Abstract
Organophosphate (OP) chemical warfare nerve agents and pesticides are potent, irreversible inhibitors of acetylcholinesterase (AChE), and paraoxon is often used as a surrogate compound in the studies of OP poisoning. For a truly effective treatment of OP poisoning, it is desirable that a protein-based OP bioscavenger can react with OP significantly faster than AChE reacting with OP to protect AChE from further inhibition reaction with OP. In the present study, our in vitro reactivity assays revealed that CocH3-Fc(M3), a potent cocaine hydrolase engineered from human butyrylcholinesterase (BChE), has a ∼20-fold improved bimolecular rate constant for the reaction with paraoxon compared to wild-type BChE. Due to the improved in vitro reactivity with paraoxon, CocH3-Fc(M3) at a modest dose of 25 mg/kg was able to effectively rescue all mice that had been injected with a lethal dose of 0.66 mg/kg paraoxon and accelerate the recovery of the mice from paraoxon-induced toxicity symptoms. All the in silico, in vitro, and in vivo data consistently suggest that CocH3-Fc(M3) can be used to effectively detoxify paraoxon.