Interaction Between Nitric Oxide Synthase and Cyclooxygenase Pathways in Osteoblastic MC3T3-E1 Cells

Abstract

Interleukin 1 (IL-1) and tumor necrosis factor ␣ (TNF-␣) have been implicated in the pathogenesis of osteoporosis. These proinflammatory cytokines induce both cyclooxygenase (COX) and nitric oxide synthase (NOS) with the release of prostaglandin (PG) and NO, respectively. The present study was undertaken to examine the interaction between COX and NOS pathways and their role in the regulation of osteoblastic function in MC3T3-E1 cells. Addition of IL-1␣ and TNF-␣ induced a marked increase in the production of both NO and PGE 2 . Reverse transcription-polymerase chain reaction analysis showed that the increase in NO production was preceded by the expression of inducible NOS mRNA. The temporal profile of PGE 2 production revealed a biphasic pattern: the first small peak at 3 h was caused by de novo synthesis of PGE 2 through inducible COX (COX-2) mRNA, while the subsequent progressive accumulation of PGE 2 was mediated through the activation of COX pathway by NO since (1) aminoguanidine (AG), a selective inhibitor of inducible NOS, significantly suppressed the PGE 2 production by IL-1␣ and TNF-␣, (2) NOC-18, an NO donor, reversed this suppression, and (3) NOC-18 increased PGE 2 production by itself. The increase in NO production in response to IL-1␣ and TNF-␣ was further stimulated by aspirin and inhibited by exogenous addition of PGE 2 , suggesting that PGE 2 produced by the cytokines, in turn, negatively modulates NO production. IL-1␣ and TNF-␣ inhibited alkaline phosphatase (ALP) activity, which was significantly reversed by AG. NOC-18 not only suppressed ALP activity by itself but also blocked the effect of AG, suggesting the role of NO in the inhibition of ALP activity. PGE 2 decreased ALP activity, and the inhibitory effect of NOC-18 was attenuated in the presence of aspirin, suggesting the involvement of PGE 2 in the negative modulation of ALP activity by NO. These results suggest that NO produced in response to proinflammatory cytokines participates in the modulation of ALP activity via the activation of COX pathway. The interaction between NO and the COX pathways may play an important role in the regulation of osteoblastic functions under physiologic as well as pathologic

Release of nitric oxide, but not prostaglandin E2, by bone cells depends on fluid flow frequency

“…In additional studies, NOS and COX, enzymes responsible for the synthesis of NO and PGE 2 , were induced by interleukin-1 (IL-1) in MC3T3-E1 cells. 46,47 In these studies it was suggested that both NO-dependent and NO-independent pathways for the production of PGE 2 exist and that the early production of PGE 2 might be independent of NO. 47 However, the stimulation of NO production by IL-1 is mediated by the inducible form of NOS (iNOS) and leads to much higher levels of NO than the stimulation by fluid flow, which runs via the constitutive form of NOS (eNOS).…”

“…46,47 In these studies it was suggested that both NO-dependent and NO-independent pathways for the production of PGE 2 exist and that the early production of PGE 2 might be independent of NO. 47 However, the stimulation of NO production by IL-1 is mediated by the inducible form of NOS (iNOS) and leads to much higher levels of NO than the stimulation by fluid flow, which runs via the constitutive form of NOS (eNOS). Nevertheless, it still needs to be established whether the delayed production of PGE 2 , which has been shown to occur in response to flow as well, 8 follows the NO release pattern.…”

Expression of Functional Metabotropic Glutamate Receptors in Primary Cultured Rat Osteoblasts

“…It is well established that bone cells are regulated in their activity both by circulating hormones (1) and by the interacting effects of a number of locally acting intercellular signals, including prostaglandins, growth factors, cytokines, and nitric oxide (2)(3)(4)(5)(6)(7)(8)(9). Recently, it has been reported that functional NMDA 1 -type glutamate receptors are expressed in a number of bone cell types, including rat and human osteoblasts and osteoclasts, MG-63 osteosarcoma cells, and in bone marrow megakaryocytes (10 -15).…”

Antitumor effects of inhibitors of nitric oxide synthase or cyclooxygenase-2 on human KB carcinoma cells overexpressing COX-2

“…Park et al (22) reported that cross-talk exists between COX and NOS in head and neck cancer cell lines. There are inter- actions between COX and NOS pathways among host tissues, not only in tumor tissue (31)(32)(33). We found that NOS inhibitor blocked COX-2 expression, and COX-2 inhibitor blocked NOS (iNOS and eNOS) expression in vivo.…”