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

Abstract

NO produced by the inducible NO synthase (NOS2) and prostanoids generated by the cyclooxygenase (COX) isoforms and terminal prostanoid synthases are major components of the host innate immune and inflammatory response. Evidence exists that pharmacological manipulation of one pathway could result in cross-modulation of the other, but the sense, amplitude, and relevance of these interactions are controversial, especially in vivo. Administration of 6 mg/kg LPS to rats i.p. resulted 6 h later in induction of NOS2 and the membrane-associated PGE synthase (mPGES) expression, and decreased constitutive COX (COX-1) expression. Low level inducible COX (COX-2) mRNA with absent COX-2 protein expression was observed. The NOS2 inhibitor aminoguanidine (50 and 100 mg/kg i.p.) dose dependently decreased both NO and prostanoid production. The LPS-induced increase in PGE2 concentration was mediated by NOS2-derived NO-dependent activation of COX-1 pathway and by induction of mPGES. Despite absent COX-2 protein, SC-236, a putative COX-2-specific inhibitor, decreased mPGES RNA expression and PGE2 concentration. Ketoprofen, a nonspecific COX inhibitor, and SC-236 had no effect on the NOS2 pathway. Our results suggest that in a model of systemic inflammation characterized by the absence of COX-2 protein expression, NOS2-derived NO activates COX-1 pathway, and inhibitors of COX isoforms have no effect on NOS2 or NOS3 (endothelial NOS) pathways. These results could explain, at least in part, the deleterious effects of NOS2 inhibitors in some experimental and clinical settings, and could imply that there is a major conceptual limitation to the use of NOS2 inhibitors during systemic inflammation.

Membrane Prostaglandin E Synthase-1: A Novel Therapeutic Target

“…TNF-␣ up-regulation of COX-2 and mPGES-1 was attenuated and augmented by interferon-␥, respectively (Wright et al, 2004). Induction of mPGES-1 by LPS (Devaux et al, 2001;Uematsu et al, 2002) was shown to be mediated by the Toll-like receptor 4/MyD88/NF-IL-6-dependent signaling pathway (Uematsu et al, 2002) and could be augmented by 9-cis-retinoic acid (Tsukamoto et al, 2004).…”

In Vivo Study on Cross Talk between Inducible Nitric-Oxide Synthase and Cyclooxygenase in Rat Gastric Mucosa: Effect of Cyclooxygenase Activity on Nitric Oxide Production

“…PCR amplification was performed by the hot starting method, using Takara Best RT-PCR (Takara). The sequences of primers used in this study were designed according to the published study (Devaux et al, 2001). The sequences of sense and antisense primers for the rat COX-2 were 5Ј-TTCAAAAGAAGTTCTGGAAAAGGT-3Ј and 5Ј-GATCATGTC-TACCTGAGTGTCTTT-3Ј, respectively, giving rise to 304-bp PCR product.…”

“…These in vitro experiments suggest that NO has the ability to lead the COX enzyme to two opposed states; activation or inactivation, depending on cell types used or experimental conditions. Several studies performed in vivo are also controversial with respect to the interaction of NO with COX activity (Paya et al, 1997;Hamilton and Warner, 1998;Devaux et al, 2001). In these studies, the iNOS inhibitors with different selectivity were used, and NO production was evaluated indirectly by measuring plasma or urinary levels of nitrite plus nitrate, which can be derived not only from endogenously produced NO but also from nitrate in a diet.…”

Inhibition of Nitric-Oxide Synthase Enhances Antigen-Induced Contractions and Increases Release of Cysteinyl-Leukotrienes in Guinea Pig Lung Parenchyma: Nitric Oxide as a Protective Factor

“…In airway macrophages, NO may in fact act on 5-LO and suppress LT synthesis (Coffey et al, 2000(Coffey et al, , 2002. The actions of NO on the COX pathway have not been completely elucidated but apparently involve both direct and indirect mechanisms (Salvemini et al, 1993;Watkins et al, 1997;Devaux et al, 2001).…”