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The pyridinium oxime therapy for treatment of organophosphate poisoning is a well established, but not sufficient method. Recent trends also focus on prophylaxis as a way of preventing even the entrance of organophosphates into the nervous system. One of the possible prophylactic methods is increasing the concentration of butyrylcholinesterase in the blood with the simultaneous administration of butyrylcholinesterase reactivators, when the enzyme is continuously reactivated by oxime. This article summarizes and sets forth the structural differences between butyrylcholinesterase and acetylcholinesterase, essential for the future design of butyrylcholinesterase reactivators. Butyrylcholinesterase lacks the reactivator aromatic binding pocket found in acetylcholinesterase, which is itself a part of the acetylcholinesterase peripheral anionic site. This difference finally renders the current acetylcholinesterase reactivators, when used in butyrylcholinesterase, non-functional. [ABSTRACT FROM AUTHOR]

Trimedoxime is a bisquaternary oxime that is widely used in the treatment of organophosphorous poisoning caused by tabun and paraoxon. We tested its affinity to acetylcholinesterase (AChE), its mechanism of interaction and effect on the cholinergic system of the rat bladder. The half maximal inhibitory concentration (IC50) of trimedoxime to recombinant AChE was found to be 82.0 mM ± 30.1 mM. This represents a weak inhibition. Its interaction with AChE seems to be very similar to obidoxime - one aromatic nucleus interacts with the peripheral anionic site and the other with the residues TYR337 and TYR341 inside the cavity. Also the oxime moiety is moving towards the catalytic triade ready for the reactivation of the inhibited AChE. In the organ bath experiment no significant effect of trimedoxime was observed on the contraction of the detrusor caused by the muscarinic agonist metacholine. [ABSTRACT FROM AUTHOR]

The article presents an in vitro study of three potential acetylcholinesterase (AChE) reactivators taken from a monoquaternary reactivator pralidoxime. The compounds used in the study include pyridinium-2-aldoxime-4- carbamoyl-N-methyl iodide, pyridinium-2-aldoxime-4-ethoxycarbonyl-N-methyl iodide, and pyridinium-2-aldoxime-5-ethoxycarbonyl-N-methyl iodide. Results showed that none of the tested oximes was able to reactivate cyclosarin-inhibited AChE.

In this work in vitro evaluation of the reactivation potency of the newly synthesized reactivators for acetylcholinesterase (AChE; EC 3.1.1.7) is described. Using this method, reactivation potency of 21 potential reactivators of AChE inhibited by the nerve agent sarin has been evaluated. We have confirmed the fact that currently the most promising AChE reactivator, HI-6, is the most effective reactivator of sarin-inhibited AChE. There are only three AChE reactivators—HI-6, TO033 and TO047—able to satisfactorily reactivate sarin-inhibited AChE at the concentration 10 -5 M, which is nontoxic for human use. On the other hand, there are 14 AChE reactivators, that are able to reactivate sarin-inhibited AChE at the concentration 10 -3 M. However, this concentration of reactivator is probably toxic for human use. [ABSTRACT FROM AUTHOR]

A comparison of one mono- and seven bisquaternary acetylcholinesterase (AChE) reactivators of acetylcholinesterase inhibited by VX agent was performed. As a source of the acetylcholinesterase, a rat brain homogenate was taken. There were significant differences in reactivation potency of all tested oximes. The oxime TO205 seems to be the most efficacious followed by TO046, HI-6, HS-6, K027, obidoxime, MMC and 2-PAM. In addition, the results of this study showed that the reactivation potency of the tested reactivators depends on many factors - such as the number of pyridinium rings, the number of oxime groups and their position, as well as the length and the shape of linkage bridge between two pyridinium rings. [ABSTRACT FROM AUTHOR]

Two methods for the synthesis of a new unsymmetric bispyridinium oxime-1-(4-hydroxyiminomethylpyridinium)-3-(carbamoylpyridinium)propane dibromide are described. In vitro efficacy of this new oxime to reactivate sarin-inhibited acetylcholinesterase has been evaluated. [Copyright &y& Elsevier]

Nerve agents (NA) pose as a great risk in the modern world. NA from the V-series, such as VX, are currently recognized as the most toxic among those compounds. However, the emergence of new classes of toxicants recently included in the Chemical Weapons Convention (CWC), such as the A-series NA, a class of organophosphorus compounds related to phosphoramidates, pose a new source of concern due to the lack of information. In order advance in the investigation on the toxicity of such toxic chemicals, we performed in vitro studies to compare representatives of the V- and A-series using affordable surrogates. Results suggest a similar inhibition potency between both agents. • Nerve agents are a great concern in the modern world. • V-series nerve agents are the most toxic organophosphorus compounds known. • There are insufficient data on A-series nerve agents. • Preliminary in vitro study comparing of V- an A-series' surrogates were performed. • Toxicity of V- an A-series' surrogates were comparable under assays' conditions. [ABSTRACT FROM AUTHOR]

Abstract: Kinetic parameters were evaluated for inhibition of native and reactivation of tabun-inhibited human erythrocyte acetylcholinesterase (AChE, EC 3.1.1.7) and human plasma butyrylcholinesterase (BChE, EC 3.1.1.8) by three bispyridinium para-aldoximes with butane (K074), but-2-ene (K075) or xylene-like linker (K114). Tested aldoximes reversibly inhibited both cholinesterases with the preference for binding to the native AChE. Both cholinesterases showed the highest affinity for K114 (K i was 0.01mM for AChE and 0.06mM for BChE). The reactivation of tabun-inhibited AChE was efficient by K074 and K075. Their overall reactivation rate constants were around 2000min−1 M−1, which is seven times higher than for the classical bispyridinium para-aldoxime TMB-4. The reactivation of tabun-inhibited AChE assisted by K114 was slow and reached 90% after 20h. Since the aldoxime binding affinity of tabun-inhibited AChE was similar for all tested aldoximes (and corresponded to their K i ), the rate of the nucleophilic displacement of the phosphoryl-moiety from the active site serine was the limiting factor for AChE reactivation. On the other hand, none of the aldoximes displayed a significant reactivation of tabun-inhibited BChE. Even after 20h, the reactivation maximum was 60% for 1mM K074 and K075, and only 20% for 1mM K114. However, lower BChE affinities for K074 and K075 compared to AChE suggest that the fast tabun-inhibited AChE reactivation by these compounds would not be obstructed by their interactions with BChE in vivo. [Copyright &y& Elsevier]

Abstract: Butyrylcholinesterase is considered to be an endogenous stoichiometric bioscavenger of organophosphorus compounds (OPs), but due to limited concentration of BChE in the organism, stoichiometric reduction of OP is not always sufficient. This can be improved by creating a pseudo-catalytic scavenger adding oximes as reactivators of inhibited exogenous BChE. In order to improve the BChE bioscavenging function in tabun or paraoxon poisoning, we tested in vitro reactivation of phosphorylated human plasma BChE by bispyridinium oximes varying in the length and type of the linker between rings, and in the position of the oxime group on the ring. Among the tested oximes, the most potent reactivators of tabun-inhibited BChE were K117 [1,1′-(2,2′-oxybis(ethane-2,1-diyl))bis(4-hydroxyiminomethyl pyridinium) bromide] and K127 [4-carbamoyl-1-(2-(2-(4-(hydroxyiminomethyl) pyridinium-1-yl)ethoxy)ethyl)pyridinium bromide]. Reactivation by these oximes (1mM) reached about 50% of control activity after only 20min; however, reactivation stopped at 70%. Reactivation of paraoxon-inhibited BChE by all of the selected oximes was slow. Using molecular mechanics, we performed docking of the oximes to tabun-inhibited BChE in order to discuss possible structural modifications of bispyridinium oximes to improve reactivation of phosphorylated BChE. [ABSTRACT FROM AUTHOR]

Abstract: The increased concern about terrorist use of nerve agents prompted us to search for new more effective oximes against tabun and soman poisoning. We investigated the interactions of five bispyridinium oximes: K027 [1-(4-hydroxyiminomethylpyridinium)-3-(4-carbamoylpyridinium) propane dibromide], K048 [1-(4-hydroxyiminomethylpyridinium)-4-(4-carbamoylpyridinium) butane dibromide], K033 [1,4-bis(2-hydroxyiminomethylpyridinium) butane dibromide], TMB-4 [1,3-bis(4-hydroxyiminomethylpyridinium) propane dibromide] and HI-6 [(1-(2-hydroxyiminomethylpyridinium)-3-(4-carbamoylpyridinium)-2-oxapropane dichloride)] with human erythrocyte acetylcholinesterase (AChE; E.C. 3.1.1.7) and their effects on tabun- and soman-poisoned mice. All the oximes reversibly inhibited AChE, and the enzyme-oxime dissociation constants were between 17 and 180μM. Tabun-inhibited AChE was completely reactivated by TMB-4, K027 and K048, with the overall reactivation rate constants of 306, 376 and 673min−1 M−1, respectively. The reactivation of tabun-inhibited AChE by K033 reached 50% after 24h, while HI-6 failed to reactivate any AChE at all. Soman-inhibited AChE was resistant to reactivation by 1mM oximes. All studied oximes protected AChE from phosphorylation with both soman and tabun. In vivo experiments showed that the studied oximes were relatively toxic to mice; K033 was the most toxic (LD50 =33.4mg/kg), while K027 was the least toxic (LD50 =672.8mg/kg). The best antidotal efficacy was obtained with K048, K027 and TMB-4 for tabun poisoning, and HI-6 for soman poisoning. Moreover, all tested oximes showed no cytotoxic effect on several cell lines in concentrations up to 0.8mM. The potency of the oximes K048 and K027 to protect mice from five-fold LD50 of tabun and their low toxicity make these compounds leading in the therapy of tabun poisoning. The combination of HI-6 and atropine is the therapy of choice for soman poisoning. [Copyright &y& Elsevier]