Research Peptide · For laboratory research use only
Also known as Long R3 IGF-1, LR3-IGF-1
IGF-1 LR3 (Long R3 IGF-I, LR3IGF-I) is a recombinant analogue of human insulin-like growth factor I. It carries an N-terminal extension made up of the first 11 residues of methionyl porcine growth hormone followed by Val-Asn, and arginine in place of glutamic acid at position 3 of the IGF-I sequence, giving 83 residues in total1.
The analogue was engineered in Adelaide in the early 1990s to bind poorly to IGF-binding proteins (IGFBPs), and most of the published research dates from that period: cell culture potency assays, rat models of catabolism and gut growth, and plasma clearance and binding studies1,2,3,4,5.
As described in the research literature
As described in the research literature, the defining property of LR3IGF-I is markedly reduced binding to IGFBPs, together with somewhat weaker binding to the type 1 IGF receptor than native IGF-I1,2. In L6 rat myoblasts the Long IGF-I analogues were more potent than IGF-I in stimulating protein and DNA synthesis and inhibiting protein breakdown, whereas in chicken embryo fibroblasts, which secrete no detectable IGFBPs, LR3IGF-I was less potent than IGF-I; the authors attributed the gain in potency to reduced IGFBP interaction1.
Plasma studies are consistent with this account. Labelled LR3IGF-I circulated mainly as free peptide in rat plasma and was cleared faster than IGF-I3, and its binding to plasma IGFBPs varied between species, being weakest in the rat4. In L6 myogenic cells, recombinant porcine IGFBP-3 suppressed proliferation stimulated by both IGF-I and LR3IGF-I, but did not suppress LR3IGF-I-stimulated differentiation6.
What published studies have examined
Protein synthesis, DNA synthesis and protein breakdown were compared across IGF-I, des(1-3)IGF-I and the Long IGF-I analogues in L6 myoblasts, H35 hepatoma cells and chicken embryo fibroblasts1. Later work examined proliferation and differentiation of L6 cells in the presence of IGFBP-36.
In dexamethasone-treated rats, body weight, nitrogen retention, muscle protein synthesis and breakdown and organ weights were compared across IGF-I, des(1-3)IGF-I and LR3IGF-I2. Small intestinal epithelial proliferation, crypt length and thymidine labelling were examined in short-term rat studies5.
Plasma clearance and tissue distribution of radiolabelled IGF-I and LR3IGF-I were measured in virgin and pregnant rats3. Association with plasma binding proteins was compared in rat, sheep, pig, human and chicken plasma4.
A doping-control case report identified His-tagged Long-R3-IGF-I in a seized vial using immunoaffinity purification, high-resolution mass spectrometry and immunoassay7.
Sources [7]
Novel recombinant fusion protein analogues of insulin-like growth factor (IGF)-I indicate the relative importance of IGF-binding protein and receptor binding for enhanced biological potency.
Francis GL, Ross M, Ballard FJ, et al. Journal of Molecular Endocrinology, 1992.
Insulin-like growth factor-I (IGF-I) and especially IGF-I variants are anabolic in dexamethasone-treated rats.
Tomas FM, Knowles SE, Owens PC, et al. The Biochemical Journal, 1992.
Plasma clearance and tissue distribution of labelled insulin-like growth factor-I (IGF-I) and an analogue LR3IGF-I in pregnant rats.
Bastian SE, Walton PE, Wallace JC, et al. The Journal of Endocrinology, 1993.
Differences in the association of insulin-like growth factor-I (IGF-I) and IGF-I variants with rat, sheep, pig, human and chicken plasma-binding proteins.
Lord AP, Bastian SE, Read LC, et al. The Journal of Endocrinology, 1994.
Administration of insulin-like growth factor-I (IGF-I) peptides for three days stimulates proliferation of the small intestinal epithelium in rats.
Steeb CB, Trahair JF, Read LC Gut, 1995.
Effect of recombinant porcine IGFBP-3 on IGF-I and long-R3-IGF-I-stimulated proliferation and differentiation of L6 myogenic cells.
Xi G, Kamanga-Sollo E, Pampusch MS, et al. Journal of Cellular Physiology, 2004.
Detection of His-tagged Long-R³-IGF-I in a black market product.
Kohler M, Thomas A, Walpurgis K, et al. Growth Hormone & IGF Research, 2010.
This page is provided for research and educational reference only. It does not constitute medical advice, dosing guidance, or a recommendation for use. All compounds are strictly for laboratory and in-vitro research purposes.