Sildenafil added to sitaxsentan in overcirculation-induced pulmonary arterial hypertension

Bone Morphogenetic Protein-Based Therapeutic Approaches

Bone morphogenetic proteins (BMPs) constitute the largest subdivision of the transforming growth factor (TGF)-β family of ligands and exert most of their effects through the canonical effectors Smad1, 5, and 8. Appropriate regulation of BMP signaling is critical for the development and homeostasis of numerous human organ systems. Aberrations in BMP pathways or their regulation are increasingly associated with diverse human pathologies, and there is an urgent and growing need to develop effective approaches to modulate BMP signaling in the clinic. In this review, we provide a wide perspective on diseases and/or conditions associated with dysregulated BMP signal transduction, outline the current strategies available to modulate BMP pathways, highlight emerging second-generation technologies, and postulate prospective avenues for future investigation.

A novel single-beat approach to assess right ventricular systolic function

Clinical assessment of right ventricular (RV) contractility in diseases such as pulmonary arterial hypertension (PAH) has been hindered by the lack of a robust methodology. Here, a novel, clinically viable, single-beat method was developed to assess end-systolic elastance (E_es), a measure of right ventricular (RV) contractility. We hypothesized that this novel approach reduces uncertainty and interobserver variability in the estimation of the maximum isovolumic pressure (P_iso), the key step in single-beat methods. The new method was designed to include a larger portion of the RV pressure data and minimize subjective adjustments by the operator. Data were obtained from right heart catheterization of PAH patients in a multicenter prospective study ( data set 1) and a single-center retrospective study ( data set 2). To obtain P_iso, three independent observers used an established single-beat method (based on the first derivative of the pressure waveform) and the novel method (based on the second derivative). Interobserver variability analysis included paired t-test, one-way ANOVA, interclass correlation (ICC) analysis, and a modified Bland-Altman analysis. The P_iso values obtained from the two methods were linearly correlated for both data set 1 ( R² = 0.74) and data set 2 ( R² = 0.91). Compared with the established method, the novel method resulted in smaller interobserver variability ( P < 0.001), nonsignificant differences between observers, and a narrower confidence interval. By reducing uncertainty and interobserved variability, this novel approach may pave the way for more effective clinical management of PAH. NEW & NOTEWORTHY A novel methodology to assess right ventricular contractility from clinical data is demonstrated. This approach significantly reduces interobserver variability in the analysis of ventricular pressure data, as demonstrated in a relatively large population of subjects with pulmonary hypertension. This study may enable more accurate clinical monitoring of systolic function in subjects with pulmonary hypertension.

A Survey of Strategies to Modulate the Bone Morphogenetic Protein Signaling Pathway: Current and Future Perspectives

Bone morphogenetic proteins (BMPs) constitute the largest subdivision of the TGF-β family of ligands and are unequivocally involved in regulating stem cell behavior. Appropriate regulation of canonical BMP signaling is critical for the development and homeostasis of numerous human organ systems, as aberrations in the BMP pathway or its regulation are increasingly associated with diverse human pathologies. In this review, we provide a wide-perspective on strategies that increase or decrease BMP signaling. We briefly outline the current FDA-approved approaches, highlight emerging next-generation technologies, and postulate prospective avenues for future investigation. We also detail how activating other pathways may indirectly modulate BMP signaling, with a particular emphasis on the relationship between the BMP and Activin/TGF-β pathways.

Right ventricular failure due to chronic pressure load: What have we learned in animal models since the NIH working group statement?

Right ventricular (RV) failure determines outcome in patients with pulmonary hypertension, congenital heart diseases and in left ventricular failure. In 2006, the Working Group on Cellular and Molecular Mechanisms of Right Heart Failure of the NIH advocated the development of preclinical models to study the pathophysiology and pathobiology of RV failure. In this review, we summarize the progress of research into the pathobiology of RV failure and potential therapeutic interventions. The picture emerging from this research is that RV adaptation to increased afterload is characterized by increased contractility, dilatation and hypertrophy. Clinical RV failure is associated with progressive diastolic deterioration and disturbed ventricular–arterial coupling in the presence of increased contractility. The pathobiology of the failing RV shows similarities with that of the LV and is marked by lack of adequate increase in capillary density leading to a hypoxic environment and oxidative stress and a metabolic switch from fatty acids to glucose utilization. However, RV failure also has characteristic features. So far, therapies aiming to specifically improve RV function have had limited success. The use of beta blockers and sildenafil may hold promise, but new therapies have to be developed. The use of recently developed animal models will aid in further understanding of the pathobiology of RV failure and development of new therapeutic strategies.

Pulmonary vasoreactivity in spontaneously hypertensive rats--effects of endothelin-1 and leptin

Background

Systemic hypertension may be associated with an increased pulmonary vascular resistance, which we hypothesized could be, at least in part, mediated by increased leptin.

Methods

Vascular reactivity to phenylephrine (1 μmol/L), endothelin-1 (10 nmol/L) and leptin (0.001–100 nmol/L) was evaluated in endothelium-intact and -denuded isolated thoracic aorta and pulmonary arteries from spontaneously hypertensive versus control Wistar rats. Arteries were sampled for pathobiological evaluation and lung tissue for morphometric evaluation.

Results

In control rats, endothelin-1 induced a higher level of contraction in the pulmonary artery than in the aorta. After phenylephrine or endothelin-1 precontraction, leptin relaxed intact pulmonary artery and aortic rings, while no response was observed in denuded arteries. Spontaneously hypertensive rats presented with increased reactivity to phenylephrine and endothelin-1 in endothelium-intact pulmonary arteries. After endothelin-1 precontraction, endothelium-dependent relaxation to leptin was impaired in pulmonary arteries from hypertensive rats. In both strains of rats, aortic segments were more responsive to leptin than pulmonary artery. In hypertensive rats, pulmonary arteries exhibited increased pulmonary artery medial thickness, associated with increased expressions of preproendothelin-1, endothelin-1 receptors type A and B, inducible nitric oxide synthase and decreased endothelial nitric oxide synthase, together with decreased leptin receptor and increased suppressor of cytokine signaling 3 expressions.

Conclusions

Altered pulmonary vascular reactivity in hypertension may be related to a loss of endothelial buffering of vasoconstriction and decreased leptin-induced vasodilation in conditions of increased endothelin-1.

Distinct loading conditions reveal various patterns of right ventricular adaptation

Right ventricular (RV) failure due to chronically abnormal loading is a main determinant of outcome in pulmonary hypertension (PH) and congenital heart disease. However, distinct types of RV loading have been associated with different outcomes. To determine whether the adaptive RV response depends on loading type, we compared hemodynamics, exercise, and hypertrophy in models of pressure overload due to pulmonary artery banding (PAB), pressure overload due to PH, combined pressure and volume overload, and isolated volume load. Ninety-four rats were subjected to either PAB, monocrotaline-induced PH (PH), aortocaval shunt (shunt), or combined monocrotaline and aortocaval shunt (PH + shunt). We performed pressure-volume analysis and voluntary exercise measurements at 4 wk. We compared PAB to PH (part I) and PH + shunt to either isolated PH or shunt (part II). In part I, enhanced contractility (end-systolic elastance and preload recruitable stroke work) was present in PH and PAB, but strongest in PAB. Frank-Starling mechanism was active in both PAB and PH. In PAB this was accompanied by diastolic dysfunction (increased end-diastolic elastance, relaxation constant), clinical signs of RV failure, and reduced exercise. These distinct responses were not attributable to differences in hypertrophy. In part II, in PH + shunt the contractility response was blunted compared with PH, which caused pseudonormalization of parameters. Additional volume overload strongly enhanced hypertrophy in PH. We conclude that different types of loading result in distinct patterns of RV adaptation. This is of importance for the approach to patients with chronically increased RV load and for experimental studies in various types of RV failure.

The role of disturbed blood flow in the development of pulmonary arterial hypertension: lessons from preclinical animal models

Pulmonary arterial hypertension (PAH) is a progressive pulmonary vasoproliferative disorder characterized by the development of unique neointimal lesions, including concentric laminar intima fibrosis and plexiform lesions. Although the histomorphology of neointimal lesions is well described, the pathogenesis of PAH and neointimal development is largely unknown. After three decades of PAH pathobiology research the focus has shifted from vasoconstriction towards a mechanism of cancer-like angioproliferation. In this concept the role of disturbed blood flow is seen as an important trigger in the development of vascular remodeling. For instance, in PAH associated with congenital heart disease, increased pulmonary blood flow (i.e., systemic-to-pulmonary shunt) is an essential trigger for the occurrence of neointimal lesions and PAH development. Still, questions remain about the exact role of these blood flow characteristics in disease progression. PAH animal models are important for obtaining insight in new pathobiological processes and therapeutical targets. However, as for any preclinical model the pathophysiological mechanism and clinical course has to be comparable to the human disease that it mimics. This means that animal models mimicking human PAH ideally are characterized by: a hit recognized in human disease (e.g., altered pulmonary blood flow), specific vascular remodeling resembling human neointimal lesions, and disease progression that leads to right ventriclular dysfunction and death. A review that underlines the current knowledge of PAH due to disturbed flow is still lacking. In this review we will summarize the current knowledge obtained from PAH animal models associated with disturbed pulmonary blood flow and address questions for future treatment strategies for PAH.

Methods for measuring right ventricular function and hemodynamic coupling with the pulmonary vasculature

The right ventricle (RV) is a pulsatile pump, the efficiency of which depends on proper hemodynamic coupling with the compliant pulmonary circulation. The RV and pulmonary circulation exhibit structural and functional differences with the more extensively investigated left ventricle (LV) and systemic circulation. In light of these differences, metrics of LV function and efficiency of coupling to the systemic circulation cannot be used without modification to characterize RV function and efficiency of coupling to the pulmonary circulation. In this article, we review RV physiology and mechanics, established and novel methods for measuring RV function and hemodynamic coupling, and findings from application of these methods to RV function and coupling changes with pulmonary hypertension. We especially focus on non-invasive measurements, as these may represent the future for clinical monitoring of disease progression and the effect of drug therapies.