Critical role of COX‐1 in prostacyclin production by human endothelial cells under modification of hydroperoxide tone

We aimed at evaluating the relative contribution of cyclooxygenase (COX) ‐1 and COX‐2 to the synthesis of prostacyclin in endothelial cells under static conditions in the presence or absence of exogenous arachidonic acid and/or altered intracellular redox balance. Selective inhibitors of either COX‐1 (SC560 and FR122047) or COX‐2 (SC236) concentration dependently (1–300 nM) reduced basal and interleukin (IL) ‐1β‐induced prostacyclin production in human umbilical vein endothelial cells by 70% or more; compound selectivity was confirmed using a whole‐blood assay (IC 50 COX‐1/COX‐2: 13 nM/930 nM for SC‐560; 9 μM/457 nM for SC‐236). The observed concomitant formation of isoprostane appeared to be associated with COX enzyme activity, while formation of COX‐1/COX‐2 heterodimers was detected by immunoprecipitation. In the presence of arachidonic acid and 12‐hydroperoxy‐eicosatetraenoic acid, either exogenous or provided by platelet activation, or after glutathione depletion, COX‐1 inhibition but not COX‐2 inhibition concentration dependently decreased prostacyclin production. Both isoforms appear to contribute to basal prostacyclin production by endothelial cells, with COX‐2 providing the hydroperoxide tone required for COX‐1 activity. Conversely, in the case of intracellular glutathione depletion or enhanced availability of arachidonic acid and hydroperoxides, selective COX‐2 inhibition did not significantly affect the production of endothelial prostacyclin. These findings contribute to a better understanding of the effects of cyclooxygenase inhibitors on prostacyclin production.—Bolego, C, Buccellati, C, Prada, A., Gaion, R. M., Folco, G., Sala, A. Critical role of COX‐1 in prostacyclin production by human endothelial cells under modification of hydroperoxide tone. FASEB J . 23, 605–612 (2009)