IGF-1 LR3
Also known as: Long R3 IGF-1, Long R3 IGF-I, LR3IGF-I, Long [R3] IGF-I, Long [Arg3] IGF-I
3 notable studies · 3 references
TLDR
IGF-1 LR3 is an engineered IGF-1 analogue with greatly reduced IGF-binding-protein affinity and potent IGF1R activity in cell and animal models, but direct controlled human evidence is essentially absent and claims about human muscle growth or an exceptionally long circulating half-life are not established by the published evidence.
Research Supports
- Studied as an experimental tool for IGF-1 receptor signaling research
- Investigated for how reduced IGF-binding-protein affinity alters IGF biology
- Examined in cell and animal models of muscle, intestinal, and organ growth
- Studied for effects on endocrine feedback involving GH, insulin, and endogenous IGF-1
Observations Reported in Research
- Ballard et al., 1993: ~5-10x more potent than IGF-1 in L6 myoblasts, but cleared from rat plasma faster
- Conlon et al., 1995 (guinea pigs): increased organ weights (adrenal, intestine, kidney, spleen) without more body-weight gain
- Dunaiski et al., 1997 (pigs): infusion reduced weight gain, food intake, and endogenous GH/IGF-I/IGFBP-3/insulin
- No published controlled human trials of LR3 itself were identified
These are brief summaries of what the referenced research examined or reported — not conclusions about safety or effectiveness, and not medical advice. See Notable Studies and Sources & References below for the full context and citations.
At a Glance
Classification: Engineered recombinant insulin-like growth factor-1 analogue; IGF-1 receptor agonist; reduced IGF-binding-protein-affinity analogue
IGF-1 LR3 is an engineered analogue of human insulin-like growth factor-1 (IGF-1). It is not ordinary IGF-1. Native human IGF-1 contains 70 amino acids. Long R3 IGF-1 contains 83 and incorporates two major modifications: substitution of arginine for glutamic acid at position 3, and addition of a 13-amino-acid N-terminal extension. These modifications greatly reduce its affinity for several IGF-binding proteins (IGFBPs), increasing biological potency in many experimental systems. The research market frequently promotes IGF-1 LR3 for muscle growth, hypertrophy, recovery, tissue repair, nutrient partitioning, and fat loss. But there is extensive human research on IGF-1 and not equivalent human clinical research on IGF-1 LR3. Published LR3 research is overwhelmingly cellular and animal research. It is not FDA-approved for human use. Commercial LONG R3 IGF-I is manufactured principally as a laboratory/cell-culture growth factor; its manufacturer explicitly states that it is not approved or permitted for human applications.
What Is IGF-1 LR3?
IGF-1 is an endogenous growth factor involved in growth, development, protein synthesis, cell proliferation, cell survival, metabolism, and tissue remodeling. Much of circulating IGF-1 is associated with IGF-binding proteins. Those proteins influence distribution, stability, clearance, tissue exposure, and receptor availability. Researchers created LR3 partly to study what happens when IGF-1 interacts much less strongly with those binding proteins. LR3 has approximately 1,000-fold lower affinity for several IGFBPs in experimental systems, including IGFBP-3 and IGFBP-4. In L6 myoblast culture, that translated into approximately 5–10-fold greater biological potency than native IGF-1. That doesn't mean LR3 is simply “10× stronger IGF-1” in a living human. Its altered binding-protein interactions also change distribution and clearance.
What Are Researchers Studying?
IGF receptor signaling
LR3 retains biological activity at the IGF-1 receptor (IGF1R). IGF1R activation influences intracellular pathways including PI3K → AKT → mTOR and RAS → RAF → MEK → ERK. These pathways participate in protein synthesis, cell survival, proliferation, differentiation, and metabolism. LR3 is therefore frequently used experimentally as a strong IGF-axis stimulus.
IGF-binding proteins
This is actually one of LR3's most scientifically important uses. Because LR3 interacts poorly with IGFBPs, researchers can compare IGF-1 versus IGF-1 LR3 to investigate how binding proteins regulate IGF biology. Experiments found LR3 to be substantially more potent than native IGF-1 in several systems despite being cleared from circulation more rapidly, not more slowly. The popular claim that LR3's defining advantage is an extremely long circulating half-life is questionable. Its name refers to its structural N-terminal extension, not proof of a dramatically longer human plasma half-life.
Muscle biology
IGF signaling plays an established role in skeletal-muscle biology. Cell studies involving LR3 have examined myoblast proliferation, myoblast differentiation, protein synthesis, and IGFBP regulation. For example, experiments in L6 myogenic cells demonstrate biological responses to both IGF-1 and LR3 and show that IGFBP-3 can modify those responses. However, IGF-1 biology is not proof that LR3 builds muscle in humans. Published controlled human hypertrophy trials of LR3 itself are lacking.
Growth and tissue development
Animal experiments demonstrate substantial growth-related activity. In rats, LR3 was more potent than IGF-1 for several growth and anticatabolic outcomes, although effects varied by tissue and administration pattern. In guinea pigs, LR3 increased relative weights of several organs without increasing overall body-weight gain. Growth is not necessarily synonymous with skeletal-muscle growth. Growth factors can affect many tissues.
Intestinal growth
IGF signaling strongly affects gastrointestinal tissue. In rats, LR3 increased intestinal mucosal mass and altered glucose absorption. Researchers concluded that increased absorption appeared largely attributable to greater intestinal tissue mass rather than increased transporter activity per unit tissue. Systemic growth-factor signaling is biologically broader than the research-market phrase “muscle growth peptide.”
Endocrine feedback
Exogenous growth-factor signaling can alter endogenous endocrine systems. In pigs, LR3 infusion reduced food intake, weight gain, circulating IGF-1, IGFBP-3, insulin, and growth-hormone secretion rather than simply accelerating growth. Endocrine systems contain feedback loops. Adding an active growth factor does not simply stack linearly on top of endogenous physiology.
How Does It Work?
LR3 acts primarily through the IGF-1 receptor. IGF1R is a receptor tyrosine kinase. Activation triggers pathways including PI3K / AKT / mTOR (protein synthesis, metabolism, survival) and RAS / MAPK (proliferation and differentiation). This is what makes LR3 especially distinctive. Native IGF-1 interacts strongly with binding proteins. LR3 interacts much less strongly with them. Consequently, more peptide can remain available to interact with receptors in some experimental environments. But reduced binding also means it can be cleared from plasma more rapidly. That is almost the opposite of the usual research-market explanation.
What Does the Research Show?
Human research
Direct human interventional evidence for IGF-1 LR3 itself is extremely limited to essentially absent in the conventional clinical literature. This must not be confused with human research involving endogenous IGF-1, recombinant human IGF-1, mecasermin, IGF-1 deficiency, growth hormone, and IGF-axis biomarkers. Those findings cannot simply be transferred to LR3. The commercial laboratory product is explicitly intended for cell culture/research rather than human use.
Animal research
LR3 has been studied in rats, pigs, guinea pigs, sheep, and mice. Research demonstrates effects involving tissue growth, organ growth, protein metabolism, intestinal growth, endocrine feedback, mammary signaling, and muscle biology. Effects vary substantially between species. For example, LR3 stimulated several growth endpoints in rats but reduced weight gain and food intake in pigs. This is an unusually good warning against simplistic human extrapolation.
In-vitro research
LR3 is extensively used in cell culture. Indeed, one of its primary legitimate commercial applications is as a growth-factor supplement for serum-free or low-serum culture media. Research has investigated myoblasts, mammary cells, intestinal cells, stem/progenitor cells, IGFBP biology, protein synthesis, and IGF1R signaling.
Notable Studies
Effects of Interactions Between IGFBPs and IGFs on the Plasma Clearance and In Vivo Biological Activities of IGFs and IGF Analogs
animalResearchers compared IGF-1 with LR3 and demonstrated that LR3 had dramatically reduced affinity for IGF-binding proteins. In L6 myoblast culture, LR3 was approximately 5–10 times more potent. In rats, it was approximately sixfold more potent than IGF-1 in several growth measurements. However, LR3 was also removed from plasma more rapidly than native IGF-1.
Limitations: Preclinical research. Potency and clearance in rats/cell culture do not establish human efficacy or pharmacokinetics.
View publication →Long [R3] Insulin-Like Growth Factor-I Reduces Growth, Plasma Growth Hormone, IGF Binding Protein-3 and Endogenous IGF-I Concentrations in Pigs
animalFour days of LR3 infusion reduced average daily weight gain and food intake while suppressing several endogenous endocrine measures, including GH, IGF-I, IGFBP-3, and insulin.
Limitations: Pig physiology cannot establish human effects. The findings also illustrate substantial species differences.
View publication →Long R3 Insulin-Like Growth Factor-I Infusion Stimulates Organ Growth but Reduces Plasma IGF-I, IGF-II and IGF Binding Protein Concentrations in the Guinea Pig
animalLR3 increased relative weights of the adrenal glands, intestine, kidneys, and spleen while reducing circulating endogenous IGFs and binding proteins. Overall body-weight gain was not significantly increased.
Limitations: Animal study with tissue-growth endpoints rather than human therapeutic outcomes.
View publication →What We Still Don't Know
Human pharmacokinetics Human half-life Safe human exposure Long-term safety Controlled human muscle-growth effects Effects on human organs during prolonged exposure Effects on glucose regulation in humans Long-term effects of sustained IGF1R activation Human cancer-related risks Whether community claims about localized versus systemic effects are accurate Whether common research-market products match the characterized laboratory reagent Whether reported bodybuilding outcomes have any reliable causal basis
Related Compounds
Recent publications
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Sources & References
- Effects of Interactions Between IGFBPs and IGFs on the Plasma Clearance and In Vivo Biological Activities of IGFs and IGF Analogs
- Conlon MA, Tomas FM, Owens PC, et al. Long R3 Insulin-Like Growth Factor-I Infusion Stimulates Organ Growth but Reduces Plasma IGF-I, IGF-II and IGF Binding Protein Concentrations in the Guinea Pig.
- Dunaiski V, Dunshea FR, Walton PE, Goddard C. Long [R3] Insulin-Like Growth Factor-I Reduces Growth, Plasma Growth Hormone, IGF Binding Protein-3 and Endogenous IGF-I Concentrations in Pigs.
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