Selank vs Semax

Selank

Selank is a synthetic seven-residue peptide, Thr-Lys-Pro-Arg-Pro-Gly-Pro, made by adding Pro-Gly-Pro to the tetrapeptide tuftsin. Tuftsin is a fragment of the heavy chain of immunoglobulin G, studied in immunology for its actions on phagocytic cells; the Pro-Gly-Pro extension was added to slow enzymatic breakdown. Selank was developed in Russia, and most published work on it comes from Russian groups. That literature consists mainly of rodent behavioural and gene-expression studies, with some small clinical studies, many of them published in Russian-language journals. Independent work outside Russia is limited.

Semax

Semax is a synthetic seven-residue peptide, Met-Glu-His-Phe-Pro-Gly-Pro, built from a short fragment of adrenocorticotropic hormone (ACTH). Its first four residues match positions 4 to 7 of ACTH; the Pro-Gly-Pro tail does not occur there in the hormone and is reported to slow breakdown by peptidases. Short ACTH fragments of this kind are described as lacking the steroid-releasing activity of the full hormone. Semax was developed by Russian researchers, and most of its literature comes from Russian groups working in rats and cell cultures. Controlled human studies are few, many are published only in Russian, and independent replication elsewhere is limited.

How Selank acts

No single receptor for Selank has been identified. Rodent studies have reported that it changes the expression of genes involved in GABAergic neurotransmission, and some experiments suggest it modulates GABA-A receptor function allosterically. It has also been reported to inhibit enkephalin-degrading enzymes in blood serum, to affect monoamine metabolism in the brain, and to alter the expression of cytokines including interleukin-6. Increased expression of brain-derived neurotrophic factor (BDNF) in the rat hippocampus has also been described. Much of this evidence comes from a small number of laboratories and awaits independent replication.

How Semax acts

No specific receptor for Semax has been identified. Studies in rats have reported higher expression of brain-derived neurotrophic factor (BDNF) and its receptor TrkB in the hippocampus, and other work has examined dopamine and serotonin turnover in the striatum. Transcriptome studies in rat models of cerebral ischaemia describe shifts in the expression of genes tied to immune and vascular processes. Because its core derives from ACTH, an interaction with melanocortin receptors has been proposed, though direct binding evidence is limited. How these separate observations connect has not been worked out.

The records side by side

• Type: Selank, Synthetic tuftsin analog (heptapeptide); Semax, Synthetic ACTH analog (heptapeptide)
• Length: Selank, 7 amino acids; Semax, 7 amino acids
• Molecular weight: Selank, 751.9 g/mol; Semax, 813.9 g/mol
• Molecular formula: Selank, C33H57N11O9; Semax, C37H51N9O10S

Reading a comparison

A comparison places two records side by side; it does not merge them. Each description above is drawn from that compound's own record, and the two were not necessarily characterised by the same methods, at the same time, or to the same level of detail. Before comparing any attribute, it is worth establishing that both records describe the substance you think they describe — names are not identifiers, and two entries sharing a name can differ in salt form, stereochemistry or the convention used to state a mass. Where a figure carries no method beside it, the comparison is between two reported numbers rather than between two measurements.