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Toxins 2016, 8(11), 329; doi:10.3390/toxins8110329

Glutathione-Conjugates of Deoxynivalenol in Naturally Contaminated Grain Are Primarily Linked via the Epoxide Group

1
Section for Chemistry and Toxicology, Norwegian Veterinary Institute, P.O. Box 750 Sentrum, Oslo 0106, Norway
2
Department of Chemistry, University of Oslo, P.O. Box 1033, Blindern, Oslo 0315, Norway
3
Division of Biotechnology and Plant Health, NIBIO—Norwegian Institute of Bioeconomy, Høgskoleveien 7, Ås 1430, Norway
4
Center for Analytical Chemistry, Department of Agrobiotechnology (IFA-Tulln), University of Natural Resources and Life Sciences, Vienna (BOKU), Tulln 3430, Austria
*
Author to whom correspondence should be addressed.
Academic Editors: Sarah De Saeger, Siska Croubels and Kris Audenaert
Received: 31 August 2016 / Revised: 2 October 2016 / Accepted: 7 November 2016 / Published: 11 November 2016
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Abstract

A glutathione (GSH) adduct of the mycotoxin 4-deoxynivalenol (DON), together with a range of related conjugates, has recently been tentatively identified by LC-MS of DON-treated wheat spikelets. In this study, we prepared samples of DON conjugated at the 10- and 13-positions with GSH, Cys, CysGly, γ-GluCys and N-acetylcysteine (NAC). The mixtures of conjugates were used as standards for LC-HRMS analysis of one of the DON-treated wheat spikelet samples, as well as 19 Norwegian grain samples of spring wheat and 16 grain samples of oats that were naturally-contaminated with DON at concentrations higher than 1 mg/kg. The artificially-contaminated wheat spikelets contained conjugates of GSH, CysGly and Cys coupled at the olefinic 10-position of DON, whereas the naturally-contaminated harvest-ripe grain samples contained GSH, CysGly, Cys, and NAC coupled mainly at the 13-position on the epoxy group. The identities of the conjugates were confirmed by LC-HRMS comparison with authentic standards, oxidation to the sulfoxides with hydrogen peroxide, and examination of product-ion spectra from LC-HRMS/MS analysis. No γ-GluCys adducts of DON were detected in any of the samples. The presence of 15-O-acetyl-DON was demonstrated for the first time in Norwegian grain. The results indicate that a small but significant proportion of DON is metabolized via the GSH-conjugation pathway in plants. To our knowledge, this is the first report of in vivo conjugation of trichothecenes via their epoxy group, which has generally been viewed as unreactive. Because conjugation at the 13-position of DON and other trichothecenes has been shown to be irreversible, this type of conjugate may prove useful as a biomarker of exposure to DON and other 12,13-epoxytrichothecenes. View Full-Text
Keywords: bioconjugation; HRMS; mercapturate; mycotoxin; trichothecene; thiol; LC-MS; metabolism; wheat; oats bioconjugation; HRMS; mercapturate; mycotoxin; trichothecene; thiol; LC-MS; metabolism; wheat; oats
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Uhlig, S.; Stanic, A.; Hofgaard, I.S.; Kluger, B.; Schuhmacher, R.; Miles, C.O. Glutathione-Conjugates of Deoxynivalenol in Naturally Contaminated Grain Are Primarily Linked via the Epoxide Group. Toxins 2016, 8, 329.

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