Spadin · Pep IQ

Spadin

TREK-1 Antagonist · Sortilin-Derived Peptide · mSP (Mini-Spadin)

"A naturally occurring peptide that blocks TREK-1 potassium channels — producing rapid antidepressant effects through a mechanism completely distinct from every approved antidepressant. TREK-1 overactivity is implicated in depression. Blocking it with spadin produces effects in mouse models comparable to fluoxetine but without the weeks-long delay. No human trials yet."

Type

17 aa peptide · endogenous sortilin fragment

Target

TREK-1 K⁺ channel · IC50 40–60 nM

Status

UK: not illegal to buy or possess · WADA: not specifically listed · US FDA: not approved · animal models only · no human trials · PE-22-28 is the optimised successor

Half-life

~7 hours (mouse) — limiting factor

Protocol summary

Community use

No converged protocol

Successor

PE-22-28 (better PK)

Stage

Preclinical · animal only

Preclinical-only

No human dose established · animal studies use IP/IV dosing · short half-life limits utility

PE-22-28 is the optimised successor fragment with better pharmacokinetics — see that entry for community use

How we read the evidence

Endogenous TREK-1 inhibitor · novel rapid-onset antidepressant mechanism · superseded in research by its own optimised fragment PE-22-28 · zero human therapeutic trials

Animal evidence

Substantial preclinical foundation but largely framed as the parent compound for PE-22-28 development. Spadin (PE 12-28) is a 17-amino-acid endogenous peptide cleaved from the propeptide of NTSR3/sortilin during receptor maturation — released into circulation as a natural fragment. Mechanism: selective inhibition of TREK-1 (TWIK-related K+ channel 1, two-pore-domain K+ channel) at IC50 ~40–60 nM. The TREK-1 antidepressant rationale: TREK-1 knockout mice show depression-resistant phenotype with enhanced serotonergic neurotransmission. Spadin demonstrated antidepressant-like effects in mouse forced swim test, learned helplessness, and corticosterone-induced models. Pharmacokinetic limitation: Veyssiere et al. demonstrated spadin activity disappears beyond ~7 hours after administration, limiting therapeutic utility — this is what motivated the PE-22-28 fragment development.

Community & clinical practice

No converged community protocol exists for spadin specifically. Most community attention has shifted to PE-22-28 (the optimised 7-aa fragment with ~330× better TREK-1 IC50 of 0.12 nM and longer in vivo activity). Where spadin is used, doses are mouse mg/kg extrapolations without human PK validation. Pep IQ does not endorse community spadin use — the parent compound has been functionally superseded by its own optimised fragment, and using the longer, less-stable peptide doesn't make biological sense.

Human trial data

No human clinical trials of spadin have been completed. All evidence is preclinical: cell culture TREK-1 patch-clamp work (Mazella et al. 2010 was the foundational paper), mouse depression models, and the Veyssiere et al. 2017 (PMC 5601071) work that compared spadin to its derivative analogs and demonstrated PE-22-28's superior potency, stability, and antidepressant activity. The development trajectory has consistently been toward truncated/modified analogs rather than parent spadin — the same pattern seen with LL-37 (where pharma moved to derivatives because the parent compound's pharmacology was suboptimal).

Regulatory status

Not approved by any regulatory agency. Sold as a research peptide by some vendors. The mechanism is genuinely novel (TREK-1 inhibition for rapid-onset antidepressant action, distinct from SSRIs and ketamine), but the compound itself has been bypassed in research in favour of PE-22-28.

Convergence

Spadin has a real and elegant mechanism — endogenous TREK-1 inhibitor with antidepressant activity in mouse models — but is functionally obsolete as a research tool because its own optimised fragment (PE-22-28) is significantly more potent, more stable, and more BBB-penetrant. Pep IQ flags this honestly: members interested in TREK-1-mediated mood support should look at PE-22-28 rather than spadin, since the development trajectory points clearly toward the smaller fragment. Spadin is the founder compound of the TREK-1 inhibitor class; PE-22-28 is the practical research tool. Both lack human trials, both are firmly experimental, but if you are going to experiment in this space, the optimised fragment is the rational choice.

Origin & The TREK-1 Story

The potassium channel nobody thought about for depression

TREK-1 (TWIK-related K⁺ channel 1, encoded by KCNK2) is a two-pore domain potassium channel expressed throughout the brain, particularly in regions relevant to depression: the hippocampus, prefrontal cortex, and raphe nuclei. Mice genetically lacking TREK-1 are resistant to depression in multiple animal models — they don't show helplessness, anhedonia, or anxiety responses to stress that wild-type mice display. This established TREK-1 as a potential antidepressant target, but the concept of blocking a potassium channel to treat depression was pharmacologically unconventional.

Spadin was discovered by Michel Lazdunski's group at the Institut de Pharmacologie Moléculaire et Cellulaire in Nice. They identified that sortilin — a multi-ligand sorting receptor — is processed to release a propeptide that naturally inhibits TREK-1 channels. This propeptide, named spadin, was then characterised as a novel endogenous antidepressant peptide. The peptide is produced when sortilin undergoes proteolytic processing in the trans-Golgi network — spadin is released and acts on TREK-1 channels in a paracrine and potentially endocrine fashion.

In rodent depression models (forced swim, tail suspension, chronic mild stress), spadin produced antidepressant effects within days — comparable to or faster than fluoxetine (which requires 2–3 weeks in mice). Unlike ketamine, spadin produced no locomotor changes, no dissociation, and no obvious off-target effects in the animal studies. A truncated version, mini-spadin (mSP), retains full TREK-1 blocking activity with improved pharmacokinetics.

Why TREK-1 matters: TREK-1 is a "leak" potassium channel — it maintains neuronal excitability close to the resting membrane potential. In the raphe nuclei, TREK-1 regulates serotonin neuron firing rate. TREK-1 overactivity hyperpolarises serotonergic neurons, reducing their firing and serotonin release — the same deficit that SSRIs try to correct by blocking serotonin reuptake. Spadin corrects the upstream problem rather than compensating downstream.

Mechanism

TREK-1 blockade — the upstream serotonin solution

How Spadin Works

TREK-1 K⁺ channel antagonism: Spadin binds the extracellular domain of TREK-1, blocking potassium efflux through the channel. This reduces hyperpolarisation of serotonergic neurons in the raphe nuclei — effectively disinhibiting them and allowing normal firing rates to be restored.

Serotonin neuron disinhibition: With TREK-1 blocked, raphe serotonergic neurons fire at normal-to-higher rates, increasing 5-HT release in projection areas including the prefrontal cortex, hippocampus, and amygdala. This is the same downstream result as SSRIs but achieved through a fundamentally different mechanism — upstream disinhibition rather than downstream reuptake blockade.

Speed advantage over SSRIs: SSRIs require weeks because they initially cause autoreceptor desensitisation that partially offsets their effect — the 5-HT₁A autoreceptors must desensitise before full antidepressant effect emerges. Spadin's mechanism bypasses this delay by directly restoring serotonergic tone without autoreceptor complications.

BDNF upregulation: Like all effective antidepressants, spadin ultimately increases hippocampal BDNF — the neurotrophin critical for neurogenesis and synaptic plasticity. This effect was confirmed in the rodent studies and provides a mechanistic link to the longer-term structural plasticity changes that underlie sustained antidepressant benefit.

Community Use — Very Limited

Where things stand

Community use of spadin is currently extremely limited — less than virtually any other compound in this book. The barriers: the science is recent (primary publications 2012–2023), synthesis and sourcing of verified spadin from research chemical suppliers is difficult, the intranasal delivery route for brain access hasn't been characterised, and the mechanism (TREK-1 channel pharmacology) is less intuitive than the BDNF or GLP-1 mechanisms that attract community attention.

Mini-spadin (mSP) has been shown to have improved stability over the full-length spadin while retaining TREK-1 blocking activity — and is the more pharmacologically attractive development candidate. If any human trials develop, they will likely use mSP rather than the full parent peptide.

⚡ What to Watch

Publications from Lazdunski and collaborating groups on spadin/mSP pharmacokinetics and in vivo optimisation. Any announcement of Phase 1 human trials — this would be the signal that the compound has cleared preclinical safety hurdles. The broader TREK-1 pharmacology field is attracting pharmaceutical interest as a depression target — any corporate TREK-1 antagonist programme that reaches clinical trials validates the target even if using a different molecule. Watch for TREK-1 in mental health pharma pipeline announcements.