Peroxynitrite, the coupling product of nitric oxide and superoxide, activates prostaglandin biosynthesis

Abstract

Peroxynitrite activates the cyclooxygenase activities of constitutive and inducible prostaglandin endoperoxide synthases by serving as a substrate for the enzymes' peroxidase activities. Activation of purified enzyme is induced by direct addition of peroxynitrite or by in situ generation of peroxynitrite from NO coupling to superoxide anion. Cu,Znsuperoxide dismutase completely inhibits cyclooxygenase activation in systems where peroxynitrite is generated in situ from superoxide. In the murine macrophage cell line RAW264.7, the lipophilic superoxide dismutase-mimetic agents, Cu(II) (3,5-diisopropylsalicylic acid) 2 , and Mn(III) tetrakis(1-methyl-4-pyridyl)porphyrin dose-dependently decrease the synthesis of prostaglandins without affecting the levels of NO synthase or prostaglandin endoperoxide synthase or by inhibiting the release of arachidonic acid. These findings support the hypothesis that peroxynitrite is an important modulator of cyclooxygenase activity in inf lammatory cells and establish that superoxide anion serves as a biochemical link between NO and prostaglandin biosynthesis.Prostaglandins and thromboxanes are important mediators of inflammation, hyperalgesia, cell growth, and hemostasis inter alia. The committed step in prostaglandin biosynthesis is the oxygenation of arachidonic acid (AA) by prostaglandin endoperoxide (PGH) synthase, a bifunctional, membrane-bound hemeprotein (1-4). Inhibition of the cyclooxygenase activity of PGH synthase is the basis for the pharmacological action of nonsteroidal antiinflammatory drugs (5, 6). Two different PGH synthases exist in vertebrates-PGH synthase-1, which is expressed constitutively and occurs in many tissues, and PGH synthase-2, which is inducible and expressed transiently (7-10). PGH synthase-2 is present at high levels in monocytes͞ macrophages, where it appears to play a major role in the production of inflammatory prostaglandins (7,11).Several recent reports demonstrate that NO stimulates prostaglandin biosynthesis in vivo, in perfused organs, and in macrophages (12-17). The stimulatory effect of NO is rapid and appears to be the result of direct activation of cyclooxygenase activity (16). However, conflicting reports exist regarding the ability of NO to stimulate purified PGH synthase, and it is possible that a derivative of NO is responsible for the activation in inflammatory cells (16,(18)(19)(20).The principal mechanism described for direct activation of the cyclooxygenase activity of PGH synthase is reaction of fatty acid hydroperoxides with the heme prosthetic group to generate a protein radical. This protein radical (probably Tyr-385) serves as the catalytic oxidant of AA (21-23). The identity of the hydroperoxides that activate PGH synthase in different cell types is uncertain because fatty acid hydroperoxides are excellent substrates for glutathione peroxidase (GSH-Px)-catalyzed reduction by glutathione (GSH) (24). The potential for control of prostaglandin biosynthesis by GSH-Px͞GSH reduction of hydroperoxide activators exhibits s...

Lipopolysaccharide-Induced Increase of Prostaglandin E2 Is Mediated by Inducible Nitric Oxide Synthase Activation of the Constitutive Cyclooxygenase and Induction of Membrane-Associated Prostaglandin E Synthase

“…Several mechanisms that could explain the activation of COX by NO have recently been reviewed by Goodwin et al (16); the most likely to explain our results is the one described by Landino and coworkers (45). In addition to increasing the synthesis of NO, LPS also causes the synthesis of reactive oxygen species such as superoxide anions (O 2 Ϫ ) that react spontaneously with NO to form the potent and versatile oxidant peroxynitrite (ONOO Ϫ ).…”

Prostaglandin Endoperoxide H Synthases

“…The physiological hydroperoxide initiator of the COX reaction is not known, although both peroxynitrite and organic peroxides are the most likely candidates depending on the cell type (66). Lipid peroxides can be formed both nonenzymatically from reactive oxygen species and polyunsaturated fatty acids in membrane lipids (67) and enzymatically through the actions of 5-, 12-, and 15-lipoxygenases, which typically oxygenate free polyunsaturated fatty acids.…”

Pivotal role of superoxide anion and beneficial effect of antioxidant molecules in murine steatohepatitis

“…31 Peroxynitrites are highly reactive metabolites with a half-life of approximately 1 second in physiological buffer. 36 They rapidly react in vivo either with lipids or with proteins to produce, in the latter case, 3-nitro-tyrosine. As already observed by others, we found elevated levels of 3-nitrotyrosine in livers of ob/ob mice 37 that were significantly decreased by SOD mimics.…”