Cysteine-iron promotes arginase activity by driving the Fenton reaction

Endothelial dysfunction in Sickle Cell Disease: Strategies for the treatment

Sickle Cell Anemia(SCA), is an inherited hemoglobinopathy characterized by the presence of an abnormal hemoglobin (HbS), being the most prevalent sickle cell disease (SCD). SCA is characterized by vascular endothelial dysfunction, which contributes significantly to various clinical conditions, including but not limited to pulmonary hypertension, priapism, cutaneous leg ulceration, and stroke. The pathophysiology of endothelial dysfunction (ED) in SCA is a multifaceted process involving a chronic inflammatory and hypercoagulable state. Key factors include hemolysis-associated elements like reduced arginine and nitric oxide (NO) availability, elevated levels of vascular adhesion molecules, the uncoupling effect of NO synthase, heightened arginase activity, an environment characterized by oxidative stress with the production of reactive oxygen and nitrogen species, and occurrences of ischemia-reperfusion injury, along with apolipoprotein A-1 depletion. The urgency for novel interventions addressing ED is evident. Presently, there is a focus on investigating small molecules that disrupt the arginine-nitric oxide pathway, exhibiting anti-inflammatory and antioxidant properties while diminishing levels of cellular and vascular adhesion molecules. In this mini-review article, we delve into the progress made in strategies for treating ED in SCD with the aim of cultivating insights for drug design.

Downregulation of eNOS and preserved endothelial function in endothelial-specific arginase 1-deficient mice

Arginase 1 (Arg1) is a ubiquitous enzyme belonging to the urea cycle that catalyzes the conversion of l-arginine into l-ornithine and urea. In endothelial cells (ECs), Arg1 was proposed to limit the availability of l-arginine for the endothelial nitric oxide synthase (eNOS) and thereby reduce nitric oxide (NO) production, thus promoting endothelial dysfunction and vascular disease. The role of EC Arg1 under homeostatic conditions is in vivo less understood. The aim of this study was to investigate the role of EC Arg1 on the regulation of eNOS, vascular tone, and endothelial function under normal homeostatic conditions in vivo and ex vivo. By using a tamoxifen-inducible EC-specific gene-targeting approach, we generated EC Arg1 KO mice. Efficiency and specificity of the gene targeting strategy was demonstrated by DNA recombination and loss of Arg1 expression measured after tamoxifen treatment in EC only. In EC Arg1 KO mice we found a significant decrease in Arg1 expression in heart and lung ECs and in the aorta, however, vascular enzymatic activity was preserved likely due to the presence of high levels of Arg1 in smooth muscle cells. Moreover, we found a downregulation of eNOS expression in the aorta, and a fully preserved systemic l-arginine and NO bioavailability, as demonstrated by the levels of l-arginine, l-ornithine, and l-citrulline as well as nitrite, nitrate, and nitroso-species. Lung and liver tissues from EC Arg1 KO mice showed respectively increase or decrease in nitrosyl-heme species, indicating that the lack of endothelial Arg1 affects NO bioavailability in these organs. In addition, EC Arg1 KO mice showed fully preserved acetylcholine-mediated vascular relaxation in both conductance and resistant vessels but increased phenylephrine-induced vasoconstriction. Systolic, diastolic, and mean arterial pressure and cardiac performance in EC Arg1 KO mice were not different from the wild-type littermate controls. In conclusion, under normal homeostatic conditions, lack of EC Arg1 expression is associated with a down-regulation of eNOS expression but a preserved NO bioavailability and vascular endothelial function. These results suggest that a cross-talk exists between Arg1 and eNOS to control NO production in ECs, which depends on both L-Arg availability and EC Arg1-dependent eNOS expression.

Arginine and Arginases Modulate Metabolism, Tumor Microenvironment and Prostate Cancer Progression

Arginine availability and activation of arginine-related pathways at cancer sites have profound effects on the tumor microenvironment, far beyond their well-known role in the hepatic urea cycle. Arginine metabolism impacts not only malignant cells but also the surrounding immune cells behavior, modulating growth, survival, and immunosurveillance mechanisms, either through an arginase-mediated effect on polyamines and proline synthesis, or by the arginine/nitric oxide pathway in tumor cells, antitumor T-cells, myeloid-derived suppressor cells, and macrophages. This review presents evidence concerning the impact of arginine metabolism and arginase activity in the prostate cancer microenvironment, highlighting the recent advances in immunotherapy, which might be relevant for prostate cancer. Even though further research is required, arginine deprivation may represent a novel antimetabolite strategy for the treatment of arginine-dependent prostate cancer.

Cyst(e)ine fortification in low crude protein diet improves growth performance of broilers by modulating serum metabolite profile

This study was aimed to explore the metabolomical mechanisms for the potentially ameliorative effect of cyst(e)ine (Cys) fortification on growth performance of broilers fed low crude protein (CP) diet. A total of 432 1-d-old broilers were randomly divided into 6 groups, each of which received one of the following diets: normal-CP diet (positive control, PC), low-CP diet (negative control, NC), NC diet fortified with 0.05%, 0.1%, 0.15% or 0.2% of Cys. Samples were collected on d 42. Results showed that increasing Cys fortification quadratically elevated (P < 0.05) the accumulative growth performance and leg muscle yield of broilers fed NC diet, with 0.1% being the optimal dose. Thus, samples from PC, NC and NC plus 0.1% Cys (NCC) groups were selected for further analysis. Both dietary CP reduction and fortification of 0.1% Cys in NC diet caused complex changes (P < 0.05) in serum amino acids and some other metabolites primarily involved in lipid metabolism. Multiple lipogenesis-related pathways were regulated (P < 0.05) following Cys fortification in NC diet, which could at least partially interpret the benefit of Cys fortification in NC diet on broiler performance. In conclusion, fortifying low-CP diet with 0.1% Cys promoted the growth performance of broilers probably through modulating serum metabolite profile.

African-centric TP53 variant increases iron accumulation and bacterial pathogenesis but improves response to malaria toxin

A variant at amino acid 47 in human TP53 exists predominantly in individuals of African descent. P47S human and mouse cells show increased cancer risk due to defective ferroptosis. Here, we show that this ferroptotic defect causes iron accumulation in P47S macrophages. This high iron content alters macrophage cytokine profiles, leads to higher arginase level and activity, and decreased nitric oxide synthase activity. This leads to more productive intracellular bacterial infections but is protective against malarial toxin hemozoin. Proteomics of macrophages reveal decreased liver X receptor (LXR) activation, inflammation and antibacterial defense in P47S macrophages. Both iron chelators and LXR agonists improve the response of P47S mice to bacterial infection. African Americans with elevated saturated transferrin and serum ferritin show higher prevalence of the P47S variant (OR = 1.68 (95%CI 1.07–2.65) p = 0.023), suggestive of its role in iron accumulation in humans. This altered macrophage phenotype may confer an advantage in malaria-endemic sub-Saharan Africa.

A polymorphism in human TP53 (P47S) that predominantly exists in individuals of African descent affects ferroptosis. Here, the authors show that this results in iron accumulation in macrophages leading to more productive infection by intracellular bacteria but improved anti-inflammatory response to the malarial toxin hemozoin.

Sources of Vascular Nitric Oxide and Reactive Oxygen Species and Their Regulation

Nitric oxide (NO) is a small free radical with critical signaling roles in physiology and pathophysiology. The generation of sufficient NO levels to regulate the resistance of the blood vessels and hence the maintenance of adequate blood flow is critical to the healthy performance of the vasculature. A novel paradigm indicates that classical NO synthesis by dedicated NO synthases is supplemented by nitrite reduction pathways under hypoxia. At the same time, reactive oxygen species (ROS), which include superoxide and hydrogen peroxide, are produced in the vascular system for signaling purposes, as effectors of the immune response, or as byproducts of cellular metabolism. NO and ROS can be generated by distinct enzymes or by the same enzyme through alternate reduction and oxidation processes. The latter oxidoreductase systems include NO synthases, molybdopterin enzymes, and hemoglobins, which can form superoxide by reduction of molecular oxygen or NO by reduction of inorganic nitrite. Enzymatic uncoupling, changes in oxygen tension, and the concentration of coenzymes and reductants can modulate the NO/ROS production from these oxidoreductases and determine the redox balance in health and disease. The dysregulation of the mechanisms involved in the generation of NO and ROS is an important cause of cardiovascular disease and target for therapy. In this review we will present the biology of NO and ROS in the cardiovascular system, with special emphasis on their routes of formation and regulation, as well as the therapeutic challenges and opportunities for the management of NO and ROS in cardiovascular disease.

Age-Related Changes in Sulfur Amino Acid Metabolism in Male C57BL/6 Mice

Alterations in sulfur amino acid metabolism are associated with an increased risk of a number of common late-life diseases, which raises the possibility that metabolism of sulfur amino acids may change with age. The present study was conducted to understand the age-related changes in hepatic metabolism of sulfur amino acids in 2-, 6-, 18- and 30-month-old male C57BL/6 mice. For this purpose, metabolite profiling of sulfur amino acids from methionine to taurine or glutathione (GSH) was performed. The levels of sulfur amino acids and their metabolites were not significantly different among 2-, 6- and 18-month-old mice, except for plasma GSH and hepatic homocysteine. Plasma total GSH and hepatic total homocysteine levels were significantly higher in 2-month-old mice than those in the other age groups. In contrast, 30-month-old mice exhibited increased hepatic methionine and cysteine, compared with all other groups, but decreased hepatic S-adenosylmethionine (SAM), S-adenosylhomocysteine and homocysteine, relative to 2-month-old mice. No differences in hepatic reduced GSH, GSH disulfide, or taurine were observed. The hepatic changes in homocysteine and cysteine may be attributed to upregulation of cystathionine β-synthase and down-regulation of γ-glutamylcysteine ligase in the aged mice. The elevation of hepatic cysteine levels may be involved in the maintenance of hepatic GSH levels. The opposite changes of methionine and SAM suggest that the regulatory role of SAM in hepatic sulfur amino acid metabolism may be impaired in 30-month-old mice.

Copper oxide nanoparticles recruit macrophages and modulate nitric oxide, proinflammatory cytokines and PGE2 production through arginase activation

AIM

In the present study, we examine the effects of copper oxide nanoparticles (CuNP) on macrophage immune response and the signaling pathways involved.

MATERIALS & METHODS

A peritonitis model was used to determine in vivo immune cells recruitment, while primary macrophages were used as an in vitro model for the cellular and molecular analysis.

RESULTS

In vivo, CuNP induce significant macrophages recruitment to the site of injection. In vitro, in LPS-stimulated primary macrophages, the co-treatment with CuNP inhibited the production of NO in a dose-dependent manner. The mechanism underlying NO and proinflammatory cytokines inhibition was associated with an increased arginase activity. Macrophage stimulation with CuNP did not provoke any cytokine secretion; however, arginase inhibition promoted TNFα and MIP-1β production. In addition, CuNP induced the expression of COX-2 and the production of PGE2 through arginase activation.

CONCLUSION

Our results demonstrate that CuNP activate arginase and suppress macrophage innate immune response.

A proteomics analysis to evaluate cytotoxicity in NRK-52E cells caused by unmodified Nano-Fe₃O₄

We synthesized unmodified Fe₃O₄ nanoparticles (NPs) with particles size from 10 nm to 100 nm. We cultured NRK-52E cell lines (rat, kidney) and treated with Fe₃O₄ NPs to investigate and evaluate the cytotoxicity of NPs for NRK-52E cells. Through global proteomics analysis using dimethyl labeling techniques and liquid phase chromatography coupled with a tandem mass spectrometer (LC-MS/MS), we characterized 435 proteins including the programmed cell death related proteins, ras-related proteins, glutathione related proteins, and the chaperone proteins such as heat shock proteins, serpin H1, protein disulfide-isomerase A4, endoplasmin, and endoplasmic reticulum resident proteins. From the statistical data of identified proteins, we believed that NPs treatment causes cell death and promotes expression of ras-related proteins. In order to avoid apoptosis, NRK-52E cell lines induce a series of protective effects such as glutathione related proteins to reduce reactive oxygen species (ROS), and chaperone proteins to recycle damaged proteins. We suggested that, in the indigenous cellular environment, Fe₃O₄ NPs treatment induced an antagonistic effect for cell lines to go to which avoids apoptosis.

Vasomotor regulation of coronary microcirculation by oxidative stress: role of arginase

Overproduction of reactive oxygen species, i.e., oxidative stress, is associated with the activation of redox signaling pathways linking to inflammatory insults and cardiovascular diseases by impairing endothelial function and consequently blood flow dysregulation due to microvascular dysfunction. This review focuses on the regulation of vasomotor function in the coronary microcirculation by endothelial nitric oxide (NO) during oxidative stress and inflammation related to the activation of L-arginine consuming enzyme arginase. Superoxide produced in the vascular wall compromises vasomotor function by not only scavenging endothelium-derived NO but also inhibiting prostacyclin synthesis due to formation of peroxynitrite. The upregulation of arginase contributes to the deficiency of endothelial NO and microvascular dysfunction in various vascular diseases by initiating or following oxidative stress and inflammation. Hydrogen peroxide, a diffusible and stable oxidizing agent, exerts vasodilator function and plays important roles in the physiological regulation of coronary blood flow. In occlusive coronary ischemia, the release of hydrogen peroxide from the microvasculature helps to restore vasomotor function of coronary collateral microvessels with exercise training. However, excessive production and prolonged exposure of microvessels to hydrogen peroxide impairs NO-mediated endothelial function by reducing L-arginine availability through hydroxyl radical-dependent upregulation of arginase. The redox signaling can be a double-edged sword in the microcirculation, which helps tissue survival in one way by improving vasomotor regulation and elicits oxidative stress and tissue injury in the other way by causing vascular dysfunction. The impact of vascular arginase on the development of vasomotor dysfunction associated with angiotensin II receptor activation, hypertension, ischemia-reperfusion, hypercholesterolemia, and inflammatory insults is discussed.

Regulation of endothelial nitric-oxide synthase (NOS) S-glutathionylation by neuronal NOS: evidence of a functional interaction between myocardial constitutive NOS isoforms

Myocardial constitutive No production depends on the activity of both endothelial and neuronal NOS (eNOS and nNOS, respectively). Stimulation of myocardial β(3)-adrenergic receptor (β(3)-AR) produces a negative inotropic effect that is dependent on eNOS. We evaluated whether nNOS also plays a role in β(3)-AR signaling and found that the β(3)-AR-mediated reduction in cell shortening and [Ca(2+)](i) transient amplitude was abolished both in eNOS(-/-) and nNOS(-/-) left ventricular (LV) myocytes and in wild type LV myocytes after nNOS inhibition with S-methyl-L-thiocitrulline. LV superoxide (O(2)(·-)) production was increased in nNOS(-/-) mice and reduced by L-N(ω)-nitroarginine methyl ester (L-NAME), indicating uncoupling of eNOS activity. eNOS S-glutathionylation and Ser-1177 phosphorylation were significantly increased in nNOS(-/-) myocytes, whereas myocardial tetrahydrobiopterin, eNOS Thr-495 phosphorylation, and arginase activity did not differ between genotypes. Although inhibitors of xanthine oxidoreductase (XOR) or NOX2 NADPH oxidase caused a similar reduction in myocardial O(2)(·-), only XOR inhibition reduced eNOS S-glutathionylation and Ser-1177 phosphorylation and restored both eNOS coupled activity and the negative inotropic and [Ca(2+)](i) transient response to β(3)-AR stimulation in nNOS(-/-) mice. In summary, our data show that increased O(2)(·-) production by XOR selectively uncouples eNOS activity and abolishes the negative inotropic effect of β(3)-AR stimulation in nNOS(-/-) myocytes. These findings provide unequivocal evidence of a functional interaction between the myocardial constitutive NOS isoforms and indicate that aspects of the myocardial phenotype of nNOS(-/-) mice result from disruption of eNOS signaling.

Oxidant-mediated modification of the cellular thiols is sufficient for arginase activation in cultured cells

Increased arginase activity in the vasculature has been implicated in the regulation of nitric oxide (NO) homeostasis, leading to the development of vascular disease and the promotion of tumor cell growth. Recently, we showed that cysteine, in the presence of iron, promotes arginase activity by driving the Fenton reaction. In the present report, we showed that induction of oxidative stress in erythroleukemic cells with the thiol-specific oxidant, diamide, led to an increase in arginase activity by 42% (P = 0.02; vs. control). By using specific antibodies, it was demonstrated that this increase correlated with an increase in arginase-1 levels in the cells and with corresponding decreases in glutathione and protein thiol levels. Treatment of cells with aurothiomalate (ATM), a protein thiol-complexing agent, diminished the activity of arginase and arginase-1 levels by 19.5 and 35.2%, respectively (vs. control) and significantly decreased both glutathione and protein thiol levels, further implicating the thiol redox system in the cellular activation of arginase. Furthermore, diamide significantly altered the kinetics of arginase, resulting in the doubling of its V(max) (vs. control). Our presented data demonstrate, for the first time that the intracellular arginase activation is may be enhanced in part, via a cellular thiol-mediated mechanism.

Sickle cell disease serum induces NADPH enzyme subunit expression and oxidant production in leukocytes

Oxidative stress plays a significant role in sickle cell disease (SCD), contributing to haemolysis, vaso-occlusive processes and endothelial dysfunction. To study the effects that the serum of SCD individuals has on the oxidative state of blood cells, sera were pooled from control individuals, steady-state SCD patients and SCD patients on hydroxyurea therapy (SCDHU), and their effects on markers of oxidative stress and damage in neutrophils isolated from healthy individuals observed. Incubation of control neutrophils, but not platelets nor red blood cells, with SCD serum (10% v/v; 2 hours) significantly augmented their production of reactive oxygen species (ROS). Increased ROS production in SCD serum-incubated neutrophils was associated with increased superoxide anion generation, apoptosis and increased nicotinamide adenine dinucleotide phosphate oxidase subunit expression. Although serum from SCDHU individuals also induced ROS generation in neutrophils, its oxidative capacity appeared to be lower. Results suggest that factors in the serum of SCD individuals contribute to ROS generation and oxidative damage in leukocytes.

Targeting stem cell niches and trafficking for cardiovascular therapy

Regenerative cardiovascular medicine is the frontline of 21st-century health care. Cell therapy trials using bone marrow progenitor cells documented that the approach is feasible, safe and potentially beneficial in patients with ischemic disease. However, cardiovascular prevention and rehabilitation strategies should aim to conserve the pristine healing capacity of a healthy organism as well as reactivate it under disease conditions. This requires an increased understanding of stem cell microenvironment and trafficking mechanisms. Engagement and disengagement of stem cells of the osteoblastic niche is a dynamic process, finely tuned to allow low amounts of cells move out of the bone marrow and into the circulation on a regular basis. The balance is altered under stress situations, like tissue injury or ischemia, leading to remarkably increased cell egression. Individual populations of circulating progenitor cells could give rise to mature tissue cells (e.g. endothelial cells or cardiomyocytes), while the majority may differentiate to leukocytes, affecting the environment of homing sites in a paracrine way, e.g. promoting endothelial survival, proliferation and function, as well as attenuating or enhancing inflammation. This review focuses on the dynamics of the stem cell niche in healthy and disease conditions and on therapeutic means to direct stem cell/progenitor cell mobilization and recruitment into improved tissue repair.

The redox state of the glutathione/glutathione disulfide couple mediates intracellular arginase activation in HCT-116 colon cancer cells

BACKGROUND

Emerging studies have implicated arginase hyperactivity in the dysregulation of nitric oxide synthesis, which can lead to the development of vascular disease and the promotion of tumor cell growth. Recently, we showed that cysteine, in the presence of molecular iron, promotes arginase activity by driving the Fenton reaction. However, the exact mechanism of arginase activation in the cell induced by oxidative stress is unknown.

AIM

The aim of the present study is to examine whether intracellular arginase is regulated by the cellular redox status of glutathione.

METHOD

To test this hypothesis, the glutathione/glutathione disulfide redox couple was altered in colon cancer cells with the thiol-specific oxidant, diamide, or the glutathione inhibitor, buthionine-(S,R)-sulfoximine, and the activity of the arginase in the cells was assessed.

RESULTS

Treatment of cells with diamide, a thiol-specific oxidant, resulted in a dose-dependent decrease in the glutathione/glutathione disulfide ratio that was associated with the loss of glutathione and a coincident increase in arginase activity and arginase-1 levels in drug-treated cells compared with untreated cells. These results show that oxidation-induced redox changes of glutathione are of sufficient magnitude to control the activity of arginase in the cells. Thus, the physiologic modulation of the glutathione/glutathione disulfide ratio could prove to be a fundamental parameter for the control of arginase activity in pathological conditions of increased oxidative stress.

CONCLUSION

This is the first evidence supporting the ex vivo regulation of arginase activity through the redox modulation of intracellular glutathione. The potential adaptive and pathological consequences of glutathione redox regulation of arginase activity are discussed.

Dysregulation of L-arginine metabolism and bioavailability associated to free plasma heme

Severe Plasmodium falciparum malaria is associated with hypoargininemia, which contributes to impaired systemic and pulmonary nitric oxide (NO) production and endothelial dysfunction. Since intravascular hemolysis is an intrinsic feature of severe malaria, we investigated whether and by which mechanisms free heme [Fe(III)-protoporphyrin IX (FP)] might contribute to the dysregulation of l-arginine (l-Arg) metabolism and bioavailability. Carrier systems “y+” [or cationic amino acid transporter (CAT)] and “y+L” transport l-Arg into red blood cells (RBC), where it is hydrolyzed to ornithine and urea by arginase (isoform I) or converted to NO^· and citrulline by endothelial nitric oxide synthase (eNOS). Our results show a significant and dose-dependent impairment of l-Arg transport into RBC pretreated with FP, with a strong inhibition of the system carrier y+L. Despite the impaired l-Arg influx, higher amounts of l-Arg-derived urea are produced by RBC preexposed to FP caused by activation of RBC arginase I. This activation appeared not to be mediated by oxidative modifications of the enzyme. We conclude that l-Arg transport across RBC membrane is impaired and arginase-mediated l-Arg consumption enhanced by free heme. This could contribute to reduced NO production in severe malaria.

Hemoglobin disorders and endothelial cell interactions

Endothelial damage and inflammation make a significant contribution to the pathophysiology of sickle cell disease (SCD) and the beta-thalassemia syndromes. Endothelial dysfunction and ensuing vasculopathy are implicated in pulmonary hypertension in the hemoglobinopathies and endothelial activation and endothelial-blood cell adhesion, accompanied by inflammatory processes and oxidative stress, are imperative to the vaso-occlusive process in SCD. Herein, we discuss the role that the endothelium plays in all of these processes and the effect that genetic modifiers and hydroxyurea therapy may have upon endothelial interactions. Therapies targeting the endothelium and endothelial interactions may represent a promising approach for treating these diseases.

Recent advances in arginine metabolism: roles and regulation of the arginases

As arginine can serve as precursor to a wide range of compounds, including nitric oxide, creatine, urea, polyamines, proline, glutamate and agmatine, there is considerable interest in elucidating mechanisms underlying regulation of its metabolism. It is now becoming apparent that the two isoforms of arginase in mammals play key roles in regulation of most aspects of arginine metabolism in health and disease. In particular, work over the past several years has focused on the roles and regulation of the arginases in vascular disease, pulmonary disease, infectious disease, immune cell function and cancer. As most of these topics have been considered in recent review articles, this review will focus more closely on results of recent studies on expression of the arginases in endothelial and vascular smooth muscle cells, post-translational modulation of arginase activity and applications of arginase inhibitors in vivo.