Raloxifene promotes prostacyclin release in human endothelial cells through a mechanism that involves cyclooxygenase-1 and -2

To examine the effects of raloxifene on prostacyclin production by human umbilical vein endothelial cells (HUVEC) and to shed light on the molecular details of that action. Cell culture for 4, 8, 16, 24, and 48 hours. University research laboratory. Source of HUVEC. Measurement of prostacyclin production and of protein levels and mRNA expression of cyclooxygenase (COX)-1 and -2. Prostacyclin production was measured by enzyme immunoassay, the mRNA expression of COX-1 was measured by quantitative real time-polymerase chain reaction, and the protein levels of COX-1 and -2 were measured by immunoblotting. Raloxifene significantly increased prostacyclin release in a time- and dose-dependent manner, being higher than control after 24 hours. Raloxifene, at 0.1–10 nM, increased the mRNA expression of COX-1 and the protein content of both COX-1 as well as COX-2. All of these effects were independent of the classical pathway for estrogen receptor (ER) activation because the treatment of cells with the ER antagonist ICI 182780 did not eliminate any of the effects. Although treatment with either the selective COX-1 inhibitor SC-560 or the selective COX-2 inhibitor NS-398 significantly diminished prostacyclin release (20% ± 5% and 24% ± 7%, respectively), co-treatment with raloxifene and either SC-560 or NS-398 was followed by a smaller increase than that achieved by raloxifene alone. The nonselective COX inhibitor indomethacin, however, reduced prostacyclin production to 37% ± 11% of control values. Raloxifene increased HUVEC prostacyclin release through a mechanism possibly distinct from the classical ER pathway and involving enhanced COX-1 and COX-2 expression and activity.