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The poisoning with organophosphorus compounds represents a life threatening danger especially in the time of terroristic menace. No universal antidote has been developed yet and other therapeutic approaches not related to reactivation of acetylcholinesterase are being investigated. This review describes the main features of the cholinergic sys-tem,...
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(1) Background: Human exposure to organophosphorus compounds employed as pesticides or as chemical warfare agents induces deleterious effects due to cholinesterase inhibition. One therapeutic approach is the reactivation of inhibited acetylcholinesterase by oximes. While currently available oximes are unable to reach the central nervous system to r...
General conditions and requirements for an internal standard useful in the determination of chemical warfare agents (CWAs) by the method of gas chromatography coupled with mass detection (GC/MS) were defined. The determination is based on a GC/MS analysis of a mixture of a CWA with an internal standard, conversion of the TIC chromatogram to a chrom...
Citations
... The currently existing therapeutic approach only addresses the symptoms of NA poisoning and is not directed towards neutralizing the NA and, therefore, could be improved [15,20]. In addition, the individual components, viz., atropine, pralidoxime, and diazepam, have their own respective limitations and side effects [3,15,16,[21][22][23][24][25][26][27][28]. Also, pyridostigmine/physostigmine-based prophylactic approaches have been developed to counteract nerve agent poisoning by masking a portion of AChE from the NA, allowing the preservation of sufficient enzyme activity to maintain the physiological function; this includes the PANPAL tablet (pyridostigmine with trihexyphenidyl and benactyzine), which could be associated with the HI-6 transdermal patch TRANSANT [29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45][46][47]. ...
Nerve agents are a class of lethal neurotoxic chemicals used in chemical warfare. In this review, we have briefly discussed a brief history of chemical warfare, followed by an exploration of the historical context surrounding nerve agents. The article explores the classification of these agents, their contemporary uses, their toxicity mechanisms, and the disadvantages of the current treatment options for nerve agent poisoning. It then discusses the possible application of enzymes as prophylactics against nerve agent poisoning, outlining the benefits and drawbacks of paraoxonase-1. Finally, the current studies on paraoxonase-1 are reviewed, highlighting that several challenges need to be addressed in the use of paraoxonase-1 in the actual field and that its potential as a prophylactic antidote against nerve agent poisoning needs to be evaluated. The literature used in this manuscript was searched using various electronic databases, such as PubMed, Google Scholar, Web of Science, Elsevier, Springer, ACS, Google Patent, and books using the keywords chemical warfare agent, Butyrylcholinesterase, enzyme, nerve agent, prophylactic, and paraoxonase- 1, with the time scale for the analysis of articles between 1960 to 2023, respectively. The study has suggested that concerted efforts by researchers and agencies must be made to develop effective countermeasures against NA poisoning and that PON1 has suitable properties for the development of efficient prophylaxis against NA poisoning.
... The compounds known as oximes, having the oxime functional group (C=NOH), are designed as reactivators/antidotes of acetylcholinesterase (AChE, EC 3.1.1.7) inhibited by highly toxic organophosphorus pesticides or warfare nerve agents (Čalić et al., 2006;Kovarik et al., 2010;Soukup et al., 2010;Worek et al., 2020). Our studies on pyridinium oximes as one of the antidote's scaffold, as well as studies from other researchers, have shown that oximes could exhibit diverse biological activities, like inducing oxidative stress, regulated cell death apoptosis, or interact with cholinergic receptors (Soukup et al., 2011;Zandona et al., 2022Zandona et al., , 2021. ...
The uncharged 3-hydroxy-2-pyridine aldoximes with protonatable tertiary amines are studied as antidotes in toxic organophosphates (OP) poisoning. Due to some of their specific structural features, we hypothesize that these compounds could exert diverse biological activity beyond their main scope of application. To examine this further, we performed an extensive cell-based assessment to determine their effects on human cells (SH-SY5Y, HEK293, HepG2, HK-2, myoblasts and myotubes) and possible mechanism of action. As our results indicated, aldoxime having a piperidine moiety did not induce significant toxicity up to 300µM within 24hours, while those with a tetrahydroisoquinoline moiety, in the same concentration range, showed time-dependent effects and stimulated mitochondria-mediated activation of the intrinsic apoptosis pathway through ERK1/2 and p38-MAPK signaling and subsequent activation of initiator caspase 9 and executive caspase 3 accompanied with DNA damage as observed already after 4hour exposure. Mitochondria and fatty acid metabolism were also likely targets of 3-hydroxy-2-pyridine aldoximes with tetrahydroisoquinoline moiety, due to increased phosphorylation of acetyl-CoA carboxylase. In silico analysis predicted kinases as their most probable target class, while pharmacophores modeling additionally predicted the inhibition of a cytochrome P450cam. Overall, if the absence of significant toxicity for piperidine bearing aldoxime highlights the potential of its further studies in medical counter-measures, the observed biological activity of aldoximes with tetrahydroisoquinoline moiety could be indicative for future design of compounds either in a negative context in OP antidotes design, or in a positive one for design of compounds for the treatment of other phenomena like cell proliferating malignancies.
... which is then unable to cleave the ACh neurotransmitter. ACh thus accumulates in the synaptic cleft causing overstimulation of cholinergic receptors with consequent respiratory failure and death (Kassa 2002;Soukup et al. 2010). Besides the effect mediated through overstimulation of peripheral nicotinic and muscarinic ACh receptors, central neurotoxicity is responsible for acute (e.g. ...
Organophosphorus compounds (OPs) involving life-threatening nerve agents (NA) have been known for several decades. Despite a clear mechanism of their lethality caused by the irreversible inhibition of acetylcholinesterase (AChE) and manifested via overstimulation of peripheral nicotinic and muscarinic acetylcholine (ACh) receptors, the mechanism for central neurotoxicity responsible for acute or delayed symptoms of the poisoning has not been thoroughly uncovered. One of the reasons is the lack of a suitable model. In our study, we have chosen the SH-SY5Y model in both the differentiated and undifferentiated state to study the effects of NAs (GB, VX and A234). The activity of expressed AChE in cell lysate assessed by Ellman’s method showed 7.3-times higher activity in differentiated SH-SY5Y cells in contrast to undifferentiated cells, and with no involvement of BuChE as proved by ethopropazine (20 µM). The activity of AChE was found to be, in comparison to untreated cells, 16-, 9.3-, and 1.9-times lower upon A234, VX, and GB (100 µM) administration respectively. The cytotoxic effect of given OPs expressed as the IC50 values for differentiated and undifferentiated SH-SY5Y, respectively, was found 12 mM and 5.7 mM (A234), 4.8 mM and 1.1 mM (VX) and 2.6 mM and 3.8 mM (GB). In summary, although our results confirm higher AChE expression in the differentiated SH-SY5Y cell model, the such higher expression does not lead to a more pronounced NA cytotoxic effect. On the contrary, higher expression of AChE may attenuate NA-induced cytotoxicity by scavenging the NA. Such finding highlights a protective role for cholinesterases by scavenging Novichoks (A-agents). Second, we confirmed the mechanism of cytotoxicity of NAs, including A-agents, can be ascribed rather to the non-specific effects of OPs than to AChE-mediated effects.
... The results of current and recent studies show that muscle responses to the effects of different concentrations of paraoxon and reversal of these effects by pralidoxime effects are significant, repetitive, and reliable. Moreover, this method was used to investigate the cholinergic-nicotinic effects of different substances, and it is considered very useful for the study of striated muscle function (16,25). ...
Background: It is generally believed that the anticholinesterase effect is induced by the organophosphate insecticide parathion only through its bioactive metabolite (i.e., paraoxon) that is created in the liver. Objectives: This study aimed to evaluate the intrinsic anticholinesterase effect of parathion, compared to its main metabolite. Methods: This study has been conducted to prepare the isolated chick biventer cervicis nerve-muscle using the twitch tension recording method. Results: According to the results, paraoxon (0.1 µM) induced a highly significant increase (more than 100%) in the twitch height, while higher concentrations (0.3 and 1 µM) induced partial or total contractures. Furthermore, parathion induced almost the same percentage of increase in the twitch height at 1 µM and partial or total contractures at 3 and 10 µM. It should be noted that pralidoxime (2-PAM), at 300 µM, reversed the effects of paraoxon and its parent (i.e., parathion). Conclusion: These results demonstrate that both parathion and its metabolite inhibit the acetylcholinesterase enzyme which can be reactivated by pralidoxime, whereas parathion is about 10 times less potent, compared to its metabolite. Therefore, the intrinsic toxic effects of parathion, regardless of its metabolite, should be considered in future studies.
... The neurotoxic poisoning must immediate administration of AChE reactivation agents which can reactivate the toxic enzymes efficiently and separate the toxicant molecules from AChE in the shortest time, so as to quickly restore the function of AChE in hydrolyzing ACh (Elsinghorst et al. 2013;Soukup et al. 2010). AChE reactivation agents include chlorophosphonium, double-complex phosphorus, and amide phosphate (HI-6). ...
Human usually uses oximes as acetylcholinesterase (AChE)-activated antidotes to treat organophosphorus (OP) compound poisoning. In addition, drugs such as atropine can also be used for its detoxification treatment. However, the natural blood-brain barrier (BBB) severely limits the penetration of these drugs into the central nervous system. As a widely used reactivator, HI-6 is difficult to penetrate the BBB due to its hydrophilicity. Therefore, we hope that a large amount of HI-6 can penetrate the BBB through the drug delivery system. They can quickly release and activate the inhibited AChE in the center. Polybutylcyanoacrylate (PBCA) has good biodegradability and biocompatibility, which ensures the safety of the treatment. Pluronic P85 gets the advantages of inhibiting P-glycoprotein (P-gp) efflux and improving drug solubility. In this study, the HI-6-loaded nanoparticles that conjugated with c(RGDyK) cyclic peptide were successfully synthesized, with encapsulation efficiency 63.69%, drug loading 6.2%, average particle size 166.9 nm, and zeta potential − 22.0 mV. The shape was round and evenly distributed. The BBB model was established by astrocytes and brain capillary endothelial cells, and the transendothelial cell resistance values of the BBB model could reach 183 Ω. The penetration effect of the c(RGDyK)-modified nanoparticles was about 4 times the free HI-6 on the BBB model in vitro. The c(RGDyK)-modified nanoparticles were more effective at targeting the brain than the unmodified nanoparticles in vivo. In addition, reactivation evaluation showed that the modified nanoparticles had a higher reactivation rate for poisoned mice, indicating that the nanoparticles modified with c(RGDyK) cyclic peptide had more central targeting. The successful implementation of this study is expected to improve the treatment level of nerve agents.
Graphical abstract
... 9,11,22−28 However, the oxime should be administered as soon as possible to prevent the process called "aging" of AChE, which is characterized by the elimination of an alkyl moiety (R1) from the OP. 11,[22][23][24][25][26]28 Among the oximes found in the literature, 1-[[2-[(E)-hydroxyiminomethyl]pyridin-1-ium-1yl]methoxymethyl]pyridin-1-ium-4-carboxamide (Asoxime chloride, or most commonly HI-6) ( Figure 1) and (NE)-N-[(1-methylpyridin-1-ium-2-yl)methylidene]hydroxylamine (pralidoxime, or most commonly 2-PAM) ( Figure 1) stand out for their efficiency in the AChE reactivation process. 11,22−26,29−35 Even with studies suggesting the importance of the quaternary nitrogen in AChE reactivation, some studies in the literature argue that the cationic oximes, which present great reactivating potential in in vitro and in vivo tests, show a significant reduction in their efficiency. ...
The deleterious effects of nerve agents over the enzymes acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) turned these compounds into the most dangerous chemical weapons known. Among the antidotes in use today against these agents, oximes in combination with other drugs are the only treatment with any action. HI-6 and 2-PAM are cationic oximes proved to be effective for the reactivation of AChE inhibited by the nerve agents VX and sarin (GB). However, when it comes to reactivation of AChE inside the central or peripheral nervous systems, charged molecules present low diffusion due to low penetration through the blood–brain barrier. Uncharged oximes appear as an interesting alternative to solve this problem, but the development and enhancement of more efficient uncharged oximes capable of reactivating human AChE is still necessary. Given the limitations for in vivo and in vitro experimental studies with nerve agents, modeling is an important tool that can contribute to a better understanding of factors that may affect the efficiency of uncharged oximes. In order to investigate the interaction and behavior of cationic and uncharged oximes, we performed here molecular docking, molecular dynamics simulations, and binding energies calculations of the known cationic oximes HI-6 and 2-PAM plus four uncharged oximes found in the literature, complexed with human AChE (HssACHE) conjugated with the nerve agents VX and GB. The uncharged oximes showed different behaviors, especially RS194B, which presented stability inside AChE-VX, but presented free binding energy lower than cationic oximes, suggesting that structural alterations could favor its interactions with these complexes. In contrast, HI-6 and 2-PAM showed higher affinities with more negative binding energy values and larger contribution of the amino acid Asp74, demonstrating the importance of the quaternary nitrogen to the affinity and interaction of oximes with AChE-GB and AChE-VX conjugates.
... The lowest yield 6 % was obtained for 2-((hydroxyamino)methyl)-1-phenethylpyridinium bromide (66) containing oxime group in C2 position of the pyridine ring with nitrogen atom substituted by 2-phenylethyl group. On the other hand, 3-((hydroxyimino)methyl)-1-phenethylpyridinium bromide (67) with oxime group in C3 position yielded 72 %. From these examples, it can be concluded that reactions are controlled by steric and electronic effects. ...
... Methoxime seems to be effective against sarin and cyclosarin, however, its efficacy seems to be lower in case of soman and tabun poisoning. Generally, counteracting tabun poisoning is an issue for any reactivator due to a higher electron density on the phosphorus atom (caused by the electron-donor effect of the substituted amino group), making a nucleophilic attack by oximate anion less probable [4,67]. Methoxime appears to be a better reactivator in vivo than one would expect from in vitro results especially when used in combination therapy with atropine and diazepam [67,68]. ...
... Generally, counteracting tabun poisoning is an issue for any reactivator due to a higher electron density on the phosphorus atom (caused by the electron-donor effect of the substituted amino group), making a nucleophilic attack by oximate anion less probable [4,67]. Methoxime appears to be a better reactivator in vivo than one would expect from in vitro results especially when used in combination therapy with atropine and diazepam [67,68]. Importantly, methoxime was highlighted, along with Hlö-7, as the best reactivator of OP-AChE in a guinea pig model [37]. ...
Acetylcholinesterase (AChE) is well-known enzyme studied in many fields of research, e.g. in Alzheimer’s disease, Parkinson’s disease, or in eco-toxicology as a biological marker. Many inhibitors of AChE have been identified in nature as well as prepared in chemical labs as a result of systematic synthetic efforts. The organophosphorus (OP) inhibitors of AChE are one of the oldest artificial inhibitors being purposely developed as military nerve agents (e.g. sarin, soman, tabun, VX, RVX). Some of the compounds with decreased toxicity are currently used in agriculture as pesticides (e.g. parathion, chlorpyrifos, paraoxon) or in the industry as softening agents and flame retardants. The common mechanism of action of all organophosphate compounds is the irreversible inhibition of AChE via a binding to the hydroxyl group of the serine residue within the active site of the enzyme. Subsequently, AChE loses its ability to fulfill its physiological role in cholinergic transmission, which leads to the cholinergic crisis with the possibility of respiratory failure and death. The reactivators of AChE are classified as strong nucleophilic agents capable to cleave the non-aged organophosphate- serine adduct and thereby restoring the activity of the enzyme. This work provides a unique overview of the most potent oximes reactivators of inhibited AChE since 1955 to the present. In this review article, we have reviewed different synthetic approaches of known and widely used oxime reactivators of AChE such as pralidoxime, methoxime, trimedoxime, obidoxime, asoxime (HI-6), HS-6, HLo-7, K027, K048, K203, K075 and BI-6. The review covers the original articles as well as patented research.
... This action is not exclusively the result of reactivation. Indeed, anticholinergic effects of the pyridinium moiety that binds to nicotinic and muscarinic receptors contribute to the pharmacological action of oximes (Soukup et al. 2010). It is noteworthy that, this side-effect led to the recent development of specific nonoxime bispyridinium antinicotinic compounds which were shown to significantly improve the efficacy of the standard antidotal treatment (Kassa et al. 2016). ...
Organophosphorus agents ( OP s) irreversibly inhibit acetylcholinesterase ( AC hE) causing a major cholinergic syndrome. The medical counter‐measures of OP poisoning have not evolved for the last 30 years with carbamates for pretreatment, pyridinium oximes‐based AC hE reactivators, antimuscarinic drugs and neuroprotective benzodiazepines for post‐exposure treatment. These drugs ensure protection of peripheral nervous system and mitigate acute effects of OP lethal doses. However, they have significant limitations. Pyridostigmine and oximes do not protect/reactivate central AC hE. Oximes poorly reactivate AC hE inhibited by phosphoramidates. In addition, current neuroprotectants do not protect the central nervous system shortly after the onset of seizures when brain damage becomes irreversible. New therapeutic approaches for pre‐ and post‐exposure treatments involve detoxification of OP molecules before they reach their molecular targets by administrating catalytic bioscavengers, among them phosphotriesterases are the most promising. Novel generation of broad spectrum reactivators are designed for crossing the blood–brain barrier and reactivate central AC hE.
This is an article for the special issue XVth International Symposium on Cholinergic Mechanisms .
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... The harmful, and even lethal, effect of OP results from phosphorylation/ phosphonylation of the serine hydroxyl group at the active site of acetylcholinesterase (AChE), which leads to the inhibition of this enzyme. The pivotal physiological role of AChE is catalyzation of acetylcholine hydrolysis in the nervous system 4,5 . OPs block the progressive cleavage and consecutive removal of acetylcholine at the neuromuscular junctions, which results in accumulation of acetylcholine 6,7 . ...
In this paper, we describe the biochemical properties and biological activity of a series of cholinesterase reactivators (symmetrical bisquaternary xylene-linked compounds, K106-K114) with ctDNA. The interaction of the studied derivatives with ctDNA was investigated using UV-Vis, fluorescence, CD and LD spectrometry, and electrophoretic and viscometric methods. The binding constants K were estimated to be in the range 1.05 × 10(5)-5.14 × 10(6) M(-1) and the percentage of hypochromism was found to be 10.64-19.28% (from UV-Vis titration). The used methods indicate that the studied samples are groove binders. Electrophoretic methods proved that the studied compounds clearly influence calf thymus Topo I (at 5 μM concentration, except for compounds K107, K111 and K114 which were effective at higher concentrations) and human Topo II (K110 partially inhibited Topo II effects even at 5 μM concentration) activity.
... Also, pesticides have the same mechanism of action as the inhibitors used in warfare and may cause, likewise to the militarily used inhibitors, death mainly by respiratory arrest. In the treatment of esterase inhibition, so called esterase reactivators are given in addition to muscarinic antagonists [92]. The mechanism of action of the reactivators is via affinity to the enzyme and the ability to bind the organophosphate which is inhibiting its active site, thereby making the site accessible to acetylcholine [93]. ...
... The exact mechanism of action of the reactivators is not totally unraveled. However, muscarinic and nicotinic receptor antagonism has been suggested [92]. ...
... However, the most common use of drugs exerting antimuscarinic receptor effects is for urge incontinence. Also, in cases of organophosphate poisoning (chemical warfare or pesticides), muscarinic receptor antagonists are indicated as antidotes [92]. ...
Background
Pharmaceuticals with targets in the cholinergic transmission have been used for decades and are still fundamental treatments in many diseases and conditions today. Both the transmission and the effects of the somatomotoric and the parasympathetic nervous systems may be targeted by such treatments. Irrespective of the knowledge that the effects of neuronal signalling in the nervous systems may include a number of different receptor subtypes of both the nicotinic and the muscarinic receptors, this complexity is generally overlooked when assessing the mechanisms of action of pharmaceuticals.
Methods
We have search of bibliographic databases for peer-reviewed research literature focused on the cholinergic system. Also, we have taken advantage of our expertise in this field to deduce the conclusions of this study.
Results
Presently, the life cycle of acetylcholine, muscarinic receptors and their effects are reviewed in the major organ systems of the body. Neuronal and non-neuronal sources of acetylcholine are elucidated. Examples of pharmaceuticals, in particular cholinesterase inhibitors, affecting these systems are discussed. The review focuses on salivary glands, the respiratory tract and the lower urinary tract, since the complexity of the interplay of different muscarinic receptor subtypes is of significance for physiological, pharmacological and toxicological effects in these organs.
Conclusion
Most pharmaceuticals targeting muscarinic receptors are employed at such large doses that no selectivity can be expected. However, some differences in the adverse effect profile of muscarinic antagonists may still be explained by the variation of expression of muscarinic receptor subtypes in different organs. However, a complex pattern of interactions between muscarinic receptor subtypes occurs and needs to be considered when searching for selective pharmaceuticals. In the development of new entities for the treatment of for instance pesticide intoxication, the muscarinic receptor selectivity needs to be considered. Reactivators generally have a muscarinic M2 receptor acting profile. Such a blockade may engrave the situation since it may enlarge the effect of the muscarinic M3 receptor effect. This may explain why respiratory arrest is the major cause for deaths by esterase blocking.
