Oxime-induced reactivation of acetylcholinesterase inhibited by organophosphinates

The comparative potency of oximes for reactivation of inhibited eel acetylcholinesterase (AChE) in vitro is dependent on the organophosphinate inhibitor. Some of the data, dealing with a reference organophosphonate, support the conclusion of other investigators that the oxime potency order is also dependent on the inhibiting phosphonate. This work was done to identify more clearly the nature of phosphinylated AChE with regard to oxime reactivation potency and the potential of phosphinates as pretreatment drugs to protect AChE against organophosphonate poisoning. We have determined the reactivation potency of four oximes--2-PAM, HI-6, TMB-4 and toxogonin--against four phosphinates--4-nitrophenyl methyl(phenyl)phosphinate (PMP), 4-nitrophenyl chloromethyl(phenyl)phosphinate (CPMP), 4-nitrophenyl trifluoromethyl(phenyl)phosphinate and 4-nitrophenyl bis(2-thienyl)phosphinate. For comparison, the phosphonate sarin (GB, isopropyl methylphosphonofluoridate) was included. Incubation of the inhibited enzyme (I-AChE) at 25 degrees C was with 0.30 microM oxime for PMP, 3.0 microM oxime for sarin and CPMP and 100 microM oxime for the two remaining phosphinates. AChE activity was assayed spectrophotometrically for 3.0 min at 272.5 nm at 25 degrees C in 0.10 M MOPS buffer (pH 7.60) using phenyl acetate as substrate. When sarin was the inhibitor (0% spontaneous recovery after a 2-h incubation), the order of oxime reactivation was 2-PAM (46%) greater than or equal to toxogonin (33%) = TMB-4 (31%) greater than HI-6 (9%) after 2-h incubations. For PMP (12% spontaneous recovery after a 2-h incubation) the oxime order was toxogonin (67%) greater than TMB-4 (53%) greater than 2-PAM (40%) after 2-h incubations.(ABSTRACT TRUNCATED AT 250 WORDS)