Reactivation by various oximes of human erythrocyte acetylcholinesterase inhibited by different organophosphorus compounds

The new bispyridinium oximes HI 6 and HLo 7 are promising antidotes against poisoning by highly toxic organophosphorus compounds, i.e. nerve agents. Until now, their ability to reactivate pesticide inhibited human acetylcholinesterase (AChE) has not been elucidated. For this purpose human erythrocyte AChE (EC 3.1.1.7) was inhibited (30 min) by chlorfenvinphos, dichlorvos, dicrotophos, heptenophos, mevinphos, monocrotophos, paraoxon, phosphamidon, trichlorfon, malaoxon, omethoate, oxydemeton-methyl or methamidophos by 85-98% of control. After removal of excess inhibitor, obidoxime, pralidoxime (2-PAM), HI 6 or HLo 7 (10, 30 or 100 mu mol/l) were added and the AChE activity was measured spectrophotometrically at various times thereafter (5-60 min). The oximes significantly, but not completely, reactivated organophosphate inhibited AChE. The velocity and extent of reactivation were dependent on the oxime and its concentration. In all cases obidoxime was superior to the three other oximes, followed by HLo 7, 2-PAM and HI 6. In most cases obidoxime and HLo 7 were most effective at 10 or 30 mu mol/l while 2-PAM and HI 6 needed 100 mu mol/l. These data suggest that 2-PAM, HI 6 and HLo 7 are less patent than obidoxime in reactivating human AChE inhibited by organophosphate pesticides.