Clinical efficacy of sitaxsentan, an endothelin-A receptor antagonist, in patients with pulmonary arterial hypertension: open-label pilot study

Identifying the Interaction Between Tuberculosis and SARS-CoV-2 Infections via Bioinformatics Analysis and Machine Learning

The number of patients with COVID-19 caused by severe acute respiratory syndrome coronavirus 2 is still increasing. In the case of COVID-19 and tuberculosis (TB), the presence of one disease affects the infectious status of the other. Meanwhile, coinfection may result in complications that make treatment more difficult. However, the molecular mechanisms underpinning the interaction between TB and COVID-19 are unclear. Accordingly, transcriptome analysis was used to detect the shared pathways and molecular biomarkers in TB and COVID-19, allowing us to determine the complex relationship between COVID-19 and TB. Two RNA-seq datasets (GSE114192 and GSE163151) from the Gene Expression Omnibus were used to find concerted differentially expressed genes (DEGs) between TB and COVID-19 to identify the common pathogenic mechanisms. A total of 124 common DEGs were detected and used to find shared pathways and drug targets. Several enterprising bioinformatics tools were applied to perform pathway analysis, enrichment analysis and networks analysis. Protein-protein interaction analysis and machine learning was used to identify hub genes (GAS6, OAS3 and PDCD1LG2) and datasets GSE171110, GSE54992 and GSE79362 were used for verification. The mechanism of protein-drug interactions may have reference value in the treatment of coinfection of COVID-19 and TB.

No Placebo Effect beyond Regression to the Mean on the Six Minute Walk Test in Pulmonary Arterial Hypertension Trials

In drug studies, patients are often included when the disease activity is high. This will make any treatment appear to lessen disease activity, although the improvement is biased by selection. This effect is known as regression towards the mean (RTM). We aimed at investigating drug trials in Pulmonary Arterial Hypertension (PAH) using the 6-minute walking distance test (6MWD) as a primary outcome for the phenomenon of RTM. An existing registry of 43 open label studies and 23 randomized controlled trials conducted between 1990 and 2009 was used as the data source. Data analysis was carried out for 18 randomized controlled trials (RCTs) and 24 open label studies out of this registry. Data were analyzed for verum and placebo arms of the RCTs separately, as well as for the open label arms. In the verum arms, the overall effect given as 33.2 m (95% CI: 25.7; 40.6]); 6MWD was slightly lower than the effect in the observational studies, with 44.6 m (95% CI: [25.4; 63.8]). After studying and interpreting the data, we found that regression towards the mean plays only a minor role in PAH studies. In particular, placebo effects in the RCTs were negligibly small, with a mean 6MWD of -2.5 m (95% CI: [-9.8; 4.7]) in the placebo arm. Therefore, our analysis indicates that results of non-randomized observational studies can be regarded as valid tools for gaining valid clinical effects in patients with PAH.

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.

Mechanisms of pulmonary vascular dysfunction in pulmonary hypertension and implications for novel therapies

Pulmonary hypertension (PH) is a serious disease characterized by various degrees of pulmonary vasoconstriction and progressive fibroproliferative remodeling and inflammation of the pulmonary arterioles that lead to increased pulmonary vascular resistance, right ventricular hypertrophy, and failure. Pulmonary vascular tone is regulated by a balance between vasoconstrictor and vasodilator mediators, and a shift in this balance to vasoconstriction is an important component of PH pathology, Therefore, the mainstay of current pharmacological therapies centers on pulmonary vasodilation methodologies that either enhance vasodilator mechanisms such as the NO-cGMP and prostacyclin-cAMP pathways and/or inhibit vasoconstrictor mechanisms such as the endothelin-1, cytosolic Ca2+, and Rho-kinase pathways. However, in addition to the increased vascular tone, many patients have a "fixed" component in their disease that involves altered biology of various cells in the pulmonary vascular wall, excessive pulmonary artery remodeling, and perivascular fibrosis and inflammation. Pulmonary arterial smooth muscle cell (PASMC) phenotypic switch from a contractile to a synthetic and proliferative phenotype is an important factor in pulmonary artery remodeling. Although current vasodilator therapies also have some antiproliferative effects on PASMCs, they are not universally successful in halting PH progression and increasing survival. Mild acidification and other novel approaches that aim to reverse the resident pulmonary vascular pathology and structural remodeling and restore a contractile PASMC phenotype could ameliorate vascular remodeling and enhance the responsiveness of PH to vasodilator therapies.

Safety, tolerability, and pharmacokinetics of the selective prostacyclin receptor agonist ralinepag in single and multiple dosing studies of an immediate-release oral formulation in healthy volunteers

Ralinepag (APD811), an oral, potent, and selective prostacyclin receptor (IP) agonist is being developed for treatment of pulmonary arterial hypertension. Two, single-center, randomized, double-blind, placebo-controlled, Phase 1 studies (single ascending dose and multiple ascending dose) evaluated an oral immediate-release capsule formulation of ralinepag in healthy subjects. Blood samples assessed plasma pharmacokinetics and safety and tolerability data monitored adverse events, vital signs, laboratory findings, physical examination, and electrocardiograms. Eighty-two healthy subjects (single ascending dose (n = 32) and multiple ascending dose (n = 50)) completed the studies. No clinically significant safety issues were observed, except one serious adverse event of atrial fibrillation considered moderate in intensity. In the single ascending dose study, ralinepag was tolerated up to 100 µg (single dose), but not 200 µg due to nausea and vomiting. Dose proportional mean ralinepag plasma exposure measures were observed. Maximum plasma concentrations were reached within 1.0–1.5 h post-dose and mean terminal elimination half-life values from 20.5–26.4 h. In the multiple ascending dose study, ralinepag tolerability decreased with increasing QD or BID dose. Dose proportional steady-state plasma exposure measures were observed where evaluable, with mean steady-state peak-to-trough ratios ranging from 3.34–4.49 (QD dosing) and 1.95–2.36 (BID dosing). Mean effective half-life values ranged from 17.5–18.4 h, reflecting ∼1.7-fold (QD dosing) and ∼2.6-fold (BID dosing) accumulation in plasma exposure. Safety and tolerability of oral immediate-release ralinepag was generally consistent with expectations for this drug class, but more individualized dose escalation appears warranted. Ralinepag exhibited favorable pharmacokinetic properties, with BID dosing producing desired minimal steady-state peak-to-trough fluctuation. Overall, results supported further clinical investigation of ralinepag and guided development of an extended-release formulation to facilitate QD dosing.

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.

Sitaxsentan for Treatment of Pulmonary Hypertension

Objective:

To review the literature pertinent to the efficacy and safety of sitaxsentan, a selective endothelin (ET)-A receptor antagonist under evaluation for the treatment of pulmonary arterial hypertension (PAH).

Data Sources:

Articles were identified through searches of the MEDLINE (1966–November 2006) and International Pharmaceutical Abstracts (1970–November 2006) databases, using the key words endothelin antagonist, pulmonary arterial hypertension, pulmonary hypertension, sitaxsentan, and TBC11251. Searches were limited to articles published in English.

Study Selection And Data Extraction:

Due to the limited number of articles on sitaxsentan, all studies captured in the search results were evaluated.

Data Synthesis:

Four studies of sitaxsentan in humans with PAH have been published to date. An uncontrolled open-label study and a randomized placebo-controlled study (STRIDE-1; Sitaxsentan to Relieve Impaired Exercise-1) showed sitaxsentan to improve exercise tolerance in patients with PAH, as evidenced by significant increases in the distance walked in 6 minutes. Significant hepatotoxicity developed in patients receiving sitaxsentan 300 mg. The benefits of sitaxsentan with respect to exercise tolerance and hemodynamics were sustained in a one year extension of the placebo-controlled study. The results of a multicenter, randomized, placebo-controlled trial of 2 doses of sitaxsentan with an open-label bosentan arm (STRIDE-2) suggested that only the 100 mg dose provided superior benefit in exercise tolerance and improvement in functional class. Treatment-related adverse effects were similar for all groups.

Conclusions:

Sitaxsentan appears to be superior to placebo in improving exercise tolerance in patients with PAH but may produce therapeutic outcomes similar to those of bosentan, a comparator agent. The optimal dose of sitaxsentan appears to be 100 mg once daily. Information about the use of sitaxsentan in a greater number of patients with PAH for longer periods is necessary to further define its place in the treatment of PAH.

Nitric Oxide Signaling and Clinical Alternatives to Nitric Oxide

Nitric oxide has been implicated in numerous biological processes, particularly those involved with the cardiovascular system. Nitric oxide production is closely regulated and influenced by a number of factors in both health and disease. Nitric oxide is involved in maintaining the vascular system in its healthy, nondiseased state by producing vasorelaxation which enhances blood flow and prevents both leukocyte and platelet adhesion to the vascular wall. Dysfunctional endothelial cell nitric oxide production has been implicated in a number of disease states, including hypertension and atherosclerosis, and has been associated with adverse cardiac events. Various recent therapies may exert their beneficial effects in part by enhancing endothelial nitric oxide bloavallability. Nitric oxide has been used therapeutically in a number of cardiorespiratory disease states. An improved understanding of the pathologic processes underlying these diseases has resulted in several alternative agents being investigated and used clinically.

Present and future treatment strategies for pulmonary arterial hypertension : focus on phosphodiesterase-5 inhibitors

Idiopathic pulmonary arterial hypertension (IPAH) is a rare progressive disorder historically associated with mortality in <3 years post-diagnosis. The etiology of PAH is complex, multifactorial, and likely involves the interplay between genetic and environmental factors. These are reviewed with emphasis on the nitric oxide pathway. Use of treatment modalities including vasodilator therapy have resulted in improved symptoms, hemodynamics, and survival in these patients. Vasodilators, including the calcium channel antagonists, prostanoids, and endothelin receptor antagonists, have been used to counteract potential imbalances in vasoactive mediators in PAH patients; all have produced improved long-term symptomatology and hemodynamics. Only the prostanoid epoprostenol has improved survival in IPAH patients. Although these medications have worked well in many patients with PAH, each of them has limitations. The phosphodiesterase-5 (PDE-5) inhibitors are a relatively new form of treatment for PAH. They are designed to potentiate the effects of cyclic guanosine monophosphate, thereby mimicking endogenous nitric oxide within the vasculature. PDE-5 inhibitors are selective pulmonary vasodilators effective in animal models of pulmonary hypertension. The published clinical studies evaluating their use have been small in size to date but appear to demonstrate benefit. The recently completed 12-week randomized placebo-controlled Sildenafil Use in Pulmonary Hypertension (SUPER-1) trial demonstrated improvement in 6-minute walk distance and hemodynamics in patients receiving sildenafil. These data suggest that the PDE-5 inhibitors are effective in treating PAH and that it is likely that their usage will increase over time. The purpose of this review is to present a current view of the pathogenesis and treatment of PAH, with an emphasis on the use of PDE-5 inhibitors in these patients.

Endothelin Blockade in Diabetic Kidney Disease

Diabetic kidney disease (DKD) remains the most common cause of chronic kidney disease and multiple therapeutic agents, primarily targeted at the renin-angiotensin system, have been assessed. Their only partial effectiveness in slowing down progression to end-stage renal disease, points out an evident need for additional effective therapies. In the context of diabetes, endothelin-1 (ET-1) has been implicated in vasoconstriction, renal injury, mesangial proliferation, glomerulosclerosis, fibrosis and inflammation, largely through activation of its endothelin A (ET_A) receptor. Therefore, endothelin receptor antagonists have been proposed as potential drug targets. In experimental models of DKD, endothelin receptor antagonists have been described to improve renal injury and fibrosis, whereas clinical trials in DKD patients have shown an antiproteinuric effect. Currently, its renoprotective effect in a long-time clinical trial is being tested. This review focuses on the localization of endothelin receptors (ET_A and ET_B) within the kidney, as well as the ET-1 functions through them. In addition, we summarize the therapeutic benefit of endothelin receptor antagonists in experimental and human studies and the adverse effects that have been described.

Selective endothelin A receptor antagonism with sitaxentan reduces neointimal lesion size in a mouse model of intraluminal injury

BACKGROUND AND PURPOSE

Endothelin (ET) receptor antagonism reduces neointimal lesion formation in animal models. This investigation addressed the hypothesis that the selective ETA receptor antagonist sitaxentan would be more effective than mixed ETA / B receptor antagonism at inhibiting neointimal proliferation in a mouse model of intraluminal injury.

EXPERIMENTAL APPROACH

Antagonism of ETA receptors by sitaxentan (1-100 nM) was assessed in femoral arteries isolated from adult, male C57Bl6 mice using isometric wire myography. Neointimal lesion development was induced by intraluminal injury in mice receiving sitaxentan (ETA antagonist; 15 mg·kg(-1) ·day(-1) ), A192621 (ETB antagonist; 30 mg·kg(-1) ·day(-1) ), the combination of both antagonists or vehicle. Treatment began 1 week before, and continued for 28 days after, surgery. Femoral arteries were then harvested for analysis of lesion size and composition.

KEY RESULTS

Sitaxentan produced a selective, concentration-dependent parallel rightward shift of ET-1-mediated contraction in isolated femoral arteries. Sitaxentan reduced neointimal lesion size, whereas ETB and combined ETA / B receptor antagonism did not. Macrophage and α-smooth muscle actin content were unaltered by ET receptor antagonism but sitaxentan reduced the amount of collagen in lesions.

CONCLUSIONS AND IMPLICATIONS

These results suggest that ETA receptor antagonism would be more effective than combined ETA /ETB receptor antagonism at reducing neointimal lesion formation.

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.

Value of preapproval safety data in predicting postapproval hepatic safety and assessing the legitimacy of class warning

OBJECTIVE

The objective of this study was to systematically evaluate whether preapproval safety data for nonhepatotoxic drugs and hepatotoxic drugs can be compared to improve preapproval prediction of postapproval hepatic safety and to assess the legitimacy of applying class warnings.

METHODS

Drugs within a therapeutic class that included at least one drug that had been withdrawn from the market because of liver toxicity or had a warning of potential liver toxicity issued by major regulatory agencies, and at least one drug free from such regulatory action, were identified and divided into two groups: drugs with and drugs without regulatory action. Preapproval clinical data [including the elevation rates of alanine aminotransferse (ALT) and withdrawal due to liver toxicity, the number of patients with combined elevation of ALT and bilirubin, and liver failure] and nonclinical data (including chemical structures, metabolic pathways, and other significant findings in animal studies) were compared between the two groups.

RESULTS

Six drug classes were assessed in this study: thiazolidinediones, cyclooxygenase-2 inhibitors, fluoroquinolones, catechol-O-methyltransferase (COMT) inhibitors, leukotriene receptor inhibitors, and endothelin receptor antagonists. In two classes (COMT inhibitors and endothelin receptor antagonists), drugs with regulatory action had significantly higher rates of ALT elevation of more than threefold and greater numbers of patients with combined elevation of ALT and bilirubin than drugs without regulatory action. Drugs with regulatory action also had chemical structures or metabolic pathways associated with the toxicity. The legitimacy of class warnings was refuted in all six classes of drugs.

CONCLUSION

Preapproval safety data may help predict postapproval hepatic safety and can be used to assess the legitimacy of applying class warnings.

Current state of endothelin receptor antagonism in hypertension and pulmonary hypertension

Endothelin 1 (ET-1), a potent vasoconstrictive substance, was discovered in 1988 by Yanagisawa and colleagues, and since then, a quarter of a century has passed. Understanding the biology of ET-1 has rapidly developed by characterizing the components of its receptors and processing enzymes. Numerous studies have revealed not only physiological but also various pathophysiological roles of the ET system. At first, ET-1 was the attractive and promising target for the treatment of hypertension owing to its potent vasoconstrictive nature and a variety of ET receptor antagonists (ERAs) were studied. However, the clinical application to treat hypertension was disappointing because of the side effects, including liver toxicity and fluid retention. On the other hand, ERAs have been established as orphan drugs for the treatment of pulmonary arterial hypertension and improved the prognosis of patients. Furthermore, multipotency of the ET system in the pathogenesis of multiple diseases has led to the development of translational research not only in the field of hypertension but in a variety of fields. Furthermore, a range of studies are ongoing to apply ERAs to clinical situations. In this article, we review the pathophysiological roles of the ET system in hypertension and pulmonary hypertension and the potential of ET receptor antagonism for the treatment of these diseases.

Clinical and molecular genetic features of hereditary pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is a rare disorder that may be hereditary (HPAH), idiopathic (IPAH), or associated with either drug-toxin exposures or other medical conditions. Familial cases have long been recognised and are usually due to mutations in the bone morphogenetic protein receptor type 2 gene (BMPR2), or, much less commonly, two other members of the transforming growth factor-β superfamily, activin-like kinase-type 1 (ALK1), and endoglin (ENG), which are associated with hereditary hemorrhagic telangiectasia. In addition, approximately 20% of patients with IPAH carry mutations in BMPR2. Clinical testing for BMPR2 mutations is available and may be offered to HPAH and IPAH patients but should be preceded by genetic counselling, since lifetime penetrance is only 10% to 20%, and there are currently no known effective preventative measures. Identification of a familial mutation can be valuable in reproductive planning and identifying family members who are not mutation carriers and thus will not require lifelong surveillance. With advances in genomic technology and with international collaborative efforts, genome-wide association studies will be conducted to identify additional genes for HPAH, genetic modifiers for BMPR2 penetrance, and genetic susceptibility to IPAH. In addition, collaborative studies of BMPR2 mutation carriers should enable identification of environmental modifiers, biomarkers for disease development and progression, and surrogate markers for efficacy end points in clinical drug development, thereby providing an invaluable resource for trials of PAH prevention.

Ironic case of hepatic dysfunction following the global withdrawal of sitaxentan

A patient with pulmonary arterial hypertension secondary to systemic sclerosis was successfully treated with sitaxentan prior to its worldwide withdrawal (because of hepatotoxicity concerns), but then ironically experienced acute hepatic dysfunction during substitute bosentan therapy, and was eventually stabilised on a phosphodiesterase-5 inhibitor.

Sitaxsentan-induced acute severe hepatitis treated with glucocorticoid therapy

Endothelin receptor antagonists are commonly used in the treatment of pulmonary hypertension. Sitaxsentan, a selective endothelin A receptor blocker, induces a mild transaminitis in approximately 3% to 5% of patients, but rarely an acute severe hepatitis. A case involving a 61-year-old female with sitaxsentan-induced acute severe liver failure is presented. Depite withdrawal of therapy, her liver tests failed to improve. After six weeks of monitoring, the patient was administered high-dose corticosteroids, with a good clinical and biochemical response. While endothelin receptor antagonists are postulated to cause hepatitis by inhibition of a bile salt transporter pump, an immune-mediated or idiosyncratic mechanism should be considered.

WHO Group 1 pulmonary arterial hypertension: current and investigative therapies

Major advances have been made in the treatment of World Health Organization Group 1 pulmonary arterial hypertension (PAH). Since the mid-1990s, nine medications have become available in the United States to target three key pathophysiologic derangements in PAH - the prostacyclin, endothelin, and nitric oxide pathways. As a group, these agents have led to improvements in functional capacity, symptoms, hemodynamics, and survival. Most patients with mild to moderate PAH are started on orally active agents such as endothelin receptor antagonists or phosphodiesterase inhibitors. Patients with more severe disease, particularly those with evidence of right heart failure, should be treated with continuous prostacyclin infusion or a combination of a prostacyclin and oral therapy. Each medication has unique properties and clinical considerations, and the selection of an appropriate therapy must be tailored to the individual patient. None of the currently available WHO Group 1 PAH therapies are curative, however, and it is the hope that new therapies in development may halt or reverse disease progression. This review will discuss the major therapeutic classes of presently available medications and their role in managing the patient with PAH. We will also review data supporting the use of combination therapy, adjuvant background therapy, and new agents currently under investigation.

Endothelin axis is upregulated in human and rat right ventricular hypertrophy

RATIONALE

Right ventricular (RV) function is the most important determinant of morbidity and mortality in pulmonary arterial hypertension (PAH). Endothelin (ET)-1 receptor antagonists (ERAs) are approved therapies for PAH. It is not known whether ERAs have effects on the RV, in addition to their vasodilating/antiproliferative effects in pulmonary arteries.

OBJECTIVE

We hypothesized that the ET axis is upregulated in RV hypertrophy (RVH) and that ERAs have direct effects on the RV myocardium.

METHODS AND RESULTS

RV myocardial samples from 34 patients with RVH were compared with 16 nonhypertrophied RV samples, and from rats with normal RV versus RVH attributable to PAH. Confocal immunohistochemistry showed that RVH myocardial ET type A (but not type B) receptor and ET-1 protein levels were increased compared with the nonhypertrophied RVs and positively correlated with the degree of RVH (RV thickness/body surface area; r(2)=0.838 and r(2)=0.818, respectively; P<0.01). These results were recapitulated in the rat model. In modified Langendorff perfusions, ERAs (BQ-123 and bosentan 10(-7,-6,-5) mol/L) decreased contractility in the hypertrophied, but not normal RV, in a dose-dependent manner (P<0.01).

CONCLUSIONS

Patients and rats with PAH have an upregulation of the myocardial ET axis in RVH. This might be a compensatory mechanism to preserve RV contractility, as the afterload increases. ERAs use might potentially worsen RV function, and this could explain some of the peripheral edema noted clinically with these agents. Further studies are required to evaluate the effects of ERAs on the RV in patients with RVH and PAH.

Prostanoids for Pulmonary Arterial Hypertension

Pulmonary arterial hypertension (PAH) is a severe condition that markedly reduces exercise capacity and survival in the affected patient population. PAH includes primary pulmonary hypertension (PPH) and pulmonary hypertension associated with collagen vascular diseases, congenital systemic-to-pulmonary shunts, portal hypertension and HIV infection. All these conditions share virtually identical obstructive pathologic changes of the pulmonary microcirculation and probably similar pathobiologic processes. The pathophysiology is characterized by a progressive increase in pulmonary vascular resistance, leading to right ventricular failure and death. Prostacyclin is an endogenous substance that is produced by vascular endothelial cells and induces vasodilatation, inhibition of platelet activity, and antiproliferative effects. A dysregulation of prostacyclin metabolic pathways has been shown in patients with PAH and this represents the rationale for the exogenous therapeutic administration of this substance. The clinical use of prostacyclin in patients with PAH has been made possible by the synthesis of stable analogs that possess different pharmacokinetic properties but share similar pharmacodynamic effects. Experience in humans has been initially collected with epoprostenol, which is a synthetic salt of prostacyclin. Epoprostenol has a short half-life in the circulation and requires continuous administration by the intravenous route by means of infusion pumps and permanent tunnelized catheters. In addition, epoprostenol is unstable at room temperature, and the complex delivery system required is associated with several adverse effects and potentially serious complications. For these reasons, alternatives to intravenous epoprostenol have been sought and this has led to the development of analogs that can be administered subcutaneously (treprostinil), orally (beraprost sodium) or by inhalation (iloprost). Three unblinded clinical trials and several uncontrolled trials have shown that treatment with epoprostenol improved symptoms and exercise capacity in New York Heart Association (NYHA) class III and IV PAH patients and also survival in patients with PPH. Subcutaneous treprostinil improved symptoms, exercise, hemodynamics and clinical events in the largest clinical trial ever performed in PAH, but local infusion site reactions limited efficacy in a proportion of patients. Oral beraprost sodium improved exercise capacity only in patients with PPH and is the only prostacyclin analog that has also been tested in NYHA class II patients. Inhaled iloprost has improved symptoms, exercise capacity and clinical events in patients with PAH and inoperable chronic thromboembolic pulmonary hypertension. The favorable effects of prostanoids observed in all studies coupled with different profiles of adverse events and tolerability for each prostacyclin analog allow the unique opportunity to select the most appropriate compound for the individual patient with PAH.

Current pathophysiological concepts and management of pulmonary hypertension

Pulmonary hypertension (PH), increasingly recognized as a major health burden, remains underdiagnosed due mainly to the unspecific symptoms. Pulmonary arterial hypertension (PAH) has been extensively investigated. Pathophysiological knowledge derives mostly from experimental models. Paradoxically, common non-PAH PH forms remain largely unexplored. Drugs targeting lung vascular tonus became available during the last two decades, notwithstanding the disease progresses in many patients. The aim of this review is to summarize recent advances in epidemiology, pathophysiology and management with particular focus on associated myocardial and systemic compromise and experimental therapeutic possibilities. PAH, currently viewed as a panvasculopathy, is due to a crosstalk between endothelial and smooth muscle cells, inflammatory activation and altered subcellular pathways. Cardiac cachexia and right ventricular compromise are fundamental determinants of PH prognosis. Combined vasodilator therapy is already mainstay for refractory cases, but drugs directed at these new pathophysiological pathways may constitute a significant advance.

Exacerbation of AIH in a patient with an AIH/systemic sclerosis overlap syndrome and pulmonary arterial hypertension treated with the endothelin-1 receptor antagonist sitaxentan

Increase of liver enzymes during therapy with endothelin receptor antagonist (ERA) because of pulmonary arterial hypertension (PAH) has been observed quite frequently the cause of which is unknown. Here we describe a female patient who suffered from autoimmune hepatitis (AIH) type I [positive for antinuclear (ANA) and antiactin antibodies] who developed systemic sclerosis (SSc) with PAH. AIH was treated with corticosteroids and azathioprine, and PAH with the ERA sitaxentan. Reactivation of AIH was observed in the course of therapy with sitaxentan as shown by an increase of liver enzymes, immunoglobulin G globulins, the reappearance of antinuclear and antiactin antibodies and the induction of a further AIH marker antibody reacting with the soluble liver/liver pancreas antigen. Therapy with ERA for pulmonary hypertension may increase the risk for development or exacerbation of AIH.

Medical management of chronic liver diseases (CLD) in children (part II): focus on the complications of CLD, and CLD that require special considerations

Treatment of the causes of many chronic liver diseases (CLDs) may not be possible. In this case, complications must be anticipated, prevented or at least controlled by the best available therapeutic modalities. There are three main goals for the management of portal hypertension: (i) prevention of the first episode of variceal bleeding largely by non-selective β-adrenoceptor antagonists, which is not generally recommended in children; (ii) control of bleeding by using a stepwise approach from the least to most invasive strategies; (iii) and prevention of re-bleeding using bypass operations, with particular enthusiasm for the use of meso-Rex bypass in the pediatric population. Hepatic encephalopathy management also consists of three main aspects: (i) ruling out other causes of encephalopathy; (ii) identifying and treating precipitating factors; and (iii) starting empiric treatment with drugs such as lactulose, rifaximin, sodium benzoate, and flumazenil. Treatment of mild ascites and peripheral edema should begin with the restriction of sodium and water, followed by careful diuresis, then large-volume paracentesis associated with colloid volume expansion in severe cases. Empiric broad spectrum antimicrobial therapy should be used for the treatment of spontaneous bacterial peritonitis, bacterial and fungal sepsis, and cholangitis, after taking appropriate cultures, with appropriate changes in therapy after sensitivity testing. Empirical therapies continue to be the standard practice for pruritus; these consist of bile acid binding agents, phenobarbital (phenobarbitone), ursodeoxycholic acid, antihistamines, rifampin (rifampicin), and carbamazepine. Partial external biliary diversion can be used in refractory cases. Once hepatorenal syndrome is suspected, treatment should be initiated early in order to prevent the progression of renal failure; approaches consist of general supportive measures, management of concomitant complications, screening for sepsis, treatment with antibiotics, use of vasopressin analogs (terlipressin), and renal replacement therapy if needed. Hepatopulmonary syndrome and portopulmonary hypertension are best managed by liver transplantation. Provision of an adequate caloric supply, nutrition, and vitamin/mineral supplements for the management of growth failure, required vaccinations, and special care for ensuring psychologic well-being should be ensured. Anticoagulation might be attempted in acute portal vein thrombosis. Some CLDs, such as extrahepatic biliary atresia (EHBA), Crigler-Najjar syndrome, and Indian childhood cirrhosis, require special considerations. For EHBA, Kasai hepatoportoenterostomy is the current standard surgical approach in combination with nutritional therapy and supplemental fat and water soluble vitamins, minerals, and trace elements. In type 1 Crigler-Najjar syndrome, extensive phototherapy is the mainstay of treatment, in association with adjuvant therapy to bind photobilirubin such as calcium phosphate, cholestyramine, or agar, until liver transplantation can be carried out. Treating Indian childhood cirrhosis with penicillamine early in the course of the disease and at doses similar to those used to treat Wilson disease decreases the mortality rate by half. New hopes for the future include extracorporeal liver support devices (the molecular adsorbent recirculating system [MARS®] and Prometheus®), hepatocyte transplantation, liver-directed gene therapy, genetically engineered enzymes, and therapeutic modalities targeting fibrogenesis. Hepapoietin, a naturally occurring cytokine that promotes hepatocyte growth, is under extensive research.

Bosentan and sildenafil in the treatment of HIV-associated pulmonary hypertension

We present the case of an HIV/HCV-coinfected patient with HIV-related pulmonary hypertension (HRPH) who experienced a good clinical and functional response to bosentan, with a subsequent switch to oral sildenafil due to increased transaminase levels. Bosentan resulted less handy in this case, probably due to both side effects and co-morbidities.

Endothelin receptor antagonists -- their role in pulmonary medicine

INTRODUCTION

Understanding of the function of endothelin-1 in the pathophysiology of endothelial disease, in particular pulmonary arterial hypertension (PAH), has paved the way for the development of endothelin-receptor antagonists (ERAs) and explains the leading role they now play in the treatment armamentarium for this disease.

BACKGROUND

Three active ERA drugs (bosentan, sitaxentan, ambrisentan) are currently approved for the treatment of PAH in France. Several randomised clinical trials have demonstrated their efficacy and safety in PAH.

PERSPECTIVES AND CONCLUSION

Besides its vasoconstrictor effect, endothelin-1 (ET-1) plays a pivotal role in cell proliferation and apoptosis. ERAs are innovative drugs potentially useful in some pulmonary disorders such as idiopathic pulmonary fibrosis or systemic sclerosis, even though the preliminary results published remain insufficient or controversial.

CONCLUSION

ERAs play a major role in the management of pulmonary vascular disease. Other drugs, still under study, could prove useful in the treatment of infiltrating pneumonias.

Pediatric pulmonary arterial hypertension: current and emerging therapeutic options

INTRODUCTION

Pulmonary arterial hypertension (PAH) is a rare disease in neonates, infants and children that is associated with significant morbidity and mortality. An adequate understanding of the controlling pathophysiologic mechanisms is lacking and although mortality has decreased as therapeutic options have increased over the past several decades, outcomes remain unacceptable.

AREAS COVERED

This review summarizes the currently available therapies for neonates, infants and children with PAH and describes emerging therapies in the context of what is known about the underlying pathophysiology of the disease.

EXPERT OPINION

All of the currently approved PAH therapies impact one of three endothelial-based pathways: nitric oxide-guanosine-3'-5'cyclic monophosphate, prostacyclin or endothelin-1. The beneficial effects of these agents may relate to their impact on pulmonary vascular tone, and/or their antiproliferative and antithrombotic properties. Fundamental advances in PAH therapy are likely to relate to: i) a better understanding of PAH subpopulations, allowing for therapies to be better tailored to individual patients and pathophysiologic processes; and ii) therapies that promote the regression of advanced structural remodeling.

Endothelin and hepatic wound healing

Liver wound healing is a coordinated response to injury caused by infections (hepatitis) or toxins (alcohol) or other processes where activation of hepatic stellate cells are a central component. During stellate cell activation, a major phenotypic transformation occurs which leads to increased production of increased extracellular matrix proteins and smooth muscle α-actin the results is organ dysfunction due to gross architectural disruption and impaired blood flow. Endothelin-1 (ET-1) is produced in increased amounts and the cellular source of ET-1 shifts from endothelial cells to stellate cells during liver injury thus setting a feedback loop which accentuates further activation, stellate cell proliferation, and production of extracellular matrix proteins. Therapy directed at intervening the ET-1 signaling pathway has significant therapeutic potential in patients with liver disease.

Recent trends in pulmonary arterial hypertension

Pulmonary hypertension is a serious and unrelenting pulmonary vascular disorder that affects the functional quality of patients and significantly decreases their life span. If diagnosed early, with the number of new therapeutic options that are available, a better quality of life can be provided for a protracted length of time. It is likely that the available treatment will change the natural course of the disease and perhaps prolong survival. As symptoms are often subtle in the early stages of the disease it is imperative that physicians are aware of the manifestations of this condition. A thorough investigation of patients suspected of this condition is essential so that appropriate treatment can be initiated promptly. The routine workup of a patient suspected to have pulmonary hypertension could easily be carried out in any well-equipped peripheral hospital in many affluent and advanced countries. However, it must be mentioned that in some less advanced countries the necessary work up can only be done in major teaching hospitals. Both pulmonologists and cardiologists should be aware of the pathophysiology of pulmonary arterial hypertension, the workup and the treatment options that are available. Patients with refractory pulmonary hypertension should be referred to these research centers for enrolment into any ongoing drug trials as well as for evaluation for heart-lung, single lung, or double lung transplantation. This paper is primarily aimed at pulmonologists and cardiologists taking care of these patients. Unless indicated otherwise this paper mainly deals with WHO group 1 pulmonary hypertension which is designated pulmonary arterial hypertension. Extensive review of the literature spanning the last 30 years was made through Medline using titles such as primary pulmonary hypertension, pulmonary arterial hypertension, secondary pulmonary hypertension, and pulmonary vascular diseases.

Management of pulmonary arterial hypertension in children

In this review we discuss the new anti- Pulmonary Arterial Hypertension [PAH] drugs and the available data on their use in paediatric PAH. Treatment of patients with PAH, children and adults, is aimed at a reduction of symptoms, survival and improvement of haemodynamics as well as exercise capacity. PAH may reflect significant different disease conditions in infants and children when compared to PAH in adults. In contrast to adult PAH, characterized mainly by idiopathic PAH and PAH associated with connective tissue disease, more than half of the cases of PAH in children are associated with congenital heart disease. Therefore, efficacy of PAH drugs in these diseases can not be extrapolated from that in adults with PAH.

Pulmonary hypertension in dogs: diagnosis and therapy

Pulmonary hypertension (PH) has been recognized as a clinical syndrome for many years in veterinary medicine, but routine accurate clinical diagnosis in dogs was greatly enhanced by widespread use of echocardiography and Doppler echocardiography. Most cases of PH in veterinary medicine can be categorized as precapillary or postcapillary. These subsets of patients often differ with regard to clinical presentation, response to therapy, and prognosis. Effective medical therapy is now available to treat this often-devastating clinical complication of common chronic diseases, making accurate diagnosis even more important to patient longevity and quality of life.

Sitaxsentan for the treatment of pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is a life-threatening, progressive condition that eventually leads to right heart failure. Endothelin receptor antagonists (ETRAs) have been shown to be a safe and efficacious treatment for PAH. Sitaxsentan is a highly selective oral ETRA that, in clinical trials, has demonstrated significant improvements in exercise capacity, functional class and pulmonary hemodynamics in PAH. Sitaxsentan has been shown to be a well tolerated and effective agent with a durable response for the treatment of PAH, and is associated with a low incidence of liver toxicity.

Advances in therapies for pediatric pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is a life-threatening disease characterized by progressive obliteration of the pulmonary vasculature, leading to right heart failure and death if left untreated. Prior to the current treatment era, pulmonary hypertension carried a poor prognosis with a high mortality rate, but its prognosis has changed over the past decades in relation to new therapeutic agents. Nevertheless, pulmonary hypertension continues to be a serious condition, which is extremely challenging to manage. The data in children are often limited owing to the small number of patients, and extrapolation from adults to children is not straightforward. While none of these new therapeutic agents have been specifically approved for children, there is evidence that each can appropriately benefit the PAH child. We review the current understanding of pediatric pulmonary hypertension, classification, diagnostic evaluation and available treatment. A description of targeted pharmacological therapy and new treatments in children is outlined.

Exercise capacity and haemodynamics in patients with sickle cell disease with pulmonary hypertension treated with bosentan: results of the ASSET studies

Doppler-defined pulmonary hypertension (PH) in sickle cell disease (SCD) is associated with 40% mortality at 40 months. To assess the effect of bosentan in SCD-PH, two randomized, double-blind, placebo-controlled, 16-week studies were initiated. Safety concerns are particularly relevant in SCD due to comorbid conditions. ASSET-1 and -2 enrolled patients with pulmonary arterial hypertension (PAH) and pulmonary venous hypertension (PH), respectively. Haemodynamics and 6-min walk distance (6MWD) were obtained at baseline and week 16. The studies were terminated due to slow site initiation and patient enrolment (n = 26). Bosentan appeared to be well tolerated. Although sample sizes were limited, in ASSET-1 at baseline, 6MWD correlated with cardiac output (CO; P = 0.006) with non-significant inverse correlations between 6MWD and pulmonary vascular resistance (PVR; P = 0.07) and between 6MWD and right atrial pressure (P = 0.08). In ASSET-2 at baseline, there was a non-significant correlation between 6MWD and CO (P = 0.06). Due to limited sample sizes, efficacy endpoints were not analysed. However, in both studies, non-significant increases in CO were observed with bosentan compared to placebo. Similarly, non-significant decreases in PVR were observed with bosentan. Limited data in SCD-PH suggest that a low 6MWD predicts a low CO. Standard-dose bosentan appears to be well tolerated. Further investigation is warranted. Clinicaltrials.gov registration numbers NCT00310830, NCT00313196, NCT00360087.

Etiology, diagnosis, and pharmacologic treatment of pediatric pulmonary hypertension

Major advances have been made in the understanding and treatment of pulmonary hypertension in the last few years. Without treatment (medication) for idiopathic pulmonary arterial hypertension, which is a rare and potentially fatal condition, the survival time is only about 3 years after diagnosis. However, if pulmonary hypertension is secondary to other causes such as congenital heart disease, it is possible to survive for 30 years or more without treatment. The condition can affect children at any age, from fetal life to adulthood. Patients with pulmonary hypertension can present to the respiratory pediatrician with unresponsive asthma, to the neurologist with faints, or to the general pediatrician with failure to thrive. Over the last few years there have been significant developments in the available therapy for managing this complicated disease. There is now a generally recognized ladder of long-term therapy for chronic pulmonary hypertension. Treatment can start with oxygen at home at night or even during the day. Next is the use of oral phosphodiesterase inhibitors, mostly type V, such as sildenafil, which enhance endogenous nitric oxide. More potent are the endothelin receptor antagonists and the most potent are the prostanoids, especially epoprostenol, which is given by constant intravenous infusion. In addition to interventional catheterization with atrial septostomy, these agents have improved the prognostic outlook. This article reviews the current knowledge about the etiology, investigation, and treatment of children with pulmonary hypertension in the clinical setting.

Treatment of pediatric pulmonary hypertension

Pulmonary hypertension was once thought to be a rare condition and only managed in specialized centers. Now however, with the advent of echocardiography, it is found in many clinical scenarios, in the neonate with chronic lung disease, in the acute setting in the intensive care unit, in connective tissue disease and in cardiology pre- and postoperatively. We have a better understanding of the pathological process and have a range of medication which is starting to be able to palliate this previously fatal condition. This review describes the areas that are known in this condition and those that are less familiar. The basic physiology behind pulmonary hypertension and pulmonary vascular disease is explained. The histopathologic process and the various diagnostic tools are described and are followed by the current and future therapy at our disposal.

Pediatric Pulmonary Hypertension: A Pharmacotherapeutic Review

Pulmonary hypertension in children is a disorder associated with increased pulmonary vascular resistance and arterial pressure, decreased cardiac output, and right-sided cardiac dysfunction that is caused by numerous etiologies. Although treatment will vary with underlying cause, pharmacological treatment has historically included inhaled nitric oxide and prostacyclin analogues. Over the past several years new agents have been added to the treatment armamentarium, including phosphodiesterase V inhibitors (eg sildenafil) and endothelin antagonists (eg bosentan). Further, more agents are currently under investigation for pulmonary hypertension in children including immunosuppressives and other endothelin antagonist entities. Limitations to treatment include the availability of appropriate, robust pediatric pharmacological data and constraints with dosage forms.

Optimizing endothelin receptor antagonist use in the management of pulmonary arterial hypertension

Endothelin receptor antagonism has emerged as an important therapeutic approach in pulmonary arterial hypertension (PAH). Bench to bedside scientific research has shown that endothelin-1 (ET-1) is overexpressed in several forms of pulmonary vascular disease and may play an important pathogenetic role in the development and progression of PAH. Oral endothelin receptor antagonists (ERAs) improved exercise capacity, functional status, pulmonary hemodymanics, and delayed the time to clinical worsening in several randomized placebo-controlled trials. Two ERAs are currently approved by the US Food and Drug Administration: bosentan, a dual ERA for patients with class III and IV PAH, and ambrisentan, a selective ERA for patients with class II and III PAH. Sitaxsentan, another selective ERA, has been approved in Europe, Canada, and Australia. The objective of this review is to evaluate the available evidence describing the pharmacology, efficacy, safety, and tolerability, and patient-focused perspectives regarding the different types of endothelin receptor antagonists. Ongoing and forthcoming randomized trials are also highlighted including the approach of combining this class of drugs with other drugs that target different cellular pathways believed to be etiologically important in PAH.