Isoprostanes and PGE2 production in human isolated pulmonary artery smooth muscle cells: concomitant and differential release.

The isoprostanes are a group of biologically active arachidonic acid metabolites initially thought to be formed under conditions of oxidative stress and independently of cyclooxygenase. However, recent studies have demonstrated isoprostane production under conditions in which cyclooxygenase is intentionally activated/induced. Here we describe for the first time formation of isoprostanes by human vascular cells via independent pathways of oxidative stress and cyclooxygenase induction. We compared the release of the isoprostane with that of the traditional prostaglandin, prostaglandin E2. Cyclooxygenase-2 induction was confirmed by Western blot. When cells were stimulated with cytokines, the release of isoprostanes was inhibited by the cyclooxygenase-1 and -2 inhibitor indomethacin as well by as the cyclooxygenase-2 selective inhibitor L-745,337. However, treatment of cells with the superoxide-producing enzyme xanthine oxidase also resulted in isoprostane release, which was not affected by cyclooxygenase inhibition, unlike PGE2 release under the same condition. Thus, two independent pathways relating to oxidative stress and cyclooxygenase-2 induction form isoprostanes. These findings may have particular importance in diseases such as sepsis and ARDS in which oxidant stress occurs and cyclooxygenase is induced.