Immunomagnetic separation and quantification of butyrylcholinesterase nerve agent adducts in human serum

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.

Optical imaging probes for selective detection of butyrylcholinesterase

Butyrylcholinesterase (BChE), a member of the human serine hydrolase family, is an essential enzyme for cholinergic neurotransmission as it catalyzes the hydrolysis of acetylcholine. It also plays central roles in apoptosis, lipid metabolism, and xenobiotic detoxification. On the other side, abnormal levels of BChE are directly associated with the formation of pathogenic states such as neurodegenerative diseases, psychiatric and cardiovascular disorders, liver damage, diabetes, and cancer. Thus, selective and sensitive detection of BChE level in living organisms is highly crucial and is of great importance to further understand the roles of BChE in both physiological and pathological processes. However, it is a very complicated task due to the potential interference of acetylcholinesterase (AChE), the other human cholinesterase, as these two enzymes share a very similar substrate scope. To this end, optical imaging probes have attracted immense attention in recent years as they have modular structures, which can be tuned precisely to satisfy high selectivity toward BChE, and at the same time they offer real time and nondestructive imaging opportunities with a high spatial and temporal resolution. Here, we summarize BChE selective imaging probes by discussing the critical milestones achieved during the development process of these molecular sensors over the years. We put a special emphasis on design principles and biological applications of highly promising new generation activity-based probes. We also give a comprehensive outlook for the future of BChE-responsive probes and highlight the ongoing challenges. This collection marks the first review article on BChE-responsive imaging agents.

Pesticide pestilence: Global scenario and recent advances in detection and degradation methods

Increased anthropogenic activities are confronted as the main cause for rising environmental and health concerns globally, presenting an indisputable threat to both environment and human well-being. Modern-day industrialization has given rise to a cascade of concurrent environmental and health challenges. The global human population is growing at an alarming rate, posing tremendous pressure on future food security, and healthy and environmentally sustainable diets for all. To feed all, the global food production needs to increase by 50% by 2050, but this increase has to occur from the limited arable land, and under the present-day climate variabilities. Pesticides have become an integral component of contemporary agricultural system, safeguarding crops from pests and diseases and their use must be reduce to fulfill the SDG (Sustainable Development Goals) agenda . However, their indiscriminate use, lengthy half-lives, and high persistence in soil and aquatic ecosystems have impacted global sustainability, overshot the planetary boundaries and damaged the pure sources of life with severe and negative impacts on environmental and human health. Here in this review, we have provided an overview of the background of pesticide use and pollution status and action strategies of top pesticide-using nations. Additionally, we have summarized biosensor-based methodologies for the rapid detection of pesticide residue. Finally, omics-based approaches and their role in pesticide mitigation and sustainable development have been discussed qualitatively. The main aim of this review is to provide the scientific facts for pesticide management and application and to provide a clean, green, and sustainable environment for future generations.

A retrospective screening method for carbamate toxicant exposure based on butyrylcholinesterase adducts in human plasma with ultra-high performance liquid chromatography-tandem mass spectrometry

Carbamate pesticides are extensively used in agriculture for their inhibition to acetylcholinesterase and damages to the insects' neural systems. Because of their toxicity, human poisoning incidents caused by carbamate pesticide exposure have occurred from time to time. What's more, some lethally toxic carbamate toxicants known as carbamate nerve agents (CMNAs) have been supplemented in Schedule 1 of the Annex on Chemicals in the Chemical Weapons Convention (CWC) by Organisation of the Prohibition of Chemical Weapons (OPCW) from 2020. And some other carbamates, like physostigmine, have been used in clinical treatment as anticholinergic drugs and their misuse may also cause damages to the body. Similar to organophosphorus toxicants, carbamate toxicants would react with butyrylcholinesterase (BChE) in plasma when entering the human body, resulting in the BChE adducts, based on which the exposure of carbamate toxicants could be detected retrospectively. In this study, methylcarbamyl nonapeptide and dimethylcarbamyl nonapeptide from pepsin digestion of BChE adducts were identified with ultra-high performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS) in product ion scan mode. Carbofuran was chosen as the target to establish the detection method of carbamate toxicant exposure based on methylcarbamyl nonapeptide digested from methylcarbamyl BChE. Procainamide-gel affinity purification, pepsin digestion and UHPLC-MS/MS analysis in multiple reaction monitoring (MRM) mode were applied. Under the optimized conditions of sample preparation and UHPLC-MS/MS MRM analysis, the limits of detection (LODs) reached 10.0 ng/mL of plasma exposed to carbofuran with satisfactory specificity. The quantitation approach was established with d₃-carbofuran-exposed plasma as the internal standard (IS) and the linearity range was 30.0-1.00 × 10³ nmol/L (R² >0.998) with the accuracy of 95.6%-107% and precision of ≤9% relative standard deviation (RSD). The applicability was also evaluated by N,N-dimethyl-carbamates with the LODs of 30.0 nmol/L for pirimicarb-exposed plasma based on dimethylcarbamyl nonapeptide. Because most of carbamate toxicants has methylcarbamyl or dimethylcarbamyl groups, this approach could be applied on the retrospective screening of carbamate toxicant exposure including CMNAs, carbamate pesticides or carbamate drugs. This study could provide an effective means in the fields of CWC verification, toxicological mechanism investigation and down-selection of potential treatment options.

Malathion detection based on polydopamine enhanced oxidase-mimetic activity of palladium nanocubes

Nowadays, fabricating simple and efficient pesticide detection methods become a research focus due to the great threat pesticide residues posed to human health and environment. Herein, we constructed a high-efficiency and sensitive colorimetric detection platform for malathion detection based on polydopamine-dressed Pd nanocubes (PDA-Pd/NCs). The Pd/NCs coated with PDA exhibited excellent oxidase-like activity, which was attributed to the substrates accumulation and accelerated electron transfer induced by PDA. What's more, we successfully achieved sensitive detection of acid phosphatase (ACP) using 3,3',5,5'-tetramethylbenzidine (TMB) as the chromogenic substrate, relying on the satisfactory oxidase activity from PDA-Pd/NCs. However, the addition of malathion could inhibit the activity of ACP and limit the production of medium AA. Therefore, we constructed a colorimetric assay for malathion based on PDA-Pd/NCs + TMB + ACP system. The wide linear range (0-8 μM) and low detection limit (0.023 μM) indicate excellent analytical performance, which is superior to most malathion analysis methods previously reported. This work not only provides a new idea for dopamine coated nano-enzyme to improve its catalytic activity, but also creates a new tactics for the detection of pesticides such as malathion.

Review: Organophosphorus toxicants, in addition to inhibiting acetylcholinesterase activity, make covalent adducts on multiple proteins and promote protein crosslinking into high molecular weight aggregates

The acute effects of exposure to organophosphorus toxicants are explained by inhibition of acetylcholinesterase activity. However, the mechanisms that explain long term illness associated with organophosphorus exposure are still under investigation. We find that organophosphorus nerve agents and organophosphorus pesticides make covalent adducts not only on the serine from acetylcholinesterase, but also on tyrosine, lysine, glutamate, serine and threonine from a variety of proteins. Almost any protein can be modified by a high dose of organophosphorus toxicant. A low dose of 10 μM chlorpyrifos oxon added to the serum-free culture medium of human neuroblastoma SH-SY5Y cells resulted in tyrosine adducts on 48 proteins immunopurified from the cell lysate. We identified the adducted proteins by mass spectrometry after immunopurifying modified proteins with a rabbit anti-diethoxyphospho-tyrosine monoclonal antibody which biased this study for tyrosine adducts. In cultured cells, the primary organophosphate targets are abundant proteins. Organophosphate-modified proteins may disrupt physiological processes. In separate experiments we identified organophosphate adducts on lysine. Organophosphylation activates the lysine for protein crosslinking. The activated lysine reacts with glutamic acid or aspartic acid protein side chains to form an isopeptide bond between proteins, resulting in high molecular weight crosslinked proteins. Crosslinked proteins form insoluble aggregates that may lead to neurogenerative disease.

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.

Verification of exposure to chemical warfare agents through analysis of persistent biomarkers in plants

The continuing threats of military conflicts and terrorism may involve the misuse of chemical weapons. The present study aims to use environmental samples to find evidence of the release of such agents at an incident scene. A novel approach was developed for identifying protein adducts in plants. Basil (Ocimum basilicum), bay laurel leaf (Laurus nobilis) and stinging nettle (Urtica dioica) were exposed to 2.5 to 150 mg m^-3 sulfur mustard, 2.5 to 250 mg m^-3 sarin, and 0.5 to 25 g m^-3 chlorine gas. The vapors of the selected chemicals were generated under controlled conditions in a dedicated set-up. After sample preparation and digestion, the samples were analyzed by liquid chromatography tandem mass spectrometry (LC-MS/MS) and liquid chromatography high resolution tandem mass spectrometry (LC-HRMS/MS), respectively. In the case of chlorine exposure, it was found that 3-chloro- and 3,5-dichlorotyrosine adducts were formed. As a result of sarin exposure, the o-isopropyl methylphosphonic acid adduct to tyrosine could be analyzed, and after sulfur mustard exposure the N1- and N3-HETE-histidine adducts were identified. The lowest vapor exposure levels for which these plant adducts could be detected, were 2.5 mg m^-3 for sarin, 50 mg m^-3 for chlorine and 12.5 mg m^-3 for sulfur mustard. Additionally, protein adducts following a liquid exposure of only 2 nmol Novichock A-234, 0.4 nmol sarin and 0.2 nmol sulfur mustard could still be observed. For both vapor and liquid exposure, the amount of adduct formed increased with the level of exposure. In all cases synthetic reference standards were used for unambiguous identification. The window of opportunity for investigation of agent exposure through the analysis of plant material was found to be remarkably long. Even three months after the actual exposure, the biomarkers could still be detected in the living plants, as well as in dried leaves. An important benefit of the current method is that a relatively simple and generic sample work-up procedure can be applied for all agents studied. In conclusion, the presented work clearly demonstrates the possibility of analyzing chemical warfare agent biomarkers in plants, which is useful for forensic reconstructions, including the investigation into alleged use in conflict areas.

Advances in Noble-Metal Nanoparticle-Based Fluorescence Detection of Organophosphorus Chemical Warfare Agents

Efficient and simple detection of chemical warfare agents (CWAs) is an essential step in minimizing the potentially lethal consequences of chemical weapons. CWAs are a family of organic chemicals that are used as chemical weapons because of their enormous severity and lethal effects when faced with unforeseen challenges. To stop the spread of CWAs, it is critical to develop a platform that detects them in a sensitive, timely, selective, and minimally invasive manner. Rapid advances in the demand for on-site sensors, metal nanoparticles, and biomarker identification for CWAs have made it possible to use fluorescence as a precise real-time and point-of-care (POCT) testing technique. For POCT-based applications, the new capabilities of micro- and nanomotors offer enormous prospects. In recent decades, significant progress has been made in the design of fluorescent sensors and the further development of noble metal nanoparticles for the detection of organophosphorus CWAs, as described in this review. Through this work, recent attempts to fabricate sensors that can detect organophosphorus CWAs through changes in their fluorescence properties have been summarized. Finally, an integrated outlook on how noble metal nanoparticles could be used to develop smart sensors for organophosphorus CWAs that communicate with and control electronic devices to monitor and improve the health of individuals.

Current Progress for Retrospective Identification of Nerve Agent Biomarkers in Biological Samples after Exposure

Organophosphorus neurotoxic agents (OPNAs) seriously damage the nervous system, inhibiting AChE activity and threatening human health and life. Timely and accurate detection of biomarkers in biomedical samples is an important means for identifying OPNA exposure, helping to recognize and clarify its characteristics and providing unambiguous forensic evidence for retrospective research. It is therefore necessary to summarize the varieties of biomarkers, recognize their various characteristics, and understand the principal research methods for these biomarkers in the retrospective detection of OPNA exposure. Common biomarkers include mainly intact agents, degradation products and protein adducts. Direct agent identification in basic experimental research was successfully applied to the detection of free OPNAs, however, this method is not applicable to actual biomedical samples because the high reactivity of OPNAs promotes rapid metabolism. Stepwise degradation products are important targets for retrospective research and are usually analyzed using a GC–MS, or an LC–MS system after derivatization. The smaller window of detection time requires that sampling be accomplished within 48 h, increasing the obstacles to determining OPNA exposure. For this reason, the focus of retrospective identification of OPNA exposure has shifted to protein adducts with a longer lifetime. Compared to the fluoride-induced reactivation method, which cannot be used for aged adducts, digestive peptide analysis is the more elegant method for detecting various adducts, identifying more active sites, exploring potential biomarkers and excavating characteristic ions. Retrospective identification of biomarkers after OPNA poisoning is of primary importance, providing unambiguous evidence for forensic analysis in actual cases and judgment of chemical accidents. At present, degradation products, the nonapeptide from BChE adducts and Y411 from human serum adducts are used successfully in actual cases of OPNA exposure. However, more potential biomarkers are still in the discovery stage, which may prove inconclusive. Therefore, there is an urgent need for research that screens biomarker candidates with high reactivity and good reliability from the potential candidates. In addition, mass spectrometry detection with high resolution and reactivity and an accurate data processing system in the scanning mode must also be further improved for the retrospective identification of unknown agents.

Identification of sulfonamide-based butyrylcholinesterase inhibitors using machine learning

Aim: This study reports the designing of BChE inhibitors through machine learning (ML), followed by in silico and in vitro evaluations. Methodology: ML technique was used to predict the virtual hit, and its derivatives were synthesized and characterized. The compounds were evaluated by using various in vitro tests and in silico methods. Results: The gradient boosting classifier predicted N-phenyl-4-(phenylsulfonamido) benzamide as an active BChE inhibitor. The derivatives of the inhibitor, i.e., compounds 34, 37 and 54 were potent BChE inhibitors and displayed blood-brain barrier permeability with no significant AChE inhibition. Conclusion: The ML prediction was effective, and the synthesized compounds showed the BChE inhibitory activity, which was also supported by the in silico studies.

Identification of sulfonamide based butyrylcholinesterase inhibitors through scaffold hopping approach

Butyrylcholinesterase (BChE), a hydrolytic enzyme, is responsible for the termination of the action of acetylcholine besides acetylcholinesterase (AChE) in the synaptic cleft of the brain. The alteration in the enzyme level, in patients with the progression of Alzheimer's disease, makes it a therapeutic target. In the present study, we developed BChE inhibitors through scaffold hopping by exploring two previously reported compounds, i.e., 1,4-bis((4-chlorophenyl) sulfonyl)-3,6-diphenylpiperazine-2,5-dione and N-(2-chlorophenyl)-4-(phenylsulfonamido)benzamide, to afford scaffold and pharmacophore fragments, respectively. The N,2-diphenyl-2-(phenylsulfonamido)acetamide derivatives, thus designed, were synthesised and screened for the inhibition of AChE and BChE enzymes. Compounds 30 and 33 were found to be most active against BChE among the derivatives, with IC₅₀ values of 7.331 ± 0.946 and 10.964 ± 0.936 μM, respectively. The compounds displayed a non-competitive mode of inhibition along with BBB permeability and good cell viability on SH-SY5Y cell line. The molecular docking analysis of the compounds with BChE showed interactions with Trp82, Trp231, Leu286, and His438. The molecular dynamics study revealed the stability of the protein-ligand complexes.

Nontargeted High-Resolution Mass Spectrometric Workflow for the Detection of Butyrylcholinesterase-Derived Adducts with Organophosphorus Toxicants and Structural Characterization of Their Phosphyl Moiety after In-Source Fragmentation

Organophosphorus (OP) nerve agents were used for chemical warfare, assassination, and attempted murder of individuals. Therefore, forensic methods are required to identify known and unknown incorporated OP poisons. Serum is tested for the presence of covalent reaction products (adducts) of the toxicant with, e.g., butyrylcholinesterase (BChE) typically by targeted analysis, thus only detecting known OP adducts. We herein present a nontargeted two-step mass spectrometry (MS)-based workflow taking advantage of a high-resolution (HR) Orbitrap mass spectrometer and its option for in-source collision-induced dissociation (IS-CID) highly valuable for the detection of unknown agents. BChE adducts are extracted by immunomagnetic separation and proteolyzed with pepsin yielding a phosphylated nonapeptide (NP) biomarker NP(OP). In step 1, the sample is separated by micro liquid chromatography (μLC) detecting the NP(OP) by nontargeted HR MS followed by data-dependent tandem-MS (ddMS2). Extracted ion chromatograms of diagnostic product ions at m/z 778.33661, 673.29402, and 602.25690 reveal the accurate mass of the NP(OP) precursor ion as well as the elemental composition of the adducted phosphyl moiety. Considering this information, a second μLC run is performed (step 2) for nonselective IS-CID of NP(OP) yielding the cleaved charged phosphyl moiety. This fragment ion is immediately subjected to targeted CID in parallel reaction monitoring (PRM). The accurate mass of its product ions allows the determination of their elemental composition and thus supports its structural elucidation. The described workflow was exemplarily applied to NP(OP) of three Tamelin esters and VX providing highly appropriate abilities for the detection of adducts even of unknown OP poisons like Novichok agents.

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.

Transthyretin as a target of alkylation and a potential biomarker for sulfur mustard poisoning: Electrophoretic and mass spectrometric identification and characterization

For the verification of exposure to the banned blister agent sulfur mustard (SM) and the better understanding of its pathophysiology, protein adducts formed with endogenous proteins represent an important field of toxicological research. SM and its analogue 2-chloroethyl ethyl sulfide (CEES) are well known to alkylate nucleophilic amino acid side chains, for example, free-thiol groups of cysteine residues. The specific two-dimensional thiol difference gel electrophoresis (2D-thiol-DIGE) technique making use of maleimide dyes allows the staining of free cysteine residues in proteins. As a consequence of alkylation by, for example, SM or CEES, this staining intensity is reduced. 2D-thiol-DIGE analysis of human plasma incubated with CEES and subsequent matrix-assisted laser desorption/ionization time-of-flight (tandem) mass-spectrometry, MALDI-TOF MS(/MS), revealed transthyretin (TTR) as a target of alkylating agents. TTR was extracted from SM-treated plasma by immunomagnetic separation (IMS) and analyzed after tryptic cleavage by microbore liquid chromatography-electrospray ionization high-resolution tandem-mass spectrometry (μLC-ESI MS/HR MS). It was found that the Cys¹⁰ -residue of TTR present in the hexapeptide C(-HETE)PLMVK was alkylated by the hydroxyethylthioethyl (HETE)-moiety, which is characteristic for SM exposure. It was shown that alkylated TTR is stable in plasma in vitro at 37°C for at least 14 days. In addition, C(-HETE)PLMVK can be selectively detected, is stable in the autosampler over 24 h, and shows linearity in a broad concentration range from 15.63 μM to 2 mM SM in plasma in vitro. Accordingly, TTR might represent a complementary protein marker molecule for the verification of SM exposure.

Verification of Exposure to Novichok Nerve Agents Utilizing a Semitargeted Human Butyrylcholinesterase Nonapeptide Assay

Novichok (NV) nerve agents were recently added to the list of Schedule 1 chemicals of the Chemical Weapons Convention. There is a well-accepted method for assessment of nerve agent exposure based on mass spectrometric analysis of a nonapeptide with the serine-198 residue modified by the nerve agent, but this approach has not yet been reported for the class of NV agents and requires the availability of reference standards, which may be a limitation for NV agent exposure assessment. Thus, a goal of this study was to first verify the utility of the nonapeptide method for the characterization of human plasma samples exposed in vitro to the NV agents A-230, A-232, and A-234. A second aim was to evaluate the possibility of identifying unknown exposures by applying precursor ion scanning in combination with high resolution mass spectrometry (HRMS). Thus, precursor ion scanning, with a generic fragment ion (m/z 778) of the nonapeptide, was used to pinpoint any modified nonapeptide, while HRMS was used for structural elucidation of the adduct moiety. By this approach, use of HRMS enabled differentiation between adducts of agents with similar molecular masses. A new unique feature that could be exploited for NV nonapeptide analysis was that the modification was released from the peptide during fragmentation in the mass spectrometer and was detected in the low-mass region of the mass spectrum. This low-mass region was extremely informative and contributed to the assignment of the structure of the particular agent used, which is especially important in case no reference materials are available. The presented method is important for verification purposes by the Organisation for Prohibition of Chemical Weapons (OPCW), e.g., in case of investigations of alleged use of NV agents, and for regular forensic investigations.

Evaluation of mass spectrometry MS/MS spectra for the presence of isopeptide crosslinked peptides

Isopeptide crosslinked proteins can be the product of transglutaminase or of exposure to organophosphorus toxicants (OP). Transglutaminase links glutamine to lysine with loss of ammonia. OP toxicants induce a link between glutamic acid and lysine with loss of water. Our goal was to establish criteria to distinguish real from false isopeptide crosslinks reported by software searches of mass spectrometry data. We used fragmentation spectra of tryptic peptides from MAP-rich tubulin Sus scrofa as a test system for detection of naturally-occurring isopeptide crosslinks. Data were analyzed with Protein Prospector. Criteria for the assignments included the presence of at least 1 crosslink specific product ion, fragment ions from both peptides, Protein Prospector scores ≥20, and best fit of the MS/MS data to the crosslinked peptide as opposed to a linear peptide. Out of 301,364 spectra, 15 potential transglutaminase-type crosslinked peptide candidates were identified. Manual evaluation of these MS/MS spectra reduced the number to 1 valid crosslink between Q112 of NFH and K368 of Tau. Immunopurification with anti-isopeptide 81D1C2 confirmed that MAP-rich tubulin contained only one isopeptide. Support for this isopeptide bond was obtained by showing that transglutaminase was capable of incorporating dansyl-aminohexyl -QQIV into K368. A model of the KIETHK-QLEAHNR isopeptide was synthesized with the aid of transglutaminase. MS/MS spectra of the model validated our interpretation of the native isopeptide. An OP-induced isopeptide bond between K163 of tubulin alpha-1A and E158 of tubulin beta-4B was induced by treating MAP-rich tubulin with 100 μM chlorpyrifos oxon. This crosslink was supported by the criteria described above and by the presence of diethoxyphospho-lysine 163 in the tubulin alpha-1A peptide. The information obtained in this work is valuable for future studies that aim to understand why exposure to OP is associated with increased risk of neurodegenerative disease.

Identification and Study of Biomarkers from Novichok-Inhibited Butyrylcholinesterase in Human Plasma

To identify biomarkers of ethyl (1-(diethylamino)ethylidene)phosphoramidofluoridate (A234)- or methyl (1-(diethylamino)ethylidene)phosphoramidofluoridate (A232)-inhibited butyrylcholinesterase (BChE), we investigated nonapeptide adducts containing the active site serine, which plays a key role in enzyme activity, using LC-MS/HRMS. Biomarkers were acquired as expected, and they exhibited a significant amount of fragment ions from the inhibiting agent itself, in contrast to the MS2 spectra of conventional nerve agents. These biomarkers had a higher abundance of [M+2H]2+ ions than [M+H]+ ions, making doubly charged ions more suitable for trace analysis.

Evidence of exposure to organophosphorus toxicants by detection of the propionylated butyrylcholinesterase-derived nonapeptide-adduct as a novel biomarker

Organophosphorus (OP) nerve agents represent a class of highly toxic chemical warfare agents banned by the Chemical Weapons Convention. Nevertheless, in the past few years they have been used repeatedly for warfare, assassination and attempted murder. In addition, the chemically related OP pesticides were frequently used for suicide and may be deployed for terroristic attacks. Therefore, sensitive and selective bioanalytical methods are indispensable to investigate biological specimens as pieces of evidence to prove poisoning. OP agents form long-lived covalent reaction products (adducts) with endogenous proteins like human serum albumin (HSA) and butyrylcholinesterase (BChE). The adducted nonapeptide (NP) obtained by proteolysis of the BChE-adduct is one of the most sensitive and important biomarkers. We herein present a novel class of NP-adducts propionylated at its N-terminal phenylalanine residue (F195). The biomarker derivative is produced by addition of propionic anhydride to the NP-adduct inducing its quantitative conversion in aqueous buffer within 5 min at room temperature. Afterwards the mixture is directly analyzed by micro-liquid chromatography-electrospray ionization tandem-mass spectrometry (µLC-ESI MS/MS). The sensitivity of the method is comparable to that of the non-derivatized NP-adduct. These characteristics make the method highly beneficial for forensic analysis especially in cases in which the OP agent does not form adducts with HSA that are typically targeted as a second biomarker of exposure. This novel procedure was successfully applied to nerve agent-spiked samples sent by the Organisation for the Prohibition of Chemical Weapons (OPCW) as well as to plasma samples of real cases of pesticide poisoning.

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.

A Method for Diagnosing Organophosphate Pesticide Exposure in Humans using Liquid Chromatography Coupled Tandem Mass Spectrometry

Organophosphate (OP) pesticides are commonly utilized worldwide for agricultural purposes and pose a health threat through air, ground, and water contamination. Here, we present a convenient method for diagnosing exposure to OP pesticides in humans. This immunoprecipitation method relies on extraction of butyrylcholinesterase (BChE), a biomarker of OP poisoning that adducts OP compounds, from human serum using agarose beads conjugated to anti-BChE antibodies. Extracted BChE was then digested with pepsin and analyzed for unadducted and OP-adducted peptides by high performance liquid chromatography coupled to tandem mass spectrometry (HPLC-MS/MS). To characterize and validate this method, pooled human plasma was exposed to parathion and dichlorvos to form diethoxyphospho, aged ethoxyphospho and dimethoxyphospho adducts with BChE. Untreated plasma was also analyzed for unadducted peptides. Additionally, samples were analyzed using Ellman's assay to measure BChE functional activity. The percent inhibition of BChE was 53.5±5.76 and 95.2±0.37%, respectively, for plasma treated with parathion for 1 hour and 24 hours. The percent inhibition was 97.2±0.98 for plasma treated with dichlorvos for 1 hour. The percent inhibition was 97.9±0.41% when the plasma treated with parathion for 1 hour, parathion for 24 hour and dichlorvos for 1 hour were mixed. Individual adducts were quantified in a single chromatographic run. Untreated plasma contained 26.4±1.87 ng/mL of unadducted BChE and no adducted peptides. In contrast, the plasma sample treated with both pesticides contained no unadducted BChE, but did contain 9.46±1.10, 10.9±0.98 and 14.1±1.10 ng/mL of diethoxyphospho, aged-ethoxy, and dimethoxyphospho peptides, respectively. The ability to identify and measure BChE and BChE adducts to parathion and dichlorvos is expected to be useful for diagnosing human exposure to multiple OP pesticides.

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.

Nanozyme Sensor Arrays Based on Heteroatom-Doped Graphene for Detecting Pesticides

Pesticides, widely used for pest control and plant growth regulation, have posed a threat to the environment and human health. Conventional methods to analyze pesticide residues are not applied to resource-limited areas because of their high cost, complexity, and requirements for expensive instruments (such as GC/MS and LC/MS). To address these challenges, herein we fabricated colorimetric nanozyme sensor arrays based on heteroatom-doped graphene for detection of aromatic pesticides. The active sites of nanozymes could be differentially masked when different pesticides were adsorbed on the graphene, which in turn resulted in the decrease of their peroxidase-mimicking activities. On the basis of this principle, five pesticides (i.e., lactofen, fluoroxypyr-meptyl, bensulfuron-methyl, fomesafen, and diafenthiuron) from 5 to 500 μM were successfully discriminated by the sensor arrays. In addition, discrimination for different concentrations of each pesticide and different ratios of two mixed pesticides were also demonstrated. The practical application of the sensor arrays was further validated by successfully discriminating the pesticides in soil samples. This work not only provides a facile and cost-effective method to detect pesticides but also makes a positive contribution to food safety and environmental protection.

Graphene oxide-based colorimetric detection of organophosphorus pesticides via a multi-enzyme cascade reaction

Size-tunable graphene oxides (GO) were synthesized as a horseradish peroxidase (HRP) mimic for colorimetric detection of organophosphorus pesticides (OPs) at nanomolar levels via a cascade reaction. A GO-based colorimetric method showed high sensitivity and stability toward OPs, which hold great potential in public health applications.

[Analysis of Countermeasures against Chemical Terrorism]

As a countermeasure against terrorism involving highly toxic chemical warfare agents, the rapid identification of the causative toxic substances is extremely important. This symposium review describes analytical methods the author's group has developed for detecting nerve gases after either high level or low level exposure. As a method for assessing human exposure to high levels of nerve gases, a technology that detects nerve gas hydrolysis products, i.e., strong anion exchange extraction-tert-butyldimethylsilyl derivatization-selectable one-dimensional or two-dimensional GC-MS, is explained. As a method for assessing human exposure to low levels of nerve gases, two technologies that detect adducts of nerve gas with blood cholinesterase, i.e., adduct purification-enzymatic digestion-LC/MS and fluoride-mediated regeneration-solid phase extraction-large volume introduction GC-MS, are explained.

Gas chromatography-mass spectrometry with spiral large-volume injection for determination of fluoridated phosphonates produced by fluoride-mediated regeneration of nerve agent adduct in human serum

A sensitive method for determination of fluoridated phosphonates produced by fluoride-mediated regeneration of nerve agent adduct in human serum was developed using gas chromatography-mass spectrometry (GCMS) with large-volume injection. The GC injection was administered using stomach-type spiral injector (LVI, AiSTI SCIENCE) enabling introduction of only target compounds from 50 μL ethyl acetate extract after purging the solvent. For GCMS analysis of sarin (GB), 670 times higher sensitivity, based on limit of detection (LOD, S/N = 3, on extracted ion chromatogram (EIC) at m/z 99), was achieved using this injection (50 μL) compared to that achieved using 1 μL split injection (ratio 20:1). Ethyl (EtGB), isopropyl (GB), n-propyl (nPrGB), isobutyl (iBuGB), pinacolyl (GD), cyclohexyl (GF) methylphosphonofluoridates, and O-ethyl N, N-dimethylphosphoramidofluoridate (GAF) were detected with low LOD (15-75 pg/mL) and sharp peak shapes (high practical plate number (defined as 5.54 x (t_R/W_h)², where t_R is the retention time and W_h is the bandwidth at half-height): 1100000-2400000) in GCMS using a polar separation column, electron ionization, and quadruple mass analyzer. During the analysis of fluoridated phosphonate-spiked ethyl acetate extract of solid phase extraction (SPE, Bond Elut NEXUS) from fluoride-mediated regeneration of blank human plasma, LOD (on EIC at m/z 99 except for GAF (m/z 126)) were 25-140 pg/mL with sharp peak shapes. The reaction recoveries in fluoride-mediated regeneration of plasma, which was inhibited by GB, GD, GA, GF, VX, and Russian VX (10 ng/mL), were 49-114% except for GD (10%). The concentration levels of 0.3-1 ng/mL of nerve agents in plasma could be determined.

Purification of recombinant human butyrylcholinesterase on Hupresin®

Affinity chromatography on procainamide-Sepharose has been an important step in the purification of butyrylcholinesterase (BChE) and acetylcholinesterase (AChE) since its introduction in 1978. The procainamide affinity gel has limitations. In the present report a new affinity gel called Hupresin® was evaluated for its ability to purify truncated, recombinant human butyrylcholinesterase (rHuBChE) expressed in a stably transfected Chinese Hamster Ovary cell line. We present a detailed example of the purification of rHuBChE secreted into 3940 mL of serum-free culture medium. The starting material contained 13,163 units of BChE activity (20.9 mg). rHuBChE was purified to homogeneity in a single step by passage over 82 mL of Hupresin® eluted with 0.1 M tetramethylammonium bromide in 20 mM TrisCl pH 7.5. The fraction with the highest specific activity of 630 units/mg contained 11 mg of BChE. Hupresin® is superior to procainamide-Sepharose for purification of BChE, but is not suitable for purifying native AChE because Hupresin® binds AChE so tightly that AChE is not released with buffers, but is desorbed with denaturing solvents such as 50% acetonitrile or 1% trifluoroacetic acid. Procainamide-Sepharose will continue to be useful for purification of AChE.

Comparison of Efficiency of Purification (from Human Plasma) of a Nerve Agent Adduct of Butyrylcholinesterase Between the Affinity Gel Method and Immunomagnetic Separation

O-ethyl S-2-diisopropylaminoethyl methyl phosphonothiolate (VX) is a highly toxic chemical warfare agent because it inhibits cholinesterase (ChE) activity in the nervous system. Inhibition of butyrylcholinesterase (BChE) activity by VX is due to formation of a phosphorylated BChE adduct; this adduct in human plasma can serve as a biomarker of exposure to nerve agents. We compared purification efficiency between the procainamide affinity gel method and immunomagnetic separation (IMS) for the nerve agent adduct of BChE in plasma and then optimized the sample preparation by purifying BChE to measure biomarkers of human exposure to organophosphorus nerve agents. The purification efficiency of IMS was 5-fold greater than that of the procainamide affinity gel method because the antibody conjugate with protein G magnetic beads ensured highly selective capture and high recovery of VX-inhibited BChE from plasma. Protein isolation and extraction of the adduct of VX-inhibited BChE from plasma were made more specific by IMS. A 50 µL of the IMS solution was enough to bind VX-inhibited BChE in up to 0.5 mL of plasma. Nonetheless, the IMS method has a limitation in terms of reutilization of the complexes antibody-magnetic beads. We expect that this approach can be used to quantify other types of organophosphorus adducts in human plasma, thus serving as a possible general assay for biomarkers of exposure to nerve agents.

Investigation of sarin(Se) reactivity against human plasma proteins using liquid chromatography-tandem mass spectrometry

Electron ionization mass spectrum of sarin(Se) was interpreted in compare of sarin MS spectrum. Inhibition of butyrylcholinesterase of human plasma by sarin and sarin(Se) was determined spectrophotometrically using modified Ellman method. It appeared that after incubation with sarin and sarin(Se), cholinesterase inhibition were 93% and 83%, respectively. Sarin, sarin(Se), and sarin(Se)-d₇ were spiked into a vial containing human plasma, and albumin adduct metabolites were identified using liquid chromatography-tandem mass spectrometry. The experiments show that these agents are attached to tyrosine on albumin in human blood. Corresponding deuterated adducts were used to confirm the proposed mechanisms for the formation of the fragments in mass spectrometry experiments.

Quantitation of saxitoxin in human urine using immunocapture extraction and LC–MS

Aim: An immunomagnetic capture protocol for use with LC–MS was developed for the quantitation of saxitoxin (STX) in human urine. Materials & methods: This method uses monoclonal antibodies coupled to magnetic beads. STX was certified reference material grade from National Research Council, Canada. Analysis was carried out using LC–MS. Results: With an extraction efficiency of 80%, accuracy and precision of 93.0–100.2% and 5.3–12.6%, respectively, and a dynamic range of 1.00–100 ng/ml, the method is well suited to quantify STX exposures based on previously reported cases. Conclusion: Compared with our previously published protocols, this method has improved selectivity, a fivefold increase in sensitivity and uses only a third of the sample volume. This method can diagnose future toxin exposures and may complement the shellfish monitoring programs worldwide.

Cobalt complexes of Biginelli derivatives as fluorescent probes for selective estimation and degradation of organophosphates in aqueous medium

Bonding between metal complexes of Biginelli derivatives and organophosphates leads to enhancement of emission intensity.

Simultaneous detection of dual biomarkers from humans exposed to organophosphorus pesticides by combination of immunochromatographic test strip and ellman assay

A novel sandwich immunoassay based immunochromatographic test strip (ICTS) has been developed for simultaneously measuring both butyrylcholinesterase (BChE) activity and the total amount of BChE (including inhibited and active enzyme) from 70 μLpost-exposure human plasma sample. The principle of this method is based on the BChE monoclonal antibody (MAb) capable of acting as both capture antibody and detection antibody. The BChE MAb which was immobilized on the test line was able to recognize both organophosphorus BChE adducts (OP-BChE) and BChE and provided equal binding affinity, permitting detection of the total enzyme amount in post-exposure human plasma samples. The formed immunocomplexes on the test line can further be excised from the test-strip for subsequent off-line measurement of BChE activity using the Ellman assay. Therefore, dual biomarkers of BChE activity and phosphorylation (OP-BChE) will be obtained simultaneously. The whole sandwich-immunoassay was performed on one ICTS, greatly reducing analytical time. The ICTS sensor showed excellent linear responses for assaying total amount of BChE and active BChE ranging from 0.22 to 3.58nM and 0.22-7.17nM, respectively. Both the signal detection limits are 0.10nM. We validated the practical application of the proposed method to measure 124 human plasma samples from orchard workers and cotton farmers with long-term exposure to organophosphorus pesticides (OPs). The results were in highly agreement with LC/MS/MS which verified our method is extremely accurate. Combining the portability and rapidity of test strip and the compatibility of BChE MAb as both capture antibody and detection antibody, the developed method provides a baseline-free, low-cost and rapid tool for in-field monitoring of OP exposures.

Use of Hupresin To Capture Red Blood Cell Acetylcholinesterase for Detection of Soman Exposure

Toxicity from acute exposure to nerve agents and organophosphorus toxicants is due to irreversible inhibition of acetylcholinesterase (AChE) in the nervous system. AChE in red blood cells is a surrogate for AChE in the nervous system. Previously we developed an immunopurification method to enrich red blood cell AChE (RBC AChE) as a biomarker of exposure. The goal of the present work was to provide an alternative RBC AChE enrichment strategy, by binding RBC AChE to Hupresin affinity gel. AChE was solubilized from frozen RBC by addition of 1% Triton X-100. Insoluble debris was removed by centrifugation. The red, but not viscous, RBC AChE solution was loaded on a Hupresin affinity column. Hemoglobin and other proteins were washed off with 3 M NaCl, while retaining AChE bound to Hupresin. Denatured AChE was eluted with 1% trifluoroacetic acid. The same protocol was used for 20 mL of RBC AChE inhibited with a soman model compound. The acid denatured protein was digested with pepsin and analyzed by liquid chromatography tandem mass spectrometry on a 6600 Triple-TOF mass spectrometer. A targeted method identified the aged soman adduct on serine 203 in peptide FGESAGAAS. It was concluded that Hupresin can be used to enrich soman-inhibited AChE solubilized from 8 mL of frozen human erythrocytes, yielding a quantity sufficient for detecting soman exposure.

Hupresin Retains Binding Capacity for Butyrylcholinesterase and Acetylcholinesterase after Sanitation with Sodium Hydroxide

Hupresin is a new affinity resin that binds butyrylcholinesterase (BChE) in human plasma and acetylcholinesterase (AChE) solubilized from red blood cells (RBC). Hupresin is available from the CHEMFORASE company. BChE in human plasma binds to Hupresin and is released with 0.1 M trimethylammonium bromide (TMA) with full activity and 10-15% purity. BChE immunopurified from plasma by binding to immobilized monoclonal beads has fewer contaminating proteins than the one-step Hupresin-purified BChE. However, when affinity chromatography on Hupresin follows ion exchange chromatography at pH 4.5, BChE is 99% pure. The membrane bound AChE, solubilized from human RBC with 0.6% Triton X-100, binds to Hupresin and remains bound during washing with sodium chloride. Human AChE is not released in significant quantities with non-denaturing solvents, but is recovered in 1% trifluoroacetic acid. The denatured, partially purified AChE is useful for detecting exposure to nerve agents by mass spectrometry. Our goal was to determine whether Hupresin retains binding capacity for BChE and AChE after Hupresin is washed with 0.1 M NaOH. A 2 mL column of Hupresin equilibrated in 20 mM TrisCl pH 7.5 was used in seven consecutive trials to measure binding and recovery of BChE from 100 mL human plasma. Between each trial the Hupresin was washed with 10 column volumes of 0.1 M sodium hydroxide. A similar trial was conducted with red blood cell AChE in 0.6% Triton X-100. It was found that the binding capacity for BChE and AChE was unaffected by washing Hupresin with 0.1 M sodium hydroxide. Hupresin could be washed with sodium hydroxide at least seven times without losing binding capacity.

Online coupling of immunoextraction, digestion, and microliquid chromatography-tandem mass spectrometry for the analysis of sarin and soman-butyrylcholinesterase adducts in human plasma

Organophosphorus nerve agent (OPNA) adducts formed with human butyrylcholinesterase (HuBuChE) can be used as biomarker of OPNA exposure. Indeed, intoxication by OPNAs can be confirmed by the LC/MS² analysis of a specific HuBuChE nonapeptide on which OPNAs covalently bind. A fast, selective, and highly sensitive online method was developed to detect sarin and soman adducts in plasma, including immunoextraction by anti-HuBuChE antibodies, pepsin digestion on immobilized enzyme reactors (IMER), and microLC/MS² analysis of the OPNA adducts. The potential of three different monoclonal antibodies, covalently grafted on sepharose, was compared for the extraction of HuBuChE. The online method developed with the most promising antibodies allowed the extraction of up to 100% of HuBuChE contained in plasma and the digestion of 45% of it in less than 40 min. Moreover, OPNA-HuBuChE adducts, aged OPNA adducts, and unadducted HuBuChE could be detected (with S/N > 2000), even in plasma spiked with a low concentration of OPNA (10 ng mL^-1). Finally, the potential of this method was compared to approaches involving other affinity sorbents, already described for HuBuChE extraction. Graphical abstract Online coupling of immunoextraction, digestion, and microliquid chromatography-tandem mass spectrometry for the analysis of organophosphorous nerve agent adducts formed with human butyrylcholinesterase.