Inhibition of Xanthine Oxidase by the Aldehyde Oxidase Inhibitor Raloxifene: Implications for Identifying Molybdopterin Nitrite Reductases

Weidert, Eric R.; Schoenborn, Scott O.; Cantú‐Medellín, Nadiezhda; Jones, None Jeff P.; Kelley, Eric E.

doi:10.1016/j.freeradbiomed.2013.10.638

Cited by 8 publications

(8 citation statements)

References 17 publications

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“…There are only a few substrates that show biotransformation by both enzymes, such as 6-deoxyclovir, 6-thioxanthine, and recently VU0409106, a lead compound for childhood developmental disorders (Krenitsky et al, 1984;Morrison et al, 2012;Choughule et al, 2014). Although some overlap exists between the substrates, there have been chemical inhibitors identified specifically for AO and XO including raloxifene (Obach, 2004), hydralazine (Strelevitz et al, 2012), allopurinol (Panoutsopoulos et al, 2004), and febuxostat (Weidert et al, 2014). Allopurinol has been widely used as a known XO inhibitor, but recently it was identified that febuxostat is a more potent inhibitor of XO than allopurinol (Malik et al, 2011).…”

Section: Discussionmentioning

confidence: 99%

Role of Molybdenum-Containing Enzymes in the Biotransformation of the Novel Ghrelin Receptor Inverse Agonist PF-5190457: A Reverse Translational Bed-to-Bench Approach

et al. 2019

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was identified as a potent and selective inverse agonist of the ghrelin receptor [growth hormone secretagogue receptor 1a (GHS-R1a)]. The present translational bed-to-bench work characterizes the biotransformation of this compound in vivo and then further explores in vitro metabolism in fractions of human liver and primary hepatocytes. Following oral administration of PF-5190457 in a phase 1b clinical study, hydroxyl metabolites of the compound were observed, including one that had not been observed in previously performed human liver microsomal incubations. PF-6870961 or (R)-1-(2-(5-(2-hydroxy-6-methylpyrimidin-4-yl)-2,3-dihydro-1H-inden-1-yl)-2,7-diazaspiro[3.5]nonan-7-yl)-2-(2-methylimidazo[2,1-b]thiazol-6-yl)ethan-1-one was biosynthesized using liver cytosol, and the site of hydroxylation was shown to be on the pyrimidine using nuclear magnetic resonance spectroscopy. The aldehyde oxidase (AO) inhibitor raloxifene and the xanthine oxidase inhibitor febuxostat inhibited the formation of PF-6870961 in human liver cytosol, suggesting both enzymes were involved in the metabolism of the drug. However, greater inhibition was observed with raloxifene, indicating AO is a dominant enzyme in the biotransformation. The intrinsic clearance of the drug in human liver cytosol was estimated to be 0.002 ml/min per milligram protein. This study provides important novel information at three levels: 1) it provides additional new information on the recently developed novel compound PF-5190457, the first GHS-R1a blocker that has moved to development in humans; 2) it provides an example of a reverse translational approach where a discovery in humans was brought back, validated, and further investigated at the bench level; and 3) it demonstrates the importance of considering the molybdenumcontaining oxidases during the development of new drug entities. SIGNIFICANCE STATEMENT PF-5190457 is a novel ghrelin receptor inverse agonist that is currently undergoing clinical development for treatment of alcohol use disorder. PF-6870961, a major hydroxyl metabolite of the compound, was observed in human plasma, but was absent in human liver microsomal incubations. PF-6870961 was biosynthesized using liver cytosol, and the site of hydroxylation on the pyrimidine ring was characterized. Inhibitors of aldehyde oxidase and xanthine oxidase inhibited the formation of PF-6870961 in human liver cytosol, suggesting both enzymes were involved in the metabolism of the drug. This information is important for patient selection in subsequent clinical studies.

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Section: Discussionmentioning

confidence: 99%

Role of Molybdenum-Containing Enzymes in the Biotransformation of the Novel Ghrelin Receptor Inverse Agonist PF-5190457: A Reverse Translational Bed-to-Bench Approach

et al. 2019

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“…Current data are based on microarray analysis, activity measurement, a HPLC assay for uric acid levels, working with PPARy agonists, which all can be influenced also by AOX, because both enzymes, XOR and AOX, are able to generate ROS (Kundu et al 2007;Kundu et al 2012). In addition, inhibitors like allopurinol and others, used for generating these data, can work on both enzymes and can create misinterpretations (see, e.g., Weidert et al 2014;Williams et al 2014). The evolution of AOX from XOR was by gene duplication and the enzymes are vicinally situated on the same chromosome (see, e.g., Krenitsky 1978).…”

Section: Discussionmentioning

confidence: 99%

Formation and degradation of lipid droplets in human adipocytes and the expression of aldehyde oxidase (AOX)

et al. 2019

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Lipid droplet (LD) binding proteins in mammary glands and in adipocytes were previously compared and striking similar sets of these specific proteins demonstrated. Xanthine oxidoreductase (XOR) together with perilipins and the lactating mammary gland protein butyrophilin play an important role in the secretion process of LDs into milk ducts. In contrast, in adipose tissue and in adipocytes, mainly perilipins have been described. Moreover, XOR was reported in mouse adipose tissue and adipocyte culture cells as "novel regulator of adipogenesis". This obvious coincidence of protein sets prompted us to revisit the formation of LDs in human-cultured adipocytes in more detail with special emphasis on the possibility of a LD association of XOR. We demonstrate by electron and immunoelectron microscopy new structural details on LD formation in adipocytes. Surprisingly, by immunological and proteomic analysis, we identify in contrast to previous data showing the enzyme XOR, predominantly the expression of aldehyde oxidase (AOX). AOX could be detected tightly linked to LDs when adipocytes were treated with starvation medium. In addition, the majority of cells show an enormous interconnected, tubulated mitochondria network. Here, we discuss that (1) XOR is involved-together with perilipins-in the secretion of LDs in alveolar epithelial cells of the lactating mammary gland and is important in the transcytosis pathway of capillary endothelial cells. (2) In cells, where LDs are not secreted, XOR cannot be detected at the protein level, whereas in contrast in these cases, AOX is often present. We detect AOX in adipocytes together with perilipins and find evidence that these proteins might direct LDs to mitochondria. Finally, we here report for the first time the exclusive and complementary localization of XOR and AOX in diverse cell types.

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“…They successfully unveiled that raloxifene as a XO inhibitor selectively targeted the joining link of both enzymes, that is, MPT nitrite reductases. Other reports also suggested that most human liver cytosol preparations lack XO activity due to which the possibility of interaction between these two protein gets dwindle . This hampers the possibility of the development of dual AOX and XO inhibitors.…”

Section: Substrates and Dual Inhibitors Of Xo And Aox Enzymesmentioning

confidence: 99%

Toward an Understanding of Structural Insights of Xanthine and Aldehyde Oxidases: An Overview of their Inhibitors and Role in Various Diseases

Kumar

Joshi

Kler

et al. 2017

Medicinal Research Reviews

101

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Almost all drug molecules become the substrates for oxidoreductase enzymes, get metabolized into more hydrophilic products and eliminated from the body. These metabolites sometime may be more potent, active, inactive, or toxic in nature compared to parent molecule. Xanthine oxidoreductase and aldehyde oxidase belong to molybdenum containing family and are well characterized for their structures and functions, in particular to their ability to oxidize/hydroxylate the xenobiotics. Their upregulated clinical levels causing oxidative stress are associated with pathways either directly involved in the progression of diseases, gout, or indirectly with the succession of other diseases such as diabetes, cancer, etc. Herein, we have put forth a comprehensive review on the xanthine and aldehyde oxidases pertaining to their structures, functions, pathophysiological role, and a comparative analysis of structural insights of xanthine and aldehyde oxidases' binding domains with endogenous ligands or inhibitors. Though both the enzymes are molybdenum containing and are likely to share some common pathways and interact with inhibitors in a similar manner but we have focused on structural prerequisites for inhibitor specificity to both the enzymes keeping in view of the existing X-ray structures. This review also provides futuristic implications in the design of inhibitors derived from inorganic complexes or small organic molecules considering the spatial features and structural insights of both the enzymes.

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Inhibition of Xanthine Oxidase by the Aldehyde Oxidase Inhibitor Raloxifene: Implications for Identifying Molybdopterin Nitrite Reductases

Cited by 8 publications

References 17 publications

Role of Molybdenum-Containing Enzymes in the Biotransformation of the Novel Ghrelin Receptor Inverse Agonist PF-5190457: A Reverse Translational Bed-to-Bench Approach

Role of Molybdenum-Containing Enzymes in the Biotransformation of the Novel Ghrelin Receptor Inverse Agonist PF-5190457: A Reverse Translational Bed-to-Bench Approach

Formation and degradation of lipid droplets in human adipocytes and the expression of aldehyde oxidase (AOX)

Toward an Understanding of Structural Insights of Xanthine and Aldehyde Oxidases: An Overview of their Inhibitors and Role in Various Diseases

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