The orally active nonpeptide selective endothelin ETA receptor antagonist YM598 prevents and reverses the development of pulmonary hypertension in monocrotaline-treated rats

Magnolol ameliorates pneumonectomy and monocrotaline-induced pulmonary arterial hypertension in rats through inhibition of angiotensin II and endothelin-1 expression

BACKGROUND

Magnolol, a major bioactive component extracted from Magnolia officinalis, exerts several beneficial effects, such as anti-inflammatory and anti-hypertensive activities.

PURPOSE

In this study, we investigated whether magnolol has a protective effect on pneumonectomy and monocrotaline-induced pulmonary arterial hypertension (PAH) in rats.

DESIGN/METHODS

The alterations of right ventricular (RV) hypertrophy, pulmonary vascular remodeling, histopathological parameters, and related gene expression and signaling pathways in lungs by magnolol treatment were studied in the PAH rats.

RESULTS

Administration of magnolol greatly ameliorated the characteristic features of PAH, including increased pulmonary arterial pressure, RV hypertrophy, and pulmonary vascular remodeling. Moreover, magnolol inhibited angiotensin-converting enzyme (ACE)/angiotensin II (Ang II)/Ang II type 1 receptor (AT-1R) cascade, whereas upregulates ACE2 in the lungs of PAH rats. The overexpression of endothelin-1 (ET-1) and ET_A receptor occurred in the PAH rats was significantly attenuated by magnolol through inhibition of Akt/ERK1/2/GSK3β/β-catenin pathway. Compared with that of untreated PAH rats, higher expression of endothelial nitric oxide synthase, and lower expression of inducible nitric oxide synthase and O₂^- production in lungs were observed in magnolol-treated PAH rats.

CONCLUSION

We demonstrated that treatment with magnolol reduces the development of PAH induced by pneumonectomy and monocrotaline in rats, and suppressing Ang II and ET-1-mediated processes may contribute to its protective effects. These findings suggest that magnolol may be a potential agent for PAH therapy.

Macitentan reverses early obstructive pulmonary vasculopathy in rats: early intervention in overcoming the survivin-mediated resistance to apoptosis

It remains unknown whether current disease-targeting therapy can histologically reverse obstructive pulmonary vasculopathy and how the timing of the therapy influences the antiremodeling effects of the compound. We test the hypothesis that a novel endothelin receptor antagonist macitentan reverses the early and/or late stages of occlusive pulmonary vascular disease (PVD) in rats. Rats with pulmonary arterial hypertension (PAH), which were produced by combined exposure to a vascular endothelial growth factor receptor inhibitor Sugen 5416 and hypobaric hypoxia for 3 wk, were assigned to receive macitentan or vehicle during 3-5 wk (early study) or during 5-8 wk (late study) after Sugen injection. Compared with vehicle-treated PAH rats and PAH rats evaluated before treatment initiation, the macitentan-treated rats showed decreases in the proportion of occlusive lesions in the early study, a finding consistent with the reversal of right ventricular systolic pressure and indexes of right ventricular hypertrophy and medial wall thickness. Macitentan ameliorated but did not reverse the proportion of occlusive lesions in the late study. Although macitentan decreased the proportion of Ki67+ lesions in both studies, macitentan increased the proportion of cleaved caspase 3+ lesions and suppressed an antiapoptotic molecule survivin expression in the early study but not in the late study. In conclusion, macitentan reversed early but not late obstructive PVD in rats. This reversal was associated with the suppression of survivin-related resistance to apoptosis and proliferation of cells in PVD.

Ambrisentan reduces pulmonary arterial hypertension but does not stimulate alveolar and vascular development in neonatal rats with hyperoxic lung injury

Ambrisentan, an endothelin receptor type A antagonist, may be a novel therapeutic agent in neonatal chronic lung disease (CLD) by blocking the adverse effects of the vasoconstrictor endothelin-1, especially pulmonary arterial hypertension (PAH)-induced right ventricular hypertrophy (RVH). We determined the cardiopulmonary effects of ambrisentan treatment (1-20 mg·kg(-1)·day(-1)) in neonatal rats with CLD in 2 models: early treatment during continuous exposure to hyperoxia for 10 days and late treatment starting on day 6 in rat pups exposed postnatally to hyperoxia for 9 days, followed by a 9-day recovery period in room air. Parameters investigated included survival, lung and heart histopathology, right ventricular function, fibrin deposition, and differential mRNA expression in the lungs. In the early treatment model, we investigated the role of nitric oxide synthase (NOS) inhibition with N(ω)-nitro-L-arginine methyl ester (L-NAME; 25 mg·kg(-1)·day(-1)) during ambrisentan treatment. In the early treatment model, ambrisentan improved survival with reduced lung fibrin and collagen III deposition, arterial medial wall thickness, and RVH. These changes were not affected by L-NAME administration. Ambrisentan did not reduce the influx of macrophages and neutrophils or prevent reduced irregular elastin expression. In the late treatment model, ambrisentan diminished PAH, RVH, and right ventricular peak pressure, demonstrating that RVH is reversible in the neonatal period. Alveolarization and vascularization were not affected by ambrisentan. In conclusion, ambrisentan prolongs survival and reduces lung injury, PAH, and RVH via a NOS-independent mechanism but does not affect inflammation and alveolar and vascular development in neonatal rats with CLD.

Effect of small hairpin RNA targeting endothelin-converting enzyme-1 in monocrotaline-induced pulmonary hypertensive rats

The purpose of this study was to investigate the therapeutic effects of small hairpin RNA (shRNA) targeting endothelin-converting enzyme (ECE)-1 in monocrotaline (MCT)-induced pulmonary hypertensive rats. Ninty-four Sprague-Dawley rats were divided into three groups: control (n = 24), MCT (n = 35) and shRNA (n = 35). Four-week survival rate in the shRNA group was significantly increased compared to that in the MCT group. The shRNA group showed a significant improvement of right ventricular (RV) pressure compared with the MCT group. The MCT and shRNA groups also showed an increase in RV/(left ventricle + septum) ratio and lung/body weight. Plasma endothelin (ET)-1 concentrations in the shRNA group were lower than those in the MCT group. Medial wall thickness of pulmonary arterioles were increased after MCT injection and was significantly decreased in the shRNA group. The number of intra-acinar muscular pulmonary arteries was decreased in the shRNA group. The mRNA expressions of ET-1 and ET receptor A (ET(A)) were significantly decreased in the shRNA group in week 4. The protein levels of ET(A) were decreased in the shRNA group in week 2. The protein levels of tumor necrosis factor-α and vascular endothelial growth factor were decreased in the shRNA group in week 4. In conclusion, the gene silencing with lentiviral vector targeting ECE-1 could be effective against hemodynamic, histopathological and gene expression changes in pulmonary hypertension.

A brief overview of mouse models of pulmonary arterial hypertension: problems and prospects

Many chronic pulmonary diseases are associated with pulmonary hypertension (PH) and pulmonary vascular remodeling, which is a term that continues to be used to describe a wide spectrum of vascular abnormalities. Pulmonary vascular structural changes frequently increase pulmonary vascular resistance, causing PH and right heart failure. Although rat models had been standard models of PH research, in more recent years the availability of genetically engineered mice has made this species attractive for many investigators. Here we review a large amount of data derived from experimental PH reports published since 1996. These studies using wild-type and genetically designed mice illustrate the challenges and opportunities provided by these models. Hemodynamic measurements are difficult to obtain in mice, and right heart failure has not been investigated in mice. Anatomical, cellular, and genetic differences distinguish mice and rats, and pharmacogenomics may explain the degree of PH and the particular mode of pulmonary vascular adaptation and also the response of the right ventricle.

The monocrotaline model of pulmonary hypertension in perspective

Severe forms of pulmonary arterial hypertension (PAH) are characterized by various degrees of remodeling of the pulmonary arterial vessels, which increases the pulmonary vascular resistance and right ventricular afterload, thus contributing to the development of right ventricle dysfunction and failure. Recent years have seen advances in the understanding of the pathobiology of PAH; however, many important questions remain unanswered. Elucidating the pathobiology of PAH continues to be critical to design new effective therapeutic strategies, and appropriate animal models of PAH are necessary to achieve the task. Although the monocrotaline rat model of PAH has contributed to a better understanding of vascular remodeling in pulmonary hypertension, we question the validity of this model as a preclinically relevant model of severe plexogenic PAH. Here we review pertinent publications that either have been forgotten or ignored, and we reexamine the monocrotaline model in the context of human forms of PAH.

Therapeutic efficacy of TBC3711 in monocrotaline-induced pulmonary hypertension

BACKGROUND

Endothelin-1 signalling plays an important role in pathogenesis of pulmonary hypertension. Although different endothelin-A receptor antagonists are developed, a novel therapeutic option to cure the disease is still needed. This study aims to investigate the therapeutic efficacy of the selective endothelin-A receptor antagonist TBC3711 in monocrotaline-induced pulmonary hypertension in rats.

METHODS

Monocrotaline-injected male Sprague-Dawley rats were randomized and treated orally from day 21 to 35 either with TBC3711 (Dose: 30 mg/kg body weight/day) or placebo. Echocardiographic measurements of different hemodynamic and right-heart hypertrophy parameters were performed. After day 35, rats were sacrificed for invasive hemodynamic and right-heart hypertrophy measurements. Additionally, histologic assessment of pulmonary vascular and right-heart remodelling was performed.

RESULTS

The novel endothelin-A receptor antagonist TBC3711 significantly attenuated monocrotaline-induced pulmonary hypertension, as evident from improved hemodynamics and right-heart hypertrophy in comparison with placebo group. In addition, muscularization and medial wall thickness of distal pulmonary vessels were ameliorated. The histologic evaluation of the right ventricle showed a significant reduction in fibrosis and cardiomyocyte size, suggesting an improvement in right-heart remodelling.

CONCLUSION

The results of this study suggest that the selective endothelin-A receptor antagonist TBC3711 demonstrates therapeutic benefit in rats with established pulmonary hypertension, thus representing a useful therapeutic approach for treatment of pulmonary hypertension.

Animal models of pulmonary arterial hypertension: the hope for etiological discovery and pharmacological cure

At present, six groups of chronic pulmonary hypertension (PH) are described. Among these, group 1 (and 1′) comprises a group of diverse diseases termed pulmonary arterial hypertension (PAH) that have several pathophysiological, histological, and prognostic features in common. PAH is a particularly severe and progressive form of PH that frequently leads to right heart failure and premature death. The diagnosis of PAH must include a series of defined clinical parameters, which extend beyond mere elevations in pulmonary arterial pressures and include precapillary PH, pulmonary hypertensive arteriopathy (usually with plexiform lesions), slow clinical onset (months or years), and a chronic time course (years) characterized by progressive deterioration. What appears to distinguish PAH from other forms of PH is the severity of the arteriopathy observed, the defining characteristic of which is “plexogenic arteriopathy.” The pathogenesis of this arteriopathy remains unclear despite intense investigation in a variety of animal model systems. The most commonly used animal models (“classic” models) are rodents exposed to either hypoxia or monocrotaline. Newer models, which involve modification of classic approaches, have been developed that exhibit more severe PH and vascular lesions, which include neointimal proliferation and occlusion of small vessels. In addition, genetically manipulated mice have been generated that have provided insight into the role of specific molecules in the pulmonary hypertensive process. Unfortunately, at present, there is no perfect preclinical model that completely recapitulates human PAH. All models, however, have provided and will continue to provide invaluable insight into the numerous pathways that contribute to the development and maintenance of PH. Use of both classic and newly developed animal models will allow continued rigorous testing of new hypotheses regarding pathogenesis and treatment. This review highlights progress that has been made in animal modeling of this important human condition.

Endothelin receptor antagonists in preclinical models of pulmonary hypertension

Pulmonary hypertension (PH), a chronic disorder of the pulmonary vasculature, is characterized by progressive elevation in pulmonary artery pressure and the ultimate development of right-sided heart failure and death. Being a rapidly progressive disease with limited therapeutic options, the pathogenesis of PH is complex and multifactorial. The pathogenesis may result from a combination of vasoconstriction, inward vascular wall remodelling and in situ thrombosis that involves dysfunction of underlying cellular pathways and mediators. Among these, the activation of endothelin (ET) system has been shown to be important in the development and perpetuation of PH. Endothelin-1 (ET-1), a potent vasoconstrictor and mitogen, exerts its biological effects by binding to two G-protein-coupled receptor isoforms, endothelin A (ETA) receptor and endothelin B (ETB) receptor. These two receptors are nonredundant and unique because of distinct localization, unique binding locations and affinities for the endothelin peptide and activation of distinct signalling pathways. Importantly, there is now substantial evidence that direct antagonism of ET receptors that can block either ETA- or ETA- and ETB receptors can be beneficial for the treatment of PH in both preclinical and clinical setting. This review provides an overview of endothelin biology, various preclinical models that have been widely used to investigate the pathophysiology of PH as well as the individual roles of the ET receptors (ETA and ETB) and their regulation in disease pathogenesis. We also review current data on the use of selective and nonselective ET receptor antagonism in the preclinical PH models.

Myocardial dysfunction and neurohumoral activation without remodeling in left ventricle of monocrotaline-induced pulmonary hypertensive rats

In monocrotaline (MCT)-induced pulmonary hypertension (PH), only the right ventricle (RV) endures overload, but both ventricles are exposed to enhanced neuroendocrine stimulation. To assess whether in long-standing PH the left ventricular (LV) myocardium molecular/contractile phenotype can be disturbed, we evaluated myocardial function, histology, and gene expression of autocrine/paracrine systems in rats with severe PH 6 wk after subcutaneous injection of 60 mg/kg MCT. The overloaded RV underwent myocardial hypertrophy ( P < 0.001) and fibrosis ( P = 0.014) as well as increased expression of angiotensin-converting enzyme (ACE) (8-fold; P < 0.001), endothelin-1 (ET-1) (6-fold; P < 0.001), and type B natriuretic peptide (BNP) (15-fold; P < 0.001). Despite the similar upregulation of ET-1 (8-fold; P < 0.001) and overexpression of ACE (4-fold; P < 0.001) without BNP elevation, the nonoverloaded LV myocardium was neither hypertrophic nor fibrotic. LV indexes of contractility ( P < 0.001) and relaxation ( P = 0.03) were abnormal, however, and LV muscle strips from MCT-treated compared with sham rats presented negative ( P = 0.003) force-frequency relationships (FFR). Despite higher ET-1 production, BQ-123 (ETA antagonist) did not alter LV MCT-treated muscle strip contractility distinctly ( P = 0.005) from the negative inotropic effect exerted on shams. Chronic daily therapy with 250 mg/kg bosentan (dual endothelin receptor antagonist) after MCT injection not only attenuated RV hypertrophy and local neuroendocrine activation but also completely reverted FFR of LV muscle strips to positive values. In conclusion, the LV myocardium is altered in advanced MCT-induced PH, undergoing neuroendocrine activation and contractile dysfunction in the absence of hypertrophy or fibrosis. Neuroendocrine mediators, particularly ET-1, may participate in this functional deterioration.

Effects of endothelin receptor antagonism on acute lung injury induced by chlorine gas

OBJECTIVE

To test the hypothesis that the endothelin system is involved in chlorine gas-induced lung injury.

DESIGN

Experimental study.

SETTING

Academic research laboratory.

SUBJECTS

Twenty-four domestic juvenile pigs.

INTERVENTIONS

Anesthetized, ventilated pigs were exposed to chlorine gas (400 parts per million in air) for 20 mins and then randomly allocated to four groups (n=6 in each group). The tezosentan pretreatment group received the dual endothelin receptor antagonist tezosentan 20 mins before and hyperoxic gas (Fio2 0.6) after chlorine gas exposure. The tezosentan postinjury treatment group received hyperoxic gas after chlorine gas exposure and tezosentan 60 mins later. Animals in the oxygen group received hyperoxic gas after chlorine gas exposure. Pigs in the fourth group (air) were ventilated with room air (Fio2 0.21) throughout the experiment.

MEASUREMENTS AND MAIN RESULTS

Hemodynamics, gas exchange, lung mechanics, and plasma endothelin-1 were evaluated for 6 hrs. Chlorine gas exposure induced an increase in circulating endothelin-1 by 90% (p<.05). The acute chlorine gas-induced rise in pulmonary vascular resistance was partly blocked by tezosentan pretreatment (p<.001). Tezosentan postinjury treatment also decreased pulmonary vascular resistance to levels significantly lower than in the air and oxygen groups (p<.001). Recovery of peak airway pressure was better in the tezosentan-treated groups than in the air group. There were significant linear relationships between circulating endothelin-1 and pulmonary vascular resistance (r=.47, p<.001) and endothelin-1 and peak airway pressure (r=.41, p<.001). These relationships were modified by tezosentan.

CONCLUSIONS

Tezosentan modified chlorine gas-induced pulmonary dysfunction, indicating that the endothelin system is involved in this mode of acute lung injury.

Upregulated Neurohumoral Factors are Associated With Left Ventricular Remodeling and Poor Prognosis in Rats With Monocrotaline-Induced Pulmonary Arterial Hypertension

BACKGROUND

Left ventricular remodeling might be involved in the pathophysiology of right ventricular hypertrophy/failure due to pulmonary arterial hypertension (PAH), while the left ventricle is considered not under pressure/volume overload.

METHODS AND RESULTS

Rats with monocrotaline-induced PAH were used in the present study to examine whether upregulated neurohumoral factors may induce left ventricular (LV) remodeling and(/or) contribute to prognosis. Morphological analysis revealed a significant increase in the weight of the free walls of both ventricles and the interventricular septum, indicating biventricular hypertrophy, although systemic blood pressure was not elevated. RNase protection assay demonstrated the activation of a fetal gene program in the cardiac muscle of the left and right ventricular free walls. Similar activation of the fetal gene program was observed in the LV of rats continuously infused with angiotensin (AT) II, although this was not the case for rats infused with isoproterenol. Measured plasma levels of ATII, noradrenaline, and brain natriuretic peptide (BNP) were all significantly elevated in the PAH rats. Furthermore, the plasma BNP level positively correlated with the ratio of heart weight to body weight and the plasma level of ATII. Not right but LV hypertrophy was significantly reduced by treatment with an AT II type 1 receptor blocker, valsartan, whereas the effect of an adrenergic alpha1 and beta1,2 blocker, carvedilol, was borderline. Survival rate in the PAH rats was significantly improved when they were treated with valsartan or carvedilol.

CONCLUSIONS

Upregulated neurohumoral factors seem to play an important role in LV remodeling without mechanical overload, and are associated with impairment of prognosis in rats with PAH.

A novel and selective endothelin ETA receptor antagonistYM598 prevents the development of chronic hypoxia-induced pulmonary hypertension in rats

The preventive effects of the novel and selective endothelin ET(A) receptor antagonist YM598 on the development of pulmonary hypertension (PH) were investigated in chronic hypoxia-induced PH rats. Oral administration of YM598 at a dose of 1 mg/kg was started on the first day of chronic hypoxia exposure for 2 and 3 weeks to investigate the effects of this compound on hemodynamic and arterial blood gas variables, respectively. Cardiopulmonary organ weights were measured at the end of the 2-week administration period. Chronic hypoxia for 2 weeks induced a marked increase in pulmonary arterial pressure, right ventricular hypertrophy, and pulmonary and systemic congestion, and a decrease in right cardiac diastolic function. Repeated oral administration of YM598 significantly suppressed the increase in pulmonary arterial pressure, right ventricular hypertrophy, and pulmonary and systemic congestion. YM598 also improved the hypoxemia which was induced by 3 weeks of exposure to hypoxia. These results suggest that repeated oral administration of YM598 to rats with chronic hypoxia effectively prevented the development of PH. Oral administration of YM598 also improved hypoxemia in this model. These data strongly suggest that YM598 will be clinically useful in the treatment of patients with either primary or secondary pulmonary hypertension.