PwPepwise

Dihexa

Brain & Focus

a.k.a. PNB-0408

Angiotensin IV analog

Dihexa (also called PNB-0408) is a small, orally active peptide derived from angiotensin IV.

§Dosing at a glance

2 protocols · from the research
What it's forDoseHow oftenHowFor how long
Peripheral nerve repair (rat, combination therapy)2–4 mg/kg—IntravenousInjected directly into a vein.—
General note2–4 mg/kg—IntramuscularInjected into a muscle.—

Approximate values pulled from the research — double-check before dosing.

§01Summary

Dihexa (also called PNB-0408) is a small, orally active peptide derived from angiotensin IV, a fragment of the body's blood pressure–regulating hormone angiotensin. Rather than acting on blood pressure, Dihexa works by binding to and amplifying the activity of hepatocyte growth factor (HGF), a naturally occurring protein that supports brain cell survival, communication, and repair. By potentiating HGF signaling through its receptor c-Met, Dihexa appears to promote the formation of new synaptic connections between neurons — the physical structures underlying learning and memory3.

In animal studies, Dihexa has been reported to improve spatial learning and memory in models of Alzheimer's disease, partially restore brain communication networks following mild traumatic brain injury, and support nerve repair when combined with stem cell therapies3,4,6,8. Preliminary evidence also suggests it may protect sensory hair cells in the inner ear from antibiotic-induced damage1. Notably, one animal study found no benefit in a Huntington's disease model, suggesting its effects may be specific to certain disease contexts5. Dihexa is of particular interest because it appears to be orally bioavailable and capable of crossing the blood-brain barrier — properties that are rare and clinically valuable for brain-targeting therapeutics3,4. Human efficacy and safety data are actively emerging.

This is the layperson summary. Mechanism, dosing, the evidence base, and the published literature are in the sections below — every claim links to its source.

§02In depth

Dihexa (N-hexanoic-Tyr-Ile-(6)-aminohexanoic amide; also designated PNB-0408) is a metabolically stabilized, low-molecular-weight peptidomimetic derived from angiotensin IV (AngIV), itself a hexapeptide fragment of angiotensin II generated through sequential aminopeptidase cleavage. Unlike AngIV, Dihexa incorporates non-natural amino acid substitutions that confer resistance to proteolytic degradation and, critically, oral bioavailability with confirmed blood-brain barrier penetration — pharmacokinetic properties that distinguish it from its parent peptide3,4.

Dihexa's primary mechanism of action involves high-affinity binding to hepatocyte growth factor (HGF), functioning as an allosteric potentiator rather than a direct receptor agonist. By dimerizing with endogenous HGF at subthreshold concentrations, Dihexa amplifies HGF's activation of its cognate receptor, the receptor tyrosine kinase c-Met (also known as MET or HGFR)3. This potentiation mechanism means Dihexa's activity is inherently dependent on the presence of endogenous HGF, a feature with important pharmacological implications for conditions characterized by HGF insufficiency. The HGF/c-Met system plays established roles in neuronal survival, axonal guidance, synaptogenesis, and neuroprotection throughout the central and peripheral nervous systems.

Downstream of c-Met activation, Dihexa engages multiple intracellular signaling cascades. In hippocampal neurons, HGF/c-Met activation by Dihexa drives spinogenesis and synaptogenesis — the physical elaboration of dendritic spines and formation of new synapses — as confirmed by knockdown of c-Met via shRNA and pharmacological blockade with HGF antagonists3. In Alzheimer's disease mouse models, the relevant downstream effector axis is PI3K/AKT, with Dihexa-induced anti-apoptotic and anti-neuroinflammatory effects abolished by the PI3K inhibitor wortmannin4. In the zebrafish lateral line hair cell model, protection from aminoglycoside ototoxicity is mediated intracellularly through parallel activation of Akt, mTOR (TOR), and MEK — confirming multi-effector involvement downstream of HGF signaling1. Notably, Dihexa's otoprotective mechanism does not involve reducing aminoglycoside uptake into hair cells, indicating that the protective action occurs at the level of intracellular survival signaling rather than drug exclusion1.

Structural integrity is essential for activity: modification of Dihexa's N-terminus with an amino group markedly attenuates its protective effects, demonstrating that the precise molecular architecture required for HGF dimerization is sensitive to chemical modification1. Brain AngIV levels are also modulated by Dihexa administration, suggesting possible interaction with the broader renin-angiotensin system within the CNS4. The compound's oral bioavailability, BBB permeability, and capacity to potentiate rather than saturate an endogenous growth factor signaling axis collectively define its pharmacological profile as an indirect neurotrophic amplifier.

§04Evidence & efficacy

Evidence base
34Studies
7Human
4Animal

Dihexa's most consistently supported preclinical effect is the promotion of hippocampal synaptogenesis and improvement of spatial learning and memory. In rodent Alzheimer's disease models (APP/PS1 mice), Dihexa has been reported to restore cognitive function in the Morris water maze, increase neuronal survival, increase synaptic protein expression, and reduce neuroinflammatory markers including IL-1β and TNF-α while elevating anti-inflammatory IL-104. These effects appear to be mediated through PI3K/AKT signaling downstream of HGF/c-Met activation, as reversal with the PI3K inhibitor wortmannin confirmed pathway dependency4.

The procognitive and synaptogenic effects of Dihexa have been independently linked to HGF/c-Met signaling in a separate mechanistic study, where orally administered Dihexa's effects in the Morris water maze were blocked by intracerebroventricular HGF antagonist administration3. In a peripheral nerve repair model, Dihexa combined with MSCs may improve motor function recovery compared to vehicle, though G-CSF outperformed Dihexa on this endpoint in one conference-reported study6,9. Preliminary electrophysiological data suggests Dihexa may partially restore interhemispheric brain connectivity following repeated mild traumatic brain injury8.

In inner ear models, Dihexa at 1 μM appeared to protect sensory hair cells from aminoglycoside toxicity via intracellular HGF signaling, with protection attenuated by co-administration of pathway inhibitors targeting Akt, TOR, and MEK1.

Importantly, Dihexa demonstrated no measurable benefit in a rat model of Huntington's disease induced by 3-nitropropionic acid, across behavioral, cognitive, and histopathological measures5, suggesting its efficacy may be model- or disease-context-specific.

§05Safety

Across all available preclinical studies, Dihexa has been administered orally, intravenously, intraperitoneally, intramuscularly, and topically without reported treatment-related adverse events1,3,4,5,6,9. In the peripheral nerve repair models, muscle atrophy (~30%) and limb flexion contractures (~60% in transplant animals) were observed but were attributed to disuse and suboptimal reinnervation rather than Dihexa toxicity9. No hematological, hepatic, renal, or systemic toxicity signals were reported in any available study.

Structural specificity appears important for activity: addition of an amino group to Dihexa's N-terminus significantly attenuated its protective effects, indicating that off-target structural variants may lose efficacy without a clear toxicity signal1. No drug interactions have been formally characterized, and no contraindications have been reported in the available literature.

Human pharmacokinetic and safety data are actively being developed, representing the primary area where the evidence base is still maturing.

§06History

Dihexa emerged from decades of research into the central nervous system effects of angiotensin peptides conducted primarily at Washington State University by John Harding, Joseph Wright, and colleagues. Initial observations in the 1980s and 1990s established that AngIV and related fragments had unexpected cognitive-enhancing effects independent of classical angiotensin receptor signaling, prompting systematic investigation into their mechanism and medicinal chemistry optimization.

The peptide's identity as an HGF/c-Met system modulator was a landmark finding reported in 2014, when Benoist and colleagues demonstrated that Dihexa and its parent compound Nle1-AngIV bind HGF with high affinity and potentiate c-Met phosphorylation — establishing the validated molecular target after years of mechanism-unknown research3. This same work confirmed oral activity and blood-brain barrier penetrance, which were critical translational milestones.

Earlier foundational work evaluating metabolically stabilized AngIV analogs for procognitive and antidementia properties established Dihexa's superiority over its predecessors in terms of stability and potency14. By 2021, independent research groups were publishing on Dihexa's efficacy in Alzheimer's transgenic mouse models and exploring PI3K/AKT as its mechanistic axis in neurodegeneration4. Peripheral applications, including nerve repair in combination with stem cell therapies, were explored in surgical and transplantation contexts beginning around the same period6.

As of 2024–2025, Dihexa has been studied across indications including Alzheimer's disease, Parkinson's disease, traumatic brain injury, ototoxicity, and peripheral nerve regeneration, with a negative result reported in a Huntington's disease model5. The compound remains in active preclinical and early translational investigation, with human clinical data still emerging.

§07References