The effect of Cu²⁺ and Zn²⁺ on the Aβ₄₂ peptide aggregation and cellular toxicity

The coordination chemistry of Cu and Zn metal ions with the amyloid β (Aβ) 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 Aβ aggregation. However, the impact of these metal ions on Aβ oligomerization and fibrillization is still not well understood, especially for the more rapidly aggregating and more neurotoxic Aβ₄₂ peptide. Here we report the effect of Cu²⁺ and Zn²⁺ on Aβ₄₂ 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 Cu²⁺ and Zn²⁺ ions inhibit Aβ₄₂ fibrillization. While presence of Cu²⁺ stabilizes Aβ₄₂ oligomers, Zn²⁺ leads to formation of amorphous, non-fibrillar aggregates. The effects of temperature, buffer, and metal ion concentration and stoichiometry were also studied. Interestingly, while Cu²⁺ increases the Aβ₄₂-induced cell toxicity, Zn²⁺ causes a significant decrease in Aβ₄₂ neurotoxicity. While previous reports have indicated that Cu²⁺ can disrupt β-sheets and lead to non-fibrillar Aβ aggregates, the neurotoxic consequences were not investigated in detail. The data presented herein including cellular toxicity studies strongly suggest that Cu²⁺ increases the neurotoxicity of Aβ₄₂ due to stabilization of soluble Aβ₄₂ oligomers.