PE-22-28

This foundational study identified spadin, a 17-residue peptide cleaved from the propeptide (PE) of the sortilin/neurotensin receptor-3 precursor, as a selective blocker of the TREK-1 two-pore-domain potassium channel, binding with roughly 10 nM affinity. In mice, spadin produced antidepressant-like effects across the forced swim, tail suspension, novelty-suppressed feeding, and learned helplessness paradigms within 4 days, faster than fluoxetine, and increased hippocampal neurogenesis and CREB phosphorylation. TREK-1 deletion abolished the effect, establishing channel inhibition as the mechanism. All data are from rodents.

Scientists discovered a natural peptide called spadin that switches off a specific potassium channel (TREK-1) in the brain, a channel linked to mood regulation. In mice, spadin lifted depression-like behavior in about 4 days, faster than the standard drug fluoxetine, and boosted the birth of new brain cells. This paper introduced the idea of treating depression by blocking TREK-1, but the work was done entirely in mice, not people. PE-22-28 is the shortened fragment (residues 22-28) derived from spadin.

This is the key study characterizing PE 22-28, a 7-residue fragment (residues 22-28 of spadin) derived from analysis of spadin's blood-degradation products. PE 22-28 inhibited TREK-1 with an IC50 of roughly 0.12 nM (versus 40-60 nM for spadin), extended in vivo activity to about 23 hours versus 7 hours, and produced antidepressant-like effects in the forced swim and novelty-suppressed feeding tests after 4-day subchronic dosing in mice. It also induced hippocampal neurogenesis and enhanced synaptogenesis, increasing PSD-95 expression in cortical neurons. All findings are preclinical.

Researchers trimmed spadin down to a much smaller 7-piece peptide called PE 22-28 that blocks the TREK-1 channel far more potently and stays active in the body roughly three times longer. In mice, it reduced depression-like behavior after only 4 days and encouraged both new brain cells and stronger connections between existing neurons. This is the main paper defining PE 22-28, and importantly it was tested only in mice, with no human data.

This review synthesizes the case for TREK-1 inhibition as a rapid-acting antidepressant strategy and traces the development from spadin to shortened analogs including PE 22-28. It details optimization approaches (sequence shortening, cyclization, retro-inverso modification) aimed at improving potency, proteolytic stability, and bioavailability, and summarizes evidence that these peptides act within about 4 days without the TREK-1-related side effects (arrhythmia, seizure) seen with global channel loss. The review is explicit that the evidence base is preclinical and that human pharmacokinetics, safety, and blood-brain-barrier penetration remain unresolved.

This is an overview article that pulls together years of research on blocking the TREK-1 channel to treat depression, following the story from spadin to its improved offspring like PE 22-28. It explains how chemists made the peptides stronger and longer-lasting, and notes they seem to work quickly in animals without the heart or seizure problems that might be expected. The authors are candid that all of this is animal research, with key questions about human safety and whether the drug reaches the human brain still unanswered.