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Nitric Oxide Activates Cyclooxygenase Enzymes

Daniela Salvemini, Thomas P. Misko, Jaime L. Masferrer, Karen Seibert, Mark G. Currie and Philip Needleman
Proceedings of the National Academy of Sciences of the United States of America
Vol. 90, No. 15 (Aug. 1, 1993), pp. 7240-7244
Stable URL: http://www.jstor.org/stable/2362688
Page Count: 5
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
Nitric Oxide Activates Cyclooxygenase Enzymes
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Abstract

We have evaluated the role of nitric oxide (NO) on the activity of the constitutive and induced forms of cyclooxygenase (COX; COX-1 and COX-2, respectively). Induction of NO synthase (NOS) and COX (COX-2) in the mouse macrophage cell line RAW264.7 by Escherichia coli lipopolysaccharide (1 μ g/ml, 18 h) caused an increase in the release of nitrite (NO- 2) and prostaglandin E2 (PGE2), products of NOS and COX, respectively. Production of both NO- 2 and PGE2 was blocked by the NOS inhibitors NG-monomethyl-L-arginine or aminoguanidine. The effects of NG-monomethyl-L-arginine or aminoguanidine were reversed by coincubation with L-Arg, the precursor for NO synthesis, but not by D-Arg. RAW264.7 cells stimulated for 18 h with lipopolysaccharide in L-Arg-free medium (to reduce NO generation by the endogenous NOS pathway) failed to release NO- 2 and accumulated at least 4-fold less PGE2 when compared to cells in the presence of L-Arg. PGE2 production elicited by a 15-min arachidonic acid treatment of lipopolysaccharide-induced RAW264.7 cells in L-Arg-deficient medium was decreased 3-fold when compared to the release obtained with cells induced in medium containing L-Arg. To examine the NO activation of the induced form of COX in the absence of an endogenous L-Arg, human fetal fibroblasts were first stimulated for 18 h with interleukin 1β. These cells released PGE2 but not NO- 2, consistent with the induction of COX but not NOS in the fibroblast. Exogenous NO either as a gaseous solution or released by a NO donor, sodium nitroprusside or glyceryl trinitrate, increased COX activity in the interleukin 1β-stimulated fibroblasts by 5-fold; these effects were abolished by coincubation with hemoglobin (10 μ M), which binds and inactivates NO, but not by methylene blue, an inhibitor of the soluble guanylate cyclase. Furthermore, sodium nitroprusside (0.25-1 mM) increased arachidonic acid-stimulated PGE2 production by murine recombinant COX-1 and COX-2. These results demonstrate that NO enhances COX activity through a mechanism independent of cGMP and suggest that, in conditions in which both the NOS and COX systems are present, there is an NO-mediated increase in the production of proinflammatory prostaglandins that may result in an exacerbated inflammatory response. The data suggest that NO directly interacts with COX to cause an increase in the enzymatic activity.

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