In vitro oxime protection of human red blood cell acetylcholinesterase inhibited by diisopropyl‐fluorophosphate

Abstract

Oximes are enzyme reactivators used in treating poisoning with organophosphorus cholinesterase (AChE) inhibitors. The oxime dose which can be safely administered is limited by the intrinsic toxicity of the substances such as their own AChE-inhibiting tendency. Clinical experience with the available oximes is disappointing. To meet this need, new AChE reactivators of potential clinical utility have been developed. The purpose of the study was to estimate in vitro both the intrinsic toxicity and the extent of possible protection conferred by established (pralidoxime, obidoxime, HI-6, methoxime, trimedoxime) and experimental (K-type) oximes, using diisopropyl-fluoro-phosphate (DFP) as an AChE inhibitor. The IC50 of DFP against human red blood cell AChE was determined ( approximately 120 nm). Measurements were then repeated in the presence of increasing oxime concentrations, leading to an apparent increase in DFP IC50. Calculated IC50 values were plotted against oxime concentrations to obtain an IC50 shift curve. The slope of this shift curve (tan alpha) was used to quantify the magnitude of the protective effect (nm IC50 increase per microm oxime). We show that, in the case of a linear relationship between oxime concentration and IC50, the binding constant K, determined using the Schild equation, equals IC50/DFP/tan alpha. Based on the values of tan alpha and of the binding constant K, some of the new K-oxime reactivators are far superior to pralidoxime (tan alpha = 0.8), obidoxime (1.5), HI-6 (0.8), trimedoxime (2.9) and methoxime (5.9), with K-107 (17), K-108 (20), and K-113 (16) being the outstanding compounds.

Oxime K027: novel low-toxic candidate for the universal reactivator of nerve agent- and pesticide-inhibited acetylcholinesterase

“…In the case of pesticides, it was able to reactivate AChE inhibited by all tested members of this family. This is in very good agreement with results shown in former studies [24][25][26][27][28][29][30][31][32][33][34][35][36] . Oxime K027 was tested at two different concentrations, which had already been selected earlier in the study of Kuca and Cabal to capture the promising compounds 7,40 .…”

“…Subsequently, they confirmed their in vitro results using in vivo studies. According to this group, oxime K027 seems to be, at present, the most promising candidate to replace obidoxime ( Figure 1) in the treatment of organophosphorus pesticide poisonings [24][25][26][27][28][29][30][31][32][33][34][35][36] . As mentioned above, in the case of nerve-agent reactivation, the obtained results were not so promising.…”

Comparative determination of the efficacy of bispyridinium oximes in paraoxon poisoning / Usporedno određivanje učinkovitosti bispiridinijevih oksima pri trovanju paraoksonom

“…Structurally, they are bispyridinium oximes that differ in the length of the connection chain between two pyridinium rings, the position of the oxime group, and the number of oxime groups in a molecule. Promising results using several of the previously mentioned oximes were obtained for poisoning by the nerve agent tabun, as well as in the case of pesticide poisoning (8,14,(19)(20)(21)(22)(23)(24)(25)(26)(27)(28)(29). Although the use of OP pesticides is under restriction in most parts of the world, especially in developed countries, some, such as parathion, are still widely (mis)used (30).…”

“…To be more precise, oximes K027 and K048 were found to be potent reactivators of the erythrocyte AChE in in vitro studies with methyl-, ethyl-paraoxon and DFP (23,(25)(26)(27)29). Thus, it seems that these compounds have a pharmacological effect indeed related to the reactivation of paraoxon-inhibited AChE, and -what is even more important -these oximes can be used at lower doses, applicable for human use.…”

Reactivation Potency of the Acetylcholinesterase Reactivator Obidoxime Is Limited

“…Obidoxime is the only accessible reactivator available for the civilian sector in the Czech Republic. Its reactivation potency is according to the literature not so good to think that it is a universal antidote [21][22][23][24] . In our in vitro experiment, we confirmed this statement.…”