In older people, low muscle mass is strongly associated with reduced functional capacity and an increased risk of disability. Myostatin is a negative regulator of muscle growth and has become an important target for pharmaceutical companies designing therapeutics to address age-associated muscle loss.
Anti-myostatin drugs increase muscle size and strength in preclinical studies. Fortetropin is a proteo-lipid complex made from fertilized egg yolk and shows anti-myostatin activity. When Fortetropin is provided as a supplement, lowered circulating myostatin levels are observed both in rodents and in young men. Fortetropin in combination with resistance exercise also lowers myostatin and increased lean body mass.
The rate of synthesis of multiple muscle proteins in vivo can be measured using tandem mass spectrometric analysis of labeling patterns after ingestion of relatively small amounts of 2 H2 O to enrich total body water. A recent study examined the effects of 21 days of Fortetropin supplementation on the fractional synthetic rate (FSR) of muscle protein in 10 healthy, older men and 10 women (1). A microbiopsy was obtained from the m. vastus lateralis on Day 21. Samples were prepared and analyzed. In healthy older men and women, daily use of fortetropin increased sysnthesis rates of mucle proteins when compared to a control group given only cheese powder. The results indicate the value of larger clinical studies to further evaluate the effectiveness of Fortetropin as therapeutic for age-associated loss of muscle mass.
Summary of Sample Prep Method
- Muscle biopsy tissue was suspended in 0.08% SDS and vortexed at low speed overnight to extract cellular proteins.
- The SDS soluble proteins were precipitated by overnight incubation at −20°C in ethanol. Pelleted proteins were rinsed twice with 90% ethanol, allowed to air dry, and resuspended in 8 M urea before trypsin digestion.
- Up to 80 µg of SDS-soluble protein sample was denatured using ProteaseMax surfactant (0.1%) and 4 M urea in 25 mM ammonium bicarbonate (pH 8).
- Proteins were reduced with TCEP (5mM) for 20 min at room temperature with vortexing and then incubated with iodoacetamide (10 mM) in the dark for 20 minutes.
- Proteins were then digested with trypsin at 37°C overnight using a 1:25 trypsin:protein mass ratio.
Evans, W. et al. (2020) Effects of Fortetropin on the Rate of Muscle Protein Synthesis in Older Men and Women: A randomized, double-blinded, placebo-controlled study. J Gerontol A Biol Sci Med Sci