Cell model comparison in the context of in vitro Parkinson studies

Pesticide exposure is associated with an increased risk of developing Parkinson’s disease (PD), though currently neurodegeneration is not covered in safety assessment of pesticides. This indicates a need for an updated safety assessment framework, preferably without the use of animal models. Death of dopaminergic (DA) neurons of the substantia nigra is a hallmark of PD. Vulnerability of these neurons to a combination of oxidative stress, mitochondrial dysfunction, and calcium dyshomeostasis is thought to underlie their selective cell death upon pesticide exposure. An in vitro model should reflect this vulnerability in order to be relevant for use in safety assessment studies. Here we assessed to what extent a commonly used PD model system displays this vulnerability. To this end, LUHMES (DA neuronal model) and HepG2 (liver model) cells were exposed to four pesticides (dinoseb, endosulfan, mancozeb, and rotenone). Cells were exposed short term (18 hours), long term (72 hours), or repeatedly (4x 6 hours with 18 hours recovery). After exposure, mitochondrial metabolic activity and cytotoxicity were determined by Alamar blue and lactate dehydrogenase assay, respectively. Both HepG2 and LUHMES cells responded similarly to dinoseb and rotenone in all scenarios. Mancozeb led to more severe inhibition of mitochondrial metabolic activity in the LUHMES cells in comparison to the HepG2 cells in all scenarios. Endosulfan led to more severe effects after short term and repeated exposure, but not long term exposure. Here we show that the expected increased vulnerability of a DA neuronal model to pesticide effects cannot be confirmed for all tested compounds. Our results demonstrate differential effects of the four pesticides in both models, which can be explained by physiological characteristics of the cell models and mechanisms of action of the pesticides. These findings highlight that to be used for safety assessment of pesticides, a chosen in vitro model should be characterized for its relevance to the expected mechanism of action of the tested compound and the mechanistic endpoint tested.