Semax vs SNAP-8 (Acetyl Octapeptide-3)

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.

SNAP-8 (Acetyl Octapeptide-3)

SNAP-8, or acetyl octapeptide-3, is a synthetic eight-residue peptide modelled on the N-terminal region of the neuronal protein SNAP-25. Its sequence, Glu-Glu-Met-Gln-Arg-Arg-Ala-Asp, extends the related acetyl hexapeptide-3 by two residues, and both ends are capped: acetylated at the N-terminus and amidated at the C-terminus. It was developed as a cosmetic ingredient, and most available data come from ingredient-level testing and small studies of topical formulations rather than independent research. Biochemical work has looked at its interaction with the SNARE complex in vitro. Whether a peptide of this size crosses intact skin to reach nerve terminals in meaningful amounts has not been well established.

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.

How SNAP-8 (Acetyl Octapeptide-3) acts

Release of neurotransmitter from a nerve terminal depends on the SNARE complex, a bundle of helices contributed by SNAP-25, syntaxin and synaptobrevin (VAMP) that draws vesicle and plasma membranes together. Acetyl octapeptide-3 copies a short stretch of the SNAP-25 N-terminus and has been proposed to compete with the native protein for a place in that bundle. Reports, mostly from ingredient developers, describe less efficient assembly of stable complexes and reduced neurotransmitter release from cultured cells. These data come largely from simplified systems, and evidence that the same interaction occurs in intact tissue is limited.

The records side by side

• Type: Semax, Synthetic ACTH analog (heptapeptide); SNAP-8 (Acetyl Octapeptide-3), Acetylated octapeptide with C-terminal amidation
• Length: Semax, 7 amino acids; SNAP-8 (Acetyl Octapeptide-3), 8 amino acids
• Molecular weight: Semax, 813.9 g/mol; SNAP-8 (Acetyl Octapeptide-3), 1075.2 g/mol
• Molecular formula: Semax, C37H51N9O10S; SNAP-8 (Acetyl Octapeptide-3), C41H70N16O16S

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.