A generic class of amyloid fibril inhibitors

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Abstract
Amyloid fibrils are large ordered fibrillar aggregates formed from mis-folded proteins. A number of human diseases are linked to the presence of amyloid deposits, including Alzheimer's disease, Parkinson's disease and type II diabetes. One therapeutic strategy for treating amyloid related diseases involves inhibiting fibril formation. Amyloid fibrils are β-sheet rich fibrillar aggregates that associate through hydrophobic interactions between precursor units. In this study, these generic physical properties of amyloid fibrils have been exploited to design a universal class of amphiphilic macromolecular inhibitors. A naturally occurring macromolecule of this structure is arabinogalactan protein (AGP), a component of gum arabic (GA). In addition, two synthetic polymers based on the proposed amphiphilic structure were synthesized and tested. These synthetic mimics, referred to as poly(norbornene glucose ester) (PNGE) and poly(norbornene gluconamide) (PNGA), possess hydrophobic polynorbornene backbones and pendent hydrophilic cyclic and open-chain glucose units, respectively. AGP, PNGE and PNGA all show inhibitory effects on in vitro amyloid fibril formation in bovine insulin (BI), hen egg white lysozyme (HEWL) and amyloid beta 1–40 (Aβ) proteins. Circular dichroism (CD) spectra of the proteins in the presence of the inhibitors suggests that amyloid fibril formation is inhibited by stabilization of the native α-helices of the proteins, as well as binding of the inhibitors to the β-sheet precursors. Based upon these results, glycosylated hydrophobic macromolecules are identified as a promising class of therapeutic agents for amyloid related diseases. Furthermore, we have determined that the intensity of the fluorescent probe thioflavin T (ThT) is dependent on both fibril morphology and the presence of the inhibitors, and is therefore not a quantitative measure of protein conversion to fibrils.

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