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

The Effects of Dietary Supplements, Nutraceutical Agents, and Physical Exercise on Myostatin Levels: Hope or Hype?

Myostatin, a secreted growth factor belonging to the transforming growth factor β (TGF-β) family, performs a role in hindering muscle growth by inhibiting protein kinase B (Akt) phosphorylation and the associated activation of hypertrophy pathways (e.g., IGF-1/PI3K/Akt/mTOR pathway). In addition to pharmacological agents, some supplements and nutraceutical agents have demonstrated modulatory effects on myostatin levels; however, the clinical magnitude must be appraised with skepticism before translating the mechanistic effects into muscle hypertrophy outcomes. Here, we review the effects of dietary supplements, nutraceutical agents, and physical exercise on myostatin levels, addressing the promise and pitfalls of relevant randomized clinical trials (RCTs) to draw clinical conclusions. RCTs involving both clinical and sports populations were considered, along with wasting muscle disorders (e.g., sarcopenia) and resistance training-induced muscle hypertrophy, irrespective of disease status. Animal models were considered only to expand the mechanisms of action, and observational data were consulted to elucidate potential cutoff values. Collectively, the effects of dietary supplements, nutraceutical agents, and physical exercise on myostatin mRNA expression in skeletal muscle and serum myostatin levels are not uniform, and there may be reductions, increases, or neutral effects. Large amounts of research using resistance protocols shows that supplements or functional foods do not clearly outperform placebo for modulating myostatin levels. Thus, despite some biological hope in using supplements or certain functional foods to decrease myostatin levels, caution must be exercised not to propagate the hope of the food supplement market, select health professionals, and laypeople.

The minor allele of the CREBRF rs373863828 p.R457Q coding variant is associated with reduced levels of myostatin in males: Implications for body composition

OBJECTIVE

The minor allele (A) of the rs373863828 variant (p.Arg457Gln) in CREBRF is restricted to indigenous peoples of the Pacific islands (including New Zealand Māori and peoples of Polynesia), with a frequency of up to 25% in these populations. This allele associates with a large increase in body mass index (BMI) but with significantly lower risk of type-2 diabetes (T2D). It remains unclear whether the increased BMI is driven by increased adiposity or by increased lean mass.

METHODS

We undertook body composition analysis using DXA in 189 young men of Māori and Pacific descent living in Aotearoa New Zealand. Further investigation was carried out in two orthologous Arg458Gln knockin mouse models on FVB/NJ and C57BL/6j backgrounds.

RESULTS

The rs373863828 A allele was associated with lower fat mass when adjusted for BMI (p < 0.05) and was associated with significantly lower circulating levels of the muscle inhibitory hormone myostatin (p < 0.05). Supporting the human data, significant reductions in adipose tissue mass were observed in the knockin mice. This was more significant in older mice in both backgrounds and appeared to be the result of reduced age-associated increases in fat mass. The older male knockin mice on C57BL/6j background also had increased grip strength (p < 0.01) and lower levels of myostatin (p < 0.05).

CONCLUSION

Overall, these results prove that the rs373863828 A-allele is associated with a reduction of myostatin levels which likely contribute to an age-dependent lowering of fat mass, at least in males.

Muscle mass and plasma myostatin after exercise training: a substudy of Renal Exercise (RENEXC)-a randomized controlled trial

BACKGROUND

Sarcopenia increases as renal function declines and is associated with higher morbidity and mortality. Myostatin is a negative regulator of muscle growth. Its expression in response to exercise is unclear. In this prespecified substudy of the Renal Exercise (RENEXC) trial, we investigated the effects of 12 months of exercise training on sarcopenia, muscle mass and plasma myostatin and the relationships between physical performance, muscle mass and plasma myostatin.

METHODS

A total of 151 non-dialysis-dependent patients (average measured glomerular filtration rate 23 ± 8 mL/min/1.73 m2), irrespective of age or comorbidity, were randomly assigned to either strength or balance in combination with endurance training. Body composition was measured with dual-energy X-ray absorptiometry. Plasma myostatin was analysed using enzyme-linked immunosorbent assay kits.

RESULTS

After 12 months, the prevalence of sarcopenia was unchanged, leg and whole-body lean mass increased significantly in the balance group and was unchanged in the strength group. Whole fat mass decreased significantly in both groups. There were no significant between-group differences in sarcopenia or body composition. Plasma myostatin levels increased significantly in both groups, with a significant difference in favour of the strength group. Plasma myostatin was significantly positively related to muscle mass and physical performance at baseline, but these relationships were attenuated after 12 months.

CONCLUSIONS

Exercise training seems to be effective in preventing sarcopenia and maintaining muscle mass in non-dialysis-dependent patients with chronic kidney disease (CKD). However, the role of plasma myostatin on muscle mass and physical performance in patients with CKD warrants further study.

Myokines in Acromegaly: An Altered Irisin Profile

INTRODUCTION

The muscle is an endocrine organ controlling metabolic homeostasis. Irisin and myostatin are key myokines mediating this process. Acromegaly is a chronic disease with a wide spectrum of complications, including metabolic disturbances.

PURPOSE

To examine the influence of acromegaly on irisin and myostatin secretion and their contribution to metabolic profile and body composition.

MATERIALS AND METHODS

In 43 patients with acromegaly and 60 controls, serum levels of irisin, myostatin, growth hormone (GH), insulin-like growth factor 1 (IGF-1), parameters of glucose, and lipid metabolism were determined. Body composition was assessed with dual-energy x-ray absorptiometry.

RESULTS

The irisin concentration was significantly lower in patients with acromegaly compared to controls (3.91 vs. 5.09 μg/ml, p = 0.006). There were no correlations between irisin and GH/IGF-1 levels. In the study group, irisin was negatively correlated with fasting insulin (r = -0.367; p = 0.042), HOMA-IR (r = -0.510; p = 0.011), and atherogenic factors: Castelli I (r = -0.416; p = 0.005), Castelli II (r = -0.400; p = 0.001), and atherogenic coefficient (AC) (r = -0.417; p = 0.05). Irisin and myostatin concentrations were also lower in acromegalics with insulin resistance than without (2.80 vs. 4.18 μg/ml, p = 0.047; 81.46 vs. 429.58 ng/L, p = 0.018, respectively). There were no differences between study group and controls in myostatin concentration. Myostatin levels negatively correlated with GH (r = -0.306; p = 0.049), HOMA-IR (r = -0.046; p = 0.411), and insulin levels (r = -0.429; p = 0.016).

CONCLUSIONS

Decreased irisin concentrations in acromegaly may suggest impaired hormonal muscle function contributing to metabolic complications in this disorder. However, learning more about the association between myostatin and GH in acromegaly requires further studies. Nevertheless, it appears that myostatin is not critical for muscle mass regulation in acromegaly.