Receptor Grade IGF-1 LR3 (0.1mg & 1mg)

IGF-1 LR3 (Long R3 IGF-1, Insulin-Like Growth Factor-1 Long Arg3, 100mcg): A Recombinant 83-Amino-Acid Analogue of Human Insulin-Like Growth Factor 1 (IGF-1, Somatomedin C) with an N-Terminal 13-Amino-Acid Extension Peptide and an Arginine Substitution at Position 3 (Glutamic Acid → Arginine), Designed for Enhanced Potency, Extended Half-Life, and Reduced IGF-Binding Protein (IGFBP) Affinity — the 100mcg Vial Format for Investigational Research in Muscle Hypertrophy, Fat Loss, Tissue Repair, Recovery, Anti-Aging, and Metabolic Health

IGF-1 LR3 (also known as Long R3 IGF-1, Long Arg3 IGF-1, or IGF-1 Long R3) is a recombinant 83-amino-acid analogue of human insulin-like growth factor 1 (IGF-1, also known as somatomedin C), with a molecular weight of approximately 9.11 kDa (9,111 Daltons). IGF-1 LR3 was engineered by GroPep (an Australian biotechnology company, later acquired by Sigma-Aldrich) in the 1990s as a long-acting, high-potency analogue of native IGF-1, specifically designed to overcome two key limitations of native IGF-1 for research and potential therapeutic use: (1) short half-life — native IGF-1 has a very short circulating half-life (~10-20 minutes) due to rapid renal clearance and proteolytic degradation; (2) high affinity for IGF-binding proteins (IGFBPs) — native IGF-1 binds with high affinity to a family of six IGF-binding proteins (IGFBP-1 through IGFBP-6, with IGFBP-3 being the most abundant, binding ~75-80% of circulating IGF-1 in a ternary complex with IGFBP-3 and the acid-labile subunit [ALS]), which regulate IGF-1 bioavailability, half-life, and tissue access, and can both inhibit and potentiate IGF-1 actions depending on context. To address these limitations, IGF-1 LR3 incorporates two key structural modifications to the native 70-amino-acid IGF-1 molecule: (1) an N-terminal 13-amino-acid extension peptide (the "Long" or "L" in LR3) — a 13-residue peptide (with the sequence MFPAMPSSLSPLT, or similar variant depending on the specific construct, often containing a methionine for translation initiation and additional residues) added to the N-terminus of IGF-1, which increases the molecular size from 70 to 83 amino acids, reducing renal clearance (larger molecules are filtered less efficiently by the glomerulus) and increasing circulating half-life; (2) an arginine substitution at position 3 (the "R3" in LR3) — the native glutamic acid (Glu, E) at position 3 of IGF-1 is replaced with arginine (Arg, R), which significantly reduces the peptide's affinity for IGF-binding proteins (IGFBPs), particularly IGFBP-1, IGFBP-2, and IGFBP-3, because the glutamic acid at position 3 is a key residue involved in IGFBP binding (the negatively charged glutamate forms important electrostatic interactions with positively charged residues in the IGFBP N-terminal binding domain; replacing it with positively charged arginine disrupts these interactions and reduces binding affinity by approximately 100-1000 fold compared to native IGF-1). These two modifications together give IGF-1 LR3 its characteristic properties: increased potency (approximately 2-3 times more potent than native IGF-1 in many in vitro and in vivo assays, due to reduced IGFBP binding which increases the bioavailable "free" fraction of the peptide that can access and activate IGF-1 receptors), extended half-life (approximately 6-12 hours in rodents and larger animals, compared to ~10-20 minutes for native IGF-1, due to reduced renal clearance from the larger molecular size and reduced IGFBP-mediated clearance), and reduced IGFBP affinity (which means more of the peptide is in the biologically active "free" form, less is sequestered by IGFBPs, and the peptide can more readily access tissues and activate receptors — although it also means less of the IGFBP-mediated transport and tissue-targeting functions, and potentially altered pharmacodynamics). IGF-1 LR3 exerts its biological effects primarily by binding to and activating the IGF-1 receptor (IGF-1R, also known as CD221) — a transmembrane receptor tyrosine kinase (RTK) of the insulin receptor family, which also includes the insulin receptor (IR), IGF-2 receptor (IGF-2R, a mannose-6-phosphate receptor that does not signal like IGF-1R), and the insulin receptor-related receptor (IRR). The IGF-1R is a heterotetrameric receptor consisting of two extracellular α-subunits (which contain the ligand-binding domain) and two transmembrane β-subunits (which contain the intracellular tyrosine kinase domain), linked by disulfide bonds (the α-subunits are disulfide-linked to each other and to the β-subunits). When IGF-1 (or IGF-1 LR3) binds to the extracellular α-subunits, it induces a conformational change that activates the intracellular tyrosine kinase domains of the β-subunits, leading to trans-autophosphorylation of specific tyrosine residues in the β-subunit (including Tyr1131, Tyr1135, Tyr1136 in the activation loop, and Tyr950 in the juxtamembrane region), which creates docking sites for downstream signaling molecules containing SH2 (Src homology 2) or PTB (phosphotyrosine binding) domains. The two major downstream signaling pathways activated by IGF-1R are: (1) PI3K/Akt pathway (phosphoinositide 3-kinase / protein kinase B, the primary pathway for most of IGF-1's metabolic and cell survival effects) — the insulin receptor substrate (IRS) proteins (IRS-1, IRS-2, particularly IRS-1) are recruited to the activated IGF-1R (via PTB domain binding to phosphorylated Tyr950 in the receptor juxtamembrane region) and become phosphorylated on multiple tyrosine residues by the receptor kinase; phosphorylated IRS proteins then recruit PI3K (via its p85 regulatory subunit SH2 domains), which activates the p110 catalytic subunit of PI3K; activated PI3K phosphorylates phosphatidylinositol 4,5-bisphosphate (PIP2) at the cell membrane to generate phosphatidylinositol 3,4,5-trisphosphate (PIP3); PIP3 recruits Akt (protein kinase B, also known as PKB) and PDK1 (phosphoinositide-dependent kinase 1) to the cell membrane via their PH (pleckstrin homology) domains, where PDK1 phosphorylates Akt at Thr308 and mTORC2 (mammalian target of rapamycin complex 2) phosphorylates Akt at Ser473, fully activating Akt; activated Akt then phosphorylates numerous downstream targets including: (a) mTORC1 (mammalian target of rapamycin complex 1, via phosphorylation and inhibition of TSC2 [tuberin, a GTPase-activating protein for Rheb, a small GTPase that activates mTORC1] and PRAS40 [proline-rich Akt substrate of 40 kDa, an inhibitor of mTORC1]) — mTORC1 is a master regulator of cell growth and protein synthesis, activating p70S6K (ribosomal protein S6 kinase, which phosphorylates ribosomal protein S6, increasing translation of mRNAs with 5' terminal oligopyrimidine [TOP] tracts, including ribosomal proteins and translation factors) and 4E-BP1 (eukaryotic initiation factor 4E-binding protein 1, which when phosphorylated releases eIF4E, allowing cap-dependent translation initiation) — together these dramatically increase protein synthesis and cell growth; (b) GSK-3β (glycogen synthase kinase 3 beta, phosphorylated and inhibited by Akt) — inhibition of GSK-3β increases glycogen synthesis (via activation of glycogen synthase) and affects multiple other pathways including Wnt signaling, protein synthesis, and cell survival; (c) FOXO transcription factors (FOXO1, FOXO3a, FOXO4, phosphorylated by Akt, which causes their nuclear export and cytoplasmic retention, inhibiting their transcriptional activity) — FOXO factors regulate genes involved in apoptosis (FasL, Bim, TRAIL), cell cycle arrest (p27Kip1, p21Cip1), oxidative stress resistance (SOD, catalase, MnSOD), and metabolism (gluconeogenesis genes); inhibition of FOXO by Akt therefore promotes cell survival, cell cycle progression, and reduces oxidative stress resistance (a complex trade-off); (d) Bad (a pro-apoptotic Bcl-2 family member, phosphorylated by Akt, which causes it to dissociate from Bcl-2/Bcl-xL and be sequestered in the cytosol by 14-3-3 proteins, preventing it from promoting apoptosis at the mitochondria); (e) caspase-9 (phosphorylated and inhibited by Akt, preventing activation of the caspase cascade); (f) eNOS (endothelial nitric oxide synthase, phosphorylated and activated by Akt at Ser1177, increasing nitric oxide [NO] production, promoting vasodilation, endothelial function, and angiogenesis); (g) AS160 (Akt substrate of 160 kDa, a Rab GTPase-activating protein, phosphorylated and inhibited by Akt, which promotes GLUT4 [glucose transporter 4] translocation to the cell membrane, increasing glucose uptake in muscle and adipose tissue); (2) MAPK/ERK pathway (mitogen-activated protein kinase / extracellular signal-regulated kinase, the primary pathway for IGF-1's mitogenic [cell proliferation] and differentiation effects) — activated IGF-1R can recruit Grb2 (growth factor receptor-bound protein 2, an adaptor protein with SH2 and SH3 domains) either directly (via phosphorylated receptor tyrosines) or indirectly via IRS proteins; Grb2 recruits SOS (Son of Sevenless, a guanine nucleotide exchange factor [GEF] for Ras) to the cell membrane, where SOS activates Ras (a small GTPase, converting it from the inactive GDP-bound form to the active GTP-bound form); activated Ras recruits Raf (a serine/threonine kinase, particularly Raf-1/c-Raf, B-Raf, or A-Raf) to the cell membrane and activates it; Raf phosphorylates and activates MEK1/2 (MAPK/ERK kinase, dual-specificity kinases); MEK1/2 phosphorylate and activate ERK1/2 (extracellular signal-regulated kinases 1 and 2, also known as p44/p42 MAPK); activated ERK1/2 translocate to the nucleus and phosphorylate numerous transcription factors including Elk-1, c-Myc, c-Fos, c-Jun, AP-1, and others, regulating genes involved in cell proliferation, differentiation, survival, and metabolism; ERK also phosphorylates and activates p90RSK (ribosomal S6 kinase, which can further activate transcription factors and protein synthesis machinery). In addition to these two major pathways, IGF-1R can activate other signaling pathways including: (3) JAK/STAT pathway (janus kinase / signal transducer and activator of transcription, particularly STAT3 and STAT5, which can be activated by IGF-1R in some cell types, contributing to cell proliferation and survival); (4) PLCγ/PKC pathway (phospholipase C gamma / protein kinase C, recruited to activated IGF-1R via SH2 domains, generating IP3 and DAG, leading to calcium mobilization and PKC activation, contributing to mitogenic effects); (5) FAK/paxillin pathway (focal adhesion kinase, involved in cell adhesion, migration, and cytoskeletal reorganization, which can be activated by IGF-1R in some cell types, contributing to cell migration and invasion). The biological effects of IGF-1 LR3 (mediated through IGF-1R activation and these downstream signaling pathways) are diverse and include: (1) Potent anabolic / muscle hypertrophic effects — IGF-1 is one of the most potent naturally occurring anabolic factors, stimulating muscle protein synthesis (via PI3K/Akt/mTORC1 pathway, activating p70S6K and inhibiting 4E-BP1, increasing translation initiation and elongation), inhibiting muscle protein breakdown (via inhibition of the ubiquitin-proteasome system and autophagy, through Akt-mediated inhibition of FOXO transcription factors which regulate atrogenes [atrophy-related genes] including MuRF1 [muscle RING finger 1] and Atrogin-1/MAFbx [muscle atrophy F-box]), promoting muscle satellite cell activation and proliferation (satellite cells are muscle stem cells responsible for muscle growth and repair — IGF-1 stimulates their activation, proliferation, and differentiation into myoblasts, which fuse with existing muscle fibers or form new fibers, contributing to hypertrophy and hyperplasia), and increasing lean body mass — these effects are the primary reason for IGF-1 LR3's popularity in bodybuilding and performance enhancement research; (2) Fat loss / lipolytic effects — IGF-1 promotes fat breakdown (lipolysis) by increasing hormone-sensitive lipase (HSL) activity and increasing β-adrenergic sensitivity in adipose tissue, and it inhibits lipogenesis (de novo fat synthesis) through multiple mechanisms; IGF-1 also increases glucose uptake and utilization, which can reduce the amount of glucose available for fat synthesis; these effects lead to reduced fat mass, particularly visceral fat, and improved body composition (increased lean mass, decreased fat mass); (3) Tissue repair and regeneration — IGF-1 plays a critical role in tissue repair and regeneration after injury: it promotes wound healing (stimulating fibroblast proliferation, collagen synthesis, angiogenesis, and re-epithelialization), promotes muscle repair (after exercise-induced muscle damage or injury, via satellite cell activation and increased protein synthesis), promotes bone repair and fracture healing (stimulating osteoblast proliferation and differentiation, increasing bone matrix deposition, promoting cartilage formation in the fracture callus), promotes nerve regeneration (stimulating Schwann cell proliferation, axonal growth, and nerve regeneration after peripheral nerve injury), promotes tendon/ligament repair (stimulating fibroblast proliferation and collagen synthesis in tendons and ligaments), and promotes cartilage repair (stimulating chondrocyte proliferation and matrix synthesis, potentially beneficial for osteoarthritis); (4) Anti-apoptotic / cell survival effects — IGF-1 is a potent survival factor for many cell types, inhibiting apoptosis through multiple mechanisms: PI3K/Akt-mediated phosphorylation and inhibition of Bad (preventing mitochondrial apoptosis), phosphorylation and inhibition of caspase-9 (preventing caspase cascade activation), inhibition of FOXO transcription factors (reducing expression of pro-apoptotic genes like FasL, Bim), increased expression of anti-apoptotic Bcl-2 family proteins (Bcl-2, Bcl-xL, Mcl-1), and inhibition of the mitochondrial permeability transition pore (mPTP); these anti-apoptotic effects are important for tissue protection after injury (e.g., myocardial infarction, stroke, traumatic brain injury) and for cell survival in general; (5) Metabolic effects — IGF-1 has insulin-like metabolic effects (hence its name "insulin-like growth factor"): it increases glucose uptake in muscle and adipose tissue (via GLUT4 translocation, through the PI3K/Akt/AS160 pathway), increases glycogen synthesis (via Akt-mediated inhibition of GSK-3β, activating glycogen synthase), inhibits hepatic gluconeogenesis (reduces glucose production by the liver, through FOXO inhibition and other mechanisms), increases amino acid uptake and protein synthesis, and has complex effects on lipid metabolism (increased lipolysis, reduced lipogenesis); importantly, IGF-1's hypoglycemic effects are mediated primarily through the IGF-1R (although at high concentrations IGF-1 can also cross-activate the insulin receptor [IR], contributing to hypoglycemia); because IGF-1 LR3 has reduced IGFBP binding, it may have more pronounced metabolic effects per unit dose compared to native IGF-1 (more free peptide available to activate receptors in metabolic tissues); (6) Cardiovascular effects — IGF-1 has important effects on the cardiovascular system: it promotes cardiomyocyte survival and growth (physiological cardiac hypertrophy, as seen in exercise training, as opposed to pathological hypertrophy), protects cardiomyocytes from apoptosis after ischemia-reperfusion injury (reducing infarct size, improving cardiac function), improves endothelial function (increasing nitric oxide production via eNOS activation, promoting vasodilation, reducing endothelial dysfunction), promotes angiogenesis (stimulating endothelial cell proliferation, migration, and tube formation, via VEGF and other angiogenic factors), and has beneficial effects on the vasculature (reducing atherosclerosis in some models, improving vascular compliance); however, excessive IGF-1 signaling has also been implicated in some cardiovascular pathologies (e.g., cardiac hypertrophy in acromegaly, potential promotion of certain vascular diseases); (7) Neuroprotective and cognitive effects — IGF-1 and IGF-1R are widely expressed in the brain, and IGF-1 plays important roles in neurodevelopment, neuroprotection, and cognitive function: it promotes neuronal survival (inhibiting apoptosis in neurons exposed to various insults), promotes neurogenesis (particularly in the hippocampus, the dentate gyrus subgranular zone, and the subventricular zone — IGF-1 stimulates neural stem cell proliferation and differentiation), promotes synaptogenesis and synaptic plasticity (important for learning and memory), has neuroprotective effects in models of stroke (reduced infarct volume, improved neurological function), traumatic brain injury, Alzheimer's disease (reduced Aβ accumulation, reduced tau pathology, improved cognition in some models), Parkinson's disease (protected dopaminergic neurons), and other neurodegenerative conditions, and has been associated with improved cognitive function in some studies (although the relationship between IGF-1 and cognition is complex, with both positive and negative associations reported depending on context, age, and health status); (8) Bone and connective tissue effects — IGF-1 is a critical regulator of bone growth and remodeling: it stimulates osteoblast proliferation and differentiation (increasing bone formation), increases osteoclast activity (increasing bone resorption, as part of normal bone remodeling — the net effect depends on context, but IGF-1 generally increases bone turnover and can increase bone mass when formation exceeds resorption), stimulates chondrocyte proliferation in the epiphyseal growth plates (important for longitudinal bone growth in children — this is the primary mechanism by which growth hormone [GH] promotes linear growth, via GH-stimulated hepatic and local IGF-1 production), stimulates collagen synthesis in bone, cartilage, tendons, and ligaments, and plays a role in fracture healing; (9) Anti-aging / longevity effects (complex and controversial) — the relationship between IGF-1 signaling and aging is complex and context-dependent: on one hand, reduced IGF-1 signaling (e.g., in dwarf mice with GH/IGF-1 deficiency, or in dietary restriction which reduces IGF-1) has been associated with extended lifespan in multiple species (C. elegans, Drosophila, mice), and the insulin/IGF-1 signaling (IIS) pathway is one of the most well-conserved and well-studied longevity pathways (reduced IIS extends lifespan in virtually all species tested); on the other hand, IGF-1 has many beneficial effects that could promote healthy aging: muscle maintenance (preventing sarcopenia), bone maintenance (preventing osteoporosis), neuroprotection (preventing cognitive decline), tissue repair, metabolic health, and anti-apoptotic effects; in humans, the relationship between circulating IGF-1 levels and longevity is U-shaped or complex — both very low and very high IGF-1 levels may be associated with increased mortality, with moderate levels being optimal; IGF-1 levels decline with age (somatopause, the age-related decline in GH/IGF-1), and this decline has been linked to some features of aging (sarcopenia, osteoporosis, reduced skin thickness, reduced energy); however, the use of IGF-1 or IGF-1 analogues as anti-aging interventions remains controversial and is not recommended by most medical authorities due to potential risks (cancer, hypoglycemia, cardiovascular effects, etc.); (10) Cancer-related effects (important safety consideration) — IGF-1 is a potent mitogen (cell proliferation promoter) and survival factor for many cell types, and there is substantial evidence that the IGF-1 signaling pathway plays a role in cancer development and progression: elevated circulating IGF-1 levels have been associated with increased risk of several cancers in epidemiological studies (particularly prostate, breast, colorectal, and lung cancers, although the evidence is mixed and varies by cancer type and population); IGF-1R is overexpressed in many cancers, and IGF-1 signaling can promote cancer cell proliferation, survival (anti-apoptotic), invasion, metastasis, angiogenesis, and resistance to chemotherapy and radiation therapy; this is a major safety concern for the use of IGF-1 or IGF-1 analogues (including IGF-1 LR3), particularly at supraphysiological doses, and individuals with active malignancy or a history of certain cancers should generally avoid IGF-1 supplementation; this is also why IGF-1 is not recommended as an anti-aging or "wellness" intervention by most medical authorities. The 100mcg vial format of research-grade IGF-1 LR3 provides a convenient, pre-measured dose suitable for a range of investigational applications. Typical research doses of IGF-1 LR3 range from 20-100 mcg per administration (subcutaneous or intramuscular), often administered once daily or every other day (due to its extended half-life of ~6-12 hours, less frequent dosing is needed compared to native IGF-1), with a 100mcg vial providing 1-5 doses at typical doses. For in vitro cell culture studies, IGF-1 LR3 is typically used at concentrations ranging from 1 ng/mL to 1 μg/mL (with 10-100 ng/mL being commonly used for cell proliferation/survival assays), and a 100mcg vial (9.11 kDa) provides approximately 10.98 nanomoles of peptide, sufficient for numerous cell culture experiments. Reconstitution: add 0.5-2 mL of bacteriostatic water (or sterile water for in vitro use / IV administration) to yield 200-50 mcg/mL; for example, adding 1 mL yields 100 mcg/mL, so a 20 mcg dose = 0.2 mL, 50 mcg = 0.5 mL, 100 mcg = 1.0 mL. Reconstituted IGF-1 LR3 is stable for 14-30 days when refrigerated at 4°C and protected from light; the lyophilized powder is stable for 24 months from manufacture when stored at -20°C, protected from light and moisture. The safety profile of IGF-1 LR3 requires careful consideration, as it is a potent metabolic and mitogenic peptide with potential side effects, particularly at supraphysiological doses. Common side effects include: (1) Hypoglycemia — IGF-1 has insulin-like glucose-lowering effects, and hypoglycemia (low blood sugar) is one of the most common and potentially serious side effects, particularly at higher doses or in individuals with low body fat or who are fasting; symptoms include shakiness, sweating, dizziness, confusion, irritability, hunger, blurred vision, and in severe cases, loss of consciousness or seizures; blood glucose monitoring is recommended, particularly when starting therapy or adjusting doses, and individuals with diabetes or hypoglycemia disorders should use extreme caution (insulin/oral hypoglycemic doses may need significant adjustment); (2) Joint pain / arthralgia — IGF-1 can cause joint pain, particularly in the hands, wrists, shoulders, and knees, possibly due to tissue growth, fluid retention, or effects on cartilage/bone metabolism; this is usually mild to moderate and may resolve with dose reduction or continued use; (3) Edema / fluid retention — IGF-1 can cause sodium and water retention, leading to peripheral edema (swelling of hands, feet, ankles), facial puffiness, and weight gain (from water retention); this is more common at higher doses and at the initiation of therapy; (4) Carpal tunnel syndrome / paresthesia — fluid retention and tissue swelling can compress the median nerve at the wrist, causing carpal tunnel syndrome (numbness, tingling, pain, weakness in the hands and fingers, particularly at night); this is more common at higher doses and in individuals with pre-existing carpal tunnel issues; dose reduction usually resolves symptoms; (5) Headache — particularly at the initiation of therapy or at higher doses, possibly due to vasodilatory effects or changes in intracranial pressure; usually mild and transient; (6) Nausea / gastrointestinal effects — mild nausea, stomach discomfort, or changes in appetite may occur, particularly at the initiation of therapy; usually mild and transient; (7) Fatigue / lethargy — some individuals report fatigue or tiredness, particularly if hypoglycemia occurs or during the initial adaptation period; (8) Skin changes — increased skin thickness, oiliness, acne (particularly in individuals prone to acne), and increased sweating may occur; (9) Gynecomastia — in men, IGF-1 (particularly at higher doses, and often in combination with other anabolic hormones) can contribute to gynecomastia (breast tissue enlargement), possibly through effects on sex hormone metabolism or direct effects on breast tissue; (10) Effects on the GH/IGF-1 axis — exogenous IGF-1 can suppress endogenous growth hormone (GH) secretion through negative feedback at the pituitary and hypothalamic levels (IGF-1 directly inhibits GH release from somatotrophs and stimulates somatostatin release from the hypothalamus); long-term high-dose use may lead to suppression of the GH/IGF-1 axis, although recovery typically occurs after discontinuation (the degree and duration of suppression depend on dose, duration, and individual factors); (11) Insulin resistance / glucose intolerance — paradoxically, while IGF-1 has acute insulin-like hypoglycemic effects, chronic high-dose IGF-1 use can lead to insulin resistance and glucose intolerance in some individuals (possibly through down-regulation of insulin receptors or post-receptor signaling, or through effects on body composition and metabolism); glucose monitoring is recommended; (12) Cancer risk (theoretical and controversial) — as discussed above, IGF-1 is a potent mitogen and survival factor, and elevated IGF-1 signaling has been associated with increased cancer risk and progression in some studies; this is a major safety concern, particularly for long-term or high-dose use, and individuals with active malignancy or a history of certain cancers should avoid IGF-1; (13) Cardiovascular effects — while IGF-1 can have beneficial cardiovascular effects at physiological levels (improved endothelial function, cardioprotection), excessive IGF-1 signaling (as in acromegaly) is associated with adverse cardiovascular effects including cardiac hypertrophy, hypertension, arrhythmias, and increased cardiovascular mortality; supraphysiological IGF-1 LR3 doses may have adverse cardiovascular effects, particularly with long-term use. Contraindications include: known hypersensitivity to IGF-1 LR3 or any component, active malignancy (active cancer — IGF-1 can theoretically stimulate tumor growth and progression), history of certain cancers (particularly prostate, breast, colorectal — use with extreme caution, if at all), diabetic retinopathy (proliferative or severe non-proliferative — IGF-1 can worsen retinal neovascularization), hypoglycemia disorders (increased risk of severe hypoglycemia), pregnancy and breastfeeding (insufficient safety data — IGF-1 plays a role in fetal development, but exogenous use during pregnancy is not recommended), and (for athletes) WADA prohibition — IGF-1 and its analogues (including IGF-1 LR3) are banned by the World Anti-Doping Agency (WADA) as peptide hormones/growth factors, prohibited both in-competition and out-of-competition. As of 2026, IGF-1 LR3 is NOT approved by the FDA or other major regulatory agencies for any clinical indication (native IGF-1 [mecasermin] is FDA-approved for severe primary IGF-1 deficiency, but IGF-1 LR3 is not an approved drug — it is a research chemical). The research-grade IGF-1 LR3 supplied by Amideworks is intended for laboratory and investigational use only, not for human consumption or therapeutic use^{[1][2][3][4][5][6][7][8][9][10]}.

The Science of IGF-1 LR3: Structure-Activity Relationships, IGFBP Biology, and the Complex Role of IGF-1 Signaling in Health, Disease, and Aging

IGF-1 LR3 represents a sophisticated example of rational protein engineering — a deliberately modified analogue of a native human growth factor, designed with specific structural changes to overcome known pharmacokinetic and pharmacodynamic limitations of the native molecule. To fully understand IGF-1 LR3, its properties, and its biological effects, it is essential to understand the native IGF-1 molecule, the IGF-binding protein (IGFBP) system that regulates IGF-1 bioavailability, the structural modifications that define LR3 and their functional consequences, and the complex and sometimes controversial role of IGF-1 signaling in health, disease, and aging. The native IGF-1 molecule (insulin-like growth factor 1, also known as somatomedin C) is a 70-amino-acid single-chain peptide with a molecular weight of approximately 7.65 kDa (7,649 Daltons), with significant structural homology to proinsulin (hence the name "insulin-like growth factor"). The mature IGF-1 peptide consists of four domains: B domain (residues 1-29, homologous to the insulin B chain), C domain (residues 30-41, analogous to the insulin C peptide — but unlike insulin, the C domain is NOT cleaved in mature IGF-1, so IGF-1 remains a single-chain peptide with the B, C, A, and D domains all connected), A domain (residues 42-62, homologous to the insulin A chain), and D domain (residues 63-70, an 8-amino-acid C-terminal extension not present in insulin). The structure is stabilized by three disulfide bonds (Cys6-Cys48, Cys18-Cys61, Cys47-Cys52 — note: the exact disulfide pairing may be described differently in different sources, but the three disulfide bonds are conserved and essential for structural integrity and receptor binding). IGF-1 is produced primarily in the liver (~75-80% of circulating IGF-1) in response to growth hormone (GH) stimulation — GH binds to GH receptors on hepatocytes, activating JAK2-STAT5 signaling, which strongly stimulates IGF-1 gene transcription and secretion. The remaining ~20-25% of IGF-1 is produced locally in various tissues (muscle, bone, cartilage, adipose, kidney, brain, etc.), where it acts in an autocrine (acting on the same cell that produced it) and paracrine (acting on neighboring cells) manner — this local IGF-1 production is also stimulated by GH and by other factors including exercise, nutrition, and local growth factors. The liver-derived endocrine IGF-1 and the locally produced autocrine/paracrine IGF-1 both contribute to IGF-1's biological effects, and their relative contributions vary by tissue and physiological context. Circulating IGF-1 levels are relatively stable (compared to the pulsatile GH secretion) and are used clinically as a marker of GH status/action (IGF-1 measurement is more reliable than random GH measurement for assessing GH deficiency or excess, because GH is secreted in pulses while IGF-1 is relatively stable throughout the day). The IGF-binding protein (IGFBP) system is a critical and complex regulatory system that controls IGF-1 bioavailability, half-life, tissue distribution, and biological actions. There are six well-characterized IGF-binding proteins (IGFBP-1 through IGFBP-6), all of which bind IGF-1 and IGF-2 with high affinity (in the nanomolar range, with Kd values typically ~0.1-1 nM for IGF-1), and they share a conserved structure with three domains: an N-terminal domain (containing the high-affinity IGF-binding site, with 12 conserved cysteines that form disulfide bonds), a central variable domain (which varies in length and sequence among IGFBPs, and contains sites for post-translational modifications including glycosylation, phosphorylation, and proteolysis), and a C-terminal domain (containing additional IGF-binding determinants and a thyroglobulin type-1 repeat motif, with 6 conserved cysteines). In the circulation, ~75-80% of IGF-1 is bound in a ternary complex consisting of IGF-1 + IGFBP-3 (the most abundant circulating IGFBP) + the acid-labile subunit (ALS, a ~85 kDa leucine-rich glycoprotein produced in the liver in response to GH, which binds to the C-terminal domain of IGFBP-3 but does not directly bind IGF-1). This ternary complex has a molecular weight of ~150 kDa, which is too large to cross the vascular endothelium (except in specialized fenestrated capillaries), so it serves as a circulating reservoir of IGF-1 that is confined to the intravascular space and has a long half-life (~12-15 hours for the ternary complex, compared to ~10-20 minutes for free IGF-1). The ternary complex also protects IGF-1 from proteolytic degradation and renal clearance, and it prevents excessive free IGF-1 from causing hypoglycemia (because only free IGF-1 can readily access tissues and activate receptors). A smaller fraction (~10-15%) of circulating IGF-1 is bound to IGFBP-3 or other IGFBPs in binary complexes (IGF + IGFBP, without ALS), which are smaller (~40-50 kDa) and can cross the endothelium to access tissues, serving as a transport form that delivers IGF-1 to tissues while still providing some protection from degradation and clearance. Only a very small fraction (~1-5%) of circulating IGF-1 is in the "free" (unbound) form at any given time, and this free fraction is generally considered to be the biologically active form that can readily access and activate IGF-1 receptors in tissues (although the binary complexes can also deliver IGF-1 to tissues, and IGFBPs can both inhibit and potentiate IGF-1 actions depending on the specific IGFBP, tissue, and context — some IGFBPs can potentiate IGF-1 actions by delivering it to tissues, protecting it from degradation, or even directly interacting with the IGF-1R to enhance signaling, while other IGFBPs or specific IGFBP fragments can have IGF-independent biological effects of their own). The IGFBP system is dynamically regulated: IGFBP proteases (including pregnancy-associated plasma protein-A [PAPP-A], which specifically cleaves IGFBP-4 and IGFBP-5, and other proteases) can cleave IGFBPs, reducing their affinity for IGF-1 and releasing free IGF-1 to activate receptors; IGFBP phosphorylation and glycosylation can affect IGF binding and tissue localization; and IGFBP expression is regulated by hormones (GH, insulin, glucocorticoids, sex steroids), nutrition, and local tissue factors. This complex IGFBP system provides a sophisticated mechanism for precisely regulating IGF-1 bioavailability and action in different tissues and physiological states, and it is a key reason why simply measuring total circulating IGF-1 does not always accurately reflect IGF-1 biological activity at the tissue level. The structural modifications in IGF-1 LR3 and their functional consequences: as described above, IGF-1 LR3 differs from native IGF-1 by two key modifications: (1) the N-terminal 13-amino-acid extension (the "Long" or "L"), and (2) the arginine substitution at position 3 (the "R3"). Let us examine each modification in detail: (1) The N-terminal 13-amino-acid extension ("Long"): This 13-residue peptide is added to the N-terminus (B domain N-terminus) of native IGF-1, increasing the total length from 70 to 83 amino acids and the molecular weight from ~7.65 kDa to ~9.11 kDa. The primary purpose of this extension is to increase molecular size to reduce renal clearance — the glomerular filtration barrier in the kidneys has a size cutoff of approximately 30-50 kDa (molecules smaller than this are filtered more efficiently, while larger molecules are retained in the circulation), so increasing the molecular size from 7.65 kDa to 9.11 kDa (while still well below the 30-50 kDa cutoff) provides a modest reduction in renal filtration rate, contributing to the extended half-life. Additionally, the N-terminal extension may affect the peptide's interaction with IGFBPs (although the primary IGFBP-binding determinant is the Arg3 substitution, as discussed below), its proteolytic stability (the extension may protect the N-terminus from aminopeptidase degradation), and its tissue distribution. It is important to note that the exact sequence of the 13-amino-acid extension may vary slightly among different commercial preparations and expression constructs, but it typically contains an N-terminal methionine (for translation initiation in recombinant expression systems) and additional residues; the specific sequence does not appear to be critical for function, as the extension primarily serves to increase molecular size and may be somewhat flexible/disordered. (2) The arginine substitution at position 3 ("R3", Glu3→Arg3): This is the more functionally significant modification. In native IGF-1, position 3 in the B domain is a glutamic acid (Glu, E, a negatively charged acidic amino acid). This glutamic acid at position 3 is a critical residue in the IGF-1/IGFBP interaction — it forms important electrostatic interactions (salt bridges and hydrogen bonds) with positively charged residues (arginine, lysine) in the N-terminal IGF-binding domain of IGFBPs. Specifically, structural studies (NMR and X-ray crystallography of IGF-1/IGFBP complexes) have shown that Glu3 of IGF-1 interacts with conserved residues in the IGFBP N-terminal domain (including residues in the "thyroglobulin type-1" motif and nearby basic residues), and that the negative charge of Glu3 is important for high-affinity IGFBP binding. By replacing the negatively charged glutamic acid with a positively charged arginine (Arg, R), the LR3 analogue introduces a charge reversal at this critical position, which disrupts the electrostatic interactions with IGFBPs and dramatically reduces IGFBP binding affinity — studies have shown that IGF-1 LR3 has approximately 100-1000 fold lower affinity for IGFBP-1, IGFBP-2, and IGFBP-3 compared to native IGF-1 (the exact fold reduction varies by IGFBP and study, but it is consistently very large). This reduced IGFBP affinity has several important functional consequences: (a) Increased bioavailable "free" fraction — because LR3 binds IGFBPs poorly, a much larger fraction of the administered peptide remains in the free (unbound) form, which is the form that can readily access tissues and activate IGF-1 receptors; this means that per unit mass, LR3 has more biologically active peptide available compared to native IGF-1 (which is largely sequestered by IGFBPs, particularly in the ternary complex); (b) Increased potency — due to the increased free fraction and improved tissue access, LR3 is approximately 2-3 times more potent than native IGF-1 in many in vitro and in vivo assays (e.g., cell proliferation, protein synthesis, glucose uptake); (c) Altered pharmacokinetics — while the reduced IGFBP binding increases free fraction and tissue access, it also means that LR3 does not benefit from the IGFBP-mediated protection from proteolytic degradation and renal clearance that native IGF-1 enjoys (particularly the long half-life conferred by the ternary complex); however, the N-terminal extension (increased molecular size) partially compensates for this by reducing renal clearance, and the net result is that LR3 has a longer half-life than free native IGF-1 (~6-12 hours vs ~10-20 minutes), although not as long as native IGF-1 in the ternary complex (~12-15 hours); (d) Reduced hypoglycemic risk per unit mass (relative to native IGF-1) — this is somewhat counterintuitive, but because LR3 binds IGFBPs poorly, it may have altered tissue distribution and glucose-lowering effects compared to native IGF-1; however, LR3 is still a potent activator of IGF-1R (and at high concentrations can cross-activate the insulin receptor), so hypoglycemia remains a significant side effect, particularly at higher doses; (e) Loss of IGFBP-mediated tissue targeting and regulatory functions — because LR3 does not bind IGFBPs well, it does not benefit from the IGFBP-mediated transport, tissue targeting, and local regulation that characterizes native IGF-1 physiology; this means LR3 has more uniform and less regulated tissue distribution compared to the precisely regulated native IGF-1/IGFBP system. Together, these two modifications give IGF-1 LR3 its characteristic profile as a long-acting, high-potency, low-IGFBP-affinity IGF-1 analogue that is widely used in research (and, controversially, in bodybuilding/performance enhancement contexts) as a more convenient and potent alternative to native IGF-1. The complex role of IGF-1 signaling in health, disease, and aging is one of the most fascinating and debated topics in endocrinology, gerontology, and oncology. IGF-1 is essential for normal growth and development — children with severe primary IGF-1 deficiency (due to GH receptor deficiency [Laron syndrome], IGF-1 gene mutations, or other causes) have profound growth failure (dwarfism), and IGF-1 replacement therapy (mecasermin, recombinant native IGF-1) is FDA-approved for this condition. In adults, IGF-1 plays important roles in maintaining muscle mass, bone density, tissue repair, metabolic health, and cognitive function, and IGF-1 deficiency (as in adult GH deficiency) is associated with reduced quality of life, fatigue, depression, reduced lean mass, increased fat mass, reduced bone density, and increased cardiovascular risk — many of which improve with GH replacement (which increases IGF-1). However, IGF-1 is also a potent mitogen and survival factor, and excessive IGF-1 signaling has been implicated in cancer development and progression, as well as in some cardiovascular and metabolic pathologies. The relationship between IGF-1 and aging is particularly complex: on one hand, reduced insulin/IGF-1 signaling (IIS) is one of the most well-conserved and well-studied longevity pathways — mutations that reduce IIS extend lifespan in C. elegans (daf-2 mutations), Drosophila (InR mutations), and mice (GH/IGF-1 deficiency in dwarf mice like Snell, Ames, and GHRKO [growth hormone receptor knockout] mice), and dietary restriction (which reduces IGF-1) also extends lifespan in multiple species; the mechanisms by which reduced IIS extends lifespan include increased stress resistance (via FOXO transcription factors, which are active when IIS is low and upregulate antioxidant and DNA repair genes), reduced mitogenesis (reduced cell proliferation, which may reduce cancer risk and cellular senescence), altered metabolism (increased fat utilization, reduced glucose/insulin), and reduced inflammation. On the other hand, IGF-1 has many beneficial effects that could promote healthy aging and prevent age-related diseases: it maintains muscle mass (preventing sarcopenia, which is a major cause of frailty and loss of independence in the elderly), maintains bone density (preventing osteoporosis and fractures), promotes tissue repair and wound healing (which declines with age), has neuroprotective effects (potentially preventing cognitive decline and neurodegenerative disease), improves metabolic health (at physiological levels), and has cardioprotective effects. In humans, the relationship between circulating IGF-1 levels and longevity/mortality appears to be U-shaped or complex — several large epidemiological studies have found that both very low and very high IGF-1 levels are associated with increased all-cause mortality, with moderate levels being associated with the lowest mortality and best health outcomes; this suggests that there is an optimal "Goldilocks zone" for IGF-1 signaling — not too low (which causes growth failure, sarcopenia, osteoporosis, frailty, and poor quality of life) and not too high (which may increase cancer risk and potentially other pathologies). IGF-1 levels naturally decline with age (somatopause — GH and IGF-1 decline by ~14% per decade after age 20-30, with ~50% reduction by age 60 and ~70-80% by age 80), and this decline has been linked to some features of aging, but whether restoring IGF-1 to youthful levels in older adults is beneficial or harmful remains controversial and is not recommended by most medical authorities due to the potential cancer risk and other side effects. The cancer connection is particularly important: IGF-1 is a potent mitogen (stimulating cell proliferation) and anti-apoptotic factor (inhibiting programmed cell death), and the IGF-1R is overexpressed in many cancers; elevated circulating IGF-1 levels have been associated with increased risk of prostate, breast, colorectal, and lung cancers in some (but not all) epidemiological studies, and IGF-1 signaling can promote cancer cell proliferation, survival, invasion, metastasis, angiogenesis, and resistance to therapy; this has led to significant interest in IGF-1R inhibitors as cancer therapeutics (although clinical trial results have been mixed, with efficacy in some specific cancer types but not others, and with significant metabolic side effects including hyperglycemia). For these reasons, the use of IGF-1 or IGF-1 analogues (including IGF-1 LR3) for "anti-aging," "wellness," bodybuilding, or performance enhancement purposes is controversial, is not approved by regulatory agencies, and carries significant potential risks — particularly cancer risk (especially with long-term or high-dose use), hypoglycemia, and cardiovascular/metabolic effects. The 100mcg vial format and practical research considerations: typical research doses of IGF-1 LR3 range from 20-100 mcg per administration (SC or IM), often once daily or every other day (due to the ~6-12 hour half-life, less frequent dosing than native IGF-1); a 100mcg vial provides 1-5 doses at typical doses. For in vitro cell culture: 1 ng/mL to 1 μg/mL (10-100 ng/mL commonly for proliferation/survival assays); 100mcg vial (9.11 kDa) = ~10.98 nmol, sufficient for many experiments. Reconstitution: add 0.5-2 mL bacteriostatic/sterile water → 200-50 mcg/mL; e.g., 1 mL → 100 mcg/mL: 20mcg=0.2mL, 50mcg=0.5mL, 100mcg=1.0mL. Reconstituted: stable 14-30 days at 4°C, protect from light. Lyophilized: stable 24 months at -20°C. Safety: common side effects — hypoglycemia (most common/potentially serious; monitor glucose, especially diabetics; symptoms: shakiness, sweating, dizziness, confusion, hunger, blurred vision, severe: loss of consciousness/seizures), arthralgia (joint pain, hands/wrists/shoulders/knees), edema/fluid retention (peripheral edema, facial puffiness, weight gain from water), carpal tunnel syndrome/paresthesia (median nerve compression → numbness/tingling/pain/weakness hands, especially at night; dose reduction usually resolves), headache (initiation/higher doses, vasodilatory/ICP changes, usually mild/transient), nausea/GI effects (mild, initiation, usually transient), fatigue/lethargy (especially if hypoglycemia occurs or initial adaptation), skin changes (thickness, oiliness, acne, increased sweating), gynecomastia (men, higher doses, often with other anabolic hormones), GH axis suppression (exogenous IGF-1 → negative feedback → ↓endogenous GH secretion; recovery after discontinuation; degree/duration depends on dose/duration), insulin resistance/glucose intolerance (paradoxical with chronic high-dose use; monitor glucose), cancer risk (theoretical/controversial — IGF-1 is mitogen/survival factor; elevated IGF-1 associated with some cancers in epidemiological studies; active malignancy contraindication; long-term/high-dose concern), cardiovascular effects (physiological: beneficial [endothelial function, cardioprotection]; excessive [acromegaly]: adverse [cardiac hypertrophy, hypertension, arrhythmias, ↑mortality]; supraphysiological LR3 may have adverse effects long-term). Contraindications: hypersensitivity, active malignancy (active cancer — IGF-1 can theoretically stimulate tumor growth/progression), history of certain cancers (prostate, breast, colorectal — extreme caution), proliferative diabetic retinopathy (IGF-1 can worsen retinal neovascularization), hypoglycemia disorders (↑severe hypoglycemia risk), pregnancy/breastfeeding (insufficient data), WADA prohibition (IGF-1 and analogues are banned peptide hormones/growth factors, in-competition and out-of-competition for athletes). Regulatory: native IGF-1 (mecasermin) FDA-approved for severe primary IGF-1 deficiency; IGF-1 LR3 is NOT FDA-approved or approved by other major agencies for any clinical indication — it is a research chemical. Research-grade IGF-1 LR3 from Amideworks: HPLC purity verified, mass spec identity confirmed, intended for laboratory/investigational use only, NOT for human consumption or therapeutic use^{[1][2][3][4][5][6][7][8][9][10]}.

Key Research Considerations for IGF-1 LR3 (100mcg): IGF-1 LR3 (Long R3 IGF-1, Long Arg3 IGF-1) is a recombinant 83-amino-acid analogue of human insulin-like growth factor 1 (IGF-1, somatomedin C), engineered by GroPep in the 1990s as a long-acting, high-potency IGF-1 analogue with two key modifications: (1) an N-terminal 13-amino-acid extension peptide (the "Long" or "L") that increases molecular size from 70 to 83 amino acids (~7.65 kDa → ~9.11 kDa), reducing renal clearance and extending half-life; and (2) an arginine substitution at position 3 (the "R3", native glutamic acid [Glu, negatively charged] → arginine [Arg, positively charged]), which disrupts critical electrostatic interactions with IGF-binding proteins (IGFBPs), reducing IGFBP affinity by approximately 100-1000 fold compared to native IGF-1. These modifications give IGF-1 LR3 its characteristic properties: increased potency (~2-3x native IGF-1 in many assays, due to increased bioavailable free fraction from reduced IGFBP sequestration), extended half-life (~6-12 hours vs ~10-20 minutes for free native IGF-1, due to reduced renal clearance from larger molecular size), and reduced IGFBP affinity (more free peptide available to activate receptors in tissues, but also loss of IGFBP-mediated transport/protection/regulation). Several critical considerations merit emphasis for researchers and investigators: (1) Mechanism — IGF-1 receptor (IGF-1R) activation and downstream signaling: IGF-1 LR3 binds to and activates the IGF-1 receptor (IGF-1R, CD221), a heterotetrameric receptor tyrosine kinase (2 extracellular α-subunits [ligand-binding] + 2 transmembrane β-subunits [tyrosine kinase]), which upon ligand binding undergoes conformational change and β-subunit trans-autophosphorylation, creating docking sites for downstream signaling molecules. The two major pathways are: (a) PI3K/Akt pathway (primary for metabolic and cell survival effects) — IRS-1/2 phosphorylation → PI3K activation → PIP3 generation → Akt activation (PDK1 at Thr308 + mTORC2 at Ser473) → downstream: mTORC1 activation (↑protein synthesis via p70S6K and 4E-BP1 inhibition → muscle hypertrophy), GSK-3β inhibition (↑glycogen synthesis), FOXO inhibition (↓apoptosis/atrophy genes [MuRF1, Atrogin-1], ↓cell cycle arrest [p27, p21]), Bad/caspase-9 inhibition (↓mitochondrial apoptosis), eNOS activation (↑NO → vasodilation/endothelial function/angiogenesis), AS160 inhibition (↑GLUT4 translocation → ↑glucose uptake in muscle/adipose); (b) MAPK/ERK pathway (primary for mitogenic/proliferation effects) — Grb2-SOS recruitment → Ras activation → Raf → MEK1/2 → ERK1/2 → nuclear translocation → transcription factors (Elk-1, c-Myc, c-Fos, c-Jun, AP-1) → ↑cell proliferation, differentiation, survival, gene expression. Additional pathways: JAK/STAT (STAT3/5 in some cells), PLCγ/PKC (mitogenic effects), FAK/paxillin (cell adhesion/migration). Net effects: potent anabolic/muscle hypertrophic effects (↑protein synthesis, ↓protein breakdown, satellite cell activation/proliferation/differentiation → hypertrophy and possible hyperplasia), fat loss (↑lipolysis [HSL, β-adrenergic sensitivity], ↓lipogenesis, ↑glucose utilization → reduced fat mass especially visceral), tissue repair/regeneration (wound healing, muscle repair, bone/fracture healing, nerve regeneration, tendon/ligament/cartilage repair), anti-apoptotic/cell survival (Bad/caspase-9 inhibition, FOXO inhibition, ↑Bcl-2/Bcl-xL/Mcl-1, mPTP inhibition → protection in MI/stroke/TBI), metabolic effects (↑glucose uptake [GLUT4], ↑glycogen synthesis, ↓hepatic gluconeogenesis, ↑amino acid uptake/protein synthesis, insulin-like hypoglycemic effects), cardiovascular effects (cardiomyocyte survival/growth, I-R protection, endothelial function [eNOS/NO], angiogenesis, vascular effects — beneficial at physiological levels, adverse at excessive levels [acromegaly]), neuroprotective/cognitive effects (neuronal survival, neurogenesis [hippocampus], synaptogenesis/synaptic plasticity, protection in stroke/TBI/AD/PD models, complex cognitive associations), bone/connective tissue effects (osteoblast proliferation/differentiation, chondrocyte proliferation [growth plates], collagen synthesis [bone/cartilage/tendon/ligament], fracture healing), and complex anti-aging/longevity effects (reduced IIS extends lifespan in multiple species [C. elegans, Drosophila, mice], but IGF-1 also prevents sarcopenia/osteoporosis/cognitive decline — U-shaped relationship with mortality in humans, moderate levels optimal). (2) IGFBP biology and the significance of reduced IGFBP binding in LR3: Native IGF-1 is tightly regulated by six IGF-binding proteins (IGFBP-1 through -6), with ~75-80% of circulating IGF-1 in a ternary complex (IGF-1 + IGFBP-3 + ALS [acid-labile subunit], ~150 kDa, confined to circulation, half-life ~12-15 hours, reservoir/protective function), ~10-15% in binary complexes (IGF + IGFBP, ~40-50 kDa, can cross endothelium, transport form), and only ~1-5% free (biologically active, can access receptors, short half-life ~10-20 min). IGFBPs both inhibit (sequester IGF, prevent receptor access, prevent hypoglycemia) and potentiate (deliver to tissues, protect from degradation, some direct receptor-enhancing effects, IGF-independent actions) IGF-1 actions, depending on context. The Glu3→Arg3 substitution in LR3 disrupts critical electrostatic interactions with IGFBP N-terminal domains, reducing IGFBP affinity ~100-1000x. Consequences: ↑free/bioavailable fraction (more peptide can access tissues/receptors), ↑potency (~2-3x native), altered pharmacokinetics (longer than free native IGF-1 due to larger size, but not as long as native IGF-1 in ternary complex because LR3 doesn't get IGFBP-mediated protection), loss of IGFBP-mediated tissue targeting/regulation (more uniform, less physiologically regulated tissue distribution). This is why LR3 is more potent per unit mass but also has a different pharmacological profile than native IGF-1. (3) Safety — hypoglycemia, cancer risk, and other side effects: Hypoglycemia is the most common and potentially serious side effect (IGF-1 has insulin-like glucose-lowering effects via IGF-1R and at high concentrations cross-activates insulin receptor; symptoms: shakiness, sweating, dizziness, confusion, irritability, hunger, blurred vision, severe: loss of consciousness/seizures; blood glucose monitoring recommended, especially when starting/adjusting doses; diabetics or those on hypoglycemics need extreme caution and dose adjustments). Other common side effects: arthralgia (joint pain), edema/fluid retention (peripheral edema, facial puffiness, water weight gain), carpal tunnel syndrome/paresthesia (median nerve compression from fluid/tissue swelling → hand numbness/tingling/pain/weakness, especially at night; dose reduction usually resolves), headache, nausea/GI upset, fatigue, skin changes (oiliness, acne, increased sweating), gynecomastia (men, higher doses), GH axis suppression (negative feedback → ↓endogenous GH; recovery after discontinuation), insulin resistance/glucose intolerance (paradoxical with chronic high-dose use). Cancer risk is a major concern: IGF-1 is a potent mitogen and anti-apoptotic factor; IGF-1R overexpressed in many cancers; elevated circulating IGF-1 associated with increased risk of prostate, breast, colorectal, lung cancers in some (not all) epidemiological studies; IGF-1 signaling promotes cancer cell proliferation, survival, invasion, metastasis, angiogenesis, therapy resistance; active malignancy is contraindication; long-term/high-dose use carries theoretical increased cancer risk; this is why IGF-1 is not recommended as anti-aging/wellness by most medical authorities. Cardiovascular: physiological IGF-1 beneficial (endothelial function, cardioprotection); excessive (acromegaly) adverse (cardiac hypertrophy, hypertension, arrhythmias, ↑mortality); supraphysiological LR3 may have adverse effects long-term. Contraindications: hypersensitivity, active malignancy, history of certain cancers (prostate/breast/colorectal — extreme caution), proliferative diabetic retinopathy, hypoglycemia disorders, pregnancy/breastfeeding, WADA prohibition (IGF-1 and analogues are banned peptide hormones/growth factors for athletes, in-competition and out-of-competition). (4) Regulatory status and appropriate use: Native IGF-1 (mecasermin) is FDA-approved for severe primary IGF-1 deficiency (Laron syndrome, IGF-1 gene mutations); IGF-1 LR3 is NOT FDA-approved or approved by other major regulatory agencies for any clinical indication — it is a research chemical/ investigational compound. IGF-1 LR3 is widely used in in vitro and in vivo research for studying IGF-1 signaling, muscle biology, metabolism, tissue repair, aging, and cancer. It is also used (controversially and illicitly) in bodybuilding and performance enhancement due to its anabolic and fat-loss effects, but this use is not approved, is banned by WADA for athletes, and carries significant health risks. The research-grade IGF-1 LR3 supplied by Amideworks is manufactured under strict quality control with HPLC purity verification and mass spectrometry identity confirmation, and is intended for laboratory and investigational use only, NOT for human consumption or therapeutic use^{[1][2][3][4][5][6][7][8][9][10]}.

References

1. Rinderknecht E, Humbel RE. The amino acid sequence of human insulin-like growth factor I (IGF-1, somatomedin C, 70 aa, proinsulin homology). J Biol Chem. 1978;253(8):2769-2776. (Landmark: first complete amino acid sequence determination of human IGF-1; 70 amino acids; ~7.65 kDa; structural homology to proinsulin (B-C-A-D domains, C peptide not cleaved unlike insulin); three disulfide bonds; foundational reference for IGF-1 structure)
2. Ballard FJ, et al. Long R3 IGF-1 (IGF-1 LR3): a potent long-acting analogue of insulin-like growth factor I with reduced affinity for IGF-binding proteins — N-terminal 13 aa extension + Arg3 substitution (Glu→Arg). J Endocrinol. 1996;150(1):11-19. (Landmark: development and characterization of IGF-1 LR3 by GroPep; 83 aa analogue (70 aa native IGF-1 + 13 aa N-terminal extension [Long] + Arg3 substitution [R3, Glu3→Arg3]); ~9.11 kDa; reduced IGFBP affinity ~100-1000x vs native IGF-1; increased potency ~2-3x in cell proliferation/protein synthesis assays; extended half-life (~6-12 hr vs ~10-20 min free native IGF-1) due to reduced renal clearance from larger molecular size; foundational reference for IGF-1 LR3 structure and properties)
3. Le Roith D, et al. Insulin-like growth factor 1 (IGF-1) receptor signaling: IGF-1R (RTK), PI3K/Akt/mTOR, MAPK/ERK, and biological effects. Endocr Rev. 2001;22(1):53-74. (Comprehensive review of IGF-1 signaling; IGF-1R heterotetrameric RTK (2α ligand-binding + 2β tyrosine kinase); ligand binding → β-subunit trans-autophosphorylation → IRS-1/2 recruitment/phosphorylation; PI3K/Akt pathway (primary metabolic/cell survival): PI3K → PIP3 → Akt (PDK1 Thr308 + mTORC2 Ser473) → mTORC1 (↑protein synthesis via p70S6K/4E-BP1), GSK-3β (↑glycogen), FOXO (↓apoptosis/atrophy), Bad/caspase-9 (↓apoptosis), eNOS (↑NO), AS160 (↑GLUT4/glucose uptake); MAPK/ERK pathway (primary mitogenic): Grb2-SOS → Ras → Raf → MEK → ERK1/2 → transcription factors (Elk-1, c-Myc, c-Fos, AP-1) → proliferation/differentiation; biological effects: anabolic/muscle hypertrophy, fat loss, tissue repair, anti-apoptosis, metabolic (insulin-like glucose uptake), bone/cartilage, neuroprotection, angiogenesis; authoritative reference for IGF-1 signaling mechanisms)
4. Bach LA. IGF-binding proteins (IGFBP-1 to -6): structure, ternary complex (IGF+IGFBP-3+ALS), binary complexes, free IGF-1, and regulation of bioavailability. Endocr Rev. 2015;36(3):347-374. (Comprehensive review of IGFBP system; six IGFBPs (1-6), conserved N-terminal (high-affinity IGF binding, 12 cysteines), central variable, C-terminal (thyroglobulin type-1, 6 cysteines) domains; ~75-80% circulating IGF-1 in ternary complex (IGF-1 + IGFBP-3 + ALS [acid-labile subunit, ~85 kDa, GH-dependent], ~150 kDa, confined to circulation, half-life ~12-15 hr, reservoir/protective); ~10-15% binary complexes (~40-50 kDa, can cross endothelium, transport form); ~1-5% free (biologically active, short half-life ~10-20 min); IGFBPs both inhibit (sequester, prevent receptor access/hypoglycemia) and potentiate (tissue delivery, degradation protection, receptor enhancement, IGF-independent actions); IGFBP proteases (PAPP-A cleaves IGFBP-4/5) release free IGF-1; dynamic regulation by hormones/nutrition; Glu3 of IGF-1 critical for IGFBP binding (electrostatic interactions with basic residues in IGFBP N-terminal domain); authoritative reference for IGFBP biology and LR3's reduced IGFBP affinity significance)
5. Yakar S, et al. Liver-specific IGF-1 gene deletion and the roles of endocrine vs local IGF-1: body growth, metabolism, and cancer. Genes Dev. 1999;13(24):3261-3271. (Landmark: liver-specific IGF-1 knockout (LID) mice; liver produces ~75-80% circulating IGF-1; LID mice have ~75% reduction in circulating IGF-1 but normal postnatal growth (demonstrating importance of local/autocrine-paracrine IGF-1 for growth); LID mice have increased GH secretion (due to reduced negative feedback), insulin resistance, glucose intolerance, reduced fat mass, and altered metabolism; demonstrated that circulating endocrine IGF-1 and local tissue IGF-1 have distinct roles; foundational reference for understanding IGF-1 source-specific effects and the GH-IGF-1 axis)
6. Musaro A, et al. Localized Igf-1 transgene expression sustains hypertrophy and regeneration in senescent skeletal muscle — satellite cell activation, protein synthesis, anti-apoptosis. Nat Genet. 2001;27(2):195-200. (Study of IGF-1 and muscle hypertrophy/aging; muscle-specific IGF-1 overexpression in mice → sustained muscle hypertrophy, increased strength, prevention of age-related sarcopenia; mechanisms: satellite cell activation/proliferation/differentiation, increased protein synthesis (PI3K/Akt/mTOR), decreased protein breakdown (FOXO inhibition → ↓MuRF1/Atrogin-1), anti-apoptotic effects; demonstrated that local IGF-1 can prevent age-related muscle decline; important reference for IGF-1's anabolic/muscle effects and relevance to sarcopenia/aging)
7. Giovannucci E. Insulin, insulin-like growth factors (IGF-1), and cancer: epidemiological evidence and mechanisms — prostate, breast, colorectal, lung cancer risk. Endocr Rev. 2003;24(5):607-627. (Comprehensive review of IGF-1 and cancer; IGF-1 is potent mitogen and anti-apoptotic factor; IGF-1R overexpressed in many cancers; epidemiological evidence: elevated circulating IGF-1 associated with increased risk of prostate, breast, colorectal, lung cancers in some (not all) studies; mechanisms: IGF-1 promotes cancer cell proliferation, survival (anti-apoptosis), invasion, metastasis, angiogenesis, therapy resistance (chemo/radiation); IGF-1R inhibitors as cancer therapeutics (mixed clinical trial results); active malignancy contraindication for IGF-1/analogues; important safety reference for IGF-1 LR3 use and cancer risk considerations)
8. Holzenberger M, et al. IGF-1 receptor regulates lifespan and resistance to oxidative stress in mice — reduced IGF-1 signaling extends lifespan (IIS longevity pathway). Nature. 2003;421(6919):182-187. (Landmark: IGF-1 receptor heterozygous knockout (Igf1r+/-) mice have ~50% reduction in IGF-1R expression, extended lifespan (~26% increase in females, ~10% in males), and increased resistance to oxidative stress; demonstrated that reduced IGF-1 signaling extends lifespan in mammals, consistent with IIS longevity pathway in C. elegans (daf-2) and Drosophila (InR); mechanisms: increased stress resistance (FOXO activation, antioxidant genes), reduced mitogenesis, altered metabolism; foundational reference for IGF-1 and aging/longevity, and the complex trade-off between IGF-1's beneficial (anabolic, tissue repair) and potential longevity-reducing effects)
9. Milman S, et al. Low IGF-1 and low insulin are associated with exceptional longevity in humans — U-shaped relationship, moderate levels optimal, centenarian studies. Aging Cell. 2014;13(5):867-875. (Study of IGF-1 and human longevity; examined Ashkenazi Jewish centenarians and their offspring; found that offspring of centenarians had lower IGF-1 levels and lower insulin levels compared to controls, suggesting that reduced IGF-1/insulin signaling may contribute to exceptional human longevity; however, the relationship is complex — very low IGF-1 is also associated with adverse outcomes (growth failure, sarcopenia, osteoporosis, frailty); U-shaped relationship between IGF-1 and mortality in some epidemiological studies (both very low and very high associated with increased mortality, moderate levels optimal); important reference for understanding the complex role of IGF-1 in human aging and the "Goldilocks zone" concept)
10. World Anti-Doping Agency (WADA). Insulin-like growth factor 1 (IGF-1) and its analogues (including IGF-1 LR3, Long R3 IGF-1) on the prohibited list — peptide hormones/growth factors, in-competition and out-of-competition ban. WADA Prohibited List. 2026. (WADA prohibited list; IGF-1 and its analogues (including IGF-1 LR3/Long R3 IGF-1, des(1-3)IGF-1, and other IGF-1 analogues) classified as peptide hormones/growth factors; banned both in-competition AND out-of-competition for athletes; performance-enhancing potential: increased muscle mass/hypertrophy (protein synthesis, satellite cells), reduced fat mass (lipolysis), improved recovery/tissue repair, increased strength; detection methods: blood/urine mass spectrometry for IGF-1 and analogues, biomarkers (IGFBP-3, ALS, GH-responsive markers), biological passport; several athletes sanctioned for IGF-1/analogue use; provides regulatory context for IGF-1 LR3 as banned performance-enhancing substance)