P21 Peptide
| Category | Compounds |
|---|---|
| Also known as | P021, CNTF-derived Peptide |
| Last updated | 2026-04-14 |
| Reading time | 3 min read |
| Tags | nootropicneurogenesiscntf-mimeticresearch |
Overview
P21, sometimes written as P021, is a small peptidomimetic derived from the active region of ciliary neurotrophic factor (CNTF). CNTF itself is a neurotrophic cytokine with therapeutic interest in neurodegenerative disease, but its clinical development was limited by poor blood-brain barrier penetration and side-effect profile. P21 was designed to capture the neurogenic activity of CNTF in a much smaller, brain-penetrant molecule.
Research on P21 — largely from laboratories associated with Khalid Iqbal and colleagues at the New York State Institute for Basic Research — describes stimulation of adult hippocampal neurogenesis, enhancement of cognitive function in mouse models of Alzheimer's disease, and reductions in tau phosphorylation. Its positioning is therefore both nootropic and neurodegeneration-focused.
P21 is commonly discussed alongside other research peptides with neurotrophic or neurogenic aims: Dihexa, Cerebrolysin, Semax, Noopept, and FGL.
Structure / Chemistry
P21 is a small peptide (typically described as a tetrapeptide amide derivative) modeled on residues within the CNTF sequence responsible for neurogenic activity. Its size and chemistry were selected to improve blood-brain barrier penetration and stability relative to the full protein.
Mechanism of Action
P21 is thought to engage leukemia inhibitory factor receptor (LIFR) signaling and downstream JAK/STAT pathways involved in neurogenesis. It increases BDNF expression and promotes proliferation and differentiation of hippocampal neural progenitor cells. In Alzheimer's disease models, downstream effects include reduced tau hyperphosphorylation and improved synaptic plasticity.
Research Summary
| Area | Finding | Reference |
|---|---|---|
| Neurogenesis | Adult hippocampal neurogenesis enhanced | Kazim et al., Neurobiol Dis 2014 |
| Alzheimer's model | Cognitive improvement in 3xTg-AD mice | Kazim et al., J Alzheimers Dis 2017 |
| Down syndrome model | Corrected learning deficits in Ts65Dn mice | Kazim et al., Mol Neurodegener 2017 |
| Tau biology | Reduced tau phosphorylation in models | Kazim et al., Neurobiol Dis 2014 |
| Stress | Reversed stress-induced cognitive deficit | Kazim et al., Transl Psychiatry 2019 |
Pharmacokinetics
P21 was designed to cross the blood-brain barrier after peripheral administration. Rodent studies have used subcutaneous or intraperitoneal routes with chronic dosing schedules. Specific half-life and human pharmacokinetic values are not well established outside preclinical work.
Common Discussion Topics
- Translation of neurogenic effects from rodent models to humans.
- Comparison with CNTF itself and reasons for the smaller peptidomimetic approach.
- Role in Alzheimer's and Down syndrome model research.
- Overlap with Dihexa as a cognitive research peptide.
- Availability and sourcing questions in the research-compound market.
Related Compounds
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Related entries
- Cerebrolysin— A porcine brain-derived peptide preparation containing low-molecular-weight neuropeptides and free amino acids, approved in over 40 countries for stroke, traumatic brain injury, and dementia, though not FDA-approved in the United States.
- Dihexa— A hexapeptide analog of angiotensin IV reported to be up to seven times more potent than BDNF at promoting hepatocyte growth factor signaling, studied primarily for cognitive enhancement and synaptogenesis in animal models.
- FGL— FGL is a short peptide mimetic of NCAM's FGFR-binding site, studied for neurotrophic, cognitive, and neuroprotective activity.
- Noopept— Noopept is a synthetic proline-containing dipeptide nootropic developed in Russia, often discussed as a more potent, orally active analog of piracetam.
- Semax— A synthetic heptapeptide analog of ACTH(4-10) developed in Russia as a nootropic and neuroprotective agent, studied for cognitive enhancement, stroke recovery, and BDNF modulation.