Improvement of bleomycin-induced pulmonary hypertension and pulmonary fibrosis by the endothelin receptor antagonist Bosentan

https://doi.org/10.1016/j.resp.2009.11.005Get rights and content

Abstract

Rationale

There is evidence that endothelin plays a key role in the development of pulmonary hypertension (PH) in pulmonary fibrosis (PF). However, the functional consequence of the unselective endothelin receptor antagonist Bosentan in PH and PF has not yet been studied. Therefore, we investigated the effects of Bosentan on the development of PH in the model of Bleomycin-induced PF in rats.

Methods

Adult male Wistar rats were randomly assigned to the following groups: untreated animals (controls), Bleomycin-induced PF (Bleomycin) and Bleomycin-induced PF treated with Bosentan (Bleomycin + Bosentan). Exercise capacity was evaluated by treadmill exercise testing. PH was assessed by right ventricular systolic pressure (RVSP) and right ventricular hypertrophy. For quantification of PF the hydroxyproline content in lung tissue (HPC) was measured.

Results

Compared to controls, animals with Bleomycin-induced PF showed a significant reduction in exercise capacity (44% vs. 100%), significantly higher RVSP (65 mmHg vs. 23 mmHg), significantly more right ventricular hypertrophy (0.55 vs. 0.24) and significantly higher HPC (60.5 vs. 14.8). Bosentan treatment in animals with Bleomycin-induced PF resulted in significantly greater exercise capacity (98% vs. 44%) and a trend towards lower RVSP (52 mmHg vs. 65 mmHg), significantly less right ventricular hypertrophy (0.34 vs. 0.55) and significantly lower HPC (16.7 vs. 60.5) compared to untreated Bleomycin-induced PF.

Conclusion

Application of Bosentan in Bleomycin rats resulted in significantly higher exercise capacity as a result of improvements in PH and PF.

Introduction

Pulmonary fibrosis (PF) is a common end stage of interstitial lung diseases, which form an etiologically heterogeneous group of diffuse inflammatory disorders affecting the pulmonary parenchyma. (American Thoracic Society/European Respiratory Society International Multidisciplinary Consensus Classification of the Idiopathic Interstitial Pneumonias, 2001). Currently, there is no adequate therapy available for patients with PF that significantly prolongs their poor life expectancy (Flaherty et al., 2003, Walter et al., 2006).

Besides the PF itself, the development of pulmonary hypertension (PH) is an important reason for mortality in patients with PF (Lettieri et al., 2006, Nadrous et al., 2005a, Nadrous et al., 2005b). The etiology of PH in PF is not well understood. Endothelin-1 (ET) is known to play a key role in the development of PH (Michel et al., 2003). The finding of increased ET-1 plasma levels in patients with PF and PH implies that endothelial dysfunction and the ET system also contributes to the development of PH in PF (Trakada et al., 2003). The ET-receptor antagonist Bosentan is a promising and approved therapy in idiopathic pulmonary arterial hypertension (Rubin et al., 2002). However, there are no studies available which have analyzed the effect of an ET receptor antagonist on PH in PF.

In addition, there is growing evidence that the ET system plays an important role in the genesis and disease progression of PF. Elevated ET-1 levels have been found in plasma and bronchoalveolar lavage fluids of PF patients (Ryu et al., 2007, Uguccioni et al., 1995). ET converting enzyme 1 and ET-1 immunohistochemical stainings of the lung correlates with disease activity of PF (Giaid et al., 1993, Saleh et al., 1997) and even precedes the development of PF (Mutsaers et al., 1998a). There is clear evidence that ET-1 can function as a profibrotic cytokine by stimulating fibroblast chemotaxis and proliferation in vitro (Mutsaers et al., 1998a, Teder and Noble, 2000). ET-1 stimulates collagen synthesis in fibroblasts in cell culture (Dawes et al., 1996). In ET-1 transgenic mice, a fibrotic alteration of lung architecture has been observed (Hocher et al., 2000). ET receptor antagonists have been shown to inhibit the effects of ET-1 on lung fibroblast proliferation (Cambrey et al., 1994), and collagen synthesis in vitro and in vivo (Dawes et al., 1996, Park et al., 1997, Rockey and Chung, 1996). A trend in delayed time to death or disease progression, and improvement in quality of life, was observed especially in patients with biopsy proven idiopathic pulmonary fibrosis treated with the unselective ET receptor antagonists Bosentan (King et al., 2008).

Thus far there have been no studies which have analyzed the effect of an ET receptor antagonist on exercise capacity and PH in PF, and conflicting results exist with respect to the effect of ET receptor antagonists on PF (Mutsaers et al., 1998b, Park et al., 1997). We, therefore, tested the hypothesis that, in rats with Bleomycin-induced PF, application of the unselective ET receptor antagonist Bosentan results in a functional improvement by reduction of the development of PH and PF.

Section snippets

Experimental groups

Adult male Wistar rats (250 g; Charles River, Sulzfeld, Germany) were randomly assigned to one of the following groups: untreated animals (controls, n = 10), Bleomycin-induced PF (Bleomycin, cell-pharm-GmbH, Hannover, Germany, intratracheal 2 units/kg, n = 9), Bleomycin-induced PF treated with Bosentan (Bleomycin + Bosentan, Actelion, Basel, Switzerland, 100 mg/kg, n = 7). Bleomycin was instilled intratracheally in narcosis (Isofluran, Florene “R”, Abbott GmbH, Wiesbaden, Germany) once to induce lung

Hemodynamics and right ventricular hypertrophy

Right ventricular hypertrophy at 4 weeks was significantly higher in the Bleomycin group compared to controls, indicated by a higher RV/(LV + S) ratio (p = 0.001, Fig. 1b) accompanied by a significantly elevated RVSP (p = 0.003, Fig. 1a). Right ventricular hypertrophy was significantly attenuated in the Bleomycin + Bosentan group compared to the untreated Bleomycin group (p = 0.003) and there was a statistically non-significant trend towards lower RVSP (p = 0.41). RV/(LV + S) (p = 0.001) and RVSP (p = 0.003)

Discussion

The present study provides the first evidence that the ET receptor antagonist Bosentan improves exercise capacity in the model of Bleomycin-induced PF in rats. This significant improvement in exercise capacity in the Bosentan-treated, Bleomycin-induced PF animals was accompanied by a trend towards lower RVSP and significantly less right ventricular hypertrophy compared to untreated animals with PF. In addition, our study revealed a significant reduction in PF by Bosentan treatment of animals

References (40)

  • A.D. Cambrey et al.

    Increased levels of endothelin-1 in bronchoalveolar lavage fluid from patients with systemic sclerosis contribute to fibroblast mitogenic activity in vitro

    Am. J. Respir. Cell. Mol. Biol.

    (1994)
  • K.R. Flaherty et al.

    Radiological versus histological diagnosis in UIP and NSIP: survival implications

    Thorax

    (2003)
  • A. Giaid et al.

    Expression of endothelin-1 in lungs of patients with cryptogenic fibrosing alveolitis

    Lancet

    (1993)
  • T.S. Hallstrand et al.

    The timed walk test as a measure of severity and survival in idiopathic pulmonary fibrosis

    Eur. Respir. J.

    (2005)
  • B. Hocher et al.

    Pulmonary fibrosis and chronic lung inflammation in ET-1 transgenic mice

    Am. J. Respir. Cell. Mol. Biol.

    (2000)
  • A. Horstmeyer et al.

    Signalling and regulation of collagen I synthesis by ET-1 and TGF-beta1

    FEBS J.

    (2005)
  • Y.J. Ryu et al.

    Bronchoalveolar lavage in fibrotic idiopathic interstitial pneumonias

    Respir Med.

    (2007)
  • M.B. Kahaleh

    Endothelin, an endothelial-dependent vasoconstrictor in scleroderma. Enhanced production and profibrotic action

    Arthritis Rheum.

    (1991)
  • T.E. King et al.

    BUILD-1: a randomized placebo-controlled trial of Bosentan in idiopathic pulmonary fibrosis

    Am. J. Respir. Crit. Care Med.

    (2008)
  • T.E. King et al.

    Predicting survival in idiopathic pulmonary fibrosis: scoring system and survival model

    Am. J. Respir. Crit. Care Med.

    (2001)
  • Cited by (38)

    • Common Vascular Toxicities of Cancer Therapies

      2019, Cardiology Clinics
      Citation Excerpt :

      The underlying pathologic condition is pulmonary fibrosis as a consequence of the stimulation and transformation of fibroblasts into collagen-producing myofibroblasts by activated alveolar macrophages and epithelial cells in a response-to-injury pattern to inflammation.109 Statins have been shown to ameliorate bleomycin-induced lung injury as have Rho kinase inhibition, endothelin receptor antagonism, arginase inhibition, and provision of inhaled or even dietary nitric oxide (NO), and sildenafil.110–117 Finally, IFN alpha can induce pulmonary vasculitis and pulmonary hypertension for unknown reasons.90

    • Pulmonary arterial hypertension: Basic knowledge for clinicians

      2016, Archives of Cardiovascular Diseases
      Citation Excerpt :

      These experimental in vivo models mimic certain histological and molecular features seen in PAH pathophysiology in humans; these include endothelial dysfunction, muscularization of previously non-muscular arterioles and increased medial thickness of normally muscularized arterioles, in situ thrombosis and the appearance of plexiform lesions [68]. Several techniques are available to induce PAH-associated alterations in animals, such as chemical agents [69,70], genetic manipulation [71,72], environmental factors [73] and surgical procedures [74] (Table 1). Currently, monocrotaline administration and chronic exposure to hypoxia are the most widely used models of PH in translational research, because of their good reproducibility and well-described histopathology.

    • Vascular Toxicities of Cancer Therapies

      2016, Clinical Cardio-oncology
    • Pulmonary hypertension in chronic obstructive and interstitial lung diseases

      2013, International Journal of Cardiology
      Citation Excerpt :

      The currently approved ET-1 receptor antagonists for PAH are the non-selective ETA and ETB receptor antagonist bosentan, and the selective ETA receptor antagonist ambrisentan. Bosentan was the first developed ET-1 receptor antagonist, and experimental studies have shown that bosentan inhibits the development of PH in chronic hypoxic rats [115] and in bleomycin induced PH [116]. Also, in human pulmonary arteries, exposure to smoke extracts resulted in up-regulation of ETA and ETB receptors, proliferation and increased vasoconstriction.

    View all citing articles on Scopus
    View full text