Phosphylated tyrosine in albumin as a biomarker of exposure to organophosphorus nerve agents

Abstract

The organophosphorus nerve agents sarin, soman, cyclosarin and tabun phosphylate a tyrosine residue on albumin in human blood. These adducts may offer relatively long-lived biological markers of nerve agent exposure that do not 'age' rapidly, and which are not degraded by therapy with oximes. Sensitive methods for the detection of these adducts have been developed using liquid chromatography-tandem mass spectrometry. Adducts of all four nerve agents were detected in the blood of exposed guinea pigs being used in studies to improve medical countermeasures. The tyrosine adducts with soman and tabun were detected in guinea pigs receiving therapy 7 days following subcutaneous administration of five times the LD(50) dose of the respective nerve agent. VX also forms a tyrosine adduct in human blood in vitro but only at high concentrations.

Pseudo-esterase Activity of Human Albumin

“…The esteratic site has been identified as Tyr-411 based on site-directed mutagenesis studies (17). Mass spectrometry (MS) 2 has identified Tyr-411 as the residue labeled by organophosphorus esters including diisopropylfluorophosphate (DFP), soman, sarin, dichlorvos, FP-biotin, and chlorpyrifos oxon (16,18) confirming the report by Sanger that a tyrosine in albumin is labeled by DFP (19),and reports that a tyrosine in albumin is labeled by the nerve agents soman, sarin, cyclosarin, and tabun (20). When albumin is labeled with 1 mol of DFP, albumin loses the fast phase of its esterase activity (the burst), supporting the conclusion that DFP and p-nitrophenyl acetate bind to the same site, namely to Tyr-411 (21).…”

“…Others have also identified tyrosine as the site of covalent binding of soman, sarin, cyclosarin, and tabun to albumin (20). Organophosphorus agents inhibit the esterase activity of butyrylcholinesterase and other serine esterases by covalent binding to the active site serine (35).…”

“…1 ml of control albumin solution was treated with 5 l of acetonitrile. A 50-l aliquot was removed into 50 l of 1% trifluoroacetic acid containing 2 l of 1 mg/ml pepsin after 5,10,15,20,30,40,50, 60 min, 6 h, 24 h, 9 days, and 14 days. The drop in pH to 1.4 stopped the reaction with p-nitrophenyl acetate.…”

Mass spectrometry identifies covalent binding of soman, sarin, chlorpyrifos oxon, diisopropyl fluorophosphate, and FP-biotin to tyrosines on tubulin: A potential mechanism of long term toxicity by organophosphorus agents

“…Enzymes are defined as serine hydrolases when their activity is inhibited by OP. On the other hand, covalent binding of OP to tyrosine has previously been reported only for albumin [16][17][18][19], papain [20] and bromelain [21]. Our previous mass spectrometry work identified the OP binding site in human albumin as Tyr 411, and in bovine albumin as Tyr 410 [9,16].…”

Detoxication of Anticholinesterase Pesticides

“…This biomarker might be especially relevant because it has proved useful for in vivo exposures, causing only 30% of AChE inhibition of several widely used OPs (azamethiphos-oxon, chlorfenvinphos-oxon, chlorpyrifos-oxon, diazoxon and malaoxon; Tarhoni et al, 2008). This biomarker has also proved relevant in vivo for exposures to the nerve agents, such as sarin, soman, cyclosarin, and tabun, and for in vitro exposures to VX (Williams et al, 2007).…”