Abnormal transition pore kinetics and cytochrome C release in muscle mitochondria of patients with chronic obstructive pulmonary disease

Effect of exercise interventions on oxygen uptake in people with chronic obstructive pulmonary disease: A network meta-analysis of randomized controlled trials

BACKGROUND

Although aerobic training leads to physiological improvements in people with chronic obstructive pulmonary disease (COPD), measured by the VO2 peak, there is no evidence as to which type of physical exercise intervention is the most effective in improving the VO2 peak or max.

OBJECTIVE

A network meta-analysis (NMA) was performed to determine the effects of different physical interventions on oxygen uptake in people with COPD.

METHODS

A literature search was performed from database inception to February 2024. Randomized controlled trials on the effectiveness of exercise programs on oxygen uptake with COPD were included. We assessed the risk of bias using the Cochrane Risk of Bias (RoB 2.0) tool and the quality of the evidence using the Grading of Recommendations, Assessment, Development, and Evaluation (GRADE) tool. Pairwise meta-analyses and NMAs were performed for direct and indirect evidence.

RESULTS

A total of 22 studies were included in this NMA. The highest effects for improvement in oxygen uptake scores were for continuous, moderate-intensity endurance exercise versus a control (effect size [ES]: 1.17; 95% CI 0.59 to 1.74), followed by continuous, high-intensity endurance exercise versus a control (ES: 0.47; 95% CI 0.08 to 0.85), and combined exercise versus a control (ES: 0.41; 95% CI 0.18 to 0.64).

CONCLUSIONS

Continuous, moderate-intensity endurance exercise should be considered the most effective strategy to improve oxygen uptake in people with COPD, followed by continuous, high-intensity endurance exercise and combined exercise. Due to the importance of VO2 as a predictor of quality of life and mortality in people with COPD, it is essential to include its assessment in clinical guidelines and to include the most effective physical activity interventions to improve it.

TRIAL REGISTRATION

PROSPERO database: CRD42023425893.

Mitochondrial damage-associated molecular patterns in chronic obstructive pulmonary disease: Pathogenetic mechanism and therapeutic target

Chronic obstructive pulmonary disease (COPD) is a common inflammatory airway disease characterized by enhanced inflammation. Recent studies suggest that mitochondrial damage-associated molecular patterns (DAMPs) may play an important role in the regulation of inflammation and are involved in a serial of inflammatory diseases, and they may also be involved in COPD. This review highlights the potential role of mitochondrial DAMPs during COPD pathogenesis and discusses the therapeutic potential of targeting mitochondrial DAMPs and their related signaling pathways and receptors for COPD. Research progress on mitochondrial DAMPs may enhance our understanding of COPD inflammation and provide novel therapeutic targets.

Targeting the mitochondria in chronic respiratory diseases

Mitochondria are one of the basic essential components for eukaryotic life survival. It is also the source of respiratory ATP. Recently published studies have demonstrated that mitochondria may have more roles to play aside from energy production. There is an increasing body of evidence which suggest that mitochondrial activities involved in normal and pathological states contribute to significant impact to the lung airway morphology and epithelial function in respiratory diseases such as asthma, COPD, and lung cancer. This review summarizes the pathophysiological pathways involved in asthma, COPD, lung cancer and highlights potential treatment strategies that target the malfunctioning mitochondria in such ailments. Mitochondria are responsive to environmental stimuli such as infection, tobacco smoke, and inflammation, which are essential in the pathogenesis of respiratory diseases. They may affect mitochondrial shape, protein production and ultimately cause dysfunction. The impairment of mitochondrial function has downstream impact on the cytosolic components, calcium control, response towards oxidative stress, regulation of genes and proteins and metabolic activities. Several novel compounds and alternative medicines that target mitochondria in asthma and chronic lung diseases have been discussed here. Moreover, mitochondrial enzymes or proteins that may serve as excellent therapeutic targets in COPD are also covered. The role of mitochondria in respiratory diseases is gaining much attention and mitochondria-based treatment strategies and personalized medicine targeting the mitochondria may materialize in the near future. Nevertheless, more in-depth studies are urgently needed to validate the advantages and efficacy of drugs that affect mitochondria in pathological states.

Integrating Mechanisms of Exacerbated Atrophy and Other Adverse Skeletal Muscle Impact in COPD

The normal decline in skeletal muscle mass that occurs with aging is exacerbated in patients with chronic obstructive pulmonary disease (COPD) and contributes to poor health outcomes, including a greater risk of death. There has been controversy about the causes of this exacerbated muscle atrophy, with considerable debate about the degree to which it reflects the very sedentary nature of COPD patients vs. being precipitated by various aspects of the COPD pathophysiology and its most frequent proximate cause, long-term smoking. Consistent with the latter view, recent evidence suggests that exacerbated aging muscle loss with COPD is likely initiated by decades of smoking-induced stress on the neuromuscular junction that predisposes patients to premature failure of muscle reinnervation capacity, accompanied by various alterations in mitochondrial function. Superimposed upon this are various aspects of COPD pathophysiology, such as hypercapnia, hypoxia, and inflammation, that can also contribute to muscle atrophy. This review will summarize the available knowledge concerning the mechanisms contributing to exacerbated aging muscle affect in COPD, consider the potential role of comorbidities using the specific example of chronic kidney disease, and identify emerging molecular mechanisms of muscle impairment, including mitochondrial permeability transition as a mechanism of muscle atrophy, and chronic activation of the aryl hydrocarbon receptor in driving COPD muscle pathophysiology.

Skeletal muscle mitochondrial adaptations induced by long-term cigarette smoke exposure

Because patients with chronic obstructive pulmonary disease (COPD) are often physically inactive, it is still unclear whether the lower respiratory capacity in the locomotor muscles of these patients is due to cigarette smoking per se or is secondary to physical deconditioning. Accordingly, the purpose of this study was to examine mitochondrial alterations in the quadriceps muscle of 10 mice exposed to 8 mo of cigarette smoke, a sedentary mouse model of emphysema, and 9 control mice, using immunoblotting, spectrophotometry, and high-resolution respirometry in permeabilized muscle fibers. Mice exposed to smoke displayed a twofold increase in the oxidative stress marker, 4-HNE, (P < 0.05) compared with control mice. This was accompanied by significant decrease in protein expression of UCP3 (65%), ANT (58%), and mitochondrial complexes II-V (∼60%-75%). In contrast, maximal ADP-stimulated respiration with complex I and II substrates (CON: 23.6 ± 6.6 and SMO: 19.2 ± 8.2 ρM·mg-1·s-1) or octanoylcarnitine (CON: 21.8 ± 9.0 and SMO: 16.5 ± 6.6 ρM·mg-1·s-1) measured in permeabilized muscle fibers, as well as citrate synthase activity, were not significantly different between groups. Collectively, our findings revealed that sedentary mice exposed to cigarette smoke for 8 mo, which is typically associated with pulmonary inflammation and emphysema, exhibited a preserved mitochondrial respiratory capacity for various substrates, including fatty acid, in the skeletal muscle. However, the mitochondrial adaptations induced by cigarette smoke favored the development of chronic oxidative stress, which can indirectly contribute to augment the susceptibility to muscle fatigue and exercise intolerance.NEW & NOTEWORTHY It is unclear whether the exercise intolerance and skeletal muscle mitochondrial dysfunction observed in patients with COPD is due to cigarette smoke exposure, per se, or if they are secondary consequences to inactivity. Herein, while long-term exposure to cigarette smoke induces oxidative stress and an altered skeletal muscle phenotype, cigarette smoke does not directly contribute to mitochondrial dysfunction. With this evidence, we demonstrate the critical role of physical inactivity in cigarette smoke-related skeletal muscle dysfunction.

Recent progress in the use of mitochondrial membrane permeability transition pore in mitochondrial dysfunction-related disease therapies

Mitochondria have various cellular functions, including ATP synthesis, calcium homeostasis, cell senescence, and death. Mitochondrial dysfunction has been identified in a variety of disorders correlated with human health. Among the many underlying mechanisms of mitochondrial dysfunction, the opening up of the mitochondrial permeability transition pore (mPTP) is one that has drawn increasing interest in recent years. It plays an important role in apoptosis and necrosis; however, the molecular structure and function of the mPTP have still not been fully elucidated. In recent years, the abnormal opening up of the mPTP has been implicated in the development and pathogenesis of diverse diseases including ischemia/reperfusion injury (IRI), neurodegenerative disorders, tumors, and chronic obstructive pulmonary disease (COPD). This review provides a systematic introduction to the possible molecular makeup of the mPTP and summarizes the mitochondrial dysfunction-correlated diseases and highlights possible underlying mechanisms. Since the mPTP is an important target in mitochondrial dysfunction, this review also summarizes potential treatments, which may be used to inhibit pore opening up via the molecules composing mPTP complexes, thus suppressing the progression of mitochondrial dysfunction-related diseases.

Early detection of skeletal muscle bioenergetic deficit by magnetic resonance spectroscopy in cigarette smoke-exposed mice

Skeletal muscle dysfunction is a common complication and an important prognostic factor in patients with chronic obstructive pulmonary disease (COPD). It is associated with intrinsic muscular abnormalities of the lower extremities, but it is not known whether there is an easy way to predict its presence. Using a mouse model of chronic cigarette smoke exposure, we tested the hypothesis that magnetic resonance spectroscopy allows us to detect muscle bioenergetic deficit in early stages of lung disease. We employed this technique to evaluate the synthesis rate of adenosine triphosphate (ATP) and characterize concomitant mitochondrial dynamics patterns in the gastrocnemius muscle of emphysematous mice. The fibers type composition and citrate synthase (CtS) and cytochrome c oxidase subunit IV (COX4) enzymatic activities were evaluated. We found that the rate of ATP synthesis was reduced in the distal skeletal muscle of mice exposed to cigarette smoke. Emphysematous mice showed a significant reduction in body weight gain, in the cross-sectional area of the total fiber and in the COX4 to CtS activity ratio, due to a significant increase in CtS activity of the gastrocnemius muscle. Taken together, these data support the hypothesis that in the early stage of lung disease, we can detect a decrease in ATP synthesis in skeletal muscle, partly caused by high oxidative mitochondrial enzyme activity. These findings may be relevant to predict the presence of skeletal bioenergetic deficit in the early stage of lung disease besides placing the mitochondria as a potential therapeutic target for the treatment of COPD comorbidities.

Cellular stress responses and dysfunctional Mitochondrial-cellular senescence, and therapeutics in chronic respiratory diseases

The abnormal inflammatory responses due to the lung tissue damage and ineffective repair/resolution in response to the inhaled toxicants result in the pathological changes associated with chronic respiratory diseases. Investigation of such pathophysiological mechanisms provides the opportunity to develop the molecular phenotype-specific diagnostic assays and could help in designing the personalized medicine-based therapeutic approaches against these prevalent diseases. As the central hubs of cell metabolism and energetics, mitochondria integrate cellular responses and interorganellar signaling pathways to maintain cellular and extracellular redox status and the cellular senescence that dictate the lung tissue responses. Specifically, as observed in chronic obstructive pulmonary disease (COPD) and pulmonary fibrosis, the mitochondria-endoplasmic reticulum (ER) crosstalk is disrupted by the inhaled toxicants such as the combustible and emerging electronic nicotine-delivery system (ENDS) tobacco products. Thus, the recent research efforts have focused on understanding how the mitochondria-ER dysfunctions and oxidative stress responses can be targeted to improve inflammatory and cellular dysfunctions associated with these pathologic illnesses that are exacerbated by viral infections. The present review assesses the importance of these redox signaling and cellular senescence pathways that describe the role of mitochondria and ER on the development and function of lung epithelial responses, highlighting the cause and effect associations that reflect the disease pathogenesis and possible intervention strategies.

Is inflammatory signaling involved in disease-related muscle wasting? Evidence from osteoarthritis, chronic obstructive pulmonary disease and type II diabetes

Muscle loss is an important feature that occurs in multiple pathologies including osteoarthritis (OA), chronic obstructive pulmonary disease (COPD) and type II diabetes (T2D). Despite differences in pathogenesis and disease-related complications, there are reasons to believe that some fundamental underlying mechanisms are inherent to the muscle wasting process, irrespective of the pathology. Recent evidence shows that inflammation, either local or systemic, contributes to the modulation of muscle mass and/or muscle strength, via an altered molecular profile in muscle tissue. However, it remains ambiguous to which extent and via which mechanisms inflammatory signaling affects muscle mass in disease. Therefore, the objective of the present review is to discuss the role of inflammation on skeletal muscle anabolism, catabolism and functionality in three pathologies that are characterized by an eventual loss in muscle mass (and muscle strength), i.e. OA, COPD and T2D. In OA and COPD, most rodent models confirmed that systemic (COPD) or muscle (OA) inflammation directly induces muscle loss or muscle dysfunctionality. However, in a patient population, the association between inflammation and muscular maladaptations are more ambiguous. For example, in T2D patients, systemic inflammation is associated with muscle loss whereas in OA patients this link has not consistently been established. T2D rodent models revealed that increased levels of advanced glycation end-products (AGEs) and a decreased mTORC1 activation play a key role in muscle atrophy, but it remains to be elucidated whether AGEs and mTORC1 are interconnected and contribute to muscle loss in T2D patients. Generally, if any, associations between inflammation and muscle are mainly based on observational and cross-sectional data. There is definitely a need for longitudinal evidence through well-powered randomized control trials that take into account confounders such as age, disease-phenotypes, comorbidities, physical (in) activity etc. This will allow to improve our understanding of the complex interaction between inflammatory signaling and muscle mass loss and hence contribute to the development of therapeutic strategies to combat muscle wasting in these diseases.

Human Cachexia Induces Changes in Mitochondria, Autophagy and Apoptosis in the Skeletal Muscle

Cachexia is a wasting syndrome characterized by the continuous loss of skeletal muscle mass due to imbalance between protein synthesis and degradation, which is related with poor prognosis and compromised quality of life. Dysfunctional mitochondria are associated with lower muscle strength and muscle atrophy in cancer patients, yet poorly described in human cachexia. We herein investigated mitochondrial morphology, autophagy and apoptosis in the skeletal muscle of patients with gastrointestinal cancer-associated cachexia (CC), as compared with a weight-stable cancer group (WSC). CC showed prominent weight loss and increased circulating levels of serum C-reactive protein, lower body mass index and decreased circulating hemoglobin, when compared to WSC. Electron microscopy analysis revealed an increase in intermyofibrillar mitochondrial area in CC, as compared to WSC. Relative gene expression of Fission 1, a protein related to mitochondrial fission, was increased in CC, as compared to WSC. LC3 II, autophagy-related (ATG) 5 and 7 essential proteins for autophagosome formation, presented higher content in the cachectic group. Protein levels of phosphorylated p53 (Ser46), activated caspase 8 (Asp384) and 9 (Asp315) were also increased in the skeletal muscle of CC. Overall, our results demonstrate that human cancer-associated cachexia leads to exacerbated muscle-stress response that may culminate in muscle loss, which is in part due to disruption of mitochondrial morphology, dysfunctional autophagy and increased apoptosis. To the best of our knowledge, this is the first report showing quantitative morphological alterations in skeletal muscle mitochondria in cachectic patients.

Bufei Jianpi Granules Reduce Quadriceps Muscular Cell Apoptosis by Improving Mitochondrial Function in Rats with Chronic Obstructive Pulmonary Disease

Background

Cell apoptosis is an important mechanism underlying skeletal muscle dysfunction in chronic obstructive pulmonary disease (COPD) patients, and mitochondrial dysfunction is recognized as a central aspect contributing to skeletal muscle deterioration. Bufei Jianpi granules have been confirmed effective for improving motor function in COPD patients, but the specific mechanism for this improved function remains unknown. This study explored the mechanisms by which Bufei Jianpi granules improve cell apoptosis and mitochondrial dysfunction in COPD.

Methods

Sprague-Dawley rats were randomized into control, model, Bufei Jianpi, and aminophylline groups. A stable COPD rat model was induced with respective repeated cigarette smoke inhalation and intragastric bacterial infection, and rats were sacrificed after 20 weeks; the quadriceps muscle was harvested from each rat. Skeletal muscle mitochondria were extracted for measurements of mitochondrial membrane potential (MMP) and mitochondrial permeability transition pore openings (mPTPs). ATP levels were determined with a firefly luciferase-based ATP assay kit. The rates of cell apoptosis were determined by the transferase-mediated deoxyuridine triphosphate-biotin nick end labeling (TUNEL) method. Cyto C and caspase-3 mRNA and protein levels were measured by qPCR and western blotting.

Results

ATP, MMP, and mPTPs were markedly decreased in COPD rats, while cell apoptosis, caspase-3, and Cyto C were increased (P<0.01). All aforementioned parameters were improved in treatment groups (P<0.05). ATP, MMP, and mPTPs were significantly higher in the Bufei Jianpi group than in the aminophylline group, while cell apoptosis, caspase-3, and Cyto C were lower (P<0.05).

Conclusions

Bufei Jianpi granules can inhibit mitochondrial dysfunction and cell apoptosis in peripheral muscles, which might be the mechanism involved in improving skeletal muscle function in COPD patients.

Role of accelerated aging in limb muscle wasting of patients with COPD

Purpose

Skeletal muscle wasting is an independent predictor of health-related quality of life and survival in patients with COPD, but the complexity of molecular mechanisms associated with this process has not been fully elucidated. We aimed to determine whether an impaired ability to repair DNA damage contributes to muscle wasting and the accelerated aging phenotype in patients with COPD.

Patients and methods

The levels of phosphorylated H2AX (γH2AX), a molecule that promotes DNA repair, were assessed in vastus lateralis biopsies from 10 COPD patients with low fat-free mass index (FFMI; COPD_L), 10 with preserved FFMI and 10 age- and gender-matched healthy controls. A panel of selected markers for cellular aging processes (CDKN2A/p16^ink4a, SIRT1, SIRT6, and telomere length) were also assessed. Markers of oxidative stress and cell damage and a panel of pro-inflammatory and anti-inflammatory cytokines were evaluated. Markers of muscle regeneration and apoptosis were also measured.

Results

We observed a decrease in γH2AX expression in COPD_L, which occurred in association with a tendency to increase in CDKN2A/p16^ink4a, and a significant decrease in SIRT1 and SIRT6 protein levels. Cellular damage and muscle inflammatory markers were also increased in COPD_L.

Conclusion

These data are in keeping with an accelerated aging phenotype as a result of impaired DNA repair and dysregulation of cellular homeostasis in the muscle of COPD_L. These data indicate cellular degeneration via stress-induced premature senescence and associated inflammatory responses abetted by the senescence-associated secretory phenotype and reflect an increased expression of markers of oxidative stress and inflammation.

Muscle atrophy in chronic obstructive pulmonary disease: molecular basis and potential therapeutic targets

Patients with chronic obstructive pulmonary disease (COPD) experience several systemic manifestations such skeletal muscle dysfunction with and without muscle mass loss. Moreover, frequent comorbidities such as nutritional abnormalities, heart failure, and pulmonary hypertension, which are frequently associated with COPD may further contribute to skeletal muscle mass loss and dysfunction. Muscle dysfunction impairs the patients' exercise capacity and quality of life as daily life activities may be hampered by this problem. Importantly, impaired muscle function and mass loss have been shown to impact negatively on the patients' prognosis and survival in several studies. Thus, this is a major clinical problem that deserves special attention in clinical settings. During the course of exacerbations muscle mass loss takes place, hence aggravating muscle status and performance even after hospital discharge, especially in the frequently exacerbator patients. Several factors and biological mechanisms are involved in the etiology of COPD muscle dysfunction. The biological mechanisms identified so far offer a niche for therapeutic interventions in the patients. In the current review, a general overview of the most relevant etiologic factors and their target biological mechanisms through which muscle mass loss and dysfunction take place in both the respiratory and lower limb muscles in COPD patients is provided. We conclude that more clinical research is still needed targeted to test several therapeutic interventions. Given its prognostic value, the assessment of skeletal muscle dysfunction should be included in the routine evaluation of patients with chronic respiratory disorders and in critical care settings.

Tandem mass tags labeled quantitative proteomics to study the effect of tobacco smoke exposure on the rat lung

BACKGROUND

The causal link between tobacco smoke exposure (TSE) and numerous severe respiratory system diseases (RSD), including chronic bronchitis, chronic obstructive pulmonary disease, and lung cancer, is well established. However, the pathogenesis of TSE-induced RSD remains incompletely understood. This research aims to detect the pathogenetic mechanisms and potential therapeutic targets of TSE-induced RSD.

METHODS

This study employed TSE model which rats were exposed to a concentration of 60% tobacco smoke in a toxicant exposure system for four weeks. Tandem mass tags (TMT) labeled quantitative proteomics combined with off-line high pH reversed-phase fractionation, and nano-liquid chromatography-mass spectrometry method (off-line high pH RPF-nano-LC-MS/MS) were adopted to detect differentially expressed proteins (DEPs) in the lung tissues of the TSE model rats and to compare them with those in control. The accuracy of the results was verified by western blot.

RESULTS

Compared with the control group, 33 proteins in the TSE model group's lung tissues showed significant differential expression. Analysis based on the Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways indicated that, several biological pathways, such as the steroid biosynthesis pathway, were involved and played significant roles in the pathogenesis of the experimental group's TSE.

CONCLUSIONS

These findings make a crucial contribution to the search for a comprehensive understanding of TSE-induced RSD's pathogenesis, and furthermore provide guidance for the diagnosis and treatment of TSE-induced RSD.

Frailty and maximal exercise capacity in adult lung transplant candidates

BACKGROUND

Frail lung transplant candidates are more likely to be delisted or die without receiving a transplant. Further knowledge of what frailty represents in this population will assist in developing interventions to prevent frailty from developing. We set out to determine whether frail lung transplant candidates have reduced exercise capacity independent of disease severity and diagnosis.

METHODS

Sixty-eight adult lung transplant candidates underwent cardiopulmonary exercise testing (CPET) and a frailty assessment (Fried's Frailty Phenotype (FFP)). Primary outcomes were peak workload and peak aerobic capacity (V˙O₂). We used linear regression to adjust for age, gender, diagnosis, and lung allocation score (LAS).

RESULTS

The mean ± SD age was 57 ± 11 years, 51% were women, 57% had interstitial lung disease, 32% had chronic obstructive pulmonary disease, 11% had cystic fibrosis, and the mean LAS was 40.2 (range 19.2-94.5). In adjusted models, peak workload decreased by 10 W (95% CI 4.7 to 14.6) and peak V˙O₂ decreased by 1.8 mL/kg/min (95% CI 0.6 to 2.9) per 1 unit increment in FFP score. After adjustment, exercise tolerance was 38 W lower (95% CI 18.4 to 58.1) and peak V˙O₂ was 8.5 mL/kg/min lower (95% CI 3.3 to 13.7) among frail participants compared to non-frail participants. Frailty accounted for 16% of the variance (R²) of watts and 19% of the variance of V˙O₂ in adjusted models.

CONCLUSION

Frailty contributes to reduced exercise capacity among lung transplant candidates independent of disease severity.

Mitochondrial Dysfunction in Airway Disease

There is increasing appreciation that mitochondria serve cellular functions beyond oxygen sensing and energy production. Accordingly, it has become important to explore noncanonical roles of mitochondria in normal and pathophysiological processes that influence airway structure and function in the context of diseases such as asthma and COPD. Mitochondria can sense upstream processes such as inflammation, infection, tobacco smoke, and environmental insults important in these diseases and in turn can respond to such stimuli through altered mitochondrial protein expression, structure, and resultant dysfunction. Conversely, mitochondrial dysfunction has downstream influences on cytosolic and mitochondrial calcium regulation, airway contractility, gene and protein housekeeping, responses to oxidative stress, proliferation, apoptosis, fibrosis, and certainly metabolism, which are all key aspects of airway disease pathophysiology. Indeed, mitochondrial dysfunction is thought to play a role even in normal processes such as aging and senescence and in conditions such as obesity, which impact airway diseases. Thus, understanding how mitochondrial structure and function play central roles in airway disease may be critical for the development of novel therapeutic avenues targeting dysfunctional mitochondria. In this case, it is likely that mitochondria of airway epithelium, smooth muscle, and fibroblasts play differential roles, consistent with their contributions to disease biology, underlining the challenge of targeting a ubiquitous cellular element of existential importance. This translational review summarizes the current state of understanding of mitochondrial processes that play a role in airway disease pathophysiology and identifying areas of unmet research need and opportunities for novel therapeutic strategies.

The Role of Mitochondria and Oxidative/Antioxidative Imbalance in Pathobiology of Chronic Obstructive Pulmonary Disease

Chronic obstructive pulmonary disease (COPD) is a common preventable and treatable disease, characterized by persistent airflow limitation that is usually progressive and associated with an enhanced chronic inflammatory response in the airways and the lung to noxious particles or gases. The major risk factor of COPD, which has been proven in many studies, is the exposure to cigarette smoke. However, it is 15-20% of all smokers who develop COPD. This is why we should recognize the pathobiology of COPD as involving a complex interaction between several factors, including genetic vulnerability. Oxidant-antioxidant imbalance is recognized as one of the significant factors in COPD pathogenesis. Numerous exogenous and endogenous sources of ROS are present in pathobiology of COPD. One of endogenous sources of ROS is mitochondria. Although leakage of electrons from electron transport chain and forming of ROS are the effect of physiological functioning of mitochondria, there are various intra- and extracellular factors which may increase this amount and significantly contribute to oxidative-antioxidative imbalance. With the coexistence with impaired antioxidant defence, all these issues lead to oxidative and carbonyl stress. Both of these states play a significant role in pathobiology of COPD and may account for development of major comorbidities of this disease.

Molecular and biological pathways of skeletal muscle dysfunction in chronic obstructive pulmonary disease

Chronic obstructive pulmonary disease (COPD) will be a major leading cause of death worldwide in the near future. Weakness and atrophy of the quadriceps are associated with a significantly poorer prognosis and increased mortality in COPD. Despite that skeletal muscle dysfunction may affect both respiratory and limb muscle groups in COPD, the latter are frequently more severely affected. Therefore, muscle dysfunction in COPD is a common systemic manifestation that should be evaluated on routine basis in clinical settings. In the present review, several aspects of COPD muscle dysfunction are being reviewed, with special emphasis on the underlying biological mechanisms. Figures on the prevalence of COPD muscle dysfunction and the most relevant etiologic contributors are also provided. Despite that ongoing research will shed light into the contribution of additional mechanisms to COPD muscle dysfunction, current knowledge points toward the involvement of a wide spectrum of cellular and molecular events that are differentially expressed in respiratory and limb muscles. Such mechanisms are thoroughly described in the article. The contribution of epigenetic events on COPD muscle dysfunction is also reviewed. We conclude that in view of the latest discoveries, from now, on new avenues of research should be designed to specifically target cellular mechanisms and pathways that impair muscle mass and function in COPD using pharmacological strategies and/or exercise training modalities.

Epigenetics and muscle dysfunction in chronic obstructive pulmonary disease

Chronic obstructive pulmonary disease (COPD) is a common, preventable, and treatable disease and a major leading cause of morbidity and mortality worldwide. In COPD, comorbidities, acute exacerbations, and systemic manifestations negatively influence disease severity and progression regardless of the respiratory condition. Skeletal muscle dysfunction, which is one of the commonest systemic manifestations in patients with COPD, has a tremendous impact on their exercise capacity and quality of life. Several pathophysiological and molecular underlying mechanisms including epigenetics (the process whereby gene expression is regulated by heritable mechanisms that do not affect DNA sequence) have been shown to participate in the etiology of COPD muscle dysfunction. The epigenetic modifications identified so far in cells include DNA methylation, histone acetylation and methylation, and noncoding RNAs such as microRNAs. Herein, we first review the role of epigenetic mechanisms in muscle development and adaptation to environmental factors in several models. Moreover, the epigenetic events reported so far to be potentially involved in muscle dysfunction and mass loss of patients with COPD are also discussed. Furthermore, the different expression profile of several muscle-enriched microRNAs in the diaphragm and vastus lateralis muscles of patients with COPD are also reviewed from results recently obtained in our group. The role of protein hyperacetylation in enhanced muscle protein catabolism of limb muscles is also discussed. Future research should focus on the full elucidation of the triggers of epigenetic mechanisms and their specific downstream biological pathways in COPD muscle dysfunction and wasting.

Targeting pro-resolution pathways to combat chronic inflammation in COPD

Chronic obstructive pulmonary disease (COPD) is an inflammatory lung condition that is associated with irreversible airflow obstruction as a consequence of small airways disease, excessive mucus production and emphysema. Paradoxically, excessive inflammation fails to control microbial pathogens that not only colonise COPD airways, but also trigger acute exacerbations, which markedly increase inflammation underlying host tissue damage. Excessive production of leukocyte mobilising cytokines such as CXCL8 (IL-8) and leukotriene B4 (LTB4) in response to environmental stimuli (cigarette smoke and microbial products) are thought to maintain chronic inflammation, in conjunction with inefficient macrophage clearance of microbes and apoptotic neutrophils. In this perspective, we discuss an alternative view on why inflammation persists with a focus on why pro-resolution mediators such as lipoxin A4 (LXA4), D-series resolving and Annexin A1 fail to effectively switch off inflammation in COPD. These pro-resolving mediators converge on the G-protein coupled receptor, ALX/FPR2. This receptor is particularly relevant to COPD as the complex milieu of exogenous and host-derived mediators within the inflamed airways include agonists that potently activate ALX/FPR2, including Serum Amyloid A (SAA) and the cathelicidin, LL-37. There is emerging evidence to suggest that ALX/FPR2 can exist in alternative receptor conformations in an agonist-biased manner, which facilitates alternate functional receptor behaviors. Hence, the development of more stable pro-resolving analogs provides therapeutic opportunities to address ALX/FPR2 conformations to counteract pathogenic signaling and promote non-phlogistic clearance pathways essential for resolution of inflammation.

Oxygen pathway modeling estimates high reactive oxygen species production above the highest permanent human habitation

The production of reactive oxygen species (ROS) from the inner mitochondrial membrane is one of many fundamental processes governing the balance between health and disease. It is well known that ROS are necessary signaling molecules in gene expression, yet when expressed at high levels, ROS may cause oxidative stress and cell damage. Both hypoxia and hyperoxia may alter ROS production by changing mitochondrial Po2 (PmO2). Because PmO2 depends on the balance between O2 transport and utilization, we formulated an integrative mathematical model of O2 transport and utilization in skeletal muscle to predict conditions to cause abnormally high ROS generation. Simulations using data from healthy subjects during maximal exercise at sea level reveal little mitochondrial ROS production. However, altitude triggers high mitochondrial ROS production in muscle regions with high metabolic capacity but limited O2 delivery. This altitude roughly coincides with the highest location of permanent human habitation. Above 25,000 ft., more than 90% of exercising muscle is predicted to produce abnormally high levels of ROS, corresponding to the "death zone" in mountaineering.

Ageing and the border between health and disease

Ageing is associated with a progressive degeneration of the tissues, which has a negative impact on the structure and function of vital organs and is among the most important known risk factors for most chronic diseases. Since the proportion of the world's population aged >60 years will double in the next four decades, this will be accompanied by an increased incidence of chronic age-related diseases that will place a huge burden on healthcare resources. There is increasing evidence that many chronic inflammatory diseases represent an acceleration of the ageing process. Chronic pulmonary diseases represents an important component of the increasingly prevalent multiple chronic debilitating diseases, which are a major cause of morbidity and mortality, particularly in the elderly. The lungs age and it has been suggested that chronic obstructive pulmonary disease (COPD) is a condition of accelerated lung ageing and that ageing may provide a mechanistic link between COPD and many of its extrapulmonary effects and comorbidities. In this article we will describe the physiological changes and mechanisms of ageing, with particular focus on the pulmonary effects of ageing and how these may be relevant to the development of COPD and its major extrapulmonary manifestations.

Obesity, metabolic syndrome, and airway disease: a bioenergetic problem?

Multiple studies have determined that obesity increases asthma risk or severity. Metabolic changes of obesity, such as diabetes or insulin resistance, are associated with asthma and poorer lung function. Insulin resistance is also found to increase asthma risk independent of body mass. Conversely, asthma is associated with abnormal glucose and lipid metabolism, insulin resistance, and obesity. Here we review our current understanding of how dietary and lifestyle factors lead to changes in mitochondrial metabolism and cellular bioenergetics, inducing various components of the cardiometabolic syndrome and airway disease.

An official American Thoracic Society/European Respiratory Society statement: update on limb muscle dysfunction in chronic obstructive pulmonary disease

BACKGROUND

Limb muscle dysfunction is prevalent in chronic obstructive pulmonary disease (COPD) and it has important clinical implications, such as reduced exercise tolerance, quality of life, and even survival. Since the previous American Thoracic Society/European Respiratory Society (ATS/ERS) statement on limb muscle dysfunction, important progress has been made on the characterization of this problem and on our understanding of its pathophysiology and clinical implications.

PURPOSE

The purpose of this document is to update the 1999 ATS/ERS statement on limb muscle dysfunction in COPD.

METHODS

An interdisciplinary committee of experts from the ATS and ERS Pulmonary Rehabilitation and Clinical Problems assemblies determined that the scope of this document should be limited to limb muscles. Committee members conducted focused reviews of the literature on several topics. A librarian also performed a literature search. An ATS methodologist provided advice to the committee, ensuring that the methodological approach was consistent with ATS standards.

RESULTS

We identified important advances in our understanding of the extent and nature of the structural alterations in limb muscles in patients with COPD. Since the last update, landmark studies were published on the mechanisms of development of limb muscle dysfunction in COPD and on the treatment of this condition. We now have a better understanding of the clinical implications of limb muscle dysfunction. Although exercise training is the most potent intervention to address this condition, other therapies, such as neuromuscular electrical stimulation, are emerging. Assessment of limb muscle function can identify patients who are at increased risk of poor clinical outcomes, such as exercise intolerance and premature mortality.

CONCLUSIONS

Limb muscle dysfunction is a key systemic consequence of COPD. However, there are still important gaps in our knowledge about the mechanisms of development of this problem. Strategies for early detection and specific treatments for this condition are also needed.

Mitochondria in lung diseases

Mitochondria are autonomous cellular organelles that oversee a variety of functions such as metabolism, energy production, calcium buffering and cell fate determination. Regulation of their morphology and diverse activities beyond energy production are being recognized as playing major roles in cellular health and dysfunction. This review is aimed at summarizing what is known regarding mitochondrial contributions to pathogenesis of lung diseases. Emphasis is given to understanding the importance of structural and functional aspects of mitochondria in both normal cellular function (based on knowledge from other cell types) and in development and modulation of lung diseases such as asthma, chronic obstructive pulmonary disease, cystic fibrosis and cancer. Emerging techniques that allow examination of mitochondria, and potential strategies to target mitochondria in the treatment of lung diseases are also discussed.

Treating neutrophilic inflammation in COPD by targeting ALX/FPR2 resolution pathways

Neutrophilic inflammation persists in COPD despite best current therapies and it is particularly resistant to inhaled glucocorticosteroids. Persistent neutrophil activation not only contributes to matrix breakdown, but can maintain inflammation through the release of endogenous damage associated molecule patterns (DAMPs). Inhibiting excessive neutrophilic inflammation is challenging as many pathogen recognition receptors can initiate migration and the targeting of downstream signaling molecules may compromise essential host defense mechanisms. Here, we discuss new strategies to combat this inflammation in COPD by focusing on the anti-inflammatory role of ALX/FPR2 receptors. ALX/FPR2 is a promiscuous G-protein coupled receptor (GPCR) responding to lipid and peptide agonists that can either switch on acute inflammation or promote resolution of inflammation. We highlight this receptor as an emerging target in the pathogenesis of COPD because known ALX/FPR2 endogenous agonists are enriched in COPD. Serum Amyloid A (SAA) has recently been discovered to be abundantly expressed in COPD and is a potent ALX/FPR2 agonist that unlike almost all other inflammatory chemoattractants, is induced by glucocorticosteroids. SAA not only initiates lung inflammation via ALX/FPR2 but can allosterically modify this receptor so that it no longer transduces pro-resolving signals from endogenous lipoxins that would otherwise promote tissue healing. We propose that there is an imbalance in endogenous and microbial ALX/FPR2 receptor agonists in the inflamed COPD lung environment that oppose protective anti-inflammatory and pro-resolution pathways. These insights open the possibility of targeting ALX/FPR2 receptors using synthetic agonists to resolve persistent neutrophilic inflammation without compromising essential host defense mechanisms.

Pathophysiology of muscle dysfunction in COPD

Muscle dysfunction often occurs in patients with chronic obstructive pulmonary disease (COPD) and may involve both respiratory and locomotor (peripheral) muscles. The loss of strength and/or endurance in the former can lead to ventilatory insufficiency, whereas in the latter it limits exercise capacity and activities of daily life. Muscle dysfunction is the consequence of complex interactions between local and systemic factors, frequently coexisting in COPD patients. Pulmonary hyperinflation along with the increase in work of breathing that occur in COPD appear as the main contributing factors to respiratory muscle dysfunction. By contrast, deconditioning seems to play a key role in peripheral muscle dysfunction. However, additional systemic factors, including tobacco smoking, systemic inflammation, exercise, exacerbations, nutritional and gas exchange abnormalities, anabolic insufficiency, comorbidities and drugs, can also influence the function of both respiratory and peripheral muscles, by inducing modifications in their local microenvironment. Under all these circumstances, protein metabolism imbalance, oxidative stress, inflammatory events, as well as muscle injury may occur, determining the final structure and modulating the function of different muscle groups. Respiratory muscles show signs of injury as well as an increase in several elements involved in aerobic metabolism (proportion of type I fibers, capillary density, and aerobic enzyme activity) whereas limb muscles exhibit a loss of the same elements, injury, and a reduction in fiber size. In the present review we examine the current state of the art of the pathophysiology of muscle dysfunction in COPD.

Mitochondrial dysfunction and therapeutic approaches in respiratory and limb muscles of cancer cachectic mice

NEW FINDINGS

What is the central question of this study? We explored whether experimental cancer-induced cachexia may alter mitochondrial respiratory chain (MRC) complexes and oxygen uptake in respiratory and peripheral muscles,and whether signalling pathways, proteasome and oxidative stress influence that process. What is the main finding and what is its importance? In cancer cachectic mice, MRC complexes and oxygen consumption were decreased in the diaphragm and gastrocnemius. Blockade of nuclear factor-κB and mitogen-activated protein kinase actions partly restored the muscle mass and force and corrected the MRC dysfunction,while concomitantly reducing tumour burden. Antioxidants improved mitochondrial oxygen consumption without eliciting effects on the loss of muscle mass and force or the tumour size,whereas bortezomib reduced tumour burden without influencing muscle mass and strength or MRC function. Abnormalities in mitochondrial content, morphology and function have been reported in several muscle-wasting conditions. We specifically explored whether experimental cancer-induced cachexia may alter mitochondrial respiratory chain (MRC) complexes and oxygen uptake in respiratory and peripheral muscles, and whether signalling pathways, proteasomes and oxidative stress may influence that process. We evaluated complex I, II and IV enzyme activities (specific activity assays) and MRC oxygen consumption (polarographic measurements) in diaphragm and gastrocnemius of cachectic mice bearing the LP07 lung tumour, with and without treatment with N-acetylcysteine, bortezomib and nuclear factor-κB (sulfasalazine) and mitogen-activated protein kinases (MAPK, U0126) inhibitors (n = 10 per group for all groups). Whole-body and muscle weights and limb muscle force were also assessed in all rodents at baseline and after 1 month. Compared with control animals, cancer cachectic mice showed a significant reduction in body weight gain, smaller sizes of the diaphragm and gastrocnemius, lower muscle strength, decreased activity of complexes I, II and IV and decreased oxygen consumption in both muscles. Blockade of nuclear factor-κB and MAPK actions restored muscle mass and force and corrected the MRC dysfunction in both muscles, while partly reducing tumour burden. Antioxidants improved mitochondrial oxygen uptake without eliciting significant effects on the loss of muscle mass and force or tumour size, whereas the proteasome inhibitor reduced tumour burden without significantly influencing muscle mass and strength or mitochondrial function. In conclusion, nuclear factor-κB and MAPK signalling pathways modulate muscle mass and performance and MRC function of respiratory and limb muscles in this model of experimental cancer cachexia, thus offering targets for therapeutic intervention.

Metabolic derangements in COPD muscle dysfunction

Mitochondrial muscle alterations are common in patients with chronic obstructive pulmonary disease (COPD) and manifest mainly as decreased oxidative capacity and excessive production of reactive oxygen species (ROS). The significant loss of oxidative capacity observed in the quadriceps of COPD patients is mainly due to reduced mitochondrial content in the fibers, a finding consistent with the characteristic loss of type I fibers observed in that muscle. Decreased oxidative capacity does not directly limit maximum performance; however, it is associated with increased lactate production at lower exercise intensity and reduced endurance. Since type I fiber atrophy does not occur in respiratory muscles, the loss of such fibers in the quadriceps could be to the result of disuse. In contrast, excessive production of ROS and oxidative stress are observed in both the respiratory muscles and the quadriceps of COPD patients. The causes of increased ROS production are not clear, and a number of different mechanisms can play a role. Several mitochondrial alterations in the quadriceps of COPD patients are similar to those observed in diabetic patients, thus suggesting a role for muscle alterations in this comorbidity. Amino acid metabolism is also altered. Expression of peroxisome proliferator-activated receptor-γ coactivator-1α mRNA is low in the quadriceps of COPD patients, which could also be a consequence of type I fiber loss; nevertheless, its response to exercise is not altered. Patterns of muscle cytochrome oxidase gene activation after training differ between COPD patients and healthy subjects, and the profile is consistent with hypoxic stress, even in nonhypoxic patients.

Abnormal lung aging in chronic obstructive pulmonary disease and idiopathic pulmonary fibrosis

Aging is a natural process characterized by progressive functional impairment and reduced capacity to respond appropriately to environmental stimuli and injury. The incidence of two common chronic respiratory diseases (chronic obstructive pulmonary disease [COPD] and idiopathic pulmonary fibrosis [IPF]) increases with advanced age. It is plausible, therefore, that abnormal regulation of the mechanisms of normal aging may contribute to the pathobiology of both COPD and IPF. This review discusses the available evidence supporting a number of aging mechanisms, including oxidative stress, telomere length regulation, cellular and immunosenescence, as well as changes in a number of antiaging molecules and the extracellular matrix, which are abnormal in COPD and/or IPF. A better understanding of these abnormalities may help in the design of novel and better therapeutic interventions for these patients.

Site of mitochondrial reactive oxygen species production in skeletal muscle of chronic obstructive pulmonary disease and its relationship with exercise oxidative stress

Exercise triggers skeletal muscle oxidative stress in patients with chronic obstructive pulmonary disease (COPD). The objective of this research was to study the specific sites of reactive oxygen species (ROS) production in mitochondria isolated from skeletal muscle of patients with COPD and its relationship with local oxidative stress induced by exercise. Vastus lateralis biopsies were obtained in 16 patients with COPD (66 ± 10 yr; FEV(1), 54 ± 12% ref) and in 14 control subjects with normal lung function who required surgery because of lung cancer (65 ± 7 yr; FEV(1), 91 ± 14% ref) at rest and after exercise. In these biopsies we isolated mitochondria and mitochondrial membrane fragments and determined in vitro mitochondrial oxygen consumption (Mit$$\stackrel{.}{\hbox{ V }}$$o(2)) and ROS production before and after inhibition of complex I (rotenone), complex II (stigmatellin), and complex III (antimycin-A). We related the in vitro ROS production during state 3 respiration), which mostly corresponds to the mitochondria respiratory state during exercise, with skeletal muscle oxidative stress after exercise, as measured by thiobarbituric acid reactive substances.State 3 Mit$$\stackrel{.}{\hbox{ V }}$$o(2) was similar in patients with COPD and control subjects (191 ± 27 versus 229 ± 46 nmol/min/mg; P = 0.058), whereas H(2)O(2) production was higher in the former (147 ± 39 versus 51 ± 8 pmol/mg/h; P < 0.001). The addition of complexI, II, and III inhibitors identify complex III as the main site of H(2)O(2) release by mitochondria in patients with COPD and in control subjects. The mitochondrial production of H(2)O(2) in state 3 respiration was related (r = 0.69; P < 0.001) to postexercise muscle thiobarbituric acid reactive substance levels. Our results show that complex III is the main site of the enhanced mitochondrial H(2)O(2) production that occurs in skeletal muscle of patients with COPD, and the latter appears to contribute to muscle oxidative damage.

Altered mitochondrial regulation in quadriceps muscles of patients with COPD

Evidence exists for locomotor muscle impairment in patients with chronic obstructive pulmonary disease (COPD), including fiber type alterations and reduced mitochondrial oxidative capacity. In this study high-resolution respirometry was used to quantify oxygen flux in permeabilized fibres from biopsies of the vastus lateralis muscle in patients with COPD and compared to healthy control subjects. The main findings of this study were that (i) routine state 2 respiration was higher in COPD; (ii) state 3 respiration in the presence of ADP was similar in both groups with substrate supply of electrons to complex I (COPD 38·28 ± 3·58 versus control 42·85 ± 3·10 pmol s(-1) mg tissue(-1) ), but O(2) flux with addition of succinate was lower in COPD patients (COPD 63·72 ± 6·33 versus control 95·73 ± 6·53 pmol s(-1) mg tissue(-1) ); (iii) excess capacity of cytochrome c oxidase in COPD patients was only ~50% that of control subjects. These results indicate that quadriceps muscle mitochondrial function is altered in patients with COPD. The regulatory mechanisms underlying these functional abnormalities remain to be uncovered.

Structural and functional changes of peripheral muscles in chronic obstructive pulmonary disease patients

PURPOSE OF REVIEW

The purpose of this review is to identify new advances in our understanding of skeletal muscle dysfunction in patients with chronic obstructive pulmonary disease (COPD).

RECENT FINDINGS

Recent studies have confirmed the relevance of muscle dysfunction as an independent prognosis factor in COPD. Animal studies have shed light on the molecular mechanisms governing skeletal muscle hypertrophy/atrophy. Recent evidence in patients with COPD highlighted the contribution of protein breakdown and mitochondrial dysfunction as pathogenic mechanisms leading to muscle dysfunction in these patients.

SUMMARY

COPD is a debilitating disease impacting negatively on health status and the functional capacity of patients. COPD goes beyond the lungs and incurs significant systemic effects among which muscle dysfunction/wasting is one of the most important. Muscle dysfunction is a prominent contributor to exercise limitation, healthcare utilization and an independent predictor of morbidity and mortality. Gaining more insight into the molecular mechanisms leading to muscle dysfunction/wasting is key for the development of new and tailored therapeutic strategies to tackle skeletal muscle dysfunction/wasting in COPD patients.