Cellular and molecular pathobiology of pulmonary arterial hypertension

Comparison of mechanical behavior among the extrapulmonary arteries from rats

Results of comparative tests on pulmonary arteries from untreated Long-Evans rats are presented from three sections of the artery: the trunk, and the right and left main extrapulmonary arteries. Analyses were conducted looking for mechanical differences between the flow (longitudinal) and circumferential directions, between the right and left main arteries, and between each of the mains and the trunk. The mechanical properties of rat pulmonary arteries were obtained with a bubble inflation technique. A flat disk of rat pulmonary artery was constrained at the periphery and inflated, and the geometry of the resulting bubble of material recorded from six different angles. To analyze the data, the area under the stress-strain curve was calculated for each test and orientation. This area, related to the strain-energy density, was calculated at stress equal to 200kPa, for the purpose of statistical comparison. The mean values for the area show that the trunk is less compliant than the main arteries; this difference is supported by histological evidence. When comparing the circumferential and longitudinal properties of the arteries, differences are found for the trunk and left main arteries, but with opposite orientations being more compliant. The mean values for the two orientations for the right main artery are statistically identical. There was indication of significant difference in mechanical properties between the trunk and the main arteries. The left main artery in the circumferential orientation is highly compliant and appears to strongly influence the likelihood that significant differences will exist when included in a statistical population. These data show that each section of the extrapulmonary arterial system should not be expected to behave identically, and they provide the baseline mechanical behavior of the pulmonary artery from normotensive rats.

Nitric oxide modulation of ETB receptor-induced vasopressin release by rat and mouse hypothalamo-neurohypophyseal explants

Endothelin (ET) peptides stimulate vasopressin (AVP) secretion via ETB receptors at hypothalamic loci. Nitric oxide modulates the actions of ET in the cardiovascular system and also influences neurotransmission and specifically suppresses firing of magnocellular neurons. The purpose of these studies was to ascertain whether nitric oxide, generated in response to ETB receptor stimulation, buffers the stimulatory effect of ET and suppresses AVP release. Studies were performed using a pharmacological approach in hypothalamo-neurohypophyseal explants from rats, and an alternative strategy using explants from mice with an inactivating mutation of neuronal NOS (nNOS−/−) and their wild-type parent strain. Whole explants in standard culture or only the hypothalamus of compartmentalized explants was exposed to the ETB selective agonist, IRL 1620 (10−13 to 10−8 M). Rat and wild-type mouse explants displayed similar responses, although absolute basal release rates were higher from murine explants. Maximal AVP release at 0.1 nM IRL 1620 was 311 ± 63 (rat) and 422 ± 112% basal·explant−1·h−1 (mouse). Sodium nitroprusside (SNP; 0.1 mM) suppressed maximal AVP release to basal values. Nω-nitro-l-arginine methyl ester (l-NAME, 0.1 μM), which did not itself stimulate AVP secretion, more than doubled the response to 1 pM IRL 1620, from 136 ± 28 to 295 ± 49% basal·explant−1·h−1 ( P < 0.05) by rat explants. Explants from wild-type mice responded similarly. Explants from nNOS−/− mice had higher basal AVP secretory rate in response to 1 pM IRL 1620: 271 ± 48 compared with 150 ± 24% basal·explant−1·h−1 ( P < 0.05) from wild-type murine explants. In the nNOS−/−, SNP suppressed stimulated release, and l-NAME exerted no additional stimulatory effect: 243 ± 38% basal·explant−1·h−1. Thus nitric oxide inhibits the AVP secretory response induced by ETB receptor activation within the hypothalamo-neurohypophyseal system and is generated primarily by the nNOS isoform. The modulation of AVP secretion by ET and also nitric oxide can take place independently from their effects on cerebral blood flow, systemic hemodynamics, or the arterial baroreflex.

Anaesthesia management for pulmonary endarterectomy

PURPOSE OF REVIEW

Options for the surgical treatment of chronic thromboembolic pulmonary hypertension are either lung transplantation or pulmonary endarterectomy. Pulmonary endarterectomy is considered permanently curative and the treatment of choice. The procedure dramatically improves functional status and provides an excellent immediate and long-term survival, much better than transplantation. Pulmonary endarterectomy, until recently performed in only a few highly specialized centres, is now spreading worldwide with good results. This review will focus on the understanding of the pathophysiology of the disease and on recent advances in assessment and treatment strategies.

RECENT FINDINGS

Recent data reinforce the thromboembolic nature of chronic thromboembolic pulmonary hypertension, and have shown that the disorder is more common than was thought and remains underdiagnosed. There has recently been a remarkable surge in the understanding of the mechanisms involved in the pathogenesis of pulmonary hypertension. Advances in diagnosis, surgical techniques, preoperative treatment, and perioperative management have improved the prognosis of this debilitating disease. New information about pretreatment and medical treatment with prostanoids and endothelin receptor antagonists is now available.

SUMMARY

Pulmonary endarterectomy can be successfully performed in selected centres using a multidisciplinary approach involving the specialities of surgery, pulmonary medicine, cardiology, radiology, anaesthesiology and critical care medicine. The largest risk factor remains the degree of operability related to a high pulmonary vascular resistance caused by permanent changes in the pulmonary vascular bed. Early operation is now recommended to prevent these irreversible changes. Further investigations are warranted to establish the role of new drugs in surgical patients with chronic thromboembolic pulmonary hypertension.

Immunoluminometric assay for measurement of the C-terminal endothelin-1 precursor fragment in human plasma

BACKGROUND

Endothelin-1 (ET-1), a potent vasoconstrictor, is difficult to measure because of its instability and its binding to receptors and plasma proteins. We report a rapid, robust way to indirectly quantify ET-1 release by measuring the C-terminal ET-1 precursor fragment (CT-proET-1) without an extraction step.

METHODS

In plasma samples from healthy individuals, patients with congestive heart failure (CHF), and patients with sepsis, we measured CT-proET-1 with a sandwich immunoluminometric assay that uses 2 polyclonal antibodies to amino acids 168-212 of pre-proET-1. We also correlated CT-proET-1 concentrations with bigET-1 measurements.

RESULTS

The assay yielded results within 3 h and showed linear dilution with an analytical detection limit of 0.4 pmol/L and an interlaboratory CV <10% for values >10 pmol/L. Ex vivo CT-proET-1 was stable (<10% loss of immunoreactivity) in EDTA-, heparin-, and citrate-plasma for at least 4 h at room temperature, 6 h at 4 degrees C, and in EDTA-plasma for at least 6 months at -20 degrees C. CT-proET-1 values followed a gaussian distribution in healthy individuals (mean, 44.3 pmol/L; range, 10.5-77.4 pmol/L) without significant differences between males and females. The correlation coefficient for CT-proET-1 vs age was 0.25 (P <0.0001). CT-proET1 was significantly (P <0.0001) increased in patients with CHF (median, 104 pmol/L; range, 50.8-315 pmol/L) and patients with sepsis (median, 189 pmol/L; range, 34.6-855 pmol/L). The correlation between CT-proET-1 and bigET-1 for 43 samples was 0.80 (P <0.0001).

CONCLUSIONS

CT-proET-1 measurement is a rapid and easy method for indirectly assessing the release of ET-1 in critically ill patients.

Transgenic mice overexpressing the 5-hydroxytryptamine transporter gene in smooth muscle develop pulmonary hypertension

One intrinsic abnormality of pulmonary artery smooth muscle cells (PA-SMCs) in human idiopathic pulmonary hypertension (iPH) is an exaggerated proliferative response to internalized serotonin (5-HT) caused by increased expression of the 5-HT transporter (5-HTT). To investigate whether 5-HTT overexpression in PA-SMCs is sufficient to produce PH, we generated transgenic mice overexpressing 5-HTT under the control of the SM22 promoter. Studies in SM22-LacZ(+) mice showed that the transgene was expressed predominantly in SMCs of pulmonary and systemic vessels. Compared with wild-type mice, SM22-5-HTT(+) mice exhibited a 3- to 4-fold increase in lung 5-HTT mRNA and protein, together with increased lung 5-HT uptake activity, but no changes in platelet 5-HTT activity or blood 5-HT levels. At 8 weeks of age, SM22-5-HTT(+) mice exhibited PH, with marked increases in right ventricular systolic pressure (RVSP), right ventricle/left ventricle+septum ratio, and muscularization of distal pulmonary vessels, but no changes in systemic arterial pressure. PH worsened with age. Except a marked decrease in Kv channels, no changes in the lung expression of mediators of pulmonary vascular remodeling were observed in SM22-5-HTT(+) mice. Compared with wild-type mice, SM22-5-HTT(+) mice showed depressed hypoxic pulmonary vasoconstriction contrasting with greater severity of hypoxia- or monocrotaline-induced PH. These results show that increased 5-HTT expression in PA-SMCs, to a level close to that found in human iPH, lead to PH in mice. They further support a central role for 5-HTT in the pathogenesis of PH, making 5-HTT a potential therapeutic target.

Circulating progenitor cells are reduced in patients with severe lung disease

Patients with chronic severe lung disease are prone to develop pulmonary vascular remodeling, possibly through pulmonary endothelial dysfunction. Circulating endothelial progenitor cells (EPCs) are involved in maintenance of endothelial homeostasis. The aim of this study was to assess whether obstructive and restrictive lung diseases are associated with modification of EPC number in peripheral blood. The study was cross-sectional and involved patients with obstructive (n = 15) and restrictive (n = 15) lung disease on oxygen therapy and 15 control subjects. Circulating EPCs were defined by the surface expression of CD34, CD133, and kinase-insert domain receptor. Results from spirometric tests, blood gas analyses, and blood cell counts have been related to EPC numbers. Patients with chronic hypoxia and severe lung disease showed lower levels of all progenitors than do control subjects. A consensual further reduction of EPC was found in restrictive patients in comparison with obstructive patients. Among restrictive patients, EPC reduction was related to reduced lung volumes and impaired alveolo-arterial diffusion, whereas progenitor cell levels were directly related to erythrocyte number. Considering obstructive patients, significant correlations were found between progenitor cell levels and bronchial obstruction and between progenitor cell levels and arterial oxygen tension. These findings demonstrate a reduction of EPCs in patients with chronic lung disease and long-lasting hypoxia. This alteration was more evident in restrictive patients and correlated to disease severity. Depletion of circulating EPCs may be involved in altered endothelial homeostasis of pulmonary circulation in these disorders.

ALK1 signalling analysis identifies angiogenesis related genes and reveals disparity between TGF-beta and constitutively active receptor induced gene expression

Background

TGF-β1 is an important angiogenic factor involved in the different aspects of angiogenesis and vessel maintenance. TGF-β signalling is mediated by the TβRII/ALK5 receptor complex activating the Smad2/Smad3 pathway. In endothelial cells TGF-β utilizes a second type I receptor, ALK1, activating the Smad1/Smad5 pathway. Consequently, a perturbance of ALK1, ALK5 or TβRII activity leads to vascular defects. Mutations in ALK1 cause the vascular disorder hereditary hemorrhagic telangiectasia (HHT).

Methods

The identification of ALK1 and not ALK5 regulated genes in endothelial cells, might help to better understand the development of HHT. Therefore, the human microvascular endothelial cell line HMEC-1 was infected with a recombinant constitutively active ALK1 adenovirus, and gene expression was studied by using gene arrays and quantitative real-time PCR analysis.

Results

After 24 hours, 34 genes were identified to be up-regulated by ALK1 signalling. Analysing ALK1 regulated gene expression after 4 hours revealed 13 genes to be up- and 2 to be down-regulated. Several of these genes, including IL-8, ET-1, ID1, HPTPη and TEAD4 are reported to be involved in angiogenesis. Evaluation of ALK1 regulated gene expression in different human endothelial cell types was not in complete agreement. Further on, disparity between constitutively active ALK1 and TGF-β1 induced gene expression in HMEC-1 cells and primary HUVECs was observed.

Conclusion

Gene array analysis identified 49 genes to be regulated by ALK1 signalling and at least 14 genes are reported to be involved in angiogenesis. There was substantial agreement between the gene array and quantitative real-time PCR data. The angiogenesis related genes might be potential HHT modifier genes. In addition, the results suggest endothelial cell type specific ALK1 and TGF-β signalling.

Hypoxia-induced pulmonary vascular remodeling requires recruitment of circulating mesenchymal precursors of a monocyte/macrophage lineage

Vascular remodeling in chronic hypoxic pulmonary hypertension includes marked fibroproliferative changes in the pulmonary artery (PA) adventitia. Although resident PA fibroblasts have long been considered the primary contributors to these processes, we tested the hypothesis that hypoxia-induced pulmonary vascular remodeling requires recruitment of circulating mesenchymal precursors of a monocyte/macrophage lineage, termed fibrocytes. Using two neonatal animal models (rats and calves) of chronic hypoxic pulmonary hypertension, we demonstrated a dramatic perivascular accumulation of mononuclear cells of a monocyte/macrophage lineage (expressing CD45, CD11b, CD14, CD68, ED1, ED2). Many of these cells produced type I collagen, expressed alpha-smooth muscle actin, and proliferated, thus exhibiting mesenchymal cell characteristics attributed to fibrocytes. The blood-borne origin of these cells was confirmed in experiments wherein circulating monocytes/macrophages of chronically hypoxic rats were in vivo-labeled with DiI fluorochrome via liposome delivery and subsequently identified in the remodeled pulmonary, but not systemic, arterial adventitia. The DiI-labeled cells that appeared in the vessel wall expressed monocyte/macrophage markers and procollagen. Selective depletion of this monocytic cell population, using either clodronate-liposomes or gadolinium chloride, prevented pulmonary adventitial remodeling (ie, production of collagen, fibronectin, and tenascin-C and accumulation of myofibroblasts). We conclude that circulating mesenchymal precursors of a monocyte/macrophage lineage, including fibrocytes, are essential contributors to hypoxia-induced pulmonary vascular remodeling.

Upregulation of profilin, cofilin-2 and LIMK2 in cultured pulmonary artery smooth muscle cells and in pulmonary arteries of monocrotaline-treated rats

Pulmonary hypertension is associated with remodeling of the smooth muscle layer of pulmonary arteries, manifested by reduced smooth muscle cell (SMC) contractility and enhanced motility and growth. These responses are underlied by increased dynamics of the peripheral actin network. Thus, we hypothesized that pulmonary hypertension is associated with upregulation of two proteins that regulate the dynamics of peripheral actin filaments, i.e., profilin and cofilin. We also analyzed the expression of LIMK2, which regulates the actin remodeling capacity of cofilin by phosphorylation. Experimental inflammation was induced by incubation of cultured pulmonary artery SMCs (PASMCs) with inflammatory mediators in vitro, and by subcutaneous administration of monocrotaline to Sprague-Dawley rats in vivo. Expression of messenger RNA (mRNA) was assessed by quantitative RT-PCR, protein levels and phosphorylation were analyzed by immunoblotting. Immune and Masson trichrome stained lung cryosections were analyzed by microscopy. PDGF, IL-1beta, ET-1 and TNFalpha upregulated the profilin, cofilin-2 and LIMK2 mRNA in cultured pulmonary artery SMCs (PASMCs). Along with the development of rat pulmonary artery and right ventricular hypertrophy, monocrotaline treatment also induced the mRNA and protein contents of profilin, cofilin-2 and LIMK2 in PASMCs. The cofilin upregulation was paralleled by a relative decrease of the phospho-cofilin content. The upregulation of profilin, cofilin and LIMK2 in experimental inflammation suggests that by intensifying the remodeling of subcortical actin filaments these proteins may contribute to the enhanced invasiveness and growth of SMCs, and to the development of increased vascular resistance and pulmonary hypertension.

Serotonin inhibits voltage-gated K+ currents in pulmonary artery smooth muscle cells: role of 5-HT2A receptors, caveolin-1, and KV1.5 channel internalization

Multiple lines of evidence indicate that serotonin (5-hydroxytryptamine [5-HT]) and voltage-gated K+ (KV) channels play a central role in the pathogenesis of pulmonary hypertension (PH). We hypothesized that 5-HT might modulate the activity of KV channels, therefore establishing a link between these pathogenetic factors in PH. Here, we studied the effects of 5-HT on KV channels present in rat pulmonary artery smooth muscle cells (PASMC) and on hKV1.5 channels stably expressed in Ltk- cells. 5-HT reduced native KV and hKV1.5 currents, depolarized cell membrane, and caused a contraction of isolated pulmonary arteries. The effects of 5-HT on KV currents and contraction were markedly prevented by the 5-HT2A receptor antagonist ketanserin. Incubation with inhibitors of phospholipase C (U73122), classic protein kinase Cs (Gö6976), or tyrosine kinases (genistein and tyrphostin 23), the cholesterol depletion agent beta-cyclodextrin or concanavalin A, an inhibitor of endocytotic processes, also prevented the effects of 5-HT. In homogenates from pulmonary arteries, 5-HT2A receptors and caveolin-1 coimmunoprecipitated with KV1.5 channels, and this was increased on stimulation with 5-HT. Moreover, KV1.5 channels were internalized when cells were stimulated with 5-HT, and this was prevented by concanavalin A. These findings indicate that activation of 5-HT2A receptors inhibits native KV and hKV1.5 currents via phospholipase C, protein kinase C, tyrosine kinase, and a caveolae pathway. KV channel inhibition accounts, at least partly, for 5-HT-induced pulmonary vasoconstriction and might play a role in PH.

Sildenafil for pulmonary arterial hypertension

Pulmonary arterial hypertension is a disease characterized by progressive obliteration of the pulmonary vasculature leading to right-ventricular failure and if untreated, death. Several effective therapies are now available for pulmonary arterial hypertension. These therapies target specific abnormalities in the endothelium, including prostacyclin and nitric oxide deficiencies, and endothelin excess. Sildenafil, a phosphodiesterase type-5 inhibitor, has garnered interest recently for the treatment of pulomonary arterial hypertension because it increases cyclic GMP – a second messenger in the nitric oxide pathway. Early studies suggested a favorable response with traditional measures of a 6-min walk and hemodynamics in pulmonary arterial hypertension patients. Recently, sildenafil was approved by the US Food and Drug Administration and the European Medicines Agency under the trade name Revatio™ (Pfizer, Inc.). Sildenafil is well tolerated and adverse events have been shown to be mild and transient. Potential benefits of sildenafil therapy include its ease of administration and safety profile.

New assignments for multitasking signal transduction inhibitors

An article presented in this issue of Molecular Pharmacology (p. 1527) provides an intriguing example of how tyrosine kinase inhibitors can be put to many uses. In this article, the action of dasatinib (BMS-354825) is contrasted with that of imatinib, a kinase inhibitor that is currently being used to treat chronic myelogenous leukemia and other disorders. Both pharmacologic inhibitors target several tyrosine kinases, including Bcr-Abl and the platelet-derived growth factor receptor (PDGFR). Up to this point, the PDGFR has not been a primary therapeutic target for this class of agents. The work of Chen and colleagues shows that dasatinib is a particularly potent inhibitor of PDGFR and that the compound also targets Src kinase. The authors suggest that this combination of activities could be useful in the treatment of vascular obstructive diseases. Although a lack of absolute specificity has typically been regarded as a pharmacologic drawback, this study exemplifies how drugs with multiple molecular targets can potentially provide a very beneficial spectrum of therapeutic activities in multiple disease states.

The serum- and glucocorticoid-inducible kinase Sgk-1 is involved in pulmonary vascular remodeling: role in redox-sensitive regulation of tissue factor by thrombin

The stress-responsive serum- and glucocorticoid-inducible kinase Sgk-1 is involved in osmoregulation and cell survival and may contribute to fibrosis and hypertension. However, the function of Sgk-1 in vascular remodeling and thrombosis, 2 major determinants of pulmonary hypertension (PH), has not been elucidated. We investigated the role of Sgk-1 in thrombin signaling and tissue factor (TF) expression and activity in pulmonary artery smooth muscle cells (PASMC). Thrombin increased Sgk-1 activity and mRNA and protein expression. H2O2 similarly induced Sgk-1 expression. Antioxidants, dominant-negative Rac, and depletion of the NADPH oxidase subunit p22phox diminished thrombin-induced Sgk-1 expression. Inhibition of p38 mitogen-activated protein kinase, phosphatidylinositol 3-kinase, and phosphoinositide-dependent kinase-1 prevented thrombin-induced Sgk-1 expression. Thrombin or Sgk-1 overexpression enhanced TF expression and procoagulant activity, whereas TF upregulation by thrombin was diminished by kinase-deficient Sgk-1 and was not detectable in fibroblasts from mice deficient in sgk-1 (sgk1(-/-)). Similarly, dexamethasone treatment failed to induce TF expression and activity in lung tissue from sgk1(-/-) mice. Transcriptional induction of TF by Sgk-1 was mediated through nuclear factor kappaB. Finally, Sgk-1 and TF proteins were detected in the media of remodeled pulmonary vessels associated with PH. These data show that thrombin potently induces Sgk-1 involving NADPH oxidases, phosphatidylinositol 3-kinase, p38 mitogen-activated protein kinase, and phosphoinositide-dependent kinase-1, and that activation of nuclear factor kappaB by Sgk-1 mediates TF expression and activity by thrombin. Because enhanced procoagulant activity can promote pulmonary vascular remodeling, and Sgk-1 and TF were present in the media of remodeled pulmonary vessels, this pathway may play a critical role in vascular remodeling in PH.

Role of angiopoietin-1 in experimental and human pulmonary arterial hypertension

INTRODUCTION

The pulmonary microvasculature, consisting mainly of an endothelial cell (EC) monolayer and scant matrix support, is incompletely muscularized. Thus, the distal pulmonary arterioles may be predisposed to regression on exposure to environmental stresses (ie, hypoxia) and may be dependent on EC survival factors, like angiopoietin (Ang) 1, to attenuate the development of pulmonary arterial hypertension (PAH). In order to clarify the link between Ang1 expression and the development of PAH in patients, we also studied messenger RNA and protein expression in lung samples from healthy control subjects and patients with idiopathic PAH (IPAH) or PAH associated with other diseases (APAH).

METHODS

Ang/Tie2 gene expression was assessed in rats that had been exposed to hypoxia (ie, 10% O2) for 1, 3, or 7 days. In a separate experiment, the cell-based gene transfer of Ang1/Ang2 was performed, and the effects were evaluated in rats with hypoxia-induced PAH.

RESULTS

Hypoxia induced significant early increases in right ventricular systolic pressure (RVSP) and right ventricle/left ventricle-plus-septum mass ratio (RV/[LV + S]), with a significant decrease in Tie2 expression. Hypoxic rats receiving Ang1 demonstrated significant improvements in RVSP and RV/(LV + S), with a partial normalization in Tie2 protein levels. Robust Ang1 expression was observed in healthy human lungs. Furthermore, there were no significant changes in the levels of Ang1 or Ang2 in IPAH or APAH samples vs those in control subjects.

CONCLUSIONS

Decreased activity of the Tie2 pathway with hypoxia may contribute to PAH, possibly by loss of EC survival signaling, which can be overcome by Ang1 gene transfer.

Molecular and cellular determinants of lung endothelial cell heterogeneity

Idiopathic pulmonary arterial hypertension is a progressive and potentially fatal disease with a limited number of therapeutic options. Two key lesions underlie the pathophysiology of this disease. The principal lesion is found in large- and intermediate-sized blood vessels and is characterized by medial and adventitial hypertrophy/hyperplasia, with distal extension of smooth-muscle layers into normally nonmuscularized vessels. The second lesion, found prominently in severe forms of pulmonary hypertension, originates in small precapillary vessel segments, commonly at blood vessel bifurcations. This "plexiform lesion" is a lumen-obliterative lesion comprised, at least in part, of cells that share endothelial cell attributes, but that have lost the "law of the monolayer." Indeed, the endothelial contribution to the (mal-)adaptive response in pulmonary hypertension is becoming increasingly apparent, with evidence that endothelium plays an important role in promoting the vasoconstriction and hyperproliferation of medial and adventitial cell layers in large- and intermediate-vessel sizes, and lumen obliteration in the plexiform lesion. Recent evidence indicates endothelial cells along the pulmonary artery and precapillary segments are phenotypically distinct and may fulfill different roles in these site-specific lesions. Thus, the present review summarizes our current understanding of pulmonary endothelial cell heterogeneity and discusses the potential role(s) of endothelial cell heterogeneity in the pathogenesis of pulmonary hypertension.

Effects of intravenous nesiritide on pulmonary vascular hemodynamics in pulmonary hypertension

BACKGROUND

Nesiritide is effective in the treatment of decompensated heart failure (HF). We evaluated the acute hemodynamic effects of nesiritide, a recombinant B-type natriuretic peptide, in patients with HF and pulmonary hypertension (PH).

METHODS AND RESULTS

Twenty patients with HF and PH (mean pulmonary arterial [PA] pressure >25 mm Hg) were enrolled: 10 with postpulmonary capillary wedge (PCW) >15 mm Hg and 10 with precapillary PH (PCW) < or =15. The pulmonary and systemic hemodynamics were determined by right heart catheterization at baseline and at 15 and 30 minutes after an intravenous nesiritide infusion (2 mcg/kg bolus and 0.01 mcg.kg.min). For the patients with postcapillary PH, the mean left ventricular ejection fraction was 28 +/- 15%. After the 30-minute nesiritide infusion, right atrial (RA) pressure decreased 48% (P < .0001), mean PA pressure decreased 29% (P < .0001), PCW pressure decreased 40% (P < .0001), cardiac index (CI) increased 35% (P = .009), pulmonary vascular resistance index (PVRI) decreased 35% (P = .01), and arteriovenous oxygen difference (AVDO(2)) decreased 27% (P = .0003). For precapillary PH patients, there was no change in RA, PA, or PCW pressure, nor any change in CI, PVRI, or AVDO(2).

CONCLUSIONS

Nesiritide acutely and significantly reduced PA pressure, PVRI, and biventricular filling pressures in patients with postcapillary PH. However, for patients with precapillary PH, nesiritide had no significant acute hemodynamic effect on the pulmonary hemodynamics. The lack of acute beneficial effects of nesiritide in patients with advanced precapillary PH may be related to their relatively fixed remodeling of the pulmonary vasculature.

Phosphodiesterase type 4 expression and anti-proliferative effects in human pulmonary artery smooth muscle cells

Background

Pulmonary arterial hypertension is a proliferative vascular disease, characterized by aberrant regulation of smooth muscle cell proliferation and apoptosis in distal pulmonary arteries. Prostacyclin (PGI₂) analogues have anti-proliferative effects on distal human pulmonary artery smooth muscle cells (PASMCs), which are dependent on intracellular cAMP stimulation. We therefore sought to investigate the involvement of the main cAMP-specific enzymes, phosphodiesterase type 4 (PDE4), responsible for cAMP hydrolysis.

Methods

Distal human PASMCs were derived from pulmonary arteries by explant culture (n = 14, passage 3–12). Responses to platelet-derived growth factor-BB (5–10 ng/ml), serum, PGI₂ analogues (cicaprost, iloprost) and PDE4 inhibitors (roflumilast, rolipram, cilomilast) were determined by measuring cAMP phosphodiesterase activity, intracellular cAMP levels, DNA synthesis, apoptosis (as measured by DNA fragmentation and nuclear condensation) and matrix metalloproteinase-2 and -9 (MMP-2, MMP-9) production.

Results

Expression of all four PDE4A-D genes was detected in PASMC isolates. PDE4 contributed to the main proportion (35.9 ± 2.3%, n = 5) of cAMP-specific hydrolytic activity demonstrated in PASMCs, compared to PDE3 (21.5 ± 2.5%), PDE2 (15.8 ± 3.4%) or PDE1 activity (14.5 ± 4.2%). Intracellular cAMP levels were increased by PGI₂ analogues and further elevated in cells co-treated with roflumilast, rolipram and cilomilast. DNA synthesis was attenuated by 1 μM roflumilast (49 ± 6% inhibition), rolipram (37 ± 6%) and cilomilast (30 ± 4%) and, in the presence of 5 nM cicaprost, these compounds exhibited EC₅₀ values of 4.4 (2.6–6.1) nM (Mean and 95% confidence interval), 59 (36–83) nM and 97 (66–130) nM respectively. Roflumilast attenuated cell proliferation and gelatinase (MMP-2 and MMP-9) production and promoted the anti-proliferative effects of PGI₂ analogues. The cAMP activators iloprost and forskolin also induced apoptosis, whereas roflumilast had no significant effect.

Conclusion

PDE4 enzymes are expressed in distal human PASMCs and the effects of cAMP-stimulating agents on DNA synthesis, proliferation and MMP production is dependent, at least in part, on PDE4 activity. PDE4 inhibition may provide greater control of cAMP-mediated anti-proliferative effects in human PASMCs and therefore could prove useful as an additional therapy for pulmonary arterial hypertension.

Activation of soluble guanylate cyclase reverses experimental pulmonary hypertension and vascular remodeling

BACKGROUND

Severe pulmonary hypertension is a disabling disease with high mortality, characterized by pulmonary vascular remodeling and right heart hypertrophy. Using wild-type and homozygous endothelial nitric oxide synthase (NOS3(-/-)) knockout mice with pulmonary hypertension induced by chronic hypoxia and rats with monocrotaline-induced pulmonary hypertension, we examined whether the soluble guanylate cyclase (sGC) stimulator Bay41-2272 or the sGC activator Bay58-2667 could reverse pulmonary vascular remodeling.

METHODS AND RESULTS

Both Bay41-2272 and Bay58-2667 dose-dependently inhibited the pressor response of acute hypoxia in the isolated perfused lung system. When wild-type (NOS3(+/+)) or NOS3(-/-) mice were housed under 10% oxygen conditions for 21 or 35 days, both strains developed pulmonary hypertension, right heart hypertrophy, and pulmonary vascular remodeling, demonstrated by an increase in fully muscularized peripheral pulmonary arteries. Treatment of wild-type mice with the activator of sGC, Bay58-2667 (10 mg/kg per day), or the stimulator of sGC, Bay41-2272 (10 mg/kg per day), after full establishment of pulmonary hypertension from day 21 to day 35 significantly reduced pulmonary hypertension, right ventricular hypertrophy, and structural remodeling of the lung vasculature. In contrast, only minor efficacy of chronic sGC activator therapies was noted in NOS3(-/-) mice. In monocrotaline-injected rats with established severe pulmonary hypertension, both compounds significantly reversed hemodynamic and structural changes.

CONCLUSIONS

Activation of sGC reverses hemodynamic and structural changes associated with monocrotaline- and chronic hypoxia-induced experimental pulmonary hypertension. This effect is partially dependent on endogenous nitric oxide generated by NOS3.

Tezosentan decreases pulmonary artery pressure and improves survival rate in an animal model of meconium aspiration

Acute pulmonary arterial hypertension in acute lung injury aggravates the clinical course and complicates treatment. Increased release and turnover of endogenous endothelin-1 is known to be a major determinant in the pathophysiology of pulmonary arterial hypertension of various etiologies. We tested whether intravenous tezosentan, a dual endothelin receptor antagonist, reduced pulmonary artery pressure in a pig model of acute lung injury induced by meconium aspiration. Acute pulmonary arterial hypertension was induced in 12 anesthetized and instrumented pigs by instillation of human pooled meconium in a 20% solution. Hemodynamic and gas exchange parameters were recorded every 30 min. Six animals received tezosentan 5 mg/kg after 0 and 90 min; six animals served as controls. Tezosentan led to a decrease of mean pulmonary artery pressure (PAP) from 33.4 +/- 4.0 mm Hg to 24.7 +/- 2.1 mm Hg and pulmonary vascular resistance (PVR) from 7.8 +/- 1.4 mm Hg.L(-1).min.m2 to 5.2 +/- 0.7 mm Hg.L(-1).min.m2. All animals treated with tezosentan survived, whereas in the control group four out of six animals died. Tezosentan improved survival and decreased pulmonary artery pressure in a porcine model of acute pulmonary arterial hypertension after meconium aspiration. Tezosentan has the potential for effective pharmacological treatment of pulmonary arterial hypertension following acute lung injury.

Pulmonary arterial hypertension

Pulmonary arterial hypertension is a disease of the small pulmonary arteries characterized by vascular narrowing and increased pulmonary vascular resistance, which eventually leads to right ventricular failure. Vasoconstriction, vascular proliferation, remodeling of the pulmonary vessels, and thrombosis are all contributing factors to the increased vascular resistance seen in this disease. Pulmonary arterial hypertension develops as a sporadic disease (idiopathic), as an inherited disorder (familial), or in association with certain conditions (collagen vascular diseases, portal hypertension, human immunodeficiency virus infection, congenital systemic-to-pulmonary shunts, ingestion of drugs or dietary products, or persistent fetal circulation). The pathogenesis of pulmonary arterial hypertension is a complicated, multifactorial process. It seems doubtful that any one factor alone is sufficient to activate the necessary pathways leading to the development of this disease. Rather, clinically apparent pulmonary arterial hypertension most likely develops after a second insult occurs in an individual who is already susceptible owing to genetic factors, environmental exposures, or acquired disorders. Currently, there is no cure for pulmonary arterial hypertension but several novel therapeutic options are now available that can improve symptoms and increase survival.

Pharmacological efficacy of CPU 86017 on hypoxic pulmonary hypertension in rats: mediated by direct inhibition of calcium channels and antioxidant action, but indirect effects on the ET-1 pathway

Endothelin-1 (ET-1) plays a key role in the pathogenesis of pulmonary hypertension. The present study was conducted to examine the effects of a novel compound p-chlorobenzyltetrahydroberberine (CPU 86017) on endothelin-1 system of hypoxia-induced pulmonary hypertension in rats. SD male rats were divided into control, untreated pulmonary hypertension, nifedipine (10 mg/kg p.o.), and CPU 86017 (80, 40, and 20 mg/kg p.o.) groups. The pulmonary hypertension was established by housing the rats in a hypoxic (10 +/- 0.5% oxygen) chamber 8 hours per day for 4 weeks. Hemodynamic and morphologic assessment exhibited a significant increase in the central vein pressure (CVP), right ventricular systolic pressure (RVSP), and pulmonary arteriole remodeling in the pulmonary hypertensive rats, which were improved by CPU 86017 80 and 40 mg/kg administration (P < 0.01). The elevated pulmonary endothelin-1 level and the over-active preproET-1 and iNOS mRNA expression were also decreased significantly (P < 0.01) in CPU 86017 groups. The maladjustment of redox enzyme system in pulmonary hypertension rats was corrected after treatment. We concluded that CPU 86017 improves pulmonary hypertension mainly to suppress the endothelin-1 pathway at the upstream and downstream via calcium antagonism and antioxidative action, then, resulting in a relief in pathogenesis of the disease.

Reversal of experimental pulmonary hypertension by PDGF inhibition

Progression of pulmonary hypertension is associated with increased proliferation and migration of pulmonary vascular smooth muscle cells. PDGF is a potent mitogen and involved in this process. We now report that the PDGF receptor antagonist STI571 (imatinib) reversed advanced pulmonary vascular disease in 2 animal models of pulmonary hypertension. In rats with monocrotaline-induced pulmonary hypertension, therapy with daily administration of STI571 was started 28 days after induction of the disease. A 2-week treatment resulted in 100% survival, compared with only 50% in sham-treated rats. The changes in RV pressure, measured continuously by telemetry, and right heart hypertrophy were reversed to near-normal levels. STI571 prevented phosphorylation of the PDGF receptor and suppressed activation of downstream signaling pathways. Similar results were obtained in chronically hypoxic mice, which were treated with STI571 after full establishment of pulmonary hypertension. Moreover, expression of the PDGF receptor was found to be significantly increased in lung tissue from pulmonary arterial hypertension patients compared with healthy donor lung tissue. We conclude that STI571 reverses vascular remodeling and cor pulmonale in severe experimental pulmonary hypertension regardless of the initiating stimulus. This regimen offers a unique novel approach for antire-modeling therapy in progressed pulmonary hypertension.

BMP signaling controls PASMC KV channel expression in vitro and in vivo

Bone morphogenetic proteins (BMPs) have been implicated in the pathogenesis of familial pulmonary arterial hypertension. The type 2 receptor (BMPR2) is required for recognition of all BMPs. Transgenic mice with a smooth muscle cell-targeted mutation in this receptor (SM22-tet-BMPR2(delx4+)) developed increased pulmonary artery pressure, associated with a modest increase in arterial muscularization, after 8 wk of transgene activation (West J, Fagan K, Steudel W, Fouty B, Lane K, Harral J, Hoedt-Miller M, Tada Y, Ozimek J, Tuder R, and Rodman DM. Circ Res 94: 1109-1114, 2004). In the present study, we show that these transgenic mice developed increased right ventricular pressures after only 1 wk of transgene activation, without significant remodeling of the vasculature. We then tested the hypothesis that the increased pulmonary artery pressure due to loss of BMPR2 signaling was mediated by reduced K(V) channel expression. There was decreased expression of K(V)1.1, K(V)1.5, and K(V)4.3 mRNA isolated from whole lung. Western blot confirmed decreased K(V)1.5 protein in these lungs. Human pulmonary artery smooth muscle cells (PASMC) treated with recombinant BMP2 had increased K(V)1.5 protein and macroscopic K(V) current density, which was blocked by anti-K(V)1.5 antibody. In vivo, nifedipine, a selective L-type Ca(2+) channel blocker, reduced RV systolic pressure in these dominant-negative BMPR2 mice to levels seen in control animals. This suggests that activation of L-type Ca(2+) channels caused by reduced K(V)1.5 mediates increased pulmonary artery pressure in these animals. These studies suggest that BMP regulates K(V) channel expression and that loss of this signaling pathway in PASMC through a mutation in BMPR2 is sufficient to cause pulmonary artery vasoconstriction.

Potent effects of aerosol compared with intravenous treprostinil on the pulmonary circulation

Inhaled vasodilator therapy for pulmonary hypertension may decrease the systemic side effects commonly observed with systemic administration. Inhaled medications only reach ventilated areas of the lung, so local vasodilation may improve ventilation-perfusion matching and oxygenation. We compared the effects of intravenous vs. aerosolized treprostinil on pulmonary and systemic hemodynamics in an unanesthetized sheep model of sustained acute pulmonary hypertension. Acute, stable pulmonary hypertension was induced in instrumented unanesthetized sheep by infusing a PGH(2) analog, U-44069. The sheep were then administered identical doses of treprostinil either intravenously or by aerosol. Systemic and pulmonary hemodynamics were recorded during each administration. Both intravenous and aerosol delivery of treprostinil reduced pulmonary vascular resistance and pulmonary arterial pressure, but the effect was significantly greater with aerosol delivery (P < 0.05). Aerosol delivery of treprostinil had minimal effects on systemic hemodynamics, whereas intravenous delivery increased heart rate and cardiac output and decreased left atrial pressure and systemic blood pressure. Aerosol delivery of the prostacyclin analog treprostinil has a greater vasodilatory effect in the lung with minimal alterations in systemic hemodynamics compared with intravenous delivery of the drug. We speculate that this may result from treprostinil stimulated production of vasodilatory mediators from pulmonary epithelium.

Proteolytic processing pattern of the endothelin-1 precursor in vivo

Endothelin-1 (ET-1) is a potent vasoconstrictor, which has been implicated in diseases involving dysfunctions of the cardiovascular system. For the biogenesis of ET-1, a larger precursor peptide (proET-1) is cleaved at two sites to give rise to bigET-1, which is subsequently cleaved to generate mature ET-1. In the present study, we investigated, which other peptides are derived from proET-1 in vivo. Six sandwich immunoassays covering various regions of proET-1 were developed and used to detect circulating proET-1 immunoreactivities in plasma of healthy subjects and septic patients. With this approach we could (a) demonstrate that, in addition to bigET-1/ET-1, three stable proET-1 fragments are generated, (b) exclude two previously discussed regions as sites for prohormone conversion and (c) show that the proteolytic processing pattern of proET-1 is unchanged under pathological conditions, which are associated with elevated levels of proET-1 fragments. The high stability and similarity in concentration of the proET-1 fragments suggest that these might be non-functional in the circulation. Stable proET-1 fragments maybe used in the future as reliable diagnostic targets to indirectly assess the release of ET-1, which might help to more selectively direct therapeutic measures.

Constrictor-induced translocation of NFAT3 in human and rat pulmonary artery smooth muscle

The transcription factor nuclear factor of activated T cells (NFAT) resides in the cytoplasm in resting cells and upon stimulation is dephosphorylated, translocates to the nucleus, and becomes transcriptionally active. NFAT is commonly activated by stimulation of receptors coupled to Ca2+mobilization; however, little is known about the regulation of NFAT in pulmonary vascular smooth muscle. The aim of this study was to investigate regulation of NFAT in human and rat intralobar pulmonary artery by two constrictors: phenylephrine (PE) and 20-hydroxyeicosatetraenoic acid (20-HETE), a cytochrome P-450 metabolite formed endogenously in lungs. Immunostaining of smooth muscle cells revealed cytoplasmic localization of NFAT in untreated cells, and PE or 20-HETE induced translocation to the nucleus, with maximal effect at 30 min. Cyclosporin A and FK-506 (both 1 μM) inhibited NFAT translocation, indicating involvement of calcineurin. Moreover, the Rho-kinase blocker Y-27632 prevented translocation. Translocation of NFAT was confirmed by Western blots, with NFAT3 the prominent isoform in pulmonary artery. Constrictors caused calcineurin-sensitive translocation of NFAT to nuclei in intact arteries, demonstrating regulation in native tissue. To investigate a role for Ca2+, cells were loaded with fura-2. Whereas PE caused an acute transient rise of [Ca2+]i, 20-HETE caused a prolonged low amplitude rise of [Ca2+]i. The involvement of Rho-kinase in PE- and 20-HETE-induced NFAT3 translocation in pulmonary artery suggests a level of control not previously recognized in smooth muscle. Constrictors of the pulmonary vasculature not only cause acute responses but also activate NFAT, which may alter gene expression in pulmonary health and disease.

Drug Insight: endothelin-receptor antagonists for pulmonary arterial hypertension in systemic rheumatic diseases

Rapid advances in the understanding of endothelin as a naturally occurring peptide with developmental and regulatory roles in normal physiology, along with a number of deleterious effects under pathologic conditions (including vasoconstriction, fibrosis, vascular hypertrophy, and inflammation) have led to the development of endothelin-receptor antagonists (ERAs). Bosentan, an antagonist with dual specificity for the endothelin-receptor subtypes A and B, has been shown to be efficacious and well tolerated in placebo-controlled clinical trials and is now approved in many countries, including the US, Canada, and Europe, for treatment of pulmonary arterial hypertension (PAH), including PAH associated with rheumatic diseases. ERAs with specificity for the endothelin-receptor subtype A, including sitaxsentan and ambrisentan, are currently undergoing investigation. This article reviews PAH associated with systemic rheumatic diseases and describes the role of ERAs in this setting.

Sildenafil citrate therapy for pulmonary arterial hypertension

BACKGROUND

Sildenafil inhibits phosphodiesterase type 5, an enzyme that metabolizes cyclic guanosine monophosphate, thereby enhancing the cyclic guanosine monophosphate-mediated relaxation and growth inhibition of vascular smooth-muscle cells, including those in the lung.

METHODS

In this double-blind, placebo-controlled study, we randomly assigned 278 patients with symptomatic pulmonary arterial hypertension (either idiopathic or associated with connective-tissue disease or with repaired congenital systemic-to-pulmonary shunts) to placebo or sildenafil (20, 40, or 80 mg) orally three times daily for 12 weeks. The primary end point was the change from baseline to week 12 in the distance walked in six minutes. The change in mean pulmonary-artery pressure and World Health Organization (WHO) functional class and the incidence of clinical worsening were also assessed, but the study was not powered to assess mortality. Patients completing the 12-week randomized study could enter a long-term extension study.

RESULTS

The distance walked in six minutes increased from baseline in all sildenafil groups; the mean placebo-corrected treatment effects were 45 m (+13.0 percent), 46 m (+13.3 percent), and 50 m (+14.7 percent) for 20, 40, and 80 mg of sildenafil, respectively (P<0.001 for all comparisons). All sildenafil doses reduced the mean pulmonary-artery pressure (P=0.04, P=0.01, and P<0.001, respectively), improved the WHO functional class (P=0.003, P<0.001, and P<0.001, respectively), and were associated with side effects such as flushing, dyspepsia, and diarrhea. The incidence of clinical worsening did not differ significantly between the patients treated with sildenafil and those treated with placebo. Among the 222 patients completing one year of treatment with sildenafil monotherapy, the improvement from baseline at one year in the distance walked in six minutes was 51 m.

CONCLUSIONS

Sildenafil improves exercise capacity, WHO functional class, and hemodynamics in patients with symptomatic pulmonary arterial hypertension.

Inhibition of phosphodiesterase 1 augments the pulmonary vasodilator response to inhaled nitric oxide in awake lambs with acute pulmonary hypertension

Phosphodiesterase 1 (PDE1) modulates vascular tone and the development of tolerance to nitric oxide (NO)-releasing drugs in the systemic circulation. Any role of PDE1 in the pulmonary circulation remains largely uncertain. We measured the expression of genes encoding PDE1 isozymes in the pulmonary vasculature and examined whether or not selective inhibition of PDE1 by vinpocetine attenuates pulmonary hypertension and augments the pulmonary vasodilator response to inhaled NO in lambs. Using RT-PCR, we detected PDE1A, PDE1B, and PDE1C mRNAs in pulmonary arteries and veins isolated from healthy lambs. In 13 lambs, the thromboxane A(2) analog U-46619 was infused intravenously to increase mean pulmonary arterial pressure to 35 mmHg. Four animals received an intravenous infusion of vinpocetine at incremental doses of 0.3, 1, and 3 mg.kg(-1).h(-1). In nine lambs, inhaled NO was administered in a random order at 2, 5, 10, and 20 ppm before and after an intravenous infusion of 1 mg.kg(-1).h(-1) vinpocetine. Administration of vinpocetine did not alter pulmonary and systemic hemodynamics or transpulmonary cGMP or cAMP release. Inhaled NO selectively reduced mean pulmonary arterial pressure, pulmonary capillary pressure, and pulmonary vascular resistance index, while increasing transpulmonary cGMP release. The addition of vinpocetine enhanced pulmonary vasodilation and transpulmonary cGMP release induced by NO breathing without causing systemic vasodilation but did not prolong the duration of pulmonary vasodilation after NO inhalation was discontinued. Our findings demonstrate that selective inhibition of PDE1 augments the therapeutic efficacy of inhaled NO in an ovine model of acute chemically induced pulmonary hypertension.

Génétique de l’hypertension artérielle pulmonaire: données récentes et applications pratiques

INTRODUCTION

Pulmonary arterial hypertension (PAHT) is defined as an increase of mean pulmonary artery pressure above 25 mmHg at rest, or 30 mmHg on exercise, due to obliteration of small calibre pulmonary arteries by proliferation of endothelial cells and smooth muscle. Beside idiopathic PAHT and that associated with other conditions, a familial form has been identified.

STATE OF THE ART

Family studies have shown an association between mutations of the BMPR2 gene and PAHT phenotypes. The products of this gene appear to be involved in vascular homeostasis and its mutations are the basis of a loss this function and, in consequence, proliferation of pulmonary vascular cells.

PERSPECTIVES

Certain characteristics, such as incomplete penetrance and genetic anticipation, lead to a complex relationship between genotype and phenotype and make genetic counselling difficult. Other members of the extended family of TGF-beta receptors are implicated in the development of the Osler-Rendu syndrome, but may also be associated with the development of PAHT.

CONCLUSION

Progress in genetics allows better understanding of the pathophysiology of this disease and could lead to new therapeutic possibilities.

[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.

The acute hemodynamic effect of IV nitroglycerin and dipyridamole in patients with pulmonary arterial hypertension: comparison with IV epoprostenol

Nitroglycerin and dipyridamole are two commonly available and well tolerated vasoactive medications. Their acute hemodynamic effects in patients with pulmonary arterial hypertension are not well defined in the current literature. The authors retrospectively analyzed the acute hemodynamic effects of IV nitroglycerin, dipyridamole, and epoprostenol in 59 patients with pulmonary arterial hypertension as determined by changes from baseline in systemic and pulmonary hemodynamic parameters. Statistical analysis was performed using the independent sample t test. A p value <0.05 was considered significant. Nitroglycerin is predominantly a vasodilator of the pulmonary vasculature with moderate systemic vasodilator effect, while dipyridamole is primarily a positive inotropic agent. Epoprostenol is a potent vasodilator of both pulmonary and systemic vessels and a strong positive inotropic agent. Nitroglycerin and dipyridamole may be useful in the acute management of pulmonary arterial hypertension.

Markers of endothelial dysfunction and severity of hypoxaemia in the Eisenmenger syndrome

Endothelial dysfunction has been reported in hypoxaemic patients with the Eisenmenger syndrome, but a direct correlation between levels of endothelial markers and the severity of hypoxaemia has not been explored. With this in mind, we compared the levels in the plasma of tissue-type plasminogen activator, thrombomodulin, and von Willebrand factor in 25 patients with the Eisenmenger syndrome. They had a median age of 31 years, and were divided into 2 groups according to their recent clinical history. Thus, 18 patients were stable, being in functional class II or III, seen as outpatients, and having peripheral saturations of oxygen of 89 plus or minus 5 percent. In contrast, 7 patients were unstable, showing episodes of symptoms placing them in functional class IV, requiring care in hospital, and manifesting saturations of oxygen of 77 plus or minus 5 percent. We were able to follow 12 patients, 8 who were stable and 4 unstable, for 24 months. At baseline, levels of von Willebrand factor were higher in the unstable patients when compared to those who were stable, at 142 plus or minus 29 and 110 plus or minus 25 units per decilitre, respectively (p equal to 0.013). This correlated positively with oxygen desaturation (p less than 0.020). The structural abnormalities also correlated positively with the magnitude of hypoxaemia (p less than 0.020). Levels remained higher in the unstable patients throughout the period of follow-up (p equal to 0.006). Tissue-type plasminogen activator was also increased, at 14.3 plus or minus 8.4 versus 6.5 plus or minus 2.7 nanograms per millilitre in controls (p less than 0.001), whereas thrombomodulin was decreased, with values of 14.4 versus 34.6 nanograms per millilitre in controls (p for median values of less than 0.001). There was no correlation with saturations of oxygen. We conclude that measurement of von Willebrand factor, as compared with tissue-type plasminogen activator and thrombomodulin, will prove a better marker of endothelial response to hypoxaemia in patients with the Eisenmenger syndrome.

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

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

Histamine-mediated increases in cytosolic [Ca2+] involve different mechanisms in human pulmonary artery smooth muscle and endothelial cells

Agonist stimulation of human pulmonary artery smooth muscle cells (PASMC) and endothelial cells (PAEC) with histamine showed similar spatiotemporal patterns of Ca(2+) release. Both sustained elevation and oscillatory patterns of changes in cytosolic Ca(2+) concentration ([Ca(2+)](cyt)) were observed in the absence of extracellular Ca(2+). Capacitative Ca(2+) entry (CCE) was induced in PASMC and PAEC by passive depletion of intracellular Ca(2+) stores with 10 microM cyclopiazonic acid (CPA; 15-30 min). The pyrazole derivative BTP2 inhibited CPA-activated Ca(2+) influx, suggesting that depletion of CPA-sensitive internal stores is sufficient to induce CCE in both PASMC and PAEC. The recourse of histamine-mediated Ca(2+) release was examined after exposure of cells to CPA, thapsigargin, caffeine, ryanodine, FCCP, or bafilomycin. In PASMC bathed in Ca(2+)-free solution, treatment with CPA almost abolished histamine-induced rises in [Ca(2+)](cyt). In PAEC bathed in Ca(2+)-free solution, however, treatment with CPA eliminated histamine-induced sustained and oscillatory rises in [Ca(2+)](cyt) but did not affect initial transient increase in [Ca(2+)](cyt). Furthermore, treatment of PAEC with a combination of CPA (or thapsigargin) and caffeine (and ryanodine), FCCP, or bafilomycin did not abolish histamine-induced transient [Ca(2+)](cyt) increases. These observations indicate that 1) depletion of CPA-sensitive stores is sufficient to cause CCE in both PASMC and PAEC; 2) induction of CCE in PAEC does not require depletion of all internal Ca(2+) stores; 3) the histamine-releasable internal stores in PASMC are mainly CPA-sensitive stores; 4) PAEC, in addition to a CPA-sensitive functional pool, contain other stores insensitive to CPA, thapsigargin, caffeine, ryanodine, FCCP, and bafilomycin; and 5) although the CPA-insensitive stores in PAEC may not contribute to CCE, they contribute to histamine-mediated Ca(2+) release.

Role of β2-adrenoceptors (ß-AR), but not ß1-, β3-AR and endothelial nitric oxide, in β-AR-mediated relaxation of rat intrapulmonary artery

The aim of this study was to analyze beta-adrenoceptor (beta-AR)-mediated relaxation in rat intralobar pulmonary artery. The relaxant responses of beta-AR agonists were characterized using beta-AR antagonists in prostaglandin F2alpha (PGF2alpha)-precontracted arteries. The role of nitric oxide (NO) and endothelium in beta-AR-mediated relaxation was also investigated. Isoprenaline (a non-selective beta-AR agonist) and salbutamol (a selective beta2-AR agonist) induced vasorelaxation. ICI 118551 (a selective beta2-AR antagonist) antagonized the effect of both isoprenaline and salbutamol (pA2 values of 9.57 and 9.51 respectively). In contrast, atenolol (1 microM) and CGP 20712A (0.1 microM), two beta1-AR antagonists, did not modify the relaxing effect of isoprenaline. The response to isoprenaline obtained in the presence of nadolol (10 microM, a beta1/beta2-AR antagonist) was not further inhibited by SR 59230A (1 microM, a selective beta3-AR antagonist). The non-beta1/beta2-AR agonists studied (BRL 37344, SR 58611A, and CGP 12177A) did not elicit vasorelaxation. Relaxation to isoprenaline and salbutamol was unaffected by L-N(G)-nitro-arginine methyl ester (100 microM, an inhibitor of NO synthase) or after endothelium removal. These results demonstrate the role of beta2-AR in mediating relaxation in rat intralobar pulmonary artery precontracted with PGF2alpha. They indicate that beta2-AR-mediated relaxation in this artery is NO- and endothelium-independent. Furthermore, they do not provide evidence of a relaxant role of either beta1- or beta3-AR in PGF2alpha-precontracted rat intrapulmonary artery.

Characteristics of attenuated endothelium-dependent relaxation seen in rabbit intrapulmonary vein following chronic nitroglycerine administration

1 This study was undertaken to determine whether long-term in vivo administration of nitroglycerine (NTG) downregulates the endothelium-dependent relaxation induced by acetylcholine (ACh) in the rabbit intrapulmonary vein and, if so, whether the type 1 angiotensin II receptor (AT(1)R) blocker valsartan normalizes this downregulated relaxation. 2 In strips treated with the cyclooxygenase inhibitor diclofenac, ACh induced a relaxation only when the endothelium was intact. A small part of this ACh-induced relaxation was inhibited by coapplication of two Ca(2+)-activated K(+)-channel blockers (charybdotoxin (CTX)+apamin) and the greater part of the response was inhibited by the nitric-oxide-synthase inhibitor N(omega)-nitro-L-arginine (L-NNA). 3 The endothelium-dependent relaxation induced by ACh, but not the endothelium-independent relaxation induced by the nitric oxide donor NOC-7, was significantly reduced in NTG-treated rabbits (versus those in NTG-nontreated control rabbits). The attenuated relaxation was normalized by coapplication of valsartan with the NTG. 4 In the vascular wall, both the amount of localized angiotensin II and the production of superoxide anion were increased by in vivo NTG treatment. These variables were normalized by coapplication of valsartan with the NTG. 5 It is suggested that long-term in vivo administration of NTG downregulates the ACh-induced endothelium-dependent relaxation, mainly through an inhibition of endothelial nitric oxide production in the rabbit intrapulmonary vein. A possible role for AT(1)R is proposed in the mechanism underlying this effect.

Prevention of pulmonary vascular remodeling and of decreased BMPR-2 expression by losartan therapy in shunt-induced pulmonary hypertension

The renin-ANG system has been reported to be overexpressed in pulmonary arterial hypertension (PAH). We investigated the effects of ANG receptor-1 blockade by losartan on hemodynamics and signaling molecules in a piglet overflow model of early PAH. Twenty-six 3-wk-old piglets were randomized to placebo or losartan therapy (1 mg.kg(-1).day(-1)) after anastomosis of the inominate to the main pulmonary artery or after a sham operation. Three months later, the animals underwent a hemodynamic evaluation, followed by pulmonary tissue sampling for morphometry, immunohistochemistry, and real-time quantitative-PCR. Chronic systemic-to-pulmonary shunting increased the pulmonary vascular resistance from 2.5 +/- 0.2 to 6.2 +/- 0.3 mmHg.l(-1).min.m(-2) and arteriolar medial thickness from 13.6 to 25.4%. These changes were associated with increased expressions of ANG II and its type 1 (AT1) and type 2 (AT2) receptors, endothelin-1 (ET-1) and its type B receptor (ETB), and angiopoietin-1, together with decreased expressions of bone morphogeneic protein receptor-1A and -2 (BMPR-1A and BMPR-2, respectively) and unchanged expression of the receptor tyrosine kinase with immunoglobulin and EGF homology domains-2 (Tie 2). Pretreatment with losartan decreased shunt-induced pulmonary vascular resistance and medial thickness by 51% and 35%, respectively. Losartan therapy was associated with persistent overexpressions of ANG II, AT2, ET-1, ETB, and angiopoietin-1 and with a return to normal of the BMPR-2 expression. These results suggest that ANG II contributes to left-to-right, shunt-induced PAH.

[Biomarkers as prognostic factors in pulmonary arterial hypertension. Rationale and study design]

CURRENT SITUATION

Pulmonary arterial hypertension (PAH) is a serious disease. Its prognostic is based on the functional status quantified by the NYHA class and the 6-min walking test, and the hemodynamic data. The algorithms of treatment are solely based on the hemodynamic data and the functional status. The main objective is to test whether basal concentrations of isoprostanes, Big endotheline 1, ADMA, high sensitivity CRP, NT-Pro-BNP and cardiac troponin T are a 3-year prognostic factor in PAH using a combined criterion: death from any cause and pulmonary or cardiopulmonary transplantation.

MATERIALS AND METHODS

This is a multicenter, prospective, prognostic, single blinded study (plasma and urinary samples being blinded). The study started in november 2003, running for 2 years, with a 3 year follow-up for each patient. The main inclusion criterion is PAH. The data analysis will use a multivariable Cox model, taking into account the functional and hemodynamic parameters.

EXPECTED RESULTS

This study will determine whether any of the biomarkers tested provides additional prognostic information in PAH in addition to the functional and hemodynamic parameters.

Pivotal role for endothelial tetrahydrobiopterin in pulmonary hypertension

BACKGROUND

Pulmonary hypertension is a fatal disease characterized by vasoconstriction and vascular remodeling. Loss of endothelial nitric oxide bioavailability is implicated in pulmonary hypertension pathogenesis. Recent evidence suggests that the cofactor tetrahydrobiopterin (BH4) is an important regulator of nitric oxide synthase enzymatic function.

METHODS AND RESULTS

In the hph-1 mouse with deficient BH4 biosynthesis, BH4 deficiency caused pulmonary hypertension, even in normoxic conditions, and greatly increased susceptibility to hypoxia-induced pulmonary hypertension. In contrast, augmented BH4 synthesis in the endothelium, by targeted transgenic overexpression of GTP-cyclohydrolase I (GCH), prevented hypoxia-induced pulmonary hypertension. Furthermore, specific augmentation of endothelial BH4 in hph-1 mice by crossing with GCH transgenic mice rescued pulmonary hypertension induced by systemic BH4 deficiency. Lung BH4 availability controlled pulmonary vascular tone, right ventricular hypertrophy, and vascular structural remodeling in a dose-dependent manner in both normoxia and hypoxia. Furthermore, BH4 availability had striking effects on the immediate vasoconstriction response to acute hypoxia. These effects of BH4 were mediated through the regulation of nitric oxide compared with superoxide synthesis by endothelial nitric oxide synthase.

CONCLUSIONS

Endothelial BH4 availability is essential for maintaining pulmonary vascular homeostasis, is a critical mediator in the pathogenesis of pulmonary hypertension, and is a novel therapeutic target.

[Physiopathology of pulmonary arterial hypertension. Cellular and molecular aspects]

The combined effects of vasoconstriction, remodelling of the pulmonary vessel walls and in situ thrombosis contribute to the increase in pulmonary vascular resistance during pulmonary arterial hypertension. Vascular remodelling involves all the sheaths of the vessel wall and all the cell types of which it is composed (endothelial cells, smooth muscle cells, fibroblasts, inflammatory cells and platelets). Excessive vasoconstriction has been related to a defect in the function of expression of the potassium channels and endothelial dysfunction. This leads to chronic insufficiency in the production of vasodilators, notably nitrogen monoxide and prostacyclin and the excessive production of vasoconstrictors such as endotheline-1. These defects contribute to the increase in vascular tonus and pulmonary vascular remodelling and represent pertinent pharmacological targets. Certain growth factors, including those of the super-family of transforming growth factor beta, angiopoietine-1 and serotonin, may play a part in the pathogenesis of pulmonary arterial hypertension.

Global gene annotation analysis and transcriptional profiling identify key biological modules in hypoxic pulmonary hypertension

Chronic hypoxic pulmonary hypertension is an important clinical disorder causing significant morbidity. Despite recent discoveries, many molecular mechanisms involved in its pathogenesis remain unexplored. We have undertaken a systematic and unbiased approach to gain global insights into this complex process. By combining transcriptional profiling with rigorous statistical methods and cluster analysis, we identified the dominant temporal patterns of gene expression during progression and regression of hypoxic pulmonary hypertension. We next integrated these results with global gene annotation analysis to identify key biological themes involved in the development and resolution of hypoxic pulmonary hypertension and vascular remodeling. This novel approach assigned biological roles to thousands of candidate genes based on their temporal expression profiles and membership in specific biological modules. Our procedure confirmed several molecular pathways and gene products known to be important in hypoxic pulmonary hypertension. Furthermore, we discovered several novel candidates and molecular mechanisms, including IQ motif containing GTPase-activating protein-1 (IQGAP1), decorin, insulin-like growth factor binding protein-3 (IGFBP3), and lactotransferrin, that may play crucial roles in hypoxic pulmonary hypertension and vascular remodeling. Our methodology of integrating transcriptional profiling, cluster analysis, and global gene annotation provides new insights into the pathophysiology of pulmonary hypertension and is applicable to other models of human disease.

Decreased whole body endogenous nitric oxide production in patients with primary pulmonary hypertension

Impaired pulmonary release of nitric oxide (NO) is one of the characteristic phenotypic changes of vascular cells in pulmonary hypertension. The aim of this study was to determine nitric oxide synthase (NOS)-dependent whole body NO production in patients with primary pulmonary hypertension. NOS-dependent whole body NO production was assessed by giving an intravenous infusion of L-[(15)N](2)-arginine (50 micromol/min for 30 min) and measuring isotopic urinary enrichment of (15)N-nitrite and (15)N-nitrate. Four female patients with no signs of infection were recruited and compared with 6 age-matched control subjects. Mean 12-hour excretion of (15)N-nitrite and (15)N-nitrate in the total urine over 36 h was smaller in patients than in control subjects (57.2 +/- 27.6 vs. 229.1 +/- 65.2 nmol/mmol creatinine, p < 0.01, Mann-Whitney U test, respectively). Neither mean 12-hour excretion of (14)N-nitrite and (14)N-nitrate (51.6 +/- 10.0 vs. 72.4 +/- 10.0 micromol/mmol creatinine, p = 0.3) nor glomerular filtration rates (84.5 +/- 15.8 vs. 129.7 +/- 16.0 ml/min, p = 0.1) were different between patients and control subjects. Our results suggest that either basal NOS-dependent whole body NO production is impaired or excess NO metabolism occurs in patients with primary pulmonary hypertension.