Cyclooxygenase-2-dependent oxidative stress mediates palmitate-induced impairment of endothelium-dependent relaxations in mouse arteries

Abstract

Palmitic acid, one of the saturated free fatty acids, impairs cardiovascular function as manifested by inducing vascular inflammation, apoptosis and over-production of reactive oxygen species (ROS) although the origin for ROS remains unclear. The present study investigated the cellular mechanisms underlying palmitate-induced impairment of endothelial function. Ex vivo treatment in tissue culture with palmitate concentration-dependently attenuated acetylcholine-induced endothelium-dependent relaxations, up-regulated the expression of cyclooxygenase-2 (COX-2) and elevated superoxide formation in mouse aortic endothelial cells (MAECs) measured by dihydroethidium (DHE) staining and electron paramagnetic resonance (EPR) spectroscopy. Superoxide scavengers, COX-2 inhibitor and thromboxane prostanoid (TP) receptor antagonist, but not COX-1 inhibitor reversed the harmful effects of palmitate. Furthermore, palmitate impaired acetylcholine-induced relaxations and raised superoxide in en face endothelium of aortas only from COX-1(-/-) mice but not from COX-2(-/-) mice. Palmitate increased the production and release of TXB2, a stable thromboxane A2 metabolite in mouse aortas, which was abolished by COX-2 inhibitor. Superoxide scavenger did not affect palmitate-induced up-regulated expression of COX-2 in MAECs. Both real time PCR and luciferase reporter gene assay confirmed COX-2 up-regulation in palmitate-treated MAECs and NF-κB was substantially involved in this up-regulation. The present study provides novel evidence that palmitate up-regulates COX-2 through NF-κB-dependent mechanism and resultant COX-2-associated oxidative stress impairs endothelium-dependent relaxations in mouse aortas.

Keywords: A23187 (PubChem CID: 11957499); Acetylcholine (PubChem CID: 187); Celecoxib (PubChem CID: 2662); Cyclooxygenase-2; DMPO (PubChem CID: 1774); DTPA (PubChem CID: 3053); Dihydroethidium (PubChem CID: 128682); Endothelium-dependent relaxations; Hypoxanthine (Pubchem CID:790); L-NAME (PubChem CID 39836); Palmitate; Parthenolide (PubChem CID: 6473881); Phenylephrine (PubChem CID: 6041); S18886 (PubChem CID: 9938840); SC-560 (PubChem CID: 4306515); Sodium palmitate (PubChem CID: 2735111); Superoxide; TEMPONE-H (PubChem CID: 98642); Tempol (PubChem CID: 137994); Thromboxane B2 (Pubchem CID: 5283137); Vitamin E (PubChem CID: 2116).