Akt-dependent phosphorylation of serine 1179 and mitogen-activated protein kinase kinase/extracellular signal-regulated kinase 1/2 cooperatively mediate activation of the endothelial nitric-oxide synthase by hydrogen peroxide

GKT137831 and hydrogen peroxide increase the release of 6-nitrodopamine from the human umbilical artery, rat-isolated right atrium, and rat-isolated vas deferens

Introduction: The human umbilical artery (HUA), rat-isolated right atrium, and rat-isolated vas deferens present a basal release of 6-nitrodopamine (6-ND). The basal release of 6-ND from these tissues was significantly decreased (but not abolished) when the tissues were pre-incubated with Nω-nitro-L-arginine methyl ester (L-NAME). Methods: In this study, the effect of the pharmacological modulation of the redox environment on the basal release of 6-ND was investigated. The basal release of 6-ND was measured using Liquid chromatography with tandem mass spectrometry (LC-MS/MS). Results and Discussion: Pre-incubation (30 min) of the tissues with GKT137831 (1 μM) caused a significant increase in the basal release of 6-ND from all tissues. In the HUA, pre-incubation with diphenyleneiodonium (DPI) (100 μM) also caused significant increases in the basal release of 6-ND. Preincubation of the HUA with hydrogen peroxide (H2O2) (100 μM) increased 6-ND basal release, whereas pre-incubation with catalase (1,000 U/mL) significantly decreased it. Pre-incubation of the HUA with superoxide dismutase (SOD) (250 U/mL; 30 min) also significantly increased the basal release of 6-ND. Preincubation of the HUA with either allopurinol (100 μM) or uric acid (1 mM) had no effect on the basal release of 6-ND. Pre-treatment of the HUA with L-NAME (100 μM) prevented the increase in the basal release of 6-ND induced by GKT137831, diphenyleneiodonium, and H2O2. The results obtained indicate a major role of endogenous H2O2 and peroxidases as modulators of 6- ND biosynthesis/release and a lack of peroxynitrite contribution.

Protective effects of phosphocreatine on human vascular endothelial cells against hydrogen peroxide-induced apoptosis and in the hyperlipidemic rat model

Phosphocreatine (PCr) has been shown to have a cardio-protective effect during cardiopulmonary resuscitation (CPR). However, little is known about its impact on atherosclerosis. In this study, we first evaluated the pharmacological effects of PCr on antioxidative defenses and mitochondrial protection against hydrogen peroxide (H2O2) induced human umbilical vascular endothelial cells (HUVECs) damage. Then we investigated the hypolipidemic and antioxidative effects of PCr on hyperlipidemic rat model. Via in vitro studies, H2O2 significantly reduced cell viability and increased apoptosis rate of HUVECs, while pretreatment with PCr abolished its apoptotic effect. PCr could reduce the generation of ROS induced by H2O2. Moreover, PCr could increase the activity of SOD and the content of NO, as well as decrease the activity of LDH and the content of MDA. PCr could also antagonize H2O2-induced up-regulation of Bax, cleaved-caspase3, cleaved-caspase9, and H2O2-induced down-regulation of Bcl-2 and p-Akt/Akt ratio. In addition, PCr reduced U937 cells' adhesion to H2O2-stimulated HUVECs. Via in vivo study, PCr could decrease MDA, TC, TG and LDL-C levels in hyperlipidemic rats. Finally, different-concentration PCr could increase the leaching of TC, HDL, and TG from fresh human atherosclerotic plaques. In conclusion, PCr could suppress H2O2-induced apoptosis in HUVECs and reduce hyperlipidemia through inhibiting ROS generation and modulating dysfunctional mitochondrial system, which might be an effective new therapeutic strategy to further prevent atherosclerosis.

Sex differences in the participation of endothelial mediators and signaling pathways involved in the vasodilator effect of a selective GPER agonist in resistance arteries of gonadectomized Wistar rats

AIM

Endothelial mechanisms underlying the vascular effects of estrogen modulated by the G protein-coupled estrogen receptor (GPER) are not well understood, especially in gonadal sex hormone deprivation. Thus, we investigated vascular function and endothelial signaling pathways involved in the selective activation of GPER in resistance arteries of gonadectomized rats.

METHODS

Gonadectomy was performed in Wistar rats of both sexes. After 21 days, the animals were euthanized. Concentration-response curves were obtained by cumulative additions of G-1 in third-order mesenteric arteries. The vasodilatory effects of G-1 were evaluated before and after endothelium removal or incubation with pharmacological inhibitors. Tissue protein expression was measured by western blotting. Assays with 4-amino-5-methylamino-2',7'-difluorofluorescein diacetate (DAF-FM) and 2',7' dichlorodihydrofluorescein-diacetate (DCF-DA) were performed in the arteries investigated. Immunolocalization was assessed by immunofluorescence.

RESULTS

G-1 induced partially endothelium-dependent relaxation in both sexes. The three isoforms of the enzyme nitric oxide synthase contributed to the production and release of nitric oxide in both gonadectomized groups, but the role of inducible nitric oxide synthase is more expressive in males. The mechanistic pathway by which endothelial nitric oxide synthase is phosphorylated appears to differ between sexes, with the rapid signaling pathway phosphatidylinositol-3-kinase/protein kinase B/endothelial nitric oxide synthase (PI3k-Akt-eNOS) being identified for males and mitogen-activated protein kinase/extracellular signal-regulated kinase/endothelial nitric oxide synthase (MEK-ERK-eNOS) for females. The contribution of hydrogen peroxide as an endothelial relaxation mediator seems to be greater in females.

CONCLUSION

These results provide new insights into the effects of estrogen-induced responses via GPER on vascular function in gonadal sex hormone deprivation.

Nitric-Oxide-Mediated Signaling in Podocyte Pathophysiology

Nitric oxide (NO) is a potent signaling molecule involved in many physiological and pathophysiological processes in the kidney. NO plays a complex role in glomerular ultrafiltration, vasodilation, and inflammation. Changes in NO bioavailability in pathophysiological conditions such as hypertension or diabetes may lead to podocyte damage, proteinuria, and rapid development of chronic kidney disease (CKD). Despite the extensive data highlighting essential functions of NO in health and pathology, related signaling in glomerular cells, particularly podocytes, is understudied. Several reports indicate that NO bioavailability in glomerular cells is decreased during the development of renal pathology, while restoring NO level can be beneficial for glomerular function. At the same time, the compromised activity of nitric oxide synthase (NOS) may provoke the formation of peroxynitrite and has been linked to autoimmune diseases such as systemic lupus erythematosus. It is known that the changes in the distribution of NO sources due to shifts in NOS subunits expression or modifications of NADPH oxidases activity may be linked to or promote the development of pathology. However, there is a lack of information about the detailed mechanisms describing the production and release of NO in the glomerular cells. The interaction of NO and other reactive oxygen species in podocytes and how NO-calcium crosstalk regulates glomerular cells’ function is still largely unknown. Here, we discuss recent reports describing signaling, synthesis, and known pathophysiological mechanisms mediated by the changes in NO homeostasis in the podocyte. The understanding and further investigation of these essential mechanisms in glomerular cells will facilitate the design of novel strategies to prevent or manage health conditions that cause glomerular and kidney damage.

Neurovascular protection by adropin in experimental ischemic stroke through an endothelial nitric oxide synthase-dependent mechanism

Adropin is a highly-conserved peptide that has been shown to preserve endothelial barrier function. Blood-brain barrier (BBB) disruption is a key pathological event in cerebral ischemia. However, the effects of adropin on ischemic stroke outcomes remain unexplored. Hypothesizing that adropin exerts neuroprotective effects by maintaining BBB integrity, we investigated the role of adropin in stroke pathology utilizing loss- and gain-of-function genetic approaches combined with pharmacological treatment with synthetic adropin peptide. Long-term anatomical and functional outcomes were evaluated using histology, MRI, and a battery of sensorimotor and cognitive tests in mice subjected to ischemic stroke. Brain ischemia decreased endogenous adropin levels in the brain and plasma. Adropin treatment or transgenic adropin overexpression robustly reduced brain injury and improved long-term sensorimotor and cognitive function in young and aged mice subjected to ischemic stroke. In contrast, genetic deletion of adropin exacerbated ischemic brain injury, irrespective of sex. Mechanistically, adropin treatment reduced BBB damage, degradation of tight junction proteins, matrix metalloproteinase-9 activity, oxidative stress, and infiltration of neutrophils into the ischemic brain. Adropin significantly increased phosphorylation of endothelial nitric oxide synthase (eNOS), Akt, and ERK1/2. While adropin therapy was remarkably protective in wild-type mice, it failed to reduce brain injury in eNOS-deficient animals, suggesting that eNOS is required for the protective effects of adropin in stroke. These data provide the first causal evidence that adropin exerts neurovascular protection in stroke through an eNOS-dependent mechanism. We identify adropin as a novel neuroprotective peptide with the potential to improve stroke outcomes.

Aging-Induced Impairment of Vascular Function: Mitochondrial Redox Contributions and Physiological/Clinical Implications

Significance: The vasculature responds to the respiratory needs of tissue by modulating luminal diameter through smooth muscle constriction or relaxation. Coronary perfusion, diastolic function, and coronary flow reserve are drastically reduced with aging. This loss of blood flow contributes to and exacerbates pathological processes such as angina pectoris, atherosclerosis, and coronary artery and microvascular disease. Recent Advances: Increased attention has recently been given to defining mechanisms behind aging-mediated loss of vascular function and development of therapeutic strategies to restore youthful vascular responsiveness. The ultimate goal aims at providing new avenues for symptom management, reversal of tissue damage, and preventing or delaying of aging-induced vascular damage and dysfunction in the first place. Critical Issues: Our major objective is to describe how aging-associated mitochondrial dysfunction contributes to endothelial and smooth muscle dysfunction via dysregulated reactive oxygen species production, the clinical impact of this phenomenon, and to discuss emerging therapeutic strategies. Pathological changes in regulation of mitochondrial oxidative and nitrosative balance (Section 1) and mitochondrial dynamics of fission/fusion (Section 2) have widespread effects on the mechanisms underlying the ability of the vasculature to relax, leading to hyperconstriction with aging. We will focus on flow-mediated dilation, endothelial hyperpolarizing factors (Sections 3 and 4), and adrenergic receptors (Section 5), as outlined in Figure 1. The clinical implications of these changes on major adverse cardiac events and mortality are described (Section 6). Future Directions: We discuss antioxidative therapeutic strategies currently in development to restore mitochondrial redox homeostasis and subsequently vascular function and evaluate their potential clinical impact (Section 7). Antioxid. Redox Signal. 35, 974-1015.

Oral Supplementation with Benzylamine Delays the Onset of Diabetes in Obese and Diabetic db-/- Mice

Substrates of semicarbazide-sensitive amine oxidase (SSAO) exert insulin-like actions in adipocytes. One of them, benzylamine (Bza) exhibits antihyperglycemic properties in several rodent models of diabetes. To further study the antidiabetic potential of this naturally occurring amine, a model of severe type 2 diabetes, the obese db-/- mouse, was subjected to oral Bza administration. To this end, db-/- mice and their lean littermates were treated at 4 weeks of age by adding 0.5% Bza in drinking water for seven weeks. Body mass, fat content, blood glucose and urinary glucose output were followed while adipocyte insulin responsiveness and gene expression were checked at the end of supplementation, together with aorta nitrites. Bza supplementation delayed the appearance of hyperglycemia, abolished polydypsia and glycosuria in obese/diabetic mice without any detectable effect in lean control, except for a reduction in food intake observed in both genotypes. The improvement of glucose homeostasis was observed in db-/- mice at the expense of increased fat deposition, especially in the subcutaneous white adipose tissue (SCWAT), without sign of worsened inflammation or insulin responsiveness and with lowered circulating triglycerides and uric acid, while NO bioavailability was increased in aorta. The higher capacity of SSAO in oxidizing Bza in SCWAT, found in the obese mice, was unaltered by Bza supplementation and likely involved in the activation of glucose utilization by adipocytes. We propose that Bza oxidation in tissues, which produces hydrogen peroxide mainly in SCWAT, facilitates insulin-independent glucose utilization. Bza could be considered as a potential agent for dietary supplementation aiming at preventing diabetic complications.

Endothelial-transcytosed myeloperoxidase activates endothelial nitric oxide synthase via a phospholipase C-dependent calcium signaling pathway

During vascular inflammation, the leukocyte-derived enzyme myeloperoxidase (MPO) is transcytosed across the endothelium and into the sub-endothelial extracellular matrix, where it promotes endothelial dysfunction by catalytically consuming nitric oxide (NO) produced by endothelial NO synthase (eNOS). In the presence of chloride ions and hydrogen peroxide (H2O2), MPO forms the oxidant hypochlorous acid (HOCl). Here we examined the short-term implications of HOCl produced by endothelial-transcytosed MPO for eNOS activity. Incubation of MPO with cultured aortic endothelial cells (ECs) resulted in its transport into the sub-endothelium. Exposure of MPO-containing ECs to low micromolar concentrations of H2O2 yielded enhanced rates of H2O2 consumption that correlated with HOCl formation and increased eNOS enzyme activity. The MPO-dependent activation of eNOS occurred despite reduced cellular uptake of the eNOS substrate l-arginine, which involved a decrease in the maximal activity (Vmax), but not substrate affinity (Km), of the major endothelial l-arginine transporter, cationic amino acid transporter-1. Activation of eNOS in MPO-containing ECs exposed to H2O2 involved a rapid elevation in cytosolic calcium and increased eNOS phosphorylation at Ser-1179 and de-phosphorylation at Thr-497. These signaling events were attenuated by intracellular calcium chelation, removal of extracellular calcium and inhibition of phospholipase C. This study shows that stimulation of endothelial-transcytosed MPO activates eNOS by promoting phospholipase C-dependent calcium signaling and altered eNOS phosphorylation at Ser-1179 and Thr-497. This may constitute a compensatory signaling response of ECs aimed at maintaining eNOS activity and NO production in the face of MPO-catalyzed oxidative stress.

Myeloperoxidase: A versatile mediator of endothelial dysfunction and therapeutic target during cardiovascular disease

Myeloperoxidase (MPO) is a prominent mammalian heme peroxidase and a fundamental component of the innate immune response against microbial pathogens. In recent times, MPO has received considerable attention as a key oxidative enzyme capable of impairing the bioactivity of nitric oxide (NO) and promoting endothelial dysfunction; a clinically relevant event that manifests throughout the development of inflammatory cardiovascular disease. Increasing evidence indicates that during cardiovascular disease, MPO is released intravascularly by activated leukocytes resulting in its transport and sequestration within the vascular endothelium. At this site, MPO catalyzes various oxidative reactions that are capable of promoting vascular inflammation and impairing NO bioactivity and endothelial function. In particular, MPO catalyzes the production of the potent oxidant hypochlorous acid (HOCl) and the catalytic consumption of NO via the enzyme's NO oxidase activity. An emerging paradigm is the ability of MPO to also influence endothelial function via non-catalytic, cytokine-like activities. In this review article we discuss the implications of our increasing knowledge of the versatility of MPO's actions as a mediator of cardiovascular disease and endothelial dysfunction for the development of new pharmacological agents capable of effectively combating MPO's pathogenic activities. More specifically, we will (i) discuss the various transport mechanisms by which MPO accumulates into the endothelium of inflamed or diseased arteries, (ii) detail the clinical and basic scientific evidence identifying MPO as a significant cause of endothelial dysfunction and cardiovascular disease, (iii) provide an up-to-date coverage on the different oxidative mechanisms by which MPO can impair endothelial function during cardiovascular disease including an evaluation of the contributions of MPO-catalyzed HOCl production and NO oxidation, and (iv) outline the novel non-enzymatic mechanisms of MPO and their potential contribution to endothelial dysfunction. Finally, we deliver a detailed appraisal of the different pharmacological strategies available for targeting the catalytic and non-catalytic modes-of-action of MPO in order to protect against endothelial dysfunction in cardiovascular disease.

NADPH Oxidase Inhibition: Preclinical and Clinical Studies in Diabetic Complications

Significance: Oxidative stress plays a critical role in the development and progression of serious micro- and macrovascular complications of diabetes. Nicotinamide adenine dinucleotide phosphate oxidase (NOX)-derived reactive oxygen species (ROS) significantly contribute to oxidative stress-associated inflammatory pathways that lead to tissue damage of different organs, including the kidneys, retina, brain, nerves, and the cardiovascular system. Recent Advances: Preclinical studies, including genetic-modified mouse models or cell culture models, have revealed the role of specific NOX isoforms in different diabetic complications, and suggested them as a promising target for the treatment of these diseases. Critical Issues: In this review, we provide an overview of the role of ROS and oxidative stress in macrovascular complications, such as stroke, myocardial infarction, coronary artery disease, and peripheral vascular disease that are all mainly driven by atherosclerosis, as well as microvascular complications, such as diabetic retinopathy, nephropathy, and neuropathy. We summarize conducted genetic deletion studies of different Nox isoforms as well as pharmacological intervention studies using NOX inhibitors in the context of preclinical as well as clinical research on diabetic complications. Future Directions: We outline the isoforms that are most promising for future clinical trials in the context of micro- and macrovascular complications of diabetes.

Oxidative Stress and Microvessel Barrier Dysfunction

Clinical and experimental evidence indicate that increased vascular permeability contributes to many disease-associated vascular complications. Oxidative stress with increased production of reactive oxygen species (ROS) has been implicated in a wide variety of pathological conditions, including inflammation and many cardiovascular diseases. It is thus important to identify the role of ROS and their mechanistic significance in microvessel barrier dysfunction under pathological conditions. The role of specific ROS and their cross talk in pathological processes is complex. The mechanisms of ROS-induced increases in vascular permeability remain poorly understood. The sources of ROS in diseases have been extensively reviewed at enzyme levels. This review will instead focus on the underlying mechanisms of ROS release by leukocytes, the differentiate effects and signaling mechanisms of individual ROS on endothelial cells, pericytes and microvessel barrier function, as well as the interplay of reactive oxygen species, nitric oxide, and nitrogen species in ROS-mediated vascular barrier dysfunction. As a counter balance of excessive ROS, nuclear factor erythroid 2 related factor 2 (Nrf2), a redox-sensitive cell-protective transcription factor, will be highlighted as a potential therapeutic target for antioxidant defenses. The advantages and limitations of different experimental approaches used for the study of ROS-induced endothelial barrier function are also discussed. This article will outline the advances emerged mainly from in vivo and ex vivo studies and attempt to consolidate some of the opposing views in the field, and hence provide a better understanding of ROS-mediated microvessel barrier dysfunction and benefit the development of therapeutic strategies.

The Roles of NO and H2S in Sperm Biology: Recent Advances and New Perspectives

After being historically considered as noxious agents, nitric oxide (NO) and hydrogen sulfide (H2S) are now listed as gasotransmitters, gaseous molecules that play a key role in a variety of cellular functions. Both NO and H2S are endogenously produced, enzymatically or non-enzymatically, and interact with each other in a range of cells and tissues. In spite of the great advances achieved in recent decades in other biological systems, knowledge about H2S function and interactions with NO in sperm biology is in its infancy. Here, we aim to provide an update on the importance of these molecules in the physiology of the male gamete. Special emphasis is given to the most recent advances in the metabolism, mechanisms of action, and effects (both physiological and pathophysiological) of these gasotransmitters. This manuscript also illustrates the physiological implications of NO and H2S observed in other cell types, which might be important for sperm function. The relevance of these gasotransmitters to several signaling pathways within sperm cells highlights their potential use for the improvement and successful application of assisted reproductive technologies.

Redox control of vascular biology

Redox control is lost when the antioxidant defense system cannot remove abnormally high concentrations of signaling molecules, such as reactive oxygen species (ROS). Chronically elevated levels of ROS cause oxidative stress that may eventually lead to cancer and cardiovascular and neurodegenerative diseases. In this review, we focus on redox effects in the vascular system. We pay close attention to the subcompartments of the vascular system (endothelium, smooth muscle cell layer) and give an overview of how redox changes influence those different compartments. We also review the core aspects of redox biology, cardiovascular physiology, and pathophysiology. Moreover, the topic-specific knowledgebase DES-RedoxVasc was used to develop two case studies, one focused on endothelial cells and the other on the vascular smooth muscle cells, as a starting point to possibly extend our knowledge of redox control in vascular biology.

Redox Regulation of the Microcirculation

The microcirculation maintains tissue homeostasis through local regulation of blood flow and oxygen delivery. Perturbations in microvascular function are characteristic of several diseases and may be early indicators of pathological changes in the cardiovascular system and in parenchymal tissue function. These changes are often mediated by various reactive oxygen species and linked to disruptions in pathways such as vasodilation or angiogenesis. This overview compiles recent advances relating to redox regulation of the microcirculation by adopting both cellular and functional perspectives. Findings from a variety of vascular beds and models are integrated to describe common effects of different reactive species on microvascular function. Gaps in understanding and areas for further research are outlined. © 2020 American Physiological Society. Compr Physiol 10:229-260, 2020.

Crosstalk Between Mitochondrial Hyperacetylation and Oxidative Stress in Vascular Dysfunction and Hypertension

Significance: Vascular dysfunction plays a key role in the development of arteriosclerosis, heart disease, and hypertension, which causes one-third of deaths worldwide. Vascular oxidative stress and metabolic disorders contribute to vascular dysfunction, leading to impaired vasorelaxation, vascular hypertrophy, fibrosis, and aortic stiffening. Mitochondria are critical in the regulation of metabolic and antioxidant functions; therefore, mitochondria-targeted treatments could be beneficial. Recent Advances: Vascular dysfunction is crucial in hypertension pathophysiology and exhibits bidirectional relationship. Metabolic disorders and oxidative stress contribute to the pathogenesis of vascular dysfunction and hypertension, which are associated with mitochondrial impairment and hyperacetylation. Mitochondrial deacetylase Sirtuin 3 (Sirt3) is critical in the regulation of metabolic and antioxidant functions. Clinical studies show that cardiovascular disease risk factors reduce Sirt3 level and Sirt3 declines with age, paralleling the increased incidence of cardiovascular disease and hypertension. An imbalance between mitochondrial acetylation and reduced Sirt3 activity contributes to mitochondrial dysfunction and oxidative stress. We propose that mitochondrial hyperacetylation drives a vicious cycle between metabolic disorders and mitochondrial oxidative stress, promoting vascular dysfunction and hypertension. Critical Issues: The mechanisms of mitochondrial dysfunction are still obscure in human hypertension. Mitochondrial hyperacetylation and oxidative stress contribute to mitochondrial dysfunction; however, regulation of mitochondrial acetylation, the role of GCN5L1 (acetyl-CoA-binding protein promoting acetyltransferase protein acetylation) acetyltransferase, Sirt3 deacetylase, and acetylation of specific proteins require further investigations. Future Directions: There is an urgent need to define molecular mechanisms and the pathophysiological role of mitochondrial hyperacetylation, identify novel pharmacological targets, and develop therapeutic approaches to reduce this phenomenon.

DHEA Treatment Effects on Redox Environment in Skeletal Muscle of Young and Aged Healthy Rats

Background:

Dehydroepiandrosterone (DHEA) is an important precursor of active ster-oid hormone, produced abundantly by the adrenal cortex with an age-dependent pattern.

Objective:

We investigated whether chronic DHEA administration impacts on redox status and on Akt protein activation in skeletal muscle during the aging process (3 and 24 months-old rats).

Methods:

Rats received one weekly dose/5 weeks of DHEA (10 mg/kg) or vehicle. Gastrocnemius muscle was removed to evaluate glutathione system, hydrogen peroxide, antioxidant enzymes, and expression of Akt kinase protein.

Results:

In the 3-months-old rats DHEA induced an increase in hydrogen peroxide when compared both to its control (276%) and the 24-months-old DHEA group (485%). Moreover, in the 24-months-old rats DHEA caused an increase in GSSG (41 and 28%), a decrease in reduced-GSH (55 and 51%), and a more oxidized redox status (reduction in GSH/GSSG ratio, 47 and 65%) when compared to 3-month-old DHEA and to 24-months-old control groups, respectively. Both older groups had increased G6PDH (2.7 fold) and GST (1.7 fold) activities when compared to younger groups, independently of any DHEA treatment. However, there was no modulation of Akt protein (phosphorylated/total isoform).

Conclusion:

The results show that chronic DHEA administration to 3 and 24-months-old rats may not present positive effects regarding the redox environment in skeletal muscle without modulation of pro-survival Akt kinase. Due to the large-scale self-administration of DHEA as an “anti-aging” die-tary supplement, it is crucial to investigate its molecular mechanisms over oxidative stress-induced related diseases.

Reactive Oxygen Comes of Age: Mechanism-Based Therapy of Diabetic End-Organ Damage

Reactive oxygen species (ROS) have been mainly viewed as unwanted by-products of cellular metabolism, oxidative stress, a sign of a cellular redox imbalance, and potential disease mechanisms, such as in diabetes mellitus (DM). Antioxidant therapies, however, have failed to provide clinical benefit. This paradox can be explained by recent discoveries that ROS have mainly essential signaling and metabolic functions and evolutionally conserved physiological enzymatic sources. Disease can occur when ROS accumulate in nonphysiological concentrations, locations, or forms. By focusing on disease-relevant sources and targets of ROS, and leaving ROS physiology intact, precise therapeutic interventions are now possible and are entering clinical trials. Their outcomes are likely to profoundly change our concepts of ROS in DM and in medicine in general.

Human umbilical artery endothelial cells from Large-for-Gestational-Age newborn have increased antioxidant efficiency and gene expression

Obesity is a public health problem worldwide, and especially in women in reproductive age where more than one in three have obesity. Maternal obesity is associated with an increased maternal, placental, and newborn oxidative stress, which has been proposed as a central factor in vascular dysfunction in large-for-gestational-age (LGA) newborn. However, cellular and molecular mechanisms behind this effect have not been elucidated. Untreated human umbilical artery endothelial cells (HUAEC) from LGA (LGA-HUAEC) presented higher O₂ ^- levels, superoxide dismutase activity and heme oxygenase 1 messenger RNA (mRNA) levels, paralleled by reduced GSH:GSSG ratio and NRF2 mRNA levels. In response to an oxidative challenge (hydrogen peroxide), only HUAEC from LGA exhibited an enhanced Glutathione Peroxidase 1 (GPX1) expression, as well as a more efficient antioxidant machinery measured by the biosensor probe, HyPer. An open state of chromatin in the TSS region of GPX1 in LGA-HUAEC was evidenced by the DNase-HS assay. Altogether, our data indicate that LGA-HUAEC have an altered cellular and molecular antioxidant system. We propose that a chronic pro-oxidant intrauterine milieu, as evidenced in pregestational obesity, could induce a more efficient antioxidant system in fetal vascular cells, which could be maintained by epigenetic mechanism during postnatal life.

Engineered Nanoparticles for Effective Redox Signaling During Angiogenic and Antiangiogenic Therapy

SIGNIFICANCE

Redox signaling plays a vital role in regulating various cellular signaling pathways and disease biology. Recently, nanomedicine (application of nanotechnology in biology and medicine) has been demonstrated to regulate angiogenesis through redox signaling. A complete understanding of redox signaling pathways influenced angiogenesis/antiangiogenesis triggered by therapeutic nanoparticles is extensively reviewed in this article. Recent Advances: In recent times, nanomedicines are regarded as the Trojan horses that could be employed for successful drug delivery, gene delivery, peptide delivery, disease diagnosis, and others, conquering barriers associated with conventional theranostic approaches.

CRITICAL ISSUES

Physiological angiogenesis is a tightly regulated process maintaining a balance between proangiogenic and antiangiogenic factors. The redox signaling is one of the main factors that contribute to this physiological balance. An aberrant redox signaling cascade can be caused by several exogenous and endogenous factors and leads to reduced or augmented angiogenesis that ultimately results in several disease conditions.

FUTURE DIRECTIONS

Redox signaling-based nanomedicine approach has emerged as a new platform for angiogenesis-related disease therapy, where nanoparticles promote angiogenesis via controlled reactive oxygen species (ROS) production and antiangiogenesis by triggering excessive ROS formation. Recently, investigators have identified different efficient nano-candidates, which modulate angiogenesis by controlling intracellular redox molecules. Considering the importance of angiogenesis in health care a thorough understanding of nanomedicine-regulated redox signaling would inspire researchers to design and develop more novel nanomaterials that could be used as an alternative strategy for the treatment of various diseases, where angiogenesis plays a vital role.

Sodium butyrate ameliorates lipopolysaccharide-induced cow mammary epithelial cells from oxidative stress damage and apoptosis

This study investigated the molecular mechanism by which sodium butyrate (NaB) causes oxidative stress damage induced by lipopolysaccharide (LPS) on cow mammary epithelial cells (MAC-T). We found that NaB significantly increased the activities of antioxidant enzymes, including superoxide dismutase, glutathione peroxidase, catalase, peroxidase, and total antioxidant capacity and decreased the reactive oxygen species production in LPS-induced MAC-T cells. NaB attenuated protein damage and reduced apoptosis in LPS-induced MAC-T cells. The messenger RNA (mRNA) levels of caspase-3, caspase-9, and Bax decreased, while the Bcl-2 mRNA level increased in LPS-induced MAC-T cells treated with NaB. Our results showed that NaB treatment increased the phosphoinositide 3-kinase (PI3K) and phospho-AKT (P-AKT) protein levels, whereas it decreased the Bax, caspase-3, and caspase-9 protein levels in LPS-induced MAC-T cells. However, the increase in PI3K and P-AKT protein levels and the decrease in Bax, caspase-3, and caspase-9 protein levels induced by NaB treatment were reversed when the cells were pretreated with LY294002 (PI3K inhibitor). These results indicate that NaB ameliorates LPS-induced oxidative damage by increasing antioxidative enzyme activities and ameliorating protein damage in MAC-T cells. In addition, NaB decreased apoptosis by inhibiting caspase-3, caspase-9, and Bax protein levels, and this action was mainly achieved via activation of the PI3K/AKT signaling pathways in LPS-induced MAC-T cells. These results provide substantial information for NaB as a chemical supplement to treat oxidative stress and its related diseases in ruminants.

Pravastatin attenuates the action of the ETS domain-containing protein ELK1 to prevent atherosclerosis in apolipoprotein E-knockout mice via modulation of extracellular signal-regulated kinase 1/2 signal pathway

Oxidative stress plays an important role in atherosclerosis, a vascular disease with high morbidity and mortality. The ETS domain-containing protein ELK1 is an oxidative stress-sensitive factor modulated by the extracellular signal-regulated kinase (ERK) 1/2 pathway. However, the role of ELK1 in the prevention of atherosclerosis by pravastatin remains unclear. In the present study, male apolipoprotein E-knockout (apoE^-/- ) mice fed a diet containing 1.25% cholesterol (w/w) were divided into two groups, one treated with pravastatin (80 mg/kg, 2-2.4 mg/mouse per day) for 8 weeks and the other not. Male C57BL/6J mice fed with a normal diet were used as a control group. Human umbilical vein endothelial cells (HUVEC) were cultured and treated with pravastatin (10 μmol/L) for 18 hours before testing for the presence or absence of 100 μmol/L H₂ O₂ (24 hours). Examination of pathological sections from mice aortas revealed that pravastatin treatment almost prevented atherosclerotic plaque formation. Pravastatin also inhibited increases in serum and aortic levels of oxidized low-density lipoprotein and aortic malondialdehyde levels and decreases in aortic reduced glutathione, and the activities of superoxide dismutase, catalase and glutathione peroxidase. H₂ O₂ -induced increases in reactive oxygen species in HUVECs were reversed by pravastatin by 48%. Pravastatin blocked the phosphorylation of ELK1 and ERK1/2 proteins and reduced mRNA levels of early growth response 1, a known atherogenic transcription factor upregulated by the ROS/ERK/ELK1 pathway, in mice. In conclusion, pravastatin attenuates the action of ELK1 induced by oxidative stress to prevent atherosclerosis, which is dependent partly on modulation of ERK1/2 signalling.

Redox regulation of gasotransmission in the vascular system: A focus on angiogenesis

Reactive oxygen species have emerged as key participants in a broad range of physiological and pathophysiological processes, not least within the vascular system. Diverse cellular functions which have been attributed to some of these pro-oxidants within the vasculature include the regulation of blood pressure, neovascularisation and vascular inflammation. We here highlight the emerging roles of the enzymatically-generated reaction oxygen species, O₂^- and H₂O₂, in the regulation of the functions of the gaseous signalling molecules: nitric oxide (NO), carbon monoxide (CO), and hydrogen sulphide (H₂S). These gasotransmitters are produced on demand from distinct enzymatic sources and in recent years it has become apparent that they are capable of mediating a number of homeostatic processes within the cardiovascular system including enhanced vasodilation, angiogenesis, wound healing and improved cardiac function following myocardial infarction. In common with O₂^- and/or H₂O₂ they signal by altering the functions of target proteins, either by the covalent modification of thiol groups or by direct binding to metal centres within metalloproteins, most notably haem proteins. The regulation of the enzymes which generate NO, CO and H₂S have been shown to be influenced at both the transcriptional and post-translational levels by redox-dependent mechanisms, while the activity and bioavailability of the gasotransmitters themselves are also subject to oxidative modification. Within vascular cells, the family of nicotinamide adenine dinucleotide phosphate oxidases (NAPDH oxidases/Noxs) have emerged as functionally significant sources of regulated O₂^- and H₂O₂ production and accordingly, direct associations between Nox-generated oxidants and the functions of specific gasotransmitters are beginning to be identified. This review focuses on the current knowledge of the redox-dependent mechanisms which regulate the generation and activity of these gases, with particular reference to their roles in angiogenesis.

Oxidative Stress and Hypertensive Diseases

It has become clear that reactive oxygen species (ROS) contribute to the development of hypertension via myriad effects. ROS are essential for normal cell function; however, they mediate pathologic changes in the brain, the kidney, and blood vessels that contribute to the genesis of chronic hypertension. There is also emerging evidence that ROS contribute to immune activation in hypertension. This article discusses these events and how they coordinate to contribute to hypertension and its consequent end-organ damage.

Role of eNOS- and NOX-containing microparticles in endothelial dysfunction in patients with obesity

OBJECTIVE

To explore the pathophysiological profile of patients who have obesity and to investigate the potential role of circulating microparticles (MPs) in endothelial dysfunction in patients who have obesity.

METHODS

The inflammatory and oxidative status and the cutaneous microvascular blood flow were characterized in 69 patients with android obesity and 46 subjects with normal weight (controls) by using laser Doppler flowmetry. Circulating MP levels were measured by flow cytometry, and endothelial nitric oxide synthase (eNOS) and NADPH oxidase (NOX) expression in MPs was investigated by Western blotting. MP effect on vascular reactivity was assessed in rat aorta rings.

RESULTS

Patients with obesity showed endothelial dysfunction, hyperglycemia, inflammation, and oxidative stress. In controls, low MP levels were positively correlated with normal microvascular function. Western blot analysis revealed reduced eNOS and increased NOX4D expression in MPs from subjects with obesity compared with controls. However, this was not correlated with endothelial dysfunction parameters and did not impair ex vivo endothelium-dependent vasodilation.

CONCLUSIONS

These results suggest that MPs do not contribute directly to endothelial dysfunction associated with obesity. Conversely, eNOS- and NOX-containing MPs could be involved in the compensatory mechanism of vascular endothelial cells to counteract the pathologic mechanisms underlying endothelial dysfunction.

Pretreatment with Astragaloside IV protects human umbilical vein endothelial cells from hydrogen peroxide induced oxidative stress and cell dysfunction via inhibiting eNOS uncoupling and NADPH oxidase - ROS - NF-κB pathway

Endothelial cell injury caused by reactive oxygen species (ROS) plays a critical role in the pathogenesis of cardiovascular disorders. Astragaloside IV (AsIV) possesses potent antioxidant properties against oxidative stress through undefined mechanism(s). We sought to investigate whether AsIV protects human umbilical vein endothelial cells (HUVECs) from hydrogen peroxide (H₂O₂) induced oxidative stress focusing on eNOS uncoupling and the NADPH oxidase - ROS - NF-κB pathway. Compared with HUVECs incubated with H₂O₂ alone, pretreatment with AsIV significantly increased the viability of HUVECs, which was accompanied with apparent increase in nitric oxide (NO) production and decrease in intracellular superoxide anion production. Furthermore, pretreatment with AsIV increased endothelial nitric oxide synthase (eNOS) dimer/monomer ratio and its critical cofactor tetrahydrobiopterin (BH₄) content, decreased Nox4 protein expression (the most abundant Nox isoform in HUVECs), inhibited translocation of NF-κB p65 subunit into nuclear fraction while enhanced the protein expression of IκB-α (the inhibitor of NF-κB p65), reduced the levels of IL-1β, IL-6, and TNF-α in HUVECs medium, and decreased iNOS protein expression. These results suggest that AsIV may protect HUVECs from H₂O₂-induced oxidative stress via inhibiting NADPH oxidase - ROS - NF-κB pathway and eNOS uncoupling.

In vitro fructose exposure overactivates NADPH oxidase and causes oxidative stress in the isolated rat aorta

Fructose acutely interferes with cardiovascular function in humans and in animals, but the mechanisms remain unclear. Thus, we tested whether fructose can affect endothelial function without the interference of its metabolic effect by exposing the rat aorta to a high fructose concentration and then evaluate the vascular responses to vasoactive agents. We observed that fructose exposure causes overactivation of NADPH oxidase, which enhances superoxide anion production and increases NO degradation. Additionally, the enhanced vasoconstrictor action of hydrogen peroxide might exacerbate contractile responses. This vasoactive imbalance might be the key role by which fructose induces vascular dysfunction.

Graphene Oxides Show Angiogenic Properties

Angiogenesis, a process resulting in the formation of new capillaries from the pre-existing vasculature plays vital role for the development of therapeutic approaches for cancer, atherosclerosis, wound healing, and cardiovascular diseases. In this report, the synthesis, characterization, and angiogenic properties of graphene oxide (GO) and reduced graphene oxide (rGO) have been demonstrated, observed through several in vitro and in vivo angiogenesis assays. The results here demonstrate that the intracellular formation of reactive oxygen species and reactive nitrogen species as well as activation of phospho-eNOS and phospho-Akt might be the plausible mechanisms for GO and rGO induced angiogenesis. The results altogether suggest the possibilities for the development of alternative angiogenic therapeutic approach for the treatment of cardiovascular related diseases where angiogenesis plays a significant role.

Csk-Induced Phosphorylation of Src at Tyrosine 530 is Essential for H2O2-Mediated Suppression of ERK1/2 in Human Umbilical Vein Endothelial Cells

Mitogen-activated protein kinases (MAPKs) are key signal transducers involved in various cellular events such as growth, proliferation, and differentiation. Previous studies have reported that H₂O₂ leads to phosphorylation of extracellular signal-regulated kinase (ERK), one of the MAPKs in endothelial cells. The current study shows that H₂O₂ suppressed ERK1/2 activation and phosphorylation at specific concentrations and times in human umbilical vein endothelial cells but not in immortalized mouse aortic endothelial cells or human astrocytoma cell line CRT-MG. Phosphorylation of other MAPK family members (i.e., p38 and JNK) was not suppressed by H₂O₂. The decrease in ERK1/2 phosphorylation induced by H₂O₂ was inversely correlated with the level of phosphorylation of Src tyrosine 530. Using siRNA, it was found that H₂O₂-induced suppression of ERK1/2 was dependent on Csk. Physiological laminar flow abrogated, but oscillatory flow did not affect, the H₂O₂-induced suppression of ERK1/2 phosphorylation. In conclusion, H₂O₂-induced Csk translocation to the plasma membrane leads to phosphorylation of Src at the tyrosine 530 residue resulting in a reduction of ERK1/2 phosphorylation. Physiological laminar flow abrogates this effect of H₂O₂ by inducing phosphorylation of Src tyrosine 419. These findings broaden our understanding of signal transduction mechanisms in the endothelial cells against oxidative stress.

Investigation of molecular mechanisms and regulatory pathways of pro-angiogenic nanorods

Angiogenesis, a process involving the growth of new blood vessels from the pre-existing vasculature, plays a crucial role in various pathophysiological conditions. We have previously demonstrated that europium hydroxide [Eu(III)(OH)3] nanorods (EHNs) exhibit pro-angiogenic properties through the generation of reactive oxygen species (ROS) and mitogen activated protein kinase (MAPK) activation. Considering the enormous implication of angiogenesis in cardiovascular diseases (CVDs) and cancer, it is essential to understand in-depth molecular mechanisms and signaling pathways in order to develop the most efficient and effective alternative treatment strategy for CVDs. However, the exact underlying mechanism and cascade signaling pathways behind the pro-angiogenic properties exhibited by EHNs still remain unclear. Herein, we report for the first time that the hydrogen peroxide (H2O2), a redox signaling molecule, generated by these EHNs activates the endothelial nitric oxide synthase (eNOS) that promotes the nitric oxide (NO) production in a PI3K (phosphoinositide 3-kinase)/Akt dependent manner, eventually triggering angiogenesis. We intensely believe that the investigation and understanding of the in-depth molecular mechanism and signaling pathways of EHNs induced angiogenesis will help us in developing an effective alternative treatment strategy for cardiovascular related and ischemic diseases where angiogenesis plays an important role.

Low-dose estrogen is as effective as high-dose treatment in rats with postmenopausal hypertension

: This study was conducted to test the hypothesis that 17β-estradiol therapy improves redox balance by decreasing reactive oxygen species production and increasing nitric oxide (NO) bioavailability, favoring Akt pathway activation and resulting in a better autonomic vascular control. Ovariectomized female Wistar rats were divided into 4 groups: (1) vehicle (VL) and animals treated with a pellet of 17β-estradiol for 21 days; (2) low dose (LE; 0.05 mg); (3) medium dose (ME; 0.2 mg); and (4) high dose (HE; 0.5 mg). Arterial pressure and its sympathetic nervous system modulation were evaluated by spectral analysis. Nitric oxide synthase and NADPH oxidase (Nox) activities, H2O2 concentration, redox status (GSH/GSSG), protein expression of Trx-1 and p-Akt/Akt were evaluated in the aorta, whereas NO metabolites were measured in the serum. Estrogen-treated groups showed a significant decrease in arterial pressure and sympathetic vascular drive. Redox status was significantly improved and NADPH oxidase and H2O2 were decreased in all estrogen-treated groups. Estrogen also induced an enhancement in NO metabolites, nitric oxide synthase activity, and Akt phosphorylation. This study demonstrated that estrogen treatment to ovariectomized rats induced cardioprotection, which was evidenced by reduced blood pressure variability and vascular sympathetic drive. These effects were associated with an improved redox balance and Akt activation, resulting in an enhanced NO bioavailability.

Phenylephrine activates eNOS Ser 1177 phosphorylation and nitric oxide signaling in renal hypertensive rat aorta

The endothelial nitric oxide synthase (eNOS) plays an important role in the control of the vascular tone. This work aimed to evaluate the role of an α1-adrenoceptor agonist phenylephrine (PE) on eNOS activity and downstream signaling pathway activation in normotensive (2K) and renal hypertensive (2K-1C) intact-endothelium rat aortas. Concentration-effect curves were performed for PE in intact-endothelium aortas from 2K and 2K-1C rats, in the absence of or in the presence of NOS or soluble guanylyl cyclase (sGC) inhibitor. Intact endothelium aortas were stimulated with PE in organ chambers and eNOS Ser(1177)/Thr(495) phosphorylation expression was evaluated by western blot. Nitric Oxide (NO) production was evaluated in isolated endothelial cells from 2K and 2K-1C rat aortas by flow-cytometry using NO selective fluorescent probe, DAF-2DA. The sGC activity/expression was also evaluated. PE-induced contractile response is lower in 2K-1C than in 2K intact-endothelium rat aorta. This is due to higher eNOS Ser(1177) phosphorylation in 2K-1C, which induces the eNOS overactivation. It was abolished by NOS or sGC inhibition. Phenylephrine reduces NO production in 2K as compared to the basal level, but it is not modified in 2K-1C. In PE-stimulated endothelial cells, the NO production is higher in 2K-1C than in 2K. Phenylephrine induces higher cGMP production in 2K-1C than in 2K, despite the lower expression of sGC in 2K-1C. Our results suggest that alpha1-adrenoceptor activation contributes to the increased activity of the enzyme eNOS by Ser(1177) phosphorylation in 2K-1C intact-endothelium aorta, which consequently decreases PE-induced contractile response.

Salidroside stimulates mitochondrial biogenesis and protects against H₂O₂-induced endothelial dysfunction

Salidroside (SAL) is an active component of Rhodiola rosea with documented antioxidative properties. The purpose of this study is to explore the mechanism of the protective effect of SAL on hydrogen peroxide- (H₂O₂-) induced endothelial dysfunction. Pretreatment of the human umbilical vein endothelial cells (HUVECs) with SAL significantly reduced the cytotoxicity brought by H₂O₂. Functional studies on the rat aortas found that SAL rescued the endothelium-dependent relaxation and reduced superoxide anion (O2^∙−) production induced by H₂O₂. Meanwhile, SAL pretreatment inhibited H₂O₂-induced nitric oxide (NO) production. The underlying mechanisms involve the inhibition of H₂O₂-induced activation of endothelial nitric oxide synthase (eNOS), adenosine monophosphate-activated protein kinase (AMPK), and Akt, as well as the redox sensitive transcription factor, NF-kappa B (NF-κB). SAL also increased mitochondrial mass and upregulated the mitochondrial biogenesis factors, peroxisome proliferator-activated receptor gamma-coactivator-1alpha (PGC-1α), and mitochondrial transcription factor A (TFAM) in the endothelial cells. H₂O₂-induced mitochondrial dysfunction, as demonstrated by reduced mitochondrial membrane potential (Δψm) and ATP production, was rescued by SAL pretreatment. Taken together, these findings implicate that SAL could protect endothelium against H₂O₂-induced injury via promoting mitochondrial biogenesis and function, thus preventing the overactivation of oxidative stress-related downstream signaling pathways.

Catalase influence in the regulation of coronary resistance by estrogen: joint action of nitric oxide and hydrogen peroxide

We tested the influence of estrogen on coronary resistance regulation by modulating nitric oxide (NO) and hydrogen peroxide (H2O2) levels in female rats. For this, estrogen levels were manipulated and the hearts were immediately excised and perfused at a constant flow using a Langendorff's apparatus. Higher estrogen levels were associated with a lower coronary resistance, increased nitric oxide bioavailability, and higher levels of H2O2. When oxide nitric synthase blockade by L-NAME was performed, no significant changes were found in coronary resistance of ovariectomized rats. Additionally, we found an inverse association between NO levels and catalase activity. Taken together, our data suggest that, in the absence of estrogen influence and, therefore, reduced NO bioavailability, coronary resistance regulation seems to be more dependent on the H2O2 that is maintained at low levels by increased catalase activity.

Nitrooleate mediates nitric oxide synthase activation in endothelial cells

Nitrated lipids such as nitrooleate (OLA-NO2) can act as endogenous peroxisome proliferator-activated receptor gamma (PPARγ) ligands to exert vascular protective effects. However, the molecular mechanisms regarding nitric oxide (NO) production and its regulation are not fully defined in the vasculature. Here, we show that OLA-NO2 increased endothelial NO release by modulating activation of endothelial nitric oxide synthase (eNOS) in endothelial cells. Treatment with OLA-NO2 (3 μM) increased NO release in a time-dependent manner. OLA-NO2 decreased protein expression of eNOS and caveolin-1 (Cav-1) but increased heat shock protein 90 (Hsp90) expression. Immunoprecipitation analysis confirmed that OLA-NO2 replaced eNOS/Cav-1 with eNOS/Hsp90 interaction, resulting in increasing eNOS activity. OLA-NO2 also induced eNOS phosphorylation at Ser633 and Ser1177 and eNOS dephosphorylation at Ser113 and Thr495. In addition, OLA-NO2 induced phosphorylation of Akt and extracellular signal-regulated protein kinase (ERK1/2), which might contribute to eNOS activation. Collectively, these results substantiate a new functional role for nitrated fatty acid, demonstrating that OLA-NO2 exerts vascular protective effects by increasing NO bioavailability through eNOS phosphorylation/dephosphorylation and interaction with associated proteins such as Hsp90 and Cav-1.

Hydrogen peroxide signaling in vascular endothelial cells

Redox signaling is implicated in different physiological and pathological events in the vasculature. Among the different reactive oxygen species, hydrogen peroxide (H₂O₂) is a very good candidate to perform functions as an intracellular messenger in the regulation of several biological events.

In this review, we summarize the main physiological sources of H₂O₂ in the endothelium and the molecular mechanisms by which it is able to act as a signaling mediator in the vasculature.

Diversity in mechanisms of endothelium-dependent vasodilation in health and disease

Small arterioles (40-150 μm) contribute to the majority of vascular resistance within organs and tissues. Under resting conditions, the basal tone of these vessels is determined by a delicate balance between vasodilator and vasoconstrictor influences. Cardiovascular homeostasis and regional tissue perfusion is largely a function of the ability of these small blood vessels to constrict or dilate in response to the changing metabolic demands of specific tissues. The endothelial cell layer of these microvessels is a key modulator of vasodilation through the synthesis and release of vasoactive substances. Beyond their vasomotor properties, these compounds importantly modulate vascular cell proliferation, inflammation, and thrombosis. Thus, the balance between local regulation of vascular tone and vascular pathophysiology can vary depending upon which factors are released from the endothelium. This review will focus on the dynamic nature of the endothelial released dilator factors depending on species, anatomic site, and presence of disease, with a focus on the human coronary microcirculation. Knowledge how endothelial signaling changes with disease may provide insights into the early stages of developing vascular inflammation and atherosclerosis, or related vascular pathologies.

A1 adenosine receptor negatively modulates coronary reactive hyperemia via counteracting A2A-mediated H2O2 production and KATP opening in isolated mouse hearts

We previously demonstrated that A2A, but not A2B, adenosine receptors (ARs) mediate coronary reactive hyperemia (RH), possibly by producing H2O2 and, subsequently, opening ATP-dependent K(+) (KATP) channels in coronary smooth muscle cells. In this study, A1 AR knockout (KO), A3 AR KO, and A1 and A3 AR double-KO (A1/A3 DKO) mice were used to investigate the roles and mechanisms of A1 and A3 ARs in modulation of coronary RH. Coronary flow of isolated hearts was measured using the Langendorff system. A1 KO and A1/A3 DKO, but not A3 KO, mice showed a higher flow debt repayment [~30% more than wild-type (WT) mice, P < 0.05] following a 15-s occlusion. SCH-58261 (a selective A2A AR antagonist, 1 μM) eliminated the augmented RH, suggesting the involvement of enhanced A2A AR-mediated signaling in A1 KO mice. In isolated coronary arteries, immunohistochemistry showed an upregulation of A2A AR (1.6 ± 0.2 times that of WT mice, P < 0.05) and a higher magnitude of adenosine-induced H2O2 production in A1 KO mice (1.8 ± 0.3 times that of WT mice, P < 0.05), which was blocked by SCH-58261. Catalase (2,500 U/ml) and glibenclamide (a KATP channel blocker, 5 μM), but not N(G)-nitro-l-arginine methyl ester, also abolished the enhanced RH in A1 KO mice. Our data suggest that A1, but not A3, AR counteracts the A2A AR-mediated CF increase and that deletion of A1 AR results in upregulation of A2A AR and/or removal of the negative modulatory effect of A1 AR, thus leading to an enhanced A2A AR-mediated H2O2 production, KATP channel opening, and coronary vasodilation during RH. This is the first report implying that A1 AR has a role in coronary RH.

Endothelial nitric oxide synthase phosphorylation at Threonine 495 and mitochondrial reactive oxygen species formation in response to a high H₂O₂ concentration

BACKGROUND

Hydrogen peroxide (H₂O₂) is produced in vessels during ischemia/reperfusion and during inflammation, both leading to vascular dysfunction. We investigated cellular pathways involved in endothelial nitric oxide synthase (eNOS) phosphorylation at Threonine 495 (Thr(495)) in human umbilical vein endothelial cells (HUVECs) exposed to H₂O₂.

METHODS

HUVECs were exposed to 400 μM H₂O₂ for 30 min. Phosphorylation at Thr(495) was assessed by Western blotting and reactive oxygen species (ROS) monitored by flow cytometry. Protein kinase C (PKC) pathways were investigated by pretreatment with PKC-β inhibitor ruboxistaurin or pan-PKC inhibitor GF109203X. In addition, we investigated ROCK and ERK pathways by MEKK1/2 inhibitor U0126 and ROCK inhibitor Y27632.

RESULTS

H₂O₂ increased eNOS phosphorylation at Thr(495) (to 176% vs. control (100%), p < 0.001) along with increased mitochondrial ROS formation (from 19.7 to 45.3%, p < 0.01). This rise in phosphorylation could be prevented by U0126 and Y27632 in a dose-dependent manner, but did not result in lowered mitochondrial ROS formation. Conversely, addition of the antioxidant N-acetyl-L-cysteine only prevented mitochondrial ROS formation but did not prevent phosphorylation of eNOS Thr(495).

CONCLUSION

H₂O₂-mediated phosphorylation of eNOS Thr(495) is mediated by ROCK and ERK activity, but not by PKC, and is uncoupled from mitochondrial ROS signaling. Furthermore, ERK inhibition increased mitochondrial ROS formation.

Impaired vasomotor function induced by the combination of hypertension and hypercholesterolemia

Although it is well known that endothelial function is compromised in the presence of either hypertension (HTN) or hypercholesterolemia (HCh), less is known about whether and how the combination of these risk factors (HTN+HCh) results in impaired endothelium-dependent dilation (EDD). The aims of this study were to evaluate the influence of HTN+HCh on vasomotor function and to identify the mechanisms that underlie the altered vascular reactivity elicited by HTN+HCh. Endothelium-dependent and -independent vasomotor responses of aortic vessels were studied in mice with diet-induced HCh and/or HTN induced by chronic administration of either angiotensin II (AngII) or deoxycorticosterone acetate-salt. HTN+HCh elicited an impairment of EDD that appeared between each risk factor alone. Incubation with catalase resulted in more severe EDD impairment. Each risk factor enhanced vascular H₂O₂ production, but a larger response was noted with HTN+HCh. An attenuated EDD was not observed in AngII type 1a receptor deficient (AT1r(-/-)) mice, but AT1r(-/-) bone marrow chimeras exhibited more profound impairment compared with wild-type. HTN+HCh does not exert an additive effect of vasomotor dysfunction compared with either risk factor alone, and both H₂O₂ and blood cell-associated AT1r contribute to the impaired EDD responses in mice with HTN+HCh.

Oxidative stress in atrial fibrillation: an emerging role of NADPH oxidase

Atrial fibrillation (AF) is the most common cardiac arrhythmia. Patients with AF have up to seven-fold higher risk of suffering from ischemic stroke. Better understanding of etiologies of AF and its thromboembolic complications are required for improved patient care, as current anti-arrhythmic therapies have limited efficacy and off target effects. Accumulating evidence has implicated a potential role of oxidative stress in the pathogenesis of AF. Excessive production of reactive oxygen species (ROS) is likely involved in the structural and electrical remodeling of the heart, contributing to fibrosis and thrombosis. In particular, NADPH oxidase (NOX) has emerged as a potential enzymatic source for ROS production in AF based on growing evidence from clinical and animal studies. Indeed, NOX can be activated by known upstream triggers of AF such as angiotensin II and atrial stretch. In addition, treatments such as statins, antioxidants, ACEI or AT1RB have been shown to prevent post-operative AF; among which ACEI/AT1RB and statins can attenuate NOX activity. On the other hand, detailed molecular mechanisms by which specific NOX isoform(s) are involved in the pathogenesis of AF and the extent to which activation of NOX plays a causal role in AF development remains to be determined. The current review discusses causes and consequences of oxidative stress in AF with a special focus on the emerging role of NOX pathways.

Hypoxia-augmented constriction of deep femoral artery mediated by inhibition of eNOS in smooth muscle

In contrast to the conventional belief that systemic arteries dilate under hypoxia, we found that α-adrenergic contraction of rat deep femoral artery (DFA) is largely augmented by hypoxia (HVCDFA) while hypoxia (3% Po2) alone had no effect. HVCDFA was consistently observed in both endothelium-intact and -denuded vessels with partial pretone by phenylephrine (PhE) or by other conditions (e.g., K+ channel blocker). Patch-clamp study showed no change in the membrane conductance of DFA myocytes by hypoxia. The RhoA-kinase inhibitor Y27632 attenuated HVCDFA. The nitric oxide synthase inhibitor [nitro-l-arginine methyl ester (l-NAME)] and soluble guanylate cyclase inhibitor [oxadiazole quinoxalin (ODQ)] strongly augmented the PhE-pretone, while neither of the agents had effect without pretone. NADPH oxidase type 4 (NOX4) inhibitors (diphenylene iodonium and plumbagin) also potentiated PhE-pretone, which was reversed by NO donor. No additive HVCDFA was observed under the pretreatment with l-NAME, ODQ, or plumbagin. Western blot and immunohistochemistry analysis showed that both NOX4 and endothelial nitric oxide synthase (eNOS) are expressed in smooth muscle layer of DFA. Various mitochondria inhibitors (rotenone, myxothiazol, and cyanide) prevented HVCDFA. From the pharmacological data, as a mechanism for HVCDFA, we suggest hypoxic inhibition of eNOS in myocytes. The putative role of NOX4 and mitochondria requires further investigation. The HVCDFA may prevent imbalance between cardiac output and skeletal blood flow under emergent hypoxia combined with increased sympathetic tone.

Contribution of oxidative stress to endothelial dysfunction in hypertension

Endothelial dysfunction is the hallmark of hypertension, which is a multifactorial disorder. In the cardiovascular system reactive oxygen species play a pivotal role in controlling the endothelial function and vascular tone. Physiologically, the endothelium-derived relaxing factors (EDRFs) and endothelium-derived contractile factors (EDCFs) that have functions on the vascular smooth muscle cells. The relaxation induced by the EDRFs nitric oxide (NO), prostacyclin, and the endothelium-derived hyperpolarization factor (EDHF) could be impaired in hypertension. The impaired ability of endothelial cells to release NO along with enhanced EDCFs production has been described to contribute to the endothelium dysfunction, which appears to lead to several cardiovascular diseases. The present review discusses the role of oxidative stress, vascular endothelium, and vascular tone control by EDRFs, mainly NO, and EDCFs in different models of experimental hypertension.

Imatinib and Nilotinib inhibit Bcr-Abl-induced ROS through targeted degradation of the NADPH oxidase subunit p22phox

Constitutive expression of the Bcr-Abl kinase in Chronic Myelogenous Leukaemia (CML) is known to produce elevated levels of Reactive Oxygen Species (ROS) which can enhance cell survival as well as generate genomic instability. Our laboratory has previously demonstrated that NADPH oxidase (Nox) activity contributes to intracellular-ROS levels in Bcr-Abl-positive cells, while inducing increased pro-survival signalling through the PI3K/Akt pathway. How Bcr-Abl signalling regulates Nox activity still remains to be elucidated. In this study, using the K562 CML cell line we showed that inhibition of Bcr-Abl signalling, by either Imatinib or Nilotinib, led to a significant reduction in ROS levels which was concurrent with the GSK-3β dependent, post-translational down-regulation of the small membrane-bound protein p22phox, an essential component of the Nox complex. Furthermore, siRNA knockdown of p22phox in these cells established its importance in ROS production and proliferation. Taken together we believe our results provide a possible link between Bcr-Abl signalling and ROS production through Nox activity and demonstrate a novel mechanism of action associated with Imatinib and Nilotinib treatment in CML.