Characterization of a rat model of right-sided heart failure induced by pulmonary trunk banding

Hypertrophy of the right ventricle by pulmonary artery banding in rats: a study of structural, functional, and transcriptomics alterations in the right and left ventricles

Introduction: Right ventricular remodeling with subsequent functional impairment can occur in some clinical conditions in adults and children. The triggering factors, molecular mechanisms, and, especially, the evolution over time are still not well known. Left ventricular (LV) changes associated with right ventricular (RV) remodeling are also poorly understood. Objectives: The study aimed to evaluate RV morphological, functional, and gene expression parameters in rats submitted to pulmonary artery banding compared to control rats, with the temporal evolution of these parameters, and to analyze the influence of RV remodeling by pulmonary artery banding in rats and their controls over time on LV geometry, histology, gene expression, and functional performance. Methods: Healthy 6-week-old male Wistar-EPM rats weighing 170-200 g were included. One day after the echocardiogram, depending on the animals undergoing the pulmonary artery banding (PAB) procedure or not (control group), they were then randomly divided into subgroups according to the follow-up time: 72 h, or 2, 4, 6, or 8 weeks. In each subgroup, the following were conducted: a new echocardiogram, a hemodynamic study, the collection of material for morphological analysis (hypertrophy and fibrosis), and molecular biology (gene expression). The results were presented as the mean ± standard deviation of the mean. A two-way ANOVA and Tukey post-test compared the variables of the subgroups and evolution follow-up times. The adopted significance level was 5%. Results: There was no significant difference among the subgroups in the percentage of water in both the lungs and the liver (the percentage of water in the lungs ranged from 76% to 78% and that of the liver ranged from 67% to 71%). The weight of the right chambers was significantly higher in PAB animals in all subgroups (RV PAB weighed from 0.34 to 0.48 g, and control subjects, from 0.17 to 0.20 g; right atrium (RA) with PAB from 0.09 to 0.14 g; and control subjects from 0.02 to 0.03 g). In the RV of PAB animals, there was a significant increase in myocyte nuclear volume (97 μm3-183.6 μm3) compared to control subjects (34.2 μm3-57.2 μm3), which was more intense in subgroups with shorter PAB follow-up time, and the fibrosis percentage (5.9%-10.4% vs. 0.96%-1.18%) was higher as the PAB follow-up time was longer. In the echocardiography result, there was a significant increase in myocardial thickness in all PAB groups (0.09-0.11 cm compared to control subjects-0.04-0.05 cm), but there was no variation in RV diastolic diameter. From 2 to 8 weeks of PAB, the S-wave (S') (0.031 cm/s and 0.040 cm/s), and fractional area change (FAC) (51%-56%), RV systolic function parameters were significantly lower than those of the respective control subjects (0.040 cm/s to 0.050 cm/s and 61%-67%). Furthermore, higher expression of genes related to hypertrophy and extracellular matrix in the initial subgroups and apoptosis genes in the longer follow-up PAB subgroups were observed in RV. On the other hand, LV weight was not different between animals with and without PAB. The nuclear volume of the PAB animals was greater than that of the control subjects (74 μm3-136 μm3; 40.8 μm3-46.9 μm3), and the percentage of fibrosis was significantly higher in the 4- and 8-week PAB groups (1.2% and 2.2%) compared to the control subjects (0.4% and 0.7%). Echocardiography showed that the diastolic diameter and LV myocardial thickness were not different between PAB animals and control subjects. Measurements of isovolumetric relaxation time and E-wave deceleration time at the echocardiography were different between PAB animals and control subjects in all subgroups, but there were no changes in diastolic function in the hemodynamic study. There was also increased expression of genes related to various functions, particularly hypertrophy. Conclusion: 1) Rats submitted to pulmonary artery banding presented RV remodeling compatible with hypertrophy. Such alterations were mediated by increased gene expression and functional alterations, which coincide with the onset of fibrosis. 2) Structural changes of the RV, such as weight, myocardial thickness, myocyte nuclear volume, and degree of fibrosis, were modified according to the time of exposure to pulmonary artery banding and related to variations in gene expression, highlighting the change from an alpha to a beta pattern from early to late follow-up times. 3) The study suggests that the left ventricle developed histological alterations accompanied by gene expression modifications simultaneously with the alterations found in the right ventricle.

A review on experimental surgical models and anesthetic protocols of heart failure in rats

Heart failure (HF) is a serious health and economic burden worldwide, and its prevalence is continuously increasing. Current medications effectively moderate the progression of symptoms, and there is a need for novel preventative and reparative treatments. The development of novel HF treatments requires the testing of potential therapeutic procedures in appropriate animal models of HF. During the past decades, murine models have been extensively used in fundamental and translational research studies to better understand the pathophysiological mechanisms of HF and develop more effective methods to prevent and control congestive HF. Proper surgical approaches and anesthetic protocols are the first steps in creating these models, and each successful approach requires a proper anesthetic protocol that maintains good recovery and high survival rates after surgery. However, each protocol may have shortcomings that limit the study's outcomes. In addition, the ethical regulations of animal welfare in certain countries prohibit the use of specific anesthetic agents, which are widely used to establish animal models. This review summarizes the most common and recent surgical models of HF and the anesthetic protocols used in rat models. We will highlight the surgical approach of each model, the use of anesthesia, and the limitations of the model in the study of the pathophysiology and therapeutic basis of common cardiovascular diseases.

Animal models of pulmonary hypertension: Getting to the heart of the problem

Despite recent therapeutic advances, pulmonary hypertension (PH) remains a fatal disease due to the development of right ventricular (RV) failure. At present, no treatments targeted at the right ventricle are available, and RV function is not widely considered in the preclinical assessment of new therapeutics. Several small animal models are used in the study of PH, including the classic models of exposure to either hypoxia or monocrotaline, newer combinational and genetic models, and pulmonary artery banding, a surgical model of pure RV pressure overload. These models reproduce selected features of the structural remodelling and functional decline seen in patients and have provided valuable insight into the pathophysiology of RV failure. However, significant reversal of remodelling and improvement in RV function remains a therapeutic obstacle. Emerging animal models will provide a deeper understanding of the mechanisms governing the transition from adaptive remodelling to a failing right ventricle, aiding the hunt for druggable molecular targets.

Transthoracic echocardiography: from guidelines for humans to cardiac ultrasound of the heart in rats

Ultrasound examination of the heart is a cornerstone of clinical evaluation of patients with established or suspected cardiovascular conditions. Advancements in ultrasound imaging technology have brought transthoracic echocardiography to preclinical murine models of cardiovascular diseases. The translational potential of cardiac ultrasound is critically important in rat models of myocardial infarction and ischemia-reperfusion injury, congestive heart failure, arterial hypertension, cardiac hypertrophy, pulmonary hypertension, right heart failure, Takotsubo cardiomyopathy, hypertrophic and dilated cardiomyopathies, developmental disorders, and metabolic syndrome. Modern echocardiographic machines capable of high-frame-rate image acquisition and fitted with high-frequency transducers allow for cardiac ultrasound in rats that yields most of the echocardiographic measurements and indices recommended by international guidelines for cardiac ultrasound in human patients. Among them are dimensions of cardiac chambers and walls, indices of systolic and diastolic cardiac function, and valvular function. In addition, measurements of cardiac dimensions and ejection fraction can be significantly improved by intravenous administration of ultrasound enhancing agents (UEAs). In this article we discuss echocardiography in rats, describe a technique for minimally invasive intravenous administration of UEAs via the saphenous vein and present a step-by-step approach to cardiac ultrasound in rats.

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.

Current animal models for the study of congestion in heart failure: an overview

Congestion (i.e., backward failure) is an important culprit mechanism driving disease progression in heart failure. Nevertheless, congestion remains often underappreciated and clinicians underestimate the importance of congestion on the pathophysiology of decompensation in heart failure. In patients, it is however difficult to study how isolated congestion contributes to organ dysfunction, since heart failure and chronic kidney disease very often coexist in the so-called cardiorenal syndrome. Here, we review the existing relevant and suitable backward heart failure animal models to induce congestion, induced in the left- (i.e., myocardial infarction, rapid ventricular pacing) or right-sided heart (i.e., aorta-caval shunt, mitral valve regurgitation, and monocrotaline), and more specific animal models of congestion, induced by saline infusion or inferior vena cava constriction. Next, we examine critically how representative they are for the clinical situation. After all, a relevant animal model of isolated congestion offers the unique possibility of studying the effects of congestion in heart failure and the cardiorenal syndrome, separately from forward failure (i.e., impaired cardiac output). In this respect, new treatment options can be discovered.

Effects of chronic treprostinil treatment on experimental right heart hypertrophy and failure

BACKGROUND

Right heart function is an important predictor of morbidity and mortality in pulmonary arterial hypertension and many CHD. We investigated whether treatment with the prostacyclin analogue treprostinil could prevent pressure overload-induced right ventricular hypertrophy and failure.

METHODS

Male Wistar rats were randomised to severe pulmonary trunk banding with a 0.5-mm banding clip (n=41), moderate pulmonary trunk banding with a 0.6-mm banding clip (n=36), or sham procedure (n=10). The banded rats were randomised to 6 weeks of treatment with a moderate dose of treprostinil (300 ng/kg/minute), a high dose of treprostinil (900 ng/kg/minute), or vehicle.

RESULTS

Pulmonary trunk banding effectively induced hypertrophy, dilatation, and decreased right ventricular function. The severely banded animals presented with decompensated heart failure with extracardial manifestations. Treatment with treprostinil neither reduced right ventricular hypertrophy nor improved right ventricular function.

CONCLUSIONS

In the pulmonary trunk banding model of pressure overload-induced right ventricular hypertrophy and failure, moderate- and high-dose treatment with treprostinil did not improve right ventricular function neither in compensated nor in decompensated right heart failure.

Transmural dispersion of repolarization and cardiac remodeling in ventricles of rabbit with right ventricular hypertrophy

INTRODUCTION

Recent publications demonstrated that rabbits with right ventricular hypertrophy (RVH) possess high sensitivity and specificity for drug-induced arrhythmias. However, the underlying mechanism has not been elucidated. This study aimed to evaluate RVH induced changes in cardiac remodeling especially the transmural dispersion of repolarization (TDR), epicardial monophasic action potentials (MAP), and hERG mRNA expression in rabbits.

METHODS

New Zealand White rabbits (n=13) were divided into 2 groups: sham operated (SHAM, n=6) and pulmonary artery banding (PAB, n=7). PAB was induced by narrowing the pulmonary artery. Twenty weeks after surgery, hemodynamic, cardiac function, electrocardiograms, and MAP were obtained from PAB compared with SHAM. After measurement, rabbits were sacrificed to collect ventricular myocardium for histopathological analysis and measurement of hERG mRNA expression by real time PCR.

RESULTS

After 20weeks, the % HW to BW ratio of whole heart and right ventricle (RV) and left and right ventricular free wall thickness was significantly increased in PAB when compared with those in SHAM. PAB has a significant electrical remodeling as demonstrated by lengthening of QT, QTc intervals, and increased Tp-Te duration. PAB also has a significant functional remodeling verified by decreased contractility index of RV and lengthened time constant of relaxation of LV. MAP of RV epicardium was significantly shortened in PAB consistently with increased hERG mRNA expression at the epicardium of RV.

DISCUSSION

The rabbit with PAB demonstrates cardiac remodeling diastolic and systolic dysfunctions. These rabbits also demonstrate increased TDR and electrical remodeling related to the change of hERG mRNA expression which may be prone to develop arrhythmias.

Iloprost improves ventricular function in the hypertrophic and functionally impaired right heart by direct stimulation

Right heart function is an important predictor of morbidity and mortality in patients suffering from pulmonary arterial hypertension and congenital heart diseases. We investigated whether the prostacyclin analog iloprost has a direct inotropic effect in the pressure-overloaded hypertrophic and dysfunctional right ventricle (RV). Rats were randomized to monocrotaline injection (60 mg/kg; [Formula: see text]), pulmonary trunk banding (PTB; [Formula: see text]), or a sham operation ([Formula: see text]). RV function was evaluated with magnetic resonance imaging, echocardiography, and invasive pressure measurements at baseline, after intravenous administration of placebo, iloprost 10 ng/kg/min, or iloprost 100 ng/kg/min (Ilo100). Infusion of Ilo100 induced a [Formula: see text] ([Formula: see text]) increase in stroke volume in the sham group and a [Formula: see text] ([Formula: see text]) increase in the PTB group. RV [Formula: see text] was elevated by [Formula: see text] ([Formula: see text]) in the sham group and by [Formula: see text] ([Formula: see text]) in the PTB group. An elevation in cardiac output of [Formula: see text] ([Formula: see text]) and an [Formula: see text] ([Formula: see text]) increase in RV systolic pressure were found in the PTB group. Iloprost caused a decrease in mean arterial blood pressure (MAP) in all groups of animals. An equal reduction in MAP induced by the arterial vasodilator nitroprusside did not improve any of the measured parameters of RV function. We conclude that iloprost has inotropic properties directly improving ventricular function in the hypertrophic and dysfunctional right heart of the rat.

Acute effects of sildenafil and dobutamine in the hypertrophic and failing right heart in vivo

Abstract The purpose of this study was to investigate whether acute intravenous administration of the phosphodiesterase type 5 (PDE-5) inhibitor sildenafil in a single clinically relevant dose improves the in vivo function of the hypertrophic and failing right ventricle (RV). Wistar rats ([Formula: see text]) were subjected to pulmonary trunk banding (PTB) causing RV hypertrophy and failure. Four weeks after surgery, they were randomized to receive an intravenous bolus dose of sildenafil (1 mg/kg; [Formula: see text]), vehicle ([Formula: see text]), or dobutamine (10 μg/kg; [Formula: see text]). Invasive RV pressures were recorded continuously, and transthoracic echocardiography was performed 1, 5, 15, 25, 35, 50, 70, and 90 minutes after injecting the bolus. Cardiac function was compared to baseline measurements to evaluate the in vivo effects of each specific treatment. The PTB procedure caused significant hypertrophy, cardiac fibrosis, and reduction in RV function evaluated by echocardiography (TAPSE) and invasive pressure measurements. Sildenafil did not improve the function of the hypertrophic failing right heart in vivo, measured by TAPSE, RV systolic pressure (RVsP), and dp/dtmax. Dobutamine improved RV function 1 minute after injection measured by TAPSE ([Formula: see text] vs. [Formula: see text] cm; [Formula: see text]), RVsP ([Formula: see text] vs. [Formula: see text] mmHg; [Formula: see text]), and dp/dtmax ([Formula: see text] vs. [Formula: see text] mmHg/s; [Formula: see text]). Acute administration of the PDE-5 inhibitor sildenafil in a single clinically relevant dose did not modulate the in vivo function of the hypertrophic failing right heart of the rat measured by echocardiography and invasive hemodynamics. In the same model, dobutamine acutely improved RV function.

Pressure load: the main factor for altered gene expression in right ventricular hypertrophy in chronic hypoxic rats

Background

The present study investigated whether changes in gene expression in the right ventricle following pulmonary hypertension can be attributed to hypoxia or pressure loading.

Methodology/Principal Findings

To distinguish hypoxia from pressure-induced alterations, a group of rats underwent banding of the pulmonary trunk (PTB), sham operation, or the rats were exposed to normoxia or chronic, hypobaric hypoxia. Pressure measurements were performed and the right ventricle was analyzed by Affymetrix GeneChip, and selected genes were confirmed by quantitative PCR and immunoblotting. Right ventricular systolic blood pressure and right ventricle to body weight ratio were elevated in the PTB and the hypoxic rats. Expression of the same 172 genes was altered in the chronic hypoxic and PTB rats. Thus, gene expression of enzymes participating in fatty acid oxidation and the glycerol channel were downregulated. mRNA expression of aquaporin 7 was downregulated, but this was not the case for the protein expression. In contrast, monoamine oxidase A and tissue transglutaminase were upregulated both at gene and protein levels. 11 genes (e.g. insulin-like growth factor binding protein) were upregulated in the PTB experiment and downregulated in the hypoxic experiment, and 3 genes (e.g. c-kit tyrosine kinase) were downregulated in the PTB and upregulated in the hypoxic experiment.

Conclusion/Significance

Pressure load of the right ventricle induces a marked shift in the gene expression, which in case of the metabolic genes appears compensated at the protein level, while both expression of genes and proteins of importance for myocardial function and remodelling are altered by the increased pressure load of the right ventricle. These findings imply that treatment of pulmonary hypertension should also aim at reducing right ventricular pressure.

Effects of phosphodiesterase-5 inhibition by sildenafil in the pressure overloaded right heart

BACKGROUND

Sustained pressure overload of the right ventricle (RV) causes RV hypertrophy and failure. Cyclic-GMP has previously been shown to modulate left ventricular hypertrophy.

AIM

To evaluate the effects of sildenafil, a phosphodiesterase-5 (PDE5) inhibitor elevating c-GMP, on myocardial hypertrophy and function in rats with RV hypertrophy.

METHODS

Rats were pulmonary trunk banded (PTB) and randomized to receive sildenafil (SIL) or vehicle (VEC) for three (n=14) and nine weeks (n=18). In addition, rats with established RV hypertrophy were randomized to SIL or VEC (n=17) three weeks after PTB. Right ventricular function was evaluated by echocardiography and RV hypertrophy by histology and RV weight.

RESULTS

Sildenafil failed to inhibit the development of RV hypertrophy when given for both 3 and 9 weeks. On the contrary, sildenafil increased RV hypertrophy after 3 weeks (RV/bodyweight: SIL 0.099+/-0.016 vs. VEC 0.081+/-0.011; p<0.05) and total heart weight after 9 weeks (SIL 1.05+/-0.10 vs. VEC 0.93+/-0.08 g; p<0.05). Sildenafil also failed to reverse established RV hypertrophy, but significantly improved RV myocardial function as measured by Tricuspid Annular Plane Systolic Excursion (TAPSE: SIL 1.85+/-0.027 vs. VEC 1.39+/-0.037 mm; p<0.05).

CONCLUSION

PDE5 inhibition by sildenafil failed to prevent or reverse RV hypertrophy in rats operated by pulmonary trunk banding. It actually increased RV hypertrophy and improved RV contractile function when given to rats with established RV hypertrophy.