What Has Published Research Reported About Dihexa?

What is dihexa?

Dihexa is a synthetic peptide-like molecule derived from angiotensin IV. McCoy and colleagues, in a 2013 paper in the Journal of Pharmacology and Experimental Therapeutics, gave its systematic name as N-hexanoic-Tyr-Ile-(6) aminohexanoic amide and described it as a chemically modified analog of the angiotensin IV tripeptide, designed for greater metabolic stability and barrier permeability (source 1). Its formula is C27H44N4O5, and a US National Center for Advancing Translational Sciences record lists an average molecular weight of 504.66 (source 11). This Steadfast Research Group profile covers the biochemical, animal-model and analytical literature. Clinical literature is outside its scope, and the sources reviewed contained no human studies of dihexa.

From the formula, the masses a laboratory would compare against a mass spectrum can be calculated. These are calculated values, not figures reported in a cited paper.

What did the 2013 development paper report?

The 2013 paper described a medicinal-chemistry series. According to its abstract, several N- and C-terminal modifications of angiotensin IV increased metabolic stability while keeping the ability to reverse scopolamine-induced deficits in Morris water maze performance in rats and to increase hippocampal synaptogenesis. Further modification produced dihexa, which the authors described as a metabolically stabilized, blood-brain-barrier-permeant analog with activity in scopolamine and aged rat models and with marked synaptogenic activity (source 1). The abstract frames these as animal-model results. This profile prints no amounts, routes or schedules from the paper, and secondary pharmacokinetic and spine-count figures that circulate online could not be confirmed from the abstract and are not reported.

The status of this paper needs care. The PubMed record for it was linked to a journal notice of concern in the search results reviewed, and none of the sources reviewed showed a retraction notice for it. Readers who cite it should check its current status on PubMed first (source 1).

What mechanism was proposed, and what happened to the papers behind it?

Two earlier papers from the same Washington State University group framed the angiotensin IV analogs as modifiers of the hepatocyte growth factor (HGF) and c-Met system. Kawas and colleagues published “Development of Angiotensin IV Analogs as Hepatocyte Growth Factor/Met Modifiers” in 2012 (source 2), and Benoist and colleagues published “The Procognitive and Synaptogenic Effects of Angiotensin IV-Derived Peptides Are Dependent on Activation of the Hepatocyte Growth Factor/c-Met System” in 2014 (source 3). A 2015 review by Wright and Harding, titled “The Brain Hepatocyte Growth Factor/c-Met Receptor System: A New Target for the Treatment of Alzheimer’s Disease,” carried the same framing in its title (source 10).

In 2021, the journal issued notices of concern on both the 2012 and the 2014 papers (sources 6 and 7). Retraction Watch reported in September 2021 that four papers co-authored by one of the researchers had received expressions of concern for possible image manipulation, pending an institutional inquiry. It also reported that a Washington State University special committee concluded that the co-author had altered images in a 2011 doctoral dissertation and in at least four papers, and that a university patent on dihexa included images from some of those papers (source 8).

The journal then retracted both papers. The retraction notices, published in the April 2025 issue of the journal, stated that a Washington State University investigation found falsified and/or fabricated data in Figures 3A and 4 of the 2012 paper (source 4), and in Figures 1B and 2A/C and in a later erratum submission for the 2014 paper (source 5). Both papers named the HGF/c-Met system in their titles, and the sources reviewed did not include another primary paper establishing that mechanism.

The notices identified specific figures, but the journal retracted each paper as a whole. This profile therefore prints no result from the 2012 or 2014 papers, and it describes them only for what the notices and the investigation reporting said about them. The 2013 paper is described at abstract level for the same reason: a reader checking the primary record should look at its notice before relying on any figure in it.

Did any other laboratory report on dihexa?

One study from a different set of institutions was found. Sun and colleagues, affiliated with China Pharmaceutical University and Nanjing First Hospital, published a 2021 paper in Brain Sciences using APP/PS1 mice. Per the abstract, the dihexa group had more brain angiotensin IV than the comparison group, performed better in the Morris water maze, and showed less glial activation and lower levels of pro-inflammatory cytokines. The authors also reported that dihexa activated the PI3K/AKT signaling pathway and that the PI3K inhibitor wortmannin reversed the anti-inflammatory and anti-apoptotic effects (source 9). This is a single mouse study read at abstract level. This profile did not assess how it relates to the retracted papers, and it does not by itself restore the earlier mechanism claims.

How do laboratories confirm dihexa identity?

No analytical paper specific to dihexa was among the sources reviewed, so the workflow below is the general one used for any research peptide. A mass spectrum is compared against the calculated values in the table above, with a [M+H]+ near 505.34 and a [M+2H]2+ near 253.17 for the formula in source 11, and an identity result is paired with a purity figure from a separate method. Because a retracted mechanism says nothing about what is in a vial, material identity depends only on batch-level analytical records. The guides to reading a peptide COA, mass spectrometry verification and HPLC purity testing cover those checks.

What terms recur in the dihexa literature?

Angiotensin IV

The parent peptide that dihexa was chemically modified from (source 1).

HGF/c-Met system

The hepatocyte growth factor and c-Met pathway named in the titles of the retracted 2012 and 2014 papers (sources 2 and 3).

Morris water maze

The spatial-learning task used in the rat and mouse experiments in sources 1 and 9.

Scopolamine model

The drug-induced deficit used as an animal model in the 2013 paper (source 1).

Notice of concern

A journal notice that raises concerns about a paper while an inquiry is pending, issued in 2021 for the papers in sources 2 and 3 (sources 6, 7 and 8).

Retraction

The 2025 journal action on the 2012 and 2014 papers, with the affected figures named in the notices (sources 4 and 5).

PI3K/AKT

The signaling pathway the 2021 mouse study linked to dihexa, tested with the inhibitor wortmannin (source 9).

What remains unresolved in the dihexa literature?

Several limits apply. The mechanism most often attached to dihexa came from two papers that were retracted in 2025, and the sources reviewed did not show a replacement mechanism confirmed by an unrelated group. The 2013 development paper is the main description of the molecule and carries a linked notice of concern in the record reviewed. The only other laboratory identified published one mouse study, read here at abstract level (source 9). The sources reviewed contained no human studies, no analytical paper on dihexa itself, and no independent measurement of its stability.

Provenance matters beyond one compound. A claim stated confidently in supplier or forum copy is only as strong as the papers under it, which is why the red flags when buying research peptides guide counts an absent evidence base as part of the screen. The sources reviewed for this profile were read at title, notice or abstract level, and vendor pages and numerical claims repeated only there were not used.