Chris Happé

Opposite Effects of Training in Rats With Stable and Progressive Pulmonary Hypertension

Background— Exercise training in pulmonary arterial hypertension (PH) is a promising adjunct to medical treatment. However, it is still unclear whether training is beneficial for all PH patients. We hypothesized that right ventricular adaptation plays a pivotal role in the response to training. Methods and Results— Two different dosages of monocrotaline were used in rats to model stable PH with preserved cardiac output and progressive PH developing right heart failure. Two weeks after injection, PH was confirmed by echocardiography, and treadmill training was initiated. Rats were trained for 4 weeks unless manifest right heart failure developed earlier. At the end of the study protocol, all rats were functionally assessed by endurance testing, echocardiography, and invasive pressure measurements. Lungs and hearts were further analyzed in quantitative histomorphologic analyses. In stable PH, exercise training was well tolerated and markedly increased exercise endurance (from 25±3.9 to 62±3.9 minutes; P<0.001). Moreover, capillary density increased significantly (from 1.21±0.12 to 1.51±0.07 capillaries per cardiomyocyte; P<0.05). However, in progressive PH, exercise training worsened survival (hazard ratio, 2.7; 95% confidence interval, 1.1 to 14.2) and increased pulmonary vascular remodeling. In addition, training induced widespread leukocyte infiltration into the right ventricle (from 135±14 to 276±18 leukocytes per 1 mm2; P<0.001). Conclusions— In our rat model, exercise training was found to be beneficial in stable PH but detrimental in progressive PH. Future studies are necessary to address the clinical implications of our findings.

SuHx rat model: partly reversible pulmonary hypertension and progressive intima obstruction

The SU5416 combined with hypoxia (SuHx) rat model features angio-obliterative pulmonary hypertension resembling human pulmonary arterial hypertension. Despite increasing use of this model, a comprehensive haemodynamic characterisation in conscious rats has not been reported. We used telemetry to characterise haemodynamic responses in SuHx rats and associated these with serial histology. Right ventricular systolic pressure (RVSP) increased to a mean±sd of 106±7 mmHg in response to SuHx and decreased but remained elevated at 72±8 mmHg upon return to normoxia. Hypoxia-only exposed rats showed a similar initial increase in RVSP, a lower maximum RVSP and near-normalisation of RVSP during subsequent normoxia. Progressive vascular remodelling consisted of a four-fold increase in intima thickness, while only minimal changes in media thickness were found. The circadian range in RVSP provided an accurate longitudinal estimate of vascular remodelling. In conclusion, in SuHx rats, re-exposure to normoxia leads to a partial decrease in pulmonary artery pressure, with persisting hypertension and pulmonary vascular remodelling characterised by progressive intima obstruction. Telemetry studies can facilitate preclinical studies to further improve our understanding of drug actions in PAH http://ow.ly/uXhjf

Bone Morphogenetic Protein Receptor Type 2 Mutation in Pulmonary Arterial Hypertension: A View on the Right Ventricle.

Background— The effect of a mutation in the bone morphogenetic protein receptor 2 (BMPR2) gene on right ventricular (RV) pressure overload in patients with pulmonary arterial hypertension is unknown. Therefore, we investigated RV function in patients who have pulmonary arterial hypertension with and without the BMPR2 mutation by combining in vivo measurements with molecular and histological analysis of human RV and left ventricular tissue. Methods and Results— In total, 95 patients with idiopathic or familial pulmonary arterial hypertension were genetically screened for the presence of a BMPR2 mutation: 28 patients had a BMPR2 mutation, and 67 patients did not have a BMPR2 mutation. In vivo measurements were assessed using right heart catheterization and cardiac MRI. Despite a similar mean pulmonary artery pressure (noncarriers 54±15 versus mutation carriers 55±9 mm Hg) and pulmonary vascular resistance (755 [483–1043] versus 931 [624–1311] dynes·s−1·cm−5), mutation carriers presented with a more severely compromised RV function (RV ejection fraction: 37.6±12.8% versus 29.0±9%: P<0.05; cardiac index 2.7±0.9 versus 2.2±0.4 L·min−1·m−2). Differences continued to exist after treatment. To investigate the role of transforming growth factor &bgr; and bone morphogenetic protein receptor II signaling, human RV and left ventricular tissue were studied in controls (n=6), mutation carriers (n=5), and noncarriers (n=11). However, transforming growth factor &bgr; and bone morphogenetic protein receptor II signaling, and hypertrophy, apoptosis, fibrosis, capillary density, inflammation, and cardiac metabolism, as well, were similar between mutation carriers and noncarriers. Conclusions— Despite a similar afterload, RV function is more severely affected in mutation carriers than in noncarriers. However, these differences cannot be explained by a differential transforming growth factor &bgr;, bone morphogenetic protein receptor II signaling, or cardiac adaptation.

Intravenous iron therapy in patients with idiopathic pulmonary arterial hypertension and iron deficiency.

In patients with idiopathic pulmonary arterial hypertension (iPAH), iron deficiency is common and has been associated with reduced exercise capacity and worse survival. Previous studies have shown beneficial effects of intravenous iron administration. In this study, we investigated the use of intravenous iron therapy in iron-deficient iPAH patients in terms of safety and effects on exercise capacity, and we studied whether altered exercise capacity resulted from changes in right ventricular (RV) function and skeletal muscle oxygen handling. Fifteen patients with iPAH and iron deficiency were included. Patients underwent a 6-minute walk test, cardiopulmonary exercise tests, cardiac magnetic resonance imaging, and a quadriceps muscle biopsy and completed a quality-of-life questionnaire before and 12 weeks after receiving a high dose of intravenous iron. The primary end point, 6-minute walk distance, was not significantly changed after 12 weeks (409 ± 110 m before vs. 428 ± 94 m after; P = 0.07). Secondary end points showed that intravenous iron administration was well tolerated and increased body iron stores in all patients. In addition, exercise endurance time (P < 0.001) and aerobic capacity (P < 0.001) increased significantly after iron therapy. This coincided with improved oxygen handling in quadriceps muscle cells, although cardiac function at rest and maximal V ͘ o 2 were unchanged. Furthermore, iron treatment was associated with improved quality of life (P < 0.05). In conclusion, intravenous iron therapy in iron-deficient iPAH patients improves exercise endurance capacity. This could not be explained by improved RV function; however, increased quadriceps muscle oxygen handling may play a role. (Trial registration: ClinicalTrials.gov identifier NCT01288651)

Histone Deacetylase Inhibition with Trichostatin a does not Reverse Severe Angioproliferative Pulmonary Hypertension in Rats (2013 Grover Conference Series)

Pulmonary arterial hypertension (PAH) is a rapidly progressive and devastating disease characterized by remodeling of lung vessels, increased pulmonary vascular resistance, and eventually right ventricular hypertrophy and failure. Because histone deacetylase (HDAC) inhibitors are agents hampering tumor growth and cardiac hypertrophy, they have been attributed a therapeutic potential for patients with PAH. Outcomes of studies evaluating the use of HDAC inhibitors in models of PAH and right ventricular pressure overload have been equivocal, however. Here we describe the levels of HDAC activity in the lungs and hearts of rats with pulmonary hypertension and right heart hypertrophy or failure, experimentally induced by monocrotaline (MCT), the combined exposure to the VEGF-R inhibitor SU5416 and hypoxia (SuHx), and pulmonary artery banding (PAB). We show that HDAC activity levels are reduced in the lungs of rat with experimentally induced hypertension, whereas activity levels are increased in the hypertrophic hearts. In contrast to what was previously found in the MCT model, the HDAC inhibitor trichostatin A had no effect on pulmonary vascular remodeling in the SuHx model. When our results and those in the published literature are taken together, it is suggested that the effects of HDAC inhibitors in humans with PAH and associated RV failure are, at best, unpredictable. Significant progress can perhaps be made by using more specific HDAC inhibitors, but before clinical tests in human PAH can be undertaken, careful preclinical studies are required to determine potential cardiotoxicity.

Left ventricular outflow tract gradient is associated with reduced capillary density in hypertrophic cardiomyopathy irrespective of genotype.

Coronary microvascular dysfunction (CMD) is an important feature of hypertrophic cardiomyopathy (HCM), which contributes negatively to symptoms and long‐term outcome. Previous in vivo imaging studies in HCM suggest that left ventricular outflow tract (LVOT) gradient and genetic status are important contributors to CMD. CMD may be caused by reduced capillary density. Here, we investigated whether a reduction in capillary density is related to genetic status or LVOT gradient severity in an in vitro study of HCM cardiac samples.

Renal Denervation Reduces Pulmonary Vascular Remodeling and Right Ventricular Diastolic Stiffness in Experimental Pulmonary Hypertension

Neurohormonal overactivation plays an important role in pulmonary hypertension (PH). In this context, renal denervation, which aims to inhibit the neurohormonal systems, may be a promising adjunct therapy in PH. In this proof-of-concept study, we have demonstrated in 2 experimental models of PH that renal denervation delayed disease progression, reduced pulmonary vascular remodeling, lowered right ventricular afterload, and decreased right ventricular diastolic stiffness, most likely by suppression of the renin-angiotensin-aldosterone system.

Pneumonectomy combined with SU5416 induces severe pulmonary hypertension in rats

The SU5416 + hypoxia (SuHx) rat model is a commonly used model of severe pulmonary arterial hypertension. While it is known that exposure to hypoxia can be replaced by another type of hit (e.g., ovalbumin sensitization) it is unknown whether abnormal pulmonary blood flow (PBF), which has long been known to invoke pathological changes in the pulmonary vasculature, can replace the hypoxic exposure. Here we studied if a combination of SU5416 administration combined with pneumonectomy (PNx), to induce abnormal PBF in the contralateral lung, is sufficient to induce severe pulmonary arterial hypertension (PAH) in rats. Sprague Dawley rats were subjected to SuPNx protocol (SU5416 + combined with left pneumonectomy) or standard SuHx protocol, and comparisons between models were made at week 2 and 6 postinitiation. Both SuHx and SuPNx models displayed extensive obliterative vascular remodeling leading to an increased right ventricular systolic pressure at week 6 Similar inflammatory response in the lung vasculature of both models was observed alongside increased endothelial cell proliferation and apoptosis. This study describes the SuPNx model, which features severe PAH at 6 wk and could serve as an alternative to the SuHx model. Our study, together with previous studies on experimental models of pulmonary hypertension, shows that the typical histopathological findings of PAH, including obliterative lesions, inflammation, increased cell turnover, and ongoing apoptosis, represent a final common pathway of a disease that can evolve as a consequence of a variety of insults to the lung vasculature.

Levosimendan prevents and reverts right ventricular failure in experimental pulmonary arterial hypertension.

Background: We investigated whether chronic levosimendan treatment can prevent and revert right ventricular (RV) failure and attenuate pulmonary vascular remodeling in a rat model of pulmonary arterial hypertension (PAH). Methods and Results: PAH was induced in rats by exposure to SU5416 and hypoxia (SuHx). The rats were randomized to levosimendan (3 mg·kg−1·d−1) initiated before SuHx (n = 10, PREV), levosimendan started 6 weeks after SuHx (n = 12, REV), or vehicle treatment (n = 10, VEH). Healthy control rats received vehicle (n = 10, CONT). Ten weeks after SuHx, RV function was evaluated by echocardiography, magnetic resonance imaging, invasive pressure–volume measurements, histology, and biochemistry. Levosimendan treatment improved cardiac output (VEH vs. PREV 77 ± 7 vs. 137 ± 6 mL/min; P < 0.0001; VEH vs. REV 77 ± 7 vs. 117 ± 10 mL/min; P < 0.01) and decreased RV afterload compared with VEH (VEH vs. PREV 219 ± 33 vs. 132 ± 20 mm Hg/mL; P < 0.05; VEH vs. REV 219 ± 33 vs. 130 ± 11 mm Hg/mL; P < 0.01). In the PREV group, levosimendan restored right ventriculoarterial coupling (VEH vs. PREV 0.9 ± 0.1 vs. 1.8 ± 0.3; P < 0.05) and prevented the development of pulmonary arterial occlusive lesions (VEH vs. PREV 37 ± 7 vs. 15 ± 6% fully occluded lesions; P < 0.05). Conclusion: Chronic treatment with levosimendan prevents and reverts the development of RV failure and attenuates pulmonary vascular remodeling in a rat model of PAH.

p38 MAPK Inhibition Improves Heart Function in Pressure-Loaded Right Ventricular Hypertrophy

Abstract Although p38 mitogen‐activated protein kinase (MAPK) is known to have a role in ischemic heart disease and many other diseases, its contribution to the pathobiology of right ventricular (RV) hypertrophy and failure is unclear. Therefore, we sought to investigate the role of p38 MAPK in the pathophysiology of pressure overload‐induced RV hypertrophy and failure. The effects of the p38 MAPK inhibitor PH797804 were investigated in mice with RV hypertrophy/failure caused by exposure to hypoxia or pulmonary artery banding. In addition, the effects of p38 MAPK inhibition or depletion (by small interfering RNA) were studied in isolated mouse RV fibroblasts. Echocardiography, invasive hemodynamic measurements, immunohistochemistry, collagen assays, immunofluorescence staining, and Western blotting were performed. Expression of phosphorylated p38 MAPK was markedly increased in mouse and human hypertrophied/failed RVs. In mice, PH797804 improved RV function and inhibited cardiac fibrosis compared with placebo. In isolated RV fibroblasts, p38 MAPK inhibition reduced transforming growth factor (TGF)‐&bgr;‐induced collagen production as well as stress fiber formation. Moreover, p38 MAPK inhibition/depletion suppressed TGF‐&bgr;‐induced SMAD2/3 phosphorylation and myocardin‐related transcription factor A (MRTF‐A) nuclear translocation, and prevented TGF‐&bgr;‐induced cardiac fibroblast transdifferentiation. Moreover, p38 MAPK inhibition in mice exposed to pulmonary artery banding led to diminished nuclear levels of MRTF‐A and phosphorylated SMAD3 in RV fibroblasts. Together, our data indicate that p38 MAPK inhibition significantly improves RV function and inhibits RV fibrosis. Inhibition of p38 MAPK in RV cardiac fibroblasts, resulting in coordinated attenuation of MRTF‐A cytoplasmic‐nuclear translocation and SMAD3 deactivation, indicates that p38 MAPK signaling contributes to distinct disease‐causing mechanisms.