Bifunctional compounds for controlling metal-mediated aggregation of the aß42 peptide.

Abnormal interactions of Cu and Zn ions with the amyloid ß (Aß) peptide are proposed to play an important role in the pathogenesis of Alzheimer's disease (AD). Disruption of these metal-peptide interactions using chemical agents holds considerable promise as a therapeutic strategy to combat this incurable disease. Reported herein are two bifunctional compounds (BFCs) L1 and L2 that contain both amyloid-binding and metal-chelating molecular motifs. Both L1 and L2 exhibit high stability constants for Cu(2+) and Zn(2+) and thus are good chelators for these metal ions. In addition, L1 and L2 show strong affinity toward Aß species. Both compounds are efficient inhibitors of the metal-mediated aggregation of the Aß(42) peptide and promote disaggregation of amyloid fibrils, as observed by ThT fluorescence, native gel electrophoresis/Western blotting, and transmission electron microscopy (TEM). Interestingly, the formation of soluble Aß(42) oligomers in the presence of metal ions and BFCs leads to an increased cellular toxicity. These results suggest that for the Aß(42) peptide-in contrast to the Aß(40) peptide-the previously employed strategy of inhibiting Aß aggregation and promoting amyloid fibril dissagregation may not be optimal for the development of potential AD therapeutics, due to formation of neurotoxic soluble Aß(42) oligomers.

The effect of Cu(2+) and Zn(2+) on the Aß42 peptide aggregation and cellular toxicity.

The coordination chemistry of Cu and Zn metal ions with the amyloid ß (Aß) peptides has attracted a lot of attention in recent years due to its implications in Alzheimer's disease. A number of reports indicate that Cu and Zn have profound effects on Aß aggregation. However, the impact of these metal ions on Aß oligomerization and fibrillization is still not well understood, especially for the more rapidly aggregating and more neurotoxic Aß42 peptide. Here we report the effect of Cu(2+) and Zn(2+) on Aß42 oligomerization and aggregation using a series of methods such as Thioflavin T (ThT) fluorescence, native gel and Western blotting, transmission electron microscopy (TEM), and cellular toxicity studies. Our studies suggest that both Cu(2+) and Zn(2+) ions inhibit Aß42 fibrillization. While presence of Cu(2+) stabilizes Aß42 oligomers, Zn(2+) leads to formation of amorphous, non-fibrillar aggregates. The effects of temperature, buffer, and metal ion concentration and stoichiometry were also studied. Interestingly, while Cu(2+) increases the Aß42-induced cell toxicity, Zn(2+) causes a significant decrease in Aß42 neurotoxicity. While previous reports have indicated that Cu(2+) can disrupt ß-sheets and lead to non-fibrillar Aß aggregates, the neurotoxic consequences were not investigated in detail. The data presented herein including cellular toxicity studies strongly suggest that Cu(2+) increases the neurotoxicity of Aß42 due to stabilization of soluble Aß42 oligomers.