Reactivation and aging of parathion-and paraoxon-inhibited human brain acetylcholinesterase in vitro

AIM To explore the differences in reactivation and aging of phosphorylated human brain AChE caused by parathion or paraoxon in vitro. METHODS Micro-spectrophotometric assay was used to determine the activity of AChE. RESULTS The pI 50 ′s inhibition of the human brain acetylcholinesterase(AChE) by parathion and paraoxon was 4.10 and 7.51, whereas the pI 90 ′s was 2.55 and 6.57, respectively. Efficacies of reactivation of parathion or paraoxon-inhibited human brain AChE by pralidoxime chloride(2-PAM), pyramidoxine(HI-6), obidoxime chloride(LuH 6) and trimedoxime(TMB 4) were obviously different. On the equivalent molar basis, the potency of LuH 6 and TMB 4 was higher in reactivition of the inhibited human brain AChE than that of 2-PAM and HI-6. The four oxime reactivators were more effective in reactivation of the paraoxon-inhibited human brain AChE than its parathion counterpart. The optimal reactivator for parathion- and paraoxon-AChE was LuH 6. The half aging time(t 0.5 ) of parathion- and paraoxon-AChE was 14 and 12 h, and the 99% aging time(t 0.99 ) was 95 and 81 h, respectively. CONCLUSION Obidoxime or trimedoxime should be used with atropine at the earliest time in the therapy of intoxication of parathion and paraoxon. Even when the acute symptoms have been well controlled, the reactivator should be consecutively used within four days.