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

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.

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.

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.

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.

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.