Vitamin E suppression of microglial activation is neuroprotective

SDS3 regulates microglial inflammation by modulating the expression of the upstream kinase ASK1 in the p38 MAPK signaling pathway

BACKGROUND

Microglia, the main innate immune cells in the central nervous system, are key drivers of neuroinflammation, which plays a crucial role in the pathogenesis of neurodegenerative diseases. The Sin3/histone deacetylase (HDAC) complex, a highly conserved multiprotein co-repressor complex, primarily performs transcriptional repression via deacetylase activity; however, the function of SDS3, which maintains the integrity of the complex, in microglia remains unclear.

METHODS

To uncover the regulatory role of the transcriptional co-repressor SDS3 in microglial inflammation, we used chromatin immunoprecipitation to identify SDS3 target genes and combined with transcriptomics and proteomics analysis to explore expression changes in cells following SDS3 knocking down. Subsequently, we validated our findings through experimental assays.

RESULTS

Our analysis revealed that SDS3 modulates the expression of the upstream kinase ASK1 of the p38 MAPK pathway, thus regulating the activation of signaling pathways and ultimately influencing inflammation.

CONCLUSIONS

Our findings provide important evidence of the contributions of SDS3 toward microglial inflammation and offer new insights into the regulatory mechanisms of microglial inflammatory responses.

Pimecrolimus protects neuron-like SH-SY5Y cells against anti-inflammatory and anti-oxidant effects of both microglial secretome and hydrogen peroxide

Calcineurin inhibitors have been found to exhibit a preventive role against neuroinflammation, which represents a crucial underlying mechanism in neurodegenerative diseases (ND). Additionally, they possess suppressive effects on the activation of apoptotic pathways, which constitute another mechanism underlying such diseases. Given that pimecrolimus, a calcineurin inhibitor, impedes the synthesis of pro-inflammatory cytokines, such as interleukin (IL)-2, IL-4, and IL-10, and influences apoptotic processes, it is noteworthy to test its potential neuroprotective properties. Thus, the objective of this investigation was to assess the potential protective effects of pimecrolimus against the degenerative consequences of both microglial secretomes and hydrogen peroxide (H2O2), an oxidant agent. The survival rates of HMC3 microglia cells, neuron-like differentiated SH-SY5Y (d-SH-SY5Y) cells, and their co-culture were determined using the 3-(4,5-Dimethylthiazol-2-yl)-2,5-Diphenyltetrazolium Bromide (MTT) method. Furthermore, the levels of pro-inflammatory cytokines IL-1β and IL-6, and anti-inflammatory cytokine IL-10 were measured using ELISA kits, besides total antioxidant and oxidant capacities in conditioned media of cells. Additionally, the effect of pimecrolimus on neurite length in these cell groups was evaluated through morphological observations. This study revealed, for the first time, that pimecrolimus exerts preventive effects on neurodegenerative processes by virtue of its anti-inflammatory and -antioxidant activities. It holds promise as a potential treatment option for ND.

α-Tocopherol Protects Lipopolysaccharide-Activated BV2 Microglia

Microglia, the resident macrophage-like population in the central nervous system, play a crucial role in the pathogenesis of many neurodegenerative disorders by triggering an inflammatory response that leads to neuronal death. Neuroprotective compounds to treat or prevent neurodegenerative diseases are a new field of study in modern medicine. Microglia are activated in response to inflammatory stimuli. The pathogenesis of various neurodegenerative diseases is closely related to the constant activation of microglia due to their fundamental role as a mediator of inflammation in the brain environment. α-Tocopherol, also known as vitamin E, is reported to possess potent neuroprotective effects. The goal of this study was to investigate the biological effects of vitamin E on BV2 microglial cells, as a possible neuroprotective and anti-inflammatory agent, following stimulation with lipopolysaccharide (LPS). The results showed that the pre-incubation of microglia with α-tocopherol can guarantee neuroprotective effects during microglial activation induced by LPS. α-Tocopherol preserved the branched morphology typical of microglia in a physiological state. It also reduced the migratory capacity; the production of pro-inflammatory and anti-inflammatory cytokines such as TNF-α and IL-10; and the activation of receptors such as TRL4 and CD40, which modulate the PI3K-Akt signaling pathway. The results of this study require further insights and research, but they present new scenarios for the application of vitamin E as an antioxidant for the purpose of greater neuroprotection in vivo for the prevention of possible neurodegenerative diseases.

Modulating neuroinflammation through molecular, cellular and biomaterial-based approaches to treat spinal cord injury

The neuroinflammatory response that is elicited after spinal cord injury contributes to both tissue damage and reparative processes. The complex and dynamic cellular and molecular changes within the spinal cord microenvironment result in a functional imbalance of immune cells and their modulatory factors. To facilitate wound healing and repair, it is necessary to manipulate the immunological pathways during neuroinflammation to achieve successful therapeutic interventions. In this review, recent advancements and fresh perspectives on the consequences of neuroinflammation after SCI and modulation of the inflammatory responses through the use of molecular-, cellular-, and biomaterial-based therapies to promote tissue regeneration and functional recovery will be discussed.

Role of Vitamin E in Neonatal Neuroprotection: A Comprehensive Narrative Review

Vitamin E (Vit E) is an essential lipophilic antioxidant and anti-inflammatory agent that has potential as a neuroprotectant in newborn infants with brain injury. Vit E has shown promise in many in vitro studies, but success in translation to in vivo animal studies and the clinical setting has been mixed, with concern of adverse effects at high intravenous doses in preterm infants. However, a recent rise in knowledge of the beneficial effects of fat emulsions containing higher levels of Vit E, along with associated improved outcomes in some neonatal co-morbidities, has led many to reconsider Vit E administration as a potential therapeutic modality to improve neurological outcomes in the setting of neonatal brain injury. This narrative review discusses Vit E's structure, mechanism(s) of action, evidence in animal models, and association with health outcomes in neonates, including both dietary and supplemental Vit E and their bioavailability and pharmacokinetics as it relates to the brain. Lastly, long-term neurodevelopmental outcomes along with gaps in current knowledge are critiqued, which to date suggests that additional translational studies in larger animal models and assessment of safety profiles of different routes and doses of administration should be explored prior to large clinical trials. Importantly, a greater understanding of the brain region(s) and cell type(s) affected by Vit E may help to target the use of Vit E as a beneficial neuroprotective agent to specific populations or types of injury seen in newborns.

Antioxidant and Neuroprotective Activity of Vitamin E Homologues: In Vitro Study

Here we present comparative data on the inhibition of lipid peroxidation by a variety of tocochromanols in liposomes. We also show for the first time the potential neuroprotective role of all the vitamin E homologues investigated on the neuronally differentiated human neuroblastoma SH-SY5Y cell line. α-Tocopherol had nearly no effect in the inhibition of lipid peroxidation, while β-, γ-, and δ-tocopherols inhibited the reaction completely when it was initiated in a lipid phase. Similar effects were observed for tocotrienol homologues. Moreover, in this respect plastochromanol-8 was as effective as β-, γ-, and δ-tocochromanols. When the prenyllipids were investigated in a 1,1-diphenyl-2-picrylhydrazyl (DPPH) test and incorporated into different lipid carriers, the radical oxidation was most pronounced in liposomes, followed by mixed micelles and the micellar system. When the reaction of tocochromanols was examined in niosomes, the oxidation was most pronounced for α-tocopherol and plastochromanol-8, followed by α-tocotrienol. Next, using retinoic acid-differentiated SH-SY5Y cells, we tested the protective effects of the compounds investigated on hydrogen peroxide (H₂O₂)-induced cell damage. We showed that tocotrienols were more active than tocopherols in the oxidative stress model. Plastochromanol-8 had a strong inhibitory effect on H₂O₂-induced lactate dehydrogenase (LDH) release and H₂O₂-induced decrease in cell viability. The water-soluble α-tocopherol phosphate had neuroprotective effects at all the concentrations analyzed. The results clearly indicate that structural differences between vitamin E homologues reflect their different biological activity and indicate their potential application in pharmacological treatments for neurodegenerative diseases. In this respect, the application of optimal tocochromanol-carrying structures might be critical.

Micronutrients May Be a Unique Weapon Against the Neurotoxic Triad of Excitotoxicity, Oxidative Stress and Neuroinflammation: A Perspective

Excitotoxicity has been implicated in many neurological disorders and is a leading cause of oxidative stress and neuroinflammation in the nervous system. Most of the research to date has focused on each of these conditions individually; however, excitotoxicity, oxidative stress, and neuroinflammation have the ability to influence one another in a self-sustaining manner, thus functioning as a "neurotoxic triad." This perspective article re-introduces the concept of the neurotoxic triad and reviews how specific dietary micronutrients have been shown to protect against not only oxidative stress, but also excitotoxicity and neuroinflammation. Future dietary interventions for neurological disorders could focus on the effects on all three aspects of the neurotoxic triad.

Interweaving epilepsy and neurodegeneration: Vitamin E as a treatment approach

Epilepsy is the most common neurological disorder, affecting nearly 50 million people worldwide. The condition can be manifested either due to genetic predisposition or acquired from acute insult which leads to alteration of cellular and molecular mechanisms. Evaluating the latest and the current knowledge in regard to the mechanisms underlying molecular and cellular alteration, hyperexcitability is a consequence of an imbalanced state wherein enhance excitatory glutamatergic and reduced inhibitory GABAergic signaling is considered to be accountable for seizures associated damage. However, neurodegeneration contributing to epileptogenesis has become increasingly appreciated. The components at the helm of neurodegenerative alterations during epileptogenesis include GABAergic neuronal and receptor changes, neuroinflammation, alteration in axonal transport, oxidative stress, excitotoxicity, and other cellular as well as functional changes. Targeting neurodegeneration with vitamin E as an antioxidant, anti-inflammatory and neuroprotective may prove to be one of the therapeutic approaches useful in managing epilepsy. In this review, we discuss and converse about the seizure-induced episodes as a link for the development of neurodegenerative and pathological consequences of epilepsy. We also put forth a summary of the potential intervention with vitamin E therapy in the management of epilepsy.

Role of Vitamin E and the Orexin System in Neuroprotection

Microglia are the first line of defense at the level of the central nervous system (CNS). Phenotypic change in microglia can be regulated by various factors, including the orexin system. Neuroinflammation is an inflammatory process mediated by cytokines, by the lack of interaction between neurotransmitters and their specific receptors, caused by systemic tissue damage or, more often, associated with direct damage to the CNS. Chronic activation of microglia could lead to long-term neurodegenerative diseases. This review aims to explore how tocopherol (vitamin E) and the orexin system may play a role in the prevention and treatment of microglia inflammation and, consequently, in neurodegenerative diseases thanks to its antioxidant properties. The results of animal and in vitro studies provide evidence to support the use of tocopherol for a reduction in microglia inflammation as well as a greater activation of the orexinergic system. Although there is much in vivo and in vitro evidence of vitamin E antioxidant and protective abilities, there are still conflicting results for its use as a treatment for neurodegenerative diseases that speculate that vitamin E, under certain conditions or genetic predispositions, can be pro-oxidant and harmful.

A Specialized Nutritional Formulation Prevents Hippocampal Glial Activation and Memory Impairment Induced by Amyloid-β Oligomers in Mice

BACKGROUND

Alzheimer's disease (AD) is the most common cause of dementia in the elderly and is characterized by progressive cognitive decline. Considerable evidence supports an important role of amyloid-β oligomers (AβOs) in the pathogenesis of AD, including the induction of aberrant glial activation and memory impairment.

OBJECTIVE

We have investigated the protective actions of a nutritional formulation, denoted AZ formulation, on glial activation and memory deficits induced by intracerebroventricular (i.c.v.) infusion of AβOs in mice.

METHODS

Two-month-old male mice were treated orally with AZ formulation or isocaloric placebo for 30 consecutive days. Microglial and astrocytic activation were analyzed by immunohistochemistry in the hippocampus 10 days after i.c.v. infusion of AβOs (n = 5 mice per experimental condition). Memory loss was assessed by the novel object recognition (NOR) test (n = 6-10 mice per experimental condition).

RESULTS

Oral treatment with the AZ formulation prevented hippocampal microglial and astrocytic activation induced by i.c.v. infusion of AβOs. The AZ formulation further protected mice from AβO-induced memory impairment.

CONCLUSION

Results suggest that administration of the AZ formulation may comprise a promising preventative and non-pharmacological strategy to reduce brain inflammation and attenuate memory impairment in AD.

Brain tocopherol levels are associated with lower activated microglia density in elderly human cortex

INTRODUCTION

Higher brain tocopherol levels have been associated with lower levels of Alzheimer's disease (AD) neuropathology; however, the underlying mechanisms are unclear.

METHODS

We studied the relations of α- and γ-tocopherol brain levels to microglia density in 113 deceased participants from the Memory and Aging Project. We used linear regression analyses to examine associations between tocopherol levels and microglia densities in a basic model adjusted for age, sex, education, apolipoprotein E (APOE)ε4 genotype (any ε4 allele vs. none) , and post-mortem time interval, and a second model additionally adjusted for total amyloid load and neurofibrillary tangle severity.

RESULTS

Higher α- and γ-tocopherol levels were associated with lower total and activated microglia density in cortical but not in subcortical brain regions. The association between cortical α-tocopherol and total microglia density remained statistically significant after adjusting for AD neuropathology.

DISCUSSION

These results suggest that the relation between tocopherols and AD might be partly explained by the alleviating effects of tocopherols on microglia activation.

Dopamine attenuates lipopolysaccharide-induced expression of proinflammatory cytokines by inhibiting the nuclear translocation of NF-κB p65 through the formation of dopamine quinone in microglia

Many reports have indicated that dopamine has immunomodulatory effects on peripheral immune cells. The purpose of this study was to reveal the immunomodulatory effect of dopamine on the expression of proinflammatory cytokines in microglial cells, which are the immune cells of the central nervous system. In murine microglial cell line BV-2 cells, pretreatment with dopamine for 24 h attenuated the lipopolysaccharide (LPS)-induced expression of proinflammatory cytokines such as tumor-necrosis factor-α, interleukin-1β, and interleukin-6. Neither (5R)-8-chloro-3-methyl-5-phenyl-1,2,4,5-tetrahydro-3-benzazepin-7-ol; hydrochloride (SCH-23390) nor sulpiride, which are dopamine D₁-like and D₂-like receptor antagonists, respectively, affected the attenuation of LPS-induced expression of cytokines by dopamine. In addition, pretreatment with neither (-)-(6aR,12bR)-4,6,6a,7,8,12b-Hexahydro-7-methylindolo[4,3-a]phenanthridin (CY208-243) nor bromocriptine, dopamine D₁-like and D₂-like receptor agonists, respectively, was effective in doing so. However, N-acetylcysteine (NAC), which inhibits dopamine oxidation to dopamine quinone, did inhibit this attenuated expression. Dopamine increased the level of quinoproteins, and this increase was inhibited by NAC. Western blot and immunocytochemical analyses revealed that dopamine inhibited LPS-induced nuclear translocation of nuclear factor-kappa B (NF-κB) p65. Dopamine also attenuated the expression of cytokines and the nuclear translocation of NF-κB p65 induced by LPS in mouse microglial cells in primary culture. These results suggest that dopamine attenuated LPS-induced expression of cytokines by inhibiting the nuclear translocation of NF-κB p65 through the formation of dopamine quinone in microglial cells.

Transferrin Enhances Microglial Phagocytic Capacity

Transferrin (Tf) is a glycoprotein playing a critical role in iron homeostasis and transport and distribution throughout the body and within tissues and cells. This molecule has been shown to accelerate the process of myelination and remyelination in the central nervous system (CNS) in vivo and induce oligodendroglial cell maturation in vitro. While the mechanisms involved in oligodendroglial precursor cell (OPC) differentiation have not been fully elucidated yet, our group has previously described the first molecular events taking place in OPC in response to extracellular Tf. Here, we show the effect of Tf on the different glial cell populations. We demonstrate that, after a CNS demyelinating injury, Tf can be incorporated by all glial cells-i.e., microglia, astrocytes, and OPC-and that, acting on microglial cells in vitro, Tf increases microglial proliferation rates and phagocytic capacity. It may be then speculated that the in vivo correlation of this process could generate a favorable microenvironment for OPC maturation and remyelination.

Excitotoxicity, neuroinflammation and oxidant stress as molecular bases of epileptogenesis and epilepsy-derived neurodegeneration: The role of vitamin E

Glutamate-mediated excitotoxicity, neuroinflammation, and oxidative stress are common underlying events in neurodegeneration. This pathogenic "triad" characterizes the neurobiology of epilepsy, leading to seizure-induced cell death, increased susceptibility to neuronal synchronization and network alterations. Along with other maladaptive changes, these events pave the way to spontaneous recurrent seizures and progressive degeneration of the interested brain areas. In vivo models of epilepsy are available to explore such epileptogenic mechanisms, also assessing the efficacy of chemoprevention and therapy strategies at the pre-clinical level. The kainic acid model of pharmacological excitotoxicity and epileptogenesis is one of the most investigated mimicking the chronicization profile of temporal lobe epilepsy in humans. Its pathogenic cues include inflammatory and neuronal death pathway activation, mitochondrial disturbances and lipid peroxidation of several regions of the brain, the most vulnerable being the hippocampus. The importance of neuroinflammation and lipid peroxidation as underlying molecular events of brain damage was demonstrated in this model by the possibility to counteract the related maladaptive morphological and functional changes of this organ with vitamin E, the main fat-soluble cellular antioxidant and "conditional" co-factor of enzymatic pathways involved in polyunsaturated lipid metabolism and inflammatory signaling. The present review paper provides an overview of the literature supporting the potential for a timely intervention with vitamin E therapy in clinical management of seizures and epileptogenic processes associated with excitotoxicity, neuroinflammation and lipid peroxidation, i.e. the pathogenic "triad".

Microenvironment Imbalance of Spinal Cord Injury

Spinal cord injury (SCI), for which there currently is no cure, is a heavy burden on patient physiology and psychology. The microenvironment of the injured spinal cord is complicated. According to our previous work and the advancements in SCI research, ‘microenvironment imbalance’ is the main cause of the poor regeneration and recovery of SCI. Microenvironment imbalance is defined as an increase in inhibitory factors and decrease in promoting factors for tissues, cells and molecules at different times and spaces. There are imbalance of hemorrhage and ischemia, glial scar formation, demyelination and re-myelination at the tissue’s level. The cellular level imbalance involves an imbalance in the differentiation of endogenous stem cells and the transformation phenotypes of microglia and macrophages. The molecular level includes an imbalance of neurotrophic factors and their pro-peptides, cytokines, and chemokines. The imbalanced microenvironment of the spinal cord impairs regeneration and functional recovery. This review will aid in the understanding of the pathological processes involved in and the development of comprehensive treatments for SCI.

l-Carnitine Inhibits Lipopolysaccharide-Induced Nitric Oxide Production of SIM-A9 Microglia Cells

Microglia are the resident immune effector cells of the central nervous system. They account for approximately 10-15% of all cells found in the brain and spinal cord, acting as macrophages, sensing and engaging in phagocytosis to eliminate toxic proteins. Microglia are dynamic and can change their morphology in response to cues from their milieu. Parkinson's disease is a neurodegenerative disease, associated with reactive gliosis, neuroinflammation, and oxidative stress. It is thought that Parkinson's disease is caused by the accumulation of abnormally folded alpha-synuclein protein, accompanied by persistent neuroinflammation, oxidative stress, and subsequent neuronal injury/death. There is evidence in the literature for mitochondrial dysfunction in Parkinson's disease as well as fatty acid beta-oxidation, involving l-carnitine. Here we investigate l-carnitine in the context of microglial activation, suggesting a potential new strategy of supplementation for PD patients. Preliminary results from our studies suggest that the treatment of activated microglia with the endogenous antioxidant l-carnitine can reverse the effects of detrimental neuroinflammation in vitro.

trans-Cinnamaldehyde Inhibits Microglial Activation and Improves Neuronal Survival against Neuroinflammation in BV2 Microglial Cells with Lipopolysaccharide Stimulation

Background

Microglial activation contributes to neuroinflammation and neuronal damage in neurodegenerative disorders including Alzheimer's and Parkinson's diseases. It has been suggested that neurodegenerative disorders may be improved if neuroinflammation can be controlled. trans-cinnamaldehyde (TCA) isolated from the stem bark of Cinnamomum cassia possesses potent anti-inflammatory capability; we thus tested whether TCA presents neuroprotective effects on improving neuronal survival by inhibiting neuroinflammatory responses in BV2 microglial cells.

Results

To determine the molecular mechanism behind TCA-mediated neuroprotective effects, we assessed the effects of TCA on lipopolysaccharide- (LPS-) induced proinflammatory responses in BV2 microglial cells. While LPS potently induced the production and expression upregulation of proinflammatory mediators, including NO, iNOS, COX-2, IL-1β, and TNF-α, TCA pretreatment significantly inhibited LPS-induced production of NO and expression of iNOS, COX-2, and IL-1β and recovered the morphological changes in BV2 cells. TCA markedly attenuated microglial activation and neuroinflammation by blocking nuclear factor kappa B (NF-κB) signaling pathway. With the aid of microglia and neuron coculture system, we showed that TCA greatly reduced LPS-elicited neuronal death and exerted neuroprotective effects.

Conclusions

Our results suggest that TCA, a natural product, has the potential of being used as a therapeutic agent against neuroinflammation for ameliorating neurodegenerative disorders.

α-Tocopherol and Hippocampal Neural Plasticity in Physiological and Pathological Conditions

Neuroplasticity is an "umbrella term" referring to the complex, multifaceted physiological processes that mediate the ongoing structural and functional modifications occurring, at various time- and size-scales, in the ever-changing immature and adult brain, and that represent the basis for fundamental neurocognitive behavioral functions; in addition, maladaptive neuroplasticity plays a role in the pathophysiology of neuropsychiatric dysfunctions. Experiential cues and several endogenous and exogenous factors can regulate neuroplasticity; among these, vitamin E, and in particular α-tocopherol (α-T), the isoform with highest bioactivity, exerts potent effects on many plasticity-related events in both the physiological and pathological brain. In this review, the role of vitamin E/α-T in regulating diverse aspects of neuroplasticity is analyzed and discussed, focusing on the hippocampus, a brain structure that remains highly plastic throughout the lifespan and is involved in cognitive functions. Vitamin E-mediated influences on hippocampal synaptic plasticity and related cognitive behavior, on post-natal development and adult hippocampal neurogenesis, as well as on cellular and molecular disruptions in kainate-induced temporal seizures are described. Besides underscoring the relevance of its antioxidant properties, non-antioxidant functions of vitamin E/α-T, mainly involving regulation of cell signaling molecules and their target proteins, have been highlighted to help interpret the possible mechanisms underlying the effects on neuroplasticity.

Hijacking microglial glutathione by inorganic arsenic impels bystander death of immature neurons through extracellular cystine/glutamate imbalance

Arsenic-induced altered microglial activity leads to neuronal death, but the causative mechanism remains unclear. The present study showed, arsenic-exposed (10 μM) microglial (N9) culture supernatant induced bystander death of neuro-2a (N2a), which was further validated with primary microglia and immature neuronal cultures. Results indicated that arsenic-induced GSH synthesis by N9 unfavorably modified the extracellular milieu for N2a by lowering cystine and increasing glutamate concentration. Similar result was observed in N9-N2a co-culture. Co-exposure of arsenic and 250 μM glutamate, less than the level (265 μM) detected in arsenic-exposed N9 culture supernatant, compromised N2a viability which was rescued by cystine supplementation. Therefore, microglia executes bystander N2a death by competitive inhibition of system Xc^- (xCT) through extracellular cystine/glutamate imbalance. We confirmed the role of xCT in mediating bystander N2a death by siRNA inhibition studies. Ex-vivo primary microglia culture supernatant from gestationally exposed mice measured to contain lower cystine and higher glutamate compared to control and N-acetyl cysteine co-treated group. Immunofluorescence staining of brain cryosections from treated group showed more dead immature neurons with no such effect on microglia. Collectively, we showed, in presence of arsenic microglia alters cystine/glutamate balance through xCT in extracellular milieu leading to bystander death of immature neurons.

Cytokine and Growth Factor Activation In Vivo and In Vitro after Spinal Cord Injury

Spinal cord injury results in a life-disrupting series of deleterious interconnected mechanisms encompassed by the primary and secondary injury. These events are mediated by the upregulation of genes with roles in inflammation, transcription, and signaling proteins. In particular, cytokines and growth factors are signaling proteins that have important roles in the pathophysiology of SCI. The balance between the proinflammatory and anti-inflammatory effects of these molecules plays a critical role in the progression and outcome of the lesion. The excessive inflammatory Th1 and Th17 phenotypes observed after SCI tilt the scale towards a proinflammatory environment, which exacerbates the deleterious mechanisms present after the injury. These mechanisms include the disruption of the spinal cord blood barrier, edema and ion imbalance, in particular intracellular calcium and sodium concentrations, glutamate excitotoxicity, free radicals, and the inflammatory response contributing to the neurodegenerative process which is characterized by demyelination and apoptosis of neuronal tissue.

Nutrients, Microglia Aging, and Brain Aging

As the life expectancy continues to increase, the cognitive decline associated with Alzheimer's disease (AD) becomes a big major issue in the world. After cellular activation upon systemic inflammation, microglia, the resident immune cells in the brain, start to release proinflammatory mediators to trigger neuroinflammation. We have found that chronic systemic inflammatory challenges induce differential age-dependent microglial responses, which are in line with the impairment of learning and memory, even in middle-aged animals. We thus raise the concept of “microglia aging.” This concept is based on the fact that microglia are the key contributor to the acceleration of cognitive decline, which is the major sign of brain aging. On the other hand, inflammation induces oxidative stress and DNA damage, which leads to the overproduction of reactive oxygen species by the numerous types of cells, including macrophages and microglia. Oxidative stress-damaged cells successively produce larger amounts of inflammatory mediators to promote microglia aging. Nutrients are necessary for maintaining general health, including the health of brain. The intake of antioxidant nutrients reduces both systemic inflammation and neuroinflammation and thus reduces cognitive decline during aging. We herein review our microglia aging concept and discuss systemic inflammation and microglia aging. We propose that a nutritional approach to controlling microglia aging will open a new window for healthy brain aging.

Dual role of superoxide dismutase 2 induced in activated microglia: oxidative stress tolerance and convergence of inflammatory responses

Microglia are activated quickly in response to external pathogens or cell debris and clear these substances via the inflammatory response. However, excessive activation of microglia can be harmful to host cells due to the increased production of reactive oxygen species and proinflammatory cytokines. Superoxide dismutase 2 (SOD2) is reportedly induced under various inflammatory conditions in the central nervous system. We herein demonstrated that activated microglia strongly express SOD2 and examined the role of SOD2, focusing on regulation of the microglial activity and the susceptibility of microglia to oxidative stress. When rat primary microglia were treated with LPS, poly(I:C), peptidoglycan, or CpG oligodeoxynucleotide, respectively, the mRNA and protein levels of SOD2 largely increased. However, an increased expression of SOD2 was not detected in the primary neurons or astrocytes, indicating that SOD2 is specifically induced in microglia under inflammatory conditions. The activated microglia showed high tolerance to oxidative stress, whereas SOD2 knockdown conferred vulnerability to oxidative stress. Interestingly, the production of proinflammatory cytokines was increased in the activated microglia treated with SOD2 siRNA compared with that observed in the control siRNA-treated cells. Pretreatment with NADPH oxidase inhibitors, diphenylene iodonium and apocynin, decreased in not only reactive oxygen species generation but also the proinflammatory cytokine expression. Notably, SOD2 knockdown largely potentiated the nuclear factor κB activity in the activated microglia. Taken together, increased SOD2 conferred tolerance to oxidative stress in the microglia and decreased proinflammatory cytokine production by attenuating the nuclear factor κB activity. Therefore, SOD2 might regulate neuroinflammation by controlling the microglial activities.

Rifampicin improves neuronal apoptosis in LPS-stimulated co‑cultured BV2 cells through inhibition of the TLR-4 pathway

Agents inhibiting microglial activation are attracting attention as candidate drugs for neuroprotection in neurodegenerative diseases. Recently, researchers have focused on the immunosuppression induced by rifampicin. Our previous study showed that rifampicin inhibits the production of lipopolysaccharide (LPS)-induced pro-inflammatory mediators and improves neuron survival in inflammation; however, the mechanism through which rifampicin inhibits microglial inflammation and its neuroprotective effects are not completely understood. In this study, we examined the effects of rifampicin on morphological changes induced by LPS in murine microglial BV2 cells. Then we investigated, in BV2 microglia, the effects of rifampicin on two signaling pathway componentss stimulated by LPS, the Toll‑like receptor-4 (TLR-4) and the nuclear factor-κB (NF-κB). In addition, we co-cultured BV2 microglia and neurons to observe the indirect neuroprotective effects of rifampicin. Rifampicin inhibited LPS-stimulated expression of the TLR-4 gene. When neurons were co-cultured with LPS-stimulated BV2 microglia, pre-treatment with rifampicin increased neuronal viability and reduced the number of apoptotic cells. Taken together, these findings suggest that rifampicin, with its anti-inflammatory properties, may be a promising agent for the treatment of neurodegenerative diseases.

Reductions of the components of the calreticulin/calnexin quality-control system by proteasome inhibitors and their relevance in a rodent model of Parkinson's disease

Evidence indicates that the ubiquitin-proteasome system and the endoplasmic retculum (ER) quality-control system work in concert to ensure that proteins are correctly folded in the ER and that misfolded proteins are retrotransported to the cytosol for degradation by proteasomes. Dysfunction of either system results in developmental abnormalities and even death in animals. This study investigates whether and how proteasome inhibition impacts the components of the calreticulin (CRT)/calnexin (CNX) glycoprotein folding machinery, a typical ER protein quality-control system, in the context of early neuronal injury. Here we report that proteasome inhibitor treatments, at nonlethal levels, reduced protein levels of CRT and ERp57 but not of CNX. These treatments increased protein levels of CRT in culture media, an effect blocked by brefeldin A, an inhibitor of protein trafficking; by contrast, ERp57 was not detected in culture media. Knockdown of CRT levels alone increased the vulnerability of SH-SY5Y, a neuronal cell line, to 6-hydroxydopamine (6-OHDA) toxicity. In a rat model of Parkinson's disease, intrastriatal 6-OHDA lesions resulted in decreased levels of CRT and ERp57 in the midbrain. These findings suggest that reduction of the components of CRT/CNX glycoprotein quality-control system may play a role in neuronal injury in Parkinson's disease and other neurodegenerative disorders associated with dysfunction of the ubiquitin-proteasome system.

Luteolin inhibits SH-SY5Y cell apoptosis through suppression of the nuclear transcription factor-κB, mitogen-activated protein kinase and protein kinase B pathways in lipopolysaccharide-stimulated cocultured BV2 cells

Microglial activation is one of the causative factors for neuroinflammation, which is associated with the pathophysiology of neurodegenerative diseases. Our previous study showed that the flavonoid luteolin inhibited several pro-inflammatory enzymes and pro-inflammatory cytokines that are induced by activated microglia; however, its effect on signaling pathways is currently unknown. The present study examined the effects of luteolin on signaling pathways stimulated by lipopolysaccharide (LPS), including Toll-like receptor-4 (TLR-4), nuclear transcription factor-κB (NF-κB), mitogen-activated protein kinase (MAPK) family and protein kinase B (Akt) pathways in murine microglial BV2 cells. In addition, BV2 microglia and SH-SY5Y neuroblastoma cells were cocultured to observe the indirect neuroprotective effects of luteolin. Luteolin inhibited the LPS-stimulated expression of TLR-4. In addition, luteolin blocked LPS-induced NF-κB, p38, JNK and Akt activation, but had no effect on ERK. When SH-SY5Y cells were cocultured with LPS-stimulated BV2 microglia, pretreatment with luteolin increased neuronal viability and reduced the number of apoptotic cells. These data suggest that luteolin has a beneficial effect on neuroinflammatory events in neurodegenerative diseases via suppression of the NF-κB, MAPK and Akt pathways in activated microglial cells.

Post-seizure α-tocopherol treatment decreases neuroinflammation and neuronal degeneration induced by status epilepticus in rat hippocampus

Vitamin E (as α-tocopherol, α-T) was shown to have beneficial effects in epilepsy, mainly ascribed to its antioxidant properties. Besides radical-induced neurotoxicity, neuroinflammation is also involved in the pathophysiology of epilepsy, since neuroglial activation and cytokine production exacerbate seizure-induced neurotoxicity and contribute to epileptogenesis. We previously showed that α-T oral supplementation before inducing status epilepticus, markedly reduces astrocytic and microglial activation, neuronal cell death and oxidative stress in the hippocampus, as observed 4 days after seizure. In order to evaluate the possibility that such a neuroprotective and anti-inflammatory effect may also provide a strategy for an acute intervention in epilepsy, in this study, seizures were induced by single intaperitoneal injection of kainic acid and, starting from 3 h after status epilepticus, rats were treated with an intraperitoneal bolus of α-T (250 mg/kg b.w.; once a day) for 4 days, that was the time after which morphological and biochemical analyses were performed on hippocampus. Post-seizure α-T administration significantly reduced astrocytosis and microglia activation, and decreased neuron degeneration and spine loss; these effects were associated with the presence of a lowered lipid peroxidation in hippocampus. These results confirm and further emphasize the anti-inflammatory and neuroprotective role of α-T in kainic acid-induced epilepsy. Moreover, the findings show that post-seizure treatment with α-T provides an effective secondary prevention against post-seizure inflammation-induced brain damages and possibly against their epileptogenic effects.

Quercetin and sesamin protect dopaminergic cells from MPP+-induced neuroinflammation in a microglial (N9)-neuronal (PC12) coculture system

A growing body of evidence indicates that the majority of Parkinson's disease (PD) cases are associated with microglia activation with resultant elevation of various inflammatory mediators and neuroinflammation. In this study, we investigated the effects of 2 natural molecules, quercetin and sesamin, on neuroinflammation induced by the Parkinsonian toxin 1-methyl-4-phenylpyridinium (MPP⁺) in a glial-neuronal system. We first established that quercetin and sesamin defend microglial cells against MPP⁺-induced increases in the mRNA or protein levels of 3 pro-inflammatory cytokines (interleukin-6, IL-1β and tumor necrosis factor-alpha), as revealed by real time-quantitative polymerase chain reaction and enzyme-linked immunoabsorbent assay, respectively. Quercetin and sesamin also decrease MPP⁺-induced oxidative stress in microglial cells by reducing inducible nitric oxide synthase protein expression as well as mitochondrial superoxide radicals. We then measured neuronal cell death and apoptosis after MPP⁺ activation of microglia, in a microglial (N9)-neuronal (PC12) coculture system. Our results revealed that quercetin and sesamin rescued neuronal PC12 cells from apoptotic death induced by MPP⁺ activation of microglial cells. Altogether, our data demonstrate that the phytoestrogen quercetin and the lignan sesamin diminish MPP⁺-evoked microglial activation and suggest that both these molecules may be regarded as potent, natural, anti-inflammatory compounds.

Zaprinast activates MAPKs, NFκB, and Akt and induces the expressions of inflammatory genes in microglia

Previously, the authors reported that zaprinast, an inhibitor of cGMP-selective phosphodiesterases, induced the secretions of TNF-α and IL-1β by microglia and enhanced the induction of iNOS by lipopolysaccharide (LPS). In this study, the signaling mechanism responsible for microglial activation by zaprinast was investigated and the effects of zaprinast and LPS on microglial activation were compared. Zaprinast was found to activate ERK1/2, p38 MAPK, JNK, NFκB, and PI3K/Akt, and subsequently, induce the mRNA expressions of IL-1α, IL-1β, TNF-α, CCL2, CCL4, CXCL1, CXCL2, and CD14. Associations between signaling pathways and gene expressions were examined by treating microglia with signal inhibitors. PDTC inhibited the induction of all the above genes by zaprinast, and SB203580 inhibited all genes except CXCL1. SP600125, PD98059, and LY294002 inhibited the induction of at least CCL2. Microglial activation by zaprinast was then compared with full-blown activation by LPS. The zaprinast-induced phosphorylations of MAPKs and IκB were less prompt than LPS-induced phosphorylations. IκB degradation by LPS was significant at 10min and did not return to normal, whereas zaprinast induced a later, transient degradation. LPS induced the mRNA expressions of IL-1β, TNF-α, IL-6, CCL2, iNOS, and COX-2, and although zaprinast significantly induced the expressions of all except IL-6 and iNOS, these inductions were far less than those induced by LPS. Collectively, zaprinast was found to upregulate microglial activity mainly via NFκB and p38 MAPK signaling and the subsequent expressions of inflammatory genes. Although, zaprinast was found to have obvious effects on microglia, these were weaker than the effects of LPS.

Involvement of Kv1.3 and p38 MAPK signaling in HIV-1 glycoprotein 120-induced microglia neurotoxicity

Inflammatory responses mediated by activated microglia play a pivotal role in the pathogenesis of human immunodeficiency virus type 1 (HIV-1)-associated neurocognitive disorders. Studies on identification of specific targets to control microglia activation and resultant neurotoxic activity are imperative. Increasing evidence indicate that voltage-gated K⁺ (K_v) channels are involved in the regulation of microglia functionality. In this study, we investigated K_v1.3 channels in the regulation of neurotoxic activity mediated by HIV-1 glycoprotein 120 (gp120)-stimulated rat microglia. Our results showed treatment of microglia with gp120 increased the expression levels of K_v1.3 mRNA and protein. In parallel, whole-cell patch-clamp studies revealed that gp120 enhanced microglia K_v1.3 current, which was blocked by margatoxin, a K_v1.3 blocker. The association of gp120 enhancement of K_v1.3 current with microglia neurotoxicity was demonstrated by experimental results that blocking microglia K_v1.3 attenuated gp120-associated microglia production of neurotoxins and neurotoxicity. Knockdown of K_v1.3 gene by transfection of microglia with K_v1.3-siRNA abrogated gp120-associated microglia neurotoxic activity. Further investigation unraveled an involvement of p38 MAPK in gp120 enhancement of microglia K_v1.3 expression and resultant neurotoxic activity. These results suggest not only a role K_v1.3 may have in gp120-associated microglia neurotoxic activity, but also a potential target for the development of therapeutic strategies.

Aging microglia: relevance to cognition and neural plasticity

Over the years it has become evident that the immune system can affect the function of the central nervous system (CNS), including altering cognitive processes. The impact of immune activation on the CNS is particularly important for aged individuals, as the brain's resident immune cells, microglia, acquire a pro-inflammatory profile. The low-grade chronic neuroinflammation that develops with normal aging likely contributes to the susceptibility to cognitive deficits and a host of age-related pathologies. Understanding why microglia show increased inflammatory activity (i.e., neuroinflammation) and identifying effective treatments to reduce microglia activation is expected to have beneficial effects on cognitive performance and measures of neural plasticity. However, microglia also promote regeneration after injury. Therefore, effective treatments must dampen inflammatory activity while preserving microglia's neuroprotective function. Discovering factors that induce neuroinflammation and investigating potential preventative therapies is expected to uncover the ways of maintaining normal microglia activity in the aged brain.

Apolipoprotein E expression is elevated by interleukin 1 and other interleukin 1-induced factors

Background

We have previously outlined functional interactions, including feedback cycles, between several of the gene products implicated in the pathogenesis of Alzheimer's disease. A number of Alzheimer-related stressors induce neuronal expression of apolipoprotein E (ApoE), β-amyloid precursor protein (βAPP), and fragments of the latter such as amyloid β-peptide (Aβ) and secreted APP (sAPP). These stressors include interleukin-1 (IL-1)-mediated neuroinflammation and glutamate-mediated excitotoxicity. Such circumstances are especially powerful when they transpire in the context of an APOE ε4 allele.

Methods

Semi-quantitative immunofluorescence imaging was used to analyze rat brains implanted with IL-1β slow-release pellets, sham pellets, or no pellets. Primary neuronal or NT2 cell cultures were treated with IL-1β, glutamate, Aβ, or sAPP; relative levels of ApoE mRNA and protein were measured by RT-PCR, qRT-PCR, and western immunoblot analysis. Cultures were also treated with inhibitors of multi-lineage kinases--in particular MAPK-p38 (SB203580), ERK (U0126), or JNK (SP600125)--prior to exposure of cultures to IL-1β, Aβ, sAPP, or glutamate.

Results

Immunofluorescence of tissue sections from pellet-implanted rats showed that IL-1β induces expression of βAPP, IL-1α, and ApoE; the latter was confirmed by western blot analysis. These protein changes were mirrored by increases in their mRNAs, as well as in those encoding IL-1β, IL-1β-converting enzyme (ICE), and tumor necrosis factor (TNF). IL-1β also increased ApoE expression in neuronal cultures. It stimulated release of sAPP and glutamate in these cultures too, and both of these agents--as well as Aβ--stimulated ApoE expression themselves, suggesting that they may contribute to the effect of IL-1β on ApoE levels. Inhibitors of MAPK-p38, ERK, and JNK inhibited ApoE induction by all these agents except glutamate, which was sensitive only to inhibitors of ERK and JNK.

Conclusion

Conditions of glial activation and hyperexcitation can elevate proinflammatory cytokines, ApoE, glutamate, βAPP, and its secreted fragments. Because each of these factors promotes glial activation and neuronal hyperexcitation, these relationships have the potential to sustain self-propagating neurodegenerative cycles that could culminate in a progressive neurodegenerative disorder such as Alzheimer's disease.

The promise of neuroprotective agents in Parkinson's disease

Parkinson’s disease (PD) is characterized by loss of dopamine neurons in the substantia nigra of the brain. Since there are limited treatment options for PD, neuroprotective agents are currently being tested as a means to slow disease progression. Agents targeting oxidative stress, mitochondrial dysfunction, and inflammation are prime candidates for neuroprotection. This review identifies Rasagiline, Minocycline, and creatine, as the most promising neuroprotective agents for PD, and they are all currently in phase III trials. Other agents possessing protective characteristics in delaying PD include stimulants, vitamins, supplements, and other drugs. Additionally, combination therapies also show benefits in slowing PD progression. The identification of neuroprotective agents for PD provides us with therapeutic opportunities for modifying the course of disease progression and, perhaps, reducing the risk of onset when preclinical biomarkers become available.

Ursolic acid attenuates lipopolysaccharide-induced cognitive deficits in mouse brain through suppressing p38/NF-κB mediated inflammatory pathways

Evidence indicates that systemic administration of lipopolysaccharide (LPS) induces brain inflammation, ultimately resulting in cognitive deficits. Ursolic acid (UA), a plant-derived pentacyclic triterpenoid, is well known to possess multiple biological functions, including antioxidant, anti-tumor and anti-inflammatory activities. In the present study, we assessed the protective effect of UA against the LPS-induced cognitive deficits in mice. We found that UA significantly improved cognitive deficits of LPS-treated mice in open field, step-through passive avoidance and Morris water maze tasks. One potential mechanism of this action was attributed to the decreased production of pro-inflammatory markers including COX-2, iNOS, TNF-α, IL-1β, IL-2 and IL-6 in LPS-treated mouse brain. Mechanistically, UA markedly inhibited LPS-induced IκBα phosphorylation and degradation, NF-κB p65 nuclear translocation and p38 activation in mouse brain, but did not affect the activation of TLR4, MyD88, ERK, JNK and Akt. Taken together, these results suggest that UA may be useful for mitigating inflammation-associated brain disorders by inhibiting pro-inflammatory factors production, at least in part, through blocking the p38/NF-κB signaling pathways.

Dietary supplementation with α-tocopherol reduces neuroinflammation and neuronal degeneration in the rat brain after kainic acid-induced status epilepticus

Vitamin E (as α-tocopherol, α-T) is proposed to alleviate glia-mediated inflammation in neurological diseases, but such a role in epilepsy is still elusive. This study investigated the effect of α-T supplementation on glial activation, neuronal cell death and oxidative stress of rat brain exposed to kainate-induced seizures. Animals were fed for 2 weeks with a α-T-enriched diet (estimated intake of 750 mg/kg/day) before undergoing status epilepticus. Compliance to supplementation was demonstrated by the remarkable increase in brain α-T. Four days after seizure, brain α-T returned to baseline and lipid peroxidation markers decreased as compared to non-supplemented rats. Status epilepticus induced a lower up-regulation of astrocytic and microglial antigens (GFAP and MHC II, respectively) and production of pro-inflammatory cytokines (IL-1β and TNF-α) in supplemented than in non-supplemented animals. This anti-inflammatory effect was associated with a lower neuronal cell death. In conclusion, α-T dietary supplementation prevents oxidative stress, neuroglial over-activation and cell death occurring after kainate-induced seizures. This evidence paves the way to an anti-inflammatory and neuroprotective role of α-T interventions in epilepsy.

Dexamethasone inhibits the Nox-dependent ROS production via suppression of MKP-1-dependent MAPK pathways in activated microglia

BACKGROUND

Nox-2 (also known as gp91phox), a subunit component of NADPH oxidases, generates reactive oxygen species (ROS). Nox-dependent ROS generation and nitric oxide (NO) release by microglia have been implicated in a variety of diseases in the central nervous system. Dexamethasone (Dex) has been shown to suppress the ROS production, NO release and inflammatory reaction of activated microglial cells. However, the underlying mechanisms remain unclear.

RESULTS

The present study showed that the increased ROS production and NO release in activated BV-2 microglial cells by LPS were associated with increased expression of Nox-2 and iNOS. Dex suppressed the upregulation of Nox-2 and iNOS, as well as the subsequent ROS production and NO synthesis in activated BV-2 cells. This inhibition caused by Dex appeared to be mediated by upregulation of MAPK phosphatase-1 (MKP-1), which antagonizes the activity of mitogen-activated protein kinases (MAPKs). Dex induced-suppression of Nox-2 and -upregulation of MKP-1 was also evident in the activated microglia from corpus callosum of postnatal rat brains. The overexpression of MKP-1 or inhibition of MAPKs (by specific inhibitors of JNK and p38 MAPKs), were found to downregulate the expression of Nox-2 and iNOS and thereby inhibit the synthesis of ROS and NO in activated BV-2 cells. Moreover, Dex was unable to suppress the LPS-induced synthesis of ROS and NO in BV-2 cells transfected with MKP-1 siRNA. On the other hand, knockdown of Nox-2 in BV-2 cells suppressed the LPS-induced ROS production and NO release.

CONCLUSION

In conclusion, it is suggested that downregulation of Nox-2 and overexpression of MKP-1 that regulate ROS and NO may form the potential therapeutic strategy for the treatment of neuroinflammation in neurodegenerative diseases.

Rifampicin inhibits microglial inflammation and improves neuron survival against inflammation

Microglial activation plays an important role in the pathophysiology of neurodegenerative diseases, and suppression of microglial activation prevents the progression of neurodegeneration. Rifampicin, a bacteriocidal antibiotic, induces immunosuppression. We hypothesized that rifampicin might be neuroprotective by inhibiting the production of pro-inflammatory mediators, thereby suppressing microglial activation. In the present study, we examined the effects of rifampicin on the production of lipopolysaccharide (LPS)-induced pro-inflammatory mediators and their signaling pathways in BV2 microglia. We also assessed the neuroprotective effects of rifampicin using a co-culture of microglia and neurons. Our results showed that rifampicin inhibited the LPS-stimulated expression of inducible nitric oxide synthase, cyclooxygenase-2, tumor necrosis factor-α, and interleukin-1β, as well as the production of nitric oxide and prostaglandin E₂. Moreover, rifampicin suppressed LPS-induced nuclear factor-kappa B activation by blocking the degradation of the inhibitor of the nuclear transcription factor NF-kappa B. Rifampicin inhibited the phosphorylation of mitogen activated protein kinases, although protein kinase B was not inhibited. Preincubation of microglia with rifampicin reduced neurotoxicity and improved neuron survival in a microglia-neuronal co-culture system. Taken together, these findings suggest that rifampicin, with its anti-inflammatory properties, might be a novel treatment for neurodegenerative diseases.

Stabilization of Nrf2 by tBHQ prevents LPS-induced apoptosis in differentiated PC12 cells

The inflammatory reaction plays an important role in the pathogenesis of the neurodegenerative disorders. tert-butylhydroquinone (tBHQ) exhibits a wide range of pharmacological activities including anti-oxidative and anti-inflammatory action. In this study, we tried to elucidate possible effects of tBHQ on lipopolysaccharide (LPS)-induced inflammatory reaction and its underlying mechanism in neuron-like PC12 cells. tBHQ inhibited LPS-induced generation of reactive oxygen species (ROS) and elevation of intracellular calcium level. It also inhibited LPS-induced cyclooxygenase 2 (COX-2), TNF-α, nuclear factor KappaB (NF-kB), and caspase-3 expression in a dose-dependent manner while stabilizing nuclear factor-erythroid 2 p45-related factor 2. Moreover, the phosphorylations of p38, ERK1/2, and JNK were suppressed by tBHQ. These results suggest that the anti-inflammatory properties of tBHQ might result from inhibition of COX-2 and TNF-α expression, inhibition of NF-kB nuclear translocation along with suppression of MAP kinases (p38, ERK1/2, and JNK) phosphorylation in PC12 cells, so may be a useful agent for prevention of inflammatory diseases.

Resveratrol differentially modulates inflammatory responses of microglia and astrocytes

BACKGROUND

Inflammatory responses in the CNS mediated by activated glial cells play an important role in host-defense but are also involved in the development of neurodegenerative diseases. Resveratrol is a natural polyphenolic compound that has cardioprotective, anticancer and anti-inflammatory properties. We investigated the capacity of resveratrol to protect microglia and astrocyte from inflammatory insults and explored mechanisms underlying different inhibitory effects of resveratrol on microglia and astrocytes.

METHODS

A murine microglia cell line (N9), primary microglia, or astrocytes were stimulated by LPS with or without different concentrations of resveratrol. The expression and release of proinflammatory cytokines (TNF-alpha, IL-1beta, IL-6, MCP-1) and iNOS/NO by the cells were measured by PCR/real-time PCR and ELISA, respectively. The phosphorylation of the MAP kinase superfamily was analyzed by western blotting, and activation of NF-kappaB and AP-1 was measured by luciferase reporter assay and/or electrophoretic mobility shift assay.

RESULTS

We found that LPS stimulated the expression of TNF-alpha, IL-1beta, IL-6, MCP-1 and iNOS in murine microglia and astrocytes in which MAP kinases, NF-kappaB and AP-1 were differentially involved. Resveratrol inhibited LPS-induced expression and release of TNF-alpha, IL-6, MCP-1, and iNOS/NO in both cell types with more potency in microglia, and inhibited LPS-induced expression of IL-1beta in microglia but not astrocytes. Resveratrol had no effect on LPS-stimulated phosphorylation of ERK1/2 and p38 in microglia and astrocytes, but slightly inhibited LPS-stimulated phosphorylation of JNK in astrocytes. Resveratrol inhibited LPS-induced NF-kappaB activation in both cell types, but inhibited AP-1 activation only in microglia.

CONCLUSION

These results suggest that murine microglia and astrocytes produce proinflammatory cytokines and NO in response to LPS in a similar pattern with some differences in signaling molecules involved, and further suggest that resveratrol exerts anti-inflammatory effects in microglia and astrocytes by inhibiting different proinflammatory cytokines and key signaling molecules.

Attenuation of proliferation in oligodendrocyte precursor cells by activated microglia

Activated microglia can influence the survival of neural cells through the release of cytotoxic factors. Here, we investigated the interaction between Toll-like receptor 4 (TLR4)-activated microglia and oligodendrocytes or their precursor cells (OPC). Primary rat or N9 microglial cells were activated by exposure to TLR4-specifc lipopolysaccharide (LPS), resulting in mitogen-activated protein kinase activation, increased CD68 and inducible nitric oxide synthase expression, and release of the proinflammatory cytokines tumor necrosis factor (TNF) and interleukin-6 (IL-6). Microglial conditioned medium (MGCM) from LPS-activated microglia attenuated primary OPC proliferation without inducing cell death. The microglial-induced inhibition of OPC proliferation was reversed by stimulating group III metabotropic glutamate receptors in microglia with the agonist L-AP4. In contrast to OPC, LPS-activated MGCM enhanced the survival of mature oligodendrocytes. Further investigation suggested that TNF and IL-6 released from TLR4-activated microglia might contribute to the effect of MGCM on OPC proliferation, insofar as TNF depletion of LPS-activated MGCM reduced the inhibition of OPC proliferation, and direct addition of TNF or IL-6 attenuated or increased proliferation, respectively. OPC themselves were also found to express proteins involved in TLR4 signalling, including TLR4, MyD88, and MAL. Although LPS stimulation of OPC did not induce proinflammatory cytokine release or affect their survival, it did trigger JNK phosphorylation, suggesting that TLR4 signalling in these cells is active. These findings suggest that OPC survival may be influenced not only by factors released from endotoxin-activated microglia but also through a direct response to endotoxins. This may have consequences for myelination under conditions in which microglial activation and cerebral infection are both implicated. , Inc.

Hyperforin is a modulator of inducible nitric oxide synthase and phagocytosis in microglia and macrophages

Upon activation, microglia, the immunocompetent cells in the brain, get highly phagocytic and release pro-inflammatory mediators like nitric oxide (NO). Excessive NO production is pivotal in neurodegenerative disorders, and there is evidence that abnormalities in NO production and inflammatory responses may at least support a range of neuropsychiatric disorders, including depression. Although extracts of St. John's wort (Hypericum perforatum L.) have been used for centuries in traditional medicine, notably for the treatment of depression, there is still considerable lack in scientific knowledge about the impact on microglia. We used N11 and BV2 mouse microglia, as well as RAW 264.7 macrophages to investigate the effects of St. John's wort extract and constituents thereof on NO production Moreover, flow cytometry and fluorescence microscopy were employed to analyze the influence on phagocytosis, transcription factor activation states, and cell motility. We found that extracts of St. John's wort efficiently suppress lipopolysaccharide-induced NO release and identified hyperforin as the responsible compound, being effective at concentrations between 0.25 and 0.75 microM. The reduced NO production was mediated by diminished inducible nitric oxide synthase expression on the mRNA and protein level. In addition, at similar concentrations, hyperforin reduced zymosan phygocytosis to 20-40% and putatively acted by downregulating the CD206 macrophage mannose receptor and modulation of cell motility. We found that the observed effects correlate with a suppression of the activated state of Nf-kappaB and phospho-CREB, while c-JUN, STAT1, and HIF-1alpha activity and cyclooxygenase-2 expression remained unaffected by hyperforin. These results reveal that hyperforin influences pro-inflammatory and immunological responses of microglia that are involved in the progression of neuropathologic disorders.

Vitamin E increases S100B-mediated microglial activation in an S100B-overexpressing mouse model of pathological aging

S100B is a calcium-binding protein released by astroglial cells of the brain capable of producing numerous extracellular effects. Although the direct molecular mechanism remains unknown, these effects can be trophic including differentiation, growth, recovery, and survival of neurons when the S100B protein is mainly oxidized and neurotoxic including apoptosis and neuroinflammatory processes marked by microglial activation when in a reduced state. S100B and its receptor RAGE (receptor for advanced glycation end products) have been found to be increased in Alzheimer's disease, Down syndrome, with tissue trauma and ischemia. In the current study, we examined the binding of the S100B receptor (RAGE) on microglial cells and the developmental effects of the antioxidant vitamin E on microglial activation and the upregulation of RAGE in an S100B over-expressing mouse model of pathological aging. We report that RAGE is co-localized on activated microglial cells and vitamin E induced dramatic increases in microglial activation as well as total microglial relative optical density that was accompanied by upregulation of the RAGE receptor, particularly in the CA1 region of the hippocampus. Our findings suggest further investigation into the potential role of vitamin E in reducing the oxidation state of the S100B protein and its influence on neuroinflammatory processes marked by microglial activation in vivo.

The p38alpha mitogen-activated protein kinase as a central nervous system drug discovery target

Protein kinases are critical modulators of a variety of cellular signal transduction pathways, and abnormal phosphorylation events can be a cause or contributor to disease progression in a variety of disorders. This has led to the emergence of protein kinases as an important new class of drug targets for small molecule therapeutics. A serine/threonine protein kinase, p38α mitogen-activated protein kinase (MAPK), is an established therapeutic target for peripheral inflammatory disorders because of its critical role in regulation of proinflammatory cytokine production. There is increasing evidence that p38α MAPK is also an important regulator of proinflammatory cytokine levels in the central nervous system, raising the possibility that the kinase may be a drug discovery target for central nervous system disorders where cytokine overproduction contributes to disease progression. Development of bioavailable, central nervous system-penetrant p38α MAPK inhibitors provides the required foundation for drug discovery campaigns targeting p38α MAPK in neurodegenerative disorders.

Blockade of chloride intracellular ion channel 1 stimulates Abeta phagocytosis

In amyloid-beta (Abeta)-stimulated microglial cells, blockade of chloride intracellular ion channel 1 (CLIC1) reverts the increase in tumor necrosis factor-alpha and nitric oxide (NO) production and results in neuroprotection of cocultured neurons. This effect could be of therapeutic efficacy in Alzheimer's disease (AD), where microglial activation may contribute to neurodegeneration, but it could reduce Abeta phagocytosis, which could facilitate amyloid plaque removal. Here, we analyzed the CLIC1 blockade effect on Abeta-stimulated mononuclear phagocytosis. In the microglial cell line BV-2, Abeta25-35 treatment enhanced fluorescent bead phagocytosis, which persisted also in the presence of IAA-94, a CLIC1 channel blocker. The same result was obtained in rat primary microglia and in BV2 cells, where CLIC1 expression had been knocked down with a plasmid producing small interfering RNAs. To address specifically the issue of Abeta phagocytosis, we treated BV-2 cells with biotinylated Abeta1-42 and measured intracellular amyloid by morphometric analysis. IAA-94-treated cells showed an increased Abeta phagocytosis after 24 hr and efficient degradation of ingested material after 72 hr. In addition, we tested Abeta1-42 phagocytosis in adult rat peritoneal macrophages. Also, these cells actively phagocytosed Abeta1-42 in the presence of IAA-94. However, the increased expression of inducible NO synthase (iNOS), stimulated by Abeta, was reverted by IAA-94. In parallel, a decrease in NO release was detected. These results suggest that blockade of CLIC1 stimulates Abeta phagocytosis in mononuclear phagocytes while inhibiting the induction of iNOS and further point to CLIC1 as a possible therapeutic target in AD.

Relationships between expression of apolipoprotein E and beta-amyloid precursor protein are altered in proximity to Alzheimer beta-amyloid plaques: potential explanations from cell culture studies

Theories regarding the initiation and progression of Alzheimer disease (AD) often consider potential roles played by elevations of beta-amyloid precursor protein (betaAPP). Because it is the source of amyloid beta-peptide, betaAPP may simply contribute more pathogenic stimulus when elevated; some analyses have, however, reported a decline in betaAPP in AD. We found a progressive increase in neuronal betaAPP expression with increasing age in the brains of nondemented individuals, whereas in AD patient samples, betaAPP antigenicity decreased in neuronal somata in a manner that correlated with accumulation of mature amyloid beta-peptide plaques. In contrast, apolipoprotein E (ApoE) expression correlated with accumulation of plaques, and even greater amounts of ApoE were detected in plaques. Induction of betaAPP by glutamate in neuronal cell cultures was found to depend upon ApoE levels or activity. Thus, elevations in expression of ApoE and betaAPP by cellular stresses are likely normally linked in vivo, and uncoupling of this link, or other pathologic events in AD initiation, may leave neurons with diminished betaAPP expression, which might in turn reduce their resistance to stressors.

Inhibition of microglial neurotoxicity by ethanol extract of Artemisia asiatica Nakai

Artemisia asiatica Nakai has been used for the treatment of infections and inflammatory disorders in traditional Oriental medicine. Previously, an ethanol extract of A. asiatica has been shown to exert antioxidative and antiinflammatory activities and to exhibit protective effects against experimentally induced damage in the gastrointestinal system, liver and pancreas. This study examined whether the ethanol extract of A. asiatica affects inflammatory activation of microglia in the central nervous system, and whether the antiinflammatory activity of A. asiatica is related to neuroprotective effects. The extract of A. asiatica inhibited inflammatory activation of mouse microglial cells as determined by the production of nitric oxide and the expression of inducible nitric oxide synthase and inflammatory cytokine. The extract also protected nerve growth factor-differentiated PC12 cells against microglial cytotoxicity, indicating that the ethanol extract of A. asiatica may be neuroprotective by inhibiting microglial neurotoxicity.

Resveratrol and quercetin, two natural polyphenols, reduce apoptotic neuronal cell death induced by neuroinflammation

Parkinson's disease (PD) is a movement disorder characterized by a progressive loss of nigrostriatal dopaminergic neurons. Microglia activation and neuroinflammation have been associated with the pathogenesis of PD. Indeed, cytokines have been proposed as candidates that mediate the apoptotic cell death of dopaminergic neurons seen in PD. In this study, we investigated the effect of two natural polyphenols, resveratrol and quercetin, on neuroinflammation. For glial cells, we observed that lipopolysaccharide (LPS)-induced mRNA levels of two proinflammatory genes, interleukin 1-alpha and tumor necrosis factor-alpha, are strongly decreased by treatments with resveratrol or quercetin. We also undertook microglial-neuronal coculture to examine the influence of resveratrol and quercetin on dopaminergic neuronal cell death evoked by LPS-activated microglia. Cytotoxicity assays were performed to evaluate the percentage of cell death, with apoptotic cells identified by both the TdT-mediated dUTP nick end labeling technique and the detection of cleaved caspase-3. We report that treatment of N9 microglial cells with resveratrol or quercetin successfully reduced the inflammation-mediated apoptotic death of neuronal cells in our coculture system. Altogether our results demonstrate that resveratrol and quercetin diminished apoptotic neuronal cell death induced by microglial activation and suggest that these two phytoestrogens may be potent antiinflammatory compounds.

Minocycline treatment following hypoxic/ischaemic injury attenuates white matter injury in a rodent model of periventricular leucomalacia

AIMS

Periventricular white matter injury in premature infants occurs following hypoxia/ischaemia and systemic infection, and results in hypomyelination, as well as neuromotor and cognitive deficits later in life. Inflammatory infiltrates are seen within human cerebral white matter from periventricular leucomalacia (PVL) cases.

METHODS

In this study, we examine the time course of CD-68+ microglial cell responses relative to cell death within white matter following hypoxia/ischaemia in a rat model of PVL. We also tested the efficacy of the minocycline, an agent that suppresses microglial activation, in this model when administered as a post-insult treatment.

RESULTS

We show that preoligodendrocyte injury in the post-natal day 6 begins within 24 h and continues for 48-96 h after hypoxia/ischaemia, and that microglial responses occur primarily over the first 96 h following hypoxia/ischaemia. Minocycline treatment over this 96 h time window following the insult resulted in significant protection against white matter injury, and this effect was concomitant with a reduction in CD-68+ microglial cell numbers.

CONCLUSIONS

These results suggest that anti-inflammatory treatments may represent a useful strategy in the treatment of PVL, where clinical conditions would favour a post-insult treatment strategy.