Chromatographic analysis of chemical warfare agents and their metabolites in biological samples

Revealing nitrogenous VX metabolites and the whole-molecule VX metabolism in the urine of guinea pigs

VX, a well-known organophosphorus nerve agent (OPNA), poses a significant threat to public safety if employed by terrorists. Obtaining complete metabolites is critical to unequivocally confirm its alleged use/exposure and elucidate its whole-molecular metabolism. However, the nitrogenous VX metabolites containing 2-diisopropylaminoethyl moiety from urinary excretion remain unknown. Therefore, this study applied a newly developed untargeted workflow platform to discover and identify them using VX-exposed guinea pigs as animal models. 2-(N,N-diisopropylamino)ethanesulfonic acid (DiPSA) was revealed as a novel nitrogenous VX metabolite in urine, and 2-(Diisopropylaminoethyl) methyl sulfide (DAEMS) was confirmed as another in plasma, indicating that VX metabolism differed between urine and plasma. It is the first report of a nitrogenous VX metabolite in urine and a complete elucidation of the VX metabolic pathway. DiPSA was evaluated as an excellent VX exposure biomarker. The whole-molecule VX metabolism in urine was characterized entirely for the first time via the simultaneous quantification of DiPSA and two known P-based biomarkers. About 52.1% and 32.4% of VX were excreted in urine as P-based and nitrogenous biomarkers within 24 h. These findings provide valuable insights into the unambiguous detection of OPNA exposure/intoxication and human and environmental exposure risk assessment.

Glutathione conjugation of sesquimustard: in vitro investigation of potential biomarkers

Sesquimustard (Q) is a powerful blistering agent that contains additional sulfur atoms. Sulfur mustard causes covalent bonding by alkylating nucleophilic groups of biologically important macromolecules such as lipids, proteins, DNA, or RNA. Most cells maintain relatively high amounts of a unique tripeptide called glutathione (GSH) (γ-glutamyl-cysteinyl glycine), which possesses a free thiol group, to prevent unwanted reactions caused by reactive chemical entities. Moreover, these thiol groups on cysteines (Cys) are the main target for alkylation. Although Q is the most potent vesicant among sulfur mustards, research studies identifying biomarkers of Q are very limited. Therefore, here in this study, we aimed to identify the GSH and Cys conjugates of Q using mass spectrometric methods and to observe the formation of these conjugates in HaCat cell culture following exposure to different doses. We identified four different conjugates of Q, which are bis-glutathionyl ethylthioethylthioethyl conjugate (GSH-ETETE-GSH), hydroxyethylthioethylthioethyl glutathione conjugate (HETETE-GSH), bis-cysteinyl ethylthioethylthioethyl conjugate (Cys-ETETE-Cys), and hydroxyethylthioethylthioethyl cysteine conjugate (HETETE-Cys). The identity of the conjugates was elucidated using liquid chromatography-high-resolution mass spectrometry (LC-HRMS). We also investigated changes in conjugate formation with exposure concentration and time elapsed after exposure in the cell culture. After exposure, GSH conjugates decreased until 1st hour, while Cys conjugates increased until 6th hour. We also observed that conjugate formation depended on the concentration of Q. This is the first study to elucidate the conjugates of Q dependent on GSH conjugation. As biomarkers are essential tools for evaluating exposure to Q, this study contributes to the limited number of studies identifying biomarkers for Q.

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.

Bile Acids: Physiological Activity and Perspectives of Using in Clinical and Laboratory Diagnostics

Bile acids play a significant role in the digestion of nutrients. In addition, bile acids perform a signaling function through their blood-circulating fraction. They regulate the activity of nuclear and membrane receptors, located in many tissues. The gut microbiota is an important factor influencing the effects of bile acids via enzymatic modification. Depending on the rate of healthy and pathogenic microbiota, a number of bile acids may support lipid and glucose homeostasis as well as shift to more toxic compounds participating in many pathological conditions. Thus, bile acids can be possible biomarkers of human pathology. However, the chemical structure of bile acids is similar and their analysis requires sensitive and specific methods of analysis. In this review, we provide information on the chemical structure and the biosynthesis of bile acids, their regulation, and their physiological role. In addition, the review describes the involvement of bile acids in various diseases of the digestive system, the approaches and challenges in the analysis of bile acids, and the prospects of their use in omics technologies.

Acoustic Wave Sensors for Detection of Blister Chemical Warfare Agents and Their Simulants

On-site detection and initial identification of chemical warfare agents (CWAs) remain difficult despite the many available devices designed for this type of analysis. Devices using well-established analytical techniques such as ion mobility spectrometry, gas chromatography coupled with mass spectrometry, or flame photometry, in addition to unquestionable advantages, also have some limitations (complexity, high unit cost, lack of selectivity). One of the emerging techniques of CWA detection is based on acoustic wave sensors, among which surface acoustic wave (SAW) devices and quartz crystal microbalances (QCM) are of particular importance. These devices allow for the construction of undemanding and affordable gas sensors whose selectivity, sensitivity, and other metrological parameters can be tailored by application of particular coating material. This review article presents the current state of knowledge and achievements in the field of SAW and QCM-based gas sensors used for the detection of blister agents as well as simulants of these substances. The scope of the review covers the detection of blister agents and their simulants only, as in the available literature no similar paper was found, in contrast to the detection of nerve agents. The article includes description of the principles of operation of acoustic wave sensors, a critical review of individual studies and solutions, and discusses development prospects of this analytical technique in the field of blister agent detection.

Array-based chemical warfare agent discrimination via organophosphorus-H2O2 reaction-regulated chemiluminescence

It has been a challenge to achieve rapid, simple, and effective discrimination of organophosphorus nerve agents (typical chemical warfare agents) due to the similar chemical properties of the targets such as sarin, soman, cyclosarin and VX. In this study, we propose a chemiluminescence sensor array that can effectively discriminate organophosphorus nerve agents by organophosphorus-H₂O₂ reaction, which produces peroxyphosphonate intermediate and regulates the chemiluminescence intensity. A simple chemiluminescence sensor array based on different chemiluminescence characteristics of the four organophosphorus nerve agents in the luminol–H₂O₂ system and layered double hydroxide–luminol–H₂O₂ system has been constructed. Four agents can be well distinguished at a concentration of 1.0 mg L⁻¹ when linear discriminant analyses and hierarchical cluster analyses are smartly combined. The high accuracy (100%) evaluation of 20 blind samples demonstrates the practicability of this proposed chemiluminescence sensor array.

A chemical warfare agent sensor array based on organophosphorus-H₂O₂ reaction-regulated chemiluminescence is proposed.

Determination of nerve agent biomarkers in human urine by a natural hydrophobic deep eutectic solvent-parallel artificial liquid membrane extraction technique

Alkyl methyl phosphonic acids (AMPAs) are the major metabolites of organophosphorus nerve agents. A method based on the use of natural hydrophobic deep eutectic solvents as supported liquid membrane in parallel artificial liquid microextraction (PALME) combined with LC-MS/MS analysis was developed and applied to their extraction from urine samples. PALME is a miniaturized liquid-phase extraction method performed in a multiwell plate format where the aqueous sample and the aqueous acceptor phase are separated by a flat membrane impregnated with an organic solvent. In this study, we investigated the possibility of replacing the harmful conventional organic solvent by an emerging green solvent, a coumarin/thymol-based deep eutectic solvent, in ordered to raise the greenness of the sample preparation method. Linear response was obtained in an interval of 0.5, 5 or 10-100 ng/ml depending on the AMPAs with a determination coefficients (R²s) ranging from 0.9751 to 0.9989 for their determination in not treated urine samples. Enrichment factors (EFs) up to 12.65 were obtained, and repeatability was within 8.90-16.28% RSD (n = 12). The limit of quantifications (LOQs: S/N ≥ 10) of the whole analytical procedure were in the range from 0.04 to 5.35 ng/ml. In addition to its good sensitivity, the presented method permitted the treatment of 192 samples in 120 min (equivalent to 37.5 s/sample), which places it as one of the most powerful preparation technique for biomonitoring of civilian or military people exposed to nerve agents in case of public health emergency. Indeed, the developed procedure combined sensitivity, high-throughput, greenness, simplicity and practicality for the determination of five acidic polar AMPAs in urine samples.

Dimeric G-Quadruplex: An Efficient Probe for Ultrasensitive Fluorescence Detection of Mustard Compounds

Some mustard compounds (mustards) are highly toxic chemical warfare agents. Some are explored as new anticancer drugs. Therefore, the fast, selective, and sensitive detection of mustards is extremely important for public security and cancer therapy. Mustards mostly target the N7 position on the guanine bases of DNA. The guanine-rich G-quadruplex DNA (G4) has been widely studied in the sensing area, and it was found that dimeric G4 (D-G4) could dramatically light up the fluorescence intensity of thioflavin T (ThT). Based on this, we used for the first time the D-G4 DNA as a selective probe for ultrasensitive fluorescence detection of nitrogen mustard (NM). When NM occupies the N7 on guanine, it can block the formation of the D-G4 structure due to the steric hindrance, and hence, it inhibits the combination of D-G4 with ThT, leading to a sharp decrease of fluorescence intensity. The proposed reaction mechanism is proved using ultraviolet-visible (UV-Vis) spectra, circular dichroism (CD) spectra, and polyacrylamide gel electrophoresis. Herein, the concentration of D-G4/ThT used is as low as 50 nM due to its highly fluorescent performance, enabling both high sensitivity and low cost. NM can be detected with a wide linear range from 10 to 2000 nM. The detection limit of NM reaches a surprisingly low concentration of 6 nM, which is 2 or 3 orders of magnitude lower than that of previously developed fluorescence methods for mustards and simulants.

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.

Analysis of Organophosphorus-Based Nerve Agent Degradation Products by Gas Chromatography-Mass Spectrometry (GC-MS): Current Derivatization Reactions in the Analytical Chemist's Toolbox

The field of gas chromatography-mass spectrometry (GC-MS) in the analysis of chemical warfare agents (CWAs), specifically those involving the organophosphorus-based nerve agents (OPNAs), is a continually evolving and dynamic area of research. The ever-present interest in this field within analytical chemistry is driven by the constant threat posed by these lethal CWAs, highlighted by their use during the Tokyo subway attack in 1995, their deliberate use on civilians in Syria in 2013, and their use in the poisoning of Sergei and Yulia Skripal in Great Britain in 2018 and Alexei Navalny in 2020. These events coupled with their potential for mass destruction only serve to stress the importance of developing methods for their rapid and unambiguous detection. Although the direct detection of OPNAs is possible by GC-MS, in most instances, the analytical chemist must rely on the detection of the products arising from their degradation. To this end, derivatization reactions mainly in the form of silylations and alkylations employing a vast array of reagents have played a pivotal role in the efficient detection of these products that can be used retrospectively to identify the original OPNA.