Cytotoxicity assay

MTT assay was aimed to investigate the effect of Aβ on cell viability. The human neuroblastoma BE(2)-C cells (ATCC #CRL-2268) were cultured at 37 °C, 5% CO₂ in the RPMI medium containing 10% FBS. Twenty thousand cells were seeding in a 96-well plate each well. ZnAβ or ADDLs diluted in the RPMI medium were added into the well and incubated for 24 hr. Then, ten µl MTT solution (5 mg/ml) was added and incubated for 3 hr for formation of formazan crystals. After incubation, the medium was carefully discarded and 100 µl DMSO was added to lyse the formazan crystals. Absorbance at 570 and 690 nm (background absorbance) were monitored by an ELISA microplate reader SpectraMax M5 (Molecular Devices, Sunnyvale, CA, USA). The difference of absorbance between 570 and 690 nm was calculated. For LDH assay, the assay was followed the instructions from the protocol of LDH assay toxicity kit (Promega, Madison, WI, USA). BE(2)-C cells were seeding the same as MTT ZnAβ or ADDLs were added and incubated for 24 hr. Next day, LDH assay was performed by monitoring the rate of substrate formation, emission at 590 nm while excitation at 560 nm. The results were replicated for 3 times. The cell lysed with 2% Triton X-100 was served as positive control for 100% cytotoxicity.