Nootropic Peptides: Selank & Semax

Selank (Thr-Lys-Pro-Arg-Pro-Gly-Pro) is a heptapeptide — a synthetic analogue of tuftsin, a naturally occurring immunomodulatory tetrapeptide (Thr-Lys-Pro-Arg). The additional Pro-Gly-Pro sequence was added to improve metabolic stability.

Tuftsin itself is produced by the spleen and plays a role in innate immunity. Selank's design leverages this natural scaffold while adding CNS-active properties not present in the parent molecule.

BDNF Modulation: Selank has been shown to increase brain-derived neurotrophic factor (BDNF) expression and secretion in neuronal cultures and in vivo. BDNF is essential for synaptic plasticity, long-term potentiation, and neuronal survival — making this a highly relevant pathway for cognitive research.

Enkephalin System: Selank inhibits enkephalin-degrading enzymes, increasing the availability of endogenous enkephalins. These natural opioid peptides play a role in stress response, anxiety regulation, and pain modulation.

GABAergic Modulation: Unlike benzodiazepines, Selank appears to modulate GABA-A receptor sensitivity without direct agonism, producing anxiolytic effects without the sedation, tolerance, or dependence associated with classical GABAergic drugs.

T-helper Cytokine Balance: Selank normalizes the Th1/Th2 cytokine ratio, reducing excessive inflammatory signaling while preserving immune function.

Preclinical studies have documented: - Anxiolytic effects comparable to diazepam in elevated plus-maze models without sedation - Memory consolidation improvements in passive and active avoidance paradigms - Stress resilience improvements in chronic mild stress models - Normalized gene expression in the hippocampus following stress exposure

Russian clinical research (limited, non-FDA-reviewed) has examined Selank in generalized anxiety disorder with reportedly positive results and favorable tolerability.

Semax (Met-Glu-His-Phe-Pro-Gly-Pro) is derived from ACTH(4-7), the biologically active core sequence of adrenocorticotropic hormone. The Pro-Gly-Pro stabilizing sequence — the same addition as in Selank — extends its biological half-life.

Semax does not stimulate cortisol production (unlike full ACTH), as it lacks the sequences required for adrenal activation. It retains and amplifies the direct CNS effects of the ACTH fragment.

BDNF and Neurotrophin Upregulation: Semax produces robust increases in BDNF, NGF (nerve growth factor), and VEGF in rodent brain tissue. The magnitude of BDNF upregulation in some studies exceeds that seen with Selank.

Dopamine and Serotonin: Semax modulates monoamine neurotransmitter release and receptor sensitivity in prefrontal cortex and hippocampus — regions central to cognitive function and mood regulation.

Neuroprotection: In models of ischemic stroke and traumatic brain injury, Semax has demonstrated significant neuroprotection, reducing infarct size and improving behavioral recovery. It is actually approved in Russia for ischemic stroke as a medical nasal spray.

Cognitive Enhancement: Working memory, attention, and information processing improvements have been documented in rodent research models. Semax is of significant interest in research on age-related cognitive decline.