Endothelin receptor antagonists in preclinical models of pulmonary hypertension

Pulmonary hypertension (PH), a chronic disorder of the pulmonary vasculature, is characterized by progressive elevation in pulmonary artery pressure and the ultimate development of right-sided heart failure and death. Being a rapidly progressive disease with limited therapeutic options, the pathogenesis of PH is complex and multifactorial. The pathogenesis may result from a combination of vasoconstriction, inward vascular wall remodelling and in situ thrombosis that involves dysfunction of underlying cellular pathways and mediators. Among these, the activation of endothelin (ET) system has been shown to be important in the development and perpetuation of PH. Endothelin-1 (ET-1), a potent vasoconstrictor and mitogen, exerts its biological effects by binding to two G-protein-coupled receptor isoforms, endothelin A (ETA) receptor and endothelin B (ETB) receptor. These two receptors are nonredundant and unique because of distinct localization, unique binding locations and affinities for the endothelin peptide and activation of distinct signalling pathways. Importantly, there is now substantial evidence that direct antagonism of ET receptors that can block either ETA- or ETA- and ETB receptors can be beneficial for the treatment of PH in both preclinical and clinical setting. This review provides an overview of endothelin biology, various preclinical models that have been widely used to investigate the pathophysiology of PH as well as the individual roles of the ET receptors (ETA and ETB) and their regulation in disease pathogenesis. We also review current data on the use of selective and nonselective ET receptor antagonism in the preclinical PH models.