Temporal profile of release of interleukin-1beta in neurotrauma

Prevalence, early predictors, and outcomes of sepsis in neurocritical illnesses: A prospective cohort study

BACKGROUND

Patients with neurocritically illness are an under-recognized population at high risk of sepsis. We aimed to investigate the prevalence, early predictors, and outcomes of sepsis in neuro-ICU.

METHODS

Daily and accumulative incidences of sepsis in neuro-ICU were explored. Demographics, medical history, baseline disease severity scores, and baseline biomarkers regarding inflammation, immunology, organ function, and nutritional status were collected and analyzed as potential predictors of sepsis. Logistic regression analyses were used to determine the independent predictors, and a nomogram was used to estimate the individual probability of sepsis in neuro-ICU.

RESULTS

153 patients were included in this study. Fifty-nine (38.6%) patients developed sepsis, and 21 (14%) patients developed septic shock. More than 86% of the septic cases occurred within the first week. Sequential organ failure assessment score ((relative risk) RR 1.334, P = .026), history of diabetes (RR 2.346, P = .049), and transferrin (RR 0.128, P = .042) on admission are independent predictors of sepsis. Septic patients had significantly higher mortality (P = .011), higher medical cost (P = .028), and a lower rate of functional independence (P = .010), compared to patients without sepsis.

CONCLUSIONS

Sepsis afflicted more than one-third of neurocritically-ill patients and occurred mostly in the first week of admission. History of diabetes, serum transferrin, and sequential organ failure assessment score on admission were early predictors. Sepsis led to significantly worse outcomes and higher medical costs.

Molecular diagnostics in neurotrauma: Are there reliable biomarkers and effective methods for their detection?

To date, a large number of studies are being carried out in the field of neurotrauma, researchers not only establish the molecular mechanisms of the course of the disorders, but are also involved in the search for effective biomarkers for early prediction of the outcome and therapeutic intervention. Particular attention is paid to traumatic brain injury and spinal cord injury, due to the complex cascade of reactions in primary and secondary injury that affect pathophysiological processes and regenerative potential of the central nervous system. Despite a wide range of methods available methods to study biomarkers that correlate with the severity and degree of recovery in traumatic brain injury and spinal cord injury, development of reliable test systems for clinical use continues. In this review, we evaluate the results of recent studies looking for various molecules acting as biomarkers in the abovementioned neurotrauma. We also summarize the current knowledge of new methods for studying biological molecules, analyzing their sensitivity and limitations, as well as reproducibility of results. In this review, we also highlight the importance of developing reliable and reproducible protocols to identify diagnostic and prognostic biomolecules.

The cephalic phase of insulin release is modulated by IL-1β

The initial cephalic phase of insulin secretion is mediated through the vagus nerve and is not due to glycemic stimulation of pancreatic β cells. Recently, IL-1β was shown to stimulate postprandial insulin secretion. Here, we describe that this incretin-like effect of IL-1β involves neuronal transmission. Furthermore, we found that cephalic phase insulin release was mediated by IL-1β originating from microglia. Moreover, IL-1β activated the vagus nerve to induce insulin secretion and regulated the activity of the hypothalamus in response to cephalic stimulation. Notably, cephalic phase insulin release was impaired in obesity, in both mice and humans, and in mice, this was due to dysregulated IL-1β signaling. Our findings attribute a regulatory role to IL-1β in the integration of nutrient-derived sensory information, subsequent neuronally mediated insulin secretion, and the dysregulation of autonomic cephalic phase responses in obesity.

Systemic inflammation in traumatic brain injury predicts poor cognitive function

Background

Traumatic brain injury (TBI) impairs cognitive function. Systemic inflammation plays important role in cognitive deficits. It remains unclear if systemic inflammation in TBI is associated with poor cognitive function.

Methods

From January 2018 to December 2020, two groups of subjects were recruited: patients with TBI (n = 120), and healthy control (n = 120), followed up to 3 months. Blood was collected from TBI patients and healthy control, and serum inflammatory cytokines including interferon‐α (IFN‐α), interleukin‐1β (IL‐1β), IL‐6, IL‐8, IL‐10, and tumor necrosis factor‐α (TNF‐α) were measured at baseline and end of 3 months. Multivariate regression was used for analysis for the relationship between cognitive function and inflammatory cytokines.

Results

Inflammatory cytokines were higher in patients with brain injury and remained high at end of 3 months. Some cytokines such as IFN‐α, IL‐1β, IL‐6, and TNF‐α were associated with worsening memory and predicted poor performance.

Conclusion

Systemic inflammation in patients with TBI predicts poor cognitive function.

Microdialysis and microperfusion electrodes in neurologic disease monitoring

Contemporary biomarker collection techniques in blood and cerebrospinal fluid have to date offered only modest clinical insights into neurologic diseases such as epilepsy and glioma. Conversely, the collection of human electroencephalography (EEG) data has long been the standard of care in these patients, enabling individualized insights for therapy and revealing fundamental principles of human neurophysiology. Increasing interest exists in simultaneously measuring neurochemical biomarkers and electrophysiological data to enhance our understanding of human disease mechanisms. This review compares microdialysis, microperfusion, and implanted EEG probe architectures and performance parameters. Invasive consequences of probe implantation are also investigated along with the functional impact of biofouling. Finally, previously developed microdialysis electrodes and microperfusion electrodes are reviewed in preclinical and clinical settings. Critically, current and precedent microdialysis and microperfusion probes lack the ability to collect neurochemical data that is spatially and temporally coincident with EEG data derived from depth electrodes. This ultimately limits diagnostic and therapeutic progress in epilepsy and glioma research. However, this gap also provides a unique opportunity to create a dual-sensing technology that will provide unprecedented insights into the pathogenic mechanisms of human neurologic disease.

Neuro-inflammatory Sequelae of Minimal Trauma in the Non-traumatized Human Brain: A Microdialysis Study

Cytokine measurement directly from the brain parenchyma by means of microdialysis has documented the activation of certain procedures in vivo, after brain trauma in humans. However, the intercalation of the micro-catheter insertion with the phenomena triggered by the head trauma renders the assessment of the findings problematic. The present study attempts to elucidate the pure effect of minimal trauma, represented by the insertion of the micro-catheter, on the non-traumatized human brain. Microdialysis catheters were implanted in 12 patients with drug-resistant epilepsy, and subjected to invasive electroencephalography with intracranial electrodes. Samples were collected during the first 5 days of monitoring. The dialysate was analyzed using bead flow cytometry, and the concentrations of interleukin (IL)-1, IL-6, IL-8, IL-10, IL-12, and tumor necrosis factor-α (TNF-α) were measured. The levels of IL-1 and IL-8 were found to be raised until 48 h post-implantation, and thereafter they reached a plateau of presumably baseline values. The temporal profile of the IL-6 variation was different, with the increase being much more prolonged, as its concentration had not returned to baseline levels at the fifth day post-insertion. TNF-α was found to be significantly raised only 2 h after implantation. IL-10 and IL-12 did not have any significant response to micro-trauma. These findings imply that the reaction of the neuro-inflammatory mechanisms of the brain exist even after minimal trauma, and is unexpectedly intense for IL-6. Questions may arise regarding the objectivity of findings attributed by some studies to inflammatory perturbation after head injury.

Role of Astrocytes in Post-traumatic Epilepsy

Traumatic brain injury, a common cause of acquired epilepsy, is typical to find necrotic cell death within the injury core. The dynamic changes in astrocytes surrounding the injury core contribute to epileptic seizures associated with intense neuronal firing. However, little is known about the molecular mechanisms that activate astrocytes during traumatic brain injury or the effect of functional changes of astrocytes on seizures. In this comprehensive review, we present our cumulated understanding of the complex neurological affection in astrocytes after traumatic brain injury. We approached the problem through describing the changes of cell morphology, neurotransmitters, biochemistry, and cytokines in astrocytes during post-traumatic epilepsy. In addition, we also discussed the relationship between dynamic changes in astrocytes and seizures and the current pharmacologic agents used for treatment. Hopefully, this review will provide a more detailed knowledge from which better therapeutic strategies can be developed to treat post-traumatic epilepsy.

Mitochondrial-Directed Antioxidant Reduces Microglial-Induced Inflammation in Murine In Vitro Model of TC-83 Infection

Venezuelan equine encephalitis virus (VEEV) is an arbovirus that is associated with robust inflammation that contributes to neurodegenerative phenotypes. In addition to triggering central nervous system (CNS) inflammation, VEEV will also induce mitochondrial dysfunction, resulting in increased cellular apoptosis. In this study, we utilize the TC-83 strain of VEEV to determine the role of mitochondrial oxidative stress in mediating inflammation elicited by murine brain microglial cells. Using an in vitro model, we show that murine microglia are susceptible to TC-83 infection, and that these cells undergo mitochondrial stress as the result of infection. We also indicate that bystander microglia contribute more significantly to the overall inflammatory load than directly infected microglia. Use of a mitochondrial targeted antioxidant, mitoquinone mesylate, greatly reduced the pro-inflammatory cytokines released by both direct infected and bystander microglia. Our data suggest that release of interleukin-1β, a key instigator of neuroinflammation during VEEV infection, may be the direct result of accumulating mitochondrial stress. This data improves our understanding inflammation elicited by murine microglia and will aid in the development of more accurate in vitro and in vivo murine model of VEEV-induced neuroinflammation.

Acute Inflammatory Biomarker Responses to Diffuse Traumatic Brain Injury in the Rat Monitored by a Novel Microdialysis Technique

Neuroinflammation is a major contributor to the progressive brain injury process induced by traumatic brain injury (TBI), and may play an important role in the pathophysiology of axonal injury. The immediate neuroinflammatory cascade cannot be characterized in the human setting. Therefore, we used the midline fluid percussion injury model of diffuse TBI in rats and a novel microdialysis (MD) method providing stable diffusion-driven biomarker sampling. Immediately post-injury, bilateral amphiphilic tri-block polymer coated MD probes (100 kDa cut off membrane) were inserted and perfused with Dextran 500 kDa-supplemented artificial cerebrospinal fluid (CSF) to optimize protein capture. Six hourly samples were analyzed for 27 inflammatory biomarkers (9 chemokines, 13 cytokines, and 5 growth factors) using a commercial multiplex biomarker kit. TBI (n = 6) resulted in a significant increase compared with sham-injured controls (n = 6) for five chemokines (eotaxin/CCL11, fractalkine/CX3CL1, LIX/CXCL5, monocyte chemoattractant protein [MCP]1α/CCL2, macrophage inflammatory protein [MIP]1α /CCL3), 10 cytokines (interleukin [IL]-1α, IL-1β, IL-4, IL-6, IL-10, IL-13, IL-17α, IL-18, interferon [IFN]-γ, tumor necrosis factor [TNF]-α), and four growth factors (epidermal growth factor [EGF], granulocyte-macrophage colony-stimulating factor [GM-CSF], leptin, vascular endothelial growth factor [VEGF]). Therefore, diffuse TBI was associated with an increased level of 18 of the 27 inflammatory biomarkers at one through six time points, during the observation period whereas the remaining 9 biomarkers were unaltered. The study shows that diffuse TBI induces an acute increase in a number of inflammatory biomarkers. The novel MD technique provides stable MD sampling suitable for further studies on the early neuroinflammatory cascade in TBI.

Neurotrauma: The Crosstalk between Neurotrophins and Inflammation in the Acutely Injured Brain

Traumatic brain injury (TBI) is a major cause of morbidity and mortality among young individuals worldwide. Understanding the pathophysiology of neurotrauma is crucial for the development of more effective therapeutic strategies. After the trauma occurs, immediate neurologic damage is produced by the traumatic forces; this primary injury triggers a secondary wave of biochemical cascades together with metabolic and cellular changes, called secondary neural injury. In the scenario of the acutely injured brain, the ongoing secondary injury results in ischemia and edema culminating in an uncontrollable increase in intracranial pressure. These areas of secondary injury progression, or areas of “traumatic penumbra”, represent crucial targets for therapeutic interventions. Neurotrophins are a class of signaling molecules that promote survival and/or maintenance of neurons. They also stimulate axonal growth, synaptic plasticity, and neurotransmitter synthesis and release. Therefore, this review focuses on the role of neurotrophins in the acute post-injury response. Here, we discuss possible endogenous neuroprotective mechanisms of neurotrophins in the prevailing environment surrounding the injured areas, and highlight the crosstalk between neurotrophins and inflammation with focus on neurovascular unit cells, particularly pericytes. The perspective is that neurotrophins may represent promising targets for research on neuroprotective and neurorestorative processes in the short-term following TBI.

Endogenous repair signaling after brain injury and complementary bioengineering approaches to enhance neural regeneration

Traumatic brain injury (TBI) affects 5.3 million Americans annually. Despite the many long-term deficits associated with TBI, there currently are no clinically available therapies that directly address the underlying pathologies contributing to these deficits. Preclinical studies have investigated various therapeutic approaches for TBI: two such approaches are stem cell transplantation and delivery of bioactive factors to mitigate the biochemical insult affiliated with TBI. However, success with either of these approaches has been limited largely due to the complexity of the injury microenvironment. As such, this review outlines the many factors of the injury microenvironment that mediate endogenous neural regeneration after TBI and the corresponding bioengineering approaches that harness these inherent signaling mechanisms to further amplify regenerative efforts.

The ischemic environment drives microglia and macrophage function

Cells of myeloid origin, such as microglia and macrophages, act at the crossroads of several inflammatory mechanisms during pathophysiology. Besides pro-inflammatory activity (M1 polarization), myeloid cells acquire protective functions (M2) and participate in the neuroprotective innate mechanisms after brain injury. Experimental research is making considerable efforts to understand the rules that regulate the balance between toxic and protective brain innate immunity. Environmental changes affect microglia/macrophage functions. Hypoxia can affect myeloid cell distribution, activity, and phenotype. With their intrinsic differences, microglia and macrophages respond differently to hypoxia, the former depending on ATP to activate and the latter switching to anaerobic metabolism and adapting to hypoxia. Myeloid cell functions include homeostasis control, damage-sensing activity, chemotaxis, and phagocytosis, all distinctive features of these cells. Specific markers and morphologies enable to recognize each functional state. To ensure homeostasis and activate when needed, microglia/macrophage physiology is finely tuned. Microglia are controlled by several neuron-derived components, including contact-dependent inhibitory signals and soluble molecules. Changes in this control can cause chronic activation or priming with specific functional consequences. Strategies, such as stem cell treatment, may enhance microglia protective polarization. This review presents data from the literature that has greatly advanced our understanding of myeloid cell action in brain injury. We discuss the selective responses of microglia and macrophages to hypoxia after stroke and review relevant markers with the aim of defining the different subpopulations of myeloid cells that are recruited to the injured site. We also cover the functional consequences of chronically active microglia and review pivotal works on microglia regulation that offer new therapeutic possibilities for acute brain injury.

Improved fracture healing in patients with concomitant traumatic brain injury: proven or not?

Over the last 3 decades, scientific evidence advocates an association between traumatic brain injury (TBI) and accelerated fracture healing. Multiple clinical and preclinical studies have shown an enhanced callus formation and an increased callus volume in patients, respectively, rats with concomitant TBI. Over time, different substances (cytokines, hormones, etc.) were in focus to elucidate the relationship between TBI and fracture healing. Until now, the mechanism behind this relationship is not fully clarified and a consensus on which substance plays the key role could not be attained in the literature. In this review, we will give an overview of current concepts and opinions on this topic published in the last decade and both clinical and pathophysiological theories will be discussed.

Brain tissue responses to neural implants impact signal sensitivity and intervention strategies

Implantable biosensors are valuable scientific tools for basic neuroscience research and clinical applications. Neurotechnologies provide direct readouts of neurological signal and neurochemical processes. These tools are generally most valuable when performance capacities extend over months and years to facilitate the study of memory, plasticity, and behavior or to monitor patients’ conditions. These needs have generated a variety of device designs from microelectrodes for fast scan cyclic voltammetry (FSCV) and electrophysiology to microdialysis probes for sampling and detecting various neurochemicals. Regardless of the technology used, the breaching of the blood–brain barrier (BBB) to insert devices triggers a cascade of biochemical pathways resulting in complex molecular and cellular responses to implanted devices. Molecular and cellular changes in the microenvironment surrounding an implant include the introduction of mechanical strain, activation of glial cells, loss of perfusion, secondary metabolic injury, and neuronal degeneration. Changes to the tissue microenvironment surrounding the device can dramatically impact electrochemical and electrophysiological signal sensitivity and stability over time. This review summarizes the magnitude, variability, and time course of the dynamic molecular and cellular level neural tissue responses induced by state-of-the-art implantable devices. Studies show that insertion injuries and foreign body response can impact signal quality across all implanted central nervous system (CNS) sensors to varying degrees over both acute (seconds to minutes) and chronic periods (weeks to months). Understanding the underlying biological processes behind the brain tissue response to the devices at the cellular and molecular level leads to a variety of intervention strategies for improving signal sensitivity and longevity.

Cellular and molecular mechanisms of injury and spontaneous recovery

Until recently, most have assumed that traumatic brain injury (TBI) was singularly associated with the overt destruction of brain tissue resulting in subsequent morbidity or death. More recently, experimental and clinical studies have shown that the pathobiology of TBI is more complex, involving a host of cellular and subcellular changes that impact on neuronal function and viability while also affecting vascular reactivity and the activation of multiple biological response pathways. Here we review the brain's response to injury, examining both focal and diffuse changes and their implications for post-traumatic brain dysfunction and recovery. TBI-induced neuronal dysfunction and death as well as the diffuse involvement of multiple fiber projections are discussed together with considerations of how local axonal membrane changes or channelopathy translate into local ionic dysregulation and axonal disconnection. Concomitant changes in the cerebral microcirculation are also discussed and their relationship with the parallel changes in the brain's metabolism is considered. These cellular and subcellular events occurring within neurons and their blood supply are correlated with multiple biological response modifiers evoked by generalized post-traumatic inflammation and the parallel activation of oxidative stress processes. The chapter closes with considerations of recovery following focal or diffuse injury. Evidence for dynamic brain reorganization/repair is presented, with considerations of traumatically induced circuit disruption and their progression to either adaptive or in some cases, maladaptive reorganization.

Immune activation promotes depression 1 month after diffuse brain injury: a role for primed microglia

BACKGROUND

Traumatic brain injury (TBI) is associated with a higher incidence of depression. The majority of individuals who suffer a TBI are juveniles and young adults, and thus, the risk of a lifetime of depressive complications is a significant concern. The etiology of increased TBI-associated depression is unclear but may be inflammatory-related with increased brain sensitivity to secondary inflammatory challenges (e.g., stressors, infection, and injury).

METHODS

Adult male BALB/c mice received a sham (n = 52) or midline fluid percussion injury (TBI; n = 57). Neuroinflammation, motor coordination (rotarod), and depressive behaviors (social withdrawal, immobility in the tail suspension test, and anhedonia) were assessed 4 hours, 24 hours, 72 hours, 7 days, or 30 days later. Moreover, 30 days after surgery, sham and TBI mice received a peripheral injection of saline or lipopolysaccharide (LPS) and microglia activation and behavior were determined.

RESULTS

Diffuse TBI caused inflammation, peripheral cell recruitment, and microglia activation immediately after injury coinciding with motor coordination deficits. These transient events resolved within 7 days. Nonetheless, 30 days post-TBI a population of deramified and major histocompatibility complex II(+) (primed) microglia were detected. After a peripheral LPS challenge, the inflammatory cytokine response in primed microglia of TBI mice was exaggerated compared with microglia of controls. Furthermore, this LPS-induced microglia reactivity 30 days after TBI was associated with the onset of depressive-like behavior.

CONCLUSIONS

These results implicate a primed and immune-reactive microglial population as a possible triggering mechanism for the development of depressive complications after TBI.

Recombinant human interleukin-1 receptor antagonist in severe traumatic brain injury: a phase II randomized control trial

Traumatic brain injury (TBI) is the commonest cause of death and disability in those aged under 40 years. Interleukin-1 receptor antagonist (IL1ra) is an endogenous competitive antagonist at the interleukin-1 type-1 receptor (IL-1R). Antagonism at the IL-1R confers neuroprotection in several rodent models of neuronal injury (i.e., trauma, stroke and excitotoxicity). We describe a single center, phase II, open label, randomized-control study of recombinant human IL1ra (rhIL1ra, anakinra) in severe TBI, at a dose of 100 mg subcutaneously once a day for 5 days in 20 patients randomized 1:1. We provide safety data (primary outcome) in this pathology, utilize cerebral microdialysis to directly determine brain extracellular concentrations of IL1ra and 41 cytokines and chemokines, and use principal component analysis (PCA) to explore the resultant cerebral cytokine profile. Interleukin-1 receptor antagonist was safe, penetrated into plasma and the brain extracellular fluid. The PCA showed a separation in cytokine profiles after IL1ra administration. A candidate cytokine from this analysis, macrophage-derived chemoattractant, was significantly lower in the rhIL1ra-treated group. Our results provide promising data for rhIL1ra as a therapeutic candidate by showing safety, brain penetration and a modification of the neuroinflammatory response to TBI by a putative neuroprotective agent in humans for the first time.

Clinical and radiological findings in long-term intracranial pressure monitoring

BACKGROUND

Advantages of telemetric devices for long-term intracranial pressure (ICP) measurement have been mentioned several times in the literature. However, descriptions of associated complications are lacking. Therefore, the presented observational study focused on clinical and radiological findings after insertion of an intraparenchymal telemetric ICP monitor.

METHODS

Between April 2010 and February 2013, 185 telemetric ICP catheters were implanted for diagnostic purposes. All patients were clinically followed. Radiological, microbiological and clinical data were analysed.

RESULTS

One brain abscess (0.5 %) and two cutaneous infections (1.1 %) occurred in 185 patients. Staphylococcus spp. could be detected in all cases. Six patients (3.2 %) suffered from single new-onset seizures and one patient (0.5 %) from a temporary hemiparesis. Intracerebral haemorrhages occurred in 15.6 %, most of the time as small punctate bleedings. Perifocal oedematous reactions surrounding inserted telemetric catheters could be observed in 46.9 %. Multiple imaging studies revealed a tendency of complete oedema resolution over time.

CONCLUSIONS

Infectious as well as haemorrhagic complication rates are well comparable with the common literature. The long-term implantation of an ICP probe does not seem to increase the risk of wound infections or brain abscess formation. Surprisingly, very high numbers of oedematous reactions after insertion of the intraparenchymal ICP monitor were seen. Reasons therefore could only be speculated upon.

The role of interleukin-1β in the pentylenetetrazole-induced kindling of seizures, in the rat hippocampus

Because the contribution of inflammatory mediators to seizure disorders is unclear, we investigated the changes in the expression of interleukin-1β (IL-β) and its receptor - IL-1 receptor type 1 (IL-1R1), tumour necrosis factor-α (TNF-α) and interleukin-6 (IL-6) in the rat hippocampus at different stages of pentylenetetrazole (PTZ)-induced kindling. The occurrence and progressive development of seizures were induced by repeated systemic administration of PTZ, a non-competitive antagonist of the γ-aminobutyric acid type A (GABAA) receptor at a subconvulsive dose of 30 mg/kg. We also examined the effects of continuous intracerebroventricular administration of IL-1β and lipopolysaccharide (LPS) in this model of epilepsy using subcutaneously implanted osmotic mini-pumps. We observed enhanced IL-1R1 expression in the dentate gyrus (DG) at different stages of kindling, whereas the elevated IL-1β level was distinctive to fully kindled seizures. We did not detect significant changes in the concentration of IL-6 or TNF-α throughout the kindling process. LPS accelerated transiently the process of kindling, while IL-1β showed a predisposition to delay kindling acquisition. Our study supports the concept of seizure-related modifications in brain cytokine production during epileptogenesis. Although some evidence indicates a proconvulsant property of IL-1β activity, it cannot be ruled out that the alterations in IL-1 system reflect the activation of endogenous protective mechanisms with respect to the kindling of seizures.

Taurine improves functional and histological outcomes and reduces inflammation in traumatic brain injury

We investigated the effect of taurine on inflammatory cytokine expression, on astrocyte activity and cerebral edema and functional outcomes, following traumatic brain injury (TBI) in rats. 72 rats were randomly divided into sham, TBI and Taurine groups. Rats subjected to moderate lateral fluid percussion injury were injected intravenously with taurine (200mg/kg) or saline immediately after injury or daily for 7days. Functional outcome was evaluated using Modified Neurological Severity Score (mNSS). Glial fibrillary acidic protein (GFAP) of the brain was measured using immunofluorescence. Concentration of 23 cytokines and chemokines in the injured cortex at 1 and 7days after TBI was assessed by Luminex xMAP technology. The results showed that taurine significantly improved functional recovery except 1day, reduced accumulation of GFAP and water content in the penumbral region at 7days after TBI. Compared with the TBI group, taurine significantly suppressed growth-related oncogene (GRO/KC) and interleukin (IL)-1β levels while elevating the levels of regulated on activation, normal T cell expressed and secreted (RANTES) at 1day. And taurine markedly decreased the level of 17 cytokine: eotaxin, Granulocyte colony-stimulating factor (G-CSF), Granulocyte-macrophage colony-stimulating factor (GM-CSF), interferon-gamma (IFN-γ), IL-1α, IL-1β, IL-4, IL-5, IL-6, IL-10, IL-12p70, IL-13, IL-17, leptin, monocyte chemotactic protein-1 (MCP-1), tumor necrosis factor-alpha (TNF-α), vascular endothelial growth factor (VEGF), and only increased the level of MIP-1α in a week. The results suggest that taurine effectively mitigates the severity of brain damage in TBI by attenuating the increase of astrocyte activity and edema as well as pro-inflammatory cytokines.

Inflammation in subarachnoid hemorrhage and delayed deterioration associated with vasospasm: a review

Delayed deterioration associated with vasospasm (DDAV) after subarachnoid hemorrhage (SAH), (often called vasospasm) continues to be both a difficult entity to treat and a leading cause of morbidity in patients. Until recently, attention was focused on alleviating the vascular spasm. Recent evidence shows that vascular spasm may not account for all the morbidity of DDAV. There is renewed interest in looking for other potential targets for therapy. Inflammation has become a promising area of research for new treatments. This review explores the evidence that inflammation is a driver of DDAV by asking three questions: (1) If inflammation is important in the pathogenesis of the disease, what part or parts of the inflammatory response are involved? (2) When does inflammation occur in SAH? (3) In what compartment of the skull does the inflammation occur, the cerebrospinal fluid and meninges, the cerebral arteries, or the brain itself?

Understanding the neuroinflammatory response following concussion to develop treatment strategies

Mild traumatic brain injuries (mTBI) have been associated with long-term cognitive deficits relating to trauma-induced neurodegeneration. These long-term deficits include impaired memory and attention, changes in executive function, emotional instability, and sensorimotor deficits. Furthermore, individuals with concussions show a high co-morbidity with a host of psychiatric illnesses (e.g., depression, anxiety, addiction) and dementia. The neurological damage seen in mTBI patients is the result of the impact forces and mechanical injury, followed by a delayed neuroimmune response that can last hours, days, and even months after the injury. As part of the neuroimmune response, a cascade of pro- and anti-inflammatory cytokines are released and can be detected at the site of injury as well as subcortical, and often contralateral, regions. It has been suggested that the delayed neuroinflammatory response to concussions is more damaging then the initial impact itself. However, evidence exists for favorable consequences of cytokine production following traumatic brain injuries as well. In some cases, treatments that reduce the inflammatory response will also hinder the brain's intrinsic repair mechanisms. At present, there is no evidence-based pharmacological treatment for concussions in humans. The ability to treat concussions with drug therapy requires an in-depth understanding of the pathophysiological and neuroinflammatory changes that accompany concussive injuries. The use of neurotrophic factors [e.g., nerve growth factor (NGF)] and anti-inflammatory agents as an adjunct for the management of post-concussion symptomology will be explored in this review.

Acute neuroimmune modulation attenuates the development of anxiety-like freezing behavior in an animal model of traumatic brain injury

Chronic anxiety is a common and debilitating result of traumatic brain injury (TBI) in humans. While little is known about the neural mechanisms of this disorder, inflammation resulting from activation of the brain's immune response to insult has been implicated in both human post-traumatic anxiety and in recently developed animal models. In this study, we used a lateral fluid percussion injury (LFPI) model of TBI in the rat and examined freezing behavior as a measure of post-traumatic anxiety. We found that LFPI produced anxiety-like freezing behavior accompanied by increased reactive gliosis (reflecting neuroimmune inflammatory responses) in key brain structures associated with anxiety: the amygdala, insula, and hippocampus. Acute peri-injury administration of ibudilast (MN166), a glial cell activation inhibitor, suppressed both reactive gliosis and freezing behavior, and continued neuroprotective effects were apparent several months post-injury. These results support the conclusion that inflammation produced by neuroimmune responses to TBI play a role in post-traumatic anxiety, and that acute suppression of injury-induced glial cell activation may have promise for the prevention of post-traumatic anxiety in humans.

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.

IL-1β is upregulated in the diabetic retina and retinal vessels: cell-specific effect of high glucose and IL-1β autostimulation

Many molecular and cellular abnormalities detected in the diabetic retina support a role for IL-1β-driven neuroinflammation in the pathogenesis of diabetic retinopathy. IL-1β is well known for its role in the induction and, through autostimulation, amplification of neuroinflammation. Upregulation of IL-1β has been consistently detected in the diabetic retina; however, the mechanisms and cellular source of IL-1β overexpression are poorly understood. The aim of this study was to investigate the effect of high glucose and IL-1β itself on IL-1β expression in microglial, macroglial (astrocytes and Müller cells) and retinal vascular endothelial cells; and to study the effect of diabetes on the expression of IL-1β in isolated retinal vessels and on the temporal pattern of IL-1β upregulation and glial reactivity in the retina of streptozotocin-diabetic rats. IL-1β was quantified by RealTime RT-PCR and ELISA, glial fibrillar acidic protein, α2-macroglobulin, and ceruloplasmin by immunoblotting. We found that high glucose induced a 3-fold increase of IL-1β expression in retinal endothelial cells but not in macroglia and microglia. IL-1β induced its own synthesis in endothelial and macroglial cells but not in microglia. In retinal endothelial cells, the high glucose-induced IL-1β overexpression was prevented by calphostin C, a protein kinase C inhibitor. The retinal vessels of diabetic rats showed increased IL-1β expression as compared to non-diabetic rats. Retinal expression of IL-1β increased early after the induction of diabetes, continued to increase with progression of the disease, and was temporally associated with upregulation of markers of glial activation. These findings point to hyperglycemia as the trigger and to the endothelium as the origin of the initial retinal upregulation of IL-1β in diabetes; and to IL-1β itself, via autostimulation in endothelial and macroglial cells, as the mechanism of sustained IL-1β overexpression. Interrupting the vicious circle triggered by IL-1β autostimulation could limit the progression of diabetic retinopathy.

The cytokine temporal profile in rat cortex after controlled cortical impact

Cerebral inflammatory responses may initiate secondary cascades following traumatic brain injury (TBI). Changes in the expression of both cytokines and chemokines may activate, regulate, and recruit innate and adaptive immune cells associated with secondary degeneration, as well as alter a host of other cellular processes. In this study, we quantified the temporal expression of a large set of inflammatory mediators in rat cortical tissue after brain injury. Following a controlled cortical impact (CCI) on young adult male rats, cortical and hippocampal tissue of the injured hemisphere and matching contralateral material was harvested at early (4, 12, and 24 hours) and extended (3 and 7 days) time points post-procedure. Naïve rats that received only anesthesia were used as controls. Processed brain homogenates were assayed for chemokine and cytokine levels utilizing an electrochemiluminescence-based multiplex ELISA platform. The temporal profile of cortical tissue samples revealed a multi-phasic injury response following brain injury. CXCL1, IFN-γ, TNF-α levels significantly peaked at four hours post-injury compared to levels found in naïve or contralateral tissue. CXCL1, IFN-γ, and TNF-α levels were then observed to decrease at least 3-fold by 12 hours post-injury. IL-1β, IL-4, and IL-13 levels were also significantly elevated at four hours post-injury although their expression did not decrease more than 3-fold for up to 24 hours post-injury. Additionally, IL-1β and IL-4 levels displayed a biphasic temporal profile in response to injury, which may suggest their involvement in adaptive immune responses. Interestingly, peak levels of CCL2 and CCL20 were not observed until after four hours post-injury. CCL2 levels in injured cortical tissue were significantly higher than peak levels of any other inflammatory mediator measured, thus suggesting a possible use as a biomarker. Fully elucidating chemokine and cytokine signaling properties after brain injury may provide increased insight into a number of secondary cascade events that are initiated or regulated by inflammatory responses.

Cytokines and innate inflammation in the pathogenesis of human traumatic brain injury

There is an increasing recognition that following traumatic brain injury, a cascade of inflammatory mediators is produced, and contributes to the pathological consequences of central nervous system injury. This review summarises the key literature from pre-clinical models that underlies our understanding of innate inflammation following traumatic brain injury before focussing on the growing evidence from human studies. In addition, the underlying molecular mediators responsible for blood brain barrier dysfunction have been discussed. In particular, we have highlighted the different sampling methodologies available and the difficulties in interpreting human data of this sort. Ultimately, understanding the innate inflammatory response to traumatic brain injury may provide a therapeutic avenue in the treatment of central nervous system disease.

Iontophoresis of a 13 kDa protein monitored by subcutaneous microdialysis in vivo

Background: The purpose of this study was to optimize parameters pertaining to microdialysis technique so as to make this method feasible for evaluating transdermal transport of macromolecules. Results: Microdialysis experiments were performed in vivo using hairless rats with daniplestim as the model protein. Two perfusion fluids – phosphate-buffered saline (PBS) and 3% dextran in PBS – were evaluated with respect to their effect on sample volume retrieval and recovery of the target protein from the microdialysis probe. Incorporation of dextran-60 in the perfusion fluid reduced fluid loss to 10% as opposed to 34% in the absence of dextran-60. Improvement in daniplestim recovery was also seen with dextran-PBS (56.5 ± 10.3%) as the perfusion fluid than with PBS alone (26.7±4.5%). Conclusion: Subcutaneous levels of daniplestim were measured following iontophoresis after improving recovery and minimizing fluid loss from the microdialysis probe.

Post-traumatic hypoxia exacerbates neurological deficit, neuroinflammation and cerebral metabolism in rats with diffuse traumatic brain injury

Background

The combination of diffuse brain injury with a hypoxic insult is associated with poor outcomes in patients with traumatic brain injury. In this study, we investigated the impact of post-traumatic hypoxia in amplifying secondary brain damage using a rat model of diffuse traumatic axonal injury (TAI). Rats were examined for behavioral and sensorimotor deficits, increased brain production of inflammatory cytokines, formation of cerebral edema, changes in brain metabolism and enlargement of the lateral ventricles.

Methods

Adult male Sprague-Dawley rats were subjected to diffuse TAI using the Marmarou impact-acceleration model. Subsequently, rats underwent a 30-minute period of hypoxic (12% O₂/88% N₂) or normoxic (22% O₂/78% N₂) ventilation. Hypoxia-only and sham surgery groups (without TAI) received 30 minutes of hypoxic or normoxic ventilation, respectively. The parameters examined included: 1) behavioural and sensorimotor deficit using the Rotarod, beam walk and adhesive tape removal tests, and voluntary open field exploration behavior; 2) formation of cerebral edema by the wet-dry tissue weight ratio method; 3) enlargement of the lateral ventricles; 4) production of inflammatory cytokines; and 5) real-time brain metabolite changes as assessed by microdialysis technique.

Results

TAI rats showed significant deficits in sensorimotor function, and developed substantial edema and ventricular enlargement when compared to shams. The additional hypoxic insult significantly exacerbated behavioural deficits and the cortical production of the pro-inflammatory cytokines IL-6, IL-1β and TNF but did not further enhance edema. TAI and particularly TAI+Hx rats experienced a substantial metabolic depression with respect to glucose, lactate, and glutamate levels.

Conclusion

Altogether, aggravated behavioural deficits observed in rats with diffuse TAI combined with hypoxia may be induced by enhanced neuroinflammation, and a prolonged period of metabolic dysfunction.

Mild stretch-induced injury increases susceptibility to interleukin-1β-induced release of matrix metalloproteinase-9 from astrocytes

Traumatic brain injury (TBI) results in the activation of glia and the release of proinflammatory cytokines, including interleukin (IL)-1β. The response of astrocytes to mild TBI has not been well studied. We used an in vitro model of cell stretch to investigate the effects of mild mechanical insult on astrocyte injury (lactate dehydrogenase and propidium iodide), and on mediators of inflammation including IL-1β, the chemokine CX3CL1, and nitrite. Here, we tested the hypothesis that a mild mechanical insult would increase susceptibility of astrocytes to delayed exposure to IL-1β, including enhanced release of the matrix metalloproteinease-9 (MMP-9). We investigated the role of the mitogen protein-activated kinase (MAPK) pathway in these responses. Cells subjected to a mild stretch show an increase in activation of the ERK1/2 and JNK pathways, and an increase in lactate dehydrogenase (LDH), but no change in the levels of inflammatory mediators. An early increase in LDH was dependent on ERK activation. Exposure to IL-1β, or to stretch alone, did not increase MMP-9. In contrast, the combination of mild stretch followed by IL-1β resulted in greater activation of the ERK pathway compared to either stimulus alone, and also resulted in an increase in the production of MMP-9 by astrocytes. Inhibition of the ERK pathway suppressed the increase in MMP-9 induced by the combination of stretch and IL-1β treatment. These results suggest that a primary mild mechanical injury renders astrocytes more susceptible to a secondary exposure to a proinflammatory cytokine such as IL-1β via the activation of the ERK pathway, and suggest a mechanism by which a mild head injury may confer increased susceptibility to neurologic injury caused by a subsequent insult.

Elevated leptin expression in rat model of traumatic spinal cord injury and femoral fracture

BACKGROUND

Few studies have reported a relationship between leptin induced by spinal cord injury (SCI) and healing bone tissue.

OBJECTIVE

To observe serum and callus leptin expression within the setting of fracture and traumatic SCI.

METHODS

Seventy-two male Sprague Dawley rats were randomized equally into four groups: control, SCI group, fracture group, and fracture/SCI group. Rats were sacrificed at 7, 14, 21, and 28 days post-fracture/SCI. Serum leptin was detected using radioimmunoassay at 1, 7, 14, 21, and 28 days, and callus formation was measured radiologically at 14, 21, and 28 days. Callus leptin was analyzed by means of immunohistochemistry.

RESULTS

Serum leptin in the fracture group, SCI group, and combined fracture/SCI group were all significantly increased compared to control group at the 1, 7, 14, and 2-day time points (P < 0.05). Serum leptin in the combined fracture/SCI group was significantly higher than in the fracture group at 7, 14, and 21 days (P < 0.05), and higher than in SCI groups at 14 and 21days after operation (P < 0.05). The percentage of leptin-positive cells in the fracture/SCI callus, and callus volume was significantly higher than in the fracture-only group (P < 0.001).

CONCLUSIONS

Overall, elevated leptin expression was demonstrated within healing bone especially in the 21 days of a rat model combining fracture and SCI. A close association exists between leptin levels and the degree of callus formation in fractures.

Neutralization of interleukin-1β reduces cerebral edema and tissue loss and improves late cognitive outcome following traumatic brain injury in mice

Increasing evidence suggests that interleukin-1β (IL-1β) is a key mediator of the inflammatory response following traumatic brain injury (TBI). Recently, we showed that intracerebroventricular administration of an IL-1β-neutralizing antibody was neuroprotective following TBI in mice. In the present study, an anti-IL-1β antibody or control antibody was administered intraperitoneally following controlled cortical injury (CCI) TBI or sham injury in 105 mice and we extended our histological, immunological and behavioral analysis. First, we demonstrated that the treatment antibody reached target brain regions of brain-injured animals in high concentrations (> 11 nm) remaining up to 8 days post-TBI. At 48 h post-injury, the anti-IL-1β treatment attenuated the TBI-induced hemispheric edema (P < 0.05) but not the memory deficits evaluated using the Morris water maze (MWM). Neutralization of IL-1β did not influence the TBI-induced increases (P < 0.05) in the gene expression of the Ccl3 and Ccr2 chemokines, IL-6 or Gfap. Up to 20 days post-injury, neutralization of IL-1β was associated with improved visuospatial learning in the MWM, reduced loss of hemispheric tissue and attenuation of the microglial activation caused by TBI (P < 0.05). Motor function using the rotarod and cylinder tests was not affected by the anti-IL-1β treatment. Our results suggest an important negative role for IL-1β in TBI. The improved histological and behavioral outcome following anti-IL-1β treatment also implies that further exploration of IL-1β-neutralizing compounds as a treatment option for TBI patients is warranted.

X-irradiation reduces the proliferation of astrocytes by cell cycle arrest

Reactive astrogliosis is one of the key components of the cellular response to CNS injury and is considered a major impediment to axonal regeneration. Our previous study demonstrated that cell cycle inhibition treatment can reduce astrocyte activation and proliferation in vivo. In this study, we examined whether reactive astrogliosis can be suppressed by X-irradiation in vitro by modulating cell cycle progression. X-irradiation with low dose (4 Gy) suppressed astrocyte proliferation as demonstrated by immunofluorescence staining with BrdU and Ki67 in monolayer astrocyte cultures and those in scratch-wound model. The proportions of BrdU (+) and Ki67 (+) cells at 12, 24, and 48 h after 4 Gy irradiation were significantly lower than those in control group. FACS analysis of monolayer astrocyte cultures showed that X-irradiation decreased the proportion of astrocytes in S phase at 12 and 24h after irradiation with a dose-dependent manner. Furthermore, after X-irradiation, higher levels of p53 were observed by western blot as compared to control astrocyte cultures. Taken together, these data support that X-irradiation can decrease astrogliosis via arresting the cell cycle progression, which might constitute an effective therapeutic intervention in diseases characterized by excessive proliferation of glial cells.

Minozac treatment prevents increased seizure susceptibility in a mouse "two-hit" model of closed skull traumatic brain injury and electroconvulsive shock-induced seizures

The mechanisms linking traumatic brain injury (TBI) to post-traumatic epilepsy (PTE) are not known and no therapy for prevention of PTE is available. We used a mouse closed-skull midline impact model to test the hypotheses that TBI increases susceptibility to seizures in a "two-hit" injury model, and that suppression of cytokine upregulation after the first hit will attenuate the increased susceptibility to the second neurological insult. Adult male CD-1 mice underwent midline closed skull pneumatic impact. At 3 and 6 h after impact or sham procedure, the mice were injected IP with either Minozac (Mzc), a suppressor of proinflammatory cytokine upregulation, or vehicle (saline). On day 7 after sham operation or TBI, seizures were induced using electroconvulsive shock (ECS), and susceptibility to seizures was measured by the current required for seizure induction. Activation of glia, neuronal injury, and metallothionein-immunoreactive cells were quantified in the hippocampus by immunohistochemical methods. Neurobehavioral function over 14-day recovery was quantified using the Barnes maze. Following TBI there was a significant increase in susceptibility to seizures induced by ECS, and this susceptibility was prevented by suppression of cytokine upregulation with Mzc. Astrocyte activation, metallothionein expression, and neurobehavioral impairment were also increased in the two-hit group subjected to combined TBI and ECS. These enhanced responses in the two-hit group were also prevented by suppression of proinflammatory cytokine upregulation with Mzc. These data implicate glial activation in the mechanisms of epileptogenesis after TBI, and identify a potential therapeutic approach to attenuate the delayed neurological sequelae of TBI.

The cytokine response to human traumatic brain injury: temporal profiles and evidence for cerebral parenchymal production

The role of neuroinflammation is increasingly being recognised in a diverse range of cerebral pathologies, including traumatic brain injury (TBI). We used cerebral microdialysis and paired arterial and jugular bulb plasma sampling to characterise the production of 42 cytokines after severe TBI in 12 patients over 5 days. We compared two microdialysis perfusates in six patients: central nervous system perfusion fluid and 3.5% human albumin solution (HAS); 3.5% HAS has a superior fluid recovery (95.8 versus 83.3%), a superior relative recovery in 18 of 42 cytokines (versus 8 of 42), and a qualitatively superior recovery profile. All 42 cytokines were recovered from the human brain. Sixteen cytokines showed a stereotyped temporal peak, at least twice the median value for that cytokine over the monitoring period; day 1: tumour necrosis factor, interleukin (IL)7, IL8, macrophage inflammatory protein (MIP)1α, soluble CD40 ligand, GRO, IL1β, platelet derived growth factor (PDGF)-AA, MIP1β, RANTES; day 2: IL1 receptor antagonist (ra). IL6, granulocyte-colony stimulating factor (G-CSF), chemokine CXC motif ligand 10 (IP10); days 4 to 5: IL12p70, IL10. Brain extracellular fluid concentrations were significantly higher than plasma concentrations for 19 cytokines: basic fibroblast growth factor (FGF2), G-CSF, IL1α, IL1β, IL1ra, IL3, IL6, IL8, IL10, IL12p40, IL12p70, IP10, monocyte chemotactic protein (MCP)1, MCP3, MIP1α, MIP1β, PDGF-AA, transforming growth factor (TGF)α and vascular endothelial growth factor. No clear arterio-jugular venous gradients were apparent. These data provide evidence for the cerebral production of these cytokines and show a stereotyped temporal pattern after TBI.

In situ detection of inflammatory mediators in post mortem human brain tissue after traumatic injury

Little is known about the molecular events following severe traumatic brain injury (TBI) in humans and to date there are no efficient therapies for the treatment of patients. In this study, the first of its kind in human tissue, a total of 21 post mortem trauma brain samples were analyzed. The inflammatory response within the brain tissue was explored by measuring the expression of various inflammatory cytokines at the mRNA and protein levels. These mediators were interleukin (IL)-1beta, IL-2, IL-4, IL-6, IL-8, IL-10, tumor necrosis factor (TNF)-alpha, interferon (IFN)-gamma, and granulocyte-macrophage colony-stimulating factor (GM-CSF). This study shows for the first time in human brain tissue that 1) pro-inflammatory mediator protein levels are significantly increased in situ following acute brain injury while anti-inflammatory cytokines protein levels remain unchanged; 2) the cerebral inflammatory response begins within minutes of acute TBI, much earlier than previously thought; 3) IL-6, IL-8, TNF-alpha, and IL-1beta mRNA levels are significantly increased following injury; 4) the rise in cytokine protein level coincides with increased levels of their mRNAs suggesting that traumatic injury elicits an immediate cerebral inflammatory response. Altogether these data confirm and extend previous observations on the release of cytokines in the cerebrospinal fluid of severe TBI patients. Finally, this study highlights the need to characterize the cell source of cytokines and elucidate their mode of action.

Elevated leptin expression in a rat model of fracture and traumatic brain injury

A few studies have reported a relationship between leptin induced by brain injury and healing of bone tissue. Our objective was to measure serum and callus leptin expression within the setting of fracture and traumatic brain injury (TBI). Sixty-four male Sprague-Dawley rats were randomised equally into four groups: control, TBI group, fracture group and fracture/TBI group. Rats were sacrificed at 2, 4, 8 and 12 weeks after fracture/TBI. Serum leptin was detected using radio-immunoassay, and callus formation was measured radiologically. Callus leptin was analysed with immunohistochemistry. Serum leptin was significantly increased in the fracture, TBI and combined fracture/TBI groups compared with the control group at 2 weeks (P &lt; 0.05). Serum leptin was significantly higher in the combined fracture/TBI group than in the fracture and TBI groups at 4 and 8 weeks (P &lt; 0.05). The percentage of leptin-positive cells in the callus and callus volume were significantly higher in the fracture/TBI group than in the fracture-only group (P &lt; 0.001). Thus, we demonstrated elevated leptin expression within healing bone, particularly in the first 8 weeks of a rat model combining fracture and TBI. A close association exists between leptin levels and the degree of callus formation in fractures.

What has inflammation to do with traumatic brain injury?

INTRODUCTION

Inflammation is an stereotypical response to tissue damage and has been extensively documented in experimental and clinical traumatic brain injury (TBI), including children.

DISCUSSION

The initiation and orchestration of inflammation in TBI, as in other tissues, is complex and multifactorial encompassing pro- and anti-inflammatory cytokines, chemokines, adhesion molecules, complement factors, reactive oxygen and nitrogen species, and other undefined factors. It is evident that inflammation can have both beneficial and detrimental effects in TBI, but the mechanisms underlying this dichotomy are mostly unknown. Modification of the inflammatory response may be neuroprotective. Monitoring inflammation is now possible with techniques such as microdialysis; however, the prognostic value of measuring inflammatory mediators in TBI is still unclear with conflicting reports. Except for corticosteroids, no anti-inflammatory agents have been tested in TBI, and the negative results with these may have been flawed by their multiple side effects. Clinical trials with anti-inflammatory agents that target multiple or central and downstream pathways are warranted in adult and pediatric TBI. This review examines the mechanisms of inflammation after TBI, monitoring, and possible routes of intervention.

In vivo electrochemical characterization and inflammatory response of multiwalled carbon nanotube-based electrodes in rat hippocampus

Stimulating neural electrodes are required to deliver charge to an environment that presents itself as hostile. The electrodes need to maintain their electrical characteristics (charge and impedance) in vivo for a proper functioning of neural prostheses. Here we design implantable multi-walled carbon nanotubes coating for stainless steel substrate electrodes, targeted at wide frequency stimulation of deep brain structures. In well-controlled, low-frequency stimulation acute experiments, we show that multi-walled carbon nanotube electrodes maintain their charge storage capacity (CSC) and impedance in vivo. The difference in average CSCs (n = 4) between the in vivo (1.111 mC cm(-2)) and in vitro (1.008 mC cm(-2)) model was statistically insignificant (p > 0.05 or P-value = 0.715, two tailed). We also report on the transcription levels of the pro-inflammatory cytokine IL-1beta and TLR2 receptor as an immediate response to low-frequency stimulation using RT-PCR. We show here that the IL-1beta is part of the inflammatory response to low-frequency stimulation, but TLR2 is not significantly increased in stimulated tissue when compared to controls. The early stages of neuroinflammation due to mechanical and electrical trauma induced by implants can be better understood by detection of pro-inflammatory molecules rather than by histological studies. Tracking of such quantitative response profits from better analysis methods over several temporal and spatial scales. Our results concerning the evaluation of such inflammatory molecules revealed that transcripts for the cytokine IL-1beta are upregulated in response to low-frequency stimulation, whereas no modulation was observed for TLR2. This result indicates that the early response of the brain to mechanical trauma and low-frequency stimulation activates the IL-1beta signaling cascade but not that of TLR2.

Therapeutic neutralization of the NLRP1 inflammasome reduces the innate immune response and improves histopathology after traumatic brain injury

Traumatic brain injury elicits acute inflammation that in turn exacerbates primary brain damage. A crucial part of innate immunity in the immune privileged central nervous system involves production of proinflammatory cytokines mediated by inflammasome signaling. Here, we show that the nucleotide-binding, leucine-rich repeat pyrin domain containing protein 1 (NLRP1) inflammasome consisting of NLRP1, caspase-1, caspase-11, apoptosis-associated speck-like protein containing a caspase recruitment domain (ASC), the X-linked inhibitor of apoptosis protein, and pannexin 1 is expressed in neurons of the cerebral cortex. Moderate parasagittal fluid-percussion injury (FPI) induced processing of interleukin-1beta, activation of caspase-1, cleavage of X-linked inhibitor of apoptosis protein, and promoted assembly of the NLRP1 inflammasome complex. Anti-ASC neutralizing antibodies administered immediately after fluid-percussion injury to injured rats reduced caspase-1 activation, X-linked inhibitor of apoptosis protein cleavage, and processing of interleukin-1beta, resulting in a significant decrease in contusion volume. These studies show that the NLRP1 inflammasome constitutes an important component of the innate central nervous system inflammatory response after traumatic brain injury and may be a novel therapeutic target for reducing the damaging effects of posttraumatic brain inflammation.

Simvastatin attenuates microglial cells and astrocyte activation and decreases interleukin-1beta level after traumatic brain injury

OBJECTIVE

Our previous studies demonstrated that simvastatin promotes neurological functional recovery after traumatic brain injury (TBI) in rat; however, the underlying mechanisms remain poorly understood. The purpose of this study was to investigate the anti-inflammatory effect of simvastatin by measuring the level of cytokines and activation of glial cells.

METHODS

Controlled cortical impact injury was performed in adult male Wistar rats. The rats were randomly divided into 3 groups: sham, saline control group, and simvastatin treatment group. Simvastatin was administered orally starting at day 1 after TBI until animals were killed at days 1, 3, 7, 14, and 35 after treatment. Functional outcome was measured using modified neurological severity scores. Enzyme-linked immunosorbent assay and immunohistochemical staining were used to measure the expression of interleukin (IL)-1beta, IL-6, and tumor necrosis factor-alpha and to identify activated microglial cells and astrocytes.

RESULTS

At days 1 and 3 after simvastatin or saline treatment, cytokine levels in the lesion boundary zone were significantly higher in the simvastatin- and saline-treated rats compared with the sham group, peaking at day 3. Simvastatin only reduced the level of IL-1beta but not IL-6 and tumor necrosis factor-alpha, compared with the saline group. Also, simvastatin significantly reduced the number of activated microglial cells and astrocytes compared with the saline control animals. There was also a trend toward improvement of modified neurological severity score, reaching statistical significance (P = 0.003) toward the end of the trial.

CONCLUSION

Our data demonstrate that TBI causes inflammatory reaction, including increased levels of IL-1beta, IL-6, and tumor necrosis factor-alpha, as well as activated microglial cells. Simvastatin selectively reduces IL-1beta expression and inhibits the activation of microglial cells and astrocytes after TBI, which might be one of the mechanisms underlying the therapeutic benefits of simvastatin treatment of TBI.

Cerebral microdialysis of interleukin (IL)-1beta and IL-6: extraction efficiency and production in the acute phase after severe traumatic brain injury in rats

BACKGROUND

As a research tool, cerebral microdialysis might be a useful technique in monitoring the release of cytokines into the extracellular fluid (ECF) following traumatic brain injury (TBI). We established extraction efficiency of Interleukin(IL)-1ss and Interleukin(IL)-6 by an in vitro microdialysis-perfusion system, followed by in vivo determination of the temporal profile of extracellular fluid cytokines after severe TBI in rats.

MATERIALS AND METHODS

In vitro experiments using a polyether sulfon (PES) microdialysis probe especially developed for recovery of macromolecules such as cytokines, were carried out to establish the extraction efficiency of IL-1ss and IL-6 from artificial cerebrospinal fluid (CSF) with defined IL-1ss and IL-6 concentrations. In vivo experiments in which rats were subjected to TBI or sham and microdialysis samples were collected from the parietal lobe for measurement of cytokines.

FINDINGS

The extraction efficiency was maximal 6.05% (range, 5.97-6.13%) at 0.5 microl/min(-1) and decreased at higher flow rates. Both cytokines were detectable in the dialysates. Highest IL-1ss levels were found within 200 min, highest IL-6 concentrations were detected at later intervals (200-400 min). No differences were found between the TBI and control groups.

CONCLUSIONS

Cerebral microdialysis allows measurement of cytokine secretion in the ECF of brain tissue in rats.

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.