Pulmonary arterial hypertension: current therapeutic strategies

Congenital Absence of the Portal Vein as a Rare Cause of Portopulmonary Hypertension-A Case Study Series

Background. Congenital absence of the portal vein (CAPV) is an extremely rare malformation that is caused by aberrant venous development during embryogenesis and is usually associated with congenital portosystemic shunts (CPSS). This hemodynamic allows mesenteric blood to bypass the liver metabolism and causes an imbalance between vasodilators and vasoconstrictors in the pulmonary circulation, which, again, might lead to the development of secondary portopulmonary hypertension (PoPH). Establishing the exact morphology of the splanchnic venous system is important when evaluating possible therapeutic options (differentiating type I and II CAPV), because some variants enable the closure of the shunt, and this represents a potential cure for pulmonary arterial hypertension (PAH). Once PoPH is diagnosed, complex care in a specialized expert centre is necessary. If possible, CPSS closure is recommended. For long-term successful patient management, specific targeted PAH therapy administration is crucial. Significant morbidity and mortality in these patients may result not only from PAH itself but also due to specific PoPH complications, such as compression of the left main coronary artery by pulmonary artery aneurysm. Case Report. We report on two patients with PoPH due to CAPV and CPSS (without any liver disease) who presented as severe PAH and who, before admission to our expert centre, were misdiagnosed as idiopathic PAH. The case reports also represent our experience with respect to the long-term follow-up and PAH-specific medical treatment of these patients, as well as the possible (even fatal) complications of these rare and complex patients.

Calcium-sensing receptor in the development and treatment of pulmonary hypertension

Calcium-sensing receptor (CaSR) is widely involved in the cell proliferation, differentiation, migration, adhesion and apoptosis, which can affect the vascular remodeling in the humanbody. The main ligand of CaSR is extracellular Ca²⁺. CaSR has the physiological significance in Ca²⁺ homeostasis. Pulmonary vascular remodeling is one of the main histopathological changes of pulmonary hypertension (PH). The abnormal proliferation of pulmonary artery smooth muscle cells (PASMCs) results in the pulmonary vascular remodeling. CaSR is an important regulator of [Ca²⁺]_i. [Ca²⁺]_i is the main cause of the excessive pulmonary vascular remodeling in patients with PH. In this review, it was conclued that the structure of CaSR was prone to explore the devolopment or the treatment of PH. It was found that the regulation of CaSR with some miRNA could inhibit the proliferation of PASMCs, and that CaSR could affect the occurrence of autophagy in PH. Therefore, CaSR would become a new therapeutic target to PH.

The effect of chloroquine on the TRPC1, TRPC6, and CaSR in the pulmonary artery smooth muscle cells in hypoxia-induced experimental pulmonary artery hypertension

Pulmonary arterial hypertension (PAH) is a life-threatening disease characterized by a constant high pulmonary artery pressure and the remodeling of the vessel. Chloroquine (CLQ) has been observed to inhibit calcium influx. The aim of this study is to investigate the effect of CLQ on transient receptor cationic proteins (TRPC1 and TRPC6) and extracellular calcium-sensitive receptor (CaSR) in a hypoxic PAH model. In this study, 8- to 12-week-old 32 male Wistar albino rats, weighing 200 to 300 g, were used. The rats were studied in four groups, including normoxy control, n = 8; normoxy CLQ (50 mg/kg/28 d), n = 8; hypoxia (HX; 10% oxygen/28 d) control, n = 8; and HX (10% oxygen/28 d) + CLQ (50 mg/kg), N = 8. Pulmonary arterial medial wall thickness, pulmonary arteriole wall, TRPC1, TRPC6, and CaSR expressions were evaluated by immunohistochemistry, polymerase chain reaction, and enzyme-linked immunosorbent assay methods. At the end of the experiment, a statistically significant increase in the medial wall thickness was observed in the hypoxic group as compared with the control group. However, in the HX + CLQ group, there was a statistically significant decrease in the vessel medial wall as compared with the HX group. In the TRPC1-, TRPC6-, and CaSR-immunopositive cell numbers, messenger RNA expressions and biochemical results showed an increase in the HX group, whereas they were decreased in the HX + CLQ group. The inhibitory effect of CLQ on calcium receptors in arterioles was observed in PAH.

Liver transplantation and cardiac illness: Current evidences and future directions

Contraindications to liver transplantation are gradually narrowing. Cardiac illness and chronic liver disease may manifest independently or may be superimposed on each other due to shared pathophysiology. Cardiac surgery involving the cardiopulmonary bypass in patients with Child-Pugh Class C liver disease is associated with a high risk of perioperative morbidity and mortality. Liver transplantation involves hemodynamic perturbations, volume shifts, coagulation abnormalities, electrolyte disturbances, and hypothermia, which may prove fatal in patients with cardiac illness depending upon the severity. Additionally, cardiovascular complications are the major cause of adverse postoperative outcomes after liver transplantation even in the absence of cardiac pathologies. Clinical decision-making has remained an unsettled issue in these clinical scenarios. The absence of randomized clinical studies has further crippled our endeavours for a consensus on the management of patients with end-stage liver disease with cardiac illness. This review seeks to address this complex clinical setting by gathering information from published literature. The management algorithm in this review may facilitate clinical decision making and augur future research.

Macrophage migration inhibitory factor (MIF) in the development and progression of pulmonary arterial hypertension

Macrophage migration inhibitory factor (MIF) has been described as a pro-inflammatory cytokine and regulator of neuro-endocrine function. It plays an important upstream role in the inflammatory cascade by promoting the release of other inflammatory cytokines such as TNF-alpha and IL-6, ultimately triggering a chronic inflammatory immune response. As lungs can synthesize and release MIF, many studies have investigated the potential role of MIF as a biomarker in assessment of patients with pulmonary arterial hypertension (PAH) and using anti-MIFs as a new therapeutic modality for PAH.

Dasatinib-induced pulmonary arterial hypertension

Drug-induced (group 1) pulmonary hypertension (PH) is an important subgroup of PH involving dasatinib as a likely related agent, which is a second-generation tyrosine kinase inhibitor (TKI) used in the treatment of chronic myeloid leukaemia (CML). The mechanism of dasatinib-induced pulmonary arterial hypertension (PAH) is unclear. However, the occurrence of PAH with late onset in CML patients suggests a chronic pathological mechanism with an insidious onset rather than an acute inflammatory or cardiac aetiology. Dasatinib has a broader effect than other TKIs; the major known difference between dasatinib and other TKIs is the additional inhibition of Src family kinases. Therefore, Src inhibition was thought to play a role in the development of dasatinib-induced PAH. However, recently, it was also speculated that chronic dasatinib therapy may cause pulmonary endothelial damage, attenuate hypoxic pulmonary vasoconstriction responses and increase susceptibility to PAH independently of the Src family kinase-induced mechanism. Dasatinib-induced PAH usually seems to be reversible with the cessation of the drug, and sometimes with PAH-specific treatment strategies. Transthoracic echocardiography can be recommended as a routine screening prior to dasatinib initiation, and this non-invasive procedure can be utilized in patients having signs and symptoms attributable to PAH during dasatinib treatment.

Calcium-Sensing Receptor Regulates Cytosolic [Ca 2+ ] and Plays a Major Role in the Development of Pulmonary Hypertension

Pulmonary arterial hypertension (PAH) is a progressive disease characterized by elevated pulmonary vascular resistance (PVR) leading to right heart failure and premature death. The increased PVR results in part from pulmonary vascular remodeling and sustained pulmonary vasoconstriction. Excessive pulmonary vascular remodeling stems from increased pulmonary arterial smooth muscle cell (PASMC) proliferation and decreased PASMC apoptosis. A rise in cytosolic free Ca²⁺ concentration ([Ca²⁺]_cyt) in PASMC is a major trigger for pulmonary vasoconstriction and a key stimulus for PASMC proliferation and migration, both contributing to the development of pulmonary vascular remodeling. PASMC from patients with idiopathic PAH (IPAH) have increased resting [Ca²⁺]_cyt and enhanced Ca²⁺ influx. Enhanced Ca²⁺ entry into PASMC due to upregulation of membrane receptors and/or Ca²⁺ channels may contribute to PASMC contraction and proliferation and to pulmonary vasoconstriction and pulmonary vascular remodeling. We have shown that the extracellular Ca²⁺-sensing receptor (CaSR), which is a member of G protein-coupled receptor (GPCR) subfamily C, is upregulated, and the extracellular Ca²⁺-induced increase in [Ca²⁺]_cyt is enhanced in PASMC from patients with IPAH in comparison to PASMC from normal subjects. Pharmacologically blockade of CaSR significantly attenuate the development and progression of experimental pulmonary hypertension in animals. Additionally, we have demonstrated that dihydropyridine Ca²⁺ channel blockers (e.g., nifedipine), which are used to treat PAH patients but are only effective in 15–20% of patients, activate CaSR resulting in an increase in [Ca²⁺]_cyt in IPAH-PASMC, but not normal PASMC. Our data indicate that CaSR functionally couples with transient receptor potential canonical (TRPC) channels to mediate extracellular Ca²⁺-induced Ca²⁺ influx and increase in [Ca²⁺]_cyt in IPAH-PASMC. Upregulated CaSR is necessary for the enhanced extracellular Ca²⁺-induced increase in [Ca²⁺]_cyt and the augmented proliferation of PASMC in patients with IPAH. This review will highlight the pathogenic role of CaSR in the development and progression of PAH.

Carfilzomib reverses pulmonary arterial hypertension

AIMS

Pulmonary arterial hypertension (PAH) remains a lethal disease with pronounced narrowing of pulmonary vessels due to abnormal cell growth. Agents that can reduce the pulmonary vascular thickness thus have therapeutic potential. The present study investigated the efficacy of carfilzomib (CFZ), a proteasome inhibitor and a cancer chemotherapeutic drug, on reversing PAH.

METHODS AND RESULTS

In two rat models of PAH, SU5416/hypoxia and SU5416/ovalbumin, CFZ effectively reversed pulmonary vascular remodelling with the promotion of apoptosis and autophagy. In human pulmonary artery smooth muscle cells, knocking down mediators of autophagy attenuated CFZ-induced cell death. The cell death role of autophagy was promoted by the participation of tumour protein p53-inducible nuclear protein 1. CFZ increased the protein ubiquitination, and siRNA knockdown of ubiquitin inhibited cell death, suggesting that CFZ-induced cell death is ubiquitin-dependent. Mass spectrometry demonstrated the ubiquitination of major vault protein and heat shock protein 90 in response to CFZ. The siRNA knockdown of these proteins enhanced CFZ-induced cell death, revealing that they are cell survival factors. CFZ reduced right-ventricular pressure and enhanced the efficacy of a vasodilator, sodium nitroprusside. While no indications of CFZ toxicity were observed in the right ventricle of PAH rats, apoptosis was promoted in the left ventricle. Apoptosis was prevented by dexrazoxane or by pifithrin-α without interfering with the efficacy of CFZ to reverse pulmonary vascular remodelling.

CONCLUSION

The addition of anti-tumour agents such as CFZ along with cardioprotectants to currently available vasodilators may be a promising way to improve PAH therapy.

Endothelial cell regulation of pulmonary vascular tone, inflammation, and coagulation

The pulmonary endothelium represents a heterogeneous cell monolayer covering the luminal surface of the entire lung vasculature. As such, this cell layer lies at a critical interface between the blood, airways, and lung parenchyma, and must act as a selective barrier between these diverse compartments. Lung endothelial cells are able to produce and secrete mediators, display surface receptor, and cellular adhesion molecules, and metabolize circulating hormones to influence vasomotor tone, both local and systemic inflammation, and coagulation functions. In this review, we will explore the role of the pulmonary endothelium in each of these systems, highlighting key regulatory functions of the pulmonary endothelial cell, as well as novel aspects of the pulmonary endothelium in contrast to the systemic cell type. The interactions between pulmonary endothelial cells and both leukocytes and platelets will be discussed in detail, and wherever possible, elements of endothelial control over physiological and pathophysiological processes will be examined.

Regulation of Cell Cycle Regulators by SIRT1 Contributes to Resveratrol-Mediated Prevention of Pulmonary Arterial Hypertension

Pulmonary arterial hypertension (PAH) is a major cause of morbidity and mortality in rheumatic diseases. Vascular remodeling due to the proliferation of pulmonary arterial smooth muscle cells (PASMCs) is central to the development of PAH. To date, it is still unclear if Silence Information Regulator 1 (SIRT1) regulates cell cycle regulators in the proliferation of PASMCs and contributes to prevention of PAH by resveratrol. In this study, we found that a significant decrease of SIRT1 expression levels in platelet-derived growth factor BB (PDGF-BB) treated human PASMCs (HPASMCs) and in monocrotaline (MCT) induced PAH rat. Overexpression of SIRT1 induced G1 phase arrest and increased p21 expression but decreased cyclin D1 expression in PDGF-BB treated HPASMCs. Moreover, resveratrol attenuated pulmonary arterial remodeling, decreased pulmonary arterial pressure, and upregulated SIRT1 and p21 expression but downregulated cyclin D1 expression in MCT induced PAH rat. Notably, knockdown of SIRT1 eliminated the regulation of resveratrol on p21 and cyclin D1 expression in PDGF-BB treated HPASMCs. These results demonstrated that SIRT1 mediated the regulation of resveratrol on the expression of cell cycle regulatory molecules. It suggests that SIRT1 exerts a protective role in PAH associated with rheumatic diseases and can be a potential treatment target.

Protein Kinase C Inhibitors as Modulators of Vascular Function and their Application in Vascular Disease

Blood pressure (BP) is regulated by multiple neuronal, hormonal, renal and vascular control mechanisms. Changes in signaling mechanisms in the endothelium, vascular smooth muscle (VSM) and extracellular matrix cause alterations in vascular tone and blood vessel remodeling and may lead to persistent increases in vascular resistance and hypertension (HTN). In VSM, activation of surface receptors by vasoconstrictor stimuli causes an increase in intracellular free Ca(2+) concentration ([Ca(2+)]i), which forms a complex with calmodulin, activates myosin light chain (MLC) kinase and leads to MLC phosphorylation, actin-myosin interaction and VSM contraction. Vasoconstrictor agonists could also increase the production of diacylglycerol which activates protein kinase C (PKC). PKC is a family of Ca(2+)-dependent and Ca(2+)-independent isozymes that have different distributions in various blood vessels, and undergo translocation from the cytosol to the plasma membrane, cytoskeleton or the nucleus during cell activation. In VSM, PKC translocation to the cell surface may trigger a cascade of biochemical events leading to activation of mitogen-activated protein kinase (MAPK) and MAPK kinase (MEK), a pathway that ultimately increases the myofilament force sensitivity to [Ca(2+)]i, and enhances actin-myosin interaction and VSM contraction. PKC translocation to the nucleus may induce transactivation of various genes and promote VSM growth and proliferation. PKC could also affect endothelium-derived relaxing and contracting factors as well as matrix metalloproteinase (MMPs) in the extracellular matrix further affecting vascular reactivity and remodeling. In addition to vasoactive factors, reactive oxygen species, inflammatory cytokines and other metabolic factors could affect PKC activity. Increased PKC expression and activity have been observed in vascular disease and in certain forms of experimental and human HTN. Targeting of vascular PKC using PKC inhibitors may function in concert with antioxidants, MMP inhibitors and cytokine antagonists to reduce VSM hyperactivity in certain forms of HTN that do not respond to Ca(2+) channel blockers.

Barrier enhancing signals in pulmonary edema

Increased endothelial permeability and reduction of alveolar liquid clearance capacity are two leading pathogenic mechanisms of pulmonary edema, which is a major complication of acute lung injury, severe pneumonia, and acute respiratory distress syndrome, the pathologies characterized by unacceptably high rates of morbidity and mortality. Besides the success in protective ventilation strategies, no efficient pharmacological approaches exist to treat this devastating condition. Understanding of fundamental mechanisms involved in regulation of endothelial permeability is essential for development of barrier protective therapeutic strategies. Ongoing studies characterized specific barrier protective mechanisms and identified intracellular targets directly involved in regulation of endothelial permeability. Growing evidence suggests that, although each protective agonist triggers a unique pattern of signaling pathways, selected common mechanisms contributing to endothelial barrier protection may be shared by different barrier protective agents. Therefore, understanding of basic barrier protective mechanisms in pulmonary endothelium is essential for selection of optimal treatment of pulmonary edema of different etiology. This article focuses on mechanisms of lung vascular permeability, reviews major intracellular signaling cascades involved in endothelial monolayer barrier preservation and summarizes a current knowledge regarding recently identified compounds which either reduce pulmonary endothelial barrier disruption and hyperpermeability, or reverse preexisting lung vascular barrier compromise induced by pathologic insults.

Protein Arginine Methyltransferases (PRMTs): promising targets for the treatment of pulmonary disorders

Protein arginine methylation is a novel posttranslational modification that plays a pivotal role in a variety of intracellular events, such as signal transduction, protein-protein interaction and transcriptional regulation, either by the direct regulation of protein function or by metabolic products originating from protein arginine methylation that influence nitric oxide (NO)-dependent processes. A growing body of evidence suggests that both mechanisms are implicated in cardiovascular and pulmonary diseases. This review will present and discuss recent research on PRMTs and the methylation of non-histone proteins and its consequences for the pathogenesis of various lung disorders, including lung cancer, pulmonary fibrosis, pulmonary hypertension, chronic obstructive pulmonary disease and asthma. This article will also highlight novel directions for possible future investigations to evaluate the functional contribution of arginine methylation in lung homeostasis and disease.

Bortezomib alleviates experimental pulmonary arterial hypertension

Vascular remodeling and endothelial dysfunction are important pathogenic features of pulmonary arterial hypertension (PAH). There is a growing body of evidence that proteasome inhibitors may be beneficial in vascular diseases by inhibiting proliferation of vascular smooth muscle cells (VSMCs) and ameliorating endothelial dysfunction. Here, we evaluated whether bortezomib (BTZ) could alleviate hypoxia- and monocrotaline (MCT)-induced PAH. BTZ (at doses from 1 to 100 μg/kg, or a dose of 100 μg/kg) was administered to mice every other day for the last 2 weeks of a 5-week hypoxia (10% O(2)) period, or to rats once daily from Day 22 to Day 34 after MCT challenge, respectively. BTZ treatment substantially suppressed elevation of right ventricular (RV) systolic pressure, RV hypertrophy, and pulmonary vascular remodeling in hypoxia-exposed mice. Similarly, BTZ treatment inhibited RV hypertrophy and vascular remodeling in MCT-injected rats. Strikingly, BTZ rescued 70% of MCT-injected rats up to Day 60, along with a considerable reduction in RV systolic pressure and suppression of vascular remodeling, whereas, among MCT-injected rats not administered BTZ, there were no survivors by Day 41. BTZ significantly suppressed proliferation of pulmonary VSMCs in vivo and in vitro. Furthermore, BTZ increased not only endothelial nitric oxide (NO) synthase (eNOS), phosphorylated eNOS, and NO production in vitro, but also eNOS and p-eNOS in hypoxia-exposed mice and MCT-injected rats, respectively. In contrast to the beneficial effects, BTZ increased active caspase-3 in cardiac ventricles of MCT-injected rats. Taken together, with caution for cardiotoxicity, BTZ could be a potential therapeutic strategy in PAH, possibly acting by inhibition of VSMC proliferation and amelioration of endothelial dysfunction.

Macrophage migration inhibitory factor mediates hypoxia-induced pulmonary hypertension

Pulmonary hypertension (PH) is a devastating disease leading to progressive hypoxemia, right ventricular failure, and death. Hypoxia can play a pivotal role in PH etiology, inducing pulmonary vessel constriction and remodeling. These events lead to increased pulmonary vessel wall thickness, elevated vascular resistance and right ventricular hypertrophy. The current study examined the association of the inflammatory cytokine macrophage migration inhibitory factor (MIF) with chronic lung disease and its role in the development of hypoxia-induced PH. We found that plasma MIF in patients with primary PH or PH secondary to interstitial lung disease (ILD) was significantly higher than in the control group (P = 0.004 and 0.007, respectively). MIF involvement with hypoxia-induced fibroblast proliferation was examined in both a human cell-line and primary mouse cells from wild-type (mif⁺/⁺) and MIF-knockout (mif⁻/⁻) mice. In vitro, hypoxia-increased MIF mRNA, extracellular MIF protein accumulation and cell proliferation. Inhibition of MIF inflammatory activity reduced hypoxia-induced cell proliferation. However, hypoxia only increased proliferation of mif⁻/⁻ cells when they were supplemented with media from mif⁺/⁺ cells. This growth increase was suppressed by MIF inhibition. In vivo, chronic exposure of mice to a normobaric atmosphere of 10% oxygen increased lung tissue expression of mRNA encoding MIF and accumulation of MIF in plasma. Inhibition of the MIF inflammatory active site, during hypoxic exposure, significantly reduced pulmonary vascular remodeling, cardiac hypertrophy and right ventricular systolic pressure. The data suggest that MIF plays a critical role in hypoxia-induced PH, and its inhibition may be beneficial in preventing the development and progression of the disease.

Decrease in pulmonary artery pressure after administration of thoracic epidural anesthesia in a patient with Marfan syndrome awaiting aortic valve replacement procedure

Thoracic epidural anesthesia is an adjunct to general anesthesia in cardiac surgery. Decrease in heart rate and blood pressure are frequently seen beneficial effects. There are several other hemodynamic effects of thoracic epidural anesthesia such as decrease in systemic vascular resistance, cardiac index, left ventricular stroke work index among others. However, the effect of thoracic epidural anesthesia on pulmonary artery pressure (PAP) has not been studied extensively in humans. Thoracic epidural anes-thesia decreased pulmonary artery pressure in experimen-tally induced pulmonary hypertension in animals. The mechanisms involved in such reduction are ill understood. We describe in this report, a significant reduction in PAP in a patient with Marfan's syndrome scheduled to under-go aortic valve replacement. The possible mechanisms of decrease in pulmonary artery pressure in the described case are, decrease in the venous return to the heart, decrease in the systemic vascular resistance, decrease in the right ventric-ular function and finally, improvement in myocardial contraction secondary to all the above. The possibility of Marfan's syndrome contributing to the decrease in PAP appears remote. The authors present this case to generate discussion about the possible mechanisms involved in thoracic epidural anesthesia producing beneficial effects in patients with secondary pulmonary hypertension. Thoracic epidural anesthesia appears to decrease pulmonary artery pressure by a combination of several mechanisms, some unknown to us. This occurrence, if studied and understood well could be put to clinical use in pulmonary hypertensives.

YC-1 attenuates hypoxia-induced pulmonary arterial hypertension in mice

BACKGROUND

Pulmonary arterial hypertension (PAH) is characterized by a progressive increase in pulmonary vascular resistance and elevation of pulmonary arterial pressure, leading to right ventricular failure and eventual death. Currently, no curative therapy for PAH is available, and the overall prognosis is very poor. Recently, direct activators of soluble guanylyl cyclase (sGC) have been tested as a novel therapeutic modality in experimental models of pulmonary arterial hypertension (PAH).

OBJECTIVE

In this study, we used in vitro and in vivo models to evaluate the therapeutic potential of 3-(5'-hydroxymethyl-2'-furyl)-1-benzylindazole (YC-1), a dual functioning chemical, as a direct activator of guanylyl cyclase and an inhibitor of hypoxia-inducible factor-1.

METHODS

We analyzed the effects of YC-1 on cell proliferation and the levels of p21 and p53 in human pulmonary artery smooth muscle cells (HPASMCs) under hypoxia. We also determined the effects of YC-1 on expression of endothelin-1 (ET-1) and phosphorylation status of endothelial nitric oxide synthase (eNOS) at Ser(1179) in human pulmonary artery endothelial cells (HPAECs) under hypoxia. In mice, hypoxic PAH was induced by exposure to normobaric hypoxic conditions for 28 days. To assess preventive or therapeutic effects, randomized mice were subjected to once daily i.p. injections of YC-1 for the entire hypoxic period (5 mg/kg) or for the last seven days of a 28-day hypoxic period (5 and 10 mg/kg). On day 28, we measured the right ventricular systolic pressure (RVSP) and determined the degrees of right ventricular hypertrophy (RVH) and vascular remodeling.

RESULTS

In HPASMCs, YC-1 inhibited hypoxia-induced proliferation and induction of p53 and p21 in a concentration-dependent manner. Also, YC-1 suppressed the hypoxia-induced expression of ET-1 mRNA and dephosphorylation of eNOS at Ser(1179) in HPAECs. In the preventive in vivo model, a daily dose of 5 mg/kg YC-1 significantly prevented the elevation of RVSP, development of RVH, and pulmonary vascular remodeling, which were caused by hypoxic exposure. In the therapeutic model, YC-1 at daily doses of 5 and 10 mg/kg alleviated RVH and pulmonary vascular remodeling but did not prevent the elevation of RVSP.

CONCLUSIONS

Our results indicate that YC-1 prevents the development of hypoxia-induced PAH in a preventive model and alleviates RVH and pulmonary vascular remodeling in a therapeutic model. Therefore, these data imply that YC-1 has therapeutic potential for use in a single or combination therapy for PAH.

Respiratory failure and hypoxemia in the cirrhotic patient including hepatopulmonary syndrome

PURPOSE OF REVIEW

Liver cirrhosis and portal hypertension present with three unique pulmonary complications that are the subject of ongoing clinical research: hepatopulmonary syndrome, portopulmonary hypertension (POPH), and hepatic hydrothorax. The present article is based on a review of the current literature on how to manage these disorders, which are highly important to both anesthesiologists and intensive care physicians.

RECENT FINDINGS

Hepatopulmonary syndrome leads to progressive hypoxemia through diffuse vasodilatation of the pulmonary microcirculation. Liver transplantation, although associated with increased mortality, is the only viable treatment. POPH occurs when vascular remodeling triggers an increase in pulmonary artery pressure and resistance. The role of liver transplantation in POPH is controversial given the excessive mortality in patients with moderate to severe POPH. Medical treatment is able to decrease pulmonary artery pressures, though multicenter randomized controlled trials showing improved outcome are lacking to date. Ultrasound plays an increasingly important role in the diagnosis of all three conditions.

SUMMARY

Patients with end-stage liver disease are at risk for respiratory failure and hypoxemia and need to be screened for hepatopulmonary syndrome, POPH, and hepatic hydrothorax. Failure to timely recognize and adequately treat these complications of cirrhosis may have severe consequences.

A novel insight into the mechanism of pulmonary hypertension involving caveolin-1 deficiency and endothelial nitric oxide synthase activation

Severe pulmonary hypertension (PH) is characterized by a progressive increase in pulmonary vascular resistance and vascular remodeling leading to right heart failure and early death. Our recent studies with the use of the novel mouse model with genetic deletions of caveolin-1 (Cav1) and endothelial nitric oxide synthase (eNOS) (NOS3) have demonstrated that persistent eNOS activation in Cav1(-/-) lungs results in tyrosine nitration of protein kinase G (PKG) and impairment of its activity, which thereby induces PH. The finding of eNOS activation and PKG nitration concomitant with Cav1 deficiency was recapitulated in lungs from patients with idiopathic pulmonary arterial hypertension. These data suggest targeting PKG nitration has potential value for the treatment of PH. Here, we will review the current knowledge about Cav1-regulated eNOS activity and its fundamental role in the pathogenesis of PH.

Pulmonary arterial hypertension

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

Soluble epoxide hydrolase as a therapeutic target for cardiovascular diseases

The cardiovascular effects of epoxyeicosatrienoic acids (EETs) include vasodilation, antimigratory actions on vascular smooth muscle cells and anti-inflammatory actions. These endogenous lipid mediators are broken down into diols by soluble epoxide hydrolase (sEH), and so inhibiting this enzyme would be expected to enhance the beneficial cardiovascular properties of EETs. sEH inhibitors (sEHIs) that are based on 1,3-disubstituted urea have been rapidly developed, and have been shown to be antihypertensive and anti-inflammatory, and to protect the brain, heart and kidney from damage. Although challenges for the future exist - including improving the drug-like properties of sEHIs and finding better ways to target sEHIs to specific tissues - the recent initiation of the first clinical trials of sEHIs has highlighted the therapeutic potential of these agents.

Novel crosstalk to BMP signalling: cGMP-dependent kinase I modulates BMP receptor and Smad activity

Integration of multiple signals into the canonical BMP/Smad pathway poses a big challenge during the course of embryogenesis and tissue homeostasis. Here, we show that cyclic guanosine 3',5'-monophosphate (cGMP)-dependent kinase I (cGKI) modulates BMP receptors and Smads, providing a novel mechanism enhancing BMP signalling. cGKI, a key mediator of vasodilation and hypertension diseases, interacts with and phosphorylates the BMP type II receptor (BMPRII). In response to BMP-2, cGKI then dissociates from the receptors, associates with activated Smads, and undergoes nuclear translocation. In the nucleus, cGKI binds with Smad1 and the general transcription factor TFII-I to promoters of BMP target genes such as Id1 to enhance transcriptional activation. Accordingly, cGKI has a dual function in BMP signalling: (1) it modulates BMP receptor/Smad activity at the plasma membrane and (2) after redistribution to the nucleus, it further regulates transcription as a nuclear co-factor for Smads. Consequently, cellular defects caused by mutations in BMPRII, found in pulmonary arterial hypertension patients, were compensated through cGKI, supporting the positive action of cGKI on BMP-induced Smad signalling downstream of the receptors.

The effects and mechanisms of mycophenolate mofetil on pulmonary arterial hypertension in rats

Pulmonary arterial hypertension (PAH) is a severe clinical and pathophysiologic syndrome with no effective treatment at present. Mycophenolate mofetil (MMF), a prodrug of mycophenolic acid (MPA), has been applied widely to the treatment of connective tissue diseases with the effect of immunosuppressant. Its anti-proliferation has been found recently. Thereby, we tried to examine the effects of MMF on rats with PAH which was induced by monocrotaline injection, so as to investigate the mechanisms of treatment on PAH by MMF. The results substantiated that MMF therapy can alleviate thickening of pulmonary arterial walls and inhibit abnormal vascular remodeling, and the MPA concentrations which demonstrated efficacy in this study are within clinical applicable range, suggesting huge potentiality of MMF in the treatment of human PAH.

Simvastatin ameliorates established pulmonary hypertension through a heme oxygenase-1 dependent pathway in rats

BACKGROUND

Simvastatin has been shown to ameliorate pulmonary hypertension by several mechanisms in experimental animal models. In this study, we hypothesized that the major benefits of simvastatin in pulmonary hypertension occur via the heme oxygenase-1 pathway.

METHODS

Simvastatin (10 mg/kgw/day) was tested in two rat models of pulmonary hypertension (PH): monocrotaline administration and chronic hypoxia. The hemodynamic changes, right heart hypertrophy, HO-1 protein expression, and heme oxygenase (HO) activity in lungs were measured in both models with and without simvastatin treatment. Tin-protoporphyrin (SnPP, 20 micromol/kg w/day), a potent inhibitor of HO activity, was used to confirm the role of HO-1.

RESULTS

Simvastatin significantly ameliorated pulmonary arterial hypertension from 38.0 +/- 2.2 mm Hg to 22.1 +/- 1.9 mm Hg in monocrotaline-induced PH (MCT-PH) and from 33.3 +/- 0.8 mm Hg to 17.5 +/- 2.9 mm Hg in chronic hypoxia-induced PH (CH-PH) rats. The severity of right ventricular hypertrophy was significantly reduced by simvastatin in MCT-PH and CH-PH rats. Co-administration with SnPP abolished the benefits of simvastatin. Simvastatin significantly increased HO-1 protein expression and HO activity in the lungs of rats with PH; however co-administration of SnPP reduced HO-1 activity only. These observations indicate that the simvastatin-induced amelioration of pulmonary hypertension was directly related to the activity of HO-1, rather than its expression.

CONCLUSION

This study demonstrated that simvastatin treatment ameliorates established pulmonary hypertension primarily through an HO-1-dependent pathway.

Endothelin receptor blockade combined with phosphodiesterase-5 inhibition increases right ventricular mitochondrial capacity in pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is often treated with endothelin (ET) receptor blockade or phosphodiesterase-5 (PDE5) inhibition. Little is known about the specific effects on right ventricular (RV) function and metabolism. We determined the effects of single and combination treatment with Bosentan [an ET type A (ET(A))/type B (ET(B)) receptor blocker] and Sildenafil (a PDE5 inhibitor) on RV function and oxidative metabolism in monocrotaline (MCT)-induced PAH. Fourteen days after MCT injection, male Wistar rats were orally treated for 10 days with Bosentan, Sildenafil, or both. RV catheterization and echocardiography showed that MCT clearly induced PAH. This was evidenced by increased RV systolic pressure, reduced cardiac output, increased pulmonary vascular resistance (PVR), and reduced RV fractional shortening. Quantitative histochemistry showed marked RV hypertrophy and fibrosis. Monotreatment with Bosentan or Sildenafil had no effect on RV systolic pressure or cardiac function, but RV fibrosis was reduced and RV capillarization increased. Combination treatment did not reduce RV systolic pressure, but significantly lowered PVR, and normalized cardiac output, RV fractional shortening, and fibrosis. Only combination treatment increased the mitochondrial capacity of the RV, as reflected by increased succinate dehydrogenase and cytochrome c oxidase activities, associated with an activation of PKG, as indicated by increased VASP phosphorylation. Moreover, significant interactions were found between Bosentan and Sildenafil on PVR, cardiac output, RV contractility, PKG activity, and mitochondrial capacity. These data indicate that the combination of Bosentan and Sildenafil may beneficially contribute to RV adaptation in PAH, not only by reducing PVR but also by acting on the mitochondria in the heart.

Treatment of sarcoidosis-associated pulmonary hypertension. A two-center experience

BACKGROUND

Pulmonary hypertension (PH) is a common complication of sarcoidosis that is associated with increased mortality. The pathogenesis of PH in sarcoidosis is uncertain, and the role of pulmonary arterial hypertension (PAH)-specific therapies remains to be determined.

METHODS

We conducted a retrospective study of patients with sarcoidosis and PH at two referral centers. New York Heart Association (NYHA) functional class, exercise capacity, hemodynamic data, pulmonary function tests, and survival were collected and analyzed.

RESULTS

Twenty-two sarcoidosis patients treated with PAH-specific therapies were identified. After a median of 11 months of follow-up, NYHA class was improved in nine subjects. Mean 6-min walk distance (n = 18) increased by 59 m (p = 0.032). Patients with a higher FVC experienced a greater increment in exercise capacity. Among 12 patients with follow-up hemodynamic data, mean pulmonary artery pressure was reduced from 48.5 +/- 4.3 to 39.4 +/- 2.8 mm Hg (p = 0.008). The 1- and 3-year transplant-free survival rates were 90% and 74%, respectively.

CONCLUSIONS

PAH-specific therapy may improve functional class, exercise capacity, and hemodynamics in PH associated with sarcoidosis. Prospective, controlled trials of PAH therapies for sarcoidosis are warranted to verify this apparent benefit. Mortality among the study population was high, highlighting the need for urgent evaluation at a lung transplant center.

Endothelin: 20 years from discovery to therapy

Since its identification as an endothelial cell-derived vasoconstrictor peptide in 1988, endothelin-1, the predominant member of the endothelin peptide family, has received considerable interest in basic medical science and in clinical medicine, which is reflected by more than 20 000 scientific publications on endothelin research in the past 20 years. The story of endothelin is unique as the gene sequences of endothelin receptors and the first receptor antagonists became available within only 4 years of the identification of the peptide sequence. The first clinical study in patients with congestive heart failure was published only 3 years thereafter. Yet, despite convincing experimental evidence of a pathogenetic role for endothelin in development, cell function, and disease, many initial clinical studies on endothelin antagonism were negative. In many of these studies, study designs or patient selection were inadequate. Today, for diseases such as pulmonary hypertension, endothelin antagonist treatment has become reality in clinical medicine, and ongoing clinical studies are evaluating additional indications, such as renal disease and cancer. Twenty years after the discovery of endothelin, its inhibitors have finally arrived in the clinical arena and are now providing us with new options to treat disease and prolong the lives of patients. Possible future indications include resistant arterial hypertension, proteinuric renal disease, cancer, and connective tissue diseases.

Characterization of Hemodynamics in Patients with Idiopathic and Thromboembolic Pulmonary Hypertension

Demographic and hemodynamic data from patients with idiopathic pulmonary arterial hypertension (IPAH) and chronic thromboembolic pulmonary hypertension (CTEPH) have not been systematically characterized to identify differences related to gender, age, race, disease severity, and drug response. Our goal was to define the distribution and relation of IPAH and CTEPH based on these criteria. Hemodynamic and demographic data from 242 IPAH patients and 90 CTEPH patients were collected and compared. IPAH incidence was greater in women, but men had a higher basal mean pulmonary arterial pressure (mPAP). mPAP was comparable among all IPAH ethnic groups. IPAH patients with no history of fenfluramine-phentermine use had a higher mPAP than users. Exercise-induced IPAH was apparent in 14.5% of IPAH patients. Only 9% of IPAH patients responded to inhaled nitric oxide with a ≥20% decrease in mPAP. Compared to CTEPH patients, mPAP was greater but average age of diagnosis was lower in IPAH patients. mPAP negatively correlated with age of diagnosis in IPAH patients only. These results indicate that elevated CO is not the main determinant of mPAP in both IPAH and CTEPH patients. However, the two patient groups differ in terms of their demographic and hemodynamic distributions, and according to the correlation between mPAP and other clinical hemodynamics and demographics.

Is sitaxsentan a good therapeutic option for pulmonary arterial hypertension associated with connective tissue disease?

Agents that indiscriminately block endothelin receptors have been shown to cause moderate improvements in the outcomes of patients who have pulmonary arterial hypertension (PAH) as a complication of connective tissue disease (CTD). Girgis et al. investigated the effects of sitaxsentan, a selective endothelin receptor type A antagonist, in patients with CTD and comcomitant PAH. After 12 weeks of treatment, patients who received sitaxsentan showed more improvement from baseline compared with those receiving placebo in terms of exercise capacity, hemodynamics and physical-health-related quality of life. At the end of the extension study (median total follow-up 26 weeks), 16 of the 41 patients with CTD had an improvement of at least one New York Heart Association functional class compared with at the start of sitaxsentan therapy. The effects of sitaxsentan observed in the CTD group were comparable to those seen in the idiopathic PAH group. The authors concluded that treatment with sitaxsentan might be beneficial in patients with PAH associated with CTD.

Pulmonary hypertension in patients with congenital portosystemic venous shunt: a previously unrecognized association

BACKGROUND

Pulmonary arterial hypertension has been reported to be observed in association with acquired portal hypertension. However, the contribution of congenital anomalies occurring in the portal system to the development of pulmonary arterial hypertension remains to be elucidated.

METHODS

Nine patients with congenital portosystemic venous shunt were studied from January 1990 through September 2005.

RESULTS

Patent ductus venosus was detected in 5 patients, including 3 patients with an absence of the portal vein. The presence of either a gastrorenal or splenorenal shunt was evident in another 4 patients. Six patients had a history of hypergalactosemia with normal enzyme activities, as seen during neonatal screening. Six (66.7%) of the 9 patients were identified to have clinically significant pulmonary arterial hypertension (mean pulmonary artery pressure: 34-79 mm Hg; pulmonary vascular resistances: 5.12-38.07 U). The median age at the onset of pulmonary arterial hypertension was 12 years and 3 months. Histologic studies of lung specimens, which were available in 4 of the 9 patients with congenital portosystemic venous shunt, showed small arterial microthrombotic lesions in 3 patients. This characteristic finding was recognized even in the congenital portosystemic venous shunt patients without PAH.

CONCLUSIONS

This study demonstrated thromboembolic pulmonary arterial hypertension to be a crucial complication in congenital portosystemic venous shunt, and this pathologic state may be latently present in patients with pulmonary arterial hypertension of unknown etiology.

Potassium channels in the regulation of pulmonary artery smooth muscle cell proliferation and apoptosis: pharmacotherapeutic implications

Maintaining the proper balance between cell apoptosis and proliferation is required for normal tissue homeostasis; when this balance is disrupted, disease such as pulmonary arterial hypertension (PAH) can result. Activity of K(+) channels plays a major role in regulating the pulmonary artery smooth muscle cell (PASMC) population in the pulmonary vasculature, as they are involved in cell apoptosis, survival and proliferation. PASMCs from PAH patients demonstrate many cellular abnormalities linked to K(+) channels, including decreased K(+) current, downregulated expression of various K(+) channels, and inhibited apoptosis. K(+) is the major intracellular cation, and the K(+) current is a major determinant of cell volume. Apoptotic volume decrease (AVD), an early hallmark and prerequisite of programmed cell death, is characterized by K(+) and Cl(-) efflux. In addition to its role in AVD, cytosolic K(+) can be inhibitory toward endogenous caspases and nucleases and can suppress mitochondrial cytochrome c release. In PASMC, K(+) channel activation accelerates AVD and enhances apoptosis, while K(+) channel inhibition decelerates AVD and inhibits apoptosis. Finally, inhibition of K(+) channels, by increasing cytosolic [Ca(2+)] as a result of membrane depolarization-mediated opening of voltage-dependent Ca(2+) channels, leads to PASMC contraction and proliferation. The goals of this review are twofold: (1) to elucidate the role of K(+) ions and K(+) channels in the proliferation and apoptosis of PASMC, with an emphasis on abnormal cell growth in human and animal models of PAH, and (2) to elaborate upon the targeting of K(+) flux pathways for pharmacological treatment of pulmonary vascular disease.

Control of phenotypic plasticity of smooth muscle cells by bone morphogenetic protein signaling through the myocardin-related transcription factors

Vascular smooth muscle cells (VSMCs), unlike other muscle cells, do not terminally differentiate. In response to injury, VSMCs change phenotype, proliferate, and migrate as part of the repair process. Dysregulation of this plasticity program contributes to the pathogenesis of several vascular disorders, such as atherosclerosis, restenosis, and hypertension. The discovery of mutations in the gene encoding BMPRII, the type II subunit of the receptor for bone morphogenetic proteins (BMPs), in patients with pulmonary arterial hypertension (PAH) provided an indication that BMP signaling may affect the homeostasis of VSMCs and their phenotype modulation. Here we report that BMP signaling potently induces SMC-specific genes in pluripotent cells and prevents dedifferentiation of arterial SMCs. The BMP-induced phenotype switch requires intact RhoA/ROCK signaling but is not blocked by inhibitors of the TGFbeta and PI3K/Akt pathways. Furthermore, nuclear localization and recruitment of the myocardin-related transcription factors (MRTF-A and MRTF-B) to a smooth muscle alpha-actin promoter is observed in response to BMP treatment. Thus, BMP signaling modulates VSMC phenotype via cross-talk with the RhoA/MRTFs pathway, and may contribute to the development of the pathological characteristics observed in patients with PAH and other obliterative vascular diseases.