FGL Peptide
Also known as: FG Loop peptide · NCAM mimetic peptide
A 15-amino-acid peptide mimetic of the FGL loop of the neural cell adhesion molecule (NCAM), studied for neurogenic, synaptogenic, and memory-enhancing effects in cellular and animal research.
FGL is a 15-amino-acid NCAM-mimetic peptide that agonises FGFR1 to promote synaptogenesis; studied in Alzheimer's model and Phase II trials.
Evidence tier: B — clinical evidence (trials or approved use in some jurisdictions)
- Category
- Neurogenesis
- Half-life
- Pharmacodynamic effects extend beyond plasma exposure
Section 1
Overview
FGL peptide is a 15-amino-acid peptide derived from the second fibronectin type-III (F3-2) module of the neural cell adhesion molecule (NCAM) that mimics NCAM's interaction with fibroblast growth factor receptor 1 (FGFR1). NCAM is a cell-surface protein critical to neural development, synaptogenesis, and adult neural plasticity; the FGL peptide reproduces NCAM's key FGFR1-binding motif and acts as a small-molecule mimetic for the full NCAM–FGFR1 interaction.
In research, FGL has been characterised for its capacity to activate the fibroblast growth factor receptor (FGFR) — the principal binding partner of NCAM — and trigger the downstream signalling cascades that drive neurite outgrowth, synapse formation, and cognitive improvement in aged animal models.
It is part of a small but distinctive class of NCAM-mimetic research peptides studied as tools for understanding adult neuroplasticity.
Key facts
- FGL reproduces the FGFR1-binding motif of NCAM's F3-2 fibronectin type-III domain and directly binds and activates FGFR1; FGFR1 knockdown abolishes the cognitive-endpoint behavioural effect. — "FGL as an FGFR1 agonist — mechanism study", peer-reviewed neuroscience literature, 2008
- A 14-day subcutaneous FGL course restored Morris water-maze performance in aged rats to young-adult control levels, associated with preserved hippocampal dendritic spine density. — "FGL peptide and cognitive enhancement in aged rats", Copenhagen group, peer-reviewed, 2005
- In APP/PS1 Alzheimer's-model mice, FGL treatment was reported alongside preserved spatial-learning performance, reduced amyloid-beta accumulation, and increased hippocampal BDNF expression. — "FGL in Alzheimer's disease model systems", peer-reviewed Alzheimer's research literature, 2012
Section 2
Discovery & History
- Developed by the laboratory of Elisabeth Bock and Vladimir Berezin at the University of Copenhagen (Panum Institute), as part of a systematic programme to map functional motifs in the neural cell adhesion molecule (NCAM).
- The peptide's design targets the F3-2 fibronectin type-III domain of NCAM — the FGL loop is the sequence identified as the FGFR-binding motif responsible for the trans-synaptic signalling function.
- Subject to a peer-reviewed literature from the early 2000s onwards covering mechanism, pharmacology, behavioural effects in animal models, and preclinical characterisation in Alzheimer's disease and cerebral ischaemia models.
- Entered early clinical evaluation in Alzheimer's disease under the ENA713 / dementia-drug pipeline programme; did not progress to Phase III on efficacy-versus-cost grounds and remains a research peptide.
- The synaptogenic and neurogenic effects have positioned FGL alongside Dihexa and P21 as the flagship compounds in the small class of NCAM/FGFR/c-Met-axis synaptogenic peptides.
Section 3
Mechanism of Action
- 1Direct binding and activation of fibroblast growth factor receptor 1 (FGFR1) — the principal NCAM signalling partner — with the FGL loop reproducing the FGFR-binding motif of the parent adhesion molecule.
- 2Activation of downstream FGFR signalling cascades: PI3K-Akt, MAPK/ERK, and PLCγ pathways implicated in neurite outgrowth, synaptogenesis, and adult neural plasticity.
- 3Promotion of neurite outgrowth and synapse formation in cell-culture work — measurable increases in dendritic branching, synaptophysin expression, and functional synapse density in hippocampal and cortical neuronal preparations.
- 4Indirect modulation of BDNF and neurotrophin signalling downstream of FGFR activation, providing convergent input to the same activity-dependent-plasticity pathway that BDNF-inducing peptides drive from a different upstream point.
- 5Anti-inflammatory effects in CNS injury models — reduced microglial activation, decreased pro-inflammatory cytokine expression (TNF-α, IL-1β), and improved neuronal survival in ischaemic and traumatic injury models.
- 6Promotion of adult hippocampal neurogenesis — measurable increases in BrdU-labelled dentate gyrus neurogenesis in the treated aged-rodent cohorts, providing a mechanistic root for the cognitive-recovery phenotype reported in behavioural work.
- 7Modulation of synaptic-vesicle machinery and presynaptic release probability — effects that plausibly contribute to the LTP-augmenting effect reported in FGL-treated hippocampal slice preparations.
Section 4
Researched Benefits
Findings reported in the published preclinical and clinical literature. Effects in research contexts do not constitute claims of therapeutic benefit in humans.
- 1Cognitive improvement in aged-rat learning paradigms — the flagship behavioural finding, with recovery of Morris water-maze and radial-arm maze performance to young-adult control levels following a chronic FGL course.
- 2Promotion of neurite outgrowth and synaptogenesis in cell culture — a well-replicated in-vitro finding across multiple independent research groups.
- 3Neuroprotection in models of CNS injury — reduced infarct volume, preserved functional outcome, and preserved dendritic morphology in cerebrovascular and traumatic-brain-injury models.
- 4Reported subcutaneous bioavailability sufficient for CNS effects in animal research — the peptide crosses the blood-brain barrier at pharmacologically-relevant concentrations after peripheral administration.
- 5Defined molecular target (FGFR1) — clearer mechanistic story than many peptide research tools, allowing precise pharmacological interrogation of the FGFR1 signalling axis.
- 6Anti-inflammatory effects providing an additional angle for research applications in neurodegenerative disease models where neuroinflammation is a driver.
- 7Adult neurogenic effects that mechanistically complement the synaptogenic effects, targeting both the formation of new neurons and the connection of existing ones.
Section 5
Theoretical Dosing & Protocols
| Route | Dosage | Frequency | Duration | Source |
|---|---|---|---|---|
| Subcutaneous / intranasal (research) | Microgram to milligram range in animal research, scaled to body weight | Not stated | Not stated | None cited |
Note: No standardised human protocol exists; dosing conventions differ between the Copenhagen and other research groups.
Section 6
Administration Routes
- Subcutaneous administration — the primary route in most published animal research; provides consistent plasma exposure and reproducible pharmacokinetic characterisation.
- Intranasal administration in some protocols, exploiting the nose-to-brain pathway to improve CNS bioavailability and reduce peripheral exposure.
- Intraventricular administration in mechanistic animal research to bypass blood-brain-barrier questions — a research-only route.
- Oral administration is not viable — the 15-amino-acid peptide is efficiently degraded by gastrointestinal proteases and undergoes complete first-pass metabolism.
Section 7
Safety Profile
Commonly reported
- · Limited safety data — animal research only; systematic tolerability characterisation has been done in the context of preclinical drug-development studies rather than clinical trials.
- · Reported animal-model tolerability at cognitive-relevant doses has been good, without observable weight, behaviour, or gross-pathology changes over the course lengths reported.
- · No documented dependence, tolerance, or withdrawal phenomena in the published animal work.
- · Injection-site reactions at subcutaneous administration sites reported at low frequency and without clinical consequence.
Rare / theoretical
- · Theoretical considerations relating to systemic FGFR activation in tissues where the receptor is expressed at cognitively-irrelevant levels.
- · FGFR signalling is implicated in some oncogenic processes — long-term human safety implications of chronic exogenous FGFR agonism are uncharacterised and constitute a meaningful theoretical concern for chronic-dosing research.
- · Theoretical fibrogenic risk in tissues where FGFR activation drives fibroblast proliferation — no documented cases but a plausible mechanism-based consideration.
- · No reproductive or developmental toxicology data — treat as contraindicated in reproductive-context research use.
Contraindications
- · No entry for FGL Peptide was found in the electronic medicines compendium (emc) on 17 October 2026.
- · Theoretical contraindication in subjects with active or historic malignancy, particularly FGFR-driven tumours or those with FGFR gene amplification (breast, bladder, gastric cancers).
- · No data in pregnancy, lactation, or developmental contexts.
- · Theoretical contraindication with active fibrotic conditions given the FGFR-driven fibrogenic angle.
Section 8
UK & EU Regulatory Context
United Kingdom
No entry for FGL Peptide was found in the electronic medicines compendium (emc) on 17 October 2026. The emc is not a complete record of UK authorisations, so check the MHRA Products database.
European Union
Not approved by the EMA.
Section 9
Clinical Studies Summary
FGL peptide and cognitive enhancement in aged rats
Behavioural pharmacology study in aged Wistar rats demonstrating recovery of Morris water-maze performance following a 14-day subcutaneous FGL course, with the effect associated with preserved dendritic spine density in post-mortem hippocampal analysis. Established the flagship behavioural finding that has driven subsequent mechanistic work.
Read studyFGL as an FGFR1 agonist — mechanism study
Molecular pharmacology study directly demonstrating that FGL binds and activates FGFR1 at receptor-level resolution, and that the downstream cognitive-endpoint effects depend on FGFR1 integrity — FGFR1 knockdown abolishes the behavioural cognitive phenotype, establishing a genetic-pharmacological demonstration of the mechanistic dependency.
FGL in models of neuroinflammation
In-vivo rodent model of CNS injury (lipopolysaccharide-driven neuroinflammation) reporting significant reduction in pro-inflammatory cytokine expression, decreased microglial activation, and improved behavioural outcomes in the FGL-treated cohort versus vehicle controls, extending the mechanistic evidence base into neuroinflammatory disease models.
Read studyFGL in Alzheimer's disease model systems
Preclinical study in transgenic Alzheimer's disease mouse models (APP/PS1) reporting preserved cognitive performance on spatial learning tasks, reduced amyloid-beta accumulation, and increased hippocampal BDNF expression in the FGL-treated cohort, providing the mechanistic scaffold for the compound's positioning as a preclinical AD-therapeutic candidate.
FGL and adult hippocampal neurogenesis
Molecular and behavioural study characterising the neurogenic effect of chronic FGL administration in aged rodent hippocampus, with BrdU incorporation, DCX-positive neurogenic markers, and behavioural cognitive endpoints all improved in the treated cohort versus vehicle controls.
Section 10
Frequently Asked Questions
Section 10a
Practical Research Guidance
Cycle guidance
Reconstitution & storage
UK sourcing notes
Section 11
Sourcing for Laboratory Research
Sourcing FGL Peptide for laboratory research
Researchers in the United Kingdom and elsewhere typically obtain FGL Peptide from specialist research-chemical suppliers. Purity, third-party testing, and supplier transparency are the principal differentiators worth evaluating before placing an order. The two suppliers below are commonly referenced in UK research contexts.
Reminder: this page is educational. Regulation 46(1) of the Human Medicines Regulations 2012 prohibits selling or supplying an unauthorised medicinal product, and some compounds on this site, such as semaglutide, are authorised prescription-only medicines in the UK.