ACE-031 (often called ACE-31 or ACE 31 in casual references) is a research compound, specifically a soluble recombinant fusion protein. It consists of the extracellular domain of the activin receptor type IIB (ActRIIB or ACVR2B) fused to the Fc portion of human IgG1. It is also known as ramatercept.
How It Works (Mechanism of Action)
ACE-031 acts as a “decoy receptor” or ligand trap. It binds to myostatin (GDF-8) and other related proteins in the TGF-β superfamily that normally inhibit muscle growth. By trapping these negative regulators, ACE-031 prevents them from signaling through the actual ActRIIB receptors on muscle cells. This promotes muscle hypertrophy (increased muscle fiber size) and can also support hyperplasia in some models, leading to greater overall muscle mass and strength. It does this across both type I (slow-twitch) and type II (fast-twitch) muscle fibers without significantly altering fiber-type distribution.
Research also suggests secondary effects on:
- Increased bone mineral density and biomarkers of bone formation.
- Reduced fat mass or altered fat metabolism.
- Potential improvements in muscle oxidative capacity and energy metabolism.
Research Findings
- Human studies: In a Phase 1 single-ascending-dose trial in healthy postmenopausal women, a single subcutaneous dose (up to 3 mg/kg) was generally well-tolerated. It led to dose-dependent increases in lean body mass (up to ~3.3%) and thigh muscle volume (~5.1% at the highest dose) measured by DXA and MRI after 29 days. Half-life was about 10–15 days. Minor side effects included injection-site reactions.
- Duchenne muscular dystrophy (DMD): A randomized trial in ambulatory boys with DMD showed some muscle-related benefits, but development faced safety concerns (e.g., potential bleeding risks or other issues in longer trials), and clinical work on ACE-031 was ultimately discontinued by the sponsors around 2013.
- Preclinical (animal) studies: In mice and other models, ACE-031 increased body weight, muscle weights (e.g., 26–46% in various muscles), and contractile force. Effects were independent of exercise in some cases and occurred without major shifts in myosin heavy chain isoforms.
It has been investigated for muscle-wasting conditions, neuromuscular diseases, age-related sarcopenia, and even metabolic aspects like insulin sensitivity or cancer-related cachexia, but it remains an experimental/research compound.
Important Notes
- Not approved for human use: ACE-031 is not FDA-approved or authorized for any clinical treatment, bodybuilding, or performance enhancement. It is sold by some peptide suppliers strictly for laboratory/research purposes (often as 1 mg or 5 mg vials for in vitro or animal studies). Use in humans, especially from black-market sources, carries unknown risks and is prohibited in sports by WADA (listed under myostatin/ActRIIB inhibitors).
