Semax (10 mg)

BDNF/TrkB and Neurotrophin Signaling

Neurotrophic Factor Upregulation — Tritium-labeled Semax binds specifically to neuronal tissue membranes with a dissociation constant (K_D) of 2.4 nM; calcium ions are required for binding activity (Dolotov et al., 2006). A single 50 μg/kg intranasal dose produces 1.4-fold BDNF protein increase, 3-fold exon III BDNF mRNA increase, and 2-fold trkB mRNA increase in rat hippocampus, accompanied by 1.6-fold TrkB tyrosine phosphorylation. In rat glial cell cultures, Semax induces 8-fold BDNF mRNA and 5-fold NGF mRNA within 30 minutes. The neurotrophin response is region-specific and time-dependent: expression initially decreases in hippocampus and retina at 20 minutes but increases in frontal cortex, with significant retinal BDNF elevation at 90 minutes.

Monoaminergic Neurotransmitter Modulation

Serotonergic and Dopaminergic System Activation — Semax rapidly activates monoaminergic systems in rodent models. Striatal 5-HIAA content increases ~25% within 2 hours; extracellular 5-HIAA rises to ~180% at 1–4 hours post-administration, indicating robust serotonergic activation (Eremin et al., 2005). Semax amplifies D-amphetamine-evoked dopamine release and locomotor activity when co-administered but does not alter basal dopamine or metabolite concentrations alone, indicating modulatory rather than direct dopaminergic action.

Melanocortin Receptor Interactions (MC4R/MC5R)

Competitive Antagonism at Melanocortin Receptors — Semax interacts with MC4R and MC5R, where it competitively antagonizes alpha-melanocyte-stimulating hormone (α-MSH). In HEK293 cells expressing human MC4R, Semax at 1 μM does not independently stimulate cAMP production but antagonizes α-MSH-induced cAMP accumulation. Despite acting at melanocortin receptors, Semax does not exhibit hormonal corticotropic activity characteristic of full-length ACTH.

Copper Chelation and Anti-Amyloid Activity

Cu²⁺ Sequestration and Aβ Fibrillation Inhibition — The Met-Glu-His N-terminal motif forms a high-affinity Cu²⁺ coordination site (conditional K_D = 1.3×10⁻¹⁵ M at pH 7.4). Semax prevents Aβ:Cu²⁺ complex formation, inhibits copper-induced amyloid-beta fibrillation concentration-dependently, extracts Cu(II) from Cu(II)-Aβ species by metal-ion stripping, and reduces ROS production through redox silencing of the Cu(II)/Cu(I) cycle. In membrane disruption assays, Semax reduced mature fibril interaction with phospholipid bilayers by up to 85%; SH-SY5Y neuronal cytoprotection against Aβ₁₋₄₂ oligomer toxicity reached ~90% (Sciacca et al., 2022; Tomasello et al., 2025).

Transcriptomic Neuroprotection in Ischemia

Inflammatory Gene Suppression and Neurotransmission Gene Activation — Filippenkov et al. (2020) identified 394 differentially expressed genes in Semax-treated ischemic rat brains at 24 hours post-ischemia-reperfusion. Semax suppressed inflammatory gene expression (Il1a, Il1b, Il6, Ccl3, Cxcl2) while activating neurotransmission-related genes, compensating for mRNA patterns disrupted during ischemia. Genome-wide RNA-Seq analysis (Medvedeva et al., 2014) showed immune response genes comprising over 50% of all affected transcripts at 24 hours, with immunoglobulin gene fold-changes exceeding 15-fold. At the protein level, Semax upregulated active CREB in subcortical structures while downregulating MMP-9, c-Fos, and active JNK in affected cortical tissue (Sudarkina et al., 2021).

Antistress Gene Expression Correction

Hippocampal Transcriptomic Restoration — In acute restraint stress models, Semax pretreatment produced over 1,500 differentially expressed genes in hippocampal tissue, correcting stress-induced transcriptomic disruptions (Filippenkov et al., 2021). In chronic unpredictable stress models, chronic Semax treatment reversed stress-induced anhedonia, body-weight gain suppression, adrenal hypertrophy, and hippocampal BDNF decreases (Inozemtseva et al., 2024).