Endothelin receptor antagonists in pulmonary arterial hypertension

Liver injury associated with endothelin receptor antagonists: a pharmacovigilance study based on FDA adverse event reporting system data

BACKGROUND

Endothelin receptor antagonists are commonly used in clinical practice, with concerns about their hepatotoxicity.

AIM

This study aimed to conduct a comprehensive pharmacovigilance study based on FDA adverse event reporting system data to evaluate the possible association between endothelin receptor antagonists and drug-induced liver injury.

METHOD

Adverse event reports from FDA adverse event reporting system between January 2004 and December 2022 were analyzed. Disproportionality algorithms, including reporting odds ratio and information component, were used to evaluate the association between endothelin receptor antagonists and liver injury. Sex- and age-stratified analyses of drug-induced liver injury events were also conducted in relation to endothelin receptor antagonists.

RESULTS

Significant associations between bosentan, macitentan, and liver injury were identified. Bosentan showed a strong link with liver injury, with reporting odds ratios for cholestatic injury at 7.59 (95% confidence interval: 6.90-8.35), hepatocellular injury at 5.63 (5.29-6.00), and serious drug-related hepatic disorders events at 1.33 (1.24-1.43). Drug-induced liver injury signals associated with bosentan were detected in all age groups. Macitentan was associated with liver injury, with reporting odds ratios for hepatic failure at 1.64 (1.39-1.94), cholestatic injury at 1.62 (1.43-1.83), and serious drug-related hepatic disorders events at 1.40 (1.29-1.51). No drug-induced liver injury signal was detected for ambrisentan, and no significant sex differences were observed in drug-induced liver injury events.

CONCLUSION

Both bosentan and macitentan are associated with liver injury. Routine monitoring of serum aminotransferase levels is recommended, especially in patients at higher risk of liver injury. Further research into drug-drug interactions involving endothelin receptor antagonists is warranted.

Endothelin receptor B-deficient mice are protected from high-fat diet-induced metabolic syndrome

OBJECTIVE

Endothelin receptor B (ETB) together with ETA mediates cellular effects of endothelin 1 (ET-1), an autocrine and endocrine peptide produced by the endothelium and other cells. It regulates vascular tone and controls kidney function. Metabolic syndrome is due to high caloric intake and is characterized by insulin resistance, dyslipidemia, and white adipose tissue (WAT) accumulation. ETA/ETB antagonism has been demonstrated to favorably influence insulin resistance. Our study explored the role of ETB in metabolic syndrome.

METHODS

Wild type (etb+/+) and rescued ETB-deficient (etb-/-) mice were fed a high-fat diet, and energy, glucose, and insulin metabolism were analyzed, and hormones and lipids measured in serum and tissues. Cell culture experiments were performed in HepG2 cells.

RESULTS

Compared to etb+/+ mice, etb-/- mice exhibited better glucose tolerance and insulin sensitivity, less WAT accumulation, lower serum triglycerides, and higher energy expenditure. Protection from metabolic syndrome was paralleled by higher hepatic production of fibroblast growth factor 21 (FGF21) and higher serum levels of free thyroxine (fT4), stimulators of energy expenditure.

CONCLUSIONS

ETB deficiency confers protection from metabolic syndrome by counteracting glucose intolerance, dyslipidemia, and WAT accumulation due to enhanced energy expenditure, effects at least in part dependent on enhanced production of thyroid hormone/FGF21. ETB antagonism may therefore be a novel therapeutic approach in metabolic syndrome.

Inhibition of Hsp110-STAT3 interaction in endothelial cells alleviates vascular remodeling in hypoxic pulmonary arterial Hypertension model

BACKGROUND

Pulmonary arterial hypertension (PAH) is a progressive and devastating disease characterized by pulmonary vascular remodeling which is associated with the malignant phenotypes of pulmonary vascular cells. Recently, the effects of heat shock protein 110 (Hsp110) in human arterial smooth muscle cells were reported. However, the underlying roles and mechanisms of Hsp110 in human pulmonary arterial endothelial cells (HPAECs) that was disordered firstly at the early stage of PAH remain unknown.

METHODS

In this research, the expression of Hsp110 in PAH human patients and rat models was investigated, and the Hsp110 localization was determined both in vivo and in vitro. The roles and mechanism of elevated Hsp110 in excessive cell proliferation and migration of HPAECs were assessed respectively exposed to hypoxia. Small molecule inhibitors targeting Hsp110-STAT3 interaction were screened via fluorescence polarization, anti-aggregation and western blot assays. Moreover, the effects of compound 6 on HPAECs abnormal phenotypes in vitro and pulmonary vascular remodeling of hypoxia-indued PAH rats in vivo by interrupting Hsp110-STAT3 interaction were evaluated.

RESULTS

Our studies demonstrated that Hsp110 expression was increased in the serum of patients with PAH, as well as in the lungs and pulmonary arteries of PAH rats, when compared to their respective healthy subjects. Moreover, Hsp110 levels were significantly elevated in HPAECs under hypoxia and mediated its aberrant phenotypes. Furthermore, boosted Hsp110-STAT3 interaction resulted in abnormal proliferation and migration via elevating p-STAT3 and c-Myc in HPAECs. Notably, we successfully identified compound 6 as potent Hsp110-STAT3 interaction inhibitor, which effectively inhibited HPAECs proliferation and migration, and significantly ameliorated right heart hypertrophy and vascular remodeling of rats with PAH.

CONCLUSIONS

Our studies suggest that elevated Hsp110 plays a vital role in HPAECs and inhibition of the Hsp110-STAT3 interaction is a novel strategy for improving vascular remodeling. In addition, compound 6 could serve as a promising lead compound for developing first-in-class drugs against PAH.

A Bioinformatic Algorithm based on Pulmonary Endoarterial Biopsy for Targeted Pulmonary Arterial Hypertension Therapy

Background

Optimal pharmacological therapy for pulmonary arterial hypertension (PAH) remains unclear, as pathophysiological heterogeneity may affect therapeutic outcomes. A ranking methodology based on pulmonary vascular genetic expression analysis could assist in medication selection and potentially lead to improved prognosis.

Objective

To describe a bioinformatics approach for ranking currently approved pulmonary arterial antihypertensive agents based on gene expression data derived from percutaneous endoarterial biopsies in an animal model of pulmonary hypertension.

Methods

We created a chronic PAH model in Micro Yucatan female swine by surgical anastomosis of the left pulmonary artery to the descending aorta. A baseline catheterization, angiography and pulmonary endoarterial biopsy were performed. We obtained pulmonary vascular biopsy samples by passing a biopsy catheter through a long 8 French sheath, introduced via the carotid artery, into 2- to 3-mm peripheral pulmonary arteries. Serial procedures were performed on days 7, 21, 60, and 180 after surgical anastomosis. RNA microarray studies were performed on the biopsy samples.

Results

Utilizing the medical literature, we developed a list of PAH therapeutic agents, along with a tabulation of genes affected by these agents. The effect on gene expression from pharmacogenomic interactions was used to rank PAH medications at each time point. The ranking process allowed the identification of a theoretical optimum three-medication regimen.

Conclusion

We describe a new potential paradigm in the therapy for PAH, which would include endoarterial biopsy, molecular analysis and tailored pharmacological therapy for patients with PAH.

Diagnosis and management of pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is a progressive disease of the pulmonary vasculature that is characterised by elevated pressures within the pulmonary vascular tree. Recent decades have witnessed a dramatic expansion in our understanding of the pathobiology and the epidemiology of PAH, and improvements in treatment options and outcomes. The prevalence of PAH is estimated to be between 48 and 55 cases per million adults. The definition was recently amended and a diagnosis of PAH now requires evidence of a mean pulmonary artery pressure >20 mmHg, a pulmonary vascular resistance >2 Wood units and a pulmonary artery wedge pressure ≤15 mmHg at right heart catheterisation. Detailed clinical assessment and a number of additional diagnostic tests are required to assign a clinical group. Biochemistry, echocardiography, lung imaging and pulmonary function tests provide valuable information to assist in the assignment of a clinical group. Risk assessment tools have been refined, and these greatly facilitate risk stratification and enhance treatment decisions and prognostication. Current therapies target three therapeutic pathways: the nitric oxide, prostacyclin and endothelin pathways. While lung transplantation remains the only curative intervention for PAH, there are a number of promising therapies under investigation which may further reduce morbidity and improve outcomes. This review describes the epidemiology, pathology and pathobiology of PAH and introduces important concepts regarding the diagnosis and risk stratification of PAH. The management of PAH is also discussed, with a special focus on PAH specific therapy and key supportive measures.

Gender Differences in Genotypic Distribution of Endothelin-1 Gene and Endothelin receptor A gene in Pulmonary Hypertension associated with Rheumatic Mitral Valve Disease

Introduction

The female gender is a risk factor for idiopathic pulmonary arterial hypertension. However, it is unknown whether females with rheumatic mitral valve disease are more predisposed to develop pulmonary hypertension compared to males.

Aim

We aimed to investigate whether there was a difference in genotypic distribution of endothelin-1 (ET-1) and endothelin receptor A (ET_A) genes between female and male patients of pulmonary hypertension associated with rheumatic mitral valve disease (PH-MVD).

Methods

We compared prevalence of ET-1 gene (Lys198Asn) and ET_A gene (His323His) polymorphisms according to gender in 123 PH-MVD subjects and 123 healthy controls.

Results

The presence of mutant Asn/Asn and either mutant Asn/Asn or heterozygous Lys/Asn genotypes of Lys198Asn polymorphism when compared to Lys/Lys in females showed significant association with higher risk (odds ratio [OR] 4.5; p =0.007 and OR 2.39; p =0.02, respectively). The presence of heterozygous C/T and either mutant T/T or heterozygous C/T genotypes of His323His polymorphism when compared to wild C/C genotype in females showed a significant association with higher risk (OR 1.96; p =0.047 and OR 2.26; p =0.01, respectively). No significant difference was seen in genotypic frequencies in males between PH-MVD subjects and controls. Logistic regression analysis showed that mutant genotype Asn/Asn (p =0.007) and heterozygous genotype Lys/Asn of Lys198Asn polymorphism (p =0.018) were independent predictors of development of PH in females.

Conclusions

ET-1 and ET_A gene polymorphisms were more prevalent in females than males in PH-MVD signifying that females with rheumatic heart disease may be more susceptible to develop PH.

BMI and Treatment Response in Patients With Pulmonary Arterial Hypertension

Background

Obesity is increasingly prevalent in pulmonary arterial hypertension (PAH) but is associated with improved survival, creating an “obesity paradox” in PAH. It is unknown if the improved outcomes could be attributable to obese patients deriving a greater benefit from PAH therapies.

Research Question

Does BMI modify treatment effectiveness in PAH?

Study Design and Methods

Using individual participant data, a meta-analysis was conducted of phase III, randomized, placebo-controlled trials of treatments for PAH submitted for approval to the U.S. Food and Drug Administration from 2000 to 2015. Primary outcomes were change in 6-min walk distance (6MWD) and World Health Organization (WHO) functional class.

Results

A total of 5,440 participants from 17 trials were included. Patients with overweight and obesity had lower baseline 6MWD and were more likely to be WHO functional class III or IV. Treatment was associated with a 27.01-m increase in 6MWD (95% CI, 21.58-32.45; P < .001) and lower odds of worse WHO functional class (OR, 0.58; 95% CI, 0.48-0.70; P < .001). For every 1 kg/m² increase in BMI, 6MWD was reduced by 0.66 m (P = .07); there was no significant effect modification of treatment response in 6MWD according to BMI (P for interaction = .34). Higher BMI was not associated with odds of WHO functional class at end of follow-up; however, higher BMI attenuated the treatment response such that every 1 kg/m² increase in BMI increased odds of worse WHO functional class by 3% (OR, 1.03; P for interaction = .06).

Interpretation

Patients with overweight and obesity had lower baseline 6MWD and worse WHO functional class than patients with normal weight with PAH. Higher BMI did not modify the treatment response for change in 6MWD, but it attenuated the treatment response for WHO functional class. PAH trials should include participants representative of all weight groups to allow for assessment of treatment heterogeneity and mechanisms.

Endothelin B Receptor Immunodynamics in Pulmonary Arterial Hypertension

Introduction

Inflammation is a major pathological feature of pulmonary arterial hypertension (PAH), particularly in the context of inflammatory conditions such as systemic sclerosis (SSc). The endothelin system and anti-endothelin A receptor (ET_A) autoantibodies have been implicated in the pathogenesis of PAH, and endothelin receptor antagonists are routinely used treatments for PAH. However, immunological functions of the endothelin B receptor (ET_B) remain obscure.

Methods

Serum levels of anti-ET_B receptor autoantibodies were quantified in healthy donors and SSc patients with or without PAH. Age-dependent effects of overexpression of prepro-endothelin-1 or ET_B deficiency on pulmonary inflammation and the cardiovascular system were studied in mice. Rescued ET_B-deficient mice (ET_B^-/-) were used to prevent congenital Hirschsprung disease. The effects of pulmonary T-helper type 2 (Th2) inflammation on PAH-associated pathologies were analyzed in ET_B^-/- mice. Pulmonary vascular hemodynamics were investigated in isolated perfused mouse lungs. Hearts were assessed for right ventricular hypertrophy. Pulmonary inflammation and collagen deposition were assessed via lung microscopy and bronchoalveolar lavage fluid analyses.

Results

Anti-ET_B autoantibody levels were elevated in patients with PAH secondary to SSc. Both overexpression of prepro-endothelin-1 and rescued ET_B deficiency led to pulmonary hypertension, pulmonary vascular hyperresponsiveness, and right ventricular hypertrophy with accompanying lymphocytic alveolitis. Marked perivascular lymphocytic infiltrates were exclusively found in ET_B^-/- mice. Following induction of pulmonary Th2 inflammation, PAH-associated pathologies and perivascular collagen deposition were aggravated in ET_B^-/- mice.

Conclusion

This study provides evidence for an anti-inflammatory role of ET_B. ET_B seems to have protective effects on Th2-evoked pathologies of the cardiovascular system. Anti-ET_B autoantibodies may modulate ET_B-mediated immune homeostasis.

A narrative review on adverse effects of dasatinib with a focus on pharmacotherapy of dasatinib-induced pulmonary toxicities

Chronic myeloid leukemia (CML), a myeloproliferative disorder caused by the over activity of BCR-ABL1 (breakpoint cluster region-Abelson), has been successfully treated by Tyrosine kinase inhibitors (TKIs). While imatinib is known as the first-line treatment of CML, in some cases other TKIs including dasatinib, nilotinib, bosutinib, and ponatinib may be preferred. Dasatinib, a second-generation TKI, inhibits multiple family kinases including BCR-ABL, SRC family kinases, receptor kinases, and TEC family kinases. It is effective against most imatinib-resistant cases except T315I mutation. Despite the superiority of dasatinib in its hematologic and cytogenetic responses in CML compared to imatinib, its potentially harmful pulmonary complications including pleural effusion (PE) and pulmonary arterial hypertension (PAH) may limit its use. Appropriate management of these serious adverse reactions is critical in both improving the quality of life and the outcome of the patient. In this narrative review, we will scrutinize the pulmonary complications of dasatinib and focus on the management of these toxicities.

Update on Medical Management of Pulmonary Arterial Hypertension

Pulmonary arterial hypertension is a rare disease characterized by pulmonary microvasculature remodeling leading to right ventricular failure and death. Medical management of pulmonary hypertension has grown increasingly complex as more therapeutic agents have been developed. Evolving treatment strategies leveraging the endothelin, nitric oxide, and prostacyclin pathways lead to improved exercise capacity and outcomes in patients; however, significant opportunities for advancement remain.

The Endothelin Receptor Antagonist Macitentan Inhibits Human Cytomegalovirus Infection

Human cytomegalovirus (HCMV) infection is an important cause of morbidity and mortality in immunocompromised patients and a major etiological factor for congenital birth defects in newborns. Ganciclovir and its pro-drug valganciclovir are the preferred drugs in use today for prophylaxis and treatment of viremic patients. Due to long treatment times, patients are at risk for developing viral resistance to ganciclovir and to other drugs with a similar mechanism of action. We earlier found that the endothelin receptor B (ETBR) is upregulated during HCMV infection and that it plays an important role in the life cycle of this virus. Here, we tested the hypothesis that ETBR blockade could be used in the treatment of HCMV infection. As HCMV infection is specific to humans, we tested our hypothesis in human cell types that are relevant for HCMV pathogenesis; i.e., endothelial cells, epithelial cells and fibroblasts. We infected these cells with HCMV and treated them with the ETBR specific antagonist BQ788 or ETR antagonists that are approved by the FDA for treatment of pulmonary hypertension; macitentan, its metabolite ACT-132577, bosentan and ambrisentan, and as an anti-viral control, we used ganciclovir or letermovir. At concentrations expected to be relevant in vivo, macitentan, ACT-132577 and BQ788 effectively inhibited productive infection of HCMV. Of importance, macitentan also inhibited productive infection of a ganciclovir-resistant HCMV isolate. Our results suggest that binding or signaling through ETBR is crucial for viral replication, and that selected ETBR blockers inhibit HCMV infection.

Comparative assessment of efficacy and safety of ambrisentan and bosentan in patients with pulmonary arterial hypertension: A meta-analysis

WHAT IS KNOWN AND OBJECTIVE

Two endothelin receptor antagonists, ambrisentan and bosentan, have been demonstrated to be effective individually compared with placebo in the treatment of patients with pulmonary arterial hypertension (PAH). This network meta-analysis compared the efficacy and safety of ambrisentan and bosentan in patients with PAH.

METHODS

Clinical trials were identified from the Cochrane Central Register of Controlled Trials (CENTRAL/CCTR), EMBASE and PubMed databases. Weighted mean differences (MD) with 95% confidence intervals (CI) were calculated for continuous outcomes (6-min walk distance [6MWD] and Borg dyspnoea index [BDI]). Hazard ratio (HR) was calculated for binary outcomes, including clinical worsening, discontinuation due to adverse events (AEs) and liver dysfunction. Surface under cumulative ranking curve (SUCRA) was used to rank the treatments in each index.

RESULTS

Five clinical trials from four published studies (total patients: n = 920) were included. Ambrisentan and bosentan showed no significant difference in 6MWD (MD: -1.32; 95% CI: -27.87, 25.31, SUCRA score: ambrisentan 0.73, bosentan 0.77), BDI (MD: -0.16; 95% CI: -0.98, 0.65, SUCRA score: ambrisentan 0.83, bosentan 0.66), clinical worsening (HR: 0.99; 95% CI: 0.33, 2.94, SUCRA score: ambrisentan 0.75, bosentan 0.74) and discontinuation due to AEs (HR: 0.84; 95% CI: 0.11, 5.86, SUCRA score: ambrisentan 0.47, bosentan 0.57). However, ambrisentan was significantly better than bosentan with respect to abnormal liver function (HR: 23.18; 95% CI: 2.24, 377.20, SUCRA score: ambrisentan 0.99, bosentan 0.02).

WHAT IS NEW AND CONCLUSION

The results of this network meta-analysis suggest that ambrisentan was similar to bosentan in efficacy, while it exhibited better tolerability with respect to abnormal liver function in comparison with bosentan, in patients with PAH.

Platelets, extracellular vesicles and coagulation in pulmonary arterial hypertension

Pulmonary arterial hypertension is a rare disease of the pulmonary vasculature, characterised pathologically by proliferation, remodelling and thrombosis in situ. Unfortunately, existing therapeutic interventions do not reverse these findings and the disease continues to result in significant morbidity and premature mortality. A number of haematological derangements have been described in pulmonary arterial hypertension which may provide insights into the pathobiology of the disease and opportunities to explore new therapeutic pathways. These include quantitative and qualitative platelet abnormalities, such as thrombocytopaenia, increased mean platelet volume and altered platelet bioenergetics. Furthermore, a hypercoagulable state and aberrant negative regulatory pathways can be observed, which could contribute to thrombosis in situ in distal pulmonary arteries and arterioles. Finally, there is increasing interest in the role of extracellular vesicle autocrine and paracrine signalling in pulmonary arterial hypertension, and their potential utility as biomarkers and novel therapeutic targets. This review focuses on the potential role of platelets, extracellular vesicles and coagulation pathways in the pathobiology of pulmonary arterial hypertension. We highlight important unanswered clinical questions and the implications of these observations for future research and pulmonary arterial hypertension-directed therapies.

Pulmonary Arterial Hypertension in Pregnancy

Pulmonary arterial hypertension is a rare disease that predominantly affects women. The pathophysiology of the disease is complex, with both genetic and hormonal influences. Pregnancy causes significant physiologic changes that may not be well tolerated with underlying pulmonary arterial hypertension, in particular leading to volume overload and increased pulmonary pressures. A multidisciplinary approach and careful monitoring are essential for appropriate management of pulmonary arterial hypertension during pregnancy. Nonetheless, outcomes are still poor, and pregnancy is considered a contraindication in patients with pulmonary arterial hypertension.

Discovery of Novel Pyrazolo[3,4-b] Pyridine Derivatives with Dual Activities of Vascular Remodeling Inhibition and Vasodilation for the Treatment of Pulmonary Arterial Hypertension

Current pulmonary arterial hypertension (PAH) therapeutic strategies mainly focus on vascular relaxation with less emphasis on vascular remodeling, which results in poor prognosis. Hence, dual pathway regulators with vasodilation effect via soluble guanylate cyclase (sGC) stimulation and vascular remodeling regulation effect by AMP-activated protein kinase (AMPK) inhibition provide more advantages and potentialities. Herein, we designed and synthesized a series of novel pyrazolo[3,4-b] pyridine derivatives based on sGC stimulator and AMPK inhibitor scaffolds. In vitro, 2 exhibited moderate vasodilation activity and higher proliferation and migration suppressive effects compared to riociguat. In vivo, 2 significantly decreased right ventricular systolic pressure (RVSP), attenuated pulmonary artery medial thickness (PAMT), and right ventricular hypertrophy (RVH) in hypoxia-induced PAH rat models (i.g.). Given the unique advantages of significant vascular remodeling inhibition and moderate vascular relaxation based on the dual pathway regulation, we proposed 2 as a promising lead for anti-PAH drug discovery.

Pharmacology of Pulmonary Arterial Hypertension: An Overview of Current and Emerging Therapies

Pulmonary arterial hypertension is a rare and devastating disease characterized by an abnormal chronic increase in pulmonary arterial pressure above 20 mmHg at rest, with a poor prognosis if not treated. Currently, there is not a single fully effective therapy, even though a dozen of drugs have been developed in the last decades. Pulmonary arterial hypertension is a multifactorial disease, meaning that several molecular mechanisms are implicated in its pathology. The main molecular pathways regulating the pulmonary vasomotor tone-endothelin, nitric oxide, and prostacyclin-are the most biologically and therapeutically explored to date. However, drugs targeting these pathways have already found their limitations. In the last years, translational research and clinical trials have made a strong effort in suggesting and testing novel therapeutic strategies for this disease. These approaches involve targeting the main molecular pathways with novel drugs, drug repurposing for novel targets, and also using combinatorial therapies. In this review, we summarize current strategies and drugs targeting the endothelin, nitric oxide, and prostacyclin pathways, as well as, the emerging new drugs proposed to cope with vascular remodelling, metabolic switch, perivascular inflammation, epigenetic modifications, estrogen deregulation, serotonin, and other neurohumoral mechanisms characteristic of this disease. Nowadays, pulmonary arterial hypertension remains an incurable disease; however, the incoming new knowledge makes us believe that new promising therapies are coming to the clinical arena soon.

Bioequivalence and Tolerability of Ambrisentan: A Pharmacokinetic Study in Mexican Healthy Male Subjects

BACKGROUND

Pulmonary arterial hypertension (PAH) is a disease characterized by a progressive rise in pulmonary vascular resistance. Ambrisentan is an oral, propanoic acid based-endothelin receptor antagonist (ERA), selective for the endothelin type-A receptor, which is approved for the treatment of PAH. The Colombia National Food and Drug Surveillance Institute regulatory criteria require demonstrating that the proposed generic product is bioequivalent to its reference-listed drug to obtain marketing approval.

OBJECTIVES

The purpose of this study was to test the bioequivalence, pharmacokinetics, and tolerability of ambrisentan 10 mg tablets.

METHODS

In this open-label, randomized, oral single-dose, two-way crossover bioequivalence study, 26 Mexican adult healthy male subjects received either the generic product of ambrisentan 10 mg or the reference product Volibris^® (ambrisentan) 10 mg tablets during each study period under fasting conditions. There was a 7-day washout period between each dosing. Ambrisentan concentrations in plasma samples were quantified using a validated ultra-performance liquid chromatography coupled with tandem mass spectrometry (UPLC-MS/MS) method. Blood samples were collected up to 72 h post-dose in each study period. The primary end points were maximum plasma concentration (C_max) and area under the plasma concentration-time (AUC_0-t) curve between 0 and 72 h for ambrisentan.

RESULTS

The ratios (90% CI) of geometric mean for ambrisentan were 104.3% (97.12-111.98%) and 100.2% (95.56-104.72%). These pharmacokinetic parameter values lie within the INVIMA-specified bioequivalence limits of 80%-125%. Nervous system disorders were the most common adverse events (AEs). All AEs were mild to moderate in nature and were resolved after follow-up or pharmacologic treatment. Both products were safe and well tolerated.

CONCLUSIONS

The test product ambrisentan 10 mg tablets is bioequivalent to the reference product Volibris^® (ambrisentan) 10 mg tablets. Both treatments were well tolerated in the Mexican male population of this study.

TRIAL REGISTRATION

COFEPRIS National Clinical Trials Registry number 183300410B0367/2018.

A non-selective endothelin receptor antagonist bosentan modulates kinetics of bone marrow-derived cells in ameliorating pulmonary hypertension in mice

The aim of this study was to investigate whether a dual endothelin receptor antagonist bosentan modulates the kinetics of bone marrow-derived stem cells in inhibiting the development of pulmonary hypertension. Bone marrow chimeric mice, transplanted with enhanced green fluorescent protein (eGFP)-positive bone marrow mononuclear cells, were exposed to hypobaric hypoxia or kept in the ambient air, and were daily treated with bosentan sodium salt or saline for 21 days. After the treatment period, right ventricular pressure was measured and pulmonary vascular morphometry was conducted. Incorporation of bone marrow-derived cells was analyzed by immunohistochemistry. Gene expression and protein level in the lung tissue were evaluated by quantitative real-time PCR and western blotting, respectively. The results showed that, in hypoxic mice, right ventricular pressure and the percentage of muscularized vessel were increased and pulmonary vascular density was decreased, each of which was reversed by bosentan. Bone marrow-derived endothelial cells and macrophages in lungs were increased by hypoxia. Bosentan promoted bone marrow-derived endothelial cell incorporation but inhibited macrophage infiltration into lungs. Quantitative real-time PCR analysis revealed that interleukin 6, stromal cell-derived factor-1, and monocyte chemoattractant protein-1 were upregulated by hypoxia, in which interleukin 6 and monocyte chemoattractant protein-1 were downregulated and stromal cell-derived factor-1 was upregulated by bosentan. Protein level of endothelial nitric oxide synthase (eNOS) in the whole lung was significantly upregulated by hypoxia, which was further upregulated by bosentan. Bosentan modulated kinetics of bone marrow-derived ECs and macrophages and related gene expression in lungs in ameliorating pulmonary hypertension in mice. Altered kinetics of bone marrow-derived stem cells may be a novel mechanism of the endothelin receptor blockade in vivo and confer a new understanding of the therapeutic basis for pulmonary hypertension.

Diagnosis and Management of Pulmonary Hypertension in Patients With CKD

Pulmonary hypertension (PH) is a highly prevalent and important condition in adults with chronic kidney disease (CKD). In this review, we summarize the definition of PH, discuss its pathophysiology and classifications, and describe diagnostic and management strategies in patients with CKD, including those with kidney failure treated by kidney replacement therapy. In the general population, PH is classified into 5 groups based on clinical presentation, pathology, hemodynamics, and management strategies. In this classification system, PH in CKD is placed in a diverse group with unclear or multifactorial mechanisms, although underlying cardiovascular disease may account for most cases. CKD may itself directly incite pulmonary circulatory dysfunction and remodeling through uremic toxins, inflammation, endothelial dysfunction, and altered vasoregulation. Despite several studies describing the higher prevalence of PH in CKD and kidney failure, along with an association with poor outcomes, high-quality evidence is not available for its diagnostic and management strategies in those with CKD. In CKD not requiring kidney replacement therapy, volume management along with treatment of underlying risk factors for PH are critical. In those receiving hemodialysis, options are limited and transition to peritoneal dialysis may be considered if recurrent hypotension precludes optimal volume control.

Newer approaches and novel drugs for inhalational therapy for pulmonary arterial hypertension

Introduction: Pulmonary arterial hypertension (PAH) is a progressive disease characterized by remodeling of small pulmonary arteries leading to increased pulmonary arterial pressure. Existing treatments acts to normalize vascular tone via three signaling pathways: the prostacyclin, the endothelin-1, and the nitric oxide. Although over the past 20 years, there has been considerable progress in terms of treatments for PAH, the disease still remains incurable with a disappointing prognosis.Areas covered: This review summarizes the pathophysiology of PAH, the advantages and disadvantages of the inhalation route, and assess the relative advantages various inhaled therapies for PAH. The recent studies concerning the development of controlled-release drug delivery systems loaded with available anti-PAH drugs have also been summarized.Expert opinion: The main obstacles of current pharmacotherapies of PAH are their short half-life, stability, and formulations, resulting in reducing the efficacy and increasing systemic side effects and unknown pathogenesis of PAH. The pulmonary route has been proposed for delivering anti-PAH drugs to overcome the shortcomings. However, the application of approved inhaled anti-PAH drugs is limited. Inhalational delivery of controlled-release nanoformulations can overcome these restrictions. Extensive studies are required to develop safe and effective drug delivery systems for PAH patients.

Volume Management in Pulmonary Arterial Hypertension Patients: An Expert Pulmonary Hypertension Clinician Perspective

Fluid volume management in patients with pulmonary arterial hypertension (PAH) is essential in preventing right ventricular failure. Volume overload may be caused by disease progression, indiscretion of dietary sodium and fluid intake, or medication side effects, and is a frequent complication in patients with PAH. Healthcare professionals (HCPs) who care for patients with PAH have a key role in monitoring, preventing, and managing volume overload. Volume management techniques in patients with PAH include managing diuretic use and electrolyte imbalances, and monitoring fluid retention that can occur from the use of endothelin receptor antagonists or calcium channel blockers. Healthcare providers can create volume management protocols as well as patient educational materials. Patients should be educated to self-monitor their daily weights, incorporate dietary restrictions, and recognize symptoms associated with volume overload. Tools to help HCPs with volume management in patients with PAH are provided in this article.Funding Actelion Pharmaceuticals US, Inc.

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

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

Macitentan in Pulmonary Arterial Hypertension: A Focus on Combination Therapy in the SERAPHIN Trial

SERAPHIN was a double-blind, placebo-controlled, event-driven phase III trial that evaluated the effects of long-term treatment with macitentan, an oral endothelin receptor antagonist, in patients with pulmonary arterial hypertension (PAH). The majority of patients were receiving PAH therapy at enrollment, providing the opportunity to evaluate the efficacy and safety of macitentan in combination with other PAH therapies (predominantly phosphodiesterase type 5 inhibitors [PDE-5i]). In patients receiving background therapy, macitentan reduced the risk of morbidity/mortality by 38% compared with placebo (hazard ratio [HR] 0.62; 95% confidence level [CL] 0.43-0.89; p = 0.009). Furthermore, patients receiving macitentan and background therapy had a 37% reduction in the risk of being hospitalized for PAH (HR 0.63; 95% CL 0.41-0.96) compared with patients receiving background therapy only (placebo arm). Macitentan treatment in combination with background therapy was also associated with improvements in exercise capacity, functional class, cardiopulmonary hemodynamics, and health-related quality of life compared with background therapy alone. The safety profile of macitentan as part of a combination therapy regimen was consistent with that of macitentan in the overall SERAPHIN population. The SERAPHIN study has provided evidence that combination therapy with macitentan and a PDE-5i is effective and well tolerated in the management of PAH. Based on these data, and those from subsequent long-term trials, combination therapy is increasingly recognized as an important treatment option for improving long-term outcomes in PAH.

CLINICAL TRIAL REGISTRATION NUMBER

NCT00660179.

COPD as an endothelial disorder: endothelial injury linking lesions in the lungs and other organs? (2017 Grover Conference Series)

Chronic obstructive pulmonary disease (COPD) is characterized by chronic expiratory airflow obstruction that is not fully reversible. COPD patients develop varying degrees of emphysema, small and large airway disease, and various co-morbidities. It has not been clear whether these co-morbidities share common underlying pathogenic processes with the pulmonary lesions. Early research into the pathogenesis of COPD focused on the contributions of injury to the extracellular matrix and pulmonary epithelial cells. More recently, cigarette smoke-induced endothelial dysfunction/injury have been linked to the pulmonary lesions in COPD (especially emphysema) and systemic co-morbidities including atherosclerosis, pulmonary hypertension, and chronic renal injury. Herein, we review the evidence linking endothelial injury to COPD, and the pathways underlying endothelial injury and the "vascular COPD phenotype" including: (1) direct toxic effects of cigarette smoke on endothelial cells; (2) generation of auto-antibodies directed against endothelial cells; (3) vascular inflammation; (4) increased oxidative stress levels in vessels inducing increases in lipid peroxidation and increased activation of the receptor for advanced glycation end-products (RAGE); (5) reduced activation of the anti-oxidant pathways in endothelial cells; (6) increased endothelial cell release of mediators with vasoconstrictor, pro-inflammatory, and remodeling activities (endothelin-1) and reduced endothelial cell expression of mediators that promote vasodilation and homeostasis of endothelial cells (nitric oxide synthase and prostacyclin); and (7) increased endoplasmic reticular stress and the unfolded protein response in endothelial cells. We also review the literature on studies of drugs that inhibit RAGE signaling in other diseases (angiotensin-converting enzyme inhibitors and angiotensin receptor blockers), or vasodilators developed for idiopathic pulmonary arterial hypertension that have been tested on cell culture systems, animal models of COPD, and/or smokers and COPD patients.

[Bosentan use in pulmonary arterial hypertension: Russian and foreign experience]

The results of evaluating the efficacy and safety of bosentan in patients with pulmonary arterial hypertension (PAH), as shown by the data of foreign randomized controlled trials and the authors' own experience, convincingly demonstrate that the introduction of the drug into clinical practice has led to a significant improvement of the possibilities of drug therapy in patients with this serious illness. Bosentan substantially improves physical activity in patients, reduces the severity of clinical symptoms, slows down the rates of disease progression, and prolongs survival in patients with different forms of PAH.

Tanshinone IIA protects against chronic intermittent hypoxia-induced myocardial injury via activating the endothelin 1 pathway

Tanshinone IIA (Tan IIA) may exert significant protective effects against heart oxidative stress damage in obstructive sleep apnoea (OSA) syndrome. Chronic intermittent hypoxia (CIH)-triggered left ventricular dysfunction is used in a rat model to mimic CIH in OSA patients. 48 rats were randomly divided into three groups: normal control (NC) group, CIH group and CIH+Tan IIA group with 16 rats in each group. At the end of experiment (day 21), the blood pressure, Plasma ET-1 and NO content, hemodynamic indexes, heart histology, myocardial apoptosis as well as the expression of eNOS, ET-1, ET_A receptor and ET_B receptor were compared among different groups. Tan IIA was able to inhibit the increase of blood pressure induced by CIH. Meanwhile, rat cardiac function in Tan IIA group was evaluated by hemodynamic indexes, histopathological examination. Higher ventricular eNOS activity was induced by Tan IIA with a reduction in both ET-1 and ET_A receptor expression. However, Tan IIA largely inhibited the decrease of ET_B receptor expression. This study demonstrated that Tan IIA has the potential to benefit rat heart against CIH via endothelin system.

A systems biology and proteomics-based approach identifies SRC and VEGFA as biomarkers in risk factor mediated coronary heart disease

Coronary heart disease (CHD) is the most common cause of death worldwide. The burden of CHD increases with risk factors such as smoking, hypertension, obesity and diabetes. Several studies have demonstrated the association of these classical risk factors with CHD. However, the mechanisms of these associations remain largely unclear due to the complexity of disease pathophysiology and the lack of an integrative approach that fails to provide a definite understanding of molecular linkage. To overcome these problems, we propose a novel systems biology approach that relates causative genes, interactomes and pathways to elucidate the risk factors mediating the molecular mechanisms and biomarkers for feasible diagnosis. The literature was mined to retrieve the causative genes of each risk factor and CHD to construct protein interactomes. The interactomes were examined to identify 298 common molecular signatures. The common signatures were mapped to the tissue network to synthesize a sub-network consisting of 82 proteins. Further, the dissection of the sub-network provides functional modules representing a diverse range of molecular functions, including the AKT/p13k, MAPK and wnt pathways. Also, the prioritization of functional modules identifies SRC, VEGFA and HIF1A as potential candidate markers. Further, we validate these candidates with the existing markers CRP, NOS3 and VCAM1 in the serum of 63 individuals, 33 with CHD and 30 controls, using ELISA. SRC, VEGFA, H1F1A, CRP and NOS3 were significantly altered in patients compared to controls. These results support the utility of these candidate markers for the diagnosis of CHD. Overall, our molecular observations indicate the influence of risk factors in the pathophysiology of CHD and identify serum markers for diagnosis.

Comparative efficacy and acceptability of endothelin receptor antagonists for pulmonary arterial hypertension: A network meta-analysis

BACKGROUND

Endothelin receptor antagonists (ERAs) such as ambrisentan, sitaxsentan, bosentan and macitentan are primary drug therapies for pulmonary arterial hypertension (PAH) patients. However, the optimal drugs for PAH remained controversial due to heterogeneous nature of randomized control trials (RCTs).

METHODS

Apart from traditional meta-analysis, network meta-analysis (NMA) was performed in this study for multiple comparisons among PAH therapies. The 6 minute walking distance (6MWD) and clinical worsening were efficacy outcomes whereas serious adverse effects (SAE) and all-cause discontinuation were acceptability outcomes. The weighted mean difference (WMD) and odds ratio (OR) along with their 95% confidence interval (95% CI) or 95% credible interval (95% CrI) were used to evaluate the positive and negative effects of these therapies on PAH patients.

RESULTS

By synthesizing direct evidence from 10 studies with a total number of 2172 patients, we discovered that all of the four PAH therapies significantly increased the average 6MWD in comparison to the placebo (P-value<0.05). Moreover, bosentan and ambrisentan both showed significant association with a decrease in the risk of clinical worsening compared to placebo. Regarding of all-cause discontinuation, ambrisentan is the only therapy which was significantly associated with a risk decrease compared to placebo. However, there was no sufficient evidence suggesting significant difference in any efficacy or acceptability outcomes between any two of the PAH therapies (P-value>0.05).

CONCLUSION

Ambrisentan could be considered as the most appropriate therapy among the four ERAs for PAH patients. Bosentan also behaved well, but it is not as safe as ambrisentan.

Selexipag in Pulmonary Arterial Hypertension: Most Updated Evidence From Recent Preclinical and Clinical Studies

Pulmonary arterial hypertension (PAH) is a relatively rare disease that, due to its chronic nature, has always been difficult to treat effectively. Selexipag is an oral prostacyclin (PGI₂ ) agonist that was approved by US Food and Drug Administration (US FDA) in December 2015 for the treatment of PAH. After its success in phase 1 and phase 2 clinical trials regarding the convenient oral twice-daily dosing and low side-effect profile, selexipag raised the hope of controlling the disease progression in PAH patients. In the recently completed multicentered phase 3 study (GRIPHON), selexipag has been shown to reduce death and hospitalization due to PAH significantly, an effect that was consistent across different ranges of maintenance dose. In the same study selexipag use was also associated with an increase in 6-minute walk distance (a measure of symptom severity) from baseline, but no significant improvement in all-cause mortality could be observed. The results of the ongoing phase 3 studies (TRITON and TRANSIT-1) are expected to throw some more light on the safety and efficacy of this novel molecule across various treatment scenarios. Hence, our article aims to summarize all the available information from preclinical and clinical studies published to date on the pharmacodynamics, pharmacokinetics, efficacy, safety (in general and in scenarios such as hepatic and renal function impairment), significant drug interactions (with warfarin and antiretroviral drugs), and clinical significance of oral selexipag in patients with PAH.

[The new endothelin receptor antagonist macitentan: Prospects for therapy of pulmonary arterial hypertension]

Pulmonary arterial hypertension (PAH) is a clinical group of severe and rare diseases with similar morphological, hemodynamic, and therapeutic characteristics. One of the novel drugs to treat PAH is macitentan, a new double endothelin ETA and ETB receptor antagonist that is characterized by special physicochemical properties, ensuring the penetration of the drug into tissues and its improved receptor-binding properties. The SERAPHIN trial has demonstrated that therapy with macitentan 10 mg versus placebo statistically significantly reduces the risk of poor outcomes and death by 45%. The treatment with macitentan 10 is observed to be highly effective regardless of the presence/absence of basic PAH-specific therapy. The drug considerably improves clinically important outcomes, including 6-minute walk distance and WHO functional class. Macitentan exerts a steady-state therapeutic effect, by improving pulmonary hemodynamics. Macitentan 10 mg statistically significantly reduces the risk of PAH, frequency of its related hospitalizations, and the number of days spent in hospital. The drug has a favorable safety profile; its most common side effects are headache, nasopharyngitis, and anemia. Macitentan is an effective first-line drug to improve long-term outcomes in patients with newly and previously diagnosed PAH.

Effect of treatment with iloprost with or without bosentan on nailfold videocapillaroscopic alterations in patients with systemic sclerosis

INTRODUCTION

Vascular involvement plays a decisive role in systemic sclerosis (SSc) pathogenesis; it is responsible for some important clinical manifestations of the disease such as Raynaud's phenomenon and digital ulcers (DU). Bosentan, a dual receptor endothelin antagonist, and iloprost, often in combination therapy, seems to be able to interfere with the scleroderma microangiopathy.

OBJECTIVES

Aim of the study was to evaluate the effect of bosentan and iloprost on scleroderma microangiopathy, analyzed by means of capillaroscopic skin ulcer risk index (CSURI), in SSc patients treated for the prevention of DU.

METHODS

Nailfold videocapillaroscopy (NVC) was performed in 95 SSc patients, treated with iloprost alone (group 1) or combination therapy with iloprost and bosentan (group 2), at baseline and after one year. In all patients CSURI was calculated according to the formula "diameter × number of megacapillaries/(total number of capillaries)²": in addition, total number of capillaries, giant capillaries, micro-hemorrhages, disorganization of the vascular array, and ramified capillaries were evaluated by means of a semiquantitative score.

RESULTS

After 12 months, we observed a reduction of the number of giant capillaries in both groups, while an increase of ramified capillaries was recorded only in group 2. CSURI improved slightly in group 2 without statistical significance; on the contrary, in group 1 a significant worsening was recorded (p ≤ 0.001).

CONCLUSIONS

Our study confirms the effectiveness of bosentan, in combination with iloprost, in SSc microangiopathy observed to NVC. Moreover, the observed findings further support the role of CSURI in the evaluation and monitoring of SSc microangiopathy.

Lung Capillary Stress Failure and Arteriolar Remodelling in Pulmonary Hypertension Associated with Left Heart Disease (Group 2 PH)

Left heart diseases (LHD) represent the most prevalent cause of pulmonary hypertension (PH), yet there are still no approved therapies that selectively target the pulmonary circulation in LHD. The increase in pulmonary capillary pressure due to LHD is a triggering event leading to physical and biological alterations of the pulmonary circulation. Acutely, mechanosensitive endothelial dysfunction and increased capillary permeability combined with reduced fluid resorption lead to the development of interstitial and alveolar oedema. From repeated cycles of such capillary stress failure originate more profound changes with pulmonary endothelial dysfunction causing increased basal and reactive pulmonary vascular tone. This contributes to pulmonary vascular remodelling with increased arterial wall thickness, but most prominently, to alveolar wall remodelling characterized by myofibroblasts proliferation with collagen and interstitial matrix deposition. Although protective against acute pulmonary oedema, alveolar wall thickening becomes maladaptive and is responsible for the development of a restrictive lung syndrome and impaired gas exchanges contributing to shortness of breath and PH. Increasing awareness of these processes is unraveling novel pathophysiologic processes that could represent selective therapeutic targets. Thus, the roles of caveolins, of the intermediate myofilament nestin and of endothelial calcium dyshomeostasis were recently evaluated in pre-clinical models. The pathophysiology of PH due to LHD (group II PH) is distinctive from other groups of PH. Therefore, therapies targeting PH due to LHD must be evaluated in that context.

Endothelial cell regulation of pulmonary vascular tone, inflammation, and coagulation

The pulmonary endothelium represents a heterogeneous cell monolayer covering the luminal surface of the entire lung vasculature. As such, this cell layer lies at a critical interface between the blood, airways, and lung parenchyma, and must act as a selective barrier between these diverse compartments. Lung endothelial cells are able to produce and secrete mediators, display surface receptor, and cellular adhesion molecules, and metabolize circulating hormones to influence vasomotor tone, both local and systemic inflammation, and coagulation functions. In this review, we will explore the role of the pulmonary endothelium in each of these systems, highlighting key regulatory functions of the pulmonary endothelial cell, as well as novel aspects of the pulmonary endothelium in contrast to the systemic cell type. The interactions between pulmonary endothelial cells and both leukocytes and platelets will be discussed in detail, and wherever possible, elements of endothelial control over physiological and pathophysiological processes will be examined.

[Approaches to therapy for pulmonary hypertension: Role of the endothelin receptor antagonist bosentan]

Pulmonary hypertension (PH) is a specific clinical group of severe and rare diseases with similar morphological, hemodynamic, and therapeutic characteristics. Despite the fact that there have been international conciliative documents and advances in drug therapy for PH, the long-term prognosis of the.disease in these patients remains rather poor. Clinical trials have demonstrated that bosentan therapy in patients with PH improves pulmonary hemodynamics and exercise endurance and delays the development of the disease. According to the data of long-term studies, as compared to the historical control, bosentan used as a first-line drug can improve survival in PH patients.

Riociguat for the treatment of pulmonary hypertension

Nitric oxide (NO) is a critical signaling molecule in the pulmonary vasculature. NO activates soluble guanylate cyclase (sGC) resulting in the synthesis of cyclic guanosine monophosphate (cGMP) - a key mediator of pulmonary artery vasodilatation that may also inhibit smooth muscle proliferation and platelet aggregation. Pulmonary hypertension, a serious, progressive and often fatal disease is characterized by NO-sGC-sGMP pathway dysregulation. Riociguat is a member of a novel therapeutic class known as soluble guanylate stimulators. Riociguat has a dual mode of action, acting in synergy with endogenous NO and also directly stimulating sGC independently of NO availability. Phase 3 randomized control trials have demonstrated that riociguat improves clinical, physiologic and hemodynamic parameters in patients with pulmonary arterial hypertension and chronic thromboembolic pulmonary hypertension. In this review we will discuss the pharmacologic properties of riociguat and its appropriate implementation into clinical practice.

Development of macitentan for the treatment of pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is a serious, chronic condition that, without early recognition and treatment, leads to progressive right heart failure and death. The dual endothelin receptor antagonist macitentan was designed through a deliberate discovery process to maximize endothelin-axis blockade while improving adverse-effect profiles compared with previous compounds. Macitentan's efficacy was demonstrated in an event-driven morbidity and mortality study of treatment-naive and background PAH therapy-treated symptomatic patients. Compared to placebo, 10 mg of macitentan significantly reduced the relative risk of morbidity and mortality by 45%, primarily by delaying PAH worsening, most prominently in World Health Organization (WHO) functional class II and III PAH patients. Macitentan reduced the incidence of the composite end point of PAH-related hospitalizations and mortality and improved WHO FC and exercise capacity (6-min walk distance). Furthermore, it significantly improved cardiopulmonary hemodynamics and quality of life, and had a favorable safety and tolerability profile. To date, this was the largest and longest prospective trial for PAH. Macitentan, currently the only approved oral PAH treatment shown to be safe and effective in delaying long-term progression and reducing PAH-related hospitalizations, has changed treatment paradigms from goal-directed to long-term outcome-oriented therapy.

Hypoxic pulmonary vasoconstriction: physiology and anesthetic implications

Hypoxic pulmonary vasoconstriction (HPV) represents a fundamental difference between the pulmonary and systemic circulations. HPV is active in utero, reducing pulmonary blood flow, and in adults helps to match regional ventilation and perfusion although it has little effect in healthy lungs. Many factors affect HPV including pH or PCO2, cardiac output, and several drugs, including antihypertensives. In patients with lung pathology and any patient having one-lung ventilation, HPV contributes to maintaining oxygenation, so anesthesiologists should be aware of the effects of anesthesia on this protective reflex. Intravenous anesthetic drugs have little effect on HPV, but it is attenuated by inhaled anesthetics, although less so with newer agents. The reflex is biphasic, and once the second phase becomes active after about an hour of hypoxia, this pulmonary vasoconstriction takes hours to reverse when normoxia returns. This has significant clinical implications for repeated periods of one-lung ventilation.

Clinical pharmacology of endothelin receptor antagonists used in the treatment of pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is a devastating life-threatening disorder characterized by elevated pulmonary vascular resistance leading to elevated pulmonary arterial pressures, right ventricular failure, and ultimately death. Vascular endothelial cells mainly produce and secrete endothelin (ET-1) in vessels that lead to a potent and long-lasting vasoconstrictive effect in pulmonary arterial smooth muscle cells. Along with its strong vasoconstrictive action, ET-1 can promote smooth muscle cell proliferation. Thus, ET-1 blockers have attracted attention as an antihypertensive drug, and the ET-1 signaling system has paved a new therapeutic avenue for the treatment of PAH. We outline the current understanding of not only the pathogenic role played by ET-1 signaling systems in the pathogenesis of PH but also the clinical pharmacology of endothelin receptor antagonists (ERA) used in the treatment of PAH.

Macitentan for the treatment of pulmonary arterial hypertension

Macitentan is the most recently approved dual endothelin-receptor antagonist (ERA) for the treatment of symptomatic pulmonary arterial hypertension. Compared to other available ERAs, it demonstrates superior receptor-binding properties, with consequently improved tissue penetration, and a longer duration of action allowing for once-daily dosing. It has a favorable adverse-effect profile, with notably no demonstrable increase in the risk of hepatotoxicity or peripheral edema, but like other ERAs, it is potentially limited by significant anemia. Phase I data have demonstrated a favorable drug-drug interaction profile and no need for dose adjustment with hepatic and renal impairment. In the pivotal SERAPHIN study, treatment of symptomatic pulmonary arterial hypertension patients with macitentan led to statistically significant improvements in functional class, exercise tolerance, and hemodynamic parameters, in addition to a reduction in morbidity in an event-driven long-term trial.

Molecular imaging of the pulmonary circulation in health and disease

The pulmonary circulation, at the unique crossroads between the left and the right heart, is submitted to large physiologic hemodynamic variations and possesses numerous important metabolic functions mediated through its vast endothelial surface. There are many pathologic conditions that can directly or indirectly affect the pulmonary vasculature and modify its physiology and functions. Pulmonary hypertension, the end result of many of these affections, is unfortunately diagnosed too late in the disease process, meaning that there is a crying need for earlier diagnosis and surrogate markers of disease progression and regression. By targeting endothelial, medial and adventitial targets of the pulmonary vasculature, novel molecular imaging agents could provide early detection of physiologic and biologic perturbation in the pulmonary circulation. This review provides the rationale for the development of molecular imaging agents for the diagnosis and follow-up of disorders of the pulmonary circulation and discusses promising targets for SPECT and positron emission tomographic imaging.

The role of endothelin-1 and endothelin receptor antagonists in inflammatory response and sepsis

Endothelin-1 (ET-1) is a potent endogenous vasoconstrictor, mainly secreted by endothelial cells. It acts through two types of receptors: ETA and ETB. Apart from a vasoconstrictive action, ET-1 causes fibrosis of the vascular cells and stimulates production of reactive oxygen species. It is claimed that ET-1 induces proinflammatory mechanisms, increasing superoxide anion production and cytokine secretion. A recent study has shown that ET-1 is involved in the activation of transcription factors such as NF-κB and expression of proinflammatory cytokines including TNF-α, IL-1, and IL-6. It has been also indicated that during endotoxaemia, the plasma level of ET-1 is increased in various animal species. Some authors indicate a clear correlation between endothelin plasma level and morbidity/mortality rate in septic patients. These pathological effects of ET-1 may be abrogated at least partly by endothelin receptor blockade. ET-1 receptor antagonists may be useful for prevention of various vascular diseases. This review summarises the current knowledge regarding endothelin receptor antagonists and the role of ET-1 in sepsis and inflammation.

Macitentan for the treatment of pulmonary arterial hypertension

Macitentan is a novel dual endothelin receptor antagonist recently approved for the treatment of symptomatic pulmonary arterial hypertension (PAH). Compared to other endothelin receptor antagonists, in vitro and in vivo studies have demonstrated that macitentan has improved tissue targeting, a longer duration of action and an improved safety profile. Macitentan is available as a once daily oral medication and has been well tolerated in clinical trials. The recently published Study with an Endothelin Receptor Antagonist in PAH to Improve cliNical Outcomes (SERAPHIN), which was the first event-driven trial ever done in PAH, also demonstrated the benefit of macitentan on reducing the likelihood of a composite endpoint of morbidity and mortality events without a significant difference in mortality.

Differentially expressed plasma microRNAs and the potential regulatory function of Let-7b in chronic thromboembolic pulmonary hypertension

Chronic thromboembolic pulmonary hypertension (CTEPH) is a progressive disease characterized by misguided thrombolysis and remodeling of pulmonary arteries. MicroRNAs are small non-coding RNAs involved in multiple cell processes and functions. During CTEPH, circulating microRNA profile endued with characteristics of diseased cells could be identified as a biomarker, and might help in recognition of pathogenesis. Thus, in this study, we compared the differentially expressed microRNAs in plasma of CTEPH patients and healthy controls and investigated their potential functions. Microarray was used to identify microRNA expression profile and qRT-PCR for validation. The targets of differentially expressed microRNAs were identified in silico, and the Gene Ontology database and Kyoto Encyclopedia of Genes and Genomes pathway database were used for functional investigation of target gene profile. Targets of let-7b were validated by fluorescence reporter assay. Protein expression of target genes was determined by ELISA or western blotting. Cell migration was evaluated by wound healing assay. The results showed that 1) thirty five microRNAs were differentially expressed in CTEPH patients, among which, a signature of 17 microRNAs, which was shown to be related to the disease pathogenesis by in silico analysis, gave diagnostic efficacy of both sensitivity and specificity >0.9. 2) Let-7b, one of the down-regulated anti-oncogenic microRNAs in the signature, was validated to decrease to about 0.25 fold in CTEPH patients. 3) ET-1 and TGFBR1 were direct targets of let-7b. Altering let-7b level influenced ET-1 and TGFBR1 expression in pulmonary arterial endothelial cells (PAECs) as well as the migration of PAECs and pulmonary arterial smooth muscle cells (PASMCs). These results suggested that CTEPH patients had aberrant microRNA signature which might provide some clue for pathogenesis study and biomarker screening. Reduced let-7b might be involved in the pathogenesis of CTEPH by affecting ET-1 expression and the function of PAECs and PASMCs.