Lewisite protein adducts

Incubation of lewisite-protein adducts with BAL is capable of transferring its metabolite 2-chlorovinylarsonous acid (CVAA) into a BAL-CVAA derivative. This derivative can be quantified using GC-MS. The method is able to detect a 1 nM lewisite exposure of human blood in vitro (Fidder et al, 2000). 

Once incorporated, unbound lewisite is quickly hydrolyzed. Its predominant metabolite is 2-chlorovinylarsonous acid, CVAA (Figure 50.8). Analytical methods to confinn lewisite exposure have, at least in the past, focused on the detection and quantification of CVAA. However, Noort et al. (2002) also pointed out that due to the high affinity of arsenic towards sulfhydryl groups, adducts of lewisite/ CVAA and cysteine residues of proteins are formed. In an in vitro study, incubating " C-labeled lewisite with human blood samples, 90% of lewisite was found in erythrocytes, whereas 25 to 50% of arsenic was bound to globin. From these protein adducts, CVAA can be released to form an adduct with the antidote British Anti-Lewisite (BAL) (Fidder et al, 2000). The authors were also able to identify a specific protein adduct of lewisite formed with the cysteine residues 93 and 112 of P-globin. See Detection of DNA and protein adducts of vesicants, below, for analytical... 

In vivo, unbound CVAA is quickly excreted via the renal pathway and cannot be detected in urine samples taken later than 12 h post-exposure. However, the biological half-life of protein adducts is much longer in blood samples taken 10 days post-exposure and treated with BAL, Fidder et al. (2000) were still able to release 10% of the CVAA-BAL concentration found on day 1. Thus, protein adducts of CVAA have an important role in the verification of potential lewisite exposure. 

From these protein adducts, CVAA can be released to form an adduct with the antidote British anti-lewisite (BAL Fidder et al., 2000). The authors were also able to identify a specific protein adduct of lewisite formed with cysteine residues 93 and 112 of p-globin. See the section "Detection of DNA and protein adducts of vesicants," later in tiiis chapter, for analytical details. Figure 56.8 summarizes the biotransformation and reversal of adduct formation by BAL. 

In view of the high affinity of arsenic for thiol functions, it can be expected that lewisite and CVAA will bind to cysteine residues of proteins. When human blood was incubated with 20 nM to 0.2 mM of [14C]lewisite, 25-50% of the dose became associated with globin (35). Electrospray tandem MS provided evidence for the presence of a CVAA-crosslink between the cysteine-93 and cysteine-112 residues in fi-globin. Whether this was the only type of adduct has not yet been completely elucidated. It must be remarked, however, that this result was in contrast with results obtained by others for the analogous phenyldichloroarsine, for which binding to human hemoglobin could not be observed. 

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