Fluoride Action Network

Fluoride reactivation-enabled sensitive quantification of tabun adducts on human serum albumin by GC-MS/MS via isotope dilution.

Source: Bioanalysis | November 15th, 2019 | Authors: Li XS, Wu JN, Yan L, Xing ZF, Liu CC, Chen B, Yuan L, Yang Y.
Location: International
Industry type: Chemical Weapons

Organophosphorus nerve agents inhibit the cholinesterase activity by phosphylation of the active site serine. The resulting phosphylated cholinesterase and adducts on human serum albumin (HSA) are appropriate biomarkers for nerve agents exposure. Several methods have been developed for the detection of nerve agents, including fluoride reactivation or alkaline cleavage. It was previously thought that some nerve agents adducts to HSA could not be detected via fluoride regeneration. In our study, the results showed that tabun (GA) adducts of HSA could be detected by fluoride regeneration. The sample preparation included acetone precipitation, washing and SPE. Deuterated tabun (d5-GA) was applied as the internal standard. The product of regenerated fluorotabun is detected with a good linearity (R2 > 0.997) in the concentration range from 0.02 to 100.0 ng/ml, small relative standard deviation (?6.89%) and favorable recoveries between 94.8 and 106.3%. The established preparation confirmed the fluorotabun was regenerated from the GA-HSA adducts.

Graphical abstract

Flow diagram for detection and quantitation of tabun adducts to human serum albumin via fluoride reactivation by GC–MS/MS using isotope dilution. HSA: Human serum albumin.

Organophosphorus nerve agents (OPNA), such as sarin (GB), soman (GD), tabun (GA) and O-ethyl-S-2-diisopropylaminoethyl methylphosphonothiolate (VX), are the most toxic organic chemicals known as their highly lethal ability [1]. OPNA are easily synthesized [2,3] that have been developed and manufactured since World War II. Even after the ratification by Chemical Weapons Convention (CWC) in Hague in 1997 [4], OPNA still cause critical concern and have already be implemented for several terrorist activities. Large stockpiles of nerve agents might still exist in many countries for possible use or as deterrence. In the Iran–Iraq conflict during the 1980s, nerve agents were thought to be used and the hydrolysis product of GB was found in bomb craters [5]. In an act of terrorism, GB gas was deliberately released in the subways of Tokyo and Masumoto by members of the Japanese cult Aum Shinrikyo in 1995. Thirteen people died, and thousands more required medical care [6,7]. In recent years, there are also still additional attacks using nerve agents, such as the killing of Kim Jong-nam in 2017 and the attacks on Russian spies in 2018. The Organisation for the Prohibition of Chemical Weapons (OPCW) also rebuild the Joint Investigative Mechanism for the use of chemical weapons in Syria.

The CWC went into effect since 1997, and specified the need for the effective extraction and analysis of chemical warfare agents and their environmental markers from environmental samples or biomarkers in the biomedical matrices [8,9]. Therefore, the sensitive detection of OPNA and the related adduct on biomolecules is of significance to confirm chemical attacks. It is reported that the exposure to OPNA rapidly result in the formation of a tight covalent bond between the agent and the serine active sites of cholinesterase. The extreme toxicity of nerve agents results from their high affinity and strong ability to inhibit cholinesterase activity by forming a covalent bond with the serine residue (Ser203 for acetylcholinesterase and Ser198 for butyrylcholinesterase, respectively) in the active site [10–13]. Also, the nerve agents can form a bond with human serum albumin (HSA; the active site is Tyr411) [14–16]. The reaction of OPNA with cholinesterase or HSA results in the loss of a primary leaving groups (fluorine for GB and GD, cyanogroup for GA and a thio-leaving group for VX and RVX, Russian VX) to form a phosphylated cholinesterase [17]. Thus, these products can act as biomarkers for OPNA poisoning and measurement of these biomarkers in plasma or urine samples can help to identify the actual OPNA [18–21]. Toward this goal, LC–MS/MS and GC–MS/MS have been widely used [22–26]. With the assistance of sample pretreatment including organic solvent precipitation, washing and SPE, the sensitive analysis of OPNA adduct in biological matrix is achieved [27].

To detect OPNA adducts, the generation of OPNA derivate is essential by reactivation techniques [28]. Among them, the fluoride reactivation technique that regenerates phosphyl groups from the cholinesterase upon the incubation with fluoride ions has been widely applied because of the easy operation [29]. Previous study suggested that the products resulting from fluoride ion regeneration were from nerve agent adducts to the cholinesterase, rather than HSA. There was strong evidence that the GB detected in exposed plasma samples was regenerated from BuChE. However, the nerve agents adducts to proteins (e.g., albumin) cannot be reactivated [30,31]…

*Read the full study at http:fluoridealert.org/wp-content/uploads/li-2019-chem-weapons.pdf


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*Read the full report online at https://www.future-science.com/doi/10.4155/bio-2019-0161  or at