Semax Peptide

Semax is a synthetic heptapeptide (Met-Glu-His-Phe-Pro-Gly-Pro, MEHFPGP) with MW 813.93 g/mol and CAS 80714-61-0. It consists of the ACTH(4-7) fragment (Met-Glu-His-Phe) with a C-terminal Pro-Gly-Pro stability tail. Developed at the Institute of Molecular Genetics, Russian Academy of Sciences, Semax is approved in Russia and Ukraine as a nootropic and neuroprotective medication.

Unlike ACTH, Semax has no steroidogenic or hormonal activity — it exclusively activates the neurotrophic and neuroprotective pathways associated with the ACTH(4-7) fragment. Research demonstrates robust BDNF and NGF upregulation, making it one of the most potent peptide-based neurotrophic enhancers studied.

BDNF/NGF Upregulation: Semax increases BDNF (Brain-Derived Neurotrophic Factor) and NGF (Nerve Growth Factor) expression in the hippocampus and cortex. BDNF promotes neuroplasticity, synaptogenesis, and long-term potentiation (LTP) — the cellular basis of memory formation.

TrkB Receptor Activation: Through BDNF upregulation, Semax indirectly activates TrkB receptors, triggering PI3K/Akt and MAPK/ERK survival and growth pathways in neurons.

Dopamine/Serotonin Modulation: Semax influences catecholamine metabolism, increasing dopamine and serotonin turnover in the prefrontal cortex and striatum, supporting attention, motivation, and mood.

Neuroprotection: Semax reduces oxidative stress in neural tissue by upregulating endogenous antioxidant enzymes and inhibiting lipid peroxidation in ischemic models.

Reconstitution vehicles: Semax dissolves readily in aqueous buffers due to its hydrophilic character (calculated logP ≈ -2.1). Suitable vehicles for in vitro research include bacteriostatic water (0.9% benzyl alcohol), preservative-free 0.9% sodium chloride, phosphate-buffered saline (pH 7.2-7.4), or sterile water for injection. For cell-culture experiments, dissolve in serum-free medium or HBSS immediately before addition to avoid extracellular degradation. Semax is freely soluble at concentrations exceeding 10 mg/mL, so dilution rather than solubility is the practical concern.

Standard preparation (5 mg vial):

• Add 1.0 mL diluent → 5 mg/mL (0.5% solution) — common stock for in vitro studies.
• Add 0.5 mL diluent → 10 mg/mL (1.0% solution) — corresponds to the concentration used in much of the Russian intranasal literature.
• Add 5.0 mL diluent → 1 mg/mL (0.1% solution) — corresponds to the lower-concentration formulation also extensively studied.

Reconstitution technique:

• Allow lyophilized vial and diluent to equilibrate to room temperature in a desiccator (prevents condensation on the cold peptide cake).
• Inject diluent down the inner wall of the vial rather than directly onto the powder — this minimizes foaming and shear stress.
• Swirl gently for 30-60 seconds; do not vortex vigorously, as cavitation introduces O₂ and accelerates Met-1 oxidation.
• Allow to stand 2-5 minutes to ensure complete dissolution; the solution should be clear and colorless.
• Where feasible, perform reconstitution under inert atmosphere (argon-purged glove bag or septum vial with N₂ overlay).

Methionine handling considerations: The N-terminal Met residue is the dominant chemical-stability liability. Practical mitigations during reconstitution:

• Use freshly opened, oxygen-low diluent. Bacteriostatic water that has been repeatedly accessed accumulates dissolved O₂.
• Consider degassing diluent by brief sonication under vacuum or by bubbling argon for 5 minutes prior to use.
• Avoid metal needles in contact with concentrated stock when possible; trace Fe/Cu from stainless steel can catalyze oxidation. Polypropylene tips are preferred for serial dilutions.
• For long working sessions, keep the reconstituted vial on ice and shielded from light.

Intranasal formulation context (preclinical / Russian literature): Much of the published Semax pharmacology is based on 0.1% and 1% intranasal solutions delivered to rodents at 50-250 μg/kg. These concentrations are referenced here only to contextualize literature dosing for in vitro and animal study design; they are not human-use instructions. For murine intranasal administration in research, 5-10 μL per nostril of 0.1% solution is a commonly cited paradigm.

Aliquoting and working stocks: Prepare single-use aliquots (10-100 μL) in low-protein-binding polypropylene tubes, snap-freeze on dry ice, and store at -20°C or -80°C. Avoid more than 2-3 freeze-thaw cycles. Working dilutions in cell culture media should be prepared fresh on the day of use.

Sterility: For cell-culture or in vivo animal studies, filter reconstituted stock through a 0.22 μm low-protein-binding PVDF or PES filter. Pre-wet the filter with vehicle and discard the first 50 μL to minimize peptide adsorption losses.

Lyophilized powder: Store at -20°C in sealed, desiccated containers for up to 24 months from date of manufacture. For long-term archival storage (>24 months), -80°C is preferred, though repeated thermal cycling between -80°C and ambient should be avoided. Lyophilized Semax (Met-Glu-His-Phe-Pro-Gly-Pro, MW 813.9 Da) is reasonably stable in the solid state due to restricted molecular mobility, but the N-terminal methionine residue remains the principal site of chemical degradation.

Reconstituted solution: Once dissolved in aqueous vehicle, store at 2-8°C and use within 10-14 days for routine research applications. For quantitative pharmacological studies requiring strict potency, aliquot and use within 7 days, as gradual oxidation of Met-1 to methionine sulfoxide can alter receptor binding kinetics and pharmacodynamics. Avoid repeated freeze-thaw of reconstituted solution; single-use aliquots stored at -20°C are preferred when extended storage is required.

Methionine oxidation — the central stability concern: The N-terminal methionine sulfur is highly susceptible to oxidation by dissolved O₂, peroxides, trace transition metals (Fe³⁺, Cu²⁺), and UV light. Oxidation produces methionine sulfoxide (Met(O)) and, under harsher conditions, methionine sulfone. Met(O)-Semax exhibits significantly reduced affinity for melanocortin receptors and altered BDNF-modulating activity, so even partial oxidation can confound experimental results.

Recommended protective measures:

• Light protection: Store in amber glass vials or wrap clear vials in foil. Avoid prolonged bench-top exposure under fluorescent lighting.
• Oxygen exclusion: Purge headspace with argon or high-purity nitrogen before sealing. Argon is preferred (denser than air, displaces O₂ more effectively).
• Desiccation: Include molecular sieve or silica desiccant in the storage container. Moisture accelerates both oxidation and peptide-bond hydrolysis.
• Antioxidant additives (research-only): Some investigators include 0.01% L-methionine or 1 mM ascorbate as a sacrificial antioxidant in reconstitution buffers; document and report any additives.
• Temperature control: Allow vials to equilibrate to room temperature in a desiccator before opening to prevent moisture condensation on cold surfaces.

Solution-phase stability data: Aqueous Semax at neutral pH (7.0-7.4) and 4°C retains >90% intact peptide by HPLC for approximately 10-14 days under inert atmosphere; at 25°C, measurable Met oxidation can occur within 48-72 hours. Acidic pH (3-5) slows oxidation but may promote slow Asp/Glu-mediated cleavage over weeks. Phosphate-buffered saline is acceptable; avoid Tris buffers containing trace metal contaminants unless EDTA (0.1 mM) is added.

Stability indicators: Visible cues of degradation include solution discoloration (yellowing), particulate formation, or odor. Analytical confirmation should rely on RP-HPLC (monitoring for the characteristic Met(O) shoulder peak eluting ~1 min earlier than parent), mass spectrometry (+16 Da adduct indicating sulfoxide), or amino acid analysis. Periodic QC of reference lots is recommended for laboratories maintaining long-term Semax stocks.

Shipping considerations: Lyophilized Semax tolerates ambient shipping for 5-7 days without significant degradation, but cold-chain shipping with gel packs is recommended for international transit or summer-month deliveries.