Targeting Heme-Oxidized Soluble Guanylate Cyclase in Experimental Heart Failure

Modulation of the nitric oxide/cGMP pathway in cardiac contraction and relaxation: Potential role in heart failure treatment

Evidence exists that heart failure (HF) has an overall impact of 1-2 % in the global population being often associated with comorbidities that contribute to increased disease prevalence, hospitalization, and mortality. Recent advances in pharmacological approaches have significantly improved clinical outcomes for patients with vascular injury and HF. Nevertheless, there remains an unmet need to clarify the crucial role of nitric oxide/cyclic guanosine 3',5'-monophosphate (NO/cGMP) signalling in cardiac contraction and relaxation, to better identify the key mechanisms involved in the pathophysiology of myocardial dysfunction both with reduced (HFrEF) as well as preserved ejection fraction (HFpEF). Indeed, NO signalling plays a crucial role in cardiovascular homeostasis and its dysregulation induces a significant increase in oxidative and nitrosative stress, producing anatomical and physiological cardiac alterations that can lead to heart failure. The present review aims to examine the molecular mechanisms involved in the bioavailability of NO and its modulation of downstream pathways. In particular, we focus on the main therapeutic targets and emphasize the recent evidence of preclinical and clinical studies, describing the different emerging therapeutic strategies developed to counteract NO impaired signalling and cardiovascular disease (CVD) development.

BAY58-2667 Activates Different Soluble Guanylyl Cyclase Species by Distinct Mechanisms that Indicate Its Principal Target in Cells is the Heme-Free Soluble Guanylyl Cyclase-Heat Shock Protein 90 Complex

Nitric oxide (NO)-unresponsive forms of soluble guanylyl cyclase (sGC) exist naturally and in disease can disable NO-sGC-cGMP signaling. Agonists like BAY58-2667 (BAY58) target these sGC forms, but their mechanisms of action in living cells are unclear. We studied rat lung fibroblast-6 cells and human airway smooth muscle cells that naturally express sGC and HEK293 cells that we transfected to express sGC and variants. Cells were cultured to build up different forms of sGC, and we used fluorescence and FRET-based measures to monitor BAY58-driven cGMP production and any protein partner exchange or heme loss events that may occur for each sGC species. We found that: (i) BAY58 activated cGMP production by the apo-sGCβ-Hsp90 species after a 5-8 minute delay that was associated with apo-sGCβ exchanging its Hsp90 partner with an sGCα subunit. (ii) In cells containing an artificially constructed heme-free sGC heterodimer, BAY58 initiated an immediate and three times faster cGMP production. However, this behavior was not observed in cells expressing native sGC under any condition. (iii) BAY58 activated cGMP production by ferric heme sGC only after a 30-minute delay, coincident with it initiating a delayed, slow ferric heme loss from sGCβ We conclude that the kinetics favor BAY58 activation of the apo-sGCβ-Hsp90 species over the ferric heme sGC species in living cells. The protein partner exchange events driven by BAY58 account for the initial delay in cGMP production and also limit the speed of subsequent cGMP production in the cells. Our findings clarify how agonists like BAY58 may activate sGC in health and disease. SIGNIFICANCE STATEMENT: A class of agonists can activate cyclic guanosine monophosphate (cGMP) synthesis by forms of soluble guanylyl cyclase (sGC) that do not respond to NO and accumulate in disease, but the mechanisms of action are unclear. This study clarifies what forms of sGC exist in living cells, which of these can be activated by the agonists, and the mechanisms and kinetics by which each form is activated. This information may help to hasten deployment of these agonists for pharmaceutical intervention and clinical therapy.

Natriuretic Peptides: It Is Time for Guided Therapeutic Strategies Based on Their Molecular Mechanisms

Natriuretic peptides (NPs) are the principal expression products of the endocrine function of the heart. They exert several beneficial effects, mostly mediated through guanylate cyclase-A coupled receptors, including natriuresis, diuresis, vasorelaxation, blood volume and blood pressure reduction, and regulation of electrolyte homeostasis. As a result of their biological functions, NPs counterbalance neurohormonal dysregulation in heart failure and other cardiovascular diseases. NPs have been also validated as diagnostic and prognostic biomarkers in cardiovascular diseases such as atrial fibrillation, coronary artery disease, and valvular heart disease, as well as in the presence of left ventricular hypertrophy and severe cardiac remodeling. Serial measurements of their levels may be used to contribute to more accurate risk stratification by identifying patients who are more likely to experience death from cardiovascular causes, heart failure, and cardiac hospitalizations and to guide tailored pharmacological and non-pharmacological strategies with the aim to improve clinical outcomes. On these premises, multiple therapeutic strategies based on the biological properties of NPs have been attempted to develop new targeted cardiovascular therapies. Apart from the introduction of the class of angiotensin receptor/neprilysin inhibitors to the current management of heart failure, novel promising molecules including M-atrial natriuretic peptide (a novel atrial NP-based compound) have been tested for the treatment of human hypertension with promising results. Moreover, different therapeutic strategies based on the molecular mechanisms involved in NP regulation and function are under development for the management of heart failure, hypertension, and other cardiovascular conditions.

Antihypertensive Effects of a Soluble Guanylate Cyclase Stimulator

We studied antihypertensive activity of an indolinone derivative (compound GRS), a soluble guanylate cyclase stimulator and a drug with previously proven antiaggregant effects. Contraction activity of isolated aorta segments of Wistar-Kyoto (WKY) rats was assessed in vitro using a mechanographic method. Addition of GRS (0.1-100 μМ) resulted in dose-dependent relaxation of endothelium-denuded aorta segments. Pretreatment of aorta smooth muscle segments with a specific inhibitor of soluble guanylate cyclase (ODQ, 1 μM) weakened the vasodilatory effect of GRS. Antihypertensive activity of the indolinone derivative GRS was studied in spontaneously hypertensive SHR rats. Single oral administration of 5 and 10 mg/kg GRS was followed by a significant dose-dependent reduction of systolic and diastolic BP in SHR rats. Antihypertensive effect of GRS in a dose of 5 mg/kg was more potent than that of the reference drug isosorbide dinitrate. GRS in a dose of 10 mg/kg did not affect systolic and diastolic BP in normotensive WKY rats.

Responses in Blood Pressure and Kidney Function to Soluble Guanylyl Cyclase Stimulation or Activation in Normal and Diabetic Rats

Introduction:

Agonists of soluble guanylate cyclase (sGC) are being developed as treatment for cardiovascular disease. Most effects of nitric oxide (NO) on glomerular and tubular function are mediated through sGC but whether sGC agonists mimic these effects is unknown.

Methods:

Renal clearance and micropuncture studies were performed in Wistar-Froemter rats (WF), with or without streptozotocin diabetes (STZ-WF), and in Goto-Kakizaki rats (GK) with mild type-2 diabetes to test for acute effects of the sGC “stimulator” BAY 41-2272, which synergizes with endogenous NO, and the “activator” runcaciguat, which generates cGMP independent of NO.

Results:

Both sGC agonists reduced arterial blood pressure (MAP). For MAP reductions <10% the drugs increased GFR in WF and STZ-WF but not in GK. Larger MAP reductions outweighed this effect and GFR declined, with better preserved GFR in STZ-WF. Changes in GFR could not be accounted for by changes in RBF, suggesting parallel changes in ultrafiltration pressure and/or ultrafiltration coefficient. The doses chosen for micropuncture in WF and GK reduced MAP by 2–10% and the net effect on single nephron GFR and ultrafiltration pressure was neutral. Effects of the drugs on tubular reabsorption were dominated by declining MAP and no natriuretic effect observed at any dose.

Discussion/Conclusion:

sGC agonists impact kidney function directly and because they reduce MAP. The direct tendency to increase GFR is most apparent for MAP reductions <10%. The direct effect is otherwise subtle and overridden when MAP declines more. Effects of sGC agonists on tubular reabsorption are dominated by effects on MAP.

Glutathione-S-Transferases as Potential Targets for Modulation of Nitric Oxide-Mediated Vasodilation

Glutathione-S-transferases (GSTs) are highly promiscuous in terms of their interactions with multiple proteins, leading to various functions. In addition to their classical detoxification roles with multi-drug resistance-related protein-1 (MRP1), more recent studies have indicated the role of GSTs in cellular nitric oxide (NO) metabolism. Vasodilation is classically induced by NO through its interaction with soluble guanylate cyclase. The ability of GSTs to biotransform organic nitrates such as nitroglycerin for NO generation can markedly modulate vasodilation, with this effect being prevented by specific GST inhibitors. Recently, other structurally distinct pro-drugs that generate NO via GST-mediated catalysis have been developed as anti-cancer agents and also indicate the potential of GSTs as suitable targets for pharmaceutical development. Further studies investigating GST biochemistry could enhance our understanding of NO metabolism and lead to the generation of novel and innovative vasodilators for clinical use.

Riociguat in pulmonary hypertension and heart failure with preserved ejection fraction: the haemoDYNAMIC trial

AIMS

The presence of pulmonary hypertension (PH) severely aggravates the clinical course of heart failure with preserved ejection fraction (HFpEF). To date, neither established heart failure therapies nor pulmonary vasodilators proved beneficial. This study investigated the efficacy of chronic treatment with the oral soluble guanylate cyclase stimulator riociguat in patients with PH-HFpEF.

METHODS AND RESULTS

The phase IIb, randomized, double-blind, placebo-controlled, parallel-group, multicentre DYNAMIC trial assessed riociguat in PH-HFpEF. Patients were recruited at five hospitals across Austria and Germany. Key eligibility criteria were mean pulmonary artery pressure ≥25 mmHg, pulmonary arterial wedge pressure >15 mmHg, and left ventricular ejection fraction ≥50%. Patients were randomized to oral treatment with riociguat or placebo (1:1). Patients started at 0.5 mg three times daily (TID) and were up-titrated to 1.5 mg TID. The primary efficacy endpoint was change from baseline to week 26 in cardiac output (CO) at rest, measured by right heart catheterization. Primary efficacy analyses were performed on the full analysis set. Fifty-eight patients received riociguat and 56 patients placebo. After 26 weeks, CO increased by 0.37 ± 1.263 L/min in the riociguat group and decreased by -0.11 ± 0.921 L/min in the placebo group (least-squares mean difference: 0.54 L/min, 95% confidence interval 0.112, 0.971; P = 0.0142). Five patients dropped out due to riociguat-related adverse events but no riociguat-related serious adverse event or death occurred.

CONCLUSION

The vasodilator riociguat improved haemodynamics in PH-HFpEF. Riociguat was safe in most patients but led to more dropouts as compared to placebo and did not change clinical symptoms within the study period.

Effects of a New Antithrombotic Drug GRS, a Soluble Guanylate Cyclase Stimulator, on Endothelial Dysfunction in Rats with Myocardial Infarction

New antithrombotic drug GRS, a soluble guanylate cyclase stimulator, after repeated administration in a dose of 10 mg/kg alleviates the symptoms of endothelial dysfunction in rats with myocardial infarction; it restores antiplatelet activity of the blood vessel wall and vasodilatory function of the endothelium without producing significant effect on endothelium-independent vasodilation. GRS also has direct antiaggregant and antihypertensive effects in therapeutic doses. The obtained data suggest that GRS can be therapeutically useful in patients with cardiovascular diseases accompanied by endothelial dysfunction.

Soluble Guanylate Cyclase Stimulators and Activators

When Furchgott, Murad, and Ignarro were honored with the Nobel prize for the identification of nitric oxide (NO) in 1998, the therapeutic implications of this discovery could not be fully anticipated. This was due to the fact that available therapeutics like NO donors did not allow a constant and long-lasting cyclic guanylyl monophosphate (cGMP) stimulation and had a narrow therapeutic window. Now, 20 years later, the stimulator of soluble guanylate cyclase (sGC), riociguat, is on the market and is the only drug approved for the treatment of two forms of pulmonary hypertension (PAH/CTEPH), and a variety of other sGC stimulators and sGC activators are in preclinical and clinical development for additional indications. The discovery of sGC stimulators and sGC activators is a milestone in the field of NO/sGC/cGMP pharmacology. The sGC stimulators and sGC activators bind directly to reduced, heme-containing and oxidized, heme-free sGC, respectively, which results in an increase in cGMP production. The action of sGC stimulators at the heme-containing enzyme is independent of NO but is enhanced in the presence of NO whereas the sGC activators interact with the heme-free form of sGC. These highly innovative pharmacological principles of sGC stimulation and activation seem to have a very broad therapeutic potential. Therefore, in both academia and industry, intensive research and development efforts have been undertaken to fully exploit the therapeutic benefit of these new compound classes. Here we summarize the discovery of sGC stimulators and sGC activators and the current developments in both compound classes, including the mode of action, the chemical structures, and the genesis of the terminology and nomenclature. In addition, preclinical studies exploring multiple aspects of their in vitro, ex vivo, and in vivo pharmacology are reviewed, providing an overview of multiple potential applications. Finally, the clinical developments, investigating the treatment potential of these compounds in various diseases like heart failure, diabetic kidney disease, fibrotic diseases, and hypertension, are reported. In summary, sGC stimulators and sGC activators have a unique mode of action with a broad treatment potential in cardiovascular diseases and beyond.

Impaired Redox and Protein Homeostasis as Risk Factors and Therapeutic Targets in Toxin-Induced Biliary Atresia

BACKGROUND & AIMS

Extrahepatic biliary atresia (BA) is a pediatric liver disease with no approved medical therapy. Recent studies using human samples and experimental modeling suggest that glutathione redox metabolism and heterogeneity play a role in disease pathogenesis. We sought to dissect the mechanistic basis of liver redox variation and explore how other stress responses affect cholangiocyte injury in BA.

METHODS

We performed quantitative in situ hepatic glutathione redox mapping in zebrafish larvae carrying targeted mutations in glutathione metabolism genes and correlated these findings with sensitivity to the plant-derived BA-linked toxin biliatresone. We also determined whether genetic disruption of HSP90 protein quality control pathway genes implicated in human BA altered biliatresone toxicity in zebrafish and human cholangiocytes. An in vivo screening of a known drug library was performed to identify novel modifiers of cholangiocyte injury in the zebrafish experimental BA model, with subsequent validation.

RESULTS

Glutathione metabolism gene mutations caused regionally distinct changes in the redox potential of cholangiocytes that differentially sensitized them to biliatresone. Disruption of human BA-implicated HSP90 pathway genes sensitized zebrafish and human cholangiocytes to biliatresone-induced injury independent of glutathione. Phosphodiesterase-5 inhibitors and other cyclic guanosine monophosphate signaling activators worked synergistically with the glutathione precursor N-acetylcysteine in preventing biliatresone-induced injury in zebrafish and human cholangiocytes. Phosphodiesterase-5 inhibitors enhanced proteasomal degradation and required intact HSP90 chaperone.

CONCLUSION

Regional variation in glutathione metabolism underlies sensitivity to the biliary toxin biliatresone and may account for the reported association between BA transplant-free survival and glutathione metabolism gene expression. Human BA can be causatively linked to genetic modulation of protein quality control. Combined treatment with N-acetylcysteine and cyclic guanosine monophosphate signaling enhancers warrants further investigation as therapy for BA.

A novel soluble guanylate cyclase activator with reduced risk of hypotension by short-acting vasodilation

Cinaciguat, a soluble guanylate cyclase (sGC) activator, was under clinical development for use in acute decompensated heart failure (ADHF), but was discontinued due to occurrence of hypotension. We hypothesized that short-term activation of sGC in ADHF patients would exert a vasodilative effect without hypotension irrespective of disease state, using a novel short-acting sGC activator, TY-55002. The objective of this study was to investigate the vasodilation and hemodynamic effects of TY-55002 in comparison with those of cinaciguat. TY-55002 and cinaciguat activated both normal and heme-oxidized sGC in a dose-dependent manner and caused rapid relaxation of phenylephrine-contracted rat aorta. However, TY-55002 had a milder effect than cinaciguat in enhancing the dose-activity response between normal and oxidized sGC. Therefore, we suggest that the pharmacological effect of TY-55002 is less subject than cinaciguat to oxidative stress associated with complications such as cardiovascular disease or diabetes. In normal dogs, the effects of intravenous TY-55002 or cinaciguat on blood pressure were evaluated in conjunction with the plasma concentrations of the compounds, and pharmacokinetic (PK)-pharmacodynamic (PD) analyses were carried out. The plasma-to-effect-site transfer rate constant (Ke0) for TY-55002 was three times greater than for cinaciguat. On the other hand, there was a small difference in blood half-life (T1/2) between the compounds. It is possible that the rapid fall in blood pressure after the initial administration of TY-55002 and the quick recovery after cessation were due to the pharmacodynamic property of the compound. In heart failure-model dogs, TY-55002 and cinaciguat improved the condition to the same degree, and the short-term action of TY-55002 was replicated. In conclusion, TY-55002 is a novel short-acting sGC activator, which offers the possibility of easy dose management without excessive hypotension. It therefore holds potential to serve as an innovative drug in the pharmacotherapy of ADHF.

The efficacy and safety of soluble guanylate cyclase stimulators in patients with heart failure: A systematic review and meta-analysis

BACKGROUND

Several randomized controlled trials (RCTs) have been investigated the benefits of soluble guanylate cyclase (sGC) stimulators in the treatment of heart failure, but a comprehensive evaluation is lacking. We performed a meta-analysis to evaluate the efficacy and safety of oral sGC stimulators (vericiguat and riociguat) in patients with heart failure.

METHODS

Studies were searched and screened in PubMed, Embase, and Cochrane Library. Eligible RCTs were included that reported mortality, the change of EuroQol Group 5-Dmensional Self-report Questionnaire (EQ-5D) US index, N-terminal pro-B-type natriuretic peptide (NT-proBNP), or serious adverse events (SAEs). Relative risk or weight mean difference (WMD) was estimated using fixed effect model or random effect model. Analysis of sensitivity and publication bias was conducted.

RESULTS

Five trials with a total of 1200 patients were included. sGC stimulators had no impact on the mortality (1.25; 95% confidence interval 0.50-3.11) and significantly improved EQ-5D US index (0.04; 95% confidence interval 0.020-0.05). Furthermore, in comparison with control group, NT-proBNP was statistically decreased in riociguat group (-0.78; 95% confidence interval -1.01 to -0.47), but not in vericiguat group (0.04, 95% confidence interval -0.18 to 0.25). There were not obverse differences in SAEs between sGC stimulators and control groups (0.90; 95% confidence interval 0.72-1.12).

CONCLUSION

Our meta-analysis suggests that sGC stimulators could improve the quality of life in patients with heart failure with good tolerance and safety, but their long-term benefits need to be observed in the future. sGC stimulators are likely to be promising add-on strategies for the treatment of heart failure.

Comparative Studies of the Dynamics Effects of BAY60-2770 and BAY58-2667 Binding with Human and Bacterial H-NOX Domains

Soluble guanylate cyclase (sGC) is a key enzyme implicated in various physiological processes such as vasodilation, thrombosis and platelet aggregation. The enzyme’s Heme-Nitric oxide/Oxygen (H-NOX) binding domain is the only sensor of nitric oxide (NO) in humans, which on binding with NO activates sGC to produce the second messenger cGMP. H-NOX is thus a hot target for drug design programs. BAY60-2770 and BAY58-2667 are two widely studied activators of sGC. Here we present comparative molecular dynamics studies to understand the molecular details characterizing the binding of BAY60-2770 and BAY58-2667 with the human H-NOX (hH-NOX) and bacterial H-NOX (bH-NOX) domains. HartreeFock method was used for parametrization of both the activators. A 50 ns molecular dynamics (MD) simulation was run to identify the functionally critical regions of the H-NOX domains. The CPPTRAJ module was used for analysis. BAY60-2770 on binding with bH-NOX, triggered rotational movement in signaling helix F and significant dynamicity in loops α and β, but in hH-NOX domain the compound showed relatively lesser aforementioned structural fluctuations. Conversely, hH-NOX ligated BAY58-2667 experienced highest transitions in its helix F due to electrostatic interactions with D84, T85 and R88 residues which are not conserved in bH-NOX. These conformational transformations might be essential to communicate with downstream PAS, CC and cyclase domains of sGC. Comparative MD studies revealed that BAY bound bHNOX dynamics varied from that of hH-NOX, plausibly due to some key residues such as R40, F74 and Y112 which are not conserved in bacteria. These findings will help to the design of novel drug leads to cure diseases associated to human sGC.

Urinary cGMP predicts major adverse renal events in patients with mild renal impairment and/or diabetes mellitus before exposure to contrast medium

BACKGROUND

The use of iodine-based contrast agents entails the risk of contrast induced nephropathy (CIN). Radiocontrast agents elicit the third most common cause of nephropathy among hospitalized patients, accounting for 11-12% of cases. CIN is connected with clinically significant consequences, including increased morbidity, prolonged hospitalization, increased risk of complications, potential need for dialysis, and increased mortality rate. The number of in-hospital examinations using iodine-based contrast media has been significantly increasing over the last decade. In order to protect patients from possible complications of such examinations, new biomarkers are needed that are able to predict a risk of contrast-induced nephropathy. Urinary and plasma cyclic guanosine monophosphate (cGMP) concentrations are influenced by renal function. Urinary cGMP is primarily of renal cellular origin. Therefore, we assessed if urinary cGMP concentration may predict major adverse renal events (MARE) after contrast media exposure during coronary angiography.

METHODS

Urine samples were prospectively collected from non-randomized consecutive patients with either diabetes or preexisting impaired kidney function receiving intra-arterial contrast medium (CM) for emergent or elective coronary angiography at the Charité Campus Mitte, University Hospital Berlin. Urinary cGMP concentration in spot urine was analyzed 24 hours after CM exposure. Patients were followed up over 90 days for occurrence of death, initiation of dialysis, doubling of plasma creatinine concentration or MARE.

RESULTS

In total, 289 consecutive patients were included into the study. Urine cGMP/creatinine ratio 24 hours before CM exposure expressed as mean±SD was predictive for the need of dialysis (no dialysis: 89.77±92.85 μM/mM, n = 277; need for dialysis: 140.3±82.90 μM/mM, n = 12, p = 0.008), death (no death during follow-up: 90.60±92.50 μM/mM, n = 280; death during follow-up: 169.88±81.52 μM/mM, n = 9; p = 0.002), and the composite endpoint MARE (no MARE: 86.02±93.17 μM/mM, n = 271; MARE: 146.64±74.68 μM/mM, n = 18, p<0.001) during the follow-up of 90 days after contrast media application. cGMP/creatinine ratio stayed significantly increased at values exceeding 120 μM/mM in patients who developed MARE, required dialysis or died.

CONCLUSIONS

Urinary cGMP/creatinine ratio ≥ 120 μM/mM before CM exposure is a promising biomarker for the need of dialysis and all-cause mortality 90 days after CM exposure in patients with preexisting renal impairment or diabetes.

Early activation of deleterious molecular pathways in the kidney in experimental heart failure with atrial remodeling

Heart failure (HF) is a major health problem with worsening outcomes when renal impairment is present. Therapeutics for early phase HF may be effective for cardiorenal protection, however the detailed characteristics of the kidney in early‐stage HF (ES‐HF), and therefore treatment for potential renal protection, are poorly defined. We sought to determine the gene and protein expression profiles of specific maladaptive pathways of ES‐HF in the kidney and heart. Experimental canine ES‐HF, characterized by de‐novo HF with atrial remodeling but not ventricular fibrosis, was induced by right ventricular pacing for 10 days. Kidney cortex (KC), medulla (KM), left ventricle (LV), and left atrial (LA) tissues from ES‐HF versus normal canines (n = 4 of each) were analyzed using RT‐PCR microarrays and protein assays to assess genes and proteins related to inflammation, renal injury, apoptosis, and fibrosis. ES‐HF was characterized by increased circulating natriuretic peptides and components of the renin‐angiotensin‐aldosterone system and decreased sodium and water excretion with mild renal injury and up‐regulation of CNP and renin genes in the kidney. Compared to normals, widespread genes, especially genes of the inflammatory pathways, were up‐regulated in KC similar to increases seen in LA. Protein expressions related to inflammatory cytokines were also augmented in the KC. Gene and protein changes were less prominent in the LV and KM. The ES‐HF displayed mild renal injury with widespread gene changes and increased inflammatory cytokines. These changes may provide important clues into the pathophysiology of ES‐HF and for therapeutic molecular targets in the kidney of ES‐HF.

Decreased Soluble Guanylate Cyclase Contributes to Cardiac Dysfunction Induced by Chronic Doxorubicin Treatment in Mice

AIMS

The use of doxorubicin, a potent chemotherapeutic agent, is limited by cardiotoxicity. We tested the hypothesis that decreased soluble guanylate cyclase (sGC) enzyme activity contributes to the development of doxorubicin-induced cardiotoxicity.

RESULTS

Doxorubicin administration (20 mg/kg, intraperitoneally [IP]) reduced cardiac sGC activity in wild-type (WT) mice. To investigate whether decreased sGC activity contributes to doxorubicin-induced cardiotoxicity, we studied mice with cardiomyocyte-specific deficiency of the sGC α1-subunit (mice with cardiomyocyte-specific deletion of exon 6 of the sGCα1 allele [sGCα1^-/-CM]). After 12 weeks of doxorubicin administration (2 mg/kg/week IP), left ventricular (LV) systolic dysfunction was greater in sGCα1^-/-CM than WT mice. To further assess whether reduced sGC activity plays a pathogenic role in doxorubicin-induced cardiotoxicity, we studied a mouse model in which decreased cardiac sGC activity was induced by cardiomyocyte-specific expression of a dominant negative sGCα1 mutant (DNsGCα1) upon doxycycline removal (Tet-off). After 8 weeks of doxorubicin administration, DNsGCα1^tg/+, but not WT, mice displayed LV systolic dysfunction and dilatation. The difference in cardiac function and remodeling between DNsGCα1^tg/+ and WT mice was even more pronounced after 12 weeks of treatment. Further impairment of cardiac function was attenuated when DNsGCα1 gene expression was inhibited (beginning at 8 weeks of doxorubicin treatment) by administering doxycycline. Furthermore, doxorubicin-associated reactive oxygen species generation was higher in sGCα1-deficient than WT hearts. Innovation and Conclusion: These data demonstrate that a reduction in cardiac sGC activity worsens doxorubicin-induced cardiotoxicity in mice and identify sGC as a potential therapeutic target. Various pharmacological sGC agonists are in clinical development or use and may represent a promising approach to limit doxorubicin-associated cardiotoxicity. Antioxid. Redox Signal. 26, 153-164.

Inhibition of soluble guanylyl cyclase by small molecules targeting the catalytic domain

Soluble guanylyl cyclase (sGC) plays a crucial role in cyclic nucleotide signaling that regulates numerous important physiological processes. To identify new sGC inhibitors that may prevent the formation of the active catalytic domain conformation, we carried out an in silico docking screen targeting a 'backside pocket' of the inactive sGC catalytic domain structure. Compounds 1 and 2 were discovered to inhibit sGC even at high/saturating nitric oxide concentrations. Both compounds also inhibit the BAY 58-2667-activated sGC as well as BAY 41-2272-stimulated sGC activity. Additional biochemical analyses showed that compound 2 also inhibits the isolated catalytic domain, thus demonstrating functional binding to this domain. Both compounds have micromolar affinity for sGC and are potential leads to develop more potent sGC inhibitors.

Chronic Activation of Heme Free Guanylate Cyclase Leads to Renal Protection in Dahl Salt-Sensitive Rats

The nitric oxide (NO)/soluble guanylate cyclase (sGC)/cyclic guanosine monophasphate (cGMP)-signalling pathway is impaired under oxidative stress conditions due to oxidation and subsequent loss of the prosthetic sGC heme group as observed in particular in chronic renal failure. Thus, the pool of heme free sGC is increased under pathological conditions. sGC activators such as cinaciguat selectively activate the heme free form of sGC and target the disease associated enzyme. In this study, a therapeutic effect of long-term activation of heme free sGC by the sGC activator cinaciguat was investigated in an experimental model of salt-sensitive hypertension, a condition that is associated with increased oxidative stress, heme loss from sGC and development of chronic renal failure. For that purpose Dahl/ss rats, which develop severe hypertension upon high salt intake, were fed a high salt diet (8% NaCl) containing either placebo or cinaciguat for 21 weeks. Cinaciguat markedly improved survival and ameliorated the salt-induced increase in blood pressure upon treatment with cinaciguat compared to placebo. Renal function was significantly improved in the cinaciguat group compared to the placebo group as indicated by a significantly improved glomerular filtration rate and reduced urinary protein excretion. This was due to anti-fibrotic and anti-inflammatory effects of the cinaciguat treatment. Taken together, this is the first study showing that long-term activation of heme free sGC leads to renal protection in an experimental model of hypertension and chronic kidney disease. These results underline the promising potential of cinaciguat to treat renal diseases by targeting the disease associated heme free form of sGC.

Cardiovascular and pharmacological implications of haem-deficient NO-unresponsive soluble guanylate cyclase knock-in mice

Oxidative stress, a central mediator of cardiovascular disease, results in loss of the prosthetic haem group of soluble guanylate cyclase (sGC), preventing its activation by nitric oxide (NO). Here we introduce Apo-sGC mice expressing haem-free sGC. Apo-sGC mice are viable and develop hypertension. The haemodynamic effects of NO are abolished, but those of the sGC activator cinaciguat are enhanced in apo-sGC mice, suggesting that the effects of NO on smooth muscle relaxation, blood pressure regulation and inhibition of platelet aggregation require sGC activation by NO. Tumour necrosis factor (TNF)-induced hypotension and mortality are preserved in apo-sGC mice, indicating that pathways other than sGC signalling mediate the cardiovascular collapse in shock. Apo-sGC mice allow for differentiation between sGC-dependent and -independent NO effects and between haem-dependent and -independent sGC effects. Apo-sGC mice represent a unique experimental platform to study the in vivo consequences of sGC oxidation and the therapeutic potential of sGC activators.

Haem-free, NO-insensitive soluble guanylate cyclase (apo-sGC) generated during oxidative stress contributes to cardiovascular pathology. By generating and characterizing apo-sGC knock-in mice, Thoonen et al. provide a scientific ground for the therapeutic concept of sGC activators, and dissect the relevance of the NO-sGC axis.

New medical therapies for heart failure

Heart failure (HF) can rightfully be called the epidemic of the 21(st) century. Historically, the only available medical treatment options for HF have been diuretics and digoxin, but the capacity of these agents to alter outcomes has been brought into question by the scrutiny of modern clinical trials. In the past 4 decades, neurohormonal blockers have been introduced into clinical practice, leading to marked reductions in morbidity and mortality in chronic HF with reduced left ventricular ejection fraction (LVEF). Despite these major advances in pharmacotherapy, our understanding of the underlying disease mechanisms of HF from epidemiological, clinical, pathophysiological, molecular, and genetic standpoints remains incomplete. This knowledge gap is particularly evident with respect to acute decompensated HF and HF with normal (preserved) LVEF. For these clinical phenotypes, no drug has been shown to reduce long-term clinical event rates substantially. Ongoing developments in the pharmacotherapy of HF are likely to challenge our current best-practice algorithms. Novel agents for HF therapy include dual-acting neurohormonal modulators, contractility-enhancing agents, vasoactive and anti-inflammatory peptides, and myocardial protectants. These novel compounds have the potential to enhance our armamentarium of HF therapeutics.

The soluble guanylate cyclase stimulator riociguat and the soluble guanylate cyclase activator cinaciguat exert no direct effects on contractility and relaxation of cardiac myocytes from normal rats

In cardiovascular diseases, reduced responsiveness of soluble guanylate cyclase (sGC) to nitric oxide (NO) upon long-term application has led to the development of NO-independent sGC stimulators (heme-dependent) and sGC activators (heme-independent). Any direct inotropic or lusitropic effects of these compounds on isolated cardiac myocytes, however, remain to be elucidated. Here, we analyzed the dose-dependent effects of clinical relevant concentrations (10(-10)-10(-5) M) of the sGC activator cinaciguat and the sGC stimulator riociguat on the contraction, relaxation, and calcium transients of isolated field-stimulated cardiac myocytes from healthy rats. For comparison, we used isoproterenol, which induced a dose-dependent significant increase in cell contractility, relaxation, and calcium transients, verapamil that significantly decreased these parameters (both at 10(-9)-10(-5) M) and 8-(4-Chlorophenylthio)-guanosine 3',5'-cyclic monophosphate (8-pCPT-cGMP) that induced a negative inotropic effect at 10(-5) M accompanied by a slight increase in relaxation. In contrast, neither cinaciguat nor riociguat significantly influenced any measured parameters. Furthermore, isoproterenol significantly increased intracellular cAMP levels that were not influenced by cinaciguat or riociguat (all at 10(-6) M). Otherwise, riociguat and cinaciguat (both at 10(-6) M) significantly enhanced intracellular cGMP generation. This accumulation was significantly augmented by cinaciguat in the presence of the sGC inhibitor 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ, 25 µM), whereas ODQ blocked cGMP generation by riociguat. However, blocking of sGC did not influence cell contractility. Our results demonstrate that, in isolated cardiac myocytes from healthy rats, the increase in cGMP levels induced by cinaciguat and riociguat at clinical relevant concentrations is not associated with acute direct effects on cell contraction and relaxation.

Small molecule and peptide therapies for chronic heart failure: a patent review (2011 - 2014)

INTRODUCTION

Chronic heart failure (CHF) is the long-term inability of the heart to meet circulatory demands under normal conditions. Effects of CHF can include increased blood volume, increased vascular resistance and compromised contractility leading to fluid retention, dyspnea and fatigue. Current standard of care for chronic systolic heart failure is directed towards managing hypoperfusion through the renin-angiotensin-aldosterone and sympathetic nervous systems. Treatment may also involve reversal of maladaptive cardiac remodeling and prevention of life-threatening arrhythmias.

AREAS COVERED

This review highlights small molecule and peptidic agents for the treatment of CHF with patents published between 2011 and 2014. Targets are subdivided into inotropic agents, ventricular remodeling, diuretics and the renin-angiotensin-aldosterone system.

EXPERT OPINION

CHF represents a large, unmet medical need where improved therapies are needed. The renin-angiotensin-aldosterone system pathway continues to be a major source of new therapies for CHF with new inotropic therapies emerging. Promising initial clinical results for a few approaches combined with the expectation of additional clinical results in the near future make this an exciting time in the pursuit of new treatments for CHF.

Cardiac endothelium-myocyte interaction: clinical opportunities for new heart failure therapies regardless of ejection fraction

Heart failure (HF) is an important global health problem with great socioeconomic burden. Outcomes remain sub-optimal. Endothelium-cardiomyocyte interactions play essential roles in cardiovascular homeostasis, and deranged endothelium-related signalling pathways have been implicated in the pathophysiology of HF. In particular, disturbances in nitric oxide (NO)-mediated pathway and neuregulin-mediated pathway have been shown to contribute to the development of HF. These signalling pathways hold the potential as pathophysiological targets for new HF therapies, and may aid in patient selection for future HF trials.

Extending the translational potential of targeting NO/cGMP-regulated pathways in the CVS

The discovery of NO as both an endogenous signalling molecule and as a mediator of the cardiovascular effects of organic nitrates was acknowledged in 1998 by the Nobel Prize in Physiology/Medicine. The characterization of its downstream signalling, mediated through stimulation of soluble GC (sGC) and cGMP generation, initiated significant translational interest, but until recently this was almost exclusively embodied by the use of PDE5 inhibitors in erectile dysfunction. Since then, research progress in two areas has contributed to an impressive expansion of the therapeutic targeting of the NO-sGC-cGMP axis: first, an increased understanding of the molecular events operating within this complex pathway and second, a better insight into its dys-regulation and uncoupling in human disease. Already-approved PDE5 inhibitors and novel, first-in-class molecules, which up-regulate the activity of sGC independently of NO and/or of the enzyme's haem prosthetic group, are undergoing clinical evaluation to treat pulmonary hypertension and myocardial failure. These molecules, as well as combinations or second-generation compounds, are also being assessed in additional experimental disease models and in patients in a wide spectrum of novel indications, such as endotoxic shock, diabetic cardiomyopathy and Becker's muscular dystrophy. There is well-founded optimism that the modulation of the NO-sGC-cGMP pathway will sustain the development of an increasing number of successful clinical candidates for years to come.

Role of soluble guanylate cyclase in renal hemodynamics and autoregulation in the rat

We studied the influence of soluble guanylate (sGC) on renal blood flow (RBF), glomerular filtration rate (GFR), and RBF autoregulation and its role in mediating the hemodynamic effects of endogenous nitric oxide (NO). Arterial pressure (AP), heart rate (HR), RBF, GFR, urine flow (UV), and the efficiency and mechanisms of RBF autoregulation were studied in anesthetized rats during intravenous infusion of sGC activator cinaciguat before and (except GFR) also after inhibition of NO synthase (NOS) by Nω-nitro-l-arginine methyl ester. Cinaciguat (0.1, 0.3, 1, 3, 10 μg·kg−1·min−1, n = 7) reduced AP and increased HR, but did not significantly alter RBF. In clearance experiments (FITC-sinistrin, n = 7) GFR was not significantly altered by cinaciguat (0.1 and 1 μg·kg−1·min−1), but RBF slightly rose (+12%) and filtration fraction (FF) fell (−23%). RBF autoregulatory efficiency (67 vs. 104%) and myogenic response (33 vs. 44 units) were slightly depressed ( n = 9). NOS inhibition ( n = 7) increased AP (+38 mmHg), reduced RBF (−53%), and greatly augmented the myogenic response in RBF autoregulation (97 vs. 35 units), attenuating the other regulatory mechanisms. These changes were reversed by 77, 78, and 90% by 1 μg·kg−1·min−1 cinaciguat. In vehicle controls ( n = 3), in which cinaciguat-induced hypotension was mimicked by aortic compression, the NOS inhibition-induced changes were not affected. We conclude that sGC activation leaves RBF and GFR well maintained despite hypotension and only slightly impairs autoregulation. The ability to largely normalize AP, RBF, RBF autoregulation, and renovascular myogenic response after NOS inhibition indicates that these hemodynamic effects of NO are predominantly mediated via sGC.

Influence of cinaciguat on gastrointestinal motility in apo-sGC mice

BACKGROUND

Cinaciguat (BAY 58-2667), an NO- and heme-independent sGC activator, was shown to be more effective when the heme-group of sGC is oxidized in vascular tissue. In apo-sGC mice (sGCβ1 (His105Phe) knockin) both sGC isoforms (sGCα1 β1 and sGCα2 β1 ) are heme-deficient and can no longer be activated by NO; these mice, showing decreased gastrointestinal nitrergic relaxation and decreased gastric emptying, can be considered as a model to study the consequence of heme-oxidation in sGC. Our aim was to compare the influence of cinaciguat, on in vitro muscle tone of gastrointestinal tissues, and on gastric emptying in WT and apo-sGC mice.

METHODS

Gastrointestinal smooth muscle strips were mounted in organ baths for isometric force recording and cGMP levels were determined by enzyme immunoassay. Protein levels of sGC subunits were assessed by immunoblotting. Gastric emptying was determined by phenol red recovery.

KEY RESULTS

Although protein levels of the sGC subunits were lower in gastrointestinal tissues of apo-sGC mice, cinaciguat induced concentration-dependent relaxations and increased cGMP levels in apo-sGC fundus and colon to a similar or greater extent than in WT mice. The sGC inhibitor ODQ increased cinaciguat-induced relaxations and cGMP levels in WT fundus and colon. In apo-sGC antrum, pylorus and jejunum, cinaciguat was not able to induce relaxations. Cinaciguat did not improve delayed gastric emptying in apo-sGC mice.

CONCLUSIONS & INFERENCES

Cinaciguat relaxes the fundus and colon efficiently when sGC is in the heme-free condition; the non-effect of cinaciguat in pylorus explains its inability to improve the delayed gastric emptying in apo-sGC mice.

Regulation of intraocular pressure by soluble and membrane guanylate cyclases and their role in glaucoma

Glaucoma is a progressive optic neuropathy characterized by visual field defects that ultimately lead to irreversible blindness (Alward, 2000; Anderson et al., 2006). By the year 2020, an estimated 80 million people will have glaucoma, 11 million of which will be bilaterally blind. Primary open-angle glaucoma (POAG) is the most common type of glaucoma. Elevated intraocular pressure (IOP) is currently the only risk factor amenable to treatment. How IOP is regulated and can be modulated remains a topic of active investigation. Available therapies, mostly geared toward lowering IOP, offer incomplete protection, and POAG often goes undetected until irreparable damage has been done, highlighting the need for novel therapeutic approaches, drug targets, and biomarkers (Heijl et al., 2002; Quigley, 2011). In this review, the role of soluble (nitric oxide (NO)-activated) and membrane-bound, natriuretic peptide (NP)-activated guanylate cyclases that generate the secondary signaling molecule cyclic guanosine monophosphate (cGMP) in the regulation of IOP and in the pathophysiology of POAG will be discussed.

Gigantic business: titin properties and function through thick and thin

The giant protein titin forms a unique filament network in cardiomyocytes, which engages in both mechanical and signaling functions of the heart. TTN, which encodes titin, is also a major human disease gene. In this review, we cover the roles of cardiac titin in normal and failing hearts, with a special emphasis on the contribution of titin to diastolic stiffness. We provide an update on disease-associated titin mutations in cardiac and skeletal muscles and summarize what is known about the impact of protein-protein interactions on titin properties and functions. We discuss the importance of titin-isoform shifts and titin phosphorylation, as well as titin modifications related to oxidative stress, in adjusting the diastolic stiffness of the healthy and the failing heart. Along the way we distinguish among titin alterations in systolic and in diastolic heart failure and ponder the evidence for titin stiffness as a potential target for pharmacological intervention in heart disease.

The chemistry and biology of soluble guanylate cyclase stimulators and activators

The vasodilatory properties of nitric oxide (NO) have been utilized in pharmacotherapy for more than 130 years. Still today, NO-donor drugs are important in the management of cardiovascular diseases. However, inhaled NO or drugs releasing NO and organic nitrates are associated with noteworthy therapeutic shortcomings, including resistance to NO in some disease states, the development of tolerance during long-term treatment, and nonspecific effects, such as post-translational modification of proteins. The beneficial actions of NO are mediated by stimulation of soluble guanylate cyclase (sGC), a heme-containing enzyme which produces the intracellular signaling molecule cyclic guanosine monophosphate (cGMP). Recently, two classes of compounds have been discovered that amplify the function of sGC in a NO-independent manner, the so-called sGC stimulators and sGC activators. The most advanced drug, the sGC stimulator riociguat, has successfully undergone Phase III clinical trials for different forms of pulmonary hypertension.

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.

Genetic modification of hypertension by sGCα1

Hypertension is an important modifiable risk factor for coronary heart disease, congestive heart failure, stroke, end-stage renal disease, and peripheral vascular disease, but many of the molecular mechanisms and genetic factors underlying the development of the most common forms of human hypertension remain to be defined. Abundant evidence suggests that nitric oxide (NO) and one of its primary targets, the cyclic guanosine monophosphate (cGMP)-generating enzyme soluble guanylate cyclase (sGC), have a critical role in regulating blood pressure. The availability of murine models of hypertension and the revolution in human genetics research (e.g., genome-wide association studies [GWAS]), resulting in the identification of dozens of genetic loci that affect normal variation in blood pressure and susceptibility to hypertension, provide a unique opportunity to dissect the mechanisms by which NO-cGMP signaling regulates blood pressure and to gain important insights into the pathogenesis of hypertension. In this review, we will give an overview of the current knowledge relating to the role of sGC in the regulation of blood pressure, discussing data obtained from genetically modified mouse models as well as from human genetic studies.

Differential expression of the pro-natriuretic peptide convertases corin and furin in experimental heart failure and atrial fibrosis

In heart failure (HF), the cardiac hormone natriuretic peptides (NPs) atrial (ANP), B-type (BNP), and C-type (CNP) play a key role to protect cardiac remodeling. The proprotein convertases corin and furin process their respective pro-NPs into active NPs. Here we define in a canine model of HF furin and corin gene and protein expression in normal and failing left atrium (LA) or ventricle (LV) testing the hypothesis that the NP proproteins convertases production is altered in experimental HF. Experimental canine HF was produced by rapid right ventricular pacing for 10 days. NPs, furin, and corin mRNA expression were determined by quantitative RT-PCR. Protein concentration or expression was determined by immunostaining, radioimmunoassay, or Western blot. Furin and corin proteins were present in normal canine LA and LV myocardium and vasculature and in smooth muscle cells. In normal canines, expression of NPs was dominant in the atrium compared with the ventricle. In experimental early stage HF characterized with marked atrial fibrosis, ANP, BNP, and CNP mRNA, and protein concentrations were higher in HF LA but not HF LV compared with normals. In LA, corin mRNA and protein expressions in HF were lower, whereas furin mRNA and protein expressions were higher than normals. NPs and furin expressions were augmented in the atrium in experimental early stage HF and, conversely, corin mRNA and protein expressions were decreased with atrial remodeling. Selective changes of these NP convertases may have significance in the regulation of pro-NP processing and atrial remodeling in early stage HF.

Heme-assisted S-nitrosation desensitizes ferric soluble guanylate cyclase to nitric oxide

Nitric oxide (NO) signaling regulates key processes in cardiovascular physiology, specifically vasodilation, platelet aggregation, and leukocyte rolling. Soluble guanylate cyclase (sGC), the mammalian NO sensor, transduces an NO signal into the classical second messenger cyclic GMP (cGMP). NO binds to the ferrous (Fe(2+)) oxidation state of the sGC heme cofactor and stimulates formation of cGMP several hundred-fold. Oxidation of the sGC heme to the ferric (Fe(3+)) state desensitizes the enzyme to NO. The heme-oxidized state of sGC has emerged as a potential therapeutic target in the treatment of cardiovascular disease. Here, we investigate the molecular mechanism of NO desensitization and find that sGC undergoes a reductive nitrosylation reaction that is coupled to the S-nitrosation of sGC cysteines. We further characterize the kinetics of NO desensitization and find that heme-assisted nitrosothiol formation of β1Cys-78 and β1Cys-122 causes the NO desensitization of ferric sGC. Finally, we provide evidence that the mechanism of reductive nitrosylation is gated by a conformational change of the protein. These results yield insights into the function and dysfunction of sGC in cardiovascular disease.

Endothelial dysfunction, arterial stiffness, and heart failure

Outcomes for heart failure (HF) patients remain suboptimal. No known therapy improves mortality in acute HF and HF with preserved ejection fraction; the most recent HF trial results have been negative or neutral. Improvement in surrogate markers has not necessarily translated into better outcomes. To translate breakthroughs with potential therapies into clinical benefit, a better understanding of the pathophysiology establishing the foundation of benefit is necessary. Vascular function plays a central role in the development and progression of HF. Endothelial function and nitric oxide availability affect myocardial function, systemic and pulmonary hemodynamics, and coronary and renal circulation. Arterial stiffness modulates ventricular loading conditions and diastolic function, key components of HF with preserved ejection. Endothelial function and arterial stiffness may therefore serve as important physiological targets for new HF therapies and facilitate patient selection for improved application of existing agents.

Tetrahydrobiopterin protects soluble guanylate cyclase against oxidative inactivation

Tetrahydrobiopterin (BH4) is a major endogenous vasoprotective agent that improves endothelial function by increasing nitric oxide (NO) synthesis and scavenging of superoxide and peroxynitrite. Therefore, administration of BH4 is considered a promising therapy for cardiovascular diseases associated with endothelial dysfunction and oxidative stress. Here we report on a novel function of BH4 that might contribute to the beneficial vascular effects of the pteridine. Treatment of cultured porcine aortic endothelial cells with nitroglycerin (GTN) or 1H-[1,2,4]-oxadiazolo[4,3-a]quinoxaline-1-one (ODQ) resulted in heme oxidation of soluble guanylate cyclase (sGC), as evident from diminished NO-induced cGMP accumulation that was paralleled by increased cGMP response to a heme- and NO-independent activator of soluble guanylate cyclase [4-([(4-carboxybutyl)[2-(5-fluoro-2-([4'-(trifluoromethyl)biphenyl-4-yl]methoxy)phenyl)ethyl]amino]methyl)benzoic acid (BAY 60-2770)]. Whereas scavenging of superoxide and/or peroxynitrite with superoxide dismutase, tiron, Mn(III)tetrakis(4-benzoic acid)porphyrin, and urate had no protective effects, supplementation of the cells with BH4, either by application of BH4 directly or of its precursors dihydrobiopterin or sepiapterin, completely prevented the inhibition of NO-induced cGMP accumulation by GTN and ODQ. Tetrahydroneopterin had the same effect, and virtually identical results were obtained with RFL-6 fibroblasts, suggesting that our observation reflects a general feature of tetrahydropteridines that is unrelated to NO synthase function and not limited to endothelial cells. Protection of sGC against oxidative inactivation may contribute to the known beneficial effects of BH4 in cardiovascular disorders associated with oxidative stress.

Nitric oxide- and heme-independent activation of soluble guanylate cyclase attenuates peroxynitrite-induced endothelial dysfunction in rat aorta

Oxidative stress interferes with nitric oxide (NO)/soluble guanylate cyclase (sGC)/cyclic guanosine monophosphate (cGMP) signalling pathway through reduction of endogenous NO and formation of the strong intermediate oxidant peroxynitrite and leads to vascular dysfunction. We evaluated the effects of oral treatment with NO- and heme-independent sGC activator cinaciguat on peroxynitrite-induced vascular dysfunction in rat aorta. Sprague-Dawley rats were treated orally 2 times at an interval of 17 hours with vehicle or with cinaciguat (10 mg/kg). One hour after the last treatment, the animals were anesthetized, the thoracic aorta was removed, and the aortic segment preparations were incubated with and without the reactive oxidant peroxynitrite (200 µmol/L, 30 minutes). Endothelium-dependent (acetylcholine), -independent (sodium nitroprusside) vasorelaxations were investigated, and histopathological examination was performed. Incubation of aortic rings with peroxynitrite significantly attenuated the maximal endothelium-dependent relaxation (R (max)) to acetylcholine (peroxynitrite, 44.5% ± 5.9% vs control, 93.2% ± 2.0%, P < .05) and decreased pD(2) values (-logEC(50), EC(50) being the concentration of acetylcholine that elicited 50% of the maximal response) for the concentration-response curves as compared to control segments. Treatment of rats with cinaciguat significantly improved the decreased acetylcholine-induced vasorelaxation after exposure of aortic rings to peroxynitrite (cinaciguat + peroxynitrite, 67.1% ± 3.5% vs peroxynitrite, 44.5% ± 5.9%, P < .05). Incubation of aortic segments with peroxynitrite caused a significant shift of the sodium nitroprusside concentration-response curves to the right without any alterations in the R (max). Moreover, exposure of aortic rings to peroxynitrite resulted in increased nitro-oxidative stress and DNA breakage which were improved by cinaciguat. Treatment of rats with cinaciguat significantly increased intracellular cGMP levels in the aortic wall. Our results show under conditions of nitro-oxidative stress when signalling in the NO/sGC/cGMP pathway is impaired, acute activation of sGC by cinaciguat might be advantageous in the treatment of endothelial dysfunction in cardiovascular disease.

Cinaciguat, a soluble guanylate cyclase activator, unloads the heart but also causes hypotension in acute decompensated heart failure

AIMS

Cinaciguat (BAY 58-2667) is a novel soluble guanylate cyclase activator. This study evaluated the haemodynamic effect and safety of cinaciguat added to standard therapy in patients with acute decompensated heart failure (ADHF).

METHODS AND RESULTS

In this placebo-controlled, phase IIb study (NCT00559650), 139 patients admitted with ADHF, pulmonary capillary wedge pressure (PCWP) ≥18 mmHg, left ventricular ejection fraction <40%, and a pre-existing need for invasive haemodynamic monitoring were randomized 2:1 to cinaciguat:placebo (continuous i.v. infusion). The dose was titrated for 8 h and maintained for 16-40 h (starting dose: 100 μg/h). At 8 h, mean PCWP changed from 25.7 ± 5.0 mmHg by -7.7 mmHg with cinaciguat and from 25.0 ± 5.3 mmHg by -3.7 mmHg with placebo (P < 0.0001). The mean right atrial pressure changed from 12.4 ± 5.3 mmHg by -2.7 mmHg with cinaciguat and from 11.8 ± 4.9 mmHg by -0.6 mmHg with placebo (P= 0.0019). Cinaciguat also decreased the pulmonary and systemic vascular resistance and the mean arterial pressure, and increased the cardiac index (all P < 0.0001 vs. placebo). Systolic blood pressure changed by -21.6 ± 17.0 mmHg with cinaciguat and -5.0 ± 14.5 mmHg with placebo. Adverse events were experienced by 71 and 45% of patients receiving cinaciguat and placebo, respectively. No adverse effects on the 30-day mortality were seen; however, the trial was stopped prematurely due to an increased occurrence of hypotension at cinaciguat doses ≥200 µg/h.

CONCLUSION

Cinaciguat unloaded the heart in patients with ADHF. However, high doses were associated with hypotension.

Nitric oxide modulation as a therapeutic strategy in heart failure

Nitric oxide (NO) is recognized as one of the most important cardiovascular signaling molecules, with multiple regulatory effects on myocardial and vascular tissue as well as on other tissues and organ systems. With the growth in understanding of the range and mechanisms of NO effects on the cardiovascular system, it is now possible to consider pharmaceutical interventions that directly target NO or key steps in NO effector pathways. This article reviews aspects of the cardiovascular effects of NO, abnormalities in NO regulation in heart failure, and clinical trials of drugs that target specific aspects of NO signaling pathways.

Cinaciguat, a soluble guanylate cyclase activator: results from the randomized, controlled, phase IIb COMPOSE programme in acute heart failure syndromes

AIMS

Cinaciguat (BAY 58-2667) is a soluble guanylate cyclase (sGC) activator that, in a previous study among patients with acute heart failure syndromes (AHFS), improved pulmonary capillary wedge pressure (PCWP) at the expense of significant hypotension at doses ≥200 µg/h. The aim of the COMPOSE programme was to investigate the safety and efficacy of fixed, low doses of intravenous cinaciguat (<200 µg/h for 24-48 h) as add-on to standard therapy in adults hospitalized with AHFS.

METHODS AND RESULTS

COMPOSE comprised three randomized, double-blind, placebo-controlled studies in patients with [COMPOSE 1 and 2 (NCT01065077 and NCT01067859)] or without [COMPOSE EARLY (NCT01064037)] a requirement for invasive haemodynamic monitoring. COMPOSE 1 and COMPOSE EARLY assessed the effects of cinaciguat (50, 100, and 150 µg/h) on haemodynamics and dyspnoea, respectively. COMPOSE 2 assessed the haemodynamic effects of 10 and 25 µg/h cinaciguat. COMPOSE was terminated early due to an excess of non-fatal hypotension and recruitment difficulties. In COMPOSE 1 (n = 12), cinaciguat reduced PCWP at 8 h compared with placebo, but there was no relevant change in cardiac index. In COMPOSE EARLY (n = 62), no meaningful difference in dyspnoea was shown between cinaciguat and placebo.

CONCLUSION

In this limited database, short-term use of intravenous cinaciguat decreased blood pressure without improving dyspnoea or cardiac index. Given the lack of effect on dyspnoea and cardiac index and the hypotensive effect seen even with low doses, it is doubtful that further studies with intravenous cinaciguat would prove beneficial in this patient population.

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.