In vitro potency of H oximes (HI-6, HLö-7), the oxime BI-6, and currently used oximes (pralidoxime, obidoxime, trimedoxime) to reactivate nerve agent-inhibited rat brain acetylcholinesterase

Novel uncharged triazole salicylaldoxime derivatives as potential acetylcholinesterase reactivators: comprehensive computational study, synthesis and in vitro evaluation

The present study aims to design and synthesise novel uncharged aldoximes and explore their reactivation abilities, structures, descriptors, and mechanisms of action, as well as assessing the interactions and stabilities in the active site of paraoxon-inhibited acetylcholinesterase enzyme using computational studies and in vitro assay. The comprehensive computational studies including quantum chemical, molecular dynamics simulations and molecular docking were conducted on paraoxon-inhibited human acetylcholinesterase to investigate the reactivation ability of the novel aldoximes and compare them with pralidoxime as a reactivator model molecule.

Molecular Modeling Study of Uncharged Oximes Compared to HI-6 and 2-PAM Inside Human AChE Sarin and VX Conjugates

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.

Advances in toxicology and medical treatment of chemical warfare nerve agents

Organophosphorous (OP) Nerve agents (NAs) are known as the deadliest chemical warfare agents. They are divided into two classes of G and V agents. Most of them are liquid at room temperature. NAs chemical structures and mechanisms of actions are similar to OP pesticides, but their toxicities are higher than these compounds. The main mechanism of action is irreversible inhibition of Acetyl Choline Esterase (AChE) resulting in accumulation of toxic levels of acetylcholine (ACh) at the synaptic junctions and thus induces muscarinic and nicotinic receptors stimulation. However, other mechanisms have recently been described. Central nervous system (CNS) depression particularly on respiratory and vasomotor centers may induce respiratory failure and cardiac arrest. Intermediate syndrome after NAs exposure is less common than OP pesticides poisoning. There are four approaches to detect exposure to NAs in biological samples: (I) AChE activity measurement, (II) Determination of hydrolysis products in plasma and urine, (III) Fluoride reactivation of phosphylated binding sites and (IV) Mass spectrometric determination of cholinesterase adducts. The clinical manifestations are similar to OP pesticides poisoning, but with more severity and fatalities. The management should be started as soon as possible. The victims should immediately be removed from the field and treatment is commenced with auto-injector antidotes (atropine and oximes) such as MARK I kit. A 0.5% hypochlorite solution as well as novel products like M291 Resin kit, G117H and Phosphotriesterase isolated from soil bacterias, are now available for decontamination of NAs. Atropine and oximes are the well known antidotes that should be infused as clinically indicated. However, some new adjuvant and additional treatment such as magnesium sulfate, sodium bicarbonate, gacyclidine, benactyzine, tezampanel, hemoperfusion, antioxidants and bioscavengers have recently been used for OP NAs poisoning.

Reactivation of VX-inhibited AChE by novel oximes having two oxygen atoms in the linker

Two newly developed AChE reactivators possessing two oxime groups in 4-position of the pyridinium rings with linkers CH(2)O(CH(2))(2)OCH(2) and CH(2)O(CH(2))(4)OCH(2) were tested for their potency to reactivate VX-inhibited AChE. Their reactivation potency was compared with currently available oximes such as pralidoxime, obidoxime and HI-6. Appropriate constants (affinity towards the intact and inhibited enzyme, reactivation rate) characterizing the reactivation process were determined. According to the data obtained, a new oxime with CH(2)O(CH(2))(2)OCH(2) linker reached as high reactivation potency as HI-6. The percentage of reactivation of the oxime with CH(2)O(CH(2))(2)OCH(2) linker was comparable to that of obidoxime at a concentration 10(-3)M. Hence, these oximes may be worthy of future development for the treatment of nerve agent intoxications, especially, with lipophilic agents such as soman and cyclosarin.

The evaluation of the neuroprotective effects of bispyridinium oximes in tabun-poisoned rats

Tabun (O-ethyl-N,N-dimethyl phosphoramidocyanidate) belongs to the group of highly toxic organophosphorus compounds that may be used as chemical warfare agents for military as well as terrorist purposes. Tabun differs from other highly toxic organophosphates by the fact that commonly used antidotes are not able adequately to prevent tabun-induced acute toxic effects. The neuroprotective effects of four bispyridinium oximes (K075, trimedoxime, HI-6, obidoxime) in combination with atropine on rats poisoned with tabun at a sublethal dose (150 microg/kg i.m.; 80% of LD50 value) were studied. Tabun-induced neurotoxicity was monitored using a functional observational battery and automatic measurement of motor activity at 24 h and 7 d following tabun challenge. The results indicated that all tested oximes combined with atropine enabled tabun-poisoned rats to survive 7 d following challenge. Trimedoxime combined with atropine was the most effective antidote in decreasing tabun-induced neurotoxicity in the case of sublethal poisonings among all oximes tested. Due to its neuroprotective effects, trimedoxime may be considered to be more suitable oxime for the antidotal treatment of acute tabun exposure than currently used oximes (obidoxime, HI-6) and the newly synthesized oxime K075.