IGF-1 LR3 (Long Arginine 3 Insulin-like Growth Factor-1), also known as LR3-IGF-1, is a synthetic, modified analog of human insulin-like growth factor 1 (IGF-1). Native IGF-1 is a hormone primarily produced in the liver in response to growth hormone (GH) and plays key roles in growth, cell proliferation, protein synthesis, and metabolism.1
Structure and Modifications
IGF-1 LR3 consists of 83 amino acids (compared to 70 in native IGF-1). The key changes are:
- Substitution of arginine for glutamic acid at position 3 (“Arg3”).
- Addition of a 13-amino-acid extension at the N-terminus (sequence: MFPAMPLLSLFVN).
These modifications drastically reduce its binding affinity to insulin-like growth factor binding proteins (IGFBPs), which normally limit IGF-1’s activity. As a result, it has greater bioavailability, improved metabolic stability, approximately 3 times higher potency than native IGF-1, and a significantly longer half-life of about 20–30 hours (versus ~12–15 hours or less for IGF-1). It retains strong agonist activity at the IGF-1 receptor.1
