Trichomonas vaginalis: metronidazole and other nitroimidazole drugs are reduced by the flavin enzyme thioredoxin reductase and disrupt the cellular redox system. Implications for nitroimidazole toxicity and resistance

Authors

  • David Leitsch,

    Corresponding author
    1. Department of Specific Prophylaxis and Tropical Medicine at the Center for Physiology, Pathophysiology and Immunology, Medical University of Vienna, A-1090 Vienna, Austria.
      *E-mail david.leitsch@meduniwien.ac.at; Tel. (+43) 14277 64871; Fax (+43) 14277 64899.
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  • Daniel Kolarich,

    1. Department of Chemistry, University of Natural Resources and Applied Life Sciences, A-1190 Vienna, Austria.
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    • Present address: Core of Biomolecular Frontiers, Macquarie University, Sydney 2109, Australia.

  • Marina Binder,

    1. Department of Specific Prophylaxis and Tropical Medicine at the Center for Physiology, Pathophysiology and Immunology, Medical University of Vienna, A-1090 Vienna, Austria.
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  • Johannes Stadlmann,

    1. Department of Chemistry, University of Natural Resources and Applied Life Sciences, A-1190 Vienna, Austria.
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  • Friedrich Altmann,

    1. Department of Chemistry, University of Natural Resources and Applied Life Sciences, A-1190 Vienna, Austria.
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  • Michael Duchêne

    1. Department of Specific Prophylaxis and Tropical Medicine at the Center for Physiology, Pathophysiology and Immunology, Medical University of Vienna, A-1090 Vienna, Austria.
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*E-mail david.leitsch@meduniwien.ac.at; Tel. (+43) 14277 64871; Fax (+43) 14277 64899.

Summary

Infections with the microaerophilic parasite Trichomonas vaginalis are treated with the 5-nitroimidazole drug metronidazole, which is also in use against Entamoeba histolytica, Giardia intestinalis and microaerophilic/anaerobic bacteria. Here we report that in T. vaginalis the flavin enzyme thioredoxin reductase displays nitroreductase activity with nitroimidazoles, including metronidazole, and with the nitrofuran drug furazolidone. Reactive metabolites of metronidazole and other nitroimidazoles form covalent adducts with several proteins that are known or assumed to be associated with thioredoxin-mediated redox regulation, including thioredoxin reductase itself, ribonucleotide reductase, thioredoxin peroxidase and cytosolic malate dehydrogenase. Disulphide reducing activity of thioredoxin reductase was greatly diminished in extracts of metronidazole-treated cells and intracellular non-protein thiol levels were sharply decreased. We generated a highly metronidazole-resistant cell line that displayed only minimal thioredoxin reductase activity, not due to diminished expression of the enzyme but due to the lack of its FAD cofactor. Reduction of free flavins, readily observed in metronidazole-susceptible cells, was also absent in the resistant cells. On the other hand, iron-depleted T. vaginalis cells, expressing only minimal amounts of PFOR and hydrogenosomal malate dehydrogenase, remained fully susceptible to metronidazole. Thus, taken together, our data suggest a flavin-based mechanism of metronidazole activation and thereby challenge the current model of hydrogenosomal activation of nitroimidazole drugs.

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