Quantitation of five organophosphorus nerve agent metabolites in serum using hydrophilic interaction liquid chromatography and tandem mass spectrometry

Development of a molecularly imprinted polymer-based electrochemical sensor for the selective detection of nerve agent VX metabolite ethyl methylphosphonic acid in human plasma and urine samples

This study focuses on the detection of ethyl methyl phosphonic acid (EMPA), a metabolite of the banned organophosphorus nerve agent VX. We developed an electrochemical sensor utilizing the molecularly imprinted polymer (MIP) based on 4-aminobenzoic acid (4-ABA) and tetraethyl orthosilicate for the selective detection of EMPA in human plasma and urine samples. The 4-ABA@EMPA/MIP/GCE sensor was constructed by a thermal polymerization process on a glassy carbon electrode and sensor characterization was performed by cyclic voltammetry and electrochemical impedance spectroscopy. The 4-ABA@EMPA/MIP/GCE sensor demonstrated impressive linear ranges 1.0 × 10-10 M-2.5 × 10-9 M for the standard solution, 1.0 × 10-10 M-2.5 × 10-9 M for the urine sample, and 1.0 × 10-10 M-1 × 10-9 M of EMPA for the plasma sample with outstanding detection limits of 2.75 × 10-11 M (standard solution), 2.11 × 10-11 M (urine), and 2.36 × 10-11 M (plasma). The sensor exhibited excellent recovery percentages ranging from 99.86 to 101.30% in urine samples and 100.62 to 101.08% in plasma samples. These findings underscore the effectiveness of the 4-ABA@EMPA/MIP/GCE as a straightforward, highly sensitive, and selective interface capable of detecting the target analyte EMPA in human plasma and urine samples.

Simultaneous analysis of degradation products of Novichok agents and conventional nerve agents in human urine by ion chromatography-tandem mass spectrometry using ammonium regeneration solution

An ion chromatography (IC)-tandem mass spectrometry (MS/MS) method to analyze nerve agent degradation products in human urine was developed. Six degradation products of conventional nerve agents and six Novichok agent degradation products were analyzed simultaneously despite their differences in hydrophilicity and acidity. Using ammonium regeneration solution improved the peak shapes greatly compared with the results obtained with the ordinary IC-MS/MS configuration. For urine samples, a simple pretreatment method of dilution with water and ultrafiltration was used. The detection limits of the nerve agent degradation products were sufficiently low (10-250 ng/mL) and the calibration curves showed acceptable linearity. Due to the absence of a derivatization step, throughput was higher than for our previous derivatization-liquid chromatography-MS/MS method.

Generic detection of organophosphorus nerve agent adducts to butyrylcholinesterase in plasma using liquid chromatography-tandem mass spectrometry combined with an improved procainamide-gel separation and pepsin digestion method

Organophosphorus nerve agent (OPNA) adducts to butyrylcholinesterase (BChE) can be applied to confirm exposure in humans. A sensitive method for generic detection of G- and V-series OPNA adducts to BChE in plasma was developed by combining an improved procainamide-gel separation (PGS) and pepsin digestion protocol with ultra-high-pressure liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS). Residual matrix interferences from prior PGS purification of OPNA-BChE adducts from plasma were found to be a critical cause of significantly reduced UHPLC-MS/MS detection sensitivity. In our developed on-column PGS approach, the matrix interference was successfully removed by adding an appropriate concentration of NaCl to the washing buffer, and it could capture ≥92.5% of the BChE in plasma. The lower pH value and the longer digestion time in all previous pepsin digestion methods were found to be a key accelerated aging factor of several adducts such as tabun (GA)-, cyclohexylsarin (GF)-, and soman (GD)-BChE nonapeptide adducts, making them difficult to detect. The aging event of several OPNA-BChE nonapeptide adducts was so successfully addressed that the formic acid level in enzymatic buffer and digestion time were lowered to 0.05% (pH 2.67) and 0.5 h, respectively, and the post-digestion reaction was immediately terminated. The improved condition parameters were optimal for pepsin digestion of all types of OPNA-BChE adducts into their individual unaged nonapeptide adducts with the highest yields, expanding the applicability of the method. The method had a nearly one-fold decrease in sample preparation time through the reduction of digestion time and removal of ultrafiltration procedure after digestion. The limit of identification (LOI) were determined respectively as 0.13 ng mL^-1, 0.28 ng mL^-1, 0.50 ng mL^-1, 0.41 ng mL^-1 and 0.91 ng mL^-1 for VX-, sarin (GB)-, GA-, GF-, and GD-exposed human plasma, being low exposure value compared to previously documented approaches. The approach was utilized to fully characterize the adducted (aged and unaged) BChE levels of five OPNAs in a series of their individual exposed concentration (1.00-400 nM) of plasma sample, and successfully detect OPNA exposure from all unknown plasma samples from OPCW's second and third biomedical proficiency tests. The OPNA-BChE adducts, their aged adducts, and unadducted BChE from OPNA-exposed plasma can simultaneously be measured using the method. The study provides a recommended diagnostic tool for generic verification of any OPNA exposure with high confidence by detecting its corresponding BChE adduct.

Analysis of degradation products of nerve agents in biological fluids by ion chromatography-tandem mass spectrometry

PURPOSE

The detection of hydrolysis products of nerve agents (alkyl methylphosphonic acids; RMPAs) in biological samples from victims is important to confirm exposure to nerve agents. However, analysis of RMPAs is difficult due to their high hydrophilicity. The aim of this study was to develop ion chromatography-tandem mass spectrometry (IC-MS/MS) methods using commercially available equipment and columns to analyze RMPAs in human urine and serum with high sensitivity and without using complicate techniques.

METHODS

A Dionex IonPac AS11-HC anion-exchange column was used to analyze six RMPAs (MPA, EMPA, IMPA, ⁱBuMPA, CHMPA, and PMPA). For pretreatments of biological fluids, we developed two pretreatment methods (Method 1: dilution and ultrafiltration; Method 2: removal of chloride ions with Ag cartridges).

RESULTS

Six RMPAs including highly hydrophilic methylphosphonic acid and ethyl methylphosphonic acid could be analyzed with sufficient retention times and peak shape. The detection limits of RMPAs were improved using Dionex OnGuard II Ba/Ag/H cartridges and MetaSEP IC-Ag cartridges (urine: 0.5-5 ng/mL; serum: 1-5 ng/mL). These methods were also applied to the test samples for the Organisation for the Prohibition of Chemical Weapons Biomedical Proficiency Tests.

CONCLUSIONS

RMPAs could be sufficiently analyzed by IC-MS/MS. In addition, the limits of detection were superior to those obtained in our previous study involving LC-MS/MS or derivatization-LC-MS/MS method. For analysis of biological samples, an appropriate pretreatment method can be chosen according to the amount of sample available for analysis and expected RMPA concentrations.

A novel approach for on-site screening of organophosphorus nerve agents based on DTNB modified AgNPs using surface-enhanced Raman spectrometry

Organophosphorus nerve agents (OPNAs), such as Sarin (GB), Tabun (GA), Soman (GD) and VX, would cause tremendous harm in military and terrorist attacks, and thus the development of simple methods for the rapid and efficient detection of these hazardous substances is of great necessity. Herein, we present a novel approach for the facile, rapid and sensitive detection of real OPNAs. The detection substrate is fabricated using functionalized silver nanoparticles (AgNPs) immobilized with acetylcholinesterase (AChE) and 5,5'-dithiobis-(2-nitrobenzoic acid) (DTNB). In the absence of OPs, AChE catalyzes the hydrolysis of acetylthiocholine (ATCh) to form thiocholine (TCh), which continues to interact quickly with DTNB to produce a very sensitive Raman probing molecule, TNB. The inhibition of the activity of AChE by OPs could induce an obvious decrease of characteristic Raman peaks of 5-thio-2-nitrobenzoic acid (TNB) at 1335 cm^-1. The introduction of DTNB as an enzyme activity indicator significantly improves the detection sensitivity with distinct characteristic Raman peaks. The LOD of GD, which is one of the most easily aged OPNAs, could reach 0.1 nM due to its strongest inhibition of AChE. Moreover, various OPNAs exhibit different SERS intensities due to their different inhibition capacities of AChE. Hence, the new strategy has great potential in public security early warning and environmental analysis.

Dimethoxytriadinylation LC-MS/MS of Novichok A-Series Degradation Products in Human Urine

Novichok A-series compounds, novel nerve agents, pose an increasing threat to citizens worldwide; however, no analytical methods have been reported for detecting their hydrolysis products. Herein, a screening method was developed to detect and identify Novichok A-series degradation products (hydrolysates of A230, A232, A234, A262, and one related compound) and alkyl methylphosphonic acids (RMPAs, conventional nerve agent hydrolysates) using liquid chromatography-tandem mass spectrometry (LC-MS/MS). We identified a suitable derivatization reagent, 4-(4,6-dimethoxy-1,3,5-triazin-2-yl)-4-methylmorpholinium chloride (DMTMM), and optimized the reaction conditions. The derivatized esters of Novichok A-series degradation products were stable and easily detected. We used this derivatization to achieve the first analytical method for Novichok hydrolysis products in urine (0.40-4.0 ng/mL). The detection limits of the RMPAs (0.1-0.4 ng/mL) were comparable to those presented in previous reports involving pentafluorobenzylation or direct LC-MS/MS. The applicability of the newly developed method was evaluated by analyzing urine samples from the OPCW Fifth Biomedical Proficiency Test.

A spore-based portable kit for on-site detection of fluoride ions

The excess residues of fluoride ions cause serious human health problems, making their detection highly valuable. In this work, a whole-cell-based biosensor was presented for the detection of fluoride ions, which can inhibit the color reaction of 3,3',5,5',-tetramethylbenzidine (TMB) catalyzed by the CotA-laccase of spore surface. This reaction for the detection of fluoride ions could be read out through UV-vis spectrophotometer, smartphone, or standard colorimetric card within 10 min. Under optimum conditions, a linear range of 1-600 μmol L^-1 with a detection limit of 0.12 μmol L^-1 (3σ/k) was achieved for fluoride ions detection by using UV-vis spectrophotometer. The biosensor coupling with smartphone had a good linear response to fluoride ions concentration in the range of 5-600 μmol L^-1 with LOD of 0.90 μmol L^-1 (3σ/k). The standard colorimetric card can be directly used for recognizing the fluoride ions level via naked-eyes. A portable kit based on a colorimetric card and smartphone was developed and has been successfully applied for fluoride ions monitoring in surface waters and groundwater. This developed method has several advantages such as rapid, outstanding selectivity and anti-interference, low-cost, ease of operation and storage, and eco-friendliness, meeting the demands of point-of-care testing of fluoride ions and disease prevention.

Untargeted and targeted analysis of sarin poisoning biomarkers in rat urine by liquid chromatography and tandem mass spectrometry

Chemical warfare agents continue to pose a real threat to humanity, despite their prohibition under the Chemical Weapons Convention. Sarin is one of the most toxic and lethal representatives of nerve agents. The methodology for the targeted analysis of known sarin metabolites has reached great heights, but little attention has been paid to the untargeted analysis of biological samples of victims exposed to this deadly poisonous substance. At present, the development of computational and statistical methods of analysis offers great opportunities for finding new metabolites or understanding the mechanisms of action or effect of toxic substances on the organism. This study presents the targeted LC-MS/MS determination of methylphosphonic acid and isopropyl methylphosphonic acid in the urine of rats exposed to a non-lethal dose of sarin, as well as the untarget urine analysis by LC-HRMS. Targeted analysis of polar acidic sarin metabolites was performed on a mixed-mode reversed-phase anion-exchange column, and untargeted analysis on a conventional reversed-phase C18 column. Isopropyl methylphosphonic acid was detected and quantified within 5 days after subcutaneous injection of sarin at a dose of 1/4 LD₅₀. A combination of generalized additive mixed models and dose-response analysis with database searches using accurate mass of precursor ions and corresponding MS/MS spectra enabled us to propose new six potential biomarkers of biological response to exposure. The results confirm the well-known fact that sarin poisoning has a significant impact on the victims' metabolome, with inhibition of acetylcholinesterase being just the first step and trigger of the complex toxicodynamic response.

Identification of 2-(diethylamino)ethylthiol dipeptide (Cys-Pro) adduct as biomarker of nerve agents VR and CVX in human plasma using liquid chromatography-high-resolution tandem mass spectrometry

Organophosphorus nerve agents pose a significant threat to human health. The most toxic compounds in this class include V-type poisonous substances such as VX, CVX, and VR. Although all stockpiles of this type of substance are subject to destruction under the Chemical Weapons Convention (CWC), there is still a risk that they could be used for criminal and terrorist purposes. The latter determines the relevance of studies aimed at identification of biomarkers that may indicate the exposure of these group substances to the organism. A liquid chromatography mass spectrometry/high-resolution mass spectrometry (LC-MS/HR MS) method for determination of trace amounts of nerve agents such as VR and CVX in human plasma was proposed. The method is based on enzymatic plasma hydrolysis with the use of pronase to form a stable adduct of 2-(diethylamino)ethylthiol with dipeptide cysteine-proline (DEAET-CP) with its subsequent determination by LC-MS/HR MS. Synthesis of DEAET-CP as reference compound was conducted using non-toxic precursors. Sample preparation of human blood plasma samples exposed to VR was carried out with the use of solid-phase extraction (SPE). Liquid chromatography (LC) separation on the reversed-phase column and mass spectrometric detection (selection of optimal transitions and detection modes) were performed. The achieved limit of detection (LOD) of VR (in the form of DEAET-CP) in human blood plasma was 0.05 ng mL^-1. The proposed approach was developed using plasma samples exposed to VR and CVX obtained in the frame of the Fifth Official Biomedical Test of the Organization for the Prohibition of Chemical Weapons (OPCW) and showed good specificity of detection.

Poisoning by organophosphorus nerve agents and pesticides: An overview of the principle strategies and current progress of mass spectrometry-based procedures for verification

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Evidence of poisoning with organophosphorus (OP) nerve agents requires biomedical verification.

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OP nerve agents undergo common biotransformation pathways producing valuable biomarkers.

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Internationally accepted methods target remaining poison, hydrolysis products and protein-adducts.

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Mass spectrometry-based methods provide optimum selectivity and sensitivity for identification.

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Methods, strategies, current proceedings, quality criteria and real cases of poisoning are presented.

Intoxication by organophosphorus (OP) poisons, like nerve agents and pesticides, is characterized by the life-threatening inhibition of acetylcholinesterase (AChE) caused by covalent reaction with the serine residue of the active site of the enzyme (phosphylation). Similar reactions occur with butyrylcholinesterase (BChE) and serum albumin present in blood as dissolved proteins. For forensic purposes, products (adducts) with the latter proteins are highly valuable long-lived biomarkers of exposure to OP agents that are accessible by diverse mass spectrometric procedures. In addition, the evidence of poison incorporation might also succeed by the detection of remaining traces of the agent itself, but more likely its hydrolysis and/or enzymatic degradation products. These relatively short-lived molecules are distributed in blood and tissue, and excreted via urine. This review presents the mass spectrometry-based methods targeting the different groups of biomarkers in biological samples, which are already internationally accepted by the Organisation for the Prohibition of Chemical Weapons (OPCW), introduces novel approaches in the field of biomedical verification, and outlines the strict quality criteria that must be fulfilled for unambiguous forensic analysis.

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.

Identification of S419 on human serum albumin as a novel biomarker for sarin and cyclosarin exposure

RATIONALE

Organophosphorus nerve agents are highly toxic because they inhibit acetylcholinesterase activity, thereby causing a series of symptomatic poisoning. Upon entering the body, nerve agents bind active amino acid residues to form phosphonylated adducts. A potentially beneficial method for specific verification of exposure of nerve agents is based on albumin adducts, which have a half-life of 18 days. This appears to be more effective than the fluoride reactivation method, based on acetylcholinesterase.

METHODS

After the exposure of human serum albumin to nine nerve agents, human serum albumin was denatured, reduced, alkylated and digested with trypsin according to standard mass spectrometry-based proteomics procedures. The phosphonylated peptides of human serum albumin were identified using positive ion electrospray ionization with a quadrupole orbitrap mass spectrometer.

RESULTS

The peptide KVPQVSTPTLVESR showed a good mass spectrometric response to the nine nerve agents. The tendency of sarin and cyclosarin was to bind to S419 on the peptide, while the other nerve agents (tabun, soman and V-type nerve agents) were shown to bind more readily to K414 on the peptide.

CONCLUSIONS

This research revealed a new site, S419, of the tryptic peptide KVPQVSTPTLVEVSR on human albumin to be a valuable biomarker for sarin/cyclosarin exposure, helping to further distinguish sarin and cyclosarin poisoning from that of other nerve agents and providing an important tool for the identification of sarin or cyclosarin in terrorist attacks.

Simultaneous determination of organophosphorus nerve agent markers in urine by IC-MS/MS using anion-exchange solid-phase extraction

In this study a comprehensive approach for determination of low molecular organophosphorus nerve agent markers - highly polar alkylphosphonic acids and much less polar alkyl methylphosphonic acids is presented. Accurate, sensitive and simultaneous determination of the nerve agent markers in human urine was performed by ion chromatography and tandem mass spectrometry using deuterated internal standards. Analysis of the urine extracts was conducted on an anion-exchanger based on poly(styrene-co-divinylbenzene) substrate with a high degree of crosslinking and a covalently-bonded branched functional layer. The use of this type of column allowed achieving high values of retention factors for alkylphosphonic acids and alkyl methylphosphonic acids due to combination of anion-exchange and hydrophobic interactions between the analytes and the stationary phase of the column. Prior to the analysis, the urine samples were purified using anion-exchange cartridges for solid-phase extraction, and high recovery values were achieved for each analyte. The developed IC-MS/MS technique was validated for linearity, limit of detection, limit of quantification, precision and accuracy using two LC-MS/MS instruments. The proposed approach was successfully tested on the urine samples, provided by the Organisation for the Prohibition of Chemical Weapons in the frame of the 4th Biomedical Proficiency Test.

Nerve agent markers screening after accumulation in garden cress (Lepidium sativum) used as a model plant object

In this research an accumulation of nerve agent markers in garden cress (Lepidium sativum) as a model plant object was studied using LC-QTOF hybrid system. For the determination of methylphosphonic acid and alkyl methylphosphonates, which are specific markers of sarin, soman, VR and VX, simple and sensitive approach was developed. Direct analysis of aqueous extracts on the reversed phase column with polar endcapping allowed to achieve satisfactory retention factor for methylphosphonic acid, which has high polarity and is usually very weakly retained on the ordinary reversed phase columns. Application of the QTOF mass spectrometer with high mass resolution led to the increase in the accuracy of the conducted measurements. The HPLC-HRMS technique developed exclusively for this study has been validated for linearity, limit of detection, limit of quantification, precision, accuracy and matrix effect prior to the analysis of plant extract samples. Hydroponic growth model was employed to examine accumulation of nerve agent markers in garden cress. It was found that after elimination of nerve agent markers from the plant growth medium, garden cress was able to store these substances for at least 5 weeks providing high retrospectivity of the analysis. Moreover, during the cress growth, no metabolization of alkyl methylphosphonates was observed. This allows not only to reveal the fact of nerve agents release into environment, but also to define its type after a long period of time.

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.

Rapid quantification of two chemical nerve agent metabolites in serum

Organophosphorus compounds (OPs) continue to represent a significant chemical threat to humans due to exposures from their use as weapons, their potential storage hazards, and from their continued use agriculturally. Existing methods for detection include ELISA and mass spectrometry. The new approach presented here provides an innovative first step toward a portable OP quantification method that surmounts conventional limitations involving sensitivity, selectivity, complexity, and portability. DNA affinity probes, or aptamers, represent an emerging technology that, when combined with a mix-and-read, free-solution assay (FSA) and a compensated interferometer (CI) can provide a novel alternative to existing OP nerve agent (OPNA) quantification methods. Here it is shown that FSA can be used to rapidly screen prospective aptamers in the biological matrix of interest, allowing the identification of a 'best-in-class' probe. It is also shown that combining aptamers with FSA-CI enables quantification of the OPNA metabolites, Sarin (NATO designation "G-series, B", or GB) and Venomous Agent X (VX) acids, rapidly with high selectivity at detection limits of sub-10 pg/mL in 25% serum (by volume in PBS). These results suggest there is potential to directly impact diagnostic specificity and sensitivity of emergency response testing methods by both simplifying sample preparation procedures and making a benchtop reader available for OPNA metabolite quantification.

Structural Insights of Stereospecific Inhibition of Human Acetylcholinesterase by VX and Subsequent Reactivation by HI-6

Over 50 years ago, the toxicity of irreversible organophosphate inhibitors targeting human acetylcholinesterase (hAChE) was observed to be stereospecific. The therapeutic reversal of hAChE inhibition by reactivators has also been shown to depend on the stereochemistry of the inhibitor. To gain clarity on the mechanism of stereospecific inhibition, the X-ray crystallographic structures of hAChE inhibited by a racemic mixture of VX (P _R/S) and its enantiomers were obtained. Beyond identifying hAChE structural features that lend themselves to stereospecific inhibition, structures of the reactivator HI-6 bound to hAChE inhibited by VX enantiomers of varying toxicity, or in its uninhibited state, were obtained. Comparison of hAChE in these pre-reactivation and post-reactivation states along with enzymatic data reveals the potential influence of unproductive reactivator poses on the efficacy of these types of therapeutics. The recognition of structural features related to hAChE's stereospecificity toward VX shed light on the molecular influences of toxicity and their effect on reactivators. In addition to providing a better understanding of the innate issues with current reactivators, an avenue for improvement of reactivators is envisioned.

Analysis of degradation products of nerve agents via post-pentafluorobenzylation liquid chromatography-tandem mass spectrometry

In the work reported here, a screening procedure was developed for the detection and identification of RMPAs (nerve agent degradation products) after pentafluorobenzylation using liquid chromatography-tandem mass spectrometry (LC-MS/MS). With this method, all RMPAs, including highly hydrophilic types such as methylphosphonic acid (MPA) and ethyl methylphosphonic acid (EMPA), were sufficiently retained in commonly used reversed-phase columns (retention times: 15.7 and 11.0 min.), and the presence of RMPAs was determined more efficiently than with the conventional direct LC-MS/MS method. The detection limits of RMPAs using this approach (<33 ng) were mostly superior to those observed with direct LC-MS/MS (<74 ng) and gas chromatography-mass spectrometry (GC-MS) after pentafluorobenzylation (<1.1 μg). The applicability of newly developed method toward real samples was evaluated via recovery tests involving urine/serum and wipe tests on various surfaces.

Investigation of dried blood sampling with liquid chromatography tandem mass spectrometry to confirm human exposure to nerve agents

A method was developed to detect and quantify organophosphate nerve agent (OPNA) metabolites in dried blood samples. Dried blood spots (DBS) and microsampling devices are alternatives to traditional blood draws, allowing for safe handling, extended stability, reduced shipping costs, and potential self-sampling. DBS and microsamplers were evaluated for precision, accuracy, sensitivity, matrix effects, and extraction recovery following collection of whole blood containing five OPNA metabolites. The metabolites of VX, Sarin (GB), Soman (GD), Cyclosarin (GF), and Russian VX (VR) were quantitated from 5.0 to 500 ng mL^-1 with precision of ≤16% and accuracy between 93 and 108% for QC samples with controlled volumes. For unknown spot volumes, OPNA metabolite concentrations were normalized to total blood protein to improve interpretation of nerve agent exposures. This study provides data to support the use of DBS and microsamplers to collect critical exposure samples quickly, safely, and efficiently following large-scale chemical exposure events.

Efficient derivatization of methylphosphonic and aminoethylsulfonic acids related to nerve agents simultaneously in soils using trimethyloxonium tetrafluoroborate for their enhanced, qualitative detection and identification by EI-GC-MS and GC-FPD

Trimethyloxonium tetrafluoroborate (TMO·BF₄) has been used in the simultaneous derivatization of phosphonic and 2-aminoethylsulfonic acids related to nerve agents in different soils for their enhanced detection and identification by electron ionization gas chromatography-mass spectrometry (EI-GC-MS). The panel of acids consisted of five Schedule 2 phosphonic acids (methyl methylphosphonic acid, ethyl methylphosphonic acid, isopropyl methylphosphonic acid, pinacolyl methylphosphonic acid and cyclohexyl methylphosphonic acid) along with two sulfonic acids, N,N-diethyl-2-aminoethylsulfonic acid and N,N-diisopropyl-2-aminoethylsulfonic acid. The acids were converted to their corresponding methyl esters at ambient temperature when present at a 10μgg^-1 concentration in three separate soils: Virginia type A soil, Ottawa sand and Nebraska EPA soil. The concentration of the acids reflects values typically encountered during proficiency tests (PTs) administered annually by the Organisation for the Prohibition of Chemical Weapons (OPCW). Derivatization times to yield detectable signals for the methyl ester products for all the acids was found to vary among all three soil samples, however, it was found that generally the most optimal time across all the matrices involved was 3h after the addition of TMO·BF₄. Concomitantly, the analysis of the samples was complemented using GC coupled to flame photometric detection (GC-FPD). The inclusion of GC-FPD in the analysis yielded stronger signals for all seven methylated analytes making their detection after merely 3h possible relative to the ones initially obtained with EI-GC-MS. Regarding the three soils employed in our study, a greater methylating efficiency was found in the Virginia type A soil and Ottawa sand yielding results that were significantly larger in magnitude to those found during the same time points for the Nebraska EPA soil sample. Prolonged reaction times (up to 72h) were explored to find the time for the highest yield of methyl ester production were found instead to be deleterious to the process showcasing the importance of the fast yielding nature of the process specifically in situations where time-sensitive analysis is crucial (e.g. OPCW-PT).

Modification of human serum albumin by the nerve agent VX: microbore liquid chromatography/electrospray ionization high-resolution time-of-flight tandem mass spectrometry method for detection of phosphonylated tyrosine and novel cysteine containing disulfide adducts

RATIONALE

Organophosphorus nerve agents still constitute a considerable threat to the health of military personnel and the civilian population. Long-term biomarkers are crucial for reliable verification of exposure to banned substances. Therefore, current research focuses on identification of endogenous protein targets showing covalent modifications by organophosphorus nerve agents (adducts).

METHODS

Purified human serum albumin and human plasma were incubated with the nerve agent VX followed by enzymatic proteolysis with pronase. Resulting peptide cleavage products were separated by microbore liquid chromatography (μLC) online coupled to positive electrospray ionization (ESI) with subsequent high-resolution time-of-flight tandem mass spectrometry (HR MS/MS) allowing identification of known and novel adducts.

RESULTS

In addition to known phosphonylation of various tyrosine residues, albumin was found to be modified at diverse cysteine residues by covalent attachment of the leaving group of VX. These novel disulfide adducts were cleaved from at least two regions of the intact protein as dipeptides containing cysteine and proline either as CP or PC. A rapid and sensitive method was developed for simultaneous detection of the diverse covalent modifications of human albumin by VX.

CONCLUSIONS

Identification of the novel leaving group adducts with human albumin expands the basic knowledge on molecular toxicology of the nerve agent VX. Furthermore, the presented μLC/ESI HR MS/MS method might be of relevance for verification of VX poisoning. Copyright © 2016 John Wiley & Sons, Ltd.

A high-throughput UHPLC-MS/MS method for the quantification of five aged butyrylcholinesterase biomarkers from human exposure to organophosphorus nerve agents

Organophosphorus nerve agents (OPNAs) are toxic compounds that are classified as prohibited Schedule 1 chemical weapons. In the body, OPNAs bind to butyrylcholinesterase (BChE) to form nerve agent adducts (OPNA-BChE). OPNA-BChE adducts can provide a reliable, long-term protein biomarker for assessing human exposure. A major challenge facing OPNA-BChE detection is hydrolysis (aging), which can continue to occur after a clinical specimen has been collected. During aging, the o-alkyl phosphoester bond hydrolyzes, and the specific identity of the nerve agent is lost. To better identify OPNA exposure events, a high-throughput method for the detection of five aged OPNA-BChE adducts was developed. This is the first diagnostic panel to allow for the simultaneous quantification of any Chemical Weapons Convention Schedule 1 OPNA by measuring the aged adducts methyl phosphonate, ethyl phosphonate, propyl phosphonate, ethyl phosphoryl, phosphoryl and unadducted BChE. The calibration range for all analytes is 2.00-250. ng/mL, which is consistent with similar methodologies used to detect unaged OPNA-BChE adducts. Each analytical run is 3 min, making the time to first unknown results, including calibration curve and quality controls, less than 1 h. Analysis of commercially purchased individual serum samples demonstrated no potential interferences with detection of aged OPNA-BChE adducts, and quantitative measurements of endogenous levels of BChE were similar to those previously reported in other OPNA-BChE adduct assays.

Simultaneous quantification of soman and VX adducts to butyrylcholinesterase, their aged methylphosphonic acid adduct and butyrylcholinesterase in plasma using an off-column procainamide-gel separation method combined with UHPLC-MS/MS

This work describes a novel and sensitive non-isotope dilution method for simultaneous quantification of organophosphorus nerve agents (OPNAs) soman (GD) and VX adducts to butyrylcholinesterase (BChE), their aged methylphosphonic acid (MeP) adduct and unadducted BChE in plasma exposed to OPNA. OPNA-BChE adducts were isolated with an off-column procainamide-gel separation (PGS) from plasma, and then digested with pepsin into specific adducted FGES^*AGAAS nonapeptide (NP) biomarkers. The resulting NPs were detected by UHPLC-MS/MS MRM. The off-column PGS method can capture over 90% of BChE, MeP-BChE, VX-BChE and GD-BChE from their respective plasma materials. One newly designed and easily synthesized phosphorylated BChE nonapeptide with one Gly-to-Ala mutation was successfully reported to serve as internal standard instead of traditional isotopically labeled BChE nonapeptide. The linear range of calibration curves were from 1.00-200ngmL^-1 for VX-NP, 2.00-200ngmL^-1 for GD-NP and MeP-NP (R²≥0.995), and 3.00-200ngmL^-1 for BChE NP (R²≥0.990). The inter-day precision had relative standard deviation (%RSD) of <8.89%, and the accuracy ranged between 88.9-120%. The limit of detection was calculated to be 0.411, 0.750, 0.800 and 1.43ngmL^-1 for VX-NP, GD-NP, MeP-NP and BChE NP, respectively. OPNA-exposed quality control plasma samples were characterized as part of method validation. Investigation of plasma samples unexposed to OPNA revealed no baseline values or interferences. Using the off-column PGS method combined with UHPLC-MS/MS, VX-NP and GD-NP adducts can be unambiguously detected with high confidence in 0.10ngmL^-1 and 0.50ngmL^-1 of exposed human plasma respectively, only requiring 0.1mL of plasma sample and taking about four hours without special sample preparation equipment. These improvements make it a simple, sensitive and robust PGS-UHPLC-MS/MS method, and this method will become an attractive alternative to immunomagnetic separation (IMS) method and a useful diagnostic tool for retrospective detection of OPNA exposure with high confidence. Furthermore, using the developed method, the adducted BChE levels from VX and GD-exposed (0.10-100ngmL^-1) plasma samples were completely characterized, and the fact that VX being more active and specific to BChE than GD was re-confirmed.

Bridging the Gap between Sample Collection and Laboratory Analysis: Using Dried Blood Spots to Identify Human Exposure to Chemical Agents

Public health response to large scale chemical emergencies presents logistical challenges for sample collection, transport, and analysis. Diagnostic methods used to identify and determine exposure to chemical warfare agents, toxins, and poisons traditionally involve blood collection by phlebotomists, cold transport of biomedical samples, and costly sample preparation techniques. Use of dried blood spots, which consist of dried blood on an FDA-approved substrate, can increase analyte stability, decrease infection hazard for those handling samples, greatly reduce the cost of shipping/storing samples by removing the need for refrigeration and cold chain transportation, and be self-prepared by potentially exposed individuals using a simple finger prick and blood spot compatible paper. Our laboratory has developed clinical assays to detect human exposures to nerve agents through the analysis of specific protein adducts and metabolites, for which a simple extraction from a dried blood spot is sufficient for removing matrix interferents and attaining sensitivities on par with traditional sampling methods. The use of dried blood spots can bridge the gap between the laboratory and the field allowing for large scale sample collection with minimal impact on hospital resources while maintaining sensitivity, specificity, traceability, and quality requirements for both clinical and forensic applications.

Evaluation of Multiple Blood Matrices for Assessment of Human Exposure to Nerve Agents

Biomedical samples may be used to determine human exposure to nerve agents through the analysis of specific biomarkers. Samples received may include serum, plasma, whole blood, lysed blood and, due to the toxicity of these compounds, postmortem blood. To quantitate metabolites resulting from exposure to sarin (GB), soman (GD), cyclosarin (GF), VX and VR, these blood matrices were evaluated individually for precision, accuracy, sensitivity and specificity. Accuracies for these metabolites ranged from 100 to 113% with coefficients of variation ranging from 2.31 to 13.5% across a reportable range of 1-100 ng/mL meeting FDA recommended guidelines for bioanalytical methods in all five matrices. Limits of detection were calculated to be 0.09-0.043 ng/mL, and no interferences were detected in unexposed matrix samples. The use of serum calibrators was also determined to be a suitable alternative to matrix-matched calibrators. Finally, to provide a comparative value between whole blood and plasma, the ratio of the five nerve agent metabolites measured in whole blood versus plasma was determined. Analysis of individual whole blood samples (n = 40), fortified with nerve agent metabolites across the reportable range, resulted in average nerve agent metabolite blood to plasma ratios ranging from 0.53 to 0.56. This study demonstrates the accurate and precise quantitation of nerve agent metabolites in serum, plasma, whole blood, lysed blood and postmortem blood. It also provides a comparative value between whole blood and plasma samples, which can assist epidemiologists and physicians with interpretation of test results from blood specimens obtained under variable conditions.

Simultaneous measurement of tabun, sarin, soman, cyclosarin, VR, VX, and VM adducts to tyrosine in blood products by isotope dilution UHPLC-MS/MS

This work describes a new specific, sensitive, and rapid stable isotope dilution method for the simultaneous detection of the organophosphorus nerve agents (OPNAs) tabun (GA), sarin (GB), soman (GD), cyclosarin (GF), VR, VX, and VM adducts to tyrosine (Tyr). Serum, plasma, and lysed whole blood samples (50 μL) were prepared by protein precipitation followed by digestion with Pronase. Specific Tyr adducts were isolated from the digest by a single solid phase extraction (SPE) step, and the analytes were separated by reversed-phase ultra high performance liquid chromatography (UHPLC) gradient elution in less than 2 min. Detection was performed on a triple quadrupole tandem mass spectrometer using time-triggered selected reaction monitoring (SRM) in positive electrospray ionization (ESI) mode. The calibration range was characterized from 0.100-50.0 ng/mL for GB- and VR-Tyr and 0.250-50.0 ng/mL for GA-, GD-, GF-, and VX/VM-Tyr (R(2) ≥ 0.995). Inter- and intra-assay precision had coefficients of variation of ≤17 and ≤10%, respectively, and the measured concentration accuracies of spiked samples were within 15% of the targeted value for multiple spiking levels. The limit of detection was calculated to be 0.097, 0.027, 0.018, 0.074, 0.023, and 0.083 ng/mL for GA-, GB-, GD-, GF-, VR-, and VX/VM-Tyr, respectively. A convenience set of 96 serum samples with no known nerve agent exposure was screened and revealed no baseline values or potential interferences. This method provides a simple and highly specific diagnostic tool that may extend the time postevent that a confirmation of nerve agent exposure can be made with confidence.