Elevated TNFalpha production in whole blood in patients with severe COPD: the potential link to disease severity

Variability in sensitivity to inflammation in muscle and lung of patients with COPD may underlie susceptibility to lung function decline

BACKGROUND

Muscle wasting and weakness (sarcopenia) are commonly associated with COPD causing frailty and reduced quality of life. The contribution of inflammation to muscle loss and the susceptibility to rapid lung function decline is debated. We hypothesised that comparing the muscle transcriptome to circulating inflammatory cytokine profiles in patients would identify any contribution of systemic inflammation to muscle atrophy.

METHODS

Quadriceps differential gene expression was determined between mild-COPD (n=28) and severe-COPD (n=51) using GSE100281. These microarray data were compared by biweight mid-correlation with lung function and plasma cytokine levels from the same patients.

RESULTS

Patients with severe COPD had reduced fat-free mass index (a measurement of muscle mass) compared with patients with mild COPD despite similar physical activity and inflammatory cytokine levels. Gene sets associated with inflammation and epithelial mesenchymal transition (EMT) were elevated in severe COPD, suggesting that inflammation may contribute to the loss of muscle mass. In patients with severe COPD, EMT and inflammation gene sets were strongly associated with circulating proinflammatory and anti-inflammatory cytokines. However, in patients with mild COPD, anti-inflammatory cytokines showed negative associations with these gene sets and associations with proinflammatory cytokines were weak. In data from lung and blood samples, patients with severe COPD had elevated inflammatory and EMT gene expression compared with patients with mild COPD suggesting that this phenomenon is not muscle-specific.

CONCLUSIONS

In patients at the severe end of the COPD spectrum, the proinflammatory response in muscle predominates, whereas in patients at the mild end of the spectrum, the anti-inflammatory response predominates. This suggestion needs confirming in a longitudinal cohort.

CC16 augmentation reduces exaggerated COPD-like disease in Cc16-deficient mice

Low Club Cell 16 kDa protein (CC16) plasma levels are linked to accelerated lung function decline in patients with chronic obstructive pulmonary disease (COPD). Cigarette smoke-exposed (CS-exposed) Cc16-/- mice have exaggerated COPD-like disease associated with increased NF-κB activation in their lungs. It is unclear whether CC16 augmentation can reverse exaggerated COPD in CS-exposed Cc16-/- mice and whether increased NF-κB activation contributes to the exaggerated COPD in CS-exposed Cc16-/- lungs. CS-exposed WT and Cc16-/- mice were treated with recombinant human CC16 (rhCC16) or an NF-κB inhibitor versus vehicle beginning at the midpoint of the exposures. COPD-like disease and NF-κB activation were measured in the lungs. RhCC16 limited the progression of emphysema, small airway fibrosis, and chronic bronchitis-like disease in WT and Cc16-/- mice partly by reducing pulmonary inflammation (reducing myeloid leukocytes and/or increasing regulatory T and/or B cells) and alveolar septal cell apoptosis, reducing NF-κB activation in CS-exposed Cc16-/- lungs, and rescuing the reduced Foxj1 expression in CS-exposed Cc16-/- lungs. IMD0354 treatment reduced exaggerated lung inflammation and rescued the reduced Foxj1 expression in CS-exposed Cc16-/- mice. RhCC16 treatment reduced NF-κB activation in luciferase reporter A549 cells. Thus, rhCC16 treatment limits COPD progression in CS-exposed Cc16-/- mice partly by inhibiting NF-κB activation and represents a potentially novel therapeutic approach for COPD.

Assessment of trace elements, systemic inflammation, and electrolytes in patients with chronic obstructive pulmonary disease

Background

Systemic inflammation, electrolytes, and trace element derangements are thought to be involved, directly or indirectly, in chronic obstructive pulmonary diseases (COPD).

Aim

Our aim is to evaluate systemic inflammation and disturbance in serum electrolytes and trace elements in patients with COPD.

Methods

This study was conducted in the Chest Department, Cardiothoracic Minia University Hospital. One hundred COPD patients and 40 healthy controls were included in the study. Sixty patients were in a stable state, while 40 patients were in acute exacerbation of chronic obstructive pulmonary disease (AECOPD). Serum C-reactive protein (CRP), TNF-α, copper (Cu), zinc (Z), Na, K, and Mg levels were measured for all participants.

Results

CRP, TNF, Cu, and Z were significantly higher in the stable group than in the control group (p-value 0.0002*, 0.0018*, 0.04*, 0.034*, respectively) with significantly higher levels during exacerbation (8.47 ± 6.3, 24.36 ± 9.53, 201 ± 39.02, 192 ± 32.3). The Cu/Z ratio was significantly lower in the exacerbation group than in the stable group (p-value 0.042*). Serum levels of Na, K, and Mg were significantly lower in the patients group than in the control group (p-value 0.024*, 0.039*,0.044*, respectively), with more reduction observed in the exacerbation group (132 ± 5.45, 3.24 ± 0.52, 1.67 ± 0.38).

Conclusion

CRP, TNF-α, Cu, and Z levels were significantly higher in stable COPD patients, with higher levels during exacerbation. The Cu/Z ratio was lower in the exacerbation group than in the stable group. Na, K, and Mg levels were lower in patients than in the control group with more reduction during exacerbation.

Accelerated immunosenescence, oxidation and inflammation lead to a higher biological age in COPD patients

Chronic obstructive pulmonary disease (COPD) is characterised by inflammatory and oxidative alterations in the lung and extrapulmonary compartments, through involvement of the immune system. Several leukocyte functions are health markers and good predictors of longevity, and high pro-inflammatory and oxidative states are related to more aged profiles. Here, we aimed to investigate the aging rate in terms of immunosenescence in COPD men with respect to healthy age-matched controls. Several neutrophil (adherence, chemotaxis, phagocytosis, superoxide anion stimulated production) and lymphocyte (adherence, chemotaxis, lymphoproliferation, natural killer activity) functions, cytokine concentrations released in response to lipopolysaccharide (tumor necrosis factor-alpha, interleukin (IL)-6, IL-8, IL-10) and redox parameters (intracellular glutathione content, basal superoxide anion level) were assessed in circulating leukocytes of men with moderate and severe stages of COPD, and compared to healthy age-matched volunteers. The biological age or aging rate in each participant was determined using the values of leukocyte functions. The results indicated impairment of immune functions in COPD patients, both in innate and adaptive immunity, and higher pro-inflammatory and oxidative states in peripheral leukocytes than controls. In general, these changes were more remarkable at the severe stage of airway obstruction. Importantly, COPD patients were found to be aging at a faster rate than age-matched healthy counterparts.

Anti-cytokines as a Strategy in Alpha-1 Antitrypsin Deficiency

For many years, the lung disease associated with alpha-1 antitrypsin (AAT) deficiency (AATD) was perceived as being secondary to an imbalance between this serine protease inhibitor and the target protease, neutrophil elastase (NE). More recently, a greater understanding of the pathways leading to lung inflammation has shed light on new potential attributes and presented AATD as an inflammatory condition in which proteases and neutrophils still play a major role, but in which pro-inflammatory cytokines, either induced by the actions of NE or by other pro-inflammatory processes normally modulated by AAT, are involved. In this review, we will look at the various cytokines centrally involved in AATD lung disease, and how a greater understanding of their contribution may help development of targeted therapies.

Transcriptome-Guided Drug Repositioning

Drug repositioning can save considerable time and resources and significantly speed up the drug development process. The increasing availability of drug action and disease-associated transcriptome data makes it an attractive source for repositioning studies. Here, we have developed a transcriptome-guided approach for drug/biologics repositioning based on multi-layer self-organizing maps (ml-SOM). It allows for analyzing multiple transcriptome datasets by segmenting them into layers of drug action- and disease-associated transcriptome data. A comparison of expression changes in clusters of functionally related genes across the layers identifies "drug target" spots in disease layers and evaluates the repositioning possibility of a drug. The repositioning potential for two approved biologics drugs (infliximab and brodalumab) confirmed the drugs' action for approved diseases (ulcerative colitis and Crohn's disease for infliximab and psoriasis for brodalumab). We showed the potential efficacy of infliximab for the treatment of sarcoidosis, but not chronic obstructive pulmonary disease (COPD). Brodalumab failed to affect dysregulated functional gene clusters in Crohn's disease (CD) and systemic juvenile idiopathic arthritis (SJIA), clearly indicating that it may not be effective in the treatment of these diseases. In conclusion, ml-SOM offers a novel approach for transcriptome-guided drug repositioning that could be particularly useful for biologics drugs.

Assessment of serum levels of DIO1 and DIO3 in patients diagnosed with COPD

PURPOSE

Chronic obstructive pulmonary disease is the most common chronic lung disease, which may be caused by different pathological processes, including inflammation. Furthermore, signs of changes in thyroid hormone levels are found in some patients. Deiodinases (DIOs) are selenoproteins (enzymes) involved in the synthesis of thyroid hormones. It has been found that these molecules are involved in inflammatory processes. We carried out this preliminary study to investigate the levels of two deiodinases, i.e. type 1 deiodinase (DIO1) and type 3 deiodinase (DIO3), and their possible association with COPD and specific clinical parameters.

PATIENTS AND METHODS

Serum levels of DIO1 and DIO3 as well as lung function parameters were measured in 50 patients suffering from COPD and 30 healthy control subjects. The Mann-Whitney U test and Pearson's correlation coefficient were used to compare and correlate data.

RESULTS

Serum levels of DIO1 and DIO3 were significantly elevated in COPD patients (97.9 ± 55.6 versus 28.2 ± 28.3 U/L for DIO1 and 19.6 ± 10.7 versus 6.4 ± 6.3 U/L for DIO3; p < 0.001). No correlation between serum levels of the examined DIOs and other sociodemographic and clinical parameters was identified in this study.

CONCLUSION

For the first time we observed that peripheral DIO1 and DIO3 concentrations were elevated in COPD; hence, we may cautiously begin considering these molecules as potential circulating biomarkers of COPD. It may also be beneficial to conduct further studies to confirm and clarify their potential role.

Relationship between Vitamin D Level and Serum TNF-α Concentration on the Severity of Chronic Obstructive Pulmonary Disease

BACKGROUND

Chronic Obstructive Pulmonary Disease (COPD) is a chronic inflammatory disease and disturbed bacterial clearance. Vitamin D deficiency is sometimes observed in COPD patients and as significant roles in increasing inflammation of airway obstruction and systemic obstruction, increasing pro-inflammatory cytokine including TNF-α, reduction of bacterial clearance and increase exacerbation risk due to infection. Also, vitamin D plays significant roles in the metabolism of calcium and mineralisation of bones and regulation system of immune. TNF-α also has essential roles in pathogenesis and inflammation of COPD. Several studies that investigate the relationship between vitamin D level and serum TNF-α concentration in COPD patients are relatively uncommon, including in Indonesia.

AIM

This study aimed to assess the relationship between vitamin D level and TNF-α concentration in patients on the severity of the chronic obstructive pulmonary disease.

METHODS

This study was a hospital-based descriptive cross-sectional study. Total samples were 50 COPD patients with the average age of older than 60 years during their enrollments at the Department of Pulmonology and Respiratory Medicine of the Dr Wahidin Sudirohusodo General Hospital Makassar in September 2018-January 2019. All procedures of the present study were reviewed and approved by the Research Ethics Committee of Medicine Faculty of Hasanuddin University. The severity of COPD was assessed according to the combination of COPD assessment stages that referred to the Global Initiative for Chronic Obstructive Lung Disease (GOLD) Guideline 2015 that consisted of the combination of scoring COPD Assessment Test (CAT), the modified Medical Research Council (mMRC) questionnaire and results of the spirometry measurement. Assessment of airway obstruction levels referred to the GOLD spirometry criteria. Determination of thoracic photographs was conducted to verify the COPD diagnosis of the severity of COPD. Determination of serum TNF-α concentration and vitamin D3 [1,25(OH)2D3] level used the ELISA method.

RESULTS

The majority of COPD patients were observed in the category of older than 60 years old accounted for 34 COPD patients (68%), and the majority of COPD patients were males accounted for 47 males with COPD (94%). The majority of COPD patients were observed in the group of D (38%). All the study subjects observed in this study were smokers, and 82% of them were in the category of heavy smokers. 21 study subjects had higher concentration of serum TNF-α (tertile 3 = 0.21-1.83 pg/dl), 20 study subjects and lower level of vitamin D (tertile 1 = 182.1-364.5 pg/dl). The majority of the study subjects (38%) were in the category of severe COPD (category D of the severity of COPD at the tertile 3) according to the GOLD Combine Assessment. Given the relationship between vitamin D level and serum TNF-α concentration on the airway obstruction, there were significant positive correlations between the increase of vitamin D levels and the increase of serum TNF-α concentrations on airway obstruction. Given the relationship between vitamin D level and serum TNF-α concentration on the severity of COPD, there were significant positive correlations between the increase of vitamin D levels (tertiles 1, 2 and 3) and the increase of serum TNF-α concentrations on the severity of COPD at p-value < 0.05. Overall, there were non-linear relationships between vitamin D level and serum TNF-α concentration on the severity of COPD.

CONCLUSIONS

Serum TNF-α concentration was positively associated with airway obstruction level and severity of COPD. Low level of vitamin D was negatively associated with airway obstruction level and severity of COPD. Vitamin D3 level (1,25(OH)2D) was negatively associated with serum TNF-α concentration and airway obstruction level and severity of COPD.

Assessment of anti-reflux treatment on pulmonary ventilation function and inflammatory cytokines in patients with stable chronic obstructive pulmonary disease combined with gastroesophageal reflux

Compelling evidence has demonstrated that systemic inflammation among patients with stable chronic obstructive pulmonary disease (COPD) is linked with increased levels of inflammatory cytokines. The aim of the present study was to investigate the effects associated with anti-reflux treatment on pulmonary ventilation function and inflammatory cytokines in patients with stable COPD and gastroesophageal reflux (GER). One hundred and thirty-six stable COPD and GER patients were recruited for the study and randomly designated into the routine treatment and the anti GER groups. Six months prior to and after treatment, pulmonary ventilation function, 6-min walk distance (6MWD) and times of acute exacerbation of COPD (AECOPD) were recorded. The levels of inflammatory cytokines IL-13, IL-18, transforming growth factor-β1 (TGF-βl) and tumor necrosis factor-α (TNF-α) in the sputum were detected by ELISA. BODE indexes, including body mass index, obstruction, dyspnea and exercise, were analyzed in order to evaluate patient prognoses. In comparison with the routine treatment group, patients in the anti-GER group displayed improved pulmonary ventilation function, increased 6MWD as well as decreases in AECOPD, levels of IL-13, IL-18, TGF-βl and TNF-α in the sputum and BODE index 6 months after treatment. The results obtained suggested a correlation between the BODE indexes after treatment and the course of disease as well as the frequency of exacerbation. The key findings of the study suggested that conventional treatment combined with anti-reflux treatment could effectively improve pulmonary ventilation function, while acting to decrease the levels of inflammatory cytokines and improve the prognosis of patients with stable COPD along with GER.

MiR-3202 protects smokers from chronic obstructive pulmonary disease through inhibiting FAIM2: An in vivo and in vitro study

Previous study found the variable miR-3202 as a potential biomarker in smoker with or without chronic obstructive pulmonary disease (COPD). This study aims to identify the molecular involvement of miR-3202 in the pathophysiology of COPD. Level of miR-3202 in blood sample of non-smoker non-COPD(C), smoker without COPD(S), smoker with stable COPD(S-COPD) and smoker with acute exacerbation COPD(AE-COPD) was observed by quantitative real-time PCR. By bioinformatics prediction, Fas apoptotic inhibitory molecule 2 (FAIM2) was identified as a potential target of miR-3202. In vitro, human bronchial epithelial (HBE) cells and cigarette smoke extract (CSE) stimulated T lymphocytes were co-cultured. Cell proliferation and apoptosis of HBE cells were determinated. In vivo, rats were exposed in cigarette smoke for 30 days and expression of miR-3202 and FAIM2 in bronchia were detected. Results showed that The miR-3202 was down-regulated in S, S-COPD and AE-COPD group when compared with C group. Decreased level of miR-3202 was also observed in CSE treated T lymphocyte. Additionally, CSE stimulation increased INF-γ and TNF-α levels and FAIM2 expression whereas inhibited Fas and FasL expressions in T lymphocytes. However, these effects were significantly suppressed by miR-3202 overexpression and enhanced by miR-3202 inhibitor. Likely to exogenous miR-3202, FAIM2 knockdown significantly inhibited HBE cells apoptosis, as well as inhibited INF-γ and TNF-α levels. In COPD rats model, miR-3202 was reduced while FAIM2 was up-regulated accordingly. Here, results suggest that high level miR-3202 in T lymphocytes may protect epithelial cells through targeting FAIM2. MiR-3202 might be used as a notable biomarker of COPD.

Theophylline action on primary human bronchial epithelial cells under proinflammatory stimuli and steroidal drugs: a therapeutic rationale approach

Theophylline is a natural compound present in tea. Because of its property to relax smooth muscle it is used in pharmacology for the treatment of airway diseases (ie, chronic obstructive pulmonary disease, asthma). However, this effect on smooth muscle is dose dependent and it is related to the development of side effects. Recently, an increasing body of evidence suggests that theophylline, at low concentrations, also has anti-inflammatory effects related to the activation of histone deacetylases. In this study, we evaluated the effects of theophylline alone and in combination with corticosteroids on human bronchial epithelial cells under inflammatory stimuli. Theophylline administrated alone was not able to reduce growth-stimulating signaling via extracellular signal-regulated kinases activation and matrix metalloproteases release, whereas it strongly counteracts this biochemical behavior when administered in the presence of corticosteroids. These data provide scientific evidence for supporting the rationale for the pharmacological use of theophylline and corticosteroid combined drug.

Anaemia in chronic obstructive pulmonary disease: an insight into its prevalence and pathophysiology

Chronic obstructive pulmonary disease (COPD) is a major health problem, with increasing morbidity and mortality. There is a growing literature regarding the extra-pulmonary manifestations of COPD, which can have a significant impact on symptom burden and disease progression. Anaemia is one of the more recently identified co-morbidities, with a prevalence that varies between 4.9% and 38% depending on patient characteristics and the diagnostic criteria used. Systemic inflammation seems to be an important factor for its establishment and repeated bursts of inflammatory mediators during COPD exacerbations could further inhibit erythropoiesis. However, renal impairment, malnutrition, low testosterone levels, growth hormone level abnormalities, oxygen supplementation, theophylline treatment, inhibition of angiotensin-converting enzyme and aging itself are additional factors that could be associated with the development of anaemia. The present review evaluates the published literature on the prevalence and significance of anaemia in COPD. Moreover, it attempts to elucidate the reasons for the high variability reported and investigates the complex pathophysiology underlying the development of anaemia in these patients.

The circulating proteinase inhibitor α-1 antitrypsin regulates neutrophil degranulation and autoimmunity

Pathological inflammation and autoimmune disease frequently involve elevated neutrophil activity in the absence of infectious agents. Tumor necrosis factor-α (TNF-α) contributes to many of the problems associated with autoimmune diseases. We investigated the ability of serum α-1 antitrypsin (AAT) to control TNF-α biosynthesis and signaling in neutrophils and assessed whether AAT deficiency (AATD) is a TNF-α-related disease. In vitro studies demonstrate that serum AAT coordinates TNF-α intracellular signaling and neutrophil degranulation of tertiary and secondary granules via modulation of ligand-receptor interactions. AATD patients homozygous for the Z allele were characterized by increased activation of the TNF-α system, as demonstrated by increased membrane TNF-α levels and increased plasma concentrations of TNF receptor 1 and neutrophil-released secondary and tertiary granule proteins. The incidence of autoantibodies directed against degranulated lactoferrin and surface protein accessible to these antibodies was increased in ZZ-AATD, leading to an enhanced rate of neutrophil reactive oxygen species production. Treatment of ZZ-AATD individuals with AAT augmentation therapy resulted in decreased membrane TNF-α expression and plasma levels of granule antigenic proteins and immunoglobulin G class autoantibodies. These results provide a mechanism by which AAT augmentation therapy affects TNF-α signaling in the circulating neutrophil, indicating promising potential of this therapy for other TNF-α-related diseases.

[Severe pneumonia due to cytomegalovirus in chronic obstructive pulmonary disease]

Severe pneumonia due to cytomegalovirus in chronic obstructive pulmonary disease.

INTRODUCTION

We describe two cases of immunocompetent patients with chronic obstructive pulmonary disease (COPD) who developed severe cytomegalovirus (CMV) pneumonia. The clinical and radiological context and CMV replication in broncho-alveolar lavage suggested a diagnosis of CMV pneumonia.

CASE HISTORIES

We report two cases in patients with moderate chronic obstructive pulmonary disease not treated with long-term steroid therapy who developed bilateral pneumonia with hypoxaemia. The only pathogen identified was CMV with replication of the virus in the broncho-alveolar lavage. Investigation failed to detect any associated immune deficiency.

CONCLUSION

Severe cytomegalovirus pneumonia could be encouraged by the existence of chronic obstructive pulmonary disease due to local inflammatory changes.

A dendrimer-based immunosensor for improved capture and detection of tumor necrosis factor-α cytokine

A dendrimer-based sandwich type enzyme-linked immunosorbent assay (ELISA) was developed for the improved detection of recombinant human tumor necrosis factor-alpha (TNF-α) for early diagnosis of perinatal diseases. Hydroxyl-terminated generation four poly(amidoamine) dendrimer (G4-OH) was used for the development of a solid phase bio-sensing platform. The surface of the ELISA plate was modified with polyethylene-glycol (PEG) and thiol-functionalized G4-OH was immobilized on the PEG-functionalized plate. A capture antibody was oxidized and covalently immobilized onto the dendrimer-modified ELISA plate, which provides favorable orientation for the antigen binding sites toward the analyte. The dendrimer-modified plate showed enhanced sensitivity, and the detection limit for TNF-α was found to be 0.48 pg mL(-1), which is significantly better than the commercially available ELISA kit. The selectivity of the dendrimer-modified ELISA plate was further evaluated with a mixture of cytokines, which showed results for similar to that of TNF-α alone. The modified plate provides a greater opportunity for the detection of a wide range of cytokines and biomarkers.

Smoking status and tumor necrosis factor-alpha mediated systemic inflammation in COPD patients

BACKGROUND

Smoking cause airway and systemic inflammation and COPD patients present low grade inflammation in peripheral blood. However, data on the influence of smoking itself on systemic inflammation in COPD patients are scarce. This study investigated the association between inflammation, smoking status, and disease.

METHODS

A cross-sectional analysis comparing 53 COPD ex-smokers, 24 COPD current smokers, 24 current smoker controls and 34 never-smoker controls was performed. Assessments included medical history, body composition, spirometry, and plasma concentration of tumor necrosis factor-alpha (TNF-alpha), interleukins (IL)-6, IL-8, and C-reactive protein (CRP).

RESULTS

Our exploratory analysis showed that serum TNF-alpha was higher in COPD current smokers [4.8(4.2-5.8)pg/mL] and in current smoker controls [4.8 (4.2-6.1) pg/mL] when compared to COPD ex-smokers [4.3 (3.9-4.9)pg/mL; p = 0.02] and to never-smoker controls [3.7 (3.4-4.0)pg/mL; p < 0.001]. Multiple regression results with and without adjustment for covariates were consistent with the hypothesis that TNF-alpha levels were associated with smoking status in both models (p < 0.001 and p < 0.001). IL-6 and CRP were significantly higher in COPD patients when compared to smoker and never-smoker controls and the multiple regression analysis confirmed the association of these mediators with disease, but not with smoking status (p < 0.001 and p < 0.001). IL-8 had only a borderline association with disease in both models (p = 0.069 and p = 0.053). No influence of disease severity, inhaled corticosteroid, fat-free mass (FFM) depletion and long term oxygen therapy (LTOT) use on systemic inflammation was found.

CONCLUSION

Smoking may influence TNF-alpha mediated systemic inflammation, which, in turn, may account for some of the benefits observed in patients with COPD who stop smoking.

COPD is not COPD is not allergy

Chronic obstructive pulmonary disease (COPD) is still a poorly understood disease. Its pathogenesis is excitingly complex and has systemic consequences caused not only by increased production of certain cytokines but also by neurohumoral activation, chronic bacterial infection, muscle wasting and cachexia. Asthma and COPD have many overlapping clinical features so it should not be surprising that in the pathogenesis of COPD mediators such as leukotrienes, complement activation, atopic or even autoimmune processes are possibly involved. The pathogenesis of cardiovascular system involvement in COPD is also multifaceted and includes chronic heart hypoxia, damage by smoking and pulmonary hypertension; it must also be viewed as a consequence of systemic inflammation and neurohormonal activation. COPD is among the leading causes of morbidity and mortality worldwide and therefore it should be studied intensively beyond the lung itself. Treatments directed at neurohumoral activation in COPD have not been fully addressed; this aspect of COPD should be better understood, as it may direct novel therapeutic approaches.