Update in Pulmonary Hypertension 2005

Peptide-coated liposomal fasudil enhances site specific vasodilation in pulmonary arterial hypertension

This study sought to develop a liposomal delivery system of fasudil—an investigational drug for the treatment of pulmonary arterial hypertension (PAH)—that will preferentially accumulate in the PAH lungs. Liposomal fasudil was prepared by film-hydration method, and the drug was encapsulated by active loading. The liposome surface was coated with a targeting moiety, CARSKNKDC, a cyclic peptide; the liposomes were characterized for size, polydispersity index, zeta potential, and storage and nebulization stability. The in vitro drug release profiles and uptake by TGF-β activated pulmonary arterial smooth muscle cells (PASMC) and alveolar macrophages were evaluated. The pharmacokinetics were monitored in male Sprague–Dawley rats, and the pulmonary hemodynamics were studied in acute and chronic PAH rats. The size, polydispersity index (PDI), and zeta potential of the liposomes were 206–216 nm, 0.058–0.084, and −20–42.7 mV, respectively. The formulations showed minimal changes in structural integrity when nebulized with a commercial microsprayer. The optimized formulation was stable for >4 weeks when stored at 4 °C. Fasudil was released in a continuous fashion over 120 h with a cumulative release of 76%. Peptide-linked liposomes were taken up at a higher degree by TGF-β activated PASMCs; but alveolar macrophages could not engulf peptide-coated liposomes. The formulations did not injure the lungs; the half-life of liposomal fasudil was 34-fold higher than that of plain fasudil after intravenous administration. Peptide-linked liposomal fasudil, as opposed to plain liposomes, reduced the mean pulmonary arterial pressure by 35–40%, without influencing the mean systemic arterial pressure. This study establishes that CAR-conjugated inhalable liposomal fasudil offers favorable pharmacokinetics and produces pulmonary vasculature specific dilatation.

Hepatopulmonary syndrome and portopulmonary hypertension

Hepatopulmonary syndrome and portopulmonary hypertension are 2 of many diseases that affect the lungs in patients with liver disease. The 2 vascular conditions are often confused. We review both hepatopulmonary syndrome and portopulmonary hypertension to better understand their pathophysiologies, clinical presentations, tools to aid in differentiating and diagnosing the disease states, treatment options, and influences on patient prognosis. We also consider patient viability for liver transplantation.

Inhaled NO and sildenafil combination in cardiac surgery patients with out-of-proportion pulmonary hypertension: acute effects on postoperative gas exchange and hemodynamics

BACKGROUND

The goal of this study was to examine the effects of coadministration of sildenafil and inhaled nitric oxide (iNO) in patients with out-of-proportion pulmonary hypertension who underwent cardiac valve replacement surgery.

METHODS AND RESULTS

Twenty consecutive cardiac surgery patients with out-of-proportion pulmonary hypertension were randomly assigned postoperatively into 2 groups: group A received 10 ppm of iNO followed by sildenafil (100 mg) orally 30 minutes later, and group B initially received sildenafil (100 mg) orally followed by 10 ppm of iNO 60 minutes later. Hemodynamic and gas exchange data were obtained at baseline, after administration of either iNO or sildenafil alone, and at 90 minutes from baseline. In group A, iNO resulted in a significant reduction in mean pulmonary artery pressure (MPAP) and pulmonary vascular resistance index (PVRI) (by 9.6% and 20.8%, respectively). In group B, sildenafil administration also resulted in a significant decrease in mean arterial pressure, MPAP, pulmonary artery occlusive pressure, PVRI, and systemic vascular resistance index but also in the PaO(2)/inspired fraction of oxygen ratio (by 18.7%, 22.0%, 15.7%, 31.6%, 21.3%, and 14%, respectively). In both groups, the coadministration of the 2 drugs resulted in a significant further reduction of mean arterial pressure, MPAP, pulmonary artery occlusive pressure, systemic vascular resistance index, and PVRI, whereas cardiac index and mixed venous oxygen saturation remained unchanged. The hypoxemia after sildenafil administration in group B improved after the coadministration of iNO, and thus PaO(2)/inspired fraction of oxygen returned to values near baseline.

CONCLUSION

In this study, the postoperative coadministration of iNO and oral sildenafil in patients with out-of-proportion pulmonary hypertension undergoing cardiac surgery is safe and results in an additive favorable effect on pulmonary arterial pressure and pulmonary vascular resistance, without systemic hypotension and ventilation/perfusion mismatch.

Prevention of bronchial hyperreactivity in a rat model of precapillary pulmonary hypertension

BACKGROUND

The development of bronchial hyperreactivity (BHR) subsequent to precapillary pulmonary hypertension (PHT) was prevented by acting on the major signalling pathways (endothelin, nitric oxide, vasoactive intestine peptide (VIP) and prostacyclin) involved in the control of the pulmonary vascular and bronchial tones.

METHODS

Five groups of rats underwent surgery to prepare an aorta-caval shunt (ACS) to induce sustained precapillary PHT for 4 weeks. During this period, no treatment was applied in one group (ACS controls), while the other groups were pretreated with VIP, iloprost, tezosentan via an intraperitoneally implemented osmotic pump, or by orally administered sildenafil. An additional group underwent sham surgery. Four weeks later, the lung responsiveness to increasing doses of an intravenous infusion of methacholine (2, 4, 8 12 and 24 μg/kg/min) was determined by using the forced oscillation technique to assess the airway resistance (Raw).

RESULTS

BHR developed in the untreated rats, as reflected by a significant decrease in ED50, the equivalent dose of methacholine required to cause a 50% increase in Raw. All drugs tested prevented the development of BHR, iloprost being the most effective in reducing both the systolic pulmonary arterial pressure (Ppa; 28%, p = 0.035) and BHR (ED50 = 9.9 ± 1.7 vs. 43 ± 11 μg/kg in ACS control and iloprost-treated rats, respectively, p = 0.008). Significant correlations were found between the levels of Ppa and ED50 (R = -0.59, p = 0.016), indicating that mechanical interdependence is primarily responsible for the development of BHR.

CONCLUSIONS

The efficiency of such treatment demonstrates that re-establishment of the balance of constrictor/dilator mediators via various signalling pathways involved in PHT is of potential benefit for the avoidance of the development of BHR.

Right ventricular function in patients with pulmonary hypertension; the value of myocardial performance index measured by tissue Doppler imaging

AIMS

Myocardial performance index (MPI) measured by conventional Doppler is routinely used to assess right ventricular (RV) systolic function in patients with pulmonary hypertension (PH). Our aim was to determine whether MPI measured by Doppler tissue imaging (tMPI) is effective in assessing RV function in these patients.

METHODS AND RESULTS

Retrospectively, we have studied 196 patients with chronic PH [pulmonary arterial systolic pressure (PASP) 81 +/- 40 mmHg] and 37 healthy volunteers (PASP of 27 +/- 7 mmHg). According to the exclusion criteria, 172 patients were included in the final study cohort. All patients were evaluated for RV systolic function by different parameters. MPI was measured by both conventional and tissue Doppler imaging. Bland-Altman analysis showed moderate agreement between MPI and tMPI (the mean difference was -0.02, absolute difference = -0.32 to 0.29; 95% intervals of agreement, percentage of average = -46.6 to 40.8%). In 50 consecutive PH patients where additional parameters were calculated, we found a significant correlation between tMPI and RV ejection fraction (r = -0.73, P< 0.0001) and RV fractional area change (r = -0.58, P< 0.0001). No significant inter- and intra-observer variability was identified.

CONCLUSION

This study demonstrated a moderate agreement between two methods of measuring MPI. A good correlation of tMPI with RV ejection fraction and RV fractional area change was found indicating that tMPI might be superior to MPI Doppler. tMPI is a parameter unaffected by RV geometry and importantly has the advantage of simultaneously recording the time intervals from the same cardiac cycle.

Iloprost inhalation redistributes pulmonary perfusion and decreases arterial oxygenation in healthy volunteers

BACKGROUND

Previous studies have shown that ventilation-perfusion matching is improved in the prone as compared with that in the supine position. Regional differences in the regulation of vascular tone may explain this. We have recently demonstrated higher production of nitric oxide in dorsal compared with ventral human lung tissue. The purpose of the present study was to investigate regional differences in actions by another vasoactive mediator, namely prostacyclin. The effects on gas exchange and regional pulmonary perfusion in different body positions were investigated at increased prostacyclin levels by inhalation of a synthetic prostacyclin analogue and decreased prostacyclin levels by unselective cyclooxygenase (COX) inhibition.

METHODS

In 19 volunteers, regional pulmonary perfusion in the prone and supine position was assessed by single photon emission computed tomography using (99m)Tc macro-aggregated albumin before and after inhalation of iloprost, a stable prostacyclin analogue, or an intravenous infusion of a non-selective COX inhibitor, diclofenac. In addition, gas distribution was assessed in seven subjects using (99m)Tc-labelled ultra-fine carbon particles before and after iloprost inhalation in the supine position.

RESULTS

Iloprost inhalation decreased arterial PaO(2) in both prone (from 14.2+/-0.5 to 11.7+/-1.7 kPa, P<0.01) and supine (from 13.7+/-1.4 to 10.9+/-2.1 kPa, P<0.01) positions. Iloprost inhalation redistributed lung perfusion from non-dependent to dependent lung regions in both prone and supine positions, while ventilation in the supine position was distributed in the opposite direction. No significant effects of non-selective COX inhibition were found in this study.

CONCLUSIONS

Iloprost inhalation decreases arterial oxygenation and results in a more gravity-dependent pulmonary perfusion in both supine and prone positions in healthy humans.

Discovery of riociguat (BAY 63-2521): a potent, oral stimulator of soluble guanylate cyclase for the treatment of pulmonary hypertension

Soluble guanylate cyclase (sGC) is a key signal-transduction enzyme activated by nitric oxide (NO). Impairments of the NO-sGC signaling pathway have been implicated in the pathogenesis of cardiovascular and other diseases. Direct stimulation of sGC represents a promising therapeutic strategy particularly for the treatment of pulmonary hypertension (PH), a disabling disease associated with a poor prognosis. Previous sGC stimulators such as the pyrazolopyridines BAY 41-2272 and BAY 41-8543 demonstrated beneficial effects in experimental models of PH, but were associated with unfavorable drug metabolism and pharmacokinetic (DMPK) properties. Herein we disclose an extended SAR exploration of this compound class to address these issues. Our efforts led to the identification of the potent sGC stimulator riociguat, which exhibits an improved DMPK profile and exerts strong effects on pulmonary hemodynamics and exercise capacity in patients with PH. Riociguat is currently being investigated in phase III clinical trials for the oral treatment of PH.

Abl knockout differentially affects p130 Crk-associated substrate, vinculin, and paxillin in blood vessels of mice

Actin polymerization has recently emerged as an important cellular process that regulates smooth muscle contraction. Abelson tyrosine kinase (Abl) has been implicated in the regulation of actin dynamics and force development in vascular smooth muscle. In the present study, the systolic blood pressure was lower in Abl(-/-) knockout mice compared with wild-type mice. The knockout of Abl diminished the tyrosine phosphorylation of p130 Crk-associated substrate (CAS, an adapter protein associated with smooth muscle contraction) in resistance arteries upon stimulation with phenylephrine or angiotensin II. The agonist-elicited enhancement of F-actin-to-G-actin ratios in arteries assessed by fluorescent microscopy was also reduced in Abl(-/-) mice. It has been known that vinculin is a structural protein that links actin filaments to extracellular matrix via transmembrane integrins, whereas paxillin is a signaling protein associated with focal contacts mediating actin cytoskeleton remodeling. The expression of vinculin and paxillin at protein and messenger levels was lower in arterial vessels from Abl knockout mice. However, the agonist-induced increase in myosin phosphorylation was not attenuated in arteries from Abl knockout mice. These results indicate that Abl differentially regulates Crk-associated substrate, vinculin, and paxillin in arterial vessels. The Abl-regulated cellular process and blood pressure are independent of myosin activation in vascular smooth muscle.

p130 Crk-associated substrate (CAS) in vascular smooth muscle

Vascular smooth muscle is a key effector in the wall of blood vessels during the pathogenesis of hypertension. Various factors directly elicit smooth muscle cell contraction, migration, growth, and hypertrophy, which lead to the progression of hypertension. Crk-associated substrate (CAS), the first discovered member of the adapter protein CAS family, has recently emerged as a critical cellular component that regulates smooth muscle functions. In this review, the molecular structure and protein interactions of the CAS family members are summarized. Evidence for the role of CAS in the regulation of vascular smooth muscle contractility, cell migration, hypertrophy, and growth is presented. Regulation of CAS by novel tyrosine kinases/phosphatases and unique downstream signaling partners of CAS are also discussed. These new findings establish the important role for CAS in regulating vascular smooth muscle functions. The CAS-associated processes may be new biological targets for the development of new treatment of cardiovascular diseases such as hypertension.

Effects of endogenous sulfur dioxide on monocrotaline-induced pulmonary hypertension in rats

AIM

The present study aimed to explore the protective effect of endogenous sulfur dioxide (SO2) in the development of monocrotaline (MCT)-induced pulmonary hypertension (PH) in rats.

METHODS

Forty Wistar rats were randomly divided into the MCT group receiving MCT treatment, the MCT+L-aspartate-beta- hydroxamate (HDX) group receiving MCT plus HDX treatment, the MCT+SO2 group receiving MCT plus SO2 donor treatment, and the control group. Mean pulmonary artery pressure (mPAP) and structural changes in pulmonary arteries were evaluated. SO2 content, aspartate aminotransferase activity, and gene expression were measured. Superoxide dismutase (SOD), glutathione peroxidase (GSH-Px), catalase (CAT), reduced glutathione (GSH), oxidized glutathione, and malondialdehyde (MDA) levels were assayed.

RESULTS

In the MCT-treated rats, mPAP and right ventricle/(left ventricle+septum) increased significantly (P<0.01), pulmonary vascular structural remodeling developed, and SOD, GSHPx, CAT, GSH, and MDA levels of lung homogenates significantly increased (P<0.01) in association with the elevated SO2 content, aspartate aminotransferase activity, and gene expression, compared with the control rats. In the MCT+HDXtreated rats, lung tissues and plasma SO2 content and aspartate aminotransferase activities decreased significantly, whereas the mPAP and pulmonary vascular structural remodeling were markedly aggravated with the decreased SOD, CAT, and GSH levels of lung tissue homogenates compared with the MCT-treated rats (P<0.01). In contrast, with the use of a SO2 donor, the pulmonary vascular structural remodeling was obviously lessened with elevated lung tissue SOD, GSH-Px, and MDA content, and plasma SOD, GSH-Px, and CAT levels.

CONCLUSION

Endogenous SO2 might play a protective role in the pathogenesis of MCT-induced PH and promote endogenous antioxidative capacities.

Differential roles of endothelin-1 ETA and ETB receptors and vasoactive intestinal polypeptide in regulation of the airways and the pulmonary vasculature in isolated rat lung

The available treatment strategies against pulmonary hypertension include the administration of endothelin-1 (ET-1) receptor subtype blockers (ET(A) and ET(B) antagonists); vasoactive intestinal polypeptide (VIP) has recently been suggested as a potential new therapeutic agent. We set out to investigate the ability of these agents to protect against the vasoconstriction and impairment of lung function commonly observed in patients with pulmonary hypertension. An ET(A) blocker (BQ123), ET(B) blocker (BQ788), a combination of these selective blockers (ET(A) + ET(B) blockers) or VIP (V6130) was administered into the pulmonary circulation in four groups of perfused normal rat lungs. Pulmonary vascular resistance (PVR) and forced oscillatory lung input impedance (Z(L)) were measured in all groups under baseline conditions and at 1 min intervals following ET-1 administrations. The airway resistance, inertance, tissue damping and elastance were extracted from the Z(L) spectra. While VIP, ET(A) blocker and combined ET(A) and ET(B) blockers significantly prevented the pulmonary vasoconstriction induced by ET-1, ET(B) blockade enhanced the ET-1-induced increases in PVR. In contrast, the ET(A) and ET(B) blockers markedly elevated the ET-1-induced increases in airway resistance, while VIP blunted this constrictor response. Our results suggest that VIP potently acts against the airway and pulmonary vascular constriction mediated by endothelin-1, while the ET(A) and ET(B) blockers exert a differential effect between airway resistance and PVR.

Anesthetic Management of Patients With Pulmonary Hypertension

Advances in the treatment of patients with chronic pulmonary hypertension have greatly improved their functional status and longevity, and increasing numbers of these complex patients are presenting for elective noncardiac surgery. In this communication we will briefly review the classification and pathophysiology of pulmonary hypertension, summarize outpatient pharmacotherapy approaches, and discuss the perioperative preparation and management of these complex patients. With an understanding of the underlying pathophysiology of the disease and pharmacology of these new therapies, combined with careful perioperative planning and care, these patients can safely undergo elective surgical procedures.

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.

Physiologic properties and regulation of the actin cytoskeleton in vascular smooth muscle

Vascular smooth muscle tone plays a fundamental role in regulating blood pressure, blood flow, microcirculation, and other cardiovascular functions. The cellular and molecular mechanisms by which vascular smooth muscle contractility is regulated are not completely elucidated. Recent studies show that the actin cytoskeleton in smooth muscle is dynamic, which regulates force development. In this review, evidence for actin polymerization in smooth muscle upon external stimulation is summarized. Protein kinases such as Abelson tyrosine kinase, focal adhesion kinase, Src, and mitogen-activated protein kinase have been documented to coordinate actin polymerization in smooth muscle. Transmembrane integrins have also been reported to link to signaling pathways modulating actin dynamics. The roles of Rho family of the small proteins that bind to guanosine triphosphate (GTP), also known as GTPases, and the actin-regulatory proteins, including Crk-associated substrate, neuronal Wiskott-Aldrich Syndrome protein, the Arp2/3 complex, and profilin, and heat shock proteins in regulating actin assembly are discussed. These new findings promote our understanding on how smooth muscle contraction is regulated at cellular and molecular levels.

Inhaled agonists of soluble guanylate cyclase induce selective pulmonary vasodilation

RATIONALE

Nitric oxide-independent agonists of soluble guanylate cyclase (sGC) have been developed.

OBJECTIVES

We tested whether inhalation of novel dry-powder microparticle formulations containing sGC stimulators (BAY 41-2272, BAY 41-8543) or an sGC activator (BAY 58-2667) would produce selective pulmonary vasodilation in lambs with acute pulmonary hypertension. We also evaluated the combined administration of BAY 41-8543 microparticles and inhaled nitric oxide (iNO). Finally, we examined whether inhaling BAY 58-2667 microparticles would produce pulmonary vasodilation when the response to iNO is impaired.

METHODS

In awake, spontaneously breathing lambs instrumented with vascular catheters and a tracheostomy tube, U-46619 was infused intravenously to increase mean pulmonary arterial pressure to 35 mm Hg.

MEASUREMENTS AND MAIN RESULTS

Inhalation of microparticles composed of either BAY 41-2272, BAY 41-8543, or BAY 58-2667 and excipients (dipalmitoylphosphatidylcholine, albumin, lactose) produced dose-dependent pulmonary vasodilation and increased transpulmonary cGMP release without significant effect on mean arterial pressure. Inhalation of microparticles containing BAY 41-8543 or BAY 58-2667 increased systemic arterial oxygenation. The magnitude and duration of pulmonary vasodilation induced by iNO were augmented after inhaling BAY 41-8543 microparticles. Intravenous administration of 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ), which oxidizes the prosthetic heme group of sGC, markedly reduced the pulmonary vasodilator effect of iNO. In contrast, pulmonary vasodilation and transpulmonary cGMP release induced by inhaling BAY 58-2667 microparticles were greatly enhanced after treatment with ODQ.

CONCLUSIONS

Inhalation of microparticles containing agonists of sGC may provide an effective novel treatment for patients with pulmonary hypertension, particularly when responsiveness to iNO is impaired by oxidation of sGC.

Portopulmonary hypertension

As a result of the success of orthotopic liver transplantation, there has been increasing interest in the diagnosis and therapeutic options for the pulmonary vascular complications of hepatic disease. These pulmonary vascular complications range from the hepatopulmonary syndrome, which is characterized by intrapulmonary vascular dilatations, to portopulmonary hypertension (POPH), which is characterized by an elevated pulmonary vascular resistance as a consequence of obstruction to pulmonary arterial blood flow. This review concentrates on POPH.

Mechanisms controlling vascular tone in pulmonary arterial hypertension: implications for vasodilator therapy

Pulmonary vasoconstriction is believed to be an early component of pulmonary arterial hypertension. Intracellular calcium concentration ([Ca(2+)](i)) is a major trigger for pulmonary vasoconstriction; however, it is now well known that contractions and relaxations may also be elicited through Ca(2+)-independent mechanisms. A variety of intracellular protein kinases and cyclic nucleotides have been identified as key determinants in controlling pulmonary vascular tone. Herein, we provide an overview of the main signaling pathways, which include protein kinase C, Rho kinases and cyclic nucleotides (cAMP and cGMP). This review also focuses on the role of store-operated Ca(2+) channels and voltage-gated K(+) channels, which are currently considered especially attractive in the pulmonary circulation and may represent new targets in the treatment of pulmonary arterial hypertension.

Increased Protein Arginine Methylation in Chronic Hypoxia

Asymmetric dimethylarginine (ADMA) is an endogenous inhibitor of nitric oxide synthesis. ADMA is generated by catabolism of proteins containing methylated arginine residues, and its levels are correlated with endothelial dysfunction in systemic cardiovascular diseases. Arginine methylation of cellular proteins is catalyzed by protein arginine methyltransferases (PRMT). The expression and localization of PRMT in the lung has not been addressed. Here, we sought to analyze the expression of PRMT isoforms in the lung and to determine whether PRMT expression is altered during exposure to chronic hypoxia (10% oxygen). Adult mice were exposed to hypoxia for up to 3 wk, and lung tissues were harvested and processed for RT-PCR, Western blotting, immunohistochemistry, and determination of tissue ADMA levels. All PRMT isoforms investigated were detected at the mRNA and protein level in mouse lung, and were localized primarily to the bronchial and alveolar epithelium. In lungs of mice subjected to chronic hypoxia, PRMT2 mRNA and protein levels were up-regulated, whereas the expression of all other PRMT isoforms remained unchanged. This was mainly due to increased expression of PRMT2 in alveolar type II cells, which did not express detectable levels of PRMT2 under normoxic conditions. Consistent with these observations, lung ADMA levels and ADMA/l-Arginine ratios were increased under hypoxic conditions. These results demonstrate that PRMTs are expressed and functional in the lung, and that hypoxia is a potent regulator of PRMT2 expression and lung ADMA concentrations. These data suggest that structural and functional changes caused by hypoxia may be linked to ADMA metabolism.

Pulmonary hypertension in children: the twenty-first century

Pulmonary hypertension is an elevation in pulmonary artery pressure that is associated with a spectrum of diseases and causes. Its clinical severity and presentation are widely varied. The field of study has changed immensely over the past several years. Significant knowledge has been gained in the pathophysiology, genetics, and vascular biology associated with pulmonary hypertension. These discoveries have contributed to medical interventions that have improved outcomes associated with pulmonary hypertension. This article reviews pulmonary hypertension in children, focusing on idiopathic pulmonary hypertension. Because most information is associated with children who have this form of the disease, formerly classified as primary pulmonary hypertension, medical therapy is discussed with a focus on this patient group. Additional therapeutic concepts relevant to other causes of pulmonary hypertension are highlighted.