Cyclic Glycine-Proline (cGP)

IGF-1 Bioavailability Regulator & Neuroprotective Peptide

Weight: 154.17 Da
Half-life: Extended stability (more stable than linear GPE precursor)
Chain: 2 amino acids (cyclic)
4 studies
2023 latest
Moderate Research
Dose 20-100 μg daily (or 300mg blackcurrant extract 2x daily)
Frequency Once daily, preferably in the morning
Cycle 4-12 weeks
Storage Room temperature in sealed container, protected from moisture and light

Community Research

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Endogenous cyclic dipeptide found in plasma, breast milk, and cerebrospinal fluid. Functions as metabolite of IGF-1, regulating its bioavailability through competitive binding to IGFBP-3. Demonstrates neuroprotective, cognitive-enhancing, and cardioprotective properties supported by clinical trials.

Mechanism of Action

Competes with IGF-1 for IGFBP-3 binding, normalizing bioavailable IGF-1 levels. Acts as positive allosteric modulator of AMPA and GABA-A receptors. Increases BDNF levels via Akt/MDM2-p53 pathway activation.

01 Neuroprotection and cognitive enhancement
02 IGF-1 optimization
03 Cardiovascular support
04 Metabolic health improvement
05 Blood-brain barrier penetration
06 Convenient oral administration

Molecular Data

Molecular Weight
154.17 Da
Chain Length
2 amino acids (cyclic)
Type
Cyclic dipeptide (2,5-diketopiperazine)
Amino Acid Sequence
One-letter: ??
H₂N
H
? 1
O ‖ C
N
H
? 2
COOH
cyc
1

cyclo(Gly

Position 1

Pro
2

Pro)

Position 2

N-terminus C-terminus
Hydrophobic
Polar
Positive (+)
Negative (-)
Modified

Research Indications

Neurological
Cognitive Enhancement effective

Higher cGP levels correlate with improved memory retention in elderly populations

Neuroprotection effective

Protects neural stem cells from oxidative stress; efficacy demonstrated in stroke models

Alzheimer's Disease moderate

Mouse studies show reduced amyloid plaque load and improved spatial memory

Parkinson's Disease moderate

Clinical study showed increased CSF cGP and reduced anxiety/depression scores

Metabolic
Type-2 Diabetes moderate

Clinical trial improved vascular complications and normalized HbA1c%

Blood Pressure Regulation moderate

Demonstrated systolic blood pressure reduction in clinical observations

Recovery
Stroke Recovery effective

Higher cGP/IGF-1 ratios associated with favorable clinical outcomes

Healthy Aging effective

Maintained ratios correlate with preserved cognitive function with age

Dosing Protocols

Preferred route with excellent bioavailability and blood-brain barrier crossing.

GoalDoseFrequencyRoute
General cognitive support20-40 μg1x dailyOral capsule
Neuroprotection/anti-aging40-50 μg1x dailyOral capsule
Metabolic/cardiovascular support40-100 μg1x dailyOral capsule
Via blackcurrant extract300 mg BCA2x dailyOral capsule

Interactions

++
IGF-1
cGP is metabolite of IGF-1; regulates bioavailability through competitive IGFBP-3 binding
synergistic
+
BPC-157
Different pathways; BPC-157 promotes tissue repair, cGP modulates IGF-1
compatible
+
Semax
Both offer neuroprotection and nootropic effects through distinct pathways
compatible
+
Selank
Complementary cognitive effects; Selank addresses anxiety, cGP optimizes IGF-1
compatible
~
GH Secretagogues
Both affect growth hormone/IGF-1 axis; monitor combined effects on levels
monitor

What to Expect

Week 1-2
Possible subtle improvements in mental clarity
Week 2-4
Enhanced cognitive function and focus may become noticeable
Week 4-8
Neuroprotective and metabolic benefits accumulating
Week 8-12
Optimal IGF-1 regulation and sustained cognitive support

Side Effects & Safety

Stop Signs - Discontinue if:

  • Allergic reactions (rash, difficulty breathing, swelling)
  • Unexpected blood glucose changes
  • Unusual fatigue or weakness

Contraindications

  • Consult healthcare provider if taking IGF-1 or growth hormone medications
  • Limited long-term human data available
  • Not studied in pregnancy

Quality Checklist

Good Signs

  • Third-party tested for purity and potency
  • Clear cGP content labeling (typically in micrograms per serving)
  • Natural blackcurrant-derived sources from New Zealand
  • Sealed containers protected from moisture and light

Warning Signs

  • Products lacking clear cGP content specification

Bad Signs

  • Extreme therapeutic claims unsupported by research
  • Vague concentration descriptions

References

  • IGF-1 Homeostasis Regulation Study
    Scientific Reports (2014)

    cGP regulates IGF-1 bioavailability through IGFBP-3 competitive binding

  • Alzheimer's Mouse Model Study
    PMC (2023)

    Significantly improved spatial memory; reduced hippocampal plaques 42.3→14.5 per mm²

  • Parkinson's Disease Clinical Study
    PMC (2018)

    Blackcurrant supplementation increased CSF cGP 74%; reduced anxiety/depression

  • Stroke Recovery & Cognitive Function Review
    PMC (2023)

    Higher cGP/IGF-1 ratios associated with favorable stroke outcomes

Related Peptides

BPC-157 compatible

Different pathways; BPC-157 promotes tissue repair, cGP modulates IGF-1

Semax compatible

Both offer neuroprotection and nootropic effects through distinct pathways

Selank compatible

Complementary cognitive effects; Selank addresses anxiety, cGP optimizes IGF-1

Disclaimer

This information is for educational and research purposes only. Consult a healthcare professional before use.