Systemic LPS administration induces brain inflammation but not dopaminergic neuronal death in the substantia nigra

Ethanol extract of Bupleurum falcatum and saikosaponins inhibit neuroinflammation via inhibition of NF-κB

ETHNOPHARMACOLOGICAL RELEVANCE

The root of Bupleurum falcatum L. (BF) has been used in traditional Korean and Chinese medicines for over 2000 years to treat infections, fever, and chronic liver diseases. Among the many active compounds in BF ethanol extract (BFE), saikosaponins exert pharmacological activities including anti-inflammatory effects. Activated microglial cells release a variety of pro-inflammatory substances, leading to neuronal cell death and neurodegenerative diseases such as Alzheimer's disease and Parkinson's disease. The aim of the present study was to investigate the mechanism of the anti-neuroinflammatory effects of BFE using lipopolysaccharide (LPS)-stimulated microglial cells and LPS-intraperitoneal injected C57BL/6 mice.

MATERIALS AND METHODS

Dried roots of BF were extracted with 70% ethanol (tenfold volume) on a stirring plate for 24h at room temperature to prepare BFE. Pure saikosaponins (SB3, SB4, and SD) were prepared by solvent extraction and column chromatography fractionation. BV2 murine microglial cells were treated with BFE or saikosaponins for 4h and stimulated with LPS. Generation of nitric oxide (NO), inflammatory cytokines, and reactive oxygen species (ROS) from activated microglial cells were monitored. The effects of BFE on NF-κB activation were determined using RT-PCR, reporter assay, and immunostaining. The in vivo effects of BFE were also assessed by immunohistochemical staining of tissue sections from LPS-injected mouse brains.

RESULTS

Treatment with BFE or saikosaponins dose-dependently attenuated LPS-induced production of NO, iNOS mRNA, and ROS by 30-50%. They reduced LPS-mediated increases in the mRNA levels of IL-6, IL-1β, and TNF-α by approximately 30-70% without affecting cell viability, and decreased LPS-mediated NF-κB activity via reducing p65/RELA mRNA, transcriptional activity, and nuclear localization of NF-κB. BFE also reduced LPS-induced activation of microglia and astrocytes in the hippocampus and substantia nigra of LPS-injected mice.

CONCLUSION

Our data suggest that BFE may be effective for reducing neuroinflammation-mediated neurodegeneration through suppressing NF-κB-mediated inflammatory pathways.

Lesion of the locus coeruleus aggravates dopaminergic neuron degeneration by modulating microglial function in mouse models of Parkinson׳s disease

The degeneration of noradrenergic neurons in the locus coeruleus (LC) commonly occurs in patients with Parkinson's disease (PD), which is characterized by a selective injury of dopaminergic neurons in the substantia nigra (SN). The pathological impact of the LC on the SN in the disease is unknown. In the present study, we used a noradrenergic toxin, N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine (DSP4), to deplete noradrenaline (NA) derived from the LC to explore its influence on degeneration or injury of dopaminergic neurons in the SN in mouse model produced by intraperitoneal injection of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) or lipopolysaccharide (LPS). Our results demonstrated that lesion of the LC could change microglial function in the brain, which led to enhanced or prolonged expression of pro-inflammatory cytokines, diminished neurotrophic factors, and weakened ability of anti-oxidation in the SN. The in vitro experiments further confirmed that NA could reduce the inflammatory reaction of microglia. The selective injury of dopaminergic neurons by inflammation, however, was due to the inflammation in different brain regions rather than the depletion of NA. Our results indicate that the lesion in the LC is an important factor in promoting dopaminergic neuron degeneration by impacting the function of microglia in the midbrain.

Nutrient and immune sensing are obligate pathways in metabolism, immunity, and disease

The growth and survival of multicellular organisms depend upon their abilities to acquire and metabolize nutrients, efficiently store and harness energy, and sense and fight infection. Systems for sensing and using nutrients have consequently coevolved alongside systems for sensing and responding to danger signals, including pathogens, and share many of the same cell signaling proteins and networks. Diets rich in carbohydrates and fats can overload these systems, leading to obesity, metabolic dysfunction, impaired immunity, and cardiovascular disease. Excessive nutrient intake promotes adiposity, typically altering adipocyte function and immune cell distribution, both of which trigger metabolic dysfunction. Here, we discuss novel mechanistic links between metabolism and immunity that underlie metabolic dysfunction in obesity. We aim to stimulate debate about how the endocrine and immune systems are connected through autocrine, paracrine, and neuroendocrine signaling in sophisticated networks that are only now beginning to be resolved. Understanding the expression and action of signaling proteins, together with modulating their receptors or pattern recognition using agonists or antagonists, will enable rational intervention in immunometabolism that may lead to novel treatments for obesity and metabolic dysfunction.

Systemic inflammation in early neonatal mice induces transient and lasting neurodegenerative effects

Background

The inflammatory mediator lipopolysaccharide (LPS) has been shown to induce acute gliosis in neonatal mice. However, the progressive effects on the murine neurodevelopmental program over the week that follows systemic inflammation are not known. Thus, we investigated the effects of repeated LPS administration in the first postnatal week in mice, a condition mimicking sepsis in late preterm infants, on the developing central nervous system (CNS).

Methods

Systemic inflammation was induced by daily intraperitoneal administration (i.p.) of LPS (6 mg/kg) in newborn mice from postnatal day (PND) 4 to PND6. The effects on neurodevelopment were examined by staining the white matter and neurons with Luxol Fast Blue and Cresyl Violet, respectively. The inflammatory response was assessed by quantifying the expression/activity of matrix metalloproteinases (MMP), toll-like receptor (TLR)-4, high mobility group box (HMGB)-1, and autotaxin (ATX). In addition, B6 CX3CR1^gfp/+ mice combined with cryo-immunofluorescence were used to determine the acute, delayed, and lasting effects on myelination, microglia, and astrocytes.

Results

LPS administration led to acute body and brain weight loss as well as overt structural changes in the brain such as cerebellar hypoplasia, neuronal loss/shrinkage, and delayed myelination. The impaired myelination was associated with alterations in the proliferation and differentiation of NG2 progenitor cells early after LPS administration, rather than with excessive phagocytosis by CNS myeloid cells. In addition to disruptions in brain architecture, a robust inflammatory response to LPS was observed. Quantification of inflammatory biomarkers revealed decreased expression of ATX with concurrent increases in HMGB1, TLR-4, and MMP-9 expression levels. Acute astrogliosis (GFAP⁺ cells) in the brain parenchyma and at the microvasculature interface together with parenchymal microgliosis (CX3CR1⁺ cells) were also observed. These changes preceded the migration/proliferation of CX3CR1⁺ cells around the vessels at later time points and the subsequent loss of GFAP⁺ astrocytes.

Conclusion

Collectively, our study has uncovered a complex innate inflammatory reaction and associated structural changes in the brains of neonatal mice challenged peripherally with LPS. These findings may explain some of the neurobehavioral abnormalities that develop following neonatal sepsis.

Plasminogen in cerebrospinal fluid originates from circulating blood

Background

Plasminogen activation is a ubiquitous source of fibrinolytic and proteolytic activity. Besides its role in prevention of thrombosis, plasminogen is involved in inflammatory reactions in the central nervous system. Plasminogen has been detected in the cerebrospinal fluid (CSF) of patients with inflammatory diseases; however, its origin remains controversial, as the blood–CSF barrier may restrict its diffusion from blood.

Methods

We investigated the origin of plasminogen in CSF using Alexa Fluor 488–labelled rat plasminogen injected into rats with systemic inflammation and blood–CSF barrier dysfunction provoked by lipopolysaccharide (LPS). Near-infrared fluorescence imaging and immunohistochemistry fluorescence microscopy were used to identify plasminogen in brain structures, its concentration and functionality were determined by Western blotting and a chromogenic substrate assay, respectively. In parallel, plasminogen was investigated in CSF from patients with Guillain-Barré syndrome (n = 15), multiple sclerosis (n = 19) and noninflammatory neurological diseases (n = 8).

Results

Endogenous rat plasminogen was detected in higher amounts in the CSF and urine of LPS-treated animals as compared to controls. In LPS-primed rats, circulating Alexa Fluor 488–labelled rat plasminogen was abundantly localized in the choroid plexus, CSF and urine. Plasminogen in human CSF was higher in Guillain-Barré syndrome (median = 1.28 ng/μl (interquartile range (IQR) = 0.66 to 1.59)) as compared to multiple sclerosis (median = 0.3 ng/μl (IQR = 0.16 to 0.61)) and to noninflammatory neurological diseases (median = 0.27 ng/μl (IQR = 0.18 to 0.35)).

Conclusions

Our findings demonstrate that plasminogen is transported from circulating blood into the CSF of rats via the choroid plexus during inflammation. Our data suggest that a similar mechanism may explain the high CSF concentrations of plasminogen detected in patients with inflammation-derived CSF barrier impairment.

Electronic supplementary material

The online version of this article (doi:10.1186/s12974-014-0154-y) contains supplementary material, which is available to authorized users.

Matrix metalloproteinase-8 plays a pivotal role in neuroinflammation by modulating TNF-α activation

Matrix metalloproteinases (MMPs) play important roles in normal brain development and synaptic plasticity, although aberrant expression of MMPs leads to brain damage, including blood-brain barrier disruption, inflammation, demyelination, and neuronal cell death. In this article, we report that MMP-8 is upregulated in LPS-stimulated BV2 microglial cells and primary cultured microglia, and treatment of MMP-8 inhibitor (M8I) or MMP-8 short hairpin RNA suppresses proinflammatory molecules, particularly TNF-α secretion. Subsequent experiments showed that MMP-8 exhibits TNF-α-converting enzyme (TACE) activity by cleaving the prodomain of TNF-α (A(74)/Q(75), A(76)/V(77) residues) and, furthermore, that M8I inhibits TACE activity more efficiently than TAPI-0, a general TACE inhibitor. Biochemical analysis of the underlying anti-inflammatory mechanisms of M8I revealed that it inhibits MAPK phosphorylation, NF-κB/AP-1 activity, and reactive oxygen species production. Further support for the proinflammatory role of microglial MMP-8 was obtained from an in vivo animal model of neuroinflammatory disorder. MMP-8 is upregulated in septic conditions, particularly in microglia. Administration of M8I or MMP-8 short hairpin RNA significantly inhibits microglial activation and expression/secretion of TNF-α in brain tissue, serum, and cerebrospinal fluid of LPS-induced septic mice. These results demonstrate that MMP-8 critically mediates microglial activation by modulating TNF-α activity, which may explain neuroinflammation in septic mouse brain.

α-Asarone Ameliorates Memory Deficit in Lipopolysaccharide-Treated Mice via Suppression of Pro-Inflammatory Cytokines and Microglial Activation

α-Asarone exhibits a number of pharmacological actions including neuroprotective, anti-oxidative, anticonvulsive, and cognitive enhancing action. The present study investigated the effects of α-asarone on pro-inflammatory cytokines mRNA, microglial activation, and neuronal damage in the hippocampus and on learning and memory deficits in systemic lipopolysaccharide (LPS)-treated C57BL/6 mice. Varying doses of α-asarone was orally administered (7.5, 15, or 30 mg/kg) once a day for 3 days before the LPS (3 mg/kg) injection. α-Asarone significantly reduced TNF-α and IL-1β mRNA at 4 and 24 hours after the LPS injection at dose of 30 mg/kg. At 24 hours after the LPS injection, the loss of CA1 neurons, the increase of TUNEL-labeled cells, and the up-regulation of BACE1 expression in the hippocampus were attenuated by 30 mg/kg of α-asarone treatment. α-Asarone significantly reduced Iba1 protein expression in the hippocampal tissue at a dose of 30 mg/kg. α-Asarone did not reduce the number of Iba1-expressing microglia on immunohistochemistry but the average cell size and percentage areas of Iba1-expressing microglia in the hippocampus were significantly decreased by 30 mg/kg of α-asarone treatment. In the Morris water maze test, α-asarone significantly prolonged the swimming time spent in the target and peri-target zones. α-Asarone also significantly increased the number of target heading and memory score in the Morris water maze. The results suggest that inhibition of pro-inflammatory cytokines and microglial activation in the hippocampus by α-asarone may be one of the mechanisms for the α-asarone-mediated ameliorating effect on memory deficits.

Glycyrrhizin alleviates neuroinflammation and memory deficit induced by systemic lipopolysaccharide treatment in mice

The present study investigated the effects of glycyrrhizin (GRZ) on neuroinflammation and memory deficit in systemic lipopolysaccharide (LPS)-treated C57BL/6 mice. Varying doses of GRZ was orally administered (10, 30, or 50 mg/kg) once a day for 3 days before the LPS (3 mg/kg) injection. At 24 h after the LPS injection, GRZ significantly reduced TNF-α and IL-1β mRNA at doses of 30 and 50 mg/kg. COX-2 and iNOS protein expressions were significantly reduced by GRZ at doses of 30 and 50 mg/kg. In the Morris water maze test, GRZ (30 mg/kg) significantly prolonged the swimming time spent in the target and peri-target zones. GRZ also significantly increased the target heading and memory score numbers. In the hippocampal tissue, GRZ significantly reduced the up-regulated Iba1 protein expression and the average cell size of Iba1-expressing microglia induced by LPS. The results indicate that GRZ ameliorated the memory deficit induced by systemic LPS treatment and the effect of GRZ was found to be mediated through the inhibition of pro-inflammatory mediators and microglial activation in the brain tissue. This study supports that GRZ may be a putative therapeutic drug on neurodegenerative diseases associated with cognitive deficits and neuroinflammation such as Alzheimer's disease.

Pro-inflammatory cytokine-mediated ferroportin down-regulation contributes to the nigral iron accumulation in lipopolysaccharide-induced Parkinsonian models

Pro-inflammatory cytokines induced by inflammation and iron accumulation in the substantia nigra (SN) have been implicated in the pathogenesis of Parkinson's disease (PD). In the present study, we aimed to investigate the relationship between inflammation and iron accumulation in a lipopolysaccharide (LPS)-induced Parkinsonian rat model. The activation of glial cells and elevated levels of pro-inflammatory cytokines were observed in the SN of LPS models, accompanied by iron deposits in the same region. Moreover, ferroportin (Fpn), the only channel for iron export, was down-regulated. SH-SY5Y dopaminergic cells were pre-incubated with conditioned media enriched in pro-inflammatory cytokines, and abnormal iron deposits and a drop of Fpn were observed. The expression of heme oxygenase-1 (HO-1) was also upregulated in vivo and in vitro. These results suggested that pro-inflammatory cytokines might induce Fpn downregulation, which leads to iron accumulation and dopaminergic neurons' degeneration in PD. HO-1 may also contribute to the iron accumulation in neurons, but its mechanism needs to be further investigated.

Herpes virus entry mediator signaling in the brain is imperative in acute inflammation-induced anorexia and body weight loss

BACKGROUND

Reduced appetite and body weight loss are typical symptoms of inflammatory diseases. A number of inflammatory stimuli are responsible for the imbalance in energy homeostasis, leading to metabolic disorders. The herpes virus entry mediator (HVEM) protein plays an important role in the development of various inflammatory diseases, such as intestinal inflammation and diet-induced obesity. However, the role of HVEM in the brain is largely unknown. This study aims to investigate whether HVEM signaling in the brain is involved in inflammation-induced anorexia and body weight loss.

METHODS

Food intake and body weight were measured at 24 hours after intraperitoneal injection of lipopolysaccharide (LPS) or intracerebroventricular injection of recombinant mouse LIGHT (also called tumor necrosis factor receptor superfamily 14, TNFSF14), an HVEM ligand, into 8- to 10-week-old male C57BL/6 mice and mice lacking HVEM expression (HVEM-/-). We also assessed LPS-induced change in hypothalamic expression of HVEM using immunohistochemistry.

RESULTS

Administration of LPS significantly reduced food intake and body weight, and moreover, increased expression of HVEM in the hypothalamic arcuate nucleus. However, LPS induced only minor decreases in food intake and body weight in HVEM-/- mice. Administration of LIGHT into the brain was very effective at decreasing food intake and body weight in wild-type mice, but was less effective in HVEM-/- mice.

CONCLUSION

Activation of brain HVEM signaling is responsible for inflammation-induced anorexia and body weight loss.

Brain inflammation and microglia: facts and misconceptions

THE INFLAMMATION THAT ACCOMPANIES ACUTE INJURY HAS DUAL FUNCTIONS: bactericidal action and repair. Bactericidal functions protect damaged tissue from infection, and repair functions are initiated to aid in the recovery of damaged tissue. Brain injury is somewhat different from injuries in other tissues in two respects. First, many cases of brain injury are not accompanied by infection: there is no chance of pathogens to enter in ischemia or even in traumatic injury if the skull is intact. Second, neurons are rarely regenerated once damaged. This raises the question of whether bactericidal inflammation really occurs in the injured brain; if so, how is this type of inflammation controlled? Many brain inflammation studies have been conducted using cultured microglia (brain macrophages). Even where animal models have been used, the behavior of microglia and neurons has typically been analyzed at or after the time of neuronal death, a time window that excludes the inflammatory response, which begins immediately after the injury. Therefore, to understand the patterns and roles of brain inflammation in the injured brain, it is necessary to analyze the behavior of all cell types in the injured brain immediately after the onset of injury. Based on our experience with both in vitro and in vivo experimental models of brain inflammation, we concluded that not only microglia, but also astrocytes, blood inflammatory cells, and even neurons participate and/or regulate brain inflammation in the injured brain. Furthermore, brain inflammation played by these cells protects neurons and repairs damaged microenvironment but not induces neuronal damage.

Lung inflammation induces IL-1β expression in hypoglossal neurons in rat brainstem

Perinatal inflammation is associated with respiratory morbidity. Immune modulation of brainstem respiratory control centers may provide a link for this pathobiology. We exposed 11-day old rats to intratracheal lipopolysaccharide (LPS, 0.5 μg/g) to test the hypothesis that intrapulmonary inflammation increases expression of the proinflammatory cytokine IL-1β within respiratory-related brainstem regions. Intratracheal LPS resulted in a 32% increase in IL-1β protein expression in the medulla oblongata. In situ hybridization showed increased intensity of IL-1β mRNA but no change in neuronal numbers. Co-localization experiments showed that hypoglossal neurons express IL-1β mRNA and immunostaining showed a 43% increase in IL-1β protein-expressing cells after LPS exposure. LPS treatment also significantly increased microglial cell numbers though they did not express IL-1β mRNA. LPS-induced brainstem expression of neuronal IL-1β mRNA and protein may have implications for our understanding of the vulnerability of neonatal respiratory control in response to a peripheral proinflammatory stimulus.

Ghrelin inhibits LPS-induced release of IL-6 from mouse dopaminergic neurones

BACKGROUND

Ghrelin is an orexigenic stomach hormone that acts centrally to increase mid-brain dopamine neurone activity, amplify dopamine signaling and protect against neurotoxin-induced dopamine cell death in the mouse substantia nigra pars compacta (SNpc). In addition, ghrelin inhibits the lipopolysaccharide (LPS)-induced release of pro-inflammatory cytokines from peripheral macrophages, T-cells and from LPS stimulated microglia. Here we sought to determine whether ghrelin attenuates pro-inflammatory cytokine release from dopaminergic neurones.

FINDINGS

The dopaminergic SN4741 cell-line, which derives from the mouse substantia nigra (SN) and expresses the ghrelin-receptor (growth hormone secretagogue receptor (GHS-R)) and the ghrelin-O-acyl transferase (GOAT) enzyme, was used to determine the neuro-immunomodulatory action of ghrelin. We induced innate immune activation via LPS challenge (1 μg/ml) of SN4741 neurones that had been pre-cultured in the presence or absence of ghrelin (1, 10, 100 nM) for 4 h. After 24 h supernatants were collected for detection of IL-1 beta (IL-1β ), TNF alpha (TNF-α) and IL-6 cytokines via enzyme linked immunosorbent assay (ELISA) analysis. Nuclear translocation of the transcription factor nuclear factor kappa B (NF-κB) was analyzed by Western blotting, and to determine viability of treatments a cell viability assay and caspase-3 immunohistochemistry were performed.We provide evidence that while IL-1β and TNF-α were not detectable under any conditions, SN4741 neurones constitutively released IL-6 under basal conditions and treatment with LPS significantly increased IL-6 secretion. Pre-treatment of neurones with ghrelin attenuated LPS-mediated IL-6 release at 24 h, an affect that was inhibited by the GHS-R antagonist [D-Lys3]-GHRP-6. However, while ghrelin pre-treatment attenuated the LPS-mediated increase in NF-κB, there was no alteration in its nuclear translocation. Cell viability assay and caspase-3 immunocytochemistry demonstrated that the results were independent from activation of cytotoxic and/or apoptotic mechanisms in the neuronal population, respectively.

CONCLUSION

Our results provide evidence that the gut-hormone, ghrelin, attenuates IL-6 secretion to LPS challenge in mid-brain dopaminergic neurones. These data suggest that ghrelin may protect against dopaminergic SN nerve cell damage or death via modulation of the innate immune response.

A new synthetic chalcone derivative, 2-hydroxy-3',5,5'-trimethoxychalcone (DK-139), suppresses the Toll-like receptor 4-mediated inflammatory response through inhibition of the Akt/NF-κB pathway in BV2 microglial cells

Microglial cells are the resident innate immune cells that sense pathogens and tissue injury in the central nervous system (CNS). Microglial activation is critical for neuroinflammatory responses. The synthetic compound 2-hydroxy-3',5,5'-trimethoxychalcone (DK-139) is a novel chalcone-derived compound. In this study, we investigated the effects of DK-139 on Toll-like receptor 4 (TLR4)-mediated inflammatory responses in BV2 microglial cells. DK-139 inhibited lipopolysaccharide (LPS)-induced TLR4 activity, as determined using a cell-based assay. DK-139 blocked LPS-induced phosphorylation of IκB and p65/RelA NF-κB, resulting in inhibition of the nuclear translocation and trans-acting activity of NF-κB in BV2 microglial cells. We also found that DK-139 reduced the expression of NF-κB target genes, such as those for COX-2, iNOS, and IL-1β, in LPS-stimulated BV2 microglial cells. Interestingly, DK-139 blocked LPS-induced Akt phosphorylation. Inhibition of Akt abrogated LPS-induced phosphorylation of p65/RelA, while overexpression of dominant-active p110CAAX enhanced p65/RelA phosphorylation as well as iNOS and COX2 expression. These results suggest that DK-139 exerts an anti-inflammatory effect on microglial cells by inhibiting the Akt/IκB kinase (IKK)/NF-κB signaling pathway.

Up-regulation of microglial cathepsin C expression and activity in lipopolysaccharide-induced neuroinflammation

Background

Cathepsin C (Cat C) functions as a central coordinator for activation of many serine proteases in inflammatory cells. It has been recognized that Cat C is responsible for neutrophil recruitment and production of chemokines and cytokines in many inflammatory diseases. However, Cat C expression and its functional role in the brain under normal conditions or in neuroinflammatory processes remain unclear. Our previous study showed that Cat C promoted the progress of brain demyelination in cuprizone-treated mice. The present study further investigated the Cat C expression and activity in lipopolysaccharide (LPS)-induced neuroinflammation in vivo and in vitro.

Methods

C57BL/6 J mice were intraperitoneally injected with either 0.9% saline or lipopolysaccharide (LPS, 5 mg/kg). Immunohistochemistry (IHC) and in situ hybridization (ISH) were used to analyze microglial activation, TNF-α, IL-1β, IL-6, iNOS mRNAs expressions and cellular localization of Cat C in the brain. Nitrite assay was used to examine microglial activation in vitro; RT-PCR and ELISA were used to determine the expression and release of Cat C. Cat C activity was analyzed by cellular Cat C assay kit. Data were evaluated for statistical significance with paired t test.

Results

Cat C was predominantly expressed in hippocampal CA2 neurons in C57BL/6 J mice under normal conditions. Six hours after LPS injection, Cat C expression was detected in cerebral cortical neurons; whereas, twenty-four hours later, Cat C expression was captured in activated microglial cells throughout the entire brain. The duration of induced Cat C expression in neurons and in microglial cells was ten days and three days, respectively. In vitro, LPS, IL-1β and IL-6 treatments increased microglial Cat C expression in a dose-dependent manner and upregulated Cat C secretion and its activity.

Conclusions

Taken together, these data indicate that LPS and proinflammatory cytokines IL-1β, IL-6 induce the expression, release and upregulate enzymatic activity of Cat C in microglial cells. Further investigation is required to determine the functional role of Cat C in the progression of neuroinflammation, which may have implications for therapeutics for the prevention of neuroinflammation-involved neurological disorders in the future.

The γ-secretase blocker DAPT impairs recovery from lipopolysaccharide-induced inflammation in rat brain

γ-Secretase is an important contributing enzyme in Alzheimer's disease and is therefore an important therapeutic target. However, the impact of γ-secretase inhibition is not well studied in acute neuroinflammation induced by systemic infection. In this study the influence of γ-secretase on the expression of some proinflammatory markers was assessed in the acute phase as well as the subsiding phase of neuroinflammation. Cerebral γ-secretase cleavage activity was measured by a fluorometric assay after lipopolysaccharide (LPS) intraperitoneal administration. Time profiles of TNF-α and COX-II expression were then determined to detect the time points relevant to the maximal inflammatory responses and the subsequent recovery phase. γ-Secretase activity coincident with TNF-α protein expression returned to its basal level till 8-12 h after systemic challenge with low dose LPS while COX-II over expression lasted for 48-72 h later. Pharmacological inhibition of γ-secretase with local or systemic administration of DAPT (N-[N-(3,5-difluorophenacetyl)-l-alanyl]-S-phenylglycine t-butyl ester) was performed to indicate the results on the developmental and sinking phases of inflammatory responses in 6 and 72 h post LPS respectively. Our results demonstrate that both local and systemic modulation of γ-secretase hyper-activity with DAPT increase the duration of TNF-α, COX-II, and NFκB induction. We consistently found mild augmented apoptosis in animals treated with DAPT as determined by measuring cleaved caspase-3 expression and by TUNEL assay 72 h following LPS injection. These results suggest that γ-secretase modulation interferes with certain immune regulatory pathways which may restrict some inflammatory transcription factors such as NFκB.

The effect of different antidepressant drugs on oxidative stress after lipopolysaccharide administration in mice

This study investigated the effect of the serotonin selective reuptake inhibitors (SSRIs) fluoxetine, sertraline, fluvoxamine and the tricyclic antidepressant (TCA) impiramine on oxidative stress in brain and liver induced by lipopolysaccharide administration in mice. Each drug was administered subcutaneously at doses of 10 or 20 mg/kg, for two days prior to intraperitoneal (i.p.) administration of lipopolysaccharide E (LPS: 200 µg/kg). Mice were euthanized 4 h after administration of the lipopolysaccharide. Lipid peroxidation (malondialdehyde; MDA), reduced glutathione (GSH) and nitric oxide (nitrite/nitrate) concentrations were measured in brain and liver. Results: The administration of lipopolysaccharide increased oxidative stress in brain and liver; it increased brain MDA by 36.1 and liver MDA by 159.8 %. GSH decreased by 34.1 % and 64.8 % and nitric oxide increased by 78.7 % and 103.8 % in brain and liver, respectively. In brain, MDA decreased after the administration of sertraline and by the lower dose of fluoxetine or fluvoxamine, but increased after the higher dose of imipramine. Reduced glutathione increased after sertraline, fluvoxamine and the lower dose of fluoxetine or imipramine. Nitric oxide decreased by sertraline, fluoxetine, fluvoxamine and by the lower dose of imipramine. In the liver, all drugs decreased MDA and increased GSH level. Nitric oxide is decreased by sertraline, fluvoxamine and by the lower dose of fluoxetine or imipramine. It is concluded that, during mild systemic inflammatory illness induced by peripheral bacterial endotoxin injection, the SSRIs fluoxetine, sertraline and fluvoxamine reduced, while the TCA impiramine increased oxidative stress induced in the brain. The SSRIs as well as imipramine reduced oxidative stress due to lipopolysaccharide in liver tissue.

The effects of trimetazidine on lipopolysaccharide-induced oxidative stress in mice

The effects of trimetazidine, a novel anti-ischemic agent, on the development of oxidative stress induced in mice with lipopolysaccharide endotoxin were investigated. The drug was administered orally once daily at doses of 1.8, 3.6 or 7.2 mg/kg for two days prior to intraperitoneal (i.p.) injection of lipopolysaccharide E (200 μg/kg) and at time of endotoxin administration. Mice were euthanized 4 h after administration of the lipopolysaccharide. Lipid peroxidation (malondialdehyde; MDA), reduced glutathione (GSH) and nitric oxide (nitrite/nitrate) concentrations were measured in brain and liver. The administration of lipopolysaccharide increased oxidative stress in both the brain and liver tissue. MDA increased by 33.9 and 107.1 %, GSH decreased by 23.9 and 84.3 % and nitric oxide increased 70.3 and 48.4 % in the brain and liver, respectively. Compared with the lipopolysaccharide control group, brain MDA decreased by 26.2 and 36.7 %, while GSH increased by 18.2 and 25.8 % after the administration of trimetazidine at 3.6 and 7.2 mg/kg, respectively. Brain nitric oxide decreased by 45.3, 50.8 and 57.0 % by trimetazidine at 1.8, 3.6 and 7.2 mg/kg, respectively. In the liver, MDA decreased by 18.7, 30.7 and 49.4 % and GSH increased by 150.3, 204.8 and 335.4 % following trimetazidine administration at 1.8, 3.6 and 7.2 mg/kg. Meanwhile, nitric oxide decreased by 17.3 % by 7.2 mg/kg of trimetazidine. These results indicate that administration of trimetazidine in the presence of mild systemic inflammatory response alleviates oxidative stress in the brain and liver.