Recovery of neuropathy target esterase activity after inhibition with mipafox and O-hexyl O-2,5-dichlorophenyl phosphoramidate in bovine chromaffin cell cultures

Neuropathy target esterase (NTE) is a membrane protein present in various tissues whose physiological function has been recently suggested to be the maintenance of phosphatidylcholine homeostasis. Inhibition and further modification of NTE by certain organophosphorus compounds (OPs) were related to the induction of the “organophosphorus induced delayed neuropathy”. Bovine chromaffin cells were cultured at 75,000 cells/well in 96-well plates and exposed to 25 μM mipafox or 3 μM O-hexyl O-2,5-dichlorophenyl phosphoramidate (HDCP) for 60 min. Inhibitors were removed by washing cells three times with Krebs solution. Then NTE activity was assayed at 0, 24, 48 and 120 h after exposure using the Biomek 1000 workstation. Immediately after mipafox treatment NTE activity represented 3% of the control (6.7 ± 1.9 mU/106 cells). At 24, 48 and 120 h after removing inhibitor, recorded activities were 33%, 42% and 111% of their respective controls (5.7 ± 3.1; 5.7 ± 1.9; 5.4 ± 0.0 mU/106 cells, respectively). Treatment with HDCP also displayed a time-dependent pattern of NTE recovery. As NTE inhibited by phosphoramidates is not reactivated in homogenized tissues, these results confirm a time-dependent regeneration of NTE after inhibition by neuropathic OPs.