Cognitive & Neurogenic Peptides (Semax, Selank, Dihexa)

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Upward Index: 02 - Compounds & Molecules MOC | Literature Dossier: Cognitive & Neurogenic Peptides (Semax, Selank, Dihexa) - References

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1. Pharmacodynamics & Mechanism of Action

Neurogenic neuropeptides bypass systemic blood-brain barrier (BBB) degradation via intranasal perineural transport along the olfactory and trigeminal nerves, directly modulating neurotrophin transcription, monoamine turnover, and spinogenesis within minutes.

• Semax (Met-Glu-His-Phe-Pro-Gly-Pro): Synthetic heptapeptide analog of the ${\text{ACTH}}_{(4\text{–}10)}$ fragment extended with a C-terminal Pro-Gly-Pro tripeptide for peptidase resistance; completely devoid of adrenal steroidogenic/cortisol activity.
  • Rapid BDNF/TrkB Surge: Within $30\text{–}180\text{ minutes}$ of intranasal administration, Semax increases hippocampal and basal forebrain BDNF protein by $+1.4\text{-fold}$, BDNF mRNA by $+3\text{-fold}$, and TrkB receptor mRNA by $+2\text{-fold}$.
  • Melanocortin & Monoamine Potentiation: Allosterically modulates MC4R/MC5R melanocortin receptors and dramatically amplifies dextroamphetamine- or activity-induced prefrontal/striatal dopamine and serotonin release without depleting vesicular pools.
• Selank (Thr-Lys-Pro-Arg-Pro-Gly-Pro): Synthetic analog of the endogenous immunomodulatory tetrapeptide Tuftsin (Thr-Lys-Pro-Arg).
  • Enkephalinase Inhibition: Potently inhibits plasma and synaptic enkephalin-degrading enzymes (neprilysin, aminopeptidase N), extending the half-life of endogenous Leu- and Met-enkephalins (natural opioid anxiolysis).
  • ${\text{GABA}}_{\text{A}}$ Transcriptomic Modulation: Alters the expression of 45 out of 84 genes involved in GABAergic/neurotransmitter signaling within $1\text{–}3\text{ hours}$ (matching the transcriptomic footprint of classical benzodiazepines without sedation, cognitive impairment, or withdrawal).
• Dihexa ($N$-hexanoic-Tyr-Ile-(6) aminohexanoic amide): Metabolically stabilized, orally and transdermally bioavailable hexapeptide derivative of Angiotensin IV.
  • HGF / c-Met Dimerization: Binds Hepatocyte Growth Factor (HGF) with picomolar affinity ($K_d\approx 65\text{ pM}$), inducing HGF dimerization and activation of its receptor tyrosine kinase c-Met in the hippocampus. In preclinical dendritic spine assays, Dihexa is roughly $10^7$ ($10\text{ million}$) times more potent than BDNF on a molar basis at inducing functional spinogenesis and glutamatergic synaptogenesis.
• P21 (Ac-DGGL^{A}G-NH2) & PE-22-28:
  • P21: Adamantane-capped CNTF (Ciliary Neurotrophic Factor) mimetic developed from Cerebrolysin epitope mapping; inhibits LIF and GSK-3$\beta$ to drive dentate gyrus neurogenesis and reduce tau hyperphosphorylation.
  • PE-22-28 (Mini-Spadin): 7-amino-acid fragment of Spadin that blocks the TREK-1 two-pore-domain potassium channel, producing rapid antidepressant and synaptogenic effects within 4 days.

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2. Pharmacokinetics & Derivative Modifications

Peptide Variant	Sequence / Cap Modification	Route	Potency & Duration Advantage
Base Semax / Selank	Unmodified N/C termini (PGP tail)	Intranasal / SubQ	Rapid onset ($15\text{ min}$); cleaved by exopeptidases into active PGP within hours
N-Acetyl Semax / Selank	N-terminal Acetylation	Intranasal / SubQ	Blocks N-terminal aminopeptidase cleavage; $\sim 30\text{–}50\%$ smoother, longer CNS curve
N-Acetyl Semax / Selank Amidate (NASA)	N-terminal Acetylation + C-terminal Amidation	Intranasal / SubQ	Blocks both aminopeptidases and carboxypeptidases; highest BBB stability and $8\text{–}12\text{ h}$ subjective duration
Dihexa	N-hexanoyl + 6-aminohexanoic amide	Transdermal (DMSO) or Oral	Extreme metabolic stability ($t_{1/2}\approx 8\text{–}12\text{ days}$); accumulates rapidly if dosed daily

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3. Dosing, Cycling & Synergies

• Standard Protocol:
  • Semax / NA-Semax-Amidate: $200\text{–}600\mu \text{g/day}$ intranasally ($100\text{–}200\mu \text{g}$ per nostril) in the morning.
  • Selank / NA-Selank-Amidate: $250\text{–}750\mu \text{g/day}$ intranasally (1–2 sprays per nostril as needed for acute executive anxiety or evening parasympathetic transition).
  • P21: $500\text{–}1,000\mu \text{g/day}$ intranasally or SubQ for 4 weeks.
  • Dihexa: $2\text{–}5\text{ mg}$ transdermally or orally, strictly limited to 1–2 times per week during targeted skill-acquisition windows (due to its $\sim 10\text{-day}$ half-life and extreme c-Met potency).
• Cycling Cadence: Run Semax/Selank in 10- to 14-day blocks followed by a 1–2 week break, or use 3–4 days per week.
• Synergies: Semax + Dopaminergics & Catecholamines (Bromantane or low-dose L-Tyrosine/caffeine—Semax potentiates dopaminergic release while protecting neurons via BDNF); Selank + GABAergics & Anxiolytics.
• Contraindications & Biomarkers to Monitor:
  • Contraindications & Oncogenic Warning (Dihexa): The HGF/c-Met axis is a primary proto-oncogenic driver of epithelial-mesenchymal transition (EMT), tumor invasion, and metastasis across carcinomas and glioblastomas; Dihexa is strictly contraindicated in any individual with active cancer, pre-cancerous lesions, or strong familial oncology history. Chronic high-dose Semax can occasionally cause transient telogen effluvium (BDNF-mediated hair follicle catagen transition) in androgen-sensitive scalps.
  • Biomarkers: Serum BDNF, hs-CRP, IL-6 (Selank suppresses elevated IL-6 in anxious patients), and comprehensive cancer screening prior to any c-Met modulator.

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4. Key Scientific Evidence Summary

• Semax Hippocampal BDNF/TrkB Induction: Dolotov et al. (2006) demonstrated in Brain Research that a single intranasal dose of Semax ($50\mu \text{g/kg}$) increased hippocampal BDNF protein by $+1.4\text{-fold}$, exon III BDNF mRNA by $+3\text{-fold}$, and TrkB mRNA by $+2\text{-fold}$ within 3 hours.
• Selank GABAergic Gene Modulation: Volkova et al. (2016) published in Frontiers in Pharmacology that Selank significantly alters the expression of 45 GABAergic/neurotransmission genes within 1 hour, correlating closely ($r=0.65\text{–}0.78$) with the acute transcriptomic profile of GABA itself without benzodiazepine side effects.
• Dihexa Synaptogenesis & Dementia Reversal: McCoy et al. (2013) demonstrated in Journal of Pharmacology and Experimental Therapeutics that oral Dihexa crossed the BBB, induced hippocampal spinogenesis at picomolar concentrations ($10^{-12}\text{ M}$), and reversed scopolamine- and age-induced spatial memory deficits in radial arm and water maze models.

See full study breakdowns in Cognitive & Neurogenic Peptides (Semax, Selank, Dihexa) - References.