inflammatory activities are not currently known. Here, we show that enhanced inflammatory cytokine production in response to lipopolysaccharide (LPS) is due to increased TGF-β-activated kinase-1 (TAK1) phosphorylation with subsequent activation of nuclear factor-κB (NF-κB). KPF attenuates LPS-mediated production of cytokines as well as activation of NF-κB. Furthermore, we identified that KPF prevents increased K63-linked polyubiquitination on TNF receptor associated factor-6 (TRAF6) and interleukin-1 receptor-associated kinase 1 (IRAK1). K63-linked polyubiquitination is a signal leading to enhanced activation of downstream pathways including TAK1. Our study shows that KPF is effective in reducing lung damage induced by LPS by modulating TRAF6 polyubiquitination. Furthermore, our findings may provide novel molecular targets to alleviate acute lung injury.

Lung fluid biomarkers for acute respiratory distress syndrome: a systematic review and meta-analysis

Background

With the development of new techniques to easily obtain lower respiratory tract specimens, bronchoalveolar lavage fluid and other lung fluids are gaining importance in pulmonary disease diagnosis. We aimed to review and summarize lung fluid biomarkers associated with acute respiratory distress syndrome diagnosis and mortality.

Methods

After searching PubMed, Embase, Web of Science, and the Cochrane Library for articles published prior to January 11, 2018, we performed a meta-analysis on biomarkers for acute respiratory distress syndrome diagnosis in at-risk patients and those related to disease mortality. From the included studies, we then extracted the mean and standard deviation of the biomarker concentrations measured in the lung fluid, acute respiratory distress syndrome etiologies, sample size, demographic variables, diagnostic criteria, mortality, and protocol for obtaining the lung fluid. The effect size was measured by the ratio of means, which was then synthesized by the inverse-variance method using its natural logarithm form and transformed to obtain a pooled ratio and 95% confidence interval.

Results

In total, 1156 articles were identified, and 49 studies were included. Increases in total phospholipases A2 activity, total protein, albumin, plasminogen activator inhibitor-1, soluble receptor for advanced glycation end products, and platelet activating factor-acetyl choline were most strongly associated with acute respiratory distress syndrome diagnosis. As for biomarkers associated with acute respiratory distress syndrome mortality, interleukin-1β, interleukin-6, interleukin-8, Kerbs von Lungren-6, and plasminogen activator inhibitor-1 were significantly increased in the lung fluid of patients who died. Decreased levels of Club cell protein and matrix metalloproteinases-9 were associated with increased odds for acute respiratory distress syndrome diagnosis, whereas decreased levels of Club cell protein and interleukin-2 were associated with increased odds for acute respiratory distress syndrome mortality.

Conclusions

This meta-analysis provides a ranking system for lung fluid biomarkers, according to their association with diagnosis or mortality of acute respiratory distress syndrome. The performance of biomarkers among studies shown in this article may help to improve acute respiratory distress syndrome diagnosis and outcome prediction.

Electronic supplementary material

The online version of this article (10.1186/s13054-019-2336-6) contains supplementary material, which is available to authorized users.

Neutrophil extracellular traps (NETs) are increased in the alveolar spaces of patients with ventilator-associated pneumonia

Background

Neutrophils release neutrophil extracellular traps (NETs) in response to invading pathogens. Although NETs play an important role in host defense against microbial pathogens, they have also been shown to play a contributing mechanistic role in pathologic inflammation in the absence of infection. Although a role for NETs in bacterial pneumonia and acute respiratory distress syndrome (ARDS) is emerging, a comprehensive evaluation of NETs in the alveolar space of critically ill patients has yet to be reported. In this study, we evaluated whether markers of NET formation in mechanically ventilated patients are associated with ventilator-associated pneumonia (VAP).

Methods

We collected bronchoalveolar lavage fluid from 100 critically ill patients undergoing bronchoscopy for clinically suspected VAP. Subjects were categorized by the absence or presence of VAP and further stratified by ARDS status. NETs (myeloperoxidase (MPO)-DNA complexes) and the NET-associated markers peroxidase activity and cell-free DNA were analyzed by enzyme-linked immunosorbent assay and colorimetric assays, respectively. Quantitative polymerase chain reaction of nuclear and mitochondrial DNA was used to determine the origin of the extruded DNA. Interleukin (IL)-8 and calprotectin were assayed as measures of alveolar inflammation and neutrophil activation. Correlations between NETs and markers of neutrophil activation were determined using Spearman’s correlation. We tested for associations with VAP and bacterial burden by logistic and linear regression, respectively, using log₁₀-transformed NETs.

Results

MPO-DNA concentrations were highly correlated with other measures of NET formation in the alveolar space, including cell-free DNA and peroxidase activity (r = 0.95 and r = 0.87, p < 0.0001, respectively). Alveolar concentrations of MPO-DNA were higher in subjects with VAP and ARDS compared with those with ARDS alone (p < 0.0001), and higher MPO-DNA was associated with increased odds of VAP (odds ratio 3.03, p < 0.0001). In addition, NET concentrations were associated with bacterial burden (p < 0.0001) and local alveolar inflammation as measured by IL-8 (r = 0.89, p < 0.0001).

Conclusions

Alveolar NETs measured by MPO-DNA complex are associated with VAP, and markers of NETosis are associated with local inflammation and bacterial burden in the lung. These results suggest that NETs contribute to inflammatory responses involved in the pathogenesis of VAP.

Electronic supplementary material

The online version of this article (10.1186/s13054-018-2290-8) contains supplementary material, which is available to authorized users.

Recent advances in understanding acute respiratory distress syndrome

Acute respiratory distress syndrome (ARDS) is characterized by acute diffuse lung injury, which results in increased pulmonary vascular permeability and loss of aerated lung tissue. This causes bilateral opacity consistent with pulmonary edema, hypoxemia, increased venous admixture, and decreased lung compliance such that patients with ARDS need supportive care in the intensive care unit to maintain oxygenation and prevent adverse outcomes. Recently, advances in understanding the underlying pathophysiology of ARDS led to new approaches in managing these patients. In this review, we want to focus on recent scientific evidence in the field of ARDS research and discuss promising new developments in the treatment of this disease.

Lung Metabolism and Inflammation during Mechanical Ventilation; An Imaging Approach

Acute respiratory distress syndrome (ARDS) is a major cause of mortality in critically ill patients. Patients are currently managed by protective ventilation and alveolar recruitment using positive-end expiratory pressure (PEEP). However, the PEEP's effect on both pulmonary metabolism and regional inflammation is poorly understood. Here, we demonstrate the effect of PEEP on pulmonary anaerobic metabolism in mechanically ventilated injured rats, using hyperpolarized carbon-13 imaging. Pulmonary lactate-to-pyruvate ratio was measured in 21 rats; 14 rats received intratracheal instillation of hydrochloric-acid, while 7 rats received sham saline. 1 hour after acid/saline instillation, PEEP was lowered to 0 cmH2O in 7 injured rats (ZEEP group) and in all sham rats; PEEP was continued in the remaining 7 injured rats (PEEP group). Pulmonary compliance, oxygen saturation, histological injury scores, ICAM-1 expression and myeloperoxidase expression were measured. Lactate-to-pyruvate ratio progressively increased in the dependent lung during mechanical ventilation at ZEEP (p < 0.001), but remained unchanged in PEEP and sham rats. Lactate-to-pyruvate ratio was correlated with hyaline membrane deposition (r = 0.612), edema severity (r = 0.663), ICAM-1 (r = 0.782) and myeloperoxidase expressions (r = 0.817). Anaerobic pulmonary metabolism increases during lung injury progression and is contained by PEEP. Pulmonary lactate-to-pyruvate ratio may indicate in-vivo neutrophil activity due to atelectasis.

Anti-IL-8 antibody potentiates the effect of exogenous surfactant in respiratory failure caused by meconium aspiration

AIM

Meconium aspiration syndrome (MAS) is life-threatening respiratory failure of newborns which can be treated by exogenous surfactant. In response to meconium, increased levels of chemokine IL-8 (CXCL8) stimulate massive neutrophil infiltration of the lungs. Local accumulation and activation of neutrophils, on-going inflammation, lung edema, and oxidative damage contribute to inactivation of endogenous and therapeutically given surfactants. Therefore, we have hypothesized that addition of monoclonal anti-IL-8 antibody into exogenous surfactant can mitigate the neutrophil-induced local injury and the secondary surfactant inactivation and may finally result in improvement of respiratory functions.

METHODS

New Zealand rabbits with intratracheal meconium-induced respiratory failure (meconium 25 mg/ml, 4 ml/kg) were divided into three groups: untreated (M), surfactant-treated (M + S), and treated with combination of surfactant and anti-IL-8 antibody (M + S + anti-IL-8). Surfactant therapy consisted of two lung lavages with diluted porcine surfactant Curosurf (10 ml/kg, 5 mg phospholipids (PL)/ml) followed by undiluted Curosurf (100 mg PL/kg) delivered by means of asymmetric high-frequency jet ventilation (f. 300/min, Ti 20%). In M + S + anti-IL-8 group, anti-IL-8 antibody (100 µg/kg) was added directly to Curosurf dose. Animals were oxygen-ventilated for additional 5 h, respiratory parameters were measured regularly. Subsequently, cell counts in bronchoalveolar lavage fluid (BAL), lung edema formation, oxidative damage, levels of interleukins (IL)-1β and IL-6 in the lung homogenate were evaluated.

RESULTS

Surfactant instillation significantly improved lung function. Addition of anti-IL-8 to surfactant further improved gas exchange and ventilation efficiency and had longer-lasting effect than surfactant-only therapy. Combined treatment showed the trend to reduce neutrophil count in BAL fluid, local oxidative damage, and levels of IL-1β and IL-6 more effectively than surfactant-alone, however, these differences were not significant.

CONCLUSION

Addition of anti-IL-8 antibody to surfactant could potentiate the efficacy of Curosurf on the gas exchange in experimental model of MAS.

Cytokine-Ion Channel Interactions in Pulmonary Inflammation

The lungs conceptually represent a sponge that is interposed in series in the bodies’ systemic circulation to take up oxygen and eliminate carbon dioxide. As such, it matches the huge surface areas of the alveolar epithelium to the pulmonary blood capillaries. The lung’s constant exposure to the exterior necessitates a competent immune system, as evidenced by the association of clinical immunodeficiencies with pulmonary infections. From the in utero to the postnatal and adult situation, there is an inherent vital need to manage alveolar fluid reabsorption, be it postnatally, or in case of hydrostatic or permeability edema. Whereas a wealth of literature exists on the physiological basis of fluid and solute reabsorption by ion channels and water pores, only sparse knowledge is available so far on pathological situations, such as in microbial infection, acute lung injury or acute respiratory distress syndrome, and in the pulmonary reimplantation response in transplanted lungs. The aim of this review is to discuss alveolar liquid clearance in a selection of lung injury models, thereby especially focusing on cytokines and mediators that modulate ion channels. Inflammation is characterized by complex and probably time-dependent co-signaling, interactions between the involved cell types, as well as by cell demise and barrier dysfunction, which may not uniquely determine a clinical picture. This review, therefore, aims to give integrative thoughts and wants to foster the unraveling of unmet needs in future research.

Interleukin-22 level is negatively correlated with neutrophil recruitment in the lungs in a Pseudomonas aeruginosa pneumonia model

Pseudomonas aeruginosa is a major threat for immune-compromised patients. Bacterial pneumonia can induce uncontrolled and massive neutrophil recruitment ultimately leading to acute respiratory distress syndrome and epithelium damage. Interleukin-22 plays a central role in the protection of the epithelium. In this study, we aimed to evaluate the role of interleukin-22 and its soluble receptor IL-22BP in an acute Pseudomonas aeruginosa pneumonia model in mice. In this model, we noted a transient increase of IL-22 during Pseudomonas aeruginosa challenge. Using an antibody-based approach, we demonstrated that IL-22 neutralisation led to increased susceptibility to infection and to lung damage correlated with an increase in neutrophil accumulation in the lungs. On the contrary, rIL-22 administration or IL-22BP neutralisation led to a decrease in mouse susceptibility and lung damage associated with a decrease in neutrophil accumulation. This study demonstrated that the IL-22/IL-22BP system plays a major role during Pseudomonas aeruginosa pneumonia by moderating neutrophil accumulation in the lungs that ultimately leads to epithelium protection.

A systematic review of diagnostic methods to differentiate acute lung injury/acute respiratory distress syndrome from cardiogenic pulmonary edema

BACKGROUND

Discriminating acute lung injury (ALI) or acute respiratory distress syndrome (ARDS) from cardiogenic pulmonary edema (CPE) is often challenging. This systematic review examines studies using biomarkers or images to distinguish ALI/ARDS from CPE.

METHODS

Three investigators independently identified studies designed to distinguish ALI/ARDS from CPE in adults. Studies were identified from PubMed, and the Cochrane Central Register of Controlled Trials database until July 3, 2017.

RESULTS

Of 475 titles and abstracts screened, 38 full texts were selected for review, and we finally included 24 studies in this systematic review: 21 prospective observational studies, two retrospective observational studies, and one retrospective combined with prospective study. These studies compared various biomarkers to differentiate subjects with ALI/ARDS and in those with CPE, and 13 calculated the area under the receiver operator characteristic curve (AUC). The most commonly studied biomarker (four studies) was brain natriuretic peptide (BNP) and the discriminatory ability ranged from AUC 0.67-0.87 but the timing of measurement varied. Other potential biomarkers or tools have been reported, but only as single studies.

CONCLUSIONS

There were no identified biomarkers or tools with high-quality evidence for differentiating ALI/ARDS from CPE. Combining clinical criteria with validated biomarkers may improve the predictive accuracy.

Cytokine-Regulation of Na+-K+-Cl- Cotransporter 1 and Cystic Fibrosis Transmembrane Conductance Regulator-Potential Role in Pulmonary Inflammation and Edema Formation

Pulmonary edema, a major complication of lung injury and inflammation, is defined as accumulation of extravascular fluid in the lungs leading to impaired diffusion of respiratory gases. Lung fluid balance across the alveolar epithelial barrier protects the distal airspace from excess fluid accumulation and is mainly regulated by active sodium transport and Cl^- absorption. Increased hydrostatic pressure as seen in cardiogenic edema or increased vascular permeability as present in inflammatory lung diseases such as the acute respiratory distress syndrome (ARDS) causes a reversal of transepithelial fluid transport resulting in the formation of pulmonary edema. The basolateral expressed Na⁺-K⁺-2Cl^- cotransporter 1 (NKCC1) and the apical Cl^- channel cystic fibrosis transmembrane conductance regulator (CFTR) are considered to be critically involved in the pathogenesis of pulmonary edema and have also been implicated in the inflammatory response in ARDS. Expression and function of both NKCC1 and CFTR can be modulated by released cytokines; however, the relevance of this modulation in the context of ARDS and pulmonary edema is so far unclear. Here, we review the existing literature on the regulation of NKCC1 and CFTR by cytokines, and-based on the known involvement of NKCC1 and CFTR in lung edema and inflammation-speculate on the role of cytokine-dependent NKCC1/CFTR regulation for the pathogenesis and potential treatment of pulmonary inflammation and edema formation.

Protein phosphatase 2A activation attenuates inflammation in murine models of acute lung injury

Acute respiratory distress syndrome (ARDS) remains a leading cause of morbidity and mortality in both adult and pediatric intensive care units. A key event in the development of ARDS is neutrophil recruitment into the lungs leading to tissue damage and destruction. Interleukin-8 (IL-8) is the major human chemokine responsible for neutrophil recruitment into the lungs. Protein phosphatase 2A (PP2A) has been shown to be a key regulator of the mitogen-activated protein kinase (MAPK) cascades, which control the production of IL-8. Previously, our laboratory employed an in vitro model to show that inhibition of PP2A results in an increase in IL-8 production in human alveolar epithelial cells. The objective of this study was to determine whether PP2A regulated this response in vivo by investigating the impact of pharmacologic activation of PP2A on chemokine production and activation of the MAPK cascade and lung injury using endotoxin- and bacterial-challenge models of ARDS in mice. N⁶-cyclopentyladenosine (N⁶-CPA) increased PP2A activity and inhibited endotoxin-induced cytokine production in a murine alveolar macrophage cell line. N⁶-CPA pretreatment in mice challenged with intratracheal endotoxin decreased chemokine production, reduced neutrophil infiltration, and attenuated lung injury. Following initiation of lung injury with live Pseudomonas aeruginosa, mice that received N⁶-CPA 4 h following bacterial challenge showed attenuated chemokine production and reduced neutrophil infiltration compared with control mice. Pharmacologic PP2A activation both limited and prevented inflammation and tissue injury in two direct injury models of ARDS. These results suggest modulation of PP2A activity as a therapeutic target in ARDS.

Age-dependent alterations in the inflammatory response to pulmonary challenge

The aging lung is increasingly susceptible to infectious disease. Changes in pulmonary physiology and function are common in older populations, and in those older than 60 years, pneumonia is the major cause of infectious death. Understanding age-related changes in the innate and adaptive immune systems, and how they affect both pulmonary and systemic responses to pulmonary challenge are critical to the development of novel therapeutic strategies for the treatment of the elderly patient. In this observational study, we examined age-associated differences in inflammatory responses to pulmonary challenge with cell wall components from Gram-positive bacteria. Thus, male Sprague–Dawley rats, aged 6 months or greater than 18 months (approximating humans of 20 and 55–65 years), were challenged, intratracheally, with lipoteichoic acid and peptidoglycan. Cellular and cytokine evaluations were performed on both bronchoalveolar lavage fluid (BAL) and plasma, 24 h post-challenge. The plasma concentration of free thyroxine, a marker of severity in non-thyroidal illness, was also evaluated. The older animals had an increased chemotactic gradient in favor of the airspaces, which was associated with a greater accumulation of neutrophils and protein. Furthermore, macrophage migration inhibitory factor (MIF), an inflammatory mediator and putative biomarker in acute lung injury, was increased in both the plasma and BAL of the older, but not young animals. Conversely, plasma free thyroxine, a natural inhibitor of MIF, was decreased in the older animals. These findings identify age-associated inflammatory/metabolic changes following pulmonary challenge that it may be possible to manipulate to improve outcome in the older, critically ill patient.

Regulation of angiopoietin-2 secretion from human pulmonary microvascular endothelial cells

INTRODUCTION

Sepsis is characterized by dysregulated systemic inflammation and cytokine storm. Angiopoietin-2 (Ang-2) is known to closely correlate with severity of sepsis-related acute lung injury and mortality. The aim of this study was to clarify the mechanisms involved in Ang-2 secretion to better understand the pathophysiology of sepsis.

MATERIALS AND METHODS

The concentration of Ang-2 was assessed in culture medium of pulmonary microvascular endothelial cells in the presence or absence of Gram-positive bacteria cell wall components [lipoteichoic acid (LTA) and peptidoglycan (PGN)] stimulation at different time points ranging from 15 minutes to 24 hours. Constitutive and LTA-PGN-stimulated Ang-2 level changes were also assessed after cells were pretreated with different pathway inhibitors for 1 hour.

RESULTS

Two distinctive mechanisms of Ang-2 secretion, constitutive and stimulated secretion, were identified. Constitutive secretion resulted in slow but continuous increase in Ang-2 in culture medium over time. It was regulated by 3'5'-cyclic adenosine monophosphate (cAMP)-protein kinase A (PKA)-Ca²⁺ and nitric oxide (NO)-3'5'-cyclic guanosine monophosphate (cGMP)-protein kinase G (PKG)-Ca²⁺ pathways and partially regulated by N-ethyl-maleimide-sensitive factor-Ca²⁺ pathways. LTA-PGN stimulation caused rapid and potent increase followed by gradual decrease of Ang-2. It was partially regulated by both Ral A-phospholipase D and NSF-Ca²⁺ pathways.

CONCLUSIONS

We demonstrated characteristics and involved pathways for two distinctive secretory mechanisms, constitutive and stimulated, of Ang-2 in pulmonary microvascular endothelial cells. Considering the close correlation of Ang-2 with sepsis outcomes, our findings provide a better understanding of an important mechanism associated with sepsis pathophysiology and identify possible therapeutic targets to improve outcomes in the potentially lethal disease.

Evidence for chemokine synergy during neutrophil migration in ARDS

Background

Acute respiratory distress syndrome (ARDS) is a life-threatening condition characterised by pulmonary oedema, respiratory failure and severe inflammation. ARDS is further characterised by the recruitment of neutrophils into the lung interstitium and alveolar space.

Objectives

The factors that regulate neutrophil infiltration into the inflamed lung and our understanding of the pathomechanisms in ARDS remain incomplete. This study aimed at determining the role of the chemokine (C-C motif) ligand (CCL)2 and CCL7 in ARDS.

Methods

CCL2 and CCL7 protein levels were measured in bronchoalveolar lavage (BAL) fluid obtained from lipopolysaccharide(LPS)-challenged human volunteers and two separate cohorts of patients with ARDS. Neutrophil chemotaxis to ARDS BAL fluid was evaluated and the contribution of each was assessed and compared with chemokine (C-X-C motif) ligand 8 (CXCL8). Chemokine receptor expression on neutrophils from blood or BAL fluid of patients with ARDS was analysed by flow cytometry.

Results

CCL2 and CCL7 were significantly elevated in BAL fluid recovered from LPS-challenged volunteers and patients with ARDS. BAL fluid from patients with ARDS was highly chemotactic for human neutrophils and neutralising either CCL2 or CCL7 attenuated the neutrophil chemotactic response. Moreover, CCL2 and CCL7 synergised with CXCL8 to promote neutrophil migration. Furthermore, neutrophils isolated from the blood or BAL fluid differentially regulated the cell surface expression of chemokine (C-X-C motif) receptor 1 and C-C chemokine receptor type 2 during ARDS.

Conclusion

This study highlights important inflammatory chemokines involved in regulating neutrophil migration, which may have potential value as therapeutic targets for the treatment of ARDS.

Interleukin-17A Is Associated With Alveolar Inflammation and Poor Outcomes in Acute Respiratory Distress Syndrome

OBJECTIVE

Interleukin-17A is a proinflammatory cytokine known to play a role in host defense and pathologic inflammation in murine models of lung injury. The relationship between interleukin-17A and inflammation in human lung injury is unknown. Our primary objective was to determine whether interleukin-17A levels are associated with alveolar measures of inflammation and injury in patients with acute respiratory distress syndrome. Our secondary objective was to test whether interleukin-17A levels are associated with acute respiratory distress syndrome-related outcomes.

DESIGN

Observational study.

SETTING

Six North American medical centers.

PATIENTS

We studied two groups of patients with acute respiratory distress syndrome: 1) patients previously enrolled in a placebo-controlled clinical trial of omega-3 fatty acids performed at five North American medical centers (n = 86, acute respiratory distress syndrome 1), and 2) patients with systemic inflammatory response syndrome admitted to an ICU who developed acute respiratory distress syndrome (n = 140, acute respiratory distress syndrome 2). In acute respiratory distress syndrome 1, we used paired serum and bronchoalveolar lavage fluid samples obtained within 48 hours of acute respiratory distress syndrome onset, whereas in acute respiratory distress syndrome 2, we used plasma obtained within the first 24 hours of ICU admission.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

We measured circulating interleukin-17A in acute respiratory distress syndrome 1 and acute respiratory distress syndrome 2. We also measured interleukin-17A, neutrophil counts, and total protein in bronchoalveolar lavage fluid from acute respiratory distress syndrome 1. We found that bronchoalveolar lavage interleukin-17A was strongly associated with higher bronchoalveolar lavage percent neutrophils (p < 0.001) and bronchoalveolar lavage total protein (p < 0.01) in acute respiratory distress syndrome1. In both acute respiratory distress syndrome 1 and acute respiratory distress syndrome 2, elevated interleukin-17A was associated with higher Sequential Organ Failure Assessment scores (p < 0.05).

CONCLUSIONS

Elevated circulating and alveolar levels of interleukin-17A are associated with increased percentage of alveolar neutrophils, alveolar permeability, and organ dysfunction in acute respiratory distress syndrome.

Neonatal Type II Alveolar Epithelial Cell Transplant Facilitates Lung Reparation in Piglets With Acute Lung Injury and Extracorporeal Life Support

OBJECTIVES

Type II alveolar epithelial cells have potential for lung growth and reparation. Extracorporeal membrane oxygenation is used as life support for lung impairment resulting from acute respiratory distress syndrome. We hypothesized that intratracheal transplantation of isogeneic primary type II alveolar epithelial cells in combination with extracorporeal membrane oxygenation may facilitate lung reparation for acute lung injury (ALI).

DESIGN

A randomized, controlled experiment.

SETTING

An animal laboratory in a university pediatric center.

SUBJECTS

Twenty-eight 4- to 6-week young piglets, weighing 7-8 kg.

INTERVENTIONS

Type II alveolar epithelial cells from neonatal male piglet lungs were isolated, purified, cultured, and labeled with chemical stain PKH26. After 3-6 hours of induction of ALI by IV endotoxin and mechanical ventilation (MV), young female piglets were allocated to five groups (n = 5): ALI-MV, ALI treated with MV; ALI-EC, ALI treated with both MV and venovenous extracorporeal membrane oxygenation; ALI-EC-T, ALI-EC protocol plus intratracheal type II alveolar epithelial cell transplant; CON-MV, healthy animals treated with MV; and CON-EC-T, healthy animals treated with venovenous extracorporeal membrane oxygenation. After 24 hours, animals were weaned from treatment for recovery in the ensuing 14 days, with their lungs assessed for injury and reparation.

MEASUREMENTS AND MAIN RESULTS

Lung injury for animals in ALI-MV was moderate to severe, whereas much milder injuries in ALI-EC-T and ALI-EC were found. More PKH26-labeled type II alveolar epithelial cells were detected by fluorescence in the lungs of ALI-EC-T than in CON-EC-T as further verified by the expression of messenger RNA of sex-determining region of Y chromosome. Electromicroscopically intact type II alveolar epithelial cells and prominent lattice-like tubular myelin were also found in ALI-EC-T and CON-MV but not in ALI-EC. The hydroxyproline level in lung tissue was significantly lower in ALI-EC-T than in ALI-EC and ALI-MV, with most of the lung histopathologic and pathobiologic manifestations in favor of ALI-EC-T.

CONCLUSIONS

The preliminary data suggested that type II alveolar epithelial cell transplant facilitated lung reparation for ALI in this model.

Resolvins Decrease Oxidative Stress Mediated Macrophage and Epithelial Cell Interaction through Decreased Cytokine Secretion

Background

Inflammation is a key hallmark of ALI and is mediated through ungoverned cytokine signaling. One such cytokine, interleukin-1beta (IL-1β) has been demonstrated to be the most bioactive cytokine in ALI patients. Macrophages are the key players responsible for IL-1β secretion into the alveolar space. Following the binding of IL-1β to its receptor, “activated” alveolar epithelial cells show enhanced barrier dysfunction, adhesion molecule expression, cytokine secretion, and leukocyte attachment. More importantly, it is an important communication molecule between the macrophage and alveolar epithelium. While the molecular determinants of this inflammatory event have been well documented, endogenous resolution processes that decrease IL-1β secretion and resolve alveolar epithelial cell activation and tissue inflammation have not been well characterized. Lipid mediator Aspirin-Triggered Resolvin D1 (AT-RvD1) has demonstrated potent pro-resolutionary effects in vivo models of lung injury; however, the contribution of the alveoli to the protective benefits of this molecule has not been well documented. In this study, we demonstrate that AT-RvD1 treatment lead to a significant decrease in oxidant induced macrophage IL-1β secretion and production, IL-1β-mediated cytokine secretion, adhesion molecule expression, leukocyte adhesion and inflammatory signaling.

Methods

THP-1 macrophages were treated with hydrogen peroxide and extracellular ATP in the presence or absence of AT-RvD1 (1000–0.1 nM). A549 alveolar-like epithelial cells were treated with IL-1β (10 ng/mL) in the presence or absence of AT-RvD1 (0.1 μM). Following treatment, cell lysate and cell culture supernatants were collected for Western blot, qPCR and ELISA analysis of pro-inflammatory molecules. Functional consequences of IL-1β induced alveolar epithelial cell and macrophage activation were also measured following treatment with IL-1β ± AT-RvD1.

Results

Results demonstrate that macrophages exposed to H₂O₂ and ATP in the presence of resolvins show decreased IL-1β production and activity. A549 cells treated with IL-1β in the presence of AT-RvD1 show a reduced level of proinflammatory cytokines IL-6 and IL-8. Further, IL-1β-mediated adhesion molecule expression was also reduced with AT-RvD1 treatment, which was correlated with decreased leukocyte adhesion. AT-RvD1 treatment demonstrated reduced MAP-Kinase signaling. Taken together, our results demonstrate AT-RvD1 treatment reduced IL-1β-mediated alveolar epithelial cell activation. This is a key step in unraveling the protective effects of resolvins, especially AT-RvD1, during injury.

The Value of Admission Serum IL-8 Monitoring and the Correlation with IL-8 (-251A/T) Polymorphism in Critically Ill Patients

Background. The clinical management of sepsis is a highly complicated process. Disruption of the immune system explains in part the major variation in sepsis outcome. IL-8 is a proinflammatory cytokine, genetic polymorphism of this cytokine could explain the outcome of sepsis. The present study was conducted to determine the value of serum IL-8 monitoring and its (-251A/T) genetic polymorphism in critically ill patients. Patients and Methods. 180 critically ill patients were allocated into two groups, 90 septic patients (sepsis group) and 90 nonseptic patients (SIRS group). Admission serum IL-8 and its (-251A/T) mutant allele were detected. Results. The admission mean value of serum IL-8 was significantly elevated in sepsis group. In both groups, the mean value of serum IL-8 in nonsurvived patients and patients with IL-8 (-251A/T) mutant allele was significantly higher. A positive correlation of survival and IL-8 (-251A/T) mutant allele was detected in both groups. The serum IL-8 distinguished wild from IL-8 (-251A/T) mutant allele at a cut-off value of 600 pg/mL. Conclusion. The admission mean value of serum IL-8 was significantly elevated in septic, nonsurvived, and patients with IL-8 (-251A/T) mutant alleles. A positive correlation of survival and IL-8 (-251A/T) mutant allele patients was detected.

Mechanism of fibroblast inflammatory responses to Pseudomonas aeruginosa elastase

Receptor tyrosine kinases, including the epidermal growth factor receptors (EGFR), are able to activate the mitogen-activated protein kinases (MAPK) via several adaptor proteins and protein kinases such as Raf. EGFR can be activated by a variety of extracellular stimuli including neutrophil elastase, but we are aware of no report as to whether Pseudomonas aeruginosa produced elastase (PE) could elicit such signalling through EGFR activation. We sought to test the inference that PE modulates inflammatory responses in human lung fibroblasts and that the process occurs by activation of the EGFR/MAPK pathways. We utilized IL-8 cytokine expression as a pathway-specific end point measure of the fibroblast inflammatory response to PE. Western blot analysis was performed to detect phosphorylation of EGFR and signal transduction intermediates. Northern blot, real-time PCR, and ELISA methods were utilized to determine cytokine gene expression levels. We found that PE induces phosphorylation of the EGFR and the extracellular signal-regulated proteins (ERK1/2) of the MAPK pathway, and nuclear translocation of NF-κB. Furthermore, enzymically active PE enhances IL-8 mRNA and protein secretion. Pretreatment of the cells with specific inhibitors of EGFR, MAPK kinase and NF-κB markedly attenuated the PE-induced signal proteins phosphorylation and IL-8 gene expression and protein secretion. Collectively, the data show that PE produced by Pseudomonas aeruginosa can modulate lung inflammation by exploiting the EGFR/ERK signalling cascades and enhancing IL-8 production in the lungs via NF-κB activation.

The mercurial nature of neutrophils: still an enigma in ARDS?

The acute respiratory distress syndrome (ARDS) is a life-threatening lung condition resulting from direct and indirect insults to the lung. It is characterized by disruption of the endothelial-epithelial barrier, alveolar damage, pulmonary edema, and respiratory failure. A key feature of ARDS is the accumulation of neutrophils in the lung microvasculature, interstitium, and alveolar space. Despite a clear association between neutrophil influx into the lung and disease severity, there is some debate as to whether neutrophils directly contribute to disease pathogenesis. The primary function of neutrophils is to provide immediate host defense against pathogenic microorganisms. Neutrophils release numerous antimicrobial factors such as reactive oxygen species, proteinases, and neutrophil extracellular traps. However, these factors are also toxic to host cells and can result in bystander tissue damage. The excessive accumulation of neutrophils in ARDS may therefore contribute to disease progression. Central to neutrophil recruitment is the release of chemokines, including the archetypal neutrophil chemoattractant IL-8, from resident pulmonary cells. However, the chemokine network in the inflamed lung is complex and may involve several other chemokines, including CXCL10, CCL2, and CCL7. This review will therefore focus on the experimental and clinical evidence supporting neutrophils as key players in ARDS and the chemokines involved in recruiting them into the lung.

Growth factors and cytokines in acute lung injury

Cytokines and growth factors play an integral role in the maintenance of immune homeostasis, the generation of protective immunity, and lung reparative processes. However, the dysregulated expression of cytokines and growth factors in response to infectious or noxious insults can initiate and perpetuate deleterious lung inflammation and fibroproliferation. In this article, we will comprehensively review the contribution of individual cytokines and growth factors and cytokine networks to key pathophysiological events in human and experimental acute lung injury (ALI), including inflammatory cell recruitment and activation, alveolar epithelial injury and repair, angiogenesis, and matrix deposition and remodeling. The application of cytokines/growth factors as prognostic indicators and therapeutic targets in human ALI is explored.

To ventilate, oscillate, or cannulate?

Ventilatory management of acute respiratory distress syndrome has evolved significantly in the last few decades. The aims have shifted from optimal gas transfer without concern for iatrogenic risks to adequate gas transfer while minimizing lung injury. This change in focus, along with improved ventilator and multiorgan system management, has resulted in a significant improvement in patient outcomes. Despite this, a number of patients develop hypoxemic respiratory failure refractory to lung-protective ventilation (LPV). The intensivist then faces the dilemma of either persisting with LPV using adjuncts (neuromuscular blocking agents, prone positioning, recruitment maneuvers, inhaled nitric oxide, inhaled prostacyclin, steroids, and surfactant) or making a transition to rescue therapies such as high-frequency oscillatory ventilation (HFOV) and/or extracorporeal membrane oxygenation (ECMO) when both these modalities are at their disposal. The lack of quality evidence and potential harm reported in recent studies question the use of HFOV as a routine rescue option. Based on current literature, the role for venovenous (VV) ECMO is probably sequential as a salvage therapy to ensure ultraprotective ventilation in selected young patients with potentially reversible respiratory failure who fail LPV despite neuromuscular paralysis and prone ventilation. Given the risk profile and the economic impact, future research should identify the patients who benefit most from VV ECMO. These choices may be further influenced by the emerging novel extracorporeal carbon dioxide removal devices that can compliment LPV. Given the heterogeneity of acute respiratory distress syndrome, each of these modalities may play a role in an individual patient. Future studies comparing LPV, HFOV, and VV ECMO should not only focus on defining the patients who benefit most from each of these therapies but also consider long-term functional outcomes.

Neutrophils in local and systemic antibody-dependent inflammatory and anaphylactic reactions

Neutrophils are notorious for their efficacy in microbial killing. Various mechanisms, such as phagocytosis, production of ROS, cytokines/chemokines and lipid mediators, degranulation of antimicrobials and enzymes, as well as NETosis contribute to this capacity. However, every incidence of neutrophil activation bears a risk to cause damage to the host. Several distinct steps, i.e., adhesion to endothelial cells, transmigration, chemotaxis, cytokine stimulation, and TLR signaling, are thought to control the extent of neutrophil activation. In the absence of a microbial stimulus, other pathways can induce neutrophil activation, among which FcR-induced activation when neutrophils encounter ICs. In these situations (inflammation, autoimmunity, allergy), neutrophils may act as primary or secondary effectors of immune reactions. In the presence of circulating ICs, neutrophils can indeed get stimulated directly in the bloodstream and trigger an immune response. Upon deposition of antibody complexes inside of tissues, neutrophils are first recruited and primed before being highly activated to amplify the ongoing inflammation. This review focuses on the engagement, activation, and responses of neutrophils to antibody ICs, inside of tissues or in the vasculature.

Tissue-specific neutrophil recruitment into the lung, liver, and kidney

The recruitment of immune cells is crucial for the development of inflammatory processes. The classical recruitment cascade of neutrophils into inflamed tissues is well understood and consists of capturing, rolling, slow rolling, arrest, postadhesion strengthening, crawling, and transmigration. While this commonly agreed paradigm might be applicable to most peripheral tissues, recruitment mechanisms may substantially vary in different organs such as the lung, liver, and kidney. These organs are highly specialized tissues with unique cell populations and structural organization, which enables them to fulfill their individual functions. The published research over the last decade has shed some light on organ-specific mechanisms of neutrophil recruitment and helped to generate a deeper understanding of the specific recruitment mechanisms involved in this process. The aim of this review is to highlight current concepts of tissue-specific differences and similarities of neutrophil recruitment into the lung, liver, and kidney.

A Bayesian Approach for Generalized Linear Models with Explanatory Biomarker Measurement Variables Subject to Detection Limit - an Application to Acute Lung Injury

Biomarkers have the potential to improve our understanding of disease diagnosis and prognosis. Biomarker levels that fall below the assay detection limits (DLs), however, compromise the application of biomarkers in research and practice. Most existing methods to handle non-detects focus on a scenario in which the response variable is subject to detection limit; only a few methods consider explanatory variables when dealing with DLs. We propose a Bayesian approach for generalized linear models with explanatory variables subject to lower, upper, or interval DLs. In simulation studies, we compared the proposed Bayesian approach to four commonly used methods in a logistic regression model with explanatory variable measurements subject to DL. We also applied the Bayesian approach and other four methods in a real study, in which a panel of cytokine biomarkers was studied for their association with acute lung injury (ALI). We found that IL8 was associated with a moderate increase in risk for ALI in the model based on the proposed Bayesian approach.

The Dual Role of TNF in Pulmonary Edema

—Pulmonary edema, a major manifestation of left ventricular heart failure, renal insufficiency, shock, diffuse alveolar damage and lung hypersensitivity states, is a significant medical problem worldwide and can be life-threatening. The proinflammatory cytokine tumor necrosis factor (TNF) has been shown to contribute to the pathogenesis and development of pulmonary edema. However, some recent studies have demonstrated surprisingly that TNF can also promote alveolar fluid reabsorption in vivo and in vitro. This protective effect of the cytokine is mediated by the lectin-like domain of the cytokine, which is spatially distinct from the TNF receptor binding sites. The TIP peptide, a synthetic mimic of the lectin-like domain of TNF, can significantly increase alveolar fluid clearance and improve lung compliance in pulmonary edema models. In this review, we will discuss the dual role of TNF in pulmonary edema.

Contribution of neutrophils to acute lung injury

Treatment of acute lung injury (ALI) and its most severe form, acute respiratory distress syndrome (ARDS), remain unsolved problems of intensive care medicine. ALI/ARDS are characterized by lung edema due to increased permeability of the alveolar-capillary barrier and subsequent impairment of arterial oxygenation. Lung edema, endothelial and epithelial injury are accompanied by an influx of neutrophils into the interstitium and broncheoalveolar space. Hence, activation and recruitment of neutrophils are regarded to play a key role in progression of ALI/ARDS. Neutrophils are the first cells to be recruited to the site of inflammation and have a potent antimicrobial armour that includes oxidants, proteinases and cationic peptides. Under pathological circumstances, however, unregulated release of these microbicidal compounds into the extracellular space paradoxically can damage host tissues. This review focuses on the mechanisms of neutrophil recruitment into the lung and on the contribution of neutrophils to tissue damage in ALI.

Pharmacotherapy for prevention and treatment of acute respiratory distress syndrome: current and experimental approaches

The acute respiratory distress syndrome (ARDS) arises from direct and indirect injury to the lungs and results in a life-threatening form of respiratory failure in a heterogeneous, critically ill patient population. Critical care technologies used to support patients with ARDS, including strategies for mechanical ventilation, have resulted in improved outcomes in the last decade. However, there is still a need for effective pharmacotherapies to treat ARDS, as mortality rates remain high. To date, no single pharmacotherapy has proven effective in decreasing mortality in adult patients with ARDS, although exogenous surfactant replacement has been shown to reduce mortality in the paediatric population with ARDS from direct causes. Several promising therapies are currently being investigated in preclinical and clinical trials for treatment of ARDS in its acute and subacute, exudative phases. These include exogenous surfactant therapy, β₂-adrenergic receptor agonists, antioxidants, immunomodulating agents and HMG-CoA reductase inhibitors (statins). Recent research has also focused on prevention of acute lung injury and acute respiratory distress in patients at risk. Drugs such as captopril, rosiglitazone and incyclinide (COL-3), a tetracycline derivative, have shown promising results in animal models, but have not yet been tested clinically. Further research is needed to discover therapies to treat ARDS in its late, fibroproliferative phase. Given the vast number of negative clinical trials to date, it is unlikely that a single pharmacotherapy will effectively treat all patients with ARDS from differing causes. Future randomized controlled trials should target specific, more homogeneous subgroups of patients for single or combination therapy.

Prognostic and pathogenetic value of combining clinical and biochemical indices in patients with acute lung injury

BACKGROUND

No single clinical or biologic marker reliably predicts clinical outcomes in acute lung injury (ALI)/ARDS. We hypothesized that a combination of biologic and clinical markers would be superior to either biomarkers or clinical factors alone in predicting ALI/ARDS mortality and would provide insight into the pathogenesis of clinical ALI/ARDS.

METHODS

Eight biologic markers that reflect endothelial and epithelial injury, inflammation, and coagulation (von Willebrand factor antigen, surfactant protein D [SP-D]), tumor necrosis factor receptor-1, interleukin [IL]-6, IL-8, intercellular adhesion molecule-1, protein C, plasminogen activator inhibitor-1) were measured in baseline plasma from 549 patients in the ARDSNet trial of low vs high positive end-expiratory pressure. Mortality was modeled with multivariable logistic regression. Predictors were selected using backward elimination. Comparisons between candidate models were based on the receiver operating characteristics (ROC) and tests of integrated discrimination improvement.

RESULTS

Clinical predictors (Acute Physiology And Chronic Health Evaluation III [APACHE III], organ failures, age, underlying cause, alveolar-arterial oxygen gradient, plateau pressure) predicted mortality with an area under the ROC curve (AUC) of 0.82; a combination of eight biomarkers and the clinical predictors had an AUC of 0.85. The best performing biomarkers were the neutrophil chemotactic factor, IL-8, and SP-D, a product of alveolar type 2 cells, supporting the concept that acute inflammation and alveolar epithelial injury are important pathogenetic pathways in human ALI/ARDS.

CONCLUSIONS

A combination of biomarkers and clinical predictors is superior to clinical predictors or biomarkers alone for predicting mortality in ALI/ARDS and may be useful for stratifying patients in clinical trials. From a pathogenesis perspective, the degree of acute inflammation and alveolar epithelial injury are highly associated with the outcome of human ALI/ARDS.

Obesity and acute lung injury

Acute lung injury (ALI) and the acute respiratory distress syndrome (ARDS) are common indications for ICU admission and mechanical ventilation. ALI/ARDS also consumes significant health care resources and is a common cause of death in ICU patients. Obesity produces changes in respiratory system physiology that could affect outcomes for ALI/ARDS patients and their response to treatment. Additionally, the biochemical alterations seen in obese patients, such as increased inflammation and altered metabolism, could affect the risk of developing ALI/ARDS in patients with another risk factor (eg, sepsis). The few studies that have examined the influence of obesity on the outcomes from ALI/ARDS are inconclusive. Furthermore, observed results could be biased by disparities in provided care.

Macrophage CD74 contributes to MIF-induced pulmonary inflammation

BACKGROUND

MIF is a critical mediator of the host defense, and is involved in both acute and chronic responses in the lung. Neutralization of MIF reduces neutrophil accumulation into the lung in animal models. We hypothesized that MIF, in the alveolar space, promotes neutrophil accumulation via activation of the CD74 receptor on macrophages.

METHODS

To determine whether macrophage CD74 surface expression contributes MIF-induced neutrophil accumulation, we instilled recombinant MIF (r-MIF) into the trachea of mice in the presence or absence of anti-CD74 antibody or the MIF specific inhibitor, ISO-1. Using macrophage culture, we examined the downstream pathways of MIF-induced activation that lead to neutrophil accumulation.

RESULTS

Intratracheal instillation of r-MIF increased the number of neutrophils as well as the concentration of macrophage inflammatory protein 2 (MIP-2) and keratinocyte-derived chemokine (KC) in BAL fluids. CD74 was found to be expressed on the surface of alveolar macrophages, and MIF-induced MIP-2 accumulation was dependent on p44/p42 MAPK in macrophages. Anti-CD74 antibody inhibited MIF-induced p44/p42 MAPK phosphorylation and MIP-2 release by macrophages. Furthermore, we show that anti-CD74 antibody inhibits MIF-induced alveolar accumulation of MIP-2 (control IgG vs. CD74 Ab; 477.1 +/- 136.7 vs. 242.2 +/- 102.2 pg/ml, p < 0.05), KC (1796.2 +/- 436.1 vs. 1138.2 +/- 310.2 pg/ml, p < 0.05) and neutrophils (total number of neutrophils, 3.33 +/- 0.93 x 104 vs. 1.90 +/- 0.61 x 104, p < 0.05) in our mouse model.

CONCLUSION

MIF-induced neutrophil accumulation in the alveolar space results from interaction with CD74 expressed on the surface of alveolar macrophage cells. This interaction induces p44/p42 MAPK activation and chemokine release. The data suggest that MIF and its receptor, CD74, may be useful targets to reduce neutrophilic lung inflammation, and acute lung injury.