Effect of Dual Endothelin Receptor Antagonist on a Retinal Degeneration Animal Model by Regulating Choroidal Microvascular Morphology

Objective. Clinical studies have found that increasing levels of plasma endothelin-1 (ET-1) might inhibit choroidal blood flow (BF) and promote choroidal vasoconstriction. This study was designed to investigate ET-1 levels and its effect on choroidal microvascular morphology in a retinitis pigmentosa (RP) animal model. Methods. Mice with retinal degeneration (rd10) were intragastrically administered bosentan, a dual endothelin receptor antagonist. We detected plasma ET-1 levels using an enzyme-linked immunosorbent assay (ELISA) kit at P14, P21, and P28 and evaluated ET-1 expression in RPE/choroid/sclera complexes using western blot and whole mount immunofluorescence staining at P28. Retinal thickness was measured using hematoxylin and eosin (H&E) staining at P28. At the same time, we also estimated choroidal microvascular densities using vascular luminal casting with a scanning electron microscope (SEM). Results. Plasma ET-1 levels were increased significantly in rd10 mice at P21 (65.48 ± 24.83 pg/ml) and P28 (85.89 ± 20.23 pg/ml) compared with C57BL/6J mice at P21 (33.52 ± 16.33 pg/ml) and P28 (42.38 ± 17.53 pg/ml); the expression of ET-1 was also upregulated in RPE/choroid/sclera complexes at P28. Bosentan inhibited ET-1 expression in plasma ( P < 0.05 ) and RPE/choroid/sclera complexes at P28 in rd10 mice. Choroidal microvascular densities were decreased in rd10 mice, and bosentan could weaken these changes. Conclusion. Plasma and local ET-1 was elevated in an animal model of RP, suggesting that it likely participates in the pathological progression of retinal degeneration and may thus provide a new intervention target. ET-1 blockade might exert its protective effect by elevating choroidal microvascular density via inhibition of ET-1.

Adolescents and adults with Fontan circulation: insights from the PREpArE-Fontan registry

The Patient Registry for Adolescents and Adults with Stable Fontan Circulation aims to describe a contemporary cohort of Fontan patients who could be eligible for a clinical trial investigating macitentan, an endothelin receptor antagonist. This international, non-interventional, multicentre, cross-sectional, observational registry enrolled patients with “stable” Fontan circulation ≥10 years following extra-cardiac conduit or lateral tunnel procedure. Main exclusion criteria were NYHA functional class IV, reoperation of Fontan circulation, or signs of disease worsening. Patient characteristics at enrolment are described; available data were collected during a single registration visit. Of the 266 screened patients, 254 were included in this analysis. At enrolment, median (interquartile range) age was 24 (20;30) years, 37%/63% of patients were from the USA/Europe, 54% were male, 54%/47% had undergone extra-cardiac conduit/lateral tunnel procedures, and 95% were in NYHA functional class I or II. History of arrhythmia was more common in older patients and patients with lateral tunnel; overall prevalence was 19%. Most laboratory values were within the normal range but mean creatinine clearance was abnormally low (87.7 ml/min). Angiotensin-converting enzyme inhibitors were used by 48% of patients and their use was associated with creatinine clearance <90 ml/min (p = 0.007), as was Fontan completion at an older age (p = 0.007). 53.4% of patients had clinical characteristics that could potentially meet an endothelin receptor antagonist trial’s eligibility criteria. The PREpArE-Fontan registry describes a cohort of patients who could potentially participate in an endothelin receptor antagonist trial and identified early subtle signs of Fontan failure, even in “stable” patients.

A clinical comparison of an endothelin receptor antagonist and phosphodiesterase-5 inhibitors for treating digital ulcers of systemic sclerosis

Objectives To assess the efficacy of an endothelin receptor antagonist (ERA) and phosphodiesterase-5 inhibitors (PDE5i) for treating systemic sclerosis (SSc)-related digital ulcers (DUs). Methods This prospective, multicenter, observational cohort study recruited patients with active SSc-related DUs from 13 medical centers in South Korea. The primary outcome was time to cardinal ulcer (CU) healing. Secondary outcomes included time to new DU occurrence. Patients were followed up 4, 8, 12, and 24 weeks after treatment initiation. Results Sixty-three patients were analyzed. Their mean age was 49.9 ± 11.4 years and 49 were female. Twenty-eight had limited SSc. Forty-nine patients received the ERA, 11 patients received a PDE5i (nine sildenafil, one udenafil, and one tadalafil), and three patients received other medication. The hazard ratio (HR) for time to CU healing in the ERA group versus the PDE5i group was 0.75 (95% CI: 0.35–1.64, p = 0.47) in an unadjusted model and 0.80 (95% CI: 0.36–1.78, p = 0.59) in a model adjusted for age, sex, use of calcium channel blockers (CCBs), total DU numbers, and initial CU area. The HR for new DU development in the ERA group versus the PDE5i group was 0.39 (95% CI: 0.16–0.93, p = 0.03) in an unadjusted model and 0.32 (95% CI: 0.13–0.81, p = 0.02) in an adjusted model. No patients receiving CCBs developed new DUs at 24 weeks. Conclusion Time to CU healing is comparable for ERA and PDE5i. An ERA is more effective in reducing new DU occurrence than PDE5i. CCBs may be effective as a background medication.

Absorption, Distribution, Metabolism, and Excretion of Aprocitentan, a Dual Endothelin Receptor Antagonist, in Humans

Background: Aprocitentan is an orally active, dual endothelin receptor antagonist that may offer a new therapeutic option for the treatment of difficult-to-control hypertension. Objective: To investigate safety, tolerability, mass balance, absorption, distribution, metabolism, and excretion of aprocitentan. Methods: : In this single-center, open-label study a single oral dose of 25 mg containing 3.7 MBq of 14C-radiolabeled aprocitentan was administered to 6 healthy male subjects to investigate safety, tolerability, mass balance, absorption, distribution, metabolism, and excretion of aprocitentan. Metabolites were identified using mass spectrometry and, where possible, confirmed and quantified with reference compounds. Results: Aprocitentan was well tolerated and there were no clinically significant findings for any safety variable. The geometric mean cumulative recovery of radioactivity from urine and feces over 14 days was 77% of the administered radioactive dose, with 52.1% cumulative recovery from urine, and 24.8% from feces. Concentrations of total radioactivity in whole blood were markedly lower compared to plasma. In plasma, 94.3% of total radioactivity was aprocitentan. In urine and feces, 5 and 2, respectively (in feces one being aprocitentan) main products were identified. Metabolism data of aprocitentan identified two main elimination pathways, glucosidation to M3 and hydrolysis to M1, representing approximately 25% and 32% of the radioactive dose, respectively. Conclusions: Based on these metabolism data, aprocitentan can be concomitantly administered without dose adjustment with drugs that are inhibitors or inducers of any metabolizing enzyme, specifically cytochrome P450 enzymes.

NT-proBNP (N-terminal prohorne of brain natriuretic peptide) as an early marker for detection of response to endothelin receptor antagonist in pulmonary arterial hypertension patients

Background Endothelin receptor antagonist (ERA) is well-established for targeted therapy of pulmonary arterial hypertension (PAH). According to the guidelines, comprehensive evaluation of responses to PAH-targeted therapy is recommended 3 to 6 months after treatment onset. Early detection of response to ERA after starting new treatment may be of clinical value to establish next therapeutic plan. Purpose We sought to investigate whether NT-proBNP plays a reliable role for early maker of responses to ERA in PAH patients. Methods Sixty four patients (age &gt;19 years old) with a confirmatory diagnosis of PAH were enrolled who were treated with ERA (bosentan or macitentan) in two tertially PAH experts centers. NT-proBNP measurements were performed at baseline, 1 month and 6 months after ERA treatment. Clinical characteristics including WHO functional class, laboratory test, and echocardiographic results were systematically collected. Result Sixty four patients were finally analyzed who completed the 6 months of follow-up. Etiology of PAH was as follows: idiopathic PAH (n=25), connective tissue disease associated PAH (n=16) and congenital heart disease assocciated PAH (n=24). Mean age was 50±15 years-old and female were predominant (75%). NTproBNP level was changed from 703pg/ml [207–2748] at baseline, 301 pg/ml [126–1314] at 1 month and 297pg/ml [106–901] at 6 months after ERA treatment. Although, NT proBNP level in overall population was significantly decreased after ERA treatment, NT proBNP level before treatment showed poor correlation with those at 6 months (R2=0.32). However, change of NT proBNP at 1 month from baseline showed strongly correlated with change of NT proBNP at 6 months from baseline with linear regression model analysis (R2 =0.90, p&lt;0.001). Conclusions Assessment of early change in nt-proBNP with only a month of treatment is associated with midterm response to ERA treatment in PAH. It can help to early decision making for early intensive therapy and rapid escalation of PAH medication in non-responsive PAH patients for initial therapy. The relationship of BNP Funding Acknowledgement Type of funding source: Private company. Main funding source(s): Handok

The Endothelin Receptor Antagonist Macitentan Ameliorates Endothelin-Mediated Vasoconstriction and Promotes Neuroprotection of Retinal Ganglion Cells in Rats

PurposeTo determine if dietary administration of the dual ETA/ ETB receptor antagonist, macitentan, could protect retinal ganglion cells (RGCs) following endothelin-1 (ET-1) mediated vasoconstriction in Brown Norway rats.MethodsAdult male and female Brown Norway rats were either untreated or treated with macitentan (5 mg/kg body weight) once a day for 3 days followed by intravitreal injection of either 4 μl of 500 μM ET-1 (2 nmole/eye) or vehicle in one eye. Imaging of the retinal vasculature using fluorescein angiography was carried out at various time points, including, 5, 10, 15, 25 and 30 minutes. Following the imaging of the vasculature, rats were either treated with macitentan (5 mg/kg/body weight in dietary gels) or untreated (control gels without medication). Following treatments, rats were euthanized, retinal flat mounts were prepared, immunostained for RGC marker Brn3a, imaged and surviving RGCs were counted in a masked manner.ResultsVasoconstrictive effects following intravitreal ET-1 injection were greatly reduced in rats administered with macitentan in the diet prior to the ET-1 administration. ET-1 intravitreal injection produced a 31% loss of RGCs which was significantly reduced in macitentan-treated rats. Following ET-1 administration, GFAP immunostaining was increased in the ganglion cell layer as well as in the retrolaminar region, suggestive of astrocytic activation by ET-1 administration. RGC numbers in macitentan treated and ET-1 injected rats were similar to that observed in control retinas.ConclusionsET-1-mediated neurodegeneration could occur through both vascular and cellular mechanisms. The endothelin receptor antagonist, macitentan, has neuroprotective effects in retinas of Brown Norway rats that occurs through different mechanisms, including, enhancement of RGC survival and reduction ET-1 mediated vasoconstriction.