Abstract
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.
Footnotes
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Send reprint requests to: Dr. Rolf M. Nüsing, Department of Pediatrics, Philipps University of Marburg, 35033 Marburg, Germany. E-mail:nuesing{at}mailer.uni-marburg.de
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↵1 This work was supported by grants from the Deutsche Forschungsgemeinschaft (Nu 73/2–1, Se 263/11–1).
- Abbreviations:
- PG
- prostaglandin
- COX
- cyclooxygenase
- NSAID
- nonsteroidal anti-inflammatory drug
- GC/MS/MS
- gas chromatography-tandem mass spectrometry
- RMC
- rat mesangial cells
- IL-1
- interleukin-1β
- TXB
- thromboxane
- HPS
- hyperprostaglandin syndrome
- RT
- reverse transcription
- PCR
- polymerase chain reaction
- Received October 28, 1996.
- Accepted May 5, 1997.
- The American Society for Pharmacology and Experimental Therapeutics
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