Increased expression of cysteinyl leukotriene receptor-1 in the brain mediates neuronal damage and astrogliosis after focal cerebral ischemia in rats

Neuromodulatory effects of leukotriene receptor antagonists: A comprehensive review

Cysteinyl leukotrienes (CysLTs) are central to the pathophysiology of asthma and various inflammatory disorders. Leukotriene receptor antagonists (LTRAs) effectively treat respiratory conditions by targeting cysteinyl leukotriene receptors, CysLT1 and CysLT2 subtypes. This review explores the multifaceted effects of LTs, extending beyond bronchoconstriction. CysLT receptors are not only present in the respiratory system but are also crucial in neuronal signaling pathways. LTRAs modulate these receptors, influencing downstream signaling, calcium levels, inflammation, and oxidative stress (OS) within neurons hinting at broader implications. Recent studies identify novel molecular targets, sparking interest in repurposing LTRAs for therapeutic use. Clinical trials are investigating their potential in neuroinflammation control, particularly in Alzheimer's disease (AD) and Parkinson's diseases (PD). However, montelukast, a long-standing LTRA since 1998, raises concerns due to neuropsychiatric adverse drug reactions (ADRs). Despite widespread use, understanding montelukast's metabolism and underlying ADR mechanisms remains limited. This review comprehensively examines LTRAs' diverse biological effects, emphasizing non-bronchoconstrictive activities. It also analyses plausible mechanisms behind LTRAs' neuronal effects, offering insights into their potential as neurodegenerative disease modulators. The aim is to inform clinicians, researchers, and pharmaceutical developers about LTRAs' expanding roles, particularly in neuroinflammation control and their promising repurposing for neurodegenerative disease management.

Leukotriene signaling in neurodegeneration: implications for treatment strategies

Leukotrienes (LTs) are a group of substances that cause inflammation. They are produced by the enzyme 5-lipoxygenase (5-LOX) from arachidonic acid. Cysteinyl LTs are a group of lipid molecules that have a prominent role in inflammatory signaling in the allergic diseases. Although they are traditionally known for their role in allergic disease, current advancements in bio-medical research have shed light on the involvement of these inflammatory mediators in diseases such as in the inflammation related to central nervous system (CNS) disorders. Among the CNS diseases, LTs, along with 5-LOX and their receptors, have been shown to be associated with multiple sclerosis (MS), Alzheimer's disease (AD), and Parkinson's disease (PD). Through a comprehensive review of current research and experimentation, this investigation provides an insight on the biosynthesis, receptors, and biological effects of LTs in the body. Furthermore, implications of leukotriene signaling in CNS and its intricate role in neurodegeneration are also studied. Through the revelation of these insights, our aim is to establish a foundation for the development of enhanced and focused therapeutic approaches in the continuous endeavor to combat neurodegeneration. Furthermore, the pharmacological inhibition of leukotriene signaling with selective inhibitors offers promising prospects for future interventions and treatments for neurodegenerative diseases.

A critical role for Macrophage-derived Cysteinyl-Leukotrienes in HIV-1 induced neuronal injury

Macrophages (MΦ) infected with human immunodeficiency virus (HIV)-1 or activated by its envelope protein gp120 exert neurotoxicity. We found previously that signaling via p38 mitogen-activated protein kinase (p38 MAPK) is essential to the neurotoxicity of HIVgp120-stimulated MΦ. However, the associated downstream pathways remained elusive. Here we show that cysteinyl-leukotrienes (CysLT) released by HIV-infected or HIVgp120 stimulated MΦ downstream of p38 MAPK critically contribute to neurotoxicity. SiRNA-mediated or pharmacological inhibition of p38 MAPK deprives MΦ of CysLT synthase (LTC4S) and, pharmacological inhibition of the cysteinyl-leukotriene receptor 1 (CYSLTR1) protects cerebrocortical neurons against toxicity of both gp120-stimulated and HIV-infected MΦ. Components of the CysLT pathway are differentially regulated in brains of HIV-infected individuals and a transgenic mouse model of NeuroHIV (HIVgp120tg). Moreover, genetic ablation of LTC4S or CysLTR1 prevents neuronal damage and impairment of spatial memory in HIVgp120tg mice. Altogether, our findings suggest a novel critical role for cysteinyl-leukotrienes in HIV-associated brain injury.

Asthma aggravates alzheimer's disease by up-regulating NF- κB signaling pathway through LTD4

Clinical studies have shown that asthma is a risk factor for dementia or Alzheimer's disease (AD). To investigate whether asthma aggravates AD in APP/PS1 mice and explore the potential mechanisms, an asthma model was established using six-month-old APP/PS1 mice, and montelukast was used as a therapeutic agent in APP/PS1 mice with asthma. The Morris water maze test showed that asthma aggravates spatial learning and memory abilities. Asthma also upregulates the NF-κB inflammatory pathway in APP/PS1 mice and promotes the expression of beta-site amyloid precursor protein cleaving enzyme 1 (BACE1), amyloid-β (Aβ) deposition, neuronal damage, synaptic plasticity deficiency, activation of microglia and astrocytes. The level of LTD4 and its receptor CysLT1R in the hippocampus of APP/PS1 mice after the asthma modeling was established was higher than that in APP/PS1 mice, suggesting that asthma may affect the pathology of AD through LTD4 and its receptor Cys-LT1R. Montelukast ameliorates these pathological changes and cognitive impairment. These results suggest that asthma aggravates AD pathology and cognitive impairment of APP/PS1 mice via upregulation of the NF-κB inflammatory pathway, and montelukast ameliorates these pathological changes.

Cross-talk between bioactive lipid mediators and the unfolded protein response in ischemic stroke

Ischemic cerebral stroke is a severe medical condition that affects about 15 million people every year and is the second leading cause of death and disability globally. Ischemic stroke results in neuronal cell death and neurological impairment. Current therapies may not adequately address the deleterious metabolic changes and may increase neurological damage. Oxygen and nutrient depletion along with the tissue damage result in endoplasmic reticulum (ER) stress, including the Unfolded Protein Response (UPR), and neuroinflammation in the affected area and cause cell death in the lesion core. The spatio-temporal production of lipid mediators, either pro-inflammatory or pro-resolving, decides the course and outcome of stroke. The modulation of the UPR as well as the resolution of inflammation promotes post-stroke cellular viability and neuroprotection. However, studies about the interplay between the UPR and bioactive lipid mediators remain elusive and this review gives insights about the crosstalk between lipid mediators and the UPR in ischemic stroke. Overall, the treatment of ischemic stroke is often inadequate due to lack of effective drugs, thus, this review will provide novel therapeutical strategies that could promote the functional recovery from ischemic stroke.

Exploring the neuroprotective effects of montelukast on brain inflammation and metabolism in a rat model of quinolinic acid-induced striatal neurotoxicity

BACKGROUND

One intrastriatal administration of quinolinic acid (QA) in rats induces a lesion with features resembling those observed in Huntington's disease. Our aim is to evaluate the effects of the cysteinyl leukotriene receptor antagonist montelukast (MLK), which exhibited neuroprotection in different preclinical models of neurodegeneration, on QA-induced neuroinflammation and regional metabolic functions.

METHODS

The right and left striatum of Sprague Dawley and athymic nude rats were injected with QA and vehicle (VEH), respectively. Starting from the day before QA injection, animals were treated with 1 or 10 mg/kg of MLK or VEH for 14 days. At 14 and 30 days post-lesion, animals were monitored with magnetic resonance imaging (MRI) and positron emission tomography (PET) using [18F]-VC701, a translocator protein (TSPO)-specific radiotracer. Striatal neuroinflammatory response was measured post-mortem in rats treated with 1 mg/kg of MLK by immunofluorescence. Rats treated with 10 mg/kg of MLK also underwent a [18F]-FDG PET study at baseline and 4 months after lesion. [18F]-FDG PET data were then used to assess metabolic connectivity between brain regions by applying a covariance analysis method.

RESULTS

MLK treatment was not able to reduce the QA-induced increase in striatal TSPO PET signal and MRI lesion volume, where we only detected a trend towards reduction in animals treated with 10 mg/kg of MLK. Post-mortem immunofluorescence analysis revealed that MLK attenuated the increase in striatal markers of astrogliosis and activated microglia in the lesioned hemisphere. We also found a significant increase in a marker of anti-inflammatory activity (MannR) and a trend towards reduction in a marker of pro-inflammatory activity (iNOS) in the lesioned striatum of MLK-compared to VEH-treated rats. [18F]-FDG uptake was significantly reduced in the striatum and ipsilesional cortical regions of VEH-treated rats at 4 months after lesion. MLK administration preserved glucose metabolism in these cortical regions, but not in the striatum. Finally, MLK was able to counteract changes in metabolic connectivity and measures of network topology induced by QA, in both lesioned and non-lesioned hemispheres.

CONCLUSIONS

Overall, MLK treatment produced a significant neuroprotective effect by reducing neuroinflammation assessed by immunofluorescence and preserving regional brain metabolism and metabolic connectivity from QA-induced neurotoxicity in cortical and subcortical regions.

The Relationship of Astrocytes and Microglia with Different Stages of Ischemic Stroke

Ischemic stroke is the predominant cause of severe morbidity and mortality worldwide. Post-stroke neuroinflammation has recently received increasing attention with the aim of providing a new effective treatment strategy for ischemic stroke. Microglia and astrocytes are major components of the innate immune system of the central nervous system. They can be involved in all phases of ischemic stroke, from the early stage, contributing to the first wave of neuronal cell death, to the late stage involving phagocytosis and repair. In the early stage of ischemic stroke, a vicious cycle exists between the activation of microglia and astrocytes (through astrocytic connexin 43 hemichannels), aggravating neuroinflammatory injury post-stroke. However, in the late stage of ischemic stroke, repeatedly activated microglia can induce the formation of glial scars by triggering reactive astrogliosis in the peri-infarct regions, which may limit the movement of activated microglia in reverse and restrict the diffusion of inflammation to healthy brain tissues, alleviating the neuroinflammatory injury poststroke. In this review, we elucidated the various roles of astrocytes and microglia and summarized their relationship with neuroinflammation. We also examined how astrocytes and microglia influence each other at different stages of ischemic stroke. Several potential therapeutic approaches targeting astrocytes and microglia in ischemic stroke have been reviewed. Understanding the details of astrocytemicroglia interaction processes will contribute to a better understanding of the mechanisms underlying ischemic stroke, contributing to the identification of new therapeutic interventions.

Montelukast reduces grey matter abnormalities and functional deficits in a mouse model of inflammation-induced encephalopathy of prematurity

Encephalopathy of prematurity (EoP) affects approximately 30% of infants born < 32 weeks gestation and is highly associated with inflammation in the foetus. Here we evaluated the efficacy of montelukast, a cysteinyl leukotriene receptor antagonist widely used to treat asthma in children, to ameliorate peripheral and central inflammation, and subsequent grey matter neuropathology and behaviour deficits in a mouse model of EoP. Male CD-1 mice were treated with intraperitoneal (i.p.) saline or interleukin-1beta (IL-1β, 40 μg/kg, 5 μL/g body weight) from postnatal day (P)1-5 ± concomitant montelukast (1-30 mg/kg). Saline or montelukast treatment was continued for a further 5 days post-injury. Assessment of systemic and central inflammation and short-term neuropathology was performed from 4 h following treatment through to P10. Behavioural testing, MRI and neuropathological assessments were made on a second cohort of animals from P36 to 54. Montelukast was found to attenuate both peripheral and central inflammation, reducing the expression of pro-inflammatory molecules (IL-1β, IL-6, TNF) in the brain. Inflammation induced a reduction in parvalbumin-positive interneuron density in the cortex, which was normalised with high-dose montelukast. The lowest effective dose, 3 mg/kg, was able to improve anxiety and spatial learning deficits in this model of inflammatory injury, and alterations in cortical mean diffusivity were not present in animals that received this dose of montelukast. Repurposed montelukast administered early after preterm birth may, therefore, improve grey matter development and outcome in EoP.

Bibliometric analysis of tumor necrosis factor in post-stroke neuroinflammation from 2003 to 2021

Objective

Tumor necrosis factor (TNF), a crucial cytokine, has important research value in post-stroke neuroinflammation (PSN). We analyzed the studies that have been conducted in this area and used bibliometric methods to predict research hotspots and identify trends regarding TNF in PSN.

Methods

Publications were accessed at the Science Citation Index Expanded 1975-2021 (SCI expanded), Web of Science Core Collection (WoSCC), on May 1, 2022. Additionally, software such as CiteSpace and VOSviewer were utilized for bibliometric analyses.

Results

In total, 1391 original articles and reviews on TNF in PSN published from 2003 to 2021 were identified. An upward trend was observed in the number of publications on TNF in PSN. These publications were primarily from 57 countries and 1446 institutions, led by China and the United States with China leading the number of publications (NP) and the US with the number of citations (NC). The League of European Research Universities (LERU) and Journal of Neuroinflammation, respectively were the most prolific branches and journals. Zhang, John H. published the most papers and Finsen, Bente had the most cited papers. One paper by Kettenmann, H. published in 2011 reached the highest level of Global Citation Score (GCS). The keyword co-occurrence and reference co-citation analyses suggest that poststroke therapy and potential mechanistic pathways are important topics related to PSN in recent years. Reference burst detection suggests new burst hotspots after 2015, focusing on pathway modulation and discovery of therapeutic targets, suggesting a substantial development in the study of TNF in PSN research.

Conclusion

The present bibliometric analysis shows a continuous trend of increasing literature related to TNF in PSN, and shows that TNF plays an important role in PSN involves multiple immune mechanisms and may contribute as a potential target for neuroprotective therapeutics after stroke. Prior to 2011, most of the research was focused on discovering the specific role of TNF in PSN, and in recent years studies have mainly targeted the exploration of the signaling pathways. Future research prospects may lie in finding key therapeutic targets in pathway of TNF in PSN.

Leukotrienes vs. Montelukast—Activity, Metabolism, and Toxicity Hints for Repurposing

Increasing environmental distress is associated with a growing asthma incidence; no treatments are available but montelukast (MTK)—an antagonist of the cysteinyl leukotrienes receptor 1—is widely used in the management of symptoms among adults and children. Recently, new molecular targets have been identified and MTK has been proposed for repurposing in other therapeutic applications, with several ongoing clinical trials. The proposed applications include neuroinflammation control, which could be explored in some neurodegenerative disorders, such as Alzheimer’s and Parkinson’s diseases (AD and PD). However, this drug has been associated with an increasing number of reported neuropsychiatric adverse drug reactions (ADRs). Besides, and despite being on the market since 1998, MTK metabolism is still poorly understood and the mechanisms underlying neuropsychiatric ADRs remain unknown. We review the role of MTK as a modulator of leukotriene pathways and systematize the current knowledge about MTK metabolism. Known toxic effects of MTK are discussed, and repurposing applications are presented comprehensively, with a focus on AD and PD.

A Dual Role for Cysteinyl Leukotriene Receptors in the Pathogenesis of Corneal Infection

Cysteinyl leukotrienes (CysLTs) have been defined as central mediators of inflammation. Despite our extensive understanding of these bioactive lipid mediators in the pathogenesis of diseases such as asthma, allergic rhinitis, and even neurological disorders, information regarding the eye is markedly lacking. As a result, this study examined the expression profiles of two major CysLT receptors, CysLT1 and CysLT2, in the cornea using experimental mouse models of Pseudomonas aeruginosa-induced keratitis with contrasting outcomes: susceptible C57BL/6 (B6) and resistant BALB/c. Postinfection, disparate levels of CysLT receptors were accompanied by distinct expression profiles for select proinflammatory and anti-inflammatory cell surface markers detected on macrophages and polymorphonuclear neutrophils between the two strains. Further, inhibition of either CysLT receptor converted the disease response of both strains, where corneal perforation was prevented in B6 mice, and BALB/c mice fared significantly worse. In addition, receptor antagonist studies revealed changes in inflammatory cell infiltrate phenotypes and an influence on downstream CysLT receptor signaling pathways. Although the B6 mouse model highlights the established proinflammatory activities related to CysLT receptor activation, results generated from BALB/c mice indicate a protective mechanism that may be essential to disease resolution. Further, basal expression levels of CysLT1 and CysLT2 were significantly higher in uninfected corneas of both mouse strains as opposed to during infection, suggestive of a novel role in homeostatic maintenance within the eye. In light of these findings, therapeutic targeting of CysLT receptors extends beyond inhibition of proinflammatory activities and may impact inflammation resolution, as well as corneal surface homeostasis.

Neuroprotective effects of CysLTR antagonist on Streptococcus pneumoniae‑induced meningitis in rats

Cysteinyl leukotrienes (CysLTs) modulate central nervous system inflammatory responses via their receptors, CysLT₁R and CysLT₂R. It has been demonstrated that CysLTR participates in the infection process of Streptococcus pneumoniae (SP)-induced meningitis. In the present study, the effects and possible underlying mechanisms of CysLTR antagonists (pranlukast and HAMI 3379) on SP meningitis were further determined. SP meningitis was induced by intracerebroventricular injection of serotype III SP in Sprague-Dawley rats which were administrated intraperitoneally with 0.1 mg/kg antagonists. The clinical disease status of rats was evaluated by body weight and behavioral changes with neurological scoring. Survival neuron density, activated microglial and astrocytes were assessed by Nissl staining and immunohistochemical staining. The expression levels of inflammatory cytokines and NLRP3 inflammasome were detected by reverse transcription-quantitative PCR and western blotting, respectively. Pranlukast and HAMI 3379 treatment markedly alleviated the clinical disease status, which was manifested by improving body weight loss and neurological deficit. Furthermore, pranlukast and HAMI 3379 treatment ameliorated neuronal injury and inhibited microgliosis and astrogliosis. In addition, significant downregulation of inflammatory cytokines and NLRP3 expression was observed in pranlukast and HAMI 3379-treated rats. These in vivo findings indicated the neuroprotective effects of CysLTR antagonists against experimental SP-induced meningitis, and the mechanism of anti-inflammatory effects may partly be by inhibiting NLRP3 inflammasome overactivation.

Brain-Specific Increase in Leukotriene Signaling Accompanies Chronic Neuroinflammation and Cognitive Impairment in a Model of Gulf War Illness

Persistent cognitive impairment is a primary central nervous system-related symptom in veterans afflicted with chronic Gulf War Illness (GWI). Previous studies in a rat model have revealed that cognitive dysfunction in chronic GWI is associated with neuroinflammation, typified by astrocyte hypertrophy, activated microglia, and enhanced proinflammatory cytokine levels. Studies in a mouse model of GWI have also shown upregulation of several phospholipids that serve as reservoirs of arachidonic acid, a precursor of leukotrienes (LTs). However, it is unknown whether altered LT signaling is a component of chronic neuroinflammatory conditions in GWI. Therefore, this study investigated changes in LT signaling in the brain of rats displaying significant cognitive impairments six months after exposure to GWI-related chemicals and moderate stress. The concentration of cysteinyl LTs (CysLTs), LTB4, and 5-Lipoxygenase (5-LOX), the synthesizing enzyme of LTs, were evaluated. CysLT and LTB4 concentrations were elevated in the hippocampus and the cerebral cortex, along with enhanced 5-LOX expression in neurons and microglia. Such changes were also associated with increased proinflammatory cytokine levels in the hippocampus and the cerebral cortex. Enhanced CysLT and LTB4 levels in the brain could also be gleaned from their concentrations in brain-derived extracellular vesicles in the circulating blood. The circulating blood in GWI rats displayed elevated proinflammatory cytokines with no alterations in CysLT and LTB4 concentrations. The results provide new evidence that a brain-specific increase in LT signaling is another adverse alteration that potentially contributes to the maintenance of chronic neuroinflammation in GWI. Therefore, drugs capable of modulating LT signaling may reduce neuroinflammation and improve cognitive function in GWI. Additional findings demonstrate that altered LT levels in the brain could be tracked efficiently by analyzing brain-derived EVs in the circulating blood.

Dihydromyricetin alleviates cerebral ischemia-reperfusion injury by attenuating apoptosis and astrogliosis in peri-infarct cortex

OBJECTIVES

In ischemic stroke, reperfusion after thrombolysis is associated with secondary brain damage. Dihydromyricetin (DHM), a flavonoid, has shown neuroprotective effects through anti-oxidant, anti-inflammatory and anti-apoptotic properties. This study investigates the potential of DHM, given postreperfusion in middle cerebral artery occlusion (MCAo) model of stroke in rats.

METHODS

MCAo surgery was performed in male Wistar rats. Reperfusion was performed after 90 min of ischemia. DHM (50 and 100 mg/kg) was administered 10-15 min and 2 h postreperfusion followed by daily dosing for 2 more days. Neurobehavioral parameters and infarct size (TTC staining) were assessed after 72 h. The effective dose (100 mg/kg) was then used to study reduction in infarct size (measured by MRI) and effect on apoptosis (evaluated by protein expression of Bax, Bcl-2 and cleaved caspase-3 and TUNEL assay) in peri-infarct cortex. Furthermore, effects of DHM on neuronal damage and activation of astrocytes were studied by immunofluorescence.

RESULTS

Poststroke DHM (100 mg/kg) administered for 3 days showed significant improvements in motor-coordination and infarct damage (TTC staining and MRI). MCAo-induced altered apoptotic proteins were normalized to a significant extent in peri-infarct cortex with DHM treatment. Data from TUNEL assay were complementary to the effects on apoptotic proteins. Additionally, DHM caused a significant reduction in the number of reactive astrocytes when compared with the MCAo group.

DISCUSSION

This study demonstrated the efficacy of subacute DHM treatment in ischemia/reperfusion injury by modulating apoptosis and astrogliosis in the peri-infarct cortex. This suggests the potential of DHM in attenuating disease progression.

Circular RNAs as Competing Endogenous RNAs in Cardiovascular and Cerebrovascular Diseases: Molecular Mechanisms and Clinical Implications

Circular RNAs (circRNAs) represent a novel class of widespread and diverse endogenous RNA molecules. This unusual class of RNA species is generated by a back-splicing event of exons or introns, resulting in a covalently closed circRNA molecule. Accumulating evidence indicates that circRNA plays an important role in the biological functions of a network of competing endogenous RNA (ceRNA). CircRNAs can competitively bind to miRNAs and abolish the suppressive effect of miRNAs on target RNAs, thus regulating gene expression at the posttranscriptional level. The role of circRNAs as ceRNAs in the pathogenesis of cardiovascular and cerebrovascular diseases (CVDs) has been recently reported and highlighted. Understanding the underlying molecular mechanism could aid the discovery of therapeutic targets or strategies against CVDs. Here, we review the progress in studying the role of circRNAs as ceRNAs in CVDs, with emphasis on the molecular mechanism, and discuss future directions and possible clinical implications.

Association between GFAP-positive astrocytes with clinically important parameters including neurological deficits and/or infarct volume in stroke-induced animals

The effect of GFAP-positive astrocytes, as positive or negative factors on stroke complications such as infarct volume and neurological deficits is currently under debate. This review was aimed to evaluate and compare the frequency of studies that showed a positive or negative relationship between astrocyte activation with the improvement of neurological deficits and/or the decrease of infarct volume. In addition, we reviewed two possible causes of differences in results including timepoint of stroke and stroke severity. Time of GFAP assessment was considered as time point and type of stroke induction and duration of stroke as stroke severity. According to our review in the most relevant English-language studies in the PubMed, Web of Science, and Google Scholar databases from 2005 to 2020, the majority of studies (77 vs. 28) showed a negative coincidence or correlation between GFAP-positive cells with neurological improvement as well as between GFAP-positive cells with infarct volume reduction. In most reviewed studies, GFAP expression was reported as a marker related to or coinciding with worse neurological function, or greater infarct volume. However, there were also studies that showed helpful effects of GFAP-positive cells on neurological function or stroke lesion. Although there are some elucidations that the difference in these findings is due to the time point of stroke and stroke severity, our review did not confirm these interpretations.

Potential Effects of Leukotriene Receptor Antagonist Montelukast in Treatment of Neuroinflammation in Parkinson's Disease

Parkinson’s disease (PD) is a neurodegenerative disorder where misfolded alpha-synuclein-enriched aggregates called Lewy bodies are central in pathogenesis. No neuroprotective or disease-modifying treatments are currently available. Parkinson’s disease is considered a multifactorial disease and evidence from multiple patient studies and animal models has shown a significant immune component during the course of the disease, highlighting immunomodulation as a potential treatment strategy. The immune changes occur centrally, involving microglia and astrocytes but also peripherally with changes to the innate and adaptive immune system. Here, we review current understanding of different components of the PD immune response with a particular emphasis on the leukotriene pathway. We will also describe evidence of montelukast, a leukotriene receptor antagonist, as a possible anti-inflammatory treatment for PD.

Caffeine and Its Neuroprotective Role in Ischemic Events: A Mechanism Dependent on Adenosine Receptors

Ischemia is characterized by a transient, insufficient, or permanent interruption of blood flow to a tissue, which leads to an inadequate glucose and oxygen supply. The nervous tissue is highly active, and it closely depends on glucose and oxygen to satisfy its metabolic demand. Therefore, ischemic conditions promote cell death and lead to a secondary wave of cell damage that progressively spreads to the neighborhood areas, called penumbra. Brain ischemia is one of the main causes of deaths and summed with retinal ischemia comprises one of the principal reasons of disability. Although several studies have been performed to investigate the mechanisms of damage to find protective/preventive interventions, an effective treatment does not exist yet. Adenosine is a well-described neuromodulator in the central nervous system (CNS), and acts through four subtypes of G-protein-coupled receptors. Adenosine receptors, especially A₁ and A_2A receptors, are the main targets of caffeine in daily consumption doses. Accordingly, caffeine has been greatly studied in the context of CNS pathologies. In fact, adenosine system, as well as caffeine, is involved in neuroprotection effects in different pathological situations. Therefore, the present review focuses on the role of adenosine/caffeine in CNS, brain and retina, ischemic events.

Montelukast alleviates inflammation in experimental autoimmune encephalomyelitis by altering Th17 differentiation in a mouse model

Montelukast is a leukotriene receptor antagonist that is known to prevent allergic rhinitis and asthma. Blocking the Cysteinyl leukotriene receptor (CysLTR1), one of the primary receptors of leukotrienes, has been demonstrated to be efficacious in ameliorating experimental autoimmune encephalomyelitis (EAE), an animal model of multiple sclerosis (MS), through disrupting chemotaxis of infiltrating T cells. However, the role of CysLTR1 in the pathogenesis of MS is not well understood. Here, we show that MS patients had higher expression of CysLTR1 in the circulation and central nervous system (CNS). The majority of CD4⁺ T cells expressed CysLTR1 in MS lesions. Among T-cell subsets, Th17 cells had the highest expression of CysLTR1, and blocking CysLTR1 signalling abrogated their development in vitro. Inhibition of CysLTR1 by montelukast suppressed EAE development in both a prophylactic and therapeutic manner and inhibited myelin loss in EAE mice. Similarly, the in vivo results showed that montelukast inhibited Th17 response in EAE mice and that Th17 cells treated with montelukast had reduced encephalitogenic in adoptive EAE. Our findings strongly suggest that targeting Th17 response by inhibiting CysLTR1 signalling could be a promising therapeutic strategy for the treatment of MS and CNS inflammatory diseases.

Microglia depletion diminishes key elements of the leukotriene pathway in the brain of Alzheimer's Disease mice

Leukotrienes (LTs) contribute to the neuropathology of chronic neurodegenerative disorders including Alzheimer’s Disease (AD), where they mediate neuroinflammation and neuronal cell-death. In consequence, blocking the action of Leukotrienes (LTs) ameliorates pathologies and improves cognitive function in animal models of neurodegeneration. Surprisingly, the source of Leukotrienes (LTs) in the brain is largely unknown. Here, we identified the Leukotriene (LT) synthesis rate-limiting enzyme 5-Lipoxygenase (5-Lox) primarily in neurons and to a lesser extent in a subpopulation of microglia in human Alzheimer´s Disease (AD) hippocampus brain sections and in brains of APP Swedish PS1 dE9 (APP-PS1) mice, a transgenic model for Alzheimer´s Disease (AD) pathology. The 5-Lipoxygenase (5-Lox) activating protein (FLAP), which anchors 5-Lipoxygenase (5-Lox) to the membrane and mediates the contact to the substrate arachidonic acid, was confined exclusively to microglia with the entire microglia population expressing 5-Lipoxygenase activating protein (FLAP). To define the contribution of microglia in the Leukotriene (LT) biosynthesis pathway, we ablated microglia using the colony stimulating factor 1 receptor (CSF1R) inhibitor PLX5622 in wildtype (WT) and APP-PS1 mice. Microglia ablation not only diminished the expression of FLAP and of the Leukotriene (LT) receptor Cysteinylleukotriene receptor 1 (CysLTR1), as expected based on their microglia cell type-specific expression, but also drastically reduced 5-Lipoxygenase (5-Lox) mRNA expression in the brain and its protein expression in neurons, in particular in wildtype (WT) mice. In conclusion i) microglia are key in Leukotriene (LT) biosynthesis, and ii) they regulate neuronal 5-Lipoxygenase (5-Lox) expression implying a yet unknown signaling mechanism between neurons and microglia.

Lipids and Lipid Mediators Associated with the Risk and Pathology of Ischemic Stroke

Stroke is a severe neurological disorder in humans that results from an interruption of the blood supply to the brain. Worldwide, stoke affects over 100 million people each year and is the second largest contributor to disability. Dyslipidemia is a modifiable risk factor for stroke that is associated with an increased risk of the disease. Traditional and non-traditional lipid measures are proposed as biomarkers for the better detection of subclinical disease. In the central nervous system, lipids and lipid mediators are essential to sustain the normal brain tissue structure and function. Pathways leading to post-stroke brain deterioration include the metabolism of polyunsaturated fatty acids. A variety of lipid mediators are generated from fatty acids and these molecules may have either neuroprotective or neurodegenerative effects on the post-stroke brain tissue; therefore, they largely contribute to the outcome and recovery from stroke. In this review, we provide an overview of serum lipids associated with the risk of ischemic stroke. We also discuss the role of lipid mediators, with particular emphasis on eicosanoids, in the pathology of ischemic stroke. Finally, we summarize the latest research on potential targets in lipid metabolic pathways for ischemic stroke treatment and on the development of new stroke risk biomarkers for use in clinical practice.

Antagonism of cysteinyl leukotrienes and their receptors as a neuroinflammatory target in Alzheimer's disease

BACKGROUND

Alzheimer's disease is a complex multifaceted neurodegenerative disorder. It is characterized by the deposition of extracellular amyloid senile plaques and intracellular neurofibrillary tangles leading to progressive dementia and death in aged adult population. Recent emerging research has highlighted a potential pharmacological role of 5-lipoxyenase-cysteinyl leukotriene pathway in molecular pathogenesis of Alzheimer's disease.

OBJECTIVE

Although cysteinyl leukotrienes and their receptors have a major clinical role in chronic respiratory inflammation, their roles in chronic neuroinflammation in Alzheimer's disease need a detailed and careful exploration.

RESULTS AND CONCLUSION

This review article highlights a novel role of cysteinyl leukotrienes and their receptors in pathophysiology of Alzheimer's disease in order to understand the underlying molecular mechanism. In addition, it summarizes the recent advances in various pre-clinical and clinical strategies used to modulate this pathway for therapeutic targeting of Alzheimer's disease.

Lipid mediators and sterile inflammation in ischemic stroke

Stroke is one of the major causes of lethality and disability, yet few effective therapies have been established for ischemic stroke. Inflammation in the ischemic brain is induced by the infiltration and subsequent activation of immune cells. Loss of cerebral blood flow and ischemic brain-cell death trigger the activation of infiltrating immune cells and drastic changes in the lipid content of the ischemic brain. In particular, polyunsaturated fatty acids and their metabolites regulate cerebral post-ischemic inflammation and ischemic stroke pathologies. In this review, we discuss the relationships between the lipid mediators and cerebral post-ischemic inflammation and their relevance to possible future therapeutic strategies targeting lipid mediators for ischemic stroke.

Modulation of neuroinflammation by cysteinyl leukotriene 1 and 2 receptors: implications for cerebral ischemia and neurodegenerative diseases

Neuroinflammation is a complex biological process and has been known to play an important role in age-related cerebrovascular and neurodegenerative disorders, such as cerebral ischemia, Alzheimer's disease, and Parkinson's disease. Cysteinyl leukotrienes (CysLTs) are potent inflammatory lipid mediators that exhibit actions mainly through activating type 1 and type 2 CysLT receptors (CysLT1 and CysLT2). Accumulating evidence shows that CysLT1 and CysLT2 are activated at different stages of pathological process in various cell types in the brain such as vascular endothelial cells, astrocytes, microglia, and neurons in response to insults. However, the precise roles and mechanisms of CysLT1 and CysLT2 in regulating the pathogenesis of cerebral ischemia, Alzheimer's disease, and Parkinson's disease are not fully understood. In this article, we focus on current advances that link activation of CysLT1 and CysLT2 to the pathological process during brain ischemia and neurodegeneration and discuss mechanisms by which CysLT1 and CysLT2 mediate inflammatory process and brain injury. Multitarget anti-inflammatory potentials of CysLT1 and CysLT2 antagonism for neuroinflammation and brain injury will also be reviewed.

A novel therapeutic potential of cysteinyl leukotrienes and their receptors modulation in the neurological complications associated with Alzheimer's disease

Cysteinyl leukotrienes (cysLTs) are member of eicosanoid inflammatory lipid mediators family produced by oxidation of arachidonic acid by action of the enzyme 5-lipoxygenase (5-LOX). 5-LOX is activated by enzyme 5-Lipoxygenase-activating protein (FLAP), which further lead to production of cysLTs i.e. leukotriene C4 (LTC4), leukotriene D4 (LTD4) and leukotriene E4 (LTE4). CysLTs then produce their potent inflammatory actions by activating CysLT1 and CysLT2 receptors. Inhibitors of cysLTs are indicated in asthma, allergic rhinitis and other inflammatory disorders. Earlier studies have associated cysLTs and their receptors in several neurodegenerative disorders diseases like, multiple sclerosis, Parkinson's disease, Huntington's disease, epilepsy and Alzheimer's disease (AD). These inflammatory lipid mediators have previously shown effects on various aggravating factors of AD. However, not much data has been elucidated to test their role against AD clinically. Herein, through this review, we have provided the current and emerging information on the role of cysLTs and their receptors in various neurological complications responsible for the development of AD. In addition, literature evidences for the effect of cysLT inhibitors on distinct aspects of abnormalities in AD has also been reviewed. Promising advancement in understanding on the role of cysLTs on the various neuromodulatory processes and mechanisms may contribute to the development of newer and safer therapy for the treatment of AD in future.

Potential role of leukotriene receptor antagonists in reducing cardiovascular and cerbrovascular risk: A systematic review of human clinical trials and in vivo animal studies

BACKGROUND

Leukotrienes are important lipid mediators of inflammation arising from arachidonic acid cascade. They are implicated in vascular inflammation and produced in different pathologic conditions as atherosclerosis, stroke and myocardial infarction. Different studies have investigated the role of leukotriene receptor antagonist (LTRA) in reducing some cardiovascular events, especially in animals. We conducted a systematic review of both in vivo animal and human studies to determine the potential role of leukotriene receptor antagonist in reducing cardiovascular and cerebrovascular events.

METHODS

Data sources: Pubmed, Embase and Cochrane database.

DATA EXTRACTION

Two reviewers independently screened potentially eligible articles and extracted relevant data.

RESULTS

A total of 28 studies were included, of which 26 were conducted in animals, and 2 in humans.

CONCLUSIONS

All animal studies reported that using a leukotriene receptor antagonist brings to a reduction of either myocardial infarction, ischemic stroke, or atherosclerosis risk. Similar results were obtained from two clinical trials on humans, suggesting a potential role of montelukast in reducing some cardiovascular diseases.

GPR17 mediates ischemia-like neuronal injury via microglial activation

GPR17 is a G (i)-coupled dual receptor, linked to P2Y and CysLT receptors stimulated by uracil nucleotides and cysteinyl leukotrienes, respectively. Recent evidence has demonstrated that GPR17 inhibition ameliorates the progression of cerebral ischemic injury by regulating neuronal death and microglial activation. The present study aimed to assess the detailed regulatory roles of this receptor in oxygen-glucose deprivation/recovery (OGD/R)-induced ischemia-like injury in vitro and explore the underlying mechanism. The results demonstrated that OGD/R induced ischemic neuronal injury and microglial activation, including enhanced phagocytosis and increased inflammatory cytokine release in neuron‑glial mixed cultures of cortical cells. GPR17 upregulation during OGD/R was spatially and temporally correlated with neuronal injury and microglial activation. In addition, GPR17 knockdown inhibited OGD/R-induced responses in neuron-glial mixed cultures. GPR17 knockdown also attenuated cell injury induced by the agonist leukotriene D₄ (LTD₄) or uridine 5′-diphosphate (UDP) in neuron-glial mixed cultures. However, GPR17 knockdown did not affect OGD/R-induced ischemic neuronal injury in primary cultures of neurons. In primary astrocyte cultures, neither GPR17 nor OGD/R induced injury. By contrast, GPR17 knockdown ameliorated OGD/R-induced microglial activation, boosting phagocytosis and inflammatory cytokine release in primary microglia cultures. Finally, the results demonstrated that the conditioned medium of microglia pretreated with OGD/R induced neuronal death, and the neuronal injury was significantly inhibited by GPR17 knockdown. These findings suggested that GPR17 may mediate ischemia-like neuronal injury and microglial activation in vitro; however, the protective effects on ischemic neuronal injury might depend upon microglial activation. Whether GPR17 regulates neuronal injury mediated by oligodendrocyte linkage remains to be investigated.

Novel insight into circular RNA HECTD1 in astrocyte activation via autophagy by targeting MIR142-TIPARP: implications for cerebral ischemic stroke

Circular RNAs (circRNAs) are highly expressed in the central nervous system and are involved in the regulation of physiological and pathophysiological processes. However, the potential role of circRNAs in stroke remains largely unknown. Here, using a circRNA microarray, we showed that circular RNA Hectd1 (circHectd1) levels were significantly increased in ischemic brain tissues in transient middle cerebral artery occlusion (tMCAO) mouse stroke models and further validated this finding in plasma samples from acute ischemic stroke (AIS) patients. Knockdown of circHectd1 expression significantly decreased infarct areas, attenuated neuronal deficits, and ameliorated astrocyte activation in tMCAO mice. Mechanistically, circHECTD1 functions as an endogenous MIR142 (microRNA 142) sponge to inhibit MIR142 activity, resulting in the inhibition of TIPARP (TCDD inducible poly[ADP-ribose] polymerase) expression with subsequent inhibition of astrocyte activation via macroautophagy/autophagy. Taken together, the results of our study indicate that circHECTD1 and its coupling mechanism are involved in cerebral ischemia, thus providing translational evidence that circHECTD1 can serve as a novel biomarker of and therapeutic target for stroke.

ABBREVIATIONS

3-MA: 3-methyladenine; ACTB: actin beta; AIS: acute ischemic stroke; AS: primary mouse astrocytes; BECN1: beclin 1, autophagy related; BMI: body mass index; circHECTD1: circRNA HECTD1; circRNAs: circular RNAs; CBF: cerebral blood flow; Con: control; DAPI: 4',6-diamidino-2-phenylindole; ECA: external carotid artery; FISH: fluorescence in situ hybridization; GAPDH: glyceraldehyde-3-phosphate dehydrogenase; Gdna: genomic DNA; GFAP: glial fibrillary acidic protein; GO: gene ontology; HDL: high-density lipoprotein; IOD: integrated optical density; LDL: low-density lipoprotein; LPA: lipoprotein(a); MAP1LC3B: microtubule-associated protein 1 light chain 3 beta; MIR142: microRNA 142; mNSS: modified neurological severity scores; MRI: magnetic resonance imaging; NIHSS: National Institute of Health Stoke Scale; OGD-R: oxygen glucose deprivation-reperfusion; PCR: polymerase chain reaction; PFA: paraformaldehyde; SQSTM1: sequestosome 1; TIPARP: TCDD inducible poly(ADP-ribose) polymerase; tMCAO: transient middle cerebral artery occlusion; TTC: 2,3,5-triphenyltetrazolium chloride; UTR: untranslated region; WT: wild type.

[Pathogenetic aspects of the development of acute focal cerebral ischemia]

Current concepts on the main mechanisms of brain damage in ischemic stroke are considered. Chemical regulation of physiological and pathological processes of maintaining cellular pool is supported by a multistep system that included compounds of different structure and complexity. A complex assessment and comparison of the processes taking place during the development of acute local cerebral ischemia (necrosis, apoptosis, autoimmune inflammatory reaction, neuroplasticity) can help in the objectification and prognosis of individual characteristics of the course and outcome of ischemic stroke. Understanding of the cascade of events that occur during the acute ischemic damage is critical for determining current and future diagnostic and therapeutic approaches.

Depletion of microglia exacerbates postischemic inflammation and brain injury

Brain ischemia elicits microglial activation and microglia survival depend on signaling through colony-stimulating factor 1 receptor (CSF1R). Although depletion of microglia has been linked to worse stroke outcomes, it remains unclear to what extent and by what mechanisms activated microglia influence ischemia-induced inflammation and injury in the brain. Using a mouse model of transient focal cerebral ischemia and reperfusion, we demonstrated that depletion of microglia via administration of the dual CSF1R/c-Kit inhibitor PLX3397 exacerbates neurodeficits and brain infarction. Depletion of microglia augmented the production of inflammatory mediators, leukocyte infiltration, and cell death during brain ischemia. Of note, microglial depletion-induced exacerbation of stroke severity did not solely depend on lymphocytes and monocytes. Importantly, depletion of microglia dramatically augmented the production of inflammatory mediators by astrocytes after brain ischemia . In vitro studies reveal that microglia restricted ischemia-induced astrocyte response and provided neuroprotective effects. Our findings suggest that neuroprotective effects of microglia may result, in part, from its inhibitory action on astrocyte response after ischemia.

Cysteinyl Leukotrienes as Potential Pharmacological Targets for Cerebral Diseases

Cysteinyl leukotrienes (CysLTs) are potent lipid mediators widely known for their actions in asthma and in allergic rhinitis. Accumulating data highlights their involvement in a broader range of inflammation-associated diseases such as cancer, atopic dermatitis, rheumatoid arthritis, and cardiovascular diseases. The reported elevated levels of CysLTs in acute and chronic brain lesions, the association between the genetic polymorphisms in the LTs biosynthesis pathways and the risk of cerebral pathological events, and the evidence from animal models link also CysLTs and brain diseases. This review will give an overview of how far research has gone into the evaluation of the role of CysLTs in the most prevalent neurodegenerative disorders (ischemia, Alzheimer's and Parkinson's diseases, multiple sclerosis/experimental autoimmune encephalomyelitis, and epilepsy) in order to understand the underlying mechanism by which they might be central in the disease progression.

The leukotriene receptor antagonist montelukast and its possible role in the cardiovascular field

BACKGROUND

Cysteinyl leukotrienes (LTC4, LTD4, and LTE4) are pro-inflammatory mediators of the 5-lipooxygenase (5-LO) pathway, that play an important role in bronchoconstriction, but can also enhance endothelial cell permeability and myocardial contractility, and are involved in many other inflammatory conditions. In the late 1990s, leukotriene receptor antagonists (LTRAs) were introduced in therapy for asthma and later on, approved for the relief of the symptoms of allergic rhinitis, chronic obstructive pulmonary disease, and urticaria. In addition, it has been shown that LTRAs may have a potential role in preventing atherosclerosis progression.

PURPOSE

The aims of this short review are to delineate the potential cardiovascular protective role of a LTRA, montelukast, beyond its traditional use, and to foster the design of appropriate clinical trials to test this hypothesis.

RESULTS AND CONCLUSIONS

What it is known about leukotriene receptor antagonists? •Leukotriene receptor antagonist, such as montelukast and zafirlukast, is used in asthma, COPD, and allergic rhinitis. • Montelukast is the most prescribed CysLT₁ antagonist used in asthmatic patients. • Different in vivo animal studies have shown that leukotriene receptor antagonists can prevent the atherosclerosis progression, and have a protective role after cerebral ischemia. What we still need to know? • Today, there is a need for conducting clinical trials to assess the role of montelukast in reducing cardiovascular risk and to further understand the mechanism of action behind this effect.

Oral administration of ampelopsin protects against acute brain injury in rats following focal cerebral ischemia

Ampelopsin (AMP) is isolated from the Chinese medicinal herb Ampelopsis grossedentata (Hand-Mazz) and has been associated with numerous biological and pharmacological activities. However, it is not clear whether AMP has a direct protective effect on cerebral ischemia reperfusion injury. Therefore, the present study investigated its role in acute brain injury following focal cerebral ischemia in rats. The current study induced transient focal cerebral ischemia by performing middle cerebral artery occlusion (MCAO) for 60 min, followed by 24 h of reperfusion. Rats were exposed to 40, 80 and 160 mg/kg AMP by oral administration 30 min prior to MCAO and the cysteinyl leukotriene receptor 1-antagonist, pranlukast (0.1 mg/kg, i.p.) was used as a positive control. Neurological deficit scores were observed and an inclined board test was used to assess behavioral dysfunction. The coronal slices were stained with 3,5-triphenyltetrazolium chloride to determine the infarct volume and brain edema. Neuronal morphology was assessed in brain sections stained with cresyl violet and degenerating neurons were identified using Fluoro-Jade B staining. Blood-brain barrier permeability was determined with immunoglobulin (Ig)G immunohistochemistry. Interleukin (IL)-1β, tumor necrosis factor-α (TNF-α) in serum and cerebrospinal fluid were measured using ELISA kits. AMP at 80 and 160 mg/kg attenuated neurological deficits, reduced infarct volume, brain edema, IgG exudation and neuron degeneration and loss. Similar to pranlukast, AMP also inhibited the MCAO-induced IL-1β and TNF-α release. Thus, AMP has a neuroprotective effect on acute brain injury following focal cerebral ischemia in rats at an effective oral dose of 80-160 mg/kg. The results of the current study indicate a therapeutic role for AMP in the treatment of ischemic stroke.

Astrocyte-derived interleukin-15 exacerbates ischemic brain injury via propagation of cellular immunity

Astrocytes are believed to bridge interactions between infiltrating lymphocytes and neurons during brain ischemia, but the mechanisms for this action are poorly understood. Here we found that interleukin-15 (IL-15) is dramatically up-regulated in astrocytes of postmortem brain tissues from patients with ischemic stroke and in a mouse model of transient focal brain ischemia. We generated a glial fibrillary acidic protein (GFAP) promoter-controlled IL-15-expressing transgenic mouse (GFAP-IL-15^tg) line and found enlarged brain infarcts, exacerbated neurodeficits after the induction of brain ischemia. In addition, knockdown of IL-15 in astrocytes attenuated ischemic brain injury. Interestingly, the accumulation of CD8⁺ T and natural killer (NK) cells was augmented in these GFAP-IL-15^tg mice after brain ischemia. Of note, depletion of CD8⁺ T or NK cells attenuated ischemic brain injury in GFAP-IL-15^tg mice. Furthermore, knockdown of the IL-15 receptor α or blockade of cell-to-cell contact diminished the activation and effector function of CD8⁺ T and NK cells in GFAP-IL-15^tg mice, suggesting that astrocytic IL-15 is delivered in trans to target cells. Collectively, these findings indicate that astrocytic IL-15 could aggravate postischemic brain damage via propagation of CD8⁺ T and NK cell-mediated immunity.

Cysteinyl leukotriene correlated with 8-isoprostane levels as predictive biomarkers for sensory dysfunction in autism

Background

Autism is a neurodevelopmental disorder that clinically presented as cognitive deficits, social impairments and sensory dysfunction. An increasing body of evidence has shown that oxidative stress and inflammation are involved in the pathophysiology of autism. Recording biomarkers as measure of the severity of autistic features might help in understanding the pathophysiology of autism.

Methods

This study investigates the plasma levels of 8-isoprostane and Cysteinyl leukotrienes (CysLTs) in 44 autistic children and 40 healthy controls. The recruited autistic patients were assessed for behavior, cognitive and sensory deficits by using different autism severity rating scales, including the Childhood Autism Rating Scales (CARS), Social responsiveness scale (SRS) and Short Sensory Profile (SSP). Receiver Operating Characteristics analysis (ROC) of the obtained data was performed to measure the predictive value of 8-isoprostane and Cysteinyl leukotrienes (CysLTs) as oxidative stress- related parameters. Pearson’s correlations between the measured parameters was also performed.

Results

The concentrations of 8-isoprostane and CysLTs in autistic patients were significantly higher than those in controls. While cognitive and social impairments did not show any significant differences, the SSP results were strongly correlated with the levels of both of the biomarkers assessed. However, autistic children showed improvements in oxidative stress status (as determined by 8-isoprostane levels) at increasing ages.

Conclusion

This study indicates that 8-isoprostane and CysLTs can be used as markers for the early recognition of autistic patients through sensory deficits phenotypes which might help early intervention.

Inflammatory Eicosanoids Increase Amyloid Precursor Protein Expression via Activation of Multiple Neuronal Receptors

Senile plaques comprised of Aβ peptides are a hallmark of Alzheimer's disease (AD) brain, as are activated glia that release inflammatory molecules, including eicosanoids. Previous studies have demonstrated that amyloid precursor protein (APP) and Aβ levels can be increased through activation of thromboxane A2-prostanoid (TP) receptors on neurons. We demonstrate that TP receptor regulation of APP expression depends on Gαq-signaling and conventional protein kinase C isoforms. Importantly, we discovered that Gαq-linked prostaglandin E2 and leukotriene D4 receptors also regulate APP expression. Prostaglandin E2 and thromboxane A2, as well as total APP levels, were found to be elevated in the brains of aged 5XFAD transgenic mice harboring Aβ plaques and activated glia, suggesting that increased APP expression resulted from eicosanoid binding to Gαq-linked neuronal receptors. Notably, inhibition of eicosanoid synthesis significantly lowered brain APP protein levels in aged 5XFAD mice. These results provide new insights into potential AD therapeutic strategies.

Astrocytes, therapeutic targets for neuroprotection and neurorestoration in ischemic stroke

Astrocytes are the most abundant cell type within the central nervous system. They play essential roles in maintaining normal brain function, as they are a critical structural and functional part of the tripartite synapses and the neurovascular unit, and communicate with neurons, oligodendrocytes and endothelial cells. After an ischemic stroke, astrocytes perform multiple functions both detrimental and beneficial, for neuronal survival during the acute phase. Aspects of the astrocytic inflammatory response to stroke may aggravate the ischemic lesion, but astrocytes also provide benefit for neuroprotection, by limiting lesion extension via anti-excitotoxicity effects and releasing neurotrophins. Similarly, during the late recovery phase after stroke, the glial scar may obstruct axonal regeneration and subsequently reduce the functional outcome; however, astrocytes also contribute to angiogenesis, neurogenesis, synaptogenesis, and axonal remodeling, and thereby promote neurological recovery. Thus, the pivotal involvement of astrocytes in normal brain function and responses to an ischemic lesion designates them as excellent therapeutic targets to improve functional outcome following stroke. In this review, we will focus on functions of astrocytes and astrocyte-mediated events during stroke and recovery. We will provide an overview of approaches on how to reduce the detrimental effects and amplify the beneficial effects of astrocytes on neuroprotection and on neurorestoration post stroke, which may lead to novel and clinically relevant therapies for stroke.

The central role of aquaporins in the pathophysiology of ischemic stroke

Stroke is a complex and devastating neurological condition with limited treatment options. Brain edema is a serious complication of stroke. Early edema formation can significantly contribute to infarct formation and thus represents a promising target. Aquaporin (AQP) water channels contribute to water homeostasis by regulating water transport and are implicated in several disease pathways. At least 7 AQP subtypes have been identified in the rodent brain and the use of transgenic mice has greatly aided our understanding of their functions. AQP4, the most abundant channel in the brain, is up-regulated around the peri-infarct border in transient cerebral ischemia and AQP4 knockout mice demonstrate significantly reduced cerebral edema and improved neurological outcome. In models of vasogenic edema, brain swelling is more pronounced in AQP4-null mice than wild-type providing strong evidence of the dual role of AQP4 in the formation and resolution of both vasogenic and cytotoxic edema. AQP4 is co-localized with inwardly rectifying K(+)-channels (Kir4.1) and glial K(+) uptake is attenuated in AQP4 knockout mice compared to wild-type, indicating some form of functional interaction. AQP4-null mice also exhibit a reduction in calcium signaling, suggesting that this channel may also be involved in triggering pathological downstream signaling events. Associations with the gap junction protein Cx43 possibly recapitulate its role in edema dissipation within the astroglial syncytium. Other roles ascribed to AQP4 include facilitation of astrocyte migration, glial scar formation, modulation of inflammation and signaling functions. Treatment of ischemic cerebral edema is based on the various mechanisms in which fluid content in different brain compartments can be modified. The identification of modulators and inhibitors of AQP4 offer new therapeutic avenues in the hope of reducing the extent of morbidity and mortality in stroke.

HAMI 3379, a CysLT2R antagonist, dose- and time-dependently attenuates brain injury and inhibits microglial inflammation after focal cerebral ischemia in rats

Cysteinyl leukotrienes (CysLTs) induce inflammatory responses by activating their receptors, CysLT1R and CysLT2R. We have reported that CysLT2R is involved in neuronal injury, astrocytosis, and microgliosis, and that intracerebroventricular (i.c.v.) injection of the selective CysLT2R antagonist HAMI 3379 protects against acute brain injury after focal cerebral ischemia in rats. In the present study, we clarified features of the protective effect of intraperitoneally-injected HAMI 3379 in rats. We found that HAMI 3379 attenuated the acute brain injury 24 h after middle cerebral artery occlusion (MCAO) with effective doses of 0.1-0.4 mg/kg and a therapeutic window of ∼1h. It attenuated the neurological deficits, and reduced infarct volume, brain edema, and neuronal loss and degeneration 24 and 72h after MCAO. RNA interference with i.c.v. injection of CysLT2R short hairpin RNA (shRNA) attenuated the acute injury as well. Also, HAMI 3379 inhibited release of the cytokines IL-1β, interferon-γ (IFN-γ), and tumor necrosis factor-α (TNF-α) into the serum and cerebrospinal fluid 24h after MCAO. Moreover, HAMI 3379 ameliorated the microglial activation and neutrophil accumulation in the ischemic regions, but did not affect astrocyte proliferation 72h after MCAO. In comparison, the CysLT1R antagonist pranlukast did not affect microglial activation and IFN-γ release, but inhibited astrocyte proliferation and reduced serum IL-4. Thus, we conclude that HAMI 3379 has a protective effect on acute and subacute ischemic brain injury, and attenuates microglia-related inflammation. CysLT2R antagonist(s) alone or in combination with CysLT1R antagonists may be a novel class of therapeutic agents in the treatment of ischemic stroke.

Cysteinyl leukotriene receptor-1 antagonists as modulators of innate immune cell function

Cysteinyl leukotrienes (cysLTs) are produced predominantly by cells of the innate immune system, especially basophils, eosinophils, mast cells, and monocytes/macrophages. Notwithstanding potent bronchoconstrictor activity, cysLTs are also proinflammatory consequent to their autocrine and paracrine interactions with G-protein-coupled receptors expressed not only on the aforementioned cell types, but also on Th2 lymphocytes, as well as structural cells, and to a lesser extent neutrophils and CD8⁺ cells. Recognition of the involvement of cysLTs in the immunopathogenesis of various types of acute and chronic inflammatory disorders, especially bronchial asthma, prompted the development of selective cysLT receptor-1 (cysLTR1) antagonists, specifically montelukast, pranlukast, and zafirlukast. More recently these agents have also been reported to possess secondary anti-inflammatory activities, distinct from cysLTR1 antagonism, which appear to be particularly effective in targeting neutrophils and monocytes/macrophages. Underlying mechanisms include interference with cyclic nucleotide phosphodiesterases, 5′-lipoxygenase, and the proinflammatory transcription factor, nuclear factor kappa B. These and other secondary anti-inflammatory mechanisms of the commonly used cysLTR1 antagonists are the major focus of the current review, which also includes a comparison of the anti-inflammatory effects of montelukast, pranlukast, and zafirlukast on human neutrophils in vitro, as well as an overview of both the current clinical applications of these agents and potential future applications based on preclinical and early clinical studies.

Protective effect of pranlukast on Aβ₁₋₄₂-induced cognitive deficits associated with downregulation of cysteinyl leukotriene receptor 1

Deposition of extracellular amyloid-β (Aβ) peptide is one of the pathological hallmarks of Alzheimer's disease (AD). Accumulation of Aβ is thought to associate with cognition deficits, neuroinflammation and apoptosis observed in AD. However, effective neuroprotective approaches against Aβ neurotoxicity are unavailable. In the present study, we analysed the effects of pranlukast, a selective cysteinyl leukotriene receptor 1 (CysLT₁R) antagonist, on the impairment of learning and memory formation induced by Aβ and the probable underlying electrophysiological and molecular mechanisms. We found that bilateral intrahippocampal injection of Aβ₁₋₄₂ resulted in a significant decline of spatial learning and memory of mice in the Morris water maze (MWM) and Y-maze tests, together with a serious depression of in vivo hippocampal long-term potentiation (LTP) in the CA1 region of the mice. Importantly, this treatment caused significant increases in CysLT₁R expression and subsequent NF-κB signaling, caspase-3 activation and Bcl-2 downregulation in the hippocampus or prefrontal cortex. Oral administration of pranlukast at 0.4 or 0.8 mg/kg for 4 wk significantly reversed Aβ₁₋₄₂-induced impairments of cognitive function and hippocampal LTP in mice. Furthermore, pranlukast reversed Aβ₁₋₄₂-induced CysLT₁R upregulation, and markedly suppressed the Aβ₁₋₄₂-triggered NF-κB pathway, caspase-3 activation and Bcl-2 downregulation in the hippocampus and prefrontal cortex in mice. Liquid chromatography-tandem mass spectrometry (LC-MS/MS) assay confirmed its presence in the brain after oral administration of pranlukast in mice. These data disclose novel findings about the therapeutic potential of pranlukast, revealing a previously unknown therapeutic possibility to treat memory deficits associated with AD.

Blocking leukotriene synthesis attenuates the pathophysiology of traumatic brain injury and associated cognitive deficits

Neuroinflammation is a component of secondary injury following traumatic brain injury (TBI) that can persist beyond the acute phase. Leukotrienes are potent, pro-inflammatory lipid mediators generated from membrane phospholipids. In the absence of injury, leukotrienes are undetectable in the brain, but after trauma they are rapidly synthesized by a transcellular event involving infiltrating neutrophils and endogenous brain cells. Here, we investigate the efficacy of MK-886, an inhibitor of 5-lipoxygenase activating protein (FLAP), in blocking leukotriene synthesis, secondary brain damage, synaptic dysfunction, and cognitive impairments after TBI. Male Sprague Dawley rats (9-11weeks) received either MK-886 or vehicle after they were subjected to unilateral moderate fluid percussion injury (FPI) to assess the potential clinical use of FLAP inhibitors for TBI. MK-886 was also administered before FPI to determine the preventative potential of FLAP inhibitors. MK-886 given before or after injury significantly blocked the production of leukotrienes, measured by reverse-phase liquid chromatography coupled to tandem mass spectrometry (RP LC-MS/MS), and brain edema, measured by T2-weighted magnetic resonance imaging (MRI). MK-886 significantly attenuated blood-brain barrier disruption in the CA1 hippocampal region and deficits in long-term potentiation (LTP) at CA1 hippocampal synapses. The prevention of FPI-induced synaptic dysfunction by MK-886 was accompanied by fewer deficits in post-injury spatial learning and memory performance in the radial arm water maze (RAWM). These results indicate that leukotrienes contribute significantly to secondary brain injury and subsequent cognitive deficits. FLAP inhibitors represent a novel anti-inflammatory approach for treating human TBI that is feasible for both intervention and prevention of brain injury and neurologic deficits.

Cysteinyl leukotriene receptor 1 mediates LTD4-induced activation of mouse microglial cells in vitro

AIM

To investigate the roles of cysteinyl leukotriene receptors CysLT1R and CysLT2R in leukotriene D4 (LTD4)-induced activation of microglial cells in vitro.

METHODS

Mouse microglial cell line BV2 was transfected with pcDNA3.1(+)-hCysLT1R or pcDNA3.1(+)-hCysLT2R. The expression of relevant mRNAs and proteins in the cells was detected using RT-PCR and Western blotting, respectively. Phagocytosis was determined with flow cytometry analysis. The release of interleukin-1β (IL-1β) from the cells was measured using an ELISA assay.

RESULTS

The expression of CysLT1R or CysLT2R was considerably increased in the transfected BV2 cells, and the receptors were mainly distributed in the plasma membrane and cytosol. Treatment of the cells expressing CysLT1R or CysLT2R with CysLT receptor agonist LTD4 (0.1-100 nmol/L) concentration-dependently enhanced the phagocytosis, and increased mRNA expression and release of IL-1β. Moreover, the responses of hCysLT1R-BV2 cells to LTD4 were significantly larger than those of hCysLT2R-BV2 or WT-BV2 cells. Pretreatment of hCysLT1R-BV2 cells with the selective CysLT1R antagonist montelukast (1 μmol/L) significantly blocked LTD4-induced phagocytosis as well as the mRNA expression and release of IL-1β, whereas the selective CysLT2R antagonist HAMI 3379 (1 μmol/L) had no such effects.

CONCLUSION

CysLT1R mediates LTD4-induced activation of BV2 cells, suggesting that CysLT1R antagonists may exert anti-inflammatory activity in brain diseases.

The role of astrocytes in mediating exogenous cell-based restorative therapy for stroke

Astrocytes have not been a major therapeutic target for the treatment of stroke, with most research emphasis on the neuron. Given the essential role that astrocytes play in maintaining physiological function of the central nervous system and the very rapid and sensitive reaction astrocytes have in response to cerebral injury or ischemic insult, we propose to replace the neurocentric view for treatment with a more nuanced astrocytic centered approach. In addition, after decades of effort in attempting to develop neuroprotective therapies, which target reduction of the ischemic lesion, there are no effective clinical treatments for stroke, aside from thrombolysis with tissue plasminogen activator, which is used in a small minority of patients. A more promising therapeutic approach, which may affect nearly all stroke patients, may be in promoting endogenous restorative mechanisms, which enhance neurological recovery. A focus of efforts in stimulating recovery post stroke is the use of exogenously administered cells. The present review focuses on the role of the astrocyte in mediating the brain network, brain plasticity, and neurological recovery post stroke. As a model to describe the interaction of a restorative cell-based therapy with astrocytes, which drives recovery from stroke, we specifically highlight the subacute treatment of stroke with multipotent mesenchymal stromal cell therapy.