Elimination kinetics and molecular reaction mechanisms of cyclosarin (GF) by an oxime substituted β-cyclodextrin derivative in vitro

Transitioning from Oxime to the Next Potential Organophosphorus Poisoning Therapy Using Enzymes

For years, organophosphorus poisoning has been a major concern of health problems throughout the world. An estimated 200,000 acute pesticide poisoning deaths occur each year, many in developing countries. Apart from the agricultural pesticide poisoning, terrorists have used these organophosphorus compounds to attack civilian populations in some countries. Recent misuses of sarin in the Syrian conflict had been reported in 2018. Since the 1950s, the therapy to overcome this health problem is to utilize a reactivator to reactivate the inhibited acetylcholinesterase by these organophosphorus compounds. However, many questions remain unanswered regarding the efficacy and toxicity of this reactivator. Pralidoxime, MMB-4, TMB-4, obidoxime, and HI-6 are the examples of the established oximes, yet they are of insufficient effectiveness in some poisonings and only a limited spectrum of the different nerve agents and pesticides are being covered. Alternatively, an option in the treatment of organophosphorus poisoning that has been explored is through the use of enzyme therapy. Organophosphorus hydrolases are a group of enzymes that look promising for detoxifying organophosphorus compounds and have recently gained much interest. These enzymes have demonstrated remarkable protective and antidotal value against some different organophosphorus compounds in vivo in animal models. Apart from that, enzyme treatments have also been applied for decontamination purposes. In this review, the restrictions and obstacles in the therapeutic development of oximes, along with the new strategies to overcome the problems, are discussed. The emerging interest in enzyme treatment with its advantages and disadvantages is described as well.

Fatal sarin poisoning in Syria 2013: forensic verification within an international laboratory network

During the United Nations fact-finding mission to investigate the alleged use of chemical warfare agents in the Syrian Arab Republic in 2013, numerous tissues from a deceased female victim, who had displayed symptoms of cholinergic crisis, were collected. The Organisation for the Prohibition of Chemical Weapons (OPCW) authorized two specialized laboratories in the Netherlands and Germany for forensic analysis of these samples. Diverse modern mass spectrometry (MS)-based procedures in combination with either liquid chromatography (LC) or gas chromatography (GC) separation were applied. A variety of biotransformation products of the nerve agent sarin was detected, including the hydrolysis product O-isopropyl methylphosphonic acid (IMPA) as well as covalent protein adducts with e.g., albumin and human butyrylcholinesterase (hBChE). IMPA was extracted after sample acidification by solid-phase extraction and directly analyzed by LC-tandem-MS with negative electrospray ionization (ESI). Protein adducts were found, either by fluoride-induced reactivation applying GC-MS techniques or by LC-MS-based detection after positive ESI for proteolyzed proteins yielding phosphonylated tyrosine residues or a specific phosphonylated hBChE-derived nonapeptide. These experimental results provided unambiguous evidence for a systemic intoxication and were the first proving the use of sarin in the ongoing bellicose conflict. This scenario underlines the requirement for qualified and specialized analytical laboratories to face repeated violation of the Chemical Weapons Convention.

Cholinesterase reactivators and bioscavengers for pre- and post-exposure treatments of organophosphorus poisoning

Organophosphorus agents (OPs) irreversibly inhibit acetylcholinesterase (AChE) 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 AChE 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 AChE. Oximes poorly reactivate AChE 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 AChE. This is an article for the special issue XVth International Symposium on Cholinergic Mechanisms.

Structure-efficiency relationships of cyclodextrin scavengers in the hydrolytic degradation of organophosphorus compounds

New derivatives of cyclodextrins were prepared in order to determine the relative importance of the structural key elements involved in the degradation of organophosphorus nerve agents. To avoid a competitive inclusion between the organophosphorus substrate and the iodosobenzoate group, responsible for its degradation, the latter group had to be covalently bound to the cyclodextrin scaffold. Although the presence of the α nucleophile iodosobenzoate was a determinant in the hydrolysis process, an imidazole group was added to get a synergistic effect towards the degradation of the agents. The degradation efficiency was found to be dependent on the relative position of the heterocycle towards the reactive group as well as on the nature of the organophosphorus derivative.

Aminoalcohol-Induced Activation of Organophosphorus Hydrolase (OPH) towards Diisopropylfluorophosphate (DFP)

Aminoalcohols have been addressed as activating buffers for alkaline phosphatase. However, there is no record on the buffer activation regarding organophosphorus hydrolase (OPH). Here we reported the activating effects of aminoalcohols on OPH-catalyzed hydrolysis of diisopropylfluorophosphate (DFP), an analog molecule of G-type warfare agents. The kinetic parametors kcat, Vmax and kcat/Km in the OPH reaction were remarkably increased in the buffers (pH 8.0, 25°C) containing aminoalcohols with C2 between nitrogen (N) and oxygen (O) in their structures, including triethanolamine (TEA), diethanolamine, monoethanolamine, 1-amino-2-propanol, 2-amino-2-methyl-1-propanol, and triisopropanolamine. In contrast, much lower or no rate-enhancing effects were observed in the adding of amines, alcohols, amine/alcohol mixtures, or 3-amino-1-propanol (C3 between N and O). The 300 mM TEA further increased DFP-degrading activities of OPH mutants F132Y and L140Y, the previously reported OPH mutants with desirable activities towards DFP. However, the treatment of ethylenediaminetetraacetate (EDTA) markedly abolished the TEA-induced activation of OPH. The product fluoride effectively inhibited OPH-catalyzed hydrolysis of DFP by a linear mixed inhibition (inhibition constant Ki ~ 3.21 mM), which was partially released by TEA adding at initial or later reaction stage. The obtained results indicate the activation of OPH by aminoalcohol buffers could be attributed to the reduction of fluoride inhibition, which would be beneficial to the hydrolase-based detoxification of organophosphofluoridate.

Experimental and computational study of the inclusion complexes of β-cyclodextrin with the chemical warfare agent soman (GD) and commonly used simulants

The inclusion complexation of the Chemical Warfare Agent soman (GD) by β-cyclodextrin is studied by both experimental and computational approaches.

Interactions of cyclodextrins and their derivatives with toxic organophosphorus compounds

The aim of this review is to provide an update on the current use of cyclodextrins against organophosphorus compound intoxications. Organophosphorus pesticides and nerve agents play a determinant role in the inhibition of cholinesterases. The cyclic structure of cyclodextrins and their toroidal shape are perfectly suitable to design new chemical scavengers able to trap and hydrolyze the organophosphorus compounds before they reach their biological target.