PE-22-28, Dihexa and Delta Sleep-Inducing Peptide (DSIP): A Research Review of the TREK-1 Blocker, the Angiotensin IV Analogue, the Nonapeptide Riddle and the Community-Forum Vocabulary Behind "semax reddit", "dihexa reddit" and "brainmelt" Labels

By the Peptide Insider Research Desk | Last updated: September 18, 2026 | Reading time: 12 min read

Three research peptides that act on the central nervous system — PE-22-28, a seven-residue TREK-1 channel blocker; Dihexa, a hexanoylated angiotensin IV analogue; and delta sleep-inducing peptide (DSIP), a nonapeptide isolated in 1977 — share a peculiarity of their search footprint. The strings that lead people to them are rarely the compound names. They are community-forum strings: semax reddit, dihexa reddit, selank reddit, ss31 reddit; protocol-seeking strings such as semax and selank dosage chart and delta sleep inducing peptide dosage; catalogue strings such as gmp selank 10mg - pekcura labs and epithalon peptides; and blend slang such as brainmelt. This review reads the primary literature on the three lead compounds — the TREK-1 knockout phenotype, the spadin-to-PE-22-28 design lineage, the retraction record around Dihexa's proposed mechanism, and the half-century “riddle” of DSIP — and then does something the forum threads cannot: it classifies every community string by the intent behind it and routes that intent to the literature-grade object that answers it. All content is provided strictly for research reference; the materials discussed are not for human or veterinary use, and nothing here describes administration to any organism.

Why Forum Vocabulary Needs a Crosswalk

A catalogue-nomenclature review handles misspellings and concatenations: the reader typed the compound wrongly and wants the compound. Community-forum strings are different. Someone searching selank peptide reddit is not confused about the spelling of Selank; they want first-person reports. Someone searching semax dosage reddit wants a protocol. Someone searching gmp selank 10mg - pekcura labs is checking a specific catalogue listing. The content that would satisfy those intents literally — anecdotes, quantities, vendor verdicts — is exactly the content a research-use-only review cannot carry. The analytical move this review makes is to separate the intent from the string: record the string as vocabulary, name the intent class, and identify the peer-reviewed study design that answers the underlying question with controls the forum thread lacks. Napoletano and colleagues, in their survey of online cognitive-enhancer communities, documented precisely this gap between self-reported experience and controlled evidence [16]; the crosswalk below is a structured response to it.

PE-22-28: From a Knockout Phenotype to a Heptapeptide

The TREK-1 story begins with genetics rather than chemistry. Heurteaux and colleagues reported in 2006 that mice lacking the background potassium channel TREK-1 (KCNK2) displayed a depression-resistant phenotype across several behavioural paradigms, with increased firing of serotonergic neurons in the dorsal raphe [1]. That observation made TREK-1 blockade a rational research target. In 2010 Mazella and colleagues identified spadin, a 17-residue peptide (PE 12-28) derived from the propeptide of the sortilin receptor NTSR3, which bound TREK-1 with roughly 10 nM affinity, blocked channel activity in COS-7 cells and hippocampal neurons, and reproduced the knockout phenotype in five behavioural models after a four-day treatment, with hippocampal neurogenesis and CREB phosphorylation as biochemical read-outs [2].

Spadin's limitation was persistence: its in vivo activity disappeared within about seven hours. Djillani and colleagues analysed spadin's blood-degradation products and designed shortened analogues, of which PE-22-28 — the seven C-terminal residues — proved the most potent. In whole-cell patch clamp on hTREK-1-expressing HEK cells, PE-22-28 inhibited the channel with an IC50 near 0.12 nM, roughly two orders of magnitude below spadin, and its activity in the forced-swim and novelty-suppressed-feeding assays lasted up to 23 hours [3]. The same group's 2019 review places TREK-1 blockade in a wider CNS context that includes neuroprotection and post-stroke depression models [4]. The literature base for PE-22-28 is narrow — effectively one laboratory, one design paper — and this review records that concentration as a feature of the evidence, not a flaw to be smoothed over.

Dihexa: A Mechanism Under Retraction

Dihexa emerged from Washington State University's angiotensin IV programme. The 2013 paper by McCoy and colleagues described a series of metabolically stabilised angiotensin IV analogues, of which Dihexa — hexanoylated at the N-terminus and amidated at the C-terminus — was reported to be orally active, blood-brain-barrier permeant and procognitive in scopolamine and aged-rat paradigms [6]. Companion papers proposed the mechanism: Dihexa was said to bind hepatocyte growth factor (HGF) and potentiate its signalling through the c-Met receptor tyrosine kinase, with synaptogenesis as the downstream effect [7][8]; Wright and Harding framed the HGF/c-Met system as a neurodegeneration target on that basis [5].

The record has since changed materially. In 2025 the Journal of Pharmacology and Experimental Therapeutics retracted the 2012 Kawas and 2014 Benoist papers that established the HGF/c-Met mechanism, and the 2013 discovery paper carries an expression of concern [6][7][8]. What survives is thinner and different: Sun and colleagues reported in 2021 that Dihexa reduced cognitive deficits in APP/PS1 transgenic mice with PI3K/AKT signalling as the identified pathway [9], and Ho and Nation's 2018 systematic review of angiotensin IV and angiotensin-(1-7) studies found consistent procognitive signals across rodent deficit models for the class as a whole, with insulin-regulated aminopeptidase (IRAP) as the most-cited target [10]. For a researcher, the operative descriptor of Dihexa is therefore “angiotensin IV analogue with a contested mechanism”, and any forum thread that still presents the HGF-mimetic story as settled is citing retracted work.

DSIP: Forty-Nine Years of an Unresolved Riddle

DSIP is the oldest of the three and the least resolved. Schoenenberger and Monnier isolated it from the cerebral venous blood of rabbits undergoing hypnogenic thalamic stimulation and published its sequence — Trp-Ala-Gly-Gly-Asp-Ala-Ser-Gly-Glu — in 1977, reporting enhanced delta-EEG activity on intraventricular infusion into recipient animals [11]. Graf and Kastin's 1984 review catalogued a sprawling set of reported effects across species, on sleep stages, neurotransmitter levels, locomotor rhythms and endocrine parameters, and noted already that the sleep effect was inconsistent [17]. Two decades later Kovalzon and Strekalova titled their review “a still unresolved riddle”: no gene encoding DSIP has been identified in mammals, no receptor has been characterised, and the peptide is rapidly degraded in plasma, which the authors proposed as one source of the inconsistent in vivo results [18]. No human-subject work is discussed in this review. The research descriptor is a nonapeptide of uncertain endogenous origin whose EEG pharmacology remains unreplicated to modern standards.

The Neighbours: Semax, Selank, Epitalon and SS-31

Four further compounds appear in the same community threads and therefore in the crosswalk. Semax, an ACTH(4-10) analogue, has been shown by Dolotov and colleagues to regulate BDNF and trkB expression in the rat hippocampus [12]; Selank, a tuftsin analogue, alters expression of GABAergic neurotransmission genes in rodent brain [13]; both are reviewed separately on this site. Epitalon (Epithalon), the tetrapeptide Ala-Glu-Asp-Gly, was reported by Khavinson and colleagues to induce telomerase catalytic-subunit expression and telomere elongation in cultured human fetal fibroblasts [14]. SS-31 (elamipretide), a mitochondria-targeted tetrapeptide, binds cardiolipin in the inner mitochondrial membrane and is reviewed by Szeto [15]. None of these is a CNS compound in the narrow sense of PE-22-28 or Dihexa — SS-31 is a mitochondrial agent, Epitalon a telomerase-pathway peptide — but the forum vocabulary groups them, and the crosswalk follows the vocabulary.

Community-Query Intent Crosswalk: Forum String → Intent Class → Literature-Grade Object

The table records every community string verbatim, classifies its intent, names the peer-reviewed object that answers the underlying question, and states the review's scope decision. Intent classes: A anecdote-seeking, B protocol-seeking, C catalogue/format, D definitional, E blend or brand slang.

Community string (verbatim)	Intent class	Underlying research question	Literature-grade object & RUO scope status
pe 22-28	D — definitional (catalogue spelling)	What is the compound and its target?	Djillani 2017 design paper; hTREK-1/HEK patch clamp, IC50 ~0.12 nM [3]; recorded as nomenclature
semax reddit, selank reddit, selank peptide reddit, selank and semax reddit	A — anecdote-seeking	What does the compound do?	Controlled rodent expression studies: BDNF/trkB for Semax [12], GABAergic genes for Selank [13]; strings recorded as vocabulary
dihexa reddit	A — anecdote-seeking	Does Dihexa act on HGF/c-Met?	Mechanism papers retracted 2025 [7][8]; discovery paper under expression of concern [6]; PI3K/AKT report [9]; recorded as vocabulary
ss31 reddit	A — anecdote-seeking	What is SS-31's target?	Cardiolipin binding at the inner mitochondrial membrane [15]; recorded as vocabulary
epithalon report reddit	A — anecdote-seeking	What has Epitalon been shown to do in vitro?	Telomerase induction in human fetal fibroblast culture [14]; recorded as vocabulary
semax and selank dosage chart, semax dosage reddit, selank dosage reddit	B — protocol-seeking	Quantity, route, schedule	Declined scope: no values supplied; research-use-only review contains no protocol content
delta sleep inducing peptide dosage	B — protocol-seeking	Quantity for DSIP	Declined scope; compound descriptor only: nonapeptide, rapid plasma degradation, no identified receptor [18]
gmp selank 10mg - pekcura labs	C — catalogue / format	Is this listing what it says?	Certificate of Analysis: identity, purity, net peptide content; vendor label recorded as nomenclature, not evaluated
epithalon peptides	C — catalogue category	Which materials fall under the label?	Tetrapeptide Ala-Glu-Asp-Gly and salt/variant forms [14]; recorded as vocabulary
what is epitalon	D — definitional	Identity of Epitalon	Khavinson 2003 primary paper [14]; recorded as nomenclature
brainmelt, brain melt	E — blend / brand slang	What is in it?	No literature object: no peer-reviewed composition; recorded as vocabulary token only

Two features of the table carry the analytical weight. First, class A strings — the “reddit” family — are answered not by rejecting the question but by naming the controlled study that addresses it, which is the substitution Napoletano and colleagues argue online communities lack [16]. Second, class B strings are the only ones for which the review declines outright, and it says so in the table rather than silently omitting them.

Evidence by Domain

Compound	Research Model	Signal Vector	Key finding	Evidence quality
PE-22-28	hTREK-1/HEK whole-cell patch clamp; mouse forced-swim and novelty-suppressed feeding	K2P channel current; immobility time; hippocampal BrdU, PSD-95	IC50 ~0.12 nM; activity to 23 h; neurogenesis markers [3]	Single-group preclinical
Spadin (parent)	COS-7, hippocampal neurons, brain slices; five mouse behavioural models	TREK-1 current; 5-HT neuron firing; CREB phosphorylation	~10 nM binding; knockout phenotype reproduced [2]	Preclinical, independent target validation [1]
Dihexa	Rat scopolamine / aged-rat paradigms; APP/PS1 mouse	Spatial learning; synaptic protein expression; PI3K/AKT	Procognitive signals [6][9]; HGF/c-Met mechanism retracted [7][8]	Compromised: retractions and expression of concern
DSIP	Rabbit intraventricular infusion; EEG	Delta-EEG power	Sequence and EEG effect [11]; inconsistent replication [17][18]	Historical, unresolved
Semax / Selank	Rat hippocampus expression studies	BDNF, trkB; GABAergic gene set	Expression changes [12][13]	Preclinical
Epitalon	Human fetal fibroblast culture	hTERT expression; telomere length	Telomerase induction [14]	In vitro, single group
SS-31	Isolated mitochondria; multiple injury models	Cardiolipin binding; cristae architecture	Cardiolipin-protective mechanism [15]	Preclinical, reviewed

Handling Considerations

All seven compounds are catalogued as lyophilised solids. DSIP's rapid plasma degradation [18] and spadin's seven-hour in vivo persistence [2][3] are pharmacological observations, not storage data, but they illustrate why peptide-stability practice matters at the bench: hydrolysis, deamidation and oxidation follow the general rules summarised by Manning and colleagues, and aqueous solutions of short peptides are handled cold, protected from light and prepared fresh [19]. Dihexa's N-hexanoyl group increases lipophilicity relative to angiotensin IV, which affects solvent choice in vitro [6]. Certificate-of-Analysis identity and purity are the only attributes a laboratory can verify for any of these materials, including anything sold under a blend label.

Where to Source for Research

PE-22-28, Dihexa, DSIP, Semax, Selank, Epitalon and SS-31 are catalogued by research-peptide suppliers as lyophilised solids under research-use-only terms. Short Chain Aminos, BioPep, Catalyst Research and Apex Research Services list CNS-research peptides, or subsets of them, with lot-specific Certificates of Analysis. Identity, purity and net-peptide-content data are the verifiable attributes for any research material; this review does not evaluate, rank or recommend suppliers, community sources or blend products, and frames sourcing only as research availability.

Frequently Asked Questions

What is pe 22-28 and how does it differ from spadin?

pe 22-28 is the catalogue spelling of PE-22-28, a seven-residue fragment of the sortilin propeptide designed by Djillani and colleagues as a shortened analogue of spadin (PE 12-28). In patch-clamp recordings on hTREK-1/HEK cells it blocked TREK-1 with an IC50 of about 0.12 nM versus roughly 40–60 nM for spadin, and its activity persisted longer in vivo [3]. It is a research reagent characterised almost entirely by a single group.

Why do semax reddit, selank reddit and selank and semax reddit appear in a research review?

semax reddit, selank reddit, selank peptide reddit and selank and semax reddit are anecdote-seeking queries: the searcher wants first-person reports. This review records them as vocabulary and routes the underlying question to the controlled literature — the ACTH(4-10) analogue Semax and the tuftsin analogue Selank each have peer-reviewed mechanistic studies [12][13] — because forum reports are uncontrolled observations, not evidence [16].

Does this review supply the semax and selank dosage chart or semax dosage reddit information?

No. semax and selank dosage chart, semax dosage reddit, selank dosage reddit and delta sleep inducing peptide dosage are protocol-seeking strings. They are recorded in the crosswalk as Declined-scope: this is a research-use-only review and it does not contain, imply or endorse quantities, routes, schedules or any use in any organism.

What does dihexa reddit ask, and what does the literature actually say about Dihexa?

dihexa reddit is an anecdote-seeking query about the angiotensin IV analogue Dihexa. The literature-grade answer is a caution: the 2012 and 2014 papers that proposed its HGF/c-Met mechanism were retracted in 2025, and the 2013 discovery paper carries an expression of concern [6][7][8]. Independent rodent work reports effects through PI3K/AKT signalling [9], and a systematic review of angiotensin IV analogues exists [10], but the mechanistic record is compromised.

What is epitalon, and what do epithalon peptides and epithalon report reddit refer to?

what is epitalon is a definitional query: Epitalon (Epithalon) is the synthetic tetrapeptide Ala-Glu-Asp-Gly, studied by Khavinson and colleagues for telomerase induction in cultured human fibroblasts [14]. epithalon peptides is a catalogue-category string for the tetrapeptide and its variants, and epithalon report reddit is an anecdote-seeking string; both are recorded as vocabulary only.

What is brainmelt or brain melt?

brainmelt (also written brain melt) is a label that surfaces alongside nootropic-peptide searches. No peer-reviewed publication defines a composition for it, and this review does not assign it one; it is recorded as a blend-slang token with no literature object. Any preparation sold under such a label can only be characterised by its own Certificate of Analysis.

What do ss31 reddit and gmp selank 10mg - pekcura labs have to do with CNS peptides?

ss31 reddit is an anecdote-seeking query about SS-31 (elamipretide), a mitochondria-targeted tetrapeptide that binds cardiolipin [15]; it appears in the same community threads as the CNS peptides and is recorded here as vocabulary. gmp selank 10mg - pekcura labs is a catalogue-format string (a quality-system descriptor, a fill mass and a vendor label) and is recorded as nomenclature; this review does not evaluate or recommend any vendor.

Works Cited

1. Heurteaux C, Lucas G, Guy N, et al. Deletion of the background potassium channel TREK-1 results in a depression-resistant phenotype. Nat Neurosci. 2006;9(9):1134-1141. doi:10.1038/nn1749
2. Mazella J, Pétrault O, Lucas G, et al. Spadin, a sortilin-derived peptide, targeting rodent TREK-1 channels: a new concept in the antidepressant drug design. PLoS Biol. 2010;8(4):e1000355. doi:10.1371/journal.pbio.1000355
3. Djillani A, Pietri M, Moreno S, et al. Shortened spadin analogs display better TREK-1 inhibition, in vivo stability and antidepressant activity. Front Pharmacol. 2017;8:643. PMID: 28955242. doi:10.3389/fphar.2017.00643
4. Djillani A, Mazella J, Heurteaux C, Borsotto M. Role of TREK-1 in health and disease, focus on the central nervous system. Front Pharmacol. 2019;10:379. doi:10.3389/fphar.2019.00379
5. Wright JW, Harding JW. The brain hepatocyte growth factor/c-Met receptor system: a new target for the treatment of Alzheimer's disease. J Alzheimers Dis. 2015;45(4):985-1000. doi:10.3233/JAD-142814
6. McCoy AT, Benoist CC, Wright JW, et al. Evaluation of metabolically stabilized angiotensin IV analogs as procognitive/antidementia agents. J Pharmacol Exp Ther. 2013;344(1):141-154. PMID: 23055539. doi:10.1124/jpet.112.199497 (expression of concern issued)
7. Benoist CC, Kawas LH, Zhu M, et al. The procognitive and synaptogenic effects of angiotensin IV-derived peptides are dependent on activation of the hepatocyte growth factor/c-Met system. J Pharmacol Exp Ther. 2014;351(2):390-402. PMID: 25187433. (Retracted 2025)
8. Kawas LH, McCoy AT, Yamamoto BJ, Wright JW, Harding JW. Development of angiotensin IV analogs as hepatocyte growth factor/Met modifiers. J Pharmacol Exp Ther. 2012;340(3):539-548. doi:10.1124/jpet.111.188136 (Retracted 2025)
9. Sun X, et al. Dihexa rescues cognitive impairment in an APP/PS1 transgenic mouse model through a PI3K/AKT-dependent mechanism. 2021. PMID: 34551989.
10. Ho JK, Nation DA. Cognitive benefits of angiotensin IV and angiotensin-(1-7): a systematic review of experimental studies. Neurosci Biobehav Rev. 2018;90:209-225. doi:10.1016/j.neubiorev.2018.05.005
11. Schoenenberger GA, Monnier M. Characterization of a delta-electroencephalogram (-sleep)-inducing peptide. Proc Natl Acad Sci U S A. 1977;74(3):1282-1286. PMID: 265572. doi:10.1073/pnas.74.3.1282
12. Dolotov OV, Karpenko EA, Inozemtseva LS, et al. Semax, an analog of ACTH(4-10) with cognitive effects, regulates BDNF and trkB expression in the rat hippocampus. Brain Res. 2006;1117(1):54-60. doi:10.1016/j.brainres.2006.07.108
13. Volkova A, Shadrina M, Kolomin T, et al. Selank administration affects the expression of some genes involved in GABAergic neurotransmission. Front Pharmacol. 2016;7:31. doi:10.3389/fphar.2016.00031
14. Khavinson VK, Bondarev IE, Butyugov AA. Epithalon peptide induces telomerase activity and telomere elongation in human somatic cells. Bull Exp Biol Med. 2003;135(6):590-592. doi:10.1023/A:1025493705728
15. Szeto HH. First-in-class cardiolipin-protective compound as a therapeutic agent to restore mitochondrial bioenergetics. Br J Pharmacol. 2014;171(8):2029-2050. doi:10.1111/bph.12461
16. Napoletano F, Schifano F, Corkery JM, et al. The psychonauts' world of cognitive enhancers. Front Psychiatry. 2020;11:546796. doi:10.3389/fpsyt.2020.546796
17. Graf MV, Kastin AJ. Delta-sleep-inducing peptide (DSIP): a review. Neurosci Biobehav Rev. 1984;8(1):83-93. PMID: 6145137. doi:10.1016/0149-7634(84)90022-8
18. Kovalzon VM, Strekalova TV. Delta sleep-inducing peptide (DSIP): a still unresolved riddle. J Neurochem. 2006;97(2):303-309. doi:10.1111/j.1471-4159.2006.03693.x
19. Manning MC, Chou DK, Murphy BM, Payne RW, Katayama DS. Stability of protein pharmaceuticals: an update. Pharm Res. 2010;27(4):544-575. PMID: 20143256. doi:10.1007/s11095-009-0045-6