Dihexa
Dihexa is a small, chemically modified peptide-like analogue of angiotensin IV developed as a metabolically stabilized research compound. It has been studied in rodent models of cognitive impairment and is not approved for any use.
Most published evidence on Dihexa comes from animal and cell studies. Findings in those models have not been established in people.
Overview
Dihexa is a synthetic, peptide-like molecule derived from angiotensin IV, a six-residue fragment of the renin-angiotensin system that earlier work had linked to learning and memory in animals. Researchers at Washington State University set out to make angiotensin IV analogues that would resist enzymatic breakdown and cross biological barriers more readily than the native fragment. Dihexa came out of that program as a shortened, end-capped structure that retains only part of the parent sequence and carries non-standard groups at both ends.
Published research on dihexa is limited and comes mainly from the originating group. Most studies use rodent models of induced memory deficits or aging, together with cell-culture work on neurons and synapse formation. There are no published controlled clinical trials of dihexa in people, and its safety in humans has not been characterized. The compound should therefore be regarded as a preclinical research tool, and reported effects as findings in animal and in-vitro systems whose relevance to people is unknown.
Structure
Dihexa is not a conventional linear peptide. It is usually described as N-hexanoic-Tyr-Ile-(6) aminohexanoic amide: a tyrosine-isoleucine dipeptide core taken from the angiotensin IV sequence (Val-Tyr-Ile-His-Pro-Phe), with a hexanoyl group capping the N-terminus and a 6-aminohexanoic acid amide replacing the C-terminal portion of the parent fragment. These modifications were intended to improve metabolic stability and lipophilicity. Because of the non-standard end groups, its mass cannot be derived from a standard amino-acid sequence alone, and identity should be checked against the specific structure.
Mechanism
The proposed mechanism centers on the hepatocyte growth factor (HGF) and c-Met receptor system rather than on classical angiotensin receptors. In cell and rodent studies, the originating group reported that dihexa binds HGF and enhances its ability to activate c-Met, and that blocking c-Met reduced effects on dendritic spine formation and on performance in memory tasks. This model is based on a small number of studies from one research network and has not been extensively replicated. The relationship of dihexa to other proposed angiotensin IV binding sites remains incompletely defined.
Research
Rodent cognition models
The main body of dihexa research uses rats with memory deficits induced by the muscarinic antagonist scopolamine, as well as aged animals, tested in spatial learning tasks such as the water maze. The originating group reported that treated animals performed better than controls in these tasks. These are small preclinical experiments, and the models capture only limited aspects of human cognitive disorders. Independent replication by other laboratories has been sparse, so the strength and generality of these findings remain uncertain.
Synaptogenesis in cell culture
In-vitro studies using cultured hippocampal neurons have examined dendritic spine density and markers of synapse formation after exposure to dihexa and related angiotensin IV analogues. Investigators reported increases in spine number and synaptic connectivity that depended on HGF and c-Met signaling. Such findings provide a mechanistic hypothesis but do not establish effects in intact animals or people. Cell-culture results also depend heavily on concentration and culture conditions, which limits direct comparison between studies.
HGF/c-Met and safety questions
Because the HGF/c-Met pathway is involved in cell growth, motility and tissue repair, and is also implicated in the biology of several cancers, researchers have noted that chronic potentiation of this pathway raises theoretical safety questions. These concerns have not been tested in long-term studies. The absence of published toxicology and human data means that the risk profile of dihexa is essentially unknown, an important caveat when interpreting the preclinical literature.
Evidence quality
Overall, the evidence for dihexa consists of a modest number of rodent and cell-culture studies, largely from one academic group, with no published randomized human trials. Characterization of research material outside the original laboratories is variable. Claims about cognitive effects in people are not supported by clinical data. The compound is best described as an experimental angiotensin IV analogue used to probe HGF/c-Met signaling in the nervous system.
Regulatory status
Dihexa is not approved by the FDA or, as far as is known, by any major regulator for any use, and it has not completed clinical development. It is not on the Section 503A bulk drug substances list, so its status for compounding should be regarded as unsupported; check current FDA guidance. Dihexa is not specifically named in the summary facts used here for anti-doping; check the current WADA Prohibited List, which also covers non-approved substances under class S0.
Status changes often. See the regulatory tracker for dated updates.
Quality and identity testing
A certificate of analysis should confirm identity by mass spectrometry against the expected mass of the full capped structure, not of an unmodified Tyr-Ile dipeptide, since the hexanoyl and aminohexanoic amide groups contribute substantially to the mass. Purity should be reported by reverse-phase HPLC with the chromatogram; the molecule is fairly hydrophobic, so retention behavior differs from typical hydrophilic peptides. NMR or MS/MS data add confidence that the end groups are correct. The tyrosine residue can be a site of oxidative degradation, and the counter-ion or salt form, if any, should be stated.
For a walkthrough of each section of a certificate, see how to read a COA.
Storage and stability
Store solid dihexa sealed at -20 °C, protected from light and moisture, and let containers reach room temperature before opening. Its limited aqueous solubility means laboratories often prepare stock solutions in an organic co-solvent such as DMSO before dilution into buffer; the choice of solvent should match the experimental system. Aliquot stock solutions to avoid repeated freeze-thaw cycles and store them at -20 °C or colder, protected from light.
Download the Dihexa data sheet (PDF): sequence, masses, expected MS ions and handling on one printable page.
Latest research
The newest PubMed-indexed papers that mention Dihexa in their title or abstract, retrieved through Europe PMC and refreshed automatically. Inclusion is not an endorsement of a paper's findings.
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Frequently asked questions
Is dihexa a peptide?
Dihexa is best described as a modified, peptide-like molecule. It contains a tyrosine-isoleucine dipeptide core taken from angiotensin IV, but both ends carry non-standard chemical groups added to improve stability. It is therefore sometimes called a peptidomimetic or angiotensin IV analogue rather than a peptide in the ordinary sense. Its classification therefore depends on the definition used.
Is dihexa FDA approved?
No. Dihexa is not approved by the FDA for any use and has not been through completed clinical trials. Its research record consists mainly of rodent and cell-culture studies, and its safety in people has not been established. Long-term toxicology data are also lacking.
How is dihexa thought to work?
The originating researchers proposed that dihexa binds hepatocyte growth factor and enhances activation of its receptor, c-Met, which in cultured neurons was associated with increased dendritic spine formation. This mechanism is based on a small number of preclinical studies and has not been widely confirmed by independent laboratories.
Related compounds
- Noopept
Noopept is a dipeptide-derived small molecule, N-phenylacetyl-L-prolylglycine ethyl ester, developed in Russia as a nootropic research compound. It has been studied mostly in rodent models, with limited clinical data, and is not approved by the FDA.
- Semax
Semax is a synthetic heptapeptide developed in Russia as an analogue of the adrenocorticotropic hormone fragment ACTH(4-7), extended with a Pro-Gly-Pro tail. It is studied for neurotrophic signaling and in models of brain injury.
- Cerebrolysin
Cerebrolysin is a preparation of low-molecular-weight peptides and amino acids derived from porcine brain proteins. It is approved in some countries for neurological conditions such as stroke and dementia, but it is not approved in the US.
- Selank
Selank is a synthetic heptapeptide developed in Russia, built from the immunomodulatory tetrapeptide tuftsin extended with a Pro-Gly-Pro tail. It is studied mainly for effects on anxiety-related behavior and immune signaling.
References
- PubMed: all indexed literature on Dihexa
- ClinicalTrials.gov: registered studies mentioning Dihexa
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