After OGD treatment, cell cytotoxicity was determined by the release of lactate dehydrogenase (LDH), a cytoplasmic enzyme released from cells. LDH release into the culture medium was detected using a CytoTox 96®Non-Radioactive Cytotoxicity Assay Kit (Promega Corporation. Madison, WI, USA). Briefly, 50 μl of each sample medium (i.e., pure culture medium for measuring background LDH release, culture media collected from control or OGD-treated cells for measuring experimental LDH release and lysis buffer-treated cells for measuring maximum LDH release) was collected to assay LDH release. The samples were incubated with reduced form of nicotinamide adenine dinucleotide and pyruvate for 30 min at room temperature and the reaction was terminated by adding Stop Solution. LDH release was assessed by measuring the absorbance of supernatants at 490 nm. Cell death rate was calculated as follows: cell death rate = (experimental LDH release-background LDH release) /(maximum LDH release-background LDH release) × 100%. The results were presented as fold increase of the control cells.