Aggregation of the amyloid-� (A�) peptide is associated with the development of Alzheimer's disease.  A� is a 39-43 residue cleavage product of the amyloid precursor protein (APP).  A� aggregates to produce insoluble plaques in the brain, which are composed of cross �-sheet structured fibrils. Various polyphenolic compounds have been shown to interfere with A� aggregation. The interaction of A� with the naturally occurring polyphenolic compounds quercetin, epigallocatechin gallate, nordihydroguaiaretic acid, curcumin, rosmarinic acid, and baicalein was investigated via circular dichroism (CD), and deep-ultraviolet resonance Raman (dUVRR) spectroscopies. Thioflavin T (ThT) fluorescence assays were used to categorize polyphenols as either inhibitors or non-inhibitors of A� aggregation. It was found that quercetin, epigallocatechin gallate, and nordihydroguaiaretic acid inhibited aggregation, while rosmarinic acid and baicalein did not. Quercetin and baicalein have similar structures, as do rosmarinic and nordihydroguaiaretic acids.  It could not be determined via ThT assay whether curcumin inhibited aggregation. However, CD spectra of A� with curcumin showed �-sheet formation.  CD and dUVRR were employed to determine if inhibitors and non-inhibitors had a similar effects on A�'s structure.

Spectroscopic investigation on the effect of naturally occurring polyphenolic compounds on the structure of the Amyloid-� peptide

248th National Meeting (2014)

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