In vivo protection of diisopropylphosphorofluoridate (DFP) poisoning by three bis-quaternary 2 -(hydroxyimino) -N -(pyridin-3-yl) acetamide derivatives in Swiss mice

This study reports efficacy of three bis pyridinium derivatives of 2-(hydroxyimino)- N-(pyridine-3-yl) acetamide in terms of survival, reactivation of brain and serum acetylcholinesterase (AChE) activity in diisopropylphosphorofluoridate (DFP) intoxicated Swiss albino male mice. LD50 of DFP (3.9 mg/kg, s.c.) and new oximes, HNK-102, HNK-106, HNK-111, (282.8, 35.0 and 35.0 mg/kg respectively, i.m.) was determined. Various doses of DFP and oximes as treatment doses with atropine (10 mg/kg, i.p.) were used to determine protection index (PI). For time dependent maximum AChE inhibition, two doses of DFP (0.20 and 2.0 LD50) were chosen. At optimized time i.e. Sixty minutes, IC50 value was calculated as 0.249 and 0.017 LD50 of brain and serum AChE, respectively. Shift of DFP induced brain AChE IC50 curves to right was observed at 0.20 LD50 treatment dose of oximes with respect to 2-PAM. These findings propose that new HNK series of oximes are effective antidote, compared to that of 2-PAM in vivo.

Total effects of contact and residual exposure of bifenthrin and λ-cyhalothrin on the predatory mite Galendromus occidentalis (Acari: Phytoseiidae)

Pyrethroid insecticides are generally regarded as acutely toxic to predatory phytoseiid mites; however, persistence of hull split spray pyrethroid residues on almond trees and their effects on phytoseiids have not been quantified over time. Hull split, the separation of the almond hull along the suture, exposes the new crop nuts to infestation by Amyelois transitella (Walker) larvae, and is the preferred timing for insecticides applied for their control. Galendromus occidentalis (Nesbitt) is the most important phytoseiid biocontrol agent for web-spinning spider mites in California (USA) almond orchards, and the impact of bifenthrin and λ-cyhalothrin pyrethroid residue on their survival, fertility, and fecundity was determined. The total effects of direct contact with esfenvalerate, permethrin, bifenthrin and λ-cyhalothrin were also evaluated for comparison. The total effects (E) of direct contact treatments of the four pyrethroids ranged from 77.8 % for esfenvalerate to 98.8 % for bifenthrin. Both bifenthrin and λ-cyhalothrin twig residue would be considered harmful (IOBC class 4) following field application at hull split timing. Bifenthrin twig residue would be considered slightly harmful (IOBC class 2) for up to 3.5 months and harmless (IOBC class 1) after 6 months. λ-cyhalothrin residue would be considered moderately harmful (IOBC class 3) for up to 3.5 months following application and harmless (IOBC class 1) after 6 months. Bifenthrin and λ-cyhalothrin twig residue on treated trees significantly reduced G. occidentalis female survival for up to 6 months post-treatment, however total effects (E) classify these residues as harmless (IOBC class 1) after 6 months. Harmful effects of direct and residual exposure following application have implications for the use of these pyrethroids in an integrated mite management program for perennial crops.

In vitro reactivation kinetics of paraoxon- and DFP-inhibited electric eel AChE using mono- and bis-pyridinium oximes

Oxime-assisted reactivation of organophosphate (OP)-inhibited acetylcholinesterase (AChE) is a crucial step in the post-inhibitory treatment of OP intoxication. The limited efficacy of oxime reactivators for all OP nerve agents and pesticides led to the development of various novel oximes and their thorough kinetic investigations. Hence, in the present investigation, we have tested 10 structurally different pyridinium oxime-based reactivators for their in vitro potency to reactivate paraoxon- and DFP-inhibited electric eel AChE. From structure activity relationship point of view, various oximes such as mono-quaternary (2-PAM, K100, K024) and bis-quaternary symmetric (obidoxime, TMB-4) and asymmetric (K027, K048, K203, K618, K628) oximes bearing different connecting linkers (oxybismethylene, trimethylene, propane, butane, butene, and xylene) have been studied. The observed kinetic data demonstrate that not only the position of oxime group is decisive for the increased reactivation ability of oximes, but the role of connecting linker is also significant. Oximes with aliphatic linkers are superior reactivators than the oximes with unsaturated and aromatic linkers. The optimal chain length for plausible reactivation ability for paraoxon- and DFP-inhibited AChE is 3 or 4 carbon-carbon connecting linker between prydinium rings.

Avoidance behaviour response and esterase inhibition in the earthworm, Lumbricus terrestris, after exposure to chlorpyrifos

The avoidance response of earthworms to polluted soils has been standardised using a simple and low-cost test, which facilitates soil toxicity screening. In this study, the avoidance response of Lumbricus terrestris was quantified in chlorpyrifos-spiked soils, depending on the pesticide concentration and exposure duration. The inhibition of acetylcholinesterase (AChE) and carboxylesterase (CbE) activities was also determined as indirect measures of pesticide bioavailability. The effects of different chlorpyrifos concentrations were examined in a standardised test (two-chamber system) with 0.6, 3 and 15 mg/kg chlorpyrifos. A modification of the test involved a pre-exposure step (24, 48 or 72 h) in soils spiked with 15 mg/kg. In both protocols, earthworms were unable to avoid the contaminated soils. However, the esterase activities showed that all earthworms were exposed to chlorpyrifos. Acetylcholinesterase activity did not change in earthworms in the standardised behavioural test (0.58 ± 0.20 U/mg protein, mean ± SD; n = 72), whereas the CbE activity was significantly inhibited (62-87 % inhibition) in earthworms exposed to 3 and 15 mg/kg. In the modified test, earthworms had greatly inhibited AChE activity (0.088 ± 0.034 U/mg protein, n = 72), which was supported by reactivation of the inhibited enzyme activity in the presence of pralidoxime (2-PAM). Similarly, the CbE activity was significantly inhibited in earthworms with all treatments. This study suggests that the avoidance behaviour test for organophosphorus-contaminated soils could be supported by specific biomarkers to facilitate a better understanding of pesticide exposure and toxicity during this test.

[Specific features of the anticonvulsant effect of memantine in mice intoxicated with a model organic phosphate]

The effect of memantine administration has been studied on the model of mice poisoning with an anticholinesterase compound. It is established that the memantine action is due to its influence on the cholinesterase activity in the brain, blood plasma, and erythrocytes in addition to its NMDA-blocking action. Memantine promotes oxime-induced erythrocyte enzyme reactivation on the model of mice poisoning with anticholinesterase compound (0.8 LD50).

Cerium chloride improves protein and carbohydrate metabolism of fifth-instar larvae of Bombyx mori under phoxim toxicity

The organophosphorus pesticide poisoning of the silkworm Bombyx mori is one of the major events causing serious damage to sericulture. Added low-dose rare earths are demonstrated to increase resistance in animals. However, very little is known about whether or not added CeCl₃ can increase resistance of silkworm to phoxim poisoning. The present findings suggested that added CeCl₃ to mulberry leaves markedly increased contents of protein, glucose and pyruvate, and carbohydrate metabolism-related enzyme activities, including lactate dehydrogenase, succinate dehydrogenase and malate dehydrogenase, and attenuated free amino acids, urea, uric acid and lactate levels and inhibited the protein metabolism-related enzymes activities, such as protease, alanine aminotransferase and aspartate aminotransferase in the haemolymph of B. mori, under phoxim toxicity. These findings suggest that added CeCl₃ may improve protein and carbohydrate metabolisms, thus leading to increases of growth and survival rate of B. mori under phoxim stress.

The history of cholinesterase reactivation: hydroxylamine and pyridinium aldoximes

Hydroxylamine (NH2OH) the substance which will turn out to be of importance to those interested in the treatment of organophosporus cholinesterase inhibitor exposure, was synthesized by Wilhem Clemens Lossen in 1865 while working in Halle as an assistant in the laboratory of Wilhelm Heinrich Heintz. The Lossen synthesis generated hydroxylamine in aqueous solution. Anhydrous hydroxylamine was prepared almost simultaneously by Lobry de Bruyn and Crismer (1891). Using hydroxylamine as a starting point Meyer synthesized aldoximes and ketoximes (1897). Lange, a PhD student of Ladenburg, isolated 2-methyl-pyridine (alpha-picoline). Some fifty years later Wilson, working in the laboratory of Nachmansohn, demonstrated the ability of hydroxylamine to reactivate cholinesterase inhibited by organophosphates. Finally Wilson and Ginsburg using 2-methyl-pyridine as a starting point synthesized the first pyridinium aldoxime reactivator of clinical relevance, pralidoxime (1955).

Correlation between butyrylcholinesterase variants and sensitivity to soman toxicity

Butyrylcholinesterase (BChE) is synthesized in the liver and found in high concentrations in blood plasma, liver, heart, pancreas, vascular endothelium, skin, brain white matter, smooth muscle cells and adipocytes. BChE is a non specific enzyme that hydrolyzes different choline esters (succinylcholine, mivacurium) and many other drugs such as aspirin, cocaine and procaine. The enzyme is also considered as a bioscavenger due to its ability to neutralize the toxic effects of organophosphorus compounds (nervous system fs agents) such as soman. BChE displays several polymorphisms that influence its serum activity; therefore they could determine the individual sensitivity to chemical nerve agents. In this study, we investigated the correlation between BChE variants and the degree of enzyme inhibition and reactivation after soman application on blood samples of 726 individuals. The blood samples of individuals expressing abnormal variants, were more sensitive to soman compared to variants of homozygotes and heterozygotes for U-allele. We found significant differences in the degree of enzyme reactivation between different variants (with and without U-presence).

A conjugate of pyridine-4-aldoxime and atropine as a potential antidote against organophosphorus compounds poisoning

A conjugate of pyridine-4-aldoxime and atropine (ATR-4-OX) was synthesized and its antidotal efficiency was tested in vitro on tabun- or paraoxon-inhibited acetylcholinesterase (AChE) of human erythrocytes as well as in vivo using soman-, tabun- or paraoxon-poisoned mice. Its genotoxic profile was assessed on human lymphocytes in vitro and was found acceptable for further research. ATR-4-OX showed very weak antidotal activity, inadequate for soman or tabun poisoning. Conversely, it was effective against paraoxon poisoning both in vitro and in vivo. All animals treated with 5 % or 25 % LD(50) doses of the new oxime survived after administration of 10.0 or 16.0 LD(50) doses of paraoxon, respectively. Based on the persistence of toxicity symptoms in mice, the atropine moiety had questionable effects in attenuating such symptoms. It appears that ATR-4-OX has a therapeutic effect related to the reactivation of phosphylated AChE, but not to receptor antagonization.

A cembranoid protects acute hippocampal slices against paraoxon neurotoxicity

Many neurotoxic organophosphates (OPs) inhibit acetylcholinesterase (AChE) and as a result can cause a life threatening cholinergic crisis. Current medical countermeasures, which typically include atropine and oximes target the cholinergic crisis and are effective in decreasing mortality but do not sufficiently protect against delayed neurological deficits. There is, therefore, a need to develop neuroprotective drugs to prevent long-term neurological deficits. We used acute hippocampal slices to test the hypothesis that 4R,6R-cembratrienediol (4R) protects against functional damage caused by the OP paraoxon (POX). To assess hippocampal function, we measured synaptically evoked population spikes (PSs). Application of 4R reversed POX inhibition of PSs and the EC(50) of this effect was 0.8 μM. Atropine alone did not protect against POX neurotoxicity, but it did enhance protection by 4R. Pralidoxime partially regenerated AChE activity and protected against POX inhibition of PSs. 4R did not regenerate AChE suggesting that under our experimental conditions, the deleterious effect of POX on hippocampal function is not directly related to AChE inhibition. In conclusion, 4R is a promising neuroprotective compound against OP neurotoxins.

The effect of oxime reactivators on muscarinic receptors: functional and binding examinations

The antidotal treatment of organophosphorus poisoning is still a problematic issue since no versatile antidote has been developed yet. In our study, we focused on an interesting property, which does not relate to the reactivation of inhibited acetylcholinesterase (AChE) of some oximes, but refers to their anti-muscarinic effects which may contribute considerably to their treatment efficacy. One standard reactivator (HI-6) and two new compounds (K027 and K203) have been investigated for their antimuscarinic properties. Anti-muscarinic effects were studies by means of an in vitro stimulated atrium preparation (functional test), the [(3)H]-QNB binding assay and G-protein coupled receptor assay (GPCR, beta-Arrestin Assay). Based on the functional data HI-6 demonstrates the highest anti-muscarinic effect. However, only when comparing [(3)H]-QNB binding results and GPCR data, K203 shows a very promising compound with regard to anti-muscarinic potency. The therapeutic impact of these findings has been discussed.

In vitro effects of acetylcholinesterase inhibitors and reactivators on Complex I of electron transport chain

OBJECTIVES

Inhibition of the enzyme acetylcholinesterase (AChE) is the main mechanism both of therapeutic action of drugs for the treatment of Alzheimer's disease and toxic action of organophosphorus compounds. Various types of oximes reactivate AChE and are commonly used as antidotes against organophosphates (pesticides, nerve agents).

METHODS

Effects both of AChE inhibitors (tacrine, 7-methoxytacrine) and oximes (pralidoxime, trimedoxime, obidoxime, methoxime, HI-6) on Complex I of electron transport chain (ETC) were examined. The enzyme activity was measured spectrophotometrically in crude mitochondrial fraction isolated from pig brain.

RESULTS

Our results showed statistically significant Complex I inhibition by tacrine, other drugs did not affect the enzyme activity significantly.

CONCLUSIONS

These observations suggest the possibility of tacrine-induced side effects related to disturbance in ETC. On the contrary, it seems that oximes do not affect cellular energetic metabolism.

Nanoparticulate transport of oximes over an in vitro blood-brain barrier model

Background

Due to the use of organophosphates (OP) as pesticides and the availability of OP-type nerve agents, an effective medical treatment for OP poisonings is still a challenging problem. The acute toxicity of an OP poisoning is mainly due to the inhibition of acetylcholinesterase (AChE) in the peripheral and central nervous systems (CNS). This results in an increase in the synaptic concentration of the neurotransmitter acetylcholine, overstimulation of cholinergic receptors and disorder of numerous body functions up to death. The standard treatment of OP poisoning includes a combination of a muscarinic antagonist and an AChE reactivator (oxime). However, these oximes can not cross the blood-brain barrier (BBB) sufficiently. Therefore, new strategies are needed to transport oximes over the BBB.

Methodology/Principal Findings

In this study, we combined different oximes (obidoxime dichloride and two different HI 6 salts, HI 6 dichloride monohydrate and HI 6 dimethanesulfonate) with human serum albumin nanoparticles and could show an oxime transport over an in vitro BBB model. In general, the nanoparticulate transported oximes achieved a better reactivation of OP-inhibited AChE than free oximes.

Conclusions/Significance

With these nanoparticles, for the first time, a tool exists that could enable a transport of oximes over the BBB. This is very important for survival after severe OP intoxication. Therefore, these nanoparticulate formulations are promising formulations for the treatment of the peripheral and the CNS after OP poisoning.

New original in vitro method to assess cholinesterase reactivity in organophosphate poisoning

Assessment of organophosphate poisoning could benefit from a safe, non-expensive, easy to perform, quick (< 1 hour) test, which evaluates the level of cholinesterase activity "in vitro" regarding to the capability of oximes to reactivate OF-blocked cholinesterase. In the proposed protocol, 0.5 mL of sample serum is incubated, prior to the evaluation of level of cholinesterase activity, with 5 microL of a Toxogonin dilution (0.125 mg) for 30 minutes at 37 degrees C. For the standardization of the newly proposed protocol, several important issues were documented in the present article. The new original method of assessing cholinesterase reactivability will consist in an advantage for the diagnosis, prognostic evaluation and therapeutic orientation in OF intoxication.

Inhibition, recovery and oxime-induced reactivation of muscle esterases following chlorpyrifos exposure in the earthworm Lumbricus terrestris

Assessment of wildlife exposure to organophosphorus (OP) pesticides generally involves the measurement of cholinesterase (ChE) inhibition, and complementary biomarkers (or related endpoints) are rarely included. Herein, we investigated the time course inhibition and recovery of ChE and carboxylesterase (CE) activities in the earthworm Lumbricus terrestris exposed to chlorpyrifos, and the ability of oximes to reactivate the phosphorylated ChE activity. Results indicated that these esterase activities are a suitable multibiomarker scheme for monitoring OP exposure due to their high sensitivity to OP inhibition and slow recovery to full activity levels following pesticide exposure. Moreover, oximes reactivated the inhibited ChE activity of the earthworms exposed to 12 and 48 mg kg(-1) chlorpyrifos during the first week following pesticide exposure. This methodology is useful for providing evidence for OP-mediated ChE inhibition in individuals with a short history of OP exposure (< or = 1 week); resulting a valuable approach for assessing multiple OP exposure episodes in the field.

Pralidoxime--the gold standard of acetylcholinesterase reactivators--reactivation in vitro efficacy

OBJECTIVE

In this work, we aim to summarize the universality of this compound, its reactivation potential when different cholinesterase inhibitors are used.

BACKGROUND

Pralidoxime is considered as a gold standard of acetylcholinesterase reactivators--antidotes used in case of nerve agent poisonings. It has been commercially available for many years. However, several studies deem this oxime an old-fashion antidote.

METHODS

Pralidoxime was synthesized at our department. The reactivating efficacy was tested on 10% (w/v) rat brain homogenate that had been incubated with appropriate inhibitor for 30 minutes to reach 96% inhibition of AChE. Then, pralidoxime was added for 10 minutes. Measurements were performed at 25 degrees C, pH 8, and 10(-3) and 10(-5) M concentrations of AChE reactivators. The activities of brain AChE were measured by a potentiostatic method.

RESULTS

No sufficient reactivation was achieved at the concentration of 10(-5) M, which is a concentration that can be reached after administration of therapeutic doses. At a higher dose (10(-3) M), pralidoxime reactivated AChE inhibited by paraoxon, chlorpyrifos, Russian VX, VX and sarin.

CONCLUSION

From the obtained results, it is clear that pralidoxime seems to be a poor reactivator of AChE inhibited by organophosphorous AChE inhibitors and thus cannot be labeled as a universal reactivator (Tab. 1, Fig. 3, Ref. 31).

Toxicity and characterization of cholinesterase-inhibition induced by diisopropyl fluorophosphate in Artemia salina larvae

The acute toxicity of diisopropyl fluorophosphate (DFP) on three age classes of Artemia salina was evaluated. An increase in toxicity of this organophosphorous (OP) compound was found following longer development of A. salina larvae. The effects of pretreatment with the non-selective muscarinic antagonist atropine, the two reversible acetylcholinesterase inhibitors physostigmine and pyridostigmine, and the cholinesterase-reactivating oxime 2-pyridine aldoxime methoiodide (2-PAM), as individual and combined pretreatments, on DFP-induced lethality in 24h Artemia were also investigated. The lethal action of DFP was not prevented by pretreatment of 24h Artemia with atropine, physostigmine, and pyridostigmine, while 2-PAM proved effective against intoxication with this OP compound. The inhibitory effects of combinations of atropine (10(-5)M) plus 2-PAM or physostigmine were greater than those elicited by either drug alone, with the maximum protection afforded being 100%. Pretreatment with 2-PAM (10(-6)M) plus physostigmine or pyridostigmine was ineffective. These results suggest that the combinations of atropine plus 2-PAM or physostigmine are effective in the prevention of the lethal effects induced by DFP in A. salina larvae.

Comparison of the oxime-induced reactivation of rhesus monkey, swine and guinea pig erythrocyte acetylcholinesterase following inhibition by sarin or paraoxon, using a perfusion model for the real-time determination of membrane-bound acetylcholinesterase activity

Recently, a dynamically working in vitro model with real-time determination of membrane-bound human acetylcholinesterase (AChE) activity was shown to be a versatile model to investigate oxime-induced reactivation kinetics of organophosphate- (OP) inhibited enzyme. In this assay, AChE was immobilized on particle filters which were perfused with acetylthiocholine, Ellman's reagent and phosphate buffer. Subsequently, AChE activity was continuously analyzed in a flow-through detector. Now, it was an intriguing question whether this model could be used with erythrocyte AChE from other species in order to investigate kinetic interactions in the absence of annoying side reactions. Rhesus monkey, swine and guinea pig erythrocytes were a stable and highly reproducible enzyme source. Then, the model was applied to the reactivation of sarin- and paraoxon-inhibited AChE by obidoxime or HI 6 and it could be shown that the derived reactivation rate constants were in good agreement to previous results obtained from experiments with a static model. Hence, this dynamic model offers the possibility to investigate highly reproducible interactions between AChE, OP and oximes with human and animal AChE.

Study of efficacy of reactivator HI 6 in reactivation of immobilized acetylcholinesterase, inhibited by organophosphorus chemical warfare agents of the "G" series

Reactivation with bis quaternary aldoxime HI-6, chemical formula 1-(2-hydroxyamino-methylpyridinium)-3-(4-carbamoylpyridinium)-2-oxapropane dichloride of immobilized enzyme acetylcholinesterase inhibited by nerve agent type "G" was studied. This aldoxime is effective in reactivation of sarin-inhibited acetylcholinesterase. Substantially lower reactivation potency was observed with cyclosarin-inhibited enzyme and almost no effect was found for that acetylcholinesterase is the enzyme complex. HI 6 is completely ineffective towards the soman-inhibited enzyme: After a 2-minute inhibition of the enzyme with soman no ability to define reactivator the inhibited enzymes and complexes.

Efficacy of structural homoloques and isomers of pralidoxime in reactivation of immobilised acetylcholinesterase inhibited with sarin, cyclosarin and soman

OBJECTIVES

Quantification of efficacy of monopyridinium isomers and homologs derived from clinically used Pralidoxime within reactivation of acetylcholinesterase inhibited with organophosphorus nerve agents.

METHODS

This work uses the colorimetric biosensor called Detehit - cotton cloth with immobilized enzyme acetylcholinesterase. Biosensor is based on the modificated Ellman's method.

RESULTS

The highest reactivation was observed with sarin-inhibited acetylcholinesterase. Substantially lower reactivation was found with the cyclosarin-inhibited enzyme whereas AChE, inhibited by soman could not be effectively reactivated under the given conditions (enzyme inhibition for 2 minutes and subsequent treatment with the reactivator for 15 minutes).

CONCLUSION

Our work gives comparison of efficacy of reactivators in dependence on the length of alkylene chain and position of aldoxime functional group. Evaluation of effectivity of aldoxime reactivators is provided by simple means. The method allows rapid in vitro evaluation of the reactivators without being disturbed by excess of the organophosphate or reactivator.

Currently Used Cholinesterase Reactivators Against Nerve Agent Intoxication: Comparison of Their Effectivity in Vitro

In vitro comparison of reactivation efficacy of five currently used oximes - pralidoxime, obidoxime, trimedoxime, methoxime, and HI-6 (at two concentrations: 10-5 and 10-3 M) - against acetylcholinesterase (AChE; E.C. 3.1.1.7) inhibited by six different nerve agents (VX, Russian VX, sarin, cyclosarin, tabun, soman) and organophosphorus insecticide chlorpyrifos was the aim of this study. As a source of AChE in the experiments, rat brain homogenate was used. According to the results obtained, no AChE reactivator was able to reach sufficient potency for AChE inhibited by all nerve agents used. Moreover, oxime HI-6 (the most effective one) was not able to reactivate tabun- and soman-inhibited AChE. Due to this fact, it could be designated as a partially broad-spectrum reactivator.

In VitroEvaluation of Acetylcholinesterase Reactivators as Potential Antidotes Against Tabun Nerve Agent Poisonings

Searching for new potent acetylcholinesterase (AChE; E.C. 3.1.1.7) reactivators (oximes) is a very time-consuming process. At our department, we are able to synthesize more than 50 new AChE reactivators per year. Owing to this fact, we have to select promising reactivators using our in vitro method (potentiometric titration, pH 8 and temperature 25 degrees C; source of cholinesterases, rat brain homogenate; time of inhibition by nerve agents, 30 min; time of reactivation, 10 min) prior to in vivo experiments. For this purpose, we are using two-phase in vitro evaluation of reactivator potency. In the first phase, reactivation potency of all newly synthesized AChE reactivators is tested at two concentrations: 10(-3) M and 10(-5) M. Afterwards, all reactivators achieving reactivation potency over 15% (especially at the concentration 10(-5) M) are tested. The second phase consists of the measurement of the relationship between concentration of the oxime and its reactivation ability. In most cases, the reactivation bell-shaped curve is obtained. The most potent AChE reactivators are selected and provided for further experiments during our development process.

Reactivation of Immobilized Acetylcholinesterase–Tabun Complex by Methoxime and Its Homologues

Using an immobilized acetylcholinesterase-tabun enzyme-inhibitor complex, the reactivation efficacy of a homologous series of bispyridinium reactivators with increasing length of the alkylene chain between the pyridinium rings has been studied. The number of the alkylene groups in the chain ranged from one to six. N,N'-Monomethylenebis(4-pyridiniumaldoxime) dibromide (MMB-4) and N,N'-trimethylenebis(4-pyridiniumaldoxime) dibromide (TMB-4) are the most efficient reactivators of the series.

Potency of Five Structurally Different Acetylcholinesterase Reactivators to Reactivate Human Brain Cholinesterases Inhibited by Cyclosarin

Acetylcholinesterase (AChE; EC 3.1.1.7) reactivators are used as a part of the antidotal therapy of organophosphorus pesticide and nerve agent intoxications. Cyclosarin is one member of the nerve agent family. In this article, we compared the reactivation potency of five structurally different AChE reactivators (pralidoxime, trimedoxime, methoxime, HS-6, and BI-6) to reactivate cyclosarin-inhibited cholinesterases of human brain. The results demonstrate that the bisquaternary monooxime reactivator BI-6 seems to be the most potent reactivator of cyclosarin-inhibited cholinesterases. Moreover, according to the results, we can describe basic structural requirements, which are necessary for the efficacious reactivation process.