Pharmacokinetic and pharmacodynamic evaluation of macitentan , a novel endothelin receptor antagonist for the treatment of pulmonary arterial hypertension

Study on the comparison between Bosentan and Macitentan in the treatment of persistent pulmonary hypertension of the newborns, simultaneously on sildenafil: A randomized double-blinded non-inferiority parallel clinical trial

BACKGROUND

Persistent Pulmonary Hypertension of the newborn (PPHN) is characterized by sustained elevated Pulmonary Artery Pressure (PAP). Drug resistance and the adverse effects of current therapeutic agents warrant investigation of other targeted therapies. Bosentan has shown benefits in affected neonates. However, trials reported the association with unwanted effects. Thus, in this study, we assess another agent in the same family, Macitentan. However, its efficacy in the treatment of PPHN is not yet reported. Hence, this study evaluated the effect of Macitentan compared to Bosentan in terms of efficacy and safety in the treatment of PPHN.

METHODS

This randomized, double-blinded non-inferiority clinical trial was conducted in Shahid Akbar Abadi hospital, Tehran, Iran. Sixty clinically stable neonates with signs suggestive of PPHN were randomly allocated into two groups (n = 30 in each group) and they received either Bosentan 1 mg/kg/dose BD (twice daily) or Macitentan 1 mg/kg/dose BD simultaneously with sildenafil. The echocardiographic and laboratory indices of efficacy and safety were compared between groups. SPAP (systolic pulmonary artery pressure) was used to assess the non-inferiority of the Macitentan compared to the Bosentan in their respective doses used in the study.

RESULTS

Participants' mean (SD) age was 3.53 (1.21) days, and 55% were female. No mortality case occurred. SPAP was reduced in both Bosentan and Macitenan groups with the mean difference in SPAP of 9 (95% CI: 7.34-10.65) in Bosentan and SPAP mean difference of 14 (95% CI: 12.12-15.86) in Macitentan group. Categorical comparison of primary outcome improvement showed that Macitentan was superior to Bosentan with a 10% non-inferiority margin. Similar results were obtained in other echocardiographic indices. Also, no significant alterations were observed in laboratory safety parameters.

CONCLUSION

Macitentan 1 mg/kg/dose BD (twice daily) is non-inferior to Bosentan 1 mg/kg/dose BD in improving echo outcomes of PPHN and it was even more effective in improving some of these. Also, it is non-inferior to Bosentan in terms of safety. TRIAL REGISTRY NUMBER: (IRCT20160120026115N9).

Long-term safety of macitentan in patients with pulmonary hypertension: A meta-analysis of randomised controlled trials

BACKGROUND

Macitentan has demonstrated its effectiveness in patients with pulmonary hypertension (PH), but its safety, especially for long-term use, needs to be further explored. This systematic review and meta-analysis aimed to determine the safety of long-term use of macitentan in patients with PH.

METHODS

A systematic search was made of PubMed, Embase, Cochrane Library and clinicaltrials.gov, without language restrictions. Randomised controlled trials (RCTs) on treatment of PH with macitentan, compared with placebo, were reviewed. Estimated effects of included studies were pooled as risk ratios (RRs), with 95% confidence intervals (CIs).

RESULTS

Six RCTs (enrolling 1003 participants) met the inclusion criteria. Anaemia (RR 3.86, 95% CI 2.05-7.30), headache (RR 1.52, 95% CI 1.02-2.26) and bronchitis (RR 2.24, 95% CI 1.30-3.87) were more frequent in the macitentan groups. There was no statistically significant difference in the proportion of patients with at least one adverse event (AE) or serious adverse event (SAE), AEs leading to discontinuation of study treatment, all-cause death, right ventricular failure (RVF) and peripheral oedema between the two groups.

CONCLUSIONS

The long-term use of macitentan is safe for patients with PH, although with a higher risk of anaemia, headache and bronchitis.

Endothelin Receptor Antagonists in Kidney Disease

Endothelin (ET) is found to be increased in kidney disease secondary to hyperglycaemia, hypertension, acidosis, and the presence of insulin or proinflammatory cytokines. In this context, ET, via the endothelin receptor type A (ET_A) activation, causes sustained vasoconstriction of the afferent arterioles that produces deleterious effects such as hyperfiltration, podocyte damage, proteinuria and, eventually, GFR decline. Therefore, endothelin receptor antagonists (ERAs) have been proposed as a therapeutic strategy to reduce proteinuria and slow the progression of kidney disease. Preclinical and clinical evidence has revealed that the administration of ERAs reduces kidney fibrosis, inflammation and proteinuria. Currently, the efficacy of many ERAs to treat kidney disease is being tested in randomized controlled trials; however, some of these, such as avosentan and atrasentan, were not commercialized due to the adverse events related to their use. Therefore, to take advantage of the protective properties of the ERAs, the use of ET_A receptor-specific antagonists and/or combining them with sodium-glucose cotransporter 2 inhibitors (SGLT2i) has been proposed to prevent oedemas, the main ERAs-related deleterious effect. The use of a dual angiotensin-II type 1/endothelin receptor blocker (sparsentan) is also being evaluated to treat kidney disease. Here, we reviewed the main ERAs developed and the preclinical and clinical evidence of their kidney-protective effects. Additionally, we provided an overview of new strategies that have been proposed to integrate ERAs in kidney disease treatment.

Endothelin-1 axes in the framework of predictive, preventive and personalised (3P) medicine

Endothelin-1 (ET-1) is involved in the regulation of a myriad of processes highly relevant for physical and mental well-being; female and male health; in the modulation of senses, pain, stress reactions and drug sensitivity as well as healing processes, amongst others. Shifted ET-1 homeostasis may influence and predict the development and progression of suboptimal health conditions, metabolic impairments with cascading complications, ageing and related pathologies, cardiovascular diseases, neurodegenerative pathologies, aggressive malignancies, modulating, therefore, individual outcomes of both non-communicable and infectious diseases such as COVID-19. This article provides an in-depth analysis of the involvement of ET-1 and related regulatory pathways in physiological and pathophysiological processes and estimates its capacity as a predictor of ageing and related pathologies,a sensor of lifestyle quality and progression of suboptimal health conditions to diseases for their targeted preventionand as a potent target for cost-effective treatments tailored to the person.

Clinical Pharmacology of Clazosentan, a Selective Endothelin A Receptor Antagonist for the Prevention and Treatment of aSAH-Related Cerebral Vasospasm

Aneurysmal subarachnoid hemorrhage (aSAH) may lead to cerebral vasospasm and is associated with significant morbidity and mortality. It represents a major unmet medical need due to few treatment options with limited efficacy. The role of endothelin-1 (ET-1) and its receptor ET_A in the pathogenesis of aSAH-induced vasospasm suggests antagonism of this receptor as promising asset for pharmacological treatment. Clazosentan is a potent ET_A receptor antagonist for intravenous use currently under development for the prevention of aSAH-induced cerebral vasospasm. The pharmacokinetics of clazosentan are characterized by an intermediate clearance, a volume of distribution similar to that of the extracellular fluid volume, dose-proportional exposure, an elimination independent of drug-metabolizing enzymes, and a disposition mainly dependent on the hepatic uptake transporter organic anion transport polypeptide 1B1/1B3. In healthy subjects, clazosentan leads to an increase in ET-1 concentration and prevents the cardiac and renal effects mediated by infusion of ET-1. In patients, it significantly reduced the incidence of moderate or severe vasospasm as well as post-aSAH vasospasm-related morbidity and mortality. Clazosentan is well tolerated up to the expected therapeutic dose of 15 mg/h and, in aSAH patients, lung complications, hypotension, and anemia were adverse events more commonly reported following clazosentan than placebo. In summary, clazosentan has a pharmacokinetic, pharmacodynamic, and safety profile suitable to become a valuable asset in the armamentarium of therapeutic modalities to prevent aSAH-induced cerebral vasospasm.

Macitentan in infants and children with pulmonary hypertensive vascular disease. Feasibility, tolerability and practical issues - a single-centre experience

Macitentan is a safe and effective substance for treatment of adults with pulmonary arterial hypertension. Data on its use in paediatric patients are limited. In this single-centre prospective study, we report on our experience with macitentan in children focusing on applicability and practical aspects. Between December 2014 and July 2018, macitentan was introduced to paediatric patients according to a dosing protocol adjusted to body weight. Blood pressure, heart rate, saturation and clinical symptoms were recorded daily during introduction. Liver function parameters and haemoglobin levels were measured at baseline, four weeks and three months after initiation and after one year of treatment. Twenty-four patients (14 male, 10 female) were enrolled for treatment with macitentan. The mean age was 10.7 ± 7.6 years (range: 0.1 year-23 years). Fifteen out of 24 patients were World Health Organization functional class (FC) II, 7 patients in FC III and 2 patients in FC IV. Twenty out of 24 patients (83%) received additional advanced therapy with sildenafil and/or prostacyclines. We had two early discontinuations because of clinical relevant oedema. In the remaining 22 patients, macitentan was well tolerated. Liver function parameters and blood count levels remained stable during the observational time. The introduction of macitentan was feasible and mostly well tolerated in paediatric patients. Special attention should be paid to oedema during introduction of the drug. To the best of our knowledge, this is the first study to report on its applicability in infants and children. However, larger prospective trials are warranted to verify these preliminary findings.

Endothelin Receptor Antagonists: Status Quo and Future Perspectives for Targeted Therapy

The endothelin axis, recognized for its vasoconstrictive action, plays a central role in the pathology of pulmonary arterial hypertension (PAH). Treatment with approved endothelin receptor antagonists (ERAs), such as bosentan, ambrisentan, or macitentan, slow down PAH progression and relieves symptoms. Several findings have indicated that endothelin is further involved in the pathogenesis of certain other diseases, making ERAs potentially beneficial in the treatment of various conditions. In addition to PAH, this review summarizes the use and perspectives of ERAs in cancer, renal disease, fibrotic disorders, systemic scleroderma, vasospasm, and pain management. Bosentan has proven to be effective in systemic sclerosis PAH and in decreasing the development of vasospasm-related digital ulcers. The selective ERA clazosentan has been shown to be effective in preventing cerebral vasospasm and delaying ischemic neurological deficits and new infarcts. Furthermore, in the SONAR (Study Of Diabetic Nephropathy With Atrasentan) trial, the selective ERA atrasentan reduced the risk of renal events in patients with diabetes and chronic kidney disease. These data suggest atrasentan as a new therapy in the treatment of diabetic nephropathy and possibly other renal diseases. Preclinical studies regarding heart failure, cancer, and fibrotic diseases have demonstrated promising effects, but clinical trials have not yet produced measurable results. Nevertheless, the potential benefits of ERAs may not be fully realized.

A network meta-analysis for safety of endothelin receptor antagonists in pulmonary arterial hypertension

Background

Currently, direct comparative safety between endothelin receptor antagonists (ERAs) in pulmonary arterial hypertension (PAH) is limited. Thus, a systematic review with network analysis was conducted.

Methods

An electronic search was performed for randomized controlled trials (RCTs) that reported the interested safety data (abnormal liver function, peripheral edema, and anemia) of ERAs in PAH. Risk ratios (RRs) with their confidence intervals (CIs) and the surface under the cumulative ranking curve (SUCRA) were calculated using a network analysis.

Results

Ten RCTs involving 2,288 patients were included. Compared with placebo, bosentan (RR, 2.93; 95% CI, 1.78-4.84) significantly increased the risk of abnormal liver function, ambrisentan (RR, 1.62; 95% CI, 1.23-2.13) significantly increased the risk of peripheral edema, and macitentan (RR, 3.42; 95% CI, 1.65-7.07) significantly increased the risk of anemia. SUCRA analysis suggested that bosentan 125 mg twice daily had the highest risk of abnormal liver function; ambrisentan 10 mg once daily had the highest risk of peripheral edema; macitentan 10 mg once daily had the highest risk of anemia.

Conclusions

Abnormal liver function (bosentan), peripheral edema (ambrisentan), and anemia (macitentan) were the safety indicators of ERAs in patients with PAH. Different monitoring parameters should be considered for individual ERA.

New drugs and emerging therapeutic targets in the endothelin signaling pathway and prospects for personalized precision medicine

During the last thirty years since the discovery of endothelin-1, the therapeutic strategy that has evolved in the clinic, mainly in the treatment of pulmonary arterial hypertension, is to block the action of the peptide either at the ET(A) subtype or both receptors using orally active small molecule antagonists. Recently, there has been a rapid expansion in research targeting ET receptors using chemical entities other than small molecules, particularly monoclonal antibody antagonists and selective peptide agonists and antagonists. While usually sacrificing oral bio-availability, these compounds have other therapeutic advantages with the potential to considerably expand drug targets in the endothelin pathway and extend treatment to other pathophysiological conditions. Where the small molecule approach has been retained, a novel strategy to combine two vasoconstrictor targets, the angiotensin AT(1) receptor as well as the ET(A) receptor in the dual antagonist sparsentan has been developed. A second emerging strategy is to combine drugs that have two different targets, the ET(A) antagonist ambrisentan with the phosphodiesterase inhibitor tadalafil, to improve the treatment of pulmonary arterial hypertension. The solving of the crystal structure of the ET(B) receptor has the potential to identify allosteric binding sites for novel ligands. A further key advance is the experimental validation of a single nucleotide polymorphism that has genome wide significance in five vascular diseases and that significantly increases the amount of big endothelin-1 precursor in the plasma. This observation provides a rationale for testing this single nucleotide polymorphism to stratify patients for allocation to treatment with endothelin agents and highlights the potential to use personalized precision medicine in the endothelin field.

Rivaroxaban and macitentan can be coadministered without dose adjustment but the combination of rivaroxaban and St John's wort should be avoided

AIMS

We assessed the potential mutual interaction of oral macitentan (cytochrome P450 (CYP) 3A4 substrate) at steady-state with single-dose oral rivaroxaban (CYP3A4 and P-glycoprotein substrate) and evaluated the effect of the CYP3A and P-glycoprotein inducer St John's wort (SJW) on the pharmacokinetics of these drugs in healthy volunteers.

METHODS

Twelve healthy volunteers completed this open-label, monocentre, two-period, one-sequence phase I clinical trial. The pharmacokinetics of macitentan (10 mg) was assessed on study days 3 (single dose), 15 (steady-state), 16 (impact of rivaroxaban) and 29 (after induction by oral SJW), and of rivaroxaban on days 2 (single dose), 16 (impact of macitentan at steady-state) and 29 (after induction by SJW). Concurrently, we quantified changes of CYP3A activity using oral microdoses of midazolam (30 μg).

RESULTS

Rivaroxaban and macitentan did not significantly change the pharmacokinetics of each other. After induction with SJW, CYP3A activity increased by 272% and geometric mean ratios of macitentan AUC decreased by 48% and of C_max by 45%. Concurrently, also geometric mean ratios of rivaroxaban AUC and C_max decreased by 25%.

CONCLUSIONS

There is no evidence for a relevant pharmacokinetic interaction between macitentan and rivaroxaban suggesting that these two drugs can be combined without dose adjustment. SJW strongly increased CYP3A activity and substantially reduced rivaroxaban and macitentan exposure while estimated net endothelin antagonism only decreased by 20%, which is considered clinically irrelevant. The combination of SJW with rivaroxaban should be avoided.

A Focus on Macitentan in the Treatment of Pulmonary Arterial Hypertension

The approval of macitentan has increased the number of pharmacological treatments of pulmonary arterial hypertension (PAH). Here, we review the effect on PAH of macitentan compared to other endothelin receptor antagonists. Drugs targeting the endothelin (ET) pathway include the selective ET_A receptor antagonist ambrisentan, the ET_A /ET_B receptor antagonists, bosentan and macitentan, which were recently approved for PAH treatment. Macitentan exhibits higher antagonistic potency than bosentan and ambrisentan in pulmonary smooth muscle cells. Compared to ambrisentan and bosentan, macitentan has a longer duration of action, reflected by the longer half-life, as well as pharmacodynamics attributed to its active metabolite, ACT-132577. The efficacy of macitentan on PAH was investigated in the phase III SERAPHIN trial (NCT00660179). Macitentan significantly reduced morbidity and mortality. It improved the 6-min. walk distance (6MWD) among PAH patients. In the AMB-320/321-E (NCT00578786) study, ambrisentan improved exercise capacity. In the EARLY study (NCT00091715), bosentan showed improvements in 6MWD which were not statistically significant. Bosentan had an effect on PAH in patients with Eisenmenger syndrome (ES) in the BREATHE-5 study (NCT00367770), while macitentan did not improve 6MWD in these patients, but there are differences regarding study size and functional class, and that 30% of the patients treated with macitentan were already in treatment with a phosphodiesterase type 5 inhibitor. Macitentan revealed a lower risk of developing peripheral oedema and hepatotoxicity in the SERAPHIN study. In summary, macitentan has an efficiency comparable to bosentan and ambrisentan in the treatment of PAH. Patients treated with macitentan exhibited less adverse effects compared to bosentan and ambrisentan. In patients with PAH associated with ES, the trials with bosentan and macitentan do not seem comparable, and it needs to be clarified whether these drugs are effective when administered as part of a combination treatment in this condition.

In Vitro Assessment of Pharmacokinetic Drug-Drug Interactions of Direct Oral Anticoagulants: Type 5-Phosphodiesterase Inhibitors Are Inhibitors of Rivaroxaban and Apixaban Efflux by P-Glycoprotein

Because of their lower bleeding risk and simplicity of use, direct oral anticoagulants (DOACs) could represent an interesting alternative to conventional anticoagulant treatment with vitamin K antagonists for patients with pulmonary arterial hypertension (PAH). P-glycoprotein (P-gp) plays a key role in DOAC pharmacokinetics. Type 5-phosphodiesterase inhibitors (PDE5is), a drug class commonly used in the treatment of PAH, have been shown to strongly inhibit P-gp. This work aimed to assess potential P-gp-mediated drug-drug interactions between PDE5is and DOACs using in vitro methods. A cellular model of drug transport assay, using P-gp-overexpressing Madin-Darby canine kidney cells (transfected with the human P-gp gene), was used to determine the bidirectional permeabilities of two DOACs (rivaroxaban and apixaban) in the absence and presence of increasing concentrations (0.5-100 µM) of three PDE5is (sildenafil, tadalafil, and vardenafil). Permeabilities and efflux ratios were calculated from DOAC concentrations, were measured with liquid chromatography coupled with mass spectrometry, and were subsequently used to determine the PDE5i percentage of inhibition and half maximal inhibitory concentration (IC₅₀ ). Rivaroxaban efflux was inhibited by 99%, 66%, and 100% with 100 µM sildenafil, tadalafil, and vardenafil, respectively. Similarly, apixaban efflux was inhibited by 97%, 74%, and 100%, respectively. The IC₅₀ values of the three PDE5is were 8, 28, and 5 µM for rivaroxaban and 23, 15, and 3 µM for apixaban, respectively. This study showed strong in vitro inhibition of DOAC efflux by PDE5is. In vivo studies are required to determine the clinical relevance of these interactions.

From the Cover: MechanisticInsights in Cytotoxic and Cholestatic Potential of the Endothelial Receptor Antagonists Using HepaRG Cells

Several endothelin receptor antagonists (ERAs) have been developed for the treatment of pulmonary arterial hypertension (PAH). Some of them have been related to clinical cases of hepatocellular injury (sitaxentan [SIT]) and/or cholestasis (bosentan [BOS]). We aimed to determine if ambrisentan (AMB) and macitentan (MAC), in addition to BOS and SIT, could potentially cause liver damage in man by use of human HepaRG cells. Our results showed that like BOS, MAC-induced cytotoxicity and cholestatic disorders characterized by bile canaliculi dilatation and impairment of myosin light chain kinase signaling. Macitentan also strongly inhibited taurocholic acid and carboxy-2',7'-dichlorofluorescein efflux while it had a much lower inhibitory effect on influx activity compared to BOS and SIT. Moreover, these three drugs caused decreased intracellular accumulation and parallel increased levels of total bile acids (BAs) in serum-free culture media. In addition, all drugs except AMB variably deregulated gene expression of BA transporters. In contrast, SIT was hepatotoxic without causing cholestatic damage, likely via the formation of reactive metabolites and AMB was not hepatotoxic. Together, our results show that some ERAs can be hepatotoxic and that the recently marketed MAC, structurally similar to BOS, can also cause cholestatic alterations in HepaRG cells. The absence of currently known or suspected cases of cholestasis in patients suffering from PAH treated with MAC is rationalized by the lower therapeutic doses and Cmax, and longer receptor residence time compared to BOS.

Functional estimation of endothelin-1 receptor antagonism by bosentan, macitentan and ambrisentan in human pulmonary and radial arteries in vitro

BACKGROUND

Endothelin receptor antagonists are approved for pulmonary arterial hypertension. Development of selective ET_A-receptor antagonists over mixed or dual receptor antagonists has depended on a range of receptor binding assays, second messenger assays and functional blood vessel assays. This study compared the 3 clinically-approved endothelin receptor antagonists in assays of human isolated pulmonary and radial arteries in vitro.

METHODS

Human isolated pulmonary (i.d. 5.5mm) and human radial (i.d. 3.23mm) artery ring segments were mounted in organ baths for isometric force measurement. Single concentration-contraction curves to endothelin-1 were constructed in the absence or presence of bosentan (1-10µM), macitentan (0.03-0.3µM) or ambrisentan (0.1-1µM).

RESULTS

All 3 endothelin antagonists caused competitive rightward shifts in the endothelin-1 concentration-response curves in both arteries. The Clark plot and analysis gave the following pK_B values: bosentan, pulmonary artery 6.28±0.13 and radial artery 6.04±0.10; macitentan, pulmonary artery 8.02±0.13 and radial artery 7.49±0.08; and ambrisentan, pulmonary artery 7.38±0.13 and radial artery 6.96±0.10.

CONCLUSIONS

Noting the maximum plasma levels attained from recommended oral doses of each antagonist in volunteers, the pK_B findings here show that there would be significant antagonism of endothelin-1 contraction in the pulmonary and radial arteries at therapeutic plasma levels. This functional assay confirms in human tissue that much higher plasma concentrations of endothelin-1 receptor antagonists are required to be effective than those predicted from binding or other biochemical assays.

Clinical Adverse Effects of Endothelin Receptor Antagonists: Insights From the Meta-Analysis of 4894 Patients From 24 Randomized Double-Blind Placebo-Controlled Clinical Trials

BACKGROUND

Evidence of the clinical safety of endothelin receptor antagonists (ERAs) is limited and derived mainly from individual trials; therefore, we conducted a meta-analysis.

METHODS AND RESULTS

After systematic searches of the Medline, Embase, and Cochrane Library databases and the ClinicalTrials.gov website, randomized controlled trials with patients receiving ERAs (bosentan, macitentan, or ambrisentan) in at least 1 treatment group were included. All reported adverse events of ERAs were evaluated. Summary relative risks and 95% CIs were calculated using random- or fixed-effects models according to between-study heterogeneity. In total, 24 randomized trials including 4894 patients met the inclusion criteria. Meta-analysis showed that the incidence of abnormal liver function (7.91% versus 2.84%; risk ratio [RR] 2.38, 95% CI 1.36-4.18), peripheral edema (14.36% versus 9.68%; RR 1.44, 95% CI 1.20-1.74), and anemia (6.23% versus 2.44%; RR 2.69, 95% CI 1.78-4.07) was significantly higher in the ERA group compared with placebo. In comparisons of individual ERAs with placebo, bosentan (RR 3.78, 95% CI 2.42-5.91) but not macitentan (RR 1.17, 95% CI 0.42-3.31) significantly increased the risk of abnormal liver function, whereas ambrisentan (RR 0.06, 95% CI 0.01-0.45) significantly decreased that risk. Bosentan (RR 1.47, 95% CI 1.06-2.03) and ambrisentan (RR 2.02, 95% CI 1.40-2.91) but not macitentan (RR 1.08, 95% CI 0.81-1.46) significantly increased the risk of peripheral edema. Bosentan (RR 3.09, 95% CI 1.52-6.30) and macitentan (RR 2.63, 95% CI 1.54-4.47) but not ambrisentan (RR 1.30, 95% CI 0.20-8.48) significantly increased the risk of anemia. ERAs were not found to increase other reported adverse events compared with placebo.

CONCLUSIONS

The present meta-analysis showed that the main adverse effects of treatment with ERAs were hepatic transaminitis (bosentan), peripheral edema (bosentan and ambrisentan), and anemia (bosentan and macitentan).

Efficacy and Safety of a Novel Endothelin Receptor Antagonist, Macitentan, in Japanese Patients With Pulmonary Arterial Hypertension

BACKGROUND

Macitentan is a novel, dual endothelin receptor antagonist with sustained receptor binding, used for the long-term treatment of pulmonary arterial hypertension (PAH). In the present study, we assessed the efficacy and safety of macitentan in Japanese patients with PAH.

METHODS AND RESULTS

Macitentan was administered at a once-daily dose of 10 mg in 30 patients. The primary endpoint was change in pulmonary vascular resistance (PVR) from baseline to week 24. Change to week 24 in the other hemodynamic parameters, 6-min walk distance (6MWD), World Health Organization (WHO) functional class, and plasmaN-terminal pro-brain natriuretic peptide (NT-pro-BNP), as well as time to clinical deterioration up to week 52 were also assessed as secondary endpoints. In the 28 patients on per-protocol analysis, PVR decreased from 667±293 to 417±214 dyn·sec·cm(-5)(P<0.0001). 6MWD increased from 427±128 to 494±116 m (P<0.0001). WHO functional class improved in 13 patients (46.4%) and was maintained in 15 patients (53.6%), and NT-pro-BNP was reduced by 18% (P<0.0001). The favorable treatment effect on PVR was apparent regardless of concomitant therapy for PAH.

CONCLUSIONS

Macitentan was efficacious and well tolerated and improved the hemodynamic parameters, exercise capacity, symptoms, and clinical biomarkers in Japanese PAH patients. Macitentan can be a valuable therapeutic option for Japanese patients with PAH. (

TRIAL REGISTRATION

JAPIC Clinical Trials Information [JapicCTI-121986].) (Circ J 2016; 80: 1478-1483).

Endothelin

The endothelins comprise three structurally similar 21-amino acid peptides. Endothelin-1 and -2 activate two G-protein coupled receptors, ETA and ETB, with equal affinity, whereas endothelin-3 has a lower affinity for the ETA subtype. Genes encoding the peptides are present only among vertebrates. The ligand-receptor signaling pathway is a vertebrate innovation and may reflect the evolution of endothelin-1 as the most potent vasoconstrictor in the human cardiovascular system with remarkably long lasting action. Highly selective peptide ETA and ETB antagonists and ETB agonists together with radiolabeled analogs have accurately delineated endothelin pharmacology in humans and animal models, although surprisingly no ETA agonist has been discovered. ET antagonists (bosentan, ambrisentan) have revolutionized the treatment of pulmonary arterial hypertension, with the next generation of antagonists exhibiting improved efficacy (macitentan). Clinical trials continue to explore new applications, particularly in renal failure and for reducing proteinuria in diabetic nephropathy. Translational studies suggest a potential benefit of ETB agonists in chemotherapy and neuroprotection. However, demonstrating clinical efficacy of combined inhibitors of the endothelin converting enzyme and neutral endopeptidase has proved elusive. Over 28 genetic modifications have been made to the ET system in mice through global or cell-specific knockouts, knock ins, or alterations in gene expression of endothelin ligands or their target receptors. These studies have identified key roles for the endothelin isoforms and new therapeutic targets in development, fluid-electrolyte homeostasis, and cardiovascular and neuronal function. For the future, novel pharmacological strategies are emerging via small molecule epigenetic modulators, biologicals such as ETB monoclonal antibodies and the potential of signaling pathway biased agonists and antagonists.