The Involvement of the Mitochondrial Amidoxime Reducing Component (mARC) in the Reductive Metabolism of Hydroxamic Acids

Abstract

The mitochondrial amidoxime reducing component is a recently discovered molybdenum enzyme in mammals which, in concert with the electron transport proteins cytochrome b5 and NADH cytochrome b5 reductase, catalyzes the reduction of -oxygenated structures. This three component enzyme system plays a major role in-reductive drug metabolism. Belonging to the group of -hydroxylated structures, hydroxamic acids are also potential substrates of the mARC-system. Hydroxamic acids show a variety of pharmacological activities and are therefore often found in drug candidates. They can also exhibit toxic properties as is the case for many aryl hydroxamic acids formed during the metabolism of arylamides. Biotransformation assays using recombinant human proteins, subcellular porcine tissue fractions as well as human cell culture were performed. Here the mARC-dependent reduction of the model compound benzhydroxamic acid is reported in addition to the reduction of three drugs. In comparison with other known substrates of the molybdenum depending enzyme system (e.g., amidoxime prodrugs) the conversion rates measured here are slower, thereby reflecting the mediocre metabolic stability and oral bioavailability of distinct hydroxamic acids. Moreover, the toxic-hydroxylated metabolite of the analgesic phenacetin, -hydroxyphenacetin, is not reduced by the mARC-system under the chosen conditions. This confirms the high toxicity of this component, as it needs to be detoxified by other pathways. This work highlights the need to monitor the-reductive metabolism of new drug candidates by the mARC-system when evaluating the metabolic stability of hydroxamic acid-containing structures or the potential risks of toxic metabolites.

Crystal structure of human mARC1 reveals its exceptional position among eukaryotic molybdenum enzymes

“…To examine the impact of these paralog-specific amino acids, we performed preliminary reductase activity assays with a potential marker substrate of hmARC1 and the hmARC2_P270S variant. The hydroxamic acid derivative CP544439, a matrix metalloproteinase inhibitor, is almost exclusively reduced by hmARC1 (10). In contrast to the almost inactive wild-type hmARC2, its P270S variant shows a remarkably higher activity toward this substrate, even though reductase activity levels are not comparable to those of hmARC1 (SI Appendix, Fig.…”

“…In this context, the mitochondrial amidoxime-reducing component (mARC) was discovered in our laboratory in 2006 as a thus-far unknown molybdenum-containing protein (3). It was identified as being an extremely effective reductase for a multitude of N-oxygenated molecules such as hydroxylamines (4), N 4 -hydroxycytosine, and N 6hydroxyadenine, including their corresponding nucleosides (5), hydroxyamidines (6), amidoxime prodrugs and hydroxyguanidines (7), oximes (8), N-oxides (8,9), hydroxamic acids (10), and sulfohydroxamic acids (11). mARC therefore plays a pivotal role as a counterpart to CYP-and FMO-mediated oxygenation reactions in metabolic cycles.…”

From the Eukaryotic Molybdenum Cofactor Biosynthesis to the Moonlighting Enzyme mARC

“…Recently, hydroxamic acids have also been proposed as substrates of human and porcine mARC [96]. Hydroxamic acids show a variety of pharmacological activities and are often used as prodrugs.…”

“…Hydroxamic acids show a variety of pharmacological activities and are often used as prodrugs. In comparison with other known substrates of mARC (e.g., amidoxime), the conversion rates measured for the hydroxamic acids were slower, thereby reflecting the low metabolic stability and oral bioavailability of distinct hydroxamic acids [96].…”

A resposta transcricional imediata ao hormônio juvenil no corpo gorduroso de larvas de Apis mellifera

“…O gene mARC codifica para uma enzima de molibdênio em mamíferos que tem sua principal função no metabolismo de n-redução de substâncias e ácidos hidroaxamicos (GINSEL et al, 2018). Em pacientes é sugerido como fator protetivo de doenças de fígado (EMDIN et al, 2019) e é descrito também como uma proteína da membrana externa das mitocôndrias em humanos (KLEIN et al, 2012).…”