Therapeutic Potential of Nitroxyl (HNO) Donors in the Management of Acute Decompensated Heart Failure

Oxidative Stress and Cerebral Vascular Tone: The Role of Reactive Oxygen and Nitrogen Species

The brain's unique characteristics make it exceptionally susceptible to oxidative stress, which arises from an imbalance between reactive oxygen species (ROS) production, reactive nitrogen species (RNS) production, and antioxidant defense mechanisms. This review explores the factors contributing to the brain's vascular tone's vulnerability in the presence of oxidative damage, which can be of clinical interest in critically ill patients or those presenting acute brain injuries. The brain's high metabolic rate and inefficient electron transport chain in mitochondria lead to significant ROS generation. Moreover, non-replicating neuronal cells and low repair capacity increase susceptibility to oxidative insult. ROS can influence cerebral vascular tone and permeability, potentially impacting cerebral autoregulation. Different ROS species, including superoxide and hydrogen peroxide, exhibit vasodilatory or vasoconstrictive effects on cerebral blood vessels. RNS, particularly NO and peroxynitrite, also exert vasoactive effects. This review further investigates the neuroprotective effects of antioxidants, including superoxide dismutase (SOD), vitamin C, vitamin E, and the glutathione redox system. Various studies suggest that these antioxidants could be used as adjunct therapies to protect the cerebral vascular tone under conditions of high oxidative stress. Nevertheless, more extensive research is required to comprehensively grasp the relationship between oxidative stress and cerebrovascular tone, and explore the potential benefits of antioxidants as adjunctive therapies in critical illnesses and acute brain injuries.

Synthesis and nitroxyl (HNO) donating properties of benzoxadiazole-based Piloty's acids

Developing functional nitroxyl (HNO) donors play a significant role in the further exploration of endogenous HNO in biochemistry and pharmacology. In this work, two novel Piloty's acids (SBD-D1 and SBD-D2) were proposed by incorporating benzoxadiazole-based fluorophores, in order to achieve the dual-function of releasing both HNO and a fluorophore in situ. Under physiological conditions, both SBD-D1 and SBD-D2 efficiently donated HNO (t_1/2 = 10.96 and 8.18 min, respectively). The stoichiometric generation of HNO was determined by both vitamin B₁₂ and phosphine compound traps. Interestingly, due to the different substitution groups on the aromatic ring, SBD-D1 with the chlorine showed no fluorescence emission, but SBD-D2 was strongly fluorescent due to the presence of the dimethylamine group. Specifically, the fluorescent signal would decrease during the release process of HNO. Moreover, theoretical calculations were performed to understand the emission difference. A strong radiation derived from benzoxadiazole with dimethylamine group due to the large transition dipole moment (∼4.3 Debye), while the presence of intramolecular charge transfer process in the donor with chlorine group caused a small transition dipole moment (<0.1 Debye). Finally, these studies would contribute to the future design and application of novel functional HNO donors for the exploration of HNO biochemistry and pharmacology.

The inorganic chemistry of the cobalt corrinoids - an update

The inorganic chemistry of the cobalt corrinoids, derivatives of vitamin B₁₂, is reviewed, with particular emphasis on equilibrium constants for, and kinetics of, their axial ligand substitution reactions. The role the corrin ligand plays in controlling and modifying the properties of the metal ion is emphasised. Other aspects of the chemistry of these compounds, including their structure, corrinoid complexes with metals other than cobalt, the redox chemistry of the cobalt corrinoids and their chemical redox reactions, and their photochemistry are discussed. Their role as catalysts in non-biological reactions and aspects of their organometallic chemistry are briefly mentioned. Particular mention is made of the role that computational methods - and especially DFT calculations - have played in developing our understanding of the inorganic chemistry of these compounds. A brief overview of the biological chemistry of the B₁₂-dependent enzymes is also given for the reader's convenience.

The Chemistry of HNO: Mechanisms and Reaction Kinetics

Azanone (HNO, also known as nitroxyl) is the protonated form of the product of one-electron reduction of nitric oxide (^•NO), and an elusive electrophilic reactive nitrogen species of increasing pharmacological significance. Over the past 20 years, the interest in the biological chemistry of HNO has increased significantly due to the numerous beneficial pharmacological effects of its donors. Increased availability of various HNO donors was accompanied by great progress in the understanding of HNO chemistry and chemical biology. This review is focused on the chemistry of HNO, with emphasis on reaction kinetics and mechanisms in aqueous solutions.

Cardioprotective Actions of Nitroxyl Donor Angeli's Salt are Preserved in the Diabetic Heart and Vasculature in the Face of Nitric Oxide Resistance

Background and Purpose

The risk of fatal cardiovascular events is increased in patients with type 2 diabetes mellitus (T2DM). A major contributor to poor prognosis is impaired nitric oxide (NO•) signalling at the level of tissue responsiveness, termed NO• resistance. This study aimed to determine if T2DM promotes NO• resistance in the heart and vasculature and whether tissue responsiveness to nitroxyl (HNO) is affected.

Experimental Approach

At 8 weeks of age, male Sprague–Dawley rats commenced a high‐fat diet. After 2 weeks, the rats received low‐dose streptozotocin (two intraperitoneal injections, 35 mg·kg⁻¹, over two consecutive days) and continued on the same diet. Twelve weeks later, isolated hearts were Langendorff‐perfused to assess responses to the NO• donor diethylamine NONOate (DEA/NO) and the HNO donor Angeli's salt. Isolated mesenteric arteries were utilised to measure vascular responsiveness to the NO• donors sodium nitroprusside (SNP) and DEA/NO, and the HNO donor Angeli's salt.

Key Results

Inotropic, lusitropic and coronary vasodilator responses to DEA/NO were impaired in T2DM hearts, whereas responses to Angeli's salt were preserved or enhanced. Vasorelaxation to Angeli's salt was augmented in T2DM mesenteric arteries, which were hyporesponsive to the relaxant effects of SNP and DEA/NO.

Conclusion and Implications

This is the first evidence that inotropic and lusitropic responses are preserved, and NO• resistance in the coronary and mesenteric vasculature is circumvented, by the HNO donor Angeli's salt in T2DM. These findings highlight the cardiovascular therapeutic potential of HNO donors, especially in emergencies such as acute ischaemia or heart failure.

Vasoprotective Actions of Nitroxyl (HNO): A Story of Sibling Rivalry

ABSTRACT

Nitroxyl (HNO), the 1 electron-reduced and protonated form of nitric oxide (NO•), has emerged as a nitrogen oxide with a suite of vasoprotective properties and therapeutic advantages over its redox sibling. Although HNO has garnered much attention due to its cardioprotective actions in heart failure, its ability to modulate vascular function, without the limitations of tolerance development and NO• resistance, is desirable in the treatment of vascular disease. HNO serves as a potent vasodilator and antiaggregatory agent and has an ability to limit vascular inflammation and reactive oxygen species generation. In addition, its resistance to scavenging by reactive oxygen species and ability to target distinct vascular signaling pathways (Kv, KATP, and calcitonin gene-related peptide) contribute to its preserved efficacy in hypertension, diabetes, and hypercholesterolemia. In this review, the vasoprotective actions of HNO will be compared with those of NO•, and the therapeutic utility of HNO donors in the treatment of angina, acute cardiovascular emergencies, and chronic vascular disease are discussed.

Kinetic Study on the Reactivity of Azanone (HNO) toward Cyclic C-Nucleophiles

Azanone (HNO) is an elusive electrophilic reactive nitrogen species of growing pharmacological and biological significance. Here, we present a comparative kinetic study of HNO reactivity toward selected cyclic C-nucleophiles under aqueous conditions at pH 7.4. We applied the competition kinetics method, which is based on the use of a fluorescein-derived boronate probe FlBA and two parallel HNO reactions: with the studied scavenger or with O₂ (k = 1.8 × 10⁴ M⁻¹s⁻¹). We determined the second-order rate constants of HNO reactions with 13 structurally diverse C-nucleophiles (k = 33–20,000 M⁻¹s⁻¹). The results show that the reactivity of HNO toward C-nucleophiles depends strongly on the structure of the scavenger. The data are supported with quantum mechanical calculations. A comprehensive discussion of the HNO reaction with C-nucleophiles is provided.

Azanone (HNO): generation, stabilization and detection

HNO (nitroxyl, azanone), joined the 'biologically relevant reactive nitrogen species' family in the 2000s. Azanone is impossible to store due to its high reactivity and inherent low stability. Consequently, its chemistry and effects are studied using donor compounds, which release this molecule in solution and in the gas phase upon stimulation. Researchers have also tried to stabilize this elusive species and its conjugate base by coordination to metal centers using several ligands, like metalloporphyrins and pincer ligands. Given HNO's high reactivity and short lifetime, several different strategies have been proposed for its detection in chemical and biological systems, such as colorimetric methods, EPR, HPLC, mass spectrometry, fluorescent probes, and electrochemical analysis. These approaches are described and critically compared. Finally, in the last ten years, several advances regarding the possibility of endogenous HNO generation were made; some of them are also revised in the present work.

Updating NO•/HNO interconversion under physiological conditions: A biological implication overview

Azanone (HNO/NO^-), also called nitroxyl, is a highly reactive compound whose biological role is still a matter of debate. A key issue that remains to be clarified regarding HNO and its biological activity is that of its endogenous formation. Given the overlap of the molecular targets and reactivity of nitric oxide (NO•) and HNO, its chemical biology was perceived to be similar to that of NO• as a biological signaling agent. However, despite their closely related reactivity, NO• and HNO's biochemical pathways are quite different. Moreover, the reduction of nitric oxide to azanone is possible but necessarily coupled to other reactions, which drive the reaction forward, overcoming the unfavorable thermodynamic barrier. The mechanism of this NO•/HNO interplay and its downstream effects in different contexts were studied recently, showing that more than fifteen moderate reducing agents react with NO• producing HNO. Particularly, it is known that the reaction between nitric oxide and hydrogen sulfide (H₂S) produces HNO. However, this rate constant was not reported yet. In this work, firstly the NO•/H₂S effective rate constant was measured as a function of the pH. Then, the implications of these chemical (non-enzymatic), biologically compatible, routes to endogenous HNO formation was discussed. There is no doubt that HNO could be (is?) a new endogenously produced messenger that mediates specific physiological responses, many of which were attributed yet to direct NO• effects.

In vivo effects of nitrosyl hydrogen on cardiac function and sarcoplasmic reticulum calcium pump (SERCA2a) in rats with heart failure after myocardial infarction

Background

Abnormal Ca2+ circulation in cardiomyocytes is an important cause of decreased myocardial contractility in failing hearts. Nitroxyl hydrogen (HNO) can oxidize Ca²⁺ cycle-related proteins, alter their biological functions, promote Ca²⁺ recovery as well as release, and enhance myocardial contractility. In this study, we aim to observe the effect of nitrosyl hydrogen (HNO) on the cardiac function of rats with heart failure and elucidate the underlying mechanism.

Methods

Twenty six male Wistar rats were randomly divided into heart failure group (HF group), Angeli's salt treatment group (HF + AS group) and sham operation group (Sham group). The HF + AS group rats were treated with HNO donor Angeli's salt by intraperitoneal injection of 1 mg/kg/d, and the rats in the HF group and the Sham group were given the same amount of normal saline. Cardiac function was measured by echocardiography before and after treatment. NT-proBNP was measured by enzyme immunoassay (ELISA) kit after treatment. Western blot were used to measure the expression of sarcoplasmic reticulum Ca²⁺-ATPase (SERCA) in protein levels in rats. The activities of SERCA2a were detected by the biochemical kit finally.

Results

We found that Nitrosyl hydrogen could significantly increase LVEF, +dp/dt, -dp/dt (P<0.05), significantly decrease NT-ProBNP and LVEDP (P<0.01), and significantly enhance the activities of SERCA2a protein (P<0.05).

Conclusions

These findings suggest that Nitrosyl hydrogen could improve the cardiac function possibly by increasing protein activities of SERCA2a in rats.

Receptor-independent modulation of cAMP-dependent protein kinase and protein phosphatase signaling in cardiac myocytes by oxidizing agents

The contraction and relaxation of the heart is controlled by stimulation of the β1-adrenoreceptor (AR) signaling cascade, which leads to activation of cAMP-dependent protein kinase (PKA) and subsequent cardiac protein phosphorylation. Phosphorylation is counteracted by the main cardiac protein phosphatases, PP2A and PP1. Both kinase and phosphatases are sensitive to intramolecular disulfide formation in their catalytic subunits that inhibits their activity. Additionally, intermolecular disulfide formation between PKA type I regulatory subunits (PKA-RI) has been described to enhance PKA's affinity for protein kinase A anchoring proteins, which alters its subcellular distribution. Nitroxyl donors have been shown to affect contractility and relaxation, but the mechanistic basis for this effect is unclear. The present study investigates the impact of several nitroxyl donors and the thiol-oxidizing agent diamide on cardiac myocyte protein phosphorylation and oxidation. Although all tested compounds equally induced intermolecular disulfide formation in PKA-RI, only 1-nitrosocyclohexalycetate (NCA) and diamide induced reproducible protein phosphorylation. Phosphorylation occurred independently of β1-AR activation, but was abolished after pharmacological PKA inhibition and thus potentially attributable to increased PKA activity. NCA treatment of cardiac myocytes induced translocation of PKA and phosphatases to the myofilament compartment as shown by fractionation, immunofluorescence, and proximity ligation assays. Assessment of kinase and phosphatase activity within the myofilament fraction of cardiac myocytes after exposure to NCA revealed activation of PKA and inhibition of phosphatase activity thus explaining the increase in phosphorylation. The data suggest that the NCA-mediated effect on cardiac myocyte protein phosphorylation orchestrates alterations in the kinase/phosphatase balance.

A new electrochemical strategy for the synthesis of a new type of sulfonamide derivatives

This study is the first report of electrochemical generation of hydroxyimino-cyclohexa-dien-ylidene haloniums and their application in the synthesis of new halo-N-hydroxysulfonamide derivatives. These compounds were obtained in a one-pot process based on the reaction of halonium acceptors with arylsulfinic acids. The method is easy to carry out, as it is performed using the carbon electrodes in a simple undivided cell. The protocol has a broad substrate scope with a tolerance for a variety of functional groups. The proposed mechanism is a ping-pong type reaction mechanism, which in its first stage the halonitroarene is reduced at the cathode to related hydroxylamine and in the second stage the cathodically generated hydroxylamine by oxidation at the anode and participating in disproportionation reaction is converted to the halonium acceptor.

Cardiovascular Therapeutic Potential of the Redox Siblings, Nitric Oxide (NO•) and Nitroxyl (HNO), in the Setting of Reactive Oxygen Species Dysregulation

Reactive oxygen species (ROS) dysregulation is a hallmark of cardiovascular disease, characterised by an imbalance in the synthesis and removal of ROS. ROS such as superoxide (•O₂^-), hydrogen peroxide (H₂O₂), hydroxyl (OH•) and peroxynitrite (ONOO^-) have a marked impact on cardiovascular function, contributing to the vascular impairment and cardiac dysfunction associated with diseases such as angina, hypertension, diabetes and heart failure. Central to the vascular dysfunction is a reduction in bioavailability and/or physiological effects of vasoprotective nitric oxide (NO•), leading to vasoconstriction, inflammation and vascular remodelling. In a cardiac context, increased ROS generation can also lead to modification of key proteins involved in cardiac contractility. Whilst playing a key role in the pathogenesis of cardiovascular disease, ROS dysregulation also limits the clinical efficacy of current therapies, such as nitrosovasodilators. As such, alternate therapies are sought. This review will discuss the impact of ROS dysregulation on the therapeutic utility of NO• and its redox sibling, nitroxyl (HNO). Both nitric oxide (NO) and nitroxyl (HNO) donors signal through soluble guanylyl cyclase (sGC). NO binds to the Fe(II) form of sGC and nitroxyl possibly to both sGC heme and thiol groups. In the vasculature, nitroxyl can also signal through voltage-dependent (K_v) and ATP-sensitive (K_ATP) K⁺ channels as well as calcitonin gene-related peptide (CGRP). In the heart, HNO directly targets critical thiols to increase myocardial contractility, an effect not seen with NO. The qualitative effects via elevation of cGMP are similar, i.e. lusitropic in the heart and inhibitory on vasoconstriction, inflammation, aggregation and vascular remodelling. Of pathophysiological significance is the fact the efficacy of NO donors is impaired by ROS, e.g. through chemical scavenging of NO, to generate reactive nitrogen oxide species (RNOS), whilst nitroxyl is apparently not.

Nitroxyl: A Novel Strategy to Circumvent Diabetes Associated Impairments in Nitric Oxide Signaling

Diabetes is associated with an increased mortality risk due to cardiovascular complications. Hyperglycemia-induced oxidative stress underlies these complications, leading to an impairment in endogenous nitric oxide (NO•) generation, together with reductions in NO• bioavailability and NO• responsiveness in the vasculature, platelets and myocardium. The latter impairment of responsiveness to NO•, termed NO• resistance, compromises the ability of traditional NO•-based therapeutics to improve hemodynamic status during diabetes-associated cardiovascular emergencies, such as acute myocardial infarction. Whilst a number of agents can ameliorate (e.g. angiotensin converting enzyme [ACE] inhibitors, perhexiline, statins and insulin) or circumvent (e.g. nitrite and sGC activators) NO• resistance, nitroxyl (HNO) donors offer a novel opportunity to circumvent NO• resistance in diabetes. With a suite of vasoprotective properties and an ability to enhance cardiac inotropic and lusitropic responses, coupled with preserved efficacy in the setting of oxidative stress, HNO donors have intact therapeutic potential in the face of diminished NO• signaling. This review explores the major mechanisms by which hyperglycemia-induced oxidative stress drives NO• resistance, and the therapeutic potential of HNO donors to circumvent this to treat cardiovascular complications in type 2 diabetes mellitus.

Nitric Oxide Resistance, Induced in the Myocardium by Diabetes, Is Circumvented by the Nitric Oxide Redox Sibling, Nitroxyl

Aim: Impairment of tissue responsiveness to exogenous and endogenous nitric oxide (NO^•), known as NO^• resistance, occurs in many cardiovascular disease states, prominently in diabetes and especially in the presence of marked hyperglycemia. In this study, we sought to determine in moderate and severe diabetes (i) whether NO^• resistance also occurs in the myocardium, and (ii) whether the NO^• redox sibling nitroxyl (HNO) circumvents this. Results: The spectrum of acute NO^• effects (induced by diethylamine-NONOate), including vasodilation, and enhanced myocardial contraction and relaxation were impaired by moderately diabetic rats ([blood glucose] ∼20 mM). In contrast, acute HNO effects (induced by isopropylamine-NONOate) were preserved even in more severe diabetes ([blood glucose] >28 mM). Intriguingly, the positive inotropic effects of HNO were significantly enhanced in diabetic rat hearts. Further, progressive attenuation of soluble guanylyl cyclase (sGC) contribution to myocardial NO^• responses occurred with increasing severity of diabetes. Nevertheless, activation of sGC by HNO remained intact in the myocardium. Innovation: Diabetes is associated with marked attenuation of vascular and myocardial effects of NO and NO donors, and this NO^• resistance is circumvented by HNO, suggesting potential therapeutic utility for HNO donors in cardiovascular emergencies in diabetics. Conclusion: These results provide the first evidence that NO^• resistance occurs in diabetic hearts, and that HNO largely circumvents this problem. Further, the positive inotropic and lusitropic effects of HNO are enhanced in a severely diabetic myocardium, a finding that warrants further mechanistic interrogation. The results support a potential role for therapeutic HNO administration in acute treatment of ischemia and/or heart failure in diabetics.

Hypertrophic Cardiomyopathy: A Vicious Cycle Triggered by Sarcomere Mutations and Secondary Disease Hits

Significance: Hypertrophic cardiomyopathy (HCM) is a cardiac genetic disease characterized by left ventricular hypertrophy, diastolic dysfunction, and myocardial disarray. Disease onset occurs between 20 and 50 years of age, thus affecting patients in the prime of their life. HCM is caused by mutations in sarcomere proteins, the contractile building blocks of the heart. Despite increased knowledge of causal mutations, the exact path from genetic defect leading to cardiomyopathy is complex and involves additional disease hits. Recent Advances: Laboratory-based studies indicate that HCM development not only depends on the primary sarcomere impairment caused by the mutation but also on secondary disease-related alterations in the heart. Here we propose a vicious mutation-induced disease cycle, in which a mutation-induced energy depletion alters cellular metabolism with increased mitochondrial work, which triggers secondary disease modifiers that will worsen disease and ultimately lead to end-stage HCM. Critical Issues: Evidence shows excessive cellular reactive oxygen species (ROS) in HCM patients and HCM animal models. Oxidative stress markers are increased in the heart (oxidized proteins, DNA, and lipids) and serum of HCM patients. In addition, increased mitochondrial ROS production and changes in endogenous antioxidants are reported in HCM. Mutant sarcomeric protein may drive excessive levels of cardiac ROS via changes in cardiac efficiency and metabolism, mitochondrial activation and/or dysfunction, impaired protein quality control, and microvascular dysfunction. Future Directions: Interventions restoring metabolism, mitochondrial function, and improved ROS balance may be promising therapeutic approaches. We discuss the effects of current HCM pharmacological therapies and potential future therapies to prevent and reverse HCM. Antioxid. Redox Signal. 31, 318-358.

Nitroxyl (HNO) targets phospholamban cysteines 41 and 46 to enhance cardiac function

Nitroxyl (HNO) positively modulates myocardial function by accelerating Ca²⁺ reuptake into the sarcoplasmic reticulum (SR). HNO-induced enhancement of myocardial Ca²⁺ cycling and function is due to the modification of cysteines in the transmembrane domain of phospholamban (PLN), which results in activation of SR Ca²⁺-ATPase (SERCA2a) by functionally uncoupling PLN from SERCA2a. However, which cysteines are modified by HNO, and whether HNO induces reversible disulfides or single cysteine sulfinamides (RS(O)NH₂) that are less easily reversed by reductants, remain to be determined. Using an ¹⁵N-edited NMR method for sulfinamide detection, we first demonstrate that Cys46 and Cys41 are the main targets of HNO reactivity with PLN. Supporting this conclusion, mutation of PLN cysteines 46 and 41 to alanine reduces the HNO-induced enhancement of SERCA2a activity. Treatment of WT-PLN with HNO leads to sulfinamide formation when the HNO donor is in excess, whereas disulfide formation is expected to dominate when the HNO/thiol stoichiometry approaches a 1:1 ratio that is more similar to that anticipated in vivo under normal, physiological conditions. Thus, ¹⁵N-edited NMR spectroscopy detects redox changes on thiols that are unique to HNO, greatly advancing the ability to detect HNO footprints in biological systems, while further differentiating HNO-induced post-translational modifications from those imparted by other reactive nitrogen or oxygen species. The present study confirms the potential of HNO as a signaling molecule in the cardiovascular system.

Stoichiometric Nitroxyl Photorelease Using the (6-Hydroxy-2-naphthalenyl)methyl Phototrigger

The design and synthesis of a photoactivatable HNO donor incorporating the (6-hydroxynaphthalen-2-yl)methyl (6,2-HNM) photocage coupled to the trifluoromethanesulfonamidoxy analogue of the well-established HNO generator Piloty's acid is described. The photoactive HNO donor stoichiometrically generates HNO (∼98%) at neutral pH conditions, and evidence for concerted C-O and N-S bond cleavage was obtained. The methanesulfonamidoxy analogue primarily undergoes undesired N-O bond cleavage.

A Chemiluminescent Probe for HNO Quantification and Real-Time Monitoring in Living Cells

Azanone (HNO) is a reactive nitrogen species with pronounced biological activity and high therapeutic potential for cardiovascular dysfunction. A critical barrier to understanding the biology of HNO and furthering clinical development is the quantification and real-time monitoring of its delivery in living systems. Herein, we describe the design and synthesis of the first chemiluminescent probe for HNO, HNOCL-1, which can detect HNO generated from concentrations of Angeli's salt as low as 138 nm with high selectivity based on the reaction with a phosphine group to form a self-cleavable azaylide intermediate. We have capitalized on this high sensitivity to develop a generalizable kinetics-based approach, which provides real-time quantitative measurements of HNO concentration at the picomolar level. HNOCL-1 can monitor dynamics of HNO delivery in living cells and tissues, demonstrating the versatility of this method for tracking HNO in living systems.

Oxidation of cardiac myofilament proteins: Priming for dysfunction?

Oxidants are produced endogenously and can react with and thereby post-translationally modify target proteins. They have been implicated in the redox regulation of signal transduction pathways conferring protection, but also in mediating oxidative stress and causing damage. The difference is that in scenarios of injury the amount of oxidants generated is higher and/or the duration of oxidant exposure sustained. In the cardiovascular system, oxidants are important for blood pressure homeostasis, for unperturbed cardiac function and also contribute to the observed protection during ischemic preconditioning. In contrast, oxidative stress accompanies all major cardiovascular pathologies and has been attributed to mediate contractile dysfunction in part by inducing oxidative modifications in myofilament proteins. However, the proportion to which oxidative modifications of contractile proteins are beneficial or causatively mediate disease progression needs to be carefully reconsidered. These antithetical aspects will be discussed in this review with special focus on direct oxidative post-translational modifications of myofilament proteins that have been described to occur in vivo and to regulate actin-myosin interactions in the cardiac myocyte sarcomere, the methodologies for detection of oxidative post-translational modifications in target proteins and the feasibility of antioxidant therapy strategies as a potential treatment for cardiac disorders.

Oxidant sensor in the cGMP-binding pocket of PKGIα regulates nitroxyl-mediated kinase activity

Despite the mechanisms for endogenous nitroxyl (HNO) production and action being incompletely understood, pharmacological donors show broad therapeutic promise and are in clinical trials. Mass spectrometry and site-directed mutagenesis showed that chemically distinct HNO donors 1-nitrosocyclohexyl acetate or Angeli’s salt induced disulfides within cGMP-dependent protein kinase I-alpha (PKGIα), an interdisulfide between Cys42 of the two identical subunits of the kinase and a previously unobserved intradisulfide between Cys117 and Cys195 in the high affinity cGMP-binding site. Kinase activity was monitored in cells transfected with wildtype (WT), Cys42Ser or Cys117/195Ser PKGIα that cannot form the inter- or intradisulfide, respectively. HNO enhanced WT kinase activity, an effect significantly attenuated in inter- or intradisulfide-deficient PKGIα. To investigate whether the intradisulfide modulates cGMP binding, real-time imaging was performed in vascular smooth muscle cells expressing a FRET-biosensor comprising the cGMP-binding sites of PKGIα. HNO induced FRET changes similar to those elicited by an increase of cGMP, suggesting that intradisulfide formation is associated with activation of PKGIα. Intradisulfide formation in PKGIα correlated with enhanced HNO-mediated vasorelaxation in mesenteric arteries in vitro and arteriolar dilation in vivo in mice. HNO induces intradisulfide formation in PKGIα, inducing the same effect as cGMP binding, namely kinase activation and thus vasorelaxation.

Vasorelaxation to the Nitroxyl Donor Isopropylamine NONOate in Resistance Arteries Does Not Require Perivascular Calcitonin Gene-Related Peptide

Nitroxyl (HNO) donors offer considerable therapeutic potential for the treatment of hypertension-related cardiovascular disorders, particularly heart failure, as they combine an inotropic action with peripheral vasodilation. Angeli's salt is the only HNO donor whose mechanism has been studied in depth, and recently, Angeli's salt vasodilation was suggested to be indirect and caused by calcitonin gene-related peptide (CGRP) released from perivascular nerves after HNO activates TRPA1 (transient receptor potential cation channel subfamily A member 1) channels. We investigated resistance artery vasorelaxation to the HNO donor, isopropylamine NONOate (IPA/NO), one of the structures providing a template for therapeutic development. Wire myography in combination with measurements of smooth muscle membrane potential was used to characterize the effect of IPA/NO in mesenteric resistance arteries. Immunohistochemistry was assessed in pressurized arteries. IPA/NO concentration dependently hyperpolarized and relaxed arteries precontracted with the α1-adrenoreceptor agonist, phenylephrine. These effects were blocked by the soluble guanylyl cyclase inhibitor, ODQ (1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one) but not by the KATP channel inhibitor, glibenclamide. Vasorelaxation persisted in the presence of raised [K+]o, used to block hyperpolarization, capsaicin to deplete perivascular CGRP, or HC030031 (2-(1,3-dimethyl-2,6-dioxo-1,2,3,6-tetrahydro-7H-purin-7-yl)-N-(4 isopropylphenyl) acetamide) to block TRPA1 receptors. Without preconstriction, hyperpolarization to IPA/NO was suppressed by glibenclamide, capsaicin, or HC030031. Hyperpolarization but not vasorelaxation to exogenous CGRP was inhibited with glibenclamide. Thus, vascular hyperpolarization is not necessary for vasorelaxation to the HNO donor IPA/NO, even though both effects are cGMP dependent. The reduced hyperpolarization after depletion of perivascular CGRP or block of TRPA1 receptors indicates some release of CGRP, but this does not contribute to HNO vasorelaxation. Therefore, HNO-TRPA1-CGRP signaling does not seem important for vasodilation to IPA/NO in resistance arteries.

Advances in chemical pharmacotherapy for managing acute decompensated heart failure

INTRODUCTION

Acute decompensated heart failure (ADHF) contributes largely to the burden of heart failure and is associated with a poorer prognosis. Although numerous clinical trials evaluated the benefit of newer medications for ADHF, most of them were not successful. Areas covered: This review focusses on the updates on recent developments in chemical pharmacotherapy for the management of ADHF. A MEDLINE search for relevant review articles and original investigations on newer drugs for ADHF provided us with necessary literature. Expert opinion: Currently, popular therapies like diuretics, vasodilators, and inotropes offer symptomatic relief but do not provide survival benefit. Although multiple medications targeting novel pathways in ADHF were studied extensively, they failed to show either symptomatic or mortality benefit in available randomized trials. Improving our understanding of the complex pathophysiology of ADHF along with designing studies which include patients who are more representative of the real-world heart failure population, standardizing methods for endpoint assessment, and evaluating the role on novel biomarkers of organ dysfunction is important to improve ADHF research. Enhancing preventive strategies like improving baseline therapy in chronic heart failure patients and developing strategies for early identification of ADHF are important as our quest for innovative ADHF pharmacotherapy continues.

The opposing roles of NO and oxidative stress in cardiovascular disease

Nitric oxide (NO) plays a pivotal role in the maintenance of cardiovascular homeostasis. A reduction in the bioavailability of endogenous NO, manifest as a decrease in the production and/or impaired signaling, is associated with many cardiovascular diseases including hypertension, atherosclerosis, stroke and heart failure. There is substantial evidence that reactive oxygen species (ROS), generated predominantly from NADPH oxidases (Nox), are responsible for the reduced NO bioavailability in vascular and cardiac pathologies. ROS can compromise NO function via a direct inactivation of NO, together with a reduction in NO synthesis and oxidation of its receptor, soluble guanylyl cyclase. Whilst nitrovasodilators are administered to compensate for the ROS-mediated loss in NO bioactivity, their clinical utility is limited due to the development of tolerance and resistance and systemic hypotension. Moreover, efforts to directly scavenge ROS with antioxidants has had limited clinical efficacy. This review outlines the therapeutic utility of NO-based therapeutics in cardiovascular diseases and describes the source and impact of ROS in these pathologies, with particular focus on the interaction with NO. Future therapeutic approaches in the treatment of cardiovascular diseases are highlighted with a focus on nitroxyl (HNO) donors as an alternative to traditional NO donors and the development of novel Nox inhibitors.