Prostaglandin E-2 (PGE(2)), an important lipid inflammatory mediator involved in the progression of vascular diseases, can be induced by hypoxia in many cell types. While folic acid has been shown to protect against inflammation in THP-1 cells during hypoxia and hypoxia-induced endothelial cell injury, whether it might do so by attenuating PGE(2) production remains unclear. To investigate this we constructed a hypoxia-induced injury model by treating human umbilical vein endothelial cells (HUVECs) with cobalt chloride (CoCl2), which mimics the effects of hypoxia. In CoCl2-treated HUVECs, folic acid significantly attenuated PGE2 production and increased vasoprotective nitric oxide (NO) content. Folic acid also decreased cyclooxygenase-2 (COX-2) and hypoxia-inducible factor 1-alpha (HIF-1 alpha) expression and altered endothelial nitric oxide synthase (eNOS) signaling by increasing p-eNOS((ser1177)) and decreasing p-eNOS((Thr495)) in a dose-dependent manner. Further investigation of the pathway demonstrated that treatment with 2-Methoxyestradiol (2-MeOE2) and celecoxib both decreased CoCl2-induced COX-2 expression but only 2-MeOE2 decreased HIF-1 alpha expression. The ability of folic acid to down regulate HIF-1 alpha and COX-2 protein levels was dramatically abrogated by L-NAME treatment, which also decreased eNOS mRNA and NO production. The NO donor sodium nitroprusside also dose dependently down-regulated HIF-1 alpha and COX-2 protein levels. Overall, these findings suggest a novel application for folic acid in attenuating CoCl2-induced PGE(2) production in HUVECs via regulation of the NO/HIF-1 alpha/COX-2 pathway. (C) 2017 Elsevier Inc. All rights reserved.