Semax is a
heptapeptide and
synthetic analogue of a fragment of
adrenocorticotropic hormone (ACTH), ACTH (4-10), of the following
amino acid sequence: Met-Glu-His-Phe-Pro-Gly-Pro ( in single-letter form). In animals, Semax rapidly elevates the levels and
expression of
brain-derived neurotrophic factor (BDNF) and its signaling receptor
tropomyosin receptor kinase B (TrkB) in the
hippocampus, and rapidly activates
serotonergic and
dopaminergic brain systems. Accordingly, it has been found to produce
antidepressant-like and
anxiolytic-like effects, attenuate the behavioral effects of exposure to
chronic stress, As such, it has been suggested that Semax may be effective in the treatment of
depression. Though the exact
mechanism of action of Semax is unclear, there is evidence that it may act through
melanocortin receptors. Specifically, there is a report of Semax
competitively antagonizing the action of
α-melanocyte-stimulating hormone (α-MSH) at the
MC4 and
MC5 receptors in both
in vitro and
in vivo experimental conditions, indicating that it may act as an
antagonist or
partial agonist of these receptors. (&alpha-MSH acts as a full agonist of all five melanocortin receptors). Semax did not antagonize α-MSH at the
MC3 receptor, though this receptor could still be a target of the drug. As a peptide, Semax has poor
oral bioavailability and hence is administered
parenterally as a
nasal spray or subcutaneous injection. ==See also==