The role of apoptosis in the pathophysiology of Acute Respiratory Distress Syndrome (ARDS): An up-to-date cell-specific review

Oxidative stress, defective proteostasis and immunometabolic complications in critically ill patients

Oxidative stress (OS) develops in critically ill patients as a metabolic consequence of the immunoinflammatory and degenerative processes of the tissues. These induce increased and/or dysregulated fluxes of reactive species enhancing their pro-oxidant activity and toxicity. At the same time, OS sustains its own inflammatory and immunometabolic pathogenesis, leading to a pervasive and vitious cycle of events that contribute to defective immunity, organ dysfunction and poor prognosis. Protein damage is a key player of these OS effects; it generates increased levels of protein oxidation products and misfolded proteins in both the cellular and extracellular environment, and contributes to forms DAMPs and other proteinaceous material to be removed by endocytosis and proteostasis processes of different cell types, as endothelial cells, tissue resident monocytes-macrophages and peripheral immune cells. An excess of OS and protein damage in critical illness can overwhelm such cellular processes ultimately interfering with systemic proteostasis, and consequently with innate immunity and cell death pathways of the tissues thus sustaining organ dysfunction mechanisms. Extracorporeal therapies based on biocompatible/bioactive membranes and new adsorption techniques may hold some potential in reducing the impact of OS on the defective proteostasis of patients with critical illness. These can help neutralizing reactive and toxic species, also removing solutes in a wide spectrum of molecular weights thus improving proteostasis and its immunometabolic corelates. Pharmacological therapy is also moving steps forward which could help to enhance the efficacy of extracorporeal treatments. This narrative review article explores the aspects behind the origin and pathogenic role of OS in intensive care and critically ill patients, with a focus on protein damage as a cause of impaired systemic proteostasis and immune dysfunction in critical illness.

Adipose-Derived exosome from Diet-Induced-Obese mouse attenuates LPS-Induced acute lung injury by inhibiting inflammation and Apoptosis: In vivo and in silico insight

BACKGROUND

Acute lung injury (ALI) is a severe clinical condition in the intensive care units, and obesity is a high risk of ALI. Paradoxically, obese ALI patients had better prognosis than non-obese patients, and the mechanism remains largely unknown.

METHODS

Mouse models of ALI and diet-induced-obesity (DIO) were used to investigate the effect of exosomes derived from adipose tissue. The adipose-derived exosomes (ADEs) were isolated by ultracentrifugation, and the role of exosomal miRNAs in the ALI was studied.

RESULTS

Compared with ADEs of control mice (C-Exo), ADEs of DIO mice (D-Exo) increased survival rate and mitigated pulmonary lesions of ALI mice. GO and KEGG analyses showed that the target genes of 40 differentially expressed miRNAs between D-Exo and C-Exo were mainly involved with inflammation, apoptosis and cell cycle. Furthermore, the D-Exo treatment significantly decreased Ly6G+ cell infiltration, down-regulated levels of pro-inflammatory cytokines (IL-6, IL-12, TNF-α, MCP-1) and chemokines (IL-8 and MIP-2), reduced pulmonary apoptosis and arrest at G0G1 phase (P < 0.01). And the protective effects of D-Exo were better than those of C-Exo (P < 0.05). Compared with the C-Exo mice, the levels of miR-16-5p and miR-335-3p in the D-Exo mice were significantly up-regulated (P < 0.05), and the expressions of IKBKB and TNFSF10, respective target of miR-16-5p and miR-335-3p by bioinformatic analysis, were significantly down-regulated in the D-Exo mice (P < 0.05).

CONCLUSIONS

Exosomes derived from adipose tissue of DIO mice are potent to attenuate LPS-induced ALI, which could be contributed by exosome-carried miRNAs. Our data shed light on the interaction between obesity and ALI.

Effect of caspase inhibitors on hemodynamics and inflammatory factors in ARDS model rats

To study the effects of caspase inhibitors on hemodynamics and inflammatory factors in acute respiratory distress syndrome (ARDS) model rats. Sixty healthy male Wistar rats were randomly divided into three groups, namely, the control group, ARDS group and ARDS + Caspase inhibitor group, with 20 rats in each group. The control group was intraperitoneally injected with 2 mL/kg saline, and the ARDS model group was established by intraperitoneally injecting 4 mg/kg Lipopolysaccharide (LPS), ARDS + Caspase inhibitor group was adminstered 20 mg/kg caspase inhibitor after intraperitoneal LPS injection. Changes in pulmonary arterial pressure (PAP) and mean arterial pressure (MAP) at 6 and 12 h before and after administration were recorded. Moreover, arterial blood gas was evaluated with a blood gas analyzer and changes in the partial pressure of O2 (PaO2), partial pressure of CO2 (PaCO2), partial pressure of O2/fraction of inspired O2 (PaO2/FiO2) were evaluated. In addition, the lung wet/dry weight (W/D) ratio and inflammatory factor levels in lung tissue were determined. Finally, pathological sections were used to determine the pulmonary artery media thickness (MT), MT percentage (MT%), and the degree of muscle vascularization. The pulmonary arterial pressure of rats was determined at several time points. Compared with the control group, the model group had a significantly increased pulmonary arterial pressure at each time point (P < 0.01), and the mean arterial pressure significantly increased at 6 h (P < 0.05). Compared with that of rats in the model group, the pulmonary arterial pressure of rats in drug administration group was significantly reduced at each time point after administration (P < 0.01), and the mean arterial pressure was significantly reduced at 6 h (P < 0.05). The arterial blood gas analysis showed that compared with those in the control group, PaO2, PaCO2 and PaO2/FiO2 in the model group were significantly reduced (P < 0.01), and PaO2, PaCO2 and PaO2/FiO2 were significantly increased after caspase inhibitor treatment (P < 0.05 or 0.01). The levels of the inflammatory mediators tumor necrosis factor-alpha (TNF-α), interleukin-1β (IL-1β) and interleukin-6 (IL-6) in the model group were significantly higher than those in the control group (P < 0.01), and they were significantly decreased after caspase inhibitor treatment (P < 0.01). In the model group, pulmonary artery MT, MT% and the degree of muscle vascularization were significantly increased (P < 0.05 or 0.01), and pulmonary artery MT and the degree of muscle vascularization were significantly reduced after caspase inhibitor treatment (P < 0.05 or 0.01). Apoptosis Repressor with a Caspase Recuitment Domain (ARC) can alleviate the occurrence and development of pulmonary hypertension (PH) by affecting hemodynamics and reducing inflammation.

Effects of sevoflurane on lung alveolar epithelial wound healing and survival in a sterile in vitro model of acute respiratory distress syndrome

Acute respiratory distress syndrome (ARDS) is a serious lung condition that often leads to hospitalization in intensive care units and a high mortality rate. Sevoflurane is a volatile anesthetic with growing interest for sedation in ventilated patients with ARDS. It has been shown to have potential lung-protective effects, such as reduced inflammation and lung edema, or improved arterial oxygenation. In this study, we investigated the effects of sevoflurane on lung injury in cultured human carcinoma-derived lung alveolar epithelial (A549) cells. We found that sevoflurane was associated with improved wound healing after exposure to inflammatory cytokines, with preserved cell proliferation but no effect on cell migration properties. Sevoflurane exposure was also associated with enhanced cell viability and active autophagy in A549 cells exposed to cytokines. These findings suggest that sevoflurane may have beneficial effects on lung epithelial injury by promoting alveolar epithelial wound healing and by influencing the survival and proliferation of A549 epithelial cells in vitro. Further research is needed to confirm these findings and to investigate the key cellular mechanisms explaining sevoflurane's potential effects on lung epithelial injury.

Monochasma savatieri Franch. protects against acute lung injury via α7nAChR-TLR4/NF-κB p65 signaling pathway based on integrated pharmacology analysis

ETHNOPHARMACOLOGICAL RELEVANCE

Acute lung injury (ALI) is a life-threatening condition with high morbidity and mortality, underscoring the urgent need for novel treatments. Monochasma savatieri Franch. (LRC) is commonly used clinically to treat wind-heat cold, bronchitis, acute pneumonia and acute gastroenteritis. However, its role in the treatment of ALI and its mechanism of action are still unclear.

AIM OF THE STUDY

This study aimed to demonstrate the pharmacological effects and underlying mechanisms of LRC extract, and provide important therapeutic strategies and theoretical basis for ALI.

MATERIALS AND METHODS

In this study, a research paradigm of integrated pharmacology combining histopathological analysis, network pharmacology, metabolomics, and biochemical assays was used to elucidate the mechanisms underlaying the effects of LRC extract on LPS-induced ALI in BALB/c mice.

RESULTS

The research findings demonstrated that LRC extract significantly alleviated pathological damage in lung tissues and inhibited apoptosis in alveolar epithelial cells, and the main active components were luteolin, isoacteoside, and aucubin. Lung tissue metabolomic and immunohistochemical methods confirmed that LRC extract could restore metabolic disorders in ALI mice by correcting energy metabolism imbalance, activating cholinergic anti-inflammatory pathway (CAP), and inhibiting TLR4/NF-κB signaling pathway.

CONCLUSIONS

This study showed that LRC extract inhibited the occurrence and development of ALI inflammation by promoting the synthesis of antioxidant metabolites, balancing energy metabolism, activating CAP and suppressing the α7nAChR-TLR4/NF-κB p65 signaling pathway. In addition, our study provided an innovative research model for exploring the effective ingredients and mechanisms of traditional Chinese medicine. To the best of our knowledge, this is the first report describing the protective effects of LRC extract in LPS-induced ALI mice.

Hispidulin exerts a protective effect against oleic acid induced-ARDS in the rat via inhibition of ACE activity and MAPK pathway

This study investigates the protective role of Hispidulin on acute respiratory distress syndrome (ARDS) in rats. Rats were divided into three groups: control, ARDS, ARDS+ Hispidulin. The ARDS models were established by injecting rats with oleic acid. Hispidulin (100 mg/kg) was injected i.p. an hour before ARDS. Myeloperoxidase (MPO), Interleukin-8 (IL-8), Mitogen-activated protein kinases (MAPK), Lipid Peroxidation (LPO), Superoxide Dismutase (SOD), Glutathione (GSH), and Angiotensin-converting enzyme (ACE) were determined by ELISA. Tumor necrosis factor-alpha (TNF-α) expression was described by RT-qPCR. Caspase-3 immunostaining was performed to evaluate apoptosis. Compared with the model group, a significant decrease was observed in the MPO, IL-8, MAPK, ACE, LPO levels, and TNF-α expression in the ARDS+ Hispidulin group. Moreover, reduced caspase-3 immunoreactivity and activity of ACE were detected in the Hispidulin+ARDS group. The protective effect of Hispidulin treatment may act through inhibition of the ACE activity and then regulation of inflammatory cytokine level and alteration of apoptosis.

Glycogen Synthase Kinase-3 Inhibition by CHIR99021 Promotes Alveolar Epithelial Cell Proliferation and Lung Regeneration in the Lipopolysaccharide-Induced Acute Lung Injury Mouse Model

Acute respiratory distress syndrome (ARDS) is a life-threatening lung injury that currently lacks effective clinical treatments. Evidence highlights the potential role of glycogen synthase kinase-3 (GSK-3) inhibition in mitigating severe inflammation. The inhibition of GSK-3α/β by CHIR99021 promoted fetal lung progenitor proliferation and maturation of alveolar epithelial cells (AECs). The precise impact of CHIR99021 in lung repair and regeneration during acute lung injury (ALI) remains unexplored. This study intends to elucidate the influence of CHIR99021 on AEC behaviour during the peak of the inflammatory phase of ALI and, after its attenuation, during the repair and regeneration stage. Furthermore, a long-term evaluation was conducted post CHIR99021 treatment at a late phase of the disease. Our results disclosed the role of GSK-3α/β inhibition in promoting AECI and AECII proliferation. Later administration of CHIR99021 during ALI progression contributed to the transdifferentiation of AECII into AECI and an AECI/AECII increase, suggesting its contribution to the renewal of the alveolar epithelial population and lung regeneration. This effect was confirmed to be maintained histologically in the long term. These findings underscore the potential of targeted therapies that modulate GSK-3α/β inhibition, offering innovative approaches for managing acute lung diseases, mostly in later stages where no treatment is available.

Particulate matter-mediated oxidative stress induces airway inflammation and pulmonary dysfunction through TXNIP/NF-κB and modulation of the SIRT1-mediated p53 and TGF-β/Smad3 pathways in mice

Exposure to particulate matter is currently recognized as a serious aggravating factor of respiratory diseases. In this study, we investigated the effects of particulate matter (PM) on the respiratory system in BALB/c mice and NCI-H292 cells. PM (0, 2.5, 5 and 20 mg/kg) was administered to mice by intra-tracheal instillation for 7 days. After a 7 day-repeated treatment of PM, we evaluated inflammatory cytokines/cell counts in bronchoalveolar lavage fluid (BALF) and conducted pulmonary histology and functional test. We also investigated the role of TXNIP/NF-κB and SIRT1-mediated p53 and TGF-β/Smad3 pathways in PM-induced airway inflammation and pulmonary dysfunction. PM caused a significant increase in pro-inflammatory cytokines, inflammatory cell counts in bronchoalveolar lavage fluid. PM-mediated oxidative stress down-regulated thioredoxin-1 and up-regulated thioredoxin-interacting protein and activation of nuclear factor-kappa B in the lung tissue and PM-treated NCI-H292 cells. PM suppressed sirtuin1 protein levels and increased p53 acetylation in PM-exposed mice and PM-treated NCI-H292 cells. In addition, PM caused inflammatory cell infiltration and the thickening of alveolar walls by exacerbating the inflammatory response in the lung tissue. PM increased levels of transforming growth factor-β, phosphorylation of Smad3 and activation of α-smooth muscle actin, and collagen type1A2 in PM-exposed mice and PM-treated NCI-H292 cells. In pulmonary function tests, PM exposure impaired pulmonary function resembling pulmonary fibrosis, characterized by increased resistance and elastance of the respiratory system, and resistance, elastance, and damping of lung tissues, whereas decreased compliance of the respiratory system, forced expired volume and forced vital capacity. Overall, PM-mediated oxidative stress caused airway inflammation and pulmonary dysfunction with pulmonary fibrosis via TXNIP pathway/NF-κB activation and modulation of the SIRT1-mediated TGF-β/Smad3 pathways. The results of this study can provide fundamental data on the potential adverse effects and underlying mechanism of pulmonary fibrosis caused by PM exposure as a public health concern. Due to the potential toxicity of PM, people with respiratory disease must be careful with PM exposure.

Synergistic Pulmonoprotective Effect of Natural Prolyl Oligopeptidase Inhibitors in In Vitro and In Vivo Models of Acute Respiratory Distress Syndrome

Acute respiratory distress syndrome (ARDS) is a highly morbid inflammatory lung disease with limited pharmacological interventions. The present study aims to evaluate and compare the potential pulmonoprotective effects of natural prolyl oligopeptidase (POP) inhibitors namely rosmarinic acid (RA), chicoric acid (CA), epigallocatechin-3-gallate (EGCG) and gallic acid (GA), against lipopolysaccharide (LPS)-induced ARDS. Cell viability and expression of pro-inflammatory mediators were measured in RAW264.7 cells and in primary murine lung epithelial and bone marrow cells. Nitric oxide (NO) production was also assessed in unstimulated and LPS-stimulated RAW264.7 cells. For subsequent in vivo experiments, the two natural products (NPs) with the most favorable effects, RA and GA, were selected. Protein, cell content and lipid peroxidation levels in bronchoalveolar lavage fluid (BALF), as well as histopathological changes and respiratory parameters were evaluated in LPS-challenged mice. Expression of key mediators involved in ARDS pathophysiology was detected by Western blotting. RA and GA favorably reduced gene expression of pro-inflammatory mediators in vitro, while GA decreased NO production in macrophages. In LPS-challenged mice, RA and GA co-administration improved respiratory parameters, reduced cell and protein content and malondialdehyde (MDA) levels in BALF, decreased vascular cell adhesion molecule-1 (VCAM-1) and the inducible nitric oxide synthase (iNOS) protein expression, activated anti-apoptotic mechanisms and down-regulated POP in the lung. Conclusively, these synergistic pulmonoprotective effects of RA and GA co-administration could render them a promising prophylactic/therapeutic pharmacological intervention against ARDS.

SARS-CoV-2 infection of polarized human airway epithelium induces necroptosis that causes airway epithelial barrier dysfunction

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is the cause the ongoing pandemic of coronavirus disease 2019 (COVID19). One key feature associated with COVID-19 is excessive pro-inflammatory cytokine production that leads to severe acute respiratory distress syndrome. Although the cytokine storm induces inflammatory cell death in the host, which type of programmed cell death mechanism that occurs in various organs and cells remains elusive. Using an in vitro culture model of polarized human airway epithelium (HAE), we observed that necroptosis, but not apoptosis or pyroptosis, plays an essential role in the damage of the epithelial barrier of polarized HAE infected with SARS-CoV-2. Pharmacological inhibitors of necroptosis, necrostatin-2 and necrosulfonamide, efficiently prevented cell death and epithelial barrier dysfunction caused by SARS-CoV-2 infection. Moreover, the silencing of genes that are involved in necroptosis, RIPK1, RIPK3, and MLKL, ameliorated airway epithelial damage of the polarized HAE infected with SARS-CoV-2. This study, for the first time, confirms that SARS-CoV-2 infection triggers necroptosis that disrupts the barrier function of human airway epithelia in vitro.

Network analysis identifies a gene biomarker panel for sepsis-induced acute respiratory distress syndrome

BACKGROUND

Acute respiratory distress syndrome (ARDS) is characterized by non-cardiogenic pulmonary edema caused by inflammation, which can lead to serious respiratory complications. Due to the high mortality of ARDS caused by sepsis, biological markers that enable early diagnosis are urgently needed for clinical treatment.

METHODS

In the present study, we used the public microarray data of whole blood from patients with sepsis-induced ARDS, patients with sepsis-alone and healthy controls to perform an integrated analysis based on differential expressed genes (DEGs) and co-expression network to identify the key genes and pathways related to the development of sepsis into ARDS that may be key targets for diagnosis and treatment.

RESULTS

Compared with controls, we identified 180 DEGs in the sepsis-alone group and 152 DEGs in the sepsis-induced ARDS group. About 70% of these genes were unique to the two groups. Functional analysis of DEGs showed that neutrophil-mediated inflammation and mitochondrial dysfunction are the main features of ARDS induced by sepsis. Gene network analysis identified key modules and screened out key regulatory genes related to ARDS. The key genes and their upstream regulators comprised a gene panel, including EOMES, LTF, CSF1R, HLA-DRA, IRF8 and MPEG1. Compared with the healthy controls, the panel had an area under the curve (AUC) of 0.900 and 0.914 for sepsis-alone group and sepsis-induced ARDS group, respectively. The AUC was 0.746 between the sepsis-alone group and sepsis-induced ARDS group. Moreover, the panel of another independent blood transcriptional expression profile dataset showed the AUC was 0.769 in diagnosing sepsis-alone group and sepsis-induced ARDS group.

CONCLUSIONS

Taken together, our method contributes to the diagnosis of sepsis and sepsis-induced ARDS. The biological pathway involved in this gene biomarker panel may also be a critical target in combating ARDS caused by sepsis.

Safflor Yellow A Protects Beas-2B Cells Against LPS-Induced Injury via Activating Nrf2

Acute lung injury and its severe form acute respiratory distress syndrome are lethal lung diseases. So far, effective therapy for the diseases is deficient and the prognosis is poor. Recently, it was found activating nuclear factor erythroid 2-related factor 2 could attenuate the injury including inflammation, oxidative stress, and apoptosis in those diseases. To discover novel therapy, we have evaluated safflor yellow A and explored the underlying mechanisms using Beas-2B cells injured by lipopolysaccharide. As a result, safflor yellow A could improve the viability of Beas-2B cells treated with lipopolysaccharide. Further investigations have revealed safflor yellow A suppressed oxidative stress induced by lipopolysaccharide via reducing reactive oxygen species and malondialdehyde, and elevating superoxide dismutase, catalase, and glutathione peroxidase. Meanwhile, the inflammation resulting from lipopolysaccharide was ameliorated through decreasing the pro-inflammatory cytokines including tumor necrosis factor-α, interleukin-1β, and interleukin-6. It was also found nuclear factor κB was inactivated by safflor yellow A. In addition, safflor yellow A downregulated cysteinyl aspartate specific proteinase-3 and Bcl-2-associated X protein and upregulated B-cell lymphoma-2 to inhibited apoptosis of Beas-2B cells induced by lipopolysaccharide. The activation of nuclear factor erythroid 2-related factor 2 was observed in Beas-2B cells, which was associated with the protective effects of safflor yellow A. And molecular docking elucidated safflor yellow A interacted with Kelch-like ECH-associated protein 1 to activate nuclear factor erythroid 2-related factor 2. These results can provide evidences for the discovery of novel therapy for further evaluation of safflor yellow A in the treatment of acute lung injury and acute respiratory distress syndrome.

Graphical Abstract

Inhibition of a Microbiota-derived Peptide Ameliorates Established Acute Lung Injury

Acute lung injury is a clinical syndrome characterized by a diffuse lung inflammation that commonly evolves into acute respiratory distress syndrome and respiratory failure. The lung microbiota is involved in the pathogenesis of acute lung injury. Corisin, a proapoptotic peptide derived from the lung microbiota, plays a role in acute lung injury and acute exacerbation of pulmonary fibrosis. Preventive therapeutic intervention with a monoclonal anticorisin antibody inhibits acute lung injury in mice. However, whether inhibition of corisin with the antibody ameliorates established acute lung injury is unknown. Here, the therapeutic effectiveness of the anticorisin antibody in already established acute lung injury in mice was assessed. Lipopolysaccharide was used to induce acute lung injury in mice. After causing acute lung injury, the mice were treated with a neutralizing anticorisin antibody. Mice treated with the antibody showed significant improvement in lung radiological and histopathological findings, decreased lung infiltration of inflammatory cells, reduced markers of lung tissue damage, and inflammatory cytokines in bronchoalveolar lavage fluid compared to untreated mice. In addition, the mice treated with anticorisin antibody showed significantly increased expression of antiapoptotic proteins with decreased caspase-3 activation in the lungs compared to control mice treated with an irrelevant antibody. In conclusion, these observations suggest that the inhibition of corisin is a novel and promising approach for treating established acute lung injury.

Pulmonary inflammatory response and immunomodulation to multiple trauma and hemorrhagic shock in pigs

BACKGROUND

Patients suffering from severe trauma experience substantial immunological stress. Lung injury is a known risk factor for the development of posttraumatic complications, but information on the long-term course of the pulmonary inflammatory response and treatment with mild hypothermia are scarce.

AIM

To investigate the pulmonary inflammatory response to multiple trauma and hemorrhagic shock in a porcine model of combined trauma and to assess the immunomodulatory properties of mild hypothermia.

METHODS

Following induction of trauma (blunt chest trauma, liver laceration, tibia fracture), two degrees of hemorrhagic shock (45 and 50%) over 90 (n = 30) and 120 min. (n = 20) were induced. Animals were randomized to hypothermia (33°C) or normothermia (38°C). We evaluated bronchoalveolar lavage (BAL) fluid and tissue levels of cytokines and investigated changes in microRNA- and gene-expression as well as tissue apoptosis.

RESULTS

We observed a significant induction of Interleukin (IL) 1β, IL-6, IL-8, and Cyclooxygenase-2 mRNA in lung tissue. Likewise, an increased IL-6 protein concentration could be detected in BAL-fluid, with a slight decrease of IL-6 protein in animals treated with hypothermia. Lower IL-10 protein levels in normothermia and higher IL-10 protein concentrations in hypothermia accompanied this trend. Tissue apoptosis increased after trauma. However, intervention with hypothermia did not result in a meaningful reduction of pro-inflammatory biomarkers or tissue apoptosis.

CONCLUSION

We observed signs of a time-dependent pulmonary inflammation and apoptosis at the site of severe trauma, and to a lower extent in the trauma-distant lung. Intervention with mild hypothermia had no considerable effect during 48 hours following trauma.

Prostaglandin D2 Attenuates Lipopolysaccharide-Induced Acute Lung Injury through the Modulation of Inflammation and Macrophage Polarization

Acute lung injury (ALI) is a well-known respiratory disease and a leading cause of death worldwide. Despite advancements in the medical field, developing complete treatment strategies against this disease is still a challenge. In the current study, the therapeutic role of prostaglandin D2 (PGD2) was investigated on lipopolysaccharide (LPS)-induced lung injury in mice models and RAW264.7 macrophages through anti-inflammatory, histopathology, immunohistochemistry, and TUNEL staining. The overproduction of cytokines by RAW264.7 macrophages was observed after stimulation with LPS. However, pretreatment with PGD2 decreased the production of cytokines. The level of inflammatory markers was significantly restored in the PGD2 treatment group (TNF-α = 58.6 vs. 78.5 pg/mL; IL-1β = 29.3 vs. 36.6 pg/mL; IL-6 = 75.4 vs. 98.2 pg/mL; and CRP = 0.84 vs. 1.14 ng/mL). The wet/dry weight ratio of the lungs was quite significant in the disease control (LPS-only treatment) group. Moreover, the histological changes as determined by haematoxylin and eosin (H&E) staining clearly showed that PGD2 treatment maintains the lung tissue architecture. The iNOS expression pattern was increased in lung tissues of LPS-treated animals, whereas, in mice treated with PGD2, the expression of iNOS protein decreased. Flow cytometry data demonstrated that LPS intoxication enhanced apoptosis, which significantly decreased with PGD2 treatment. In conclusion, all these observations indicate that PGD2 provides an anti-inflammatory response in RAW264.7 macrophages and in ALI, and they suggest a therapeutic potential in lung pathogenesis.

Knockdown of circ_0001679 alleviates lipopolysaccharide-induced MLE-12 lung cell injury by regulating the miR-338-3p/ mitogen-activated protein kinase 1 axis

The upregulation of circ_0001679 was reported in lipopolysaccharide (LPS)-induced lung injury mouse model, but its functional roles and mechanisms in LPS-induced lung injury remain to be investigated. In this study, we aimed to explore the potential role of circ_0001679 in septic acute lung injury. We initially established an in vitro lung cell injury model using LPS-treated MLE-12 cells. siRNAs targeting circRNA_0001679 were employed to stably knock down circRNA_0001679, followed by functional assays to investigate the effect of circRNA_0001679 silencing. The levels of inflammatory cytokines such as IL-6, IL-β and TNF-α (Tumor necrosis factor-α) were detected by ELISA (Enzyme-linked immunosorbent assay). Meanwhile, protein levels of Bcl-2, cleaved-caspase 3, Bax, and MAPK1 (Mitogen-Activated Protein Kinase 1) proteins expression level were measured by Western blot. We found that Circ_0001679 was upregulated in LPS-induced MLE-12 cells, and silencing circ_0001679 attenuated the growth inhibition and suppressed apoptosis induced by LPS. Circ_0001679 knockdown also lowered levels of IL-6, IL-β and TNF-α, and prevent the activation of cleaved-caspase 3 protein. We further revealed that circ_0001679 functioned as a sponge of miR-338-3p to negatively regulate miR-338-3p activity. miR-338-3p downregulated its downstream target MAPK1, while the upregulation of circ_0001679 maintained a high-level expression of MAPK1 by suppressing miR-338-3p. Collectively, our study indicates that circ_0001679/miR-338-3p/MAPK1 axis may play an important role in the pathogenesis of acute lung injury (ALI).

Blockade of caspase cascade overcomes malaria-associated acute respiratory distress syndrome in mice

Malaria is an enormous burden on global health that caused 409,000 deaths in 2019. Severe malaria can manifest in the lungs, an illness known as acute respiratory distress syndrome (ARDS). Not much is known about the development of malaria-associated ARDS (MA-ARDS), especially regarding cell death in the lungs. We had previously established a murine model that mimics various human ARDS aspects, such as pulmonary edema, hemorrhages, pleural effusion, and hypoxemia, using DBA/2 mice infected with Plasmodium berghei ANKA. Here, we explored the mechanisms and the involvement of apoptosis in this syndrome. We found that apoptosis contributes to the pathogenesis of MA-ARDS, primarily as facilitators of the alveolar-capillary barrier breakdown. The protection of pulmonary endothelium by inhibiting caspase activation could be a promising therapeutic strategy to prevent the pathogenicity of MA-ARDS. Therefore, intervention in the programmed death cell mechanism could help patients not to develop severe malaria.

Cyclooxygenase-2 deficiency attenuates lipopolysaccharide-induced inflammation, apoptosis, and acute lung injury in adult mice

Many lung diseases are caused by an excessive inflammatory response, and inflammatory lung diseases are often modeled using lipopolysaccharide (LPS) in mice. Cyclooxygenase-2 (COX-2) encoded by the Ptgs2 gene is induced in response to inflammatory stimuli including LPS. The objective of this study was to test the hypothesis that mice deficient in COX-2 (Ptgs2-/-) will be protected from LPS-induced lung injury. Wild-type (WT; CD1 mice) and Ptgs2-/- mice (on a CD1 background) were treated with LPS or vehicle for 24 h. LPS treatment resulted in histological evidence of lung injury, which was attenuated in the Ptgs2-/- mice. LPS treatment increased the mRNA levels for tumor necrosis factor-α, interleukin-10, and monocyte chemoattractant protein-1 in the lungs of WT mice, and the LPS-induced increases in these levels were attenuated in the Ptgs2-/- mice. The protein levels of active caspase-3 and caspase-9 were lower in the LPS-treated lungs of Ptgs2-/- mice than in LPS-treated WT mice, as were the number of terminal deoxynucleotide transferase dUTP nick end labeling-positive cells in lung sections. LPS exposure resulted in a greater lung wet-to-dry weight ratio (W/D) in WT mice, suggestive of pulmonary edema, while in LPS-treated Ptgs2-/- mice, the W/D was not different from controls and less than in LPS-treated WT mice. These results demonstrate that COX-2 is involved in the inflammatory response to LPS and suggest that COX-2 not only acts as a downstream participant in the inflammatory response, but also acts as a regulator of the inflammatory response likely through a feed-forward mechanism following LPS stimulation.

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.

Protective Effect of Fluorofenidone Against Acute Lung Injury Through Suppressing the MAPK/NF-κB Pathway

Acute lung injury (ALI) is a severe disease that presents serious damage and excessive inflammation in lungs with high mortality without effective pharmacological therapy. Fluorofenidone (AKFPD) is a novel pyridone agent that has anti-fibrosis, anti-inflammation, and other pharmacological activities, while the effect of fluorofenidone on ALI is unclarified. Here, we elucidated the protective effects and underlying mechanism of fluorofenidone on lipopolysaccharide (LPS)-induced ALI. In this study, fluorofenidone alleviated lung tissue structure injury and reduced mortality, decreased the pulmonary inflammatory cell accumulation and level of inflammatory cytokines IL-1β, IL-6, and TNF-α in the bronchoalveolar lavage fluid, and attenuated pulmonary apoptosis in LPS-induced ALI mice. Moreover, fluorofenidone could block LPS-activated phosphorylation of ERK, JNK, and P38 and further inhibited the phosphorylation of IκB and P65. These results suggested that fluorofenidone can significantly contrast LPS-induced ALI through suppressing the activation of the MAPK/NF-κB signaling pathway, which indicates that fluorofenidone could be considered as a novel therapeutic candidate for ALI.

The role of necroptosis in common respiratory diseases in children

Studies have shown that necroptosis (NEC) relies on a unique gene-regulated molecular pathway to cause cell death. With the development of knockout mouse models and specific molecular inhibitors of necrotic proteins, this cell death pathway has been considered one of the important causes of the pathogenesis of human diseases. In this review, we explored the possible roles and mechanisms of NEC in common respiratory diseases in children, such as acute lung injury, acute respiratory distress syndrome, pulmonary infection, childhood asthma, pulmonary hypertension, etc., in order to provide new ideas for the prevention and treatment of such diseases.

24-Dehydrocholesterol Reductase alleviates oxidative damage-induced apoptosis in alveolar epithelial cells via regulating Phosphatidylinositol-3-Kinase/Protein Kinase B activation

Apoptosis of alveolar epithelial cells during acute lung injury (ALI)/acute respiratory distress syndrome (ARDS) is a critical pathological event that seriously endangers the health of patients. Suppressing apoptosis of alveolar epithelial cells was shown to alleviate functional damage of lung, and modulator of the reactive oxygen species (ROS)-induced apoptosis becomes a promising approach to the ALI therapy. Previous little studies showed that DHCR24 possessed anti-oxidative and anti-apoptotic property in ALI. Thus, H₂O₂ was utilized to mimic oxidative damage in vitro in alveolar epithelial cell line A549 in the present study. Our results exhibited that H₂O₂ treatment of A549 cells reduced the level of SOD and increased the level of ROS. Moreover, H₂O₂ inhibited Bcl-2 expression in A549 cells, but increased Bax and the activity of Caspase-3. In addition, the apoptosis rate in the H₂O₂ treatment group also increased significantly. And the expression of 24-dehydrocholesterol reductase (DHCR24) was markedly reduced in the H₂O₂ treatment group. Overexpression of DHCR24 can remarkably inhibit H₂O₂-induced oxidative stress and apoptosis. We found that overexpression of DHCR24 increased the phosphorylation level of PI3K and AKT, however, the PI3K inhibitor LY294002 (LY) eliminated the protective effect of DHCR24 in ALI. DHCR24 was down-regulated in H₂O₂-induced ALI, and overexpression of DHCR24 could inhibit H₂O₂-induced oxidative stress and apoptosis of A549 cells by activating the Phosphatidylinositol-3-Kinase/Protein Kinase B (PI3K/AKT) signaling pathway. The above exhibited a protective effect of DHCR24 on alveolar epithelial cells exposed to oxidative stress-mediated apoptosis and provided a novel therapeutic method for ALI.

Association between inflammatory biomarkers and acute respiratory distress syndrome or acute lung injury risk : A systematic review and meta-analysis

Background

The relationship between acute respiratory distress syndrome (ARDS)/acute lung injury (ALI) and levels of certain inflammatory factors remains controversial. The purpose of this meta-analysis was to summarize the available studies evaluating the association between levels of inflammatory factors and ARDS/ALI incidence.

Methods

We searched the PubMed, EmBase, and Cochrane databases for studies published up to July 2017. For each inflammatory factor, a random effects model was employed to pool results from different studies.

Results

We identified 63 studies that included 6243 patients in our meta-analysis. Overall, the results indicated that the levels of angiopoietin (ANG)-2 (standard mean difference, SMD: 1.34; P < 0.001), interleukin (IL)-1β (SMD: 0.92; P = 0.012), IL‑6 (SMD: 0.66; P = 0.005), and tumor necrosis factor (TNF)-α (SMD: 0.98; P = 0.001) were significantly higher in patients with ARDS/ALI than in unaffected individuals. No significant differences were observed between patients with ARDS/ALI and unaffected individuals in terms of the levels of IL‑8 (SMD: 0.61; P = 0.159), IL-10 (SMD: 1.10; P = 0.231), and plasminogen activator inhibitor (PAI)-1 (SMD: 0.70; P = 0.060).

Conclusions

ARDS/ALI is associated with a significantly elevated levels of ANG‑2, IL-1β, IL‑6, and TNF‑α, but not with IL‑8, IL-10, and PAI‑1 levels.

Supplementary Information

The online version of this article (10.1007/s00508-021-01971-3) contains supplementary material, which is available to authorized users.

Cabozantinib ameliorates lipopolysaccharide-induced lung inflammation and bleomycin--induced early pulmonary fibrosis in mice

The lung, as the primary organ for gas exchange in mammals, is the main target organ for many pathogens and allergens, which may cause acute lung injury. A certain proportion of acute lung injury may progress into irreversible pulmonary fibrosis. Both acute lung injury and pulmonary fibrosis have high mortality rates and few effective treatments. Cabozantinib is a multi-target small molecule tyrosine kinase inhibitor and has been approved for the treatment of multiple malignant solid tumors. In this study, we explored the role of cabozantinib in acute lung injury and pulmonary fibrosis in vivo and in vitro. In the lipopolysaccharide and bleomycin induced mouse lung injury models, cabozantinib significantly improved the pathological state and reduced the infiltration of inflammatory cells in the lung tissues. In the bleomycin induced pulmonary fibrosis model, cabozantinib significantly reduced the area of pulmonary fibrosis and improved lung function in mice. The results of in vitro studies showed that cabozantinib could inhibit the inflammatory response and apoptosis of alveolar epithelial cells by inhibiting the activation of TLR4/NF-κB and NLRP3 inflammasome pathways. At the same time, cabozantinib could inhibit the activation of lung fibroblasts through suppressing the TGF-β1/Smad pathway, and promote the apoptosis of fibroblasts. In summary, cabozantinib could alleviate lung injury through regulating the TLR4 /NF-κB/NLRP3 inflammasome pathway, and alleviate pulmonary fibrosis by inhibiting the TGF-β1/Smad3 signaling pathway.

Mechanisms Underlying the Effects of Lianhua Qingwen on Sepsis-Induced Acute Lung Injury: A Network Pharmacology Approach

Background and Purpose: Sepsis is a life-threatening condition associated with secondary multiple organ injury. Acute lung injury (ALI) caused by sepsis has high morbidity and mortality in critical care units. Lianhua Qingwen (LHQW) is a traditional Chinese medicine composing of 11 herbs and 2 medicinal minerals. LHQW exhibits anti-inflammatory activity and is effective in treating pneumonia. Our study aimed to evaluate the effect of LHQW on sepsis-induced ALI and its underlying mechanism.

Materials and Methods: A network pharmacology approach was used to predict the bioactive components and effective targets of LHQW in treating ALI. We established ALI model C57/BL6 mice via an intraperitoneal injection of LPS and inhibited p53 expression by pifithrin-α, in order to validate the mechanism by which LHQW exerted protective role in ALI. Hematoxylin-eosin staining was conducted to assess the severity of lung injury. The severity of inflammation was evaluated based on MPO (myeloperoxidase) activity. TUNEL assay was employed to detect apoptotic cells. The levels of p53 and caspase-3 were tested by immunohistochemical staining and Western blotting. The expression levels of Bcl-2, Bax, cytochrome C and caspase-9 were detected by Western blotting.

Results: A total of 80 genes were associated with LHQW in the treatment of ALI. After PPI network construction, four active components (quercetin, luteolin, kaempferol and wogonin) and 10 target genes (AKT1, TP53, IL6, VEGFA, TNF, JUN, STAT3, MAPK8, MAPK1, and EGF) were found to be essential for ALI treatment. GO and KEGG analyses indicated that apoptosis pathway was mainly involved in the LHQW-ALI network. Animal experiments showed that LHQW was able to attenuate LPS-induced ALI, and medium-dose LHQW exhibited the most prominent effect. LHQW could inhibit the overexpression of p53 induced by LPS and suppress p53-mediated intrinsic apoptotic pathways by decreasing the levels of Bax, caspase-3 and caspase-9, increasing the expression of Bcl-2, and attenuating the release of cytochrome C in ALI mice.

Conclusion: This study reveals that LHQW may alleviate LPS-induced ALI via inhibiting p53-mediated intrinsic apoptosis pathways.

Postnatal Sepsis and Bronchopulmonary Dysplasia in Premature Infants: Mechanistic Insights into "New BPD"

Bronchopulmonary dysplasia (BPD) is a debilitating disease in premature infants resulting from lung injury that disrupts alveolar and pulmonary vascular development. Despite the use of lung-protective ventilation and targeted oxygen therapy, BPD rates have not significantly changed over the last decade. Recent evidence suggests that sepsis and conditions initiating the systemic inflammatory response syndrome in preterm infants are key risk factors for BPD. However, the mechanisms by which sepsis-associated systemic inflammation and microbial dissemination program aberrant lung development are not fully understood. Progress has been made within the last 5 years with the inception of animal models allowing mechanistic investigations into neonatal acute lung injury and alveolar remodeling due to endotoxemia and NEC. These recent studies begin to unravel the pathophysiology of early endothelial immune activation via pattern recognition receptors such as Toll Like Receptor 4 and disruption of critical lung developmental processes such as angiogenesis, extracellular matrix deposition, and ultimately alveologenesis. Here we review scientific evidence from preclinical models of neonatal sepsis-induced lung injury to new data emerging from clinical literature.

Potential therapeutic interventions of plant-derived isoflavones against acute lung injury

Acute lung injury (ALI) is a life-threatening syndrome that possibly leads to high morbidity and mortality as no therapy exists. Several natural ingredients with negligible adverse effects have recently been investigated to possibly inhibit the inflammatory pathways associated with ALI at the molecular level. Isoflavones, as phytoestrogenic compounds, are naturally occurring bioactive compounds that represent the most abundant category of plant polyphenols (Leguminosae family). A broad range of therapeutic activities of isoflavones, including antioxidants, chemopreventive, anti-inflammatory, antiallergic and antibacterial potentials, have been extensively documented in the literature. Our review exclusively focuses on the possible anti-inflammatory, antioxidant role of botanicals'-derived isoflavones against ALI and their immunomodulatory effect in experimentally induced ALI. Despite the limited scope covering their molecular mechanisms, isoflavones substantially contributed to protecting from ALI via inhibiting toll-like receptor 4 (TLR4)/Myd88/NF-κB pathway and subsequent cytokines, chemokines, and adherent proteins. Nonetheless, future research is suggested to fill the gap in elucidating the protective roles of isoflavones to alleviate ALI concerning antioxidant potentials, inhibition of the inflammatory pathways, and associated molecular mechanisms.

Tumor necrosis factor α‑induced protein 8‑like 2 contributes to penehyclidine hydrochloride pretreatment against lipopolysaccharide‑induced acute lung injury in a mouse model

The aim of the present study was to investigate the effect of penehyclidine hydrochloride (PHC) pretreatment on mice with lipopolysaccharide (LPS)‑induced acute lung injury (ALI) and its possible underlying mechanisms. Mice were randomly separated into six groups: i) Sham group; ii) LPS group; iii) LPS + PHC group; iv) tumor necrosis factor a‑induced protein 8‑like protein 2 (TIPE2) group; v) LPS + TIPE2 group; and vi) LPS + TIPE2 + PHC group. The ALI model was induced using LPS through intratracheal injection. The mice received adenovirus gene to induce the overexpression of TIPE2. After mice were sacrificed, lung injury indices were assessed, and arterial blood, bronchoalveolar lavage fluid and lung tissues were collected for subsequent assays. Expression levels of related proteins were detected by using western blotting. It was found that compared with the sham group, the mice treated with LPS showed increased lung injury and dysfunctions of gas exchange. However, these trends were significantly ameliorated in the LPS + PHC group. Evaluation of protein expression in lung tissues showed that the increased expression of nuclear NF‑κB p65 and p‑c‑Jun N‑terminal kinase (JNK) induced by LPS were suppressed in the LPS + PHC group and the expression of TIPE2 was increased. The mice that received adenovirus gene to induce TIPE2 overexpression could also showed protective effects compared with the mice in the LPS group. However, the expression of TIPE2 decreased rather than increased in LPS group. In the mice pretreated with PHC, the expression of TIPE2 increased in mice with LPS‑induced ALI. To conclude, PHC pretreatment could inhibit the occurrence of inflammation and apoptosis in LPS‑induced ALI. This process may be related to the activation of TIPE2 and the inhibition of NF‑κB and JNK signaling pathway in the lungs of mice.

Phospholipases A2 as biomarkers in ARDS

Acute respiratory distress syndrome (ARDS) is a multifactorial life-threatening lung injury, characterized by diffuse lung inflammation and increased alveolocapillary barrier permeability. The different stages of ARDS have distinctive biochemical and clinical profiles. Despite the progress of our understanding on ARDS pathobiology, the mechanisms underlying its pathogenesis are still obscure. Herein, we review the existing literature about the implications of phospholipases 2 (PLA2s), a large family of enzymes that catalyze the hydrolysis of fatty acids at the sn-2 position of glycerophospholipids, in ARDS-related pathology. We emphasize on the versatile way of participation of different PLA2s isoforms in the distinct ARDS subgroup phenotypes by either potentiating lung inflammation and damage or by preserving the normal lung. Current research supports that PLA2s are associated with the progression and the outcome of ARDS. We herein discuss the transcellular communication of PLA2s through secreted extracellular vesicles and suggest it as a new mechanism of PLA2s involvement in ARDS. Thus, the elucidation of the spatiotemporal features of PLA2s expression may give new insights and provide valuable information about the risk of an individual to develop ARDS or advance to more severe stages, and potentially identify PLA2 isoforms as biomarkers and target for pharmacological intervention.

LncRNA OIP5-AS1 knockdown or miR-223 overexpression can alleviate LPS-induced ALI/ARDS by interfering with miR-223/NLRP3-mediated pyroptosis

BACKGROUND

Acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) are life-threatening diseases and endothelial barrier injury is an important contributor to the pathogenesis of ALI/ARDS. LncRNA has been proved to participate in the progression of ALI/ARDS. Our study aimed to investigate the function of lncRNA OIP5-AS1 in LPS-induced ALI/ARDS.

METHODS

OIP5-AS1 and miR-223 levels were detected by PCR in the serum of ALI/ARDS patients or healthy donors. MTT assay were performed to detect the proliferation of HPMECs. Flow cytometry were performed to detect the apoptosis of HPMECs. The protein levels of NLRP3, ASC, GSDMD-N, caspase-1 were measured by western blot to detect the pyroptosis of HPMECs. IL-1β, IL-6, IL-18 and IL-10 was detected by ELISA to measure the inflammatory response of HPMECs. And production of ROS, SOD and MDA was measured to determine the oxidative stress of HPMECs. Targets of OIP5-AS1 and miR-223 were predicted by StarBase and confirmed by dual-luciferase reporter assay.

RESULTS

We found that OIP5-AS1 was upregulated, while miR-223 was downregulated in the serum of ALI/ARDS patients and LPS-treated HPMECs. Functionally, knockdown of OIP5-AS1 induced proliferation and inhibited apoptosis, pyroptosis, inflammatory response and oxidative stress of LPS-treated HPMECs. Interestingly, miR-223 was a target of OIP5-AS1 and miR-223 inhibition abolished the effects of si-OIP5-AS1 on LPS-induced HPMECs. More importantly, miR-223 directly targeted NLRP3, miR-223 overexpression also promoted proliferation and inhibited apoptosis, pyroptosis, inflammatory response and oxidative stress of LPS-treated HPMECs and which was abolished by NLRP3 overexpression. Finally, we found that OIP5-AS1 knockdown and miR-223 overexpression could both alleviate LPS-induced ALI/ARDS in vivo.

CONCLUSION

Together, we find that LncRNA OIP5-AS1 aggravates LPS-induced ALI/ARDS via miR-223/NLRP3 axis and provides new targets for ALI/ARDS therapy.

Rat model of smoke inhalation-induced acute lung injury

BACKGROUND

Acute lung injury (ALI)/acute respiratory distress syndrome (ARDS) is a lethal disease with limited therapeutic options and an unacceptably high mortality rate. Understanding the complex pathophysiological processes involved in the development of ALI/ARDS is critical for developing novel therapeutic strategies. Smoke inhalation (SI) injury is the leading cause of morbidity and mortality in patients with burn-associated ALI/ARDS; however, to our knowledge few reliable, reproducible models are available for pure SI animal model to investigate therapeutic options for ALI/ARDS without the confounding variables introduced by cutaneous burn or other pathology.

OBJECTIVE

To develop a small animal model of pure SI-induced ALI and to use this model for eventual testing of novel therapeutics for ALI.

METHODS

Rats were exposed to smoke using a custom-made smoke generator. Peripheral oxygen saturation (SpO₂), heart rate, arterial blood gas, and chest X-ray (CXR) were measured before and after SI. Wet/dry weight (W/D) ratio, lung injury score and immunohistochemical staining of cleaved caspase 3 were performed on harvested lung tissues of healthy and SI animals.

RESULTS

The current study demonstrates the induction of ALI in rats after SI as reflected by a significant, sustained decrease in SpO₂ and the development of diffuse bilateral pulmonary infiltrates on CXR. Lung tissue of animals exposed to SI showed increased inflammation, oedema and apoptosis as reflected by the increase in W/D ratio, injury score and cleaved caspase 3 level of the harvested tissues compared with healthy animals.

CONCLUSION

We have successfully developed a small animal model of pure SI-induced ALI. This model is offered to the scientific community as a reliable model of isolated pulmonary SI-induced injury without the confounding variables of cutaneous injury or other systemic pathology to be used for study of novel therapeutics or other investigation.

Differential effects of the Src family tyrosine kinases Yes and Fyn on lipopolysaccharide-induced lung injury in ice

Endothelial cell apoptosis is an early event in the development of acute lung injury (ALI). We have previously found that the Src family tyrosine kinase (STK) Yes activates caspase-3, whereas the STK Fyn inhibits caspase-3 activation in cultured pulmonary endothelial cells. We hypothesized that deficiency in Yes or Fyn in mice would have differential effects on lipopolysaccharide (LPS)-induced ALI. Mice were treated with LPS (10 mg/kg ip) for 24 h. Histological evidence of lung injury was greater in LPS-treated wild-type mice than in vehicle-treated wild-type mice, and the LPS-induced histological evidence of lung injury was attenuated in yes^-/- mice and enhanced in fyn^-/- mice. In wild-type or fyn^-/- mice, LPS resulted in greater lung wet-to-dry weight ratios than in controls, whereas in yes^-/- mice lung, wet-to-dry weight was similar between LPS and controls. LPS-exposed fyn^-/- mice had greater respiratory system resistance and lower respiratory system compliance than did LPS-exposed wild-type mice. TUNEL positive cells in the lung following LPS treatment were greater in the fyn^-/- mice and lower in the yes^-/- mice compared with that in the wild-type mice. Following LPS treatment lung protein levels of PECAM-1 were lower in fyn^-/- mice than in controls or yes^-/- mice. LPS treatment increased cleaved caspase-3 protein levels in wild-type mice, whereas LPS-induced caspase-3 activation was attenuated in yes^-/- mice and enhanced in fyn^-/- mice. These results indicate that LPS-induced ALI is positively mediated via Yes-related mechanisms and negatively mediated by Fyn-related mechanisms.

Necrosis Rather Than Apoptosis is the Dominant form of Alveolar Epithelial Cell Death in Lipopolysaccharide-Induced Experimental Acute Respiratory Distress Syndrome Model

Alveolar epithelial cell (AEC) death, which is classified as apoptosis or necrosis, plays a critical role in the pathogenesis of acute respiratory distress syndrome (ARDS). In addition to apoptosis, some types of necrosis are known to be molecularly regulated, and both apoptosis and necrosis can be therapeutic targets for diseases. However, the relative contribution of apoptosis and necrosis to AEC death during ARDS has not been elucidated. Here, we evaluated which type of AEC death is dominant and whether regulated necrosis is involved in lipopolysaccharide (LPS)-induced lung injury, an experimental ARDS model. In the bronchoalveolar lavage fluid from the LPS-induced lung injury mice, both the levels of cytokeratin 18-M65 antigen (a marker of total epithelial cell death) and cytokeratin 18-M30 antigen (an epithelial apoptosis marker) were increased. The M30/M65 ratio, which is an indicator of the proportion of apoptosis to total epithelial cell death, was significantly lower than that in healthy controls. In addition, the number of propidium iodide-positive, membrane-disrupted cells was significantly higher than the number of TUNEL-positive apoptotic cells in the lung sections of lung injury mice. Activated neutrophils seemed to mediate AEC death. Finally, we demonstrated that necroptosis, a regulated necrosis pathway, is involved in AEC death during LPS-induced lung injury. These results indicate that necrosis including necroptosis, rather than apoptosis, is the dominant type of AEC death in LPS-induced lung injury. Although further studies investigating human ARDS subjects are necessary, targeting necrosis including its regulated forms might represent a more efficient approach to protecting the alveolar epithelial barrier during ARDS.

Virus Caused Imbalance of Type I IFN Responses and Inflammation in COVID-19

The global expansion of coronavirus disease 2019 (COVID-19) caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has emerged as one of the greatest public health challenges and imposes a great threat to human health. Innate immunity plays vital roles in eliminating viruses through initiating type I interferons (IFNs)-dependent antiviral responses and inducing inflammation. Therefore, optimal activation of innate immunity and balanced type I IFN responses and inflammation are beneficial for efficient elimination of invading viruses. However, SARS-CoV-2 manipulates the host's innate immune system by multiple mechanisms, leading to aberrant type I IFN responses and excessive inflammation. In this review, we will emphasize the recent advances in the understanding of the crosstalk between host innate immunity and SARS-CoV-2 to explain the imbalance between inflammation and type I IFN responses caused by viral infection, and explore potential therapeutic targets for COVID-19.

Protective Effect of Dexmedetomidine on Acute Lung Injury via the Upregulation of Tumour Necrosis Factor-α-Induced Protein-8-like 2 in Septic Mice

The aim of the present study was to investigate whether TIPE2 participates in the protective actions of dexmedetomidine (DEX) in a mouse model of sepsis-induced acute lung injury (ALI). We administered TIPE2 adeno-associated virus (AAV-TIPE2) intratracheally into the lungs of mice. Control mice were infected with an adeno-associated virus expressing no transgene. Three weeks later, an animal model of caecal ligation-perforation (CLP)-induced sepsis was established. DEX was administered intravenously 30 min after CLP. Twenty-four hours after sepsis, lung injury was assayed by lung histology, the ratio of polymorphonuclear leukocytes (PMNs) to total cells in the bronchoalveolar lavage fluid (BALF), myeloperoxidase (MPO) activity, BALF protein content and the lung wet-to-dry (W/D) weight ratio. Proinflammatory factor levels in the BALF of mice were measured. The protein expression levels in lung tissues were analysed by Western blotting. The results showed that DEX treatment markedly mitigated sepsis-induced lung injury, which was characterized by the deterioration of histopathology, histologic scores, the W/D weight ratio and total protein levels in the BALF. Moreover, DEX markedly attenuated sepsis-induced lung inflammation, as evidenced by the decrease in the number of PMNs in the BALF, lung MPO activity and proinflammatory cytokines in the BALF. In addition, DEX dramatically prevented sepsis-induced pulmonary cell apoptosis in mice, as reflected by decreases in the number of TUNEL-positive cells, the protein expression of cleaved caspase-9 and cleaved caspase 3 and the Bax/Bcl-2 ratio. In addition, evaluation of protein expression showed that DEX blocked sepsis-activated JNK phosphorylation and NF-κB p65 nuclear translocation. Similar results were also observed in the TIPE2 overexpression group. Our study demonstrated that DEX inhibits acute inflammation and apoptosis in a murine model of sepsis-stimulated ALI via the upregulation of TIPE2 and the suppression of the activation of the NF-κB and JNK signalling pathways.

MicroRNA-486-5p Promotes Acute Lung Injury via Inducing Inflammation and Apoptosis by Targeting OTUD7B

The aim of this article is to study the effect of miR-486-5p in acute lung injury (ALI). MiR-486-5p expression in peripheral blood was determined in ALI patients and healthy volunteers by qRT-PCR. ALI mouse model were reproduced by LPS treatment, and miR-486-5p NC and miRNA-486 inhibitors were injected through trachea. ALI patients' peripheral blood and LPS-induced acute lung injury in mice had significantly higher miR-486-5p levels than control subjects. Inhibition of miR-486-5p by injection with antagomiR-486-5p markedly reduced LPS-induced lung inflammation. Moreover, knockdown of miR-486-5p can reduce protects A549 cell against LPS-induced injury and its corresponding inflammatory response. In addition, Mechanistic analysis indicated that miR-486-5p on the occurrence of ALI is related to the inhibition of OTUD7B activity, which induces the downregulation of inflammatory in ALI. Our results identified miR-486-5p independently associated with ALI. miR-486-5p can mediate the formation of ALI by promoting inflammation.

Antibody-induced procoagulant platelets in severe COVID-19 infection

Severe COVID-19 is associated with increased antibody-mediated procoagulant platelets.

Procoagulant platelets and platelet apoptosis in severe COVID-19 is correlated with D-dimer and higher incidence of thromboembolisms.

The pathophysiology of COVID-19–associated thrombosis seems to be multifactorial. We hypothesized that COVID-19 is accompanied by procoagulant platelets with subsequent alteration of the coagulation system. We investigated depolarization of mitochondrial inner transmembrane potential (ΔΨm), cytosolic calcium (Ca²⁺) concentration, and phosphatidylserine (PS) externalization. Platelets from COVID-19 patients in the intensive care unit (ICU; n = 21) showed higher ΔΨm depolarization, cytosolic Ca²⁺, and PS externalization compared with healthy controls (n = 18) and non-ICU COVID-19 patients (n = 4). Moreover, significant higher cytosolic Ca²⁺ and PS were observed compared with a septic ICU control group (ICU control; n = 5). In the ICU control group, cytosolic Ca2⁺ and PS externalization were comparable with healthy controls, with an increase in ΔΨm depolarization. Sera from COVID-19 patients in the ICU induced a significant increase in apoptosis markers (ΔΨm depolarization, cytosolic Ca²⁺, and PS externalization) compared with healthy volunteers and septic ICU controls. Interestingly, immunoglobulin G fractions from COVID-19 patients induced an Fcγ receptor IIA–dependent platelet apoptosis (ΔΨm depolarization, cytosolic Ca²⁺, and PS externalization). Enhanced PS externalization in platelets from COVID-19 patients in the ICU was associated with increased sequential organ failure assessment score (r = 0.5635) and D-dimer (r = 0.4473). Most importantly, patients with thrombosis had significantly higher PS externalization compared with those without. The strong correlations between markers for apoptosic and procoagulant platelets and D-dimer levels, as well as the incidence of thrombosis, may indicate that antibody-mediated procoagulant platelets potentially contributes to sustained increased thromboembolic risk in ICU COVID-19 patients.

Phosphodiesterase Inhibitors in Acute Lung Injury: What Are the Perspectives?

Despite progress in understanding the pathophysiology of acute lung damage, currently approved treatment possibilities are limited to lung-protective ventilation, prone positioning, and supportive interventions. Various pharmacological approaches have also been tested, with neuromuscular blockers and corticosteroids considered as the most promising. However, inhibitors of phosphodiesterases (PDEs) also exert a broad spectrum of favorable effects potentially beneficial in acute lung damage. This article reviews pharmacological action and therapeutical potential of nonselective and selective PDE inhibitors and summarizes the results from available studies focused on the use of PDE inhibitors in animal models and clinical studies, including their adverse effects. The data suggest that xanthines as representatives of nonselective PDE inhibitors may reduce acute lung damage, and decrease mortality and length of hospital stay. Various (selective) PDE3, PDE4, and PDE5 inhibitors have also demonstrated stabilization of the pulmonary epithelial-endothelial barrier and reduction the sepsis- and inflammation-increased microvascular permeability, and suppression of the production of inflammatory mediators, which finally resulted in improved oxygenation and ventilatory parameters. However, the current lack of sufficient clinical evidence limits their recommendation for a broader use. A separate chapter focuses on involvement of cyclic adenosine monophosphate (cAMP) and PDE-related changes in its metabolism in association with coronavirus disease 2019 (COVID-19). The chapter illuminates perspectives of the use of PDE inhibitors as an add-on treatment based on actual experimental and clinical trials with preliminary data suggesting their potential benefit.

Experimental Models of Acute Lung Injury: their Advantages and Limitations

Acute damage to the lung may originate from various direct and indirect reasons. Direct lung injury may be caused by pneumonia, near-drowning, aspiration, inhalation of toxic gases etc., while indirect lung injury is secondary, following any severe extra-pulmonary disease, e.g. sepsis, acute pancreatitis, or severe trauma. Due to a complex pathophysiology of the acute lung injury, the treatment is also extremely complicated and except for lung-protective ventilation there have been no specific treatment approaches recommended. An urgent need for a reliable and sufficiently effective treatment forces the researchers into testing novel therapeutic strategies. However, most of these determinations should be done in the laboratory conditions using animals. Complex methods of preparation of various experimental models of the acute lung injury has gradually developed within decades. Nowadays, there have been the models of direct, indirect, or mixed lung injury well established, as well as the models evoked by a combination of two triggering factors. Although the applicability of the results from animal experiments to patients might be limited by many factors, animal models are essential for understanding the patho-physiology of acute lung injury and provide an exceptional opportunity to search for novel therapeutical strategies.

Soluble cluster of differentiation 74 regulates lung inflammation through the nuclear factor-κB signaling pathway

The soluble form of the migration inhibitory factor receptor cluster of differentiation 74 (sCD74) has previously been shown to be elevated during the development of acute lung injury (ALI) in mice. However, the biological role of increased sCD74 in ALI remans poorly understood. Synthesized recombinant sCD74 protein was administered to mice intratracheally. Pro-inflammatory genes in lung tissue and the inflammatory factors in bronchoalveolar lavage fluid (BALF) were analyzed using RT-PCR and ELISA, respectively. Additionally, RAW264.7, A549, and human umbilical vein endothelial cells (HUVEC) were treated with sCD74, and the resulting pro-inflammatory factor protein and gene expression levels were analyzed in the supernatants and cell lysates. Meanwhile, the level of nuclear factor (NF)-κB components in cell lysates after stimulating macrophages with sCD74 was also assessed. After administration of 0.5 mg/kg body weight sCD74 to mice, the expression of Tnfa, Mip2, and Il6 increased in lung tissues after 2 h by 2.1-, 3.4-, and 2.8-fold, respectively. Moreover, the BALF concentrations of TNF-α and MIP-2 reached maximal levels of 560 and 107 pg/mL at 8 h compared to those in the saline group, respectively. Similarly, TNFA, MIP2, and IL6 expression increased by 4.0-, 11.8-, and 2.6-fold, respectively, 2 h after stimulating macrophages with 1000 ng/mL sCD74. The levels of phospho-IκB and phospho-p65 were also significantly increased in the cytoplasm and nucleus of macrophages following sCD74 stimulation. Taken together, these results suggest that sCD74 is a critical cellular factor involved in the lung acute inflammatory response through nuclear factor-κB signaling.

Effect of different dosages of dexamethasone therapy on lung function and inflammation in an early phase of acute respiratory distress syndrome model

Inflammation associated with acute respiratory distress syndrome (ARDS) can damage the alveolar epithelium and surfactant and worsen the respiratory failure. Glucocorticoids (GC) appear to be a rational therapeutic approach, but the effect is still unclear, especially for early administration and low-dose. In this study we compared two low doses of dexamethasone in early phase of surfactant-depleted model of acute respiratory distress syndrome (ARDS). In the study, lung-lavaged New Zealand rabbits with respiratory failure (PaO(2)<26.7 kPa in FiO(2) 1.0) were treated with intravenous dexamethasone (DEX): 0.5 mg/kg (DEX-0.5) and 1.0 mg/kg (DEX-1.0), or were untreated (ARDS). Animals without ARDS served as controls. Respiratory parameters, lung edema, leukocyte shifts, markers of inflammation and oxidative damage in the plasma and lung were evaluated. Both doses of DEX improved the lung function vs. untreated animals. DEX-1.0 had faster onset with significant improvement in gas exchange and ventilation efficiency vs. DEX-0.5. DEX-1.0 showed a trend to reduce lung neutrophils, local oxidative damage, and levels of TNFalpha, IL-6, IL-8 more effectively than DEX-0.5 vs. ARDS group. Both dosages of dexamethasone significantly improved the lung function and suppressed inflammation in early phase ARDS, while some additional enhancement was observed for higher dose (1 mg/kg) of DEX.

Effects of nitric oxide donor on the lung functions in a saline lavage-induced model of ARDS

Acute respiratory distress syndrome (ARDS) is characterized by acute hypoxemia, neutrophil-mediated inflammation, and lung edema formation. Whereas lung damage might be alleviated by nitric oxide (NO), goal of this study was to evaluate if intratracheal NO donor S-nitroso-N-acetylpenicillamine (SNAP) can positively influence the lung functions in experimental model of ARDS. New Zealand rabbits with respiratory failure induced by saline lavage (30 ml/kg, 9+/-3 times) were divided into: ARDS group without therapy, ARDS group treated with SNAP (7 mg/kg i.t.), and healthy Control group. During 5 h of ventilation, respiratory parameters (blood gases, ventilatory pressures) were estimated. After anesthetics overdosing, left lung was saline-lavaged and cell count, cell viability and protein content in bronchoalveolar lavage fluid (BALF) were measured. Right lung tissue was used for estimation of wet/dry weight ratio, concentration of NO metabolites, and histomorphological investigation. Repetitive lung lavage induced lung injury, worsened gas exchange, and damaged alveolar-capillary membrane. Administration of SNAP reduced cell count in BALF, lung edema formation, NO metabolites, and histopathological signs of injury, and improved respiratory parameters. Treatment with intratracheal SNAP alleviated lung injury and edema and improved lung functions in a saline-lavaged model of ARDS suggesting a potential of NO donors also for patients with ARDS.

COVID-19 and pneumonia: a role for the uPA/uPAR system

Here, we highlight recent findings on the urokinase plasminogen activator (uPA)/uPA receptor (uPAR) system that suggest its potential role as a main orchestrator of fatal progression to pulmonary, kidney, and heart failure in patients with coronavirus. Patients with prolonged background inflammation can present aberrant inflammatory reactions, well recognized as the main factors that can result in death and probably sustained by a dysregulated uPA/uPAR system. SuPAR, the soluble form of uPAR, represents a biomarker of disease progression, and its levels correlate well with comorbidities associated with the death of patients with coronavirus. New drugs that regulate the uPA/uPAR system could help treat the severe complications of highly pathogenic human coronaviruses (hCoVs), including pandemic coronavirus 2019 (COVID-19).

MicroRNA-92a serves as a risk factor in sepsis-induced ARDS and regulates apoptosis and cell migration in lipopolysaccharide-induced HPMEC and A549 cell injury

AIMS

Sepsis-induced acute respiratory distress syndrome (ARDS) is a common, high mortality complication in intensive care unit (ICU) patients. MicroRNA-92a (miR-92a) plays a role in many diseases, but its association with sepsis-induced ARDS is unclear.

MATERIALS AND METHODS

We enrolled 53 patients, including 17 with sepsis only, and 36 with sepsis-induced ARDS. Lipopolysaccharide (LPS) was used to stimulate pulmonary microvascular endothelial cells (HPMEC) and alveolar epithelial A549 cells, which were used to investigate the miR-92a roles in ARDS. MiR-92a expression levels in patient serum and cells were quantified using quantitative reverse transcription-polymerase chain reaction (RT-PCR), and protein expression was examined using Western blotting. The effect of miR-92a on apoptosis was examined using flow cytometry. Wound healing and transwell migration assays were used to evaluate cell migration.

KEY FINDINGS

Serum miR-92a expression was higher in patients with sepsis-induced ARDS, when compared to patients with sepsis only. After LPS treatment in cells, miR-92a expression was higher when compared with control group, cell apoptosis and inflammatory responses were increased and cell migration was inhibited. However, cell apoptosis and inflammatory responses were decreased and cell migration was enhanced after miR-92a downregulation, when compared with inhibitor negative control (NC) group. Moreover, phosphorylated-Akt and phosphorylated-mTOR expression were increased after miR-92a inhibition.

SIGNIFICANCE

Our study provides evidence that circulating serum miR-92a could act as a risk factor for sepsis-induced ARDS. MiR-92a inhibition attenuated the adverse effects of LPS on ARDS through the Akt/mTOR signaling pathway.

Iron overload causes a mild and transient increase in acute lung injury

Recent studies have demonstrated a strong link between acute respiratory distress syndrome (ARDS) and the levels of iron and iron-related proteins in the lungs. However, the role of iron overload in ARDS development has yet to be characterized. In this study, we compared the highly iron-overloaded hepcidin knockout mice (HKO) to their iron-sufficient wild-type (WT) littermates in a model of sterile acute lung injury (ALI) induced by treatment with oropharyngeal (OP) LPS. There were no major differences in systemic inflammatory response or airway neutrophil infiltration between the two groups at the time of maximal injury (days 2 and 3) or during the recovery phase (day 7). Hepcidin knockout mice had transiently increased bronchoalveolar lavage fluid (BALF) protein and MPO activity in the lung and BALF on day 3, indicating worse vascular leakage and increased neutrophil activity, respectively. The increased ALI severity in iron-overloaded mice may be a result of increased apoptosis of lung tissue, as evidenced by an increase in cleaved capsase-3 protein in lung homogenates from HKO mice versus WT mice on day 3. Altogether, our data suggest that even severe iron overload has a relatively minor and transient effect in LPS-induced ALI.

Lipid-Protein and Protein-Protein Interactions in the Pulmonary Surfactant System and Their Role in Lung Homeostasis

Pulmonary surfactant is a lipid/protein complex synthesized by the alveolar epithelium and secreted into the airspaces, where it coats and protects the large respiratory air–liquid interface. Surfactant, assembled as a complex network of membranous structures, integrates elements in charge of reducing surface tension to a minimum along the breathing cycle, thus maintaining a large surface open to gas exchange and also protecting the lung and the body from the entrance of a myriad of potentially pathogenic entities. Different molecules in the surfactant establish a multivalent crosstalk with the epithelium, the immune system and the lung microbiota, constituting a crucial platform to sustain homeostasis, under health and disease. This review summarizes some of the most important molecules and interactions within lung surfactant and how multiple lipid–protein and protein–protein interactions contribute to the proper maintenance of an operative respiratory surface.