IGF-1 LR3 (Long R3 IGF-I, also written LR3IGF-I) is a modified form of human insulin-like growth factor I. It keeps the 70-amino-acid IGF-I sequence with one substitution, arginine in place of glutami...
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Certificate of Analysis included with every order.
Technical Specifications
Purity
≥98%
Form
Lyophilized Powder
Storage
-20°C
About IGF-1 LR3
IGF-1 LR3 (Long R3 IGF-I, also written LR3IGF-I) is a modified form of human insulin-like growth factor I. It keeps the 70-amino-acid IGF-I sequence with one substitution, arginine in place of glutamic acid at position 3, and adds an N-terminal extension peptide derived from the first 11 amino acids of methionyl porcine growth hormone, joined by a Val-Asn linker.[1][11] Pepitiva supplies IGF-1 LR3 as a lyophilized powder (1 mg vials, ≥98% purity) for in vitro and preclinical research.
Why it was made
Native IGF-I circulates bound to a family of six IGF-binding proteins (IGFBPs), which hold it with high affinity and can inhibit its action.[10] IGF-1 LR3 was designed in the early 1990s as a research reagent that binds these proteins very poorly: IGF-I has roughly 1000-fold higher affinity than LR3IGF-I for IGFBP-3 and IGFBP-4.[1][3] That makes it a tool for separating receptor effects from binding-protein effects in cell culture and animal models.
Regulatory status
IGF-1 LR3 is not an approved medicine for human or veterinary use; it was developed and is used as a laboratory reagent, and its effects in humans have not been described.[1][8][9] A recombinant form of native human IGF-I (mecasermin) is a separate, approved drug.[12]
For research use only. Not for human consumption.
Quality & Storage
≥98% purity. Lyophilized Powder. Storage: -20°C. For research purposes only.
Mechanism of Action
Receptor binding versus binding-protein escape
IGF-1 LR3 acts through the type 1 IGF receptor, but it does not bind that receptor better than IGF-I. In one study it bound the type 1 receptor about 3-fold less well than IGF-I, and Arg3 analogues bound slightly less well than IGF-I to the receptor on L6 myoblasts while binding IGFBP-2 very poorly.[2][4] Its higher potency in most systems comes from reduced IGFBP binding, not from stronger receptor binding.[1][2]
Potency depends on the binding proteins present
Cells that secrete IGFBPs: in L6 rat myoblasts the Long IGF-I analogues were more potent than IGF-I at stimulating protein and DNA synthesis and inhibiting protein breakdown; LR3IGF-I was 5- to 10-fold more potent.[1][3]
Cells without detectable IGFBPs: in chicken embryo fibroblasts, LR3IGF-I was less potent than IGF-I.[1]
Faster clearance, not a longer half-life
Because it associates poorly with plasma IGFBPs, LR3IGF-I was removed from the blood of rats much more rapidly than IGF-I; in pregnant rats, where IGFBP levels are markedly reduced, IGF-I clearance became almost as rapid as that of LR3IGF-I.[3] Higher potency in vivo therefore reflects greater free availability to tissues, not prolonged circulation.
Research Applications
Preclinical findings
Catabolic state in rats (1992): in dexamethasone-treated rats, LR3IGF-I and des(1-3)IGF-I were about 2.5-fold more potent than IGF-I at restoring body weight and nitrogen retention, and the IGF peptides increased gut weight by up to 45%.[4]
Growth in normal rats (1993): over 14 days LR3IGF-I increased weight gain, nitrogen retention and food conversion efficiency at a substantially lower dose than IGF-I, while body proportions were maintained.[5]
Glucose lowering in pigs and marmosets (1997): IGF-I variants with weak IGFBP binding were 2- to 3-fold more potent than IGF-I at lowering plasma glucose and suppressed glucose for longer; LR3IGF-I was the only variant more potent than IGF-I at lowering plasma amino acids.[6]
Alzheimer model mice (2025): 7 months of intranasal LR3-IGF-1 in male 5XFAD mice improved body composition and some features of cortical amyloid pathology, but did not preserve behavior or memory; in BV-2 microglial cells it enhanced uptake of amyloid-β 1-42.[7]
Laboratory research applications
IGF/IGFBP biology: comparing native IGF-I with a ligand that escapes binding-protein control.[1][10]
Myoblast protein and DNA synthesis assays: the L6 model in which the analogue was first characterized.[1]
Glucose and amino acid metabolism: acute hypoglycaemic and metabolic responses in animal models.[6]
Analytical and anti-doping methods: mass-spectrometric identification of Long R3 IGF-I and its variants in seized products.[8]
GH/IGF-1 axis comparisons: IGF-1 LR3 acts downstream of growth hormone, whereas sermorelin and tesamorelin act on the GHRH receptor and ipamorelin on the ghrelin receptor to release the animal's own growth hormone.
Reported adverse effects of unregulated GH/IGF-1-axis peptides include dysglycaemia and other endocrine-metabolic disturbances, and mitogenic concerns remain unproven but biologically plausible.[9] This product is sold for laboratory research only.
Storage & Handling Guidelines
Proper storage and handling are essential to maintain peptide integrity and ensure reliable research results. All Pepitiva Biolabs peptides are supplied as lyophilized (freeze-dried) powder, which provides excellent long-term stability when stored correctly. Store lyophilized peptides at -20°C for long-term storage or 2-8°C for short-term use. Once reconstituted, peptide solutions should be stored at 2-8°C and used within the timeframe specified in the product documentation. Always use sterile bacteriostatic water for reconstitution and handle peptides in a clean laboratory environment to prevent contamination. Avoid repeated freeze-thaw cycles, as thermal stress can cause peptide degradation and loss of biological activity.
Quality Control & Certification
This product is manufactured under strict quality control protocols and has been verified through comprehensive analytical testing. Each batch undergoes reverse-phase HPLC analysis for purity determination and electrospray ionization mass spectrometry (ESI-MS) for molecular identity confirmation. A detailed Certificate of Analysis (COA) is available for download, documenting purity percentage, molecular weight verification, appearance, and recommended storage conditions. Pepitiva Biolabs maintains batch-level traceability from synthesis through delivery, ensuring complete transparency and quality assurance for your research.
Frequently Asked Questions
What is IGF-1 LR3?
A modified human IGF-I with arginine instead of glutamic acid at position 3 and an N-terminal extension peptide taken from porcine growth hormone. The changes make it bind IGF-binding proteins very poorly.
What is the difference between IGF-1 LR3 and IGF-1?
Native IGF-I (70 amino acids) is held by IGF-binding proteins; IGF-1 LR3 binds them about 1000-fold less strongly. It is not a stronger receptor binder: it binds the type 1 IGF receptor somewhat less well than IGF-I.
Does IGF-1 LR3 have a longer half-life than IGF-1?
Not in the rat clearance studies. LR3IGF-I was cleared from plasma much more rapidly than IGF-I, because it does not form complexes with plasma IGF-binding proteins. Its higher potency comes from greater availability to tissues.
What does LR3 stand for?
Long R3: "Long" refers to the N-terminal extension peptide and "R3" to the arginine (R) substituted at position 3 of the IGF-I sequence.
Is IGF-1 LR3 FDA approved?
No. IGF-1 LR3 was developed as a laboratory reagent and is not approved for human or veterinary use. Recombinant native IGF-I (mecasermin) is a different, approved drug.
How should IGF-1 LR3 be stored?
Keep the lyophilized powder at −20 °C, protected from light and moisture.
Is this product approved for human use?
No. This product is intended exclusively for in vitro scientific research and laboratory use. It is not approved for human or veterinary use, not intended for diagnostic or therapeutic purposes, and should not be administered to humans or animals under any circumstances.
How do I reconstitute this peptide?
Add sterile bacteriostatic water slowly to the vial, directing the stream against the glass wall rather than directly onto the lyophilized powder. Gently swirl the vial until the powder is fully dissolved — do not shake vigorously. The recommended reconstitution volume depends on your desired concentration. Refer to the product documentation for specific guidance.
Can I get a Certificate of Analysis (COA)?
Yes. A Certificate of Analysis is included with every order and is also available for download from the product page. The COA documents HPLC purity, mass spectrometry identity confirmation, batch number, production date, and storage recommendations.
Scientific References
Francis GL, Ross M, Ballard FJ, et al. 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. J Mol Endocrinol. 1992;8(3):213-223. PubMed
King R, Wells JR, Krieg P, et al. Production and characterization of recombinant insulin-like growth factor-I (IGF-I) and potent analogues of IGF-I, with Gly or Arg substituted for Glu3, following their expression in Escherichia coli as fusion proteins. J Mol Endocrinol. 1992;8(1):29-41. PubMed
Ballard FJ, Walton PE, Bastian S, et al. Effects of interactions between IGFBPs and IGFs on the plasma clearance and in vivo biological activities of IGFs and IGF analogs. Growth Regul. 1993;3(1):40-44. PubMed
Tomas FM, Knowles SE, Owens PC, et al. Insulin-like growth factor-I (IGF-I) and especially IGF-I variants are anabolic in dexamethasone-treated rats. Biochem J. 1992;282 Pt 1:91-97. PubMed
Tomas FM, Knowles SE, Chandler CS, et al. Anabolic effects of insulin-like growth factor-I (IGF-I) and an IGF-I variant in normal female rats. J Endocrinol. 1993;137(3):413-421. PubMed
Tomas FM, Walton PE, Dunshea FR, Ballard FJ. IGF-I variants which bind poorly to IGF-binding proteins show more potent and prolonged hypoglycaemic action than native IGF-I in pigs and marmoset monkeys. J Endocrinol. 1997;155(2):377-386. PubMed
Engel MG, Narayan S, Cui MH, et al. Intranasal long R3 insulin-like growth factor-1 treatment promotes amyloid plaque remodeling in cerebral cortex but fails to preserve cognitive function in male 5XFAD mice. J Alzheimers Dis. 2025;103(1):113-126. PubMed
Kohler M, Thomas A, Walpurgis K, et al. Detection of His-tagged Long-R³-IGF-I in a black market product. Growth Horm IGF Res. 2010;20(5):386-390. PubMed
Dominikowski A, Rękoś Z, Olejarz M, et al. The emerging landscape of performance-enhancing peptides modulating GH-IGF1 axis: bridging the gap between clinical evidence and patient self-administration. Front Endocrinol (Lausanne). 2026;17:1822475. PubMed
Baxter RC. Insulin-like growth factor (IGF)-binding proteins: interactions with IGFs and intrinsic bioactivities. Am J Physiol Endocrinol Metab. 2000;278(6):E967-E976. PubMed
U.S. Food and Drug Administration. Drugs@FDA: application 021839 (mecasermin recombinant); original approval August 30, 2005. Source
Sources are peer-reviewed publications indexed in PubMed and trial registrations on ClinicalTrials.gov. Each citation was checked against its PubMed record.
For research use only. Not for human consumption.
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