IGF-1-LR3

IGF-1 LR3 is an engineered version of insulin-like growth factor 1, the protein through which much of growth hormone's activity is actually carried out. Growth hormone reaching the liver prompts IGF-1 production, and IGF-1 is what then acts on tissue. This compound is the downstream messenger itself rather than anything that prompts its release.

Two changes separate it from natural IGF-1. The third amino acid is replaced by arginine, and thirteen extra residues are added to the front of the chain. Both serve one purpose: to weaken the protein's grip on the binding proteins that normally hold it. In the bloodstream, almost all IGF-1 is bound to carriers and inactive, released only where and when it is needed.

Loosening that grip leaves far more of the molecule free and active, and extends its working life substantially. This is why the analogue is a standard reagent in laboratory cell culture and bioprocessing, where a reliable, long-lasting growth signal in the medium is the requirement. It is among the few compounds in this catalogue whose main use is genuinely as a laboratory material.

• Binding proteins as a control system: Six IGF-binding proteins govern how much IGF-1 is available at any moment. An analogue that escapes them is the cleanest way to ask what that control system actually contributes.

• A dependable culture reagent: Cells grown outside the body need growth signals supplied in the medium. Because it resists the binding proteins and persists, it gives a steadier stimulus than natural IGF-1, and is used routinely on that basis.

• The receptor, studied directly: The IGF-1 receptor is closely related to the insulin receptor and the two overlap in signalling. Work on that relationship needs a stable, potent ligand, which is one of this molecule's standard roles.

• Downstream, not upstream: Unlike the releasing peptides in this category, it does not ask the pituitary for anything. It allows the effects of the end signal to be separated from the machinery that normally produces it.

Most hormones travel free in blood. IGF-1 does not: around ninety-nine per cent of it is held by binding proteins, which act as both a reservoir and a brake. Holding the hormone prevents it acting everywhere at once, extends how long the supply lasts, and allows release to be targeted. The consequence is that the amount of IGF-1 present says little about how much is actually working.

The modifications in this analogue reduce how firmly those binding proteins can hold it. Less bound means more free, and more free means a stronger and longer signal at the receptor from the same quantity. The engineering did not make the molecule more potent at its receptor — it removed the restraint that normally limits access to it.

At the receptor, IGF-1 activates pathways governing cell growth, protein synthesis and survival. These are the same pathways insulin acts through, which is why the two systems are studied together and why a tool that persists is useful: signalling of this kind is measured over hours, and a natural ligand cleared within minutes makes that difficult to observe.

As a laboratory reagent the evidence is essentially complete. The modifications, the reduced binding-protein affinity, the extended half-life and the receptor activity are all characterised, and the analogue is manufactured commercially for cell culture on the strength of it. In that setting it does exactly what it is documented to do.

Its evidence base is as a laboratory reagent, where the modifications, the reduced binding-protein affinity, the extended half-life and the receptor activity are all characterised and it is manufactured commercially for cell culture on that basis. There is no approved use in whole organisms, and it is supplied for laboratory research only. In culture it does exactly what it is documented to do, which is why it is a standard component of defined media.

The releasing peptides sit upstream of this one. CJC-1295 and Ipamorelin, supplied together as CJC-1295 + Ipamorelin, prompt the pituitary to release growth hormone, which prompts the liver to produce IGF-1. This compound is the end of that chain, supplied directly.

That distinction is the useful one. A study asking what IGF-1 does uses IGF-1; a study asking what the axis does when it is stimulated uses a releasing peptide, and the answers are not interchangeable.