Sulfur Mustard Adducts with Albumin

Sulfur mustard was shown by Noort et al. (24) to alkylate the cysteine-34 residue in human serum albumin. The site of alkylation was identified in a tryptic digest of albumin from blood exposed to [14C] sulfur mustard. The cysteine-34 residue is the only free cysteine residue in human serum albumin and has a relatively low pKa, caused by intramolecular stabilization of the thiolate anion. It has previously been identified as a nucleophilic site capable of reacting with various electrophiles (25,26). 

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Noort and colleagues (2008) investigated the persistence of sulfur mustard adducts to albumin and hemoglobin in rats. The albumin adduct (S -2-hydroxyethylthioethyl)-Cys-Pro-Tyr was detectable up to 7 days after the exposure, while the adduct to the N-terminal valine in hemoglobin was still detected after 28 days. The decrease of adduct concentration corresponded with albumin half-life and the hfetime of the rat erythrocyte, respectively. 

Another interesting development is comprehensive GC-MS. Comprehensive GC offers great selectivity and resolution and is ideal for complex samples such as biomedical samples. Its combination with time-of-flight mass spectrometry offers the possibility to analyze in full-scan mode, not target-directed, with the availability of a full mass spectrum that will meet the forensic standards. The utility has been demonstrated for the detection of CWAs in complicated matrices such as fuel (Reichenbach et al., 2003). The method has also been used for the analysis of regenerated sarin in inhibited plasma (van der Meer et al., 2010). Finally, it may be expected that the sample preparation will be more or less automated. Recently, a promising result was published by Carol-Visser et al. (2008), who described the digestion and analysis of sulfur mustard adducts in albumin and the sarin adduct to BuChE. 

Analysis of Blood Samples. Urinary metabolites undergo relatively rapid elimination from the body, whereas blood components offer biomarkers that have the potential to be used for verification of sulfur mustard exposure long after the exposure incident. Three different approaches have been used for blood biomarker analysis. The intact macromolecule such as protein or DNA with the sulfur mustard adducts still attached can be analyzed. To date, this approach has only been demonstrated for hemoglobin using in vitro experiments. For proteins, an alternate approach is to enzymatically digest them to produce a smaller peptide with the sulfur mustard adduct still attached. Methods of this type have been developed for both hemoglobin and albumin. A third approach has been to cleave the sulfur mustard adduct from the macromolecule and analyze in a fashion similar to that used for free metabolites found in the urine. The later two approaches have both been successfully used to verify human exposure of sulfur mustard. 

Sulfur mustard forms adducts with the blood proteins hemoglobin and albumin. Adducts with histidine residues are the most abundant after exposure of hemoglobin in vitro to sulfur mustard. Analysis of adducted histidine by GC/MS is hampered by poor thermal stability of volatile derivatives. A sensitive method was developed using LC/ESI/MS/MS after... 

The analytical procedure for S-[2-[(hydroxyethyl) thio]ethyl-Cys-Pro-Phe was successfully applied to blood samples from nine Iranian casualties of the Iraq-Iran war, all exhibiting skin injuries compatible with exposure to sulfur mustard. The blood samples were collected 8-9 days after the alleged exposure and stored at — 70 °C. The albumin adduct was detected in all cases, at levels estimated as corresponding to those after in vitro exposure of human blood to mustard concentrations ranging from 0.4-1.8 xM. 

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