Catalytic detoxification of nerve agent and pesticide organophosphates by butyrylcholinesterase assisted with non-pyridinium oximes

Abstract

SYNOPSIS We present here a comprehensive in vitro, ex vivo and in vivo study on hydrolytic detoxification of nerve agent and pesticide organophosphates (OPs) catalyzed by purified human butyrylcholinesterase (hBChE) in combination with novel non-pyridinium oxime reactivators. We identified 2-trimethylammonio-6-hydroxybenzaldehyde oxime (TAB2OH) as an efficient reactivator of OP-hBChE conjugates formed by the nerve agents, VX and cyclosarin, and the pesticide, paraoxon. It was also functional in reactivation of sarin and tabun inhibited hBChE. A three to five-fold enhancement of in vitro reactivation of VX, cyclosarin and paraoxon inhibited hBChE was observed, when compared to the commonly used N-methylpyridinium aldoxime reactivator, 2PAM. Kinetic analysis showed the enhancement resulted from improved molecular recognition of corresponding OP-hBChE conjugates by TAB2OH. The unique features of TAB2OH stem from an exocyclic quaternary nitrogen and a hydroxyl, both ortho to an oxime group on a benzene ring. pH dependences reveal participation of the hydroxyl (pKa=7.6) forming an additional ionizing nucleophile to potentiate the oxime (pKa=10) at physiological pH. The TAB2OH protective indices in therapy of sarin and paraoxon exposed mice were enhanced by 30% – 60% when they were treated with a combination of TAB2OH and sub-stoichiometric hBChE. These results establish that oxime-assisted catalysis is feasible for OP bioscavenging.

Pseudocatalytic scavenging of the nerve agent VX with human blood components and the oximes obidoxime and HI-6

“…Current research is directed to develop primarily new BChE-specific reactivators to turn plasma BChE into a pseudocatalytic scavenger or to even augment this process by administration of recombinant BChE (Kovarik et al 2010;Radić et al 2013;Elsinghorst et al 2013;Nachon et al 2013;Sit et al 2014). As a short-term solution, administration of the licensed obidoxime or HI-6 as oxime in advanced development together with additionalby itself stoichiometric-AChE and/or BChE from blood products is a practical approach to elevate the oximemediated pseudocatalytic breakdown of VX in the vascular compartment to decrease the toxic body load and improve physical recovery.…”

“…By now the reactivation of nerve agent-inhibited BChE using the approved (bis-)pyridinium oximes obidoxime or pralidoxime is rather weak (Aurbek et al 2009;Elsinghorst et al 2013). Current research is directed toward synthesizing oximes with new scaffolds combining high affinity and reactivatability toward BChE in plasma to generate an effective pseudocatalytic scavenger (Kovarik et al 2010;Radić et al 2013;Sit et al 2014). …”

Sarin (GB, O-isopropyl methylphosphonofluoridate) neurotoxicity: critical review

“…It acts as a bioscavenger, like a sponge to absorb and degrade OP compounds (e.g. nerve agents and insecticides, Radić et al, 2013; Abou-Donia et al, 2016). Although BChE represents the most promising stoichiometric bioscavenger for protecting against acute cardiac and neurological toxicity from OPs, it is unsuitable for clinical use due to the large quantities that are needed to treat a single patient (Saxena et al 2008).…”

HLö-7 - A REVIEW OF ACETYLCHOLINESTERASE REACTIVATOR AGAINST ORGANOPHOSPHOROUS INTOXICATION

“…9). 6,[28][29][30] 75 Uncharged reactivators represent a new hope in the therapy of OP intoxication. However, their potential implication in the OP-countermeasure is still on the long road ahead.…”