Dihexa (N-hexanoic-Tyr-Ile-(6) aminohexanoic amide) is a synthetic peptide analogue developed at Washington State University (formerly the McCoy lab, now at Oregon Health & Science University). It was designed as a potent, orally bioavailable agonist of the HGF/c-Met signaling system — a pathway that plays a critical role in synaptic formation and cognitive function.
Origins and Design
Dihexa was derived from angiotensin IV (Ang IV) and its parent compound Norleucine-1-Ang IV, through a series of structure-activity relationship studies aimed at identifying the minimum active sequence with maximum CNS penetration and oral bioavailability.
The hexanoic acid modification dramatically improves lipophilicity, enabling oral administration — a critical advantage over most peptides that require parenteral routes. This was intentional: the goal was a CNS-active peptide that could be studied orally in aging and neurodegeneration models.
Mechanism: HGF/c-Met Axis
Dihexa's primary target is the hepatocyte growth factor (HGF) / c-Met receptor system. While named for its liver biology, HGF/c-Met signaling is highly active in the brain, particularly in the hippocampus.
HGF/c-Met and synaptic plasticity:
- c-Met activation drives dendritic spine formation and stabilization
- It promotes synaptogenesis — the formation of new synaptic connections
- It upregulates NMDA receptor trafficking to the synapse
- It enhances LTP (long-term potentiation) — the cellular correlate of memory formation
Dihexa has been described as a "super potent" HGF/c-Met agonist with affinity reportedly ~1 million times greater than HGF itself for promoting synaptogenesis in hippocampal cultures.
Cognitive Research Findings
The original Dihexa publications (Wright et al.) used the Morris Water Maze and passive avoidance paradigms in aged rat models:
- Aged rats treated with Dihexa performed comparably to young rats in spatial memory tasks
- Improvements were observed in both acquisition (learning) and retention (recall)
- Hippocampal synaptophysin levels (a marker of synaptic density) were significantly elevated in treated animals
- Effects persisted beyond the treatment period in some protocols, suggesting structural rather than purely functional changes
These findings positioned Dihexa as a candidate for Alzheimer's disease and age-related cognitive decline research.
Oral Bioavailability: A Key Advantage
Dihexa's oral bioavailability is a major research advantage. Most peptides are degraded in the GI tract and require injection. Dihexa's modified structure allows it to survive digestion and cross the blood-brain barrier.
This makes it uniquely accessible for chronic dosing protocols and for research contexts where injection is not feasible. Studies have administered it via drinking water, gavage, and subcutaneous injection — all with demonstrable CNS effects.
Current Research Landscape
Dihexa remains a primarily preclinical compound. No human clinical trials have been completed. Its extraordinary potency in animal models has generated significant interest, but also appropriate caution — the consequences of potent synaptogenesis at non-optimal brain regions or developmental stages are not fully characterized.
Current research directions include: Alzheimer's disease models, traumatic brain injury, post-stroke cognitive recovery, and the basic biology of HGF/c-Met in adult neuroplasticity.
Published References
Research Use Only. All content is for informational and educational purposes regarding preclinical research. None of the compounds discussed have been approved by the FDA for human therapeutic use. This information does not constitute medical advice.