Prevention of SU5416-Induced Pulmonary Hypertension in a TGF beta Dependent Genetic Mouse Model of Scleroderma Using the Endothelin Receptor Antagonist Macitentan.

Background/Purpose: Pulmonary arterial hypertension (PAH) is an important complication of systemic sclerosis (SSc) that occurs in around 10% of cases. We have previously shown that a TGFbeta dependent transgenic mouse strain (TβRIIΔk-fib) is susceptible to organ based pathology relevant to SSc and that pulmonary endothelial injury is associated with development of PH with perturbed VEGF, BMP and endothelin signalling. In this study, we have prevented the development of PH in this mouse strain using macitentan, a potent endothelin receptor antagonist recently licensed to treat PAH in connective tissue disease based upon a significant effect on morbidity and mortality in PAH. Methods: SU5416, a VEGF receptor inhibitor, was administered to all TβRIIΔk-fib transgenic (TG) mice and littermate wildtype (WT) animals to induce endothelial injury with subsequent endoluminal proliferation and PH in transgenic mice only. Mice were treated with either 50mg/kg macitentan daily by oral gavage or vehicle alone (n=8 each group). The development of PH in each group was assessed by histology and immunohistochemistry of vessel architecture, in vivo haemodynamic studies and RV mass index measurements. Results: Compared with WT littermates, after SU5416, all TG mice developed a prominent perivascular chronic inflammatory infiltrate and smooth muscle layer hypertrophy, as previously described. RV mass index was elevated in TG animals receiving vehicle compared to other groups (TG vehicle 0.29±0.007, TG macitentan 0.24±0.007, p