Abstract 16016: Role For Macitentan in Angiogenesis of Right Ventricle, Peripheral Muscle and Lungs in Pulmonary Arterial Hypertension

Abstract

Background: Pulmonary arterial hypertension (PAH) is a vascular disease characterized by remodeling of distal pulmonary arteries (PA) leading to increased mean PA pressure, subsequent right ventricular (RV) failure and ultimately death of patients. Impaired angiogenesis is now recognized as a major factor in PAH etiology. It contributes not only to the decrease in lung perfusion but also to a rarefaction of the capillary network within the skeletal muscle and RV leading to exercise intolerance and RV failure. Several studies have suggested that endothelin-1 (ET-1) contributes to decrease angiogenesis in PAH. In light of these observations, we hypothesized that macitentan, an ET-1 receptors blocker, improves PAH by promoting angiogenesis in lungs, RV and skeletal muscles. Methods/Results: In the Sugen/hypoxia rat model of PAH, we demonstrated by right catheterization in closed chest rats that compared to vehicle treated animals, daily treatment during two weeks with macitentan (30 mg/kg) decreases significantly mean PA pressure (n=8-20; p<0.01) and total pulmonary resistance (n=8-20; p<0.05) and improves cardiac output, stroke volume (n=7-17; p<0.05) and RV hypertrophy measured by echo (n=6-10; p<0.05). These effects were associated with an increase of 2.9 fold in lung blood perfusion (n=6), 4.1 fold in quadriceps perfusion (n=5-7) and 1.5 fold in right ventricle perfusion (n=5-6) measured in vivo by micro CT angiogram (p<0.05). Both in vivo lectin perfusion (n=4-10; p<0.05) and immunologic CD31 staining (n=4-5; p<0.05) confirmed these findings. In the lungs, the hemodynamic and perfusion improvements were associated with decreased vascular remodeling (H&E) (n=6-17; p<0.01). In vitro, using primary cultured human endothelial cells isolated from distal PA (PAEC) and RV (RVEC), we showed that macitentan decreases PAH-PAEC proliferation (Ki67 assay) and resistance to apoptosis (TUNEL assay), while increasing angiogenesis capacity of healthy PAEC and RVEC (matrigel assay). Conclusion: Our data provide structural and functional evidence that ET-1 receptor inhibition with macitentan may improve PAH by promoting angiogenesis.