Glutamate-stimulated peroxynitrite production in a brain-derived endothelial cell line is dependent on N-methyl-D-aspartate (NMDA) receptor activation

The Emerging Role of N-Methyl-D-Aspartate (NMDA) Receptors in the Cardiovascular System: Physiological Implications, Pathological Consequences, and Therapeutic Perspectives

N-methyl-D-aspartate receptors (NMDARs) are ligand-gated ion channels that are activated by the neurotransmitter glutamate, mediate the slow component of excitatory neurotransmission in the central nervous system (CNS), and induce long-term changes in synaptic plasticity. NMDARs are non-selective cation channels that allow the influx of extracellular Na⁺ and Ca²⁺ and control cellular activity via both membrane depolarization and an increase in intracellular Ca²⁺ concentration. The distribution, structure, and role of neuronal NMDARs have been extensively investigated and it is now known that they also regulate crucial functions in the non-neuronal cellular component of the CNS, i.e., astrocytes and cerebrovascular endothelial cells. In addition, NMDARs are expressed in multiple peripheral organs, including heart and systemic and pulmonary circulations. Herein, we survey the most recent information available regarding the distribution and function of NMDARs within the cardiovascular system. We describe the involvement of NMDARs in the modulation of heart rate and cardiac rhythm, in the regulation of arterial blood pressure, in the regulation of cerebral blood flow, and in the blood-brain barrier (BBB) permeability. In parallel, we describe how enhanced NMDAR activity could promote ventricular arrhythmias, heart failure, pulmonary artery hypertension (PAH), and BBB dysfunction. Targeting NMDARs could represent an unexpected pharmacological strategy to reduce the growing burden of several life-threatening cardiovascular disorders.

Domino reaction of neurovascular unit in neuropathic pain after spinal cord injury

The mechanism of neuropathic pain after spinal cord injury is complex, and the communication between neurons, glia, and blood vessels in neurovascular units significantly affects the occurrence and development of neuropathic pain. After spinal cord injury, a domino chain reaction occurs in the neuron-glia-vessel, which affects the permeability of the blood-spinal cord barrier and jointly promotes the development of neuroinflammation. This article discusses the signal transduction between neuro-glial-endothelial networks from a multidimensional point of view and reviews its role in neuropathic pain after spinal cord injury.

Increased plasma glutamate in non-smokers with vasospastic angina pectoris is associated with plasma cystine and antioxidant capacity

Objectives. Endothelial dysfunction caused by oxidative stress plays an important role in the development of vasospastic angina pectoris (VSAP). Glutamate causes endothelial dysfunction by generating oxidative stress, and it inhibits cystine import into endothelial cells via the cystine/glutamate antiporter (X_C^-), which leads to depletion of antioxidant glutathione. However, whether glutamate and cystine are implicated in the pathogenesis of VSAP remains unclear. We investigated plasma glutamate and cystine levels, oxidative stress markers and antioxidant capacity in non-smoker patients with VSAP to determine whether glutamate and cystine are associated with the development of VSAP. We assessed 49 non-smokers assigned to groups with (n = 27) and without (n = 22) VSAP, and also measured plasma glutamate, cystine, nitrotyrosine, reactive oxygen metabolites and biological antioxidant potential. Results. Plasma glutamate and cystine values were significantly higher in the group with, than without VSAP (59.8 ± 25.7 vs. 43.5 ± 18.7 µmol/L, p = .016 and 35.3 ± 14.2 vs. 25.2 ± 9.1 µmol/L, p = .0056, respectively). Plasma glutamate and cystine values were significantly and positively associated (r = 0.32, p = .027). Levels of the oxidative stress markers nitrotyrosine and reactive oxygen metabolites, and biological antioxidant potential of as a measure of antioxidant capacity, did not significantly differ between the two groups. However, glutamate and biological antioxidant potential values were significantly and negatively associated (r = -0.3, p = .036). Conclusion. Plasma glutamate levels were increased in patients with VSAP who did not smoke, and they were positively associated with plasma cystine and negatively associated with the biological antioxidant potential levels.

The Amino Acid-mTORC1 Pathway Mediates APEC TW-XM-Induced Inflammation in bEnd.3 Cells

The blood-brain barrier (BBB) is key to establishing and maintaining homeostasis in the central nervous system (CNS); meningitis bacterial infection can disrupt the integrity of BBB by inducing an inflammatory response. The changes in the cerebral uptake of amino acids may contribute to inflammatory response during infection and were accompanied by high expression of amino acid transporters leading to increased amino acid uptake. However, it is unclear whether amino acid uptake is changed and how to affect inflammatory responses in mouse brain microvascular endothelial (bEnd.3) cells in response to Avian Pathogenic Escherichia coli TW-XM (APEC XM) infection. Here, we firstly found that APEC XM infection could induce serine (Ser) and glutamate (Glu) transport from extracellular into intracellular in bEnd.3 cells. Meanwhile, we also shown that the expression sodium-dependent neutral amino acid transporter 2 (SNAT2) for Ser and excitatory amino acid transporter 4 (EAAT4) for Glu was also significantly elevated during infection. Then, in amino acid deficiency or supplementation medium, we found that Ser or Glu transport were involving in increasing SNAT2 or EAAT4 expression, mTORC1 (mechanistic target of rapamycin complex 1) activation and inflammation, respectively. Of note, Ser or Glu transport were inhibited after SNAT2 silencing or EAAT4 silencing, resulting in inhibition of mTORC1 pathway activation, and inflammation compared with the APEC XM infection group. Moreover, pEGFP-SNAT2 overexpression and pEGFP-EAAT4 overexpression in bEnd.3 cells all could promote amino acid uptake, activation of the mTORC1 pathway and inflammation during infection. We further found mTORC1 silencing could inhibit inflammation, the expression of SNAT2 and EAAT4, and amino acid uptake. Taken together, our results demonstrated that APEC TW-XM infection can induce Ser or Glu uptake depending on amino acid transporters transportation, and then activate amino acid-mTORC1 pathway to induce inflammation in bEnd.3 cells.

Anti-NR2 glutamate receptor antibodies as an early biomarker of cerebral small vessel disease

OBJECTIVES

Cerebral small vessel disease (SVD) associated with age and vascular risk factors is one of the leading causes of cognitive disorders as well as ischemic and hemorrhagic strokes. The pathogenesis of this disease has not been fully understood yet. The previously established association of the antibodies against the NR2 subunit of the NMDA receptor (NR2ab) with the mechanisms of SVD such as ischemia and blood-brain barrier (BBB) disruption, might suggest their importance in the brain damage.

DESIGN & METHODS

We studied the NR2ab serum level in 70 patients (45 females, 61.1 ± 6.3 y.o.) with different severity of cognitive impairment and MRI features of SVD and 20 healthy volunteers (12 females, 58.5 ± 6.4 y.o.).

RESULTS

The elevated level of NR2ab was associated with subjective cognitive impairment (SCI) (p = 0.028) and mild cognitive impairment (MCI) (p = 0.017), Fazekas grade (F) 2 (p = 0,002) and F3 (p = 0,009) of white matter hyperintensities (WMH) and the numbers of lacunes in the cerebral white matter (less than 5) (p = 0,039).

CONCLUSION

The detected increase in serum NR2ab level in patients with SCI, as well as the minimal amount of white matter lacunes, is most likely caused by hypoxia-induced endothelial damage in the early stage of SVD. Normal NR2ab values in patients with F1 WMH, the increased NR2ab level in patients with F2 and F3 WMH and those with the minimal number of lacunes can indicate that NR2bs are involved in diffuse brain damage due to hypoxia-induced loss of BBB integrity.

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.

Circulating tPA contributes to neurovascular coupling by a mechanism involving the endothelial NMDA receptors

The increase of cerebral blood flow evoked by neuronal activity is essential to ensure enough energy supply to the brain. In the neurovascular unit, endothelial cells are ideally placed to regulate key neurovascular functions of the brain. Nevertheless, some outstanding questions remain about their exact role neurovascular coupling (NVC). Here, we postulated that the tissue-type plasminogen activator (tPA) present in the circulation might contribute to NVC by a mechanism dependent of its interaction with endothelial N-Methyl-D-Aspartate Receptor (NMDAR). To address this question, we used pharmacological and genetic approaches to interfere with vascular tPA-dependent NMDAR signaling, combined with laser speckle flowmetry, intravital microscopy and ultrafast functional ultrasound in vivo imaging. We found that the tPA present in the blood circulation is capable of potentiating the cerebral blood flow increase induced by the activation of the mouse somatosensorial cortex, and that this effect is mediated by a tPA-dependent activation of NMDAR expressed at the luminal part of endothelial cells of arteries. Although blood molecules, such as acetylcholine, bradykinin or ATP are known to regulate vascular tone and induce vessel dilation, our present data provide the first evidence that circulating tPA is capable of influencing neurovascular coupling (NVC).

Simvastatin, edaravone and dexamethasone protect against kainate-induced brain endothelial cell damage

BACKGROUND

Excitotoxicity is a central pathological pathway in many neurological diseases with blood-brain barrier (BBB) dysfunction. Kainate, an exogenous excitotoxin, induces epilepsy and BBB damage in animal models, but the direct effect of kainate on brain endothelial cells has not been studied in detail. Our aim was to examine the direct effects of kainate on cultured cells of the BBB and to test three anti-inflammatory and antioxidant drugs used in clinical practice, simvastatin, edaravone and dexamethasone, to protect against kainate-induced changes.

METHODS

Primary rat brain endothelial cell, pericyte and astroglia cultures were used to study cell viability by impedance measurement. BBB permeability was measured on a model made from the co-culture of the three cell types. The production of nitrogen monoxide and reactive oxygen species was followed by fluorescent probes. The mRNA expression of kainate receptors and nitric oxide synthases were studied by PCR.

RESULTS

Kainate damaged brain endothelial cells and made the immunostaining of junctional proteins claudin-5 and zonula occludens-1 discontinuous at the cell border indicating the opening of the barrier. The permeability of the BBB model for marker molecules fluorescein and albumin and the production of nitric oxide in brain endothelial cells were increased by kainate. Simvastatin, edaravone and dexamethasone protected against the reduced cell viability, increased permeability and the morphological changes in cellular junctions caused by kainate. Dexamethasone attenuated the elevated nitric oxide production and decreased the inducible nitric oxide synthase (NOS2/iNOS) mRNA expression increased by kainate treatment.

CONCLUSION

Kainate directly damaged cultured brain endothelial cells. Simvastatin, edaravone and dexamethasone protected the BBB model against kainate-induced changes. Our results confirmed the potential clinical usefulness of these drugs to attenuate BBB damage.

VEGFD Protects Retinal Ganglion Cells and, consequently, Capillaries against Excitotoxic Injury

In the central nervous system, neurons and the vasculature influence each other. While it is well described that a functional vascular system is trophic to neurons and that vascular damage contributes to neurodegeneration, the opposite scenario in which neural damage might impact the microvasculature is less defined. In this study, using an in vivo excitotoxic approach in adult mice as a tool to cause specific damage to retinal ganglion cells, we detected subsequent damage to endothelial cells in retinal capillaries. Furthermore, we detected decreased expression of vascular endothelial growth factor D (VEGFD) in retinal ganglion cells. In vivo VEGFD supplementation via neuronal-specific viral-mediated expression or acute intravitreal delivery of the mature protein preserved the structural and functional integrity of retinal ganglion cells against excitotoxicity and, additionally, spared endothelial cells from degeneration. Viral-mediated suppression of expression of the VEGFD-binding receptor VEGFR3 in retinal ganglion cells revealed that VEGFD exerts its protective capacity directly on retinal ganglion cells, while protection of endothelial cells is the result of upheld neuronal integrity. These findings suggest that VEGFD supplementation might be a novel, clinically applicable approach for neuronal and vascular protection.

Astrocyte-Derived Paracrine Signals: Relevance for Neurogenic Niche Regulation and Blood-Brain Barrier Integrity

Astrocytes are essential for proper regulation of the central nervous system (CNS). Importantly, these cells are highly secretory in nature. Indeed they can release hundreds of molecules which play pivotal physiological roles in nervous tissues and whose abnormal regulation has been associated with several CNS disorders. In agreement with these findings, recent studies have provided exciting insights into the key contribution of astrocyte-derived signals in the pleiotropic functions of these cells in brain health and diseases. In the future, deeper analysis of the astrocyte secretome is likely to further increase our current knowledge on the full potential of these cells and their secreted molecules not only as active participants in pathophysiological events, but as pharmacological targets or even as therapeutics for neurological and psychiatric diseases. Herein we will highlight recent findings in our and other laboratories on selected molecules that are actively secreted by astrocytes and contribute in two distinct functions with pathophysiological relevance for the astroglial population: i) regulation of neural stem cells (NSCs) and their progeny within adult neurogenic niches; ii) modulation of the blood–brain barrier (BBB) integrity and function.

The Concentration of Memantine in the Cerebrospinal Fluid of Alzheimer's Disease Patients and Its Consequence to Oxidative Stress Biomarkers

Memantine is a noncompetitive N-methyl-d-aspartate (NMDA) receptor antagonist utilized as a palliative cure for Alzheimer’s disease. This is the second study examining the memantine concentrations in cerebrospinal fluid. The previously published study enrolled six patients, and three of them were theoretically in a steady state. In our study, we enrolled 22 patients who regularly used a standard therapeutic dose of memantine (20 mg/day, oral administration) before the sample collection. Patients were divided into four groups, according to the time of plasma and cerebrospinal fluid collection: 6, 12, 18, and 24 h after memantine administration. The cerebrospinal fluid samples were also assessed for selected oxidative stress parameters (malondialdehyde, 3-nitrotyrosine, glutathione, non-protein thiols, and non-protein disulfides). The plasma/cerebrospinal fluid (CSF) ratio for all time intervals were within the range of 45.89% (6 h) to 55.60% (18 h), which corresponds with previously published findings in most patients. The other aim of our study was to deduce whether the achieved “real” memantine concentration in the central compartment was sufficient to block NMDA receptors. The IC₅₀ value of memantine as an NMDA antagonist is in micromolar range; the lowest limit is 112 ng/ml (GluN2C), and this value was achieved only in three cases. The memantine cerebrospinal fluid concentration did not reach one quarter of the IC₅₀ value in five cases (one patient was excluded for noncompliance); therefore, the potency of memantine as a therapeutic effect in patients may be questionable. However, it appears that memantine therapy positively affected the levels of some oxidative stress parameters, especially non-protein thiols and 3-nitrotyrosine.

Astrocytes drive cortical vasodilatory signaling by activating endothelial NMDA receptors

Astrocytes express neurotransmitter receptors that serve as sensors of synaptic activity and initiate signals leading to activity-dependent local vasodilation and increases in blood flow. We previously showed that arteriolar vasodilation produced by activation of cortical astrocytes is dependent on endothelial nitric oxide synthase (eNOS) and endogenous agonists of N-methyl-D-aspartate (NMDA) receptors. Here, we tested the hypothesis that these effects are mediated by NMDA receptors expressed by brain endothelial cells. Primary endothelial cultures expressed NMDA receptor subunits and produced nitric oxide in response to co-agonists, glutamate and D-serine. In cerebral cortex in situ, immunoelectron microscopy revealed that endothelial cells express the GluN1 NMDA receptor subunit at basolateral membrane surfaces in an orientation suitable for receiving intercellular messengers from brain cells. In cortical slices, activation of astrocytes by two-photon flash photolysis of a caged Ca²⁺ compound or application of a metabotropic glutamate receptor agonist caused endothelial NO generation and local vasodilation. These effects were mitigated by NMDA receptor antagonists and conditional gene silencing of endothelial GluN1, indicating at least partial dependence on endothelial NMDA receptors. Our observations identify a novel astrocyte-endothelial vasodilatory signaling axis that could contribute to endothelium-dependent vasodilation in brain functional hyperemia.

Gliotransmitters and cytokines in the control of blood-brain barrier permeability

The contribution of astrocytes and microglia to the regulation of neuroplasticity or neurovascular unit (NVU) is based on the coordinated secretion of gliotransmitters and cytokines and the release and uptake of metabolites. Blood-brain barrier (BBB) integrity and angiogenesis are influenced by perivascular cells contacting with the abluminal side of brain microvessel endothelial cells (pericytes, astrocytes) or by immune cells existing (microglia) or invading the NVU (macrophages) under pathologic conditions. The release of gliotransmitters or cytokines by activated astroglial and microglial cells is provided by distinct mechanisms, affects intercellular communication, and results in the establishment of microenvironment controlling BBB permeability and neuroinflammation. Glial glutamate transporters and connexin and pannexin hemichannels working in the tight functional coupling with the purinergic system serve as promising molecular targets for manipulating the intercellular communications that control BBB permeability in brain pathologies associated with excessive angiogenesis, cerebrovascular remodeling, and BBB-mediated neuroinflammation. Substantial progress in deciphering the molecular mechanisms underlying the (patho)physiology of perivascular glia provides promising approaches to novel clinically relevant therapies for brain disorders. The present review summarizes the current understandings on the secretory machinery expressed in glial cells (glutamate transporters, connexin and pannexin hemichannels, exocytosis mechanisms, membrane-derived microvesicles, and inflammasomes) and the role of secreted gliotransmitters and cytokines in the regulation of NVU and BBB permeability in (patho)physiologic conditions.

A Two-Photon Fluorescent Probe for Imaging Endogenous ONOO- near NMDA Receptors in Neuronal Cells and Hippocampal Tissues

In this study, we developed a two-photon fluorescent probe for detection of peroxynitrite (ONOO^-) near the N-methyl-d-aspartate (NMDA) receptor. This naphthalimide-based probe contains a boronic acid reactive group and an ifenprodil-like tail, which serves as an NMDA receptor targeting unit. The probe displays high sensitivity and selectivity, along with a fast response time in aqueous solution. More importantly, the probe can be employed along with two-photon fluorescence microscopy to detect endogenous ONOO^- near NMDA receptors in neuronal cells as well as in hippocampal tissues. The results suggest that the probe has the potential of serving as a useful imaging tool for studying ONOO^- related diseases in the nervous system.

Conventional and electronic cigarettes dysregulate the expression of iron transporters and detoxifying enzymes at the brain vascular endothelium: In vivo evidence of a gender-specific cellular response to chronic cigarette smoke exposure

It is well established that tobacco smoking is associated with vascular endothelial dysfunction in a causative and dose dependent manner primarily related to the tobacco smoke (TS) content of reactive oxygen species (ROS), nicotine, and oxidative stress (OS) -driven inflammation. Preclinical studies have also shown that nicotine (the principal e-liquid's ingredient used in e-cigarettes (e-Cigs) can also cause OS, exacerbation of cerebral ischemia and secondary brain injury. Likewise, chronic e-Cig vaping could be prodromal to vascular endothelial dysfunctions. Herein, we provide direct evidence that similarly to TS, e-Cig promotes mitochondrial depolarization in primary brain vascular endothelial cells as well as the vascular endothelial cell line bEnd3. In addition, both TS and e-Cig exposure upregulated the transmembrane iron exporter Slc40a1 (crucial to maintain cellular iron and redox homeostasis) and that of porphyrin importer Abcb6 (linked to accelerated atherosclerosis). We then investigated in vivo whether gender plays a role in how chronic TS affect vascular endothelial functions. Our results clearly show chronic TS exposure differentially impacts the expression levels of Phase-II enzymes as well as the iron transporters previously investigated in vitro. Although the physiological implications of the gender-specific differential responses to TS are not fully clear, they do demonstrate that gender is a risk factor that needs to be investigated when assessing the potential impact of chronic smoking and perhaps e-Cig vaping.

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.

Mechanisms of glutamate toxicity in multiple sclerosis: biomarker and therapeutic opportunities

Research advances support the idea that excessive activation of the glutamatergic pathway plays an important part in the pathophysiology of multiple sclerosis. Beyond the well established direct toxic effects on neurons, additional sites of glutamate-induced cell damage have been described, including effects in oligodendrocytes, astrocytes, endothelial cells, and immune cells. Such toxic effects could provide a link between various pathological aspects of multiple sclerosis, such as axonal damage, oligodendrocyte cell death, demyelination, autoimmunity, and blood-brain barrier dysfunction. Understanding of the mechanisms underlying glutamate toxicity in multiple sclerosis could help in the development of new approaches for diagnosis, treatment, and follow-up in patients with this debilitating disease. While several clinical trials of glutamatergic modulators have had disappointing results, our growing understanding suggests that there is reason to remain optimistic about the therapeutic potential of these drugs.

Neuroendothelial NMDA receptors as therapeutic targets in experimental autoimmune encephalomyelitis

Multiple sclerosis is among the most common causes of neurological disability in young adults. Here we provide the preclinical proof of concept of the benefit of a novel strategy of treatment for multiple sclerosis targeting neuroendothelial N-methyl-D-aspartate glutamate receptors. We designed a monoclonal antibody against N-methyl-D-aspartate receptors, which targets a regulatory site of the GluN1 subunit of N-methyl-D-aspartate receptor sensitive to the protease tissue plasminogen activator. This antibody reverted the effect of tissue plasminogen activator on N-methyl-D-aspartate receptor function without affecting basal N-methyl-D-aspartate receptor activity (n = 21, P < 0.01). This antibody bound N-methyl-D-aspartate receptors on the luminal surface of neurovascular endothelium in human tissues and in mouse, at the vicinity of tight junctions of the blood-spinal cord barrier. Noteworthy, it reduced human leucocyte transmigration in an in vitro model of the blood-brain barrier (n = 12, P < 0.05). When injected during the effector phase of MOG-induced experimental autoimmune encephalomyelitis (n = 24), it blocked the progression of neurological impairments, reducing cumulative clinical score (P < 0.001) and mean peak score (P < 0.001). This effect was observed in wild-type animals but not in tissue plasminogen activator knock-out animals (n = 10). This therapeutic effect was associated to a preservation of the blood-spinal cord barrier (n = 6, P < 0.001), leading to reduced leucocyte infiltration (n = 6, P < 0.001). Overall, this study unveils a critical function of endothelial N-methyl-D-aspartate receptor in multiple sclerosis, and highlights the therapeutic potential of strategies targeting the protease-regulated site of N-methyl-D-aspartate receptor.

In Vitro Study of L-Glutamate and L-Glutamine Transport in Retinal Pericytes: Involvement of Excitatory Amino Acid Transporter 1 and Alanine-Serine-Cysteine Transporter 2

L-Glutamate (L-Glu) is known to be a relaxant of pericytes and to induce changes in microcirculatory hemodynamics. Since the concentration of L-Glu which induces the dilation of retinal capillaries is reported to be high compared with the estimated concentration in the retinal interstitial fluid, it is hypothesized that some systems involving concentrative L-Glu release are present in retinal pericytes. The purpose of this study was to investigate the existence of L-Glu-storing systems, which contribute to autocrine L-Glu release, in retinal pericytes using conditionally immortalized rat retinal pericytes (TR-rPCT1 cells), which express mRNAs of L-Glu-synthesizing enzymes from L-glutamine (L-Gln). TR-rPCT1 cells express the mRNAs of vesicular L-Glu transporter 1 (VGLUT1), indicating that L-Glu in the cytoplasm is taken up into VGLUT1-expressing vesicles of retinal pericytes. L-Glu and L-Gln are taken up into TR-rPCT1 cells via Na(+)-dependent saturable process(es) with a Km value of 22.4 µM and 163 µM, respectively. The [(3)H]L-Glu uptake was inhibited by ca. 50% in the presence of D-aspartate, a substrate of excitatory amino acid transporter (EAAT) subtypes, whereas substrates of alanine-serine-cysteine transporter (ASCT) subtypes exhibited only a weak inhibitory effect on [(3)H]L-Glu uptake compared with D-aspartate. Regarding the L-Gln uptake by TR-rPCT1 cells, the inhibitory effect of ASCT substrates on the [(3)H]L-Gln uptake was stronger than that of substrates of other neutral amino acid transport systems. Consequently, it was determined that EAAT1 and ASCT2 play a role in the transport of L-Glu and L-Gln, respectively, from retinal interstitial fluid to the cytoplasm of retinal pericytes.

The plasminogen activation system in neuroinflammation

The plasminogen activation (PA) system consists in a group of proteases and protease inhibitors regulating the activation of the zymogen plasminogen into its proteolytically active form, plasmin. Here, we give an update of the current knowledge about the role of the PA system on different aspects of neuroinflammation. These include modification in blood-brain barrier integrity, leukocyte diapedesis, removal of fibrin deposits in nervous tissues, microglial activation and neutrophil functions. Furthermore, we focus on the molecular mechanisms (some of them independent of plasmin generation and even of proteolysis) and target receptors responsible for these effects. The description of these mechanisms of action may help designing new therapeutic strategies targeting the expression, activity and molecular mediators of the PA system in neurological disorders involving neuroinflammatory processes. This article is part of a Special Issue entitled: Neuro Inflammation edited by Helga E. de Vries and Markus Schwaninger.

The Neuroprotective Effect of Lithium in cannabinoid Dependence is Mediated through Modulation of Cyclic AMP, ERK1/2 and GSK-3β Phosphorylation in Cerebellar Granular Neurons of Rat

Lithium (Li), a glycogen synthase kinase-3β (GSK-3β) inhibitor, has used to attenuate the cannabinoid-induced dependence/withdrawal signs, but molecular mechanisms related to this are unclear. Recent studies indicate the involvement of upstream extracellular signal kinase1/2 (ERK1/2) and downstream GSK-3β pathways in the development of cannabinoid-induced dependence. This is mediated through cannabinoid receptor 1 (CB1) enriched in cerebellar granular neurons (CGNs). Accordingly, the present study aimed to investigate the mechanism of modulatory/neuroprotective effects of Li on a cannabinoid agonist (WIN 55,212-2 (WIN))-induced dependence, through quantitative analysis of some involved proteins such as ERK1/2, GSK-3β and related signaling pathways including their phosphorylated forms; and cAMP level as the other molecular mechanisms leading to dependence, in CGNs model. The CGNs were prepared from 7-day-old Wistar rat pup in a 12-well plate, pretreated with Li (1mM) and an ERK1/2 inhibitor SL327 (SL, 10 µM). The WIN (1 µM) was added 30 minutes prior to treatment and AM251 (AM, 1 µM), as a cannabinoid antagonist was co-treated with WIN. The cAMP level, as an indicator of cannabinoid-induced dependence, was measured by ELISA following forskolin (FSK) stimulation. Western blot analyses determined the phosphorylated forms of ERK1/2 (p-ERK1/2), GSK-3β (p-GSK-3β) as well as their total expressions in various treatment times and doses in CGNs. WIN alone could down regulate the cAMP/p-ERK1/2 cascade compared to AM treatment. However, P-GSK-3β was up-regulated with Li and WIN or with SL and Li pretreatment to AM-induced cellular response, which was the highest 60 minutes after CGNs exposure. Results further suggested the potential role of Li pretreatment to diminish the development of cannabinoid-induced dependence/neuronal injury through possible mechanisms of modulating the cAMP/p-ERK1/2 cascade independent of p-GSK-3β signaling pathway in-vitro.

Memantine alleviates brain injury and neurobehavioral deficits after experimental subarachnoid hemorrhage

Subarachnoid hemorrhage (SAH) causes brain injury via glutamate excitotoxicity, which leads to an excessive Ca(2+) influx and this starts an apoptotic cascade. Memantine has been proven to reduce brain injury in several types of brain insults. This study investigated the neuro-protective potential of memantine after SAH and explored the underlying mechanisms. An endovascular perforation rat model of SAH was used and Sprague-Dawley rats were randomized into sham surgery, SAH + vehicle, and SAH + memantine groups. The effects of memantine on SAH were evaluated by assessing the neuro-behavioral functions, blood-brain barrier (BBB) permeability and neuronal cell preservation. The mechanisms of action of memantine, with its N-methyl-D-aspartate (NMDA) antagonistic characteristics on nitric oxide synthase (NOS) expression and peroxynitrite formation, were also investigated. The apoptotic cascade after SAH was suppressed by memantine. Neuronal NOS (nNOS) expression, peroxynitrite formation, and subsequent oxidative/nitrosative stress were also reduced. Memantine effectively preserved BBB integrity, rescued neuronal injury, and improved neurological outcome in experimental SAH. Memantine has neuro-protective potential in experimental SAH and may help combat SAH-induced brain damage in the future.

Blood-brain barrier disruption induced by hemoglobin in vivo: Involvement of up-regulation of nitric oxide synthase and peroxynitrite formation

Accumulating evidence has demonstrated that up-regulation of nitric oxide synthase (NOS) and subsequent peroxynitrite (ONOO(-)) formation exert a devastating effect on the damage of BBB in multiple diseases. However, considerably less attention has been focused on the role of NOS/ONOO(-) in BBB disruption after intracerebral hemorrhage (ICH). Using an experimental stroke model by injecting hemoglobin (Hb) into the caudate nucleus of male Sprague Dawley rats, we explored the role of NOS/ONOO(-) in BBB disruption after ICH. Brain edema content, behavioral changes, alterations of TJ proteins (claudin-5 and ZO-1), expression of neuronal NOS (nNOS), inducible NOS (iNOS) and endothelial NOS (eNOS), formation of 3-nitrotyrosine (3-NT), as well as NO production were investigated. Hb in the rat brain led to a significant brain edema production and neurological deficits. Overexpressed NOS was concomitant with large quantities of 3-NT formation. Moreover, sites of enhanced nNOS, iNOS, eNOS and 3-NT immunoreactivity were colocalized with diminished or discontinuous ZO-1 and/or claudin-5 staining as evidenced by Western blot and immunofluorescence, indicating the involvement of NOS and ONOO(-) in the BBB disruption. Meaningfully, levels of 3-NT in serum, which had a similar tendency with that of in brain tissues (r=0.934, P<0.001), had a marked correlation with brain edema content (r=0.782, P<0.001) and neurological deficits (r=0.851, P<0.001). We concluded that ONOO(-) formation by the upregulation of NOS may play a central role in promoting the BBB damage following ICH. Moreover, ONOO(-) may be a promising biomarker for the judgment or prediction of brain injury and clinical prognosis after ICH.

Inhibition of NR2B-Containing N-methyl-D-Aspartate Receptors (NMDARs) in Experimental Autoimmune Encephalomyelitis, a Model of Multiple Sclerosis

Neurodegeneration is the pathophysiological basis for permanent neurological disabilities in multiple sclerosis (MS); thus neuroprotection is emerging as a therapeutic approach in MS research. Modulation of excitotoxicity by inhibition of NMDARs has been suggested for neuroprotection, but selective antagonisation of the NR2B subtype of these receptors, a subtype believed to play a more pivotal role in neurodegeneration, has not been tested in MS. In this study inhibition of NR2B-containing NMDAR was evaluated on the animal model of MS, experimental autoimmune encephalomyelitis (EAE). EAE induction was done using MOG in C57BL/6 mice. Therapeutic administration of different doses of highly selective NR2B-containing NMDAR inhibitor (RO25-6981) was compared with memantine (non-selective NMDAR antagonist) and vehicle. Neurological deficits in EAE animals were more efficiently decreased by selective inhibition of NR2B-containing NMDARs. Histological studies of the spinal cords also showed decreased inflammation, myelin degradation and neuro-axonal degeneration when RO25-6981was administered with higher doses. The effects were dose dependent. Regarding the role of NR2B-containing NMDARs in excitotoxicity, selective inhibition of these receptor subtypes seems to modulate the neurological disabilities and pathological changes in EAE. Further elucidation of the exact mechanism of action as well as more experimental studies can suggest NR2B-containing NMDAR inhibition as a potentially effective treatment strategy for slowing down the clinical deterioration of disability in MS.

Neurovascular unit dysfunction with blood-brain barrier hyperpermeability contributes to major depressive disorder: a review of clinical and experimental evidence

About one-third of people with major depressive disorder (MDD) fail at least two antidepressant drug trials at 1 year. Together with clinical and experimental evidence indicating that the pathophysiology of MDD is multifactorial, this observation underscores the importance of elucidating mechanisms beyond monoaminergic dysregulation that can contribute to the genesis and persistence of MDD. Oxidative stress and neuroinflammation are mechanistically linked to the presence of neurovascular dysfunction with blood-brain barrier (BBB) hyperpermeability in selected neurological disorders, such as stroke, epilepsy, multiple sclerosis, traumatic brain injury, and Alzheimer’s disease. In contrast to other major psychiatric disorders, MDD is frequently comorbid with such neurological disorders and constitutes an independent risk factor for morbidity and mortality in disorders characterized by vascular endothelial dysfunction (cardiovascular disease and diabetes mellitus). Oxidative stress and neuroinflammation are implicated in the neurobiology of MDD. More recent evidence links neurovascular dysfunction with BBB hyperpermeability to MDD without neurological comorbidity. We review this emerging literature and present a theoretical integration between these abnormalities to those involving oxidative stress and neuroinflammation in MDD. We discuss our hypothesis that alterations in endothelial nitric oxide levels and endothelial nitric oxide synthase uncoupling are central mechanistic links in this regard. Understanding the contribution of neurovascular dysfunction with BBB hyperpermeability to the pathophysiology of MDD may help to identify novel therapeutic and preventative approaches.

Endothelial calcium dynamics, connexin channels and blood-brain barrier function

Situated between the circulation and the brain, the blood-brain barrier (BBB) protects the brain from circulating toxins while securing a specialized environment for neuro-glial signaling. BBB capillary endothelial cells exhibit low transcytotic activity and a tight, junctional network that, aided by the cytoskeleton, restricts paracellular permeability. The latter is subject of extensive research as it relates to neuropathology, edema and inflammation. A key determinant in regulating paracellular permeability is the endothelial cytoplasmic Ca(2+) concentration ([Ca(2+)]i) that affects junctional and cytoskeletal proteins. Ca(2+) signals are not one-time events restricted to a single cell but often appear as oscillatory [Ca(2+)]i changes that may propagate between cells as intercellular Ca(2+) waves. The effect of Ca(2+) oscillations/waves on BBB function is largely unknown and we here review current evidence on how [Ca(2+)]i dynamics influence BBB permeability.

Brain-reactive antibodies and disease

Autoimmune diseases currently affect 5-7% of the world's population; in most diseases there are circulating autoantibodies. Brain-reactive antibodies are present in approximately 2-3% of the general population but do not usually contribute to brain pathology. These antibodies penetrate brain tissue only early in development or under pathologic conditions. This restriction on their pathogenicity and the lack of correlation between serum titers and brain pathology have, no doubt, contributed to a delayed appreciation of the contribution of autoantibodies in diseases of the central nervous system. Nonetheless, it is increasingly clear that antibodies can cause damage in the brain and likely initiate or aggravate multiple neurologic conditions; brain-reactive antibodies contribute to symptomatology in autoimmune disease, infectious disease, and malignancy.

Prenatal alcohol exposure affects vasculature development in the neonatal brain

OBJECTIVE

In humans, antenatal alcohol exposure elicits various developmental disorders, in particular in the brain. Numerous studies focus on the deleterious effects of alcohol on neural cells. Although recent studies suggest that alcohol can affect angiogenesis in adults, the impact of prenatal alcohol exposure on brain microvasculature remains poorly understood.

METHODS

We used a mouse model to investigate effects of prenatal alcohol exposure on the cortical microvascular network in vivo and ex vivo and the action of alcohol, glutamate, and vascular endothelial growth factor A (VEGF) on activity, plasticity, and survival of microvessels. We used quantitative reverse transcriptase polymerase chain reaction, Western blot, immunohistochemistry, calcimetry, and videomicroscopy. We characterized the effect of prenatal alcohol exposure on the cortical microvascular network in human controls and fetal alcohol syndrome (FAS)/partial FAS (pFAS) patients at different developmental stages.

RESULTS

In mice, prenatal alcohol exposure induced a reduction of cortical vascular density, loss of the radial orientation of microvessels, and altered expression of VEGF receptors. Time-lapse experiments performed on brain slices revealed that ethanol inhibited glutamate-induced calcium mobilization in endothelial cells, affected plasticity, and promoted death of microvessels. These effects were prevented by VEGF. In humans, we evidenced a stage-dependent alteration of the vascular network in the cortices of fetuses with pFAS/FAS. Whereas no modification was observed from gestational week 20 (WG20) to WG22, the radial organization of cortical microvessels was clearly altered in pFAS/FAS patients from WG30 to WG38.

INTERPRETATION

Prenatal alcohol exposure affects cortical angiogenesis both in mice and in pFAS/FAS patients, suggesting that vascular defects contribute to alcohol-induced brain abnormalities.

Drug delivery to the brain in Alzheimer's disease: consideration of the blood-brain barrier

The successful treatment of Alzheimer's disease (AD) will require drugs that can negotiate the blood-brain barrier (BBB). However, the BBB is not simply a physical barrier, but a complex interface that is in intimate communication with the rest of the central nervous system (CNS) and influenced by peripheral tissues. This review examines three aspects of the BBB in AD. First, it considers how the BBB may be contributing to the onset and progression of AD. In this regard, the BBB itself is a therapeutic target in the treatment of AD. Second, it examines how the BBB restricts drugs that might otherwise be useful in the treatment of AD and examines strategies being developed to deliver drugs to the CNS for the treatment of AD. Third, it considers how drug penetration across the AD BBB may differ from the BBB of normal aging. In this case, those differences can complicate the treatment of CNS diseases such as depression, delirium, psychoses, and pain control in the AD population.

Coactivation of NMDA receptors by glutamate and D-serine induces dilation of isolated middle cerebral arteries

N-methyl-D-aspartate (NMDA) receptors are glutamate-gated cation channels that mediate excitatory neurotransmission in the central nervous system. In addition to glutamate, NMDA receptors are also activated by coagonist binding of the gliotransmitter, D-serine. Neuronal NMDA receptors mediate activity-dependent blood flow regulation in the brain. Our objective was to determine whether NMDA receptors expressed by brain endothelial cells can induce vasodilation of isolated brain arteries. Adult mouse middle cerebral arteries (MCAs) were isolated, pressurized, and preconstricted with norepinephrine. N-methyl-D-aspartate receptor agonists, glutamate and NMDA, significantly dilated MCAs in a concentration-dependent manner in the presence of D-serine but not alone. Dilation was significantly inhibited by NMDA receptor antagonists, D-2-amino-5-phosphonopentanoate and 5,7-dichlorokynurenic acid, indicating a response dependent on NMDA receptor glutamate and D-serine binding sites, respectively. Vasodilation was inhibited by denuding the endothelium and by selective inhibition or genetic knockout of endothelial nitric oxide synthase (eNOS). We also found evidence for expression of the pan-NMDA receptor subunit, NR1, in mouse primary brain endothelial cells, and for the NMDA receptor subunit NR2C in cortical arteries in situ. Overall, we conclude that NMDA receptor coactivation by glutamate and D-serine increases lumen diameter in pressurized MCA in an endothelial and eNOS-dependent mechanism.

Metabotropic glutamate receptor 5 mediates phosphorylation of vascular endothelial cadherin and nuclear localization of β-catenin in response to homocysteine

Elevated plasma homocysteine (Hcy) is an independent risk factor for vascular disease and stroke in part by causing generalized endothelial dysfunction. A receptor that is sensitive to Hcy and its intracellular signaling systems has not been identified. β-catenin is a pleiotropic regulator of transcription and cell function. Using a brain microvascular endothelial cell line (bEnd.3), we tested the hypothesis that Hcy causes receptor-dependent nuclear translocation of β-catenin. Hcy increased phosphorylation of Y731 on vascular endothelial cadherin (VE-cadherin), a site involved in coupling β-catenin to VE-cadherin. This was blocked by inhibition of either metabotropic glutamate receptor 5 (mGluR5) or ionotropic glutamate receptor (NMDAr) and by shRNA knockdown of mGluR5. Expression of these receptors was confirmed by flow cytometry, immunohistochemistry, and western blotting. Directed pharmacology with specific agonists elucidated a signaling cascade where Hcy activates mGluR5 which activates NMDAr with subsequent PKC activation and uncoupling of the VE-cadherin/β-catenin complex. Moreover, Hcy caused a shift in localization of β-catenin from membrane-bound VE-cadherin to the cell nucleus, where it bound DNA, including a regulatory region of the gene for claudin-5, leading to reduced expression of claudin-5. Nuclear localization, DNA binding of β-catenin, and reduced claudin-5 expression were blocked by inhibition of mGluR5. Knockdown of mGluR5 expression with shRNA also rescued claudin-5 expression from the effects of Hcy treatment. These data uniquely identify mGluR5 as a master switch that drives β-catenin nuclear localization in vascular endothelium and regulates cell-cell coupling in response to elevated Hcy levels. These studies dissect a pharmacological opportunity for developing new therapeutic strategies in HHcy.

HIF-1 is involved in high glucose-induced paracellular permeability of brain endothelial cells

Experimental evidence from human patients and animal models of diabetes has demonstrated that hyperglycemia increases blood-brain barrier (BBB) permeability, which is associated with increased risk of neurological dysfunction. However, the mechanism underlying high glucose-induced BBB disruption is not understood. Here we investigated the role of hypoxia-inducible factor-1 (HIF-1) in high glucose-induced endothelial permeability in vitro using mouse brain microvascular endothelial cells (b.End3). Our results demonstrated that high glucose (30 mM) upregulated the protein level of HIF-1α, the regulatable subunit of HIF-1, and increased the transcriptional activity of HIF-1 in the endothelial cells. At the same time, high glucose increased the paracellular permeability associated with diminished expression and disrupted continuity of tight junction proteins occludin and zona occludens protein-1 (ZO-1) of the endothelial cells. Upregulating HIF-1 activity by cobalt chloride increased the paracellular permeability of the endothelial cells exposed to normal glucose (5.5 mM). In contrast, downregulating HIF-1 activity by HIF-1α inhibitors and HIF-1α specific siRNA ameliorated the increased paracellular permeability and the alterations of distribution pattern of occludin and ZO-1 induced by high glucose. In addition, high glucose increased expression of vascular endothelial growth factor (VEGF), a downstream gene of HIF-1. Inhibiting VEGF improved the expression pattern of occludin and ZO-1, and attenuated the endothelial leakage. Furthermore, key results were confirmed in human brain microvascular endothelial cells. These results strongly indicate that HIF-1 plays an important role in high glucose-induced BBB dysfunction. The results will help us understand the molecular mechanisms involved in hyperglycemia-induced BBB dysfunction and neurological outcomes.

Stress-induced hyperalgesia is associated with a reduced and delayed GABA inhibitory control that enhances post-synaptic NMDA receptor activation in the spinal cord

GABA and glutamate are both affected by stress and are involved in nociception. Thus, we determined whether stress-induced enhancement of inflammatory hyperalgesia is mediated by an imbalance between glutamate and GABA neurotransmission. Male rats were subjected daily to 10 to 20 minutes per day of either forced swimming (FS) or sham swimming for 3 consecutive days; nonconditioned rats served as controls. Some rats were treated i.p. with ketamine (5 mg/kg), diazepam (2 mg/kg), flumazenil (0.1 mg/kg), or vehicle (0.9% NaCl), 30 to 60 minutes before each conditioning session or nociception assessment. Pain behavior, spinal nociceptive neuronal activation and GABA and glutamate release were respectively evaluated by the formalin test, the expression of c-Fos and in vivo microdialysis of superficial laminae of the lumbar spinal cord, 48 hours after the last conditioning session. Nitric oxide metabolites (NO(x)) were determined as markers of post-synaptic NMDA receptor activation. FS stress enhanced formalin-induced hyperalgesia, increased pain-elicited c-Fos expression, decreased basal and delayed pain-induced GABA release, and increased basal and induced glutamate release. Hyperalgesia and c-Fos overexpression were blocked only by prestress treatment with diazepam and post-stress treatment with ketamine, whereas changes in GABA and glutamate release were reversed by prestress treatment with diazepam. Diazepam effects were blocked by flumazenil. NO(x) increased in lumbar spinal cord of FS rats by a mechanism antagonized by ketamine. Thus, stress-induced hyperalgesia is initiated by a decreased and delayed GABA release and GABA-A receptor activation, whereas it is maintained by increased glutamate release and NMDA glutamate receptor activation at the spinal level.

Inflammation induced neurological handicap processes in multiple sclerosis: new insights from preclinical studies

Multiple sclerosis (MS) is described as originating from incompletely explained neuroinflammatory processes, dysfunction of neuronal repair mechanisms and chronicity of inflammation events. Blood-borne immune cell infiltration and microglia activation are causing both neuronal destruction and myelin loss, which are responsible for progressive motor deficiencies, organic and cognitive dysfunctions. MRI as a non-invasive imaging method offers various ways to visualise de- and remyelination, neuronal loss, leukocyte infiltration, blood-brain barrier modification and new sensors are emerging to detect inflammatory lesions at an early stage. We describe studies performed on experimental autoimmune encephalomyelitis (EAE) animal models of MS that shed new light on mechanisms of functional impairments to understand the neurological handicap in MS. We focus on examples of neuroinflammation-mediated inhibition of CNS repair involving adult neurogenesis in the sub-ventricular zone and hippocampus and such experimentally observed inhibitions could reflect deficient plasticity and activation of compensatory mechanisms in MS. In parallel with cognitive decline, organic deficits such as bladder dysfunction are described in most of MS patients. Neuropharmacological interventions, electrical stimulation of nerves, MRI and histopathology follow-up studies helped in understanding the operating events to remodel the neurological networks and to compensate the inflammatory lesions both in spinal cord and in cortical regions. At the molecular level, the local production of reactive products is a well-described phenomenon: oxidative species disturb cellular physiology and generate new molecular epitopes that could further promote immune reactions. The translational research from EAE animal models to MS patient cohorts helps in understanding the mechanisms of the neurological handicap and in development of new therapeutic concepts in MS.

Oxidative stress upregulates the NMDA receptor on cerebrovascular endothelium

N-methyl-d-aspartate receptor (NMDA-R)-mediated oxidative stress has been implicated in blood-brain barrier (BBB) disruption in a variety of neuropathological diseases. Although some interactions between both phenomena have been elucidated, possible influences of reactive oxygen species (ROS) on the NMDA-R itself have so far been neglected. The objective of this study was to examine how the cerebroendothelial NMDA-R is affected by exposure to oxidative stress and to assess possible influences on BBB integrity. RT-PCR confirmed several NMDA-R subunits (NR1, NR2B-D) expressed in the bEnd3 cell line (murine cerebrovascular endothelial cells). NR1 protein expression after exposure to ROS was observed via in-cell Western. The functionality of the expressed NMDA-R was determined by measuring DiBAC fluorescence in ROS-preexposed cells upon stimulation with the specific agonist NMDA. Finally, the effects on barrier integrity were evaluated using the ECIS system to detect changes in monolayer impedance upon NMDA-R stimulation after exposure to ROS. The expression of NR1 significantly (p<0.001) increased 72 h after 30 min exposure to superoxide (+33.8+/-7.5%), peroxynitrite (+84.9+/-10.7%), or hydrogen peroxide (+92.8+/-7.6%), resulting in increased cellular response to NMDA-R stimulation and diminished monolayer impedance. We conclude that oxidative stress upregulates NMDA-R on cerebrovascular endothelium and thus heightens susceptibility to glutamate-induced BBB disruption.

Newborn- and adult-derived brain microvascular endothelial cells show age-related differences in phenotype and glutamate-evoked protease release

Few data are available on the involvement of brain microvascular endothelial cells (BMECs) in excitotoxic neonatal brain lesions. Therefore, we developed an original approach for investigating mouse-derived BMECs in vitro. We hypothesized that newborn and adult BMEC cultures would show age-related differences in phenotype and sensitivity to glutamate. Expression of the monocarboxylate transporter, MCT1, was higher in neonatal than in adult BMECs, whereas expression of the glucose transporter, GLUT1, was higher in adult than in neonatal BMECs that overexpressed the N-methyl-D-aspartate receptor NR1 subunit (NMDAR1) compared with adult BMECs. The ability of neonatal and adult BMECs to be activated by glutamate was confirmed through intracellular calcium ([Ca2+]i) recording. The glutamate-induced [Ca2+]i increase was blocked by the selective NMDAR antagonist, MK-801. Significant glutamate-evoked concentration-dependent release of tissue-type plasminogen activator (t-PA) and matrix metalloproteinases (MMPs) activities was found in supernatants of neonatal, but not in adult BMECs. The glutamate-mediated release of t-PA, MMP-2, and MMP-9 proteolytic activities in neonatal BMECs was blocked by MK-801. Conceivably, this protease release from neonatal BMECs may participate in neonatal brain lesions.

A comparative evaluation of the response to peroxynitrite by a brain endothelial cell line and control of the effects by drug targeting

The potent oxidant peroxynitrite (ONOO(-)) is formed after the combination of nitric oxide with superoxide and has been closely associated with the pathology of inflammatory disease. In particular, the generation of ONOO(-) has been linked to central nervous system disorders including Alzheimer's and Parkinson's disease, multiple sclerosis and bacterial and viral meningitis. Specifically, ONOO(-) has been implicated in the loss of blood-brain barrier (BBB) integrity during neuroinflammation, but the precise mechanisms through which the molecule acts to mediate neurovascular breakdown have not been established. The disruptive effects of ONOO(-) could be mediated by either direct or indirect actions on the endothelial cells that comprise the major component of the BBB. The current study has comparatively assessed the direct toxic effects of ONOO(-) on the brain endothelial cell line, b.End3 and C6 astrocytoma and NA neuroblastoma preparations. b.End3 cells were relatively resistant to ONOO(-)-induced cell death compared with C6 and NA cultures. The indirect involvement of ONOO(-) in neuroendothelial disruption was pharmacologically determined via adhesion molecule expression and immunocompetent cell attachment to b.End3 cells. ONOO(-)-targeted drugs, including the selective free radical scavenger, uric acid, the decomposition catalyst 5,10,15,20-tetrakis (4-sulphonatophenyl) porphyrinatoiron (III) (FeTPPS) and the poly(ADP-ribose) polymerase inhibitor N-(6-oxo-5,6-dihydrophenanthridin-2-yl)-(N,N-dimethylamino) acetamide hydrochloride (PJ34) revealed that ONOO(-) was only partly involved in E-selectin, ICAM-1 and VCAM-1 expression on b.End3 cells and also cytokine-induced T-lymphocyte attachment to the cell line. The results indicate that ONOO(-) contributes to b.End3 cell disruption but is not exclusively responsible for the breakdown of neuroendothelial function.

Neurodegeneration in multiple sclerosis: the role of oxidative stress and excitotoxicity

In multiple sclerosis (MS) disability results from neuronal and axonal loss, the hallmark of neurodegenerative diseases (ND). Neurodegeneration is initiated by microglia activation and mediated by oxidative stress and excitotoxicity. The same sequence of events has been consistently observed in MS. However, microglia activation correlates with a marked cell infiltration in MS but not in ND. In both pathological states, peroxynitrite is the common initiating factor of oxidative stress and excitotoxicity and is thus a potential interesting therapeutic target. Oxidative stress leads to multiple lipid and protein damages via peroxidation and nitration processes. The pathomechanisms of excitotoxicity are complex involving glutamate overload, ionic channel dysfunction, calcium overload, mitochondriopathy, proteolytic enzyme production and activation of apoptotic pathways. The inflammatory component in MS is important for the design of therapeutic strategies. Inflammation not only causes axonal and neuronal loss but it also initiates the degenerative cascade in the early stage of MS. Potent anti-inflammatory agents are now available and it is not unreasonable to think that an early blockade of inflammatory processes might also block associated degenerative mechanisms and delay disability progression. The development of neuroprotective drugs is more problematic. Indeed, given the multiple and parallel mechanisms involved in neurodegeneration, modulation of a single specific pathway will likely yield a partial benefit if any.

Fluvastatin prevents glutamate-induced blood-brain-barrier disruption in vitro

Glutamate is an important excitatory amino acid in the central nervous system. Under pathological conditions glutamate levels dramatically increase. Aim of the present study was to examine whether the HMG-CoA inhibitor fluvastatin prevents glutamate-induced blood-brain-barrier (BBB) disruption. Measurements of transendothelial electrical resistance (TEER) were performed to analyze BBB integrity in an in vitro co-culture model of brain endothelial and glial cells. Myosin light chain (MLC) phosphorylation was detected by immunohistochemistry, or using the in-cell western technique. Intracellular Ca2+ and reactive oxygen species (ROS) levels were analyzed using the fluorescence dyes Ca-green or DCF. Glutamate induced a time- (1-3 h) and concentration- (0.25-1 mmol/l) dependent decrease of TEER values that was blocked by the NMDA-receptor antagonist MK801, the Ca2+ chelator BAPTA, the NAD(P)H-oxidase inhibitor apocynin and the MLC-kinase inhibitor ML-7. Furthermore we observed a concentration-dependent increase of intracellular Ca2+ and ROS after glutamate application. Glutamate caused an increase of MLC phosphorylation that was antagonized by apocynin, or BAPTA, indicating that Ca2+ and ROS signaling is involved in the activation of the contractile machinery. Fluvastatin (10-25 micromol/l) completely abolished the glutamate-induced barrier disruption and oxidative stress. The BBB-protecting effect of fluvastatin was completely lost if the cells were treated with the nitric oxide (NO) synthase inhibitor L-NMMA (300 micromol/l). In the present study we demonstrated that glutamate-induced BBB disruption involves Ca2+ signalling via NMDA receptors, which is followed by an increased ROS generation by the NAD(P)H-oxidase. This oxidative stress then activates the MLC kinase. Fluvastatin preserves barrier function in a NO-dependent way and reduces glutamate-induced oxidative stress.

Memantine reduces oxidative damage and enhances long-term recognition memory in aged rats

Many neurodegenerative diseases, including Alzheimer's (AD), Parkinson's (PD) and Huntington's diseases (HD), are caused by different mechanisms but may share a common pathway to neuronal injury as a result of the overstimulation of glutamate receptors. It has been suggested that this pathway can be involved in generation of cognitive deficits associated with normal aging. Previous studies performed in our laboratory have demonstrated that aged rats presented recognition memory deficits. The aim of the present study was to evaluate the effect of memantine, a low-affinity N-methyl-D-aspartate (NMDA) receptor antagonist, on age-induced recognition memory deficits. Additionally, parameters of oxidative damage in cerebral regions related to memory formation were evaluated. In order to do that, male Wistar rats (24 months old) received daily injections of saline solution or memantine (20 mg/kg i.p.) during 21 days. The animals were submitted to a novel object recognition task 1 week after the last injection. Memantine-treated rats showed normal recognition memory while the saline group showed long-term recognition memory deficits. The results show that memantine is able to reverse age-induced recognition memory deficits. We also demonstrated that memantine reduced the oxidative damage to proteins in cortex and hippocampus, two important brain regions involved in memory formation. Thus, the present findings suggest that, at least in part, age-induced cognitive deficits are related to oxidative damage promoted by NMDA receptor overactivation.