IGF-1 LR3

What Is IGF-1 LR3?

IGF-1 LR3 (Long R3 IGF-1) is a synthetic, modified form of insulin-like growth factor 1, the downstream mediator of most of growth hormone's tissue-growth effects. Two changes distinguish it from native IGF-1: an arginine substitution for glutamic acid at position 3 (R3) and a 13-amino-acid N-terminal extension (Long), bringing the total length to 83 residues against 70 for the endogenous peptide. Both modifications sharply reduce binding to the six IGF binding proteins that normally sequester circulating IGF-1 and inactivate it within minutes.

The result is a molecule that escapes IGFBP capture, remains free in circulation, and engages IGF-1 receptors for roughly 20 to 30 hours instead of about 10 minutes, with approximately 2- to 3-fold greater potency per molecule than native IGF-1 in the published cell assays. Downstream, IGF-1 receptor activation drives the PI3K/AKT/mTOR pathway that governs muscle protein synthesis, MAPK signalling for satellite cell proliferation, and GLUT4 translocation for glucose uptake. The aggressive glucose uptake into muscle is also the source of the hypoglycaemia signal reported in the literature. IGF-1 LR3 was originally developed as a cell-culture reagent and has no human clinical development history.