Mast cell blocking reduces brain edema and hematoma volume and improves outcome after experimental intracerebral hemorrhage

Role and mechanisms of mast cells in brain disorders

Mast cells serve as crucial effector cells within the innate immune system and are predominantly localized in the skin, airways, gastrointestinal tract, urinary and reproductive tracts, as well as in the brain. Under physiological conditions, brain-resident mast cells secrete a diverse array of neuro-regulatory mediators to actively participate in neuroprotection. Meanwhile, as the primary source of molecules causing brain inflammation, mast cells also function as the "first responders" in brain injury. They interact with neuroglial cells and neurons to facilitate the release of numerous inflammatory mediators, proteases, and reactive oxygen species. This process initiates and amplifies immune-inflammatory responses in the brain, thereby contributing to the regulation of neuroinflammation and blood-brain barrier permeability. This article provides a comprehensive overview of the potential mechanisms through which mast cells in the brain may modulate neuroprotection and their pathological implications in various neurological disorders. It is our contention that the inhibition of mast cell activation in brain disorders could represent a novel avenue for therapeutic breakthroughs.

Preliminary Analysis of Aging-Related Genes in Intracerebral Hemorrhage by Integration of Bulk and Single-Cell RNA Sequencing Technology

Background

Aging is recognized as the key risk for intracerebral hemorrhage (ICH). The detailed mechanisms of aging in ICH warrant exploration. This study aimed to identify potential aging-related genes associated with ICH.

Methods

ICH-specific aging-related genes were determined by the intersection of differentially expressed genes (DEGs) between perihematomal tissues and corresponding contralateral parts of four patients with ICH (GSE24265) and 349 aging-related genes obtained from the Aging Atlas database. Gene Ontology (GO), Kyoto Encyclopedia of Genes and Genomes (KEGG) and Gene Set Enrichment Analysis (GSEA) analyses were performed to identify the potential biological functions and pathways in which these ICH-specific aging-related genes may be involved. Then, PPI network was established to identify the hub genes of ICH-specific aging-related genes. Meanwhile, miRNA-mRNA and transcription factor (TF)-mRNA regulatory networks were constructed to further explore the ICH-specific aging-related genes regulation. The relationship between these hub genes and immune infiltration was also further explored. Additional single-cell RNA-seq analysis (scRNA-seq, GSE167593) was used to locate the hub genes in different cell types. Besides, expression levels of the hub genes were validated using clinical samples from our institute and another GEO dataset (GSE206971).

Results

This study identified 24 ICH-specific aging-related genes, including 22 up-regulated and 2 down-regulated genes. The results of GO and KEGG suggested that the ICH-specific aging-related genes mainly enriched in immunity and inflammation-related pathways, suggesting that aging may affect the ich pathogenesis by regulating inflammatory and immune-related pathways.

Conclusion

Our study revealed 24 ICH-specific aging-related genes and their functions highly pertinent to ICH pathogenesis, providing new insights into the impact of aging on ICH.

Combined effect of trifluoperazine and sodium cromoglycate on reducing acute edema and limiting lasting functional impairments after spinal cord injury in rats

Edema formation is one of the very first events to occur after spinal cord injury (SCI) leading to an increase of the intrathecal pressure and consequently to serious spinal tissue and functional impairments. Current edema treatments are still symptomatic and/or non-specific. Since edema formation mechanisms are mainly described as vasogenic and cytotoxic, it becomes crucial to understand the interplay between these two subtypes. Acting on key targets to inhibit edema formation may reduce secondary damage and related functional impairments. In this study, we characterize the edema kinetic after T9-10 spinal contusion. We use trifluoperazine (TFP) to block the expression and the functional subcellular localization of aquaporin-4 supposed to be implicated in the cytotoxic edema formation. We also use sodium cromoglycate (SCG) to deactivate mast cell degranulation known to be implicated in the vasogenic edema formation. Our results show a significant reduction of edema after TFP treatment and after TFP-SCG combined treatment compared to control. This reduction is correlated with limited onset of initial sensorimotor impairments particularly after combined treatment. Our results highlight the importance of potential synergetic targets in early edema therapy after SCI as part of tissue sparing strategies.

Immune compartments at the brain's borders in health and neurovascular diseases

Recent evidence implicates cranial border immune compartments in the meninges, choroid plexus, circumventricular organs, and skull bone marrow in several neuroinflammatory and neoplastic diseases. Their pathogenic importance has also been described for cardiovascular diseases such as hypertension and stroke. In this review, we will examine the cellular composition of these cranial border immune niches, the potential pathways through which they might interact, and the evidence linking them to cardiovascular disease.

Potential role of IGF-1/GLP-1 signaling activation in intracerebral hemorrhage

IGF-1 and GLP-1 receptors are essential in all tissues, facilitating defense by upregulating anabolic processes. They are abundantly distributed throughout the central nervous system, promoting neuronal proliferation, survival, and differentiation. IGF-1/GLP-1 is a growth factor that stimulates neurons' development, reorganization, myelination, and survival. In primary and secondary brain injury, the IGF-1/GLP-1 receptors are impaired, resulting in further neuro complications such as cerebral tissue degradation, neuroinflammation, oxidative stress, and atrophy. Intracerebral hemorrhage (ICH) is a severe condition caused by a stroke for which there is currently no effective treatment. While some pre-clinical studies and medications are being developed as symptomatic therapies in clinical trials, there are specific pharmacological implications for improving post-operative conditions in patients with intensive treatment. Identifying the underlying molecular process and recognizing the worsening situation can assist researchers in developing effective therapeutic solutions to prevent post-hemorrhagic symptoms and the associated neural dysfunctions. As a result, in the current review, we have addressed the manifestations of the disease that are aggravated by the downregulation of IGF-1 and GLP-1 receptors, which can lead to ICH or other neurodegenerative disorders. Our review summarizes that IGF-1/GLP-1 activators may be useful for treating ICH and its related neurodegeneration.

ER Stress is Involved in Mast Cells Degranulation via IRE1α/miR-125/Lyn Pathway in an Experimental Intracerebral Hemorrhage Mouse Model

The degranulation of mast cells accounts for the development of neuroinflammation following intracerebral hemorrhage (ICH). Inhibition of IRE1α, a sensor signaling protein related to endoplasmic reticulum stress, has been shown to exert anti-inflammatory effects in several neurological diseases. The objective of this study was to investigate the effects of IRE1α inhibition on mast cells degranulation in an ICH mouse model and to explore the contribution of miR-125/Lyn pathway in IRE1α-mediated mast cells degranulation. Male mice were subjected to ICH by intraparenchymal injection of autologous blood. STF083010, an inhibitor of IRE1α, was administered intranasally at 1 h after ICH induction. AntimiR-125 was delivered by intracerebroventricular (i.c.v.) injection prior to ICH induction to elucidate the possible mechanisms. Western blot analysis, immunofluorescence staining, neurological test, hematoma volume, brain water content, toluidine blue staining and reverse transcription quantitative real-time polymerase chain reaction (RT-qPCR) were performed. Endogenous phosphorylated IRE1α (p-IRE1α), tryptase, interleukin-17A (IL-17A), tumor necrosis factor α (TNF-α) and tryptase mRNA were increased in time dependent manner while miR-125b-2-3p was decreased after ICH. Inhibition of IRE1α, with STF083010, remarkably reduced brain water content, improved neurological function, decreased hematoma volume, upregulated the expression of miR-125b-2-3p, decreased the number of mast cells, and downregulated the protein expression of Lyn kinase, XBP1s (spliced X-box binding protein-1), tryptase, IL-17A and TNF-α. The downregulation of Lyn kinase, tryptase, IL-17A, TNF-α, and decreased mast cells number were reversed by antimiR-125. The present findings demonstrate that IRE1α inhibition attenuates mast cells degranulation and neuroinflammation, at least partially, through IRE1α/miR-125/Lyn signaling pathway after ICH.

Anticoagulation targeting membrane-bound anionic phospholipids improves outcomes of traumatic brain injury in mice

Severe traumatic brain injury (TBI) often causes an acute systemic hypercoagulable state that rapidly develops into consumptive coagulopathy. We have recently demonstrated that TBI-induced coagulopathy (TBI-IC) is initiated and disseminated by brain-derived extracellular vesicles (BDEVs) and propagated by extracellular vesicles (EVs) from endothelial cells and platelets. Here, we present results from a study designed to test the hypothesis that anticoagulation targeting anionic phospholipid-expressing EVs prevents TBI-IC and improves the outcomes of mice subjected to severe TBI. We evaluated the effects of a fusion protein (ANV-6L15) for improving the outcomes of TBI in mouse models combined with in vitro experiments. ANV-6L15 combines the phosphatidylserine (PS)-binding annexin V (ANV) with a peptide anticoagulant modified to preferentially target extrinsic coagulation. We found that ANV-6L15 reduced intracranial hematoma by 70.2%, improved neurological function, and reduced death by 56.8% in mice subjected to fluid percussion injury at 1.9 atm. It protected the TBI mice by preventing vascular leakage, tissue edema, and the TBI-induced hypercoagulable state. We further showed that the extrinsic tenase complex was formed on the surfaces of circulating EVs, with the highest level found on BDEVs. The phospholipidomic analysis detected the highest levels of PS on BDEVs, as compared with EVs from endothelial cells and platelets (79.1, 15.2, and 3.5 nM/mg of protein, respectively). These findings demonstrate that TBI-IC results from a trauma-induced hypercoagulable state and may be treated by anticoagulation targeting on the anionic phospholipid-expressing membrane of EVs from the brain and other cells.

Mast Cells Mediate Inflammatory Injury and Aggravate Neurological Impairment in Experimental Subarachnoid Hemorrhage Through Microglial PAR-2 Pathway

Subarachnoid hemorrhage (SAH) is a devastating cerebrovascular disease with high mortality and disability. Aberrant neuroinflammation has been identified as a critical factor accounting for the poor prognosis of SAH patients. Mast cells (MCs), the sentinel cells of the immune system, play a critical in the early immune reactions and participate in multiple pathophysiological process. However, the exact role of MCs on the pathophysiological process after SAH has not been fully understood. The current study was conducted to determine the role of MCs and MC stabilization in the context of SAH. Mouse SAH model was established by endovascular perforation process. Mice received saline or cromolyn (MC stabilizer) or compound 48/80 (MCs degranulator). Post-SAH evaluation included neurobehavioral test, western blot, immunofluorescence, and toluidine blue staining. We demonstrated that SAH induced MCs activation/degranulation. Administration of MC stabilizer cromolyn conferred a better neurologic outcome and decreased brain edema when compared with SAH+vehicle group. Furthermore, cromolyn significantly inhibited neuroinflammatory response and alleviated neuronal damage after SAH. However, pharmacological activation of MCs with compound 48/80 dramatically aggravated SAH-induced brain injury and exacerbated neurologic outcomes. Notably, pharmacological inhibition of microglial PAR-2 significantly reversed MCs-induced inflammatory response and neurological impairment. Additionally, the effect of MCs-derived tryptase in mediating neuroinflammation was also abolished by the microglial PAR-2 blockage in vitro. Taken together, MCs yielded inflammatory injury through activating microglia-related neuroinflammation after SAH. These data shed light on the notion that MCs might be a novel and promising therapeutic target for SAH.

Potential therapeutic targets for intracerebral hemorrhage-associated inflammation: An update

Intracerebral hemorrhage (ICH) is a subtype of stroke with high mortality and disability but no specific or effective treatment. In the last two decades, much has been learned about the pathologic mechanisms of ICH. It is now known that after ICH onset, immune and inflammatory responses contribute to blood-brain barrier disruption, edema development, and cell death processes, jointly resulting in secondary brain injury. However, the translation of potential therapies from preclinical to clinical success has been disappointing. With the development of new laboratory technology, recent progress has been made in the understanding of ICH pathomechanisms, and promising therapeutic targets have been identified. This review provides an update of recent progress on ICH and describes the prospects for further preclinical studies in this field. Our goal is to discuss new therapeutic targets and directions for the treatment of ICH and promote the effective transformation from preclinical to clinical trials.

Neuroprotective potential of solanesol in a combined model of intracerebral and intraventricular hemorrhage in rats

Intracerebral hemorrhage (ICH) may be caused by trauma, aneurysm and arteriovenous malformation, as can any bleeding within the intracranial vault, including brain parenchyma and adjacent meningeal spaces (aneurism and atreovenous malformation). ICH is the cerebral stroke with the least treatable form. Over time, intraventricular hemorrhage (IVH) is associated with ICH, which contributes to hydrocephalus, and the major cause of most hemorrhagic death (Due to the cerebral hemorrhage and post hemorrhagic surgeries). Most patients suffer from memory impairment, grip strength, posture, and cognitive dysfunctions attributable to cerebral hemorrhage or post-brain hemorrhagic surgery. Nevertheless, a combined model of ICH based IVH is not present pre-clinically. Autologous blood (ALB) injection (20 μl/5 min) in the rat brain triggers hemorrhage, such as factors that further interfere with the normal functioning of neuroinflammatory cytokines, oxidative stress, and neurotransmitter dysfunction, such as CoQ10 insufficiency and dysregulation of mitochondrial ETC-complexes. For the prevention of post-brain hemorrhagic behavioral and neurochemical dysfunctions, there is no specific drug treatment available, only available therapy used to provide symptomatic relief. The current study reveals that long-term administration of Solanesol (SNL) 40 and 60 mg/kg alone and in combination with available drug therapy Donepezil (DNP) 3 mg/kg, Memantine (MEM) 20 mg/kg, Celecoxib (CLB) 20 mg/kg, Pregabalin (PGB) 30 mg/kg, may provide the neuroprotective effect by improving behavioral and neurochemical deficits, and gross pathological changes in ALB induced combined experimental model of ICH-IVH in post brain hemorrhagic conditions in rats. Thus, SNL can be a potential therapeutic approach to improve neuronal mitochondrial dysfunction associated with post brain hemorrhagic behavioral and neurochemical alterations.

The Role of Mast Cells in Intracerebral Hemorrhage

Mast cells are first responders to intracerebral hemorrhage. They release potent mediators that can disrupt the blood-brain barrier promoting injury, vasogenic edema formation, and hematoma exacerbation. Also, mast cells recruit other inflammatory cells that maintain and amplify brain damage. Given their early role in the cascade of events in intracerebral hemorrhage, mast cells may offer an alternative target for antichemotactic interventions.

The Role of Mast Cells in Stroke

Mast cells (MCs) are densely granulated perivascular resident cells of hematopoietic origin. Through the release of preformed mediators stored in their granules and newly synthesized molecules, they are able to initiate, modulate, and prolong the immune response upon activation. Their presence in the central nervous system (CNS) has been documented for more than a century. Over the years, MCs have been associated with various neuroinflammatory conditions of CNS, including stroke. They can exacerbate CNS damage in models of ischemic and hemorrhagic stroke by amplifying the inflammatory responses and promoting brain–blood barrier disruption, brain edema, extravasation, and hemorrhage. Here, we review the role of these peculiar cells in the pathophysiology of stroke, in both immature and adult brain. Further, we discuss the role of MCs as potential targets for the treatment of stroke and the compounds potentially active as MCs modulators.

Targeting mast cell as a neuroprotective strategy

Background: Mast cells (MCs) are perivascularly located immune cells of haematopoietic origin. Emerging evidences suggest that the activation of MCs play important roles in the pathogenesis of blood brain barrier disruption, neuroinflammation, and neurodegeneration. Objectives: In this review, we aimed to discuss the detrimental effects of MCs in response to various types of brain injury, as well as the therapeutic potential and neuroprotective effects of targeting the activation and degranulation of MCs, particularly in the management of the acute phase. Methods: An extensive online literature search was conducted through Pubmed/Central on March 2018. Then, we comprehensively summarized the effects of the activation of brain MCs in acute brain injury along with current pharmacological strategies targeting at the activation of MCs. Results: The review of the current literature indicated that the activation and degranulation of brain MCs significantly contribute to the acute pathological process following different types of brain injury including focal and global cerebral ischaemia, intracerebral haemorrhage, subarachnoid haemorrhage, and traumatic brain injury. Conclusions: Brain MCs significantly contribute to the acute pathological processes following brain injury. In that regard, targeting brain MCs may provide a novel strategy for neuroprotection.

Sodium cromoglycate reduces short- and long-term consequences of status epilepticus in rats

Several studies indicate that sodium cromoglycate (CG) induces neuroprotective effects in acute neurological conditions. The present study focused on investigating if the use of CG in rats during the post-status epilepticus (post-SE) period reduces the acute and long-term consequences of seizure activity. Our results revealed that animals that received a single dose of CG (50 mg/kg s.c.: subcutaneously) during the post-SE period showed a lower number of neurons in the process of dying in the dentate gyrus, hilus, cornu ammonis 1 (CA1), and CA3 of the dorsal hippocampus than the rats that received the vehicle. However, this effect was not evident in layers V-VI of the sensorimotor cortex or the lateral-posterior thalamic nucleus. A second experiment showed that animals that received CG subchronically (50 mg/kg s.c. every 12 h for 5 days followed by 24 mg/kg/day s.c. for 14 days using osmotic minipumps) after SE presented fewer generalized convulsive seizures and less neuronal damage in the lateral-posterior thalamic nucleus but not in the hippocampus or cortex. Our data indicate that CG can be used as a therapeutic strategy to reduce short- and long-term neuronal damage in the hippocampus and thalamus, respectively. The data also indicate that CG can reduce the expression of generalized convulsive spontaneous seizures when it is given during the latent period of epileptogenesis.

Optimized tPA: A non-neurotoxic fibrinolytic agent for the drainage of intracerebral hemorrhages

Intracerebral hemorrhage (ICH) is the most severe form of stroke. Catheter-delivered thrombolysis with recombinant tissue-type plasminogen activator (rtPA) for the drainage of ICH is currently under evaluation in a phase III clinical trial (MISTIE III). However, in a pig model of ICH, in situ fibrinolysis with rtPA was reported to increase peri-lesional edema by promoting N-methyl-D-aspartate (NMDA)-dependent excitotoxicity. In the present study, we engineered a non-neurotoxic tPA variant, OptPA, and investigated its safety and efficacy for in situ fibrinolysis in a rat model of ICH. Magnetic resonance imaging analyses of hematoma and edema volumes, behavioral tasks and histological analyses were performed to measure the effects of treatments. In vitro, OptPA was equally fibrinolytic as rtPA without promoting NMDA-dependent neurotoxicity. In vivo, in situ fibrinolysis using OptPA reduced hematoma volume, like rtPA, but it also reduced the evolution of peri-hematomal neuronal death and subsequent edema progression. Overall, this preclinical study demonstrates beneficial effects of OptPA compared to rtPA for the drainage of ICH.

An Inflammation-Centric View of Neurological Disease: Beyond the Neuron

Inflammation is a complex biological response fundamental to how the body deals with injury and infection to eliminate the initial cause of cell injury and effect repair. Unlike a normally beneficial acute inflammatory response, chronic inflammation can lead to tissue damage and ultimately its destruction, and often results from an inappropriate immune response. Inflammation in the nervous system (“neuroinflammation”), especially when prolonged, can be particularly injurious. While inflammation per se may not cause disease, it contributes importantly to disease pathogenesis across both the peripheral (neuropathic pain, fibromyalgia) and central [e.g., Alzheimer disease, Parkinson disease, multiple sclerosis, motor neuron disease, ischemia and traumatic brain injury, depression, and autism spectrum disorder] nervous systems. The existence of extensive lines of communication between the nervous system and immune system represents a fundamental principle underlying neuroinflammation. Immune cell-derived inflammatory molecules are critical for regulation of host responses to inflammation. Although these mediators can originate from various non-neuronal cells, important sources in the above neuropathologies appear to be microglia and mast cells, together with astrocytes and possibly also oligodendrocytes. Understanding neuroinflammation also requires an appreciation that non-neuronal cell—cell interactions, between both glia and mast cells and glia themselves, are an integral part of the inflammation process. Within this context the mast cell occupies a key niche in orchestrating the inflammatory process, from initiation to prolongation. This review will describe the current state of knowledge concerning the biology of neuroinflammation, emphasizing mast cell-glia and glia-glia interactions, then conclude with a consideration of how a cell's endogenous mechanisms might be leveraged to provide a therapeutic strategy to target neuroinflammation.

IVIG activates FcγRIIB-SHIP1-PIP3 Pathway to stabilize mast cells and suppress inflammation after ICH in mice

Following intracerebral hemorrhage (ICH), the activation of mast cell contributes to brain inflammation and brain injury. The mast cell activation is negatively regulated by an inhibitory IgG-receptor. It's signals are mediated by SHIP (Src homology 2-containing inositol 5' phosphatase), in particular SHIP1, which activation leads to hydrolyzation of PIP3 (Phosphatidylinositol (3,4,5)-trisphosphate (PtdIns(3,4,5)P₃, leading to the inhibition of calcium mobilization and to the attenuation of mast cell activation. Intravenous immunoglobulin (IVIG) is a FDA-approved drug containing IgG. We hypothesized that IVIG will attenuate the ICH-induced mast cell activation via FcγRIIB/SHIP1 pathway, resulting in a decrease of brain inflammation, protection of the blood-brain-barrier, and improvement of neurological functions after ICH. To prove this hypothesis we employed the ICH collagenase mouse model. We demonstrated that while ICH induced mast cell activation/degranulation, IVIG attenuated post-ICH mast cell activation. Mast cell deactivation resulted in reduced inflammation, consequently attenuating brain edema and improving of neurological functions after ICH. Furthermore using siRNA-induced in vivo knockdown approach we demonstrated that beneficial effects of IVIG were mediated, at least partly, via SHIP1/PIP3 pathway. We conclude that IVIG treatment represents a promising therapeutic approach potentially able to decrease mortality and morbidity after ICH in experimental models.

Impact of Inflammation on the Blood-Neural Barrier and Blood-Nerve Interface: From Review to Therapeutic Preview

A number of nervous system disorders are characterized by a state of inflammation (neuroinflammation) in which members of the innate immune system, most notably mast cells and microglia-acting as single entities and in unison-produce inflammatory molecules that play major roles. A neuroinflammatory environment can weaken not only blood-nerve and blood-brain barrier (BBB) integrity but also that of the blood-spinal cord barrier. Mast cells, with their distribution in peripheral nerves and the central nervous system, are positioned to influence blood-nerve barrier characteristics. Being close also to the perivasculature and on the brain side of the BBB, the mast cell is well positioned to disrupt BBB function. Interestingly, tissue damage and/or stress activates homeostatic mechanisms/molecules expressed by mast cells and microglia, and includes N-acylethanolamines. Among the latter, N-palmitoylethanolamine has distinguished itself as a key component in supporting homeostasis of the organism against external stressors capable of provoking inflammation. This review will discuss the pathobiology of neuroinflammation with emphasis on mast cells and microglia, their roles in BBB health, and novel therapeutic opportunities, including nanoscale delivery for targeting these immune cells with a view to maintain the BBB.

Mast Cell Infiltration in Human Brain Metastases Modulates the Microenvironment and Contributes to the Metastatic Potential

Metastatic brain tumors continue to be a clinical problem, despite new therapeutic advances in cancer treatment. Brain metastases (BMs) are among the most common mass lesions in the brain that are resistant to chemotherapies, have a very poor prognosis, and currently lack any efficient diagnostic tests. Predictions estimate that about 40% of lung and breast cancer patients will develop BM. Despite this, very little is known about the immunological and genetic aberrations that drive tumorigenesis in BM. In this study, we demonstrate the infiltration of mast cells (MCs) in a large cohort of human BM samples with different tissues of origin for primary cancer. We applied patient-derived BM cell models to the study of BM cell-MC interactions. BM cells when cocultured with MCs demonstrate enhanced growth and self-renewal capacity. Gene set enrichment analyses indicate increased expression of signal transduction and transmembrane proteins related genes in the cocultured BM cells. MCs exert their effect by release of mediators such as IL-8, IL-10, matrix metalloprotease 2, and vascular endothelial growth factor, thereby permitting metastasis. In conclusion, we provide evidence for a role of MCs in BM. Our findings indicate MCs' capability of modulating gene expression in BM cells and suggest that MCs can serve as a new target for drug development against metastases in the brain.

Neuroinflammation, Mast Cells, and Glia: Dangerous Liaisons

The perspective of neuroinflammation as an epiphenomenon following neuron damage is being replaced by the awareness of glia and their importance in neural functions and disorders. Systemic inflammation generates signals that communicate with the brain and leads to changes in metabolism and behavior, with microglia assuming a pro-inflammatory phenotype. Identification of potential peripheral-to-central cellular links is thus a critical step in designing effective therapeutics. Mast cells may fulfill such a role. These resident immune cells are found close to and within peripheral nerves and in brain parenchyma/meninges, where they exercise a key role in orchestrating the inflammatory process from initiation through chronic activation. Mast cells and glia engage in crosstalk that contributes to accelerate disease progression; such interactions become exaggerated with aging and increased cell sensitivity to stress. Emerging evidence for oligodendrocytes, independent of myelin and support of axonal integrity, points to their having strong immune functions, innate immune receptor expression, and production/response to chemokines and cytokines that modulate immune responses in the central nervous system while engaging in crosstalk with microglia and astrocytes. In this review, we summarize the findings related to our understanding of the biology and cellular signaling mechanisms of neuroinflammation, with emphasis on mast cell-glia interactions.

Contribution of mast cells to injury mechanisms in a mouse model of pediatric traumatic brain injury

The cognitive and behavioral deficits caused by traumatic brain injury (TBI) to the immature brain are more severe and persistent than injuries to the adult brain. Understanding this developmental sensitivity is critical because children under 4 years of age of sustain TBI more frequently than any other age group. One of the first events after TBI is the infiltration and degranulation of mast cells (MCs) in the brain, releasing a range of immunomodulatory substances; inhibition of these cells is neuroprotective in other types of neonatal brain injury. This study investigates for the first time the role of MCs in mediating injury in a P7 mouse model of pediatric contusion-induced TBI. We show that various neural cell types express histamine receptors and that histamine exacerbates excitotoxic cell death in primary cultured neurons. Cromoglycate, an inhibitor of MC degranulation, altered the inflammatory phenotype of microglia activated by TBI, reversing several changes but accentuating others, when administered before TBI. However, without regard to the time of cromoglycate administration, inhibiting MC degranulation did not affect cell loss, as evaluated by ventricular dilatation or cleaved caspase-3 labeling, or the density of activated microglia, neurons, or myelin. In double-heterozygous cKit mutant mice lacking MCs, this overall lack of effect was confirmed. These results suggest that the role of MCs in this model of pediatric TBI is restricted to subtle effects and that they are unlikely to be viable neurotherapeutic targets. © 2016 Wiley Periodicals, Inc.

Experimental animal models and inflammatory cellular changes in cerebral ischemic and hemorrhagic stroke

Stroke, including cerebral ischemia, intracerebral hemorrhage, and subarachnoid hemorrhage, is the leading cause of long-term disability and death worldwide. Animal models have greatly contributed to our understanding of the risk factors and the pathophysiology of stroke, as well as the development of therapeutic strategies for its treatment. Further development and investigation of experimental models, however, are needed to elucidate the pathogenesis of stroke and to enhance and expand novel therapeutic targets. In this article, we provide an overview of the characteristics of commonly-used animal models of stroke and focus on the inflammatory responses to cerebral stroke, which may provide insights into a framework for developing effective therapies for stroke in humans.

T cell deficiency in spinal cord injury: altered locomotor recovery and whole-genome transcriptional analysis

BACKGROUND

T cells undergo autoimmunization following spinal cord injury (SCI) and play both protective and destructive roles during the recovery process. T cell-deficient athymic nude (AN) rats exhibit improved functional recovery when compared to immunocompetent Sprague-Dawley (SD) rats following spinal cord transection.

METHODS

In the present study, we evaluated locomotor recovery in SD and AN rats following moderate spinal cord contusion. To explain variable locomotor outcome, we assessed whole-genome expression using RNA sequencing, in the acute (1 week post-injury) and chronic (8 weeks post-injury) phases of recovery.

RESULTS

Athymic nude rats demonstrated greater locomotor function than SD rats only at 1 week post-injury, coinciding with peak T cell infiltration in immunocompetent rats. Genetic markers for T cells and helper T cells were acutely enriched in SD rats, while AN rats expressed genes for T(h)2 cells, cytotoxic T cells, NK cells, mast cells, IL-1a, and IL-6 at higher levels. Acute enrichment of cell death-related genes suggested that SD rats undergo secondary tissue damage from T cells. Additionally, SD rats exhibited increased acute expression of voltage-gated potassium (Kv) channel-related genes. However, AN rats demonstrated greater chronic expression of cell death-associated genes and less expression of axon-related genes. Immunostaining for macrophage markers revealed no T cell-dependent difference in the acute macrophage infiltrate.

CONCLUSIONS

We put forth a model in which T cells facilitate early tissue damage, demyelination, and Kv channel dysregulation in SD rats following contusion SCI. However, compensatory features of the immune response in AN rats cause delayed tissue death and limit long-term recovery. T cell inhibition combined with other neuroprotective treatment may thus be a promising therapeutic avenue.

Phosphoinositide 3-Kinase Gamma Contributes to Neuroinflammation in a Rat Model of Surgical Brain Injury

Neuroinflammation plays an important role in the pathophysiology of surgical brain injury (SBI). Phosphoinositide 3-kinase gamma (PI3Kγ), predominately expressed in immune and endothelial cells, activates multiple inflammatory responses. In the present study, we investigated the role of PI3Kγ and PI3Kγ-activated phosphodiesterase 3B (PDE3B) in neuroinflammation in a rat model of SBI. One hundred and fifty-two male Sprague Dawley rats (weight 280-350 g) were subjected to a partial right frontal lobe corticotomy model of SBI. A PI3Kγ pharmacological inhibitor (AS252424 or AS605240) was administered intraperitoneally. PI3Kγ siRNA, human recombinant active-PI3Kγ protein, or human recombinant active-PDE3B protein were administered intracerebroventricularly. Post-SBI assessments included neurobehavioral tests, brain water content, Western blot, and immunohistochemistry. Endogenous PI3Kγ levels were increased within peri-resection brain tissues after SBI, accompanied by increased brain water content and neurological functional deficits. There was a trend toward increased endogenous PDE3B phosphorylation after SBI. The selective PI3Kγ inhibitors AS252424 and AS605240 reduced brain water content surrounding corticotomy and improved neurological function after SBI. SBI increased and PI3Kγ inhibitor decreased levels of myeloperoxidase, cluster of differentiation 3, mast cell degranulation, E-selectin, and IL-1 in peri-resection brain tissues. Direct administration of human recombinant active-PI3Kγ protein and active-PDE3B protein countered the protective effect of AS252424. PI3Kγ siRNA reduced PI3Kγ levels, decreased brain water content within peri-resection brain tissues, and improved neurological function after SBI. Collectively, our findings suggest that PI3Kγ contributed to neuroinflammation after SBI. The use of selective PI3Kγ inhibitors may be a novel approach to ameliorating SBI via their anti-inflammation effects. Significance statement: Life-saving or elective neurosurgeries often involve unavoidable damages to neighboring, nondiseased brain tissues. Such surgical brain injury (SBI) is attributable exclusively to the neurosurgical procedure itself and may cause postoperative complications that exacerbate neurological function. Although the importance of this medical problem is fully acknowledged, intraoperative administration of adjunctive treatment such as steroids and mannitol to patients undergoing neurosurgery appear not to be efficient remedies for SBI. To date, the issue of perioperative neuroprotection specifically against SBI has not been well studied. Using a clinically relevant rat model of SBI, we are exploring a new neuroprotective strategy targeting phosphoinositide 3-kinase gamma (PI3Kγ). PI3Kγ activates multiple inflammatory responses. By attenuating neuroinflammation, selective PI3Kγ inhibition would limit postoperative complications and benefit neurological outcomes.

The crucial role of mast cells in blood-brain barrier alterations

Mast cells are critical regulators of the pathogenesis of the central nervous system diseases, including stroke, multiple sclerosis, and traumatic brain injury, and brain tumors. Here, we have summarized the literature data concerning the involvement of mast cells in blood-brain barrier alterations, and we have suggested a possible role of angiogenic mediators stored in mast cell granules in the vasoproliferative reactions occurring in these pathological conditions. It is conceivable to hypothesize that mast cells might be regarded in a future perspective as a new target for the adjuvant treatment of neurodegenerative diseases and brain tumors through the selective inhibition of angiogenesis, tissue remodeling and tumor-promoting molecules, favoring the secretion of cytotoxic cytokines and preventing mast cell-mediated immune suppression.

Toxic role of prostaglandin E2 receptor EP1 after intracerebral hemorrhage in mice

Inflammatory mechanisms mediated by prostaglandins may contribute to the progression of intracerebral hemorrhage (ICH)-induced brain injury, but they are not fully understood. In this study, we examined the effect of prostaglandin E2 receptor EP1 (EP1R) activation and inhibition on brain injury in mouse models of ICH and investigated the underlying mechanism of action. ICH was induced by injecting collagenase, autologous blood, or thrombin into the striatum of middle-aged male and female mice and aged male mice. Effects of selective EP1R agonist ONO-DI-004, antagonist SC51089, and nonspecific Src family kinase inhibitor PP2 were evaluated by a combination of histologic, magnetic resonance imaging (MRI), immunofluorescence, molecular, cellular, and behavioral assessments. EP1R was expressed primarily in neurons and axons but not in astrocytes or microglia after ICH induced by collagenase. In middle-aged male mice subjected to collagenase-induced ICH, EP1R inhibition mitigated brain injury, brain edema, cell death, neuronal degeneration, neuroinflammation, and neurobehavioral deficits, whereas its activation exacerbated these outcomes. EP1R inhibition also was protective in middle-aged female mice and aged male mice after collagenase-induced ICH and in middle-aged male mice after blood- or thrombin-induced ICH. EP1R inhibition also reduced oxidative stress, white matter injury, and brain atrophy and improved functional outcomes. Histologic results were confirmed by MRI. Src kinase phosphorylation and matrix metalloproteinase-9 activity were increased by EP1R activation and decreased by EP1R inhibition. EP1R regulated matrix metalloproteinase-9 activity through Src kinase signaling, which mediated EP1R toxicity after collagenase-induced ICH. We conclude that prostaglandin E2 EP1R activation plays a toxic role after ICH through mechanisms that involve the Src kinases and the matrix metalloproteinase-9 signaling pathway. EP1R inhibition could be a novel therapeutic strategy to improve outcomes after ICH.

Evidence that meningeal mast cells can worsen stroke pathology in mice

Stroke is the leading cause of adult disability and the fourth most common cause of death in the United States. Inflammation is thought to play an important role in stroke pathology, but the factors that promote inflammation in this setting remain to be fully defined. An understudied but important factor is the role of meningeal-located immune cells in modulating brain pathology. Although different immune cells traffic through meningeal vessels en route to the brain, mature mast cells do not circulate but are resident in the meninges. With the use of genetic and cell transfer approaches in mice, we identified evidence that meningeal mast cells can importantly contribute to the key features of stroke pathology, including infiltration of granulocytes and activated macrophages, brain swelling, and infarct size. We also obtained evidence that two mast cell-derived products, interleukin-6 and, to a lesser extent, chemokine (C-C motif) ligand 7, can contribute to stroke pathology. These findings indicate a novel role for mast cells in the meninges, the membranes that envelop the brain, as potential gatekeepers for modulating brain inflammation and pathology after stroke.

A novel combined model of intracerebral and intraventricular hemorrhage using autologous blood-injection in rats

Intracerebral hemorrhage (ICH) is the least treatable form of stroke and is associated with the worst prognosis. In up to 40% of cases, ICH is further complicated by intraventricular hemorrhage (IVH), which predisposes to hydrocephalus, and increases case-mortality to 80%. However, IVH is not present in widely used preclinical models of ICH. Here, we characterize a novel rat model of combined ICH and IVH. Rats were injected with different volumes of autologous whole blood into the right deep basal ganglia region (100μL, 150μL, 200μL, and 250μL, n=10 per group). MRI was performed immediately, and at 24, 48, 72h, and 1week after blood injection, along with neurological evaluations. Injected blood volume reliably correlated with blood volumes measured from MRI obtained after blood injection. Brain edema was most prominent in the ⩾200μL groups, peaking at 48h in all groups, being statistically different between the ⩾200μL and <200μL groups at all-time points. Presence of hydrocephalus was detected in most of the animals, most clearly in the 200μL and 250μL groups, both being statistically different from the 100μL group at all-time points, with tendency to worsen during the whole follow-up period. Most deteriorating neurological and behavioral outcomes as well as the highest mortality rates were detected in groups injected with 200μL and 250μL of autologous blood, 40% and 70%, respectively. These volumes were most similar to the clinical scenario of combined ICH and IVH, demonstrating that this novel rat model is a promising starting point for future ICH+IVH research.

Evolution of intracerebral hemorrhage after intravenous tPA: reversal of harmful effects with mast cell stabilization

Thrombolysis with tissue plasminogen activator (tPA) traditionally demands baseline imaging to rule out intracerebral hemorrhage (ICH), which causes delays in treatment. Preventing possible adverse effects of tPA on ICH would allow rapid on-site thrombolysis in patients with presumed acute ischemic stroke, reducing onset-to-treatment times. We examined how intravenous tPA alters ICH evolution during an extended follow-up, and how mast cell stabilization affects this process. Intracerebral hemorrhage was induced in rats by collagenase injection. Rats received either saline (n=10), tPA (n=13), tPA+low-dose cromoglycate (n=10), or tPA+high-dose cromoglycate (n=10). Magnetic resonance imaging was performed at 24, 48, and 72 hours after ICH induction, together with neurologic evaluations. During 72 hours of follow-up, tPA administration did not significantly increase hematoma volume (mean±s.d. 83.5±14.3 versus 66.7±14.7 μL; P=0.256) or hemispheric expansion (14.5±5.0 versus 11.5±5.0%; P=0.457) compared with saline. However, tPA-treated animals had worse neurologic outcomes (P<0.05), and mortality (8/13 versus 3/10). Combining tPA with high-dose cromoglycate mitigated hemispheric expansion (7.4±1.7 versus 14.5±5.0%; P=0.01), improved neurologic outcome (P<0.001) and decreased mortality (1/10; P<0.05) compared with tPA alone. Our results suggest tPA increases neurologic deficit in ICH, an effect that was abolished by concomitant mast cell stabilization. Further studies are needed to establish the clinical relevance of these findings.

Mast cells protect from post-traumatic spinal cord damage in mice by degrading inflammation-associated cytokines via mouse mast cell protease 4

Mast cells (MCs) are found abundantly in the central nervous system and play a complex role in neuroinflammatory diseases such as multiple sclerosis and stroke. In the present study, we show that MC-deficient Kit(W-sh/W-sh) mice display significantly increased astrogliosis and T cell infiltration as well as significantly reduced functional recovery after spinal cord injury compared to wildtype mice. In addition, MC-deficient mice show significantly increased levels of MCP-1, TNF-α, IL-10 and IL-13 protein levels in the spinal cord. Mice deficient in mouse mast cell protease 4 (mMCP4), an MC-specific chymase, also showed increased MCP-1, IL-6 and IL-13 protein levels in spinal cord samples and a decreased functional outcome after spinal cord injury. A degradation assay using supernatant from MCs derived from either mMCP4(-/-) mice or controls revealed that mMCP4 cleaves MCP-1, IL-6, and IL-13 suggesting a protective role for MC proteases in neuroinflammation. These data show for the first time that MCs may be protective after spinal cord injury and that they may reduce CNS damage by degrading inflammation-associated cytokines via the MC-specific chymase mMCP4.

Possible involvement of TLRs and hemichannels in stress-induced CNS dysfunction via mastocytes, and glia activation

In the central nervous system (CNS), mastocytes and glial cells (microglia, astrocytes and oligodendrocytes) function as sensors of neuroinflammatory conditions, responding to stress triggers or becoming sensitized to subsequent proinflammatory challenges. The corticotropin-releasing hormone and glucocorticoids are critical players in stress-induced mastocyte degranulation and potentiation of glial inflammatory responses, respectively. Mastocytes and glial cells express different toll-like receptor (TLR) family members, and their activation via proinflammatory molecules can increase the expression of connexin hemichannels and pannexin channels in glial cells. These membrane pores are oligohexamers of the corresponding protein subunits located in the cell surface. They allow ATP release and Ca²⁺ influx, which are two important elements of inflammation. Consequently, activated microglia and astrocytes release ATP and glutamate, affecting myelinization, neuronal development, and survival. Binding of ligands to TLRs induces a cascade of intracellular events leading to activation of several transcription factors that regulate the expression of many genes involved in inflammation. During pregnancy, the previous responses promoted by viral infections and other proinflammatory conditions are common and might predispose the offspring to develop psychiatric disorders and neurological diseases. Such disorders could eventually be potentiated by stress and might be part of the etiopathogenesis of CNS dysfunctions including autism spectrum disorders and schizophrenia.

Hydrogen inhalation ameliorated mast cell-mediated brain injury after intracerebral hemorrhage in mice

OBJECTIVE

Hydrogen inhalation was neuroprotective in several brain injury models. Its mechanisms are believed to be related to antioxidative stress. We investigated the potential neurovascular protective effect of hydrogen inhalation especially effect on mast cell activation in a mouse model of intracerebral hemorrhage.

DESIGN

Controlled in vivo laboratory study.

SETTING

Animal research laboratory.

SUBJECTS

One hundred seventy-one 8-week-old male CD-1 mice were used.

INTERVENTIONS

Collagenase-induced intracerebral hemorrhage model in 8-week-old male CD-1 mice was used. Hydrogen was administrated via spontaneous inhalation. The blood-brain barrier permeability and neurologic deficits were investigated at 24 and 72 hours after intracerebral hemorrhage. Mast cell activation was evaluated by Western blot and immuno-staining. The effects of hydrogen inhalation on mast cell activation were confirmed in an autologous blood injection model intracerebral hemorrhage.

MEASUREMENT AND MAIN RESULTS

At 24 and 72 hours post intracerebral hemorrhage, animals showed blood-brain barrier disruption, brain edema, and neurologic deficits, accompanied with phosphorylation of Lyn kinase and release of tryptase, indicating mast cell activation. Hydrogen treatment diminished phosphorylation of Lyn kinase and release of tryptase, decreased accumulation and degranulation of mast cells, attenuated blood-brain barrier disruption, and improved neurobehavioral function.

CONCLUSION

Activation of mast cells following intracerebral hemorrhage contributed to increase of blood-brain barrier permeability and brain edema. Hydrogen inhalation preserved blood-brain barrier disruption by prevention of mast cell activation after intracerebral hemorrhage.

The role of mast cells in neuroinflammation

Mast cells (MCs) are densely granulated perivascular resident cells of hematopoietic origin and well known for their pathogenetic role in allergic and anaphylactic reactions. In addition, they are also involved in processes of innate and adaptive immunity. MCs can be activated in response to a wide range of stimuli, resulting in the release of not only pro-inflammatory, but also anti-inflammatory mediators. The patterns of secreted mediators depend upon the given stimuli and microenvironmental conditions, accordingly MCs have the ability to promote or attenuate inflammatory processes. Their presence in the central nervous system (CNS) has been recognized for more than a century. Since then a participation of MCs in various pathological processes in the CNS has been well documented. They can aggravate CNS damage in models of brain ischemia and hemorrhage, namely through increased blood-brain barrier damage, brain edema and hemorrhage formation and promotion of inflammatory responses to such events. In contrast, recent evidence suggests that MCs may have a protective role following traumatic brain injury by degrading pro-inflammatory cytokines via specific proteases. In neuroinflammatory diseases such as multiple sclerosis, the role of MCs seems to be ambiguous. MCs have been shown to be damaging, neuroprotective, or even dispensable, depending on the experimental protocols used. The role of MCs in the formation and progression of CNS tumors such as gliomas is complex and both positive and negative relationships between MC activity and tumor progression have been reported. In summary, MCs and their secreted mediators modulate inflammatory processes in multiple CNS pathologies and can thereby either contribute to neurological damage or confer neuroprotection. This review intends to give a concise overview of the regulatory roles of MCs in brain disease.

Vascular protection to increase the safety of tissue plasminogen activator for stroke

Thrombolytic therapy with tissue plasminogen activator (tPA) remains the most effective treatment for acute ischemic stroke, but can cause vascular damage leading to edema formation and hemorrhagic transformation (HT). In this review, we discuss how tPA contributes to the pathogenesis of vascular damage and highlight evidence to support combination therapy of tPA with pharmacological agents that are vascular protective. There is an unmet need to develop therapeutic interventions which target the underlying mechanisms of vascular damage after acute ischemic stroke in order to prevent HT and improve the safety and impact of tPA.

Mast cells protect from post-traumatic brain inflammation by the mast cell-specific chymase mouse mast cell protease-4

Mast cells (MCs) are found abundantly in the brain and the meninges and play a complex role in neuroinflammatory diseases, such as stroke and multiple sclerosis. Here, we show that MC-deficient Kit/Kit mice display increased neurodegeneration in the lesion area after brain trauma. Furthermore, MC-deficient mice display significantly more brain inflammation, namely an increased presence of macrophages/microglia, as well as dramatically increased T-cell infiltration at days 4 and 14 after injury, combined with increased astrogliosis at day 14 following injury. The number of proliferating Ki67 macrophages/microglia and astrocytes around the lesion area is more than doubled in these MC-deficient mice. In parallel, MC-deficient Kit mice display increased presence of macrophages/microglia at day 4, and persistent astrogliosis at day 4 and 14 after brain trauma. Further analysis of mice deficient in one of the most relevant MC proteases, i.e., mouse mast cell protease 4 (mMCP-4), revealed that astrogliosis and T-cell infiltration are significantly increased in mMCP-4-knockout mice. Finally, treatment with an inhibitor of mMCP-4 significantly increased macrophage/microglia numbers and astrogliosis. These data suggest that MCs exert protective functions after trauma, at least in part via mMCP-4, by suppressing exacerbated inflammation via their proteases.

Chemokines and their receptors in intracerebral hemorrhage

Intracerebral hemorrhage (ICH) is a devastating clinical event which results in a high rate of disability and death. At present, no effective treatment is available for ICH. Accumulating evidence suggests that inflammatory responses contribute significantly to the ICH-induced secondary brain outcomes. During ICH, inflammatory cells accumulate at the ICH site attracted by gradients of chemokines. This review summarizes recent progress in ICH studies and the chemoattractants that act during the injury and focuses on and introduces the basic biology of the chemokine monocyte chemoattractant protein-1 (MCP1) and its role in the progression of ICH. Better understanding of MCP1 signaling cascade and the compensation after its inhibition could shed light on the development of effective treatments for ICH.

Neuroprotective effects of lithium treatment following hypoxic-ischemic brain injury in neonatal rats

PURPOSE

Increasing evidence indicates that lithium is a neuroprotective agent against transient focal and global ischemic injury in the adult animal. In the developing brain, lithium has shown protective effects against neuroapoptosis induced by drugs. This study was designed to investigate the neuroprotective effects of lithium on hypoxic-ischemic brain injury in the neonatal rat.

METHODS

Seven-day-old Sprague-Dawley rats underwent hypoxic-ischemic injury (HII) induced by ligation of the common carotid artery followed by exposure to ~2.5 h of hypoxia (~7% oxygen). After HII, rat pups were randomly assigned into two groups: a control group (n = 21), which received a daily subcutaneous injection of 0.9% normal saline for 14 days following HII; and a lithium group (n = 32), treated with daily injection of lithium chloride. N-acetylaspartate/creatinine, choline/creatinine, lipid/creatinine ratios at 1.3 ppm (Lip(1.3)/Cr) and 0.9 ppm (Lip(0.9)/Cr) lipid peaks were evaluated by proton magnetic resonance spectroscopy on the day of HII and on days 7 and 14 after HII. Infarct ratios based on magnetic resonance images were also determined at the same time points.

RESULTS

Seven days after HII, the Lip(1.3)/Cr and Lip(0.9)/Cr ratios as well as the infarct ratio were significantly lower in the lithium group than in the control group. The Lip(1.3)/Cr and Lip(0.9)/Cr ratios were significantly correlated with infarct ratio.

CONCLUSION

This study showed that post-HII treatment with lithium may have a neuroprotective effect in the immature brain. Further studies are needed to elucidate the mechanism of neuroprotective properties of lithium against HII-induced neonatal brain damage.

Systemic inflammatory challenges compromise survival after experimental stroke via augmenting brain inflammation, blood- brain barrier damage and brain oedema independently of infarct size

BACKGROUND

Systemic inflammation impairs outcome in stroke patients and experimental animals via mechanisms which are poorly understood. Circulating inflammatory mediators can activate cerebrovascular endothelium or glial cells in the brain and impact on ischaemic brain injury. One of the most serious early clinical complications of cerebral ischaemia is brain oedema, which compromises survival in the first 24-48 h. It is not understood whether systemic inflammatory challenges impair outcome after stroke by increasing brain injury only or whether they have direct effects on brain oedema, cerebrovascular inflammation and blood-brain barrier damage.

METHODS

We used two different systemic inflammatory stimuli, acute endotoxin treatment and anaphylaxis to study mechanisms of brain injury after middle cerebral artery occlusion (MCAo). Ischaemic brain injury, blood-brain barrier damage and oedema were analysed by histological techniques. Systemic cytokine responses and inflammatory changes in the brain were analysed by cytometric bead array, immunofluorescence, in situ hibridization and quantitative real-time PCR.

RESULTS

Systemic inflammatory challenges profoundly impaired survival in the first 24 h after experimental stroke in mice, independently of an increase in infarct size. Systemic lipopolysaccharide (LPS) dose-dependently increased mortality (50-100%) minutes to hours after cerebral ischaemia. Acute anaphylactic challenge in ovalbumin-sensitised mice affected stroke more seriously when induced via intraperitoneal administration compared to intravenous. Both LPS and anaphylaxis induced inflammatory changes in the blood and in the brain prior to experimental stroke. Plasma cytokine levels were significantly higher after LPS, while increased IL-10 levels were seen after anaphylaxis. After MCAo, both LPS and anaphylaxis increased microglial interleukin-1α (IL-1α) expression and blood-brain barrier breakdown. LPS caused marked granulocyte recruitment throughout the ipsilateral hemisphere. To investigate whether reduction of ischaemic damage can improve outcome in systemic inflammation, controlled hypothermia was performed. Hypothermia reduced infarct size in all treatment groups and moderately improved survival, but failed to reduce excess oedema formation after anaphylaxis and LPS-induced neuroinflammation.

CONCLUSIONS

Our results suggest that systemic inflammatory conditions induce cerebrovascular inflammation via diverse mechanisms. Increased brain inflammation, blood-brain barrier injury and brain oedema formation can be major contributors to impaired outcome in mice after experimental stroke with systemic inflammatory stimuli, independently of infarct size.

Cerebral mast cells mediate blood-brain barrier disruption in acute experimental ischemic stroke through perivascular gelatinase activation

BACKGROUND AND PURPOSE

Perivascularly positioned cerebral mast cells (MC) have been shown to participate in acute blood-brain barrier disruption and expansive brain edema following experimental transient cerebral ischemia. However, the underlying molecular mechanisms remain unknown. Because proteolytic gelatinase enzymes, matrix metalloproteinases (MMP)-2 and MMP-9, are thought to have a central role in compromising the integrity of the blood-brain barrier following ischemia, we examined whether cerebral MCs influence gelatinase activity in ischemic cerebral microvasculature.

METHODS

Rats underwent 60 minutes of middle cerebral artery occlusion followed by 3-hour reperfusion, and were treated with a MC-stabilizing (cromoglycate), or MC-degranulating (compound 48/80) agent, or vehicle. Genetically manipulated, MC-deficient WsRc(Ws/Ws) rats and their wild-type littermates (WT) underwent the same procedures. Cerebral edema and extravasation of Evans blue albumin were measured. Gelatinase activity was visualized by in situ zymography and was quantified with computerized high-throughput image and data analysis.

RESULTS

Activated MCs showed secretion of gelatinase-positive granules. Genetic MC deficiency decreased global gelatinase-active area (-69%, compared with WT; P<0.001) and the mean gelatinase activity of the ischemic microvasculature (-57% compared with WT; P=0.002). MC stabilization with cromoglycate decreased the percentage of microvessels with high gelatinase activity (-36% compared with saline; P<0.05). Compound 48/80 showed increased area of in situ zymography activity in the ischemic lesion (+55% compared with saline; P<0.001). Microvascular gelatinase activity correlated with brain swelling (r=0.84; P<0.001; and r=0.61; P=0.02).

CONCLUSIONS

Our data demonstrate that cerebral MCs participate in regulation of acute microvascular gelatinase activation and consequent blood-brain barrier disruption following transient cerebral ischemia.

Treatment of intracerebral hemorrhage in animal models: meta-analysis

OBJECTIVE

Interventions that improve functional outcome after acute intracerebral hemorrhage (ICH) in animals might benefit humans. Therefore, we systematically reviewed the literature to find studies of nonsurgical treatments tested in animal models of ICH.

METHODS

In July 2009 we searched Ovid Medline (from 1950), Embase (from 1980), and ISI Web of Knowledge (from 1969) for controlled animal studies of nonsurgical interventions given after the induction of ICH that reported neurobehavioral outcome. We assessed study quality and performed meta-analysis using a weighted mean difference random effects model.

RESULTS

Of 13,343 publications, 88 controlled studies described the effects of 64 different medical interventions (given a median of 2 hours after ICH induction) on 38 different neurobehavioral scales in 2,616 treated or control animals (median 14 rodents per study). Twenty-seven (31%) studies randomized treatment allocation, and 7 (8%) reported allocation concealment; these studies had significantly smaller effect sizes than those without these attributes (p < 0.001). Of 64 interventions stem cells, calcium channel blockers, anti-inflammatory drugs, iron chelators, and estrogens improved both structural outcomes and neurobehavioral scores in >1 study. Meta-regression revealed that together, structural outcome and the intervention used accounted for 65% of the observed heterogeneity in neurobehavioral score (p < 0.001, adjusted r(2) = 0.65).

INTERPRETATION

Further animal studies of the interventions that we found to improve both functional and structural outcomes in animals, using better experimental designs, could target efforts to translate effective treatments for ICH in animals into randomized controlled trials in humans.

Preclinical and clinical research on inflammation after intracerebral hemorrhage

Intracerebral hemorrhage (ICH) is one of the most lethal stroke subtypes. Despite the high morbidity and mortality associated with ICH, its pathophysiology has not been investigated as well as that of ischemic stroke. Available evidence from preclinical and clinical studies suggests that inflammatory mechanisms are involved in the progression of ICH-induced secondary brain injury. For example, in preclinical ICH models, microglial activation has been shown to occur within 1h, much earlier than neutrophil infiltration. Recent advances in our understanding of neuroinflammatory pathways have revealed several new molecular targets, and related therapeutic strategies have been tested in preclinical ICH models. This review summarizes recent progress made in preclinical models of ICH, surveys preclinical and clinical studies of inflammatory cells (leukocytes, macrophages, microglia, and astrocytes) and inflammatory mediators (matrix metalloproteinases, nuclear factor erythroid 2-related factor 2, heme oxygenase, and iron), and highlights the emerging areas of therapeutic promise.

Mast cells as early responders in the regulation of acute blood-brain barrier changes after cerebral ischemia and hemorrhage

The inflammatory response triggered by stroke has been viewed as harmful, focusing on the influx and migration of blood-borne leukocytes, neutrophils, and macrophages. This review hypothesizes that the brain and meninges have their own resident cells that are capable of fast host response, which are well known to mediate immediate reactions such as anaphylaxis, known as mast cells (MCs). We discuss novel research suggesting that by acting rapidly on the cerebral vessels, this cell type has a potentially deleterious role in the very early phase of acute cerebral ischemia and hemorrhage. Mast cells should be recognized as a potent inflammatory cell that, already at the outset of ischemia, is resident within the cerebral microvasculature. By releasing their cytoplasmic granules, which contain a host of vasoactive mediators such as tumor necrosis factor-alpha, histamine, heparin, and proteases, MCs act on the basal membrane, thus promoting blood-brain barrier (BBB) damage, brain edema, prolonged extravasation, and hemorrhage. This makes them a candidate for a new pharmacological target in attempts to even out the inflammatory responses of the neurovascular unit, and to stabilize the BBB after acute stroke.

Decompressive surgery for severe brain edema

Decompressive surgery has since long been a promising therapeutic approach for patients with acute severe brain injury at risk to develop severe brain edema. The underlying rationale of removing part of the cranium is to create space for the expanding brain to prevent secondary damage to vital brain tissue. However, until recently, randomized controlled trials that demonstrate the efficacy of decompressive surgery or benefit for outcome were missing. This has changed since the results of 3 randomized trials on hemicraniectomy in malignant infarction of the middle cerebral artery have been published in 2007. In this article, the current evidence for decompressive surgery in the treatment of cerebral ischemia, intracranial hemorrhage, traumatic brain injury, inflammatory diseases, or severe metabolic derangements is reviewed. Although there is increasing evidence for the efficacy of decompressive surgery in reducing intracranial pressure and even mortality, a critical point remains the definition of good or acceptable outcome.

Inflammation and the neurovascular unit in the setting of focal cerebral ischemia

Responses to focal cerebral ischemia by neurons and adjacent microvessels are rapid, simultaneous, and topographically related. Recent observations indicate the simultaneous appearance of proteases by components of nearby microvessels that are also expressed by neurons in the ischemic territory, implying that the events could be coordinated. The structural relationship of neurons to their microvascular supply, the direct functional participation of glial cells, and the observation of a highly ordered microvessel-neuron response to ischemia suggest that these elements are arranged in and behave in a unitary fashion, the neurovascular unit. Their roles as a unit in the stimulation of cellular inflammation and the generation of inflammatory mediators during focal cerebral ischemia have not been explored yet. However, components of the neurovascular unit both generate and respond to these influences under the conditions of ischemia. Here we briefly explore the potential inter-relationships of the components of the neurovascular unit with respect to their potential roles in ischemia-induced inflammatory responses.