PE-22-28 blocks TREK-1 and showed antidepressant-like effects in mice

What is PE-22-28?

PE-22-28 is a synthetic seven-amino-acid analog of spadin that blocks the TREK-1 potassium channel ^[1]⁠^[2]. Spadin is a 17-amino-acid peptide originally derived from the pro-domain of sortilin ^[2]. PE-22-28 is spadin shortened to its most active seven-residue core, the sequence GVSWGLR.

Spadin's pharmacological job is to block TREK-1, a two-pore-domain potassium channel that sits on neurons and dampens their excitability. PE-22-28 does the same job in a smaller molecule.

Is PE-22-28 a BDNF mimetic?

PE-22-28 is not a BDNF mimetic: its primary characterization paper describes TREK-1 channel blockade, not TrkB activation or neurotrophin receptor agonism ^[1].

The forum narrative describes PE-22-28 as a "loop 4 dipeptide mimetic" that activates TrkB receptors. That mechanism comes from an entirely different research program, one that traces back to Russian peptide chemistry but targets neurotrophin signaling directly rather than a potassium channel. Conflating the two programs produces a coherent-sounding story with no basis in the paper that characterizes PE-22-28 ^[1].

Claims that PE-22-28 is "a safer alternative to BDNF" take a different compound's proposed mechanism and attach it to this one. The evidence on BDNF injections covers BDNF itself.

Why do researchers target TREK-1 for depression?

Researchers target TREK-1 because mice with the channel genetically deleted show a depression-resistant phenotype across five behavioral models ^[3]. The knockout mice also show increased serotonergic firing and blunted stress-hormone responses ^[3].

That knockout result is the mechanistic rationale the entire spadin program rests on ^[3]. The program's logic: block the channel with a drug and get a pharmacological version of that resistance.

How does PE-22-28 compare with spadin?

PE-22-28 blocks human TREK-1 roughly 300 to 500-fold more potently than spadin and lasts longer in vivo ^[1]. In the primary characterization paper, PE-22-28 blocked human TREK-1 with an IC50 of 0.12 nM, while spadin required 40 to 60 nM for comparable inhibition ^[1].

PE-22-28's estimated duration of action in rodents was 23 hours, versus about 7 hours for full-length spadin ^[1]. The shortening is a legitimate and interesting piece of medicinal-chemistry optimization: a shorter peptide that is more potent at its target and more stable in circulation.

What do mouse studies of PE-22-28 show?

Mice treated with PE-22-28 showed significantly reduced immobility time in the forced swim test, a standard, if debated, rodent proxy for antidepressant-like activity ^[1]. Sub-chronic treatment over four days induced measurable hippocampal neurogenesis ^[1]. That result echoes spadin, which acts through enhanced CREB phosphorylation and increased serotonergic neuron firing in the dorsal raphe nucleus ^[2].

The PE-22-28 evidence base is small, consistent, and entirely preclinical. Three papers form its lineage: the 2006 knockout study establishing TREK-1 as a causal target in mice ^[3], the 2010 paper characterizing spadin ^[2], and the 2017 paper introducing PE-22-28 as the optimized shortened analog ^[1].

The findings are real and replicated within the lab. They are also entirely internal to one research group's mouse work.

Has PE-22-28 been tested in humans?

No published study has tested PE-22-28 in humans, and no paper in the PE-22-28 literature reports human data of any kind ^[1]⁠^[2]⁠^[3]⁠^[4]. A 2019 review by the same research group states plainly that clinical trials had not been initiated at the time of writing. The review describes human testing as a future objective, not an ongoing effort ^[4].

The E (Minimal) grade is the accurate description of that record, not a conservative hedge. Forced swim test immobility is a specific endpoint, validated imperfectly as a screening tool for antidepressant drug candidates in rodents. It is not a measure of human mood, motivation, or cognitive performance, and reduced immobility in a mouse does not predict what a compound will do in a person at any dose, by any route.

Online claims stretch specific rodent endpoints, forced swim immobility and novelty suppressed feeding, into general claims about memory and focus in healthy adults. The source papers do not attempt that leap themselves. The evidence on Semax for cognitive enhancement covers a related nootropic claim.

Is PE-22-28 safe?

PE-22-28's safety in humans is unknown: no human safety study, adverse event data, or dose-limiting toxicity finding has been published.

The online narrative treats "well tolerated" as established, but no human safety study exists to establish tolerability in the species that matters. The only concerns on record are theoretical ones, and they follow logically from systemically blocking a potassium channel that is expressed outside the brain as well as in it.

Where do PE-22-28 dosing protocols come from?

The 100 to 300 mcg PE-22-28 protocols posted online trace to no study: no dose-ranging study exists in any species, and no human dose has been published. No human pharmacokinetic study and no safety trial at any dose exist. Online human dose schedules are not derived from any published pharmacokinetic or trial evidence.

The entire quantitative record for PE-22-28 is an in vitro IC50 of 0.12 nM against human TREK-1 ^[1], a comparative potency figure against spadin ^[1], an in vivo duration-of-action estimate in rodents ^[1], and behavioral outcome data from mouse assays ^[1]⁠^[2]. None of those figures is a human dose.

Route is a second gap. None of the cited papers establishes intranasal delivery for PE-22-28, so nasal dosing claims stack an unaddressed extrapolation on top of an unproven species jump. No study addresses whether PE-22-28 survives peripheral proteolysis or crosses the blood-brain barrier in humans at any dose.

The 23-hour stability figure comes from animal pharmacokinetics ^[1], not human data. Stability in a mouse says little about oral, subcutaneous, or intranasal bioavailability in a person. How nasal peptides reach the brain covers the nasal route in general terms.

What is still unknown about PE-22-28?

PE-22-28's human pharmacokinetics, its dose-response relationship, and its effect on human mood or cognition are all unknown:

• Human pharmacokinetics. Absorption, half-life, and blood-brain barrier penetration remain unpublished at any tested dose.
• Dose-response. No dose-response relationship exists in any species, by any route other than the one the original mouse study used.
• Translational validity. Whether TREK-1 blockade produces anything resembling the rodent behavioral changes in human mood or cognition has never been tested, because it has never been attempted in a clinical trial ^[4].

Rodent findings could reasonably inform human use only after three steps: a human pharmacokinetic study establishing absorption and half-life by an actual route of administration, a dose-ranging safety trial, and then a controlled trial measuring a validated human outcome rather than an animal behavioral proxy. None of those studies exists yet. PE-22-28 remains an early-stage rodent neuropharmacology candidate with a specific and interesting mechanism, not a characterized human nootropic.