Temporal profiles of cerebrospinal fluid leukotrienes, brain edema and inflammatory response following experimental brain injury

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.

Chronic consumption of a high linoleic acid diet during pregnancy, lactation and post-weaning period increases depression-like behavior in male, but not female offspring

Polyunsaturated fatty acids (PUFAs) play an essential role in brain development. Emerging data have suggested a possible link between an imbalance in PUFAs and cognitive behavioral deficits in offspring. A diet rich in high linoleic acid (HLA), typically from preconception to lactation, leads to an increase in the ratio of omega-6 (n-6) to omega-3 (n-3) fatty acids in the fetus. Arising research has suggested that a deficiency in omega-3 fatty acids is a potential risk factor for inducing autism spectrum disorder (ASD)-like behavioral deficits. However, the impact of a high n- diet during preconception, pregnancy, lactation, and post-weaning on the brain development of adolescent offspring are yet to be determined. This study examined whether consumption of an HLA diet during pregnancy, lactation, and post-weaning induced social and cognitive impairments in female and male offspring rats that resemble autistic phenotypes in humans. Female Wistar Kyoto rats were fed with either HLA or low linoleic acid (LLA) control diet for 10 weeks before mating, then continued with the same diet throughout the pregnancy and lactation period. Female and male offspring at 5 weeks old were subjected to behavioral tests to assess social interaction behavior and depression-/anxiety-like behavior. Our result showed that chronic consumption of an HLA diet did not affect sociability and social recognition memory, but induced depression-like behavior in male but not in female offspring.

Arachidonic Acid Derivatives and Neuroinflammation

Neuroinflammation is characterized by dysregulated inflammatory responses localized within the brain and spinal cord. Neuroinflammation plays a pivotal role in the onset of several neurodegenerative disorders and is considered a typical feature of these disorders. Microglia perform primary immune surveillance and macrophage-like activities within the central nervous system. Activated microglia are predominant players in the central nervous system response to damage related to stroke, trauma, and infection. Moreover, microglial activation per se leads to a proinflammatory response and oxidative stress. During the release of cytokines and chemokines, cyclooxygenases and phospholipase A2 are stimulated. Elevated levels of these compounds play a significant role in immune cell recruitment into the brain. Cyclic phospholipase A2 plays a fundamental role in the production of prostaglandins by releasing arachidonic acid. In turn, arachidonic acid is biotransformed through different routes into several mediators that are endowed with pivotal roles in the regulation of inflammatory processes. Some experimental models of neuroinflammation exhibit an increase in cyclic phospholipase A2, leukotrienes, and prostaglandins such as prostaglandin E2, prostaglandin D2, or prostacyclin. However, findings on the role of the prostacyclin receptors have revealed that their signalling suppresses Th2-mediated inflammatory responses. In addition, other in vitro evidence suggests that prostaglandin E2 may inhibit the production of some inflammatory cytokines, attenuating inflammatory events such as mast cell degranulation or inflammatory leukotriene production. Based on these conflicting experimental data, the role of arachidonic acid derivatives in neuroinflammation remains a challenging issue.

Protein biomarkers of epileptogenicity after traumatic brain injury

Traumatic brain injury (TBI) is a major risk factor for acquired epilepsy. Post-traumatic epilepsy (PTE) develops over time in up to 50% of patients with severe TBI. PTE is mostly unresponsive to traditional anti-seizure treatments suggesting distinct, injury-induced pathomechanisms in the development of this condition. Moderate and severe TBIs cause significant tissue damage, bleeding, neuron and glia death, as well as axonal, vascular, and metabolic abnormalities. These changes trigger a complex biological response aimed at curtailing the physical damage and restoring homeostasis and functionality. Although a positive correlation exists between the type and severity of TBI and PTE, there is only an incomplete understanding of the time-dependent sequelae of TBI pathobiologies and their role in epileptogenesis. Determining the temporal profile of protein biomarkers in the blood (serum or plasma) and cerebrospinal fluid (CSF) can help to identify pathobiologies underlying the development of PTE, high-risk individuals, and disease modifying therapies. Here we review the pathobiological sequelae of TBI in the context of blood- and CSF-based protein biomarkers, their potential role in epileptogenesis, and discuss future directions aimed at improving the diagnosis and treatment of PTE.

Implication of the Kallikrein-Kinin system in neurological disorders: Quest for potential biomarkers and mechanisms

Neurological disorders represent major health concerns in terms of comorbidity and mortality worldwide. Despite a tremendous increase in our understanding of the pathophysiological processes involved in disease progression and prevention, the accumulated knowledge so far resulted in relatively moderate translational benefits in terms of therapeutic interventions and enhanced clinical outcomes. Aiming at specific neural molecular pathways, different strategies have been geared to target the development and progression of such disorders. The kallikrein-kinin system (KKS) is among the most delineated candidate systems due to its ubiquitous roles mediating several of the pathophysiological features of these neurological disorders as well as being implicated in regulating various brain functions. Several experimental KKS models revealed that the inhibition or stimulation of the two receptors of the KKS system (B1R and B2R) can exhibit neuroprotective and/or adverse pathological outcomes. This updated review provides background details of the KKS components and their functions in different neurological disorders including temporal lobe epilepsy, traumatic brain injury, stroke, spinal cord injury, Alzheimer's disease, multiple sclerosis and glioma. Finally, this work will highlight the putative roles of the KKS components as potential neurotherapeutic targets and provide future perspectives on the possibility of translating these findings into potential clinical biomarkers in neurological disease.

Ultra-Performance Liquid Chromatography-Mass Spectrometry Analysis of Free and Esterified Oxygenated Derivatives from Docosahexaenoic Acid in Rat Brain

Docosahexaenoic acid (DHA), a prominent long-chain fatty acid of the omega-3 family, is present at high amount in brain tissues, especially in membrane phospholipids. This polyunsaturated fatty acid is the precursor of various oxygenated lipid mediators involved in diverse physiological and pathophysiological processes. Characterization of DHA-oxygenated metabolites is therefore crucial for better understanding the biological roles of DHA. In this study, we identified and measured, by ultrahigh-performance liquid chromatography coupled with tandem mass spectrometry, a number of oxygenated products derived from DHA in exsanguinated and nonexsanguinated brains. These metabolites were found both in free form and esterified in phospholipids. Interestingly, both (R)- and (S)-monohydroxylated fatty acid stereoisomers were observed free and esterified in phospholipids. Monohydroxylated metabolites were the main derivatives; however, measurable amounts of dihydroxylated products such as protectin DX were detected. Moreover, exsanguination allowed discriminating brain oxygenated metabolites from those generated in blood. These results obtained in healthy rats allowed an overview on the brain oxygenated metabolism of DHA, which deserves further research in pathophysiological conditions, especially in neurodegenerative diseases.

Multiple mechanisms underlying neuroprotection by secretory phospholipase A2 preconditioning in a surgically induced brain injury rat model

BACKGROUND

Intra-operative bleeding, post-operative brain edema and neuroinflammation are major complications in patients with surgical brain injury (SBI). Phospholipase A2 (PLA2) is the upstream enzyme which initiates the PLA2, 5-lipoxygenase (5-LOX) and leukotriene B4 (LTB4) inflammatory pathway. We hypothesized PLA2preconditioning (PPC) prior to SBI can activate endogenous anti-inflammatory responses to protect against SBI. This study evaluated if PPC can ameliorate neurosurgical complications and elucidated PPC-mediated possible protective mechanisms in a rat SBI model.

METHODS

Total 105 adult male Sprague Dawley rats were used for this study. SBI was induced by partial resection of the right frontal lobe. PLA2 or 0.9% NaCl was injected via rats' tail vein for 3 consecutive days prior to SBI. For mechanism study, a selective PLA2 inhibitor, Manoalide and 5-LOX inhibitor, Zileuton were injected intravenously with PPC to elucidate the role of PLA2 and 5-LOX in PPC-mediated anti-inflammatory effects. Brain water content (BWC) and lung water content, neurological tests, ELISA, western blot, immunohistochemistry, white blood cells (WBC) count, and spectrophotometric assay for intra-operative hemorrhage volume were evaluated.

RESULTS

First, PPC reduced brain water content, intra-operative bleeding, and improved neurological function after SBI. Second, PPC decreased 5-LOX expression and brain leukocyte infiltration, while increasing glial fibrillary acidic protein (GFAP) expression in the peri-resection brain tissue after SBI. Third, PPC induced peripheral inflammation represented by mild pulmonary inflammation and increased peripheral blood WBC count and LTB4 level. Lastly, PPC increased blood glucose concentration and glucocorticoid levels after SBI. In addition, PPC mediated above-mentioned changes were partially reversed by administration of PLA2 inhibitor, Manoalide and 5-LOX inhibitor, Zileuton.

CONCLUSIONS

PPC conferred neuroprotection against SBI via multi-target involvement induced anti-inflammatory mechanisms.

Naja sputatrix Venom Preconditioning Attenuates Neuroinflammation in a Rat Model of Surgical Brain Injury via PLA2/5-LOX/LTB4 Cascade Activation

Inflammatory preconditioning is a mechanism in which exposure to small doses of inflammatory stimuli prepares the body against future massive insult by activating endogenous protective responses. Phospholipase A2/5-lipoxygenase/leukotriene-B4 (PLA2/5-LOX/LTB4) axis is an important inflammatory signaling pathway. Naja sputatrix (Malayan spitting cobra) venom contains 15% secretory PLA2 of its dry weight. We investigated if Naja sputatrix venom preconditioning (VPC) reduces surgical brain injury (SBI)-induced neuroinflammation via activating PLA2/5-LOX/LTB4 cascade using a partial frontal lobe resection SBI rat model. Naja sputatrix venom sublethal dose was injected subcutaneously for 3 consecutive days prior to SBI. We observed that VPC reduced brain edema and improved neurological function 24 h and 72 h after SBI. The expression of pro-inflammatory mediators in peri-resection brain tissue was reduced with VPC. Administration of Manoalide, a PLA2 inhibitor or Zileuton, a 5-LOX inhibitor with VPC reversed the protective effects of VPC against neuroinflammation. The current VPC regime induced local skin inflammatory reaction limited to subcutaneous injection site and elicited no other toxic effects. Our findings suggest that VPC reduces neuroinflammation and improves outcomes after SBI by activating PLA2/5-LOX/LTB4 cascade. VPC may be beneficial to reduce post-operative neuroinflammatory complications after brain surgeries.

Macrophages and Phospholipases at the Intersection between Inflammation and the Pathogenesis of HIV-1 Infection

Persistent low grade immune activation and chronic inflammation are nowadays considered main driving forces of the progressive immunologic failure in effective antiretroviral therapy treated HIV-1 infected individuals. Among the factors contributing to this phenomenon, microbial translocation has emerged as a key driver of persistent immune activation. Indeed, the rapid depletion of gastrointestinal CD4⁺ T lymphocytes occurring during the early phases of infection leads to a deterioration of the gut epithelium followed by the translocation of microbial products into the systemic circulation and the subsequent activation of innate immunity. In this context, monocytes/macrophages are increasingly recognized as an important source of inflammation, linked to HIV-1 disease progression and to non-AIDS complications, such as cardiovascular disease and neurocognitive decline, which are currently main challenges in treated patients. Lipid signaling plays a central role in modulating monocyte/macrophage activation, immune functions and inflammatory responses. Phospholipase-mediated phospholipid hydrolysis leads to the production of lipid mediators or second messengers that affect signal transduction, thus regulating a variety of physiologic and pathophysiologic processes. In this review, we discuss the contribution of phospholipases to monocyte/macrophage activation in the context of HIV-1 infection, focusing on their involvement in virus-associated chronic inflammation and co-morbidities.

Dynamic regulation of aquaporin-4 water channels in neurological disorders

Aquaporin-4 water channels play a central role in brain water regulation in neurological disorders. Aquaporin-4 is abundantly expressed at the astroglial endfeet facing the cerebral vasculature and the pial membrane, and both its expression level and subcellular localization significantly influence brain water transport. However, measurements of aquaporin-4 levels in animal models of brain injury often report opposite trends of change at the injury core and the penumbra. Furthermore, aquaporin-4 channels play a beneficial role in brain water clearance in vasogenic edema, but a detrimental role in cytotoxic edema and exacerbate cell swelling. In light of current evidence, we still do not have a complete understanding of the role of aquaporin-4 in brain water transport. In this review, we propose that the regulatory mechanisms of aquaporin-4 at the transcriptional, translational, and post-translational levels jointly regulate water permeability in the short and long time scale after injury. Furthermore, in order to understand why aquaporin-4 channels play opposing roles in cytotoxic and vasogenic edema, we discuss experimental evidence on the dynamically changing osmotic gradients between blood, extracellular space, and the cytosol during the formation of cytotoxic and vasogenic edema. We conclude with an emerging picture of the distinct osmotic environments in cytotoxic and vasogenic edema, and propose that the directions of aquaporin-4-mediated water clearance in these two types of edema are distinct. The difference in water clearance pathways may provide an explanation for the conflicting observations of the roles of aquaporin-4 in edema resolution.

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.

Lipid mediators in plasma of autism spectrum disorders

Background

Inflammation is increasingly recognized as being of both physiological and pathological importance in the immature brain. Cerebellar pathology occurs in autism, as a neurodevelopmental disorder with genetic and environmental origins. The genesis of this disorder is still not understood but inflammation in utero or early in childhood is an environmental risk factor.

Methods

Prostaglandin E2 (PGE2), cysteinyl leukotriene as two important lipid mediators together with 8 isoprostane as marker of oxidative stress were measured using ELISA in plasma of 20 male autistic patients compared to 19 age and gender matching control participants.

Results

PGE2, leukotrienes and isoprostanes recorded significantly elevated levels in autistics compared to controls. Role of these measured parameters in inflammation and autoimmunity as two etiological factors in autism were discussed in details.

Conclusion

Receiver Operating Characteristic (ROC) curve analysis shows satisfactory values of area under the curve (AUC) which could reflect the high degree of specificity and sensitivity of the altered PGE2, leukotrienes and isoprostanes as predictive biomarkers in autistic patients from Saudi Arabia.

Carvacrol together with TRPC1 elimination improve functional recovery after traumatic brain injury in mice

Death of Central Nervous System (CNS) neurons following traumatic brain injury (TBI) is a complex process arising from a combination of factors, many of which are still unknown. It has been found that inhibition of transient receptor potential (TRP) channels constitutes an effective strategy for preventing death of CNS neurons following TBI. TRP channels are classified into seven related subfamilies, most of which are Ca(2+) permeable and involved in many cellular functions, including neuronal cell death. We hypothesized that TRP channels of the TRPC subfamily may be involved in post-TBI pathophysiology and that the compound 5-isopropyl-2-methylphenol (carvacrol), by inhibition of TRP channels, may exert neuroprotective effect after TBI. To test these suppositions, carvacrol was given to mice after TBI and its effect on their functional recovery was followed for several weeks. Our results show that neurological recovery after TBI was significantly enhanced by application of carvacrol. To better define the type of the specific channel involved, the effect of carvacrol on the extent and speed of recovery after TBI was compared among mice lacking TRPC1, TRPC3, or TRPC5, relative to wild type controls. We found that neurological recovery after TBI was significantly enhanced by combining carvacrol with TRPC1 elimination, but not by the absence of TRPC3 or TRPC5, showing a synergistic effect between carvacrol application and TRPC1 elimination. We conclude that TRPC1-sensitive mechanisms are involved in TBI pathology, and that inhibition of this channel by carvacrol enhances recovery and should be considered for further studies in animal models and humans.

Experimental traumatic brain injury

Traumatic brain injury, a leading cause of death and disability, is a result of an outside force causing mechanical disruption of brain tissue and delayed pathogenic events which collectively exacerbate the injury. These pathogenic injury processes are poorly understood and accordingly no effective neuroprotective treatment is available so far. Experimental models are essential for further clarification of the highly complex pathology of traumatic brain injury towards the development of novel treatments. Among the rodent models of traumatic brain injury the most commonly used are the weight-drop, the fluid percussion, and the cortical contusion injury models. As the entire spectrum of events that might occur in traumatic brain injury cannot be covered by one single rodent model, the design and choice of a specific model represents a major challenge for neuroscientists. This review summarizes and evaluates the strengths and weaknesses of the currently available rodent models for traumatic brain injury.

Injury-related production of cysteinyl leukotrienes contributes to brain damage following experimental traumatic brain injury

The leukotrienes belong to a family of biologically active lipids derived from arachidonate that are often involved in inflammatory responses. In the central nervous system, a group of leukotrienes, known as the cysteinyl leukotrienes, is generated in brain tissue in response to a variety of acute brain injuries. Although the exact clinical significance of this excess production remains unclear, the cysteinyl leukotrienes may contribute to injury-related disruption of the brain-blood barrier and exacerbate secondary injury processes. In the present study, the formation and role of cysteinyl leukotrienes was explored in the fluid percussion injury model of traumatic brain injury in rats. The results showed that levels of the cysteinyl leukotrienes were elevated after fluid percussion injury with a maximal formation 1 hour after the injury. Neutrophils contributed to cysteinyl leukotriene formation in the injured brain hemisphere, potentially through a transcellular biosynthetic mechanism. Furthermore, pharmacological reduction of cysteinyl leukotriene formation after the injury, using MK-886, resulted in reduction of brain lesion volumes, suggesting that the cysteinyl leukotrienes play an important role in traumatic brain injury.

Development of a platelet-activating factor antagonist for HIV-1 associated neurocognitive disorders

The neuroregulatory activities of PMS-601, a platelet activating factor antagonist, were investigated in laboratory and animal models of HIV-1 encephalitis (HIVE). For the former, PMS-601 reduced monocyte-derived macrophage pro-inflammatory secretions, multinucleated giant cell (MGC) formation, and neuronal loss independent of antiretroviral responses. PMS-601 treatment of HIVE severe combined immunodeficient mice showed reduced microgliosis, MGCs and neurodegeneration. These observations support the further development of PMS-601 as an adjunctive therapy for HIV-1 associated neurocognitive disorders.

Protective effect of hyperbaric oxygen therapy on experimental brain contusions

BACKGROUND

We evaluated the effect of hyperbaric oxygen therapy (HBO) on experimental brain contusions in rats using magnetic resonance imaging (MRI).

MATERIALS AND METHODS

Ten Sprague-Dawley rats were investigated at 24 h and 72 h after controlled cortical impact injury. One hour after trauma, 5 rats were treated for 60 min with 100% oxygen at 2.5 absolute atmosphere (ATA), 5 were kept at normobaric room air. MRI was performed longitudinally at 24 h and 72 h after injury. Lesion volume was determined in T2 weighted MRI scans. Relative apparent diffusion coefficient (ADC) changes were calculated in comparison to the contralateral side.

RESULTS

Following HBO, T2 lesion volume was smaller at 24 h versus controls (63.1 +/- 16.5 mm3 vs. 87.4 +/- 13.8 mm3, p < 0.05), and decreased further at 72 h (46.8 +/- 17.8 mm3 vs. 92.5 +/- 13.1 mm3, p < 0.01). At 24 h, the mean relative ADC change in the lesion area decreased from + 26.8 +/- 2.3% in controls to + 2.3 +/- 12.2% in HBO animals (p < 0.01). At 72 h, the HBO effect on relative ADC values was less when compared to 24 h.

DISCUSSION

A 60-minute exposure to hyperbaric oxygen starting 1 h after impact injury significantly attenuated lesion growth and relative increase of ADC values within the contused area for up to 72 h. Thus, a "single-shot" HBO treatment seems to have long-lasting neuroprotective effects on the contused brain and its penumbra.

CYP4Fs expression in rat brain correlates with changes in LTB4 levels after traumatic brain injury

Cytochrome P450 (CYP) 4Fs constitute a subgroup of the cytochrome P450 superfamily and are involved in cellular protection and metabolism of numerous molecules, including drugs, toxins, and eicosanoids. CYP4Fs are widely distributed in rat brain with each isoform having a unique distribution pattern throughout different brain regions. The present study shows that traumatic brain injury (TBI) triggers inflammation and elicits changes in mRNA expression of CYP4Fs in the frontal and occipital lobes and the hippocampus. At 24 h post-injury, almost all CYP4F mRNA expression is suppressed compared with sham control throughout these three regions, while at 2 weeks post-injury, all CYP4F mRNAs increase, reaching levels higher than those at 24 h post-injury or uninjured controls. These changes in CYP4F levels inversely correlate with levels of leukotriene B4 (LTB4) levels in the brain following injury at the same time points. TBI also causes changes in CYP4F protein expression and localization around the injury site. CYP4F1 and CYP4F6 immunoreactivity increases in surrounding astrocytes, while CYP4F4 immunoreactivity shifts from endothelia of cerebral vessels to astrocytes.

Time-dependent alterations of cholinergic markers after experimental traumatic brain injury

Traumatic brain injury (TBI) is one of the leading causes of death and disability. Cognitive deficits are believed to be connected with impairments of the cholinergic system. The present study was conducted to evaluate the cholinergic system in a model of focal brain injury with special attention to the time course of posttraumatic events in critical brain regions. Three groups of male Sprague-Dawley rats (post-TBI survival time: 2 h, 24 h and 72 h) were subjected to sham-operation (control) or controlled cortical impact injury. Receptor densities were determined on frozen ipsilateral sagittal brain sections with [(3)H]epibatidine (nicotinic acetylcholine receptors) and [(3)H]QNB (muscarinic acetylcholine receptors). The density of the vesicular acetylcholine transporter (vAChT) was evaluated with (-)[(3)H]vesamicol. Compared to control, vAChT was lowered (up to 50%) at each time point after trauma, with reductions in olfactory tubercle, basal forebrain, motor cortex, putamen, thalamic and hypothalamic areas and the gigantocellular reticular nucleus. Time-dependent reductions of about 20% of nAChR-density in the thalamus, hypothalamus, olfactory tubercle, gigantocellular reticular nucleus and motor cortex were observed post-TBI at 24 and 72 h. The same brain regions showed reductions of mAChR at 24 and 72 h after trauma with additional decreases in the corpus callosum, basal forebrain and anterior olfactory nucleus. In conclusion, cholinergic markers showed significant time-dependent impairments after TBI. Considering the role of the cholinergic system for cognitive processes in the brain, it seems likely that these impairments contribute to clinically relevant cognitive deficits.

Alterations of acetylcholinesterase activity after traumatic brain injury in rats

OBJECTIVE

The cholinergic system is highly vulnerable to traumatic brain injury (TBI). However, limited information is available to what extent the degrading enzyme acetylcholinesterase (AChE) is involved. The present study addresses this question.

METHOD

Thirty-six anaesthetized Sprague-Dawley rats were subjected to sham operation or to TBI using controlled cortical impact (CCI). The AChE activity was histochemically determined in frozen brain slices at 2, 24 and 72 hours after TBI.

RESULTS

High enzyme activity was observed in regions rich in cholinergic innervation such as the olfactory tubercle, basal forebrain, putamen and superior colliculi. Low activity was found in the cortex, cerebellum and particularly in the white matter. A decrease of AchE activity (20-35%) was found in the hippocampus and hypothalamus already at 2 hours after TBI. An increase of approximately 30% was found in the basal forebrain at 2 and 24 hours. No changes occurred at 72 hours.

CONCLUSION

The findings are consistent with impairment of the cholinergic neurotransmission after TBI and suggest the involvement of the AChE in short-term regulatory mechanisms.

Transcellular biosynthesis of cysteinyl leukotrienes in rat neuronal and glial cells

Leukotrienes are mediators of inflammation that belong to a family of lipids derived from arachidonic acid by the action of 5-lipoxygenase. Leukotrienes have been detected in the central nervous system in association with different pathological events, but little is known about their biosynthesis or function in the brain. When rat neurons and glial cells in primary culture were stimulated with the calcium ionophore, no significant biosynthesis of leukotrienes was detected using liquid chromatography/mass spectrometry (LC/MS) techniques. However, when exogenous LTA(4) was added to these cultured cells, both neurons and glia were able to synthesize LTC(4). Activated neutrophils are known to supply LTA(4) to other cells for transcellular biosynthesis of cysteinyl-leukotrienes. Since neutrophils can infiltrate brain tissue after stroke or traumatic brain injury, we examined whether neutrophils play a similar role in the central nervous system. When peripheral blood neutrophils were co-cultured with rat neurons, glia cells, and then stimulated with calcium ionophore, a robust production of LTC(4), LTD(4), and LTE(4) was observed, revealing that neurons and glia can participate in the transcellular mechanism of leukotriene biosynthesis. The formation of LTC(4) through this mechanism may be relevant in the genesis and progression of the inflammatory response as a result of brain injury.

Pranlukast, a cysteinyl leukotriene receptor 1 antagonist, protects mice against brain cold injury

We have reported the neuroprotective effect of cysteinyl leukotriene receptor 1 (CysLT1) antagonists on cerebral ischemia. Here, we further determined the protective effect of pranlukast, a CysLT1 receptor antagonist, on brain cold injury in mice. Brains were injured by placing a cooled metal probe on the skull surface for 30 s. We found that pranlukast significantly reduced cold-induced lesion volume (0.3 mg/kg) and the percentage increase in lesioned hemisphere volume (0.03-0.3 mg/kg) 24 h after injury, but did not show any effect 72 h after injury. Pranlukast also significantly inhibited neuron loss 24 h (0.1 mg/kg) and 72 h (0.1-0.3 mg/kg) after injury, and decreased the density of degenerated neurons 24 h (0.01-0.3 mg/kg) and 72 h (0.03-0.3 mg/kg) after injury. In addition, pranlukast (0.1-0.3 mg/kg) significantly reduced endogenous IgG exudation both 24 h and 72 h after injury. Thus, this study indicates the protective effect of pranlukast on brain cold injury.

Leukotriene D4 induces brain edema and enhances CysLT2 receptor-mediated aquaporin 4 expression

Cysteinyl leukotrienes (including LTC(4), LTD(4), and LTE(4)), potent inflammatory mediators, can induce brain-blood barrier (BBB) disruption and brain edema. These reactions are mediated by their receptors, CysLT(1) and CysLT(2) receptors. On the other hand, aquaporin 4 (AQP4) primarily modulates brain water homeostasis and edema after various injuries. Here, we aimed to determine whether AQP4 is involved in LTD(4)-induced brain edema. LTD(4) (1ng in 0.5mul PBS) microinjection into the cortex increased endogenous IgG exudation (BBB disruption) and water content (brain edema), and enhanced AQP4 expression in mouse brain. The selective CysLT(1) receptor antagonist pranlukast inhibited the IgG exudation, but not the increased water content and AQP4 expression induced by LTD(4). In the cultured rat astrocytes, LTD(4) (10(-9)-10(-7)M, for 24h) similarly enhanced AQP4 expression. The enhanced AQP4 expression was inhibited by Bay u9773, a non-selective CysLT(1)/CysLT(2) receptor antagonist, but not by pranlukast. LTD(4) (10(-9)-10(-7)M) also induced the mRNA expression of CysLT(2) (not CysLT(1)) receptor in astrocytes. These results indicate that LTD(4) modulates brain edema; CysLT(1) receptor mediates vasogenic edema while CysLT(2) receptor may mediate cytotoxic edema via up-regulating AQP4 expression.

Spatio-temporal properties of 5-lipoxygenase expression and activation in the brain after focal cerebral ischemia in rats

The role of 5-lipoxygenase (5-LOX) in brain injury after cerebral ischemia has been reported; however, the spatio-temporal properties of 5-LOX expression and the enzymatic activation are unclear. To determine these properties, we observed post-ischemic 5-LOX changes from 3 h to 14 days after reperfusion in rats with transient focal cerebral ischemia induced by 30 min of middle cerebral artery occlusion. We found that the expression of 5-LOX, both mRNA and protein, was increased in the ischemic core 12-24 h after reperfusion, and in the boundary zone adjacent to the ischemic core 7-14 days after reperfusion. The increased 5-LOX was primarily localized in the neurons in the ischemic core at 24 h, but in the proliferated astrocytes in the boundary zone 14 days after reperfusion. As 5-LOX metabolites, the level of cysteinyl-leukotrienes in the ischemic brain was substantially increased 3 h to 24 h, near control at 3 days, and moderately increased again 7 days after reperfusion; whereas the level of LTB(4) was increased mildly 3 h but substantially 7-14 days after reperfusion. Thus, we conclude that 5-LOX expression and the enzymatic activity are increased after focal cerebral ischemia, and spatio-temporally involved in neuron injury in the acute phase and astrocyte proliferation in the late phase.

Cyclooxygenases, lipoxygenases, and epoxygenases in CNS: Their role and involvement in neurological disorders

Three enzyme systems, cyclooxygenases that generate prostaglandins, lipoxygenases that form hydroxy derivatives and leukotrienes, and epoxygenases that give rise to epoxyeicosatrienoic products, metabolize arachidonic acid after its release from neural membrane phospholipids by the action of phospholipase A(2). Lysophospholipids, the other products of phospholipase A(2) reactions, are either reacylated or metabolized to platelet-activating factor. Under normal conditions, these metabolites play important roles in synaptic function, cerebral blood flow regulation, apoptosis, angiogenesis, and gene expression. Increased activities of cyclooxygenases, lipoxygenases, and epoxygenases under pathological situations such as ischemia, epilepsy, Alzheimer's disease, Parkinson disease, amyotrophic lateral sclerosis, and Creutzfeldt-Jakob disease produce neuroinflammation involving vasodilation and vasoconstriction, platelet aggregation, leukocyte chemotaxis and release of cytokines, and oxidative stress. These are closely associated with the neural cell injury which occurs in these neurological conditions. The metabolic products of docosahexaenoic acid, through these enzymes, generate a new class of lipid mediators, namely docosatrienes and resolvins. These metabolites antagonize the effect of metabolites derived from arachidonic acid. Recent studies provide insight into how these arachidonic acid metabolites interact with each other and other bioactive mediators such as platelet-activating factor, endocannabinoids, and docosatrienes under normal and pathological conditions. Here, we review present knowledge of the functions of cyclooxygenases, lipoxygenases, and epoxygenases in brain and their association with neurodegenerative diseases.

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

Cysteinyl leukotrienes are potent pro-inflammatory mediators. Cysteinyl leukotriene receptor 1 is one of the two cysteinyl leukotriene receptors cloned. We recently reported that cysteinyl leukotriene receptor 1 antagonists protected against cerebral ischemic injury, and an inducible expression of cysteinyl leukotriene receptor 1 was found in neuron- and glial-appearing cells after traumatic injury in human brain. To determine the role of cysteinyl leukotriene receptor 1 in ischemic brain injury, we investigated the temporal and spatial profile of cysteinyl leukotriene receptor 1 expression in rat brain from 3 h to 14 days after 30 min of middle cerebral artery occlusion, and observed the effect of pranlukast, a cysteinyl leukotriene receptor 1 antagonist, on the ischemic injury. We found that cysteinyl leukotriene receptor 1 mRNA expression was up-regulated in the ischemic core both 3-12 h and 7-14 days, and in the boundary zone 7-14 days after reperfusion. In the ischemic core, cysteinyl leukotriene receptor 1 was primarily localized in neurons 24 h, and in macrophage/microglia 14 days after reperfusion; while in the boundary zone it was localized in proliferated astrocytes 14 days after reperfusion. Pranlukast attenuated neurological deficits, reduced infarct volume and ameliorated neuron loss in the ischemic core 24 h after reperfusion; it reduced infarct volume, ameliorated neuron loss and inhibited astrocyte proliferation in the boundary zone 14 days after reperfusion. Thus, we conclude that cysteinyl leukotriene receptor 1 mediates acute neuronal damage and subacute/chronic astrogliosis after focal cerebral ischemia.

Activation of 5-lipoxygenase after oxygen-glucose deprivation is partly mediated via NMDA receptor in rat cortical neurons

5-Lipoxygenase (5-LOX) is the enzyme metabolizing arachidonic acid to produce pro-inflammatory leukotrienes. We have reported that 5-LOX is translocated to the nuclear envelope after ischemic-like injury in PC12 cells. In the present study, we determined whether 5-LOX is activated (translocation and production of leukotrienes) after oxygen-glucose deprivation (OGD) in primary rat cortical neurons; if so, whether this activation is mediated by NMDA receptor. After OGD, 5-LOX was translocated to the nuclear envelope as detected by immunoblotting, immunostaining and green fluorescent protein-5-LOX transfection. 5-LOX metabolites, cysteinyl-leukotrienes (CysLTs) but not leukotriene B4, in the culture media were increased 0.5-1.5 h after recovery. Similarly, NMDA (100 microm) also induced 5-LOX translocation, and increased the production of CysLTs during 0.5-1 h NMDA exposure. Both OGD and NMDA reduced neuron viability. NMDA receptor antagonist MK-801 inhibited almost all the responses to OGD and NMDA; whereas 5-LOX activating protein inhibitor MK-886 and 5-LOX inhibitor caffeic acid inhibited the reduction of neuron viability and the production of CysLTs, but did not affect 5-LOX translocation. From these results, we conclude that OGD can activate 5-LOX in primary rat cortical neurons, and that this activation may be partly mediated via activating NMDA receptor.

Pranlukast, a cysteinyl leukotriene receptor-1 antagonist, protects against chronic ischemic brain injury and inhibits the glial scar formation in mice

We have recently reported the neuroprotective effect of pranlukast (ONO-1078), a cysteinyl leukotriene receptor-1 (CysLT1) antagonist, on cerebral ischemia in rats and mice. In this study, we further determined whether the effect of pranlukast is long lasting and related to the formation of a glial scar in cerebral ischemic mice. Focal cerebral ischemia was induced by middle cerebral artery occlusion (MCAO). After ischemia, pranlukast (0.1 mg/kg) was injected intraperitoneally for 5 consecutive days. Neurological deficits and sensorimotor function were determined during 70 days after ischemia. Brain lesion and glial scar formation were detected at the end of the experiment. Pranlukast did not reduce mortality, but significantly improved neurological deficits and promoted sensorimotor recovery during 70 days. At the end of the experiment, pranlukast significantly reduced lesion volume, and increased neuron densities in the cortex and hippocampal CA1 region in the ischemic hemispheres. Importantly, pranlukast also remarkably reduced the thickness of a scar wall in the ischemic hemispheres. These findings indicate that pranlukast has a long-lasting protective effect on focal cerebral ischemia in mice, and inhibit the ischemia-induced glial scar formation, providing further evidence of the therapeutic potential of pranlukast in the treatment of ischemic stroke.

Distribution of cysteinyl leukotriene receptor 2 in human traumatic brain injury and brain tumors

AIM

To determine the distribution of cysteinyl leukotriene receptor 2 (CysLT2), one of the cysteinyl leukotriene receptors, in human brains with traumatic injury and tumors.

METHODS

Brain specimens were obtained from patients who underwent brain surgery. CysLT2 in brain tissues was examined using immunohistochemical analysis.

RESULTS

CysLT2 was expressed in the smooth muscle cells (not in the endothelial cells) of arteries and veins. CysLT2 was also expressed in the granulocytes in both vessels and in the brain parenchyma. In addition, CysLT2 was detected in neuron- and glial-appearing cells in either the late stages of traumatic injury or in the area surrounding the tumors. Microvessels regenerated 8 d after trauma and CysLT2 expression was recorded in their endothelial cells.

CONCLUSION

CysLT2 is distributed in vascular smooth muscle cells and granulocytes, and brain trauma and tumor can induce its expression in vascular endothelial cells and in a number of other cells.

Brain tissue biomechanics in cortical contusion injury: a finite element analysis

The controlled cortical impact model has been used extensively to study focal traumatic brain injury. Although the impact variables can be well defined, little is known about the biomechanical trauma as delivered to different brain regions. This knowledge however could be valuable for interpretation of experiment (immunohistochemistry etc.), especially regarding the comparison of the regional biomechanical severity level to the regional magnitude of the trauma sequel under investigation. We used finite element (FE) analysis, based on high resolution T2-weighted MRI images of rat brain, to simulate displacement, mean stress, and shear stress of brain during impact. Young's Modulus E, to describe tissue elasticity, was assigned to each FE in three scenarios: in a constant fashion (E = 50 kPa), or according to the MRI intensity in a linear (E = [10, 100] kPa) and inverse-linear fashion (E = [100, 10] kPa). Simulated tissue displacement did not vary between the 3 scenarios, however mean stress and shear stress were largely different. The linear scenario showed the most likely distribution of stresses. In summary, FE analysis seems to be a suitable tool for biomechanical simulation, however, to be closest to reality tissue elasticity needs to be determined with a more specific approach, e.g. by means of MRI elastography.

Montelukast, a Cysteinyl Leukotriene Receptor-1 Antagonist, Dose- and Time-Dependently Protects against Focal Cerebral Ischemia in Mice

Our previous studies showed that cysteinyl leukotriene receptor-1 (CysLT1) antagonist pranlukast has a neuroprotective effect on cerebral ischemia in rats and mice. However, whether the neuroprotective effect of pranlukast is its special action or a common action of CysLT1 receptor antagonists remains to be clarified. This study was performed to determine whether montelukast, another CysLT1 receptor antagonist, has the neuroprotective effect on focal cerebral ischemia in mice, and to observe its dose- and time-dependent properties. Permanent focal cerebral ischemia was induced by middle cerebral artery occlusion (MCAO). Montelukast was injected intraperitoneally either as multiple doses (once a day for 3 days and 30 min before MCAO) or as a single dose (at 30 min before, 30 min after, or 1 h after MCAO), respectively, and pranlukast and edaravone were used as controls. The neurological deficits, infarct volumes, brain edema, neuron density, and Evans blue extravasation in the brain were determined 24 h after MCAO. Pretreatments with multiple doses or a single dose of montelukast (0.1 and 1.0 mg/kg) before MCAO significantly attenuated all the ischemic insults. Post-treatment with a single dose of montelukast (0.1 and 1.0 mg/kg) at 30 min after MCAO also significantly decreased brain edema and infarct volume, but not neurological deficits. However, post-treatment with a single dose of montelukast at 1 h after MCAO had no significant effect. Pranlukast showed the same effects as montelukast, but edaravone attenuated the ischemic insults only with multiple doses before MCAO. Thus, montelukast has a dose- and time-dependent neuroprotective effect on permanent focal cerebral ischemia in mice, with an effective dose range of 0.1-1.0 mg/kg and a therapeutic window of 30 min. These findings further support the therapeutic potential of CysLT1 receptor antagonists in the treatment of cerebral ischemia at earlier phases.

Expression of cysteinyl leukotriene receptor 1 in human traumatic brain injury and brain tumors

Cysteinyl leukotrienes (CysLTs) are potent proinflammatory mediators. CysLT receptor 1 (CysLT(1)) is one of the two CysLT receptors that has been cloned. Although the expression of CysLT(1) in the brain has been demonstrated by Northern blot and RT-PCR analyses, the location of CysLT(1) in the brain remains unknown. The objective of this study was to examine the distribution of CysLT(1) by immunohistochemical analysis in human brains with traumatic injury or tumors. CysLT(1) was expressed intensely in the microvascular endothelial cells in both normal and abnormal conditions. At 8 days after traumatic injury, microvascular regeneration was found and all of the endothelial cells highly expressed CysLT(1). In gray and white matters of the normal regions of the brain, CysLT(1) was expressed weekly or not at all. However, the CysLT(1) expression increased in the neuron- and glial-appearing cells in gray and white matters after traumatic brain injury. CysLT(1) was also detected in astrocytoma, ganglioglioma and metastatic adenocarcinoma, and the expression in the neuron- and glial-appearing cells around brain tumors increased robustly.