Hydrogen peroxide decreases endothelial nitric oxide synthase promoter activity through the inhibition of AP-1 activity

Endothelial cell-specific roles for tetrahydrobiopterin in myocardial function, cardiac hypertrophy, and response to myocardial ischemia-reperfusion injury

The cofactor tetrahydrobiopterin (BH4) is a critical regulator of nitric oxide synthase (NOS) function and redox signaling, with reduced BH4 implicated in multiple cardiovascular disease states. In the myocardium, augmentation of BH4 levels can impact on cardiomyocyte function, preventing hypertrophy and heart failure. However, the specific role of endothelial cell BH4 biosynthesis in the coronary circulation and its role in cardiac function and the response to ischemia has yet to be elucidated. Endothelial cell-specific Gch1 knockout mice were generated by crossing Gch1fl/fl with Tie2cre mice, generating Gch1fl/flTie2cre mice and littermate controls. GTP cyclohydrolase protein and BH4 levels were reduced in heart tissues from Gch1fl/flTie2cre mice, localized to endothelial cells, with normal cardiomyocyte BH4. Deficiency in coronary endothelial cell BH4 led to NOS uncoupling, decreased NO bioactivity, and increased superoxide and hydrogen peroxide productions in the hearts of Gch1fl/flTie2cre mice. Under physiological conditions, loss of endothelial cell-specific BH4 led to mild cardiac hypertrophy in Gch1fl/flTie2cre hearts. Endothelial cell BH4 loss was also associated with increased neuronal NOS protein, loss of endothelial NOS protein, and increased phospholamban phosphorylation at serine-17 in cardiomyocytes. Loss of cardiac endothelial cell BH4 led to coronary vascular dysfunction, reduced functional recovery, and increased myocardial infarct size following ischemia-reperfusion injury. Taken together, these studies reveal a specific role for endothelial cell Gch1/BH4 biosynthesis in cardiac function and the response to cardiac ischemia-reperfusion injury. Targeting endothelial cell Gch1 and BH4 biosynthesis may provide a novel therapeutic target for the prevention and treatment of cardiac dysfunction and ischemia-reperfusion injury.NEW & NOTEWORTHY We demonstrate a critical role for endothelial cell Gch1/BH4 biosynthesis in coronary vascular function and cardiac function. Loss of cardiac endothelial cell BH4 leads to coronary vascular dysfunction, reduced functional recovery, and increased myocardial infarct size following ischemia/reperfusion injury. Targeting endothelial cell Gch1 and BH4 biosynthesis may provide a novel therapeutic target for the prevention and treatment of cardiac dysfunction, ischemia injury, and heart failure.

NF-κB-dependent repression of Sox18 transcription factor requires the epigenetic regulators histone deacetylases 1 and 2 in acute lung injury

In acute lung injury (ALI), the NF-κB-mediated downregulation of Sox18 gene expression leads to the disruption of the pulmonary endothelial barrier. Previous studies have suggested that the action of NF-κB as a transcriptional repressor also requires the action of class I histone deacetylases (HDACs). Thus, the purpose of this study was to investigate and further delineate the mechanism of Sox18 repression during lipopolysaccharide (LPS) induced ALI. Using selective inhibitors and specific siRNA-driven depletion of HDACs 1-3 in human lung microvascular endothelial cells (HLMVEC) we were able to demonstrate a critical role for HDACs 1 and 2 in the LPS-mediated repression of Sox18 gene expression and the loss of endothelial monolayer integrity. Moreover, our data demonstrate that HDAC1 associates with a transcription-repressive complex within the NF-κB-binding site of Sox18 promoter. Further, we were able to show that the selective inhibitor of HDAC1, tacedinaline, significantly reduced the endothelial permeability and injury associated with LPS challenge in the mouse lung. Taken together, our data demonstrate, for the first time, that transcription repressors HDACs 1 and 2 are involved in pathological mechanism of ALI and can be considered as therapeutic targets.

Potential Advantages of Peroxoborates and Their Ester Adducts Over Hydrogen Peroxide as Therapeutic Agents in Oral Healthcare Products: Chemical/Biochemical Reactivity Considerations In Vitro, Ex Vivo And In Vivo

Peroxides present in oral healthcare products generally exert favourable protective activities against the development and progression of tooth decay, plaque, gingivitis, and halitosis, etc. However, despite the high level of research focus on hydrogen and carbamide peroxides as therapeutically active (and tooth-whitening) agents, to date the use of alternative chemical forms of peroxides such as peroxoborates for these purposes has received only scant attention. Intriguingly, peroxoborate and its esters with polyols, such as glycerol, have a very diverse chemistry/biochemistry in aqueous solution, for which there is an increasing amount of evidence that it remains distinctive from that of hydrogen peroxide; such properties include self-associative and hydrolytic equilibria, and their abilities to participate in electrophile- or nucleophile-scavenging, metal ion-complexing, redox and free radical reactions, for example. Therefore, the purpose of this detailed commentary is to evaluate both differences and similarities between the molecular/biomolecular reactivities of peroxoborate species and hydrogen peroxide in vitro, ex-vivo and in vivo. It encompasses brief sectional accounts regarding the molecular heterogeneity of peroxoborates, the release of bioactive agents therefrom, and their oxidative attack on oral cavity biomolecules (the nucleophilic or electrophilic character of these oxidations are discussed). Further areas explored are the abilities of borates and peroxoborates to enhance the solubility of iron ions in aqueous solution, their involvements in free radical biochemistry (particularly the complexation of oxygen radical-promoting transition metal ions by, and antioxidant properties of, peroxoborate-polyol ester adducts), and the specific inhibition of protease enzymes. Further aspects focus on the tooth-whitening, oral malodor neutralizing, and potential mutagenic and genotoxic properties of peroxoborates, along with possible mechanisms for these processes. The abilities of peroxoborates, and peroxides in general, to modulate the activities of inflammatory mediators and vitamins, antioxidant or otherwise, are also explored.

Reactive Oxygen Species (ROS), Intimal Thickening, and Subclinical Atherosclerotic Disease

Arteriosclerosis causes significant morbidity and mortality worldwide. Central to this process is the development of subclinical non-atherosclerotic intimal lesions before the appearance of pathologic intimal thickening and advanced atherosclerotic plaques. Intimal thickening is associated with several risk factors, including oxidative stress due to reactive oxygen species (ROS), inflammatory cytokines and lipid. The main ROS producing systems in-vivo are reduced nicotinamide dinucleotide phosphate (NADPH) oxidase (NOX). ROS effects are context specific. Exogenous ROS induces apoptosis and senescence, whereas intracellular ROS promotes stem cell differentiation, proliferation, and migration. Lineage tracing studies using murine models of subclinical atherosclerosis have revealed the contributory role of medial smooth muscle cells (SMCs), resident vascular stem cells, circulating bone-marrow progenitors and endothelial cells that undergo endothelial-mesenchymal-transition (EndMT). This review will address the putative physiological and patho-physiological roles of ROS in controlling vascular cell fate and ROS contribution to vascular regeneration and disease progression.

Carbon monoxide prevents TNF-α-induced eNOS downregulation by inhibiting NF-κB-responsive miR-155-5p biogenesis

Heme oxygenase-1-derived carbon monoxide prevents inflammatory vascular disorders. To date, there is no clear evidence that HO-1/CO prevents endothelial dysfunction associated with the downregulation of endothelial NO synthesis in human endothelial cells stimulated with TNF-α. Here, we found that the CO-releasing compound CORM-2 prevented TNF-α-mediated decreases in eNOS expression and NO/cGMP production, without affecting eNOS promoter activity, by maintaining the functional activity of the eNOS mRNA 3′-untranslated region. By contrast, CORM-2 inhibited MIR155HG expression and miR-155-5p biogenesis in TNF-α-stimulated endothelial cells, resulting in recovery of the 3′-UTR activity of eNOS mRNA, a target of miR-155-5p. The beneficial effect of CORM-2 was blocked by an NF-κB inhibitor, a miR-155-5p mimic, a HO-1 inhibitor and siRNA against HO-1, indicating that CO rescues TNF-α-induced eNOS downregulation through NF-κB-responsive miR-155-5p expression via HO-1 induction; similar protective effects of ectopic HO-1 expression and bilirubin were observed in endothelial cells treated with TNF-α. Moreover, heme degradation products, except iron and N-acetylcysteine prevented H₂O₂-mediated miR-155-5p biogenesis and eNOS downregulation. These data demonstrate that CO prevents TNF-α-mediated eNOS downregulation by inhibiting redox-sensitive miR-155-5p biogenesis through a positive forward circuit between CO and HO-1 induction. This circuit may play an important preventive role in inflammatory endothelial dysfunction associated with human vascular diseases.

AP-1 Inhibition by SR 11302 Protects Human Hepatoma HepG2 Cells from Bile Acid-Induced Cytotoxicity by Restoring the NOS-3 Expression

The harmful effects of bile acid accumulation occurring during cholestatic liver diseases have been associated with oxidative stress increase and endothelial nitric oxide synthase (NOS-3) expression decrease in liver cells. We have previously reported that glycochenodeoxycholic acid (GCDCA) down-regulates gene expression by increasing SP1 binding to the NOS-3 promoter in an oxidative stress dependent manner. In the present study, we aimed to investigate the role of transcription factor (TF) AP-1 on the NOS-3 deregulation during GCDCA-induced cholestasis. The cytotoxic response to GCDCA was characterized by 1) the increased expression and activation of TFs cJun and c-Fos; 2) a higher binding capability of these at position -666 of the NOS-3 promoter; 3) a decrease of the transcriptional activity of the promoter and the expression and activity of NOS-3; and 4) the expression increase of cyclin D1. Specific inhibition of AP-1 by the retinoid SR 11302 counteracted the cytotoxic effects induced by GCDCA while promoting NOS-3 expression recovery and cyclin D1 reduction. NOS activity inhibition by L-NAME inhibited the protective effect of SR 11302. Inducible NOS isoform was no detected in this experimental model of cholestasis. Our data provide direct evidence for the involvement of AP-1 in the NOS-3 expression regulation during cholestasis and define a critical role for NOS-3 in regulating the expression of cyclin D1 during the cell damage induced by bile acids. AP-1 appears as a potential therapeutic target in cholestatic liver diseases given its role as a transcriptional repressor of NOS-3.

Glycated human serum albumin induces NF-κB activation and endothelial nitric oxide synthase uncoupling in human umbilical vein endothelial cells

AIMS

Non-enzymatic glycated proteins could mediate diabetes vascular complications, but the molecular mechanisms are unknown. Our objective was to find new targets involved in the glycated human serum albumin (gHSA)-enhanced extracellular reactive oxygen species (ROS) production in human endothelial cells.

METHODS & RESULTS

Some nuclear factors and phosphorylation cascades were analysed. gHSA activated nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB), which up-regulated NOX4 and P22PHOX and enhanced ROS production. Pharmacological inhibition of NF-κB reversed gHSA-enhanced NOX4 expression and decreased gHSA-induced ROS production in extra- and intracellular spaces. The inhibition of activator protein-1 (AP-1) induced a rise in NOX4 and P22PHOX subunit expression and a down-regulation of endothelial nitric oxide synthase (eNOS). AP-1 inhibition also enhanced extracellular ROS production in the presence of serum albumin, but not with gHSA. These results were explained by the eNOS uncoupling induced by gHSA, also demonstrated in this study. Phosphatidylinositol 3-kinase or mitogen-activated protein kinase kinase 1/2 did not show to be involved in gHSA-induced ROS production.

CONCLUSIONS

All together, the results suggested that gHSA-enhanced ROS production in endothelium is mediated by: 1) NF-κB activation and subsequence up-regulation of NADPH oxidase, 2) eNOS uncoupling. AP-1, although is not directly affected by gHSA, is another target for regulating NADPH oxidase and eNOS expression in endothelial cells.

Cyclic stretch stimulates mitochondrial reactive oxygen species and Nox4 signaling in pulmonary artery smooth muscle cells

This study was designed to determine whether cyclic stretch induces a persistent pulmonary hypertension of the newborn (PPHN) phenotype of increased NADPH oxidase (Nox) 4 signaling in control pulmonary artery smooth muscle cells (PASMC), and to identify the signal transduction molecules involved. To achieve this, PPHN was induced in lambs by antenatal ligation of the ductus arteriosus at 128 days gestation. After 9 days, lungs and PASMC were isolated from control (twin) and PPHN lambs. Control PASMC were exposed to cyclic stretch at 1 Hz and 15% elongation for 24 h. Stretch-induced Nox4 expression was attenuated by inhibition of mitochondrial complex III and NF-κB, and stretch-induced protein thiol oxidation was attenuated by Nox4 small interfering RNA and complex III inhibition. NF-κB activity was increased by stretch in a complex III-dependent fashion, and stretch-induced cyclin D1 expression was attenuated by complex III inhibition and Nox4 small interfering RNA. This is the first study to show that cyclic stretch increases Nox4 expression via mitochondrial complex III-induced activation of NF-κB in fetal PASMC, resulting in ROS signaling and increased cyclin D1 expression. Targeting these signaling molecules may attenuate pulmonary vascular remodeling associated with PPHN.

Mangiferin activates the Nrf2-ARE pathway and reduces etoposide-induced DNA damage in human umbilical cord mononuclear blood cells

CONTEXT

Mangiferin (2-C-β-d-gluco-pyranosyl-1,3,6,7-tetrahydroxyxanthone) is a well-known natural antioxidant distributed in various plants of the Anacardiaceae and Gentianaceae families. Mangiferin can inhibit carcinogen-induced lung or colon tumor formation in experimental animals. However, the molecular mechanisms of its chemopreventive activity remain unexplored.

OBJECTIVE

This study aimed to investigate the effects of mangiferin on chemical carcinogen-induced DNA damage and Nrf2-ARE signaling in hematopoietic cells.

MATERIALS AND METHODS

Mononuclear cells (MNCs) were isolated from human umbilical cord blood (hUCB). DNA damage was evaluated by comet and micronucleus assays. The expression of Nrf2 and NQO1 was examined by immunofluorescence and western blotting. An electrophoretic mobility shift assay (EMSA) was used to detect the binding activity of Nrf2 with NQO1-ARE sequences.

RESULTS

We found that mangiferin treatment significantly reduced DNA damage in etoposide-treated MNCs, which was verified by decreased olive tail moment (OTM) and micronucleus (MN) frequency. Mangiferin treatment significantly promoted Nrf2 translocation into the nucleus and increased nuclear Nrf2 expression. Moreover, NQO1, an Nrf2 signaling target, was significantly upregulated by mangiferin treatment, and the binding activity of Nrf2 with NQO1-ARE sequences was elevated after mangiferin treatment.

DISCUSSION AND CONCLUSION

Mangiferin activated Nrf2 signaling, upregulated NQO1 expression, and significantly reduced etoposide-induced DNA damage. Thus, mangiferin is a potential cytoprotective agent for hematopoietic cells.

Looking into a conceptual framework of ROS-miRNA-atrial fibrillation

Atrial fibrillation (AF) has been recognized as a major cause of cardiovascular-related morbidity and mortality. MicroRNAs (miRNAs) represent recent additions to the collection of biomolecules involved in arrhythmogenesis. Reactive oxygen species (ROS) have been independently linked to both AF and miRNA regulation. However, no attempts have been made to investigate the possibility of a framework composed of ROS–miRNA–AF that is related to arrhythmia development. Therefore, this review was designed as an attempt to offer a new approach to understanding AF pathogenesis. The aim of this review was to find and to summarize possible connections that exist among AF, miRNAs and ROS to understand the interactions among the molecular entities underlying arrhythmia development in the hopes of finding unappreciated mechanisms of AF. These findings may lead us to innovative therapies for AF, which can be a life-threatening heart condition. A systemic literature review indicated that miRNAs associated with AF might be regulated by ROS, suggesting the possibility that miRNAs translate cellular stressors, such as ROS, into AF pathogenesis. Further studies with a more appropriate experimental design to either prove or disprove the existence of an ROS–miRNA–AF framework are strongly encouraged.

Sox18 preserves the pulmonary endothelial barrier under conditions of increased shear stress

Shear stress secondary to increased pulmonary blood flow (PBF) is elevated in some children born with congenital cardiac abnormalities. However, the majority of these patients do not develop pulmonary edema, despite high levels of permeability inducing factors. Previous studies have suggested that laminar fluid shear stress can enhance pulmonary vascular barrier integrity. However, little is known about the mechanisms by which this occurs. Using microarray analysis, we have previously shown that Sox18, a transcription factor involved in blood vessel development and endothelial barrier integrity, is up-regulated in an ovine model of congenital heart disease with increased PBF (shunt). By subjecting ovine pulmonary arterial endothelial cells (PAEC) to laminar flow (20 dyn/cm(2) ), we identified an increase in trans-endothelial resistance (TER) across the PAEC monolayer that correlated with an increase in Sox18 expression. Further, the TER was also enhanced when Sox18 was over-expressed and attenuated when Sox18 expression was reduced, suggesting that Sox18 maintains the endothelial barrier integrity in response to shear stress. Further, we found that shear stress up-regulates the cellular tight junction protein, Claudin-5, in a Sox18 dependent manner, and Claudin-5 depletion abolished the Sox18 mediated increase in TER in response to shear stress. Finally, utilizing peripheral lung tissue of 4 week old shunt lambs with increased PBF, we found that both Sox18 and Claudin-5 mRNA and protein levels were elevated. In conclusion, these novel findings suggest that increased laminar flow protects endothelial barrier function via Sox18 dependent up-regulation of Claudin-5 expression.

Role of interferon alpha in endothelial dysfunction: insights into endothelial nitric oxide synthase-related mechanisms

Systemic lupus erythematosus (SLE) is an autoimmune disease that is characterized by the production of autoantibodies against nuclear antigens such as double-stranded DNA. Lupus predominantly affects women (ratio, 9:1). Moreover, premenopausal women with SLE are 50 times more likely to have a myocardial infarction. Although specific risk factors for advanced cardiovascular complications have not been identified in this patient population, endothelial dysfunction is highly prevalent. Recent studies show that the type I interferon signature gene expression coincides with impaired brachial artery flow-mediated dilation and diminished endothelial progenitor cell circulation, both markers of impaired endothelial function. Although many factors promote the development of vascular endothelial dysfunction, all pathways converge on the diminished activity of endothelial nitric oxide synthase (eNOS) and loss of nitric oxide (NO) bioavailability. Studies examining the effects of type I interferons on eNOS and NO in SLE are missing. This literature review examines the current literature regarding the role of type I interferons in cardiovascular disease and its known effects on regulators of eNOS and NO bioavailability that are important for proper endothelial cell function.

Sp1 modification of human endothelial nitric oxide synthase promoter increases the hypoxia-stimulated activity

Human endothelial nitric oxide synthase (eNOS) gene has a TATA-less weak promoter with a low activity. The aim of this study was to increase eNOS promoter activity by modification. Human eNOS promoter was modified by inserting a Sp1 element at a -74 bp site and function of the modified promoter was investigated via a hypoxia model induced by cobalt chloride in human umbilical vein endothelial cells. The results demonstrated that the Sp1-modified promoter resulted in a significant increase of normalized luciferase activity in the presence of hypoxia. There was a correlation between the transcriptional activity of the Sp1-modified promoter and the level of eNOS expression with enhancement of nitric oxide production. Together, these data indicate that human eNOS promoter activity is increased by inserting Sp1 binding site into the GC-rich region of the promoter in response to hypoxia, suggesting that this provides an approach to ameliorate microcirculation barrier of some cardiovascular disease and to study its mechanistic process.

Endothelin-1 stimulates catalase activity through the PKCδ-mediated phosphorylation of serine 167

Our previous studies have shown that endothelin-1 (ET-1) stimulates catalase activity in endothelial cells and in lambs with acute increases in pulmonary blood flow (PBF), without altering gene expression. The purpose of this study was to investigate the molecular mechanism by which this occurs. Exposing pulmonary arterial endothelial cells to ET-1 increased catalase activity and decreased cellular hydrogen peroxide (H2O2) levels. These changes correlated with an increase in serine-phosphorylated catalase. Using the inhibitory peptide δV1.1, this phosphorylation was shown to be protein kinase Cδ (PKCδ) dependent. Mass spectrometry identified serine 167 as the phosphorylation site. Site-directed mutagenesis was used to generate a phospho-mimic (S167D) catalase. Activity assays using recombinant protein purified from Escherichia coli or transiently transfected COS-7 cells demonstrated that S167D catalase had an increased ability to degrade H2O2 compared to the wild-type enzyme. Using a phospho-specific antibody, we were able to verify that pS167 catalase levels are modulated in lambs with acute increases in PBF in the presence and absence of the ET receptor antagonist tezosentan. S167 is located on the dimeric interface, suggesting it could be involved in regulating the formation of catalase tetramers. To evaluate this possibility we utilized analytical gel filtration to examine the multimeric structure of recombinant wild-type and S167D catalase. We found that recombinant wild-type catalase was present as a mixture of monomers and dimers, whereas S167D catalase was primarily tetrameric. Further, the incubation of wild-type catalase with PKCδ was sufficient to convert wild-type catalase into a tetrameric structure. In conclusion, this is the first report indicating that the phosphorylation of catalase regulates its multimeric structure and activity.

Shear-induced endothelial mechanotransduction: the interplay between reactive oxygen species (ROS) and nitric oxide (NO) and the pathophysiological implications

Hemodynamic shear stress, the blood flow-generated frictional force acting on the vascular endothelial cells, is essential for endothelial homeostasis under normal physiological conditions. Mechanosensors on endothelial cells detect shear stress and transduce it into biochemical signals to trigger vascular adaptive responses. Among the various shear-induced signaling molecules, reactive oxygen species (ROS) and nitric oxide (NO) have been implicated in vascular homeostasis and diseases. In this review, we explore the molecular, cellular, and vascular processes arising from shear-induced signaling (mechanotransduction) with emphasis on the roles of ROS and NO, and also discuss the mechanisms that may lead to excessive vascular remodeling and thus drive pathobiologic processes responsible for atherosclerosis. Current evidence suggests that NADPH oxidase is one of main cellular sources of ROS generation in endothelial cells under flow condition. Flow patterns and magnitude of shear determine the amount of ROS produced by endothelial cells, usually an irregular flow pattern (disturbed or oscillatory) producing higher levels of ROS than a regular flow pattern (steady or pulsatile). ROS production is closely linked to NO generation and elevated levels of ROS lead to low NO bioavailability, as is often observed in endothelial cells exposed to irregular flow. The low NO bioavailability is partly caused by the reaction of ROS with NO to form peroxynitrite, a key molecule which may initiate many pro-atherogenic events. This differential production of ROS and RNS (reactive nitrogen species) under various flow patterns and conditions modulates endothelial gene expression and thus results in differential vascular responses. Moreover, ROS/RNS are able to promote specific post-translational modifications in regulatory proteins (including S-glutathionylation, S-nitrosylation and tyrosine nitration), which constitute chemical signals that are relevant in cardiovascular pathophysiology. Overall, the dynamic interplay between local hemodynamic milieu and the resulting oxidative and S-nitrosative modification of regulatory proteins is important for ensuing vascular homeostasis. Based on available evidence, it is proposed that a regular flow pattern produces lower levels of ROS and higher NO bioavailability, creating an anti-atherogenic environment. On the other hand, an irregular flow pattern results in higher levels of ROS and yet lower NO bioavailability, thus triggering pro-atherogenic effects.

Apelin attenuates oxidative stress in human adipocytes

It has been recently recognized that the increased oxidative stress (ROS overproduction) in obese condition is a key contributor to the pathogenesis of obesity-associated metabolic diseases. Apelin is an adipocytokine secreted by adipocytes, and known for its anti-obesity and anti-diabetic properties. In obesity, both oxidative stress and plasma level of apelin are increased. However, the regulatory roles of apelin on oxidative stress in adipocytes remain unknown. In the present study, we provide evidence that apelin, through its interaction with apelin receptor (APJ), suppresses production and release of reactive oxygen species (ROS) in adipocytes. This is further supported by the observations that apelin promotes the expression of anti-oxidant enzymes via MAPK kinase/ERK and AMPK pathways, and suppresses the expression of pro-oxidant enzyme via AMPK pathway. We further demonstrate that apelin is able to relieve oxidative stress-induced dysregulations of the expression of anti- and pro-oxidant enzymes, mitochondrial biogenesis and function, as well as release of pro- and anti-inflammatory adipocytokines. This study, for the first time, reveals the antioxidant properties of apelin in adipocytes, and suggests its potential as a novel therapeutic target for metabolic diseases.

Brief hyperoxia increases mitochondrial oxidation and increases phosphodiesterase 5 activity in fetal pulmonary artery smooth muscle cells

AIMS

Oxygen is a pulmonary vasodilator, but data suggest high O(2) concentrations impede that response. We previously reported 24 h of 100% O(2) increased phosphodiesterase 5 (PDE5) activity in fetal pulmonary artery smooth muscle cells (FPASMC) and in ventilated neonatal lambs. PDE5 degrades cyclic GMP (cGMP) and inhibits nitric oxide (NO)-mediated cGMP-dependent vasorelaxation. We sought to determine the mechanism by which hyperoxia initiates reactive oxygen species (ROS) production and regulates PDE5.

RESULTS

Thirty minutes of hyperoxia increased mitochondrial ROS versus normoxia (30.3±1.7% vs. 21.1±2.8%), but had no effect on cytosolic ROS, measured by roGFP, a ratiometric protein thiol redox sensor. Hyperoxia increased PDE5 activity (220±39%) and decreased cGMP responsiveness to NO (37±17%). Mitochondrial catalase overexpression attenuated hyperoxia-induced mitochondrial roGFP oxidation, compared to FPASMC infected with empty adenoviral vector (50±3% of control) or mitochondrial superoxide dismutase. MitoTEMPO, mitochondrial catalase, and DT-3, a cGMP-dependent protein kinase I alpha inhibitor, decreased PDE5 activity (32±13%, 26±21%, and 63±10% of control, respectively), and restored cGMP responsiveness to NO (147±16%,172±29%, and 189±43% of control, respectively). C57Bl6 mice exposed to 90%-100% O(2) for 45 min±mechanical ventilation had increased PA PDE5 activity (206±39% and 235±75%, respectively).

INNOVATION

This is the first description that hyperoxia induces ROS in the mitochondrial matrix prior to the cytosol. Our results indicate that short hyperoxia exposures can produce significant changes in critical cellular signaling pathways.

CONCLUSIONS

These results indicate that mitochondrial matrix oxidant signals generated during hyperoxia, specifically H(2)O(2), activate PDE5 in a cGMP-dependent protein kinase-dependent manner in pulmonary vascular smooth muscle cells.

Ginsenoside Rb1 reverses H2O2-induced senescence in human umbilical endothelial cells: involvement of eNOS pathway

OBJECTIVE

Senescence of endothelial cells has been implicated in endothelial dysfunction and atherogenesis. This study investigated the effects of Rb1, a major ginsenoside in ginseng, on H2O2-induced senescence in primary human umbilical vein endothelial cells (HUVECs).

METHODS AND RESULTS

Real-time PCR and Western blot were used to detect the mRNA and protein expression, respectively. H2O2 (40∼100 μmol/L) effectively increased SA-β-gal activity and PAI-1 mRNA levels, two important senescence related biomarkers, in HUVECs, which were dramatically inhibited by Rb1 pre-incubation. Furthermore, Rb1 administration reversed the H2O2-decreased protein and mRNA levels of eNOS and its phosphorylation at Ser-1177, and the increased eNOS phosphorylation at Thr-495. As a result, Rb1 pretreatment restored the NO generation, as assayed by nitrate reductase method. However, pretreatment with L-NAME, a NOS inhibitor, abolished all the inhibitory effects of Rb1 on senescence. Importantly, Rb1 modulated the H2O2-altered caveolin-1 and pAkt, two most important regulators of eNOS expression and activity, in HUVECs.

CONCLUSIONS

We showed that Rb1 effectively protects HUVECs from senescence through eNOS modulation.

Oxidative stress induced interleukin-32 mRNA expression in human bronchial epithelial cells

Background

Chronic obstructive pulmonary disease (COPD) is characterized by airflow obstruction and persistent inflammation in the airways and lung parenchyma. Oxidative stress contributes to the pathogenesis of COPD. Interleukin (IL)-32 expression has been reported to increase in the lung tissue of patients with COPD. Here, we show that IFNγ upregulated IL-32 expression and that oxidative stress augmented IFNγ-induced-IL-32 expression in airway epithelial cells. We further investigated transcriptional regulation responsible for IFNγ induced IL-32 expression in human airway epithelial cells.

Methods

Human bronchial epithelial (HBE) cells were stimulated with H₂O₂ and IFNγ, and IL-32 expression was evaluated. The cell viability was confirmed by MTT assay. The intracellular signaling pathways regulating IL-32 expression were investigated by examining the regulatory effects of MAPK inhibitors and JAK inhibitor after treatment with H₂O₂ and IFNγ, and by using a ChIP assay to identify transcription factors (i.e. c-Jun, CREB) binding to the IL-32 promoter. Promoter activity assays were conducted after mutations were introduced into binding sites of c-Jun and CREB in the IL-32 promoter. IL-32 expression was also examined in HBE cells in which the expression of either c-Jun or CREB was knocked out by siRNA of indicated transcription factors.

Results

There were no significant differences of cell viability among groups. After stimulation with H₂O₂ or IFNγ for 48 hours, IL-32 expression in HBE cells was increased by IFNγ and synergistically upregulated by the addition of H₂O₂. The H₂O₂ augmented IFNγ induced IL-32 mRNA expression was suppressed by a JNK inhibitor, but not by MEK inhibitor, p38 inhibitor, and JAK inhibitor I. Significant binding of c-Jun and CREB to the IL-32 promoter was observed in the IFNγ + H₂O₂ stimulated HBE cells. Introducing mutations into the c-Jun/CREB binding sites in the IL-32 promoter prominently suppressed its transcriptional activity. Further, knocking down CREB expression by siRNA resulted in significant suppression of IL-32 induction by IFNγ and H₂O₂ in HBE cells.

Conclusion

IL-32 expression in airway epithelium may be augmented by inflammation and oxidative stress, which may occur in COPD acute exacerbation. c-Jun and CREB are key transcriptional factors in IFNγ and H₂O₂ induced IL-32 expression.

Hydrogen peroxide regulates extracellular superoxide dismutase activity and expression in neonatal pulmonary hypertension

We previously demonstrated that superoxide and H(2)O(2) promote pulmonary arterial vasoconstriction in a lamb model of persistent pulmonary hypertension of the newborn (PPHN). Because extracellular superoxide dismutase (ecSOD) augments vasodilation, we hypothesized that H(2)O(2)-mediated ecSOD inactivation contributes to pulmonary arterial vasoconstriction in PPHN lambs. ecSOD activity was decreased in pulmonary arterial smooth muscle cells (PASMCs) isolated from PPHN lambs relative to controls. Exposure to 95% O(2) to mimic hyperoxic ventilation reduced ecSOD activity in control PASMCs. In both cases, these events were associated with increased protein thiol oxidation, as detected by the redox sensor roGFP. Accordingly, exogenous H(2)O(2) decreased ecSOD activity in control PASMCs, and PEG-catalase restored ecSOD activity in PPHN PASMCs. In intact animal studies, ecSOD activity was decreased in fetal PPHN lambs, and in PPHN lambs ventilated with 100% O(2) relative to controls. In ventilated PPHN lambs, administration of a single dose of intratracheal PEG-catalase enhanced ecSOD activity, reduced superoxide levels, and improved oxygenation. We propose that H(2)O(2) generated by PPHN and hyperoxia inactivates ecSOD, and intratracheal catalase enhances enzyme function. The associated decrease in extracellular superoxide augments vasodilation, suggesting that H(2)O(2) scavengers may represent an effective therapy in the clinical management of PPHN.

eNOS activation and NO function: structural motifs responsible for the posttranslational control of endothelial nitric oxide synthase activity

Rather than being a constitutive enzyme as was first suggested, endothelial nitric oxide synthase (eNOS) is dynamically regulated at the transcriptional, posttranscriptional, and posttranslational levels. This review will focus on how changes in eNOS function are conferred by various posttranslational modifications. The latest knowledge regarding eNOS targeting to the plasma membrane will be discussed as the role of protein phosphorylation as a modulator of catalytic activity. Furthermore, new data are presented that provide novel insights into how disruption of the eNOS dimer prevents eNOS uncoupling and the production of superoxide under conditions of elevated oxidative stress and identifies a novel regulatory region we have termed the 'flexible arm'.

Regulation of the Pulmonary Circulation in the Fetus and Newborn

During the development of the pulmonary vasculature in the fetus, many structural and functional changes occur to prepare the lung for the transition to air breathing. The development of the pulmonary circulation is genetically controlled by an array of mitogenic factors in a temporo-spatial order. With advancing gestation, pulmonary vessels acquire increased vasoreactivity. The fetal pulmonary vasculature is exposed to a low oxygen tension environment that promotes high intrinsic myogenic tone and high vasocontractility. At birth, a dramatic reduction in pulmonary arterial pressure and resistance occurs with an increase in oxygen tension and blood flow. The striking hemodynamic differences in the pulmonary circulation of the fetus and newborn are regulated by various factors and vasoactive agents. Among them, nitric oxide, endothelin-1, and prostaglandin I2 are mainly derived from endothelial cells and exert their effects via cGMP, cAMP, and Rho kinase signaling pathways. Alterations in these signaling pathways may lead to vascular remodeling, high vasocontractility, and persistent pulmonary hypertension of the newborn.

Mitochondrial oxidant stress increases PDE5 activity in persistent pulmonary hypertension of the newborn

In the pulmonary vasculature, phosphodiesterase-5 (PDE5) degrades cGMP and inhibits nitric oxide-mediated, cGMP-dependent vasorelaxation. We previously reported that ventilation with 100% O2 increased PDE5 activity in pulmonary arteries (PAs) of pulmonary hypertension lambs (PPHN) more than in control lambs. In the present study, PA smooth muscle cells (PASMCs) from PPHN lambs had increased basal PDE5 activity, decreased cGMP-responsiveness to NO, and increased mitochondrial matrix oxidant stress compared to control PASMC. Hyperoxia (24 h) increased PDE5 activity and mitochondrial matrix oxidant stress above baseline to a similar degree in PPHN and control PASMC. Mitochondrially targeted catalase decreased PDE5 activity at baseline and after hyperoxia in PPHN PASMC. Similarly, catalase treatment of PPHN lambs ventilated with 100% O2 decreased PDE5 activity and increased cGMP in PA. We conclude that baseline PDE5 activity and oxidative stress is increased in PPHN PASMC, and scavenging H2O2 is sufficient to block oxidant-mediated increases in PDE5 activity in PPHN.

A novel role for caveolin-1 in regulating endothelial nitric oxide synthase activation in response to H2O2 and shear stress

Previous studies have shown that acute increases in oxidative stress induced by the addition of hydrogen peroxide (H(2)O(2)) can increase endothelial nitric oxide synthase (eNOS) catalytic activity via an increase in the phosphorylation of eNOS at serine 1177. However, it is unclear how increased H(2)O(2) affects nitric oxide (NO) signaling when endothelial cells are exposed to biomechanical forces. Thus, the purpose of this study was to evaluate the acute effects of H(2)O(2) on NO signaling in the presence or absence of laminar shear stress. We found that acute sustained increases in cellular H(2)O(2) levels in bovine aortic endothelial cells did not alter basal NO generation but the NO produced in response to shear stress was significantly increased. This amplification in NO signaling was found to correlate with an H(2)O(2)-induced increase in eNOS localized to the plasma membrane and an increase in total caveolin-1 protein levels. We further demonstrated that overexpressing caveolin-1 increased eNOS localized to the plasma membrane again without altering total eNOS protein levels. We also found that caveolin-1 overexpression increased NO generation in response to shear stress but only in the presence of H(2)O(2). Conversely, depleting caveolin-1 with an siRNA decreased eNOS localized to the plasma membrane and abolished the enhanced NO generation. Finally, we found that expressing a caveolin-1 binding-site deletion mutant of eNOS in COS-7 cells decreased its plasma membrane localization and resulted in attenuated NO production in response to calcium activation. In conclusion, we have identified a new role for caveolin-1 in enhancing eNOS trafficking to the plasma membrane that seems to be involved in priming eNOS for flow-mediated activation under conditions of oxidative stress. To our knowledge, this is the first report that H(2)O(2) modulates eNOS activity by altering its subcellular location and that caveolin-1 can play a stimulatory role in NO signaling.

Hydrogen peroxide decreases endothelial nitric oxide synthase promoter activity through the inhibition of Sp1 activity

We have previously shown that endothelial nitric oxide synthase (eNOS) promoter activity is decreased in endothelial cells in response to the addition of hydrogen peroxide (H(2)O(2)), and this involves, at least in part, the inhibition of AP-1 activity. Thus, the objective of this study was to determine if other cis-element(s) and transcription factor(s) are involved in the oxidant-mediated downregulation of eNOS. Our initial experiments indicated that although H(2)O(2) treatment increased eNOS mRNA levels in ovine pulmonary arterial endothelial cells (OPAECs), there was a significant decrease in the promoter activity of an eNOS promoter construct containing 840 bp of upstream sequence. However, a truncated promoter construct that lacked the AP-1 element (650 bp) was also inhibited by H(2)O(2). A similar effect was observed when the 650 bp human eNOS promoter construct was transfected into human PAECs. We also found that although exposure of the cells to PEG-catalase prevented the inhibitory effect on eNOS promoter activity, the hydroxyl radical scavenger, deferoxamine myslate, did not. Nor could we identify an increase in hydroxyl radical levels in cells exposed to H(2)O(2). Exposure of PAECs caused a significant increase in labile zinc levels in response to H(2)O(2). As the eNOS promoter has a cis-element for Sp1 binding, we evaluated the role of Sp1 in response to H(2)O(2). As previously reported, mutation of the Sp1 consensus lead to the complete loss of eNOS promoter activity, confirming the key role of Sp1 in regulating basal eNOS promoter activity. In addition, we found, using electrophoretic mobility and supershift assays, that H(2)O(2) decreased Sp1 binding. Finally, using chromatin immunoprecipitation analysis, we found a significant decrease in Sp1 binding to the eNOS promoter in vivo in response to treatment with H(2)O(2). Together, these data suggest that the inhibition of Sp1 activity, possibly through loss of zinc in the protein, plays a role in the H(2)O(2)-induced inhibition of eNOS promoter activity.

Molecular mechanisms and clinical applications of nordihydroguaiaretic acid (NDGA) and its derivatives: an update

Creosote bush, Larrea tridentata, is known as chaparral or greasewood in the United States and as gobernadora or hediondilla in Mexico. Nordihydroguaiaretic acid (NDGA), the main metabolite of the creosote bush, has been shown to have promising applications in the treatment of multiple diseases, including cardiovascular diseases, neurological disorders and cancers. Creosote bush is a promising agent of North American herbal medicine, and it has extensive pharmacological effects and specific mechanisms of actions. This review provides an update of recent in vitro and in vivo research about NDGA and describes experimental studies using NDGA as antioxidant. Also, potential medical uses based on the effects of NDGA on the cardiovascular, immune and neurological systems; cancer; tissue engineering; as well as pharmacokinetics and toxicity are discussed.

Endothelin-1 impairs nitric oxide signaling in endothelial cells through a protein kinase Cdelta-dependent activation of STAT3 and decreased endothelial nitric oxide synthase expression

In an ovine model of persistent pulmonary hypertension of the newborn (PPHN), endothelin-1 (ET-1) expression is increased, while endothelial nitric oxide synthase (eNOS) expression is decreased. However, the molecular mechanisms by which ET-1 attenuates eNOS expression in endothelial cells are not completely understood. Thus, the goal of this study was to determine if the overexpression of ET-1 decreases eNOS expression in pulmonary arterial endothelial cells isolated from fetal lambs. To increase the ET-1 expression, cells were transfected with a plasmid coding for Prepro-ET-1, a precursor of ET-1. After overexpression of Prepro-ET-1, ET-1 levels in the culture medium were significantly increased (control = 805.3 +/- 69.8; Prepro-ET-1 overexpression = 1351 +/- 127.9). eNOS promoter activity, protein levels, and NO generation were all significantly decreased by the overexpression of Prepro-ET-1. The decrease in transcription correlated with increased activity of protein kinase Cdelta (PKCdelta) and STAT3. Further, DNA binding activity of STAT3 was also increased by Prepro-ET-1 overexpression. The increase in STAT3 activity and decrease in eNOS promoter activity were inhibited by the overexpression of dominant negative mutants of PKCdelta or STAT3. Further, a 2 bp mutation in the STAT3 binding site in the eNOS promoter inhibited STAT3 binding and led to enhanced promoter activity in the presence of Prepro-ET-1 overexpression. In conclusion, ET-1 secretion is increased by Prepro-ET-1 overexpression. This results in activation of PKCdelta, which phosphorylates STAT3, increasing its binding to the eNOS promoter. This in turn decreases eNOS promoter activity, protein levels, and NO production. Thus, ET-1 can reduce eNOS expression and NO generation in fetal pulmonary artery endothelial cells through PKCdelta-mediated activation of STAT3.

Alterations in lung arginine metabolism in lambs with pulmonary hypertension associated with increased pulmonary blood flow

Previous studies demonstrate impaired nitric oxide (NO) signaling in children and animal models with congenital heart defects and increased pulmonary blood flow. However, the molecular mechanisms underlying these alterations remain incompletely understood. The purpose of this study was to determine if early changes in arginine metabolic pathways could play a role in the reduced NO signaling demonstrated in our lamb model of congenital heart disease with increased pulmonary blood flow (Shunt lambs). The activities of the arginine recycling enzymes, argininosuccinate synthetase (ASS) and argininosuccinate lyase (ASL) were both decreased in lung tissues of Shunt lambs while arginase activity was increased. Associated with these alterations, lung L-arginine levels were decreased. These changes correlated with an increase in NO synthase-derived reactive oxygen species (ROS) generation. This study provides further insights into the molecular mechanisms leading to decreased NO signaling in Shunt lambs and suggests that altered arginine metabolism may play a role in the development of the endothelial dysfunction associated with pulmonary hypertension secondary to increased pulmonary blood flow.

Estradiol increases guanosine 5'-triphosphate cyclohydrolase expression via the nitric oxide-mediated activation of cyclic adenosine 5'-monophosphate response element binding protein

A number of studies have demonstrated that estradiol can stimulate endothelial nitric oxide synthase expression and activity, resulting in enhanced nitric oxide (NO) generation. However, its effect on the NO synthase cofactor, tetrahydrobiopterin are less clear. Cellular tetrahydrobiopterin levels are regulated, at least in part, by GTP cyclohydrolase 1 (GCH1). Thus, the purpose of this study was to determine the effect of estradiol on GCH1 expression and the regulatory mechanisms in pulmonary arterial endothelial cells. Our data indicate that 17beta-estradiol (E2) increases GCH1 transcription in a dose- and time-dependent manner, whereas estrogen receptor antagonism or NO synthase inhibition attenuated E2-stimulated GCH1 expression. Analysis of the GCH1 promoter fragment responsive to E2 revealed the presence of a cAMP response element, and we found that E2 triggers a rapid but transient elevation of phospho-cAMP response element-binding protein (CREB; <1 h) followed by a second sustained rise after 6 h. EMSA analysis revealed an increase in the binding of CREB during E2 treatment and mutation of the cAMP response element in the GCH1 promoter attenuated the E2-mediated increase in transcription. Furthermore, inhibition of the cAMP-dependent kinase, protein kinase A (PKA) completely abolished the E2-stimulated GCH1 promoter activity, whereas the stimulation of cAMP levels with forskolin increased GCH1 promoter activity, indicating the key role of cAMP in regulating GCH1 promoter activity. In conclusion, our results demonstrate that estradiol can modulate GCH1 expression via NO-mediated activation of CREB in pulmonary arterial endothelial cells. These findings provide new insight into the vascular protective effect of estradiol.

GTP cyclohydrolase I expression is regulated by nitric oxide: role of cyclic AMP

Our previous studies have demonstrated that nitric oxide (NO) leads to nitric oxide synthase (NOS) uncoupling and an increase in NOS-derived superoxide. However, the cause of this uncoupling has not been adequately resolved. The pteridine cofactor tetrahydrobiopterin (BH(4)) is a critical determinant of endothelial NOS (eNOS) activity and coupling, and GTP cyclohydrolase I (GCH1) is the rate-limiting enzyme in its generation. Thus the initial purpose of this study was to determine whether decreases in BH(4) could underlie, at least in part, the NO-mediated uncoupling of eNOS we have observed both in vitro and in vivo. Initially we evaluated the effect of inhaled NO levels on GCH1 expression and BH(4) levels in the intact lamb. Contrary to our hypothesis, we found that there was a significant increase in both plasma BH4 levels and peripheral lung GCH1 protein levels. Furthermore, in vitro, we found that exposure to the NO donor spermine NONOate (SPNONO) led to an increase in GCH1 protein and BH(4) levels in both COS-7 and pulmonary arterial endothelial cells. However, SPNONO treatment also caused a significant increase in phospho-cAMP response element binding protein (CREB) levels, as detected by Western blot analysis, and significantly increased cAMP levels, as detected by enzyme immunoassay. Furthermore, utilizing GCH1 promoter fragments fused to a luciferase reporter gene, we found that GCH1 promoter activity was enhanced by SPNONO in a CREB-dependent manner, and electromobility shift assays revealed an NO-dependent increase in the nuclear binding of CREB. These data suggest that NO increases BH(4) levels through a cAMP/CREB-mediated increase in GCH1 transcription and that the eNOS uncoupling associated with exogenous NO does not involved reduced BH(4) levels.

Fibroblast growth factor 9 prevents MPP+-induced death of dopaminergic neurons and is involved in melatonin neuroprotection in vivo and in vitro

Oxidative stress and down-regulated trophic factors are involved in the pathogenesis of nigrostriatal dopamine(DA)rgic neurodegeneration in Parkinson's disease. Fibroblast growth factor 9 (FGF9) is a survival factor for various cell types; however, the effect of FGF9 on DA neurons has not been studied. The antioxidant melatonin protects DA neurons against neurotoxicity. We used MPP(+) to induce neuron death in vivo and in vitro and investigated the involvement of FGF9 in MPP(+) intoxication and melatonin protection. We found that MPP(+) in a dose- and time-dependent manner inhibited FGF9 mRNA and protein expression, and caused death in primary cortical neurons. Treating neurons in the substantia nigra and mesencephalic cell cultures with FGF9 protein inhibited the MPP(+)-induced cell death of DA neurons. Melatonin co-treatment attenuated MPP(+)-induced FGF9 down-regulation and DA neuronal apoptosis in vivo and in vitro. Co-treating DA neurons with melatonin and FGF9-neutralizing antibody prevented the protective effect of melatonin. In the absence of MPP(+), the treatment of FGF9-neutralizing antibody-induced DA neuronal apoptosis whereas FGF9 protein reduced it indicating that endogenous FGF9 is a survival factor for DA neurons. We conclude that MPP(+) down-regulates FGF9 expression to cause DA neuron death and that the prevention of FGF9 down-regulation is involved in melatonin-provided neuroprotection.