Toxicokinetics of the nerve agent (+/-)-VX in anesthetized and atropinized hairless guinea pigs and marmosets after intravenous and percutaneous administration

Effective skin decontamination with RSDL® (reactive skin decontamination lotion kit) following dermal exposure to a Novichok class nerve agent

In recent years, various poisoning incidents have been reported, involving the alleged use of the so-called Novichok agents, resulting in their addition to the Schedule I list of the Organisation for the Prohibition of Chemical Warfare (OPCW). As the physicochemical properties of these agents are different from the 'classical' nerve agents, such as VX, research is needed to evaluate whether and to what extent existing countermeasures are effective. Here, we evaluated the therapeutic potential of RSDL® (Reactive Skin Decontamination Lotion Kit) for the neutralization of percutaneous toxicity caused by Novichok agents, both in vitro and in vivo. Experiments showed the three selected Novichok agents (A230, A232, A234) could be degraded by RSDL lotion, but at a different rate. The half-life of A234, in the presence of an excess of RSDL lotion, was 36 min, as compared to A230 (<5 min) and A232 (18 min). Following dermal exposure of guinea pigs to A234, application of the RSDL kit was highly effective in preventing intoxication, even when applied up until 30 min following exposure. Delayed use of the RSDL kit until the appearance of clinical signs of intoxication (3-4 h) was not able to prevent intoxication progression and deaths. This study determines RSDL decontamination as an effective treatment strategy for dermal exposure to the Novichok agent A234 and underscores the importance of early, forward use of skin decontamination, as rapidly as possible.

The phosphylated butyrylcholinesterase-derived tetrapeptide GlyGluSerAla proves exposure to organophosphorus agents with enantioselectivity

We herein present for the first time the phosphylated (*) tetrapeptide (TP)-adduct GlyGluSer198*Ala generated from butyrylcholinesterase (BChE) with proteinase K excellently suited for the verification of exposure to toxic organophosphorus nerve agents (OPNA). Verification requires bioanalytical methods mandatory for toxicological and legal reasons. OPNA react with BChE by phosphonylation of the active site serine residue (Ser198) forming one of the major target protein adducts for verification. After its enzymatic cleavage with pepsin, the nonapeptide (NP) PheGlyGluSer*AlaGlyAlaAlaSer is typically produced as biomarker. Usually OPNA occur as racemic mixtures of phosphonic acid derivatives with the stereocenter at the phosphorus atom, e.g. (±)-VX. Both enantiomers react with BChE, but the adducted NP does not allow their chromatographic distinction. In contrast, the herein introduced TP-adducts appeared as two peaks when using a stationary reversed phase (1.8 µm) in micro-liquid chromatography-electrospray ionisation tandem-mass spectrometry (µLC-ESI MS/MS) analysis. These two peaks represent diastereomers of the (+)- and (-)-OPNA adducted to the peptide that comprises chiral L-amino acids exclusively. Concentration- and time-dependent effects of adduct formation with (±)-VX and its pure enantiomers (+)- and (-)-VX as well as with (±)-cyclosarin (GF) were investigated in detail characterising enantioselective adduct formation, stability, ageing and spontaneous reactivation. The method was also successfully applied to samples from a real case of pesticide poisoning as well as to samples of biomedical proficiency tests provided by the Organisation for the Prohibition of Chemical Weapons.

"Catch-up" therapy: combining antidotal treatment with dermal application of AHA following percutaneous VX poisoning in the domestic swine

Low-volatility organophosphorus chemical warfare agents (OP CWAs) are cholinesterase inhibitors which easily absorb into the skin, leading to the formation of a dermal depot from which they slowly enter the bloodstream. This leads to sustained cholinergic hyperstimulation, which if untreated may lead to death. However, current available countermeasures are not adequate to neutralize the agent residing in the dermal depot. Accordingly, we evaluated the efficacy of the potassium salt of acetohydroxamic acid (880 mg/ml in DMSO/H2O 1:4, AHAK), as a potential "catch-up" therapy lotion intended to neutralize the dermal depot, by penetrating the skin and decomposing it before it reaches the bloodstream. To that end, we compared the clinical outcome following skin surface decontamination combined with antidotal treatment, to that following the same antidotal treatment combined with dermal application of AHAK at the site of VX exposure, against percutaneous poisoning by a lethal neat dose (4 mg/kg) of the low-volatility nerve agent VX, in an unanesthetized swine model. Following skin surface decontamination and antidotal treatment, recurrence of intoxication signs and a prolonged recovery time were observed. In contrast, similar antidotal treatment combined with dermal application of AHAK significantly reduced intoxication signs recurrences and accordingly medical supervision duration needed, paralleled by a significantly faster recovery of whole blood cholinesterase activity. An initial evaluation demonstrated the safety of prolonged whole-body AHAK application. Hence, the AHAK lotion may act as an efficient "catch-up" therapy against percutaneous poisoning by low-volatility OP CWAs, improving the clinical outcome and reducing the burden on medical staff.

Evidence of nerve agent VX exposure in rat plasma by detection of albumin-adducts in vitro and in vivo

VX is a highly toxic organophosphorus nerve agent that reacts with a variety of endogenous proteins such as serum albumin under formation of adducts that can be targeted by analytical methods for biomedical verification of exposure. Albumin is phosphonylated by the ethyl methylphosphonic acid moiety (EMP) of VX at various tyrosine residues. Additionally, the released leaving group of VX, 2-(diisopropylamino)ethanethiol (DPAET), may react with cysteine residues in diverse proteins. We developed and validated a microbore liquid chromatography-electrospray ionization high-resolution tandem mass spectrometry (µLC-ESI MS/HR MS) method enabling simultaneous detection of three albumin-derived biomarkers for the analysis of rat plasma. After pronase-catalyzed cleavage of rat plasma proteins single phosphonylated tyrosine residues (Tyr-EMP), the Cys34(-DPAET)Pro dipeptide as well as the rat-specific LeuProCys448(-DPAET) tripeptide were obtained. The time-dependent adduct formation in rat plasma was investigated in vitro and biomarker formation during proteolysis was optimized. Biomarkers were shown to be stable for a minimum of four freeze-and-thaw cycles and for at least 24 h in the autosampler at 15 °C thus making the adducts highly suited for bioanalysis. Cys34(-DPAET)Pro was superior compared to the other serum biomarkers considering the limit of identification and stability in plasma at 37 °C. For the first time, Cys34(-DPAET)Pro was detected in in vivo specimens showing a time-dependent concentration increase after subcutaneous exposure of rats underlining the benefit of the dipeptide disulfide biomarker for sensitive analysis.

Toxicokinetics of plasmatic VX in a swine model: comparison of a simple enzymatic titration method with a mass spectrometry method

Recent events have shown that organophosphorus nerve agents (OPNAs) are a serious threat. Cholinesterase inhibition by OPNAs results in acetylcholine accumulation, a cholinergic crisis leading to death if untreated. Efficacy assessment of new medical countermeasures against OPNAs relies on translational animal models. We developed a swine model of percutaneous VX intoxication and a simple plate reader-based enzymatic method to quantify plasmatic VX over time. Juvenile pigs anesthetized with sevoflurane were poisoned with a single supralethal (n = 5; 1200 μg/kg) or sublethal (n = 6; 320 μg/kg) percutaneous dose of VX. These intoxicated animals were compared to 7 control animals. Repeated blood sampling was performed up to 6 h post-intoxication. Blood cholinesterase activities were measured using the Ellman assay. Nanomolar plasma concentrations of VX were measured by exogenous butyrylcholinesterase added to an aliquot of plasma. As expected, we observed a steady increase in plasma concentration of VX over time concomitant to a decrease in blood cholinesterase activities for all intoxicated pigs. Despite the simplicity of the enzymatic method, the results obtained are in good agreement with those of the liquid chromatography-mass spectrometry method. This method is also applicable to other OPNAs such as novichoks with minor adaptations.

Post-VX exposure treatment of rats with engineered phosphotriesterases

The biologically stable and highly toxic organophosphorus nerve agent (OP) VX poses a major health threat. Standard medical therapy, consisting of reactivators and competitive muscarinic receptor antagonists, is insufficient. Recently, two engineered mutants of the Brevundimonas diminuta phosphotriesterase (PTE) with enhanced catalytic efficiency (k_cat/K_M = 21 to 38 × 10⁶ M⁻¹ min⁻¹) towards VX and a preferential hydrolysis of the more toxic P(−) enantiomer were described: PTE-C23(R152E)-PAS(100)-10-2-C3(I106A/C59V/C227V/E71K)-PAS(200) (PTE-2), a single-chain bispecific enzyme with a PAS linker and tag having enlarged substrate spectrum, and 10-2-C3(C59V/C227V)-PAS(200) (PTE-3), a stabilized homodimeric enzyme with a double PASylation tag (PAS-tag) to reduce plasma clearance. To assess in vivo efficacy, these engineered enzymes were tested in an anesthetized rat model post-VX exposure (~ 2LD₅₀) in comparison with the recombinant wild-type PTE (PTE-1), dosed at 1.0 mg kg⁻¹ i.v.: PTE-2 dosed at 1.3 mg kg⁻¹ i.v. (PTE-2.1) and 2.6 mg kg⁻¹ i.v. (PTE-2.2) and PTE-3 at 1.4 mg kg⁻¹ i.v. Injection of the mutants PTE-2.2 and PTE-3, 5 min after s.c. VX exposure, ensured survival and prevented severe signs of a cholinergic crisis. Inhibition of erythrocyte acetylcholinesterase (AChE) could not be prevented. However, medulla oblongata and diaphragm AChE activity was partially preserved. All animals treated with the wild-type enzyme, PTE-1, showed severe cholinergic signs and died during the observation period of 180 min. PTE-2.1 resulted in the survival of all animals, yet accompanied by severe signs of OP poisoning. This study demonstrates for the first time efficient detoxification in vivo achieved with low doses of heterodimeric PTE-2 as well as PTE-3 and indicates the suitability of these engineered enzymes for the development of highly effective catalytic scavengers directed against VX.

Do cold weather temperatures affect the efficacy of skin decontamination?

Skin decontamination in cold weather temperatures might be challenging due to the aggravating circumstances. However, no information is available on the efficacy of commonly used procedures in winter conditions. Therefore, the efficacy of the reactive skin decontamination lotion (RSDL) and soapy water decontamination following skin exposure to the nerve agent VX was evaluated at three ambient air temperatures (-5°C, -15°C and room temperature). Experiments were performed in vitro using human dermatomed skin. The ability of RSDL to degrade VX at the three different air temperatures was separately evaluated. The ambient air temperature in experiments without decontamination did not influence the penetration rate of VX through skin. RSDL decontamination was highly efficient in removing VX from skin when performed in all three ambient temperatures, despite the slower agent degradation rate of VX at the lower temperatures. Decontamination with soapy water at RT resulted in an increased skin penetration of VX compared with the control without decontamination; however, in colder temperatures the VX skin penetration was similar to the corresponding control without decontamination. At RT, dry removal prior to washing with soapy water did not improve decontamination of VX compared with washing solely with soapy water. This study demonstrated high efficacy of RSDL decontamination following skin exposure to VX also at cold temperatures. The previously reported 'wash-in' effect of soapy water on VX skin penetration was reduced at cold temperatures. Altogether, this study found a scientific basis to establish guidelines for skin decontamination of chemical casualties at cold weather temperatures.

A delayed treatment model for the evaluation of scopolamine for VX nerve agent intoxication

Most research on medical countermeasures for nerve agent exposure assumes a military scenario, in which (autoinjector) treatment is envisaged to be available immediately. In a civilian setting however, treatment is delayed until arrival of first-aid responders. This may significantly affect treatment efficacy and the requirements for secondary intensive care. The aim of the current study was to develop a guinea pig model to evaluate the efficacy of delayed treatment following nerve agent exposure. We identified a trigger-to-treat based on a progressive stage of the toxidrome following VX exposure, which was associated with the subsiding of clonic movements. This paradigm resulted in treatment consistently being administered between 15 and 25 min post-exposure. Using the model, we investigated the potential for the anticholinergic scopolamine to act as a delayed treatment either as a standalone treatment, or as an adjunct to delayed treatment with Standard of Care (SOC), containing atropine, 2-PAM, and midazolam. The study provides a framework for a small animal model for evaluating the efficacy of treatment administered at a specific stage of the toxidrome, when immediate treatment is absent. As an adjunct, scopolamine treatment did not result in improved survival, but did show a beneficial effect on recovery, in terms of general posture. As a standalone treatment, scopolamine showed a significant, dose-responsive, beneficial effect on survival and recovery. These promising results warrant additional studies to investigate which observed physiological improvements are relevant for the recovery process and residual injury.

Extended retrospective detection of regenerated sarin (GB) in rabbit blood and the IMPA metabolite in urine: a pharmacokinetics study

Long-term retrospective monitoring of exposure to organophosphorus nerve agents is challenging. We recently developed two highly sensitive analytical methods for regenerated sarin (GB) nerve agent in blood and its primary metabolite, isopropyl-methylphosphonic acid (IMPA), in urine. These methods were implemented in a toxicokinetics study carried out with sarin injected (i.v.) to rabbits at doses corresponding to 0.1, 0.5 or 0.9 LD₅₀. The time frame for monitoring regenerated sarin from blood was 70 days for 0.1 LD₅₀ and 0.5 LD₅₀ and 77 days for 0.9 LD_50, where rapid elimination occurred in the first 8 days with an initial average half-life of 1.2 days, followed by a second, slower elimination, with a terminal average half-life of 8.4 days. The time frame for monitoring IMPA in urine was 7, 15 and 16 days for 0.1 LD₅₀, 0.5 LD₅₀ and 0.9 LD₅₀ intoxications, respectively. Rapid elimination of IMPA in urine occurred after exposure, with an average half-life of ~ 0.8 days on days 2-6. For the first time, a slower elimination route for IMPA, with an average half-life of ~ 4 days from day 6 onwards, was revealed. Both IMPA and regenerated sarin pharmacokinetics exhibit linearity with dose. The overlaid pharmacokinetic profiles of regenerated sarin in blood along with IMPA in urine emphasize the dominance of IMPA with a rapid decay in urine in the first week and the slower long-term decay of protein-bound sarin later in blood. To our knowledge, the two new sensitive methods exhibit the longest monitoring time frame reported in biological samples.

Early Detection of Exposure to Toxic Chemicals Using Continuously Recorded Multi-Sensor Physiology

Early detection of exposure to a toxic chemical, e.g., in a military context, can be life-saving. We propose to use machine learning techniques and multiple continuously measured physiological signals to detect exposure, and to identify the chemical agent. Such detection and identification could be used to alert individuals to take appropriate medical counter measures in time. As a first step, we evaluated whether exposure to an opioid (fentanyl) or a nerve agent (VX) could be detected in freely moving guinea pigs using features from respiration, electrocardiography (ECG) and electroencephalography (EEG), where machine learning models were trained and tested on different sets (across subject classification). Results showed this to be possible with close to perfect accuracy, where respiratory features were most relevant. Exposure detection accuracy rose steeply to over 95% correct during the first five minutes after exposure. Additional models were trained to correctly classify an exposed state as being induced either by fentanyl or VX. This was possible with an accuracy of almost 95%, where EEG features proved to be most relevant. Exposure detection models that were trained on subsets of animals generalized to subsets of animals that were exposed to other dosages of different chemicals. While future work is required to validate the principle in other species and to assess the robustness of the approach under different, realistic circumstances, our results indicate that utilizing different continuously measured physiological signals for early detection and identification of toxic agents is promising.

Efficient agent degradation within skin is important for decontamination of percutaneously exposed VX

AIM OF THE STUDY

Following percutaneous exposure to the nerve agent VX, the remaining intact agent within the skin after decontamination is of great concern. Consequently, this leads to prolonged agent release to the blood circulation resulting in sustained intoxication, which may complicate the medical management. The decontamination procedure used should therefore possess the ability for agent removal both on and within the skin. The efficacy of three decontamination procedures was evaluated by measuring VX and the primary degradation product ethyl methyl phosphonic acid (EMPA) penetrated through human skin and the amount remaining within the skin.

MATERIALS AND METHODS

Decontamination was initiated 5 min post-exposure to VX on human dermatomed skin. Experiments were conducted using an in vitro skin penetration model and the amount remaining within the skin was determined by combining the tape-stripping technique and acetylcholinesterase activity measurements.

RESULTS

In control experiments without decontamination, higher amounts of VX were recovered in the deeper layers of skin compared to EMPA, which was primarily located in the stratum corneum. Both Reactive Skin Decontamination Lotion (RSDL) and the RSDL training kit (TRSDL) significantly reduced the amount of VX within the skin and decreased the penetration through the skin. However, the degradation ability of RSDL was demonstrated to be beneficial by the reduction of intact agents remaining in the skin compared to TRSDL without agent degradation capability. Soapy water decontamination caused a "wash-in" effect of VX with decreased agent amounts within stratum corneum but increased the amount VX penetrated through the skin.

CONCLUSION

Efficient skin decontamination of VX requires skin decontaminants reaching deeper layers of the skin, and that both absorption and degradation properties are important. In addition, the "wash-in" effect by using soapy water may enhance VX release to the blood circulation.

Detection of Chemical Weapon Nerve Agents in Bone by Liquid Chromatography-Mass Spectrometry

A recently proposed model for the incorporation of xenobiotics of forensic interest into the human skeleton suggests nerve agent metabolites may incorporate into bone at relatively elevated concentrations based on their unique chemical properties. To test the hypothesis that nerve agent metabolites interact with bone, methods for the extraction, isolation and semi-quantitative detection of nerve agent metabolites (MPA, EMPA, IMPA, iBuMPA, CMPA and PMPA, corresponding to the nerve agents VX, Russian VX, sarin, cyclosarin and soman, respectively) from osseous tissue were developed using liquid chromatography-mass spectrometry with both quadrupole time-of-flight and triple quadrupole (QqQ) instruments. The optimized methods were validated on the QqQ instrument. Despite high ion suppression, the achieved limits of detection (5-20 pg/g for four analytes; 350 pg/g for the fifth analyte) were lower than many of those published for the same analytes in other biomatrices, including serum and urine. These methods were tested on the skeletal remains of minipigs exposed to the chemical weapon VX in vivo. The VX metabolite was detected in multiple minipig bone samples; to the authors' knowledge, this is the first time in vivo nerve agent exposure has been detected from bone. Further, detected concentrations and diaphyseal-to-epiphyseal area count ratios reflect animal exposure history. Although the results are limited, they are promising, indicating that nerve agent metabolites may interact with bone as a pharmacokinetic compartment and can be extracted from bone postmortem. Additional studies, assessing the effects of different agents, exposure pathways and taphonomic variables, are needed; however, these results suggest the method may be used with human bone to detect use of chemical weapons from postmortem biomatrices even well after a suspected attack. More general implications for both nerve agent toxicology and skeletal toxicology are also discussed.

Enantioselective in-vitro elimination kinetics of nerve agents in blood monitored by derivatization and LC-MS/MS analysis

We present a simple method for chiral separation and analysis of organophosphorus nerve agents and apply it to monitor the enantioselective blood elimination kinetics of sarin in-vitro. The method is implemented in standard reverse phase LC-MS operating conditions, relieving the user of the dedicated operating conditions frequently demanded in chiral LC-MS analysis. The method consists of formation of diastereomers by a rapid derivatization with (R)-2-(1 aminoethyl) phenol, followed by LC-MS/MS analysis. Derivatization enantioselectivity was studied by comparing the reaction of optically pure sarin and racemic sarin, proving no substantial enantiomeric preference in the reaction and demonstrating the enantiomeric discrimination abilities of the technique. Enantioselective sarin elimination pathways were probed in-vitro by following the fast elimination kinetics of the two sarin enantiomers as well as its hydrolysis metabolite (isopropyl methyl-phosphonic acid, IMPA) in whole blood and plasma compared to water. Sarin enantiomers showed the known marked differences in elimination kinetics with rapid elimination of the (+) enantiomer and slower elimination of the (-) enantiomer in whole blood and plasma as well as dose-dependent kinetics (faster elimination at lower concentrations). We found that small amounts of acetonitrile in plasma prevent the rapid elimination of the (+) enantiomer, resulting in similar, slower elimination kinetics for both enantiomers.

In Vitro Interaction of Organophosphono- and Organophosphorothioates with Human Acetylcholinesterase

The implementation of the Chemical Weapons Convention (CWC) in 1997 was a milestone in the prohibition of chemical warfare agents (CWA). Yet, the repeated use of CWA underlines the ongoing threat to the population. Organophosphorus (OP) nerve agents still represent the most toxic CWA subgroup. Defensive research on nerve agents is mainly focused on the "classical five", namely tabun, sarin, soman, cyclosarin and VX, although Schedule 1 of the CWC covers an unforeseeable number of homologues. Likewise, an uncounted number of OP pesticides have been produced in previous decades. Our aim was to determine the in vitro inhibition kinetics of selected organophosphono- and organophosphorothioates with human AChE, as well as hydrolysis of the agents in human plasma and reactivation of inhibited AChE, in order to derive potential structure-activity relationships. The investigation of the interactions of selected OP compounds belonging to schedule 1 (V-agents) and schedule 2 (amiton) of the CWC with human AChE revealed distinct structural effects of the P-alkyl, P-O-alkyl and N,N-dialkyl residues on the inhibitory potency of the agents. Irrespective of structural modifications, all tested V-agents presented as highly potent AChE inhibitors. The high stability of the tested agents in human plasma will most likely result in long-lasting poisoning in vivo, having relevant consequences for the treatment regimen. In conclusion, the results of this study emphasize the need to investigate the biological effects of nerve agent analogues in order to assess the efficacy of available medical countermeasures.

Organophosphorus compounds and oximes: a critical review

Organophosphorus (OP) pesticides and nerve agents still pose a threat to the population. Treatment of OP poisoning is an ongoing challenge and burden for medical services. Standard drug treatment consists of atropine and an oxime as reactivator of OP-inhibited acetylcholinesterase and is virtually unchanged since more than six decades. Established oximes, i.e. pralidoxime, obidoxime, TMB-4, HI-6 and MMB-4, are of insufficient effectiveness in some poisonings and often cover only a limited spectrum of the different nerve agents and pesticides. Moreover, the value of oximes in human OP pesticide poisoning is still disputed. Long-lasting research efforts resulted in the preparation of countless experimental oximes, and more recently non-oxime reactivators, intended to replace or supplement the established and licensed oximes. The progress of this development is slow and none of the novel compounds appears to be suitable for transfer into advanced development or into clinical use. This situation calls for a critical analysis of the value of oximes as mainstay of treatment as well as the potential and limitations of established and novel reactivators. Requirements for a straightforward identification of superior reactivators and their development to licensed drugs need to be addressed as well as options for interim solutions as a chance to improve the therapy of OP poisoning in a foreseeable time frame.

Broad Spectrum Treatment for Ocular Insult Induced by Organophosphate Chemical Warfare Agents

Warfare organophosphates nerve agents constitute one of the prime threats to mankind on the battlefield and in the scenario of civilian terror. Exposure to organophosphate (OP) nerve agents dose-dependently result in incapacitation. They affect multiple organs, but the eye is one of the first and most frequently affected. Ocular OP insult may result in long-term miosis, impaired visual function, and ocular pain thus inducing functional incapacitation. The currently recommended military medical doctrine of using 1% atropine eye drops is far from being the optimal treatment. Although effective in reducing ocular pain and the miotic response, this treatment induces long-term mydriasis and cycloplegia promoting photophobia and restricted accommodation, which may result in further impairment in visual function. An optimal treatment must ameliorate the long-term ocular insult enabling rapid return of normal visual function, while avoiding the induction of mydriasis and cycloplegia side effects, which could possibly worsen the visual performance. Optimal treatment should also keep effects of misuse to a minimum. Work done in recent years examined treatments with various anticholinergic drugs alone or used in combination with oxime treatments and may offer improved efficacy in ameliorating the ocular insult. This review is a summary of the applied research in animals and will discuss clinical implications and possible alterations in treatment protocols following OP exposure. Taken together the data points toward the use of topical low concentrations of potent anticholinergic ophthalmic drops such as atropine or homatropine, which rapidly ameliorate the long-term OP-induced ocular insult.

Structural and kinetic evidence of aging after organophosphate inhibition of human Cathepsin A

Human Cathepsin A (CatA) is a lysosomal serine carboxypeptidase of the renin-angiotensin system (RAS) and is structurally similar to acetylcholinesterase (AChE). CatA can remove the C-terminal amino acids of endothelin I, angiotensin I, Substance P, oxytocin, and bradykinin, and can deamidate neurokinin A. Proteomic studies identified CatA and its homologue, SCPEP1, as potential targets of organophosphates (OP). CatA could be stably inhibited by low µM to high nM concentrations of racemic sarin (GB), soman (GD), cyclosarin (GF), VX, and VR within minutes to hours at pH 7. Cyclosarin was the most potent with a kinetically measured dissociation constant (K_I) of 2 µM followed by VR (K_I = 2.8 µM). Bimolecular rate constants for inhibition by cyclosarin and VR were 1.3 × 10³ M^-1sec^-1 and 1.2 × 10³ M^-1sec^-1, respectively, and were approximately 3-orders of magnitude lower than those of human AChE indicating slower reactivity. Notably, both AChE and CatA bound diisopropylfluorophosphate (DFP) comparably and had K_I^DFP = 13 µM and 11 µM, respectively. At low pH, greater than 85% of the enzyme spontaneously reactivated after OP inhibition, conditions under which OP-adducts of cholinesterases irreversibly age. At pH 6.5 CatA remained stably inhibited by GB and GF and <10% of the enzyme spontaneously reactivated after 200 h. A crystal structure of DFP-inhibited CatA was determined and contained an aged adduct. Similar to AChE, CatA appears to have a "backdoor" for product release. CatA has not been shown previously to age. These results may have implications for: OP-associated inflammation; cardiovascular effects; and the dysregulation of RAS enzymes by OP.

Ocular surface histopathological insult following sarin and VX exposure and potential treatments in the rat model

Eye exposure to organophosphate (OP) chemical warfare irreversible acetylcholinesterase inhibitors, results in long-term miosis and impaired visual function. In contrast to the well-documented miotic and ciliary muscle spasm observed following chemical warfare, OP ocular exposure, little is known regarding the ocular surface histopathological insult. The aim of the present study was to determine the degree of the ocular surface insult following sarin or VX ocular exposure and to evaluate potential anti-cholinergic treatments in counteracting this insult. Rats that were whole body exposed to various sarin concentrations (0.049-43 μg/L; 5 min exposure), showed a dose-dependent miotic response and light reflex impairment. Following whole body sarin exposure, a dose dependent ocular surface histopathological insult was developed. A week following exposure to a low concentration of 0.05 μg/L, conjunctival pathology was observed, while corneal insult was noticed only following exposure to a concentration of 0.5 μg/L and above. Both tissues presented poorer outcomes when exposed to higher sarin concentrations. In contrast, eyes topically exposed to 1 μg sarin demonstrated no ocular insult a week following exposure. On the contrary, topical exposure to 1 μg VX resulted in a significant corneal insult. Anticholinergic treatments such as 0.1% atropine or 2% homatropine, given shortly following VX exposure, counteracted this insult. The results of this study show that not only do anti-cholinergic treatments counteract the miotic response, but also prevent the histopathological insult observed when given shortly following OP exposure.

The Application of a Single-Column GC-MS-MS Method for the Rapid Analysis of Chemical Warfare Agents and Breakdown Products

The development of one comprehensive gas chromatographic-triple quadrupole mass spectrometric (GC-MS-MS) method for the analysis of nerve agents and their breakdown products can pose a challenge due to significant differences in analyte volatility. Nerve agent breakdown products typically have a low volatility, requiring a derivatization step prior to analysis by gas chromatography (GC). However, nerve agent parent compounds are generally more volatile, which eliminates the need for derivatization and allows for direct analysis. Therefore, the analysis of these analytes is typically performed using separate analytical methods. This may require the use of multiple columns composed of different stationary phases to ensure the most efficient separation. With the wide selection of GC columns and derivatizing agents, it is potentially possible to develop a single-column/analytical method that is suitable for the detection of nerve agents and their breakdown products. We evaluated six nerve agents (tabun, sarin, soman, cyclosarin, VX and Russian VX) and the six corresponding breakdown products (EDPA, IMPA, PMPA, CMPA EMPA and MMPA). Chromatographic separation and multiple-reaction mode electron ionization detection of the nerve agents and silylated breakdown product derivatives were performed using an Agilent 7890 A gas chromatography (GC) equipped with a mid-polarity column, coupled to a 7000 triple quadrupole mass spectrometry system. A fast (12.5 min), highly sensitive (picogram) and selective method was achieved. The feasibility of this method for nerve agent and breakdown product detection in real samples was demonstrated using nerve agent-spiked human plasma at various exposure times (3 min, 1 h and 24 h). Five of the six nerve agents and all six breakdown products were successfully detected. This robust method has utility as a rapid screening tool to identify a specific nerve agent in a potential exposure event by simultaneous detection of the parent and or its corresponding breakdown product in plasma.

Environmental exposure to organophosphorus nerve agents

Exposure to organophosphorus nerve agents, the most deadly chemical warfare agents, is possible in a variety of situations, such as destruction of chemical warfare agents, terrorist attacks, armed conflicts or accidents in research laboratories and storage facilities. Hundreds of thousands of tons of chemical munitions were disposed of at the sea in the post World War II period, with European, Russian, Japanese and US coasts being the most affected. Sulfur mustard, Lewisite and nerve agents appear to be the most frequently chemical warfare agents disposed of at the sea. Addressing the overall environmental risk, it has been one of the priorities of the world community since that time. Aside from confirming exposure to nerve agents in the alleged use for forensic purposes, the detection and identification of biological markers of exposure are also needed for the diagnosis and treatment of poisoning, in addition to occupational health monitoring for specific profiles of workers. When estimating detrimental effects of acute or potential chronic sub-lethal doses of organophosphorus nerve agents, released accidentally or intentionally into the environment, it is necessary to understand the wide spectra of physical, chemical and toxicological properties of these agents, and predict their ultimate fate in environmental systems.

Bioscavenger is effective as a delayed therapeutic intervention following percutaneous VX poisoning in the guinea-pig

The prolonged systemic exposure that follows skin contamination with low volatility nerve agents, such as VX, requires treatment to be given over a long time due to the relatively short half-lives of the therapeutic compounds used. Bioscavengers, such as butyrylcholinesterase (BChE), have been shown to provide effective post-exposure protection against percutaneous nerve agent when given immediately on signs of poisoning and to reduce reliance on additional treatments. In order to assess the benefits of administration of bioscavenger at later times, its effectiveness was assessed when administration was delayed for 2h after the appearance of signs of poisoning in guinea-pigs challenged with VX (4×LD₅₀). VX-challenged animals received atropine, HI-6 and avizafone on signs of poisoning and 2h later the same combination with or without bioscavenger. Five out of 6 animals which received BChE 2h after the appearance of signs of poisoning survived to the end of the study at 48h, compared with 6 out of 6 which received BChE immediately on signs. All the animals (n=6+6) that received only MedCM, without the addition of BChE, died within 10h of poisoning. The toxicokinetics of a sub-lethal challenge of percutaneous VX were determined in untreated animals. Blood VX concentration peaked at approximately 4h after percutaneous dosing with 0.4×LD₅₀; VX was still detectable at 36h and had declined to levels below the lower limit of quantification (10pg/mL) by 48h in 7 of 8 animals, with the remaining animal having a concentration of 12pg/mL. These studies confirm the persistent systemic exposure to nerve agent following percutaneous poisoning and demonstrate that bioscavenger can be an effective component of treatment even if its administration is delayed.

Oximes in organophosphate poisoning: 60 years of hope and despair

The high number of annual fatalities following suicidal poisoning by organophosphorus (OP) pesticides and the recent homicidal use of the chemical warfare nerve agent sarin against civilian population in Syria underlines the continuous threat by these highly toxic agents. The need for an effective treatment of OP poisoning resulted in the implementation of a combination therapy with the muscarinic receptor antagonist atropine and an oxime for the reactivation of OP-inhibited acetylcholinesterase (AChE). Since the invention of the first clinically used oxime pralidoxime (2-PAM) in the 1950s ongoing research attempted to identify more effective oximes. In fact, several thousand oximes were synthesized in the past six decades. These include charged and non-charged compounds, mono- and bispyridinium oximes, asymmetric oximes, oximes with different substitutes and more recently non-oxime reactivators. Multiple in vitro and in vivo studies investigated the potential of oximes to reactivate OP-inhibited AChE and to reverse OP-induced cholinergic signs. Depending on the experimental model, the investigated species and the tested OP largely variable results were obtained by different laboratories. These findings and the inconsistent effectiveness of oximes in the treatment of OP-pesticide poisoned patients led to a continuous discussion on the value of oximes. In order to provide a forward-looking evaluation of the significance of oximes in OP poisoning multiple aspects, including intrinsic toxicity, in vitro reactivation potency, efficacy and pharmacokinetics, as well as the impact of the causative OP have to be considered. The different influencing factors in order to define the benefit and limitations of oximes in OP poisoning will be discussed.

HI-6 assisted catalytic scavenging of VX by acetylcholinesterase choline binding site mutants

The high toxicity of organophosphorus compounds originates from covalent inhibition of acetylcholinesterase (AChE), an essential enzyme in cholinergic neurotransmission. Poisonings that lead to life-threatening toxic manifestations require immediate treatment that combines administration of anticholinergic drugs and an aldoxime as a reactivator of AChE. An alternative approach to reduce the in vivo toxicity of OPs focuses on the use of bioscavengers against the parent organophosphate. Our previous research showed that AChE mutagenesis can enable aldoximes to substantially accelerate the reactivation of OP-enzyme conjugates, while dramatically slowing down rates of OP-conjugate dealkylation (aging). Herein, we demonstrate an efficient HI-6-assisted VX detoxification, both ex vivo in human blood and in vivo in mice by hAChE mutants modified at the choline binding site (Y337A and Y337A/F338A). The catalytic scavenging of VX in mice improved therapeutic outcomes preventing lethality and resulted in a delayed onset of toxicity symptoms.

In vitro human skin penetration model for organophosphorus compounds with different physicochemical properties

A flow-through diffusion cell was validated for in vitro human epidermal penetration studies of organophosphorus compounds (OPCs) applied by infinite dosing. By testing OPCs with similar molecular weight but different physicochemical properties, it was shown that hydrophilic and lipophilic properties are major determinants for the penetration rate. Lipophilic OPCs displayed maximum cumulative penetration in the 20-75% agent concentration range whereas the hydrophilic OPCs displayed maximum cumulative penetration at 10 or 20% agent concentration. Low penetration was observed for all agents at 1% agent concentration or when applied as neat agents. The impact of the receptor solution composition was evaluated by comparing the penetration using receptor solutions of different ratios of ethanol and water. For diluted OPCs, a high concentration of ethanol in the receptor solution significantly increased the penetration compared to lower concentrations. When OPCs were applied as neat agents, the composition of the receptor solution only affected the penetration for one of four tested compounds. In conclusion, the flow-through diffusion cell was useful for examining the penetration of OPCs through the epidermal membrane. It was also demonstrated that the penetration rates of OPCs are strongly influenced by dilution in water and the receptor fluid composition.

Oxidative decontamination of chemical warfare agent VX and its simulant using N,N-dichlorovaleramide

The efficient, operationally simple and safe oxidative decontamination of chemical warfare agent O-ethyl-S-2-(N,N-diisopropylaminoethyl)methylphosphonothioate (VX) and its non-toxic simulant O,S-diethyl methylphosphonothioate (OSDEMP) has been reported.

Showering effectiveness for human hair decontamination of the nerve agent VX

In this work, our goals were to establish whether hair decontamination by showering one hour post-exposure to the highly toxic organophosphate nerve agent VX was effective, whether it required the addition of a detergent to water and, if it could be improved by using the adsorbent Fuller's Earth (FE) or the Reactive Skin Decontamination Lotion (RSDL) 30 min prior to showering. Hair exposure to VX and decontamination was performed by using an in vitro model. Hair showering led to 72% reduction of contamination. Addition of detergent to water slightly increased the decontamination effectiveness. Hair treatment with FE or RSDL improved the decontamination rate. Combination of FE use and showering, which yielded a decontamination factor of 41, was demonstrated to be the most effective hair decontamination procedure. Hair wiping after showering was shown to contribute to hair decontamination. Altogether, our results highlighted the importance of considering hair decontamination as an important part of body surface decontamination protocols.

Natural Detoxification Capacity to Inactivate Nerve Agents Sarin and VX in the Rat Blood

BACKGROUND

The method of continual determination of the rat blood cholinesterase activity was developed to study the changes of the blood cholinesterases following different intervetions.

AIMS

The aim of this study is registration of cholinesterase activity in the rat blood and its changes to demonstrate detoxification capacity of rats to inactivate sarin or VX in vivo.

METHODS

The groups of female rats were premedicated (ketamine and xylazine) and cannulated to a. femoralis. Continual blood sampling (0.02 ml/min) and monitoring of the circulating blood cholinesterase activity were performed. Normal activity was monitored 1-2 min and then the nerve agent was administered i.m. (2×LD50). Using different time intervals of the leg compression and relaxation following the agent injection, cholinesterase activity was monitored and according to the inhibition obtained, detoxification capacity was assessed.

RESULTS

Administration of sarin to the leg, then 1 and 5 min compression and 20 min later relaxation showed that further inhibition in the blood was not observed. On the other hand, VX was able to inhibit blood cholinesterases after this intervention.

CONCLUSIONS

The results demonstrated that sarin can be naturally detoxified on the contrary to VX. Described method can be used as model for other studies dealing with changes of cholinesterases in the blood following different factors.

Evidence of VX nerve agent use from contaminated white mustard plants

The Chemical Weapons Convention prohibits the development, production, acquisition, stockpiling, retention, transfer or use of chemical weapons by Member States. Verification of compliance and investigations into allegations of use require accurate detection of chemical warfare agents (CWAs) and their degradation products. Detection of CWAs such as organophosphorus nerve agents in the environment relies mainly upon the analysis of soil. We now present a method for the detection of the nerve agent VX and its hydrolysis products by gas chromatography and liquid chromatography mass spectrometry of ethanol extracts of contaminated white mustard plants (Sinapis alba) which retained the compounds of interest for up to 45 days. VX is hydrolysed by the plants to ethyl methylphosphonic acid and then to methylphosphonic acid. The utility of white mustard as a nerve agent detector and remediator of nerve agent-polluted sites is discussed. The work described will help deter the employment of VX in conflict.

Acute toxicity of some nerve agents and pesticides in rats

OBJECTIVES

Highly toxic organophosphorus compounds (V- and G-nerve agents) were originally synthesized for warfare or as agricultural pesticides. Data on their acute toxicity are rare and patchy. Therefore, there is a need for integrated summary comparing acute toxicity of organophosphates using different administration routes in the same animal model with the same methodology. Based on original data, a summary of in vivo acute toxicity of selected V- and G-nerve agents (tabun, sarin, soman, VX, Russian VX) and organophosphates paraoxon (POX) and diisopropyl fluorophosphate (DFP) in rats has been investigated.

MATERIALS AND METHODS

Male Wistar rats were exposed to organophosphates in several administration routes (i.m., i.p., p.o, s.c., p.c.). The acute toxicity was evaluated by the assessment of median lethal dose (LD50, mg kg(-1)) 2, 4, and 24 hours post exposure.

RESULTS

V-agents were the most toxic presented with LD50 ranged from 0.0082 mg kg(-1) (VX, i.m.) to 1.402 mg kg(-1) (Russian VX, p.o.), followed by G-agents (LD50 = 0.069 mg kg(-1)/soman, i.m./ - 117.9 mg kg(-1)/sarin, p.c./), organophosphate POX and DFP (LD50 = 0.321 mg kg(-1)/POX, i.m./ - 420 mg kg(-1)/DFP, p.c./). Generally, i.m. administration was the most toxic throughout all tested agents and ways of administration (LD50 = 0.0082 mg kg(-1)/VX/ - 1.399 mg kg(-1)/DFP/) whereas p.c. way was responsible for lowest acute toxicity (LD50 = 0.085 mg kg(-1)/VX/ - 420 mg kg(-1)/DFP/).

CONCLUSION

The acute toxicity of selected organophosphorus compounds is summarized throughout this study. Although the data assessed in rats are rather illustrative prediction for human, it presents a valuable contribution, indicating the toxic potential and harmfulness of organophosphates.

New modified β-cyclodextrin derivatives as detoxifying agents of chemical warfare agents (I). Synthesis and preliminary screening: evaluation of the detoxification using a half-quantitative enzymatic assay

Current treatments of organophosphorus nerve agents poisoning are imperfect, and more efficient medical countermeasures need to be developed. Chemical scavengers based on β-cyclodextrin displayed promising results, but further investigations have to be performed to evaluate the possibility of application of substituted cyclodextrins as potential detoxification agents. Herein, five new cyclodextrins scavengers were synthesized. New optimal conditions for regioselectively monosubstitution of β-cyclodextrin at O-2 position were then studied to access to key intermediates. After these optimizations, a new series of three permethylated derivatives was developed, and two compounds bearing an α-nucleophilic group via a three carbon atoms linker were prepared. The ability of these five scavengers to detoxify nerve agents (cyclosarin, soman, tabun and VX) was evaluated by a semi-quantitative biological assay. All the modified cyclodextrins significantly decreased the inhibitory effect of chemical warfare G agents on acetylcholinesterase activity. For this purpose, we showed that the specific interactions between the organophosphorus compound and the oligosaccharidic moiety of the scavenger played a pivotal role in the detoxification process.

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.

New tools in diagnosis and biomonitoring of intoxications with organophosphorothioates: case studies with chlorpyrifos and diazinon

Organophosphate (OP) pesticides are neurotoxic compounds that are widely used in agriculture. Classical methods for monitoring OP exposure comprise the measurement of intact OP, its metabolites or cholinesterase activity. Newly developed methods focus on the analysis of the OP adduct bound to proteins such as butyrylcholinesterase (BuChE) and albumin. These adducts can be analyzed by means of fluoride reactivation or by analysis with LC-MS/MS of the pepsin or pronase digest of butyrylcholinesterase and albumin, respectively. The utility of these methods is illustrated through the analysis of plasma samples obtained from patients taken 1-49 days after ingestion of the organophosphate pesticides chlorpyrifos and/or diazinon. Thus, in this particular case several independent methodologies were applied to the biomedical samples, all pointing to the same exposure.