MK-801 and 7-Ni attenuate the activation of brain NF-κB induced by LPS

Attenuation of Vanadium-Induced Neurotoxicity in Rat Hippocampal Slices (In Vitro) and Mice (In Vivo) by ZA-II-05, a Novel NMDA-Receptor Antagonist

Exposure to heavy metals, such as vanadium, poses an ongoing environmental and health threat, heightening the risk of neurodegenerative disorders. While several compounds have shown promise in mitigating vanadium toxicity, their efficacy is limited. Effective strategies involve targeting specific subunits of the NMDA receptor, a glutamate receptor linked to neurodegenerative conditions. The potential neuroprotective effects of ZA-II-05, an NMDA receptor antagonist, against vanadium-induced neurotoxicity were explored in this study. Organotypic rat hippocampal slices, and live mice, were used as models to comprehensively evaluate the compound's impact. Targeted in vivo fluorescence analyses of the hippocampal slices using propidium iodide as a marker for cell death was utilized. The in vivo study involved five dams, each with eight pups, which were randomly assigned to five experimental groups (n = 8 pups). After administering treatments intraperitoneally over six months, various brain regions were assessed for neuropathologies using different immunohistochemical markers. High fluorescence intensity was observed in the hippocampal slices treated with vanadium, signifying cell death. Vanadium-exposed mice exhibited demyelination, microgliosis, and neuronal cell loss. Significantly, treatment with ZA-II-05 resulted in reduced cellular death in the rat hippocampal slices and preserved cellular integrity and morphological architecture in different anatomical regions, suggesting its potential in countering vanadium-induced neurotoxicity.

Characterization of the Dahl salt-sensitive rat as a rodent model of inherited, widespread, persistent pain

Animal models are essential for studying the pathophysiology of chronic pain disorders and as screening tools for new therapies. However, most models available do not reproduce key characteristics of clinical persistent pain. This has limited their ability to accurately predict which new medicines will be clinically effective. Here, we characterize the Dahl salt-sensitive (SS) rat strain as the first rodent model of inherited widespread hyperalgesia. We show that this strain exhibits physiological phenotypes known to contribute to chronic pain, such as neuroinflammation, defective endogenous pain modulation, dysfunctional hypothalamic-pituitary-adrenal axis, increased oxidative stress and immune cell activation. When compared with Sprague Dawley and Brown Norway rats, SS rats have lower nociceptive thresholds due to increased inflammatory mediator concentrations, lower corticosterone levels, and high oxidative stress. Treatment with dexamethasone, the reactive oxygen species scavenger tempol, or the glial inhibitor minocycline attenuated the pain sensitivity in SS rats without affecting the other strains while indomethacin and gabapentin provided less robust pain relief. Moreover, SS rats presented impaired diffuse noxious inhibitory controls and an exacerbated response to the proalgesic mediator PGE₂, features of generalized pain conditions. These data establish this strain as a novel model of spontaneous, widespread hyperalgesia that can be used to identify biomarkers for chronic pain diagnosis and treatment.

Neuroprotective action of α-Klotho against LPS-activated glia conditioned medium in primary neuronal culture

The α-Klotho is an anti-aging protein that, when overexpressed, extends the life span in humans and mice. It has an anti-inflammatory and protective action on renal cells by inhibiting NF-κB activation and production of inflammatory cytokines in response to TNF-α. Furthermore, studies have shown the neuroprotective effect of α-Klotho against neuroinflammation on different conditions, such as aging, animal models of neurodegenerative diseases, and ischemic brain injury. This work aimed to evaluate the effects of α-Klotho protein on primary glial cell culture against the proinflammatory challenge with LPS and how this could interfere with neuronal health. Cortical mixed glial cells and purified astrocytes were pretreated with α- α-Klotho and stimulated with LPS followed by TNFα, IL-1β, IL-6, IFN-γ levels, and NF-κB activity analysis. Conditioned medium from cortical mixed glia culture treated with LPS (glia conditioned medium (GCM) was used to induce neuronal death of primary cortical neuronal culture and evaluate if GCM-KL (medium from glia culture pretreated α-Klotho followed by LPS stimulation) or GCM + LPS in the presence of KL can reverse the effect. LPS treatment in glial cells induced an increase in proinflammatory mediators such as TNF-α, IL-1β, IL-6, and IFN-γ, and activation of astrocyte NF-κB. GCM treated-cortical neuronal culture induced a concentration-dependent neuronal death. Pretreatment with α-Klotho decreased TNF-α and IL-6 production, reverted NF-κB activation, and decreased neuronal death induced by GCM. In addition, KL incubation together with GCM + LPS completely reverts the neuronal toxicity induced by low concentration of GCM-LPS. These data suggest an anti-inflammatory and neuroprotective effect of α-Klotho protein in the CNS. This work demonstrated the therapeutic potential of α-Klotho in pathological processes which involves a neuroinflammatory component.

Immunomodulatory effects of thalidomide in an experimental brain death liver donor model

Brain death is characterized by a generalized inflammatory response that results in multiorgan damage. This process is mainly mediated through cytokines, which amplify graft immunogenicity. We investigated the immunological response in a brain death liver donor model and analysed the effects of thalidomide, a drug with powerful immunomodulatory properties. Brain death was induced in male Lewis rats. We studied three groups: Control (sham-operated rats in which trepanation was performed without inserting the balloon catheter), BD (rats subjected to brain death by increasing intracranial pressure) and BD + Thalid (BD rats receiving thalidomide after brain death). After 6 h, serum levels of AST, ALT, LDH, and ALP as well as systemic and hepatic levels of TNF-α, IL1-β, IL-6, and IL-10 were analysed. We also determined the mRNA expression of MHC Class I and Class II, NF-κB, and macrophage infiltration. NF-κB was also examined by electrophoretic mobility shift assay. Thalidomide treatment significantly reduced serum levels of hepatic enzymes and TNF-α, IL-1-β, and IL-6. These cytokines were evaluated at either the mRNA expression or protein level in liver tissue. In addition, thalidomide administration resulted in a significant reduction in macrophages, MHC Class I and Class II, and NF-κB activation. This study reveals that thalidomide significantly inhibited the immunologic response and graft immunogenicity, possibly through suppression of NF-κB activation.

An Overview of NO Signaling Pathways in Aging

Nitric Oxide (NO) is a potent signaling molecule involved in the regulation of various cellular mechanisms and pathways under normal and pathological conditions. NO production, its effects, and its efficacy, are extremely sensitive to aging-related changes in the cells. Herein, we review the mechanisms of NO signaling in the cardiovascular system, central nervous system (CNS), reproduction system, as well as its effects on skin, kidneys, thyroid, muscles, and on the immune system during aging. The aging-related decline in NO levels and bioavailability is also discussed in this review. The decreased NO production by endothelial nitric oxide synthase (eNOS) was revealed in the aged cardiovascular system. In the CNS, the decline of the neuronal (n)NOS production of NO was related to the impairment of memory, sleep, and cognition. NO played an important role in the aging of oocytes and aged-induced erectile dysfunction. Aging downregulated NO signaling pathways in endothelial cells resulting in skin, kidney, thyroid, and muscle disorders. Putative therapeutic agents (natural/synthetic) affecting NO signaling mechanisms in the aging process are discussed in the present study. In summary, all of the studies reviewed demonstrate that NO plays a crucial role in the cellular aging processes.

The α2 Na+/K+-ATPase isoform mediates LPS-induced neuroinflammation

Na⁺/K⁺-ATPase is a transmembrane ion pump that is essential for the maintenance of ion gradients and regulation of multiple cellular functions. Na⁺/K⁺-ATPase has been associated with nuclear factor kappa B (NFκB) signalling, a signal associated with lipopolysaccharides (LPSs)-induced immune response in connection with activated Toll-like receptor 4 (TLR4) signalling. However, the contribution of Na⁺/K⁺-ATPase to regulating inflammatory responses remains elusive. We report that mice haploinsufficient for the astrocyte-enriched α₂Na⁺/K⁺-ATPase isoform (α₂^+/G301R mice) have a reduced proinflammatory response to LPS, accompanied by a reduced hypothermic reaction compared to wild type litter mates. Following intraperitoneal injection of LPS, gene expressions of Tnf-α, Il-1β, and Il-6 was reduced in the hypothalamus and hippocampus from α₂^+/G301R mice compared to α₂^+/+ littermates. The α₂^+/G301R mice experienced increased expression of the gene encoding an antioxidant enzyme, NRF2, in hippocampal astrocytes. Our findings indicate that α₂Na⁺/K⁺-ATPase haploinsufficiency negatively modulates LPS-induced immune responses, highlighting a rational pharmacological target for reducing LPS-induced inflammation.

Stress and brain immunity: Microglial homeostasis through hypothalamus-pituitary-adrenal gland axis and sympathetic nervous system

Stress has been well documented to bring about various clinical disorders, ranging from neurodegeneration, such as Parkinson’s (PD) and Alzheimer’s diseases (AD), to metabolic disorders including diabetes mellitus. Importantly, microglia, immunocompetent cells in the brain, have been shown to be involved in these clinical disorders. In the recent studies aiming to clarify the microglial responses, microglia are found to be quite responsive to stressful events, such as acute, subchronic, chronic stress, and social defeat stress. However, the mechanisms of these stress response on microglial activation have been not fully understood. In response to stress exposure, both the hypothalamic-pituitary-adrenal (HPA) axis and the sympathetic nervous system (SNS) are simultaneously activated, with the former inducing glucocorticoids (GCs) and the latter noradrenaline (NA), respectively. However, the effects of these stress-induced GCs and NA have not been consistent. The GCs, conventionally known to act on microglia as immunosuppressant, is also reported to act on it as stimulator. Similarly, the NA has been reported to act on microglia as stimulator or inhibitor depending on environmental conditions. Since any kinds of stress upregulate the HPA axis and SNS, with the levels of upregulation variable depending on the stress type, it is plausible that microglia is closely regulated by these two stress pathways. In this review, we discuss the microglial responses induced by various stresses as well as the possible mechanism by which stress induces microglial activation.

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The present study introduces the mechanism by which microglial activation occurs following acute stress.

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The present study suggests that microglial activation may be regulated through the HPA axis and sympathetic nervous system.

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The present study suggests that microglia may be inhibited by glucocorticoids, while activated by noradrenaline under physiological conditions.

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The present study suggests the hypothesis that the HPA axis may interact with sympathetic nervous system to maintain microglial homeostasis.

Klotho deficiency aggravates sepsis-related multiple organ dysfunction

Sepsis-induced organ failure is characterized by a massive inflammatory response and oxidative stress. Acute kidney injury (AKI) occurs in approximately half of patients in septic shock, and the mortality associated with sepsis-induced AKI is unacceptably high. Klotho is a protein expressed by renal cells and has anti-senescence properties. Klotho has also been shown to protect the kidneys in ischemia-reperfusion injury and to have antioxidant properties. To analyze the role of Klotho in sepsis-related organ dysfunction and AKI, we used a cecal ligation and puncture (CLP) model of sepsis in heterozygous Klotho-haploinsufficient mice and their wild-type littermates (CLP- Kl/+ and CLP-WT mice, respectively). In comparison with the CLP-WT mice, CLP- Kl/+ mice showed lower survival, impaired renal function, impaired hepatic function, greater oxidative stress, upregulation of inflammatory pathways (at the systemic and kidney tissue levels), and increased NF-κB activation. It is noteworthy that CLP- Kl/+ mice also showed lower heart-rate variability, less sympathetic activity, impaired baroreflex sensitivity to sodium nitroprusside, and a blunted blood pressure response to phenylephrine. We also demonstrated that sepsis creates a state of acute Klotho deficiency. Given that low Klotho expression exacerbates sepsis and multiple organ dysfunction, Klotho might play a protective role in sepsis, especially in elderly individuals in whom Klotho expression is naturally reduced.

Ouabain attenuates oxidative stress and modulates lipid composition in hippocampus of rats in lipopolysaccharide-induced hypocampal neuroinflammation in rats

Our study aimed to analyze the effect of ouabain (OUA) administration on lipopolysaccharide (LPS)-induced changes in hippocampus of rats. Oxidative parameters were analyzed in Wistar rats after intraperitoneal injection of OUA (1.8 µg/kg), LPS (200 µg/kg), or OUA plus LPS or saline. To reach our goal, activities of superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GPX), in addition to levels of reduced glutathione (GSH), protein carbonyl (PCO) and lipid peroxidation (LPO) were evaluated. We also analyzed the membrane lipid profile and some important lipids for the nervous system, such as phosphatidylethanolamine (PE), phosphatidylcholine (PC), phosphatidylinositol (PI), phosphatidic acid and sphingomyelin. The group that received only LPS showed increased oxidative stress, as evidenced by an increase in LPO (about twice), PCO (about three times) levels, and CAT activity (80%). Conversely, administration of LPS decreased GSH levels (55%), and GPx activity (30%), besides a reduction in the amount of PI (60%) and PC (45%). By other side, OUA alone increased the amount of PI (45%), PE (85%), and PC (70%). All harmful effects recorded were attenuated by OUA, suggesting a protective effect against LPS-induced oxidative stress. The relevance of our results extends beyond changes in oxidative parameters induced by LPS, because nanomolar doses of OUA may be useful in neurodegenerative models. Other studies on other cardenolides and substances related issues, as well as the development of new molecules derived from OUA, could also be useful in general oxidative and/or cellular stress, a condition favoring the appearance of neuronal pathologies.

Topical Dexamethasone Administration Impairs Protein Synthesis and Neuronal Regeneration in the Olfactory Epithelium

Chronic inflammatory process in the nasal mucosa is correlated with poor smell perception. Over-activation of immune cells in the olfactory epithelium (OE) is generally associated with loss of olfactory function, and topical steroidal anti-inflammatory drugs have been largely used for treating such condition. Whether this therapeutic strategy could directly affect the regenerative process in the OE remains unclear. In this study, we show that nasal topical application of dexamethasone (DEX; 200 or 800 ng/nostril), a potent synthetic anti-inflammatory steroid, attenuates OE lesion caused by Gram-negative bacteria lipopolysaccharide (LPS) intranasal infusion. In contrast, repeated DEX (400 ng/nostril) local application after lesion establishment limited the regeneration of olfactory sensory neurons after injury promoted by LPS or methimazole. Remarkably, DEX effects were observed when the drug was infused as 3 consecutive days regimen. The anti-inflammatory drug does not induce OE progenitor cell death, however, disturbance in mammalian target of rapamycin downstream signaling pathway and impairment of protein synthesis were observed during the course of DEX treatment. In addition, in vitro studies conducted with OE neurospheres in the absence of an inflammatory environment showed that glucocorticoid receptor engagement directly reduces OE progenitor cells proliferation. Our results suggest that DEX can interfere with the intrinsic regenerative cellular mechanisms of the OE, raising concerns on the use of topical anti-inflammatory steroids as a risk factor for progressive olfactory function impairment.

Regulatory and Mechanistic Actions of Glucocorticoids on T and Inflammatory Cells

Glucocorticoids (GCs) play an important role in regulating the inflammatory and immune response and have been used since decades to treat various inflammatory and autoimmune disorders. Fine-tuning the glucocorticoid receptor (GR) activity is instrumental in the search for novel therapeutic strategies aimed to reduce pathological signaling and restoring homeostasis. Despite the primary anti-inflammatory actions of GCs, there are studies suggesting that under certain conditions GCs may also exert pro-inflammatory responses. For these reasons the understanding of the GR basic mechanisms of action on different immune cells in the periphery (e.g., macrophages, dendritic cells, neutrophils, and T cells) and in the brain (microglia) contexts, that we review in this chapter, is a continuous matter of interest and may reveal novel therapeutic targets for the treatment of immune and inflammatory response.

Intravenous immunoglobulin for the treatment of childhood encephalitis

BACKGROUND

Encephalitis is a syndrome of neurological dysfunction due to inflammation of the brain parenchyma, caused by an infection or an exaggerated host immune response, or both. Attenuation of brain inflammation through modulation of the immune response could improve patient outcomes. Biological agents such as immunoglobulin that have both anti-inflammatory and immunomodulatory properties may therefore be useful as adjunctive therapies for people with encephalitis.

OBJECTIVES

To assess the efficacy and safety of intravenous immunoglobulin (IVIG) as add-on treatment for children with encephalitis.

SEARCH METHODS

The Cochrane Multiple Sclerosis and Rare Diseases of the CNS group's Information Specialist searched the following databases up to 30 September 2016: CENTRAL, MEDLINE, Embase, CINAHL, ClinicalTrials.gov, and the WHO ICTRP Search Portal. In addition, two review authors searched Science Citation Index Expanded (SCI-EXPANDED) & Conference Proceedings Citation Index - Science (CPCI-S) (Web of Science Core Collection, Thomson Reuters) (1945 to January 2016), Global Health Library (Virtual Health Library), and Database of Abstracts of Reviews of Effects (DARE).

SELECTION CRITERIA

Randomised controlled trials (RCTs) comparing IVIG in addition to standard care versus standard care alone or placebo.

DATA COLLECTION AND ANALYSIS

Two review authors independently selected articles for inclusion, extracted relevant data, and assessed quality of trials. We resolved disagreements by discussion among the review authors. Where possible, we contacted authors of included studies for additional information. We presented results as risk ratios (RR) or mean differences (MD) with 95% confidence intervals (CI).

MAIN RESULTS

The search identified three RCTs with 138 participants. All three trials included only children with viral encephalitis, one of these included only children with Japanese encephalitis, a specific form of viral encephalitis. Only the trial of Japanese encephalitis (22 children) contributed to the primary outcome of this review and follow-up in that study was for three to six months after hospital discharge. There was no follow-up of participants in the other two studies. We identified one ongoing trial.For the primary outcomes, the results showed no significant difference between IVIG and placebo when used in the treatment of children with Japanese encephalitis: significant disability (RR 0.75, 95% CI 0.22 to 2.60; P = 0.65) and serious adverse events (RR 1.00, 95% CI 0.07 to 14.05; P = 1.00).For the secondary outcomes, the study of Japanese encephalitis showed no significant difference between IVIG and placebo when assessing significant disability at hospital discharge (RR 1.00, 95% CI 0.60 to 1.67). There was no significant difference (P = 0.53) in Glasgow Coma Score at discharge between IVIG (median score 14; range 3 to 15) and placebo (median 14 score; range 7 to 15) in the Japanese encephalitis study. The median length of hospital stay in the Japanese encephalitis study was similar for IVIG-treated (median 13 days; range 9 to 21) and placebo-treated (median 12 days; range 6 to 18) children (P = 0.59).Pooled analysis of the results of the other two studies resulted in a significantly lower mean length of hospital stay (MD -4.54 days, 95% CI -7.47 to -1.61; P = 0.002), time to resolution of fever (MD -0.97 days, 95% CI -1.25 to -0.69; P < 0.00001), time to stop spasms (MD -1.49 days, 95% CI -1.97 to -1.01; P < 0.00001), time to regain consciousness (MD -1.10 days, 95% CI -1.48 to -0.72; P < 0.00001), and time to resolution of neuropathic symptoms (MD -3.20 days, 95% CI -3.34 to -3.06; P < 0.00001) in favour of IVIG when compared with standard care.None of the included studies reported other outcomes of interest in this review including need for invasive ventilation, duration of invasive ventilation, cognitive impairment, poor adaptive functioning, quality of life, number of seizures, and new diagnosis of epilepsy.The quality of evidence was very low for all outcomes of this review.

AUTHORS' CONCLUSIONS

The findings suggest a clinical benefit of adjunctive IVIG treatment for children with viral encephalitis for some clinical measures (i.e. mean length of hospital stay, time (days) to stop spasms, time to regain consciousness, and time to resolution of neuropathic symptoms and fever. For children with Japanese encephalitis, IVIG had a similar effect to placebo when assessing significant disability and serious adverse events.Despite these findings, the risk of bias in the included studies and quality of the evidence make it impossible to reach any firm conclusions on the efficacy and safety of IVIG as add-on treatment for children with encephalitis. Furthermore, the included studies involved only children with viral encephalitis, therefore findings of this review cannot be generalised to all forms of encephalitis. Future well-designed RCTs are needed to assess the efficacy and safety of IVIG in the management of children with all forms of encephalitis. There is a need for internationally agreed core outcome measures for clinical trials in childhood encephalitis.

Alpha 2 Na+,K+-ATPase silencing induces loss of inflammatory response and ouabain protection in glial cells

Ouabain (OUA) is a cardiac glycoside that binds to Na⁺,K⁺-ATPase (NKA), a conserved membrane protein that controls cell transmembrane ionic concentrations and requires ATP hydrolysis. At nM concentrations, OUA activates signaling pathways that are not related to its typical inhibitory effect on the NKA pump. Activation of these signaling pathways protects against some types of injury of the kidneys and central nervous system. There are 4 isoforms of the alpha subunit of NKA, which are differentially distributed across tissues and may have different physiological roles. Glial cells are important regulators of injury and inflammation in the brain and express the α1 and α2 NKA isoforms. This study investigated the role of α2 NKA in OUA modulation of the neuroinflammatory response induced by lipopolysaccharide (LPS) in mouse primary glial cell cultures. LPS treatment increased lactate dehydrogenase release, while OUA did not decrease cell viability and blocked LPS-induced NF-κB activation. Silencing α2 NKA prevented ERK and NF-κB activation by LPS. α2 NKA also regulates TNF-α and IL-1β levels. The data reported here indicate a significant role of α2 NKA in regulating central LPS effects, with implications in the associated neuroinflammatory processes.

Chronic nicotine treatment decreases LPS signaling through NF-κB and TLR-4 modulation in the hippocampus

The hippocampus is a brain region that is rich in nicotinic acetylcholine receptors (nAChRs), especially the α7 subtype. The hippocampus is severely affected in disorders that have a neuroinflammatory component, such as Alzheimer's disease, Parkinson's disease, and schizophrenia. Previous studies demonstrated both in vivo and in vitro that nicotine inhibits immunological responses, including those that are triggered by the inflammatory agent lipopolysaccharide (LPS), the endotoxin of Gram-negative bacteria. The present study investigated whether chronically administered nicotine interferes with the nuclear binding of nuclear factor-κB (NF-κB) and the expression of LPS-induced inflammatory response genes. The results indicated that chronic nicotine administration (0.1mg/kg, s.c., 14days) inhibited the LPS-induced nuclear binding of NF-κB and mRNA expression levels of Tnf, Il1b, Nos2, and Tlr4. The presence of both the selective α7 nAChR antagonist methyllycaconitine (MLA; 5.0mg/kg i.p., 14days) and the nonselective nAChR antagonist mecamylamine (Meca; 1.0mg/kg, s.c., 14days) reversed the inhibitory effects of nicotine. These results suggest that the chronic activation of α7- and α_xβ_y-containing nAChRs reduces acute inflammatory responses in the brain.

Age-related neuroinflammation and changes in AKT-GSK-3β and WNT/ β-CATENIN signaling in rat hippocampus

Aging is a multifactorial process associated with an increased susceptibility to neurodegenerative disorders which can be related to chronic inflammation. Chronic inflammation, however, can be characterized by the persistent elevated glucocorticoid (GCs) levels, activation of the proinflammatory transcription factor NF-кB, as well as an increase in cytokines. Interestingly, both NF-кB and cytokines can be even modulated by Glycogen Synthase Kinase 3 beta (GSK-3β) activity, which is a key protein that can intermediate inflammation and metabolism, once it has a critical role in AKT signaling pathway, and can also intermediate WNT/β-CATENIN signaling pathway. The aim of this study was to verify age-related changes in inflammatory status, as well as in the AKT and WNT signaling pathways. Results showed an age-related increase in neuroinflammation as indicated by NF-кB activation, TNF-α and GCs increased levels, a decrease in AKT activation and an increase in GSK-3β activity in both 12- and 24- month old animals. Aging also seems to induce a progressive decrease in canonical WNT/β-CATENIN signaling pathway once there is a decrease in DVL-2 levels and in the transcription of Axin2 gene. Little is known about the DVL-2 regulation as well as its roles in WNT signaling pathway, but for the first time it was suggested that DVL-2 expression can be changed along aging.

Glucocorticoids: Protectors of the Brain during Innate Immune Responses

The innate immune response is a coordinated set of reactions involving cells of myeloid lineage and a network of signaling molecules. Such a response takes place in the CNS during trauma, stroke, spinal cord injury, and neurodegenerative diseases, suggesting that macrophages/microglia are the cells that perpetuate the progressive neuronal damage. However, there is accumulating evidence that these cells and their secreted proinflammatory molecules have more beneficial effects than detrimental consequences for the neuronal elements. Indeed, a timely controlled innate immune response may limit toxicity in swiftly eliminating foreign materials and debris that are known to interfere with recovery and regeneration. Each step of the immune cascade is under the tight control of stimulatory and inhibitory signals. Glucocorticoids (GCs) act as the critical negative feedback on all myeloid cells, including those present within the brain parenchyma. Because too little is like too much, both an inappropriate feedback of GCs on microglia and high circulating GC levels in stressed individuals have been associated with deleterious consequences for the brain. In this review, the authors discuss both sides of the story with a particular emphasis on the neuro-protective role of endogenous GCs during immune challenges and the problems in determining whether GCs can be a good therapy for the treatment of neuropathological conditions.

Relevance of chronic stress and the two faces of microglia in Parkinson's disease

This review is aimed to highlight the importance of stress and glucocorticoids (GCs) in modulating the inflammatory response of brain microglia and hence its potential involvement in Parkinson’s disease (PD). The role of inflammation in PD has been reviewed extensively in the literature and it is supposed to play a key role in the course of the disease. Historically, GCs have been strongly associated as anti-inflammatory hormones. However, accumulating evidence from the peripheral and central nervous system have clearly revealed that, under specific conditions, GCs may promote brain inflammation including pro-inflammatory activation of microglia. We have summarized relevant data linking PD, neuroinflamamation and chronic stress. The timing and duration of stress response may be critical for delineating an immune response in the brain thus probably explain the dual role of GCs and/or chronic stress in different animal models of PD.

Altered KLOTHO and NF-κB-TNF-α Signaling Are Correlated with Nephrectomy-Induced Cognitive Impairment in Rats

Renal insufficiency can have a negative impact on cognitive function. Neuroinflammation and changes in klotho levels associate with chronic kidney disease (CKD) and may play a role in the development of cognitive impairment (CI). The present study evaluates the correlation of cognitive deficits with neuroinflammation and soluble KLOTHO in the cerebral spinal fluid (CSF) and brain tissue of nephrectomized rats (Nx), with 5/6 renal mass ablation. Nx and sham Munich Wistar rats were tested over 4 months for locomotor activity, as well as inhibitory avoidance or novel object recognition, which started 30 days after the surgery. EMSA for Nuclear factor-κB and MILLIPLEXMAP or ELISA kit were used to evaluate cytokines, glucocorticoid and KLOTHO levels. Nx animals that showed a loss in aversive-related memory and attention were included in the CI group (Nx-CI) (n=14) and compared to animals with intact learning (Nx-M n=12 and Sham n=20 groups). CSF and tissue samples were collected 24 hours after the last behavioral test. The results show that the Nx-groups have increased NF-κB binding activity and tumor necrosis factor-alpha (TNF-α) levels in the hippocampus and frontal cortex, with these changes more pronounced in the Nx-CI group frontal cortex. In addition, the Nx-CI group showed significantly increased CSF glucocorticoid levels and TNF-α /IL-10 ratio compared to the Sham group. Klotho levels were decreased in Nx-CI frontal cortex but not in hippocampus, when compared to Nx-M and Sham groups. Overall, these results suggest that neuroinflammation mediated by frontal cortex NF-κB, TNF-α and KLOTHO signaling may contribute to Nx-induced CI in rats.

Effects of intermittent fasting on age-related changes on Na,K-ATPase activity and oxidative status induced by lipopolysaccharide in rat hippocampus

Chronic neuroinflammation is a common characteristic of neurodegenerative diseases, and lipopolysaccharide (LPS) signaling is linked to glutamate-nitric oxide-Na,K-ATPase isoforms pathway in central nervous system (CNS) and also causes neuroinflammation. Intermittent fasting (IF) induces adaptive responses in the brain that can suppress inflammation, but the age-related effect of IF on LPS modulatory influence on nitric oxide-Na,K-ATPase isoforms is unknown. This work compared the effects of LPS on the activity of α1,α2,3 Na,K-ATPase, nitric oxide synthase gene expression and/or activity, cyclic guanosine monophosphate, 3-nitrotyrosine-containing proteins, and levels of thiobarbituric acid-reactive substances in CNS of young and older rats submitted to the IF protocol for 30 days. LPS induced an age-related effect in neuronal nitric oxide synthase activity, cyclic guanosine monophosphate, and levels of thiobarbituric acid-reactive substances in rat hippocampus that was linked to changes in α2,3-Na,K-ATPase activity, 3-nitrotyrosine proteins, and inducible nitric oxide synthase gene expression. IF induced adaptative cellular stress-response signaling pathways reverting LPS effects in rat hippocampus of young and older rats. The results suggest that IF in both ages would reduce the risk for deficits on brain function and neurodegenerative disorders linked to inflammatory response in the CNS.

Signaling function of Na,K-ATPase induced by ouabain against LPS as an inflammation model in hippocampus

BACKGROUND

Ouabain (OUA) is a newly recognized hormone that is synthesized in the adrenal cortex and hypothalamus. Low doses of OUA can activate a signaling pathway by interaction with Na,K-ATPase, which is protective against a number of insults. OUA has central and peripheral anti-inflammatory effects. Lipopolysaccharide (LPS), via toll-like receptor 4 activation, is a widely used model to induce systemic inflammation. This study used a low OUA dose to evaluate its effects on inflammation induced by LPS injection in rats.

METHODS

Adult male Wistar rats received acute intraperitoneal (ip) OUA (1.8 μg/kg) or saline 20 minutes before LPS (200 μg/kg, ip) or saline injection. Some of the animals had their femoral artery catheterized in order to assess arterial blood pressure values before and after OUA administration. Na,K-ATPase activity, cytokine mRNA levels, apoptosis-related proteins, NF-κB activation brain-derived neurotrophic factor BDNF, corticosterone and TNF-α levels were measured.

RESULTS

OUA pretreatment decreased mRNA levels of the pro-inflammatory cytokines, inducible nitric oxide synthase (iNOS) and IL-1β, which are activated by LPS in the hippocampus, but with no effect on serum measures of these factors. None of these OUA effects were linked to Na,K-ATPase activity. The involvement of the inflammatory transcription factor NF-κB in the OUA effect was indicated by its prevention of LPS-induced nuclear translocation of the NF-κB subunit, RELA (p65), as well as the decreased cytosol levels of the NF-κB inhibitor, IKB, in the hippocampus. OUA pretreatment reversed the LPS-induced glial fibrillary acidic protein (GFAP) activation and associated inflammation in the dentate gyrus. OUA also prevented LPS-induced increases in the hippocampal Bax/Bcl2 ratio suggesting an anti-apoptotic action in the brain.

CONCLUSION

Our results suggest that a low dose of OUA has an important anti-inflammatory effect in the rat hippocampus. This effect was associated with decreased GFAP induction by LPS in the dentate gyrus, a brain area linked to adult neurogenesis.

Intermittent fasting attenuates lipopolysaccharide-induced neuroinflammation and memory impairment

BACKGROUND

Systemic bacterial infections often result in enduring cognitive impairment and are a risk factor for dementia. There are currently no effective treatments for infection-induced cognitive impairment. Previous studies have shown that intermittent fasting (IF) can increase the resistance of neurons to injury and disease by stimulating adaptive cellular stress responses. However, the impact of IF on the cognitive sequelae of systemic and brain inflammation is unknown.

METHODS

Rats on IF for 30 days received 1 mg/kg of lipopolysaccharide (LPS) or saline intravenously. Half of the rats were subjected to behavioral tests and the other half were euthanized two hours after LPS administration and the hippocampus was dissected and frozen for analyses.

RESULTS

Here, we report that IF ameliorates cognitive deficits in a rat model of sepsis by a mechanism involving NF-κB activation, suppression of the expression of pro-inflammatory cytokines, and enhancement of neurotrophic support. Treatment of rats with LPS resulted in deficits in cognitive performance in the Barnes maze and inhibitory avoidance tests, without changing locomotor activity, that were ameliorated in rats that had been maintained on the IF diet. IF also resulted in reduced levels of mRNAs encoding the LPS receptor TLR4 and inducible nitric oxide synthase (iNOS) in the hippocampus. Moreover, IF prevented LPS-induced elevation of IL-1α, IL-1β and TNF-α levels, and prevented the LPS-induced reduction of BDNF levels in the hippocampus. IF also significantly attenuated LPS-induced elevations of serum IL-1β, IFN-γ, RANTES, TNF-α and IL-6 levels.

CONCLUSIONS

Taken together, our results suggest that IF induces adaptive responses in the brain and periphery that can suppress inflammation and preserve cognitive function in an animal model of systemic bacterial infection.

The HPA - Immune Axis and the Immunomodulatory Actions of Glucocorticoids in the Brain

In response to physiological and psychogenic stressors, the hypothalamic–pituitary–adrenal (HPA) axis orchestrates the systemic release of glucocorticoids (GCs). By virtue of nearly ubiquitous expression of the GC receptor and the multifaceted metabolic, cardiovascular, cognitive, and immunologic functions of GCs, this system plays an essential role in the response to stress and restoration of an homeostatic state. GCs act on almost all types of immune cells and were long recognized to perform salient immunosuppressive and anti-inflammatory functions through various genomic and non-genomic mechanisms. These renowned effects of the steroid hormone have been exploited in the clinic for the past 70 years and synthetic GC derivatives are commonly used for the therapy of various allergic, autoimmune, inflammatory, and hematological disorders. The role of the HPA axis and GCs in restraining immune responses across the organism is however still debated in light of accumulating evidence suggesting that GCs can also have both permissive and stimulatory effects on the immune system under specific conditions. Such paradoxical actions of GCs are particularly evident in the brain, where substantial data support either a beneficial or detrimental role of the steroid hormone. In this review, we examine the roles of GCs on the innate immune system with a particular focus on the CNS compartment. We also dissect the numerous molecular mechanisms through which GCs exert their effects and discuss the various parameters influencing the paradoxical immunomodulatory functions of GCs in the brain.

Suppression of adrenal gland-derived epinephrine enhances the corticosterone-induced antinociceptive effect in the mouse formalin test

BACKGROUND

There is both clinical and experimental evidence to support the application of corticosterone in the management of inflammation and pain. Corticosterone has been used to treat painful inflammatory diseases and can produce antinociceptive effects. Epinephrine is synthesized from norepinephrine by the enzyme phenylethanolamine N-methyltransferase (PNMT) and works as an endogenous adrenoceptor ligand secreted peripherally by the adrenal medulla. It is currently unclear whether corticosterone's antinociceptive effect is associated with the modulation of peripheral epinephrine.

METHODS

We first determined whether exogenous corticosterone treatment actually produced an antinociceptive effect in a formalin-induced pain model, and then examined whether this corticosterone-induced antinociceptive effect was altered by suppression of adrenal-derived epinephrine, using the following three suppression methods: (1) inhibition of the PNMT enzyme; (2) blocking peripheral epinephrine receptors; and (3) adrenalectomy.

RESULTS

Exogenous treatment with corticosterone at a high dose (50 mg/kg), but not at lower doses (5, 25 mg/kg), significantly reduced pain responses in the late phase. Moreover, injection of 2,3-dichloro-a-methylbenzylamine, a PNMT enzyme inhibitor, (10 mg/kg) before corticosterone treatment caused a leftward shift in the dose-response curve for corticosterone and injection of propranolol (5 mg/kg), but not phentolamine, also shifted the dose-response curve to the left during the late phase. Chemical sympathectomy with 6-hydroxydopamine had no effect on corticosterone-induced antinociceptive effect, but injection of a low dose of corticosterone produced an antinociceptive effect in adrenalectomized animals.

CONCLUSIONS

These results demonstrate that suppression of epinephrine, derived from adrenal gland, enhances the antinociceptive effect of exogenous corticosterone treatment in an inflammatory pain model.

Microglial cells are involved in the susceptibility of NADPH oxidase knockout mice to 6-hydroxy-dopamine-induced neurodegeneration

We explored the impact of Nox-2 in modulating inflammatory-mediated microglial responses in the 6-hydroxydopamine (6-OHDA)-induced Parkinson’s disease (PD) model. Nox1 and Nox2 gene expression were found to increase in striatum, whereas a marked increase of Nox2 expression was observed in substantia nigra (SN) of wild-type (wt) mice after PD induction. Gp91^phox-/- 6-OHDA-lesioned mice exhibited a significant reduction in the apomorphine-induced rotational behavior, when compared to wt mice. Immunolabeling assays indicated that striatal 6-OHDA injections reduced the number of dopaminergic (DA) neurons in the SN of wt mice. In gp91^phox-/- 6-OHDA-lesioned mice the DA degeneration was negligible, suggesting an involvement of Nox in 6-OHDA-mediated SN degeneration. Gp91^phox-/- 6-OHDA-lesioned mice treated with minocycline, a tetracycline derivative that exerts multiple anti-inflammatory effects, including microglial inhibition, exhibited increased apomorphine-induced rotational behavior and degeneration of DA neurons after 6-OHDA injections. The same treatment also increased TNF-α release and potentiated NF-κB activation in the SN of gp91^phox-/--lesioned mice. Our results demonstrate for the first time that inhibition of microglial cells increases the susceptibility of gp91^phox-/- 6-OHDA lesioned mice to develop PD. Blockade of microglia leads to NF-κB activation and TNF-α release into the SN of gp91^phox-/- 6-OHDA lesioned mice, a likely mechanism whereby gp91^phox-/- 6-OHDA lesioned mice may be more susceptible to develop PD after microglial cell inhibition. Nox2 adds an essential level of regulation to signaling pathways underlying the inflammatory response after PD induction.

Modulation of pineal melatonin synthesis by glutamate involves paracrine interactions between pinealocytes and astrocytes through NF-κB activation

The glutamatergic modulation of melatonin synthesis is well known, along with the importance of astrocytes in mediating glutamatergic signaling in the central nervous system. Pinealocytes and astrocytes are the main cell types in the pineal gland. The objective of this work was to investigate the interactions between astrocytes and pinealocytes as a part of the glutamate inhibitory effect on melatonin synthesis. Rat pinealocytes isolated or in coculture with astrocytes were incubated with glutamate in the presence of norepinephrine, and the melatonin content, was quantified. The expression of glutamate receptors, the intracellular calcium content and the NF-κB activation were analyzed in astrocytes and pinealocytes. TNF-α's possible mediation of the effect of glutamate was also investigated. The results showed that glutamate's inhibitory effect on melatonin synthesis involves interactions between astrocytes and pinealocytes, possibly through the release of TNF-α. Moreover, the activation of the astrocytic NF-κB seems to be a necessary step. In astrocytes and pinealocytes, AMPA, NMDA, and group I metabotropic glutamate receptors were observed, as well as the intracellular calcium elevation. In conclusion, there is evidence that the modulation of melatonin synthesis by glutamate involves paracrine interactions between pinealocytes and astrocytes through the activation of the astrocytic NF-κB transcription factor and possibly by subsequent TNF-α release.

Functional imaging of Rel expression in inflammatory processes using bioluminescence imaging system in transgenic mice

c-Rel plays important roles in many inflammatory diseases. Revealing the dynamic expression of c-Rel in disease processes in vivo is critical for understanding c-Rel functions and for developing anti-inflammatory drugs. In this paper, a transgenic mouse line, B6-Tg(c-Rel-luc)(Mlit), which incorporated the transgene firefly luciferase driven by a 14.5-kb fragment containing mouse c-Rel gene Rel promoter, was generated to monitor Rel expression in vivo. Luciferase expression could be tracked in living mice by the method of bioluminescence imaging in a variety of inflammatory processes, including LPS induced sepsis and EAE disease model. The luciferase expression in transgenic mice was comparable to the endogenous Rel expression and could be suppressed by administration of anti-inflammatory drug dexamethasone or aspirin. These results indicate that the B6-Tg(c-Rel-luc)(Mlit) mouse is a valuable animal model to study Rel expression in physiological and pathological processes, and the effects of various drug treatments in vivo.

Thalidomide suppresses inflammation in adenine-induced CKD with uraemia in mice

BACKGROUND

Persistent systemic inflammation has been widely recognized in patients with chronic kidney disease (CKD), and is associated with increased risk of morbidity and mortality. Intervention therapies aiming for the blockade of inflammatory cytokines are considered attractive approaches for CKD patients with signs of chronic inflammation. In this context, thalidomide, due to its potent anti-inflammatory and immunomodulatory properties, may represent an alternative strategy of treatment. In the present study, we developed an experimental model of CKD with uraemia in mice, induced by a diet rich in adenine, which causes progressive renal dysfunction, resembling the human uraemic features. Inflammatory parameters were analysed in this model of CKD and the potential beneficial effects of thalidomide as an anti-inflammatory drug was also investigated.

METHODS

C57/BL-6 mice were fed with an adenine-containing diet during a period of 6 weeks. Thirty mice were divided into three groups: Control group (animals receiving normal diet), ADE group (mice receiving adenine-containing diet) and ADE + TLD group (CKD mice receiving thalidomide, 30 mg/kg/day, by gavage). Besides biochemical and histopathological changes, local and systemic inflammatory parameters were also analysed, including expression of cytokines interleukin (IL)-1β, tumour necrosis factor-α, IL-6, IL-4 and IL-10 in kidney samples by real-time RT-PCR and quantification of serum levels of cytokines. Finally, the electrophoretic mobility shift assay (EMSA) for NF-κB was also examined.

RESULTS

Adenine-fed mice developed advanced CKD characterized by a marked increase in serum urea, creatinine, phosphorus and intact parathyroid hormone (iPTH) levels. In addition, histological changes of tubulointerstitial injury, characterized by deposition of crystals in the kidney, accompanied by tubular dilatation, degeneration of proximal tubular epithelium with loss of the brush border, inflammatory cellular infiltration, foreign-body granuloma formation and interstitial fibrosis were also evident. By immunohistochemistry, Mac-2- and α-SMA-positive cells were identified in the tubulointerstitial compartment. Treatment with thalidomide significantly reduced serum urea, creatinine, phosphorus and iPTH levels and protected against tubulointerstitial injury. Local and systemic inflammation in the mice model of adenine-induced CKD was confirmed by the findings of significantly high expression of cytokine mRNA levels and NF-κB activation in the kidney tissue as well as marked increased serum levels of inflammatory cytokines. Thalidomide treatment significantly reduced gene expression of these cytokines and the activation of the NF-κB in the renal tissue and the circulating levels of cytokines.

CONCLUSIONS

Dietary adenine caused advanced CKD with uraemia in mice providing a useful experimental model to study molecular and morphological changes associated with this disease. The negative impact of inflammation in this CKD model was overcome by the marked anti-inflammatory effects of thalidomide, promoting renal protection.

The neuroendocrine control of the innate immune system in health and brain diseases

The innate immune reaction takes place in the brain during immunogenic challenges, injury, and disease. Such a response is highly regulated by numerous anti-inflammatory mechanisms that may directly affect the ultimate consequences of such a reaction within the cerebral environment. The neuroendocrine control of this innate immune system by glucocorticoids is critical for the delicate balance between cell survival and damage in the presence of inflammatory mediators. Glucocorticoids play key roles in regulating the expression of inflammatory genes, and they also have the ability to modulate numerous functions that may ultimately lead to brain damage or repair after injury. Here we review these mechanisms and discuss data supporting both neuroprotective and detrimental roles of the neuroendocrine control of innate immunity.

Role of IKK/NF-κB signaling in extinction of conditioned place aversion memory in rats

The inhibitor κB protein kinase/nuclear factor κB (IKK/NF-κB) signaling pathway is critical for synaptic plasticity. However, the role of IKK/NF-κB in drug withdrawal-associated conditioned place aversion (CPA) memory is unknown. Here, we showed that inhibition of IKK/NF-κB by sulphasalazine (SSZ; 10 mM, i.c.v.) selectively blocked the extinction but not acquisition or expression of morphine-induced CPA in rats. The blockade of CPA extinction induced by SSZ was abolished by sodium butyrate, an inhibitor of histone deacetylase. Thus, the IKK/NF-κB signaling pathway might play a critical role in the extinction of morphine-induced CPA in rats and might be a potential pharmacotherapy target for opiate addiction.

Adipose tissue inflammation and cancer cachexia: possible role of nuclear transcription factors

Cancer cachexia is a multifaceted syndrome whose aetiology is extremely complex and is directly related to poor patient prognosis and survival. Changes in lipid metabolism in cancer cachexia result in marked reduction of total fat mass, increased lipolysis, total oxidation of fatty acids, hyperlipidaemia, hypertriglyceridaemia, and hypercholesterolaemia. These changes are believed to be induced by inflammatory mediators, such as tumour necrosis factor-α (TNF-α) and other factors. Attention has recently been drawn to the current theory that cachexia is a chronic inflammatory state, mainly caused by the host's reaction to the tumour. Changes in expression of numerous inflammatory mediators, notably in white adipose tissue (WAT), may trigger several changes in WAT homeostasis. The inhibition of adipocyte differentiation by PPARγ is paralleled by the appearance of smaller adipocytes, which may partially account for the inhibitory effect of PPARγ on inflammatory gene expression. Furthermore, inflammatory modulation and/or inhibition seems to be dependent on the IKK/NF-κB pathway, suggesting that a possible interaction between NF-κB and PPARγ is required to modulate WAT inflammation induced by cancer cachexia. In this article, current literature on the possible mechanisms of NF-κB and PPARγ regulation of WAT cells during cancer cachexia are discussed. This review aims to assess the role of a possible interaction between NF-κB and PPARγ in the setting of cancer cachexia as well as its significant role as a potential modulator of chronic inflammation that could be explored therapeutically.

Influence of N-methyl-D-aspartate receptors on ouabain activation of nuclear factor-κB in the rat hippocampus

It has been shown that ouabain (OUA) can activate the Na,K-ATPase complex and mediate intracellular signaling in the central nervous system (CNS). Inflammatory stimulus increases glutamatergic transmission, especially at N-methyl-D-aspartate (NMDA) receptors, which are usually coupled to the activation of nitric oxide synthase (NOS). Nuclear factor-κB (NF-κB) activation modulates the expression of genes involved in development, plasticity, and inflammation. The present work investigated the effects of OUA on NF-κB binding activity in rat hippocampus and the influence of this OUA-Na,K-ATPase signaling cascade in NMDA-mediated NF-κB activation. The findings presented here are the first report indicating that intrahippocampal administration of OUA, in a concentration that did not alter Na,K-ATPase or NOS activity, induced an activation of NF-κB, leading to increases in brain-derived neurotrophic factor (Bdnf), inducible NOS (iNos), tumor necrosis factor-α (Tnf-α), and B-cell leukemia/lymphoma 2 (Bcl2) mRNA levels. This response was not linked to any significant signs of neurodegeneration as showed via Fluoro-Jade B and Nissl stain. Intrahippocampal administration of NMDA induced NF-κB activation and increased NOS and α(2/3) -Na,K-ATPase activities. NMDA treatment further increased OUA-induced NF-κB activation, which was partially blocked by MK-801, an antagonist of NMDA receptor. These results suggest that OUA-induced NF-κB activation is at least in part dependent on Na,K-ATPase modulatory action of NMDA receptor in hippocampus. The interaction of these signaling pathways could be associated with biological mechanisms that may underlie the basal homeostatic state linked to the inflammatory signaling cascade in the brain.

Antimicrobial responses in the male reproductive tract of lipopolysaccharide challenged rats

PROBLEM

Innate immune machinery including the Toll-like receptors (TLRs) confers the first line of defense mechanisms to counter pathogenic microorganisms that enter the body. The male reproductive tract is vulnerable to infection and the role of TLRs and the antimicrobial responses that operate to counter infections in this organ system are poorly understood.

METHOD OF STUDY

Caput and cauda epididymides, testes and seminal vesicles were collected at 0, 3, 6, 9, 12, 15 and 24 h from rats injected intraperitoneally with a single dose of LPS. Plasma testosterone was measured using ELISA. Expression pattern of defensins and Spag11 isoforms were analysed using RT-PCR. Immunohistochemical analyses was performed to determine SPAG11E protein expression following LPS treatment.

RESULTS

We provide the first line of evidence that the male reproductive tract induces the expression of Sperm Associated Antigen 11 (Spag11) mRNA variants and defensins when challenged with lipopolysaccharide (LPS) with a concomitant increase in protein expression. However, there was an inverse relationship between induction of antimicrobial gene expression and plasma testosterone. An increase in the mRNA levels of proinflammatory cytokines was observed parallel to the induction of Spag11 variants and majority of defensin expression in the male reproductive tract.

CONCLUSION

The increase in Spag11 and defensin mRNA in response to LPS administration demonstrates their importance in protecting the male reproductive tract during infection. Results of this study help to understand male reproductive tract innate immune defense mechanisms and to design novel peptide antibiotics to prevent sexually transmitted diseases.

Glucocorticoids exacerbate lipopolysaccharide-induced signaling in the frontal cortex and hippocampus in a dose-dependent manner

Although the anti-inflammatory actions of glucocorticoids (GCs) are well established, evidence has accumulated showing that proinflammatory GC effects can occur in the brain, in a poorly understood manner. Using electrophoretic mobility shift assay, real-time PCR, and immunoblotting, we investigated the ability of varying concentrations of corticosterone (CORT, the GC of rats) to modulate lipopolysaccharide (LPS)-induced activation of NF-κB (nuclear factor κB), expression of anti- and proinflammatory factors and of the MAP (mitogen-activated protein) kinase family [ERK (extracellular signal-regulated kinase), p38, and JNK/SAPK (c-Jun N-terminal protein kinase/stress-activated protein kinase)], and AKT. In the frontal cortex, elevated CORT levels were proinflammatory, exacerbating LPS effects on NF-κB, MAP kinases, and proinflammatory gene expression. Milder proinflammatory GCs effects occurred in the hippocampus. In the absence of LPS, elevated CORT levels increased basal activation of ERK1/2, p38, SAPK/JNK, and AKT in both regions. These findings suggest that GCs do not uniformly suppress neuroinflammation and can even enhance it at multiple levels in the pathway linking LPS exposure to inflammation.

Microglial activation is inhibited by corticosterone in dopaminergic neurodegeneration

The present study compared 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced microglial activation in 3 different groups, sham-operated (SHM) mice, adrenalectomized mice (ADX), and ADX mice administered with corticosterone (ADX + CORT), to investigate the roles of glucocorticoids on microglial activation and dopaminergic neurodegeneration. Acute MPTP treatment induced moderate tyrosine hydroxylase (TH)-immunoreactive neuronal loss in the substantia nigra (SN) of SHM mice; this neuronal loss was significantly enhanced in ADX mice, but eventually recovered following the administration of corticosterone. Consistent with neuronal findings, acute MPTP treatment induced microglial activation in the SN from 1-3 days post injection in SHM mice. Interestingly, microglial activation was further enhanced and occasionally showed a phagocytic morphology in ADX mice that showed no circulating corticosterone. Furthermore, the activated microglia was significantly suppressed by the administration of corticosterone to ADX mice. Moreover, a confocal microscopic study demonstrated that the expression of inducible nitric oxide synthase protein, exclusively colocalized with activated microglia in the SN in ADX mice, was substantially decreased by the administration of corticosterone. Thus, the present study, using in-vivo adrenalectomy for a dopaminergic neurodegeneration model, successfully demonstrated the neuroprotective effects of corticosterone by microglial inhibition.

TNF alpha production in morphine-treated human neural cells is NF-kappaB-dependent

The cytokine tumor necrosis factor alpha (TNFalpha) is a key factor in several inflammatory diseases and its levels increase in response to a variety of internal or external stimuli. The regulation of the TNFalpha promoter is mediated by several transcription factors including the nuclear factor kappa B protein (NF-kappaB). This study examines the role of NF-kappaB in the regulation of TNFalpha production by morphine in microglia. Using reverse transcriptase polymerase chain reaction, we demonstrated the presence of morphine receptors in these cells. We next demonstrated the ability of morphine to promote TNFalpha production and secretion by these cells using a cytokine array assay. Transient transfection experiments led to the identification of the region located between nucleotides -751 and -615 within the TNFalpha promoter as being responsive to morphine treatment. The DNA sequence of this region contains a motif indicative of a potential NF-kappaB binding site. The use of a small interfering RNA directed against p65, a subunit of NF-kappaB, demonstrated that TNFalpha induction by morphine is NF-kappaB-dependent. All of the effects of morphine were reversed by the morphine inhibitor, naloxone. These data provide important insights into the effects of morphine on microglia.

Activation of toll-like receptor 4 (TLR4) by in vivo and in vitro exposure of rat epididymis to lipopolysaccharide from Escherichia Coli

This study provides the first evidence that rat epididymis is fully capable of initiating an inflammatory response to lipopolysaccharide (LPS) from Escherichia coli through activation of Toll-like receptor 4 (TLR4). TLR4 functionality was demonstrated by in vivo LPS challenge, which induced a time- and dose-dependent activation of the transcription factor nuclear factor kappa B (NFKB) in caput and cauda epididymides. NFKB activation by LPS in caput epididymidis was abrogated when rats were pretreated with the NFKB inhibitor PDTC, confirming the specificity of this response. Within 2 h of LPS treatment (0.01 and 1 mg/kg, i.v.), NFKB activation in caput and cauda was accompanied by upregulation of Il1b, Nfkbia, and Cd14, but not Tlr4, mRNA. These effects, however, were not sustained after 24 h of LPS treatment. Lipopolysaccharide systemic effects were not restricted to epididymides, since Il1b, Nfkbia, and Cd14 mRNAs were also upregulated in other male reproductive tissues from LPS-treated rats (1 mg/kg, i.v., 2 h). Constitutive TLR4 was immunolocalized in some, but not all, epididymal epithelial cells and in interstitial cells, some of them identified as resident ED2-positive macrophages. No change in TLR4 immunostaining pattern was observed when epididymides from control and LPS-treated rats were compared (1 mg/kg, i.v., 2 h and 24 h). Significant NFKB activation was also achieved within 1 min of in vitro incubation of caput epididymidis with LPS (0.01-5 mug/ml), confirming that components for TLR4 signaling cascade activation are fully active in this tissue. This study contributes to a better understanding of the innate immune response in the epididymis and other tissues from the male reproductive tract.

Role of nitric oxide in the brain during lipopolysaccharide-evoked systemic inflammation

Although the inducible isoform of nitric oxide synthase (iNOS) is a well-established source of nitric oxide (NO*) during inflammation of the central nervous system (CNS), little is known about the involvement of constitutive isoforms of NOS (cNOS) in the inflammatory process. The aim of this study was to compare the responses of the expression and activity of iNOS and the two cNOS isoforms, neuronal and endothelial (nNOS and eNOS, respectively), in the brain to systemic inflammation and their roles in the cascade of events leading to degeneration and apoptosis. A systemic inflammatory response in C57BL/6 mice was induced by intraperitoneal injection of lipopolysaccharide [LPS; 1 mg/kg body weight (b.w.)]. The relative roles of the NOS isoforms were evaluated after injection of NG-nitro-L-arginine (NNLA; 30 mg/kg b.w.), which preferentially inhibits cNOS, or 1400W (5 mg/kg b.w.), an inhibitor of iNOS. Biochemical and morphological alterations were analyzed up to 48 hr after administration of LPS. Systemic LPS administration evoked significant ultrastructural alterations in brain capillary vessels, neuropils, and intracellular organelles of neurons, astrocytes, and microglia. Apoptotic/autophagic processes occurred in many neurons of the substantia nigra (SN), which coincided with exclusive enhancement of iNOS expression and activity in this brain region. Moreover, inhibitors of both iNOS and cNOS prevented LPS-evoked release of apoptosis-inducing factor (AIF) from SN mitochondria. Collectively, the results indicate that synthesis of NO* by both the inducible and constitutive NOS isoforms contribute to the activation of apoptotic pathways in the brain during systemic inflammation.

Neuroprotective role of the innate immune system by microglia

Innate immunity is a rapid series of reactions to pathogens, cell injuries and toxic proteins. A key component of this natural response is the production of inflammatory mediators by resident microglia and infiltrating macrophages. There is accumulating evidence that inflammation contributes to acute injuries and more chronic CNS diseases, though other studies have shown that inhibition of microglia is, in contrast, associated with more damages or less repair. The controversies regarding the neuroprotective and neurodegenerative properties of microglia may depend on the experimental approaches. Neurotoxic substances are frequently used to produce animal models of acute injuries or diseases and they may activate microglia either directly or indirectly by their ability to cause neuronal death and demyelination. Whether microglia and the immune response play a direct role in such processes still remains an open question. On the other hand, there are data supporting the role of resident microglia and those derived from the bone marrow in the stimulation of myelin repair, removal of toxic proteins from the CNS and the prevention of neurodegeneration in chronic brain diseases. The ability of glucocorticoids to provide a negative feedback on nuclear factor kappa B pathways in microglia may be a determinant mechanism underlying the ultimate fate of the inflammatory response in the CNS. This review presents new concepts regarding the neuroprotective role of the innate immune response in the brain and how microglia can be directed to improve recovery after injuries and prevent/delay neurodegeneration.

Chronic lithium administration attenuates up-regulated brain arachidonic acid metabolism in a rat model of neuroinflammation

Neuroinflammation, caused by a 6-day intracerebroventricular infusion of lipopolysaccharide (LPS) in rats, is associated with the up-regulation of brain arachidonic acid (AA) metabolism markers. Because chronic LiCl down-regulates markers of brain AA metabolism, we hypothesized that it would attenuate increments of these markers in LPS-infused rats. Incorporation coefficients k* of AA from plasma into brain, and other brain AA metabolic markers, were measured in rats that had been fed a LiCl or control diet for 6 weeks, and subjected in the last 6 days on the diet to intracerebroventricular infusion of artificial CSF or of LPS. In rats on the control diet, LPS compared with CSF infusion increased k* significantly in 28 regions, whereas the LiCl diet prevented k* increments in 18 of these regions. LiCl in CSF infused rats increased k* in 14 regions, largely belonging to auditory and visual systems. Brain cytoplasmic phospholipase A(2) activity, and prostaglandin E(2) and thromboxane B(2) concentrations, were increased significantly by LPS infusion in rats fed the control but not the LiCl diet. Chronic LiCl administration attenuates LPS-induced up-regulation of a number of brain AA metabolism markers. To the extent that this up-regulation has neuropathological consequences, lithium might be considered for treating human brain diseases accompanied by neuroinflammation.

Reduced basal and lipopolysaccharide-stimulated adenosine A1 receptor expression in the brain of nuclear factor-kappaB p50-/- mice

Adenosine promotes cytoprotection under conditions of infection, ischemic preconditioning and oxidative stress. Previous studies from our laboratory indicate that the expression of the adenosine A1 receptor (A1AR) is induced by oxidative stress via activation of nuclear factor (NF)-kappaB. The prototypic transcription factor is composed of homo- or heterodimers of p50 and p65 subunits. To determine the role of NF-kappaB in the regulation of the A1AR in vivo, we compared the A1AR RNA and protein levels in the brains of mice lacking the p50 subunit of NF-kappaB (p50-/- mice) and age-matched B6129PF2/J (F2) controls. Radioligand binding assays in the cortex revealed a significantly lower number of A(1)AR (maximal binding capacity, Bmax) in the cortex of p50-/- mice (151+/-62 fmol/mg protein) versus 479+/-181 fmol/mg protein in the F2 (N=5 per strain, P<0.05), but no change in the equilibrium dissociation constant. Similar reductions in A1AR were measured in the hippocampus, brain stem and hypothalamus and in peripheral tissues, such as the adrenal gland, kidney and spleen. Estimation of the A1AR following purification by antibody affinity columns also indicated reduced A1AR in the p50-/- mice cortex, as compared with the F2 mice. A1AR immunocytochemistry indicates distinct neuronal labeling in the F2 cortex, which was substantially reduced in similar sections obtained from p50-/- mice. The p50-/- mice expressed lower levels of A1AR mRNA than F2 mice, as determined by real time PCR. Quantitation of the A1AR transducing G proteins by Western blotting show significantly less Galphai3, no change in Galphai1, but higher levels of Galphao and Gbeta in the cortices of p50-/-, as compared with F2 mice. Administration of bacterial lipopolysaccharide (LPS), an activator of NF-kappaB, increased A1AR expression in the cortices of F2 mice but not p50-/- mice. Cortical neurons cultures prepared from p50-/- mice showed a greater degree of apoptosis, compared with neurons from F2 mice. Activation of the A1AR reduced apoptosis with greater efficacy in cultures from F2 than p50-/- mice. Taken together, these data support a role for NF-kappaB in determining both the basal and LPS-stimulated A1AR expression in vivo which could contribute to neuronal survival.