N-methyl-d-aspartate receptor activation in human cerebral endothelium promotes intracellular oxidant stress

Redefining Roles: A Paradigm Shift in Tryptophan-Kynurenine Metabolism for Innovative Clinical Applications

The tryptophan-kynurenine (KYN) pathway has long been recognized for its essential role in generating metabolites that influence various physiological processes. Traditionally, these metabolites have been categorized into distinct, often opposing groups, such as pro-oxidant versus antioxidant, excitotoxic/neurotoxic versus neuroprotective. This dichotomous framework has shaped much of the research on conditions like neurodegenerative and neuropsychiatric disorders, as well as cancer, where metabolic imbalances are a key feature. The effects are significantly influenced by various factors, including the concentration of metabolites and the particular cellular milieu in which they are generated. A molecule that acts as neuroprotective at low concentrations may exhibit neurotoxic effects at elevated levels. The oxidative equilibrium of the surrounding environment can alter the function of KYN from an antioxidant to a pro-oxidant. This narrative review offers a comprehensive examination and analysis of the contemporary understanding of KYN metabolites, emphasizing their multifaceted biological functions and their relevance in numerous physiological and pathological processes. This underscores the pressing necessity for a paradigm shift in the comprehension of KYN metabolism. Understanding the context-dependent roles of KYN metabolites is vital for novel therapies in conditions like Alzheimer's disease, multiple sclerosis, and cancer. Comprehensive pathway modulation, including balancing inflammatory signals and enzyme regulation, offers promising avenues for targeted, effective treatments.

Extracellular vesicles as nanotheranostic platforms for targeted neurological disorder interventions

Central Nervous System (CNS) disorders represent a profound public health challenge that affects millions of people around the world. Diseases such as Alzheimer's disease (AD), Parkinson's disease (PD), and traumatic brain injury (TBI) exemplify the complexities and diversities that complicate their early detection and the development of effective treatments. Amid these challenges, the emergence of nanotechnology and extracellular vesicles (EVs) signals a new dawn for treating and diagnosing CNS ailments. EVs are cellularly derived lipid bilayer nanosized particles that are pivotal in intercellular communication within the CNS and have the potential to revolutionize targeted therapeutic delivery and the identification of novel biomarkers. Integrating EVs with nanotechnology amplifies their diagnostic and therapeutic capabilities, opening new avenues for managing CNS diseases. This review focuses on examining the fascinating interplay between EVs and nanotechnology in CNS theranostics. Through highlighting the remarkable advancements and unique methodologies, we aim to offer valuable perspectives on how these approaches can bring about a revolutionary change in disease management. The objective is to harness the distinctive attributes of EVs and nanotechnology to forge personalized, efficient interventions for CNS disorders, thereby providing a beacon of hope for affected individuals. In short, the confluence of EVs and nanotechnology heralds a promising frontier for targeted and impactful treatments against CNS diseases, which continue to pose significant public health challenges. By focusing on personalized and powerful diagnostic and therapeutic methods, we might improve the quality of patients.

Evidence Implicating Blood-Brain Barrier Impairment in the Pathogenesis of Acquired Epilepsy following Acute Organophosphate Intoxication

Organophosphate (OP) poisoning can trigger cholinergic crisis, a life-threatening toxidrome that includes seizures and status epilepticus. These acute toxic responses are associated with persistent neuroinflammation and spontaneous recurrent seizures (SRS), also known as acquired epilepsy. Blood-brain barrier (BBB) impairment has recently been proposed as a pathogenic mechanism linking acute OP intoxication to chronic adverse neurologic outcomes. In this review, we briefly describe the cellular and molecular components of the BBB, review evidence of altered BBB integrity following acute OP intoxication, and discuss potential mechanisms by which acute OP intoxication may promote BBB dysfunction. We highlight the complex interplay between neuroinflammation and BBB dysfunction that suggests a positive feedforward interaction. Lastly, we examine research from diverse models and disease states that suggest mechanisms by which loss of BBB integrity may contribute to epileptogenic processes. Collectively, the literature identifies BBB impairment as a convergent mechanism of neurologic disease and justifies further mechanistic research into how acute OP intoxication causes BBB impairment and its role in the pathogenesis of SRS and potentially other long-term neurologic sequelae. Such research is critical for evaluating BBB stabilization as a neuroprotective strategy for mitigating OP-induced epilepsy and possibly seizure disorders of other etiologies. SIGNIFICANCE STATEMENT: Clinical and preclinical studies support a link between blood-brain barrier (BBB) dysfunction and epileptogenesis; however, a causal relationship has been difficult to prove. Mechanistic studies to delineate relationships between BBB dysfunction and epilepsy may provide novel insights into BBB stabilization as a neuroprotective strategy for mitigating epilepsy resulting from acute organophosphate (OP) intoxication and non-OP causes and potentially other adverse neurological conditions associated with acute OP intoxication, such as cognitive impairment.

Blood-brain barrier damage and new onset refractory status epilepticus: An exploratory study using dynamic contrast-enhanced magnetic resonance imaging

OBJECTIVE

This study was undertaken to characterize the blood-brain barrier (BBB) dysfunction in patients with new onset refractory status epilepticus (NORSE) using dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI).

METHODS

This study included three groups of adult participants: patients with NORSE, encephalitis patients without status epilepticus (SE), and healthy subjects. These participants were retrospectively included from a prospective DCE-MRI database of neurocritically ill patients and healthy subjects. The BBB permeability (Ktrans) in the hippocampus, basal ganglia, thalamus, claustrum, periventricular white matter, and cerebellum were measured and compared between these three groups.

RESULTS

A total of seven patients with NORSE, 14 encephalitis patients without SE, and nine healthy subjects were included in this study. Among seven patients with NORSE, only one had a definite etiology (autoimmune encephalitis), and the rest were cryptogenic. Etiology of encephalitis patients without SE included viral (n = 2), bacterial (n = 8), tuberculous (n = 1), cryptococcal (n = 1), and cryptic (n = 2) encephalitis. Of these 14 encephalitis patients without SE, three patients had seizures. Compared to healthy controls, NORSE patients had significantly increased Ktrans values in the hippocampus (.73 vs. .02 × 10^-3 /min, p = .001) and basal ganglia (.61 vs. .003 × 10^-3 /min, p = .007) and a trend in the thalamus (.24 vs. .08 × 10^-3 /min, p = .017). Compared to encephalitis patients without SE, NORSE patients had significantly increased Ktrans values in the thalamus (.24 vs. .01 × 10^-3 /min, p = .002) and basal ganglia (.61 vs. .004 × 10^-3 /min, p = .013).

SIGNIFICANCE

This exploratory study demonstrates that BBBs of NORSE patients were impaired diffusely, and BBB dysfunction in the basal ganglia and thalamus plays an important role in the pathophysiology of NORSE.

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.

Electroacupuncture of the trigeminal nerve causes N-methyl-D-aspartate receptors to mediate blood-brain barrier opening and induces neuronal excitatory changes

The blood-brain barrier (BBB) is an important structure for maintaining environmental stability in the central nervous system (CNS). Our previous study showed that specific parameters of electroacupuncture (EA) at the head points Shuigou (GV26) and Baihui (GV20) can open the BBB; however, the mechanism by which stimulation of body surface acupuncture points on the head results in peripheral stimulation and affects the status of the central BBB and the neuronal excitatory changes has not been elucidated. We used laser spectroscopy, the In Vivo Imaging System (IVIS), immunofluorescence and immunoblotting to verified the role of the trigeminal nerve in BBB opening during EA, and we applied the central N-methyl-D-aspartate (NMDA) receptors blocker MK-801 to verify the mediating role of NMDA receptors in EA-induced BBB opening. Next, electroencephalogram (EEG) and in vivo calcium imaging techniques were applied to verify the possible electrical patterns of BBB opening promoted by different intensities of EA stimulation. The results showed that the trigeminal nerve plays an important role in the alteration of BBB permeability promoted by EA stimulation of the head acupoints. Brain NMDA receptors play a mediating role in promoting BBB permeability during EA of the trigeminal nerve, which may affect the expression of the TJ protein occludin, and thus alter BBB permeability. The analysis of the electrical mechanism showed that there was no significant change in the rhythm of local field potentials (LFP) in different brain regions across frequency bands immediately after EA of the trigeminal nerve at different intensities. However, the local primary somatosensory (S1BF) area corresponding to the trigeminal nerve showed a transient reduction in the delta rhythm of LFP with no change in the high-frequency band, and the action potential (spike) with short inter spike interval (ISI) varied with EA intensity. Meanwhile, EA of the trigeminal nerve resulted in rhythmic changes in calcium waves in the S1BF region, which were influenced by different EA intensities. This study provides a research perspective and a technical approach to further explore the mechanism of EA-induced BBB opening and its potential clinical applications.

The Prevention and Reversal of a Phenytoin-Resistant Model by N-acetylcysteine Therapy Involves the Nrf2/P-Glycoprotein Pathway at the Blood-Brain Barrier

The transporter hypothesis is one of the most popular hypotheses of drug-resistant epilepsy (DRE). P-glycoprotein (P-gp), a channel protein at the blood-brain barrier (BBB), plays an important role in the transport of some anti-seizure drugs from brain tissue into vessels, which reduces drug concentrations and diminishes the effects of drug treatment. We performed this study to test whether P-gp is overexpressed in DRE and identify ways to prevent and reverse DRE. In this study, we established a phenytoin (PHT)-resistant mouse model and revealed that P-gp was overexpressed at the BBB in PHT-resistant mice. The P-gp inhibitor nimodipine decreased the resistance of phenytoin. Antioxidative preventive treatment with N-acetylcysteine (NAC) prevented the mice from entering a PHT-resistant state, and NAC therapy tended to reverse PHT resistance into sensitivity. We were also able to induce PHT resistance by activating the Nrf2/P-gp pathway, which indicates that oxidative stress plays an important role in drug resistance. Taken together, these findings suggest that antioxidative therapy may be a promising strategy for overcoming DRE.

The Involvement of Long Non-coding RNA and Messenger RNA Based Molecular Networks and Pathways in the Subacute Phase of Traumatic Brain Injury in Adult Mice

Traumatic brain injury (TBI) is a complex injury with a multi-faceted recovery process. Long non-coding RNAs (lncRNAs) are demonstrated to be involved in central nervous system (CNS) disorders. However, the roles of lncRNAs in long-term neurological deficits post-TBI are poorly understood. The present study depicted the microarray’s lncRNA and messenger RNA (mRNA) profiles at 14 days in TBI mice hippocampi. LncRNA and mRNA microarray was used to identify differentially expressed genes. Quantitative real-time polymerase chain reaction (qRT-PCR) was employed to validate the microarray results. Bioinformatics analysis [including Gene Ontology (GO), the Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway, lncRNA-mRNA co-expression network, and lncRNA-miRNA-mRNA network] were applied to explore the underlying mechanism. A total of 264 differentially expressed lncRNAs and 232 expressed mRNAs were identified (fold change > 1.5 and P-value < 0.05). Altered genes were enriched in inflammation, immune response, blood–brain barrier, glutamatergic neurological effects, and neuroactive ligand-receptor, which may be associated with TBI-induced pathophysiologic changes in the long-term neurological deficits. The lncRNAs-mRNAs co-expression network was generated for 74 lncRNA-mRNA pairs, most of which are positive correlations. The lncRNA-miRNA-mRNA interaction network included 12 lncRNAs, 59 miRNAs, and 25 mRNAs. Numerous significantly altered lncRNAs and mRNAs in mice hippocampi were enriched in inflammation and immune response. Furthermore, these dysregulated lncRNAs and mRNAs may be promising therapeutic targets to overcome obstacles in long-term recovery following TBI.

Cerebral and systemic hemodynamic effect of recurring seizures

The increase in neuronal activity induced by a single seizure is supported by a rise in the cerebral blood flow and tissue oxygenation, a mechanism called neurovascular coupling (NVC). Whether cerebral and systemic hemodynamics are able to match neuronal activity during recurring seizures is unclear, as data from rodent models are at odds with human studies. In order to clarify this issue, we used an invasive brain and systemic monitoring to study the effects of chemically induced non-convulsive seizures in sheep. Despite an increase in neuronal activity as seizures repeat (Spearman’s ρ coefficient 0.31, P < 0.001), ictal variations of cerebral blood flow remained stable while it progressively increased in the inter-ictal intervals (ρ = 0.06, P = 0.44 and ρ = 0.22; P = 0.008). We also observed a progressive reduction in the inter-ictal brain tissue oxygenation (ρ =  − 0.18; P = 0.04), suggesting that NVC was unable to compensate for the metabolic demand of these closely repeating seizures. At the systemic level, there was a progressive reduction in blood pressure and a progressive rise in cardiac output (ρ =  − 0.22; P = 0.01 and ρ = 0.22; P = 0.01, respectively), suggesting seizure-induced autonomic dysfunction.

NMDAR in bladder smooth muscle is not a pharmacotherapy target for overactive bladder in mice

Overactive bladder (OAB) is a common condition that affects a significant patient population. The N-methyl-D-aspartate receptor (NMDAR) has a role in developing bladder overactivity, pharmacological inhibition of which inhibits bladder overactivity. The common pathogenesis of OAB involves bladder smooth muscle (BSM) overactivity. In this study, a smooth muscle-specific NMDAR knockout (SMNRKO) mouse model was generated. The bladders from SMNRKO mice displayed normal size and weight with an intact bladder wall and well-arranged BSM bundles. Besides, SMNRKO mice had normal voiding patterns and urodynamics and BSM contractility, indicating that NMDAR in BSM was not essential for normal physiological bladder morphology and function. Unexpectedly, cyclophosphamide (CYP)-treated SMNRKO and wild-type (WT) mice had similar pathological changes in the bladder. Furthermore, SMNRKO mice displayed similar altered voiding patterns and urodynamic abnormalities and impaired BSM contractility compared with WT mice after CYP treatment. MK801 partially reversed the pathological bladder morphology and improved bladder dysfunction induced by CYP, but did not cause apparent differences between WT mice and SMNRKO mice, suggesting that NMDAR in BSM was not involved in pathological bladder morphology and function. Moreover, the direct instillation of NMDAR agonists or antagonists into the CYP-induced OAB did not affect bladder urodynamic function, indicating that NMDAR in BSM was not the pharmacotherapy target of MK801 for CYP-induced cystitis. The findings indicated that NMDAR in BSM was not essential for normal physiological or pathological bladder morphology and function, and MK801 improving pathological bladder function was not mediated by an action on NMDAR in BSM.

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.

Memantine, NMDA Receptor Antagonist, Attenuates ox-LDL-Induced Inflammation and Oxidative Stress via Activation of BDNF/TrkB Signaling Pathway in HUVECs

Atherosclerosis is a chronic cardiovascular disease and contributes to pathogenesis of most myocardial infarction and ischemic stroke. Additionally, N-methyl-D-aspartate (NMDA) receptor plays a crucial role in myocardial infarction and ischemic strokes. The aim of our study was to investigate the underlying mechanisms of memantine (MEM), the blocker of NMDA receptors, in the development of atherosclerosis. In our study, human umbilical vascular endothelial cells (HUVECs) were stimulated with low-density lipoprotein (ox-LDL) to establish an atherosclerotic cell model. Cell Counting Kit-8 (CCK-8) assay and TUNEL staining were performed to detect the cell activity and apoptosis of HUVECs, respectively. The levels of inflammatory cytokines and malondialdehyde and the activities of lactate dehydrogenase (LDH), superoxide dismutase (SOD), and caspase-1 were quantified with commercial assay kits. Finally, qRT-PCR assay and western blot analysis were carried out to determine the mRNA and protein expressions of inflammation-related genes in HUVECs. The results of the present study suggested that ox-LDL stimulation induced decreased viability of HUVECs, excessive inflammation, and oxidative stress, while these effects were counteracted by MEM treatment. Interestingly, MEM triggered the activation of BDNF/TrkB signaling pathway in HUVECs, and K252a, the inhibitor of the BDNF/TrkB pathway, abolished the suppressive effect of MEM on ox-LDL-induced inflammation, oxidative stress, and apoptosis in HUVECs. Overall, MEM attenuated ox-LDL-induced inflammation, oxidative stress, and apoptosis via activation of BDNF/TrkB signaling pathway in HUVECs, indicating that MEM may be defined as a novel and effective agent for atherosclerosis treatment.

TMS-Induced Controlled BBB Opening: Preclinical Characterization and Implications for Treatment of Brain Cancer

Proper neuronal function requires strict maintenance of the brain's extracellular environment. Therefore, passage of molecules between the circulation and brain neuropil is tightly regulated by the blood-brain barrier (BBB). While the BBB is vital for normal brain function, it also restricts the passage of drugs, potentially effective in treating brain diseases, into the brain. Despite previous attempts, there is still an unmet need to develop novel approaches that will allow safe opening of the BBB for drug delivery. We have recently shown in experimental rodents and in a pilot human trial that low-frequency, high-amplitude repetitive transcranial magnetic stimulation (rTMS) allows the delivery of peripherally injected fluorescent and Gd-based tracers into the brain. The goals of this study were to characterize the duration and safety level of rTMS-induced BBB opening and test its capacity to enhance the delivery of the antitumor growth agent, insulin-like growth factor trap, across the BBB. We employed direct vascular and magnetic resonance imaging, as well as electrocorticography recordings, to assess the impact of rTMS on brain vascular permeability and electrical activity, respectively. Our findings indicate that rTMS induces a transient and safe BBB opening with a potential to facilitate drug delivery into the brain.

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.

Blood-brain barrier dysfunction in status epileptics: Mechanisms and role in epileptogenesis

The blood-brain barrier (BBB), a unique anatomical and physiological interface between the central nervous system (CNS) and the peripheral circulation, is essential for the function of neural circuits. Interactions between the BBB, cerebral blood vessels, neurons, astrocytes, microglia, and pericytes form a dynamic functional unit known as the neurovascular unit (NVU). The NVU-BBB crosstalk plays a key role in the regulation of blood flow, response to injury, neuronal firing, and synaptic plasticity. Blood-brain barrier dysfunction (BBBD), a hallmark of brain injury, is a prominent finding in status epilepticus. Blood-brain barrier dysfunction is observed within the first hour of status epilepticus, and in epileptogenic brain regions, may last for months. Blood-brain barrier dysfunction was shown to have a role in astroglial dysfunction, neuroinflammation, increasing neural excitability, reduction of seizure threshold, excitatory synaptogenesis, impaired plasticity, and epileptogenesis. A key signaling pathway associated with BBBD-induced neurovascular dysfunction is the transforming growth factor beta (TGF-β) proinflammatory pathway, activated by the extravasation of serum albumin into the brain when BBB functions are compromised. Specific small molecules blocking TGF-β, and the nonspecific, Food and Drug Administration (FDA) approved blocker and angiotensin antagonist losartan, were shown to reduce BBBD and block epileptogenesis. With these encouraging preclinical data, we have developed imaging approach to quantitatively assess BBBD as a diagnostic, predictive, and pharmacodynamic biomarker after brain injury. Clinical trials in the foreseen future are expected to test the feasibility of BBB-targeted diagnostic coupled therapy in status epileptics and seizure disorders. This article is part of the Special Issue "Proceedings of the 7th London-Innsbruck Colloquium on Status Epilepticus and Acute Seizures".

Cytosolic phospholipase A2 is a key regulator of blood-brain barrier function in epilepsy

Blood-brain barrier dysfunction in epilepsy contributes to seizures and resistance to antiseizure drugs. Reports show that seizures increase brain glutamate levels, leading to barrier dysfunction. One component of barrier dysfunction is overexpression of the drug efflux transporters P-glycoprotein (P-gp) and breast cancer resistance protein (BCRP). Based on our previous studies, we hypothesized that glutamate released during seizures activates cytosolic phospholipase A2 (cPLA2), resulting in P-gp and BCRP overexpression. We exposed isolated rat brain capillaries to glutamate ex vivo and used an in vivo-ex vivo approach of isolating brain capillaries from rats after status epilepticus (SE) and in chronic epileptic (CE) rats. Glutamate increased cPLA2, P-gp, and BCRP protein and activity levels in isolated brain capillaries. We confirmed the role of cPLA2 in the signaling pathway in brain capillaries from male and female mice lacking cPLA2. We also demonstrated, in vivo, that cPLA2 inhibition prevents overexpression of P-gp and BCRP at the blood-brain barrier in rats after status epilepticus and in CE rats. Our data support the hypothesis that glutamate signals cPLA2 activation, resulting in overexpression of blood-brain barrier P-gp and BCRP.-Hartz, A. M. S., Rempe, R. G., Soldner, E. L. B., Pekcec, A., Schlichtiger, J., Kryscio, R., Bauer, B. Cytosolic phospholipase A2 is a key regulator of blood-brain barrier function in epilepsy.

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.

Inhibition of VEGF-Flk-1 binding induced profound biochemical alteration in the hippocampus of a rat model of BBB breakdown by spider venom. A preliminary assessment using FT-IR spectroscopy

Phoneutria nigriventer spider venom (PNV) contains ion channels-acting neuropeptides that in rat induces transitory blood-brain barrier breakdown (BBBb) in hippocampus in parallel with VEGF upregulation. We investigated whether VEGF has a neuroprotective role by inhibiting its binding to receptor Flk-1 by itraconazole (ITZ). FT-IR spectroscopy examined the biochemical status of hippocampus and evaluated BBBb in rats administered PNV or ITZ/PNV at periods with greatest toxicity (1-2h), recovery (5h) and visual absence of symptoms (24h), and compared to saline and ITZ controls. The antifungal treatment before venom intoxication aggravated the venom effects and increased BBB damage. FT-IR spectra of venom, hippocampi of controls, PNV and ITZ-PNV showed a 1400 cm^-1 band linked to symmetric stretch of carboxylate and 1467 cm^-1 band (CH₂ bending: mainly lipids) that were considered biomarker and reference bands, respectively. Inhibition of VEGF/Flk-1 binding produced marked changes in lipid/protein stability at 1-2h. The largest differences were observed in spectra regions assigned to lipids, both symmetric (2852 cm^-1) and asymmetric (2924 and 2968 cm^-1). Quantitative analyses showed greatest increases in the 1400 cm^-1/1467 cm^-1 ratio also at 1h. Such changes at period of rats' severe intoxication referred to wavenumber region from 3106 cm^-1 to 687 cm^-1 assigning for C-H and N-H stretching of protein, Amide I, C=N cytosine, N-H adenine, Amide II, CH₂ bending: mainly lipids, C-O stretch: glycogen, polysaccharides, glycolipids, z-type DNA, C-C, C-O and CH out-of-plane bending vibrations. We conclude that VEGF has a neuroprotective role and can be a therapeutic target in PNV envenomation. FT-IR spectroscopy showed to be instrumental for monitoring biochemical changes in this model of P. nigriventer venom-induced BBB disruption.

Matrix Metalloproteinase-Mediated Blood-Brain Barrier Dysfunction in Epilepsy

The blood-brain barrier is dysfunctional in epilepsy, thereby contributing to seizure genesis and resistance to antiseizure drugs. Previously, several groups reported that seizures increase brain glutamate levels, which leads to barrier dysfunction. One critical component of barrier dysfunction is brain capillary leakage. Based on our preliminary data, we hypothesized that glutamate released during seizures mediates an increase in matrix-metalloproteinase (MMP) expression and activity levels, thereby contributing to barrier leakage. To test this hypothesis, we exposed isolated brain capillaries from male Sprague Dawley rats to glutamate ex vivo and used an in vivo/ex vivo approach of isolated brain capillaries from female Wistar rats that experienced status epilepticus as an acute seizure model. We found that exposing isolated rat brain capillaries to glutamate increased MMP-2 and MMP-9 protein and activity levels, and decreased tight junction protein levels, which resulted in barrier leakage. We confirmed these findings in vivo in rats after status epilepticus and in brain capillaries from male mice lacking cytosolic phospholipase A₂ Together, our data support the hypothesis that glutamate released during seizures signals an increase in MMP-2 and MMP-9 protein expression and activity levels, resulting in blood-brain barrier leakage.SIGNIFICANCE STATEMENT The mechanism leading to seizure-mediated blood-brain barrier dysfunction in epilepsy is poorly understood. In the present study, we focused on defining this mechanism in the brain capillary endothelium. We demonstrate that seizures trigger a pathway that involves glutamate signaling through cytosolic phospholipase A₂, which increases MMP levels and decreases tight junction protein expression levels, resulting in barrier leakage. These findings may provide potential therapeutic avenues within the blood-brain barrier to limit barrier dysfunction in epilepsy and decrease seizure burden.

NMDA-Type Glutamate Receptor Activation Promotes Vascular Remodeling and Pulmonary Arterial Hypertension

BACKGROUND

Excessive proliferation and apoptosis resistance in pulmonary vascular cells underlie vascular remodeling in pulmonary arterial hypertension (PAH). Specific treatments for PAH exist, mostly targeting endothelial dysfunction, but high pulmonary arterial pressure still causes heart failure and death. Pulmonary vascular remodeling may be driven by metabolic reprogramming of vascular cells to increase glutaminolysis and glutamate production. The N-methyl-d-aspartate receptor (NMDAR), a major neuronal glutamate receptor, is also expressed on vascular cells, but its role in PAH is unknown.

METHODS

We assessed the status of the glutamate-NMDAR axis in the pulmonary arteries of patients with PAH and controls through mass spectrometry imaging, Western blotting, and immunohistochemistry. We measured the glutamate release from cultured pulmonary vascular cells using enzymatic assays and analyzed NMDAR regulation/phosphorylation through Western blot experiments. The effect of NMDAR blockade on human pulmonary arterial smooth muscle cell proliferation was determined using a BrdU incorporation assay. We assessed the role of NMDARs in vascular remodeling associated to pulmonary hypertension, in both smooth muscle-specific NMDAR knockout mice exposed to chronic hypoxia and the monocrotaline rat model of pulmonary hypertension using NMDAR blockers.

RESULTS

We report glutamate accumulation, upregulation of the NMDAR, and NMDAR engagement reflected by increases in GluN1-subunit phosphorylation in the pulmonary arteries of human patients with PAH. K_v channel inhibition and type A-selective endothelin receptor activation amplified calcium-dependent glutamate release from human pulmonary arterial smooth muscle cell, and type A-selective endothelin receptor and platelet-derived growth factor receptor activation led to NMDAR engagement, highlighting crosstalk between the glutamate-NMDAR axis and major PAH-associated pathways. The platelet-derived growth factor-BB-induced proliferation of human pulmonary arterial smooth muscle cells involved NMDAR activation and phosphorylated GluN1 subunit localization to cell-cell contacts, consistent with glutamatergic communication between proliferating human pulmonary arterial smooth muscle cells via NMDARs. Smooth-muscle NMDAR deficiency in mice attenuated the vascular remodeling triggered by chronic hypoxia, highlighting the role of vascular NMDARs in pulmonary hypertension. Pharmacological NMDAR blockade in the monocrotaline rat model of pulmonary hypertension had beneficial effects on cardiac and vascular remodeling, decreasing endothelial dysfunction, cell proliferation, and apoptosis resistance while disrupting the glutamate-NMDAR pathway in pulmonary arteries.

CONCLUSIONS

These results reveal a dysregulation of the glutamate-NMDAR axis in the pulmonary arteries of patients with PAH and identify vascular NMDARs as targets for antiremodeling treatments in PAH.

Glutamate-Mediated Blood-Brain Barrier Opening: Implications for Neuroprotection and Drug Delivery

The blood-brain barrier is a highly selective anatomical and functional interface allowing a unique environment for neuro-glia networks. Blood-brain barrier dysfunction is common in most brain disorders and is associated with disease course and delayed complications. However, the mechanisms underlying blood-brain barrier opening are poorly understood. Here we demonstrate the role of the neurotransmitter glutamate in modulating early barrier permeability in vivo Using intravital microscopy, we show that recurrent seizures and the associated excessive glutamate release lead to increased vascular permeability in the rat cerebral cortex, through activation of NMDA receptors. NMDA receptor antagonists reduce barrier permeability in the peri-ischemic brain, whereas neuronal activation using high-intensity magnetic stimulation increases barrier permeability and facilitates drug delivery. Finally, we conducted a double-blind clinical trial in patients with malignant glial tumors, using contrast-enhanced magnetic resonance imaging to quantitatively assess blood-brain barrier permeability. We demonstrate the safety of stimulation that efficiently increased blood-brain barrier permeability in 10 of 15 patients with malignant glial tumors. We suggest a novel mechanism for the bidirectional modulation of brain vascular permeability toward increased drug delivery and prevention of delayed complications in brain disorders.

SIGNIFICANCE STATEMENT

In this study, we reveal a new mechanism that governs blood-brain barrier (BBB) function in the rat cerebral cortex, and, by using the discovered mechanism, we demonstrate bidirectional control over brain endothelial permeability. Obviously, the clinical potential of manipulating BBB permeability for neuroprotection and drug delivery is immense, as we show in preclinical and proof-of-concept clinical studies. This study addresses an unmet need to induce transient BBB opening for drug delivery in patients with malignant brain tumors and effectively facilitate BBB closure in neurological disorders.

Connexin Channels at the Glio-Vascular Interface: Gatekeepers of the Brain

Neuronal survival, electrical signaling and synaptic activity require a well-balanced micro-environment in the central nervous system. This is achieved by the blood-brain barrier (BBB), an endothelial barrier situated in the brain capillaries, that controls near-to-all passage in and out of the brain. The endothelial barrier function is highly dependent on signaling interactions with surrounding glial, neuronal and vascular cells, together forming the neuro-glio-vascular unit. Within this functional unit, connexin (Cx) channels are of utmost importance for intercellular communication between the different cellular compartments. Connexins are best known as the building blocks of gap junction (GJ) channels that enable direct cell-cell transfer of metabolic, biochemical and electric signals. In addition, beyond their role in direct intercellular communication, Cxs also form unapposed, non-junctional hemichannels in the plasma membrane that allow the passage of several paracrine messengers, complementing direct GJ communication. Within the NGVU, Cxs are expressed in vascular endothelial cells, including those that form the BBB, and are eminent in astrocytes, especially at their endfoot processes that wrap around cerebral vessels. However, despite the density of Cx channels at this so-called gliovascular interface, it remains unclear as to how Cx-based signaling between astrocytes and BBB endothelial cells may converge control over BBB permeability in health and disease. In this review we describe available evidence that supports a role for astroglial as well as endothelial Cxs in the regulation of BBB permeability during development as well as in disease states.

Osteonecrosis in children with acute lymphoblastic leukemia

The morbidity and toxicity associated with current intensive treatment protocols for acute lymphoblastic leukemia in childhood become even more important as the vast majority of children can be cured and become long-term survivors. Osteonecrosis is one of the most common therapy-related and debilitating side effects of anti-leukemic treatment and can adversely affect long-term quality of life. Incidence and risk factors vary substantially between study groups and therapeutic regimens. We therefore analyzed 22 clinical trials of childhood acute lymphoblastic leukemia in terms of osteonecrosis incidence and risk factors. Adolescent age is the most significant risk factor, with patients >10 years old at the highest risk. Uncritical modification or even significant reduction of glucocorticoid dosage cannot be recommended at this stage. A novel and innovative approach to reduce osteonecrosis-associated morbidity might be systematic early screening for osteonecrosis by serial magnetic resonance images. However, discriminating patients at risk of functional impairment and debilitating progressive joint disease from asymptomatic patients still remains challenging.

Identification of Target Genes Involved in Wound Healing Angiogenesis of Endothelial Cells with the Treatment of a Chinese 2-Herb Formula

Angiogenesis is vitally important in diabetic wound healing. We had previously demonstrated that a Chinese 2-herb formula (NF3) significantly stimulated angiogenesis of HUVEC in wound healing. However, the molecular mechanism has not yet been elucidated. In line with this, global expression profiling of NF3-treated HUVEC was performed so as to assess the regulatory role of NF3 involved in the underlying signaling pathways in wound healing angiogenesis. The microarray results illustrated that different panels of differentially expressed genes were strictly governed in NF3-treated HUVEC in a time-regulated manner. The microarray analysis followed by qRT-PCR and western blotting verification of NF3-treated HUVEC at 6 h revealed the involvement of various genes in diverse biological process, e.g., MAP3K14 in anti-inflammation; SLC5A8 in anti-tumorogenesis; DNAJB7 in protein translation; BIRC5, EPCAM, INSL4, MMP8 and NPR3 in cell proliferation; CXCR7, EPCAM, HAND1 and MMP8 in migration; CXCR7, EPCAM and MMP8 in tubular formation; and BIRC5, CXCR7, EPCAM, HAND1, MMP8 and UBD in angiogenesis. After 16 h incubation of NF3, other sets of genes were shown with differential expression in HUVEC, e.g., IL1RAPL2 and NR1H4 in anti-inflammation; miR28 in anti-tumorogenesis; GRIN1 and LCN1 in anti-oxidation; EPB41 in intracellular signal transduction; PRL and TFAP2A in cell proliferation; miR28, PRL and SCG2 in cell migration; PRL in tubular formation; and miR28, NR1H4 and PRL in angiogenesis. This study provided concrete scientific evidence in support of the regulatory role of NF3 on endothelial cells involved in wound healing angiogenesis.

Genetics of glucocorticoid-associated osteonecrosis in children with acute lymphoblastic leukemia

Glucocorticoids are important therapy for acute lymphoblastic leukemia (ALL) and their major adverse effect is osteonecrosis. Our goal was to identify genetic and nongenetic risk factors for osteonecrosis. We performed a genome-wide association study of single nucleotide polymorphisms (SNPs) in a discovery cohort comprising 2285 children with ALL, treated on the Children's Oncology Group AALL0232 protocol (NCT00075725), adjusting for covariates. The minor allele at SNP rs10989692 (near the glutamate receptor GRIN3A locus) was associated with osteonecrosis (hazard ratio = 2.03; P = 3.59 × 10(-7)). The association was supported by 2 replication cohorts, including 361 children with ALL on St. Jude's Total XV protocol (NCT00137111) and 309 non-ALL patients from Vanderbilt University's BioVU repository treated with glucocorticoids (odds ratio [OR] = 1.87 and 2.26; P = .063 and .0074, respectively). In a meta-analysis, rs10989692 was also highest ranked (P = 2.68 × 10(-8)), and the glutamate pathway was the top ranked pathway (P = 9.8 × 10(-4)). Osteonecrosis-associated glutamate receptor variants were also associated with other vascular phenotypes including cerebral ischemia (OR = 1.64; P = 2.5 × 10(-3)), and arterial embolism and thrombosis (OR = 1.88; P = 4.2 × 10(-3)). In conclusion, osteonecrosis was associated with inherited variations near glutamate receptor genes. Further understanding this association may allow interventions to decrease osteonecrosis. These trials are registered at www.clinicaltrials.gov as #NCT00075725 and #NCT00137111.

Status epilepticus, blood-brain barrier disruption, inflammation, and epileptogenesis

Over the last 15 years, attention has been focused on dysfunction of the cerebral vasculature and inflammation as important players in epileptogenic processes, with a specific emphasis on failure of the blood-brain barrier (BBB; Fig. 1) (Seiffert et al., 2004; Marchi et al., 2007; Oby and Janigro, 2006; van Vliet et al., 2014; Vezzani et al., 2011) [3-7]. Here, we discuss how the BBB is disrupted as a consequence of SE and how this BBB breakdown may be involved in epileptogenesis. This article is part of a Special Issue entitled "Status Epilepticus".

Memantine Attenuates Delayed Vasospasm after Experimental Subarachnoid Hemorrhage via Modulating Endothelial Nitric Oxide Synthase

Delayed cerebral vasospasm is an important pathological feature of subarachnoid hemorrhage (SAH). The cause of vasospasm is multifactorial. Impairs nitric oxide availability and endothelial nitric oxide synthase (eNOS) dysfunction has been reported to underlie vasospasm. Memantine, a low-affinity uncompetitive N-methyl-d-aspartate (NMDA) blocker has been proven to reduce early brain injury after SAH. This study investigated the effect of memantine on attenuation of vasospasm and restoring eNOS functionality. Male Sprague-Dawley rats weighing 350–450 g were randomly divided into three weight-matched groups, sham surgery, SAH + vehicle, and SAH + memantine groups. The effects of memantine on SAH were evaluated by assessing the severity of vasospasm and the expression of eNOS. Memantine effectively ameliorated cerebral vasospasm by restoring eNOS functionality. Memantine can prevent vasospasm in experimental SAH. Treatment strategies may help combat SAH-induced vasospasm in the future.

Methamphetamine effects on blood-brain barrier structure and function

Methamphetamine (Meth) is a widely abuse psychostimulant. Traditionally, studies have focused on the neurotoxic effects of Meth on monoaminergic neurotransmitter terminals. Recently, both in vitro and in vivo studies have investigated the effects of Meth on the BBB and found that Meth produces a decrease in BBB structural proteins and an increase in BBB permeability to various molecules. Moreover, preclinical studies are validated by clinical studies in which human Meth users have increased concentrations of toxins in the brain. Therefore, this review will focus on the structural and functional disruption of the BBB caused by Meth and the mechanisms that contribute to Meth-induced BBB disruption. The review will reveal that the mechanisms by which Meth damages dopamine and serotonin terminals are similar to the mechanisms by which the blood-brain barrier (BBB) is damaged. Furthermore, this review will cover the factors that are known to potentiate the effects of Meth (McCann et al., 1998) on the BBB, such as stress and HIV, both of which are co-morbid conditions associated with Meth abuse. Overall, the goal of this review is to demonstrate that the scope of damage produced by Meth goes beyond damage to monoaminergic neurotransmitter systems to include BBB disruption as well as provide a rationale for investigating therapeutics to treat Meth-induced BBB disruption. Since a breach of the BBB can have a multitude of consequences, therapies directed toward the treatment of BBB disruption may help to ameliorate the long-term neurodegeneration and cognitive deficits produced by Meth and possibly even Meth addiction.

The effects of the modulation of NMDA receptors by homocysteine thiolactone and dizocilpine on cardiodynamics and oxidative stress in isolated rat heart

In light of the limited data concerning the role of N-methyl-D-aspartate (NMDA) receptors in cardiac function, the aim of the present study was to determine the role of NMDA receptors in cardiac function, as well as the possible role played by the oxidative stress induced by the overstimulation of NMDA receptors in isolated rat heart. The hearts of male, Wistar albino rats (n = 24, 12 in each experimental group, BM 180-200 g) were retrogradely perfused at a constant perfusion pressure (70 cm H₂O₂), using the Langendorff technique, and cardiodynamic parameters were determined during the subsequent administration of DL-homocysteine thiolactone (DL-Hcy TLHC) alone, the combination of DL-Hcy TLHC and dizocilpine (MK-801), and MK-801 alone. In the second experimental group, the order of the administration of each of the substances was reversed. The oxidative stress biomarkers, including thiobarbituric acid reactive substances (TBARS), NO(2)(-), O(2)(-) and H₂O₂, were each determined spectrophotometrically. DL-Hcy TLHC and MK-801 depressed cardiac function. DL-Hcy TLHC decreased oxidative stress, a finding that contrasted with the results of the experiments in which MK-801 was administered first. The findings of this study were suggestive of the likely role played by NMDA receptors in the regulation of cardiac function and coronary circulation in isolated rat heart.

Genetic variants of glutamate receptor gene family in Taiwanese Kawasaki disease children with coronary artery aneurysms

BACKGROUND

Patients with Kawasaki disease (KD), a pediatric systemic vasculitis, may develop coronary artery aneurysm (CAA) as a complication. To investigate the role of glutamate receptors in KD and its CAA development, we performed genetic association studies.

METHODS AND RESULTS

We examined the whole family of glutamate receptors by genetic association studies in a Taiwanese cohort of 262 KD patients. We identified glutamate receptor ionotropic, kainate 1 (GRIK1) as a novel susceptibility locus associated with CAA formation in KD. Statistically significant differences were noted for factors like fever duration, 1st Intravenous immunoglobulin (IVIG) used time (number of days after the first day of fever) and the GRIK1 (rs466013, rs425507, and rs38700) genetic variants. This significant association persisted even after using multivariate regression analysis (Full model: for rs466013: odds ratio =2.12; 95% CI =1.22-3.65; for rs425507: odds ratio =2.16; 95% CI =1.26-3.76; for rs388700: odds ratio =2.16; 95% CI =1.26-3.76).

CONCLUSIONS

We demonstrated that GRIK1 polymorphisms are associated CAA formation in KD, even when adjusted for fever duration and IVIG used time, and may also serve as a genetic marker for the CAA formation in KD.

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 pathophysiology in traumatic brain injury

The blood-brain barrier (BBB) is formed by tightly connected cerebrovascular endothelial cells, but its normal function also depends on paracrine interactions between the brain endothelium and closely located glia. There is a growing consensus that brain injury, whether it is ischemic, hemorrhagic, or traumatic, leads to dysfunction of the BBB. Changes in BBB function observed after injury are thought to contribute to the loss of neural tissue and to affect the response to neuroprotective drugs. New discoveries suggest that considering the entire gliovascular unit, rather than the BBB alone, will expand our understanding of the cellular and molecular responses to traumatic brain injury (TBI). This review will address the BBB breakdown in TBI, the role of blood-borne factors in affecting the function of the gliovascular unit, changes in BBB permeability and post-traumatic edema formation, and the major pathophysiological factors associated with TBI that may contribute to post-traumatic dysfunction of the BBB. The key role of neuroinflammation and the possible effect of injury on transport mechanisms at the BBB will also be described. Finally, the potential role of the BBB as a target for therapeutic intervention through restoration of normal BBB function after injury and/or by harnessing the cerebrovascular endothelium to produce neurotrophic growth factors will be discussed.

Association between GRIN3A gene polymorphism in Kawasaki disease and coronary artery aneurysms in Taiwanese children

Kawasaki disease (KD) is pediatric systemic vasculitis with the classic complication of coronary artery aneurysm (CAA). It is the leading cause of acquired cardiovascular diseases in children. Some severe cases present with multi-organ involvement or neurological dysfunction. To identify the role of the glutamate receptor, ionotropic, N-methyl-d-aspartate 3A (GRIN3A) in KD, we investigated genetic variations in GRIN3A in a Taiwanese cohort of 262 KD patients (76 with and 186 without CAA complications). We used univariate and multivariate regression analyses to identify the associations between clinical characteristics and GRIN3A genetic variations in KD. According to univariate regression analysis, CAA formation in KD was significantly associated with fever duration (p < 0.0001), first Intravenous immunoglobulin (IVIG) used (days after day one of fever) (p < 0.0001), and the GRIN3A (rs7849782) genetic variant (p < 0.001). KD patients with GG+GC genotype showed a lower rate of developing CAA (GG+GC genotype: odds ratio = 0.26; 95% CI = 0.14–0.46). Significant associations were identified between KD with CAA complication and the GRIN3A (rs7849782) genetic variant by using multivariate regression analysis. Specifically, significant correlations were observed between KD with CAA complications and the presence of GG+GC genotypes for the GRIN3A rs7849782 single-nucleotide polymorphism (full model: odds ratio = 0.25; 95% CI = 0.14–0.46). Our results suggest that a polymorphism of the GRIN3A gene may play a role in KD pathogenesis.

Venous endothelial injury in central nervous system diseases

The role of the venous system in the pathogenesis of inflammatory neurological/neurodegenerative diseases remains largely unknown and underinvestigated. Aside from cerebral venous infarcts, thromboembolic events, and cerebrovascular bleeding, several inflammatory central nervous system (CNS) diseases, such as multiple sclerosis (MS), acute disseminated encephalomyelitis (ADEM), and optic neuritis, appear to be associated with venous vascular dysfunction, and the neuropathologic hallmark of these diseases is a perivenous, rather than arterial, lesion. Such findings raise fundamental questions about the nature of these diseases, such as the reasons why their pathognomonic lesions do not develop around the arteries and what exactly are the roles of cerebral venous inflammation in their pathogenesis. Apart from this inflammatory-based view, a new hypothesis with more focus on the hemodynamic features of the cerebral and extracerebral venous system suggests that MS pathophysiology might be associated with the venous system that drains the CNS. Such a hypothesis, if proven correct, opens new therapeutic windows in MS and other neuroinflammatory diseases. Here, we present a comprehensive review of the pathophysiology of MS, ADEM, pseudotumor cerebri, and optic neuritis, with an emphasis on the roles of venous vascular system programming and dysfunction in their pathogenesis. We consider the fundamental differences between arterial and venous endothelium, their dissimilar responses to inflammation, and the potential theoretical contributions of venous insufficiency in the pathogenesis of neurovascular diseases.

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.

High t-PA release by neonate brain microvascular endothelial cells under glutamate exposure affects neuronal fate

Glutamate excitotoxicity is a consolidated hypothesis in neonatal brain injuries and tissue plasminogen activator (t-PA) participates in the processes through proteolytic and receptor mediated effects. In brain microvascular endothelial cell (nBMEC) cultures from neonates, t-PA content and release upon glutamate are higher than in adult (aBMECs) cultures. Owing to the variety of t-PA substrates and receptor targets, the study was aimed at determining the putative roles of endothelial t-PA in the neonatal brain parenchyma under glutamate challenge. Basal t-PA release was 4.4 fold higher in nBMECs vs aBMECs and glutamate was 20 fold more potent to allow Evans blue vascular permeability in neonate microvessels indicating that, under noxious glutamate (50 μM) exposure, high amounts of endothelial t-PA stores may be mobilized and may access the nervous parenchyma. Culture media from nBMECS or aBMECs challenged by excitotoxic glutamate were applied to neuron cultures at DIV 11. While media from adult cells did not evoke more LDH release in neuronal cultures that under glutamate alone, media from nBMECs enhanced 2.2 fold LDH release. This effect was not observed with media from t-PA(-/-) nBMECs and was inhibited by hr-PAI-1. In Cortical slices from 10 day-old mice, hrt-PA associated with glutamate evoked neuronal necrosis in deeper (more mature) layers, an effect reversed by NMDA receptor GluN1 amino-terminal domain antibody capable of inhibiting t-PA potentiation of the receptor. In superficial layers (less mature), hrt-PA alone inhibited apoptosis, an effect reversed by the EGF receptor antagonist AG1478. Applied to immature neurons in culture (DIV5), media from nBMEC rescued 85.1% of neurons from cell death induced by serum deprivation. In cortical slices, the anti-apoptotic effect of t-PA fitted with age dependent localization of less mature neurons. These data suggest that in the immature brain, propensity of vessels to release high amounts of t-PA may not only impact vascular integrity but may also influence neuronal fate, via regulation of apoptosis in immature cells and, as in adult by potentiating glutamate toxicity in mature neurons. The data point out putative implication of microvessels in glutamate neurotoxicity in the development, and justify research towards vessel oriented neuroprotection strategies in neonates.

Emerging roles of endothelial cells in multiple sclerosis pathophysiology and therapy

Although multiple sclerosis (MS) has traditionally been viewed and researched as an immune-mediated demyelinating and neurodegenerative disease of the human central nervous system (CNS), its highly complex pathogenesis clearly includes a significant vascular inflammatory component and many therapeutic approaches achieve benefit by direct or indirect effects on cerebrovascular endothelial cells. Cerebral endothelial cells create and separate the compartments of the peripheral circulation and CNS creating the blood-brain barrier (BBB), a selectively permeable boundary layer between these spaces. Interactions between activated leukocytes and cerebral endothelium play essential roles in mediating their trans-BBB diapedesis during normal immune surveillance and during pathogenesis of neuroinflammatory diseases like MS. Extravasation of activated and committed leukocytes from the peripheral circulation through the endothelial layer of the BBB into the CNS milieu is the most fundamental step in formation of MS lesions. During MS pathogenesis, once the activated leukocytes enter the CNS environment, they propagate a massive wave of destruction which culminates in the loss of both myelin/oligodendrocyte complex and neurodegeneration. Multiple clinical and basic scientific observations support endothelial cell 'stress' and apoptosis as a hallmark characteristic of MS. The manipulation of the endothelial biology aiming to block trans-endothelial migration of activated immune cells into the CNS is a potent form of treatment for MS achieving significant reductions in disease activity and new lesion formation. In particular, endothelial microparticles are now well-recognized as important biomarkers and mediators of this type of stress. In this review, we discuss recent findings and new advances in our knowledge regarding leukocyte migration through the endothelial frontier of the BBB and how this can be exploited toward treating MS patients.

The crossroads of neuroinflammation in infectious diseases: endothelial cells and astrocytes

Homeostasis implies constant operational defence mechanisms, against both external and internal threats. Infectious agents are prominent among such threats. During infection, the host elicits the release of a vast array of molecules and numerous cell-cell interactions are triggered. These pleiomorphic mediators and cellular effects are of prime importance in the defence of the host, both in the systemic circulation and at sites of tissue injury, for example, the blood-brain barrier (BBB). Here, we focus on the interactions between the endothelium, astrocytes, and the molecules they release. Our review addresses these interactions during infectious neurological diseases of various origins, especially cerebral malaria (CM). Two novel elements of the interplay between endothelium and astrocytes, microparticles and the kynurenine pathway, will also be discussed.

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.

Pathogenic implications of iron accumulation in multiple sclerosis

Iron, an essential element used for a multitude of biochemical reactions, abnormally accumulates in the CNS of patients with multiple sclerosis (MS). The mechanisms of abnormal iron deposition in MS are not fully understood, nor do we know whether these deposits have adverse consequences, that is, contribute to pathogenesis. With some exceptions, excess levels of iron are represented concomitantly in multiple deep gray matter structures often with bilateral representation, whereas in white matter, pathological iron deposits are usually located at sites of inflammation that are associated with veins. These distinct spatial patterns suggest disparate mechanisms of iron accumulation between these regions. Iron has been postulated to promote disease activity in MS by various means: (i) iron can amplify the activated state of microglia resulting in the increased production of proinflammatory mediators; (ii) excess intracellular iron deposits could promote mitochondria dysfunction; and (iii) improperly managed iron could catalyze the production of damaging reactive oxygen species (ROS). The pathological consequences of abnormal iron deposits may be dependent on the affected brain region and/or accumulation process. Here, we review putative mechanisms of enhanced iron uptake in MS and address the likely roles of iron in the pathogenesis of this disease.

Effects of NMDA receptor modulators on a blood-brain barrier in vitro model

Changes of the functionality of the blood-brain barrier (BBB) have been reported in the context of several brain related diseases such as multiple sclerosis, epilepsy, Alzheimer's disease and stroke. Several publications indicated the presence and functionality of the NMDA receptor (NMDAR) at the brain endothelium and a possible involvement of the NMDAR in the above-mentioned diseases. Recently, it was shown that the application of the NMDAR antagonist MK801 can block several adverse effects at the BBB in vitro, but also that MK801 can significantly change the proteome of brain endothelial cells without simultaneous stimulation of NMDAR by glutamate. Based on these reports we investigated if NMDAR antagonists MK801 and D-APV can affect the intracellular calcium level (Ca²⁺i) of an in vitro BBB model based on human cell line ECV304 on their own and compared these results to effects mediated by NMDAR agonists glutamate and NMDA. Treatment of ECV304 cells for 30 min with glutamate resulted in no significant change of Ca²⁺i. On the contrary, application of NMDA and NMDAR antagonists D-APV and MK801 led to a significant and concentration dependent decrease of Ca²⁺i. Further studies revealed that glutamate was able to decrease the transendothelial electrical resistance (TEER) of the BBB in vitro model, whereas NMDA and D-APV were able to increase TEER. Analysis of the protein expression levels of tight junctional molecules ZO-1 and occludin showed a complex regulation after application of NMDAR modulators. In summary, it was shown that NMDAR antagonists can alter BBB key properties in vitro on their own. Moreover, although qPCR results confirmed the presence of NMDA receptor subunits NR1, NR2A, NR2B and NR2C, membrane binding studies failed to prove the typical plasma membrane localization and functionality in human BBB cell line ECV304.

Neurovascular protective effect of FeTPPs in N-methyl-D-aspartate model: similarities to diabetes

We have previously shown a causal role of peroxynitrite in mediating retinal ganglion cell (RGC) death in diabetic and neurotoxicity models. In the present study, the role of peroxynitrite in altering the antioxidant and antiapoptotic thioredoxin (Trx) system will be investigated as well as the subsequent effects on glial activation and capillary degeneration. Excitotoxicity of the retina was induced by intravitreal injection of N-methyl-d-aspartate (NMDA) in rats, which also received the peroxynitrite decomposition catalyst FeTPPs. RGC loss was assessed by terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling and GC count. Glial activation and nitrotyrosine were assessed by immunohistochemistry. Acellular capillaries and pericytes were counted in retinal trypsin digest. NMDA-induced peroxynitrite formation caused RGC loss, which was associated with enhanced expression of Trx and its endogenous inhibitor thioredoxin interacting protein. The results also showed enhanced thioredoxin interacting protein/Trx binding and disruption of the Trx/apoptosis signal-regulating kinase 1 "inhibitory complex," leading to release of apoptosis signal-regulating kinase 1 and activation of the apoptotic pathway, as evidenced by p38 MAPK and poly-ADP-ribose polymerase activation. Furthermore, NMDA caused glial activation and compromised retinal vasculature, as indicated by acellular-capillary formation and pericyte loss. Treatment with FeTPPs blocked these effects. In conclusion, NMDA-induced retinal neuro/vascular injury is mediated by peroxynitrite-altered Trx antioxidant defense, which in turn activates the apoptosis signal-regulating kinase-1 apoptotic pathway. In addition to acute RGC death, an NMDA model can be a useful tool to study glial activation and capillary degeneration in retinal neurodegenerative disorders, including diabetic retinopathy.

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.

The effects of NMDA receptor antagonists over intestinal ischemia/reperfusion injury in rats

Intestinal ischemia/reperfusion causes severe injury and alters motility. N-methyl-D-aspartate (NMDA) receptor antagonists have been shown to reduce ischemia/reperfusion injury in the nervous system, and in other organs. In this study, we set out to investigate the effects of NMDA receptor antagonists over intestinal ischemia/reperfusion injury. Male Wistar rats were randomly divided into four groups: (1) a control, sham-operated group; (2) an intestinal ischemia/reperfusion group subjected to 45 min ischemia and 1h reperfusion; (3) a group treated with 10 mg/kg ketamine before ischemia/reperfusion; and (4) a group treated with 10 mg/kg memantine before ischemia/reperfusion. Intestinal samples were taken for histological evaluation. Serum levels of aspartate aminotransferase (AST), alanine aminotransferase (ALT), lactate dehydrogenase (LDH), malondialdehyde (MDA), total antioxidant capacity, tumor necrosis factor alpha (TNF-alpha), P-selectin and antithrombin III (ATIII) were measured. Intestinal transit time was determined to evaluate intestinal motility. Fecal pellet output and animal weight were also registered daily for 7 days post-ischemia. After reperfusion, AST, LDH, TNF-alpha and P-selectin levels were elevated, ATIII levels were depleted, and ALT levels were unchanged in serum. Additionally, levels of MDA were increased and total antioxidant capacity was reduced in serum, indicating oxidative stress. Intestinal mucosa showed severe injury. Ketamine, but not memantine, diminished these alterations. Intestinal motility and fecal pellet output were also altered after ischemia/reperfusion. Both drugs abolished the alterations in motility. In conclusion, ketamine's protective effects over ischemia/reperfusion do not appear to be NMDA mediated, but they could be playing a role in protecting the intestine against ischemia-induced functional changes.