A simple acetylcholinesterase inhibition assay for the quantification of the nerve agent VX: Application in a Franz cell model with rat skin and various decontaminants.

Abstract

The medical community continues to regard organophosphate nerve agent poisoning as a significant concern. Due to the lack of therapeutic options for the nicotinic signs and symptoms for certain agents (e.g. tabun), decontamination remains a pivotal aspect of patient care. Current models to study skin penetration of nerve agents and the respective decontamination rely on expensive, laborious and not readily available methods, i.e. GC-MS-MS and LC-MS-MS. Hence, we used a photometric acetylcholinesterase (AChE) inhibition assay for the quantification of nerve agents, relying on VX as a model substance. Inhibition curves were determined in a time dependent manner and consecutively slopes of the tangents and the calculated standard curve were used for quantification. The concentration dependent rate constant of VX with human AChE (k₁) and the inhibitor concentration [IX] were used to plot 1/k₁ against 1/[IX]-(1-α). α equals [S]/(K_m+[S]), [S] being the substrate and K_m the Michaelis-Menten-constant. A Franz cell model served as an example to determine the robustness and suitability of the assay to study penetration rates and the success of decontamination. The inhibition assay delivers robust results, even when the decontamination protocol interferes with the colorimetric Ellman assay. Hence, we provide a generic, low-cost method for the quantification of nerve agents in a model studying the decontamination of nerve agents.