P021 vs Semax

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.

Semax

Semax is a synthetic seven-residue peptide, Met-Glu-His-Phe-Pro-Gly-Pro, built from a short fragment of adrenocorticotropic hormone (ACTH). Its first four residues match positions 4 to 7 of ACTH; the Pro-Gly-Pro tail does not occur there in the hormone and is reported to slow breakdown by peptidases. Short ACTH fragments of this kind are described as lacking the steroid-releasing activity of the full hormone. Semax was developed by Russian researchers, and most of its literature comes from Russian groups working in rats and cell cultures. Controlled human studies are few, many are published only in Russian, and independent replication elsewhere is limited.

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.

How Semax acts

No specific receptor for Semax has been identified. Studies in rats have reported higher expression of brain-derived neurotrophic factor (BDNF) and its receptor TrkB in the hippocampus, and other work has examined dopamine and serotonin turnover in the striatum. Transcriptome studies in rat models of cerebral ischaemia describe shifts in the expression of genes tied to immune and vascular processes. Because its core derives from ACTH, an interaction with melanocortin receptors has been proposed, though direct binding evidence is limited. How these separate observations connect has not been worked out.

The records side by side

• Type: P021, Peptidomimetic; Semax, Synthetic ACTH analog (heptapeptide)
• Length: P021, 5 amino acids; Semax, 7 amino acids
• Molecular weight: P021, 578.7 g/mol; Semax, 813.9 g/mol
• Molecular formula: P021, C27H42N6O8; Semax, C37H51N9O10S

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.