Exercise-induced lactate increase in relation to muscle substrates in patients with chronic obstructive pulmonary disease

Brown adipose tissue activation is not related to hypermetabolism in emphysematous chronic obstructive pulmonary disease patients

BACKGROUND

Brown adipose tissue (BAT) has been primarily researched as a potential target for mitigating obesity. However, the physiological significance of BAT in relation to cachexia remains poorly understood. The objective of this study was to investigate the putative contribution of BAT on different components of energy metabolism in emphysematous chronic obstructive pulmonary disease (COPD) patients.

METHODS

Twenty COPD patients (mean ± SD age 62 ± 6, 50% female, median [range] BMI 22.4 [15.1-32.5] kg/m² and 85% low FFMI) were studied. Basal metabolic rate (BMR) was assessed by ventilated hood, total daily energy expenditure (TDEE) by doubly labelled water and physical activity by triaxial accelerometry. BMR was adjusted for fat-free mass (FFM) as assessed by deuterium dilution. Analysis of BAT and WAT was conducted in a subset of ten patients and six age-matched, gender-matched and BMI-matched healthy controls. BAT glucose uptake was assessed by means of cold-stimulated integrated [18F]FDG positron-emission tomography and magnetic resonance imaging. WAT was collected from subcutaneous abdominal biopsies to analyse metabolic and inflammatory gene expression levels. Lung function was assessed by spirometry and body plethysmography and systemic inflammation by high sensitivity C-reactive protein.

RESULTS

Mean TDEE was 2209 ± 394 kcal/day, and mean BMR was 1449 ± 214 kcal/day corresponding to 120% of predicted. FFM-adjusted BMR did not correlate with lung function or C-reactive protein. Upon cooling, energy expenditure increased, resulting in a non-shivering thermogenesis of (median [range]) 20.1% [3.3-41.3] in patients and controls. Mean BAT glucose uptake was comparable between COPD and controls (1.5 [0.1-6.2] vs. 1.1 [0.7-3.9]). In addition, no correlation was found between BMR adjusted for FFM and BAT activity or between cold-induced non-shivering energy expenditure and BAT activity. Gene expression levels of the brown adipocyte or beige markers were also comparable between the groups. No (serious) adverse events were reported.

CONCLUSIONS

Although COPD patients were hypermetabolic at rest, no correlation was found between BMR or TDEE and BAT activity. Furthermore, both BAT activity and gene expression levels of the brown adipocyte or beige markers were comparable between COPD patients and controls.

Metabolic profiling of organic and fatty acids in chronic and autoimmune diseases

Metabolomics is a powerful tool of omics that permits the simultaneous identification of metabolic perturbations in several autoimmune and chronic diseases. Several parameters can affect a metabolic profile, from the population characteristics to the selection of the analytical method. In the current chapter, we summarize the main analytical methods and results of the metabolic profiling of fatty and organic acids performed in human metabolomic studies for asthma, COPD, psoriasis and Hashimoto's thyroiditis. We discuss the most significant metabolic alterations associated with these diseases, after comparison of either a single patient's group with healthy controls or several patient's subgroups of different disease severity and phenotype with healthy controls or of a patient's group before and after treatment. Finally, we present critical metabolic patterns that are associated with each disease and their potency for the unraveling of disease pathogenesis, prediction, diagnosis, patient stratification and treatment selection.

Comprehensive metabolic flux analysis to explain skeletal muscle weakness in COPD

BACKGROUND & AIMS

Metabolic characterization of a well-defined group of patients could be a powerful tool in revealing metabolic signatures to explain limb muscle weakness in chronic diseases. Studies are currently limited in Chronic Obstructive Pulmonary Disease (COPD) to the identification of differential amino acid concentrations but lack comprehensive analysis of the flux through relevant muscle function related metabolic pathways.

METHODS

In 23 stable patients with moderate to very severe COPD and 19 healthy controls, a comprehensive metabolic flux analysis was conducted by administering an intravenous pulse and primed constant infusion of multiple stable tracers of amino acids known to play a role in muscle health. Blood samples were obtained to calculate production (WBP) and interconversion rates, and plasma concentrations of these amino acids. Lower and upper limb muscle strength, muscle mass, lung function, physical activity level, and disease history and characteristics were assessed.

RESULTS

The COPD group was characterized by lower and upper limb muscle weakness (P < 0.01) despite preserved muscle mass. Higher values were found in COPD for plasma glutamine, WBP of leucine (P < 0.001), 3-methylhistidine (P < 0.01) (marker of enhanced myofibrillar protein breakdown), citrulline (P < 0.05), and arginine to citrulline conversion (P < 0.05) (reflecting enhanced nitric oxide synthesis). Plasma concentration of β-hydroxy β-methylbutyrate (HMB with anticatabolic, anabolic and contractile properties), WBP of glycine (precursor of creatine and glutathione), and transcutaneous O₂ saturation explained up to 79% and 65% of the variation in strength of the lower and upper limb muscles, respectively, in COPD.

CONCLUSIONS

Comprehensive metabolic flux analysis revealed a homogenous metabolic signature in stable patients with COPD and a specific metabolic profile in those with skeletal muscle weakness.

CLINICAL TRIAL REGISTRY

ClinicalTrials.gov; No. NCT01787682; URL: www.clinicaltrials.gov.

Metabolic Fingerprint of Chronic Obstructive Lung Diseases: A New Diagnostic Perspective

Chronic obstructive lung disease (COLD) is a group of airway diseases, previously known as emphysema and chronic bronchitis. The heterogeneity of COLD does not allow early diagnosis and leads to increased morbidity and mortality. The increasing number of COLD incidences stresses the need for precision medicine approaches that are specific to the patient. Metabolomics is an emerging technology that allows for the discrimination of metabolic changes in the cell as a result of environmental factors and specific genetic background. Thus, quantification of metabolites in human biofluids can provide insights into the metabolic state of the individual in real time and unravel the presence of, or predisposition to, a disease. In this article, the advantages of and potential barriers to putting metabolomics into clinical practice for COLD are discussed. Today, metabolomics is mostly lab-based, and research studies with novel COLD-specific biomarkers are continuously being published. Several obstacles in the research and the market field hamper the translation of these data into clinical practice. However, technological and computational advances will facilitate the clinical interpretation of data and provide healthcare professionals with the tools to prevent, diagnose, and treat COLD with precision in the coming decades.

Imaging approaches to understand disease complexity: chronic obstructive pulmonary disease as a clinical model

The clinical manifestations of chronic obstructive pulmonary disease (COPD) reflect an aggregate of multiple pulmonary and extrapulmonary processes. It is increasingly clear that full assessment of these processes is essential to characterize disease burden and to tailor therapy. Medical imaging has advanced such that it is now possible to obtain in vivo insight in the presence and severity of lung disease-associated features. In this review, we have assembled data from multiple disciplines of medical imaging research to review the role of imaging in characterization of COPD. Topics include imaging of the lungs, body composition, and extrapulmonary tissue metabolism. The primary focus is on imaging modalities that are widely available in clinical care settings and that potentially contribute to describing COPD heterogeneity and enhance our insight in underlying pathophysiological processes and their structural and functional effects.

Proteasome activity related with the daily physical activity of COPD patients

BACKGROUND

COPD is a debilitating disease that affects patients' daily lives. One's daily physical activity (DPA) decreases due to multifactorial causes, and this decrease is correlated with a poor prognosis in COPD patients. Muscle wasting may at least be partly due to increased activity of the ubiquitin proteasome pathway and apoptosis.

METHODS

This study investigated the relationships among DPA, circulating proteasome activity, and protein carbonyl in COPD patients and healthy subjects (HSs). This study included 57 participants (42 patients and 15 healthy subjects). Ambulatory DPA was measured using actigraphy, and oxygen saturation was measured with a pulse oximeter.

RESULTS

COPD patients had lower DPA, lower 6 min walking distance (6MWD), lower delta saturation pulse oxygenation (SpO₂) during the 6MWT, and lower delta SpO₂ during DPA than HSs. COPD patients had higher proteasome activity and protein carbonyl than HSs. Circulating proteasome activity was significantly negatively correlated with DPA (r=-0.568, P<0.05) in COPD patients, whereas delta SpO₂ during the 6MWT was significantly positively correlated with proteasome activity (r=0.685, P<0.05) in HSs. Protein carbonyl was significantly negatively correlated with the body mass index (r=-0.318, P<0.05), mid-arm circumference (r=0.350, P<0.05), calf circumference (r=0.322, P<0.05), forced expiratory volume in the first second (r=-0.441, P<0.01), and 6MWD (r=-0.313, P<0.05) in COPD patients. Our results showed no significant difference in inflammatory markers (interleukin-6 and tumor necrosis factor-α) or ubiquitin between the two groups.

CONCLUSION

COPD patients had lower DPA levels and higher circulating proteasome activity than HSs, and a negative correlation of DPA with circulating proteasome activity.

Clinical management of chronic obstructive pulmonary disease patients with muscle dysfunction

Muscle dysfunction is frequently observed in chronic obstructive pulmonary disease (COPD) patients, contributing to their exercise limitation and a worsening prognosis. The main factor leading to limb muscle dysfunction is deconditioning, whereas respiratory muscle dysfunction is mostly the result of pulmonary hyperinflation. However, both limb and respiratory muscles are also influenced by other negative factors, including smoking, systemic inflammation, nutritional abnormalities, exacerbations and some drugs. Limb muscle weakness is generally diagnosed through voluntary isometric maneuvers such as handgrip or quadriceps muscle contraction (dynamometry); while respiratory muscle loss of strength is usually recognized through a decrease in maximal static pressures measured at the mouth. Both types of measurements have validated reference values. Respiratory muscle strength can also be evaluated determining esophageal, gastric and transdiaphragmatic maximal pressures although there is a lack of widely accepted reference equations. Non-volitional maneuvers, obtained through electrical or magnetic stimulation, can be employed in patients unable to cooperate. Muscle endurance can also be assessed, generally using repeated submaximal maneuvers until exhaustion, but no validated reference values are available yet. The treatment of muscle dysfunction is multidimensional and includes improvement in lifestyle habits (smoking abstinence, healthy diet and a good level of physical activity, preferably outside), nutritional measures (diet supplements and occasionally, anabolic drugs), and different modalities of general and muscle training.

Cachexia in chronic obstructive pulmonary disease: new insights and therapeutic perspective

Cachexia and muscle wasting are well recognized as common and partly reversible features of chronic obstructive pulmonary disease (COPD), adversely affecting disease progression and prognosis. This argues for integration of weight and muscle maintenance in patient care. In this review, recent insights are presented in the diagnosis of muscle wasting in COPD, the pathophysiology of muscle wasting, and putative mechanisms involved in a disturbed energy balance as cachexia driver. We discuss the therapeutic implications of these new insights for optimizing and personalizing management of COPD-induced cachexia.

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

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

Oxygen desaturation during the six-minute walk test in COPD patients

OBJECTIVE

To evaluate the behavior of oxygen saturation curves throughout the six-minute walk test (6MWT) in patients with COPD.

METHODS

We included 85 patients, all of whom underwent spirometry and were classified as having moderate COPD (modCOPD, n = 30) or severe COPD (sevCOPD, n = 55). All of the patients performed a 6MWT, in a 27-m corridor with continuous SpO2 and HR monitoring by telemetry. We studied the SpO2 curves in order to determine the time to a 4% decrease in SpO2, the time to the minimum SpO2 (Tmin), and the post-6MWT time to return to the initial SpO2, the last designated recovery time (RT). For each of those curves, we calculated the slope.

RESULTS

The mean age in the modCOPD and sevCOPD groups was 66 ± 10 years and 62 ± 11 years, respectively. At baseline, SpO2 was > 94% in all of the patients; none received supplemental oxygen during the 6MWT; and none of the tests were interrupted. The six-minute walk distance did not differ significantly between the groups. The SpO2 values were lowest in the sevCOPD group. There was no difference between the groups regarding RT. In 71% and 63% of the sevCOPD and modCOPD group patients, respectively, a ≥ 4% decrease in SpO2 occurred within the first minute. We found that FEV1% correlated significantly with the ΔSpO2 (r = -0.398; p < 0.001), Tmin (r = -0.449; p < 0.001), and minimum SpO2 (r = 0.356; p < 0.005).

CONCLUSIONS

In the sevCOPD group, in comparison with the modCOPD group, SpO2 was lower and the Tmin was greater, suggesting a worse prognosis in the former.

Correlation of BMI and oxygen saturation in stable COPD in Northern India

Background:

Chronic obstructive pulmonary disease (COPD) is associated with clinically relevant extra pulmonary manifestations; one of them is weight loss. However, there are very few studies from North India available in relation to body mass index (BMI) and Oxygen saturation (SpO₂) with COPD.

Aims:

To study the prevalence of undernutrition among stable COPD patients and correlation of COPD severity with SpO₂ and BMI.

Settings and Design:

A prospective study was carried out at a tertiary care hospital.

Subjects and Methods:

COPD patients were diagnosed and staged as per global initiative for chronic obstructive lung disease (GOLD) guidelines. SpO₂ was measured using pulse oxymeter and BMI categorization was done as per new classification for Asian Indians (2009). Statistical analysis was done using Statistical Package for Social Sciences Version 15.0.

Results:

Out of 147 COPD patients, 85 (57.8%) were undernourished. The prevalence of undernourished BMI was 25%, 50.8%, 61.7%, and 80% in stage I, II, III and IV respectively; statistically significant (P < 0.050). The mean SpO₂ was 95.50 ± 1.41, 95.05 ± 2.42, 94.37 ± 2.28 and 93.05 ± 1.39 in stage I, II, III and IV respectively; statistically significant (F = 4.723; P = 0.004).

Conclusions:

The overall prevalence of under nutrition among COPD patients was 57.8%. With increasing COPD stage the BMI and median SpO₂ value decreased in progressive manner. Association of SpO₂ and COPD stages could be explored further in order to suggest an additional marker of disease severity that would add a new dimension in the management of COPD.

Pathophysiology of muscle dysfunction in COPD

Muscle dysfunction often occurs in patients with chronic obstructive pulmonary disease (COPD) and may involve both respiratory and locomotor (peripheral) muscles. The loss of strength and/or endurance in the former can lead to ventilatory insufficiency, whereas in the latter it limits exercise capacity and activities of daily life. Muscle dysfunction is the consequence of complex interactions between local and systemic factors, frequently coexisting in COPD patients. Pulmonary hyperinflation along with the increase in work of breathing that occur in COPD appear as the main contributing factors to respiratory muscle dysfunction. By contrast, deconditioning seems to play a key role in peripheral muscle dysfunction. However, additional systemic factors, including tobacco smoking, systemic inflammation, exercise, exacerbations, nutritional and gas exchange abnormalities, anabolic insufficiency, comorbidities and drugs, can also influence the function of both respiratory and peripheral muscles, by inducing modifications in their local microenvironment. Under all these circumstances, protein metabolism imbalance, oxidative stress, inflammatory events, as well as muscle injury may occur, determining the final structure and modulating the function of different muscle groups. Respiratory muscles show signs of injury as well as an increase in several elements involved in aerobic metabolism (proportion of type I fibers, capillary density, and aerobic enzyme activity) whereas limb muscles exhibit a loss of the same elements, injury, and a reduction in fiber size. In the present review we examine the current state of the art of the pathophysiology of muscle dysfunction in COPD.

Casein protein results in higher prandial and exercise induced whole body protein anabolism than whey protein in chronic obstructive pulmonary disease

Exercise is known to improve physical functioning and health status in Chronic Obstructive Pulmonary Disease (COPD). Recently, disturbances in protein turnover and amino acid kinetics have been observed after exercise in COPD. The objective was to investigate which dairy protein is able to positively influence the protein metabolic response to exercise in COPD. 8 COPD patients and 8 healthy subjects performed a cycle test on two days while ingesting casein or whey protein. Whole body protein breakdown (WbPB), synthesis (WbPS), splanchnic amino acid extraction (SPE), and NetWbPS (=WbPS-WbPB) were measured using stable isotope methodology during 20 min of exercise (at 50% peak work load of COPD group). The controls performed a second exercise test at the same relative workload. Exercise was followed by 1 h of recovery. In the healthy group, WbPS, SPE, and NetPS were higher during casein than during whey feeding (P<.01). WbPS and NetPS were higher during exercise, independent of exercise intensity (P<.01). NetPS was higher during casein feeding in COPD due to lower WbPB (P<.05). Higher SPE was found during exercise during casein and whey feeding in COPD (P<.05). Lactate levels during exercise were higher in COPD (P<.05) independent of the protein. Post-exercise, lower NetPS values were found independent of protein type in both groups. Casein resulted in more protein anabolism than whey protein which was maintained during and following exercise in COPD. Optimizing protein intake might be of importance for muscle maintenance during daily physical activities in COPD.

Respiratory diseases and muscle dysfunction

Many respiratory diseases lead to impaired function of skeletal muscles, influencing quality of life and patient survival. Dysfunction of both respiratory and limb muscles in chronic obstructive pulmonary disease has been studied in depth, and seems to be caused by the complex interaction of general (inflammation, impaired gas exchange, malnutrition, comorbidity, drugs) and local factors (changes in respiratory mechanics and muscle activity, and molecular events). Some of these factors are also present in cystic fibrosis and asthma. In obstructive sleep apnea syndrome, repeated exposure to hypoxia and the absence of reparative rest are believed to be the main causes of muscle dysfunction. Deconditioning appears to be crucial for the functional impairment observed in scoliosis. Finally, cachexia seems to be the main mechanism of muscle dysfunction in advanced lung cancer. A multidimensional therapeutic approach is recommended, including pulmonary rehabilitation, an adequate level of physical activity, ventilatory support and nutritional interventions.

Preserved muscle metaboreflex in chronic obstructive pulmonary disease

The objective of this study was to measure the magnitude of the muscle metaboreflex in people with chronic obstructive pulmonary disease (COPD) compared with healthy controls and to assess the relationships between disease severity, exercise capacity, and the magnitude of the muscle metaboreflex. Nine people with mild-to-severe COPD and 11 age- and gender-matched healthy controls performed isometric handgrip exercise (IHG), followed by postexercise circulatory occlusion (PECO) while hemodynamic changes were measured. Continuous measures of heart rate, arterial pressure, leg blood flow, leg vascular resistance, and total peripheral resistance were obtained. Participants then performed a cycle test to exhaustion. Heart rate, blood pressure, and blood flow responses during IHG and PECO were similar between the COPD group and healthy controls (p > 0.05). There was no association between disease severity or exercise capacity and the magnitude of the muscle metaboreflex. We observed a preserved muscle metaboreflex in mild-to-severe COPD, suggesting the metaboreflex is not a contributing factor to the development of exercise intolerance in this population.

Glucose and pyruvate metabolism in severe chronic obstructive pulmonary disease

The mechanisms leading to weight loss in patients with chronic obstructive pulmonary disease (COPD) are poorly understood but may involve alterations in macronutrient metabolism. Changes in muscle oxidative capacity and lactate production during exercise suggest glucose metabolism may be altered in COPD subjects. The objective of this study was to determine differences in the rates of glucose production and clearance, the rate of glycolysis (pyruvate production), and oxidative and nonoxidative pyruvate disposal in subjects with severe COPD compared with healthy controls. The in vivo rates of glucose production and clearance were measured in 14 stable outpatients with severe COPD (seven with low and seven with preserved body mass indexes) and 7 healthy controls using an intravenous infusion of [(2)H(2)]glucose. Additionally, pyruvate production and oxidative and non-oxidative pyruvate disposal were measured using intravenous infusions of [(13)C]bicarbonate and [(13)C]pyruvate. Endogenous glucose flux and glucose clearance were significantly faster in the combined COPD subjects (P = 0.002 and P < 0.001, respectively). This difference remained significant when COPD subjects were separated by body mass index. Pyruvate flux and oxidation were significantly higher in the combined COPD subjects than controls (P = 0.02 for both), but there was no difference in nonoxidative pyruvate disposal or plasma lactate concentrations between the two groups. In subjects with severe COPD, there are alterations in glucose metabolism leading to increased glucose production and faster glucose metabolism by glycolysis and oxidation compared with controls. However, no difference in glucose conversion to lactate via pyruvate reduction is observed.

Increased postabsorptive and exercise-induced whole-body glucose production in patients with chronic obstructive pulmonary disease

Skeletal muscle biopsy studies have consistently shown a decreased oxidative phenotype in patients with moderate to severe chronic obstructive pulmonary disease (COPD). Limited information is available regarding potential adaptations or abnormalities in anaerobic metabolism and glucose homeostasis. Whole-body glucose production was assessed at rest and during exercise in COPD patients with moderate disease severity (forced expiratory volume in 1 second, 52% ± 3%), prestratified into normal-weight (n = 7; body mass index [BMI], 27.5 ± 0.9 kg·m(-2)) and underweight subjects (n = 6; BMI, 20.6 ± 0.7 kg·m(-2)), and in 8 healthy controls matched for age and BMI with the normal-weight COPD group. Glucose tolerance was normal in all subjects. Rate of appearance (R(a)) of glucose at rest and during submaximal cycling exercise was measured in postabsorptive state by infusion of stable isotope tracer [6,6-(2)H(2)]glucose. Resting glucose R(a) was significantly enhanced in underweight COPD patients compared with controls (16.7 ± 0.3 vs 15.1 ± 0.4 μmol·kg fat-free mass(-1)·min(-1), P < .05) and was inversely related to fat-free mass (r = -0.75, P < .01). Furthermore, the exercise-induced increase in glucose R(a) was enhanced in COPD patients (81.9% ± 3.4% vs 72.1% ± 2.0%, P = .05), resulting in elevated end-of-exercise glucose output. Differences were most pronounced in underweight patients, who were also characterized by enhanced plasma catecholamine levels and decreased insulin concentrations (all, P < .05). In normal-weight patients, there was evidence for decreased insulin sensitivity assessed by homeostatic modeling technique. Whole-body glucose production is increased in underweight COPD patients with normal glucose tolerance. It is hypothesized that lowered body weight in COPD has unique effects on glucose uptake despite reduced skeletal muscle oxidative capacity, relative hypoxemia, and sympathetic activation.

No effect of glutamine ingestion on indices of oxidative metabolism in stable COPD

COPD patients have reduced muscle glutamate which may contribute to an impaired response of oxidative metabolism to exercise. We hypothesised that prior glutamine supplementation would enhance V(O2) peak, V(O2) at lactate threshold and speed pulmonary oxygen uptake kinetics in COPD. 13 patients (9 males, age 66±5 years, mean±SD) with severe COPD (mean FEV(1) 0.88±0.23l, 33±7% predicted) performed on separate days ramp cycle-ergometry (5-10 W min(-1)) to volitional exhaustion and subsequently square-wave transitions to 80% estimated lactate threshold (LT) following consumption of either placebo (CON) or 0.125 g kg bm(-1) of glutamine (GLN) in 5 ml kg bm(-1) placebo. Oral glutamine had no effect on peak or V(O2) at LT, {V(O2) peak: CON=0.70±0.1 l min(-1) vs. GLN=0.73±0.2 l min(-1); LT: CON=0.57±0.1 l min(-1) vs. GLN=0.54±0.1 lmin(-1)} or V(O2) kinetics {tau: CON=68±22 s vs. GLN=68±16 s}. Ingestion of glutamine before exercise did not improve indices of oxidative metabolism in this patient group.

Systemic effects of chronic obstructive pulmonary disease

Chronic obstructive pulmonary disease (COPD) is associated with important extrapulmonary, or systemic, effects. There is systemic as well as pulmonary inflammation in COPD and this, together with systemic oxidative stress, contributes to their development. Skeletal muscle dysfunction contributes to exercise limitation. There is a loss of muscle mass and a reduction in the proportion of type 1 fibers. Sedentarism, hypoxia, corticosteroid therapy, nutritional depletion and systemic inflammation may contribute to its development. Weight loss is another important effect. It is associated with a worse prognosis, which changes with therapy and may be due to reductions in calorie intake, changes in intermediate metabolism and effects of systemic inflammation. Cardiovascular disease is a frequent cause of death in COPD and coronary artery disease, left ventricular failure and arrhythmias are systemic effects of COPD, as well as comorbidities sharing a common etiology. Exacerbations of COPD may increase the risk of coronary events by increasing the level of systemic inflammation. Osteoporosis is more common in COPD (even after adjusting for corticosteroid usage) and may be due to a combination of inactivity and the effects of systemic inflammation. COPD is also associated with systemic endothelial dysfunction and CNS abnormalities (including depression), which may also be due to the effects of systemic inflammation. These systemic effects respond to COPD treatments, including pulmonary rehabilitation, nutritional supplementation and inhaled corticosteroids, as well as specific drugs, such as bisphosphonates or diuretics. There is growing evidence that novel approaches, such as the use of statins, may also be of value.

Fat-free mass change after nutritional rehabilitation in weight losing COPD: role of insulin, C-reactive protein and tissue hypoxia

BACKGROUND

Fat-free mass (FFM) depletion marks the imbalance between tissue protein synthesis and breakdown in chronic obstructive pulmonary disease (COPD). To date, the role of essential amino acid supplementation (EAAs) in FFM repletion has not been fully acknowledged. A pilot study was undertaken in patients attending pulmonary rehabilitation.

METHODS

28 COPD patients with dynamic weight loss > 5% over the last 6 months were randomized to receive EAAs embedded in a 12-week rehabilitation program (EAAs group n = 14), or to the same program without supplementation (C group n = 14). Primary outcome measures were changes in body weight and FFM, using dual X-ray absorptiometry (DEXA).

RESULTS

At the 12th week, a body weight increment occurred in 92% and 15% of patients in the EAAs and C group, respectively, with an average increase of 3.8 +/- 2.6 kg (P = 0.0002) and -0.1 +/- 1.1 kg (P = 0.81), respectively. A FFM increment occurred in 69% and 15% of EAAs and C patients, respectively, with an average increase of 1.5 +/- 2.6 kg (P = 0.05) and -0.1 +/- 2.3 kg (P = 0.94), respectively. In the EAAs group, FFM change was significantly related to fasting insulin (r(2) 0.68, P < 0.0005), C-reactive protein (C-RP) (r(2) = 0.46, P < 0.01), and oxygen extraction tension (PaO(2x)) (r(2) = 0.46, P < 0.01) at end of treatment. These three variables were highly correlated in both groups (r > 0.7, P < 0.005 in all tests).

CONCLUSIONS

Changes in FFM promoted by EAAs are related to cellular energy and tissue oxygen availability in depleted COPD. Insulin, C-RP, and PaO(2x) must be regarded as clinical markers of an amino acid-stimulated signaling to FFM accretion.

Correlation of levels of obstruction in COPD with lactate and six-minute walk test

Chronic obstructive pulmonary disease (COPD) is a leading cause of morbid-mortality world wide, leading not only to pulmonary damage but also to multisystemic impairment, with repercussions on skeletal muscles and the ability to undertake effort, as measured in the six-minute walk test (6-MWT).

AIMS

To correlate the level of obstruction in COPD with lactate concentration and heart rate (HR) at rest, and distance walked. To correlate distance walked with blood gas analysis and correlate desaturation in 6-MWT with post 6-MWT lactate concentration and heart rate.

METHODS

COPD patients underwent spirometry, blood gas analysis and 6-MWT to evaluate distance walked, heart rate, capillary lactate (CL) concentration pre- and post 6-MWT, and desaturation with 6-MWT.

RESULTS

91 patients with all levels of obstruction were evaluated. HR and CL increased significantly post 6-MWT. The decrease in peripheral saturation of haemoglobin to oxygen observed with 6-MWT was also significant. The distance walked was shorter the greater the obstruction. The correlation analysis was significantly positive between FEV1 and distance walked, negative between FEV(1) and HR at rest and negative between distance walked and PaCO(2), and not significant for the other variables.

CONCLUSIONS

Increased obstruction in COPD and higher PaCO(2) values contribute to a reduction in distance walked in 6-MWT. The level of obstruction in COPD leads to a haemodynamic impairment with increased HR at rest of these patients.

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.

Plasma branched-chain amino acid levels and muscle energy metabolism in patients with chronic obstructive pulmonary disease

BACKGROUND & AIMS

Although several studies have shown that plasma concentrations of branched-chain amino acids (BCAAs) are reduced in patients with chronic obstructive pulmonary disease (COPD), little is understood about how low concentrations of BCAAs limit exercise in such patients. The present study investigated whether plasma BCAAs are related to energy metabolism in exercising muscle using (31)P-magnetic resonance spectroscopy (MRS).

METHODS

We analyzed the plasma amino acid profiles of 23 male patients with COPD (aged 69.2+/-5.1 years) and of 7 healthy males (aged 64.1+/-6.0 years). We normalized the exercise intensity of repetitive lifting by adjusting the weight to 7% of the maximal grip power. The intracellular pH and the phosphocreatine (PCr) index (PCr/(PCr+Pi); Pi, inorganic phosphate) were calculated from MR spectra. We evaluated the relationship between intracellular pH and PCr index at the completion of exercise and the plasma BCAA concentration.

RESULTS

Glutamine concentrations were elevated in patients with COPD compared with healthy individuals. Plasma concentrations of BCAAs correlated with intracellular pH and PCr index at the completion of exercise.

CONCLUSIONS

The findings are consistent with the notion that BCAAs affect muscle energy metabolism during exercise in patients with COPD.

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.

Future trends in preoperative evaluation

Preoperative evaluation before lung resection has been frequently addressed in modern medical literature. Actual or predicted pulmonary volumes are considered relevant to predict the risk of surgery. Nevertheless, ppoFEV1 underestimates the real functional loss in the immediate postoperative period when most of the complications occur. Not all patients, however, have comparable functional changes after lobectomy. Minimal impairment or even improvements have been demonstrated in COPD cases after lobectomy. Efforts should be directed to an accurate prediction of the immediate postoperative pulmonary volumes for a better evaluation of high-risk patients caused by respiratory impairment. Future developments are needed on the role of measuring preoperative DLCO and how to evaluate a patient's general cardiorespiratory status. Evidence underlines the relevance of routine evaluation of preoperative DLCO at rest or, better, during exercise for a thorough assessment of patient's capability to adapt to a stressful situation (Fig. 3). Only by improving knowledge about the general condition of the patient, can one assess the physiologic response to surgery. Widespread use of sophisticated or simple exercise tests and measurements or daily activity using motion detectors can identify high-risk patients with otherwise acceptable pulmonary volumes. Another suggested investigation issue is to develop different relevant outcome parameters, not only from the surgeon's point of view but also from the patient's perspective, such as postoperative QOL-related variables or delayed outcomes. Finally, multidisciplinary investigation teams, including experts in mathematical modeling, are essential to improve the quality and validity of the developed models. Although knowledge about perioperative physiologic changes has increased, clinicians are still far from finding a way to put all this knowledge down and make it applicable for an individual patient. Multicentric cooperation and evaluation of large prospectively recorded databases are essential to develop evidence-based clinical guidelines on preoperative evaluation.

Metabolic and functional effects of glutamate intake in patients with chronic obstructive pulmonary disease (COPD)

BACKGROUND & AIMS

Patients with chronic obstructive pulmonary disease (COPD) often suffer from skeletal muscle weakness due to muscle wasting and altered muscle metabolism. Decreased muscle glutamate concentration in COPD is consistently reported and is associated with decreased muscle glutathione concentration and early lactic acidosis. We hypothesized that an increased availability of glutamate via glutamate ingestion increases muscle glutamate concentration leading to acute improvements in skeletal muscle energy metabolism and function.

METHODS

Two experiments were conducted. In experiment 1, in two groups of 6 male COPD patients (FEV(1): 44.8+/-3.4%pred) and 6 healthy controls, blood samples and muscle biopsies were taken at 0 and 80 min after repeated glutamate (30 mg/kg BW) or control ingestion (1.25 ml/kg BW), and after 20 min cycling at 50% peak workload. In experiment 2, in 10 COPD patients (FEV(1): 36.1+/-2.5%pred), the effect of the two drinks was tested on cycle endurance time and contractile quadriceps fatigue measured by magnetic stimulation before and after cycling at 75% peak workload.

RESULTS

Glutamate ingestion increased plasma (p<0.01) but not muscle glutamate concentration. Muscle total and reduced glutathione and plasma lactate concentration were not affected by glutamate ingestion. Glutamate ingestion did not influence contractile muscle fatigue and endurance time.

CONCLUSION

Continuous oral glutamate ingestion for 80 min did not lead to an acute effect on skeletal muscle substrate metabolism and muscle performance in COPD patients and in age-matched healthy controls.

C-reactive protein correlates with tissue oxygen availability in patients with stable COPD

BACKGROUND

Arterial oxygen tension, oxygen delivery to tissue, and systemic inflammation are recognized as pivotal factors in the progression of chronic obstructive pulmonary disease (COPD). However, interconnections between systemic inflammation and tissue oxygen availability are scantly investigated. Tissue oxygen availability depends on arterial PaO2, oxygen concentration, hemoglobin oxygen affinity (P50), and hemoglobin oxygen binding capacity (ceHb). As the integrated changes of those indices are summarized by oxygen extraction tension (PaO2x), the objective of this study was to explore the association between C-reactive protein (CRP) blood levels and either PaO2x or each of its determinants, in stable COPD.

MATERIALS AND METHODS

Blood CRP and oxygen status of arterial blood were measured at rest while breathing room air in 44 moderate to severe stable COPD patients. PaO2x was calculated along the shape of oxygen binding curve as the oxygen tension resulting from removal of 2.3 mmol of oxygen per liter of blood. Multiple linear regression analysis was performed with PaO2, ceHb, and P50 as independent variables, and CRP as the dependent variable, adjusting for age and sex. The analysis was repeated using PaO2x as a sole independent variable.

RESULTS

Multiple linear regression analysis indicated that ceHb, PaO2, and P50, were significant and independent predictors of CRP (R2 = 0.52, p < 0.0001). PaO2x alone was an even stronger predictor of CRP (R2 = 0.62, p < 0.0001).

CONCLUSIONS

These findings indicate that physiological determinants of tissue oxygen availability are independently associated with CRP blood levels. Thus, improvement of tissue oxygen availability is a central therapeutic option to modulate the severity of systemic inflammatory processes in patients with COPD.

Phenotypes of chronic obstructive pulmonary disease

The current clinical classification of smoking-related lung disease fails to take into account the heterogeneity of chronic obstructive pulmonary disease (COPD). With an increased understanding of pathophysiologic variation, COPD now clearly represents a spectrum of overlapping diseases with important extrapulmonary consequences. A "phenotype" describes the outward physical manifestations of a particular disease, and compromises anything that is part of the observable structure, function or behavior of an individual. Such phenotypic distinctions in COPD include: frequent exacerbator, pulmonary cachectic, rapid decliner, airways hyperresponsiveness, impaired exercise tolerance, and emphysema versus airways disease. These variable manifestations, each with unique prognostic, clinical and physiologic ramifications, represent distinct phenotypes within COPD. While all of these phenotypes have smoking as a common risk factor, the other risk factors that determine these phenotypes remain poorly understood. An individual smoker has variable expression of each phenotype and there is mounting evidence that COPD phenotypes have different clinical outcomes. These phenotypes can be broadly classified into one of three groups: clinical, physiologic and radiographic. This review presents the evidence for the spectrum of COPD phenotypes with a focused discussion on the pathophysiologic, epidemiologic and clinical significance of each subtype.

Effects of exercise training on quadriceps muscle gene expression in chronic obstructive pulmonary disease

Exercise capacity and training response are limited in chronic obstructive pulmonary disease (COPD), but the extent to which this is related to altered skeletal muscle function is not fully understood. To test the hypothesis that muscle gene expression is altered in COPD, we performed needle biopsies from the vastus lateralis of six COPD patients and five sedentary age-matched healthy men, before and after 3 mo of exercise training. RNA was hybridized to Affymetrix U133A Genechip arrays. In addition, peak O2 uptake and other functional parameters (e.g., 6-min walk) were measured before and after training. The 6-min walk test increased significantly following training in both groups (53.6 ± 18.6 m in controls, P = 0.045; 37.1 ± 6.7 m in COPD, P = 0.002), but peak O2 uptake increased only in controls (19.4 ± 4.5%, P = 0.011). Training significantly altered muscle gene expression in both groups, but the number of affected genes was lower in the COPD patients (231) compared with controls (573). Genes related to energy pathways had higher expression in trained controls. In contrast, oxidative stress, ubiquitin proteasome, and COX gene pathways had higher expression in trained COPD patients, and some genes (e.g., COX11, COX15, and MAPK-9) were upregulated by training only in COPD patients. We conclude that both COPD and control subjects demonstrated functional responses to training but with somewhat different patterns in muscle gene expression. The pathways that are uniquely induced by exercise in COPD (e.g., ubiquitin proteasome and COX) might indicate a greater degree of tissue stress (perhaps by altered O2 and CO2 dynamics) than in controls.

Nutritional modulation as part of the integrated management of chronic obstructive pulmonary disease

Weight loss is a frequent complication in patients with chronic obstructive pulmonary disease (COPD) and is a determining factor for functional capacity, health status and mortality. Weight loss in COPD is a consequence of an inbalance between increased energy requirements and dietary intake. Both metabolic and mechanical inefficiency may contribute to elevated energy expenditure during physical activity, while systemic inflammation has been associated with hypermetabolism at rest. Disease-specific symptoms and systemic inflammation may impair appetite and dietary intake. Altered intermediary metabolism may cause disproportionate wasting of fat-free mass in some patients. A combination of nutritional support and exercise as an anabolic stimulus appears to be the best approach to obtaining marked functional improvement. Patients responding to this treatment even demonstrated a decreased mortality. The effectiveness of anti-catabolic modulation requires further investigation.

Enzyme Catalytic Activities in Chronic Obstructive Pulmonary Disease

BACKGROUND

Altered muscle amino acid metabolism resulting in skeletal muscle dysfunction is one of the systemic effects of chronic obstructive pulmonary disease (COPD) associated with systemic oxidative stress and inflammation. The aim of the study was to investigate the existence and extent of changes in the activities of the enzymes catalyzing transamination reactions (aminotransferases), the enzyme involved in bone rearrangement (alkaline phosphatase), and the enzyme reflecting hypoxia that is characteristic of these patients (lactate dehydrogenase). In addition, the effect of cigarette smoking on these enzyme activities was also assessed.

METHODS

Enzyme activities such as alanine aminotransferase, aspartate aminotransferase, alkaline phosphatase, gamma-glutamyltransferase and lactate dehydrogenase were determined by standard analysis in sera of 29 COPD patients (FEV(1) = 46.6 +/- 12.1%) and 58 healthy subjects (21 nonsmokers, 17 ex-smokers and 20 smokers).

RESULTS

The activity of aspartate aminotransferase and alanine aminotransferase was significantly decreased, and the activity of lactate dehydrogenase increased in sera of COPD patients as compared with the group of healthy nonsmokers. According to centile values, the activity of alkaline phosphatase, gamma-glutamyltransferase and lactate dehydrogenase was increased in 50, 5, and 50% of COPD patients, respectively.

CONCLUSIONS

Study results revealed significant changes in the activities of transamination enzymes in patient sera, thus supporting the reports on altered amino acid metabolism in skeletal muscle in COPD. The elevated activity of alkaline phosphatase provides additional evidence for altered bone rearrangement in these patients. Smoking was not found to have any major effect on these enzyme activities in the present study.

Effect of glutamate ingestion on whole-body glutamate turnover in healthy elderly and patients with chronic obstructive pulmonary disease

OBJECTIVE

Decreased whole-body glutamate turnover is found in healthy elderly and in patients with chronic obstructive pulmonary disease (COPD). Glutamate supplementation as an option to increase whole-body glutamate turnover and, hence, glutamate availability has never been investigated. In the present study, we developed a protocol based on repeated glutamate ingestion to increase plasma glutamate concentration to a steady-state level without inducing toxic side effects and to evaluate the effect of repeated glutamate ingestion on whole-body glutamate turnover in patients with COPD and healthy elderly.

METHODS

In part 1, the response of plasma glutamate concentration was determined in young healthy volunteers who repeatedly ingested a glutamate solution. The tolerance of the glutamate drink was evaluated in 26 healthy volunteers by a food tolerance questionnaire. In part 2, eight male patients with COPD and eight healthy elderly ingested the glutamate drink, an isomolar amount of a glutamine drink, or only water to test the effect on plasma glutamate concentration and whole-body glutamate turnover.

RESULTS

In part 1, repeated ingestion of 30 mg of glutamate per kilogram of body weight every 20 min increased plasma glutamate concentration five-fold to steady-state level within 80 min and without any side effects. In part 2, repeated ingestion of glutamate significantly increased whole-body glutamate turnover in healthy controls and patients with COPD, although the increase was smaller in patients with COPD than in controls.

CONCLUSION

We found that repeated ingestion of 30 mg of glutamate per kilogram of body weight every 20 min can increase glutamate availability in healthy elderly and patients with COPD, who are likely more dependent on external glutamate ingestion than are young adults.

The systemic inflammatory response to exercise in adults with cystic fibrosis

Exercise is associated with release of inflammatory mediators in the circulation and there is evidence that the exercising muscles and tendons are sources of interleukin-6. Due to the catabolic effects of some cytokines, increased release in circulation might contribute to alterations in body composition in adults with cystic fibrosis. We hypothesised that exercise of moderate intensity would generate increased blood concentrations of some inflammatory mediators. We investigated the change in blood concentrations of interleukin-6, tumour necrosis factor alpha and their soluble receptors after a structured exercise (box stepping) of intensity similar to that encountered during activities of daily living in 12 adults with cystic fibrosis and mean (95% confidence interval) FEV1 55.6 (44.4, 66.8)% predicted, body mass index 23.0 (21.3, 24.6) kg/m2 and 12 healthy subjects. The increments post-exercise for all inflammatory mediators and lactate corrected for the work performed until voluntary exhaustion were greater for patients, while the total work was less for patients (all p<0.01). Daytime variability of the inflammatory mediators was assessed in eight patients and was less than the change due to exercise. We report greater increments in circulating concentrations of some cytokines with moderate exercise in adults with cystic fibrosis compared to healthy subjects.

Decreased whole-body and splanchnic glutamate metabolism in healthy elderly men and patients with chronic obstructive pulmonary disease in the postabsorptive state and in response to feeding

Decreased plasma and muscle glutamate concentrations have been observed in patients with chronic obstructive pulmonary disease (COPD), suggesting disturbances in glutamate metabolism. The present study was conducted to further examine glutamate metabolism in 8 male COPD patients (68 +/- 4 y) by measurement of whole-body (WB) glutamate production and splanchnic glutamate extraction in the postabsorptive state as well as in response to feeding. Because COPD is particularly prevalent in the elderly and aging per se may also affect glutamate metabolism, 2 male control groups were included: 8 healthy elderly (63 +/- 3 y) and 8 young (22 +/- 1 y) subjects. On 2 test days, the stable isotope L-15N-glutamate was infused i.v. or enterally according to a primed constant and continuous infusion protocol. After 90 min of infusion, subjects ingested a carbohydrate-protein drink (28% milk protein, 72% maltodextrin) every 20 min for 2 h. Arterialized-venous blood samples were taken at the end of the postabsorptive and feeding periods. Postabsorptive WB glutamate production and splanchnic glutamate extraction were significantly lower in the elderly and COPD patients than in the young (P < 0.01). Feeding further decreased WB endogenous glutamate production in the elderly and COPD patients, with COPD patients tending (P = 0.07) to have a greater decrease. Splanchnic glutamate extraction increased during feeding in the elderly (P < 0.05) but did not change in COPD patients. In conclusion, aging reduces postabsorptive WB endogenous glutamate production and splanchnic glutamate extraction. COPD does not affect postabsorptive WB glutamate metabolism but may influence splanchnic glutamate metabolism during feeding.

Raised CRP levels mark metabolic and functional impairment in advanced COPD

BACKGROUND

C-reactive protein (CRP) is often used as a clinical marker of acute systemic inflammation. Since low grade inflammation is evident in chronic diseases such as chronic obstructive pulmonary disease (COPD), new methods have been developed to enhance the sensitivity of CRP assays in the lower range. A study was undertaken to investigate the discriminative value of high sensitivity CRP in COPD with respect to markers of local and systemic impairment, disability, and handicap.

METHODS

Plasma CRP levels, interleukin 6 (IL-6) levels, body composition, resting energy expenditure (REE), exercise capacity, health status, and lung function were determined in 102 patients with clinically stable COPD (GOLD stage II-IV). The cut off point for normal versus raised CRP levels was 4.21 mg/l.

RESULTS

CRP levels were raised in 48 of 102 patients. In these patients, IL-6 (p<0.001) and REE (adjusted for fat-free mass, p = 0.002) were higher while maximal (p = 0.040) and submaximal exercise capacity (p = 0.017) and 6 minute walking distance (p = 0.014) were lower. The SGRQ symptom score (p = 0.003) was lower in patients with raised CRP levels, as were post-bronchodilator FEV1 (p = 0.031) and reversibility (p = 0.001). Regression analysis also showed that, when adjusted for FEV1, age and sex, CRP was a significant predictor for body mass index (p = 0.044) and fat mass index (p = 0.016).

CONCLUSIONS

High sensitivity CRP is a marker for impaired energy metabolism, functional capacity, and distress due to respiratory symptoms in COPD.

Polyunsaturated fatty acids improve exercise capacity in chronic obstructive pulmonary disease

BACKGROUND

Muscle wasting and decreased muscle oxidative capacity commonly occur in patients with chronic obstructive pulmonary disease (COPD). Polyunsaturated fatty acids (PUFA) have been shown to mediate several inflammatory and metabolic pathways which may be involved in the pathogenesis of muscle impairment in COPD. The aim of this study was to investigate the effect of PUFA modulation on systemic inflammation, reversal of muscle wasting, and functional status in COPD.

METHODS

Eighty patients with COPD (57 men) with forced expiratory volume in 1 second (FEV1) 37.3 (13.8)% predicted received 9 g PUFA or placebo daily in a double blind randomised fashion during an 8 week rehabilitation programme. Body composition (bioelectrical impedance), functional capacity (lung function, incremental cycle ergometry test, submaximal cycle test, isokinetic quadriceps strength) and inflammatory markers (C-reactive protein (CRP), interleukin (IL)-6 and tumour necrosis factor (TNF)-alpha) were assessed at baseline and after 8 weeks.

RESULTS

Both groups had similar increases in weight, fat-free mass (FFM), and muscle strength. The peak load of the incremental exercise test increased more in the PUFA group than in the placebo group (difference in increase 9.7 W (95% CI 2.5 to 17.0), p = 0.009) even after adjustment for FFM. The duration of the constant work rate test also increased more in patients receiving PUFA (difference in increase 4.3 min (95% CI 0.6 to 7.9), p = 0.023). The positive effects of PUFA could not be attributed to a decrease in systemic levels of CRP, IL-6 and TNF-alpha.

CONCLUSIONS

This is the first study to show beneficial effects of PUFA on exercise capacity in patients with COPD.

Skeletal muscle glutamate metabolism in health and disease: state of the art

PURPOSE OF REVIEW

Glutamate is an amino acid of interest because it participates in many metabolic pathways. However, there is evidence that skeletal muscle glutamate metabolism is disturbed in disease. This review presents current knowledge regarding the metabolic function and regulation of glutamate in skeletal muscle under physiological and pathophysiological circumstances. Furthermore, several options for modulating muscle glutamate concentration in order to improve glutamate metabolism are discussed.

RECENT FINDINGS

The high correlation between muscle glutamate concentration and muscle glutathione concentration suggests that glutamate plays a determining role in the glutathione synthesis pathway. During exercise, glutamate plays a central role in energy provision because it participates in the tricarboxylic acid and the purine nucleotide cycles. However, a consistent finding in several diseases is reduced skeletal muscle glutamate. Remarkably, only few studies focused on modulation of muscle glutamate status either by exercise or by nutritional supplementation. There are several options for modulating glutamate metabolism, but the specific effects of the individual options require further elucidation. Nutritional supplementation of glutamate or its precursors glutamine, (ornithine) alpha-ketoglutarate, or the branched chain amino acids can influence muscle glutamate status.

SUMMARY

Specific intervention studies must be conducted to investigate the effect of supplementation on skeletal muscle glutamate turnover and its related metabolic and functional consequences in healthy individuals and in patients with acute or chronic disease.

Response of whole-body protein and urea turnover to exercise differs between patients with chronic obstructive pulmonary disease with and without emphysema

BACKGROUND

Exercise is known to improve physical capacity and muscle mass in patients with chronic obstructive pulmonary disease (COPD). However, recent evidence suggests that exercise may also negatively influence metabolism in COPD.

OBJECTIVE

The objective was to investigate whether exercise influences whole-body protein metabolism differently in COPD patients and control subjects and to elucidate the effect of the specific underlying lung disease.

DESIGN

Whole-body protein synthesis and breakdown and urea synthesis were measured by using stable-isotope methods in 14 male patients with severe COPD (forced expiratory volume in 1 s: 37 +/- 12% of predicted) and in 8 male control subjects during and after 20 min of exercise. Subjects were normal weight [body mass index (in kg/m2) of COPD patients and control subjects: 25.8 +/- 3.9 and 25.7 +/- 4.4, respectively]. The COPD group was selected to include patients with (Emph+, n = 7) and without (Emph-, n = 7) emphysema. Absolute workload was 35 +/- 5 W, corresponding to 17 +/- 2%, 33 +/- 9%, and 52 +/- 14% of the maximal obtained workload in the control, Emph-, and Emph+ groups.

RESULTS

Exercise induced a 9% increase in protein synthesis and breakdown in the Emph- and control groups, which normalized postexercise. In the Emph+ group, protein turnover did not change significantly during exercise but decreased postexercise (+/- 10%). Exercise did not change net protein breakdown (protein breakdown - synthesis) or urea synthesis, except in the Emph+ group, which showed a 14% reduction in urea synthesis postexercise (P < 0.05).

CONCLUSION

Low-intensity exercise suppresses whole-body protein and urea turnover in COPD patients with emphysema and needs to be considered when maximal anabolism is targeted through a combination of exercise and nutrition.

Weight loss in chronic obstructive pulmonary disease. Mechanisms and implications

Weight loss occurs frequently in patients with chronic obstructive pulmonary disease (COPD). Although the precise cellular mechanisms underlying weight loss in COPD are unclear, this is a clinically relevant phenomenon because it contributes to limit the exercise capacity of these patients and, therefore, it jeopardizes their quality of life. More importantly, it is a negative prognostic factor that is independent of the degree of lung function impairment present. Thus, weight loss in COPD constitutes a new therapeutic target. This article reviews the mechanisms and potential consequences of weight loss in COPD and highlights areas that needed future research. It is hoped that a better understanding of its pathogenesis may eventually contribute to the development of new therapeutic strategies that contribute to improve the well-being and/or long-term prognosis of patients suffering from this devastating disease and, potentially, from others characterized also by unexplained weight loss.

Altered amino acid metabolism in chronic obstructive pulmonary disease: new therapeutic perspective?

PURPOSE OF REVIEW

Wasting of muscle mass, commonly present in patients with chronic obstructive pulmonary disease, is a complex process involving changes in the control of intermediary metabolism as well as in muscle cell status. Although research exploring intermediary metabolism in chronic obstructive pulmonary disease is still in its infancy, there is an increased interest in a potential role for amino acids in modulating muscle anabolism. This review aims at summarizing and critically evaluating the available clinical studies examining alterations in amino acid profile in plasma and skeletal muscle of patients with chronic obstructive pulmonary disease.

RECENT FINDINGS

All studies show pronounced alterations in plasma and muscle amino acid status in patients with chronic obstructive pulmonary disease but no consistent "disease specific" pattern for most amino acids. Variability is likely influenced by the heterogeneity of the disease with respect to lung function and nutritional state. Nevertheless, general consistency exists in chronic obstructive pulmonary disease with respect to (1) a reduced plasma branched-chain amino acid level, and (2) a decreased muscle glutamate concentration. Alterations in branched-chain amino acid metabolism appear to be influenced by the degree of muscle wasting, while the reduction in muscle glutamate is related to the diffusing capacity as a hallmark of emphysema. The reduction in glutamate status is associated with reduced muscle glutathione levels and appears to be linked to enhanced glycolysis as evidenced from an accelerated increase in plasma lactate during exercise.

SUMMARY

Underlying mechanisms of the observed alterations in amino acid profile in chronic obstructive pulmonary disease, and the influences of disease associated mediators such as chronic low-grade inflammation and (chronic and intermittent) hypoxia are speculative and need to be explored in experimental study designs.

Chronic obstructive pulmonary disease. 5: systemic effects of COPD

The role of body cell mass wasting, muscle wasting, and changes in muscle metabolism in the pathogenesis of chronic obstructive pulmonary disease is reviewed.

Pulmonary cachexia

Weight loss is a frequent complication in patients with chronic obstructive pulmonary disease (COPD) and is a determining factor of functional capacity, health status, and mortality. Weight loss in COPD is a consequence of increased energy requirements unbalanced by dietary intake. Both metabolic and mechanical inefficiency contribute to the elevated energy expenditure during physical activity, while systemic inflammation is a determinant of hypermetabolism at rest. A disbalance between protein synthesis and protein breakdown may cause a disproportionate depletion of fat-free mass in some patients. Nutritional support is indicated for depleted patients with COPD because it provides not only supportive care, but direct intervention through improvement in respiratory and peripheral skeletal muscle function and in exercise performance. A combination of oral nutritional supplements and exercise or anabolic stimulus appears to be the best treatment approach to obtaining significant functional improvement. Patients responding to this treatment even demonstrated a decreased mortality. Poor response was related to the effects of systemic inflammation on dietary intake and catabolism. The effectiveness of anticatabolic modulation requires further investigation.

Effect of exercise on concentrations of free amino acids in pools of type I and type II fibres in human muscle with reduced glycogen stores

A few animal studies have shown that some amino acid concentrations vary between different muscle fibre types. In the present study, amino acid concentrations were measured in separate pools of different fibre types in human skeletal muscle, with reduced glycogen stores, before and after sustained exercise. Five subjects exercised at a submaximal work rate for 60 min and then at a maximal rate for 20 min. Biopsy samples were taken from the vastus lateralis muscle before and after exercise; they were freeze-dried and individual fibres were dissected out. Fragments of these fibres were stained for myosin-adenosine triphosphatase (ATPase) and identified as type I or type II fibres. The concentrations of free amino acids were measured by high performance liquid chromatography (HPLC) in perchloric acid (PCA) extracts containing pools of either type of fibre. After exercise, glycogen was decreased in type I fibres (53%) and in four subjects also in type II fibres. The concentrations of most amino acids were similar in the two fibre types before exercise, but the glutamate, aspartate and arginine levels were 10% higher in type II than in type I fibres. After exercise, the glutamate concentration was decreased by 45% in both fibre types and the branched-chain amino acids (BCAA) were decreased in type II fibres (14%). Exercise caused an increase by 25-30% in tyrosine concentration in both type I and type II fibres. The results show that amino acids can be measured in pools of fibre fragments and suggest that amino acid metabolism play an important role in both type I and type II fibres during exercise.