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Abstract
Renalase was recently described as a new flavoprotein that functions as FAD/NADH-dependent oxidase and, in contrast to other monoamine oxidases, is secreted into plasma and urine. Recombinant renalase was found to exert powerful and rapid hypotensive effects when administered intravenously on rats and this was suggested to be mediated by circulating catecholamines degradation. However there is no concrete evidence that directly supports the hypothesis that renalase metabolizes catecholamines. In this study we aimed to evaluate the catecholamines-degrading renalase activity by three different technical approaches: 1) Amplex Red Monoamine Oxidase Assay, which evaluates the rate of resaruzin reduction by renalase oxidative activity; 2) assessment of catecholamines consumptions by high-pressure liquid chromatography (HPLC) with electrochemical-detection (ED) and 3) assessment of product formation by HPLC with photodiode array-detection (DAD). Using the Amplex Red MAO Assay, all three catecholamines were degraded by recombinant renalase overtime, being adrenaline the preferred substrate, followed by noradrenaline and dopamine. In addition using HPLC-ED, it was observed the consumption of all three catecholamines by recombinant renalase, which were oxidized to the correspondent aminochromes, as observed by DAD. However the role of renalase as catalyzer of aminochromes production is still undefined. In summary, the data presented in this study propose by different methodologies the involvement of renalase in catecholamine metabolization.
Highlights
Renalase was recently described as a new flavoprotein, that functions as FAD-dependent oxidase and, in contrast to other monoamine oxidases, is secreted into plasma and urine where it was suggested to metabolize catecholamines [1, 2]
The amine oxidase activity was inhibited by a renalase antibody [1], supporting the notion that the rate of resaruzin reduction measured by the Amplex Red Monoamine Oxidase Assay Kit could be used as an indirect measure of renalase oxidase activity [3, 4]
In the present study we evaluate catecholamines degradation renalase activity by 1) the rate of resaruzin reduction measured by the Amplex Red Monoamine Oxidase Assay Kit; 2) the consumption of the substrate measured by HPLCED and 3) the formation of the respective catalyse reaction end-products measured by HPLC-DAD
Summary
Renalase was recently described as a new flavoprotein, that functions as FAD-dependent oxidase and, in contrast to other monoamine oxidases, is secreted into plasma and urine where it was suggested to metabolize catecholamines [1, 2]. The amine oxidase activity was inhibited by a renalase antibody [1], supporting the notion that the rate of resaruzin reduction measured by the Amplex Red Monoamine Oxidase Assay Kit could be used as an indirect measure of renalase oxidase activity [3, 4] These findings were strongly questioned by Boomsma and Tipton [5], who pointed out that the rate of hydrogen peroxide (H2O2) generation, determined by this method, was far too low to be. Based on these findings it has been suggested that renalase act as a catecholamine-degrading enzyme, via either O2-dependent or NADH-dependent mechanisms, and recently it was suggested as possible metabolic end-products aminochromes [10]
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