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

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.