Cellular pathophysiology and therapy of pulmonary hypertension

Molecular recognition and activation of the prostacyclin receptor by anti-pulmonary arterial hypertension drugs

The prostacyclin (PGI2) receptor (IP) is a Gs-coupled receptor associated with blood pressure regulation, allergy, and inflammatory response. It is a main therapeutic target for pulmonary arterial hypertension (PAH) and several other diseases. Here we report cryo-electron microscopy (cryo-EM) structures of the human IP-Gs complex bound with two anti-PAH drugs, treprostinil and MRE-269 (active form of selexipag), at global resolutions of 2.56 and 2.41 angstrom, respectively. These structures revealed distinct features governing IP ligand binding, receptor activation, and G protein coupling. Moreover, comparison of the activated IP structures uncovered the mechanism and key residues that determine the superior selectivity of MRE-269 over treprostinil. Combined with molecular docking and functional studies, our structures provide insight into agonist selectivity, ligand recognition, receptor activation, and G protein coupling. Our results provide a structural template for further improving IP-targeting drugs to reduce off-target activation of prostanoid receptors and adverse effects.

Role of the Purinergic P2Y2 Receptor in Pulmonary Hypertension

Pulmonary arterial hypertension (PAH), group 1 pulmonary hypertension (PH), is a fatal disease that is characterized by vasoconstriction, increased pressure in the pulmonary arteries, and right heart failure. PAH can be described by abnormal vascular remodeling, hyperproliferation in the vasculature, endothelial cell dysfunction, and vascular tone dysregulation. The disease pathomechanisms, however, are as yet not fully understood at the molecular level. Purinergic receptors P2Y within the G-protein-coupled receptor family play a major role in fluid shear stress transduction, proliferation, migration, and vascular tone regulation in systemic circulation, but less is known about their contribution in PAH. Hence, studies that focus on purinergic signaling are of great importance for the identification of new therapeutic targets in PAH. Interestingly, the role of P2Y2 receptors has not yet been sufficiently studied in PAH, whereas the relevance of other P2Ys as drug targets for PAH was shown using specific agonists or antagonists. In this review, we will shed light on P2Y receptors and focus more on the P2Y2 receptor as a potential novel player in PAH and as a new therapeutic target for disease management.

Management of prostacyclin side effects in adult patients with pulmonary arterial hypertension

Therapies that target the prostacyclin pathway are considered effective, yet are complex to dose and may cause dose-limiting side effects for patients with pulmonary arterial hypertension (PAH). Careful side effect management and the ability to discern side effects from worsening disease are essential in order for patients to continue, and benefit from, prostacyclin therapy. This manuscript was developed through a collaborative effort of allied health providers with extensive experience in managing patients with PAH who are treated with medications that target the prostacyclin pathway. This article provides an overview of individual prostacyclin pathway therapies approved in the United States, side effects most commonly associated with these therapies, and practical suggestions for side effect management. Most patients will experience significant side effects on prostacyclin therapy. Creating a proactive and careful side effect management program will increase the likelihood that patients are able to stay on therapy and receive the benefits afforded by prostacyclin therapy.

Inhibition of kinin B1 receptors attenuates pulmonary hypertension and vascular remodeling

This study examined whether the kinin B1 receptor is involved in the pathogenesis of pulmonary hypertension, and whether its inhibition could reduce inflammation, pulmonary hypertension, vascular remodeling, and right heart dysfunction. Male Wistar rats underwent left pneumonectomy. Seven days later, the rats were injected subcutaneously with monocrotaline (60 mg/kg). The rats were then randomly assigned to receive treatment with vehicle or with BI113823 (a selective B1 receptor antagonist, 30 mg/kg, twice per day) via oral gavage from the day of monocrotaline injection to day 28. By day 28, BI113823-treated rats had significantly lower mean pulmonary artery pressure, less right ventricular hypertrophy, and pulmonary arterial neointimal formation than that of the vehicle-treated rats. Real-time polymerase chain reaction revealed that there was a significant increase in mRNA expression of B1 receptors in the lungs of monocrotaline-challenged pneumonectomized rats. Treatment with BI113823 significantly reduced macrophage recruitment, as measured via bronchoalveolar lavage. It also markedly reduced CD-68 positive macrophages and proliferating cell nuclear antigen positive cells in the perivascular areas, reduced expression of inducible nitric oxide synthase, matrix metalloproteinase 2 and 9, and B1 receptors compared with measurements in vehicle-treated rats. These findings demonstrate that kinin B1 receptors represent a novel therapeutic target for pulmonary arterial hypertension.

Serum levels of tumor necrosis factor-related apoptosis-inducing ligand correlate with the severity of pulmonary hypertension

Pulmonary hypertension (PH) is a rapidly progressive disease that eventually leads to right heart failure and death. Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) and its receptors (TRAIL-Rs) play an important role in the survival, migration, and proliferation of vascular smooth muscle cells. However, the association between serum TRAIL levels and PH is unknown. In this study, we assayed the serum soluble TRAIL (sTRAIL) levels in 78 patients with PH and 80 controls. The sTRAIL concentrations were elevated in the PH patients compared with the controls (138.76 ± 6.60 pg/mL vs. 80.14 ± 3.38 pg/mL, p < 0.0001). The presence of sTRAIL levels of >103 pg/mL could discriminate PH patients from healthy individuals, with a sensitivity of 75.6% and specificity of 81.2%. Moreover, elevated sTRAIL concentrations were associated with eventual pathological complications; this is consistent with the finding that sTRAIL levels decreased in patients who responded to treatment. In a hypoxia-induced PH mouse model, sTRAIL levels were significantly higher compared with those in normoxia mice, and clearly decreased when the mice were treated with treprostinil. The sTRAIL levels were positively correlated with right ventricular systolic pressure and the index of right ventricular hypertrophy. In conclusion, serum sTRAIL could be a biomarker for diagnosis and effective therapy for PH patients.

Endothelin-1 driven proliferation of pulmonary arterial smooth muscle cells is c-fos dependent

Pulmonary hypertension (PH) is characterized by enhanced pulmonary artery smooth muscle cell (PASMC) proliferation leading to vascular remodeling. Although, multiple factors have been associated with pathogenesis of PH the underlying mechanisms are not fully understood. Here, we hypothesize that already very short exposure to hypoxia may activate molecular cascades leading to vascular remodeling. Microarray studies from lung homogenates of mice exposed to only 3h of hypoxia revealed endothelin-1 (ET-1) and connective tissue growth factor (CTGF) as the most upregulated genes, and the mitogen-activated protein kinase (MAPK) pathway as the most differentially regulated pathway. Evaluation of these results in vitro showed that ET-1 but not CTGF stimulation of human PASMCs increased DNA synthesis and expression of proliferation markers such as Ki67 and cell cycle regulator, cyclin D1. Moreover, ET-1 treatment elevated extracellular signal-regulated kinase (Erk)-dependent c-fos expression and phosphorylation of c-fos and c-jun transcription factors. Silencing of c-fos with siRNA abrogated the ET-1-induced proliferation of PASMCs. Expression and immunohistochemical analyses revealed higher levels of total and phosphorylated c-fos and c-jun in the vessel wall of lung samples of human idiopathic pulmonary arterial hypertension patents, hypoxia-exposed mice and monocrotaline-treated rats as compared to control subjects. These findings shed the light on the involvement of c-fos/c-jun in the proliferative response of PASMCs to ET-1 indicating that already very short hypoxia exposure leads to the regulation of mediators involved in vascular remodeling underlying PH.

Iloprost for idiopathic pulmonary arterial hypertension

Idiopathic pulmonary arterial hypertension is a rare but serious and life-threatening disease that leads to right heart failure and death within 2.8 years without specific treatment. This review focuses on the stable prostacyclin analog iloprost, its biologic action and pharmacology and, finally, on its clinical development, efficacy and safety in patients with idiopathic pulmonary arterial hypertension, which led to its approval for this indication. Furthermore, this review assesses the role of iloprost compared with other newly developed drugs, such as the endothelin receptor antagonist bosentan and the phosphodiesterase-5 inhibitor sildenafil, as well as other modes of application of prostacyclin and its analogs for the treatment of idiopathic pulmonary arterial hypertension. Based on the different modes of action of these substances, a combination of these treatments could be most promising for the future.

Right ventricular systolic pressure measurements in combination with harvest of lung and immune tissue samples in mice

The function of the right heart is to pump blood through the lungs, thus linking right heart physiology and pulmonary vascular physiology. Inflammation is a common modifier of heart and lung function, by elaborating cellular infiltration, production of cytokines and growth factors, and by initiating remodeling processes. Compared to the left ventricle, the right ventricle is a low-pressure pump that operates in a relatively narrow zone of pressure changes. Increased pulmonary artery pressures are associated with increased pressure in the lung vascular bed and pulmonary hypertension. Pulmonary hypertension is often associated with inflammatory lung diseases, for example chronic obstructive pulmonary disease, or autoimmune diseases. Because pulmonary hypertension confers a bad prognosis for quality of life and life expectancy, much research is directed towards understanding the mechanisms that might be targets for pharmaceutical intervention. The main challenge for the development of effective management tools for pulmonary hypertension remains the complexity of the simultaneous understanding of molecular and cellular changes in the right heart, the lungs and the immune system. Here, we present a procedural workflow for the rapid and precise measurement of pressure changes in the right heart of mice and the simultaneous harvest of samples from heart, lungs and immune tissues. The method is based on the direct catheterization of the right ventricle via the jugular vein in close-chested mice, first developed in the late 1990s as surrogate measure of pressures in the pulmonary artery. The organized team-approach facilitates a very rapid right heart catheterization technique. This makes it possible to perform the measurements in mice that spontaneously breathe room air. The organization of the work-flow in distinct work-areas reduces time delay and opens the possibility to simultaneously perform physiology experiments and harvest immune, heart and lung tissues. The procedural workflow outlined here can be adapted for a wide variety of laboratory settings and study designs, from small, targeted experiments, to large drug screening assays. The simultaneous acquisition of cardiac physiology data that can be expanded to include echocardiography and harvest of heart, lung and immune tissues reduces the number of animals needed to obtain data that move the scientific knowledge basis forward. The procedural workflow presented here also provides an ideal basis for gaining knowledge of the networks that link immune, lung and heart function. The same principles outlined here can be adapted to study other or additional organs as needed.

Erythrocyte-derived ATP and perfusion distribution: role of intracellular and intercellular communication

In complex organisms, both intracellular and intercellular communication are critical for the appropriate regulation of the distribution of perfusion to assure optimal O(2) delivery and organ function. The mobile erythrocyte is in a unique position in the circulation as it both senses and responds to a reduction in O(2) tension in its environment. When erythrocytes enter a region of the microcirculation in which O(2) tension is reduced, they release both O(2) and the vasodilator, ATP, via activation of a specific and dedicated signaling pathway that requires increases in cAMP, which are regulated by PDE3B. The ATP released initiates a conducted vasodilation that results in alterations in the distribution of perfusion to meet the tissue's metabolic needs. This delivery mechanism is modulated by both positive and negative feedback regulators. Importantly, defects in low O(2) -induced ATP release from erythrocytes have been observed in several human disease states in which impaired vascular function is present. Understanding of the role of erythrocytes in controlling perfusion distribution and the signaling pathways that are responsible for ATP release from these cells makes the erythrocyte a novel therapeutic target for the development of new approaches for the treatment of vascular dysfunction.

Opposing roles of leukotrienes and prostaglandins in fibrotic lung disease

Lung fibrosis is a devastating disease that involves a variable degree of inflammation, alveolar epithelial injury, fibroblast hyperplasia and the deposition of extracellular matrix. Standard therapies that consist of corticosteroids and immunosuppressive agents offer little benefit and most patients experience a progressive deterioration in lung function which is ultimately fatal within 2-5 years of diagnosis. New pathogenetic insights and therapeutic approaches are badly needed. Eicosanoids are lipid mediators derived from arachidonic acid metabolism, the best studied of which are prostaglandins and leukotrienes. Although these mediators are primarily known for their roles in asthma, pain, fever and vascular responses, they also exert relevant effects on immune and inflammatory cells as well as structural cells such as epithelial cells and fibroblasts - cell types which participate in fibrogenesis. In general, leukotrienes promote while prostaglandin E(2) opposes fibrogenic responses. Lung fibrosis is associated with increased production of leukotrienes and decreased production of prostaglandin E(2). Furthermore, responses to prostaglandin E(2) are altered in fibrotic conditions. This review highlights the role of this leukotriene/prostaglandin imbalance in the evolution of fibrotic lung disease, offers insights into the mechanisms that underlie the dysregulated responses and discusses approaches for therapeutic targeting of eicosanoids in these conditions.

Upregulation of Oct-4 isoforms in pulmonary artery smooth muscle cells from patients with pulmonary arterial hypertension

Oct-4 is a transcription factor considered to be one of the defining pluripotency markers in embryonic stem cells. Its expression has also been demonstrated in adult stem cells, tumorigenic cells, and, most recently and controversially, in somatic cells. Oct-4 pseudogenes also contribute to carcinogenesis. Oct-4 may be involved in the excessive proliferation of pulmonary arterial smooth muscle cells (PASMC) in patients with idiopathic pulmonary arterial hypertension (IPAH), contributing to the pathogenesis of IPAH. In this study, we show that Oct-4 isoforms are upregulated in IPAH-PASMC. Human embryonic stem cells (H9 line) and human PASMC from normotensive subjects were used throughout the investigation as positive and negative controls. In addition to significant upregulation of Oct-4 in a population of IPAH-PASMC, HIF-2alpha, a hypoxia-inducible transcription factor that has been shown to bind to the Oct-4 promoter and induces its expression and transcriptional activity, was also increased. Interestingly, a substantial upregulation of Oct-4 isoforms and HIF-2alpha was also observed in normal PASMC exposed to chronic hypoxia. In conclusion, the data suggest that both Oct-4 isoforms are upregulated and potentially have a significant role in the development of vascular abnormalities associated with the pathogenesis of IPAH and in pulmonary hypertension triggered by chronic hypoxia.

Preserved pulmonary vasodilative properties of aerosolized brain natriuretic peptide

INTRODUCTION

Inhalation of vasoactive substances is an effective treatment of pulmonary hypertension. The B-type natriuretic peptide (BNP) leads to relaxation of smooth muscle cells, caused by an increased formation of cyclic guanosine monophosphate (cGMP). The biologic activity of BNP using an inhalative approach has not been addressed.

METHODS

In order to assess the vasorelaxing capacity of exogenous BNP in the isolated ventilated and buffer perfused rabbit lung model, a stable pulmonary vasoconstriction was established by either the application of endothelin-1 or the thromboxane A(2) mimetic U46619. This was followed by an intravascular or aerosol application of BNP. CGMP was measured in the recirculating buffer fluid using a radioimmunoassay technique.

RESULTS

During a stable plateau of U46619 induced pulmonary vasoconstriction (mean pulmonary artery pressure, PAP 25.5+/-0.23 mmHg), the intravascular administration of BNP induced a rapid vasodilation (mean PAP 18.13+/-0.95 mmHg, p<0.001). This vasodilation was dose dependent and was paralleled by a 6-fold increase of cGMP. When BNP was aerosolized, pulmonary vasoconstriction was also significantly alleviated in the U46619 model (mean PAP 22+/-2.1 mmHg) and during endothelin-1 induced vasoconstriction (mean PAP 17.1+/-2.47 mmHg). Correspondingly, inhalation caused a significant augmentation of cGMP levels was.

CONCLUSION

The vasodilative capability of BNP as an indicator of the biologic activity of this peptide is preserved during its aerosolization. Presumably these vascular actions are caused at least in part by an increased availability of cGMP.

Inhaled iloprost for the control of pulmonary hypertension

Pulmonary arterial hypertension (PAH) is a life-threatening disease characterized by an elevated pulmonary arterial pressure and vascular resistance with a poor prognosis. Various pulmonary and extrapulmonary causes are now recognized to exist separately from the idiopathic form of pulmonary hypertension. An imbalance in the presence of vasoconstrictors and vasodilators plays an important role in the pathophysiology of the disease, one example being the lack of prostacyclin. Prostacyclin and its analogues are potent vasodilators with antithrombotic, antiproliferative and anti-inflammatory qualities, all of which are important factors in the pathogenesis of precapillary pulmonary hypertension. Iloprost is a stable prostacyclin analogue available for intravenous and aerosolized application. Due to the severe side effects of intravenous administration, the use of inhaled iloprost has become a mainstay in PAH therapy. However, owing to the necessity for 6 to 9 inhalations a day, oral treatment is often preferred as a first-line therapy. Numerous studies proving the efficacy and safety of inhaled iloprost have been performed. It is therefore available for a first-line therapy for PAH. The combination with endothelin-receptor antagonists or sildenafil has shown encouraging effects. Further studies with larger patient populations will have to demonstrate the use of combination therapy for long-term treatment of pulmonary hypertension.

The 'sweet' and 'bitter' involvement of glycosaminoglycans in lung diseases: pharmacotherapeutic relevance

The extracellular matrix (ECM) plays a significant role in the structure and function of the lung. The ECM is a three-dimensional fibre mesh, comprised of various interconnected and intercalated macromolecules, among which are the glycosaminoglycans (GAG). GAG are long, linear and highly charged, heterogeneous polysaccharides that are composed of a variable number of repeating disaccharide units (macromolecular sugars) and most of them, as their name implies, have a sweet taste. In the lung, GAG support the structure of the interstitium, the subepithelial tissue and the bronchial walls, and are secreted in the airway secretions. Besides maintaining lung tissue structure, GAG also play an important role in lung function as they regulate hydration and water homeostasis, modulate the inflammatory response and influence lung tissue repair and remodelling. However, depending on their size and/or degree of sulphation, and their immobilization or solubilization in the ECM, specific GAG in the lung either live up to their sweet taste/name, supporting normal lung physiology, or they are associated to 'bitter' effects, related to lung pathology. The present review discusses the biological role of GAG in the lung as well as the involvement of these molecules in various respiratory diseases. Given the great structural diversity of GAG, understanding the changes in GAG expression that occur in lung diseases may lead to novel targets for pharmacological intervention in order to prevent and/or to treat a range of lung diseases.

Upregulation of vascular calcium channels in neonatal piglets with hypoxia-induced pulmonary hypertension

Inhibition of voltage-gated, L-type Ca(2+) (Ca(L)) channels by clinical calcium channel blockers provides symptomatic improvement to some pediatric patients with pulmonary arterial hypertension (PAH). The present study investigated whether abnormalities of vascular Ca(L) channels contribute to the pathogenesis of neonatal PAH using a newborn piglet model of hypoxia-induced PAH. Neonatal piglets exposed to chronic hypoxia (CH) developed PAH by 21 days, which was evident as a 2.1-fold increase in pulmonary vascular resistance in vivo compared with piglets raised in normoxia (N). Transpulmonary pressures (DeltaPtp) in the corresponding isolated perfused lungs were 20.5 +/- 2.1 mmHg (CH) and 11.6 +/- 0.8 mmHg (N). Nifedipine reduced the elevated DeltaPtp in isolated lungs of CH piglets by 6.4 +/- 1.3 mmHg but only reduced DeltaPtp in lungs of N piglets by 1.9 +/- 0.2 mmHg. Small pulmonary arteries from CH piglets also demonstrated accentuated Ca(2+)-dependent contraction, and Ca(2+) channel current was 3.94-fold higher in the resident vascular muscle cells. Finally, although the level of mRNA encoding the pore-forming alpha(1C)-subunit of the Ca(L) channel was similar between small pulmonary arteries from N and CH piglets, a profound and persistent upregulation of the vascular alpha(1C) protein was detected by 10 days in CH piglets at a time when pulmonary vascular resistance was only mildly elevated. Thus chronic hypoxia in the neonate is associated with the anomalous upregulation of Ca(L) channels in small pulmonary arteries in vivo and the resulting abnormal Ca(2+)-dependent resistance may contribute to the pathogenesis of PAH.

Prostaglandins differentially affect osteogenic differentiation of human adipose tissue-derived mesenchymal stem cells

Adipose tissue-derived mesenchymal stem cells (AT-MSCs) are currently used for bone tissue engineering. AT-MSCs undergoing osteogenic differentiation respond to mechanical loading with increased cyclooxygenase-2 gene expression, a key enzyme in prostaglandin (PG) synthesis. PGs are potent multifunctional regulators in bone, exhibiting stimulatory and inhibitory effects on bone formation and resorption. PGE(2), but not PGI(2) or PGF(2), recruits osteoprogenitors from the bone marrow space and influences their differentiation. We hypothesize that PGE(2), PGI(2), and PGF(2) may differentially regulate osteogenic differentiation of human AT-MSCs. PGE(2), PGI(2), and PGF(2) (0.01-10 microM) affected osteogenic differentiation, but not proliferation of AT-MSCs after 4-14 days. Only PGF(2) (0.01-10 microM) increased alkaline phosphatase (ALP) activity at day 4. PGE(2) (10 microM), PGI(2) (0.01-10 microM), and PGF(2) (10 microM) decreased ALP activity, whereas PGF(2) (0.1 microM) increased ALP activity at day 14. PGF(2) (0.01-0.1 microM) and PGI(2) (0.01 microM) upregulated osteopontin gene expression, and PGF(2) (0.01 microM) upregulated alpha1(I)procollagen gene expression at day 4. PGE(2) and PGF(2) (10 microM) at day 4 and PGF(2) (1 microM) at day 14 downregulated runt-related transcription factor-2 gene expression. We conclude that PGE(2), PGI(2), and PGF(2) differentially affect osteogenic differentiation of AT-MSCs, with PGF(2) being the most potent. Thus, locally produced PGF(2) might be most beneficial in promoting osteogenic differentiation of AT-MSCs, resulting in enhanced bone formation for bone tissue engineering.

Chronic thromboembolic and pulmonary arterial hypertension share acute vasoreactivity properties

BACKGROUND

Pulmonary arterial hypertension (PAH) and chronic thromboembolic pulmonary hypertension (CTEPH) are the major classes of pulmonary hypertensive disorders according to the World Health Organization; both lead to right heart failure and death. A better understanding of disease mechanisms has led to the suggestion that the thromboembolic and nonthromboembolic types of pulmonary hypertension may share pathophysiologic features. We therefore compared acute vasoreactivity and proximal pulmonary artery compliance in patients with PAH and CTEPH during the initial diagnostic heart catheterization.

METHODS

Right heart catheterization using a flow-directed Swan-Ganz catheter was performed in patients with CTEPH (n = 22) and PAH (n = 35). Pulmonary hemodynamics were assessed at baseline, during the inhalation of 40 ppm of nitric oxide, and 30 min after the inhalation of 10 mug of iloprost. To assess the proximal pulmonary artery compliance, the pulse pressure (PP) [systolic-diastolic pressure] and the fractional PP (PPf) [divided by the mean pressure] were calculated.

RESULTS

Both vasodilators produced similar hemodynamic improvement, and the difference between CTEPH and PAH was not significant. The baseline PP and PPf did not vary between the two groups.

CONCLUSION

Patients with PAH and CTEPH show similar acute vasoreactivity to inhaled nitric oxide and iloprost, and have similar pulmonary artery compliance. These findings support the presence of some shared pathophysiologic pathways in both disorders and may lead to therapeutic implications in patients with inoperable CTEPH.

Iloprost inhalation solution for the treatment of pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is a condition that is characterised by increased pulmonary arterial pressure and vascular resistance that can lead to right ventricular failure and death. A variety of disturbances in pulmonary vascular endothelial and smooth muscle function are present in PAH, including reduced production of vasodilator and antiproliferative substances, such as nitric oxide and prostacyclin, and an overproduction of mitogens, such as endothelin. As a result of these observations, therapies have been developed for PAH that specifically target these pathogenic processes, including prostacyclin analogues and endothelin receptor antagonists. This article reviews iloprost inhalation solution, the most recently approved form of prostacyclin therapy that is delivered directly to the lungs by inhalation.

HIV-1 TAT represses transcription of the bone morphogenic protein receptor-2 in U937 monocytic cells

The bone morphogenetic protein receptor-2 (BMPR2) is a member of the transforming growth factor-beta receptor family and is expressed on the surface of several cell types including endothelial cells and macrophages. Recently, a cause for familial primary pulmonary hypertension (FPPH) has been identified as mutations in the gene encoding BMPR2. Three forms of pulmonary hypertension (PH) exist, including PPH, FPPH, and PH secondary to other etiologies (sporadic PH) such as drug abuse and human immunodeficiency virus (HIV) infection. It is interesting that these subtypes are histologically indistinguishable. The macrophage is a key target cell for HIV-1, significantly altering macrophage cell function upon infection. HIV-1 trans-activator of transcription (Tat), an immediate-early product of the HIV-1 lifecycle, plays an important role in mediating HIV-induced modulation of host cell function. Our laboratory has previously shown that Tat represses mannose receptor transcription in macrophages. In the current study, we examined activity from the BMPR2 promoter in the macrophage cell line U937 and potential regulation by Tat. Transfection of U937 cells with BMPR2 promoter-reporter constructs revealed dose-dependent repression of BMPR2 promoter activity in the presence of Tat. Experiments using truncations of the BMPR2 promoter localized Tat-mediated repression to the first 208 bases of the promoter. Decreased BMPR2 transcription resulted in altered downstream signaling. Similar to mothers against decapentaplegics (SMAD) phosphorylation and SMAD6 expression, in response to BMP2 treatment, were down-regulated after Tat treatment. Finally, HIV-1 infection and treatment with Tat protein of the U937 human monocytic cell line resulted in a decreased, endogenous BMPR2 transcript copy number.

[Lung function testing in patients with pulmonary arterial hypertension]

OBJECTIVE

The main objective was to describe the results of lung function testing in a series of 120 patients with pulmonary arterial hypertension, and the secondary objective was to compare these findings with hemodynamic variables.

PATIENTS AND METHODS

This was a descriptive study of lung function in 120 patients with stable pulmonary arterial hypertension (Evian/Venice groups 1 and 4) studied until January 2002 in the Pulmonary Hypertension and Lung Transplant Working Group attached to the Cardiology Department of the Hospital Universtario 12 de Octubre in Madrid, Spain. Data were collected retrospectively for the first 47 patients (1981 to 1995) and prospectively thereafter for the remaining 73 patients. The diagnosis was idiopathic arterial hypertension or hypertension associated with collagenosis, chronic pulmonary embolism, cardiac shunt, or toxic oil syndrome (30 cases).

RESULTS

In the group as a whole, forced vital capacity, forced expiratory volume in 1 second, and total lung capacity were normal; mean (SD) values revealed low carbon dioxide diffusing capacity (67.6% [23.2%]), and moderate hypoxemia (65.8 [15.4] mm Hg). No significant associations were observed between lung function and hemodynamic parameters. Mean age in the toxic oil syndrome group was lower (33.7 [11.4] years), and these patients had higher mean scores on the New York Heart Association scale (3.3 [0.5]) and for pulmonary vascular resistance (20.3 [8.1] kPa.L(-1).s).

CONCLUSIONS

Lung function was studied in a series of 120 patients with pulmonary arterial hypertension (Evian/ Venice groups 1 and 4), 30 of whom had toxic oil syndrome. No significant associations were found between lung function and hemodynamic parameters.

Inhaled tolafentrine reverses pulmonary vascular remodeling via inhibition of smooth muscle cell migration

BACKGROUND

The aim of the study was to assess the chronic effects of combined phosphodiesterase 3/4 inhibitor tolafentrine, administered by inhalation, during monocrotaline-induced pulmonary arterial hypertension (PAH) in rats.

METHODS

CD rats were given a single subcutaneous injection of monocrotaline to induce PAH. Four weeks after, rats were subjected to inhalation of tolafentrine or sham nebulization in an unrestrained, whole body aerosol exposure system. In these animals (i) the acute pulmonary vasodilatory efficacy of inhaled tolafentrine (ii) the anti-remodeling effect of long-term inhalation of tolafentrine (iii) the effects of tolafentrine on the expression profile of 96 genes encoding cell adhesion and extracellular matrix regulation were examined. In addition, the inhibitory effect of tolafentrine on ex vivo isolated pulmonary artery SMC cell migration was also investigated.

RESULTS

Monocrotaline injection provoked severe PAH (right ventricular systolic pressure increased from 25.9 +/- 4.0 to 68.9 +/- 3.2 after 4 weeks and 74.9 +/- 5.1 mmHg after 6 weeks), cardiac output depression and right heart hypertrophy. The media thickness of the pulmonary arteries and the proportion of muscularization of small precapillary resistance vessels increased dramatically, and the migratory response of ex-vivo isolated pulmonary artery smooth muscle cells (PASMC) was increased. Micro-arrays and subsequent confirmation with real time PCR demonstrated upregulation of several extracellular matrix regulation and adhesion genes, such as matrixmetalloproteases (MMP) 2, 8, 9, 10, 11, 12, 20, Icam, Itgax, Plat and serpinb2. When chronically nebulized from day 28 to 42 (12 daily aerosol maneuvers), after full establishment of severe pulmonary hypertension, tolafentrine reversed about 60% of all hemodynamic abnormalities, right heart hypertrophy and monocrotaline-induced structural lung vascular changes, including the proportion of pulmonary artery muscularization. The upregulation of extracellular matrix regulation and adhesion genes was reduced by nearly 80% by inhalation of the tolafentrine. When assessed in vitro, tolafentrine blocked the enhanced PASMC migratory response.

CONCLUSION

In conclusion, we demonstrate for the first time that inhalation of combined PDE3/4 inhibitor reverses pulmonary hypertension fully developed in response to monocrotaline in rats. This "reverse-remodeling" effect includes structural changes in the lung vascular wall and key molecular pathways of matrix regulation, concomitant with 60% normalization of hemodynamics.

[Pulmonary hypertension: pathophysiology, genetics and functional genomics]

Novel discoveries of the genetic basis of pulmonary hypertension have recently inspired a whole new area of research in pulmonary medicine. The finding that germ-line mutations in the BMPR2 locus, encoding a transmembrane receptor of the TGF beta superfamily, are the cause for familial and partly idiopathic pulmonary arterial hypertension has provided new clues for our understanding of this complex, yet highly localized disease. The TGF beta superfamily comprises more than 40 different growth and differentiation factors essential in the control of proliferation and differentiation of most cell types. In this review, we summarize the novel genetic and functional genomic findings to provide an outlook for the understanding of this disease.

Eicosanoids: mediators and therapeutic targets in fibrotic lung disease

Fibrosis is a common end-stage sequella of a number of acute and chronic lung diseases. Current concepts of pathogenesis implicate dysregulated interactions between epithelial cells and mesenchymal cells. Although investigative efforts have documented important roles for cytokines and growth factors in the pathogenesis of fibrotic lung diseases, these observations have not as yet been translated into efficacious therapies, and there is a pressing need for new pathogenetic insights and therapeutic approaches for these devastating disorders. Eicosanoids are lipid mediators derived from arachidonic acid, the most studied of which are the prostaglandins and leukotrienes. Although they are primarily known for their roles in asthma, pain, fever and vascular responses, present evidence indicates that eicosanoids exert relevant effects on immune/inflammatory, as well as structural, cells pertinent to fibrogenesis. In general, leukotrienes promote, whereas prostaglandin E(2) opposes, fibrogenic responses. An imbalance of eicosanoids also exists in pulmonary fibrosis, which favours the production of leukotrienes over prostaglandin E(2). This review highlights the role of this imbalance in the evolution of fibrotic lung disease, discusses the mechanisms by which it may arise and considers approaches for therapeutic targeting of eicosanoids in these conditions.

Specific inhibition of p38 mitogen-activated protein kinase with FR167653 attenuates vascular proliferation in monocrotaline-induced pulmonary hypertension in rats

OBJECTIVES

p38 mitogen-activated protein kinase is associated with many clinical entities characterized by inflammation. We postulated that inhibition of p38 mitogen-activated protein kinase with FR167653 attenuates inflammation and the development of pulmonary hypertension in monocrotaline-treated rats.

METHODS

Rats were divided into 4 groups: (1) the control group (daily 0.9% saline), (2) the FR group (daily FR167653, 2 mg . kg(-1) . d(-1)), (3) the MCT group (daily 0.9% saline the day after a single monocrotaline dose, 60 mg/kg), and (4) the MCT+FR group (daily FR167653, 2 mg . kg(-1) . d(-1), the day after a single MCT dose). Body weight, pulmonary artery pressure, and morphometric changes of the pulmonary artery with the histopathologic method were observed weekly for 4 weeks. Also, p38 mitogen-activated protein kinase activity and inflammatory cytokine expression in the lung were measured.

RESULTS

Four weeks after monocrotaline administration, mean pulmonary artery pressure in the MCT+FR group was lower than in the MCT group (MCT+FR vs MCT: 24.7 +/- 1.9 vs 36.5 +/- 2.1 mm Hg; P < .05). In morphometric analysis the percentage of medial wall thickness and the percentage of muscularization in the MCT+FR group were reduced compared with those in the MCT group after 4 weeks (P < .05); however, the number of macrophages was not significantly different. p38 mitogen-activated protein kinase activity was significantly attenuated in the MCT+FR group compared with in the MCT group (7.2 +/- 0.52 vs 2.1 +/- 0.23 fold-increase, P < .05, at 1 week). Although mRNA levels of tumor necrosis factor alpha and interleukin 1beta were reduced in the MCT+FR group compared with in the MCT group (tumor necrosis factor alpha: 1.18 +/- 0.36 vs 3.05 +/- 1.12 fold-increase, P < .05, at 2 weeks; interleukin 1beta: 2.2 +/- 0.34 vs 4.4 +/- 1.09 fold-increase, P < .05, at 1 week), FR167653 did not suppress increased monocyte chemotactic protein 1 mRNA expression induced by monocrotaline (3.2 +/- 0.62 vs 3.1 +/- 0.42 fold-increase, at 1 week).

CONCLUSION

FR167653 significantly attenuates the expression of inflammatory cytokines, ultimately preventing the progression of pulmonary hypertension. These results suggest that p38 mitogen-activated protein kinase might play a central role in the molecular events that underlie the development and progression of pulmonary hypertension.

The construction of endothelial cellular biosensing system for the control of blood pressure drugs

In order to assess blood pressure control drugs, the endothelial cellular biosensing system for assessing blood pressure control drugs was constructed. This system consists of human umbilical vein endothelial cells (HUVEC) on a polyion-coated gold electrode, a platinum counter electrode and an Ag/AgCl reference electrode. Nitric oxide (NO) as an indicator of blood vessel relaxation was detected with a polyion-coated electrode in the system. The NO detection limit of this electrode was 8.4 nM by differential pulse voltammetry (DPV). The drugs of blood pressure control (acetylcholine chloride (AcChCl), NOC 7 and NG-monomethyl-L-arginine (L-NMMA)) were assessed with this endothelial cellular biosensing system. One milli molar of AcChCl make NO released from HUVEC stimulated by activating endothelial nitric oxide synthase (eNOS) in HUVEC. In the case of 5 mM of L-NMMA, NO releasing was inhibited by inhibiting eNOS activation by 1 mM of AcChCl. NOC 7 immediately released NO regardless of eNOS activation in endothelial cells.

Insights into the redox control of blood coagulation: role of vascular NADPH oxidase-derived reactive oxygen species in the thrombogenic cycle

Various cardiovascular diseases including thrombosis, atherosclerosis, (pulmonary) hypertension and diabetes, are associated with disturbed coagulation. Alterations in the vessel wall common to many cardiovascular disorders have been shown to initiate the activity of the coagulation system, but also to be the result of an abnormal coagulation system. The primary link between the coagulation and the vascular system appears to be tissue factor (TF), which is induced on the surface of vascular cells and initiates the extrinsic pathway of the blood coagulation cascade, leading to the formation of thrombin. Thrombin can also interact with the vascular wall via specific receptors and can increase vascular TF expression. Such a "thrombogenic cycle" may be essentially involved in the pathogenesis of cardiovascular disorders associated with an abnormal coagulation. Therefore, the identification of the signaling pathways regulating this cycle and each of its relevant connecting links is of fundamental importance for the understanding of these disorders and their putative therapeutic potential. Reactive oxygen species (ROS) and the ROS-generating NADPH oxidases have been shown to play important roles as signaling molecules in the vasculature. In this review, we summarize the data supporting a substantial role of ROS in promoting a thrombogenic cycle in the vascular system.

Ion transport across Xenopus alveolar epithelium is regulated by extracellular ATP, UTP and adenosine

Native alveolar epithelium from Xenopus lung was used for electrophysiological Ussing chamber experiments to investigate ion transport regulation. The tissue exhibits a considerable absorption of Na(+) ions and this transepithelial transport is largely up-regulated after treatment of donor animals with ACTH. Extracellular ATP, UTP and adenosine were tested for their regulating effects and all three increased I(sc), which was mainly due to a stimulation of amiloride sensitive Na(+) transport (increase of I(ami) 32% for ATP, 21% for UTP, 25% for adenosine). Solely the effect of UTP was completely abolished in the presence of amiloride. In contrast, the effects of ATP or adenosine disappeared under Cl(-)-free conditions. ATP and UTP proved to have additive effects and pyridoxalphosphate-6-azophenyl-2',4'-disulfonic acid (PPADS), an antagonist of purinergic receptors, inhibited selectively the effect of UTP on I(sc). Further, I(sc) was increased by the P2X selective agonist beta,gamma-meATP. We were able to demonstrate, that extracellular purines and pyrimidines play a possible role as auto/paracrine messengers for alveolar ion transport regulation in Xenopus lung.

Prostacyclin and its analogues in the treatment of pulmonary hypertension

Prostacyclin and its analogues (prostanoids) are potent vasodilators and possess antithrombotic and antiproliferative properties. All of these properties help to antagonize the pathological changes that take place in the small pulmonary arteries of patients with pulmonary hypertension. Indeed, several prostanoids have been shown to be efficacious to treat pulmonary hypertension, while the main mechanism underlying the beneficial effects remains unknown. There are indications of beneficial combination effects of prostaglandins and phosphodiesterase inhibitors and endothelin receptor antagonists. This speaks in favor of combination therapies for pulmonary hypertension in the future. The mode of application of prostanoids used in randomized controlled studies has been quite variable: continuous i.v. infusion of prostacyclin, continuous s.c. infusion of treprostinil, p.o. application of beraprost, and inhaled application of iloprost. In addition, the applied doses were quite different, ranging from 0.25 ng/kg/min for inhaled iloprost to 30-50 ng/kg/min for i.v. prostacyclin. While the principal pharmacological properties of all prostanoids are very similar due to a main action on IP receptors, there are considerable differences in pharmacokinetics and metabolism, with half-lives of 2 min for prostacyclin and about 34 min for treprostinil for i.v. infused drugs and half-lives of about 85 min for s.c. infused treprostinil. In addition, the adverse effects largely depend on the doses used and the mode of application, although there is great variability between subjects. It remains to be determined which patients will profit most from which substance (or combination) and mode of application.

What you should know about pulmonary hypertension

Pulmonary hypertension is a fatal disease that often goes unrecognized until it becomes severe and debilitating. Early recognition allows for earlier treatment and improved quality of life for those affected. Early signs and symptoms include dyspnea and fatigue, and treatment options range from oral therapy with bosentan to intravenous therapy with epoprostenol. Work-up of pulmonary hypertension and its secondary causes are also reviewed.

Severe pulmonary hypertension: a frequent complication of stem cell transplantation for malignant infantile osteopetrosis

This report describes eight infants who developed acute severe pulmonary arterial hypertension (PAH) at days -2 to +89 after allogeneic stem cell transplantation (SCT) for malignant infantile osteopetrosis (MIOP). They were taken from a total of 28 children (frequency 29%) transplanted for this disease at three institutions between 1996 and 2002. Typical presentations were acute dyspnoea, hypoxia and brady/tachycardia usually in the absence of fever, crepitations or other evidence of infection. Six patients (75%) required assisted ventilation and five (62%) died. There was clinical or pathological evidence of veno-occlusive disease (VOD) in three children, but absence of VOD in the remaining five suggests that a separate disease process may be responsible for the PAH. Responses to nitric oxide (NO), defibrotide (DF), nicardipine and steroids in varying combinations were disappointing. Three children showed sustained improvement after administration of epoprostenol (EP, prostacyclin) in conjunction with NO and/or DF and remain well and free of PAH 25, 31 and 32 months post-transplant. PAH must therefore be excluded in any child who becomes acutely breathless after SCT for osteopetrosis.

Phosphodiesterase inhibitors for persistent pulmonary hypertension of the newborn: a review

Persistent pulmonary hypertension of the newborn (PPHN) is a complex syndrome with multiple causes, with an incidence of 0.43-6.8/1,000 live births and a mortality of 10-20%. Survivors have high morbidity in the forms of neurodevelopmental and audiological impairment, cognitive delays, hearing loss, and a high rate of rehospitalization. The optimal approach to the management of PPHN remains controversial. Inhaled nitric oxide (iNO) is currently regarded as the gold standard therapy, but with as many as 30% of cases failing to respond, has not proven to be the single magic bullet. Given the complex pathophysiology of the disease, any such magic bullet is unlikely. A number of recent studies have suggested a role for specific phosphodiesterase (PDE) inhibitors in the management of PPHN. Sildenafil, a specific PDE5 inhibitor, appears the most promising of such agents. We aim to review the current status and limitations of iNO and the potential of PDE inhibitors in the management of PPHN. The reasons why caution is warranted before specific PDE5 inhibitors like sildenafil are labelled as potential magic bullets for PPHN will be discussed. The need for randomized-controlled trials to determine the safety, efficacy, and long-term outcome following treatment with sildenafil in PPHN is emphasized.