Regulation of synthesis of prostacyclin and HETEs in human endothelial cells

Human umbilical endothelial cells in culture synthesize prostacyclin (PGI₂), 15-hydroxyeicosatetraenoic acid (15-HETE), and 12-hydroxyeicosatetraenoic acid (12-HETE). The synthesis of these eicosanoids was measured by specific radioimmunoassays after stimulation by arachidonic acid, A23187, bradykinin, melittin, or histamine. Under all conditions, the synthesis of PGI₂ paralleled and exceeded the synthesis of 15-HETE and 12-HETE. Idomethacin inhibited arachidonic acid-stimulated PGI₂ and 15-HETE synthesis but enhanced 12-HETE synthesis. Meclofenamate gave similar qualitative results. Drugs that act as inhibitors of lipoxygenase in some tissues, such as nordihydroguaiaretic acid (NDGA), caffeic acid, esculin-diethylcarbamazine, quercetin, and 5,8,11,14-eicosatetrayenoic acid (ETYA) were nonspecific in their inhibition of PGI₂, 12-HETE, and 15-HETE synthesis. For example, NDGA inhibited arachidonic acid-stimulated release with a 50% inhibitory concentration (IC₅₀) of 0.39 μM for PGI₂, 0.25 μM for 15-HETE, and 0.10 μM for 12-HETE. These results show that endothelial cells metabolize both endogenous and exogenous arachidonic acid to PGI₂, 15-HETE, and 12-HETE. These data also suggest, based on results with inhibitors, that PGI₂ and 15-HETE are products of cyclooxygenase, whereas 12-HETE is produced via a different enzymatic pathway, most likely a lipoxygenase pathway.