MPP+ was chosen to induce apoptosis and α-synuclein expression in this experiment because it had been successfully used in several other studies. However, a closer analysis of these other studies shows that the amount of MPP+ used to obtain high α-synuclein expression were unrealistic for a Parkinson’s disease model. In this experiment, 500 µM was the exposure level; whereas other studies have used mM concentrations of MPP+. However, in this study, cells treated with MPP+ had one of the lowest total protein concentrations because so many of the cells had died and broken down due to exposure to the neurotoxin.
It is important to keep in mind that the intent of this experiment was to investigate potential clinical treatments for Parkinson’s disease through studying the effects of guanosine on alpha synuclein. To create a more realistic model, a smaller amount of MPP+ was used because the onset of Parkinson’s disease is not immediate. Often, by the time the disease has been diagnosed or even when symptoms first become noticeable, 70 to 80% of the disease has progressed. The natural destruction of dopaminergic cells is slow. Also, α-synuclein aggregation (in Lewy bodies) in neuroblastoma is a standard cellular symptom of Parkinson’s disease, so MPP+, neurotoxin used in this model, had to induce expression of the protein.
Although rendered statistically insignificant by the unexpected MPP+ results, the lack of α-synuclein expression in the samples treated with guanosine is interesting and consistent with other studies that have proven that guanosine protects against apoptosis. In this experiment, guanosine appeared to prevent apoptotic aggregation of α-synuclein. Previous studies have shown that it promotes mitosis and is not as pro-apoptotic as adenine-based purines.