ACE-031: Reference Overview and Reconstitution Notes

ACE-031 (ramatercept) is an experimental protein being studied for its effects on muscle mass. It is for research only and has not been approved by the FDA.

ACE-031

What it is

ACE-031, also called ramatercept, is a man-made protein built from two connected parts. One part is copied from a human cell receptor (a docking site found on the surface of cells) called activin receptor type IIB (ActRIIB). The other part comes from a common antibody protein called IgG1. The two parts are joined to form a single molecule.

It belongs to a group of lab tools called soluble receptor "ligand trap" biologics. Think of a ligand trap like a decoy target: it catches certain signaling molecules before they can reach their real destination. ACE-031 is not a short peptide, even though it is often grouped alongside peptides in commercial catalogs.

Research context and categorization

Researchers classify ACE-031 as a myostatin and activin pathway modulator. In plain terms, it interferes with certain signals that control muscle growth. It works like a decoy receptor, floating through the bloodstream and grabbing signaling proteins before they can attach to real cell-surface receptors (the docking sites on cells). The proteins it catches, including myostatin and activin, belong to a large protein family called the TGF-beta superfamily.

Myostatin acts like a brake on muscle growth. It tells the body to limit how much muscle it builds. Because ACE-031 blocks myostatin from reaching its target, it is commonly studied in connection with muscle mass and strength.

Clinical Trials and Safety

Researchers once studied ACE-031 as a possible tool for muscle-wasting conditions. It reached human clinical trials (organized studies in people) for Duchenne muscular dystrophy (a serious genetic disease that progressively weakens muscles) and was also studied in post-menopausal participants.

It is important to note that ACE-031 is not FDA-approved. The company that developed it stopped its muscular dystrophy trial after participants experienced vascular-related side effects. These included nosebleeds, small swollen blood vessels, and gum bleeding.

Later research linked these side effects to the fact that ACE-031 also affects other signaling proteins beyond myostatin. One of them is BMP9, a protein that helps keep blood vessels stable (a state called homeostasis, meaning the body's normal steady balance). Any uses described here are investigational, meaning they are still being studied and are not proven or approved benefits.

Key point: ACE-031 is not FDA-approved, and its clinical development was stopped after participants in trials experienced vascular-related side effects.

Status

• Regulatory status: Research-only and not FDA-approved. Clinical development was discontinued and no marketing approval exists.
• Sport status: Prohibited under the WADA Prohibited List (the World Anti-Doping Agency's global list of banned substances in sport). It falls under section S4.3, which covers myostatin inhibitors and activin receptor type II inhibitors in the hormone and metabolic modulators class. It is banned at all times, both in-competition and out-of-competition.

Reconstitution notes (general)

A lyophilized (freeze-dried) protein comes as a dry powder inside a sealed vial. To use it at the lab bench, you add a liquid called a diluent to dissolve the powder. The concentration (how strong the resulting solution is) equals the milligrams of powder in the vial divided by the milliliters of liquid added. For example, a vial mixed with 2 mL of liquid will be half as strong as the same vial mixed with only 1 mL.

A reconstitution calculator is available at peptide calculator to convert vial size and diluent volume into a working concentration.

Dilution and handling notes (compound-specific)

ACE-031 comes as a white freeze-dried powder. Like other freeze-dried proteins, you mix it with liquid before using it at the lab bench. Vials are commonly sold in small sizes such as 1 mg, with larger 10 mg sizes also available.

A common example: a 10 mg vial mixed with about 2 mL of liquid gives roughly 5 mg/mL. Using only about 1 mL gives a more concentrated roughly 10 mg/mL solution. Using less liquid makes the solution stronger, but leaves a smaller total volume and less room for measurement error.

Handling Quirks

Two handling quirks are worth noting:

• Gentle reconstitution: ACE-031 is a large protein, not a small short-chain peptide. Large proteins are more fragile and easier to damage. Point the stream of liquid at the inside wall of the vial and let the powder dissolve on its own. Do not shake it hard, and do not let it foam. Shaking and foaming can cause the protein to clump together (called aggregation), which makes it unusable. Dissolving may take several minutes. A properly mixed solution will look clear or only very slightly cloudy. That faint pearly haze is called opalescent and is normal.
• Diluent selection: Bacteriostatic water contains a preservative called benzyl alcohol. Some sources say this preservative can reduce protein stability over time. Because of this, plain sterile water is sometimes preferred, even though it has no preservative and supports a shorter in-use window. Check the specific product's documentation for guidance on which liquid to use.

Handling and storage

Proper storage and handling protocols include the following:

• Store reconstituted material in the refrigerator at 2 to 8 C, away from direct light.
• Wipe the vial stopper with an alcohol swab before drawing from it, and label the vial with the date it was mixed.
• A refrigerated in-use window of roughly 4 weeks is commonly cited for reconstituted material.
• Discard the solution if it becomes cloudy or discolored, or if you see visible particles or floaters.

Related reading

• Amycretin
• ARA-290
• Cagrilintide
• How Reconstitution Works
• How Long Does a Reconstituted Vial Last?

Tools and supplies

• peptide calculator
• Bacteriostatic Water 30 ml
• Gansulin Metal Reusable Pen
• 3 ml Glass Cartridges (10-pack)
• Complete Starter Kit

Reminder: research and educational reference only. Preppin Peppers sells hardware and materials, not peptides. Not medical, dosing, or health advice, not evaluated by the FDA, and not intended for human or animal use.

Frequently asked questions

What is ACE-031 (ramatercept) and how does it work mechanistically?

ACE-031 is a soluble ActRIIB-IgG1 fusion protein that acts as a ligand trap, sequestering myostatin and other TGF-beta superfamily ligands before they bind cell-surface receptors, thereby modulating muscle-growth signaling pathways.

Why was ACE-031 clinical development discontinued?

Trials were halted after participants experienced vascular side effects, nosebleeds, telangiectasias, and gum bleeding, attributed to off-target inhibition of BMP9, a protein required for blood vessel homeostasis.

What is ACE-031's regulatory and WADA doping status?

ACE-031 has no FDA approval or marketing authorization. It is prohibited at all times under WADA Prohibited List section S4.3, which covers myostatin inhibitors and activin receptor type II inhibitors.

More in our bacteriostatic water and diluents collection.

What the research community gets wrong about ACE-031 (ramatercept)

• It is not a peptide. ACE-031 is a large fusion protein (an ActRIIB piece joined to an antibody fragment). Catalogs list it next to short peptides, but at the bench it behaves like a big, fragile protein and is far easier to damage than a small peptide.
• It does not trap only myostatin. People call it a myostatin blocker, but the same decoy also grabs other proteins in the TGF-beta family, including activin and BMP9. That wider reach is what showed up as blood vessel effects (nosebleeds, small dilated vessels, gum bleeding) in the human studies.
• Do not mix it like a small peptide. Hard shaking and foaming can make the protein clump together (aggregation), which ruins the vial. Aim the liquid at the inside wall and let the powder dissolve on its own, which can take several minutes.
• Bacteriostatic water is not automatically the best diluent. The benzyl alcohol preservative in it can lower stability for some large proteins, so the specific product's own documentation should decide which liquid to use, not habit.
• It is not interchangeable with other ActRII traps. ACE-031 is not the same molecule as luspatercept or other activin-receptor decoys. The receptor version and the mix of proteins each one catches differ, so handling notes for one do not carry over to another.

From our bench: If you have reconstituted an ActRIIB-IgG1 fusion like ACE-031, we want your real notes. When you aimed the diluent at the vial wall and let it stand, how long did the powder take to fully dissolve, and did the finished solution look clear or slightly opalescent (that faint pearly haze)? Send your bench observations, along with your diluent, vial size, and storage temperature, and we may add them here with credit.

Sources

1. Bacteriostatic Water for Injection, USP , FDA/DailyMed label (0.9% benzyl alcohol)
2. Duerkop et al., Biotechnol J 2018 , Impact of Cavitation, High Shear Stress and Air/Liquid Interfaces on Protein Aggregation
3. Sigma-Aldrich (Merck) , Handling and Storage Guidelines for Peptides and Proteins
4. Campbell C, et al. Myostatin inhibitor ACE-031 treatment of ambulatory boys with Duchenne muscular dystrophy: a randomized, placebo-controlled clinical trial. Muscle Nerve. 2017 (PubMed 27462804)
5. Attie KM, et al. A single ascending-dose study of muscle regulator ACE-031 in healthy volunteers. Muscle Nerve. 2013 (PubMed 23169607)
6. ACE-031, a soluble activin type IIB receptor, increases muscle mass and strength in the common marmoset (Callithrix jacchus). PLoS One, 2026 (PMC12904423)