7 8 dihydroxyflavone

7,8-dihydroxyflavone, wogonin, quercetin, and apigenin were purchased from Sigma-Aldrich, St. Louis, Mosby, MO, United States. Congo red (Sigma-Aldrich, St. Louis, Mosby, MO, United States), known to bind to the cross β-sheet structure of amyloid fibrils (Sipe and Cohen, 2000 (link)), was included for comparison. For biochemical Tau aggregation inhibition test, bacterial expressed proaggregator ΔK280 Tau_RD (Gln²⁴⁴–Glu³⁷² of 441-residue human Tau) was prepared as described (Lin et al., 2020 (link)). ΔK280 Tau_RD protein (20 μM in final 50 μl) was incubated with tested compounds (5–10 μM in 150 mM sodium chloride (NaCl) and 20 mM tris(hydroxymethyl)aminomethane-hydrochloride (Tris–HCl), pH 8.0) at 37°C for 48 h. Then, thioflavin T (5 μM final concentration; Sigma-Aldrich, St. Louis, Mosby, MO, United States), a dye exhibiting enhanced fluorescence upon binding to diverse types of amyloid fibrils (Biancalana and Koide, 2010 (link)), was added and incubated for 25 min at room temperature. The formed aggregates reflected by thioflavin T fluorescence intensity was recorded at excitation 420 nm and emission 485 nm by using the FLx800 Fluorescence Microplate Reader (BioTek Instruments Incorporation, Winooski, VT, United States). Half maximal effective concentration (EC₅₀) was calculated using the interpolation method.

2,2-Diphenyl-1-picrylhydrazyl radical (DPPH^●), 2,2-Diphenyl-1-picrylhydrazin (DPPH), 2,4,6-Tris(2-pyridyl)-s-triazine (TPTZ), FeCl₂·4H₂O, FeCl₃·6H₂O, TROLOX, quercetin, rutin, baicalein, morin, 7,8-dihydroxyflavone, (−)-epicatechin, (+)-catechin, l-ascorbic acid, tannic acid, crocin, -caroten, purpurin, silibinin, olivetol, gallic acid, caffeic acid, protocatechuic acid, avenanthramides A, B, and C, flavone, ergocalciferol, lipoic acid, biotin, thiamin, indole-3-carbinol, astaxanthin, uric acid, sodium acetate, ethanol, and acetic acid were purchased from Merck /Sigma/ (St. Louis, MO, USA).

2,2-Diphenyl-1-picrylhydrazyl radical (DPPH^●), 2,2-Diphenyl-1-picrylhydrazin (DPPH), 2,4,6-Tris(2-pyridyl)-s-triazine (TPTZ), FeCl₂·4H₂O, FeCl₃·6H₂O, TROLOX, quercetin, rutin, baicalein, morin, 7,8-dihydroxyflavone, (−)-epicatechin, (+)-catechin, l-ascorbic acid, tannic acid, crocin, -caroten, purpurin, silibinin, olivetol, gallic acid, caffeic acid, protocatechuic acid, avenanthramides A, B, and C, flavone, ergocalciferol, lipoic acid, biotin, thiamin, indole-3-carbinol, astaxanthin, uric acid, sodium acetate, ethanol, and acetic acid were purchased from Merck /Sigma/ (St. Louis, MO, USA).