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Reactions of benzene oxide with thiols including glutathione

Lookup NU author(s): Martine Barnes, Dr Christine Bleasdale, Professor William Clegg, Professor William Watson, Emeritus Professor Bernard Golding

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Abstract

S-Phenylmercapturic acid is a minor metabolite of benzene used as a biomarker for human benzene exposures. The reaction of intracellular glutathione with benzene oxide-oxepin, the initial metabolite of benzene, is presumed to give 1-(S-glutathionyl)-cyclohexa-3,5-dien-2-ol, which undergoes dehydration to S-phenylglutathione, the precursor of S-phenylmercapturic acid. To validate the proposed route to S-phenylglutathione, reactions of benzene oxide-oxepin with glutathione and other sulfur nucleophiles have been studied. The reaction of benzene oxide with an excess of aqueous sodium sulfide, followed by acetylation, gave bis-(6-trans-5-acetoxycyclohexa-1,3-dienyl)sulfide, the structure of which was proved by X-ray crystallography. Reactions of benzene oxide-oxepin in a 95:5 (v/v) mixture of phosphate buffer in D2O with (CD 3)2SO were monitored by 1H NMR spectroscopy. In the absence of glutathione, the half-life of benzene oxide-oxepin was ca. 34 min at 25 °C and pD 7.0. The half-life was not affected in the range of 2-15 mM glutathione in the presence and absence of a commercial sample of human glutathione S-transferase (at pH 7.0, 8.0, 8.5, or 10.0). The adduct 1-(S-glutathionyl)-cyclohexa-3,5-diene-2-ol was identified in these reaction mixtures, especially at higher pH, by mass spectrometry and by its acid-catalyzed decomposition to S-phenylglutathione. Incubation of benzene oxide with N-acetyl-L-cysteine at 37 °C and pH 10.0 and subsequent mass spectrometric analysis of the mixture showed formation of pre-S- phenylmercapturic acid and the dehydration product, S-phenylmercapturic acid. The data validate the premise that benzene oxide-oxepin can be captured by glutathione to give (1R,2R)- and/or (1S,2S)-1-(S-glutathionyl)-cyclohexa-3,5- dien-2-ol, which dehydrate to S-phenylglutathione. The capture is a relatively inefficient process at pH 7 that is accelerated at higher pH. These studies account for the observation that the metabolism of benzene is dominated by the formation of phenol. The pathway leading to S-phenylmercapturic acid is necessarily minor on account of the low efficiency of benzene oxide capture by glutathione at pH 7 vs spontaneous rearrangement to phenol.

Publication metadata

Author(s): Henderson AP, Barnes ML, Bleasdale C, Cameron R, Clegg W, Heath SL, Lindstrom AB, Rappaport SM, Waidyanatha S, Watson WP, Golding BT

Publication type: Article

Publication status: Published

Journal: Chemical Research in Toxicology

Year: 2005

Volume: 18

Issue: 2

Pages: 265-270

Print publication date: 01/02/2005

ISSN (print): 0893-228X

ISSN (electronic): 1520-5010

Publisher: American Chemical Society

URL: http://dx.doi.org/10.1021/tx049781y

DOI: 10.1021/tx049781y

PubMed id: 15720131

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