Abnormal sarcoplasmic reticulum Ca2+-sequestering properties in skeletal muscle in chronic obstructive pulmonary disease

Role of nutrition in patients with coexisting chronic obstructive pulmonary disease and sarcopenia

Chronic obstructive pulmonary disease (COPD) is one of the most common chronic diseases in the elderly population and is characterized by persistent respiratory symptoms and airflow obstruction. During COPD progression, a variety of pulmonary and extrapulmonary complications develop, with sarcopenia being one of the most common extrapulmonary complications. Factors that contribute to the pathogenesis of coexisting COPD and sarcopenia include systemic inflammation, hypoxia, hypercapnia, oxidative stress, protein metabolic imbalance, and myocyte mitochondrial dysfunction. These factors, individually or in concert, affect muscle function, resulting in decreased muscle mass and strength. The occurrence of sarcopenia severely affects the quality of life of patients with COPD, resulting in increased readmission rates, longer hospital admission, and higher mortality. In recent years, studies have found that oral supplementation with protein, micronutrients, fat, or a combination of nutritional supplements can improve the muscle strength and physical performance of these patients; some studies have also elucidated the possible underlying mechanisms. This review aimed to elucidate the role of nutrition among patients with coexisting COPD and sarcopenia.

Sarcopenia in pulmonary diseases is associated with elevated sarcoplasmic reticulum stress and myonuclear disorganization

Chronic obstructive pulmonary disease (COPD) is frequently associated with age-related muscle loss or sarcopenia. However, the exact molecular mechanism of muscle loss in COPD remains elusive. We investigated the association of chronic dysregulation of sarcoplasmic reticulum (SR) protein homeostasis (a condition called SR stress) and myonuclear disorganization with sarcopenia in patients with COPD. Markers of SR stress and their downstream consequences, including apoptosis and inflammation, were upregulated in patients with COPD. The maximal SR Ca²⁺ ATPase (SERCA) activity was significantly reduced in advanced COPD as compared to healthy controls. Single muscle fiber diameter and cytoplasmic domain per myonucleus were significantly smaller in patients with advanced COPD than in healthy controls. Increased disruption of myonuclear organization was found in the COPD patients as compared to healthy controls. These changes in SR dysfunction were accompanied by elevated global levels of oxidative stress, including lipid peroxidation and mitochondrial reactive oxygen species (ROS) production. Altogether, our data suggest that muscle weakness in advanced COPD is in part associated with the disruption of SR protein and calcium homeostasis and their pathological consequences.

Resveratrol prevents palmitic-acid-induced cardiomyocyte contractile impairment

Long-chain saturated fatty acids, especially palmitic acid (PA), contribute to cardiomyocyte lipotoxicity. This study tests the effects of PA on adult rat cardiomyocyte contractile function and proteins associated with calcium regulating cardiomyocyte contraction and relaxation. Adult rat cardiomyocytes were pretreated with resveratrol (Resv) and then treated with PA. For the reversal study, cardiomyocytes were incubated with PA prior to treatment with Resv. Cardiomyocyte contractility, ratio of rod- to round-shaped cardiomyocytes, and Hoechst staining were used to measure functional and morphological changes in cardiomyocytes. Protein expression of sarco-endoplasmic reticulum ATPase 2a (SERCA2a), native phospholamban (PLB) and phosphorylated PLB (pPLB ser16 and pPLB thr17), and troponin I (TnI) and phosphorylated TnI (pTnI) were measured. SERCA2a activity was also measured. Our results show that PA (200 μM) decreased the rate of cardiomyocyte relaxation, reduced the number of rod-shaped cardiomyocytes, and increased the number of cells with condensed nuclei; pre-treating cardiomyocytes with Resv significantly prevented these changes. Post-treatment with Resv did not reverse morphological changes induced by PA. Protein expression levels of SERCA2a, PLB, pPLBs, TnI, and pTnI were unchanged by PA or Resv. SERCA2a activity assay showed that V_max and Iono ratio were increased with PA and pre-treatment with Resv prevented this increase. In conclusion, our results show that Resv protect cardiomyocytes from contractile dysfunction induced by PA.

The Effect of the Stretch-Shortening Cycle in the Force-Velocity Relationship and Its Association With Physical Function in Older Adults With COPD

This study aimed to evaluate the effect of the stretch-shortening cycle (SSC) on different portions of the force–velocity (F–V) relationship in older adults with and without chronic obstructive pulmonary disease (COPD), and to assess its association with physical function. The participants were 26 older adults with COPD (79 ± 7 years old; FEV₁ = 53 ± 36% of predicted) and 10 physically active non-COPD (77 ± 4 years old) older adults. The F–V relationship was evaluated in the leg press exercise during a purely concentric muscle action and compared with that following an eccentric muscle action at 10% intervals of maximal unloaded shortening velocity (V₀). Vastus lateralis (VL) muscle thickness, pennation angle (PA), and fascicle length (FL) were assessed by ultrasound. Habitual gait speed was measured over a 4-m distance. COPD subjects exhibited lower physical function and concentric maximal muscle power (P_max) values compared with the non-COPD group (both p < 0.05). The SSC increased force and power values among COPD participants at 0–100 and 1–100% of V₀, respectively, while the same was observed among non-COPD participants only at 40–90 and 30–90% of V₀, respectively (all p < 0.05). The SSC induced greater improvements in force, but not power, among COPD compared with non-COPD subjects between 50 and 70% of V₀ (all p < 0.05). Thus, between-group differences in muscle power were not statistically significant after the inclusion of the SSC (p > 0.05). The SSC-induced potentiation at 50–100% of V₀ was negatively associated with physical function (r = -0.40–0.50), while that observed at 80–100% of V₀ was negatively associated with VL muscle thickness and PA (r = -0.43–0.52) (all p < 0.05). In conclusion, older adults with COPD showed a higher SSC-induced potentiation compared with non-COPD subjects, which eliminated between-group differences in muscle power when performing SSC muscle actions. The SSC-induced potentiation was associated with lower physical function, VL muscle thickness, and VL PA values. The SSC-induced potentiation may help as a compensatory mechanism in those older subjects with a decreased ability to produce force/power during purely concentric muscle actions.

Oxidative stress-induced dysregulation of excitation-contraction coupling contributes to muscle weakness

BACKGROUND

We have previously shown that the deletion of the superoxide scavenger, CuZn superoxide dismutase, in mice (Sod1^-/- mice) results in increased oxidative stress and an accelerated loss of skeletal muscle mass and force that mirror the changes seen in old control mice. The goal of this study is to define the effect of oxidative stress and ageing on muscle weakness and the Excitation Contraction (EC) coupling machinery in age-matched adult (8-10 months) wild-type (WT) and Sod1^-/- mice in comparison with old (25-28 months) WT mice.

METHODS

In vitro contractile assays were used to measure muscle contractile parameters. The activity of the sarcoplasmic reticulum Ca²⁺ ATPase (SERCA) pump was measured using an NADH-linked enzyme assay. Immunoblotting and immunofluorescence techniques were used to measure protein expression, and real-time reverse transcription PCR was used to measure gene expression.

RESULTS

The specific force generated by the extensor digitorum longus muscle was reduced in the Sod1^-/- and old WT mice compared with young WT mice along with significant prolongation of time to peak force, increased half relaxation time, and disruption of intracellular calcium handling. The maximal activity of the SERCA calcium uptake pump was significantly reduced in gastrocnemius muscle from both old WT (≈14%) and adult Sod1^-/- (≈33%) mice compared with young WT mice along with increased expression of sarcolipin, a known inhibitor of SERCA activity. Protein levels of the voltage sensor and calcium uptake channel proteins dihydropyridine receptor α1 and SERCA2 were significantly elevated (≈45% and ≈57%, respectively), while the ratio of calstabin, a channel stabilizing protein, to ryanodine receptor was significantly reduced (≈21%) in Sod1^-/- mice compared with young WT mice. The changes in calcium handling were accompanied by substantially elevated levels of global protein carbonylation and lipid peroxidation.

CONCLUSIONS

Our data suggest that the muscle weakness in Sod1^-/- and old WT mice is in part driven by reactive oxygen species-mediated EC uncoupling and supports a role for reduced SERCA pump activity in compromised muscle function. The novel quantitative mechanistic data provided here can lead to potential therapeutic interventions of SERCA dysfunction for sarcopenia and muscle diseases.

Cigarette smoke directly impairs skeletal muscle function through capillary regression and altered myofibre calcium kinetics in mice

KEY POINTS

Cigarette smoke components directly alter muscle fatigue resistance and intracellular muscle fibre Ca2+ handling independent of a change in lung structure. Changes in muscle vascular structure are associated with a depletion of satellite cells. Sarcoplasmic reticulum Ca2+ uptake is substantially impaired in myofibres during fatiguing contractions in mice treated with cigarette smoke extract.

ABSTRACT

Cigarette smokers exhibit exercise intolerance before a decline in respiratory function. In the present study, the direct effects of cigarette smoke on limb muscle function were tested by comparing cigarette smoke delivered to mice by weekly injections of cigarette smoke extract (CSE), or nose-only exposure (CS) 5 days each week, for 8 weeks. Cigarette smoke delivered by either route did not alter pulmonary airspace size. Muscle fatigue measured in situ was 50% lower in the CSE and CS groups than in control. This was accompanied by 34% and 22% decreases in soleus capillary-to-fibre ratio of the CSE and CS groups, respectively, and a trend for fewer skeletal muscle actin-positive arterioles (P = 0.07). In addition, fewer quiescent satellite cells (Nes+Pax7+) were associated with soleus fibres in mice with skeletal myofibre VEGF gene deletion (decreased 47%) and CS exposed (decreased 73%) than with control fibres. Contractile properties of isolated extensor digitorum longus and soleus muscles were impaired. In flexor digitorum brevis myofibres isolated from CSE mice, fatigue resistance was diminished by 43% compared to control and CS myofibres, and this was accompanied by a pronounced slowing in relaxation, an increase in intracellular Ca2+ accumulation, and a slowing in sarcoplasmic reticulum Ca2+ uptake. These data suggest that cigarette smoke components may impair hindlimb muscle vascular structure, fatigue resistance and myofibre calcium handling, and these changes ultimately affect contractile efficiency of locomotor muscles independent of a change in lung function.

Different oxidative status and expression of calcium channel components in stress-induced dysfunctional chicken muscle

The objective of this study was to assess the effects of transport stress at high ambient temperatures on the oxidation status and the expression of essential elements responsible for the Ca transport (sarco- (endo-) plasmic reticulum Ca-ATPase (SERCA1) and the ryanodine receptor (RyR) in (PM) muscles of broilers. Briefly, Arbor Acres broiler chickens ( = 112) were randomly categorized into 2 treatments: unstressed control (C) and 0.5 h transport (T). Each treatment consisted of 8 replicates of 7 birds each. Birds were transported according to a designed protocol. PM muscle samples in T group were collected and classified as normal (T-NOR) or pale, soft, and exudative-like (T-PSE) using meat quality parameters. The results indicated that production of corticosterone (CORT) and reactive oxygen species (ROS) increased significantly after transportation ( < 0.05). Thiobarbituric acid reactive substance values and carbonyl contents increased significantly in the T group ( < 0.05). Moreover, the extent of lipid peroxidation and protein oxidation was more severe in the T-PSE group compared to the T-NOR group ( < 0.05). The mRNA and protein expression of SERCA1 and αRyR increased in the T-NOR group but decreased significantly in the T-PSE group compared to the CON group ( < 0.05). The mRNA expression of βRyR was found to be enhanced in the T-NOR group compared to the CON group, whereas there was no difference in the T-PSE group ( < 0.05). The results indicate that short-distance transport of broilers affects their physiological responses and biochemical changes which may lead to different oxidative states and, importantly, to different expressions of SERCA and RyR. These induced changes in abnormal sarcoplasmic Ca homeostasis have significant implications for the development of PSE-like meat.

Skeletal muscle dysfunction in idiopathic pulmonary arterial hypertension

Despite improvements in survival with disease-targeted therapies, the majority of patients with pulmonary arterial hypertension (PAH) have persistent exercise intolerance that results from impaired cardiac function and skeletal muscle dysfunction. Our intent was to understand the molecular mechanisms mediating skeletal muscle dysfunction in PAH. A total of 12 patients with PAH and 10 matched control subjects were assessed. Patients with PAH demonstrated diminished exercise capacity (lower oxygen uptake max, lower anaerobic threshold and higher minute ventilation/CO2) compared with control subjects. Quadriceps muscle cross-sectional area was significantly smaller in patients with PAH. The vastus lateralis muscle was biopsied to enable muscle fiber morphometric assessment and to determine expression levels/activation of proteins regulating (1) muscle mass, (2) mitochondria biogenesis and shaping machinery, and (3) excitation-contraction coupling. Patients with PAH demonstrated a decreased type I/type II muscle fiber ratio, with a smaller cross-sectional area in the type I fibers. Diminished AKT and p70S6 kinase phosphorylation, with increased atrogin-1 and muscle RING-finger protein-1 transcript levels, were evident in the PAH muscle, suggesting engagement of cellular signaling networks stimulating ubiquitin-proteasome-mediated proteolysis of muscle, with concurrent depression of networks mediating muscle hypertrophy. Although there were no differences in expression/activation of proteins associated with mitochondrial biogenesis or fission (MTCO2 [cytochrome C oxidase subunit II]/succinate dehydrogenase flavoprotein subunit A, mitochondrial transcription factor A, nuclear respiratory factor-1/dynamin-related protein 1 phosphorylation), protein levels of a positive regulator of mitochondrial fusion, Mitofusin2, were significantly lower in patients with PAH. Patients with PAH demonstrated increased phosphorylation of ryanodine receptor 1 receptors, suggesting that altered sarcoplasmic reticulum Ca(++) sequestration may impair excitation-contraction coupling in the PAH muscle. These data suggest that muscle dysfunction in PAH results from a combination of muscle atrophy and intrinsically impaired contractility.

Ca²⁺-pumping impairment during repetitive fatiguing contractions in single myofibers: role of cross-bridge cycling

The energy cost of contractions in skeletal muscle involves activation of both actomyosin and sarcoplasmic reticulum (SR) Ca²⁺-pump (SERCA) ATPases, which together determine the overall ATP demand. During repetitive contractions leading to fatigue, the relaxation rate and Ca²⁺ pumping become slowed, possibly because of intracellular metabolite accumulation. The role of the energy cost of cross-bridge cycling during contractile activity on Ca²⁺-pumping properties has not been investigated. Therefore, we inhibited cross-bridge cycling by incubating isolated Xenopus single fibers with N-benzyl-p-toluene sulfonamide (BTS) to study the mechanisms by which SR Ca²⁺ pumping is impaired during fatiguing contractions. Fibers were stimulated in the absence (control) and presence of BTS and cytosolic calcium ([Ca²⁺]c) transients or intracellular pH (pHi) changes were measured. BTS treatment allowed normal [Ca²⁺]c transients during stimulation without cross-bridge activation. At the time point that tension was reduced to 50% in the control condition, the fall in the peak [Ca²⁺]c and the increase in basal [Ca²⁺]c did not occur with BTS incubation. The progressively slower Ca²⁺ pumping rate and the fall in pHi during repetitive contractions were reduced during BTS conditions. However, when mitochondrial ATP supply was blocked during contractions with BTS present (BTS + cyanide), there was no further slowing in SR Ca²⁺ pumping during contractions compared with the BTS-alone condition. Furthermore, the fall in pHi was significantly less during the BTS + cyanide condition than in the control conditions. These results demonstrate that factors related to the energetic cost of cross-bridge cycling, possibly the accumulation of metabolites, inhibit the Ca²⁺ pumping rate during fatiguing contractions.

ICU-acquired weakness: mechanisms of disability

PURPOSE OF REVIEW

ICU-acquired weakness (ICUAW) is now recognized as a major complication of critical illness. There is no doubt that ICUAW is prevalent - some might argue ubiquitous - after critical illness, but its true role, the interaction with preexisting nerve and muscle lesions as well as its contribution to long-term functional disability, remains to be elucidated.

RECENT FINDINGS

In this article, we review the current state-of-the-art of the basic pathophysiology of nerve and muscle weakness after critical illness and explore the current literature on ICUAW with a special emphasis on the most important mechanisms of weakness.

SUMMARY

Variable contributions of structural and functional changes likely contribute to both early and late myopathy and neuropathy, although the specifics of the temporality of both processes, and the influence patient comorbidities, age, and nature of the ICU insult have on them, remain to be determined.

Metabolic derangements in COPD muscle dysfunction

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

Intensive care unit-acquired weakness: clinical phenotypes and molecular mechanisms

Intensive care unit-acquired weakness (ICUAW) begins within hours of mechanical ventilation and may not be completely reversible over time. It represents a major functional morbidity of critical illness and is an important patient-centered outcome with clear implications for quality of life and resumption of prior work and lifestyle. There is heterogeneity in functional outcome related to ICUAW across various patient populations after an episode of critical illness. This state-of-the art review argues that this observed heterogeneity may represent a clinical spectrum of disability in which there are recognizable clinical phenotypes for outcome according to age, burden of comorbid illness, and ICU length of stay. It further argues that these functional outcomes are modified by mood, cognition, and caregiver physical and mental health. This proposed construct of clinical phenotypes will be used as a framework for a review of the current literature on the molecular biology of muscle and nerve injury. This translational approach for the development of models pairing clinical phenotypes for different functional outcomes after critical illness with molecular mechanism of injury may offer unique insights into the diagnosis and treatment of muscle and nerve lesions.

[Diaphragm and skeletal muscle dysfunction in COPD]

INTRODUCTION

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

STATE OF THE ART

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

PERSPECTIVES

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

CONCLUSIONS

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

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

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

Impact of pulmonary system limitations on locomotor muscle fatigue in patients with COPD

We examined the effects of respiratory muscle work [inspiratory (W(r-insp)); expiratory (W(r-exp))] and arterial oxygenation (Sp(O(2))) on exercise-induced locomotor muscle fatigue in patients with chronic obstructive pulmonary disease (COPD). Eight patients (FEV, 48 +/- 4%) performed constant-load cycling to exhaustion (Ctrl; 9.8 +/- 1.2 min). In subsequent trials, the identical exercise was repeated with 1) proportional assist ventilation + heliox (PAV); 2) heliox (He:21% O(2)); 3) 60% O(2) inspirate (hyperoxia); or 4) hyperoxic heliox mixture (He:40% O(2)). Five age-matched healthy control subjects performed Ctrl exercise at the same relative workload but for 14.7 min ( approximately best COPD performance). Exercise-induced quadriceps fatigue was assessed via changes in quadriceps twitch force (Q(tw,pot)) from before to 10 min after exercise in response to supramaximal femoral nerve stimulation. During Ctrl, absolute workload (124 +/- 6 vs. 62 +/- 7 W), W(r-insp) (207 +/- 18 vs. 301 +/- 37 cmH(2)O x s x min(-1)), W(r-exp) (172 +/- 15 vs. 635 +/- 58 cmH(2)O x s x min(-1)), and Sp(O(2)) (96 +/- 1% vs. 87 +/- 3%) differed between control subjects and patients. Various interventions altered W(r-insp), W(r-exp), and Sp(O(2)) from Ctrl (PAV: -55 +/- 5%, -21 +/- 7%, +6 +/- 2%; He:21% O(2): -16 +/- 2%, -25 +/- 5%, +4 +/- 1%; hyperoxia: -11 +/- 2%, -17 +/- 4%, +16 +/- 4%; He:40% O(2): -22 +/- 2%, -27 +/- 6%, +15 +/- 4%). Ten minutes after Ctrl exercise, Q(tw,pot) was reduced by 25 +/- 2% (P < 0.01) in all COPD and 2 +/- 1% (P = 0.07) in healthy control subjects. In COPD, DeltaQ(tw,pot) was attenuated by one-third after each interventional trial; however, most of the exercise-induced reductions in Q(tw,pot) remained. Our findings suggest that the high susceptibility to locomotor muscle fatigue in patients with COPD is in part attributable to insufficient O(2) transport as a consequence of exaggerated arterial hypoxemia and/or excessive respiratory muscle work but also support a critical role for the well-known altered intrinsic muscle characteristics in these patients.

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

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

Inhibition of mTOR attenuates store-operated Ca2+ entry in cells from endarterectomized tissues of patients with chronic thromboembolic pulmonary hypertension

Pulmonary vascular remodeling occurs in patients with chronic thromboembolic pulmonary hypertension (CTEPH). One factor contributing to this vascular wall thickening is the proliferation of pulmonary artery smooth muscle cells (PASMC). Store-operated Ca(2+) entry (SOCE) and cytosolic free Ca(2+) concentration ([Ca(2+)](cyt)) in PASMC are known to be important in cell proliferation and vascular remodeling in pulmonary hypertension. Rapamycin is widely known for its antiproliferative effects in injured coronary arteries. Although several reports have suggested favorable effects of rapamycin in animal models of pulmonary hypertension, no reports have been published to date in human tissues. Here we report that rapamycin has an inhibitory effect on SOCE and an antiproliferative effect on PASMC derived from endarterectomized tissues of CTEPH patients. Cells were isolated from endarterectomized tissues obtained from patients undergoing pulmonary thromboendarterectomy (PTE). Immunohistochemical analysis indicated high deposition of platelet-derived growth factor (PDGF) in tissue sections from PTE tissues and increased PDGF receptor expression. PDGF transiently phosphorylated Akt, mammalian target of rapamycin (mTOR), and p70S6 kinase in CTEPH cells from CTEPH patients. Acute treatment (30 min) with rapamycin (10 nM) slightly increased cyclopiazonic acid (10 microM)-induced Ca(2+) mobilization and significantly reduced SOCE. Chronic treatment (24 h) with rapamycin reduced Ca(2+) mobilization and markedly inhibited SOCE. The inhibitory effects of rapamycin on SOCE were less prominent in control cells. Rapamycin also significantly reduced PDGF-stimulated cell proliferation. In conclusion, the data from this study indicate the importance of the mTOR pathway in the development of pulmonary vascular remodeling in CTEPH and suggest a potential therapeutic benefit of rapamycin (or inhibition of mTOR) in these patients.

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

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

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

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

Altered metabolic and transporter characteristics of vastus lateralis in chronic obstructive pulmonary disease

To investigate energy metabolic and transporter characteristics in resting muscle of patients with moderate to severe chronic obstructive pulmonary disease [COPD; forced expiratory volume in 1 s (FEV(1)) = 42 +/- 6.0% (mean +/- SE)], tissue was extracted from resting vastus lateralis (VL) of 9 COPD patients and compared with that of 12 healthy control subjects (FEV(1) = 114 +/- 3.4%). Compared with controls, lower (P < 0.05) concentrations (mmol/kg dry wt) of ATP (19.6 +/- 0.65 vs. 17.8 +/- 0.69) and phosphocreatine (81.3 +/- 2.3 vs. 69.1 +/- 4.2) were observed in COPD, which occurred in the absence of differences in the total adenine nucleotide and total creatine pools. Higher concentrations were observed in COPD for several glycolytic metabolites (glucose-1-phosphate, glucose-6-phosphate, fructose-6-phosphate, pyruvate) but not lactate. Glycogen storage was not affected by the disease (289 +/- 20 vs. 269 +/- 20 mmol glucosyl units/kg dry wt). Although no difference between groups was observed for the glucose transporter GLUT1, GLUT4 was reduced by 28% in COPD. For the monocarboxylate transporters, MCT4 was 35% lower in COPD, with no differences observed for MCT1. These results indicate that in resting VL, moderate to severe COPD results in a reduction in phosphorylation potential, an apparent elevation of glycolytic flux rate, and a potential defect in glucose and lactate transport as a result of reduced levels of the principal isoforms.