Sodium butyrate suppresses interferon-gamma-, but not lipopolysaccharide-mediated induction of nitric oxide and tumor necrosis factor-alpha in microglia

Influence of antipsychotic drugs on microglia-mediated neuroinflammation in schizophrenia: perspectives in an astrocyte-microglia co-culture model

Schizophrenia is a severe mental disorder with a strong lifetime impact on patients' health and wellbeing. Usually, symptomatic treatment includes typical or atypical antipsychotics. Study findings show an involvement of low-grade inflammation (blood, brain parenchyma, and cerebrospinal fluid) in schizophrenia. Moreover, experimental and neuropathological evidence suggests that reactive microglia, which are the main resident immune cells of the central nervous system (CNS), have a negative impact on the differentiation and function of oligodendrocytes, glial progenitor cells, and astrocytes, which results in the disruption of neuronal networks and dysregulated synaptic transmission, contributing to the pathophysiology of schizophrenia. Here, the role of microglial cells related to neuroinflammation in schizophrenia was discussed to be essential. This review aims to summarize the evidence for the influence of antipsychotics on microglial inflammatory mechanisms in schizophrenia. Furthermore, we propose an established astrocyte-microglia co-culture model for testing regulatory mechanisms and examining the effects of antipsychotics on glia-mediated neuroinflammation. This could lead to a better understanding of how typical and atypical antipsychotics can be used to address positive and negative symptoms in schizophrenia and comorbidities like inflammatory diseases or the status of low-grade inflammation.

Sodium butyrate activates the KATP channels to regulate the mechanism of Parkinson's disease microglia model inflammation

BACKGROUND

Parkinson's disease (PD) is a common neurodegenerative disorder. Microglia-mediated neuroinflammation has emerged as an involving mechanism at the initiation and development of PD. Activation of adenosine triphosphate (ATP)-sensitive potassium (KATP ) channels can protect dopaminergic neurons from damage. Sodium butyrate (NaB) shows anti-inflammatory and neuroprotective effects in some animal models of brain injury and regulates the KATP channels in islet β cells. In this study, we aimed to verify the anti-inflammatory effect of NaB on PD and further explored potential molecular mechanisms.

METHODS

We established an in vitro PD model in BV2 cells using 1-methyl-4-phenylpyridinium (MPP+ ). The effects of MPP+ and NaB on BV2 cell viability were detected by cell counting kit-8 assays. The morphology of BV2 cells with or without MPP+ treatment was imaged via an optical microscope. The expression of Iba-1 was examined by the immunofluorescence staining. The intracellular ATP content was estimated through the colorimetric method, and Griess assay was conducted to measure the nitric oxide production. The expression levels of pro-inflammatory cytokines and KATP channel subunits were evaluated by reverse transcription-quantitative polymerase chain reaction and western blot analysis.

RESULTS

NaB (5 mM) activated the KATP channels through elevating Kir6.1 and Kir6.1 expression in MPP+ -challenged BV2 cells. Both NaB and pinacidil (a KATP opener) suppressed the MPP+ -induced activation of BV2 cells and reduced the production of nitrite and pro-inflammatory cytokines in MPP+ -challenged BV2 cells.

CONCLUSION

NaB treatment alleviates the MPP+ -induced inflammatory responses in microglia via activation of KATP channels.

The Role of Gut Microbiome-Derived Short-Chain Fatty Acid Butyrate in Hepatobiliary Diseases

The short-chain fatty acid butyrate, produced from fermentable carbohydrates by gut microbiota in the colon, has multiple beneficial effects on human health. At the intestinal level, butyrate regulates metabolism, helps in the transepithelial transport of fluids, inhibits inflammation, and induces the epithelial defense barrier. The liver receives a large amount of short-chain fatty acids via the blood flowing from the gut via the portal vein. Butyrate helps prevent nonalcoholic fatty liver disease, nonalcoholic steatohepatitis, inflammation, cancer, and liver injuries. It ameliorates metabolic diseases, including insulin resistance and obesity, and plays a direct role in preventing fatty liver diseases. Butyrate has different mechanisms of action, including strong regulatory effects on the expression of many genes by inhibiting the histone deacetylases and modulating cellular metabolism. The present review highlights the wide range of beneficial therapeutic and unfavorable adverse effects of butyrate, with a high potential for clinically important uses in several liver diseases.

Two New Phomaligols from the Marine-Derived Fungus Aspergillus flocculosus and Their Anti-Neuroinflammatory Activity in BV-2 Microglial Cells

Two new phomaligols, deketo-phomaligol A (1) and phomaligol E (2), together with six known compounds (3-8) were isolated from the culture broth of the marine-derived fungus Aspergillus flocculosus. Compound 1 was first isolated as a phomaligol derivative possessing a five-membered ring. The structures and absolute configurations of the new phomaligols were determined by detailed analyses of mass spectrometry (MS), nuclear magnetic resonance (NMR) data, optical rotation values and electronic circular dichroism (ECD). In addition, the absolute configurations of the known compounds 3 and 4 were confirmed by chemical oxidation and comparison of optical rotation values. Isolated compounds at a concentration of 100 μM were screened for inhibition of nitric oxide (NO) production in lipopolysaccharide (LPS)-induced BV-2 microglial cells. Among the compounds, 4 showed moderate anti-neuroinflammatory effects with an IC50 value of 56.6 μM by suppressing the production of pro-inflammatory mediators in activated microglial cells without cytotoxicity.

Herpes Simplex Virus Type 1 and Other Pathogens are Key Causative Factors in Sporadic Alzheimer's Disease

This review focuses on research in epidemiology, neuropathology, molecular biology, and genetics regarding the hypothesis that pathogens interact with susceptibility genes and are causative in sporadic Alzheimer's disease (AD). Sporadic AD is a complex multifactorial neurodegenerative disease with evidence indicating coexisting multi-pathogen and inflammatory etiologies. There are significant associations between AD and various pathogens, including Herpes simplex virus type 1 (HSV-1), Cytomegalovirus, and other Herpesviridae, Chlamydophila pneumoniae, spirochetes, Helicobacter pylori, and various periodontal pathogens. These pathogens are able to evade destruction by the host immune system, leading to persistent infection. Bacterial and viral DNA and RNA and bacterial ligands increase the expression of pro-inflammatory molecules and activate the innate and adaptive immune systems. Evidence demonstrates that pathogens directly and indirectly induce AD pathology, including amyloid-β (Aβ) accumulation, phosphorylation of tau protein, neuronal injury, and apoptosis. Chronic brain infection with HSV-1, Chlamydophila pneumoniae, and spirochetes results in complex processes that interact to cause a vicious cycle of uncontrolled neuroinflammation and neurodegeneration. Infections such as Cytomegalovirus, Helicobacter pylori, and periodontal pathogens induce production of systemic pro-inflammatory cytokines that may cross the blood-brain barrier to promote neurodegeneration. Pathogen-induced inflammation and central nervous system accumulation of Aβ damages the blood-brain barrier, which contributes to the pathophysiology of AD. Apolipoprotein E4 (ApoE4) enhances brain infiltration by pathogens including HSV-1 and Chlamydophila pneumoniae. ApoE4 is also associated with an increased pro-inflammatory response by the immune system. Potential antimicrobial treatments for AD are discussed, including the rationale for antiviral and antibiotic clinical trials.

Basal transcription is regulated by lipopolysaccharide and glucosamine via the regulation of DNA binding of RNA polymerase II in RAW264.7 cells

AIMS

The objective of this study is to investigate glucosamine (GlcN) as a transcriptional regulator of iNOS and other genes in association with the dynamic O-GlcNAcylation of RNA polymerase II (RNAPII).

MAIN METHODS

The LPS- and/or GlcN-stimulated transcriptional activities of various Gal4-binding site/TATA-box-containing reporter constructs were measured.

KEY FINDINGS

Basal transcriptional activities of nuclear factor-κB (NF-κB) and nitric oxide synthase (iNOS) reporter plasmids are inhibited by GlcN in RAW264.7 cells. Furthermore, GlcN suppressed whereas lipopolysaccharide (LPS) stimulated the basal activity of Gal4-binding site/TATA-box-containing reporter constructs. LPS reduced the O-linked N-acetylglucosamine modification (O-GlcNAcylation) of RNAPII, but enhanced the binding of this enzyme to the iNOS promoter. In contrast, GlcN enhanced RNAPII O-GlcNAcylation, but inhibited iNOS promoter binding. Furthermore, the basal activities of reporter plasmids containing activator protein 1 (AP1), E2F, or cyclic AMP response element (CRE) binding sites were consistently inhibited by GlcN in a dose-dependent manner. However, GlcN did not inhibit the phorbol 12-myristate 13-acetate- (PMA-) or forskolin-induced transcriptional activities of AP1 and CRE. The transcriptional activity of transforming growth factor alpha (TGF-α) was slightly increased by both LPS and GlcN.

SIGNIFICANCE

In conclusion, our data demonstrate that LPS activates, whereas GlcN suppresses, basal activities of transcription through the regulation of RNAPII O-GlcNAcylation and DNA binding.

The impact of neuroimmune changes on development of amyloid pathology; relevance to Alzheimer's disease

Neuroinflammatory changes are a characteristic of several, if not all, neurodegenerative diseases including Alzheimer's disease and are typified by increased microglial activation. Microglia express several receptors making them highly reactive and plastic cells, and, at least in vitro, they adopt different phenotypes in a manner analogous to their peripheral counterparts, macrophages. Microglia also express numerous cell surface proteins enabling them to interact with cells and the evidence indicates that maintenance of microglia in a quiescent state relies, at least to some extent, on an interaction with neurons by means of specific ligand-receptor pairs, for example CD200-CD200R. It is clear that microglia also interact with T cells and recent evidence indicates that co-incubation of microglia with T helper type 1 cells markedly increases their activation. Under normal conditions, small numbers of activated T cells gain entry to the brain and are involved in immune surveillance but infiltration of significant numbers of T cells occurs in disease and following injury. The consequences of T cell infiltration appear to depend on the conditions, with descriptions of both neurodestructive and neuroprotective effects in animal models of different diseases. This review will discuss the modulatory effect of T cells on microglia and the impact of infiltration of T cells into the brain with a focus on Alzheimer's disease, and will propose that infiltration of interferon-γ-producing cells may be an important factor in triggering inflammation that is pathogenic and destructive.

Valproic acid attenuates microgliosis in injured spinal cord and purinergic P2X4 receptor expression in activated microglia

Peripheral injection with a high dose of valproic acid (VPA), a histone deacetylase (HDAC) inhibitor, into animals with mild or moderate spinal cord injury (SCI) for 1 week can reduce spinal cord tissue loss and promote hindlimb locomotor recovery. A purinergic adenosine triphosphate (ATP) receptor subtype, P2X4 receptor (P2X4 R), has been considered as a potential target to diminish SCI-associated inflammatory responses. In this study, using a minipump-based infusion system, we found that intraspinal infusion with VPA for 3 days into injured spinal cord significantly improved hindlimb locomotion of rats with severe SCI induced by a 10-g NYU impactor dropping from the height of 50 mm onto the spinal T9/10 segment. The neuronal fibers in the injured spinal cord tissues were significantly preserved in VPA-treated rats compared with those observed in vehicle-treated animals. Moreover, the accumulation of microglia/macrophages and astrocytes in the injured spinal cord was attenuated in the animal group receiving VPA infusion. VPA also significantly reduced P2X4 R expression post-SCI. Furthermore, in vitro study indicated that VPA, but not the other HDAC inhibitors, sodium butyrate and trichostatin A (TSA), caused downregulation of P2X4 R in microglia activated with lipopolysaccharide (LPS). Moreover, p38 mitogen-activated protein kinase (MAPK)-triggered signaling was involved in the effect of VPA on the inhibition of P2X4 R gene expression. In addition to the findings from others, our results also provide important evidence to show the inhibitory effect of VPA on P2X4 R expression in activated microglia, which may contribute to reduction of SCI-induced gliosis and subsequently preservation of spinal cord tissues. © 2013 Wiley Periodicals, Inc.

Molecular mechanism of capillarisin-mediated inhibition of MyD88/TIRAP inflammatory signaling in in vitro and in vivo experimental models

ETHNOPHARMACOLOGICAL RELEVANCE

Artemisia capillaris Thunberg (Compositae) have been used as traditional medicine as a diuretic, liver protective agent, and for amelioration of inflammatory and analgesic disorders. The present study was carried out to establish the scientific rationale for treating inflammation and to find active principles from A. capillaris. The aim of the present study is to investigate the possible anti-inflammatory mechanism of the major component (capillarisin) isolated from A. capillaris via inhibition of MyD88/TIRAP inflammatory signaling both in vitro and in vivo models.

MATERIALS AND METHODS

The nitrite, PGE(2), and TNF-α productions were evaluated by Griess reagent and ELISA kits. The protein and mRNA expression levels were investigated by Western blot and RT-PCR. The NF-κB and AP-1 DNA-binding was performed by electrophoretic mobility shift assay. The CFA- and carrageenan-induced paw edema was performed in ICR mice in which 20 and 80 mg/kg body weight of capillarisin was administered intraperitoneally (i.p.).

RESULTS

The results demonstrated that pretreatment with capillarisin effectively inhibited the LPS-induced activation of NF-κB, Akt, and MAP kinase-activated inflammatory genes, which is mediated by MyD88 and TIRAP. Treatment with capillarisin reduced the mRNA and protein levels of iNOS and COX-2 in RAW 264.7 cells as assessed by RT-PCR and Western blot. Capillarisin suppressed LPS-induced inhibitory kappa kinase (IKK) phosphorylation and the degradation of inhibitory kappa B (IκBα) and prevented the nuclear translocation of p65 and p50. Capillarisin also exhibited a promising inhibitory effect on the LPS-induced NF-κB and AP-1 DNA binding activity based on an electrophoretic mobility shift assay. The LPS-induced activation of p-JNK, p-p38, p-ERK, and p-Akt was significantly inhibited. In addition, the TNF-α level in the media was effectively reduced by capillarisin. In vivo experimental analysis revealed that capillarisin (20 and 80 mg/kg, i.p.) inhibited complete Freund's adjuvant (CFA)-and carrageenan-induced paw edema, nitrite production in plasma, and TNF-α, a pro-inflammatory cytokine production.

CONCLUSION

The results presented here demonstrate that capillarisin has consistent anti-inflammatory properties and acts by inhibiting inflammatory mediators in in vitro and in vivo experimental models, and suggest its potential utility in the control of inflammatory disorders.

Natural plant products and extracts that reduce immunoexcitotoxicity-associated neurodegeneration and promote repair within the central nervous system

Our understanding of the pathophysiological and biochemical basis of a number of neurological disorders has increased enormously over the last three decades. Parallel with this growth of knowledge has been a clearer understanding of the mechanism by which a number of naturally occurring plant extracts, as well as whole plants, can affect these mechanisms so as to offer protection against injury and promote healing of neurological tissues. Curcumin, quercetin, green tea catechins, balcalein, and luteolin have been extensively studied, and they demonstrate important effects on cell signaling that go far beyond their antioxidant effects. Of particular interest is the effect of these compounds on immunoexcitotoxicity, which, the authors suggest, is a common mechanism in a number of neurological disorders. By suppressing or affecting microglial activation states as well as the excitotoxic cascade and inflammatory mediators, these compounds dramatically affect the pathophysiology of central nervous system disorders and promote the release and generation of neurotrophic factors essential for central nervous system healing. We discuss the various aspects of these processes and suggest future directions for study.

Structural insights into RipC, a putative citrate lyase β subunit from a Yersinia pestis virulence operon

Yersinia pestis remains a threat, with outbreaks of plague occurring in rural areas and its emergence as a weapon of bioterrorism; thus, an improved understanding of its various pathogenicity pathways is warranted. The rip (required for intracellular proliferation) virulence operon is required for Y. pestis survival in interferon-γ-treated macrophages and has been implicated in lowering macrophage-produced nitric oxide levels. RipC, one of three gene products from the rip operon, is annotated as a citrate lyase β subunit. Furthermore, the Y. pestis genome lacks genes that encode citrate lyase α and γ subunits, suggesting a unique functional role of RipC in the Y. pestis rip-mediated survival pathway. Here, the 2.45 Å resolution crystal structure of RipC revealed a homotrimer in which each monomer consists of a (β/α)(8) TIM-barrel fold. Furthermore, the trimeric state was confirmed in solution by size-exclusion chromatography. Through sequence and structure comparisons with homologous proteins, it is proposed that RipC is a putative CoA- or CoA-derivative binding protein.

Glucosamine exerts a neuroprotective effect via suppression of inflammation in rat brain ischemia/reperfusion injury

We investigated the neuroprotective effect of glucosamine (GlcN) in a rat middle cerebral artery occlusion model. At the highest dose used, intraperitoneal GlcN reduced infarct volume to 14.3% ± 7.4% that of untreated controls and afforded a reduction in motor impairment and neurological deficits. Neuroprotective effects were not reproduced by other amine sugars or acetylated-GlcN, and GlcN suppressed postischemic microglial activation. Moreover, GlcN suppressed lipopolysaccharide (LPS)-induced upregulation of proinflammatory mediators both in vivo and in culture systems using microglial or macrophage cells. The anti-inflammatory effects of GlcN were mainly attributable to its ability to inhibit nuclear factor kappaB (NF-κB) activation. GlcN inhibited LPS-induced nuclear translocation and DNA binding of p65 to both NF-κB consensus sequence and NF-κB binding sequence of inducible nitric oxide synthase promoter. In addition, we found that GlcN strongly repressed p65 transactivation in BV2 cells using Gal4-p65 chimeras system. P65 displayed increased O-GlcNAcylation in response to LPS; this effect was also reversed by GlcN. The LPS-induced increase in p65 O-GlcNAcylation was paralleled by an increase in interaction with O-GlcNAc transferase, which was reversed by GlcN. Finally, our results suggest that GlcN or its derivatives may serve as novel neuroprotective or anti-inflammatory agents.

Valproic acid enhances microglial phagocytosis of amyloid-beta(1-42)

Alzheimer's disease (AD) is a prevalent neurodegenerative disorder manifested by memory loss, confusion and changes in mood. A principal pathology of this debilitating disorder is extracellular deposits of amyloid-beta (Abeta) protein. The "amyloid hypothesis" postulates that a build-up of Abeta protein is responsible for neuronal loss and the ensuing symptoms of AD. One possible mechanism of Abeta clearance, and hence AD therapy, is phagocytosis of Abeta protein by microglial cells. Microglia are the brain's resident immune cells and phagocytosis is one of their innate functions. We are interested in identifying molecules that augment microglial-mediated phagocytosis of Abeta protein. We used the rodent BV-2 microglial cell line which readily phagocytose fluorescent latex beads and synthetic Abeta(1-42) peptide. BV-2 cells treated with the neuroactive drug valproic acid (VPA) showed greatly enhanced phagocytic activity for both latex beads and Abeta. VPA also reduced microglial viability by inducing apoptosis, as previously reported. The relevance of these in vitro results to the treatment of AD is unclear but further investigation into the effects of VPA on the clearance of Abeta through enhanced microglial phagocytosis is warranted.

Cilostazol is anti-inflammatory in BV2 microglial cells by inactivating nuclear factor-kappaB and inhibiting mitogen-activated protein kinases

BACKGROUND AND PURPOSE

Cilostazol is a specific inhibitor of 3'-5'-cyclic adenosine monophosphate (cAMP) phosphodiesterase, which is widely used to treat ischemic symptoms of peripheral vascular disease. Although cilostazol has been shown to exhibit vasodilator properties as well as antiplatelet and anti-inflammatory effects, its cellular mechanism in microglia is unknown. In the present study, we assessed the anti-inflammatory effect of cilostazol on the production of pro-inflammatory mediators in lipopolysaccharide (LPS)-stimulated murine BV2 microglia.

EXPERIMENTAL APPROACH

We examined the effects of cilostazol on LPS-induced nuclear factor-kappaB (NF-kappaB) activation and phosphorylation of mitogen-activated protein kinases (MAPKs).

KEY RESULTS

Cilostazol suppressed production of nitric oxide (NO), prostaglandin E(2) (PGE(2)) and the proinflammatory cytokines, interleukin-1 (IL-1), tumour necrosis factor-alpha, and monocyte chemoattractant protein-1 (MCP-1), in a concentration-dependent manner. Inhibitory effects of cilostazol were not affected by treatment with an adenylate cyclase inhibitor, SQ 22536, indicating that these actions of cilostazol were cAMP-independent. Cilostazol significantly inhibited the DNA binding and transcriptional activity of NF-kappaB. Moreover, cilostazol blocked signalling upstream of NF-kappaB activation by inhibiting extracellular signal-regulated kinases 1 and 2 (ERK1/2) and c-Jun N-terminal kinase (JNK), but without affecting the activity of p38 MAPK.

CONCLUSION AND IMPLICATIONS

Our results demonstrate that suppression of the NF-kappaB, ERK, JNK signalling pathways may inhibit LPS-induced NO and PGE(2) production. Therefore, cilostazol may have therapeutic potential for neurodegenerative diseases by inhibiting pro-inflammatory mediators and cytokine production in activated microglia.

Induction of glioma apoptosis by microglia-secreted molecules: The role of nitric oxide and cathepsin B

Microglia contributes significantly to brain tumor mass, particularly in astrocytic gliomas. Here, we examine the cytotoxic effects of soluble components secreted from microglia culture on glioma cells. Microglia conditioned culture medium (MCM) actively stimulated apoptotic death of glioma cells, and the effects of MCM prepared from LPS- or IFN-gamma-activated microglia were more pronounced. The cytotoxic effects were glioma-specific in that primary cultured rat astrocytes were not affected by MCM. A donor of peroxynitrite induced glioma-specific cell death. In addition, NO synthase inhibitor suppressed glioma cell death induced by activated MCM, indicating that NO is one of the key molecules responsible for glioma cytotoxicity mediated by activated MCM. However, since unstimulated resting microglia produces low or very limited level of NO, MCM may contain other critical molecule(s) that induce glioma apoptosis. To identify the proteins secreted in MCM, proteomic analysis was performed on control or activated medium. Among over 200 protein spots detected by Coomassie blue staining, we identified 26 constitutive and 28 LPS- or IFN-gamma-regulated MCM proteins. Several cathepsin proteases were markedly expressed, which were reduced upon activation. In particular, suppression of cathepsin B by the chemical inhibitors significantly reversed MCM-induced glioma cell death, implying a critical role of this protease in cytotoxicity. Our findings provide evidence on the functional implications of specific microglial-secreted proteins in glioma cytotoxicity, as well as a basis to develop a proteomic databank of both basal and activation-related proteins in microglia.

Complementary roles of tumor necrosis factor alpha and interferon gamma in inducible microglial nitric oxide generation

Proinflammatory cytokines and pathogen components activate microglia to release several substances such as nitric oxide (NO) produced after the induction of type II nitric oxide synthase (iNOS). The present study was designed to elucidate the interaction between the proinflammatory cytokines interferon gamma (IFN-gamma) and tumor necrosis factor alpha (TNF-alpha) on iNOS expression and NO production in microglial cells. In primary mouse microglial cells exposure to IFN-gamma (5 and 10 ng/ml; 48 h) or TNF-alpha (20 ng/ml; 48 h) alone were unable to induce iNOS expression; however, when cells were exposed to both cytokines together, the expression of this enzyme and the NO production in culture media were found significantly increased. In the BV-2 microglial cell line, IFN-gamma and TNF-alpha were shown to cooperate in nuclear factor kappa B (NF-kappa B) activation, an essential transcription factor for iNOS gene transcription. Importantly, IFN-gamma induced NF-kappa B binding to DNA was totally dependent on the endogenous TNF-alpha released via MEK/ERK signalling pathway. Thus, exposure of BV-2 cells to IFN-gamma in the presence of the selective MEK inhibitor U0126 or a neutralizing anti-TNF-alpha antibody significantly reduced IFN-gamma dependent NF-kappa B activation and iNOs expression. In addition, by activating the Jak/STAT pathway IFN-gamma potentiated TNF-alpha induced NF-kappa B binding to DNA and activated additional transcription factors (i.e. IRF-1) known to be essential for iNOs gene expression. The present findings demonstrate that the proinflammatory cytokines IFN-gamma and TNF-alpha have complementary roles on iNOS expression in microglial cells and this might be relevant to understand the molecular mechanisms of microglial activation associated with the pathogenesis of several neuroinflammatory disorders in which increased levels of IFN-gamma and TNF-alpha have been reported.

Suppression of caspase-11 expression by histone deacetylase inhibitors

It has been well documented that histone deacetylase inhibitors suppress inflammatory gene expression. Therefore, we investigated whether histone deacetylase inhibitors modulate the expression of caspase-11 that is known as an inducible caspase regulating both inflammation and apoptosis. In the present study, we show that sodium butyrate and trichostatin A, two structurally unrelated inhibitors of histone deacetylase (HDAC), effectively suppressed the induction of caspase-11 in mouse embryonic fibroblasts stimulated with lipopolysaccharides. Sodium butyrate inhibited the activation of upstream signaling events for the caspase-11 induction such as activation of p38 mitogen-activated protein kinase and c-Jun N-terminal kinase, degradation of inhibitor of kappaB, and activation of nuclear factor-kappaB. These results suggest that the HDAC inhibitor suppressed cytosolic signaling events for the induction of caspase-11 by inhibiting the deacetylation of non-histone proteins.

Lipopolysaccharide is a frequent and significant contaminant in microglia-activating factors

Lipopolysaccharide (LPS/endotoxin) is a potent immunologic stimulant. Many commercial-grade reagents used in research are not screened for LPS contamination. LPS induces a wide spectrum of proinflammatory responses in microglia, the immune cells of the brain. Recent studies have demonstrated that a broad range of endogenous factors including plasma-derived proteins and bioactive phospholipids can also activate microglia. However, few of these studies have reported either the LPS levels found in the preparations used or the effect of LPS inhibitors such as polymyxin B (PMX) on factor-induced responses. Here, we used the Limulus amoebocyte lysate assay to screen a broad range of commercial- and pharmaceutical-grade proteins, peptides, lipids, and inhibitors commonly used in microglia research for contamination with LPS. We then characterized the ability of PMX to alter a representative set of factor-induced microglial activation parameters including surface antigen expression, metabolic activity/proliferation, and NO/cytokine/chemokine release in both the N9 microglial cell line and primary microglia. Significant levels of LPS contamination were detected in a number of commercial-grade plasma/serum- and nonplasma/serum-derived proteins, phospholipids, and synthetic peptide preparations, but not in pharmaceutical-grade recombinant proteins or pharmacological inhibitors. PMX had a significant inhibitory effect on the microglia-activating potential of a number of commercial-, but not pharmaceutical-grade, protein preparations. Novel PMX-resistant responses to alpha(2)-macroglobulin and albumin were incidentally observed. Our results indicate that LPS is a frequent and significant contaminant in commercial-grade preparations of previously reported microglia-activating factors. Careful attention to LPS levels and appropriate controls are necessary for future studies in the neuroinflammation field.

C6 glioma cell insoluble matrix components enhance interferon-gamma-stimulated inducible nitric-oxide synthase/nitric oxide production in BV2 microglial cells

Microglia are the primary central nervous system immune effector cells. Microglial activation is linked to interactions with extracellular cytokines and the extracellular matrix (ECM). Astrocytomas are characterized by their diffuse nature, which is regulated by insoluble ECM components produced by the tumor cells that are largely absent from normal central nervous system tissue. The present study examined the influence of astrocytoma (C6 rat glioma) insoluble matrix components on interferon-gamma (IFN-gamma)-mediated inducible nitric-oxide synthase (iNOS) induction in microglial cells. We found that IFN-gamma-stimulated iNOS induction and nitric oxide release was greater in microglia cultured on C6 glioma cell-derived matrices compared with microglia cultured on primary rat astrocyte-derived matrices. Culture of microglia on C6 glioma cell-derived matrices also led to activation of STAT1, augmentation of IFN-gamma-induced STAT-3 activation, and an increase in IFN-gamma-activated site (GAS)-luciferase reporter activity. In addition, culture of microglia on C6 glioma cell-derived matrices activated NF-kappaB DNA binding activity and transcriptional activity. The results suggest that insoluble matrix components derived from malignant glioma cells can regulate microglia activation. These factors may include ECM components, such as fibronectin, collagen, laminin, vitronectin, and other nondiffusible compounds, and laminin seems to a critical regulator of this process. Microglia activation and subsequent brain inflammation may influence tumor growth, treatment, and metastasis. Better understanding of the regulation of microglial activation by astrocytoma-derived insoluble matrix components may be important in the development of immune-based treatment strategies against malignant brain tumors.

Treatment with dexamethasone and vitamin D3 attenuates neuroinflammatory age-related changes in rat hippocampus

Among the changes which occur in the brain with age is an increase in hippocampal concentration of proinflammatory cytokines like interleukin-1beta (IL-1beta) and an increase in IL-1beta-induced signaling. Here we demonstrate that the increase in IL-1beta concentration is accompanied by an increase in expression of IL-1 type I receptor (IL-1RI) and an age-related increase in microglial activation, as shown by increased expression of the cell surface marker, major histocompatibility complex II (MHCII) and increased MHCII staining. The evidence indicates that these age-related changes were abrogated in hippocampus of aged rats treated with dexamethasone and vitamin D3. Similarly, the age-related increases in activation of the stress-activated protein kinase, c-Jun N-terminal kinase (JNK), as well as caspase-3 and PARP were all attenuated in hippocampal tissue prepared from rats that received dexamethasone and vitamin D3. The data indicate that dexamethasone and vitamin D3 ameliorated the age-related increase in IFNgamma and suggest that IFNgamma may be the trigger leading to microglial activation, since it increases MHCII mRNA and IL-1beta release from cultured glia. In parallel with its ability to decrease microglial activation in vivo, we report that treatment of cultured glia with dexamethasone and vitamin D3 blocked the lipopolysaccharide increased MHCII mRNA and IL-1beta concentration, while the IL-1beta-induced increases in activation of JNK and caspase 3 in cultured neurons were also reversed by treatment with dexamethasone and vitamin D3. The data suggest that the antiinflammatory effect of dexamethasone and vitamin D3 derives from their ability to downreguate microglial activation.

Valproic acid and other histone deacetylase inhibitors induce microglial apoptosis and attenuate lipopolysaccharide-induced dopaminergic neurotoxicity

Valproic acid (VPA), a widely prescribed drug for seizures and bipolar disorder, has been shown to be an inhibitor of histone deacetylase (HDAC). Our previous study has demonstrated that VPA pretreatment reduces lipopolysaccharide (LPS)-induced dopaminergic (DA) neurotoxicity through the inhibition of microglia over-activation. The aim of this study was to determine the mechanism underlying VPA-induced attenuation of microglia over-activation using rodent primary neuron/glia or enriched glia cultures. Other histone deacetylase inhibitors (HDACIs) were compared with VPA for their effects on microglial activity. We found that VPA induced apoptosis of microglia cells in a time- and concentration-dependent manner. VPA-treated microglial cells showed typical apoptotic hallmarks including phosphatidylserine externalization, chromatin condensation and DNA fragmentation. Further studies revealed that trichostatin A (TSA) and sodium butyrate (SB), two structurally dissimilar HDACIs, also induced microglial apoptosis. The apoptosis of microglia was accompanied by the disruption of mitochondrial membrane potential and the enhancement of acetylation levels of the histone H3 protein. Moreover, pretreatment with SB or TSA caused a robust decrease in LPS-induced pro-inflammatory responses and protected DA neurons from damage in mesencephalic neuron-glia cultures. Taken together, our results shed light on a novel mechanism whereby HDACIs induce neuroprotection and underscore the potential utility of HDACIs in preventing inflammation-related neurodegenerative disorders such as Parkinson's disease.

Sodium butyrate prevents lethality of severe sepsis in rats

This study was performed to investigate a novel strategy to pharmacologically inhibit high-mobility group box 1 protein (HMGB1) expression with sodium butyrate, a short-chain fatty acid. Using a sepsis model induced by cecal ligation and puncture (CLP), 100 male Wistar rats were randomly divided into 4 groups as follows: control group (10 rats), sham operation group (10 rats), CLP group (further randomized into 2, 6, 12, 24, 48, and 72 h post-CLP subgroups, each 10 rats), and sodium butyrate treatment group (further randomized into 12 and 24 h post-CLP subgroups, each 10 rats). Animals of all groups were killed at designated time points, and blood and tissue samples from livers, lungs, kidneys, and small intestines were harvested to determine organ damage-related variables, and HMGB1 mRNA expression was assessed by the reverse-transcription-polymerase chain reaction. In addition, we observed the effect of treatment with sodium butyrate on survival rate in septic rats. The results showed that early treatment with sodium butyrate can markedly reduce serum alanine aminotransferase, creatinine levels at 12 h, and pulmonary myeloperoxidase activity at 24 h post-CLP, and significantly improve the 1- to 6-day survival rates in animals subjected to CLP (P < 0.05-0.01). These findings suggest that HMGB1 is excessively expressed and produced in sepsis. Sodium butyrate can markedly inhibit HMGB1 mRNA expression and may have protective effect on multiple organ damage in sepsis.

IL-4 attenuates the neuroinflammation induced by amyloid-beta in vivo and in vitro

It has been shown that Abeta inhibits long-term potentiation (LTP) in the rat hippocampus and this is accompanied by an increase in hippocampal concentration of IL-1beta. Abeta also increases microglial activation, which is the likely cell source of IL-1beta. Because IL-4 attenuates the effects of IL-1beta in hippocampus, and microglial activation is inhibited by minocycline, we assessed the ability of both IL-4 and minocycline to modulate the effects of Abeta on LTP and IL-1beta concentration. Following treatment with Abeta, IL-4 or minocycline, rats were assessed for their ability to sustain LTP in perforant path-granule cell synapses. We report that the Abeta-induced inhibition of LTP was associated with increases in expression of MHCII, JNK phosphorylation and IL-1beta concentration, and that these changes were attenuated by treatment of rats with IL-4 and minocycline. We also report that Abeta-induced increases in expression of MHCII and IL-1beta were similarly attenuated by IL-4 and minocycline in glial cultures prepared from neonatal rats. These data suggest that glial cell activation and the consequent increase in IL-1beta concentration mediate the inhibitory effect of Abeta on LTP and indicate that IL-4, by down-regulating glial cell activation, antagonizes the effects of Abeta.

The age-related attenuation in long-term potentiation is associated with microglial activation

It is well established that inflammatory changes contribute to brain ageing, and an increased concentration of proinflammatory cytokine, interleukin-1beta (IL-1beta), has been reported in the aged brain associated with a deficit in long-term potentiation (LTP) in rat hippocampus. The precise age at which changes are initiated is unclear. In this study, we investigate parallel changes in markers of inflammation and LTP in 3-, 9- and 15-month-old rats. We report evidence of increased hippocampal concentrations of the proinflammatory cytokines IL-1alpha, IL-18 and interferon-gamma (IFNgamma), which are accompanied by deficits in LTP in the older rats. We also show an increase in expression of markers of microglial activation, CD86, CD40 and intercellular adhesion molecules (ICAM). Associated with these changes, we observed a significant impairment of hippocampal LTP in the same rats. The importance of microglial activation in the attenuation of long-term potentiation (LTP) was demonstrated using an inhibitor of microglial activation, minocycline; partial restoration of LTP in 15-month-old rats was observed following administration of minocycline. We propose that signs of neuroinflammation are observed in middle age and that these changes, which are characterized by microglial activation, may be triggered by IL-18.

Insoluble matrix components of glioma cells suppress LPS-mediated iNOS/NO induction in microglia

This study examines the influence of insoluble matrix components of glioma (astrocytoma) cells on LPS-mediated inducible nitric oxide (NO)/NO synthase (iNOS) induction in microglia cells. Insoluble matrix components prepared from C6 rat glioma cells strongly suppressed iNOS induction and subsequent NO release induced by LPS. Matrices prepared from several glioma cell lines displayed similar inhibitory effects on LPS-induced NO/iNOS induction, whereas matrices from primary cultured rat astrocytes had a minimal influence. Of the various purified ECM materials examined, collagen suppressed LPS-mediated iNOS/NO induction in microglia. C6 matrices potentiated LPS-induced NF-kappaB DNA binding/transcriptional activity, suggesting that the suppression of LPS-induced iNOS by C6 matrices is NF-kappaB independent. C6 matrices inhibited LPS-mediated activation of p38 and JNK MAP kinases. This study shows that non-diffusible factors derived from astrocytoma cells in the brain are critically involved in the suppression of microglial cell activation. Our results indicate that activation of microglia can be regulated by various cellular and pathological environmental conditions, not only through cell-cell contact or soluble factors, but also via insoluble matrix components.

Up-regulation of microglial CD11b expression by nitric oxide

Increased expression of CD11b, the beta-integrin marker of microglia, represents microglial activation during neurodegenerative inflammation. However, the molecular mechanism behind increased microglial CD11b expression is poorly understood. The present study was undertaken to explore the role of nitric oxide (NO) in the expression of CD11b in microglial cells. Bacterial lipopolysaccharide (LPS) induced the production of NO and increased the expression of CD11b in mouse BV-2 microglial cells and primary microglia. Either a scavenger of NO (PTIO) or an inhibitor of inducible nitric-oxide synthase (L-NIL) blocked this increase in microglial CD11b expression. Furthermore, co-microinjection of PTIO with LPS was also able to suppress LPS-mediated expression of CD11b and loss of dopaminergic neuronal fibers and neurotransmitters in striatum in vivo. Similarly, other inducers of NO production such as interferon-gamma, interleukin-1beta, human immunodeficiency virus type-1 gp120, and double-stranded RNA (poly(IC)) also increased the expression of CD11b in microglia through NO. The role of NO in the expression of CD11b was corroborated further by the expression of microglial CD11b by GSNO, an NO donor. Because NO transduces many intracellular signals via guanylate cyclase (GC), we investigated the role of GC, cyclic GMP (cGMP), and cGMP-activated protein kinase (PKG) in microglial expression of CD11b. Inhibition of LPS- and GSNO-mediated up-regulation of CD11b either by NS2028 (a specific inhibitor of GC) or by KT5823 and Rp-8-bromo-cGMP (specific inhibitors of PKG), and increase in CD11b expression either by 8-bromo-cGMP or by MY-5445 (a specific inhibitor of cGMP phosphodiesterase) alone suggest that NO increases microglial expression of CD11b via GC-cGMP-PKG. In addition, GSNO induced the activation of cAMP response element-binding protein (CREB) via PKG that was involved in the up-regulation of CD11b. This study illustrates a novel biological role of NO in regulating the expression of CD11b in microglia through GC-cGMP-PKG-CREB pathway that may participate in the pathogenesis of devastating neurodegenerative disorders.

Butyrate differentially regulates cytokines and proliferation in porcine peripheral blood mononuclear cells

Although butyrate modulates proliferation and cytokine production by PBMC in some species, the role of butyrate as a regulator of immunocyte function in the pig has not been studied. Therefore, the primary objective of this study was to determine whether butyrate influences peripheral blood mononuclear cell (PBMC) proliferation, cytokine secretion and mRNA expression in the pig in vitro. We also sought to determine whether alterations in cytokine production attributable to butyrate were associated with changes in the expression of suppressor of cytokine signaling-3 (SOCS3). Porcine PBMC were isolated from venous blood and stimulated with concanavalin A (ConA) in the presence or absence of sodium butyrate at 0.2 or 2.0 mM. Butyrate at 2.0 mM suppressed (P<0.05) ConA-induced PBMC proliferation and led to a paradoxical increase (P<0.05) in IL-2 mRNA expression. The secretion and mRNA expression of interferon-gamma (IFN-gamma) by ConA-activated PBMC was increased (P<0.05) by butyrate at 2.0 mM. Exposing activated PBMC to butyrate at 2.0 mM decreased (P<0.05) the secretion of interleukin-10 (IL-10). In contrast, butyrate at 0.2 mM increased (P<0.05) both IL-10 secretion and mRNA expression. Activation of porcine PBMC with ConA increased (P<0.05) the expression of SOCS3 mRNA, and butyrate treatment further augmented (P<0.05) SOCS3 mRNA expression in a dose-dependent manner. Mechanistically, pretreatment with the adenyl cyclase inhibitor 2,5-dideoxyadenosine abolished (P<0.05) the inhibitory effect of 2.0 mM butyrate on IL-10 secretion, and partially reversed (P<0.05) the increase in IFN-gamma secretion induced by 2.0mM butyrate. These data indicate that the effect of butyrate on cytokine production by porcine PBMC is dose-dependent, and that butyrate increases the expression of SOCS3 in activated PBMC. In addition, we provide evidence that the effects of butyrate on IFN-gamma and IL-10 production are mediated in part via a cAMP-dependent mechanism.

Interaction between interferon ? and insulin-like growth factor-1 in hippocampus impacts on the ability of rats to sustain long-term potentiation

There is compelling evidence to suggest that inflammation significantly contributes to neurodegenerative changes. Consistent with this is the observation that several neurodegenerative disorders are accompanied by an increase in the concentration of interleukin (IL)-1beta. IL-1beta has a negative impact on synaptic plasticity and therefore an increased concentration of IL-1beta, such as that in the hippocampus of the aged rat, is associated with a deficit in long-term potentiation (LTP). IL-1beta is derived mainly from activated microglia but the trigger leading to this activation, specifically in the aged brain, remains to be identified. Here we examined the possibility that interferon (IFN)gamma may stimulate microglial activation and increase IL-1beta concentration, thereby inhibiting LTP. The IFNgamma concentration was increased in hippocampus prepared from aged, compared with young, rats and inversely correlated with the ability of rats to sustain LTP. Intracerebroventricular injection of IFNgamma inhibited LTP, and increased microglial activation was observed in both IFNgamma-injected and aged rats. The age-related increase in IFNgamma was accompanied by a decrease in the hippocampal concentration of insulin-like growth factor (IGF)-1. The evidence presented suggests that IGF-1 acts to antagonize the IFNgamma-induced microglial activation, the accompanying increase in IL-1beta concentration and the consequent deficit in LTP.

Repression of interferon-γ-induced inducible nitric oxide synthase (iNOS) gene expression in microglia by sodium butyrate is mediated through specific inhibition of ERK signaling pathways

We have reported recently that sodium butyrate suppressed IFN-gamma, but not the LPS-mediated induction of nitric oxide and TNF-alpha in microglia via the specific inhibition of NF-kappaB. In order to further determine the upstream signaling mechanism involved in the IFN-gamma-specific down-regulation of iNOS by sodium butyrate in microglia, this study investigated the effect of sodium butyrate on the MAP kinase activities. Sodium butyrate significantly repressed the phosphorylation of ERK induced by IFN-gamma, but had little effect on that induced by LPS. This suggests that sodium butyrate suppresses the IFN-gamma-induced iNOS expression by inhibiting the ERK to NF-kappaB pathway. In addition, it was found that sodium butyrate suppressed the IFN-gamma-induced interferon regulatory factor 1 (IRF-1) expression via the inhibition of ERK. Therefore, the ERK signaling pathway appears to play a key role in the sodium butyrate-mediated down-regulation of iNOS in the IFN-gamma-stimulated microglia.

Distinct signaling pathways for induction of type II NOS by IFNγ and LPS in BV-2 microglial cells

Nitric oxide (NO) release upon microglial cell activation has been implicated in the tissue injury and cell death in many neurodegenerative diseases. Recent studies have indicated the ability of interferon-gamma (IFNgamma) and lipopolysaccharides (LPS) to independently induce type II nitric oxide synthase (iNOS) expression and NO production in BV-2 microglial cells. However, a detailed comparison between the signaling pathways activating iNOS by these two agents has not been accomplished. Analysis of PKC isoforms revealed mainly the presence of PKCdelta, iota and lambda in BV-2 cells. Although both IFNgamma and LPS could specifically enhance the tyrosine phosphorylation of PKCdelta, treatment with IFNgamma induced a steady increase of phospho-PKCdelta for up to 1h, whereas treatment with LPS elevated phospho-PKCdelta levels only transiently, with peak activity at 5 min. Rottlerin, a specific inhibitor for PKCdelta, dose-dependently inhibited IFNgamma- and LPS-induced NO production. Despite the common involvement of PKCdelta, IFNgamma- but not LPS-induced NO production involved extracellular signal-regulated kinases (ERK1/2) cascade and IFNgamma-induced phosphorylation of ERK1/2 was mediated through PKC. On the other hand, LPS- but not IFNgamma-induced NO production was through stimulation of NF-kappaB activation and nuclear translocation to interact with DNA. These results demonstrated distinct signaling pathways for induction of iNOS by IFNgamma and LPS in BV-2 microglial cells.

Transcriptional therapy with the histone deacetylase inhibitor trichostatin A ameliorates experimental autoimmune encephalomyelitis

We demonstrate that the histone deacetylase (HDAC) inhibitor drug trichostatin A (TSA) reduces spinal cord inflammation, demyelination, neuronal and axonal loss and ameliorates disability in the relapsing phase of experimental autoimmune encephalomyelitis (EAE), a model of multiple sclerosis (MS). TSA up-regulates antioxidant, anti-excitotoxicity and pro-neuronal growth and differentiation mRNAs. TSA also inhibits caspase activation and down-regulates gene targets of the pro-apoptotic E2F transcription factor pathway. In splenocytes, TSA reduces chemotactic, pro-Th1 and pro-proliferative mRNAs. A transcriptional imbalance in MS may contribute to immune dysregulation and neurodegeneration, and we identify HDAC inhibition as a transcriptional intervention to ameliorate this imbalance.