Amyloid-β interactions with chondroitin sulfate-derived monosaccharides and disaccharides -: Implications for drug development

In Alzheimer's disease, the major pathological features are diffuse and senile plaques that are primarily composed of the amyloid-beta (A beta) peptide. It has been proposed that proteoglycans and glycosaminoglycans (GAG) facilitate amyloid fibril formation and/or stabilize the plaque aggregates. To develop effective therapeutics based on A beta -GAG interactions, understanding the A beta binding motif on the GAG chain is imperative. Using electron microscopy, fluorescence spectroscopy, and competitive inhibition ELISAs, we have evaluated the ability of chondroitin sulfate-derived monosaccharides and disaccharides to induce the structural changes in A beta that are associated with GAG interactions. Our results demonstrate that the disaccharides GalNAc-4-sulfate(4S), Delta UA-GalNAc-6-sulfate(6S), and Delta UA-GalNAc-4,6-sulfate(4S,6S), the iduronic acid-2-sulfate analogues, and the monosaccharides D-GalNAc-4S, D-GalNAc-6S, and D-GalNAc-4S,6S, but not D-GalNAc, D-GlcNAc, or Delta UA-GalNAc, induce the fibrillar features of A beta -GAG interactions. The binding affinities of all chondroitin sulfate derived saccharides mimic those of the intact GAG chains. The sulfated monosaccharides and disaccharides compete with the intact chondroitin sulfate and heparin GAGs for A beta binding, as illustrated by competitive inhibition ELISAs. Therefore, the development of therapeutics based on the model of A beta -chondroitin sulfate binding may lead to effective inhibitors of the GAG-induced amyloid formation that is observed in vitro.