IGF-1 LR3

Also known as: Long R3 IGF-1, Long Arg3 IGF-1

**Mechanism of Action** IGF-1 LR3 (Long R3 IGF-1) is a synthetic analog of insulin-like growth factor-1 engineered with an arginine substitution at position 3 and a 13-amino-acid N-terminal extension. This modification significantly reduces binding to insulin-like growth factor-binding proteins (IGFBPs), thereby prolonging its half-life and enhancing bioavailability. The peptide acts primarily by activating the IGF-1 receptor (IGF-1R), a tyrosine kinase receptor that initiates downstream signaling cascades, including the PI3K/Akt and MAPK/ERK pathways. These pathways promote protein synthesis, satellite cell activation, and myonuclear accretion, leading to muscle hypertrophy and reduced catabolism. **Key Research Findings** Preclinical studies demonstrate that IGF-1 LR3 induces greater myotube hypertrophy and proliferation in vitro compared to native IGF-1, attributed to sustained receptor activation. In rodent models, systemic administration increases lean body mass, muscle fiber cross-sectional area, and functional strength, with effects observed in both skeletal and cardiac muscle. However, prolonged activation of IGF-1R raises concerns regarding mitogenic potential, as elevated IGF-1 signaling is linked to accelerated tumor growth in certain cancer models. Limited human data exist, with most evidence derived from animal studies or anecdotal reports. **Clinical Relevance** IGF-1 LR3 remains an experimental compound with no approved therapeutic indications. Its potent anabolic effects have attracted interest for conditions involving muscle wasting (e.g., cachexia, sarcopenia), but safety concerns—including hypoglycemia, acromegalic-like effects, and potential carcinogenicity—preclude clinical use. Regulatory status varies, but it is not approved for human consumption by major health authorities. For research purposes only — not medical advice.

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