Modulation of myocardial contraction by peroxynitrite

Increased chaperone activity of human α‌B-crystallin with incomplete oxidation as a new defense mechanism against oxidative stress

Previous research has shown that production of the high levels of oxidants overwhelms the body's antioxidant defense system during diabetes mellitus. Under this circumstance, ocular lens proteins are one of the main molecular targets for oxidative damage. In the present study, the individual effect of partial and extensive oxidation on the structure and function of human αB-crystallin was investigated using electrophoresis and various spectroscopic methods. The results of our study suggested that widespread oxidation causes loss of the chaperone activity of this protein, while partial oxidation significantly enhances this activity. Our studies also suggested that partial and extensive oxidation induces the formation of different structures in this protein. In fact, the chaperone-active and chaperone-inactive states of this protein are respectively associated with a minor and extensive structural alteration. Moreover, the oligomeric size distribution shows an inverse relationship with the chaperone activity of this protein. Increasing the chaperone activity of this protein during partial oxidation may be a natural defense mechanism to overcome the damages caused by oxidative stress, especially in diabetes and other pathological diseases.

The expanding roles of neuronal nitric oxide synthase (NOS1)

The nitric oxide synthases (NOS; EC 1.14.13.39) use L-arginine as a substrate to produce nitric oxide (NO) as a by-product in the tissue microenvironment. NOS1 represents the predominant NO-producing enzyme highly enriched in the brain and known to mediate multiple functions, ranging from learning and memory development to maintaining synaptic plasticity and neuronal development, Alzheimer's disease (AD), psychiatric disorders and behavioral deficits. However, accumulating evidence indicate both canonical and non-canonical roles of NOS1-derived NO in several other tissues and chronic diseases. A better understanding of NOS1-derived NO signaling, and identification and characterization of NO-metabolites in non-neuronal tissues could become useful in diagnosis and prognosis of diseases associated with NOS1 expression. Continued investigation on the roles of NOS1, therefore, will synthesize new knowledge and aid in the discovery of small molecules which could be used to titrate the activities of NOS1-derived NO signaling and NO-metabolites. Here, we address the significance of NOS1 and its byproduct NO in modifying pathophysiological events, which could be beneficial in understanding both the disease mechanisms and therapeutics.

An emerging perspective on sex differences: Intersecting S-nitrosothiol and aldehyde signaling in the heart

Cardiovascular disease is the leading cause of the death for both men and women. Although baseline heart physiology and the response to disease are known to differ by sex, little is known about sex differences in baseline molecular signaling, especially with regard to redox biology. In this review, we describe current research on sex differences in cardiac redox biology with a focus on the regulation of nitric oxide and aldehyde signaling. Furthermore, we argue for a new perspective on cardiovascular sex differences research, one that focuses on baseline redox biology without the elimination or disruption of sex hormones.

A selenoprotein T-derived peptide protects the heart against ischaemia/reperfusion injury through inhibition of apoptosis and oxidative stress

AIM

Selenoprotein T (SelT or SELENOT) is a novel thioredoxin-like enzyme whose genetic ablation in mice results in early embryonic lethality. SelT exerts an essential cytoprotective action during development and after injury through its redox-active catalytic site. This study aimed to determine the expression and regulation of SelT in the mammalian heart in normal and pathological conditions and to evaluate the cardioprotective effect of a SelT-derived peptide, SelT43-52(PSELT) encompassing the redox motif which is key to its function, against ischaemia/reperfusion(I/R) injury.

METHODS

We used the isolated Langendorff rat heart model and different analyses by immunohistochemistry, Western blot and ELISA.

RESULTS

We found that SelT expression is very abundant in embryo but is undetectable in adult heart. However, SelT expression was tremendously increased after I/R. PSELT (5 nmol/L) was able to induce pharmacological post-conditioning cardioprotection as evidenced by a significant recovery of contractility (dLVP) and reduction of infarct size (IS), without changes in cardiac contracture (LVEDP). In contrast, a control peptide lacking the redox site did not confer cardioprotection. Immunoblot analysis showed that PSELT-dependent cardioprotection is accompanied by a significant increase in phosphorylated Akt, Erk-1/2 and Gsk3α-β, and a decrement of p38MAPK. PSELT inhibited the pro-apoptotic factors Bax, caspase 3 and cytochrome c and stimulated the anti-apoptotic factor Bcl-2. Furthermore, PSELT significantly reduced several markers of I/R-induced oxidative and nitrosative stress.

CONCLUSION

These results unravel the role of SelT as a cardiac modulator and identify PSELT as an effective pharmacological post-conditioning agent able to protect the heart after ischaemic injury.

Kcnj11 Ablation Is Associated With Increased Nitro-Oxidative Stress During Ischemia-Reperfusion Injury: Implications for Human Ischemic Cardiomyopathy

BACKGROUND

Despite increased secondary cardiovascular events in patients with ischemic cardiomyopathy (ICM), the expression of innate cardiac protective molecules in the hearts of patients with ICM is incompletely characterized. Therefore, we used a nonbiased RNAseq approach to determine whether differences in cardiac protective molecules occur with ICM.

METHODS AND RESULTS

RNAseq analysis of human control and ICM left ventricular samples demonstrated a significant decrease in KCNJ11 expression with ICM. KCNJ11 encodes the Kir6.2 subunit of the cardioprotective K_ATP channel. Using wild-type mice and kcnj11-deficient (kcnj11-null) mice, we examined the effect of kcnj11 expression on cardiac function during ischemia-reperfusion injury. Reactive oxygen species generation increased in kcnj11-null hearts above that found in wild-type mice hearts after ischemia-reperfusion injury. Continuous left ventricular pressure measurement during ischemia and reperfusion demonstrated a more compromised diastolic function in kcnj11-null compared with wild-type mice during reperfusion. Analysis of key calcium-regulating proteins revealed significant differences in kcnj11-null mice. Despite impaired relaxation, kcnj11-null hearts increased phospholamban Ser16 phosphorylation, a modification that results in the dissociation of phospholamban from sarcoendoplasmic reticulum Ca²⁺, thereby increasing sarcoendoplasmic reticulum Ca²⁺-mediated calcium reuptake. However, kcnj11-null mice also had increased 3-nitrotyrosine modification of the sarcoendoplasmic reticulum Ca²⁺-ATPase, a modification that irreversibly impairs sarcoendoplasmic reticulum Ca²⁺ function, thereby contributing to diastolic dysfunction.

CONCLUSIONS

KCNJ11 expression is decreased in human ICM. Lack of kcnj11 expression increases peroxynitrite-mediated modification of the key calcium-handling protein sarcoendoplasmic reticulum Ca²⁺-ATPase after myocardial ischemia-reperfusion injury, contributing to impaired diastolic function. These data suggest a mechanism for ischemia-induced diastolic dysfunction in patients with ICM.

Ischemia/Reperfusion Injury following Acute Myocardial Infarction: A Critical Issue for Clinicians and Forensic Pathologists

Acute myocardial infarction (AMI) is a leading cause of morbidity and mortality. Reperfusion strategies are the current standard therapy for AMI. However, they may result in paradoxical cardiomyocyte dysfunction, known as ischemic reperfusion injury (IRI). Different forms of IRI are recognized, of which only the first two are reversible: reperfusion-induced arrhythmias, myocardial stunning, microvascular obstruction, and lethal myocardial reperfusion injury. Sudden death is the most common pattern for ischemia-induced lethal ventricular arrhythmias during AMI. The exact mechanisms of IRI are not fully known. Molecular, cellular, and tissue alterations such as cell death, inflammation, neurohumoral activation, and oxidative stress are considered to be of paramount importance in IRI. However, comprehension of the exact pathophysiological mechanisms remains a challenge for clinicians. Furthermore, myocardial IRI is a critical issue also for forensic pathologists since sudden death may occur despite timely reperfusion following AMI, that is one of the most frequently litigated areas of cardiology practice. In this paper we explore the literature regarding the pathophysiology of myocardial IRI, focusing on the possible role of the calpain system, oxidative-nitrosative stress, and matrix metalloproteinases and aiming to foster knowledge of IRI pathophysiology also in terms of medicolegal understanding of sudden deaths following AMI.

Cross-talk between lipid and protein carbonylation in a dynamic cardiomyocyte model of mild nitroxidative stress

Reactive oxygen and nitrogen species (ROS/RNS) play an important role in the regulation of cardiac function. Increase in ROS/RNS concentration results in lipid and protein oxidation and is often associated with onset and/or progression of many cardiovascular disorders. However, interplay between lipid and protein modifications has not been simultaneously studied in detail so far. Biomolecule carbonylation is one of the most common biomarkers of oxidative stress. Using a dynamic model of nitroxidative stress we demonstrated rapid changes in biomolecule carbonylation in rat cardiomyocytes. Levels of carbonylated species increased as early as 15min upon treatment with the peroxynitrite donor, 3-morpholinosydnonimine (SIN-1), and decreased to values close to control after 16h. Total (lipids+proteins) vs. protein-specific carbonylation showed different dynamics, with a significant increase in protein-bound carbonyls at later time points. Treatment with SIN-1 in combination with inhibitors of proteasomal and autophagy/lysosomal degradation pathways allowed confirmation of a significant role of the proteasome in the degradation of carbonylated proteins, whereas lipid carbonylation increased in the presence of autophagy/lysosomal inhibitors. Electrophilic aldehydes and ketones formed by lipid peroxidation were identified and relatively quantified using LC-MS/MS. Molecular identity of reactive species was used for data-driven analysis of their protein targets. Combination of different enrichment strategies with LC-MS/MS analysis allowed identification of more than 167 unique proteins with 332 sites modified by electrophilic lipid peroxidation products. Gene ontology analysis of modified proteins demonstrated enrichment of several functional categories including proteins involved in cytoskeleton, extracellular matrix, ion channels and their regulation. Using calcium mobilization assays, the effect of nitroxidative stress on the activity of several ion channels was further confirmed.

Alu RNA accumulation in hyperglycemia augments oxidative stress and impairs eNOS and SOD2 expression in endothelial cells

Endothelial dysfunction resulting from oxidative stress and inflammation plays a dominant role in hyperglycemia-induced vasculopathy. While double-stranded RNA (dsRNA) accumulates in redox and inflammatory conditions, its precise role in hyperglycemia-associated endothelial dysfunction remains unclear. This study aimed to investigate whether and how endogenous dsRNA contributes to endothelial dysfunction via oxidative stress. We used a dsRNA-specific antibody J2 to detect and immunoprecipitate cellular dsRNA. Acquired dsRNA was recognized by cDNA library construction and DNA sequencing. Quantitative PCR, ELISA and immunoassays were performed to identify changes induced by acquired dsRNA in primary human umbilical vein endothelial cells (HUVEC). Our data showed that endogenous dsRNA homologous to Alu Sc subfamily accumulated in hyperglycemic HUVEC. Comparing Alu-transfected HUVEC with high-glucose treated HUVEC, we found that Alu RNA elicited the production of reactive oxygen species (ROS) and up-regulated interleukin-1β (IL-1β) expression and secretion in a similar manner as high-glucose treatment. Moreover, Alu RNA impeded the expression of endothelial nitric oxide synthase (eNOS) and superoxide dismutase 2 (SOD2), increased ROS production and activated nuclear factor NFκB by chemically scavenging ROS and inactivation of NFκB. The repressed expression of eNOS and SOD2 resulted from Alu RNA-mediated negative regulatory mechanisms. Our study uncovered endogenous Alu RNA accumulation in hyperglycemic endothelial cells that provoked endothelial oxidative stress and dysfunction by suppressing SOD2 and eNOS expression at both transcription and translation levels via NFκB signaling pathway. These findings suggest a novel regulatory mechanism that involves endogenous dsRNA in endothelial oxidative stress and dysfunction.

Phosphoinositide 3-kinase gamma controls inflammation-induced myocardial depression via sequential cAMP and iNOS signalling

AIMS

Sepsis-induced myocardial depression (SIMD), an early and frequent event of infection-induced systemic inflammatory response syndrome (SIRS), is characterized by reduced contractility irrespective of enhanced adrenergic stimulation. Phosphoinositide-3 kinase γ (PI3Kγ) is known to prevent β-adrenergic overstimulation via its scaffold function by activating major cardiac phosphodiesterases and restricting cAMP levels. However, the role of PI3Kγ in SIRS-induced myocardial depression is unknown. This study is aimed at determining the specific role of lipid kinase-dependent and -independent functions of PI3Kγ in the pathogenesis of SIRS-induced myocardial depression.

METHODS AND RESULTS

PI3Kγ knockout mice (PI3Kγ(-/-)), mice expressing catalytically inactive PI3Kγ (PI3Kγ(KD/KD)), and wild-type mice (P3Kγ(+/+)) were exposed to lipopolysaccharide (LPS)-induced systemic inflammation and assessed for survival, cardiac autonomic nervous system function, and left ventricular performance. Additionally, primary adult cardiomyocytes were used to analyse PI3Kγ effects on myocardial contractility and inflammatory response. SIRS-induced adrenergic overstimulation induced a transient hypercontractility state in PI3Kγ(-/-) mice, followed by reduced contractility. In contrast, P3Kγ(+/+) mice and PI3Kγ(KD/KD) mice developed an early and ongoing myocardial depression despite exposure to similarly increased catecholamine levels. Compared with cells from P3Kγ(+/+) and PI3Kγ(KD/KD) mice, cardiomyocytes from PI3Kγ(-/-) mice showed an enhanced and prolonged cAMP-mediated signalling upon norepinephrine and an intensified LPS-induced proinflammatory response characterized by nuclear factor of activated T-cells-mediated inducible nitric oxide synthase up-regulation.

CONCLUSIONS

This study reveals the lipid kinase-independent scaffold function of PI3Kγ as a mediator of SIMD during inflammation-induced SIRS. Activation of cardiac phosphodiesterases via PI3Kγ is shown to restrict myocardial hypercontractility early after SIRS induction as well as the subsequent inflammatory responses.

Abnormal Ca(2+) cycling in failing ventricular myocytes: role of NOS1-mediated nitroso-redox balance

SIGNIFICANCE

Heart failure (HF) results from poor heart function and is the leading cause of death in Western society. Abnormalities of Ca(2+) handling at the level of the ventricular myocyte are largely responsible for much of the poor heart function.

RECENT ADVANCES

Although studies have unraveled numerous mechanisms for the abnormal Ca(2+) handling, investigations over the past decade have indicated that much of the contractile dysfunction and adverse remodeling that occurs in HF involves oxidative stress.

CRITICAL ISSUES

Regrettably, antioxidant therapy has been an immense disappointment in clinical trials. Thus, redox signaling is being reassessed to elucidate why antioxidants failed to treat HF.

FUTURE DIRECTIONS

A recently identified aspect of redox signaling (specifically the superoxide anion radical) is its interaction with nitric oxide, known as the nitroso-redox balance. There is a large nitroso-redox imbalance with HF, and we suggest that correcting this imbalance may be able to restore myocyte contraction and improve heart function.

Interaction between neuronal nitric oxide synthase signaling and temperature influences sarcoplasmic reticulum calcium leak: role of nitroso-redox balance

RATIONALE

Although nitric oxide (NO) signaling modulates cardiac function and excitation-contraction coupling, opposing results because of inconsistent experimental conditions, particularly with respect to temperature, confound the ability to elucidate NO signaling pathways. Here, we show that temperature significantly modulates NO effects.

OBJECTIVE

To test the hypothesis that temperature profoundly affects nitroso-redox equilibrium, thereby affecting sarcoplasmic reticulum (SR) calcium (Ca(2+)) leak.

METHODS AND RESULTS

We measured SR Ca(2+) leak in cardiomyocytes from wild-type (WT), NO/redox imbalance (neuronal nitric oxide synthase-deficient mice-1 [NOS1(-/-)]), and hyper S-nitrosoglutathione reductase-deficient (GSNOR(-/-)) mice. In WT cardiomyocytes, SR Ca(2+) leak increased because temperature decreased from 37°C to 23°C, whereas in NOS1(-/-) cells, the leak suddenly increased when the temperature surpassed 30°C. GSNOR(-/-) cardiomyocytes exhibited low leak throughout the temperature range. Exogenously added NO had a biphasic effect on NOS1(-/-) cardiomyocytes; reducing leak at 37°C but increasing it at subphysiological temperatures. Oxypurinol and Tempol diminished the leak in NOS1(-/-) cardiomyocytes. Cooling from 37°C to 23°C increased reactive oxygen species generation in WT but decreased it in NOS1(-/-) cardiomyocytes. Oxypurinol further reduced reactive oxygen species generation. At 23°C in WT cells, leak was decreased by tetrahydrobiopterin, an essential NOS cofactor. Cooling significantly increased SR Ca(2+) content in NOS1(-/-) cells but had no effect in WT or GSNOR(-/-).

CONCLUSIONS

Ca(2+) leak and temperature are normally inversely proportional, whereas NOS1 deficiency reverses this effect, increasing leak and elevating reactive oxygen species production because temperature increases. Reduced denitrosylation (GSNOR deficiency) eliminates the temperature dependence of leak. Thus, temperature regulates the balance between NO and reactive oxygen species which in turn has a major effect on SR Ca(2+).

Targeting NOS as a therapeutic approach for heart failure

Nitric oxide is a key signaling molecule in the heart and is produced endogenously by three isoforms of nitric oxide synthase, neuronal NOS (NOS1), endothelial NOS (NOS3), and inducible NOS (NOS2). Nitric oxide signals via cGMP-dependent or independent pathways to modulate downstream proteins via specific post translational modifications (i.e. cGMP-dependent protein kinase phosphorylation, S-nitrosylation, etc.). Dysfunction of NOS (i.e. altered expression, location, coupling, activity, etc.) exists in various cardiac disease conditions, such as heart failure, contributing to the contractile dysfunction, adverse remodeling, and hypertrophy. This review will focus on the signaling pathways of each NOS isoform during health and disease, and discuss current and potential therapeutic approaches targeting nitric oxide signaling to treat heart disease.

ROS-responsive activatable photosensitizing agent for imaging and photodynamic therapy of activated macrophages

The optical properties of macrophage-targeted theranostic nanoparticles (MacTNP) prepared from a Chlorin e6 (Ce6)-hyaluronic acid (HA) conjugate can be activated by reactive oxygen species (ROS) in macrophage cells. MacTNP are nonfluorescent and nonphototoxic in their native state. However, when treated with ROS, especially peroxynitrite, they become highly fluorescent and phototoxic. In vitro cell studies show that MacTNP emit near-infrared (NIR) fluorescence inside activated macrophages. The NIR fluorescence is quenched in the extracellular environment. MacTNP are nontoxic in macrophages up to a Ce6 concentration of 10 μM in the absence of light. However, MacTNP become phototoxic upon illumination in a light dose-dependent manner. In particular, significantly higher phototoxic effect is observed in the activated macrophage cells compared to human dermal fibroblasts and non-activated macrophages. The ROS-responsive MacTNP, with their high target-to-background ratio, may have a significant potential in selective NIR fluorescence imaging and in subsequent photodynamic therapy of atherosclerosis with minimum side effects.