Dihexa vs P021

Dihexa

Dihexa is a small-molecule analogue of angiotensin IV, studied in animal and cell models of cognition, hair-cell damage and nerve repair. Its published structure is not a simple peptide chain but a two-residue core carrying a hexanoyl group at one end and an aminohexanoic amide at the other. Much of the founding work came from a single laboratory, and two of those papers now carry a retraction and an expression of concern. Later studies by other groups used zebrafish, rats and mice, and one of them reported no protective effect in its model.

P021

P021 is a peptidomimetic derived from ciliary neurotrophic factor, carrying an adamantylated glycine at its C-terminus. Its originators describe a four-residue core identified by epitope mapping of the most active region of CNTF, with the adamantane-bearing residue added to increase blood-brain barrier permeability and reduce breakdown by exopeptidases. Nearly all published work comes from one group in New York, in rat and transgenic mouse models of ageing, Alzheimer-type pathology and Down syndrome. An independent 2024 study in a model of CDKL5 deficiency reported changes in cultured cells but no matching change in mice.

How Dihexa acts

Published work describes dihexa as acting on the hepatocyte growth factor system rather than on an angiotensin receptor. In zebrafish lateral line hair cells, protection against aminoglycoside damage was attenuated by an HGF antagonist and by inhibitors of Akt, TOR and MEK, which the authors read as evidence that c-Met signalling is involved. A 2021 study in APP/PS1 mice attributed its effects to the PI3K and AKT pathway. The 2014 paper that first proposed direct HGF binding has since been retracted, so this account rests on the later work.

How P021 acts

The published account is indirect. P021 is described as a mimetic of a small active region of ciliary neurotrophic factor, and the reported downstream step is raised expression of brain-derived neurotrophic factor, with an associated fall in glycogen synthase kinase-3 beta activity reported in a triple-transgenic mouse model. Changes in neurogenesis and in dendritic and synaptic markers are attributed to that route. An independent 2024 study in Cdkl5 knockout mice found no rise in BDNF, so the proposed route has not been reproduced in every model tested.

The records side by side

• Type: Dihexa, Peptidomimetic; P021, Peptidomimetic
• Length: Dihexa, not recorded; P021, 5 amino acids
• Molecular weight: Dihexa, 504.7 g/mol; P021, 578.7 g/mol
• Molecular formula: Dihexa, C27H44N4O5; P021, C27H42N6O8

Reading a comparison

A comparison places two records side by side; it does not merge them. Each description above is drawn from that compound's own record, and the two were not necessarily characterised by the same methods, at the same time, or to the same level of detail. Before comparing any attribute, it is worth establishing that both records describe the substance you think they describe — names are not identifiers, and two entries sharing a name can differ in salt form, stereochemistry or the convention used to state a mass. Where a figure carries no method beside it, the comparison is between two reported numbers rather than between two measurements.