Chemico-Biological Interactions 187 (2010) 259–264 Contents lists available at ScienceDirect Chemico-Biological Interactions journal homepage: www.elsevier.com/locate/chembioint Evaluation of medical countermeasures against organophosphorus compounds: The value of experimental data and computer simulations Franz Worek a,∗ , Nadine Aurbek a , Nadja M. Herkert a , Harald John a , Michael Eddleston b , Peter Eyer c , Horst Thiermann a a Bundeswehr Institute of Pharmacology and Toxicology, Munich, Germany b National Poisons Information Service-Edinburgh, Royal Infirmary of Edinburgh, Edinburgh, UK c Walther-Straub-Institute of Pharmacology and Toxicology, Ludwig-Maximilians-University Munich, Munich, Germany article info Article history: Available online 13 November 2009 Keywords: Organophosphorus compounds Oximes AChE Reactivation Computer model abstract Despite extensive research for more than six decades on medical countermeasures against poisoning by organophosphorus compounds (OP) the treatment options are meagre. The presently established acetyl- cholinesterase (AChE) reactivators (oximes), e.g. obidoxime and pralidoxime, are insufficient against a number of nerve agents and there is ongoing debate on the benefit of oxime treatment in human OP pes- ticide poisoning. Up to now, the therapeutic efficacy of oximes was mostly evaluated in animal models but substantial species differences prevent direct extrapolation of animal data to humans. Hence, it was considered essential to establish relevant experimental in vitro models for the investigation of oximes as antidotes and to develop computer models for the simulation of oxime efficacy in different scenarios of OP poisoning. Kinetic studies on the various interactions between erythrocyte AChE from various species, structurally different OP and different oximes provided a basis for the initial assessment of the ability of oximes to reactivate inhibited AChE. In the present study, in vitro enzyme-kinetic and pharmacokinetic data from a minipig model of dimethoate poisoning and oxime treatment were used to calculate dynamic changes of AChE activities. It could be shown that there is a close agreement between calculated and in vivo AChE activities. Moreover, computer simulations provided insight into the potential and limitations of oxime treatment. In the end, such data may be a versatile tool for the ongoing discussion of the pros and cons of oxime treatment in human OP pesticide poisoning. © 2009 Elsevier Ireland Ltd. All rights reserved. 1. Introduction Worldwide 3 million annual cases of human poisoning by organophosphorus (OP) pesticides with up to 300,000 fatalities are estimated [1]. These numbers and the persisting threat of use of pesticides or highly toxic OP-based nerve agents by terrorists [2] emphasizes the urgent need for effective therapy. Standard treat- ment of OP poisoning comprises an anticholinergic, e.g. atropine, and an acetylcholinesterase (AChE) reactivator (oxime) [3,4]. This therapeutic approach was developed in the early 1950s; over the following decades, efforts were put into the development of more effective oximes and improved treatment protocols [5]. Despite the fact that oximes are regarded a major component for causal drug therapy of OP poisoning there is an ongoing debate on the therapeutic value of oximes [6,7]. A vast amount of experi- ∗ Corresponding author at: Bundeswehr Institute of Pharmacology and Toxicol- ogy, Neuherbergstrasse 11, 80937 Munich, Germany. Tel.: +49 89 3168 2930; fax: +49 89 3168 2333. E-mail address: FranzWorek@Bundeswehr.org (F. Worek). mental in vitro and in vivo data clearly demonstrates the ability of oximes to reactivate OP-inhibited AChE and gives insight into the potential and limitations of individual compounds [4]. However, surprisingly few data from well designed clinical trials are available and the findings of these studies are not consistent [8–11]. The major mechanism of OP is covalent binding to AChE leading to inhibition of the enzyme and subsequent cholinergic overstim- ulation [12]. Human and animal AChE is easily available by using erythrocytes or tissue as enzyme source. Hence, it is possible to analyse the various reactions between AChE, OP and oximes in vitro and to determine the distinct kinetic constants [4]. In the past, much work has been done with AChE from different species demon- strating substantial differences in the kinetic properties of oximes between human and animal AChE [13–15]. Although these data provided a valuable basis for the evaluation of the ability of oximes to reactivate OP-inhibited AChE it remained uncertain whether erythrocyte AChE may reflect the different reactions at synaptic (muscle) AChE. Recently, use of a perfusion model for the real-time determination of membrane-bound AChE activity [16] enabled the comparison of human erythrocyte and muscle AChE with respect to reactivation of OP-inhibited enzyme by oximes. This study clearly 0009-2797/$ – see front matter © 2009 Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.cbi.2009.11.009