Educational reference, not medical advice. This page summarizes information from published research and regulatory filings for educational purposes. It is not a recommendation to use any compound and should not replace guidance from a licensed healthcare provider. Most peptides discussed here are not approved for the uses described.
What it is
FGL (sometimes written FGLL) is a synthetic 15-amino-acid peptide derived from the second fibronectin-type-III module of the neural cell adhesion molecule (NCAM). It was designed to mimic the structural motif on NCAM that engages the fibroblast growth factor receptor (FGFR), thereby triggering FGFR signaling without requiring the full NCAM protein.
The sequence is taken from the loop region of the FN3 module thought to be central to NCAM's role in axonal outgrowth and synaptic plasticity. The peptide is small enough to cross the blood-brain barrier after subcutaneous or intranasal administration in rodents, which is one reason it has remained an active research tool despite never advancing to clinical development.
History
FGL was characterized by Vladimir Berezin, Elisabeth Bock, and colleagues at the University of Copenhagen in the early 2000s. The defining paper by Cambon and colleagues in Journal of Neuroscience (2004) demonstrated that the peptide promotes synaptogenesis in cultured hippocampal neurons, enhances presynaptic function, and facilitates spatial-memory consolidation in rats.
Over the next decade the same group and collaborators published a series of papers extending the profile: rescue of FGFR phosphorylation in NCAM-deficient mice (Aonurm-Helm 2010), anti-inflammatory effects in aged-rodent brain (Downer 2010), facilitation of AMPA receptor synaptic delivery as a mechanism for cognitive enhancement (Knafo 2012), and modulation of striatal plasticity (Dallérac 2011). An attempt to advance FGL toward clinical development was made by ENKAM Pharmaceuticals, a Danish spin-out, but the program did not reach a published Phase I trial.
Regulatory status
FGL has no approved medical use. It has not been the subject of a published Phase I trial registered with the FDA or EMA. It is sold only through research-chemical suppliers, with not-for-human-use labeling.
How researchers describe its action
The proposed mechanism centers on FGFR activation via the NCAM-mimicking face of the peptide:
- FGFR engagement. FGL binds FGFR-1 (and to a lesser extent other FGFR family members), triggering receptor dimerization and downstream MAPK/PI3K signaling — the same canonical FGFR pathway activated by endogenous FGF ligands.
- Synaptogenesis. Cell-culture work shows that FGL promotes formation of presynaptic terminals and modulates synaptic transmission.
- AMPA receptor trafficking. The Knafo et al. 2012 paper identified facilitated synaptic insertion of AMPA receptors as a molecular correlate of FGL's procognitive effects in rats.
- Anti-inflammatory effects. Downer and colleagues described attenuation of LPS-induced and age-related neuroinflammatory changes in rodent brain.
These findings are uniformly preclinical. Mechanism data in human tissue is not available.
Half-life and dosing intervals
Published pharmacokinetics for FGL are limited. The peptide is small and crosses the blood-brain barrier reasonably well in rodents after subcutaneous or intranasal administration. Plasma half-life estimates fall in the range of 1 to 4 hours, with central nervous system concentrations declining over a similar timeframe.
Dosing in rodent studies varies. The Cambon 2004 paper used subcutaneous administration of 1 to 10 mg/kg in rats; subsequent studies have used intranasal dosing in the low-microgram range per nostril. There is no established human dose.
Reconstitution example
Research-grade FGL is sold as a lyophilized powder, typically in 5 mg or 10 mg vials. A 5 mg vial reconstituted with 1 mL of bacteriostatic water or saline yields 5 mg/mL. For intranasal administration in research applications, this concentration is often further diluted depending on the dose targeted.
Vial's calculator handles the mass-to-volume conversion when you enter the vial mass and water volume.
What to know
- Strictly preclinical. All efficacy data comes from cell culture and rodent studies. No Phase I human trial has been published.
- Designed for blood-brain barrier crossing. The small size and intentional design of FGL allow CNS penetration after peripheral administration, which is part of why the peptide has remained a useful research probe.
- Storage. Lyophilized FGL is stable refrigerated and most stable frozen. Once reconstituted, refrigerate and use within the stability window quoted by the supplier (typically 1 to 2 weeks).
- FGFR pathway considerations. Sustained FGFR activation has implications in unrelated literature (FGFR signaling is involved in some tumor types); long-term safety of exogenous FGFR-activating peptides has not been characterized in any human study.
- Naming. "FGL" and "FGLL" are used interchangeably for the same 15-amino-acid peptide; older Berezin and Bock papers use both designations.
Sources
- 1.Cambon K, Hansen SM, Venero C, Herrero AI, Skibo G, Berezin V, Bock E, Sandi C (2004). A synthetic neural cell adhesion molecule mimetic peptide promotes synaptogenesis, enhances presynaptic function, and facilitates memory consolidation. Journal of Neuroscience.
- 2.Aonurm-Helm A, Berezin V, Bock E, Zharkovsky A (2010). NCAM-mimetic, FGL peptide, restores disrupted fibroblast growth factor receptor (FGFR) phosphorylation and FGFR mediated signaling in neural cell adhesion molecule (NCAM)-deficient mice. Brain Research.
- 3.Downer EJ, Cowley TR, Lyons A, Mills KH, Berezin V, Bock E, Lynch MA (2010). A novel anti-inflammatory role of NCAM-derived mimetic peptide, FGL. Neurobiology of Aging.
- 4.Knafo S, Venero C, Sánchez-Puelles C, Pereda-Peréz I, Franco A, Sandi C, Suárez LM, Solís JM, Alonso-Nanclares L, Martín ED, Merino-Serrais P, Borcel E, Li S, Chen Y, Esteban JA (2012). Facilitation of AMPA receptor synaptic delivery as a molecular mechanism for cognitive enhancement by the NCAM-derived peptide FGL. PLoS Biology.
- 5.Dallérac G, Zerwas M, Novikova T, Callu D, Leblanc-Veyrac P, Bock E, Berezin V, Rampon C, Doyère V (2011). Updating temporal expectancy of an aversive event engages striatal plasticity under amygdala control: long-term plasticity facilitated by FGL. Learning & Memory.