Inducible NOS inhibition reverses tobacco-smoke-induced emphysema and pulmonary hypertension in mice

Compartment-specific remodeling patterns in end-stage chronic obstructive pulmonary disease with and without severe pulmonary hypertension

BACKGROUND

In patients with end-stage chronic obstructive pulmonary disease (COPD), severe pulmonary hypertension (PH) is frequently associated with less severe airway obstruction as compared to mild or no PH. However, the histologic correlate of this finding is not clear. We aimed to quantify remodeling of pulmonary arteries, airways, and parenchyma in random samples of explanted end-stage COPD lungs.

METHODS

We quantified remodeling of small pulmonary arteries, small airways, and the degree of emphysema (mean interseptal distance [MID]) with dedicated software. As primary objective, we compared COPD patients with severe PH (SevPH-COPD) with age- and sex-matched MildPH-COPD. For comparison, we also investigated COPD lungs with no PH (NoPH-COPD), idiopathic PAH (IPAH), and healthy donors.

RESULTS

We included n = 17 SevPH-COPD (mPAP = 43 [39-45]mm Hg), n = 17 MildPH-COPD (mPAP = 28 [24-31]mm Hg), n = 5 NoPH-COPD (mPAP = 18 [16-19]mm Hg), n = 10 IPAH (mPAP = 72 [65-91]mm Hg), and n = 10 healthy donor lungs. SevPH-COPD versus MildPH-COPD was characterized by better preserved forced vital capacity (51% vs 40% predicted, p < 0.05), less emphysema (MID 169 µm vs 279 µm, p < 0.001), and less PAS-positive and CD45-positive mucosa cells (15% vs 22%, p = 0.063% and 5% vs 7%, p = 0.058) suggesting less airway inflammation. In COPD patients, intimal and medial thickening were strongly correlated with mPAP (r = 0.676, p < 0.001 and r = 0.595, p < 0.001). MID was negatively correlated with mPAP (r = -0.556, p < 0.001) and was highest in NoPH-COPD (mean 281 µm), suggesting that emphysema per se is not associated with PH.

CONCLUSIONS

End-stage COPD with severe PH is characterized by pronounced pulmonary vascular remodeling, less inflammation of small airways, and less emphysema as compared to COPD with mild PH or no PH, suggesting that COPD with severe PH may represent a unique phenotype of COPD.

Predictive Value of Smoking Index Combined with NT-proBNP for Patients with Pulmonary Hypertension Due to Chronic Lung Disease: A Retrospective Study

Purpose

Smoking is a major risk factor for the group 3 PH. NT-proBNP is a biomarker for risk stratification in PH. This study aims to investigate the effects of smoking status and smoking index (SI) on group 3 PH and to evaluate the value of SI and SI combined with NT-proBNP in early diagnosis and prediction of disease severity.

Patients and Methods

Four hundred patients with group 3 PH at the First Hospital of Shanxi Medical University between January 2020 and December 2021 were enrolled and divided into two groups: mild (30 mmHg ≤ pulmonary artery systolic pressure (PASP)≤50 mmHg) and non-mild (PASP >50 mmHg). The effect of smoking on group 3 PH was analyzed using univariate analysis, and logistic analysis was conducted to evaluate the risk of group 3 PH according to smoking status and SI. Spearman correlation coefficient was used to test the correlation between SI and the index of group 3 PH severity. The predictive value of SI was evaluated using a receiver operating characteristic (ROC) curve.

Results

Correlation and logistic analyses showed that SI was associated with PH severity. Smoking status (P=0.009) and SI (P=0.039) were independent risk factors for non-mild group 3 PH, and ROC showed that the predictive value of SI (AUC:0.596) for non-mild PH was better than that of the recognized pro-brain natriuretic peptide (NT-proBNP) (AUC:0.586). SI can be used as a single predictive marker. SI and NT-proBNP can be formulated as prediction models for screening non-mild clinical cases (AUC:0.628).

Conclusion

SI is a potentially ideal non-invasive predictive marker for group 3 PH. SI and NT-proBNP could be used to develop a prediction model for screening non-mild PH cases. This can greatly improve the predictive specificity of the established PH marker, NT-proBNP.

GLI1+ Cells Contribute to Vascular Remodeling in Pulmonary Hypertension

BACKGROUND

The precise origin of newly formed ACTA2+ (alpha smooth muscle actin-positive) cells appearing in nonmuscularized vessels in the context of pulmonary hypertension is still debatable although it is believed that they predominantly derive from preexisting vascular smooth muscle cells (VSMCs).

METHODS

Gli1Cre-ERT2; tdTomatoflox mice were used to lineage trace GLI1+ (glioma-associated oncogene homolog 1-positive) cells in the context of pulmonary hypertension using 2 independent models of vascular remodeling and reverse remodeling: hypoxia and cigarette smoke exposure. Hemodynamic measurements, right ventricular hypertrophy assessment, flow cytometry, and histological analysis of thick lung sections followed by state-of-the-art 3-dimensional reconstruction and quantification using Imaris software were used to investigate the contribution of GLI1+ cells to neomuscularization of the pulmonary vasculature.

RESULTS

The data show that GLI1+ cells are abundant around distal, nonmuscularized vessels during steady state, and this lineage contributes to around 50% of newly formed ACTA2+ cells around these normally nonmuscularized vessels. During reverse remodeling, cells derived from the GLI1+ lineage are largely cleared in parallel to the reversal of muscularization. Partial ablation of GLI1+ cells greatly prevented vascular remodeling in response to hypoxia and attenuated the increase in right ventricular systolic pressure and right heart hypertrophy. Single-cell RNA sequencing on sorted lineage-labeled GLI1+ cells revealed an Acta2high fraction of cells with pathways in cancer and MAPK (mitogen-activated protein kinase) signaling as potential players in reprogramming these cells during vascular remodeling. Analysis of human lung-derived material suggests that GLI1 signaling is overactivated in both group 1 and group 3 pulmonary hypertension and can promote proliferation and myogenic differentiation.

CONCLUSIONS

Our data highlight GLI1+ cells as an alternative cellular source of VSMCs in pulmonary hypertension and suggest that these cells and the associated signaling pathways represent an important therapeutic target for further studies.

GPS2 ameliorates cigarette smoking-induced pulmonary vascular remodeling by modulating the ras-Raf-ERK axis

BACKGROUND

Mitogen-activated protein kinase (MAPK)signaling-mediated smoking-associated pulmonary vascular remodeling (PVR) plays an important role in the pathogenesis of group 3 pulmonary hypertension (PH). And G protein pathway suppressor 2 (GPS2) could suppress G-protein signaling such as Ras and MAPK, but its role in cigarette smoking -induced PVR (CS-PVR) is unclear.

METHODS

An in vivo model of smoke-exposed rats was constructed to assess the role of GPS2 in smoking-induced PH and PVR. In vitro, the effects of GPS2 overexpression and silencing on the function of human pulmonary arterial smooth cells (HPASMCs) and the underlying mechanisms were explored.

RESULTS

GPS2 expression was downregulated in rat pulmonary arteries (PAs) and HPASMCs after CS exposure. More importantly, CS-exposed rats with GPS2 overexpression had lower right ventricular systolic pressure (RVSP), right ventricular hypertrophy index (RVHI), and wall thickness (WT%) than those without. And enhanced proliferation and migration of HPASMCs induced by cigarette smoking extract (CSE) can be evidently inhibited by overexpressed GPS2. Besides, GPS2siRNA significantly enhanced the proliferation, and migration of HPASMCs as well as activated Ras and Raf/ERK signaling, while these effects were inhibited by zoledronic acid (ZOL). In addition, GPS2 promoter methylation level in rat PAs and HPASMCs was increased after CS exposure, and 5-aza-2-deoxycytidine (5-aza) inhibited CSE-induced GPS2 hypermethylation and downregulation in vitro.

CONCLUSIONS

GPS2 overexpression could improve the CS-PVR, suggesting that GPS2 might serve as a novel therapeutic target for PH-COPD in the future.

Immune Dysregulation in Chronic Obstructive Pulmonary Disease

Chronic obstructive pulmonary disease (COPD) is a disease whose incidence increase with age and is characterised by chronic inflammation and significant immune dysregulation. Inhalation of toxic substances cause oxidative stress in the lung tissue as well as airway inflammation, under the recruitment of chemokines, immune cells gathered and are activated to play a defensive role. However, persistent inflammation damages the immune system and leads to immune dysregulation, which is mainly manifested in the reduction of the body's immune response to antigens, and immune cells function are impaired, further destroy the respiratory defensive system, leading to recurrent lower respiratory infections and progressive exacerbation of the disease, thus immune dysregulation play an important role in the pathogenesis of COPD. This review summarizes the changes of innate and adaptive immune-related cells during the pathogenesis of COPD, aiming to control COPD airway inflammation and improve lung tissue remodelling by regulating immune dysregulation, for further reducing the risk of COPD progression and opening new avenues of therapeutic intervention in COPD.

Impact of inhalation exposure to cigarette smoke on the pathogenesis of pulmonary hypertension primed by monocrotaline in rats

Extensive, long-term exposure to cigarette smoke (CS) was recently suggested to be a risk factor for pulmonary hypertension, although further validation is required. The vascular effects of CS share similarities with the etiology of pulmonary hypertension, including vascular inflammation and remodeling. Thus, we examined the influence of CS exposure on the pathogenesis of monocrotaline (MCT)-induced pulmonary hypertension, hypothesizing that smoking might accelerate the development of primed pulmonary hypertension. CS was generated from 3R4F reference cigarettes, and rats were exposed to CS by inhalation at total particulate matter concentrations of 100-300 μg/L for 4 h/day, 7 days/week for 4 weeks. Following 1 week of initial exposure, rats received 60 mg/kg MCT and were sacrificed and analyzed after an additional 3 weeks of exposure. MCT induced hypertrophy in pulmonary arterioles and increased the Fulton index, a measure of right ventricular hypertrophy. Additional CS exposure exacerbated arteriolar hypertrophy but did not further elevate the Fulton index. No significant alterations were observed in levels of endothelin-1 and vascular endothelial growth factor, or in hematological and serum biochemical parameters. Short-term inhalation exposure to CS exacerbated arteriolar hypertrophy in the lung, although this effect did not directly aggravate the overworked heart under the current experimental conditions.

Endogenous Nitric Oxide Can Enhance Oxidative Stress Caused by Air Pollutants and Explain Higher Susceptibility of Individuals with Inflammatory Disorders

Air pollution causes morbidity and excess mortality. In the epithelial lining fluid of the respiratory tract, air pollutants trigger a chemical reaction sequence that causes the formation of noxious hydroxyl radicals that drive oxidative stress. For hitherto unknown reasons, individuals with pre-existing inflammatory disorders are particularly susceptible to air pollution. Through detailed multiphase chemical kinetic analysis, we show that the commonly elevated concentrations of endogenous nitric oxide in diseased individuals can increase the production of hydroxyl radicals via peroxynitrite formation. Our findings offer a molecular rationale of how adverse health effects and oxidative stress caused by air pollutants may be exacerbated by inflammatory disorders.

Quantitative Assessment Characteristics of Small Pulmonary Vessel Remodelling in Populations at High Risk for COPD and Smokers Using Low-Dose CT

Purpose

To explore the morphological alterations in small pulmonary vessels in populations at high risk for chronic obstructive pulmonary disease (COPD) and smokers based on multiple computed tomography (CT) quantitative parameters.

Patients and Methods

A total of 1969 Three Major Chest Diseases Screening Study participants with available demographic data and smoking history who underwent low-dose chest CT from 2018 to 2020 were included. All subjects were divided into normal, high risk for COPD, and COPD groups according to their pulmonary function test (PFT) results. Furthermore, the three groups were further subdivided into never-smokers, current smokers, and former smokers subgroups according to their smoking history. Quantitative parameters, such as the number, area at 6 mm~24 mm subpleura and volume of small pulmonary vessels, were extracted by computer software. Differences in small pulmonary vessel parameters among the groups were compared using two-way ANOVA.

Results

The number, area at 6 mm~24 mm subpleura and volume of small pulmonary vessels in the group at high risk for COPD were lower than those in the normal group (P<0.05). The number, area at 6 mm~24 mm subpleura and volume of small pulmonary vessels in the COPD group were higher than those in the normal group (P<0.05). The number, area of small pulmonary vessels at 6 mm~12 mm subpleura in current smokers with high risk for COPD were higher than those in former smokers with high risk for COPD (P<0.05).

Conclusion

The number, area, and volume of small pulmonary vessels in populations at high risk for COPD were decreased. Smoking cessation may impede structural changes in small pulmonary vessels in populations at high risk for COPD.

Phenotypes and treatment outcomes in idiopathic pulmonary arterial hypertension patients with comorbidities

Idiopathic pulmonary arterial hypertension (IPAH) is often diagnosed in elderly patients with many comorbidities. Whereas a clear treatment strategy and risk assessment is recommended for patients with rare classical IPAH, monotherapy with phosphodiesterase type 5 inhibitors or endothelin receptor antagonists followed by regular follow-up and individualised therapy should be used for patients with many cardiopulmonary comorbidities. Here, we focus on these patients with IPAH and comorbidities, present a review of the literature with a focus on recently published work and summarise factors that may help to provide guidance for individualised treatment approaches in such patients.

[Pathophysiology, diagnosis, prognosis and treatment of pulmonary hypertension associated with chronic lung disease]

The pathophysiology of pulmonary hypertension associated with chronic lung disease (PH-CLD) is complex, multifactorial, and not consistent among pulmonary diseases. However, pulmonary vasculopathy triggered by various factors, such as chronic alveolar hypoxia or cigarette smoking, seems to play a central role in the pathogenesis of PH-CLD. While the initial workup of PH-CLD is usually complicated by an overlap of symptoms of PH and the underlying lung disease, PH-CLD should be considered when there is a discrepancy between symptoms (especially exertional dyspnea) and pulmonary function tests. Clinical suspicion of PH-CLD can be strengthened by noninvasive diagnostic tools such as transthoracic echocardiography (TTE) or N-terminal pro-B-type natriuretic peptide (NT-pro-BNP). However, a right heart catheterization should only be performed in specialized centers to establish the diagnosis if therapeutic consequences for the patient were expected.The basic treatment of PH-CLD is optimal management of the underlying lung disease. Among the existing interventional and registry-based studies, only a small number of data suggests favorable outcomes when treating PH-CLD patients with PAH-specific medications. Some publications even suggest negative effects. Nevertheless, recent data on inhaled vasoactive therapy in PH-CLD showed positive results for inhaled Treprostinil, although long-term data for this therapeutic approach are still lacking. Treatment of PH-CLD patients with PAH-specific drugs should only be performed in specialized centers and preferably in the context of clinical trials.

Fibroblast growth factor 10 reverses cigarette smoke- and elastase-induced emphysema and pulmonary hypertension in mice

BACKGROUND

COPD is an incurable disease and a leading cause of death worldwide. In mice, fibroblast growth factor (FGF)10 is essential for lung morphogenesis, and in humans, polymorphisms in the human FGF10 gene correlate with an increased susceptibility to develop COPD.

METHODS

We analysed FGF10 signalling in human lung sections and isolated cells from healthy donor, smoker and COPD lungs. The development of emphysema and PH was investigated in Fgf10+/- and Fgfr2b+/- (FGF receptor 2b) mice upon chronic exposure to cigarette smoke. In addition, we overexpressed FGF10 in mice following elastase- or cigarette smoke-induced emphysema and pulmonary hypertension (PH).

RESULTS

We found impaired FGF10 expression in human lung alveolar walls and in primary interstitial COPD lung fibroblasts. In contrast, FGF10 expression was increased in large pulmonary vessels in COPD lungs. Consequently, we identified impaired FGF10 signalling in alveolar walls as an integral part of the pathomechanism that leads to emphysema and PH development: mice with impaired FGF10 signalling (Fgf10+/- and Fgfr2b+/- ) spontaneously developed lung emphysema, PH and other typical pathomechanistic features that generally arise in response to cigarette smoke exposure.

CONCLUSION

In a therapeutic approach, FGF10 overexpression successfully restored lung alveolar and vascular structure in mice with established cigarette smoke- and elastase-induced emphysema and PH. FGF10 treatment triggered an initial increase in the number of alveolar type 2 cells that gradually returned to the basal level when the FGF10-mediated repair process progressed. Therefore, the application of recombinant FGF10 or stimulation of the downstream signalling cascade might represent a novel therapeutic strategy in the future.

Cigarette Smoke-Induced Reactive Oxygen Species Formation: A Concise Review

Smoking is recognized as a significant risk factor for numerous disorders, including cardiovascular diseases, respiratory conditions, and various forms of cancer. While the exact pathogenic mechanisms continue to be explored, the induction of oxidative stress via the production of excess reactive oxygen species (ROS) is widely accepted as a primary molecular event that predisposes individuals to these smoking-related ailments. This review focused on how cigarette smoke (CS) promotes ROS formation rather than the pathophysiological repercussions of ROS and oxidative stress. A comprehensive analysis of existing studies revealed the following key ways through which CS imposes ROS burden on biological systems: (1) ROS, as well as radicals, are intrinsically present in CS, (2) CS constituents generate ROS through chemical reactions with biomolecules, (3) CS stimulates cellular ROS sources to enhance production, and (4) CS disrupts the antioxidant system, aggravating the ROS generation and its functions. While the evidence supporting these mechanisms is chiefly based on in vitro and animal studies, the direct clinical relevance remains to be fully elucidated. Nevertheless, this understanding is fundamental for deciphering molecular events leading to oxidative stress and for developing intervention strategies to counter CS-induced oxidative stress.

Pulmonary hypertension associated with lung disease: new insights into pathomechanisms, diagnosis, and management

Patients with chronic lung diseases, particularly interstitial lung disease and chronic obstructive pulmonary disease, frequently develop pulmonary hypertension, which results in clinical deterioration, worsening of oxygen uptake, and an increased mortality risk. Pulmonary hypertension can develop and progress independently from the underlying lung disease. The pulmonary vasculopathy is distinct from that of other forms of pulmonary hypertension, with vascular ablation due to loss of small pulmonary vessels being a key feature. Long-term tobacco exposure might contribute to this type of pulmonary vascular remodelling. The distinct pathomechanisms together with the underlying lung disease might explain why treatment options for this condition remain scarce. Most drugs approved for pulmonary arterial hypertension have shown no or sometimes harmful effects in pulmonary hypertension associated with lung disease. An exception is inhaled treprostinil, which improves exercise capacity in patients with interstitial lung disease and pulmonary hypertension. There is a pressing need for safe, effective treatment options and for reliable, non-invasive diagnostic tools to detect and characterise pulmonary hypertension in patients with chronic lung disease.

The vascular perspective on acute and chronic lung disease

The pulmonary vasculature has been frequently overlooked in acute and chronic lung diseases, such as acute respiratory distress syndrome (ARDS), pulmonary fibrosis (PF), and chronic obstructive pulmonary disease (COPD). The primary emphasis in the management of these parenchymal disorders has largely revolved around the injury and aberrant repair of epithelial cells. However, there is increasing evidence that the vascular endothelium plays an active role in the development of acute and chronic lung diseases. The endothelial cell network in the capillary bed and the arterial and venous vessels provides a metabolically highly active barrier that controls the migration of immune cells, regulates vascular tone and permeability, and participates in the remodeling processes. Phenotypically and functionally altered endothelial cells, and remodeled vessels, can be found in acute and chronic lung diseases, although to different degrees, likely because of disease-specific mechanisms. Since vascular remodeling is associated with pulmonary hypertension, which worsens patient outcomes and survival, it is crucial to understand the underlying vascular alterations. In this Review, we describe the current knowledge regarding the role of the pulmonary vasculature in the development and progression of ARDS, PF, and COPD; we also outline future research directions with the hope of facilitating the development of mechanism-based therapies.

CEACAM6 as a Novel Therapeutic Target to Boost HO-1-mediated Antioxidant Defense in COPD

Rationale: Tobacco smoking and air pollution are primary causes of chronic obstructive pulmonary disease (COPD). However, only a minority of smokers develop COPD. The mechanisms underlying the defense against nitrosative/oxidative stress in nonsusceptible smokers to COPD remain largely unresolved. Objectives: To investigate the defense mechanisms against nitrosative/oxidative stress that possibly prevent COPD development or progression. Methods: Four cohorts were investigated: 1) sputum samples (healthy, n = 4; COPD, n = 37), 2) lung tissue samples (healthy, n = 13; smokers without COPD, n = 10; smoker+COPD, n = 17), 3) pulmonary lobectomy tissue samples (no/mild emphysema, n = 6), and 4) blood samples (healthy, n = 6; COPD, n = 18). We screened 3-nitrotyrosine (3-NT) levels, as indication of nitrosative/oxidative stress, in human samples. We established a novel in vitro model of a cigarette smoke extract (CSE)-resistant cell line and studied 3-NT formation, antioxidant capacity, and transcriptomic profiles. Results were validated in lung tissue, isolated primary cells, and an ex vivo model using adeno-associated virus-mediated gene transduction and human precision-cut lung slices. Measurements and Main Results: 3-NT levels correlate with COPD severity of patients. In CSE-resistant cells, nitrosative/oxidative stress upon CSE treatment was attenuated, paralleled by profound upregulation of heme oxygenase-1 (HO-1). We identified carcinoembryonic antigen cell adhesion molecule 6 (CEACAM6) as a negative regulator of HO-1-mediated nitrosative/oxidative stress defense in human alveolar type 2 epithelial cells (hAEC2s). Consistently, inhibition of HO-1 activity in hAEC2s increased the susceptibility toward CSE-induced damage. Epithelium-specific CEACAM6 overexpression increased nitrosative/oxidative stress and cell death in human precision-cut lung slices on CSE treatment. Conclusions: CEACAM6 expression determines the hAEC2 sensitivity to nitrosative/oxidative stress triggering emphysema development/progression in susceptible smokers.

Dynamic association of ambient air pollution with incidence and mortality of pulmonary hypertension: A multistate trajectory analysis

BACKGROUND

There is little evidence regarding the association between ambient air pollution and incidence and the mortality of pulmonary hypertension (PH).

METHODS

We included 494,750 participants at baseline in the UK Biobank study. Exposures to PM2.5, PM10, NO2, and NOx were estimated at geocoded participants' residential addresses, utilizing pollution data provided by UK Department for Environment, Food and Rural Affairs (DEFRA). The outcomes were the incidence and mortality of PH. We used multivariate multistate models to investigate the impacts of various ambient air pollutants on both incidence and mortality of PH.

RESULTS

During a median follow-up of 11.75 years, 2517 participants developed incident PH, and 696 died. We observed that all ambient air pollutants were associated with increased incidence of PH with different magnitudes, with adjusted hazard ratios (HRs) [95% confidence intervals (95% CIs)] for each interquartile range (IQR) increase of 1.73 (1.65, 1.81) for PM2.5, 1.70 (1.63, 1.78) for PM10, 1.42 (1.37, 1.48) for NO2, and 1.35 (1.31, 1.40) for NOx. Furthermore, PM2.5, PM10, NO2 and NO2 influenced the transition from PH to death, and the corresponding HRs (95% CIs) were 1.35 (1.25, 1.45), 1.31 (1.21, 1.41), 1.28 (1.20, 1.37) and 1.24 (1.17, 1.32), respectively.

CONCLUSION

The results of our study indicate that exposure to various ambient air pollutants might play key but differential roles in both the incidence and mortality of PH.

Myeloid-derived suppressor cells and pulmonary hypertension

Pulmonary hypertension (PH) is a chronic pulmonary vascular disorder characterized by an increase in pulmonary vascular resistance and pulmonary arterial pressure. The detailed molecular mechanisms remain unclear. In recent decades, increasing evidence shows that altered immune microenvironment, comprised of immune cells, mesenchymal cells, extra-cellular matrix and signaling molecules, might induce the development of PH. Myeloid-derived suppressor cells (MDSCs) have been proposed over 30 years, and the functional importance of MDSCs in the immune system is appreciated recently. MDSCs are a heterogeneous group of cells that expand during cancer, chronic inflammation and infection, which have a remarkable ability to suppress T-cell responses and may exacerbate the development of diseases. Thus, targeting MDSCs has become a novel strategy to overcome immune evasion, especially in tumor immunotherapy. Nowadays, severe PH is accepted as a cancer-like disease, and MDSCs are closely related to the development and prognosis of PH. Here, we review the relationship between MDSCs and PH with respect to immune cells, cytokines, chemokines and metabolism, hoping that the key therapeutic targets of MDSCs can be identified in the treatment of PH, especially in severe PH.

Nicotine promotes e-cigarette vapour-induced lung inflammation and structural alterations

BACKGROUND

Electronic cigarette (e-cigarette) vapour is gaining popularity as an alternative to tobacco smoking and can induce acute lung injury. However, the specific role of nicotine in e-cigarette vapour and its long-term effects on the airways, lung parenchyma and vasculature remain unclear.

RESULTS

In vitro exposure to nicotine-containing e-cigarette vapour extract (ECVE) or to nicotine-free e-cigarette vapour extract (NF ECVE) induced changes in gene expression of epithelial cells and pulmonary arterial smooth muscle cells (PASMCs), but ECVE in particular caused functional alterations (e.g. a decrease in human and mouse PASMC proliferation by 29.3±5.3% and 44.3±8.4%, respectively). Additionally, acute inhalation of nicotine-containing e-cigarette vapour (ECV) but not nicotine-free e-cigarette vapour (NF ECV) increased pulmonary endothelial permeability in isolated lungs. Long-term in vivo exposure of mice to ECV for 8 months significantly increased the number of inflammatory cells, in particular lymphocytes, compared to control and NF ECV in the bronchoalveolar fluid (BALF) (ECV: 853.4±150.8 cells·mL-1; control: 37.0±21.1 cells·mL-1; NF ECV: 198.6±94.9 cells·mL-1) and in lung tissue (ECV: 25.7±3.3 cells·mm-3; control: 4.8±1.1 cells·mm-3; NF ECV: 14.1±2.2 cells·mm-3). BALF cytokines were predominantly increased by ECV. Moreover, ECV caused significant changes in lung structure and function (e.g. increase in airspace by 17.5±1.4% compared to control), similar to mild tobacco smoke-induced alterations, which also could be detected in the NF ECV group, albeit to a lesser degree. In contrast, the pulmonary vasculature was not significantly affected by ECV or NF ECV.

CONCLUSIONS

NF ECV components induce cell type-specific effects and mild pulmonary alterations, while inclusion of nicotine induces significant endothelial damage, inflammation and parenchymal alterations.

The Role of Oxidative Stress and Antioxidants in Cardiovascular Comorbidities in COPD

Oxidative stress driven by several environmental and local airway factors associated with chronic obstructive bronchiolitis, a hallmark feature of COPD, plays a crucial role in disease pathomechanisms. Unbalance between oxidants and antioxidant defense mechanisms amplifies the local inflammatory processes, worsens cardiovascular health, and contributes to COPD-related cardiovascular dysfunctions and mortality. The current review summarizes recent developments in our understanding of different mechanisms contributing to oxidative stress and its countermeasures, with special attention to those that link local and systemic processes. Major regulatory mechanisms orchestrating these pathways are also introduced, with some suggestions for further research in the field.

Contribution of adaptive immunity to human COPD and experimental models of emphysema

The pathophysiology of chronic obstructive pulmonary disease (COPD) and the undisputed role of innate immune cells in this condition have dominated the field in the basic research arena for many years. Recently, however, compelling data suggesting that adaptive immune cells may also contribute to the progressive nature of lung destruction associated with COPD in smokers have gained considerable attention. The histopathological changes in the lungs of smokers can be limited to the large or small airways, but alveolar loss leading to emphysema, which occurs in some individuals, remains its most significant and irreversible outcome. Critically, however, the question of why emphysema progresses in a subset of former smokers remained a mystery for many years. The recognition of activated and organized tertiary T- and B-lymphoid aggregates in emphysematous lungs provided the first clue that adaptive immune cells may play a crucial role in COPD pathophysiology. Based on these findings from human translational studies, experimental animal models of emphysema were used to determine the mechanisms through which smoke exposure initiates and orchestrates adaptive autoreactive inflammation in the lungs. These models have revealed that T helper (Th)1 and Th17 subsets promote a positive feedback loop that activates innate immune cells, confirming their role in emphysema pathogenesis. Results from genetic studies and immune-based discoveries have further provided strong evidence for autoimmunity induction in smokers with emphysema. These new findings offer a novel opportunity to explore the mechanisms underlying the inflammatory landscape in the COPD lung and offer insights for development of precision-based treatment to halt lung destruction.

Tensions in Taxonomies: Current Understanding and Future Directions in the Pathobiologic Basis and Treatment of Group 1 and Group 3 Pulmonary Hypertension

In the over 100 years since the recognition of pulmonary hypertension (PH), immense progress and significant achievements have been made with regard to understanding the pathophysiology of the disease and its treatment. These advances have been mostly in idiopathic pulmonary arterial hypertension (IPAH), which was classified as Group 1 Pulmonary Hypertension (PH) at the Second World Symposia on PH in 1998. However, the pathobiology of PH due to chronic lung disease, classified as Group 3 PH, remains poorly understood and its treatments thus remain limited. We review the history of the classification of the five groups of PH and aim to provide a state-of-the-art review of the understanding of the pathogenesis of Group 1 PH and Group 3 PH including insights gained from novel high-throughput omics technologies that have revealed heterogeneities within these categories as well as similarities between them. Leveraging the substantial gains made in understanding the genomics, epigenomics, proteomics, and metabolomics of PAH to understand the full spectrum of the complex, heterogeneous disease of PH is needed. Multimodal omics data as well as supervised and unbiased machine learning approaches after careful consideration of the powerful advantages as well as of the limitations and pitfalls of these technologies could lead to earlier diagnosis, more precise risk stratification, better predictions of disease response, new sub-phenotype groupings within types of PH, and identification of shared pathways between PAH and other types of PH that could lead to new treatment targets. © 2023 American Physiological Society. Compr Physiol 13:4295-4319, 2023.

Airway Smooth Muscle Regulated by Oxidative Stress in COPD

Since COPD is a heterogeneous disease, a specific anti-inflammatory therapy for this disease has not been established yet. Oxidative stress is recognized as a major predisposing factor to COPD related inflammatory responses, resulting in pathological features of small airway fibrosis and emphysema. However, little is known about effects of oxidative stress on airway smooth muscle. Cigarette smoke increases intracellular Ca²⁺ concentration and enhances response to muscarinic agonists in human airway smooth muscle. Cigarette smoke also enhances proliferation of these cells with altered mitochondrial protein. Hydrogen peroxide and 8-isoprostans are increased in the exhaled breath condensate in COPD. These endogenous oxidants cause contraction of tracheal smooth muscle with Ca²⁺ dynamics through Ca²⁺ channels and with Ca²⁺ sensitization through Rho-kinase. TNF-α and growth factors potentiate proliferation of these cells by synthesis of ROS. Oxidative stress can alter the function of airway smooth muscle through Ca²⁺ signaling. These phenotype changes are associated with manifestations (dyspnea, wheezing) and pathophysiology (airflow limitation, airway remodeling, airway hyperresponsiveness). Therefore, airway smooth muscle is a therapeutic target against COPD; oxidative stress should be included in treatable traits for COPD to advance precision medicine. Research into Ca²⁺ signaling related to ROS may contribute to the development of a novel agent for COPD.

iNOS Deletion in Alveolar Epithelium Cannot Reverse the Elastase-Induced Emphysema in Mice

BACKGROUND

Chronic obstructive pulmonary disease (COPD) is the third leading cause of death worldwide. In addition to chronic bronchitis and emphysema, patients often develop at least mild pulmonary hypertension (PH). We previously demonstrated that inhibition of inducible nitric oxide synthase (iNOS) prevents and reverses emphysema and PH in mice. Interestingly, strong iNOS upregulation was found in alveolar epithelial type II cells (AECII) in emphysematous murine lungs, and peroxynitrite, which can be formed from iNOS-derived NO, was shown to induce AECII apoptosis in vitro. However, the specific cell type(s) that drive(s) iNOS-dependent lung regeneration in emphysema/PH has (have) not been identified yet.

AIM

we tested whether iNOS knockout in AECII affects established elastase-induced emphysema in mice.

METHODS

four weeks after a single intratracheal instillation of porcine pancreatic elastase for the induction of emphysema and PH, we induced iNOS knockout in AECII in mice, and gave an additional twelve weeks for the potential recovery.

RESULTS

iNOS knockout in AECII did not reduce elastase-induced functional and structural lung changes such as increased lung compliance, decreased mean linear intercept and increased airspace, decreased right ventricular function, increased right ventricular systolic pressure and increased pulmonary vascular muscularization. In vitro, iNOS inhibition did not reduce apoptosis of AECII following exposure to a noxious stimulus.

CONCLUSION

taken together, our data demonstrate that iNOS deletion in AECII is not sufficient for the regeneration of emphysematous murine lungs, and suggest that iNOS expression in pulmonary vascular or stromal cells might be critically important in this regard.

Impact of Protein Nitration on Influenza Virus Infectivity and Immunogenicity

Influenza viruses are deadly respiratory pathogens of special importance due to their long history of global pandemics. During influenza virus infections, the host responds by producing interferons, which activate interferon-stimulated genes (ISGs) inside target cells. One of these ISGs is inducible nitric oxide synthase (iNOS). iNOS produces nitric oxide (NO) from arginine and molecular oxygen inside the cell. NO can react with superoxide radicals to form reactive nitrogen species, principally peroxynitrite. While much work has been done studying the many roles of nitric oxide in influenza virus infections, the direct effect of peroxynitrite on influenza virus proteins has not been determined. Manipulations of NO, either by knocking out iNOS or chemically inhibiting NO, produced no change in virus titers in mouse models of influenza infection. However, peroxynitrite has a known antimicrobial effect on various bacteria and parasites, and the reason for its lack of antimicrobial effect on influenza virus titers in vivo remains unclear. Therefore, we wished to test the direct effect of nitration of influenza virus proteins. We examined the impact of nitration on virus infectivity, replication, and immunogenicity. We observed that the nitration of influenza A virus proteins decreased virus infectivity and replication ex vivo. We also determined that the nitration of influenza virus hemagglutinin protein can reduce antibody responses to native virus protein. However, our study also suggests that nitration of influenza virus proteins in vivo is likely not extensive enough to inhibit virus functions substantially. These findings will help clarify the role of peroxynitrite during influenza virus infections. IMPORTANCE Nitric oxide and peroxynitrite produced during microbial infections have diverse and seemingly paradoxical functions. While nitration of lung tissue during influenza virus infection has been observed in both mice and humans, the direct effect of protein nitration on influenza viruses has remained elusive. We addressed the impact of nitration of influenza virus proteins on virus infectivity, replication, and immunogenicity. We observed that ex vivo nitration of influenza virus proteins reduced virus infectivity and immunogenicity. However, we did not detect nitration of influenza virus hemagglutinin protein in vivo. These results contribute to our understanding of the roles of nitric oxide and peroxynitrite in influenza virus infections.

Characterization of pulmonary vascular remodeling and MicroRNA-126-targets in COPD-pulmonary hypertension

BACKGROUND

Despite causing increased morbidity and mortality, pulmonary hypertension (PH) in chronic obstructive pulmonary disease (COPD) patients (COPD-PH) lacks treatment, due to incomplete understanding of its pathogenesis. Hypertrophy of pulmonary arterial walls and pruning of the microvasculature with loss of capillary beds are known features of pulmonary vascular remodeling in COPD. The remodeling features of pulmonary medium- and smaller vessels in COPD-PH lungs are less well described and may be linked to maladaptation of endothelial cells to chronic cigarette smoking (CS). MicroRNA-126 (miR126), a master regulator of endothelial cell fate, has divergent functions that are vessel-size specific, supporting the survival of large vessel endothelial cells and inhibiting the proliferation of microvascular endothelial cells. Since CS decreases miR126 in microvascular lung endothelial cells, we set out to characterize the remodeling by pulmonary vascular size in COPD-PH and its relationship with miR126 in COPD and COPD-PH lungs.

METHODS

Deidentified lung tissue was obtained from individuals with COPD with and without PH and from non-diseased non-smokers and smokers. Pulmonary artery remodeling was assessed by ⍺-smooth muscle actin (SMA) abundance via immunohistochemistry and analyzed by pulmonary artery size. miR126 and miR126-target abundance were quantified by qPCR. The expression levels of ceramide, ADAM9, and endothelial cell marker CD31 were assessed by immunofluorescence.

RESULTS

Pulmonary arteries from COPD and COPD-PH lungs had significantly increased SMA abundance compared to non-COPD lungs, especially in small pulmonary arteries and the lung microvasculature. This was accompanied by significantly fewer endothelial cell markers and increased pro-apoptotic ceramide abundance. miR126 expression was significantly decreased in lungs of COPD individuals. Of the targets tested (SPRED1, VEGF, LAT1, ADAM9), lung miR126 most significantly inversely correlated with ADAM9 expression. Compared to controls, ADAM9 was significantly increased in COPD and COPD-PH lungs, predominantly in small pulmonary arteries and lung microvasculature.

CONCLUSION

Both COPD and COPD-PH lungs exhibited significant remodeling of the pulmonary vascular bed of small and microvascular size, suggesting these changes may occur before or independent of the clinical development of PH. Decreased miR126 expression with reciprocal increase in ADAM9 may regulate endothelial cell survival and vascular remodeling in small pulmonary arteries and lung microvasculature in COPD and COPD-PH.

Targeting VEGF-A/VEGFR2 Y949 Signaling-Mediated Vascular Permeability Alleviates Hypoxic Pulmonary Hypertension

BACKGROUND

Pulmonary hypertension (PH) is associated with increased expression of VEGF-A (vascular endothelial growth factor A) and its receptor, VEGFR2 (vascular endothelial growth factor 2), but whether and how activation of VEGF-A signal participates in the pathogenesis of PH is unclear.

METHODS

VEGF-A/VEGFR2 signal activation and VEGFR2 Y949-dependent vascular leak were investigated in lung samples from patients with PH and mice exposed to hypoxia. To study their mechanistic roles in hypoxic PH, we examined right ventricle systolic pressure, right ventricular hypertrophy, and pulmonary vasculopathy in mutant mice carrying knock-in of phenylalanine that replaced the tyrosine at residual 949 of VEGFR2 (Vefgr2^Y949F) and mice with conditional endothelial deletion of Vegfr2 after chronic hypoxia exposure.

RESULTS

We show that PH leads to excessive pulmonary vascular leak in both patients and hypoxic mice, and this is because of an overactivated VEGF-A/VEGFR2 Y949 signaling axis. In the context of hypoxic PH, activation of Yes1 and c-Src and subsequent VE-cadherin phosphorylation in endothelial cells are involved in VEGFR2 Y949-induced vascular permeability. Abolishing VEGFR2 Y949 signaling by Vefgr2^Y949F point mutation was sufficient to prevent pulmonary vascular permeability and inhibit macrophage infiltration and Rac1 activation in smooth muscle cells under hypoxia exposure, thereby leading to alleviated PH manifestations, including muscularization of distal pulmonary arterioles, elevated right ventricle systolic pressure, and right ventricular hypertrophy. It is important that we found that VEGFR2 Y949 signaling in myeloid cells including macrophages was trivial and dispensable for hypoxia-induced vascular abnormalities and PH. In contrast with selective blockage of VEGFR2 Y949 signaling, disruption of the entire VEGFR2 signaling by conditional endothelial deletion of Vegfr2 promotes the development of PH.

CONCLUSIONS

Our results support the notion that VEGF-A/VEGFR2 Y949-dependent vascular permeability is an important determinant in the pathogenesis of PH and might serve as an attractive therapeutic target pathway for this disease.

Deletion of classical transient receptor potential 1, 3 and 6 alters pulmonary vasoconstriction in chronic hypoxia-induced pulmonary hypertension in mice

Chronic hypoxia-induced pulmonary hypertension (CHPH) is a severe disease that is characterized by increased proliferation and migration of pulmonary arterial smooth muscle cells (PASMCs) leading to pulmonary vascular remodeling. The resulting increase in pulmonary vascular resistance (PVR) causes right ventricular hypertrophy and ultimately right heart failure. In addition, increased PVR can also be a consequence of hypoxic pulmonary vasoconstriction (HPV) under generalized hypoxia. Increased proliferation and migration of PASMCs are often associated with high intracellular Ca²⁺ concentration. Recent publications suggest that Ca²⁺-permeable nonselective classical transient receptor potential (TRPC) proteins-especially TRPC1 and 6-are crucially involved in acute and sustained hypoxic responses and the pathogenesis of CHPH. The aim of our study was to investigate whether the simultaneous deletion of TRPC proteins 1, 3 and 6 protects against CHPH-development and affects HPV in mice. We used a mouse model of chronic hypoxia as well as isolated, ventilated and perfused mouse lungs and PASMC cell cultures. Although right ventricular systolic pressure as well as echocardiographically assessed PVR and right ventricular wall thickness (RVWT) were lower in TRPC1, 3, 6-deficient mice, these changes were not related to a decreased degree of pulmonary vascular muscularization and a reduced proliferation of PASMCs. However, both acute and sustained HPV were almost absent in the TRPC1, 3, 6-deficient mice and their vasoconstrictor response upon KCl application was reduced. This was further validated by myographical experiments. Our data revealed that 1) TRPC1, 3, 6-deficient mice are partially protected against development of CHPH, 2) these changes may be caused by diminished HPV and not an altered pulmonary vascular remodeling.

Identification of exercise-regulated genes in mice exposed to cigarette smoke

Cigarette smoke (CS) is the major risk factor for COPD and is linked to cardiopulmonary dysfunction. Exercise training as part of pulmonary rehabilitation is recommended for all COPD patients. It has several physiological benefits, but the mechanisms involved remain poorly defined. Here, we employed transcriptomic profiling and examined lung endothelium to investigate novel interactions between exercise and CS on cardiopulmonary alterations. Mice were exposed to 20 weeks of CS, CS + 6 weeks of high-intensity interval training on a treadmill, or control. Lung and cardiac (left and right ventricle) tissue were harvested and RNA-sequencing was performed and validated with RT-qPCR. Immunohistochemistry assessed pulmonary arteriolar changes. Transcriptome analysis between groups revealed 37 significantly regulated genes in the lung, 21 genes in the left ventricle, and 43 genes in the right ventricle (likelihood-ratio test). Validated genes that showed interaction between exercise and CS included angiotensinogen (p = 0.002) and resistin-like alpha (p = 0.019) in left ventricle, with prostacyclin synthetase different in pulmonary arterioles (p = 0.004). Transcriptomic profiling revealed changes in pulmonary and cardiac tissue following exposure to CS, with exercise training exerting rescue effects. Exercise-regulated genes included angiotensinogen and resistin-like alpha, however, it remains unclear if these represent potential candidate genes or biomarkers that could play a role during pulmonary rehabilitation.

Phenotyping of idiopathic pulmonary arterial hypertension: a registry analysis

BACKGROUND

Among patients meeting diagnostic criteria for idiopathic pulmonary arterial hypertension (IPAH), there is an emerging lung phenotype characterised by a low diffusion capacity for carbon monoxide (DLCO) and a smoking history. The present study aimed at a detailed characterisation of these patients.

METHODS

We analysed data from two European pulmonary hypertension registries, COMPERA (launched in 2007) and ASPIRE (from 2001 onwards), to identify patients diagnosed with IPAH and a lung phenotype defined by a DLCO of less than 45% predicted and a smoking history. We compared patient characteristics, response to therapy, and survival of these patients to patients with classical IPAH (defined by the absence of cardiopulmonary comorbidities and a DLCO of 45% or more predicted) and patients with pulmonary hypertension due to lung disease (group 3 pulmonary hypertension).

FINDINGS

The analysis included 128 (COMPERA) and 185 (ASPIRE) patients with classical IPAH, 268 (COMPERA) and 139 (ASPIRE) patients with IPAH and a lung phenotype, and 910 (COMPERA) and 375 (ASPIRE) patients with pulmonary hypertension due to lung disease. Most patients with IPAH and a lung phenotype had normal or near normal spirometry, a severe reduction in DLCO, with the majority having no or a mild degree of parenchymal lung involvement on chest computed tomography. Patients with IPAH and a lung phenotype (median age, 72 years [IQR 65-78] in COMPERA and 71 years [65-76] in ASPIRE) and patients with group 3 pulmonary hypertension (median age 71 years [65-77] in COMPERA and 69 years [63-74] in ASPIRE) were older than those with classical IPAH (median age, 45 years [32-60] in COMPERA and 52 years [38-64] in ASPIRE; p<0·0001 for IPAH with a lung phenotype vs classical IPAH in both registries). While 99 (77%) patients in COMPERA and 133 (72%) patients in ASPIRE with classical IPAH were female, there was a lower proportion of female patients in the IPAH and a lung phenotype cohort (95 [35%] COMPERA; 75 [54%] ASPIRE), which was similar to group 3 pulmonary hypertension (336 [37%] COMPERA; 148 [39%] ASPIRE]). Response to pulmonary arterial hypertension therapies at first follow-up was available from COMPERA. Improvements in WHO functional class were observed in 54% of patients with classical IPAH, 26% of patients with IPAH with a lung phenotype, and 22% of patients with group 3 pulmonary hypertension (p<0·0001 for classical IPAH vs IPAH and a lung phenotype, and p=0·194 for IPAH and a lung phenotype vs group 3 pulmonary hypertension); median improvements in 6 min walking distance were 63 m, 25 m, and 23 m for these cohorts respectively (p=0·0015 for classical IPAH vs IPAH and a lung phenotype, and p=0·64 for IPAH and a lung phenotype vs group 3 pulmonary hypertension), and median reductions in N-terminal-pro-brain-natriuretic-peptide were 58%, 27%, and 16% respectively (p=0·0043 for classical IPAH vs IPAH and a lung phenotype, and p=0·14 for IPAH and a lung phenotype vs group 3 pulmonary hypertension). In both registries, survival of patients with IPAH and a lung phenotype (1 year, 89% in COMPERA and 79% in ASPIRE; 5 years, 31% in COMPERA and 21% in ASPIRE) and group 3 pulmonary hypertension (1 year, 78% in COMPERA and 64% in ASPIRE; 5 years, 26% in COMPERA and 18% in ASPIRE) was worse than survival of patients with classical IPAH (1 year, 95% in COMPERA and 98% in ASPIRE; 5 years, 84% in COMPERA and 80% in ASPIRE; p<0·0001 for IPAH with a lung phenotype vs classical IPAH in both registries).

INTERPRETATION

A cohort of patients meeting diagnostic criteria for IPAH with a distinct, presumably smoking-related form of pulmonary hypertension accompanied by a low DLCO, resemble patients with pulmonary hypertension due to lung disease rather than classical IPAH. These observations have pathogenetic, diagnostic, and therapeutic implications, which require further exploration.

FUNDING

COMPERA is funded by unrestricted grants from Acceleron, Bayer, GlaxoSmithKline, Janssen, and OMT. The ASPIRE Registry is supported by Sheffield Teaching Hospitals NHS Foundation Trust, Sheffield, UK.

Emerging phenotypes of pulmonary hypertension associated with COPD: a field guide

PURPOSE OF REVIEW

Pulmonary hypertension (PH) is a common complication of chronic obstructive lung disease (COPD), but clinical presentation is variable and not always 'proportional' to the severity of the obstructive disease. This review aims to analyze heterogeneity in clinical features of PH-COPD, providing a guide for diagnosis and management according to phenotypes.

RECENT FINDINGS

Recent works have focused on severe PH in COPD, providing insights into the characteristics of patients with predominantly vascular disease. The recently recognized 'pulmonary vascular phenotype', characterized by severe PH and mild airflow obstruction with severe hypoxemia, has markedly worse prognosis and may be a candidate for large trials with pulmonary vasodilators. In severe PH, which might be best described by a pulmonary vascular resistance threshold, there may also be a need to distinguish patients with mild COPD (pulmonary vascular phenotype) from those with severe COPD ('Severe COPD-Severe PH' phenotype).

SUMMARY

Correct phenotyping is key to appropriate management of PH associated with COPD. The lack of evidence regarding the use of pulmonary vasodilators in PH-COPD may be due to the existence of previously unrecognized phenotypes with different responses to therapy. This review offers the clinician caring for patients with COPD and PH a phenotype-focused approach to diagnosis and management, aimed at personalized care.

Therapeutic Potential of Small Molecules Targeting Oxidative Stress in the Treatment of Chronic Obstructive Pulmonary Disease (COPD): A Comprehensive Review

Chronic obstructive pulmonary disease (COPD) is an increasing and major global health problem. COPD is also the third leading cause of death worldwide. Oxidative stress (OS) takes place when various reactive species and free radicals swamp the availability of antioxidants. Reactive nitrogen species, reactive oxygen species (ROS), and their counterpart antioxidants are important for host defense and physiological signaling pathways, and the development and progression of inflammation. During the disturbance of their normal steady states, imbalances between antioxidants and oxidants might induce pathological mechanisms that can further result in many non-respiratory and respiratory diseases including COPD. ROS might be either endogenously produced in response to various infectious pathogens including fungi, viruses, or bacteria, or exogenously generated from several inhaled particulate or gaseous agents including some occupational dust, cigarette smoke (CS), and air pollutants. Therefore, targeting systemic and local OS with therapeutic agents such as small molecules that can increase endogenous antioxidants or regulate the redox/antioxidants system can be an effective approach in treating COPD. Various thiol-based antioxidants including fudosteine, erdosteine, carbocysteine, and N-acetyl-L-cysteine have the capacity to increase thiol content in the lungs. Many synthetic molecules including inhibitors/blockers of protein carbonylation and lipid peroxidation, catalytic antioxidants including superoxide dismutase mimetics, and spin trapping agents can effectively modulate CS-induced OS and its resulting cellular alterations. Several clinical and pre-clinical studies have demonstrated that these antioxidants have the capacity to decrease OS and affect the expressions of several pro-inflammatory genes and genes that are involved with redox and glutathione biosynthesis. In this article, we have summarized the role of OS in COPD pathogenesis. Furthermore, we have particularly focused on the therapeutic potential of numerous chemicals, particularly antioxidants in the treatment of COPD.

Increased Methyl-CpG-Binding Domain Protein 2 Promotes Cigarette Smoke-Induced Pulmonary Hypertension

Pulmonary hypertension (PH) is a chronic vascular proliferative disorder. While cigarette smoke (CS) plays a vital part in PH related to chronic obstructive pulmonary disease (COPD). Methyl-CpG-Binding Domain Protein 2 (MBD2) has been linked to multiple proliferative diseases. However, the specific mechanisms of MBD2 in CS-induced PH remain to be elucidated. Herein, the differential expression of MBD2 was tested between the controls and the PH patients’ pulmonary arteries, CS-exposed rat models’ pulmonary arteries, and primary human pulmonary artery smooth muscle cells (HPASMCs) following cigarette smoke extract (CSE) stimulation. As a result, PH patients and CS-induced rats and HPASMCs showed an increase in MBD2 protein expression compared with the controls. Then, MBD2 silencing was used to investigate the function of MBD2 on CSE-induced HPASMCs’ proliferation, migration, and cell cycle progression. As a consequence, CSE could induce HPASMCs’ increased proliferation and migration, and cell cycle transition, which were suppressed by MBD2 interference. Furthermore, RNA-seq, ChIP-qPCR, and MassARRAY were conducted to find out the downstream mechanisms of MBD2 for CS-induced pulmonary vascular remodeling. Subsequently, RNA-seq revealed MBD2 might affect the transcription of BMP2 gene, which furtherly altered the expression of BMP2 protein. ChIP-qPCR demonstrated MBD2 could bind BMP2’s promotor. MassARRAY indicated that MBD2 itself could not directly affect DNA methylation. In sum, our results indicate that increased MBD2 expression promotes CS-induced pulmonary vascular remodeling. The fundamental mechanisms may be that MBD2 can bind BMP2’s promoter and downregulate its expression. Thus, MBD2 may promote the occurrence of the CS-induced PH.

Ethanol Extract of Sargassum siliquastrum Inhibits Lipopolysaccharide-Induced Nitric Oxide Generation by Downregulating the Nuclear Factor-Kappa B Signaling Pathway

Sargassum siliquastrum (SS) is an edible brown seaweed widely consumed in Korea and considered a functional food source. Previous studies have reported various biological activities of SS extracts, including antioxidant and hepatoprotective properties. In the present study, we examined the anti-inflammatory effects of the SS extract and assessed the underlying mechanism of action. The SS extract significantly inhibited lipopolysaccharide (LPS)-induced nitric oxide (NO) production in a dose-dependent manner (% of NO production at 500 μg/mL: 60.1 ± 0.9%), with no obvious toxicity. Furthermore, the SS extract inhibited mRNA and protein expression levels of inducible NO synthase, as well as LPS-induced expression and production of proinflammatory cytokines such as IL-1β, IL-6, or TNF-α (IL-6 production (ng/mL) : LPS−: 0.7 ± 0.3; LPS+: 68.1 ± 2.8; LPS + SS extract: 51.9 ± 1.2; TNF-α production (ng/mL) : LPS−: 0.3 ± 0.1; LPS+: 23.0 ± 0.1; LPS + SS extract: 18.2 ± 10.8). Mechanistically, the SS extract attenuated LPS-induced activation of the nuclear factor kappa-light-chain-enhancer of activated B cells (nuclear factor-kappa B, NF-κB) signaling pathway such as phosphorylation of NF-κB p65 and degradation of IκB-α, thereby blocking LPS-induced activation of NF-κB transcriptional activity. The SS extract also enhanced LPS-induced heme oxygenase-1 expression and attenuated LPS-induced cellular reactive oxygen species production (% of ROS production at 500 μg/mL: 52.2 ± 1.3%). Collectively, these findings suggest that the SS extract elicits anti-inflammatory effects in mouse macrophage cells.

Oxidative Stress in Chronic Obstructive Pulmonary Disease

There is a marked increase in oxidative stress in the lungs of patients with COPD, as measured by increased exhaled 8-isoprostane, ethane, and hydrogen peroxide in the breath. The lung may be exposed to exogenous oxidative stress from cigarette smoking and indoor or outdoor air pollution and to endogenous oxidative stress from reactive oxygen species released from activated inflammatory cells, particularly neutrophils and macrophages, in the lungs. Oxidative stress in COPD may be amplified by a reduction in endogenous antioxidants and poor intake of dietary antioxidants. Oxidative stress is a major driving mechanism of COPD through the induction of chronic inflammation, induction of cellular senescence and impaired autophagy, reduced DNA repair, increased autoimmunity, increased mucus secretion, and impaired anti-inflammatory response to corticosteroids. Oxidative stress, therefore, drives the pathology of COPD and may increase disease progression, amplify exacerbations, and increase comorbidities through systemic oxidative stress. This suggests that antioxidants may be effective as disease-modifying treatments. Unfortunately, thiol-based antioxidants, such as N-acetylcysteine, have been poorly effective, as they are inactivated by oxidative stress in the lungs, so there is a search for more effective and safer antioxidants. New antioxidants in development include mitochondria-targeted antioxidants, NOX inhibitors, and activators of the transcription factor Nrf2, which regulates several antioxidant genes.

Group 3 Pulmonary Hypertension: From Bench to Bedside

Pulmonary hypertension (PH) because of chronic lung disease is categorized as Group 3 PH in the most recent classification system. Prevalence of these diseases is increasing over time, creating a growing need for effective therapeutic options. Recent approval of the first pulmonary arterial hypertension therapy for the treatment of Group 3 PH related to interstitial lung disease represents an encouraging advancement. This review focuses on molecular mechanisms contributing to pulmonary vasculopathy in chronic hypoxia, the pathology and epidemiology of Group 3 PH, the right ventricular dysfunction observed in this population and clinical trial data that inform the use of pulmonary vasodilators in Group 3 PH.

The Latest in Animal Models of Pulmonary Hypertension and Right Ventricular Failure

Pulmonary hypertension (PH) describes heterogeneous population of patients with a mean pulmonary arterial pressure >20 mm Hg. Rarely, PH presents as a primary disorder but is more commonly part of a complex phenotype associated with comorbidities. Regardless of the cause, PH reduces life expectancy and impacts quality of life. The current clinical classification divides PH into 1 of 5 diagnostic groups to assign treatment. There are currently no pharmacological cures for any form of PH. Animal models are essential to help decipher the molecular mechanisms underlying the disease, to assign genotype-phenotype relationships to help identify new therapeutic targets, and for clinical translation to assess the mechanism of action and putative efficacy of new therapies. However, limitations inherent of all animal models of disease limit the ability of any single model to fully recapitulate complex human disease. Within the PH community, we are often critical of animal models due to the perceived low success upon clinical translation of new drugs. In this review, we describe the characteristics, advantages, and disadvantages of existing animal models developed to gain insight into the molecular and pathological mechanisms and test new therapeutics, focusing on adult forms of PH from groups 1 to 3. We also discuss areas of improvement for animal models with approaches combining several hits to better reflect the clinical situation and elevate their translational value.

Myeloid-cell-specific deletion of inducible nitric oxide synthase protects against smoke-induced pulmonary hypertension in mice

BACKGROUND

Pulmonary hypertension (PH) is a common complication of COPD, associated with increased mortality and morbidity. Intriguingly, pulmonary vascular alterations have been suggested to drive emphysema development. Previously, we identified inducible nitric oxide synthase (iNOS) as an essential enzyme for development and reversal of smoke-induced PH and emphysema, and showed that iNOS expression in bone-marrow-derived cells drives pulmonary vascular remodelling, but not parenchymal destruction. In this study, we aimed to identify the iNOS-expressing cell type driving smoke-induced PH and to decipher pro-proliferative pathways involved.

METHODS

To address this question we used 1) myeloid-cell-specific iNOS knockout mice in chronic smoke exposure and 2) co-cultures of macrophages and pulmonary artery smooth muscle cells (PASMCs) to decipher underlying signalling pathways.

RESULTS

Myeloid-cell-specific iNOS knockout prevented smoke-induced PH but not emphysema in mice. Moreover, iNOS deletion in myeloid cells ameliorated the increase in expression of CD206, a marker of M2 polarisation, on interstitial macrophages. Importantly, the observed effects on lung macrophages were hypoxia-independent, as these mice developed hypoxia-induced PH. In vitro, smoke-induced PASMC proliferation in co-cultures with M2-polarised macrophages could be abolished by iNOS deletion in phagocytic cells, as well as by extracellular signal-regulated kinase inhibition in PASMCs. Crucially, CD206-positive and iNOS-positive macrophages accumulated in proximity of remodelled vessels in the lungs of COPD patients, as shown by immunohistochemistry.

CONCLUSION

In summary, our results demonstrate that iNOS deletion in myeloid cells confers protection against PH in smoke-exposed mice and provide evidence for an iNOS-dependent communication between M2-like macrophages and PASMCs in underlying pulmonary vascular remodelling.

Tetramethylpyrazine Improves Monocrotaline-Induced Pulmonary Hypertension through the ROS/iNOS/PKG-1 Axis

Background

Tetramethylpyrazine (TMP), a potent anti-free radical and anti-inflammations substance, has been demonstrated to possess a direct vessel relaxation property. This study aimed to evaluate the effect of TMP treatment in pulmonary hypertension (PH) and test the hypothesis that TMP prevents or reverses the process of PH.

Methods

Rats (n = 36) injected with 50 mg/kg of monocrotaline (MCT) subcutaneously 4 weeks to develop PH were then randomized to TMP (5 mg/kg per day) for another 4 weeks. Hemodynamics was evaluated via the right ventricle. Pulmonary vessels structural remodeling and inflammation were examined by histologic and transmission electron microscopy observation. The expression of inducible nitric oxide synthase (iNOS) and cGMP-dependent protein kinases 1 (PKG-1) was detected by immunohistochemical staining and Western blot. Generation of reactive oxygen species (ROS) and antioxidation species was measured by biochemical analyses.

Results

MCT increased PH and right ventricle hypertrophy. TMP alleviated pulmonary arterial pressure elevation, leukocyte infiltration, and structural remodeling of pulmonary arterials induced by MCT successfully. TMP treatment significantly increased the PKG-1 expression and suppressed the iNOS expression. The activity of superoxide dismutase (SOD), glutathione peroxidase (GSH), and catalase (CAT) was significantly higher than control group, while malondialdehyde (MDA) levels were lower compared with MCT group.

Conclusion

TMP can suppress established MCT-induced PH through the ROS/iNOS/PKG axis. The underlying mechanisms may be associated with its anti-inflammatory, antioxidant, and antiproliferative properties in pulmonary arterial.

Role of oxidative stress in the pathogenesis of COPD

Chronic inhalation of cigarette smoke is a prominent cause of chronic obstructive pulmonary disease (COPD) and provides an important source of exogenous oxidants. In addition, several inflammatory and structural cells are a source of endogenous oxidants in the lower airways of COPD patients, even in former smokers. This suggests that oxidants play a key role in the pathogenesis of COPD. This oxidative stress is counterbalanced by the protective effects of the various endogenous antioxidant defenses of the lower airways. A large amount of data from animal models and patients with COPD have shown that both the stable phase of the disease, and during exacerbations, have increased oxidative stress in the lower airways compared with age-matched smokers with normal lung function. Thus, counteracting the increased oxidative stress may produce clinical benefits in COPD patients. Smoking cessation is currently the most effective treatment of COPD patients and reduces oxidative stress in the lower airways. In addition, many drugs used to treat COPD have some antioxidant effects, however, it is still unclear if their clinical efficacy is related to pharmacological modulation of the oxidant/antioxidant balance. Several new antioxidant compounds are in development for the treatment of COPD.

Dysregulated Cell Signaling in Pulmonary Emphysema

Pulmonary emphysema is characterized by the destruction of alveolar septa and irreversible airflow limitation. Cigarette smoking is the primary cause of this disease development. It induces oxidative stress and disturbs lung physiology and tissue homeostasis. Alveolar type II (ATII) cells have stem cell potential and can repair the denuded epithelium after injury; however, their dysfunction is evident in emphysema. There is no effective treatment available for this disease. Challenges in this field involve the large complexity of lung pathophysiological processes and gaps in our knowledge on the mechanisms of emphysema progression. It implicates dysregulation of various signaling pathways, including aberrant inflammatory and oxidative responses, defective antioxidant defense system, surfactant dysfunction, altered proteostasis, disrupted circadian rhythms, mitochondrial damage, increased cell senescence, apoptosis, and abnormal proliferation and differentiation. Also, genetic predispositions are involved in this disease development. Here, we comprehensively review studies regarding dysregulated cell signaling, especially in ATII cells, and their contribution to alveolar wall destruction in emphysema. Relevant preclinical and clinical interventions are also described.

Spontaneous pulmonary emphysema in mice lacking all three nitric oxide synthase isoforms

The roles of endogenous nitric oxide (NO) derived from the entire NO synthases (NOSs) system have yet to be fully elucidated. We addressed this issue in mice in which all three NOS isoforms were deleted. Under basal conditions, the triple n/i/eNOSs^−/− mice displayed significantly longer mean alveolar linear intercept length, increased alveolar destructive index, reduced lung elastic fiber content, lower lung field computed tomographic value, and greater end-expiratory lung volume as compared with wild-type (WT) mice. None of single NOS^−/− or double NOSs^−/− genotypes showed such features. These findings were observed in the triple n/i/eNOSs^−/− mice as early as 4 weeks after birth. Cyclopaedic and quantitative comparisons of mRNA expression levels between the lungs of WT and triple n/i/eNOSs^−/− mice by cap analysis of gene expression (CAGE) revealed that mRNA expression levels of three Wnt ligands and ten Wnt/β-catenin signaling components were significantly reduced in the lungs of triple n/i/eNOSs^−/− mice. These results provide the first direct evidence that complete disruption of all three NOS genes results in spontaneous pulmonary emphysema in juvenile mice in vivo possibly through down-regulation of the Wnt/β-catenin signaling pathway, demonstrating a novel preventive role of the endogenous NO/NOS system in the occurrence of pulmonary emphysema.

Retinal tissue develops an inflammatory reaction to tobacco smoke and electronic cigarette vapor in mice

Cigarette smoke has been identified as a major risk factor for the development of age-related macular degeneration (AMD). As an alternative to conventional cigarettes (C-cigarette), electronic cigarettes (E-cigarette) have been globally promoted and are currently widely used. The increasing usage of E-cigarettes raises concerns with regard to short- (2 weeks), medium- (3 months), and long- (8 months) term consequences related to retinal tissue. In this report, a controlled study in mouse models was conducted to probe the comprehensive effects of E-cigarette vapor on retina, retinal pigmented epithelium (RPE), and choroidal tissues by (1) comparing the effects of C-cigarette smoke and E-cigarette vapor on retina separately and (2) determining the effects of E-cigarette vapor on the RPE and analyzing the changes with regard to inflammatory (IL-1β, TNFα, iNOS) and angiogenic (VEGF, PEDF) mediators in retina/RPE/choroid by ELISA assays. The data showed that C-cigarette smoke exposure promoted an inflammatory reaction in the retina in vivo. Mice exposed to E-cigarette (nicotine-free) vapor developed inflammatory and angiogenic reactions more pronounced in RPE and choroid as compared to retinal tissue, while nicotine-containing E-cigarette vapor caused even a more serious reaction. Both inflammatory and pro-angiogenic reactions increased with the extension of exposure time. These results demonstrate that exposure to C-cigarette smoke is harmful to the retina. Likewise, the exposure to E-cigarette vapor (with or without nicotine) increases the occurrence and progression of inflammatory and angiogenic stimuli in the retina, which might also be related to the onset of wet AMD in humans. KEY MESSAGES: C-cigarette smoke exposure promotes an inflammatory reaction in the retina in vivo. Mice exposed to E-cigarette (nicotine-free) vapor develop inflammatory and angiogenic reactions more pronounced in RPE and choroid compared to retinal tissue, while nicotine-containing E-cigarette vapor causes even a more serious reaction. Both inflammatory and pro-angiogenic reactions increase with the extension of E-cigarette vapor exposure time.

Phospholipase A2 receptor 1 promotes lung cell senescence and emphysema in obstructive lung disease

BACKGROUND

Cell senescence is a key process in age-associated dysfunction and diseases, notably chronic obstructive pulmonary disease (COPD). We previously identified phospholipase A2 receptor 1 (PLA2R1) as a positive regulator of cell senescence acting via Janus kinase (JAK)/signal transducer and activator of transcription (STAT) signalling. Its role in pathology, however, remains unknown. Here, we assessed PLA2R1-induced senescence in COPD and lung emphysema pathogenesis.

METHODS

We assessed cell senescence in lungs and cultured lung cells from patients with COPD and controls subjected to PLA2R1 knockdown, PLA2R1 gene transduction and treatment with the JAK1/2 inhibitor ruxolitinib. To assess whether PLA2R1 upregulation caused lung lesions, we developed transgenic mice overexpressing PLA2R1 (PLA2R1-TG) and intratracheally injected wild-type mice with a lentiviral vector carrying the Pla2r1 gene (LV-PLA2R1 mice).

RESULTS

We found that PLA2R1 was overexpressed in various cell types exhibiting senescence characteristics in COPD lungs. PLA2R1 knockdown extended the population doubling capacity of these cells and inhibited their pro-inflammatory senescence-associated secretory phenotype (SASP). PLA2R1-mediated cell senescence in COPD was largely reversed by treatment with the potent JAK1/2 inhibitor ruxolitinib. Five-month-old PLA2R1-TG mice exhibited lung cell senescence, and developed lung emphysema and lung fibrosis together with pulmonary hypertension. Treatment with ruxolitinib induced reversal of lung emphysema and fibrosis. LV-PLA2R1-treated mice developed lung emphysema within 4 weeks and this was markedly attenuated by concomitant ruxolitinib treatment.

CONCLUSIONS

Our data support a major role for PLA2R1 activation in driving lung cell senescence and lung alterations in COPD. Targeting JAK1/2 may represent a promising therapeutic approach for COPD.