Evaluation of the combination of endothelin receptor antagonists (ERA) and phosphodiesterase-5 inhibitors for the treatment of pulmonary arterial hypertension (PAH) in pathologic human pulmonary arteries in an ex-vivo organ bath model
Introduction
Pulmonary arterial hypertension (PAH) is a progressive disease characterized by elevated pressure (mean pulmonary artery pressure (mPAP) ≥ 25 mmHg) in the lung arteries [1]. Compensatory right ventricular overload may then result in right heart failure [2]. Proliferation of smooth muscle cells, fibroblasts, and endothelial cells, fibrosis and increased vasoconstriction contribute to the increase in vascular resistance [3,4]. Prognosis is poor in the absence of treatment with a mean 5-year-survival rate of 34%, whereas an early therapy onset reduces right heart failure and improves the prognosis [1,5,6]. PAH therapy may include both immediate effects such as vasodilation and improved oxygen supply, and long-term effects targeted at the suppression of excess cell proliferation. Medical therapy options include different vasodilators (ERA and PDE-5 inhibitors) and calcium-antagonists and additionally supportive and preventive therapy such as anticoagulation, diuretics and oxygen [7]. A specific PAH therapy for WHO functional class II and III includes the endothelin receptor antagonists (ERA) ambrisentan, bosentan and macitentan, furthermore the phosphodiesterase-5 (PDE-5) inhibitors tadalafil and sildenafil and in off-label use vardenafil as well as the soluble guanylyl cyclase stimulator Riociguat [1,[7], [8], [9]].
Bosentan is a non-selective type A and B ERA with a higher affinity to type A receptors, which has been in clinical use since 2002 [7]. Bosentan therapy is effective for PAH treatment and is not associated with an increase of mortality or of adverse events [10]. Vasodilator effects of bosentan on isolated human pulmonary arteries and veins were reported previously [11]. Macitentan is also a dual ERA and has been available since 2014 [12]. This compound has a lower liver toxicity and was shown to reduce morbidity and mortality of PAH patients [13]. Besides sildenafil and tadalafil, the two PDE-5 inhibitors currently approved for PAH treatment, vardenafil is another option of this substance class. Although a clinical trial showed its safety and efficacy in PAH treatment, it is currently approved for the treatment of erectile dysfunction only [14]. Vardenafil's short lifetime dose does not permit a once-per-day regimen in PAH treatment. Nevertheless, the compound is of interest as it shows the most potent vasodilator effect on isolated human pulmonary arteries [15]. Thus this work focuses on Vardenafil although it is currently used as an off label therapy option [8].
Long-term treatment of PAH with approved medications provided as monotherapy is often limited by a lack of drug efficacy in low to medium-risk patients or a lack of effect in high-risk patients [7]. Current guidelines advise the combination of drugs using different mechanisms of action in case of an insufficient therapeutic effect of monotherapy [13,16,17]. The AMBITION trial established clinical benefits of a combination of the ETA-specific ERA ambrisentan and the PDE-5 inhibitor tadalafil [18]. We have demonstrated the superiority of other combinations of ERA and PDE-5 inhibitors using readily available pulmonary vessels of patients without elevated pulmonary blood pressure in an ex-vivo model [11,12,15,19,20]. However, the vascular changes which contribute to the elevated pulmonary pressure in PAH patients may stem from, or result in, alterations of vasoconstrictor and vasodilator pathways. Therefore the purpose of the present study was to confirm these combination vasodilator effects of the ERA macitentan and bosentan as well as of the PDE-5 inhibitor vardenafil in pulmonary vessels of patients who underwent lung transplantation (LTX) owing to end-stage lung disease. In contrast to former studies which were aimed at investigating impacts of medication on patients, our work focuses on effects of vasodilative medication directly on pulmonary arteries. Experiments were intended to investigate, whether PDE-5 inhibition-mediated vasodilation, in addition to antiproliferation, is likely to be salutary in diseased pulmonary arteries. Observation of the substance class focused on the most potent vasodilator of the clinically available PDE-5 inhibitors.
Section snippets
Study design
Study patients were recruited among patients scheduled for LTX at the University Hospital Munich, Campus Groβhadern from October 2016 to November 2019. Patients were eligible if they were at least 18 years of age and able to provide written informed consent. Exclusion criteria included preoperative chemo- or radiotherapy, tumour infiltration and known infectious diseases such as HIV or Hepatitis C. Pulmonary arteries (segment length approx. 3 cm, internal diameter up to 10 mm) were dissected
Study patients
Pulmonary arteries of 51 patients were suitable for organ bath experiments. Of these, 13 patients had to be excluded from analysis owing to inadequate contractile function. The demographic data of the remaining 38 study patients are shown in Table 1. The study group included three patients with proven PAH (mPAP> 25 mmHg). A total of 36 patients had invasive measurements of the mean pulmonary artery pressures with a mPAP of 24.1 ± 10.1 mmHg (range 14–63 mmHg).
Bosentan and vardenafil
Three series of experiments were
Discussion
With PAH being incurable, the main goal of PAH therapy is to reduce the risk status of patients and to demote their WHO functional class, resulting in a better quality of life [7]. Most of the previous studies targeting PAH treatment were clinical-pharmacological studies or animal experiments [4]. The lack of human ex-vivo studies prompted us to examine the effects of drugs already being prescribed in a human ex-vivo model.
Thus, vardenafil was the strongest vasodilator in our previous
Conclusions
The non-selective ETA/ETB receptor antagonists macitentan and bosentan were potent in regulating vasoconstriction in pathologic human pulmonary arteries, which is the key problem of PAH. Showing better effects than single vardenafil administration, both ERA have a major role in PAH treatment. These data confirm our previous results in non-pathologic human pulmonary arteries. Dual ERA and vardenafil administration was superior to either single drug only in one particular combination owing to the
Ethical approval
All procedures performed in studies involving human participants were accordance with the ethical standards of the ethics committees of the University of Regensburg (file no. 11-101-0133) and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards.
Informed consent
Informed consent was obtained from all individual participants prior to study enrollment.
Author credit roles
Englert, Leonie: Writing- Original Draft, Writing- Review and Editing.
Stadlbauer, Christian: Data Curation.
Spaeth, Mirjam: Investigation.
Hofman, Hans-Stefan: Supervision, Project administration, Conceptualization.
Schneider, Christian: Resources.
Hatz, Rudolf: Resources.
Preissler, Gerhard: Resources.
Michel, Sebastian: Resources.
Golovchenko, Svitlana: Supervision, Resources.
Ried, Michael: Supervision, Project administration, Conceptualization.
Hoenicka, Markus: Methodology, Conceptualization,
Declaration of competing interest
The authors declare that they have no conflict of interest.
Acknowledgements
Bosentan and Macitentan were provided by the company “Actelion Pharmaceuticals Deutschland GmbH” (cooperation contract: “MED-2013-249-Hoenicka”), all other substances were bought by our team.
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