What it is
Cyclic glycine-proline is 2 amino acids, glycine and proline, joined in a ring. The body makes it. It forms when the first 3 amino acids break off the end of IGF-1 and then curl into a ring. It is found in human blood and in the fluid around the brain and spine. It is also found in some foods, such as blackcurrants. It helps control how much IGF-1 is free to act in the body. Most research comes from a group at the University of Auckland in New Zealand. See the IGF-1 LR3 entry for a related compound. Other names: cGP, cyclo(Gly-Pro).
What researchers study it for
- How much free IGF-1 is in the blood
- Memory and plaques in Alzheimer's model mice
- Recovery after stroke
- Whether it reaches the brain when taken by mouth
What the studies found
1. It competes with IGF-1 for the same carrier protein.
Most IGF-1 in the blood rides on a carrier protein called IGFBP-3. IGF-1 that is attached cannot act. A 2014 study showed cGP attaches to IGFBP-3 too. This pushes IGF-1 off and changes how much is free. The authors use the ratio of cGP to IGF-1 as a measure of IGF-1 activity. Lab data.
2. Alzheimer's model mice did better on memory tests and had fewer plaques.
A 2023 study from a lab in India gave cGP through the nose to mice bred to develop Alzheimer's-like changes. The mice did better in a water maze memory test. Amyloid plaques in their brains went down. This lab is separate from the New Zealand group. Mouse data only.
3. A lower cGP-to-IGF-1 ratio after stroke went with worse recovery.
A 2019 study measured blood levels in 34 stroke patients and 50 people without stroke. Stroke patients had lower cGP and a lower cGP-to-IGF-1 ratio. The ratio rose over 90 days of recovery. A higher ratio at the start went with better scores at 90 days. This shows a link, not that cGP caused better recovery. Human data.
4. A blackcurrant extract raised cGP in the brain fluid of Parkinson's patients.
A 2018 study gave 11 men with Parkinson's disease a blackcurrant extract by mouth for 28 days. The extract is a natural source of cGP. cGP went up in the fluid around the brain and spine. Levels there tracked levels in the blood. This shows cGP can reach the brain from the gut. The study was small and had no comparison group. Human data.
How much research exists
One key lab study, one mouse study, and two small human studies. Most of the work comes from one group in New Zealand. No controlled human trial of cGP by itself has been published.
Facts
- Formula: C7H10N2O2
- Weight: about 154 g/mol
- CAS number: 19179-12-5 (could not confirm)
- Sequence: cyclo(Gly-Pro), a ring of glycine and proline
- Time in the blood: never measured for cGP given from outside the body
- Storage: powder in the freezer, away from moisture.
Legal status
Not approved by the FDA or any other agency as a drug. Blackcurrant extracts that contain it are sold as supplements.
For research use only. Not for human use. Nothing here is medical advice.