# P21 — Research Peptide Profile

> P21 (P021) is a CNTF-mimetic peptide that increased dentate gyrus neurogenesis and reduced tau pathology in Alzheimer-model mice. No human trials exist.

Source: https://peptpedia.org/peptide/p21 | Published: 2026-09-18 | Last updated: 2026-09-18

P21 (P021) is a CNTF-mimetic peptide (Ac-DGGL(A)G-NH2) that pairs a 4-residue fragment of ciliary neurotrophic factor with an adamantane-cage glycine for stability and brain penetration. In transgenic Alzheimer mice, chronic oral treatment increased dentate gyrus neurogenesis, reduced tau hyperphosphorylation, and rescued cognition. It has never been given to humans in a published study, and all in vivo work comes from a single research group.

## Overview

P21 (P021) is a synthetic neurotrophic peptide mimetic designed by the Iqbal and Grundke-Iqbal group at the New York State Institute for Basic Research in Developmental Disabilities. It consists of an N-acetylated tetrapeptide (Asp-Gly-Gly-Leu) corresponding to a biologically active region of human ciliary neurotrophic factor (CNTF residues 148-151), C-terminally fused to an adamantane-cage glycine mimetic amide that increases stability and lipophilicity; the primary literature writes it as Ac-DGGL(A)G-NH2 (PubChem CID 56599151; C27H42N6O8; CAS 1246751-68-7). The design goal was explicit: a small, blood-brain-barrier-permeable compound that mimics the neurogenesis-promoting action of CNTF without CNTF's size, instability, and inflammatory liabilities. The 2010 FEBS Letters discovery study showed peripheral administration improved learning and memory and boosted dentate gyrus neurogenesis in normal adult mice. Follow-up work in 3xTg-AD Alzheimer mice reported disease-modifying effects after chronic oral dosing: reduced tau hyperphosphorylation, rescued neurogenesis and synaptic plasticity deficits, improved cognition, and, in a prevention design, reduced mortality. Aged-rat cerebrospinal fluid studies showed reduced tau levels and no detectable immune reaction. All published in vivo evidence comes from the same research group, and no human study of any kind has been published.

## Molecular Profile

- **Category:** cognitive-enhancement
- **Molecular formula:** C27H42N6O8
- **Molecular weight:** 578.7 g/mol
- **CAS number:** 1246751-68-7
- **Amino acid sequence:** Ac-DGGL(A)G-NH2 (N-acetyl Asp-Gly-Gly-Leu with a C-terminal adamantane-cage glycine mimetic amide)
- **Also known as:** P021, P-21, Peptide 021, Ac-DGGL(A)G-NH2
- **Half-life:** Not formally published; designed for metabolic stability via the adamantane cage and end caps, and orally active in diet studies
- **Solubility:** Formulated for oral dietary administration in animal studies
- **Storage:** No validated stability data; lyophilized peptides of this class are typically stored at -20°C.

## Mechanism of Action

P021 acts as a neurotrophic factor mimetic rather than through a single defined receptor. In 3xTg-AD mice it increased hippocampal BDNF expression, engaging the BDNF/TrkB/PI3K/AKT axis and inhibiting glycogen synthase kinase-3-beta (GSK3-beta), the principal tau kinase; this provides a mechanistic link to the observed reduction in abnormal tau hyperphosphorylation (PMID: 25046994). In the dentate gyrus it enhanced neurogenesis and the maturation of newly born neurons in the granular cell layer and subgranular zone, coupling neurogenesis to improved synaptic plasticity measures (PMID: 20600002). The compound is blood-brain-barrier permeable after oral dosing, attributed to the adamantane cage and end caps, and reduced brain total tau and CSF tau toward young-adult levels in aged rats (PMID: 26401692). Amyloid effects are limited: soluble A-beta levels fell in 3xTg-AD mice but plaque load only trended down, consistent with reduced A-beta generation rather than clearance.

## Key Research Findings

- P021 is a rationally designed CNTF mimetic: the CNTF(148-151) fragment DGGL with N-acetyl and a C-terminal adamantane-cage glycine amide, giving oral, brain-penetrant activity.
- Chronic oral treatment of 3xTg-AD mice reduced tau hyperphosphorylation via the BDNF/TrkB/GSK3-beta axis and rescued cognition, neurogenesis, and synaptic plasticity; a prevention-start design also markedly reduced mortality.
- In aged rats it normalized elevated CSF tau to young-adult levels without a detectable immune reaction, a notable tolerability signal for a peptide.
- The entire evidence base is one research group's mouse and rat work; there is no human study and no independent replication, which caps confidence in the headline claims.

## Safety & Tolerability

P021 has no human safety data of any kind; it has been studied only in rodents. Within that limit, the published record is favorable: chronic oral administration for up to 12-18 months was tolerated in transgenic mice, and an aged-rat study explicitly found no detectable immune reaction. The concentration of all evidence in a single research group, with no independent replication, is itself a safety-relevant caveat.

**Human data status:** No human trials, human pharmacokinetics, or human exposure data exist. The compound has been administered only to mice and rats in published research.

**Regulatory status:** Not approved anywhere; a preclinical research compound with no registered clinical trial.

- Twelve months of chronic oral P021 in 3xTg-AD mice produced disease-modifying effects without reported toxicity, and the prevention-start study additionally reported markedly reduced mortality in treated animals. (evidence tier: animal; [PMID 25046994](https://pubmed.ncbi.nlm.nih.gov/25046994/))
- In aged rats, chronic oral P021 reduced elevated CSF tau to young-adult levels and, notably for a peptide drug candidate, did not induce any detectable immune reaction. (evidence tier: animal; [PMID 26401692](https://pubmed.ncbi.nlm.nih.gov/26401692/))
- Treatment from birth to postnatal day 120 in 3xTg-AD mice prevented Alzheimer-like behavior and synaptic dysfunction; developmental-stage exposure showed no reported adverse effect in that study. (evidence tier: animal; [PMID 34057082](https://pubmed.ncbi.nlm.nih.gov/34057082/))
- All published P021 in vivo work originates from a single research group (Iqbal/Grundke-Iqbal, NYS Institute for Basic Research); independent replication has not been published, and vendor dosing schedules have no pharmacokinetic basis. (evidence tier: theoretical)

## Dosing Information (Research Context)

Published mouse studies administered P021 chronically by the oral route, admixed into formulated diet at 60 nmol of peptide per gram of diet for up to 12 months in 3xTg-AD treatment and prevention studies. The 2010 discovery study used peripheral (intraperitoneal) injection over 4 weeks in adult mice. No human dosing exists; the compound has never been administered to humans in a published study.

| Route | Dose | Frequency | Notes |
| --- | --- | --- | --- |
| Oral, admixed in diet (mouse) | 60 nmol/g of formulated diet | Continuous, weeks to 12 months | 3xTg-AD chronic treatment, prevention, and early-development studies (PMID: 25046994, 28387677, 34057082) |
| Intraperitoneal (mouse) | Peripheral dosing over 4 weeks | Per protocol | Discovery study in normal adult C57Bl6 mice (PMID: 20600002) |

## Researched Effects

- **Adult Hippocampal Neurogenesis** (evidence: moderate): The discovery study showed that peripherally administered P021 increased neurogenesis and maturation of newborn neurons in the granular cell layer and subgranular zone of the dentate gyrus in normal adult C57Bl6 mice, alongside improved learning, short-term, and spatial reference memory (PMID: 20600002). Neurogenesis rescue was later replicated in 3xTg-AD mice, where the compound restored deficits rather than augmenting baseline. This is the defining and best-documented effect of the peptide, though all demonstrations come from one research group.
- **Tau Pathology Reduction** (evidence: moderate): Chronic oral P021 significantly reduced abnormal hyperphosphorylation and accumulation of tau at major Alzheimer neurofibrillary-pathology sites in 3xTg-AD mice, mechanistically tied to BDNF-mediated inhibition of GSK3-beta (PMID: 25046994). In aged Fisher rats, chronic treatment reduced brain total tau and brought elevated CSF tau down to young-adult levels (PMID: 26401692). Two convergent models support the tau effect; no human biomarker data exists.
- **Cognitive Rescue in Alzheimer Models** (evidence: moderate): In 3xTg-AD mice treated for 12 months from 9-10 months of age, P021 rescued deficits in cognition, neurogenesis, and synaptic plasticity at both moderate and severe pathology stages (PMID: 25046994). A prevention study starting treatment at 3 months, before overt pathology, prevented neurodegeneration, A-beta and tau pathologies, episodic memory impairment, and markedly reduced mortality (PMID: 28387677). Treatment initiated during early postnatal development likewise prevented Alzheimer-like behavior and synaptic dysfunction (PMID: 34057082).
- **Synaptic Plasticity Enhancement** (evidence: moderate): Beyond neuron birth, the discovery study reported improved synaptic plasticity alongside the memory gains, and chronic oral treatment later rescued synaptic plasticity deficits in 3xTg-AD mice together with cognition and neurogenesis (PMID: 20600002, 25046994). The coupling of neurogenesis with synaptic recovery is the basis for the group's neurotrophic-compound therapeutic framework.
- **Amyloid-Beta Effects** (evidence: preliminary): The amyloid dimension is deliberately modest: in 3xTg-AD mice, P021 significantly decreased soluble A-beta levels but produced only a trend toward reduced CA1 plaque load, a pattern the authors interpreted as reduced A-beta generation rather than plaque clearance (PMID: 25046994). Claims of anti-amyloid action beyond this are not supported by the published data.

## Research Applications

- Alzheimer's Disease Research
- Neurogenesis Studies
- Neurotrophic Factor Mimetics
- Cognitive Aging Research
- Tau Pathology Research

## Key Studies

### Neurotrophic peptides incorporating adamantane improve learning and memory, promote neurogenesis and synaptic plasticity in mice

Li B, Wanka L, Blanchard J, et al. — *FEBS Letters* (2010) — [PMID 20600002](https://pubmed.ncbi.nlm.nih.gov/20600002/) | [doi:10.1016/j.febslet.2010.06.025](https://doi.org/10.1016/j.febslet.2010.06.025)

The discovery paper: the Iqbal group designed P21 (Ac-DGGLAG-NH2), a CNTF-derived peptide incorporating an adamantane-containing glycine mimetic, to mimic neurotrophin action while surviving peripheral administration. Given peripherally to normal adult C57Bl6 mice, P21 enhanced learning, short-term and spatial reference memory, induced neurogenesis and maturation of newborn neurons in the dentate gyrus granular layer and subgranular zone, and increased synaptic markers. It established both the compound and the adamantane-stabilization design principle.

### Disease modifying effect of chronic oral treatment with a neurotrophic peptidergic compound in a triple transgenic mouse model of Alzheimer's disease

Kazim SF, Blanchard J, Dai CL, et al. — *Neurobiology of Disease* (2014) — [PMID 25046994](https://pubmed.ncbi.nlm.nih.gov/25046994/) | [doi:10.1016/j.nbd.2014.07.001](https://doi.org/10.1016/j.nbd.2014.07.001)

The flagship efficacy study: 3xTg-AD and wild-type female mice received P021 (Ac-DGGL(A)G-NH2) or vehicle diet for 12 months starting at 9-10 months of age, covering moderate to severe pathology stages. Treatment significantly reduced abnormal tau hyperphosphorylation and accumulation at major neurofibrillary sites, decreased soluble A-beta (with only a trend on plaques, implying reduced generation rather than clearance), and rescued cognition, neurogenesis, and synaptic plasticity deficits. The mechanism was traced to increased BDNF expression with downstream inhibition of GSK3-beta activity.

### Elevated Tau Level in Aged Rat Cerebrospinal Fluid Reduced by Treatment with a Neurotrophic Compound

Khatoon S, Chalbot S, Bolognin S, et al. — *Journal of Alzheimer's Disease* (2015) — [PMID 26401692](https://pubmed.ncbi.nlm.nih.gov/26401692/) | [doi:10.3233/JAD-142799](https://doi.org/10.3233/JAD-142799)

This aged-Fisher-rat study produced three notable findings: P021 is blood-brain-barrier permeable; chronic oral treatment reduced brain total tau and brought the age-elevated CSF tau level down to that of young adult rats (CSF A-beta/A-betaPP, also elevated with age, was not reduced); and P021 induced no detectable immune reaction, an important early tolerability signal for a peptide therapeutic. The CSF tau finding frames a translational biomarker strategy the authors proposed for future trials.

### Prevention of Amyloid-beta and Tau Pathologies, Associated Neurodegeneration, and Cognitive Deficit by Early Treatment with a Neurotrophic Compound

Baazaoui N, Iqbal K — *Journal of Alzheimer's Disease* (2017) — [PMID 28387677](https://pubmed.ncbi.nlm.nih.gov/28387677/) | [doi:10.3233/JAD-170075](https://doi.org/10.3233/JAD-170075)

A secondary-prevention experiment: continuous P021 treatment of 3xTg-AD mice was started at 3 months of age, during the synaptic compensation period months before overt pathology. Followed at 9, 15, and 18 months of treatment, treated animals showed prevention of neurodegeneration (Fluorojade C), of A-beta and tau pathologies (immunohistochemistry and Western blot), and of episodic memory impairment (novel object recognition at 16-17 months), plus a marked reduction in mortality rate. It is the strongest claim in the P021 literature and awaits independent replication.

### Neurotrophic Treatment Initiated During Early Postnatal Development Prevents the Alzheimer-Like Behavior and Synaptic Dysfunction

Wei W, Liu Y, Dai CL, et al. — *Journal of Alzheimer's Disease* (2021) — [PMID 34057082](https://pubmed.ncbi.nlm.nih.gov/34057082/) | [doi:10.3233/JAD-201599](https://doi.org/10.3233/JAD-201599)

Extending the prevention paradigm to its limit, this study treated 3xTg-AD and wild-type female mice with P021 in diet (60 nmol/g formulated diet) from birth to postnatal day 120. Early-development treatment prevented the emergence of Alzheimer-like cognitive deficits and synaptic dysfunction. The paper also documents the compound's identity precisely: Ac-DGGL(A)G-NH2, monoisotopic molecular weight 578.3 (average 578.7), corresponding to human CNTF residues 148-151 with C-terminal adamantylated glycine added to increase stability and lipophilicity.

## Frequently Asked Questions

### What is P21 and how is it related to CNTF?

P21 (P021) is a synthetic mimetic of ciliary neurotrophic factor. It takes a 4-amino-acid active-region fragment of human CNTF (residues 148-151, Asp-Gly-Gly-Leu) and adds an N-terminal acetyl group and a C-terminal adamantane-cage glycine mimetic amide, written Ac-DGGL(A)G-NH2. The goal was to keep CNTF's neurogenesis-promoting activity in a small, stable, brain-penetrant compound, avoiding full-length CNTF's delivery and inflammatory problems.

### Has P21 been tested in humans?

No. Every published P021 study is preclinical, conducted in mice or rats, and all in vivo work comes from a single research group (the Iqbal group at the NYS Institute for Basic Research). There is no human pharmacokinetic, safety, or efficacy data, no registered clinical trial, and no independent replication of the headline Alzheimer-mouse findings.

### What did the Alzheimer mouse studies actually show?

In 3xTg-AD mice, 12 months of oral P021 from 9-10 months of age reduced tau hyperphosphorylation and soluble amyloid, rescued cognition, neurogenesis, and synaptic plasticity (PMID: 25046994). Started at 3 months before pathology appeared, it prevented neurodegeneration, both pathologies, and memory impairment, and markedly reduced mortality (PMID: 28387677). Mechanistically, the effect ran through increased BDNF and inhibition of the tau kinase GSK3-beta.

### What is the adamantane group for?

Adamantane is a rigid lipophilic hydrocarbon cage. Fusing it to the peptide's C-terminus (as an adamantane-glycine mimetic) increases resistance to proteolytic degradation and raises lipophilicity, which the design study credits for the compound's oral activity and blood-brain barrier permeability. The same stabilization idea is used, without published validation, in vendor peptides like Adamax.

### Does P21 clear amyloid plaques?

No, and the primary data says so plainly. In 3xTg-AD mice, P021 significantly lowered soluble A-beta levels but produced only a nonsignificant trend toward reduced CA1 plaque load, which the authors interpreted as reduced A-beta generation rather than plaque clearance (PMID: 25046994). Its pathology effect is predominantly on tau, neurogenesis, and synaptic plasticity.

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This content is for educational and research purposes only. It is not medical advice, and the compounds covered are research chemicals not approved for human use unless explicitly stated otherwise.

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