Emphysema-induced reductions in locomotory skeletal muscle contractile function

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.

Pulmonary Emphysema Impairs Male Reproductive Physiology Due To Testosterone and Oxidative Stress Imbalance in Mesocricetus auratus

This study evaluated whether pulmonary emphysema affects sperm quality, male reproductive organs, and testosterone levels in adult male hamsters. Mesocricetus auratus males (130-150 g) were subdivided into a control group (C group) and an emphysema group (E group). The C group received an intratracheal instillation of saline solution (0.3 mL/100 g of body weight), and the E group received papain (40 mg/100 g of body weight). After 60 days, the biometric, pulmonary, and reproductive parameters of each group were evaluated. The E group developed pulmonary emphysema, which decreased body weight and sperm quality compared to the C group. In oxidative stress-related assays, lipid peroxidation was increased in the testis and epididymis (caput and cauda) in the E group compared with the C group. However, only the caput epididymis showed a reduction in glutathione levels. Pulmonary emphysema also affected the testicle by inducing an increase in abnormal seminiferous tubules, accompanied by a decrease in seminiferous epithelium height. Spermatogenesis kinetics were also modified by pulmonary emphysema. The number of Leydig and Sertoli cells decreased in the E group, accompanied by an increase in the nuclear volume of Leydig cells. Testosterone concentration was increased in the E group. Similarly, pulmonary emphysema altered epididymal components in all regions. In conclusion, pulmonary emphysema affected the reproductive system in this experimental model, as shown by testicular and epididymal morphophysiology changes, hormonal alteration, and oxidative stress imbalance, inducing the loss of correct function in the male reproductive system.

Oxygen delivery and the restoration of the muscle energetic balance following exercise: implications for delayed muscle recovery in patients with COPD

Patients with chronic obstructive pulmonary disease (COPD) experience a delayed recovery from skeletal muscle fatigue following exhaustive exercise that likely contributes to their progressive loss of mobility. As this phenomenon is not well understood, this study sought to examine postexercise peripheral oxygen (O₂) transport and muscle metabolism dynamics in patients with COPD, two important determinants of muscle recovery. Twenty-four subjects, 12 nonhypoxemic patients with COPD and 12 healthy subjects with a sedentary lifestyle, performed dynamic plantar flexion exercise at 40% of the maximal work rate (WR_max) with phosphorus magnetic resonance spectroscopy (³¹P-MRS), near-infrared spectroscopy (NIRS), and vascular Doppler ultrasound assessments. The mean response time of limb blood flow at the offset of exercise was significantly prolonged in patients with COPD (controls: 56 ± 27 s; COPD: 120 ± 87 s; P < 0.05). In contrast, the postexercise time constant for capillary blood flow was not significantly different between groups (controls: 49 ± 23 s; COPD: 51 ± 21 s; P > 0.05). The initial postexercise convective O₂ delivery (controls: 0.15 ± 0.06 l/min; COPD: 0.15 ± 0.06 l/min) and the corresponding oxidative adenosine triphosphate (ATP) demand (controls: 14 ± 6 mM/min; COPD: 14 ± 6 mM/min) in the calf were not significantly different between controls and patients with COPD (P > 0.05). The phosphocreatine resynthesis time constant (controls: 46 ± 20 s; COPD: 49 ± 21 s), peak mitochondrial phosphorylation rate, and initial proton efflux were also not significantly different between groups (P > 0.05). Therefore, despite perturbed peripheral hemodynamics, intracellular O₂ availability, proton efflux, and aerobic metabolism recovery in the skeletal muscle of nonhypoxemic patients with COPD are preserved following plantar flexion exercise and thus are unlikely to contribute to the delayed recovery from exercise in this population.

Oxidative and proteolysis-related parameters of skeletal muscle from hamsters with experimental pulmonary emphysema: a comparison between papain and elastase induction

The objective of this study was to investigate whether emphysema induced by elastase or papain triggers the same effects on skeletal muscle, related to oxidative stress and proteolysis, in hamsters. For this purpose, we evaluated pulmonary lesions, body weight, muscle loss, oxidative stress (thiobarbituric acid-reactive substances, total and oxidized glutathiones, chemiluminescence stimulated by tert-butyl hydroperoxide and carbonyl proteins), chymotrypsin-like and calpain-like proteolytic activities and muscle fibre cross-sectional area in the gastrocnemius muscles of emphysemic hamsters. Two groups of animals received different intratracheal inductions of experimental emphysema: by 40 mg/ml papain (EP) or 5.2 IU/100 g animal (EE) elastase (n = 10 animals/group). The control group received intratracheal instillation of 300 μl sterile NaCl 0.9%. Compared with the control group, the EP group had reduced muscle weight (18.34%) and the EE group had increased muscle weight (8.37%). Additionally, tert-butyl hydroperoxide-initiated chemiluminescence, carbonylated proteins and chymotrypsin-like proteolytic activity were all elevated in the EP group compared to the CS group, while total glutathione was decreased compared to the EE group. The EE group showed more fibres with increased cross-sectional areas and increased calpain-like activity. Together, these data show that elastase and papain, when used to induce experimental models of emphysema, lead to different speeds and types of adaptation. These findings provide more information on choosing a suitable experimental model for studying skeletal muscle adaptations in emphysema.

Lung injury-dependent oxidative status and chymotrypsin-like activity of skeletal muscles in hamsters with experimental emphysema

BACKGROUND

Peripheral skeletal muscle is altered in patients suffering from emphysema and chronic obstructive pulmonary disease (COPD). Oxidative stress have been demonstrated to participate on skeletal muscle loss of several states, including disuse atrophy, mechanical ventilation, and chronic diseases. No evidences have demonstrated the occurance in a severity manner.

METHODS

We evaluated body weight, muscle loss, oxidative stress, and chymotrypsin-like proteolytic activity in the gastrocnemius muscle of emphysemic hamsters. The experimental animals had 2 different severities of lung damage from experimental emphysema induced by 20 mg/mL (E20) and 40 mg/mL (E40) papain.

RESULTS

The severity of emphysema increased significantly in E20 (60.52 ± 2.8, p < 0.05) and E40 (52.27 ± 4.7; crossed the alveolar intercepts) groups. As compared to the control group, there was a reduction on body (171.6 ± 15.9 g) and muscle weight (251.87 ± 24.87 mg) in the E20 group (157.5 ± 10.3 mg and 230.12 ± 23.52 mg, for body and muscle weight, respectively), which was accentuated in the E40 group (137.4 ± 7.2 g and 197.87 ± 10.49 mg, for body and muscle weight, respectively). Additionally, the thiobarbituric acid reactive substances (TBARS), tert-butyl hydroperoxide-initiated chemiluminescence (CL), carbonylated proteins, and chymotrypsin-like proteolytic activity were elevated in the E40 group as compared to the E20 group (p < 0.05 for all comparisons). The severity of emphysema significantly correlated with the progressive increase in CL (r = -0.95), TBARS (r = -0.98), carbonyl proteins (r = -0.99), and chymotrypsin-like proteolytic activity (r = -0.90). Furthermore, augmentation of proteolytic activity correlated significantly with CL (r = 0.97), TBARS (r = 0.96), and carbonyl proteins (r = 0.91).

CONCLUSIONS

Taken together, the results of the present study suggest that muscle atrophy observed in this model of emphysema is mediated by increased muscle chymotrypsin-like activity, with possible involvement of oxidative stress in a severity-dependent manner.

Long-term nose-only cigarette smoke exposure induces emphysema and mild skeletal muscle dysfunction in mice

Mouse models of chronic obstructive pulmonary disease (COPD) focus on airway inflammation and lung histology, but their use has been hampered by the lack of pulmonary function data in their assessment. Systemic effects such as muscle dysfunction are also poorly modeled in emphysematous mice. We aimed to develop a cigarette-smoke-induced emphysema mouse model in which serial lung function and muscular dysfunction could be assessed, allowing the disease to be monitored more appropriately. C57Bl6 mice were nose-only exposed to cigarette smoke or filtered air for 3–6 months. Lung function tests were repeated in the same mice after 3 and 6 months of cigarette smoke or air exposure and compared with lung histological changes. Contractile properties of skeletal muscles and muscle histology were also determined at similar time points in separate groups of mice. Serial lung function measurements documented hyperinflation after 3 and 6 months of cigarette smoke exposure, with a significant 31–37% increase in total lung capacity (TLC) and a significant 26–35% increase in compliance (Cchord) when compared with animals exposed to filtered air only (P<0.001 after 3 and after 6 months). These functional changes preceded the changes in mean linear intercept, which became only significant after 6 months of cigarette smoke exposure and which correlated very well with TLC (r=0.74, P=0.004) and Cchord (r=0.79, P=0.001). After 6 months of cigarette smoke exposure, a significant fiber-type shift from IIa to IIx/b was also observed in the soleus muscle (P<0.05), whereas a 20% reduction of force was present at high stimulation frequencies (80 Hz; P=0.09). The extensor digitorum longus (EDL) muscle was not affected by cigarette smoke exposure. These serial pulmonary function variables are sensitive outcomes to detect emphysema progression in a nose-only cigarette-smoke-exposed animal model of COPD. In this model, muscular changes became apparent only after 6 months, particularly in muscles with a mixed fiber-type composition.

Treatment with a corticotrophin releasing factor 2 receptor agonist modulates skeletal muscle mass and force production in aged and chronically ill animals

Background

Muscle weakness is associated with a variety of chronic disorders such as emphysema (EMP) and congestive heart failure (CHF) as well as aging. Therapies to treat muscle weakness associated with chronic disease or aging are lacking. Corticotrophin releasing factor 2 receptor (CRF2R) agonists have been shown to maintain skeletal muscle mass and force production in a variety of acute conditions that lead to skeletal muscle wasting.

Hypothesis

We hypothesize that treating animals with a CRF2R agonist will maintain skeletal muscle mass and force production in animals with chronic disease and in aged animals.

Methods

We utilized animal models of aging, CHF and EMP to evaluate the potential of CRF2R agonist treatment to maintain skeletal muscle mass and force production in aged animals and animals with CHF and EMP.

Results

In aged rats, we demonstrate that treatment with a CRF2R agonist for up to 3 months results in greater extensor digitorum longus (EDL) force production, EDL mass, soleus mass and soleus force production compared to age matched untreated animals. In the hamster EMP model, we demonstrate that treatment with a CRF2R agonist for up to 5 months results in greater EDL force production in EMP hamsters when compared to vehicle treated EMP hamsters and greater EDL mass and force in normal hamsters when compared to vehicle treated normal hamsters. In the rat CHF model, we demonstrate that treatment with a CRF2R agonist for up to 3 months results in greater EDL and soleus muscle mass and force production in CHF rats and normal rats when compared to the corresponding vehicle treated animals.

Conclusions

These data demonstrate that the underlying physiological conditions associated with chronic diseases such as CHF and emphysema in addition to aging do not reduce the potential of CRF2R agonists to maintain skeletal muscle mass and force production.

Exercise capacity in hamsters with elastase-induced emphysema compared to normal controls

The purpose of this study was to determine whether hamsters with elastase-induced emphysema (EMP) would demonstrate a reduction in exercise capacity compared to control (CON) hamsters and whether changes in activity levels, muscle function and structure could explain any changes in exercise capacity. Peak oxygen consumption and daily activity levels were measured on two occasions. Inspiratory capacity under deep anesthesia, in vitro measurements of muscle force and fatigability for the diaphragm (DIA) and extensor digitorum longus (EDL) and fiber proportions, muscle cross-sectional area and fiber specific SDH activity from the DIA, EDL and vastus lateralis (VLA) were obtained. Inspiratory capacity was 60% higher in the EMP compared to CON hamsters (p=0.0004). Activity levels and exercise capacity were not significantly different between EMP and CON hamsters. Muscle strength and fatigability, fiber proportions, muscle cross-sectional area and fiber specific SDH activity were similar between EMP and CON hamsters. In conclusion, in hamsters, elastase-induced emphysema did not reduce maximal exercise capacity.

Exercise tolerance and dyspnea in patients with chronic obstructive pulmonary disease

Background/Aim. Peripheral muscle weakness and nutritional disorders, firstly loss of body weight, are common findings in patients with chronic obstructive pulmonary disease (COPD). The aim of this study was to analyse the impact of pulmonary function parameters, nutritional status and state of peripheral skeletal muscles on exercise tolerance and development of dyspnea in COPD patients. Methods. Thirty COPD patients in stable state of disease were analyzed. Standard pulmonary function tests, including spirometry, body pletysmography, and measurements of diffusion capacity were performed. The 6-minute walking distance test (6MWD) was done in order to assess exercise tolerance. Level of dyspnea was measured with Borg scale. In all patients midthigh muscle cross-sectional area (MTCSA) was measured by computerized tomography scan. Nutritional status of patients was estimated according to body mass index (BMI). Results. Statistically significant correlations were found between parameters of pulmonary function and exercise tolerance. Level of airflow limitation and lung hyperinflation had significant impact on development of dyspnea at rest and especially after exercise. Significant positive correlation was found between MTCSA and exercise tolerance. Patients with more severe airflow limitation, lung hyperinflation and reduced diffusion capacity had significantly lower MTCSA. Conclusion. Exercise tolerance in COPD patients depends on severity of bronchoobstruction, lung hyperinflation and MTCSA. Severity of bronchoobstruction and lung hyperinflation have significant impact on dyspnea level.

Maximal force is unaffected by emphysema-induced atrophy in extensor digitorium longus

Patients with chronic obstructive pulmonary disease (COPD) demonstrate a limited exercise capacity. It is unknown whether muscle fiber atrophy and subsequent decrease in force production contributes to this functional limitation. Therefore, the purpose of this investigation was to determine whether emphysema-induced muscle fiber atrophy leads to a reduction in locomotory muscle force production. Maximal muscle force production and fiber cross-sectional area were measured in the almost exclusively fast-twitch extensor digitorium longus muscles at 4 and 8 months following saline (control, n=8/time period) or elastase (emphysema, n=15/time period) instillation in the lungs of hamsters. Excised lung volume increased 145 and 161% with emphysema at 4 and 8 months, respectively (both P<0.01). Muscle mass, maximal force, and fiber cross-section were unaltered at 4 months. However, absolute mass (-15%) and fiber cross-sectional area (-18%) were reduced at 8 months (both P<0.01). Surprisingly, maximal force was preserved in emphysema animals. These data demonstrate that maximal muscle force may be preserved in the face of emphysema-induced fiber atrophy.

Apoptosis and Id2 expression in diaphragm and soleus muscle from the emphysematous hamster

During chronic obstructive pulmonary disease (COPD) diaphragm and peripheral muscle weakness occur. Muscle remodeling and wasting may be a result of apoptosis and changes in muscle-specific transcription factors, such as MyoD, altering muscle-specific gene transcription and muscle regenerative capacity. To investigate this, we instilled under ketamine/xylazine anesthesia porcine elastase in the lungs of hamsters to induce emphysema. The emphysematous hamster is an accepted model for COPD. In the diaphragm and peripheral muscles we assessed the occurrence of apoptosis, and in the diaphragm and soleus also the expression of MyoD and inhibitor of differentiation protein 2 (Id2). There was no significant muscle atrophy in emphysematous hamsters. The mRNA levels of TNF-alpha and markers of apoptosis were significantly elevated in the diaphragm and soleus muscles during emphysema. This was accompanied by an increased presence of nucleosomes in the cytosol. Caspase 3 activity and the DNA-binding activity of the p65 subunit of NF-kappaB, however, were unaltered in all muscles. The protein expression of MyoD and Id2 were decreased and increased in the diaphragm and the soleus muscle, respectively. Thus, despite the absence of muscle atrophy in emphysematous hamsters, there was evidence of increased TNF-alpha expression, apoptosis, and altered muscle-specific transcriptional regulation as reflected by decreased MyoD and elevated Id2 levels at least in the soleus and diaphragm muscle. These alterations may impair the regenerative capacity of skeletal muscles and ultimately contribute to muscle wasting.

Gene expression profiling in lung tissues from mice exposed to cigarette smoke, lipopolysaccharide, or smoke plus lipopolysaccharide by inhalation

The purpose of this study was to investigate whether coexposure to lipopolysacchride (LPS) will heighten the inflammatory response and other pulmonary lesions in mice exposed to cigarette smoke, and thus to evaluate the potential use of this LPS-compromised mouse model as a model for chronic obstructive pulmonary disease (COPD) investigation. AKR/J male mice were exposed to HEPA-filtered air (sham control group), cigarette smoke (smoke group), LPS (LPS group), or smoke plus LPS (smoke-LPS group) by nose-only inhalation. Lungs were collected at the end of the 3-wk exposure and processed for microarray analysis. Clustering and network analysis showed decreased heat-shock response and chaperone activity, increased immune and inflammatory response, and increased mitosis in all three exposed groups. Two networks/function modules were exclusively found in the smoke-LPS group, that is, the downregulated muscle development/muscle contraction process and the upregulated reactive oxygen species production process. Notably, the number of genes and function modules/networks associated with inflammation was reduced in the smoke-LPS group compared to the LPS group. The most upregulated gene in the smoke group, MMP12, is a matrix metalloproteinase that preferentially degrades elastin and has been implicated in COPD development. NOXO1, which was upregulated in all three treatment groups, positively regulates the expression of a subunit of NADPH oxidase (NOX1), a major source of reactive oxygen species, and may play an important role in the pathogenesis of COPD. Serum amyloid A1, which is an acute-phase systemic inflammation marker and can be induced by LPS exposure, was significantly upregulated in the LPS and smoke-LPS groups. MARCO, a scavenger receptor expressed in macrophages that may play a significant role in LPS-induced inflammatory response, was upregulated in the LPS group and the smoke-LPS group, but not in the smoke group. In conclusion, gene expression profiling identified genes and function modules that may be related to COPD pathogenesis and may be useful as biomarkers to monitor COPD progression. In addition, an LPS-compromised mouse model showed potential as a useful tool for studying cigarette smoke-associated COPD.