Nitroxyl improves cellular heart function by directly enhancing cardiac sarcoplasmic reticulum Ca2+ cycling

Nitroxyl donating and visualization with a coumarin-based fluorescence probe

Nitroxyl (HNO), the single-electron reduction product of nitric oxide (NO), has attracted great interest in the treatment of congestive heart failure in clinical trials. In this paper, we describe the first coumarin-based compound N-hydroxy-2-oxo-2H-chromene-6-sulfonamide (CD1) as a dualfunctional HNO donor, which can release both an HNO signaling molecule and a fluorescent reporter. Under physiological conditions (pH 7.4 and 37 °C), the CD1 HNO donor can readily decompose with a half-life of ∼90 min. The corresponding stoichiometry HNO from the CD1 donor was confirmed using both Vitamin B12 and phosphine compound traps. In addition to HNO releasing, specifically, the degradation product 2-oxo-2H-chromene-6-sulfinate (CS1) was generated as a fluorescent marker during the decomposition. Therefore, the HNO amount released in situ can be accurately monitored through fluorescence generation. As compared to the CD1 donor, the fluorescence intensity increased by about 4.9-fold. The concentration limit of detection of HNO releasing was determined to be ∼0.13 μM according to the fluorescence generation of CS1 at physiological conditions. Moreover, the bioimaging of the CD1 donor was demonstrated in the cell culture of HeLa cells, where the intracellular fluorescence signals were observed, inferring the site of HNO release. Finally, we anticipate that this novel coumarin-based CD1 donor opens a new platform for exploring the biology of HNO.

Azobenzene-based colorimetric and fluorometric chemosensor for nitroxyl releasing

The precise release and characterization of nitroxyl (HNO) gas signaling molecule remain a challenge due to its short lifetime to date. To solve this issue, an azobenzene-based HNO donor (Azo-D1) was proposed as a colorimetric and fluorometric chemosensor for HNO releasing, to release both HNO and an azobenzene fluorescent reporter together. Specifically, the Azo-D1 has an HNO release half-life of ∼68 min under physiological conditions. The characteristic color change from the original orange to the yellow color indicated the decomposition of the donor molecule. In addition, the stoichiometry release of HNO was qualitatively and quantitatively verified through the classical phosphine compound trap. As compared with the donor molecule by itself, the decomposed product demonstrates a maximum fluorescence emission at 424 nm, where the increase of fluorescence intensity by 6.8 times can be applied to infer the real-time concentration of HNO. Moreover, cellular imaging can also be achieved using this Azo-D1 HNO donor through photoexcitation at 405 and 488 nm, where the real-time monitoring of HNO release was achieved without consuming the HNO source. Finally, the Azo-D1 HNO donor would open a new platform in the exploration of the biochemistry and the biology of HNO.

Expanding the Frontiers of Guardian Antioxidant Selenoproteins in Cardiovascular Pathophysiology

Significance: Physiological levels of reactive oxygen and nitrogen species (ROS/RNS) function as fundamental messengers for many cellular and developmental processes in the cardiovascular system. ROS/RNS involved in cardiac redox-signaling originate from diverse sources, and their levels are tightly controlled by key endogenous antioxidant systems that counteract their accumulation. However, dysregulated redox-stress resulting from inefficient removal of ROS/RNS leads to inflammation, mitochondrial dysfunction, and cell death, contributing to the development and progression of cardiovascular disease (CVD). Recent Advances: Basic and clinical studies demonstrate the critical role of selenium (Se) and selenoproteins (unique proteins that incorporate Se into their active site in the form of the 21st proteinogenic amino acid selenocysteine [Sec]), including glutathione peroxidase and thioredoxin reductase, in cardiovascular redox homeostasis, representing a first-line enzymatic antioxidant defense of the heart. Increasing attention has been paid to emerging selenoproteins in the endoplasmic reticulum (ER) (i.e., a multifunctional intracellular organelle whose disruption triggers cardiac inflammation and oxidative stress, leading to multiple CVD), which are crucially involved in redox balance, antioxidant activity, and calcium and ER homeostasis. Critical Issues: This review focuses on endogenous antioxidant strategies with therapeutic potential, particularly selenoproteins, which are very promising but deserve more detailed and clinical studies. Future Directions: The importance of selective selenoproteins in embryonic development and the consequences of their mutations and inborn errors highlight the need to improve knowledge of their biological function in myocardial redox signaling. This could facilitate the development of personalized approaches for the diagnosis, prevention, and treatment of CVD. Antioxid. Redox Signal. 40, 369-432.

Oxidative stress in early metabolic syndrome impairs cardiac RyR2 and SERCA2a activity and modifies the interplay of these proteins during Ca2+ waves

We investigated how oxidative stress (OS) alters Ca2+ handling in ventricular myocytes in early metabolic syndrome (MetS) in sucrose-fed rats. The effects of N-acetyl cysteine (NAC) or dl-Dithiothreitol (DTT) on systolic Ca2+ transients (SCaTs), diastolic Ca2+ sparks (CaS) and Ca2+ waves (CaW), recorded by confocal techniques, and L-type Ca2+ current (ICa), assessed by whole-cell patch clamp, were evaluated in MetS and Control cells. MetS myocytes exhibited decreased SCaTs and CaS frequency but unaffected CaW propagation. In Control cells, NAC/DTT reduced RyR2/SERCA2a activity blunting SCaTs, CaS frequency and CaW propagation, suggesting that basal ROS optimised Ca2+ signalling by maintaining RyR2/SERCA2a function and that these proteins facilitate CaW propagation. Conversely, NAC/DTT in MetS recovered RyR2/SERCA2a function, improving SCaTs and CaS frequency, but unexpectedly decreasing CaW propagation. We hypothesised that OS decreases RyR2/SERCA2a activity at early MetS, and while decreased SERCA2a favours CaW propagation, diminished RyR2 restrains it.

Endogenous plant nitroxyl, a new component of nitric oxide biology

Nitroxyl (HNO), a one-electron reduced and protonated congener of nitric oxide (•NO), was recently discovered in Arabidopsis thaliana. Due to its distinct chemical properties, we believe HNO must be further studied to determine how many physiological processes it impacts.

Targeting calcium regulators as therapy for heart failure: focus on the sarcoplasmic reticulum Ca-ATPase pump

Impaired myocardial Ca2+ cycling is a critical contributor to the development of heart failure (HF), causing changes in the contractile function and structure remodeling of the heart. Within cardiomyocytes, the regulation of sarcoplasmic reticulum (SR) Ca2+ storage and release is largely dependent on Ca2+ handling proteins, such as the SR Ca2+ ATPase (SERCA2a) pump. During the relaxation phase of the cardiac cycle (diastole), SERCA2a plays a critical role in transporting cytosolic Ca2+ back to the SR, which helps to restore both cytosolic Ca2+ levels to their resting state and SR Ca2+ content for the next contraction. However, decreased SERCA2a expression and/or pump activity are key features in HF. As a result, there is a growing interest in developing therapeutic approaches to target SERCA2a. This review provides an overview of the regulatory mechanisms of the SERCA2a pump and explores potential strategies for SERCA2a-targeted therapy, which are being investigated in both preclinical and clinical studies.

Effects of intestinal bacteria on cardiovascular disease

In the long process of human evolution, the Intestinal Bacteria has become intimately related to human health, producing many metabolites in the intestines that can affect cardiovascular disease. Today, the incidence of cardiovascular disease is rising, its treatment is becoming increasingly important, and new therapeutic targets are needed. Here we describe the effects of trimethylamine oxide (TMAO), lipid metabolism, phenolic compounds, indole sulfate (IS), oleuropein (OL), and hydroxytyrosol (HT) on atherosclerosis, heart failure, hypertension, and other cardiovascular diseases, as well as their mechanism of action. This study provides new ideas, new methods, and new directions for the treatment of cardiovascular disease.

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.

Reactive Oxygen Species Induced Pathways in Heart Failure Pathogenesis and Potential Therapeutic Strategies

With respect to structural and functional cardiac disorders, heart failure (HF) is divided into HF with reduced ejection fraction (HFrEF) and HF with preserved ejection fraction (HFpEF). Oxidative stress contributes to the development of both HFrEF and HFpEF. Identification of a broad spectrum of reactive oxygen species (ROS)-induced pathways in preclinical models has provided new insights about the importance of ROS in HFrEF and HFpEF development. While current treatment strategies mostly concern neuroendocrine inhibition, recent data on ROS-induced metabolic pathways in cardiomyocytes may offer additional treatment strategies and targets for both of the HF forms. The purpose of this article is to summarize the results achieved in the fields of: (1) ROS importance in HFrEF and HFpEF pathophysiology, and (2) treatments for inhibiting ROS-induced pathways in HFrEF and HFpEF patients. ROS-producing pathways in cardiomyocytes, ROS-activated pathways in different HF forms, and treatment options to inhibit their action are also discussed.

A bifunctional fluorescent probe based on "AND logic" for the simultaneous recognition of H2S/HNO and its bioimaging applications

The reaction of NO and H₂S to form HNO is a classical pathway in physiological conditions. The reported single recognition-type fluorescent probes are difficult to track precisely the relationships of H₂S and HNO. It is necessary to develop a bifunctional fluorescence probe (NJA) for monitoring simultaneously the production of endogenous HNO and H₂S. Using 7-Nitrobenzofurazan (NBD) and 2-(diphenylphosphine) benzoate as recognition sites, the obatined NJA can detect specifically HS^- and HNO. The detection limit of HS^- and HNO are 0.46 μM and 1.42 μM, respectively. Based on the dual recognition sites and input signals of the probe, a molecular "AND" logic gate was established to detect successfully H₂S and HNO in MCF-7 cells. NJA based on "AND logic" provided a simple and robust tool for monitoring the production of endogenous HNO correlative with H₂S and NO in living cells.

Solid-gas reactions for nitroxyl (HNO) generation in the gas phase

We present a novel nitroxyl (HNO) generation method, which avoids the need of using a liquid system or extreme experimental conditions. This method consists of the reaction between a gaseous base and an HNO donor (Piloty's acid) in the solid phase, allowing the formation of gaseous HNO in a fast and economical way. Detection of HNO was carried out indirectly, measuring the nitrous oxide (N₂O) byproduct of HNO dimerization using infrared spectroscopy, and directly, using mass spectrometry techniques and an electrochemical HNO sensor.

Melatonin, Its Metabolites and Their Interference with Reactive Nitrogen Compounds

Melatonin and several of its metabolites are interfering with reactive nitrogen. With the notion of prevailing melatonin formation in tissues that exceeds by far the quantities in blood, metabolites come into focus that are poorly found in the circulation. Apart from their antioxidant actions, both melatonin and N¹-acetyl-5-methoxykynuramine (AMK) downregulate inducible and inhibit neuronal NO synthases, and additionally scavenge NO. However, the NO adduct of melatonin redonates NO, whereas AMK forms with NO a stable product. Many other melatonin metabolites formed in oxidative processes also contain nitrosylatable sites. Moreover, AMK readily scavenges products of the CO₂-adduct of peroxynitrite such as carbonate radicals and NO₂. Protein AMKylation seems to be involved in protective actions.

Nitroaromatic Antibiotics as Nitrogen Oxide Sources

Nitroaromatic antibiotics show activity against anaerobic bacteria and parasites, finding use in the treatment of Heliobacter pylori infections, tuberculosis, trichomoniasis, human African trypanosomiasis, Chagas disease and leishmaniasis. Despite this activity and a clear need for the development of new treatments for these conditions, the associated toxicity and lack of clear mechanisms of action have limited their therapeutic development. Nitroaromatic antibiotics require reductive bioactivation for activity and this reductive metabolism can convert the nitro group to nitric oxide (NO) or a related reactive nitrogen species (RNS). As nitric oxide plays important roles in the defensive immune response to bacterial infection through both signaling and redox-mediated pathways, defining controlled NO generation pathways from these antibiotics would allow the design of new therapeutics. This review focuses on the release of nitrogen oxide species from various nitroaromatic antibiotics to portend the increased ability for these compounds to positively impact infectious disease treatment.

Nitric Oxide Donors as Potential Drugs for the Treatment of Vascular Diseases Due to Endothelium Dysfunction

Endothelial dysfunction and consequent vasoconstriction are a common condition in patients with hypertension and other cardiovascular diseases. Endothelial cells produce and release vasodilator substances that play a pivotal role in normal vascular tone. The mechanisms underlying endothelial dysfunction are multifactorial. However, enhanced reactive oxygen species (ROS) production and consequent vasoconstriction instead of endothelium-derived relaxant generation and consequent vasodilatation contribute to this dysfunction considerably. The main targets of the drugs that are currently used to treat vascular diseases concerning enzyme activities and protein functions that are impaired by endothelial nitric oxide synthase (eNOS) uncoupling and ROS production. Nitric oxide (NO) bioavailability can decrease due to deficient NO production by eNOS and/or NO release to vascular smooth muscle cells, which impairs endothelial function. Considering the NO cellular mechanisms, tackling the issue of eNOS uncoupling could avoid endothelial dysfunction: provision of the enzyme cofactor tetrahydrobiopterin (BH4) should elicit NO release from NO donors, to activate soluble guanylyl cyclase. This should increase cyclic guanosine-monophosphate (cGMP) generation and inhibit phosphodiesterases (especially PDE5) that selectively degrade cGMP. Consequently, protein kinase-G should be activated, and K+ channels should be phosphorylated and activated, which is crucial for cell membrane hyperpolarization and vasodilation and/or inhibition of ROS production. The present review summarizes the current concepts about the vascular cellular mechanisms that underlie endothelial dysfunction and which could be the target of drugs for the treatment of patients with cardiovascular disease.

Interaction among Hydrogen Sulfide and Other Gasotransmitters in Mammalian Physiology and Pathophysiology

Hydrogen sulfide (H₂S), nitric oxide (NO), carbon monoxide (CO), and sulfur dioxide (SO₂) were previously considered as toxic gases, but now they are found to be members of mammalian gasotransmitters family. Both H₂S and SO₂ are endogenously produced in sulfur-containing amino acid metabolic pathway in vivo. The enzymes catalyzing the formation of H₂S are mainly CBS, CSE, and 3-MST, and the key enzymes for SO₂ production are AAT1 and AAT2. Endogenous NO is produced from L-arginine under catalysis of three isoforms of NOS (eNOS, iNOS, and nNOS). HO-mediated heme catabolism is the main source of endogenous CO. These four gasotransmitters play important physiological and pathophysiological roles in mammalian cardiovascular, nervous, gastrointestinal, respiratory, and immune systems. The similarity among these four gasotransmitters can be seen from the same and/or shared signals. With many studies on the biological effects of gasotransmitters on multiple systems, the interaction among H₂S and other gasotransmitters has been gradually explored. H₂S not only interacts with NO to form nitroxyl (HNO), but also regulates the HO/CO and AAT/SO₂ pathways. Here, we review the biosynthesis and metabolism of the gasotransmitters in mammals, as well as the known complicated interactions among H₂S and other gasotransmitters (NO, CO, and SO₂) and their effects on various aspects of cardiovascular physiology and pathophysiology, such as vascular tension, angiogenesis, heart contractility, and cardiac protection.

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.

Effects of a Novel Nitroxyl Donor in Acute Heart Failure: The STAND-UP AHF Study

OBJECTIVES

The primary objective was to identify well-tolerated doses of cimlanod in patients with acute heart failure (AHF). Secondary objectives were to identify signals of efficacy, including biomarkers, symptoms, and clinical events.

BACKGROUND

Nitroxyl (HNO) donors have vasodilator, inotropic and lusitropic effects. Bristol-Myers Squibb-986231 (cimlanod) is an HNO donor being developed for acute heart failure (AHF).

METHODS

This was a phase IIb, double-blind, randomized, placebo-controlled trial of 48-h treatment with cimlanod compared with placebo in patients with left ventricular ejection fraction ≤40% hospitalized for AHF. In part I, patients were randomized in a 1:1 ratio to escalating doses of cimlanod or matching placebo. In part II, patients were randomized in a 1:1:1 ratio to either of the 2 highest tolerated doses of cimlanod from part I or placebo. The primary endpoint was the rate of clinically relevant hypotension (systolic blood pressure <90 mm Hg or patients became symptomatic).

RESULTS

In part I (n = 100), clinically relevant hypotension was more common with cimlanod than placebo (20% vs. 8%; relative risk [RR]: 2.45; 95% confidence interval [CI]: 0.83 to 14.53). In part II (n = 222), the incidence of clinically relevant hypotension was 18% for placebo, 21% for cimlanod 6 μg/kg/min (RR: 1.15; 95% CI: 0.58 to 2.43), and 35% for cimlanod 12 μg/kg/min (RR: 1.9; 95% CI: 1.04 to 3.59). N-terminal pro-B-type natriuretic peptide and bilirubin decreased during infusion of cimlanod treatment compared with placebo, but these differences did not persist after treatment discontinuation.

CONCLUSIONS

Cimlanod at a dose of 6 μg/kg/min was reasonably well-tolerated compared with placebo. Cimlanod reduced markers of congestion, but this did not persist beyond the treatment period. (Evaluate the Safety and Efficacy of 48-Hour Infusions of HNO (Nitroxyl) Donor in Hospitalized Patients With Heart Failure [STANDUP AHF]; NCT03016325).

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.

Treatments targeting inotropy

Acute heart failure (HF) and in particular, cardiogenic shock are associated with high morbidity and mortality. A therapeutic dilemma is that the use of positive inotropic agents, such as catecholamines or phosphodiesterase-inhibitors, is associated with increased mortality. Newer drugs, such as levosimendan or omecamtiv mecarbil, target sarcomeres to improve systolic function putatively without elevating intracellular Ca2+. Although meta-analyses of smaller trials suggested that levosimendan is associated with a better outcome than dobutamine, larger comparative trials failed to confirm this observation. For omecamtiv mecarbil, Phase II clinical trials suggest a favourable haemodynamic profile in patients with acute and chronic HF, and a Phase III morbidity/mortality trial in patients with chronic HF has recently begun. Here, we review the pathophysiological basis of systolic dysfunction in patients with HF and the mechanisms through which different inotropic agents improve cardiac function. Since adenosine triphosphate and reactive oxygen species production in mitochondria are intimately linked to the processes of excitation-contraction coupling, we also discuss the impact of inotropic agents on mitochondrial bioenergetics and redox regulation. Therefore, this position paper should help identify novel targets for treatments that could not only safely improve systolic and diastolic function acutely, but potentially also myocardial structure and function over a longer-term.

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.

Mechanisms Associated to Nitroxyl (HNO)-Induced Relaxation in the Intestinal Smooth Muscle

The pharmacological properties of nitroxyl (HNO) donors in the gastrointestinal tract are unknown. We investigated the properties of this molecule in the regulation of gastrointestinal contractility focusing on its possible interaction with other gaseous signaling molecules such as NO and H₂S. Organ bath, Ca²⁺ imaging, and microelectrode recordings were performed on rat intestinal samples, using Angeli’s salt as HNO donor. Angeli’s salt caused a concentration-dependent relaxation of longitudinal or circular muscle strips of the ileum and the proximal colon. This relaxation was strongly inhibited by the Rho-kinase inhibitor Y-27632 (10 μM), by the reducing agent DTT or by the inhibitor of soluble guanylate cyclase (sGC) ODQ (10 μM) alone or in combination with the inhibitors of the endogenous synthesis of H₂S β-cyano-L-alanine (5 mM) and amino-oxyacetate (5 mM). Preventing endogenous synthesis of NO by the NO synthase inhibitor L-NAME (200 μM) did not affect the relaxation induced by HNO. HNO induced an increase in cytosolic Ca²⁺ concentration in colonic myocytes. It also elicited myocyte membrane hyperpolarization that amounted to −10.6 ± 1.1 mV. ODQ (10 μM) and Apamin (1 μM), a selective inhibitor of small conductance Ca²⁺-activated K⁺ channels (SKca), strongly antagonized this effect. We conclude that HNO relaxes the gastrointestinal tract musculature by hyperpolarizing myocytes via activation of the sGC/cGMP pathway similarly to NO, not only inhibiting the RhoK and activating MLCP as do both NO and H₂S but also increasing cytosolic Ca²⁺ for activation of SK_Ca contributing to hyperpolarization.

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.

Leveraging Signaling Pathways to Treat Heart Failure With Reduced Ejection Fraction

Advances in the treatment of heart failure with reduced ejection fraction due to systolic dysfunction are engaging an ever-expanding compendium of molecular signaling targets. Well established approaches modifying hemodynamics and cell biology by neurohumoral receptor blockade are evolving, exploring the role and impact of modulating intracellular signaling pathways with more direct myocardial effects. Even well-tread avenues are being reconsidered with new insights into the signaling engaged and thus opportunity to treat underlying myocardial disease. This review explores therapies that have proven successful, those that have not, those that are moving into the clinic but whose utility remains to be confirmed, and those that remain in the experimental realm. The emphasis is on signaling pathways that are tractable for therapeutic manipulation. Of the approaches yet to be tested in humans, we chose those with a well-established experimental history, where clinical translation may be around the corner. The breadth of opportunities bodes well for the next generation of heart failure therapeutics.

An isophorone-fused near-infrared fluorescent probe with a large Stokes shift for imaging endogenous nitroxyl in living cells and zebrafish

Nitroxyl (HNO) plays an important role in multiple physiological and pathological processes, but the detailed generation mechanism of the endogenous HNO still remained to explore and perfect further. There is an urgent need to develop an excellent fluorescent probe for selective recognition and sensitive detection of HNO in biological systems. Near-infrared (NIR) fluorescent probes with a large Stokes shift are an ideal tool for bioimaging applications. Here, we have developed a NIR fluorescent probe with a large Stokes shift, namely, NIR-HNO, to monitor HNO in cells and zebrafish. NIR-HNO consists of an isophorone-fused NIR fluorescence reporter and a diphenylphosphinobenzoyl HNO-responsive unit. Based on an aza-ylide intramolecular ester aminolysis reaction, NIR-HNO showed a rapid selective NIR fluorescent turn-on response for HNO, high sensitivity (detection limit was 39.6 nM), and large Stokes shift (265 nm). The biological imaging results indicate that NIR-HNO is a good candidate for imaging of endogenous HNO in living systems.

Nitroxyl as a Potential Theranostic in the Cancer Arena

Significance: As one-electron reduced molecule of nitric oxide (NO), nitroxyl (HNO) has gained enormous attention because of its novel physiological or pharmacological properties, ranging from cardiovascular protective actions to antitumoricidal effects. Recent Advances: HNO is emerging as a new entity with therapeutic advantages over its redox sibling, NO. The interests in the chemical, pharmacological, and biological characteristics of HNO have broadened our current understanding of its role in physiology and pathophysiology. Critical Issues: In particular, the experimental evidence suggests the therapeutic potential of HNO in tumor pharmacology, such as neuroblastoma, gastrointestinal tumor, ovarian, lung, and breast cancers. Indeed, HNO donors have been demonstrated to attenuate tumor proliferation and angiogenesis. Future Directions: In this review, the generation and detection of HNO are outlined, and the roles of HNO in cancer progression are further discussed. We anticipate that the completion of this review might give novel insights into the roles of HNO in cancer pharmacology and open up a novel field of cancer therapy based on HNO.

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.

Incubation with sodium nitrite attenuates fatigue development in intact single mouse fibres at physiological P O 2

KEY POINTS

Dietary nitrate supplementation increases plasma nitrite concentration, which provides an oxygen-independent source of nitric oxide and can delay skeletal muscle fatigue. Nitrate supplementation has been shown to increase myofibre calcium release and force production in mouse skeletal muscle during contractions at a supra-physiological oxygen tension, but it is unclear whether nitrite exposure can delay fatigue development and improve myofibre calcium handling at a near-physiological oxygen tension. Single mouse muscle fibres acutely treated with nitrite had a lower force and cytosolic calcium concentration during single non-fatiguing contractions at a near-physiological oxygen tension. Nitrite treatment delayed fatigue development during repeated fatiguing isometric contractions at near-physiological, but not at supra-physiological, oxygen tension in combination with better maintenance of myofilament calcium sensitivity and sarcoplasmic reticulum calcium pumping. These findings improve understanding of the mechanisms by which increased skeletal muscle nitrite exposure might be ergogenic and imply that this is related to improved calcium handling.

ABSTRACT

Dietary nitrate (NO₃ ^- ) supplementation, which increases plasma nitrite (NO₂ ^- ) concentration, has been reported to attenuate skeletal muscle fatigue development. Sarcoplasmic reticulum (SR) calcium (Ca²⁺ ) release is enhanced in isolated single skeletal muscle fibres following NO₃ ^- supplementation or NO₂ ^- incubation at a supra-physiological P O 2 but it is unclear whether NO₂ ^- incubation can alter Ca²⁺ handling and fatigue development at a near-physiological P O 2 . We hypothesised that NO₂ ^- treatment would improve Ca²⁺ handling and delay fatigue at a physiological P O 2 in intact single mouse skeletal muscle fibres. Each muscle fibre was perfused with Tyrode solution pre-equilibrated with either 20% ( P O 2 ∼150 Torr) or 2% O₂ ( P O 2  = 15.6 Torr) in the absence and presence of 100 µM NaNO₂ . At supra-physiological P O 2 (i.e. 20% O₂ ), time to fatigue was lowered by 34% with NaNO₂ (control: 257 ± 94 vs. NaNO₂ : 159 ± 46 s, Cohen's d = 1.63, P < 0.05), but extended by 21% with NaNO₂ at 2% O₂ (control: 308 ± 217 vs. NaNO₂ : 368 ± 242 s, d = 1.14, P < 0.01). During the fatiguing contraction protocol completed with NaNO₂ at 2% O₂ , peak cytosolic Ca²⁺ concentration ([Ca²⁺ ]_c ) was not different (P > 0.05) but [Ca²⁺ ]_c accumulation between contractions was lower, concomitant with a greater SR Ca²⁺ pumping rate (P < 0.05) compared to the control condition. These results demonstrate that increased exposure to NO₂ ^- blunts fatigue development at near-physiological, but not at supra-physiological, P O 2 through enhancing SR Ca²⁺ pumping rate in single skeletal muscle fibres. These findings extend our understanding of the mechanisms by which increased NO₂ ^- exposure can mitigate skeletal muscle fatigue development.

Hurdles to Cardioprotection in the Critically Ill

Cardiovascular disease is the largest contributor to worldwide mortality, and the deleterious impact of heart failure (HF) is projected to grow exponentially in the future. As heart transplantation (HTx) is the only effective treatment for end-stage HF, development of mechanical circulatory support (MCS) technology has unveiled additional therapeutic options for refractory cardiac disease. Unfortunately, despite both MCS and HTx being quintessential treatments for significant cardiac impairment, associated morbidity and mortality remain high. MCS technology continues to evolve, but is associated with numerous disturbances to cardiac function (e.g., oxidative damage, arrhythmias). Following MCS intervention, HTx is frequently the destination option for survival of critically ill cardiac patients. While effective, donor hearts are scarce, thus limiting HTx to few qualifying patients, and HTx remains correlated with substantial post-HTx complications. While MCS and HTx are vital to survival of critically ill cardiac patients, cardioprotective strategies to improve outcomes from these treatments are highly desirable. Accordingly, this review summarizes the current status of MCS and HTx in the clinic, and the associated cardiac complications inherent to these treatments. Furthermore, we detail current research being undertaken to improve cardiac outcomes following MCS/HTx, and important considerations for reducing the significant morbidity and mortality associated with these necessary treatment strategies.

Novel approaches to the management of chronic systolic heart failure: future directions and unanswered questions

Despite improvements in outcomes in the last few decades for heart failure (HF) with reduced ejection fraction (HFrEF), there still remains a need for novel therapies as many patients incompletely recover with existing therapies and progress to advanced HF. In this review, we will discuss recent advances in the management of HFrEF with a focus on upcoming therapies that hold the greatest promise for clinical use. We will discuss novel pharmacological therapies and areas of uncertainty with existing therapies. We will also discuss the potential utility and controversy surrounding novel interventions for HF such as percutaneous mitral valve repair, atrial fibrillation ablation, and other emerging interventions with positive signals for benefit in HFrEF. Finally, we will summarize the current state of stem cell and gene therapy for HFrEF and future directions.

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Rationale and design for the development of a novel nitroxyl donor in patients with acute heart failure

Hospitalisation for acute heart failure remains a major public health problem with high prevalence, morbidity, mortality, and cost. Prior attempts to develop new therapies for this condition have not been successful. Nitroxyl (HNO) plays a unique role in cardiovascular physiology by direct post-translational modification of thiol residues on target proteins, specifically SERCA2a, phospholamban, the ryanodine receptor and myofilament proteins in cardiomyocytes. In animal models, these biological effects lead to vasodilatation, increased inotropy and lusitropy, but without tachyphylaxis, pro-arrhythmia or evidence of increased myocardial oxygen demand. BMS-986231 is an HNO donor being developed as a therapy for heart failure, and initial studies in patients with heart failure support the potential clinical value of these physiological effects. In this manuscript, we describe the ongoing phase II development programme for BMS-986231, which consists of three related randomised placebo-controlled clinical trials, StandUP-AHF, StandUP-Imaging and StandUP-Kidney, which are designed to provide evidence of tolerability and efficacy as well as confirm the anticipated physiological effects in patients with heart failure with reduced ejection fraction. These studies will set the stage for the further study of BMS-986231 in future phase III clinical trials.

Tracking nitroxyl-derived posttranslational modifications of phospholamban in cardiac myocytes

Mundiña-Weilenmann and Mattiazzi examine new work revealing the mechanism by which nitroxide modifies uptake of Ca²⁺ into the SR.

A Mononuclear, Nonheme FeII-Piloty's Acid (PhSO2NHOH) Adduct: An Intermediate in the Production of {FeNO}7/8 Complexes from Piloty's Acid

Reaction of the mononuclear nonheme complex [Fe^II(CH₃CN)(N3PyS)]BF₄ (1) with an HNO donor, Piloty's acid (PhSO₂NHOH, P.A.), at low temperature affords a high-spin ( S = 2) Fe^II-P.A. intermediate (2), characterized by ⁵⁷Fe Mössbauer and Fe K-edge X-ray absorption (XAS) spectroscopies, with interpretation of both supported by DFT calculations. The combined methods indicate that P.A. anion binds as the N-deprotonated tautomer (PhSO₂NOH^-) to [Fe^II(N3PyS)]⁺, leading to 2. Complex 2 is the first spectroscopically characterized example, to our knowledge, of P.A. anion bound to a redox-active metal center. Warming of 2 above -60 °C yields the stable {FeNO}⁷ complex [Fe(NO)(N3PyS)]BF₄ (4), as evidenced by ¹H NMR, ATR-IR, and Mössbauer spectroscopies. Isotope labeling experiments with ¹⁵N-labeled P.A. confirm that the nitrosyl ligand in 4 derives from P.A. In contrast, addition of a second equivalent of a strong base leads to S-N cleavage and production of an {FeNO}⁸ species, the deprotonated analog of an Fe-HNO complex. This work has implications for the targeted delivery of HNO/NO^-/NO· to nonheme Fe centers in biological and synthetic applications, and suggests a new role for nonheme Fe^II complexes in the assisted degradation of HNO donor molecules.

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.

A Phase 1 Randomized Study of Single Intravenous Infusions of the Novel Nitroxyl Donor BMS-986231 in Healthy Volunteers

Nitroxyl (HNO) is a reactive nitrogen molecule that has potential therapeutic benefits for patients with acute heart failure. The results of the first‐in‐human study for BMS‐986231, a novel HNO donor, are reported. The aim of this sequential cohort study was to evaluate the safety, tolerability, and pharmacokinetic profile of BMS‐986231 after 24‐ and 48‐hour intravenous infusions in healthy volunteers. Eighty subjects were randomized and dosed. Seven cohorts (stratum A) received BMS‐986231 0.1, 0.33, 1, 3, 5, 10, and 15 μg/kg/min or placebo, infused over 24 hours. An additional cohort (stratum B) received 10 μg/kg/min or placebo, infused over 48 hours. Adverse events (AEs) were reported for 30 days after completion of infusion. Blood/urine samples were collected at regular intervals; other parameters (blood pressure, heart rate/rhythm, cardiac index) were also assessed. Headaches were the most commonly reported drug‐related AE (48%) in those who received BMS‐986231, although their severity was reduced by hydration. No other significant drug‐related AEs were noted. BMS‐986231 was associated with dose‐dependent and well‐tolerated reductions in systolic and diastolic blood pressure versus baseline; cardiac index, as measured noninvasively, was increased. BMS‐986231 had no clinically significant effect on heart rate/rhythm or laboratory parameters. Its mean elimination half‐life was 0.7‐2.5 hours. BMS‐986231 was safe and well‐tolerated for up to 24 hours (15 μg/kg/min) or 48 hours (10 μg/kg/min), with a favorable hemodynamic profile observed. Ongoing studies continue to evaluate the potential benefit of BMS‐986231 in patients with acute heart failure.

A recent history of nitroxyl chemistry, pharmacology and therapeutic potential

Due to the excitement surrounding the discovery of NO as an endogenously generated signalling molecule, a number of other nitrogen oxides were also investigated as possible physiological mediators. Among these was nitroxyl (HNO). Over the past 25 years or so, a significant amount of work by this laboratory and many others has disclosed that HNO possesses unique chemical properties and important pharmacological utility. Indeed, the pharmacological potential for HNO as a treatment for heart failure, among other uses, has garnered this curious molecule a considerable amount of recent attention. This review summarizes the events that led to this recent attention as well as poses important questions that are still to be answered with regards to understanding the chemistry and biology of HNO. LINKED ARTICLES: This article is part of a themed section on Nitric Oxide 20 Years from the 1998 Nobel Prize. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.2/issuetoc.

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.

Intravenous Infusion of the Novel HNO Donor BMS-986231 Is Associated With Beneficial Inotropic, Lusitropic, and Vasodilatory Properties in 2 Canine Models of Heart Failure

The effects of the nitroxyl donor BMS-986231 on hemodynamics, left ventricular (LV) function, and pro-arrhythmic potential were assessed using canine heart failure models. BMS-986231 significantly (p < 0.05) increased LV end-systolic elastance, pre-load-recruitable stroke work, ejection fraction, stroke volume, cardiac output, ratio of early-to-late filling time integrals, and early mitral valve inflow velocity deceleration time. BMS-986231 significantly decreased LV filling pressures, end-diastolic stiffness, the time-constant of relaxation, end-diastolic wall stress, systemic vascular resistance, and myocardial oxygen consumption. BMS-986231 had little effect on heart rate and did not induce de novo arrhythmias. Thus, BMS-986231 has beneficial inotropic, lusitropic, and vasodilatory effects.

Reaction-Based Fluorescent Probes for the Imaging of Nitroxyl (HNO) in Biological Systems

Nitroxyl (HNO) has been identified as an important signaling molecule in biological systems and plays critical roles in many physiological processes. Fluorescence imaging could provide a robust approach to explore the biological formation of HNO and its physiological functions. Herein, we summarize the organic reaction types for constructing HNO probes and specifically focus on review of the recent advances in the development of the reaction-based HNO probes and their imaging applications in living systems.

The Anti-Cancer Multikinase Inhibitor Sorafenib Impairs Cardiac Contractility by Reducing Phospholamban Phosphorylation and Sarcoplasmic Calcium Transients

Tyrosine-kinase inhibitors (TKIs) have revolutionized cancer therapy in recent years. Although more targeted than conventional chemotherapy, TKIs exhibit substantial cardiotoxicity, often manifesting as hypertension or heart failure. Here, we assessed myocyte intrinsic cardiotoxic effects of the TKI sorafenib and investigated underlying alterations of myocyte calcium homeostasis. We found that sorafenib reversibly decreased developed force in auxotonically contracting human myocardia (3 µM: -25 ± 4%, 10 µM: -29 ± 7%, 30 µM: -43 ± 12%, p < 0.01), reduced peak cytosolic calcium concentrations in isolated cardiomyocytes (10 µM: 52 ± 8.1% of baseline, p < 0.001), and slowed cytosolic calcium removal kinetics (RT50, RT10, Tau, p < 0.05). Beta-adrenergic stimulation induced augmentation of calcium transient (CaT) amplitude was attenuated in sorafenib-treated cells (2.7 ± 0.3-fold vs. 3.6 ± 0.2-fold in controls, p < 0.001). Sarcoplasmic reticulum (SR) calcium content was reduced to 67 ± 4% (p < 0.01), and SR calcium re-uptake slowed (p < 0.05). Sorafenib significantly reduced serine 16 phosphorylation of phospholamban (PLN, p < 0.05), while PLN threonine 17 and CaMKII (T286) phosphorylation were not altered. Our data demonstrate that sorafenib acutely impairs cardiac contractility by reducing S16 PLN phosphorylation, leading to reduced SR calcium content, CaT amplitude, and slowed cytosolic calcium removal. These results indicate myocyte intrinsic cardiotoxicity irrespective of effects on the vasculature and chronic cardiac remodeling.

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.

Development and cellular application of visible-light-controllable HNO releasers based on caged Piloty's acid

Novel visible-light-controllable HNO releasers was developed based on a caged form of Piloty's acid, and applied for cellular systems.

CXL-1020, a Novel Nitroxyl (HNO) Prodrug, Is More Effective than Milrinone in Models of Diastolic Dysfunction-A Cardiovascular Therapeutic: An Efficacy and Safety Study in the Rat

The nitroxyl (HNO) prodrug, CXL-1020, induces vasorelaxation and improves cardiac function in canine models and patients with systolic heart failure (HF). HNO's unique mechanism of action may be applicable to a broader subset of cardiac patients. This study investigated the load-independent safety and efficacy of CXL-1020 in two rodent (rat) models of diastolic heart failure and explored potential drug interactions with common HF background therapies. In vivo left-ventricular hemodynamics/pressure-volume relationships assessed before/during a 30 min IV infusion of CXL-1020 demonstrated acute load-independent positive inotropic, lusitropic, and vasodilatory effects in normal rats. In rats with only diastolic dysfunction due to bilateral renal wrapping (RW) or pronounced diastolic and mild systolic dysfunction due to 4 weeks of chronic isoproterenol exposure (ISO), CXL-1020 attenuated the elevated LV filling pressures, improved the end diastolic pressure volume relationship, and accelerated relaxation. CXL-1020 facilitated Ca²⁺ re-uptake and enhanced myocyte relaxation in isolated cardiomyocytes from ISO rats. Compared to milrinone, CXL-1020 more effectively improved Ca²⁺ reuptake in ISO rats without concomitant chronotropy, and did not enhance Ca²⁺ entry via L-type Ca²⁺ channels nor increase myocardial arrhythmias/ectopic activity. Acute-therapy with CXL-1020 improved ventricular relaxation and Ca²⁺ cycling, in the setting of chronic induced diastolic dysfunction. CXL-1020's lusitropic effects were greater than those seen with the cAMP-dependent agent milrinone, and unlike milrinone it did not produce chronotropy or increased ectopy. HNO is a promising new potential therapy for both systolic and diastolic heart failure.

NO and HNO donors, nitrones, and nitroxides: Past, present, and future

The biological effects attributed to nitric oxide (^• NO) and nitroxyl (HNO) have been extensively studied, propelling their array of putative clinical applications beyond cardiovascular disorders toward other age-related diseases, like cancer and neurodegenerative diseases. In this context, the unique properties and reactivity of the N-O bond enabled the development of several classes of compounds with potential clinical interest, among which ^• NO and HNO donors, nitrones, and nitroxides are of particular importance. Although primarily studied for their application as cardioprotective agents and/or molecular probes for radical detection, continuous efforts have unveiled a wide range of pharmacological activities and, ultimately, therapeutic applications. These efforts are of particular significance for diseases in which oxidative stress plays a key pathogenic role, as shown by a growing volume of in vitro and in vivo preclinical data. Although in its early stages, these efforts may provide valuable guidelines for the development of new and effective N-O-based drugs for age-related disorders. In this report, we review recent advances in the chemistry of NO and HNO donors, nitrones, and nitroxides and discuss its pharmacological significance and potential therapeutic application.

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.