Selective Endothelin Receptor Research Articles

#2661 High albuminuria in CKD: prevalence and characteristics in a real-world clinical setting

Abstract Background and Aims Chronic kidney disease (CKD) is estimated to affect 1 in 10 adults globally. CKD is associated with increased morbidity, mortality and decreased quality of life, and places a financial burden on the healthcare system. Furthermore, persistently high albuminuria is associated with an especially high risk of renal and cardiovascular complications in patients with CKD. With recent advances in therapeutic approaches for CKD management, both with sodium–glucose co-transporter-2 inhibitors (SGLT2i) and endothelin receptor antagonists as add-on to renin–angiotensin system blockade, it is important to highlight patients with persistent urine albumin-creatinine ratio (UACR; ≥700 mg/g). In patients with UACR >700 mg/g, a novel and highly selective endothelin receptor A antagonist (zibotentan) plus the SGLT2i dapagliflozin significantly reduced albuminuria versus dapagliflozin plus placebo (ZENITH-CKD trial). Hence, it is important to understand the prevalence and characteristics of patients with CKD and high albuminuria in a real-world clinical setting. Methods We used a large USA claims database (Optum's de-identified Clinformatics® Data Mart Database [CDM]) to identify patients aged ≥18 years with a CKD diagnosis and a UACR measurement ≥200 mg/g. Patients were indexed on 1st January 2022 and grouped into two UACR groups: ≥700UACR group (≥700 mg/g) and <700UACR group (200–699 mg/g). Continuous variables were calculated as medians with interquartile range (IQR). Baseline characteristics and comorbidities included age, sex, median UACR, median estimated glomerular filtration rate (eGFR) and a history of heart failure. Results Of 53,306 patients with CKD and UACR ≥200 mg/g, 22,504 (42%) were in the ≥700UACR group and 30,802 (58%) in the <700UACR group (Fig. 1). Patients were more frequently men in both groups (57%). Median UACR was 1459 mg/g (IQR 977–2473) in the ≥700UACR group and 341 mg/g (IQR 256–474) in the <700UACR group. Patients in the ≥700UACR group were slightly younger (72 vs 74 years), had a higher frequency of heart failure (42% vs 34%) and lower eGFR (37 mL/min/1.73 m2 [IQR 21–55] vs 49 mL/min/1.73 m2 [IQR 34–67]) compared to the <700UACR group. Conclusions In this contemporary study of patients with albuminuric CKD, more than 4 out of 10 had UACR levels ≥700 mg/g. These patients were slightly younger, had more severe CKD, and greater prevalence of cardiorenal disease compared to those with UACR 200–699 mg/g. Patients with UACR levels ≥700 mg/g have an urgent need for improved risk management.

Combination therapy for kidney disease in people with diabetes mellitus.

Diabetic kidney disease (DKD), defined as co-existing diabetes and chronic kidney disease in the absence of other clear causes of kidney injury, occurs in approximately 20-40% of patients with diabetes mellitus. As the global prevalence of diabetes has increased, DKD has become highly prevalent and a leading cause of kidney failure, accelerated cardiovascular disease, premature mortality and global health care expenditure. Multiple pathophysiological mechanisms contribute to DKD, and single lifestyle or pharmacological interventions have shown limited efficacy at preserving kidney function. For nearly two decades, renin-angiotensin system inhibitors were the only available kidney-protective drugs. However, several new drug classes, including sodium glucose cotransporter-2 inhibitors, a non-steroidal mineralocorticoid antagonist and a selective endothelin receptor antagonist, have now been demonstrated to improve kidney outcomes in people with type 2 diabetes mellitus. In addition, emerging preclinical and clinical evidence of the kidney-protective effects of glucagon-like-peptide-1 receptor agonists has led to the prospective testing of these agents for DKD. Research and clinical efforts are geared towards using therapies with potentially complementary efficacy in combination to safely halt kidney disease progression. As more kidney-protective drugs become available, the outlook for people living with DKD should improve in the next few decades.

Anti-Anginal Efficacy of Zibotentan in the Coronary Slow-Flow Phenomenon.

Patients with coronary microvascular disorders often experience recurrent angina for which there are limited evidence-based therapies. These patients have been found to exhibit increased plasma levels of endothelin; thus, selective endothelin-A (Et-A) receptor blockers such as zibotentan may be an effective anti-anginal therapy in these patients. The study evaluated the impact of a 10 mg daily dose of zibotentan on spontaneous angina episodes in patients with the coronary slow-flow phenomenon who had refractory angina (i.e., experiencing angina at least three times/week despite current anti-anginal therapy). Using a randomized, double-blind, placebo-controlled, crossover trial design with 4-week treatment periods, 18 patients (63.2 ± 9.9 years, 33% females) were recruited. The primary endpoint was angina frequency as measured by an angina diary, with secondary endpoints including nitrate consumption, angina duration/severity and the Seattle Angina Questionnaire (SAQ) domains. During the 4 weeks of therapy, angina frequency significantly improved with zibotentan therapy (placebo 41.4 (58.5) vs. zibotentan 29.2 (31.6), p < 0.05), and sublingual nitrate consumption significantly reduced (placebo 11.8 (15.2) vs. zibotentan 8.8 (12.9), p < 0.05. Zibotentan improved the frequency of spontaneous angina episodes and reduced sublingual nitrate consumption in patients unresponsive to standard anti-anginal therapy.

Insulin resistance, kidney outcomes and effects of the endothelin receptor antagonist atrasentan in patients with type 2 diabetes and chronic kidney disease

BackgroundInsulin resistance (IR) is a pathophysiologic hallmark of type 2 diabetes and associated with the presence of chronic kidney disease (CKD). Experimental studies suggest that endothelin-1 increases IR. We assessed the association between IR and cardio-renal outcomes and the effect of the selective endothelin receptor antagonist atrasentan on IR in patients with type 2 diabetes and CKD.MethodsWe used data from the RADAR and SONAR trials that recruited participants with type 2 diabetes and CKD [eGFR 25–75 mL/min/1.73 m², urine albumin-to-creatinine ratio of 300–5000 mg/g]. IR was calculated using the homeostatic model assessment (HOMA-IR). The association between HOMA-IR and the pre-specified cardio-renal outcomes was assessed using multivariable Cox proportional hazards regression, and effects of atrasentan on HOMA-IR by a linear mixed effect model.ResultsIn the SONAR trial, each log-unit increase in HOMA-IR was associated with an increased risk of the composite cardio-renal outcome [hazard ratio 1.32 (95%CI 1.09,1.60; p = 0.004)], kidney outcome [hazard ratio 1.30 (95%CI 1.00,1.68; p-value = 0.048)], and the kidney or all-cause mortality outcome [hazard ratio 1.25 (95%CI 1.01,1.55; p-value = 0.037)]. After 12 weeks treatment in the RADAR trial (N = 123), atrasentan 0.75 mg/day and 1.25 mg/day compared to placebo reduced HOMA-IR by 19.1 (95%CI -17.4, 44.3) and 26.7% (95%CI -6.4, 49.5), respectively. In the SONAR trial (N = 1914), atrasentan 0.75 mg/day compared to placebo reduced HOMA-IR by 9.6% (95%CI 0.6, 17.9).ConclusionsMore severe IR is associated with increased risk of cardio-renal outcomes. The endothelin receptor antagonist atrasentan reduced IR.Trial registrationRADAR trial (Reducing Residual Albuminuria in Subjects With Diabetes and Nephropathy With AtRasentan): NCT01356849.SONAR trial (The Study Of Diabetic Nephropathy With AtRasentan) NCT01858532.

Arterial stiffness, endothelial dysfunction and impaired fibrinolysis are pathogenic mechanisms contributing to cardiovascular risk in ANCA-associated vasculitis

Cardiovascular disease is a complication of systemic inflammatory diseases including anti-neutrophil cytoplasm antibody-associated vasculitis (AAV). The mechanisms of cardiovascular morbidity in AAV are poorly understood, and risk-reduction strategies are lacking. Therefore, in a series of double-blind, randomized case-control forearm plethysmography and crossover systemic interventional studies, we examined arterial stiffness and endothelial function in patients with AAV in long-term disease remission and in matched healthy volunteers (32 each group). The primary outcome for the case-control study was the difference in endothelium-dependent vasodilation between health and AAV, and for the crossover study was the difference in pulse wave velocity (PWV) between treatment with placebo and selective endothelin-A receptor antagonism. Parallel invitro studies of circulating monocytes and platelets explored mechanisms. Compared to healthy volunteers, patients with AAV had 30% reduced endothelium-dependent vasodilation and 50% reduced acute release of endothelial active tissue plasminogen activator (tPA), both significant in the case-control study. Patients with AAV had significantly increased arterial stiffness (PWV: 7.3 versus 6.4 m/s). Plasma endothelin-1 was two-fold higher in AAV and independently predicted PWV and tPA release. Compared to placebo, both selective endothelin-A and dual endothelin-A/B receptor blockade reduced PWV and increased tPA release in AAV in the crossover study. Mechanistically, patients with AAV had increased platelet activation, more platelet-monocyte aggregates, and altered monocyte endothelin receptor function, reflecting reduced endothelin-1 clearance. Patients with AAV in long-term remission have elevated cardiovascular risk and endothelin-1 contributes to this. Thus, our data support a role for endothelin-blockers to reduce cardiovascular risk by reducing arterial stiffness and increasing circulating tPA activity.

Research in Brief

Edward Stern and colleagues conducted a three-part study to assess the safety and efficacy of zibotentan, a highly selective endothelin receptor antagonist, in systemic sclerosis-associated chronic kidney disease. 13 patients with an estimated glomerular filtration rate (eGFR) greater than 45 mL/min were randomly assigned (1:1) to zibotentan (n=6) or placebo (n=7) for 26 weeks. No effect was seen on serum VCAM1, but eGFR increased in patients receiving zibotentan and decreased in those receiving placebo.

Effects of Selective Endothelin Receptor Antagonist on Vegf Signaling System in Diabetic Penis: A Possible Clinical Implication for Diabetes Induced Erectile Dysfunction

Erectile dysfunction (ED) affects around 50 percent of male diabetic patients due to vascular and neuropathic complications arising from diabetes. Vascular endothelial growth factor (VEGF) has been extensively investigated for its pathogenic relevance in various diabetes complications, and we have already noted that VEGF signaling is significantly reduced at the insulin-resistant stage in the penis of type II diabetic rat model. The present research used a three-week streptozotocin (STZ)-induced diabetic (DM) rat model to determine the expression of VEGF with NO mechanism in penile tissue and subsequently investigated its impact endothelin antagonism on these shifts. Citrate saline vehicle or STZ (65 mg/kg IP) was administered to male Sprague-Dawley rats (weight 453 ± 23 g). Hyperglycemia confirmed diabetes, and then after 1 week of diabetes, animals were divided into receiving endothelin-A (ET-A) receptor antagonists (TA-0201, 1 mg/kg) or saline by osmotic minipump for 2 weeks and then sacrificed. Significantly improved glucose levels in DM rats (405 ± 103 mg/dL) relative to non-DM rats (120 ± 8 mg/dL) and higher local ET-1 levels in DM penis by 20% are observed. A 30 percent decline in penile tissue expression of VEGF was observed in DM rats and improved by an antagonist with ET. Penile NO and eNOS levels in DM rats decreased, while ET-A receptor antagonist significantly increased. Therefore, we infer that ET antagonism seemed able to restore the down-regulated VEGF and was possibly efficient in restoring the decreased levels of NO and eNOS in DM.

Ambrisentan use in a HIV-1 infected patient with end-stage renal disease and pulmonary hypertension: minimal removal by hemodialysis - a case report

BackgroundAmbrisentan is a selective endothelin receptor antagonist used for the treatment of pulmonary arterial hypertension (PAH). Little is known about ambrisentan removal by hemodialysis in patients with end-stage renal disease (ESRD).Case presentationA 53-year-old woman with HIV/hepatitis C virus (HCV) co-infection, PAH and ESRD on regular hemodialyis was admitted in our hospital due to refractory heart failure while on treatment with bosentan (125 mg twice daily) and tadalafil (20 mg once daily) for PAH and antiretroviral treatment (cART) including darunavir/cobicistat (800/150 mg once daily). Excessive exposure to bosentan due to drug interactions between bosentan and darunavir/cobicistat was suspected. Bosentan was replaced by ambrisentan, with progressive improvement in her clinical condition. Pre- and postdialyzer cocentrations of ambrisentan in plasma were determined and hemodialysis extraction ratio for ambrisentan was 2%.ConclusionsOur results suggest that hemodialysis results in minimal ambrisentan removal, and therefore no specific ambrisentan dosage adjustment seems to be required in ESRD patients undergoing hemodialysis.

Comparison of the protective effects of selective endothelin-a receptor antagonist, ambrisentan, and dual endothelin-A/B receptor antagonist, bosentan, in experimental renal ischemia reperfusion injury.

This study aims to compare the protective effects of ambrisentan, a selective endothelin typeA receptor antagonist, and bosentan, a dual endothelin typeA/B receptor antagonist, on experimental renal ischemia reperfusion injury. The study sample consisted of 21 female rats, which were divided into 3 groups: Control, Ambrisentan and Bosentan. For the ischemia-reperfusion injury model, left‑kidney nephrectomy was performed after sacrificing the animals. In the immunohistochemical examination, caspase-3 was examined, and then the apoptotic index was determined. In the biochemical examination, the activities of malondialdehyde (MDA), superoxide dismutase (SOD), glutathione peroxidase, and the levels of nitrite (NOx), TNF-α, and IL-1β were determined. There were statistically significant differences between the groups in terms of total injury score grade in range of 0‒3 (p=0.001).The glomerular and tubular apoptotic indices were higher in the control group as compared to those of the ambrisentan and bosentan groups (p=0.001).There were no statistically significant differences in terms of SOD, CAT, GPx, MDA, IL-1β and TNF-α measurements among the groups (p>0.05). In the experimentally created renal ischemia reperfusion model, both ambrisentan and bosentan increased the NOx level, decreased the apoptosis, and protected the kidney from renal ischemia reperfusion injury. However, no significant superiority was found between ambrisentan and bosentan in terms of their protective effects (Tab. 3, Fig. 2, Ref. 31).

Co-targeting of endothelin-A and vitamin D receptors: a novel strategy to ameliorate cisplatin-induced nephrotoxicity.

Although modulation of the vitamin D receptor (VDR) and endothelin-A receptor (ETAR) has previously been reported to offer renoprotection against cisplatin-induced nephrotoxicity, the possible interaction between the ET-1 and vitamin D pathways remains obscure. Therefore, the present study addressed the possible interaction between these signalling pathways using BQ-123 (a selective ETAR blocker) and alfacalcidol (a vitamin D3 analogue) separately or in combination. Male Sprague-Dawley rats were divided into the following groups: control (DMSO orally), cisplatin (single dose of 6 mg/kg ip; nephrotoxicity model), cisplatin + BQ-123 (1 mg/kg BQ-123 ip 1 h before and 1 day after cisplatin), cisplatin + alfacalcidol (50 ng/kg alfacalcidol orally 5 days before and 14 days after cisplatin), and cisplatin + BQ-123+alfacalcidol. Nephrotoxicity was evaluated 96 h and 14 days following cisplatin administration. Both BQ-123 and alfacalcidol counteracted cisplatin-induced nephrotoxic changes. Specifically, they reduced serum creatinine and urea levels; renal tumour necrosis factor-alpha (TNF-α), transforming growth factor-beta1 (TGF-β1), and phosphorylated nuclear factor-kappa B (pNF-κB) content; and caspase-3 activity. They downregulated ET-1 and ETAR expression and ameliorated cisplatin-induced acute tubular necrosis. In addition, the treatments have increased VDR and endothelin-B receptor (ETBR) expression; however, BQ-123 did not affect ETBR. The effect of the combination regimen surpassed that of each drug alone. These findings highlight the potential cross-talk between vitamin D and ET-1 pathways and pave the way for future preclinical/clinical studies to explore further mechanisms involved in this cross-talk.

Atrasentan and renal events in patients with type 2 diabetes and chronic kidney disease (SONAR): a double-blind, randomised, placebo-controlled trial

Short-term treatment for people with type 2 diabetes using a low dose of the selective endothelin A receptor antagonist atrasentan reduces albuminuria without causing significant sodium retention. We report the long-term effects of treatment with atrasentan on major renal outcomes. We did this double-blind, randomised, placebo-controlled trial at 689 sites in 41 countries. We enrolled adults aged 18-85 years with type 2 diabetes, estimated glomerular filtration rate (eGFR) 25-75 mL/min per 1·73 m2 of body surface area, and a urine albumin-to-creatinine ratio (UACR) of 300-5000 mg/g who had received maximum labelled or tolerated renin-angiotensin system inhibition for at least 4 weeks. Participants were given atrasentan 0·75 mg orally daily during an enrichment period before random group assignment. Those with a UACR decrease of at least 30% with no substantial fluid retention during the enrichment period (responders) were included in the double-blind treatment period. Responders were randomly assigned to receive either atrasentan 0·75 mg orally daily or placebo. All patients and investigators were masked to treatment assignment. The primary endpoint was a composite of doubling of serum creatinine (sustained for ≥30 days) or end-stage kidney disease (eGFR <15 mL/min per 1·73 m2 sustained for ≥90 days, chronic dialysis for ≥90 days, kidney transplantation, or death from kidney failure) in the intention-to-treat population of all responders. Safety was assessed in all patients who received at least one dose of their assigned study treatment. The study is registered with ClinicalTrials.gov, number NCT01858532. Between May 17, 2013, and July 13, 2017, 11 087 patients were screened; 5117 entered the enrichment period, and 4711 completed the enrichment period. Of these, 2648 patients were responders and were randomly assigned to the atrasentan group (n=1325) or placebo group (n=1323). Median follow-up was 2·2 years (IQR 1·4-2·9). 79 (6·0%) of 1325 patients in the atrasentan group and 105 (7·9%) of 1323 in the placebo group had a primary composite renal endpoint event (hazard ratio [HR] 0·65 [95% CI 0·49-0·88]; p=0·0047). Fluid retention and anaemia adverse events, which have been previously attributed to endothelin receptor antagonists, were more frequent in the atrasentan group than in the placebo group. Hospital admission for heart failure occurred in 47 (3·5%) of 1325 patients in the atrasentan group and 34 (2·6%) of 1323 patients in the placebo group (HR 1·33 [95% CI 0·85-2·07]; p=0·208). 58 (4·4%) patients in the atrasentan group and 52 (3·9%) in the placebo group died (HR 1·09 [95% CI 0·75-1·59]; p=0·65). Atrasentan reduced the risk of renal events in patients with diabetes and chronic kidney disease who were selected to optimise efficacy and safety. These data support a potential role for selective endothelin receptor antagonists in protecting renal function in patients with type 2 diabetes at high risk of developing end-stage kidney disease. AbbVie.

Role of ambrisentan (selective endothelin-A receptor antagonist) on cigarette smoke exposure induced cognitive impairment in Danio rerio

BackgroundCigarette smoke is exogenous modifiable factors to changes the neurovascular complication. The chronic exposure of cigarette smoke enhances neurocognitive dysfunction. AimsThe present study is focused on evaluating the role of ambrisentan (selective endothelin-A receptor antagonist) on cigarette smoke-induced cognitive impairment in Danio rerio. Main methodsThe cognitive dysfunction was developed by cigarette smoke exposure (CSE; 10 min in 25 ml of CSE per day) for five days. The selective endothelin-A receptor antagonist i.e., ambrisentan (2.5 to 5 mg/kg; i.p. for five consecutive days) was used for testing of CSE induced cognitive dysfunction. In addition, treatment of reference drug i.e., donepezil (10 mg/kg; i.p. for five consecutive days) was used for this cognitive function study. The cognitive functions were assessed by light and dark chamber; color recognition; partition preference; horizontal compartment; and T-Maze tests. Further, the CSE induced biomarkers changes of the zebrafish brain samples were estimated. Key findingsThe treatment of ambrisentan showed a potential ameliorative effect against the CSE induced cognitive functions along with attenuation of biochemical changes. The results are comparable to donepezil-treated groups. SignificanceTherefore, ambrisentan can be considered for the attenuation of CSE induced impairment neurocognitive functions due to its reduction of free radical scavenging and neuroinflammatory actions as well as regulation of cholinergic neurotransmitter functions.

Effect of Ambrisentan Therapy on the Expression of Endothelin Receptor, Endothelial Nitric Oxide Synthase and NADPH Oxidase 4 in Monocrotaline-induced Pulmonary Arterial Hypertension Rat Model.

Background and ObjectivesElevated endothelin (ET)-1 level is strongly correlated with the pathogenesis of pulmonary arterial hypertension (PAH). Expression level of nicotinamide adenine dinucleotide phosphate oxidase (NOX) 4 is increased in the PAH patients. Ambrisentan, a selective endothelin receptor A (ERA) antagonist, is widely used in PAH therapy. The current study was undertaken to evaluate the effects of ambrisentan treatment in the monocrotaline (MCT)-induced PAH rat model.MethodsRats were categorized into control group (C), monocrotaline group (M) and ambrisentan group (Am). The M and Am were subcutaneously injected 60 mg/kg MCT at day 0, and in Am, ambrisentan was orally administered the day after MCT injection for 4 weeks. The right ventricle (RV) pressure was measured and pathological changes of the lung tissues were observed by Victoria blue staining. Protein expressions of ET-1, ERA, endothelial nitric oxide synthase (eNOS) and NOX4 were confirmed by western blot analysis.ResultsAmbrisentan treatment resulted in a recovery of the body weight and RV/left ventricle+septum at week 4. The RV pressure was lowered at weeks 2 and 4 after ambrisentan administration. Medial wall thickening of pulmonary arterioles and the number of intra-acinar arteries were also attenuated by ambrisentan at week 4. Protein expression levels of ET-1 and eNOS were recovered at weeks 2 and 4, and ERA levels recovered at week 4.ConclusionsAmbrisentan administration resulted in the recovery of ET-1, ERA and eNOS protein expression levels in the PAH model. However, the expression level of NOX4 remained unaffected after ambrisentan treatment.

Isolation, identification, characterization, synthesis and quality control strategy of new process-related impurities in ambrisentan

Ambrisentan is a highly selective endothelin-A receptor antagonist for the treatment of pulmonary arterial hypertension (PAH). The analysis of the process-related impurities will help not only to optimize the process parameters but also to develop reasonable analytical methods and set the quality standard for a quality control strategy in pharmaceutical manufacturing. During the manufacture of ambrisentan, five unknown impurities were detected in pilot batches ranging from 0.05% to 0.15% by HPLC. All of these impurities were isolated and synthesized successfully and were identified and characterized by LC–MS, HRMS, ESI-MS/MS(Q-Tof), 1D-NMR (1H, 13C, DEPT) and 2D-NMR (COSY, HSQC, HMBC) techniques. The formation mechanisms that yield these impurities are discussed for the first time. Quality control strategies to deal with these impurities are developed to obtain bulk drug of ICH-grade quality.

Baseline characteristics and enrichment results from the SONAR trial.

AimThe SONAR trial uses an enrichment design based on the individual response to the selective endothelin receptor antagonist atrasentan on efficacy (the degree of the individual response in the urinary albumin‐to‐creatinine ratio [UACR]) and safety/tolerability (signs of sodium retention and acute increases in serum creatinine) to assess the effects of this agent on major renal outcomes. The patient population and enrichment results are described here.MethodsPatients with type 2 diabetes with an estimated glomerular filtration rate (eGFR) within 25 to 75 mL/min/1.73 m2 and UACR between 300 and 5000 mg/g were enrolled. After a run‐in period, eligible patients received 0.75 mg/d of atrasentan for 6 weeks. A total of 2648 responder patients in whom UACR decreased by ≥30% compared to baseline were enrolled, as were 1020 non‐responders with a UACR decrease of <30%. Patients who experienced a weight gain of >3 kg and in whom brain natriuretic peptide exceeded ≥300 pg/mL, or who experienced an increase in serum creatinine >20% (0.5 mg/dL), were not randomized.ResultsBaseline characteristics were similar for atrasentan responders and non‐responders. Upon entry to the study, median UACR was 802 mg/g in responders and 920 mg/g in non‐responders. After 6 weeks of treatment with atrasentan, the UACR change in responders was −48.8% (95% CI, −49.8% to −47.9%) and in non‐responders was −1.2% (95% CI, −6.4% to 3.9%). Changes in other renal risk markers were similar between responders and non‐responders except for a marginally greater reduction in systolic blood pressure and eGFR in responders.ConclusionsThe enrichment period has successfully identified a population with a profound UACR reduction without clinical signs of sodium retention in whom a large atrasentan effect on clinically important renal outcomes is possible. The SONAR trial aims to establish whether atrasentan confers renal protection.

Pulmonary hypertension: reasonable selection of specific therapy

Pulmonary hypertension is characterized with persistent increase in pulmonary vascular resistance leading to progressive worsening of right ventricular failure and death. The basis for pulmonary arterial hypertension is structural changes in pulmonary arteries and arterioles caused by endothelial dysfunction. Endothelin-1 is the main pathogenic trigger of pulmonary hypertension and potential target for therapeutic exposure. The efficacy of endothelin receptor antagonists is proved in various preclinical and clinical studies. In patients with pulmonary arterial hypertension, the efficacy of dual and selective endothelin receptor antagonists is comparable despite the varied activity against various receptors. Bosentan is the most widely used pulmonary vasodilator which improves exercise tolerance and decelerates disease progression.

Highly Selective Endothelin-1 Receptor A Inhibition Prevents Bleomycin-Induced Pulmonary Inflammation and Fibrosis in Mice

Background: Pulmonary fibrosis is a chronic disease, which progressively leads to respiratory failure and ultimately death. Endothelin-1 (ET-1), a vasoconstrictor secreted by endothelial cells, promotes vasoconstriction by activation of its receptors A and B. Objectives: We addressed the role of highly selective ET-1 receptor A (ETA) inhibition in the pathogenesis of experimental pulmonary fibrosis by bleomycin (BLM). Methods: BLM sulfate (2 U/mL) or saline was intratracheally administered to C57/Bl6 mice (4 groups; n = 5-11/group). Pretreatment with the highly selective ETA receptor inhibitor sitaxentan (15 mg/kg/day) was started 1 day prior to BLM injection and continued for the duration of the experiment. Lung mechanics were assessed prior to sacrifice at days 7, 14, and 21 after BLM, followed by procurement of bronchoalveolar lavage fluid (BALF), blood, and lung tissue samples. Results: Time-dependent effects of BLM exposure included decreased static compliance and increased lung elastance, airspace inflammation and microvascular permeability, histological acute lung injury and fibrosis, and lung collagen deposition. Pretreatment with highly selective ETA receptor inhibitor had no adverse effect on control mice but improved lung mechanics and lung injury score in addition to decreasing BALF pleocytosis, protein content, and collagen deposition in BLM-treated mice. Mortality from BLM reached 40% and occurred primarily during the inflammatory stage of the model but was abrogated by sitaxentan pretreatment. Conclusions: We conclude that in our BLM-induced pulmonary fibrosis model, prophylactic highly selective ETA inhibition improves survival, preserves lung function, attenuates lung injury, and reduces collagen deposition.

Ambrisentan: a review of its use in pulmonary arterial hypertension.

Pulmonary arterial hypertension (PAH) is a progressive disease defined by an elevation in pulmonary arterial pressure that can lead to right heart failure and death. Ambrisentan is a selective endothelin receptor antagonist approved for the treatment of idiopathic, heritable PAH and connective tissue disease-associated PAH. Ambrisentan has been shown to improve exercise capacity and hemodynamics with an acceptable side-effect profile. It has also proven to be safely used in combination with other PAH-specific medications, especially with phosphodiesterase-5 inhibitors. In the recent randomized trial, AMBITION, it was shown that upfront combination therapy of ambrisentan and tadalafil significantly decreased the risk of clinical failure compared with monotherapy. This review describes the drug profile of ambrisentan and its safety and efficacy in the treatment of PAH.

Long-Term Endothelin-A Receptor Antagonism Provides Robust Renal Protection in Humanized Sickle Cell Disease Mice.

Sickle cell disease (SCD)-associated nephropathy is a major source of morbidity and mortality in patients because of the lack of efficacious treatments targeting renal manifestations of the disease. Here, we describe a long-term treatment strategy with the selective endothelin-A receptor (ETA) antagonist, ambrisentan, designed to interfere with the development of nephropathy in a humanized mouse model of SCD. Ambrisentan preserved GFR at the level of nondisease controls and prevented the development of proteinuria, albuminuria, and nephrinuria. Microscopy studies demonstrated prevention of podocyte loss and structural alterations, the absence of vascular congestion, and attenuation of glomerulosclerosis in treated mice. Studies in isolated glomeruli showed that treatment reduced inflammation and oxidative stress. At the level of renal tubules, ambrisentan treatment prevented the increased excretion of urinary tubular injury biomarkers. Additionally, the treatment strategy prevented tubular brush border loss, diminished tubular iron deposition, blocked the development of interstitial fibrosis, and prevented immune cell infiltration. Furthermore, the prevention of albuminuria in treated mice was associated with preservation of cortical megalin expression. In a separate series of identical experiments, combined ETA and ETB receptor antagonism provided only some of the protection observed with ambrisentan, highlighting the importance of exclusively targeting the ETA receptor in SCD. Our results demonstrate that ambrisentan treatment provides robust protection from diverse renal pathologies in SCD mice, and suggest that long-term ETA receptor antagonism may provide a strategy for the prevention of renal complications of SCD.

Inhibition of infarction-induced sympathetic innervation with endothelin receptor antagonism via a PI3K/GSK-3β-dependent pathway

Although endothelin (ET)-1 has been shown to upregulate nerve growth factor (NGF) expression, the molecular mechanisms are largely unknown. Phosphatidylinositol 3-kinase (PI3K)/Akt/glycogen synthase kinase (GSK)-3β signal has been implicated in the regulation of NGF. We investigated whether selective ET receptor blockers attenuated cardiac sympathetic reinnervation through restoring PI3K/Akt/GSK-3β activity. After ligation of the left anterior descending artery, male Wistar rats were randomized to either vehicle, atrasentan (an ETA receptor antagonist) or A-192621 (an ETB receptor antagonist) for 4 weeks. Sympathetic hyperinnervation after infarction was confirmed by myocardial norepinephrine measurement and immunofluorescent analysis. Post infarction was associated with increased reactive oxygen species (ROS), as measured by myocardial superoxide levels and dihydroethidine fluorescence staining. This was paralleled by a significant upregulation of NGF expression on mRNA and protein levels in the vehicle-treated rats, which reduced after administering atrasentan, not A-192621. Arrhythmic scores in the vehicle-treated rats were significantly higher than those treated with atrasentan. In an in vivo study atrasentan-induced decreased NGF was associated with activation of PI3K/Akt signaling pathway, which was further confirmed by the ex vivo study showing the restoration of NGF levels after coadministration of PI3K inhibitors (wortmannin and LY294002). Lithium chloride, an inhibitor of GSK-3β, did not provide additional attenuated NGF levels compared with atrasentan alone. Finally, atrasentan-attenuated NGF levels were reversed in the presence of peroxynitrite generator. ETA receptor antagonism is a mediator to attenuate sympathetic hyperinnervation probably through restoration of PI3K/Akt/GSK-3β/ROS signaling pathway, a potential pharmacological target for arrhythmias after infarction.