What Is IGF-1 LR3 Peptide?
IGF-1 LR3 peptide, also known as Long R3 IGF-I, is a synthetic analogue of insulin-like growth factor-I (IGF-I). It is a modified form of the naturally occurring IGF-I peptide and belongs to the insulin-like growth factor family.
The Long R3 form contains two defining structural modifications. An arginine substitution at position 3 and a 13-amino-acid extension at the N-terminus. These changes distinguish Long R3 IGF-I from native IGF-I at the molecular level.
Research Overview Table
Chemical and Molecular Characteristics
IGF-1 LR3 is a modified analogue of IGF-I. It contains an arginine substitution for glutamate at position 3 and a 13-amino-acid extension at the N-terminus. Published structural studies describe the extension as hydrophobic.
Structural analysis found that the main IGF-I domain closely resembles native IGF-I, while the N-terminal extension shows greater conformational flexibility.
Certificates:
Mechanism of Action Under Investigation
Long R3 IGF-I has been studied in relation to the type 1 insulin-like growth factor receptor (IGF-1R). Cell experiments found that Long R3 IGF-I activates IGF-1R, with researchers measuring receptor phosphorylation after exposure to the analogue. Studies also examined the effect of IGF-binding protein-3 on this response and found that IGFBP-3 reduced Long R3 IGF-I-induced IGF-1R phosphorylation by binding the analogue outside the cell.
Researchers have also examined signaling events downstream of IGF-1R. One study found that Long R3 IGF-I activated IRS-2 in cultured cells. Another study using fetal sheep cardiomyocytes found that blocking either PI3K or ERK prevented the increase in BrdU uptake produced by Long R3 IGF-I, linking those pathways to the response measured in that experimental model.
Researchers have investigated these events through receptor phosphorylation assays, immunoprecipitation, Western blotting, ligand-binding experiments, and pathway-specific inhibitors.
Scientific Research Context
Researchers study IGF-1 LR3 as a modified IGF-I analogue in laboratory research. The published literature includes in vitro research, preclinical animal studies, and limited human-related research. Evidence has progressed from laboratory and preclinical investigation to limited human research, but the overall evidence base remains predominantly preclinical. Human research remains limited and does not establish a clinical research program for IGF-1 LR3.
IGF-1 LR3 Biology and Biological Pathways
Primary Biological Function
IGF-1 LR3 is studied within the biology of the IGF-I system, which regulates cellular growth, differentiation, protein turnover, and survival. Researchers use Long R3 IGF-I to examine these processes because its modified structure changes its interaction with IGF-binding proteins while retaining activity within the IGF-I system.
Relevant Metabolic or Signaling Pathways
The main pathways associated with IGF-I biology include PI3K/AKT and Ras/MAPK signaling. These pathways connect IGF-1R activity with cellular processes such as protein metabolism, growth, differentiation, and survival. Long R3 IGF-I research has examined PI3K and ERK signaling in experimental cells, including fetal sheep cardiomyocytes. Researchers investigate these pathways to define how IGF-I signaling relates to cellular responses.
Tissue-Specific Biology
Researchers have investigated IGF-1 LR3 in skeletal muscle, intestinal tissue, mammary tissue, cardiac tissue, and mammary arteries. Animal studies have also examined the gut, kidneys, adrenal glands, and spleen.
Experimental Biomarkers
Researchers measure IGF-related biomarkers to characterize biological responses to Long R3 IGF-I. These include IGF-I, IGF-II, IGFBP-3, insulin, growth hormone, phosphorylated AKT, ERK, and IRS proteins. Researchers select these markers based on the biological system under investigation and use them to characterize changes within the IGF signaling environment.
Laboratory Investigation Methods
Published IGF-1 LR3 studies use cell culture, ligand-binding assays, receptor phosphorylation assays, immunoprecipitation, Western blotting, and RT-PCR. These methods measure receptor phosphorylation, ligand interactions, protein signaling, and gene expression. Animal models also appear in the published IGF-1 LR3 literature.
Experimental Models Used in Published Research
Published IGF-1 LR3 research includes cultured myogenic cells, rat intestinal models, guinea pigs, pigs, and isolated mammary arteries. The models range from isolated cells and tissues to intact animals. Each has limitations related to its experimental setting and its ability to represent human biology.
Cell-Based Models
Porcine embryonic myogenic cells and L6 myogenic cells are represented in the published Long R3 IGF-I literature. The main limitation of these cultured models is their isolation from the other tissues, organs, and circulating factors present in an intact organism.
Intestinal Models
Rats are the intestinal animal model reported in published Long R3 IGF-I studies. The main limitation is species specificity, because rat intestinal physiology does not fully represent human intestinal biology.
Guinea Pig Models
Female guinea pigs appear in published Long R3 IGF-I research as whole-animal models. The main limitation is species specific physiology, which limits direct translation of observations from guinea pigs to human biology.
Pig Models
Finisher pigs are the whole-animal model reported in published Long R3 IGF-I studies. The main limitation is the physiological difference between pigs and humans, which limits how directly observations from this model apply to human biology.
Mammary Artery Models
Isolated bovine and ovine mammary arteries represent the tissue model reported in Long R3 IGF-I research. The main limitation is that isolated artery preparations do not reproduce the broader interactions and whole-body regulation present in an intact animal.
IGF-1 LR3 Published Research
Intestinal Growth and Function
Published research has examined Long R3 IGF-I in relation to intestinal growth and intestinal glucose absorption. Studies investigated changes in intestinal mucosal growth and the absorption of 3-O-methyl-D-glucose. Research also examined intestinal development in newborn animals receiving dietary Long R3 IGF-I.
Organ Growth
Long R3 IGF-I has been studied in relation to organ growth. The published study found higher fractional weights of the adrenal glands, gut, kidneys, and spleen, while overall body weight gain remained unchanged.
Endocrine and Metabolic Responses
Studies have examined Long R3 IGF-I in relation to circulating IGF-I, IGF-II, IGF-binding proteins, glucose, insulin, and other metabolic measurements. Research has also compared responses associated with Long R3 IGF-I and growth hormone administration.
Cellular Growth
Cell-based research has investigated Long R3 IGF-I in relation to cell proliferation and IGF-binding protein activity. Published studies examined how IGFBP-5 affected Long R3 IGF-I-associated proliferation in porcine embryonic myogenic cells. Other work examined Long R3 IGF-I responses in cultured human fibroblasts in relation to endogenous IGF-binding protein production.
Mammary Biology
Lactation and mammary gland function have also been examined in studies of Long R3 IGF-I. One study assessed lactation capacity and changes in mammary tissue following exposure to the analogue.
Vascular Biology
Published research has also examined Long R3 IGF-I in relation to mammary artery vascular responses. Experimental work investigated vascular responses to the analogue and examined the role of endothelial nitric oxide production in those responses.
Limitations of Current Research
Evidence Is Predominantly Preclinical
The Long R3 IGF-I literature is made up mainly of cell, tissue, and animal studies. Published research includes work in cultured cells, rodents, livestock, and other experimental systems. A human plasma study has also examined Long R3 IGF-I analytically, but it did not provide clinical evidence.
Human Clinical Evidence
Human clinical evidence for Long R3 IGF-I is limited. Published human research has focused mainly on detecting Long R3 IGF-I and its metabolites rather than evaluating the compound in controlled clinical studies.
Species Differences
The Long R3 IGF-I literature includes findings that differ across animal species. For example, one study reported increased fractional organ weights, while another reported reduced growth and lower circulating IGF-I, IGFBP-3 and growth hormone concentrations. These differences limit direct comparison and make cross species interpretation difficult.
Study Design Limitations
The studies differ in species, exposure periods, experimental conditions and research endpoints. Some use isolated cells or tissues, while others use intact animals. Because the study designs vary, findings from one study cannot always be compared directly with findings from another.
Independent Replication
The available literature does not provide enough closely matched studies to establish consistent replication across every major research question. Several areas rely on individual experimental studies with specific models and conditions. This makes it difficult to determine whether individual observations remain consistent across different laboratories and experimental settings.
Long-Term Evidence
Long-term evidence remains limited relative to the broader research literature. However, it is not accurate to describe all studies as short-term. A recent study followed male 5XFAD mice for seven months while investigating intranasal Long R3 IGF-I. Longer-duration research therefore exists, but it remains limited compared with the amount of short-duration experimental work.
Analytical Documentation
HPLC can assess chromatographic purity and help separate Long R3 IGF-I from related substances. LC-MS adds molecular-mass information and can support compound identification.
NMR can provide structural information for suitable protein samples, although it does not need to be treated as a routine test for every Long R3 IGF-I preparation. A Certificate of Analysis (CoA) provides batch-specific analytical results and reported specifications, such as identity and purity.
Together, these records help document the material used in laboratory research. They verify product identity and quality, not biological performance.
Storage and Laboratory Handling
Store IGF-1 LR3 at 2–8°C, as specified on the Certificate of Analysis. Keep the material properly sealed during storage and handling to reduce contamination risk.
Qualified laboratory personnel should handle the material using appropriate laboratory practices and clean handling procedures. Maintain the stated storage conditions throughout laboratory storage.
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