Loss of quadriceps muscle oxidative phenotype and decreased endurance in patients with mild-to-moderate COPD

Effects and long-term outcomes of endurance versus resistance training as an adjunct to standard medication in patients with stable COPD: a multicenter randomized trial

BACKGROUND

Comparisons between endurance training (ET) and resistance training (RT) have produced equivocal findings in chronic obstructive pulmonary disease (COPD) patients. The purpose of our study is to investigate the effectiveness and long-term outcomes of adding ET and RT to conventional medical treatment in patients with COPD. A secondary objective is to investigate the clinical improvements resulting from exercise training in patients with different disease severities.

METHODS

The study was a multicenter, prospective trial in people with stable COPD. The cohort was randomized to three groups: individualized medical treatment group (MT), MT + endurance training group (MT + ET) and MT + resistance training group (MT + RT). Exercise was performed 3 times weekly over a 12-week period. The endpoints of exercise capacity, health-related quality of life, COPD symptoms, lung function, and anxiety and depression questionnaires were re-evaluated at baseline, at the completion of the intervention and at 6 and 12-month follow-up. According to the COPD assessment tool offered by GOLD guidelines, patients were stratified into GOLD A and B groups and GOLD C and D groups for further subgroup analysis.

RESULTS

The intention-to-treat (ITT) population included 366 patients, 328 of them completed the study protocol over 12 months (the PP-population). There were no significant differences in the primary outcome, quality of life, between patients who underwent medical treatment (MT) alone, MT + endurance training (MT + ET), or MT + resistance training (MT + RT) at the completion of the intervention, 6-, or 12-month follow-up. Additionally, no significant differences were observed between MT, MT + RT, or MT + ET groups concerning the primary outcome, exercise capacity (3MWD), after initial 3 months of intervention. However, a small statistically significant difference was noted in favor of MT + ET compared to MT + RT at 12 months (ITT: Δ3MWD in ET vs RT = 5.53 m, 95% confidence interval: 0.87 to 13.84 m, P = 0.03) (PP: Δ3MWD in ET vs RT = 7.67 m, 95% confidence interval: 0.93 to 16.27 m, P = 0.04). For patients in the GOLD C and D groups, improvement in quality of life following ET or RT was significantly superior to medical intervention alone. Furthermore, upon completion of the exercise regimen, RT exhibited a greater improvement in anxiety compared to ET in these patients (ITT: ΔHAD-A at 3-month: RT = -1.63 ± 0.31 vs ET = -0.61 ± 0.33, p < 0.01) (PP: ΔHAD-A at 3-month: RT = -1.80 ± 0.36 vs ET = -0.75 ± 0.37, p < 0.01).

CONCLUSIONS

Our study presents evidence of the beneficial effects of ET and RT in combination with standard medical treatment, as well as the long-term effects over time after the intervention. While the statistically significant effect favoring ET over RT in terms of exercise capacity was observed, it should be interpreted cautiously. Patients in severe stages of COPD may derive greater benefits from either ET or RT and should be encouraged accordingly. These findings have implications for exercise prescription in patients with COPD.

TRIAL REGISTRATION

ChiCTR-INR-16009892 (17, Nov, 2016).

Heart failure worsens leg muscle strength and endurance in coexistence patients with COPD and heart failure reduced ejection fraction

Purpose: Exercise intolerance and dyspnoea are clinical symptoms in both heart failure (HF) reduced ejection fraction (HFrEF) and chronic obstructive pulmonary disease (COPD), which are suggested to be associated with musculoskeletal dysfunction. We tested the hypothesis that HFrEF + COPD patients would present lower muscle strength and greater fatigue compared to compared to the COPD group. Methods: We included 25 patients with HFrEF + COPD (100% male, age 67.8 ± 6.9) and 25 patients with COPD alone (100% male, age 66.1 ± 9.1). In both groups, COPD severity was determined as moderate-to-severe according to the GOLD classification (FEV1/FVC < 0.7 and predicted post-bronchodilator FEV1 between 30%-80%). Knee flexor-extensor muscle performance (torque, work, power and fatigue) were measured by isokinetic dynamometry in age and sex-matched patients with HFrEF + COPD and COPD alone; Functional capacity was assessed by the cardiopulmonary exercise test, the 6-min walk test (6MWT) and the four-minute step test. Results: The COPD group exhibited reduced lung function compared to the HFrEF + COPD group, as evidenced by lower FEV1/FVC (58.0 ± 4.0 vs. 65.5 ± 13.9; p < 0.0001, respectively) and FEV1 (51.3 ± 17.0 vs. 62.5 ± 17.4; p = 0.026, respectively) values. Regarding musculoskeletal function, the HFrEF + COPD group showed a knee flexor muscles impairment, however this fact was not observed in the knee extensors muscles. Power peak of the knee flexor corrected by muscle mass was significantly correlated with the 6MWT (r = 0.40; p < 0.05), number of steps (r = 0.30; p < 0.05) and work ratepeak (r = 0.40; p < 0.05) in the HFrEF + COPD and COPD groups. Conclusion: The presence of HFrEF in patients with COPD worsens muscular weakness when compared to isolated COPD.

Microalgae Produce Antioxidant Molecules with Potential Preventive Effects on Mitochondrial Functions and Skeletal Muscular Oxidative Stress

In recent years, microalgae have become a source of molecules for a healthy life. Their composition of carbohydrates, peptides, lipids, vitamins and carotenoids makes them a promising new source of antioxidant molecules. Skeletal muscle is a tissue that requires constant remodeling via protein turnover, and its regular functioning consumes energy in the form of adenosine triphosphate (ATP), which is produced by mitochondria. Under conditions of traumatic exercise or muscular diseases, a high production of reactive oxygen species (ROS) at the origin of oxidative stress (OS) will lead to inflammation and muscle atrophy, with life-long consequences. In this review, we describe the potential antioxidant effects of microalgae and their biomolecules on mitochondrial functions and skeletal muscular oxidative stress during exercises or in musculoskeletal diseases, as in sarcopenia, chronic obstructive pulmonary disease (COPD) and Duchenne muscular dystrophy (DMD), through the increase in and regulation of antioxidant pathways and protein synthesis.

Skeletal Muscle Mitochondrial Dysfunction in Chronic Obstructive Pulmonary Disease: Underlying Mechanisms and Physical Therapy Perspectives

Skeletal muscle dysfunction (SMD) is a prevalent extrapulmonary complication and a significant independent prognostic factor in patients with chronic obstructive pulmonary disease (COPD). Mitochondrial dysfunction is one of the core factors that damage structure and function in COPD skeletal muscle and is closely related to smoke exposure, hypoxia, and insufficient physical activity. The currently known phenotypes of mitochondrial dysfunction are reduced mitochondrial content and biogenesis, impaired activity of mitochondrial respiratory chain complexes, and increased mitochondrial reactive oxygen species production. Significant progress has been made in research on physical therapy (PT), which has broad prospects for treating the abovementioned potential mitochondrial-function changes in COPD skeletal muscle. In terms of specific types of PT, exercise therapy can directly act on mitochondria and improve COPD SMD by increasing mitochondrial density, regulating mitochondrial biogenesis, upregulating mitochondrial respiratory function, and reducing oxidative stress. However, improvements in mitochondrial-dysfunction phenotype in COPD skeletal muscle due to different exercise strategies are not entirely consistent. Therefore, based on the elucidation of this phenotype, in this study, we analyzed the effect of exercise on mitochondrial dysfunction in COPD skeletal muscle and the regulatory mechanism thereof. We also provided a theoretical basis for exercise programs to rehabilitate this condition.

Impaired muscle stem cell function and abnormal myogenesis in acquired myopathies

Skeletal muscle possesses a high plasticity and a remarkable regenerative capacity that relies mainly on muscle stem cells (MuSCs). Molecular and cellular components of the MuSC niche, such as immune cells, play key roles to coordinate MuSC function and to orchestrate muscle regeneration. An abnormal infiltration of immune cells and/or imbalance of pro- and anti-inflammatory cytokines could lead to MuSC dysfunctions that could have long lasting effects on muscle function. Different genetic variants were shown to cause muscular dystrophies that intrinsically compromise MuSC function and/or disturb their microenvironment leading to impaired muscle regeneration that contributes to disease progression. Alternatively, many acquired myopathies caused by comorbidities (e.g., cardiopulmonary or kidney diseases), chronic inflammation/infection, or side effects of different drugs can also perturb MuSC function and their microenvironment. The goal of this review is to comprehensively summarize the current knowledge on acquired myopathies and their impact on MuSC function. We further describe potential therapeutic strategies to restore MuSC regenerative capacity.

Role of Nrf2 and exercise in alleviating COPD-induced skeletal muscle dysfunction

Chronic obstructive pulmonary disease (COPD) is a complex chronic respiratory disease with cumulative impacts on multiple systems, exhibiting significant extrapulmonary impacts, and posing a serious public health problem. Skeletal muscle dysfunction is one of the most pronounced extrapulmonary effects in patients with COPD, which severely affects patient prognosis and mortality primarily through reduced productivity resulting from muscle structural and functional alterations. Although the detailed pathogenesis of COPD has not been fully determined, some researchers agree that oxidative stress plays a significant role. Oxidative stress not only catalyzes the progression of pulmonary symptoms but also drives the development of skeletal muscle dysfunction. Nuclear factor erythroid 2-related factor 2 (Nrf2), is a key transcription factor that regulates the antioxidant response and plays an enormous role in combating oxidative stress. In this review, we have summarized current research on oxidative stress damage to COPD skeletal muscle and analyzed the role of Nrf2 in improving skeletal muscle dysfunction in COPD through exercise. The results suggest that oxidative stress drives the occurrence and development of skeletal muscle dysfunction in COPD. Exercise may improve skeletal muscle dysfunction in patients with COPD by promoting the dissociation of Kelch-like ECH-associated protein 1 (Keap1) and Nrf2, inducing sequestosome1(p62) phosphorylation to bind with Keap1 competitively leading to Nrf2 stabilization and improving dynamin-related protein 1-dependent mitochondrial fission. Nrf2 may be a key target for exercise anti-oxidative stress to alleviate skeletal muscle dysfunction in COPD.

Impaired regenerative capacity contributes to skeletal muscle dysfunction in chronic obstructive pulmonary disease

Locomotor skeletal muscle dysfunction is a relevant comorbidity of chronic obstructive pulmonary disease (COPD) and is strongly associated with worse clinical outcomes including higher mortality. Over the last decades, a large body of literature helped characterize the process, defining the disruptive muscle phenotype caused by COPD that involves reduction in muscle mass, force-generation capacity, fatigue-tolerance, and regenerative potential following injury. A major limitation in the field has been the scarcity of well-calibrated animal models to conduct mechanistic research based on loss- and gain-of-function studies. This article provides an overall description of the process, the tools available to mechanistically investigate it, and the potential role of mitochondrially driven metabolic signals on the regulation muscle regeneration after injury in COPD. Finally, a description of future avenues to further expand on the area is proposed based on very recent evidence involving mitochondrial metabolic cues affecting myogenesis.

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.

Chronic aryl hydrocarbon receptor activity phenocopies smoking-induced skeletal muscle impairment

BACKGROUND

Chronic obstructive pulmonary disease (COPD) patients exhibit skeletal muscle atrophy, denervation, and reduced mitochondrial oxidative capacity. Whilst chronic tobacco smoke exposure is implicated in COPD muscle impairment, the mechanisms involved are ambiguous. The aryl hydrocarbon receptor (AHR) is a ligand-activated transcription factor that activates detoxifying pathways with numerous exogenous ligands, including tobacco smoke. Whereas transient AHR activation is adaptive, chronic activation can be toxic. On this basis, we tested the hypothesis that chronic smoke-induced AHR activation causes adverse muscle impact.

METHODS

We used clinical patient muscle samples, and in vitro (C2C12 myotubes) and in vivo models (mouse), to perform gene expression, mitochondrial function, muscle and neuromuscular junction morphology, and genetic manipulations (adeno-associated virus-mediated gene transfer).

RESULTS

Sixteen weeks of tobacco smoke exposure in mice caused muscle atrophy, neuromuscular junction degeneration, and reduced oxidative capacity. Similarly, smoke exposure reprogrammed the muscle transcriptome, with down-regulation of mitochondrial and neuromuscular junction genes. In mouse and human patient specimens, smoke exposure increased muscle AHR signalling. Mechanistically, experiments in cultured myotubes demonstrated that smoke condensate activated the AHR, caused mitochondrial impairments, and induced an AHR-dependent myotube atrophy. Finally, to isolate the role of AHR activity, expression of a constitutively active AHR mutant without smoke exposure caused atrophy and mitochondrial impairments in cultured myotubes, and muscle atrophy and neuromuscular junction degeneration in mice.

CONCLUSIONS

These results establish that chronic AHR activity, as occurs in smokers, phenocopies the atrophy, mitochondrial impairment, and neuromuscular junction degeneration caused by chronic tobacco smoke exposure.

Isokinetic testing of quadriceps function in COPD: feasibility, responsiveness, and minimal important differences in patients undergoing pulmonary rehabilitation

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Evaluation of isokinetic quadriceps testing in COPD is needed to assess its efficacy.

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Isokinetic testing was performed incorrectly in a quarter of patients with COPD.

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Quadriceps peak torque and total work improved following pulmonary rehabilitation.

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Minimal important differences for peak torque and total work were determined.

Background

Isokinetic testing of peripheral muscle function is valid and reliable in patients with chronic obstructive pulmonary disease (COPD).

Objective

To evaluate whether and to what extent isokinetic testing of quadriceps function meets pre-defined test criteria in patients with COPD; to determine the response to pulmonary rehabilitation (PR), and to calculate minimal important differences (MIDs) of isokinetic quadriceps function.

Methods

Retrospective analysis of 2033 patients with COPD (age: 65±9 years, body mass index: 26±6 kg/m², FEV₁: 49±22% predicted) who followed a comprehensive PR program. Pre and post PR isokinetic quadriceps function was assessed with 30 maximal extension-flexion contractions at an angular speed of 90°/s on a computerized dynamometer. The chosen anchors were 6-min walk test and COPD assessment test.

Results

Pre PR, 27% of the patients performed the isokinetic test incorrectly. In male and female patients with a correct pre and post PR isokinetic test, peak torque (Δ=10±13 Nm or 9% and Δ=7±9 Nm or 10%, respectively) and total work (Δ=263±270 J or 14% and Δ=198±190 J or 15%, respectively) improved significantly. There was no change in work fatigue index following PR. Using distribution-based calculations, MID estimates for peak torque and total work ranged between 6–7 Nm and 97–135 J in males and between 4–5 Nm and 62–99 J in females.

Conclusions

Based on the current test criteria, three in four patients with COPD performed the isokinetic quadriceps test correctly during baseline PR assessment. Furthermore, peak torque and total work, but not work fatigue index, were responsive to PR and sex-specific MIDs were established.

Working memory training efficacy in COPD: the randomised, double-blind, placebo-controlled Cogtrain trial

BACKGROUND

Cognitive impairment is highly prevalent in COPD and is associated with a sedentary lifestyle, unhealthy diet and increased cognitive stress susceptibility. Enhancement of cognitive performance by working memory training (WMT) may reverse these effects. Therefore, this study aimed to investigate the efficacy of WMT in COPD on cognitive performance, healthy lifestyle behaviours and cognitive stress susceptibility.

METHODS

The double-blind randomised, placebo-controlled Cogtrain trial consisted of a 12-week training phase comprising 30 active or sham WMT sessions, followed by a second 12-week maintenance phase with 12 sessions. Measurements took place at baseline and after the first and second phases. The primary outcome was cognitive performance. Secondary outcomes were the recall of prespecified healthy lifestyle goals, physical capacity and activity, dietary quality and cognitive stress susceptibility. Motivation towards exercising and healthy eating and psychological wellbeing were exploratory outcomes.

RESULTS

Sixty-four patients with moderate COPD (45% male, aged 66.2±7.2 years, median forced expiratory volume in 1 s 60.6% predicted) were randomised. WMT significantly increased patients' performance on the trained tasks in the first phase, which remained stable in the second phase. Of the 17 cognitive outcome measures, only one measure of memory improved after the first phase and one measure of reaction time after the second phase. This intervention did not influence physical capacity and activity, recall of prespecified healthy lifestyle goals, psychological wellbeing or cognitive stress susceptibility.

CONCLUSION

WMT improved performance on the trained tasks but not overall cognitive performance, healthy lifestyle behaviours or cognitive stress susceptibility in patients with COPD.

Carnosine, oxidative and carbonyl stress, antioxidants and muscle fiber characteristics of quadriceps muscle of patients with COPD

BACKGROUND

Oxidative/carbonyl stress is elevated in lower-limb muscles of patients with Chronic Obstructive Pulmonary Disease (COPD). Carnosine is a skeletal muscle antioxidant particularly present in fast-twitch fibers.

AIMS

To compare muscle carnosine, oxidative/carbonyl stress, antioxidants and fiber characteristics between patients with COPD and healthy controls (HCs), and between patients after stratification for airflow limitation (mild/moderate vs. severe/very-severe). To investigate correlates of carnosine in patients with COPD.

METHODS

A vastus lateralis muscle biopsy was obtained from 40 patients with stable COPD and 20 age/sex matched HCs. Carnosine, oxidative/carbonyl stress, antioxidants, fiber characteristics, quadriceps strength and endurance (QE), VO₂peak (incremental cycle test) and physical activity (PA) were determined.

RESULTS

Patients with COPD had a similar carnosine concentration (4.16 mmol/kg wet weight (WW) (SD 1.93)) to HCs (4.64 mmol/kgWW (SD 1.71)) and significantly higher percentage of fast-twitch fibers and lower QE, VO₂peak and PA vs. HCs. Patients with severe/very-severe COPD had a 30% lower carnosine concentration (3.24 mmol/kgWW (SD 1.79); n=15) vs. patients with mild/moderate COPD (4.71 mmol/kgWW (SD 1.83); n=25; P=0.02) and significantly lower VO₂peak and PA vs. patients with mild/moderate COPD. Carnosine correlated significantly with QE (r_s=0.427), VO₂peak (r_s=0.334), PA (r_s=0.379) and lung function parameters in patients with COPD.

CONCLUSION

Despite having the highest proportion of fast-twitch fibers, patients with severe/very-severe COPD displayed a 30% lower muscle carnosine concentration compared to patients with mild/moderate COPD. As no oxidative/carbonyl stress markers, nor antioxidants were affected, the observed carnosine deficiency is thought to be a possible first sign of muscle redox balance abnormalities.

Succinate Dehydrogenase (SDH)-subunit C Regulates Muscle Oxygen Consumption and Fatigability in an Animal Model of Pulmonary Emphysema

Patients with pulmonary emphysema often develop locomotor muscle dysfunction, which is independently associated with disability and higher mortality in that population. Muscle dysfunction entails reduced force-generation capacity which partially depends on fibers' oxidative potential, yet very little mechanistic research has focused on muscle respiration in pulmonary emphysema. Using a recently established animal model of pulmonary emphysema-driven skeletal muscle dysfunction, we found downregulation of succinate dehydrogenase (SDH) subunit C in association with lower oxygen consumption and fatigue-tolerance in locomotor muscles. Reduced SDH activity has been previously observed in muscles from patients with pulmonary emphysema and we found that SDHC is required to support respiration in cultured muscle cells. Moreover, in-vivo gain of SDH function in emphysema animals muscles resulted in better oxygen consumption rate (OCR) and fatigue tolerance. These changes correlated with a larger number of relatively more oxidative type 2-A and 2X fibers, and a reduced amount of 2B fibers. Our data suggests that SDHC is a key regulator of respiration and fatigability in pulmonary emphysema-driven skeletal muscles, which could be impactful to develop strategies aimed at attenuating this comorbidity.

Bufei Jianpi Formula Improves Mitochondrial Function and Suppresses Mitophagy in Skeletal Muscle via the Adenosine Monophosphate-Activated Protein Kinase Pathway in Chronic Obstructive Pulmonary Disease

Skeletal muscle dysfunction, a striking systemic comorbidity of chronic obstructive pulmonary disease (COPD), is associated with declines in activities of daily living, reductions in health status and prognosis, and increases in mortality. Bufei Jianpi formula (BJF), a traditional Chinese herbal formulation, has been shown to improve skeletal muscle tension and tolerance via inhibition of cellular apoptosis in COPD rat models. This study aimed to investigate the mechanisms by which BJF regulates the adenosine monophosphate-activated protein kinase (AMPK) pathway to improve mitochondrial function and to suppress mitophagy in skeletal muscle cells. Our study showed that BJF repaired lung function and ameliorated pathological impairment in rat lung and skeletal muscle tissues. BJF also improved mitochondrial function and reduced mitophagy via the AMPK signaling pathway in rat skeletal muscle tissue. In vitro, BJF significantly improved cigarette smoke extract-induced mitochondrial functional impairment in L6 skeletal muscle cells through effects on mitochondrial membrane potential, mitochondrial permeability transition pores, adenosine triphosphate production, and mitochondrial respiration. In addition, BJF led to upregulated expression of mitochondrial biogenesis markers, including AMPK-α, PGC-1α, and TFAM and downregulation of mitophagy markers, including LC3B, ULK1, PINK1, and Parkin, with increased expression of downstream markers of the AMPK pathway, including mTOR, PPARγ, and SIRT1. In conclusion, BJF significantly improved skeletal muscle and mitochondrial function in COPD rats and L6 cells by promoting mitochondrial biogenesis and suppressing mitophagy via the AMPK pathway. This study suggests that BJF may have therapeutic potential for prophylaxis and treatment of skeletal muscle dysfunction in patients with COPD.

Cardiorespiratory responses to high-intensity skeletal muscle metaboreflex activation in chronic obstructive pulmonary disease

BACKGROUND

Augmented skeletal muscle metaboreflex activation may accompany chronic obstructive pulmonary disease (COPD). The maintained metaboreflex control of mean arterial pressure (MAP) that has been reported may reflect limited evaluation using only one moderate bout of static handgrip (HG) and following postexercise ischaemia (PEI).

OBJECTIVE

We tested the hypothesis that cardiovascular and respiratory responses to high-intensity static HG and isolated metaboreflex activation during PEI are augmented in COPD patients.

METHODS

Ten patients with moderate to severe COPD and eight healthy age- and BMI-matched controls performed two-minute static HG at moderate (30% maximal voluntary contraction; MVC) and high (40% MVC) intensity followed by PEI.

RESULTS

Despite similar ratings of perceived exertion, arm muscle mass and strength, COPD patients demonstrated lower MAP responses during both HG intensities compared with controls (time × group interaction, p < .05). Indeed, during high-intensity HG at 40% MVC, peak MAP responses were significantly lower in COPD patients (ΔMAP: COPD 41 ± 9 mmHg vs. controls 56 ± 14 mmHg, p < .05). Notably, no group differences in MAP were observed during PEI (e.g. 40% MVC PEI: ΔMAP COPD 33 ± 9 mmHg vs. controls 33 ± 6 mmHg, p > .05). We found no between-group differences in heart rate, respiratory rate, or estimated minute ventilation during HG or PEI.

CONCLUSION

These results suggest that the pressor response to high-intensity HG is blunted in COPD patients. Moreover, despite inducing a strong cardiovascular and respiratory stimulus, skeletal muscle metaboreflex activation evoked similar responses in COPD patients and controls.

Role of acute exacerbations in skeletal muscle impairment in COPD

Introduction: Muscle impairments are prevalent in COPD and have adverse clinical implications in terms of physical performance capacity, disease burden, quality of life and even mortality. During acute exacerbations of COPD (AECOPDs) the respiratory symptoms worsen and this might also apply to the muscle impairments. Areas covered: This report includes a review of both clinical and pre-clinical peer-reviewed literature of the past 20 years found in PubMed providing a comprehensive view on the role of AECOPD in muscle dysfunction in COPD, the putative underlying mechanisms and the treatment perspectives. Expert opinion: The contribution of AECOPD and its recurrent nature to muscle impairment in COPD cannot be ignored and can be attributed to the acutely intensifying and converging disease-related drivers of muscle deterioration, in particular disuse, systemic inflammation and corticosteroid treatment. The search for novel treatment options should focus on the AECOPD-enhanced drivers of muscle dysfunction as well as on the underlying, mainly catabolic, mechanisms. Considering the impact of AECOPD on muscle function, and that of muscle impairment on the recurrence of exacerbations, counteracting muscle deterioration in AECOPD provides an unprecedented therapeutic opportunity.

The role of peripheral muscle fatigability on exercise intolerance in COPD

INTRODUCTION

Exercise limitation in chronic obstructive pulmonary disease (COPD) is multi-factorial; however, growing evidence indicates that muscle dysfunction may contribute in some patients.

AREAS COVERED

This work outlines current evidence for and against increased peripheral muscle fatigability in COPD through a comprehensive review of relevant literature available on PubMed/MEDLINE until May 2020. The authors first discuss key methodological issues relative to muscle fatigue assessment by non-volitional techniques, particularly magnetic stimulation. The authors then provide a detailed discussion of critical studies to have objectively measured skeletal muscle fatigue in individuals with COPD.

EXPERT OPINION

Current evidence indicates that localized (knee extension) and cycling exercise are associated with increased quadriceps fatigability in most COPD patients. Increased fatigability, however, has not been consistently found in response to walking, likely reflecting the tendency of 'central' respiratory constraints to overshadow potential functional impairments in the appendicular muscles in this form of exercise. Thus, addressing skeletal muscle abnormalities may be critical to translate improvements in lung mechanics (e.g., due to bronchodilator therapy) into better exercise tolerance. The positive effects of pulmonary rehabilitation on muscle fatigability are particularly encouraging and suggest a role for these measurements to test the efficacy of emerging adjunct training strategies focused on the peripheral muscles.

Hypercapnia-Driven Skeletal Muscle Dysfunction in an Animal Model of Pulmonary Emphysema Suggests a Complex Phenotype

Patients with chronic pulmonary conditions such as chronic obstructive pulmonary disease (COPD) often develop skeletal muscle dysfunction, which is strongly and independently associated with poor outcomes including higher mortality. Some of these patients also develop chronic CO₂ retention, or hypercapnia, which is also associated with worse prognosis. While muscle dysfunction in these settings involve reduction of muscle mass and disrupted fibers’ metabolism leading to suboptimal muscle work, mechanistic research in the field has been limited by the lack of adequate animal models. Over the last years, we have established a rodent model of COPD-induced skeletal muscle dysfunction that allowed a disaggregated interrogation of the cellular and physiological effects driven by COPD from the ones unique to hypercapnia. We found that while COPD and hypercapnia synergistically contribute to muscle atrophy, they are antagonistic processes regarding fibers respiratory capacity. We propose that AMP-activated protein kinase (AMPK) is a crucial regulator of CO₂ signaling in hypercapnic muscles, which leads to both net protein catabolism and improved mitochondrial respiration to support a transition into a substrate-rich, fuel-efficient metabolic mode that allows muscle cells cope with the CO₂ toxicity.

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.

Locomotor Muscles in COPD: The Rationale for Rehabilitative Exercise Training

Exercise training as part of pulmonary rehabilitation is arguably the most effective intervention to improve tolerance to physical exertion in patients with chronic obstructive pulmonary disease (COPD). Owing to the fact that exercise training has modest effects on exertional ventilation, operating lung volumes and respiratory muscle performance, improving locomotor muscle structure and function are key targets for pulmonary rehabilitation in COPD. In the current concise review, we initially discuss whether patients’ muscles are exposed to deleterious factors. After presenting corroboratory evidence on this regard (e.g., oxidative stress, inflammation, hypoxemia, inactivity, and medications), we outline their effects on muscle macro- and micro-structure and related functional properties. We then finalize by addressing the potential beneficial consequences of different training strategies on these muscle-centered outcomes. This review provides, therefore, an up-to-date outline of the rationale for rehabilitative exercise training approaches focusing on the locomotor muscles in this patient population.

Resveratrol and metabolic health in COPD: A proof-of-concept randomized controlled trial

BACKGROUND

Patients with COPD are often characterized by disturbed metabolic health which is reflected in altered body composition. Current studies in healthy subjects suggest that resveratrol improves metabolic health by enhancing muscle mitochondrial function and adipose tissue morphology. The primary objective was to investigate the effect of four weeks resveratrol supplementation on muscle mitochondrial function in patients with COPD. Secondary objectives were to investigate the effect of resveratrol on adipose tissue inflammatory and metabolic gene expression, systemic inflammation and body composition in patients with COPD.

METHODS

In a double-blind randomized placebo-controlled proof-of-concept study, 21 COPD patients (FEV₁: 53 ± 15% predicted; age: 67 ± 9 years and BMI: 24.5 ± 3.3 kg/m²) received resveratrol (150 mg/day) or placebo for four weeks. Before and after intervention, blood samples, quadriceps muscle and subcutaneous abdominal fat biopsies were obtained for metabolic and inflammatory profiling. Body composition was assessed by dual energy X-ray absorptiometry.

RESULTS

Muscle mitochondrial biogenesis regulators AMPK, SIRT1 and PGC-1α as well as mitochondrial respiration, Oxphos complexes, oxidative enzyme activities and kynurenine aminotransferases were not improved by resveratrol. Plasma high-sensitive C-reactive protein and kynurenine did not change after resveratrol supplementation. Adipose tissue inflammatory markers were unaffected by resveratrol, while markers of glycolysis and lipolysis were significantly increased compared to placebo supplementation. Body weight decreased after resveratrol supplementation (resveratrol -0.95 ± 1.01 kg vs placebo -0.16 ± 0.66 kg, p = 0.049) due to a reduction in lean mass (resveratrol -1.79 ± 1.67 kg vs 0.37 ± 0.86 kg, p = 0.026).

CONCLUSION

We do not confirm previously reported positive effects of resveratrol on skeletal muscle mitochondrial function in patients with COPD, but show an unexpected decline in lean mass.

CLINICAL TRIAL REGISTRY

Clinicaltrials.gov NCT02245932.

Effects of combining functional exercises with exercise training on daily physical activities and functionality in patients with COPD: a protocol for a randomized clinical trial

Introduction

Functional training has been shown to be a viable alternative for the elderly and patients with chronic obstructive pulmonary disease (COPD). However, whether the combination of this type of training with aerobic and resistance training, commonly performed in pulmonary rehabilitation (PR) programs, induces more pronounced effects on daily physical activities and functionality remains unclear. The aims of the study will be to evaluate the short-term and sustained effects of the combination of a functional circuit program with a training program consisting of aerobic and resistance exercise.

Methods

In this randomized controlled trial, patients with COPD will be randomly assigned (1:1:1) to an 8-week training program to follow one of the three a priori defined groups: (I) resistance and aerobic and functional exercises, (II) a conventional program including only resistance and aerobic exercises, or (III) a usual care program. Patients will be evaluated before and upon completion of 8 weeks of training regarding physical activity in daily life (PADL) using an activity monitor (accelerometer), activities of daily living (London Chest Activity of Daily Living), functional exercise capacity (6-minute walk test), and muscle strength (dynamometry). Additionally, the sustained effects of the interventions will be evaluated 22 weeks after commencing the study.

Discussion

The inclusion of a protocol of functional physical training in the training conventionally performed by patients with COPD as an alternative to increase PADL and functionality may provide subsidies for the treatment of these patients, representing an advance and impacting on the physical training of patients with COPD.

Trial registration

Brazilian Clinical Trials Registry (ReBEC) ID: RBR-3zmh3r. Registered: March 7, 2018.

Impaired Skeletal Muscle Kynurenine Metabolism in Patients with Chronic Obstructive Pulmonary Disease

Background: Loss of peripheral muscle oxidative phenotype, cognitive impairment, and depression are well-recognized systemic manifestations of chronic obstructive pulmonary disease (COPD). Kynurenine (KYN), known to be associated with disturbed mental health, can be metabolized in muscle by kynurenine aminotransferases (KAT) 1–4. These KATs are regulated by peroxisome proliferator-activated receptor gamma (PPARγ) coactivator-1α (PGC1α). We hypothesize that impaired PGC1α signaling in COPD is associated with reduced muscle KAT expression and increased KYN plasma levels. Methods: Retrospective collected and metabolically phenotyped muscle tissue and blood obtained from 29 well-characterized COPD patients and 15 healthy controls were analyzed. KYN was measured in plasma and KAT1–4 expression and major constituents of PGC1α signaling were assessed in quadriceps muscle biopsies. Results: Circulating KYN levels were increased in COPD. Furthermore, both gene and protein expression levels of KAT4 were reduced in muscle tissue from COPD patients. Finally, in the whole group (even when controlled for airflow obstruction) and in each subgroup separately, KAT4 gene expression correlated significantly with constituents of the PGC1α signaling pathway. Conclusions: These data support our hypothesis that KYN plasma levels are elevated in COPD through impaired KYN clearance in muscle. Our findings show a pathway via which exercise training and/or nutritional modulation may improve physical and mental health in COPD patients.

Quadriceps miR-542-3p and -5p are elevated in COPD and reduce function by inhibiting ribosomal and protein synthesis

Reduced physical performance reduces quality of life in patients with chronic obstructive pulmonary disease (COPD). Impaired physical performance is, in part, a consequence of reduced muscle mass and function, which is accompanied by mitochondrial dysfunction. We recently showed that miR-542-3p and miR-542-5p were elevated in a small cohort of COPD patients and more markedly in critical care patients. In mice, these microRNAs (miRNAs) promoted mitochondrial dysfunction suggesting that they would affect physical performance in patients with COPD, but we did not explore the association of these miRNAs with disease severity or physical performance further. We therefore quantified miR-542-3p/5p and mitochondrial rRNA expression in RNA extracted from quadriceps muscle of patients with COPD and determined their association with physical performance. As miR-542-3p inhibits ribosomal protein synthesis its ability to inhibit protein synthesis was also determined in vitro. Both miR-542-3p expression and -5p expression were elevated in patients with COPD (5-fold P < 0.001) and the degree of elevation associated with impaired lung function (transfer capacity of the lung for CO in % and forced expiratory volume in 1 s in %) and physical performance (6-min walk distance in %). In COPD patients, the ratio of 12S rRNA to 16S rRNA was suppressed suggesting mitochondrial ribosomal stress and mitochondrial dysfunction and miR-542-3p/5p expression was inversely associated with mitochondrial gene expression and positively associated with p53 activity. miR-542-3p suppressed RPS23 expression and maximal protein synthesis in vitro. Our data show that miR-542-3p and -5p expression is elevated in COPD patients and may suppress physical performance at least in part by inhibiting mitochondrial and cytoplasmic ribosome synthesis and suppressing protein synthesis. NEW & NOTEWORTHY miR-542-3p and -5p are elevated in the quadriceps muscle of patients with chronic obstructive pulmonary disease (COPD) in proportion to the severity of their lung disease. These microRNAs inhibit mitochondrial and cytoplasmic protein synthesis suggesting that they contribute to impaired exercise performance in COPD.

Quality of resistance training description in COPD trials: study protocol for a systematic review

INTRODUCTION

Limb muscle dysfunction is a common manifestation in patients with chronic obstructive pulmonary disease (COPD). Optimising of limb muscle function is therefore an important goal during pulmonary rehabilitation of patients with COPD. Resistance training (RT) is the best available intervention to achieve this goal. Previous systematic reviews on RT primarily focused on methodological quality. However, the intervention holds the essence of each experimental study. Replication of RT interventions requires clear, complete and accessible reporting of the essential components. The American College of Sports Medicine (ACSM) provides evidence-based guidelines for RT prescription and recommends RT models specific to desired outcomes, that is, improvements in strength, muscular hypertrophy, power or local muscle endurance. The aim of this review is to investigate if the application of the RT principles and key training variables is described sufficiently in current evidence on the effects of RT interventions in patients with COPD.

METHODS AND ANALYSIS

Any research study (randomised, non-randomised controlled, controlled pre-post studies and observational studies) with an RT intervention in patients with COPD will be considered for this systematic review. Potentially relevant studies published in English from inception to 1 October 2017 will be identified from Embase, Cochrane Library, Cumulative Index of Nursing and Allied Health Literature (CINAHL) and Physiotherapy Evidence Database (PEDro). Studies exploring the effects of RT following a single session and RT interventions limited to other respiratory chronic diseases will not be included. Additionally, studies including non-COPD participants will be excluded, if the COPD data are not separated. Pairs of reviewers will independently extract data using data collecting sheets. Quality appraisal of RT description will be performed in timeframes according to the latest published ACSM position statement on exercise or RT.

ETHICS AND DISSEMINATION

This protocol is a systematic review and therefore ethical approval is not required. The results of this review will be disseminated through peer-reviewed publication and presented at scientific conferences.

PROSPERO REGISTRATION NUMBER

CRD42017067403.

Molecular signalling towards mitochondrial breakdown is enhanced in skeletal muscle of patients with chronic obstructive pulmonary disease (COPD)

Loss of skeletal muscle mitochondrial oxidative capacity is well-established in patients with COPD, but the role of mitochondrial breakdown herein is largely unexplored. Currently, we studied if mitochondrial breakdown signalling is increased in skeletal muscle of COPD patients and associates with the loss of mitochondrial content, and whether it is affected in patients with iron deficiency (ID) or systemic inflammation. Therefore, mitophagy, autophagy, mitochondrial dynamics and content markers were analysed in vastus lateralis biopsies of COPD patients (N = 95, FEV₁% predicted: 39.0 [31.0–53.6]) and healthy controls (N = 15, FEV₁% predicted: 112.8 [107.5–125.5]). Sub-analyses were performed on patients stratified by ID or C-reactive protein (CRP). Compared with controls, COPD patients had lower muscle mitochondrial content, higher BNIP3L and lower FUNDC1 protein, and higher Parkin protein and gene-expression. BNIP3L and Parkin protein levels inversely correlated with mtDNA/gDNA ratio and FEV₁% predicted. ID-COPD patients had lower BNIP3L protein and higher BNIP3 gene-expression, while high CRP patients had higher BNIP3 and autophagy-related protein levels. In conclusion, our data indicates that mitochondrial breakdown signalling is increased in skeletal muscle of COPD patients, and is related to disease severity and loss of mitochondrial content. Moreover, systemic inflammation is associated with higher BNIP3 and autophagy-related protein levels.

Ventilation distribution, pulmonary diffusion and peripheral muscle endurance as determinants of exercise intolerance in elderly patients with chronic obstructive pulmonary disease

Chronic obstructive pulmonary disease (COPD) is a progressive and disabling disease that has been associated with aging. Several factors may potentially impair performance during exercise in elderly patients with COPD. This study was conducted to evaluate what characteristics related to lung function, peripheral muscle strength and endurance can predict the performance of elderly patients with COPD during cardiopulmonary exercise testing (CPET). Forty elderly patients with COPD underwent resting lung function tests, knee isokinetic dynamometry, and CPET. Three models were developed to explain the variability in peak oxygen uptake (VO(2) peak) after controlling for age as an independent confounder. The pulmonary function model showed the highest explained variance (65.6 %); in this model, ventilation distribution (p<0.001) and pulmonary diffusion (0.013) were found to be independent predictors. Finally, the models that included the muscle strength and endurance variables presented explained variances of 51 % and 57.4 %, respectively. In these models that involved muscular dysfunction, however, only the endurance variables were found to be independent predictors (p<0.05). In conclusion, ventilation distribution and pulmonary diffusion, but not the degree of airway obstruction, independently predict CPET performance in elderly patients with COPD. In addition, peripheral muscle endurance, but not strength, also predicts CPET performance in these subjects.

Altered skeletal muscle mitochondrial phenotype in COPD: disease vs. disuse

Patients with chronic obstructive pulmonary disease (COPD) exhibit an altered skeletal muscle mitochondrial phenotype, which often includes reduced mitochondrial density, altered respiratory function, and elevated oxidative stress. As this phenotype may be explained by the sedentary lifestyle that commonly accompanies this disease, the aim of this study was to determine whether such alterations are still evident when patients with COPD are compared to control subjects matched for objectively measured physical activity (PA; accelerometry). Indexes of mitochondrial density [citrate synthase (CS) activity], respiratory function (respirometry in permeabilized fibers), and muscle oxidative stress [4-hydroxynonenal (4-HNE) content] were assessed in muscle fibers biopsied from the vastus lateralis of nine patients with COPD and nine PA-matched control subjects (CON). Despite performing similar levels of PA (CON: 18 ± 3, COPD: 20 ± 7 daily minutes moderate-to-vigorous PA; CON: 4,596 ± 683, COPD: 4,219 ± 763 steps per day, P > 0.70), patients with COPD still exhibited several alterations in their mitochondrial phenotype, including attenuated skeletal muscle mitochondrial density (CS activity; CON 70.6 ± 3.8, COPD 52.7 ± 6.5 U/mg, P < 0.05), altered mitochondrial respiration [e.g., ratio of complex I-driven state 3 to complex II-driven state 3 (CI/CII); CON: 1.20 ± 0.11, COPD: 0.90 ± 0.05, P < 0.05), and oxidative stress (4-HNE; CON: 1.35 ± 0.19, COPD: 2.26 ± 0.25 relative to β-actin, P < 0.05). Furthermore, CS activity ( r = 0.55), CI/CII ( r = 0.60), and 4-HNE ( r = 0.49) were all correlated with pulmonary function, assessed as forced expiratory volume in 1 s ( P < 0.05), but not PA ( P > 0.05). In conclusion, the altered mitochondrial phenotype in COPD is present even in the absence of differing levels of PA and appears to be related to the disease itself. NEW & NOTEWORTHY Chronic obstructive pulmonary disease (COPD) is associated with debilitating alterations in the function of skeletal muscle mitochondria. By comparing the mitochondrial phenotype of patients with COPD to that of healthy control subjects who perform the same amount of physical activity each day, this study provides evidence that many aspects of the dysfunctional mitochondrial phenotype observed in COPD are not merely due to reduced physical activity but are likely related to the disease itself.

Adaptive remodeling of skeletal muscle energy metabolism in high-altitude hypoxia: Lessons from AltitudeOmics

Metabolic responses to hypoxia play important roles in cell survival strategies and disease pathogenesis in humans. However, the homeostatic adjustments that balance changes in energy supply and demand to maintain organismal function under chronic low oxygen conditions remain incompletely understood, making it difficult to distinguish adaptive from maladaptive responses in hypoxia-related pathologies. We integrated metabolomic and proteomic profiling with mitochondrial respirometry and blood gas analyses to comprehensively define the physiological responses of skeletal muscle energy metabolism to 16 days of high-altitude hypoxia (5260 m) in healthy volunteers from the AltitudeOmics project. In contrast to the view that hypoxia down-regulates aerobic metabolism, results show that mitochondria play a central role in muscle hypoxia adaptation by supporting higher resting phosphorylation potential and enhancing the efficiency of long-chain acylcarnitine oxidation. This directs increases in muscle glucose toward pentose phosphate and one-carbon metabolism pathways that support cytosolic redox balance and help mitigate the effects of increased protein and purine nucleotide catabolism in hypoxia. Muscle accumulation of free amino acids favor these adjustments by coordinating cytosolic and mitochondrial pathways to rid the cell of excess nitrogen, but might ultimately limit muscle oxidative capacity in vivo Collectively, these studies illustrate how an integration of aerobic and anaerobic metabolism is required for physiological hypoxia adaptation in skeletal muscle, and highlight protein catabolism and allosteric regulation as unexpected orchestrators of metabolic remodeling in this context. These findings have important implications for the management of hypoxia-related diseases and other conditions associated with chronic catabolic stress.

Resveratrol for patients with chronic obstructive pulmonary disease: hype or hope?

PURPOSE OF REVIEW

Chronic obstructive pulmonary disease (COPD) is a progressive lung disease with a high prevalence of extrapulmonary manifestations and, frequently, cardiovascular comorbidity. Resveratrol is a food-derived compound with anti-inflammatory, antioxidant, metabolic and cardioprotective potential. Therefore, resveratrol might improve the pulmonary as well as extrapulmonary pathology in COPD. In this review, we will evaluate knowledge on the effects of resveratrol on lung injury, muscle metabolism and cardiovascular risk profile and discuss if resveratrol is a hype or hope for patients with COPD.

RECENT FINDINGS

Experimental models of COPD consistently show decreased inflammation and oxidative stress in the lungs after resveratrol treatment. These beneficial anti-inflammatory and antioxidant properties of resveratrol can indirectly also improve both skeletal and respiratory muscle impairment in COPD. Recent clinical studies in non-COPD populations show improved mitochondrial oxidative metabolism after resveratrol treatment, which could be beneficial for both lung and muscle impairment in COPD. Moreover, preclinical studies suggest cardioprotective effects of resveratrol but results of clinical studies are inconclusive.

SUMMARY

Resveratrol might be an interesting therapeutic candidate to counteract lung and muscle impairments characteristic to COPD. However, there is no convincing evidence that resveratrol will significantly decrease the cardiovascular risk in patients with COPD.

MicroRNA-542 Promotes Mitochondrial Dysfunction and SMAD Activity and Is Elevated in Intensive Care Unit-acquired Weakness

RATIONALE

Loss of skeletal muscle mass and function is a common consequence of critical illness and a range of chronic diseases, but the mechanisms by which this occurs are unclear.

OBJECTIVES

To identify microRNAs (miRNAs) that were increased in the quadriceps of patients with muscle wasting and to determine the molecular pathways by which they contributed to muscle dysfunction.

METHODS

miRNA-542-3p/5p (miR-542-3p/5p) were quantified in the quadriceps of patients with chronic obstructive pulmonary disease and intensive care unit-acquired weakness (ICUAW). The effect of miR-542-3p/5p was determined on mitochondrial function and transforming growth factor-β signaling in vitro and in vivo.

MEASUREMENTS AND MAIN RESULTS

miR-542-3p/5p were elevated in patients with chronic obstructive pulmonary disease but more markedly in patients with ICUAW. In vitro, miR-542-3p suppressed the expression of the mitochondrial ribosomal protein MRPS10 and reduced 12S ribosomal RNA (rRNA) expression, suggesting mitochondrial ribosomal stress. miR-542-5p increased nuclear phospho-SMAD2/3 and suppressed expression of SMAD7, SMURF1, and PPP2CA, proteins that inhibit or reduce SMAD2/3 phosphorylation, suggesting that miR-542-5p increased transforming growth factor-β signaling. In mice, miR-542 overexpression caused muscle wasting, and reduced mitochondrial function, 12S rRNA expression, and SMAD7 expression, consistent with the effects of the miRNAs in vitro. Similarly, in patients with ICUAW, the expression of 12S rRNA and of the inhibitors of SMAD2/3 phosphorylation were reduced, indicative of mitochondrial ribosomal stress and increased transforming growth factor-β signaling. In patients undergoing aortic surgery, preoperative levels of miR-542-3p/5p were positively correlated with muscle loss after surgery.

CONCLUSIONS

Elevated miR-542-3p/5p may cause muscle atrophy in intensive care unit patients through the promotion of mitochondrial dysfunction and activation of SMAD2/3 phosphorylation.

Hand grip endurance test relates to clinical state and prognosis in COPD patients better than 6-minute walk test distance

Purpose

Patients with COPD present peripheral muscle dysfunction and atrophy, expressed as muscle strength and endurance reduction. The goal of this study was direct dynamometric assessment of hand grip endurance and strength in relation to the stage of disease, multidimensional predictors of mortality, and 6-minute walk test (6MWT). To the best of our knowledge, there has been no previous study determining these parameters.

Patients and methods

In this observational study, 58 consecutive outpatients with stable COPD and 25 volunteers without respiratory problems were compared. All COPD subjects underwent a comprehensive examination to determine COPD severity, prognostic scales, and 6MWT. Body composition, basic spirometric parameters, and hand grip strength and endurance were determined in all study participants.

Results

Patients in the COPD group had a 15% decrease in maximum strength (P=0.012) and a 28% decrease in area under the force/time curve (AUC) of the endurance test (P<0.001) compared to the control group. Dynamometric parameters were significantly negatively associated with the stage of disease and values of multivariable prediction indexes, and positively associated with the results of 6MWT. In most cases, closer associations were found with AUC than with 6MWT and in the gender-specific groups.

Conclusion

Both hand grip strength and endurance are impaired in COPD patients in comparison with the control group. In particular, AUC could be considered as an attractive option not only to assess exercise capacity but also as a predictive marker with a better prognostic value than 6MWT in COPD patients. This is the first study to observe the dependence of hand grip endurance on combined COPD assessment.

Does peripheral arterial occlusive disease influence muscle strength and exercise capacity in COPD patients?

Background

The pathophysiology of chronic obstructive pulmonary disease (COPD) is complex and understanding of it has been changing in recent years, with regard to its multisystemic manifestations, especially peripheral dysfunction and its influence on intolerance to exercise.

Objectives

To evaluate the relationship between peripheral arterial occlusive disease (PAOD) and peripheral muscle strength and exercise capacity in COPD patients.

Methods

We conducted a cross-sectional study of 35 patients with COPD who were evaluated with the Ankle-Brachial Index, handgrip strength test, 1 repetition maximum (1RM) of knee extensors and flexors, and distance covered in the incremental shuttle walking test (dISWT).

Results

COPD patients with coexisting PAOD had lower dominant handgrip strength test results (33.00 vs. 26.66 kgf, p = 0.02) and worse performance in the dISWT (297.32 vs. 219.41 m, p = 0.02) when compared to the COPD patients without PAOD. Strong correlations were found between the result of the handgrip strength test and both the dISWT (r = 0.78; p < 0.001) and the 1RM/knee extension (r = 0.71; p = 0.03); and also between the dISWT and both the 1RM/knee extension (r = 0.72; p = 0.02) and the 1RM/knee flexion (r = 0.92; p < 0.001). The linear regression model showed that the dISWT variable alone explains 15.3% of the Ankle-Brachial Index result (p = 0.01).

Conclusion

COPD patients with PAOD exhibit reduced muscle strength and lower exercise capacity than COPD patients without PAOD.

Tumor necrosis factor-like weak inducer of apoptosis regulates quadriceps muscle atrophy and fiber-type alteration in a rat model of chronic obstructive pulmonary disease

Background

In chronic obstructive pulmonary disease (COPD), weakness and muscle mass loss of the quadriceps muscle has been demonstrated to predict survival and mortality rates of patients. Tumor necrosis factor (TNF)-like weak inducer of apoptosis (TWEAK), as a member of the TNF superfamily, has recently been identified as a key regulator of skeletal muscle wasting and metabolic dysfunction. So our aim was to study the role of TWEAK during quadriceps muscle atrophy and fiber-type transformation in COPD model rats and its possible pathway.

Methods

Forty-four healthy male adult Wistar rats were randomly divided into two groups: A normal control group (n = 16) and a COPD model group (n = 28). The COPD group was exposed to cigarette smoke for 90 d and injected with porcine pancreatic elastase on day 15, whereas the control group was injected with saline alone. Following treatment, weights of the quadriceps muscles were measured and hematoxylin and eosin staining was performed to identify structural changes in lung and quadriceps muscle tissue. Immunohistochemical staining was also conducted to determine the localization of TWEAK, nuclear factor (NF)-κB, muscle ring finger (MuRF)-1 and proliferator-activated coactivator (PGC)-1a proteins in the quadriceps muscle, and western blotting was used to assess the level of protein expression.

Results

Compared with controls, COPD model rats exhibited significantly lower quadriceps muscle weight (P < 0.05) accompanied by fiber atrophy and disordered fiber arrangement, a wide gap between adjacent muscle fibers, a significant reduction in nuclear number (P < 0.05) and an uneven size distribution. The proportion of fiber types was also significantly altered (P < 0.05). In addition, TWEAK expression in the quadriceps muscle of COPD model rats was significantly higher than that in control rats (P < 0.05), and was significantly associated with quadriceps atrophy and fiber-type alteration (P < 0.05). Levels of NF-κB, MuRF1 and PGC-1α expression also significantly differed between the two groups (P < 0.05).

Conclusions

Collectively these data suggest that increased levels of TWEAK may lead to skeletal muscle atrophy and fiber-type alteration, which in turn may be associated with activation of the ubiquitin-proteasome pathway, involving NF-κB, MuRF1 and PGC-1α as potential regulatory factors. These preliminary results in rats suggest that TWEAK may be a therapeutic target for the treatment of muscle atrophy in COPD.

Systemic effects of chronic obstructive pulmonary disease in young-old adults' life-space mobility

PURPOSE

The objective was to assess whether dyspnea, peripheral muscle strength and the level of physical activity are correlated with life-space mobility of older adults with COPD.

PATIENTS AND METHODS

Sixty patients over 60 years of age (40 in the COPD group and 20 in the control group) were included. All patients were evaluated for lung function (spirometry), life-space mobility (University of Alabama at Birmingham Study of Aging Life-Space Assessment), dyspnea severity (Modified Dyspnea Index), peripheral muscle strength (handgrip dynamometer), level of physical activity and number of daily steps (accelerometry). Groups were compared using unpaired t-test. Pearson's correlation was used to test the association between variables.

RESULTS

Life-space mobility (60.41±16.93 vs 71.07±16.28 points), dyspnea (8 [7-9] vs 11 [10-11] points), peripheral muscle strength (75.16±14.89 vs 75.50±15.13 mmHg), number of daily steps (4,865.4±2,193.3 vs 6,146.8±2,376.4 steps), and time spent in moderate to vigorous activity (197.27±146.47 vs 280.05±168.95 minutes) were lower among COPD group compared to control group (p<0.05). The difference was associated with the lower mobility of COPD group in the neighborhood.

CONCLUSION

Life-space mobility is decreased in young-old adults with COPD, especially at the neighborhood level. This impairment is associated to higher dyspnea, peripheral muscle weakness and the reduced level of physical activity.

Leg blood flow is impaired during small muscle mass exercise in patients with COPD

Skeletal muscle blood flow is regulated to match the oxygen demand and dysregulation could contribute to exercise intolerance in patients with chronic obstructive pulmonary disease (COPD). We measured leg hemodynamics and metabolites from vasoactive compounds in muscle interstitial fluid and plasma at rest, during one-legged knee-extensor exercise, and during arterial infusions of sodium nitroprusside (SNP) and acetylcholine (ACh), respectively. Ten patients with moderate to severe COPD and eight age- and sex-matched healthy controls were studied. During knee-extensor exercise (10 W), leg blood flow was lower in the patients compared with the controls (1.82 ± 0.11 vs. 2.36 ± 0.14 l/min, respectively; P < 0.05), which compromised leg oxygen delivery (372 ± 26 vs. 453 ± 32 ml O2/min, respectively; P < 0.05). At rest, plasma endothelin-1 (vasoconstrictor) was higher in the patients with COPD ( P < 0.05) and also tended to be higher during exercise ( P = 0.07), whereas the formation of interstitial prostacyclin (vasodilator) was only increased in the controls. There was no difference between groups in the nitrite/nitrate levels (vasodilator) in plasma or interstitial fluid during exercise. Moreover, patients and controls showed similar vasodilatory capacity in response to both endothelium-independent (SNP) and endothelium-dependent (ACh) stimulation. The results suggest that leg muscle blood flow is impaired during small muscle mass exercise in patients with COPD possibly due to impaired formation of prostacyclin and increased levels of endothelin-1.

NEW & NOTEWORTHY This study demonstrates that chronic obstructive pulmonary disease (COPD) is associated with a reduced blood flow to skeletal muscle during small muscle mass exercise. In contrast to healthy individuals, interstitial prostacyclin levels did not increase during exercise and plasma endothelin-1 levels were higher in the patients with COPD.

Increased Myogenic and Protein Turnover Signaling in Skeletal Muscle of Chronic Obstructive Pulmonary Disease Patients With Sarcopenia

BACKGROUND

Sarcopenia was recently recognized as an independent condition by an International Classification of Diseases, Tenth Revision, Clinical Modification code, and is a frequently observed comorbidity in chronic obstructive pulmonary disease (COPD). Muscle mass is primarily dictated by the balance between protein degradation and synthesis, but their relative contribution to sarcopenia is unclear.

OBJECTIVE

We aimed to assess potential differential molecular regulation of protein degradation and synthesis, as well as myogenesis, in the skeletal muscle of COPD patients with and without sarcopenia.

METHODS

Muscle biopsies were obtained from the vastus lateralis muscle. Patients with COPD were clustered based on sarcopenia defined by low appendicular skeletal muscle mass index (nonsarcopenic COPD, n = 53; sarcopenic COPD, n = 39), and compared with healthy nonsarcopenic controls (n = 13). The mRNA and protein expression of regulators and mediators of ubiquitin-proteasome system (UPS), autophagy-lysosome system (autophagy), and protein synthesis were analyzed. Furthermore, mRNA expression of myogenesis markers was assessed.

RESULTS

UPS signaling was unaltered, whereas indices of UPS regulation (eg, FOXO1 protein; p-FOXO3/FOXO3), autophagy signaling (eg, LC3BII/I; p-ULK1[Ser757]/ULK1), and protein synthesis signaling (eg, AKT1; p-GSK3B/GSK3B; p-4E-BP1/4E-BP1) were increased in COPD. These alterations were even more pronounced in COPD patients with sarcopenia (eg, FOXO1 protein; p-FOXO1/FOXO1; LC3BII/I; p-ULK(Ser555); p-AKT1/AKT1; AKT1; p-4E-BP1). Furthermore, myogenic signaling (eg, MYOG) was increased in COPD despite a concomitant increase of myostatin (MSTN) mRNA expression, with no difference between sarcopenic and nonsarcopenic COPD patients.

CONCLUSION

Together with elevated myogenic signaling, the increase in muscle protein turnover signaling in COPD, which is even more prominent in COPD patients with sarcopenia, reflects molecular alterations associated with muscle repair and remodeling.

Eccentric Ergometer Training Promotes Locomotor Muscle Strength but Not Mitochondrial Adaptation in Patients with Severe Chronic Obstructive Pulmonary Disease

Eccentric ergometer training (EET) is increasingly being proposed as a therapeutic strategy to improve skeletal muscle strength in various cardiorespiratory diseases, due to the principle that lengthening muscle actions lead to high force-generating capacity at low cardiopulmonary load. One clinical population that may particularly benefit from this strategy is chronic obstructive pulmonary disease (COPD), as ventilatory constraints and locomotor muscle dysfunction often limit efficacy of conventional exercise rehabilitation in patients with severe disease. While the feasibility of EET for COPD has been established, the nature and extent of adaptation within COPD muscle is unknown. The aim of this study was therefore to characterize the locomotor muscle adaptations to EET in patients with severe COPD, and compare them with adaptations gained through conventional concentric ergometer training (CET). Male patients were randomized to either EET (n = 8) or CET (n = 7) for 10 weeks and matched for heart rate intensity. EET patients trained on average at a workload that was three times that of CET, at a lower perception of leg fatigue and dyspnea. EET led to increases in isometric peak strength and relative thigh mass (p < 0.01) whereas CET had no such effect. However, EET did not result in fiber hypertrophy, as morphometric analysis of muscle biopsies showed no increase in mean fiber cross-sectional area (p = 0.82), with variability in the direction and magnitude of fiber-type responses (20% increase in Type 1, p = 0.18; 4% decrease in Type 2a, p = 0.37) compared to CET (26% increase in Type 1, p = 0.04; 15% increase in Type 2a, p = 0.09). EET had no impact on mitochondrial adaptation, as revealed by lack of change in markers of mitochondrial biogenesis, content and respiration, which contrasted to improvements (p < 0.05) within CET muscle. While future study is needed to more definitively determine the effects of EET on fiber hypertrophy and associated underlying molecular signaling pathways in COPD locomotor muscle, our findings promote the implementation of this strategy to improve muscle strength. Furthermore, contrasting mitochondrial adaptations suggest evaluation of a sequential paradigm of eccentric followed by concentric cycling as a means of augmenting the training response and attenuating skeletal muscle dysfunction in patients with advanced COPD.

Heterogeneity of blood flow and metabolism during exercise in patients with chronic obstructive pulmonary disease

The study investigated whether the capacity to regulate muscle blood flow (Q) relative to metabolic demand (VO₂) is impaired in COPD. Using six NIRS optodes over the upper, middle and lower vastus lateralis in 6 patients, (FEV₁:46±12%predicted) we recorded from each: a) Q by indocyanine green dye injection, b) VO₂/Q ratios based on fractional tissue O₂ saturation and c) VO₂ as their product, during constant-load exercise (at 20%, 50% and 80% of peak capacity) in normoxia and hyperoxia (F_IO₂:1.0). At 50 and 80%, relative dispersion (RD) for Q, but not for VO₂, was greater in normoxia (0.67±0.07 and 0.79±0.08, respectively) compared to hyperoxia (0.57±0.12 and 0.72±0.07, respectively). In both conditions, RD for VO₂ and Q significantly increased throughout exercise; however, RD of VO₂/Q ratio was minimal (normoxia: 0.12-0.08 vs hyperoxia: 0.13-0.09). Muscle Q and VO₂ appear closely matched in COPD patients, indicating a minimal impact of heterogeneity on muscle oxygen availability at submaximal levels of exercise.

Skeletal muscle mitophagy in chronic disease: implications for muscle oxidative capacity?

PURPOSE OF REVIEW

Loss of skeletal muscle oxidative capacity is a common feature of chronic diseases such as chronic obstructive pulmonary disease, type 2 diabetes, and congestive heart failure. It may lead to physical impairments and has been suggested to contribute to metabolic inflexibility-induced cardiometabolic risk. The mechanism underlying loss of muscle oxidative capacity is incompletely understood. This review discusses the role of mitophagy as a driving force behind the loss of skeletal muscle oxidative capacity in these patients.

RECENT FINDINGS

Mitophagy has been studied to a very limited extent in human skeletal muscle. There are, however, clear indications that disease-related factors, including hypoxia, systemic inflammation, muscle inactivity, and iron deficiency are able to induce mitophagy, and that these factors trigger mitophagy via different regulatory mechanisms. Although mitophagy may lead to mitochondrial loss, it is also required to maintain homeostasis through clearance of damaged mitochondria.

SUMMARY

Based on available evidence, we propose that enhanced mitophagy is involved in chronic disease-induced loss of muscle oxidative capacity. Clearly more research is required to confirm this role and to establish to what extent mitophagy is pathological or a part of physiological adaptation to maintain muscle health.

Effect of endurance versus resistance training on quadriceps muscle dysfunction in COPD: a pilot study

Introduction

Exercise is an important countermeasure to limb muscle dysfunction in COPD. The two major training modalities in COPD rehabilitation, endurance training (ET) and resistance training (RT), may both be efficient in improving muscle strength, exercise capacity, and health-related quality of life, but the effects on quadriceps muscle characteristics have not been thoroughly described.

Methods

Thirty COPD patients (forced expiratory volume in 1 second: 56% of predicted, standard deviation [SD] 14) were randomized to 8 weeks of ET or RT. Vastus lateralis muscle biopsies were obtained before and after the training intervention to assess muscle morphology and metabolic and angiogenic factors. Symptom burden, exercise capacity (6-minute walking and cycle ergometer tests), and vascular function were also assessed.

Results

Both training modalities improved symptom burden and exercise capacity with no difference between the two groups. The mean (SD) proportion of glycolytic type IIa muscle fibers was reduced after ET (from 48% [SD 11] to 42% [SD 10], P<0.05), whereas there was no significant change in muscle fiber distribution with RT. There was no effect of either training modality on muscle capillarization, angiogenic factors, or vascular function. After ET the muscle protein content of phosphofructokinase was reduced (P<0.05) and the citrate synthase content tended increase (P=0.08) but no change was observed after RT.

Conclusion

Although both ET and RT improve symptoms and exercise capacity, ET induces a more oxidative quadriceps muscle phenotype, counteracting muscle dysfunction in COPD.

Respiratory constraints during activities in daily life and the impact on health status in patients with early-stage COPD: a cross-sectional study

In patients with chronic obstructive pulmonary disease (COPD), exercise capacity is reduced, resulting over time in physical inactivity and worsened health status. It is unknown whether ventilatory constraints occur during activities of daily life (ADL) in early stages of COPD. The aim of this study was to assess respiratory mechanics during ADL and to study its consequences on dyspnoea, physical activity and health status in early-stage COPD compared with healthy controls. In this cross-sectional study, 39 early-stage COPD patients (mean FEV₁ 88±s.d. 12% predicted) and 20 controls performed 3 ADL: climbing stairs, vacuum cleaning and displacing groceries in a cupboard. Respiratory mechanics were measured during ADL. Physical activity was measured with accelerometry. Health status was assessed by the Nijmegen Clinical Screening Instrument. Compared with controls, COPD patients had greater ventilatory inefficiency and higher ventilatory requirements during ADL (P<0.05). Dyspnoea scores were increased in COPD compared with controls (P<0.001). During ADL, >50% of the patients developed dynamic hyperinflation in contrast to 10–35% of the controls. Higher dyspnoea was scored by patients with dynamic hyperinflation. Physical activity was low but comparable between both groups. From the patients, 55–84% experienced mild-to-severe problems in health status compared with 5–25% of the controls. Significant ventilatory constraints already occur in early-stage COPD patients during common ADL and result in increased dyspnoea. Physical activity level is not yet reduced, but many patients already experience limitations in health status. These findings reinforce the importance of early diagnosis of COPD and assessment of more than just spirometry.

Why and How Limb Muscle Mass and Function Should Be Measured in Patients with Chronic Obstructive Pulmonary Disease

Impaired limb muscle function is a common occurrence in patients with chronic obstructive pulmonary disease (COPD), and it negatively influences exercise tolerance, quality of life, and even survival. Assessment of limb muscle mass and function in COPD is highly encouraged; it should include the quadriceps muscle, but other lower and upper limb muscles may also be evaluated to provide valuable information. Quantification of muscle mass as well as assessment of muscle strength and endurance are suggested. Bioelectrical impedance and dual-energy X-ray absorption can be realistically used in the clinical environment to monitor body composition. Although sophisticated computerized dynamometers provide the most accurate assessment, simple exercise and testing equipment are valid alternatives and they should help in implementing limb muscle function assessment in clinical settings. Isometric measurements, using strain-gauges or hand-held dynamometers, should be favored for their simplicity, availability, and quality of information provided. This perspective provides a rationale for the evaluation of limb muscle mass and function in COPD in routine clinical practice. In addition, measurement techniques used to assess limb muscle mass, strength, endurance, and fatigue in various clinical settings are discussed.

Role of Protein Carbonylation in Skeletal Muscle Mass Loss Associated with Chronic Conditions

Muscle dysfunction, characterized by a reductive remodeling of muscle fibers, is a common systemic manifestation in highly prevalent conditions such as chronic heart failure (CHF), chronic obstructive pulmonary disease (COPD), cancer cachexia, and critically ill patients. Skeletal muscle dysfunction and impaired muscle mass may predict morbidity and mortality in patients with chronic diseases, regardless of the underlying condition. High levels of oxidants may alter function and structure of key cellular molecules such as proteins, DNA, and lipids, leading to cellular injury and death. Protein oxidation including protein carbonylation was demonstrated to modify enzyme activity and DNA binding of transcription factors, while also rendering proteins more prone to proteolytic degradation. Given the relevance of protein oxidation in the pathophysiology of many chronic conditions and their comorbidities, the current review focuses on the analysis of different studies in which the biological and clinical significance of the modifications induced by reactive carbonyls on proteins have been explored so far in skeletal muscles of patients and animal models of chronic conditions such as COPD, disuse muscle atrophy, cancer cachexia, sepsis, and physiological aging. Future research will elucidate the specific impact and sites of reactive carbonyls on muscle protein content and function in human conditions.