IGF-1 LR3 : données probantes, mécanisme et limites

IGF-1 LR3, also called Long R3 IGF-I, is a synthetic analog of human insulin-like growth factor 1. It has an extension at one end of the molecule and a substitution at position 3. These changes greatly reduce its binding to IGF binding proteins, which normally carry and regulate IGF-1 in the blood.

It is a different molecule from mecasermin, the recombinant IGF-1 medicine approved in the United States as INCRELEX. Findings for one cannot be transferred to the other.

Because IGF-1 LR3 binds the carrier proteins poorly, more of it may stay free to act on tissues. In rats, IGF-1 analogs that bind these proteins poorly were substantially more potent than IGF-1 at stimulating growth. This is preclinical evidence.

Other species did not respond the same way. The authors of the pig experiments suggest that in older animals, these analogs may suppress the body's own growth hormone secretion through feedback. No human study has tested the mechanism.

In guinea pigs, a week-long infusion increased the relative weight of the gut, kidneys, spleen, and adrenal glands without increasing overall growth. It also lowered blood levels of IGF-I, IGF-II, and IGF binding proteins.

In older pigs, long-term administration under the skin reduced growth and food intake, while newborn pigs grew faster. In the same pig experiments, IGF analogs given into a vein lowered blood glucose, with the strongest effect from analogs that bound the carrier proteins least.

No human efficacy trial exists. The only human-sample work in the library is an anti-doping method that detects IGF-1 LR3 and its breakdown products in plasma.

Human safety is unknown because no human safety study has been published in the cited record. The animal findings raise questions rather than answer them: growth of some organs without overall growth, lowered blood glucose, and suppressed natural IGF levels.

Products sold outside an approved channel have no regulatory check on identity or purity. These unknowns cannot be resolved by an educational profile.

IGF-1 LR3 is not approved as a therapeutic by FDA or Health Canada. WADA prohibits IGF-1 and its synthetic analogues at all times, and anti-doping laboratories have developed methods to detect IGF-1 LR3 and its metabolites in plasma.