Franz Rischard

Pathogenic role of calcium-sensing receptors in the development and progression of pulmonary hypertension

An increase in cytosolic free Ca(2+) concentration ([Ca(2+)]cyt) in pulmonary arterial smooth muscle cells (PASMC) is a major trigger for pulmonary vasoconstriction and a critical stimulation for PASMC proliferation and migration. Previously, we demonstrated that expression and function of calcium sensing receptors (CaSR) in PASMC from patients with idiopathic pulmonary arterial hypertension (IPAH) and animals with experimental pulmonary hypertension (PH) were greater than in PASMC from normal subjects and control animals. However, the mechanisms by which CaSR triggers Ca(2+) influx in PASMC and the implication of CaSR in the development of PH remain elusive. Here, we report that CaSR functionally interacts with TRPC6 to regulate [Ca(2+)]cyt in PASMC. Downregulation of CaSR or TRPC6 with siRNA inhibited Ca(2+)-induced [Ca(2+)]cyt increase in IPAH-PASMC (in which CaSR is upregulated), whereas overexpression of CaSR or TRPC6 enhanced Ca(2+)-induced [Ca(2+)]cyt increase in normal PASMC (in which CaSR expression level is low). The upregulated CaSR in IPAH-PASMC was also associated with enhanced Akt phosphorylation, whereas blockade of CaSR in IPAH-PASMC attenuated cell proliferation. In in vivo experiments, deletion of the CaSR gene in mice (casr(-/-)) significantly inhibited the development and progression of experimental PH and markedly attenuated acute hypoxia-induced pulmonary vasoconstriction. These data indicate that functional interaction of upregulated CaSR and upregulated TRPC6 in PASMC from IPAH patients and animals with experimental PH may play an important role in the development and progression of sustained pulmonary vasoconstriction and pulmonary vascular remodeling. Blockade or downregulation of CaSR and/or TRPC6 with siRNA or miRNA may be a novel therapeutic strategy to develop new drugs for patients with pulmonary arterial hypertension.

Transition from parenteral to oral treprostinil in pulmonary arterial hypertension

BACKGROUND Parenteral prostanoids are effective treatment for pulmonary arterial hypertension, but long-term pump infusion systems have significant delivery-related safety and convenience limitations. METHODS Subjects with a favorable risk profile transitioned from parenteral to oral treprostinil using a protocol-driven titration during 5 days of inpatient observation. Baseline and Week 24 assessments included 6-minute walk distance, echocardiogram, right heart catheterization, pharmacokinetics, treatment satisfaction and quality of life. Thirty-three subjects (76% female, mean age 50 years) enrolled; 85% were using subcutaneous treprostinil with a median dose of 57 (range 25 to 111) ng/kg/min. Participants were using background, approved non-prostanoid therapy, including 9 on 2 oral therapies; baseline right atrial pressure and cardiac output were in the normal range. All 33 subjects transitioned to oral treprostinil therapy within 4 weeks, but 2 transitioned back to parenteral drug before Week 24. At Week 24, subjects were taking a median total daily dose of 44 (15 to 75) mg, with 25 of 31 using a 3-times-daily regimen at 7- to 9-hour intervals. RESULTS The 6-minute walk distance was preserved (median +17 m [-98 to 95 m]) at its baseline of 446 m. Hemodynamic variables, including pulmonary vascular resistance, were similar at Week 24 except for mixed venous saturation, which dropped from a median of 71% to 68% (p < 0.001). Overall quality of life and treatment satisfaction measures did not change; however, mood-related symptom and treatment convenience subscores improved. Common adverse effects included headache, nausea, flushing and diarrhea. CONCLUSIONS Lower risk patients managed on parenteral treprostinil may be candidates for transition to a more convenient, oral form of the drug.

Simple functional imaging of the right ventricle in pulmonary hypertension: Can right ventricular ejection fraction be improved?

a Pittsburgh Heart, Lung, Blood and Vascular Medicine Institute, University of Pittsburgh, Pittsburgh, PA, USA b Department of Pulmonary and Critical Care, University of Arizona: Tucson, Tucson, AZ, USA c Faculty of Medicine, Free University of Brussels, Brussels, Belgium d Bioengineering, University of Colorado, Denver, CO, USA e Division of Cardiology, Departments of Medicine and Bioengineering, University of Pittsburgh and UPMC Heart & Vascular Institute, United States

PVDOMICS: A Multi-Center Study to Improve Understanding of Pulmonary Vascular Disease Through Phenomics

The National Institutes of Health (NIH)/National Heart, Lung and Blood institute (NHLBI) launched an initiative, PVDOMICS (Redefining Pulmonary Hypertension through Pulmonary Vascular Disease Phenomics) that aims to augment the current pulmonary hypertension (PH) classification based on shared biological features. PVDOMICS will enroll 1500 participants with PH and disease and healthy comparators. Enrollees will undergo deep clinical phenotyping, and blood will be acquired for comprehensive omic analyses that will focus on discovery of molecular-based subtypes of pulmonary vascular disease (PVD) through application of high dimensional model-based clustering methods. In addition to an updated, molecular classification of PVD, the phenomic data generated will be a rich resource to the broad community of heart and lung disease investigators. Editorial, see p 1106 PH is a hemodynamic condition that causes increased blood pressure in the pulmonary arteries and the right heart leading to adverse clinical outcomes. The current World Symposium on Pulmonary Hypertension (WSPH) classification of PH is based on a combination of patient characteristics, clinical features, and cardiopulmonary hemodynamics, and these features are used to inform treatment options.1 Aside from heritable pulmonary arterial hypertension, this classification is not tied to molecular or cellular pathobiologic mechanism to explain the pathogenesis of PH. The NIH has a vested interest in understanding the causes and natural history of PH, as well as the discovery of effective treatment options. Since the first large NIH registry of patients with pulmonary arterial hypertension >30 years ago,2 significant advances in scientific knowledge and translational medicine have occurred, highlighting a need for updating the current clinical classification system. The NHLBI has sponsored several workshops focusing on PVD research strategic planning over the past decade. PVD encompasses PH and PVD without PH, for example, pulmonary vasculitis and pathological pulmonary vascular remodeling without hemodynamic criteria for PH. Experts identified the need …

What’s new: the management of acute right ventricular decompensation of chronic pulmonary hypertension

In healthy individuals, the right ventricular-pulmonary circulation is a low-pressure, high-compliance system. In high afterload states, the right ventricle (RV) adapts by increasing contractility (homeometric autoregulation) and preload (heterometric autoregulation) [1, 2]. Pulmonary hypertension (PH), defined as a mean pulmonary artery pressure [25 mmHg, results from any physiologic process that increases RV afterload, most commonly left ventricular (LV) disease resulting in a high left atrial pressure and post-capillary pulmonary venous congestion [3]. Pre-capillary PH (PAH) results from high RV loading despite normal pulmonary venous pressure. PAH may present with RV dysfunction, a physiologic state where the RV ventriculo-vascular unit is unable to perform some necessary functions. However, many patients with PAH present to the intensive care unit (ICU) in overt RV failure. In this condition, regardless of etiology, the RV is unable to meet increased loading demands leading to RV dilation, tricuspid regurgitation, and increased right atrial pressure reducing forward flow, coronary perfusion, and perhaps systemic hypotension [4]. This presents unique problems for hemodynamic optimization, intubation, and ventilator management. This paper offers strategies to address the complicated physiology of PH with RV failure in the ICU. See Fig. 1 for a summary of our recommendations.

Ischemia and ischemic preconditioning in the buffer-perfused pigeon heart.

Isolated pigeon hearts were perfused with Krebs-Henseleit bicarbonate buffer with 1.25 mM Ca++ at a pressure of 60 cm H2O and paced at 210 beats per min. After an equilibration perfusion of 30 min, hearts were subjected to 10 min global ischemia and then reperfused for 30 min. Left ventricular +dP/dtmax, systolic, and end diastolic pressures differed significantly from baseline values during reperfusion as did the release of lactate dehydrogenase (LDH). When the hearts were preconditioned by interruption of flow for two 2.5-min intervals, followed by 10 min of ischemia and then reperfusion, the short periods of ischemia, followed by reperfusion, protected the hearts against the longer bout of ischemia as evidenced by significant differences between the left ventricular (LV) pressure, +dP/dtmax, LV end diastolic pressure and LDH values obtained from the hearts of control vs. preconditioned hearts. Substitution of 1 microM adenosine for the preconditioning ischemia also resulted in the preconditioning response. Ischemic preconditioning (IP) was not blocked by addition of 100 microM 8-(-p-sulfophenyl) theophylline, an adenosine receptor antagonist. Therefore, isolated, perfused bird hearts can be preconditioned, and the mechanism may involve adenosine receptors, although their activation is not necessary for i.p. to occur. Factors in addition to adenosine are likely involved.

Endothelial HIF-2α contributes to severe pulmonary hypertension due to endothelial-to-mesenchymal transition

Pulmonary vascular remodeling characterized by concentric wall thickening and intraluminal obliteration is a major contributor to the elevated pulmonary vascular resistance in patients with idiopathic pulmonary arterial hypertension (IPAH). Here we report that increased hypoxia-inducible factor 2α (HIF-2α) in lung vascular endothelial cells (LVECs) under normoxic conditions is involved in the development of pulmonary hypertension (PH) by inducing endothelial-to-mesenchymal transition (EndMT), which subsequently results in vascular remodeling and occlusive lesions. We observed significant EndMT and markedly increased expression of SNAI, an inducer of EndMT, in LVECs from patients with IPAH and animals with experimental PH compared with normal controls. LVECs isolated from IPAH patients had a higher level of HIF-2α than that from normal subjects, whereas HIF-1α was upregulated in pulmonary arterial smooth muscle cells (PASMCs) from IPAH patients. The increased HIF-2α level, due to downregulated prolyl hydroxylase domain protein 2 (PHD2), a prolyl hydroxylase that promotes HIF-2α degradation, was involved in enhanced EndMT and upregulated SNAI1/2 in LVECs from patients with IPAH. Moreover, knockdown of HIF-2α (but not HIF-1α) with siRNA decreases both SNAI1 and SNAI2 expression in IPAH-LVECs. Mice with endothelial cell (EC)-specific knockout (KO) of the PHD2 gene, egln1 (egln1EC-/-), developed severe PH under normoxic conditions, whereas Snai1/2 and EndMT were increased in LVECs of egln1EC-/- mice. EC-specific KO of the HIF-2α gene, hif2a, prevented mice from developing hypoxia-induced PH, whereas EC-specific deletion of the HIF-1α gene, hif1a, or smooth muscle cell (SMC)-specific deletion of hif2a, negligibly affected the development of PH. Also, exposure to hypoxia for 48-72 h increased protein level of HIF-1α in normal human PASMCs and HIF-2α in normal human LVECs. These data indicate that increased HIF-2α in LVECs plays a pathogenic role in the development of severe PH by upregulating SNAI1/2, inducing EndMT, and causing obliterative pulmonary vascular lesions and vascular remodeling.

Exercise-Induced Pulmonary Hypertension: Translating Pathophysiological Concepts Into Clinical Practice

&NA; Exercise stress testing of the pulmonary circulation for the diagnosis of latent or early‐stage pulmonary hypertension (PH) is gaining acceptance. There is emerging consensus to define exercise‐induced PH by a mean pulmonary artery pressure > 30 mm Hg at a cardiac output < 10 L/min and a total pulmonary vascular resistance> 3 Wood units at maximum exercise, in the absence of PH at rest. Exercise‐induced PH has been reported in association with a bone morphogenetic receptor‐2 gene mutation, in systemic sclerosis, in left heart conditions, in chronic lung diseases, and in chronic pulmonary thromboembolism. Exercise‐induced PH is a cause of decreased exercise capacity, may precede the development of manifest PH in a proportion of patients, and is associated with a decreased life expectancy. Exercise stress testing of the pulmonary circulation has to be dynamic and rely on measurements of the components of the pulmonary vascular equation during, not after exercise. Noninvasive imaging measurements may be sufficiently accurate in experienced hands, but suffer from lack of precision, so that invasive measurements are required for individual decision‐making. Exercise‐induced PH is caused either by pulmonary vasoconstriction, pulmonary vascular remodeling, or by increased upstream transmission of pulmonary venous pressure. This differential diagnosis is clinical. Left heart disease as a cause of exercise‐induced PH can be further ascertained by a pulmonary artery wedge pressure above or below 20 mm Hg at a cardiac output < 10 L/min or a pulmonary artery wedge pressure‐flow relationship above or below 2 mm Hg/L/min during exercise.

Pulmonary Circulatory – Right Ventricular Uncoupling: New Insights Into Pulmonary Hypertension Pathophysiology

The pulmonary circulatory – right ventricular uncoupling is a key pathophysiological feature of pulmonary hypertension. Uncoupling develops when the ventricular contractility is not matched to its afterload due to a discordant response of the RV to increased afterload, or to an impaired right ventricular function. In this chapter we reported the methods which were developed to quantify the right ventricular –pulmonary artery (RV-PA) coupling in patients with PH and in experimental models of PH. The RV pressure-volume loop analysis are the gold standard to quantify RV-PA coupling metrics but more simple and less invasive methods were developed. We also reported how the RV-PA coupling metrics may be used to improve the phenotyping of patients and experimental models with PH. RV-PA coupling was also used to quantify the pharmacological effects of treatments in animal models with PH and to improve the understanding of the pathophysiological differences in different PH types. In recent studies, RV-PA coupling quantification with imaging methods showed interesting application to prognosis stratification of patients with PH.

How prostacyclin therapy improves right ventricular function in pulmonary arterial hypertension

Within recent years, right ventricular (RV) function has been recognised as a major determinant of outcome in pulmonary arterial hypertension (PAH) [1, 2]. Clinical [3] and in vitro experimental [4, 5] data suggest that prostacyclins, the treatment of choice for most severely ill PAH patients [6], might have a positive inotropic effect on RV function, and reduce pulmonary vascular resistance (PVR). Nevertheless, inotropic effects are difficult to demonstrate in vivo, as ventricular contractility adjusts to afterload to preserve ventricular-arterial coupling [7]. In fact, the ratio of ventricular end-systolic elastance (Ees), a measure of in vivo contractility, to pulmonary arterial elastance (Ea) or the “coupling ratio” (Ees/Ea), was restored by epoprostenol in a model of load-induced acute RV failure; however, this was explained by a reduction in afterload [8]. Prostacyclin reduces right ventricular contractility, but improves ejection fraction and exercise capacity in PAH http://ow.ly/m5S830dpcZv