Is endothelin targeting finally ready for prime time?

The endothelin family of peptides has long been recognized as a physiological regulator of diverse biological functions and mechanistically involved in various disease states, encompassing, among others, the cardiovascular system, the kidney, and the nervous system. Pharmacological blockade of the endothelin system, however, has encountered strong obstacles in its entry into the clinical mainstream, having obtained only a few proven indications until recently. This translational gap has been attributable predominantly to the relevant side effects associated with endothelin receptor antagonism (ERA), particularly fluid retention. Of recent, however, an expanding understanding of the pathophysiological processes involving endothelin, in conjunction with the development of new antagonists of endothelin receptors or adjustment of their doses, has driven a flourish of new clinical trials. The favorable results of some of them have extended the proven indications for ET targeting to a variety of clinical conditions, including resistant arterial hypertension and glomerulopathies. In addition, on the ground of strong preclinical evidence, other studies are ongoing to test the potential benefits of ERA in combination with other treatments, such as sodium-glucose co-transporter 2 inhibition in fluid retentive states or anti-cancer therapies in solid tumors. Furthermore, antibodies providing long-term blockade of endothelin receptors are under testing to overcome the short half-life of most small molecule endothelin antagonists. These efforts may yet bring new life to the translation of endothelin targeting strategies in clinical practice.

Current Status of Endothelin Receptor Antagonists in Pulmonary Arterial Hypertension: A Combined Study Results and Pharmacology-Based Review

Pulmonary arterial hypertension (PAH) affects a wide range of people globally and has a poor prognosis despite many advancements in available treatment options. Among the available treatments, endothelin receptor antagonists (ERA) are among the most widely used drugs. These drugs have been evaluated in scientific trials. We included free full texts in the English language from the last ten years and reviewed them. We are writing this review to amalgamate the pharmacological aspects and the previous studies on ERAs to demonstrate a comprehensive overview of the current status of ERAs for PAH treatment. We focused on the structure, pharmacodynamics, pharmacokinetics, and efficacy and safety of the three most widely used ERAs: Bosentan, Ambrisentan, and Macitentan. These drugs have different receptor affinities, bioavailability, excretion routes, and different levels of safety profiles. There are three available studies, the RCT, the ARIES series, and the SERAPHIN studies, for assessing the safety and efficacy of Bosentan, Ambrisentan, and Macitentan, respectively. All the studies and some additional studies for combination therapy have proven all three drugs effective in treating PAH. The side effects (SE) varied from headache and hepatic enzyme elevation to worsening the PAH status of varied severities. Although these studies provided valuable insight into the role of ERAs, there is still enough scope for more studies on ERAs, both as monotherapy and combination therapy for PAH.

Pathogenic Mechanisms of Pulmonary Arterial Hypertension: Homeostasis Imbalance of Endothelium-Derived Relaxing and Contracting Factors

Pulmonary arterial hypertension (PAH) is a progressive and fatal disease. Sustained pulmonary vasoconstriction and concentric pulmonary vascular remodeling contribute to the elevated pulmonary vascular resistance and pulmonary artery pressure in PAH. Endothelial cells regulate vascular tension by producing endothelium-derived relaxing factors (EDRFs) and endothelium-derived contracting factors (EDCFs). Homeostasis of EDRF and EDCF production has been identified as a marker of the endothelium integrity. Impaired synthesis or release of EDRFs induces persistent vascular contraction and pulmonary artery remodeling, which subsequently leads to the development and progression of PAH. In this review, the authors summarize how EDRFs and EDCFs affect pulmonary vascular homeostasis, with special attention to the recently published novel mechanisms related to endothelial dysfunction in PAH and drugs associated with EDRFs and EDCFs.

Recent Advances in the Treatment of Pulmonary Arterial Hypertension

Pulmonary arterial hypertension (PAH) is a disease in which stenosis or obstruction of the pulmonary arteries (PAs) causes an increase in PA pressure, leading to right-sided heart failure and death. Basic research has revealed a decrease in the levels of endogenous vasodilators, such as prostacyclin, and an increase in the levels of endogenous vasoconstrictors, such as endothelin, in patients with PAH, leading to the development of therapeutic agents. Currently, therapeutic agents for PAH target three pathways that are selective for PAs: the prostacyclin, endothelin, and nitric oxide pathways. These treatments improve the prognosis of PAH patients. In this review, we introduce new drug therapies and provide an overview of the current therapeutic agents.

Endothelin and the Cardiovascular System: The Long Journey and Where We Are Going

Simple Summary

In this review, we describe the basic functions of endothelin and related molecules, including their receptors and enzymes. Furthermore, we discuss the important role of endothelin in several cardiovascular diseases, the relevant clinical evidence for targeting the endothelin pathway, and the scope of endothelin-targeting treatments in the future. We highlight the present uses of endothelin receptor antagonists and the advancements in the development of future treatment options, thereby providing an overview of endothelin research over the years and its future scope.

Abstract

Endothelin was first discovered more than 30 years ago as a potent vasoconstrictor. In subsequent years, three isoforms, two canonical receptors, and two converting enzymes were identified, and their basic functions were elucidated by numerous preclinical and clinical studies. Over the years, the endothelin system has been found to be critical in the pathogenesis of several cardiovascular diseases, including hypertension, pulmonary arterial hypertension, heart failure, and coronary artery disease. In this review, we summarize the current knowledge on endothelin and its role in cardiovascular diseases. Furthermore, we discuss how endothelin-targeting therapies, such as endothelin receptor antagonists, have been employed to treat cardiovascular diseases with varying degrees of success. Lastly, we provide a glimpse of what could be in store for endothelin-targeting treatment options for cardiovascular diseases in the future.

Association of Endothelin-Converting Enzyme and Endothelin-1 Gene Polymorphisms with Essential Hypertension in Malay Ethnics

Objectives

Endothelin-1 (ET-1), the most potent endogenous vasoconstrictor, generated by enzymatic cleavage catalyzed by an endothelin-converting enzyme (ECE), plays a significant role in the regulation of hypertension.

Methods

This study investigates the effect of endothelin-1 (Lys198Asn/rs5370) and ECE (rs212526 C/T) gene polymorphisms with essential hypertension (EH) among Malay ethnics. To determine the association of gene polymorphism, 177 hypertensives and controls (196) were genotyped using Taqman method.

Results

A significant difference was observed in ET-1 rs5370 and ECE rs212526 gene polymorphisms between EH and control subjects (P < 0.001). A significantly high body mass index (BMI), waist-to-hip ratio, fasting plasma glucose, hemoglobin A1c, systolic and diastolic blood pressure, and lipid profiles were observed among the EH patients when compared to controls (P < 0.05). Moreover, T allele (rs5370) carriers in males have a high risk for EH. There was no significant association between gender in ECE C/T polymorphisms (P > 0.05).

Conclusion

Based on our result, it is evident that the T allele of ET-1 rs5370 polymorphism and C allele of ECE rs212526 have a significant genetic risk factor in EH among Malay subjects, and BMI and age are associated with hypertension.

The Causal Relationship between Endothelin-1 and Hypertension: Focusing on Endothelial Dysfunction, Arterial Stiffness, Vascular Remodeling, and Blood Pressure Regulation

Hypertension (HTN) is one of the most prevalent diseases worldwide and is among the most important risk factors for cardiovascular and cerebrovascular complications. It is currently thought to be the result of disturbances in a number of neural, renal, hormonal, and vascular mechanisms regulating blood pressure (BP), so crucial importance is given to the imbalance of a number of vasoactive factors produced by the endothelium. Decreased nitric oxide production and increased production of endothelin-1 (ET-1) in the vascular wall may promote oxidative stress and low-grade inflammation, with the development of endothelial dysfunction (ED) and increased vasoconstrictor activity. Increased ET-1 production can contribute to arterial aging and the development of atherosclerotic changes, which are associated with increased arterial stiffness and manifestation of isolated systolic HTN. In addition, ET-1 is involved in the complex regulation of BP through synergistic interactions with angiotensin II, regulates the production of catecholamines and sympathetic activity, affects renal hemodynamics and water–salt balance, and regulates baroreceptor activity and myocardial contractility. This review focuses on the relationship between ET-1 and HTN and in particular on the key role of ET-1 in the pathogenesis of ED, arterial structural changes, and impaired vascular regulation of BP. The information presented includes basic concepts on the role of ET-1 in the pathogenesis of HTN without going into detailed analyses, which allows it to be used by a wide range of specialists. Also, the main pathological processes and mechanisms are richly illustrated for better understanding.

Endothelial cells in the pathogenesis of pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is a devastating disease that involves pulmonary vasoconstriction, small vessel obliteration, large vessel thickening and obstruction, and development of plexiform lesions. PAH vasculopathy leads to progressive increases in pulmonary vascular resistance, right heart failure and, ultimately, premature death. Besides other cell types that are known to be involved in PAH pathogenesis (e.g. smooth muscle cells, fibroblasts and leukocytes), recent studies have demonstrated that endothelial cells (ECs) have a crucial role in the initiation and progression of PAH. The EC-specific role in PAH is multi-faceted and affects numerous pathophysiological processes, including vasoconstriction, inflammation, coagulation, metabolism and oxidative/nitrative stress, as well as cell viability, growth and differentiation. In this review, we describe how EC dysfunction and cell signalling regulate the pathogenesis of PAH. We also highlight areas of research that warrant attention in future studies, and discuss potential molecular signalling pathways in ECs that could be targeted therapeutically in the prevention and treatment of PAH.

Mechanism of herbal medicine on hypertensive nephropathy (Review)

Hypertensive nephropathy is the most common complication of hypertension, and is one of the main causes of end-stage renal disease (ESRD) in numerous countries. The basic pathological feature of hypertensive nephropathy is arteriolosclerosis followed by renal parenchymal damage. The etiology of this disease is complex, and its pathogenesis is mainly associated with renal hemodynamic changes and vascular remodeling. Despite the increased knowledge on the pathogenesis of hypertensive nephropathy, the current clinical treatment methods are still not effective in preventing the development of the disease to ESRD. Herbal medicine, which is used to relieve symptoms, can improve hypertensive nephropathy through multiple targets. Since there are few clinical studies on the treatment of hypertensive nephropathy with herbal medicine, this article aims to review the progress on the basic research on the treatment of hypertensive nephropathy with herbal medicine, including regulation of the renin angiotensin system, inhibition of sympathetic excitation, antioxidant stress and anti-inflammatory protection of endothelial cells, and improvement of obesity-associated factors. Herbal medicine with different components plays a synergistic and multi-target role in the treatment of hypertensive nephropathy. The description of the mechanism of herbal medicine in the treatment of hypertensive nephropathy will contribute towards the progress of modern medicine.

Predictive model of bosentan-induced liver toxicity in Japanese patients with pulmonary arterial hypertension

Bosentan, an endothelin receptor antagonist, has been widely used as a first-line medication for the treatment of pulmonary arterial hypertension (PAH). It has been shown to improve symptoms of hypertension, exercise capacity, and hemodynamics and prolong time to clinical worsening. However, liver dysfunction is a major side effect of bosentan treatment that could hamper the optimal management of patients with PAH. Previously, we demonstrated, using drug metabolism enzymes and transporters analysis, that the carbohydrate sulfotransferase 3 (CHST3) and CHST13 alleles are significantly more frequent in patients with elevated aminotransferases during therapy with bosentan than they are in patients without liver toxicity. In addition, we constructed a pharmacogenomics model to predict bosentan-induced liver injury in patients with PAH using two single-nucleotide polymorphisms and two nongenetic factors. The purpose of the present study was to externally validate the predictive model of bosentan-induced liver toxicity in Japanese patients. We evaluated five cases of patients treated with bosentan, and one presented with liver dysfunction. We applied mutation alleles of CHST3 and CHST13, serum creatinine, and age to our model to predict liver dysfunction. The sensitivity and specificity were calculated as 100% and 50%, respectively. Considering that PAH is a rare disease, multicenter collaboration would be necessary to validate our model.

Pazopanib, Cabozantinib, and Vandetanib in the Treatment of Progressive Medullary Thyroid Cancer with a Special Focus on the Adverse Effects on Hypertension

Medullary thyroid cancer (MTC) is a rare malignancy with a poor prognosis. First line therapy is surgery, which is the only curative method of the disease. However, in non-operable cases or with tumor progression and metastases, a systemic treatment is necessary. This form of cancer is often insensitive to conventional chemotherapy, but the use of tyrosine kinase inhibitors (TKIs), such as pazopanib, cabozantinib, and vandetanib, has shown promising results with an increase in progression-free survival and prolonged lifetime. Therefore, we focused on the pharmacological characteristics of TKIs, their mechanism of action, their application as a secondary treatment option for MTC, their efficacy as a cancer drug treatment, and reviewed the ongoing clinical trials. TKIs also act systemically causing various adverse events (AEs). One common AE of this treatment is hypertension, known to be associated with cardiovascular disease and can therefore potentially worsen the well-being of the treated patients. The available treatment strategies of drug-induced hypertension were discussed. The mechanism behind the development of hypertension is still unclear. Therefore, the treatment of this AE remains symptomatic. Thus, future studies are necessary to investigate the link between tumor growth inhibition and hypertension. In addition, optimized, individual treatment strategies should be implemented.

CHST3 and CHST13 polymorphisms as predictors of bosentan-induced liver toxicity in Japanese patients with pulmonary arterial hypertension

Bosentan, an endothelin receptor antagonist, has been widely used as a first-line drug for the treatment of pulmonary arterial hypertension (PAH). In addition, bosentan is approved for patients with digital ulcers related to systemic sclerosis. Liver dysfunction is a major adverse effect of bosentan and may lead to discontinuation of therapy. The purpose of this study was to identify genomic biomarkers to predict bosentan-induced liver injury. A total of 69 PAH patients were recruited into the study. An exploratory analysis of 1936 single-nucleotide polymorphisms (SNPs) in 231 genes involved in absorption, distribution, metabolism, and elimination of multiple medications using Affimetrix DMET™ (Drug Metabolism Enzymes and Transporters) chips was performed. We extracted 16 SNPs (P <  0.05) using the Jonckheere-Terpstra trend test and multiplex logistic analysis; we identified two SNPs in two genes, CHST3 and CHST13, which are responsible for proteoglycan sulfation and were significantly associated with bosentan-induced liver injury. We constructed a predictive model for bosentan-induced liver injury (area under the curve [AUC]: 0.89, sensitivity: 82.61%, specificity: 86.05%) via receiver operating curve (ROC) analysis using 2 SNPs and 2 non-genetic factors. Two SNPs were identified as potential predictive markers for bosentan-induced liver injury in Japanese patients with pulmonary arterial hypertension. This is the first pharmacogenomics study linking proteoglycan sulfating genes to drug-induced liver dysfunction, a frequently observed clinical adverse effect of bosentan therapy. These results may provide a way to personalize PAH medicine as well as provide novel mechanistic insights to drug-induced liver dysfunction.

Blockade of Endothelin-1 Receptor Type B Ameliorates Glucose Intolerance and Insulin Resistance in a Mouse Model of Obstructive Sleep Apnea

Obstructive sleep apnea (OSA) is associated with insulin resistance (IR) and glucose intolerance. Elevated endothelin-1 (ET-1) levels have been observed in OSA patients and in mice exposed to intermittent hypoxia (IH). We examined whether pharmacological blockade of type A and type B ET-1 receptors (ETA and ETB) would ameliorate glucose intolerance and IR in mice exposed to IH. Subcutaneously implanted pumps delivered BQ-123 (ETA antagonist; 200 nmol/kg/day), BQ-788 (ETB antagonist; 200 nmol/kg/day) or vehicle (saline or propyleneglycol [PG]) for 14 days in C57BL6/J mice (10/group). During treatment, mice were exposed to IH (decreasing the FiO2 from 20.9% to 6%, 60/h) or intermittent air (IA). After IH or IA exposure, insulin (0.5 IU/kg) or glucose (1 mg/kg) was injected intraperitoneally and plasma glucose determined after injection and area under glucose curve (AUC) was calculated. Fourteen-day IH increased fasting glucose levels (122 ± 7 vs. 157 ± 8 mg/dL, PG: 118 ± 6 vs. 139 ± 8; both p < 0.05) and impaired glucose tolerance (AUCglucose: 19,249 ± 1105 vs. 29,124 ± 1444, PG AUCglucose: 18,066 ± 947 vs. 25,135 ± 797; both p < 0.05) in vehicle-treated animals. IH-induced impairments in glucose tolerance were partially ameliorated with BQ-788 treatment (AUCglucose: 21,969 ± 662; p < 0.05). Fourteen-day IH also induced IR (AUCglucose: 7185 ± 401 vs. 8699 ± 401; p < 0.05). Treatment with BQ-788 decreased IR under IA (AUCglucose: 5281 ± 401, p < 0.05) and reduced worsening of IR with IH (AUCglucose: 7302 ± 401, p < 0.05). There was no effect of BQ-123 on IH-induced impairments in glucose tolerance or IR. Our results suggest that ET-1 plays a role in IH-induced impairments in glucose homeostasis.

[Pharmacoeconomic aspects of macitentan in the therapy of pulmonary arterial hypertension]

AIM

To provide a pharmacoeconomic estimate of macitentan versus bosentan in therapy for pulmonary arterial hypertension (PAH).

SUBJECT AND METHODS

An analysis was carried out on the basis of a social perspective for patients, whose mean age was 50 years. A budget impact analysis was performed without discounting; with the time horizon of the study being 5 years. Assessing the cost- effectiveness of endothelin receptor antagonists used a Markov model based on the meta-analysis of clinical trials. The cost of bosentan was calculated from the 2016 registered prices with VAT. That of macitentan was estimated from the expected price of 170,000 rubles per 10-mg dose pack #28 if the drug is included in the List of Essential Medicines with VAT. The cost of sildenafil and iloprost was consistent with the January-to-November 2016 auctio.

RESULTS

At cost-effectiveness assessment costs and outcomes were both discounted at an annual rate of 3,5%.

RESULTS

After 5 years of therapy with macitentan in patients with baseline Functional Class (FC) II PAH, the proportion of patients with FC I-II was shown to be 2.6% more than that during therapy with bosentan (20.1 and 17.5%, respectively), and that of the died patients was 1.5% lower (69.5 and 71%, respectively). In baseline FC III PAH following 5 years, the proportion of patients with FC III PAH on initial macitentan treatment was 1% more than that on bosentan therapy (8.1 and 7.1%, respectively), and that of the died patients was 0.5% lower (87.2, and 87.7%, respectively). The cost-effectiveness analysis shows that therapy with macitentan versus bosentan not only causes some increase in life expectancy in terms of quality of life (by 0.414 and 0.230 QALYs in FC II and III PAH, respectively), but also results in a small cost decrease in FC II and III PAH (by 11,000 and 16,000 rubles per patient, respectively). Thus, macitentan is a dominant alternative versus bosentan. The budget impact analysis indicates that when bosentan is replaced with macitentan, the reduction in health care costs in the Russian Federation will amount to 1.9 million rubles over 5 years, and in all budgetary costs will be 14.7 million rubles.

CONCLUSION

Treatment with macitentan in patients with FC II-III PAH is more cost-effective than that with bosentan and does not require an increase in budget costs.

TSP1-CD47 signaling is upregulated in clinical pulmonary hypertension and contributes to pulmonary arterial vasculopathy and dysfunction

AIMS

Thrombospondin-1 (TSP1) is a ligand for CD47 and TSP1-/- mice are protected from pulmonary hypertension (PH). We hypothesized the TSP1-CD47 axis is upregulated in human PH and promotes pulmonary arterial vasculopathy.

METHODS AND RESULTS

We analyzed the molecular signature and functional response of lung tissue and distal pulmonary arteries (PAs) from individuals with (n = 23) and without (n = 16) PH. Compared with controls, lungs and distal PAs from PH patients showed induction of TSP1-CD47 and endothelin-1/endothelin A receptor (ET-1/ETA) protein and mRNA. In control PAs, treatment with exogenous TSP1 inhibited vasodilation and potentiated vasoconstriction to ET-1. Treatment of diseased PAs from PH patients with a CD47 blocking antibody improved sensitivity to vasodilators. Hypoxic wild type (WT) mice developed PH and displayed upregulation of pulmonary TSP1, CD47, and ET-1/ETA concurrent with down regulation of the transcription factor cell homolog of the v-myc oncogene (cMyc). In contrast, PH was attenuated in hypoxic CD47-/- mice while pulmonary TSP1 and ET-1/ETA were unchanged and cMyc was overexpressed. In CD47-/- pulmonary endothelial cells cMyc was increased and ET-1 decreased. In CD47+/+ cells, forced induction of cMyc suppressed ET-1 transcript, whereas suppression of cMyc increased ET-1 signaling. Furthermore, disrupting TSP1-CD47 signaling in pulmonary smooth muscle cells abrogated ET-1-stimulated hypertrophy. Finally, a CD47 antibody given 2 weeks after monocrotaline challenge in rats upregulated pulmonary cMyc and improved aberrations in PH-associated cardiopulmonary parameters.

CONCLUSIONS

In pre-clinical models of PH CD47 targets cMyc to increase ET-1 signaling. In clinical PH TSP1-CD47 is upregulated, and in both, contributes to pulmonary arterial vasculopathy and dysfunction.

Association of oral endothelin receptor antagonists with risks of cardiovascular events and mortality: meta-analysis of randomized controlled trials

BACKGROUND

Endothelin receptor antagonists (ERAs) are widely used in a variety of disorders, including pulmonary artery hypertension, systemic sclerosis, diabetic and kidney diseases, and several tumors. However, reported adverse events, especially increased risks of cardiovascular disease (CVD) morbidity and mortality, have cast doubt on their potential clinical application. Therefore, we conducted this meta-analysis to confirm whether ERAs increased CVD risk and mortality.

METHODS

We systematically searched PubMed (1966-2015), EMBASE (1974-2015), ClinicalTrials.gov, and the Cochrane Controlled Clinical Trials Register Database for randomized controlled trials published between Jan 1, 1990 and Mar 18, 2015. Inclusion criteria included a study duration of more than 3 weeks, the use of a randomized control group receiving an oral ERA or placebo, and the availability of outcome data for cardiovascular events and all-cause death.

RESULTS

A total of 33 trials met the inclusion criteria. There were 8098 cases in the ERA group and 5074 cases in the placebo group. Compared with the control group, the risk ratio (RR) for all-cause death in the ERA group was 0.983 [95% confidence interval (CI), 0.883 to 1.094, P = 0.754]. The summary RR for cardiovascular events was 1.651 in the ERA group (95% CI, 1.164 to 2.34, P = 0.005). The pooled results showed that ERAs treatment could lead to more edema, anemia, and abnormal transaminase levels. Also, there was an increased proportion of discontinued therapy in the ERA treatment because of side effects (RR = 1.322, 95% CI, 1.036 to 1.686, P = 0.025). There were no significant differences in the experienced episodes of headache and dyspnea between the active therapy and control groups.

CONCLUSIONS

ERAs therapy is not significantly associated with increased all-cause death, but there are more cardiovascular events and edema or fluid retention, anemia, and liver enzymes disorder. Large clinical randomized controlled studies are needed to further confirm the safety of the clinical application of ERAs.

Portopulmonary hypertension

Portopulmonary hypertension (PoPH) refers to the condition that pulmonary arterial hypertension (PAH) occur in the stetting of portal hypertension. The development of PoPH is thought to be independent of the severity of portal hypertension or the etiology or severity of liver disease. PoPH results from excessive vasoconstriction, vascular remodeling, and proliferative and thrombotic events within the pulmonary circulation that lead to progressive right ventricular failure and ultimately to death. Untreated PoPH is associated with a poor prognosis. As PoPH is frequently asymptomatic or symptoms are generally non-specific, patients should be actively screened for the presence of PoPH. Two-dimensional transthoracic echocardiography is a useful non-invasive screening tool, but a definitive diagnosis requires invasive hemodynamic confirmation by right heart catheterization. Despite a dearth of randomized, prospective data, an ever-expanding clinical experience shows that patients with PoPH benefit from therapy with PAH-specific medications including with endothelin receptor antagonists, phosphodiesterase-5 inhibitors, and/or prostanoids. Due to high perioperative mortality, transplantation should be avoided in those patients who have severe PoPH that is refractory to medical therapy.

Endothelin-1 shifts the mediator of bradykinin-induced relaxation from NO to H2 O2 in resistance arteries from patients with cardiovascular disease

BACKGROUND AND PURPOSE

We tested the hypothesis that in resistance arteries from cardiovascular disease (CVD) patients, effects of an endothelium-dependent vasodilator depend on the contractile stimulus.

EXPERIMENTAL APPROACH

Arteries dissected from parietal pericardium of cardiothoracic surgery patients were studied by myography and imaging techniques. Segments were sub-maximally contracted by K(+) , the TxA2 analogue U46619 or endothelin-1 (ET-1).

KEY RESULTS

Relaxing effects of Na-nitroprusside were comparable, but those of bradykinin (BK) were bigger in the presence of ET-1 compared with K(+) or U46619. BK-induced relaxation was (i) abolished by L-NAME in K(+) -contracted arteries, (ii) partly inhibited by L-NAME in the presence of U46619 and (iii) not altered by indomethacin, L-NAME plus inhibitors of small and intermediate conductance calcium-activated K(+) channels, but attenuated by catalase, in ET-1-contracted arteries. This catalase-sensitive relaxation was unaffected by inhibitors of NADPH oxidases or allopurinol. Exogenous H2 O2 caused a larger relaxation of ET-1-induced contractions than those evoked by K(+) or U46619 in the presence of inhibitors of other endothelium-derived relaxing factors. Catalase-sensitive staining of cellular ROS with CellROX Deep Red was significantly increased in the presence of both 1 μM BK and 2 nM ET-1 but not either peptide alone.

CONCLUSIONS AND IMPLICATIONS

In resistance arteries from patients with CVD, exogenous ET-1 shifts the mediator of relaxing responses to the endothelium-dependent vasodilator BK from NO to H2 O2 and neither NADPH oxidases, xanthine oxidase nor NOS appear to be involved in this effect. This might have consequences for endothelial dysfunction in conditions where intra-arterial levels of ET-1 are enhanced.

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.

Epigenetic modulation as a therapeutic approach for pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is a rare but progressive and currently incurable disease, which is characterized by vascular remodeling in association with muscularization of the arterioles, medial thickening and plexiform lesion formation. Despite our advanced understanding of the pathogenesis of PAH and the recent therapeutic advances, PAH still remains a fatal disease. In addition, the susceptibility to PAH has not yet been adequately explained. Much evidence points to the involvement of epigenetic changes in the pathogenesis of a number of human diseases including cancer, peripheral hypertension and asthma. The knowledge gained from the epigenetic study of various human diseases can also be applied to PAH. Thus, the pursuit of novel therapeutic targets via understanding the epigenetic alterations involved in the pathogenesis of PAH, such as DNA methylation, histone modification and microRNA, might be an attractive therapeutic avenue for the development of a novel and more effective treatment. This review provides a general overview of the current advances in epigenetics associated with PAH, and discusses the potential for improved treatment through understanding the role of epigenetics in the development of PAH.

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

INTRODUCTION

Pulmonary arterial hypertension (PAH) is a chronic disorder of the pulmonary vasculature characterized by elevated mean pulmonary arterial pressure eventually leading to right-sided heart failure and premature death. Macitentan is an oral, once-daily, dual endothelin (ET)A and ETB receptor antagonist with high affinity and sustained receptor binding that was approved in the USA, Europe, Canada, and Switzerland for the treatment of PAH.

AREAS COVERED

This review discusses the pharmacokinetics (PK) and pharmacodynamics (PD) of macitentan and its drug interaction potential based on preclinical and clinical data.

EXPERT OPINION

Up to date, macitentan is the only registered treatment for PAH that significantly reduced morbidity and mortality as a combined endpoint in a long-term event-driven study. The safety profile of macitentan is favorable with respect to hepatic safety and edema/fluid retention and may be better than that of other ET receptor antagonists such as bosentan and ambrisentan. The PK profile supports a once-a-day dosing regimen. Macitentan has limited interactions with other drugs. Based on these characteristics macitentan is an important new addition to the treatment of PAH.