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Cyclic Glycine-Proline (cGP)

Cognitive & Neurological · ['cGP', 'cyclo(Gly-Pro)', 'cyclic glycyl-proline', 'cycloprolylglycine']

A naturally occurring cyclic dipeptide cleaved from the N-terminus of IGF-1 that regulates IGF-1 bioavailability by competing for IGFBP-3 binding, studied for neuroprotective and neurodevelopmental effects.

🔬 Research use only — not for human or veterinary use. K4 Elite does not provide dosing instructions.
Molecular Formula
C7H10N2O2
Molecular Weight
154.17 g/mol
PubChem
CID 126154 ↗
Research Level
Well Researched
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Cyclic Glycine-Proline (cGP) chemical structure

Cyclic glycine-proline (cGP) is a small cyclic dipeptide (a diketopiperazine of glycine and proline) that occurs naturally as a metabolite cleaved from the N-terminal tripeptide of insulin-like growth factor-1 (IGF-1). It is also the active cyclic metabolite associated with the nootropic Noopept and is found ubiquitously, including in some marine and plant sources.

PubChem lists the L-proline stereoisomer under CID 126154 with molecular formula C7H10N2O2 and a molecular weight of about 154.17 g/mol. Because it is small, lipophilic, and enzymatically stable, the research literature describes it as orally available with reported brain uptake.

All information here is drawn from published preclinical and clinical research and is provided for research and reference use only.

cGP is described as a homeostatic regulator of IGF-1 function. It retains affinity for IGF-binding protein-3 (IGFBP-3) and competes with IGF-1 for IGFBP-3 binding. By shifting this binding equilibrium, cGP is proposed to modulate the amount of bioavailable, functional IGF-1 in circulation; the molar ratio of cGP to IGF-1 is used in the literature as an index of bioavailable IGF-1.

Through this IGF-1-normalizing effect, cGP has been associated in animal and cell studies with promotion of neurogenesis, synaptic function, and vascular remodeling, and with inhibition of inflammation, apoptosis, and vascular damage.

  • IGF-1 homeostasis: Studies showing cGP alters IGFBP-3 binding to regulate bioavailable IGF-1 (McNeill et al., Sci Rep 2014).
  • Neuroprotection: Animal models of ischemia and brain injury examining neuroprotective and vascular-remodeling effects.
  • Neurodevelopment: Studies of maternally administered cGP increasing offspring IGF-1 bioavailability and novelty recognition.
  • Ageing brain / cognition: Reviews and studies of cGP in age-related neurological conditions and IGF-1 normalization.
  • Metabolic and dietary contexts: Work on cGP and synaptophysin in high-fat-diet obese rat models.
📋 How published studies were conducted — a research reference summarizing study designs from the literature. This is not usage, dosing, or administration guidance. K4 Elite does not provide dosing instructions; determining any research protocol is the sole responsibility of the qualified researcher.

Guan et al. / McNeill et al., Scientific Reports (2014): Reported that cGP regulates IGF-1 homeostasis by altering the binding of IGFBP-3 to IGF-1, establishing the competitive-binding mechanism. Reported for reference only.

Maternal administration study, Endocrinology (2016): Reported that maternally administered cGP increased IGF-1 bioavailability and novelty recognition in developing offspring in a rodent model. Described for information only; any dosing figures are experimental parameters, not recommendations.

Ageing-brain review (PMC9919809): A review summarized cGP's role in normalizing IGF-1 function in the ageing brain and age-related neurological conditions, and noted that clinical trials of cGP analogues have been explored for developmental neurological conditions such as Rett and Fragile X syndromes. Reporting only.

Combinations examined in the research literature. Descriptive only — not a recommendation to combine compounds.

IGF-1 / IGFBP-3 systemSynergistic
cGP directly modulates IGF-1 bioavailability through IGFBP-3 binding; its activity is defined relative to this system.
Noopept (Omberacetam)Neutral
cGP is described as an active cyclic metabolite of Noopept, so their reported pharmacology overlaps.
Other IGF-1 pathway modulatorsCaution
Compounds that alter IGF-1 signaling could theoretically interact with cGP's homeostatic role in research settings.
Neurotrophic peptides (BDNF-pathway agents)Compatible
Studied within overlapping neuroprotection and neurogenesis research frameworks.

References are being compiled for this entry.

Where does cGP come from?
It is a naturally occurring cyclic dipeptide cleaved from the N-terminus of IGF-1, and is also the cyclic metabolite associated with the nootropic Noopept; it is found across many biological sources.
How does cGP affect IGF-1?
It competes with IGF-1 for binding to IGFBP-3, shifting the balance of bound versus free IGF-1 and thereby helping to normalize the amount of bioavailable IGF-1 in the research literature.
Why is cGP described as neuroprotective in studies?
Through its IGF-1-normalizing effect, animal and cell studies associate cGP with neurogenesis, synaptic function, and vascular remodeling, and with reduced inflammation and apoptosis.
Have cGP analogues been in clinical trials?
Reviews note that cGP analogue trials have been explored for developmental neurological conditions such as Rett and Fragile X syndromes; this entry reports that only and makes no efficacy claims.
Is cGP approved or intended for consumption?
No. This entry is for research and reference use only. cGP is not presented as an approved drug or supplement here, and nothing in it is medical advice or a usage recommendation.
Disclaimer: This profile summarizes published preclinical and laboratory research for reference only. It is not medical advice and makes no claim of safety or efficacy in humans. Determining any research protocol is the sole responsibility of the qualified researcher. Products are sold strictly for in-vitro research and have not been evaluated by the FDA.