Selank, Semax, TB-4 and Dihexa in Neurocognitive Research
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Introduction
Cognition represents a multidimensional construct encompassing episodic memory, working memory, executive functioning and inhibitory control, spatial learning, language comprehension, processing speed, and reading fluency. Central to these processes is synaptic plasticity—the capacity of neuronal networks to modify in response to novel input. These modifications may be transient, lasting milliseconds to hours, or more persistent, extending over months to years. Transient mechanisms include facilitation, augmentation, and potentiation, each enhancing neurotransmitter release and supporting short-term learning and adaptation.
Cognitive decline is strongly associated with aging, systemic illnesses (e.g., diabetes, hypertension, dyslipidemia, obesity), neurotoxic exposures (alcohol, smoking), and reduced physical activity. Structural markers of decline include reductions in cortical thickness and subcortical volume, estimated at 0.5–1% annually, alongside progressive axonal degeneration and plaque accumulation. Epidemiological data suggest that mild cognitive impairment occurs in 21.5–71.3 cases per 1,000 person-years, with progression to dementia when impairments disrupt daily functioning. Currently, approximately 50 million individuals worldwide live with dementia, and prevalence is projected to triple by 2050. This escalating burden underscores the urgent need for novel therapeutic approaches.
Peptides such as Selank, Semax, Thymosin Beta-4, and Dihexa have emerged as candidates with potential to support neurocognitive function through diverse mechanisms.
Selank
Clinical Overview
Selank, a heptapeptide analog with structural similarity to melanocortins, exhibits anxiolytic, antidepressant, and neurotropic activity. Its therapeutic role has been most studied in the context of anxiety and stress-related disorders.
Mechanism of Action
Selank modulates neurotransmission via melanocortin-like pathways, producing anxiolytic and nootropic effects.
Semax
Clinical Overview
Semax, derived from the adrenocorticotropic hormone fragment ACTH(4–10), is a neuroactive peptide.
Mechanism of Action
Semax enhances neuroplasticity via modulation of the brain-derived neurotrophic factor (BDNF)/trkB signaling axis, promoting neuronal survival, synaptogenesis, and cognitive performance.
Research Evidence
In animal studies, intranasal administration of Semax (50 μg/kg) produced significant increases in hippocampal BDNF protein expression (1.4-fold) and trkB phosphorylation (1.6-fold), with associated elevations in BDNF and trkB mRNA levels. Behavioral testing revealed enhanced learning, as evidenced by increased conditioned avoidance responses. These findings position Semax as a potential neuroprotective and cognition-enhancing agent.
Combined Use of Selank and Semax
The combination of Selank and Semax has been investigated for synergistic effects on learning capacity, exploratory behavior, neuroregeneration, and neuromuscular performance.
Thymosin Beta-4
Clinical Overview
Thymosin Beta-4 (Tβ4) is a naturally occurring peptide secreted by the thymus and distributed in skeletal and smooth muscle tissue. It is upregulated following tissue injury and plays a key role in repair and regeneration.
Mechanism of Action
Tβ4 functions as a G-actin-sequestering molecule, regulating cytoskeletal remodeling, angiogenesis, cell migration, and anti-inflammatory processes. It has been evaluated in contexts ranging from cardiovascular repair to musculoskeletal injury recovery.
Research Evidence
In experimental traumatic brain injury models, Tβ4 administration promoted angiogenesis, neurogenesis, oligodendrogenesis, and axonal remodeling. These restorative processes translated into improved functional outcomes, supporting its potential as a neuroprotective intervention in central nervous system trauma.
Dihexa
Clinical Overview
Dihexa is a small peptide analog derived from Angiotensin IV, developed to cross the blood-brain barrier and exert potent synaptogenic activity.
Mechanism of Action
Dihexa binds with high affinity to hepatocyte growth factor (HGF), potentiating c-Met receptor activation. This interaction facilitates synaptogenesis and enhances neuronal connectivity.
Research Evidence
Preclinical studies demonstrated that Dihexa enhances hippocampal spinogenesis and synaptogenesis in a manner comparable to HGF itself. Cognitive improvements, including enhanced spatial learning in the Morris water maze, were abolished when HGF signaling was antagonized, confirming the dependency of Dihexa’s procognitive effects on the HGF/c-Met pathway.
Conclusion
Selank, Semax, Thymosin Beta-4, and Dihexa are studied in models of cognitive function and neurodegeneration. Each demonstrates distinct mechanisms—ranging from modulation of neurotrophic signaling to synaptogenesis and tissue repair. Preclinical and early clinical work remains at an exploratory stage.
REFERENCES
- Benoist, C. C., Kawas, L. H., Zhu, M., Tyson, K. A., Stillmaker, L., Appleyard, S. M., Wright, J. W., Wayman, G. A., & Harding, J. W. (2014). The procognitive and synaptogenic effects of angiotensin IV-derived peptides are dependent on activation of the hepatocyte growth factor/c-met system. The Journal of pharmacology and experimental therapeutics, 351(2), 390–402. https://doi.org/10.1124/jpet.114.218735 (Retraction published J Pharmacol Exp Ther. 2025 Apr;392(4):103567. doi: 10.1016/j.jpet.2025.103567.)
- P-1114 – Rapid and slow response during treatment of generalized anxiety disorder with peptide anxiolytic selank
- Semax, an analog of ACTH(4–10) with cognitive effects, regulates BDNF and trkB expression in the rat hippocampus
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