injectable ACE-031 – an underground example is shown above – is a synthetic activin receptor type IIB. Muscle cells have this receptor too: it’s intended for proteins like myostatin, GDF11 and activin A and B. If myostatin attaches itself to an activin receptor type IIB, then the growth of muscle fibres is inhibited. Under the ‘right’ conditions myostatin actually breaks down muscle.
If you inject ACE-031 this doesn’t happen at all. The synthetic activin receptor type IIB filters out the muscle inhibiting proteins and deactivates them.
In 2007 Acceleron Pharma still had high expectations for ACE-031. At that point the company only had animal studies to back them up. But in 2013 they published the results of a human study, in which 48 healthy women aged from 45-75 had been given a single injection containing 0.02, 0.05, 0.1, 0.3, 1 or 3 mg ACE-031 per kg bodyweight. The substance remained in circulation in the body for a number of weeks: the half-life was 10-15 days.
But the single injection did lead to muscle growth. The 3-mg/kg dose led to an increase in muscle of volume of 5 percent, it boosted lean body mass by 3 percent [just over a kilogram], and seemed to also reduce fat mass-
The injection reduced the leptin concentration and boosted that of adiponectin. This would suggest that ACE-031 breaks down fat mass.
Moreover, the myostatin inhibitor boosted the concentration of bone specific alkaline phosphatase [BSAP] in the blood and reduced that of C-terminal type 1 collagen telopeptide [CTX]. This would suggest that ACE-031 strengthens bones. Acceleron has demonstrated these effects in animal studies using RAP-031, the mouse variant of ACE-031. [Endocrinology. 2010 Sep; 151(9): 4289-300.]