Effects of nitric oxide and nitric oxide‐derived species on prostaglandin endoperoxide synthase and prostaglandin biosynthesis

Abstract

Prostaglandins and NO. are important mediators of inflammation and other physiological and pathophysiological processes. Continuous production of these molecules in chronic inflammatory conditions has been linked to development of autoimmune disorders, coronary artery disease, and cancer. There is mounting evidence for a biological relationship between prostanoid biosynthesis and NO. biosynthesis. Upon stimulation, many cells express high levels of nitric oxide synthase (NOS) and prostaglandin endoperoxide synthase (PGHS). There are reports of stimulation of prostaglandin biosynthesis in these cells by direct interaction between NO. and PGHS, but this is not universally observed. Clarification of the role of NO. in PGHS catalysis has been attempted by examining NO. interactions with purified PGHS, including binding to its heme prosthetic group, cysteines, and tyrosyl radicals. However, a clear picture of the mechanism of PGHS stimulation by NO. has not yet emerged. Available studies suggest that NO. may only be a precursor to the molecule that interacts with PGHS. Peroxynitrite (from O2.-+NO.) reacts directly with PGHS to activate prostaglandin synthesis. Furthermore, removal of O2.- from RAW 267.4 cells that produce NO. and PGHS inhibits prostaglandin biosynthesis to the same extent as NOS inhibitors. This interaction between reactive nitrogen species and PGHS may provide new approaches to the control of inflammation in acute and chronic settings.

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

“…To explain this paradigm, we investigated a potential effect of SC-236 on another enzyme responsible for prostanoid synthesis. PGE 2 is described as the main modulator of immune and inflammatory reactions (16), and was the most abundant PG produced following LPS injection in our experiments. Because AG totally abolished the LPS-mediated increase in 6-k-PGF 1␣ and TXB 2 , but had partial effects on PGE 2 concentration, we focused on the enzyme specifically responsible for the synthesis of PGE 2 .…”

“…Five micrograms of total RNA in 10 l of diethyl pyrocarbonate-treated water were mixed with 5 mM MgCl 2 , 1ϫ PCR buffer II, 1 mM dNTP, 2.5 M oligo(dT) 16 , 1 U/ l RNase inhibitor (GeneAmp RNA PCR kit; PE Applied Biosystems, Courtaboeuf, France), and 0.25 U/ l DNase I (Pharmacia Biotech, Orsay, France) to a final volume of 20 l, and incubated for 30 min at 37°C, followed by 5 min at 75°C. After 5 min on ice, the RNA was mixed with 2.5 U/ l murine leukemia virus reverse transcriptase (PE Applied Biosystems) and incubated for 45 min at 42°C, followed by 5 min at 90°C for denaturation of murine leukemia virus reverse transcriptase.…”

“…Specifically, studies performed in rats in vivo have shown that NOS2-produced NO either activates PG synthesis (42) or has no effect (52). The results of these conflicting reports have been recently reviewed by Goodwin et al (16). The effects of NO on COX activity depend not only on experimental conditions, cell types, inhibitors, and inducers of NO synthesis used, but also on the isoforms of NOS and COX taken into account.…”

“…Several in vitro reports have suggested that NO activates COX activity, but these observations are still controversial, and in vivo data are scarce (for a recent review, see Ref. 16). Moreover, it has been suggested in vitro that the COX products could modulate NOS2 activation through increased cAMP content in cells expressing NOS2 (reviewed in Ref.…”

Chronic inflammation and oxidative stress in human carcinogenesis

“…79 M1G adducts have been found in human tissues at levels as high as 1.2 adducts per 106 bases (which corresponds to 6,000 adducts per cell). M1G has been detected in human breast tissue by 32 phospho-postlabeling as well as in rodent tissues. 80 Moreover, M1G has been demonstrated to be mutagenic in Escherichia coli, through the transversions to T and transitions to A.…”