Riociguat: Mode of Action and Clinical Development in Pulmonary Hypertension

Qifu yixin prescription ameliorates cardiac fibrosis by activating soluble guanylate cyclase (sGC) in heart failure

ETHNOPHARMACOLOGICAL RELEVANCE

Qifu yixin prescription (QYP), an effective traditional Chinese medicine formula, has been utilized in the clinical treatment of cardiovascular diseases for over two decades and has been granted a national invention patent in China. It has demonstrated the ability to improve clinical symptoms in patients with heart failure. However, its precise effects and underlying molecular mechanisms remain unclear.

AIM OF THE STUDY

To evaluate the efficacy of QYP in treating HF and the underlying mechanisms.

MATERIALS AND METHODS

The heart failure (HF) model in mice was established using transverse aortic constriction (TAC), while neonatal rat cardiac fibroblasts (CFs) were utilized for in vitro experiments. The bioactive compounds in QYP were identified through high-performance liquid chromatography (HPLC). Cardiac hypertrophy, function, and fibrosis were assessed using morphological observations, echocardiography, and histomorphometric analyses. To investigate the underlying mechanisms by which QYP alleviates HF, transcriptomic analysis was conducted, and network pharmacology was employed to explore its potential mechanisms of action. Mechanistically, the expression levels of sGC, PKG, ERK, and p-ERK were analyzed using western blotting, immunohistochemistry, and immunofluorescence. Molecular docking was conducted to assess the binding affinity of the compounds of QYP to sGC. Additionally, the effects of QYP on CFs were investigated through cell-based assays.

RESULTS

We identified 33 bioactive compounds in QYP. Histomorphometric and transcriptomic analyses indicated that QYP alleviates cardiac fibrosis in HF. Network pharmacological analysis suggested that the sGC/cGMP/PKG and MAPK pathways are key mechanisms underlying the effects of QYP on cardiac fibrosis. The findings confirmed that QYP activates sGC, leading to the inhibition of ERK phosphorylation. Molecular docking revealed that the compounds of QYP exhibit strong binding affinity to sGC. Additionally, cell-based experiments demonstrated that QYP effectively suppresses CFs activation by stimulating sGC.

CONCLUSIONS

These results indicate QYP improves cardiac fibrosis in HF by activating sGC to inhibit ERK phosphorylation. We propose that QYP is a potential treatment for HF with anti-fibrotic properties.

Novel insights into the potential applications of stem cells in pulmonary hypertension therapy

Pulmonary hypertension (PH) refers to a group of deadly lung diseases characterized by vascular lesions in the microvasculature and a progressive increase in pulmonary vascular resistance. The prevalence of PH has increased over time. Currently, the treatment options available for PH patients have limited efficacy, and none of them can fundamentally reverse pulmonary vascular remodeling. Stem cells represent an ideal seed with proven efficacy in clinical studies focusing on liver, cardiovascular, and nerve diseases. Since the potential therapeutic effect of mesenchymal stem cells (MSCs) on PH was first reported in 2006, many studies have demonstrated the efficacy of stem cells in PH animal models and suggested that stem cells can help slow the deterioration of lung tissue. Existing PH treatment studies basically focus on the paracrine action of stem cells, including protein regulation, exosome pathway, and cell signaling; however, the specific mechanisms have not yet been clarified. Apoptotic and afunctional pulmonary microvascular endothelial cells (PMVECs) and alveolar epithelial cells (AECs) are two fundamental promoters of PH although they have not been extensively studied by researchers. This review mainly focuses on the supportive communication and interaction between PMVECs and AECs as well as the potential restorative effect of stem cells on their injury. In the future, more studies are needed to prove these effects and explore more radical cures for PH.

Severe thrombocytopenia associated to bevacizumab in a patient with scleroderma, gastrointestinal angiodysplasias and refractory gastrointestinal bleeding

This case report discusses the medical history of a 64-year-old woman diagnosed with scleroderma and diffuse gastrointestinal angiodysplasia. The patient received bevacizumab (BVZ) therapy to address gastrointestinal bleeding that was unresponsive to endoscopic treatment. Subsequently, she developed severe thrombocytopenia. Although there were suspicions of an immune-mediated mechanism resulting from BVZ treatment, the laboratory results did not provide conclusive evidence. The patient underwent transfusions, received gamma globulin, and was treated with Romiplostim. Over time, her platelet levels gradually improved, and the bleeding was successfully controlled. It's worth noting that BVZ-induced thrombocytopenia is a relatively rare yet severe adverse effect. Recognizing and understanding the mechanisms behind thrombocytopenia is essential for developing safer treatment approaches. Further research is required to identify potential risk factors associated with this condition.

The nitric oxide-soluble guanylate cyclase-cGMP pathway in pulmonary hypertension: from PDE5 to soluble guanylate cyclase

The nitric oxide (NO)-soluble guanylate cyclase (sGC)-cyclic guanosine monophosphate (cGMP) pathway plays a key role in the pathogenesis of pulmonary hypertension (PH). Targeted treatments include phosphodiesterase type 5 inhibitors (PDE5i) and sGC stimulators. The sGC stimulator riociguat is approved for the treatment of pulmonary arterial hypertension (PAH) and chronic thromboembolic pulmonary hypertension (CTEPH). sGC stimulators have a dual mechanism of action, enhancing the sGC response to endogenous NO and directly stimulating sGC, independent of NO. This increase in cGMP production via a dual mechanism differs from PDE5i, which protects cGMP from degradation by PDE5, rather than increasing its production. sGC stimulators may therefore have the potential to increase cGMP levels under conditions of NO depletion that could limit the effectiveness of PDE5i. Such differences in mode of action between sGC stimulators and PDE5i could lead to differences in treatment efficacy between the classes. In addition to vascular effects, sGC stimulators have the potential to reduce inflammation, angiogenesis, fibrosis and right ventricular hypertrophy and remodelling. In this review we describe the evolution of treatments targeting the NO-sGC-cGMP pathway, with a focus on PH.

Recognition, diagnosis, and operability assessment of chronic thromboembolic pulmonary hypertension (CTEPH): A global cross-sectional scientific survey (CLARITY)

Early recognition and diagnosis of chronic thromboembolic pulmonary hypertension (CTEPH) is crucial for improving prognosis and reducing the disease burden. Established clinical practice guidelines describe interventions for the diagnosis and evaluation of CTEPH, yet limited insight remains into clinical practice variation and barriers to care. The CTEPH global cross-sectional scientific survey (CLARITY) was developed to gather insights into the current diagnosis, treatment, and management of CTEPH and to identify unmet medical needs. This paper focuses on the recognition and diagnosis of CTEPH and the referral and evaluation of these patients. The survey was offered to hospital-based medical specialists through Scientific Societies and other medical organizations, from September 2021 to May 2022. Response data from 353 physicians showed that self-reported awareness of CTEPH increased over the past 10 years among 96% of respondents. Clinical practices in acute pulmonary embolism (PE) follow-up and CTEPH diagnosis differed among respondents. While 50% of respondents working in a nonexpert center reported to refer patients to an expert pulmonary hypertension/CTEPH center when CTEPH is suspected, 51% of these physicians did not report referral of patients with a confirmed diagnosis for further evaluation. Up to 50% of respondents involved in the evaluation of referred patients have concluded a different operability status than that indicated by the referring center. This study indicates that early diagnosis and timely treatment of CTEPH is challenged by suboptimal acute PE follow-up and patient referral practices. Nonadherence to guideline recommendations may be impacted by various barriers to care, which were shown to vary by geographical region.

The risk profile change in patients with severe chronic thromboembolic pulmonary hypertension treated with subcutaneous treprostinil

Chronic thromboembolic pulmonary hypertension (CTEPH) is successfully treatable with pulmonary endarterectomy (PEA), balloon pulmonary angioplasty, and medical therapy. Registry to Evaluate Early and Long-Term Pulmonary Arterial Hypertension Disease Management risk score (RRS) is able to predict long-term outcome in inoperable patients or in patients with residual PH after surgery. We performed a post hoc analysis of RRS in patients who were enrolled in the CTREPH study (NCT01416636), a randomized, double-blind clinical trial comparing high-dose and low-dose subcutaneous (SC) treprostinil in patients with severe CTEPH that was classified by an interdisciplinary CTEPH team as nonoperable, or as persistent or recurrent pulmonary hypertension after PEA. Baseline mean RRS was similar in both treatment groups (8.7 in high-dose arm vs. 8.6 in low-dose arm), but mean RRS change from baseline to Week 24 was greater in the high-dose treprostinil group than in the low-dose treprostinil group (-0.88 vs. -0.17). The difference in RRS change from baseline to Week 24 between high dose versus low dose was statistically significant with mean difference of -0.70 (95% confidence interval: -1.36 to -0.05, p = 0.0352), and was driven mainly by improvement of World Health Organization functional class and N-terminal pro-brain natriuretic peptide concentration. SC treprostinil therapy administered in standard dose had positive effect on the risk profile measured by RRS in patients with inoperable or persistent/recurrent severe CTEPH. Although our study was limited by the small sample size and post hoc nature, assessment of risk profile is of great importance to this particular patient population with very poor prognosis.

The role of riociguat in combination therapies for pulmonary arterial hypertension

Effective clinical decision-making in initial treatment selection and switching or escalations of therapy for pulmonary arterial hypertension (PAH) depends on multiple factors including the patient's risk profile. Data from clinical trials suggest that switching from a phosphodiesterase-5 inhibitor (PDE5i) to the soluble guanylate cyclase stimulator riociguat may provide clinical benefit in patients not reaching treatment goals. In this review, we cover the clinical evidence for riociguat combination regimens for patients with PAH and discuss their evolving role in upfront combination therapy and switching from a PDE5i as an alternative to escalating therapy. Specifically, we review current evidence which suggests or provides a hypothesis for 1) the potential use of riociguat plus endothelin receptor antagonist combinations for upfront combination therapy in patients with PAH at intermediate to high risk of 1-year mortality and 2) the benefits of switching to riociguat from a PDE5i in patients who are not achieving treatment goals with PDE5i-based dual combination therapy and at intermediate risk.

Pathophysiology and Treatment of Chronic Thromboembolic Pulmonary Hypertension

Chronic thromboembolic pulmonary hypertension (CTEPH) is a condition in which an organic thrombus remains in the pulmonary artery (PA) even after receiving anticoagulation therapy for more than 3 months and is complicated by pulmonary hypertension (PH), leading to right-sided heart failure and death. CTEPH is a progressive pulmonary vascular disease with a poor prognosis if left untreated. The standard treatment for CTEPH is pulmonary endarterectomy (PEA), which is usually performed only in specialized centers. In recent years, balloon pulmonary angioplasty (BPA) and drug therapy for CTEPH have also shown good results. This review discusses the complex pathogenesis of CTEPH and presents the standard of care, PEA, as well as a new device called BPA, which is showing remarkable progress in efficacy and safety. Additionally, several drugs are now demonstrating established evidence of efficacy in treating CTEPH.

Stimulation of soluble guanylate cyclase by vericiguat reduces skeletal muscle atrophy of mice following chemotherapy

Background: The chemotherapeutic doxorubicin (DOX) promotes severe skeletal muscle atrophy, which induces skeletal muscle weakness and fatigue. Soluble guanylate cyclase (sGC) contributes to a variety of pathophysiological processes, but whether it is involved in DOX-induced skeletal muscle atrophy is unclear. The present study aimed to stimulate sGC by vericiguat, a new oral sGC stimulator, to test its role in this process. Methods: Mice were randomly divided into four groups: control group, vericiguat group, DOX group, and DOX + vericiguat group. Exercise capacity was evaluated before the mice were sacrificed. Skeletal muscle atrophy was assessed by histopathological and molecular biological methods. Protein synthesis and degradation were monitored in mice and C2C12 cells. Results: In this study, a significant decrease in exercise capacity and cross-sectional area (CSA) of skeletal muscle fibers was found in mice following DOX treatment. Furthermore, DOX decreased sGC activity in mice and C2C12 cells, and a positive correlation was found between sGC activity and CSA of skeletal muscle fibers in skeletal muscle. DOX treatment also impaired protein synthesis, shown by puromycin detection, and activated ubiquitin-proteasome pathway. Following sGC stimulation, the CSA of muscle fibers was elevated, and exercise capacity was enhanced. Stimulation of sGC also increased protein synthesis and decreased ubiquitin-proteasome pathway. In terms of the underlying mechanisms, AKT/mTOR and FoxO1 pathways were impaired following DOX treatment, and stimulation of sGC restored the blunted pathways. Conclusion: These results unravel sGC stimulation can improve skeletal muscle atrophy and increase the exercise capacity of mice in response to DOX treatment by enhancing protein synthesis and inhibiting protein degradation. Stimulation of sGC may be a potential treatment of DOX-induced skeletal muscle dysfunction.

Riociguat and the right ventricle in pulmonary arterial hypertension and chronic thromboembolic pulmonary hypertension

Pulmonary arterial hypertension (PAH) and chronic thromboembolic pulmonary hypertension (CTEPH) are progressive diseases that can lead to right heart failure and death. Right ventricular dysfunction, hypertrophy and maladaptive remodelling are consequences of increased right ventricular (RV) afterload in PAH and CTEPH and are indicative of long-term outcomes. Because RV failure is the main cause of morbidity and mortality in PAH and CTEPH, successful treatments should lead to improvements in RV parameters. Riociguat is a soluble guanylate cyclase stimulator approved for the treatment of PAH and inoperable or persistent/recurrent CTEPH after pulmonary endarterectomy. This review examines the current evidence showing the effect of riociguat on the right ventricle, with particular focus on remodelling, function and structural parameters in preclinical models and patients with PAH or CTEPH.

Balloon pulmonary angioplasty versus riociguat in inoperable chronic thromboembolic pulmonary hypertension (MR BPA): an open-label, randomised controlled trial

BACKGROUND

Treatment options for patients with chronic thromboembolic pulmonary hypertension ineligible for pulmonary endarterectomy (inoperable CTEPH) include balloon pulmonary angioplasty (BPA) and riociguat. However, these two treatment options have not been compared prospectively. We aimed to compare the safety and efficacy of BPA and riociguat in patients with inoperable CTEPH.

METHODS

This open-label, randomised controlled trial was conducted at four high-volume CTEPH centres in Japan. Patients aged 20-80 years with inoperable CTEPH (mean pulmonary arterial pressure ≥25 to <60 mm Hg and pulmonary artery wedge pressure ≤15 mm Hg) and WHO functional class II or III were randomly assigned (1:1) to BPA or riociguat via a computer program located at the registration centre using a minimisation method with biased-coin assignment. In the BPA group, the aim was for BPA to be completed within 4 months of the initial date of the first procedure. BPA was repeated until mean pulmonary arterial pressure decreased to less than 25 mm Hg. The frequency of BPA procedures depended on the difficulty and number of the lesions. In the riociguat group, 1·0 mg riociguat was administered orally thrice daily. When the systolic blood pressure was maintained at 95 mm Hg or higher, the dose was increased by 0·5 mg every 2 weeks up to a maximum of 2·5 mg thrice daily; dose adjustment was completed within 4 months of the date of the first dose. The primary endpoint was change in mean pulmonary arterial pressure from baseline to 12 months, measured in the full analysis set (patients who were enrolled and randomly assigned to one of the study treatments, and had at least one assessment after randomisation). BPA-related complications and indices related to clinical worsening were recorded throughout the study period. Adverse events were recorded throughout the study period and evaluated in the safety analysis set (patients who were enrolled and randomely assigned to one of the study treatments, and had received part of or all the study treatments). This trial is registered in the Japan Registry of Clinical Trials (jRCT; jRCTs031180239) and is completed.

FINDINGS

Between Jan 8, 2016, and Oct 31, 2019, 61 patients with inoperable CTEPH were enrolled and randomly assigned to BPA (n=32) or riociguat (n=29). Patients in the BPA group underwent an average of 4·7 (SD 1·6) BPA procedures. In the riociguat group, the mean maintenance dose was 7·0 (SD 1·0) mg/day at 12 months. At 12 months, mean pulmonary arterial pressure had improved by -16·3 (SE 1·6) mm Hg in the BPA group and -7·0 (1·5) mm Hg in the riociguat group (group difference -9·3 mm Hg [95% CI -12·7 to -5·9]; p<0·0001). A case of clinical worsening of pulmonary hypertension occurred in the riociguat group, whereas none occurred in the BPA group. The most common adverse event was haemosputum, haemoptysis, or pulmonary haemorrhage, affecting 14 patients (44%) in the BPA group and one (4%) in the riociguat group. In 147 BPA procedures done in 31 patients, BPA-related complications were observed in 17 procedures (12%) in eight patients (26%).

INTERPRETATION

Compared with riociguat, BPA was associated with a greater improvement in mean pulmonary arterial pressure in patients with inoperable CTEPH at 12 months, although procedure-related complications were reported. These findings support BPA as a reasonable option for inoperable CTEPH in centres with experienced BPA operators, with attention to procedure-related complications.

FUNDING

Bayer Yakuhin.

TRANSLATION

For the Japanese translation of the abstract see Supplementary Materials section.

BMI and Treatment Response in Patients With Pulmonary Arterial Hypertension: A Meta-analysis

BACKGROUND

Obesity is increasingly prevalent in pulmonary arterial hypertension (PAH) but is associated with improved survival, creating an "obesity paradox" in PAH. It is unknown if the improved outcomes could be attributable to obese patients deriving a greater benefit from PAH therapies.

RESEARCH QUESTION

Does BMI modify treatment effectiveness in PAH?

STUDY DESIGN AND METHODS

Using individual participant data, a meta-analysis was conducted of phase III, randomized, placebo-controlled trials of treatments for PAH submitted for approval to the U.S. Food and Drug Administration from 2000 to 2015. Primary outcomes were change in 6-min walk distance (6MWD) and World Health Organization (WHO) functional class.

RESULTS

A total of 5,440 participants from 17 trials were included. Patients with overweight and obesity had lower baseline 6MWD and were more likely to be WHO functional class III or IV. Treatment was associated with a 27.01-m increase in 6MWD (95% CI, 21.58-32.45; P < .001) and lower odds of worse WHO functional class (OR, 0.58; 95% CI, 0.48-0.70; P < .001). For every 1 kg/m2 increase in BMI, 6MWD was reduced by 0.66 m (P = .07); there was no significant effect modification of treatment response in 6MWD according to BMI (P for interaction = .34). Higher BMI was not associated with odds of WHO functional class at end of follow-up; however, higher BMI attenuated the treatment response such that every 1 kg/m2 increase in BMI increased odds of worse WHO functional class by 3% (OR, 1.03; P for interaction = .06).

INTERPRETATION

Patients with overweight and obesity had lower baseline 6MWD and worse WHO functional class than patients with normal weight with PAH. Higher BMI did not modify the treatment response for change in 6MWD, but it attenuated the treatment response for WHO functional class. PAH trials should include participants representative of all weight groups to allow for assessment of treatment heterogeneity and mechanisms.

Soluble Guanylate Cyclase Stimulators (Riociguat) in Pulmonary Hypertension: Data from Real-Life Clinical Practice in a 3-Year Follow-Up

BACKGROUND

Pulmonary hypertension (PH) is a rare and complex disease with poor prognosis, which requires lifelong treatment.

OBJECTIVE

To describe 3-year follow-up real-life data on treatment with soluble guanylate cyclase stimulators (Riociguat) of patients with PH, measuring current risk assessment parameters.

METHODS

This study retrospectively collected clinical and epidemiological data of patients with PH of group 1 (pulmonary arterial hypertension) and group 4 (chronic thromboembolic PH). Non-invasive and invasive parameters corresponding to the risk assessment were analyzed at baseline and follow-up. Statistical analyses were performed using the SPSS 18.0 software, and p-values < 0.050 were considered statistically significant.

RESULTS

In total, 41 patients receiving riociguat were included in the study. Of them, 31 had already completed 3 years of treatment and were selected for the following analysis. At baseline, 70.7% of patients were in WHO functional class III or IV. After 3 years of treatment, the WHO functional class significantly improved in all patients. In addition, the median of the 6-minute walk test (6MWT) significantly increased from 394 ± 91 m at baseline to 458 ± 100 m after 3 years of follow-up (p= 0.014). The three-year survival rate was 96.7%.

CONCLUSION

In our real-life cohort, most patients with PH treated with riociguat showed stable or improved risk parameters, especially in the 6MWT, at 3 years of follow-up.

Riociguat in the Treatment of Pulmonary Arterial Hypertension in Mexico

Pulmonary arterial hypertension (PAH) is a severe clinical condition that significantly affects patients' quality of life and survival. Since the emergence of prostanoids 45 years ago, different drugs acting on vasoconstriction/vasodilation mechanisms have been developed for the treatment of PAH. Current evidence shows that better results occur when combined therapy is initiated up-front with periodic and systematized evaluations for escalation and switching. Among these strategies, riociguat has a relevant role, supported by the results of several clinical studies. This document issues recommendations by a panel of experts who analysed and discussed the indications and limitations for riociguat in PAH in different institutions of the Mexican health system.

Novel use of riociguat in infants with severe pulmonary arterial hypertension unable to wean from inhaled nitric oxide

INTRODUCTION

Riociguat, an oral soluble guanylate cyclase stimulator, has been approved for use in adults with pulmonary arterial hypertension (PAH) and chronic thromboembolic pulmonary hypertension. However, there is limited data on its therapeutic use in children.

CASE PRESENTATION

We report the case of two infants with severe suprasystemic pulmonary hypertension who were successfully treated with riociguat after failure to wean off inhaled nitric oxide (iNO) despite combination PAH therapy. Case 1 is a 6-month-old term male with TBX4 deletion who presented with severe hypoxemic respiratory failure and severe PAH immediately after birth. Initial cardiac catheterization showed PVRi 15.5 WU*m2. Marked hypoxemia and PAH persisted despite aggressive therapy with sildenafil, bosentan, intravenous treprostinil, and milrinone. The infant required high doses of inhaled nitric oxide (60 ppm) and manifested significant post-ductal hypoxemia and hemodynamic instability with any attempt at weaning. After discontinuation of sildenafil, initiation, and very slow uptitration of riociguat, the patient was able to maintain hemodynamic stability and wean from nitric oxide over 6 weeks with persistently severe but not worsened pulmonary hypertension. Case 2 is a 4-month-old term male with compound heterozygous SLC25A26 mutation and severe pulmonary hypertension. Initial cardiac catheterization showed PVRi 28.2 WU*m2. After uptitration of sildenafil, bosentan, and IV treprostinil, serial echocardiograms continued to demonstrate near-systemic pulmonary hypertension. He failed multiple attempts to wean off typical doses of iNO (10-20 ppm) over the following weeks with tachypnea, hypoxemia, and worsening pulmonary hypertension on echocardiogram despite continued aggressive combination targeted therapy. After a 24-h sildenafil washout, he was initiated and uptitrated on riociguat with concomitant, successful wean of nitric oxide over one week that was well tolerated. No serious adverse effects in the titration period were observed.

CONCLUSION

Riociguat may be considered as an adjuvant therapeutic agent in selected children with severe PAH who are poorly responsive to sildenafil therapy and unable to wean from iNO.

Runcaciguat, a novel soluble guanylate cyclase activator, shows renoprotection in hypertensive, diabetic, and metabolic preclinical models of chronic kidney disease

Chronic kidney diseaQueryse (CKD) is associated with oxidative stress which can interrupt the nitric oxide (NO)/soluble guanylyl cyclase (sGC) signaling and decrease cyclic guanosine monophosphate (cGMP) production. Low cGMP concentrations can cause kidney damage and progression of CKD. The novel sGC activator runcaciguat targets the oxidized and heme-free form of sGC, restoring cGMP production under oxidative stress. The purpose of this study is to investigate if runcaciguat could provide an effective treatment for CKD. Runcaciguat was used for the treatment not only in rat CKD models with different etiologies and comorbidities, namely of hypertensive rats, the renin transgenic (RenTG) rat, and angiotensin-supplemented (ANG-SD) rat, but also in rats with diabetic and metabolic CKD, the Zucker diabetic fatty (ZDF) rat. The treatment duration was 2 to 42 weeks and runcaciguat was applied orally in doses from 1 to 10 mg/kg/bid. In these different rat CKD models, runcaciguat significantly reduced proteinuria (urinary protein to creatinine ratio; uPCR). These effects were also significant at doses which did not or only moderately decrease systemic blood pressure. Moreover, runcaciguat significantly decreased kidney injury biomarkers and attenuated morphological kidney damages. In RenTG rats, runcaciguat improved survival rates and markers of heart injury. These data demonstrate that the sGC activator runcaciguat exhibits cardio-renal protection at doses which did not reduce blood pressure and was effective in hypertensive as well as diabetic and metabolic CKD models. These data, therefore, suggest that runcaciguat, with its specific mode of action, represents an efficient treatment approach for CKD and associated CV diseases.

Update on Medical Management of Pulmonary Arterial Hypertension

Pulmonary arterial hypertension is a rare disease characterized by pulmonary microvasculature remodeling leading to right ventricular failure and death. Medical management of pulmonary hypertension has grown increasingly complex as more therapeutic agents have been developed. Evolving treatment strategies leveraging the endothelin, nitric oxide, and prostacyclin pathways lead to improved exercise capacity and outcomes in patients; however, significant opportunities for advancement remain.

Repurposing Riociguat to Target a Novel Paracrine Nitric Oxide-TRPC6 Pathway to Prevent Podocyte Injury

Increased expression and activity of the Ca²⁺ channel transient receptor potential channel 6 (TRPC6) is associated with focal segmental glomerulosclerosis, but therapeutic strategies to target TRPC6 are currently lacking. Nitric oxide (NO) is crucial for normal glomerular function and plays a protective role in preventing glomerular diseases. We investigated if NO prevents podocyte injury by inhibiting injurious TRPC6-mediated signaling in a soluble guanylate cyclase (sGC)-dependent manner and studied the therapeutic potential of the sGC stimulator Riociguat. Experiments were performed using human glomerular endothelial cells and podocytes. Podocyte injury was induced by Adriamycin incubation for 24 h, with or without the NO-donor S-Nitroso-N-acetyl-DL-penicillamine (SNAP), the sGC stimulator Riociguat or the TRPC6 inhibitor Larixyl Acetate (LA). NO and Riociguat stimulated cGMP synthesis in podocytes, decreased Adriamycin-induced TRPC6 expression, inhibited the Adriamycin-induced TRPC6-mediated Ca²⁺ influx and reduced podocyte injury. The protective effects of Riociguat and NO were blocked when sGC activity was inhibited with 1H-[1,2,4]Oxadiazolo[4,3-a]quinoxalin-1-one (ODQ) or when TRPC6 activity was inhibited by LA. Our data demonstrate a glomerular (e)NOS-NO-sGC-cGMP-TRPC6 pathway that prevents podocyte injury, which can be translated to future clinical use by, e.g., repurposing the market-approved drug Riociguat.

Haemodynamic effects of riociguat in CTEPH and PAH: a 10-year observational study

Background

Long-term treatment with riociguat has been shown to enhance exercise capacity in patients with pulmonary arterial hypertension (PAH) and inoperable or persistent/recurrent chronic thromboembolic pulmonary hypertension (CTEPH). This study sought to evaluate the long-term haemodynamic effects of riociguat in patients with PAH and inoperable CTEPH.

Methods

During this single-centre long-term observational study, riociguat was administered at a three-times-daily dose of up to 2.5 mg. The primary outcome was pulmonary vascular resistance (PVR). The secondary outcomes included mean pulmonary arterial pressure (PAP), cardiac index, mortality, clinical worsening events, 6-min walk distance (6MWD) and World Health Organization functional class (WHO FC).

Results

37 patients (CTEPH n=19; PAH n=18) were included. The median follow-up period was 96 months. The survival estimates for all the patients at 1/3/5/8 years were 0.97/0.86/0.72/0.61, without significant differences between patients with CTEPH and PAH. At the final data cut-off, PVR decreased (1232±462 dyn·s·cm^–5versus 835±348 dyn·s·cm^–5, p<0.001), cardiac index increased (1.7±0.4 L·min⁻¹·m⁻²versus 2.4±0.5 L·min⁻¹·m⁻², p<0.001), 6MWD increased by 43.1±59.6 m, and WHO FC improved/stabilised/worsened in 40%/35%/25% of patients versus baseline. Improvement in PAP was not shown. Compared with patients in WHO FC I/II and III/IV at baseline, the 8-year clinical worsening-free survival estimates were 0.51 versus 0.19 (p=0.026).

Conclusions

Riociguat improved PVR and cardiac index for up to 8 years, but not PAP. WHO FC may have certain predictive value for the long-term prognosis.

In patients with PAH and inoperable CTEPH, riociguat improved pulmonary vascular resistance and cardiac index for 8 years, but not pulmonary arterial pressure. World Health Organization functional class may have predictive value for long-term prognosis.https://bit.ly/3dTf4ft

Riociguat for the treatment of Phe508del homozygous adults with cystic fibrosis

BACKGROUND

Riociguat is a first-in-class soluble guanylate cyclase stimulator for which preclinical data suggested improvements in cystic fibrosis transmembrane conductance regulator (CFTR) function.

METHODS

This international, multicenter, two-part, Phase II study of riociguat enrolled adults with cystic fibrosis (CF) homozygous for Phe508del CFTR. Part 1 was a 28-day, randomized, double-blind, placebo-controlled study in participants not receiving CFTR modulator therapy. Twenty-one participants were randomized 1:2 to placebo or oral riociguat (0.5 mg three times daily [tid] for 14 days, increased to 1.0 mg tid for the subsequent 14 days). The primary and secondary efficacy endpoints were change in sweat chloride concentration and percent predicted forced expiratory volume in 1 second (ppFEV₁), respectively, from baseline to Day 14 and Day 28 with riociguat compared with placebo.

RESULTS

Riociguat did not alter CFTR activity (change in sweat chloride) or lung function (change in ppFEV₁) at doses up to 1.0 mg tid after 28 days. The most common drug-related adverse event (AE) was headache occurring in three participants (21%); serious AEs occurred in one participant receiving riociguat (7%) and one participant receiving placebo (14%). This safety profile was consistent with the underlying disease and the known safety of riociguat for its approved indications.

CONCLUSIONS

The Rio-CF study was terminated due to lack of efficacy and the changing landscape of CF therapeutic development. The current study⁠, within its limits of a small sample size, did not provide evidence that riociguat could be a valid treatment option for CF.

CLINICAL TRIAL REGISTRATION NUMBER

NCT02170025.

Riociguat: Clinical research and evolving role in therapy

Riociguat is a first-in-class soluble guanylate cyclase stimulator, approved for the treatment of adults with pulmonary arterial hypertension (PAH), inoperable chronic thromboembolic pulmonary hypertension (CTEPH), or persistent or recurrent CTEPH after pulmonary endarterectomy. Approval was based on the results of the phase III PATENT-1 (PAH) and CHEST-1 (CTEPH) studies, with significant improvements in the primary endpoint of 6-minute walk distance vs placebo of +36 m and +46 m, respectively, as well as improvements in secondary endpoints such as pulmonary vascular resistance and World Health Organization functional class. Riociguat acts as a stimulator of cyclic guanosine monophosphate synthesis rather than as an inhibitor of cGMP metabolism. As with other approved therapies for PAH, riociguat has antifibrotic, antiproliferative and anti-inflammatory effects, in addition to vasodilatory properties. This has led to further clinical studies in patients who do not achieve a satisfactory clinical response with phosphodiesterase type-5 inhibitors. Riociguat has also been evaluated in patients with World Health Organization group 2 and 3 pulmonary hypertension, and other conditions including diffuse cutaneous systemic sclerosis, Raynaud's phenomenon and cystic fibrosis. This review evaluates the results of the original clinical trials of riociguat for the treatment of PAH and CTEPH, and summarises the body of work that has examined the safety and efficacy of riociguat for the treatment of other types of pulmonary hypertension.

Chronic Obstructive Pulmonary Disease and the Cardiovascular System: Vascular Repair and Regeneration as a Therapeutic Target

Chronic obstructive pulmonary disease (COPD) is a major cause of morbidity and mortality worldwide and encompasses chronic bronchitis and emphysema. It has been shown that vascular wall remodeling and pulmonary hypertension (PH) can occur not only in patients with COPD but also in smokers with normal lung function, suggesting a causal role for vascular alterations in the development of emphysema. Mechanistically, abnormalities in the vasculature, such as inflammation, endothelial dysfunction, imbalances in cellular apoptosis/proliferation, and increased oxidative/nitrosative stress promote development of PH, cor pulmonale, and most probably pulmonary emphysema. Hypoxemia in the pulmonary chamber modulates the activation of key transcription factors and signaling cascades, which propagates inflammation and infiltration of neutrophils, resulting in vascular remodeling. Endothelial progenitor cells have angiogenesis capabilities, resulting in transdifferentiation of the smooth muscle cells via aberrant activation of several cytokines, growth factors, and chemokines. The vascular endothelium influences the balance between vaso-constriction and -dilation in the heart. Targeting key players affecting the vasculature might help in the development of new treatment strategies for both PH and COPD. The present review aims to summarize current knowledge about vascular alterations and production of reactive oxygen species in COPD. The present review emphasizes on the importance of the vasculature for the usually parenchyma-focused view of the pathobiology of COPD.

Higher susceptibility to heme oxidation and lower protein stability of the rare α1C517Yβ1 sGC variant associated with moyamoya syndrome

NO sensitive soluble guanylyl cyclase (sGC) plays a key role in mediating physiological functions of NO. Genetic alterations of the GUCY1A3 gene, coding for the α1 subunit of sGC, are associated with several cardiovascular dysfunctions. A rare sGC variant with Cys517 → Tyr substitution in the α1subunit, has been associated with moyamoya disease and achalasia. In this report we characterize the properties of this rare sGC variant. Purified α1C517Yβ1 sGC preserved only ~25% of its cGMP-forming activity and showed an elevated Km for GTP substrate. However, the mutant enzyme retained a high affinity for and robust activation by NO, similar to wild type sGC. Purified α1C517Yβ1 enzyme was more sensitive to specific sGC heme oxidizers and less responsive to heme reducing agents. When expressed in COS7 cells, α1C517Yβ1 sGC showed a much stronger response to cinaciguat or gemfibrozil, which targets apo-sGC or sGC with ferric heme, as compared to its NO response or the relative response of the wild type sGC. A stronger response to cinaciguat was also observed for purified α1C517Yβ1 in the absence of reducing agents. In COS7 cells, αCys517β sGC was less stable than the wild type enzyme under normal conditions and exhibited accelerated degradation upon induction of cellular oxidative stress. We conclude that diminished cGMP-forming activity of this sGC variant is aggravated by its high susceptibility to oxidative stress and diminished protein stability. The combination of these deficiencies contributes to the severity of observed moyamoya and achalasia symptoms in human carriers of this rare α1C517Yβ1 sGC variant.

Tracing the path of inhaled nitric oxide: Biological consequences of protein nitrosylation

Nitric oxide (NO) is a comprehensive regulator of vascular and airway tone. Endogenous NO produced by nitric oxide synthases regulates multiple signaling cascades, including activation of soluble guanylate cyclase to generate cGMP, relaxing smooth muscle cells. Inhaled NO is an established therapy for pulmonary hypertension in neonates, and has been recently proposed for the treatment of hypoxic respiratory failure and acute respiratory distress syndrome due to COVID-19. In this review, we summarize the effects of endogenous and exogenous NO on protein S-nitrosylation, which is the selective and reversible covalent attachment of a nitrogen monoxide group to the thiol side chain of cysteine. This posttranslational modification targets specific cysteines based on the acid/base sequence of surrounding residues, with significant impacts on protein interactions and function. S-nitrosothiol (SNO) formation is tightly compartmentalized and enzymatically controlled, but also propagated by nonenzymatic transnitrosylation of downstream protein targets. Redox-based nitrosylation and denitrosylation pathways dynamically regulate the equilibrium of SNO-proteins. We review the physiological roles of SNO proteins, including nitrosohemoglobin and autoregulation of blood flow through hypoxic vasodilation, and pathological effects of nitrosylation including inhibition of critical vasodilator enzymes; and discuss the intersection of NO source and dose with redox environment, in determining the effects of protein nitrosylation.

cGMP Signaling in Cardiovascular Diseases: Linking Genotype and Phenotype

Cyclic guanosine 3',5'-monophosphate (cGMP) is the key second messenger molecule in nitric oxide signaling. Its rapid generation and fate, but also its role in mediating acute cellular functions has been extensively studied. In the past years, genetic studies suggested an important role for cGMP in affecting the risk of chronic cardiovascular diseases, for example, coronary artery disease and myocardial infarction. Here, we review the role of cGMP in atherosclerosis and other cardiovascular diseases and discuss recent genetic findings and identified mechanisms. Finally, we highlight open questions and promising research topics.

NO-sensitive guanylyl cyclase in the lung

In the late 1960s, several labatories identified guanylyl cyclase (GC) as the cGMP-producing enzyme. Subsequently, two different types of GC were described that differed in their cellular localization. Primarily found in the cytosol, nitric oxide (NO)-sensitive guanylyl cyclase (NO-GC) acts as receptor for the signalling molecule NO, in contrast the membrane-bound isoenzyme is activated by natriuretic peptides. The lung compared with other tissues exhibits the highest expression of NO-GC. The enzyme has been purified from lung for biochemical analysis. Although expressed in smooth muscle cells (SMCs) and in pericytes, the function of NO-GC in lung, especially in pericytes, is still not fully elucidated. However, pharmacological compounds that target NO-GC are available and have been implemented for the therapy of pulmonary arterial hypertension. In addition, NO-GC has been suggested as drug target for the therapy of asthma, acute respiratory distress syndrome and pulmonary fibrosis.

Strategies for the management of pulmonary arterial hypertension in patients with congenital heart disease

Background

Pulmonary hypertension (PH) is commonly seen in adults who have congenital heart disease (CHD). Therapy is available for pulmonary arterial hypertension (PAH) and has greatly benefitted many patients with PAH related to CHD (PAH-CHD) over the last 15 years, with evidence of improved quality of life and prognosis in those with Eisenmenger syndrome and repaired PAH-CHD.

In this review, we describe the standard management and advanced therapies for PAH, which are available in specialist PH centres around the UK and Ireland, and how these are used in PAH-CHD. Decisions around the choice of therapy are governed by commissioning and available evidence.

Conclusion

We explain the different pathways for action and the variety of medications now at our disposal to help this important group of patients.

Stimulation of soluble guanylyl cyclase (sGC) by riociguat attenuates heart failure and pathological cardiac remodelling

BACKGROUND AND PURPOSE

Heart failure is associated with an impaired NO-soluble guanylyl cyclase (sGC)-cGMP pathway and its augmentation is thought to be beneficial for its therapy. We hypothesized that stimulation of sGC by the sGC stimulator riociguat prevents pathological cardiac remodelling and heart failure in response to chronic pressure overload.

EXPERIMENTAL APPROACH

Transverse aortic constriction or sham surgery was performed in C57BL/6N mice. After 3 weeks of transverse aortic constriction when heart failure was established, animals receive either riociguat or its vehicle for 5 additional weeks. Cardiac function was evaluated weekly by echocardiography. Eight weeks after surgery, histological analyses were performed to evaluate remodelling and the transcriptome of the left ventricles (LVs) was analysed by RNA sequencing. Cell culture experiments were used for mechanistically studies.

KEY RESULTS

Transverse aortic constriction resulted in a continuous decrease of LV ejection fraction and an increase in LV mass until week 3. Five weeks of riociguat treatment resulted in an improved LV ejection fraction and a decrease in the ratio of left ventricular mass to total body weight (LVM/BW), myocardial fibrosis and myocyte cross-sectional area. RNA sequencing revealed that riociguat reduced the expression of myocardial stress and remodelling genes (e.g. Nppa, Nppb, Myh7 and collagen) and attenuated the activation of biological pathways associated with cardiac hypertrophy and heart failure. Riociguat reversed pathological stress response in cultivated myocytes and fibroblasts.

CONCLUSION AND IMPLICATIONS

Stimulation of the sGC reverses transverse aortic constriction-induced heart failure and remodelling, which is associated with improved myocardial gene expression.

IRAG1 Deficient Mice Develop PKG1β Dependent Pulmonary Hypertension

PKGs are serine/threonine kinases. PKG1 has two isoforms-PKG1α and β. Inositol trisphosphate receptor (IP₃R)-associated cGMP-kinase substrate 1 (IRAG1) is a substrate for PKG1β. IRAG1 is also known to further interact with IP₃RI, which mediates intracellular Ca²⁺ release. However, the role of IRAG1 in PH is not known. Herein, WT and IRAG1 KO mice were kept under normoxic or hypoxic (10% O₂) conditions for five weeks. Animals were evaluated for echocardiographic variables and went through right heart catheterization. Animals were further sacrificed to prepare lungs and right ventricular (RV) for immunostaining, western blotting, and pulmonary artery smooth muscle cell (PASMC) isolation. IRAG1 is expressed in PASMCs and downregulated under hypoxic conditions. Genetic deletion of IRAG1 leads to RV hypertrophy, increase in RV systolic pressure, and RV dysfunction in mice. Absence of IRAG1 in lung and RV have direct impacts on PKG1β expression. Attenuated PKG1β expression in IRAG1 KO mice further dysregulates other downstream candidates of PKG1β in RV. IRAG1 KO mice develop PH spontaneously. Our results indicate that PKG1β signaling via IRAG1 is essential for the homeostasis of PASMCs and RV. Disturbing this signaling complex by deleting IRAG1 can lead to RV dysfunction and development of PH in mice.

The effect of Riociguat on cardiovascular function and efficiency in healthy, juvenile pigs

INTRODUCTION

Riociguat is a soluble guanylate cyclase stimulator approved for the treatment of pulmonary hypertension. Its effect on cardiometabolic efficiency is unknown. A potential cardiac energy sparing effect of this drug could imply a positive prognostic effect, particularly in patients with right heart failure from pulmonary hypertension.

METHOD

We infused Riociguat in six healthy juvenile pigs and measured the integrated cardiovascular effect and myocardial oxygen consumption. To assess the interplay with NO-blockade on cardiac function and efficiency we also administered the NO-blocker L- NAME to the animals after Riociguat.

RESULTS AND DISCUSSION

Infusion of 100 µg/kg Riociguat gave modest systemic vasodilatation seen as a drop in coronary and systemic vascular resistance of 36% and 26%, respectively. Right and left ventriculoarterial coupling index (Ees/Ea), stroke work efficiency (SWeff), and the relationship between left ventricular myocardial oxygen consumption (MVO₂ ) and total mechanical work (pressure-volume area; PVA) were unaffected by Riociguat. In contrast, systemic and pulmonary vasoconstriction induced by L-NAME (15 mg/kg) shifted the Ees/Ea ratio toward reduced SWeff in both systemic and pulmonary circulation. However, there was no surplus oxygen consumption, that was measured by the MVO₂ /PVA relationship after L-NAME in Riociguat-treated pigs. This suggests that Riociguat can reduce the NO-related cardiometabolic inefficiency previously observed by blocking the NO pathway.

Specific O-GlcNAc modification at Ser-615 modulates eNOS function

Idiopathic pulmonary arterial hypertension (IPAH) is a progressive and devastating disease characterized by vascular smooth muscle and endothelial cell proliferation leading to a narrowing of the vessels in the lung. The increased resistance in the lung and the higher pressures generated result in right heart failure. Nitric Oxide (NO) deficiency is considered a hallmark of IPAH and altered function of endothelial nitric oxide synthase (eNOS), decreases NO production. We recently demonstrated that glucose dysregulation results in augmented protein serine/threonine hydroxyl-linked N-Acetyl-glucosamine (O-GlcNAc) modification in IPAH. In diabetes, dysregulated glucose metabolism has been shown to regulate eNOS function through inhibition of Ser-1177 phosphorylation. However, the link between O-GlcNAc and eNOS function remains unknown. Here we show that increased protein O-GlcNAc occurs on eNOS in PAH and Ser-615 appears to be a novel site of O-GlcNAc modification resulting in reduced eNOS dimerization. Functional characterization of Ser-615 demonstrated the importance of this residue on the regulation of eNOS activity through control of Ser-1177 phosphorylation. Here we demonstrate a previously unidentified regulatory mechanism of eNOS whereby the O-GlcNAc modification of Ser-615 results in reduced eNOS activity and endothelial dysfunction under conditions of glucose dysregulation.

Riociguat in the Treatment of Chronic Thromboembolic Pulmonary Hypertension: An Evidence-Based Review of Its Place in Therapy

Chronic thromboembolic pulmonary hypertension (CTEPH) is classified as group-4 pulmonary hypertension caused by organized thrombi in pulmonary arteries and vasculopathy in nonoccluded areas leading to right heart failure and death. In addition to chronic anticoagulation therapy, each patient with CTEPH should receive treatment assessment starting with evaluation for pulmonary endarterectomy (PEA), which is the guideline recommended treatment. There is increasing experience with balloon pulmonary angioplasty (BPA) for inoperable patients; this option, like PEA, is reserved for specialized centers with expertise in this treatment method. Inoperable patients are candidates for targeted drug therapy. Riociguat remains the only approved medical therapy for CTEPH patients deemed inoperable or with persistent pulmonary hypertension after PEA. The role of riociguat therapy preoperatively or in tandem with BPA is currently under investigation. The purpose of this review is to evaluate the safety and efficacy of riociguat in the treatment of CTEPH.

Pulmonary vasodilation in acute pulmonary embolism - a systematic review

Acute pulmonary embolism is the third most common cause of cardiovascular death. Pulmonary embolism increases right ventricular afterload, which causes right ventricular failure, circulatory collapse and death. Most treatments focus on removal of the mechanical obstruction caused by the embolism, but pulmonary vasoconstriction is a significant contributor to the increased right ventricular afterload and is often left untreated. Pulmonary thromboembolism causes mechanical obstruction of the pulmonary vasculature coupled with a complex interaction between humoral factors from the activated platelets, endothelial effects, reflexes and hypoxia to cause pulmonary vasoconstriction that worsens right ventricular afterload. Vasoconstrictors include serotonin, thromboxane, prostaglandins and endothelins, counterbalanced by vasodilators such as nitric oxide and prostacyclins. Exogenous administration of pulmonary vasodilators in acute pulmonary embolism seems attractive but all come with a risk of systemic vasodilation or worsening of pulmonary ventilation-perfusion mismatch. In animal models of acute pulmonary embolism, modulators of the nitric oxide-cyclic guanosine monophosphate-protein kinase G pathway, endothelin pathway and prostaglandin pathway have been investigated. But only a small number of clinical case reports and prospective clinical trials exist. The aim of this review is to give an overview of the causes of pulmonary embolism-induced pulmonary vasoconstriction and of experimental and human investigations of pulmonary vasodilation in acute pulmonary embolism.

Pulmonary hypertension in chronic obstructive pulmonary disease

Even mild pulmonary hypertension (PH) is associated with increased mortality and morbidity in patients with chronic obstructive pulmonary disease (COPD). However, the underlying mechanisms remain elusive; therefore, specific and efficient treatment options are not available. Therapeutic approaches tested in the clinical setting, including long-term oxygen administration and systemic vasodilators, gave disappointing results and might be only beneficial for specific subgroups of patients. Preclinical studies identified several therapeutic approaches for the treatment of PH in COPD. Further research should provide deeper insight into the complex pathophysiological mechanisms driving vascular alterations in COPD, especially as such vascular (molecular) alterations have been previously suggested to affect COPD development. This review summarizes the current understanding of the pathophysiology of PH in COPD and gives an overview of the available treatment options and recent advances in preclinical studies. LINKED ARTICLES: This article is part of a themed issue on Risk factors, comorbidities, and comedications in cardioprotection. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v178.1/issuetoc.

Emerging Drug Classes and Their Potential Use in Hypertension

Despite the availability of multiple antihypertensive drugs targeting the different pathways implicated in its pathophysiology, hypertension remains poorly controlled worldwide, and its prevalence is increasing because of the aging of the population and the obesity epidemic. Although nonadherence to treatment contributes to uncontrolled hypertension, it is likely that not all the pathophysiological mechanisms are neutralized by the various classes of antihypertensive treatment currently available, and, the counter-regulatory mechanisms triggered by these treatments may decrease their blood pressure–lowering effect. The development of new antihypertensive drugs acting on new targets, with different modes of action, therefore, remains essential, to improve blood pressure control and reduce the residual burden of cardiovascular risks further. However, the difficulties encountered in the conception, development, costs, and delivery to the market of new classes of antihypertensive agents highlights the hurdles that must be overcome to release and to evaluate their long-term safety and efficacy for hypertension only, especially because of the market pressure of cheap generic drugs. New chemical entities with blood pressure–lowering efficacy are thus being developed more for heart failure or diabetic kidney disease, 2 diseases pathophysiologically associated with hypertension. These include dual angiotensin II receptor-neprilysin inhibitors, soluble guanylate cyclase stimulators, nonsteroidal dihydropyridine-based mineralocorticoid receptor antagonists, as well as sodium-glucose cotransporter 2 inhibitors. However, centrally acting aminopeptidase A inhibitors and endothelin receptor antagonists have a dedicated program of development for hypertension. All these emergent drug classes and their potential use in hypertension are reviewed here.

Clinical Pharmacokinetic and Pharmacodynamic Profile of Riociguat

Oral riociguat is a soluble guanylate cyclase (sGC) stimulator that targets the nitric oxide (NO)–sGC–cyclic guanosine monophosphate pathway with a dual mode of action: directly by stimulating sGC, and indirectly by increasing the sensitivity of sGC to NO. It is rapidly absorbed, displays almost complete bioavailability (94.3%), and can be taken with or without food and as crushed or whole tablets. Riociguat exposure shows pronounced interindividual (60%) and low intraindividual (30%) variability in patients with pulmonary arterial hypertension (PAH) or chronic thromboembolic pulmonary hypertension (CTEPH), and is therefore administered using an individual dose-adjustment scheme at treatment initiation. The half-life of riociguat is approximately 12 h in patients and approximately 7 h in healthy individuals. Riociguat and its metabolites are excreted via both renal (33–45%) and biliary routes (48–59%), and dose adjustment should be performed with particular care in patients with moderate hepatic impairment or mild to severe renal impairment (no data exist for patients with severe hepatic impairment). The pharmacodynamic effects of riociguat reflect the action of a vasodilatory agent, and the hemodynamic response to riociguat correlated with riociguat exposure in patients with PAH or CTEPH in phase III population pharmacokinetic/pharmacodynamic analyses. Riociguat has a low risk of clinically relevant drug interactions due to its clearance by multiple cytochrome P450 (CYP) enzymes and its lack of effect on major CYP isoforms and transporter proteins at therapeutic levels. Riociguat has been approved for the treatment of PAH and CTEPH that is inoperable or persistent/recurrent after surgical treatment.

A focus on riociguat in the treatment of pulmonary arterial hypertension

Current treatment of pulmonary arterial hypertension (PAH) targets three signalling pathways: the nitric oxide (NO) pathway, the endothelin pathway and the prostacyclin pathway. Riociguat is a soluble guanylate cyclase stimulator, acting via the NO pathway in a new way: unlike other common drugs targeting this pathway (eg tadalafil and sildenafil), riociguat acts independently of endogenous NO. This MiniReview focuses on PAH treatment with riociguat and on its advantages and disadvantages compared with other drugs targeting the NO pathway. In the PATENT-1 trial (NCT00810693), riociguat improved significantly the 6-minute walking distance in patients suffering from PAH, with a mean difference (MD) of 36 m compared with a placebo group. The results are comparable to those found for its competitors tadalafil (MD of 33 m) and sildenafil (MD of 50 m) in the PHIRST-1 trial (NCT00125918) and the SUPER-1 trial (NCT00644605). No obvious advantages were found regarding pharmacokinetic features and adverse events. In the RESPITE study (NCT02007629), patients with PAH with insufficient response to treatment with tadalafil or sildenafil were switched to riociguat. These results indicate that riociguat might be superior regarding efficacy to PDE-5 inhibitors in a patient group, where endogenous NO production might be insufficient. This finding was further examined in the REPLACE study (NCT02891850). Moreover, riociguat has shown promising anti-proliferative, anti-inflammatory and anti-fibrotic effects in animal models. Further investigations are needed to determine whether this applies also to human beings. Taken together, riociguat induces vasodilation of the pulmonary arteries and leads to an improvement in the ability to carry out physical activity.

Risk assessment in pulmonary arterial hypertension and chronic thromboembolic pulmonary hypertension

Background

Current pulmonary hypertension treatment guidelines recommend use of a risk stratification model encompassing a range of parameters, allowing patients to be categorised as low, intermediate or high risk. Three abbreviated versions of this risk stratification model were previously evaluated in patients with pulmonary arterial hypertension (PAH) in the French, Swedish and COMPERA registries. Our objective was to investigate the three abbreviated risk stratification methods for patients with mostly prevalent PAH and chronic thromboembolic pulmonary hypertension (CTEPH), in patients from the PATENT-1/2 and CHEST-1/2 studies of riociguat.

Methods

Risk was assessed at baseline and at follow-up in PATENT-1 and CHEST-1. Survival and clinical worsening-free survival were assessed in patients in each risk group/strata.

Results

With all three methods, riociguat improved risk group/strata in patients with PAH after 12 weeks. The French non-invasive and Swedish/COMPERA methods discriminated prognosis for survival and clinical worsening-free survival at both baseline and follow-up. Furthermore, patients achieving one or more low-risk criteria or a low-risk stratum at follow-up had a significantly reduced risk of death and clinical worsening compared with patients achieving no low-risk criteria or an intermediate-risk stratum. Similar results were obtained in patients with inoperable or persistent/recurrent CTEPH.

Conclusions

This analysis confirms and extends the results of the registry analyses, supporting the value of goal-oriented treatment in PAH. Further assessment of these methods in patients with CTEPH is warranted.

Riociguat improves risk group in patients with PAH and CTEPH according to three abbreviated versions of the ESC/ERS risk stratification model (results of a post hoc analysis)http://ow.ly/Herk30o8lKM

Long-term clinical value and outcome of riociguat in chronic thromboembolic pulmonary hypertension

Background

To improve clinical outcome, patients with inoperable and residual chronic thromboembolic pulmonary hypertension (CTEPH) can be treated with riociguat. The aim of this study is to explore long-term outcomes and to compare our 'real world' data with previous research.

Methods

We included all consecutive patients with technical inoperable and residual CTEPH, in whom riociguat therapy was initiated from January 2014 onwards, with patients followed till January 2019. Survival, clinical worsening (CW), functional class (FC), N-terminal pro brain natriuretic peptide (NT-proBNP) and 6-minute walking distance (6MWD) were described yearly after riociguat initiation.

Results

Thirty-six patients (50% female, mean age 64.9 ± 12.1 years, 54% WHO FC III/IV and 6MWD 337 ± 138 m could be included, with a mean follow-up of 2.3 ± 1.2 years. Survival and CW-free survival three years after initiation of riociguat were 94% and 78%, respectively. The 6MWD per 10 m at baseline was a significant predictor (HR 0.90 [0.83-0.97], p = 0.009) for CW. At three years follow-up the WHO FC and 6MWD improved and NT-proBNP decreased compared to baseline.

Conclusion

Our study confirms that riociguat is an effective treatment in patients with technical inoperable and residual CTEPH at long-term follow-up. Although our results are consistent with previous studies, more 'real world' research is necessary to confirm long-term results.

EXPRESS: Switching to riociguat: A potential treatment strategy for the management of CTEPH and PAH

Currently, five classes of drug are approved for the treatment of pulmonary arterial hypertension (PAH): phosphodiesterase 5 inhibitors (PDE5i); endothelin receptor antagonists; prostacyclin analogs; the IP receptor agonist selexipag; and the soluble guanylate cyclase (sGC) stimulator riociguat. For patients with inoperable or persistent/recurrent chronic thromboembolic pulmonary hypertension (CTEPH), riociguat is currently the only approved pharmacotherapy. Despite the development of evidence-based guidelines on appropriate use of specific drugs, in clinical practice patients are often prescribed PAH-targeted therapies off label or at inadequate doses.

PDE5i are the most often prescribed class of drugs as initial therapy, either alone or in combination with other drug classes. However, a proportion of patients receiving PAH therapies do not reach or maintain treatment goals. As PDE5i and riociguat target different molecules in the nitric oxide-sGC-cyclic guanosine monophosphate (NO-sGC-cGMP) signaling pathway, for patients with PAH without an initial or sustained response to PDE5i, there is a biological rationale for switching to riociguat. However, robust data from randomized controlled trials on the safety and efficacy of switching are lacking, as is formal guidance for clinicians. Here we review studies of sequential combination therapy, and trial data and case studies that have investigated switching between PAH-approved therapies, particularly from PDE5i to riociguat in patients with PAH with an insufficient response to PDE5i, and in patients with CTEPH who were receiving off-label treatment. These studies summarize the current evidence and practical real-life experience on the concept of switching treatments.

Diagnosis and treatment of pediatric pulmonary arterial hypertension

INTRODUCTION

Pediatric pulmonary arterial hypertension (PAH) remains a rare and severe disease with a poor prognosis. PAH may be idiopathic, heritable or associated with systemic conditions in particular associated with congenital heart disease. Areas covered: A thorough and extensive diagnostic approach is required for a correct diagnosis. The outcome has improved over the last decade with a better diagnostic approach and with the initiation of new targeted therapies. However, there is still significant progress to achieve as there is still no cure for this devastating disease. Expert opinion: Adapted clinical studies to define the best therapeutic approach are needed. Even if the treatment approach is still mainly derived from adult data and expert consensus, several studies and registries are currently underway and should deliver important information in the next future. This review aims to give an overview of the current diagnosis and treatment strategies of PAH.

Practical management of riociguat in patients with pulmonary arterial hypertension

Riociguat is one of several approved therapies available for patients with pulmonary arterial hypertension (PAH). Treatment should be initiated and monitored at an expert center by a physician experienced in treating PAH, and the dose adjusted in the absence of signs and symptoms of hypotension. In certain populations, including patients with hepatic or renal impairment, the elderly, and smokers, riociguat exposure may differ, and dose adjustments should therefore be made with caution according to the established scheme. Common adverse events are often easily managed, particularly if they are discussed before starting therapy. Combination therapy with riociguat and other PAH-targeted agents is feasible and generally well tolerated, although the coadministration of phosphodiesterase type 5 inhibitors (PDE5i) and riociguat is contraindicated. An open-label, randomized study is currently ongoing to assess whether patients who do not achieve treatment goals while receiving PDE5i may benefit from switching to riociguat. In this review, we provide a clinical view on the practical management of patients with PAH receiving riociguat, with a focus on the opinions and personal experience of the authors. The reviews of this paper are available via the supplemental material section.

Methods of Pharmacological Treatment of Chronic Thromboembolic Pulmonary Hypertension Current Approaches to the Patients Management

In this paper we have discussed epidemiology, pathogenesis, and approaches to treatment of chronic thromboembolic pulmonary hypertension (CTEPH). CTEPH is a unique potentially curable form of pulmonary hypertension. The gold standard of CTEPH treatment is pulmonary thromboendarterectomy. However, about 40% of patients with CTEPH are inoperable due to distal surgically inaccessible lesions of the pulmonary vasculature, severe hemodynamic impairments, or other contraindications. In addition, nearly half of patients have persistent or recurrent pulmonary hypertension following surgery. Current guidelines support the use of pharmacotherapy in these patients. In the article we have presented results of main clinical studies of targeted drugs therapy (endothelin receptor antagonists, prostanoids, phosphodiesterase type 5 inhibitors, soluble guanylate cyclase stimulators) of patients with CTEPH. The only drug that has demonstrated robust clinical efficacy in terms of improvment hemodynamic parameters, exercise capacity and patients' quality of life is the stimulator of the soluble guanylate cyclase riociguat. The efficacy and safety of riociguat have been investigated in short-term and long-term studies with follow-up up to 6 years. Results of these studies have constituted the basis forits approval by the regulatory authorities of more than 50 countries for the treatment of inoperable CTEPH and persistent or recurrent CTEPH after pulmonary thromboendarterectomy. In the European Union, USA and many other countries, riociguat is the only pharmacological agent approved for these indications.

Characterization and regulation of wild-type and mutant TASK-1 two pore domain potassium channels indicated in pulmonary arterial hypertension

Key points

The TASK‐1 channel gene (KCNK3) has been identified as a possible disease‐causing gene in heritable pulmonary arterial hypertension (PAH).

In the present study, we show that novel mutated TASK‐1 channels, seen in PAH patients, have a substantially reduced current compared to wild‐type TASK‐1 channels.

These mutated TASK‐1 channels are located at the plasma membrane to the same degree as wild‐type TASK‐1 channels.

ONO‐RS‐082 and alkaline pH 8.4 both activate TASK‐1 channels but do not recover current through mutant TASK‐1 channels.

We show that the guanylate cyclase activator, riociguat, a novel treatment for PAH, enhances current through TASK‐1 channels but does not recover current through mutant TASK‐1 channels.

Abstract

Pulmonary arterial hypertension (PAH) affects ∼15–50 people per million. KCNK3, the gene that encodes the two pore domain potassium channel TASK‐1 (K2P3.1), has been identified as a possible disease‐causing gene in heritable PAH. Recently, two new mutations have been identified in KCNK3 in PAH patients: G106R and L214R. The present study aimed to characterize the functional properties and regulation of wild‐type (WT) and mutated TASK‐1 channels and determine how these might contribute to PAH and its treatment. Currents through WT and mutated human TASK‐1 channels transiently expressed in tsA201 cells were measured using whole‐cell patch clamp electrophysiology. Localization of fluorescence‐tagged channels was visualized using confocal microscopy and quantified with in‐cell and on‐cell westerns. G106R or L214R mutated channels were located at the plasma membrane to the same degree as WT channels; however, their current was markedly reduced compared to WT TASK‐1 channels. Functional current through these mutated channels could not be restored using activators of WT TASK‐1 channels (pH 8.4, ONO‐RS‐082). The guanylate cyclase activator, riociguat, enhanced current through WT TASK‐1 channels; however, similar to the other activators investigated, riociguat did not have any effect on current through mutated TASK‐1 channels. Thus, novel mutations in TASK‐1 seen in PAH substantially alter the functional properties of these channels. Current through these channels could not be restored by activators of TASK‐1 channels. Riociguat enhancement of current through TASK‐1 channels could contribute to its therapeutic benefit in the treatment of PAH.

The TASK‐1 channel gene (KCNK3) has been identified as a possible disease‐causing gene in heritable pulmonary arterial hypertension (PAH).

In the present study, we show that novel mutated TASK‐1 channels, seen in PAH patients, have a substantially reduced current compared to wild‐type TASK‐1 channels.

These mutated TASK‐1 channels are located at the plasma membrane to the same degree as wild‐type TASK‐1 channels.

ONO‐RS‐082 and alkaline pH 8.4 both activate TASK‐1 channels but do not recover current through mutant TASK‐1 channels.

We show that the guanylate cyclase activator, riociguat, a novel treatment for PAH, enhances current through TASK‐1 channels but does not recover current through mutant TASK‐1 channels.

A Randomized, Placebo-Controlled, Multiple-Ascending-Dose Study to Assess the Safety, Tolerability, Pharmacokinetics, and Pharmacodynamics of the Soluble Guanylate Cyclase Stimulator Praliciguat in Healthy Subjects

Nitric oxide (NO)-soluble guanylate cyclase (sGC)-cyclic guanosine monophosphate (cGMP) signaling is central to the regulation of several physiological processes, including blood flow and inflammation. Deficient NO signaling is implicated in multiple diseases. sGC stimulators are small molecules that enhance sGC activity, particularly in combination with NO. In a randomized, placebo-controlled phase 1 study, the safety, tolerability, pharmacokinetics, and pharmacodynamics of multiple ascending doses of the sGC stimulator praliciguat were assessed in 44 healthy adults. Four cohorts of 11 subjects (8 praliciguat, 3 placebo) received once-daily praliciguat for 14 days before up-titrating for 7 days (treatment sequences: 15/30 mg, 20/40 mg, 30/40 mg, and weight-based). All doses were tolerated. No serious or severe adverse events (AEs) were reported. The most common AEs in praliciguat recipients were headache and symptoms consistent with blood pressure (BP) lowering/vasodilation. There were no laboratory, vital sign, electrocardiographic, or platelet function findings indicative of a safety concern. Pharmacokinetics were dose proportional, with an effective half-life of 24-37 hours, supporting once-daily dosing. Praliciguat produced dose-related increases in plasma cGMP consistent with stimulation of sGC. Repeated once-daily dosing showed sustained decreases in BP. Results support evaluation of praliciguat for the treatment of conditions associated with deficient NO signaling.

Cyclic nucleotide-dependent inhibitory signaling interweaves with activating pathways to determine platelet responses

Platelets are regulated by extracellular cues that impact on intracellular signaling. The endothelium releases prostacyclin and nitric oxide which stimulate the synthesis of cyclic nucleotides cAMP and cGMP leading to platelet inhibition. Other inhibitory mechanisms involve immunoreceptor tyrosine-based inhibition motif-containing receptors, intracellular receptors and receptor desensitization. Inhibitory cyclic nucleotide pathways are traditionally thought to represent a passive background system keeping platelets in a quiescent state. In contrast, cyclic nucleotides are increasingly seen to be dynamically involved in most aspects of platelet regulation. This review focuses on crosstalk between activating and cyclic nucleotide-mediated inhibitory pathways highlighting emerging new hub structures and signaling mechanisms. In particular, interactions of plasma membrane receptors like P2Y12 and GPIb/IX/V with the cyclic nucleotide system are described. Furthermore, differential regulation of the RGS18 complex, second messengers, protein kinases, and phosphatases are presented, and control over small G-proteins by guanine-nucleotide exchange factors and GTPase-activating proteins are outlined. Possible clinical implications of signaling crosstalk are discussed.