Nitric oxide regulates the heart by spatial confinement of nitric oxide synthase isoforms

Protein S-Nitrosylation: Determinants of Specificity and Enzymatic Regulation of S-Nitrosothiol-Based Signaling

SIGNIFICANCE

Protein S-nitrosylation, the oxidative modification of cysteine by nitric oxide (NO) to form protein S-nitrosothiols (SNOs), mediates redox-based signaling that conveys, in large part, the ubiquitous influence of NO on cellular function. S-nitrosylation regulates protein activity, stability, localization, and protein-protein interactions across myriad physiological processes, and aberrant S-nitrosylation is associated with diverse pathophysiologies. Recent Advances: It is recently recognized that S-nitrosylation endows S-nitroso-protein (SNO-proteins) with S-nitrosylase activity, that is, the potential to trans-S-nitrosylate additional proteins, thereby propagating SNO-based signals, analogous to kinase-mediated signaling cascades. In addition, it is increasingly appreciated that cellular S-nitrosylation is governed by dynamically coupled equilibria between SNO-proteins and low-molecular-weight SNOs, which are controlled by a growing set of enzymatic denitrosylases comprising two main classes (high and low molecular weight). S-nitrosylases and denitrosylases, which together control steady-state SNO levels, may be identified with distinct physiology and pathophysiology ranging from cardiovascular and respiratory disorders to neurodegeneration and cancer.

CRITICAL ISSUES

The target specificity of protein S-nitrosylation and the stability and reactivity of protein SNOs are determined substantially by enzymatic machinery comprising highly conserved transnitrosylases and denitrosylases. Understanding the differential functionality of SNO-regulatory enzymes is essential, and is amenable to genetic and pharmacological analyses, read out as perturbation of specific equilibria within the SNO circuitry.

FUTURE DIRECTIONS

The emerging picture of NO biology entails equilibria among potentially thousands of different SNOs, governed by denitrosylases and nitrosylases. Thus, to elucidate the operation and consequences of S-nitrosylation in cellular contexts, studies should consider the roles of SNO-proteins as both targets and transducers of S-nitrosylation, functioning according to enzymatically governed equilibria.

Rethinking Endothelial Dysfunction as a Crucial Target in Fighting Heart Failure

Endothelial dysfunction is characterized by nitric oxide dysregulation and an altered redox state. Oxidative stress and inflammatory markers prevail, thus promoting atherogenesis and hypertension, important risk factors for the development and progression of heart failure. There has been a reemerging interest in the role that endothelial dysfunction plays in the failing circulation. Accordingly, patients with heart failure are being clinically assessed for endothelial dysfunction via various methods, including flow-mediated vasodilation, peripheral arterial tonometry, quantification of circulating endothelial progenitor cells, and early and late endothelial progenitor cell outgrowth measurements. Although the mechanisms underlying endothelial dysfunction are intimately related to cardiovascular disease and heart failure, it remains unclear whether targeting endothelial dysfunction is a feasible strategy for ameliorating heart failure progression. This review focuses on the pathophysiology of endothelial dysfunction, the mechanisms linking endothelial dysfunction and heart failure, and the various diagnostic methods currently used to measure endothelial function, ultimately highlighting the therapeutic implications of targeting endothelial dysfunction for the treatment of heart failure.

The HNO- radical anion: A proposed intermediate in diazeniumdiolate synthesis using nitric oxide and alkoxides

The strategy of synthesizing diazeniumdiolates (X-N(O)=NO^-) through the coexistence of nitric oxide and alkoxides (RO^-) was introduced by Wilhelm Traube 120 years ago. Today, despite the wide use of diazeniumdiolate derivatives to release nitric oxide in the treatment of cancer, the first step of the reaction mechanism for diazeniumdiolate synthesis remains a mystery and is thought to be complex. We have studied the gas-phase reactions of nitric oxide with alkoxides at room temperature. An electron-coupled hydrogen transfer is observed, and the radical anion HNO^- is the only ionic product in these reactions. HNO^- can further react with nitric oxide to form N₂O and HO^-.

Age Induced Nitroso-Redox Imbalance Leads to Subclinical Hypogonadism in Male Mice

Objective: The cause of age-related changes in testosterone remains unclear. We hypothesized that increased nitroso-redox imbalance with aging could affect testosterone production. Materials and Methods: We measured several markers of nitroso-redox imbalance (4-HNE, 3-NT, and NT) in serum of S-nitrosoglutathione reductase knock out (GSNOR KO) mice that have increased nitroso-redox imbalance and compared these to wild-type (WT) mice. We evaluated the impact of age-induced nitroso-redox imbalance on serum luteinizing hormone (LH) and testosterone (T) in WT young (<2 months), middle-aged (2-6 months), and aged (>12 months) mice. Finally, to elucidate the susceptibility of testes to nitroso-redox imbalance, we measured 4-HNE protein levels in the testes of WT and KO mice. Results: We identified 4-HNE as a reliable marker of nitroso-redox imbalance, as evidenced by increased protein levels in serum of GSNOR KO mice compared with WT mice. We demonstrated that 4-HNE serum protein levels increase in WT mice with age but do not accumulate in the testes. We also found that T levels were similar in all age groups. Interestingly, we found that serum LH levels in aged and middle-aged mice were increased when compared to young mice (n = 5) consistent with the phenotype of subclinical hypogonadism. Conclusions: Increased serum 4-HNE and LH levels without changes in T with age suggest that nitroso-redox imbalance is associated with subclinical hypogonadism in aged mice. Recognizing the relationship and etiology of a currently poorly understood classification of hypogonadism could be a paradigm shift in how age-related testosterone change is diagnosed and treated.

Redox Dependent Modifications of Ryanodine Receptor: Basic Mechanisms and Implications in Heart Diseases

Heart contraction vitally depends on tightly controlled intracellular Ca regulation. Because contraction is mainly driven by Ca released from the sarcoplasmic reticulum (SR), this organelle plays a particularly important role in Ca regulation. The type two ryanodine receptor (RyR2) is the major SR Ca release channel in ventricular myocytes. Several cardiac pathologies, including myocardial infarction and heart failure, are associated with increased RyR2 activity and diastolic SR Ca leak. It has been suggested that the increased RyR2 activity plays an important role in arrhythmias and contractile dysfunction. Several studies have linked increased SR Ca leak during myocardial infarction and heart failure to the activation of RyR2 in response to oxidative stress. This activation might include direct oxidation of RyR2 as well as indirect activation via phosphorylation or altered interactions with regulatory proteins. Out of ninety cysteine residues per RyR2 subunit, twenty one were reported to be in reduced state that could be potential targets for redox modifications that include S-nitrosylation, S-glutathionylation, and disulfide cross-linking. Despite its clinical significance, molecular mechanisms of RyR dysfunction during oxidative stress are not fully understood. Herein we review the most recent insights into redox-dependent modulation of RyR2 during oxidative stress and heart diseases.

Neuronal nitric oxide synthase (nNOS) splice variant function: Insights into nitric oxide signaling from skeletal muscle

Defects in neuronal nitric oxide synthase (nNOS) splice variant localization and signaling in skeletal muscle are a firmly established pathogenic characteristic of many neuromuscular diseases, including Duchenne and Becker muscular dystrophy (DMD and BMD, respectively). Therefore, substantial efforts have been made to understand and therapeutically target skeletal muscle nNOS isoform signaling. The purpose of this review is to summarize recent salient advances in understanding of the regulation, targeting, and function of nNOSμ and nNOSβ splice variants in normal and dystrophic skeletal muscle, primarily using findings from mouse models. The first focus of this review is how the differential targeting of nNOS splice variants creates spatially and functionally distinct nitric oxide (NO) signaling compartments at the sarcolemma, Golgi complex, and cytoplasm. Particular attention is given to the functions of sarcolemmal nNOSμ and limitations of current nNOS knockout models. The second major focus is to review current understanding of cGMP-mediated nNOS signaling in skeletal muscle and its emergence as a therapeutic target in DMD and BMD. Accordingly, we address the preclinical and clinical successes and setbacks with the testing of phosphodiesterase 5 inhibitors to redress nNOS signaling defects in DMD and BMD. In summary, this review of nNOS function in normal and dystrophic muscle aims to advance understanding how the messenger NO is harnessed for cellular signaling from a skeletal muscle perspective.

Cardioprotective effect of 2,3-dehydrosilybin preconditioning in isolated rat heart

2,3-dehydrosilybin (DHS) is a minor component of silymarin, Silybum marianum seed extract, used in some dietary supplements. One of the most promising activities of this compound is its anticancer and cardioprotective activity that results, at least partially, from its cytoprotective, antioxidant, and chemopreventive properties. The present study investigated the cardioprotective effects of DHS in myocardial ischemia and reperfusion injury in rats. Isolated hearts were perfused by the Langendorff technique with low dose DHS (100 nM) prior to 30 min of ischemia induced by coronary artery occlusion. After 60 min of coronary reperfusion infarct size was determined by triphenyltetrazolium staining, while lactatedehydrogenase activity was evaluated in perfusate samples collected at several timepoints during the entire perfusion procedure. Signalosomes were isolated from a heart tissue after reperfusion and involved signalling proteins were detected. DHS reduced the extent of infarction compared with untreated control hearts at low concentration; infarct size as proportion of ischemic risk zone was 7.47 ± 3.1% for DHS versus 75.3 ± 4.8% for ischemia. This protective effect was comparable to infarct limitation induced by ischemic preconditioning (22.3 ± 4.5%). Selective inhibition of Src-family kinases with PP2 (4-Amino-3-(4-chlorophenyl)-1-(t-butyl)-1H-pyrazolo[3,4-d]pyrimidine) abrogated the protection afforded by DHS. This study provides experimental evidence that DHS can mediate Src-kinase-dependent cardioprotection against myocardial damage produced by ischemia/reperfusion injury.

Proarrhythmic Remodeling of Calcium Homeostasis in Cardiac Disease; Implications for Diabetes and Obesity

A rapid growth in the incidence of diabetes and obesity has transpired to a major heath issue and economic burden in the postindustrial world, with more than 29 million patients affected in the United States alone. Cardiovascular defects have been established as the leading cause of mortality and morbidity of diabetic patients. Over the last decade, significant progress has been made in delineating mechanisms responsible for the diminished cardiac contractile function and enhanced propensity for malignant cardiac arrhythmias characteristic of diabetic disease. Rhythmic cardiac contractility relies upon the precise interplay between several cellular Ca²⁺ transport protein complexes including plasmalemmal L-type Ca²⁺ channels (LTCC), Na⁺-Ca²⁺ exchanger (NCX1), Sarco/endoplasmic Reticulum (SR) Ca²⁺-ATPase (SERCa2a) and ryanodine receptors (RyR2s), the SR Ca²⁺ release channels. Here we provide an overview of changes in Ca²⁺ homeostasis in diabetic ventricular myocytes and discuss the therapeutic potential of targeting Ca²⁺ handling proteins in the prevention of diabetes-associated cardiomyopathy and arrhythmogenesis.

Proarrhythmic Remodeling of Calcium Homeostasis in Cardiac Disease; Implications for Diabetes and Obesity

A rapid growth in the incidence of diabetes and obesity has transpired to a major heath issue and economic burden in the postindustrial world, with more than 29 million patients affected in the United States alone. Cardiovascular defects have been established as the leading cause of mortality and morbidity of diabetic patients. Over the last decade, significant progress has been made in delineating mechanisms responsible for the diminished cardiac contractile function and enhanced propensity for malignant cardiac arrhythmias characteristic of diabetic disease. Rhythmic cardiac contractility relies upon the precise interplay between several cellular Ca²⁺ transport protein complexes including plasmalemmal L-type Ca²⁺ channels (LTCC), Na⁺-Ca²⁺ exchanger (NCX1), Sarco/endoplasmic Reticulum (SR) Ca²⁺-ATPase (SERCa2a) and ryanodine receptors (RyR2s), the SR Ca²⁺ release channels. Here we provide an overview of changes in Ca²⁺ homeostasis in diabetic ventricular myocytes and discuss the therapeutic potential of targeting Ca²⁺ handling proteins in the prevention of diabetes-associated cardiomyopathy and arrhythmogenesis.

Interplay Between Sub-Cellular Alterations of Calcium Release and T-Tubular Defects in Cardiac Diseases

Asynchronous Ca²⁺ release promotes non-homogeneous myofilament activation, leading to mechanical dysfunction, as well as initiation of propagated calcium waves and arrhythmias. Recent advances in microscopy techniques have allowed for optical recordings of local Ca²⁺ fluxes and action potentials from multiple sub-cellular domains within cardiac cells with unprecedented spatial and temporal resolution. Since then, sub-cellular local information of the spatio-temporal relationship between Ca²⁺ release and action potential propagation have been unlocked, providing novel mechanistic insights in cardiac excitation-contraction coupling (ECC). Here, we review the promising perspectives arouse from repeatedly probing Ca²⁺ release at the same sub-cellular location while simultaneously probing multiple locations at the same time within a single cardiac cell. We also compare the results obtained in three different rodent models of cardiac diseases, highlighting disease-specific mechanisms. Slower local Ca²⁺ release has been observed in regions with defective action potential conduction in diseased cardiac cells. Moreover, significant increment of Ca²⁺ variability (both in time and in space) has been found in diseased cardiac cells but does not directly correlate with local electrical defects nor with the degree of structural aberrations of the cellular membrane system, suggesting a role for other players of the ECC machinery. We finally explore exciting opportunities provided by the technology for studying different cardiomyocyte populations, as well as for dissecting the mechanisms responsible for subcellular spatio-temporal variability of Ca²⁺ release.

Voltage-Dependent Sarcolemmal Ion Channel Abnormalities in the Dystrophin-Deficient Heart

Mutations in the gene encoding for the intracellular protein dystrophin cause severe forms of muscular dystrophy. These so-called dystrophinopathies are characterized by skeletal muscle weakness and degeneration. Dystrophin deficiency also gives rise to considerable complications in the heart, including cardiomyopathy development and arrhythmias. The current understanding of the pathomechanisms in the dystrophic heart is limited, but there is growing evidence that dysfunctional voltage-dependent ion channels in dystrophin-deficient cardiomyocytes play a significant role. Herein, we summarize the current knowledge about abnormalities in voltage-dependent sarcolemmal ion channel properties in the dystrophic heart, and discuss the potentially underlying mechanisms, as well as their pathophysiological relevance.

Resistance exercise mediates remote ischemic preconditioning by limiting cardiac eNOS uncoupling

BACKGROUND

Currently viewed as a complementary non-pharmacological intervention for preventing cardiac disorders, long-term aerobic training produces cardioprotection through remote ischemic preconditioning (RIPC) mechanisms. However, RIPC triggered by acute exercise remains poorly understood. Although resistance exercise (RE) has been highly recommended by several public health guidelines, there is no evidence showing that RE mediates RIPC. Hence, we investigated whether RE induces cardiac RIPC through nitric oxide synthase (NOS)-dependent mechanism.

METHODS AND RESULTS

Acute RE at 40% of the maximal load augmented systemic nitrite levels, associated with increased cardiac eNOS phosphorylation, without affecting nNOS activity. Using an experimental model of myocardial infarction (MI) through ischemia-reperfusion (IR), RE fully prevented the loss of cardiac contractility and the extent of MI size compared to non-exercised (NE) rats. Moreover, RE mitigated aberrant ST-segment and reduced life-threatening arrhythmias induced by IR. Importantly, inhibition of NOS abolished the RE-mediated cardioprotection. After IR, NE rats showed increased cardiac eNOS activity, associated with reduced dimer/monomer ratio. Supporting the pivotal role of eNOS coupling during MI, non-exercised rats displayed a marked generation of reactive oxygen species (ROS) and oxidative-induced carbonylation of proteins, whereas RE prevented these responses. We validated our data demonstrating a restoration of physiological ROS levels in NE + IR cardiac sections treated with BH₄, a cofactor oxidatively depleted during eNOS uncoupling, while cardiac ROS generation from exercised rats remained unchanged, suggesting no physiological needs of supplemental eNOS cofactors.

CONCLUSION

Together, our findings strongly indicate that RE mediates RIPC by limiting eNOS uncoupling and mitigates myocardial IR injury.

Arrhythmogenic Mechanisms in Heart Failure: Linking β-Adrenergic Stimulation, Stretch, and Calcium

Heart failure (HF) is associated with elevated sympathetic tone and mechanical load. Both systems activate signaling transduction pathways that increase cardiac output, but eventually become part of the disease process itself leading to further worsening of cardiac function. These alterations can adversely contribute to electrical instability, at least in part due to the modulation of Ca²⁺ handling at the level of the single cardiac myocyte. The major aim of this review is to provide a definitive overview of the links and cross talk between β-adrenergic stimulation, mechanical load, and arrhythmogenesis in the setting of HF. We will initially review the role of Ca²⁺ in the induction of both early and delayed afterdepolarizations, the role that β-adrenergic stimulation plays in the initiation of these and how the propensity for these may be altered in HF. We will then go onto reviewing the current data with regards to the link between mechanical load and afterdepolarizations, the associated mechano-sensitivity of the ryanodine receptor and other stretch activated channels that may be associated with HF-associated arrhythmias. Furthermore, we will discuss how alterations in local Ca²⁺ microdomains during the remodeling process associated the HF may contribute to the increased disposition for β-adrenergic or stretch induced arrhythmogenic triggers. Finally, the potential mechanisms linking β-adrenergic stimulation and mechanical stretch will be clarified, with the aim of finding common modalities of arrhythmogenesis that could be targeted by novel therapeutic agents in the setting of HF.

Role of Nitric Oxide in the Cardiovascular and Renal Systems

The gasotransmitters are a family of gaseous signaling molecules which are produced endogenously and act at specific receptors to play imperative roles in physiologic and pathophysiologic processes. As a well-known gasotransmitter along with hydrogen sulfide and carbon monoxide, nitric oxide (NO) has earned repute as a potent vasodilator also known as endothelium-derived vasorelaxant factor (EDRF). NO has been studied in greater detail, from its synthesis and mechanism of action to its physiologic, pathologic, and pharmacologic roles in different disease states. Different animal models have been applied to investigate the beneficial effects of NO as an antihypertensive, renoprotective, and antihypertrophic agent. NO and its interaction with different systems like the renin–angiotensin system, sympathetic nervous system, and other gaseous transmitters like hydrogen sulfide are also well studied. However, links that appear to exist between the endocannabinoid (EC) and NO systems remain to be fully explored. Experimental approaches using modulators of its synthesis including substrate, donors, and inhibitors of the synthesis of NO will be useful for establishing the relationship between the NO and EC systems in the cardiovascular and renal systems. Being a potent vasodilator, NO may be unique among therapeutic options for management of hypertension and resulting renal disease and left ventricular hypertrophy. Inclusion of NO modulators in clinical practice may be useful not only as curatives for particular diseases but also for arresting disease prognoses through its interactions with other systems.

Cross-Sectional Associations between Homoarginine, Intermediate Phenotypes, and Atrial Fibrillation in the Community-The Gutenberg Health Study

Homoarginine has come into the focus of interest as a biomarker for cardiovascular disease. Atrial fibrillation (AF) causes a substantial increase in morbidity and mortality. Whether circulating homoarginine is associated with occurrence or persistence of AF and may serve as a new predictive biomarker remains unknown. We measured plasma levels of homoarginine in the population-based Gutenberg health study (3761 patients included, of them 51.7% males), mean age 55.6 ± 10.9 years-old. Associations between homoarginine and intermediate electrocardiographic and echocardiographic phenotypes and manifest AF were examined. Patients with AF (124 patients, of them 73.4% males) had a mean age 64.8 ± 8.6 years-old compared to a mean age of 55.3 ± 10.9 in the population without AF (p-value < 0.001) and showed a less beneficial risk factor profile. The median homoarginine levels in individuals with and without AF were 1.9 μmol/L (interquartile range (IQR) 1.5–2.5) and 2.0 μmol/L (IQR 1.5–2.5), respectively, p = 0.56. In multivariable-adjusted regression analyses homoarginine was not statistically significantly related to electrocardiographic variables. Among echocardiographic variables beta per standard deviation increase was −0.12 (95% confidence interval (CI) −0.23–(−0.02); p = 0.024) for left atrial area and −0.01 (95% CI −0.02–(−0.003); p = 0.013) for E/A ratio. The odds ratio between homoarginine and AF was 0.91 (95% CI 0.70–1.16; p = 0.45). In our large, population-based cross-sectional study, we did not find statistically significant correlations between lower homoarginine levels and occurrence or persistence of AF or most standard electrocardiographic phenotypes, but some moderate inverse associations with echocardiographic left atrial size and E/A. Homoarginine may not represent a strong biomarker to identify individuals at increased risk for AF. Further investigations will be needed to elucidate the role of homoarginine and cardiac function.

nNOS splice variants differentially regulate myofilament function but are dispensable for intracellular calcium and force transients in cardiac papillary muscles

Cardiac muscle expresses three neuronal nitric oxide synthase (nNOS) splice variants: nNOSα, nNOSμ and nNOSβ. The functions of these nNOS splice variants in cardiac muscle, particularly myofilament-associated nNOSβ are unclear. To decipher cardiac nNOS splice variant function we investigated myofilament function and intracellular calcium and force transients in demembranated and intact papillary muscles from two lines of nNOS knockout mice. The first line (KN1) lacks nNOSα and nNOSμ. The second line (KN2) lacks active nNOSα, nNOSμ and nNOSβ. Demembranated KN1 papillary muscles exhibited reduced myofilament ATPase activity (-35%) and specific force (-10%) relative to controls. Demembranated KN2 muscles exhibited a smaller decrease in myofilament ATPase activity (-21%), but a greater reduction in specific force (-26%) relative to controls. Myofilament calcium sensitivity in demembranated KN1 and KN2 papillary muscles was similar to controls. Thus, papillary muscle-expressed nNOS splice variants are necessary for control levels of myofilament ATPase activity and force generation, but dispensable for myofilament calcium sensitivity. The greater reduction in myofilament ATPase relative to specific force in KN1, but not KN2 muscle, reduced the energy cost of muscle contraction, suggesting that nNOSβ increased the energetic efficiency of contraction in the absence of nNOSμ and nNOSα. Analyses of intact KN1 and KN2 papillary muscles showed that both intracellular calcium transients and their evoked force transients were similar to controls at stimulation frequencies between 1 and 3 Hz. Therefore, nNOS was dispensable for baseline excitation-contraction coupling. In summary, these data suggest that nNOS splice variants differentially regulate myofilament function, but not baseline calcium handling in papillary muscles. More importantly, they suggest that nNOSβ is a novel modulator of myofilament function, and ultimately the energetic efficiency of cardiac papillary muscle contraction.

Specificity in nitric oxide signalling

Reactive nitrogen species (RNS) and their cognate redox signalling networks pervade almost all facets of plant growth, development, immunity, and environmental interactions. The emerging evidence implies that specificity in redox signalling is achieved by a multilayered molecular framework. This encompasses the production of redox cues in the locale of the given protein target and protein tertiary structures that convey the appropriate local chemical environment to support redox-based, post-translational modifications (PTMs). Nascent nitrosylases have also recently emerged that mediate the formation of redox-based PTMs. Reversal of these redox-based PTMs, rather than their formation, is also a major contributor of signalling specificity. In this context, the activities of S-nitrosoglutathione (GSNO) reductase and thioredoxin h5 (Trxh5) are a key feature. Redox signalling specificity is also conveyed by the unique chemistries of individual RNS which is overlaid on the structural constraints imposed by tertiary protein structure in gating access to given redox switches. Finally, the interactions between RNS and ROS (reactive oxygen species) can also indirectly establish signalling specificity through shaping the formation of appropriate redox cues. It is anticipated that some of these insights might function as primers to initiate their future translation into agricultural, horticultural, and industrial biological applications.

Asymmetric dimethylarginine (ADMA) as an important risk factor for the increased cardiovascular diseases and heart failure in chronic kidney disease

Patients with chronic kidney disease have an increased cardiovascular morbidity and mortality. It has been recognized that the traditional cardiovascular risk factors could only partially explain the increased cardiovascular morbidity and mortality in patients with chronic kidney disease. Asymmetric dimethylarginine (ADMA) and N-monomethy l-arginine (L-NMMA) are endogenous inhibitors of nitric oxide synthases that attenuate nitric oxide production and enhance reactive oxidative specie generation. Increased plasma ADMA and/or L-NMMA are strong and independent risk factor for chronic kidney disease, and various cardiovascular diseases such as hypertension, coronary artery disease, atherosclerosis, diabetes, and heart failure. Both ADMA and L-NMMA are also eliminated from the body through either degradation by dimethylarginine dimethylaminohydrolase-1 (DDAH1) or urine excretion. This short review will exam the literature of ADMA and L-NMMA degradation and urine excretion, and the role of chronic kidney diseases in ADMA and L-NMMA accumulation and the increased cardiovascular disease risk. Based on all available data, it appears that the increased cardiovascular morbidity in chronic kidney disease may relate to the dramatic increase of systemic ADMA and L-NMMA after kidney failure.

Aucubin protects against pressure overload-induced cardiac remodelling via the β3 -adrenoceptor-neuronal NOS cascades

BACKGROUND AND PURPOSE

Aucubin, the predominant component of Eucommia ulmoides Oliv., has been shown to have profound effects on oxidative stress. As oxidative stress has previously been demonstrated to contribute to acute and chronic myocardial injury, we tested the effects of aucubin on cardiac remodelling and heart failure.

EXPERIMENTAL APPROACH

Initially, H9c2 cardiomyocytes and neonatal rat cardiomyocytes pretreated with aucubin (1, 3, 10, 25 and 50 μM) were challenged with phenylephrine. Secondly, the transverse aorta was constricted in C57/B6 and neuronal NOS (nNOS)-knockout mice, then aucubin (1 or 5 mg·kg^-1 body weight day^-1 ) was injected i.p. for 25 days. Hypertrophy was evaluated by assessing morphological changes, echocardiographic parameters, histological analyses and hypertrophic markers. Oxidative stress was evaluated by examining ROS generation, oxidase activity and NO generation. NOS expression was determined by Western blotting.

KEY RESULTS

Aucubin effectively suppressed cardiac remodelling; in mice, aucubin substantially inhibited pressure overload-induced cardiac hypertrophy, fibrosis and inflammation, whereas knocking out nNOS abolished these cardioprotective effects of aucubin. Blocking or knocking down the β₃ -adrenoceptor abolished the protective effects of aucubin in vitro. Furthermore, aucubin enhanced the protective effects of a β₃ -adrenoceptor agonist in vitro by increasing cellular cAMP levels, whereas treatment with an adenylate cyclase (AC) inhibitor abolished the cardioprotective effects of aucubin.

CONCLUSIONS AND IMPLICATIONS

Aucubin suppresses oxidative stress during cardiac remodelling by increasing the expression of nNOS in a process that requires activation of the β₃ -adrenoceptor/AC/cAMP pathway. These findings suggest that aucubin could have potential as a treatment for cardiac remodelling and heart failure.

Molecular Profile of Priapism Associated with Low Nitric Oxide Bioavailability

Priapism is a disorder in which prolonged penile erection persists uncontrollably, potentially leading to tissue damage. Priapism commonly afflicts patient populations with severely low nitric oxide (NO) bioavailability. Because NO is a primary mediator of erection, the molecular mechanisms involved in priapism pathophysiology associated with low NO bioavailability are not well-understood. The objective of this study was to identify dysregulated molecular targets and signaling pathways in penile tissue of a mouse model of low NO bioavailability that have potential relevance to priapism. Neuronal plus endothelial NO synthase double knockout mice (NOS1/3^-/-) were used as a model of low NO bioavailability. Priapic-like activity was demonstrated in the NOS1/3^-/- mice relative to wild-type (WT) mice by the measurement of prolonged erections following cessation of electrical stimulation of the cavernous nerve. Penile tissue was processed and analyzed by reverse-phase liquid chromatography tandem mass spectrometry. As a result, 1279 total proteins were identified and quantified by spectral counting, 46 of which were down-regulated and 110 of which were up-regulated in NOS1/3^-/- versus WT (P < 0.05). Ingenuity Pathway Analysis of differentially expressed proteins revealed increased protein kinase A and G-protein coupled receptor signaling in NOS1/3^-/- penises, which represent potential mechanisms contributing to priapism for secondary to low NO bioavailability.

Nitric oxide signalling in cardiovascular health and disease

Nitric oxide (NO) signalling has pleiotropic roles in biology and a crucial function in cardiovascular homeostasis. Tremendous knowledge has been accumulated on the mechanisms of the nitric oxide synthase (NOS)-NO pathway, but how this highly reactive, free radical gas signals to specific targets for precise regulation of cardiovascular function remains the focus of much intense research. In this Review, we summarize the updated paradigms on NOS regulation, NO interaction with reactive oxidant species in specific subcellular compartments, and downstream effects of NO in target cardiovascular tissues, while emphasizing the latest developments of molecular tools and biomarkers to modulate and monitor NO production and bioavailability.

Gaseous Signaling Molecules in Cardiovascular Function: From Mechanisms to Clinical Translation

Carbon monoxide (CO), hydrogen sulfide (H₂S), and nitric oxide (NO) constitute endogenous gaseous molecules produced by specific enzymes. These gases are chemically simple, but exert multiple effects and act through shared molecular targets to control both physiology and pathophysiology in the cardiovascular system (CVS). The gases act via direct and/or indirect interactions with each other in proteins such as heme-containing enzymes, the mitochondrial respiratory complex, and ion channels, among others. Studies of the major impacts of CO, H₂S, and NO on the CVS have revealed their involvement in controlling blood pressure and in reducing cardiac reperfusion injuries, although their functional roles are not limited to these conditions. In this review, the basic aspects of CO, H₂S, and NO, including their production and effects on enzymes, mitochondrial respiration and biogenesis, and ion channels are briefly addressed to provide insight into their biology with respect to the CVS. Finally, potential therapeutic applications of CO, H₂S, and NO with the CVS are addressed, based on the use of exogenous donors and different types of delivery systems.

Plastics and cardiovascular health: phthalates may disrupt heart rate variability and cardiovascular reactivity

Plastics have revolutionized medical device technology, transformed hematological care, and facilitated modern cardiology procedures. Despite these advances, studies have shown that phthalate chemicals migrate out of plastic products and that these chemicals are bioactive. Recent epidemiological and research studies have suggested that phthalate exposure adversely affects cardiovascular function. Our objective was to assess the safety and biocompatibility of phthalate chemicals and resolve the impact on cardiovascular and autonomic physiology. Adult mice were implanted with radiofrequency transmitters to monitor heart rate variability, blood pressure, and autonomic regulation in response to di-2-ethylhexyl-phthalate (DEHP) exposure. DEHP-treated animals displayed a decrease in heart rate variability (-17% SD of normal beat-to-beat intervals and -36% high-frequency power) and an exaggerated mean arterial pressure response to ganglionic blockade (31.5% via chlorisondamine). In response to a conditioned stressor, DEHP-treated animals displayed enhanced cardiovascular reactivity (-56% SD major axis Poincarè plot) and prolonged blood pressure recovery. Alterations in cardiac gene expression of endothelin-1, angiotensin-converting enzyme, and nitric oxide synthase may partly explain these cardiovascular alterations. This is the first study to show an association between phthalate chemicals that are used in medical devices with alterations in autonomic regulation, heart rate variability, and cardiovascular reactivity. Because changes in autonomic balance often precede clinical manifestations of hypertension, atherosclerosis, and conduction abnormalities, future studies are warranted to assess the downstream impact of plastic chemical exposure on end-organ function in sensitive patient populations. This study also highlights the importance of adopting safer biomaterials, chemicals, and/or surface coatings for use in medical devices.NEW & NOTEWORTHY Phthalates are widely used in the manufacturing of consumer and medical products. In the present study, di-2-ethylhexyl-phthalate exposure was associated with alterations in heart rate variability and cardiovascular reactivity. This highlights the importance of investigating the impact of phthalates on health and identifying suitable alternatives for medical device manufacturing.

Advanced glycation end products reduce the calcium transient in cardiomyocytes by increasing production of reactive oxygen species and nitric oxide

Advanced glycation end products (AGE) are central to the development of cardiovascular complications associated with diabetes mellitus. AGE may alter cellular function through cross‐linking of cellular proteins or by activating the AGE receptor (RAGE). However, the signalling molecules involved during AGE stimulation in cardiomyocytes remain unclear. Here, we investigated the effects of AGE treatment on intracellular calcium homeostasis of isolated cardiomyocytes and studied the activation of signalling molecules involved in this process. Treatment of cardiomyocytes with AGE for 24 h resulted in a dose‐dependent reduction in calcium transient amplitude, reaching a maximum 50% reduction at a dose of 1 mg·mL⁻¹. This was accompanied with a 32% reduction in sarcoplasmic reticulum calcium content but without any detectable changes in the expression of major calcium channels. Mechanistically, we observed a significant increase in the production of reactive oxygen species (ROS) in AGE‐treated cardiomyocytes and enhancement of NADPH oxidase activity. This was accompanied with activation of p38 kinase and nuclear translocation of NF‐κB, and subsequently induction of inducible NO synthase (iNOS) expression, leading to excessive nitric oxide production. Overall, our data reveal the molecular signalling that may underlie the alteration of intracellular calcium homeostasis in cardiac myocytes due to AGE stimulation. This may provide new insights into the pathophysiological mechanisms of the development of diabetic cardiomyopathy.

Estrogens Protect Calsequestrin-1 Knockout Mice from Lethal Hyperthermic Episodes by Reducing Oxidative Stress in Muscle

Oxidative stress has been proposed to play a key role in malignant hyperthermia (MH), a syndrome caused by excessive Ca²⁺ release in skeletal muscle. Incidence of mortality in male calsequestrin-1 knockout (CASQ1-null) mice during exposure to halothane and heat (a syndrome closely resembling human MH) is far greater than that in females. To investigate the possible role of sex hormones in this still unexplained gender difference, we treated male and female CASQ1-null mice for 1 month, respectively, with Premarin (conjugated estrogens) and leuprolide (GnRH analog) and discovered that during exposure to halothane and heat Premarin reduced the mortality rate in males (79-27% and 86-20%), while leuprolide increased the incidence of mortality in females (18-73% and 24-82%). We then evaluated the (a) responsiveness of isolated muscles to temperature and caffeine, (b) sarcoplasmic reticulum (SR) Ca²⁺ release in single fibers, and (c) oxidative stress and the expression levels of main enzymes involved in the regulation of the redox balance in muscle. Premarin treatment reduced the temperature and caffeine sensitivity of EDL muscles, normalized SR Ca²⁺ release, and reduced oxidative stress in males, suggesting that female sex hormones may protect mice from lethal hyperthermic episodes by reducing both the SR Ca²⁺ leak and oxidative stress.

The genetic variation rs12143842 in NOS1AP increases idiopathic ventricular tachycardia risk in Chinese Han populations

Genome-wide association studies identified that the common T of rs12143842 in NOS1AP is associated with a QT/QTc interval in European populations. In this study, we test the association between the variation rs12143842 in NOS1AP and idiopathic ventricular tachycardia (IVT). A case-control association study examining rs12143842 was performed in two independent cohorts. The Northern cohort enrolled 277 IVT patients and 728 controls from a Chinese Gene ID population. The Central cohort enrolled 301 IVT patients and 803 matched controls. Genotyping was performed using high-resolution melt analysis. The minor T allele of the rs12143842 SNP was significantly associated with decreased IVT risk in the Northern cohort (adjusted P = 0.024, OR 0.71(0.52~0.96)), and this association was replicated in an independent Central Gene ID cohort (adjusted P = 0.029, OR 0.78 (0.62~0.97)). The association was more significant in the combined population (adjusted P = 0.001, OR 0.76 (0.64~0.90)). The P values for the genotypic association were significant for the dominant (P < 0.001) and additive (P = 0.001) models. The minor T allele for the SNP rs12143842 in NOS1AP is significantly associated with IVT. NOS1AP might be a novel gene affecting IVT, and further functional studies should be performed.

Effects of hydrogen sulfide on inducible nitric oxide synthase activity and expression of cardiomyocytes in diabetic rats

The aim of the present study was to investigate the effects of hydrogen sulfide (H₂S) on the activity and expression of inducible nitric oxide synthase (iNOS) in the myocardial tissue of type 1 diabetic rats. Rats were divided randomly into four groups: Normal control (NC), diabetes mellitus (DM), DM+DL-Proparglygylcine (DM+PAG) and DM+sodium hydrosulfide (DM+NaHS) groups. Type 1 diabetes was induced in the respective groups by a single intraperitoneal (i.p.) injection of streptozotocin. Rats in the DM+PAG and DM+NaHS groups were injected with PAG and NaHS (i.p.) once a day, respectively. The level of fasting blood glucose (FBG), the heart-weight to body-weight (HW/BW) ratio and the ventricular hemodynamic parameters were measured. The activities of serum total NOS (tNOS), iNOS, lactate dehydrogenase (LDH), creatine kinase (CK) and creatine kinase MB isozyme (CK-MB), and the content of nitric oxide (NO) were detected. The contents of myocardial malondialdehyde (MDA) and NO, and the activities of superoxide dismutase (SOD), tNOS and iNOS were determined. The myocardial tissue was examined for histological and ultrastructural alterations. The expression level of iNOS at the transcriptional and translational levels in the myocardial tissue was estimated. The level of FBG was increased in the DM group compared with the NC group, verifying the diabetic condition of the rats. The function of the left ventricle, the myocardial histological alterations and ultrastructures were damaged in the DM group. The DM group additionally demonstrated an increase in the serum NO content and tNOS, iNOS, LDH, CK and CK-MB activities. The myocardial MDA, NO content and tNOS levels were additionally increased in this group. The iNOS activity was increased significantly whereas the myocardial SOD activity was decreased. The increase in the iNOS activity was supported by an enhanced expression level of myocardial iNOS mRNA and protein in the DM group. In the DM+PAG group, in the absence of H₂S, the dysfunction of the left ventricle and the oxidative stress injury were increased compared with the DM group. The activity and the expression of tNOS and iNOS were increased significantly. However, the rats in the DM+PAG group demonstrated the opposite effects. In conclusion, H₂S exhibits a protective effect on the myocardium in type 1 diabetic rats, which may be associated with the suppression of iNOS activity and expression, a decrease in the NO content and the inhibition of oxidative stress injury.

Nitric oxide signalling and neuronal nitric oxide synthase in the heart under stress

Nitric oxide (NO) is an imperative regulator of the cardiovascular system and is a critical mechanism in preventing the pathogenesis and progression of the diseased heart. The scenario of bioavailable NO in the myocardium is complex: 1) NO is derived from both endogenous NO synthases (endothelial, neuronal, and/or inducible NOSs [eNOS, nNOS, and/or iNOS]) and exogenous sources (entero-salivary NO pathway) and the amount of NO from exogenous sources varies significantly; 2) NOSs are located at discrete compartments of cardiac myocytes and are regulated by distinctive mechanisms under stress; 3) NO regulates diverse target proteins through different modes of post-transcriptional modification (soluble guanylate cyclase [sGC]/cyclic guanosine monophosphate [cGMP]/protein kinase G [PKG]-dependent phosphorylation, S-nitrosylation, and transnitrosylation); 4) the downstream effectors of NO are multidimensional and vary from ion channels in the plasma membrane to signalling proteins and enzymes in the mitochondria, cytosol, nucleus, and myofilament; 5) NOS produces several radicals in addition to NO (e.g. superoxide, hydrogen peroxide, peroxynitrite, and different NO-related derivatives) and triggers redox-dependent responses. However, nNOS inhibits cardiac oxidases to reduce the sources of oxidative stress in diseased hearts. Recent consensus indicates the importance of nNOS protein in cardiac protection under pathological stress. In addition, a dietary regime with high nitrate intake from fruit and vegetables together with unsaturated fatty acids is strongly associated with reduced cardiovascular events. Collectively, NO-dependent mechanisms in healthy and diseased hearts are better understood and shed light on the therapeutic prospects for NO and NOSs in clinical applications for fatal human heart diseases.

Endogenous nitric oxide formation in cardiac myocytes does not control respiration during β-adrenergic stimulation

KEY POINTS

In the heart, endothelial nitric oxide (NO) controls oxygen consumption in the working heart through paracrine mechanisms. While cardiac myocytes contain several isoforms of NO synthases, it is unclear whether these can control respiration in an intracrine fashion. A long-standing controversy is whether a NOS exists within mitochondria. By combining fluorescence technologies with electrical field stimulation or the patch-clamp technique in beating cardiac myocytes, we identified a neuronal NO synthase (nNOS) as the most relevant source of intracellular NO during β-adrenergic stimulation, while no evidence for a mitochondria-located NOS was obtained. The amounts of NO produced by non-mitochondrial nNOS were insufficient to regulate respiration during β-adrenergic stimulation, arguing against intracrine control of respiration by NO within cardiac myocytes.

ABSTRACT

Endothelial nitric oxide (NO) controls cardiac oxygen (O₂ ) consumption in a paracrine way by slowing respiration at the mitochondrial electron transport chain. While NO synthases (NOSs) are also expressed in cardiac myocytes, it is unclear whether they control respiration in an intracrine way. Furthermore, the existence of a mitochondrial NOS is controversial. Here, by combining fluorescence imaging with electrical field stimulation, the patch-clamp method and knock-out technology, we determined the sources and consequences of intracellular NO formation during workload transitions in isolated murine and guinea pig cardiac myocytes and mitochondria. Using 4-amino-5-methylamino-2',7'-difluorofluorescein diacetate (DAF) as a fluorescent NO-sensor that locates to the cytosol and mitochondria, we observed that NO increased by ∼12% within 3 min of β-adrenergic stimulation in beating cardiac myocytes. This NO stems from neuronal NOS (nNOS), but not endothelial (eNOS). After patch clamp-mediated dialysis of cytosolic DAF, the remaining NO signals (mostly mitochondrial) were blocked by nNOS deletion, but not by inhibiting the mitochondrial Ca²⁺ uniporter with Ru360. While in isolated mitochondria exogenous NO inhibited respiration and reduced the NAD(P)H redox state, pyridine nucleotide redox states were unaffected by pharmacological or genetic disruption of endogenous nNOS or eNOS during workload transitions in cardiac myoctyes. We conclude that under physiological conditions, nNOS is the most relevant source for NO in cardiac myocytes, but this nNOS is not located in mitochondria and does not control respiration. Therefore, cardiac O₂ consumption is controlled by endothelial NO in a paracrine, but not intracrine, fashion.

Cardioprotective Action of Ginkgo biloba Extract against Sustained β-Adrenergic Stimulation Occurs via Activation of M2/NO Pathway

Ginkgo biloba is the most popular phytotherapic agent used worldwide for treatment of several human disorders. However, the mechanisms involved in the protective actions of Ginkgo biloba on cardiovascular diseases remain poorly elucidated. Taking into account recent studies showing beneficial actions of cholinergic signaling in the heart and the cholinergic hypothesis of Ginkgo biloba-mediated neuroprotection, we aimed to investigate whether Ginkgo biloba extract (GBE) promotes cardioprotection via activation of cholinergic signaling in a model of isoproterenol-induced cardiac hypertrophy. Here, we show that GBE treatment (100 mg/kg/day for 8 days, v.o.) reestablished the autonomic imbalance and baroreflex dysfunction caused by chronic β-adrenergic receptor stimulation (β-AR, 4.5 mg/kg/day for 8 days, i.p.). Moreover, GBE prevented the upregulation of muscarinic receptors (M₂) and downregulation of β₁-AR in isoproterenol treated-hearts. Additionally, we demonstrated that GBE prevents the impaired endothelial nitric oxide synthase activity in the heart. GBE also prevented the pathological cardiac remodeling, electrocardiographic changes and impaired left ventricular contractility that are typical of cardiac hypertrophy. To further investigate the mechanisms involved in GBE cardioprotection in vivo, we performed in vitro studies. By using neonatal cardiomyocyte culture we demonstrated that the antihypertrophic action of GBE was fully abolished by muscarinic receptor antagonist or NOS inhibition. Altogether, our data support the notion that antihypertrophic effect of GBE occurs via activation of M₂/NO pathway uncovering a new mechanism involved in the cardioprotective action of Ginkgo biloba.

Reactive Oxygen Species/Nitric Oxide Mediated Inter-Organ Communication in Skeletal Muscle Wasting Diseases

SIGNIFICANCE

Cachexia is defined as a complex metabolic syndrome that is associated with underlying illness and a loss of muscle with or without loss of fat mass. This disease is associated with a high incidence with chronic diseases such as heart failure, cancer, chronic obstructive pulmonary disease (COPD), and acquired immunodeficiency syndrome (AIDS), among others. Since there is currently no effective treatment available, cachectic patients have a poor prognosis. Elucidation of the underlying mechanisms is, therefore, an important medical task. Recent Advances: There is accumulating evidence that the diseased organs such as heart, lung, kidney, or cancer tissue secrete soluble factors, including Angiotensin II, myostatin (growth differentiation factor 8 [GDF8]), GDF11, tumor growth factor beta (TGFβ), which act on skeletal muscle. There, they induce a set of genes called atrogenes, which, among others, induce the ubiquitin-proteasome system, leading to protein degradation. Moreover, elevated reactive oxygen species (ROS) levels due to modulation of NADPH oxidases (Nox) and mitochondrial function contribute to disease progression, which is characterized by loss of muscle mass, exercise resistance, and frailty.

CRITICAL ISSUES

Although substantial progress was achieved to elucidate the pathophysiology of cachexia, effectice therapeutic strategies are urgently needed.

FUTURE DIRECTIONS

With the identification of key components of the aberrant inter-organ communication leading to cachexia, studies in mice and men to inhibit ROS formation, induction of anti-oxidative superoxide dismutases, and upregulation of muscular nitric oxide (NO) formation either by pharmacological tools or by exercise are promising approaches to reduce the extent of skeletal muscle wasting. Antioxid. Redox Signal. 26, 700-717.

Mechanisms of the cyclic nucleotide cross-talk signaling network in cardiac L-type calcium channel regulation

Regulation of L-type Calcium (Ca2+) Channel (LCC) gating is critical to shaping the cardiac action potential (AP) and triggering the initiation of excitation-contraction (EC) coupling in cardiac myocytes. The cyclic nucleotide (cN) cross-talk signaling network, which encompasses the β-adrenergic and the Nitric Oxide (NO)/cGMP/Protein Kinase G (PKG) pathways and their interaction (cross-talk) through distinctively-regulated phosphodiesterase isoenzymes (PDEs), regulates LCC current via Protein Kinase A- (PKA) and PKG-mediated phosphorylation. Due to the tightly-coupled and intertwined biochemical reactions involved, it remains to be clarified how LCC gating is regulated by the signaling network from receptor to end target. In addition, the large number of EC coupling-related phosphorylation targets of PKA and PKG makes it difficult to quantify and isolate changes in L-type Ca2+ current (ICaL) responses regulated by the signaling network. We have developed a multi-scale, biophysically-detailed computational model of LCC regulation by the cN signaling network that is supported by experimental data. LCCs are modeled with functionally distinct PKA- and PKG-phosphorylation dependent gating modes. The model exhibits experimentally observed single channel characteristics, as well as whole-cell LCC currents upon activation of the cross-talk signaling network. Simulations show 1) redistribution of LCC gating modes explains changes in whole-cell current under various stimulation scenarios of the cN cross-talk network; 2) NO regulation occurs via potentiation of a gating mode characterized by prolonged closed times; and 3) due to compensatory actions of cross-talk and antagonizing functions of PKA- and PKG-mediated phosphorylation of LCCs, the effects of individual inhibitions of PDEs 2, 3, and 4 on ICaL are most pronounced at low levels of β-adrenergic stimulation. Simulations also delineate the contribution of the following two mechanisms to overall LCC regulation, which have otherwise been challenging to distinguish: 1) regulation of PKA and PKG activation via cN cross-talk (Mechanism 1); and 2) LCC interaction with activated PKA and PKG (Mechanism 2). These results provide insights into how cN signals transduced via the cN cross-talk signaling network are integrated via LCC regulation in the heart.

Sex Differences in Metabolic Cardiomyopathy

In contrast to ischemic cardiomyopathies which are more common in men, women are over-represented in diabetic cardiomyopathies. Diabetes is a risk factor for cardiovascular disease; however, there is a sexual dimorphism in this risk factor: heart disease is five times more common in diabetic women but only two-times more common in diabetic men. Heart failure with preserved ejection fraction, which is associated with metabolic syndrome, is also more prevalent in women. This review will examine potential mechanisms for the sex differences in metabolic cardiomyopathies. Sex differences in metabolism, calcium handling, nitric oxide, and structural proteins will be evaluated. Nitric oxide synthase and PPARα exhibit sex differences and have also been proposed to mediate the development of hypertrophy and heart failure. We focused on a role for these signalling pathways in regulating sex differences in metabolic cardiomyopathies.

Dissipative energy loss within the left ventricle detected by vector flow mapping in diabetic patients with controlled and uncontrolled blood glucose levels

Diabetes mellitus (DM) is related to increased risks of cardiovascular diseases, such as myocardial infarction, diabetic cardiomyopathy and secondary hypertension. Dissipative energy loss (EL) derived from vector flow mapping (VFM) is thought to reflect the efficiency of blood flow and has been deemed to be an index for the evaluation of left ventricular function. Our study aimed to investigate the value of dissipative EL in diabetic patients with controlled and uncontrolled blood glucose by VFM. Eighty-eight patients with DM and 58 age-matched healthy controls were recruited. All of the patients received echocardiography examinations. VFM analyses were executed to calculate the EL values according to the apical four-chamber examinations from the left ventricle (LV) view. Our results showed that diastolic EL was compromised in the controlled-blood glucose (59.19 mV/m vs. 32.68 mV/m, p = 0.039) patients and was more dramatically increased in the uncontrolled blood glucose group (88.84 mV/m vs. 32.68 mV/m, p < 0.001) compared with the healthy controls. The impairment of systolic EL was observed only in the uncontrolled blood glucose patients (39.65 mV/m vs. 20.29 mV/m, p < 0.001) and not in the controlled blood glucose patients (29.25 mV/m vs. 20.29 mV/m, p = 0.072). Multivariate backward stepwise linear regression analysis revealed that the HbA1c level was independently related to the diastolic EL (β = 0.233, p = 0.026) and systolic EL (β = 0.237, p = 0.023). VFM is feasible and reproducible for assessing LV dissipative EL in DM patients with normal LVEF values in whom diastolic EL may be a more vulnerable indicator of early LV cardiac dysfunction in patients with DM. However, LV systolic EL may be a sensitive indicator of preclinical LV dysfunction for patients with DM with uncontrolled blood glucose levels. Uncontrolled blood glucose, which is independently correlated with subclinical LV dysfunction, may lead to increases in systolic EL and diastolic EL in LV.

Blood Pressure in Healthy Humans Is Regulated by Neuronal NO Synthase

NO is physiologically generated by endothelial and neuronal NO synthase (nNOS) isoforms. Although nNOS was first identified in brain, it is expressed in other tissues, including perivascular nerves, cardiac and skeletal muscle. Increasing experimental evidence suggests that nNOS has important effects on cardiovascular function, but its composite effects on systemic hemodynamics in humans are unknown. We undertook the first human study to assess the physiological effects of systemic nNOS inhibition on basal hemodynamics. Seventeen healthy normotensive men aged 24±4 years received acute intravenous infusions of an nNOS-selective inhibitor, S-methyl-l-thiocitrulline, and placebo on separate occasions. An initial dose-escalation study showed that S-methyl-l-thiocitrulline (0.1–3.0 µmol/kg) induced dose-dependent changes in systemic hemodynamics. The highest dose of S-methyl-l-thiocitrulline (3.0 µmol/kg over 10 minutes) significantly increased systemic vascular resistance (+42±6%) and diastolic blood pressure (67±1 to 77±3 mm Hg) when compared with placebo (both P<0.01). There were significant decreases in heart rate (60±4 to 51±3 bpm; P<0.01) and left ventricular stroke volume (59±6 to 51±6 mL; P<0.01) but ejection fraction was unaltered. S-methyl-l-thiocitrulline had no effect on radial artery flow-mediated dilatation, an index of endothelial NOS activity. These results suggest that nNOS-derived NO has an important role in the physiological regulation of basal systemic vascular resistance and blood pressure in healthy humans.

Regulation of Cell Calcium and Role of Plasma Membrane Calcium ATPases

The plasma membrane Ca²⁺ ATPase (PMCA pump) is a member of the superfamily of P-type pumps. It has 10 transmembrane helices and 2 cytosolic loops, one of which contains the catalytic center. Its most distinctive feature is a C-terminal tail that contains most of the regulatory sites including that for calmodulin. The pump is also regulated by acidic phospholipids, kinases, a dimerization process, and numerous protein interactors. In mammals, four genes code for the four basic isoforms. Isoform complexity is increased by alternative splicing of primary transcripts. Pumps 2 and 3 are expressed preferentially in the nervous system. The pumps coexist with more powerful systems that clear Ca²⁺ from the bulk cytosol: their role is thus the regulation of Ca²⁺ in selected subplasma membrane microdomains, where a number of important Ca²⁺-dependent enzymes interact with them. Malfunctions of the pump lead to disease phenotypes that affect the nervous system preferentially.

The Subcellular Localisation of Neuronal Nitric Oxide Synthase Determines the Downstream Effects of NO on Myocardial Function

Aims

In healthy hearts, the neuronal nitric oxide synthase (nNOS) is predominantly localized to the sarcoplasmic reticulum (SR), where it regulates the ryanodine receptor Ca2+ release channel (RyR2) and phospholamban (PLB) phosphorylation, and to a lesser extent to the sarcolemmal membrane where it inhibits the L-type Ca2+ current (I Ca). However, in failing hearts, impaired relaxation and depressed inotropy are associated with a larger proportion of nNOS being localized to the sarcolemmal membrane. Whether there is a causal relationship between altered myocardial function and subcellular localization of nNOS remains to be assessed.

Methods and results

Adenoviruses (AdV) encoding for a human nNOS.eGFP fusion protein or eGFP were injected into the left ventricle (LV) of nNOS−/− mice. nNOS.eGFP localized to the sarcolemmal and t-tubular membrane and immunoprecipitated with syntrophin and caveolin-3 but not with RyR2. Myocardial transduction of nNOS.eGFP resulted in a significantly increased NOS activity (10-fold, P < 0.01), a 20% increase in myocardial tetrahydrobiopterin (BH4) (P < 0.05), and a 30% reduction in superoxide production (P < 0.001). LV myocytes transduced with nNOS.eGFP showed a significantly lower basal and β-adrenergic stimulated I Ca, [Ca2+]i transient amplitude and cell shortening (vs. eGFP). All differences between groups were abolished after NOS inhibition. In contrast, nNOS.eGFP had no effect on RyR nitrosylation, PLB phosphorylation or the rate of myocardial relaxation and [Ca2+]i decay.

Conclusion

Our findings indicate that nNOS-mediated regulation of myocardial excitation–contraction (E–C) coupling is exquisitely dependent on nNOS subcellular localization and suggests a partially adaptive role for sarcolemmal nNOS in the human failing myocardium.

Association evidence of CCTTT repeat polymorphism in the iNOS promoter and the risk of atrial fibrillation in Taiwanese

Inducible nitric oxide synthase (iNOS) plays an important role in the pathogenesis of atrial fibrillation (AF). The iNOS promoter has a CCTTT-repeat length polymorphism that can determine the level of gene transcription. This study enrolled 200 AF patients and 240 controls. The length of CCTTT-repeat polymorphism in the iNOS promoter region was examined by polymerase chain reactions, with the alleles with ≤11 repeats designated as S and alleles with ≥12 repeats designated as L alleles. AF patients carried significantly higher frequencies of the LL genotype than control subjects (40.0% versus 28.3%, P = 0.010). Multivariate analysis showed that the presence of LL genotype was significantly associated with AF (odds ratio: 1.87, 95% CI = 1.10–3.17, P = 0.021). In vitro, transient transfection assay in HL-1 atrial myocytes showed that the responsiveness of iNOS transcriptional activity to tachypacing was correlated with the length of the CCTTT-repeats. Right atrial tissues from patients with chronic AF were investigated with immunoconfocal microscopy. Patients with LL genotype exhibited greater oxidative stress and substrate remodeling in their atria than those with non-LL genotypes. Our results suggest that the iNOS microsatellite polymorphism may contribute to the genetic background of AF in Chinese-Taiwanese patients.

Nitric oxide: what's new to NO?

Nitric oxide (NO) is one of the critical components of the vasculature, regulating key signaling pathways in health. In macrovessels, NO functions to suppress cell inflammation as well as adhesion. In this way, it inhibits thrombosis and promotes blood flow. It also functions to limit vessel constriction and vessel wall remodeling. In microvessels and particularly capillaries, NO, along with growth factors, is important in promoting new vessel formation, a process termed angiogenesis. With age and cardiovascular disease, animal and human studies confirm that NO is dysregulated at multiple levels including decreased production, decreased tissue half-life, and decreased potency. NO has also been implicated in diseases that are related to neurotransmission and cancer although it is likely that these processes involve NO at higher concentrations and from nonvascular cell sources. Conversely, NO and drugs that directly or indirectly increase NO signaling have found clinical applications in both age-related diseases and in younger individuals. This focused review considers recently reported advances being made in the field of NO signaling regulation at several levels including enzymatic production, receptor function, interacting partners, localization of signaling, matrix-cellular and cell-to-cell cross talk, as well as the possible impact these newly described mechanisms have on health and disease.

Mechanotransduction and Metabolism in Cardiomyocyte Microdomains

Efficient contractions of the left ventricle are ensured by the continuous transfer of adenosine triphosphate (ATP) from energy production sites, the mitochondria, to energy utilization sites, such as ionic pumps and the force-generating sarcomeres. To minimize the impact of intracellular ATP trafficking, sarcomeres and mitochondria are closely packed together and in proximity with other ultrastructures involved in excitation-contraction coupling, such as t-tubules and sarcoplasmic reticulum junctions. This complex microdomain has been referred to as the intracellular energetic unit. Here, we review the literature in support of the notion that cardiac homeostasis and disease are emergent properties of the hierarchical organization of these units. Specifically, we will focus on pathological alterations of this microdomain that result in cardiac diseases through energy imbalance and posttranslational modifications of the cytoskeletal proteins involved in mechanosensing and transduction.

Perspectives and challenges of antioxidant therapy for atrial fibrillation

Atrial fibrillation (AF) is the most common sustained arrhythmia associated with significant morbidity and mortality. The mechanisms underlying the pathogenesis of AF are poorly understood, although electrophysiological remodeling has been described as an important initiating step. There is growing evidence that oxidative stress is involved in the pathogenesis of AF. Many known triggers of oxidative stress, such as age, diabetes, smoking, and inflammation, are linked with an increased risk of arrhythmia. Numerous preclinical studies and clinical trials reported the importance of antioxidant therapy in the prevention of AF, using vitamins C and E, polyunsaturated fatty acids, statins, or nitric oxide donors. The aim of our work is to give a current overview and analysis of opportunities, challenges, and benefits of antioxidant therapy in AF.

Uniform low-level dystrophin expression in the heart partially preserved cardiac function in an aged mouse model of Duchenne cardiomyopathy

Dystrophin deficiency results in Duchenne cardiomyopathy, a primary cause of death in Duchenne muscular dystrophy (DMD). Gene therapy has shown great promise in ameliorating the cardiac phenotype in mouse models of DMD. However, it is not completely clear how much dystrophin is required to treat dystrophic heart disease. We and others have shown that mosaic dystrophin expression at the wild-type level, depending on the percentage of dystrophin positive cardiomyocytes, can either delay the onset of or fully prevent cardiomyopathy in dystrophin-null mdx mice. Many gene therapy strategies will unlikely restore dystrophin to the wild-type level in a cardiomyocyte. To determine whether low-level dystrophin expression can reduce the cardiac manifestations in DMD, we examined heart histology, ECG and hemodynamics in 21-m-old normal BL6 and two strains of BL6-background dystrophin-deficient mice. Mdx3cv mice show uniform low-level expression of a near full-length dystrophin protein in every myofiber while mdx4cv mice have no dystrophin expression. Immunostaining and western blot confirmed marginal level dystrophin expression in the heart of mdx3cv mice. Although low-level expression did not reduce myocardial histopathology, it significantly ameliorated QRS prolongation and normalized diastolic hemodynamic deficiencies. Our study demonstrates for the first time that low-level dystrophin can partially preserve heart function.

The Relationship between Estrogen and Nitric Oxide in the Prevention of Cardiac and Vascular Anomalies in the Developing Zebrafish (Danio Rerio)

It has been known that both estrogen (E2) and nitric oxide (NO) are critical for proper cardiovascular system (CVS) function. It has also been demonstrated that E2 acts as an upstream effector in the nitric oxide (NO) pathway. Results from this study indicate that the use of a nitric oxide synthase (NOS) inhibitor (NOSI) which targets specifically neuronal NOS (nNOS or NOS1), proadifen hydrochloride, caused a significant depression of fish heart rates (HR) accompanied by increased arrhythmic behavior. However, none of these phenotypes were evident with either the inhibition of endothelial NOS (eNOS) or inducible NOS (iNOS) isoforms. These cardiac arrhythmias could also be mimicked by inhibition of E2 synthesis with the aromatase inhibitor (AI), 4-OH-A, in a manner similar to that of nNOSI. In both scenarios, by using an NO donor (DETA-NO) in either NO + nNOSI or E2 + AI co-treatments, fish could be significantly rescued from decreased HR and increased arrhythmias. However, the addition of an NOS inhibitor (L-NAME) to the E2 + AI co-treatment fish prevented the rescue of low heart rates and arrhythmias, which strongly implicates the NO pathway as a downstream E2 targeted molecule for the maintenance of healthy cardiomyocyte contractile conditions in the developing zebrafish. Cardiac arrhythmias could be mimicked by the S-nitrosylation pathway inhibitor DTT (1,4-dithiothreitol) but not by ODQ (1H-[1–3]oxadiazolo[4,3-a]quinoxalin-1-one), the inhibitor of the NO receptor molecule sGC in the cGMP-dependent pathway. In both the nNOSI and AI-induced arrhythmic conditions, 100% of the fish expressed the phenotype, but could be rapidly rescued with maximum survival by a washout with dantrolene, a ryanodine Ca²⁺ channel receptor blocker, compared to the time it took for rescue using a control salt solution. In addition, of the three NOS isoforms, eNOS was the one most implicated in the maintenance of an intact developing fish vascular system. In conclusion, results from this study have shown that nNOS is the prominent isoform that is responsible, in part, for maintaining normal heart rates and prevention of arrhythmias in the developing zebrafish heart failure model. These phenomena are related to the upstream stimulatory regulation by E2. On the other hand, eNOS has a minimal effect and iNOS has little to no influence on this phenomenon. Data also suggests that nNOS acts on the zebrafish cardiomyocytes through the S-nitrosylation pathway to influence the SR ryanidine Ca²⁺ channels in the excitation-coupling phenomena. In contrast, eNOS is the prominent isoform that influences blood vessel development in this model.

Associations of Macro- and Microvascular Endothelial Dysfunction With Subclinical Ventricular Dysfunction in End-Stage Renal Disease

Patients with end-stage renal disease (ESRD) suffer high rates of heart failure and cardiovascular mortality, and we lack a thorough understanding of what, if any, modifiable factors contribute to cardiac dysfunction in these high-risk patients. To evaluate endothelial function as a potentially modifiable cause of cardiac dysfunction in ESRD, we investigated cross-sectional associations of macro- and microvascular dysfunction with left and right ventricular dysfunction in a well-controlled ESRD cohort. We performed comprehensive echocardiography, including tissue Doppler imaging and speckle-tracking echocardiography of the left and right ventricle, in 149 ESRD patients enrolled in an ongoing prospective, observational study. Of these participants, 123 also underwent endothelium-dependent flow-mediated dilation of the brachial artery (macrovascular function). Microvascular function was measured as the velocity time integral of hyperemic blood flow after cuff deflation. Impaired flow-mediated dilation was associated with higher left ventricular mass, independently of age and blood pressure: per 2-fold lower flow-mediated dilation, left ventricular mass was 4.1% higher (95% confidence interval, 0.49-7.7; P=0.03). After adjustment for demographics, blood pressure, comorbidities, and medications, a 2-fold lower velocity time integral was associated with 9.5% higher E/e' ratio (95% confidence interval, 1.0-16; P=0.03) and 6.7% lower absolute right ventricular longitudinal strain (95% confidence interval, 2.0-12; P=0.003). Endothelial dysfunction is a major correlate of cardiac dysfunction in ESRD, particularly diastolic and right ventricular dysfunction, in patients whose volume status is well controlled. Future investigations are needed to determine whether therapies targeting the vascular endothelium could improve cardiac outcomes in ESRD.

Nitric Oxide Signaling and Clinical Alternatives to Nitric Oxide

Nitric oxide has been implicated in numerous biological processes, particularly those involved with the cardiovascular system. Nitric oxide production is closely regulated and influenced by a number of factors in both health and disease. Nitric oxide is involved in maintaining the vascular system in its healthy, nondiseased state by producing vasorelaxation which enhances blood flow and prevents both leukocyte and platelet adhesion to the vascular wall. Dysfunctional endothelial cell nitric oxide production has been implicated in a number of disease states, including hypertension and atherosclerosis, and has been associated with adverse cardiac events. Various recent therapies may exert their beneficial effects in part by enhancing endothelial nitric oxide bloavallability. Nitric oxide has been used therapeutically in a number of cardiorespiratory disease states. An improved understanding of the pathologic processes underlying these diseases has resulted in several alternative agents being investigated and used clinically.