IGF-1 LR3

Engineered 83-amino-acid analog of insulin-like growth factor 1 with reduced binding-protein affinity, used in growth research.

Overview

IGF-1 LR3 (Long Arginine-3 IGF-1) is an engineered analog of human insulin-like growth factor 1 produced by recombinant technology. It carries an arginine-for-glutamate substitution at position 3 and an N-terminal extension, changes that markedly reduce its binding to the IGF-binding proteins that normally buffer native IGF-1. The result is a longer-acting, more bioavailable IGF-1 receptor agonist in research systems. It is used widely in cell-culture work and in animal growth studies, and it circulates in research-peptide markets as a lyophilized product.

Mechanism

IGF-1 LR3 activates the IGF-1 receptor, triggering the same anabolic and mitogenic signaling cascades as native IGF-1, including PI3K-Akt and MAPK pathways. Because it binds IGF-binding proteins poorly, a larger fraction of the administered dose is available to signal at the receptor, which is the basis for its high potency and extended action in experimental models.

Dosing

In research settings IGF-1 LR3 is given by subcutaneous injection, commonly once daily in rodent protocols at microgram-range doses specified in the individual studies. It is also a standard supplement in serum-free cell-culture media. No approved human use exists; dosing must come from the primary literature.

Expected Effects

increased lean-mass signals and reduced protein breakdown in animal models
support of cell proliferation in culture systems
elevated anabolic signaling relative to native IGF-1 at equivalent doses in experimental systems
effects on glucose handling, reflecting IGF-1 receptor crosstalk with insulin signaling

Side Effects & Tolerability

Published human safety data are essentially absent for LR3 specifically. By analogy with IGF-1 biology, concerns include hypoglycemia, fluid retention, and mitogenic effects on tissues, so long-term exposure studies would be required before any human research use could be justified.

Storage

Lyophilized IGF-1 LR3 should be stored desiccated, protected from light, and kept frozen at -20 deg C or below. Reconstituted solutions should be refrigerated at 2-8 deg C and used within a short period, avoiding repeated freeze-thaw cycles.