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Rixen S, Havemeyer A, Tyl-Bielicka A, Pysniak K, Gajewska M, Kulecka M, Ostrowski J, Mikula M, Clement B. Mitochondrial amidoxime-reducing component 2 (MARC2) has a significant role in N-reductive activity and energy metabolism. J Biol Chem 2019; 294:17593-17602. [PMID: 31554661 DOI: 10.1074/jbc.ra119.007606] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2019] [Revised: 09/19/2019] [Indexed: 01/29/2023] Open
Abstract
The mitochondrial amidoxime-reducing component (MARC) is a mammalian molybdenum-containing enzyme. All annotated mammalian genomes harbor two MARC genes, MARC1 and MARC2, which share a high degree of sequence similarity. Both molybdoenzymes reduce a variety of N-hydroxylated compounds. Besides their role in N-reductive drug metabolism, only little is known about their physiological functions. In this study, we characterized an existing KO mouse model lacking the functional MARC2 gene and fed a high-fat diet and also performed in vivo and in vitro experiments to characterize reductase activity toward known MARC substrates. MARC2 KO significantly decreased reductase activity toward several N-oxygenated substrates, and for typical MARC substrates, only small residual reductive activity was still detectable in MARC2 KO mice. The residual detected reductase activity in MARC2 KO mice could be explained by MARC1 expression that was hardly unaffected by KO, and we found no evidence of significant activity of other reductase enzymes. These results clearly indicate that MARC2 is mainly responsible for N-reductive biotransformation in mice. Striking phenotypical features of MARC2 KO mice were lower body weight, increased body temperature, decreased levels of total cholesterol, and increased glucose levels, supporting previous findings that MARC2 affects energy pathways. Of note, the MARC2 KO mice were resistant to high-fat diet-induced obesity. We propose that the MARC2 KO mouse model could be a powerful tool for predicting MARC-mediated drug metabolism and further investigating MARC's roles in energy homeostasis.
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Affiliation(s)
- Sophia Rixen
- Department of Pharmaceutical and Medicinal Chemistry, Pharmaceutical Institute, Christian Albrechts University, 24118 Kiel, Germany
| | - Antje Havemeyer
- Department of Pharmaceutical and Medicinal Chemistry, Pharmaceutical Institute, Christian Albrechts University, 24118 Kiel, Germany
| | - Anita Tyl-Bielicka
- Department of Genetics, Maria Sklodowska-Curie Institute, Cancer Center, 02-781 Warsaw, Poland
| | - Kazimiera Pysniak
- Department of Genetics, Maria Sklodowska-Curie Institute, Cancer Center, 02-781 Warsaw, Poland
| | - Marta Gajewska
- Department of Genetics, Maria Sklodowska-Curie Institute, Cancer Center, 02-781 Warsaw, Poland
| | - Maria Kulecka
- Department of Gastroenterology, Hepatology, and Clinical Oncology, Centre of Postgraduate Medical Education, 02-781 Warsaw, Poland
| | - Jerzy Ostrowski
- Department of Genetics, Maria Sklodowska-Curie Institute, Cancer Center, 02-781 Warsaw, Poland.,Department of Gastroenterology, Hepatology, and Clinical Oncology, Centre of Postgraduate Medical Education, 02-781 Warsaw, Poland
| | - Michal Mikula
- Department of Genetics, Maria Sklodowska-Curie Institute, Cancer Center, 02-781 Warsaw, Poland
| | - Bernd Clement
- Department of Pharmaceutical and Medicinal Chemistry, Pharmaceutical Institute, Christian Albrechts University, 24118 Kiel, Germany
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Ginsel C, Plitzko B, Froriep D, Stolfa DA, Jung M, Kubitza C, Scheidig AJ, Havemeyer A, Clement B. The Involvement of the Mitochondrial Amidoxime Reducing Component (mARC) in the Reductive Metabolism of Hydroxamic Acids. Drug Metab Dispos 2018; 46:1396-1402. [DOI: 10.1124/dmd.118.082453] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2018] [Accepted: 07/11/2018] [Indexed: 12/18/2022] Open
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Schneider J, Girreser U, Havemeyer A, Bittner F, Clement B. Detoxification of Trimethylamine N-Oxide by the Mitochondrial Amidoxime Reducing Component mARC. Chem Res Toxicol 2018; 31:447-453. [PMID: 29856598 DOI: 10.1021/acs.chemrestox.7b00329] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
Although known for years, the toxic effects of trimethylamine N-oxide (TMAO), a physiological metabolite, were just recently discovered and are currently under investigation. It is known that elevated TMAO plasma levels correlate with an elevated risk for cardiovascular disease (CVD). Even though there is a general consensus about the existence of a causal relationship between TMAO and CVD, the underlying mechanisms are not fully understood. TMAO is an oxidation product of the hepatic flavin-containing monooxygenases (FMO), mainly of isoform 3, and it is conceivable that humans also have an enzyme reversing this toxification by reducing TMAO to its precursor trimethylamine (TMA). All prokaryotic enzymes that use TMAO as a substrate have molybdenum-containing cofactors in common. Such molybdenum-containing enzymes also exist in mammals, with the so-called mitochondrial amidoxime reducing component (mARC) representing the most recently discovered mammalian molybdenum enzyme. The enzyme has been found to exist in two isoforms, mARC1 and mARC2, both being capable of reducing a variety of N-oxygenated compounds, including nonphysiological N-oxides. To investigate whether the two isoforms of this enzyme are able to reduce and detoxify TMAO, we developed a suitable analytical method and tested TMAO reduction with a recombinant enzyme system. We found that one of the two recombinant human mARC proteins, namely, hmARC1, reduces TMAO to TMA. The N-reductive activity is relatively low and identified via the kinetic parameters with Km = (30.4 ± 9.8) mM and Vmax = (100.5 ± 12.2) nmol/(mg protein·min). Nevertheless, the ubiquitous tissue expression of hmARC1 allows a continuous reduction of TMAO whereas the counter-reaction, the production of TMAO through FMO3, can take place only in the liver where FMO3 is expressed. TMAO reduction in porcine liver subfractions showed the characteristic enrichment of N-reductive activity in the outer mitochondrial membrane. TMAO reduction was also found in human cell cultures. These findings indicate the role of hmARC1 in the metabolomic pathway of TMAO, which might contribute to the prevention of CVD. This also hints at a physiological function of the molybdenum enzyme, which remains mainly unknown to date.
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Affiliation(s)
- Jennifer Schneider
- Department of Pharmaceutical and Medicinal Chemistry , Pharmaceutical Institute of the Christian-Albrechts-University of Kiel , 24118 Kiel , Germany
| | - Ulrich Girreser
- Department of Pharmaceutical and Medicinal Chemistry , Pharmaceutical Institute of the Christian-Albrechts-University of Kiel , 24118 Kiel , Germany
| | - Antje Havemeyer
- Department of Pharmaceutical and Medicinal Chemistry , Pharmaceutical Institute of the Christian-Albrechts-University of Kiel , 24118 Kiel , Germany
| | - Florian Bittner
- Federal Research Centre for Cultivated Plants , Julius Kuehn Institute , 06484 Quedlinburg , Germany
| | - Bernd Clement
- Department of Pharmaceutical and Medicinal Chemistry , Pharmaceutical Institute of the Christian-Albrechts-University of Kiel , 24118 Kiel , Germany
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Kubitza C, Ginsel C, Bittner F, Havemeyer A, Clement B, Scheidig AJ. T4 lysozyme-facilitated crystallization of the human molybdenum cofactor-dependent enzyme mARC. Acta Crystallogr F Struct Biol Commun 2018; 74:337-344. [PMID: 29870017 PMCID: PMC5987741 DOI: 10.1107/s2053230x18006921] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2018] [Accepted: 05/04/2018] [Indexed: 12/12/2022] Open
Abstract
The human mitochondrial amidoxime reducing component (hmARC) is a molybdenum cofactor-dependent enzyme that is involved in the reduction of a diverse range of N-hydroxylated compounds of either physiological or xenobiotic origin. In this study, the use of a fusion-protein approach with T4 lysozyme (T4L) to determine the structure of this hitherto noncrystallizable enzyme by X-ray crystallography is described. A set of four different hmARC-T4L fusion proteins were designed. Two of them contained either an N-terminal or a C-terminal T4L moiety fused to hmARC, while the other two contained T4L as an internal fusion partner tethered to the hmARC enzyme between two predicted secondary-structure elements. One of these internal fusion constructs could be expressed and crystallized successfully. The hmARC-T4L crystals diffracted to 1.7 Å resolution using synchrotron radiation and belonged to space group P212121 with one molecule in the asymmetric unit. Initial attempts to solve the structure by molecular replacement using T4L did not result in electron-density distributions that were sufficient for model building and interpretation of the hmARC moiety. However, this study emphasizes the utility of the T4L fusion-protein approach, which can be used for the crystallization and structure determination of membrane-bound proteins as well as soluble proteins.
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Affiliation(s)
- Christian Kubitza
- Structural Biology, Zoological Institute, Kiel University, Am Botanischen Garten 1–9, 24118 Kiel, Germany
| | - Carsten Ginsel
- Pharmaceutical Institute, Kiel University, Gutenbergstrasse 76, 24118 Kiel, Germany
| | - Florian Bittner
- Julius Kuehn Institute, Federal Research Centre for Cultivated Plants, Erwin-Baur-Strasse 27, 06484 Quedlinburg, Germany
| | - Antje Havemeyer
- Pharmaceutical Institute, Kiel University, Gutenbergstrasse 76, 24118 Kiel, Germany
| | - Bernd Clement
- Pharmaceutical Institute, Kiel University, Gutenbergstrasse 76, 24118 Kiel, Germany
| | - Axel J. Scheidig
- Structural Biology, Zoological Institute, Kiel University, Am Botanischen Garten 1–9, 24118 Kiel, Germany
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Kalimuthu P, Havemeyer A, Clement B, Kubitza C, Scheidig AJ, Bernhardt PV. Human mitochondrial amidoxime reducing component (mARC): An electrochemical method for identifying new substrates and inhibitors. Electrochem commun 2017. [DOI: 10.1016/j.elecom.2017.10.003] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
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Plitzko B, Havemeyer A, Bork B, Bittner F, Mendel R, Clement B. Defining the Role of the NADH-Cytochrome-b5 Reductase 3 in the Mitochondrial Amidoxime Reducing Component Enzyme System. ACTA ACUST UNITED AC 2016; 44:1617-21. [PMID: 27469001 DOI: 10.1124/dmd.116.071845] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2016] [Accepted: 07/27/2016] [Indexed: 11/22/2022]
Abstract
The importance of the mitochondrial amidoxime reducing component (mARC)-containing enzyme system in N-reductive metabolism has been studied extensively. It catalyzes the reduction of various N-hydroxylated compounds and therefore acts as the counterpart of cytochrome P450- and flavin-containing monooxygenase-catalyzed oxidations at nitrogen centers. This enzyme system was found to be responsible for the activation of amidoxime and N-hydroxyguanidine prodrugs in drug metabolism. The synergy of three components (mARC, cytochrome b5, and the appropriate reductase) is crucial to exert the N-reductive catalytic effect. Previous studies have demonstrated the involvement of the specific isoforms of the molybdoenzyme mARC and the electron transport protein cytochrome b5 in N-reductive metabolism. To date, the corresponding reductase involved in N-reductive metabolism has yet to be defined because previous investigations have presented ambiguous results. Using small interfering RNA-mediated knockdown in human cells and assessing the stoichiometry of the enzyme system reconstituted in vitro, we provide evidence that NADH-cytochrome-b5 reductase 3 is the principal reductase involved in the mARC enzyme system and is an essential component of N-reductive metabolism in human cells. In addition, only minimal levels of cytochrome-b5 reductase 3 protein are sufficient for catalysis, which impeded previous attempts to identify the reductase.
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Affiliation(s)
- Birte Plitzko
- Department of Pharmaceutical and Medicinal Chemistry, Christian-Albrechts University of Kiel, Kiel, Germany (B.P., A.H., B.C.); and Department of Plant Biology, Braunschweig University of Technology, Braunschweig, Germany (B.B., F.B., R.M.)
| | - Antje Havemeyer
- Department of Pharmaceutical and Medicinal Chemistry, Christian-Albrechts University of Kiel, Kiel, Germany (B.P., A.H., B.C.); and Department of Plant Biology, Braunschweig University of Technology, Braunschweig, Germany (B.B., F.B., R.M.)
| | - Bettina Bork
- Department of Pharmaceutical and Medicinal Chemistry, Christian-Albrechts University of Kiel, Kiel, Germany (B.P., A.H., B.C.); and Department of Plant Biology, Braunschweig University of Technology, Braunschweig, Germany (B.B., F.B., R.M.)
| | - Florian Bittner
- Department of Pharmaceutical and Medicinal Chemistry, Christian-Albrechts University of Kiel, Kiel, Germany (B.P., A.H., B.C.); and Department of Plant Biology, Braunschweig University of Technology, Braunschweig, Germany (B.B., F.B., R.M.)
| | - Ralf Mendel
- Department of Pharmaceutical and Medicinal Chemistry, Christian-Albrechts University of Kiel, Kiel, Germany (B.P., A.H., B.C.); and Department of Plant Biology, Braunschweig University of Technology, Braunschweig, Germany (B.B., F.B., R.M.)
| | - Bernd Clement
- Department of Pharmaceutical and Medicinal Chemistry, Christian-Albrechts University of Kiel, Kiel, Germany (B.P., A.H., B.C.); and Department of Plant Biology, Braunschweig University of Technology, Braunschweig, Germany (B.B., F.B., R.M.)
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Plitzko B, Havemeyer A, Kunze T, Clement B. The pivotal role of the mitochondrial amidoxime reducing component 2 in protecting human cells against apoptotic effects of the base analog N6-hydroxylaminopurine. J Biol Chem 2015; 290:10126-35. [PMID: 25713076 DOI: 10.1074/jbc.m115.640052] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/21/2015] [Indexed: 12/27/2022] Open
Abstract
N-Hydroxylated nucleobases and nucleosides as N-hydroxylaminopurine (HAP) or N-hydroxyadenosine (HAPR) may be generated endogenously in the course of cell metabolism by cytochrome P450, by oxidative stress or by a deviating nucleotide biosynthesis. These compounds have shown to be toxic and mutagenic for procaryotic and eucaryotic cells. For DNA replication fidelity it is therefore of great importance that organisms exhibit effective mechanisms to remove such non-canonical base analogs from DNA precursor pools. In vitro, the molybdoenzymes mitochondrial amidoxime reducing component 1 and 2 (mARC1 and mARC2) have shown to be capable of reducing N-hydroxylated base analogs and nucleoside analogs to the corresponding canonical nucleobases and nucleosides upon reconstitution with the electron transport proteins cytochrome b5 and NADH-cytochrome b5 reductase. By RNAi-mediated down-regulation of mARC in human cell lines the mARC-dependent N-reductive detoxication of HAP in cell metabolism could be demonstrated. For HAPR, on the other hand, the reduction to adenosine seems to be of less significance in the detoxication pathway of human cells as HAPR is primarily metabolized to inosine by direct dehydroxylamination catalyzed by adenosine deaminase. Furthermore, the effect of mARC knockdown on sensitivity of human cells to HAP was examined by flow cytometric quantification of apoptotic cell death and detection of poly (ADP-ribose) polymerase (PARP) cleavage. mARC2 was shown to protect HeLa cells against the apoptotic effects of the base analog, whereas the involvement of mARC1 in reductive detoxication of HAP does not seem to be pivotal.
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Affiliation(s)
- Birte Plitzko
- From the Department of Pharmaceutical and Medicinal Chemistry, Pharmaceutical Institute, Christian-Albrechts-University of Kiel, 24118 Kiel, Germany
| | - Antje Havemeyer
- From the Department of Pharmaceutical and Medicinal Chemistry, Pharmaceutical Institute, Christian-Albrechts-University of Kiel, 24118 Kiel, Germany
| | - Thomas Kunze
- From the Department of Pharmaceutical and Medicinal Chemistry, Pharmaceutical Institute, Christian-Albrechts-University of Kiel, 24118 Kiel, Germany
| | - Bernd Clement
- From the Department of Pharmaceutical and Medicinal Chemistry, Pharmaceutical Institute, Christian-Albrechts-University of Kiel, 24118 Kiel, Germany
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Bauch E, Reichmann D, Mendel RR, Bittner F, Manke AM, Kurz P, Girreser U, Havemeyer A, Clement B. Electrochemical and mARC-catalyzed enzymatic reduction of para-substituted benzamidoximes: consequences for the prodrug concept "amidoximes instead of amidines". ChemMedChem 2014; 10:360-7. [PMID: 25512261 DOI: 10.1002/cmdc.201402437] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/10/2014] [Indexed: 11/05/2022]
Abstract
The mitochondrial amidoxime reducing component (mARC) activates amidoxime prodrugs by reduction to the corresponding amidine drugs. This study analyzes relationships between the chemical structure of the prodrug and its metabolic activation and compares its enzyme-mediated vs. electrochemical reduction. The enzyme kinetic parameters KM and Vmax for the N-reduction of ten para-substituted derivatives of the model compound benzamidoxime were determined by incubation with recombinant proteins and subcellular fractions from pig liver followed by quantification of the metabolites by HPLC. A clear influence of the substituents at position 4 on the chemical properties of the amidoxime function was confirmed by correlation analyses of (1) H NMR chemical shifts and the redox potentials of the 4-substituted benzamidoximes with Hammett's σ. However, no clear relationship between the kinetic parameters for the enzymatic reduction and Hammett's σ or the lipophilicity could be found. It is thus concluded that these properties as well as the redox potential of the amidoxime can be largely ignored during the development of new amidoxime prodrugs, at least regarding prodrug activation.
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Affiliation(s)
- Eva Bauch
- Department of Pharmaceutical and Medicinal Chemistry, Christian Albrechts University Kiel, Gutenbergstraße 76, 24118 Kiel (Germany)
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Ott G, Plitzko B, Krischkowski C, Reichmann D, Bittner F, Mendel RR, Kunze T, Clement B, Havemeyer A. Reduction of Sulfamethoxazole Hydroxylamine (SMX-HA) by the Mitochondrial Amidoxime Reducing Component (mARC). Chem Res Toxicol 2014; 27:1687-95. [DOI: 10.1021/tx500174u] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Affiliation(s)
- Gudrun Ott
- Department
of Pharmaceutical and Medicinal Chemistry, Pharmaceutical Institute, Christian-Albrechts-University of Kiel, Gutenbergstrasse 76, D-24118 Kiel, Germany
| | - Birte Plitzko
- Department
of Pharmaceutical and Medicinal Chemistry, Pharmaceutical Institute, Christian-Albrechts-University of Kiel, Gutenbergstrasse 76, D-24118 Kiel, Germany
| | - Carmen Krischkowski
- Department
of Pharmaceutical and Medicinal Chemistry, Pharmaceutical Institute, Christian-Albrechts-University of Kiel, Gutenbergstrasse 76, D-24118 Kiel, Germany
| | - Debora Reichmann
- Department
of Plant Biology, Braunschweig University of Technology, Humboldtstrasse
1, D-38106 Braunschweig, Germany
| | - Florian Bittner
- Department
of Plant Biology, Braunschweig University of Technology, Humboldtstrasse
1, D-38106 Braunschweig, Germany
| | - Ralf R. Mendel
- Department
of Plant Biology, Braunschweig University of Technology, Humboldtstrasse
1, D-38106 Braunschweig, Germany
| | - Thomas Kunze
- Department
of Pharmaceutical and Medicinal Chemistry, Pharmaceutical Institute, Christian-Albrechts-University of Kiel, Gutenbergstrasse 76, D-24118 Kiel, Germany
| | - Bernd Clement
- Department
of Pharmaceutical and Medicinal Chemistry, Pharmaceutical Institute, Christian-Albrechts-University of Kiel, Gutenbergstrasse 76, D-24118 Kiel, Germany
| | - Antje Havemeyer
- Department
of Pharmaceutical and Medicinal Chemistry, Pharmaceutical Institute, Christian-Albrechts-University of Kiel, Gutenbergstrasse 76, D-24118 Kiel, Germany
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Jakobs HH, Mikula M, Havemeyer A, Strzalkowska A, Borowa-Chmielak M, Dzwonek A, Gajewska M, Hennig EE, Ostrowski J, Clement B. The N-reductive system composed of mitochondrial amidoxime reducing component (mARC), cytochrome b5 (CYB5B) and cytochrome b5 reductase (CYB5R) is regulated by fasting and high fat diet in mice. PLoS One 2014; 9:e105371. [PMID: 25144769 PMCID: PMC4140751 DOI: 10.1371/journal.pone.0105371] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2014] [Accepted: 07/21/2014] [Indexed: 12/11/2022] Open
Abstract
The mitochondrial amidoxime reducing component mARC is the fourth mammalian molybdenum enzyme. The protein is capable of reducing N-oxygenated structures, but requires cytochrome b5 and cytochrome b5 reductase for electron transfer to catalyze such reactions. It is well accepted that the enzyme is involved in N-reductive drug metabolism such as the activation of amidoxime prodrugs. However, the endogenous function of the protein is not fully understood. Among other functions, an involvement in lipogenesis is discussed. To study the potential involvement of the protein in energy metabolism, we tested whether the mARC protein and its partners are regulated due to fasting and high fat diet in mice. We used qRT-PCR for expression studies, Western Blot analysis to study protein levels and an N-reductive biotransformation assay to gain activity data. Indeed all proteins of the N-reductive system are regulated by fasting and its activity decreases. To study the potential impact of these changes on prodrug activation in vivo, another mice experiment was conducted. Model compound benzamidoxime was injected to mice that underwent fasting and the resulting metabolite of the N-reductive reaction, benzamidine, was determined. Albeit altered in vitro activity, no changes in the metabolite concentration in vivo were detectable and we can dispel concerns that fasting alters prodrug activation in animal models. With respect to high fat diet, changes in the mARC proteins occur that result in increased N-reductive activity. With this study we provide further evidence that the endogenous function of the mARC protein is linked with lipid metabolism.
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Affiliation(s)
- Heyka H. Jakobs
- Department of Pharmaceutical and Medicinal Chemistry, Christian-Albrechts-Universität zu Kiel, Kiel, Germany
| | - Michal Mikula
- Department of Genetics, Maria Sklodowska-Curie Memorial Cancer Center and Institute of Oncology, Warsaw, Poland
| | - Antje Havemeyer
- Department of Pharmaceutical and Medicinal Chemistry, Christian-Albrechts-Universität zu Kiel, Kiel, Germany
| | - Adriana Strzalkowska
- Department of Genetics, Maria Sklodowska-Curie Memorial Cancer Center and Institute of Oncology, Warsaw, Poland
| | - Monika Borowa-Chmielak
- Department of Genetics, Maria Sklodowska-Curie Memorial Cancer Center and Institute of Oncology, Warsaw, Poland
| | - Artur Dzwonek
- Department of Genetics, Maria Sklodowska-Curie Memorial Cancer Center and Institute of Oncology, Warsaw, Poland
| | - Marta Gajewska
- Department of Genetics, Maria Sklodowska-Curie Memorial Cancer Center and Institute of Oncology, Warsaw, Poland
| | - Ewa E. Hennig
- Department of Genetics, Maria Sklodowska-Curie Memorial Cancer Center and Institute of Oncology, Warsaw, Poland
- Department of Gastroenterology and Hepatology, Medical Center for Postgraduate Education, Warsaw, Poland
| | - Jerzy Ostrowski
- Department of Genetics, Maria Sklodowska-Curie Memorial Cancer Center and Institute of Oncology, Warsaw, Poland
- Department of Gastroenterology and Hepatology, Medical Center for Postgraduate Education, Warsaw, Poland
| | - Bernd Clement
- Department of Pharmaceutical and Medicinal Chemistry, Christian-Albrechts-Universität zu Kiel, Kiel, Germany
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Jakobs HH, Froriep D, Havemeyer A, Mendel RR, Bittner F, Clement B. The Mitochondrial Amidoxime Reducing Component (mARC): Involvement in Metabolic Reduction ofN-Oxides, Oximes andN-Hydroxyamidinohydrazones. ChemMedChem 2014; 9:2381-7. [DOI: 10.1002/cmdc.201402127] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2014] [Indexed: 11/12/2022]
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Ott G, Reichmann D, Boerger C, Cascorbi I, Bittner F, Mendel RR, Kunze T, Clement B, Havemeyer A. Functional characterization of protein variants encoded by nonsynonymous single nucleotide polymorphisms in MARC1 and MARC2 in healthy Caucasians. Drug Metab Dispos 2014; 42:718-25. [PMID: 24423752 DOI: 10.1124/dmd.113.055202] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
Human molybdenum-containing enzyme mitochondrial amidoxime reducing component (mARC), cytochrome b5 type B, and NADH cytochrome b5 reductase form an N-reductive enzyme system that is capable of reducing N-hydroxylated compounds. Genetic variations are known, but their functional relevance is unclear. Our study aimed to investigate the incidence of nonsynonymous single nucleotide polymorphisms (SNPs) in the mARC genes in healthy Caucasian volunteers, to determine saturation of the protein variants with molybdenum cofactor (Moco), and to characterize the kinetic behavior of the protein variants by in vitro biotransformation studies. Genotype frequencies of six SNPs in the mARC genes (c.493A>G, c.560T>A, c.736T>A, and c.739G>C in MARC1; c.730G>A and c.735T>G in MARC2) were determined by pyrosequencing in a cohort of 340 healthy Caucasians. Protein variants were expressed in Escherichia coli. Saturation with Moco was determined by measurement of molybdenum by inductively coupled mass spectrometry. Steady state assays were performed with benzamidoxime. The six variants were of low frequency in this Caucasian population. Only one homozygous variant (c.493A; MARC1) was detected. All protein variants were able to bind Moco. Steady state assays showed statistically significant decreases of catalytic efficiency values for the mARC-2 wild type compared with the mARC-1 wild type (P < 0.05) and for two mARC-2 variants compared with the mARC-2 wild type (G244S, P < 0.05; C245W, P < 0.05). After simultaneous substitution of more than two amino acids in the mARC-1 protein, N-reductive activity was decreased 5-fold. One homozygous variant of MARC1 was detected in our sample. The encoded protein variant (A165T) showed no different kinetic parameters in the N-reduction of benzamidoxime.
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Affiliation(s)
- Gudrun Ott
- Department of Pharmaceutical and Medicinal Chemistry, Pharmaceutical Institute, Christian-Albrechts-University of Kiel, Kiel, Germany (G.O., T.K., B.C., A.H.); Department of Plant Biology, Technical University of Braunschweig, Braunschweig, Germany (D.R., F.B., R.-R.M.); and Institute of Experimental and Clinical Pharmacology, University Hospital Schleswig-Holstein, Campus Kiel, Kiel, Germany (C.B., I.C.)
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Plitzko B, Ott G, Reichmann D, Henderson CJ, Wolf CR, Mendel R, Bittner F, Clement B, Havemeyer A. The involvement of mitochondrial amidoxime reducing components 1 and 2 and mitochondrial cytochrome b5 in N-reductive metabolism in human cells. J Biol Chem 2013; 288:20228-37. [PMID: 23703616 PMCID: PMC3711290 DOI: 10.1074/jbc.m113.474916] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/09/2013] [Revised: 05/23/2013] [Indexed: 12/26/2022] Open
Abstract
The mitochondrial amidoxime reducing component mARC is a recently discovered molybdenum enzyme in mammals. mARC is not active as a standalone protein, but together with the electron transport proteins NADH-cytochrome b5 reductase (CYB5R) and cytochrome b5 (CYB5), it catalyzes the reduction of N-hydroxylated compounds such as amidoximes. The mARC-containing enzyme system is therefore considered to be responsible for the activation of amidoxime prodrugs. All hitherto analyzed mammalian genomes code for two mARC genes (also referred to as MOSC1 and MOSC2), which share high sequence similarities. By RNAi experiments in two different human cell lines, we demonstrate for the first time that both mARC proteins are capable of reducing N-hydroxylated substrates in cell metabolism. The extent of involvement is highly dependent on the expression level of the particular mARC protein. Furthermore, the mitochondrial isoform of CYB5 (CYB5B) is clearly identified as an essential component of the mARC-containing N-reductase system in human cells. The participation of the microsomal isoform (CYB5A) in N-reduction could be excluded by siRNA-mediated down-regulation in HEK-293 cells and knock-out in mice. Using heme-free apo-CYB5, the contribution of mitochondrial CYB5 to N-reductive catalysis was proven to strictly depend on heme. Finally, we created recombinant CYB5B variants corresponding to four nonsynonymous single nucleotide polymorphisms (SNPs). Investigated mutations of the heme protein seemed to have no significant impact on N-reductive activity of the reconstituted enzyme system.
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Affiliation(s)
- Birte Plitzko
- From the Department of Pharmaceutical and Medicinal Chemistry, Pharmaceutical Institute, Christian-Albrechts-University of Kiel, 24118 Kiel, Germany
| | - Gudrun Ott
- From the Department of Pharmaceutical and Medicinal Chemistry, Pharmaceutical Institute, Christian-Albrechts-University of Kiel, 24118 Kiel, Germany
| | - Debora Reichmann
- the Department of Plant Biology, Braunschweig University of Technology, 38023 Braunschweig, Germany, and
| | - Colin J. Henderson
- the University of Dundee Medical Research Institute, Jacqui Wood Cancer Centre, Ninewells Hospital and Medical School, Dundee DD1 9SY, Scotland, United Kingdom
| | - C. Roland Wolf
- the University of Dundee Medical Research Institute, Jacqui Wood Cancer Centre, Ninewells Hospital and Medical School, Dundee DD1 9SY, Scotland, United Kingdom
| | - Ralf Mendel
- the Department of Plant Biology, Braunschweig University of Technology, 38023 Braunschweig, Germany, and
| | - Florian Bittner
- the Department of Plant Biology, Braunschweig University of Technology, 38023 Braunschweig, Germany, and
| | - Bernd Clement
- From the Department of Pharmaceutical and Medicinal Chemistry, Pharmaceutical Institute, Christian-Albrechts-University of Kiel, 24118 Kiel, Germany
| | - Antje Havemeyer
- From the Department of Pharmaceutical and Medicinal Chemistry, Pharmaceutical Institute, Christian-Albrechts-University of Kiel, 24118 Kiel, Germany
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Froriep D, Clement B, Bittner F, Mendel RR, Reichmann D, Schmalix W, Havemeyer A. Activation of the anti-cancer agent upamostat by the mARC enzyme system. Xenobiotica 2013; 43:780-4. [DOI: 10.3109/00498254.2013.767481] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
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Altmann KS, Havemeyer A, Beitz E, Clement B. Dimethylarginine-dimethylaminohydrolase-2 (DDAH-2) does not metabolize methylarginines. Chembiochem 2012; 13:2599-604. [PMID: 23125090 DOI: 10.1002/cbic.201200499] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2012] [Indexed: 01/18/2023]
Abstract
Free endogenous methylarginines, N(ω)-monomethyl-L-arginine (L-NMMA) and N(ω),N(ω')-dimethyl-L-arginine (ADMA), inhibit NO synthases (NOSs) and are metabolized by dimethylargininedimethylaminohydrolase (DDAH). A postulated metabolism has been shown several times for DDAH-1, but the involvement of DDAH-2 in the degradation of ADMA and L-NMMA is still a matter of debate. Determination of the isoform-specific DDAH protein expression profiles in various porcine tissue types shows a correlation of DDAH activity only with DDAH-1 levels. DDAH activity (measured as L-citrulline formation from the conversion of methylarginines and alternative DDAH substrates) was detected in DDAH-1-rich porcine tissue types, that is, kidney, liver, and brain, but not in DDAH-2-rich porcine fractions, that is, spleen and thyroid. Furthermore, several ex vivo studies showed DDAH activity to be important for L-citrulline formation in porcine tissue and indicated the absence of an endogenous DDAH inhibitor in porcine tissue. This study provides new insights into tissue distributions as well as substrate selectivity for both DDAH isoforms. Although DDAH-1 is known to metabolize the endogenous NOS inhibitors L-NMMA and ADMA, a physiological function for DDAH-2 has yet to be determined. Hence, determining DDAH activity by methylarginine conversion is not suitable for analyzing isoform selectivity of DDAH-1 inhibitors as postulated.
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Affiliation(s)
- Karin S Altmann
- Department of Pharmaceutical and Medicinal Chemistry, Pharmaceutical Institute, Christian-Albrechts-Universität Kiel, Gutenbergstrasse 76, 24118 Kiel, Germany
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Krompholz N, Krischkowski C, Reichmann D, Garbe-Schönberg D, Mendel RR, Bittner F, Clement B, Havemeyer A. The mitochondrial Amidoxime Reducing Component (mARC) is involved in detoxification of N-hydroxylated base analogues. Chem Res Toxicol 2012; 25:2443-50. [PMID: 22924387 DOI: 10.1021/tx300298m] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The "mitochondrial Amidoxime Reducing Component" (mARC) is the newly discovered fourth molybdenum enzyme in mammals. All hitherto analyzed mammals express two mARC proteins, referred to as mARC1 and mARC2. Together with their electron transport proteins cytochrome b(5) and NADH cytochrome b(5) reductase, they form a three-component enzyme system and catalyze the reduction of N-hydroxylated prodrugs. Here, we demonstrate the reductive detoxification of toxic and mutagenic N-hydroxylated nucleobases and their corresponding nucleosides by the mammalian mARC-containing enzyme system. The N-reductive activity was found in all tested tissues with the highest detectable conversion rates in liver, kidney, thyroid, and pancreas. According to the presumed localization, the N-reductive activity is most pronounced in enriched mitochondrial fractions. In vitro assays with the respective recombinant three-component enzyme system show that both mARC isoforms are able to reduce N-hydroxylated base analogues, with mARC1 representing the more efficient isoform. On the basis of the high specific activities with N-hydroxylated base analogues relative to other N-hydroxylated substrates, our data suggest that mARC proteins might be involved in protecting cellular DNA from misincorporation of toxic N-hydroxylated base analogues during replication by converting them to the correct purine or pyrimidine bases, respectively.
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Affiliation(s)
- Nina Krompholz
- Pharmaceutical Institute, Christian-Albrechts-University of Kiel, Germany 24118
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Wahl B, Reichmann D, Niks D, Krompholz N, Havemeyer A, Clement B, Messerschmidt T, Rothkegel M, Biester H, Hille R, Mendel RR, Bittner F. Biochemical and spectroscopic characterization of the human mitochondrial amidoxime reducing components hmARC-1 and hmARC-2 suggests the existence of a new molybdenum enzyme family in eukaryotes. J Biol Chem 2010; 285:37847-59. [PMID: 20861021 PMCID: PMC2988388 DOI: 10.1074/jbc.m110.169532] [Citation(s) in RCA: 81] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2010] [Revised: 09/17/2010] [Indexed: 11/06/2022] Open
Abstract
The mitochondrial amidoxime reducing component mARC is a newly discovered molybdenum enzyme that is presumed to form the catalytical part of a three-component enzyme system, consisting of mARC, heme/cytochrome b(5), and NADH/FAD-dependent cytochrome b(5) reductase. mARC proteins share a significant degree of homology to the molybdenum cofactor-binding domain of eukaryotic molybdenum cofactor sulfurase proteins, the latter catalyzing the post-translational activation of aldehyde oxidase and xanthine oxidoreductase. The human genome harbors two mARC genes, referred to as hmARC-1/MOSC-1 and hmARC-2/MOSC-2, which are organized in a tandem arrangement on chromosome 1. Recombinant expression of hmARC-1 and hmARC-2 proteins in Escherichia coli reveals that both proteins are monomeric in their active forms, which is in contrast to all other eukaryotic molybdenum enzymes that act as homo- or heterodimers. Both hmARC-1 and hmARC-2 catalyze the N-reduction of a variety of N-hydroxylated substrates such as N-hydroxy-cytosine, albeit with different specificities. Reconstitution of active molybdenum cofactor onto recombinant hmARC-1 and hmARC-2 proteins in the absence of sulfur indicates that mARC proteins do not belong to the xanthine oxidase family of molybdenum enzymes. Moreover, they also appear to be different from the sulfite oxidase family, because no cysteine residue could be identified as a putative ligand of the molybdenum atom. This suggests that the hmARC proteins and sulfurase represent members of a new family of molybdenum enzymes.
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Affiliation(s)
- Bettina Wahl
- From the Department of Plant Biology, Technische Universität Braunschweig, 38023 Braunschweig, Germany
| | - Debora Reichmann
- From the Department of Plant Biology, Technische Universität Braunschweig, 38023 Braunschweig, Germany
| | - Dimitri Niks
- the Department of Biochemistry, University of California, Riverside, California 92521
| | - Nina Krompholz
- the Pharmaceutical Institute, Department of Pharmaceutical and Medicinal Chemistry, Christian-Albrechts-Universität Kiel, 24118 Kiel, Germany, and
| | - Antje Havemeyer
- the Pharmaceutical Institute, Department of Pharmaceutical and Medicinal Chemistry, Christian-Albrechts-Universität Kiel, 24118 Kiel, Germany, and
| | - Bernd Clement
- the Pharmaceutical Institute, Department of Pharmaceutical and Medicinal Chemistry, Christian-Albrechts-Universität Kiel, 24118 Kiel, Germany, and
| | | | | | - Harald Biester
- Environmental Geology, Technische Universität Braunschweig, 38023 Braunschweig, Germany
| | - Russ Hille
- the Department of Biochemistry, University of California, Riverside, California 92521
| | - Ralf R. Mendel
- From the Department of Plant Biology, Technische Universität Braunschweig, 38023 Braunschweig, Germany
| | - Florian Bittner
- From the Department of Plant Biology, Technische Universität Braunschweig, 38023 Braunschweig, Germany
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Havemeyer A, Grünewald S, Wahl B, Bittner F, Mendel R, Erdélyi P, Fischer J, Clement B. Reduction of N-Hydroxy-sulfonamides, Including N-Hydroxy-valdecoxib, by the Molybdenum-Containing Enzyme mARC. Drug Metab Dispos 2010; 38:1917-21. [DOI: 10.1124/dmd.110.032813] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
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Havemeyer A, Bittner F, Wollers S, Mendel R, Kunze T, Clement B. Identification of the Missing Component in the Mitochondrial Benzamidoxime Prodrug-converting System as a Novel Molybdenum Enzyme. J Biol Chem 2006; 281:34796-802. [PMID: 16973608 DOI: 10.1074/jbc.m607697200] [Citation(s) in RCA: 127] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Amidoximes can be used as prodrugs for amidines and related functional groups to enhance their intestinal absorption. These prodrugs are reduced to their active amidines. Other N-hydroxylated structures are mutagenic or responsible for toxic effects of drugs and are detoxified by reduction. In this study, a N-reductive enzyme system of pig liver mitochondria using benzamidoxime as a model substrate was identified. A protein fraction free from cytochrome b5 and cytochrome b5 reductase was purified, enhancing 250-fold the minor benzamidoxime-reductase activity catalyzed by the membrane-bound cytochrome b5/NADH cytochrome b5 reductase system. This fraction contained a 35-kDa protein with homologies to the C-terminal domain of the human molybdenum cofactor sulfurase. Here it was demonstrated that this 35-kDa protein contains molybdenum cofactor and forms the hitherto ill defined third component of the N-reductive complex in the outer mitochondrial membrane. Thus, the 35-kDa protein represents a novel group of molybdenum proteins in eukaryotes as it forms the catalytic part of a three-component enzyme complex consisting of separate proteins. Supporting these findings, recombinant C-terminal domain of the human molybdenum cofactor sulfurase exhibited N-reductive activity in vitro, which was strictly dependent on molybdenum cofactor.
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Affiliation(s)
- Antje Havemeyer
- Pharmaceutical Institute, Department of Pharmaceutical and Medicinal Chemistry, Christian-Albrechts-University of Kiel, 24118 Kiel, Germany
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Clement B, Mau S, Deters S, Havemeyer A. HEPATIC, EXTRAHEPATIC, MICROSOMAL, AND MITOCHONDRIAL ACTIVATION OF THEN-HYDROXYLATED PRODRUGS BENZAMIDOXIME, GUANOXABENZ, AND RO 48-3656 ([[1-[(2S)-2-[[4-[(HYDROXYAMINO)IMINOMETHYL]BENZOYL]AMINO]-1-OXOPROPYL]-4-PIPERIDINYL]OXY]-ACETIC ACID). Drug Metab Dispos 2005; 33:1740-7. [PMID: 16118330 DOI: 10.1124/dmd.105.005249] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
In previous studies, it was shown that liver microsomes from rabbit, rat, pig, and human are involved in the reduction of N-hydroxylated amidines, guanidines, and amidinohydrazones of various drugs and model compounds (Drug Metab Rev 34: 565-579). One responsible enzyme system, the microsomal benzamidoxime reductase, consisting of cytochrome b5, its reductase, and a cytochrome P450 isoenzyme, was isolated from pig liver microsomes (J Biol Chem 272:19615-19620). Further investigations followed to establish whether such enzyme systems are also present in microsomes of other organs such as brain, lung, and intestine. In addition, the mitochondrial reduction in human and porcine liver and kidney preparations was studied. The reductase activities were measured by following the reduction of benzamidoxime to benzamidine, guanoxabenz to guanabenz, and Ro 48-3656 ([[1-[(2S)-2-[[4-[(hydroxyamino)iminomethyl]benzoyl]amino]-1-oxopropyl]-4-piperidinyl]oxy]-acetic acid) to Ro 44-3888 ([[1-[(2S)-2-[[4-(aminoiminomethyl)benzoyl]amino]-1-oxopropyl]-4-piperidinyl]oxy]-acetic acid). Interestingly, preparations of all tested organs were capable of reducing the three compounds. The highest specific rates were found in kidney followed by liver, brain, lung, and intestine, and usually the mitochondrial reduction rates were superior. From the determined characteristics, similarities between the enzyme systems in the different organs and organelles were detected. Furthermore, properties of the benzamidoxime reductase located in the outer membrane of pig liver mitochondria were studied. In summary, these results demonstrate that in addition to the microsomal reduction, mitochondria are involved to a great extent in the activation of amidoxime prodrugs. The importance of extrahepatic metabolism in the reduction of N-hydroxylated prodrugs is demonstrated.
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Affiliation(s)
- Bernd Clement
- Institute of Pharmacy, Christian-Albrechts-University of Kiel, Kiel, Germany.
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Clement B, Behrens D, Amschler J, Matschke K, Wolf S, Havemeyer A. Reduction of sulfamethoxazole and dapsone hydroxylamines by a microsomal enzyme system purified from pig liver and pig and human liver microsomes. Life Sci 2005; 77:205-19. [PMID: 15862605 DOI: 10.1016/j.lfs.2004.12.028] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/25/2004] [Accepted: 12/22/2004] [Indexed: 11/17/2022]
Abstract
Biotransformation involving nitrogen are of pharmacological and toxicological relevance. In principle, nitrogen containing functional groups can undergo all the known biotransformation processes such as oxidation, reduction, hydrolysis and formation of conjugates. For the N-reduction of benzamidoxime an oxygen-insensitive liver microsomal enzyme system that required cytochrome b5, NADH-cytochrome b5 reductase and a cytochrome P450 isoenzyme of the subfamily 2D has been described. In previous studies it was demonstrated that N-hydroxylated derivates of strongly basic functional groups are easily reduced by this enzyme system. The N-hydroxylation of sulfonamides such sulfamethoxazole (SMX) and dapsone (DDS) to sulfamethoxazole-hydroxylamine (SMX-HA) and dapsone-hydroxylamine (DDS-N-OH), respectively is the first step in the formation of reactive metabolites. Therefore it seemed reasonable to study the potential of cytochrome b5, NADH-cytochrome b5 reductase and CYP2D to detoxify these N-hydroxylated metabolites by N-reduction. Metabolites were analysed by HPLC analysis. SMX-HA and DDS-N-OH are reduced by cytochrome b5, NADH-cytochrome b5 reductase and CYP2D but also only by cytochrome b5 and NADH-cytochrome b5 reductase without addition of CYP2D. The reduction rate for SMX-HA by cytochrome b5, NADH-cytochrome b5 reductase and CYP2D was 0,65 +/- 0,1 nmol SMX/min/mg protein. The reduction rate by b5 and b5 reductase was 0,37 +/- 0,15 nmol SMX/min/mg protein. For DDS-N-OH the reduction rate by cytochrome b5, NADH-cytochrome b5 reductase and CYP2D was 1.79 +/- 0.85 nmol DDS/min/mg protein and by cytochrome b5 and NADH-cytochrome b5 reductase 1.25 +/- 0.15 nmol DDS/min/mg protein. Cytochrome b5, NADH-cytochrome b5 reductase are therefore involved in the detoxification of these reactive hydroxylamines and CYP2D increased the N-reduction.
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Affiliation(s)
- Bernd Clement
- Pharmazeutisches Institut, Christian-Albrechts-Universität, Gutenbergstr. 76, D-24118 Kiel, Germany.
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