Identification of fermented tea (Camellia sinensis) polyphenols and their inhibitory activities against amyloid-beta aggregation

Abstract

Thirty-three phenolic compounds were identified from the extract of fermented tea (Camellia sinensis L.), including three undescribed flavonoids, namely quamoreokchaside I–II and kamoreokchaside I, along with thirty known compounds. All isolates were tested to evaluate their inhibitory effects against amyloid-beta (Aβ) aggregation through thioflavin-T (ThT) fluorescence-based assay and transmission electron microscopy (TEM). Among the isolates, three tea polyphenols, including (–)-catechin gallate (CG), (–)-epicatechin gallate (ECG), and (–)-epigallocatechin gallate (EGCG), significantly decreased Aβ aggregation at a concentration of 10 μg ml−1, compared to the positive control, Aβ alone. The anti-Aβ aggregation effects of CG, ECG, and EGCG were confirmed again via TEM, which were consistent with the ThT fluorescence-based assay. Moreover, CG and ECG provided stronger protection on SH-SY5Y cells against Aβ-induced cytotoxicity than EGCG. Remarkably, CG showed more potent inhibitory activity than EGCG, the best-known anti-Aβ aggregation agent from tea products.