Reactivation of zebrafish acetylcholinesterase by novel oxime compounds following inhibition by organophosphate pesticides
- Erica Fradinger, Associate Professor of Biology, Whittier College
- Palmer Taylor, Dean of Pharmacy, Skaggs School of Pharmacy and Pharmaceutical Sciences, University of California San Diego Skaggs School of Pharmacy and Pharmaceutical Sciences
- Zoran Radić, Associate Project Scientist, University of California San Diego Skaggs School of Pharmacy and Pharmaceutical Sciences
Organophosphates (OPs) are a class of pesticides and nerve agents whose mechanism of toxicity involves irreversible inhibition of acetylcholinesterase (AChE). This leads to hyperstimulation by cholinergic neurons due to a slower catalytic hydrolysis of acetylcholine released at the synaptic cleft. Current antidotal treatment involves the use of oxime reactivators such as 2-PAM, which have limited efficacy in vivo due to their inability to cross the blood-brain barrier. Similarly, passage of 2-PAM as a quaternary antidote into the circulation and CNS of fish may be limiting. Here, we examine the suitability of the zebrafish (Danio rerio) model system for in vitro and in vivo tests of antidotal efficacy by comparing the inhibition and reactivation kinetics of purified human AChE with zebrafish AChE isolated from tissue homogenates. Inhibition kinetics for zebrafish AChE was determined for two OPs, chlorpyrifos oxon and dichlorvos. Chlorpyrifos oxon was found to be a more potent inhibitor of AChE activity than dichlorvos. We then compared the zebrafish AChE reactivation kinetics of two tertiary amine containing oximes, to the quaternary antidote, 2-PAM. All three oximes reactivated zebrafish AChE after OP inhibition, enabling us to begin to compare in vitro reactivation kinetics with protection from OP toxicity. Data revealed that zebrafish AChE demonstrated similar inhibition and reactivation kinetics to human AChE. Therefore, the zebrafish emerges as an appropriate and convenient model system for the in vivo study of novel oxime AChE reactivators.