Pre-treatment, but not simultaneous treatment, of sinomenine inhibits oligomeric Aβ (ADDL)-induced increase in level of reactive oxygen species (ROS) in microglial BV2 cells. ROS levels were determined using the DCFDA reagent. A. BV2 cells were pre-treated with different concentrations of sinomenine before addition of ADDL. ADDL significantly increased the level of ROS in BV2 cells. However, pre-treatment with sinomenine inhibited ADDL-induced increase in ROS level (n = 6 in all groups). B. BV2 cells were either pre-treated with sinomenine before ADDL addition (Sinomenine pre-treatment) or treated with sinomenine and ADDL simultaneously (Simultaneous addition). Whereas pre-treatment of sinomenine inhibited ADDL-induced ROS generation, simultaneous treatment of sinomenine had no effect on ADDL-induced ROS level (n = 7 in all groups). There was no significant difference between ADDL and ADDL + sinomenine groups when simultaneous addition was performed. In Figures 1A, 2, 5, 6 and 8, the effects of sinomenine alone were also examined. Compared to control, sinomenine alone had no significant effects. Asterisks denote significant differences (p < 0.05).