University of Oulu

Mariam Esmaeeli, Manfred Nimtz, Lothar Jänsch, Lloyd W. Ruddock and Silke Leimkühler. Drug Metabolism and Disposition June 2023, 51 (6) 764-770; DOI:

Inactivation of human aldehyde oxidase by small sulfhydryl-containing reducing agents

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Author: Esmaeeli, Mariam1; Nimtz, Manfred2; Jänsch, Lothar2;
Organizations: 1Institute of Biochemistry and Biology, Department of Molecular Enzymology, University of Potsdam, Potsdam, Germany
2Helmholtz Center for Infection Research, Inhoffenstraße 7, Braunschweig, Germany
3Faculty of Biochemistry and Molecular Medicine, University of Oulu, Aapistie A, Oulu, Finland
Format: article
Version: published version
Access: open
Online Access: PDF Full Text (PDF, 0.8 MB)
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Language: English
Published: American Society for Pharmacology and Experimental Therapeutics, 2023
Publish Date: 2023-09-29


Human aldehyde oxidase (hAOX1) is a molybdoflavoenzyme that belongs to the xanthine oxidase (XO) family. hAOX1 is involved in phase I drug metabolism, but its physiologic role is not fully understood to date, and preclinical studies consistently underestimated hAOX1 clearance. In the present work, we report an unexpected effect of the common sulfhydryl-containing reducing agents, e.g., dithiothreitol (DTT), on the activity of hAOX1 and mouse aldehyde oxidases. We demonstrate that this effect is due to the reactivity of the sulfido ligand bound at the molybdenum cofactor with the sulfhydryl groups. The sulfido ligand coordinated to the Mo atom in the XO family of enzymes plays a crucial role in the catalytic cycle and its removal results in the total inactivation of these enzymes. Because liver cytosols, S9 fractions, and hepatocytes are commonly used to screen the drug candidates for hAOX1, our study suggests that DTT treatment of these samples should be avoided, otherwise false negative results by an inactivated hAOX1 might be obtained.

SIGNIFICANCE STATEMENT This work characterizes the inactivation of human aldehyde oxidase (hAOX1) by sulfhydryl-containing agents and identifies the site of inactivation. The role of dithiothreitol in the inhibition of hAOX1 should be considered for the preparation of hAOX1-containing fractions for pharmacological studies on drug metabolism and drug clearance.

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Series: Drug metabolism and disposition
ISSN: 0090-9556
ISSN-E: 1521-009X
ISSN-L: 0090-9556
Volume: 51
Issue: 6
Pages: 764 - 770
DOI: 10.1124/dmd.122.001244
Type of Publication: A1 Journal article – refereed
Field of Science: 1182 Biochemistry, cell and molecular biology
Funding: This work was supported by the Deutsche Forschungsgemeinschaft [Grant LE1171/8-3].
Dataset Reference: The authors declare that all the data supporting the findings of this study are available within the paper and its supplemental data.
Copyright information: © 2023 by The Author(s). This is an open access article distributed under the CC BY Attribution 4.0 International license.