IGF-1 is a peptide consisting of 70 amino acids with a molecular weight of 7649 Da. IGF-1 has an A and B chain connected by disulfide bonds, like insulin, which is how it gets its name. The structural similarity to insulin explains the ability of IGF-1 to bind (with low affinity) to the insulin receptor. IGF-1 is secreted by many tissues and the secretory site seems to determine its actions. Most IGF-1
is secreted by the liver and is transported to other tissues, acting as an endocrine hormone. IGF-1 is also secreted by other tissues, including cartilaginous cells, and acts locally as a paracrine hormone.
Most of the IGF-1 produced by the liver is secreted for its proliferative and growth effects. Lower IGF-1 and growth hormone are often associated with excess body fat. IGF-1 and other proteins in the IGF family are growth factors that stimulate the proliferation and survival of various cell types including muscle, bone, and cartilage tissue. IGF-1 plays an important role in childhood growth and continues to have anabolic effects in adults. A synthetic analog of IGF-1, mecasermin is commercially available and is used for the treatment of growth failure. Therapeutic administration of IGF-1 is associated with reversing insulin sensitivity, reducing weight and increasing metabolic expenditure as well as potential reversal of degeneration of spinal cord motor neuron axons in certain peripheral neuropathies.
IGF-1 LR3 has a modified amino acid sequence compared to biological IGF-1. It has an additionally arginine at amino acid position 2. By making this change, it gives the molecule higher potency and a much longer half-life. For this reason, it is commonly used as long-acting version for the same therapeutic reasons as the IGF-1.