Anti-inflammatory effects of fucoidan through inhibition of NF-κB, MAPK and Akt activation in lipopolysaccharide-induced BV2 microglia cells

Fucoidan, a sulfated polysaccharide extracted from brown seaweed, displays a wide variety of internal biological activities; however, the cellular and molecular mechanisms underlying fucoidan’s anti-inflammatory activity remain poorly understood. In this study, we investigated the inhibitory effects of fucoidan on production of lipopolysaccharide (LPS)-induced pro-inflammatory mediators in BV2 microglia. Our data indicated that fucoidan treatment significantly inhibited excessive production of nitric oxide (NO) and prostaglandin E₂ (PGE₂) in LPS-stimulated BV2 microglia. It also attenuated expression of inducible nitric oxide synthase (iNOS), cyclooxygenase (COX)-2, monocyte chemoattractant protein-1 (MCP-1), and pro-inflammatory cytokines, including interleukin-1β (IL-1β) and tumor necrosis factor (TNF)-α. Moreover, fucoidan exhibited anti-inflammatory properties by suppression of nuclear factor-kappa B (NF-κB) activation and down-regulation of extracellular signal-regulated kinase (ERK), c-Jun N-terminal kinase (JNK), p38 mitogen-activated protein kinase (MAPK), and AKT pathways. These finding suggest that fucoidan may offer substantial therapeutic potential for treatment of neurodegenerative diseases that are accompanied by microglial activation.     

吡格列酮对脂多糖诱导星形胶质细胞诱导型一氧化氮合酶表达的抑制作用

目的 研究吡格列酮(Pio)对脂多糖 (LPS) 诱导星形胶质细胞(AC)诱导型一氧化氮合酶(iNOS)的抑制作用及其作用机制。方法 AC分别加入Pio 0.1, 1.0和10.0 μmol·L^-1, c-Jun氨基端激酶(JNK)抑制剂SP600125 20.0 μmol·L^-1, p38丝裂原活化蛋白激酶(p38MAPK)抑制剂SB203580 20.0 μmol·L^-1或过氧化物酶体增殖物激活受体γ(PPARγ)抑制剂GW9662 10.0 μmol·L^-1,1 h以后加入LPS 10.0 mg·L^-1, 继续作用24 h。Griess法测定培养AC上清液中一氧化氮(NO)含量。免疫印迹法和免疫荧光法检测iNOS的表达水平。结果 与正常对照组相比,LPS 10.0 mg·L^-1组iNOS表达水平和NO分泌水平均显著增高(P<0.01)。Pio 0.1, 1.0和10.0 μmol·L^-1可明显抑制LPS诱导的iNOS表达上调及NO分泌增加(P<0.05),Pio 10.0 μmol·L^-1组iNOS蛋白表达水平由LPS组1.711±0.283下降到0.157±0.082(P<0.01),NO分泌量由LPS组(16.63±2.25)μmol·L^-1下降到(6.92±1.30)μmol·L^-1(P<0.01)。GW9662 10.0 μmol·L^-1可抑制Pio 1.0 μmol·L^-1的上述作用,iNOS蛋白表达水平由Pio 1.0 μmol·L^-1组0.562±0.100增加到0.847±0.088(P<0.01),NO分泌量由(9.27±1.23)μmol·L^-1增加到(15.54±2.30)μmol·L^-1(P<0.01)。SB203580 20.0 μmol·L^-1和SP600125 20.0 μmol·L^-1的作用与Pio作用相似,使iNOS蛋白表达水平降低到0.434±0.082和0.434±0.076,NO分泌量下降到(11.53±2.40)μmol·L^-1和(8.81±0.58)μmol·L^-1;而单独应用SB203580 20.0 μmol·L^-1和SP600125 20.0 μmol·L^-1对AC的iNOS表达和NO分泌没有影响。结论 Pio能通过抑制LPS诱导的大鼠皮质AC的iNOS表达,从而减少NO的分泌,这种抑制作用可能与其激活PPARγ和阻断JNK和p38MARK信号转导通路有关。     

Involvement of protein kinase Cdelta and extracellular signal-regulated kinase-2 in the suppression of microglial inducible nitric oxide synthase expression by N-[3,4-dimethoxycinnamoyl]-anthranilic acid (tranilast)

Excess nitric oxide (NO) in the brain released by microglial cells contributes to neuronal damage in various pathologies of the central nervous system (CNS) including neurodegenerative diseases and multiple sclerosis. N-[3,4-Dimethoxycinnamoyl]-anthranilic acid (tranilast, TNL) is an anti-allergic compound which suppresses the activation of monocytes. We show that inducible nitric oxide synthase (iNOS) mRNA and protein expression and the release of NO from N9 microglial cells stimulated with the bacterial endotoxin lipopolysaccharide (LPS) are inhibited when the cells are exposed to TNL. TNL fails to modulate LPS-stimulated nuclear factor-kappaB (NF-kappaB) reporter gene activity and phosphorylation of inhibitory kappaB (IkappaB), indicating that NF-kappaB is not involved in the TNL-mediated suppression of LPS-induced iNOS expression. Moreover, TNL inhibits LPS-induced phosphorylation of extracellular signal-regulated kinase 2 (ERK-2). Finally, TNL abolishes translocation of protein kinase Cdelta (PKCdelta) to the nucleus and suppresses the phosphorylation of the PKCdelta substrate, myristoylated alanin-rich C kinase substrate (MARCKS). We conclude that the anti-allergic compound TNL suppresses microglial iNOS induction by LPS via inhibition of a signalling pathway involving PKCdelta and ERK-2.     

Anti-inflammatory effects of fluoxetine in lipopolysaccharide(LPS)-stimulated microglial cells

Recent evidence has suggested that microglial activation plays an important role in the pathogenesis of depression. Activated microglia can secrete various pro-inflammatory cytokines and neurotoxic mediators, which may contribute to the development and maintenance of depression. Thus, inhibition of microglial activation may have a therapeutic benefit in the treatment of depression. In the present study, using BV2 microglial cell line and primary microglial culture, we investigated if fluoxetine, the most widely used antidepressant, can inhibit microglia activation. Our results showed that fluoxetine significantly inhibited lipopolysaccharide (LPS)-induced production of tumor necrosis factor-alpha (TNF-α), interleukin- 6 (IL-6) and nitric oxide (NO). By RT-PCR, the mRNA level of these pro-inflammatory cytokines and iNOS was also attenuated by fluoxetine. We further investigated the intracellular signaling mechanism regulating the production of pro-inflammatory cytokines and NO from LPS-activated microglia. The results showed that fluoxetine inhibited IκB-a degradation, phosphorylation and nuclear translocation of the p65 subunit of NF-κB, and phosphorylation of p38 mitogen-activated protein kinase (MAPK) in the LPS-stimulated microglia. Taken together, our results suggest that the therapeutic effects of fluoxetine are partially mediated by modulating microglial activation.     

Hypoxia-induced iNOS expression in microglia is regulated by the PI3-kinase/Akt/mTOR signaling pathway and activation of hypoxia inducible factor-1alpha

Exposure to hypoxia induced microglia activation and animal studies have shown that neuronal cell death is correlated with microglial activation following cerebral ischemia. Thus, it is likely that toxic inflammatory mediators produced by activated microglia under hypoxic conditions may exacerbate neuronal injury following cerebral ischemia. The hypoxia-inducible factor-1 (HIF-1) is primarily involved in the sensing and adapting of cells to changes in the O(2) level, which is regulated by many physiological functions. However, the role of HIF-1 in microglia activation under hypoxia has not yet been defined. In the current work, we investigate the signaling pathways of HIF-1alpha involved in the regulation of hypoxia-induced overexpression of inducible NO synthase (iNOS) in microglia. Exposure of primary rat microglial cultures as well as established microglial cell line BV-2 to hypoxia induced the expression of iNOS, indicating that hypoxia could lead to the inflammatory activation of microglia. iNOS induction was accompanied with NO production. Moreover, the molecular analysis of these events indicated that iNOS expression was regulated by the phosphatidylinositol 3-kinase (PI3-kinase)/AKT/ mammalian target of rapamycin (mTOR) signaling pathway and activation of hypoxia inducible factor-1alpha (HIF-1alpha). Thus, during cerebral ischemia, hypoxia may not only directly damage neurons, but also promote neuronal injury indirectly via microglia activation. In this study, we demonstrated that hypoxia induced iNOS expression by regulation of HIF-1alpha in microglia.     

石菖蒲抑制脂多糖诱导的神经胶质细胞炎性反应及其机制

目的 观察石菖蒲对脂多糖(lipopolysaccharide,LPS)诱导的大鼠原代神经胶质细胞炎性反应的抑制作用并探讨其可能机制.方法 分离提取大鼠原代神经胶质细胞,用LPS刺激2h后分别加入不同浓度的石菖蒲含药血清,采用硝酸还原酶法检测石菖蒲对一氧化氮的影响,运用酶联免疫吸附法(ELISA)测定培养上清液中IL-1 β、IL-8、TNF-α水平,通过实时逆转录聚合酶链反应(RT-PCR)测定细胞中诱导型一氧化氮合酶(iNOS) mRNA表达.结果 LPS能够激活神经胶质细胞,不同浓度的石菖蒲含药大鼠血清在不影响细胞存活率的情况下,可以显著降低细胞培养上清液中NO、IL-1β、IL-8、TNF-α水平,抑制细胞内iNOS mRNA表达(P＜0.05).结论 石菖蒲的神经保护机制可能与抑制胶质细胞炎症反应有关.     

Inhibitory action of minocycline on lipopolysaccharide-lnduced release of nitric oxide and prostaglandin E2 in BV2 microglial cells

Microglia are the major inflammatory cells in the central nervous system and become activated in response to brain injuries such as ischemia, trauma, and neurodegenerative diseases including Alzheimer's disease (AD). Moreover, activated microglia are known to release a variety of proinflammatory cytokines and oxidants such as nitric oxide (NO). Minocycline is a semisynthetic second-generation tetracycline that exerts anti-inflammatory effects that are completely distinct form its antimicrobial action. In this study, the inhibitory effects of minocycline on NO and prostaglandin E2 (PGE2) release was examined in lipopolysaccharides (LPS)-challenged BV2 murine microglial cells. Further, effects of minocycline on inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2) expression levels were also determined. The results showed that minocycline significantly inhibited NO and PGE2 production and iNOS and COX-2 expression in BV2 microglial cells. These findings suggest that minocycline should be evaluated as potential therapeutic agent for various pathological conditions due to the excessive activation of microglia.     

Wogonin attenuates endotoxin‐induced prostaglandin E2 and nitric oxide production via Src‐ERK1/2‐NFκB pathway in BV‐2 microglial cells

Microglia are the major component of intrinsic brain immune system in neuroinflammation. Although wogonin expresses anti‐inflammatory function in microglia, little is known about the molecular mechanisms of the protective effect of wogonin against microglia activation. The aim of this study was to evaluate how wogonin exerts its anti‐inflammatory function in BV2 microglial cells after LPS/INFγ administration. Wogonin not only inhibited LPS/ INFγ‐induced PGE2 and NO production without affecting cell viability but also exhibited parallel inhibition on LPS/INFγ‐induced expression of iNOS and COX‐2 in the same concentration range. While LPS/INFγ‐induced expression of P‐p65 and P‐IκB was inhibited by wogonin — only weak inhibition on P‐p38 and P‐JNK were observed, whereas it significantly attenuated the P‐ERK1/2 and its upstream activators P‐MEK1/2 and P‐Src in a parallel concentration‐dependent manner. These results indicated that the blockade of PGE2 and NO production by wogonin in LPS/INFγ‐stimulated BV2 cells is attributed mainly to interference in the Src‐MEK1/2‐ERK1/2‐NFκB‐signaling pathway. © 2013 Wiley Periodicals, Inc. Environ Toxicol 29: 1162–1170, 2014.     

Effect of a selective inducible nitric oxide synthase inhibitor on intraocular nitric oxide production in endotoxin-induced uveitis rabbits: in vivo intraocular microdialysis study

Inducible nitric oxide (NO) synthase (iNOS) is believed to contribute to the pathogenesis of endotoxin-induced uveitis (EIU). In the present study, we investigated the inhibitory effects of N(G)-nitro-L-arginine methyl ester (L-NAME), a non-selective NOS inhibitor, and S,S'-1,4-phenylene-bis(1,2-ethanediyl)bis-isothiourea (PBITU), a potent and selective iNOS inhibitor, on intraocular NO production in EIU rabbits using an in vivo intraocular microdialysis technique. The flare level in the anterior chamber increased from 1h after the injection of 100 micro g/kg lipopolysaccharide (LPS), and continued to increase for 24h. Aqueous humor protein concentrations were significantly increased at 24h after LPS-injection. These changes were significantly reduced by L-NAME (10mg/kg) and PBITU (1mg/kg), but not by D-NAME (10mg/kg). The increase in NO(2)(-) and NO(3)(-) levels in the dialysate induced by LPS was significantly inhibited by L-NAME (10mg/kg) and PBITU (1mg/kg), but not by D-NAME (10mg/kg). These results suggest that activation of iNOS may play a key role in the development of EIU, and selective inhibitors of iNOS may have therapeutic applications in the treatment of EIU.     

Manganese potentiates in vitro production of proinflammatory cytokines and nitric oxide by microglia through a nuclear factor kappa B-dependent mechanism.

Recent evidence suggests that the mechanism of manganese (Mn) neurotoxicity involves activation of microglia and/or astrocytes; as a consequence, neurons adjacent to the activated microglia may be injured. Mn modulation of proinflammatory cytokine expression by microglia has not been investigated. Therefore, the objectives of this research were to (1) assess whether Mn induces proinflammatory cytokine expression and/or modulates lipopolysaccharide (LPS)-induced expression of proinflammatory cytokines and (2) investigate possible mechanisms for such an induction. N9 microglia were exposed in vitro to increasing concentrations (50-1000 microM) of Mn in the presence or absence of LPS (10, 100, or 500 ng/ml). After various incubation times (up to 48 h), media levels of several cytokines and nitric oxide (NO) were determined, as was the expression of the inducible form of NO synthase (iNOS). Lactate dehydrogenase (LDH) release into the medium and the cellular uptake of Neutral Red were used as general measures for cytotoxicity. In the absence of LPS, Mn moderately increased interleukin-6 and tumor necrosis factor alpha (TNF-a) production only at higher Mn concentrations, which were cytotoxic. At all LPS doses, however, proinflammatory cytokine production was dose-dependently increased by Mn. Similarly, LPS-induced NO production and iNOS expression were substantially enhanced by Mn. Pharmacological manipulations indicated that nuclear factor kappa B (NFkappaB) activation is critical for the observed enhancement of cytokine and NO production. Within the context of inflammation, increased production of proinflammatory cytokines and NO by Mn could be an important part of the mechanism by which Mn exerts its neurotoxicity.     

Inhibition of macrophage migration inhibitory factor (MIF) tautomerase activity suppresses microglia‐mediated inflammatory responses

Macrophage migration inhibitory factor (MIF), a pleiotropic pro‐inflammatory cytokine, is a key regulator in both innate and acquired immunity systems. MIF has become a promising drug target for inflammatory diseases. Apart from its cytokine activities, MIF is known to act as a d ‐dopachrome tautomerase. Our previous work has identified that 3‐[(biphenyl‐4‐ylcarbonyl)carbamothioyl]amino benzoic acid (Z‐590) exhibited a potent inhibitory activity against MIF. In this study, we investigate the effect of Z‐590 on lipopolysaccharide (LPS)‐activated microglial cell activation. Our results demonstrate that Z‐590 significantly decreases the production of nitric oxide (NO), tumour necrosis factor‐alpha (TNF‐α), interleukin (IL)‐6, IL‐1β, cyclooxygenase (COX‐2), inducible nitric oxide synthase (iNOS) as well as reactive oxygen species (ROS) involved in inhibiting MAKPs signalling pathway in LPS‐stimulated microglia cells. Furthermore, Z‐590 reduced cytotoxicity of activated microglia toward HT‐22 hippocampal cells in a microglia‐conditioned medium system. Taken together, these results indicate that MIF inhibitor Z‐590 elicits a potent inhibitor for microglia‐mediated neuroinflammation.     

Down-regulation of microglial cyclo-oxygenase-2 and inducible nitric oxide synthase expression by lipocortin 1

1. Activated microglial cells are believed to play an active role in most brain pathologies, during which they can contribute to host defence and repair but also to the establishment of tissue damage. These actions are largely mediated by microglial secretory products, among which are prostaglandins (PGs) and nitric oxide (NO). 2. The anti-inflammatory protein, lipocortin 1 (LC1) was reported to have neuroprotective action and to be induced by glucocorticoids in several brain structures, with a preferential expression in microglia. In this paper we tested whether the neuroprotective effect of LC1 could be explained by an inhibitory effect on microglial activation. 3. We have previously shown that bacterial endotoxin (LPS) strongly stimulates PGE2 and NO production in rat primary microglial cultures, by inducing the expression of the key enzymes cyclo-oxygenase-2 (COX-2) and inducible nitric oxide synthase (iNOS), respectively. 4. Dexamethasone (DEX, 1-100 nM) and LC1-derived N-terminus peptide (peptide Ac2-26, 1-100 microg ml(-1)) dose-dependently inhibited the production of both PGE2 and NO from LPS-stimulated microglia. The inhibitory effects of DEX on NO and of the peptide on NO and PGE2 synthesis were partially abrogated by a specific antiserum, raised against the N-terminus of human LC1. The peptide Ac2-26 did not affect arachidonic acid release from control and LPS-stimulated microglial cultures. 5. Western blot experiments showed that the LPS-induced expression of COX-2 and iNOS was effectively down-regulated by DEX (100 nM) and peptide Ac2-26 (100 microg ml(-1)). 6. In conclusion, our findings support the hypothesis that LC1 may foster neuroprotection by limiting microglial activation, through autocrine and paracrine mechanisms.     

Adenosine kinase inhibitor attenuates the expression of inducible nitric oxide synthase in glial cells

The present study demonstrates the anti-inflammatory effect of adenosine kinase inhibitor (ADKI) in glial cells. Treatment of glial cells with IC51, an ADKI, stimulated the extracellular adenosine release and reduced the LPS/IFNgamma-mediated production of NO, and induction of iNOS and TNF-alpha gene expression. The recovery of IC51-mediated inhibition of iNOS expression by adenosine transport inhibitor, S-(4-nitrobenzyl)-6-thioinosine (NBTI), and the inhibition of LPS/IFNgamma-induced iNOS gene expression by exogenous adenosine indicate a role for adenosine release in IC51-mediated iNOS expression. The rescue of IC51-mediated inhibition of iNOS expression by adenosine receptor antagonist for A2A, 8-(3-chlorostyryl)caffeine (CSC) and alloxazine for A2B, further supports a role for interaction of adenosine and its receptors in anti-inflammatory activity. The IC51-mediated induction of cAMP levels, downstream target of A2A and A2B, and inhibition of LPS/IFNgamma-induced expression of iNOS by forskolin, a cAMP activator, document a role for cAMP mediated pathway in anti-inflammatory activity of IC51. Taken together, these studies document that IC51-mediated inhibition of iNOS expression is through activation of adenosine receptors, which activates A2A and A2B resulting in increased cAMP levels following LPS/IFNgamma stimulation. Moreover, the lack of effect of IC51 or adenosine on NFkappaB DNA binding activity and its transactivity indicates that the inhibition of iNOS expression mediated by IC51 may be through an NFkappaB independent pathway.     

Resveratrol inhibits nitric oxide and TNF-alpha production by lipopolysaccharide-activated microglia

Upon activation, brain macrophages, the microglia, release proinflammatory mediators that play important roles in eliciting neuroinflammatory responses associated with neurodegenerative diseases. As resveratrol, an antioxidant component of grape, has been reported to exert anti-inflammatory activities on macrophages, we investigated its effects on the production of TNF-alpha (TNF-alpha) and nitric oxide (NO) by lipopolysaccharide (LPS)-activated microglia. Exposure of cultured rat cortical microglia and a mouse microglial cell line N9 to LPS increased their release of TNF-alpha and NO, which was significantly inhibited by resveratrol. Further studies revealed that resveratrol suppressed LPS-induced degradation of IkappaBalpha, expression of iNOS and phosphorylation of p38 mitogen-activated protein kinases (MAPKs) in N9 microglial cells. These results demonstrate a potent suppressive effect of resveratrol on proinflammatory responses of microglia, suggesting a therapeutic potential for this compound in neurodegenerative diseases accompanied by microglial activation.     

Myrrh mediates haem oxygenase-1 expression to suppress the lipopolysaccharide-induced inflammatory response in RAW264.7 macrophages

Objectives To elucidate a novel anti‐inflammatory mechanism of myrrh against lipopolysaccharide (LPS)‐induced inflammation. Methods RAW264.7 macrophages were cultured in DMEM and then cells were treated with LPS or LPS plus a myrrh methanol extract (MME) for 24 h. The culture medium was collected for determination of nitric oxide (NO), prostaglandin (PG)E₂, interleukin (IL)‐1β, and tumour necrosis factor (TNF)‐α, and cells were harvested by lysis buffer for Western blot analysis. Key findings Our data showed that treatment with the MME (1～100 µg/ml) did not cause cytotoxicity or activate haem oxygenase‐1 (HO‐1) protein synthesis in RAW264.7 macrophages. Furthermore, the MME inhibited LPS‐stimulated NO, PGE₂, IL‐1β and TNF‐α release and inducible nitric oxide synthase (iNOS) and cyclooxygenase (COX)‐2 protein expression. Zn(II) protoporphyrin IX, a specific inhibitor of HO‐1, blocked the inhibition of iNOS and COX‐2 expression by the MME. Conclusions These results suggest that among mechanisms of the anti‐inflammatory response, the MME inhibited the production of NO, PGE₂, IL‐1β and TNF‐α by downregulating iNOS and COX‐2 gene expression in macrophages and worked through the action of HO‐1.