Modulation of MAPK and NF-954;B Signaling Pathways by Antioxidant Therapy in Skeletal Muscle of Heart Failure Rats.

BACKGROUND/AIMS: Although increased oxidative stress plays a role in heart failure (HF)-induced skeletal myopathy, signaling pathways involved in muscle changes and the role of antioxidant agents have been poorly addressed. We evaluated the effects of N-acetylcysteine (NAC) on intracellular signaling pathways potentially modulated by oxidative stress in soleus muscle from HF rats. METHODS AND RESULTS: Four months after surgery, rats were assigned to Sham, myocardial infarction (MI)-C (without treatment), and MI-NAC (treated with N-acetylcysteine) groups. Two months later, echocardiogram showed left ventricular dysfunction in MI-C; NAC attenuated diastolic dysfunction. Oxidative stress was evaluated in serum and soleus muscle; malondialdehyde was higher in MI-C than Sham and did not differ between MI-C and MI-NAC. Oxidized glutathione concentration in soleus muscle was similar in Sham and MI-C, and lower in MI-NAC than MI-C (Sham 0.168 ± 0.056; MI-C 0.223 ± 0.073; MI-NAC 0.136 ± 0.023 nmol/mg tissue; p = 0.014). Western blot showed increased p-JNK and decreased p38, ERK1/2, and p-ERK1/2 in infarcted rats. NAC restored ERK1/2. NF-954;B p65 subunit was reduced; p-Ser276 in p65 and I954;B was increased; and p-Ser536 unchanged in MI-C compared to Sham. NAC did not modify NF-954;B p65 subunit, but decreased p-Ser276 and p-Ser536. CONCLUSION: N-acetylcysteine modulates MAPK and NF-954;B signaling pathways in soleus muscle of HF rats.

Influence of N- acetylcysteine on oxidative stress in slow-twitch soleus muscle of heart failure rats.

BACKGROUND: Chronic heart failure is characterized by decreased exercise capacity with early exacerbation of fatigue and dyspnea. Intrinsic skeletal muscle abnormalities can play a role in exercise intolerance. Causal or contributing factors responsible for muscle alterations have not been completely defined. This study evaluated skeletal muscle oxidative stress and NADPH oxidase activity in rats with myocardial infarction (MI) induced heart failure. METHODS AND RESULTS: Four months after MI, rats were assigned to Sham, MI-C (without treatment), and MI-NAC (treated with N-acetylcysteine) groups. Two months later, echocardiogram showed left ventricular dysfunction in MI-C; NAC attenuated diastolic dysfunction. In soleus muscle, glutathione peroxidase and superoxide dismutase activity was decreased in MI-C and unchanged by NAC. 3-nitrotyrosine was similar in MI-C and Sham, and lower in MI-NAC than MI-C. Total reactive oxygen species (ROS) production was assessed by HPLC analysis of dihydroethidium (DHE) oxidation fluorescent products. The 2-hydroxyethidium (EOH)/DHE ratio did not differ between Sham and MI-C and was higher in MI-NAC. The ethidium/DHE ratio was higher in MI-C than Sham and unchanged by NAC. NADPH oxidase activity was similar in Sham and MI-C and lower in MI-NAC. Gene expression of p47(phox) was lower in MI-C than Sham. NAC decreased NOX4 and p22(phox) expression. CONCLUSIONS: We corroborate the case that oxidative stress is increased in skeletal muscle of heart failure rats and show for the first time that oxidative stress is not related to increased NADPH oxidase activity.

Early Spironolactone Treatment Attenuates Heart Failure Development by Improving Myocardial Function and Reducing Fibrosis in Spontaneously Hypertensive Rats.

BACKGROUND: We evaluated the role of the aldosterone blocker spironolactone in attenuating long-term pressure overload-induced cardiac remodeling and heart failure (HF) in spontaneously hypertensive rats (SHR). METHODS AND RESULTS: Thirteen month-old male SHR were assigned to control (SHR-C, n=20) or spironolactone (SHR-SPR, 20 mg/kg/day, n=24) groups for six months. Normotensive Wistar-Kyoto rats (WKY, n=15) were used as controls. Systolic blood pressure was higher in SHR groups and unchanged by spironolactone. Right ventricular hypertrophy, which characterizes HF in SHR, was less frequent in SHR-SPR than SHR-C. Echocardiographic parameters did not differ between SHR groups. Myocardial function was improved in SHR-SPR compared to SHR-C [developed tension: WKY 4.85±0.68; SHR-C 5.22±1.64; SHR-SPR 6.80±1.49 g/mm2; -dT/dt: WKY 18.0 (16.0­19.0); SHR-C 20.8 (18.4­25.1); SHR-SPR 28.9 (24.2­34.6) g/mm2/s]. Cardiomyocyte cross-sectional area and total collagen concentration (WKY 1.06±0.34; SHR-C 1.85±0.63; SHR-SPR 1.28±0.39 µg/mg wet tissue) were greater in SHR-C than WKY and SHR-SPR. Type 3 collagen expression was lower in SHR-C than WKY and unchanged by spironolactone. Soluble collagen, type I collagen, and lysyl oxidase did not differ between groups. CONCLUSION: Early spironolactone treatment decreases heart failure development frequency by improving myocardial systolic and diastolic function and attenuating hypertrophy and fibrosis in spontaneously hypertensive rats.

Long-term low intensity physical exercise attenuates heart failure development in aging spontaneously hypertensive rats.

BACKGROUND: Physical exercise is a strategy to control hypertension and attenuate pressure overload-induced cardiac remodeling. The influence of exercise on cardiac remodeling during uncontrolled hypertension is not established. We evaluated the effects of a long-term low intensity aerobic exercise protocol on heart failure (HF) development and cardiac remodeling in aging spontaneously hypertensive rats (SHR). METHODS: Sixteen month old SHR (n=50) and normotensive Wistar-Kyoto (WKY, n=35) rats were divided into sedentary (SED) and exercised (EX) groups. Rats exercised in treadmill at 12 m/min, 30 min/day, 5 days/week, for four months. The frequency of HF features was evaluated at euthanasia. STATISTICAL ANALYSES: ANOVA and Tukey or Mann-Whitney, and Goodman test. RESULTS: Despite slightly higher systolic blood pressure, SHR-EX had better functional capacity and lower HF frequency than SHR-SED. Echocardiography and tissue Doppler imaging showed no differences between SHR groups. In SHR-EX, however, left ventricular (LV) systolic diameter, larger in SHR-SED than WKY-SED, and endocardial fractional shortening, lower in SHR-SED than WKY-SED, had values between those in WKY-EX and SHR-SED not differing from either group. Myocardial function, assessed in LV papillary muscles, showed improvement in SHR-EX over SHR-SED and WKY-EX. LV myocardial collagen fraction and type I and III collagen gene expression were increased in SHR groups. Myocardial hydroxyproline concentration was lower in SHR-EX than SHR-SED. Lysyl oxidase gene expression was higher in SHR-SED than WKY-SED. CONCLUSION: Exercise improves functional capacity and reduces decompensated HF in aging SHR independent of elevated arterial pressure. Improvement in functional status is combined with attenuation of LV and myocardial dysfunction and fibrosis.

Heart failure-induced diaphragm myopathy.

BACKGROUND: Intracellular signaling pathways involved in skeletal myosin heavy chain (MyHC) isoform alterations during heart failure (HF) are not completely understood. We tested the hypothesis that diaphragm expression of mitogen-activated protein kinases (MAPK) and myogenic regulatory factors is changed in rats with myocardial infarction (MI) induced HF. METHODS: Six months after MI rats were subjected to transthoracic echocardiography. After euthanasia, infarcted rats were subdivided in MI/HF- group (with no HF evidence; n=10), and MI/HF+ (with right ventricular hypertrophy and lung congestion; n=10). Sham-operated rats were used as controls (n=10). MyHC isoforms were analyzed by electrophoresis. STATISTICAL ANALYSIS: ANOVA and Pearson correlation. RESULTS: MI/HF- had left cardiac chambers dilation with systolic and diastolic left ventricular dysfunction. Cardiac injury was more intense in MI/HF+ than MI/HF-. MyHC I isoform percentage was higher in MI/HF+ than MI/HF-, and IIb isoform lower in MI/HF+ than Sham. Left atrial diameter-to-body weight ratio positively correlated with MyHC I (p=0.005) and negatively correlated with MyHC IIb (p=0.02). TNF-α serum concentration positively correlated with MyHC I isoform. Total and phosphorylated ERK was lower in MI/HF- and MI/HF+ than Sham. Phosphorylated JNK was lower in MI/HF- than Sham. JNK and p38 did not differ between groups. Expression of NF-κB and the myogenic regulatory factors MyoD, myogenin, and MRF4 was similar between groups. CONCLUSION: Diaphragm MyHC fast-to-slow shift is related to cardiac dysfunction severity and TNF-α serum levels in infarcted rats. Reduced ERK expression seems to participate in MyHC isoform changes. Myogenic regulatory factors and NF-κB do not modulate diaphragm MyHC distribution during chronic HF.

Aldosterone blockade reduces mortality without changing cardiac remodeling in spontaneously hypertensive rats.

BACKGROUND: The role of aldosterone blockers during transition from long-term compensated hypertrophy to dilated failure is not completely understood. In this study we evaluated the effects of early administration of spironolactone on cardiac remodeling, myocardial function, and mortality in spontaneously hypertensive rats (SHR). METHODS: Sixteen-month-old SHR received no treatment (SHR-C, n=72) or spironolactone (SHR-SPR, 20 mg/kg/day, n=34) for six months. Echocardiogram was performed before and after treatment. Myocardial function was analyzed in left ventricular (LV) papillary muscle preparations. Myocardial collagen and hydroxyproline concentration were evaluated by morphometry and spectrophotometry, respectively. LV gene expression was assessed by real time RT-PCR. STATISTICS: Student's t test; Log rank test (Kaplan Meyer). RESULTS: SHR-C and SHR-SPR presented mortality rates of 71 and 38%, respectively (p=0.004). Systolic arterial pressure did not differ between groups (SHR-C 199±43; SHR-SPR 200±35 mmHg). Initial and final echocardiograms did not show significant differences in cardiac structures or LV function between groups. Myocardial function was similar between groups at basal and after inotropic stimulation. Collagen fractional area, hydroxyproline concentration, gene expression for α- and ß-myosin heavy chain, atrial natriuretic peptide, and Serca2a were not different between groups. CONCLUSION: Early spironolactone administration reduces mortality without changing cardiac remodeling in spontaneous hypertensive rats.

Aldosterone is not involved in the ventricular remodeling process induced by tobacco smoke exposure.

BACKGROUND/AIMS: Renin-angiotensin-aldosterone system blockade with a mineralocorticoid-receptor antagonist has not yet been studied in exposure to tobacco smoke (TS) models. Thus, this study investigated the role of spironolactone on cardiac remodeling induced by exposure to tobacco smoke. METHODS: Male Wistar rats were divided into 4 groups: a control group (group C, n=11); a group with 2 months of cigarette smoke exposure (group TS-C, n=13); a group that received spironolactone 20 mg/kg of diet/day and no cigarette smoke exposure (group TS-S, n=13); and a group with 2 months of cigarette smoke exposure and spironolactone supplementation (group S, n=12). The rats were observed for a period of 60 days, during which morphological, biochemical and functional analyses were performed. RESULTS: There was no difference in invasive mean arterial pressure among the groups. There were no interactions between tobacco smoke exposure and spironolactone in the morphological and functional analysis. However, in the echocardiographic analysis, the TS groups had left chamber enlargement, higher left ventricular mass index and higher isovolumetric relaxation time corrected by heart rate compared with the non-TS groups. In vitro left ventricular diastolic function also worsened in the TS groups and was not influenced by spironolactone. In addition, there were no differences in myocardial levels of IFN-γ, TNF-α, IL-10, ICAM-1 and GLUT4 [TS: OR 0.52, 95%CI (-0.007; 0.11); Spironolactone: OR -0.01, 95%CI (-0.07;0.05)]. CONCLUSION: Our data do not support the participation of aldosterone in the ventricular remodeling process induced by exposed to cigarette smoke.

Myostatin and follistatin expression in skeletal muscles of rats with chronic heart failure.

Skeletal muscle abnormalities can contribute to decreased exercise capacity in heart failure. Although muscle atrophy is a common alteration in heart failure, the mechanisms responsible for muscle mass reduction are not clear. Myostatin, a member of TGF-beta family (transforming growth factor), regulates muscle growth and mass. Several studies have shown a negative correlation between myostatin expression and muscle mass. The aim of this study was to evaluate myostatin expression in skeletal muscles of rats with heart failure. As myostatin gene expression can be modulated by follistatin, we also evaluated its expression. Heart failure was induced by myocardial infarction (MI, n = 10); results were compared to Sham-operated group (n = 10). Ventricular function was assessed by echocardiogram. Gene expression was analyzed by real-time PCR and protein levels by Western blotting in the soleus and gastrocnemius muscles; fibre trophism was evaluated by morphometric analysis. MI group presented heart failure evidence such as pleural effusion and right ventricular hypertrophy. Left ventricular dilation and dysfunction were observed in MI group. In the soleus muscle, cross-sectional area (P = 0.006) and follistatin protein levels (Sham 1.00 +/- 0.36; MI 0.18 +/- 0.06 arbitrary units; P = 0.03) were lower in MI and there was a trend for follistatin gene expression to be lower in MI group (P = 0.085). There was no change in myostatin expression between groups. In gastrocnemius, all MI group parameters were statistically similar to the Sham. In conclusion, our data show that during chronic heart failure, decreased skeletal muscle trophism is combined with unchanged myostatin and reduced follistatin expression.

Clinical impact of body composition phenotypes in patients with COPD: a retrospective analysis.

BACKGROUND/OBJECTIVES: Abnormal body composition is an independent determinant of COPD outcomes. To date, it is already known that patient stratification into body composition phenotypes are associated with important outcomes, such as exercise capacity and inflammation, but there are no data comparing physical activity and muscle strength among these phenotypes. Thus, the aim of this study was to compare clinical characteristics and physical function in patients with COPD stratified into body composition phenotypes. SUBJECTS/METHODS: Two-hundred and seventy stable COPD patients were classified according to the 10th and 90th percentiles of sex-age-BMI-specific reference values for fat-free and fat mass indexes into four groups: Normal body composition (NBC), Obese, Sarcopenic, and Sarcopenic-obese (SO). Patients underwent assessment of exercise capacity, peripheral and respiratory muscle strength, physical activity, dyspnea severity, functional status, and symptoms of anxiety and depression. RESULTS: The prevalence of patients classified as NBC, Obese, Sarcopenic, and SO was 39%, 13%, 21%, or 27%, respectively. SO presented lower 6MWT compared with NBC (P < 0.05). Sarcopenic and SO groups presented worse muscle strength compared with NBC (P < 0.05). Sarcopenic group presented more time in moderate-to-vigorous physical activity compared to all other groups (P < 0.05) and less sedentary time when compared with NBC and obese groups (P < 0.05). There were no differences regarding dyspnea severity, functional status, and symptoms of anxiety and depression (P > 0.16). Sarcopenic and SO groups had, respectively, 7.8 [95% CI: 1.6-37.7] and 9.5 [2.2-41.7] times higher odds to have a 6MWT equal or lower to 350 meters. CONCLUSIONS: Body composition phenotypes are associated with physical function in patients with COPD. Sarcopenic-obese patients were the most impaired.

Effects of growth hormone on cardiac remodeling and soleus muscle in rats with aortic stenosis-induced heart failure.

BACKGROUND: Skeletal muscle wasting is often observed in heart failure (HF). The growth hormone (GH)/insulin-like growth factor-1 (IGF-1) axis is impaired in HF. In this study, we evaluated the effects of GH on soleus muscle and cardiac remodeling in rats with aortic stenosis (AS)-induced HF. METHODS: AS was created by placing a stainless-steel clip on the ascending aorta. After clinically detecting HF, GH (2 mg/kg/day) was subcutaneously injected for 14 days (AS-GH group). Results were compared with those from Sham and non-treated AS groups. Transthoracic echocardiogram was performed before and after treatment. Protein expression was evaluated by Western blot and satellite cells activation by immunofluorescence. Statistical analyzes: ANOVA and Tukey or Kruskal-Wallis and Student-Newman-Keuls. RESULTS: Before treatment both AS groups presented a similar degree of cardiac injury. GH prevented body weight loss and attenuated systolic dysfunction. Soleus cross-sectional fiber areas were lower in both AS groups than Sham (Sham 3,556±447; AS 2,882±422; AS-GH 2,868±591 µm2; p=0.016). GH increased IGF-1 serum concentration (Sham 938±83; AS 866±116; AS-GH 1167±166 ng/mL; p<0.0001) and IGF-1 muscle protein expression and activated PI3K protein. Neural cell adhesion molecule (NCAM) immunofluorescence was increased in both AS groups. Catabolism-related intracellular pathways did not differ between groups. CONCLUSION: Short-term growth hormone attenuates left ventricular systolic dysfunction in rats with aortic stenosis-induced HF. Despite preserving body weight, increasing serum and muscular IGF-1 levels, and stimulating PI3K muscle expression, GH does not modulate soleus muscle trophism, satellite cells activation or intracellular pathways associated with muscle catabolism.

Effects of late exercise on cardiac remodeling and myocardial calcium handling proteins in rats with moderate and large size myocardial infarction.

BACKGROUND: Physical exercise attenuates myocardial infarction (MI)-induced cardiac remodeling. However, it is unsettled whether late exercise modulates post-infarction cardiac remodeling differentially according to infarct size. We investigated the effects of exercise started at late stage heart failure on cardiac remodeling in rats with moderate and large sized MI. METHODS: Three months after MI, rats were assigned into sedentary and exercise groups. Exercise rats underwent treadmill for three months. After assessing infarct size by histological analysis, rats were subdivided into four groups: moderate MI sedentary (Mod MI-Sed; n=7), Mod MI exercised (Mod MI-Ex; n=7), Large MI-Sed (n=11), and Large MI-Ex (n=10). RESULTS: Before exercise, MI-induced cardiac changes were demonstrated by comparing results to a Sham group; alterations were more intense in rats with large than moderate MI size. Systolic function, evaluated by echocardiogram using the variation in LV fractional area change between after and before exercise, was improved in exercise than sedentary groups. Calsequestrin expression increased in exercised compared to sedentary groups. L-type calcium channel was higher in Mod MI-Ex than Mod MI-Sed. SERCA2a, phospholamban, and Na(+)/Ca(2+) exchanger expression did not differ between groups. CONCLUSION: Late exercise improves systolic function and modulates intracellular calcium signaling proteins in rats with moderate and large MI.

Beneficial Effects of Physical Exercise on Functional Capacity and Skeletal Muscle Oxidative Stress in Rats with Aortic Stenosis-Induced Heart Failure.

Objective. We evaluated the influence of exercise on functional capacity, cardiac remodeling, and skeletal muscle oxidative stress, MAPK, and NF-κB pathway in rats with aortic stenosis- (AS-) induced heart failure (HF). Methods and Results. Eighteen weeks after AS induction, rats were assigned into sedentary control (C-Sed), exercised control (C-Ex), sedentary AS (AS-Sed), and exercised AS (AS-Ex) groups. Exercise was performed on treadmill for eight weeks. Statistical analyses were performed with Goodman and ANOVA or Mann-Whitney. HF features frequency and mortality did not differ between AS groups. Exercise improved functional capacity, assessed by maximal exercise test on treadmill, without changing echocardiographic parameters. Soleus cross-sectional areas did not differ between groups. Lipid hydroperoxide concentration was higher in AS-Sed than C-Sed and AS-Ex. Activity of antioxidant enzymes superoxide dismutase and glutathione peroxidase was changed in AS-Sed and restored in AS-Ex. NADPH oxidase activity and gene expression of its subunits did not differ between AS groups. Total ROS generation was lower in AS-Ex than C-Ex. Exercise modulated MAPK in AS-Ex and did not change NF-κB pathway proteins. Conclusion. Exercise improves functional capacity in rats with AS-induced HF regardless of echocardiographic parameter changes. In soleus, exercise reduces oxidative stress, preserves antioxidant enzyme activity, and modulates MAPK expression.

Echocardiographic detection of congestive heart failure in postinfarction rats.

In studies of congestive heart failure (CHF) treatment, it is essential to select animals with a similar degree of cardiac dysfunction. However, this is difficult to establish without hemodynamic evaluation in rat postinfarction-induced CHF. This study aimed to diagnose CHF in long-term follow-up postinfarction rats using only echocardiographic criteria through a J-tree cluster analysis and Fisher's linear discriminant function. Two sets of sham and infarcted rats were studied. The first was used to perform cluster analysis and the second to prospectively validate the results. Six months after inducing myocardial infarction (MI), rats were subjected to transthoracic echocardiography. Infarct size was measured by histological analysis. Six echocardiographic variables were used in the cluster analysis: left ventricular (LV) systolic dimension, LV diastolic dimension-to-body weight ratio, left atrial diameter-to-body weight ratio, LV posterior wall shortening velocity, E wave, and isovolumetric relaxation time. Cluster analysis joined the rats into one sham and two MI groups. One MI cluster had more severe anatomical and echocardiographic changes and was called MI with heart failure (MI/HF+, n = 24, infarct size: 42.7 ± 5.8%). The other had less severe changes and was called MI without heart failure (MI/HF-, n = 11, infarct size: 32.3 ± 9.9%; P < 0.001 vs. MI/HF+). Three rats with small infarct size (21.6 ± 2.2%) presenting mild cardiac alterations were misallocated in the sham group. Fisher's linear discriminant function was built using these groups and used to prospectively classify additional groups of sham-operated (n = 20) and infarcted rats (n = 57) using the same echocardiographic parameters. The discriminant function therefore detected CHF with 100% specificity and 80% sensitivity considering allocation in MI/HF+ and sham group, and 100% specificity and 58.8% sensitivity considering MI/HF+ and MI/HF- groups, taking into account pathological criteria of CHF diagnosis. Echocardiographic analysis can be used to accurately predict congestive heart failure in postinfarction rats.

Miostatina e redução da massa muscular em doenças crônicas / Myostatin and muscle mass in chronic diseases

JUSTIFICATIVA E OBJETIVOS: A miostatina, também conhecida como fator de crescimento e diferenciação-8 (GDF-8), regula o crescimento de músculos esqueléticos durante o desenvolvimento embrionário e na vida adulta. Foi descoberta em pesquisas para identificar novos membros da superfamília fator transformador do crescimento-Beta (TGF-Beta) de fatores de diferenciação e crescimento celular. Os objetivos deste estudo consistiram em descrever o histórico e as características da miostatina, resumo de estudos sobre mecanismo de ação em condições fisiológicas e patológicas, por meio de estudos em humanos e modelos experimentais em animais, bem como as perspectivas futuras de utilização terapêutica de antagonistas da miostatina. CONTEÚDO: Estudos sobre os efeitos da miostatina mostraram correlação negativa entre sua expressão e massa muscular, sugerindo que possa estar envolvida na indução de hipotrofia e inibição do crescimento da musculatura esquelética. O mecanismo de ação da miostatina também foi avaliado, experimentalmente, em várias doenças como insuficiência cardíaca, neoplasias, cirrose, distrofias musculares, uremia e denervação. Os resultados sugerem que amiostatina exerce ações relevantes na redução da musculatura esquelética associada a estas condições. Também em humanos, os estudos realizados com indivíduos saudáveis e em pacientes com doenças crônicas reforçam este conceito. Entre as perspectivas para o futuro, ainda em fase de investigação experimental, há possibilidades terapêuticas que permitam antagonizar a ação da miostatina e reverter ou impedir a perda de massa muscular associada a doenças crônicas. Entre elas incluem-se anticorpos monoclonais anti-miostatina, propeptídeo da miostatina resistente à clivagem, forma solúvel do receptor activina tipo IIB e folistatina...

BACKGROUND AND OBJECTIVES: Myostatin, or GDF-8 (growth and differentiation factor-8), regulates muscle growth during development and adult life. Myostatin was originally identified in a screen for novel members of the transforming growth factor-Beta (TGF-Beta) superfamily of growth and differentiation factors. In this short review we describe myostatin characteristics, summary of studies on myostatin during physiological and pathological settings in human and experimental animal?s studies and future directions on myostatin antagonism.CONTENTS: Studies about the myostatin effects have shown a negative correlation between myostatin expression and muscle mass suggesting its involvement on muscle growth inhibition and atrophy. Myostatin has also been experimentally evaluated in several diseases such as heart failure, cancer, cirrhosis, muscular dystrophy, uremia, and denervation. The results suggest that myostatin can play an important role on chronic disease-associated skeletal muscle wasting. Although human studies are sparse, evaluation performed in healthy individuals and chronically diseased patients reinforces this hypothesis. Considering future perspectives, there is therapeutic potential to inhibit myostatin activity and treat or prevent muscle loss associated with chronic diseases. This includes myostatin neutralizing antibodies, protease resistant form of the myostatin propeptide, soluble version of the activin RIIB receptor, and follistatin. CONCLUSION: Experimental studies validate myostatin inhibition as a therapeutic approach to muscular dystrophy and chronic disease-associated muscle wasting.