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The effect of steviol on differentiated rat PC-12 cells induced by MPP+

Background: The 1-methyl-4-phenylpyridinium ion (MPP+) is a neurotoxin. It inhibits mitochondrial complex I by interfering with oxidative phosphorylation in mitochondria. That causes ATP depletion and eventual cell apoptosis. Objective: This study investigates steviol's effect, a major metabolite of stevia obtained from Stevia rebaudiana, on MPP+-induced apoptosis of differentiated rat adrenal pheochromocytoma (PC-12) cells. Methods: The PC12 cells were differentiated into neuronal cells by adding nerve growth factor and then treated with MPP+ and steviol in different concentrations; twenty-four hours later, two in vitro toxicity assays. 3-(4,5-Dimethylthiazol-2-Yl)-2,5-Diphenyltetrazolium Bromide (MTT) and Lactate Dehydrogenase Leakage assays (LDH) were conducted to detect the cells’ viability. Results: The present study demonstrated that steviol caused statistically significant cell damage and inhibited the proliferation of the differentiated rat PC-12 cell line in a dose-dependent manner. Furthermore, the results from MTT and LDH assays complemented the outcome of our experiments that steviol acted synergistically in the presence of MPP+ to increase cell death in differentiated rat PC-12 cells. Conclusion: The data obtained from MTT and LDH assays indicated that steviol acted synergistically in the presence of MPP+ free radicals, increasing cytotoxicity. Both assays revealed that steviol aggravated the cytotoxicity produced by MPP+ in differentiated rat PC-12 cells. However, as the MTT assay does not correspond to mitochondrial dysfunction, it may give a poor estimate of cytotoxicity of steviol as compared to the LDH assay that quantifies the damage to the cell membrane, especially when there are small-scale variations in cellular reduction capacity.