Cytochrome oxidase activity and mitochondrial gene expression in skeletal muscle of patients with chronic obstructive pulmonary disease

Main Pathogenic Mechanisms and Recent Advances in COPD Peripheral Skeletal Muscle Wasting

Chronic obstructive pulmonary disease (COPD) is a worldwide prevalent respiratory disease mainly caused by tobacco smoke exposure. COPD is now considered as a systemic disease with several comorbidities. Among them, skeletal muscle dysfunction affects around 20% of COPD patients and is associated with higher morbidity and mortality. Although the histological alterations are well characterized, including myofiber atrophy, a decreased proportion of slow-twitch myofibers, and a decreased capillarization and oxidative phosphorylation capacity, the molecular basis for muscle atrophy is complex and remains partly unknown. Major difficulties lie in patient heterogeneity, accessing patients' samples, and complex multifactorial process including extrinsic mechanisms, such as tobacco smoke or disuse, and intrinsic mechanisms, such as oxidative stress, hypoxia, or systemic inflammation. Muscle wasting is also a highly dynamic process whose investigation is hampered by the differential protein regulation according to the stage of atrophy. In this review, we report and discuss recent data regarding the molecular alterations in COPD leading to impaired muscle mass, including inflammation, hypoxia and hypercapnia, mitochondrial dysfunction, diverse metabolic changes such as oxidative and nitrosative stress and genetic and epigenetic modifications, all leading to an impaired anabolic/catabolic balance in the myocyte. We recapitulate data concerning skeletal muscle dysfunction obtained in the different rodent models of COPD. Finally, we propose several pathways that should be investigated in COPD skeletal muscle dysfunction in the future.

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.

Effects of photobiomodulation as an adjunctive treatment in chronic obstructive pulmonary disease: a narrative review

Chronic obstructive pulmonary disease (COPD) is a disease characterized by chronic airway inflammation and remodeling and lung parenchymal inflammation and destruction, which result in many pulmonary and extrapulmonary manifestations. The anti-inflammatory effect of photobiomodulation (PBM) has been reported in previous studies. This review was conducted to evaluate the direct effect of PBM on lung inflammation in COPD. The other effects of PBM on modulation of peripheral and respiratory muscle metabolism and angiogenesis in lung tissues were also discussed. The databases of PubMed, Cochrane Library, and Google Scholar were searched to find the relevant studies. Keywords included PBM and related terms, COPD-related signs, and lung inflammation. A total of 12 articles were selected and reviewed in this study. Based on the present review, PBM is helpful in reducing lung inflammation through decreasing the inflammatory cytokines and chemokines at multiple levels and increasing anti-inflammatory cytokines. In addition, PBM also improves both peripheral and respiratory muscle metabolism and promote angiogenesis. This review demonstrated that PBM is a promising adjunctive treatment modality for COPD management which merits further validation.

Mitochondrial Ribosome Dysfunction in Human Alveolar Type II Cells in Emphysema

Pulmonary emphysema is characterized by airspace enlargement and the destruction of alveoli. Alveolar type II (ATII) cells are very abundant in mitochondria. OXPHOS complexes are composed of proteins encoded by the mitochondrial and nuclear genomes. Mitochondrial 12S and 16S rRNAs are required to assemble the small and large subunits of the mitoribosome, respectively. We aimed to determine the mechanism of mitoribosome dysfunction in ATII cells in emphysema. ATII cells were isolated from control nonsmokers and smokers, and emphysema patients. Mitochondrial transcription and translation were analyzed. We also determined the miRNA expression. Decreases in ND1 and UQCRC2 expression levels were found in ATII cells in emphysema. Moreover, nuclear NDUFS1 and SDHB levels increased, and mitochondrial transcribed ND1 protein expression decreased. These results suggest an impairment of the nuclear and mitochondrial stoichiometry in this disease. We also detected low levels of the mitoribosome structural protein MRPL48 in ATII cells in emphysema. Decreased 16S rRNA expression and increased 12S rRNA levels were observed. Moreover, we analyzed miR4485-3p levels in this disease. Our results suggest a negative feedback loop between miR-4485-3p and 16S rRNA. The obtained results provide molecular mechanisms of mitoribosome dysfunction in ATII cells in emphysema.

Current views in chronic obstructive pulmonary disease pathogenesis and management

Chronic obstructive pulmonary disease (COPD) is a progressive lung dysfunction caused mainly by inhaling toxic particles and cigarette smoking (CS). The continuous exposure to ruinous molecules can lead to abnormal inflammatory responses, permanent damages to the respiratory system, and irreversible pathological changes. Other factors, such as genetics and aging, influence the development of COPD. In the last decade, accumulating evidence suggested that mitochondrial alteration, including mitochondrial DNA damage, increased mitochondrial reactive oxygen species (ROS), abnormal autophagy, and apoptosis, have been implicated in the pathogenesis of COPD. The alteration can also extend to epigenetics, namely DNA methylation, histone modification, and non-coding RNA. This review will discuss the recent progressions in COPD pathology, pathophysiology, and molecular pathways. More focus will be shed on mitochondrial and epigenetic variations related to COPD development and the role of nanomedicine as a potential tool for the prevention and treatment of this disease.

Mitochondrial ribosomal stress in lung diseases

Mitochondria are involved in a variety of critical cellular functions, and their impairment drives cell injury. The mitochondrial ribosome (mitoribosome) is responsible for the protein synthesis of mitochondrial DNA encoded genes. These proteins are involved in oxidative phosphorylation, respiration, and ATP production required in the cell. Mitoribosome components originate from both mitochondrial and nuclear genomes. Their dysfunction can be caused by impaired mitochondrial protein synthesis or mitoribosome misassembly, leading to a decline in mitochondrial translation. This decrease can trigger mitochondrial ribosomal stress and contribute to pulmonary cell injury, death, and diseases. This review focuses on the contribution of the impaired mitoribosome structural components and function to respiratory disease pathophysiology. We present recent findings in the fields of lung cancer, chronic obstructive pulmonary disease, interstitial lung disease, and asthma. We also include reports on the mitoribosome dysfunction in pulmonary hypertension, high altitude pulmonary edema, bacterial and viral infections. Studies of the mitoribosome alterations in respiratory diseases can lead to novel therapeutic targets.

Gender specific airway gene expression in COPD sub-phenotypes supports a role of mitochondria and of different types of leukocytes

Chronic obstructive pulmonary disease (COPD) is a destructive inflammatory disease and the genes expressed within the lung are crucial to its pathophysiology. We have determined the RNAseq transcriptome of bronchial brush cells from 312 stringently defined ex-smoker patients. Compared to healthy controls there were for males 40 differentially expressed genes (DEGs) and 73 DEGs for females with only 26 genes shared. The gene ontology (GO) term “response to bacterium” was shared, with several different DEGs contributing in males and females. Strongly upregulated genes TCN1 and CYP1B1 were unique to males and females, respectively. For male emphysema (E)-dominant and airway disease (A)-dominant COPD (defined by computed tomography) the term “response to stress” was found for both sub-phenotypes, but this included distinct up-regulated genes for the E-sub-phenotype (neutrophil-related CSF3R, CXCL1, MNDA) and for the A-sub-phenotype (macrophage-related KLF4, F3, CD36). In E-dominant disease, a cluster of mitochondria-encoded (MT) genes forms a signature, able to identify patients with emphysema features in a confirmation cohort. The MT-CO2 gene is upregulated transcriptionally in bronchial epithelial cells with the copy number essentially unchanged. Both MT-CO2 and the neutrophil chemoattractant CXCL1 are induced by reactive oxygen in bronchial epithelial cells. Of the female DEGs unique for E- and A-dominant COPD, 88% were detected in females only. In E-dominant disease we found a pronounced expression of mast cell-associated DEGs TPSB2, TPSAB1 and CPA3. The differential genes discovered in this study point towards involvement of different types of leukocytes in the E- and A-dominant COPD sub-phenotypes in males and females.

Mitochondrial dysfunction in airways and quadriceps muscle of patients with chronic obstructive pulmonary disease

BACKGROUND

Mitochondrial damage and dysfunction have been reported in airway and quadriceps muscle cells of patients with chronic obstructive pulmonary disease (COPD). We determined the concomitance of mitochondrial dysfunction in these cells in COPD.

METHODS

Bronchial biopsies were obtained from never- and ex-smoker volunteers and COPD patients (GOLD Grade 2) and quadriceps muscle biopsies from the same volunteers in addition to COPD patients at GOLD Grade 3/4 for measurement of mitochondrial function.

RESULTS

Decreased mitochondrial membrane potential (ΔΨm), increased mitochondrial reactive oxygen species (mtROS) and decreased superoxide dismutase 2 (SOD2) levels were observed in mitochondria isolated from bronchial biopsies from Grade 2 patients compared to healthy never- and ex-smokers. There was a significant correlation between ΔΨm and FEV₁ (% predicted), transfer factor of the lung for carbon monoxide (TLCO_C % predicted), 6-min walk test and maximum oxygen consumption. In addition, ΔΨm was also associated with decreased expression levels of electron transport chain (ETC) complex proteins I and II. In quadriceps muscle of Grade 2 COPD patients, a significant increase in total ROS and mtROS was observed without changes in ΔΨm, SOD2 or ETC complex protein expression. However, quadriceps muscle of GOLD Grade 3/4 COPD patients showed an increased mtROS and decreased SOD2 and ETC complex proteins I, II, III and V expression.

CONCLUSIONS

Mitochondrial dysfunction in the airways, but not in quadriceps muscle, is associated with airflow obstruction and exercise capacity in Grade 2 COPD. Oxidative stress-induced mitochondrial dysfunction in the quadriceps may result from similar disease processes occurring in the lungs.

Acute effects of photobiomodulation therapy applied to respiratory muscles of chronic obstructive pulmonary disease patients: a double-blind, randomized, placebo-controlled crossover trial

To investigate the effects of photobiomodulation applied to respiratory muscles on lung function, thoracoabdominal mobility, respiratory muscle strength, and functional capacity in COPD patients. This is a randomized double-blind crossover clinical trial. Twelve male COPD patients participated in the study. Participants were randomly allocated to receive two photobiomodulation sessions, 1 week apart: (1) an effective photobiomodulation session applied at the main respiratory muscles by means of a cluster with 69 light-emitting diodes (LEDs), containing 35 red (630 ± 10 nm; 10 mW; 0.2 cm²) and 34 near-infrared (830 ± 20 nm; 10 mW; 0.2 cm²) LEDs and (2) a sham photobiomodulation session, following the same procedures without emitting light. The primary outcomes were pulmonary function (spirometric indexes); thoracoabdominal mobility (cirtometry); respiratory muscle strength (maximal respiratory pressures), assessed at three moments: (1) baseline, (2) 1 h after intervention, and (3) 24 h after intervention; and the functional capacity, assessed by the 6-min walk test (6MWT) at baseline and 24 h after intervention. No significant interactions were found for spirometric variables, maximal respiratory pressures, and cirtometry. However, there was a Time × Condition interaction (F = 18.63; p = 0.001; η²_p = 0.62) in the walked distance on the 6MWT, with a significant increase after photobiomodulation intervention (p < 0.01) compared with the baseline. Photobiomodulation applied to respiratory muscles was effective in improving acute functional capacity in COPD patients. To the best of our knowledge, this is the first study assessing the effects of photobiomodulation applied to respiratory muscles in patients with COPD.

Effects of Roflumilast on Rehospitalization and Mortality in Patients

Introduction: Hospitalization for chronic obstructive pulmonary disease (COPD) exacerbation portends the greatest risk of rehospitalization and mortality. Treatments that prevent hospitalizations could significantly lessen COPD morbidity and mortality. Methods: We performed a prospective, randomized, double-blind, placebo-controlled study of roflumilast 500 ug daily versus placebo in patients hospitalized for acute COPD exacerbation. Primary outcome was time to all-cause mortality or non-elective rehospitalization at 180 days post-randomization. Secondary outcomes were death or hospitalization from a respiratory cause, quality of life, change in health status, forced expiratory volume in 1 second (FEV1) and roflumilast tolerance. Results: A total of 64 patients with moderate to severe COPD (FEV1, 37.6 ± 16.4% predicted; 61% female, 61.6 ± 7.9 years old) were assigned to roflumilast or placebo. No deaths occurred in the follow-up period. There was no difference in the time to first readmission between the roflumilast and placebo groups (46.1 days versus 47.3 days respectively, p=0.93). There were 29 and 30 readmissions in the roflumilast and placebo groups, respectively (p=0.47). The St George's Respiratory Questionnaire (SGRQ) decreased 10.8 points and 7.8 points in the roflumilast and placebo groups, respectively and were not different. EuroQuality of Life Five Dimension scale (EQ5D) scores improved, but not significantly in either group. Weight loss and nausea were more common with roflumilast but not different from placebo. Change in glycosylated hemoglobin percentage (HgbA1C%) was not different between groups. Sub-analysis for the impact of chronic bronchitis did not affect outcomes. Conclusion: In this pilot study conducted in patients hospitalized with an exacerbation of COPD, roflumilast did not affect time to all-cause rehospitalization, quality of life, FEV1 or any other measured parameter.

Genomics and response to long-term oxygen therapy in chronic obstructive pulmonary disease

Chronic obstructive pulmonary disease (COPD) is a leading cause of death worldwide, and long-term oxygen therapy has been shown to reduce mortality in COPD patients with severe hypoxemia. However, the Long-term Oxygen Treatment Trial (LOTT), a large randomized trial, found no benefit of oxygen therapy in COPD patients with moderate hypoxemia. We hypothesized that there may be differences in response to oxygen which depend on genotype or gene expression. In a genome-wide time-to-event analysis of the primary outcome of death or hospitalization in 331 subjects, 97 single nucleotide polymorphisms (SNPs) showed evidence of interaction with oxygen therapy at P < 1e-5, including 7 SNPs near arylsulfatase B (ARSB; P = 6e-6). In microarray expression profiling on 51 whole blood samples from 37 individuals, at screening and/or at 12-month follow-up, ARSB expression was associated with the primary outcome depending on oxygen treatment. The significant SNPs were conditional expression quantitative trait loci for ARSB expression. In a network analysis of genes affected by long-term oxygen, two observed clusters including 26 co-expressed genes were enriched in mitochondrial function. Using data from the observational COPDGene Study, we validated the expression of 25 of these 26 genes, plus ARSB. The effect of long-term oxygen therapy in COPD varied based on ARSB expression and genotype. ARSB has previously been shown to be associated with hypoxemia in human bronchial and colonic epithelial cells and in a mouse model. In peripheral blood, long-term oxygen treatment affected expression of mitochondrial-related genes, a biologically relevant pathway in COPD. SNPs and expression of ARSB are associated with response to long-term oxygen in COPD. The ARSB SNPs were expression quantitative trait loci depending on oxygen therapy. Genes differentially expressed by long-term oxygen were enriched in mitochondrial functions. This suggests a potential biomarker to personalize use of long-term oxygen in COPD.

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.

Mitochondrial dysfunction in inflammatory responses and cellular senescence: pathogenesis and pharmacological targets for chronic lung diseases

Mitochondria are dynamic organelles, which couple the various cellular processes that regulate metabolism, cell proliferation and survival. Environmental stress can cause mitochondrial dysfunction and dynamic changes including reduced mitochondrial biogenesis, oxidative phosphorylation and ATP production, as well as mitophagy impairment, which leads to increased ROS, inflammatory responses and cellular senescence. Oxidative stress, inflammation and cellular senescence all have important roles in the pathogenesis of chronic lung diseases, such as chronic obstructive pulmonary disease, pulmonary fibrosis and bronchopulmonary dysplasia. In this review, we discuss the current state on how mitochondrial dysfunction affects inflammatory responses and cellular senescence, the mechanisms of mitochondrial dysfunction underlying the pathogenesis of chronic lung diseases and the potential of mitochondrial transfer and replacement as treatments for these diseases.

Alterations in Skeletal Muscle Oxidative Phenotype in Mice Exposed to 3 Weeks of Normobaric Hypoxia

Skeletal muscle of patients with chronic respiratory failure is prone to loss of muscle mass and oxidative phenotype. Tissue hypoxia has been associated with cachexia and emphysema in humans. Experimental research on the role of hypoxia in loss of muscle oxidative phenotype, however, has yielded inconsistent results. Animal studies are frequently performed in young animals, which may hinder translation to generally older aged patients. Therefore, in this study, we tested the hypothesis that hypoxia induces loss of skeletal muscle oxidative phenotype in a model of aged (52 weeks) mice exposed to 3 weeks of hypoxia. Additional groups of young (4 weeks) and adult (12 weeks) mice were included to examine age effects. To verify hypoxia-induced cachexia, fat pad and muscle weights as well as muscle fiber cross-sectional areas were determined. Muscle oxidative phenotype was assessed by expression and activity of markers of mitochondrial metabolism and fiber-type distribution. A profound loss of muscle and fat was indeed accompanied by a slightly lower expression of markers of muscle oxidative capacity in the aged hypoxic mice. In contrast, hypoxia-associated changes of fiber-type composition were more prominent in the young mice. The differential response of the muscle of young, adult, and aged mice to hypoxia suggests that age matters and that the aged mouse is a better model for translation of findings to elderly patients with chronic respiratory disease. Furthermore, the findings warrant further mechanistic research into putative accelerating effects of hypoxia-induced loss of oxidative phenotype on the cachexia process in chronic respiratory disease.

Mitochondria in lung disease

Mitochondria are a distinguishing feature of eukaryotic cells. Best known for their critical function in energy production via oxidative phosphorylation (OXPHOS), mitochondria are essential for nutrient and oxygen sensing and for the regulation of critical cellular processes, including cell death and inflammation. Such diverse functional roles for organelles that were once thought to be simple may be attributed to their distinct heteroplasmic genome, exclusive maternal lineage of inheritance, and ability to generate signals to communicate with other cellular organelles. Mitochondria are now thought of as one of the cell's most sophisticated and dynamic responsive sensing systems. Specific signatures of mitochondrial dysfunction that are associated with disease pathogenesis and/or progression are becoming increasingly important. In particular, the centrality of mitochondria in the pathological processes and clinical phenotypes associated with a range of lung diseases is emerging. Understanding the molecular mechanisms regulating the mitochondrial processes of lung cells will help to better define phenotypes and clinical manifestations associated with respiratory disease and to identify potential diagnostic and therapeutic targets.

Mitochondrial iron chelation ameliorates cigarette smoke-induced bronchitis and emphysema in mice

Chronic obstructive pulmonary disease (COPD) is linked to both cigarette smoking and genetic determinants. We have previously identified iron-responsive element-binding protein 2 (IRP2) as an important COPD susceptibility gene and have shown that IRP2 protein is increased in the lungs of individuals with COPD. Here we demonstrate that mice deficient in Irp2 were protected from cigarette smoke (CS)-induced experimental COPD. By integrating RNA immunoprecipitation followed by sequencing (RIP-seq), RNA sequencing (RNA-seq), and gene expression and functional enrichment clustering analysis, we identified Irp2 as a regulator of mitochondrial function in the lungs of mice. Irp2 increased mitochondrial iron loading and levels of cytochrome c oxidase (COX), which led to mitochondrial dysfunction and subsequent experimental COPD. Frataxin-deficient mice, which had higher mitochondrial iron loading, showed impaired airway mucociliary clearance (MCC) and higher pulmonary inflammation at baseline, whereas mice deficient in the synthesis of cytochrome c oxidase, which have reduced COX, were protected from CS-induced pulmonary inflammation and impairment of MCC. Mice treated with a mitochondrial iron chelator or mice fed a low-iron diet were protected from CS-induced COPD. Mitochondrial iron chelation also alleviated CS-induced impairment of MCC, CS-induced pulmonary inflammation and CS-associated lung injury in mice with established COPD, suggesting a critical functional role and potential therapeutic intervention for the mitochondrial-iron axis in COPD.

Muscle dysfunction in chronic obstructive pulmonary disease: update on causes and biological findings

Respiratory and/or limb muscle dysfunction, which are frequently observed in chronic obstructive pulmonary disease (COPD) patients, contribute to their disease prognosis irrespective of the lung function. Muscle dysfunction is caused by the interaction of local and systemic factors. The key deleterious etiologic factors are pulmonary hyperinflation for the respiratory muscles and deconditioning secondary to reduced physical activity for limb muscles. Nonetheless, cigarette smoke, systemic inflammation, nutritional abnormalities, exercise, exacerbations, anabolic insufficiency, drugs and comorbidities also seem to play a relevant role. All these factors modify the phenotype of the muscles, through the induction of several biological phenomena in patients with COPD. While respiratory muscles improve their aerobic phenotype (percentage of oxidative fibers, capillarization, mitochondrial density, enzyme activity in the aerobic pathways, etc.), limb muscles exhibit the opposite phenotype. In addition, both muscle groups show oxidative stress, signs of damage and epigenetic changes. However, fiber atrophy, increased number of inflammatory cells, altered regenerative capacity; signs of apoptosis and autophagy, and an imbalance between protein synthesis and breakdown are rather characteristic features of the limb muscles, mostly in patients with reduced body weight. Despite that significant progress has been achieved in the last decades, full elucidation of the specific roles of the target biological mechanisms involved in COPD muscle dysfunction is still required. Such an achievement will be crucial to adequately tackle with this relevant clinical problem of COPD patients in the near-future.

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.

Pulmonary rehabilitation: the reference therapy for undernourished patients with chronic obstructive pulmonary disease

Chronic obstructive pulmonary disease (COPD) combines the deleterious effects of chronic hypoxia, chronic inflammation, insulin-resistance, increased energy expenditure, muscle wasting, and exercise deconditioning. As for other chronic disorders, loss of fat-free mass decreased survival. The preservation of muscle mass and function, through the protection of the mitochondrial oxidative metabolism, is an important challenge in the management of COPD patients. As the prevalence of the disease is increasing and the medical advances make COPD patients live longer, the prevalence of COPD-associated nutritional disorders is expected to increase in future decades. Androgenopenia is observed in 40% of COPD patients. Due to the stimulating effects of androgens on muscle anabolism, androgenopenia favors loss of muscle mass. Studies have shown that androgen substitution could improve muscle mass in COPD patients, but alone, was insufficient to improve lung function. Two multicentric randomized clinical trials have shown that the association of androgen therapy with physical exercise and oral nutritional supplements containing omega-3 polyinsaturated fatty acids, during at least three months, is associated with an improved clinical outcome and survival. These approaches are optimized in the field of pulmonary rehabilitation which is the reference therapy of COPD-associated undernutrition.

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.

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

Being well-established in advanced chronic obstructive pulmonary disease (COPD), skeletal muscle dysfunction and its underlying pathology have been scarcely investigated in patients with mild-to-moderate airflow obstruction. We hypothesized that a loss of oxidative phenotype (oxphen) associated with decreased endurance is present in the skeletal muscle of patients with mild-to-moderate COPD. In quadriceps muscle biopsies from 29 patients with COPD (forced expiratory volume in 1 s [FEV1] 58 ± 16%pred, body mass index [BMI] 26 ± 4 kg/m2) and 15 controls (BMI 25 ± 3 kg/m2) we assessed fiber type distribution, fiber cross-sectional areas (CSA), oxidative and glycolytic gene expression, OXPHOS protein levels, metabolic enzyme activity, and levels of oxidative stress markers. Quadriceps function was assessed by isokinetic dynamometry, body composition by dual-energy X-ray absorptiometry, exercise capacity by an incremental load test, and physical activity level by accelerometry. Compared with controls, patients had comparable fat-free mass index, quadriceps strength, and fiber CSA, but quadriceps endurance was decreased by 29% ( P = 0.002). Patients with COPD had a clear loss of muscle oxphen: a fiber type I-to-II shift, decreased levels of OXPHOS complexes IV and V subunits (47% and 31%, respectively; P < 0.05), a decreased ratio of 3-hydroxyacyl-CoA dehydrogenase/phosphofructokinase (PFK) enzyme activities (38%, P < 0.05), and decreased peroxisome proliferator-activated receptor-γ coactivator-1α (40%; P < 0.001) vs. increased PFK (67%; P < 0.001) gene expression levels. Within the patient group, markers of oxphen were significantly positively correlated with quadriceps endurance and inversely with the increase in plasma lactate relative to work rate during the incremental test. Levels of protein carbonylation, tyrosine nitration, and malondialdehyde protein adducts were comparable between patients and controls. However, among patients, oxidative stress levels were significantly inversely correlated with markers of oxphen and quadriceps endurance. Reduced muscle endurance associated with underlying loss of muscle oxphen is already present in patients with mild-to-moderate COPD without muscle wasting.

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.

COPD elicits remodeling of the diaphragm and vastus lateralis muscles in humans

A profound remodeling of the diaphragm and vastus lateralis (VL) occurs in patients with moderate-to-severe chronic obstructive pulmonary disease (COPD). In this mini-review, we discuss the following costal diaphragm remodeling features noted in patients with moderate-to-severe COPD: 1) deletion of serial sarcomeres, 2) increased proportion of slow-twitch fibers, 3) fast-to-slow isoform shift in sarco(endo)plasmic reticulum Ca(2+)-ATPase, 4) increased capacity of oxidative metabolism, 5) oxidative stress, and 6) myofiber atrophy. We then present the sole feature of diaphragm remodeling noted in mild-to-moderate COPD under the heading "MyHC and contractile remodeling noted in mild-to-moderate COPD." The importance of VL remodeling in COPD patients as a prognostic indicator as well as a major determinant of the ability to carry out activities of daily living is well accepted. We present the remodeling of the VL noted in COPD patients under the following headings: 1) Decrease in proportion of slow-twitch fibers, 2) Decreased activity of oxidative pathways, 3) Oxidative and nitrosative stress, and 4) Myofiber atrophy. For each of the remodeling features noted in both the VL and costal diaphragm of COPD patients, we present mechanisms that are currently thought to mediate these changes as well as the pathophysiology of each remodeling feature. We hope that our mechanistic presentation stimulates research in this area that focuses on improving the ability of COPD patients to carry out increased activities of daily living.

Injury of peripheral muscles in smokers with chronic obstructive pulmonary disease

Muscle injury has clinical relevance in diseased individuals because it is associated with muscle dysfunction in terms of decreased strength and/or endurance. This study was aimed at answering three questions: whether the presence of chronic obstructive pulmonary disease (COPD) is associated with peripheral muscle injury; whether muscle injury is associated with some of the relevant functional impairment in the muscles; and whether muscle injury can be solely justified by deconditioning. Twenty-one male COPD patients were eligible for the study. Seven healthy volunteers recruited from the general population were included as controls. Function of the quadriceps muscle was assessed through specific single-leg exercise (strength and endurance). Cellular (light microscopy) and subcellular (electron microscopy) techniques were used to evaluate muscle injury on biopsies from the vastus lateralis muscle. Signs of injury were found in muscles from both control and COPD patients, not only in cases showing severe airflow obstruction but also in the mild or moderate stages of the disease. Current smoking and presence of COPD were significantly associated with increased injury of the muscle as assessed by light and electron microscopy techniques. The authors conclude that peripheral muscle injury is evident in mild, moderate, and severe stages of COPD even in the absence of respiratory failure, hypercapnia, chronic steroid treatment, low body weight, or some coexisting disease. These findings support the theory that systemic factors with deleterious effect are acting on peripheral muscles of smokers with COPD, increasing the susceptibility of the muscle fibers to membrane and sarcomere injury.

Skeletal muscle oxidative metabolism in an animal model of pulmonary emphysema: formoterol and skeletal muscle dysfunction

Skeletal muscle dysfunction is a significant contributor to exercise limitation in pulmonary emphysema. This study investigated skeletal muscle oxidative metabolism before and after aerosol exposure to a long-acting β-agonist (LABA), such as formoterol, in the pallid mouse (B6.Cg-Pldnpa/J), which has a deficiency in serum α(1)-antitrypsin (α(1)-PI) and develops spontaneous pulmonary emphysema. C57 BL/6J and its congener pallid mice of 8-12 and 16 months of age were treated with vehicle or formoterol aerosol challenge for 120 seconds. Morphological and morphometric studies and evaluations of mitochondrial adenosine diphosphate-stimulated respiration and of cytochrome oxidase activity on skeletal muscle were performed. Moreover, the mtDNA content in skeletal muscle and the mediators linked to muscle mitochondrial function and biogenesis, as well as TNF-α and peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α), were also evaluated. The lungs of pallid mice at 12 and 16 months of age showed patchy areas of airspace enlargements, with the destruction of alveolar septa. No significant differences were observed in basal values of mitochondrial skeletal muscle oxidative processes between C57 BL/6J and pallid mice. Exposure to LABA significantly improved mitochondrial skeletal muscle oxidative processes in emphysematous mice, where the mtDNA content was significantly higher with respect to 8-month-old pallid mice. This effect was compared with a significant increase of PGC-1α in skeletal muscles of 16-month-old pallid mice, with no significant changes in TNF-α concentrations. In conclusion, in emphysematous mice that showed an increased mtDNA content, exposure to inhaled LABA can improve mitochondrial skeletal muscle oxidative processes. PGC-1α may serve as a possible mediator of this effect.

Role of mtDNA haplogroups in COPD susceptibility in a southwestern Han Chinese population

The interplay of a complex genetic basis with the environmental factors of chronic obstructive pulmonary disease (COPD) may account for the differences in individual susceptibility to COPD. Mitochondrial DNA (mtDNA) contributes to an individual's ability to resist oxidation, an important determinant that affects COPD susceptibility. To investigate whether mtDNA haplogroups play important roles in COPD susceptibility, the frequencies of mtDNA haplogroups and an 822-bp mtDNA deletion in 671 COPD patients and 724 control individuals from southwestern China were compared. Multivariate logistic regression analysis revealed that, whereas mtDNA haplogroups A and M7 might be associated with an increased risk for COPD (OR=1.996, 95% CI=1.149-2.831, p=0.006, and OR=1.754, 95% CI=1.931-2.552, p=0.021, respectively), haplogroups F, D, and M9 might be associated with a decreased risk for COPD in this population (OR=0.554, 95% CI=0.390-0.787, p=0.001; OR=0.758, 95% CI=0.407-0.965, p=0.002; and OR=0.186, 95% CI=0.039-0.881, p=0.034, respectively). Additionally, the increased frequency of the 822-bp mtDNA deletion in male cigarette-smoking subjects among COPD patients and controls of haplogroup D indicated that haplogroup D might increase an individual's susceptibility to DNA damage from external reactive oxygen species derived from heavy cigarette smoking. We conclude that haplogroups A and M7 might be risk factors for COPD, whereas haplogroups D, F, and M9 might decrease the COPD risk in this Han Chinese population.

The clinical COPD questionnaire correlated with BODE index-A cross-sectional study

The Global initiative for Chronic Obstructive Lung Disease (GOLD) staging has widely used in the stratification of the severity of COPD, while BODE (body mass index, airflow obstruction, dyspnea, and exercise capacity) index was proven superior to FEV1 in predicting mortality, exacerbation and disease severity in patients with COPD. Clinical COPD Questionnaire (CCQ), a questionnaire with ten items categorized into three domains (symptoms, functional state and mental state) was developed to measure health status of COPD patients. However, little is known about the relationship between CCQ score and BODE index. We performed a prospective study with the inclusion of 89 patients who were clinically stable after a 6-week-therapy for COPD symptoms comparing their health status assessed by CCQ, BODE index and GOLD staging. We found that the total CCQ score was correlated with BODE score (P < 0.001) and GOLD staging (P < 0.001); of three CCQ domains, the functional status correlated the most with BODE index (rS = 0.670) and GOLD staging (rS = 0.531), followed by symptoms (rS = 0.482; rS = 0.346, respectively), and mental status (rS = 0.340; rS = 0.236, respectively). Our data suggest that CCQ is a reliable and convenient alternative tool to evaluate the severity of COPD.

Should androgenic anabolic steroids be considered in the treatment regime of selected chronic obstructive pulmonary disease patients?

PURPOSE OF REVIEW

Chronic obstructive pulmonary disease (COPD) is a widespread disease with high morbidity rates. Advanced stages can be complicated by unintentional weight loss and muscle wasting, which may contribute to increased morbidity and mortality. Reversal of weight loss increases muscle strength and exercise capacity and improves survival. This can partly be achieved by nutritional support, preferably combined with increase in exercise. Androgenic anabolic steroids (AASs), of which testosterone is the parent hormone, increase muscle size and strength. Due to these anabolic effects, AASs may emerge as a treatment option in COPD patients suffering from muscle wasting.

RECENT FINDINGS

Seven trials investigated the effects of AAS in patients with COPD. Some studies also included nutritional therapy and/or a pulmonary rehabilitation program. Compared with placebo, AASs increase lean body mass (LBM) and muscle size. However, no consistent effects on muscle strength, exercise capacity, or pulmonary function are seen.

SUMMARY

AASs increase LBM in patients with advanced stages of COPD. No consistent beneficial effect on other endpoints was demonstrated in the reviewed trials. However, probably higher doses of AASs are needed to exert a clinically meaningful effect on muscle strength or exercise capacity. Currently, no evidence is available to recommend AASs to all patients with COPD. In individual cases, treatment with AASs can be considered, particularly in men with advanced COPD, moderate-to-severe functional impairment, muscle wasting and on chronic corticosteroid therapy. Treatment with AASs should preferably be combined with a rehabilitation program and nutritional support. AASs should not be used in women or in men with symptomatic heart disease. When treatment with AASs is considered, intramuscular nandrolone-decanoate is preferred in a dose of 50-200 mg per week for a period of 12 weeks. However, the efficacy of AAS treatment in COPD patients needs further clarification in well designed, adequately powered clinical studies.

[Diaphragm and skeletal muscle dysfunction in COPD]

INTRODUCTION

Chronic obstructive pulmonary disease (COPD) is often accompanied by skeletal muscle alterations, resulting in enhanced morbidity and mortality.

STATE OF THE ART

Many studies have highlighted important structural and biochemical modifications in limb and respiratory muscles in COPD. Reviewing the similarities and differences between the two most studied muscles in COPD, the quadriceps and the diaphragm, may provide important clues about the mechanisms dictating muscle changes that occur in this disease.

PERSPECTIVES

Though these two muscle groups share a common systemic environment, discrepancies are observed in their respective alterations. These phenotypic differences suggest that, in addition to systemic factors, the local microenvironment must participate in the reorganization seen in these two muscles in COPD.

CONCLUSIONS

The current review introduces the alterations observed in the quadriceps and diaphragm in the context of COPD and suggests possible signaling pathways involved in the development of muscle dysfunction.

Excessive visceral fat accumulation in advanced chronic obstructive pulmonary disease

BACKGROUND

Previous studies have suggested links between chronic obstructive pulmonary disease (COPD), cardiovascular disease, and abdominal obesity. Although abdominal visceral fat is thought to be associated with cardiovascular risk factors, the degree of visceral fat accumulation in patients with COPD has not been directly studied. The aim of this study was to investigate the abdominal visceral fat accumulation and the association between visceral fat and the severity and changes in emphysema in COPD patients.

METHODS

We performed clinical and laboratory tests, including pulmonary function, dyspnea score, and the six-minute walking test in COPD patients (n = 101) and control, which included subjects with a smoking history but without airflow obstruction (n = 62). We used computed tomography to evaluate the abdominal visceral fat area (VFA), subcutaneous fat area (SFA), and the extent of emphysema.

RESULTS

The COPD group had a larger VFA than the control group. The prevalence of non-obese subjects with an increased VFA was greater in the Global Initiative for Chronic Obstructive Lung Disease Stages III and IV than in the other stages of COPD. The extent of emphysema was inversely correlated with waist circumference and SFA. However, VFA did not decrease with the severity of emphysema. VFA was positively correlated with the degree of dyspnea.

CONCLUSION

COPD patients have excessive visceral fat, which is retained in patients with more advanced stages of COPD or severe emphysema despite the absence of obesity.

Pulmonary rehabilitation improves exercise capacity and quality of life in underweight patients with chronic obstructive pulmonary disease

BACKGROUND AND OBJECTIVE

An estimated 20-40% of COPD patients are underweight. We sought to confirm the physiological and psychosocial benefits of pulmonary rehabilitation programmes (PRP) in underweight compared with non-underweight patients with COPD.

METHODS

Twenty-two underweight COPD patients with BMI <20 kg/m(2), and 22 non-underweight COPD patients, who were matched for FEV(1) and age, were studied. All patients had moderate-to-very severe COPD. All patients participated in 12-week, hospital-based outpatient PRP consisting of two sessions per week. Baseline and post-PRP status were evaluated by spirometry, cardiopulmonary exercise testing, ventilatory muscle strength and the St. George's Respiratory Questionnaire (SGRQ).

RESULTS

At baseline, the age distribution and airflow obstruction were similar in underweight and non-underweight patients with COPD. Baseline exercise capacity, inspiratory muscle strength and SGRQ total and symptoms scores were significantly lower in the underweight patients (all P < 0.05). After the PRP, there was significant weight gain in the underweight COPD patients (mean increase 0.8 kg, P = 0.01). There were also significant improvements in peak oxygen uptake, peak workload and the SGRQ total, symptoms, activity and impact scores in both underweight and non-underweight patients with COPD (all P < 0.05).

CONCLUSIONS

Underweight patients with COPD have impaired exercise capacity and health-related quality of life (HRQL). Exercise training with supplemental oxygen may result in significant weight gains and improvements in exercise capacity and HRQL. Exercise training is indicated for underweight patients with COPD.

Evidence that a higher ATP cost of muscular contraction contributes to the lower mechanical efficiency associated with COPD: preliminary findings

Impaired metabolism in peripheral skeletal muscles potentially contributes to exercise intolerance in chronic obstructive pulmonary disease (COPD). We used (31)P-magnetic resonance spectroscopy ((31)P-MRS) to examine the energy cost and skeletal muscle energetics in six patients with COPD during dynamic plantar flexion exercise compared with six well-matched healthy control subjects. Patients with COPD displayed a higher energy cost of muscle contraction compared with the controls (control: 6.1 ± 3.1% of rest·min(-1)·W(-1), COPD: 13.6 ± 8.3% of rest·min(-1)·W(-1), P = 0.01). Although, the initial phosphocreatine resynthesis rate was also significantly attenuated in patients with COPD compared with controls (control: 74 ± 17% of rest/min, COPD: 52 ± 13% of rest/min, P = 0.04), when scaled to power output, oxidative ATP synthesis was similar between groups (6.5 ± 2.3% of rest·min(-1)·W(-1) in control and 7.8 ± 3.9% of rest·min(-1)·W(-1) in COPD, P = 0.52). Therefore, our results reveal, for the first time that in a small subset of patients with COPD a higher ATP cost of muscle contraction may substantially contribute to the lower mechanical efficiency previously reported in this population. In addition, it appears that some patients with COPD have preserved mitochondrial function and normal energy supply in lower limb skeletal muscle.

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.

Cellular assessment of muscle in COPD: case studies of two males

The objective of this paper is to provide an overview of the recent developments in muscle physiology and biochemistry in general, and with respect to chronic obstructive pulmonary disease (COPD) specifically. As a way of illustration, we have presented data on the remodeling that occurs in vastus lateralis in two patients with COPD (COPD #1, forced expiratory volume in one second/forced vital capacity [FEV₁/FVC] = 63%; COPD #2, FEV₁/FVC = 41%) exhibiting differences in muscle wasting as compared to healthy controls (CON; FEV₁/FVC = 111 ± 2.2%, n = 4). Type I fibers percentages were lower in both COPD #1 (16.7) and COPD #2 (24.9) compared to CON (57.3 ± 5.2). Cross sectional area of the type I fibers of the patients ranged between 65%–68% of CON and for the type II subtypes (IIA, IIAX, IIX) between 74% and 89% (COPD #1) and 17%–32% (COPD #2). A lower number of capillary contacts were observed for all fiber types in COPD #1 but not COPD #2. Lower concentrations of adenosine triphosphate (ATP) (24%–26%) and phosphocreatine (18%–20%), but not lactate occurred in COPD. In contrast to COPD #1, who displayed normal glucose transporter content, GLUT1 and GLUT4 were only 71% and 54%, respectively of CON in COPD #2. Lower monocarboxylate contents were found for MCT1 in both COPD #1 (63%) and COPD #2 (41%) and for MCT4 (78%) in COPD #1. Maximal oxidative enzyme activities (V_max) for COPD #2 ranged between 37% (succinic dehydrogenase) and 70% (cytochrome C oxidase) of CON. For the cytosolic enzymes, V_max ranged between 89% (hexokinase) to 31% (pyruvate kinase) of CON. Depressions were also observed in V_max of the Na⁺-K⁺-ATPase for COPD #1 (66% of CON) but not COPD #2 (92% of CON) while V_max of the Ca²⁺-ATPase was near normal in COPD #1 (84% CON). It is concluded that disturbances can occur in muscle to a wide range of excitation, contraction and metabolic processes in COPD.

Time-dependent effects of short-term training on muscle metabolism during the early phase of exercise

In this study, we investigated the hypothesis that the metabolic adaptations observed during steady-state exercise soon after the onset of training would be displayed during the nonsteady period of moderate exercise and would occur in the absence of increases in peak aerobic power (Vo2peak) and in muscle oxidative potential. Nine untrained males [age = 20.8 +/- 0.70 (SE) yr] performed a cycle task at 62% Vo2peak before (Pre-T) and after (Post-T) training for 2 h/day for 5 days at task intensity. Tissue samples extracted from the vastus lateralis at 0 min (before exercise) and at 10, 60, and 180 s of exercise, indicated that at Pre-T, reductions (P < 0.05) in phosphocreatine and increases (P < 0.05) in creatine, inorganic phosphate, calculated free ADP, and free AMP occurred at 60 and 180 s but not at 10 s. At Post-T, the concentrations of all metabolites were blunted (P < 0.05) at 60 s. Training also reduced (P < 0.05) the increase in lactate and the lactate-to-pyruvate ratio observed during exercise at Pre-T. These adaptations occurred in the absence of change in Vo2peak (47.8 +/- 1.7 vs. 49.2 +/- 1.7 mlxkg(-1)xmin(-1)) and in the activities (molxkg protein(-1)xh(-1)) of succinic dehydrogenase (3.48 +/- 0.21 vs. 3.77 +/- 0.35) and citrate synthase (7.48 +/- 0.61 vs. 8.52 +/- 0.65) but not cytochrome oxidase (70.8 +/- 5.1 vs. 79.6 +/- 6.6 U/g protein; P < 0.05). It is concluded that the tighter metabolic control observed following short-term training is initially expressed during the nonsteady state, probably as a result of increases in oxidative phosphorylation that is not dependent on changes in Vo2peak while the role of oxidative potential remains uncertain.

Comparative assessment of the quadriceps and the diaphragm in patients with COPD

Chronic obstructive pulmonary disease (COPD) and other chronic diseases such as heart failure are accompanied by skeletal muscle alterations that further enhance morbidity and mortality in affected individuals. Several studies have highlighted important structural and biochemical modifications in limb and respiratory muscles in COPD. Reviewing the similarities and differences between the two most studied muscles in COPD, the quadriceps and the diaphragm, may be helpful in providing important clues about the mechanisms underlying muscle changes associated with this disease. Although oxidative stress is present in both muscles, other muscle alterations are clearly distinct between the quadriceps and the diaphragm. For example, the oxidative metabolism varies in opposite directions, the diaphragm exhibiting increased resistance to fatigue while the quadriceps in COPD is characterized by premature fatigability. Differences in muscle phenotypic expression between the diaphragm and the quadriceps indicate that, in addition to systemic factors, the local microenvironment must participate in the reorganization seen in these two skeletal muscles in COPD.

Skeletal muscle dysfunction in patients with chronic obstructive pulmonary disease

Chronic obstructive pulmonary disease (COPD) is a debilitating disease characterized by inflammation-induced airflow limitation and parenchymal destruction. In addition to pulmonary manifestations, patients with COPD develop systemic problems, including skeletal muscle and other organ-specific dysfunctions, nutritional abnormalities, weight loss, and adverse psychological responses. Patients with COPD often complain of dyspnea on exertion, reduced exercise capacity, and develop a progressive decline in lung function with increasing age. These symptoms have been attributed to increases in the work of breathing and in impairments in gas exchange that result from airflow limitation and dynamic hyperinflation. However, there is mounting evidence to suggest that skeletal muscle dysfunction, independent of lung function, contributes significantly to reduced exercise capacity and poor quality of life in these patients. Limb and ventilatory skeletal muscle dysfunction in COPD patients has been attributed to a myriad of factors, including the presence of low grade systemic inflammatory processes, nutritional depletion, corticosteroid medications, chronic inactivity, age, hypoxemia, smoking, oxidative and nitrosative stresses, protein degradation and changes in vascular density. This review briefly summarizes the contribution of these factors to overall skeletal muscle dysfunction in patients with COPD, with particular attention paid to the latest advances in the field.

Clinical predictors of the efficacy of a pulmonary rehabilitation programme in patients with COPD

OBJECTIVES

To identify predictors of success for an 8week pulmonary rehabilitation programme (PRP) in patients with chronic obstructive pulmonary disease (COPD).

METHODS

Sixty patients were stratified in subgroups according to baseline findings: airway obstruction (FEV(1) >/= or <50% pred), pulmonary hyperinflation (TLC > or <or=120% pred), BMI value (BMI > or <or=25), cardiovascular (CV) comorbidity, and resting PaO(2) (PaO(2) >/= or <60mmHg). Outcome measurements of PRP were: >54m increase in 6min walking test (6MWT), or >4points reduction in total score of S. George Respiratory Questionnaire (SGRQ). Logistic regression analysis was used.

RESULTS

After PRP there was a significant improvement in exercise tolerance and quality of life, which correlated with baseline FEV(1)/VC, PaO(2), SpO(2), 6MWT and SGRQ. SGRQ significantly decreased and 6MWT significantly increased after PRP in all subgroups, except for patients with CV comorbidities. Both univariate and multivariate logistic regression analyses showed that BMI>25 and resting PaO(2)<60mmHg were independent predictors of PRP efficacy in terms of improvement of 6MWT, but not of SGRQ scores.

CONCLUSIONS

Clinical and functional baseline findings do not predict the response to PRP in COPD. The greater efficacy in patients with BMI>25 or with PaO(2)<60mmHg may be due to a greater deconditioning in overweight patients, and to a larger room for improvement in hypoxemic patients.

Muscle fiber type characteristics in females with chronic obstructive pulmonary disease. A preliminary study

Chronic obstructive pulmonary disease (COPD) is known to elicit intrinsic abnormalities in male skeletal muscle. However, it is unclear to what extent these changes occur in women and whether they are fiber-type specific. We investigated fiber-type specific differences in selected histochemical properties in muscle obtained from women with moderate to severe COPD compared to healthy control (CON) women. Tissue was obtained from the vastus lateralis in five COPD patients (age 66.9 +/- 2.6 years; FEV1 = 43 +/- 7%) and eight CON (age 68 +/- 4.9 years; FEV1 = 113 +/- 4.2%). Compared to CON, the distribution (30.6 +/- 5.2 vs. 57.9 +/- 4.6%) and cross sectional area of type I (CSA, 5660 +/- 329 vs. 3586 +/- 257 microm2) and type IIA (2770 +/- 302 vs. 2099 +/- 206 microm2) were lower (P < 0.05) and higher (P < 0.05), respectively, in COPD. Disease state did not alter either the distribution or CSA of the IIA, IIAX or type X subtypes. Although differences were found between fiber types in the number of capillary contacts (n) (I > IIAX, IIX; IIA > IIX) and the capillaries per CSA (microm210(-3)) (I < IIA, IIAX, IIX), no differences were found between CON and COPD. Succinic dehydrogenase activity and sarcoplasmic reticulum (SR) Ca2+-ATPase activity, measured photometrically (OD units), were higher (P < 0.05), and lower (P < 0.05), respectively, in type I compared to the type II fiber subtypes. These properties were not altered with COPD. COPD in females is accompanied by a higher percent of type II fibers, a larger CSA of type I and type IIA fibers, both of which occur in the absence of differences in oxidative potential and the potential for SR Ca2+-sequestration.

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

Skeletal muscle dysfunction (SMD) is frequent in patients with chronic obstructive pulmonary disease (COPD). Mitochondrial abnormalities appear to play a role in the pathogenesis of SMD. The mitochondrion permeability transition pore (MPTP) facilitates the leakage of mitochondrial matrix constituents, such as cytochrome c (cyto-c), and triggers apoptosis, known to occur in skeletal muscle of patients with COPD. Our objective was to study MPTP kinetics and cyto-c release in skeletal muscle mitochondria of patients with COPD. Mitochondria were isolated from the vastus lateralis (VL), external intercostalis (EI), and latissimus dorsi (LD) in 11 patients with COPD (66 +/- 9 yr; FEV(1) 66 +/- 13%) and 15 smokers with normal lung function (64 +/- 6 yr; FEV(1) 95 +/- 11%) who required thoracic surgery for a localized lung neoplasm. MPTP kinetics were determined spectrophotometrically (time to reach V'max, V'max and mitochondrial swelling) and cyto-c release by enzyme-linked immunosorbent assay. MPTP kinetics and cyto-c release were abnormal in patients with COPD in the three muscles studied. In addition, V'max of VL mitochondria was significantly related (P < 0.01) to BMI (r = -0.75 COPD, -0.67 control) and aerobic capacity (r = -0.70 COPD, -0.60 control) for the COPD group. MPTP kinetics and cyto-c release are abnormal in skeletal and respiratory muscles of patients with moderate COPD, suggesting a systemic mechanism(s) occurring early during the course of the disease.

Pulmonary dysfunction and skeletal muscle changes in horses with RAO

BACKGROUND

Chronic pulmonary diseases (recurrent airway obstruction [RAO]) have been reported to alter skeletal muscle cells in humans. The purpose of this study was to evaluate a potential relationship between pulmonary and muscle variables in horses with a clinical diagnosis of RAO. Muscle biopsies from healthy horses and from horses with RAO were investigated and the relationship between the severity of lung disease and the degree of muscular changes was determined.

HYPOTHESIS

We hypothesized that chronic pulmonary disease can lead to changes of the skeletal muscle in horses.

ANIMALS

Fifteen healthy horses (control) and 50 horses with RAO were examined.

METHODS

In a prospective clinical trial, a complete lung examination was performed in all horses. In all horses, muscle enzyme activity at rest and after exercise and muscle biopsies from the M. gluteus medius were examined.

RESULTS

None of the horses had clinical or histologic signs of primary or neurogenic myopathies. According to the clinical, endoscopic, and radiographic findings and with a scoring system, the horses with RAO were grouped according to the severity of pulmonary findings (15 horses mild, 24 horses moderate, 11 horses severe RAO). Pathologic changes of the skeletal muscle (fiber atrophy or fiber hypertrophy, myofibrillar degeneration, hyperplasia of mitochondria, and ragged-red-like fibers) were identified in most horses with RAO but in only a few individual control horses. In addition, a marked depletion of muscle glycogen storage was evident in the RAO horses but not in the control group. Other pathologic changes of skeletal muscle such as centralized nuclei and regenerating fibers were rare, but were more frequent in horses with lung diseases than in the control group. The degree of muscle cell changes was also graded with a scoring system and correlated with the severity of pulmonary disease (r= 0.55).

CONCLUSION

Chronic pulmonary disease in horses is associated with structural changes in skeletal muscle.

CLINICAL IMPORTANCE

Because chronic pulmonary disease may affect muscles, early and effective therapy may prevent these changes. This finding could be of clinical importance but requires further studies.

Organization of metabolic pathways in vastus lateralis of patients with chronic obstructive pulmonary disease

The objective of this study was to determine whether patients with chronic obstructive lung disease (COPD) display differences in organization of the metabolic pathways and segments involved in energy supply compared with healthy control subjects. Metabolic pathway potential, based on the measurement of the maximal activity (Vmax) of representative enzymes, was assessed in tissue extracted from the vastus lateralis in seven patients with COPD (age 67 ± 4 yr; FEV1/FVC = 44 ± 3%, where FEV1is forced expiratory volume in 1 s and FVC is forced vital capacity; means ± SE) and nine healthy age-matched controls (age 68 ± 2 yr; FEV1/FVC = 75 ± 2%). Compared with control, the COPD patients displayed lower ( P < 0.05) Vmax(mol·kg protein−1·h−1) for cytochrome c oxidase (COX; 21.2 ± 2.0 vs. 28.7 ± 2.2) and 3-hydroxyacyl-CoA dehydrogenase (HADH; 2.54 ± 0.14 vs. 3.74 ± 0.12) but not citrate synthase (CS; 2.20 ± 0.16 vs. 3.19 ± 0.5). While no differences between groups were observed in Vmaxfor creatine phosphokinase, phosphorylase (PHOSPH), phosphofructokinase (PFK), pyruvate kinase, and lactate dehydrogenase, hexokinase (HEX) was elevated in COPD ( P < 0.05). Enzyme activity ratios were higher ( P < 0.05) for HEX/CS, HEX/COX, PHOSPH/HADH and PFK/HADH in COPD compared with control. It is concluded that COPD patients exhibit a reduced potential for both the electron transport system and fat oxidation and an increased potential for glucose phosphorylation while the potential for glycogenolysis and glycolysis remains normal. A comparison of enzyme ratios indicated greater potentials for glucose phosphorylation relative to the citric acid cycle and the electron transport chain and glycogenolysis and glycolysis relative to β-oxidation.