SNAP-8 (Acetyl Octapeptide-3): Sequence, SNARE Chemistry and Research Literature

SNAP-8 is a synthetic octapeptide whose eight residues, Glu-Glu-Met-Gln-Arg-Arg-Ala-Asp, are lifted verbatim from positions 12 to 19 of human SNAP-25, the synaptosomal-associated protein of 25 kilodaltons catalogued at UniProt P60880. Chemical modification is confined to the two ends: an acetyl group on the amino terminus, a primary amide on the carboxyl terminus.

Both caps are deliberate synthetic choices rather than incidental. Removing the free alpha-amino group and the free alpha-carboxyl group eliminates the charges that aminopeptidases and carboxypeptidases recognise at peptide ends, and it also removes two zwitterionic termini that would otherwise sit at the boundaries of a sequence already carrying three acidic and two basic side chains. What remains is a molecule of 1075.2 g/mol whose net charge at neutral pH comes entirely from side chains.

The INCI-style naming around this compound is inconsistent enough to matter for procurement records. PubChem CID 76283482 lists acetyl octapeptide-3, acetyl octapeptide-1, acetyl octapeptide-8 and acetyl glutamyl heptapeptide-3 as synonyms for one and the same structure, alongside the trade designation SNAP-8. Recording CAS 868844-74-0 or the CID, rather than a trivial name, removes the ambiguity between catalogues.

SNAP-8 borrows its sequence from a protein whose assembly biology is unusually well described. SNAP-25 contributes two of the four helices in the neuronal SNARE bundle, pairing with syntaxin-1 and the vesicle protein VAMP2. That four-helix trans complex zippers from its amino-terminal end toward its carboxyl-terminal end, drawing two lipid bilayers together closely enough to fuse.

Work published in the Journal of Neurochemistry in 2004 by Blanes-Mira and colleagues examined this directly with short synthetic peptides drawn from the SNAP-25 amino-terminal region. The segment spanning 22Ala to 44Ile proved essential to complex formation, and peptides designed from that region suppressed assembly in a manner that tracked how much alpha-helical structure each peptide adopted in solution. Critically, the peptides only abolished complex formation when added before assembly began; once the aggregate had formed, they could not disassemble it. The same peptides disrupted the binary SNAP-25 and syntaxin intermediate and inhibited calcium-dependent exocytosis from permeabilized cells.

That order-of-addition constraint is the mechanistically interesting result, because it distinguishes a competitive assembly modulator from a protease. Botulinum neurotoxins cleave SNAP-25 covalently; a peptide that competes for a docking interface does not, and any effect it produces reverses as the peptide is degraded or cleared.

The SNAP-25 assembly picture has continued to move. A 2026 report in Cell Reports found that SNAP25 undergoes liquid-liquid phase separation in vitro and in living cells, with the linker between its two SNARE motifs required for condensation and regulated by palmitoylation. Those condensates recruited syntaxin-1 and VAMP2 into ternary coacervates that facilitated complex assembly, and two encephalopathy-associated variants, I67N and I192N, blocked condensate fusion and suppressed assembly. Whether short amino-terminal peptides interact with this condensate step has not been reported.

SNAP-8 and acetyl hexapeptide-8 are nested sequences rather than independent molecules. Acetyl hexapeptide-8 is Ac-EEMQRR-NH2, covering SNAP-25 residues 12 to 17. SNAP-8 covers residues 12 to 19, appending alanine and aspartate. The extension adds roughly 42 g/mol, one additional carboxylate, and two more positions of contact with any binding surface the sequence engages.

The hexapeptide is the version with primary literature behind it. Blanes-Mira and colleagues reported in the International Journal of Cosmetic Science in 2002 that Ac-EEMQRR-NH2 inhibited neurotransmitter release with a potency described as comparable to botulinum neurotoxin A, though with much lower efficacy, and that the mechanism traced to interference with formation or stability of the SNARE complex. The same paper reported skin topography analysis on volunteers using a 10% oil-in-water emulsion over 30 days, with wrinkle depth reduced by up to 30%.

No equivalent peer-reviewed mechanistic characterisation of the octapeptide has been published. Comparative claims that the longer sequence engages the SNARE interface more effectively than the hexapeptide circulate widely in supplier literature and are repeated in the introduction of at least one analytical paper, but the underlying comparison does not appear as a peer-reviewed dataset. Treating the two peptides as equivalent in mechanism is an assumption from sequence homology, not a measured result.

One chemical difference is worth noting independently of biology. The added aspartate raises the net negative charge and the polar surface area of an already highly hydrophilic molecule, which works against passive transport across a lipid-rich barrier. Longer and more charged does not mean more permeant.

Permeation is the dominant constraint on SNAP-8 and its shorter relative, and the numbers are stark. At 1075.2 g/mol the octapeptide sits roughly twice the mass conventionally cited as the practical ceiling for passive diffusion through intact stratum corneum, and its five ionisable side chains make it strongly hydrophilic against a lipid-ordered barrier.

The most concrete measurements come from Kraeling and colleagues, publishing in Cutaneous and Ocular Toxicology in 2015 on the hexapeptide. Working with flow-through diffusion cells on hairless guinea pig skin and human cadaver skin, the study applied a 10% cosmetic formulation and recovered most of the peptide from the surface wash. Retention in the stratum corneum reached 0.54% of the applied amount in guinea pig skin and 0.22% in human skin. Epidermal recovery was 0.01% in both species. No peptide was detected in the dermis or in the receptor fluid.

A 2025 review in the International Journal of Molecular Sciences reached the same conclusion from the wider literature: hydrophilicity and molecular size restrict passage through the lipophilic stratum corneum, low penetration limits bioavailability, and formulation strategy rather than the peptide itself is the variable that governs any measured effect. Any published figure for a finished product is therefore a statement about a delivery system as much as about a sequence.

The 2025 Expert Panel for Cosmetic Ingredient Safety review of acetyl hexapeptide-8 amide sits alongside this. The panel concluded that the available data supported cosmetic use at concentrations up to 0.005%, and judged the record insufficient to reach a conclusion at concentrations above that figure.

Delivery work is where the recent publication record on SNAP-8 and its hexapeptide relative is concentrated, following one logic: if the barrier will not pass the molecule, the barrier or the carrier must change. Four approaches recur across 2020 to 2026 papers: dissolving microneedle arrays, ionic liquid co-assemblies, penetration-enhancing carrier peptides, and deep eutectic solvent systems.

Microneedle arrays are the only format in which the octapeptide itself appears in a clinical publication. Avcil and colleagues reported in the Journal of Cosmetic Dermatology in 2020 on hyaluronic acid microneedle patches containing acetyl octapeptide-3 together with palmitoyl tripeptide-5, an arginine and lysine polypeptide, adenosine and seaweed extracts. Over 12 weeks, instrumental measurement recorded fine lines and wrinkles decreased by 25.8%, hydration increased by 15.4%, and dermal density and thickness increased by 14.2% and 12.9% respectively. Because five actives were present, the octapeptide's individual contribution cannot be resolved from that design.

The 2026 work by Feng and colleagues in the International Journal of Biological Macromolecules shows how far the format has been pushed on the hexapeptide. A hyaluronic acid and polyvinyl alcohol matrix at a 3:2 ratio, cast by two-step vacuum-assisted micromolding, reached 20% loading for acetyl hexapeptide-8 and delivered 11.29% cumulative transdermal transfer across Bama miniature pig skin, higher than the aqueous solution comparator. In a UV and D-galactose photoaging mouse model the arrays raised superoxide dismutase activity and lowered malondialdehyde.

Solvent engineering is the other active line. Wang and colleagues reported in the Journal of Materials Chemistry B in 2025 that co-assembling the hexapeptide with a malic acid-derived ionic liquid produced 24-hour cumulative permeation 3.10 times that of the free peptide, with simulations attributing the gain to cation interactions with the lipid matrix. A 2026 Biomaterials Advances paper combined self-assembled tripeptide nanoparticles with a betaine, glycerol and propylene glycol deep eutectic solvent, reporting reduced acetylcholine secretion and suppressed sodium and calcium channel activity alongside weakened stratum corneum tight junctions.

Model systems have advanced in parallel. A 2025 paper in ACS Biomaterials Science and Engineering built a sensory neurone-integrated skin spheroid specifically to evaluate neuropeptide delivery systems, and is the closest published approximation to a functional readout for this peptide class outside a human study.

SNAP-8 has a strikingly small primary literature of its own. A PubMed search on acetyl octapeptide-3 returns only a handful of records, of which one clinical paper and one analytical paper actually concern the molecule. Everything else routinely cited in connection with the octapeptide is either about SNAP-25 biology or about the shorter hexapeptide.

That gap has three practical consequences for anyone reading the field. First, the widely repeated comparative potency claims against acetyl hexapeptide-8 have no peer-reviewed source that can be checked. Second, the single clinical dataset in which the octapeptide appears is a multi-ingredient patch, so no isolated effect size exists. Third, no published permeation study has measured the octapeptide itself across human skin, so its permeation is inferred from a shorter, smaller and less charged molecule that already penetrates poorly.

What is genuinely well established is narrower and more chemical: the sequence, mass and registry identity of the molecule; its exact correspondence to a defined span of SNAP-25; the assembly-stage mechanism by which SNAP-25 amino-terminal peptides interfere with SNARE complex formation in cell-free and permeabilized-cell systems; and a validated method for quantifying the octapeptide down to 0.0125 nanograms per millilitre.

SNAP-8 is supplied for laboratory research only. No regulatory authority has approved the octapeptide as a drug, and material sold to laboratories carries research-use labelling stating that it is not for human or veterinary use.

SNAP-8 is supplied as a white to off-white lyophilized powder and is freely water-soluble, which follows directly from its side-chain complement of three carboxylates and two guanidinium groups. Material catalogues list storage of the dry powder at minus 20 degrees Celsius, protected from light and moisture, with aqueous stocks held frozen and kept sealed against atmospheric water.

One structural feature governs most of the chemical caution around this sequence. Methionine at position three is the single sulfur-containing residue in the molecule, and thioether sulfur is the most readily oxidised side chain in the standard amino acid set. Oxidation to the sulfoxide adds 16 mass units and is detectable by mass spectrometry as an M plus 16 species, which is why identity confirmation on this peptide is normally run by mass spectrometry rather than by retention time alone. Exposure to peroxides, transition metal ions and prolonged air contact in solution all accelerate that route.

For quantification, the reference method is the liquid chromatography with tandem mass spectrometry procedure published by Ji and colleagues in the Journal of Analytical Science and Technology in 2020, which built a multiple reaction monitoring dataset specifically for acetyl octapeptide-3. Reported figures of merit were linearity of r at or above 0.9971, a quantification limit of 0.0125 nanograms per millilitre, repeatability of 0.02 to 0.12% relative standard deviation and accuracy between minus 1.68 and 1.44% relative error. Those numbers set a practical floor for detecting the peptide in formulation matrices and in permeation experiments.

Purity on research-grade material is normally specified at or above 98% by reversed-phase HPLC, with the expected molecular mass of 1075.2 g/mol confirmed against the C41H70N16O16S formula. Because acetyl hexapeptide-8 shares the first six residues, a truncated impurity from incomplete chain assembly differs from the target by only 187 mass units and is chromatographically close; separation conditions should be checked to resolve the two rather than assumed.

SNAP-8 is intended for laboratory research use only. It is not a drug, food or cosmetic ingredient supplied for consumer application, and it is not for human or veterinary use.