Epithelial cell death is an important contributor to oxidant-mediated acute lung injury

RTA408 alleviates lipopolysaccharide-induced acute lung injury via inhibiting Bach1-mediated ferroptosis

The approved traditional Asian medicine RTA408 (Omaveloxolone) has demonstrated potent anti-inflammatory properties in the treatment of Friedreich's ataxia. However, its effect on lipopolysaccharide (LPS)-induced acute lung injury (ALI) remains poorly understood. This study aims to evaluate the effect of RTA408 on LPS-induced ALI and elucidate its underlying mechanisms. In this study, in vivo experiments demonstrated that RTA408 significantly ameliorated LPS-induced mouse ALI, characterized by reduced pathological damage and neutrophil infiltration as well as decreased lung edema of murine lung tissues. Moreover, LPS administration induced ferroptosis in ALI mice, evidenced by increased MDA levels, reduced GSH and SOD activity, and decreased expression of ferroptosis repressors (GPX4 and SLC7A11), whereas RTA408 reversed these changes. Consistently, RTA408 reduced ferroptosis and improved cell damage in LPS-stimulated MLE-12 cells, as evidenced by decreased ROS and MDA levels, increased SOD, GSH activity and ferroptosis repressors expression. Meanwhile, the protective effective of RTA408 on LPS-induced oxidative damage was blocked by ferroptosis inhibitor ferrostatin-1 (Fer-1). Mechanistic studies demonstrated that RTA408 inhibited the expression and nuclear translocation of Bach1, and the anti-ferroptosis effect was diminished by Bach1 siRNA or Bach1 knockout (Bach1-/-) mice. Furthermore, Bach1-/- mice exhibited attenuated ALI induced by LPS compared to wild-type (WT) mice, and the protective effect of RTA408 on LPS-challenged ALI was not observed in Bach1-/- mice. In conclusion, our data suggested that RTA408 alleviates LPS-induced ALI by interfering Bach1-mediated ferroptosis and might be a novel candidate for LPS-induced ALI/ARDS therapy.

Deciphering regulatory patterns in a mouse model of hyperoxia-induced acute lung injury

Background

Oxygen therapy plays a pivotal role in treating critically ill patients in the intensive care unit (ICU). However, excessive oxygen concentrations can precipitate hyperoxia, leading to damage in multiple organs, with a notable effect on the lungs. Hyperoxia condition may lead to hyperoxia-induced acute lung injury (HALI), deemed as a milder form of acute respiratory distress syndrome (ARDS). Given its clinical importance and practical implications, there is a compelling need to investigate the underlying pathogenesis and comprehensively understand the regulatory mechanisms implicated in the development of HALI.

Results

In this study, we conducted a mouse model with HALI and performed regulatory mechanism analysis using RNA-seq on both HALI and control group. Comprehensive analysis revealed 727 genes of significant differential expression, including 248 long non-coding RNAs (lncRNAs). Also, alternative splicing events were identified from sequencing results. Notably, we observed up-regulation or abnormal alternative splicing of genes associated with immune response and ferroptosis under hyperoxia conditions. Utilizing weighted gene co-expression network analysis (WGCNA), we ascertained that genes involved in immune response formed a distinct cluster, showcasing an up-regulated pattern in hyperoxia, consistent with previous studies. Furthermore, a competing endogenous RNA (ceRNA) network was constructed, including 78 differentially expressed mRNAs and six differentially expressed lncRNAs, including H19. These findings uncover the intricate interplay of multiple transcriptional regulatory mechanisms specifically tailored to the pulmonary defense against HALI, substantiating the importance of these non-coding RNAs in this disease context.

Conclusions

Our results provide new insights into the potential mechanisms and underlying pathogenesis in the development of HALI at the post-transcriptional level. The findings of this study reveal potential regulatory interactions and biological roles of specific lncRNAs and genes, such as H19 and Sox9, encompassing driven gene expression patterns, alternative splicing events, and lncRNA-miRNA-mRNA ceRNA networks. These findings may pave the way for advancing therapeutic strategies and reducing the risk associated with oxygen treatment for patients.

FAM134B deletion exacerbates apoptosis and epithelial-to-mesenchymal transition in rat lungs exposed to hyperoxia

Oxygen therapy is widely used in clinical practice; however, prolonged hyperoxia exposure may result in hyperoxic acute lung injury (HALI). In this study, we investigated the role of FAM134B in hyperoxia-induced apoptosis, cell proliferation, and epithelial-to-mesenchymal transition (EMT) using RLE-6TN cells and rat lungs. We also studied the effect of CeO2-NPs on RLE-6TN cells and lungs following hyperoxia exposure. FAM134B was inhibited in RLE-6TN cells and rat lungs following hyperoxia exposure. Overexpressing FAM134B promoted cell proliferation, and reduced EMT and apoptosis following hyperoxia exposure. FAM134B activation increased ER-phagy, decreased apoptosis, improved lung structure damage, and decreased collagen fiber deposition to limit lung injury. These effects could be reversed by PI3K/AKT pathway inhibitor LY294002. Additionally, CeO2-NPs protected RLE-6TN cells and lung damage following hyperoxia exposure by ameliorating impaired ER-phagy. Therefore, FAM134B restoration is a potential therapeutic target for the HALI. Moreover, CeO2-NPs can be used for the treatment of HALI.

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.

Sigma-1 receptor regulates the endoplasmic reticulum stress pathway in the protective mechanism of dexmedetomidine against hyperoxia-induced lung injury

Perioperative hyperoxia therapy is of great significance to save the lives of patients, but little is known about the possible mechanisms that induce hyperoxia-induced acute lung injury (HALI) and the measures for clinical prevention and treatment. In this experiment, the models were established with a feeding chamber with automatic regulation of oxygen concentration. The results showed that with the increase in inhaled oxygen concentration and the prolongation of exposure time, the severity of lung injury also increases significantly, reaching the diagnostic indication of HALI after 48 h of inhaling 95 % oxygen concentration. Subsequently, according to the dynamic changes of apoptosis in lung specimens, and the expression changes in Sig-1R-regulated ER stress pathway proteins (Sig-1R, GRP78, p-PERK, ATF6, IRE1, Caspase-12, ATF4, CHOP, Caspase-3 and p-JNK), it was confirmed that the Sig-1R-regulated ER stress signaling pathway was involved in the occurrence of HALI. To explore the preventive and therapeutic effects of routine clinical medication on HALI during the perioperative period, our research group selected dexmedetomidine (Dex) with lung protection. The experimental results revealed that Dex partially reversed the changes in the expression levels of Sig-1R-regulated ER stress pathway proteins. These results preliminarily confirmed that Dex may inhibit apoptosis induced by high oxygen concentration through the Sig-1R-regulated ER stress signaling pathway, thus playing a protective role in HALI.

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.

Alveolar Mitochondrial Quality Control During Acute Respiratory Distress Syndrome

Acute respiratory distress syndrome (ARDS) is a leading cause of respiratory failure and death in patients in the intensive care unit. Experimentally, acute lung injury resolution depends on the repair of mitochondrial oxidant damage by the mitochondrial quality control (MQC) pathways, mitochondrial biogenesis, and mitophagy, but nothing is known about this in the human lung. In a case-control autopsy study, we compared the lungs of subjects dying of ARDS (n = 8; cases) and age-/gender-matched subjects dying of nonpulmonary causes (n = 7; controls). Slides were examined by light microscopy and immunofluorescence confocal microscopy, randomly probing for co-localization of citrate synthase with markers of oxidant stress, mitochondrial DNA damage, mitophagy, and mitochondrial biogenesis. ARDS lungs showed diffuse alveolar damage with edema, hyaline membranes, and neutrophils. Compared with controls, a high degree of mitochondrial oxidant damage was seen in type 2 epithelial (AT2) cells and alveolar macrophages by 8-hydroxydeoxyguanosine and malondialdehyde co-staining with citrate synthase. In ARDS, antioxidant protein heme oxygenase-1 and DNA repair enzyme N-glycosylase/DNA lyase (Ogg1) were found in alveolar macrophages but not in AT2 cells. Moreover, MAP1 light chain-3 (LC3) and serine/threonine-protein kinase (Pink1) staining were absent in AT2 cells, suggesting a mitophagy failure. Nuclear respiratory factor-1 staining was missing in the alveolar region, suggesting impaired mitochondrial biogenesis. Widespread hyperproliferation of AT2 cells in ARDS could suggest defective differentiation into type 1 cells. ARDS lungs show profuse mitochondrial oxidant DNA damage but little evidence of MQC activity in AT2 epithelium. Because these pathways are important for acute lung injury resolution, our findings support MQC as a novel pharmacologic target for ARDS resolution.

Apoptotic cell death in disease-Current understanding of the NCCD 2023

Apoptosis is a form of regulated cell death (RCD) that involves proteases of the caspase family. Pharmacological and genetic strategies that experimentally inhibit or delay apoptosis in mammalian systems have elucidated the key contribution of this process not only to (post-)embryonic development and adult tissue homeostasis, but also to the etiology of multiple human disorders. Consistent with this notion, while defects in the molecular machinery for apoptotic cell death impair organismal development and promote oncogenesis, the unwarranted activation of apoptosis promotes cell loss and tissue damage in the context of various neurological, cardiovascular, renal, hepatic, infectious, neoplastic and inflammatory conditions. Here, the Nomenclature Committee on Cell Death (NCCD) gathered to critically summarize an abundant pre-clinical literature mechanistically linking the core apoptotic apparatus to organismal homeostasis in the context of disease.

NLRX1 knockdown attenuates pro-apoptotic signaling and cell death in pulmonary hyperoxic acute injury

Hyperoxia is frequently used for treating acute respiratory failure, but it can cause acute lung injury. Nucleotide-binding domain and leucine-rich-repeat-containing family member X1 (NLRX1) is localized in mitochondria and involved in production of reactive oxygen species, inflammation, and apoptosis, which are the features of hyperoxic acute lung injury (HALI). The contribution of NLRX1 to HALI has not previously been addressed. Thus, to investigate the role of NLRX1 in hyperoxia, we generated a murine model of HALI in wild-type (WT) and NLRX1^-/- mice by exposure to > 95% oxygen for 72 h. As a result, NLRX1 expression was elevated in mice exposed to hyperoxia. In acute lung injury, levels of inflammatory cells, protein leakage, cell cytotoxicity, and pro-inflammatory cytokines were diminished in NLRX1^-/- mice compared to WT mice. In a survival test, NLRX1^-/- mice showed reduced mortality under hyperoxic conditions, and apoptotic cell death and caspase expression and activity were also lower in NLRX1^-/- mice. Furthermore, levels of the MAPK signaling proteins ERK 1/2, JNK, and p38 were decreased in NLRX1-deficient mice than in WT mice exposed to hyperoxia. The study shows that a genetic deficit in NLRX1 can suppress hyperoxia-induced apoptosis, suggesting that NLRX1 acts as a pivotal regulator of HALI.

Advanced development and mechanism of sepsis-related acute respiratory distress syndrome

The introduction of the Sepsis 3.0 guidelines in 2016 improved our understanding of sepsis diagnosis and therapy. Personalized treatment strategies and nursing methods for sepsis patients are recommended in the "Save Sepsis Campaign" in 2021. However, mortality in sepsis patients remains high. Patients with sepsis-related acute respiratory distress syndrome account for around 30% of them, with fatality rates ranging from 30 to 40%. Pathological specimens from individuals with sepsis-related ARDS frequently demonstrate widespread alveolar damage, and investigations have revealed that pulmonary epithelial and pulmonary endothelial injury is the underlying cause. As a result, the purpose of this work is to evaluate the mechanism and research progress of pulmonary epithelial and pulmonary endothelial damage in sepsis-related ARDS, which may provide new directions for future research, diagnosis, and therapy.

Epidermal Growth Factor Receptor Inhibition Is Protective in Hyperoxia-Induced Lung Injury

Aims

Studies have linked severe hyperoxia, or prolonged exposure to very high oxygen levels, with worse clinical outcomes. This study investigated the role of epidermal growth factor receptor (EGFR) in hyperoxia-induced lung injury at very high oxygen levels (>95%).

Results

Effects of severe hyperoxia (100% oxygen) were studied in mice with genetically inhibited EGFR and wild-type littermates. Despite the established role of EGFR in lung repair, EGFR inhibition led to improved survival and reduced acute lung injury, which prompted an investigation into this protective mechanism. Endothelial EGFR genetic knockout did not confer protection. EGFR inhibition led to decreased levels of cleaved caspase-3 and poly (ADP-ribosyl) polymerase (PARP) and decreased terminal dUTP nick end labeling- (TUNEL-) positive staining in alveolar epithelial cells and reduced ERK activation, which suggested reduced apoptosis in vivo. EGFR inhibition decreased hyperoxia (95%)-induced apoptosis and ERK in murine alveolar epithelial cells in vitro, and CRISPR-mediated EGFR deletion reduced hyperoxia-induced apoptosis and ERK in human alveolar epithelial cells in vitro. Innovation. This work defines a protective role of EGFR inhibition to decrease apoptosis in lung injury induced by 100% oxygen. This further characterizes the complex role of EGFR in acute lung injury and outlines a novel hyperoxia-induced cell death pathway that warrants further study.

Conclusion

In conditions of severe hyperoxia (>95% for >24 h), EGFR inhibition led to improved survival, decreased lung injury, and reduced cell death. These findings further elucidate the complex role of EGFR in acute lung injury.

Oxygen toxicity: cellular mechanisms in normobaric hyperoxia

In clinical settings, oxygen therapy is administered to preterm neonates and to adults with acute and chronic conditions such as COVID-19, pulmonary fibrosis, sepsis, cardiac arrest, carbon monoxide poisoning, and acute heart failure. In non-clinical settings, divers and astronauts may also receive supplemental oxygen. In addition, under current standard cell culture practices, cells are maintained in atmospheric oxygen, which is several times higher than what most cells experience in vivo. In all the above scenarios, the elevated oxygen levels (hyperoxia) can lead to increased production of reactive oxygen species from mitochondria, NADPH oxidases, and other sources. This can cause cell dysfunction or death. Acute hyperoxia injury impairs various cellular functions, manifesting ultimately as physiological deficits. Chronic hyperoxia, particularly in the neonate, can disrupt development, leading to permanent deficiencies. In this review, we discuss the cellular activities and pathways affected by hyperoxia, as well as strategies that have been developed to ameliorate injury.

Antioxidants as Therapeutic Agents in Acute Respiratory Distress Syndrome (ARDS) Treatment-From Mice to Men

Acute respiratory distress syndrome (ARDS) is a major cause of patient mortality in intensive care units (ICUs) worldwide. Considering that no causative treatment but only symptomatic care is available, it is obvious that there is a high unmet medical need for a new therapeutic concept. One reason for a missing etiologic therapy strategy is the multifactorial origin of ARDS, which leads to a large heterogeneity of patients. This review summarizes the various kinds of ARDS onset with a special focus on the role of reactive oxygen species (ROS), which are generally linked to ARDS development and progression. Taking a closer look at the data which already have been established in mouse models, this review finally proposes the translation of these results on successful antioxidant use in a personalized approach to the ICU patient as a potential adjuvant to standard ARDS treatment.

Oxygen Toxicity to the Immature Lung-Part I: Pathomechanistic Understanding and Preclinical Perspectives

In utero, the fetus and its lungs develop in a hypoxic environment, where HIF-1α and VEGFA signaling constitute major determinants of further development. Disruption of this homeostasis after preterm delivery and extrauterine exposure to high fractions of oxygen are among the key events leading to bronchopulmonary dysplasia (BPD). Reactive oxygen species (ROS) production constitutes the initial driver of pulmonary inflammation and cell death, altered gene expression, and vasoconstriction, leading to the distortion of further lung development. From preclinical studies mainly performed on rodents over the past two decades, the deleterious effects of oxygen toxicity and the injurious insults and downstream cascades arising from ROS production are well recognized. This article provides a concise overview of disease drivers and different therapeutic approaches that have been successfully tested within experimental models. Despite current studies, clinical researchers are still faced with an unmet clinical need, and many of these strategies have not proven to be equally effective in clinical trials. In light of this challenge, adapting experimental models to the complexity of the clinical situation and pursuing new directions constitute appropriate actions to overcome this dilemma. Our review intends to stimulate research activities towards the understanding of an important issue of immature lung injury.

Oxygen Toxicity to the Immature Lung-Part II: The Unmet Clinical Need for Causal Therapy

Oxygen toxicity continues to be one of the inevitable injuries to the immature lung. Reactive oxygen species (ROS) production is the initial step leading to lung injury and, subsequently, the development of bronchopulmonary dysplasia (BPD). Today, BPD remains the most important disease burden following preterm delivery and results in life-long restrictions in lung function and further important health sequelae. Despite the tremendous progress in the pathomechanistic understanding derived from preclinical models, the clinical needs for preventive or curative therapies remain unmet. This review summarizes the clinical progress on guiding oxygen delivery to the preterm infant and elaborates future directions of research that need to take into account both hyperoxia and hypoxia as ROS sources and BPD drivers. Many strategies have been tested within clinical trials based on the mechanistic understanding of ROS actions, but most have failed to prove efficacy. The majority of these studies were tested in an era before the latest modes of non-invasive respiratory support and surfactant application were introduced or were not appropriately powered. A comprehensive re-evaluation of enzymatic, antioxidant, and anti-inflammatory therapies to prevent ROS injury is therefore indispensable. Strategies will only succeed if they are applied in a timely and vigorous manner and with the appropriate outcome measures.

Short exposure to hyperoxia causes cultured lung epithelial cell mitochondrial dysregulation and alveolar simplification in mice

BACKGROUND

Prolonged exposure to high oxygen concentrations in premature infants, although lifesaving, can induce lung oxidative stress and increase the risk of developing BPD, a form of chronic lung disease. The lung alveolar epithelium is damaged by sustained hyperoxia, causing oxidative stress and alveolar simplification; however, it is unclear what duration of exposure to hyperoxia negatively impacts cellular function.

METHODS

Here we investigated the role of a very short exposure to hyperoxia (95% O₂, 5% CO₂) on mitochondrial function in cultured mouse lung epithelial cells and neonatal mice.

RESULTS

In epithelial cells, 4 h of hyperoxia reduced oxidative phosphorylation, respiratory complex I and IV activity, utilization of mitochondrial metabolites, and caused mitochondria to form elongated tubular networks. Cells allowed to recover in air for 24 h exhibited a persistent global reduction in fuel utilization. In addition, neonatal mice exposed to hyperoxia for only 12 h demonstrated alveolar simplification at postnatal day 14.

CONCLUSION

A short exposure to hyperoxia leads to changes in lung cell mitochondrial metabolism and dynamics and has a long-term impact on alveolarization. These findings may help inform our understanding and treatment of chronic lung disease.

IMPACT

Many studies use long exposures (up to 14 days) to hyperoxia to mimic neonatal chronic lung disease. We show that even a very short exposure to hyperoxia leads to long-term cellular injury in type II-like epithelial cells. This study demonstrates that a short (4 h) period of hyperoxia has long-term residual effects on cellular metabolism. We show that neonatal mice exposed to hyperoxia for a short time (12 h) demonstrate later alveolar simplification. This work suggests that any exposure to clinical hyperoxia leads to persistent lung dysfunction.

Human Umbilical Cord-Derived Mesenchymal Stem Cells for Acute Respiratory Distress Syndrome

OBJECTIVES

To investigate the safety, feasibility, and possible adverse events of single-dose human umbilical cord-derived mesenchymal stem cells in patients with moderate-to-severe acute respiratory distress syndrome.

DESIGN

Prospective phase I clinical trial.

SETTING

Medical center in Kaohsiung, Taiwan.

PATIENTS

Moderate-to-severe acute respiratory distress syndrome with a PaO2/FIO2 ratio less than 200.

INTERVENTIONS

Scaling for doses was required by Taiwan Food and Drug Administration as follows: the first three patients received low-dose human umbilical cord-derived mesenchymal stem cells (1.0 × 10 cells/kg), the next three patients with intermediate dose (5.0 × 10 cells/kg), and the final three patients with high dose (1.0 × 10 cells/kg) between December 2017 and August 2019.

MEASUREMENTS AND MAIN RESULTS

Nine consecutive patients were enrolled into the study. In-hospital mortality was 33.3% (3/9), including two with recurrent septic shock and one with ventilator-induced severe pneumomediastinum and subcutaneous emphysema. No serious prespecified cell infusion-associated or treatment-related adverse events was identified in any patient. Serial flow-cytometric analyses of circulating inflammatory biomarkers (CD14CD33/CD11b+CD16+/CD16+MPO+/CD11b+MPO+/CD14CD33+) and mesenchymal stem cell markers (CD26+CD45-/CD29+CD45-/CD34+CD45-/CD44+CD45-/CD73+CD45-/CD90+CD45-/CD105+CD45-/CD26+CD45-) were notably progressively reduced (p for trend < 0.001), whereas the immune cell markers (Helper-T-cell/Cytotoxity-T-cell/Regulatory-T-cell) were notably increased (p for trend < 0.001) after cell infusion.

CONCLUSIONS

The result of this phase I clinical trial showed that a single-dose IV infusion of human umbilical cord-derived mesenchymal stem cells was safe with favorable outcome in nine acute respiratory distress syndrome patients.

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.

The association between urinary aluminum and lung function among an urban adult population: A repeated-measure longitudinal study

OBJECTIVES

To investigate the cross-sectional and longitudinal associations between aluminum exposure and lung function and the risk of chronic obstructive pulmonary disease (COPD).

METHODS

The repeated-measure study was developed with 3917 adults from the Wuhan-Zhuhai cohort and they were followed-up after 3 years and 6 years. Urinary aluminum and lung function were measured at each period. Linear mixed models were used to estimate the exposure-response relationship between urinary aluminum and lung function. COX regression models were used to evaluate the association of urinary aluminum with the risk of COPD.

RESULTS

A total of 6996 observations including 2251 (32.2%) males with a mean age of 54.8 years were included. In the cross-sectional analyses, each 1-unit increase in log-transformed urinary aluminum was associated with a -33.34 mL (95% confidence interval (CI) -45.71 to -20.96) change in forced vital capacity (FVC) and a -17.89 mL (-27.80 to -7.97) change in forced expiratory volume in 1 s (FEV1). The follow-up analyses detected a negative association between urinary aluminum and the annual change of FVC (-6.73 mL/year, 95% CI -10.92 to -2.54), while the association of annual decline of FEV1 with urinary aluminum was statistically insignificant (-2.26 mL/year, -5.76 to 1.23). In the adjusted COX regression model, each 1-unit increase in log-transformed urinary aluminum was associated with a 29% increase in the incident risk of COPD (hazard ratio 1.29, 95% CI 1.04-1.62).

INCLUSION

Increased urinary aluminum was associated with lung function reduction and the increased risk of COPD in a general urban population.

Clusterin Deficiency Exacerbates Hyperoxia-Induced Acute Lung Injury

Exposure to high oxygen concentrations leads to generation of excessive reactive oxygen species, causing cellular injury and multiple organ dysfunctions and is associated with a high mortality rate. Clusterin (CLU) is a heterodimeric glycoprotein that mediates several intracellular signaling pathways, including cell death and inflammation. However, the role of CLU in the pathogenesis of hyperoxic acute lung injury (HALI) is unknown. Wild-type (WT) and CLU-deficient mice and cultured human airway epithelial cells were used. Changes in cell death- and inflammation-related molecules with or without hyperoxia exposure in cells and animals were determined. Hyperoxia induced an increase in CLU expression in mouse lungs and human airway epithelial cells. Mice lacking CLU had increased HALI and mortality rate compared with WT mice. In vitro, CLU-disrupted cells showed enhanced release of cytochrome c, Bax translocation, cell death and inflammatory cytokine expression. However, treatment with recombinant CLU attenuated hyperoxia-induced apoptosis. Moreover, the Kyoto Encyclopedia of Genes and Genomes and Gene Ontology analyses revealed metabolic pathways, hematopoietic cell lineage, response to stress and localization and regulation of immune system that were differentially regulated between WT and CLU-/- mice. These results demonstrate that prolonged hyperoxia-induced lung injury is associated with CLU expression and that CLU replenishment may alleviate hyperoxia-induced cell death.

Cardiopulmonary Resuscitation-associated Lung Edema (CRALE). A Translational Study

Rationale: Cardiopulmonary resuscitation is the cornerstone of cardiac arrest (CA) treatment. However, lung injuries associated with it have been reported.Objectives: To assess 1) the presence and characteristics of lung abnormalities induced by cardiopulmonary resuscitation and 2) the role of mechanical and manual chest compression (CC) in its development.Methods: This translational study included 1) a porcine model of CA and cardiopulmonary resuscitation (n = 12) and 2) a multicenter cohort of patients with out-of-hospital CA undergoing mechanical or manual CC (n = 52). Lung computed tomography performed after resuscitation was assessed qualitatively and quantitatively along with respiratory mechanics and gas exchanges.Measurements and Main Results: The lung weight in the mechanical CC group was higher compared with the manual CC group in the experimental (431 ± 127 vs. 273 ± 66, P = 0.022) and clinical study (1,208 ± 630 vs. 837 ± 306, P = 0.006). The mechanical CC group showed significantly lower oxygenation (P = 0.043) and respiratory system compliance (P < 0.001) compared with the manual CC group in the experimental study. The variation of right atrial pressure was significantly higher in the mechanical compared with the manual CC group (54 ± 11 vs. 31 ± 6 mm Hg, P = 0.001) and significantly correlated with lung weight (r = 0.686, P = 0.026) and respiratory system compliance (r = -0.634, P = 0.027). Incidence of abnormal lung density was higher in patients treated with mechanical compared with manual CC (37% vs. 8%, P = 0.018).Conclusions: This study demonstrated the presence of cardiopulmonary resuscitation-associated lung edema in animals and in patients with out-of-hospital CA, which is more pronounced after mechanical as opposed to manual CC and correlates with higher swings of right atrial pressure during CC.

Mitochondrial Dysfunction and Permeability Transition in Neonatal Brain and Lung Injuries

This review discusses the potential mechanistic role of abnormally elevated mitochondrial proton leak and mitochondrial bioenergetic dysfunction in the pathogenesis of neonatal brain and lung injuries associated with premature birth. Providing supporting evidence, we hypothesized that mitochondrial dysfunction contributes to postnatal alveolar developmental arrest in bronchopulmonary dysplasia (BPD) and cerebral myelination failure in diffuse white matter injury (WMI). This review also analyzes data on mitochondrial dysfunction triggered by activation of mitochondrial permeability transition pore(s) (mPTP) during the evolution of perinatal hypoxic-ischemic encephalopathy. While the still cryptic molecular identity of mPTP continues to be a subject for extensive basic science research efforts, the translational significance of mitochondrial proton leak received less scientific attention, especially in diseases of the developing organs. This review is focused on the potential mechanistic relevance of mPTP and mitochondrial dysfunction to neonatal diseases driven by developmental failure of organ maturation or by acute ischemia-reperfusion insult during development.

MCTR3 reduces LPS-induced acute lung injury in mice via the ALX/PINK1 signaling pathway

Acute lung injury (ALI), a common respiratory distress syndrome in the intensive care unit (ICU), is mainly caused by severe infection and shock. Epithelial and capillary endothelial cell injury, interstitial edema and inflammatory cell infiltration are the main pathological changes observed in ALI animal models. Maresin conjugates in tissue regeneration (MCTR) are a new family of anti-inflammatory proteins. MCTR3 is a key enhancer of the host response, that promotes tissue regeneration and reduces infection; however, its role and mechanism in ALI are still unclear. The purpose of our research was to assess the protective effects of MCTR3 against ALI and its underlying mechanism. The work in this study was conducted in a murine model and the pulmonary epithelial cell line MLE-12. In vivo, MCTR3 (2 ng/g) was given 2 h after lipopolysaccharide (LPS) injection. We found that the treatment of mice with LPS-induced ALI with MCTR3 significantly reduced the cell number and protein levels in the bronchoalveolar lavage fluid (BALF); decreased the production of inflammatory cytokines; alleviated oxidative stress and cell apoptosis, consequently decreased lung injury; and restored pulmonary function. These protective effects of MCTR3 were dependent on down-regulation of the PTEN-induced putative kinase 1 (PINK1) pathway. Additionally, in MLE-12 cells stimulated with LPS, MCTR3 inhibited cell death, inflammatory cytokine levels and oxidative stress via the ALX/PINK1 signaling pathway. Thus, we conclude that MCTR3 protected against LPS-induced ALI partly through inactivation of the ALX/PINK1 mediated mitophagy pathway.

Electroacupuncture Pretreatment Alleviates LPS-Induced Acute Respiratory Distress Syndrome via Regulating the PPAR Gamma/NF-Kappa B Signaling Pathway

Electroacupuncture (EA) is reported to possess anti-inflammatory properties and has beneficial effects on acute respiratory distress syndrome (ARDS). However, the underlying mechanisms of the effects of EA on ARDS remain unclear. This study aims to investigate the protective effect of EA on LPS-induced ARDS. In this study, Sprague-Dawley male rats were treated with EA at Hegu (LI4) for 45 minutes before LPS instillation (0.4 mg/kg, 100 ul). H&E staining, wet-to-dry weight (W/D) ratio, PaO₂, and protein content in BALF were employed to determine the function of lung tissues. Inflammatory cytokines in serum and BALF were detected by enzyme-linked immunoassay assay (ELISA). The levels of oxidative stress markers were detected to determine the oxidative stress status. Cell apoptosis was observed by terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL) staining and western blot. Here, we found that EA pretreatment effectively alleviated lung pathological damage. Moreover, EA suppressed the oxidative stress damage by upregulating glutathione and superoxide dismutase and downregulating malondialdehyde. EA pretreatment also regulated apoptosis-related proteins, such as Bax and Bcl-2. We found that peroxisome proliferators-activated receptors γ (PPARγ) play a critical role during ARDS, EA up-regulated the expression of PPARγ, which inhibited the activation of nuclear factor-kappa B (NF-κB) and decreased the inflammatory cytokines (interleukin-1β, interleukin-6, and tumor necrosis factor-α). When rats were treated with GW9662, a selective PPARγ antagonist, these effects of EA were reversed. Our study demonstrated that EA pretreatment had a beneficial effect on LPS-induced ARDS in rats by anti-inflammatory, antioxidative, and antiapoptotic properties which was regulated via PPARγ/NF-κB signaling pathway.

Cross-sectional and longitudinal associations between urinary zinc and lung function among urban adults in China

Background

Exposure to zinc was suggested to be associated with pulmonary damage, but whether zinc exposure affects lung function remains unclear.

Objectives

To quantify the association between urinary zinc and lung function and explore the potential mechanisms.

Methods

Urinary zinc and lung function were measured in 3917 adults from the Wuhan-Zhuhai cohort and were repeated after 3 years of follow-up. Indicators of systemic inflammation (C reactive protein), lung epithelium integrity (club cell secretory protein-16) and oxidative damage (8-hydroxy-2′-deoxyguanosine and 8-isoprostane) were measured at baseline. Linear mixed models were used to estimate the exposure–response relationship between urinary zinc and lung function. Mediation analyses were conducted to assess mediating roles of inflammation and oxidative damage in above relationships.

Results

Each 1-unit increase in log-transformed urinary zinc values was associated with a 35.72 mL decrease in forced vital capacity (FVC) and a 24.89 mL decrease in forced expiratory volume in 1 s (FEV1) in the baseline analyses. In the follow-up analyses, there was a negative association between urinary zinc and FVC among participants with persistent high urinary zinc levels, with an estimated change of −93.31 mL (95% CI −178.47 to −8.14). Furthermore, urinary zinc was positively associated with restrictive ventilatory impairment. The mediation analyses suggested that C reactive protein mediated 8.62% and 8.71% of the associations of urinary zinc with FVC and FEV1, respectively.

Conclusion

Urinary zinc was negatively associated with lung function, and the systemic inflammation may be one of the underlying mechanisms.

Tie-2 Cre-Mediated Deficiency of Extracellular Signal-Regulated Kinase 2 Potentiates Experimental Bronchopulmonary Dysplasia-Associated Pulmonary Hypertension in Neonatal Mice

Bronchopulmonary dysplasia (BPD)-associated pulmonary hypertension (PH) is a significant lung morbidity of infants, and disrupted lung angiogenesis is a hallmark of this disease. We observed that extracellular signal-regulated kinases (ERK) 1/2 support angiogenesis in vitro, and hyperoxia activates ERK1/2 in fetal human pulmonary microvascular endothelial cells (HPMECs) and in neonatal murine lungs; however, their role in experimental BPD and PH is unknown. Therefore, we hypothesized that Tie2 Cre-mediated deficiency of ERK2 in the endothelial cells of neonatal murine lungs would potentiate hyperoxia-induced BPD and PH. We initially determined the role of ERK2 in in vitro angiogenesis using fetal HPMECs. To disrupt endothelial ERK2 signaling in the lungs, we decreased ERK2 expression by breeding ERK2^flox/flox mice with Tie-Cre mice. One-day-old endothelial ERK2-sufficient (eERK2^+/+) or –deficient (eERK2^+/−) mice were exposed to normoxia or hyperoxia (FiO₂ 70%) for 14 d. We then performed lung morphometry, gene and protein expression studies, and echocardiography to determine the extent of inflammation, oxidative stress, and development of lungs and PH. The knockdown of ERK2 in HPMECs decreased in vitro angiogenesis. Hyperoxia increased lung inflammation and oxidative stress, decreased lung angiogenesis and alveolarization, and induced PH in neonatal mice; however, these effects were augmented in the presence of Tie2-Cre mediated endothelial ERK2 deficiency. Therefore, we conclude that endothelial ERK2 signaling is necessary to mitigate hyperoxia-induced experimental BPD and PH in neonatal mice. Our results indicate that endothelial ERK2 is a potential therapeutic target for the management of BPD and PH in infants.

Oxidative Stress in Pulmonary Fibrosis

Oxidative stress has been linked to various disease states as well as physiological aging. The lungs are uniquely exposed to a highly oxidizing environment and have evolved several mechanisms to attenuate oxidative stress. Idiopathic pulmonary fibrosis (IPF) is a progressive age-related disorder that leads to architectural remodeling, impaired gas exchange, respiratory failure, and death. In this article, we discuss cellular sources of oxidant production, and antioxidant defenses, both enzymatic and nonenzymatic. We outline the current understanding of the pathogenesis of IPF and how oxidative stress contributes to fibrosis. Further, we link oxidative stress to the biology of aging that involves DNA damage responses, loss of proteostasis, and mitochondrial dysfunction. We discuss the recent findings on the role of reactive oxygen species (ROS) in specific fibrotic processes such as macrophage polarization and immunosenescence, alveolar epithelial cell apoptosis and senescence, myofibroblast differentiation and senescence, and alterations in the acellular extracellular matrix. Finally, we provide an overview of the current preclinical studies and clinical trials targeting oxidative stress in fibrosis and potential new strategies for future therapeutic interventions. © 2020 American Physiological Society. Compr Physiol 10:509-547, 2020.

Impairment of Fatty Acid Oxidation in Alveolar Epithelial Cells Mediates Acute Lung Injury

Profound impairment in cellular oxygen consumption, referred to as cytopathic dysoxia, is one of the pathological hallmarks in the lungs of patients with pathogen-induced acute lung injury (ALI). However, the underlying mechanism for this functional defect remains largely unexplored. In this study, we found that primary mouse alveolar epithelial cells (AECs) conducted robust fatty acid oxidation (FAO). More importantly, FAO was strikingly impaired in AECs of mice with LPS-induced ALI. The metabolic deficiency in these cells was likely due to decreased expression of key mediators involved in FAO and mitochondrial bioenergenesis, such as peroxisome proliferator-activated receptor γ coactivator (PGC)-1α, carnitine palmitoyltransferase 1A, and medium-chain acyl-CoA dehydrogenase (CAD). We found that treatment of alveolar epithelial line MLE-12 cells with BAL fluids from mice with ALI decreased FAO, and this effect was largely replicated in MLE-12 cells treated with the proinflammatory cytokine TNF-α, which was consistent with downregulations of PGC-1α, carnitine palmitoyltransferase 1A, long-chain CAD, and medium-chain CAD in the same treated cells. Furthermore, we found that the BAL fluids from ALI mice and TNF-α inhibited MLE-12 bioenergenesis and promoted cell apoptosis. In delineation of the role of FAO in ALI in vivo, we found that conditional ablation of AEC PGC-1α aggravated LPS-induced ALI. In contrast, fenofibrate, an activator of the PPAR-α/PGC-1α cascade, protected mice from this pathology. In summary, these data suggest that FAO is essential to AEC bioenergenesis and functional homeostasis. This study also indicates that FAO impairment-induced AEC dysfunction is an important contributing factor to the pathogenesis of ALI.

Peroxiredoxins and Beyond; Redox Systems Regulating Lung Physiology and Disease

Significance: The lung is a unique organ, as it is constantly exposed to air, and thus it requires a robust antioxidant defense system to prevent the potential damage from exposure to an array of environmental insults, including oxidants. The peroxiredoxin (PRDX) family plays an important role in scavenging peroxides and is critical to the cellular antioxidant defense system. Recent Advances: Exciting discoveries have been made to highlight the key features of PRDXs that regulate the redox tone. PRDXs do not act in isolation as they require the thioredoxin/thioredoxin reductase/NADPH, sulfiredoxin (SRXN1) redox system, and in some cases glutaredoxin/glutathione, for their reduction. Furthermore, the chaperone function of PRDXs, controlled by the oxidation state, demonstrates the versatility in redox regulation and control of cellular biology exerted by this class of proteins. Critical Issues: Despite the long-known observations that redox perturbations accompany a number of pulmonary diseases, surprisingly little is known about the role of PRDXs in the etiology of these diseases. In this perspective, we review the studies that have been conducted thus far to address the roles of PRDXs in lung disease, or experimental models used to study these diseases. Intriguing findings, such as the secretion of PRDXs and the formation of autoantibodies, raise a number of questions about the pathways that regulate secretion, redox status, and immune response to PRDXs. Future Directions: Further understanding of the mechanisms by which individual PRDXs control lung inflammation, injury, repair, chronic remodeling, and cancer, and the importance of PRDX oxidation state, configuration, and client proteins that govern these processes is needed.

miR‑21‑5p ameliorates hyperoxic acute lung injury and decreases apoptosis of AEC II cells via PTEN/AKT signaling in rats

Inhibiting apoptosis of type II alveolar epithelial cells (AEC II) is an effective way to decrease hyperoxic acute lung injury (HALI); however, the specific underlying molecular mechanisms have not yet been fully elucidated. Although miRNA‑21‑5p has previously been reported to decrease H2O2‑induced AEC II apoptosis by targeting PTEN in vitro, whether miR‑21‑5p can decrease HALI in vivo and the downstream molecular mechanisms remain unclear. In the present study, rats were endotracheally administered with an miR‑21‑5p‑encoding (AAV‑6‑miR‑21‑5p) or a negative control adenovirus vector, and then a HALI model was established by exposure to hyperoxia. At 3 weeks following the administration of AAV‑6‑miR‑21‑5p, the severity of HALI was decreased, as evidenced by the improved outcome of the oxygenation index, respiratory index, wet/dry weight ratio and pathological scores of the HALI lungs. To further investigate the underlying mechanisms, AEC II cells were isolated from the lungs of the experimental rats and cultured. The expression levels of miR‑21‑5p and its target gene, PTEN, were detected, as well as the levels of phosphorylated and total AKT. In addition, the apoptosis rate of AEC II was detected by flow cytometry. The results demonstrated that AAV‑6‑miR‑21‑5p administration increased the miR‑21‑5p levels in primary AEC II cells, while it decreased the expression levels of PTEN. miR‑21‑5p overexpression also increased AKT phosphorylation in AEC II cells from the HALI lungs compared with that of the HALI alone group and the control virus group. The present study indicated that miR‑21‑5p ameliorated HALI in vivo, which may have resulted from the inhibition of PTEN/AKT‑induced apoptosis of AEC II cells. These findings suggest that miR‑21‑5p and PTEN/AKT signaling might serve as potential targets for HALI treatment.

Oxygen radical disease in the newborn, revisited: Oxidative stress and disease in the newborn period

Thirty years ago, there was an emerging appreciation for the significance of oxidative stress in newborn disease. This prompted a renewed interest in the impact of oxygen therapy for the newborn in the delivery room and beyond, especially in premature infants. Today, the complexity of oxidative stress both in normal regulation and pathology is better understood, especially as it relates to neonatal mitochondrial oxidative stress responses to hyperoxia. Mitochondria are recipients of oxidative damage and have a propensity for oxidative self-injury that has been implicated in the pathogenesis of neonatal lung diseases. Similarly, both intrauterine growth restriction (IUGR) and macrosomia are associated with mitochondrial dysfunction and oxidative stress. Additionally, reoxygenation with 100% O₂ in a hypoxic-ischemic newborn lamb model increased the production of pro-inflammatory cytokines in the brain. Moreover, the interplay between inflammation and oxidative stress in the newborn is better understood because of animal studies. Transcriptomic analyses have found a number of genes to be differentially expressed in murine models of bronchopulmonary dysplasia (BPD). Epigenetic changes have also been detected both in animal models of BPD and premature infants exposed to oxygen. Antioxidant therapy to prevent newborn disease has not been very successful; however, new therapeutic principles, like melatonin, are under investigation.

In Vitro Consequences of Electronic-Cigarette Flavoring Exposure on the Immature Lung

Background: The developing lung is uniquely susceptible and may be at increased risk of injury with exposure to e-cigarette constituents. We hypothesize that cellular toxicity and airway and vascular responses with exposure to flavored refill solutions may be altered in the immature lung. Methods: Fetal, neonatal, and adult ovine pulmonary artery smooth muscle cells (PASMC) were exposed to popular flavored nicotine-free e-cigarette refill solutions (menthol, strawberry, tobacco, and vanilla) and unflavored solvents: propylene glycol (PG) or vegetable glycerin (VG). Viability was assessed by lactate dehydrogenase assay. Brochodilation and vasoreactivity were determined on isolated ovine bronchial rings (BR) and pulmonary arteries (PA). Results: Neither PG or VG impacted viability of immature or adult cells; however, exposure to menthol and strawberry flavored solutions increased cell death. Neonatal cells were uniquely susceptible to menthol flavoring-induced toxicity, and all four flavorings demonstrated lower lethal doses (LD50) in immature PASMC. Exposure to flavored solutions induced bronchodilation of neonatal BR, while only menthol induced airway relaxation in adults. In contrast, PG/VG and flavored solutions did not impact vasoreactivity with the exception of menthol-induced relaxation of adult PAs. Conclusion: The immature lung is uniquely susceptible to cellular toxicity and altered airway responses with exposure to common flavored e-cigarette solutions.

Fatty acid synthase downregulation contributes to acute lung injury in murine diet-induced obesity

The prevalence of obesity is rising worldwide and obese patients comprise a specific population in the intensive care unit. Acute respiratory distress syndrome (ARDS) incidence is increased in obese patients. Exposure of rodents to hyperoxia mimics many of the features of ARDS. In this report, we demonstrate that high fat diet induced obesity increases the severity of hyperoxic acute lung injury in mice in part by altering fatty acid synthase (FASN) levels in the lung. Obese mice exposed to hyperoxia had significantly reduced survival and increased lung damage. Transcriptomic analysis of lung homogenates identified Fasn as one of the most significantly altered mitochondrial associated genes in mice receiving 60% compared to 10% fat diet. FASN protein levels in the lung of high fat diet mice were lower by immunoblotting and immunohistochemistry. Depletion of FASN in type II alveolar epithelial cells resulted in altered mitochondrial bioenergetics and more severe lung injury with hyperoxic exposure, even upon the administration of a 60% fat diet. This is the first study to show that a high fat diet leads to altered FASN expression in the lung and that both a high fat diet and reduced FASN expression in alveolar epithelial cells promote lung injury.

Melatonin prevents lung injury by regulating apelin 13 to improve mitochondrial dysfunction

Pulmonary fibrosis is a progressive disease characterized by epithelial cell damage, fibroblast proliferation, excessive extracellular matrix (ECM) deposition, and lung tissue scarring. Melatonin, a hormone produced by the pineal gland, plays an important role in multiple physiological and pathological responses in organisms. However, the function of melatonin in the development of bleomycin-induced pulmonary injury is poorly understood. In the present study, we found that melatonin significantly decreased mortality and restored the function of the alveolar epithelium in bleomycin-treated mice. However, pulmonary function mainly depends on type II alveolar epithelial cells (AECIIs) and is linked to mitochondrial integrity. We also found that melatonin reduced the production of reactive oxygen species (ROS) and prevented apoptosis and senescence in AECIIs. Luzindole, a nonselective melatonin receptor antagonist, blocked the protective action of melatonin. Interestingly, we found that the expression of apelin 13 was significantly downregulated in vitro and in vivo and that this downregulation was reversed by melatonin. Furthermore, ML221, an apelin inhibitor, disrupted the beneficial effects of melatonin on alveolar epithelial cells. Taken together, these results suggest that melatonin alleviates lung injury through regulating apelin 13 to improve mitochondrial dysfunction in the process of bleomycin-induced pulmonary injury.

The hormone melatonin could protect lung cells from the damage associated with respiratory diseases such as pulmonary fibrosis. Several studies have linked such damage with abnormal activity of the mitochondria, with these essential metabolic organelles churning out damaging ‘reactive oxygen species’ (ROS), compounds that induce premature cell aging and death. Melatonin can mitigate ROS production, and researchers led by Haihai Liang at China’s Harbin Medical University have demonstrated that it can prevent injury to airway epithelial cells in a mouse model of lung disease. Melatonin treatment countered much of the damage, resulting in significantly longer survival, and the team identified a target molecule in the mitochondria that may be responsible for this effect. This approach could offer hope for a family of diseases with a poor prognosis and limited treatment options.

Acute respiratory distress syndrome

The acute respiratory distress syndrome (ARDS) is a common cause of respiratory failure in critically ill patients and is defined by the acute onset of noncardiogenic pulmonary oedema, hypoxaemia and the need for mechanical ventilation. ARDS occurs most often in the setting of pneumonia, sepsis, aspiration of gastric contents or severe trauma and is present in ~10% of all patients in intensive care units worldwide. Despite some improvements, mortality remains high at 30-40% in most studies. Pathological specimens from patients with ARDS frequently reveal diffuse alveolar damage, and laboratory studies have demonstrated both alveolar epithelial and lung endothelial injury, resulting in accumulation of protein-rich inflammatory oedematous fluid in the alveolar space. Diagnosis is based on consensus syndromic criteria, with modifications for under-resourced settings and in paediatric patients. Treatment focuses on lung-protective ventilation; no specific pharmacotherapies have been identified. Long-term outcomes of patients with ARDS are increasingly recognized as important research targets, as many patients survive ARDS only to have ongoing functional and/or psychological sequelae. Future directions include efforts to facilitate earlier recognition of ARDS, identifying responsive subsets of patients and ongoing efforts to understand fundamental mechanisms of lung injury to design specific treatments.

Cell Death in the Lung: The Apoptosis-Necroptosis Axis

Regulated cell death is a major mechanism to eliminate damaged, infected, or superfluous cells. Previously, apoptosis was thought to be the only regulated cell death mechanism; however, new modalities of caspase-independent regulated cell death have been identified, including necroptosis, pyroptosis, and autophagic cell death. As an understanding of the cellular mechanisms that mediate regulated cell death continues to grow, there is increasing evidence that these pathways are implicated in the pathogenesis of many pulmonary disorders. This review summarizes our understanding of regulated cell death as it pertains to the pathogenesis of chronic obstructive pulmonary disease, asthma, idiopathic pulmonary fibrosis, acute respiratory distress syndrome, and pulmonary arterial hypertension.

Shock Wave Therapy Enhances Mitochondrial Delivery into Target Cells and Protects against Acute Respiratory Distress Syndrome

This study tested the hypothesis that shock wave therapy (SW) enhances mitochondrial uptake into the lung epithelial and parenchymal cells to attenuate lung injury from acute respiratory distress syndrome (ARDS). ARDS was induced in rats through continuous inhalation of 100% oxygen for 48 h, while SW entailed application 0.15 mJ/mm² for 200 impulses at 6 Hz per left/right lung field. In vitro and ex vivo studies showed that SW enhances mitochondrial uptake into lung epithelial and parenchyma cells (all p < 0.001). Flow cytometry demonstrated that albumin levels and numbers of inflammatory cells (Ly6G+/CD14+/CD68+/CD11^b/c+) in bronchoalveolar lavage fluid were the highest in untreated ARDS, were progressively reduced across SW, Mito, and SW + Mito (all p < 0.0001), and were the lowest in sham controls. The same profile was also seen for fibrosis/collagen deposition, levels of biomarkers of oxidative stress (NOX-1/NOX-2/oxidized protein), inflammation (MMP-9/TNF-α/NF-κB/IL-1β/ICAM-1), apoptosis (cleaved caspase 3/PARP), fibrosis (Smad3/TGF-β), mitochondrial damage (cytosolic cytochrome c) (all p < 0.0001), and DNA damage (γ-H2AX+), and numbers of parenchymal inflammatory cells (CD11+/CD14+/CD40L+/F4/80+) (p < 0.0001). These results suggest that SW-assisted Mito therapy effectively protects the lung parenchyma from ARDS-induced injury.

Efferocytosis of apoptotic alveolar epithelial cells is sufficient to initiate lung fibrosis

Type II alveolar epithelial cell (AEC) apoptosis is a prominent feature of fibrotic lung diseases and animal models of pulmonary fibrosis. While there is growing recognition of the importance of AEC injury and apoptosis as a causal factor in fibrosis, the underlying mechanisms that link these processes remain unknown. We have previously shown that targeting the type II alveolar epithelium for injury by repetitively administering diphtheria toxin to transgenic mice expressing the diphtheria toxin receptor off of the surfactant protein C promoter (SPC-DTR) develop lung fibrosis, confirming that AEC injury is sufficient to cause fibrosis. In the present study, we find that SPC-DTR mice develop increased activation of caspase 3/7 after initiation of diphtheria toxin treatment consistent with apoptosis within AECs. We also find evidence of efferocytosis, the uptake of apoptotic cells, by alveolar macrophages in this model. To determine the importance of efferocytosis in lung fibrosis, we treated cultured alveolar macrophages with apoptotic type II AECs and found that the uptake induced pro-fibrotic gene expression. We also found that the repetitive intrapulmonary administration of apoptotic type II AEC or MLE-12 cells induces lung fibrosis. Finally, mice lacking a key efferocytosis receptor, CD36, developed attenuated fibrosis in response to apoptotic MLE-12 cells. Collectively, these studies support a novel mechanism linking AEC apoptosis with macrophage pro-fibrotic activation via efferocytosis and reveal previously unrecognized therapeutic targets.

Mitochondrial Dysfunction in Pulmonary Fibrosis

The aging of the human population has resulted in an unprecedented increase in the incidence and prevalence of age-related diseases, including those of the lung. Idiopathic pulmonary fibrosis is a disease of aging, and is characterized by a progressive decline in lung function and high mortality. Recent studies suggest that mitochondrial dysfunction, which can accompany aging phenotypes, may contribute to the pathogenesis of idiopathic pulmonary fibrosis. In this review, we explore current evidence for mitochondrial dysfunction in alveolar epithelial cells, fibroblasts, and immune cells that participate in the fibrotic process. Further, the fates of these cell populations and the potential to target mitochondrial dysfunction as a therapeutic strategy are discussed.

WISP-3/CCN6 inhibits apoptosis by regulating caspase pathway after hyperoxia in lung epithelial cells

Cell death is a normal phenomenon in the course of biological development, moreover, which is also a prominent feature in lung exposed to hyperoxia. Severe hypoxia occurs in ALI/ARDS patients, who generally require high concentration oxygen therapy assisted by mechanical ventilation. Nevertheless, high oxygen can cause excessive reactive oxygen species (ROS), leading to apoptosis in lung epithelial cells, which has been reported in our previous study. Herein, the correlation between increments of ROS and CCN6 expression was negative in CCN6-mediated the mitochondria dependent, intrinsic apoptotic pathway. Our latest research explained that CCN6 can inhibit caspase-8 mediated extrinsic apoptotic pathway to protect cells from hyperoxia-induced apoptosis. As demonstrated by Western Blot Analysis, Caspase 8 cleavage and Caspase 3 cleavage in CCN6-depleted cells exceeded the control group treated with high oxygen (48 h). And deletion of CCN6 enhanced caspase-8 activation after hyperoxia shown by Flow Cytometry. Although, it is unclear how CCN6 participated in the regulation of apoptotic pathways, the future targeted therapy drugs inhibiting CCN6 may be useful in the treatment of ALI/ARDS.

A role for heat shock factor 1 in hypercapnia-induced inhibition of inflammatory cytokine expression

Hypercapnia, elevated levels of CO₂ in the blood, is a known marker for poor clinical prognosis and is associated with increased mortality in patients hospitalized with both bacterial and viral pneumonias. Although studies have established a connection between elevated CO₂ levels and poor pneumonia outcomes, a mechanistic basis of this association has not yet been established. We previously reported that hypercapnia inhibits expression of key NF-κB-regulated, innate immune cytokines, TNF-α, and IL-6, in LPS-stimulated macrophages in vitro and in mice during Pseudomonas pneumonia. The transcription factor heat shock factor 1 (HSF1) is important in maintaining proteostasis during stress and has been shown to negatively regulate NF-κB activity. In this study, we tested the hypothesis that HSF1 activation in response to hypercapnia results in attenuated NF-κB-regulated gene expression. We found that hypercapnia induced the protein expression and nuclear accumulation of HSF1 in primary murine alveolar macrophages and in an alveolar macrophage cell line (MH-S). In MH-S cells treated with short interfering RNA targeting Hsf1, LPS-induced IL-6 and TNF-α release were elevated during exposure to hypercapnia. Pseudomonas-infected Hsf1^+/+ (wild-type) mice, maintained in a hypercapnic environment, showed lower levels of IL-6 and TNF-α in bronchoalveolar lavage fluid and IL-1β in lung tissue than did infected mice maintained in room air. In contrast, infected Hsf1^+/- mice exposed to either hypercapnia or room air had similarly elevated levels of those cytokines. These results suggest that hypercapnia-mediated inhibition of NF-κB cytokine production is dependent on HSF1 expression and/or activation.-Lu, Z., Casalino-Matsuda, S. M., Nair, A., Buchbinder, A., Budinger, G. R. S., Sporn, P. H. S., Gates, K. L. A role for heat shock factor 1 in hypercapnia-induced inhibition of inflammatory cytokine expression.

Hyperoxia-mediated transcriptional activation of cytochrome P4501A1 (CYP1A1) and decreased susceptibility to oxygen-mediated lung injury in newborn mice

Hyperoxia contributes to the development of bronchopulmonary dysplasia (BPD) in premature infants. In this study, we tested the hypothesis that newborn transgenic mice carrying the human CYP1A1-Luc promoter will display transcriptional activation of the human CYP1A1 promoter in vivo upon exposure to hyperoxia, and that these mice will be less susceptible to hyperoxic lung injury and alveolar simplification than similarly exposed wild type (WT) mice. Newborn WT (CD-1) or transgenic mice carrying a 13.2 kb human CYP1A1 promoter and the luciferase (Luc) reporter gene (CYP1A1-luc) were maintained in room air or exposed to hyperoxia (85% O2) for 7-14 days. Hyperoxia exposure of CYP1A1-Luc mice for 7 and 14 days resulted in 4- and 30-fold increases, respectively, in hepatic Luc (CYP1A1) expression, compared to room air controls. In lung, hyperoxia caused a 2-fold induction of reporter Luc at 7 days, but the induction declined after 14 days. The newborn CYP1A1-Luc mice were less susceptible to lung injury and alveolar simplification than similarly exposed wild type (WT) CD-1 mice. Also, the CYP1A1-Luc mice showed increased levels of hepatic and pulmonary CYP1A1 expression and hepatic CYP1A2 activity after hyperoxia exposure. Hyperoxia also increased NADP(H) quinone reductase (NQO1) pulmonary gene expression in both CD-1 and CYP1A1-Luc mice at both time points, but this was more pronounced in the latter at 14 days. Our results support the hypothesis that hyperoxia activates the human CYP1A1 promoter in newborn mice, and that increased endogenous expression of CYP1A1 and NADP(H) quinone reductase (NQO1) contributes to the decreased susceptibilities to hyperoxic lung injury in the transgenic animals. This is the first report providing evidence of hyperoxia-mediated transcriptional activation of the human CYP1A1 promoter in newborn mice, and this in conjunction with decreased lung injury, suggests that these phenomena have important implications for BPD.

Effective protection against acute respiratory distress syndrome/sepsis injury by combined adipose-derived mesenchymal stem cells and preactivated disaggregated platelets

This study assessed whether combining adipose-derived mesenchymal stem cells (ADMSC) with preactivated, disaggregated shape-changed platelets (PreD-SCP) was superior to either therapy alone for protecting rat lung from acute respiratory distress syndrome (ARDS) complicated by sepsis. ARDS and sepsis were induced through 100% oxygen inhalation and peritoneal administration of 1.5 mg/kg lipopolysaccharide (LPS), respectively. Adult-male Sprague-Dawley rats (n=40) were randomized into sham-control (SC), ARDS-LPS, ARDS-LPS-ADMSC (1.2x10⁶ cells), ARDS-LPS-PreD-SCP (3.0x10⁸, intravenous administration), and ARDS-LPS-ADMS/PreD-SCP groups, and were sacrificed 72 h after 48 h ARDS induction. Lung injury scores (LIS) and collagen deposition were highest in ARDS-LPS, lowest in SC, higher in ARDS-LPS+ADMSC than in ARDS-LPS+PreD-SCP and ARDS-LPS+ADMS/PreD-SCP, and higher in ARDS-LPS+PreD-SCP than in ARDS-LPS+ADMS/PreD-SCP (all p<0.0001). Alveolar-sac numbers, oxygen saturation, endothelial marker levels, and mitochondrial cytochrome-C levels exhibited opposite patterns with respect to LIS (all p<0.001). Levels of inflammatory, oxidative-stress, apoptosis, mitochondrial/DNA damage, and MAPK and Akt signaling markers exhibited patterns identical to that of LIS (all p<0.001). Anti-oxidant and anti-inflammatory protein levels increased progressively from SC to ARDS-LPS+ADMS/PreD-SCP (all p<0.0001). These findings indicate combined ADMSC/PreD-SCP was superior to either therapy alone for protecting rat lung from ARDS-sepsis injury.

A novel fine tuning scheme of miR-200c in modulating lung cell redox homeostasis

Oxidative stress induces miR-200c, the predominant microRNA (miRNA) in lung tissues; however, the antioxidant role and biochemistry of such induction have not been clearly defined. Therefore, a lung adenocarcinoma cell line (A549) and a normal lung fibroblast (MRC-5) were used as models to determine the effects of miR-200c expression on lung antioxidant response. Hydrogen peroxide (H₂O₂) upregulated miR-200c, whose overexpression exacerbated the decrease in cell proliferation, retarded the progression of cells in the G2/M-phase, and increased oxidative stress upon H₂O₂ stimulation. The expression of three antioxidant proteins, superoxide dismutase (SOD)-2, haem oxygenase (HO)-1, and sirtuin (SIRT) 1, was reduced upon H₂O₂ stimulation in miR-200c-overexpressed A549 cells. This phenomenon of increased oxidative stress and antioxidant protein downregulation also occurs simultaneously in miR-200c overexpressed MRC-5 cells. Molecular analysis revealed that miR-200c inhibited the gene expression of HO-1 by directly targeting its 3'-untranslated region. The downregulation of SOD2 and SIRT1 by miR-200c was mediated through zinc finger E-box-binding homeobox 2 (ZEB2) and extracellular signal-regulated kinase 5 (ERK5) pathways, respectively, where knockdown of ZEB2 or ERK5 decreased the expression of SOD2 or SIRT1 in A549 cells. LNA anti-miR-200c transfection in A549 cells inhibited the endogenous miR-200c expression, resulting in increased expressions of antioxidant proteins, reduced oxidative stress and recovered cell proliferation upon H₂O₂ stimulation. These findings indicate that miR-200c fine-tuned the antioxidant response of the lung cells to oxidative stress through several pathways, and thus this study provides novel information concerning the role of miR-200c in modulating redox homeostasis of lung.

Perioperative hyperoxia: perhaps a malady in disguise

Oxygen is an element, which is used liberally during several medical procedures. The use of oxygen during perioperative care is a controversial issue. Anesthesiologists use oxygen to prevent hypoxemia during surgical procedures, but the effects of its liberal use can be harmful. Another argument for using high oxygen concentrations is to prevent surgical site infections by increasing oxygen levels at the incision site. Although inconclusive, literature concerning the use of high oxygen concentrations during anesthesia show that this approach may cause hemodynamic changes, altered microcirculation and increased oxidative stress. In intensive care it has been shown that high oxygen concentrations may be associated with increased mortality in certain patient populations such as post cardiac arrest patients. In this paper, a review of literature had been undertaken to warn anesthesiologists about the potential harmful effects of high oxygen concentrations.

Lung protection by inhalation of exogenous solubilized extracellular matrix

Decellularized extracellular matrix (ECM) contains complex tissue-specific components that work in concert to promote tissue repair and constructive remodeling and has been used experimentally and clinically to accelerate epithelial wound repair, leading us to hypothesize that lung-derived ECM could mitigate acute lung injury. To explore the therapeutic potential of ECM for noninvasive delivery to the lung, we decellularized and solubilized porcine lung ECM, then characterized the composition, concentration, particle size and stability of the preparation. The ECM preparation at 3.2 mg/mL with average particle size <3 μm was tested in vitro on human A549 lung epithelial cells exposed to 95% O2 for 24 hours, and in vivo by tracheal instillation or nebulization into the lungs of rats exposed intermittently or continuously to 90% O2 for a cumulative 72 hours. Our results showed that the preparation was enriched in collagen, reduced in glycosaminoglycans, and contained various bioactive molecules. Particle size was concentration-dependent. Compared to the respective controls treated with cell culture medium in vitro or saline in vivo, ECM inhalation normalized cell survival and alveolar morphology, and reduced hyperoxia-induced apoptosis and oxidative damage. This proof-of-concept study established the methodology, feasibility and therapeutic potential of exogenous solubilized ECM for pulmonary cytoprotection, possibly as an adjunct or potentiator of conventional therapy.

Senegenin Ameliorate Acute Lung Injury Through Reduction of Oxidative Stress and Inhibition of Inflammation in Cecal Ligation and Puncture-Induced Sepsis Rats

The purpose of this study was to assess the protective effect of senegenin on acute lung injury (ALI) in rats induced by sepsis. Rat ALI model was reproduced by cecal ligation and puncture (CLP). All rats were randomly divided into five groups: group 1 (control), group 2 (CLP), group 3 (CLP + senegenin 15 mg/kg), group 4 (CLP + senegenin 30 mg/kg), and group 5 (CLP + senegenin 60 mg/kg). CLP + senegenin groups received senegenin by gavage daily for consecutive 5 days, respectively, while the mice in control and CLP groups were given an equivalent volume of saline. We detected the lung wet/dry weight ratios and the histopathology of the lung. The levels of lung tissue myeloperoxidase (MPO), malondialdehyde (MDA), superoxide dismutase (SOD), and glutathione (GSH) were determined. Meanwhile, the nuclear factor-kappa B (NF-κB) activation, tumor necrosis factor-alpha (TNF-α), and interleukin-1β (IL-1β) levels were studied. The results demonstrated that senegenin treatment significantly attenuated CLP-induced lung injury, including reduction of lung wet/dry weight ratio, protein leak, infiltration of leukocytes, and MPO activity. In addition, senegenin markedly decreased MDA content and increased SOD activity and GSH level. Serum levels of TNF-α and IL-1β were also decreased by senegenin administration. Furthermore, senegenin administration inhibited the nuclear translocation of NF-κB in the lungs. These findings indicate that senegenin exerts protective effects on CLP-induced septic rats. Senegenin may be a potential therapeutic agent against sepsis.

Detoxification of Mitochondrial Oxidants and Apoptotic Signaling Are Facilitated by Thioredoxin-2 and Peroxiredoxin-3 during Hyperoxic Injury

Mitochondria play a fundamental role in the regulation of cell death during accumulation of oxidants. High concentrations of atmospheric oxygen (hyperoxia), used clinically to treat tissue hypoxia in premature newborns, is known to elicit oxidative stress and mitochondrial injury to pulmonary epithelial cells. A consequence of oxidative stress in mitochondria is the accumulation of peroxides which are detoxified by the dedicated mitochondrial thioredoxin system. This system is comprised of the oxidoreductase activities of peroxiredoxin-3 (Prx3), thioredoxin-2 (Trx2), and thioredoxin reductase-2 (TrxR2). The goal of this study was to understand the role of the mitochondrial thioredoxin system and mitochondrial injuries during hyperoxic exposure. Flow analysis of the redox-sensitive, mitochondrial-specific fluorophore, MitoSOX, indicated increased levels of mitochondrial oxidant formation in human adenocarcinoma cells cultured in 95% oxygen. Increased expression of Trx2 and TrxR2 in response to hyperoxia were not attributable to changes in mitochondrial mass, suggesting that hyperoxic upregulation of mitochondrial thioredoxins prevents accumulation of oxidized Prx3. Mitochondrial oxidoreductase activities were modulated through pharmacological inhibition of TrxR2 with auranofin and genetically through shRNA knockdown of Trx2 and Prx3. Diminished Trx2 and Prx3 expression was associated with accumulation of mitochondrial superoxide; however, only shRNA knockdown of Trx2 increased susceptibility to hyperoxic cell death and increased phosphorylation of apoptosis signal-regulating kinase-1 (ASK1). In conclusion, the mitochondrial thioredoxin system regulates hyperoxic-mediated death of pulmonary epithelial cells through detoxification of oxidants and regulation of redox-dependent apoptotic signaling.