Acetylcholinesterase and Neuropathy Target Esterase Inhibitions in Neuroblastoma Cells to Distinguish Organophosphorus Compounds Causing Acute and Delayed Neurotoxicity

The differential inhibition of the target esterases acetylcholinesterase (AChE) and neuropathy target esterase (NTE, neurotoxic esterase) by organophosphorus compounds (OPs) is followed by distinct neurological consequences in exposed subjects. The present study demonstrates that neuroblastoma cell lines (human SH-SY5Y and murine NB41A3) can be used to differentiate between neuropathic OPs (i.e., those inhibiting NTE and causing organophosphorus-induced delayed neuropathy) and acutely neurotoxic OPs (i.e., those highly capable of inhibiting AChE). In these experiments, concentration–response data indicated that the capability to inhibit AChE was over 100× greater than the capability to inhibit NTE for acutely toxic, nonneuropathic OPs (e.g., paraoxon and malaoxon) in both cell lines. Inhibition of AChE was greater than inhibition of NTE, without overlap of the concentration–response curves, for OPs which are more likely to cause acute, rather than delayed, neurotoxic effectsin vivo(e.g., chlorpyrifos-oxon, dichlorvos, and trichlorfon). In contrast, concentrations inhibiting AChE and NTE overlapped for neuropathy-causing OPs. For example, apparent IC50 values for NTE inhibition were less than 9.6-fold the apparent IC50 values for AChE inhibition when cells were exposed to the neuropathy-inducing OPs diisopropyl phosphorofluoridate, cyclic tolyl saligenin phosphate, phenyl saligenin phosphate, mipafox, dibutyl dichlorovinyl phosphate, and di-octyl-dichlorovinyl phosphate. In all cases, esterase inhibition occurred at lower concentrations than those needed for cytoxicity. These results suggest that either mouse or human neuroblastoma cell lines can be considered usefulin vitromodels to distinguish esterase-inhibiting OP neurotoxicants.