Characterization of cholyl-leu-val-phe-phe-ala-OH as an inhibitor of amyloid beta-peptide polymerization

Abstract

Cholyl-LVFFA-OH (1, PPI-368) is an organic-modified peptide based on the sequence of amyloid beta-peptide (Aβ). It is a potent and selective inhibitor of A β polymerization that blocks the formation of neurotoxic species of Aβ. In a nucleation-dependent polymerization assay of 50μM Aβ1-40 equimolar concentrations of PPI-368 block polymerization based on turbidity and electron microscopy. Monomeric Aβ1-40 and Aβ1-42 are non-toxic when incubated with neuronal cell lines, but become toxic during polymerization. PPI-368 coordinately delays the onset of polymerization and the formation of neurotoxic Aβ species for both peptides. In a polymerization extension assay seeded with pre-formed Aβ polymer, similar inhibition and dose-dependency phenomena are observed with PPI-368. Radiolabeled PPI-368 is incorporated into fibrils during polymerization demonstrating binding to Aβ peptide within a fibrillar structure. Gel-filtration studies show progressive disappearance of Aβ monomer and concomitant appearance of soluble higher molecular weight oligomers. In the presence of submolar concentrations of PPI-368, monomeric Aβ is still present and oligomers are not observed. PPI-368 does not inhibit the polymerization of other amyloidogenic proteins such as transthyretin (TTR) or islet amyloid polypeptide(IAPP20-29).