Regulation of chemokines and chemokine receptors after experimental closed head injury

Traumatic brain injury: molecular biomarkers, genetics, secondary consequences, and medical management

Traumatic brain injury (TBI) has reached epidemic proportions worldwide. The consequences of TBI can be severe even with repetitive mild trauma. If death and coma are avoided, the consequences of TBI in the long term typically involve dizziness, sleep disturbances, headache, seizures, cognitive impairment, focal deficits, depression, and anxiety. The severity of brain injury is a significant predictor of outcome. However, the heterogenous nature of the injury makes prognosis difficult. The present review of the literature focuses on the genetics of TBI including genome wide (GWAS) data and candidate gene associations, among them brain-derived neurotrophic factor (BDNF) with TBI and development of post-traumatic epilepsy (PTE). Molecular biomarkers of TBI are also discussed with a focus on proteins and the inflammatory protein IL1-β. The secondary medical sequela to TBI of cognitive impairment, PTE, headache and risk for neurodegenerative disorders is also discussed. This overview of TBI concludes with a review and discussion of the medical management of TBI and the medicines used for and being developed at the preclinical and clinical stages for the treatment of TBI and its host of life-debilitating symptoms.

Chemokine Receptors CC Chemokine Receptor 5 and C-X-C Motif Chemokine Receptor 4 Are New Therapeutic Targets for Brain Recovery after Traumatic Brain Injury

Recently, chemokine receptor CC chemokine receptor 5 (CCR5) was found to be a negative modulator of learning and memory. Its inhibition improved outcome after stroke and traumatic brain injury (TBI). To better understand its role after TBI and establish therapeutic strategies, we investigated the effect of reduced CCR5 signaling as a neuroprotective strategy and of the temporal changes of CCR5 expression after TBI in different brain cell types. To silence CCR5 expression, ccr5 short hairpin RNA (shRNA) or dsred shRNA (control) was injected into the cornu ammonis (CA) 1 and CA3 regions of the hippocampus 2 weeks before induction of closed-head injury in mice. Animals were then monitored for 32 days and euthanized at different time points to assess lesion area, inflammatory components of the glial response (immunohistochemistry; IHC), cytokine levels (enzyme-linked immunosorbent array), and extracellular signal-regulated kinase (ERK) phosphorylation (western blot). Fluorescence-activated cell sorting (FACS) analysis was performed to study post-injury temporal changes of CCR5 and C-X-C motif chemokine receptor 4 (CXCR4) expression in cortical and hippocampal cell populations (neurons, astrocytes, and microglia). Phosphorylation of the N-methyl-d-aspartate subunit 1 (NR1) subunit of N-methyl-d-aspartate (western blot) and cAMP-response-element-binding protein (CREB; IHC) were also assessed. The ccr5 shRNA mice displayed reduced lesion area, dynamic alterations in levels of inflammation-related CCR5 ligands and cytokines, and higher levels of phosphorylated ERK. The ccr5 shRNA also reduced astrocytosis in the lesioned and sublesioned cortex. FACS analysis revealed increased cortical CCR5 and CXCR4 expression in CD11b-positive cells, astrocytes, and neurons, which was most evident in cells expressing both receptors, at 3 and 11 days post-injury. The lowest levels of phosphorylated NR1 and phosphorylated CREB were found at day 3 post-injury, suggesting that this is the critical time point for therapeutic intervention.

Mild Traumatic Brain Injury Causes Nociceptive Sensitization through Spinal Chemokine Upregulation

High rates of acute and chronic pain are associated with traumatic brain injury (TBI), but mechanisms responsible for the association remain elusive. Recent data suggest dysregulated descending pain modulation circuitry could be involved. Based on these and other observations, we hypothesized that serotonin (5-HT)-dependent activation of spinal CXC Motif Chemokine Receptor 2 (CXCR2) may support TBI-related nociceptive sensitization in a mouse model of mild TBI (mTBI). We observed that systemic 5-HT depletion with p-chlorophenylalanine attenuated mechanical hypersensitivity seen after mTBI. Likewise, selective spinal 5-HT fiber depletion with 5,7-dihydroxytryptamine (5,7-DHT) reduced hypersensitivity after mTBI. Consistent with a role for spinal 5-HT₃ serotonin receptors, intrathecal ondansetron administration after TBI dose-dependently attenuated nociceptive sensitization. Also, selective CXCR2 antagonist SCH527123 treatment attenuated mechanical hypersensitivity after mTBI. Furthermore, spinal CXCL1 and CXCL2 mRNA and protein levels were increased after mTBI as were GFAP and IBA-1 markers. Spinal 5,7-DHT application reduced both chemokine expression and glial activation. Our results suggest dual pathways for nociceptive sensitization after mTBI, direct 5-HT effect through 5-HT₃ receptors and indirectly through upregulation of chemokine signaling. Designing novel clinical interventions against either the 5-HT₃ mediated component or chemokine pathway may be beneficial in treating pain frequently seen in patients after mTBI.

A Systematic Review of Closed Head Injury Models of Mild Traumatic Brain Injury in Mice and Rats

Mild TBI (mTBI) is a significant health concern. Animal models of mTBI are essential for understanding mechanisms, and pathological outcomes, as well as to test therapeutic interventions. A variety of closed head models of mTBI that incorporate different aspects (i.e., biomechanics) of the mTBI have been reported. The aim of the current review was to compile a comprehensive list of the closed head mTBI rodent models, along with the common data elements, and outcomes, with the goal to summarize the current state of the field. Publications were identified from a search of PubMed and Web of Science and screened for eligibility following PRISMA guidelines. Articles were included that were closed head injuries in which the authors classified the injury as mild in rats or mice. Injury model and animal-specific common data elements, as well as behavioral and histological outcomes, were collected and compiled from a total of 402 articles. Our results outline the wide variety of methods used to model mTBI. We also discovered that female rodents and both young and aged animals are under-represented in experimental mTBI studies. Our findings will aid in providing context comparing the injury models and provide a starting point for the selection of the most appropriate model of mTBI to address a specific hypothesis. We believe this review will be a useful starting place for determining what has been done and what knowledge is missing in the field to reduce the burden of mTBI.

The Chemokine Receptor CXCR2 Supports Nociceptive Sensitization after Traumatic Brain Injury

Abstract

Chronic pain after traumatic brain injury (TBI) is very common, but the mechanisms linking TBI to pain and the pain-related interactions of TBI with peripheral injuries are poorly understood. Chemokine receptors play an important role in both pain and brain injury. In the current work, we pursued the hypothesis that the epigenetically regulated CXC chemokine receptor 2 (CXCR2) is a crucial modulator of nociceptive sensitization induced by TBI. For these studies, we used the rat lateral fluid percussion model of TBI. Histone actyltransferase activity was blocked using anacardic acid beginning immediately following injury, or delayed for seven days prior to administration. The selective CXCR2 antagonist SCH527123 administered systemically or intrathecally was used to probe the role of chemokine signaling on mechanical hindpaw sensitization after TBI. The expression of the CXCR2 receptor was accomplished using real-time PCR, immunohistochemistry, and Western blotting, while epigenetic regulation was assessed using chromatin immunoprecipitation assay. The spinal levels of several pain-related mediators including CXCL1, an endogenous ligand for CXCR2, as well as brain-derived neurotrophic factor and prodynorphin were measured by enzyme-linked immunosorbent assay. We observed that anacardic acid potently blocked and reversed mechanical hindpaw sensitization after TBI. The same drug was able to prevent the upregulation of CXCR2 after TBI, but did not affect the spinal expression of other pain mediators. On the other hand, both systemically and intrathecally administered SCH527123 reversed hindpaw allodynia after TBI. Most of the spinal CXCR2 appeared to be expressed by spinal cord neurons. Chromatin immunoprecipitation experiments demonstrated TBI-enhanced association of the CXCR2 promoter with acetylated-H3K9 histone protein that was also reversible using anacardic acid. Taken together, our findings suggested that TBI causes the upregulation of spinal CXCR2 through an epigenetic mechanism ultimately supporting nociceptive sensitization. The use of CXCR2 antagonists may, therefore, be useful in pain resulting from TBI.

Hemorrhagic shock shifts the serum cytokine profile from pro- to anti-inflammatory after experimental traumatic brain injury in mice

Secondary insults, such as hemorrhagic shock (HS), worsen outcome from traumatic brain injury (TBI). Both TBI and HS modulate levels of inflammatory mediators. We evaluated the addition of HS on the inflammatory response to TBI. Adult male C57BL6J mice were randomized into five groups (n=4 [naïve] or 8/group): naïve; sham; TBI (through mild-to-moderate controlled cortical impact [CCI] at 5 m/sec, 1-mm depth), HS; and CCI+HS. All non-naïve mice underwent identical monitoring and anesthesia. HS and CCI+HS underwent a 35-min period of pressure-controlled hemorrhage (target mean arterial pressure, 25-27 mm Hg) and a 90-min resuscitation with lactated Ringer's injection and autologous blood transfusion. Mice were sacrificed at 2 or 24 h after injury. Levels of 13 cytokines, six chemokines, and three growth factors were measured in serum and in five brain tissue regions. Serum levels of several proinflammatory mediators (eotaxin, interferon-inducible protein 10 [IP-10], keratinocyte chemoattractant [KC], monocyte chemoattractant protein 1 [MCP-1], macrophage inflammatory protein 1alpha [MIP-1α], interleukin [IL]-5, IL-6, tumor necrosis factor alpha, and granulocyte colony-stimulating factor [G-CSF]) were increased after CCI alone. Serum levels of fewer proinflammatory mediators (IL-5, IL-6, regulated upon activation, normal T-cell expressed, and secreted, and G-CSF) were increased after CCI+HS. Serum level of anti-inflammatory IL-10 was significantly increased after CCI+HS versus CCI alone. Brain tissue levels of eotaxin, IP-10, KC, MCP-1, MIP-1α, IL-6, and G-CSF were increased after both CCI and CCI+HS. There were no significant differences between levels after CCI alone and CCI+HS in any mediator. Addition of HS to experimental TBI led to a shift toward an anti-inflammatory serum profile--specifically, a marked increase in IL-10 levels. The brain cytokine and chemokine profile after TBI was minimally affected by the addition of HS.

Traumatic Brain Injury pathophysiology and treatments: early, intermediate, and late phases post-injury

Traumatic Brain Injury (TBI) affects a large proportion and extensive array of individuals in the population. While precise pathological mechanisms are lacking, the growing base of knowledge concerning TBI has put increased emphasis on its understanding and treatment. Most treatments of TBI are aimed at ameliorating secondary insults arising from the injury; these insults can be characterized with respect to time post-injury, including early, intermediate, and late pathological changes. Early pathological responses are due to energy depletion and cell death secondary to excitotoxicity, the intermediate phase is characterized by neuroinflammation and the late stage by increased susceptibility to seizures and epilepsy. Current treatments of TBI have been tailored to these distinct pathological stages with some overlap. Many prophylactic, pharmacologic, and surgical treatments are used post-TBI to halt the progression of these pathologic reactions. In the present review, we discuss the mechanisms of the pathological hallmarks of TBI and both current and novel treatments which target the respective pathways.

The role of markers of inflammation in traumatic brain injury

Within minutes of a traumatic impact, a robust inflammatory response is elicited in the injured brain. The complexity of this post-traumatic squeal involves a cellular component, comprising the activation of resident glial cells, microglia, and astrocytes, and the infiltration of blood leukocytes. The second component regards the secretion immune mediators, which can be divided into the following sub-groups: the archetypal pro-inflammatory cytokines (Interleukin-1, Tumor Necrosis Factor, Interleukin-6), the anti-inflammatory cytokines (IL-4, Interleukin-10, and TGF-beta), and the chemotactic cytokines or chemokines, which specifically drive the accumulation of parenchymal and peripheral immune cells in the injured brain region. Such mechanisms have been demonstrated in animal models, mostly in rodents, as well as in human brain. Whilst the humoral immune response is particularly pronounced in the acute phase following Traumatic brain injury (TBI), the activation of glial cells seems to be a rather prolonged effect lasting for several months. The complex interaction of cytokines and cell types installs a network of events, which subsequently intersect with adjacent pathological cascades including oxidative stress, excitotoxicity, or reparative events including angiogenesis, scarring, and neurogenesis. It is well accepted that neuroinflammation is responsible of beneficial and detrimental effects, contributing to secondary brain damage but also facilitating neurorepair. Although such mediators are clear markers of immune activation, to what extent cytokines can be defined as diagnostic factors reflecting brain injury or as predictors of long term outcome needs to be further substantiated. In clinical studies some groups reported a proportional cytokine production in either the cerebrospinal fluid or intraparenchymal tissue with initial brain damage, mortality, or poor outcome scores. However, the validity of cytokines as biomarkers is not broadly accepted. This review article will discuss the evidence from both clinical and laboratory studies exploring the validity of immune markers as a correlate to classification and outcome following TBI.

The role of markers of inflammation in traumatic brain injury

Within minutes of a traumatic impact, a robust inflammatory response is elicited in the injured brain. The complexity of this post-traumatic squeal involves a cellular component, comprising the activation of resident glial cells, microglia, and astrocytes, and the infiltration of blood leukocytes. The second component regards the secretion immune mediators, which can be divided into the following sub-groups: the archetypal pro-inflammatory cytokines (Interleukin-1, Tumor Necrosis Factor, Interleukin-6), the anti-inflammatory cytokines (IL-4, Interleukin-10, and TGF-beta), and the chemotactic cytokines or chemokines, which specifically drive the accumulation of parenchymal and peripheral immune cells in the injured brain region. Such mechanisms have been demonstrated in animal models, mostly in rodents, as well as in human brain. Whilst the humoral immune response is particularly pronounced in the acute phase following Traumatic brain injury (TBI), the activation of glial cells seems to be a rather prolonged effect lasting for several months. The complex interaction of cytokines and cell types installs a network of events, which subsequently intersect with adjacent pathological cascades including oxidative stress, excitotoxicity, or reparative events including angiogenesis, scarring, and neurogenesis. It is well accepted that neuroinflammation is responsible of beneficial and detrimental effects, contributing to secondary brain damage but also facilitating neurorepair. Although such mediators are clear markers of immune activation, to what extent cytokines can be defined as diagnostic factors reflecting brain injury or as predictors of long term outcome needs to be further substantiated. In clinical studies some groups reported a proportional cytokine production in either the cerebrospinal fluid or intraparenchymal tissue with initial brain damage, mortality, or poor outcome scores. However, the validity of cytokines as biomarkers is not broadly accepted. This review article will discuss the evidence from both clinical and laboratory studies exploring the validity of immune markers as a correlate to classification and outcome following TBI.

LPS-induced microglial secretion of TNFα increases activity-dependent neuronal apoptosis in the neonatal cerebral cortex

During the pre- and neonatal period, the cerebral cortex reveals distinct patterns of spontaneous synchronized activity, which is critically involved in the formation of early networks and in the regulation of neuronal survival and programmed cell death (apoptosis). During this period, the cortex is also highly vulnerable to inflammation and in humans prenatal infection may have a profound impact on neurodevelopment causing long-term neurological deficits. Using in vitro and in vivo multi-electrode array recordings and quantification of caspase-3 (casp-3)-dependent apoptosis, we demonstrate that lipopolysaccharide-induced inflammation causes rapid alterations in the pattern of spontaneous burst activities, which subsequently leads to an increase in apoptosis. We show that these inflammatory effects are specifically initiated by the microglia-derived pro-inflammatory cytokine tumor necrosis factor α and the chemokine macrophage inflammatory protein 2. Our data demonstrate that inflammation-induced modifications in spontaneous network activities influence casp-3-dependent cell death in the developing cerebral cortex.

Guilty molecules, guilty minds? The conflicting roles of the innate immune response to traumatic brain injury

Traumatic brain injury (TBI) is a complex disease in the most complex organ of the body, whose victims endure lifelong debilitating physical, emotional, and psychosocial consequences. Despite advances in clinical care, there is no effective neuroprotective therapy for TBI, with almost every compound showing promise experimentally having disappointing results in the clinic. The complex and highly interrelated innate immune responses govern both the beneficial and deleterious molecular consequences of TBI and are present as an attractive therapeutic target. This paper discusses the positive, negative, and often conflicting roles of the innate immune response to TBI in both an experimental and clinical settings and highlights recent advances in the search for therapeutic candidates for the treatment of TBI.

Challenging the role of adaptive immunity in neurotrauma: Rag1(-/-) mice lacking mature B and T cells do not show neuroprotection after closed head injury

The role of adaptive immunity in contributing to post-traumatic neuroinflammation and neuropathology after head injury remains largely unexplored. The present study was designed to investigate the pathophysiological sequelae of closed head injury in Rag1(-/-) mice devoid of mature B and T lymphocytes. C57BL/6 wild-type and Rag1(-/-) mice were subjected to experimental closed head injury, using a standardized weight-drop device. Outcome parameters consisted of neurological scoring, quantification of blood-brain barrier (BBB) function, measurement of inflammatory markers and mediators of apoptosis in serum and brain tissue, and assessment of neuronal cell death, astrogliosis, and tissue destruction. There was no difference between wild-type and Rag1(-/-) mice with regard to injury severity and neurological impairment for up to 7 days after head injury. The extent of BBB dysfunction was in a similar range for both groups. Quantification of complement activation fragments in serum revealed significantly attenuated C3a levels in Rag1(-/-) mice compared to wild-type animals. In contrast, the levels of pro- and anti-inflammatory cytokines and pro-apoptotic and anti-apoptotic mediators remained in a similar range for both groups, and the histological analysis of brain sections did not reveal a difference in reactive astrogliosis, tissue destruction, and neuronal cell death in Rag1(-/-) compared to wild-type mice. These findings suggest that adaptive immunity is not of crucial importance for initiating and sustaining the inflammatory neuropathology after closed head injury. The attenuated extent of post-traumatic complement activation seen in Rag1(-/-) mice implies a cross-talk between innate and adaptive immune responses, which requires further investigation in future studies.

Peripheral immune cells in the pathology of traumatic brain injury?

PURPOSE OF REVIEW

This review will consider the reasons why the inhibition of leucocyte recruitment after traumatic brain injury has not been demonstrated but should remain an area of active interest.

RECENT FINDINGS

Focal lesions to the brain display a characteristic inflammatory response with infiltration of peripheral immune cells after injury. These cells are believed to be important because they contain and release a multitude of inflammatory mediators associated with increased tissue injury. Furthermore a large body of evidence from ischaemic injuries suggests that inhibition of leucocyte recruitment can reduce injury and improve outcome. However, therapeutic efficacy has not been demonstrated in clinical trials and for traumatic injuries the results are less convincing.

SUMMARY

A greater appreciation of the timing of assessment, leucocyte subsets and the extended inflammatory response will be discussed.

Deficiency of the chemokine receptor CXCR2 attenuates neutrophil infiltration and cortical damage following closed head injury

The contribution of infiltrated neutrophils to secondary damage following traumatic brain injury remains controversial. Chemokines that regulate neutrophil migration by signaling through the CXCR2 receptor are markedly elevated by brain injury and are associated with the propagation of secondary damage. This study thus investigated the function of CXCR2 in posttraumatic inflammation and secondary degeneration by examining Cxcr2-deficient (Cxcr2(-/-)) mice over 14 days following closed head injury (CHI). We demonstrate a significant attenuation of neutrophil infiltration in Cxcr2(-/-) mice at 12 hours and 7 days after CHI, despite increased levels of CXC neutrophil-attracting chemokines in the lesioned cortex. This coincides with reduced tissue damage, neuronal loss, and cell death in Cxcr2(-/-) mice compared to wild-type controls, with heterozygotes showing intermediate responses. In contrast, blood-brain barrier permeability and functional recovery did not appear to be affected by Cxcr2 deletion. This study highlights the deleterious contribution of neutrophils to posttraumatic neurodegeneration and demonstrates the importance of CXC chemokine signaling in this process. Therefore, CXCR2 antagonistic therapeutics currently in development for other inflammatory conditions may also be of benefit in posttraumatic neuroinflammation.

Role of chemokines in CNS health and pathology: a focus on the CCL2/CCR2 and CXCL8/CXCR2 networks

Chemokines and their receptors have crucial roles in the trafficking of leukocytes, and are of particular interest in the context of the unique immune responses elicited in the central nervous system (CNS). The chemokine system CC ligand 2 (CCL2) with its receptor CC receptor 2 (CCR2), as well as the receptor CXCR2 and its multiple ligands CXCL1, CXCL2 and CXCL8, have been implicated in a wide range of neuropathologies, including trauma, ischemic injury and multiple sclerosis. This review aims to overview the current understanding of chemokines as mediators of leukocyte migration into the CNS under neuroinflammatory conditions. We will specifically focus on the involvement of two chemokine networks, namely CCL2/CCR2 and CXCL8/CXCR2, in promoting macrophage and neutrophil infiltration, respectively, into the lesioned parenchyma after focal traumatic brain injury. The constitutive brain expression of these chemokines and their receptors, including their recently identified roles in the modulation of neuroprotection, neurogenesis, and neurotransmission, will be discussed. In conclusion, the value of evidence obtained from the use of Ccl2- and Cxcr2-deficient mice will be reported, in the context of potential therapeutics inhibiting chemokine activity which are currently in clinical trial for various inflammatory diseases.

CD38 facilitates recovery from traumatic brain injury

Traumatic brain injury (TBI) is a major cause of death and disability worldwide. It causes progressive tissue atrophy and consequent neurological dysfunctions. TBI is accompanied by neuroinflammation, a process mediated largely by microglia. CD38 is an ectoenzyme that promotes transmembrane signaling via the synthesis of potent calcium mobilizing agents or via its receptor activity. CD38 is expressed in the brain in various cell types including microglia. In previous studies, we showed that CD38 regulates microglial activation and response to chemokines. In view of the important role of neuroinflammation in TBI and the effects of CD38 on microglial responses, the present study examines the role of CD38 in the recovery of mice from closed head injury (CHI), a model of focal TBI. For this purpose, CD38-deficient and wild-type (WT) mice were subjected to a similar severity of CHI and the effect of the injury on neurobehavioral and cognitive functions was assessed by the Neurological Severity Score (NSS) and the Object Recognition Test, at various time points post-injury. The results show that recovery after CHI (as indicated by the NSS) was significantly lower in CD38-deficient mice than in WT mice and that the object recognition performance after injury was significantly impaired in injured CD38-deficient mice than in WT mice. In addition, we also observed that the amount of activated microglia/macrophages at the injury site was significantly lower in CD38-deficient mice compared with WT mice. Taken together, our findings indicate that CD38 plays a beneficial role in the recovery of mice from CHI and that this effect is mediated, at least in part, via the effect of CD38 on microglia responses.

The temporal expression, cellular localization, and inhibition of the chemokines MIP-2 and MCP-1 after traumatic brain injury in the rat

The expression of the neutrophil chemokine macrophage inflammatory protein-2 (MIP-2/CXCL2) and the monocyte chemokine monocyte chemotactic protein-1 (MCP-1/CCL2) have been described in glial cells in vitro but their origin following TBI has not been established. Furthermore, little is known of the modulation of these chemokines. Chemokine expression was investigated in male Sprague-Dawley rats following moderate lateral fluid percussion injury (LFPI). At 0, 4, 8, 12, and 24 h after injury, brains were harvested and MIP-2/CXCL2 and MCP-1/CCL2 levels measured by ELISA. To investigate the inhibition of chemokine expression a second cohort of animals received dexamethasone (1-15mg/kg), FK506 (1mg/kg), or vehicle, systemically, immediately after injury. These animals were sacrificed at the time of peak chemokine expression. A third cohort of animals was also sacrificed at the time of peak chemokine expression and immunohistochemistry performed for MIP-2/CXCL2 and MCP-1/CCL2. Following LFPI, chemokines were increased in the ipsilateral hemisphere, MIP-2/CXCL2 peaking at 4 h and MCP-1/CCL2 peaking at 8-12 h post-injury. Dexamethasone significantly reduced cortical MCP-1/CCL2, but not MIP-2/CXCL2 concentrations. FK506 did not inhibit chemokine expression. In undamaged brain, chemokine expression was localized to cells with a neuronal morphology. For MIP-2/CXCL2 this was supported by double staining for the neuronal antigen NeuN. In contused tissue, increased MIP-2/CXCL2 and MCP-1/CCL2 staining was visible in cells with the morphology of degenerating neurons. MIP-2/CXCL2 and MCP-1/CCL2 are increased after injury, and neurons appear to be the source of this expression. Chemokine expression was selectively inhibited by dexamethasone. The implications of this are discussed.

Serum IL-8 and MCP-1 concentration do not identify patients with enlarging contusions after traumatic brain injury

BACKGROUND

Cerebral contusions contain numerous leukocytes, and a temporal relationship exists among cerebral chemokine expression, leukocyte recruitment, and contusion enlargement. This would suggest a role for chemokines in contusion development. However, it has not been established if serum concentrations of chemokines such as interleukin-8 (IL-8) or monocyte chemoattractant protein-1 (MCP-1) change with contusion enlargement.

METHODS

Eighteen adult patients with severe contusional traumatic brain injury, on computerized tomography, were identified. Patients with diffuse injuries or extradural and subdural hematomas associated with mass effect were not included in the study. Daily serum samples were taken for the measurement of IL-8 and MCP-1 concentrations for up to 11 days postinjury.

RESULTS

In the patients who died while in intensive care, IL-8 and MCP-1 were significantly greater than in those patients discharged (18 [0-202] vs. 0 [0-156] pg/mL and 498 [339-1,063] vs. 368 [86-11,289] pg/mL for IL-8 and MCP-1, respectively). No difference was seen in serum chemokine levels in patients who deteriorated with contusion enlargement compared with those that did not. The IL-8 and MCP-1 concentrations did not change significantly over time either in the group as a whole or in the subgroup of patients who deteriorated.

CONCLUSIONS

These inflammatory mediators may be predictive of a poor outcome in patients with traumatic brain injury in which contusions are the predominant abnormality. However, they do not distinguish those patients who will deteriorate because of contusion enlargement.

IGF-1 and pAKT signaling promote hippocampal CA1 neuronal survival following injury to dentate granule cells

Insulin-like growth factor-1 (IGF-1) protects neurons from apoptosis and in vivo offers neuroprotective support to hippocampal CA1 pyramidal neurons following ischemia or seizure. IGF-1 signals through IGF-1 receptors activating phosphytidylinositol 3-kinase (PI3K)/Akt or pMAPK pathways. IGF-1 can be induced with injury and microglia and astrocytes may serve as a source of this neurotrophic factor to promote neuronal survival. An acute systemic injection of trimethyltin (TMT; 2 mg/kg, ip) to mice induces apoptosis of dentate granule neurons within 24 h and a differential response of microglia with ramified microglia present in the CA-1 region. Using this model, we studied the role of IGF-1 in the survival of CA-1 pyramidal neurons under conditions of altered synaptic input due to changes in the dentate gyrus. Within 24 h of injection, IGF-1 mRNA levels were elevated in the hippocampus and IGF-1 protein detected in both astrocytes and microglia. IGF-1 was redistributed within the CA-1 neurons corresponding with an increase in cytoplasmic pAkt, elevated PKBalpha/Akt protein levels, and a decrease in the antagonist, Rho. pMAPK was not detected in CA-1 neurons and ERK2 showed a transient decrease followed by a significant increase, suggesting a lack of recruitment of the pMAPK signaling pathway for neuronal survival. In mice deficient for IGF-1, a similar level of apoptosis was observed in dentate granule neurons as compared to wildtype; however, TMT induced a significant level CA-1 neuronal death, further supporting a role for IGF-1 in the survival of CA-1 neurons.

Characterization of the pharmacokinetics of human recombinant erythropoietin in blood and brain when administered immediately after lateral fluid percussion brain injury and its pharmacodynamic effects on IL-1beta and MIP-2 in rats

This study sought to determine the bio-availability of recombinant human erythropoietin (EPO) in the brain and blood and its effects on the cerebral concentrations of the inflammatory mediators interleukin-1beta (IL-1beta) and macrophage-inflammation protein-2 (MIP-2) following lateral fluid percussion brain injury (FPI) in the rat. After induction of moderate FPI (1.6-1.8 atm), EPO was injected intraperitoneally (IP) or intravenously (IV) at doses of 1000-5000 U/kg in a randomized and blinded manner. Animals were then sacrificed at time points (4, 8, 12, 24 h) post-trauma, and the brain concentrations of EPO, IL-1beta, and MIP-2 were determined. EPO administration leads to a dose-dependent increase in the brain concentration of the drug; however, this could only be detected at doses of 3000 and 5000 U/kg. The cerebral concentration peaked in the first 4 h following trauma. EPO concentrations were significantly higher and decreased more slowly in the traumatized cortex compared to the contralateral side (p<0.0125). IV EPO (5000 U/kg) produced slightly higher concentrations of EPO than same doses injected IP; however, this was not significant. At a dose of 5000 U/kg, EPO significantly reduced the increase in IL-1beta at 8 and 12 h in both cortical sides. It also reduced the increase in MIP-2 but only after 8 h, on the contralateral side and after 12 h on the ipsilateral side. Our results suggest that EPO crosses the blood-brain barrier (BBB) by 4 h after trauma and is localized primarily in the traumatized cortex. Further, it has biological efficacy at 8 h on several inflammatory proteins, yet must be employed at high doses to cross the BBB.

The genomic profile of the cerebral cortex after closed head injury in mice: effects of minocycline

Microarray analysis was used to delineate gene expression patterns and profile changes following traumatic brain injury (TBI) in mice. A parallel microarray analysis was carried out in mice with TBI that were subsequently treated with minocycline, a drug proposed as a neuroprotectant in other neurological disorders. The aim of this comparison was to identify pathways that may be involved in secondary injury processes following TBI and potential specific pathways that could be targeted with second generation therapeutics for the treatment of neurotrauma patients. Gene expression profiles were measured with the compugen long oligo chip and real-time PCR was used to validate microarray findings. A pilot study of effect of minocycline on gene expression following TBI was also carried out. Gene ontology comparison analysis of sham TBI and minocycline treated brains revealed biological pathways with more genes differentially expressed than predicted by chance. Among 495 gene ontology categories, the significantly different gene ontology groups included chemokines, genes involved in cell surface receptor-linked signal transduction and pro-inflammatory cytokines. Expression levels of some key genes were validated by real-time quantitative PCR. This study confirms that multiple regulatory pathways are affected following brain injury and demonstrates for the first time that specific genes and molecular networks are affected by minocycline following brain injury.

Increased expression of the gamma-secretase components presenilin-1 and nicastrin in activated astrocytes and microglia following traumatic brain injury

Gamma-secretase is an aspartyl protease composed of four proteins: presenilin (PS), nicastrin (Nct), APH1, and PEN2. These proteins assemble into a membrane complex that cleaves a variety of substrates within the transmembrane domain. The gamma-secretase cleavage products play an important role in various biological processes such as embryonic development and Alzheimer's disease (AD). The major role of gamma-secretase in brain pathology has been linked to AD and to the production of the amyloid beta-peptide. However, little is known about the possible role of gamma-secretase following acute brain insult. Here we examined by immunostaining the expression patterns of two gamma-secretase components, PS1 and Nct, in three paradigms of brain insult in mice: closed head injury, intracerebroventricular injection of LPS, and brain stabbing. Our results show that in naïve and sham-injured brains expression of PS1 and Nct is restricted mainly to neurons. However, following insult, the expression of both proteins is also observed in nonneuronal cells, consisting of activated astrocytes and microglia. Furthermore, the proteins are coexpressed within the same astrocytes and microglia, implying that these cells exhibit an enhanced gamma-secretase activity following brain damage. In view of the important role played by astrocytes and microglia in brain disorders, our findings suggest that gamma-secretase may participate in brain damage and repair processes by regulating astrocyte and microglia activation and/or function.

Transient blockage of the CD11d/CD18 integrin reduces contusion volume and macrophage infiltration after traumatic brain injury in rats

The early inflammatory response to traumatic brain injury (TBI) may result in secondary damage. The purpose of this study was to evaluate the effects of a transient treatment employing a blocking monoclonal antibody (mAb) to the CD11d/CD18 integrin on histopathological outcome and macrophage infiltration following TBI. A parasagittal fluid percussion (FP) brain injury (1.8-2.1 atm) was induced in male Sprague-Dawley rats. Rats were randomized into two trauma groups, treated (N=7) and nontreated (N=8) animals. In the treated group, a mAb to the CD11d subunit of the CD11d/CD18 integrin was administered 30 min, 24 and 48 h after brain injury. Control animals received an isotype-matched irrelevant mAb using the same dose and treatment regimen. At 3 days after TBI, animals were perfusion-fixed for histopathological and immunocytochemical analysis. The anti-CD11d mAb treatment reduced contusion areas as well as overall contusion volume compared to vehicle treated animals. For example, overall contusion volume was reduced from 2.7+/-0.5 mm(3) (mean+/-SEM) to 1.4+/-0.4 with treatment (p<0.05). Immunocytochemical studies identifying CD68 immunoreactive macrophages showed that treatment caused significant attenuation of leukocyte infiltration into the contused cortical areas. These data emphasize the beneficial effects of blocking inflammatory cell recruitment into the injured brain on histopathological outcome following traumatic brain injury.

Changes in extracellular concentrations of some cytokines, chemokines, and neurotrophic factors after insertion of intracerebral microdialysis catheters in neurosurgical patients

OBJECTIVE

The extracellular levels of eight different inflammatory agents were analyzed during the initial 36 hours after insertion of microdialysis catheters in patients.

METHODS

Cerebral extracellular fluid from 38 patients who were treated in a neurosurgical intensive care unit for severe brain injury was collected every 6 hours for 36 hours. The concentration of interleukin (IL)-1 beta, IL-6, IL-8, macrophage inflammatory protein-1 beta, regulated on activation, normal T-cell expressed and secreted (RANTES), fibroblast growth factor-2, and vascular endothelial growth factor was determined by a multiplex assay, and IL-10 was determined by enzyme-linked immunosorbent assay.

RESULTS

This is the first report regarding the presence of IL-10, IL-8, macrophage inflammatory protein-1 beta, regulated on activation, T-cell expressed and secreted, vascular endothelial growth factor, and fibroblast growth factor-2 in the tissue level proper of the living human brain. The study also provides new information regarding the response of IL-1 beta and IL-6 after insertion of a microdialysis catheter. The study confirms that the intriguing patterns of interplay between different components of the inflammatory response studied in laboratory settings are present in the human brain. This was most clearly observed in the variations in response between the three different chemokines investigated, as well as in the rapid and transient response of fibroblast growth factor-2.

CONCLUSION

The data presented illustrate the opportunity to monitor biochemical events of possible importance in the human brain and indicate the potential of such monitoring in neurosurgical intensive care. The study also underlines that any analysis of events in the brain involving mechanical invasiveness needs to take into account biochemical changes that are directly related to the manipulation of brain tissue.

Multiplex assessment of cytokine and chemokine levels in cerebrospinal fluid following severe pediatric traumatic brain injury: effects of moderate hypothermia

This study performed a comprehensive analysis of cerebrospinal fluid (CSF) cytokine levels after severe traumatic brain injury (TBI) in children using a multiplex bead array assay and to evaluate the effects of moderate hypothermia on cytokine levels. To this end, samples were collected during two prospective randomized controlled trials of therapeutic moderate hypothermia in pediatric TBI. Thirty-six children with severe TBI (Glasgow Coma Scale [GCS] score of <or=8) and 10 children with negative diagnostic lumbar punctures. All children with TBI had continuous monitoring of intracranial pressure and CSF drainage via an intraventricular catheter. Moderate hypothermia (32-33 degrees C) was maintained for 48 h in 17 patients, and they were slowly re-warmed at 48-72 h. A multiplex bead array assay was used to analyze serial CSF samples (<18 h, 24 +/- 6 h, 48 +/- 6 h, and 72 +/- 6 h) for 21 pro-and anti-inflammatory cytokines and chemokines. Interleukin (IL)-8 and transforming growth factor beta were measured by enzyme-linked immunosorbant assay (ELISA). There was a strong correlation (Spearman correlation coefficient = 0.92, p < 0.001) between multiplex assay and ELISA for IL-8. Pro-inflammatory IL-1beta, -6 and -12p70, anti-inflammatory IL-10 and chemokines IL-8 and MIP-1alpha were increased after TBI compared to controls, p < 0.05; however, there was no association between cytokines and age, gender, initial GCS, or outcome. Hypothermia did not attenuate the increases in CSF cytokine levels after TBI versus normothermia. This investigation confirmed that the multiplex bead array assay is a useful method to measure CSF cytokine levels. Severe TBI in infants and children induces increases in pro- and anti-inflammatory cytokines and chemokines. It is the first clinical report of increased levels of MIP-1alpha after TBI in any patient population and the most comprehensive assessment of cytokines after TBI to date. Moderate therapeutic hypothermia did not attenuate the increase in CSF cytokine levels in children after TBI.

[The relevance of the inflammatory response in the injured brain]

Research efforts in recent years have defined traumatic brain injury (TBI) as a predominantly immunological and inflammatory disorder. This perception is based on the fact that the overwhelming neuroinflammatory response in the injured brain contributes to the development of posttraumatic edema and to neuropathological sequelae which are, in large part, responsible for the adverse outcome. While the "key" mediators of neuroinflammation, such as the cytokine cascade and the complement system, have been clearly defined by studies in experimental TBI models, their exact pathways of interaction and pathophysiological implications remain to be further elucidated. This lack of knowledge is partially due to the concept of a "dual role" of the neuroinflammatory response after TBI. This notion implies that specific inflammatory molecules may mediate diverse functions depending on their local concentration and kinetics of expression in the injured brain. The inflammation-induced effects range from beneficial aspects of neuroprotection to detrimental neurotoxicity. The lack of success in pushing anti-inflammatory therapeutic concepts from"bench to bedside" for patients with severe TBI strengthens the further need for advances in basic research on the molecular aspects of the neuroinflammatory network in the injured brain. The present review summarizes the current knowledge from experimental studies in this field of research and discusses potential future targets of investigation.

Acute brain injury triggers MyD88-dependent, TLR2/4-independent inflammatory responses

Endogenous molecules released from disrupted cells and extracellular matrix degradation products activate Toll-like receptors (TLRs) and, thus, might contribute to immune activation after tissue injury. Here, we show that aseptic, cold-induced cortical injury triggered an acute immune response that involves increased production of multiple cytokines/chemokines accompanied by neutrophil recruitment to the lesion site. We observed selective reductions in injury-induced cytokine/chemokine expression as well as in neutrophil accumulation in mice lacking the common TLR signaling adaptor MyD88 compared with wild-type mice. Notably, attenuation of the immune response was paralleled by a reduction in lesion size. Neutrophil depletion of wild-type mice and transplantation of MyD88-deficient bone marrow into lethally irradiated wild-type recipients had no substantial impact on injury-induced expression of cytokines/chemokines and on lesion development. In contrast to MyD88 deficiency, double deficiency of TLR2 and TLR4 -- despite the two receptors being activated by specific endogenous molecules associated to danger and signal through MyD88 -- altered neither immune response nor extent of tissue lesion size on injury. Our data indicate modulation of the neuroinflammatory response and lesion development after aseptic cortical injury through MyD88-dependent but TLR2/4-independent signaling by central nervous system resident nonmyeloid cells.

IFN-gamma-induced chemokines synergize with pertussis toxin to promote T cell entry to the central nervous system

Inflammation of the CNS, which occurs during multiple sclerosis and experimental autoimmune encephalomyelitis, is characterized by increased levels of IFN-gamma, a cytokine not normally expressed in the CNS. To investigate the role of IFN-gamma in CNS, we used intrathecal injection of a replication-defective adenovirus encoding murine IFN-gamma (AdIFNgamma) to IFN-gamma-deficient (GKO) mice. This method resulted in stable, long-lived expression of IFN-gamma that could be detected in cerebrospinal fluid using ELISA and Luminex bead immunoassay. IFN-gamma induced expression in the CNS of message and protein for the chemokines CXCL10 and CCL5, to levels comparable to those seen during experimental autoimmune encephalomyelitis. Other chemokines (CXCL2, CCL2, CCL3) were not induced. Mice lacking the IFN-gammaR showed no response, and a control viral vector did not induce chemokine expression. Chemokine expression was predominantly localized to meningeal and ependymal cells, and was also seen in astrocytes and microglia. IFN-gamma-induced chemokine expression did not lead to inflammation. However, when pertussis toxin was given i.p. to mice infected with the IFN-gamma vector, there was a dramatic increase in the number of T lymphocytes detected in the CNS by flow cytometry. This increase in blood-derived immune cells in the CNS did not occur with pertussis toxin alone, and did not manifest as histologically detectable inflammatory pathology. These results show that IFN-gamma induces a characteristic glial chemokine response that by itself is insufficient to promote inflammation, and that IFN-gamma-induced CNS chemoattractant signals can synergize with a peripheral infectious stimulus to drive T cell entry into the CNS.

Transient neuroprotection by minocycline following traumatic brain injury is associated with attenuated microglial activation but no changes in cell apoptosis or neutrophil infiltration

Cerebral inflammation and apoptotic cell death are two processes implicated in the progressive tissue damage that occurs following traumatic brain injury (TBI), and strategies to inhibit one or both of these pathways are being investigated as potential therapies for TBI patients. The tetracycline derivative minocycline was therapeutically effective in various models of central nervous system injury and disease, via mechanisms involving suppression of inflammation and apoptosis. We therefore investigated the effect of minocycline in TBI using a closed head injury model. Following TBI, mice were treated with minocycline or vehicle, and the effect on neurological outcome, lesion volume, inflammation and apoptosis was evaluated for up to 7 days. Our results show that while minocycline decreases lesion volume and improves neurological outcome at 1 day post-trauma, this response is not maintained at 4 days. The early beneficial effect is likely not due to anti-apoptotic mechanisms, as the density of apoptotic cells is not affected at either time-point. However, protection by minocycline is associated with a selective anti-inflammatory response, in that microglial activation and interleukin-1beta expression are reduced, while neutrophil infiltration and expression of multiple cytokines are not affected. These findings demonstrate that further studies on minocycline in TBI are necessary in order to consider it as a novel therapy for brain-injured patients.

Immune cell recruitment following acoustic trauma

Acoustic trauma induces cochlear inflammation. We hypothesized that chemokines are involved in the recruitment of leukocytes as part of a wound healing response. The cochleas of NIH-Swiss mice, exposed to octave-band noise (8-16 kHz, at 118 dB) for 2h, were examined after the termination of exposure. Leukocytes were identified immunohistochemically with antibodies to CD45 and F4/80. Gene array analysis followed by RT-PCR was performed on cochlear tissue to identify up-regulation of chemokine and adhesion molecule mRNA. The expression of the adhesion molecule ICAM-1 was also investigated immunohistochemically. Few CD45- or F4/80-positive leukocytes were observed in the non-exposed cochlea. Following acoustic trauma however, the number of CD45-positive cells was dramatically increased especially after 2 and 4 days, after which time the numbers decreased. F4/80-positive cells also increased in number over the course of a week. Gene array analysis indicated increased expression of monocyte chemoattractant protein 5 (MCP-5), monocyte chemoattractant protein 1 (MCP-1), macrophage inflammatory protein-1beta (MIP-1beta) and ICAM-1. RT-PCR, performed using primers for the individual mRNA sequences, confirmed the increased expression of MCP-1, MCP-5, MIP-1beta, and ICAM-1 relative to non-exposed mice. In the normal cochlea, ICAM-1 immunohistochemical expression was observed in venules, spiral ligament fibrocytes and in endosteal cells of the scala tympani. Expression increased to include more of the spiral ligament and endosteal cells after acoustic trauma. A cochlear inflammatory response is initiated in response to acoustic trauma and involves the recruitment of circulating leukocytes to the inner ear.

Relative effects of mannitol and hypertonic saline on calpain activity, apoptosis and polymorphonuclear infiltration in traumatic focal brain injury

The purpose of this study was to compare the relative effects of mannitol and hypertonic saline (HTS) on calpain activity, apoptosis and neuroinflammatory response induced by experimental cortical contusion. Four groups of 5 Sprague-Dawley male rats were submitted to focal brain injury produced by exposing the parietal cortex to dynamic cortical deformation. Groups were defined by rescucitation fluids administered 30 min post-injury as follows: group 1-0.9% normal saline 2 ml/kg; group 2-mannitol 20% 0.5 g/kg; group 3-HTS 2 ml/kg; group 4-HTS 4 ml/kg. At 72 h, animals were sacrificed. Paraffin-mounted sections of were stained for mu-Calpain, TUNEL, active caspase 3 and myeloperoxidase. There was no difference in the lesion size between the different groups. In contrast, there was a significant reduction in calpain and apoptosis activity and in the neuroinflammatory response in animals receiving HTS. Although mannitol proved to significantly decrease the neuroinflammatory response and calpain activity, it did not affect apoptosis, and its effect was significantly less than that of HTS. Importantly, the effect of HTS was mostly independent from the infused volume. Our results show that HTS promotes cell survival and reduces secondary brain damage following TBI. This protective effect was evidenced at rather small infused volumes, proved to encompass several cellular and molecular mechanisms involved in secondary cell death and could not be related to relief of intracranial pressure. These findings suggest that the high osmolality of HTS may have protective effects besides its impact on brain edema.

Migration of perilesional microglia after focal brain injury and modulation by CC chemokine receptor 5: an in situ time-lapse confocal imaging study

Microglia rapidly become reactive in response to diverse stimuli and are thought to be prominent participants in the pathophysiology of both acute injury and chronic neurological diseases. However, mature microglial reactions to a focal lesion have not been characterized dynamically in adult vertebrate tissue. Here, we present a detailed analysis of long-distance perilesional microglial migration using time-lapse confocal microscopy in acutely isolated living slices from adult brain-injured mice. Extensive migration of perilesional microglia was apparent by 24 h after injury and peaked at 3 d. Average instantaneous migration speeds of approximately 5 microm/min and peak speeds >10 microm/min were observed. Collective, directed migration toward the lesion edge was not observed as might be expected in the presence of chemoattractive gradients. Rather, migration was autonomous and could be modeled as a random walk. Pharmacological blockade of the cysteine-cysteine chemokine receptor 5 reduced migration velocity and the number of perilesional migratory microglia without affecting directional persistence, suggesting a novel role for chemokines in modulation of discrete migratory parameters. Finally, activated microglia in the denervated hippocampal stratum oriens did not migrate extensively, whereas human immunodeficiency virus-1 tat-activated microglia migrated nearly twice as fast as those at the stab lesion, indicating a nonuniform microglial response to different stimuli. Understanding the characteristics and specific molecular mechanisms underlying microglial migration after neural injury could reveal novel targets for therapeutic strategies for modulating neuroinflammation in human diseases.

Erythropoietin is neuroprotective, improves functional recovery, and reduces neuronal apoptosis and inflammation in a rodent model of experimental closed head injury

Traumatic brain injury (TBI) is a leading cause of morbidity and mortality in young people in industrialized countries. Although various anti-inflammatory and antiapoptotic modalities have shown neuroprotective effects in experimental models of TBI, to date, no specific pharmacological agent aimed at blocking the progression of secondary brain damage has been approved for clinical use. Erythropoietin (Epo) belongs to the cytokine superfamily and has traditionally been viewed as a hematopoiesis-regulating hormone. The newly discovered neuroprotective properties of Epo lead us to investigate its effect in TBI in a mouse model of closed head injury. Recombinant human erythropoietin (rhEpo) was injected at 1 and 24 h after TBI, and the effect on recovery of motor and cognitive functions, tissue inflammation, axonal degeneration, and apoptosis was evaluated up to 14 days. Motor deficits were lower, cognitive function was restored faster, and less apoptotic neurons and caspase-3 expression were found in rhEpo-treated as compared with vehicle-treated animals (P<0.05). Axons at the trauma area in rhEpo-treated mice were relatively well preserved compared with controls (shown by their density; P<0.01). Immunohistochemical analysis revealed a reduced activation of glial cells by staining for GFAP and complement receptor type 3 (CD11b/CD18) in the injured hemisphere of Epo- vs. vehicle-treated animals. We propose that further studies on Epo in TBI should be conducted in order to consider it as a novel therapy for TBI.

Increased expression of chemokine KC, an interleukin-8 homologue, in a model of oxygen-induced retinopathy

PURPOSE

The purpose of this study was to determine the retinal expression of angiogenic chemokines/cytokines in a mouse model of oxygen-induced retinopathy.

METHODS

C57BL/6 (B6) mice were exposed to 75% oxygen from postnatal day 7 (P7) to P12 and then recovered in room air. Reverse transcription-polymerase chain reaction (RT-PCR) was used to determine relative mRNA levels of KC, macrophage inflammatory protein-2 (MIP-2), interleukin-1alpha (IL-1alpha), and interferon gamma (IFN-gamma). Immunohistochemistry was used to localize KC in the retina. IL-1alpha was also injected into the vitreous of mouse eyes, and KC expression was examined by RT-PCR, enzyme-linked immunosorbent assay (ELISA), and immunohistochemistry.

RESULTS

KC expression at both the mRNA and protein levels was increased in P14, P17, and P21 of hyperoxia-injured eyes. KC immunoreactivity was localized along the nerve fiber layer and in radial Müller cell processes. IL-1alpha mRNA was modestly increased in hyperoxia-injured eyes on P14 and P17. INF-gamma mRNA was not detected in the retina. Adult mouse eyes injected with IL-1alpha demonstrated increased levels of both KC mRNA and protein, with KC immunoreactivity localized to Müller cell processes.

CONCLUSIONS

Oxygen-induced injury to the developing retina results in the induction of the CXC chemokine KC at both the mRNA and protein levels during the peak time points of neovascularization, suggesting a possible role in the pathogenesis of retinopathy of prematurity.

Recombinant erythropoietin down-regulates IL-6 and CXCR4 genes in TNF-alpha-treated primary cultures of human microvascular endothelial cells: implications for multiple sclerosis

In multiple sclerosis (MS), disruption of the blood-brain barrier might lead to new gadolinium-enhanced lesion formation in the brain and cause acute relapses. Current therapeutic options for acute relapses in MS are limited. The effect of recombinant erythropoietin (rEPO) on cytokine gene expression in TNF-alpha-treated human brain microvascular endothelial cells was studied. The cells were controls (untreated), exposed for either 6 or 24 h to TNF-alpha or TNF-alpha/rEPO. Of the 96 genes studied, interleukin-6 (IL-6), IL-1beta, CXCR4, and IL-1alpha genes were down-regulated when treated with TNF-alpha/rEPO for 6 h as compared with TNF-alpha alone. At 24 h, IL-6 and CXCR4 gene expression was 4.24 and 2.98, respectively. Quantitative RT-PCR analysis showed down-regulation by 3.86 and 1.9 for IL-6 and CXCR4 genes, respectively. Our findings suggest that further studies are warranted to evaluate the use of EPO in minimizing acute relapses in MS.

Molecular profiles of mRNA levels in laser capture microdissected murine hippocampal regions differentially responsive to TMT-induced cell death

Using a chemical-induced model of dentate granule (DG) cell death, cDNA microarray analysis was used to identify gene profiles from the laser-captured microdissected (LCM) hippocampal DG cell region versus the CA pyramidal cell layer (CA) from 21-day-old male CD1 mice injected with trimethyltin hydroxide (TMT; 3.0 mg/kg, i.p.). At 6 h post-TMT, lectin + microglia displaying a reactive morphology were in contact with active caspase 3+ neurons. By 18 h, amoeboid microglia and signs of phagocytosis, and a mild astrocytic response were present in the DG. There was no evidence of IgG extravasation in the hippocampus, or cell death and glial reactivity in the CA. Atlas 1.2K Clontech array detected 115 genes changed in the hippocampus with TMT and included genes associated with immediate-early responses, calcium homeostasis, cellular signaling, cell cycle, immunomodulation and DNA repair. Early responses localized to LCM DG samples consisted of elevations in inflammatory factors such as tumor necrosis factor-alpha and receptors, as well as MIP1alpha, CD14, CD18, and a decrease in factors associated with calcium buffering. By 18 h, in the DG, changes occurred in transcripts associated with apoptosis, cell adhesion, DNA repair, cell proliferation and growth. In the CA, a differential level of elevation was seen in CD86 antigen, zinc finger protein 38 and DNA damage inducible transcript 3. A significant number of genes was decreased at these early time points in both hippocampal regions.

Closed head injury--an inflammatory disease?

Closed head injury (CHI) remains the leading cause of death and persisting neurological impairment in young individuals in industrialized nations. Research efforts in the past years have brought evidence that the intracranial inflammatory response in the injured brain contributes to the neuropathological sequelae which are, in large part, responsible for the adverse outcome after head injury. The presence of hypoxia and hypotension in the early resuscitative period of brain-injured patients further aggravates the inflammatory response in the brain due to ischemia/reperfusion-mediated injuries. The profound endogenous neuroinflammatory response after CHI, which is phylogenetically aimed at defending the intrathecal compartment from invading pathogens and repairing lesioned brain tissue, contributes to the development of cerebral edema, breakdown of the blood-brain barrier, and ultimately to delayed neuronal cell death. However, aside from these deleterious effects, neuroinflammation has been recently shown to mediate neuroreparative mechanisms after brain injury as well. This "dual effect" of neuroinflammation was the focus of extensive experimental and clinical research in the past years and has lead to an expanded basic knowledge on the cellular and molecular mechanisms which regulate the intracranial inflammatory response after CHI. Thus, head injury has recently evolved as an inflammatory and immunological disease much more than a pure traumatological, neurological, or neurosurgical entity. The present review will summarize the so far known mechanisms of posttraumatic neuroinflammation after CHI, based on data from clinical and experimental studies, with a special focus on the role of pro-inflammatory cytokines, chemokines, and the complement system.

The chemokine fractalkine in patients with severe traumatic brain injury and a mouse model of closed head injury

The potential role of the chemokine Fractalkine (CX3CL1) in the pathophysiology of traumatic brain injury (TBI) was investigated in patients with head trauma and in mice after experimental cortical contusion. In control individuals, soluble (s)Fractalkine was present at low concentrations in cerebrospinal fluid (CSF) (12.6 to 57.3 pg/mL) but at much higher levels in serum (21,288 to 74,548 pg/mL). Elevation of sFractalkine in CSF of TBI patients was observed during the whole study period (means: 29.92 to 535.33 pg/mL), whereas serum levels remained within normal ranges (means: 3,100 to 59,159 pg/mL). Based on these differences, a possible passage of sFractalkine from blood to CSF was supported by the strong correlation between blood-brain barrier dysfunction (according to the CSF-/serum-albumin quotient) and sFractalkine concentrations in CSF (R = 0.706; P < 0.01). In the brain of mice subjected to closed head injury, neither Fractalkine protein nor mRNA were found to be augmented; however, Fractalkine receptor (CX3CR1) mRNA steadily increased peaking at 1 week postinjury (P < 0.05, one-way analysis of variance). This possibly implies the receptor to be the key factor determining the action of constitutively expressed Fractalkine. Altogether, these data suggest that the Fractalkine-CX3CR1 protein system may be involved in the inflammatory response to TBI, particularly for the accumulation of leukocytes in the injured parenchyma.

Widely expressed transcripts for chemokine receptor CXCR1 in identified glutamatergic, ?-aminobutyric acidergic, and cholinergic neurons and astrocytes of the rat brain: A single-cell reverse transcription-multiplex polymerase chain reaction study

Increasing evidence suggests that the chemokine interleukin (IL)-8/CXCL8 plays important roles in CNS development, neuronal survival, modulation of excitability, and neuroimmune response. Recently, we have shown that CXCL8 can acutely modulate ion channel activity in septal neurons expressing receptors CXCR1 and/or CXCR2. This was a surprising finding, insofar as CXCR1 expression had not been described for the mammalian brain. Here we investigated whether CXCR1 transcripts are present in other brain regions, whether they are expressed at the single-cell level in molecularly identified neurons and astrocytes, and how they are regulated during early postnatal development. In addition, possible cellular colocalization of CXCR1 and CXCR2 transcripts was examined. Semiquantitative reverse transcription-polymerase chain reaction (RT-PCR) revealed that CXCR1 mRNAs were expressed in the septum, striatum, hippocampus, cerebellum, and cortex (temporoparietal and entorhinal) at different levels and appeared to be regulated independently from CXCR2 during development. By using RT multiplex PCR on acutely dissociated cells from these brain regions, we show that CXCR1 transcripts were expressed in 83% of 84 sampled neurons displaying cholinergic (choline acetyltransferase mRNAs), gamma-aminobutyric acidergic (glutamic acid decarboxylases 65 and 67 mRNAs), or glutamatergic (vesicular glutamate transporters 1 and 2 mRNAs) phenotypes. CXCR1 and CXCR2 transcripts were colocalized in 45% of neurons sampled and also were present in some glial fibrillary acidic protein mRNA-expressing astrocytes. This is the first study to demonstrate the widespread expression of CXCR1 transcripts in the brain and suggests that CXCR1 may have hitherto unsuspected roles in neuromodulation and inflammation.

Elevated intracranial IL-18 in humans and mice after traumatic brain injury and evidence of neuroprotective effects of IL-18-binding protein after experimental closed head injury

Proinflammatory cytokines are important mediators of neuroinflammation after traumatic brain injury. The role of interleukin (IL)-18, a new member of the IL-1 family, in brain trauma has not been reported to date. The authors investigated the posttraumatic release of IL-18 in murine brains following experimental closed head injury (CHI) and in CSF of CHI patients. In the mouse model, intracerebral IL-18 was induced within 24 hours by ether anesthesia and sham operation. Significantly elevated levels of IL-18 were detected at 7 days after CHI and in human CSF up to 10 days after trauma. Published data imply that IL-18 may play a pathophysiological role in inflammatory CNS diseases; therefore its inhibition may ameliorate outcome after CHI. To evaluate the functional aspects of IL-18 in the injured brain, mice were injected systemically with IL-18-binding protein (IL-18BP), a specific inhibitor of IL-18, 1 hour after trauma. IL-18BP-treated mice showed a significantly improved neurological recovery by 7 days, accompanied by attenuated intracerebral IL-18 levels. This demonstrates that inhibition of IL-18 is associated with improved recovery. However, brain edema at 24 hours was not influenced by IL-18BP, suggesting that inflammatory mediators other than IL-18 induce the early detrimental effects of intracerebral inflammation.

Inflammatory response in acute traumatic brain injury: a double-edged sword

Inflammation is an important part of the pathophysiology of traumatic brain injury. Although the central nervous system differs from the other organs because of the almost complete isolation from the blood stream mediated by the blood-brain barrier, the main steps characterizing the immune activation within the brain follow a scenario similar to that in other organs. The key players in these processes are the numerous immune mediators released within minutes of the primary injury. They guide a sequence of events including expression of adhesion molecules, cellular infiltration, and additional secretion of inflammatory molecules and growth factors, resulting in either regeneration or cell death. The question is this: to what extent is inflammation beneficial for the injured brain tissue, and how does it contribute to secondary brain damage and progressive neuronal loss? This review briefly reports recent evidence supporting the dual, the beneficial, or the deleterious role of neuroinflammation after traumatic brain injury.