Build Blend includes IGF-1 LR3, a synthetic analog of insulin-like growth factor 1 (IGF-1). Researchers developed this modified peptide to study how changes in IGF-binding protein interactions affect biological activity.
Its structure differs from natural human IGF-1. These changes give IGF-1 LR3 a much lower affinity for several IGF-binding proteins. This property can increase its biological activity in certain laboratory and animal models.
Research has examined IGF-1 LR3 in cell cultures and animal studies. However, these findings do not establish its safety or effectiveness in humans. IGF-1 LR3 is not an FDA-approved drug, and it has no established clinical use or approved human dosing guidelines.
What Is IGF-1 LR3?
IGF-1 LR3 is a modified version of insulin-like growth factor 1. Its structure includes an additional 13 amino acids at the N-terminus and an arginine substitution at position three.
These changes distinguish it from native IGF-1. They also reduce its binding affinity for several IGF-binding proteins (IGFBPs).
IGF-binding proteins normally regulate IGF-1 activity, transport, and availability. They help control how much IGF-1 remains available to interact with cellular receptors.
IGF-1 LR3 binds less strongly to these proteins. This difference can increase its availability for receptor interactions in experimental systems.
However, greater biological activity in an animal model does not prove greater clinical benefit in humans.
Mechanism of Action
IGF-1 LR3 is associated with the insulin-like growth factor signaling system. Its proposed activity involves several biological processes.
IGF-1 Receptor Interaction
IGF-1 normally interacts with the IGF-1 receptor (IGF-1R), a receptor tyrosine kinase found on many cell types.
Receptor activation can stimulate intracellular pathways linked to cell growth, metabolism, and survival. Two important signaling pathways include:
- PI3K/Akt pathway: Involved in cellular metabolism, survival, and protein synthesis.
- MAPK pathway: Involved in cell growth, differentiation, and proliferation.
IGF-1 LR3 can interact with the IGF signaling system. However, its activity and receptor interactions may differ from native IGF-1.
Reduced Binding to IGF-Binding Proteins
IGFBPs regulate the movement and availability of IGF molecules in biological systems. Native IGF-1 has a strong affinity for several of these binding proteins.
Research shows that LR3IGF-I has substantially lower affinity for IGFBP-3 and other binding proteins. This difference can increase its biological potency in certain experimental models.
Cellular Growth and Protein Metabolism
Researchers have studied IGF-1 signaling in relation to protein metabolism and tissue growth. Experimental findings suggest that LR3IGF-1 can influence these processes in animal models.
However, these results do not establish predictable changes in human muscle mass, strength, or physical performance.
What Does Current Research Show?
Most published research on IGF-1 LR3 comes from laboratory experiments and animal models. Human clinical evidence for this specific analog remains insufficient.
Research on IGF-Binding Proteins
A 1993 study compared IGF-I with LR3IGF-I and examined their interactions with IGF-binding proteins.
The researchers found that LR3IGF-I had approximately 1,000 times lower binding affinity for certain IGF-binding proteins. In cultured muscle cells, this reduced binding was associated with greater biological potency.
This study helps explain the molecular differences between native IGF-1 and its LR3 analog. It does not establish outcomes in human treatment.
Animal Research on Biological Activity
A 1996 study examined the effects of injected LR3IGF-I in normal and catabolic rats. Researchers compared its activity with native IGF-I over seven days.
The results showed greater activity for LR3IGF-I across several growth-related measurements. However, its effects on muscle loss were less pronounced than some other measurements suggested.
These findings provide information about its activity in rats. They cannot establish equivalent effects in human subjects.
Research on Blood Glucose Effects
A 1997 study examined IGF-I analogs, including LR3IGF-I, in pigs and marmoset monkeys.
The researchers reported that several analogs produced stronger reductions in blood glucose than native IGF-I. LR3IGF-I showed notable glucose-lowering activity in these animal models.
This finding is important because IGF-related activity can affect glucose regulation. It also highlights a potential safety concern rather than proof of a clinical benefit.
Human Clinical Evidence
The available research does not establish the safety or effectiveness of IGF-1 LR3 in humans. Studies of native IGF-1 cannot automatically support claims about this modified analog.
Mecasermin, sold under the brand name Increlex, is an FDA-approved form of recombinant human IGF-1 for specific pediatric patients with severe primary IGF-1 deficiency. It is not IGF-1 LR3, and its approval does not extend to LR3 products.
Safety and Regulatory Considerations
IGF-1 LR3 has no established human safety profile. Its effects on glucose regulation and cellular growth require particular attention.
- Hypoglycemia: Increased IGF activity can lower blood glucose levels.
- Abnormal tissue growth: IGF-1 signaling plays a role in cell growth and proliferation.
- Neoplasm concerns: Elevated IGF-1 activity raises concerns about potential effects on existing or developing tumors.
- Fluid retention: Increased activity within the growth hormone and IGF system may affect fluid balance.
- Organ-related effects: Changes in IGF signaling can influence several tissues and organ systems.
The FDA lists concerns such as neoplasm risk, glucose intolerance, intracranial hypertension, fluid retention, and pancreatitis in its discussion of risks associated with elevated IGF-1 and approved growth hormone therapies. These are relevant class-related concerns, not a confirmed adverse-event profile for IGF-1 LR3.
IGF-1 LR3 is not FDA-approved for human use. An FDA warning letter from 2020 specifically identified IGF-1 LR3 among bulk substances used by a pharmacy in products that did not qualify for the applicable section 503A compounding exemptions. The FDA also explains that compounded drugs are not FDA-approved; the agency does not review their safety, effectiveness, or quality before marketing.
Important distinction: FDA approval of mecasermin does not mean that IGF-1 LR3 has FDA approval. These compounds have different structures and regulatory statuses.
