Peroxynitrite provides the peroxide tone for PGHS-2-dependent prostacyclin synthesis in vascular smooth muscle cells.
Endotoxin-treated vascular smooth muscle cells (VSMCs) were recently shown to release high amounts of prostacyclin (PGI2) dependent on the induction of prostaglandin endoperoxide synthase-2 (PGHS-2). In contrast to endothelial PGI2-synthase, for which nitration and inhibition by peroxynitrite was reported, addition of SIN-1 as a peroxynitrite-generating system did not cause inhibition but rather doubled PGI2 release by VSMC. The hypothesis of peroxynitrite supplementing an unsaturated peroxide tone for PGHS-2 was supported by H2O2 exerting the same effect. Studies performed with purified PGHS-2 revealed maximal elevation of enzyme activity in the presence of equimolar concentrations of *NO and *O2-, which together form peroxynitrite, while excessive production of either one radical was inhibitory. Most importantly, 6-keto-PGF1alpha formation by intact VSMC depended on a nearly equimolar generation of *NO and *O2- for providing the endogenous peroxide tone. These findings, together with the observation that an excess of exogenously added *NO, as well as uric acid as a scavenger of peroxynitrite potently reduced PGI2 release, underlined the role of peroxynitrite as the dominating and rate-limiting intracellular mediator of peroxide tone in VSMC. The results allow us to postulate a new cross-talk between the *NO and the prostanoid pathways with a crucial role for peroxynitrite in providing the peroxide tone for a continuous activation of PGHS-2.
Schildknecht
Stefan
S
Department of Biology, University of Konstanz, 78457 Konstanz, Germany.
Bachschmid
Markus
M
Ullrich
Volker
V
D000818:Animals; D002417:Cattle; D002478:Cells, Cultured; D051546:Cyclooxygenase 2 / Q000502:physiology*; D011464:Epoprostenol / Q000096:biosynthesis*; D006861:Hydrogen Peroxide / Q000378:metabolism*; D008981:Molsidomine / Q000031:analogs & derivatives / Q000494:pharmacology; D009131:Muscle, Smooth, Vascular / Q000166:cytology / Q000378:metabolism*; D032389:Myocytes, Smooth Muscle / Q000378:metabolism*; D009569:Nitric Oxide / Q000378:metabolism; D019001:Nitric Oxide Synthase / Q000378:metabolism; D009589:Nitrogen Oxides / Q000494:pharmacology; D030421:Peroxynitrous Acid / Q000502:physiology*; D013096:Spermine / Q000031:analogs & derivatives / Q000494:pharmacology; D013481:Superoxides / Q000378:metabolism
D009589:Nitrogen Oxides; D013481:Superoxides; C091861:spermine nitric oxide complex; D030421:Peroxynitrous Acid; D013096:Spermine; D009569:Nitric Oxide; C002385:linsidomine; D006861:Hydrogen Peroxide; D008981:Molsidomine; D011464:Epoprostenol; D019001:Nitric Oxide Synthase; D051546:Cyclooxygenase 2