An experiment of nature: genetic L-arginine deficiency and NO insufficiency

The Mechanisms of L-Arginine Metabolism Disorder in Endothelial Cells

L-arginine is a key metabolite for nitric oxide production by endothelial cells, as well as signaling molecule of the mTOR signaling pathway. mTOR supports endothelial cells homeostasis and regulates activity of L-arginine-metabolizing enzymes, endothelial nitric oxide synthase, and arginase II. Disruption of the L-arginine metabolism in endothelial cells leads to the development of endothelial dysfunction. Conflicting results of the use of L-arginine supplement to improve endothelial function reveals a controversial role of the amino acid in the endothelial cell biology. The review is aimed at analysis of the current data on the role of L-arginine metabolism in the development of endothelial dysfunction.

The Association Between Concentrations of Arginine, Ornithine, Citrulline and Major Depressive Disorder: A Meta-Analysis

Alterations in the peripheral (e.g., serum, plasma, platelet) concentrations of arginine and its related catabolic products (i.e., ornithine, citrulline) in the urea and nitric oxide cycles have been reported to be associated with major depressive disorder (MDD). The meta-analysis herein aimed to explore the association between the concentration of peripheral arginine, its catabolic products and MDD, as well as to discuss the possible role of arginine catabolism in the onset and progression of MDD. PubMed, EMBASE, PsycINFO and Web of Science were searched from inception to June 2020. The protocol for the meta-analysis herein has been registered at the Open Science Framework [https://doi.org/10.17605/osf.io/7fn59]. In total, 745 (47.5%) subjects with MDD and 823 (52.5%) healthy controls (HCs) from 13 articles with 16 studies were included. Fifteen of the included studies assessed concentrations of peripheral arginine, eight assessed concentrations of ornithine, and six assessed concentrations of citrulline. Results indicated that: (1) the concentrations of arginine, ornithine, and citrulline were not significantly different between individuals with MDD and HCs when serum, plasma and platelet are analyzed together, (2) in the subgroups of serum samples, the concentrations of arginine were lower in individuals with MDD than HCs, and (3) concurrent administration of psychotropic medications may be a confounding variable affecting the concentrations of arginine, ornithine, and citrulline. Our findings herein do not support the hypothesis that arginine catabolism between individuals with MDD and HCs are significantly different. The medication status and sample types should be considered as a key future research avenue for assessing arginine catabolism in MDD.

Atherosclerosis Linked to Aberrant Amino Acid Metabolism and Immunosuppressive Amino Acid Catabolizing Enzymes

Cardiovascular disease is the leading global health concern and responsible for more deaths worldwide than any other type of disorder. Atherosclerosis is a chronic inflammatory disease in the arterial wall, which underpins several types of cardiovascular disease. It has emerged that a strong relationship exists between alterations in amino acid (AA) metabolism and the development of atherosclerosis. Recent studies have reported positive correlations between levels of branched-chain amino acids (BCAAs) such as leucine, valine, and isoleucine in plasma and the occurrence of metabolic disturbances. Elevated serum levels of BCAAs indicate a high cardiometabolic risk. Thus, BCAAs may also impact atherosclerosis prevention and offer a novel therapeutic strategy for specific individuals at risk of coronary events. The metabolism of AAs, such as L-arginine, homoarginine, and L-tryptophan, is recognized as a critical regulator of vascular homeostasis. Dietary intake of homoarginine, taurine, and glycine can improve atherosclerosis by endothelium remodeling. Available data also suggest that the regulation of AA metabolism by indoleamine 2,3-dioxygenase (IDO) and arginases 1 and 2 are mediated through various immunological signals and that immunosuppressive AA metabolizing enzymes are promising therapeutic targets against atherosclerosis. Further clinical studies and basic studies that make use of animal models are required. Here we review recent data examining links between AA metabolism and the development of atherosclerosis.

Role of Arginase 2 as a potential pharmacological target for the creation of new drugs to correct cardiovascular diseases

Introduction: The review provides relevant information about arginase 2, the role of this enzyme in the formation of endothelial dysfunction and, as a consequence, the development of cardiovascular diseases.

History of the discovery of arginase and its functions: The discovery of arginase took place long before its active study as a substance that affects the formation of endothelial dysfunction.

Role of arginase 2 in the development of a number of cardiovascular diseases: The role of NO synthase and arginase 2 in the formation of oxidative stress is determined. The pathophysiological mechanisms of the development of a number of cardiovascular diseases, such as coronary heart disease, atherosclerosis, and aortic aneurysm, are described. The modern possibilities of treatment of endothelial dysfunction in the pathology of the cardiovascular system and the possibility of creation of new drugs are considered. An increase in the activity of arginase 2 was proven to occur in the case of the development of coronary heart disease (CHD), hypertension, type II diabetes mellitus, hypercholesterolemia, as well as in the process of aging. According to the WHO, coronary heart disease and apoplectic attack have topped the list of causes of death worldwide over the past 15 years.

Arginase 2 as a potential pharmacological target: The purpose of this literature review is to determine the possibilities of use of arginase 2 as a new target for the pharmacological correction of cardiovascular diseases.

Coagulation Disturbances in Patients with Argininemia

BACKGROUND

Argininemia is an autosomal recessive urea cycle disorder (UCD). Unlike other UCD, hyperammonemia is rarely seen. Patients usually present in childhood with neurological symptoms. Uncommon presentations like neonatal cholestasis or cirrhosis have been reported. Although transient elevations of liver transaminases and coagulopathy have been reported during hyperammonemia episodes, a permanent coagulopathy has never been reported.

METHODS

In this retrospective study, coagulation disturbances are examined in 6 argininemia patients. All of the patients were routinely followed up for hepatic involvement due to argininemia. Laboratory results, including liver transaminases, albumin, prothrombin time (PT), international normalized ratio (INR), activated partial thromboplastin time (aPTT), and clotting factor levels, were assessed in all of the patients.

RESULTS

All of the patients had a prolonged PT and an increased INR, while none of the patients had a prolonged aPTT. Five patients had slightly elevated liver transaminases. A liver biopsy was performed in 1 patient but neither cirrhosis nor cholestasis was documented. Five of the 6 patients had low factor VII and factor IX levels, while other clotting factors were normal.

CONCLUSIONS

Argininemia patients should be investigated for coagulation disorders even if there is no apparent liver dysfunction or major bleeding symptoms.

Threshold levels of extracellular l-arginine that trigger NOS-mediated ROS/RNS production in cardiac ventricular myocytes

l-Arginine (L-Arg) is the substrate for nitric oxide synthase (NOS) to produce nitric oxide (NO), a signaling molecule that is key in cardiovascular physiology and pathology. In cardiac myocytes, L-Arg is incorporated from the circulation through the functioning of system-y⁺ cationic amino acid transporters. Depletion of L-Arg leads to NOS uncoupling, with O₂ rather than L-Arg as the terminal electron acceptor, resulting in superoxide formation. The reactive oxygen species (ROS) superoxide (O₂˙^-), combined with NO, may lead to the production of the reactive nitrogen species (RNS) peroxynitrite (ONOO^-), which is recognized as a major contributor to myocardial depression. In this study we aimed to determine the levels of external L-Arg that trigger ROS/RNS production in cardiac myocytes. To this goal, we used a two-step experimental design in which acutely isolated cardiomyocytes were loaded with the dye coelenterazine that greatly increases its fluorescence quantum yield in the presence of ONOO^- and O₂˙^- Cells were then exposed to different concentrations of extracellular L-Arg and changes in fluorescence were followed spectrofluorometrically. It was found that below a threshold value of ~100 µM, decreasing concentrations of L-Arg progressively increased ONOO^-/ O₂˙^--induced fluorescence, an effect that was not mimicked by d-arginine or l-lysine and was fully blocked by the NOS inhibitor l-NAME. These results can be explained by NOS aberrant enzymatic activity and provide an estimate for the levels of circulating L-Arg below which ROS/RNS-mediated harmful effects arise in cardiac muscle.

Environmental origins of hypertension: phylogeny, ontogeny and epigenetics

Hypertension and renal parenchymal disease are intricately linked. Primary renal parenchymal disease can impact on sodium and volume regulation and lead to hypertension, while arterial hypertension can induce renal parenchymal injury and precipitate renal dysfunction. The examination for clues to the environmental origins of renal disease and hypertension necessitates an approach that integrates epidemiology, clinical medicine, developmental biology, environmental science and epigenetics, such that the manner in which genes and the environment interact can be better understood to pave the way for innovative management paradigms with regards to prevention, diagnosis and treatment. This review summarizes the extant literature and provides cogent arguments for the need to evaluate chronic adult onset disease models such as hypertension and renal disease from the modern perspective that takes into account prenatal exposures, the intrauterine environment and development, postnatal growth and transgenerational epigenetic modifications with their attendant future disease risk from the individual to the population level.

Arginase deficiency with new phenotype and a novel mutation: contemporary summary

In areas without expanded newborn screening, instead of presenting neonatally, patients with arginase deficiency typically present with spastic paraplegia in early childhood. Diagnosis of this rare neurometabolic disease poses the first challenge because it is often misdiagnosed as cerebral palsy during initial stages. We describe arginase deficiency in a 20-year-old woman with spastic paraplegia, progressive dystonia, dementia, peripheral neuropathy, epilepsy, liver cirrhosis, and non-B/non-C hepatocellular carcinoma. A novel homozygous mutation NM_000045.2 (ARG1):c.673del (p.Arg225GlyfsX5) was detected. We suggest that all children presenting with progressive neurodegeneration or spastic paraplegia in the absence of risk factors for cerebral palsy should be screened for inborn errors of metabolism, including arginase deficiency. For monitoring urea cycle defects, noninvasive imaging screening for liver fibrosis and hepatocellular carcinoma can help ensure early detection, with potential treatment implications.

Protective effect of Melothria maderaspatana leaf fraction on electrolytes, catecholamines, endothelial nitric oxide synthase and endothelin-1 peptide in uninephrectomized deoxycorticosterone acetate-salt hypertensive rats

This study was designed to investigate the protective effect of ethyl acetate fraction of Melothria maderaspatana (EAFM) leaf on electrolytes, catecholamines, endothelial nitric oxide synthase (eNOS) and endothelin-1 (ET-1) peptide in uninephrectomized deoxycorticosterone acetate (DOCA)-salt hypertensive rats. Administration of DOCA-salt significantly increased the systolic and diastolic blood pressure and treatment with EAFM significantly lowered the blood pressure. In DOCA-salt rats, the levels of sodium and chloride increased significantly while potassium level decreased and administration of EAFM brought these parameters to normality. The levels of epinephrine and norepinephrine increased significantly in DOCA-salt rats and administration of EAFM significantly decreased these parameters to normality. DOCA-salt hypertensive rats exhibited significantly decreased L: -arginine and nitrite + nitrate levels and administration of EAFM brought these parameters to normality. DOA-salt hypertensive rats showed down-regulation of eNOS and up-regulation of ET-1 protein expressions in heart and kidney, and treatment with EAFM prevented down-regulation of eNOS and significantly down-regulated the ET-1 protein expressions. In conclusion, EAFM provides good blood pressure control by enhancing potassium and decreasing sodium levels, decreasing levels of epinephrine and norepinephrine, and preventing down-regulation of eNOS and significantly down-regulating ET-1 protein expression.

Vascular Nitric Oxide: Formation and Function

Nitric oxide (NO) is a structurally simple, highly versatile molecule that was originally discovered over 30 years ago as an endothelium-derived relaxing factor. In addition to its vasorelaxing effects, NO is now recognized as a key determinant of vascular health, exerting antiplatelet, antithrombotic, and anti-inflammatory properties within the vasculature. This short-lived molecule exerts its inhibitory effect on vascular smooth muscle cells and platelets largely through cyclic guanosine monophosphate-dependent mechanisms, resulting in a multitude of molecular effects by which platelet activation and aggregation are prevented. The biosynthesis of NO occurs via the catalytic activity of NO synthase, an oxidoreductase found in many cell types. NO insufficiency can be attributed to limited substrate/cofactor availability as well as interactions with reactive oxygen species. Impaired NO bioavailability represents the central feature of endothelial dysfunction, a common abnormality found in many vascular diseases. In this review, we present an overview of NO synthesis and biochemistry, discuss the mechanisms of action of NO in regulating platelet and endothelial function, and review the effects of vascular disease states on NO bioavailability.

Arginase: a critical regulator of nitric oxide synthesis and vascular function

1. Arginase is the focal enzyme of the urea cycle hydrolysing L-arginine to urea and L-ornithine. Emerging studies have identified arginase in the vasculature and have implicated this enzyme in the regulation of nitric oxide (NO) synthesis and the development of vascular disease. 2. Arginase inhibits the production of NO via several potential mechanisms, including competition with NO synthase (NOS) for the substrate L-arginine, uncoupling of NOS resulting in the generation of the NO scavenger, superoxide and peroxynitrite, repression of the translation and stability of inducible NOS protein, inhibition of inducible NOS activity via the generation of urea and by sensitization of NOS to its endogenous inhibitor asymmetric dimethyl-L-arginine. 3. Upregulation of arginase inhibits endothelial NOS-mediated NO synthesis and may contribute to endothelial dysfunction in hypertension, ageing, ischaemia-reperfusion and diabetes. 4. Arginase also redirects the metabolism of L-arginine to L-ornithine and the formation of polyamines and L-proline, which are essential for smooth muscle cell growth and collagen synthesis. Therefore, the induction of arginase may also promote aberrant vessel wall remodelling and neointima formation. 5. Arginase represents a promising novel therapeutic target that may reverse endothelial and smooth muscle cell dysfunction and prevent vascular disease.

Nitric oxide insufficiency and atherothrombosis

Nitric oxide (NO) is a structurally simple compound that participates in a wide range of biological reactions to maintain normal endothelial function and an antithrombotic intravascular milieu. Among its principal effects are the regulation of vascular tone, vascular smooth muscle cell proliferation, endothelial-leukocyte interactions, and the antiplatelet effects of the endothelium. Impaired NO bioavailability represents the central feature of endothelial dysfunction, the earliest stage in the atherosclerotic process, and also contributes to the pathogenesis of acute vascular syndromes by predisposing to intravascular thrombosis. The causes of NO insufficiency can be grouped into two fundamental mechanisms: inadequate synthesis and increased inactivation of NO. Polymorphisms in the endothelial NO synthase gene and decreased substrate or cofactor availability for this enzyme are the main mechanisms that compromise the synthesis of NO. Inactivation of NO occurs mainly through its interaction with reactive oxygen species and can be favored by a deficiency of antioxidant enzymes such as glutathione peroxidase. In this review, we present an overview of NO synthesis and biological chemistry, discuss the mechanisms of action of NO in regulating endothelial and platelet function, and explore the causes of NO insufficiency, as well as the evidence linking these causes to the pathophysiology of endothelial dysfunction and atherothrombosis.

Recurrent fatal pulmonary alveolar proteinosis after heart-lung transplantation in a child with lysinuric protein intolerance

We present a case of recurrent pulmonary alveolar proteinosis after heart-lung transplantation in a child with lysinuric protein intolerance. The recurrence of the pulmonary disease provides further insight regarding the possible pathogenesis of pulmonary alveolar proteinosis and therapeutic options for this complication.

Regulation of amino acid and glucose transporters in endothelial and smooth muscle cells

While transport processes for amino acids and glucose have long been known to be expressed in the luminal and abluminal membranes of the endothelium comprising the blood-brain and blood-retinal barriers, it is only within the last decades that endothelial and smooth muscle cells derived from peripheral vascular beds have been recognized to rapidly transport and metabolize these nutrients. This review focuses principally on the mechanisms regulating amino acid and glucose transporters in vascular endothelial cells, although we also summarize recent advances in the understanding of the mechanisms controlling membrane transport activity and expression in vascular smooth muscle cells. We compare the specificity, ionic dependence, and kinetic properties of amino acid and glucose transport systems identified in endothelial cells derived from cerebral, retinal, and peripheral vascular beds and review the regulation of transport by vasoactive agonists, nitric oxide (NO), substrate deprivation, hypoxia, hyperglycemia, diabetes, insulin, steroid hormones, and development. In view of the importance of NO as a modulator of vascular tone under basal conditions and in disease and chronic inflammation, we critically review the evidence that transport of L-arginine and glucose in endothelial and smooth muscle cells is modulated by bacterial endotoxin, proinflammatory cytokines, and atherogenic lipids. The recent colocalization of the cationic amino acid transporter CAT-1 (system y(+)), nitric oxide synthase (eNOS), and caveolin-1 in endothelial plasmalemmal caveolae provides a novel mechanism for the regulation of NO production by L-arginine delivery and circulating hormones such insulin and 17beta-estradiol.