Differential effects of cyclooxygenase-2 (COX-2) inhibitors on endoplasmic reticulum (ER) stress in human coronary artery endothelial cells

Selective cyclooxygenase-2 (COX-2) inhibitor rofecoxib was pulled off the market because of its association with increased risk of adverse cardiovascular effects. The precise underlying mechanism for the differential effects of COX-2 inhibitors on cardiovascular risk is not known. Since endoplasmic reticulum (ER) stress is implicated in atherogenesis, we examined the effects of COX-2 inhibitors on ER stress in primary human coronary artery endothelial cells (HCAEC), human umbilical vein endothelial cells (HUVEC), and human pulmonary artery endothelial cells (HPAEC). ER stress was measured in HCAEC treated with either tunicamycin (TM) or high-concentrations (27.5 mM) of dextrose (HD) using the secreted alkaline phosphatase (ES-TRAP) assay. Markers of the unfolded protein response (UPR) such as activating transcription factor 6 (ATF6), glucose-regulated protein 78 (GRP78), inositol-requiring enzyme 1α (IRE1α), phospho-IRE1α, protein kinase R (PKR)-like endoplasmic reticulum kinase (PERK), and phospho-PERK were measured by Western blot. Treatment of HCAEC with TM and HD decreased secreted alkaline phosphatase activity indicating increased ER stress. Treatment of cells exposed to TM or HD with celecoxib, meloxicam, ibuprofen, and acetylsalicylic acid, but not rofecoxib, resulted in a dose-dependent decrease in ER stress. High-dextrose and TM increased IRE1α and PERK phosphorylation and ATF6 and GRP78 expression. Treatment with celecoxib, but not rofecoxib, inhibited these markers of the UPR. Treatment with selective COX-2 inhibitors, with the exception of rofecoxib, suppressed ER stress as measured with both alkaline phosphatase activity assays and markers for the UPR. The inability of rofecoxib to inhibit ER stress, unlike the other cyclooxygenase inhibitors tested, may have contributed to its unfavorable effects on cardiovascular outcomes.