Semax vs Selank: Two Russian Heptapeptides, Two Different Research Questions

Semax (Met-Glu-His-Phe-Pro-Gly-Pro) derives from the ACTH(4-10) fragment and is studied for neurotrophin (BDNF) expression, stress and attention-related endpoints. Selank (Thr-Lys-Pro-Arg-Pro-Gly-Pro) derives from the immunopeptide tuftsin and is studied for anxiolytic-type behaviour and stress adaptation. Both were developed at the Institute of Molecular Genetics in Moscow and both carry a Pro-Gly-Pro tail for enzymatic stability.

Shared design, different parents

Both peptides come from the same Moscow research lineage and use the same trick: take a short biologically active fragment and add Pro-Gly-Pro at the C-terminus to slow enzymatic breakdown. That is where the similarity ends.

Semax starts from ACTH(4-10) — residues 4 to 10 of adrenocorticotropic hormone, a fragment long known to have central-nervous-system activity without ACTH's hormonal effect. Its sequence is Met-Glu-His-Phe-Pro-Gly-Pro (813.9 g/mol).

Selank starts from tuftsin — Thr-Lys-Pro-Arg, a tetrapeptide fragment of immunoglobulin G with immune-signalling activity. Its sequence is Thr-Lys-Pro-Arg-Pro-Gly-Pro (751.9 g/mol).

Mechanisms studied

Semax research centres on neurotrophins. A 2007 *Neuroscience Letters* study reported altered BDNF and related gene expression in rat brain [1]; later work compared nootropic agents' effects on hippocampal and cortical BDNF [2], examined antidepressant-like and antistress effects alongside other ACTH(4-10) analogs [3], and looked at intracellular calcium dynamics [4].

Selank research centres on anxiolytic-type behaviour. A 2018 review collects the molecular work [5]; foundational studies placed it among tuftsin-family peptides regulating adaptive behaviour under stress [6]; and a 2014 rat study examined it in a modelled withdrawal setting [7].

Research models compared

• Neurotrophin / gene expression: Semax [1][2]
• Anxiolytic-type behavioural assays: Selank [5][6]
• Stress models: both, from different angles — Semax for antistress and early-life-stress endpoints [3], Selank for stress adaptation [6]
• Withdrawal models: Selank [7]

Specifications side by side

• Parent: ACTH(4-10) · tuftsin
• Sequence: MEHFPGP · TKPRPGP
• Molecular weight: 813.9 g/mol · 751.9 g/mol
• Format: Semax 30 mg vial, $55 · Selank 10 mg vial, $50
• Testing: independent HPLC/MS, batch COA, both

Rodent and cell research only. Neither compound is approved by the FDA; APX Labs products are for research use only and nothing here is a claim of effect.

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