The Fas/FasL pathway impairs the alveolar fluid clearance in mouse lungs

Necroptosis in alveolar epithelial cells drives lung inflammation and injury caused by SARS-CoV-2 infection

COVID-19, caused by SARS-CoV-2 infection, results in irreversible or fatal lung injury. We assumed that necroptosis of virus-infected alveolar epithelial cells (AEC) could promote local inflammation and further lung injury in COVID-19. Since CD8+ lymphocytes induced AEC cell death via cytotoxic molecules such as FAS ligands, we examined the involvement of FAS-mediated cell death in COVID-19 patients and murine COVID-19 model. We identified the occurrence of necroptosis and subsequent release of HMGB1 in the admitted patients with COVID-19. In the mouse model of COVID-19, lung inflammation and injury were attenuated in Fas-deficient mice compared to Fas-intact mice. The infection enhanced Type I interferon-inducible genes in both groups, while inflammasome-associated genes were specifically upregulated in Fas-intact mice. The treatment with necroptosis inhibitor, Nec1s, improved survival rate, lung injury, and systemic inflammation. SARS-CoV-2 induced necroptosis causes cytokine induction and lung damage, and its inhibition could be a novel therapeutic strategy for COVID-19.

Unmasking the complex roles of hypocalcemia in cancer, COVID-19, and sepsis: Engineered nanodelivery and diagnosis

Calcium (Ca2+) homeostasis is essential for maintaining physiological processes in the body. Disruptions in Ca2+ signaling can lead to various pathological conditions including inflammation, fibrosis, impaired immune function, and accelerated senescence. Hypocalcemia, a common symptom in diseases such as acute respiratory distress syndrome (ARDS), cancer, septic shock, and COVID-19, can have both potential protective and detrimental effects. This article explores the multifaceted role of Ca2+ dysregulation in inflammation, fibrosis, impaired immune function, and accelerated senescence, contributing to disease severity. Targeting Ca2+ signaling pathways may provide opportunities to develop novel therapeutics for age-related diseases and combat viral infections. However, the role of Ca2+ in viral infections is complex, and evidence suggests that hypocalcemia may have a protective effect against certain viruses, while changes in Ca2+ homeostasis can influence susceptibility to viral infections. The effectiveness and safety of Ca2+ supplements in COVID-19 patients remain a subject of ongoing research and debate. Further investigations are needed to understand the intricate interplay between Ca2+ signaling and disease pathogenesis.

Cardiogenic Pulmonary Edema in Emergency Medicine

Cardiogenic pulmonary edema (CPE) is characterized by the development of acute respiratory failure associated with the accumulation of fluid in the lung's alveolar spaces due to an elevated cardiac filling pressure. All cardiac diseases, characterized by an increasing pressure in the left side of the heart, can cause CPE. High capillary pressure for an extended period can also cause barrier disruption, which implies increased permeability and fluid transfer into the alveoli, leading to edema and atelectasis. The breakdown of the alveolar-epithelial barrier is a consequence of multiple factors that include dysregulated inflammation, intense leukocyte infiltration, activation of procoagulant processes, cell death, and mechanical stretch. Reactive oxygen and nitrogen species (RONS) can modify or damage ion channels, such as epithelial sodium channels, which alters fluid balance. Some studies claim that these patients may have higher levels of surfactant protein B in the bloodstream. The correct approach to patients with CPE should include a detailed medical history and a physical examination to evaluate signs and symptoms of CPE as well as potential causes. Second-level diagnostic tests, such as pulmonary ultrasound, natriuretic peptide level, chest radiograph, and echocardiogram, should occur in the meantime. The identification of the specific CPE phenotype is essential to set the most appropriate therapy for these patients. Non-invasive ventilation (NIV) should be considered early in the treatment of this disease. Diuretics and vasodilators are used for pulmonary congestion. Hypoperfusion requires treatment with inotropes and occasionally vasopressors. Patients with persistent symptoms and diuretic resistance might benefit from additional approaches (i.e., beta-agonists and pentoxifylline). This paper reviews the pathophysiology, clinical presentation, and management of CPE.

Human Identical Sequences, hyaluronan, and hymecromone ─ the new mechanism and management of COVID-19

COVID-19 caused by SARS-CoV-2 has created formidable damage to public health and market economy. Currently, SARS-CoV-2 variants has exacerbated the transmission from person-to-person. Even after a great deal of investigation on COVID-19, SARS-CoV-2 is still rampaging globally, emphasizing the urgent need to reformulate effective prevention and treatment strategies. Here, we review the latest research progress of COVID-19 and provide distinct perspectives on the mechanism and management of COVID-19. Specially, we highlight the significance of Human Identical Sequences (HIS), hyaluronan, and hymecromone ("Three-H") for the understanding and intervention of COVID-19. Firstly, HIS activate inflammation-related genes to influence COVID-19 progress through NamiRNA-Enhancer network. Accumulation of hyaluronan induced by HIS-mediated HAS2 upregulation is a substantial basis for clinical manifestations of COVID-19, especially in lymphocytopenia and pulmonary ground-glass opacity. Secondly, detection of plasma hyaluronan can be effective for evaluating the progression and severity of COVID-19. Thirdly, spike glycoprotein of SARS-CoV-2 may bind to hyaluronan and further serve as an allergen to stimulate allergic reaction, causing sudden adverse effects after vaccination or the aggravation of COVID-19. Finally, antisense oligonucleotides of HIS or inhibitors of hyaluronan synthesis (hymecromone) or antiallergic agents could be promising therapeutic agents for COVID-19. Collectively, Three-H could hold the key to understand the pathogenic mechanism and create effective therapeutic strategies for COVID-19.

Single Nucleotide Variant in FAS Associates With Organ Failure and Soluble Fas Cell Surface Death Receptor in Critical Illness

OBJECTIVES

Multiple organ failure in critically ill patients is associated with poor prognosis, but biomarkers contributory to pathogenesis are unknown. Previous studies support a role for Fas cell surface death receptor (Fas)-mediated apoptosis in organ dysfunction. Our objectives were to test for associations between soluble Fas and multiple organ failure, identify protein quantitative trait loci, and determine associations between genetic variants and multiple organ failure.

DESIGN

Retrospective observational cohort study.

SETTING

Four academic ICUs at U.S. hospitals.

PATIENTS

Genetic analyses were completed in a discovery (n = 1,589) and validation set (n = 863). Fas gene expression and flow cytometry studies were completed in outpatient research participants (n = 250).

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

In discovery and validation sets of critically ill patients, we tested for associations between enrollment plasma soluble Fas concentrations and Sequential Organ Failure Assessment score on day 3. We conducted a genome-wide association study of plasma soluble Fas (discovery n = 1,042) and carried forward a single nucleotide variant in the FAS gene, rs982764, for validation (n = 863). We further tested whether the single nucleotide variant in FAS (rs982764) was associated with Sequential Organ Failure Assessment score, FAS transcriptional isoforms, and Fas cell surface expression. Higher plasma soluble Fas was associated with higher day 3 Sequential Organ Failure Assessment scores in both the discovery (β = 4.07; p < 0.001) and validation (β = 6.96; p < 0.001) sets. A single nucleotide variant in FAS (rs982764G) was associated with lower plasma soluble Fas concentrations and lower day 3 Sequential Organ Failure Assessment score in meta-analysis (-0.21; p = 0.02). Single nucleotide variant rs982764G was also associated with a lower relative expression of the transcript for soluble as opposed to transmembrane Fas and higher cell surface expression of Fas on CD4+ T cells.

CONCLUSIONS

We found that single nucleotide variant rs982764G was associated with lower plasma soluble Fas concentrations in a discovery and validation population, and single nucleotide variant rs982764G was also associated with lower organ dysfunction on day 3. These findings support further study of the Fas pathway as a potential mediator of organ dysfunction in critically ill patients.

Gene Therapy for Acute Respiratory Distress Syndrome

Acute respiratory distress syndrome (ARDS) is a devastating clinical syndrome that leads to acute respiratory failure and accounts for over 70,000 deaths per year in the United States alone, even prior to the COVID-19 pandemic. While its molecular details have been teased apart and its pathophysiology largely established over the past 30 years, relatively few pharmacological advances in treatment have been made based on this knowledge. Indeed, mortality remains very close to what it was 30 years ago. As an alternative to traditional pharmacological approaches, gene therapy offers a highly controlled and targeted strategy to treat the disease at the molecular level. Although there is no single gene or combination of genes responsible for ARDS, there are a number of genes that can be targeted for upregulation or downregulation that could alleviate many of the symptoms and address the underlying mechanisms of this syndrome. This review will focus on the pathophysiology of ARDS and how gene therapy has been used for prevention and treatment. Strategies for gene delivery to the lung, such as barriers encountered during gene transfer, specific classes of genes that have been targeted, and the outcomes of these approaches on ARDS pathogenesis and resolution will be discussed.

Inhaled β2 Adrenergic Agonists and Other cAMP-Elevating Agents: Therapeutics for Alveolar Injury and Acute Respiratory Disease Syndrome?

Inhaled long-acting β-adrenergic agonists (LABAs) and short-acting β-adrenergic agonists are approved for the treatment of obstructive lung disease via actions mediated by β2 adrenergic receptors (β2-ARs) that increase cellular cAMP synthesis. This review discusses the potential of β2-AR agonists, in particular LABAs, for the treatment of acute respiratory distress syndrome (ARDS). We emphasize ARDS induced by pneumonia and focus on the pathobiology of ARDS and actions of LABAs and cAMP on pulmonary and immune cell types. β2-AR agonists/cAMP have beneficial actions that include protection of epithelial and endothelial cells from injury, restoration of alveolar fluid clearance, and reduction of fibrotic remodeling. β2-AR agonists/cAMP also exert anti-inflammatory effects on the immune system by actions on several types of immune cells. Early administration is likely critical for optimizing efficacy of LABAs or other cAMP-elevating agents, such as agonists of other Gs-coupled G protein-coupled receptors or cyclic nucleotide phosphodiesterase inhibitors. Clinical studies that target lung injury early, prior to development of ARDS, are thus needed to further assess the use of inhaled LABAs, perhaps combined with inhaled corticosteroids and/or long-acting muscarinic cholinergic antagonists. Such agents may provide a multipronged, repurposing, and efficacious therapeutic approach while minimizing systemic toxicity. SIGNIFICANCE STATEMENT: Acute respiratory distress syndrome (ARDS) after pulmonary alveolar injury (e.g., certain viral infections) is associated with ∼40% mortality and in need of new therapeutic approaches. This review summarizes the pathobiology of ARDS, focusing on contributions of pulmonary and immune cell types and potentially beneficial actions of β2 adrenergic receptors and cAMP. Early administration of inhaled β2 adrenergic agonists and perhaps other cAMP-elevating agents after alveolar injury may be a prophylactic approach to prevent development of ARDS.

The bioactivity of soluble Fas ligand is modulated by key amino acids of its stalk region

We have previously reported that the 26-amino acid N-terminus stalk region of soluble Fas ligand (sFasL), which is separate from its binding site, is required for its biological function. Here we investigate the mechanisms that link the structure of the sFasL stalk region with its function. Using site-directed mutagenesis we cloned a mutant form of sFasL in which all the charged amino acids of the stalk region were changed to neutral alanines (mut-sFasL). We used the Fas-sensitive Jurkat T-cell line and mouse and human alveolar epithelial cells to test the bioactivity of sFasL complexes, using caspase-3 activity and Annexin-V externalization as readouts. Finally, we tested the effects of mut-sFasL on lipopolysaccharide-induced lung injury in mice. We found that mutation of all the 8 charged amino acids of the stalk region into the non-charged amino acid alanine (mut-sFasL) resulted in reduced apoptotic activity compared to wild type sFasL (WT-sFasL). The mut-sFasL attenuated WT-sFasL function on the Fas-sensitive human T-cell line Jurkat and on primary human small airway epithelial cells. The inhibitory mechanism was associated with the formation of complexes of mut-sFasL with the WT protein. Intratracheal administration of the mut-sFasL to mice 24 hours after intratracheal Escherichia coli lipopolysaccharide resulted in attenuation of the inflammatory response 24 hours later. Therefore, the stalk region of sFasL has a critical role on bioactivity, and changes in the structure of the stalk region can result in mutant variants that interfere with the wild type protein function in vitro and in vivo.

Circulating sFasL Levels Predict the Severity and Outcome of Burn Injury: A Prospective Observational Study

BACKGROUND

Severe burn injury activates shock, inflammation, and blood cell system, but inappropriate reactions may lead to adverse outcomes. Soluble Fas ligand (sFasL) participates in apoptosis and inflammatory response. The circulating sFasL levels we investigated in association with the burn severity, shock, inflammation, blood cells, and mortality in patients with severe burns.

METHODS

A total of 56 patients with severe burns were recruited. The levels of sFasL and the biomarkers reflecting shock, organ damage, inflammation, and blood cells at 48 h postburn were analyzed. We compared the practical situation of patients that stratified by median sFasL levels and investigated the predictive value of sFasL for mortality.

RESULTS

High circulating sFasL levels were associated with the higher degrees of burn index, shock index, lactate, N-terminal probrain natriuretic peptide, total bilirubin, blood urea nitrogen, creatinine, tumor necrosis factor-α, interleukin-1β, interleukin-8, intercellular adhesion molecule 1, and complement 3, and the lower degrees of oxygenation index, lymphocytes, and platelets. Multiple linear regression analysis showed that the higher tumor necrosis factor-α (P < 0.001) and the lower oxygenation index (P = 0.031) and lymphocytes (P = 0.043) were associated with the higher sFasL. High sFasL (a unit is 50 ng/L) (odds ratio [OR] 5.50 [95% CI 1.04-29.20], P = 0.045) was an independent predictor of increased mortality by multivariate logistic regression analysis.

CONCLUSIONS

High circulating sFasL at 48 h postburn in patients with severe burns reflect shock, proinflammatory response, organ damage, and lymphocyte reductions and predict 30-day mortality.

Ischemia-reperfusion Injury in the Transplanted Lung: A Literature Review

Lung ischemia-reperfusion injury (LIRI) and primary graft dysfunction are leading causes of morbidity and mortality among lung transplant recipients. Although extensive research endeavors have been undertaken, few preventative and therapeutic treatments have emerged for clinical use. Novel strategies are still needed to improve outcomes after lung transplantation. In this review, we discuss the underlying mechanisms of transplanted LIRI, potential modifiable targets, current practices, and areas of ongoing investigation to reduce LIRI and primary graft dysfunction in lung transplant recipients.

Role of Receptor for Advanced Glycation End Products in Regulating Lung Fluid Balance in Lipopolysaccharide-induced Acute Lung Injury and Infection-Related Acute Respiratory Distress Syndrome

Receptor for advanced glycation end products (RAGE) is implicated in inflammatory responses in acute lung injury (ALI)/acute respiratory distress syndrome (ARDS), but its role in pulmonary edema formation remains unclear, especially in infection-related ARDS mainly caused by pneumonia or sepsis. In this study, we investigated the role of RAGE in alveolar fluid regulation by using RAGE gene knockout (RAGE) mice in a murine ALI model induced by lipopolysaccharide (LPS), and by comparing soluble RAGE (sRAGE) levels in serum and bronchial alveolar lavage fluid between ARDS patients and control subjects. We found that RAGE knockout significantly improved alveolar fluid clearance and reduced pulmonary vascular albumin leakage upon LPS challenge. Furthermore, LPS-induced substantial decrease in lung expression of sodium-potassium ATPase (Na,K-ATPase), epithelial sodium channel, and zonula occluden-1 (ZO-1) were fully or partially restored by the deletion of RAGE. In addition to this, LPS-induced lung leukocyte infiltration and inflammatory cytokine and chemokine release were all attenuated in RAGE mice as compared to wide-type mice. In infection-related ARDS patients, both serum and bronchial alveolar lavage fluid levels of the sRAGE were much higher than those in control subjects, and they were positively correlated with pulmonary vascular permeability and levels of interleukin (IL)-6, IL-8, and macrophage inflammatory protein (MIP)-2. Taken together, we provided the first direct evidence for the essential role of RAGE in regulating lung fluid balance in infection-related ARDS/ALI. The underlying mechanisms may involve the downregulation of both ion-channel and tight junction proteins mediated by RAGE signaling in bacterial endotoxin-induced lung injury.

Activation of mas restores hyperoxia-induced loss of lung epithelial barrier function through inhibition of apoptosis

BACKGROUND

Neonatal therapy with a high concentration of oxygen (hyperoxia) is a known cause of bronchopulmonary dysplasia (BPD). BPD is characterized by increased pulmonary permeability and diffuse infiltration of various inflammatory cells. Disruption of the epithelial barrier may lead to altered pulmonary permeability and airways fluid accumulation. Mas receptor is a component of the renin angiotensin system and is the receptor for the protective endogenous peptide angiotensin 1-7. The activation of the Mas receptor was previously shown to have protective pulmonary responses. However, the effect of Mas receptor activation on epithelial barrier integrity has not been tested.

OBJECTIVE

To determine the effects of hyperoxia with or without Mas receptor activation on epithelial cell barrier integrity.

DESIGN/METHODS

Human epithelial cell line A549 was cultured on transwell polycarbonate porous membrane to confluence and treated with 95% oxygen (hyperoxia) for 72 hours with or without the Mas receptor agonist (AVE0991), or the apoptotic inhibitors Z-VAD-FMK or aurintricarboxylic acid. The cells were then challenged with Rhodamine labeled bovine serum albumin (Rh-BSA) on one side of the membrane. Fluorescent quantitation of Rh-BSA (albumin flux) was performed on the media in the other side of the membrane 3 hours later and was compared with 21% oxygen (Normoxia) control group. A549 cells were also cultured with or without AVE0991 in hyperoxia or normoxia and used for nuclear fragmentation apoptosis assay using propidium iodide staining.

RESULTS

Hyperoxia induced an increase in albumin flux that was significantly prevented by AVE0991 treatment and by the apoptosis inhibitors. AVE0991 also significantly decreased the hyperoxia-induced nuclear fragmentation.

CONCLUSION

These results suggest that hyperoxia causes a disruption in the epithelial barrier integrity, and that this disruption is inhibited by the Mas receptor agonist AVE0991 through inhibition of epithelial apoptosis. These results reveal a novel potential drug for BPD and pulmonary edema treatment.

Penehyclidine hydrochloride exerts protective effects in rats with acute lung injury via the Fas/FasL signaling pathway

Acute lung injury (ALI) is a critical syndrome that is associated with high morbidity and mortality rates. The activation of the Fas/Fas ligand (FasL) signaling pathway may be an important pathophysiological mechanism during ALI development. Penehyclidine hydrochloride (PHC) has been revealed to exhibit anti-apoptotic properties and may attenuate the observed systemic inflammatory response. The present study was performed to elucidate the molecular mechanism of PHC in the regulation of the Fas/FasL signaling pathway in rats with ALI. An ALI rat model was constructed by inducing blunt chest trauma and hemorrhagic shock (T/HS), with PHC administration prior to or following T/HS. At 6 h following T/HS, blood samples and lung tissues were collected. Western blotting, arterial blood gas analysis, ELISA, hematoxylin and eosin staining, terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling staining and biochemical indicator analysis were performed to determine the degree of lung injury and the key signaling pathways associated with lung damage. The results indicated that the administration of PHC following T/HS effectively attenuates lung injury by improving pulmonary oxygenation, decreasing histopathological damage, decreasing polymorphonuclear neutrophil count and decreasing Fas, FasL, caspase-8, caspase-3, tumor necrosis factor-α, interleukin (IL)-6 and IL-1β expression. The results indicated that PHC exhibits anti-apoptotic functions and exerts protective effects in ALI rats induced by T/HS, which may be attributed to the inhibition of the Fas/FasL signaling pathway.

Fas activation alters tight junction proteins in acute lung injury

Background:The acute respiratory distress syndrome (ARDS) is characterized by protein-rich oedema in the alveolar spaces, a feature in which Fas-mediated apoptosis of the alveolar epithelium has been involved. Objective:To determine whether Fas activation increases protein permeability by mechanisms involving disruption of the paracellular tight junction (TJ) proteins in the pulmonary alveoli. Methods: Protein permeability and the expression of TJ proteins were assessed in vivo in wild-type and Fas-deficient lpr mice 16 hours after the intratracheal instillation of recombinant human soluble Fas ligand (rh-sFasL), and at different time points in vitro in human pulmonary alveolar epithelial cells (HPAEpiC) exposed to rh-sFasL Results:Activation of the Fas pathway increased protein permeability in mouse lungs and altered the expression of the TJ proteins occludin and zonula occludens-1 in the alveolar-capillary membrane in vivo and in human alveolar epithelial cell monolayers in vitro. Blockade of caspase-3, but not inhibition of tyrosine kinase dependent pathways, prevented the alterations in TJ protein expression and permeability induced by the Fas/FasL system in human alveolar cell monolayers in vitro. We also observed that both the Fas-induced increase of protein permeability and disruption of TJ proteins occurred before cell death could be detected in the cell monolayers in vitro. Conclusion:Targeting caspase pathways could prevent the disruption of TJs and reduce the formation of lung oedema in the early stages of ARDS.

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.

New insights into the mechanisms of pulmonary edema in acute lung injury

Appearance of alveolar protein-rich edema is an early event in the development of acute respiratory distress syndrome (ARDS). Alveolar edema in ARDS results from a significant increase in the permeability of the alveolar epithelial barrier, and represents one of the main factors that contribute to the hypoxemia in these patients. Damage of the alveolar epithelium is considered a major mechanism responsible for the increased pulmonary permeability, which results in edema fluid containing high concentrations of extravasated macromolecules in the alveoli. The breakdown of the alveolar-epithelial barrier is a consequence of multiple factors that include dysregulated inflammation, intense leukocyte infiltration, activation of pro-coagulant processes, cell death and mechanical stretch. The disruption of tight junction (TJ) complexes at the lateral contact of epithelial cells, the loss of contact between epithelial cells and extracellular matrix (ECM), and relevant changes in the communication between epithelial and immune cells, are deleterious alterations that mediate the disruption of the alveolar epithelial barrier and thereby the formation of lung edema in ARDS.

Inhibition of Prolyl Hydroxylase Attenuates Fas Ligand-Induced Apoptosis and Lung Injury in Mice

Alveolar epithelial injury and increased alveolar permeability are hallmarks of acute respiratory distress syndrome. Apoptosis of lung epithelial cells via the Fas/Fas ligand (FasL) pathway plays a critical role in alveolar epithelial injury. Activation of hypoxia-inducible factor (HIF)-1 by inhibition of prolyl hydroxylase domain proteins (PHDs) is a possible therapeutic approach to attenuate apoptosis and organ injury. Here, we investigated whether treatment with dimethyloxalylglycine (DMOG), an inhibitor of PHDs, could attenuate Fas/FasL-dependent apoptosis in lung epithelial cells and lung injury. DMOG increased HIF-1α protein expression in vitro in MLE-12 cells, a murine alveolar epithelial cell line. Treatment of MLE-12 cells with DMOG significantly suppressed cell surface expression of Fas and attenuated FasL-induced caspase-3 activation and apoptotic cell death. Inhibition of the HIF-1 pathway by echinomycin or small interfering RNA transfection abolished these antiapoptotic effects of DMOG. Moreover, intraperitoneal injection of DMOG in mice increased HIF-1α expression and decreased Fas expression in lung tissues. DMOG treatment significantly attenuated caspase-3 activation, apoptotic cell death in lung tissue, and the increase in alveolar permeability in mice instilled intratracheally with FasL. In addition, inflammatory responses and histopathological changes were also significantly attenuated by DMOG treatment. In conclusion, inhibition of PHDs protects lung epithelial cells from Fas/FasL-dependent apoptosis through HIF-1 activation and attenuates lung injury in mice.

Intratracheal Administration of Small Interfering RNA Targeting Fas Reduces Lung Ischemia-Reperfusion Injury

OBJECTIVES

Lung ischemia-reperfusion injury is the main cause of primary graft dysfunction after lung transplantation and results in increased morbidity and mortality. Fas-mediated apoptosis is one of the pathologic mechanisms involved in the development of ischemia-reperfusion injury. We hypothesized that the inhibition of Fas gene expression in lungs by intratracheal administration of small interfering RNA could reduce lung ischemia-reperfusion injury in an ex vivo model reproducing the procedural sequence of lung transplantation.

DESIGN

Prospective, randomized, controlled experimental study.

SETTING

University research laboratory.

SUBJECTS

C57/BL6 mice weighing 28-30 g.

INTERVENTIONS

Ischemia-reperfusion injury was induced in lungs isolated from mice, 48 hours after treatment with intratracheal small interfering RNA targeting Fas, control small interfering RNA, or vehicle. Isolated lungs were exposed to 6 hours of cold ischemia (4°C), followed by 2 hours of warm (37°C) reperfusion with a solution containing 10% of fresh whole blood and mechanical ventilation with constant low driving pressure.

MEASUREMENTS AND MAIN RESULTS

Fas gene expression was significantly silenced at the level of messenger RNA and protein after ischemia-reperfusion in lungs treated with small interfering RNA targeting Fas compared with lungs treated with control small interfering RNA or vehicle. Silencing of Fas gene expression resulted in reduced edema formation (bronchoalveolar lavage protein concentration and lung histology) and improvement in lung compliance. These effects were associated with a significant reduction of pulmonary cell apoptosis of lungs treated with small interfering RNA targeting Fas, which did not affect cytokine release and neutrophil infiltration.

CONCLUSIONS

Fas expression silencing in the lung by small interfering RNA is effective against ischemia-reperfusion injury. This approach represents a potential innovative strategy of organ preservation before lung transplantation.

A new experimental model of acid- and endotoxin-induced acute lung injury in rats

The majority of the animal models of acute lung injury (ALI) are focused on the acute phase. This limits the studies of the mechanisms involved in later phases and the effects of long-term treatments. Thus the goal of this study was to develop an experimental ALI model of aspiration pneumonia, in which diffuse alveolar damage continues for 72 h. Rats were intratracheally instilled with one dose of HCl (0.1 mol/l) followed by another instillation of one dose of LPS (0, 10, 20, 30, or 40 μg/g body weight) 2 h later, which models aspiration of gastric contents that progresses to secondary lung injury from bacteria or bacterial products. The rats were euthanized at 24, 48, and 72 h after the last instillation. The results showed that HCl and LPS at all doses caused activation of inflammatory responses, increased protein permeability and apoptosis, and induced mild hypoxemia in rat lungs at 24 h postinstillation. However, this lung damage was present at 72 h only in rats receiving HCl and LPS at the doses of 30 and 40 μg/g body wt. Mortality (∼50%) occurred in the first 48 h and only in the rats treated with HCl and LPS at the highest dose (40 μg/g body wt). In conclusion, intratracheal instillation of HCl followed by LPS at the dose of 30 μg/g body wt results in severe diffuse alveolar damage that continues at least 72 h. This rat model of aspiration pneumonia-induced ALI will be useful for testing long-term effects of new therapeutic strategies in ALI.

With-No-Lysine Kinase 4 Mediates Alveolar Fluid Regulation in Hyperoxia-Induced Lung Injury

OBJECTIVES

To investigate mechanisms involved in the regulation of epithelial ion channels and alveolar fluid clearance in hyperoxia-induced lung injury.

DESIGN

Laboratory animal experiments.

SETTING

Animal care facility procedure room in a medical center.

SUBJECTS

Wild-type, STE20/SPS1-related proline/alanine-rich kinase knockout (SPAK(-/-)), and with-no-lysine kinase 4 knockin (WNK4(D561A/+)) mice.

INTERVENTIONS

Mice were exposed to room air or 95% hyperoxia for 60 hours.

MEASUREMENTS AND MAIN RESULTS

Exposure to hyperoxia for 60 hours increased the lung expression of with-no-lysine kinase 4 and led to STE20/SPS1-related proline/alanine-rich kinase and sodium-potassium-chloride cotransporter phosphorylation, which resulted in the suppression of alveolar fluid clearance and increase of lung edema. WNK4(D561A/+) mice at the baseline presented an abundance of epithelium sodium channel and high levels of STE20/SPS1-related proline/alanine-rich kinase and sodium-potassium-chloride cotransporter phosphorylation. Compared with the wild-type group, hyperoxia caused greater epithelium sodium channel expression in WNK4(D561A/+) mice, but no significant difference in STE20/SPS1-related proline/alanine-rich kinase and sodium-potassium-chloride cotransporter phosphorylation. The functional inactivation of sodium-potassium-chloride cotransporter by gene knockout in SPAK(-/-) mice yielded a lower severity of lung injury and longer animal survival, whereas constitutive expression of with-no-lysine kinase 4 exacerbated the hyperoxia-induced lung injury. Pharmacologic inhibition of sodium-potassium-chloride cotransporter by inhaled furosemide improved animal survival in WNK4(D561A/+) mice. By contrast, inhibition of epithelium sodium channel exacerbated the hyperoxia-induced lung injury and animal death.

CONCLUSIONS

With-no-lysine kinase 4 plays a crucial role in the regulation of epithelial ion channels and alveolar fluid clearance, mainly via phosphorylation and activation of STE20/SPS1-related proline/alanine-rich kinase and sodium-potassium-chloride cotransporter.

The caspase inhibitor zVAD increases lung inflammation in pneumovirus infection in mice

Severe respiratory syncytial virus (RSV) disease is a frequent cause of acute respiratory distress syndrome (ARDS) in young children, and is associated with marked lung epithelial injury and neutrophilic inflammation. Experimental studies on ARDS have shown that inhibition of apoptosis in the lungs reduces lung epithelial injury. However, the blockade of apoptosis in the lungs may also have deleterious effects by hampering viral clearance, and importantly, by enhancing or prolonging local proinflammatory responses. The aim of this study was to determine the effect of the broad caspase inhibitor Z-VAD(OMe)-FMK (zVAD) on inflammation and lung injury in a mouse pneumovirus model for severe RSV disease. Eight- to 11-week-old female C57BL/6OlaHsd mice were inoculated with the rodent-specific pneumovirus pneumonia virus of mice (PVM) strain J3666 and received multiple injections of zVAD or vehicle (control) during the course of disease, after which they were studied for markers of apoptosis, inflammation, and lung injury on day 7 after infection. PVM-infected mice that received zVAD had a strong increase in neutrophil numbers in the lungs, which was associated with decreased neutrophil apoptosis. Furthermore, zVAD treatment led to higher concentrations of several proinflammatory cytokines in the lungs and more weight loss in PVM-infected mice. In contrast, zVAD did not reduce apoptosis of lung epithelial cells and did not affect the degree of lung injury, permeability, and viral titers in PVM disease. We conclude that zVAD has an adverse effect in severe pneumovirus disease in mice by enhancing the lung proinflammatory response.

How to measure alterations in alveolar barrier function as a marker of lung injury

The alveolar capillary membrane maintains the proper water and solute content of the epithelial lining fluid at the alveolar air-liquid interface, which is critical for adequate gas exchange in the lung. This is possible due to the alveolar fluid clearance (AFC) capacity of this membrane that assists in the removal of salt and water from the alveolar air spaces. The alveolar capillary membrane also provides a barrier that restricts the passage of proteins and water from the interstitial and vascular compartments into the alveolar air spaces. This restricted passage is due to the presence of tight junctions between adjacent alveolar epithelial cells. Severe injury to the alveolar epithelial/endothelial membrane results in increased protein permeability and impairment of AFC, which leads to the formation of protein-rich edema with the consequent deterioration of gas exchange. Many animal models of lung injury, focused on damage of the alveolar-capillary membrane, assess the AFC capacity and the barrier function. We describe a simple method to assess the AFC rate in normal and pathological conditions in mice. We also describe two complementary methods to assess the alveolar-capillary barrier function, which require measuring the concentration of endogenous plasma proteins in bronchoalveolar lavage fluid and detection of tight-junction proteins in lung tissue by immunofluorescence.

Novel regulators of endothelial barrier function

Endothelial barrier function is an essential and tightly regulated process that ensures proper compartmentalization of the vascular and interstitial space, while allowing for the diffusive exchange of small molecules and the controlled trafficking of macromolecules and immune cells. Failure to control endothelial barrier integrity results in excessive leakage of fluid and proteins from the vasculature that can rapidly become fatal in scenarios such as sepsis or the acute respiratory distress syndrome. Here, we highlight recent advances in our understanding on the regulation of endothelial permeability, with a specific focus on the endothelial glycocalyx and endothelial scaffolds, regulatory intracellular signaling cascades, as well as triggers and mediators that either disrupt or enhance endothelial barrier integrity, and provide our perspective as to areas of seeming controversy and knowledge gaps, respectively.

Astaxanthin inhibits apoptosis in alveolar epithelial cells type II in vivo and in vitro through the ROS-dependent mitochondrial signalling pathway

Oxidative stress is an important molecular mechanism underlying lung fibrosis. The mitochondrion is a major organelle for oxidative stress in cells. Therefore, blocking the mitochondrial signalling pathway may be the best therapeutic manoeuver to ameliorate lung fibrosis. Astaxanthin (AST) is an excellent antioxidant, but no study has addressed the pathway of AST against pulmonary oxidative stress and free radicals by the mitochondrion-mediated signalling pathway. In this study, we investigated the antioxidative effects of AST against H₂O₂- or bleomycin (BLM)-induced mitochondrial dysfunction and reactive oxygen species (ROS) production in alveolar epithelial cells type II (AECs-II) in vivo and in vitro. Our data show that AST blocks H₂O₂- or BLM-induced ROS generation and dose-dependent apoptosis in AECs-II, as characterized by changes in cell and mitochondria morphology, translocation of apoptotic proteins, inhibition of cytochrome c (Cyt c) release, and the activation of caspase-9, caspase-3, Nrf-2 and other cytoprotective genes. These data suggest that AST inhibits apoptosis in AECs-II cells through the ROS-dependent mitochondrial signalling pathway and may be of potential therapeutic value in lung fibrosis treatment.

The effects of salbutamol on epithelial ion channels depend on the etiology of acute respiratory distress syndrome but not the route of administration

Introduction

We investigated the effects of intravenous and intratracheal administration of salbutamol on lung morphology and function, expression of ion channels, aquaporin, and markers of inflammation, apoptosis, and alveolar epithelial/endothelial cell damage in experimental pulmonary (p) and extrapulmonary (exp) mild acute respiratory distress syndrome (ARDS).

Methods

In this prospective randomized controlled experimental study, 56 male Wistar rats were randomly assigned to mild ARDS induced by either intratracheal (n = 28, ARDSp) or intraperitoneal (n = 28, ARDSexp) administration of E. coli lipopolysaccharide. Four animals with no lung injury served as controls (NI). After 24 hours, animals were anesthetized, mechanically ventilated in pressure-controlled mode with low tidal volume (6 mL/kg), and randomly assigned to receive salbutamol (SALB) or saline 0.9% (CTRL), intravenously (i.v., 10 μg/kg/h) or intratracheally (bolus, 25 μg). Salbutamol doses were targeted at an increase of ≈ 20% in heart rate. Hemodynamics, lung mechanics, and arterial blood gases were measured before and after (at 30 and 60 min) salbutamol administration. At the end of the experiment, lungs were extracted for analysis of lung histology and molecular biology analysis. Values are expressed as mean ± standard deviation, and fold changes relative to NI, CTRL vs. SALB.

Results

The gene expression of ion channels and aquaporin was increased in mild ARDSp, but not ARDSexp. In ARDSp, intravenous salbutamol resulted in higher gene expression of alveolar epithelial sodium channel (0.20 ± 0.07 vs. 0.68 ± 0.24, p < 0.001), aquaporin-1 (0.44 ± 0.09 vs. 0.96 ± 0.12, p < 0.001) aquaporin-3 (0.31 ± 0.12 vs. 0.93 ± 0.20, p < 0.001), and Na-K-ATPase-α (0.39 ± 0.08 vs. 0.92 ± 0.12, p < 0.001), whereas intratracheal salbutamol increased the gene expression of aquaporin-1 (0.46 ± 0.11 vs. 0.92 ± 0.06, p < 0.001) and Na-K-ATPase-α (0.32 ± 0.07 vs. 0.58 ± 0.15, p < 0.001). In ARDSexp, the gene expression of ion channels and aquaporin was not influenced by salbutamol. Morphological and functional variables and edema formation were not affected by salbutamol in any of the ARDS groups, regardless of the route of administration.

Conclusion

Salbutamol administration increased the expression of alveolar epithelial ion channels and aquaporin in mild ARDSp, but not ARDSexp, with no effects on lung morphology and function or edema formation. These results may contribute to explain the negative effects of β2-agonists on clinical outcome in ARDS.