Pulmonary and systemic vasodilator responses to the soluble guanylyl cyclase activator, BAY 60-2770, are not dependent on endogenous nitric oxide or reduced heme

Endothelial and Vascular Smooth Muscle Dysfunction in Hypertension

The development of essential hypertension involves several factors. Vascular dysfunction, characterized by endothelial dysfunction, low-grade inflammation and structural remodeling, plays an important role in the initiation and maintenance of essential hypertension. Although the mechanistic pathways by which essential hypertension develops are poorly understood, several pharmacological classes available on the clinical settings improve blood pressure by interfering in the cardiac output and/or vascular function. This review is divided in two major sections. The first section depicts the major molecular pathways as renin angiotensin aldosterone system (RAAS), endothelin, nitric oxide signalling pathway and oxidative stress in the development of vascular dysfunction. The second section describes the role of some pharmacological classes such as i) RAAS inhibitors, ii) dual angiotensin receptor-neprilysin inhibitors, iii) endothelin-1 receptor antagonists, iv) soluble guanylate cyclase modulators, v) phosphodiesterase type 5 inhibitors and vi) sodium-glucose cotransporter 2 inhibitors in the context of hypertension. Some classes are already approved in the treatment of hypertension, but others are not yet approved. However, due to their potential benefits these classes were included.

Pharmacological developments in antihypertensive treatment through nitric oxide-cGMP modulation

Treatment of hypertension until now has been directed at inhibition of vasoconstriction, of cardiac contractility and of blood volume regulation. Despite the arsenal of drugs available for this purpose, the control of target blood pressure is still a difficult goal to reach in outpatients. The nitric oxide-cyclic guanosine monophosphate signaling is one of the most important mediators of vasodilation. It might therefore be a potential and most welcome drug target for optimization of the treatment of hypertension. In this chapter we review the problems that can occur in this signaling system, the attempts that have been made to correct these problems, and those that are still under investigation. Recently developed, clinically safe medicines that are currently approved for other applications, such as myocardial infarction, await to be tested for essential systemic hypertension. We conclude that despite many years of research without translation, stimulation of nitric oxide-cyclic guanosine monophosphate is still a viable strategy in the prevention of the health risk posed by chronic hypertension.

Hsp90 in Human Diseases: Molecular Mechanisms to Therapeutic Approaches

The maturation of hemeprotein dictates that they incorporate heme and become active, but knowledge of this essential cellular process remains incomplete. Studies on chaperon Hsp90 has revealed that it drives functional heme maturation of inducible nitric oxide synthase (iNOS), soluble guanylate cyclase (sGC) hemoglobin (Hb) and myoglobin (Mb) along with other proteins including GAPDH, while globin heme maturations also need an active sGC. In all these cases, Hsp90 interacts with the heme-free or apo-protein and then drives the heme maturation by an ATP dependent process before dissociating from the heme-replete proteins, suggesting that it is a key player in such heme-insertion processes. As the studies on globin maturation also need an active sGC, it connects the globin maturation to the NO-sGC (Nitric oxide-sGC) signal pathway, thereby constituting a novel NO-sGC-Globin axis. Since many aggressive cancer cells make Hbβ/Mb to survive, the dependence of the globin maturation of cancer cells places the NO-sGC signal pathway in a new light for therapeutic intervention. Given the ATPase function of Hsp90 in heme-maturation of client hemeproteins, Hsp90 inhibitors often cause serious side effects and this can encourage the alternate use of sGC activators/stimulators in combination with specific Hsp90 inhibitors for better therapeutic intervention.

The sGC stimulator BAY-747 and activator runcaciguat can enhance memory in vivo via differential hippocampal plasticity mechanisms

Soluble guanylate cyclase (sGC) requires a heme-group bound in order to produce cGMP, a second messenger involved in memory formation, while heme-free sGC is inactive. Two compound classes can increase sGC activity: sGC stimulators acting on heme-bound sGC, and sGC activators acting on heme-free sGC. In this rodent study, we investigated the potential of the novel brain-penetrant sGC stimulator BAY-747 and sGC activator runcaciguat to enhance long-term memory and attenuate short-term memory deficits induced by the NOS-inhibitor L-NAME. Furthermore, hippocampal plasticity mechanisms were investigated. In vivo, oral administration of BAY-747 and runcaciguat to male Wistar rats enhanced memory acquisition in the object location task (OLT), while only BAY-747 reversed L-NAME induced memory impairments in the OLT. Ex vivo, both BAY-747 and runcaciguat enhanced hippocampal GluA1-containing AMPA receptor (AMPAR) trafficking in a chemical LTP model for memory acquisition using acute mouse hippocampal slices. In vivo only runcaciguat acted on the glutamatergic AMPAR system in hippocampal memory acquisition processes, while for BAY-747 the effects on the neurotrophic system were more pronounced as measured in male mice using western blot. Altogether this study shows that sGC stimulators and activators have potential as cognition enhancers, while the underlying plasticity mechanisms may determine disease-specific effectiveness.

Capillary hemodynamics and contracting skeletal muscle oxygen pressures in male rats with heart failure: Impact of soluble guanylyl cyclase activator

In heart failure with reduced ejection fraction (HFrEF), nitric oxide-soluble guanylyl cyclase (sGC) pathway dysfunction impairs skeletal muscle arteriolar vasodilation and thus capillary hemodynamics, contributing to impaired oxygen uptake (V̇O2) kinetics. Targeting this pathway with sGC activators offers a new treatment approach to HFrEF. We tested the hypotheses that sGC activator administration would increase the O2 delivery (Q̇O2)-to-V̇O2 ratio in the skeletal muscle interstitial space (PO2is) of HFrEF rats during twitch contractions due, in part, to increases in red blood cell (RBC) flux (fRBC), velocity (VRBC), and capillary hematocrit (Hctcap). HFrEF was induced in male Sprague-Dawley rats via myocardial infarction. After 3 weeks, rats were treated with 0.3 mg/kg of the sGC activator BAY 60-2770 (HFrEF + BAY; n = 11) or solvent (HFrEF; n = 9) via gavage b.i.d for 5 days prior to phosphorescence quenching (PO2is, in contracting muscle) and intravital microscopy (resting) measurements in the spinotrapezius muscle. Intravital microscopy revealed higher fRBC (70 ± 9 vs 25 ± 8 RBC/s), VRBC (490 ± 43 vs 226 ± 35 μm/s), Hctcap (16 ± 1 vs 10 ± 1%) and a greater number of capillaries supporting flow (91 ± 3 vs 82 ± 3%) in HFrEF + BAY vs HFrEF (all P < 0.05). Additionally, PO2is was especially higher during 12-34s of contractions in HFrEF + BAY vs HFrEF (P < 0.05). Our findings suggest that sGC activators improved resting Q̇O2 via increased fRBC, VRBC, and Hctcap allowing for better Q̇O2-to-V̇O2 matching during the rest-contraction transient, supporting sGC activators as a potential therapeutic to target skeletal muscle vasomotor dysfunction in HFrEF.

Emerging antenatal therapies for congenital diaphragmatic hernia-induced pulmonary hypertension in preclinical models

Congenital diaphragmatic hernia (CDH)-related deaths are the largest contributor to in-hospital neonatal deaths in children with congenital malformations. Morbidity and mortality in CDH are directly related to the development of pulmonary hypertension (PH). Current treatment consists of supportive measures. To date, no pharmacotherapy has been shown to effectively reverse the hallmark finding of pulmonary vascular remodeling that is associated with pulmonary hypertension in CDH (CDH-PH). As such, there is a great need for novel therapies to effectively manage CDH-PH. Our review aims to evaluate emerging therapies, and specifically focuses on those that are still under investigation and not approved for clinical use by the Food and Drug Administration. Therapies were categorized into antenatal pharmacotherapies or antenatal regenerative therapies and assessed on their method of administration, safety profile, the effect on pulmonary vascular pathophysiology, and overall efficacy. In general, emerging antenatal pharmaceutical and regenerative treatments primarily aim to alleviate pulmonary vascular remodeling by restoring normal function and levels of key regulatory factors involved in pulmonary vascular development and/or in promoting angiogenesis. Overall, while these emerging therapies show great promise for the management of CDH-PH, most require further assessment of safety and efficacy in preclinical models before translation into the clinical setting. IMPACT: Emerging antenatal therapies for congenital diaphragmatic hernia-induced pulmonary hypertension (CDH-PH) show promise to effectively mitigate vascular remodeling in preclinical models. Further investigation is needed in preclinical and human studies to evaluate safety and efficacy prior to translation into the clinical arena. This review offers a comprehensive and up-to-date summary of emerging therapies currently under investigation in experimental animal models. There is no cure for CDH-PH. This review explores emerging therapeutic options for the treatment of CDH-PH and evaluates their impact on key molecular pathways and clinical markers of disease to determine efficacy in the preclinical stage.

The soluble guanylate cyclase stimulator, 1-nitro-2-phenylethane, reverses monocrotaline-induced pulmonary arterial hypertension in rats

AIMS

We examined the effects of treatment with 1-nitro-2-phenylethane (NP), a novel soluble guanylate cyclase stimulator, on monocrotaline (MCT)-induced PAH in rats.

MAIN METHODS

At day 0, male adult rats were injected with a single subcutaneous (s.c.) dose of monocrotaline (60 mg/kg). Control (CNT) rats received an equal volume of monocrotaline's vehicle only (s.c.). Four weeks later, MCT-treated rats were treated orally for 14 days with NP (50 mg/kg/day) (MCT-NP group) or its vehicle (Tween 2%) (MCT-V group). At the end of the treatment period and before invasive hemodynamic study, rats of all experimental groups were examined by echocardiography.

KEY FINDINGS

With respect to CNT rats, MCT-V rats showed significant; (1) increases in pulmonary artery (PA) diameter, RV free wall thickness and end-diastolic RV area, and increase of Fulton index; (2) decreases in maximum pulmonary flow velocity, PA acceleration time (PAAT), PAAT/time of ejection ratio, and velocity-time integral; (3) increases in estimated mean pulmonary arterial pressure; (4) reduction of maximal relaxation to acetylcholine in aortic rings, and (5) increases in wall thickness of pulmonary arterioles. All these measured parameters were significantly reduced or even abolished by oral treatment with NP.

SIGNIFICANCE

NP reversed endothelial dysfunction and pulmonary vascular remodeling, which in turn reduced ventricular hypertrophy. NP reduced pulmonary artery stiffness, normalized the pulmonary artery diameter and alleviated RV enlargement. Thus, NP may represent a new therapeutic or a complementary approach to treatment of PAH.

A new paradigm for gaseous ligand selectivity of hemoproteins highlighted by soluble guanylate cyclase

Nitric oxide (NO), carbon monoxide (CO), and oxygen (O₂) are important physiological messengers whose concentrations vary in a remarkable range, [NO] typically from nM to several μM while [O₂] reaching to hundreds of μM. One of the machineries evolved in living organisms for gas sensing is sensor hemoproteins whose conformational change upon gas binding triggers downstream response cascades. The recently proposed "sliding scale rule" hypothesis provides a general interpretation for gaseous ligand selectivity of hemoproteins, identifying five factors that govern gaseous ligand selectivity. Hemoproteins have intrinsic selectivity for the three gases due to a neutral proximal histidine ligand while proximal strain of heme and distal steric hindrance indiscriminately adjust the affinity of these three gases for heme. On the other hand, multiple-step NO binding and distal hydrogen bond donor(s) specifically enhance affinity for NO and O₂, respectively. The "sliding scale rule" hypothesis provides clear interpretation for dramatic selectivity for NO over O₂ in soluble guanylate cyclase (sGC) which is an important example of sensor hemoproteins and plays vital roles in a wide range of physiological functions. The "sliding scale rule" hypothesis has so far been validated by all experimental data and it may guide future designs for heme-based gas sensors.

The selective PGI2 receptor agonist selexipag ameliorates Sugen 5416/hypoxia-induced pulmonary arterial hypertension in rats

Pulmonary arterial hypertension (PAH) is a lethal disease characterized by a progressive increase in pulmonary artery pressure due to an increase in vessel tone and occlusion of vessels. The endogenous vasodilator prostacyclin and its analogs are used as therapeutic agents for PAH. However, their pharmacological effects on occlusive vascular remodeling have not been elucidated yet. Selexipag is a recently approved, orally available and selective prostacyclin receptor agonist with a non-prostanoid structure. In this study, we investigated the pharmacological effects of selexipag on the pathology of chronic severe PAH in Sprague-Dawley and Fischer rat models in which PAH was induced by a combination of injection with the vascular endothelial growth factor receptor antagonist Sugen 5416 and exposure to hypoxia (SuHx). Oral administration of selexipag for three weeks significantly improved right ventricular systolic pressure and right ventricular (RV) hypertrophy in Sprague-Dawley SuHx rats. Selexipag attenuated the proportion of lung vessels with occlusive lesions and the medial wall thickness of lung arteries, corresponding to decreased numbers of Ki-67-positive cells and a reduced expression of collagen type 1 in remodeled vessels. Administration of selexipag to Fischer rats with SuHx-induced PAH reduced RV hypertrophy and mortality caused by RV failure. These effects were probably based on the potent prostacyclin receptor agonistic effect of selexipag on pulmonary vessels. Selexipag has been approved and is used in the clinical treatment of PAH worldwide. It is thought that these beneficial effects of prostacyclin receptor agonists on multiple aspects of PAH pathology contribute to the clinical outcomes in patients with PAH.

Nitric Oxide-cGMP Signaling in Hypertension: Current and Future Options for Pharmacotherapy

For the treatment of systemic hypertension, pharmacological intervention in nitric oxide-cyclic guanosine monophosphate signaling is a well-explored but unexploited option. In this review, we present the identified drug targets, including oxidases, mitochondria, soluble guanylyl cyclase, phosphodiesterase 1 and 5, and protein kinase G, important compounds that modulate them, and the current status of (pre)clinical development. The mode of action of these compounds is discussed, and based upon this, the clinical opportunities. We conclude that drugs that directly target the enzymes of the nitric oxide-cyclic guanosine monophosphate cascade are currently the most promising compounds, but that none of these compounds is under investigation as a treatment option for systemic hypertension.

Beneficial Effects of Soluble Guanylyl Cyclase Stimulation and Activation in Sickle Cell Disease Are Amplified by Hydroxyurea: In Vitro and In Vivo Studies

The complex pathophysiology of sickle cell anemia (SCA) involves intravascular hemolytic processes and recurrent vaso-occlusion, driven by chronic vascular inflammation, which result in the disease’s severe clinical complications, including recurrent painful vaso-occlusive episodes. Hydroxyurea, the only drug frequently used for SCA therapy, is a cytostatic agent, although it appears to exert nitric oxide/soluble guanylyl cyclase (sGC) modulating activity. As new drugs that can complement or replace the use of hydroxyurea are sought to further reduce vaso-occlusive episode frequency in SCA, we investigated the effects of the sGC agonists BAY 60-2770 (sGC activator) and BAY 41-2272 (sGC stimulator) in the presence or absence of hydroxyurea on SCA vaso-occlusive mechanisms and cell recruitment both ex vivo and in vivo. These agents significantly reduced stimulated human SCA neutrophil adhesive properties ex vivo in association with the inhibition of surface β2-integrin activation. A single administration of BAY 60-2770 or BAY 41-2272 decreased tumor necrosis factor cytokine–induced leukocyte recruitment in a mouse model of SCA vaso-occlusion. Importantly, the in vivo actions of both agonists were significantly potentiated by the coadministration of hydroxyurea. Erythroid cell fetal hemoglobin (HbF) elevation is also a major goal for SCA therapy. BAY 41-2272 but not BAY 60-2770 at the concentrations employed significantly induced γ-globin gene transcription in association with HbF production in cultured erythroleukemic cells. In conclusion, sGC agonist drugs could represent a promising approach as therapy for SCA, for use either as stand-alone treatments or in combination with hydroxyurea.

Therapies that enhance pulmonary vascular NO-signaling in the neonate

There are several pulmonary hypertensive diseases that affect the neonatal population, including persistent pulmonary hypertension of the newborn (PPHN) and bronchopulmonary dysplasia (BPD)-associated pulmonary hypertension (PH). While the indication for inhaled nitric oxide (iNO) use is for late-preterm and term neonates with PPHN, there is a suboptimal response to this pulmonary vasodilator in ~40% of patients. Additionally, there are no FDA-approved treatments for BPD-associated PH or for preterm infants with PH. Therefore, investigating mechanisms that alter the nitric oxide-signaling pathway has been at the forefront of pulmonary vascular biology research. In this review, we will discuss the various mechanistic pathways that have been targets in neonatal PH, including NO precursors, soluble guanylate cyclase modulators, phosphodiesterase inhibitors and antioxidants. We will review their role in enhancing NO-signaling at the bench, in animal models, as well as highlight their role in the treatment of neonates with PH.

Modulation of nitric oxide-stimulated soluble guanylyl cyclase activity by cytoskeleton-associated proteins in vascular smooth muscle

Soluble guanylyl cyclase (sGC, EC 4.6.1.2) is a key enzyme in the regulation of vascular tone. In view of the therapeutic interest of the NO/cGMP pathway, drugs were developed that either increase the NO sensitivity of the enzyme or activate heme-free apo-sGC. However, modulation of sGC activity by endogenous agents is poorly understood. In the present study we show that the maximal activity of NO-stimulated purified sGC is significantly increased by cytosolic preparations of porcine coronary arteries. Purification of the active principle by several chromatographic steps resulted in a protein mixture consisting of 100, 70, and 40 kDa bands on SDS polyacrylamide gel electrophoresis. The respective proteins were identified by LC-MS/MS as gelsolin, annexin A6, and actin, respectively. Further purification resulted in loss of activity, indicating an interaction of sGC with a protein complex rather than a single protein. The partially purified preparation had no effect on basal sGC activity or enzyme activation by the heme mimetic BAY 60-2770, suggesting a specific effect on the conformation of the NO-bound heterodimeric holoenzyme. Since the three proteins identified are all related to contractile elements of smooth muscle, our data suggest that regulation of vascular tone involves a modulatory interaction of sGC with the cytoskeleton.

Discovery and development of sGC stimulators for the treatment of pulmonary hypertension and rare diseases

The NO/sGC/cGMP signaling cascade plays a pivotal role in regulation of cardiovascular, cardiopulmonary and cardiorenal diseases and impairment of this cascade results in severe pathologies. Therefore, pharmacological interventions, targeting this pathway are promising strategies for treating a variety of diseases. Nitrates, supplementing NO and, PDE5 inhibitors preventing cGMP degradation, are used for angina pectoris treatment and the treatment of pulmonary arterial hypertension (PAH), respectively. More recently, a new class of drugs which directly stimulate the sGC enzyme and trigger NO-independent cGMP production was introduced and termed sGC stimulators. In 2013, the first sGC stimulator, riociguat, was approved for the treatment of PAH and chronic thromboembolic pulmonary hypertension (CTEPH). Since cGMP targets multiple intracellular downstream targets, sGC stimulators have shown - beyond the well characterized vasodilatation - anti-fibrotic, anti-inflammatory and anti-proliferative effects. These additional modes of action might extend the therapeutic potential of this drug class substantially. This review summarizes the NO/sGC/cGMP signaling cascades, the discovery and the mode of action of sGC stimulators. Furthermore, the preclinical evidence and development of riociguat for the treatment of PAH and CTEPH is reviewed. Finally, a summary of the antifibrotic effects of sGC stimulators, especially the most recent finding for skin fibrosis are included which may indicate efficacy in fibrotic diseases like Systemic Sclerosis (SSc).

Acute stimulation of the soluble guanylate cyclase does not impact on left ventricular capacitance in normal and hypertrophied porcine hearts in vivo

Experimental data indicate that stimulation of the nitric oxide-soluble guanylate cyclase(sGC)-cGMP-PKG pathway can increase left ventricular (LV) capacitance via phosphorylation of the myofilamental protein titin. We aimed to test whether acute pharmacological sGC stimulation with BAY 41-8543 would increase LV capacitance via titin phosphorylation in healthy and deoxycorticosteroneacetate (DOCA)-induced hypertensive pigs. Nine healthy Landrace pigs and 7 pigs with DOCA-induced hypertension and LV concentric hypertrophy were acutely instrumented to measure LV end-diastolic pressure-volume relationships (EDPVRs) at baseline and during intravenous infusion of BAY 41-8543 (1 and 3 μg·kg^-1·min^-1 for 30 min, respectively). Separately, in seven healthy and six DOCA pigs, transmural LV biopsies were harvested from the beating heart to measure titin phosphorylation during BAY 41-8543 infusion. LV EDPVRs before and during BAY 41-8543 infusion were superimposable in both healthy and DOCA-treated pigs, whereas mean aortic pressure decreased by 20-30 mmHg in both groups. Myocardial titin phosphorylation was unchanged in healthy pigs, but total and site-specific (Pro-Glu-Val-Lys and N2-Bus domains) titin phosphorylation was increased in DOCA-treated pigs. Bicoronary nitroglycerin infusion in healthy pigs ( n = 5) induced a rightward shift of the LV EDPVR, demonstrating the responsiveness of the pathway in this model. Acute systemic sGC stimulation with the sGC stimulator BAY 41-8543 did not recruit an LV preload reserve in both healthy and hypertrophied LV porcine myocardium, although it increased titin phosphorylation in the latter group. Thus, increased titin phosphorylation is not indicative of increased in vivo LV capacitance. NEW & NOTEWORTHY We demonstrate that acute pharmacological stimulation of soluble guanylate cyclase does not increase left ventricular compliance in normal and hypertrophied porcine hearts. Effects of long-term soluble guanylate cyclase stimulation with oral compounds in disease conditions associated with lowered myocardial cGMP levels, i.e., heart failure with preserved ejection fraction, remain to be investigated.

Methods to investigate structure and activation dynamics of GC-1/GC-2

Soluble guanylyl cyclase (sGC) is a heterodimeric enzyme consisting of one α and one β subunit. The α1β1 (GC-1) and α2β1 (GC-2) heterodimers are important for NO signaling in humans and catalyse the conversion from GTP to cGMP. Each sGC subunit consists of four domains. Several crystal structures of the isolated domains are available. However, crystals of full-length sGC have failed to materialise. In consequence, the detailed three dimensional structure of sGC remains unknown to date. Different techniques including stopped-flow spectroscopy, Förster-resonance energy transfer, direct fluorescence, analytical ultracentrifugation, chemical cross-linking, small-angle X-ray scattering, electron microscopy, hydrogen-deuterium exchange and protein thermal shift assays, were used to collect indirect information. Taken together, this circumstantial evidence from different groups brings forth a plausible model of sGC domain arrangement, spatial orientation and dynamic rearrangement upon activation. For analysis of the active conformation the stable binding mode of sGC activators has a significant methodological advantage over the transient, elusive, complex and highly concentration dependent effects of NO in many applications. The methods used and the results obtained are reviewed and discussed in this article.

Redox regulation of soluble guanylyl cyclase

The nitric oxide/soluble guanylyl cyclase (NO-sGC) signaling pathway regulates the cardiovascular, neuronal, and gastrointestinal systems. Impaired sGC signaling can result in disease and system-wide organ failure. This review seeks to examine the redox control of sGC through heme and cysteine regulation while discussing therapeutic drugs that target various conditions. Heme regulation involves mechanisms of insertion of the heme moiety into the sGC protein, the molecules and proteins that control switching between the oxidized (Fe³⁺) and reduced states (Fe²⁺), and the activity of heme degradation. Modifications to cysteine residues by S-nitrosation on the α1 and β1 subunits of sGC have been shown to be important in sGC signaling. Moreover, redox balance and localization of sGC is thought to control downstream effects. In response to altered sGC activity due to changes in the redox state, many therapeutic drugs have been developed to target decreased NO-sGC signaling. The importance and relevance of sGC continues to grow as sGC dysregulation leads to numerous disease conditions.

Search for an animal model to investigate selective pulmonary vasodilation

Pulmonary arterial hypertension is a life-threatening disease with a poor prognosis. Oral treatment with vasodilators is often limited by systemic hypotension. Inhalation of vasodilators offers the opportunity for selective pulmonary vasodilation. Testing selective pulmonary vasodilation by inhaled nitric oxide or alternative substances in animal models requires an increased pulmonary vascular tone. The aim of this study was to identify animal models that are suitable for investigating selective pulmonary vasodilation. To do so, a haemodynamic stable pulmonary hypertension was initiated, with a 30 min duration deemed to be a sufficient time interval before and after a possible intervention. In anaesthetized and mechanically-ventilated Sprague-Dawley rats pulmonary hypertension was induced either by acute hypoxia due to reduction of the inspired oxygen fraction from 0.21 to 0.1 ( n = 6), a fixed infusion rate of the thromboxane analogue U46619 (240 ng/min; n = 6) or a monocrotaline injection (MCT; 60 mg/kg applied 23 days before the investigation; n = 7). The animals were instrumented to measure right ventricular and systemic arterial pressures. Acute hypoxia caused a short, and only transient, increase of pulmonary artery pressure as well as profound systemic hypotension which suggested haemodynamic instability. U46619 infusion induced variable changes in the pulmonary and systemic vascular tone without sufficient stabilization within 30 min. MCT provoked sustained pulmonary hypertension with normal systemic pressure values and inhalation of nitric oxide caused selective pulmonary vasodilation. In conclusion, out of the three examined rat animal models only MCT-induced pulmonary hypertension is a solid and reliable model for investigating selective pulmonary vasodilation.

Nebivolol has a beneficial effect in monocrotaline-induced pulmonary hypertension

Pulmonary hypertension is a rare disorder that, without treatment, is progressive and fatal within 3–4 years. Current treatment involves a diverse group of drugs that target the pulmonary vascular bed. In addition, strategies that increase nitric oxide (NO) formation have a beneficial effect in rodents and patients. Nebivolol, a selective β1 adrenergic receptor-blocking agent reported to increase NO production and stimulate β3 receptors, has vasodilator properties suggesting that it may be beneficial in the treatment of pulmonary hypertension. The present study was undertaken to determine whether nebivolol has a beneficial effect in monocrotaline-induced (60 mg/kg) pulmonary hypertension in the rat. These results show that nebivolol treatment (10 mg/kg, once or twice daily) attenuates pulmonary hypertension, reduces right ventricular hypertrophy, and improves pulmonary artery remodeling in monocrotaline-induced pulmonary hypertension. This study demonstrates the presence of β3 adrenergic receptor immunoreactivity in pulmonary arteries and airways and that nebivolol has pulmonary vasodilator activity. Studies with β3 receptor agonists (mirabegron, BRL 37344) and antagonists suggest that β3 receptor-mediated decreases in systemic arterial pressure occur independent of NO release. Our results suggest that nebivolol, a selective vasodilating β1 receptor antagonist that stimulates β3 adrenergic receptors and induces vasodilation by increasing NO production, may be beneficial in treating pulmonary hypertensive disorders.

Soluble guanylyl cyclase-activated cyclic GMP-dependent protein kinase inhibits arterial smooth muscle cell migration independent of VASP-serine 239 phosphorylation

Coronary artery disease (CAD) accounts for over half of all cardiovascular disease-related deaths. Uncontrolled arterial smooth muscle (ASM) cell migration is a major component of CAD pathogenesis and efforts aimed at attenuating its progression are clinically essential. Cyclic nucleotide signaling has long been studied for its growth-mitigating properties in the setting of CAD and other vascular disorders. Heme-containing soluble guanylyl cyclase (sGC) synthesizes cyclic guanosine monophosphate (cGMP) and maintains vascular homeostasis predominantly through cGMP-dependent protein kinase (PKG) signaling. Considering that reactive oxygen species (ROS) can interfere with appropriate sGC signaling by oxidizing the cyclase heme moiety and so are associated with several CVD pathologies, the current study was designed to test the hypothesis that heme-independent sGC activation by BAY 60-2770 (BAY60) maintains cGMP levels despite heme oxidation and inhibits ASM cell migration through phosphorylation of the PKG target and actin-binding vasodilator-stimulated phosphoprotein (VASP). First, using the heme oxidant ODQ, cGMP content was potentiated in the presence of BAY60. Using a rat model of arterial growth, BAY60 significantly reduced neointima formation and luminal narrowing compared to vehicle (VEH)-treated controls. In rat ASM cells BAY60 significantly attenuated cell migration, reduced G:F actin, and increased PKG activity and VASP Ser239 phosphorylation (pVASP·S239) compared to VEH controls. Site-directed mutagenesis was then used to generate overexpressing full-length wild type VASP (FL-VASP/WT), VASP Ser239 phosphorylation-mimetic (FL-VASP/239D) and VASP Ser239 phosphorylation-resistant (FL-VASP/239A) ASM cell mutants. Surprisingly, FL-VASP/239D negated the inhibitory effects of FL-VASP/WT and FL-VASP/239A cells on migration. Furthermore, when FL-VASP mutants were treated with BAY60, only the FL-VASP/239D group showed reduced migration compared to its VEH controls. Intriguingly, FL-VASP/239D abrogated the stimulatory effects of FL-VASP/WT and FL-VASP/239A cells on PKG activity. In turn, pharmacologic blockade of PKG in the presence of BAY60 reversed the inhibitory effect of BAY60 on naïve ASM cell migration. Taken together, we demonstrate for the first time that BAY60 inhibits ASM cell migration through cGMP/PKG/VASP signaling yet through mechanisms independent of pVASP·S239 and that FL-VASP overexpression regulates PKG activity in rat ASM cells. These findings implicate BAY60 as a potential pharmacotherapeutic agent against aberrant ASM growth disorders such as CAD and also establish a unique mechanism through which VASP controls PKG activity.

Activation of soluble guanylyl cyclase by BAY 58-2667 improves bladder function in cyclophosphamide-induced cystitis in mice

Activators of soluble guanylyl cyclase (sGC) interact directly with its prosthetic heme group, enhancing the enzyme responsiveness in pathological conditions. This study aimed to evaluate the effects of the sGC activator BAY 58-2667 on voiding dysfunction, protein expressions of α1 and β1 sGC subunits and cGMP levels in the bladder tissues after cyclophosphamide (CYP) exposure. Female C57BL/6 mice (20-25 g) were injected with CYP (300 mg/kg ip) to induce cystitis. Mice were pretreated or not with BAY 58-2667 (1 mg/kg, gavage), given 1 h before CYP injection. The micturition patterns and in vitro bladder contractions were evaluated at 24 h. In freely moving mice, the CYP injection produced reduced the micturition volume and increased the number of urine spots. Cystometric recordings in CYP-injected mice revealed significant increases in basal pressure, voiding frequency, and nonvoiding contractions (NVCs), along with decreases in bladder capacity, intercontraction interval, and compliance. BAY 58-2667 significantly prevented the micturition alterations observed in both freely moving mice and cystometry and normalized the reduced in vitro carbachol-induced contractions in the CYP group. Reduced protein expressions of α1 and β1 sGC subunits and of cGMP levels were observed in the CYP group, all of which were prevented by BAY 58-2667. CYP exposure significantly increased reactive-oxygen species (ROS) generation in both detrusor and urothelium, and this was normalized by BAY 58-2667. The increased myeloperoxidase and cyclooxygenase-2 activities in the bladders of the CYP group remained unchanged by BAY 58-2667. Activators of sGC may constitute a novel and promising therapeutic approach for management of interstitial cystitis.

Soluble guanylate cyclase: a new therapeutic target for pulmonary arterial hypertension and chronic thromboembolic pulmonary hypertension

Nitric oxide (NO) activates soluble guanylate cyclase (sGC) by binding its prosthetic heme group, thereby catalyzing cyclic guanosine monophosphate (cGMP) synthesis. cGMP causes vasodilation and may inhibit smooth muscle cell proliferation and platelet aggregation. The NO-sGC-cGMP pathway is disordered in pulmonary arterial hypertension (PAH), a syndrome in which pulmonary vascular obstruction, inflammation, thrombosis, and constriction ultimately lead to death from right heart failure. Expression of sGC is increased in PAH but its function is reduced by decreased NO bioavailability, sGC oxidation and the related loss of sGC's heme group. Two classes of sGC modulators offer promise in PAH. sGC stimulators (e.g., riociguat) require heme-containing sGC to catalyze cGMP production, whereas sGC activators (e.g., cinaciguat) activate heme-free sGC. Riociguat is approved for PAH and yields functional and hemodynamic benefits similar to other therapies. Its main serious adverse effect is dose-dependent hypotension. Riociguat is also approved for inoperable chronic thromboembolic pulmonary hypertension.

Oxidative stress associated with middle aging leads to sympathetic hyperactivity and downregulation of soluble guanylyl cyclase in corpus cavernosum

Impairment of nitric oxide (NO)-mediated cavernosal relaxations in middle age contributes to erectile dysfunction. However, little information is available about the alterations of sympathetic neurotransmission and contraction in erectile tissue at middle age. This study aimed to evaluate the alterations of the contractile machinery associated with tyrosine hydroxylase (TH) in rat corpus cavernosum (RCC) at middle age, focusing on the role of superoxide anion. Male Wistar young (3.5-mo) and middle-aged (10-mo) rats were used. Electrical-field stimulation (EFS)- and phenylephrine-induced contractions were obtained in RCC strips. Levels of reactive-oxygen species (ROS) and TH mRNA expression, as well as protein expressions for α1/β1-subunits of soluble guanylyl cyclase (sGC), in RCC were evaluated. The neurogenic contractile responses elicited by EFS (4–32 Hz) were greater in RCC from the middle-aged group that was accompanied by elevated TH mRNA expression ( P < 0.01). Phenylephrine-induced contractions were also greater in the middle-aged group. A 62% increase in ROS generation in RCC from middle-aged rats was observed. The mRNA expression for the α1A-adrenoceptor remained unchanged among groups. Protein levels of α1/β1-sGC subunits were decreased in RCC from the middle-aged compared with young group. The NADPH oxidase inhibitor apocynin (85 mg·rat−1·day−1, 4 wk) fully restored the enhanced ROS production, TH mRNA expressions, and α1/β1-subunit sGC expression, indicating that excess of superoxide anion plays a major role in the sympathetic hyperactivity and hypercontractility in erectile tissue at middle age. Reduction of oxidative stress by dietary antioxidants may be an interesting approach to treat erectile dysfunction in aging population.

Vascular dysfunctions in the isolated aorta of double-transgenic hypertensive mice developing aortic aneurysm

Angiotensin-II and oxidative stress are involved in the genesis of aortic aneurysms, a phenomenon exacerbated by endothelial nitric oxide synthase (eNOS) deletion or uncoupling. The purpose of this work was to study the endothelial function in wild-type C57BL/6 (BL) and transgenic mice expressing the h-angiotensinogen and h-renin genes (AR) subjected to either a control, or a high-salt diet plus a treatment with a NO-synthase inhibitor, N-ω-nitro-L-arginine-methyl-ester (L-NAME; BLSL and ARSL). BLSL showed a moderate increase in blood pressure, while ARSL became severely hypertensive. Seventy-five percent of ARSL developed aortic aneurysms, characterized by major histo-morphological changes and associated with an increase in NADP(H) oxidase-2 (NOX2) expression. Contractile responses (KCl, norepinephrine, U-46619) were similar in the four groups of mice, and relaxations were not affected in BLSL and AR. However, in ARSL, endothelium-dependent relaxations (acetylcholine, UK-14304) were significantly reduced, and this dysfunction was similar in aortae without or with aneurysms. The endothelial impairment was unaffected by catalase, superoxide-dismutase mimetic, radical scavengers, cyclooxygenase inhibition, or TP-receptor blockade and could not be attributed to sGC oxidation. Thus, ARSL is a severe hypertension model developing aortic aneurysm. A vascular dysfunction, involving both endothelial (reduced role of NO) and smooth muscle cells, precedes aneurysms formation and, paradoxically, does not appear to involve oxidative stress.

Endothelin-1 and endothelin-2 initiate and maintain contractile responses by different mechanisms in rat mesenteric and cerebral arteries

BACKGROUND AND PURPOSE

Endothelin (ET)-1 and ET-2 cause potent long-lasting vasoconstrictions by tight binding to smooth muscle ETA receptors. We tested the hypotheses that different mechanisms mediate initiation and maintenance of arterial contractile responses to ET-1 and ET-2 and that this differs among vascular beds.

EXPERIMENTAL APPROACH

Segments of rat mesenteric resistance artery (MRA) and basilar artery (BA) were studied in wire myographs with and without functional antagonists.

KEY RESULTS

Sensitivity and maximum of MRA contractile responses to ET-1 were not, or only moderately, reduced by stimulation of soluble GC, AC or K(+) -channels and by an inhibitor of receptor-operated ion channels. However, each of these reduced maintenance of ET-1 effects and relaxed ET-1-induced contractions in MRA. A calcium channel antagonist did not alter sensitivity, maximum and maintenance of ET-1 effects, but relaxed ET-1-induced contractions in MRA. A PLC inhibitor prevented contractile responses to ET-1 and ET-2 in MRA and BA, and relaxed ET-1- and ET-2-induced responses in MRA and ET-1 effects in BA. A Rho-kinase inhibitor did not modify sensitivity, maximum and maintenance of responses to both peptides in both arteries but relaxed ET-2, but not ET-1, effects in MRA and ET-1 effects in BA.

CONCLUSIONS AND IMPLICATIONS

PLC played a key role in arterial contractile responses to ETs, but ET-1 and ET-2 initiated and maintained vasoconstriction through different mechanisms, and these differed between MRA and BA. Selective functional antagonism may be considered for agonist- and vascular bed selective pharmacotherapy of ET-related diseases.

The soluble guanylyl cyclase activator BAY 60-2770 potently relaxes the pulmonary artery on congenital diaphragmatic hernia rabbit model

PURPOSE

Congenital diaphragmatic hernia (CDH) is associated with pulmonary hypertension which is often difficult to manage, and a significant cause of morbidity and mortality. In this study, we have used a rabbit model of CDH to evaluate the effects of BAY 60-2770 on the in vitro reactivity of left pulmonary artery.

METHODS

CDH was performed in New Zealand rabbit fetuses (n = 10 per group) and compared to controls. Measurements of body, total and left lung weights (BW, TLW, LLW) were done. Pulmonary artery rings were pre-contracted with phenylephrine (10 μM), after which cumulative concentration-response curves to glyceryl trinitrate (GTN; NO donor), tadalafil (PDE5 inhibitor) and BAY 60-2770 (sGC activator) were obtained as well as the levels of NO (NO3/NO2).

RESULTS

LLW, TLW and LBR were decreased in CDH (p < 0.05). In left pulmonary artery, the potency (pEC50) for GTN was markedly lower in CDH (8.25 ± 0.02 versus 9.27 ± 0.03; p < 0.01). In contrast, the potency for BAY 60-2770 was markedly greater in CDH (11.7 ± 0.03 versus 10.5 ± 0.06; p < 0.01). The NO2/NO3 levels were 62 % higher in CDH (p < 0.05).

CONCLUSION

BAY 60-2770 exhibits a greater potency to relax the pulmonary artery in CDH, indicating a potential use for pulmonary hypertension in this disease.

Prolonged therapy with the soluble guanylyl cyclase activator BAY 60-2770 restores the erectile function in obese mice

INTRODUCTION

Cardiovascular and endocrine-metabolic diseases associated with increased oxidative stress such as obesity lead to erectile dysfunction (ED). Activators of soluble guanylyl cyclase (sGC) such as BAY 60-2770 reactivate the heme-oxidized sGC in vascular diseases.

AIM

This study aimed to evaluate the effects of 2-week oral intake with BAY 60-2270 on a murine model of obesity-associated ED.

METHODS

C57BL/6 male mice were fed for 12 weeks with standard chow or high-fat diet. Lean and obese mice were treated with BAY 60-2770 (1 mg/kg/day, 2 weeks).

MAIN OUTCOME MEASURES

Measurements of intracavernosal pressure (ICP), along with acetylcholine (10(-9) to 10(-5)  M) and electrical field stimulation (EFS; 4-10 Hz)-induced corpus cavernosum relaxations in vitro, were obtained. Levels of cyclic guanosine monophosphate (cGMP), reactive oxygen species (ROS), and sGC protein expressions in cavernosal tissues were measured.

RESULTS

Cavernous nerve stimulation caused frequency-dependent ICP increases, which were significantly lower in obese compared with lean mice (P < 0.05). Two-week therapy with BAY 60-2770 fully reversed the decreased ICP in obese group. Acetylcholine-induced cavernosal relaxations were 45% lower (P < 0.001) in obese mice, which were fully restored by BAY 60-2770 treatment. Likewise, the EFS-induced relaxations in obese mice were restored by BAY 60-2770. Basal cGMP content in erectile tissue was 68% lower (P < 0.05) in obese mice, an effect normalized by BAY 60-2770. Levels of ROS were 52% higher (P < 0.05) whereas protein expression of α1 sGC subunit was reduced in cavernosal tissue of obese mice, both of which were normalized by BAY 60-2770. In lean group, BAY 60-2770 did not significantly affect any functional, biochemical, or molecular parameter analyzed.

CONCLUSIONS

Two-week therapy with BAY 60-2770 restores the erectile function in obese mice that is associated with reduced ROS levels, up-regulation of α1 sGC subunit, and increased cGMP levels in the erectile tissue.

Vasodilator responses to acetylcholine are not mediated by the activation of soluble guanylate cyclase or TRPV4 channels in the rat

The effects of 1H-[1,2,4]-oxadizaolo[4,3-]quinoxaline-1-one (ODQ), an inhibitor of the activation of soluble guanylate cyclase (sGC) on responses to NO donors acetylcholine (ACh) and bradykinin (BK) were investigated in the pulmonary and systemic vascular beds of the rat. In these studies the administration of ODQ in a dose of 5 mg/kg iv attenuated vasodilator responses to five different NO donors without inhibiting responses to ACh and BK in the systemic and pulmonary vascular beds of the rat. Vasodilator responses to ACh were not inhibited by l-NAME or the transient receptor vanilloid type 4 (TRPV4) antagonist GSK-2193874, which attenuated vasodilator responses to the TRPV4 agonist GSK-1016790A. ODQ did not inhibit vasodilator responses to agents reported to act in an NO-independent manner or to vasoconstrictor agents, and ODQ did not increase blood methemoglobin levels, suggesting that off target effects were minimal. These results show that ODQ in a dose that inhibited NO donor-mediated responses did not alter vasodilator responses to ACh in the pulmonary and systemic vascular beds and did not alter systemic vasodilator responses to BK. The present results indicate that decreases in pulmonary and systemic arterial pressures in response to ACh are not mediated by the activation of sGC or TRPV4 channels and that ODQ can be used to study the role of the activation of sGC in mediating vasodilator responses in the rat.

Direct sGC activation bypasses NO scavenging reactions of intravascular free oxy-hemoglobin and limits vasoconstriction

AIMS

Hemoglobin-based oxygen carriers (HBOC) provide a potential alternative to red blood cell (RBC) transfusion. Their clinical application has been limited by adverse effects, in large part thought to be mediated by the intravascular scavenging of the vasodilator nitric oxide (NO) by cell-free plasma oxy-hemoglobin. Free hemoglobin may also cause endothelial dysfunction and platelet activation in hemolytic diseases and after transfusion of aged stored RBCs. The new soluble guanylate cyclase (sGC) stimulator Bay 41-8543 and sGC activator Bay 60-2770 directly modulate sGC, independent of NO bioavailability, providing a potential therapeutic mechanism to bypass hemoglobin-mediated NO inactivation.

RESULTS

Infusions of human hemoglobin solutions and the HBOC Oxyglobin into rats produced a severe hypertensive response, even at low plasma heme concentrations approaching 10 μM. These reactions were only observed for ferrous oxy-hemoglobin and not analogs that do not rapidly scavenge NO. Infusions of L-NG-Nitroarginine methyl ester (L-NAME), a competitive NO synthase inhibitor, after hemoglobin infusion did not produce additive vasoconstriction, suggesting that vasoconstriction is related to scavenging of vascular NO. Open-chest hemodynamic studies confirmed that hypertension occurred secondary to direct effects on increasing vascular resistance, with limited negative cardiac inotropic effects. Intravascular hemoglobin reduced the vasodilatory potency of sodium nitroprusside (SNP) and sildenafil, but had no effect on vasodilatation by direct NO-independent activation of sGC by BAY 41-8543 and BAY 60-2770.

INNOVATION AND CONCLUSION

These data suggest that both sGC stimulators and sGC activators could be used to restore cyclic guanosine monophosphate-dependent vasodilation in conditions where cell-free plasma hemoglobin is sufficient to inhibit endogenous NO signaling.

Modulation of soluble guanylate cyclase for the treatment of erectile dysfunction

Nitric oxide (NO) is the principal mediator of penile erection, and PDE-5 inhibitors are the first-line agents used to treat erectile dysfunction (ED). When NO formation or bioavailability is decreased by oxidative stress and PDE-5 inhibitors are no longer effective, a new class of agents called soluble guanylate cyclase (sGC) stimulators like BAY 41-8543 will induce erection. sGC stimulators bind to the normally reduced, NO-sensitive form of sGC to increase cGMP formation and promote erection. The sGC stimulators produce normal erectile responses when NO formation is inhibited and the nerves innervating the corpora cavernosa are damaged. However, with severe oxidative stress, the heme iron on sGC can be oxidized, rendering the enzyme unresponsive to NO or sGC stimulators. In this pathophysiological situation, another newly developed class of agents called sGC activators can increase the catalytic activity of the oxidized enzyme, increase cGMP formation, and promote erection. The use of newer agents that stimulate or activate sGC to promote erection and treat ED is discussed in this brief review article.

Analysis of erectile responses to imatinib in the rat

OBJECTIVE

To investigate the erectile and cardiovascular responses to the tyrosine kinase inhibitor imatinib in the rat.

MATERIALS AND METHODS

The effect of intracavernosal injection of imatinib on the intracavernosal pressure (ICP), ICP/mean arterial pressure (MAP) ratio, area under the curve, and duration of the increase in ICP and the effect of intravenous injection of imatinib on the MAP, cardiac output, and total peripheral resistance were investigated. The effect of the nitric oxide synthase inhibitor NG-nitro-L-arginine methyl ester on the responses to imatinib was investigated.

RESULTS

Intracavernosal injection of imatinib produced significant dose-related increases in the ICP, ICP/MAP ratio, area under the curve, and duration of the increase in ICP and decreases in the MAP. The erectile responses to imatinib were rapid in onset and short in duration. The erectile responses to imatinib were not significantly altered by NG-nitro-L-arginine methyl ester or cavernosal nerve crush injury, and imatinib was significantly less potent than the nitric oxide donor sodium nitroprusside in inducing erection. Intravenous injection of imatinib produced significant dose-related decreases in the MAP without significantly changing the cardiac output, and imatinib was significantly less potent than sodium nitroprusside in decreasing the MAP. Systemic vascular resistance was decreased in a significant dose-related manner, and the vasodilator responses to imatinib were not altered by NG-nitro-L-arginine methyl ester.

CONCLUSION

The present results have indicated that imatinib has significant erectile and systemic vasodilator activity in the rat that is not dependent on nitric oxide release. Another tyrosine kinase inhibitor, nilotinib, also increased the ICP and decreased the MAP in the rat. These data suggest that tyrosine kinases might play a constitutive role in maintaining penile tumescence and the baseline vasoconstrictor tone in the peripheral vascular bed.

Imatinib attenuates monocrotaline pulmonary hypertension and has potent vasodilator activity in pulmonary and systemic vascular beds in the rat

Cardiovascular responses to the tyrosine kinase inhibitor imatinib were investigated in the rat. Intravenous injections of 0.3-30 mg/kg imatinib produced small decreases in pulmonary arterial pressure, larger dose-dependent decreases in systemic arterial pressure, and no change or small increases in cardiac output, suggesting that the systemic vasodilator response is more pronounced under baseline conditions. When pulmonary arterial pressure was increased with U-46619 or N(ω)-nitro-L-arginine methyl ester (L-NAME), intravenous injections of imatinib produced larger dose-dependent decreases in pulmonary arterial pressure. Imatinib attenuated the acute hypoxic pulmonary vasoconstrictor response. Vasodilator responses to imatinib were not inhibited by meclofenamate, glybenclamide, or rolipram, suggesting that cyclooxygenase, ATP-sensitive K(+) (KATP) channels, and cAMP were not involved in mediating the response. In a 21-day prevention study, imatinib treatment (50 mg/kg ip) attenuated the increase in pulmonary arterial pressure, right ventricular hypertrophy, and small vessel remodeling induced by monocrotaline. Imatinib reduced PDGF receptor phosphorylation and PDGF-stimulated thymidine incorporation in rat pulmonary artery smooth muscle cells. These data suggest that the beneficial effect of imatinib in pulmonary hypertension may involve inhibition of PDGF tyrosine kinase receptor-mediated effects on smooth muscle cell proliferation and on vasoconstrictor tone. These results indicate that imatinib has nonselective vasodilator activity in the pulmonary and systemic vascular beds similar to the Rho kinase inhibitor fasudil and the calcium entry antagonist isradipine. The present results are consistent with the hypothesis that imatinib may inhibit a constitutively active tyrosine kinase vasoconstrictor pathway in the pulmonary and systemic vascular beds in the rat.

Pathophysiology of hypertension in the absence of nitric oxide/cyclic GMP signaling

The nitric oxide (NO)-cyclic guanosine monophosphate (cGMP) signaling system is a well-characterized modulator of cardiovascular function, in general, and blood pressure, in particular. The availability of mice mutant for key enzymes in the NO-cGMP signaling system facilitated the identification of interactions with other blood pressure modifying pathways (e.g. the renin-angiotensin-aldosterone system) and of gender-specific effects of impaired NO-cGMP signaling. In addition, recent genome-wide association studies identified blood pressure-modifying genetic variants in genes that modulate NO and cGMP levels. Together, these findings have advanced our understanding of how NO-cGMP signaling regulates blood pressure. In this review, we will summarize the results obtained in mice with disrupted NO-cGMP signaling and highlight the relevance of this pathway as a potential therapeutic target for the treatment of hypertension.

Insights into BAY 60-2770 activation and S-nitrosylation-dependent desensitization of soluble guanylyl cyclase via crystal structures of homologous nostoc H-NOX domain complexes

The soluble guanylyl cyclase (sGC) is an important receptor for nitric oxide (NO). Nitric oxide activates sGC several hundred fold to generate cGMP from GTP. Because of sGC's salutary roles in cardiovascular physiology, it has received substantial attention as a drug target. The heme domain of sGC is key to its regulation as it not only contains the NO activation site but also harbors sites for NO-independent sGC activators as well an S-nitrosylation site (β1 C122) involved in desensitization. Here we report the crystal structure of the activator BAY 60-2770 bound to the Nostoc H-NOX domain that is homologous to sGC. The structure reveals that BAY 60-2770 has displaced the heme and acts as a heme mimetic via carboxylate-mediated interactions with the conserved YxSxR motif as well as hydrophobic interactions. Comparisons with the previously determined BAY 58-2667 bound structure reveal that BAY 60-2770 is more ordered in its hydrophobic tail region. sGC activity assays demonstrate that BAY 60-2770 has about 10% higher fold maximal stimulation compared to BAY 58-2667. S-Nitrosylation of the BAY 60-2770 substituted Nostoc H-NOX domain causes subtle changes in the vicinity of the S-nitrosylated C122 residue. These shifts could impact the adjacent YxSxR motif and αF helix and as such potentially inhibit either heme incorporation or NO-activation of sGC and thus provide a structural basis for desensitization.

The selective Rho-kinase inhibitor azaindole-1 has long-lasting erectile activity in the rat

OBJECTIVE

To investigate the effects of the selective Rho-associated protein kinase (ROCK) inhibitor azaindole-1 on erectile function under physiologic and pathophysiologic conditions in the rat.

METHODS

The effect of intracavernosal (i.c.) injections of azaindole-1 on change in intracavernous pressure (ICP), ICP/mean arterial pressure (MAP), area under the curve (AUC), and response duration were investigated in the anesthetized rat under control conditions and when nonadrenergic noncholinergic neurotransmission and cholinergic function or soluble guanylyl cyclase (sGC) were inhibited or after cavernosal nerve crush injury.

RESULTS

The i.c. injections of azaindole-1 produced dose-related increases in ICP/MAP and AUC that were long-lasting at the highest doses studied compared with the prototypical ROCK inhibitor fasudil. Erectile responses were not altered by 7-nitroindazole and atropine in doses that reduced the response to cavernosal nerve stimulation by 86%, indicating that they were independent of NO release by cavernosal nerves or activation of muscarinic receptors in the corpora cavernosa. Erectile responses to azaindole-1 were not altered by the sGC inhibitor ODQ in a dose that attenuated responses to the NO donor sodium nitroprusside, indicating that they were independent of an action on sGC. The erectile response to i.c. injections of azaindole-1 or Y-27632, which was reported to be NO/cyclic guanosine monophosphate-dependent, was not attenuated after cavernosal nerve crush injury.

CONCLUSION

The present studies indicate that azaindole-1 has long-lasting erectile activity that is independent of NO release, muscarinic receptor, or sGC activation or the integrity of the cavernosal nerves.

The sGC activator BAY 60-2770 has potent erectile activity in the rat

Nitric oxide (NO) is the principal mediator of penile erection, and soluble guanylate cyclase (sGC) is the receptor for NO. In pathophysiological conditions when sGC is inactivated and not responsive to NO or sGC stimulators a new class of agents called sGC activators increase the activity of NO-insensitive sGC and produce erection. The aim of this study was to investigate erectile responses to BAY 60-2770, a sGC activator, under physiological and pathophysiological conditions. In the present study increases in intracavernosal pressure (ICP) in response to intracavernosal (ic) injections of BAY 60-2770 were investigated under baseline conditions, when sGC was inhibited by 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ), when nitric oxide synthase (NOS) was inhibited by N-nitro-L-arginine methyl ester (L-NAME), and after cavernosal nerve crush injury. Under baseline conditions ic injections of BAY 60-2770 increase ICP, ICP/mean arterial pressure (MAP), and area under the ICP curve (AUC) and produce small decreases in MAP at the highest doses studied. BAY 60-2770 was very potent in its ability to induce erection and responses to BAY 60-2770 were enhanced by ODQ which attenuates erectile responses to sodium nitroprusside (SNP), diethylamine NONOate (DEA/NO), and cavernosal nerve stimulation. Responses to BAY 60-2770 were not altered by L-NAME or cavernosal nerve crush injury. These data indicate that BAY 60-2770 has potent erectile activity that is enhanced by ODQ and show that responses to BAY 60-2770 are not attenuated by NOS inhibition or cavernosal nerve injury. These results suggest that BAY 60-2770 would be effective in the treatment of erectile dysfunction when NO bioavailability is reduced, after pelvic nerve injury, and when sGC is oxidized.

Activation of haem-oxidized soluble guanylyl cyclase with BAY 60-2770 in human platelets lead to overstimulation of the cyclic GMP signaling pathway

BACKGROUND AND AIMS

Nitric oxide-independent soluble guanylyl cyclase (sGC) activators reactivate the haem-oxidized enzyme in vascular diseases. This study was undertaken to investigate the anti-platelet mechanisms of the haem-independent sGC activator BAY 60-2770 in human washed platelets. The hypothesis that sGC oxidation potentiates the anti-platelet activities of BAY 60-2770 has been tested.

METHODS

Human washed platelet aggregation and adhesion assays, as well as flow cytometry for α(IIb)β(3) integrin activation and Western blot for α1 and β1 sGC subunits were performed. Intracellular calcium levels were monitored in platelets loaded with a fluorogenic calcium-binding dye (FluoForte).

RESULTS

BAY 60-2770 (0.001-10 µM) produced significant inhibition of collagen (2 µg/ml)- and thrombin (0.1 U/ml)-induced platelet aggregation that was markedly potentiated by the sGC inhibitor ODQ (10 µM). In fibrinogen-coated plates, BAY 60-2770 significantly inhibited platelet adhesion, an effect potentiated by ODQ. BAY 60-2770 increased the cGMP levels and reduced the intracellular Ca(2+) levels, both of which were potentiated by ODQ. The cell-permeable cGMP analogue 8-Br-cGMP (100 µM) inhibited platelet aggregation and Ca(2+) levels in an ODQ-insensitive manner. The cAMP levels remained unchanged by BAY 60-2770. Collagen- and thrombin-induced α(IIb)β(3) activation was markedly inhibited by BAY 60-2770 that was further inhibited by ODQ. The effects of sodium nitroprusside (3 µM) were all prevented by ODQ. Incubation with ODQ (10 µM) significantly reduced the protein levels of α1 and β1 sGC subunits, which were prevented by BAY 60-2770.

CONCLUSION

The inhibitory effects of BAY 60-2770 on aggregation, adhesion, intracellular Ca(2+) levels and α(IIb)β(3) activation are all potentiated in haem-oxidizing conditions. BAY 60-2770 prevents ODQ-induced decrease in sGC protein levels. BAY 60-2770 could be of therapeutic interest in cardiovascular diseases associated with thrombotic complications.

Environmentally persistent free radicals decrease cardiac function and increase pulmonary artery pressure

Epidemiological studies have consistently linked inhalation of particulate matter (PM) to increased cardiac morbidity and mortality, especially in at risk populations. However, few studies have examined the effect of PM on baseline cardiac function in otherwise healthy individuals. In addition, airborne PM contain environmentally persistent free radicals (EPFR) capable of redox cycling in biological systems. The purpose of this study was to determine whether nose-only inhalation of EPFRs (20 min/day for 7 days) could decrease baseline left ventricular function in healthy male Sprague-Dawley rats. The model EPFR tested was 1,2-dichlorobenzene chemisorbed to 0.2-μm-diameter silica/CuO particles at 230°C (DCB230). Inhalation of vehicle or silica particles served as controls. Twenty-four hours after the last exposure, rats were anesthetized (isoflurane) and ventilated (3 l/min), and left ventricular function was assessed using pressure-volume catheters. Compared with controls, inhalation of DCB230 significantly decreased baseline stroke volume, cardiac output, and stroke work. End-diastolic volume and end-diastolic pressure were also significantly reduced; however, ventricular contractility and relaxation were not changed. DCB230 also significantly increased pulmonary arterial pressure and produced hyperplasia in small pulmonary arteries. Plasma levels of C-reactive protein were significantly increased by exposure to DCB230, as were levels of heme oxygenase-1 and SOD2 in the left ventricle. Together, these data show that inhalation of EPFRs, but not silica particles, decreases baseline cardiac function in healthy rats by decreasing cardiac filling, secondary to increased pulmonary resistance. These EPFRs also produced systemic inflammation and increased oxidative stress markers in the left ventricle.

The Rho kinase inhibitor azaindole-1 has long-acting vasodilator activity in the pulmonary vascular bed of the intact chest rat

Responses to a selective azaindole-based Rho kinase (ROCK) inhibitor (azaindole-1) were investigated in the rat. Intravenous injections of azaindole-1 (10–300 µg/kg), produced small decreases in pulmonary arterial pressure and larger decreases in systemic arterial pressure without changing cardiac output. Responses to azaindole-1 were slow in onset and long in duration. When baseline pulmonary vascular tone was increased with U46619 or L-NAME, the decreases in pulmonary arterial pressure in response to the ROCK inhibitor were increased. The ROCK inhibitor attenuated the increase in pulmonary arterial pressure in response to ventilatory hypoxia. Azaindole-1 decreased pulmonary and systemic arterial pressures in rats with monocrotaline-induced pulmonary hypertension. These results show that azaindole-1 has significant vasodilator activity in the pulmonary and systemic vascular beds and that responses are larger, slower in onset, and longer in duration when compared with the prototypical agent fasudil. Azaindole-1 reversed hypoxic pulmonary vasoconstriction and decreased pulmonary and systemic arterial pressures in a similar manner in rats with monocrotaline-induced pulmonary hypertension. These data suggest that ROCK is involved in regulating baseline tone in the pulmonary and systemic vascular beds, and that ROCK inhibition will promote vasodilation when tone is increased by diverse stimuli including treatment with monocrotaline.

Immunohistochemical and functional characterization of nitric oxide signaling pathway in isolated aorta from Crotalus durissus terrificus

We characterized the nitric oxide (NO)-cyclic GMP-phosphodiesterase-5 (PDE5) pathway in Crotalus durissus terrificus aorta. Concentration responses curves to acetylcholine (ACh), sodium nitroprusside (SNP), BAY41-2272 (soluble guanylyl cyclase [sGC] stimulator), BAY60-2770 (sGC activator) and tadalafil (PDE5 inhibitor) were constructed in phenylephrine (10 μM)-precontracted tissues with intact (E(+)) or denuded (E(-)) endothelium. ACh (0.0001-10 μM) and SNP (0.0001-10 μM) relaxed aorta, which were reduced by the NO synthase (L-NAME,100 μM) or the sGC inhibitors (ODQ, 10 μM). Tadalafil (0.0001-10 μM) relaxed E(+) rings with potency (pEC(50)) and maximal response (E(max)) values of 7.34±0.02 and 105±8%, respectively. E(-) or ODQ treatment significantly (P<0.05) reduced tadalafil relaxations (66±18% and 71±7%, respectively). BAY41-2272 (0.0001-300 nM) produced concentration-dependent relaxations in E(+) rings, which were reduced by addition of either ODQ or L-NAME (16.0- and 5.2-fold rightward shifts, respectively). The relaxation of BAY60-2770 was markedly potentiated by ODQ and L-NAME (41.0- and 9.7-fold leftward shifts, respectively), whereas in E(-) the pEC(50) values were shifted by 7-fold to the right. Immunohistochemistry, followed validation by transcriptomic analysis, revealed the presence of eNOS in endothelium, whereas nNOS was observed only in perivascular nerves. sGC and PDE5 were expressed in smooth muscle. Thus, NO-sGC-PDE5 pathway is evolutionarily present in Crotalus sp. vessels, and has a remarkable degree of functional similarity to mammalian vessels.

Analysis of responses to glyceryl trinitrate and sodium nitrite in the intact chest rat

Responses to glyceryl trinitrate/nitroglycerin (GTN), S-nitrosoglutathione (GSNO), and sodium nitrite were compared in the intact chest rat. The iv injections of GTN, sodium nitrite, and GSNO produced dose-dependent decreases in pulmonary and systemic arterial pressures. In as much as cardiac output was not reduced, the decreases in pulmonary and systemic arterial pressures indicate that GTN, sodium nitrite, and GSNO have significant vasodilator activity in the pulmonary and systemic vascular beds in the rat. Responses to GTN were attenuated by cyanamide, but not allopurinol, whereas responses to nitrite formed by the metabolism of GTN were attenuated by allopurinol and cyanamide. The results with allopurinol and cyanamide suggest that only mitochondrial aldehyde dehydrogenase is involved in the bioactivation of GTN, sodium nitrite, and GSNO, whereas both pathways are involved in the bioactivation of nitrite anion in the intact rat. The comparison of vasodilator activity indicates that GSNO and GTN are more than 1000-fold more potent than sodium nitrite in decreasing pulmonary and systemic arterial pressures in the rat. Following administration of 1H-[1,2,4]-oxadizaolo[4,3-]quinoxaline-1-one (ODQ), responses to GTN were significantly attenuated, indicating that responses are mediated by the activation of soluble guanylyl cyclase. These data suggest that the reduction of nitrite to nitric oxide formed from the metabolism of GTN, cannot account for the vasodilator activity of GTN in the intact rat and that another mechanism; perhaps the formation of an S-NO, may mediate the vasodilator response to GTN in this species.

Peroxynitrite has potent pulmonary vasodilator activity in the rat

Peroxynitrite (PN) worsens pathological conditions associated with oxidative stress. However, beneficial effects have also been reported. PN has been shown to demonstrate vasodilator as well as vasoconstrictor properties that are dependent upon the experimental conditions and the vascular bed studied. PN-induced vascular smooth muscle relaxation may involve the formation of nitric oxide (NO) donors. The present results show that PN has significant vasodilator activity in the pulmonary and systemic vascular beds, and that responses to PN were not attenuated by L-penicillamine (L-PEN), a PN scavenger, whereas responses to sodium nitroprusside (SNP) were decreased. PN had a small inhibitory effect on decreases in arterial pressure in response to the NO donors diethylammonium (Z)-1-(N,N-diethylamino)diazen-1-ium-1,2-diolate (DEA/NO) and S-nitrosoglutathione (GSNO). PN partially reversed hypoxic pulmonary vasoconstriction. PN responses were attenuated by the soluble guanylate cyclase (sGC) inhibitor, 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ) and responses to PN and the PN precursor, 3-morpholinosydnonimine (SIN-1), were different. These data show that PN has potent pulmonary vasodilator activity in the rat, and provide evidence that a PN interaction with S-nitrosothiols is not the major mechanism mediating the response. These data suggest that responses to PN are mediated by the activation of sGC, and that PN has a small inhibitory effect on NO responses.

Stimulators and activators of soluble guanylate cyclase: review and potential therapeutic indications

The heme-protein soluble guanylyl cyclase (sGC) is the intracellular receptor for nitric oxide (NO). sGC is a heterodimeric enzyme with α and β subunits and contains a heme moiety essential for binding of NO and activation of the enzyme. Stimulation of sGC mediates physiologic responses including smooth muscle relaxation, inhibition of inflammation, and thrombosis. In pathophysiologic states, NO formation and bioavailability can be impaired by oxidative stress and that tolerance to NO donors develops with continuous use. Two classes of compounds have been developed that can directly activate sGC and increase cGMP formation in pathophysiologic conditions when NO formation and bioavailability are impaired or when NO tolerance has developed. In this report, we review current information on the pharmacology of heme-dependent stimulators and heme-independent activators of sGC in animal and in early clinical studies and the potential role these compounds may have in the management of cardiovascular disease.

Pressure-overload-induced subcellular relocalization/oxidation of soluble guanylyl cyclase in the heart modulates enzyme stimulation

RATIONALE

Soluble guanylyl cyclase (sGC) generates cyclic guanosine monophophate (cGMP) upon activation by nitric oxide (NO). Cardiac NO-sGC-cGMP signaling blunts cardiac stress responses, including pressure-overload-induced hypertrophy. The latter itself depresses signaling through this pathway by reducing NO generation and enhancing cGMP hydrolysis.

OBJECTIVE

We tested the hypothesis that the sGC response to NO also declines with pressure-overload stress and assessed the role of heme-oxidation and altered intracellular compartmentation of sGC as potential mechanisms.

METHODS AND RESULTS

C57BL/6 mice subjected to transverse aortic constriction (TAC) developed cardiac hypertrophy and dysfunction. NO-stimulated sGC activity was markedly depressed, whereas NO- and heme-independent sGC activation by BAY 60-2770 was preserved. Total sGCα(1) and β(1) expression were unchanged by TAC; however, sGCβ(1) subunits shifted out of caveolin-enriched microdomains. NO-stimulated sGC activity was 2- to 3-fold greater in Cav3-containing lipid raft versus nonlipid raft domains in control and 6-fold greater after TAC. In contrast, BAY 60-2770 responses were >10 fold higher in non-Cav3 domains with and without TAC, declining about 60% after TAC within each compartment. Mice genetically lacking Cav3 had reduced NO- and BAY-stimulated sGC activity in microdomains containing Cav3 for controls but no change within non-Cav3-enriched domains.

CONCLUSIONS

Pressure overload depresses NO/heme-dependent sGC activation in the heart, consistent with enhanced oxidation. The data reveal a novel additional mechanism for reduced NO-coupled sGC activity related to dynamic shifts in membrane microdomain localization, with Cav3-microdomains protecting sGC from heme-oxidation and facilitating NO responsiveness. Translocation of sGC out of this domain favors sGC oxidation and contributes to depressed NO-stimulated sGC activity.

IRAG and novel PKG targeting in the cardiovascular system

Signaling by nitric oxide (NO) determines several cardiovascular functions including blood pressure regulation, cardiac and smooth muscle hypertrophy, and platelet function. NO stimulates the synthesis of cGMP by soluble guanylyl cyclases and thereby activates cGMP-dependent protein kinases (PKGs), mediating most of the cGMP functions. Hence, an elucidation of the PKG signaling cascade is essential for the understanding of the (patho)physiological aspects of NO. Several PKG signaling pathways were identified, meanwhile regulating the intracellular calcium concentration, mediating calcium desensitization or cytoskeletal rearrangement. During the last decade it emerged that the inositol trisphosphate receptor-associated cGMP-kinase substrate (IRAG), an endoplasmic reticulum-anchored 125-kDa membrane protein, is a main signal transducer of PKG activity in the cardiovascular system. IRAG interacts specifically in a trimeric complex with the PKG1β isoform and the inositol 1,4,5-trisphosphate receptor I and, upon phosphorylation, reduces the intracellular calcium release from the intracellular stores. IRAG motifs for phosphorylation and for targeting to PKG1β and 1,4,5-trisphosphate receptor I were identified by several approaches. The (patho)physiological functions for the regulation of smooth muscle contractility and the inhibition of platelet activation were perceived. In this review, the IRAG recognition, targeting, and function are summarized compared with PKG and several PKG substrates in the cardiovascular system.

Pediatric pulmonary arterial hypertension: current and emerging therapeutic options

INTRODUCTION

Pulmonary arterial hypertension (PAH) is a rare disease in neonates, infants and children that is associated with significant morbidity and mortality. An adequate understanding of the controlling pathophysiologic mechanisms is lacking and although mortality has decreased as therapeutic options have increased over the past several decades, outcomes remain unacceptable.

AREAS COVERED

This review summarizes the currently available therapies for neonates, infants and children with PAH and describes emerging therapies in the context of what is known about the underlying pathophysiology of the disease.

EXPERT OPINION

All of the currently approved PAH therapies impact one of three endothelial-based pathways: nitric oxide-guanosine-3'-5'cyclic monophosphate, prostacyclin or endothelin-1. The beneficial effects of these agents may relate to their impact on pulmonary vascular tone, and/or their antiproliferative and antithrombotic properties. Fundamental advances in PAH therapy are likely to relate to: i) a better understanding of PAH subpopulations, allowing for therapies to be better tailored to individual patients and pathophysiologic processes; and ii) therapies that promote the regression of advanced structural remodeling.