Emerging medical therapies for pulmonary arterial hypertension

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.

Regio- and Stereocontrolled Dieckmann Approach to Treprostinil-Inspired, Polycyclic Scaffold For Building Macrocyclic Diversity

We developed a regio- and stereocontrolled Dieckmann cyclization approach to the synthesis of a novel, natural-product-like scaffold that was inspired from treprostinil (UT-15). This was further utilized in a diversity-based, 15-membered macrocyclic synthesis of two different sets of hybrid compounds. The amino acid moiety embedded in the macrocyclic skeleton allow exploring various chiral side chain groups within the ring.

Saudi Guidelines on the Diagnosis and Treatment of Pulmonary Hypertension: Pulmonary arterial hypertension associated with connective tissue diseases

The explosive growth of medical literature on pulmonary hypertension (PH) has led to a steady increase in awareness of this disease within the medical community during the past decade. The recent revision of the classification of PH is presented in in the main guidelines.

Group 1 PH or pulmonary arterial hypertension (PAH) is a heterogeneous group and includes PH due to inheritable, drug-induced, and toxin-induced causes and to such underlying systemic causes as connective tissue diseases, human immunodeficiency viral infection, portal hypertension, congenital heart disease, and schistosomiasis.

Systemic sclerosis (SSc) is an autoimmune multisystem disorder, which affects over 240 persons per million in the United States.[1] Its manifestations are not confined to the skin but may also involve the lungs, kidneys, peripheral circulation, musculoskeletal system, gastrointestinal tract, and heart.

The outcome of PAH associated with SSc is worse when compared to other subtypes of PAH.

In this review, we summarize available information about the pulmonary vascular and cardiac manifestations of SSc with special emphasis on their prognostic implications as well as the peculiarity of their detection.

Therapies for scleroderma-related pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH), a common complication of systemic sclerosis, carries a very severe prognosis and is one of the leading causes of death in patients who suffer from it. Indeed, response to modern medical therapy has been disappointing in scleroderma-related PAH compared with other forms of PAH from the WHO group 1 classification of diseases, despite similar histological changes involving the pulmonary vasculature. This review discusses specific features of scleroderma-related PAH, currently available and US FDA-approved therapy for this syndrome, as well as potential future therapeutic developments based on newly acquired knowledge of this disorder.

Pulmonary arterial hypertension in connective tissue diseases

Pulmonary arterial hypertension (PAH) may complicate diverse connective tissue diseases (CTDs). Approximately 10% of patients with systemic sclerosis develop PAH, the prevalence being much lower in other CTDs. However, PAH is an important contributor to morbidity and mortality in all forms of CTD. Despite similarities in presentation, hemodynamic perturbations, and pathogenesis, patients with CTD-associated PAH (CTD-PAH) usually have a poorer response to PAH-specific medications and poorer prognosis than patients with idiopathic PAH (IPAH). Select patients with CTD-PAH may be candidates for lung transplantation, but results are less favorable than for IPAH because of comorbidities and complications specifically associated with CTD.

The cost to managed care of managing pulmonary hypertension

OBJECTIVE

To estimate direct medical costs and resource use for commercially-insured patients within two pulmonary hypertension sub-groups: pulmonary arterial hypertension (PAH) and chronic thromboembolic pulmonary hypertension (CTEPH).

RESEARCH DESIGN AND METHODS

Using a retrospective cohort design, subjects (≥18 years) with ICD-9 code 416.0 (PAH or CTEPH) or 416.8 (CTEPH) were identified during 2004-2009 within the MarketScan database. The date of the first observed claim was the index date. Each PAH and CTEPH patient was matched to one-to-five controls without PAH and CTEPH on age, gender, region, and payer type. Patients and controls were continuously enrolled for at least 12 months pre- and 12 months post-index date. Per-patient-per-month costs and resource use were compared using Wilcoxon rank-sum test.

RESULTS

PAH patients (1647) and controls (6352) were identified (mean age 63 years, 73% female). Total monthly costs before PAH diagnosis were: PAH patients $2064 vs controls $1094. After PAH diagnosis, PAH patients had significantly higher monthly costs and resource use vs controls: Total costs $4021 vs $1533, outpatient visits 1.1 vs 0.8, inpatient visits 0.7 vs 0.2, prescriptions 3.6 vs 2.7, all p-values <0.05. One hundred and forty-six CTEPH patients and 558 controls were identified (mean age 64 years, 54.8% female). Total monthly costs in the period before CTEPH diagnosis were higher for CTEPH patients ($3895) than controls ($1177). After CTEPH diagnosis, CTEPH patients had significantly higher monthly costs and resource use vs controls: Total costs $6198 vs $1579, Outpatient visits 1.2 vs 0.8, inpatient visits 2 vs 0.2, prescriptions 4.2 vs 2.8, all p-values <0.05.

KEY LIMITATIONS

Identification of PAH is complicated, as there exists no precise ICD-9-CM code for the condition. CTEPH diagnosis was based upon claims data and was not verified clinically.

CONCLUSIONS

CTEPH and PAH patients incurred higher costs and used more resources than controls in the baseline and follow-up periods.

Excess costs associated with patients with pulmonary arterial hypertension in a US privately insured population

BACKGROUND

Pulmonary arterial hypertension (PAH) is a rare but fatal disease. Little is known about the economic burden associated with PAH patients in the US.

OBJECTIVES

The objective of this study was to estimate excess direct costs associated with privately insured PAH patients in the US.

METHODS

From a privately insured claims database (>8 million beneficiaries, 2002-7), 471 patients with PAH were identified using the criteria: two or more claims for primary pulmonary hypertension (PH), International Classification of Diseases, ninth edition, clinical modification (ICD-9-CM) code 416.0; no left heart disease, lung diseases, chronic thromboembolic PH or miscellaneous PH diagnoses within 12 months prior or 1 month after the initial PH claim (index date); one or more claim for right heart catheterization (RHC) within 6 months prior to any PH claim or one or more claim for echocardiogram within 6 months prior to a specialist-diagnosed PH claim; aged 18-64 years. Patients with PAH were matched demographically to controls without PH. Patients were followed as long as continuously eligible; mean follow-up of PAH patients was 24.8 months. Chi-squared tests were used to compare baseline co-morbidities. Wilcoxon rank-sum tests were used to compare direct (medical and pharmaceutical) patient-month costs to insurers.

RESULTS

The average age for PAH patients was 52.2 years, and 55.8% were women. Compared with controls, PAH patients had significantly higher baseline rates of co-morbidities (e.g. essential hypertension, diabetes mellitus and congestive heart failure) and a higher mean Charlson Co-morbidity Index score. Mean direct patient-month costs (year 2007 values) were $US2023 for PAH patients and $US498 for controls (p < 0.0001), yielding excess costs of $US1525. Sensitivity analysis restricting the sample to patients diagnosed following RHC yielded a 64% increase in excess costs relative to the original sample. Regarding cost drivers, inpatient services accounted for 45%, outpatient and other services for 38% and prescription drugs for 15% of total direct healthcare costs per patient-month in PAH patients. Circulatory/respiratory system-related patient-month costs were $US724 among PAH patients and $US114 among controls (p < 0.0001).

CONCLUSIONS

Patients with PAH had substantially higher costs and co-morbidity than controls, with circulatory/respiratory system-related costs accounting for 40% of excess costs. The high burden of illness suggests opportunities for savings from improved management.

Lung involvement in systemic sclerosis

Scleroderma is a multisystem disease characterized by a severe inflammatory process and exuberant fibrosis. Lung involvement is a frequent complication and a leading cause of morbidity and mortality in this syndrome. Two major pulmonary syndromes are associated with scleroderma; a pulmonary vascular disorder evolving over time into relatively isolated pulmonary arterial hypertension (PAH), and interstitial lung disease (ILD). Each syndrome, when present, is a cause of morbidity and significantly reduces survival of scleroderma patients when compared to patients free of lung complication. When pulmonary hypertension and ILD are combined, survival is further reduced. Current therapy appears to have no meaningful effect on either condition and, thus, there is a need for better understanding of underlying pathogenic mechanisms. This review focuses on clinical, diagnostic, and therapeutic features of PAH and ILD as well as other frequent but less debilitating lung complications of scleroderma.

Propylthiouracil attenuates monocrotaline-induced pulmonary arterial hypertension in rats

BACKGROUND

Propylthiouracil (PTU) enhances nitric oxide production and inhibits smooth muscle cell proliferation, suggesting a possible role in the prevention of pulmonary arterial hypertension (PAH).

METHODS AND RESULTS

The 30 male Sprague-Dawley rats were randomized to receive saline injection only (group 1), monocrotaline (MCT) (70 mg/kg) only (group 2) or MCT + 0.1% PTU in drinking water (group 3) given on day 5 after MCT administration. By day 35, western blot showed lower connexin43 (Cx43) and membranous protein kinase C-epsilon expressions in the right ventricle (RV) of group 2 animals than in the other groups (all P<0.05). Conversely, Cx43 expression in the lung was higher in group 2 than in other groups (all P<0.02). Additionally, mRNA expressions of matrix metalloproteinase-9, tissue necrotic factor-alpha, and caspase-3 were higher, whereas Bcl-2 and endothelial nitric oxide synthase were lower, in the lungs and RV of group 2 rats than in the other groups (all P<0.05). Moreover, the numbers of alveolar sacs and lung arterioles were also reduced in group 2 than in other groups (all P<0.05), and RV systolic pressure and RV weight were increased in group 2 compared with other groups (all P<0.001).

CONCLUSIONS

PTU effectively attenuates complications associated with MCT-induced PAH.

Early combined treatment with cilostazol and bone marrow-derived endothelial progenitor cells markedly attenuates pulmonary arterial hypertension in rats

We investigated whether early combined cilostazol and bone marrow-derived endothelial progenitor cell (BMDEPC) treatment offers synergistic benefit in ameliorating monocrotaline (MCT)-induced pulmonary arterial hypertension (PAH) in rats. Male Sprague-Dawley rats (n = 10/group) were randomized to receive saline injection only (group 1), MCT (70 mg/kg) (group 2), and MCT plus cilostazol (20 mg/kg/day) (group 3), MCT plus BMDEPCs (2.0 x 10(6) cells) (group 4), and MCT plus combined cilostazol/BMDEPCs (group 5). Intravenous BMDEPCs and oral cilostazol were given on day 3 after MCT administration. By day 42, connexin43 protein expression in right ventricle (RV) was reduced in group 2 compared with other groups and also was decreased in groups 3 and 4 compared with groups 1 and 5 (all p < 0.05). In addition, mRNA expressions of matrix metalloproteinase-9, tumor necrosis factor-alpha, and caspase-3 were higher, whereas Bcl-2 and endothelial nitric-oxide synthase were lower in lung and RV in group 2 compared with the other groups (all p < 0.05). The number of alveolar sacs and lung arterioles was lower in group 2 than in other groups and lower in groups 3 and 4 than in group 5 (all p < 0.05). RV systolic pressure (RVSP) and weight were increased in group 2 compared with the other groups (all p < 0.0001). Moreover, RVSP and RV-to-left ventricle plus septum weight ratio were higher in groups 3 and 4 than in groups 1 and 5 (p < 0.001) but showed no difference between groups 1 and 5. In conclusion, early combined autologous BMDEPC/cilostazol treatment is superior to BMDEPC or cilostazol only for preventing MCT-induced PAH.

Cilostazol therapy attenuates monocrotaline-induced pulmonary arterial hypertension in rat model

BACKGROUND

Pulmonary arterial hypertension (PAH) is characterized by a progressive increase in pulmonary vascular resistance caused by a proliferation of vascular endothelial and smooth muscle cells, resulting in occlusion of the lumen of small pulmonary arteries. Cilostazol, with its antiproliferative effects on vascular endothelial and smooth muscle cells, may ameliorate monocrotaline (MCT)-induced PAH in rats.

METHODS AND RESULTS

Male Sprague - Dawley rats (n=10/each group) were randomized to receive MCT (75 mg/kg) only (group 1), MCT plus cilostazol (20 mg .kg(-1 ). day(-1)) (group 2) and saline injection only (group 3). Hemodynamic measurement on day 28 following MCT treatment indicated the development of significant PAH on MCT-treated groups (p<0.0001). Cilostazol was given to group 2 orally on days 28-90. By day 90 following MCT treatment, the right ventricular (RV) systolic blood pressure and RV hypertrophy were significantly higher in group 1 than in groups 2 and 3 (all values of p<0.01). Additionally, connexin43 and endothelial nitric oxide synthase gene expressions of lung and RV, and Bcl-2 protein expression of RV, were significantly lower in group 1 than in groups 2 and 3 (all values of p<0.01). Furthermore, the number of alveolar sac and small arterioles of the lung were significantly lower in group 1 than in groups 2 and 3 (all values of p<0.01).

CONCLUSION

Cilostazol therapy effectively attenuates of MCT-induced PAH.

Amlodipine prevents monocrotaline-induced pulmonary arterial hypertension and prolongs survival in rats independent of blood pressure lowering

1. The present study was designed to examine the role of amlodipine in preventing and reversing monocrotaline (MCT)-induced pulmonary arterial hypertension (PAH) in rats. 2. Rats were injected with MCT (40 mg/kg, s.c.) and randomly given either 6 mg/kg per day of amlodipine in drinking water or placebo for 3 weeks. Any animals treated with MCT that survived for 3 weeks were given either amlodipine or placebo for the next 3 weeks. 3. Blood pressure was not different between the groups. Amlodipine immediately following MCT markedly inhibited PAH with severe pulmonary vascular remodelling. The survival rate at 3 weeks after treatment was increased significantly in the amlodipine group compared with the placebo group (77%vs 43%; P < 0.01). The placebo group showed markedly diminished expression of endothelial nitric oxide synthase (eNOS) protein and mRNA levels, increased numbers of proliferating cell nuclear antigen-positive cells, enhanced mRNA expression of matrix metalloproteinase-2 and pro-inflammatory cytokines in the lung tissue and upregulation of P-selectin on the endothelium of the pulmonary arteries, whereas these effects were suppressed in the amlodipine-treated group. Furthermore, late treatment with amlodipine did not palliate PAH or improve survival. 4. Amlodipine inhibited the development of PAH and improved survival in rats independent of its effect on lowering blood pressure. These effects were associated with marked inhibition of the downregulation of eNOS and improvement of pulmonary vascular endothelial activation, as well as anti-inflammatory, antiproliferative and antifibrotic effects in the lung tissue. However, amlodipine failed to reverse established PAH. This study may provide an insight into therapeutic strategy of amlodipine in PAH.

Low-dose oral sildenafil for patients with pulmonary hypertension: a cost-effective solution in countries with limited resources

INTRODUCTION

Pulmonary arterial hypertension, both primary and secondary, continues to pose a therapeutic problem. In this study, we evaluate the efficacy and safety of a low-dose of oral sildenafil in 10 patients with pulmonary arterial hypertension.

METHODS

We administered a single daily dose of 0.5 milligrams per kilogram of sildenafil for 3 months to 10 patients with pulmonary arterial hypertension. Their average age was 26.8 years. Diagnoses were primary pulmonary arterial hypertension in 3 patients, and secondary pulmonary arterial hypertension due to congenital cardiac disease in the remaining 7 patients. Outcome measures included the clinical state, the mean pulmonary arterial pressure, and the indexed pulmonary vascular resistance; the latter two assessed at the beginning and at the end of the treatment period by cardiac catheterization. We also analysed the cost of the treatment.

RESULTS

Oral treatment was well tolerated, and resulted in an improvement of the functional capacity in 9 of the 10 patients. Pulmonary arterial pressure decreased from 70 to 60 millimetres of mercury (p equal to 0.05), and indexed pulmonary vascular resistance decreased from 21.8 to 15.8 Wood units per square metre (p equal to 0.006). The mean cost per patient for 3 months on oral treatment with sildenafil was 120.99 American dollars.

CONCLUSIONS

A low dose of 0.5 milligrams per kilogram per day of oral sildenafil, instead of 1 to 4 milligrams per kilogram per day, provided early clinical and haemodynamic improvements, and proved less expensive. Additional experience is now required to define more reliably the true long-term benefits of this therapy.

Hypoxic pulmonary hypertension (HPH) and iptakalim, a novel ATP-sensitive potassium channel opener targeting smaller arteries in hypertension

Hypoxic pulmonary hypertension (HPH) is a serious and potentially devastating chronic disorder of the pulmonary circulation. Attempts to use drugs in the therapy of hypoxic pulmonary hypertension indicated the importance of prevention or reduction of vasoconstriction as well as of the reversal of remodeling within the cardiovascular system. Iptakalim (2,3-dimethyl-N-(1-methylethyl)-2-butylamine), a novel ATP-sensitive potassium channel opener, has the desired effects on hypoxic pulmonary arteries. Iptakalim decreases the elevated mean pressure in pulmonary arteries, and attenuates remodeling in the right ventricle, pulmonary arteries and airways. Moreover, iptakalim has selective antihypertensive effects: it significantly lowers arterial pressure in hypertensive animals, but has little if any effect in normotensive animals. In HPH iptakalim has selective effects on smaller arteries. Long-term iptakalim therapy decreases expression of sulfonylurea receptor 2 and of mRNA of inwardly rectifying potassium channel in smaller arteries of spontaneously hypertensive rats. Iptakalim inhibits the effects of endothelin-1, reduces the intracellular calcium concentration and inhibits the cell cycle in smooth muscle cells of pulmonary arteries. There is no evidence for the development of tolerance to the long-lasting antihypertensive action of iptakalim. At therapeutic doses iptakalim has no effects on the central nervous, respiratory, digestive, or endocrine systems. It has a broad therapeutic range, so that it can be safely used in the therapy of HPH.

Bosentan therapy of pulmonary arterial hypertension in connective tissue diseases

BACKGROUND

Pulmonary arterial hypertension (PAH) is a life-threatening and debilitating complication of several connective tissue diseases. We aimed to evaluate the effects of long-term treatment with bosentan, an oral dual endothelin ET(A)/ET(B) receptor antagonist, in a cohort of patients with PAH related to connective tissue diseases.

MATERIALS AND METHODS

In the present prospective, noncontrolled study, 13 patients (nine with systemic sclerosis, two with systemic lupus erythematosus, one with mixed connective tissue disease and one with overlap syndrome including scleroderma and myositis), mostly nonresponders to prostanoids therapy, were treated for 1 year with bosentan. Cardiac haemodynamics and the diagnosis of PAH were performed by Doppler ultrasound examination. Exercise capacity was assessed by 6-min walking test at baseline and at 3, 6 and 12 months of therapy.

RESULTS

During bosentan treatment, progressive improvement of exercise capacity was observed. Walk distance increased in seven patients, remained unchanged in three and slightly decreased in three patients. A progressive significant decrease of right ventricular systolic pressure was also observed, whereas pulmonary artery mean pressure remained unchanged. Adverse effects related to bosentan (elevation of hepatic aminotransferases) were noted in two patients.

CONCLUSION

Long-term treatment with bosentan was effective in improving exercise capacity and pulmonary haemodynamics in patients with PAH related to connective tissue diseases.

Sildenafil: from angina to erectile dysfunction to pulmonary hypertension and beyond

In less than 20 years, the first selective type 5 phosphodiesterase inhibitor, sildenafil, has evolved from a potential anti-angina drug to an on-demand oral treatment for erectile dysfunction (Viagra), and more recently to a new orally active treatment for pulmonary hypertension (Revatio). Here we describe the key milestones in the development of sildenafil for these diverse medical conditions, discuss the advances in science and clinical medicine that have accompanied this journey and consider possible future indications for this versatile drug.

Cognitive, emotional, and quality of life outcomes in patients with pulmonary arterial hypertension

Background

The effects of pulmonary arterial hypertension on cardiovascular and physical function are well documented. Limited information exists regarding the effects of pulmonary arterial hypertension on cognitive function despite patient reports of problems with memory and attention. Our primary purpose was to determine if a prospectively identified cohort of pulmonary arterial hypertension patients had cognitive sequelae. Our secondary purpose was to determine the relationships between cognitive sequelae and neuropsychological test scores with depression, anxiety, and quality of life.

Methods

Forty-six adults with pulmonary arterial hypertension underwent assessment of cognitive function, depression, anxiety, and quality of life using standardized neuropsychological tests and questionnaires. The patients' scores were compared to normal population data. Medical, affective, neuropsychological, and quality of life data for patients with and without cognitive sequelae were compared using analysis of variance, Chi-square, or Fisher exact tests for categorical data. Correlations assessed relationships between neuropsychological test scores, depression, anxiety, quality of life, and medical data.

Results

Cognitive sequelae occurred in 58% (27/46) of the pulmonary arterial hypertension patients. Patients with cognitive sequelae had worse verbal learning, delayed verbal memory, executive function, and fine motor scores compared to patients without cognitive sequelae. Twenty-six percent of patients had moderate to severe depression and 19% had moderate to severe anxiety. Depression, anxiety and quality of life were not different for patients with or without cognitive sequelae. Our patients had decreased quality of life, which was associated with worse working memory.

Conclusion

Patients with pulmonary arterial hypertension have cognitive impairments, depression, anxiety, and decreased quality of life. Depression, anxiety, and quality of life were similar for patients with cognitive sequelae compared to those without cognitive sequelae. Decreased quality of life was associated with worse verbal and working memory. Clinicians should be aware of adverse brain related outcomes in PAH patients. Attention to proximal determinants and possible interventions to prevent or reduce cognitive and emotional morbidity and decreased quality of life are warranted and should be an emphasis in outcomes research.

Effects of Nicorandil on Monocrotaline-Induced Pulmonary Arterial Hypertension in Rats

We investigated whether nicorandil might prevent and reverse monocrotaline (MCT)-induced pulmonary arterial hypertension. Rats were injected with 50 mg/kg of MCT subcutaneously and randomized to either 7.5 mg/kg/d of nicorandil in drinking water or placebo for 3 weeks. Animals that were treated with MCT and survived for 3 weeks were assigned to either nicorandil or placebo. Nicorandil markedly attenuated pulmonary arterial hypertension with severe structural remodeling of the pulmonary vessels. The survival rate at 3 weeks after treatment was significantly increased in the nicorandil group compared with the placebo group (73% versus 39%, P<0.05). In the placebo group, endothelial nitric oxide synthase (eNOS) protein was significantly decreased, the numbers of the CD45-positive cells and those of the proliferating cell nuclear antigen-positive cells were increased in the lung tissue, and P-selectin was intensely expressed on the endothelium of the pulmonary arteries. These features were prevented by nicorandil. Late treatment with nicorandil did not palliate established pulmonary arterial hypertension nor improved survival. Thus, nicorandil inhibited development of MCT-induced pulmonary arterial hypertension but failed to reverse it. These effects were associated with marked up-regulation of diminished lung eNOS protein along with improvement of pulmonary vascular endothelial activation and anti-inflammatory and anti-proliferative effects in the lung tissue.

Clinical pharmacology of bosentan, a dual endothelin receptor antagonist

Bosentan, a dual endothelin receptor antagonist, is indicated for the treatment of patients with pulmonary arterial hypertension (PAH). Following oral administration, bosentan attains peak plasma concentrations after approximately 3 hours. The absolute bioavailability is about 50%. Food does not exert a clinically relevant effect on absorption at the recommended dose of 125 mg. Bosentan is approximately 98% bound to albumin and, during multiple-dose administration, has a volume of distribution of 30 L and a clearance of 17 L/h. The terminal half-life after oral administration is 5.4 hours and is unchanged at steady state. Steady-state concentrations are achieved within 3-5 days after multiple-dose administration, when plasma concentrations are decreased by about 50% because of a 2-fold increase in clearance, probably due to induction of metabolising enzymes. Bosentan is mainly eliminated from the body by hepatic metabolism and subsequent biliary excretion of the metabolites. Three metabolites have been identified, formed by cytochrome P450 (CYP) 2C9 and 3A4. The metabolite Ro 48-5033 may contribute 20% to the total response following administration of bosentan. The pharmacokinetics of bosentan are dose-proportional up to 600 mg (single dose) and 500 mg/day (multiple doses). The pharmacokinetics of bosentan in paediatric PAH patients are comparable to those in healthy subjects, whereas adult PAH patients show a 2-fold increased exposure. Severe renal impairment (creatinine clearance 15-30 mL/min) and mild hepatic impairment (Child-Pugh class A) do not have a clinically relevant influence on the pharmacokinetics of bosentan. No dosage adjustment in adults is required based on sex, age, ethnic origin and bodyweight. Bosentan should generally be avoided in patients with moderate or severe hepatic impairment and/or elevated liver aminotransferases. Ketoconazole approximately doubles the exposure to bosentan because of inhibition of CYP3A4. Bosentan decreases exposure to ciclosporin, glibenclamide, simvastatin (and beta-hydroxyacid simvastatin) and (R)- and (S)-warfarin by up to 50% because of induction of CYP3A4 and/or CYP2C9. Coadministration of ciclosporin and bosentan markedly increases initial bosentan trough concentrations. Concomitant treatment with glibenclamide and bosentan leads to an increase in the incidence of aminotransferase elevations. Therefore, combined use with ciclosporin and glibenclamide is contraindicated and not recommended, respectively. The possibility of reduced efficacy of CYP2C9 and 3A4 substrates should be considered when coadministered with bosentan. No clinically relevant interaction was detected with the P-glycoprotein substrate digoxin. In healthy subjects, bosentan doses >300 mg increase plasma levels of endothelin-1. The drug moderately reduces blood pressure, and its main adverse effects are headache, flushing, increased liver aminotransferases, leg oedema and anaemia. In a pharmacokinetic-pharmacodynamic study in PAH patients, the haemodynamic effects lagged the plasma concentrations of bosentan.

Cyclic nucleotide phosphodiesterase activity, expression, and targeting in cells of the cardiovascular system

Cyclic AMP (cAMP) and cGMP regulate a myriad of cellular functions, such as metabolism, contractility, motility, and transcription in virtually all cell types, including those of the cardiovascular system. Considerable effort over the last 20 years has allowed identification of the cellular components involved in the synthesis of cyclic nucleotides, as well as effectors of cyclic nucleotide-mediated signaling. More recently, a central role for cyclic nucleotide phosphodiesterase (PDE) has also been elaborated in many cell types, including those involved in regulating the activities of the cardiovascular system. In this review, we introduce the PDE families whose members are expressed in cells of the cardiovascular system including cardiomyocytes, vascular smooth muscle cells, and vascular endothelial cells. Because cell behavior is a dynamic process influenced by numerous factors, we will attempt to emphasize how changes in the activity, expression, and targeting of PDE influence cyclic nucleotide-mediated regulation of the behavior of these cells.