The need to recognize the pulmonary circulation and the right ventricle as an integrated functional unit: facts and hypotheses (2013 Grover Conference series)

Chronic hypoxia-induced alterations of the right ventricular myocardium are not aggravated by alimentary obesity in the mouse

BACKGROUND AND AIMS

Obesity is a risk factor of cardiopulmonary disorders including left and right ventricular dysfunction and pulmonary hypertension (PH), and PH is associated with right ventricular (RV) hypertrophy and failure. Here, we tested the hypothesis that alterations of the RV capillary network under PH induced by chronic hypoxia are aggravated by alimentary obesity, thereby representing a predisposition for subsequent RV dysfunction.

METHODS AND RESULTS

Male, 6-week-old C57BL/6N mice were assigned to one of the following groups: control diet (CD), CD/hypoxia (CD-Hyp), high-fat diet (HFD), HFD/hypoxia (HFD-Hyp). Mice were fed CD or HFD for 30 weeks, CD-Hyp and HFD-Hyp mice were exposed to normobaric hypoxia (13 % O2) during the last 3 weeks of the experiments. Hearts were prepared for light and electron microscopy and right atria and RVs were analyzed by design-based stereology. HFD and hypoxia independently increased RV and cardiomyocyte volume. These changes were further enhanced in HFD-Hyp. The ratio between RV and body weights was similar in CD and HFD but enhanced in both hypoxia groups to a similar extent. The total length of capillaries was elevated in proportion with the RV hypertrophy, thus the area of myocardium supplied by an average capillary was similar in all groups. Similarly, the thickness of the capillary endothelium was not altered by HFD or hypoxia.

CONCLUSION

In conclusion, in experimental PH capillaries of the RV myocardium showed similar adaptations in lean and obese mice. Thus, under chronic hypoxic conditions, obesity had no adverse effect on the capillarization of the right ventricle.

Use of Prostaglandin E1 in the Management of Congenital Diaphragmatic Hernia-A Review

Congenital diaphragmatic hernia (CDH) is a rare congenital anomaly, whose presentation is complicated by pulmonary hypertension (PH), pulmonary hypoplasia, and myocardial dysfunction, each of which have significant impact on short-term clinical management and long-term outcomes. Despite many advances in therapy and surgical technique, optimal CDH management remains a topic of debate, due to the variable presentation, complex pathophysiology, and continued impact on morbidity and mortality. One of the more recent management strategies is the use of prostaglandin E1 (PGE1) infusion in the management of PH associated with CDH. PGE1 is widely used in the NICU in critical congenital cardiac disease to maintain ductal patency and facilitate pulmonary and systemic blood flow. In a related paradigm, PGE1 infusion has been used in situations of supra-systemic right ventricular pressures, including CDH, with the therapeutic intent to maintain ductal patency as a "pressure relief valve" to reduce the effective afterload on the right ventricle (RV), optimize cardiac function and support pulmonary and systemic blood flow. This paper reviews the current evidence for use of PGE1 in the CDH population and the opportunities for future investigations.

Supra-coronary aortic banding improves right ventricular function in experimental pulmonary arterial hypertension in rats by increasing systolic right coronary artery perfusion

AIM

Pulmonary arterial hypertension (PAH) results in right ventricular (RV) dysfunction owing, in part, to RV ischemia. The relative contribution of RV microvascular rarefaction vs reduced right coronary artery perfusion pressure (RCA-PP) to RV ischemia remains unknown. We hypothesize that increasing RCA-PP improves RV function in PAH by increasing RV systolic perfusion.

METHODS

Supra-coronary aortic banding (SAB) or sham surgery was performed on male Sprague-Dawley rats. Seven to ten days later, rats received either monocrotaline (MCT; 60 mg/kg) or saline. After 1 month, echocardiography, cardiac catheterization, ^99m Tc-sestamibi single-photon emission computed tomography (SPECT) and microsphere infusion studies were performed. The RV was harvested for measurement of hypertrophy (RVH), fibrosis and immunoblotting, and the lung was harvested for pulmonary artery (PA) histology.

RESULTS

Supra-coronary aortic banding increased systolic pressures in proximal aorta and systolic RCA-PP in SAB + MCT vs MCT rats (114 ± 12 vs 5 ± 9 mm Hg), without altering diastolic RCA-PP. SAB + MCT rats had improved RV function vs MCT rats, evident from their significantly increased cardiac output (CO), RV free wall (RVFW) thickening, tricuspid annular plane systolic excursion (TAPSE) and RV-PA coupling indices. RV-PA coupling indices and CO correlated directly with systolic RCA-PP. RV perfusion was increased in SAB + MCT vs MCT rats and correlated well with CO; whereas microvascular rarefaction was unaltered. SAB + MCT rats had less RVH and fibrosis and lower PA pressures vs MCT rats. SAB + MCT rats had significantly lower RV pyruvate kinase muscle isoform 2/1 ratios than MCT rats, consistent with restoration of oxidative metabolism.

CONCLUSION

A SAB-induced increase in systolic RCA-PP improves RV perfusion and function in MCT rats. Maintaining systolic RCA perfusion can preserve RV function in PAH.

Establishment of adult right ventricle failure in ovine using a graded, animal-specific pulmonary artery constriction model

BACKGROUND

Right ventricle failure (RVF) is associated with serious cardiac and pulmonary diseases that contribute significantly to the morbidity and mortality of patients. Currently, the mechanisms of RVF are not fully understood and it is partly due to the lack of large animal models in adult RVF. In this study, we aim to establish a model of RVF in adult ovine and examine the structure and function relations in the RV.

METHODS

RV pressure overload was induced in adult male sheep by revised pulmonary artery constriction (PAC). Briefly, an adjustable hydraulic occluder was placed around the main pulmonary artery trunk. Then, repeated saline injection was performed at weeks 0, 1, and 4, where the amount of saline was determined in an animal-specific manner. Healthy, age-matched male sheep were used as additional controls. Echocardiography was performed bi-weekly and on week 11 post-PAC, hemodynamic and biological measurements were obtained.

RESULTS

This PAC methodology resulted in a marked increase in RV systolic pressure and decreases in stroke volume and tricuspid annular plane systolic excursion, indicating signs of RVF. Significant increases in RV chamber size, wall thickness, and Fulton's index were observed. Cardiomyocyte hypertrophy and collagen accumulation (particularly type III collagen) were evident, and these structural changes were correlated with RV dysfunction.

CONCLUSION

In summary, the animal-specific, repeated PAC provided a robust approach to induce adult RVF, and this ovine model will offer a useful tool to study the progression and treatment of adult RVF that is translatable to human diseases.

Fischer rats exhibit maladaptive structural and molecular right ventricular remodelling in severe pulmonary hypertension: a genetically prone model for right heart failure

Aims

The ability of the right ventricle (RV) to adapt to increased afterload is the major determinant of survival in patients with pulmonary hypertension (PH). In this study, we explored the effect of genetic background on RV adaptation and survival in a rat model of severe pulmonary arterial hypertension (PAH).

Methods and results

PH was induced by a single injection of SU5416 (SU) in age-matched Sprague Dawley (SD) or Fischer rats, followed by a 3-week exposure to chronic hypoxia (SUHx). SD and Fischer rats exhibited similar elevations in RV systolic pressure, number of occlusive pulmonary vascular lesions, and RV hypertrophy (RV/LV+S) in response to SUHx. However, no Fischer rats survived beyond 7 weeks compared with complete survival for SD rats. This high early mortality of Fischer rats was associated with significantly greater RV dilatation and reduced ejection fraction, cardiac output, and exercise capacity at 4 weeks post-SU. Moreover, microarray analysis revealed that over 300 genes were uniquely regulated in the RV in the severe PAH model in the Fischer compared with SD rats, mainly related to angiogenesis and vascular homoeostasis, fatty acid metabolism, and innate immunity. A focused polymerase chain reaction array confirmed down-regulation of angiogenic genes in the Fischer compared with SD RV. Furthermore, Fischer rats demonstrated significantly lower RV capillary density compared with SD rats in response to SUHx.

Conclusion

Fischer rats are prone to develop RV failure in response to increased afterload. Moreover, the high mortality in the SUHx model of severe PAH was caused by a failure of RV adaptation associated with lack of adequate microvascular angiogenesis, together with metabolic and immunological responses in the hypertrophied RV.

Epigenetic Metabolic Reprogramming of Right Ventricular Fibroblasts in Pulmonary Arterial Hypertension: A Pyruvate Dehydrogenase Kinase-Dependent Shift in Mitochondrial Metabolism Promotes Right Ventricular Fibrosis

RATIONALE

Right ventricular (RV) fibrosis in pulmonary arterial hypertension contributes to RV failure. While RV fibrosis reflects changes in the function of resident RV fibroblasts (RVfib), these cells are understudied.

OBJECTIVE

Examine the role of mitochondrial metabolism of RVfib in RV fibrosis in human and experimental pulmonary arterial hypertension.

METHODS AND RESULTS

Male Sprague-Dawley rats received monocrotaline (MCT; 60 mg/kg) or saline. Drinking water containing no supplement or the PDK (pyruvate dehydrogenase kinase) inhibitor dichloroacetate was started 7 days post-MCT. At week 4, treadmill testing, echocardiography, and right heart catheterization were performed. The effects of PDK activation on mitochondrial dynamics and metabolism, RVfib proliferation, and collagen production were studied in RVfib in cell culture. Epigenetic mechanisms for persistence of the profibrotic RVfib phenotype in culture were evaluated. PDK expression was also studied in the RVfib of patients with decompensated RV failure (n=11) versus control (n=7). MCT rats developed pulmonary arterial hypertension, RV fibrosis, and RV failure. MCT-RVfib (but not left ventricular fibroblasts) displayed excess mitochondrial fission and had increased expression of PDK isoforms 1 and 3 that persisted for >5 passages in culture. PDK-mediated decreases in pyruvate dehydrogenase activity and oxygen consumption rate were reversed by dichloroacetate (in RVfib and in vivo) or siRNA targeting PDK 1 and 3 (in RVfib). These interventions restored mitochondrial superoxide and hydrogen peroxide production and inactivated HIF (hypoxia-inducible factor)-1α, which was pathologically activated in normoxic MCT-RVfib. Redox-mediated HIF-1α inactivation also decreased the expression of TGF-β1 (transforming growth factor-beta-1) and CTGF (connective tissue growth factor), reduced fibroblast proliferation, and decreased collagen production. HIF-1α activation in MCT-RVfib reflected increased DNMT (DNA methyltransferase) 1 expression, which was associated with a decrease in its regulatory microRNA, miR-148b-3p. In MCT rats, dichloroacetate, at therapeutic levels in the RV, reduced phospho-pyruvate dehydrogenase expression, RV fibrosis, and hypertrophy and improved RV function. In patients with pulmonary arterial hypertension and RV failure, RVfib had increased PDK1 expression.

CONCLUSIONS

MCT-RVfib manifest a DNMT1-HIF-1α-PDK-mediated, chamber-specific, metabolic memory that promotes collagen production and RV fibrosis. This epigenetic mitochondrial-metabolic pathway is a potential antifibrotic therapeutic target.

Neuregulin-1 attenuates right ventricular diastolic stiffness in experimental pulmonary hypertension

We have previously shown that treatment with recombinant human neuregulin-1 (rhNRG-1) improves pulmonary arterial hypertension (PAH) in a monocrotaline (MCT)-induced animal model, by decreasing pulmonary arterial remodelling and endothelial dysfunction, as well as by restoring right ventricular (RV) function. Additionally, rhNRG-1 treatment showed direct myocardial anti-remodelling effects in a model of pressure loading of the RV without PAH. This work aimed to study the intrinsic cardiac effects of rhNRG-1 on experimental PAH and RV pressure overload, and more specifically on diastolic stiffness, at both the ventricular and cardiomyocyte level. We studied the effects of chronic rhNRG-1 treatment on ventricular passive stiffness in RV and LV samples from MCT-induced PAH animals and in the RV from animals with compensated and decompensated RV hypertrophy, through a mild and severe pulmonary artery banding (PAB). We also measured passive tension in isolated cardiomyocytes and quantified the expression of myocardial remodelling-associated genes and calcium handling proteins. Chronic rhNRG-1 treatment decreased passive tension development in RV and LV isolated from animals with MCT-induced PAH. This decrease was associated with increased phospholamban phosphorylation, and with attenuation of the expression of cardiac maladaptive remodelling markers. Finally, we showed that rhNRG-1 therapy decreased RV remodelling and cardiomyocyte passive tension development in PAB-induced RV hypertrophy animals, without compromising cardiac function, pointing to cardiac-specific effects in both hypertrophy stages. In conclusion, we demonstrated that rhNRG-1 treatment decreased RV intrinsic diastolic stiffness, through the improvement of calcium handling and cardiac remodelling signalling.

Increased Drp1-Mediated Mitochondrial Fission Promotes Proliferation and Collagen Production by Right Ventricular Fibroblasts in Experimental Pulmonary Arterial Hypertension

Introduction: Right ventricular (RV) fibrosis contributes to RV failure in pulmonary arterial hypertension (PAH). The mechanisms underlying RV fibrosis in PAH and the role of RV fibroblasts (RVfib) are unknown. Activation of the mitochondrial fission mediator dynamin-related protein 1 (Drp1) contributes to dysfunction of RV myocytes in PAH through interaction with its binding partner, fission protein 1 (Fis1). However, the role of mitochondrial fission in RVfib and RV fibrosis in PAH is unknown. Objective: We hypothesize that mitochondrial fission is increased in RVfib of rats with monocrotaline (MCT)-induced PAH. We evaluated the contribution of Drp1 and Drp1-Fis1 interaction to RVfib proliferation and collagen production in culture and to RV fibrosis in vivo. Methods: Vimentin (+) RVfib were enzymatically isolated and cultured from the RVs of male Sprague-Dawley rats that received MCT (60 mg/kg) or saline. Mitochondrial morphology, proliferation, collagen production, and expression of Drp1, Drp1 binding partners and mitochondrial fusion mediators were measured. The Drp1 inhibitor mitochondrial division inhibitor 1 (Mdivi-1), P110, a competitive peptide inhibitor of Drp1-Fis1 interaction, and siRNA targeting Drp1 were assessed. Subsequently, prevention and regression studies tested the antifibrotic effects of P110 (0.5 mg/kg) in vivo. At week 4 post MCT, echocardiography and right heart catheterization were performed. The RV was stained for collagen. Results: Mitochondrial fragmentation, proliferation rates and collagen production were increased in MCT-RVfib versus control-RVfib. MCT-RVfib had increased expression of activated Drp1 protein and a trend to decreased mitofusin-2 expression. Mdivi-1 and P110 inhibited mitochondrial fission, proliferation and collagen III expression in MCT-RVfib. However, P110 was only effective at high doses (1 mM). siDrp1 also reduced fission in MCT-RVfib. Despite promising results in cell therapy, in vivo therapy with P110 failed to prevent or regress RV fibrosis in MCT rats, perhaps due to failure to achieve adequate P110 levels or to the greater importance of interaction of Drp1 with other binding partners. Conclusion: PAH RVfib have increased Drp1-mediated mitochondrial fission. Inhibiting Drp1 prevents mitochondrial fission and reduces RVfib proliferation and collagen production. This is the first description of disordered mitochondrial dynamics in RVfib and suggests that Drp1 is a potential new antifibrotic target.

Urocortin-2 improves right ventricular function and attenuates pulmonary arterial hypertension

Aims

Pulmonary arterial hypertension (PAH) is a devastating disease and treatment options are limited. Urocortin-2 (Ucn-2) has shown promising therapeutic effects in experimental and clinical left ventricular heart failure (HF). Our aim was to analyse the expression of Ucn-2 in human and experimental PAH, and to investigate the effects of human Ucn-2 (hUcn-2) administration in rats with monocrotaline (MCT)-induced pulmonary hypertension (PH).

Methods and results

Tissue samples were collected from patients with and without PAH and from rats with MCT-induced PH. hUcn-2 (5 μg/kg, bi-daily, i.p., for 10 days) or vehicle was administered to male wistar rats subjected to MCT injection or to pulmonary artery banding (PAB) to induce right ventricular (RV) overload without PAH. Expression of Ucn-2 and its receptor was increased in the RV of patients and rats with PAH. hUcn-2 treatment reduced PAH in MCT rats, resulting in decreased morbidity, improved exercise capacity and attenuated pulmonary arterial and RV remodelling and dysfunction. Additionally, RV gene expression of hypertrophy and failure signalling pathways were attenuated. hUcn-2 treatment also attenuated PAB-induced RV hypertrophy.

Conclusions

Ucn-2 levels are altered in human and experimental PAH. hUcn-2 treatment attenuates PAH and RV dysfunction in MCT-induced PH, has direct anti-remodelling effects on the pressure-overloaded RV, and improves pulmonary vascular function.

Maintained right ventricular pressure overload induces ventricular-arterial decoupling in mice

NEW FINDINGS

What is the central question of this study? The aim was to investigate whether complementary assessment of non-invasive ultrasound imaging together with closed chest-derived intracardiac pressure-volume catheterization is applicable to mice for an in-depth characterization of right ventricular (RV) function even upon maintained pressure overload. What is the main finding and its importance? Characterization of RV function by the complementary use of echocardiographic imaging together with pressure-volume catheterization reveals ventricular-arterial decoupling upon maintained pressure overload, where RV systolic function correlates with ventricular-arterial coupling rather than contractility, whereas diastolic function correlates well with RV diastolic pressure. This combined approach allows us to phenotype RV function and dysfunction better in genetically modified and/or pharmacologically treated mice. Assessment of right ventricular (RV) function in rodents is a challenge because of the complex RV anatomy and structure. To date, the best characterization of RV function has been achieved by accurate cardiovascular phenotyping, involving a combination of non-invasive imaging and intracardiac pressure-volume measurements. We sought to investigate the feasibility of two complementary phenotyping techniques for the evaluation of RV function in an experimental mouse model of sustained RV pressure overload. Mice underwent either sham surgery (n = 5) or pulmonary artery banding (n = 8) to induce isolated RV pressure overload. After 3 weeks, indices of RV function were assessed by echocardiography (Vevo2100) and closed chest-derived invasive pressure-volume measurements (PVR-1030). Pulmonary artery banding resulted in RV hypertrophy and dilatation accompanied by systolic and diastolic dysfunction. Invasive RV haemodynamic measurements demonstrated an increased end-systolic elastance and arterial elastance after pulmonary artery banding compared with sham operation, resulting in ventricular-arterial decoupling. Regression analysis revealed that tricuspid annular plane systolic excursion is correlated with ventricular-arterial coupling (r² = 0.77, P = 0.002) rather than with RV contractility (r² = -0.61, P = 0.07). Furthermore, the isovolumic relaxation time to ECG-derived R-R interval and the ratio of the early diastolic peak velocity measured by pulsed wave Doppler to the early diastolic peak obtained during tissue Doppler imaging correlate well with RV end-diastolic pressure (r² = 0.87, P = 0.0001 and r² = 0.82, P = 0.0009, respectively). Commonly used indices of systolic RV function are associated with RV-arterial coupling rather than contractility, whereas diastolic indices well correlate with end-diastolic pressure when there is maintained pressure overload.

Mesenchymal stromal cell therapy reduces lung inflammation and vascular remodeling and improves hemodynamics in experimental pulmonary arterial hypertension

Background

Experimental research has reported beneficial effects of mesenchymal stromal cell (MSC) therapy in pulmonary arterial hypertension (PAH). However, these studies either were based on prophylactic protocols or assessed basic remodeling features without evaluating possible mechanisms. We analyzed the effects of MSC therapy on lung vascular remodeling and hemodynamics and its possible mechanisms of action in monocrotaline (MCT)-induced PAH.

Methods

Twenty-eight Wistar rats were randomly divided into two groups. In the PAH group, animals received MCT 60 mg/kg intraperitoneally, while a control group received saline (SAL) instead. On day 14, both groups were further randomized to receive 10⁵ adipose-derived MSCs or SAL intravenously (n = 7/group). On day 28, right ventricular systolic pressure (RVSP) and the gene expression of mediators associated with apoptosis, inflammation, fibrosis, Smad-1 levels, cell proliferation, and endothelial–mesenchymal transition were determined. In addition, lung histology (smooth muscle cell proliferation and plexiform-like injuries), CD68⁺ and CD163⁺ macrophages, and plasma levels of vascular endothelial growth factor (VEGF) and platelet-derived growth factor (PDGF) were evaluated.

Results

In the PAH group, adipose-derived MSCs, compared to SAL, reduced mean RVSP (29 ± 1 vs 39 ± 2 mmHg, p < 0.001), lung tissue collagen fiber content, smooth muscle cell proliferation, CD68⁺ macrophages, interleukin-6 expression, and the antiapoptotic mediators Bcl-2 and survivin. Conversely, expression of the proapoptotic mediator procaspase-3 and plasma VEGF increased, with no changes in PDGF. In the pulmonary artery, MSCs dampened the endothelial–mesenchymal transition.

Conclusion

In MCT-induced PAH, MSC therapy reduced lung vascular remodeling, thus improving hemodynamics. These beneficial effects were associated with increased levels of proapoptotic markers, mesenchymal-to-endothelial transition, reduced cell proliferation markers, and inflammation due to a shift away from the M1 phenotype.

Electronic supplementary material

The online version of this article (doi:10.1186/s13287-017-0669-0) contains supplementary material, which is available to authorized users.

Therapeutic effect of prostaglandin E1 in monocrotaline-induced pulmonary arterial hypertension rats

Pulmonary arterial hypertension (PAH) is a severe pulmonary vascular disease characterized by sustained increase in pulmonary arterial pressure and excessive thickening and remodeling of distal small pulmonary arteries. During disease progression, PAH include increase in mean pulmonary arterial pressure, right ventricular (RV) enlargement, increased pulmonary vascular resistance, and smooth muscle hypertrophy in pulmonary arterioles. Several anti-PAH therapies targeting various pathways involved in PAH progression have been approved by the Food and Drug Adminstration. However, many of the currently available anti-PAH drugs suffer from a number of limitations, including short biological half-life, and poor pulmonary selectivity. Prostaglandin E1 (PGE1) is a potent vasodilator with selectivity toward pulmonary circulation when it is administered via the pulmonary route. However, PGE1 has a very short half-life of 5–10 minutes. Therefore, we hypothesized that long-term effect of PGE1 could reduce mal-adaptive structural remodeling of the lung and heart and prevent ventricular arrhythmias in monocrotaline-induced rat model of PAH. Our results revealed that PGE1 reduced ventricular hypertrophy, protein expressions of endothelin-1 and endothelin receptor A, and the expression of fibrosis. These results support the notion that PGE1 can improve the functional properties of RV, highlighting its potential benefits for heart and lung impairment.

Altered mTOR and Beclin-1 mediated autophagic activation during right ventricular remodeling in monocrotaline-induced pulmonary hypertension

Background

Right ventricular structure and function is a major predictor of outcomes in pulmonary hypertension (PH), yet the underlying mechanisms remain poorly understood. Growing evidence suggests the importance of autophagy in cardiac remodeling; however, its dynamics in the process of right ventricle(RV) remodeling in PH has not been fully explored. We sought to study the time course of cardiomyocyte autophagy in the RV in PH and determine whether mammalian target of rapamycin (mTOR) and Beclin-1 hypoxia-related pro-autophagic pathways are underlying mechanisms.

Methods

Rats were studied at 2, 4, and 6 weeks after subcutaneous injection of 60 mg/kg monocrotaline (MCT) (MCT-2 W, 4 W, 6 W) or vehicle (CON-2 W, 4 W, 6 W). Cardiac hemodynamics and RV function were assessed in rats. Autophagy structures and markers were assessed using transmission electron microscope, RT-qPCR, immunohistochemistry staining, and western blot analyses. Western blot was also used to quantify the expression of mTOR and Beclin-1 mediated pro-autophagy signalings in the RV.

Results

Two weeks after MCT injection, pulmonary artery systolic pressure increased and mild RV hypertrophy without RV dilation was observed. RV enlargement presented at 4 weeks with moderately decreased function, whereas typical characteristics of RV decompensation and failure occurred at 6 weeks thus demonstrating the progression of RV remodeling in the MCT model. A higher LC3 (microtubule- associated protein light chain 3) II/I ratio, upregulated LC3 mRNA and protein levels, as well as accumulation of autophagosomes in RV of MCT rats indicated autophagy induction. Autophagy activation was coincident with increased pulmonary artery systolic pressure. Pro-autophagy signaling pathways were activated in a RV remodeling stage-dependent manner since phospho-AMPK (adenosine monophosphate-activated protein kinase)-α were primarily upregulated and phospho-mTOR suppressed in the RV at 2 and 4 weeks post-MCT injection, whearas, BNIP3 (Bcl2-interacting protein 3) and beclin-1 expression were relatively low during these stages, they were significantly upregulated after 6 weeks in this model.

Conclusions

Our findings provide evidence of sustained activation of autophagy in RV remodeling of MCT induced PH model, while pro-autophagic signaling pathways varied depending on the phase.

Pulmonary Perfusion and Ventilation during Cardiopulmonary Bypass Are Not Associated with Improved Postoperative Outcomes after Cardiac Surgery

OBJECTIVES

Clinical trials of either pulmonary perfusion or ventilation during cardiopulmonary bypass (CBP) are equivocal. We hypothesized that to achieve significant improvement in outcomes both interventions had to be concurrent.

DESIGN

Retrospective case-control study.

SETTINGS

Major academic tertiary referral medical center.

PARTICIPANTS

Two hundred seventy-four consecutive patients who underwent open heart surgery with CBP 2009-2013.

INTERVENTIONS

The outcomes of 86 patients who received pulmonary perfusion and ventilation during CBP were retrospectively compared to the control group of 188 patients.

MEASUREMENTS AND MAIN RESULTS

Respiratory complications rates were similar in both groups (33.7 vs. 33.5%), as were the rates of postoperative pneumonia (4.7 vs. 4.3%), pleural effusions (13.9 vs. 12.2%), and re-intubations (9.3 vs. 9.1%). Rates of adverse postoperative cardiac events including ventricular tachycardia (9.3 vs. 8.5%) and atrial fibrillation (33.7 vs. 28.2%) were equivalent in both groups. Incidence of sepsis (8.1 vs. 5.3%), postoperative stroke (2.3 vs. 2.1%), acute kidney injury (2.3 vs. 3.7%), and renal failure (5.8 vs. 3.7%) was likewise comparable. Despite similar transfusion requirements, coagulopathy (12.8 vs. 5.3%, p = 0.031) and the need for mediastinal re-exploration (17.4 vs. 9.6%, p = 0.0633) were observed more frequently in the pulmonary perfusion and ventilation group, but the difference did not reach the statistical significance. Intensive care unit (ICU) and hospital stays, and the ICU readmission rates (7.0 vs. 8.0%) were similar in both groups.

CONCLUSION

Simultaneous pulmonary perfusion and ventilation during CBP were not associated with improved clinical outcomes.

Distinct right ventricle remodeling in response to pressure overload in the rat

Pulmonary arterial hypertension (PAH), the most serious chronic disorder of the pulmonary circulation, is characterized by pulmonary vasoconstriction and remodeling, resulting in increased afterload on the right ventricle (RV). In fact, RV function is the main determinant of prognosis in PAH. The most frequently used experimental models of PAH include monocrotaline- and chronic hypoxia-induced PAH, which primarily affect the pulmonary circulation. Alternatively, pulmonary artery banding (PAB) can be performed to achieve RV overload without affecting the pulmonary vasculature, allowing researchers to determine the RV-specific effects of their drugs/interventions. In this work, using two different degrees of pulmonary artery constriction, we characterize, in full detail, PAB-induced adaptive and maladaptive remodeling of the RV at 3 wk after PAB surgery. Our results show that application of a mild constriction resulted in adaptive hypertrophy of the RV, with preserved systolic and diastolic function, while application of a severe constriction resulted in maladaptive hypertrophy, with chamber dilation and systolic and diastolic dysfunction up to the isolated cardiomyocyte level. By applying two different degrees of constriction, we describe, for the first time, a reliable and short-duration PAB model in which RV adaptation can be distinguished at 3 wk after surgery. We characterize, in full detail, structural and functional changes of the RV in its response to moderate and severe constriction, allowing researchers to better study RV physiology and transition to dysfunction and failure, as well as to determine the effects of new therapies.

Challenges and opportunities in treating inflammation associated with pulmonary hypertension

INTRODUCTION

Inflammatory cells are present in the lungs from patients with many, if not all, forms of severe pulmonary hypertension.

AREAS COVERED

Historically the first inflammatory cell identified in the pulmonary vascular lesions was the mast cell. T and B lymphocytes, as well as macrophages, are present in and around the pulmonary arterioles and many patients have elevated blood levels of interleukin 1 and 6; some patients show elevated levels of leukotriene B4. An overlap between collagen-vascular disease-associated pulmonary arterial hypertension (PAH) and idiopathic PAH exists, yet only a few studies have been designed that evaluate the effect of anti-inflammatory treatments. Here we review the pertinent data that connect PAH and inflammation/autoimmune dysregulation and evaluate experimental models of severe PAH with an emphasis on the Sugen/athymic rat model of severe PAH. Expert commentary: We postulate that there are several inflammatory phenotypes and predict that there will be several anti-inflammatory treatment strategies for severe PAH.

Reduced immunoreactivities of B-type natriuretic peptide in pulmonary arterial hypertension rats after ranolazine treatment

Pulmonary arterial hypertension (PAH) is a severe pulmonary vascular disease characterized by sustained increase in the pulmonary arterial pressure and excessive thickening and remodeling of the distal small pulmonary arteries. During disease progression, structural remodeling of the right ventricular (RV) impairs pump function, creates pro-arrhythmic substrates and triggers for arrhythmias. Notably, RV failure and lethal arrhythmias are major contributors to cardiac death in PAH that are not directly addressed by currently available therapies. Ranolazine (RAN) is an anti-anginal, anti-ischemic drug that has cardioprotective effects of heart dysfunction. RAN also has anti-arrhythmic effects due to inhibition of the late sodium current in cardiomyocytes. Therefore, we hypothesized that RAN could reduce the mal-adaptive structural remodeling of the RV, and prevent triggered ventricular arrhythmias in the monocrotaline-induced rat model of PAH. RAN reduced ventricular hypertrophy, reduced levels of B-type natriuretic peptide, and decreased the expression of fibrosis. In addition, RAN prevented cardiovascular death in rat model of PAH. These results support the notion that RAN can improve the functional properties of the RV, highlighting its potential benefits in the setting of heart impairment.

The right ventricle and pulmonary hypertension

In patients with pulmonary hypertension (PH), the primary cause of death is right ventricular (RV) failure. Improvement in RV function is therefore one of the most important treatment goals. In order to be able to reverse RV dysfunction and also prevent RV failure, a detailed understanding of the pathobiology of RV failure and the underlying mechanisms concerning the transition from a pressure-overloaded adapted right ventricle to a dilated and failing right ventricle is required. Here, we propose that insufficient RV contractility, myocardial fibrosis, capillary rarefaction, and a disturbed metabolism are important features of a failing right ventricle. Furthermore, an overview is provided about the potential direct RV effects of PH-targeted therapies and the effects of RV-directed medical treatments.

Neuregulin-1 improves right ventricular function and attenuates experimental pulmonary arterial hypertension

AIMS

Pulmonary arterial hypertension (PAH) is a serious disease that affects both the pulmonary vasculature and the right ventricle (RV). Current treatment options are insufficient. The cardiac neuregulin (NRG)-1/ErbB system is deregulated during heart failure, and treatment with recombinant human NRG-1 (rhNRG-1) has been shown to be beneficial in animal models and in patients with left ventricular (LV) dysfunction. This study aimed to evaluate the effects of rhNRG-1 in RV function and pulmonary vasculature in monocrotaline (MCT)-induced PAH and RV hypertrophy (RVH).

METHODS AND RESULTS

Male wistar rats (7- to 8-weeks old, n = 78) were injected with MCT (60 mg/kg, s.c.) or saline and treated with rhNRG-1 (40 µg/kg/day) or vehicle for 1 week, starting 2 weeks after MCT administration. Another set of animals was submitted to pulmonary artery banding (PAB) or sham surgery, and followed the same protocol. MCT administration resulted in the development of PAH, pulmonary arterial and RV remodelling, and dysfunction, and increased RV markers of cardiac damage. Treatment with rhNRG-1 attenuated RVH, improved RV function, and decreased RV expression of disease markers. Moreover, rhNRG-1 decreased pulmonary vascular remodelling and attenuated MCT-induced endothelial dysfunction. The anti-remodelling effects of rhNRG-1 were confirmed in the PAB model, where rhNRG-1 treatment was able to attenuate PAB-induced RVH.

CONCLUSION

rhNRG-1 treatment attenuates pulmonary arterial and RV remodelling, and dysfunction in a rat model of MCT-induced PAH and has direct anti-remodelling effects on the pressure-overloaded RV.