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      Homoarginine and inhibition of human arginase activity: kinetic characterization and biological relevance

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          Abstract

          The inhibition of arginase, resulting in higher arginine (ARG) availability for nitric oxide synthesis, may account for the putative protective effect of homoarginine (HOMOARG) against atherosclerosis and cardiovascular disease. However, uncertainty exists regarding the significance of HOMOARG-induced arginase inhibition in vivo. A novel UPLC-MS method, measuring the conversion of ARG to ornithine (ORN), was developed to determine arginase 1 and arginase 2 inhibition by HOMOARG, lysine (LYS), proline (PRO), agmatine (AG), asymmetric dimethylarginine (ADMA), symmetric dimethylarginine (SDMA), and NG-Monomethyl-L-arginine (L-NMMA). Plasma HOMOARG, ARG and ORN concentrations were further measured in 50 healthy older adults >65 years (27 males and 23 females). HOMOARG inhibited arginase 1 with IC 50 and K i values of 8.14 ± 0.52 mM and 6.1 ± 0.50 mM, and arginase 2 with IC 50 and K i values of 2.52 ± 0.01 mM and 1.73 ± 0.10 mM, respectively. Both arginase isoforms retained 90% activity vs. control when physiological HOMOARG concentrations (1–10 µM) were used. In partial correlation analysis, plasma HOMOARG was not associated with ARG (P = 0.38) or ARG/ORN ratio (P = 0.73) in older adults. Our results suggest that arginase inhibition is unlikely to play a significant role in the reported cardio-protective effects of HOMOARG.

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          Dysregulated arginine metabolism, hemolysis-associated pulmonary hypertension, and mortality in sickle cell disease.

          Sickle cell disease is characterized by a state of nitric oxide resistance and limited bioavailability of l-arginine, the substrate for nitric oxide synthesis. We hypothesized that increased arginase activity and dysregulated arginine metabolism contribute to endothelial dysfunction, pulmonary hypertension, and patient outcomes. To explore the role of arginase in sickle cell disease pathogenesis, pulmonary hypertension, and mortality. Plasma amino acid levels, plasma and erythrocyte arginase activities, and pulmonary hypertension status as measured by Doppler echocardiogram were prospectively obtained in outpatients with sickle cell disease. Patients were followed up for survival up to 49 months. Urban tertiary care center and community clinics in the United States between February 2001 and March 2005. Two hundred twenty-eight patients with sickle cell disease, aged 18 to 74 years, and 36 control participants. Plasma amino acid levels, plasma and erythrocyte arginase activities, diagnosis of pulmonary hypertension, and mortality. Plasma arginase activity was significantly elevated in patients with sickle cell disease, with highest activity found in patients with secondary pulmonary hypertension. Arginase activity correlated with the arginine-ornithine ratio, and lower ratios were associated with greater severity of pulmonary hypertension and with mortality in this population (risk ratio, 2.5; 95% confidence interval [CI], 1.2-5.2; P = .006). Global arginine bioavailability, characterized by the ratio of arginine to ornithine plus citrulline, was also strongly associated with mortality (risk ratio, 3.6; 95% CI, 1.5-8.3; P<.001). Increased plasma arginase activity was correlated with increased intravascular hemolytic rate and, to a lesser extent, with markers of inflammation and soluble adhesion molecule levels. These data support a novel mechanism of disease in which hemolysis contributes to reduced nitric oxide bioavailability and endothelial dysfunction via release of erythrocyte arginase, which limits arginine bioavailability, and release of erythrocyte hemoglobin, which scavenges nitric oxide. The ratios of arginine to ornithine and arginine to ornithine plus citrulline are independently associated with pulmonary hypertension and increased mortality in patients with sickle cell disease.
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              Global characterization of in vivo enzyme catalytic rates and their correspondence to in vitro kcat measurements.

              Turnover numbers, also known as kcat values, are fundamental properties of enzymes. However, kcat data are scarce and measured in vitro, thus may not faithfully represent the in vivo situation. A basic question that awaits elucidation is: how representative are kcat values for the maximal catalytic rates of enzymes in vivo? Here, we harness omics data to calculate kmax(vivo), the observed maximal catalytic rate of an enzyme inside cells. Comparison with kcat values from Escherichia coli, yields a correlation ofr(2)= 0.62 in log scale (p < 10(-10)), with a root mean square difference of 0.54 (3.5-fold in linear scale), indicating that in vivo and in vitro maximal rates generally concur. By accounting for the degree of saturation of enzymes and the backward flux dictated by thermodynamics, we further refine the correspondence between kmax(vivo) and kcat values. The approach we present here characterizes the quantitative relationship between enzymatic catalysis in vitro and in vivo and offers a high-throughput method for extracting enzyme kinetic constants from omics data.
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                Author and article information

                Contributors
                arduino.mangoni@flinders.edu.au
                Journal
                Sci Rep
                Sci Rep
                Scientific Reports
                Nature Publishing Group UK (London )
                2045-2322
                27 February 2018
                27 February 2018
                2018
                : 8
                : 3697
                Affiliations
                [1 ]Department of Clinical Pharmacology, College of Medicine and Public Health, Flinders University and Flinders Medical Centre, Adelaide, Australia
                [2 ]ISNI 0000 0001 2153 2936, GRID grid.48815.30, Faculty of Health and Life Sciences, , De Montfort University, ; Leicester, United Kingdom
                [3 ]ISNI 0000 0001 2193 314X, GRID grid.8756.c, Institute of Cardiovascular and Medical Sciences, , University of Glasgow, ; Glasgow, United Kingdom
                [4 ]ISNI 0000 0004 0367 2697, GRID grid.1014.4, Flinders Centre for Innovation in Cancer, College of Medicine and Public Health, , Flinders University, ; Adelaide, Australia
                Author information
                http://orcid.org/0000-0001-8969-9636
                http://orcid.org/0000-0002-3714-9381
                Article
                22099
                10.1038/s41598-018-22099-x
                5829263
                29487337
                82d80563-6a30-4411-a159-75d8ff66b961
                © The Author(s) 2018

                Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/.

                History
                : 21 September 2017
                : 16 February 2018
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