Endothelin Receptor Research Articles

Clinical adverse events to letairis: a real-world drug safety study based on FDA Adverse Event Reporting System (FAERS)

ABSTRACT Background Letairis (ambrisentan), an endothelin receptor antagonist (ERA), is a critical medication for pulmonary arterial hypertension (PAH). Despite its efficacy, its safety profile is under scrutiny, warranting a detailed analysis. Research design and methods This study leveraged the FDA Adverse Event Reporting System (FAERS) from Q1 2007 to Q4 2023, focusing on Letairis as the primary suspect in adverse events. Employing advanced data mining techniques, such as Reporting Odds Ratio (ROR), Proportional Reporting Ratio (PRR), Bayesian Confidence Propagation Neural Network (BCPNN), and Multi-item Gamma Poisson Shrinker (MGPS), the study aimed to uncover safety signals. Results A total of 43,774 cases were identified, with Letairis implicated in 16,038,963 adverse event reports. There was a notable predominance of female patients (75.30%), with a median age around 64 years. Severe outcomes, including hospitalization (51.63%) and fatalities (20.44%), were prevalent. Signal strength analysis highlighted concerns in infections and infestations, as well as cardiac disorders. Conclusion The analysis underscores the need for vigilant pharmacovigilance and highlights Letairis’s potential to induce serious AEs, particularly in female and elderly populations. These findings are instrumental in guiding clinical practice and future drug safety assessments.

Complex regulation of tau phosphorylation by the endothelin system in brain microvascular endothelial cells (BMVECs): link to barrier function.

Endothelin-1 (ET-1), the most potent vasoconstrictor identified to date, contributes to cerebrovascular dysfunction. ET-1 levels in postmortem brain specimens from individuals diagnosed with Alzheimer's disease (AD) and related dementias (ADRD) were shown to be related to cerebral hypoxia and disease severity. ET-1-mediated vascular dysfunction and ensuing cognitive deficits have also been reported in experimental models of AD and ADRD. Moreover, studies also showed that ET-1 secreted from brain microvascular endothelial cells (BMVECs) can affect neurovascular unit integrity in an autocrine and paracrine manner. Vascular contributions to cognitive impairment and dementia (VCID) is a leading ADRD cause known to be free of neuronal tau pathology, a hallmark of AD. However, a recent study reported cytotoxic hyperphosphorylated tau (p-tau) accumulation, which fails to bind or stabilize microtubules in BMVECs in VCID. Thus, the study aimed to determine the impact of ET-1 on tau pathology, microtubule organization, and barrier function in BMVECs. Cells were stimulated with 1 μM ET-1 for 24 h in the presence/absence of ETA (BQ123; 20 μM) or ETB (BQ788; 20 μM) receptor antagonists. Cell lysates were assayed for an array of phosphorylation site-specific antibodies and microtubule organization/stabilization markers. ET-1 stimulation increased p-tau Thr231 but decreased p-tau Ser199, Ser262, Ser396, and Ser214 levels only in the presence of ETA or ETB antagonism. ET-1 also impaired barrier function in the presence of ETA antagonism. These novel findings suggest that (1) dysregulation of endothelial tau phosphorylation may contribute to cerebral microvascular dysfunction and (2) the ET system may be an early intervention target to prevent hyperphosphorylated tau-mediated disruption of BMVEC barrier function.

Endothelin receptor B is required for the blood pressure-lowering effect of G protein-coupled estrogen receptor 1 in ovariectomized rats.

Activation of G protein-coupled estrogen receptor 1 (GPER1) elicits antihypertensive actions in different animal models. The endothelin-1 signaling system plays a fundamental role in blood pressure regulation. Lack of functional endothelin receptor B (ETB) evokes hypertension and salt sensitivity. GPER1 and ETB interact to promote urinary sodium excretion in female rats. We hypothesized that activation of GPER1 protects against hypertension and salt sensitivity induced by ETB antagonism in female rats. Female Sprague-Dawley rats were implanted with radiotelemetry. Animals were then subjected to ovariectomy and simultaneously implanted with minipumps to deliver either the GPER1 agonist G1 or its corresponding vehicle. Two weeks post surgery, we initiated treatment of rats with the ETB antagonist A-192621. Animals were maintained on a normal-salt diet and then challenged with a high-salt diet for an additional 5 days. Assessment of mean arterial blood pressure revealed an increase in vehicle-treated, but not G1-treated, rats in response to ovariectomy. A-192621 increased blood pressure in normal-salt diet-fed vehicle- and G1-treated rats. G1 improved the circadian blood pressure rhythms that were disrupted in A-192621-treated ovariectomized rats. Thus, although systemic GPER1 activation did not protect ovariectomized rats from hypertension and salt sensitivity induced by ETB antagonism, it maintained circadian blood pressure rhythms. Functional ETB is required to elicit the antihypertensive actions of GPER1. Additional studies are needed to improve our understanding of the interaction between G protein-coupled receptors in regulating circadian blood pressure rhythm.NEW & NOTEWORTHY Systemic G protein-coupled estrogen receptor 1 (GPER1) activation in rats prevents the increase in blood pressure evoked by ovariectomy. Blockade of endothelin receptor B negates the blood pressure-lowering impact of GPER1 in ovariectomized rats. Endothelin receptor B plays an important role in mediating the blood pressure-lowering action of GPER1 activation in female rats.

Urinary Clusterin as a Pharmacodynamic Response Biomarker for the Endothelin Receptor Antagonist Atrasentan

Urinary Clusterin as a Pharmacodynamic Response Biomarker for the Endothelin Receptor Antagonist Atrasentan

Formulation Optimization and Evaluation of Patented Solid Lipid Nanoparticles of Ambrisentan for Pulmonary Arterial Hypertension.

Ambrisentan is a new endothelin receptor antagonist extensively used to manage pulmonary or pulmonary arterial hypertension. The therapeutic efficacy of Ambrisentan is limited due to its reduced solubility, higher log P (3.4), and thus less bioavailability. The recent investigation was concentrated on the improvement of solubility, and bioavailability of Ambrisentan for the therapy of hypertension via solid lipid nanoparticles (SLN) administered orally. XRD evaluated the compatibility of Ambrisentan with lipids with FTIR, DSC, and crystalline nature. The SLN was developed by High-pressure homogenization method. The Glyceryl monostearate and Tween 80 indicated the highest solubility, hence selected. The optimization was performed with Box-Behnken Design considering the concentration of GMS (X1), Tween 80 (X2), stirring speed (X3) as independent factors and particle size (Y1), entrapment efficiency (Y2) as dependent factors. The Patents on the SLN are Indian 202321053691, U.S. Patent, 10,973,798B2, U.S. Patent 10,251,960B2, U.S. Patent 2021/0069121A1 and U.S. Patent 2022/0151945A1. The optimized batch F1 showed particle size (130 nm), ZP (-18.9 mV), and entrapment efficiency (85.73 %). The dual release pattern (prompt and sustained) was achieved with the SLNloaded Ambrisentan for about 24 hours. The lyophilized sample was subjected to SEM, which also revealed a spherical shape of a colloidal dispersion with a particle size of 126 nm. Hence, the F1 batch is highly recommended for solid oral delivery and also for the pilot-plant scale-up. A marked improvement in the solubility and dissolution of Ambrisentan was attained with the SLN. Moreover, the sustained delivery via the oral route enabled the patient's comfort, compliance, and therapeutic efficacy.

Study Design and Baseline Characteristics of ALIGN, a Randomized Controlled Study of Atrasentan in Patients With IgA Nephropathy

IntroductionEndothelin A (ETA) receptor activation is a driver of proteinuria, kidney inflammation and fibrosis in IgA nephropathy (IgAN). Atrasentan, a selective ETA receptor antagonist, has potential to reduce proteinuria and preserve kidney function in IgAN. ALIGN (NCT04573478) is a phase 3, randomized, double-blind, placebo-controlled clinical trial of atrasentan in patients with IgAN at high risk of kidney function loss. MethodsEligibility criteria for the ALIGN main stratum included patients with biopsy-proven IgAN, total protein excretion ≥1g/d, eGFR ≥30 mL/min/1.73m2, receiving a maximally-tolerated stable dose of a renin-angiotensin system inhibitor (RASi). An exploratory stratum enrolled participants also receiving a stable dose of sodium glucose cotransporter-2 inhibitors (SGLT2i). Participants were randomized to 0.75 mg atrasentan or placebo orally daily for 132 weeks followed by a 4-week wash-out period. The primary outcome is proteinuria change from baseline (24h urine protein–creatinine ratio UPCR) to Week 36 in the main stratum. Key secondary endpoints include eGFR change from baseline to Week 136, safety and tolerability. ResultsEnrolment occurred across 20 countries; 404 patients are randomized: 340 in the main stratum and 64 in the SGLT2i stratum. At baseline in the main stratum, mean age was 44.7 years, 42.4% were female, mean eGFR and median UPCR were 58.9 mL/min/1.73 m2 and 1.4 g/g, respectively. ConclusionThe ongoing ALIGN trial evaluates the efficacy and safety of atrasentan in a representative global IgAN population at risk for disease progression despite optimized RASi therapy and includes an exploratory stratum evaluating atrasentan use in combination with an SGLT2i.

Iron TAMs: The fallen protectors.

A new study by Folkert et al. (https://doi.org/10.1084/jem.20230420) defines an "iron-rich" subset of tumor-associated macrophages (iTAMs). The metabolism of heme leads to the degradation of the transcriptional repressor Bach1 and shapes the transcriptional profile of iTAMs. The endothelin receptor B in iTAMs signals tumor-supportive functions.

An iron-rich subset of macrophages promotes tumor growth through a Bach1-Ednrb axis.

We define a subset of macrophages in the tumor microenvironment characterized by high intracellular iron and enrichment of heme and iron metabolism genes. These iron-rich tumor-associated macrophages (iTAMs) supported angiogenesis and immunosuppression in the tumor microenvironment and were conserved between mice and humans. iTAMs comprise two additional subsets based on gene expression profile and location-perivascular (pviTAM) and stromal (stiTAM). We identified the endothelin receptor type B (Ednrb) as a specific marker of iTAMs and found myeloid-specific deletion of Ednrb to reduce tumor growth and vascular density. Further studies identified the transcription factor Bach1 as a repressor of the iTAM transcriptional program, including Ednrb expression. Heme is a known inhibitor of Bach1, and, correspondingly, heme exposure induced Ednrb and iTAM signature genes in macrophages. Thus, iTAMs are a distinct macrophage subset regulated by the transcription factor Bach1 and characterized by Ednrb-mediated immunosuppressive and angiogenic functions.

CGS-21680 defers cisplatin-induced AKI-CKD transition in C57/BL6 mice

Acute kidney injury (AKI), with a high mortality and morbidity, is known as a risk factor for developing progressive chronic kidney disease (CKD). Targeting transition of AKI to CKD displays an excellent therapeutic potential. This study aims at investigating the role of CGS-21680, selective A2AR agonist, in deferring Cis-induced AKI-CKD transition. The AKI-CKD transition model was induced in C57/BL6 mice by repeated low doses of Cis (2.5 mg/kg i.p for 5 consecutive days in two cycles with a recovery phase of 16 days between two cycles). CGS-21680 was administered daily for 6 weeks (0.1 mg/kg, i.p). Urine, blood, and kidney were collected at three different time points to track the disease progression. CGS-21680 administration preserved kidney function and attenuated tubular damage as evidenced by hematoxylin-eosin (H&E) histopathology. CGS-21680 significantly restored oxidative status as reflected by reduced malondialdehyde (MDA) content and increased total antioxidant capacity (TAC). CGS-21680 showed anti-inflammatory effect as indicated by decreased TNF-α and iNOS. Additionally, CGS-21680 ameliorated endothelial dysfunction and enhanced renal vasodilation as evidenced by upregulation of endothelial nitric oxide synthase (eNOS) and nitric oxide (NO) expression and down regulation of endothelin-1 (ET-1) and its receptor endothelin-A (ET-A) receptor expression. CGS-21680 also attenuated renal fibrosis as reflected by the reduction of percentage of fibrosis in Masson's trichome-stained renal sections and down regulation of transforming growth factor beta1 (TGF-β1) protein expression in IHC-stained renal sections. In conclusion, CGS-21680 could defer Cis-induced AKI-CKD transition via its vasodilatory, antioxidant, anti-inflammatory, and anti-fibrotic effects.

Right Ventricular Hypertrophy in Spontaneously Hypertensive Rats (SHR/NHsd) Is Associated with Inter-Individual Variations of the Pulmonary Endothelin System.

Spontaneously hypertensive rats (SHRs) develop severe hypertension and subsequently left ventricular hypertrophy. Whether they also develop right ventricular hypertrophy is not clear. We analyzed 76 female SHRs (strain SHR/NHsd) and observed severe right ventricular hypertrophy in 7% of these rats (SHR-RVH). Right ventricular hypertrophy did not correlate with the age of the rats and was already seen in one rat at the pre-hypertensive state. The current study investigated the molecular fingerprint of the lung and right ventricle from SHR-RVH and compared this first to SHRs that did develop left but not right ventricular hypertrophy, and second to normotensive rats without hypertrophy. Rats with right ventricular hypertrophy had a decreased expression of the endothelin-B receptor (EDNRB) in the lung, together with an increased protein content of endothelin-1 and an increased expression of ACTA2A. Furthermore, in the right ventricle, a down-regulation of the endothelin-A receptor (EDNRA) was found, consistent with a mild phenotype. The data suggest that in a sub-group of SHR/NHsd rats, low expression of the endothelin clearance receptor (endothelin-B receptor) in the lung triggers an increase in vascular resistance to the right ventricle that then triggers hypertrophy. Our study is the first description of a genetic variant in a defined SHR strain.

Macitentan and Tadalafil Combination Therapy in Incident and Prevalent Pulmonary Arterial Hypertension: Real-World Evidence from the OPUS/OrPHeUS Studies.

Historically, patients recently (≤6months) diagnosed with pulmonary arterial hypertension (PAH; incident) have had poorer survival than those with a longer (>6months) time from PAH diagnosis (prevalent). Despite guideline recommendations for initial combination therapy for most patients with PAH, many are initiated and maintained on monotherapy. Real-world evidence to evaluate the benefit of early combination treatment in newly-diagnosed patients is lacking. Patients with PAH initiating combination therapy with the endothelin receptor antagonist macitentan and the phosphodiesterase-5 inhibitor tadalafil (M+T) were identified from the combined dataset of the US, multicenter OPUS (prospective, observational drug registry; NCT02126943) and OrPHeUS (retrospective, medical chart review; NCT03197688) studies (2013-2020). Descriptive analyses were performed for the incident and prevalent cohorts, as well as the subcohort of incident patients who received M+T as first-line combination therapy (incident initial combination). In OPUS/OrPHeUS, 1336 patients with PAH received M+T during the observation period. For the incident [n=453 (33.9%)], incident initial combination [n=272 (20.4%)], and prevalent [n=837 (62.6%)] cohorts: median (Q1, Q3) M+T exposure was 14.2 (4.2, 27.5), 12.2 (3.2, 25.5), and 14.7 (4.5, 28.0) months. 12-month Kaplan-Meier estimates (95% confidence limits) for survival were 91.2% (87.7, 93.7), 88.5% (83.2, 92.2), and 92.9% (90.6, 94.6), for patients free from hospitalization were 59.4% (54.1, 64.4), 56.3% (49.1, 62.9), and 62.3% (58.5, 65.9), and for patients persisting on combination therapy were 68.6% (63.9, 72.8), 65.0% (58.8, 70.6) and 66.9% (63.5, 70.0). Adverse events (OPUS only) were reported in 77.8%, 80.2%, and 80.3% of patients, respectively, with no unexpected adverse events observed. Despite a historically worse prognosis, incident patients receiving M+T, including as initial combination therapy, had similar survival and hospitalization as prevalent patients. Safety profiles were similar across cohorts. Together, these data support the use of early combination therapy with macitentan and tadalafil.

Early Addition of Selexipag to Double Therapy for Pulmonary Arterial Hypertension

A subgroup analysis of a randomized clinical trial established the efficacy of selexipag plus background therapy (monotherapy or double oral therapy [DOT]) vs placebo plus background therapy and found that the addition of selexipag within 6 months had an added benefit. However, the timing of selexipag addition to DOT and the incremental benefit in clinical practice is not well studied. To compare triple oral therapy (TOT) consisting of selexipag, endothelin receptor antagonist (ERA), and phosphodiesterase type 5 inhibitor (PDE5i) vs DOT consisting of ERA and PDE5i. This comparative effectiveness study was conducted using data from the US Komodo claims database to emulate a randomized trial. Patients aged 18 years or older with pulmonary arterial hypertension (PAH) treated with ERA plus PDE5i with records from July 2015 through June 2022 were duplicated to TOT and DOT and artificially censored when observed treatment deviated from assigned treatment. Hypothetical randomization was emulated using inverse probability of treatment weighting, and the study accounted for censoring-induced selection bias using inverse probability of censoring weighting. A pooled logistic model estimated the per-protocol difference between treatment groups. Data were analyzed from November 2022 through July 2023. TOT (addition of selexipag within 3, 6, and 12 months of initiating DOT) vs DOT. Adjusted risk of all-cause hospitalization, PAH-related hospitalization, and PAH-related disease progression over a 2-year follow-up. A total of 2966 patients with PAH (mean [SD] age, 54.3 [14.0] years; 2125 female [71.6%]) met eligibility criteria. Adding selexipag within 6 months of ongoing DOT was associated with a reduction in risk for all-cause hospitalization (adjusted hazard ratio [aHR], 0.82; 95% CI, 0.72-0.94), PAH-related hospitalization (aHR, 0.81; 95% CI, 0.70-0.95), and PAH-related progression (aHR, 0.82; 95% CI, 0.70-0.95) vs DOT alone. There were no associations if selexipag was initiated within 12 months for all-cause hospitalization, PAH-related hospitalization, or PAH-related disease progression. The association remained with a greater decrease in risk for disease progression vs DOT for selexipag initiation within 3 months (aHR, 0.74; 95% CI, 0.61-0.90). This study found that early selexipag addition to ERA plus PDE5i was associated with a reduction in risk of hospitalization and disease progression. These findings suggest that delays in selexipag initiation likely contribute to suboptimal patient and health system outcomes.

The Gq/11 family of Gα subunits is necessary and sufficient for lower jaw development.

Vertebrate jaw development is coordinated by highly conserved ligand-receptor systems such as the peptide ligand Endothelin 1 (Edn1) and Endothelin receptor type A (Ednra), which are required for patterning of lower jaw structures. The Edn1/Ednra signaling pathway establishes the identity of lower jaw progenitor cells by regulating expression of numerous patterning genes, but the intracellular signaling mechanisms linking receptor activation to gene regulation remain poorly understood. As a first step towards elucidating this mechanism, we examined the function of the Gq/11 family of Gα subunits in zebrafish using pharmacological inhibition and genetic ablation of Gq/11 activity and transgenic induction of a constitutively active Gq protein in edn1 -/- embryos. Genetic loss of Gq/11 activity fully recapitulated the edn1 -/- phenotype, with genes encoding G11 being most essential. Furthermore, inducing Gq activity in edn1 -/- embryos not only restored Edn1/Ednra-dependent jaw structures and gene expression signatures but also caused homeosis of the upper jaw structure into a lower jaw-like structure. These results indicate that Gq/11 is necessary and sufficient to mediate the lower jaw patterning mechanism for Ednra in zebrafish.

Blood pressure management strategies and podocyte health.

Hypertension (HTN) is one of the key global cardiovascular risk factors, which is tightly linked to kidney health and disease development. Podocytes, glomerular epithelial cells that play a pivotal role in maintenance of the renal filtration barrier, are significantly affected by increased glomerular capillary pressure in HTN. Damage or loss of these cells causes proteinuria, which marks the initiation of the HTN-driven renal damage. It goes without saying that effective BP management should not only mitigate cardiovascular risks but also preserve renal function by protecting podocyte integrity. This review offers a comprehensive examination of current blood pressure (BP) management strategies and their implications for podocyte structure and function and emphasizes strategies for the reduction of proteinuria in HTN. We explore primary and secondary antihypertensive agents, including ACE inhibitors, ARBs, calcium channel blockers, diuretics, as well as newer therapies (SGLT2 blocking and endothelin receptor antagonism), emphasizing their mechanistic roles in safeguarding podocytes and curtailing proteinuria.

Blockade of endothelin receptors mitigates SARS-CoV-2-induced osteoarthritis.

Joint pain and osteoarthritis can occur as coronavirus disease 2019 (COVID-19) sequelae after infection. However, little is known about the damage to articular cartilage. Here we illustrate knee joint damage after wild-type, Delta and Omicron variants of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection in vivo. Rapid joint injury with cystic lesions at the osteochondral junction was observed in two patients with post-COVID osteoarthritis and recapitulated in a golden Syrian hamster model. SARS-CoV-2-activated endothelin-1 signalling increased vascular permeability and caused viral spike proteins leakage into the subchondral bone. Osteoclast activation, chondrocyte dropout and cyst formation were confirmed histologically. The US Food and Drug Administration-approved endothelin receptor antagonist, macitentan, mitigated cystic lesions and preserved chondrocyte number in the acute phase of viral infection in hamsters. Delayed macitentan treatment at post-acute infection phase alleviated chondrocyte senescence and restored subchondral bone loss. It is worth noting that it could also attenuate viral spike-induced joint pain. Our work suggests endothelin receptor blockade as a novel therapeutic strategy for post-COVID arthritis.

Endothelin-1 down-regulates nuclear factor erythroid 2-related factor-2 and contributes to perivascular adipose tissue dysfunction in obesity.

Perivascular adipose tissue (PVAT) negatively regulates vascular muscle contraction. However, in the context of obesity, the PVAT releases vasoconstrictor substances that detrimentally affect vascular function. A pivotal player in this scenario is the peptide endothelin-1 (ET-1), which induces oxidative stress and disrupts vascular function. The present study postulates that obesity augments ET-1 production in the PVAT, decreases the function of the nuclear factor erythroid 2-related factor-2 (Nrf2) transcription factor, further increasing reactive oxygen species (ROS) generation, culminating in PVAT dysfunction. Male C57BL/6 mice were fed either a standard or a high-fat diet for 16 weeks. Mice were also treated with saline or a daily dose of 100 mg·kg-1 of the ETA and ETB receptor antagonist Bosentan, for 7 days. Vascular function was evaluated in thoracic aortic rings, with and without PVAT. Mechanistic studies utilized PVAT from all groups and cultured WT-1 mouse brown adipocytes. PVAT from obese mice exhibited increased ET-1 production, increased ECE1 and ETA gene expression, loss of the anticontractile effect, as well as increased ROS production, decreased Nrf2 activity, and downregulated expression of Nrf2-targeted antioxidant genes. PVAT of obese mice also exhibited increased expression of Tyr216-phosphorylated-GSK3β and KEAP1, but not BACH1 - negative Nrf2 regulators. Bosentan treatment reversed all these effects. Similarly, ET-1 increased ROS generation and decreased Nrf2 activity in brown adipocytes, events mitigated by BQ123 (ETA receptor antagonist). These findings place ET-1 as a major contributor to PVAT dysfunction in obesity and highlight that pharmacological control of ET-1 effects restores PVAT's cardiovascular protective role.

Pressing Update: Aprocitentan for the Treatment of Hypertension.

This article reviews the published data including the pharmacology, efficacy, and safety of aprocitentan, a novel endothelin receptor antagonist developed to treat hypertension in conjunction with additional agents. A literature search was conducted from drug discovery until May 2024 through PubMed, MEDLINE, and National Institutes of Health Clinical Trials Registry utilizing the following search terms: Tryvio, aprocitentan, hypertension, resistant hypertension, endothelin receptor antagonist, and ACT-132577. All relevant English-language studies, or studies that could be appropriately translated into English, containing the pharmacology, pharmacokinetics, safety, and efficacy of aprocitentan, were selected for review. In the setting of resistant hypertension, aprocitentan has shown significant reductions in blood pressure in both medical office and 24-hour ambulatory settings at 4 weeks with a sustained effect at 40 weeks. Studies evaluating cardiovascular risk reduction have not been conducted at this time. Fluid retention and edema were the most frequent adverse events reported in clinical studies with aprocitentan. As a class, endothelin receptor antagonists may cause fetal harm; aprocitentan should be used with caution to avoid embryo-fetal toxicity. Owing to the existent barriers for the treatment of resistant hypertension, aprocitentan presents itself as an effective option when added to traditional antihypertensives. This single-strength, once-daily regimen may serve as an appealing option to both patients and prescribers. Aprocitentan is a safe and effective medication for the treatment of hypertension when added to other pharmacological therapies.

Investigation of pulmonary artery and circulating endothelin-1 expression in dogs with pulmonary hypertension secondary to myxomatous mitral valve disease.

Pulmonary hypertension (PH) is a condition characterized by abnormally elevated pressure in the pulmonary vasculature. It is a common complication of myxomatous mitral valve disease (MMVD) in dogs. Several vasoactive substances, including endothelin-1 (ET-1), have been suggested to contribute to pathological changes in the pulmonary arteries of patients with PH. This study aimed to examine the local and systemic expression of ET-1 in dogs with PH secondary to MMVD. Lung tissues were collected from 20 client-owned dogs during the first stage of the study and divided into three groups: normal dogs (n = 5), MMVD dogs (n = 8), and MMVD+PH dogs (n = 7). The expression of ET-1 and endothelin A receptor (ETAR) in the pulmonary arteries was determined using immunohistochemistry. Blood samples were collected from 61 client-owned dogs for the second stage of the study and divided into three groups: normal (n = 22), MMVD (n = 20), and MMVD+PH (n = 19). Plasma ET-1 concentration was measured using a sandwich enzyme-linked immunosorbent assay. There was no difference in ET-1 and ETAR expression in the pulmonary arteries among the three groups. Similarly, there was no difference in the plasma ET-1 concentration between the groups. In addition, no correlation was found between the immunohistochemical expression of ET-1 and ETAR and the thickness of the pulmonary arteries or between the plasma ET-1 level and echocardiographic variables. The lack of difference in the expression of ET-1 and ETAR in the pulmonary arteries and in the circulating ET-1 concentration among the studied groups suggests that ET-1 may not be related to the pathological development of PH secondary to MMVD in dogs. Due to the small sample size in this study, further research is needed to confirm these findings.

Effect of endothelin-1 on the blood pressure response to acute hypoxia and hyperoxia in healthy young men.

Endothelin-1 (ET-1) and its receptors are linked to increases in sensitivity of the chemoreceptors to hypoxic stress and the development of hypertension in preclinical models. We hypothesized ET receptor antagonism would lower resting blood pressure (BP) as well as the acute BP response to chemoreflex stress. Twenty-four men (31 ± 5 years, 26 ± 3 kg/m2) completed two study visits (control, bosentan). On each visit, BP was assessed under three conditions: (1) normoxia (FiO2 0.21), (2) chemoreflex excitation via hypoxia (FiO2 0.05-0.21), (3) chemoreflex inhibition via hyperoxia (FiO2 1.00). Bosentan increased plasma ET-1 (0.94 ± 0.90 to 1.27 ± 0.62 pg/mL, p = 0.004), supporting receptor blockade. Resting diastolic (73 ± 5 to 69 ± 7 mmHg, p = 0.007) and mean (93 ± 7 to 88 ± 7 mmHg, p = 0.005) BP were reduced following bosentan compared to control with no change in systolic BP (p = 0.507). The mean BP response to both acute hypoxia (-0.48 ± 0.38 to -0.25 ± 0.31 mmHg/%, p = 0.004) and hyperoxia (area under the curve -93 ± 108 to -27 ± 66 AU, p = 0.018) were attenuated following bosentan. Acute ET receptor inhibition attenuates the rise in BP during chemoreflex excitation as well as the fall in BP during chemoreflex inhibition in healthy young men. These data support a role for ET-1 in control of resting BP, possibly through a chemoreceptor-mediated mechanism.

Abstract 35: The Dual Endothelin-1 Antagonist Aprocitentan Attenuates Mitochondrial Oxidative Stress in Human Cardiac Fibroblasts

Endothelin-1 (ET-1) is a peptide hormone primarily produced by endothelial cells that functions as a potent vasoconstrictor through two receptors, ETA and ETB. While most research on ET-1 has focused on endothelial dysfunction and hypertension, increasing evidence shows that ET-1 is also involved in other physiological processes such as cell proliferation, inflammation, and tissue remodeling. Dysregulation of ET-1 has been implicated in the pathogenesis of various diseases, including heart failure, atherosclerosis, fibrosis, systemic sclerosis, and cancer. Aprocitentan (also known as ACT-132577) is a relatively new dual ET-1 receptor antagonist that prevents ET-1 from binding to both endothelin receptors and has been shown to significantly reduce blood pressure in patients with resistant hypertension. Our hypothesis was that aprocitentan could reduce the proliferation rate and mitochondrial ROS production induced by TGF-β in human cardiac fibroblasts (HCFs). HCFs were isolated from hearts from fully de-identified cadaveric donors and cultured in cardiac fibroblast growth medium. HCFs were treated with aprocitentan (4 μM) and/or TGF-β1 (10 ng/ml) for 72 hours (doses and times identified in preliminary dose-response and time-course assays). Aprocitentan reduced the TGF-β1-induced proliferation rate in HCFs by approximately 23% ( Figure 1A ). Our study also aimed to determine if aprocitentan could mitigate mitochondrial dysfunction. Since the mitochondrion is a major source of reactive oxygen species (ROS), which can promote myofibroblast differentiation, mitochondrial properties in HCFs were assessed using MitoTracker Green and MitoSOX staining. TGF-β1 treatment increased mitochondrial ROS production, which was significantly reduced by aprocitentan ( Figure 1BC ); furthermore, aprocitentan reduced mitochondrial fragmentation induced by TGF-β1 treatment ( Figure 1D ). To the best of our knowledge, we are the first to demonstrate that aprocitentan can reduce the increased production of mitochondrial ROS, mitochondrial fragmentation, and cell proliferation rate induced by TGF-β1 in HCFs. This discovery could pave the way for new research and therapeutic strategies for treating fibrosis in cardiovascular disorders.