Analysis of the effects of androgens and training on myostatin propeptide and follistatin concentrations in blood and skeletal muscle using highly sensitive immuno PCR

Resistance training attenuates circulating FGF-21 and myostatin and improves insulin resistance in elderly men with and without type 2 diabetes mellitus: A randomised controlled clinical trial

Fibroblast growth factor 21 (FGF-21) and myostatin have been proposed to be potential therapeutic target for insulin resistance in age-related metabolic disorders including type 2 diabetes (T2D). Moreover, despite the potential metabolic effect of resistance training on insulin resistance, aging, and T2D; the effect of this type of exercise training on FGF-21 and myostatin in elderly men with and without T2D are unknown. Forty-four elderly men were assigned to either the RT training (RT; without T2D: 12, with TD2 = 10) or the control group (C; without T2D: 12, with TD2 = 10). The RT group performed 12-wk resistance training intervention, 3 days/wk, 10 repetitions with 70% 1RM. At the baseline, the elderly men with T2D had a higher FGF-21 (p = 0.002) and myostatin (p = 0.02) concentrations and lower muscle strength (p = 0.01) than the elderly men without T2D. RT resulted in significant decrease in FGF-21 and myostatin concentration and increase in muscle strength in both elderly men with and without T2D (P = 0.001, for all) as well as decrease in HOMA-IR in only elderly men without T2D (P = 0.001). There was no significant difference in the RT-induced FGF-21 reduction between elderly men with and without T2D (p = 0.77, p = 0.28, respectively), but, RT caused a larger reduction in circulating myostatin in elderly men without T2D than with T2D (P = 0.007). Taken together, our results demonstrated that 12 weeks of RT induced an overall significant reduction of FGF-21 and myostatin in elderly men with and without T2D; with higher reduction of myostatin in elderly men without T2D.

Why is low body fat rarely seen in large-sized male athletes?

OBJECTIVES

It is unknown why low body fat is rarely seen in large-sized athletes (>100 kg body mass). The aim of this review was to examine the relationship between body mass and body composition (fat mass and fat-free mass) in elite male athletes, and to discuss the possible reasons why low body fat is rarely seen in large-sized male athletes.

METHODS

A search using two electronic databases was conducted. Eighteen studies estimated body composition in elite athletes by dual-energy X-ray absorptiometry, totaling 2249 elite male athletes and 72 data points.

RESULTS

Our results indicated that low body fat (eg, less than 10% body fat) was rarely seen in large-sized male athletes over 100 kg body mass. The larger the body mass, the higher the fat-free mass, with fat-free mass leveling off when body mass exceeds approximately 120 kg.

CONCLUSION

Possible reasons for this are unknown but we provide some ideas for why this might occur. The two different stages to consider with respect to skeletal muscle growth: the amount of growth during development and the amount of growth as a result of long-term resistance training. In certain sporting events, a large body mass may be favored. However, the large-sized athletes have to balance any potential positive influence of body mass on sports performance with the potential negative factors associated with body fat accumulation. Further research is warranted, as there is currently limited evidence on this topic.

A Sensitive and Selective Immunoassay for the Quantitation of Serum Latent Myostatin after In Vivo Administration of SRK-015, a Selective Inhibitor of Myostatin Activation

Myostatin, a member of the transforming growth factor β (TGFβ) superfamily, is a key regulator of skeletal muscle mass and a therapeutic target for muscle wasting diseases. We developed a human monoclonal antibody, SRK-015, that selectively binds to and inhibits proteolytic processing of myostatin precursors, thereby preventing growth factor release from the latent complex. As a consequence of antibody binding, latent myostatin accumulates in the circulation of animals treated with SRK-015 or closely related antibodies, suggesting that quantitation of latent myostatin in serum may serve as a biomarker for target engagement. To accurately measure SRK-015 target engagement, we developed a sensitive plate-based electrochemiluminescent immunoassay to quantitate latent myostatin in serum samples. The assay selectively recognizes latent myostatin without cross-reactivity to promyostatin, mature myostatin, or closely related members of the TGFβ superfamily. To enable use of the assay in samples from animals dosed with SRK-015, we incorporated a low-pH step that dissociates SRK-015 from latent myostatin, improving drug tolerance of the assay. The assay meets inter- and intra-assay accuracy and precision acceptance criteria, and it has a lower limit of quantitation (LLOQ) of 10 ng/mL. We then tested serum samples from a pharmacology study in cynomolgus monkeys treated with SRK-015. Serum latent myostatin increases after treatment with SRK-015, reaches a dose-dependent plateau approximately 20 days after dosing, and trends back toward baseline after cessation of antibody dosing. Taken together, these data suggest that this assay can be used to accurately measure levels of the primary circulating form of myostatin in population-based or pharmacodynamic studies.

GH replacement titrated to serum IGF-1 does not reduce concentrations of myostatin in blood or skeletal muscle

OBJECTIVE

Traditional weight-based regimens of GH replacement are more effective at reversing the loss of skeletal muscle in GH-deficient adults than currently recommended regimens, where the dose of GH is increased to restore serum concentrations of IGF-1. While weight-based regimens increase concentrations of IGF-1 and decrease concentrations of myostatin, it is not known whether the reduced effectiveness of individually titrated GH regimens is due to ongoing hypersecretion of myostatin. Consequently, the aims of this study were to determine whether concentrations of myostatin in blood and skeletal muscle are increased in GH-deficient adults, and whether these concentrations are decreased by GH replacement regimens titrated to restore serum IGF-1.

DESIGN

Twenty-six GH deficient adults (18 men and 8 women) were treated with individualised regimens of recombinant human GH aiming to achieve serum concentrations of IGF-1 within one standard deviation of the age- and gender-adjusted mean. Plasma concentrations of myostatin were measured at baseline and after 6 months of treatment were compared to fifteen healthy controls (9 men and 6 women). Skeletal muscle biopsies were performed in 19 of these GH-deficient adults (15 men and 4 women) and 10 of the healthy controls (6 men and 4 women). Expression of IGF-1 and myostatin mRNA was determined by qPCR.

RESULTS

Concentrations of IGF-1 in serum and mRNA in skeletal muscle were reduced, and concentrations of myostatin in plasma and mRNA in skeletal muscle were increased in GH-deficient adults at baseline (P < .05 versus healthy controls). Despite restoring concentrations of IGF-1, GH replacement did not reduce concentrations of myostatin in either blood or skeletal muscle. Concentrations of IGF-1 and myostatin in both blood and skeletal muscle were positively correlated in GH-deficient adults at baseline (P < .05), but not in GH-replete adults.

CONCLUSIONS

Concentrations of myostatin in blood and skeletal muscle are increased in GH-deficient adults. Despite normalising concentrations of IGF-1, individualised regimens of GH replacement do not reduce concentrations of myostatin in blood or skeletal muscle. Ongoing hypersecretion of myostatin may explain why individually titrated GH replacement regimens are less effective than higher weight-based regimens in increasing skeletal muscle mass.

Serum reference value of two potential doping candidates-myostatin and insulin-like growth factor-I in the healthy young male

Background

Myostatin negatively regulates muscle growth, and its inhibition by suitable proteins can increase muscle bulk and exercise performance. However, the reference values of serum myostatin in athletes performing strength training are still lacking.

Methods

A cross-sectional study recruiting28 male collegiate athletes performing strength training and 29 age-matched normal controls was conducted.

The serum concentration of myostatin and insulin-like growth factor 1 (IGF-1), grip strength, and body composition were the main outcome measures. We used regression models to analyze the correlation between serum markers and the physiological parameters. The athlete group had greater height, weight, body mass index (BMI), fat mass percentage, fat-free mass, muscle mass, waist girth, grip strength, and estimated daily energy expenditure.

Results

The IGF-1 concentration was higher in the athlete group (324 ± 80 vs. 263 ± 134 ng/ml), but the myostatin levels did not differ (12.1 ± 3.7 vs. 12.4 ± 3.5 ng/ml). The reference value for IGF-1 among the healthy young males was 293 ± 114 ng/ml, correlated with age and height; the value for myostatin was 12.3 ± 3.6 ng/ml, correlated negatively with BMI, fat mass percentage, and waist girth after adjustment for age.

Conclusion

Myostatin level is negatively related to fat percentage, and serum IGF-1 is positively related to height. The reference values could provide a basis for future doping-related study.

Highly sensitive ligand-binding assays in pre-clinical and clinical applications: immuno-PCR and other emerging techniques

Recombinant DNA technology and corresponding innovations in molecular biology, chemistry and medicine have led to novel therapeutic biomacromolecules as lead candidates in the pharmaceutical drug development pipelines. While monoclonal antibodies and other proteins provide therapeutic potential beyond the possibilities of small molecule drugs, the concomitant demand for supportive bioanalytical sample testing creates multiple novel challenges. For example, intact macromolecules can usually not be quantified by mass-spectrometry without enzymatic digestion and isotopically labeled internal standards are costly and/or difficult to prepare. Classical ELISA-type immunoassays, on the other hand, often lack the sensitivity required to obtain pharmacokinetics of low dosed drugs or pharmacodynamics of suitable biomarkers. Here we summarize emerging state-of-the-art ligand-binding assay technologies for pharmaceutical sample testing, which reveal enhanced analytical sensitivity over classical ELISA formats. We focus on immuno-PCR, which combines antibody specificity with the extremely sensitive detection of a tethered DNA marker by quantitative PCR, and alternative nucleic acid-based technologies as well as methods based on electrochemiluminescence or single-molecule counting. Using case studies, we discuss advantages and drawbacks of these methods for preclinical and clinical sample testing.

Effects of elastic band resistance training and nutritional supplementation on muscle quality and circulating muscle growth and degradation factors of institutionalized elderly women: the Vienna Active Ageing Study (VAAS)

PURPOSE

Regular resistance exercise training and a balanced diet may counteract the age-related muscular decline on a molecular level. The aim of this study was to investigate the influence of elastic band resistance training and nutritional supplementation on circulating muscle growth and degradation factors, physical performance and muscle quality (MQ) of institutionalized elderly.

METHODS

Within the Vienna Active Ageing Study, 91 women aged 83.6 (65.0-92.2) years were randomly assigned to one of the three intervention groups (RT, resistance training; RTS, resistance training plus nutritional supplementation; CT, cognitive training). Circulating levels of myostatin, activin A, follistatin, IGF-1 and GDF-15, as well as MQ and functional parameters were tested at baseline as well as after 3 and 6 months of intervention.

RESULTS

MQ of lower extremities significantly increased in the RT group (+14 %) and RTS group (+12 %) after 6 months. Performance improved in the RT and RTS groups for chair stand test (RT: +18 %; RTS: +15 %). Follistatin increased only in the RT group (+18 %) in the latter phase of the intervention, accompanied by a decrease in the activin A-to-follistatin ratio (-7 %). IGF-1, myostatin and GDF-15 levels were not affected by the intervention.

CONCLUSION

Our data confirm that strength training improves physical performance and MQ even in very old institutionalized women. This amelioration appears to be mediated by blocking muscle degradation pathways via follistatin rather than inducing muscle growth through the IGF-1 pathway. As plasma levels of biomarkers reflect an overall status of various organ systems, future studies of tissue levels are suggested.

Myostatin as a mediator of sarcopenia versus homeostatic regulator of muscle mass: insights using a new mass spectrometry-based assay

BACKGROUND

Myostatin is a protein synthesized and secreted by skeletal muscle that negatively regulates muscle mass. The extent to which circulating myostatin levels change in the context of aging is controversial, largely due to methodological barriers.

METHODS

We developed a specific and sensitive liquid chromatography with tandem mass spectrometry (LC-MS/MS) assay to measure concentrations of myostatin and two of its key inhibitors, follistatin-related gene (FLRG) protein and growth and serum protein-1 (GASP-1) in 80 younger (<40 years), 80 older (>65 years), and 80 sarcopenic older women and men.

RESULTS

Older women had 34 % higher circulating concentrations of myostatin than younger women. Per unit of lean mass, both older and sarcopenic older women had >23 % higher myostatin levels than younger women. By contrast, younger men had higher myostatin concentrations than older men with and without sarcopenia. Younger men had approximately twofold higher concentrations of myostatin than younger women; however, older women and sarcopenic older women had significantly higher relative myostatin levels than the corresponding groups of men. In both sexes, sarcopenic older subjects had the highest concentrations of FLRG. Circulating concentrations of myostatin exhibited positive, but not robust, correlations with relative muscle mass in both sexes.

CONCLUSIONS

Our data suggest that myostatin may contribute to the higher prevalence of sarcopenia in women but acts as a homeostatic regulator of muscle mass in men. Moreover, this new LC-MS/MS-based approach offers a means to determine the extent to which myostatin serves as a biomarker of muscle health in diverse conditions of muscle loss and deterioration.

RNA sequencing identifies upregulated kyphoscoliosis peptidase and phosphatidic acid signaling pathways in muscle hypertrophy generated by transgenic expression of myostatin propeptide

Myostatin (MSTN), a member of the transforming growth factor-β superfamily, plays a crucial negative role in muscle growth. MSTN mutations or inhibitions can dramatically increase muscle mass in most mammal species. Previously, we generated a transgenic mouse model of muscle hypertrophy via the transgenic expression of the MSTN N-terminal propeptide cDNA under the control of the skeletal muscle-specific MLC1 promoter. Here, we compare the mRNA profiles between transgenic mice and wild-type littermate controls with a high-throughput RNA sequencing method. The results show that 132 genes were significantly differentially expressed between transgenic mice and wild-type control mice; 97 of these genes were up-regulated, and 35 genes were down-regulated in the skeletal muscle. Several genes that had not been reported to be involved in muscle hypertrophy were identified, including up-regulated myosin binding protein H (mybph), and zinc metallopeptidase STE24 (Zmpste24). In addition, kyphoscoliosis peptidase (Ky), which plays a vital role in muscle growth, was also up-regulated in the transgenic mice. Interestingly, a pathway analysis based on grouping the differentially expressed genes uncovered that cardiomyopathy-related pathways and phosphatidic acid (PA) pathways (Dgki, Dgkz, Plcd4) were up-regulated. Increased PA signaling may increase mTOR signaling, resulting in skeletal muscle growth. The findings of the RNA sequencing analysis help to understand the molecular mechanisms of muscle hypertrophy caused by MSTN inhibition.

Skeletal muscle is an endocrine organ

Skeletal muscle plays a key role in postural retention as well as locomotion for maintaining the physical activities of human life. Skeletal muscle has a second role as an elaborate energy production and consumption system that influences the whole body's energy metabolism. Skeletal muscle is a specific organ that engenders a physical force, and exercise training has been known to bring about multiple benefits for human health maintenance and/or improvement. The mechanisms underlying the improvement of the human physical condition have been revealed: skeletal muscle synthesizes and secretes multiple factors, and these muscle-derived factors, so-called as myokines, exert beneficial effects on peripheral and remote organs. In this short review, we focus on the third aspect of skeletal muscle function - namely, the release of multiple types of myokines, which constitute a broad network for regulating the function of remote organs as well as skeletal muscle itself. We conclusively show that skeletal muscle is one of the endocrine organs and that understanding the mechanisms of production and secretion of myokines may lead to a new pharmacological approach for treatment of clinical disorders.

Emerging technologies to increase ligand binding assay sensitivity

Ligand binding assays (LBAs) have been the method of choice for protein analyte measurements for more than four decades. Over the years, LBA methods have improved in sensitivity and achieved larger dynamic ranges by using alternative detection systems and new technologies. As a consequence, the landscape and application of immunoassay platforms has changed dramatically. The introduction of bead-based methods, coupled with single molecule detection standardization and the ability to amplify assay signals, has improved the sensitivity of many immunoassays, in some cases by several logs of magnitude. Three promising immunoassay platforms are described in this article: Single Molecule Counting (SMC™) from Singulex Inc, Single Molecule Arrays (Simoa™) from Quanterix Corporation, and Immuno-PCR (Imperacer®) from Chimera Biotec GmbH. These platforms have the potential to significantly improve immunoassay sensitivity and thereby address the bioanalytical needs and challenges faced during biopharmaceutical drug development.

A satellite cell-specific knockout of the androgen receptor reveals myostatin as a direct androgen target in skeletal muscle

Androgens have well-established anabolic actions on skeletal muscle, although the direct effects of the androgen receptor (AR) in muscle remain unclear. We generated satellite cell-specific AR-knockout (satARKO) mice in which the AR is selectively ablated in satellite cells, the muscle precursor cells. Total-limb maximal grip strength is decreased by 7% in satARKO mice, with soleus muscles containing ∼10% more type I fibers and 10% less type IIa fibers than the corresponding control littermates. The weight of the perineal levator ani muscle is markedly reduced (-52%). Thus, muscle AR is involved in fiber-type distribution and force production of the limb muscles, while it is a major determinant of the perineal muscle mass. Surprisingly, myostatin (Mstn), a strong inhibitor of skeletal muscle growth, is one of the most androgen-responsive genes (6-fold reduction in satARKO) through direct transcription activation by the AR. Consequently, muscle hypertrophy in response to androgens is augmented in Mstn-knockout mice. Our finding that androgens induce Mstn signaling to restrain their own anabolic actions has implications for the treatment of muscle wasting disorders.-Dubois, V., Laurent, M. R., Sinnesael, M., Cielen, N., Helsen, C., Clinckemalie, L., Spans, L., Gayan-Ramirez, G., Deldicque, L., Hespel, P., Carmeliet, G., Vanderschueren, D., and Claessens, F. A satellite cell-specific knockout of the androgen receptor reveals myostatin as a direct androgen target in skeletal muscle.

Combinatory effects of siRNA-induced myostatin inhibition and exercise on skeletal muscle homeostasis and body composition

Abstract Inhibition of myostatin (Mstn) stimulates skeletal muscle growth, reduces body fat, and induces a number of metabolic changes. However, it remains unexplored how exercise training modulates the response to Mstn inhibition. The aim of this study was to investigate how siRNA-mediated Mstn inhibition alone but also in combination with physical activity affects body composition and skeletal muscle homeostasis. Adult mice were treated with Mstn-targeting siRNA and subjected to a treadmill-based exercise protocol for 4 weeks. Effects on skeletal muscle and fat tissue, expression of genes, and serum concentration of proteins involved in myostatin signaling, skeletal muscle homeostasis, and lipid metabolism were investigated and compared with Mstn(-/-) mice. The combination of siRNA-mediated Mstn knockdown and exercise induced skeletal muscle hypertrophy, which was associated with an upregulation of markers for satellite cell activity. SiRNA-mediated Mstn knockdown decreased visceral fat and modulated lipid metabolism similar to effects observed in Mstn(-/-) mice. Myostatin did not regulate its own expression via an autoregulatory loop, however, Mstn knockdown resulted in a decrease in the serum concentrations of myostatin propeptide, leptin, and follistatin. The ratio of these three parameters was distinct between Mstn knockdown, exercise, and their combination. Taken together, siRNA-mediated Mstn knockdown in combination with exercise stimulated skeletal muscle hypertrophy. Each intervention or their combination induced a specific set of adaptive responses in the skeletal muscle and fat metabolism which could be identified by marker proteins in serum.

Endocrine and clinical correlates of myostatin serum concentration in men--the STRAMBO study

CONTEXT

Myostatin is expressed mainly in skeletal muscle cells and acts as an inhibitor of muscle growth and differentiation. However, data on the determinants of serum myostatin concentrations in humans are limited.

OBJECTIVE

The aim of the study was to assess the correlates of serum myostatin concentrations in men.

DESIGN

We conducted a cross-sectional analysis of the STRAMBO cohort.

SETTING

Men holding private health insurance coverage with Mutuelle de Travailleurs de la Région Lyonnaise were included in the study.

PARTICIPANTS

A total of 1121 male volunteers aged 20-87 yr participated in the study.

INTERVENTIONS

Nonfasting blood samples were collected.

MAIN OUTCOME MEASURES

We measured the association of the investigated variables with circulating myostatin levels.

RESULTS

Serum myostatin levels increased slightly with age until 57 yr and then decreased. Circulating myostatin levels showed circannual variation, with the highest concentration in spring. In men older than 57 yr, serum myostatin levels decreased across increasing quartiles of body mass index and of total central and peripheral fat mass (P<0.05 to <0.001). Serum myostatin levels were positively correlated with serum levels of 25-hydroxycholecalciferol (25OHD), even after adjustment for season. Average myostatin levels were 0.47 sd higher in men with 25OHD above 40 ng/ml, compared with those with 25OHD below 20 ng/ml (P<0.05). Current smokers had lower myostatin concentration. Neither current physical activity nor serum levels of PTH, testosterone, and 17β-estradiol were associated with myostatin concentrations.

CONCLUSIONS

In men, circulating myostatin levels show seasonal changes and are associated with age, body mass index, fat mass, smoking, and 25OHD levels.

Myostatin and its association with abdominal obesity, androgen and follistatin levels in women with polycystic ovary syndrome

STUDY QUESTION

What is the role of myostatin and its relationship with obesity, androgens and follistatin levels in women with polycystic ovary syndrome (PCOS)? SUMMARY ANSWERS: The myostatin level was positively correlated to the risk of abdominal obesity, but negatively associated with circulating levels of dehydroepiandrosterone sulfate (DHEAS) and follistatin in women with PCOS.

WHAT IS KNOWN AND WHAT THIS PAPER ADDS

Myostatin is a well-known negative regulator of skeletal muscle and is involved in metabolism; however, little is known about the role of myostatin in women with PCOS. In this study, we found that the myostatin level was positively related to the risk of abdominal obesity, but negatively related to the circulating levels of DHEAS and follistatin in women with PCOS. Such a relationship might imply a potential regulatory role of androgens and follistatin in the metabolism of skeletal muscle in women with PCOS.

DESIGN

A cross-sectional case-control study.

PARTICIPANTS AND SETTING

A total of 239 untreated, consecutive women with PCOS and 38 healthy volunteer women without PCOS were enrolled and studied in a tertiary medical center.

MAIN RESULTS AND THE ROLE OF CHANCE

Myostatin level was higher in women with PCOS than those without PCOS (16.6±15.6 and 14.2±9.7, P=0.025), but were not significantly different between non-obese women with and without PCOS after considering the effect of obesity (P=0.09). Stepwise multivariate regression analysis in women revealed that only the presence of PCOS (β=0.256, P=0.0001), total testosterone (β=0.159, P=0.031), DHEAS (β=-0.188, P=0.0003) and follistatin (β=-0.171, P=0.0001) levels were left in the final model and were significantly related to the myostatin level after considering all the explanatory variables. By using stepwise multivariate regression analysis, the total testosterone levels (β=0.196, P=0.003) were positively, but the DHEAS (β=-0.196, P<0.0001) and follistatin (β=-0.151, P=0.0001) levels were negatively, related to myostatin levels in women with PCOS after adjustment for age, anthropometric measurements, insulin sensitivity index and hormonal profiles. The high myostatin level was associated with the increased risk of abdominal obesity after further adjusting the androgens and follistatin levels in women with PCOS.

LIMITATION, REASONS FOR CAUTION

This study is a cross-sectional case-control design, and therefore, cannot answer the cause-effect relationship among the androgens, follistatin and myostatin levels. The small sample size and non-obese control group may also limit the application of the conclusion of the present study to general population other than women with PCOS. In addition, lack of data regarding muscle mass is another limitation in this study that prevents clarification of the relationship between myostatin, lean mass and obesity and therefore restricts the clinical application of the results.

WIDER IMPLICATIONS OF THE FINDINGS

Future studies to investigate the efficacy of exercise and lifestyle modification in treating women with PCOS should consider the myostatin, follistatin and androgen levels as well as the effect of muscle mass and BMI.

STUDY FUNDING/COMPETING INTEREST

This study was supported by grants NSC97-2314-B002-079-MY3, NSC98-2314-B002-105-MY3 and NSC 100-2314-B002-027-MY3 from the National Science Council of Taiwan. There is no competing interest declared in this study.

Plasma myostatin measured by a competitive ELISA using a highly specific antiserum

BACKGROUND

Understanding the (patho)physiology of the negative muscle regulator myostatin (Myo) is important for patients with skeletal muscle disorders or cardiac disease. However, a reliable tool for measuring plasma Myo immunoreactivity is still lacking.

METHODS

Human full-length proMyo was used to raise a polyclonal rabbit antiserum for a competitive Myo ELISA that was validated in patients with decompensated congestive heart failure (CHF) and in control patients (n=20 each).

RESULTS

The Myo antiserum detected all subunits of human proMyo. The calibration curve showed an optimal range between 0.3 and 83.3 ng/ml (7.5-2100 pmol/l), with no cross-reactivity to growth differentiation factor-11, follistatin and follistatin-related gene protein. The inter-assay and intra-assay variances in human serum were ≤15% and ≤10%, respectively; the detection limit was 270 pg/ml (6.75 pmol/l). The assay showed excellent linearity in human plasma. Plasma NT-proBNP and Myo were significantly elevated in decompensated CHF compared with control patients and decreased significantly upon recompensating therapy.

CONCLUSION

We describe the development of the first ELISA for myostatin immunoreactivity and its validation during recompensating therapy for CHF. This assay will be valuable for investigating neurological and cardiac diseases and states of cachexia, insulin resistance, and obesity.