Semax is a synthetic heptapeptide analogue of a fragment of adrenocorticotropic hormone (ACTH), modified at its C-terminus with a Pro-Gly-Pro tripeptide to resist enzymatic degradation. Laboratory studies use it to examine neurotrophin signalling, gene expression in brain tissue and the pharmacology of melanocortin-derived peptides in cell culture and rodent models. Its sequence is short, but its stability, charge and sulphur-containing residue make handling and verification important. This article summarises its structure, proposed mechanisms, the published research areas and the analytical and storage standards needed for reproducible work. It is written for laboratory researchers and offers no guidance on human use.
What is Semax?
Semax is classified as a synthetic neuropeptide and a melanocortin-derived analogue. Its sequence is Met-Glu-His-Phe-Pro-Gly-Pro, usually written MEHFPGP. The first four residues correspond to positions 4 to 7 of ACTH, and the heptapeptide is therefore described as an analogue of ACTH(4-10) in which the original C-terminal residues are replaced by the tripeptide Pro-Gly-Pro. The molecular formula is approximately C37H51N9O10S and the molecular weight is about 814 Da for the free peptide.
The reason for the design lies in the biology of the parent fragment. ACTH(4-10) is a short sequence that lacks the corticotropic and pigmenting activity of full-length ACTH but was reported in the 1970s and 1980s to influence learning and attention-related behaviour in rodents. The fragment is cleared within minutes by peptidases. Adding Pro-Gly-Pro at the C-terminus was reported to slow this degradation considerably, because proline-rich sequences are poor substrates for many exopeptidases. The Pro-Gly-Pro tripeptide is itself studied as a biologically active fragment, derived from collagen and related proteins.
The peptide was developed in Russia at the Institute of Molecular Genetics of the Russian Academy of Sciences, by a group associated with Igor Ashmarin, Nikolai Myasoedov and colleagues, in the 1980s and 1990s. A pharmaceutical formulation has been registered for specific clinical uses in Russia and some neighbouring countries. That product is manufactured and supplied under national pharmaceutical standards, and research-grade material is not equivalent to it. To the author’s understanding, Semax is not authorised as a medicine in the United Kingdom, and this should be checked against current Medicines and Healthcare products Regulatory Agency (MHRA) records. The MHRA has issued warnings about unlicensed products marketed for human use.
Researchers will meet the compound described as Semax, Semax acetate and, for the C-terminal tripeptide alone, PGP. Because the names are used loosely, the certificate of analysis should state the sequence and mass. The material is relevant here only as a laboratory research reagent.
Mechanism of action
No single receptor has been conclusively identified for Semax, and this is the most important point to understand about its mechanism. The literature describes several proposed routes, and some of them rest on observations from a small number of research groups.
The first proposed route concerns the melanocortin system. ACTH and related peptides act on the five melanocortin receptors, which are class A G protein-coupled receptors coupled to cyclic AMP signalling. The fragment on which Semax is based lacks the core His-Phe-Arg-Trp motif that gives full melanocortin receptor activity, so its activity at these receptors is limited, and reports of melanocortin-mediated effects should be checked against receptor-specific controls.
The second proposed route involves neurotrophin signalling. Studies in rodents reported that exposure to the peptide altered expression of brain-derived neurotrophic factor (BDNF) and of its receptor TrkB in the hippocampus, and altered related signalling in cell systems. These are measurements of gene and protein expression in a specific model.
The third proposed route concerns neurotransmitter systems. Reports describe effects on serotonergic and dopaminergic signalling in rodent brain tissue, and inhibition of enkephalin-degrading enzymes has also been suggested as a contribution, since enkephalinase activity can be affected by short peptides. These findings are not uniformly replicated.
The fourth route is transcriptional. Microarray and RNA sequencing studies in rats reported that the peptide changed the expression of large sets of genes, including genes associated with immune and vascular function, in brain tissue after experimental interventions. Such analyses generate hypotheses rather than prove causal pathways.
In cell-based work, “dosage” means molar concentration in the medium, which depends on net peptide content, adsorption to plasticware and protease activity in any serum used. Because Semax is much more stable than native ACTH(4-10) but is not immune to degradation, its stability in the chosen medium should be checked. Scrambled-sequence controls and the Pro-Gly-Pro tripeptide alone are useful comparators, because they allow the contribution of the C-terminal extension to be separated from that of the ACTH-derived portion.
What the research shows
The literature on Semax is substantial for a peptide of its size, but it is concentrated in a few research groups, most of them in Russia. Four areas are summarised below in general terms. Readers should consult the primary papers for methods, concentrations and statistics, because commercial summaries often overstate findings.
The first area is the original design and characterisation. Papers from the Russian Academy of Sciences groups in the late 1980s and 1990s described analogues of ACTH(4-10) extended with Pro-Gly-Pro and compared their stability and behavioural effects with those of the parent fragment in rodents. They reported that the extended peptide persisted longer in biological preparations. The early literature can be explored through a PubMed search on ACTH(4-10) analogue Semax and Pro-Gly-Pro.
The second area is neurotrophin expression. A 2006 paper by Dolotov and colleagues in Brain Research reported that Semax altered the expression of BDNF and TrkB in the rat hippocampus, and examined effects in cultured cells. Exposures in the animal experiments were expressed per kilogram of body weight, and the route of administration affected the results, so the values should be taken from the primary paper. This was a rodent and cell study, and it is described only as part of the scientific record. It can be located through a PubMed search for Semax effects on BDNF and trkB expression in rodent hippocampus.
The third area is gene expression profiling. Studies led by groups in Moscow reported transcriptome changes in rat brain tissue after experimental focal cerebral ischaemia, with and without the peptide, and described changes in genes involved in immune response and vascular function. These are large-scale expression analyses in animals. They are hypothesis-generating and say nothing about any effect outside the experimental model.
The fourth area is enzymatic stability and metabolism. Biochemical studies examined how the peptide is broken down in plasma and tissue extracts and identified the C-terminal tripeptide as a relatively stable product. This work explains the logic of the Pro-Gly-Pro extension and supports the use of the tripeptide as a control.
A recurring limitation runs through this body of work. Most primary studies come from a small number of laboratories, routes and exposures vary widely, results from the heptapeptide and its metabolites are sometimes conflated, and the exact material used is not always characterised analytically. Independent replication would strengthen the evidence, and reproducibility depends on knowing exactly what was in the vial.
Research applications
In the laboratory, Semax is used in several contexts. The most common is neuroscience research in cell culture and tissue preparations, where it is a test compound in studies of neurotrophin expression, neuronal survival under stress and gene expression in neuronal and glial cells. Good practice is to include scrambled-sequence and Pro-Gly-Pro controls.
A second context is peptide pharmacology. The peptide is used as an example of how a short C-terminal extension can stabilise a fragment of a larger hormone, and researchers developing other protease-resistant peptides use it as a comparator in plasma stability assays.
A third context is animal models, which require institutional ethical review and, in the United Kingdom, authorisation under the Animals (Scientific Procedures) Act 1986. Study design should include vehicle controls, blinded assessment and analytical confirmation of the material administered.
A fourth context is analytical chemistry. A heptapeptide containing methionine, histidine and two prolines is a useful test case for liquid chromatography and mass spectrometry methods, including those that must separate oxidised forms, and reference material of defined identity and purity supports method development and the detection of unlicensed peptide products.
Purity, storage and handling
Although Semax is short, its chemistry has traps. The methionine at the N-terminus oxidises readily to the sulphoxide, adding 16 Da, and can do so during cleavage from the resin, during purification and during storage. The glutamic acid and histidine side chains require appropriate protection during synthesis, and the Pro-Gly-Pro sequence at the C-terminus can form diketopiperazine by-products through cyclisation of the terminal dipeptide, a known side reaction in sequences ending in proline. Reversed-phase high-performance liquid chromatography (HPLC) with UV detection at 214 or 220 nm is the standard purity method, and a main peak of at least 98 per cent is commonly expected. The phenylalanine and histidine residues give weak absorbance near 254 to 260 nm, so a second wavelength can help to identify the peptide. For a peptide this small and polar, retention may be modest and impurities can elute close to the main peak, so a shallow gradient is needed. A stated purity is meaningful only if the method and chromatogram are available.
HPLC must be paired with mass spectrometry. The expected mass is about 814 Da. A species 16 Da higher indicates the methionine sulphoxide, which is the most common impurity, and a species lacking a residue indicates a deletion product. A clean peak at the wrong mass is a clean peak of the wrong compound.
A batch-specific certificate of analysis matters because purity, peptide content and oxidation level vary between synthesis runs and with storage. It should carry a lot number matching the vial, the HPLC trace or purity value, the observed and theoretical masses, the test date and ideally the salt form and net peptide content. Lyophilised powders contain counterions and residual water, so the weighed mass is not the mass of peptide, and ignoring this introduces systematic errors into any concentration-response comparison. For a peptide of only 814 Da, the counterion can account for a particularly large fraction of the powder’s mass, so the salt form deserves attention.
Because methionine oxidation proceeds readily once the peptide is in solution, batch-level verification matters more here than with a sequence lacking oxidisable residues. UK laboratories sourcing Semax should expect a batch-specific certificate of analysis that states the mass found and the salt form, with lyophilised storage at -20°C, and the same documentation standard applies when weighing any best peptides supplier uk claim, since a supplier’s analytical record rather than its search ranking shows whether the vial matches its stated specification.
Lyophilised Semax is generally stored at -20°C in a sealed container with desiccant, and many laboratories use -80°C for long-term archives. Vials should reach room temperature before opening so that condensation does not form on the cold powder. After reconstitution, stability falls. Standard practice is to dissolve the peptide in sterile water or a suitable buffer, divide the solution into single-use aliquots and freeze them to avoid repeated freeze-thaw cycles. Refrigerated storage at 2 to 8°C is sometimes used for solutions consumed within days, but the acceptable period should be validated for the assay concerned, preferably by re-running HPLC and mass spectrometry on stored solution. Degassed buffers can slow methionine oxidation, and sealing vials under inert gas is a further precaution some laboratories take.
Light sensitivity is a secondary but genuine concern. The histidine, phenylalanine and methionine residues can undergo photo-oxidation, so amber vials or dark storage are advisable, and prolonged exposure to bright laboratory lighting should be avoided. Peptides also adsorb to glass and some plastics at low concentrations, so low-bind tubes are preferred for dilute working solutions.
Labelling is a final indicator of quality. Clear naming, sequence, molecular weight, lot number, salt form and an unambiguous research-only statement suggest a supplier that understands its market, while any wording that implies use in humans is a warning sign and raises regulatory concerns in the United Kingdom.
Frequently asked questions
What is Semax used for in laboratory research?
It is used as a test compound in neuroscience studies of neurotrophin expression and gene regulation in cultured cells and approved animal models, in comparative studies of protease-resistant peptides and as a reference in analytical methods. It is a research reagent and not an authorised medicine in the United Kingdom.
What is the sequence and molecular weight of Semax?
Semax is a heptapeptide with the sequence Met-Glu-His-Phe-Pro-Gly-Pro, usually written MEHFPGP, and a molecular weight of about 814 Da. It is an analogue of ACTH(4-10) with a Pro-Gly-Pro C-terminal extension. The certificate of analysis should show a mass spectrometry result matching this value.
How should Semax be stored for research?
Keep lyophilised peptide at -20°C, or -80°C for long-term archiving, in a sealed, dry, light-protected container. Allow vials to reach room temperature before opening. After reconstitution, aliquot and freeze the solution to limit freeze-thaw cycles and methionine oxidation.
How can I verify the purity of a Semax batch?
Request a batch-specific certificate of analysis showing HPLC purity and a mass spectrometry result near 814 Da, with the salt form and a lot number matching the vial. A mass 16 Da higher suggests oxidation. For critical work, independent testing by an accredited laboratory confirms identity.
Semax is supplied for in-vitro laboratory research only and is not intended for human or veterinary use.
