Cellular and Molecular Responses to Ethyl-Parathion in Undifferentiated SH-SY5Y Cells Provide Neurotoxicity Pathway Indicators for Organophosphorus Impacts.

High-fidelity non-animal screening methods are needed that can rapidly and accurately characterize organophosphorus compound (OP)-induced neurotoxicity. Herein, the efficacy of human neuroblastoma cell line (SH-SY5Y) to provide molecular and cellular responses characteristic of the OP neurotoxicity pathway was investigated in response to the OP-model compound, ethyl-parathion. Undifferentiated SH-SY5Y cells were exposed to ethyl-parathion for 30 minutes at 0 (control), 0.5, 2.5, 5, 10, and 25 µg/ml. Dose-responsive reductions in cell viability were observed with significant reductions at ≥ 10 µg/ml. From these results, ethyl-parathion exposures of 0 (control), 5, and 10 µg/ml were selected to examine bioindicators underlying the OP neurotoxicity pathway including: reactive oxygen species (ROS), cell membrane peroxidation, mitochondrial membrane potential, and apoptosis. Ethyl-parathion elicited highly significant increases in ROS relative to controls (p < 0.01) at both exposure concentrations, confirmed using N-acetyl cysteine (NAC) as a ROS quencher which alleviated ROS increases. A response characteristic of increased ROS exposure, cell membrane-lipid peroxidation, significantly increased (p < 0.05) at the highest ethyl-parathion exposure (10 µg/ml). As a likely consequence of membrane-lipid peroxidation, ethyl-parathion-induced reductions in mitochondrial membrane potential (MMP) were observed with significant effects at 10 µg/ml, reducing MMP by 58.2%. As a culmination of these cellular-damage indicators, apoptosis progression was investigated by phosphatidylserine translocation where ethyl-parathion induced dose-responsive, highly significant (p < 0.01) increases at both 5 and 10 µg/ml. Overall, the mechanistic responses observed in undifferentiated SH-SY5Y cells corresponded with in vivo mammalian results demonstrating potential for this non-animal model to provide accurate OP neurotoxicology screening.