Abstract
Despite major advances in the treatment of pulmonary arterial hypertension including the use of endothelial antagonists, the disease remains deadly. The right ventricle plays an important role in the development of pulmonary arterial hypertension as it faces changing loads due to pulmonary and vascular disorders. Varying experimental animal models of pulmonary arterial hypertension have been designed to mimic and reflect the complex symptoms and mechanisms of PAH to develop human therapies. This research seeks to explore PAH therapy using animal models targeting endothelin-1 antagonists, with a specific focus on ventricular and cellular studies.Pulmonary arterial hypertension is a severe vascular and progressive condition characterized by elevated mean pulmonary arterial pressure (mPAP) >25mmHg and pulmonary vascular resistance (PVR), finally leading to right heart ventricular failure and ultimately death. Ventricular remodelling, hypertrophy, abnormal vasoconstriction, and cellular dysfunction are some of the many manifestations and symptoms peculiar to PAH. Macitentan an endothelial antagonist was used, and the effectiveness was evaluated in this study. In chapter 3, using Sugen-Hypoxia rat models (Su/Hx), repeat Cardiac Magnetic Resonance (CMR) scans was used to determine right ventricular dysfunction and track subsequent changes when treated with Macitentan. The effectiveness of Macitentan in pulmonary circulation was investigated using rat pulmonary arteries (main and inter-lobal arteries) in chapter 4. Considering the role pulmonary arterial fibroblast cells play in the remodelling and vasoconstriction of the pulmonary vasculature, chapter 5 was focused on the efficacy of Macitentan in reducing the migration and proliferation of rat pulmonary arterial fibroblast cells (RPAFs).
Sprague Dawley rats were dosed with either vehicle or Macitentan for 3 weeks (30mg/kg) daily with control rats receiving vehicle only. All rats underwent three CMR scans; before treatment, two weeks into treatment, and finally at the end of the study to determine and track any changes. A separate group was used treated as above and underwent haemodynamic measurements. In the second part of this study, wire myography was used to determine pulmonary vascular reactivity of main and inter-lobal pulmonary arteries from 2- to 3-month-old Sprague Dawley rats using Endothelin-1 as a vasoconstrictor. Using cervical dislocation, rats were euthanised using a rod and arteries were dissected from the animals. The vasoreactivity of Macitentan was then investigated. Finally, cell culture was then used to investigate the role of Macitentan in rat pulmonary arterial fibroblast cells (RPAFs). RPAFs were then explanted from the pulmonary arteries of Sprague Dawley rats and were exposed to normoxic and hypoxic conditions (5% O2) for 24hrs. Using scratch assays and an automated cell counter, proliferation and migration of these cells was analysed to determine the effects of Macitentan.
Using repeat CMR measurements, Macitentan was found to significantly reverse RV hypertrophy by reducing RV mass as well as reducing left ventricular eccentricity index. It was also shown to lower RV systolic pressure and significantly increase RV ejection fraction. This study also showed that Macitentan influenced the vasoreactivity of the main and inter-lobal pulmonary arteries as an effective vasodilator in the pulmonary vasculature. Finally, the study further revealed the inhibitory effect of Macitentan in the proliferation and migration of RPAFs under hypoxic conditions and its effectiveness in mitigating the remodelling of the vasculature and reversal of the symptoms of PAH.
This study has demonstrated the effectiveness of repeat CMR in analysing the structural changes in the right ventricles of rat Su/Hx model and subsequently measure the changes in response to treatment using Macitentan. It has further demonstrated that Macitentan may be an effective vasodilator in the pulmonary circulatory system. Furthermore, Macitentan may be useful as an inhibitory agent in the cellular pulmonary remodelling of the vasculature as a result of hypoxia. These findings support previous and ongoing studies on the efficacy of Macitentan as a useful therapy in the treatment of PAH. However, further research should be undertaken to further understand molecular effects of the drug to optimize treatment and minimize any adverse effects.
| Date of Award | 2024 |
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| Original language | English |
| Awarding Institution |
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| Supervisor | David Welsh (Supervisor) & Yvonne Dempsie (Supervisor) |