Abstract

Tau protein and Aβ-amyloid have been studied as pathological aggregations, which form neurofibrillary tangles and amyloid plaques in Alzheimer’s disease brain. Tau protein plays a critical role in neuron that binds to microtubules and assists with their formation and stabilization. However, unbinding of hyperphosphorylated tau and microtubules leads to unstable and disintegrating state of neuron. The free tau proteins form neurofibrillary tangles. The purpose of this study is to screen in vitro the the tau-aggregation inhibitory activity of nine methanol extracts of Psidium guajava leaf, Nelumbo nucifera leaf; wild Ipomoea aquatic, Cleome rutidosperma aerial parts, Artocarpus altilis leaf, cultivated Ipomoea aquatic, Centella asiatica leaf, Mimosa pudica L. aerial parts, Nelumbo nucifera seed pod collected in the Mekong Delta. Nine herbs were collected, dried and extracted with methanol. The half maximal inhibitory concentration (IC50) of methanol extracts was measured by Thioflavin T assay at various concentrations. Silica gel column chromatography was employed to fractionate the Psidium guajava leaf crude extract. Nine methanol extracts were proved to reduce the tau aggregation in vitro. Extracts from leaves of Psidium guajava, Artocarpus altilis and Nelumbo nucifera impressively inhibited the tau aggregation with IC50 at 0.39 mg/mL, 1.05 mg/mL and 1.24 mg/mL, respectively. Methylene blue was used as a positive control, with IC50 at 1.35 μM. The five examined fractions of guava leaf were proved to inhibit the tau aggregation ranging from 33.70 % to 48.49 %, except the 100 % of hexane fraction showed almost no effect on the tau aggregation inhibitor.