Follistatin-344

What it is

Follistatin-344 is a recombinant form of the naturally occurring follistatin protein, which binds and neutralizes myostatin and related TGF-beta family growth factors. Myostatin is a protein that limits skeletal muscle growth. Most of the muscle data comes from animal gene-therapy and transgenic models rather than injected protein.

Human clinical evidence for injected follistatin is essentially absent, and whether subcutaneous injection produces meaningful systemic activity is unresolved. In the PeptidesAI encyclopedia it is categorized under growth hormone and healing.

How it's thought to work

Follistatin-344 binds myostatin (GDF-8) and related ligands such as activin, preventing them from signalling through the ActRIIB receptor. Removing that brake on muscle growth increases muscle mass in animal models.

In a mouse study, binding of myostatin to the ActRIIB receptor was inhibited by follistatin, and transgenic mice engineered to make follistatin in skeletal muscle showed large increases in muscle mass comparable to myostatin knockout mice.

What the research says

Animal gene-therapy and transgenic studies show large increases in muscle mass. There are no human clinical trials of injected follistatin protein for muscle growth, and it is not FDA-approved.

In a phase 1/2a trial in six people with Becker muscular dystrophy, follistatin delivered by gene therapy (an adeno-associated virus vector carrying the FS344 form, injected into the thigh muscles) was reported to improve the six-minute walk distance in four of the six. This was gene therapy, not an injected protein.

Reported side effects

Human safety data for injected follistatin is essentially absent. Broad interference with the TGF-beta/activin family of signaling proteins is a theoretical concern given those pathways' roles in tissue regulation.

Reconstitution

Follistatin-344 is supplied as a lyophilized (freeze-dried) powder and is typically reconstituted with bacteriostatic (BAC) water before use. It commonly comes in 1 mg vials. The amount of peptide in the vial is fixed; the water added only changes how concentrated the solution is.

Worked example. A 1 mg vial is 1,000 mcg. Reconstituted with 1 mL of BAC water, that works out to 1,000 mcg ÷ 1 mL = 1,000 mcg/mL. On a U-100 insulin syringe, where each unit is 0.01 mL, each unit holds 1,000 × 0.01 = 10 mcg. Use the peptide reconstitution calculator to work out the concentration and units for any vial size and water volume.

Important notes

Follistatin-344 has very limited human data. It is not FDA-approved and is listed as prohibited by the World Anti-Doping Agency (WADA).

Sources

1. Regulation of myostatin activity and muscle growth. Lee SJ et al. Proceedings of the National Academy of Sciences, 2001. Preclinical
2. A phase 1/2a follistatin gene therapy trial for becker muscular dystrophy. Mendell JR et al. Molecular Therapy, 2015. Human trial

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Frequently asked questions

These questions cover the same ground as the sections above, in a shorter format.

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