Kanematsu M, Ikeda K, Yamada Y
Department of Geriatric Research, National Institute for Longevity Sciences, Aichi, Japan.
J Bone Miner Res. 1997 Nov;12(11):1789-96. doi: 10.1359/jbmr.1997.12.11.1789.
Interleukin 1 (IL-1) and tumor necrosis factor alpha (TNF-alpha) 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 alpha and TNF-alpha induced a marked increase in the production of both NO and PGE2. 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 PGE2 production revealed a biphasic pattern: the first small peak at 3 h was caused by de novo synthesis of PGE2 through inducible COX (COX-2) mRNA, while the subsequent progressive accumulation of PGE2 was mediated through the activation of COX pathway by NO since (1) aminoguanidine (AG), a selective inhibitor of inducible NOS, significantly suppressed the PGE2 production by IL-1 alpha and TNF-alpha, (2) NOC-18, an NO donor, reversed this suppression, and (3) NOC-18 increased PGE2 production by itself. The increase in NO production in response to IL-1 alpha and TNF-alpha was further stimulated by aspirin and inhibited by exogenous addition of PGE2, suggesting that PGE2 produced by the cytokines, in turn, negatively modulates NO production. IL-1 alpha and TNF-alpha 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. PGE2 decreased ALP activity, and the inhibitory effect of NOC-18 was attenuated in the presence of aspirin, suggesting the involvement of PGE2 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 conditions.
白细胞介素1（IL-1）和肿瘤坏死因子α（TNF-α）与骨质疏松症的发病机制有关。这些促炎细胞因子分别诱导环氧化酶（COX）和一氧化氮合酶（NOS），并释放前列腺素（PG）和NO。本研究旨在探讨COX和NOS途径之间的相互作用及其在调节MC3T3-E1细胞成骨细胞功能中的作用。添加IL-1α和TNF-α可显著增加NO和PGE2的产生。逆转录-聚合酶链反应分析表明，NO产生的增加先于诱导型NOS mRNA的表达。PGE2产生的时间模式呈现双相性：3小时时的第一个小峰值是由诱导型COX（COX-2）mRNA从头合成PGE2引起的，而随后PGE2的逐渐积累是由NO激活COX途径介导的，因为（1）诱导型NOS的选择性抑制剂氨基胍（AG）显著抑制IL-1α和TNF-α诱导的PGE2产生，（2）NO供体NOC-18可逆转这种抑制作用，（3）NOC-18自身可增加PGE2的产生。阿司匹林进一步刺激了IL-1α和TNF-α诱导的NO产生增加，而外源性添加PGE2则抑制了这种增加，这表明细胞因子产生的PGE2反过来对NO产生负调节作用。IL-1α和TNF-α抑制碱性磷酸酶（ALP）活性，而AG可显著逆转这种抑制作用。NOC-18不仅自身抑制ALP活性，还阻断了AG的作用，这表明NO在抑制ALP活性中起作用。PGE2降低了ALP活性，在阿司匹林存在的情况下，NOC-18的抑制作用减弱，这表明PGE2参与了NO对ALP活性的负调节作用。这些结果表明，对促炎细胞因子产生的NO通过激活COX途径参与ALP活性的调节。NO和COX途径之间的相互作用可能在生理和病理条件下成骨细胞功能的调节中起重要作用。
