Medical Aspects of Chemical Warfare (2008) - The Black Vault

Medical Aspects of Chemical Warfarelittle change in tissue total GSH concentration, butthe reduced GSH levels fell significantly and GSSGlevels increased significantly. 168,169 In these studies, thereduced GSH as percent of total was 41% less than thecontrol subject. The collection of lung tissue samplesfrom humans that are thought to have been exposedto phosgene is impractical, but the collection of bronchoalveolarlavage fluid is possible. Sciuto has reportedon the concentrations of GSSG, GSH, and total GSH inthe bronchoalveolar lavage fluid of rodents with severechanges in the GSH redox state following phosgeneinhalation. 170,171 Increases in total GSH levels were observedin both studies, but the redox state of the GSHwas not reported. It can be anticipated that increasedlevels of the oxidized form of GSH would be a betterindicator of phosgene exposure, but at this time onlytotal GSH has been correlated with phosgene inhalationin lavage fluid. It should also be noted that in Sciuto’sreported studies, there was no discrimination betweenGSSG and GSCOSG. Because these two species are similarin structure, it is unclear whether the reported detectionof GSSG includes some component from GSCOSG.The detection of GSCOSG, increased GSSG levels,and decreased GSH levels following phosgene exposuremay hold promise for detecting phosgene exposure,but there are considerable obstacles to some ofthese approaches. The levels of total GSH and changesin GSH redox state in animal models were determinedshortly after exposure to phosgene; however, the lifetimeof GSCOSG is not known, and even though thelevels of total GSH in mice exposed to phosgene weresignificantly higher than in controls up to 24 hourspostexposure, the GSH levels were only marginallyabove controls at times up to 7 days postexposure. 171Furthermore, there are large variations in GSH andGSSH levels in human subjects, so predetermined baselinelevels should be required for each patient. 162,163 Theformation of GSCOGS may be specific for phosgene (orchlorinated compounds that metabolize to phosgene).A reference range study of GSCOSG levels in peoplewith no known exposure to phosgene is required touse this biomarker for phosgene exposure.Cysteine AdductsPhosgene reportedly forms an adduct with thethiol amino acid cysteine. 172 Cysteine is a buildingblock of GSH and is the rate-limiting step in generatingGSH for antioxidant tissue protection. 173 As in thecase of GSH, cysteine can be reduced to the disulfidecysteine dimer cystine. Cysteine is generated in thebody by the conversion of methionine through thecystathionine pathway. Average concentrations ofcysteine in humans are typically lower than GSH andhave been approximated at 250 µm in plasma and 400µm in urine. 174The reaction of phosgene and cysteine in vitro wasfirst reported by Kubic and Anders, and the productwas identified as 2-oxothiazolidine-4-carboxylic acid(known as OTZ, OTC, or procysteine). 172 OTZ wasformed by incubating hepatic microsomal fractionswith chloroform, nicotinamide adenosine dinucleotidephosphate, and cysteine (Figure 22-14). 172 Isotopicstudies showed that chloroform was first metabolizedto phosgene by cytochrome P-450. The phosgene thenreacted with cysteine to form OTZ. Synthetic routes toOTZ also have indicated the generation from cysteineand phosgene. 175OTZ is a prodrug of cysteine and is rapidly convertedby 5-oxoprolinase to cysteine in vivo. 173 Studieshave indicated that the lifetime of OTZ in the humanbody varies from 3 to 8 hours. 173,176 OTZ’s rapid eliminationlimits its usefulness as a biomarker for phosgeneunless samples are obtained quickly after a suspectedexposure.Other possible markers for phosgene exposure maybe the reduction of cysteine to its disulfide, cystine,upon exposure to phosgene. However, this reactionis not specific to phosgene exposure. The formationof the acylated dimer cysteine-CO-cysteine has beenshown in vitro when cysteine is treated with phosgenein solution, and this reaction occurs even in the presenceof GSH. 166Small Molecule AdductsInhaled phosgene reportedly reacts with other componentsin the lungs. In 1933 treatment of lung pulpwith phosgene was found to form the chlorocarbonicester of cholesterol. 177 Kling 177 also indicated that thehydrophilic character of the fats was destroyed in thecells because of the loss of free sterols and suggestedthat caused acute pulmonary edema.Phosgene forms adducts with phospholipids. In aOHNOOHChemical Formula: C 4 H 5 NO 3 SMolecular Weight: 147.15Fig. 22-14. Structure of 2-oxothiazolidine-4-carboxylic acid.S736