Generation of 8-epi-prostaglandin F-2 alpha in isolated rat kidney glomeruli by a radical-independent mechanism

1 Isoprostanes comprise a group of free radical-catalyzed products of arach idonic acid. However, there is recent evidence pointing towards an enzyme-d ependent formation of isoprostanes. 2 With the use of isolated rat glomeruli we addressed the mechanisms of iso prostane generation. Synthesis of prostanoids and isoprostanes, including 8 -epi-PGF(2 alpha), was studied under conditions favouring radical formation . 3 Cultured glomeruli formed different proslanoids including 8-epi-PGF(2 alp ha). Upon LPS challenge cyclo-oxygenase (COX)-2 expression was enhanced, an d this was paralleled by a 2-9-fold increase in prostanoid formation, inclu ding isoprostanes. Addition of COX-isoform unselective inhibitors (diclofen ac, indompthacin) or a selective inhibitor (NS-398) suppressed the synthesi s of prostanoids, 8-epi-PGF(2 alpha) and total isoprostane fraction; howeve r, inhibition of the latter was less pronounced. 4 Antioxidants such as butylated hydroxytoluene (BHT), nordihydroguaiaretic acid (NDGA), or dimethylurea exhibited an only minimal inhibitory effect o n 8-epi-PGF(2 alpha) synthesis. Moreover, ROS-generating drugs (menadione, methylviologen) or NADPH-driven radical formation were unable to cause the generation of significant amounts of 8-epi-PGF(2 alpha) by rat glomeruli. I n contrast, the total isoprostane fraction could be increased by menadione addition. 5 These data provide further evidence for a radical-independent, but COX-de pendent formation of 8-epi-PGF(2 alpha) in renal tissue. Regarding the othe r isoprostanes, both radicals and COX enzymes contribute to their formation . Based on our data we assume that elevated release of vasoactive 8-epi-PGF (2 alpha) has to be expected under conditions when the prostanoid system in the kidney is stimulated, e.g. under inflammatory conditions. Regarding re nal oxidative injuries, the usefulness of 8-epi-PGF(2 alpha) as a represent ative marker molecule of oxidative stress has to be questioned.