Metabolic dysfunction in pulmonary hypertension: from basic science to clinical practice.

Pulmonary hypertension (PH) is an often-fatal vascular disease of unclear molecular origins. The pulmonary vascular remodelling which occurs in PH is characterised by elevated vasomotor tone and a pro-proliferative state, ultimately leading to right ventricular dysfunction and heart failure. Guided in many respects by prior evidence from cancer biology, recent investigations have identified metabolic aberrations as crucial components of the disease process in both the pulmonary vessels and the right ventricle. Given the need for improved diagnostic and therapeutic options for PH, the development or repurposing of metabolic tracers and medications could provide an effective avenue for preventing or even reversing disease progression. In this review, we describe the metabolic mechanisms that are known to be dysregulated in PH; we explore the advancing diagnostic testing and imaging modalities that are being developed to improve diagnostic capability for this disease; and we discuss emerging drugs for PH which target these metabolic pathways.

Clinical trials with endothelin receptor antagonists: what went wrong and where can we improve?

In the early 1990s, within three years of cloning of endothelin receptors, orally active endothelin receptor antagonists (ERAs) were tested in humans and the first clinical trial of ERA therapy in humans was published in 1995. ERAs were subsequently tested in clinical trials involving heart failure, pulmonary arterial hypertension, resistant arterial hypertension, stroke/subarachnoid hemorrhage and various forms of cancer. The results of most of these trials - except those for pulmonary arterial hypertension and scleroderma-related digital ulcers - were either negative or neutral. Problems with study design, patient selection, drug toxicity, and drug dosing have been used to explain or excuse failures. Currently, a number of pharmaceutical companies who had developed ERAs as drug candidates have discontinued clinical trials or further drug development. Given the problems with using ERAs in clinical medicine, at the Twelfth International Conference on Endothelin in Cambridge, UK, a panel discussion was held by clinicians actively involved in clinical development of ERA therapy in renal disease, systemic and pulmonary arterial hypertension, heart failure, and cancer. This article provides summaries from the panel discussion as well as personal perspectives of the panelists on how to proceed with further clinical testing of ERAs and guidance for researchers and decision makers in clinical drug development on where future research efforts might best be focused.

Future perspectives for the treatment of pulmonary arterial hypertension.

Over the past 2 decades, pulmonary arterial hypertension has evolved from a uniformly fatal condition to a chronic, manageable disease in many cases, the result of unparalleled development of new therapies and advances in early diagnosis. However, none of the currently available therapies is curative, so the search for new treatment strategies continues. With a deeper understanding of the genetics and the molecular mechanisms of pulmonary vascular disorders, we are now at the threshold of entering a new therapeutic era. Our working group addressed what can be expected in the near future. The topics span the understanding of genetic variations, novel antiproliferative treatments, the role of stem cells, the right ventricle as a therapeutic target, and strategies and challenges for the translation of novel experimental findings into clinical practice.

Identification of putative endothelial progenitor cells (CD34+CD133+Flk-1+) in endarterectomized tissue of patients with chronic thromboembolic pulmonary hypertension.

Chronic thromboembolic pulmonary hypertension (CTEPH) is characterized by a fibrotic thrombus persisting and obliterating the lumen of pulmonary arteries; its pathogenesis remains poorly defined. This study investigates a potential contribution for progenitor cell types in the development of vascular obliteration and remodeling in CTEPH patients. Endarterectomized tissue from patients undergoing pulmonary thromboendarterectomy was collected and examined for the structure and cellular composition. Our data show an organized fibrin network structure in unresolved thromboemboli and intimal remodeling in vascular wall tissues, characterized by smooth muscle alpha-actin (SM-alphaA)-positive cell proliferation in proximal regions (adjacent to thromboemboli) and neoangiogenesis/recanalization in distal regions (downstream from thromboemboli). Cells that are positively stained with CD34 and fetal liver kinase-1 (Flk-1) (CD34(+)Flk-1(+)) were identified in both the proximal and distal vascular tissues; a subpopulation of CD34(+)Flk-1(+)CD133(+) cells were further identified by immunostaining. Triple-positive cells are indicative of a population of putative endothelial progenitor cells or potential colony-forming units of endothelial cells. In addition, inflammatory cells (CD45(+)) and collagen-secreting cells (procollagen-1(+)) were detected in the proximal vascular wall. Some of the CD34(+) cells in CTEPH cells isolated from proximal regions were also positive for SM-alphaA. Our data indicate that putative progenitor cell types are present in the neointima of occluded vessels of CTEPH patients. It is possible that the microenvironment provided by thromboemboli may promote these putative progenitor cells to differentiate and enhance intimal remodeling.

Acute effects of the combination of sildenafil and inhaled treprostinil on haemodynamics and gas exchange in pulmonary hypertension.

BACKGROUND: Inhaled treprostinil was recently developed for the treatment of pulmonary arterial hypertension (PAH). We investigated the safety and acute haemodynamic effects of the combination oral sildenafil and inhaled treprostinil in an open label study in patients with precapillary pulmonary hypertension. METHODS AND PATIENTS: Inhaled nitric oxide (20ppm; n=50), sildenafil (50mg; n=50) and inhaled treprostinil (15microg; n=25 or 30microg; n=25) were applied in subsequent order during right heart catheter investigation to consecutive patients with pulmonary arterial hypertension (PAH; n=28), non-operable chronic thromboembolic pulmonary hypertension (CTEPH; n=17) and pulmonary fibrosis associated pulmonary hypertension (n=5). RESULTS: Inhaled nitric oxide reduced pulmonary vascular resistance (PVR) to 87.3+/-5.1% of baseline values, reduced mean pulmonary arterial pressure (PAP) to 89.7+/-3.5% and increased cardiac output (CO) to 102.4+/-2.9%. Sildenafil reduced PVR to 80.1+/-5.0%, mPAP to 86.5+/-2.9% and increased CO to 103.8+/-3.2%. Treprostinil, inhaled 1h after sildenafil, reduced PVR to 66.3+/-3.8%, mPAP to 77.8+/-3.3%, and increased CO to 107.1+/-3.3% (mean+/-95% confidence interval). Subgroup analysis showed similar acute haemodynamic effects in PAH and CTEPH patients. Ventilation/perfusion distribution measurement in six patients with pre-existing gas exchange limitations was not changed by sildenafil and treprostinil. Relevant side effects were not observed. CONCLUSION: The combination of sildenafil and inhaled treprostinil was well tolerated and induced additive, pulmonary selective vasodilatation in pulmonary hypertension patients. This could be of relevance also for long-term treatment of PAH and CTEPH patients.

Pulmonary arterial hypertension.

Significant advances in the treatment of pulmonary arterial hypertension (PAH) have occurred over the last 10 years, starting with the approval of epoprostenol in 1998. Subsequently, multiple additional medications have received approval, including a subcutaneous prostacyclin, an inhaled prostacyclin, and oral medications in 2 separate classes. Over this same period, the classification of pulmonary hypertension has been revised with changes including the substitution of the term idiopathic for primary PAH and an expanded list of conditions felt to be associated with the development of PAH. Long-term follow-up studies have provided better information on prognosis and expected outcomes with treatment, with particularly valuable data on reassessment of prognosis after treatment with epoprostenol. Combination therapy is more frequently being used, and limited data on novel therapies such as stem cell transplantation have been published. The purpose of this review is to describe the current state of evidence for the diagnosis, prognosis, and treatment of the patient with PAH.

Treatment of pulmonary arterial hypertension due to scleroderma: challenges for the future.

Although progress has been made in treatment of pulmonary arterial hypertension, serious challenges remain. This article provides an overview of the challenges faced in treatment of PAH caused by scleroderma. It also provides a glimpse into the future, based on recent developments in the field that hold promise for enhancing the treatment of this disease.

Safety and efficacy of inhaled treprostinil as add-on therapy to bosentan in pulmonary arterial hypertension.

OBJECTIVES: This study evaluated the safety and efficacy of inhaled treprostinil as add-on therapy to oral bosentan in patients with pulmonary arterial hypertension (PAH). BACKGROUND: The addition of a long-acting prostacyclin analogue via the inhaled route might be a safe and effective strategy to optimize therapy in PAH patients on bosentan. METHODS: Twelve patients with symptomatic PAH despite bosentan received either 30 microg of inhaled treprostinil 4 times daily (n = 6) or 45 microg 4 times daily (n = 6), via an ultrasonic nebulizer. Six-min walk distance (6MWD), functional class, and hemodynamics were assessed at baseline and 12 weeks. RESULTS: One patient was excluded from analysis due to the subsequent finding of pulmonary capillary hemangiomatosis. In the remaining 11 patients, inhaled treprostinil was safe and well tolerated. Inhaled treprostinil was associated with an increase in 6MWD at 12 weeks (baseline 339 +/- 86, 12 week, 1 h post-inhalation 406 +/- 121 m, 67-m change, p = 0.01). An improvement in 6MWD of 49 m from baseline was noted during the trough period, just before inhalation of treprostinil (p = 0.009). The 6MWD improvement of at least 10% was noted in 1 of 6 patients receiving 30 microg versus 5 of 6 receiving 45 microg. Over 12 weeks, significant decreases were noted in mean pulmonary arterial pressure (-10%) and in pulmonary vascular resistance (-26%). Functional class improved from III to II in 9 of 11 patients. CONCLUSIONS: This trial suggests that inhaled treprostinil is safe, well tolerated, and associated with significant improvements in exercise capacity, functional class, and pulmonary hemodynamics in symptomatic patients with PAH on bosentan.

Clinical classification of pulmonary hypertension.

In 1998, during the Second World Symposium on Pulmonary Hypertension (PH) held in Evian, France, a clinical classification of PH was proposed. The aim of the Evian classification was to individualize different categories sharing similarities in pathophysiological mechanisms, clinical presentation, and therapeutic options. The Evian classification is now well accepted and widely used in clinical practice, especially in specialized centers. In addition, this classification has been used by the U.S. Food and Drug Administration and the European Agency for Drug Evaluation for the labeling of newly approved medications in PH. In 2003, during the Third World Symposium on Pulmonary Arterial Hypertension held in Venice, Italy, it was decided to maintain the general architecture and philosophy of the Evian classification. However, some modifications have been proposed, mainly to abandon the term "primary pulmonary hypertension" and to replace it with "idiopathic pulmonary hypertension"; to reclassify pulmonary veno-occlusive disease and pulmonary capillary hemangiomatosis; to update risk factors and associated conditions for pulmonary arterial hypertension and to propose guidelines in order to improve the classification of congenital systemic-to-pulmonary shunts.

High prevalence of elevated clotting factor VIII in chronic thromboembolic pulmonary hypertension.

Chronic thromboembolic pulmonary hypertension (CTEPH) is an enigmatic disorder lacking signs, symptoms and classical risk factors for venous thromboembolism. The objective of the prospective case controlled study, carried out at the Pulmonary Hypertension Unit, University Hospital Vienna, Austria, was to investigate whether plasma FVIII is elevated in CTEPH patients. The study examined 122 consecutive patients diagnosed with CTEPH. Plasma FVIII was measured and compared with plasma FVIII of healthy controls (n = 82) and of patients with nonthromboembolic pulmonary arterial hypertension (PAH, n = 88). Results show that CTEPH patients had higher FVIII levels than controls (233 +/- 83IU/dl versus 123 +/- 40IU/dl, p < 0.0001) and PAH patients (158 +/- 61IU/dl, p < 0.0001). Plasma FVIII one year after surgery (212 +/- 94IU/dl) was statistically unchanged compared with preoperative values (FVIII: 226 +/- 88IU/dl, n = 25). FVIII > 230IU/dl was more prevalent in CTEPH patients (41%) than in controls (5%, p < 0.0001) and PAH patients (22%, p = 0.022). We can conclude that elevated plasma FVIII is the first prothrombotic factor identified in a large proportion of CTEPH patients.

Bone morphogenetic proteins induce apoptosis in human pulmonary vascular smooth muscle cells.

Pulmonary vascular medial hypertrophy in primary pulmonary hypertension (PPH) is mainly caused by increased proliferation and decreased apoptosis in pulmonary artery smooth muscle cells (PASMCs). Mutations of the bone morphogenetic protein (BMP) receptor type II (BMP-RII) gene have been implicated in patients with familial and sporadic PPH. The objective of this study was to elucidate the apoptotic effects of BMPs on normal human PASMCs and to examine whether BMP-induced effects are altered in PASMCs from PPH patients. Using RT-PCR, we detected six isoforms of BMPs (BMP-1 through -6) and three subunits of BMP receptors (BMP-RIa, -RIb, and -RII) in PASMCs. Treatment of normal PASMCs with BMP-2 or -7 (100-200 nM, 24-48 h) markedly increased the percentage of cells undergoing apoptosis. The BMP-2-mediated apoptosis in normal PASMCs was associated with a transient activation or phosphorylation of Smad1 and a marked downregulation of the antiapoptotic protein Bcl-2. In PASMCs from PPH patients, the BMP-2- or BMP-7-induced apoptosis was significantly inhibited compared with PASMCs from patients with secondary pulmonary hypertension. These results suggest that the antiproliferative effect of BMPs is partially due to induction of PASMC apoptosis, which serves as a critical mechanism to maintain normal cell number in the pulmonary vasculature. Inhibition of BMP-induced PASMC apoptosis in PPH patients may play an important role in the development of pulmonary vascular medial hypertrophy in these patients.

Differential effects of stable prostacyclin analogs on smooth muscle proliferation and cyclic AMP generation in human pulmonary artery.

Primary pulmonary hypertension is characterized by increased pulmonary vascular resistance and smooth muscle proliferation. Stable analogs are increasingly being used to treat this disease, although no data exists comparing their effects on proliferation. We therefore investigated the antiproliferative activity of several prostacyclin (PGI(2)) analogs on human pulmonary arterial smooth muscle cells, including UT-15 and iloprost, analogs that have recently completed successful clinical trials. Serum-induced proliferation, as assessed by [(3)H]thymidine incorporation (30 h) or cell number (48 h), was significantly inhibited with a 10-fold difference in potency, ranking in effectiveness UT-15 > iloprost > cicaprost > beraprost. Effects were reversed by the adenylyl cyclase inhibitor, 2,5'dideoxyadenosine (DDA) but not SQ22536. Intracellular cyclic AMP (cAMP) was elevated by all analogs and inhibited by DDA, although SQ22536 was a highly variable inhibitor, suggesting that different pathways might mediate cAMP generation. UT-15 produced a significantly larger and more sustained increase in cAMP compared with other analogs, with iloprost being the weakest elevator. Thus, PGI(2) analogs potently inhibit proliferation of human pulmonary artery, probably via a cAMP-dependent pathway, although cAMP elevation in itself is not a good predictor of antiproliferative potency.

Nitric oxide induces apoptosis by activating K+ channels in pulmonary vascular smooth muscle cells.

Nitric oxide (NO) is an endogenous endothelium-derived relaxing factor that regulates vascular smooth muscle cell proliferation and apoptosis. This study investigated underlying mechanisms involved in NO-induced apoptosis in human and rat pulmonary artery smooth muscle cells (PASMC). Exposure of PASMC to NO, which was derived from the NO donor S-nitroso-N-acetyl-penicillamine, increased the percentage of cells undergoing apoptosis. Increasing extracellular K+ concentration to 40 mM or blocking K+ channels with 1 mM tetraethylammonia (TEA), 100 nM iberiotoxin (IBTX), and 5 mM 4-aminopyridine (4-AP) significantly inhibited the NO-induced apoptosis. In single PASMC, NO reversibly increased K+ currents through the large-conductance Ca(2+)-activated K+ (K(Ca)) channels, whereas TEA and IBTX markedly decreased the K(Ca) currents. In the presence of TEA, NO also increased K+ currents through voltage-gated K+ (K(v)) channels, whereas 4-AP significantly decreased the K(v) currents. Opening of K(Ca) channels with 0.3 mM dehydroepiandrosterone increased K(Ca) currents, induced apoptosis, and further enhanced the NO-mediated apoptosis. Furthermore, NO depolarized the mitochondrial membrane potential. These observations indicate that NO induces PASMC apoptosis by activating K(Ca) and K(v) channels in the plasma membrane. The resulting increase in K+ efflux leads to cytosolic K+ loss and eventual apoptosis volume decrease and apoptosis. NO-induced apoptosis may also be related to mitochondrial membrane depolarization in PASMC.