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What Is IGF-1?
IGF-1 (Insulin-like Growth Factor 1, also called Somatomedin C) is a 70-amino acid peptide hormone structurally similar to insulin. It's primarily produced by the liver in response to growth hormone (GH) stimulation and mediates many of GH's anabolic effects on tissues throughout the body.
Key Characteristics
- Role: Primary mediator of growth hormone effects
- Structure: Similar to insulin (hence "insulin-like")
- Binding: Circulates bound to IGFBPs (binding proteins)
- Effects: Growth, anabolic, anti-apoptotic
GH → IGF-1 Axis
Understanding the GH/IGF-1 relationship:
- GH stimulates liver to produce IGF-1
- IGF-1 provides negative feedback on GH release
- Many GH effects are mediated through IGF-1
- Some GH effects are direct (not IGF-1 dependent)
- IGF-1 is used clinically as marker of GH status
Biological Functions
- Growth: Essential for linear growth in children
- Anabolic: Protein synthesis in muscle
- Metabolic: Glucose uptake, fat metabolism
- Cell survival: Anti-apoptotic effects
- Brain: Neurogenesis and neuroprotection
Clinical Use
Mecasermin (recombinant IGF-1) is FDA-approved for:
- Primary IGF-1 deficiency (GH insensitivity)
- Laron syndrome (GH receptor defect)
- GH gene deletion with antibodies to GH
Variants and Analogs
| Compound | Description | Notes |
|---|---|---|
| IGF-1 | Native 70 aa | Short half-life |
| IGF-1 LR3 | 83 aa, modified | Research; longer half-life |
| IGF-1 DES | 67 aa, truncated | Research; more potent locally |
| MGF | Mechano-Growth Factor | IGF-1 splice variant |
IGF-1 and Aging/Longevity
Interestingly, the IGF-1/longevity relationship is complex:
- Low IGF-1 associated with extended lifespan in some species
- Laron syndrome patients (no IGF-1) have low cancer rates
- High IGF-1 may increase certain cancer risks
- The "growth-longevity tradeoff" concept
Medical Use Only
IGF-1 (Mecasermin) is a prescription medication with significant side effects including hypoglycemia, increased intracranial pressure, and potential cancer risk concerns. Research forms like IGF-1 LR3 are not approved for human use. IGF-1 use is banned in sports.
Summary
IGF-1 is the key downstream mediator of growth hormone's effects on tissues. While essential for normal growth and development, it also raises interesting questions about the tradeoff between growth/anabolism and longevity. Clinical use is limited to specific deficiency states due to side effect concerns.