Selank Peptide: Potential Support for Neurotransmitters and Neurotrophins

Selank is a synthetic heptapeptide, and the seven amino acids in its structure are in the configuration of Thr-Lys-Pro-Arg-Pro-Gly-Pro (TKPRPGP). The peptide appears to be a modified analogue of the endogenously occurring tetrapeptide Tuftsin (TKPR). However, Selank incorporates an additional tripeptide fragment, Pro-Gly-Pro (PGP), at the C-terminal end. The inclusion of this PGP sequence has been investigated for its hypothetical support for the physicochemical properties of the molecule, particularly in relation to hydrophilicity, lipophilicity, and interactions with lipid-rich barriers such as the BB barrier.

Research conducted in laboratory settings may suggest that the PGP motif may facilitate interactions with membrane transport systems, including potential receptor-mediated uptake or active transport mechanisms. Beyond these structural modifications, laboratory studies have examined Selank peptide capacity to engage with multiple signaling pathways in central nervous tissues. Experimental data indicates possible actions on systems such as GABAergic, serotonergic, and enkephalinergic signaling, as well as on the regulation of neurotrophic factor (aka neutrophins) synthesis.

 

Research

Selank Peptide: Potential Interaction with Enkephalinergic Signaling

Enkephalinergic signaling refers to the activity of enkephalins, which are short endogenous opioid peptides that bind mainly to δ- and μ-opioid receptors on the nerve cells. These peptides are quickly degraded by a set of peptidases collectively known as enkephalinases. Because of their rapid turnover, the duration and strength of enkephalin signaling depend not only on peptide release and receptor affinity, but also on how quickly they are broken down.

Studies have suggested that Selank peptide may interact with enkephalinergic signaling through modulation of enkephalin degradation. Experimental data collected by Zozulya et al. indicates that Selank may concentration-dependently inhibit the enzymatic hydrolysis of enkephalins. The researchers comment that “Selank was more potent than peptidase inhibitors bacitracin and puromycin in inhibiting enkephalinases” in laboratory settings, implying a relatively high affinity for targets within the enkephalin-degrading enzyme system.⁽¹⁾

Since enkephalins are rapidly metabolized by multiple plasma peptidases, even subtle interference with their hydrolysis might prolong their half-life and thereby support their interaction with opioid receptors. By slowing down this degradation process, Selank may act as an exogenous enkephalinase modulator. In this way, it might be posited that Selank contributes to a functional stimulation of the opioid system not by directly activating receptors, but by stabilizing endogenous peptides.

Radioreceptor assays conducted by Meshavkin et al. also suggest indirect support, as Selank peptide actions appeared to be fully antagonized by naloxone, a non-selective opioid receptor blocker, even though the peptide does not compete for binding at the corresponding δ- and μ-opioid receptors.⁽²⁾ The data reinforces the hypothesis that Selank peptide activity involves the regulation of enkephalin metabolism. By limiting the degradation of enkephalins, Selank might extend their signaling lifetime, thereby potentially altering the functional crosstalk between enkephalinergic and dopaminergic systems.

Selank Peptide: Potential Support for GABAergic Signaling

GABAergic signaling is mediated by γ-aminobutyric acid (GABA), which is considered the principal inhibitory neurotransmitter in the interactions of nerve cells. Experimental data by Volkova et al. suggest that Selank may be “associated with allosteric modulation of the GABAergic system.” Specifically, the peptide may alter the binding of radiolabeled GABA to its receptors without supporting receptor affinity, leading to the proposal that Selank may function as an allosteric modulator of some subclasses of GABA receptors.⁽³⁾ This hypothesis is further supported by gene expression analyses showing overlapping transcriptional changes following exposure to either Selank or GABA.

When Volkova et al. examined the expression of neurotransmission-related genes in cortical tissue, Selank also appeared to modulate the mRNA levels of numerous GABA receptor subunits and transporters. Some of these actions resembled those induced by GABA itself, while other actions were unique to Selank. Another notable finding by Volkova et al. was that Selank appeared to continuously produce transcriptional changes at later time points when GABA’s actions had largely subsided.

This delayed activity might reflect secondary signaling cascades initiated by Selank, potentially extending beyond direct GABA receptor modulation. In line with this, Selank also interacts with genes linked to dopaminergic and serotonergic signaling, hinting at cross-talk between mitigatory and other neurotransmitter systems. Altogether, these findings suggest that Selank may engage the GABAergic system in a manner partly overlapping with, yet not identical to, GABA itself.

Selank Peptide: Potential Support on Serotonergic Signaling

Laboratory experiments by Nadorova et al. suggest that Selank may support various serotonergic parameters in a state-dependent manner, including the levels of the main neurotransmitter serotonin (5-HT), which mediates the signaling.⁽⁴⁾ When tested under baseline conditions, Selank did not appear to markedly alter the concentrations of 5-HT or its primary metabolite across several brain regions, suggesting little support for serotonergic tone in the absence of perturbation.

In comparison, Selank apparently prevented this accumulation in structures such as the frontal cortex, hypothalamus, and amygdala under conditions where 5-HT levels were observed to be elevated in laboratory settings. This pattern may be explained by a reduction in 5-HT synthesis, or by modulation of turnover, given the accompanying changes in the 5-hydroxyindoleacetic acid (5-HIAA)/5-HT ratio, where 5-HIAA is the main breakdown product of 5-HT. One possibility is that Selank interacts indirectly with serotonergic receptor pathways.

Another line of interpretation is that Selank does not act solely within the serotonin system but may shift broader neurotransmitter balance. Previous reports note support on dopaminergic indices at higher concentrations and alterations in amino acid transmitter levels (e.g., glutamate and GABA) at lower concentrations. Since both dopamine and excitatory/mitigatory amino acids are tightly interconnected with serotonin circuits, Selank peptide apparent action might reflect a coordinated support on multiple transmitter systems rather than a strictly serotonergic mechanism.

Selank Peptide: Potential Support on Neurotrophic Factor Signaling

Research by Inozemtseva et al. suggests that Selank may also interact with neurotrophic factor signaling, particularly brain-derived neurotrophic factor (BDNF).⁽⁵⁾ BDNF is a well-characterized growth factor that appears to regulate synaptic plasticity, memory-related processes, and neuronal survival through binding to TrkB receptors. Its expression is dynamically regulated at both the transcriptional and translational levels, and small shifts in BDNF availability may alter long- and short-term synaptic functions.

Experimental work by Inozemtseva et al. has suggested that Selank may alter hippocampal BDNF expression in a time-dependent manner. At the transcriptional level, Selank exposure was associated with an increase in BDNF mRNA several hours after administration, suggesting a potential stimulation of neurotrophin gene transcription. Interestingly, the protein levels appeared to drop briefly at one time point but later rose above baseline. This timing difference may suggest that Selank might support both fast-acting regulatory processes, possibly through immediate signaling cascades, and slower genomic mechanisms that might eventually increase BDNF protein production.

Observations like these by Inozemtseva et al. raise the possibility that Selank may interact with the molecular machinery governing neurotrophin expression rather than acting as a direct receptor ligand. By modulating BDNF transcription and translation dynamics, Selank may indirectly support neuronal plasticity-related pathways. The pattern resembles what has been described for other regulatory peptides with nootropic activity, reinforcing the hypothesis that Selank engages multiple signaling axes, including opioid peptides, GABAergic transmission, and neurotrophin regulation.

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References:

1. Zozulya AA, Kost NV, Yu Sokolov O, Gabaeva MV, Grivennikov IA, Andreeva LN, Zolotarev YA, Ivanov SV, Andryushchenko AV, Myasoedov NF, Smulevich AB. The inhibitory effect of Selank on enkephalin-degrading enzymes as a possible mechanism of its anxiolytic activity. Bull Exp Biol Med. 2001 Apr;131(4):315-7. doi: 10.1023/a:1017979514274. PMID: 11550013.
2. Meshavkin VK, Kost NV, Sokolov OY, Zolotarev YA, Myasoedov NF, Zozulya AA. Naloxone-blocked depriming effect of anxiolytic selank on apomorphine-induced behavioral manifestations of hyperfunction of dopamine system. Bull Exp Biol Med. 2006 Nov;142(5):598-600. doi: 10.1007/s10517-006-0428-1. PMID: 17415472.
3. Volkova A, Shadrina M, Kolomin T, Andreeva L, Limborska S, Myasoedov N, Slominsky P. Selank Administration Affects the Expression of Some Genes Involved in GABAergic Neurotransmission. Front Pharmacol. 2016 Feb 18;7:31. doi: 10.3389/fphar.2016.00031. PMID: 26924987; PMCID: PMC4757669.https://doi.org/10.3389/fphar.2016.00031
4. Nadorova AV, Kolik LG, Klodt PM, Narkevich VB, Naplyokova PL, Kozlovskaya MM, Kudrin VS. The relationship between the anxiolytic action of selank and the level of serotonin in brain structures during the modeling of alcohol abstinence in rats. Neurochemical journal. 2014 Apr;8(2):115-20.
5. Inozemtseva LS, Karpenko EA, Dolotov OV, Levitskaya NG, Kamensky AA, Andreeva LA, Grivennikov IA. Intranasal administration of the peptide Selank regulates BDNF expression in the rat hippocampus in vivo. Dokl Biol Sci. 2008 Jul-Aug;421:241-3. doi: 10.1134/s0012496608040066. PMID: 18841804.