Excitotoxicity in glial cells

N-acetylcysteine amide and di- N-acetylcysteine amide protect retinal cells in culture via an antioxidant action

Reactive oxygen species (ROS) play a significant role in toxicity to the retina in a variety of diseases. N-acetylcysteine (NAC), N-acetylcysteine amide (NACA) and the dimeric di-N-acetylcysteine amide (diNACA) were evaluated in terms of protecting retinal cells, in vitro, in a variety of stress models. Three types of rat retinal cell cultures were utilized in the study: macroglial-only cell cultures, neuron-only retinal ganglion cell (RGC) cultures, and mixed cultures containing retinal glia and neurons. Ability of test agents to attenuate oxidative stress in all cultures was ascertained. In addition, capability of agents to protect against a variety of alternate clinically-relevant stressors, including excitotoxins and mitochondrial electron transport chain inhibitors, was also evaluated. Capacity of test agents to elevate cellular levels of reduced glutathione under normal and compromised conditions was also determined. NAC, NACA and diNACA demonstrated concentration-dependent cytoprotection against oxidative stress in all cultures. These three compounds, however, had differing effects against a variety of alternate insults to retinal cells. The most protective agent was NACA, which was most potent against the most stressors (including oxidative stress, mitochondrial impairment by antimycin A and azide, and glutamate-induced excitotoxicity). Similar to NAC, NACA increased glutathione levels in non-injured cells, although diNACA did not, suggesting a different, unknown mechanism of antioxidant activity for the latter. In support of this, diNACA was the only agent to attenuate rotenone-induced toxicity in mitochondria. NAC, NACA and diNACA exhibited varying degrees of antioxidant activity, i.e., protected cultured rat retinal cells from a variety of stressors which were designed to mimic aspects of the pathology of different retinal diseases. A general rank order of activity was observed: NACA ≥ diNACA > NAC. These results warrant further exploration of NACA and diNACA as antioxidant therapeutics for the treatment of retinal diseases, particularly those involving oxidative stress. Furthermore, we have defined the battery of tests carried out as the "Wood, Chidlow, Wall and Casson (WCWC) Retinal Antioxidant Indices"; we believe that these are of great value for screening molecules for potential to reduce retinal oxidative stress in a range of retinal diseases.

Molars to Medicine: A Focused Review on the Pre-Clinical Investigation and Treatment of Secondary Degeneration following Spinal Cord Injury Using Dental Stem Cells

Spinal cord injury (SCI) can result in the permanent loss of mobility, sensation, and autonomic function. Secondary degeneration after SCI both initiates and propagates a hostile microenvironment that is resistant to natural repair mechanisms. Consequently, exogenous stem cells have been investigated as a potential therapy for repairing and recovering damaged cells after SCI and other CNS disorders. This focused review highlights the contributions of mesenchymal (MSCs) and dental stem cells (DSCs) in attenuating various secondary injury sequelae through paracrine and cell-to-cell communication mechanisms following SCI and other types of neurotrauma. These mechanistic events include vascular dysfunction, oxidative stress, excitotoxicity, apoptosis and cell loss, neuroinflammation, and structural deficits. The review of studies that directly compare MSC and DSC capabilities also reveals the superior capabilities of DSC in reducing the effects of secondary injury and promoting a favorable microenvironment conducive to repair and regeneration. This review concludes with a discussion of the current limitations and proposes improvements in the future assessment of stem cell therapy through the reporting of the effects of DSC viability and DSC efficacy in attenuating secondary damage after SCI.

Hepatopancreatic metabolic disorders and their implications in the development of Alzheimer's disease and vascular dementia

Dementia has been faced with significant public health challenges and economic burdens that urges the need to develop safe and effective interventions. In recent years, an increasing number of studies have focused on the relationship between dementia and liver and pancreatic metabolic disorders that result in diseases such as diabetes, obesity, hypertension and dyslipidemia. Previous reports have shown that there is a plausible correlation between pathologies caused by hepatopancreatic dysfunctions and dementia. Glucose, insulin and IGF-1 metabolized in the liver and pancreas probably have an important influence on the pathophysiology of the most common dementias: Alzheimer's and vascular dementia. This current review highlights recent studies aimed at identifying convergent mechanisms, such as insulin resistance and other diseases, linked to altered hepatic and pancreatic metabolism, which are capable of causing brain changes that ultimately lead to dementia.

Cuscuta epithymum Murr. crude extract pre-conditioning protects C6 cells from L-glutamate-induced neurotoxicity

BACKGROUND

Cuscuta epithymum Murr. (C. epithymum), as an herbal medicine, has played an anti-cancerous role in various studies; however, its possible neuroprotective effects have been neglected. Here, we aimed to investigate the protective effects of C. epithymum seeds crude extract and different fractions on rat glioblastoma cells (C6) in L-glutamate oxidative condition.

METHODS

Initially, the total phenolic content of C. epithymum crude extract and the fractions (all produced by maceration method) was determined. Subsequently, C6 cells were pre-treated with the various concentrations of crude extract and fractions 24 h before L-glutamate exposure. Likewise, C6 cells were treated with the same concentrations of crude extract and fractions 24 h after exposure to L-glutamate. The cell viability and morphology were compared in crude extract and fractions groups, then superoxide dismutase (SODs) activity, reactive oxygen species (ROS), and malondialdehyde (MDA) levels were measured. The flow cytometry test was used to study C. epithymum crude extract's effects on the cell cycle and also to quantify the apoptosis, necrosis, and live cells population in different groups.

RESULTS

C. epithymum crude extract and fractions (hexanoic, dichloromethanolic, and methanolic) had concentration-dependent cytotoxicity (IC50:126.47, 2101.96, 140.97, and 218.96 µg/ml, respectively). The crude extract and methanolic fraction contained phenolic compounds (55.99 ± 2.795 and 50.80 ± 2.969 mg gallic acid/g extract), while in hexanoic and dichloromethanolic fractions, the phenolic content was undetectable. In the cell viability assay, in comparison to fractions, the crude extract showed a more protective effect against glutamate-induced oxidative condition (P < 0.0001). The crude extract increased the SODs activity (P < 0.001) and decreased MDA and ROS levels (P < 0.0001) in comparison to the glutamate group. The crude extract significantly increased the population of cells in G1 (from 63.04 to 76.29) and decreased the percentage of cells in G2 (from 11.56 to 6.7) and S phase (from 25.4 to 17.01). In addition, it decreased the apoptotic and necrotic cell populations (from 34 to 17.1) and also increased the percentage of live cells (from 66.8 to 83.4 percent) in the flow cytometry test.

CONCLUSION

C. epithymum crude extract plays a neuroprotective role by activating the defense mechanisms in cell against the oxidative condition.

Novel Multipotent Amantadine-M30D Hybrids with Highly Selective Butyrylcholinesterase Inhibition and Neuroprotective Effects as Effective Anti-Alzheimer's Agents

As a contribution to the development of new dual/multifunctional drugs, a novel therapeutical scaffold merging key structural features from memantine and M30D was designed, synthesized, and explored for its AChE/BuChE inhibitory activity and neuroprotective effects. All synthetized hybrids were not able to inhibit AChE, but most of them exhibit inhibition with high selectivity toward butyrylcholinesterase (BuChE). Notably, among the tested compounds, amantadine/M30D hybrids with six, seven, nine, and twelve methylene groups in the spacer (5d, 5e, 5f, and 5g) not only highlighted having the best potency and selective butyrylcholinesterase inhibition greater than 83% but also, particularly 5e and 5d, elicited considerable neuroprotection when evaluated in pretreatment conditions, by reducing injury effects caused by glutamate with maximum protection reached about 47.82 ± 0.81% (5e) and 42 ± 2.20% (5d) in comparison with memantine (37.27 ± 2.69%). Likewise, we chose 5e as the hit compound, which in a glutamate excitotoxity coculture model prevented astroglia reactivity and neuronal death, as well as a 91% restoration of calcium levels and an increasing ATP level in both pre-/post-treatments of 61.48 ± 4.60 and 45.16 ± 10.55%, respectively. Regarding docking studies, a blockade of the NMDA channel pore by 5e would explain its neuroprotective response. Finally, the hit compound 5e exhibited in vitro blood-brain barrier (BBB) permeability and human plasma stability, as well as an optimal in silico neuropharmacokinetic profile. From a therapeutic perspective, merging key pharmacophoric features from memantine and M30D provides a new medicinal scaffold with dual-/multifunctional properties and human plasma stability for the future development of potential drugs for treating AD.

Central nervous system macrophages in progressive multiple sclerosis: relationship to neurodegeneration and therapeutics

There are over 15 disease-modifying drugs that have been approved over the last 20 years for the treatment of relapsing–remitting multiple sclerosis (MS), but there are limited treatment options available for progressive MS. The development of new drugs for the treatment of progressive MS remains challenging as the pathophysiology of progressive MS is poorly understood.

The progressive phase of MS is dominated by neurodegeneration and a heightened innate immune response with trapped immune cells behind a closed blood–brain barrier in the central nervous system. Here we review microglia and border-associated macrophages, which include perivascular, meningeal, and choroid plexus macrophages, during the progressive phase of MS. These cells are vital and are largely the basis to define lesion types in MS. We will review the evidence that reactive microglia and macrophages upregulate pro-inflammatory genes and downregulate homeostatic genes, that may promote neurodegeneration in progressive MS. We will also review the factors that regulate microglia and macrophage function during progressive MS, as well as potential toxic functions of these cells. Disease-modifying drugs that solely target microglia and macrophage in progressive MS are lacking. The recent treatment successes for progressive MS include include B-cell depletion therapies and sphingosine-1-phosphate receptor modulators. We will describe several therapies being evaluated as a potential treatment option for progressive MS, such as immunomodulatory therapies that can target myeloid cells or as a potential neuroprotective agent.

The role of inflammasomes in vascular cognitive impairment

There is an increasing prevalence of Vascular Cognitive Impairment (VCI) worldwide, and several studies have suggested that Chronic Cerebral Hypoperfusion (CCH) plays a critical role in disease onset and progression. However, there is a limited understanding of the underlying pathophysiology of VCI, especially in relation to CCH. Neuroinflammation is a significant contributor in the progression of VCI as increased systemic levels of the proinflammatory cytokine interleukin-1β (IL-1β) has been extensively reported in VCI patients. Recently it has been established that CCH can activate the inflammasome signaling pathways, involving NLRP3 and AIM2 inflammasomes that critically regulate IL-1β production. Given that neuroinflammation is an early event in VCI, it is important that we understand its molecular and cellular mechanisms to enable development of disease-modifying treatments to reduce the structural brain damage and cognitive deficits that are observed clinically in the elderly. Hence, this review aims to provide a comprehensive insight into the molecular and cellular mechanisms involved in the pathogenesis of CCH-induced inflammasome signaling in VCI.

Targeting CDK5 in Astrocytes Promotes Calcium Homeostasis Under Excitotoxic Conditions

Glutamate excitotoxicity triggers overactivation of CDK5 and increases calcium influx in neural cells, which promotes dendritic retraction, spine loss, increased mitochondrial calcium from the endoplasmic reticulum, and neuronal death. Our previous studies showed that CDK5 knockdown (KD) in astrocytes improves neurovascular integrity and cognitive functions and exerts neuroprotective effects. However, how CDK5-targeted astrocytes affect calcium regulation and whether this phenomenon is associated with changes in neuronal plasticity have not yet been analyzed. In this study, CDK5 KD astrocytes transplanted in CA3 remained at the injection site without proliferation, regulated calcium in the CA1 hippocampal region after excitotoxicity by glutamate in ex vivo hippocampal slices, improving synapsin and PSD95 clustering. These CDK5 KD astrocytes induced astrocyte stellation and neuroprotection after excitotoxicity induced by glutamate in vitro. Also, these effects were supported by CDK5 inhibition (CDK5i) in vitro through intracellular stabilization of calcium levels in astrocytes. Additionally, these cells in cocultures restored calcium homeostasis in neurons, redistributing calcium from somas to dendrites, accompanied by dendrite branching, higher dendritic spines and synapsin-PSD95 clustering. In summary, induction of calcium homeostasis at the CA1 hippocampal area by CDK5 KD astrocytes transplanted in the CA3 area highlights the role of astrocytes as a cell therapy target due to CDK5-KD astrocyte-mediated synaptic clustering, calcium spreading regulation between both areas, and recovery of the intracellular astrocyte-neuron calcium imbalance and plasticity impairment generated by glutamate excitotoxicity.

Understanding the Connection Between Common Stroke Comorbidities, Their Associated Inflammation, and the Course of the Cerebral Ischemia/Reperfusion Cascade

Despite the enormous progress in the understanding of the course of the ischemic stroke over the last few decades, a therapy that effectively protects neurovascular units (NVUs) and significantly improves neurological functions in stroke patients has still not been achieved. The reasons for this state are unclear, but it is obvious that the cerebral ischemia and reperfusion cascade is a highly complex phenomenon, which includes the intense neuroinflammatory processes, and comorbid stroke risk factors strongly worsen stroke outcomes and likely make a substantial contribution to the pathophysiology of the ischemia/reperfusion, enhancing difficulties in searching of successful treatment. Common concomitant stroke risk factors (arterial hypertension, diabetes mellitus and hyperlipidemia) strongly drive inflammatory processes during cerebral ischemia/reperfusion; because these factors are often present for a long time before a stroke, causing low-grade background inflammation in the brain, and already initially disrupting the proper functions of NVUs. Broad consideration of this situation in basic research may prove to be crucial for the success of future clinical trials of neuroprotection, vasculoprotection and immunomodulation in stroke. This review focuses on the mechanism by which coexisting common risk factors for stroke intertwine in cerebral ischemic/reperfusion cascade and the dysfunction and disintegration of NVUs through inflammatory processes, principally activation of pattern recognition receptors, alterations in the expression of adhesion molecules and the subsequent pathophysiological consequences.

Neuroprotective mechanisms of mangiferin in neurodegenerative diseases

The central nervous system (CNS) regulates and coordinates an extensive array of complex processes requiring harmonious regulation of specific genes. CNS disorders represent a large burden on society and cause enormous disability and economic losses. Traditional Chinese medicine (TCM) has been used for many years in the treatment of neurological illnesses, such as Alzheimer's disease, Parkinson's disease, stroke, and depression, as the combination of TCM and Western medicine has superior therapeutic efficacy and minimal toxic side effects. Mangiferin (MGF) is an active compound of the traditional Chinese herb rhizome anemarrhenae, which has antioxidant, anti-inflammation, anti-lipid peroxidation, immunomodulatory, and anti-apoptotic functions in the CNS. MGF has been demonstrated to have therapeutic effects in CNS diseases through a multitude of mechanisms. This review outlines the latest research on the neuroprotective ability of MGF and the diverse molecular mechanisms involved.

CDK5 Targeting as a Therapy for Recovering Neurovascular Unit Integrity in Alzheimer's Disease

The neurovascular unit (NVU) is responsible for synchronizing the energetic demand, vasodynamic changes, and neurochemical and electrical function of the brain through a closed and interdependent interaction of cell components conforming to brain tissue. In this review, we will focus on cyclin-dependent kinase 5 (CDK5) as a molecular pivot, which plays a crucial role in the healthy function of neurons, astrocytes, and the endothelium and is implicated in the cross-talk of cellular adhesion signaling, ion transmission, and cytoskeletal remodeling, thus allowing the individual and interconnected homeostasis of cerebral parenchyma. Then, we discuss how CDK5 overactivation affects the integrity of the NVU in Alzheimer's disease (AD) and cognitive impairment; we emphasize how CDK5 is involved in the excitotoxicity spreading of glutamate and Ca2+ imbalance under acute and chronic injury. Additionally, we present pharmacological and gene therapy strategies for producing partial depletion of CDK5 activity on neurons, astrocytes, or endothelium to recover neuroplasticity and neurotransmission, suggesting that the NVU should be the targeted tissue unit in protective strategies. Finally, we conclude that CDK5 could be effective due to its intervention on astrocytes by its end feet on the endothelium and neurons, acting as an intermediary cell between systemic and central communication in the brain. This review provides integrated guidance regarding the pathogenesis of and potential repair strategies for AD.

Datumetine exposure alters hippocampal neurotransmitters system in C57BL/6 mice

Our previous study showed that datumetine modulates NMDAR activity with long term exposure leading to memory deficit and altered NMDAR signaling. We aim to explore the neurotransmitters perturbations of acute datumetine-NMDAR interaction. Fifteen C57/BL6 mice were used for the study, they are divided into three groups of 5 animals each. Animals were administered DMSO (DMSO/Control), 0.25 mg/kg body weight of datumetine (0.25 Datumetine) and 1 mg/kg bodyweight of datumetine (1.0 Datumetine) intraperitoneally for 14 days. At the end of treatment, animals were euthanized in isofluorane chamber, perfused transcardially with 1XPBS followed by PFA. Immunofluorescence procedure was done to check the distribution of neurons, astrocytes, microglia and major neuronal subtypes in the hippocampus. Expansion and electron microscopy techniques were used to assess the condition of the synapses. Quantitative data were expressed as mean ± SEM and analyzed using ANOVA with Tukey post hoc using p < 0.05 as significant. Datumetine increased the expression of CD11b, GFAP, vGlut1, GABA, CHRNA7 and TH while expression of TrPH and NeuN were reduced in the hippocampus compared to control animals. Synaptic loss was evident in datumetine exposed animals with reduced synaptic vesicles accompanied by a thickness of postsynaptic density than that of control animals. This study concludes that acute datumetine exposure alters hippocampal neurotransmitter systems.

Ischemia-Triggered Glutamate Excitotoxicity From the Perspective of Glial Cells

A plethora of neurological disorders shares a final common deadly pathway known as excitotoxicity. Among these disorders, ischemic injury is a prominent cause of death and disability worldwide. Brain ischemia stems from cardiac arrest or stroke, both responsible for insufficient blood supply to the brain parenchyma. Glucose and oxygen deficiency disrupts oxidative phosphorylation, which results in energy depletion and ionic imbalance, followed by cell membrane depolarization, calcium (Ca²⁺) overload, and extracellular accumulation of excitatory amino acid glutamate. If tight physiological regulation fails to clear the surplus of this neurotransmitter, subsequent prolonged activation of glutamate receptors forms a vicious circle between elevated concentrations of intracellular Ca²⁺ ions and aberrant glutamate release, aggravating the effect of this ischemic pathway. The activation of downstream Ca²⁺-dependent enzymes has a catastrophic impact on nervous tissue leading to cell death, accompanied by the formation of free radicals, edema, and inflammation. After decades of “neuron-centric” approaches, recent research has also finally shed some light on the role of glial cells in neurological diseases. It is becoming more and more evident that neurons and glia depend on each other. Neuronal cells, astrocytes, microglia, NG2 glia, and oligodendrocytes all have their roles in what is known as glutamate excitotoxicity. However, who is the main contributor to the ischemic pathway, and who is the unsuspecting victim? In this review article, we summarize the so-far-revealed roles of cells in the central nervous system, with particular attention to glial cells in ischemia-induced glutamate excitotoxicity, its origins, and consequences.

Corticotropin-releasing factor protects against ammonia neurotoxicity in isolated larval zebrafish brains

The physiological roles of corticotropin-releasing factor (CRF) have recently been extended to cytoprotection. Here, to determine whether CRF is neuroprotective in fish, the effects of CRF against high environmental ammonia (HEA)-mediated neurogenic impairment and cell death were investigated in zebrafish. In vivo, exposure of 1 day post-fertilization (dpf) embryos to HEA only reduced the expression of the determined neuron marker neurod1 In contrast, in 5 dpf larvae, HEA increased the expression of nes and sox2, neural progenitor cell markers, and reduced the expression of neurog1, gfap and mbpa, proneuronal cell, radial glia and oligodendrocyte markers, respectively, and neurod1 The N-methyl-d-aspartate (NMDA) receptor inhibitor MK801 rescued the HEA-induced reduction in neurod1 in 5 dpf larvae but did not affect the HEA-induced transcriptional changes in other neural cell types, suggesting that hyperactivation of NMDA receptors specifically contributes to the deleterious effects of HEA in determined neurons. As observed in vivo, HEA exposure elicited marked changes in the expression of cell type-specific markers in isolated 5 dpf larval brains. The addition of CRF reversed the in vitro effects of HEA on neurod1 expression and prevented an HEA-induced increase in cell death. Finally, the protective effects of CRF against HEA-mediated neurogenic impairment and cell death were prevented by the CRF type 1 receptor selective antagonist antalarmin. Together, these results provide novel evidence that HEA has developmental time- and cell type-specific neurotoxic effects, that NMDA receptor hyperactivation contributes to HEA-mediated impairment of determined neurons, and that CRF has neuroprotective properties in the larval zebrafish brain.

Suppression of the Peripheral Immune System Limits the Central Immune Response Following Cuprizone-Feeding: Relevance to Modelling Multiple Sclerosis

Cuprizone (CPZ) preferentially affects oligodendrocytes (OLG), resulting in demyelination. To investigate whether central oligodendrocytosis and gliosis triggered an adaptive immune response, the impact of combining a standard (0.2%) or low (0.1%) dose of ingested CPZ with disruption of the blood brain barrier (BBB), using pertussis toxin (PT), was assessed in mice. 0.2% CPZ(±PT) for 5 weeks produced oligodendrocytosis, demyelination and gliosis plus marked splenic atrophy (37%) and reduced levels of CD4 (44%) and CD8 (61%). Conversely, 0.1% CPZ(±PT) produced a similar oligodendrocytosis, demyelination and gliosis but a smaller reduction in splenic CD4 (11%) and CD8 (14%) levels and no splenic atrophy. Long-term feeding of 0.1% CPZ(±PT) for 12 weeks produced similar reductions in CD4 (27%) and CD8 (43%), as well as splenic atrophy (33%), as seen with 0.2% CPZ(±PT) for 5 weeks. Collectively, these results suggest that 0.1% CPZ for 5 weeks may be a more promising model to study the ‘inside-out’ theory of Multiple Sclerosis (MS). However, neither CD4 nor CD8 were detected in the brain in CPZ±PT groups, indicating that CPZ-mediated suppression of peripheral immune organs is a major impediment to studying the ‘inside-out’ role of the adaptive immune system in this model over long time periods. Notably, CPZ(±PT)-feeding induced changes in the brain proteome related to the suppression of immune function, cellular metabolism, synaptic function and cellular structure/organization, indicating that demyelinating conditions, such as MS, can be initiated in the absence of adaptive immune system involvement.

Overexpression of VLA-4 in glial-restricted precursors enhances their endothelial docking and induces diapedesis in a mouse stroke model

The loss of oligodendrocytes after stroke is one of the major causes of secondary injury. Glial-restricted progenitors (GRPs) have remylenating potential after intraparenchymal cerebral transplantation. The intraarterial (IA) injection route is an attractive gateway for global brain delivery, but, after IA infusion, naive GRPs fail to bind to the cerebral vasculature. The aim of this study was to test whether overexpression of Very Late Antigen-4 (VLA-4) increases endothelial docking and cerebral homing of GRPs in a stroke model. Mouse GRPs were co-transfected with DNA plasmids encoding VLA-4 subunits (α4, β1). The adhesion capacity and migration were assessed using a microfluidic assay. In vivo imaging of the docking and homing of IA-infused cells was performed using two-photon microscopy in a mouse middle cerebral artery occlusion (MCAO) model. Compared to naïve GRPs, transfection of GRPs with VLA-4 resulted in >60% higher adhesion (p < 0.05) to both purified Vascular Cell Adhesion Molecule-11 (VCAM-11) and TNFα-induced endothelial VCAM-1. VLA-4⁺GRPs displayed a higher migration in response to a chemoattractant gradient. Following IA infusion, VLA-4⁺GRPs adhered to the vasculature at three-fold greater numbers than naïve GRPs. Multi-photon imaging confirmed that VLA-4 overexpression increases the efficiency of GRP docking and leads to diapedesis after IA transplantation. This strategy may be further exploited to increase the efficacy of cellular therapeutics.

Recovery of Neurovascular Unit Integrity by CDK5-KD Astrocyte Transplantation in a Global Cerebral Ischemia Model

Astrocytes play metabolic and structural support roles and contribute to the integrity of the blood-brain barrier (BBB), linking communication between neurons and the endothelium. Cyclin-dependent kinase 5 (CDK5) likely exerts a dual effect on the endothelium and astrocytes due to its involvement in migration and angiogenesis; the overactivation of CDK5 is associated with dysfunction in glutamate recapture and hypoxia. Recently, we proposed that CDK5-targeted astrocytes facilitate the recovery of neurological and motor function in transplanted ischemic rats. In the current study, we treated cerebral ischemic rats and endothelial cells exposed to glutamate toxicity with CDK5 knock-down (CDK5-KD) astrocytes to determine the role of CDK5 in neurovascular integrity. We found that the effects of CDK5-KD were sustained for 4 months, preventing neuronal and astrocyte loss, facilitating the recovery of the BBB via the production of BDNF by endogenous astrocytes (GFP^-) surrounding vessels in the motor cortex and the corpus callosum of global ischemic rats, and improving neurological performance. These findings were supported by the in vitro findings of increased transendothelial resistance, p120-ctn+ adhesion and reduced intercellular gaps induced by a CDK5 inhibitor (roscovitine) in bEnd.3 cells in a glutamate-toxicity model. Additionally, CDK5-KD astrocytes in co-culture protected the endothelial cell viability, increased BDNF release from astrocytes, increased BDNF immunoreactivity in neighboring astrocytes and endothelial cells and enhanced cell adhesion in a glutamate-toxicity model. Altogether, these findings suggest that a CDK5 reduction in astrocytes protects the endothelium, which promotes BDNF release, endothelial adhesion, and the recovery of neurovascular unit integrity and brain function in ischemic rats.

Exploring the potential of natural and synthetic neuroprotective steroids against neurodegenerative disorders: A literature review

Neurodegeneration is a complex process, which leads to progressive brain damage due to loss of neurons. Despite exhaustive research, the cause of neuronal loss in various degenerative disorders is not entirely understood. Neuroprotective steroids constitute an important line of attack, which could play a major role against the common mechanisms associated with various neurodegenerative disorders like Alzheimer's disease, Parkinson's disease, Huntington's disease, and amyotrophic lateral sclerosis. Natural endogenous steroids induce the neuroprotection by protecting the nerve cells from neuronal injury through multiple mechanisms, therefore the structural modifications of the endogenous steroids could be helpful in the generation of new therapeutically useful neuroprotective agents. The review article will keep the readers apprised of the detailed description of natural as well as synthetic neuroprotective steroids from the medicinal chemistry point of view, which would be helpful in drug discovery efforts aimed toward neurodegenerative diseases.

Acute death of astrocytes in blast-exposed rat organotypic hippocampal slice cultures

Blast traumatic brain injury (bTBI) affects civilians, soldiers, and veterans worldwide and presents significant health concerns. The mechanisms of neurodegeneration following bTBI remain elusive and current therapies are largely ineffective. It is important to better characterize blast-evoked cellular changes and underlying mechanisms in order to develop more effective therapies. In the present study, our group utilized rat organotypic hippocampal slice cultures (OHCs) as an in vitro system to model bTBI. OHCs were exposed to either 138 ± 22 kPa (low) or 273 ± 23 kPa (high) overpressures using an open-ended helium-driven shock tube, or were assigned to sham control group. At 2 hours (h) following injury, we have characterized the astrocytic response to a blast overpressure. Immunostaining against the astrocytic marker glial fibrillary acidic protein (GFAP) revealed acute shearing and morphological changes in astrocytes, including clasmatodendrosis. Moreover, overlap of GFAP immunostaining and propidium iodide (PI) indicated astrocytic death. Quantification of the number of dead astrocytes per counting area in the hippocampal cornu Ammonis 1 region (CA1), demonstrated a significant increase in dead astrocytes in the low- and high-blast, compared to sham control OHCs. However only a small number of GFAP-expressing astrocytes were co-labeled with the apoptotic marker Annexin V, suggesting necrosis as the primary type of cell death in the acute phase following blast exposure. Moreover, western blot analyses revealed calpain mediated breakdown of GFAP. The dextran exclusion additionally indicated membrane disruption as a potential mechanism of acute astrocytic death. Furthermore, although blast exposure did not evoke significant changes in glutamate transporter 1 (GLT-1) expression, loss of GLT-1-expressing astrocytes suggests dysregulation of glutamate uptake following injury. Our data illustrate the profound effect of blast overpressure on astrocytes in OHCs at 2 h following injury and suggest increased calpain activity and membrane disruption as potential underlying mechanisms.

Neuroprotection Induced by Transplanted CDK5 Knockdown Astrocytes in Global Cerebral Ischemic Rats

Cerebral ischemia is a cerebrovascular episode that generates a high incidence of death and physical and mental disabilities worldwide. Excitotoxicity, release of free radicals, and exacerbated immune response cause serious complications in motor and cognitive areas during both short and long time frames post-ischemia. CDK5 is a kinase that is widely involved in the functions of neurons and astrocytes, and its over-activation is implicated in neurodegenerative processes. In this study, we evaluated the brain parenchymal response to the transplantation of CDK5-knockdown astrocytes into the somatosensory cortex after ischemia in rats. Male Wistar rats were subjected to the two-vessel occlusion (2VO) model of global cerebral ischemia and immediately transplanted with shCDK5miR- or shSCRmiR-transduced astrocytes or with untransduced astrocytes (Control). Our findings showed that animals transplanted with shCDK5miR astrocytes recovered motor and neurological performance better than with those transplanted with WT or shSCRmiR astrocytes. Cell transplantation produced an overall prevention of neuronal loss, and CDK5-knockdown astrocytes significantly increased the immunoreactivity (IR) of endogenous GFAP in branches surrounding blood vessels, accompanied by the upregulation of PECAM-1 IR in the walls of vessels in the motor and somatosensory regions and by an increase in Ki67 IR in the subventricular zone (SVZ), partially associated with the production of BDNF. Together, our data suggest that transplantation of shCDK5miR astrocytes protects the neurovascular unit in ischemic rats, allowing the motor and neurological function recovery.

Purinergic signalling in brain ischemia

Ischemia is a multifactorial pathology characterized by different events evolving in the time. After ischemia a primary damage due to the early massive increase of extracellular glutamate is followed by activation of resident immune cells, i.e microglia, and production or activation of inflammation mediators. Protracted neuroinflammation is now recognized as the predominant mechanism of secondary brain injury progression. Extracellular concentrations of ATP and adenosine in the brain increase dramatically during ischemia in concentrations able to stimulate their respective specific P2 and P1 receptors. Both ATP P2 and adenosine P1 receptor subtypes exert important roles in ischemia. Although adenosine exerts a clear neuroprotective effect through A1 receptors during ischemia, the use of selective A1 agonists is hampered by undesirable peripheral effects. Evidence up to now in literature indicate that A2A receptor antagonists provide protection centrally by reducing excitotoxicity, while agonists at A2A (and possibly also A2B) and A3 receptors provide protection by controlling massive infiltration and neuroinflammation in the hours and days after brain ischemia. Among P2X receptors most evidence indicate that P2X7 receptor contribute to the damage induced by the ischemic insult due to intracellular Ca(2+) loading in central cells and facilitation of glutamate release. Antagonism of P2X7 receptors might represent a new treatment to attenuate brain damage and to promote proliferation and maturation of brain immature resident cells that can promote tissue repair following cerebral ischemia. Among P2Y receptors, antagonists of P2Y12 receptors are of value because of their antiplatelet activity and possibly because of additional anti-inflammatory effects. Moreover strategies that modify adenosine or ATP concentrations at injury sites might be of value to limit damage after ischemia. This article is part of the Special Issue entitled 'Purines in Neurodegeneration and Neuroregeneration'.

Oligodendrocytes Are Targets of HIV-1 Tat: NMDA and AMPA Receptor-Mediated Effects on Survival and Development

Myelin pallor in HIV(+) individuals can occur very early during the disease process. While myelin damage might partly originate from HIV-induced vascular changes, the timing suggests that myelin and/or oligodendrocytes (OLs) may be directly affected. Histological (Golgi-Kopsch, electron microscopy) and biochemical studies have revealed an increased occurrence of abnormal OL/myelin morphology and dysregulated myelin protein expression in transgenic mice expressing the HIV-1 transactivator of transcription (Tat) protein. This suggests that viral proteins by themselves might cause OL injury. Since Tat interacts with NMDARs, we hypothesized that activation of NMDARs and subsequent disruption of cytoplasmic Ca(2+) ([Ca(2+)]i) homeostasis might be one cause of white matter injury after HIV infection. In culture, HIV-1 Tat caused concentration-dependent death of immature OLs, while more mature OLs remained alive but had reduced myelin-like membranes. Tat also induced [Ca(2+)]i increases and Thr-287 autophosphorylation of Ca(2+)/calmodulin-dependent protein kinase II β (CaMKIIβ) in OLs. Tat-induced [Ca(2+)]i was attenuated by the NMDAR antagonist MK801, and also by the AMPA/kainate receptor antagonist CNQX. Importantly, both MK801 and CNQX blocked Tat-induced death of immature OLs, but only MK801 reversed Tat effects on myelin-like membranes. These results suggest that OLs can be direct targets of HIV proteins released from infected cells. Although viability and membrane production are both affected by glutamatergic receptor-mediated Ca(2+) influx, and possibly the ensuing CaMKIIβ activation, the roles of AMPARs and NMDARs appear to be different and dependent on the stage of OL differentiation.

SIGNIFICANCE STATEMENT

Over 33 million individuals are currently infected by HIV. Among these individuals, ∼60% develop HIV-associated neurocognitive disorders. Myelin damage and white matter injury have been frequently reported in HIV patients but not extensively studied. Clinical studies using combined antiretroviral therapy (cART) together with adjunctive "anti-inflammatory" drugs show no improvement over cART alone, suggesting existence of injury mechanisms in addition to inflammation. In our studies, oligodendrocytes exhibited rapid increases in intracellular Ca(2+) level upon HIV-1 transactivator of transcription (Tat) exposure. Thus, immature and mature oligodendrocytes can be direct targets of Tat. Since ionotropic glutamate receptor antagonists can partially or fully reverse the detrimental effects of Tat, glutamate receptors could be a potential therapeutic target for white matter damage in HIV patients.

Endoplasmic reticulum quality control and dysmyelination

Dysmyelination contributes to several human diseases including multiple sclerosis, Charcot-Marie-Tooth, leukodystrophies, and schizophrenia and can result in serious neurological disability. Properly formed, compacted myelin sheaths are required for appropriate nerve conduction velocities and the health and survival of neurons. Many different molecular mechanisms contribute to dysmyelination and many of these mechanisms originate at the level of the endoplasmic reticulum. The endoplasmic reticulum is a critical organelle for myelin biosynthesis and maintenance as the site of myelin protein folding quality control, Ca2+ homeostasis, cholesterol biosynthesis, and modulation of cellular stress. This review paper highlights the role of the endoplasmic reticulum and its resident molecules as an upstream and dynamic contributor to myelin and myelin pathologies.

CDK5 knockdown in astrocytes provide neuroprotection as a trophic source via Rac1

Astrocytes perform metabolic and structural support functions in the brain and contribute to the integrity of the blood-brain barrier. Astrocytes influence neuronal survival and prevent gliotoxicity by capturing glutamate (Glu), reactive oxygen species, and nutrients. During these processes, astrocytic morphological changes are supported by actin cytoskeleton remodeling and require the involvement of Rho GTPases, such as Rac1. The protein cyclin-dependent kinase 5 (CDK5) may have a dual effect on astrocytes because it has been shown to be involved in migration, senescence, and the dysfunction of glutamate recapture; however, its role in astrocytes remains unclear. Treating a possible deregulation of CDK5 with RNAi is a strategy that has been proposed as a therapy for neurodegenerative diseases. Models of glutamate gliotoxicity in the C6 astroglioma cell line, primary cultures of astrocytes, and co-cultures with neurons were used to analyze the effects of CDK5 RNAi in astrocytes and the role of Rac1 in neuronal viability. In C6 cells and primary astrocytes, CDK5 RNAi prevented the cell death generated by glutamate-induced gliotoxicity, and this finding was corroborated by pharmacological inhibition with roscovitine. This effect was associated with the appearance of lamellipodia, protrusions, increased cell area, stellation, Rac1 activation, BDNF release, and astrocytic protection in neurons that were exposed to glutamate excitotoxicity. Interestingly, Rac1 inhibition in astrocytes blocked BDNF upregulation and the astrocyte-mediated neuroprotection. Actin cytoskeleton remodeling and stellation may be a functional phenotype for BDNF release that promotes neuroprotection. In summary, our findings suggest that CDK5- knockdown in astrocytes acts as a trophic source for neuronal protection in a Rac1-dependent manner.

Understanding the pathophysiology of traumatic brain injury and the mechanisms of action of neuroprotective interventions

Traumatic brain injury continues to be a major socioeconomic problem, costing the United States $76.5 billion in the year of 2000. Despite the advances in the field of medicine, there are still no definitive treatments for traumatic brain injury. Goal of therapy is still gearing toward supportive cares such as intracranial pressure monitoring, lowering intracranial pressure, correcting cerebral ischemia, and manipulating serum osmolarity. The search for effective treatment in human studies has been unfruitful. In this review, the mechanisms of primary and secondary brain injury are discussed along with potential neuroprotective interventions such as hyperosmolar therapies, hypothermia, statins, and cyclosporin A.

From demyelination to remyelination: the road toward therapies for spinal cord injury

Myelin integrity is crucial for central nervous system (CNS) physiology while its preservation and regeneration after spinal cord injury (SCI) is key to functional restoration. Disturbance of nodal organization acutely after SCI exposes the axon and triggers conduction block in the absence of overt demyelination. Oligodendrocyte (OL) loss and myelin degradation follow as a consequence of secondary damage. Here, we provide an overview of the major biological events and underlying mechanisms leading to OL death and demyelination and discuss strategies to restrain these processes. Another aspect which is critical for SCI repair is the enhancement of endogenously occurring spontaneous remyelination. Recent findings have unveiled the complex roles of innate and adaptive immune responses in remyelination and the immunoregulatory potential of the glial scar. Moreover, the intimate crosstalk between neuronal activity, oligodendrogenesis and myelination emphasizes the contribution of rehabilitation to functional recovery. With a view toward clinical applications, several therapeutic strategies have been devised to target SCI pathology, including genetic manipulation, administration of small therapeutic molecules, immunomodulation, manipulation of the glial scar and cell transplantation. The implementation of new tools such as cellular reprogramming for conversion of one somatic cell type to another or the use of nanotechnology and tissue engineering products provides additional opportunities for SCI repair. Given the complexity of the spinal cord tissue after injury, it is becoming apparent that combinatorial strategies are needed to rescue OLs and myelin at early stages after SCI and support remyelination, paving the way toward clinical translation.

Redox biology in normal cells and cancer: restoring function of the redox/Fyn/c-Cbl pathway in cancer cells offers new approaches to cancer treatment

This review discusses a unique discovery path starting with novel findings on redox regulation of precursor cell and signaling pathway function and identification of a new mechanism by which relatively small changes in redox status can control entire signaling networks that regulate self-renewal, differentiation, and survival. The pathway central to this work, the redox/Fyn/c-Cbl (RFC) pathway, converts small increases in oxidative status to pan-activation of the c-Cbl ubiquitin ligase, which controls multiple receptors and other proteins of central importance in precursor cell and cancer cell function. Integration of work on the RFC pathway with attempts to understand how treatment with systemic chemotherapy causes neurological problems led to the discovery that glioblastomas (GBMs) and basal-like breast cancers (BLBCs) inhibit c-Cbl function through altered utilization of the cytoskeletal regulators Cool-1/βpix and Cdc42, respectively. Inhibition of these proteins to restore normal c-Cbl function suppresses cancer cell division, increases sensitivity to chemotherapy, disrupts tumor-initiating cell (TIC) activity in GBMs and BLBCs, controls multiple critical TIC regulators, and also allows targeting of non-TICs. Moreover, these manipulations do not increase chemosensitivity or suppress division of nontransformed cells. Restoration of normal c-Cbl function also allows more effective harnessing of estrogen receptor-α (ERα)-independent activities of tamoxifen to activate the RFC pathway and target ERα-negative cancer cells. Our work thus provides a discovery strategy that reveals mechanisms and therapeutic targets that cannot be deduced by standard genetics analyses, which fail to reveal the metabolic information, isoform shifts, protein activation, protein complexes, and protein degradation critical to our discoveries.

Neuroinflammation as a possible link between cannabinoids and addiction

OBJECTIVE

Substance dependence disorder is a chronically relapsing condition characterised by neurobiological changes leading to loss of control in restricting a substance intake, compulsion and withdrawal syndrome. In the past few years, (endo)cannabinoids have been raised as a possible target in the aetiology of drug addiction. On the other hand, although the exact mechanisms of the genesis of addiction remain poorly understood, it is possible that neuroinflammation might also play a role in the pathophysiology of this condition. Studies demonstrated that (endo)cannabinoids act as immunomodulators by inhibiting cytokines production and microglial cell activation. Thus, in the present review, we explore the possible role of neuroinflammation on the therapeutic effects of cannabinoids on drug addiction.

METHODS

We conducted an evidence-based review of the literature in order to assess the role of cannabinoids on the neuroinflammatory hypothesis of addiction (terms: addiction, cannabinoids and inflammation). We searched PubMed and BioMedCentral databases up to April 2014 with no date restrictions.

RESULTS

In all, 165 eligible articles were included in the present review. Existing evidence suggests that disruption in cannabinoid signalling during the drug addiction process leads to microglial activation and neuroinflammation.

CONCLUSION

The literature showed that inflammation and changes in endocannabinod signalling occur in drug abuse; however, it remains uncertain whether these changes are causally or coincidentally associated with addiction. Additional studies, therefore, are needed to elucidate the contribution of neuroinflammation on the behavioural and neuroprotective effects of cannabinoids on drug addiction.

Loss of SIRT4 decreases GLT-1-dependent glutamate uptake and increases sensitivity to kainic acid

Glutamate transport is a critical process in the brain that maintains low extracellular levels of glutamate to allow for efficient neurotransmission and prevent excitotoxicity. Loss of glutamate transport function is implicated in epilepsy, traumatic brain injury, and amyotrophic lateral sclerosis. It remains unclear whether or not glutamate transport can be modulated in these disease conditions to improve outcome. Here, we show that sirtuin (SIRT)4, a mitochondrial sirtuin, is up-regulated in response to treatment with the potent excitotoxin kainic acid. Loss of SIRT4 leads to a more severe reaction to kainic acid and decreased glutamate transporter expression and function in the brain. Together, these results indicate a critical and novel stress response role for SIRT4 in promoting proper glutamate transport capacity and protecting against excitotoxicity.

Adenosine A2A receptors modulate acute injury and neuroinflammation in brain ischemia

The extracellular concentration of adenosine in the brain increases dramatically during ischemia. Adenosine A_2A receptor is expressed in neurons and glial cells and in inflammatory cells (lymphocytes and granulocytes). Recently, adenosine A_2A receptor emerged as a potential therapeutic attractive target in ischemia. Ischemia is a multifactorial pathology characterized by different events evolving in the time. After ischemia the early massive increase of extracellular glutamate is followed by activation of resident immune cells, that is, microglia, and production or activation of inflammation mediators. Proinflammatory cytokines, which upregulate cell adhesion molecules, exert an important role in promoting recruitment of leukocytes that in turn promote expansion of the inflammatory response in ischemic tissue. Protracted neuroinflammation is now recognized as the predominant mechanism of secondary brain injury progression. A_2A receptors present on central cells and on blood cells account for important effects depending on the time-related evolution of the pathological condition. Evidence suggests that A_2A receptor antagonists provide early protection via centrally mediated control of excessive excitotoxicity, while A_2A receptor agonists provide protracted protection by controlling massive blood cell infiltration in the hours and days after ischemia. Focus on inflammatory responses provides for adenosine A_2A receptor agonists a wide therapeutic time-window of hours and even days after stroke.

Ventral tegmental area/substantia nigra and prefrontal cortex rodent organotypic brain slices as an integrated model to study the cellular changes induced by oxygen/glucose deprivation and reperfusion: effect of neuroprotective agents

Unveiling the roles of distinct cell types in brain response to insults is a partially unsolved challenge and a key issue for new neuroreparative approaches. In vivo models are not able to dissect the contribution of residential microglia and infiltrating blood-borne monocytes/macrophages, which are fundamentally undistinguishable; conversely, cultured cells lack original tissue anatomical and functional complexity, which profoundly alters reactivity. Here, we tested whether rodent organotypic co-cultures from mesencephalic ventral tegmental area/substantia nigra and prefrontal cortex (VTA/SN-PFC) represent a suitable model to study changes induced by oxygen/glucose deprivation and reperfusion (OGD/R). OGD/R induced cytotoxicity to both VTA/SN and PFC slices, with higher VTA/SN susceptibility. Neurons were highly affected, with astrocytes and oligodendrocytes undergoing very mild damage. Marked reactive astrogliosis was also evident. Notably, OGD/R triggered the activation of CD68-expressing microglia and increased expression of Ym1 and Arg1, two markers of "alternatively" activated beneficial microglia. Treatment with two well-known neuroprotective drugs, the anticonvulsant agent valproic acid and the purinergic P2-antagonist PPADS, prevented neuronal damage. Thus, VTA/SN-PFC cultures are an integrated model to investigate OGD/R-induced effects on distinct cells and easily screen neuroprotective agents. The model is particularly adequate to dissect the microglia phenotypic shift in the lack of a functional vascular compartment.

NMDA Receptors in Glial Cells: Pending Questions

Glutamate receptors of the N-methyl-D-aspartate (NMDA) type are involved in many cognitive processes, including behavior, learning and synaptic plasticity. For a long time NMDA receptors were thought to be the privileged domain of neurons; however, discoveries of the last 25 years have demonstrated their active role in glial cells as well. Despite the large number of studies in the field, there are many unresolved questions connected with NMDA receptors in glia that are still a matter of debate. The main objective of this review is to shed light on these controversies by summarizing results from all relevant works concerning astrocytes, oligodendrocytes and polydendrocytes (also known as NG2 glial cells) in experimental animals, further extended by studies performed on human glia. The results are divided according to the study approach to enable a better comparison of how findings obtained at the mRNA level correspond with protein expression or functionality. Furthermore, special attention is focused on the NMDA receptor subunits present in the particular glial cell types, which give them special characteristics different from those of neurons – for example, the absence of Mg²⁺ block and decreased Ca²⁺ permeability. Since glial cells are implicated in important physiological and pathophysiological roles in the central nervous system (CNS), the last part of this review provides an overview of glial NMDA receptors with respect to ischemic brain injury.

Oligodendroglia and neurotrophic factors in neurodegeneration

Myelination by oligodendroglial cells (OLs) enables the propagation of action potentials along neuronal axons, which is essential for rapid information flow in the central nervous system. Besides saltatory conduction, the myelin sheath also protects axons against inflammatory and oxidative insults. Loss of myelin results in axonal damage and ultimately neuronal loss in demyelinating disorders. However, accumulating evidence indicates that OLs also provide support to neurons via mechanisms beyond the insulating function of myelin. More importantly, an increasing volume of reports indicates defects of OLs in numerous neurodegenerative diseases, sometimes even preceding neuronal loss in pre-symptomatic episodes, suggesting that OL pathology may be an important mechanism contributing to the initiation and/or progression of neurodegeneration. This review focuses on the emerging picture of neuronal support by OLs in the pathogenesis of neurodegenerative disorders through diverse molecular and cellular mechanisms, including direct neuron-myelin interaction, metabolic support by OLs, and neurotrophic factors produced by and/or acting on OLs.

Overexpression of GRP78 protects glial cells from endoplasmic reticulum stress

Endoplasmic reticulum (ER) stress induces apoptotic cell death by causing the accumulation of structurally abnormal proteins. The 78-kDa glucose-regulated protein (GRP78) is an ER chaperone that regulates protein folding in the ER and has been suggested to contribute to cell survival. Using the rat C6 glioma cell line and flow cytometry, we assessed GRP78 expression following tunicamycin- and glutamate-induced ER stress. The results showed that GRP78 expression is upregulated following ER stress and has protective effects on injured glial cells. Annexin V and propidium iodide labeling revealed cells transiently expressing GRP78 prior to injury were protected against high-concentrations of tunicamycin and glutamate within 72 h. Our findings support the hypothesis that GRP78 inhibits cell death associated with ER stress.

Cellular changes underlying hyperoxia-induced delay of white matter development

Impaired neurological development in premature infants frequently arises from periventricular white matter injury (PWMI), a condition associated with myelination abnormalities. Recently, exposure to hyperoxia was reported to disrupt myelin formation in neonatal rats. To identify the causes of hyperoxia-induced PWMI, we characterized cellular changes in the white matter (WM) using neonatal wild-type 2-3-cyclic nucleotide 3-phosphodiesterase-enhanced green fluorescent protein (EGFP) and glial fibrillary acidic protein (GFAP)-EGFP transgenic mice exposed to 48 h of 80% oxygen from postnatal day 6 (P6) to P8. Myelin basic protein expression and CC1(+) oligodendroglia decreased after hyperoxia at P8, but returned to control levels during recovery between P12 and P15. At P8, hyperoxia caused apoptosis of NG2(+)O4(-) progenitor cells and reduced NG2(+) cell proliferation. This was followed by restoration of the NG2(+) cell population and increased oligodendrogenesis in the WM after recovery. Despite apparent cellular recovery, diffusion tensor imaging revealed WM deficiencies at P30 and P60. Hyperoxia did not affect survival or proliferation of astrocytes in vivo, but modified GFAP and glutamate-aspartate transporter expression. The rate of [(3)H]-d-aspartic acid uptake in WM tissue was also decreased at P8 and P12. Furthermore, cultured astrocytes exposed to hyperoxia showed a reduced capacity to protect oligodendrocyte progenitor cells against the toxic effects of exogenous glutamate. This effect was prevented by 2,3-dioxo-6-nitro-1,2,3,4-tetrahydrobenzo[f]quinoxaline-7-sulfonamide treatment. Our analysis reveals a role for altered glutamate homeostasis in hyperoxia-induced WM damage. Understanding the cellular dynamics and underlying mechanisms involved in hyperoxia-induced PWMI will allow for future targeted therapeutic intervention.

Selective adenosine A2A receptor agonists and antagonists protect against spinal cord injury through peripheral and central effects

BACKGROUND

Permanent functional deficits following spinal cord injury (SCI) arise both from mechanical injury and from secondary tissue reactions involving inflammation. Enhanced release of adenosine and glutamate soon after SCI represents a component in the sequelae that may be responsible for resulting functional deficits. The role of adenosine A2A receptor in central ischemia/trauma is still to be elucidated. In our previous studies we have demonstrated that the adenosine A2A receptor-selective agonist CGS21680, systemically administered after SCI, protects from tissue damage, locomotor dysfunction and different inflammatory readouts. In this work we studied the effect of the adenosine A2A receptor antagonist SCH58261, systemically administered after SCI, on the same parameters. We investigated the hypothesis that the main action mechanism of agonists and antagonists is at peripheral or central sites.

METHODS

Spinal trauma was induced by extradural compression of SC exposed via a four-level T5-T8 laminectomy in mouse. Three drug-dosing protocols were utilized: a short-term systemic administration by intraperitoneal injection, a chronic administration via osmotic minipump, and direct injection into the spinal cord.

RESULTS

SCH58261, systemically administered (0.01 mg/kg intraperitoneal. 1, 6 and 10 hours after SCI), reduced demyelination and levels of TNF-α, Fas-L, PAR, Bax expression and activation of JNK mitogen-activated protein kinase (MAPK) 24 hours after SCI. Chronic SCH58261 administration, by mini-osmotic pump delivery for 10 days, improved the neurological deficit up to 10 days after SCI. Adenosine A2A receptors are physiologically expressed in the spinal cord by astrocytes, microglia and oligodendrocytes. Soon after SCI (24 hours), these receptors showed enhanced expression in neurons. Both the A2A agonist and antagonist, administered intraperitoneally, reduced expression of the A2A receptor, ruling out the possibility that the neuroprotective effects of the A2A agonist are due to A2A receptor desensitization. When the A2A antagonist and agonist were centrally injected into injured SC, only SCH58261 appeared neuroprotective, while CGS21680 was ineffective.

CONCLUSIONS

Our results indicate that the A2A antagonist protects against SCI by acting on centrally located A2A receptors. It is likely that blockade of A2A receptors reduces excitotoxicity. In contrast, neuroprotection afforded by the A2A agonist may be primarily due to peripheral effects.

Effect of berberine and Berberis aetnensis C. Presl. alkaloid extract on glutamate-evoked tissue transglutaminase up-regulation in astroglial cell cultures

Berberis aetnensis C. Presl. is a bushy-spiny shrub common on Mount Etna (Sicily, Italy), containing various alkaloids with several pharmacological properties. This study assessed the effect of berberine and of the alkaloid extract of B. aetnensis roots on the glutamate-evoked tissue transglutaminase (TG2) up-regulation in rat astrocyte primary cultures, used as an in vitro model of excitotoxicity. The findings show that the alkaloid extract of B. aetnensis roots consists mainly of berberine. Furthermore, berberine and the alkaloid extract of B. aetnensis roots were able to restore the oxidative status modified by glutamate and the levels of TG2 to control values. It was found that berberine or the alkaloid extract of B. aetnensis roots are able to ameliorate the excessive production of glutamate, protein misfolding and aggregation, mitochondrial fragmentation, and neurodegeneration. Thus, it is suggested that berberine and the alkaloid extract of B. aetnensis roots, may represent a natural therapeutic strategy in the neuropathological conditions associated with excitotoxicity.

Effect of resveratrol on gliotransmitter levels and p38 activities in cultured astrocytes

Accumulating evidence suggests that resveratrol may have beneficial effects against traumatic brain injury. However, its effect on the regulation of extracellular levels of gliotransmitter and on the activation of p38 MAPK in astrocytes is still unknown. We have examined whether resveratrol regulates extracellular levels of gliotransmitter as well as the activation of p38 MAPK in cultured astrocytes before and after stretch injury. The extracellular levels of glutamate, D-/L-serine and D-serine were apparently reduced by 100 μM resveratrol in control astrocyte cultures. The dramatic increase of glutamate and D-serine release induced by stretch injury was also clearly inhibited by resveratrol. Resveratrol mediates this response by reduction of release through inhibition of extracellular calcium influx and increment of gliotransmitter uptake through enhancement of amino acid transporter expressed in the membrane of astrocyte. In addition, resveratrol definitely reduced the activation of p38 MAPK in cultured astrocytes following stretch injury. AMPA receptor is involved in the activation of p38 following injury. Conversely, the levels of glutamine and glycine were not obviously affected by resveratrol before and after injury. Intracellular levels of glutamate and D-serine are not apparently changed by stretch injury. Collectively, our data suggest that resveratrol might play an important role in protection of the nervous system after injury by decreasing the extracellular levels of gliotransmitter and inhibiting activation of p38 MAPK following injury.

Synthesis and resolution of cis-(+/-)-methyl (1R,2S/1S,2R)-2-[(4-hydroxy-4-phenylpiperidin-1-yl)methyl]-1-(4-methylphenyl)cyclopropanecarboxylate [(+/-)-PPCC)]: new sigma receptor ligands with neuroprotective effect

The enantiomers of cis-(+/-)-methyl (1R,2S/1S,2R)-2-[(4-hydroxy-4-phenylpiperidin-1-yl)methyl]-1-(4-methylphenyl)cyclopropanecarboxylate [1, (+/-)-PPCC], a selective sigma ligand, were synthesized. The (+)- and (-)-enantiomers bind predominantly to sigma(1) receptors and have a reduced sigma(2) affinity. Both individually restore the astroglial oxidative status modified by glutamate, counteracting also transglutaminase-2 overexpression. They exhibited in vivo anti-opioid effects on kappa opioid (KOP) receptor-mediated analgesia. Our findings demonstrate that the enantiomers display mainly sigma(1) agonist activity and that they have neuroprotective effects.