Figure 2. Effects of metformin pretreatment on the viability of MPP⁺-treated differentiated SH-SY5Y cells. Cell viability was determined by the MTT assay. Cells were pretreated with metformin (2000 µM and 500 µM) for 1 h before exposure to MPP⁺ (1000 µM) for 24 h.The data are expressed as the means ± SEM from five independent experiments, each of which included five replicates. *** P < 0.001 versus control; ### P < 0.001 versus MPP⁺-treated cells.