— Research note —
Dihexa
Orally bioavailable angiotensin IV analog investigated as a small-molecule hepatocyte growth factor mimetic in preclinical neuroscience research.
Dihexa (N-hexanoyl-Tyr-Ile-(6) aminohexanoic amide) is a small-molecule oligopeptide derivative developed by the Harding and Wright laboratories at Washington State University in the early 2010s. The compound was designed within a structure-activity exploration of the angiotensin IV (Ang IV) hexapeptide, which had been characterized in earlier research as engaging an insulin-regulated aminopeptidase (IRAP) and producing cognitive effects in rodent models. Dihexa retains key pharmacophoric features of Ang IV while incorporating modifications that confer oral bioavailability, blood-brain barrier penetration, and substantially enhanced potency.
The molecule has been characterized in research models as a potent facilitator of hepatocyte growth factor (HGF)/c-Met receptor signaling, with effects on synaptogenesis and synaptic plasticity reported in hippocampal preparations. In behavioral studies in aged rats and rodent models of cognitive impairment, dihexa administration has been associated with improvements in spatial learning and memory endpoints, attributed mechanistically to enhanced synaptogenesis in the hippocampus.
The compound has attracted interest as a research tool because its potency in synaptogenesis assays (active at picomolar concentrations in some preparations) and its oral activity distinguish it from earlier Ang IV analogs and from many neurotrophic factors that require parenteral administration. Dihexa serves as a probe for studies of HGF/c-Met signaling in the central nervous system and as a reference compound for academic investigations of synaptogenesis-promoting molecules.
Dihexa is supplied here for laboratory research use only and is not intended for human consumption. Its primary research applications include cognitive pharmacology in aged rodent models, characterization of HGF/c-Met signaling in neurons, and structure-activity studies of angiotensin-derived neuropeptide analogs.
Mechanism
Dihexa has been characterized as a small-molecule facilitator of hepatocyte growth factor (HGF) binding to its receptor c-Met. The proposed mechanism involves the compound forming a complex with HGF that enhances its affinity for c-Met, effectively functioning as a positive allosteric modulator of HGF/c-Met interactions. Engagement of c-Met activates downstream tyrosine kinase signaling, including ERK and PI3K/Akt pathways implicated in neuronal survival and synaptic plasticity.
In hippocampal preparations, dihexa has been reported to increase dendritic spine density and to enhance synaptogenesis at concentrations in the picomolar to nanomolar range. These effects have been associated with improved synaptic transmission in electrophysiological recordings. Behavioral effects in aged rodents include preservation of spatial learning in Morris water maze paradigms, with mechanistic attribution to the synaptogenic effects in hippocampal circuits. The molecule retains aspects of Ang IV pharmacology, including binding to IRAP, though the relevance of IRAP engagement to the cognitive effects observed remains an area of continued investigation.
Research history
The Harding and Wright laboratories at Washington State University investigated angiotensin IV-derived compounds in the 1990s and 2000s, building on earlier characterization of Ang IV as a cognitive enhancer in rodent models. The identification of IRAP as the Ang IV binding site by Albiston, Chai, and colleagues provided a molecular target hypothesis that informed subsequent medicinal chemistry programs.
Dihexa was disclosed in publications from 2012 onward as an optimized small-molecule analog with oral bioavailability and brain penetration. The compound's potent synaptogenic effects in hippocampal preparations and behavioral effects in aged rodents were reported in subsequent publications. The proposed mechanism involving HGF/c-Met positive allosteric modulation emerged from biochemical studies of HGF binding in the presence of the compound.
Subsequent research has examined dihexa in models of Alzheimer's disease, Parkinson's disease, and traumatic brain injury, with publications continuing to appear from the Harding/Wright group and independent laboratories. The compound has not advanced to formal clinical research but continues to serve as a reference probe for academic investigations of cognitive pharmacology, HGF/c-Met signaling, and synaptogenesis-promoting molecules.
References
- McCoy AT, et al. 2013. Evaluation of metabolically stabilized angiotensin IV analogs as procognitive/antidementia agents. J Pharmacol Exp Ther. PMID: 23197776
- Benoist CC, et al. 2014. The procognitive and synaptogenic effects of angiotensin IV-derived peptides are dependent on activation of the hepatocyte growth factor/c-Met system. J Pharmacol Exp Ther. PMID: 24403517
- Wright JW, Harding JW. 2015. The brain hepatocyte growth factor/c-Met receptor system: a new target for the treatment of Alzheimer's disease. J Alzheimers Dis. PMID: 25812853
- Albiston AL, et al. 2001. Evidence that the angiotensin IV (AT(4)) receptor is the enzyme insulin-regulated aminopeptidase. J Biol Chem. PMID: 11335713
- Wright JW, Harding JW. 2013. The brain RAS and Alzheimer's disease. Exp Neurol. PMID: 23159991
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Information presented in third-person scientific context. Research use only. Not medical advice; not for human consumption.