Cytochrome P450 epoxygenase-derived 5,6-epoxyeicosatrienoic acid relaxes pulmonary arteries in normoxia but promotes sustained pulmonary vasoconstriction in hypoxia

Abstract

Aims: The aim of the study was to investigate the role of cytochrome P450 (CYP) epoxygenase-derived epoxyeicosatrienoic acids (EETs) in sustained hypoxic pulmonary vasoconstriction (HPV).

Methods: Vasomotor responses of isolated mouse intrapulmonary arteries (IPAs) were assessed using wire myography. Key findings were verified by haemodynamic measurements in isolated perfused and ventilated mouse lungs.

Results: Pharmacological inhibition of EET synthesis with MS-PPOH, application of the EET antagonist 14,15-EEZE or deficiency of CYP2J isoforms suppressed sustained HPV. In contrast, knockdown of EET-degrading soluble epoxide hydrolase or its inhibition with TPPU augmented sustained HPV almost twofold. All EET regioisomers elicited relaxation in IPAs pre-contracted with thromboxane mimetic U46619. However, in the presence of KCl-induced depolarization, 5,6-EET caused biphasic contraction in IPAs and elevation of pulmonary vascular tone in isolated lungs, whereas other regioisomers had no effect. In patch-clamp experiments, hypoxia elicited depolarization in pulmonary artery smooth muscle cells (PASMCs), and 5,6-EET evoked inward whole cell currents in PASMCs depolarized to the hypoxic level, but not at their resting membrane potential.

Conclusions: The EET pathway substantially contributes to sustained HPV in mouse pulmonary arteries. 5,6-EET specifically appears to be involved in HPV, as it is the only EET regioisomer able to elicit not only relaxation, but also sustained contraction in these vessels. 5,6-EET-induced pulmonary vasoconstriction is enabled by PASMC depolarization, which occurs in hypoxia. The discovery of the dual role of 5,6-EET in the regulation of pulmonary vascular tone may provide a basis for the development of novel therapeutic strategies for treatment of HPV-related diseases.

Keywords: cytochrome P450 epoxygenase; epoxyeicosatrienoic acid; hypoxia; hypoxic pulmonary vasoconstriction; pulmonary arteries; soluble epoxide hydrolase.