Neutrophils do not mediate blood-brain barrier permeability early after controlled cortical impact in rats

Elucidating the neuroimmunology of traumatic brain injury: methodological approaches to unravel intercellular communication and function

The neuroimmunology of traumatic brain injury (TBI) has recently gained recognition as a crucial element in the secondary pathophysiological consequences that occur following neurotrauma. Both immune cells residing within the central nervous system (CNS) and those migrating from the periphery play significant roles in the development of secondary brain injury. However, the precise mechanisms governing communication between innate and adaptive immune cells remain incompletely understood, partly due to a limited utilization of relevant experimental models and techniques. Therefore, in this discussion, we outline current methodologies that can aid in the exploration of TBI neuroimmunology, with a particular emphasis on the interactions between resident neuroglial cells and recruited lymphocytes. These techniques encompass adoptive cell transfer, intra-CNS injection(s), selective cellular depletion, genetic manipulation, molecular neuroimaging, as well as in vitro co-culture systems and the utilization of organoid models. By incorporating key elements of both innate and adaptive immunity, these methods facilitate the examination of clinically relevant interactions. In addition to these preclinical approaches, we also detail an emerging avenue of research that seeks to leverage human biofluids. This approach enables the investigation of how resident and infiltrating immune cells modulate neuroglial responses after TBI. Considering the growing significance of neuroinflammation in TBI, the introduction and application of advanced methodologies will be pivotal in advancing translational research in this field.

In-vivo time course of organ uptake and blood-brain-barrier permeation of poly(L-lactide) and poly(perfluorodecyl acrylate) nanoparticles with different surface properties in unharmed and brain-traumatized rats

Background

Traumatic brain injury (TBI) has a dramatic impact on mortality and quality of life and the development of effective treatment strategies is of great socio-economic relevance. A growing interest exists in using polymeric nanoparticles (NPs) as carriers across the blood-brain barrier (BBB) for potentially effective drugs in TBI. However, the effect of NP material and type of surfactant on their distribution within organs, the amount of the administrated dose that reaches the brain parenchyma in areas with intact and opened BBB after trauma, and a possible elicited inflammatory response are still to be clarified.

Methods

The organ distribution, BBB permeation and eventual inflammatory activation of polysorbate-80 (Tw80) and sodiumdodecylsulfate (SDS) stabilized poly(L-lactide) (PLLA) and poly(perfluorodecyl acrylate) (PFDL) nanoparticles were evaluated in rats after intravenous administration. The NP uptake into the brain was assessed under intact conditions and after controlled cortical impact (CCI).

Results

A significantly higher NP uptake at 4 and 24 h after injection was observed in the liver and spleen, followed by the brain and kidney, with minimal concentrations in the lungs and heart for all NPs. A significant increase of NP uptake at 4 and 24 h after CCI was observed within the traumatized hemisphere, especially in the perilesional area, but NPs were still found in areas away from the injury site and the contralateral hemisphere. NPs were internalized in brain capillary endothelial cells, neurons, astrocytes, and microglia. Immunohistochemical staining against GFAP, Iba1, TNFα, and IL1β demonstrated no glial activation or neuroinflammatory changes.

Conclusions

Tw80 and SDS coated biodegradable PLLA and non-biodegradable PFDL NPs reach the brain parenchyma with and without compromised BBB by TBI, even though a high amount of NPs are retained in the liver and spleen. No inflammatory reaction is elicited by these NPs within 24 h after injection. Thus, these NPs could be considered as potentially effective carriers or markers of newly developed drugs with low or even no BBB permeation.

PHLPP Inhibitor NSC74429 Is Neuroprotective in Rodent Models of Cardiac Arrest and Traumatic Brain Injury

Pleckstrin homology domain and leucine rich repeat protein phosphatase (PHLPP) knockout mice have improved outcomes after a stroke, traumatic brain injury (TBI), and decreased maladaptive vascular remodeling following vascular injury. Thus, small-molecule PHLPP inhibitors have the potential to improve neurological outcomes in a variety of conditions. There is a paucity of data on the efficacy of the known experimental PHLPP inhibitors, and not all may be suited for targeting acute brain injury. Here, we assessed several PHLPP inhibitors not previously explored for neuroprotection (NSC13378, NSC25247, and NSC74429) that had favorable predicted chemistries for targeting the central nervous system (CNS). Neuronal culture studies in staurosporine (apoptosis), glutamate (excitotoxicity), and hydrogen peroxide (necrosis/oxidative stress) revealed that NSC74429 at micromolar concentrations was the most neuroprotective. Subsequent testing in a rat model of asphyxial cardiac arrest, and in a mouse model of severe TBI, showed that serial dosing of 1 mg/kg of NSC74429 over 3 days improved hippocampal survival in both models. Taken together, NSC74429 is neuroprotective across multiple insult mechanisms. Future pharmacokinetic and pharmacodynamic (PK/PD) studies are warranted to optimize dosing, and mechanistic studies are needed to determine the percentage of neuroprotection mediated by PHLPP1/2 inhibition, or potentially from the modulation of PHLPP-independent targets.

Unveiling Leukocyte Extracellular Traps in Inflammatory Responses of the Central Nervous System

Over the past nearly two decades, increasing evidence has uncovered how immune cells can actively extrude genetic material to entrap invading pathogens or convey sterile inflammatory signals that contribute to shaping immune responses. Originally identified in neutrophils, the release of decondensed chromatin fibers decorated with antimicrobial proteins, called extracellular traps (ETs), has been recognized as a specific form of programmed inflammatory cell death, which is now known to occur in several other leukocytes. Subsequent reports have shown that self-DNA can be extruded from immune cells even in the absence of cell death phenomena. More recent data suggest that ETs formation could exacerbate neuroinflammation in several disorders of the central nervous system (CNS). This review article provides an overview of the varied types, sources, and potential functions of extracellular DNA released by immune cells. Key evidence suggesting the involvement of ETs in neurodegenerative, traumatic, autoimmune, and oncological disorders of the CNS will be discussed, outlining ongoing challenges and drawing potentially novel lines of investigation.

Localization of Multi-Lamellar Vesicle Nanoparticles to Injured Brain Tissue in a Controlled Cortical Impact Injury Model of Traumatic Brain Injury in Rodents

Severe traumatic brain injury (TBI), such as that suffered by patients with cerebral contusion, is a major cause of death and disability in young persons. Effective therapeutics to treat or mitigate the effects of severe TBI are lacking, in part because drug delivery to the injured brain remains a challenge. Promising therapeutics targeting secondary injury mechanisms may have poor pharmacokinetics/pharmacodynamics, unwanted side effects, or high hydrophobicity. To address these challenges, we have developed a multi-lamellar vesicle nanoparticle (MLV-NP) formulation with a narrow size distribution (243 nm in diameter, 0.09 polydispersity index) and the capability of encapsulating hydrophobic small molecule drugs for delivery to the injured brain. To demonstrate the utility of these particles, we produced dual-fluorescent labeled nanoparticles containing the organic dyes, coumarin 153 and rhodamine B, that were delivered intravenously to Sprague-Dawley rats and C57Bl6/J mice at 1, 1 and 4, 24, or 48 h after controlled cortical impact injury. Distribution of particles was measured at 5, 25, 48, or 49 h post-injury by fluorescence microscopy of coronal brain sections. In all cases of MLV administration, a 1.2- to 1.9-fold enhancement of ipsilateral fluorescence signal was observed compared to the contralateral cortex. Enhanced fluorescence was also observed in the injured hippocampal tissue in these animals. MLV-NPs administered at 1 h were observed intracellularly in the injured hemisphere at 48 h, suggesting the possibility of concentrated drug delivery to injured cells. These results suggest that MLV-NP delivery of therapeutic agents may be a viable strategy for treating cerebral contusion TBI.

Biomimetic Nanoparticles as a Theranostic Tool for Traumatic Brain Injury

Traumatic brain injury (TBI) triggers both central and peripheral inflammatory responses. Existing pharmacological drugs are unable to effectively and quickly target the brain inflamed regions, setting up a major roadblock towards effective brain trauma treatments. Nanoparticles (NPs) have been used in multiple diseases as drug delivery tools with remarkable success due to their rapid diffusion and specificity in the target organ. Here, leukocyte-based biomimetic NPs are fabricated as a theranostic tool to directly access inflamed regions in a TBI mouse model. This NP systemic delivery is visualized using advanced in vivo imaging techniques, including intravital microscopy and in vivo imaging system. The results demonstrate selective targeting of NPs to the injured brain and increased NPs accumulation among the peripheral organs 24 h after TBI. Interestingly, increased microglial proliferation, decreased macrophage infiltration, and reduced brain lesion following the NPs treatments compared to sham vehicle-treated mice are also found. In summary, the results suggest that NPs represent a promising future theranostic tool for TBI treatment.

Inflammation in Traumatic Brain Injury

There is an increasing evidence that inflammation contributes to clinical and functional outcomes in traumatic brain injury (TBI). Many successful target-engaging, lesion-reducing, symptom-alleviating, and function-improving interventions in animal models of TBI have failed to show efficacy in clinical trials. Timing and immunological context are paramount for the direction, quality, and intensity of immune responses to TBI and the resulting neuroanatomical, clinical, and functional course. We present components of the immune system implicated in TBI, potential immune targets, and target-engaging interventions. The main objective of our article is to point toward modifiable molecular and cellular mechanisms that may modify the outcomes in TBI, and contribute to increasing the translational value of interventions that have been identified in animal models of TBI.

The role of the immune system during regeneration of the central nervous system

Central nervous system damage in mammals leads to neuronal cell death, axonal degeneration, and formation of a glial scar resulting in functional and behavioral defects. Other vertebrates, like fish and salamanders, have retained the ability to functionally regenerate after central nervous system injury. To date research from many research organisms has led to a more concise understanding of the response of local neural cells to injury. However, it has become clear that non-neural cells of the immune system play an important role in determining the tissue response to injury. In this review we briefly consider the mammalian response to injury compared to organisms with the natural ability to regenerate. We then discuss similarities and differences in how cells of the innate and adaptive immune system respond and contribute to tissue repair in various species.

The emerging role of neutrophils as modifiers of recovery after traumatic injury to the developing brain

The innate immune response plays a critical role in traumatic brain injury (TBI), contributing to ongoing pathogenesis and worsening long-term outcomes. Here we focus on neutrophils, one of the "first responders" to TBI. These leukocytes are recruited to the injured brain where they release a host of toxic molecules including free radicals, proteases, and pro-inflammatory cytokines, all of which promote secondary tissue damage. There is mounting evidence that the developing brain is more vulnerable to injury that the adult brain. This vulnerability to greater damage from TBI is, in part, attributed to relatively low antioxidant reserves coupled with an early robust immune response. The latter is reflected in enhanced sensitivity to cytokines and a prolonged recruitment of neutrophils into both cortical and subcortical regions. This review considers the contribution of neutrophils to early secondary pathogenesis in the injured developing brain and raises the distinct possibility that these leukocytes, which exhibit phenotypic plasticity, may also be poised to support wound healing. We provide a basic review of the development, life cycle, and granular contents of neutrophils and evaluate their potential as therapeutic targets for early neuroprotection and functional recovery after injury at early age. While neutrophils have been broadly studied in neurotrauma, we are only beginning to appreciate their diverse roles in the developing brain and the extent to which their acute manipulation may result in enduring neurological recovery when TBI is superimposed upon brain development.

Quantitative and qualitative assessment of glymphatic flux using Evans blue albumin

BACKGROUND

The glymphatic system is a proposed pathway for clearance of proteins and macromolecules from brain, and disrupted glymphatic flux is implicated in neurological disease. We capitalized on colorimetric, fluorescent, and protein-binding properties of Evans blue to evaluate glymphatic flux.

NEW METHOD

Twenty-five μL of 1% Evans blue-labeled albumin (EBA) in artificial cerebrospinal fluid (aCSF) was injected into the intracisternal space of anesthetized postnatal day 17 rats. Serum was collected at various time points after injection (n = 37) and EBA was measured spectrophotometrically. In separate rats (n = 3), a cranial window was placed over the parietal cortex and EBA transit was evaluated using in vivo multiphoton microscopy. Separate rats (n = 6) were processed for immunohistochemistry to examine localization of EBA. In some rats, intracranial pressure (ICP) was increased via intracisternal injection of aCSF.

RESULTS

EBA was detected in serum as early as 30 min, was maximal at 4 h, and was undetectable at 72 h after intracisternal injection. Using intra-vital microscopy and immunohistochemistry EBA could be tracked from CSF to perivascular locations. Consistent with removal via glymphatic flux, increasing ICP to 40 mmHg accelerated transit of EBA from CSF to blood.

COMPARISON WITH EXISTING METHODS

Transit of EBA from CSF to serum could be quantified spectrophotometrically without radioactive labeling. Glymphatic flux could also be qualitatively evaluated using EBA fluorescence.

CONCLUSION

We present a novel technique for simultaneous quantitative and qualitative evaluation of glymphatic flux in rats.

Glibenclamide Produces Region-Dependent Effects on Cerebral Edema in a Combined Injury Model of Traumatic Brain Injury and Hemorrhagic Shock in Mice

Cerebral edema is critical to morbidity/mortality in traumatic brain injury (TBI) and is worsened by hypotension. Glibenclamide may reduce cerebral edema by inhibiting sulfonylurea receptor-1 (Sur1); its effect on diffuse cerebral edema exacerbated by hypotension/resuscitation is unknown. We aimed to determine if glibenclamide improves pericontusional and/or diffuse edema in controlled cortical impact (CCI) (5m/sec, 1 mm depth) plus hemorrhagic shock (HS) (35 min), and compare its effects in CCI alone. C57BL/6 mice were divided into five groups (n = 10/group): naïve, CCI+vehicle, CCI+glibenclamide, CCI+HS+vehicle, and CCI+HS+glibenclamide. Intravenous glibenclamide (10 min post-injury) was followed by a subcutaneous infusion for 24 h. Brain edema in injured and contralateral hemispheres was subsequently quantified (wet-dry weight). This protocol brain water (BW) = 80.4% vehicle vs. 78.3% naïve, p < 0.01) but was not reduced by glibenclamide (I%BW = 80.4%). Ipsilateral edema also developed in CCI alone (I%BW = 80.2% vehicle vs. 78.3% naïve, p < 0.01); again unaffected by glibenclamide (I%BW = 80.5%). Contralateral (C) %BW in CCI+HS was increased in vehicle (78.6%) versus naive (78.3%, p = 0.02) but unchanged in CCI (78.3%). At 24 h, glibenclamide treatment in CCI+HS eliminated contralateral cerebral edema (C%BW = 78.3%) with no difference versus naïve. By 72 h, contralateral cerebral edema had resolved (C%BW = 78.5 ± 0.09% vehicle vs. 78.3 ± 0.05% naïve). Glibenclamide decreased 24 h contralateral cerebral edema in CCI+HS. This beneficial effect merits additional exploration in the important setting of TBI with polytrauma, shock, and resuscitation. Contralateral edema did not develop in CCI alone. Surprisingly, 24 h of glibenclamide treatment failed to decrease ipsilateral edema in either model. Interspecies dosing differences versus prior studies may play an important role in these findings. Mechanisms underlying brain edema may differ regionally, with pericontusional/osmolar swelling refractory to glibenclamide but diffuse edema (via Sur1) from combined injury and/or resuscitation responsive to this therapy. TBI phenotype may mandate precision medicine approaches to treat brain edema.

Effects of astragalus polysaccharide on the adhesion-related immune response of endothelial cells stimulated with CSFV in vitro

Background

Astragalus polysaccharide (APS) has immunomodulatory activities on porcine peripheral blood mononuclear cells. The immunomodulatory effects of APS on porcine endothelial cells (ECs) expose to classical swine fever virus (CSFV) remain unknown.

Methods

The virus was titrated using an indirect immune biotin enzyme standard method to confirm that porcine ECs were susceptible to CSFV infection and to determine the TCID50 of CSFV (C-strain). Porcine ECs were cultured with CSFV in the presence of APS. Relative quantitative PCR was used to assess the mRNA expression of factors that influence EC adhesion and immunity.

Results

The expression of adhesion factors mRNA increased following stimulation with CSFV; this effect was inhibited by pre-exposing the cells to APS. In addition, the expression of growth factors and some immune factors increased after infection with CSFV; this increase in tissue factor (TF), transforming growth factor (TGF-β), and interleukin-8 (IL-8) could be inhibited by the addition of APS. The immune response mediated by Toll-like receptor 4 (TLR4) in ECs may be unregulated by CSFV as it was also inhibited by pre-treatment with APS.

Discussion

The addition of APS to the culture can obviously regulate the expression of molecules related to the adhesion, growth, and immune response of ECs, as well as the production of cytokines. Therefore, it may have the potential to be an effective component in vaccines against CSFV.

Neuroimmunology of Traumatic Brain Injury: Time for a Paradigm Shift

Traumatic brain injury (TBI) is a leading cause of morbidity and disability, with a considerable socioeconomic burden. Heterogeneity of pathoanatomical subtypes and diversity in the pathogenesis and extent of injury contribute to differences in the course and outcome of TBI. Following the primary injury, extensive and lasting damage is sustained through a complex cascade of events referred to as "secondary injury." Neuroinflammation is proposed as an important manipulable aspect of secondary injury in animal and human studies. Because neuroinflammation can be detrimental or beneficial, before developing immunomodulatory therapies, it is necessary to better understand the timing and complexity of the immune responses that follow TBI. With a rapidly increasing body of literature, there is a need for a clear summary of TBI neuroimmunology. This review presents our current understanding of the immune response to TBI in a chronological and compartment-based manner, highlighting early changes in gene expression and initial signaling pathways that lead to activation of innate and adaptive immunity. Based on recent advances in our understanding of innate immune cell activation, we propose a new paradigm to study innate immune cells following TBI that moves away from the existing M1/M2 classification of activation states toward a stimulus- and disease-specific understanding of polarization state based on transcriptomic and proteomic profiling.

Emerging Roles for the Immune System in Traumatic Brain Injury

Traumatic brain injury (TBI) affects an ever-growing population of all ages with long-term consequences on health and cognition. Many of the issues that TBI patients face are thought to be mediated by the immune system. Primary brain damage that occurs at the time of injury can be exacerbated and prolonged for months or even years by chronic inflammatory processes, which can ultimately lead to secondary cell death, neurodegeneration, and long-lasting neurological impairment. Researchers have turned to rodent models of TBI in order to understand how inflammatory cells and immunological signaling regulate the post-injury response and recovery mechanisms. In addition, the development of numerous methods to manipulate genes involved in inflammation has recently expanded the possibilities of investigating the immune response in TBI models. As results from these studies accumulate, scientists have started to link cells and signaling pathways to pro- and anti-inflammatory processes that may contribute beneficial or detrimental effects to the injured brain. Moreover, emerging data suggest that targeting aspects of the immune response may offer promising strategies to treat TBI. This review will cover insights gained from studies that approach TBI research from an immunological perspective and will summarize our current understanding of the involvement of specific immune cell types and cytokines in TBI pathogenesis.

Insight into Pre-Clinical Models of Traumatic Brain Injury Using Circulating Brain Damage Biomarkers: Operation Brain Trauma Therapy

Operation Brain Trauma Therapy (OBTT) is a multicenter pre-clinical drug screening consortium testing promising therapies for traumatic brain injury (TBI) in three well-established models of TBI in rats--namely, parasagittal fluid percussion injury (FPI), controlled cortical impact (CCI), and penetrating ballistic-like brain injury (PBBI). This article presents unique characterization of these models using histological and behavioral outcomes and novel candidate biomarkers from the first three treatment trials of OBTT. Adult rats underwent CCI, FPI, or PBBI and were treated with vehicle (VEH). Shams underwent all manipulations except trauma. The glial marker glial fibrillary acidic protein (GFAP) and the neuronal marker ubiquitin C-terminal hydrolase (UCH-L1) were measured by enzyme-linked immunosorbent assay in blood at 4 and 24 h, and their delta 24-4 h was calculated for each marker. Comparing sham groups across experiments, no differences were found in the same model. Similarly, comparing TBI + VEH groups across experiments, no differences were found in the same model. GFAP was acutely increased in injured rats in each model, with significant differences in levels and temporal patterns mirrored by significant differences in delta 24-4 h GFAP levels and neuropathological and behavioral outcomes. Circulating GFAP levels at 4 and 24 h were powerful predictors of 21 day contusion volume and tissue loss. UCH-L1 showed similar tendencies, albeit with less robust differences between sham and injury groups. Significant differences were also found comparing shams across the models. Our findings (1) demonstrate that TBI models display specific biomarker profiles, functional deficits, and pathological consequence; (2) support the concept that there are different cellular, molecular, and pathophysiological responses to TBI in each model; and (3) advance our understanding of TBI, providing opportunities for a successful translation and holding promise for theranostic applications. Based on our findings, additional studies in pre-clinical models should pursue assessment of GFAP as a surrogate histological and/or theranostic end-point.

Emerging Roles for the Immune System in Traumatic Brain Injury

Traumatic brain injury (TBI) affects an ever-growing population of all ages with long-term consequences on health and cognition. Many of the issues that TBI patients face are thought to be mediated by the immune system. Primary brain damage that occurs at the time of injury can be exacerbated and prolonged for months or even years by chronic inflammatory processes, which can ultimately lead to secondary cell death, neurodegeneration, and long-lasting neurological impairment. Researchers have turned to rodent models of TBI in order to understand how inflammatory cells and immunological signaling regulate the post-injury response and recovery mechanisms. In addition, the development of numerous methods to manipulate genes involved in inflammation has recently expanded the possibilities of investigating the immune response in TBI models. As results from these studies accumulate, scientists have started to link cells and signaling pathways to pro- and anti-inflammatory processes that may contribute beneficial or detrimental effects to the injured brain. Moreover, emerging data suggest that targeting aspects of the immune response may offer promising strategies to treat TBI. This review will cover insights gained from studies that approach TBI research from an immunological perspective and will summarize our current understanding of the involvement of specific immune cell types and cytokines in TBI pathogenesis.

Resuscitation with Valproic Acid Alters Inflammatory Genes in a Porcine Model of Combined Traumatic Brain Injury and Hemorrhagic Shock

Traumatic brain injury and hemorrhagic shock (TBI+HS) elicit a complex inflammatory response that contributes to secondary brain injury. There is currently no proven pharmacologic treatment for TBI+HS, but modulation of the epigenome has been shown to be a promising strategy. The aim of this study was to investigate whether valproic acid (VPA), a histone deacetylase inhibitor, modulates the expression of cerebral inflammatory gene profiles in a large animal model of TBI+HS. Ten Yorkshire swine were subjected to computer-controlled TBI+HS (40% blood volume). After 2 h of shock, animals were resuscitated with Hextend (HEX) or HEX+VPA (300 mg/kg, n = 5/group). Six hours after resuscitation, brains were harvested, RNA was isolated, and gene expression profiles were measured using a porcine microarray. Ingenuity Pathway Analysis® (IPA), gene ontology (GO), Parametric Gene Set Enrichment Analysis (PGSEA), and DAVID (Database for Annotation, Visualization, and Integrated Discovery) were used for pathway analysis. Key microarray findings were verified using real-time polymerase chain reaction (PCR). IPA analysis revealed that VPA significantly down-regulated the complement system (p < 0.001), natural killer cell communication (p < 0.001), and dendritic cell maturation (p < 0.001). DAVID analysis indicated that a cluster of inflammatory pathways held the highest rank and gene enrichment score. Real-time PCR data confirmed that VPA significantly down-expressed genes that ultimately regulate nuclear factor-kB (NF-kB)-mediated production of cytokines, such as TYROBP, TREM2, CCR1, and IL-1β. This high-throughput analysis of cerebral gene expression shows that addition of VPA to the resuscitation protocol significantly modulates the expression of inflammatory pathways in a clinically realistic model of TBI+HS.

Markers for blood-brain barrier integrity: how appropriate is Evans blue in the twenty-first century and what are the alternatives?

In recent years there has been a resurgence of interest in brain barriers and various roles their intrinsic mechanisms may play in neurological disorders. Such studies require suitable models and markers to demonstrate integrity and functional changes at the interfaces between blood, brain, and cerebrospinal fluid. Studies of brain barrier mechanisms and measurements of plasma volume using dyes have a long-standing history, dating back to the late nineteenth-century. Their use in blood-brain barrier studies continues in spite of their known serious limitations in in vivo applications. These were well known when first introduced, but seem to have been forgotten since. Understanding these limitations is important because Evans blue is still the most commonly used marker of brain barrier integrity and those using it seem oblivious to problems arising from its in vivo application. The introduction of HRP in the mid twentieth-century was an important advance because its reaction product can be visualized at the electron microscopical level, but it also has limitations. Advantages and disadvantages of these markers will be discussed together with a critical evaluation of alternative approaches. There is no single marker suitable for all purposes. A combination of different sized, visualizable dextrans and radiolabeled molecules currently seems to be the most appropriate approach for qualitative and quantitative assessment of barrier integrity.

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.

Contributions of the immune system to the pathophysiology of traumatic brain injury - evidence by intravital microscopy

Traumatic brain injury (TBI) results in immediate brain damage that is caused by the mechanical impact and is non-reversible. This initiates a cascade of delayed processes which cause additional—secondary—brain damage. Among these secondary mechanisms, the inflammatory response is believed to play an important role, mediating actions that can have both protective and detrimental effects on the progression of secondary brain damage. Histological data generated extensive information; however, this is only a snapshot of processes that are, in fact, very dynamic. In contrast, in vivo microscopy provides detailed insight into the temporal and spatial patterns of cellular dynamics. In this review, we aim to summarize data which was generated by in vivo microscopy, specifically investigating the immune response following brain trauma, and its potential effects on secondary brain damage.

Blood-brain barrier pathophysiology in traumatic brain injury

The blood-brain barrier (BBB) is formed by tightly connected cerebrovascular endothelial cells, but its normal function also depends on paracrine interactions between the brain endothelium and closely located glia. There is a growing consensus that brain injury, whether it is ischemic, hemorrhagic, or traumatic, leads to dysfunction of the BBB. Changes in BBB function observed after injury are thought to contribute to the loss of neural tissue and to affect the response to neuroprotective drugs. New discoveries suggest that considering the entire gliovascular unit, rather than the BBB alone, will expand our understanding of the cellular and molecular responses to traumatic brain injury (TBI). This review will address the BBB breakdown in TBI, the role of blood-borne factors in affecting the function of the gliovascular unit, changes in BBB permeability and post-traumatic edema formation, and the major pathophysiological factors associated with TBI that may contribute to post-traumatic dysfunction of the BBB. The key role of neuroinflammation and the possible effect of injury on transport mechanisms at the BBB will also be described. Finally, the potential role of the BBB as a target for therapeutic intervention through restoration of normal BBB function after injury and/or by harnessing the cerebrovascular endothelium to produce neurotrophic growth factors will be discussed.

Selectins and their ligands as potential immunotherapeutic targets in neurological diseases

Selectins are a family of adhesion receptors that bind to highly glycosylated molecules expressed on the surface of leukocytes and endothelial cells. The interactions between selectins and their ligands control tethering and rolling of leukocytes on the vascular wall during the process of leukocyte migration into the tissues under physiological and pathological conditions. In recent years, it has been shown that leukocyte recruitment in the CNS plays a pivotal role in diseases such as multiple sclerosis, ischemic stroke, epilepsy and traumatic brain injury. In this review, we discuss the role of selectins in leukocyte–endothelial interactions in the pathogenesis of neurological diseases, highlighting new findings suggesting that selectins and their ligands may represent novel potential therapeutic targets for the treatment of CNS diseases.

In vivo temporal and spatial profile of leukocyte adhesion and migration after experimental traumatic brain injury in mice

Background

Leukocytes are believed to be involved in delayed cell death following traumatic brain injury (TBI). However, data demonstrating that blood-borne inflammatory cells are present in the injured brain prior to the onset of secondary brain damage have been inconclusive. We therefore investigated both the interaction between leukocytes and the cerebrovascular endothelium using in vivo imaging and the accumulation of leukocytes in the penumbra following experimentally induced TBI.

Methods

Experimental TBI was induced in C57/Bl6 mice (n = 42) using the controlled cortical impact (CCI) injury model, and leukocyte-endothelium interactions (LEI) were quantified using both intravital fluorescence microscopy (IVM) of superficial vessels and 2-photon microscopy of cortical vessels for up to 14 h post-CCI. In a separate experimental group, leukocyte accumulation and secondary lesion expansion were analyzed in mice that were sacrificed 15 min, 2, 6, 12, 24, or 48 h after CCI (n = 48). Finally, leukocyte adhesion was blocked with anti-CD18 antibodies, and the effects on LEI and secondary lesion expansion were determined 16 (n = 12) and 24 h (n = 21), respectively, following TBI.

Results

One hour after TBI leukocytes and leukocyte-platelet aggregates started to roll on the endothelium of pial venules, whereas no significant LEI were observed in pial arterioles or in sham-operated mice. With a delay of >4 h, leukocytes and aggregates did also firmly adhere to the venular endothelium. In deep cortical vessels (250 μm) LEIs were much less pronounced. Transmigration of leukocytes into the brain parenchyma only became significant after the tissue became necrotic. Treatment with anti-CD18 antibodies reduced adhesion by 65%; however, this treatment had no effect on secondary lesion expansion.

Conclusions

LEI occurred primarily in pial venules, whereas little or no LEI occurred in arterioles or deep cortical vessels. Inhibiting LEI did not affect secondary lesion expansion. Importantly, the majority of migrating leukocytes entered the injured brain parenchyma only after the tissue became necrotic. Our results therefore suggest that neither intravascular leukocyte adhesion nor the migration of leukocytes into cerebral tissue play a significant role in the development of secondary lesion expansion following TBI.

Neuro-glial and systemic mechanisms of pathological responses in rat models of primary blast overpressure compared to "composite" blast

A number of experimental models of blast brain injury have been implemented in rodents and larger animals. However, the variety of blast sources and the complexity of blast wave biophysics have made data on injury mechanisms and biomarkers difficult to analyze and compare. Recently, we showed the importance of rat position toward blast generated by an external shock tube. In this study, we further characterized blast producing moderate traumatic brain injury and defined "composite" blast and primary blast exposure set-ups. Schlieren optics visualized interaction between the head and a shock wave generated by external shock tube, revealing strong head acceleration upon positioning the rat on-axis with the shock tube (composite blast), but negligible skull movement upon peak overpressure exposure off-axis (primary blast). Brain injury signatures of a primary blast hitting the frontal head were assessed and compared to damage produced by composite blast. Low to negligible levels of neurodegeneration were found following primary blast compared to composite blast by silver staining. However, persistent gliosis in hippocampus and accumulation of GFAP/CNPase in circulation was detected after both primary and composite blast. Also, markers of vascular/endothelial inflammation integrin alpha/beta, soluble intercellular adhesion molecule-1, and L-selectin along with neurotrophic factor nerve growth factor-beta were increased in serum within 6 h post-blasts and persisted for 7 days thereafter. In contrast, systemic IL-1, IL-10, fractalkine, neuroendocrine peptide Orexin A, and VEGF receptor Neuropilin-2 (NRP-2) were raised predominantly after primary blast exposure. In conclusion, biomarkers of major pathological pathways were elevated at all blast set-ups. The most significant and persistent changes in neuro-glial markers were found after composite blast, while primary blast instigated prominent systemic cytokine/chemokine, Orexin A, and Neuropilin-2 release, particularly when primary blast impacted rats with unprotected body.

Neutrophil depletion reduces edema formation and tissue loss following traumatic brain injury in mice

Background

Brain edema as a result of secondary injury following traumatic brain injury (TBI) is a major clinical concern. Neutrophils are known to cause increased vascular permeability leading to edema formation in peripheral tissue, but their role in the pathology following TBI remains unclear.

Methods

In this study we used controlled cortical impact (CCI) as a model for TBI and investigated the role of neutrophils in the response to injury. The outcome of mice that were depleted of neutrophils using an anti-Gr-1 antibody was compared to that in mice with intact neutrophil count. The effect of neutrophil depletion on blood-brain barrier function was assessed by Evan's blue dye extravasation, and analysis of brain water content was used as a measurement of brain edema formation (24 and 48 hours after CCI). Lesion volume was measured 7 and 14 days after CCI. Immunohistochemistry was used to assess cell death, using a marker for cleaved caspase-3 at 24 hours after injury, and microglial/macrophage activation 7 days after CCI. Data were analyzed using Mann-Whitney test for non-parametric data.

Results

Neutrophil depletion did not significantly affect Evan's blue extravasation at any time-point after CCI. However, neutrophil-depleted mice exhibited a decreased water content both at 24 and 48 hours after CCI indicating reduced edema formation. Furthermore, brain tissue loss was attenuated in neutropenic mice at 7 and 14 days after injury. Additionally, these mice had a significantly reduced number of activated microglia/macrophages 7 days after CCI, and of cleaved caspase-3 positive cells 24 h after injury.

Conclusion

Our results suggest that neutrophils are involved in the edema formation, but not the extravasation of large proteins, as well as contributing to cell death and tissue loss following TBI in mice.

Severity profile of penetrating ballistic-like brain injury on neurofunctional outcome, blood-brain barrier permeability, and brain edema formation

This study evaluated the injury severity profile of unilateral, frontal penetrating ballistic-like brain injury (PBBI) on neurofunctional outcome, blood-brain barrier (BBB) permeability, and brain edema formation. The degree of injury severity was determined by the delivery of a water-pressure pulse designed to produce a temporary cavity by rapid (<40 ms) expansion of the probe's elastic balloon calibrated to equal 5%, 10%, 12.5%, or 15% of total rat brain volume (control groups consisted of sham surgery or insertion of the probe only). Neurofunctional assessments revealed motor and cognitive deficits related to the degree of injury severity, with the most clear-cut profile of PBBI injury severity depicted by the Morris water maze (MWM) results. A biphasic pattern of BBB leakage was detected in the injured hemisphere at all injury severity levels at 4 h post-injury, and again at 48-72 h post-injury, which remained evident out to 7 days post-PBBI in the 10% and 12.5% PBBI groups. Likewise, significant brain edema was detected in the injured hemisphere by 4 h post-injury and remained elevated out to 7 days post-injury in the 10% and 12.5% PBBI groups. However, following 5% PBBI, significant levels of edema were only detected from 24 h to 48h post-injury. These results identify an injury severity profile of BBB permeability, brain edema, and neurofunctional impairment that provides sensitive and clinically relevant outcome metrics for studying potential therapeutics.

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.

Associations between cerebrospinal fluid protein concentrations, serum albumin concentrations and intracranial pressure in neurotrauma and intracranial haemorrhage

Recent evidence suggests that using intravenous isotonic albumin solution for haemodynamic resuscitation in neurotrauma is associated with adverse outcomes. This study assessed the correlations between cerebrospinal fluid protein concentrations, serum albumin concentrations and intracranial pressure in a cohort of neurosurgical patients. After obtaining ethics committee approval, correlations between concomitant cerebrospinal fluid protein concentrations, serum albumin concentrations and the mean daily intracranial pressure of 63 consecutive neurosurgical patients, grouped as neurotrauma or intracranial haemorrhage, admitted between 1 January and 31 December 2007, were assessed. The mean daily intracranial pressure was significantly associated with cerebrospinal fluid protein concentrations (Spearman correlation coefficient [SCC] = 0.496, P = 0.001), white cell counts (SCC = 0.359, P = 0.001), red cell counts (SCC = 0.399, P = .0O01) and serum albumin concentrations (SCC = 0.431, P = 0.001) in patients with neurotrauma (n=23). Cerebrospinal fluid protein concentrations were also significantly associated with concomitant serum albumin concentrations (SCC = 0.393, P = 0.001) in these patients. In patients with intracranial haemorrhage (n=40), the mean daily intracranial pressure was only significantly associated with cerebrospinal fluid white cell and red cell counts but not cerebrospinal fluid protein and serum albumin concentrations. In summary, intracranial pressure is correlated with cerebrospinal fluid protein and serum albumin concentrations in patients with severe neurotrauma, and these suggest that blood-brain barrier may not be completely intact after severe neurotrauma.

Modulation of blood-brain barrier permeability by neutrophils: in vitro and in vivo studies

The blood-brain barrier (BBB) restricts solute permeability across healthy cerebral endothelial cells. However, during inflammation, permeability is increased and can lead to deleterious cerebral edema. Neutrophils are early cellular participants in acute inflammation, but their effect on BBB permeability is unclear. To study this, neutrophils were applied in a resting and activated state to in vitro and in vivo models of the BBB. In vitro, human neutrophils (5 x 10(6)/ml) were activated with tumor necrosis factor (100 U/ml) and leukotriene B(4) (10(-7) mol/l). Untreated neutrophils reduced permeability across the human brain endothelial cell line hCMEC/D3. Activated neutrophils returned permeability to baseline, an effect blocked by the reactive oxygen scavengers superoxide dismutase (10 U/ml) and catalase (1000 U/ml). In vivo, human neutrophils (2.5 x1 0(5) in 4 microl) were injected into the striatum of anesthetized juvenile Wistar rats, and BBB permeability measured 30 min later. This was compared to control injections (4 microl) of vehicle (0.9% saline) and arachidonic acid (10(-3) mol/l). The injection generated a small hematoma around the injection tract (<3 microl). Untreated neutrophils induced significantly lower permeability in their vicinity than activated neutrophils, with a trend to lowered permeability compared to the vehicle control. Neither untreated nor activated neutrophils induced permeability increases, while arachidonic acid increased permeability as a positive control. This study further delineates the effect of neutrophils on the BBB, and demonstrates that resting neutrophils induce acute reductions in permeability while activated neutrophils have a neutral effect. The in vivo model reiterates some aspects of acute intracerebral hemorrhage.

Antiinflammatory and neuroprotective actions of COX2 inhibitors in the injured brain

Overexpression of COX2 appears to be both a marker and an effector of neural damage after a variety of acquired brain injuries, and in natural or pathological aging of the brain. COX2 inhibitors may be neuroprotective in the brain by reducing prostanoid and free radical synthesis, or by directing arachidonic acid down alternate metabolic pathways. The arachidonic acid shunting hypothesis proposes that COX2 inhibitors' neuroprotective effects may be mediated by increased formation of potentially beneficial eicosanoids. Under conditions where COX2 activity is inhibited, arachidonic acid accumulates or is converted to eicosanoids via lipoxygenases and cytochrome P450 (CYP) epoxygenases. Several P450 eicosanoids have been demonstrated to have beneficial effects in the brain and/or periphery. We suspect that arachidonic acid shunting may be as important to functional recovery after brain injuries as altered prostanoid formation per se. Thus, COX2 inhibition and arachidonic acid shunting have therapeutic implications beyond the suppression of prostaglandin synthesis and free radical formation.

Selective early cardiolipin peroxidation after traumatic brain injury: an oxidative lipidomics analysis

OBJECTIVE

Enhanced lipid peroxidation is well established in traumatic brain injury. However, its molecular targets, identity of peroxidized phospholipid species, and their signaling role have not been deciphered.

METHODS

Using controlled cortical impact as a model of traumatic brain injury, we employed a newly developed oxidative lipidomics approach to qualitatively and quantitatively characterize the lipid peroxidation response.

RESULTS

Electrospray ionization and matrix-assisted laser desorption/ionization mass spectrometry analysis of rat cortical mitochondrial/synaptosomal fractions demonstrated the presence of highly oxidizable molecular species containing C(22:6) fatty acid residues in all major classes of phospholipids. However, the pattern of phospholipid oxidation at 3 hours after injury displayed a nonrandom character independent of abundance of oxidizable species and included only one mitochondria-specific phospholipid, cardiolipin (CL). This selective CL peroxidation was followed at 24 hours by peroxidation of other phospholipids, most prominently phosphatidylserine, but also phosphatidylcholine and phosphatidylethanolamine. CL oxidation preceded appearance of biomarkers of apoptosis (caspase-3 activation, terminal deoxynucleotidyltransferase-mediated dUTP nick end labeling-positivity) and oxidative stress (loss of glutathione and ascorbate).

INTERPRETATION

The temporal sequence combined with the recently demonstrated role of CL hydroperoxides (CL-OOH) in in vitro models of apoptosis suggest that CL-OOH may be both a key in vivo trigger of apoptotic cell death and a therapeutic target in experimental traumatic brain injury.

Effects of Crystalloid-Colloid Solutions on Traumatic Brain Injury

The purpose of this study was to compare the effects of crystalloid and crystalloid-colloid solutions administered at different times after isolated traumatic brain injury. Male Sprague-Dawley rats were randomized to receive one of three intravenous treatments (4 mL/kg body weight) at 10 min or 6 h after moderate traumatic brain injury. Treatments included hypertonic saline, hypertonic albumin, and normal albumin. Moderate injuries were produced using the controlled cortical impact injury model set at 2.0 mm, 4.0 m/sec, and 130 msec. Tissue damage and cerebral edema were measured to evaluate the effect of treatments for traumatic brain injury. Blood brain barrier permeability was assessed at different time points after injury to identify a mechanism for treatment effectiveness. Injury volume was the smallest for animals treated with hypertonic albumin at 6 h after injury compared to all other treatments and administration times. Ipsilateral brain water content was significantly attenuated with immediate normal saline-albumin treatment. The presence of colloid in the infusion solutions was associated with an improvement in tissue damage and edema following isolated head injury while hypertonic saline alone, when given immediately after injury, worsened tissue damage and edema. When hypertonic saline was administered at 6 h after injury, tissue damage and edema were not worsened. In conclusion, the presence of colloid in solutions used to treat traumatic brain injury and the timing of treatment have a significant impact on tissue damage and edema.

(Peri)vascular production and action of pro-inflammatory cytokines in brain pathology

In response to tissue injury or infection, the peripheral tissue macrophage induces an inflammatory response through the release of IL-1β (interleukin-1β) and TNFα (tumour necrosis factor α). These cytokines stimulate macrophages and endothelial cells to express chemokines and adhesion molecules that attract leucocytes into the peripheral site of injury or infection. The aims of the present review are to (i) discuss the relevance of brain (peri)vascular cells and compartments to bacterial meningitis, HIV-1-associated dementia, multiple sclerosis, ischaemic and traumatic brain injury, and Alzheimer's disease, and (ii) to provide an overview of the production and action of pro-inflammatory cytokines by (peri)vascular cells in these pathologies of the CNS (central nervous system). The brain (peri)vascular compartments are highly relevant to pathologies affecting the CNS, as infections are almost exclusively blood-borne. Insults disrupt blood and energy flow to neurons, and active brain-to-blood transport mechanisms, which are the bottleneck in the clearance of unwanted molecules from the brain. Perivascular macrophages are the most reactive cell type and produce IL-1β and TNFα after infection or injury to the CNS. The main cellular target for IL-1β and TNFα produced in the brain (peri)vascular compartment is the endothelium, where these cytokines induce the expression of adhesion molecules and promote leucocyte infiltration. Whether this and other effects of IL-1 and TNF in the brain (peri)vascular compartments are detrimental or beneficial in neuropathology remains to be shown and requires a clear understanding of the role of these cytokines in both damaging and repair processes in the CNS.

Hyperbaric oxygen therapy reduces neuroinflammation and expression of matrix metalloproteinase-9 in the rat model of traumatic brain injury

The acute inflammatory response plays an important role in secondary brain damage after traumatic brain injury (TBI). Neutrophils provide the main source of matrix metalloproteinases (MMPs) which also play a deleterious role in TBI. Numerous preclinical studies have suggested that hyperbaric oxygen therapy (HBOT) may by beneficial in various noncerebral and cerebral inflammatory diseases. The goal of this study was to evaluate the effects of HBOT on inflammatory infiltration and the expression of MMPs in correlation with secondary cell death in the rat model of dynamic cortical deformation (DCD). Twenty animals underwent DCD with subsequent HBOT (2.8 ATA, two sessions of 45 min each); 10 animals: DCD and normobaric oxygenation (1 ATA), 10 animals: not treated after DCD. Cell death was evaluated by TUNEL. Neutrophils were revealed by myeloperoxidase staining. Immunohistochemical staining for MMP-2 and -9 and tissue inhibitors of MMP-1 (TIMP-1) and -2 was also performed and the results were quantitatively evaluated by image analysis. In the animals treated by HBOT, a significant decrease in the number of TUNEL-positive cells and neutrophilic inflammatory infiltration was seen in comparison with nontreated animals and those treated by normobaric oxygen. The expression of MMP-9 was also significantly lower in the treated group. Staining for MMP-2 and TIMP-2 did not change significantly. Our results demonstrate that HBOT decreased the extent of secondary cell death and reactive neuroinflammation in the TBI model. The decline of MMP-9 expression after HBOT may also contribute to protection of brain tissue in the perilesional area. Further research should be centred on the evaluation of long-term functional and morphological results of HBOT.

Effect of granulocyte colony-stimulating factor on functional and histopathologic outcome after traumatic brain injury in mice

OBJECTIVE

Granulocyte colony-stimulating factor has been used to reduce the risk of sepsis in patients with traumatic brain injury. However, granulocyte colony-stimulating factor exerts potent pro- and anti-inflammatory effects that could influence secondary injury, and outcome, after traumatic brain injury. Our objective was to determine the effect of granulocyte colony-stimulating factor on histopathologic, motor, and cognitive outcome after experimental traumatic brain injury in mice.

DESIGN

Experimental study.

SETTING

Research laboratory at the Massachusetts General Hospital, Boston, MA.

SUBJECTS

Forty-eight adult male C57Bl/6 mice.

INTERVENTIONS

Mice (8 wks of age, n = 16/group) were administered granulocyte colony-stimulating factor or saline subcutaneously twice per day for 7 days after controlled cortical impact or sham injury (n = 16). Absolute neutrophil counts, motor function, Morris water maze performance, and lesion volume were determined after controlled cortical impact or sham injury.

MEASUREMENTS AND MAIN RESULTS

At the time of controlled cortical impact, body weight, brain and body temperature, and systemic absolute neutrophil counts did not differ between groups. Compared with control, systemic absolute neutrophil count was increased more than ten-fold in granulocyte colony-stimulating factor-treated mice on posttrauma days 2 and 7 (p < .05, repeated-measures analysis of variance) but did not differ between groups by day 14. There were no differences between groups in tests of motor function or histopathologic outcome. However, compared with control, mice given granulocyte colony-stimulating factor had improved Morris water maze performance after controlled cortical impact (p < .05, repeated-measures analysis of variance) but not sham injury.

CONCLUSIONS

The data suggest a small beneficial effect of granulocyte colony-stimulating factor on functional outcome after traumatic brain injury in adult mice but do not show differences in histopathology or motor outcome between treated and control groups.

Neutrophils both reduce and increase permeability in a cell culture model of the blood-brain barrier

This study was carried out to determine the effects that human neutrophils have on permeability across a model of the blood-brain barrier (BBB) formed by primary cultures of bovine brain microvessel endothelial cells (BBMEC). Transendothelial electrical resistance (TEER) was used to measure changes in permeability across BBMEC monolayers in a dual compartment system, during neutrophil interactions. When neutrophils (5 x 10(6)/ml) were applied to monolayers, TEER increased (permeability decreased). Adenosine was implicated, since the TEER increase was blocked by adenosine deaminase (1 U/ml) and the adenosine A2 receptor antagonist ZM 241385 (at 10(-6) M but not 10(-8) M, implicating A2B receptors). Oxygen free radicals were implicated as the TEER increase was blocked by combined catalase (100 U/ml) and superoxide dismutase (60 U/ml). When a gradient of the bacterial chemoattractant peptide formyl methionyl leucine phenylalanine (fMLP, 10(-7) M) was applied to neutrophils, the TEER decreased (permeability increased), concurrent with migration. When fMLP (10(-7) M) was added to the neutrophils, without migration, no change occurred. The TEER decrease was blocked by loading endothelium with the calcium buffer BAPTA (10 microM) and partially blocked by the serine protease inhibitor aprotinin (20 microg/ml). Measures to block the potential extracellular triggers heparin binding protein, glutamate, oxygen free radicals and binding to intercellular cell adhesion molecule-1 (ICAM-1) were ineffective. These data indicate that neutrophils both reduce and increase permeability in a cell culture model of the BBB, correlated to their proximity and migration through the endothelium. They explore the role of neutrophils in BBB breakdown, and the formation or amelioration of vasogenic cerebral edema.

The role of inflammatory processes in the pathophysiology and treatment of brain and spinal cord trauma

Traumatic injury to the brain and spinal cord results in an early inflammatory response that is initiated by the release of proinflammatory cytokines followed by the infiltration and accumulation of polymorphonuclear leukocytes (PMNLs). The role of the inflammatory cascade on traumatic outcome remains controversial. Pleiotropic cytokines appear to function both protectively and destructively. The induction of cytokines can lead to the expression of the inducible form of nitric oxide synthase (iNOS), which in turn provokes the release of excessive amounts of nitric oxide (NO) that may participate in the pathogenesis of tissue injury. Hypothermia has been reported by various groups to be neuroprotective in brain and spinal cord trauma. We studied the effect of therapeutic hypothermia on cerebral IL-1beta concentrations, PMNL accumulation and iNOS activity after traumatic brain injury (TBI) and spinal cord injury (SCI). Based on current data therapeutic hypothermia may protect in models of traumatic injury by modulating deleterious inflammatory processes.

Traumatic Cerebral Vascular Injury: The Effects of Concussive Brain Injury on the Cerebral Vasculature

In terms of human suffering, medical expenses, and lost productivity, head injury is one of the major health care problems in the United States, and inadequate cerebral blood flow is an important contributor to mortality and morbidity after traumatic brain injury. Despite the importance of cerebral vascular dysfunction in the pathophysiology of traumatic brain injury, the effects of trauma on the cerebral circulation have been less well studied than the effects of trauma on the brain. Recent research has led to a better understanding of the physiologic, cellular, and molecular components and causes of traumatic cerebral vascular injury. A more thorough understanding of the direct and indirect effects of trauma on the cerebral vasculature will lead to improvements in current treatments of brain trauma as well as to the development of novel and, hopefully, more effective therapeutic strategies.

Administration of either anti-intercellular adhesion molecule-1 or a nonspecific control antibody improves recovery after traumatic brain injury in the rat

Intercellular adhesion molecule-1 (ICAM-1) is an endothelial protein that facilitates invasion of leukocytes into the CNS in response to injury or inflammation. ICAM-1 expression correlates with the severity of clinical head injuries, but its importance in secondary injury events is not fully understood. Therefore, we evaluated ICAM-1 expression and the effect of anti-ICAM-1 treatment on motor recovery and neutrophil invasion after traumatic brain injury induced via the lateral fluid-percussion method in the rat. ICAM-1 was expressed in large and small blood vessels within the injured cortex at 10 and 24 h after injury. Repeated administration of anti-ICAM-1 antibody (clone 1A29) at 1, 10, and again at 24 h after injury significantly improved performance in two of three motor tests, compared to saline controls. Equal doses of nonspecific control antibody (IgG) also significantly improved motor test scores, compared to saline controls. Cortical myeloperoxidase activity, an indicator of neutrophil invasion, was significantly reduced 26 h after injury in animals treated with anti-ICAM-1. Animals treated with IgG showed a trend toward reduction that did not reach significance. These data suggest that ICAM-1 may be involved in neutrophil invasion and neurological dysfunction after TBI, but also implicate a role for a nonspecific antibody effect in improved functional outcome.

Interleukin-1beta messenger ribonucleic acid and protein levels after fluid-percussion brain injury in rats: importance of injury severity and brain temperature

OBJECTIVE

Posttraumatic temperature manipulations have been reported to significantly influence the inflammatory response to traumatic brain injury (TBI). The purpose of this study was to determine the temporal and regional profiles of messenger ribonucleic acid (mRNA) expression and protein levels for the proinflammatory cytokine interleukin-1beta (IL-1beta), after moderate or severe TBI. The effects of posttraumatic hypothermia (33 degrees C) or hyperthermia (39.5 degrees C) on these consequences of TBI were then determined.

METHODS

Male Sprague-Dawley rats underwent fluid-percussion brain injury. In the first phase of the study, rats were killed 15 minutes or 1, 3, or 24 hours after moderate TBI (1.8-2.2 atmospheres), for reverse transcription-polymerase chain reaction analysis. Other groups of rats were killed 1, 3, 24, or 72 hours after moderate or severe TBI (2.4-2.7 atmospheres), for protein analysis. In the second phase, rats underwent moderate fluid-percussion brain injury, followed immediately by 3 hours of posttraumatic normothermia (37 degrees C), hyperthermia (39.5 degrees C), or hypothermia (33 degrees C), and were then killed, for analyses of protein levels and mRNA expression. Brain samples, including cerebral cortex, hippocampus, thalamus, and cerebellum, were dissected and stored at -80 degrees C until analyzed.

RESULTS

The findings indicated that mRNA levels were increased (P < 0.05) as early as 1 hour after TBI and remained elevated up to 3 hours after moderate TBI. Although both moderate and severe TBI induced increased levels of IL-1beta (P < 0.05), increased protein levels were also noted in remote brain structures after severe TBI. Posttraumatic hypothermia attenuated IL-1beta protein levels, compared with normothermia (P < 0.05), although the levels remained elevated in comparison with sham values. In contrast, hyperthermia had no significant effect on IL-1beta levels, compared with normothermic values. Posttraumatic temperature manipulations had no significant effect on IL-1beta mRNA levels.

CONCLUSION

Injury severity determines the degree of IL-1beta protein level elevation after TBI. The effects of posttraumatic hypothermia on IL-1beta protein levels (an important mediator of neurodegeneration after TBI) may partly explain the established effects of posttraumatic temperature manipulations on inflammatory processes after TBI.

Effect of posttraumatic hyperglycemia on contusion volume and neutrophil accumulation after moderate fluid-percussion brain injury in rats

The purpose of this study was to evaluate the effects of posttraumatic hyperglycemia on contusion volume and neutrophil accumulation following moderate traumatic brain injury (TBI) in rats. A parasagittal fluid-percussion (F-P) brain injury (1.8-2.1 atm) was induced in male Sprague-Dawley rats. Rats were then randomized into four trauma groups (n = 7/group) by the timing of dextrose injection (2.0 gm/kg/ip), which included (1) early (E) group: 5 min after TBI; (2) delayed (D) group: 4 h after TBI; (3) 24-h group: 24 h after TBI; or (4) control (C) group: no dextrose injection. A sham operated control group also received dextrose to document physiological parameters (n = 4). Rats were perfusion fixed 3 days following TBI, and the brains were processed for routine histopathological and immunocytochemical analysis. Contusion areas and volumes, as well as the frequency of myeloperoxidase immunoreactive polymorphonuclear leukocytes (PMNLs) were determined. Dextrose injections significantly increased blood glucose levels (p < 0.005) in all treated groups. Although acute hyperglycemia following TBI did not significantly affect total contusion volume, contusion area was significantly elevated in the early treatment group. In addition, early posttraumatic hyperglycemia enhanced neutrophil accumulation in the area of the cortical contusion (p < 0.005). In contrast, delayed induced hyperglycemia (i.e., 4 h, 24 h) did not significantly affect histopathological outcome or neutrophil accumulation. Taken together, these findings indicate that acute but not delayed hyperglycemia aggravates histopathological outcome and increased accumulation of PMNLs. Posttraumatic hyperglycemia in the acute phase may worsen traumatic outcome by enhancing secondary injury processes, including inflammation.

Acute systemic administration of interleukin-10 suppresses the beneficial effects of moderate hypothermia following traumatic brain injury in rats

Traumatic injury to the central nervous system initiates inflammatory processes such as the synthesis of proinflammatory mediators that contribute to secondary tissue damage. Hence, administration of anti-inflammatory cytokines, such as interleukin-10 (IL-10) may be neuroprotective. Moderate hypothermia (30-32 degrees C) also decreases the pro-inflammatory response to traumatic brain injury (TBI). Thus, we hypothesized that the combination of IL-10 and hypothermia would provide synergistic neuroprotective effects after TBI. To test this hypothesis, fifty isoflurane-anesthetized rats underwent a controlled cortical impact (2.7 mm tissue deformation at 4 m/s) or sham injury and then were randomly assigned to one of five conditions (TBI/VEH Normothermia (37 degrees C), TBI/VEH Hypothermia (32 degrees C for 3 h), TBI/IL-10 Normothermia, TBI/IL-10 Hypothermia, and Sham/VEH Normothermia). Human IL-10 (5 microg) or VEH was administered (i.p.) 30 min after surgery. Function was assessed by established motor and cognitive tests on post-operative days 1-5 and 14-18, respectively. Cortical lesion volume and hippocampal CA(1)/CA(3) cell survival were quantified at 4 weeks. Brain sections from 15 additional rats were immunohistochemically assessed (MoAB RP-3) to determine neutrophil accumulation at 5 h after TBI. The administration of IL-10 after TBI produced an approximately 75% reduction in the number of RP-3-positive cells in both the normothermic and hypothermic groups vs. the normothermic vehicle-treated group (P<0.05), but did not improve functional outcome. In contrast, hypothermia alone enhanced both motor and cognitive function and increased CA(3) neuronal survival after TBI. Contrary to our hypothesis, systemic administration of IL-10 combined with hypothermia did not provide synergistic neuroprotective effects after TBI. Rather, IL-10 administration suppressed the beneficial effects produced by hypothermia alone after TBI. The mechanism(s) for the negative effects of IL-10 combined with hypothermia after TBI remain to be determined.

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.

Neuroprotective profile of enoxaparin, a low molecular weight heparin, in in vivo models of cerebral ischemia or traumatic brain injury in rats: a review

The development of treatments for acute neurodegenerative diseases (stroke and brain trauma) has focused on (i) reestablishing blood flow to ischemic areas as quickly as possible (i.e. mainly antithrombotics or thrombolytics for stroke therapy) and (ii) on protecting neurons from cytotoxic events (i.e. neuroprotective therapies such as anti-excitotoxic or anti-inflammatory agents for stroke and neurotrauma therapies). This paper reviews the preclinical data for enoxaparin in in vivo models of ischemia and brain trauma in rats. Following a photothrombotic lesion in the rat, enoxaparin significantly reduced edema at 24 h after lesion when the treatment was started up to 18 h after insult. Enoxaparin was also tested after an ischemic insult using the transient middle cerebral artery occlusion (tMCAO) model in the rat. Enoxaparin, 2 x 1.5 mg/kg i.v., significantly reduced the lesion size and improved the neuroscore when the treatment was started up to 5 h after ischemia. Enoxaparin, administered at 5 h after insult, reduced cortical lesion size in a dose-dependent manner. In permanent MCAO, enoxaparin (5 and 24 h after insult) significantly reduced lesion size and improved neuroscore. A slight and reversible elevation of activated partial thromboplastin time (APTT) suggests that enoxaparin is neuroprotective at a non-hemorrhagic dose. Traumatic brain injury (TBI) is often accompanied by secondary ischemia due in part to edema-induced compression of blood vessels. When enoxaparin, at 0.5 mg/kg i.v. + 4 x 1 mg/kg s.c., was administered later than 30 h after TBI, it significantly reduced edema in hippocampus and parietal cortex. At one week after TBI the lesion size was significantly reduced and the neurological deficit significantly improved in enoxaparin treated animals. Finally, the cognitive impairment was significantly improved by enoxaparin at 48 h to 2 weeks after TBI. The anticoagulant properties of unfractionated heparin and specifically enoxaparin can explain their anti-ischemic effects in experimental models. Furthermore, unfractionated heparin and specifically enoxaparin, have, in addition to anticoagulant, many other pharmacological effects (i.e. reduction of intracellular Ca2+ release; antioxidant effect; anti-inflammatory or neurotrophic effects) that could act in synergy to explain the neuroprotective activity of enoxaparin in acute neurodegenerative diseases. Finally, we demonstrated, that in different in vivo models of acute neurodegenerative diseases, enoxaparin reduces brain edema and lesion size and improves motor and cognitive functional recovery with a large therapeutic window of opportunity (compatible with a clinical application). Taking into account these experimental data in models of ischemia and brain trauma, the clinical use of enoxaparin in acute neurodegenerative diseases warrants serious consideration.

Infusion of prostacyclin following experimental brain injury in the rat reduces cortical lesion volume

Endothelial-derived prostacyclin is an important regulator of microvascular function, and its main actions are inhibition of platelet/leukocyte aggregation and adhesion, and vasodilation. Disturbances in endothelial integrity following traumatic brain injury (TBI) may result in insufficient prostacyclin production and participate in the pathophysiological sequelae of brain injury. The objective of this study was to evaluate the potential therapeutic effects of a low-dose prostacyclin infusion on cortical lesion volume, CA3 neuron survival and functional outcome following TBI in the rat. Anesthetized animals (sodium pentobarbital, 60 mg/kg, i.p.) were subjected to a lateral fluid percussion brain injury (2.5 atm) or sham injury. Following TBI, animals were randomized to receive a constant infusion of either prostacyclin (1 ng/kg x min(-1) i.v.) or vehicle over 48 h. All sham animals received vehicle (n = 6). Evaluation of neuromotor function, lesion volume, and CA3 neuronal loss was performed blindly. By 7 days postinjury, cortical lesion volume was significantly reduced by 43% in the prostacyclin-treated group as compared to the vehicle treated group (p < 0.01; n = 12 prostacyclin, n = 12 vehicle). No differences were observed in neuromotor function (48 h and 7 days following TBI), or in hippocampal cell loss (7 days following TBI) between the prostacyclin- and vehicle-treated groups. We conclude that prostacyclin in a low dose reduces loss of neocortical neurons following TBI and may be a potential clinical therapeutic agent to reduce neuronal cell death associated with brain trauma.