What is PE-22-28 and how does it differ from SSRIs?

PE-22-28 (Mini-Spadin, GVSWGLR) allosterically blocks TREK-1 background K+ channels in DRN serotonergic neurons, directly depolarizing 5-HT cell bodies and bypassing the 5-HT1A autoreceptor feedback that delays SSRI efficacy. Antidepressant effects and hippocampal neurogenesis appear within 4 days in rodent models vs. 3–6 weeks for SSRIs.

What is the molecular structure of PE-22-28?

Sequence: GVSWGLR (7 amino acids); derived from Sortilin propeptide residues 22–28 (Mini-Spadin). Molecular formula: C35H54N12O9S; MW ~773.89–802.94 Da. TREK-1 IC50 ~0.12 nM (~400× more potent than native Spadin). Effect duration >24 hours per dose.

What is the selectivity profile of PE-22-28?

PE-22-28 is selective for TREK-1 (K2P2.1) over TREK-2, TRAAK, TRESK, and TASK-1. It does not block the hERG channel at research concentrations. Mechanism is allosteric antagonism of arachidonic acid-induced activation, not pore blockade. (PMC5601071)

What cardiac safety concerns exist for TREK-1 inhibition?

TREK-1 contributes to ventricular repolarization reserve. TREK-1 knockout mice show QT interval prolongation. A human gain-of-function TREK-1 mutation (I267T) is linked to RVOT tachycardia. Preclinical studies in healthy mice have not shown overt cardiac toxicity, but patients with pre-existing QT prolongation, arrhythmias, or concurrent QT-prolonging drugs are at theoretical elevated risk. (PMC9815770)

How does PE-22-28 affect bladder and gastrointestinal smooth muscle?

TREK-1 is the primary K2P channel in bladder detrusor muscle. Blockade prevents relaxation and induces spontaneous contractions; TREK-1 KO mice exhibit bladder hypertrophy and overactivity. In intestinal smooth muscle, TREK-1 blockade increases contractility. Subjects with OAB, interstitial cystitis, or cramping IBS subtypes are at theoretical risk for exacerbation. (PMC4214657)

PE-22-28

Name: PE-22-28 (Mini-Spadin) 7 MG Lyophilized Peptide
Brand: Kaiser BioMed
SKU: P-079

Description

Summary Abstract

PE-22-28 (Mini-Spadin; GVSWGLR; C₃₅H₅₄N₁₂O₉S; MW ~773–803 Da) is a synthetic heptapeptide derived from the C-terminal active fragment (residues 22–28) of Spadin, itself a propeptide of Sortilin (Neurotensin Receptor 3/NTSR3). It is the most potent and pharmacokinetically optimized analog in the Spadin series, inhibiting the TWIK-related potassium channel 1 (TREK-1; K2P2.1) with an IC₅₀ of ~0.12 nM — approximately 400-fold more potent than native Spadin. TREK-1 is a background K⁺ leak channel constitutively expressed in serotonergic neurons of the dorsal raphe nucleus (DRN), where its tonic activity maintains a hyperpolarized resting state. By allosterically blocking TREK-1, PE-22-28 depolarizes DRN 5-HT neurons, overriding inhibitory 5-HT_1A autoreceptor feedback and driving a rapid increase in serotonergic firing. This cascade engages the cAMP/PKA/pCREB axis within hippocampal targets, upregulating BDNF mRNA and protein within 4 days — far shorter than the 3–6 week timeline of SERT-blocking antidepressants. PE-22-28 also stimulates hippocampal neurogenesis (BrdU+ progenitor doubling), increases PSD-95/synapsin expression, and has shown infarct-size reduction in rodent ischemia/reperfusion models. Its effect duration exceeds 24 hours per dose, supporting once-daily dosing in preclinical protocols. The primary systemic safety considerations relate to TREK-1 expression in cardiac and smooth muscle tissue, detailed in the Safety section.

Research Applications

PE-22-28’s selective TREK-1 antagonism supports investigation in:

Major Depressive Disorder (MDD) / Treatment-Resistant Depression: Mechanism completely orthogonal to SERT inhibitors, MAOIs, and TCAs — potential utility in monoaminergic non-responders. Rapid onset (4 days in rodent models vs. 3–6 weeks for SSRIs) offers a fundamentally distinct temporal profile.
Hippocampal Neurogenesis Kinetics: PE-22-28 induces BrdU+ progenitor doubling in the dentate gyrus within 4 days, providing a rapid-induction model for studying activity-dependent neurogenesis and its relationship to mood regulation.
Ischemic Neuroprotection: Rodent stroke models demonstrate reduced infarct volume and improved neurological scores following PE-22-28 administration, mediated by downstream BDNF/PI3K/Akt activation.
Ion Channel Pharmacology (K2P Biology): PE-22-28’s high selectivity for TREK-1 over TREK-2, TRAAK, TRESK, and TASK-1 makes it a precise tool for dissecting the physiological roles of individual K2P subunits in CNS and peripheral tissues.
Cognitive Impairment / Stress-Induced Deficits: Stress-induced dendritic atrophy and PSD-95 loss in the hippocampus are reversed by BDNF upregulation; PE-22-28’s rapid neurogenic induction makes it a candidate probe for examining plasticity restoration timelines.

Contraindications and Safety Considerations

Cardiac Conduction Disorders: TREK-1 contributes to ventricular repolarization reserve. Blockade carries a theoretical risk of QT prolongation and Torsades de Pointes, particularly in patients with pre-existing Long QT syndrome, arrhythmias, silent channelopathies, or those co-administering QT-prolonging drugs. TREK-1 knockout mice exhibit prolonged QT intervals.
Overactive Bladder / Interstitial Cystitis: TREK-1 is the dominant K2P channel in the bladder detrusor. Its blockade prevents smooth muscle relaxation and triggers spontaneous contractions, potentially inducing urinary urgency or frequency.
Irritable Bowel Syndrome (IBS-C / Cramping Subtypes): TREK-1 maintains ileal and colonic smooth muscle relaxation; blockade may increase contractility and exacerbate cramping symptoms.
Epilepsy: While preclinical data suggest context-dependent neuroprotection, global K2P modulation carries a theoretical risk of altered seizure thresholds. The relationship is complex and patient-specific risk cannot be excluded.
Pregnancy: No teratogenicity data are available. Use is contraindicated in the absence of safety data.

Mechanism of Action

TREK-1 Allosteric Antagonism

PE-22-28 binds an extracellular domain of the TREK-1 channel (K2P2.1), locking it in a closed conformation and specifically blocking activation by arachidonic acid (AA). Unlike classical pore blockers (e.g., Ba²⁺), PE-22-28 is a state-dependent allosteric inhibitor that preferentially silences channels that are active or lipid-stimulated, potentially providing greater on-demand modulation than constitutive blockade.

DRN Serotonergic Depolarization

TREK-1 tonically hyperpolarizes DRN 5-HT neurons. Blockade by PE-22-28 removes this leak current, depolarizing these neurons and lowering the action potential threshold (rheobase). Critically, this mechanism bypasses the 5-HT_1A autoreceptor feedback loop that delays SSRI efficacy. Enhanced serotonergic firing propagates to the hippocampus and prefrontal cortex (PFC), engaging postsynaptic Gs-coupled 5-HT receptors.

cAMP / PKA / pCREB / BDNF Cascade

Postsynaptic 5-HT receptor activation (5-HT₄/5-HT₇) → cAMP elevation → PKA → CREB phosphorylation at Ser-133 (pCREB) → BDNF transcription. Elevated hippocampal BDNF activates TrkB → PI3K/Akt and MAPK/ERK, driving neuronal survival, PSD-95/synapsin upregulation, and BrdU+ progenitor proliferation in the dentate gyrus subgranular zone.

Rapid Neurogenesis vs. SSRIs

PE-22-28 doubles the number of BrdU+ dentate gyrus progenitors within 4 days. SSRIs require 14+ days for comparable neurogenic effects because they first trigger autoreceptor-mediated inhibition. PE-22-28 bypasses this delay by acting upstream — at the membrane potential of the DRN neuron — rather than at the reuptake transporter.

Key Features & Specifications

PE-22-28 represents the rational optimization of the Spadin series for maximal TREK-1 potency and in vivo stability:

IC₅₀ ~0.12 nM — ~400× more potent than native Spadin

Selective for TREK-1 over TREK-2, TRAAK, TRESK, TASK-1

Effect duration >24 hours — once-daily dosing in preclinical models

Antidepressant onset 4 days vs. 3–6 weeks for SSRIs

Neurogenesis doubled (BrdU+) within 4 days

7 MG lyophilized (SKU P-079)

Chemical Analysis

Property	Specification Reference Data
Sequence	Gly-Val-Ser-Trp-Gly-Leu-Arg (GVSWGLR)
Parent Peptide	Spadin (YAPLPRWSGPIGVSWGLR) — Sortilin propeptide residues 22–28
Molecular Formula	C₃₅H₅₄N₁₂O₉S (free base; salt form adds counterion mass)
Molecular Weight	~773.89 Da (free base) to ~802.94 Da (TFA salt form)
CAS Number	Not formally registered in primary databases; investigational heptapeptide
Synonyms	Mini-Spadin, PE 22-28, GVSWGLR heptapeptide, Sortilin propeptide 22-28
Target / Affinity	TREK-1 (K2P2.1/KCNK2) allosteric antagonist; IC₅₀ ~0.12 nM
Form / Variation	7 MG Lyophilized (SKU P-079)

Storage, Safety, and Handling

Storage Protocol

Store lyophilized PE-22-28 at −20 °C or below, desiccated and protected from light. Reconstitute in sterile bacteriostatic water or sterile PBS immediately before use; aliquot and freeze at −80 °C to avoid repeat freeze-thaw degradation. At −20 °C in the lyophilized state, peptide stability is maintained for 24+ months in validated cold-chain conditions. The heptapeptide core is relatively hydrophilic; avoid exposure to oxidizing conditions that could affect the Trp residue.

Handling & Compliance

Handle with standard laboratory PPE. The primary systemic safety concerns are cardiac (QT prolongation risk in compromised hearts) and smooth muscle (bladder/gut depolarization). At the microgram doses used in preclinical research, healthy-subject pharmacovigilance has not identified cardiac or urological adverse events. PE-22-28 is not approved by any regulatory agency. No formal LD50 or teratogenicity studies have been published. All protocols require institutional review board or ethics committee approval. Do not administer to subjects with pre-existing cardiac conduction disorders, OAB, IBS, epilepsy, or during pregnancy without specific risk assessment.