Arginase inhibition improves coronary microvascular function and reduces infarct size following ischaemia-reperfusion in a rat model

Sodium valproate treatment reverses endothelial dysfunction in aorta from rabbits with acute myocardial infarction

Sodium valproate (VPA), a histone deacetylase (HDAC) inhibitor, could be a promising candidate to treat acute myocardial infarction (AMI). In this study, AMI was induced in New Zealand White rabbits by occluding the left circumflex coronary artery for 1 h, followed by reperfusion. The animals were distributed into three experimental groups: the sham-operated group (SHAM), the AMI group and the AMI + VPA group (AMI treated with VPA 500 mg/kg/day). After 5 weeks, abdominal aorta was removed and used for isometric recording of tension in organ baths or protein expression by Western blot, and plasma for the determination of nitrate/nitrite (NOx) levels by colorimetric assay. Our results indicated that AMI induced a reduction of the endothelium-dependent response to acetylcholine without modifying the endothelium-independent response to sodium nitroprusside, leading to endothelial dysfunction. VPA treatment reversed AMI-induced endothelial dysfunction and even increased NO sensitivity in vascular smooth muscle. This response was consistent with an antioxidant effect of VPA, as it was able to reverse the superoxide dismutase 1 (SOD 1) down-regulation induced by AMI. Our experiments also ruled out that the VPA mechanism was related to eNOS, iNOS, sGC and arginase expression or changes in NOx plasma levels. Therefore, we conclude that VPA improves vasodilation by increasing NO bioavailability, likely due to its antioxidant effect. Since endothelial dysfunction was closely related to AMI, VPA treatment could increase aortic blood flow, making it a potential agent in reperfusion therapy that can prevent the vascular damage.

Neutrophil degranulation and myocardial infarction

Myocardial infarction (MI) is one of the most common cardiac emergencies with high morbidity and is a leading cause of death worldwide. Since MI could develop into a life-threatening emergency and could also seriously affect the life quality of patients, continuous efforts have been made to create an effective strategy to prevent the occurrence of MI and reduce MI-related mortality. Numerous studies have confirmed that neutrophils play important roles in inflammation and innate immunity, which provide the first line of defense against microorganisms by producing inflammatory cytokines and chemokines, releasing reactive oxygen species, and degranulating components of neutrophil cytoplasmic granules to kill pathogens. Recently, researchers reported that neutrophils are closely related to the severity and prognosis of patients with MI, and neutrophil to lymphocyte ratio in post-MI patients had predictive value for major adverse cardiac events. Neutrophils have been increasingly recognized to exert important functions in MI. Especially, granule proteins released by neutrophil degranulation after neutrophil activation have been suggested to involve in the process of MI. This article reviewed the current research progress of neutrophil granules in MI and discusses neutrophil degranulation associated diagnosis and treatment strategies.

Inhibiting the ROCK Pathway Ameliorates Acute Lung Injury in Mice following Myocardial Ischemia/reperfusion

To clarify the role of Y-27632, a selective inhibitor of Rho-associated coiled-coil forming protein kinase (ROCK), in acute lung injury (ALI) induced by myocardial ischemia/reperfusion (I/R). Mice were randomized into Sham, I/R, and Y-27632 (10, 20 or 30 mg/kg) + I/R groups, and hemodynamics, infarcted area, the protein concentration, neutrophils in bronchoalveolar lavage fluid (BALF), malondialdehyde (MDA), superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) levels were assessed. Pathological changes were evaluated by hematoxylin-eosin (HE) staining; protein and gene expression were measured by Western blotting, enzyme-linked immunosorbent assay (ELISA), immunohistochemistry and quantitative real-time reverse-transcription polymerase chain reaction (qRT-PCR); and apoptosis was assessed by terminal deoxynucleotidyl transferase (TdT)-mediated dUTP nick-end labeling (TUNEL) staining. ROCK1 and ROCK2 expression was up-regulated in lung tissues of I/R mice compared to sham mice. Y-27632 decreased the protein concentration and the neutrophils in BALF in I/R mice, improved hemodynamics and reduced infarct size (IS)/area at risk (AAR) ratio. In addition, pathological changes in lung tissues of Y-27632-treated mice were mitigated, and these alterations were accompanied by decreases in MDA levels in lung tissues and increases in SOD and GSH-Px levels. Moreover, in I/R group, the number of apoptotic cells in lung tissue was higher than that in sham group, and p53, Caspase-3 and Bax expression was up-regulated; however, following treatment with Y-27632 (10, 20 and 30 mg/kg), these changes were reversed. Inhibition of ROCK pathway by Y-27632 ameliorated ALI in myocardial I/R mice by mitigating oxidative stress, inflammation and cell apoptosis.

The role of arginase in the microcirculation in cardiovascular disease

In the microcirculation, the exchange of nutrients, water, gas, hormones, and waste takes place, and it is divided into the three main sections arterioles, capillaries, and venules. Disturbances in the microcirculation can be measured using surrogate parameters or be visualized either indirectly or directly.Arginase is a manganese metalloenzyme hydrolyzing L-arginine to urea and L-ornithine. It is located in different cell types, including vascular cells, but also in circulating cells such as red blood cells. A variety of pro-inflammatory factors, as well as interleukins, stimulate increased arginase expression. An increase in arginase activity consequently leads to a consumption of L-arginine needed for nitric oxide (NO) production by endothelial NO synthase. A vast body of evidence convincingly showed that increased arginase activity is associated with endothelial dysfunction in larger vessels of the vascular tree. Of note, arginase also influences the microcirculation. Arginase inhibition leads to an increase in the bioavailability of NO and reduces superoxide levels, resulting in improved endothelial function. Arginase inhibition might, therefore, be a potent treatment strategy in cardiovascular medicine. Recently, red blood cells emerged as an influential player in the development from increased arginase activity to endothelial dysfunction. As red blood cells directly interact with the microcirculation in gas exchange, this could constitute a potential link between arginase activity, endothelial dysfunction and microcirculatory disturbances.The aim of this review is to summarize recent findings revealing the role of arginase in regulating vascular function with particular emphasis on the microcirculation.

Arginase 2 is a mediator of ischemia-reperfusion injury in the kidney through regulation of nitrosative stress

Kidney ischemia-reperfusion injury is a major cause of acute kidney injury (AKI). Following reduced kidney perfusion, the pathological overproduction of reactive oxygen and reactive nitrogen species play a substantial role in the development of kidney ischemia-reperfusion injury. Arginase 2 (ARG2) competes with nitric oxide synthase for the same substrate, L-arginine, and is implicated in the regulation of reactive nitrogen species. Therefore, we investigated the role of ARG2 in kidney ischemia-reperfusion injury using human proximal tubule cells (HK-2) and a mouse model of kidney ischemia-reperfusion injury. ARG2 was predominantly expressed in kidney tubules of the cortex, which was increased after ischemia-reperfusion injury. In HK-2 cells, ARG2 was expressed in punctate form in the cytoplasm and upregulated after hypoxia-reoxygenation. ARG2 knockdown reduced the level of reactive oxygen species and 3-nitrotyrosine after hypoxia-reoxygenation injury compared with control siRNA. Consistent with these results, in Arg2 knockout mice, abnormal kidney function and the increased acute tubular necrosis score induced by ischemia-reperfusion injury was significantly reduced without any obvious blood pressure changes. Additionally, an accumulation of 3-nitrotyrosine and apoptosis of renal tubule cells were attenuated in Arg2 knockout mice compared with wild-type mice. Inhibition of arginase by N^ω-hydroxy-nor-_L-arginine alleviated kidney ischemia-reperfusion injury like the results found in Arg2 knockout mice. Thus, ARG2 plays a pivotal role in ischemia-reperfusion-induced AKI by means of nitrosative stress. Hence, an ARG2-specific inhibitor may effectively treat kidney ischemia-reperfusion injury.

Improvement in endothelial function in cardiovascular disease - Is arginase the target?

Endothelial dysfunction represents an early change in the vascular wall in areas prone to atherosclerotic plaque formation and is present in association with several risk factors for cardiovascular disease. The underlying mechanisms behind endothelial dysfunction are multifactorial and complex. Arginase has emerged as a key player in the regulation of endothelial integrity by the ability of reciprocally inhibits nitric oxide formation and promoting oxidative stress. A chain of evidence suggest that arginase is implicated in the pathogenesis underlying endothelial dysfunction induced by several cardiovascular risk factors and established cardiovascular disease including diabetes, hypercholesteremia, ischemia/reperfusion, atherosclerosis, obesity, ageing and hypertension. Recent data has unveiled a key role of arginase as one of the key mechanisms underlying endothelial dysfunction in diabetes and may serve as a potential therapeutic target in previously overlooked compartments including red blood cells. The current review is devoted to discuss arginase as a key mediator in endothelial dysfunction and the potential for therapeutic possibilities to target this enzyme in various diseases, especially type 2 diabetes, atherosclerosis and ischemia/reperfusion with focus on translational and clinical aspects. Moreover, approaches of how and in which patient group(s) arginase may be targeted in future clinical trials are discussed.

Changes of the coronary arteries and cardiac microvasculature with aging: Implications for translational research and clinical practice

Aging results in functional and structural changes in the cardiovascular system, translating into a progressive increase of mechanical vessel stiffness, due to a combination of changes in micro-RNA expression patterns, autophagy, arterial calcification, smooth muscle cell migration and proliferation. The two pivotal mechanisms of aging-related endothelial dysfunction are oxidative stress and inflammation, even in the absence of clinical disease. A comprehensive understanding of the aging process is emerging as a primary concern in literature, as vascular aging has recently become a target for prevention and treatment of cardiovascular disease. Change of life-style, diet, antioxidant regimens, anti-inflammatory treatments, senolytic drugs counteract the pro-aging pathways or target senescent cells modulating their detrimental effects. Such therapies aim to reduce the ineluctable burden of age and contrast aging-associated cardiovascular dysfunction. This narrative review intends to summarize the macrovascular and microvascular changes related with aging, as a better understanding of the pathways leading to arterial aging may contribute to design new mechanism-based therapeutic approaches to attenuate the features of vascular senescence and its clinical impact on the cardiovascular system.

Role of Nitric Oxide Carried by Hemoglobin in Cardiovascular Physiology: Developments on a Three-Gas Respiratory Cycle

A continuous supply of oxygen is essential for the survival of multicellular organisms. The understanding of how this supply is regulated in the microvasculature has evolved from viewing erythrocytes (red blood cells [RBCs]) as passive carriers of oxygen to recognizing the complex interplay between Hb (hemoglobin) and oxygen, carbon dioxide, and nitric oxide-the three-gas respiratory cycle-that insures adequate oxygen and nutrient delivery to meet local metabolic demand. In this context, it is blood flow and not blood oxygen content that is the main driver of tissue oxygenation by RBCs. Herein, we review the lines of experimentation that led to this understanding of RBC function; from the foundational understanding of allosteric regulation of oxygen binding in Hb in the stereochemical model of Perutz, to blood flow autoregulation (hypoxic vasodilation governing oxygen delivery) observed by Guyton, to current understanding that centers on S-nitrosylation of Hb (ie, S-nitrosohemoglobin; SNO-Hb) as a purveyor of oxygen-dependent vasodilatory activity. Notably, hypoxic vasodilation is recapitulated by native S-nitrosothiol (SNO)-replete RBCs and by SNO-Hb itself, whereby SNO is released from Hb and RBCs during deoxygenation, in proportion to the degree of Hb deoxygenation, to regulate vessels directly. In addition, we discuss how dysregulation of this system through genetic mutation in Hb or through disease is a common factor in oxygenation pathologies resulting from microcirculatory impairment, including sickle cell disease, ischemic heart disease, and heart failure. We then conclude by identifying potential therapeutic interventions to correct deficits in RBC-mediated vasodilation to improve oxygen delivery-steps toward effective microvasculature-targeted therapies. To the extent that diseases of the heart, lungs, and blood are associated with impaired tissue oxygenation, the development of new therapies based on the three-gas respiratory system have the potential to improve the well-being of millions of patients.

Molecular Understanding of the Cardiomodulation in Myocardial Infarction and the Mechanism of Vitamin E Protections

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Myocardial infarction is a major cause of deaths globally. Modulation of several molecular mechanisms occurs during the initial stages of myocardial ischemia prior to permanent cardiac tissue damage, which involves both pathogenic as well as survival pathways in the cardiomyocyte. Currently, there is increasing evidence regarding the cardioprotective role of vitamin E in alleviating the disease. This fat-soluble vitamin does not only act as a powerful antioxidant; but it also has the ability to regulate several intracellular signalling pathways including HIF-1, PPAR-γ, Nrf-2, and NF-κB that influence the expression of a number of genes and their protein products. Essentially, it inhibits the molecular progression of tissue damage and preserves myocardial tissue viability. This review aims to summarize the molecular understanding of the cardiomodulation in myocardial infarction as well as the mechanism of vitamin E protection.

Deuterium oxide protects against myocardial injury induced by ischemia and reperfusion in rats

Objectives. Although deuterium oxide (D₂O) has preservative property on the extracted organ, whether D₂O also protects the in situ myocardial injury remains unknown. Using cardiac microdialysis, local administration of D₂O through dialysis probe was applied in situ rat heart. We examined the effect of the D₂O on the myocardial injury induced ischemia, reperfusion, and chemical hypoxia. Methodology. We measured dialysate myoglobin levels during 30 min of coronary occlusion and reperfusion in the absence and presence of D₂O. Furthermore, to confirm the effect of D₂O on NaCN induced myocardial injury, we measured the dialysate myoglobin levels with local perfusion of NaCN in the absence and presence of D₂O. Results. The dialysate myoglobin levels increased from 177 ± 45 ng/mL at baseline to 3030 ± 1523 ng/mL during 15-30 min of coronary occlusion and further increased to 8588 ± 1684ng/mL at 0-15 min of reperfusion. The dialysate myoglobin levels with 60 min local perfusion of NaCN increased to 1214 ± 279 ng/mL. D₂O attenuated myocardial myoglobin release during 15-30 min of coronary occlusion and 0-30 min of reperfusion and 15-60 min of local perfusion of NaCN. Conclusions. D₂O might have a beneficial effect of myocardium against ischemia, reperfusion and chemical hypoxia.

The Arginase Pathway in Neonatal Brain Hypoxia-Ischemia

Brain damage after hypoxia-ischemia (HI) occurs in an age-dependent manner. Neuroprotective strategies assumed to be effective in adults might have deleterious effects in the immature brain. In order to create effective therapies, the complex pathophysiology of HI in the developing brain requires exploring new mechanisms. Critical determinants of neuronal survival after HI are the extent of vascular dysfunction, inflammation, and oxidative stress, followed later by tissue repair. The key enzyme of these processes in the human body is arginase (ARG) that acts via the bioavailability of nitric oxide, and the synthesis of polyamines and proline. ARG is expressed throughout the brain in different cells. However, little is known about the effect of ARG in pathophysiological states of the brain, especially hypoxia-ischemia. Here, we summarize the role of ARG during neurodevelopment as well as in various brain pathologies.

Arginase: A Multifaceted Enzyme Important in Health and Disease

The arginase enzyme developed in early life forms and was maintained during evolution. As the last step in the urea cycle, arginase cleaves l-arginine to form urea and l-ornithine. The urea cycle provides protection against excess ammonia, while l-ornithine is needed for cell proliferation, collagen formation, and other physiological functions. In mammals, increases in arginase activity have been linked to dysfunction and pathologies of the cardiovascular system, kidney, and central nervous system and also to dysfunction of the immune system and cancer. Two important aspects of the excessive activity of arginase may be involved in diseases. First, overly active arginase can reduce the supply of l-arginine needed for the production of nitric oxide (NO) by NO synthase. Second, too much l-ornithine can lead to structural problems in the vasculature, neuronal toxicity, and abnormal growth of tumor cells. Seminal studies have demonstrated that increased formation of reactive oxygen species and key inflammatory mediators promote this pathological elevation of arginase activity. Here, we review the involvement of arginase in diseases affecting the cardiovascular, renal, and central nervous system and cancer and discuss the value of therapies targeting the elevated activity of arginase.

Arginase-2 mediates renal ischemia-reperfusion injury

Novel therapeutic interventions for preventing or attenuating kidney injury following ischemia-reperfusion injury (IRI) remain a focus of significant interest. Currently, there are no definitive therapeutic or preventive approaches available for ischemic acute kidney injury (AKI). Our objective is to determine 1) whether renal arginase activity or expression is increased in renal IRI, and 2) whether arginase plays a role in development of renal IRI. The impact of arginase activity and expression on renal damage was evaluated in male C57BL/6J (wild type) and arginase-2 (ARG2)-deficient (Arg2^-/- ) mice subjected to bilateral renal ischemia for 28 min, followed by reperfusion for 24 h. ARG2 expression and arginase activity significantly increased following renal IRI, paralleling the increase in kidney injury. Pharmacological blockade or genetic deficiency of Arg2 conferred kidney protection in renal IRI. Arg2^-/- mice had significantly attenuated kidney injury and lower plasma creatinine and blood urea nitrogen levels after renal IRI. Blocking arginases using S-(2-boronoethyl)-l-cysteine (BEC) 18 h before ischemia mimicked arginase deficiency by reducing kidney injury, histopathological changes and kidney injury marker-1 expression, renal apoptosis, kidney inflammatory cell recruitment and inflammatory cytokines, and kidney oxidative stress; increasing kidney nitric oxide (NO) production and endothelial NO synthase (eNOS) phosphorylation, kidney peroxisome proliferator-activated receptor-γ coactivator-1α expression, and mitochondrial ATP; and preserving kidney mitochondrial ultrastructure compared with vehicle-treated IRI mice. Importantly, BEC-treated eNOS-knockout mice failed to reduce blood urea nitrogen and creatinine following renal IRI. These findings indicate that ARG2 plays a major role in renal IRI, via an eNOS-dependent mechanism, and that blocking ARG2 activity or expression could be a novel therapeutic approach for prevention of AKI.

Arginase 2 promotes neurovascular degeneration during ischemia/reperfusion injury

Retinal ischemia is a major cause of visual impairment and blindness and is involved in various disorders including diabetic retinopathy, glaucoma, optic neuropathies and retinopathy of prematurity. Neurovascular degeneration is a common feature of these pathologies. Our lab has previously reported that the ureahydrolase arginase 2 (A2) is involved in ischemic retinopathies. Here, we are introducing A2 as a therapeutic target to prevent neurovascular injury after retinal ischemia/reperfusion (I/R) insult. Studies were performed with mice lacking both copies of A2 (A2^−/−) and wild-type (WT) controls (C57BL6J). I/R insult was conducted on the right eye and the left eye was used as control. Retinas were collected for analysis at different times (3 h–4 week after injury). Neuronal and microvascular degeneration were evaluated using NeuN staining and vascular digests, respectively. Glial activation was evaluated by glial fibrillary acidic protein expression. Necrotic cell death was studied by propidium iodide labeling and western blot for RIP-3. Arginase expression was determined by western blot and quantitative RT-PCR. Retinal function was determined by electroretinography (ERG). A2 mRNA and protein levels were increased in WT I/R. A2 deletion significantly reduced ganglion cell loss and microvascular degeneration and preserved retinal morphology after I/R. Glial activation, reactive oxygen species formation and cell death by necroptosis were significantly reduced by A2 deletion. ERG showed improved positive scotopic threshold response with A2 deletion. This study shows for the first time that neurovascular injury after retinal I/R is mediated through increased expression of A2. Deletion of A2 was found to be beneficial in reducing neurovascular degeneration after I/R.

Reperfusion injury and reactive oxygen species: The evolution of a concept

Reperfusion injury, the paradoxical tissue response that is manifested by blood flow-deprived and oxygen-starved organs following the restoration of blood flow and tissue oxygenation, has been a focus of basic and clinical research for over 4-decades. While a variety of molecular mechanisms have been proposed to explain this phenomenon, excess production of reactive oxygen species (ROS) continues to receive much attention as a critical factor in the genesis of reperfusion injury. As a consequence, considerable effort has been devoted to identifying the dominant cellular and enzymatic sources of excess ROS production following ischemia-reperfusion (I/R). Of the potential ROS sources described to date, xanthine oxidase, NADPH oxidase (Nox), mitochondria, and uncoupled nitric oxide synthase have gained a status as the most likely contributors to reperfusion-induced oxidative stress and represent priority targets for therapeutic intervention against reperfusion-induced organ dysfunction and tissue damage. Although all four enzymatic sources are present in most tissues and are likely to play some role in reperfusion injury, priority and emphasis has been given to specific ROS sources that are enriched in certain tissues, such as xanthine oxidase in the gastrointestinal tract and mitochondria in the metabolically active heart and brain. The possibility that multiple ROS sources contribute to reperfusion injury in most tissues is supported by evidence demonstrating that redox-signaling enables ROS produced by one enzymatic source (e.g., Nox) to activate and enhance ROS production by a second source (e.g., mitochondria). This review provides a synopsis of the evidence implicating ROS in reperfusion injury, the clinical implications of this phenomenon, and summarizes current understanding of the four most frequently invoked enzymatic sources of ROS production in post-ischemic tissue.

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Reperfusion injury is implicated in a variety of human diseases and disorders.

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Evidence implicating ROS in reperfusion injury continues to grow.

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Several enzymes are candidate sources of ROS in post-ischemic tissue.

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Inter-enzymatic ROS-dependent signaling enhances the oxidative stress caused by I/R.

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FoxO4 promotes early inflammatory response upon myocardial infarction via endothelial Arg1

RATIONALE

Inflammation in post-myocardial infarction (MI) is necessary for myocyte repair and wound healing. Unfortunately, it is also a key component of subsequent heart failure pathology. Transcription factor forkhead box O4 (FoxO4) regulates a variety of biological processes, including inflammation. However, its role in MI remains unknown.

OBJECTIVE

To test the hypothesis that FoxO4 promotes early post-MI inflammation via endothelial arginase 1 (Arg1).

METHODS AND RESULTS

We induced MI in wild-type and FoxO4(-/-) mice. FoxO4(-/-) mice had a significantly higher post-MI survival, better cardiac function, and reduced infarct size. FoxO4(-/-) hearts had significantly fewer neutrophils, reduced expression of cytokines, and competitive nitric oxide synthase inhibitor Arg1. We generated conditional FoxO4 knockout mice with FoxO4 deleted in cardiac mycoytes or endothelial cells. FoxO4 endothelial cell-specific knockout mice showed significant post-MI improvement of cardiac function and reduction of neutrophil accumulation and cytokine expression, whereas FoxO4 cardiac mycoyte-specific knockout mice had no significant difference in cardiac function and post-MI inflammation from those of control littermates. FoxO4 binds the Foxo-binding site in the Arg1 promoter and activates Arg1 transcription. FoxO4 knockdown in human aortic endothelial cells upregulated nitric oxide on ischemia and suppressed monocyte adhesion that can be reversed by ectopic-expression of Arg1. Furthermore, chemical inhibition of Arg1 in wild-type mice had similar cardioprotection and reduced inflammation after MI as FoxO4 inactivation and administration of nitric oxide synthase inhibitor to FoxO4 KO mice reversed the beneficial effects of FoxO4 deletion on post-MI cardiac function.

CONCLUSIONS

FoxO4 activates Arg1 transcription in endothelial cells in response to MI, leading to downregulation of nitric oxide and upregulation of neutrophil infiltration to the infarct area.

Arginase: an old enzyme with new tricks

Arginase has roots in early life-forms. It converts L-arginine to urea and ornithine. The former provides protection against NH3; the latter serves to stimulate cell growth and other physiological functions. Excessive arginase activity in mammals has been associated with cardiovascular and nervous system dysfunction and disease. Two relevant aspects of this elevated activity may be involved in these disease states. First, excessive arginase activity reduces the supply of L-arginine needed by nitric oxide (NO) synthase to produce NO. Second, excessive production of ornithine leads to vascular structural problems and neural toxicity. Recent research has identified inflammatory agents and reactive oxygen species (ROS) as drivers of this pathologic elevation of arginase activity and expression. We review the involvement of arginase in cardiovascular and nervous system dysfunction, and discuss potential therapeutic interventions targeting excess arginase.

Arginase as a Critical Prooxidant Mediator in the Binomial Endothelial Dysfunction-Atherosclerosis

Arginase is a metalloenzyme which hydrolyzes L-arginine to L-ornithine and urea. Since its discovery, in the early 1900s, this enzyme has gained increasing attention, as literature reports have progressively pointed to its critical participation in regulating nitric oxide bioavailability. Indeed, accumulating evidence in the following years would picture arginase as a key player in vascular health. Recent studies have highlighted the arginase regulatory role in the progression of atherosclerosis, the latter an essentially prooxidant state. Apart from the fact that arginase has been proven to impair different metabolic pathways, and also as a consequence of this, the repercussions of the actions of such enzyme go further than first thought. In fact, such metalloenzyme exhibits direct implications in multiple cardiometabolic diseases, among which are hypertension, type 2 diabetes, and hypercholesterolemia. Considering the epidemiological repercussions of these clinical conditions, arginase is currently seen under the spotlights of the search for developing specific inhibitors, in order to mitigate its deleterious effects. That said, the present review focuses on the role of arginase in endothelial function and its participation in the establishment of atherosclerotic lesions, discussing the main regulatory mechanisms of the enzyme, also highlighting the potential development of pharmacological strategies in related cardiovascular diseases.

Arginase induction and activation during ischemia and reperfusion and functional consequences for the heart

Induction and activation of arginase is among the fastest responses of the heart to ischemic events. Induction of arginase expression and enzyme activation under ischemic conditions shifts arginine consumption from nitric oxide formation (NO) to the formation of ornithine and urea. In the heart such a switch in substrate utilization reduces the impact of the NO/cGMP-pathway on cardiac function that requires intact electromechanical coupling but at the same time it induces ornithine-dependent pathways such as the polyamine metabolism. Both effects significantly reduce the recovery of heart function during reperfusion and thereby limits the success of reperfusion strategies. In this context, changes in arginine consumption trigger cardiac remodeling in an unfavorable way and increases the risk of arrhythmia, specifically in the initial post-ischemic period in which arginase activity is dominating. However, during the entire ischemic period arginase activation might be a meaningful adaptation that is specifically relevant for reperfusion following prolonged ischemic periods. Therefore, a precise understanding about the underlying mechanism that leads to arginase induction as well as of it's mechanistic impact on post-ischemic hearts is required for optimizing reperfusion strategies. In this review we will summarize our current understanding of these processes and give an outlook about possible treatment options for the future.

Increased arginase levels contribute to impaired perfusion after cardiopulmonary resuscitation

OBJECTIVES

The postcardiac arrest syndrome occurs after global hypoxia leading to microcirculatory impairment. Nitric oxide (NO) is a key molecule regulating microvascular function. The enzyme arginase has been suggested to modulate microvascular function by regulating NO metabolism. Therefore, we investigated whether arginase increases following global hypoxia and resuscitation and tested whether arginase inhibition influences altered microcirculation in resuscitated patients.

METHODS

To determine the effect of global hypoxia on circulating arginase levels, fourteen healthy subjects were exposed to hypoxia in a normobaric hypoxia chamber (FiO² = 9·9%). In addition, 31 resuscitated patients were characterized clinically, and arginase 1 was measured on days 1 and 3. In eight resuscitated patients, a microcirculatory analysis was performed using a sidestream darkfield microcirculation camera. Perfused capillary density (PCD) was recorded before and after sublingual incubation of N-omega-hydroxy-nor-l-arginine (nor-NOHA) alone or together with the NOS inhibitor NG-monomethyl-l-arginine (l-NMMA).

RESULTS

Circulating arginase 1 levels increased in healthy volunteers following global hypoxia in the hypoxic chamber (P < 0·01). In addition, arginase 1 levels were higher on day 1 (69·1 ± 83·3 ng/mL) and on day 3 (44·2 ± 65·6 ng/mL) after resuscitation than in control subjects (P < 0·001). Incubation of the sublingual mucosa with nor-NOHA increased microcirculatory perfusion (P < 0·001). This effect was inhibited by co-incubation with K-NMMA.

CONCLUSIONS

Circulating arginase 1 levels are increased following exposure to global hypoxia and in patients who have been successfully resuscitated after cardiac arrest. Topical arginase inhibition improves microcirculatory perfusion following resuscitation. This is of potential therapeutic importance for the postcardiac arrest syndrome.

Ageing and microvasculature

A decline in the function of the microvasculature occurs with ageing. An impairment of endothelial properties represents a main aspect of age-related microvascular alterations. Endothelial dysfunction manifests itself through a reduced angiogenic capacity, an aberrant expression of adhesion molecules and an impaired vasodilatory function. Increased expression of adhesion molecules amplifies the interaction with circulating factors and inflammatory cells. The latter occurs in both conduit arteries and resistance arterioles. Age-related impaired function also associates with phenotypic alterations of microvascular cells, such as endothelial cells, smooth muscle cells and pericytes. Age-related morphological changes are in most of cases organ-specific and include microvascular wall thickening and collagen deposition that affect the basement membrane, with the consequent perivascular fibrosis. Data from experimental models indicate that decreased nitric oxide (NO) bioavailability, caused by impaired eNOS activity and NO inactivation, is one of the causes responsible for age-related microvascular endothelial dysfunction. Consequently, vasodilatory responses decline with age in coronary, skeletal, cerebral and vascular beds. Several therapeutic attempts have been suggested to improve microvascular function in age-related end-organ failure, and include the classic anti-atherosclerotic and anti-ischemic treatments, and also new innovative strategies. Change of life style, antioxidant regimens and anti-inflammatory treatments gave the most promising results. Research efforts should persist to fully elucidate the biomolecular basis of age-related microvascular dysfunction in order to better support new therapeutic strategies aimed to improve quality of life and to reduce morbidity and mortality among the elderly patients.

The role of arginase and rho kinase in cardioprotection from remote ischemic perconditioning in non-diabetic and diabetic rat in vivo

Background

Pharmacological inhibition of arginase and remote ischemic perconditioning (RIPerc) are known to protect the heart against ischemia/reperfusion (IR) injury.

Purpose

The objective of this study was to investigate whether (1) peroxynitrite-mediated RhoA/Rho associated kinase (ROCK) signaling pathway contributes to arginase upregulation following myocardial IR; (2) the inhibition of this pathway is involved as a cardioprotective mechanism of remote ischemic perconditioning and (3) the influence of diabetes on these mechanisms.

Methods

Anesthetized rats were subjected to 30 min left coronary artery ligation followed by 2 h reperfusion and included in two protocols. In protocol 1 rats were randomized to 1) control IR, 2) RIPerc induced by bilateral femoral artery occlusion for 15 min during myocardial ischemia, 3) RIPerc and administration of the nitric oxide synthase inhibitor N^G-monomethyl-L-arginine (L-NMMA), 4) administration of the ROCK inhibitor hydroxyfasudil or 5) the peroxynitrite decomposition catalyst FeTPPS. In protocol 2 non-diabetic and type 1 diabetic rats were randomosed to IR or RIPerc as described above.

Results

Infarct size was significantly reduced in rats treated with FeTPPS, hydroxyfasudil and RIPerc compared to controls (P<0.001). FeTPPS attenuated both ROCK and arginase activity (P<0.001 vs. control). Similarly, RIPerc reduced arginase and ROCK activity, peroxynitrite formation and enhanced phospho-eNOS expression (P<0.05 vs. control). The cardioprotective effect of RIPerc was abolished by L-NMMA. The protective effect of RIPerc and its associated changes in arginase and ROCK activity were abolished in diabetes.

Conclusion

Arginase is activated by peroxynitrite/ROCK signaling cascade in myocardial IR. RIPerc protects against IR injury via a mechanism involving inhibition of this pathway and enhanced eNOS activation. The beneficial effect and associated molecular changes of RIPerc is abolished in type 1 diabetes.

Effect of arginase inhibition on ischemia-reperfusion injury in patients with coronary artery disease with and without diabetes mellitus

BACKGROUND

Arginase competes with nitric oxide synthase for their common substrate L-arginine. Up-regulation of arginase in coronary artery disease (CAD) and diabetes mellitus may reduce nitric oxide bioavailability contributing to endothelial dysfunction and ischemia-reperfusion injury. Arginase inhibition reduces infarct size in animal models. Therefore the aim of the current study was to investigate if arginase inhibition protects from endothelial dysfunction induced by ischemia-reperfusion in patients with CAD with or without type 2 diabetes (

CLINICAL TRIAL REGISTRATION NUMBER

NCT02009527).

METHODS

Male patients with CAD (n = 12) or CAD + type 2 diabetes (n = 12), were included in this cross-over study with blinded evaluation. Endothelium-dependent vasodilatation was assessed by flow-mediated dilatation (FMD) of the radial artery before and after 20 min ischemia-reperfusion during intra-arterial infusion of the arginase inhibitor (Nω-hydroxy-nor-L-arginine, 0.1 mg/min) or saline.

RESULTS

The forearm ischemia-reperfusion was well tolerated. Endothelium-independent vasodilatation was assessed by sublingual nitroglycerin. Ischemia-reperfusion decreased FMD in patients with CAD from 12.7±5.2% to 7.9±4.0% during saline administration (P<0.05). Nω-hydroxy-nor-L-arginine administration prevented the decrease in FMD in the CAD group (10.3±4.3% at baseline vs. 11.5±3.6% at reperfusion). Ischemia-reperfusion did not significantly reduce FMD in patients with CAD + type 2 diabetes. However, FMD at reperfusion was higher following nor-NOHA than following saline administration in both groups (P<0.01). Endothelium-independent vasodilatation did not differ between the occasions.

CONCLUSIONS

Inhibition of arginase protects against endothelial dysfunction caused by ischemia-reperfusion in patients with CAD. Arginase inhibition may thereby be a promising therapeutic strategy in the treatment of ischemia-reperfusion injury.

Arginase II is a target of miR-17-5p and regulates miR-17-5p expression in human pulmonary artery smooth muscle cells

Vascular remodeling and smooth muscle cell proliferation are hallmark pathogenic features of pulmonary artery hypertension. MicroRNAs, endogenously expressed small noncoding RNAs, regulate gene expression at the posttranscriptional level. It has previously been shown that miR-17 overexpression in cultured human pulmonary artery smooth muscle cell (hPASMC) resulted in increased viable cell number. Previously, we have found that arginase II promotes hypoxia-induced proliferation in hPASMC. Therefore, we hypothesized that miR-17 would be upregulated by hypoxia in hPASMC and would result in greater arginase II expression. We found that levels of miR-17-5p and arginase II were significantly greater in cultured hPASMC exposed to 1% O2 for 48 h than in hPASMC exposed to 21% O2 for 48 h. Furthermore, inhibiting miR-17-5p expression decreased hypoxia-induced arginase II protein levels in hPASMC. Conversely, overexpressing miR-17-5p resulted in greater arginase II protein levels. Somewhat surprisingly, arginase II inhibition was associated with lower miR-17-5p expression in both normoxic and hypoxic hPASMC, whereas overexpressing arginase II resulted in greater miR-17-5p expression in hPASMC. These findings suggest that hypoxia-induced arginase II expression is not only regulated by miR-17-5p but also that there is a feedback loop between arginase II and miR-17-5p in hPASMC. We also found that the arginase II-mediated regulation of miR-17-5p was independent of either p53 or c-myc. We also found that l-arginine, the substrate for arginase II, and l-ornithine, the amino acid product of arginase II, were not involved in the regulation of miR-17-5p expression.

Levosimendan improves contractility in vivo and in vitro in a rodent model of post-myocardial infarction heart failure

AIM

As few studies have presented a thorough analysis of the effect of levosimendan (LEV) on contractility, our purpose was to investigate in vivo cardiac function as well as in vitro cardiomyocyte function and calcium (Ca(2+) ) handling following LEV treatment.

METHODS

Rats with post-myocardial infarction heart failure (HF) induced by ligation of the left anterior descending coronary artery and sham-operated animals were randomized to the infusion of LEV (2.4 μg kg(-1) min(-1) ) or vehicle for 40 min. Echocardiographic examination was coupled to pressure-volume sampling in the left ventricle before (B) and after (40 min) infusion. Isolated left ventricular cardiomyocytes were studied in an epifluorescence microscope.

RESULTS

HF LEV (n = 6), HF vehicle (n = 7), sham LEV (n = 5) and sham vehicle (n = 6) animals were included. LEV infusion compared to vehicle in HF animals reduced left ventricular end-diastolic pressure and mean arterial pressure (both P < 0.001) and improved the slope of the preload-recruitable stroke work (P < 0.05). Administrating LEV to HF cardiomyocytes in vitro improved fractional shortening and Ca(2+) sensitivity index ratio, and increased the diastolic Ca(2+) (all P < 0.01).

CONCLUSION

In HF animals, LEV improved the contractility by increasing the Ca(2+) sensitivity. Furthermore loading conditions were changed, and LEV could consequently change organ perfusion. An observed increase in diastolic Ca(2+) following LEV treatment and clinical implications of this should be further addressed.

Contribution of calpain to myoglobin efflux from cardiomyocytes during ischaemia and after reperfusion in anaesthetized rats

AIM

Calpain activation has a putative role in ischaemia-reperfusion injury of cardiomyocytes. This study clarified the in vivo contribution of calpain to disruption of cardiomyocyte sarcolemma during ischaemia and after reperfusion in anaesthetized rats.

METHODS

Using a microdialysis technique in the hearts of anaesthetized rats, we investigated the effects of the calpain inhibitors on myocardial interstitial myoglobin level in the ischaemic region during coronary occlusion and after reperfusion. The calpain inhibitors were administered locally via a dialysis probe. Two durations of coronary occlusion were tested.

RESULTS

Thirty-minute coronary occlusion: dialysate myoglobin concentration increased markedly from 385 ± 46 ng mL(-1) at baseline to 3701 ± 527 ng mL(-1) at 20-30 min of occlusion. After reperfusion, dialysate myoglobin concentration further increased, reaching a peak (12 296 ± 1564 ng mL(-1) ) at 10-20 min post-reperfusion and then declined gradually. The calpain inhibitors, MDL-28170 and SNJ-1945 did not change dialysate myoglobin concentration during occlusion but attenuated the increase after reperfusion to 6826 ± 1227 and 8130 ± 938 ng mL(-1) at 10-20 min post-reperfusion (P < 0.05), respectively. Ninety-minute coronary occlusion: dialysate myoglobin concentration increased from 516 ± 33 ng mL(-1) at baseline to 5463 ± 387 ng mL(-1) at 80-90 min after occlusion. After reperfusion, there was no significant increase in dialysate myoglobin concentration. MDL-28170 did not affect dialysate myoglobin concentration during occlusion or after reperfusion.

CONCLUSION

Calpain contributes to sarcolemmal disruption immediately after reperfusion following 30-min coronary occlusion, but has little effects during ischaemia and after reperfusion in 90-min coronary occlusion.

Adalimumab ameliorates abdominal aorta cross clamping which induced liver injury in rats

The aim of this study was to investigate the possible protective effects of adalimumab (ADA) on cell damage in rat liver tissue during ischemia/reperfusion (I/R) injury of infrarenal abdominal aorta. Thirty male Wistar-albino rats were divided into three groups: control, I/R, and I/R+ADA, each group containing 10 animals. Laparotomy without I/R injury was performed in the control group animals. Laparotomy in the I/R group was followed by two hours of infrarenal abdominal aortic cross ligation and then two hours of reperfusion. ADA (50 mg/kg) was administered intraperitoneally as a single dose, to the I/R+ADA group, five days before I/R. The tumor necrosis factor-alpha (TNF-α) (pg/mg protein) and nitric oxide (NO) (µmol/g protein) levels in the I/R group (430.8 ± 70.1, 8.0 ± 1.1, resp.) were significantly higher than those in the I/R+ADA group (338.0 ± 71.6, P = 0.006; 6.3 ± 1.2, P = 0.008) and the control group (345.5 ± 53.3, P = 0.008; 6.5 ± 1.5, P = 0.010, resp.). I/R causes severe histopathological injury to the liver tissue, but ADA leads to much less histopathological changes. ADA treatment significantly decreased the severity of liver I/R injury. ADA pretreatment may have protective effects on experimental liver injury.

Adalimumab ameliorates abdominal aorta cross clamping which induced liver injury in rats

The aim of this study was to investigate the possible protective effects of adalimumab (ADA) on cell damage in rat liver tissue during ischemia/reperfusion (I/R) injury of infrarenal abdominal aorta. Thirty male Wistar-albino rats were divided into three groups: control, I/R, and I/R+ADA, each group containing 10 animals. Laparotomy without I/R injury was performed in the control group animals. Laparotomy in the I/R group was followed by two hours of infrarenal abdominal aortic cross ligation and then two hours of reperfusion. ADA (50 mg/kg) was administered intraperitoneally as a single dose, to the I/R+ADA group, five days before I/R. The tumor necrosis factor-alpha (TNF-α) (pg/mg protein) and nitric oxide (NO) (µmol/g protein) levels in the I/R group (430.8 ± 70.1, 8.0 ± 1.1, resp.) were significantly higher than those in the I/R+ADA group (338.0 ± 71.6, P = 0.006; 6.3 ± 1.2, P = 0.008) and the control group (345.5 ± 53.3, P = 0.008; 6.5 ± 1.5, P = 0.010, resp.). I/R causes severe histopathological injury to the liver tissue, but ADA leads to much less histopathological changes. ADA treatment significantly decreased the severity of liver I/R injury. ADA pretreatment may have protective effects on experimental liver injury.

Arginase as a target for treatment of myocardial ischemia-reperfusion injury

Two distinct enzymes of arginase (1 and 2) are critically regulating nitric oxide (NO) bioavailability by competing with NO synthase for their common substrate l-arginine. Increased expression and activity of arginase is observed in atherosclerosis and myocardial ischemia-reperfusion (I/R). Several studies have demonstrated a key pathophysiological role of increased activity of arginase during I/R. Pharmacological inhibition of arginase results in restoration of NO availability and salvage of myocardium during I/R. Arginase inhibition might be a promising therapeutic strategy for the limitation of myocardial injury in acute myocardial infarction. Current understanding of the role of arginase and efficacy of arginase inhibition during myocardial I/R is reviewed in the present article.