PT - JOURNAL ARTICLE AU - Thomas Klein AU - Felix Reutter AU - Horst Schweer AU - Hannsjörg W. Seyberth AU - Rolf M. Nüsing TI - Generation of the Isoprostane 8-Epi-prostaglandin F<sub>2α</sub> <em>In Vitro</em> and <em>In Vivo via</em> the Cyclooxygenases DP - 1997 Sep 01 TA - Journal of Pharmacology and Experimental Therapeutics PG - 1658--1665 VI - 282 IP - 3 4099 - http://jpet.aspetjournals.org/content/282/3/1658.short 4100 - http://jpet.aspetjournals.org/content/282/3/1658.full SO - J Pharmacol Exp Ther1997 Sep 01; 282 AB - F2-Isoprostanes are isomers of the prostaglandin PGF2α. At least one compound of this group, 8-epi-PGF2α, exhibits biological activity, and therefore special interest is focused on the mechanism of isoprostane formation: enzyme catalyzed or radical mediated. We analyzed the formation of isoprostanes in vitro and in vivo. In both systems, purified cyclooxygenase isoenzymes and cell models specific for the cyclooxygenase isoenzymes, 8-epi-PGF2α formation could be totally suppressed by cyclooxygenase inhibitors. Indomethacin inhibited concentration-dependent 8-epi-PGF2α formation in platelets stimulated with calcium ionophore, arachidonic acid or thrombin. Nordihydroguaiaretic acid, an antioxidant, blocked isoprostane formation with a similar IC50 value as thromboxane B2 synthesis, pointing toward cyclooxygenase as the primary target of inhibition. Based on the turnover number, cyclooxygenase-2 formed higher levels of 8-epi-PGF2α than cyclooxygenase-1. Endogenous 8-epi-PGF2α production in rat mesangial cells correlated well with the mRNA and protein expression of cyclooxygenase-2 during interleukin-1 induction. However, in contrast to human platelets, which produced different forms of isoprostanes, rat mesangial cells appeared to form only 8-epi-PGF2α. Further, this indicates that mesangial cells may represent a cellular origin for renal 8-epi-PGF2αformation. Next, we analyzed the formation of isoprostanes in humans. A direct correlation was observed between indomethacin treatment and the decrease in 8-epi-PGF2α and isoprostane levels, but compared with other prostanoids the inhibition was less pronounced. In summary, based on the in vitro studies, a clear cyclooxygenase-dependent formation of isoprostanes, especially 8-epi-PGF2α, was observed. However, in vivoadditional formation via cyclooxygenase enzyme-independent mechanisms is likely. The American Society for Pharmacology and Experimental Therapeutics