Surface Plasmon Resonance Imaging of Amyloid-β Aggregation Kinetics in the Presence of Epigallocatechin Gallate and Metals

A number of human protein misfolding disorders, including Alzheimer's disease (AD), are closely related to the accumulation of beta-sheet-rich amyloid fibrils or aggregates. Neuronal toxicity in AD has been linked to the interactions of amyloid-beta (A beta) with metals, especially Zn2+, Cu2+, and Fe3+, which leads to the production of reactive oxygen species. Nucleation-dependent A beta aggregation, or "seeding", is thought to propagate fibril formation. In this surface plasmon resonance imaging (SPRi) study, we have 5, shown that the fibril seeds formed with the incubation of A beta in the presence of metals are better at promoting monomer elongation compared to A beta alone or in the presence of a well-described polyphenol, (-)-epigallocatechin-3-gallate (EGCG). This is a novel attempt to simultaneously monitor the effects of multiple modulators on fibril elongation using a single chip. EGCG was shown in transmission electron microscopy (TEM) and thioflavin T (ThT) studies to promote the formation of off-pathway, highly stable unstructured oligomers, supporting the SPRi results. These findings suggest that SPRi provides a promising platform as a screening tool for small molecules that can affect the aggregation pathways in neurodegenerative diseases.