Simultaneous Quantification of Biomarkers for Bis-(2-chloroethyl) Sulfide and 1,2-Bis(2-chloroethylthio) Ethane Exposure in Human Urine at Trace Exposure Levels by Gas Chromatography Tandem Mass Spectrometry via Simultaneous Incubation and Extraction

Sulfur mustard [HD; bis-(2-chloroethyl) sulfide] and other analogues are a kind of highly toxic vesicant and have been prohibited by the Organization for the Prohibition of Chemical Weapons (OPCW) since 1997. Exposures to HD could generate several adducts in the plasma and hydrolysis products in the urine, which are widely applied as biomarkers to identify HD exposure in forensic analysis. Several methods have been developed for the detection of related biomarkers. However, most methods are based on complex derivatization, and not enough attention is paid to HD analogues. A modified and convenient analytical method reported herein includes simultaneous incubation and organic solvent extraction. The biomarkers such as thiodiglycol and 1,2-bis (2-hydroxyethylthio) are transferred to HD and 1,2-bis(2-chloroethylthio) ethane via hydrochloric acid at the appropriate temperature. The analytes are analyzed by gas chromatography tandem mass spectrometry (GC-MS/MS) with 2-chloroethyl ethyl sulfide (2-CEES) applied as the internal standard. The interday and intraday study according to FDA rules has been achieved to evaluate the accuracy and precision of the method. The two targets are detected with a good linearity (R2 > 0.99) in the concentration ranges from 5 to 1000 ng/mL and 10 to 1000 ng/mL, with small relative standard deviations (RSD ≤6.62% and RSD ≤6.93%) and favorable recoveries between 90.3 and 107.3% and between 89.4 and 108.7%, respectively. The established method can be used for retrospective detection of sulfur mustards in biological samples and successfully applied in the biomedical proficiency testing organized by the OPCW.

Simultaneous quantification of multiple amino acid adducts from sulfur mustard-modified human serum albumin in plasma at trace exposure levels by ultra-high performance liquid chromatography-triple quadrupole mass spectrometry after propionyl derivatization

Sulfur mustard (HD) is a highly toxic vesicant and is prohibited by the Organisation for the Prohibition of Chemical Weapons (OPCW). HD can modify human serum albumin (HSA) to generate hydroxyethylthioethyl (HETE) adducts, which could be utilized as biomarkers for verifying HD exposure in forensic analysis. Here, five amino acid adducts generated from pronase digestion of HD-exposed human serum albumin (HD-HSA) in plasma were selected as biomarkers to retrospectively detect HD exposure. HD-HSA was precipitated from plasma with acetone, digested by pronase, derivatized with propionic anhydride (PA), and analysed with ultra-high performance liquid chromatography coupled with triple quadrupole mass spectrometry (UHPLC-TQ MS). The limits of detection (LODs) and limits of quantification (LOQs) of the HD exposure concentrations were evaluated as 1.00 ng/mL at S/N≥3 and 3.00 ng/mL at S/N≥10, respectively, which are approximately 60 times lower than those of the reported method. The approach shows good linearity (R²≥0.997) from 3.00 ng/mL to 10.0 µg/mL of HD-exposed human plasma with satisfactory precision and accuracy. The developed approach was applied to analysing samples from the 6^th OPCW Biomedical Proficiency Test (BioPT). The study showed that the developed approach was also suitable for analysing human plasma samples that were exposed to six of HD analogues, which were common impurities in sulfur mustard mixtures. Moreover, the method was successfully applied to plasma from other species, including rabbits, rats and cattle. This study provides a reliable and sensitive tool for the retrospective detection of vesicants exposure based on multiple biomarkers.

A proteomics strategy for the identification of multiple sites in sulfur mustard-modified HSA and screening potential biomarkers for retrospective analysis of exposed human plasma

A major challenge for the unequivocal verification of alleged exposure to sulfur mustard (HD) lies in identifying its multiple modifications on endogenous proteins and utilizing these modified proteins to achieve accurate, sensitive, and rapid detection for retrospective analysis of HD exposure. As the most abundant protein in human plasma, human serum albumin (HSA) can react with many xenobiotics, such as HD, to protect the body from damage. The HSA adducts induced by HD have been used as biomarkers for the verification of HD exposure. In this study, the modification sites on HSA by HD were identified through application of the bottom-up strategy used in proteomics, and 41 modified sites were discovered with seven types of amino acids, of which 3 types were not previously reported. Then, different enzymes, including pepsin, endoproteinase Glu-C, and pronase, were applied to digest HD-HSA to produce adducts with hydroxyethylthioethyl (HETE) groups, which may be used as potential biomarkers for HD exposure. As candidates for retrospective analysis, sixteen adducts were obtained and characterized with ultra-high-pressure liquid chromatography coupled with quadrupole-Orbitrap mass spectrometry (UHPLC-QE Focus MS). These potential biomarkers were evaluated in human plasma that was exposed in vitro to HD and five of its analogues. This study integrated the identification of modification sites through application of the bottom-up strategy of proteomics and screening biomarkers, providing a novel strategy for retrospective detection of the exposure of xenobiotic chemicals.