Endothelin‐1 (ET‐1) stimulates superoxide production by eNOS following exposure of vascular endothelial cells to endotoxin

Abstract

Microcirculation is hypersensitized to ET-1 following endotoxin (LPS) treatment leading to an increased vasopressor response. This is in part related to decreased activation of eNOS by ET-1. eNOS can be uncoupled from nitric Oxide (NO) production to produce superoxide (O2−). We have previously reported that LPS treatment of Human Umbilical Vein Endothelial Cells (HUVEC) significantly impairs ET-1-induced NO production by eNOS. This is associated with an increase in O2−production. Thus increased O2− in the absence of adequate NO production may contribute to vascular dysregulation following inflammatory stress. In this study we tested whether decreased availability of the cofactor tetrahydrobiopterin (BH4) following LPS treatment might explain eNOS uncoupling and production of O2− in endothelial cells. HUVEC were subjected to 6h treatment with LPS (250ng/ml) or LPS and a BH4 precursor, sepiapterin (100μM) followed by 30 min ET-1 treatment (10nM). Sepiapterin significantly decreased O2− production in both unstimulated and ET-1-stimulated LPS groups, but did not restore NO production. ET-1 treatment following LPS stress significantly monomerized the eNOS homodimer which was reversed by sepiapterin loading. In conclusion, we have demonstrated that pretreatment of vascular endothelial cells with LPS not only abrogates activation of NO production by eNOS following ET-1 stimulation, but also turns the eNOS enzyme into a superoxide generator due to a functional deficiency in the cofactor BH4. ET-1-induced eNOS activation switches from NO to O2− production. This source of O2− may be important for altered regulation of endothelial cell function. Supported by DK38201