Selank and Semax are frequently mentioned together. Both are short synthetic neuropeptides developed at the Institute of Molecular Genetics of the Russian Academy of Sciences, both end in the same stabilizing Pro-Gly-Pro tail, and both are administered intranasally in the Russian clinical literature. They are, however, derived from different parent molecules and studied for different primary effects. This article compares them side by side. For single-compound summaries, see our Selank overview and Semax overview.
Structure and Origin
| Selank | Semax | |
|---|---|---|
| Sequence | Thr-Lys-Pro-Arg-Pro-Gly-Pro (7 aa) | Met-Glu-His-Phe-Pro-Gly-Pro (7 aa) |
| Parent molecule | Tuftsin (Thr-Lys-Pro-Arg), an immunomodulatory tetrapeptide from the IgG heavy chain | ACTH(4-7) fragment of adrenocorticotropic hormone |
| Added stabilizer | Pro-Gly-Pro tail | Pro-Gly-Pro tail |
| Hormonal activity | Not a hormone analog | Reported to lack the corticotropic (adrenal-stimulating) activity of ACTH |
The Pro-Gly-Pro tail is a design feature: it is intended to slow degradation by peptidases, because short peptides are otherwise cleared in minutes. The comparison is a good example of a common strategy, taking a short bioactive fragment and engineering stability onto it.
What Each Is Studied For
Semax has been studied mainly for neurotrophin signaling and for models of cerebral ischemia. Dolotov and colleagues reported that Semax increased BDNF protein and trkB receptor mRNA expression in the rat hippocampus (Brain Res 2006;1117:54-60). Medvedeva and colleagues used genome-wide transcriptional analysis in a rat focal-ischemia model and reported that Semax altered expression of genes related to the immune and vascular systems (BMC Genomics 2014;15:228). In Russia, Semax is registered for use in certain neurological conditions; it is not approved by the FDA.
Selank has been studied mainly in anxiety models and for effects on the GABAergic system and immune signaling. Volkova and colleagues reported that Selank administration altered the expression of several genes involved in GABAergic neurotransmission in rat brain tissue (Front Pharmacol 2016;7:31). The wider literature, reviewed by Kolomin and colleagues, also describes effects on enkephalin metabolism and cytokine expression (Neurosci Med 2013;4:223-252). In Russia it is registered for anxiety-spectrum disorders; it is not approved by the FDA.
Shared Features
- Both are described as modulating neurotrophin and neurotransmitter-related gene expression in rodent brain.
- Both were developed and clinically studied primarily in Russia, with the bulk of human data published in Russian-language journals.
- Both have been delivered intranasally in the primary literature, which raises their own research questions about nose-to-brain transport and the fraction that reaches the CNS.
How They Differ for a Researcher
- Biological question. Semax maps to neurotrophin, ischemia and cognitive-process models; Selank maps to anxiety, GABAergic and immune-modulation models.
- Parent-molecule logic. Because Semax derives from ACTH, researchers need to confirm the absence of melanocortin and adrenal effects in their own system; Selank's tuftsin lineage points toward immune endpoints.
- Readouts. BDNF/trkB expression is the classic Semax readout; GABA-pathway gene expression and behavioral anxiety paradigms are the classic Selank readouts.
The Evidence Gaps
- Language and geography. Much of the original clinical work is in Russian-language journals produced by a related network of laboratories, which limits access and independent replication.
- Gene expression is not function. Both compounds are supported heavily by transcript-level changes in rodent tissue; these do not by themselves demonstrate behavioral or clinical effects.
- Limited controlled Western trials. There are few large, pre-registered, double-blind trials in international journals for either compound.
- Dose and route. Intranasal delivery in rodents and humans is hard to compare, and brain exposure is rarely measured directly.
Sources
- Dolotov OV, et al. Semax, an analog of ACTH(4-10) with cognitive effects, regulates BDNF and trkB expression in the rat hippocampus. Brain Res 2006;1117:54-60. PubMed
- Medvedeva EV, et al. The peptide Semax affects the expression of genes related to the immune and vascular systems in rat brain focal ischemia: genome-wide transcriptional analysis. BMC Genomics 2014;15:228.
- Volkova A, et al. Selank administration affects the expression of some genes involved in GABAergic neurotransmission. Front Pharmacol 2016;7:31.
- Kolomin T, Shadrina M, Slominsky P, Limborska S, Myasoedov N. A new generation of drugs: synthetic peptides based on natural regulatory peptides. Neurosci Med 2013;4:223-252.
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