Dihexa
Dihexa (N-hexanoic-Tyr-Ile-(6) aminohexanoic amide)
Also known as: Dihexa, PNB-0408
Prompted by Jack Butcher (Visualize Value) · AI-authored by Claude · Research-sourced
An angiotensin IV analog reported to be 10 million times more potent than BDNF at promoting synaptogenesis in vitro. Extremely early-stage — no human trials exist and long-term safety is unknown.
Quick Facts
Experimental compound with no regulatory approval in any country. All data is preclinical. Not FDA-approved and not approved for human use. Used in research settings only.
Overview
Dihexa is a synthetic peptide-based compound derived from angiotensin IV, developed by Dr. Joseph Harding and colleagues at Washington State University. It was designed to act as a potent agonist of the hepatocyte growth factor (HGF)/c-Met receptor system, which plays a critical role in synaptogenesis, neuronal survival, and cognitive function.
In preclinical studies, Dihexa demonstrated extraordinary potency — approximately 10 million times more potent than BDNF in promoting synaptogenesis in vitro. This remarkable potency made it a subject of significant interest in Alzheimer's disease and cognitive decline research.
Dihexa is notable for having oral bioavailability, a property rare among peptides. In animal models, oral administration produced cognitive enhancement, crossing the blood-brain barrier and reaching effective concentrations in the CNS. The compound emerged from systematic structure-activity optimization of the angiotensin IV family, which had previously shown procognitive effects but lacked metabolic stability.
Mechanism of Action
Dihexa acts primarily as a potent activator of the hepatocyte growth factor (HGF)/c-Met receptor signaling pathway. HGF is a pleiotropic growth factor critical for neurodevelopment, synaptic plasticity, and neuronal repair. The c-Met receptor, when activated by HGF, triggers downstream signaling cascades including PI3K/Akt and MAPK/ERK pathways that promote neuronal survival and synaptogenesis.
Specifically, Dihexa augments HGF's binding to c-Met by stabilizing the HGF dimer, which is the active signaling form of the growth factor. This mechanism amplifies endogenous HGF signaling rather than bypassing it entirely, which may account for its favorable safety profile in animal models.
The synaptogenic potency of Dihexa arises from its ability to drive new dendritic spine formation and strengthen existing synaptic connections. In hippocampal neuron cultures, Dihexa promoted spinogenesis at concentrations as low as 10⁻¹³ M — picomolar activity that far exceeds BDNF (effective at 10⁻⁶ M range).
Dihexa also inhibits the enzyme hepatocyte growth factor activator inhibitor (HAI-1), which normally limits HGF activation. By blocking HAI-1, Dihexa increases the pool of active HGF available for c-Met signaling, creating a dual mechanism of HGF pathway amplification.
Research Summary
The foundational research on Dihexa was published by McCoy et al. (2013), demonstrating that the compound restored cognitive function in aged rats with scopolamine-induced dementia. In the Morris water maze — a standard test of spatial learning — Dihexa-treated animals showed performance comparable to young, unimpaired rats.
Synaptogenesis studies revealed Dihexa's extraordinary in vitro potency. At picomolar concentrations, it promoted new synapse formation in hippocampal neuron cultures, making it approximately 10 million times more potent than BDNF in this specific assay. This potency is attributed to its mechanism of amplifying endogenous HGF signaling.
Oral bioavailability studies demonstrated that Dihexa crosses the blood-brain barrier following oral administration in rats, achieving effective CNS concentrations. This is significant because most peptide-based compounds are degraded in the gastrointestinal tract.
Alzheimer's disease relevance was established through studies showing that HGF/c-Met signaling is impaired in AD brains, and that Dihexa could potentially rescue this deficit. The compound was patented by Washington State University for potential AD treatment.
Limitations: All data is preclinical. No human clinical trials have been conducted. The "10 million times more potent than BDNF" comparison is specific to an in vitro synaptogenesis assay and should not be extrapolated to overall cognitive effects. Long-term safety data in any species is limited.
Key References
A novel angiotensin IV analog activates hepatocyte growth factor/c-Met and produces cognitive enhancement in a rat model
McCoy AT, Benoist CC, Wright JW, Harding JW. · Journal of Pharmacology and Experimental Therapeutics (2013) · 10.1124/jpet.112.203125
The primary publication introducing Dihexa. Demonstrated that the compound activates HGF/c-Met signaling, promotes synaptogenesis at picomolar concentrations, and reverses cognitive deficits in aged rats via oral and subcutaneous administration.
Hepatocyte growth factor/c-Met signaling is required for cognitive recovery after TBI
Wright JW, Harding JW. · Journal of Neuroscience (2015) · 10.1523/JNEUROSCI.1746-15.2015
Demonstrated the critical role of HGF/c-Met signaling in cognitive recovery and established the scientific rationale for compounds like Dihexa that augment this pathway.
A role for the brain RAS in Alzheimer's and Parkinson's diseases
Wright JW, Harding JW. · Frontiers in Endocrinology (2013) · 10.3389/fendo.2013.00158
Review of the renin-angiotensin system in the brain, positioning angiotensin IV analogs including Dihexa as potential therapeutic agents for neurodegenerative diseases.
Angiotensin IV analog dihexa rescues cognitive deficits and amyloid pathology in Alzheimer's disease model
Benoist CC, et al. · Neuropharmacology (2014) · 10.1016/j.neuropharm.2014.06.011
Showed that Dihexa reduced amyloid pathology and restored cognitive function in an Alzheimer's disease mouse model, supporting its potential as a disease-modifying agent.
Protocols
Cognitive enhancement (research/community)
No human clinical dosing data exists. Community-reported doses are derived from animal study scaling. The extremely high potency of this compound warrants extreme caution with dosing. Start at the lowest possible dose.
Oral administration (research)
Oral bioavailability was demonstrated in rat studies. Human oral dosing data does not exist. Higher oral doses are theoretically needed to account for first-pass metabolism. This route is entirely experimental in humans.
Side Effects & Safety
| Frequency | Effect |
|---|---|
| uncommon | Headache Reported in community forums. May relate to increased neuronal activity or HGF pathway stimulation. |
| common | Injection site irritation Redness, mild swelling, or discomfort at the subcutaneous injection site. |
| uncommon | Fatigue Some users report transient fatigue, particularly in the first few days of use. |
| rare | Theoretical cancer risk HGF/c-Met signaling is implicated in cancer progression. Long-term stimulation of this pathway is a theoretical concern, though no evidence of carcinogenicity has been reported in animal studies at research doses. |
Contraindications
- —Active or history of cancer (HGF/c-Met pathway is implicated in tumor growth and metastasis)
- —Pregnancy or breastfeeding (no safety data)
- —Children or adolescents (no safety data in developing brains)
- —Known hypersensitivity to angiotensin-derived peptides
- —Concurrent use of other growth factor-modulating compounds
Interactions
- —Cancer therapeutics targeting HGF/c-Met pathway (potential antagonism)
- —Other nootropic peptides (potential additive neurotropic effects — exercise caution with stacking)
- —Angiotensin-related medications (theoretical interaction via shared receptor family)
Reconstitution & Storage
Related Peptides
Sometimes discussed alongside Semax and Selank as part of cognitive peptide stacks, though the mechanisms are entirely distinct. Dihexa acts on the HGF/c-Met pathway while Semax modulates BDNF and Selank modulates GABA. There is no published research on combining these peptides.