Lipofuscin accumulation in the vastus lateralis muscle in patients with chronic obstructive pulmonary disease

Musculoskeletal crosstalk in chronic obstructive pulmonary disease and comorbidities: Emerging roles and therapeutic potentials

Chronic Obstructive Pulmonary Disease (COPD) is a multifaceted respiratory disorder characterized by progressive airflow limitation and systemic implications. It has become increasingly apparent that COPD exerts its influence far beyond the respiratory system, extending its impact to various organ systems. Among these, the musculoskeletal system emerges as a central player in both the pathogenesis and management of COPD and its associated comorbidities. Muscle dysfunction and osteoporosis are prevalent musculoskeletal disorders in COPD patients, leading to a substantial decline in exercise capacity and overall health. These manifestations are influenced by systemic inflammation, oxidative stress, and hormonal imbalances, all hallmarks of COPD. Recent research has uncovered an intricate interplay between COPD and musculoskeletal comorbidities, suggesting that muscle and bone tissues may cross-communicate through the release of signalling molecules, known as "myokines" and "osteokines". We explored this dynamic relationship, with a particular focus on the role of the immune system in mediating the cross-communication between muscle and bone in COPD. Moreover, we delved into existing and emerging therapeutic strategies for managing musculoskeletal disorders in COPD. It underscores the development of personalized treatment approaches that target both the respiratory and musculoskeletal aspects of COPD, offering the promise of improved well-being and quality of life for individuals grappling with this complex condition. This comprehensive review underscores the significance of recognizing the profound impact of COPD on the musculoskeletal system and its comorbidities. By unravelling the intricate connections between these systems and exploring innovative treatment avenues, we can aspire to enhance the overall care and outcomes for COPD patients, ultimately offering hope for improved health and well-being.

Lipofuscin Granule Accumulation Requires Autophagy Activation

Lipofuscins are oxidized lipid and protein complexes that accumulate during cellular senescence and tissue aging, regarded as markers for cellular oxidative damage, tissue aging, and certain aging-associated diseases. Therefore, understanding their cellular biological properties is crucial for effective treatment development. Through traditional microscopy, lipofuscins are readily observed as fluorescent granules thought to accumulate in lysosomes. However, lipofuscin granule formation and accumulation in senescent cells are poorly understood. Thus, this study examined lipofuscin accumulation in human fibroblasts exposed to various stressors. Our results substantiate that in glucose-starved or replicative senescence cells, where elevated oxidative stress levels activate autophagy, lipofuscins predominately appear as granules that co-localize with autolysosomes due to lysosomal acidity or impairment. Meanwhile, autophagosome formation is attenuated in cells experiencing oxidative stress induced by a doxorubicin pulse and chase, and lipofuscin fluorescence granules seldom manifest in the cytoplasm. As Torin-1 treatment activates autophagy, granular lipofuscins intensify and dominate, indicating that autophagy activation triggers their accumulation. Our results suggest that high oxidative stress activates autophagy but fails in lipofuscin removal, leaving an abundance of lipofuscin-filled impaired autolysosomes, referred to as residual bodies. Therefore, future endeavors in treating lipofuscin pathology-associated diseases and dysfunctions through autophagy activation demand meticulous consideration.

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.

Nitrosative and Oxidative Stress, Reduced Antioxidant Capacity, and Fiber Type Switch in Iron-Deficient COPD Patients: Analysis of Muscle and Systemic Compartments

We hypothesized that a rise in the levels of oxidative/nitrosative stress markers and a decline in antioxidants might take place in systemic and muscle compartments of chronic obstructive pulmonary disease (COPD) patients with non-anemic iron deficiency. In COPD patients with/without iron depletion (n = 20/group), markers of oxidative/nitrosative stress and antioxidants were determined in blood and vastus lateralis (biopsies, muscle fiber phenotype). Iron metabolism, exercise, and limb muscle strength were assessed in all patients. In iron-deficient COPD compared to non-iron deficient patients, oxidative (lipofuscin) and nitrosative stress levels were greater in muscle and blood compartments and proportions of fast-twitch fibers, whereas levels of mitochondrial superoxide dismutase (SOD) and Trolox equivalent antioxidant capacity (TEAC) decreased. In severe COPD, nitrosative stress and reduced antioxidant capacity were demonstrated in vastus lateralis and systemic compartments of iron-deficient patients. The slow- to fast-twitch muscle fiber switch towards a less resistant phenotype was significantly more prominent in muscles of these patients. Iron deficiency is associated with a specific pattern of nitrosative and oxidative stress and reduced antioxidant capacity in severe COPD irrespective of quadriceps muscle function. In clinical settings, parameters of iron metabolism and content should be routinely quantify given its implications in redox balance and exercise tolerance.

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.

Understanding the role of smoking and chronic excess alcohol consumption on reduced caloric intake and the development of sarcopenia

This narrative review provides mechanistic insight into the biological link between smoking and/or chronic excess alcohol consumption, and increased risk of developing sarcopenia. Although the combination of excessive alcohol consumption and smoking is often associated with ectopic adipose deposition, this review is focused on the context of a reduced caloric intake (leading to energy deficit) that also may ensue due to either lifestyle habit. Smoking is a primary cause of periodontitis and chronic obstructive pulmonary disease that both induce swallowing difficulties, inhibit taste and mastication, and are associated with increased risk of muscle atrophy and mitochondrial dysfunction. Smoking may contribute to physical inactivity, energy deficit via reduced caloric intake, and increased systemic inflammation, all of which are factors known to suppress muscle protein synthesis rates. Moreover, chronic excess alcohol consumption may result in gut microbiota dysbiosis and autophagy-induced hyperammonemia, initiating the up-regulation of muscle protein breakdown and down-regulation of muscle protein synthesis via activation of myostatin, AMPK and REDD1, and deactivation of IGF-1. Future research is warranted to explore the link between oral healthcare management and personalised nutrition counselling in light of potential detrimental consequences of chronic smoking on musculoskeletal health outcomes in older adults. Experimental studies should investigate the impact of smoking and chronic excess alcohol consumption on the gut-brain axis, and explore biomarkers of smoking-induced oral disease progression. The implementation of behavioural change interventions and health policies regarding smoking and alcohol intake habits may mitigate the clinical and financial burden of sarcopenia on the healthcare system.

Oxidative stress causes muscle structural alterations via p38 MAPK signaling in COPD mouse model

INTRODUCTION

Sarcopenia is a complication of Chronic Obstructive Pulmonary Disease (COPD) that negatively affects physical activity and quality of life. However, the underlying mechanism by which COPD affects skeletal muscles remains to be elucidated. Therefore, we investigated the association between oxidative stress and structural alterations in muscles in elastase-induced emphysema mouse models.

MATERIALS AND METHODS

Twelve-week-old male C57BL/6J mice were treated with either intratracheal porcine pancreatic elastase (PPE) dissolved in saline, or saline alone. The mice were euthanized 12 weeks after treatment, and the lungs and limb muscles were used for protein analysis of oxidative stress, p38 mitogen-activated protein kinase (p38 MAPK) signaling pathway and muscle atrophy signaling pathway related with oxidative stress. Furthermore, C57BL/6J mice treated with PPE or saline were analyzed for the effects of oral administration of astaxanthin or p38 inhibitor.

RESULTS

The weight of the soleus muscle, proportion of type I muscle fibers, and cross-sectional areas of muscle fibers in the PPE group were lower than those in the control group. Oxidative stress marker levels in the PPE group were elevated in skeletal muscles. The p38 MAPK signaling pathway was activated in the soleus muscles, leading to the activation of the ubiquitin-proteasome system and autophagy. Astaxanthin and p38 inhibitors attenuated alterations in muscle structure through the deactivation of the p38 MAPK signaling pathway.

CONCLUSIONS

This study provides first evidence in COPD mouse model that oxidative stress trigger a series of muscle structural changes. Our findings suggest a novel target for sarcopenia in COPD.

Pathogenesis of sarcopenia in chronic obstructive pulmonary disease

Chronic obstructive pulmonary disease (COPD) is a common pulmonary disease characterized by persistent respiratory symptoms and airflow obstruction. In addition to lung diseases, chronic obstructive pulmonary disease (COPD) is often associated with other organ diseases, and sarcopenia is one of the common diseases. In recent years, multiple factors have been proposed to influence muscle dysfunction in COPD patients, including systemic and local inflammation, oxidative stress, hypoxia, hypercapnia, protein synthesis, catabolic imbalance, nutritional changes, disuse, ageing, and the use of medications such as steroids. These factors alone or in combination can lead to a reduction in muscle mass and cross-sectional area, deterioration of muscle bioenergy metabolism, defects in muscle repair and regeneration mechanisms, apoptosis and other anatomical and/or functional pathological changes, resulting in a decrease in the muscle’s ability to work. This article reviews the research progress of possible pathogenesis of sarcopenia in COPD.

Involvement of Parkin-mediated mitophagy in the pathogenesis of chronic obstructive pulmonary disease-related sarcopenia

BACKGROUND

Sarcopenia is characterized by the loss of skeletal muscle mass and strength and is associated with poor prognosis in patients with chronic obstructive pulmonary disease (COPD). Cigarette smoke (CS) exposure, a major cause for COPD, induces mitochondrial damage, which has been implicated in sarcopenia pathogenesis. The current study sought to examine the involvement of insufficient Parkin-mediated mitophagy, a mitochondrion-selective autophagy, in the mechanisms by which dysfunctional mitochondria accumulate with excessive reactive oxygen species (ROS) production in the development of COPD-related sarcopenia.

METHODS

The involvement of Parkin-mediated mitophagy was examined using in vitro models of myotube formation, in vivo CS-exposure model using Parkin^-/- mice, and human muscle samples from patients with COPD-related sarcopenia.

RESULTS

Cigarette smoke extract (CSE) induced myotube atrophy with concomitant 30% reduction in Parkin expression levels (P < 0.05). Parkin-mediated mitophagy regulated myotube atrophy by modulating mitochondrial damage and mitochondrial ROS production. Increased mitochondrial ROS was responsible for myotube atrophy by activating Muscle Ring Finger 1 (MuRF-1)-mediated myosin heavy chain (MHC) degradation. Parkin^-/- mice with prolonged CS exposure showed enhanced limb muscle atrophy with a 31.7% reduction in limb muscle weights (P < 0.01) and 2.3 times greater MuRF-1 expression (P < 0.01) compared with wild-type mice with concomitant accumulation of damaged mitochondria and oxidative modifications in 4HNE expression. Patients with COPD-related sarcopenia exhibited significantly reduced Parkin but increased MuRF-1 protein levels (35% lower and 2.5 times greater protein levels compared with control patients, P < 0.01 and P < 0.05, respectively) and damaged mitochondria accumulation demonstrated in muscles. Electric pulse stimulation-induced muscle contraction prevented CSE-induced MHC reduction by maintaining Parkin levels in myotubes.

CONCLUSIONS

Taken together, COPD-related sarcopenia can be attributed to insufficient Parkin-mediated mitophagy and increased mitochondrial ROS causing enhanced muscle atrophy through MuRF-1 activation, which may be at least partly preventable through optimal physical exercise.

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.

Redox changes in obesity, metabolic syndrome, and diabetes

"Life is an instantaneous encounter of circulating matter and flowing energy" (Jean Giaja, Serbian physiologist), is one of the most elegant definitions not only of life but the relationship of redox biology and metabolism. Their evolutionary liaison has created inseparable yet dynamic homeostasis in health, which, when disrupted, leads to disease. This interconnection is even more pertinent today, in an era of increasing metabolic diseases of epidemic proportions such as obesity, metabolic syndrome, and diabetes. Despite great advances in understanding the molecular mechanisms of redox and metabolic regulation, we face significant challenges in preventing, diagnosing, and treating metabolic diseases. The etiological association and temporal overlap of these syndromes present significant challenges for the discrimination of appropriate clinical biomarkers for diagnosis, treatment, and outcome prediction. These multifactorial, multiorgan metabolic syndromes with complex etiopathogenic mechanisms are accompanied by disturbed redox equilibrium in target tissues and circulation. Free radicals and reactive species are considered both a causal factor and a consequence of disease status. Thus, determining the subtypes and levels of free radicals and reactive species, oxidatively damaged biomolecules (lipids, proteins, and nucleic acids) and antioxidant defense components as well as redox-sensitive transcription factors and fluxes of redox-dependent metabolic pathways will help define existing and establish novel redox biomarkers for stratifying metabolic diseases. This review aims to discuss diverse redox/metabolic aspects in obesity, metabolic syndrome, and diabetes, with the imperative to help establish a platform for emerging and future redox-metabolic biomarkers research in precision medicine. Future research warrants detailed investigations into the status of redox biomarkers in healthy subjects and patients, including the use of emerging 'omic' profiling technologies (e.g., redox proteomes, lipidomes, metabolomes, and transcriptomes), taking into account the influence of lifestyle (diet, physical activity, sleep, work patterns) as well as circadian ~24h fluctuations in circulatory factors and metabolites.

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.

Mitochondrial electron transport chain, ROS generation and uncoupling (Review)

The mammalian mitochondrial electron transport chain (ETC) includes complexes I-IV, as well as the electron transporters ubiquinone and cytochrome c. There are two electron transport pathways in the ETC: Complex I/III/IV, with NADH as the substrate and complex II/III/IV, with succinic acid as the substrate. The electron flow is coupled with the generation of a proton gradient across the inner membrane and the energy accumulated in the proton gradient is used by complex V (ATP synthase) to produce ATP. The first part of this review briefly introduces the structure and function of complexes I-IV and ATP synthase, including the specific electron transfer process in each complex. Some electrons are directly transferred to O₂ to generate reactive oxygen species (ROS) in the ETC. The second part of this review discusses the sites of ROS generation in each ETC complex, including sites I_F and I_Q in complex I, site II_F in complex II and site III_Qo in complex III, and the physiological and pathological regulation of ROS. As signaling molecules, ROS play an important role in cell proliferation, hypoxia adaptation and cell fate determination, but excessive ROS can cause irreversible cell damage and even cell death. The occurrence and development of a number of diseases are closely related to ROS overproduction. Finally, proton leak and uncoupling proteins (UCP_S) are discussed. Proton leak consists of basal proton leak and induced proton leak. Induced proton leak is precisely regulated and induced by UCPs. A total of five UCPs (UCP1-5) have been identified in mammalian cells. UCP1 mainly plays a role in the maintenance of body temperature in a cold environment through non-shivering thermogenesis. The core role of UCP2-5 is to reduce oxidative stress under certain conditions, therefore exerting cytoprotective effects. All diseases involving oxidative stress are associated with UCPs.

2D-DIGE proteomic analysis of vastus lateralis from COPD patients with low and normal fat free mass index and healthy controls

BACKGROUND

Chronic obstructive pulmonary disease (COPD) is associated with several extra-pulmonary effects of which skeletal muscle wasting is one of the most common and contributes to reduced quality of life, increased morbidity and mortality. The molecular mechanisms leading to muscle wasting are not fully understood. Proteomic analysis of human skeletal muscle is a useful approach for gaining insight into the molecular basis for normal and pathophysiological conditions.

METHODS

To identify proteins involved in the process of muscle wasting in COPD, we searched differentially expressed proteins in the vastus lateralis of COPD patients with low fat free mass index (FFMI), as a surrogate of muscle mass (COPDL, n = 10) (FEV1 33 ± 4.3% predicted, FFMI 15 ± 0.2 Kg.m-2), in comparison to patients with COPD and normal FFMI (COPDN, n = 8) and a group of age, smoking history, and sex matched healthy controls (C, n = 9) using two-dimensional fluorescence difference in gel electrophoresis (2D-DIGE) technology, combined with mass spectrometry (MS). The effect of silencing DOT1L protein expression on markers of cell arrest was analyzed in skeletal muscle satellite cells (HSkMSCs) in vitro and assessed by qPCR and Western blotting.

RESULTS

A subset of 7 proteins was differentially expressed in COPDL compared to both COPDN and C. We found an increased expression of proteins associated with muscle homeostasis and protection against oxidative stress, and a decreased expression of structural muscle proteins and proteins involved in myofibrillogenesis, cell proliferation, cell cycle arrest and energy production. Among these was a decreased expression of the histone methyltransferase DOT1L. In addition, silencing of the DOT1L gene in human skeletal muscle satellite cells in vitro was significantly related to up regulation of p21 WAF1/Cip1/CDKN1A, a marker of cell arrest and ageing.

CONCLUSIONS

2D-DIGE coupled with MS identified differences in the expression of several proteins in the wasted vastus lateralis that are relevant to the disease process. Down regulation of DOT1L in the vastus lateralis of COPDL patients may mediate the muscle wasting process through up regulation of markers of cell arrest and senescence.

Interactions between muscle stem cells, mesenchymal-derived cells and immune cells in muscle homeostasis, regeneration and disease

Recent evidence has revealed the importance of reciprocal functional interactions between different types of mononuclear cells in coordinating the repair of injured muscles. In particular, signals released from the inflammatory infiltrate and from mesenchymal interstitial cells (also known as fibro-adipogenic progenitors (FAPs)) appear to instruct muscle stem cells (satellite cells) to break quiescence, proliferate and differentiate. Interestingly, conditions that compromise the functional integrity of this network can bias muscle repair toward pathological outcomes that are typically observed in chronic muscular disorders, that is, fibrotic and fatty muscle degeneration as well as myofiber atrophy. In this review, we will summarize the current knowledge on the regulation of this network in physiological and pathological conditions, and anticipate the potential contribution of its cellular components to relatively unexplored conditions, such as aging and physical exercise.

Gait mechanics in patients with chronic obstructive pulmonary disease

BACKGROUND

Chronic obstructive pulmonary disease (COPD) is characterized by the frequent association of disease outside the lung. The objective of this study was to determine the presence of biomechanical gait abnormalities in COPD patients compared to healthy controls while well rested and without rest.

METHODS

Patients with COPD (N = 17) and aged-matched, healthy controls (N = 21) walked at their self-selected pace down a 10-meter walkway while biomechanical gait variables were collected. A one-minute rest was given between each of the five collected trials to prevent tiredness (REST condition). Patients with COPD then walked at a self-selected pace on a treadmill until the onset of self-reported breathlessness or leg tiredness. Subjects immediately underwent gait analysis with no rest between each of the five collected trials (NO REST condition). Statistical models with and without covariates age, gender, and smoking history were used.

RESULTS

After adjusting for covariates, COPD patients demonstrated more ankle power absorption in mid-stance (P = 0.006) than controls during both conditions. Both groups during NO REST demonstrated increased gait speed (P = 0.04), stride length (P = 0.03), and peak hip flexion (P = 0.04) with decreased plantarflexion moment (P = 0.04) and increased knee power absorption (P = 0.04) as compared to REST. A significant interaction revealed that peak ankle dorsiflexion moment was maintained from REST to NO REST for COPD but increased for controls (P < 0.01). Stratifying by disease severity did not alter these findings, except that step width decreased in NO REST as compared to REST (P = 0.01). Standardized effect sizes of significant effects varied from 0.5 to 0.98.

CONCLUSIONS

Patients with COPD appear to demonstrate biomechanical gait changes at the ankle as compared to healthy controls. This was seen not only in increased peak ankle power absorption during no rest but was also demonstrated by a lack of increase in peak ankle dorsiflexion moment from the REST to the NO REST condition as compared to the healthy controls. Furthermore, a wider step width has been associated with fall risk and this could account for the increased incidence of falls in patients with COPD.

S-nitrosoglutathione reductase deficiency-induced S-nitrosylation results in neuromuscular dysfunction

AIMS

Nitric oxide (NO) production is implicated in muscle contraction, growth and atrophy, and in the onset of neuropathy. However, many aspects of the mechanism of action of NO are not yet clarified, mainly regarding its role in muscle wasting. Notably, whether NO production-associated neuromuscular atrophy depends on tyrosine nitration or S-nitrosothiols (SNOs) formation is still a matter of debate. Here, we aim at assessing this issue by characterizing the neuromuscular phenotype of S-nitrosoglutathione reductase-null (GSNOR-KO) mice that maintain the capability to produce NO, but are unable to reduce SNOs.

RESULTS

We demonstrate that, without any sign of protein nitration, young GSNOR-KO mice show neuromuscular atrophy due to loss of muscle mass, reduced fiber size, and neuropathic behavior. In particular, GSNOR-KO mice show a significant decrease in nerve axon number, with the myelin sheath appearing disorganized and reduced, leading to a dramatic development of a neuropathic phenotype. Mitochondria appear fragmented and depolarized in GSNOR-KO myofibers and myotubes, conditions that are reverted by N-acetylcysteine treatment. Nevertheless, although atrogene transcription is induced, and bulk autophagy activated, no removal of damaged mitochondria is observed. These events, alongside basal increase of apoptotic markers, contribute to persistence of a neuropathic and myopathic state.

INNOVATION

Our study provides the first evidence that GSNOR deficiency, which affects exclusively SNOs reduction without altering nitrotyrosine levels, results in a clinically relevant neuromuscular phenotype.

CONCLUSION

These findings provide novel insights into the involvement of GSNOR and S-nitrosylation in neuromuscular atrophy and neuropathic pain that are associated with pathological states; for example, diabetes and cancer.

Skeletal muscle adiposity is associated with physical activity, exercise capacity and fibre shift in COPD

Quadriceps muscle phenotype varies widely between patients with chronic obstructive pulmonary disease (COPD) and cannot be determined without muscle biopsy. We hypothesised that measures of skeletal muscle adiposity could provide noninvasive biomarkers of muscle quality in this population. In 101 patients and 10 age-matched healthy controls, mid-thigh cross-sectional area, percentage intramuscular fat and skeletal muscle attenuation were calculated using computed tomography images and standard tissue attenuation ranges: fat -190- -30 HU; skeletal muscle -29-150 HU. Mean±sd percentage intramuscular fat was higher in the patient group (6.7±3.5% versus 4.3±1.2%, p = 0.03). Both percentage intramuscular fat and skeletal muscle attenuation were associated with physical activity level, exercise capacity and type I fibre proportion, independent of age, mid-thigh cross-sectional area and quadriceps strength. Combined with transfer factor of the lung for carbon monoxide, these variables could identify >80% of patients with fibre type shift with >65% specificity (area under the curve 0.83, 95% CI 0.72-0.95). Skeletal muscle adiposity assessed by computed tomography reflects multiple aspects of COPD related muscle dysfunction and may help to identify patients for trials of interventions targeted at specific muscle phenotypes.

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.

Normal black kidney

A black kidney has 3 major differential diagnoses: hemosiderosis, lipofuscin pigment and melanotic renal cell carcinoma. Excluding lipofuscin, the other 2 are accompanied by an abnormal renal function. We report on a 25-year-old man who intended to donate a kidney to his cousin. On the operating room table when we incised the left flank region and exposed the kidney, we found a firm and black kidney so the operation was cancelled due to potential vascular injuries. Days after the incomplete procedure, we reviewed the donor's biochemistry and imaging to reassess his renal function, but the results showed quite normal renal function again. The result of Ham test was also negative. Two weeks later, we began the operation, removed the same left kidney and found that it was in the same conditions as it was before. We took the opportunity to send needle biopsies of the kidney for histopathologic analysis. The analysis showed a melanotic kidney without pathological changes in glomeruli and interstitium and vessels. A black kidney may result in hemosiderin, lipofuscin or melanin deposits in the kidney, which can confirm the diagnosis; however, special tests for underlying disease and renal function should be considered. Some causes of black kidney lead to abnormal function, but our patients's kidney returned to normal.

The Effect of a Short Duration, High Intensity Exercise Intervention on Gait Biomechanics in Patients With COPD: Findings From a Pilot Study

Previous work has shown that patients with chronic obstructive pulmonary disease (COPD) demonstrate changes in their gait biomechanics as compared to controls. This pilot study was designed to explore the possibility that biomechanical alterations present in COPD patients might be amenable to treatment by exercise training of skeletal muscle. This study investigated the effect of a 6-week exercise intervention on gait biomechanics in patients with COPD under both a rest and a non-rested condition. Seven patients with COPD underwent a supervised cardio-respiratory and strength training protocol 2-3 times per week for 6-weeks for a total of 16-sessions. Spatiotemporal, kinematic and kinetic gait variables were collected prior to and post intervention. All patients demonstrated significant improvements in strength following the intervention. The knee joint biomechanics demonstrated a significant main effect for intervention and for condition. Step width demonstrated a significant interaction as it decreased from pre- to post-intervention under the rest condition and increased under the non-rested condition. It does appear that being pushed (non-rested) has a strong influence at the knee joint. The quadriceps muscles, the primary knee extensors, have been shown to demonstrate muscular abnormalities in patients with COPD and the intervention may have influenced gait patterns through an effect on this skeletal muscle structure and function. Additionally, the intervention influenced step width closer to a more healthy value. Patients with COPD are more likely to fall and step width is a risk factor for falling suggesting the intervention may address fall risk. Whether a longer duration intervention would have more profound effects remains to be tested.

Musculoskeletal disorders in chronic obstructive pulmonary disease

Chronic obstructive pulmonary disease (COPD) is a lung disease characterized by airway obstruction and inflammation but also accompanied by several extrapulmonary consequences, such as skeletal muscle weakness and osteoporosis. Skeletal muscle weakness is of major concern, since it leads to poor functional capacity, impaired health status, increased healthcare utilization, and even mortality, independently of lung function. Osteoporosis leads to fractures and is associated with increased mortality, functional decline, loss of quality of life, and need for institutionalization. Therefore, the presence of the combination of these comorbidities will have a negative impact on daily life in patients with COPD. In this review, we will focus on these two comorbidities, their prevalence in COPD, combined risk factors, and pathogenesis. We will try to prove the clustering of these comorbidities and discuss possible preventive or therapeutic strategies.

Muscular senescence in cetaceans: adaptation towards a slow muscle fibre phenotype

Sarcopenia, or senile muscle atrophy, is the slow and progressive loss of muscle mass with advancing age that constitutes the most prevalent form of muscle atrophy. The effects of ageing on skeletal muscle have been extensively studied in humans and laboratory animals (mice), while the few reports on wild animals are based on short-lived mammals. The present study describes the age-related changes in cetacean muscles regarding the three factors that determine muscle mass: fibre size, fibre number, and fibre type. We show that the skeletal muscle fibres in cetaceans change with advancing age, evolving towards a slower muscle phenotype. We suggest that this physiological evolution constitutes an adaptation that allows these marine mammals to perform prolonged, deep dives.

The value of muscle biopsies in Pompe disease: identifying lipofuscin inclusions in juvenile- and adult-onset patients

Background

Pompe disease, an inherited deficiency of lysosomal acid alpha-glucosidase (GAA), is a metabolic myopathy with heterogeneous clinical presentations. Late-onset Pompe disease (LOPD) is a debilitating progressive muscle disorder that can occur anytime from early childhood to late adulthood. Enzyme replacement therapy (ERT) with recombinant human GAA is currently available for Pompe patients. Although ERT shows some benefits, the reversal of skeletal muscle pathology - lysosomal glycogen accumulation and autophagic buildup - remains a challenge. In this study, we examined the clinical status and muscle pathology of 22 LOPD patients and one atypical infantile patient on ERT to understand the reasons for muscle resistance to ERT.

Results

The patients were divided into three groups for analysis, based on the age of onset and diagnosis: adult-onset patients, juvenile-onset patients, and those identified through newborn screening (NBS). The areas of autophagic buildup found in patients’ biopsies of all three groups, contained large autofluorescent inclusions which we show are made of lipofuscin, an indigestible intralysosomal material typically associated with ageing. These inclusions, analysed by staining, spectral analysis, time-resolved Fluorescence Lifetime Imaging (FLIM), and Second Harmonic Generation (SHG) imaging, were the major pathology remaining in many fibers after ERT. The best outcome of ERT both clinically and morphologically was observed in the NBS patients.

Conclusions

The muscle biopsy, in spite of its shortcomings, allowed us to recognize an underreported, ERT-resistant pathology in LOPD; numerous lysosomes and autolysosomes loaded with lipofuscin appear to be a hallmark of LOPD skeletal muscle. Lipofuscin accumulation - a result of inefficient lysosomal degradation - may in turn exacerbate both lysosomal and autophagic abnormalities.

Angiogenesis-related factors in skeletal muscles of COPD patients: roles of angiopoietin-2

The role of angiogenesis factors in skeletal muscle dysfunction in patients with chronic obstructive pulmonary disease (COPD) is unknown. The first objective of this study was to assess various pro- and antiangiogenic factor and receptor expressions in the vastus lateralis muscles of control subjects and COPD patients. Preliminary inquiries revealed that angiopoietin-2 (ANGPT2) is overexpressed in limb muscles of COPD patients. ANGPT2 promotes skeletal satellite cell survival and differentiation. Factors that are involved in regulating muscle ANGPT2 production are unknown. The second objective of this study was to evaluate how oxidants and proinflammatory cytokines influence muscle-derived ANGPT2 expression. Angiogenic gene expressions in human vastus lateralis biopsies were quantified with low-density real-time PCR arrays. ANGPT2 mRNA expressions in cultured skeletal myoblasts were quantified in response to proinflammatory cytokine and H2O2 exposure. Ten proangiogenesis genes, including ANGPT2, were significantly upregulated in the vastus lateralis muscles of COPD patients. ANGPT2 mRNA levels correlated negatively with forced expiratory volume in 1 s and positively with muscle wasting. Immunoblotting confirmed that ANGPT2 protein levels were significantly greater in muscles of COPD patients compared with control subjects. ANGPT2 expression was induced by interferon-γ and -β and by hydrogen peroxide, but not by tumor necrosis factor. We conclude that upregulation of ANGPT2 expression in vastus lateralis muscles of COPD patients is likely due to oxidative stress and represents a positive adaptive response aimed at facilitating myogenesis and angiogenesis.

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.

Protein carbonylation in skeletal muscles: impact on function

Relatively low levels of reactive oxygen species (ROS) produced inside resting skeletal muscles play important functions in cell signaling. When ROS production increases to levels beyond the buffering capacity of muscle antioxidant systems, a state of oxidative stress develops, which leads to skeletal muscle contractile dysfunction. A clear association between oxidative stress and depressed skeletal muscle performance has been described in several acute and chronic conditions, such as systemic inflammation and chronic obstructive lung diseases. The observation that the levels of oxidant-derived posttranslational protein modifications, including protein carbonylation, are elevated inside skeletal muscle fibers when oxidative stress develops suggest that these modifications play important roles in regulating muscle function. This proposal is supported by recent studies that unveiled that several myofilament (myosin heavy chain and actin), mitochondrial (aconitase, creatine kinase), and cytosolic (enolase, aldolase and glyceraldehyde 3-phosphate dehydrogenase and carbonic anhydrase III) proteins are carbonylated inside skeletal muscle fibers in many animal models of muscle dysfunction, and in humans with impaired skeletal muscle contractility. However, the functional importance of carbonylation in determining the function of muscle-specific proteins and the precise contribution of carbonylation-induced dysfunction of these proteins to overall muscle contractile deficit in various pathologies remain to be determined.

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.

The mitochondrial phenotype of peripheral muscle in chronic obstructive pulmonary disease: disuse or dysfunction?

RATIONALE

Peripheral muscle alterations have been recognized to contribute to disability in chronic obstructive pulmonary disease (COPD).

OBJECTIVES

To describe the mitochondrial phenotype in a moderate to severe COPD population and age-matched controls.

METHODS

Three primary aspects of mitochondrial function were assessed in permeabilized locomotor muscle fibers.

MEASUREMENTS AND MAIN RESULTS

Respiration rates per milligram of fiber weight were significantly lower in COPD muscle compared with healthy age-matched control muscle under various respiratory states. However, when variations in mitochondrial volume were taken into account by normalizing respiration per unit of citrate synthase activity, differences between the two groups were abolished, suggesting the absence of specific mitochondrial respiratory impairment in COPD. H(2)O(2) production per mitochondrion was higher both under basal and ADP-stimulated states, suggesting that mitochondria from COPD muscle have properties that potentiate H(2)O(2) release. Direct assessment of mitochondrial sensitivity to Ca(2+)-induced opening of the permeability transition pore (PTP) indicated that mitochondria from patients with COPD were more resistant to PTP opening than their counterparts in control subjects.

CONCLUSIONS

Comparison of these results with those of studies comparing healthy glycolytic with oxidative muscle suggests that these differences may be attributable to greater type II fiber expression in COPD muscle, as mitochondria within this fiber type have respiratory function similar to that of mitochondria from type I fibers, and yet are intrinsically prone to greater release of H(2)O(2) and more resistant to PTP opening. These results thus argue against the presence of pathological mitochondrial alterations in this category of patients with COPD.

Hypoxia: the third wheel between nerve and muscle

Skeletal muscles not only obey carefully all motor commands received via motor nerves from nervous system, but also are ready to modify their structure and function to be more suited to the tasks assigned by nervous system. Thus, nervous system appears as the major modulator of the muscle structure and function. Other factors, however, may interfere with the nerve-muscle partnership and among them, hypoxia plays a pivotal role because skeletal muscles exhibit a great variability of the oxygen fluxes and because hypoxia per se has a powerful influence on muscle fibers. The adaptation of skeletal muscles to nerve-induced activity is particularly evident with low frequency tonic patterns and examples are given by chronic low frequency stimulation and by endurance training. Adaptation includes fiber type transitions towards a slow-oxidative phenotype, increased mitochondrial density and increased capillary/fiber ratio. Hypoxia can trigger some of such changes and this has suggested that low oxygen tension at fiber level might be a mediator, possibly based on HIF and VEGF, of the muscle adaptation to increased contractile activity. Chronic hypoxia can, however, induce opposite modifications, such as a fiber type transition from slow-oxidative to fast-glycolytic and mitochondrial loss. In such conditions, the increased contractile activity can antagonize hypoxia effects. Thus, hypoxia can play a double role in the nerve-muscle relationship, either reinforcing the nerve influence or antagonizing it. This short review aims to re-examine the ambiguous relationships between nerve-induced contractile activity and hypoxic conditions and to suggest possible interpretations of the double role played by hypoxia.

Oxidative and nitrosative stress in the diaphragm of patients with COPD

COPD is associated with an increased load on the diaphragm. Since chronic muscle loading results in changes in antioxidant capacity and formation of reactive oxygen and reactive nitrogen species, we hypothesized that COPD has a similar effect on the diaphragm, which is related to the severity of COPD. Catalase activity was determined spectrophotometrically. Levels of 4-hydroxy-2-nonenal (HNE)-protein adducts and 3-nitrotyrosine (NT) formation were measured using western blotting. Levels of malondialdehyde (MDA) were assessed by high-performance liquid chromatography. We found that catalase activity was ~89% higher in the diaphragm of severe COPD patients (FEV₁ 37 ± 5% predicted) compared with non-COPD patients. MDA levels, a marker for lipid peroxidation, were significantly lower in the diaphragm of COPD patients compared with non-COPD patients, whereas the level of HNE-protein adducts was equal in both groups. NT formation was not different between groups. However, increasing hyperinflation and NT formation were inversely correlated. These results indicate that in COPD the diaphragm adapts to a higher work load by increasing catalase activity, resulting in a reduction in oxidative damage to lipids and tyrosine nitration of proteins.

Diaphragm adaptations in patients with COPD

Inspiratory muscle weakness in patients with COPD is of major clinical relevance. For instance, maximum inspiratory pressure generation is an independent determinant of survival in severe COPD. Traditionally, inspiratory muscle weakness has been ascribed to hyperinflation-induced diaphragm shortening. However, more recently, invasive evaluation of diaphragm contractile function, structure, and biochemistry demonstrated that cellular and molecular alterations occur, of which several can be considered pathologic of nature. Whereas the fiber type shift towards oxidative type I fibers in COPD diaphragm is regarded beneficial, rendering the overloaded diaphragm more resistant to fatigue, the reduction of diaphragm fiber force generation in vitro likely contributes to diaphragm weakness. The reduced diaphragm force generation at single fiber level is associated with loss of myosin content in these fibers. Moreover, the diaphragm in COPD is exposed to oxidative stress and sarcomeric injury. This review postulates that the oxidative stress and sarcomeric injury activate proteolytic machinery, leading to contractile protein wasting and, consequently, loss of force generating capacity of diaphragm fibers in patients with COPD. Interestingly, several of these presumed pathologic alterations are already present early in the course of the disease (GOLD I/II), although these patients appear not limited in their daily life activities. Treatment of diaphragm dysfunction in COPD is complex since its etiology is unclear, but recent findings indicate the ubiquitin-proteasome pathway as a prime target to attenuate diaphragm wasting in COPD.

Muscle fibre type shifting in the vastus lateralis of patients with COPD is associated with disease severity: a systematic review and meta-analysis

BACKGROUND

Skeletal muscle dysfunction is a common feature in chronic obstructive pulmonary disease (COPD) which is associated with intrinsic muscular abnormalities. One of the most consistently reported alterations is a shift from fibre type I to II in the vastus lateralis of these patients. Surprisingly, the relationship between this shift and the severity and phenotype of COPD remains unclear. A study was conducted to determine whether vastus lateralis muscle fibre type proportions are associated with COPD disease severity and to provide reference values for the proportions of fibre types in the vastus lateralis in COPD.

METHODS

A systematic review and a meta-analysis were conducted in which muscle fibre type data and markers of disease severity were collected from the literature.

RESULTS

The forced expiratory volume in 1 s (FEV(1)), the ratio of FEV(1) to forced vital capacity (FVC) and body mass index were positively associated with the proportion of type I fibres in COPD. A proportion of 51% for vastus lateralis fibre type I and 13% for fibre type IIX were calculated from the combined data as normal values for patients with typical GOLD stage 3-4 COPD aged 60-70 years. Based on these reference values, a proportion of fibre type I <27% and of fibre type IIX >29% were defined as pathologically abnormal.

CONCLUSIONS

This review sheds new light on the relationship between skeletal muscle abnormalities and important hallmarks of the disease in severe COPD, and identifies absence of data in GOLD stages 1-2. This review also provides reference values on fibre type composition for diagnostic purposes in COPD.

Diagnostic usefulness of B-type natriuretic peptide and functional consequences of muscle alterations in COPD and chronic heart failure

COPD affects up to one third of patients with chronic heart failure. The coexistence of COPD and chronic heart failure presents clinicians with diagnostic and therapeutic challenges. Measurement of B-type natriuretic peptide plasma levels facilitates the diagnosis of acute dyspnea in patients known to have both COPD and chronic heart failure. Patients with COPD or chronic heart failure have skeletal muscle abnormalities that limit functional capacity independently from primary organ failure. Exercise training reverses skeletal muscle abnormalities in patients with COPD or chronic heart failure and may be particularly indicated in patients with coexistent COPD and chronic heart failure.

Exercise training restores uncoupling protein-3 content in limb muscles of patients with chronic obstructive pulmonary disease

Oxidative capacity and uncoupling protein-3 (UCP3) content are reduced in limb muscles of patients with chronic obstructive pulmonary disease (COPD). It has been hypothesized that the physiological role of UCP3 is to protect mitochondria against lipotoxicity in cases where fatty acid influx exceeds the capacity to oxidize them. Exercise training improves oxidative capacity and reduces UCP3 protein content in healthy subjects, but the response of UCP3 to training in COPD is unknown. We studied the effect of exercise training on UCP3 content in limb muscles of COPD patients. For this, seven healthy age-matched subjects and thirteen patients with COPD were studied. All patients were admitted to an 8-wk exercise training intervention. Exercise capacity was assessed by means of an incremental cycle ergometry test. Biopsies were taken from the vastus lateralis in which UCP3 and lipid peroxidation levels were determined by Western blotting. Citrate synthase and 3-hydroxyacyl-CoA dehydrogenase (HAD; an enzyme involved in fatty acid oxidation) were measured as indexes of muscle oxidative capacity. UCP3 in COPD was approximately 50% lower compared with healthy age-matched controls. In COPD, training induced upregulation of UCP3 [from 67.7 (SD 41.8) to 113.8 (SD 104.2) arbitrary units (AU), P = 0.062], especially in the patients who showed no increase in HAD activity [from 80.9 (SD 52.6) to 167.9 (SD 109.1) AU, P = 0.028], whereas lipid peroxidation levels remained unaltered. We conclude that exercise-training can restore muscle UCP3 protein level in COPD, and the nature of this response complies with the hypothesis that UCP3 may protect against lipotoxicity.

Muscle-targeted deletion of VEGF and exercise capacity in mice

Methods to study exercise are evolving from classically integrative organ approaches towards the more fundamental cellular reactions. While in vitro cellular and molecular methods are well established, only recently has in vivo molecular manipulation been widely used. This review discusses two complementary methods for determining in vivo the significance of one gene thought important to exercise: vascular endothelial growth factor (VEGF). Because VEGF deletion is embryonically lethal, its study requires conditional and/or organ-targeted strategies. We inactivated the muscle VEGF gene in two ways:

Hemosiderin deposits in chronic graft-vs.-host disease related myopathy

Chronic graft-vs.-host disease (cGVHD) occurs in 20-50% of patients who survive for at least 100 d after allogeneic stem cell transplantation (SCT). cGVHD includes scleroderma-like skin changes, chronic cholangitis, obstructive lung disease and general wasting syndrome. Polymyositis or myopathy are rare manifestations of cGVHD with approximately 40 reported cases. Polymyositis accompanied by hemosiderin deposits in cGVHD has been reported only once, and there are no reports on lipofuscin deposits in skeletal muscle cells in cGVHD. We report here on a 56-yr-old male who underwent allogeneic SCT in 1999 for osteomyelofibrosis and progressive hematopoietic insufficiency. In February 2004, the patient was hospitalized for progressive muscular weakness with loss of the ability to walk. Laboratory tests demonstrated normal values for serum creatine kinase, aldolase and lactic dehydrogenase; the ferritin level was highly elevated. The femoral muscle biopsy showed mostly perifascicular atrophy as well as numerous subsarcolemmal hemosiderin and lipofuscin deposits. Intravenous administration of the chelating agent deferoxamine was ineffective. Three weeks later the patient died of aspiration pneumonia. Interestingly, autopsy disclosed moderate hemosiderin deposits in the liver, the organ usually involved in hemosiderosis.

Hypoxaemia enhances peripheral muscle oxidative stress in chronic obstructive pulmonary disease

BACKGROUND

Because oxidative stress affects muscle function, the underlying mechanism to explain exercise induced peripheral muscle oxidative stress in patients with chronic obstructive pulmonary disease (COPD) is clinically relevant. This study investigated whether chronic hypoxaemia in COPD worsens peripheral muscle oxidative stress and whether an abnormal muscle inflammatory process is associated with it.

METHODS

Nine chronically hypoxaemic and nine non-hypoxaemic patients performed repeated knee extensions until exhaustion. Biopsy specimens were taken from the vastus lateralis muscle before and 48 hours after exercise. Muscle oxidative stress was evaluated by lipid peroxidation (lipofuscin and thiobarbituric acid reactive substances (TBARs)) and oxidised proteins. Inflammation was evaluated by quantifying muscle neutrophil and tumour necrosis factor (TNF)-alpha levels.

RESULTS

When both groups were taken together, arterial oxygen pressure was positively correlated with quadriceps endurance time (n = 18, r = 0.57; p < 0.05). At rest, quadriceps lipofuscin inclusions were significantly greater in hypoxaemic patients than in non-hypoxaemic patients (2.9 (0.2) v 2.0 (0.3) inclusions/fibre; p < 0.05). Exercise induced a greater increase in muscle TBARs and oxidised proteins in hypoxaemic patients than in non-hypoxaemic patients (40.6 (9.1)% v 10.1 (5.8)% and 51.2 (11.9)% v 3.7 (12.2)%, respectively, both p = 0.01). Neutrophil levels were significantly higher in hypoxaemic patients than in non-hypoxaemic patients (53.1 (11.6) v 21.5 (11.2) counts per fibre x 10(-3); p < 0.05). Exercise did not alter muscle neutrophil levels in either group. Muscle TNF-alpha was not detected at baseline or after exercise.

CONCLUSION

Chronic hypoxaemia was associated with lower quadriceps endurance time and worsened muscle oxidative stress at rest and after exercise. Increased muscle neutrophil levels could be a source of the increased baseline oxidative damage. The involvement of a muscle inflammatory process in the exercise induced oxidative stress of patients with COPD remains to be shown.

Oxidative Stress and Respiratory Muscle Dysfunction in Severe Chronic Obstructive Pulmonary Disease

RATIONALE

Oxidative stress is involved in the skeletal muscle dysfunction observed in patients with severe chronic obstructive pulmonary disease (COPD). We hypothesized that the diaphragms of such patients might generate greater levels of oxidants than those neutralized by antioxidants.

OBJECTIVES

To assess the levels of both oxidative and nitrosative stress and different antioxidants in the diaphragms of those patients, and to analyze potential relationships with lung and respiratory muscle dysfunctions.

METHODS AND MEASUREMENTS

We conducted a case-control study in which reactive carbonyl groups, hydroxynonenal-protein adducts, antioxidant enzyme levels, nitric oxide synthases, and 3-nitrotyrosine formation were detected using immunoblotting and immunhistochemistry in diaphragm specimens (thoracotomy) obtained from six patients with severe COPD, six patients with moderate COPD, and seven control subjects.

MAIN RESULTS

Diaphragms of patients with severe COPD showed both higher protein carbonyl groups and hydroxynonenal-protein adducts than control subjects. When only considering patients with COPD, negative correlations were found between carbonyl groups and airway obstruction, and between hydroxynonenal-protein adducts and respiratory muscle strength. Although diaphragmatic neuronal nitric oxide synthase did not differ among the three groups and no inducible nitric oxide synthase was detected in any muscle, muscle endothelial nitric oxide synthase was lower in patients with severe COPD than in control subjects. Muscle nitrotyrosine levels were similar in both patients with severe COPD and control subjects.

CONCLUSIONS

This study shows that oxidative stress rather than nitric oxide is likely to be involved in the respiratory muscle dysfunction in severe COPD.

Altered antioxidant status in peripheral skeletal muscle of patients with COPD

Despite the growing field of interest in the role of pulmonary oxidative stress in chronic obstructive pulmonary disease (COPD), barely any data are available with respect to antioxidant capacity in the peripheral musculature of these patients. The main objective of this study was to assess in detail the antioxidant status in skeletal muscle of patients with COPD. Biopsies from the vastus lateralis of 21 patients with COPD and 12 healthy age-matched controls were analysed. Total antioxidant capacity, vitamin E, glutathione, and uric acid levels were determined and the enzyme activities of superoxide dismutase, glutathione reductase, glutathione peroxidase, and glutathione-S-transferase were measured. Malondialdehyde was measured as an index of lipid peroxidation. The total antioxidant capacity and the uric acid levels were markedly higher in COPD patients than in healthy controls (25%, P = 0.006 and 24%, P = 0.029, respectively). Glutathione-S-transferase activity was also increased (35%; P = 0.044) in patients compared to healthy subjects. Vitamin E level was lower in patients than in controls (P < 0.05). The malondialdehyde level was not different between the two groups. It can be concluded that the muscle total antioxidant capacity is increased in patients with COPD. Together with the reduced vitamin E levels, the increased glutathione-S-transferase activity and normal levels of lipid peroxidation products, these findings suggest that the antioxidant system may be exposed to and subsequently triggered by elevated levels of reactive oxygen species.

Emphysema-induced reductions in locomotory skeletal muscle contractile function

Patients with COPD suffer from locomotory skeletal muscle contractile dysfunction. This may be due to the disease per se or as a result of some confounding factor. Therefore, the purpose of this investigation was to determine whether emphysema: (1) reduces force production; (2) increases fatigability; and (3) impairs the speed of recovery in locomotory skeletal muscle in an accepted animal model in which many confounding variables can be controlled. To explore this issue, in situ mechanical properties of gastrocnemius were measured in Syrian Golden hamsters 8 months after intratracheal instillation of either saline (control, n = 5) or elastase (emphysema, n = 7). Emphysema increased excised lung volume (80%; P < 0.01), increased fatigability (control, 25% reduction in maximal strength after 4 min of repeated contractions; emphysema, 55% reduction; P < 0.05) and decreased the recovery rate (half-times of recovery: control, 7 +/- 7 s; emphysema, 92 +/- 92 s; P < 0.05) of gastrocnemius muscle. In contrast, emphysema had no effect on maximal force, whether related to body mass or muscle mass, or force-velocity characteristics of gastrocnemius muscle. These data demonstrate that emphysema, independent of physical activity levels, pharmacological intervention, and/or nutritional status, can increase fatigability and impair the speed of recovery of locomotory skeletal muscle contractile function which may contribute to exercise intolerance of COPD patients.

Respiratory muscle fibres: specialisation and plasticity

Skeletal muscles are composed of fibres of different types, each type being identified by the isoform of myosin heavy chain which is expressed as slow 1, fast 2A, fast 2X, and fast 2B. Slow fibres are resistant to fatigue due to their highly oxidative metabolism whereas 2X and 2B fibres are easily fatiguable and fast 2A fibres exhibit intermediate fatigue resistance. Slow fibres and fast fibres are present in equal proportions in the adult human diaphragm while intercostal muscles contain a higher proportion of fast fibres. A small fibre size, abundance of capillaries, and a high aerobic oxidative enzyme activity are typical features of diaphragm fibres and give them the resistance to fatigue required by their continuous activity. Because of their fibre composition, intercostal muscles are less resistant to fatigue. The structural and functional characteristics of respiratory muscle fibres are not fixed, however, and can be modified in response to several physiological and pathological conditions such as training (adaptation to changes in respiratory load), adaptation to hypoxia, age related changes, and changes associated with respiratory diseases. The properties of respiratory muscle fibres can also be modified by pharmacological agents such as beta2 agonists and corticosteroids used for the treatment of respiratory diseases.