IGF-DES 1mg Review

Des(1-3) IGF-1, catalogued here as IGF-DES 1mg, is a naturally occurring N-terminally truncated variant of human insulin-like growth factor-1 (IGF-1). The truncation removes the three-residue sequence Gly-Pro-Glu from the N-terminus, and that seemingly minor edit produces a peptide with substantially different binding behavior toward the six IGF-binding proteins (IGFBPs) that normally sequester circulating IGF-1. The result is a research tool that generates a larger fraction of "free," receptor-accessible ligand than the parent hormone does under equivalent conditions, making it approximately 5-10 times more potent than native IGF-1 in many cell-proliferation assays and 2-3 times more potent in large-animal hypoglycemia models. ^[1]

This review examines the evidence base behind those claims: where the literature is solid, where it is thin, and what that means for researchers evaluating IGF-DES as a laboratory reagent. Because the compound touches oncology, metabolic disease, muscle biology, and bone physiology, the downstream signaling pathways and tissue-specific effects merit detailed treatment. The pharmacokinetics section pays particular attention to the practical consequences of reduced IGFBP binding on half-life and tissue distribution. The purity and verification section outlines what a credible certificate of analysis (CoA) should contain and how to cross-check vendor claims with third-party mass spectrometry.

Editor's Verdict

Apollo Peptide Sciences provides this compound at $80.00 per 1 mg lyophilized vial, which is competitive for the category. The 1 mg vial size suits most in-vitro screening work, where per-experiment consumption is measured in micrograms. For longitudinal rodent studies, researchers should budget for multiple vials. See our full IGF-DES product listing for the current affiliate-linked vendor page.

Specifications

What It Is: Chemistry, Origin, and Sequence Detail

Natural occurrence and discovery

Des(1-3) IGF-1 is not purely a synthetic invention. It was first isolated from bovine colostrum in the 1980s by Francis and colleagues, who noted that a minor fraction of IGF-1-immunoreactive material in colostrum migrated differently on gel electrophoresis from the intact 70-residue species. ^[2] Subsequent sequencing confirmed the N-terminal truncation. Later work identified the peptide in porcine uterus and in human brain tissue, establishing that it is a physiologically generated species rather than an artifact of peptide chemistry. ^[1] The proteolytic enzyme or enzymes responsible for in-vivo generation of des(1-3) IGF-1 have not been definitively characterized, although some evidence points toward brain-specific metalloendoproteases acting on the Gly1-Pro2 bond.

The biological rationale for a truncated IGF-1 form in brain and uterus is worth dwelling on. Both tissues use IGF-1 as a local trophic factor, and both express substantial quantities of IGFBPs. A locally generated form that evades IGFBP sequestration would provide a mechanism to create microenvironments of elevated free IGF-1 activity without raising systemic hormone levels. This is conceptually analogous to the role played by IGFBP proteases (PAPP-A, kallikreins) in releasing IGF-1 from high-affinity complexes at specific tissue sites. ^[3]

Structural relationship to native IGF-1

Native human IGF-1 is a 70-amino-acid, 7.65 kDa peptide organized into four domains (B, C, A, D) that fold into a three-helix bundle stabilized by three intra-chain disulfide bonds: Cys6-Cys48, Cys18-Cys61, and Cys47-Cys52 (native numbering). ^[4] The B-domain (residues 1-29) forms an extended N-terminal alpha helix that is the primary binding interface for both IGFBP-1 through IGFBP-6 and the IGF-1 receptor. Within that domain, the first three residues, Gly1-Pro2-Glu3, form a flexible solvent-exposed loop segment that makes critical contacts with multiple IGFBPs but contributes minimally to direct IGF-1R engagement. ^[1]

Removal of Gly-Pro-Glu therefore does two things simultaneously. First, it disrupts the IGFBP contact region sufficiently to reduce affinity for IGFBP-1, -2, -3, -4, and -5 by one to two orders of magnitude in competitive binding assays. Second, because those residues are not part of the primary receptor-binding epitope on helices 1 and 3, receptor binding affinity is largely preserved. ^{[1] [5]} Structural modeling and X-ray crystallography of related truncated IGF-1 variants indicate that the B-domain helix simply starts three residues later (at Thr4 in native numbering, renumbered Thr1 in des(1-3) IGF-1), with the remainder of the folded structure, including all three disulfides, remaining intact. ^[4]

This makes des(1-3) IGF-1 a natural "IGFBP-bypass" experiment: the receptor pharmacophore is intact, the sequestration mechanism is attenuated, and the resulting "bioavailability amplification" can be studied in isolation from any confounding changes in receptor affinity.

Synthetic production and reconstitution chemistry

Research-grade des(1-3) IGF-1 is produced by recombinant expression in E. coli followed by refolding under redox conditions that establish the three native disulfide bonds, or by total solid-phase peptide synthesis (SPPS) with orthogonal Cys protection strategies. Recombinant methods are more common for 67-residue peptides because SPPS yield and purity fall off sharply above ~50 residues. ^[4]

Lyophilized powder should be reconstituted in sterile water (preferred for aqueous assays) or 0.6% acetic acid (preferred when protein aggregation is a concern at neutral pH). Researchers should consult the reconstitution guide for detailed technique, including the importance of gentle swirling rather than vortexing and of allowing adequate equilibration time before use. IGF-1 family peptides are susceptible to oxidation of the single methionine residue (Met59 in des(1-3) numbering) and to non-specific adsorption onto plastic surfaces at low concentrations; working stocks below 100 ng/mL should include carrier protein (0.1% BSA) to minimize adsorption losses.

Mechanism of Action

IGF-1 receptor binding and activation

The primary molecular target of des(1-3) IGF-1 is the type 1 insulin-like growth factor receptor (IGF-1R), a heterotetrameric receptor tyrosine kinase (RTK) consisting of two extracellular alpha-subunits and two membrane-spanning beta-subunits linked by disulfide bonds. ^[6] Ligand binding induces conformational changes that bring the two kinase domains of the beta-subunits into proximity, enabling trans-autophosphorylation at Tyr1131, Tyr1135, and Tyr1136 within the activation loop. ^[7] This converts the kinase from an autoinhibited state, where the unphosphorylated loop occludes the substrate-binding cleft, to an active conformation capable of phosphorylating downstream substrates.

Des(1-3) IGF-1 binds IGF-1R with affinity essentially equivalent to native IGF-1, since the receptor contact residues in helices 1 and 3 of the B-domain and in the A-domain are preserved in the truncated form. ^{[1] [5]} Several receptor cross-reactivity studies confirm that des(1-3) IGF-1 also binds the insulin receptor (IR), though with considerably lower affinity (approximately 100-fold less than for IGF-1R). Hybrid IGF-1R/IR receptors, which are abundant in metabolic tissues, bind des(1-3) IGF-1 with intermediate affinity and may contribute to glycemic effects observed in animal studies. ^[8]

PI3K/Akt signaling axis

Upon IGF-1R activation, the phosphorylated tyrosine residues in the juxtamembrane region recruit insulin receptor substrate proteins (IRS-1, IRS-2) and the Shc adapter. IRS-1 and IRS-2 are then phosphorylated on multiple tyrosine residues, creating docking sites for the SH2 domain of the p85 regulatory subunit of phosphoinositide 3-kinase (PI3K). ^[7] The catalytic p110 subunit phosphorylates phosphatidylinositol-4,5-bisphosphate to phosphatidylinositol-3,4,5-trisphosphate (PIP3), which recruits PDK1 and Akt to the membrane. PDK1 phosphorylates Akt at Thr308, and the mTORC2 complex phosphorylates Akt at Ser473, achieving full activation.

Active Akt phosphorylates a broad substrate set with anabolic consequences: it inhibits FOXO transcription factors (reducing atrogene expression), activates mTORC1 (stimulating ribosomal biogenesis and protein synthesis via S6K1 and 4E-BP1), and phosphorylates GSK-3beta, which relieves inhibition of glycogen synthase and eIF2B. ^{[7] [6]} In skeletal muscle, this PI3K/Akt/mTORC1 axis is the canonical driver of hypertrophy, and its activation by IGF-1 family peptides in rodent and cell models is well established. Because des(1-3) IGF-1 activates IGF-1R with equivalent intrinsic efficacy to native IGF-1, and does so at a higher effective free concentration (by virtue of reduced IGFBP binding), the net downstream PI3K/Akt signal is amplified relative to equimolar doses of native IGF-1 in systems where IGFBPs are present. ^[1]

MAPK/ERK signaling and mitogenesis

The second major downstream cascade involves Ras activation through Grb2/SOS recruitment to phospho-Shc, leading to sequential phosphorylation of Raf, MEK1/2, and ERK1/2. ^[7] Phospho-ERK1/2 translocates to the nucleus and activates transcription factors including Elk-1, c-Fos/c-Jun (AP-1), and CREB, driving expression of cyclin D1, cyclin E, and other cell-cycle entry genes. This MAPK arm is responsible for the mitogenic effects of IGF-1 and its analogues: increased DNA synthesis, cell proliferation, and in transformed cells, contributions to anchorage-independent growth. ^[6]

The mitogenic potency of des(1-3) IGF-1 in cell culture is routinely reported as 5-10 times greater than native IGF-1 in assays conducted in the presence of serum (which contains IGFBPs). ^[1] When the same experiments are performed in serum-free, IGFBP-free conditions, the difference largely disappears, confirming that the potency advantage is attributable entirely to IGFBP evasion rather than intrinsically superior receptor agonism. ^[5] This is a critical point for interpreting in-vitro data: the choice of assay matrix (serum vs. serum-free) substantially changes the apparent relative potency.

Tissue distribution and secondary signaling

IGF-1R is expressed in virtually all differentiated cell types, but expression density varies considerably. Skeletal muscle satellite cells, osteoblasts, chondrocytes, hepatocytes, neurons, cardiomyocytes, and adipocytes express particularly high levels, consistent with the broad anabolic and growth-promoting roles attributed to IGF-1 signaling. ^[4] Because des(1-3) IGF-1 is not sequestered in a ternary IGFBP-3/ALS complex, the fraction that reaches tissues after administration in vivo is higher than for native IGF-1, producing tissue distributions skewed toward high-perfusion organs and tissues with dense capillary beds.

In brain tissue, where the peptide naturally occurs, des(1-3) IGF-1 can cross the blood-brain barrier more readily than native IGF-1 (which is largely IGFBP-3-bound and too large in complex form to cross efficiently). IGF-1R signaling in neurons activates PI3K/Akt to promote survival, differentiation, and synaptic plasticity. Intracerebroventricular (ICV) administration in rodent neonates has been used to study neurotrophic effects. ^[8] These neurotrophic actions are the basis for ongoing research interest in des(1-3) IGF-1 as a model compound for CNS injury and neurodevelopmental research.

What the Research Says

Study 1: Ballard et al. (1996), potency characterization in cell proliferation and animal models

The most-cited primary characterization of des(1-3) IGF-1 relative to native IGF-1 was conducted by Ballard and colleagues, who used a combination of receptor binding assays, cell proliferation studies, and in-vivo pig models to generate a comprehensive potency profile. ^[1] The receptor binding work confirmed that removal of Gly-Pro-Glu had no meaningful effect on IGF-1R affinity (IC50 values were statistically indistinguishable in serum-free displacement assays), while IGFBP-3 binding affinity was reduced by approximately 70-fold. In bovine mammary epithelial cell proliferation assays conducted in the presence of 10% fetal bovine serum (which contains IGFBPs), des(1-3) IGF-1 was 6.4 times more potent than native IGF-1 on a molar basis.

The pig experiments used glucose-clamped, catheterized Landrace pigs to compare hypoglycemic potency and duration. Intravenous infusion of des(1-3) IGF-1 produced glucose-lowering that was approximately 2.5-fold greater in magnitude and persisted roughly 40% longer than equimolar native IGF-1 infusion. Plasma clearance was faster for des(1-3) IGF-1, which is consistent with the loss of the IGFBP-3/ALS ternary complex that normally extends the circulating half-life of native IGF-1 to 12-16 hours. The apparent paradox of greater pharmacodynamic effect despite faster clearance is explained by the higher fraction of free (receptor-accessible) peptide throughout the shorter circulating period.

The study's main limitation is its use of supraphysiological doses required for measurable hypoglycemia in pigs, which makes translating the potency ratio to lower-dose physiological scenarios uncertain. Nevertheless, the receptor-binding and cell-proliferation data, being conducted across a full concentration range with EC50 comparisons, provide the most robust quantitative basis for the commonly cited "5-10x potency" claim.

Study 2: Tomas et al. (1993), protein metabolism in sheep

Tomas and colleagues administered des(1-3) IGF-1 by subcutaneous infusion to sheep over a 7-day period, measuring nitrogen balance (a proxy for net protein synthesis), muscle protein fractional synthesis rate (FSR), and IGF-1 receptor occupancy in muscle biopsies. ^[9] At literature-reported research doses in this ovine model, des(1-3) IGF-1 increased nitrogen retention by 20-30% compared with saline controls, and muscle FSR was elevated by approximately 15%. Critically, native IGF-1 at the same molar dose produced nitrogen retention increases of only 10-12%, confirming the in-vivo superiority of the truncated variant in terms of net anabolic effect on skeletal muscle protein metabolism.

The study design included post-infusion washout measurements that showed a more rapid return of nitrogen balance to baseline after des(1-3) IGF-1 compared with rhIGF-1, consistent with shorter pharmacological duration of action. This reinforces the concept that the peptide trades persistence for potency. From a research standpoint, this study is important because it demonstrates that the IGFBP-bypass mechanism operates in a physiologically intact large mammal, not merely in cultured cells or in-vitro binding assays. Limitations include the absence of a dose-response characterization (a single dose level was used), the use of continuous subcutaneous infusion rather than bolus dosing, and the fact that sheep IGFBPs may differ quantitatively from human IGFBPs in relevant respects.

Study 3: Gutierrez-Hartmann et al. and the KID knock-in mouse model (Elis et al., 2011)

One of the most mechanistically informative sets of data comes from the knock-in mouse (KID) model generated by Elis and colleagues. ^[5] In this model, the endogenous mouse Igf1 gene was replaced at the genomic level with a sequence encoding des(1-3) IGF-1 (knock-in des, or KID), so that the only circulating IGF-1 variant produced was the truncated form. This approach is conceptually powerful: it separates the effect of IGFBP evasion from any pharmacokinetic differences introduced by exogenous administration, allowing the question "what happens when endogenous IGF-1 is always in its IGFBP-low-affinity form?" to be answered in a genetically clean system.

KID mice showed body length 6-8% greater than wild-type controls at 8 weeks, increased femur length, higher trabecular bone volume fraction by microCT, and increased kidney and spleen mass, all consistent with elevated effective IGF-1 bioactivity despite total serum IGF-1 concentrations that were similar to or lower than wild-type. Liver-derived IGF-1 in KID mice was rapidly cleared (consistent with reduced IGFBP-3 binding), so circulating concentrations were modestly suppressed relative to wild-type, yet bone and body length were greater. This dissociation between serum IGF-1 concentration and growth effect is the key finding: what matters biologically is free, receptor-accessible IGF-1, not total immunoreactive IGF-1.

The study also characterized insulin sensitivity. KID mice showed modestly enhanced insulin sensitivity and lower fasting glucose than controls, in accordance with higher free-IGF-1 bioactivity at metabolic tissues. Importantly, no malignant transformation was observed during the observation window (up to 14 months), though the study was not powered as a cancer bioassay. Limitations include the purely murine genetic context, the constitutive nature of the knock-in (no conditional tissue-specific controls), and the relatively short observation window for carcinogenesis endpoints.

Study 4: Tomas et al. (1991), hypoglycemia dose-response in sheep and comparison with R3-IGF-1

In a companion study to the 1993 protein-metabolism work, Tomas and colleagues compared des(1-3) IGF-1 with native IGF-1 and with R3-IGF-1 (an analogue with a Glu3-to-Arg substitution, preserving length but also reducing IGFBP affinity) in terms of hypoglycemic potency across a dose range in sheep. ^[10] Des(1-3) IGF-1 produced a dose-dependent fall in blood glucose with an ED50 approximately 2-3 times lower than native IGF-1, consistent with Ballard's pig data. R3-IGF-1 showed intermediate potency between native IGF-1 and des(1-3) IGF-1, which is expected given its intermediate IGFBP-binding profile.

The time-course data from this study are particularly instructive. After a single intravenous bolus, blood glucose nadir for des(1-3) IGF-1 occurred earlier (approximately 30-45 minutes post-injection) and returned to baseline faster (approximately 2-3 hours) than for native IGF-1 (nadir at 60-90 minutes, return to baseline at 4-6 hours). R3-IGF-1, whose longer amino acid chain maintains some IGFBP binding and thus a modest circulating half-life, showed an intermediate time course. These data make des(1-3) IGF-1 a useful tool for studying acute IGF-1R activation without the prolonged hypoglycemic window that complicates interpretation with native IGF-1 in rodent and large-animal models.

Study 5: Gallaher et al., neonatal neurological models

Gallaher and colleagues used intracerebroventricular administration of des(1-3) IGF-1 in neonatal rat pups to investigate neurotrophic and neuroprotective effects following hypoxic-ischemic brain injury. ^[8] The study used a 45-minute unilateral carotid ligation model followed by hypoxic exposure (8% O2), then a single ICV injection of either des(1-3) IGF-1 or vehicle 2 hours after the insult. At 72 hours, histological scoring of cortical and hippocampal injury showed significant reduction in infarct volume in des(1-3) IGF-1-treated pups (literature-reported research doses in neonatal rat models typically range from 2 to 50 micrograms ICV). The neuroprotective effect was not seen with IGFBP-3 co-administration at concentrations sufficient to re-sequester the peptide, providing strong functional evidence that the protective effect depended on receptor-accessible (IGFBP-unbound) ligand.

This study is mechanistically important for two reasons. First, it demonstrates that des(1-3) IGF-1's superior IGFBP evasion is pharmacologically meaningful in CNS tissue specifically, where native IGF-1 has difficulty reaching receptor-expressing neurons when administered systemically due to the IGFBP-rich cerebrospinal fluid environment. Second, it provides a model-system precedent for studying CNS IGF-1R biology with a pharmacologically clean tool (high receptor activity, low IGFBP confounding). Limitations include the model-specific nature of the findings (neonatal rat hypoxia-ischemia may not generalize to adult neurological conditions) and the use of direct ICV delivery rather than peripheral administration.

Pharmacokinetics

Understanding the pharmacokinetic (PK) profile of des(1-3) IGF-1 is essential for designing experiments with meaningful and reproducible exposure windows. Several features of its PK diverge substantially from native IGF-1 because of the IGFBP-binding differences.

Plasma half-life

Native IGF-1 has a plasma half-life of approximately 12-16 hours when measured as total immunoreactive IGF-1, because the ternary complex with IGFBP-3 and ALS dramatically slows renal and hepatic clearance. ^[3] The free-IGF-1 component (approximately 1-5% of total) has a half-life closer to 10 minutes in the absence of rebinding to IGFBPs. Des(1-3) IGF-1 cannot form the stabilizing ternary complex and binds all IGFBPs with greatly reduced affinity, so its effective pharmacokinetic behavior resembles free native IGF-1 rather than the full ternary complex. Studies in pigs and sheep report plasma half-life estimates of 20-40 minutes for des(1-3) IGF-1 after intravenous bolus administration. ^{[1] [10]}

The short half-life is not merely an academic PK detail: it determines sampling time points in in-vivo experiments and the frequency of dosing required to maintain sustained receptor occupancy. For rodent studies aiming at prolonged anabolic stimulation, multiple daily administrations or continuous subcutaneous infusion are needed to compensate for the rapid clearance.

Volume of distribution and tissue penetration

Because des(1-3) IGF-1 is not retained in the IGFBP-3/ALS ternary complex, it distributes more rapidly into peripheral tissues and crosses the capillary endothelium more readily than native IGF-1. Estimates from sheep pharmacokinetic studies suggest a volume of distribution approximately 2-3 times larger than for native IGF-1 after IV bolus. ^[10] The elevated Vd is consistent with faster and more extensive tissue penetration, including to CNS compartments, skeletal muscle interstitium, and bone marrow. This broad tissue distribution is pharmacologically advantageous for studies targeting peripheral tissues but complicates dose-effect interpretation because a given serum concentration does not represent the same receptor exposure as it would for native IGF-1.

Routes of administration in research models

In published research, des(1-3) IGF-1 has been administered by intravenous (IV) bolus, subcutaneous (SC) infusion, intramuscular injection, and intracerebroventricular (ICV) injection in animal models. Oral bioavailability, like that of all peptides above approximately 500 Da, is essentially nil due to gastric protease degradation. ^[9] Subcutaneous absorption is generally efficient for small to mid-size peptides at the concentrations used in research, with bioavailability in rodent models estimated at 50-70% based on area-under-the-curve comparisons with IV dosing for related IGF-1 analogues.

Metabolism and elimination

Like all peptide hormones, des(1-3) IGF-1 is subject to proteolytic catabolism by circulating endopeptidases, receptor-mediated endocytosis and lysosomal degradation after receptor binding, and glomerular filtration followed by tubular catabolism. Because it lacks the IGFBP-3/ALS shelter, it is considerably more exposed to circulating proteases than native IGF-1. Specific cleavage sites have not been fully mapped for des(1-3) IGF-1, but the major sites identified for native IGF-1 (cleavage between residues 26-29 in the C-domain and between residues 49-51 in the A-domain) are likely relevant. ^[4]

Researchers conducting time-course studies should account for the rapid plasma elimination when designing sample collection intervals. Blood draws at 5, 15, 30, 60, and 120 minutes post-administration will capture the full PK profile for des(1-3) IGF-1, whereas for native IGF-1 the relevant window extends to 24-48 hours. This difference has implications for radioimmunoassay and ELISA-based plasma quantitation: standard total-IGF-1 assays that use acid-ethanol extraction to displace IGFBPs will underestimate des(1-3) IGF-1 concentrations if the peptide has already been cleared before extraction.

Purity and Verification

What a credible CoA should contain

Researchers sourcing research peptides are well-served by understanding what constitutes a rigorous certificate of analysis and what minimal information is insufficient to validate peptide identity and purity. A high-quality CoA for des(1-3) IGF-1 should contain at minimum the following elements.

HPLC chromatogram with area-percent purity. Reversed-phase HPLC (typically C18 column, water/acetonitrile gradient with 0.1% TFA) should show a single dominant peak with area percentage at or above 98%. The chromatogram itself, not merely the stated purity number, should be available. Retention time should be consistent across lot numbers.

Mass spectrometry confirmation. ESI-MS or MALDI-TOF data showing molecular ion peaks consistent with the theoretical molecular weight of des(1-3) IGF-1 (approximately 7,370 Da, or the appropriate multiply-charged ion series in ESI). For a 67-residue peptide, the molecular weight confirmation is critical because at this size, a truncation artifact or missed disulfide bond will shift the mass measurably.

Residual solvent and counterion content. Trifluoroacetate counterion from HPLC purification is potentially cytotoxic at high concentrations in cell culture; vendors who have exchanged to acetate or formate counterions provide CoAs specifying this. Residual organic solvents (acetonitrile, DMF) should be within ICH Q3C limits.

Endotoxin testing (LAL assay). For any peptide used in animal injections, endotoxin levels should be below 1 EU/mg. Vendors who supply research-grade (not clinical-grade) material may not routinely perform LAL testing; researchers using injectable preparations should verify this independently or perform their own limulus amebocyte lysate testing.

Lot-specific identity and release date. Peptide stability is lot-specific; release dates allow researchers to track shelf-life and to correlate any potency drift with peptide age and storage conditions.

Apollo Peptide Sciences provides lot-specific HPLC and MS data. Researchers are encouraged to request the CoA for the specific lot number before placing an order, as this is standard practice for research-grade materials procurement.

Independent verification strategies

Laboratory managers with access to analytical instrumentation should consider independent verification of vendor CoAs, particularly for high-value experiments where peptide quality directly affects reproducibility. Several practical approaches exist.

In-house HPLC. If the laboratory has access to a C18 reverse-phase HPLC column and UV detector (214 nm for peptide bond absorption), a quick analytical run on a small aliquot of the received material against the vendor chromatogram provides a first-pass identity and purity check. Retention time shifts of more than 1 minute (under identical gradient conditions) suggest a batch inconsistency worth investigating.

Intact-mass LC-MS. For definitive identity confirmation, submitting a microgram-scale sample to a core proteomics facility for LC-MS intact mass measurement is cost-effective and unambiguous. The theoretical average mass of des(1-3) IGF-1 (67 residues, 3 disulfides) is approximately 7,370 Da; any significant deviation indicates an incorrect product or a manufacturing defect.

Cell-based potency assay. The most functionally relevant verification is a cell-based assay measuring IGF-1R phosphorylation or downstream Akt phosphorylation in a cell line known to express IGF-1R (e.g., MCF-7, C2C12 myoblasts, or NIH-3T3 cells). A concentration-response curve from 0.1 to 100 ng/mL should produce an EC50 in the range reported in published literature (approximately 1-5 ng/mL in serum-containing conditions). Significant rightward shift suggests peptide degradation or misfolding.

See our supplier evaluation guide for a more detailed framework for assessing vendor quality management systems, and our CoA reading guide for interpretation of analytical data.

Dosage and Reconstitution

Reconstitution protocol

The 1 mg lyophilized vial should be reconstituted following standard peptide reconstitution principles. For a full protocol, consult the peptide reconstitution guide. A brief summary specific to des(1-3) IGF-1 follows.

Allow the sealed vial to reach room temperature before opening, to prevent condensation on the lyophilized cake. Add reconstitution solvent (sterile water or 0.6% acetic acid) slowly down the inner wall of the vial, avoiding direct contact with the cake, which can cause foaming. For most laboratory uses, a stock concentration of 0.1 mg/mL (100 micrograms per mL) is practical: add 10 mL of solvent to the 1 mg vial. This concentration is compatible with standard micropipette volumes and minimizes freeze-thaw degradation on aliquoting.

Gently swirl (do not vortex) and allow 15-20 minutes for complete dissolution. Visual clarity does not guarantee full dissolution for larger peptides; using the full equilibration time is important. Divide into single-use aliquots of 100-200 microliters in low-binding (polypropylene) 0.5 mL tubes. Store aliquots at -80°C if not to be used within one week.

Literature-reported research doses: worked examples

The following examples are drawn from published animal studies and are provided to help researchers contextualize the literature. They are animal-equivalent doses from experimental contexts and should not be interpreted as human dosing recommendations.

Example 1: Rodent in-vivo subcutaneous injection (hypothetical nitrogen balance experiment)

In sheep studies (Tomas et al., 1993), SC infusion doses of approximately 1-2 micrograms per kilogram per hour were used to achieve measurable anabolic effects on nitrogen balance over 7 days. ^[9] To understand the per-dose equivalent in a 25-gram mouse: 1 microgram per kg per hour translates to 0.025 micrograms per hour for a 25 g mouse, or approximately 0.6 micrograms per day if the hourly rate is maintained continuously. Scaling this to a twice-daily injection model, each injection would contain approximately 0.3 micrograms (300 nanograms) in a volume typically of 100-200 microliters for subcutaneous injection in rodents. From a 0.1 mg/mL (100 ng/microliter) stock, 3 microliters would deliver 300 nanograms.

Example 2: Cell culture proliferation assay

Published IGF-1 analogue cell proliferation assays (e.g., bovine mammary epithelial, C2C12 myoblast) typically use a concentration range of 1 to 1,000 ng/mL for dose-response characterization. At the commonly cited EC50 of approximately 2-3 ng/mL for des(1-3) IGF-1 in serum-containing medium, ^[1] a 10 ng/mL working concentration provides a robust supramaximal stimulus. From a 0.1 mg/mL (100 micrograms/mL, or 100,000 ng/mL) stock, a 1:10,000 dilution is needed: serial dilution (1:100 twice) achieves this practically with minimal pipetting error.

Example 3: Neonatal rat ICV administration

The Gallaher neonatal rat neuroprotection model used ICV doses in the range of 2-50 micrograms in a total injection volume of 2-5 microliters. ^[8] From a 1 mg/mL (1,000 ng/microliter) reconstituted stock: 2-5 microliters of the stock delivers 2-5 micrograms; for 50 micrograms, 50 microliters of the stock solution would be used (or reconstitution at higher concentration). Researchers designing ICV experiments should consult neuroanatomy references for accurate lateral ventricle coordinates by postnatal day and should use a calibrated Hamilton syringe for small-volume precision.

For detailed guidance on calculating volumes from reconstituted peptide stocks, consult the dosage calculation guide.

Storage considerations after reconstitution

Reconstituted des(1-3) IGF-1 in neutral aqueous buffer is susceptible to oxidation of Met59 (in des(1-3) numbering) and to disulfide scrambling if reducing agents are present. Researchers should avoid reconstitution in buffers containing DTT or beta-mercaptoethanol. Addition of 0.1% BSA to the reconstitution solvent stabilizes the peptide at concentrations below 100 ng/mL by reducing adsorption to plastic. Avoid multiple freeze-thaw cycles: more than three cycles will degrade biological activity measurably.

Side Effects and Safety

Preclinical safety signals and extrapolation

The safety profile of des(1-3) IGF-1 in laboratory animals has not been characterized with the rigor of a formal toxicology package (GLP repeated-dose toxicity, genotoxicity, reproductive toxicity). Available information is extrapolated from native IGF-1 animal and clinical pharmacology, from the knock-in mouse model, and from pharmacological reasoning.

The most significant theoretical risk is promotion of neoplastic growth. IGF-1R is overexpressed or hyper-activated in a wide range of human malignancies including breast, colorectal, prostate, lung, and hepatocellular carcinoma. ^[11] Epidemiological data show that higher circulating IGF-1 concentrations are associated with modestly elevated risks of several cancers. Because des(1-3) IGF-1 generates higher free-IGF-1 bioactivity than native IGF-1 at equivalent doses, it carries an amplified theoretical mitogenic and tumor-promoting risk relative to the parent hormone. The KID knock-in mouse study did not observe malignancy during a 14-month observation window, ^[5] but this is insufficient to characterize a carcinogenic risk profile, particularly given the relatively limited lifespan of the observation window and the constitutive low-level expression rather than pharmacological over-activation.

Hypoglycemia is the most acutely dangerous pharmacological effect. Des(1-3) IGF-1 at sufficiently high doses produces dose-dependent glucose lowering via IGF-1R and IR partial agonism in insulin-sensitive tissues. Severe acute hypoglycemia can cause seizures, cardiac arrhythmia, and death. Animal studies demonstrate a 2-3 fold shift in the hypoglycemic dose-response curve compared with native IGF-1, meaning acute toxicity from glucose lowering would be expected to occur at lower doses. ^[10]

Organ hypertrophy at sustained high exposures is demonstrated in the knock-in mouse model, where kidney and spleen masses were significantly increased relative to wild-type. ^[5] Chronic stimulation of IGF-1R in renal mesangial cells promotes glomerular hypertrophy; in the heart, sustained IGF-1R signaling can cause pathological (as opposed to physiological) cardiac hypertrophy under conditions of concurrent hemodynamic stress. ^[12]

Potential endocrine disruption through negative feedback on the GH/IGF-1 axis is also relevant. Exogenous IGF-1 (and by extension des(1-3) IGF-1) suppresses pituitary GH secretion via negative feedback at both the hypothalamic (suppressing GHRH, stimulating somatostatin) and pituitary levels. ^[4] Chronic suppression of GH could have secondary effects on body composition, thyroid function, and adrenal axis responsiveness.

Drug and assay interference considerations

In research settings, the short plasma half-life of des(1-3) IGF-1 relative to native IGF-1 creates specific assay interference risks. Standard clinical immunoassay kits for total IGF-1 use acid-ethanol extraction to displace IGFBPs; this technique was validated for native IGF-1 and may not reliably capture des(1-3) IGF-1 at equivalent sensitivity. Researchers measuring endogenous or exogenous des(1-3) IGF-1 in plasma should use assays specifically validated for the truncated form, or use liquid chromatography-mass spectrometry (LC-MS) methods that distinguish the peptide species by mass rather than antibody recognition. ^[3]

How It Compares

The IGF-1 research peptide landscape includes several analogues that differ from native IGF-1 in IGFBP affinity, receptor affinity, half-life, and practical utility for specific experimental contexts.

Des(1-3) IGF-1 vs. LR3-IGF-1

LR3-IGF-1 (long R3 IGF-1) is the most commonly used IGFBP-reduced IGF-1 analogue in cell culture research because its 13-amino-acid N-terminal leader sequence confers a plasma half-life of approximately 2-6 hours, compared with 20-40 minutes for des(1-3) IGF-1. ^[9] For in-vitro work where sustained receptor stimulation across a 24-96 hour incubation is needed, LR3-IGF-1 is the preferable tool: it requires fewer media changes and maintains more consistent receptor occupancy. For experiments specifically interrogating the acute kinetics of IGF-1R activation, where rapid clearance and a defined short stimulus window are experimental design goals, des(1-3) IGF-1 is more appropriate.

In terms of IGFBP affinity, both compounds show similarly reduced binding relative to native IGF-1, though LR3-IGF-1 is somewhat more consistent across all IGFBP family members due to the bulky N-terminal leader. Des(1-3) IGF-1 is the natural variant, which gives it an argument for being the more physiologically relevant research tool when studying what nature's own IGFBP-bypass mechanism looks like pharmacologically.

Des(1-3) IGF-1 vs. native IGF-1

For experiments where the research question is "what does IGF-1 do in the presence of IGFBPs?", native IGF-1 is the appropriate comparator and des(1-3) IGF-1 is the experimental arm. The approximately 5-10x potency advantage seen in serum-containing assays provides sufficient dynamic range to observe significant effects at doses where native IGF-1 is still largely IGFBP-sequestered. ^[1] If the experimental system contains no IGFBPs (serum-free, defined media), the two compounds are pharmacologically interchangeable at IGF-1R, and native IGF-1 is cheaper and more abundantly characterized in the literature.

Des(1-3) IGF-1 vs. R3-IGF-1

R3-IGF-1 is a single-amino-acid substitution variant that retains the full 70-residue length of native IGF-1 but has the Glu3-to-Arg change that disrupts several IGFBP contact points. Its IGFBP binding is reduced relative to native IGF-1 but not as completely as for des(1-3) IGF-1, producing intermediate potency in serum-containing assays. ^[10] R3-IGF-1 is somewhat easier to produce synthetically due to its standard amide-bond backbone, whereas des(1-3) IGF-1 requires careful attention to N-terminal sequencing during synthesis or recombinant expression to confirm the exact 3-residue deletion. For most in-vitro cell culture applications, R3-IGF-1 is the more widely available and lower-cost option; des(1-3) IGF-1 is preferred when studying the natural truncation variant specifically, as occurs in brain or uterine tissue biology, or when maximum IGFBP evasion is required.

Where to Buy

Researchers sourcing IGF-DES 1mg should prioritize vendors who provide lot-specific HPLC and mass spectrometry data, maintain a cold chain during shipping, and operate a traceable quality management system. Before ordering, review the criteria outlined in the peptide supplier evaluation guide.

Apollo Peptide Sciences is the affiliated vendor for this compound. See the IGF-DES product page for current pricing, lot availability, and the direct CoA request process. The product page also links to the vendor's standard documentation package, which includes HPLC purity traces and intact-mass confirmation.

When comparing vendor pricing in this category, note that the relevant metric is cost per microgram of confirmed-purity peptide, not raw vial price. A nominally cheaper vial with 90% purity contains 10% less active material than stated, which distorts dose calculations. For a 1 mg vial at 98% purity, approximately 980 micrograms of active peptide is available. At Apollo Peptide Sciences' $80.00 per vial, this translates to approximately $0.082 per microgram at stated purity. Comparing this figure across vendors with their respective CoA purity values allows like-for-like cost comparison.

IGF-DES is not a compound available through standard biochemical reagent suppliers (Sigma-Aldrich, Cayman Chemical) at the 1 mg scale and research-peptide price point. Specialty research peptide vendors are the appropriate procurement channel. Researchers in European jurisdictions should verify import regulations for research peptides before ordering, as customs classification varies by country.

Open Research Questions

Several significant gaps in the des(1-3) IGF-1 literature warrant specific discussion, both to orient researchers toward areas where new data would be valuable and to contextualize the limitations of existing claims.

Precise IGFBP subtype selectivity. While it is established that des(1-3) IGF-1 has greatly reduced affinity for IGFBP-3 (the major circulating IGFBP), the quantitative affinity data for IGFBP-1, -2, -4, -5, and -6 are variable across published studies and have not been systematically characterized in a single experimental design with standardized assay conditions. The consequence is uncertainty about which IGFBP-expressing tissue compartments will show the greatest "bioavailability amplification" with des(1-3) IGF-1, compared with LR3 or R3 variants.

In-vivo pharmacokinetics in rodents. Most pharmacokinetic data come from pig and sheep models. Rodent PK data (Cmax, AUC, Vd, t1/2) after subcutaneous injection in mice and rats are not well characterized in the primary literature, yet rodents are the most common species used in des(1-3) IGF-1 research. The absence of murine PK data makes dose selection for rodent studies dependent on allometric scaling from large-animal data, which introduces uncertainty.

Long-term carcinogenic potential. The theoretical risk that sustained IGF-1R overstimulation promotes tumor formation has not been directly tested for des(1-3) IGF-1 in a controlled lifetime bioassay. The KID knock-in model provides reassurance at constitutive low-level expression but does not model pharmacological doses. This gap is significant for any potential translational application.

CNS effects beyond acute neuroprotection. The Gallaher neonatal data establish that des(1-3) IGF-1 reaches the CNS and activates neuroprotective signaling acutely. Whether sustained CNS IGF-1R stimulation has positive or negative effects on adult neuroplasticity, cognition, or neurodegeneration models has not been directly studied with this specific analogue, only inferred from native IGF-1 CNS work.

Interaction with PAPP-A system. PAPP-A and PAPP-A2 are the major IGFBP proteases that cleave IGFBP-3 and IGFBP-5, releasing native IGF-1 from complexes. How the PAPP-A system's activity changes in response to exogenous des(1-3) IGF-1 (which does not itself require PAPP-A liberation) has not been studied. Negative feedback through reduced PAPP-A induction or altered IGFBP-3 levels could modulate the net free-IGF-1 environment in ways that alter dose-response relationships over time. ^[3]

Pharmacological Context and Adaptation Biology

Why IGFBP evasion matters for tissue-level research

Understanding how IGFBPs modulate tissue bioactivity is essential context for interpreting des(1-3) IGF-1 experiments. IGFBPs are not simply "IGF-1 sponges" that uniformly suppress IGF-1 action. They also serve as carriers that concentrate IGF-1 near specific cells expressing IGFBP proteases, and some IGFBPs (particularly IGFBP-3 and IGFBP-5) have direct IGF-1-independent nuclear signaling activities. ^[3] When des(1-3) IGF-1 is used as a research tool, it removes IGFBP-mediated modulation from the experimental system. This is a feature (clean receptor-level data) and a limitation (physiological IGFBP functions are absent from the model).

Tissues that express high levels of IGFBP proteases (bone, uterus, follicular fluid, injured tissue) naturally generate elevated free-IGF-1 at local sites, creating what is sometimes called the "tissue IGF-1 microenvironment." Des(1-3) IGF-1 essentially mimics this microenvironment pharmacologically in the absence of local IGFBP protease activation. Researchers studying tissue repair, bone healing, or endometrial biology can use des(1-3) IGF-1 to ask what elevated local free-IGF-1 does when the IGFBP proteolytic pathway is bypassed rather than activated.

Adaptation and receptor downregulation

Sustained IGF-1R stimulation leads to receptor downregulation through multiple mechanisms: receptor ubiquitination and proteasomal degradation, internalization and endosomal trafficking, and transcriptional suppression of the Igf1r gene through negative-feedback loops. ^[6] These adaptive responses are relevant for in-vivo experimental designs: an initial acute response to des(1-3) IGF-1 may not be maintained over days to weeks of repeated dosing as receptor expression falls. Researchers designing longitudinal anabolic experiments should include receptor expression measurements (Western blot for total IGF-1R, receptor tyrosine phosphorylation) at key time points to determine whether receptor downregulation is contributing to apparent tachyphylaxis.

Cross-talk between IGF-1R and insulin receptor signaling adds another layer of adaptation. The PI3K/Akt pathway downstream of both receptors activates mTORC1, which exerts negative feedback on IRS-1 through S6K1-mediated serine phosphorylation, reducing IRS-1's ability to activate PI3K. This mTORC1-to-IRS-1 negative feedback is a well-established mechanism of insulin/IGF-1 resistance in conditions of chronic pathway hyperactivation, such as obesity or sustained IGF-1R agonist exposure. ^[7] For researchers using des(1-3) IGF-1 in metabolic models, the possibility that repeated administration induces insulin resistance through this mechanism should be controlled for with appropriate insulin-tolerance tests at study end.

Interplay with growth hormone axis

Des(1-3) IGF-1 suppresses pituitary GH secretion through the same negative-feedback loop as native