Skeletal muscle myosin heavy chains in heart failure: correlation between magnitude of the isozyme shift, exercise capacity, and gas exchange measurements

Improving functional capacity in heart failure: the need for a multifaceted approach

PURPOSE OF REVIEW

Functional capacity is a broad term that describes a person's ability to perform the daily activities that require physical exertion. Patients diagnosed with heart failure, regardless of cause, demonstrate a compromised functional capacity. The ability to perform aerobic activities is a central, but not complete, determinant of functional capacity. Muscular strength and endurance are other important elements of functional capacity. It is well established that patients with heart failure demonstrate attenuated muscular strength and endurance as a consequence of their disease process. Typically, a heart failure patient's ability to perform daily activities that are either aerobic or resistive in nature is compromised and contributes to the decline in functional capacity.

RECENT FINDINGS

There is an abundance of literature demonstrating that exercise training improves aerobic capacity and muscular strength and endurance in those with heart failure. These training benefits translate to an improvement in functional capacity and an enhanced ability to perform activities of daily living. There are several approaches to exercise training in the heart failure population, each of which has implications for the degree to which functional capacity can be improved.

SUMMARY

This review summarizes the current body of literature related to exercise training as a means of optimizing functional capacity in patients with heart failure.

Alteration in skeletal muscle afferents in rats with chronic heart failure

An exaggerated exercise pressor reflex (EPR) contributes to exercise intolerance and excessive sympatho-excitation in the chronic heart failure (CHF) state. However, the components of this reflex that are responsible for the exaggerated EPR in CHF remain unknown. To determine whether muscle afferent function is altered in CHF, we recorded the discharge of group III and IV afferents in response to static contraction, passive stretch and hindlimb intra-arterial injection of capsaicin in sham and CHF rats. We also investigated the roles of purinergic 2X receptor (P2X) and the transient receptor potential vanilloid 1 (VR1) in mediating the altered sensitivity of muscle afferents. Compared with sham rats, CHF rats exhibited greater responses of group III afferents to contraction and stretch whereas the responses of group IV afferents to contraction and capsaicin were blunted. Hindlimb intra-arterial infusion of pyridoxal phosphate-6-azophenyl-2,4-disulfonic acid (PPADS), a P2X antagonist, attenuated the responses of group III afferents to contraction and stretch in CHF rats to a greater extent than in sham rats. Western blot data showed that P2X3 receptors were significantly upregulated in doral root ganglion (DRG) of CHF rats whereas VR1 receptors were significantly downregulated. Immunohistochemical evidence showed that immunostaining of the P2X3 receptors was more intense in both IB4-positive (C-fibre) and NF200-positive (A-fibre) neurons in DRG of CHF rats whereas the immunostaining of the VR1 receptors was decreased in IB4-positive neurons. These data suggest that group III afferents are sensitized whereas group IV afferents are desensitized in CHF, which is related to the dysfunction of P2X and VR1 receptors.

Resistance training increases 6-minute walk distance in people with chronic heart failure: a systematic review

QUESTION

Does resistance training, either alone or as an adjunct to aerobic training, improve cardiac function, exercise capacity and quality of life in people with chronic heart failure?

DESIGN

Systematic review with meta-analysis of randomised trials.

PARTICIPANTS

Adults with stable chronic heart failure.

INTERVENTION

Progressive resistance exercise training, alone or as an adjunct to aerobic training.

OUTCOME MEASURES

Cardiac function, exercise capacity and quality of life.

RESULTS

241 participants from eight trials performed 2 to 6 months of moderate-intensity resistance training (50-75% of 1RM). Most programs consisted of 5 to 6 exercises for large limb and trunk muscles with two sets of 8 to 12 repetitions, three times a week. Resistance training significantly increased 6-minute walk distance (WMD 52 m, 95% CI 19 to 85) but not peak oxygen consumption (WMD 1.4 ml/kg/min, 95% CI -0.3 to 3.1). When used as an adjunct to aerobic training, resistance training did not significantly alter left ventricular ejection fraction (WMD -0.5%, 95% CI -4.3 to 3.3), peak oxygen consumption (WMD -0.7 ml/kg/min, 95% CI -2.3 to 1.0), or Minnesota Living with Heart Failure Questionnaire scores (WMD -0.9, 95% CI -5.4 to 3.7), compared with aerobic training alone.

CONCLUSION

Resistance training increased 6-minute walk distance compared to no training, but had no other benefits on cardiac function, exercise capacity, or quality of life if used alone or as an adjunct to aerobic training in people with chronic heart failure. However, further high quality, large scale, randomised trials are needed.

Mechanisms underlying skeletal muscle weakness in human heart failure: alterations in single fiber myosin protein content and function

BACKGROUND

Patients with chronic heart failure (HF) frequently experience skeletal muscle weakness that limits physical function. The mechanisms underlying muscle weakness, however, have not been clearly defined.

METHODS AND RESULTS

This study examined the hypothesis that HF promotes a loss of myosin protein from single skeletal muscle fibers, which in turn reduces contractile performance. Ten patients with chronic HF and 10 controls were studied. Muscle atrophy was not evident in patients, and groups displayed similar physical activity levels, suggesting that observed differences reflect the effects of HF and not muscle atrophy or disuse. In single muscle fibers, patients with HF showed reduced myosin heavy chain protein content (P<0.05) that manifested as a reduction in functional myosin-actin cross-bridges (P<0.05). No evidence was found for a generalized loss of myofilament protein, suggesting a selective loss of myosin. Accordingly, single muscle fiber maximal Ca(2+)-activated tension was reduced in myosin heavy chain I fibers in patients (P<0.05). However, tension was maintained in myosin heavy chain IIA fibers in patients because a greater proportion of available myosin heads were bound to actin during Ca(2+) activation (P<0.01).

CONCLUSIONS

Collectively, our results show that HF alters the quantity and functionality of the myosin molecule in skeletal muscle, leading to reduced tension in myosin heavy chain I fibers. Loss of single fiber myosin protein content represents a potential molecular mechanism underlying muscle weakness and exercise limitation in patients with HF.

Implications of chronic heart failure on peripheral vasculature and skeletal muscle before and after exercise training

The pathophysiology of chronic heart failure (CHF) is typically conceptualized in terms of cardiac dysfunction. However, alterations in peripheral blood flow and intrinsic skeletal muscle properties are also now recognized as mechanisms for exercise intolerance that can be modified by therapeutic exercise. This overview focuses on blood delivery, oxygen extraction and utilization that result from heart failure. Related features of inflammation, changes in skeletal muscle signaling pathways, and vulnerability to skeletal muscle atrophy are discussed. Specific focus is given to the ways in which perfusion and skeletal muscle properties affect exercise intolerance and how peripheral improvements following exercise training increase aerobic capacity. We also identify gaps in the literature that may constitute priorities for further investigation.

Diaphragm single-fiber weakness and loss of myosin in congestive heart failure rats

Diaphragm weakness commonly occurs in patients with congestive heart failure (CHF) and is an independent predictor of mortality. However, the pathophysiology of diaphragm weakness is poorly understood. We hypothesized that CHF induces diaphragm weakness at the single-fiber level by decreasing myosin content. In addition, we hypothesized that myofibrillar Ca(2+) sensitivity is decreased and cross-bridge kinetics are slower in CHF diaphragm fibers. Finally, we hypothesized that loss of myosin in CHF diaphragm weakness is associated with increased proteolytic activities of caspase-3 and the proteasome. In skinned diaphragm single fibers of rats with CHF, induced by left coronary artery ligation, maximum force generation was reduced by approximately 35% (P < 0.01) compared with sham-operated animals for slow, 2a, and 2x fibers. In these CHF diaphragm fibers, myosin heavy chain content per half-sarcomere was concomitantly decreased (P < 0.01). Ca(2+) sensitivity of force generation and the rate constant of tension redevelopment were significantly reduced in CHF diaphragm fibers compared with sham-operated animals for all fiber types. The cleavage activity of the proteolytic enzyme caspase-3 and the proteasome were approximately 30% (P < 0.05) and approximately 60% (P < 0.05) higher, respectively, in diaphragm homogenates from CHF rats than from sham-operated rats. The present study demonstrates diaphragm weakness at the single-fiber level in a myocardial infarct model of CHF. The reduced maximal force generation can be explained by a loss of myosin content in all fiber types and is associated with activation of caspase-3 and the proteasome. Furthermore, CHF decreases myofibrillar Ca(2+) sensitivity and slows cross-bridge cycling kinetics in diaphragm fibers.

Effect of heart transplantation on skeletal muscle metabolic enzyme reserve and fiber type in end-stage heart failure patients

BACKGROUND

Skeletal muscle myopathy is a hallmark of chronic heart failure (HF). Phenotypic changes involve shift in myosin heavy chain (MHC) fiber type from oxidative, MHC type I, towards more glycolytic MHC IIx fibers, reductions in oxidative enzyme activity, and increase in glycolytic enzyme activity. However, it is unknown if muscle myopathy is reversed following heart transplantation. The purpose of this study was to determine the effect of heart transplantation on skeletal muscle metabolic enzyme reserve and MHC fiber type in end-stage HF patients.

METHODS

Thirteen HF subjects were prospectively studied before and two months after heart transplantation and a subgroup (n = 6) at eight months after transplantation. Skeletal muscle biopsy of the vastus lateralis was performed and relative MHC composition was determined using sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Lactate dehydrogenase (LDH), citrate synthase (CS), and 3-hydroxyacyl-CoA-dehydrogenase (HACoA) enzyme activity assays were performed to assess glycolytic, oxidative, and beta-oxidative metabolic enzyme reserves, respectively.

RESULTS

Lactate dehydrogenase activity (130.5 +/- 13.3 vs. 106.1 +/- 13.2 micromol/g wet wt/min, p < 0.05), CS activity (14.0 +/- 1.2 vs. 9 +/- 0.9 micromol/g wet wt/min, p < 0.05), and HACoA activity (4.5 +/- 0.48 vs. 3.6 +/- 0.3 micromol/g wet wt/min, p < 0.05) decreased two months after heart transplantation. At eight months, LDH activity was restored (139.0 +/- 11 micromol/g wet wt/min), but not CS or HACoA activity compared with before transplantation. There was no significant change in muscle %MHC type I (28.7 +/- 3.5% vs. 25.3 +/- 3.0%, p = NS), %MHC type IIa (33.2 +/- 2.0% vs. 34.6 +/- 1.9%, p = NS), or %MHC type IIx (38.1 +/- 2.8% vs. 40.1 +/- 3.7%, p = NS) fiber type two months after heart transplantation. However, %MHC type I (19.3 +/- 6.6%) was decreased and %MHC type IIx (51.0 +/- 6.5%) was increased at eight months after (p < 0.05) compared with before transplantation.

CONCLUSIONS

Skeletal muscle glycolytic, oxidative, and beta-oxidative enzymatic reserves are diminished early after heart transplantation, with reduced oxidative capacity persisting late in the first year. The myopathic MHC phenotype present in end-stage HF persists early in the post-operative state and declines further by eight months.

Biomechanical efficiency is decreased in heart failure during low-level steady state and maximal ramp exercise

BACKGROUND

Previous studies of biomechanical efficiency (external work/energy input--Watt/O(2) consumed) in heart failure (HF) using cardiopulmonary exercise testing (CPET) and magnetic resonance spectroscopy (MRS) have had discordant results with increased efficiency by CPET and decreased efficiency by MRS.

AIMS

Compare biomechanical efficiency of HF subjects and normal controls during steady state (SS=35 W for 6 min) and ramp cycle ergometer exercise. The hypothesis was that HF subjects would have impaired biomechanical efficiency that correlated with HF symptoms.

METHODS

Biomechanical efficiency used the actual Vo(2) during exercise and recovery. Gross (Vo(2) above zero), Net (Vo(2) above the resting Vo(2)) and Work (Vo(2) above the unloaded pedaling Vo(2)) efficiencies were calculated.

RESULTS

HF subjects had an 18% higher Vo(2) during SS exercise (P=0.029). Biomechanical efficiency was reduced during SS exercise (gross -15%, P=0.019, net -15%, P=0.062, and work -35%, P=0.002). Gross Efficiency during SS exercise had the strongest correlation with HF symptoms (r=0.55). During ramp exercise gross (-26%), net (-10%) and work (-8%) biomechanical efficiency were all reduced (all P<0.05). The slope of the Vo(2)/Watt relationship during ramp exercise had the best correlation with HF symptoms (r=0.46).

CONCLUSIONS

HF subjects have an increased O(2) cost/Watt during SS and ramp exercise that correlates with HF symptoms of fatigue and breathlessness. Methods to improve biomechanical efficiency in HF subjects by exercise training or medications may improve the symptoms and the impaired exercise capacity associated with HF.

Maximum oxygen uptake corrected for skeletal muscle mass accurately predicts functional improvements following exercise training in chronic heart failure

BACKGROUND

Skeletal muscle mass and peak oxygen uptake are important predictors of functional status and outcome in patients with stable chronic heart failure.

AIMS

To assess changes in skeletal muscle mass and peak oxygen uptake following an exercise training program.

METHODS

Thirty-six patients with moderate stable chronic heart failure were randomly allocated to either a bicycle ergometer (bike) or functional electrical muscle stimulators (FES) applied to quadriceps and gastrocnemius muscles to be used daily for six weeks. Dual-energy X-ray absorptionometry (DEXA) scanning was performed before and after training along with symptom limited cardiopulmonary exercise test, quadriceps strength and fatigue resistance, and 6-min walk test.

RESULTS

Both exercise modalities resulted in improvements in treadmill exercise time, leg strength, 6-min walk test and peak oxygen uptake per kilogram of skeletal muscle. Despite significant improvements in functional capacity, there were no significant changes in body composition for total skeletal muscle mass, leg muscle mass or total body fat content. Skeletal muscle mass was strongly predictive of maximum oxygen uptake at baseline (r=0.61, p<0.001) and after exercise training (r=0.68, p<0.001).

CONCLUSIONS

In moderate stable chronic heart failure, exercise training using bicycle ergometer or FES results in favourable qualitative rather than quantitative changes in skeletal muscle. Correction of maximum oxygen uptake for skeletal muscle mass rather than total body mass is a more sensitive measure of changes associated with exercise training.

The effect of moderate exercise training on skeletal muscle myosin heavy chain distribution in chronic heart failure

BACKGROUND

The myosin heavy chain (MHC) is altered in chronic heart failure (CHF), but the effect of exercise on MHC expression in CHF patients is not understood. The aim of the present study was to show the effect of aerobic exercise on MHC distribution in patients with CHF.

METHODS

Patients (n=17) with stable NYHA class I-III CHF were randomised into training and control groups. For a period of three months, the training group cycled on an ergometric cycle 3 times a week for 30 min, the control group continued as they did previously. Both a baseline and a final 3 month graded maximal exercise test and exercise endurance test with constant submaximal work load were performed. Muscle samples, obtained from vastus lateralis muscle at baseline and after 3 months from the 8 patients in the training group and the 9 in the control group, were analysed for MHC distribution using SDS-polyacrylamide gel electrophoresis.

RESULTS

Baseline MHC distributions were similar in both groups and training did not alter the MHC distribution. Exercise duration, at constant submaximal work load, improved from 14.9+/-7.1 to 26.9+/-9.6 min (p<0.01 for the change between the groups). Training did not improve peak oxygen consumption.

CONCLUSION

No correlation between the change in exercise capacity and MHC distribution appeared despite the significant improvement of exercise duration.

Depression of force production and ATPase activity in different types of human skeletal muscle fibers from patients with chronic heart failure

Isometric force production and ATPase activity were determined simultaneously in single human skeletal muscle fibers (n = 97) from five healthy volunteers and nine patients with chronic heart failure (CHF) at 20 degrees C. The fibers were permeabilized by means of Triton X-100 (1% vol/vol). ATPase activity was determined by enzymatic coupling of ATP resynthesis to the oxidation of NADH. Calcium-activated actomyosin (AM) ATPase activity was obtained by subtracting the activity measured in relaxing (pCa = 9) solutions from that obtained in maximally activating (pCa = 4.4) solutions. Fiber type was determined on the basis of myosin heavy chain isoform composition by polyacrylamide SDS gel electrophoresis. AM ATPase activity per liter cell volume (+/-SE) in the control and patient group, respectively, amounted to 134 +/- 24 and 77 +/- 9 microM/s in type I fibers (n = 11 and 16), 248 +/- 17 and 188 +/- 13 microM/s in type IIA fibers (n = 14 and 32), 291 +/- 29 and 126 +/- 21 microM/s in type IIA/X fibers (n = 3 and 5), and 325 +/- 32 and 205 +/- 21 microM/s in type IIX fibers (n = 7 and 9). The maximal isometric force per cross-sectional area amounted to 64 +/- 7 and 43 +/- 5 kN/m(2) in type I fibers, 86 +/- 11 and 58 +/- 4 kN/m(2) in type IIA fibers, 85 +/- 6 and 42 +/- 9 kN/m(2) in type IIA/X fibers, and 90 +/- 5 and 59 +/- 5 kN/m(2) in type IIX fibers in the control and patient group, respectively. These results indicate that, in CHF patients, significant reductions occur in isometric force and AM ATPase activity but that tension cost for each fiber type remains the same. This suggests that, in skeletal muscle from CHF patients, a decline in density of contractile proteins takes place and/or a reduction in the rate of cross-bridge attachment of approximately 30%, which exacerbates skeletal muscle weakness due to muscle atrophy.

Effect of resistance exercise on skeletal muscle myopathy in heart transplant recipients

The purpose of this study was to determine the efficacy of resistance exercise in reversing skeletal muscle myopathy in heart transplant recipients. Myopathy, engendered by both heart failure and immunosuppression with glucocorticoids, is a post-transplant complication. The sequelae of myopathic disease includes fiber-type shifts and deficits in aerobic metabolic capability. We randomly assigned patients to either 6 months of resistance exercise (training group; n = 8) or a control (control group; n = 7) group. Exercise was initiated at 2 months after transplant. Biopsy of the right vastus lateralis was performed before and after the 6-month intervention. Myosin heavy chain (MHC) composition was assessed using sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Biochemical assays were performed to determine citrate synthase, 3-hydroxyacyl-CoA-dehydrogenase, and lactate dehydrogenase activity. There were no group differences (p >or=0.05) in MHC composition and enzymatic reserve at baseline. Improvements in the training group for citrate cynthase (+40%), 3-hydroxyacyl-CoA-dehydrogenase (+10%), and lactate dehydrogenase activity (+48%) were significantly greater (p <or=0.05) than in the control group (+10%, -15%, and +20%, respectively). Oxidative type 1 MHC isoform concentration increased significantly in the training group (+73%, p <or=0.05) but decreased in the control group (-28%; p <or=0.05). Glycolytic type 2x MHC isoform increased significantly (17%; p <or=0.05) in the control group but decreased (-33%; p <or=0.05) in the training group. This is the first study to demonstrate that resistance training elicits myofibrillar shifts from less oxidative type II fibers to more oxidative fatigue-resistant type I fibers in heart transplant recipients. Resistance exercise initiated early in the post-transplant period is efficacious in changing skeletal muscle phenotype through increases in enzymatic reserve and shifts in fiber morphology.

Physiology of the abnormal response of heart failure patients to exercise

Chronic heart failure is associated with reduced exercise capacity. Altered diastolic function and reduced chronotropic response play an important role. However, there is no clear correlation between any hemodynamic parameter and exercise capacity. Peripheral factors, long overlooked, seem to play a major role. Altered peripheral vasodilatation, involving endothelial abnormalities, alters the optimal distribution of blood flow. Muscular abnormalities are constant: aside from muscle atrophy, altered muscle metabolism results in an altered utilization of oxygen. A comprehensive understanding of all these determinants of exercise response is important to optimize the care of the patient. Sole improvement of cardiac function may be insufficient to correct their exercise intolerance; regular training may well have beneficial effects on exercise capacity, functional impairment, and quality of life.

Skeletal muscle abnormalities in chronic heart failure patients: relation to exercise capacity and therapeutic implications

Recent studies suggest that changes in the periphery, like those occurring in the skeletal muscles of patients with chronic heart failure, might play an important role in the origin of symptoms and exercise intolerance in this condition. Biochemical and histologic changes in the skeletal muscles of chronic heart failure patients relate with the degree of exercise intolerance better than hemodynamics parameters. A reduction in skeletal muscle mass represents another important determinant of exercise intolerance in chronic heart failure patients. The relationship between skeletal muscle changes and exercise intolerance suggests the possibility of modifying the peripheral changes in order to improve functional capacity in chronic heart failure patients. Recent studies have shown that the administration of angiotensin-converting enzyme inhibitors and angiotensin II receptor blockers can improve the properties of the skeletal muscles. Similarly, exercise training allows improvement in peak oxygen consumption, which parallels important biochemical and histologic changes in the skeletal muscles.

Differential effects of exercise training in men and women with chronic heart failure

BACKGROUND

Abnormalities of myosin heavy chain (MHC) isoforms, enzyme activity, and capillarity contribute to the exercise intolerance that is characteristic of patients with heart failure. To what extent these changes can be reversed with exercise training and whether differences exist in the responses of men and women remains uncertain. We described and compared the effects of exercise training on exercise capacity and skeletal muscle histochemistry in men and women with chronic heart failure.

METHODS

Fifteen patients (10 male) undergoing standard medical therapy completed a 14- to 24-week exercise training program. Peak oxygen consumption, MHC isoforms, capillary density, and selected metabolic enzymes were assessed before and after training.

RESULTS

Peak oxygen consumption was improved 14% (P <.05); however, this increase was mostly because of the improvement observed in men versus women (+20% versus +2%, respectively, P <.01). At baseline, MHC I content was lower in men than in women (33% +/- 3% vs 49.6% +/- 5.5%, P <.05). MHC I improved with training in men, to 45.6% +/- 4.5% (+38%, P <.05), versus women (-3%, P =.82), and the increase in men tended (P =.12) to be significant when compared with that in women. There were no significant changes in capillary density or muscle enzyme activity with training in the group as a whole or in men and women separately.

CONCLUSION

Among patients with chronic heart failure, improvements in peak exercise capacity may be more pronounced in men than in women. This difference in response of functional capacity to training paralleled differences observed between men and women for changes in MHC I isoforms.

L-Carnitine: a potential treatment for blocking apoptosis and preventing skeletal muscle myopathy in heart failure

Skeletal muscle in congestive heart failure is responsible for increased fatigability and decreased exercise capacity. A specific myopathy with increased expression of fast-type myosins, myocyte atrophy, secondary to myocyte apoptosis triggered by high levels of circulating tumor necrosis factor-alpha (TNF-alpha) has been described. In an animal model of heart failure, the monocrotaline-treated rat, we have observed an increase of apoptotic skeletal muscle nuclei. Proapoptotic agents, caspase-3 and -9, were increased, as well as serum levels of TNF-alpha and its second messenger sphingosine. Treatment of rats with L-carnitine, known for its protective effect on muscle metabolism injuries, was found to inhibit caspases and to decrease the levels of TNF-alpha and sphingosine, as well as the number of apoptotic myonuclei. Staurosporine was used in in vitro experiments to induce apoptosis in skeletal muscle cells in culture. When L-carnitine was applied to skeletal muscle cells, before staurosporine treatment, we observed a reduction in apoptosis. These findings show that L-carnitine can prevent apoptosis of skeletal muscles cells and has a role in the treatment of congestive heart failure-associated myopathy.

Comparison of ventilatory expired gas parameters used to predict hospitalization in patients with heart failure

BACKGROUND

Several ventilatory expired gas measures obtained during exercise testing demonstrate prognostic value in the heart failure (HF) population. Comparison of prognostic efficacy between pertinent measures is sparse.

METHODS

The ability of various expressions of peak oxygen consumption (VO2), the relationship between minute ventilation (VE) and carbon dioxide production (VCO2), and the partial pressure of end-tidal carbon dioxide (P(ET)CO2) were assessed to determine which measure(s) best predicted cardiac-related hospitalization over a 1-year period in subjects diagnosed with HF.

RESULTS

Univariate Cox regression analysis found that several expressions of peak VO 2, VE-VCO2 relationship, and P(ET)CO2 were significant predictors of hospitalization. Multivariate Cox regression analysis revealed that the VE/VCO2 slope significantly predicted hospitalization (chi2 = 29.1, P <.00001). Peak VO 2 and P(ET)CO2 did not provide additional predictive value.

CONCLUSIONS

The prognostic superiority of the VE/VCO2 slope over peak VO2 may be a result of the latter measure's partial dependence on subject effort and skeletal muscle function.

Apoptosis in the skeletal muscle of rats with heart failure is associated with increased serum levels of TNF-alpha and sphingosine

Skeletal muscle in congestive heart failure (CHF) is responsible for increased fatigability, decreased endurance and exercise capacity. A specific myopathy with increased expression of fast myosin heavy chains (MHCs), myocyte atrophy, secondary to myocyte apoptosis, that is triggered by high levels of circulating tumor necrosis factor (TNF-alpha) has been described. However, a direct effect of TNF-alpha on skeletal muscle has not been described yet. In this paper we put forward the hypothesis that TNF-alpha plays an indirect effect on skeletal myocytes. In an animal model of CHF, the monocrotaline-treated rat, we have observed a significant (P<0.001) increase of circulating TNF-alpha that is paralleled by increased serum levels of the endogenous second messenger, sphingosine (SPH), (from 0.71+/-0.15 to 1.32+/-0.39 nmoles/ml, P<0.01). In the tibialis anterior (TA) muscle we found a marked increase of myocyte apoptosis (from 1.4+/-2.4 to 40.1+/-39.5 nuclei/mm(3), P<0.04). We correlated plasma levels of TNF-alpha with those of SPH and in turn with the magnitude of apoptosis. Linear regression showed a significant correlation between TNF-alpha, SPH, and apoptosis (r(2)=0.74, P=0.004 and r(2)=0.87, P=0.001 respectively). Analysis of covariance showed that TNF-alpha and SPH were independently correlated with the number of apoptotic nuclei (P=0.0001). In parallel in vitro experiments, where increasing concentrations of SPH were applied to skeletal muscle cells in culture, we observed a dose-dependent increase in apoptosis. These results suggest that TNF-alpha-induced SPH production may be responsible for skeletal muscle apoptosis. The link between TNF-alpha and skeletal muscle apoptosis could be represented by the second messenger SPH, which can directly induce apoptosis in these cells.

Skeletal muscle mass independently predicts peak oxygen consumption and ventilatory response during exercise in noncachectic patients with chronic heart failure

OBJECTIVES

We sought to assess whether skeletal muscle mass might be a predictor of peak oxygen consumption (Vo2) and relation of the ventilation to carbon dioxide production (VE/VCo2) slope in patients with chronic heart failure (CHF) independent of clinical conditions, neurohormonal activation and resting hemodynamics.

BACKGROUND

A variety of abnormalities characterize skeletal muscle and contribute to exercise intolerance in patients with CHF. Skeletal muscle mass is a determinant of peak Vo2 both in healthy patients and in patients with CHF, but there are no reports on the independent predictive value of this parameter, which can be measured with great accuracy by whole-body dual energy X-ray absorptiometry (DEXA). The influence of skeletal muscle mass on VE/VCo2 slope is not known either.

METHODS

We prospectively evaluated 120 consecutive noncachectic patients with CHF. Every patient underwent a cardiopulmonary exercise test, an echo-Doppler examination and an evaluation of neurohormonal activation and body composition as assessed by DEXA.

RESULTS

At the univariate analysis, New York Heart Association (NYHA) class (p < 0.0001), age (p < 0.0001), male gender (p < 0.0001) and plasma renin (p < 0.0001) significantly related with peak Vo2. There was a significant correlation between lean mass and absolute peak Vo2 (r = 0.70, p < 0.0001) and VE/VCo2 slope (r = -0.27; p < 0.01). At the multivariate analysis, lean mass predicted peak Vo2 and VE/VCo2 slope independently of NYHA functional class, age, gender, neurohormonal activation and resting hemodynamics.

CONCLUSIONS

Skeletal muscle mass is an independent predictor of peak Vo2 and VE/VCo2 slope in stable noncachectic patients with CHF. Future studies will determine whether an increase in skeletal muscle mass in the individual patient might result in an improvement in parameters of exercise capacity.

Apoptosis and changes in contractile protein pattern in the skeletal muscle in heart failure

Chronic heart failure is characterized as a clinical disorder by exercise intolerance. There are two factors that are independently responsible for the reduced exercise capacity: (a) a shift from myosin heavy chain 1 (MHC1) to MHC2a and MHC2b and (b) muscle atrophy. We have demonstrated, both in experimental models of heart failure and in man, that the more severe the heart failure, the greater the magnitude of skeletal muscle apoptosis. In the monocrotaline treated rat, that develops a severe right-sided heart failure, the increased number of apoptotic nuclei was paralleled by increasing levels of circulating TNFalpha. In agreement with some recent observations showing that sphingolipids can mediate programmed cell death, we found that in animals with heart failure and high number of apoptotic nuclei, circulating levels of sphingosine were significantly increased. In a study conducted in patients with heart failure we found a correlation between exercise capacity limitation and skeletal myocytes apoptosis. There was also a correlation between degree of muscle atrophy and magnitude of apoptosis. The shift in MHCs, although with a different mechanism, is also responsible for the reduced exercise capacity in these patients. In fact there is a strong correlation between indices of severity of CHF and MHC composition. Muscle fatigue, appears earlier in patients that have a greater skeletal muscle expression of 'fast' MHCs. We have also demonstrated that MHCs shift and apoptosis can be prevented by using angiotensin II converting enzyme inhibitors and angiotensin II receptor blockers.

Apoptosis in the skeletal muscle of patients with heart failure: investigation of clinical and biochemical changes

OBJECTIVE

To investigate the contribution of apoptosis in the development of the skeletal myopathy in chronic heart failure.

DESIGN

The electrophoretic pattern of myosin heavy chains (MHC), fibre cross sectional area, number of in situ nick end labelling (TUNEL) positive apoptotic myocyte nuclei, and the tissue levels of caspase-3, Bcl-2, and ubiquitin were determined in biopsies taken from the vastus lateralis muscle. The study involved nine patients with severe chronic heart failure caused by ischaemic heart disease and hibernating myocardium and five controls.

RESULTS

In chronic heart failure patients the vastus lateralis showed a significant increase of MHC(2a) and MHC(2b) and a greater degree of fibre atrophy, as demonstrated by the decreased cross sectional area. There was also an increased number of TUNEL positive apoptotic myocyte nuclei. Tissue concentrations of Bcl-2 were decreased, while those of caspase-3 and ubiquitin were increased. Peak oxygen consumption (VO(2)) was negatively correlated with the number of TUNEL positive nuclei and the fibre cross sectional area. There was a correlation between the number of apoptotic nuclei and the fibre cross sectional area, but no correlation between myosin heavy chains and number of apoptotic nuclei.

CONCLUSIONS

Myocyte apoptosis occurs in the skeletal muscle of patients with chronic heart failure, and its magnitude is associated with the severity of exercise capacity limitation and the degree of muscle atrophy. Muscle atrophy contributes to the limitation of exercise capacity, together with the increased synthesis of fast, more fatiguable myosin heavy chains.

Apoptosis and atrophy in rat slow skeletal muscles in chronic heart failure

Congestive heart failure is characterized by a skeletal muscle myopathy with muscle bulk loss. The mechanisms responsible for these changes are not clear at present. We have investigated the role of apoptosis in the rat "slow" soleus muscle during the development of heart failure, which was induced by injection of monocrotaline (30 mg/kg). We looked at the time course of apoptosis by studying six animals at each of the following time points: 0, 17, 24, and 30 days. We found a decreased expression of the antiapoptotic protein Bcl-2, which was accompanied by a rise of proapoptotic caspase-3. Ubiquitin levels did not change. DNA nick-end labeling showed an increased number of apoptotic nuclei both in myofibers and interstitial cells when heart failure occurred. At variance with previous observations in the fast-twitch tibialis anterior muscle in the same animals, in which tumor necrosis factor-alpha (TNF-alpha) increased at the time that apoptosis occurred, the magnitude of apoptosis is lower in soleus muscle and there is no appearance of muscle atrophy. In soleus muscle, apoptosis is accompanied by activation of the caspase-3 system. There is no activation of the TNF-alpha- and ubiquitin-dependent protein waste. In conclusion, slow muscles are less prone to develop apoptosis than fast muscles. Muscle atrophy appears earlier in these latter ones.

Improved exercise tolerance after losartan and enalapril in heart failure: correlation with changes in skeletal muscle myosin heavy chain composition

BACKGROUND

In congestive heart failure, fatigue-resistant, oxidative, slow type I fibers are decreased in leg skeletal muscle, contributing to exercise capacity (EC) limitation. The mechanisms by which ACE inhibitors and AII antagonists improve EC is still unclear. We tested the hypothesis that improvement in EC is related to changes in skeletal muscle composition toward type I fibers.

METHODS AND RESULTS

Eight patients with congestive heart failure, NYHA classes I through IV, were treated for 6 months with enalapril (E) 20 mg/d, and another 8 with losartan (L) 50 mg/d. EC was assessed with maximal cardiopulmonary exercise testing at baseline and after treatment. Myosin heavy chain (MHC) composition of the gastrocnemius was studied after electrophoretic separation of slow MHC1, fast oxidative MHC2a, and fast glycolytic MHC2b isoforms from needle microbiopsies obtained at baseline and after 6 months. EC improved in both groups. Peak V(O2) increased from 21.0+/-4.7 to 27.6+/-4.3 mL . kg-1 . min -1 (P=0.011) in the L group and from 17.5+/-5.0 to 25.0+/-5.5 mL . kg-1 . min -1 (P=0.014) in the E group. Similarly, ventilatory threshold changed from 15.0+/-4.0 to 19.9+/-4.9 mL (P=0. 049) with L and from 12.0+/-1.9 to 15.4+/-3.5 mL (P=0.039) with E. MCH1 increased from 61.2+/-11.2% to 75.4+/-7.6% with L (P=0.012) and from 60.6+/-13.1% to 80.1+/-10.9% (P=0.006) with E. Similarly, MHC2a decreased from 21.20+/-9.5% to 12.9+/-4.4% (P=0.05) with L and from 19.9+/-7.8% to 11.8+/-7.9% (P=0.06) with E. MHC2b changed from 17. 5+/-6.5% to 11.7+/-5.2% (P=0.07) with L and from 19.5+/-6.4% to 8. 1+/-4.6% (P=0.0015) with E. There was a significant correlation between net changes in MHC1 and absolute changes in peak V(O2) (r2=0.29, P=0.029) and a trend to significance for MHC2a and 2b.

CONCLUSIONS

Six months' treatment with L and with E produces an improvement in EC of similar magnitude. These changes are accompanied by a reshift of MHCs of leg skeletal muscle toward the slow, more fatigue-resistant isoforms. Magnitude of MHC1 changes correlates with the net peak V(O2) gain, which suggests that improved EC may be caused by favorable biochemical changes occurring in the skeletal muscle.