What Is PE 22-28?

PE 22-28, also written PE-22-28 or PE22-28, is a synthetic seven-amino-acid peptide derived from the C-terminal portion of spadin, a longer sortilin-derived peptide studied as an inhibitor of the two-pore-domain potassium channel TREK-1.

Researchers created shortened spadin analogues to identify the minimum sequence that retained TREK-1 inhibition while improving potency and biological persistence. Among the tested fragments, PE 22-28 was reported as the shortest and most potent core sequence.

🧬 Molecular Structure

🧪 Amino-acid sequence

Gly-Val-Ser-Trp-Gly-Leu-Arg-OH

One-letter notation:

GVSWGLR

Terminal chemistry

The published reference sequence is generally represented with a free N-terminal glycine and a free C-terminal arginine carboxyl group. Acetylated, amidated, biotinylated, lipidated, or substituted forms are distinct analogues and should not be labeled simply as native PE 22-28 without qualification.

Structural characteristics

• Seven standard L-amino acids
• Linear peptide
• No cysteine or disulfide bonds
• One tryptophan residue
• Basic C-terminal arginine
• Hydrophobic valine, tryptophan, and leucine residues

⚛️ Molecular Weight and 🧫 Formula

Acetate salt

Commercial research material is sometimes sold as an acetate salt. The reported formula weight then depends on the amount of associated acetate and water. The peptide’s net content must therefore be distinguished from total vial mass.

📅 Discovery Timeline and Research History

1996–1997: Sortilin and neurotensin receptor-3 characterized

Sortilin was identified as a receptor and trafficking protein involved in neurotensin biology, protein sorting, neuronal signaling, and later proneurotrophin pathways.

2010: Spadin described

Spadin, corresponding to residues PE 12-28 of the sortilin propeptide, was reported to inhibit TREK-1 and produce rapid antidepressant-like effects in mice.

2010–2014: Neurogenesis and synaptic research expands

Spadin was reported to increase hippocampal neurogenesis, synaptogenesis, and selected plasticity markers.

2015: TREK-1 blockade and serotonergic signaling

Independent pharmacological work strengthened the relationship between TREK-1 inhibition, antidepressant-like behavior, and CREB–BDNF signaling.

2017: Shortened spadin analogues published

A library of 22 shortened and modified peptides was screened. PE 22-28 emerged as a seven-residue core with an IC₅₀ near 0.12 nM, compared with approximately 40 nM for spadin in the reported assay.

2017: Antidepressant-like and plasticity findings

PE 22-28 and selected analogues reduced depressive-like behavior and increased hippocampal neurogenesis and PSD-95 expression in mice.

2018–2019: TREK-1 reviews and analog development

Reviews positioned shortened spadin analogues as high-affinity research tools and possible leads for novel antidepressant development.

Current status

No recognized phase 1–3 human clinical-development program or FDA-approved PE 22-28 product has been established.

Sortilin, Propeptide, and Spadin Origins

Sortilin

Sortilin, also called neurotensin receptor-3, is a type-I membrane protein involved in intracellular trafficking, neurotrophin signaling, lipoprotein metabolism, and neuronal function.

Sortilin propeptide

Newly synthesized sortilin contains an N-terminal propeptide that is cleaved during maturation. A portion of this propeptide can regulate TREK-1.

Spadin

Spadin is a 17-amino-acid peptide corresponding to residues 12–28 of the sortilin propeptide. Its name was derived from “sortilin-derived peptide with antidepressant effect.”

PE 22-28

PE 22-28 is the seven-amino-acid C-terminal fragment of spadin:

GVSWGLR

Why shortening mattered

Removing nonessential N-terminal residues increased apparent TREK-1-blocking potency and produced a smaller synthesis target. However, shorter sequence does not automatically guarantee better human absorption, brain delivery, or safety.

TREK-1 Biology

What TREK-1 is

TREK-1, encoded by KCNK2, is a two-pore-domain potassium channel also called K2P2.1. It contributes to background potassium currents that stabilize the resting membrane potential.

Channel activation

TREK-1 responds to membrane stretch, temperature, intracellular acidosis, polyunsaturated fatty acids, lysophospholipids, anesthetics, and cellular signaling pathways.

Brain distribution

TREK-1 is expressed in hippocampal, cortical, serotonergic, sensory, and other neuronal populations.

Physiological roles

• Neuronal excitability
• Mood-related circuitry
• Pain and mechanosensation
• Temperature responses
• Ischemic tolerance
• Anesthetic actions
• Neuroprotection

Therapeutic tension

Blocking TREK-1 may enhance antidepressant-like signaling and neurogenesis, while TREK-1 activation can protect neurons during ischemia and excessive excitation. Effects may therefore differ by disease, timing, and tissue.

🧠 Mechanism of Action

1. TREK-1 channel inhibition

PE 22-28 was reported to inhibit human TREK-1 expressed in HEK293 cells with an IC₅₀ of approximately 0.12 nM.

2. Increased membrane excitability

Reducing a background potassium conductance can depolarize neurons and increase responsiveness to synaptic input.

3. Channel internalization

Spadin has been reported to promote TREK-1 internalization. Whether PE 22-28 reproduces the same trafficking mechanism to the same extent requires careful direct testing.

4. Serotonergic and hippocampal signaling

TREK-1 deficiency or blockade can increase firing of dorsal-raphe serotonin neurons and alter downstream hippocampal plasticity.

5. CREB and BDNF-related pathways

Antidepressant-like effects of TREK-1 blockade have been associated with CREB phosphorylation, BDNF expression, and neuroplasticity.

🎯 Target and Pathway Profile

Antidepressant-Like Research

Rodent behavioral assays

PE 22-28 was evaluated in commonly used preclinical tests, including the forced-swim test, novelty-suppressed feeding, and learned-helplessness paradigms.

Reported findings

Repeated low-dose administration reduced immobility, shortened latency to feed, and improved escape behavior in mice.

Rapid-onset concept

Spadin-family compounds produced effects after several days in animal experiments, faster than the several-week delay historically associated with many conventional antidepressants.

Behavioral tests are not depression diagnoses

Forced-swim immobility and feeding latency measure stress-coping or motivational behavior, not the full human syndrome of major depressive disorder.

No human antidepressant evidence

No randomized controlled human trial has established efficacy for depression, anxiety, bipolar depression, treatment-resistant depression, or suicidality.

Neurogenesis and Synaptogenesis Research

Hippocampal neurogenesis

PE 22-28 and selected analogues increased markers of cell proliferation and immature neurons in the dentate gyrus.

PSD-95

Mouse hippocampal studies reported increased PSD-95, a postsynaptic scaffold protein commonly used as a synaptogenesis-related marker.

Spadin precedent

Earlier spadin research reported increased neurogenesis, dendritic spine maturation, and synaptic proteins.

Potential relationship to mood

Hippocampal neurogenesis is associated with stress adaptation and some antidepressant responses, but it is not the sole mechanism of depression treatment.

No proof of human neuron growth

No human imaging, cerebrospinal-fluid, histological, or clinical evidence demonstrates that PE 22-28 increases neurogenesis or synapse formation in people.

Serotonin, CREB, and BDNF Pathways

TREK-1 and serotonin neurons

TREK-1 is expressed in dorsal-raphe serotonergic neurons. Genetic deletion increases their firing and produces antidepressant-like behavior in mice.

Indirect serotonergic action

PE 22-28 is not an SSRI and has not been shown to block the serotonin transporter directly.

5-HT1A interaction research

Pharmacological TREK-1 blockade may interact synergistically with 5-HT1A receptor activation through shared CREB–BDNF pathways.

CREB

CREB regulates genes involved in neuronal survival, learning, stress adaptation, and synaptic plasticity.

BDNF

BDNF supports neuronal plasticity and is often altered by antidepressant treatment, but increases in BDNF are neither unique to effective antidepressants nor sufficient to prove clinical efficacy.

Ischemia and Neuronal-Injury Research

TREK-1 can be neuroprotective

TREK-1 activation hyperpolarizes neurons and can reduce excitotoxicity during ischemia, seizures, or metabolic stress.

Apparent conflicting claims

Some commercial databases attribute reduced stroke deficits or cell death to PE 22-28 or related spadin analogues. These findings must be distinguished from the established protective role of TREK-1 activation in acute ischemia.

Timing may determine outcome

Chronic TREK-1 blockade may promote plasticity and mood-related signaling, while acute blockade during energy failure could theoretically increase excitability.

No stroke treatment evidence

PE 22-28 is not an approved neuroprotective therapy and must not replace emergency stroke evaluation, reperfusion, antiplatelet therapy, or rehabilitation.

Pancreatic Beta-Cell and Peripheral Research

TREK-1 outside the brain

TREK-1 is expressed in sensory, smooth-muscle, vascular, pancreatic, and other tissues.

Beta-cell survival claims

Some research summaries report reduced apoptotic death of pancreatic beta cells with PE 22-28 in ischemia-related models. The exact direct evidence base is much smaller than the depression literature and should not be generalized.

Insulin secretion

Background potassium channels influence membrane excitability and secretion, but PE 22-28 has not been established as a diabetes therapy.

Muscle and bladder claims

Commercial articles sometimes extrapolate to smooth-muscle or bladder function. Direct PE 22-28 evidence is sparse and does not establish clinical utility.

Channel Selectivity and Physiological Tradeoffs

TREK-1 selectivity

The 2017 analogue study reported substantially higher potency for TREK-1 than spadin and lower effects at related TREK-2 and TRAAK channels.

Absolute selectivity is not proven

A peptide may interact with unrelated channels, receptors, membranes, transporters, or proteins not included in the original screen.

Pain and sensory effects

TREK-1 contributes to pain processing and mechanosensation. Long-term blockade could alter sensory thresholds.

Anesthesia and temperature

TREK-1 participates in volatile-anesthetic actions and thermosensation. The significance of sustained inhibition is unknown.

Seizure and excitability concern

Reducing background potassium current can increase neuronal excitability, creating a theoretical seizure or excitotoxicity concern that requires formal testing.

Stability and Pharmacokinetic Limitations

Spadin duration

Spadin’s in-vivo activity was reported to decline within hours, motivating the development of shorter and modified analogues.

PE 22-28 persistence

The 2017 study reported improved in-vivo stability and behavioral activity relative to spadin, with effects observed well beyond the parent peptide’s shorter window.

Exact half-life

Commercial claims of a greater-than-24-hour half-life should not be treated as established human pharmacokinetics. Behavioral persistence is not identical to plasma half-life.

Brain delivery

Rodent behavioral effects imply that active peptide or downstream signaling reaches relevant circuits, but the precise route, transport mechanism, brain concentration, and metabolite activity remain incompletely characterized.

Human pharmacokinetics

Absorption, bioavailability, half-life, clearance, tissue distribution, and blood–brain barrier exposure are unknown in humans.

Evidence Limitations and Clinical Interpretation

Single primary analogue paper

The most direct PE 22-28 evidence is concentrated in the 2017 shortened-spadin analogue study.

Parent-peptide extrapolation

Many claims are inherited from spadin, genetic TREK-1 knockout models, or unrelated TREK-1 blockers.

Behavioral-model limitations

Rodent stress tests do not fully reproduce human depression, trauma, bipolar disorder, or treatment resistance.

Limited toxicology

Comprehensive safety pharmacology, reproductive, developmental, genotoxic, carcinogenic, seizure-liability, cardiovascular, and chronic-organ studies are not established.

No human trials

No controlled human efficacy, dose-ranging, pharmacokinetic, or safety study has been established.

Publication concentration

Much of the spadin and PE 22-28 literature comes from a connected group of investigators, increasing the importance of independent replication.

Safety and Regulatory Considerations

No established human safety profile

No approved label defines dose, route, contraindications, interactions, pregnancy safety, psychiatric monitoring, or chronic adverse effects.

Potential neurological risks

• Agitation or anxiety
• Sleep disruption
• Headache
• Altered pain or temperature sensation
• Excess neuronal excitability
• Seizure liability
• Mood switching in susceptible individuals

Psychiatric risk

Any experimental compound promoted for mood must be evaluated for suicidality, mania, mixed states, psychosis, withdrawal effects, and interactions with antidepressants or stimulants.

Drug interactions

Interactions with SSRIs, SNRIs, MAO inhibitors, lithium, antipsychotics, anticonvulsants, sedatives, stimulants, or anesthetics are unknown.

Product-quality risk

Unapproved material may contain deletion sequences, D-amino-acid epimers, oxidized tryptophan, incorrect salt content, endotoxin, residual solvents, or inaccurate peptide quantity.

Regulatory status

PE 22-28 is not FDA approved.

🧪 Laboratory Testing Methods

📄 How to Interpret a PE 22-28 COA

1. Verify the complete seven-amino-acid sequence: GVSWGLR.
2. Confirm terminal chemistry: Free N-terminus and C-terminal carboxyl group unless a specific analogue is intended.
3. Confirm formula and molecular weight: C₃₅H₅₅N₁₁O₉ and approximately 773.89 g/mol for the free peptide.
4. Account for acetate and water: Salt and moisture increase total vial weight without increasing peptide content.
5. Use MS/MS sequencing: HPLC and intact mass alone cannot prove residue order.
6. Review truncations and deletion sequences: Seven-residue synthesis can still produce closely related impurities.
7. Review tryptophan oxidation and amino-acid epimerization.
8. Measure net peptide content: A “99% purity” result is not the labeled number of milligrams.
9. Require functional TREK-1 testing: Ideally include TREK-2, TRAAK, and broader ion-channel counter-screens.
10. Do not infer efficacy: A COA cannot prove antidepressant effects, neurogenesis, brain penetration, rapid onset, or human safety.

📊 PE 22-28 vs Spadin vs Sortilin Propeptide

PE 22-28 vs SSRI vs Ketamine vs Psilocybin

PE 22-28 vs Other Potassium-Channel Targets

PE 22-28 vs Approved Depression Care

🔗 Related Peptides, Channels, and Pathways

• Spadin: 17-amino-acid parent peptide.
• Sortilin / NTSR3: Protein from whose propeptide spadin was derived.
• TREK-1 / KCNK2: Primary potassium-channel target.
• TREK-2 and TRAAK: Related K2P channels used in selectivity testing.
• CREB and BDNF: Plasticity-associated downstream pathways.
• 5-HT1A: Serotonin receptor linked to TREK-1-blockade synergy.
• PSD-95: Postsynaptic marker increased in preclinical research.
• G/A-PE 22-28: Analogue in which a glycine is replaced with alanine.

🖼️ Original Diagram Specifications

Diagram 1: PE 22-28 molecular sequence

Show the linear GVSWGLR peptide with free N- and C-termini and hydrophobic, polar, aromatic, and basic residues labeled.

Diagram 2: Sortilin-to-PE 22-28 development

Show sortilin precursor → propeptide → spadin/PE 12-28 → PE 22-28/GVSWGLR.

Diagram 3: TREK-1 channel blockade

Show background potassium efflux through TREK-1, membrane stabilization, PE 22-28 binding, reduced K⁺ current, and increased neuronal excitability.

Diagram 4: Antidepressant-like pathway

Show TREK-1 inhibition → dorsal-raphe firing → serotonin-network activity → CREB/BDNF → hippocampal plasticity.

Diagram 5: Neurogenesis and synaptogenesis

Show dentate-gyrus progenitors, DCX-positive neurons, dendritic maturation, PSD-95, and synapse formation.

Diagram 6: Benefit–risk tradeoff

Show mood and plasticity signaling on one side and possible hyperexcitability, seizure, pain, temperature, and ischemia-related risks on the other.

Diagram 7: COA workflow

Show sequence, intact mass, MS/MS, chiral analysis, tryptophan oxidation, acetate correction, net content, TREK-1 potency, related-channel selectivity, microbiology, and stability.

❓ Frequently Asked Questions

Is PE 22-28 a peptide?

Yes. It is a synthetic linear heptapeptide.

What is its exact sequence?

Gly-Val-Ser-Trp-Gly-Leu-Arg, or GVSWGLR.

Is it 22 to 28 amino acids long?

No. It contains seven amino acids. The name identifies its location within the longer spadin sequence.

What is its molecular formula?

C₃₅H₅₅N₁₁O₉ for the free peptide.

What is its molecular weight?

Approximately 773.89 g/mol.

What does PE 22-28 target?

Its primary reported target is the TREK-1 two-pore-domain potassium channel.

How potent is it?

The published cell assay reported an IC₅₀ near 0.12 nM.

Is PE 22-28 an SSRI?

No. It does not primarily inhibit the serotonin transporter.

Does it work rapidly?

Rodent antidepressant-like effects appeared after a short treatment period, but rapid human efficacy has not been established.

Does it increase neurogenesis?

Mouse studies reported increased hippocampal neurogenesis markers. Human evidence is unavailable.

Is PE 22-28 FDA approved?

No.

Has it been tested in humans?

No established controlled human clinical trial was identified.

Could it increase seizure risk?

That remains unknown, but increasing neuronal excitability creates a theoretical concern requiring formal safety testing.

Is PE 22-28 the same as spadin?

No. It is a shorter seven-residue fragment of the 17-residue spadin peptide.

Does 99% HPLC purity prove identity?

No. Sequence, stereochemistry, mass, net content, oxidation, and functional channel activity require separate confirmation.

Final Thoughts

PE 22-28 is a well-defined seven-amino-acid experimental peptide derived from the C-terminal region of spadin. Its principal scientific significance is exceptionally potent inhibition of the TREK-1 background potassium channel in a published cell assay.

Preclinical studies report antidepressant-like behavioral effects, increased hippocampal neurogenesis, and higher PSD-95 expression. However, the evidence remains concentrated in rodent and cellular research, and many broader claims are extrapolated from spadin, TREK-1 knockout animals, or other channel blockers.

Legitimate PE 22-28 material should be verified for its GVSWGLR sequence, free terminal chemistry, exact mass, tryptophan oxidation, amino-acid stereochemistry, deletion peptides, acetate and water content, net peptide quantity, TREK-1 potency, related-channel selectivity, broader ion-channel liabilities, route-specific microbiological quality, and stability.

📚 References

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Identity, sequence, spadin origin, TREK-1 pharmacology, antidepressant-like behavior, neurogenesis, synaptogenesis, serotonergic signaling, safety, and analytical evidence were reviewed in July 2026. PE 22-28 remains an unapproved investigational peptide.