Bosentan inhibits cigarette smoke-induced endothelin receptor expression in pulmonary arteries

Abstract

The endothelin (ET) system contributes to lung vascular tension and remodelling in smokers and chronic obstructive pulmonary disease (COPD) patients.This study examined the effect of cigarette smoke (CS) on ET receptor A (ETA) and B (ETB) expression in human pulmonary artery smooth muscle cells (HPASMCs) and human small intrapulmonary arteries, as well as their functional consequences.CS extract (CSE) increased ETA and ETB expression in HPASMCs and small intrapulmonary arteries, which was attenuated by bosentan, the ETA antagonist BQ123 and the ETB antagonist BQ788, and by blocking ET-1 with a monoclonal antibody against ET-1, suggesting a feed-forward mechanism mediated by ET-1 release. ET receptor (ETR) antagonism attenuated the CSE-induced HPASMC proliferation. Furthermore, CSE exposure increased the acute ET-1-induced small intrapulmonary artery contraction, which was attenuated by bosentan, BQ123 and BQ788. Pulmonary arteries from smokers and COPD patients showed a higher expression of ETA and ETB than those of nonsmoker patients.These results show a novel mechanism by which ETR blockade attenuates CS-induced ETR overexpression and, subsequently, small intrapulmonary artery tension. These data may be of potential value to explain therapeutic effects of bosentan in some forms of disproportionate pulmonary hypertension in COPD patients.KEYWORDS: Bosentan, cigarette smoke, endothelin receptor, human pulmonary artery smooth muscle cells, precision-cut lung slice P ulmonary hypertension (PH) is a relatively common form of cigarette smoke (CS)-induced lung disease. PH develops in ,6% of subjects with chronic obstructive pulmonary disease (COPD) but is present in ,40% of patients with a forced expiratory volume in 1 s of ,1 L [1, 2]. The pathogenesis of PH in COPD is unclear. Current studies suggest that PH is caused by the direct effects of CS on the intrapulmonary vessels by the secretion of a number of vasoconstrictive/proliferative peptides, such as endothelin (ET) or vascular endothelial growth factor, which subsequently contribute to vascular remodelling and the development of PH [3]. The circulating levels of ET-1 are elevated after exposure to CS in humans [4] and it has been shown that ET-1 correlates with pulmonary systolic pressure in COPD patients with PH [5], suggesting that ET-1 is involved in CS-induced vascular remodelling. ET-1 activates two receptors, ETA and ETB, which are located in pulmonary artery smooth muscle cells (PASMCs), whilst exclusively ETB are present in endothelial cells. Both ETA and ETB mediate proliferation and contractility in PASMCs from small pulmonary arteries, while endothelial ETB mediates vasodilation in normal pulmonary arteries. ETB upregulation has been observed in human blood vessels from patients with ischaemic heart disease [6], hypertension [7] and severe PH [8]. More recently, it has been shown that CS extract (CSE) induces ETA and ETB overexpression in resistant cerebral arteries from rats by a mechanism implicating the activation of the intracellular m...

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