Bilirubin inhibits the up-regulation of inducible nitric oxide synthase by scavenging reactive oxygen species generated by the toll-like receptor 4-dependent activation of NADPH oxidase.
Bilirubin inhibits the up-regulation of inducible nitric oxide synthase by scavenging reactive oxygen species generated by the toll-like receptor 4-dependent activation of NADPH oxidase.
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DOI：
10.1016/j.redox.2015.06.008
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发表时间：
2015-08
期刊：
影响因子：
11.4
通讯作者：
Zucker SD
中科院分区：
文献类型：
--
作者：
Idelman G;Smith DLH;Zucker SD
先前已有研究表明，胆红素可阻止诱导型一氧化氮合酶（iNOS）在LPS作用下的上调。本研究探讨了这种效应是否通过toll样受体-4 （TLR4）信号的调节来发挥作用。通过测量细胞硝酸盐和超氧化物的产生，分别评估lps刺激的RAW 264.7小鼠巨噬细胞的iNOS和NADPH氧化酶（Nox）活性。TLR4抑制剂抑制了硝酸盐的生成和对LPS的响应，表明iNOS和Nox的激活依赖于TLR4。虽然用超氧化物歧化酶（SOD）和胆红素处理能有效地消除脂多糖介导的生成，但胆红素和peg -过氧化氢酶能抑制过氧化氢和硝酸盐的释放，而SOD则不能，这表明iNOS的激活主要依赖于细胞内的H2O2。LPS处理增加了氧化还原敏感转录因子缺氧诱导因子-1α (HIF-1α)的核易位，这一作用被胆红素消除。转染HIF-1α特异性缺氧反应元件被破坏的小鼠iNOS报告结构的细胞对LPS的反应迟钝，支持HIF-1α介导nox依赖性iNOS表达。胆红素，而不是SOD，阻断了细胞中干扰素-β的产生，而白细胞介素-6的产生不受影响。这些数据支持胆红素通过清除nox衍生的活性氧来阻止HIF-1α的激活，从而抑制tlr4介导的iNOS上调。胆红素还通过ros独立机制抑制干扰素-β的释放。这些发现表征了胆红素抗炎作用的潜在机制。胆红素通过清除NADPH氧化酶衍生的活性氧来阻断TLR4信号。胆红素特异性抑制trif依赖性TLR4信号通路。诱导型一氧化氮合酶的LPS激活是由HIF-1α介导的。巨噬细胞表现出HIF-1α和芳烃受体途径的相互调节。揭示了胆红素抗炎作用的潜在机制。
It has been previously shown that bilirubin prevents the up-regulation of inducible nitric oxide synthase (iNOS) in response to LPS. The present study examines whether this effect is exerted through modulation of Toll-Like Receptor-4 (TLR4) signaling. LPS-stimulated iNOS and NADPH oxidase (Nox) activity in RAW 264.7 murine macrophages was assessed by measuring cellular nitrate and superoxide () production, respectively. The generation of both nitrate and in response to LPS was suppressed by TLR4 inhibitors, indicating that activation of iNOS and Nox is TLR4-dependent. While treatment with superoxide dismutase (SOD) and bilirubin effectively abolished LPS-mediated production, hydrogen peroxide and nitrate release were inhibited by bilirubin and PEG-catalase, but not SOD, supporting that iNOS activation is primarily dependent upon intracellular H2O2. LPS treatment increased nuclear translocation of the redox-sensitive transcription factor Hypoxia Inducible Factor-1α (HIF-1α), an effect that was abolished by bilirubin. Cells transfected with murine iNOS reporter constructs in which the HIF-1α-specific hypoxia response element was disrupted exhibited a blunted response to LPS, supporting that HIF-1α mediates Nox-dependent iNOS expression. Bilirubin, but not SOD, blocked the cellular production of interferon-β, while interleukin-6 production remained unaffected. These data support that bilirubin inhibits the TLR4-mediated up-regulation of iNOS by preventing activation of HIF-1α through scavenging of Nox-derived reactive oxygen species. Bilirubin also suppresses interferon-β release via a ROS-independent mechanism. These findings characterize potential mechanisms for the anti-inflammatory effects of bilirubin. Bilirubin blocks TLR4 signaling by scavenging NADPH oxidase-derived reactive oxygen species. Bilirubin specifically inhibits the TRIF-dependent TLR4 signaling pathway. LPS activation of inducible nitric oxide synthase is mediated by HIF-1α. Macrophages exhibit reciprocal regulation of HIF-1α and aryl hydrocarbon receptor pathways. Potential mechanisms underlying the anti-inflammatory effects of bilirubin are delineated.