Reversal of inducible nitric oxide synthase uncoupling unmasks tolerance to ischemia/reperfusion injury in the diabetic rat heart

Exploring the therapeutic potential of tetrahydrobiopterin for heart failure with preserved ejection fraction: A path forward

A large number of patients are affected by classical heart failure (HF) symptomatology with preserved ejection fraction (HFpEF) and multiorgan syndrome. Due to high morbidity and mortality rate, hospitalization and mortality remain serious socioeconomic problems, while the lack of effective pharmacological or device treatment means that HFpEF presents a major unmet medical need. Evidence from clinical and basic studies demonstrates that systemic inflammation, increased oxidative stress, and impaired mitochondrial function are the common pathological mechanisms in HFpEF. Tetrahydrobiopterin (BH4), beyond being an endogenous co-factor for catalyzing the conversion of some essential biomolecules, has the capacity to prevent systemic inflammation, enhance antioxidant resistance, and modulate mitochondrial energy production. Therefore, BH4 has emerged in the last decade as a promising agent to prevent or reverse the progression of disorders such as cardiovascular disease. In this review, we cover the clinical progress and limitations of using downstream targets of nitric oxide (NO) through NO donors, soluble guanylate cyclase activators, phosphodiesterase inhibitors, and sodium-glucose co-transporter 2 inhibitors in treating cardiovascular diseases, including HFpEF. We discuss the use of BH4 in association with HFpEF, providing new evidence for its potential use as a pharmacological option for treating HFpEF.

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.

NADPH Oxidases in Diastolic Dysfunction and Heart Failure with Preserved Ejection Fraction

Nicotinamide adenine dinucleotide phosphate (NADPH) oxidases regulate production of reactive oxygen species (ROS) that cause oxidative damage to cellular components but also regulate redox signaling in many cell types with essential functions in the cardiovascular system. Research over the past couple of decades has uncovered mechanisms by which NADPH oxidase (NOX) enzymes regulate oxidative stress and compartmentalize intracellular signaling in endothelial cells, smooth muscle cells, macrophages, cardiomyocytes, fibroblasts, and other cell types. NOX2 and NOX4, for example, regulate distinct redox signaling mechanisms in cardiac myocytes pertinent to the onset and progression of cardiac hypertrophy and heart failure. Heart failure with preserved ejection fraction (HFpEF), which accounts for at least half of all heart failure cases and has few effective treatments to date, is classically associated with ventricular diastolic dysfunction, i.e., defects in ventricular relaxation and/or filling. However, HFpEF afflicts multiple organ systems and is associated with systemic pathologies including inflammation, oxidative stress, arterial stiffening, cardiac fibrosis, and renal, adipose tissue, and skeletal muscle dysfunction. Basic science studies and clinical data suggest a role for systemic and myocardial oxidative stress in HFpEF, and evidence from animal models demonstrates the critical functions of NOX enzymes in diastolic function and several HFpEF-associated comorbidities. Here, we discuss the roles of NOX enzymes in cardiovascular cells that are pertinent to the development and progression of diastolic dysfunction and HFpEF and outline potential clinical implications.

Nitrosative Stress and Human Disease: Therapeutic Potential of Denitrosylation

Proteins dynamically contribute towards maintaining cellular homeostasis. Posttranslational modification regulates the function of target proteins through their immediate activation, sudden inhibition, or permanent degradation. Among numerous protein modifications, protein nitrosation and its functional relevance have emerged. Nitrosation generally initiates nitric oxide (NO) production in association with NO synthase. NO is conjugated to free thiol in the cysteine side chain (S-nitrosylation) and is propagated via the transnitrosylation mechanism. S-nitrosylation is a signaling pathway frequently involved in physiologic regulation. NO forms peroxynitrite in excessive oxidation conditions and induces tyrosine nitration, which is quite stable and is considered irreversible. Two main reducing systems are attributed to denitrosylation: glutathione and thioredoxin (TRX). Glutathione captures NO from S-nitrosylated protein and forms S-nitrosoglutathione (GSNO). The intracellular reducing system catalyzes GSNO into GSH again. TRX can remove NO-like glutathione and break down the disulfide bridge. Although NO is usually beneficial in the basal context, cumulative stress from chronic inflammation or oxidative insult produces a large amount of NO, which induces atypical protein nitrosation. Herein, we (1) provide a brief introduction to the nitrosation and denitrosylation processes, (2) discuss nitrosation-associated human diseases, and (3) discuss a possible denitrosylation strategy and its therapeutic applications.

Natural and synthetic antioxidants targeting cardiac oxidative stress and redox signaling in cardiometabolic diseases

Cardiometabolic diseases (CMDs) are metabolic diseases (e.g., obesity, diabetes, atherosclerosis, rare genetic metabolic diseases, etc.) associated with cardiac pathologies. Pathophysiology of most CMDs involves increased production of reactive oxygen species and impaired antioxidant defense systems, resulting in cardiac oxidative stress (OxS). To alleviate OxS, various antioxidants have been investigated in several diseases with conflicting results. Here we review the effect of CMDs on cardiac redox homeostasis, the role of OxS in cardiac pathologies, as well as experimental and clinical data on the therapeutic potential of natural antioxidants (including resveratrol, quercetin, curcumin, vitamins A, C, and E, coenzyme Q10, etc.), synthetic antioxidants (including N-acetylcysteine, SOD mimetics, mitoTEMPO, SkQ1, etc.), and promoters of antioxidant enzymes in CMDs. As no antioxidant indicated for the prevention and/or treatment of CMDs has reached the market despite the large number of preclinical and clinical studies, a sizeable translational gap is evident in this field. Thus, we also highlight potential underlying factors that may contribute to the failure of translation of antioxidant therapies in CMDs.

The Role of Oxidative Stress in Cardiac Disease: From Physiological Response to Injury Factor

Reactive oxygen species (ROS) are highly reactive chemical species containing oxygen, controlled by both enzymatic and nonenzymatic antioxidant defense systems. In the heart, ROS play an important role in cell homeostasis, by modulating cell proliferation, differentiation, and excitation-contraction coupling. Oxidative stress occurs when ROS production exceeds the buffering capacity of the antioxidant defense systems, leading to cellular and molecular abnormalities, ultimately resulting in cardiac dysfunction. In this review, we will discuss the physiological sources of ROS in the heart, the mechanisms of oxidative stress-related myocardial injury, and the implications of experimental studies and clinical trials with antioxidant therapies in cardiovascular diseases.

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

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

Inducible Nitric Oxide Synthase and L-Arginine Optimizes Nitric Oxide Bioavailability in Ischemic Tissues Under Diabetes Mellitus Type 1

BACKGROUND

The mechanisms influencing the balance of nitric oxide (NO) bioavailability in tissues are negatively affected under diabetic and also under ischemic conditions. Free tissue transplantation for diabetic patients has to deal with both ischemic and diabetic circumstances, which lead to a significantly decrease in providing NO, thus increasing ischemia-reperfusion injury. In previous studies, we could prove that enhancing NO bioavailability leads to attenuated ischemia-reperfusion injury macrocirculatory and microcirculatory alterations in healthy and also in diabetes type 2 rats. This study is evaluating the role of inducible nitric oxide synthase in different dosages and L-arginine under diabetes type 1 conditions.

METHODS

Diabetic type 1 conditions were established via streptozotocin over a period of 4 weeks and verified via blood sugar, insulin, and C-peptide levels. Vascular pedicle isolated rat skin flap model that underwent 3 hours of ischemia was used. At 30 minutes before ischemia, normal saline, inducible nitric oxide synthase (NOS) (1/2 IE), and L-arginine (50 mg/kg body weight) were administered systemically. Ischemia/reperfusion (I/R)-induced alterations were measured 5 days after the operation.

RESULTS

The inducible NOS (iNOS) attenuated I/R-induced alterations under diabetic type 1 conditions significantly with vitality rates of 16.1% compared with control group (5.5%). Best results could be achieved with the combination of iNOS (1 IE) and L-arginine displaying vitality rates of 43%. Increased dosage of inducible nitric oxide (2 IE) led to decreased vitality rates (22.2%/27.4% without/with L-arginine).

CONCLUSIONS

Supporting the mechanisms of NO bioavailability via exogenous application of iNOS and L-arginine significantly attenuated I/R-induced alterations in a skin flap rat model. This pharmacologic preconditioning could be an easy and effective interventional strategy to uphold conversation of L-arginine to NO even on ischemic and type 1 diabetic conditions.

Overexpression of inducible nitric oxide synthase in the diabetic heart compromises ischemic postconditioning

Ischemia postconditioning (PTC) can reduce myocardial ischemia/reperfusion injury. However, the effectiveness of PTC cardioprotection is reduced or lost in diabetes and the mechanisms are largely unclear. Hyperglycemia can induce overexpression of inducible nitric oxide synthesis (iNOS) in the myocardium of diabetic subjects. However, it is unknown whether or not iNOS especially its overexpression plays an important role in the loss of cardioprotection of PTC in diabetes. C57BL6 and iNOS^-/- mice were treated with streptozotocin to induce diabetes. Part of diabetic C57BL6 mice were also treated with an iNOS specific inhibitor, 1400 W. Mice were subjected to myocardial ischemia/ reperfusion with/without PTC. The hemodynamic parameters, plasma levels of cardiac troponin T (cTnT), TNF-α, IL-6 and nitric oxide (NO) were monitored. The myocardial infarct size, superoxide anion (O₂^-) generation, nitrotyrosine production and apoptosis were measured. The expression of phosphorylated Akt, endothelial NOS (eNOS), iNOS and Erk1/2 in ischemic heart were detected by immunoblot analysis. In diabetic C57BL6 and iNOS^-/- mice, the post-ischemic hemodynamics were impaired, the cTnT, TNF-α, IL-6 level, myocardial infarct size, apoptotic index, O₂^- and nitrotyrosine generation were increased and the Akt/eNOS signal pathways were inhibited. PTC improved hemodynamic parameters, reduced cTnT level, myocardial infarct size, apoptotic index, O₂^- and nitrotyrosine generation and activated Akt/eNOS and Erk1/2 signal pathways in both non-diabetic C57BL6 and iNOS^-/- mice as well as diabetic iNOS^-/- mice, but not in diabetic C57BL6 mice. PTC also increased NO production in both non-diabetic and diabetic C57BL6 and iNOS^-/- mice, and enhanced iNOS expression in non-diabetic C57BL6 mice. 1400 W restored the cardioprotection of PTC in diabetic C57BL6 mice. Our data demonstrated that PTC reduced myocardial ischemia/reperfusion injury in non-diabetic mice but not C57BL6 diabetic mice. Deletion of iNOS restored the cardioprotection of PTC in diabetic mice. Our findings suggest that iNOS plays a key role in the reduction of cardioprotection of PTC in diabetes and may provide a therapeutic target for diabetic patients.

The role of reactive oxygen species in the pathophysiology of cardiovascular diseases and the clinical significance of myocardial redox

Acute and chronic excessive intracellular increase of reactive oxygen species (ROS) is involved in the development and progression of cardiovascular diseases. ROS are by-products of various oxidative physiological and biochemical processes. Sources of ROS are mitochondrial respiration, NADH/NADPH oxidase, xanthine oxidoreductase or the uncoupling of nitric oxide synthase (NOS) in vascular cells. ROS mediate various signaling pathways that underlie cardiovascular pathophysiology. The delicate equilibrium between free-radical generation and antioxidant defense is altered in favor of the former, thus leading to redox imbalance, oxidative stress, and increased cellular injury. An understanding of the pathophysiological mechanisms mediated by oxidative stress is crucial to the prevention and treatment of cardiovascular diseases.

Insights for Oxidative Stress and mTOR Signaling in Myocardial Ischemia/Reperfusion Injury under Diabetes

Diabetes mellitus (DM) displays a high morbidity. The diabetic heart is susceptible to myocardial ischemia/reperfusion (MI/R) injury. Impaired activation of prosurvival pathways, endoplasmic reticulum (ER) stress, increased basal oxidative state, and decreased antioxidant defense and autophagy may render diabetic hearts more vulnerable to MI/R injury. Oxidative stress and mTOR signaling crucially regulate cardiometabolism, affecting MI/R injury under diabetes. Producing reactive oxygen species (ROS) and reactive nitrogen species (RNS), uncoupling nitric oxide synthase (NOS), and disturbing the mitochondrial quality control may be three major mechanisms of oxidative stress. mTOR signaling presents both cardioprotective and cardiotoxic effects on the diabetic heart, which interplays with oxidative stress directly or indirectly. Antihyperglycemic agent metformin and newly found free radicals scavengers, Sirt1 and CTRP9, may serve as promising pharmacological therapeutic targets. In this review, we will focus on the role of oxidative stress and mTOR signaling in the pathophysiology of MI/R injury in diabetes and discuss potential mechanisms and their interactions in an effort to provide some evidence for cardiometabolic targeted therapies for ischemic heart disease (IHD).

Treatment with high dose of atorvastatin reduces vascular injury in diabetic rats

BACKGROUND

Previous reports showed conflicting results regarding the treatment effects of statin on Diabetes mellitus (DM). We investigated how treatment with high dose of atorvastatin affects the impaired vascular function in diabetic rats.

METHODS

Atorvastatin (80mg/kg/day, oral gavage, 4 weeks) or its vehicle was administered to male control or streptozotocin (STZ)-induced diabetic rats. Aortic segments were used to investigate the vascular reactivity, protein expression of cyclooxygenase-2 (COX-2) and nicotinamide adenine dinucleotide phosphate oxidase (NADPH oxidase) 1 (NOX1) and superoxide anions levels.

RESULTS

Atorvastatin treatment did not affect glycemia levels. In diabetic rats, the vascular reactivity to phenylephrine increased compared with controls and the atorvastatin treatment reduced this response. Removal of the endothelium increased the response to phenylephrine in control rats, but not in the diabetic group. Atorvastatin increased the endothelial modulation in diabetic rats. L-NAME (100μM) increased the reactivity in all groups, but this effect was greater in atorvastatin-treated diabetic rats. Indomethacin (10μM) and NS398 (1μM) decreased the contractile response in diabetic rats and atorvastatin reversed these effects, without changing COX-2 expression. Apocynin (30μM) decreased the phenylephrine response in diabetic rats, which also showed increased NOX1 and superoxide anions; these effects were prevented by atorvastatin treatment.

CONCLUSIONS

The results suggest that treatment with high dose of atorvastatin, independent of glycemia, improves endothelial function in aortas from diabetic rats by reducing the constrictor prostanoids derived from COX-2 and by reducing the oxidative stress by NADPH oxidase, as well as a possible increasing of nitric oxide participation.

Rotenone-stimulated superoxide release from mitochondrial complex I acutely augments L-type Ca2+ current in A7r5 aortic smooth muscle cells

Voltage-gated L-type Ca(2+) current (ICa,L) induces contraction of arterial smooth muscle cells (ASMCs), and ICa,L is increased by H2O2 in ASMCs. Superoxide released from the mitochondrial respiratory chain (MRC) is dismutated to H2O2 We studied whether superoxide per se acutely modulates ICa,L in ASMCs using cultured A7r5 cells derived from rat aorta. Rotenone is a toxin that inhibits complex I of the MRC and increases mitochondrial superoxide release. The superoxide content of mitochondria was estimated using mitochondrial-specific MitoSOX and HPLC methods, and was shown to be increased by a brief exposure to 10 μM rotenone. ICa,L was recorded with 5 mM BAPTA in the pipette solution. Rotenone administration (10 nM to 10 μM) resulted in a greater ICa,L increase in a dose-dependent manner to a maximum of 22.1% at 10 μM for 1 min, which gradually decreased to 9% after 5 min. The rotenone-induced ICa,L increase was associated with a shift in the current-voltage relationship (I-V) to a hyperpolarizing direction. DTT administration resulted in a 17.9% increase in ICa,L without a negative shift in I-V, and rotenone produced an additional increase with a shift. H2O2 (0.3 mM) inhibited ICa,L by 13%, and additional rotenone induced an increase with a negative shift. Sustained treatment with Tempol (4-hydroxy tempo) led to a significant ICa,L increase but it inhibited the rotenone-induced increase. Staurosporine, a broad-spectrum protein kinase inhibitor, partially inhibited ICa,L and completely suppressed the rotenone-induced increase. Superoxide released from mitochondria affected protein kinases and resulted in stronger ICa,L preceding its dismutation to H2O2 The removal of nitric oxide is a likely mechanism for the increase in ICa,L.

Protein S-nitrosylation in preconditioning and postconditioning

The coronary artery disease is a leading cause of death and morbidity worldwide. This disease has a complex pathophysiology that includes multiple mechanisms. Among these is the oxidative/nitrosative stress. Paradoxically, oxidative/nitrosative signaling plays a major role in cardioprotection against ischemia/reperfusion injury. In this context, the gas transmitter nitric oxide may act through several mechanisms, such as guanylyl cyclase activation and via S-nitrosylation of proteins. The latter is a covalent modification of a protein cysteine thiol by a nitric oxide-group that generates an S-nitrosothiol. Here, we report data showing that nitric oxide and S-nitrosylation of proteins play a pivotal role not only in preconditioning but also in postconditioning cardioprotection.

S-Nitrosoglutathione-mediated STAT3 regulation in efficacy of radiotherapy and cisplatin therapy in head and neck squamous cell carcinoma

S-nitrosoglutathione (GSNO) is an endogenous nitric oxide (NO) carrier that plays a critical role in redox based NO signaling. Recent studies have reported that GSNO regulates the activities of STAT3 and NF-κB via S-nitrosylation dependent mechanisms. Since STAT3 and NF-κB are key transcription factors involved in tumor progression, chemoresistance, and metastasis of head and neck cancer, we investigated the effect of GSNO in cell culture and mouse xenograft models of head and neck squamous cell carcinoma (HNSCC). For the cell culture studies, three HNSCC cell lines were tested (SCC1, SCC14a and SCC22a). All three cell lines had constitutively activated (phosphorylated) STAT3 (Tyr⁷⁰⁵). GSNO treatment of these cell lines reversibly decreased the STAT3 phosphorylation in a concentration dependent manner. GSNO treatment also decreased the basal and cytokine-stimulated activation of NF-κB in SCC14a cells and reduced the basal low degree of nitrotyrosine by inhibition of inducible NO synthase (iNOS) expression. The reduced STAT3/NF-κB activity by GSNO treatment was correlated with the decreased cell proliferation and increased apoptosis of HNSCC cells. In HNSCC mouse xenograft model, the tumor growth was reduced by systemic treatment with GSNO and was further reduced when the treatment was combined with radiation and cisplatin. Accordingly, GSNO treatment also resulted in decreased levels of phosphorylated STAT3. In summary, these studies demonstrate that GSNO treatment blocks the NF-κB and STAT3 pathways which are responsible for cell survival, proliferation and that GSNO mediated mechanisms complement cispaltin and radiation therapy, and thus could potentiate the therapeutic effect in HNSCC.

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S-nitrosoglutathione (GSNO) inhibits activations of STAT3 and NF-κB in HNSCC cells.

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GSNO induces cell cycle arrest and apoptosis of HNSCC cells.

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GSNO decreases iNOS and VEGF production in HNSCC cells.

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GSNO enhances efficacy of chemoradiation therapy in HNSCC mouse xenograft model.

Cardiac NO signalling in the metabolic syndrome

It is well documented that metabolic syndrome (i.e. a group of risk factors, such as abdominal obesity, elevated blood pressure, elevated fasting plasma glucose, high serum triglycerides and low cholesterol level in high-density lipoprotein), which raises the risk for heart disease and diabetes, is associated with increased reactive oxygen and nitrogen species (ROS/RNS) generation. ROS/RNS can modulate cardiac NO signalling and trigger various adaptive changes in NOS and antioxidant enzyme expressions/activities. While initially these changes may represent protective mechanisms in metabolic syndrome, later with more prolonged oxidative, nitrosative and nitrative stress, these are often exhausted, eventually favouring myocardial RNS generation and decreased NO bioavailability. The increased oxidative and nitrative stress also impairs the NO-soluble guanylate cyclase (sGC) signalling pathway, limiting the ability of NO to exert its fundamental signalling roles in the heart. Enhanced ROS/RNS generation in the presence of risk factors also facilitates activation of redox-dependent transcriptional factors such as NF-κB, promoting myocardial expression of various pro-inflammatory mediators, and eventually the development of cardiac dysfunction and remodelling. While the dysregulation of NO signalling may interfere with the therapeutic efficacy of conventional drugs used in the management of metabolic syndrome, the modulation of NO signalling may also be responsible for the therapeutic benefits of already proven or recently developed treatment approaches, such as ACE inhibitors, certain β-blockers, and sGC activators. Better understanding of the above-mentioned pathological processes may ultimately lead to more successful therapeutic approaches to overcome metabolic syndrome and its pathological consequences in cardiac NO signalling.

Protective effect of sodium nitroprusside on the rat small intestine transplanted mucosa

The intestinal mucosal epithelium is extremely susceptible to even brief periods of ischemia. Mucosal barrier damage, which is associated with ischemia/reperfusion (I/R) injury and consequently bacterial translocation, remains a major obstacle for clinically successful small bowel transplantation (SBT). Previous studies have demonstrated a protective effect of nitric oxide (NO) on other transplanted organs and NO mediated intestinal protection has also been reported in vitro. The aim of this study was to evaluate the effect of sodium nitroprusside (SNP), NO donor, on graft mucosal histology and molecular markers of function after SBT in rats. We used SNP in different period of heterotopic SBT rats. The groups consisted of SBT, pre-SNP group, and post-SNP group. Interestingly, the pre-SNP graft samples exhibited less damage compared to the SBT and post-SNP samples. In addition, mucosal samples from the pre-SNP group showed higher Na(+)-K(+)-ATPase activity and higher levels of laminin expression compared to the SBT and post-SNP samples. The findings of the present study reveal that SNP given before graft ischemia/reperfusion injury has a protective effect on mucosal histology and molecular markers of function in the transplanted small intestine.

Protective vascular and cardiac effects of inducible nitric oxide synthase in mice with hyperhomocysteinemia

Diet-induced hyperhomocysteinemia produces endothelial and cardiac dysfunction and promotes thrombosis through a mechanism proposed to involve oxidative stress. Inducible nitric oxide synthase (iNOS) is upregulated in hyperhomocysteinemia and can generate superoxide. We therefore tested the hypothesis that iNOS mediates the adverse oxidative, vascular, thrombotic, and cardiac effects of hyperhomocysteinemia. Mice deficient in iNOS (Nos2-/-) and their wild-type (Nos2+/+) littermates were fed a high methionine/low folate (HM/LF) diet to induce mild hyperhomocysteinemia, with a 2-fold increase in plasma total homocysteine (P<0.001 vs. control diet). Hyperhomocysteinemic Nos2+/+ mice exhibited endothelial dysfunction in cerebral arterioles, with impaired dilatation to acetylcholine but not nitroprusside, and enhanced susceptibility to carotid artery thrombosis, with shortened times to occlusion following photochemical injury (P<0.05 vs. control diet). Nos2-/- mice had decreased rather than increased dilatation responses to acetylcholine (P<0.05 vs. Nos2+/+ mice). Nos2-/- mice fed control diet also exhibited shortened times to thrombotic occlusion (P<0.05 vs. Nos2+/+ mice), and iNOS deficiency failed to protect from endothelial dysfunction or accelerated thrombosis in mice with hyperhomocysteinemia. Deficiency of iNOS did not alter myocardial infarct size in mice fed the control diet but significantly increased infarct size and cardiac superoxide production in mice fed the HM/LF diet (P<0.05 vs. Nos2+/+ mice). These findings suggest that endogenous iNOS protects from, rather than exacerbates, endothelial dysfunction, thrombosis, and hyperhomocysteinemia-associated myocardial ischemia-reperfusion injury. In the setting of mild hyperhomocysteinemia, iNOS functions to blunt cardiac oxidative stress rather than functioning as a source of superoxide.

Are nitric oxide-mediated protein modifications of functional significance in diabetic heart? ye'S, -NO', wh'Y-NO't?

Protein modifications effected by nitric oxide (NO) primarily in conjunction with reactive oxygen species (ROS) include tyrosine nitration, cysteine S-nitrosylation, and glutathionylation. The physiological and pathological relevance of these three modifications is determined by the amino acids on which these modifications occur -cysteine and tyrosine, for instance, ranging from altering structural integrity/catalytic activity of proteins or by altering propensity towards protein degradation. Even though tyrosine nitration is a well-established nitroxidative stress marker, instilled as a footprint of oxygen- and nitrogen-derived oxidants, newer data suggest its wider role in embryonic heart development and substantiate the need to focus on elucidating the underlying mechanisms of reversibility and specificity of tyrosine nitration. S-nitrosylation is a covalent modification in specific cysteine residues of proteins and is suggested as one of the ways in which NO contributes to its ubiquitous signalling. Several sensitive and specific techniques including biotin switch assay and mass spectrometry based analysis make it possible to identify a large number of these modified proteins, and provide a great deal of potential S-nitrosylation sites. The number of studies that have documented nitrated proteins in diabetic heart is relatively much less compared to what has been published in the normal physiology and other cardiac pathologies. Nevertheless, elucidation of nitrated proteome of diabetic heart has revealed the presence of many mitochondrial and cytosolic proteins of functional importance. But, the existence of different models of diabetes and analyses at diverse stages of this disease have impeded scientists from gaining insights that would be essential to understand the cardiac complications during diabetes. This review summarizes NO mediated protein modifications documented in normal and abnormal heart physiology including diabetes.

Tetrahydrobiopterin in cardiovascular health and disease

Tetrahydrobiopterin (BH4) functions as a cofactor for several important enzyme systems, and considerable evidence implicates BH4 as a key regulator of endothelial nitric oxide synthase (eNOS) in the setting of cardiovascular health and disease. BH4 bioavailability is determined by a balance of enzymatic de novo synthesis and recycling, versus degradation in the setting of oxidative stress. Augmenting vascular BH4 levels by pharmacological supplementation has been shown in experimental studies to enhance NO bioavailability. However, it has become more apparent that the role of BH4 in other enzymatic pathways, including other NOS isoforms and the aromatic amino acid hydroxylases, may have a bearing on important aspects of vascular homeostasis, inflammation, and cardiac function. This article reviews the role of BH4 in cardiovascular development and homeostasis, as well as in pathophysiological processes such as endothelial and vascular dysfunction, atherosclerosis, inflammation, and cardiac hypertrophy. We discuss the therapeutic potential of BH4 in cardiovascular disease states and attempt to address how this modulator of intracellular NO-redox balance may ultimately provide a powerful new treatment for many cardiovascular diseases.

Nitric oxide synthase regulation of cardiac excitation-contraction coupling in health and disease

Significant advances in our understanding of the ability of nitric oxide synthases (NOS) to modulate cardiac function have provided key insights into the role NOS play in the regulation of excitation-contraction (EC) coupling in health and disease. Through both cGMP-dependent and cGMP-independent (e.g. S-nitrosylation) mechanisms, NOS have the ability to alter intracellular Ca(2+) handling and the myofilament response to Ca(2+), thereby impacting the systolic and diastolic performance of the myocardium. Findings from experiments using nitric oxide (NO) donors and NOS inhibition or gene deletion clearly implicate dysfunctional NOS as a critical contributor to many cardiovascular disease states. However, studies to date have only partially addressed NOS isoform-specific effects and, more importantly, how subcellular localization of NOS influences ion channels involved in myocardial EC coupling and excitability. In this review, we focus on the contribution of each NOS isoform to cardiac dysfunction and on the role of uncoupled NOS activity in common cardiac disease states, including heart failure, diabetic cardiomyopathy, ischemia/reperfusion injury and atrial fibrillation. We also review evidence that clearly indicates the importance of NO in cardioprotection. This article is part of a Special Issue entitled "Redox Signalling in the Cardiovascular System".

Methylglyoxal modulates endothelial nitric oxide synthase-associated functions in EA.hy926 endothelial cells

BACKGROUND

Increased levels of the sugar metabolite methylglyoxal (MG) in vivo were shown to participate in the pathophysiology of vascular complications in diabetes. Alterations of endothelial nitric oxide synthase (eNOS) activity by hypophosphorylation of the enzyme and enhanced monomerization are found in the diabetic milieu, and the regulation of this still remains undefined. Using various pharmacological approaches, we elucidate putative mechanisms by which MG modulates eNOS-associated functions of MG-stimulated superoxide O₂•⁻ production, phosphorylation status and eNOS uncoupling in EA.hy926 human endothelial cells.

METHODS

In cultured EA.hy926 endothelial cells, the effects of MG treatment, tetrahydrobiopterin (BH4; 100 μM) and sepiapterin (20 μM) supplementation, NOS inhibition by N(G)-nitro-L-arginine methyl ester (L-NAME; 50 μM), and inhibition of peroxynitrite (ONOO⁻) formation (300 μM Tempol plus 50 μM L-NAME) on eNOS dimer/monomer ratios, Ser-1177 eNOS phosphorylation and 3-nitrotyrosine (3NT) abundance were quantified using immunoblotting. O₂•⁻-dependent fluorescence was determined using a commercially available kit and tissue biopterin levels were measured by fluorometric HPLC analysis.

RESULTS

In EA.hy926 cells, MG treatment significantly enhanced O₂•⁻ generation and 3NT expression and reduced Ser-1177 eNOS phosphorylation, eNOS dimer/monomer ratio and cellular biopterin levels indicative of eNOS uncoupling. These effects were significantly mitigated by administration of BH4, sepiapterin and suppression of ONOO⁻ formation. L-NAME treatment significantly blunted eNOS-derived O₂•⁻ generation but did not modify eNOS phosphorylation or monomerization.

CONCLUSION

MG triggers eNOS uncoupling and hypophosphorylation in EA.hy926 endothelial cells associated with O₂•⁻ generation and biopterin depletion. The observed effects of the glycolysis metabolite MG presumably account, at least in part, for endothelial dysfunction in diabetes.

Diabetic cardiomyopathy: pathophysiology and clinical features

Since diabetic cardiomyopathy was first reported four decades ago, substantial information on its pathogenesis and clinical features has accumulated. In the heart, diabetes enhances fatty acid metabolism, suppresses glucose oxidation, and modifies intracellular signaling, leading to impairments in multiple steps of excitation–contraction coupling, inefficient energy production, and increased susceptibility to ischemia/reperfusion injury. Loss of normal microvessels and remodeling of the extracellular matrix are also involved in contractile dysfunction of diabetic hearts. Use of sensitive echocardiographic techniques (tissue Doppler imaging and strain rate imaging) and magnetic resonance spectroscopy enables detection of diabetic cardiomyopathy at an early stage, and a combination of the modalities allows differentiation of this type of cardiomyopathy from other organic heart diseases. Circumstantial evidence to date indicates that diabetic cardiomyopathy is a common but frequently unrecognized pathological process in asymptomatic diabetic patients. However, a strategy for prevention or treatment of diabetic cardiomyopathy to improve its prognosis has not yet been established. Here, we review both basic and clinical studies on diabetic cardiomyopathy and summarize problems remaining to be solved for improving management of this type of cardiomyopathy.

Site-specific antioxidative therapy for prevention of atherosclerosis and cardiovascular disease

Oxidative stress has been implicated in pathophysiology of aging and age-associated disease. Antioxidative medicine has become a practice for prevention of atherosclerosis. However, limited success in preventing cardiovascular disease (CVD) in individuals with atherosclerosis using general antioxidants has prompted us to develop a novel antioxidative strategy to prevent atherosclerosis. Reducing visceral adipose tissue by calorie restriction (CR) and regular endurance exercise represents a causative therapy for ameliorating oxidative stress. Some of the recently emerging drugs used for the treatment of CVD may be assigned as site-specific antioxidants. CR and exercise mimetic agents are the choice for individuals who are difficult to continue CR and exercise. Better understanding of molecular and cellular biology of redox signaling will pave the way for more effective antioxidative medicine for prevention of CVD and prolongation of healthy life span.

Oxidative stress and myocardial injury in the diabetic heart

Reactive oxygen or nitrogen species play an integral role in both myocardial injury and repair. This dichotomy is differentiated at the level of species type, amount and duration of free radical generated. Homeostatic mechanisms designed to prevent free radical generation in the first instance, scavenge, or enzymatically convert them to less toxic forms and water, playing crucial roles in the maintenance of cellular structure and function. The outcome between functional recovery and dysfunction is dependent upon the inherent ability of these homeostatic antioxidant defences to withstand acute free radical generation, in the order of seconds to minutes. Alternatively, pre-existent antioxidant capacity (from intracellular and extracellular sources) may regulate the degree of free radical generation. This converts reactive oxygen and nitrogen species to the role of second messenger involved in cell signalling. The adaptive capacity of the cell is altered by the balance between death or survival signal converging at the level of the mitochondria, with distinct pathophysiological consequences that extends the period of injury from hours to days and weeks. Hyperglycaemia, hyperlipidaemia and insulin resistance enhance oxidative stress in the diabetic myocardium that cannot adapt to ischaemia-reperfusion. Altered glucose flux, mitochondrial derangements and nitric oxide synthase uncoupling in the presence of decreased antioxidant defence and impaired prosurvival cell signalling may render the diabetic myocardium more vulnerable to injury, remodelling and heart failure.

Diabetes-induced increased oxidative stress in cardiomyocytes is sustained by a positive feedback loop involving Rho kinase and PKCβ2

We previously reported that acute inhibition of the RhoA/Rho kinase (ROCK) pathway normalized contractile function of diabetic rat hearts, but the underlying mechanism is unclear. Protein kinase C (PKC) β(2) has been proposed to play a major role in diabetic cardiomyopathy at least in part by increasing oxidative stress. Further evidence suggests that PKC positively regulates RhoA expression through induction of inducible nitric oxide synthase (iNOS) in diabetes. However, in preliminary studies, we found that inhibition of ROCK itself reduced RhoA expression in diabetic hearts. We hypothesized that there is an interaction between RhoA/ROCK and PKCβ(2) in the form of a positive feedback loop that sustains their activation and the production of reactive oxygen species (ROS). This was investigated in cardiomyocytes isolated from diabetic and control rat hearts, incubated with or without cytochalasin D or inhibitors of ROCK, RhoA, PKCβ(2), or iNOS. Inhibition of RhoA and ROCK markedly attenuated the diabetes-induced increases in PKCβ(2) activity and iNOS and RhoA expression in diabetic cardiomyocytes, while having no effect in control cells. Inhibition of PKCβ(2) and iNOS also normalized RhoA expression and ROCK overactivation, whereas iNOS inhibition reversed the increase in PKCβ(2) activity. Each of these treatments also normalized the diabetes-induced increase in production of ROS. Actin cytoskeleton disruption attenuated the increased expression and/or activity of all of these targets in diabetic cardiomyocytes. These data suggest that, in the diabetic heart, the RhoA/ROCK pathway contributes to contractile dysfunction at least in part by sustaining PKCβ(2) activation and ROS production via a positive feedback loop that requires an intact cytoskeleton.

Preconditioning and acute effects of flavonoids in protecting cardiomyocytes from oxidative cell death

While flavonoids can reportedly protect against cardiac ischemia-reperfusion injury, the relative effectiveness of different flavonoids and the mechanisms involved are unclear. We compared protection by different flavonoids using rat embryonic ventricular H9c2 cells subjected to simulated ischemia-reperfusion (IR) and to tert-butyl hydroperoxide (t-buOOH). Characterization of the IR model showed the relative contributions of glucose, serum, and oxygen deprivation to cell death. With long-term (2-3 day) pretreatment before IR the best protection was given by catechin, epigallocatechin gallate, proanthocyanidins, and ascorbate, which protected at all doses. Quercetin protected (34%) at 5 μM but was cytotoxic at higher doses. Cyanidin protected mildly (10-15%) at 5 and 20 μM, while delphinidin had no effect at 5 μM and was cytotoxic at higher doses. Comparing long-term and acute protection by catechin, a higher concentration was needed for benefit with acute (1 hr) pretreatment. With a pure oxidative stress (t-buOOH) only quercetin significantly protected with 3-day pretreatment, while with short-term (1 h) pretreatments protection was best with quercetin and epigallocatechin gallate. The results suggest catechins to be especially useful as IR preconditioning agents, while quercetin and epigallocatechin gallate may be the most protective acutely in situations of oxidative stress.

Regulation of nitric oxide generation by up-regulated arginase I in rat spinal cord injury

Recently, arginase is suggested to regulate nitric oxide production by competing with nitric oxide synthase for the same substrate, L-arginine, in experimental asthma. We investigated the role of arginase and its relationship to nitric oxide production after spinal cord injury. Rats were subjected to laminectomy and complete transection of their spinal cords (injury group) or laminectomy only (sham group). In the injury group, arginase I was increased in the macrophages at the transection edge, and the peak was observed 48 h after spinal cord injury. However, nitric oxide production decreased significantly in the injury group despite increased nitric oxide synthase2 mRNA expression compared with the sham group. We also demonstrated the reduction in L-arginine concentrations, which was inversely associated with changes in arginase activity. Therefore, arginase appeared to regulate nitric oxide production by consuming L-arginine. The regulation of arginase activity and L-arginine levels may improve nitroxidative stress and reduce tissue damage in spinal cord injury.

Nitric oxide synthase in post-ischaemic remodelling: new pathways and mechanisms

The three isoforms of nitric oxide synthase (NOS), spatially confined in specific intracellular compartments in cardiac cells, have distinct roles in the regulation of contractility in pathophysiological situations. Recently, evidence has emerged that implicates NOS in modulating myocardial remodelling during cardiac stress, including after ischaemic insults. As long as they remain in a coupled state the NOS mostly attenuate hypertrophic remodelling through both cGMP-dependent and independent mechanisms. We review the evidence provided from the phenotype of genetic mouse models as well as from in vitro cell experiments dissecting the signalling effectors involved in the NOS-mediated regulation that justify new therapeutic interventions on the NOS-cGMP axis to attenuate the development of heart failure.

The role of oxidative stress in the pathophysiology of gestational diabetes mellitus

Normal human pregnancy is considered a state of enhanced oxidative stress. In pregnancy, it plays important roles in embryo development, implantation, placental development and function, fetal development, and labor. However, pathologic pregnancies, including gestational diabetes mellitus (GDM), are associated with a heightened level of oxidative stress, owing to both overproduction of free radicals and/or a defect in the antioxidant defenses. This has important implications on the mother, placental function, and fetal well-being. Animal models of diabetes have confirmed the important role of oxidative stress in the etiology of congenital malformations; the relative immaturity of the antioxidant system facilitates the exposure of embryos and fetuses to the damaging effects of oxidative stress. Of note, there are only a few clinical studies evaluating the potential beneficial effects of antioxidants in GDM. Thus, whether or not increased antioxidant intake can reduce the complications of GDM in both mother and fetus needs to be explored. This review provides an overview and updated data on our current understanding of the complications associated with oxidative changes in GDM.

Sepiapterin enhances angiogenesis and functional recovery in mice after myocardial infarction

Uncoupling of nitric oxide synthase (NOS) has been implicated in left ventricular (LV) remodeling and dysfunction after myocardial infarction (MI). We hypothesized that inducible NOS (iNOS) plays a crucial role in LV remodeling after MI, depending on its coupling status. MI was created in wild-type, iNOS-knockout (iNOS(-/-)), endothelial NOS-knockout (eNOS(-/-)), and neuronal NOS-knockout (nNOS(-/-)) mice. iNOS and nNOS expressions were increased after MI associated with an increase in nitrotyrosine formation. The area of myocardial fibrosis and LV end-diastolic volume and ejection fraction were more deteriorated in eNOS(-/-) mice compared with other genotypes of mice 4 wk after MI. The expression of GTP cyclohydrolase was reduced, and tetrahydrobiopterin (BH(4)) was depleted in the heart after MI. Oral administration of sepiapterin after MI increased dihydrobiopterin (BH(2)), BH(4), and BH(4)-to-BH(2) ratio in the infarcted but not sham-operated heart. The increase in BH(4)-to-BH(2) ratio was associated with inhibition of nitrotyrosine formation and an increase in nitrite plus nitrate. However, this inhibition of NOS uncoupling was blunted in iNOS(-/-) mice. Sepiapterin increased capillary density and prevented LV remodeling and dysfunction after MI in wild-type, eNOS(-/-), and nNOS(-/-) but not iNOS(-/-) mice. N(ω)-nitro-L-arginine methyl ester abrogated sepiapterin-induced increase in nitrite plus nitrate and angiogenesis and blocked the beneficial effects of sepiapterin on LV remodeling and function. These results suggest that sepiapterin enhances angiogenesis and functional recovery after MI by activating the salvage pathway for BH(4) synthesis and increasing bioavailable nitric oxide predominantly derived from iNOS.

Ascorbic acid and N-acetyl cysteine prevent uncoupling of nitric oxide synthase and increase tolerance to ischemia/reperfusion injury in diabetic rat heart

Oxidative stress may cause a loss of tetrahydrobiopterin (BH4), a co-factor of nitric oxide synthase (NOS), decrease the bioavailability of NO and aggravate ischemia/reperfusion (I/R) injury in diabetic heart. We hypothesized that ascorbic acid (AA) and N-acetyl cysteine (NAC) protect the diabetic heart from I/R injury by increasing BH4/dihydrobiopterin (BH2) ratio and inhibiting uncoupling of NOS. Diabetes mellitus was induced in rats by streptozotocin treatment, and the hearts were isolated and perfused. BH4 and BH4/BH2 ratio decreased in the diabetic heart associated with increased production of superoxide and nitrotyrosine (NT). Treatment with AA or NAC significantly increased BH4/BH2 ratio in the diabetic heart associated with decreased production of superoxide and NT and increased generation of nitrate plus nitrite (NOx). Pre-treatment with AA or NAC before 30 min ischemia followed by 120 min reperfusion improved left ventricular (LV) function and reduced infarct size in the diabetic but not non-diabetic hearts. The NOS inhibitor, L-NAME, inhibited the increase in the generation of superoxide, NT and NOx, but aggravated LV function and increased infarct size in the diabetic heart. L-NAME also abrogated the increase in NOx and improvement of LV function and the infarct size-limiting effect induced by AA or NAC in the diabetic heart. These results suggest that AA and NAC increase BH4/BH2 ratio and prevent NOS uncoupling in the diabetic heart. Resultant increase in the bioavailability of NO renders the diabetic heart toleratant to I/R injury.

Redox regulation of mitochondrial ATP synthase: implications for cardiac resynchronization therapy

RATIONALE

Cardiac resynchronization therapy (CRT) is an effective clinical treatment for heart failure patients with conduction delay, impaired contraction, and energetics. Our recent studies have revealed that mitochondrial posttranslational modifications (PTM) may contribute to its benefits, motivating the present study of the oxidative regulation of mitochondrial ATP synthase.

OBJECTIVES

We tested whether CRT alteration of ATP synthase function is linked to cysteine (Cys) oxidative PTM (Ox-PTM) of specific ATP synthase subunits.

METHODS AND RESULTS

Canine left ventricular myocardium was collected under conditions to preserve Ox-PTM from control, dyssynchronous heart failure (DHF), or hearts that had undergone CRT. In-gel ATPase activity showed that CRT increased ATPase activity by approximately 2-fold (P<0.05) over DHF, approaching control levels, and this effect was recapitulated with a reducing agent. ATP synthase function and 3 Ox-PTM: disulfide bond, S-glutathionylation and S-nitrosation were assessed. ATP synthase from DHF hearts contained 2 novel disulfide bonds, between ATP synthase α subunits themselves and between α and γ subunits, both of which were decreased in CRT hearts (4.38 ± 0.13- and 4.23 ± 0.36-fold, respectively, P<0.01). S-glutathionylation of ATP synthase α subunit occurred in DHF hearts and was decreased by CRT (1.56 ± 0.16-fold, P<0.04). In contrast, S-nitrosation of ATP synthase α subunit in DHF hearts was lower than in CRT hearts (1.53 ± 0.19-fold, P<0.05). All modifications occurred at ATP synthase α subunit Cys294 and Cys to Ser mutation indicated that this residue is critical for ATP synthase function.

CONCLUSIONS

A selective Cys in ATP synthase α subunit is targeted by multiple Ox-PTM suggesting that this Cys residue may act as a redox sensor modulating ATP synthase function.