IGF1-LR3

Detection of His-tagged Long-R³-IGF-I in a black market product.

Kohler M, Thomas A, Walpurgis K, Terlouw K, Schänzer W, Thevis M., Growth Hormone & IGF Research, 2010;20(5):386-390

published

Material identity not established. The material this case report identified was Long-R³-IGF-I carrying a His₆ tag on its C-terminus, joined by a Leu-Glu linker — a tagged version of the molecule, not the untagged analogue. It is recorded here because the vial was sold as this compound; the finding is about what was in that vial.

• A vial obtained from the black market was analysed by immunoaffinity purification, nano-UPLC and high-resolution, high-accuracy mass spectrometry of the intact and trypsinated substance, and by an enzyme-linked immunosorbent assay. The mass spectra characterised the protein as Long-R³-IGF-I with a His₆ tag attached to the C terminus by the linker amino acids Leu-Glu.
• The authors state that His tags are commonly added to proteins during synthesis to allow convenient and complete purification and are removed enzymatically when attached at the N terminus; that the effects of His-tagged Long-R³-IGF-I in humans have not been elucidated or described; and that the product may be a by-product of biochemical studies rather than material made for people. They also note that black-market products frequently do not contain the substances they declare.

Solution structure and backbone dynamics of long-[Arg(3)]insulin-like growth factor-I.

Laajoki LG, Francis GL, Wallace JC, Carver JA, Keniry MA., The Journal of Biological Chemistry, 2000;275(14):10009-10015

published

• Reports the solution structure of ¹⁵N-labelled Long-[Arg3]-IGF-I — described as IGF-I modified by a Glu3 to Arg mutation and a 13-amino-acid extension appended to the N terminus — determined by high-resolution NMR and restrained molecular dynamics to a precision of 0.82 ± 0.28 Å root mean square deviation for the backbone heavy atoms in the three alpha-helices, and 3.5 ± 0.9 Å for all backbone heavy atoms excluding the 8 N-terminal and 8 C-terminal residues.
• The IGF-I domain of the structure is reported as consistent with earlier studies of IGF-I, with minor changes remote from the N terminus; the major variations occur at the N terminus, with a substantial reorientation of the N-terminal three residues of the IGF-I domain. The authors interpret these results in terms of the analogue's lower binding affinity for insulin-like growth factor-binding proteins.
• Backbone dynamics, studied by ¹⁵N nuclear spin relaxation and the heteronuclear nuclear Overhauser enhancement, indicated a considerable degree of flexibility even within the alpha-helices, with an average (¹H)¹⁵N NOE of 0.55 for those regions; the largest enhancements were in the helices, lower values in the C-domain loop separating helix 1 from helix 2, and negative values in the N-terminal extension and at the C terminus.

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, Milner SJ, Senn C, McNeil KA, Wallace JC, King R, Wells JR., Journal of Molecular Endocrinology, 1992;8(3):213-223

published

• Describes an Escherichia coli expression system for IGF-I fusion peptide analogues, among them [Met1]-pGH(1-11)-Val-Asn-[Arg3]-IGF-I, referred to as Long [Arg3]-IGF-I: the human IGF-I sequence with Glu-3 replaced by arginine, preceded by the first 11 amino acids of methionyl porcine growth hormone and Val-Asn. The authors report that the hydrophobic N-terminal extension appears to help the analogue fold correctly compared with normal-length IGFs.
• In L6 rat myoblasts, all the analogues were more potent than authentic IGF-I at stimulating protein and DNA synthesis and inhibiting protein breakdown. In cell lines secreting IGF-binding proteins into the medium, the order of potency was Long [Arg3]-IGF-I and des(1-3)IGF-I, then Long [Gly3]-IGF-I, then Long IGF-I, then IGF-I.
• In chicken embryo fibroblasts, a cell line that does not secrete detectable IGF-binding proteins into the medium, Long [Arg3]-IGF-I was less potent than IGF-I. In H35 hepatoma cells, where the IGFs act through the insulin receptor, the Long IGF-I analogues kept a similar potency relative to IGF-I to the one seen in the L6 myoblasts. The authors state that the increased potency of N-terminal analogues is due to changes in the degree of their interactions with IGF-binding proteins.

IGF-1 LR3 does not promote growth in late-gestation growth-restricted fetal sheep.

White A, Stremming J, Wesolowski SR, Al-Juboori SI, Dobrinskikh E, Limesand SW, Brown LD, Rozance PJ., American Journal of Physiology. Endocrinology and Metabolism, 2025;328(1):E116-E125

published

• Fetal body weights, insulin, glucose, oxygen and glucose-stimulated insulin secretion were not different between the two groups.
• Amino acid concentrations decreased in the IGF-1 LR3 group (baseline versus final individual means comparison P = 0.0232) but not in the vehicle group (P = 0.3866). The authors report this as a reduction in circulating amino acids, notably branched-chain amino acids, and conclude that the one-week course did not increase growth in growth-restricted fetuses.

Engel et al., 2025 (title withheld on this site; see the publication record)

Engel MG, Narayan S, Cui MH, Branch CA, Zhang X, Gandy SE, Ehrlich M, Huffman DM., Journal of Alzheimer's Disease, 2025;103(1):113-126

published

• In male 5XFAD mice it did not significantly alter cognitive symptoms, as assessed by multiple assays. The authors conclude that it fails to preserve aspects of behaviour or memory and that these data do not support it as a monotherapy.
• In cortex, the reported changes in pathology were a reduction in filamentous plaques and an increase in inert plaques, corresponding with a reduction in low molecular weight amyloid-β oligomers.

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, Ballard FJ., The Journal of Endocrinology, 1993;138(2):327-336

published

• IGF-I was cleared from plasma more rapidly in pregnant than in virgin rats: metabolic clearance rate 2.88 ± 0.12 versus 0.90 ± 0.05 ml/min per kg. LR3IGF-I was cleared more rapidly than IGF-I, and at similar rates in both groups: 9.19 ± 0.15 ml/min per kg in pregnant and 9.84 ± 0.28 in virgin animals.
• The majority of LR3IGF-I was detected as free peptide, while in virgin rat plasma labelled IGF-I was mainly associated with the 150 kDa complex and in pregnant rat plasma with lower molecular weight binding proteins of approximately 30 to 50 kDa. More LR3IGF-I tracer than IGF-I tracer was detected in kidneys, ovaries and adrenals of virgin rats and in the ovaries and adrenals of pregnant rats; less was detected in placenta, fetus and fetal plasma.