Pulmonary arterial hypertension: future directions: report of a National Heart, Lung and Blood Institute/Office of Rare Diseases workshop

Overexpressed lncRNA AC068039.4 Contributes to Proliferation and Cell Cycle Progression of Pulmonary Artery Smooth Muscle Cells Via Sponging miR-26a-5p/TRPC6 in Hypoxic Pulmonary Arterial Hypertension

BACKGROUND

Hypoxic pulmonary hypertension (HPH) is a devastating and incurable disease characterized by pulmonary vascular remodeling, resulting in right heart failure and even death. Accumulated evidence has confirmed long coding RNAs (lncRNAs) are involved in hypoxia-induced pulmonary vascular remodeling in HPH. The exact mechanism of lncRNA in hypoxic pulmonary hypertension remains unclear.

METHODS

Microarray analysis was applied to investigate the profiles of lncRNA expression in pulmonary artery smooth muscle cells (PASMCs) cultured under hypoxia and normoxia condition. qRT-PCR was performed for the expression of lncRNAs, miRNA, and mRNAs, western blot analysis was employed for the detection of the expression of proteins. CCK-8 and transwell chamber assay were applied for the assessment of PASMC proliferation and migration, respectively. Besides, flow cytometry was performed for assessments of cell cycle progression. The binding between AC068039.4 and miR-26a-5p, miR-26a-5p, and TRPC6 3'UTR was detected by dual luciferase reporter assay.

RESULTS

A total of 1,211 lncRNAs (698 up-regulated and 513 down-regulated) were differently expressed in hypoxia-induced PASMCs. Consistent with microarray analysis, quantitative PCR verified that AC068039.4 was obviously up-regulated in hypoxia-induced PASMCs. Knocking down AC068039.4 alleviated proliferation and migration of PASMCs and regulated cell cycle progression through inhibiting cells entering the G0/G1 cell cycle phase. Further experiment indicated AC068039.4 promoted hypoxic PASMCs proliferation via sponging miR-26-5p. In addition, transient receptor potential canonical 6 (TRPC6) was confirmed to be a target gene of miR-26a-5p.

CONCLUSION

In conclusion, downregulation of lncRNA AC068039.4 inhibited pulmonary vascular remodeling through AC068039.4/miR-26a-5p/TRPC6 axis, providing new therapeutic insights for the treatment of HPH.

Association between cytokines and functional, hemodynamic parameters, and clinical outcomes in pulmonary arterial hypertension

To assess the relationship of cytokines with functional and clinical outcomes in pulmonary arterial hypertension (PAH). Endothelial dysfunction and vascular inflammation are characteristic of PAH. We investigated whether markers of angiogenesis and inflammation associated with functional, hemodynamic parameters, and clinical outcomes in PAH. PAH patients (n = 206) were pooled from two clinical trials: TRUST-1 and FREEDOM-C2. Baseline and post-treatment cytokine levels were correlated to baseline clinical and hemodynamic parameters, were assessed in clinical subgroups, and were associated with clinical outcomes. In 206 patients (mean age = 48 years; 74% women) with WHO group-1 PAH, most cytokine levels were higher in those with 6-min walking distance (6MWD) < median (335 m) vs. those above median, including Ang-1 (11.9 ± 10.1 vs. 5.9 ± 6.0 ng/mL), Ang-2 (14.3 ± 11.8 vs. 12.2 ± 11.2 ng/mL), and MMP-9 (221 ± 262.3 vs. 119 ± 171 ng/mL). Baseline 6MWD inversely correlated with Ang-1 (r = −0.27, P < 0.0001), Ang-2 (r = −0.20, P = 0.004), and MMP-9 (r = −0.27, P < 0.0001). MMP-9 levels differed significantly by NYHA functional class (P = 0.001) suggesting an association between MMP-9 and subjective PAH severity. Mean Ang-2 levels were higher in those with baseline right atrial pressure (RAP) > 15 mmHg compared to those with RAP < 15 mmHg (23,841 vs. 11,020 pg/mL). Baseline RAP was associated with change in MMP-9 levels (r = −0.53, P = 0.03). Finally, baseline Ang-1, VEGF and MMP-9 levels were associated with risk of death and hospitalization at 16-week follow-up. Inflammatory cytokines and vascular angiogenesis markers are associated with baseline functional, hemodynamic parameters in PAH, and predict death and hospitalization. Larger prospective studies are needed to confirm the utility of cytokines in PAH.

A rabbit model of progressive chronic right ventricular pressure overload

OBJECTIVES

Right ventricular (RV) failure from increased pressure loading is a frequent consequence of acquired and congenital heart diseases. However, the mechanisms involved in their pathophysiology are still unclear, and few data exist on RV pressure-loading models and early versus late effects on RV and left ventricular responses. We characterized a rabbit model of chronic RV pressure overload and early-late effects on biventricular function.

METHODS

Twenty-one New Zealand white rabbits were randomized into 3 groups: (i) sham, (ii) pulmonary artery (PA) banding (PAB) for 3 weeks (PAB3W) and (iii) PAB for 6 weeks (PAB6W). Progressive RV pressure overload was created by serial band inflation using an adjustable device. Molecular, echocardiographic and haemodynamic studies were performed.

RESULTS

RV pressure overload was achieved with clinical manifestations of RV failure. Heart and liver weights were significantly higher after PAB. PAB-induced echocardiographic ventricular remodelling increased wall thickness and stress and ventricular dilation. Cardiac output (ml/min) (sham 172.4 ± 42.86 vs PAB3W 103.1 ± 23.14 vs PAB6W 144 ± 60.9, P = 0.0027) and systolic and diastolic functions decreased; with increased RV end-systolic and end-diastolic pressures (mmHg) (sham 1.6 ± 0.66 vs PAB3W 3.9 ± 1.8 vs PAB6W 5.2 ± 2.2, P = 0.0103), despite increased contractility [end-systolic pressure-volume relationship (mmHg/ml), sham 3.76 ± 1.76 vs PAB3W 12.21 ± 3.44 vs PAB6W 19.4 ± 6.88, P < 0.0001]. Functional parameters further worsened after PAB6W versus PAB3W. LV contractility increased in both the PAB groups, despite worsening of other invasive measures of systolic and diastolic functions.

CONCLUSIONS

We describe a novel, unique model of chronic RV pressure overload leading to early biventricular dysfunction and fibrosis with further progression at 6 weeks. These findings can aid in guiding management.

Validation of the Gatortail method for accurate sizing of pulmonary vessels from 3D medical images

PURPOSE

Detailed characterization of changes in vessel size is crucial for the diagnosis and management of a variety of vascular diseases. Because clinical measurement of vessel size is typically dependent on the radiologist's subjective interpretation of the vessel borders, it is often prone to high inter- and intra-user variability. Automatic methods of vessel sizing have been developed for two-dimensional images but a fully three-dimensional (3D) method suitable for vessel sizing from volumetric X-ray computed tomography (CT) or magnetic resonance imaging has heretofore not been demonstrated and validated robustly.

METHODS

In this paper, we refined and objectively validated Gatortail, a method that creates a mathematical geometric 3D model of each branch in a vascular tree, simulates the appearance of the virtual vascular tree in a 3D CT image, and uses the similarity of the simulated image to a patient's CT scan to drive the optimization of the model parameters, including vessel size, to match that of the patient. The method was validated with a 2-dimensional virtual tree structure under deformation, and with a realistic 3D-printed vascular phantom in which the diameter of 64 branches were manually measured 3 times each. The phantom was then scanned on a conventional clinical CT imaging system and the images processed with the in-house software to automatically segment and mathematically model the vascular tree, label each branch, and perform the Gatortail optimization of branch size and trajectory. Previously proposed methods of vessel sizing using matched Gaussian filters and tubularity metrics were also tested. The Gatortail method was then demonstrated on the pulmonary arterial tree segmented from a human volunteer's CT scan.

RESULTS

The standard deviation of the difference between the manually measured and Gatortail-based radii in the 3D physical phantom was 0.074 mm (0.087 in-plane pixel units for image voxels of dimension 0.85 × 0.85 × 1.0 mm) over the 64 branches, representing vessel diameters ranging from 1.2 to 7 mm. The linear regression fit gave a slope of 1.056 and an R² value of 0.989. These three metrics reflect superior agreement of the radii estimates relative to previously published results over all sizes tested. Sizing via matched Gaussian filters resulted in size underestimates of >33% over all three test vessels, while the tubularity-metric matching exhibited a sizing uncertainty of >50%. In the human chest CT data set, the vessel voxel intensity profiles with and without branch model optimization showed excellent agreement and improvement in the objective measure of image similarity.

CONCLUSIONS

Gatortail has been demonstrated to be an automated, objective, accurate and robust method for sizing of vessels in 3D non-invasively from chest CT scans. We anticipate that Gatortail, an image-based approach to automatically compute estimates of blood vessel radii and trajectories from 3D medical images, will facilitate future quantitative evaluation of vascular response to disease and environmental insult and improve understanding of the biological mechanisms underlying vascular disease processes.

Assessment of microRNA and gene dysregulation in pulmonary hypertension by endoarterial biopsy

MicroRNAs (miRNAs) may regulate a number of genes, each of which may have a variety of functions. We utilized an endoarterial biopsy catheter to assess the dysregulation of miRNAs in a porcine shunt model of pulmonary hypertension (PH). Two Yucatan micropigs underwent surgical anastomosis of the left pulmonary artery to the descending aorta. Endoarterial biopsy samples were obtained at baseline, and at regular intervals during the progression of PH. RNA, isolated from biopsy samples, was analyzed by Illumina miRNA expression microarrays (containing ∼1200 human miRNAs), Affymetrix Porcine GeneChips, Bioconductor, and GeneSpring. We examined a total of 925 genes in a PH whole genome microarray. Biopsy samples showed that 39 miRNAs were downregulated and 34 miRNAs were upregulated compared to baseline. The number of PH-associated genes reported to be controlled by each of the dysregulated miRNAs was in the range of 1–113. The five miRNAs that had the largest number of PH-associated genes were: miR-548c-3p, miR-520d-3p, miR-130a-5p, miR-30a-3p, and miR-let-7g-3p. Several of the dysregulated miRNAs have been associated with molecular pathways and biologic processes involved in PH. Among 29 miRNAs, which were predicted to be dysregulated by a systems biology approach, we found four that were dysregulated in our porcine shunt model. An endoarterial biopsy technique was successful in showing that a large number of miRNAs are dysregulated in a porcine shunt model of PH. Many of these miRNAs control multiple PH-associated genes, molecular pathways, and biologic processes. Endoarterial biopsy offers potential experimental and clinical diagnostic value.

Shared gene expression patterns in mesenchymal progenitors derived from lung and epidermis in pulmonary arterial hypertension: identifying key pathways in pulmonary vascular disease

Rapid access to lung-derived cells from stable subjects is a major challenge in the pulmonary hypertension field, given the relative contraindication of lung biopsy. In these studies, we sought to demonstrate the importance of evaluating a cell type that actively participates in disease processes, as well as the potential to translate these findings to vascular beds in other nonlung tissues, in this instance perivascular skin mesenchymal cells (MCs). We utilized posttransplant or autopsy lung explant-derived cells (ABCG2-expressing mesenchymal progenitor cells [MPCs], fibroblasts) and skin-derived MCs to test the hypothesis that perivascular ABCG2 MPCs derived from pulmonary arterial hypertension (PAH) patient lung and skin would express a gene profile reflective of ongoing vascular dysfunction. By analyzing the genetic signatures and pathways associated with abnormal ABCG2 lung MPC phenotypes during PAH and evaluating them in lung- and skin-derived MCs, we have identified potential predictor genes for detection of PAH as well as a targetable mechanism to restore MPCs and microvascular function. These studies are the first to explore the utility of expanding the study of ABCG2 MPC regulation of the pulmonary microvasculature to the epidermis, in order to identify potential markers for adult lung vascular disease, such as PAH.

Endothelial hyperpermeability in severe pulmonary arterial hypertension: role of store-operated calcium entry

Here, we tested the hypothesis that animals with severe pulmonary arterial hypertension (PAH) display increased sensitivity to vascular permeability induced by activation of store-operated calcium entry. To test this hypothesis, wild-type and transient receptor potential channel 4 (TRPC4) knockout Fischer 344 rats were given a single injection of Semaxanib (SU5416; 20 mg/kg) followed by 3 wk of exposure to hypoxia (10% oxygen) and a return to normoxia (21% oxygen) for an additional 2-3 wk. This Semaxanib/hypoxia/normoxia (i.e., SU5416/hypoxia/normoxia) treatment caused PAH, as evidenced by development of right ventricular hypertrophy, pulmonary artery medial hypertrophy, and occlusive lesions within precapillary arterioles. Pulmonary artery pressure was increased fivefold in Semaxanib/hypoxia/normoxia-treated animals compared with untreated, Semaxanib-treated, and hypoxia-treated controls, determined by isolated perfused lung studies. Thapsigargin induced a dose-dependent increase in permeability that was dependent on TRPC4 in the normotensive perfused lung. This increase in permeability was accentuated in PAH lungs but not in Semaxanib- or hypoxia-treated lungs. Fluid accumulated in large perivascular cuffs, and although alveolar fluid accumulation was not seen in histological sections, Evans blue dye conjugated to albumin was present in bronchoalveolar lavage fluid of hypertensive but not normotensive lungs. Thus PAH is accompanied by a TRPC4-dependent increase in the sensitivity to edemagenic agents that activate store-operated calcium entry.

Pulmonary Arteriopathy and Idiopathic Pulmonary Arterial Hypertension in Six Dogs

Pulmonary arteriopathy (PA) is the pathologic hallmark in human medicine of diffuse constrictive (medial and intimal remodeling) or multifocal complex (plexiform and dilatative lesions) arterial lesions, or both, that lead to irreversible obliteration of the arterial lumen. Clinically, PA leads to pulmonary arterial hypertension (PAH), of which idiopathic (IPAH) is one of the 5 subsets, and ultimately, to right-sided heart failure (RHF). Clinical and pathologic findings from 6 dogs with diagnosis of IPAH and PA were reviewed. These dogs were of various pure (5/6, 83%) and mixed (1/6, 17%) breeding, 5 months to 9 years (mean 5.2 years) old, and predominantly female (4/6, 67%) and reproductively intact (4/6, 67%). Doppler echocardiography ( n = 5) indicated increased pulmonary arterial pressures during systole (70-135 mm Hg, mean 98 mm Hg) and diastole (35-80 mm Hg, mean 58 mm Hg). All 6 dogs had right ventricular pressure overload, right ventricular eccentric hypertrophy, and RHF. Histologic examination confirmed the clinical diagnosis of IPAH in all dogs, revealing PA characterized by 1 of the 4 main human histologic subsets: 1) isolated medial hypertrophy (1/6, 17%); 2) medial hypertrophy-intimal thickening without the plexiform lesion (1/6, 17%); 3) medial hypertrophyintimal thickening concurrent with the plexiform lesion, which often was regionally clustered and situated near branching points of the respiratory artery, the poststenotic dilatation lesion, and vasculitis (4/6, 66%); and 4) isolated arteritis (1/6, 17%). Ancillary lesions similar to those in humans also complicated the PA (5/6, 83%). The complex lesions and ancillary exudative alveolitis seemed to be important indicators of severe, likely rapidly progressive and fatal, IPAH.

Inflammatory mechanisms in the pathogenesis of pulmonary arterial hypertension

Inflammation is a prominent feature of human and experimental pulmonary hypertension (PH) as suggested by infiltration of various inflammatory cells and increased expression of certain cytokines in remodeled pulmonary vessels. Macrophages, T and B lymphocytes, and dendritic cells are found in the vascular lesions of idiopathic pulmonary arterial hypertension (PAH) as well as in PAH associated with connective tissue diseases or infectious etiologies such as HIV. In addition, PAH is often characterized by the presence of circulating chemokines and cytokines, increased expression of growth (such as VEGF and PDGF) and transcriptional (e.g., nuclear factor of activated T cells or NFAT) factors, and viral protein components (e.g., HIV-1 Nef), which directly contribute to further recruitment of inflammatory cells and the pulmonary vascular remodeling process. These inflammatory pathways may thus serve as potential specific therapeutic targets. This article provides an overview of inflammatory pathways involving chemokines and cytokines as well as growth factors, highlighting their potential role in pulmonary vascular remodeling and the possibility of future targeted therapy.

Experimental and transgenic models of pulmonary hypertension

Pulmonary hypertension in human patients can result from increased pulmonary vascular tone, pressure transferred from the systemic circulation, dropout of small pulmonary vessels, occlusion of vessels with thrombi or intimal lesions, or some combination of all of these. Different animal models have been designed to reflect these different mechanistic origins of disease. Pulmonary hypertension models may be roughly grouped into tone-related models, inflammation-related models, and genetic models with unusual or mixed mechanism. Models of tone generally use hypoxia as a base, and then modify this with either genetic modifications (SOD, NOS, and caveolin) or with drugs (Sugen), although some genetic modifications of tone-related pathways can result in spontaneous pulmonary hypertension (Hph-1). Inflammation-related models can use either toxic chemicals (monocrotaline, bleomycin), live pathogens (stachybotrys, schistosomiasis), or genetic modifications (IL-6, VIP). Additional genetic models rely on alterations in metabolism (adiponectin), cell migration (S100A4), the serotonin pathway, or the BMP pathway. While each of these shares molecular and pathologic symptoms with different classes of human pulmonary hypertension, in most cases the molecular etiology of human pulmonary hypertension is unknown, and so the relationship between any model and human disease is unclear. There is thus no best animal model of pulmonary hypertension; instead, investigators must select the model most related to the specific pathology they are studying.

Evaluation of the Effects of Atorvastatin on the Treatment of Secondary Pulmonary Hypertension due to Chronic Obstructive Pulmonary Diseases: A Randomized Controlled Trial

Background

Since pulmonary hypertension (PH) in patients with chronic obstructive pulmonary diseases (COPD) causes poor prognosis and inflammatory process involved in PH, it is supposed that Statins with anti-inflammatory effects might be useful in the treatment of PH.

Objectives

The aim of this study was to evaluate the influence of Atorvastatin on the treatment of pulmonary hypertension in patients with COPD.

Patients and Methods

A registered (IRCT201108257411N1), triple-blind, randomized controlled trial was performed in Rasoule Akram hospital, Tehran, from 2009 to 2011. Forty five patients with secondary pulmonary hypertension due to COPD were recruited and randomized to two groups receiving either Atorvastatin 40 mg/d or placebo in addition to their current treatment for 6 months. The outcomes including systolic pulmonary arterial hypertension (SPAH), cardiac output (CO), right ventricular size (RVS), CRP, 6 min walk distance test (6MWD), and spirometry parameters were measured after 6 months.

Results

Baseline characteristics were similar in both groups. After 6 months, pulmonary hypertension changed from 48.5 ± 6.9 to 42.9 ± 9.3 mmHg for Atorvastatin users and from 49.7 ± 11.4 to 48.2 ± 14.6 mmHg for Placebo users (P = 0.19, CI - 13.57 - 2.89), 6MWD after 6 months was 339 ± 155 meters in case group versus 340 ± 106 meters in control group (P = 0.98, CI - 92.58 - 91.15). There were no significant changes in other outcomes including CRP, RVS, CO and spirometry parameters.

Conclusions

Although we found a trend towards decreasing SPAH and improving 6MWD, no statistically significant shift were detected in our outcomes due to inadequate sample size.

Vascular histomolecular analysis by sequential endoarterial biopsy in a shunt model of pulmonary hypertension

The molecular mechanisms of pulmonary arterial hypertension (PAH) remain ill-defined. The aims of this study were to obtain sequential endoarterial biopsy samples in a surgical porcine model of PAH and assess changes in histology and mRNA expression during the disease progression. Differentially expressed genes were then analyzed as potential pharmacological targets. Four Yucatan micro-pigs underwent surgical anastomosis of the left pulmonary artery to the descending aorta. Endovascular samples were obtained with a biopsy catheter at baseline (before surgery) and from the left lung 7, 60, and 180 days after surgery. RNA was isolated from biopsy samples, amplified and analyzed. Dysregulated genes were linked to drugs with potential to treat or prevent PAH. With the development of PAH in our model, we identified changes in histology and in the expression of several genes with known or investigational inhibitors and several novel genes for PAH. Gene dysregulation displayed time-related variations during disease progression. Endoarterial biopsy provides a new method of assessing pulmonary vascular histology and gene expression in PAH. This analysis could identify novel applications for existing and new PAH drugs. The detection of stage- and disease-specific variation in gene expression could lead to individualized therapies.

Differential effects of formoterol on thrombin- and PDGF-induced proliferation of human pulmonary arterial vascular smooth muscle cells

Background

Increased pulmonary arterial vascular smooth muscle (PAVSM) cell proliferation is a key pathophysiological component of pulmonary vascular remodeling in pulmonary arterial hypertension (PH). The long-acting β₂-adrenergic receptor (β₂AR) agonist formoterol, a racemate comprised of (R,R)- and (S,S)-enantiomers, is commonly used as a vasodilator in chronic obstructive pulmonary disease (COPD). PH, a common complication of COPD, increases patients’ morbidity and reduces survival. Recent studies demonstrate that formoterol has anti-proliferative effects on airway smooth muscle cells and bronchial fibroblasts. The effects of formoterol and its enantiomers on PAVSM cell proliferation are not determined. The goals of this study were to examine effects of racemic formoterol and its enantiomers on PAVSM cell proliferation as it relates to COPD-associated PH.

Methods

Basal, thrombin-, PDGF- and chronic hypoxia-induced proliferation of primary human PAVSM cells was examined by DNA synthesis analysis using BrdU incorporation assay. ERK1/2, mTORC1 and mTORC2 activation were determined by phosphorylation levels of ERK1/2, ribosomal protein S6 and S473-Akt using immunoblot analysis.

Results

We found that (R,R) and racemic formoterol inhibited basal, thrombin- and chronic hypoxia-induced proliferation of human PAVSM cells while (S,S) formoterol had lesser inhibitory effect. The β₂AR blocker propranolol abrogated the growth inhibitory effect of formoterol. (R,R), but not (S,S) formoterol attenuated basal, thrombin- and chronic hypoxia-induced ERK1/2 phosphorylation, but had little effect on Akt and S6 phosphorylation levels. Formoterol and its enantiomers did not significantly affect PDGF-induced DNA synthesis and PDGF-dependent ERK1/2, S473-Akt and S6 phosphorylation in human PAVSM cells.

Conclusions

Formoterol inhibits basal, thrombin-, and chronic hypoxia-, but not PDGF-induced human PAVSM cell proliferation and ERK1/2, but has little effect on mTORC1 and mTORC2 signaling. Anti-proliferative effects of formoterol depend predominantly on its (R,R) enantiomer and require the binding with β₂AR. These data suggest that (R,R) formoterol may be considered as potential adjuvant therapy to inhibit PAVSM cell proliferation in COPD-associated PH.

Congenital heart disease and pulmonary hypertension

Many patients with congenital heart disease and systemic-to-pulmonary shunts develop pulmonary arterial hypertension (PAH), particularly if the cardiac defect is left unrepaired. A persistent increase in pulmonary blood flow may lead to obstructive arteriopathy and increased pulmonary vascular resistance, a condition that can lead to reversal of shunt and cyanosis (Eisenmenger syndrome). Cardiac catheterization is crucial to confirm diagnosis and facilitate treatment. Bosentan is the only medication to date to be compared with placebo in a randomized controlled trial specifically targeting congenital heart disease-associated PAH. Lung transplantation with repair of the cardiac defect or combined heart-lung transplantation is reserved for recalcitrant cases.

Clinical perspectives with long-term pulsed inhaled nitric oxide for the treatment of pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is a chronic, progressive disease of the pulmonary vasculature with a high morbidity and mortality. Its pathobiology involves at least three interacting pathways – prostacyclin (PGI₂), endothelin, and nitric oxide (NO). Current treatments target these three pathways utilizing PGI₂ and its analogs, endothelin receptor antagonists, and phosphodiesterase type-5 (PDE-5) inhibitors. Inhaled nitric oxide (iNO) is approved for the treatment of hypoxic respiratory failure associated with pulmonary hypertension in term/near-term neonates. As a selective pulmonary vasodilator, iNO can acutely decrease pulmonary artery pressure and pulmonary vascular resistance without affecting cardiac index or systemic vascular resistance. In addition to delivery via the endotracheal tube, iNO can also be administered as continuous inhalation via a facemask or a pulsed nasal delivery. Consistent with a deficiency in endogenously produced NO, long-term pulsed iNO dosing appears to favorably affect hemodynamics in PAH patients, observations that appear to correlate with benefit in uncontrolled settings. Clinical studies and case reports involving patients receiving long-term continuous pulsed iNO have shown minimal risk in terms of adverse events, changes in methemoglobin levels, and detectable exhaled or ambient NO or NO₂. Advances in gas delivery technology and strategies to optimize iNO dosing may enable broad-scale application to long-term treatment of chronic diseases such as PAH.

Erythropoietin, but not asialoerythropoietin or carbamyl-erythropoietin, attenuates monocrotaline-induced pulmonary hypertension in rats

Erythropoietin (EPO) has long been utilized for the treatment of renal anemia. The erythropoietin receptor (EPOR) is also expressed in the cardiovascular and central nervous systems in addition to an erythroid lineage, to provide an organoprotective role against several types of cellular stress. Pulmonary hypertension (PH) is a poor prognostic disease caused by primary and secondary pulmonary vascular injury. We observed the effects of EPO derivatives on monocrotaline-induced PH in rats on the supposition that EPO may protect small arteries from injury. Asialoerythropoietin (AEPO) lacks sialic acids in the termini of carbohydrate chains that results in rapid clearance from blood. Carbamyl-erythropoietin (CEPO) interacts with EPOR/βc heterodimers, but not with EPOR homodimers expressed in erythroid cells. Monocrotaline-injected rats were treated with continuous intravenous injection of 2500 ng/kg/day of EPO, AEPO, or CEPO for 21 days, and lung histology, cardiac function, and mRNA expression in the lungs were examined. Wall thickening of small arteries in the lungs and PH were improved by administration of EPO, but not by its non-hematopoietic derivatives, AEPO, or CEPO. Erythropoietin administration increased mRNA expression of the anti-apoptotic molecule, Bcl-xL, and maintained expression of the CD31 antigen. We conclude that lungs may express EPOR homoreceptors, but not heteroreceptors. Adequate serum erythropoietin levels may be essential for pulmonary protective effects.

Targeting the vasoprotective axis of the renin-angiotensin system: a novel strategic approach to pulmonary hypertensive therapy

A decade has passed since the discovery of angiotensin-converting enzyme 2 (ACE2), a component of the ACE2–angiotensin (Ang)-(1-7)–Mas counterregulatory axis of the renin angiotensin system (RAS). ACE2 is considered an endogenous regulator of the vasoconstrictive, proliferative, fibrotic, and proinflammatory effects of the ACE–Ang II–angiotensin II type 1 receptor (AT₁R) axis. Both animal and clinical studies have emerged to define a role for ACE2 in pulmonary arterial hypertension (PAH). There is scientific evidence supporting the concept that ACE2 maintains the RAS balance and plays a protective role in PAH. The activation of pulmonary ACE2 could influence the pathogenesis of PAH and serve as a novel therapeutic target in PAH. Current therapeutic strategies and interventions have limited success, and PAH remains a fatal disease. Thus, more research that establishes the novel therapeutic potential and defines the mechanism of the ACE2–Ang-(1-7)–Mas counterregulatory axis in PAH is needed.

Simvastatin has beneficial effect on pulmonary artery hypertension by inhibiting NF-κB expression

Whether Simvastatin has beneficial effect on pulmonary artery hypertension (PAH) remains unclear. This study aimed to explore the effect of simvastatin on PAH and the underlying mechanism. Male SD rats were randomized into three groups: control group, PAH model group, and treatment group with the intervention of the Simvastatin (n = 10, each group). Rat PVSMCs were isolated from pulmonary artery, cultured in vitro, and subjected to different treatment with PDGF, and/or Simvastatin or parthenolide. The mean pulmonary arterial pressure (mPAP), endomembrane proliferation in the pneumono-arteriole, and scores of the average angiemphraxis (VOS) were measured. The expression of NF-κB at mRNA and protein levels in the artery and PVSMCs was evaluated by fluorescent quantitative PCR, immunohistochemistry, and Western blot. Our results showed that mPAP, endomembrane proliferation in the pneumono-arteriole and VOS increased significantly in PAH model group compared with control group (P < 0.05). NF-κB expression was significantly higher in PAH model group than control group (P < 0.05), and also higher in the stimulated PVSMCs than control PVSMCs (P < 0.05). With the intervention of simvastatin, mPAP, endomembrane proliferation in the pneumono-arteriole and VOS decreased dramatically, compared with model group (P < 0.05). NF-κB expression was significantly decreased in both the artery and PVSMCs (P < 0.05). In conclusion, our study provides experimental evidence that NF-κB plays an important role in the occurrence of pulmonary artery hypertension and Simvastatin has beneficial effect on pulmonary artery hypertension by inhibiting the expression of NF-κB.

Pulmonary arterial hypertension: pathobiology, diagnosis, treatment, and emerging therapies

Pulmonary hypertension is a rare disorder caused by vasoconstriction of the pulmonary arteries that leads to elevation of pulmonary vascular resistance, right ventricular failure, and ultimately death. Hypertrophy and proliferation of the pulmonary vascular endothelium leads to remodeling of this vascular system, resulting in a progressive disorder. In the past decade the molecular mechanisms and pathobiology of this disorder has become clearer. In addition, a host of new medical treatments and therapies are now available for what has been previously known to be a devastating disorder. Although much needs to be learned, this review will discuss our current knowledge, results of clinical trials, along with treatment options and emerging therapies available for the treatment of this disorder.

Treatment of pediatric pulmonary hypertension with simvastatin: an observational study

BACKGROUND

Animal studies and an adult human case series suggest that statins may have a role in the treatment of pulmonary hypertension. We reviewed the results of empirical therapy for children at Primary Children's Medical Center to determine whether simvastatin had a favorable effect on non-invasive estimates of pulmonary arterial pressure.

MATERIALS AND METHODS

The medical records of children with pulmonary hypertension who were treated with simvastatin were reviewed. Mean measurements of the gradient of tricuspid valve regurgitation before and after treatment were compared by a paired t-test. A favorable response to simvastatin was defined as a 20% decrease in the average measurement of the gradient of tricuspid valve regurgitation or a 20% decrease in right ventricular anterior wall thickness when tricuspid valve regurgitation resolved during treatment. Potential factors associated with a favorable response to simvastatin were identified with a Fisher exact test.

RESULTS

Twelve children, 4-15 years of age, had adequate Doppler velocity waveforms to reliably measure gradients of tricuspid valve regurgitation during a period of 1 year before treatment. Eleven patients had gradients of tricuspid valve regurgitation that could be measured during a period of 1 year after treatment. Patients were treated with simvastatin 0.09-0.28 mg/kg/day. Collectively, there was no difference between the average measurements of the gradient of tricuspid valve regurgitation before and after treatment (66 ± 21 mmHg vs. 63 ± 28 mmHg). Three of the five patients with clinical findings consistent with alveolar hypoxia and none of the seven patients without clinical findings consistent with alveolar hypoxia had a favorable response to treatment with simvastatin (P = 0.05).

CONCLUSION

Simvastatin may decrease pulmonary arterial pressure in a subset of patients with pulmonary hypertension.

Role of lipoxygenase metabolites of arachidonic acid in enhanced pulmonary artery contractions of female rabbits

Pulmonary arterial hypertension is characterized by elevated pulmonary artery pressure and vascular resistance. In women the incidence is 4-fold greater than that in men. Studies suggest that sustained vasoconstriction is a factor in increased vascular resistance. Possible vasoconstrictor mediators include arachidonic acid-derived lipoxygenase (LO) metabolites. Our studies in rabbits showed enhanced endothelium-dependent contractions to arachidonic acid in pulmonary arteries from females compared with males. Because treatment with a nonspecific LO inhibitor reduced contractions in females but not males, the present study identified which LO isoform contributes to sex-specific pulmonary artery vasoconstriction. The 15- and 5- but not 12-LO protein expressions were greater in females. Basal and A23187-stimulated release of 15-, 5-, and 12-hydroxyeicosatetraenoic acids (HETEs) from females and males were measured by liquid chromatography/mass spectrometry. Only 15-HETE synthesis was greater in females compared with males under both basal and stimulated conditions. Vascular contractions to 15-HETE were enhanced in females compared with males (maximal contraction: 44±6%versus 25±3%). The specific 15-LO inhibitor PD146176 (12 μmol/L) decreased arachidonic acid-induced contractions in females (maximal contraction: 93±4% versus 57±10%). If male pulmonary arteries were incubated with estrogen (1 μmol/L, 18 hours), protein expression of 15-LO and 15-HETE production increased. Mechanisms to explain the increased incidence of pulmonary hypertension in women are not known. Results suggest that the 15-LO pathway is different between females and males and is regulated by estrogen. Understanding this novel sex-specific mechanism may provide insight into the increased incidence of pulmonary hypertension in females.

Proteomic 2D DIGE profiling of human vascular endothelial cells exposed to environmentally relevant concentration of endocrine disruptor PCB153 and physiological concentration of 17β-estradiol

Considering the recent studies that question previously reported cardio-protective effects of estrogen, there is a growing concern that endocrine disruptors may also contribute to the pathology of cardiovascular disease. PCB153 is one of the most commonly found polychlorinated biphenyls, and based on epidemiological studies, has been implicated in cardiovascular disease. The endocrine disruptor PCB153 has been reported to bind the estrogen receptor alpha, induce vessel formation, and increase the formation of reactive oxygen species in endothelial cells. Since PCB153-induced phenotypic changes are similar to estradiol, we postulated that PCB153 activates redox signaling pathways common to 17β-estradiol. Whether the effect of PCB153 on the proteome is comparable to 17β-estradiol is not known. Therefore we investigated the proteome of human microvascular endothelial cells exposed to PCB153 (100 ng/ml) for 24 h. Using 2D DIGE coupled to MALDI-time of flight (TOF)/TOF MS, we found 96 protein spots significantly (greater than 1.5-fold) modulated by experimental treatments. Mass spectrometry identified 11 of 13 protein spots with high confidence protein score CI that was greater than 95%. Of the identified proteins, lamin A/C and far upstream element-binding protein (FUBP1) were regulated similarly by both treatments. FUBP1 is of particular interest because it controls c-myc. While lamin A/C modulates transcription factor AP-1 function. Interestingly, both c-myc and AP-1 are redox-sensitive transcription factors known to regulate genes required for cell growth. Network analysis of these proteins showed transforming growth factor β-1 and c-myc to play central roles. While our findings do not reveal any mechanisms involved in PCB153-induced vascularization, the identified network does provide a potential target pathway for further mechanistic studies of these relationships.

Gene expression profile of endothelial cells exposed to estrogenic environmental compounds: implications to pulmonary vascular lesions

AIMS

The cardiovascular system is an important target of estrogenic compounds. Considering the recent studies that question previously reported cardio-protective effects of estrogen, there is a growing concern that estrogenic environmental compounds may contribute to the pathology of vascular lesion formation.

MAIN METHODS

Real-time quantitative PCR was used to monitor the expression of genes involved in vascularization. Using Bayesian network modeling, we determined a gene network that estrogenic chemicals modulate in human vascular endothelial cells.

KEY FINDINGS

We showed that planar and coplanar polychlorinated biphenyls (PCBs) induce the expression of different genes compared to estradiol. Non-planar PCB congener 153 induced NOTCH3 which is a new finding as well as CCL2 and IL8 similar to what has been reported by other non-planar PCBs in endothelial cells. Our gene network indicated that experimental treatments signal a network containing TGF-beta receptor and NOTCH3; molecules biologically relevant to signaling pulmonary vascular lesions.

SIGNIFICANCE

We report in the present study that exposure of vascular endothelial cells to environmentally relevant concentrations of estrogenic PCBs induce gene networks implicated in the process of inflammation and adhesion. Our data suggest that PCBs can promote vascular lesion formation by activating gene networks involved in endothelial cell adhesion, cell growth, and pro-inflammatory molecules which were different from natural estrogen. Since inflammation and adhesion are a hallmark in the pathology of endothelial cell dysfunction, reconstructing gene networks provide insight into the potential mechanisms that may contribute to the vascular risks associated with estrogenic environmental chemicals.

Gene delivery of cytochrome p450 epoxygenase ameliorates monocrotaline-induced pulmonary artery hypertension in rats

Pulmonary arterial hypertension (PAH) is a life-threatening disease that leads to progressive pulmonary hypertension, right heart failure, and death. Endothelial dysfunction and inflammation were implicated in the pathogenesis of PAH. Epoxyeicosatrienoic acids (EETs), products of the cytochrome P450 epoxygenase metabolism of arachidonic acid, are potent vasodilators that possess anti-inflammatory and other protective properties in endothelial cells. We investigated whether gene delivery with the human cytochrome P450 epoxygenase 2J2 (CYP2J2) ameliorates monocrotaline (MCT)-induced pulmonary hypertension in rats. Significant pulmonary hypertension developed 3 weeks after the administration of MCT, but gene therapy with CYP2J2 significantly attenuated the development of pulmonary hypertension and pulmonary vascular remodeling, without causing changes in systemic arterial pressure or heart rate. These effects were associated with increased pulmonary endothelial NO synthase (eNOS) expression and its activity, inhibition of inflammation in the lungs, and transforming growth factor (TGF)-β/type II bone morphogenetic protein receptor (BMPRII)-drosophila mothers against decapentaplegic proteins (Smads) signaling. Collectively, these data suggest that gene therapy with CYP2J2 may have potential as a novel therapeutic approach to this progressive and oftentimes lethal disorder.

Simvastatin restores down-regulated GATA-6 expression in pulmonary hypertensive rats

Vascular smooth muscle cell proliferation has been known to be predominant in vascular remodeling of pulmonary hypertensive. The GATA family proteins, a group of zinc finger transcription factors, play an important role during cell proliferation. The aim of present study was to investigate the expression of GATA-6 gene in experimental pulmonary hypertensive rats and explore the effect of regulation of GATA-6 expression by simvastatin on pulmonary vascular remodeling. The male Sprague-Dawley rats model was established with receiving pneumonectomy and monocrotaline (MCT) administration. Right pulmonary artery remodeling in these animals was compared with untreated rats or rats receiving simvastatin. The level of GATA-6 mRNA and protein expression was detected by reverse transcriptase–polymerase chain reaction (RT-PCR) and Western blotting, respectively. Pneumonectomized, MCT-treated rats had significantly increased mean pulmonary arterial pressure (mPAP), RV/(LV + S) ratio (ratio of the right ventricular to left ventricular and septum weights), vascular occlusion scores (VOSs), and percent media wall thickness on day 35, all the indices were significantly decreased after simvastatin administration in these rats. The level of GATA-6 mRNA and protein were markedly decreased in these pneumonectomy and MCT-treated rats, and they were significantly up-regulated in these rats after receiving simvastatin. These results indicate that the development and progression of pulmonary hypertension is prevented by simvastatin by up-regulating GATA-6 expression in the lung tissue.

Pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is a devastating disease with significant disability and mortality, and it has much higher prevalence than previously thought. During the past 15 years, we have witnessed remarkable advances in our understanding of pathogenesis, in diagnostic process and in the development of disease-specific treatments for PAH. Nowadays, the diagnosis is more clearly defined, non-invasive markers of disease severity can be widely applied, and finally we can adopt evidence-based treatment. Newer drugs availability has resulted in radical change in the management of this disease. The article reviews established approaches to evaluation and treatment of this disorder.

Thrombin induces fibronectin-specific migration of pulmonary microvascular endothelial cells: requirement of calcium/calmodulin-dependent protein kinase II

Pulmonary arterial hypertension (PAH) is a progressive disease of excess vasoconstriction and vascular cell proliferation that results in increased pulmonary vascular resistance and right heart failure. We have previously shown (66) that tissue factor expression is increased in the abnormal vessels of patients and rats with PAH. We hypothesized that tissue factor and its downstream mediator, thrombin, would promote migration of endothelial cells (EC) and the vascular pathology of PAH. Immunostaining revealed EC and a fibronectin-enriched matrix within the "plexiform-like" lesions in a rat model of severe PAH. In a modified Boyden assay, protease-activated receptor 1 (PAR1; thrombin receptor) stimulation by agonist peptide or thrombin induced pulmonary microvascular EC (PMVEC) migration when the cells were interacting with fibronectin, but not with other extracellular matrix proteins. Thrombin/fibronectin-induced migration was confirmed in wound healing and angiogenesis assays and was abrogated by the PAR1 antagonist SCH79797 and soluble RGD peptide. This fibronectin dependence was unique to PAR1 activation; other EC agonists evaluated did not induce migration on any matrix, and 10% FBS stimulated similar levels of migration on all matrix proteins tested. Thrombin/fibronectin stimulated autophosphorylation of calcium/calmodulin dependent protein kinase II (CaMKII) in PMVEC, and inhibitors of CaMKII blocked thrombin-induced migration on fibronectin, but had no effect on migration induced by 10% FBS. In contrast, EC isolated from the proximal pulmonary artery migrated in response to most agonists independent of the matrix substrate. Our findings illustrate EC heterogeneity in a single tissue and indicate a novel role for CaMKII in mediating EC migration. Because PMVEC have been shown to have impressive proliferative potential, thrombin/fibronectin-stimulated migration of these cells to a site of injured endothelium is a potential mechanism by which thrombin contributes to the development of vascular lesions in PAH.

A functional single-nucleotide polymorphism in the TRPC6 gene promoter associated with idiopathic pulmonary arterial hypertension

BACKGROUND

Excessive proliferation of pulmonary artery smooth muscle cells (PASMCs) plays an important role in the development of idiopathic pulmonary arterial hypertension (IPAH), whereas a rise in cytosolic Ca2+ concentration triggers PASMC contraction and stimulates PASMC proliferation. Recently, we demonstrated that upregulation of the TRPC6 channel contributes to proliferation of PASMCs isolated from IPAH patients. This study sought to identify single-nucleotide polymorphisms (SNPs) in the TRPC6 gene promoter that are associated with IPAH and have functional significance in regulating TRPC6 activity in PASMCs.

METHODS AND RESULTS

Genomic DNA was isolated from blood samples of 237 normal subjects and 268 IPAH patients. Three biallelic SNPs, -361 (A/T), -254(C/G), and -218 (C/T), were identified in the 2000-bp sequence upstream of the transcriptional start site of TRPC6. Although the allele frequencies of the -361 and -218 SNPs were not different between the groups, the allele frequency of the -254(C-->G) SNP in IPAH patients (12%) was significantly higher than in normal subjects (6%; P<0.01). Genotype data showed that the percentage of -254G/G homozygotes in IPAH patients was 2.85 times that of normal subjects. Moreover, the -254(C-->G) SNP creates a binding sequence for nuclear factor-kappaB. Functional analyses revealed that the -254(C-->G) SNP enhanced nuclear factor-kappaB-mediated promoter activity and stimulated TRPC6 expression in PASMCs. Inhibition of nuclear factor-kappaB activity attenuated TRPC6 expression and decreased agonist-activated Ca2+ influx in PASMCs of IPAH patients harboring the -254G allele.

CONCLUSIONS

These results suggest that the -254(C-->G) SNP may predispose individuals to an increased risk of IPAH by linking abnormal TRPC6 transcription to nuclear factor-kappaB, an inflammatory transcription factor.

Pulmonary hypertension: diagnosis and management

Pulmonary arterial hypertension is a progressive, symptomatic, and ultimately fatal disorder for which substantial advances in treatment have been made during the past decade. Effective management requires timely recognition and accurate diagnosis of the disorder and appropriate selection among therapeutic alternatives. Despite progress in treatment, obstacles remain that impede the achievement of optimal outcomes. The current article provides an overview of the pathobiologic mechanisms of pulmonary arterial hypertension, including genetic substrates and molecular and cellular mechanisms, and describes the clinical manifestations and classification of pulmonary arterial hypertension. The article also reviews established approaches to evaluation and treatment, with emphasis on the appropriate application of calcium channel blockers, prostacyclin analogues, endothelin receptor antagonists, and phosphodiesterase 5 inhibitors. In addition, the authors discuss unresolved issues that may complicate patient management, such as the clinical importance of mild or exercise-related pulmonary arterial hypertension, and they identify avenues by which treatment may advance in the future through the use of combination treatment, outcomes assessment, and exploration of alternative pharmacologic strategies.

Pulmonary hypertension: diagnosis and management

Pulmonary arterial hypertension is a progressive, symptomatic, and ultimately fatal disorder for which substantial advances in treatment have been made during the past decade. Effective management requires timely recognition and accurate diagnosis of the disorder and appropriate selection among therapeutic alternatives. Despite progress in treatment, obstacles remain that impede the achievement of optimal outcomes. The current article provides an overview of the pathobiologic mechanisms of pulmonary arterial hypertension, including genetic substrates and molecular and cellular mechanisms, and describes the clinical manifestations and classification of pulmonary arterial hypertension. The article also reviews established approaches to evaluation and treatment, with emphasis on the appropriate application of calcium channel blockers, prostacyclin analogues, endothelin receptor antagonists, and phosphodiesterase 5 inhibitors. In addition, the authors discuss unresolved issues that may complicate patient management, such as the clinical importance of mild or exercise-related pulmonary arterial hypertension, and they identify avenues by which treatment may advance in the future through the use of combination treatment, outcomes assessment, and exploration of alternative pharmacologic strategies.

Synergistic heterozygosity for TGFbeta1 SNPs and BMPR2 mutations modulates the age at diagnosis and penetrance of familial pulmonary arterial hypertension

PURPOSE

We hypothesized that functional TGFbeta1 SNPs increase TGFbeta/BMP signaling imbalance in BMPR2 mutation heterozygotes to accelerate the age at diagnosis, increase the penetrance and SMAD2 expression in familial pulmonary arterial hypertension.

METHODS

Single nucleotide polymorphism genotypes of BMPR2 mutation heterozygotes, age at diagnosis, and penetrance of familial pulmonary arterial hypertension were compared and SMAD2 expression was studied in lung sections.

RESULTS

BMPR2 mutation heterozygotes with least active -509 or codon 10 TGFbeta1 SNPs had later mean age at diagnosis of familial pulmonary arterial hypertension (39.5 and 43.2 years) than those with more active genotypes (31.6 and 33.1 years, P = 0.03 and 0.02, respectively). Kaplan-Meier analysis also showed that those with the less active single nucleotide polymorphisms had later age at diagnosis. BMPR2 mutation heterozygotes with nonsense-mediated decay resistant BMPR2 mutations and the least, intermediate and most active -509 TGFbeta1 SNP genotypes had penetrances of 33, 72, and 80%, respectively (P = 0.003), whereas those with 0-1, 2, or 3-4 active single nucleotide polymorphism alleles had penetrances of 33, 72, and 75% (P = 0.005). The relative expression of TGFbeta1 dependent SMAD2 was increased in lung sections of those with familial pulmonary arterial hypertension compared with controls.

CONCLUSIONS

The TGFbeta1 SNPs studied modulate age at diagnosis and penetrance of familial pulmonary arterial hypertension in BMPR2 mutation heterozygotes, likely by affecting TGFbeta/BMP signaling imbalance. This modulation is an example of Synergistic Heterozygosity.

Pulmonary arterial remodeling induced by a Th2 immune response

Pulmonary arterial remodeling characterized by increased vascular smooth muscle density is a common lesion seen in pulmonary arterial hypertension (PAH), a deadly condition. Clinical correlation studies have suggested an immune pathogenesis of pulmonary arterial remodeling, but experimental proof has been lacking. We show that immunization and prolonged intermittent challenge via the airways with either of two different soluble antigens induced severe muscularization in small- to medium-sized pulmonary arteries. Depletion of CD4(+) T cells, antigen-specific T helper type 2 (Th2) response, or the pathogenic Th2 cytokine interleukin 13 significantly ameliorated pulmonary arterial muscularization. The severity of pulmonary arterial muscularization was associated with increased numbers of epithelial cells and macrophages that expressed a smooth muscle cell mitogen, resistin-like molecule alpha, but surprisingly, there was no correlation with pulmonary hypertension. Our data are the first to provide experimental proof that the adaptive immune response to a soluble antigen is sufficient to cause severe pulmonary arterial muscularization, and support the clinical observations in pediatric patients and in companion animals that muscularization represents one of several injurious events to the pulmonary artery that may collectively contribute to PAH.

Evidence-based pharmacologic management of pulmonary arterial hypertension

BACKGROUND

Pulmonary arterial hypertension (PAH) is a debilitating chronic disorder of the pulmonary vasculature characterized by elevated mean pulmonary arterial pressure, right-sided heart failure, and early mortality.

OBJECTIVES

This paper reviews the available information on PAH, including its pathophysiology, classification of its severity, current treatment options, drug interactions, pharmacokinetics, and cost considerations. The results of clinical trials of the available treatments are summarized, and a suggested treatment algorithm is provided as a guide to the medical management of PAH.

METHODS

Pertinent articles were identified by a search of MEDLINE through May 2007 using the terms primary pulmonary hypertension, pulmonary arterial hypertension, prostacyclin, pulmonary vasodilators, endothelin-receptor antagonists, and phosphodiesterase inhibitors. Trials with prospective, randomized designs were given precedence, and prospective studies having nonrandomized, open-label designs or using historical controls were included if they contributed useful knowledge. Retrospective studies were not included.

RESULTS

In two 12-week, randomized, open-label trials in patients with moderate to severe PAH (N = 81 and N = 111), exercise capacity, measured on the 6-minute walk test (6-MWT), was significantly improved with intravenous epoprostenol compared with conventional therapy (+31 vs -29 m, respectively, in one study [P = 0.002]; +46 vs -48 m in the other [P < 0.001]). In one of these trials, intravenous epoprostenol also was associated with a significant survival benefit (P < 0.003). In a 12-week, randomized, doubleblind, placebo-controlled trial in 470 patients with moderate to severe PAH, subcutaneous treprostinil plus conventional therapy was associated with a significant improvement on the 6-MWT compared with conventional therapy alone (+10 vs 0 m, respectively; P = 0.006). In a 16-week, randomized, double-blind, placebo-controlled trial in 213 patients with mild to moderate symptoms, the oral endothelin-receptor antagonist bosentan was associated with a significant improvement on the 6-MWT compared with placebo (+36 vs -8 m, respectively; P </= 0.001) and significantly less clinical worsening at 28 weeks (9/144 vs 14/69; P = 0.002). In a 12-week, prospective, randomized, double-blind, placebo-controlled trial in 277 patients with PAH, sildenafil 20, 40, and 80 mg TID were associated with significant improvements on the 6-MWT compared with placebo (all, P < 0.001). In a prospective trial in 76 patients with idiopathic PAH, the inhaled prostacyclin iloprost was associated with overall survival rates of 93%, 79%, 70%, 59%, 59%, and 49% at 3 months and 1, 2, 3, 4, and 5 years, respectively. In an early trial in 64 patients receiving highdose calcium channel blockers, those who had responded to initial drug challenge (defined as a > 20% decrease in pulmonary arterial pressure and pulmonary vascular resistance immediately after challenge) had a survival rate of 94% at 1, 3, and 5 years.

CONCLUSIONS

Patients who respond to an acute trial of a vasodilator may be treated with an oral calcium channel blocker, whereas oral therapies such as sildenafil and bosentan have been effective in patients with mild to moderate symptoms. Infusions of the prostacyclin analogues epoprostenol and treprostinil appear to be the treatment of choice for moderate to severe PAH, and agents with alternate routes of delivery such as inhaled iloprost may be advantageous in adjunctive roles. Future trials that focus on the long-term effects of currently available agents, as well as on combination therapy, are needed.

Rho kinase-mediated vasoconstriction in rat models of pulmonary hypertension

There is current controversy regarding whether vasoconstriction plays a significant role in the elevated pressure of severe, advanced stages of pulmonary hypertension. Results of acute vasodilator testing using conventional vasodilators in such patients suggest there is only a minor contribution of vasoconstriction. However, there is a possibility that these results may underestimate the contribution of vasoconstriction because the most effective vasodilators have not yet been tested. This issue has not been addressed even experimentally, due mainly to a lack of appropriate animal models. A few animal models that mimic the pathology of human severe pulmonary hypertension more closely (i.e., development of occlusive neointimal lesions in small pulmonary arteries/arterioles) have been introduced, including rat models of left lung pneumonectomy plus monocrotaline injection and vascular endothelial growth factor inhibition plus exposure to chronic hypoxia. We have observed that Rho kinase inhibitors, a novel class of potent vasodilators, reduce the high pulmonary artery pressure of these models acutely and markedly, suggesting that vasoconstriction can significantly be involved in pulmonary hypertension with severely remodeled (occluded) pulmonary vessels. This chapter describes methods used for evaluation of the involvement of Rho kinase-mediated vasoconstriction in rat models of pulmonary hypertension.

Comparison of lung proteome profiles in two rodent models of pulmonary arterial hypertension

We studied the lung proteome changes in two widely used models of pulmonary arterial hypertension (PAH): monocrotaline (MCT) injection and chronic hypoxia (CH); untreated rats were used as controls (n = 6/group). After 28 days, invasive right ventricular systolic pressure (RVSP) was measured. Lungs were immunostained for alpha-smooth muscle actin (alphaSMA). 2-DE (n = 4/group) followed by nano-LC-MS/MS was applied for protein identification. Western blotting was used additionally if possible. RVSP was significantly increased in MCT- and CH-rats (MCT 62.5 +/- 4.4 mmHg, CH 62.2 +/- 4.1 mmHg, control 25.0 +/- 1.7 mmHg, p<0.001). This was associated with an increase of alphaSMA positive vessels. In both groups, there was a significantly increased expression of proteins associated with the contractile apparatus (diphosphoHsp27 (p<0.001), Septin2 (p<0.001), F-actin capping protein (p<0.01), and tropomyosin beta (p<0.02)). In CH, proteins of the nitric oxide (Hsc70; p = 0.002), carbon monoxide (biliverdin reductase; p = 0.005), and vascular endothelial growth factor (VEGF) pathway (annexin 3; p<0.001) were significantly increased. In MCT, proteins involved in serotonin synthesis (14-3-3; p = 0.02), the enhanced unfolded protein response (ERp57; p = 0.02), and intracellular chloride channels (CLIC 1; p = 0.002) were significantly elevated. Therefore, MCT- and CH-induced vasoconstriction and remodeling seemed to be mediated via different signaling pathways. These differences should be considered in future studies using either PAH model.