What Is Selank | Tuftsin-Analog Peptide for Neuroscience Research

Selank is a synthetic heptapeptide (Thr-Lys-Pro-Arg-Pro-Gly-Pro). Most published work comes from in vitro and rodent studies.

A small number of published human comparator studies also exist, but their limited size and lack of broad independent replication do not establish general clinical safety or efficacy. Much of the mechanistic literature comes from overlapping research groups, and broad independent replication remains limited; the evidence should therefore not be weighted as equivalent to multi-center, independently replicated findings.

Molecular Identity

The free-acid peptide moiety listed by PubChem is H-Thr-Lys-Pro-Arg-Pro-Gly-Pro-OH, usually written as TKPRPGP. PubChem lists CAS 129954-34-3, molecular formula C₃₃H₅₇N₁₁O₉, average molecular weight 751.9 g/mol, monoisotopic exact mass 751.4341 Da, and PubChem CID 11765600.

Research batches may be supplied as acetate (e.g., the diacetate salt is listed in PubChem supplier synonyms as TP-7 diacetate) or other counter-ion forms, which should be identified and quantified separately from the peptide moiety.^[1]

The sequence contains three proline residues. Its first four amino acids, Thr-Lys-Pro-Arg, match the tuftsin sequence, and Pro-Gly-Pro is added at the C terminus.

Published research therefore describes Selank as a synthetic tuftsin-analog peptide.^[2]

The chemical form must stay consistent across the product label, COA, molecular formula, molecular weight, and mass spectrum. A C-terminally amidated peptide is not the same chemical form as the free-acid Selank listed above and requires its own verified identity data.

The theoretical monoisotopic neutral mass of free-acid Selank is 751.4341 Da; calculated charge-state ions for mass-spectrometric reference are [M+H]⁺ m/z 752.4413, [M+2H]²⁺ m/z 376.7243, and [M+3H]³⁺ m/z 251.4853. The average molecular weight of 751.9 g/mol should not be used alone as the high-resolution MS acceptance target.

Counter-ions should be characterized separately where relevant.

What GABA-Related Studies Show

One rat study (male Wistar rats, single intranasal 300 μg/kg, frontal cortex at 1 and 3 hours) found changes in several frontal-cortex genes involved in neurotransmission after Selank exposure. Some of the affected genes were linked to GABA signaling.

This suggests a possible connection with the GABA system, but it does not identify one confirmed receptor or explain the full mechanism.^[2]

Vyunova et al. (2018) used a radioligand-receptor method with isolated brain cell plasma membranes and found that Selank affected [³H]GABA binding in a concentration-dependent manner as a positive allosteric modulator. The study also reported that Selank was able to block the modulatory activity of diazepam and olanzapine; the locations of their binding sites and the peptide binding site apparently differ but may partially overlap.

The authors hypothesized that one of Selank’s molecular mechanisms may involve subtype-selective, concentration-dependent allosteric modulation of GABA receptors.

The exact receptor subtype and binding site are still not known.^[3]

Results have also differed between mouse strains and between laboratory dosing routes. In one study, BALB/c and C57BL/6 mice (300 μg/kg/day, 5 consecutive days, intranasal vs. intraperitoneal) did not show the same behavioral or receptor-binding changes.

This means the findings should not be treated as one fixed effect that appears in every model.^[4]

Tests such as the elevated plus maze measure anxiety-like behavior in rodents. They are useful research tools, but they do not measure human clinical benefit, human safety, dependence, withdrawal, or side effects.^[5]

BDNF and Brain-Chemistry Findings

A rat study (intranasal 250 or 500 μg/kg, hippocampus at 1, 3, and 24 hours) reported that Selank changed brain-derived neurotrophic factor (BDNF) expression with clear time- and dose-dependence: BDNF mRNA increased approximately 1.5- to 2-fold at 3 hours, while BDNF protein decreased by approximately 40% at 3 hours under the 500 μg/kg condition and increased by approximately 30% at 24 hours. The safest description is that Selank regulated BDNF under the tested conditions.

It should not be described as always or permanently increasing BDNF.^[6]

In a different rat model involving long-term ethanol exposure (0.3 mg/kg/day intraperitoneal for 7 days), researchers reported that Selank prevented ethanol-associated BDNF elevation in the hippocampus and frontal cortex rather than simply raising BDNF, and changes in memory-related test results were also observed. These findings apply only to that specific animal model and do not prove a general memory or cognitive benefit.^[7]

A mouse study also found changes in norepinephrine and dopamine metabolites after Selank exposure. Some dopamine-related changes went in opposite directions in BALB/c and C57BL/6 mice.

It is therefore more accurate to say that Selank changed some monoamine measurements in these models, rather than claiming that it simply raises or lowers one neurotransmitter.^[8]

Enzyme Findings

Kost et al. (2001) tested Selank against enkephalin-degrading enzymes from human serum in vitro. Selank showed an IC₅₀ of about 20 μM, while Semax showed an IC₅₀ of about 10 μM; for comparison, puromycin had an IC₅₀ of 10 mM in the same system.

Pentapeptide fragments of both peptides were also active, while the tested three-, four-, and six-amino-acid fragments were not. This means the study did not show that the Pro-Gly-Pro tripeptide alone caused the effect.

It also did not prove that the same effect occurs in a living animal or person.^[9]

Laboratory Handling

• Dry peptide: Follow the storage condition on the batch documentation. General peptide-handling guidance supports storing lyophilized peptides at −20°C to −80°C for long-term laboratory storage. Keep the container sealed, dry, and away from direct light.^[10]
• Before opening: Let a cold, sealed vial reach room temperature in a dry environment before opening it. This helps reduce moisture condensation entering the vial.^[10]
• Solvent: Choose the solvent from a validated laboratory protocol and confirm that it fits the required concentration, pH, salt level, and assay. Water, buffered aqueous media, saline-containing media, or preservative-containing solutions should not be treated as universally interchangeable solvents for every experiment.
• Prepared solution: Stability depends on the peptide concentration, solvent, pH, container, temperature, and storage time. Use small laboratory aliquots when suitable and avoid repeated freeze-thaw cycles. Do not give a fixed refrigerated or frozen shelf life without supporting stability data.^[10][11]
• Concentration calculations: Any mass, volume, or molar calculation must be labeled as laboratory configuration information only. It must not be presented as a human or veterinary dose.

How to Read a Peptide COA

A certificate of analysis is batch-specific quality information. It does not prove that a material is safe for people, clinically effective, or suitable for veterinary use.

• Mass spectrometry: Identity should be evaluated against the theoretical monoisotopic mass and the expected charge-state or adduct m/z values of the stated peptide moiety. The average molecular weight of 751.9 g/mol should not be used by itself as the high-resolution MS acceptance target. Mass spectrometry supports identity, but it does not prove purity by itself. Counter-ions such as acetate or TFA should be characterized separately where relevant.
• HPLC purity: HPLC area percentage shows the relative chromatographic peak area under one test method. It is not automatically the same as the actual mass percentage of peptide in the vial.
• Peptide content: Water, counter-ions such as acetate or TFA, residual solvents, and inorganic salts can lower the actual peptide content even when the HPLC area purity is high.
• Impurities: A useful COA should address the tests that matter for that batch, which may include related peptide impurities, water, residual solvents, and counter-ion content.
• Batch match: The lot number, sequence, terminal form, theoretical mass, chromatogram, mass spectrum, and test date must all refer to the same material.

Peer-reviewed work on synthetic peptide reference standards notes that identity, purity, water, counter-ions, and handling all affect the assigned purity or peptide-content value of a peptide material.^[12] As a general quality principle, ICH Q6A defines a specification as a set of tests, test methods, and acceptance criteria rather than a single result.^[13]

ICH Q1A(R2) and Q6A are cited here only as general pharmaceutical-quality principles. Their citation does not imply that a research-use-only material has been manufactured, tested, or released as a regulated drug substance.

Limits of the Evidence

The available Selank studies use different test systems, animal strains, routes, doses, tissues, and time points. Their results should not be combined into one certain mechanism or used as proof of a human benefit.

Much of the mechanistic literature comes from overlapping research groups, and broad independent replication remains limited. A small number of published human comparator studies exist (e.g., Selank vs. medazepam and Selank vs. phenazepam) but are limited in size and do not establish general clinical safety or efficacy.

Words such as “anxiolytic,” “nootropic,” “anti-stress,” or “cognitive enhancement” should only be used when describing the measured endpoint of a cited laboratory or animal study.

Research Use Only Disclaimer

Research Use Only: All NEXALUME LABS products are intended and labeled solely for laboratory research use. They are not intended, manufactured, tested, or released for human or veterinary administration.

This article provides general scientific information regarding standard laboratory in vitro and in vivo research contexts only, and does not constitute a validated experimental protocol, medical guidance, clinical guidance, veterinary guidance, or treatment advice.