title: Cytokine-induced prostaglandin E2 synthesis and cyclooxygenase-2 activity are regulated both by a nitric oxide-dependent and -independent mechanism in rat osteoblasts in vitro.
abstract: Osteoblasts respond to stimulation with interleukin-1 (IL-1), tumor necrosis factor-alpha (TNF-alpha), and interferon-gamma (IFN-gamma) by production of nitric oxide and prostaglandins (PGs). In this study the relationship between nitric oxide and PG synthesis was investigated after cytokine stimulation of cultured rat osteoblasts. IL-1, TNF-alpha, IFN-gamma, and exogenous sodium nitroprusside, a nitric oxide donor, all stimulated PGE2 production in a dose-dependent manner. PGE2 production was blocked by L-nitro-arginine methyl ester, an inhibitor of nitric oxide production, after IFN-gamma stimulation and was partially blocked after TNF-alpha stimulation. However, IL-1-induced PGE2 was unaffected. Similarly, expression of the cyclooxygenase-2 protein was stimulated by cytokines, and IFN-gamma-induced expression was again blocked by L-nitro-arginine methyl ester. In contrast, all cytokines induced the cyclooxygenase-2 mRNA expression independently of nitric oxide production, although exogenous sodium nitroprusside was able to induce the cyclooxygenase-2 mRNA in the absence of cytokines. The results show that nitric oxide can induce PG synthesis and cyclooxygenase-2 expression and may regulate cyclooxygenase-2 expression at both transcriptional and post-transcriptional levels. In addition, the data show the existence of both nitric oxide-dependent and -independent pathways of PG synthesis after cytokine stimulation of osteoblasts. The results suggest that nitric oxide may be an important mediator of PG production in inflammatory bone diseases.
authors.affiliation: Department of Periodontology, Faculty of Clinical Dentistry, St. Bartholomews and the Royal London School of Medicine and Dentistry, London E1, United Kingdom.
authors.forename: F J
authors.initials: FJ
authors.lastname: Hughes
authors.forename: L D
authors.initials: LD
authors.lastname: Buttery
authors.forename: M V
authors.initials: MV
authors.lastname: Hukkanen
authors.forename: A
authors.initials: A
authors.lastname: O'Donnell
authors.forename: J
authors.initials: J
authors.lastname: Maclouf
authors.forename: J M
authors.initials: JM
authors.lastname: Polak
mesh_terms: D000818:Animals; D002478:Cells, Cultured; D051546:Cyclooxygenase 2; D015232:Dinoprostone / Q000096:biosynthesis*; D004790:Enzyme Induction; D007371:Interferon-gamma / Q000494:pharmacology; D007375:Interleukin-1 / Q000494:pharmacology; D007527:Isoenzymes / Q000096:biosynthesis / Q000378:metabolism*; D019331:NG-Nitroarginine Methyl Ester / Q000494:pharmacology; D009569:Nitric Oxide / Q000378:metabolism*; D019001:Nitric Oxide Synthase / Q000096:biosynthesis / Q000378:metabolism; D052247:Nitric Oxide Synthase Type II; D009599:Nitroprusside / Q000494:pharmacology; D010006:Osteoblasts / Q000187:drug effects / Q000378:metabolism*; D011451:Prostaglandin-Endoperoxide Synthases / Q000096:biosynthesis / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology
chemical_list: D007375:Interleukin-1; D007527:Isoenzymes; D012333:RNA, Messenger; D014409:Tumor Necrosis Factor-alpha; D009599:Nitroprusside; D009569:Nitric Oxide; D007371:Interferon-gamma; D019001:Nitric Oxide Synthase; D052247:Nitric Oxide Synthase Type II; C496318:Nos2 protein, rat; D051546:Cyclooxygenase 2; D011451:Prostaglandin-Endoperoxide Synthases; D015232:Dinoprostone; D019331:NG-Nitroarginine Methyl Ester