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

Subclinical brain manifestations of repeated mild traumatic brain injury are changed by chronic exposure to sleep loss, caffeine, and sleep aids

INTRODUCTION

After mild traumatic brain injury (mTBI), the brain is labile for weeks and months and vulnerable to repeated concussions. During this time, patients are exposed to everyday circumstances that, in themselves, affect brain metabolism and blood flow and neural processing. How commonplace activities interact with the injured brain is unknown. The present study in an animal model investigated the extent to which three commonly experienced exposures-daily caffeine usage, chronic sleep loss, and chronic sleep aid medication-affect the injured brain in the chronic phase.

METHODS

Subclinical trauma by repeated mTBIs was produced by our head rotational acceleration injury model, which causes brain injury consistent with the mechanism of concussion in humans. Forty-eight hours after a third mTBI, chronic administrations of caffeine, sleep restriction, or zolpidem (sedative hypnotic) began and were continued for 70 days. On Days 30 and 60 post injury, resting state functional magnetic resonance imaging (fMRI) and diffusion tensor imaging (DTI) were performed.

RESULTS

Chronic caffeine, sleep restriction, and zolpidem each changed the subclinical brain characteristics of mTBI at both 30 and 60 days post injury, detected by different MRI modalities. Each treatment caused microstructural alterations in DTI metrics in the insular cortex and retrosplenial cortex compared with mTBI, but also uniquely affected other gray and white matter regions. Zolpidem administration affected the largest number of individual structures in mTBI at both 30 and 60 days, and not necessarily toward normalization (sham treatment). Chronic sleep restriction changed local functional connectivity at 30 days in diametrical opposition to chronic caffeine ingestion, and both treatment outcomes were different from sham, mTBI-only and zolpidem comparisons. The results indicate that commonly encountered exposures modify subclinical brain activity and structure long after healing is expected to be complete.

CONCLUSIONS

Changes in activity and structure detected by fMRI are widely understood to reflect changes in the functions of the affected region which conceivably underlie mTBI neuropathology and symptomatology in the chronic phase after injury.

ROS-responsive biomimetic nanosystem camouflaged by hybrid membranes of platelet-exosomes engineered with neuronal targeting peptide for TBI therapy

Recovery and survival following traumatic brain injury (TBI) depends on optimal amelioration of secondary injuries at lesion site. Delivering mitochondria-protecting drugs to neurons may revive damaged neurons at sites secondarily traumatized by TBI. Pioglitazone (PGZ) is a promising candidate for TBI treatment, limited by its low brain accumulation and poor targetability to neurons. Herein, we report a ROS-responsive nanosystem, camouflaged by hybrid membranes of platelets and engineered extracellular vesicles (EVs) (C3-EPm-|TKNPs|), that can be used for targeted delivery of PGZ for TBI therapy. Inspired by intrinsic ability of macrophages for inflammatory chemotaxis, engineered M2-like macrophage-derived EVs were constructed by fusing C3 peptide to EVs membrane integrator protein, Lamp2b, to confer them with ability to target neurons in inflamed lesions. Platelets provided hybridized EPm with capabilities to target hemorrhagic area caused by trauma via surface proteins. Consequently, C3-EPm-|PGZ-TKNPs| were orientedly delivered to neurons located in the traumatized hemisphere after intravenous administration, and triggered the release of PGZ from TKNPs via oxidative stress. The current work demonstrate that C3-EPm-|TKNPs| can effectively deliver PGZ to alleviate mitochondrial damage via mitoNEET for neuroprotection, further reversing behavioral deficits in TBI mice. Our findings provide proof-of-concept evidence of C3-EPm-|TKNPs|-derived nanodrugs as potential clinical approaches against neuroinflammation-related intracranial diseases.

Concussion: Beyond the Cascade

Sport concussion affects millions of athletes each year at all levels of sport. Increasing evidence demonstrates clinical and physiological recovery are becoming more divergent definitions, as evidenced by several studies examining blood-based biomarkers of inflammation and imaging studies of the central nervous system (CNS). Recent studies have shown elevated microglial activation in the CNS in active and retired American football players, as well as in active collegiate athletes who were diagnosed with a concussion and returned to sport. These data are supportive of discordance in clinical symptomology and the inflammatory response in the CNS upon symptom resolution. In this review, we will summarize recent advances in the understanding of the inflammatory response associated with sport concussion and broader mild traumatic brain injury, as well as provide an outlook for important research questions to better align clinical and physiological recovery.

Microenvironmental Variations After Blood-Brain Barrier Breakdown in Traumatic Brain Injury

Traumatic brain injury (TBI) is linked to several pathologies. The blood-brain barrier (BBB) breakdown is considered to be one of the initial changes. Further, the microenvironmental alteration following TBI-induced BBB breakdown can be multi-scaled, constant, and dramatic. The microenvironmental variations after disruption of BBB includes several pathological changes, such as cerebral blood flow (CBF) alteration, brain edema, cerebral metabolism imbalances, and accumulation of inflammatory molecules. The modulation of the microenvironment presents attractive targets for TBI recovery, such as reducing toxic substances, inhibiting inflammation, and promoting neurogenesis. Herein, we briefly review the pathological alterations of the microenvironmental changes following BBB breakdown and outline potential interventions for TBI recovery based on microenvironmental modulation.

Tailored Therapeutic Doses of Dexmedetomidine in Evolving Neuroinflammation after Traumatic Brain Injury

BACKGROUND

Understanding the secondary damage mechanisms of traumatic brain injury (TBI) is essential for developing new therapeutic approaches. Neuroinflammation has a pivotal role in secondary brain injury after TBI. Activation of NLRP3 inflammasome complexes results in the secretion of proinflammatory mediators and, in addition, later in the response, microglial activation and migration of the peripheral immune cells into the injured brain are observed. Therefore, these components involved in the inflammatory process are becoming a new treatment target in TBI. Dexmedetomidine (Dex) is an effective drug, widely used over the past few years in neurocritical care units and during surgical operations for sedation and analgesia, and has anti-inflammatory effects, which are shown in in vivo studies. The aim of this original research is to discuss the anti-inflammatory effects of different Dex doses over time in TBI.

METHODS

Brain injury was performed by using a weight-drop model. Half an hour after the trauma, intraperitoneal saline was injected into the control groups and 40 and 200 μg/kg of Dex were given to the drug groups. Neurological evaluations were performed with the modified Neurological Severity Score before being killed. Then, the mice were killed on the first or the third day after TBI and histopathologic (hematoxylin-eosin) and immunofluorescent (Iba1, NLRP3, interleukin-1β, and CD3) findings of the brain tissues were examined. Nonparametric data were analyzed by using the Kruskal-Wallis test for multiple comparisons, and the Mann-Whitney U-test was done for comparing two groups. The results are presented as mean ± standard error of mean.

RESULTS

The results showed that low doses of Dex suppress NLRP3 and interleukin-1β in both terms. Additionally, high doses of Dex cause a remarkable decrease in the migration and motility of microglial cells and T cells in the late phase following TBI. Interestingly, the immune cells were influenced by only high-dose Dex in the late phase of TBI and it also improves neurologic outcome in the same period.

CONCLUSIONS

In the mice head trauma model, different doses of Dex attenuate neuroinflammation by suppressing distinct components of the neuroinflammatory process in a different timecourse that contributes to neurologic recovery. These results suggest that Dex may be an appropriate choice for sedation and analgesia in patients with TBI.

Doxycycline alleviates acute traumatic brain injury by suppressing neuroinflammation and apoptosis in a mouse model

Traumatic brain injury (TBI) is one of the significant causes of death among young people worldwide. Doxycycline (DOX), an antibiotic with anti-inflammatory effects, has not been used as a therapeutic agent to modify the inflammatory response after the traumatic brain injury. In this study, intraperitoneal administration of DOX reduced significantly the acute inflammatory markers like IL-6 and CD3, microglial migration to the damaged area marked with Iba-1, and neuronal apoptosis assessed with TUNEL assay at 72 h after the trauma. The low dose, 10 mg/kg of DOX had a dominant anti-inflammatory effect; while the high dose, 100 mg/kg of DOX, was more effective in decreasing neuronal apoptosis. In early hours after the head trauma, use of a low dose (10 mg/kg) of DOX for decreasing the acute form of inflammation followed by a high dose (100 mg/kg) for the anti-apoptotic effects particularly in severe head traumas, would be a promising approach to alleviate the brain injury.

Traumatic Brain Injury Broadly Affects GABAergic Signaling in Dentate Gyrus Granule Cells

Traumatic brain injury (TBI) causes cellular and molecular alterations that contribute to neuropsychiatric disease and epilepsy. GABAergic dysfunction figures prominently in the pathophysiology of TBI, yet the effects of TBI on tonic inhibition in hippocampus remain uncertain. We used a mouse model of severe TBI [controlled cortical impact (CCI)] to investigate GABAergic signaling in dentate gyrus granule cells (DGGCs). Basal tonic GABA currents were not affected by CCI. However, tonic currents induced by the δ subunit-selective GABA_A receptor agonist 4,5,6,7-tetrahydroisoxazolo[5,4-c]pyridin-3-ol (THIP; 10 μm) were reduced by 44% in DGGCs ipsilateral to CCI (CCI-ipsi), but not in contralateral DGGCs. Reduced THIP currents were apparent one week after injury and persisted up to 15 weeks. The frequency of spontaneous IPSCs (sIPSCs) was reduced in CCI-ipsi cells, but the amplitude and kinetics of sIPSCs were unaffected. Immunohistochemical analysis showed reduced expression of GABA_A receptor δ subunits and GABA_B receptor B2 subunits after CCI, by 43% and 40%, respectively. Activation of postsynaptic GABA_B receptors caused a twofold increase in tonic currents, and this effect was markedly attenuated in CCI-ipsi cells (92% reduction). GABA_B receptor-activated K⁺ currents in DGGCs were also significantly reduced in CCI-ipsi cells, confirming a functional deficit of GABA_B receptors after CCI. Results indicate broad disruption of GABAergic signaling in DGGCs after CCI, with deficits in both phasic and tonic inhibition and GABA_B receptor function. These changes are predicted to disrupt operation of hippocampal networks and contribute to sequelae of severe TBI, including epilepsy.

Influence of Organic Solvents on Secondary Brain Damage after Experimental Traumatic Brain Injury

Many compounds tested for a possible neuroprotective effect after traumatic brain injury (TBI) are not readily soluble and therefore organic solvents need to be used as a vehicle. It is, however, unclear whether these organic solvents have intrinsic pharmacological effects on secondary brain damage and may therefore interfere with experimental results. Thus, the aim of the current study was to evaluate the effect of four widely used organic solvents, dimethylsulfoxide (DMSO), Miglyol 812 (Miglyol^®), polyethyleneglycol 40 (PEG 40), and N-2-methyl-pyrrolidone (NMP) on outcome after TBI in mice. A total of 143 male C57Bl/6 mice were subjected to controlled cortical impact (CCI). Contusion volume, brain edema formation, and neurological function were assessed 24 h after TBI. Test substances or saline were injected intraperitoneally (i.p.) 10 min before CCI. DMSO, Miglyol, and PEG 40 had no effect on post-traumatic contusion volume after CCI; NMP, however, significantly reduced contusion volume and brain edema formation at different concentrations. The use of DMSO, Miglyol, and PEG 40 is unproblematic for studies investigating neuroprotective treatment strategies as they do not influence post-traumatic brain damage. NMP seems to have an intrinsic neuroprotective effect that should be considered when using this agent in pharmacological experiments; further, a putative therapeutic effect of NMP needs to be elucidated in future studies.

Longitudinal Characterization of Blood-Brain Barrier Permeability after Experimental Traumatic Brain Injury by In Vivo 2-Photon Microscopy

Vasogenic brain edema (VBE) formation remains an important factor determining the fate of patients with traumatic brain injury (TBI). The spatial and temporal development of VBE, however, remains poorly understood because of the lack of sufficiently sensitive measurement techniques. To close this knowledge gap, we directly visualized the full time course of vascular leakage after TBI by in vivo 2-photon microscopy (2-PM). Male C57BL/6 mice (n = 6/group, 6-8 weeks old) were assigned randomly to sham operation or brain trauma by controlled cortical impact. A cranial window was prepared, and tetramethylrhodamine-dextran (TMRM, MW 40,000 Da) was injected intravenously to visualize blood plasma 4 h, 24 h, 48 h, 72 h, or seven days after surgery or trauma. Three regions with increasing distance to the primary contusion were investigated up to a depth of 300 μm by 2-PM. No TMRM extravasation was detected in sham-operated mice, while already 4 h after TBI vascular leakage was significantly increased (p < 0.05 vs. sham) and reached its maximum at 48 h after injury. Vascular leakage was most pronounced in the vicinity of the contusion. The rate of extravasation showed a biphasic pattern, peaking 4 h and 48-72 h after trauma. Taken together, longitudinal quantification of vascular leakage after TBI in vivo demonstrates that VBE formation after TBI develops in a biphasic manner suggestive of acute and delayed mechanisms. Further studies using the currently developed dynamic in vivo imaging modalities are needed to investigate these mechanisms and potential therapeutic strategies in more detail.

Depletion of regulatory T cells increases T cell brain infiltration, reactive astrogliosis, and interferon-γ gene expression in acute experimental traumatic brain injury

Background

Traumatic brain injury (TBI) is a major cause of death and disability. T cells were shown to infiltrate the brain during the first days after injury and to exacerbate tissue damage. The objective of this study was to investigate the hitherto unresolved role of immunosuppressive, regulatory T cells (Tregs) in experimental TBI.

Methods

“Depletion of regulatory T cell” (DEREG) and wild type (WT) C57Bl/6 mice, treated with diphtheria toxin (DTx) to deplete Tregs or to serve as control, were subjected to the controlled cortical impact (CCI) model of TBI. Neurological and motor deficits were examined until 5 days post-injury (dpi). At the 5 dpi endpoint, (immuno-) histological, protein, and gene expression analyses were carried out to evaluate the consequences of Tregs depletion. Comparison of parametric or non-parametric data between two groups was done using Student’s t test or the Mann-Whitney U test. For multiple comparisons, p values were calculated by one-way or two-way ANOVA followed by specific post hoc tests.

Results

The overall neurological outcome at 5 dpi was not different between DEREG and WT mice but more severe motor deficits occurred transiently at 1 dpi in DEREG mice. DEREG and WT mice did not differ in the extent of brain damage, blood-brain barrier (BBB) disruption, or neuronal excitotoxicity, as examined by lesion volumetry, immunoglobulin G (IgG) extravasation, or calpain-generated αII-spectrin breakdown products (SBDPs), respectively. In contrast, increased protein levels of glial fibrillary acidic protein (GFAP) and GFAP+ astrocytes in the ipsilesional brain tissue indicated exaggerated reactive astrogliosis in DEREG mice. T cell counts following anti-CD3 immunohistochemistry and gene expression analyses of Cd247 (CD3 subunit zeta) and Cd8a (CD8a) further indicated an increased number of T cells infiltrating the brain injury sites of DEREG mice compared to WT. These changes coincided with increased gene expression of pro-inflammatory interferon-γ (Ifng) in DEREG mice compared to WT in the injured brain.

Conclusions

The results show that the depletion of Tregs attenuates T cell brain infiltration, reactive astrogliosis, interferon-γ gene expression, and transiently motor deficits in murine acute traumatic brain injury.

PET Evaluation of Microglial Activation in Non-neurodegenerative Brain Diseases

PURPOSE OF THE REVIEW

Microglial cell activation is an important component of neuroinflammation, and it is generally well accepted that chronic microglial activation is indicative of accumulating tissue damage in neurodegenerative conditions, particularly in the earlier stages of disease. Until recently, there has been less focus on the role of neuroinflammation in other forms of neurological and neuropsychiatric conditions. Through this review, we hope to demonstrate the important role TSPO PET imaging has played in illuminating the pivotal role of neuroinflammation and microglial activation underpinning these conditions.

RECENT FINDINGS

TSPO is an 18 kDa protein found on the outer membrane of mitochondria and can act as a marker of microglial activation using nuclear imaging. Through the development of radiopharmaceuticals targeting TSPO, researchers have been able to better characterise the spatial-temporal evolution of chronic neurological conditions, ranging from the focal autoimmune reactions seen in multiple sclerosis to the Wallerian degeneration at remote parts of the brain months following acute cerebral infarction. Development of novel techniques to investigate neuroinflammation within the central nervous system, for the purposes of diagnosis and therapeutics, has flourished over the past few decades. TSPO has proven itself a robust and sensitive biomarker of microglial activation and neuroimaging affords a minimally invasive technique to characterise neuroinflammatory processes in vivo.

Bazedoxifene protects cerebral autoregulation after traumatic brain injury and attenuates impairments in blood-brain barrier damage: involvement of anti-inflammatory pathways by blocking MAPK signaling

OBJECTIVE

Traumatic brain injury (TBI) is a significant cause of death and long-term deficits in motor and cognitive functions for which there are currently no effective chemotherapeutic drugs. Bazedoxifene (BZA) is a third-generation selective estrogen receptor modulator (SERM) and has been investigated as a treatment for postmenopausal osteoporosis. It is generally safe and well tolerated, with favorable endometrial and breast safety profiles. Recent findings have shown that SERMs may have therapeutic benefits; however, the role of BZA in the treatment of TBI and its molecular and cellular mechanisms remain poorly understood. The aim of the present study was to examine the neuroprotective effects of BZA on early TBI in rats and to explore the underlying mechanisms of these effects.

MATERIALS AND METHODS

TBI was induced using a modified weight-drop method. Neurological deficits were evaluated according to the neurological severity score (NSS). Morris water maze and open-field behavioral tests were used to test cognitive functions. Brain edema was measured by brain water content, and impairments in the blood-brain barrier (BBB) were evaluated by expression analysis of tight junction-associated proteins, such as occludin and zonula occludens-1 (ZO-1). Neuronal injury was assessed by hematoxylin and eosin (H&E) staining. LC-MS/MS analysis was performed to determine the ability of BZA to cross the BBB.

RESULTS

Our results indicated that BZA attenuated the impaired cognitive functions and the increased BBB permeability of rats subjected to TBI through activation of inflammatory cascades. In vivo experiments further revealed that BZA provided this neuroprotection by suppressing TBI-induced activation of the MAPK/NF-κB signaling pathway. Thus, mechanically, the anti-inflammatory effects of BZA in TBI may be partially mediated by blocking the MAPK signaling pathway.

CONCLUSIONS

These findings suggest that BZA might attenuate neurological deficits and BBB damage to protect against TBI by blocking the MAPK/NF-κB signaling pathway.

The Role of Microglia in the Etiology and Evolution of Chronic Traumatic Encephalopathy

Chronic traumatic encephalopathy (CTE) is a progressive neurodegenerative disease that presents as a late sequela from traumatic brain injury (TBI). TBI is a growing and under-recognized public health concern with a high degree of morbidity and large associated global costs. While the immune response to TBI is complex, its contribution to the development of CTE remains largely unknown. In this review, we summarize the current understanding of the link between CTE and the resident innate immune system of the brain-microglia. We discuss the neuropathology underlying CTE including the creation and aggregation of phosphorylated tau protein into neurofibrillary tangles and the formation of amyloid beta deposits. We also present how microglia, the resident innate immune cells of the brain, drive the continuous low-level inflammation associated with the insidious onset of CTE. In this review, we conclude that the latency period between the index brain injury and the long-term development of CTE presents an opportunity for therapeutic intervention. Encouraging advances with microtubule stabilizers, cis p-tau antibodies, and the ability to therapeutically alter the inflammatory state of microglia have shown positive results in both animal and human trials. Looking forward, recent advancements in next-generation sequencing technology for the study of genomic, transcriptomic, and epigenetic information will provide an opportunity for significant advancement in our understanding of prorepair and pro-injury gene signatures allowing for targeted intervention in this highly morbid injury process.

Inversion of neurovascular coupling after subarachnoid hemorrhage in vivo

Subarachnoid hemorrhage (SAH) induces acute changes in the cerebral microcirculation. Recent findings ex vivo suggest neurovascular coupling (NVC), the process that increases cerebral blood flow upon neuronal activity, is also impaired after SAH. The aim of the current study was to investigate whether this occurs also in vivo. C57BL/6 mice were subjected to either sham surgery or SAH by filament perforation. Twenty-four hours later NVC was tested by forepaw stimulation and CO₂ reactivity by inhalation of 10% CO₂. Vessel diameter was assessed in vivo by two-photon microscopy. NVC was also investigated ex vivo using brain slices. Cerebral arterioles of sham-operated mice dilated to 130% of baseline upon CO₂ inhalation or forepaw stimulation and cerebral blood flow (CBF) increased. Following SAH, however, CO₂ reactivity was completely lost and the majority of cerebral arterioles showed paradoxical constriction in vivo and ex vivo resulting in a reduced CBF response. As previous results showed intact NVC 3 h after SAH, the current findings indicate that impairment of NVC after cerebral hemorrhage occurs secondarily and is progressive. Since neuronal activity-induced vasoconstriction (inverse NVC) is likely to further aggravate SAH-induced cerebral ischemia and subsequent brain damage, inverse NVC may represent a novel therapeutic target after SAH.

Acute changes in neurovascular reactivity after subarachnoid hemorrhage in vivo

Subarachnoid hemorrhage causes acute and long-lasting constrictions of pial arterioles. Whether these vessels dilate normally to neuronal activity is of great interest since a mismatch between delivery and consumption of glucose and oxygen may cause additional neuronal damage. Therefore, we investigated neurovascular reactivity of pial and parenchymal arterioles after experimental subarachnoid hemorrhage. C57BL/6 mice were subjected to subarachnoid hemorrhage by filament perforation or sham surgery. Neurovascular reactivity was assessed 3 h later by forepaw stimulation or inhalation of 10% CO₂ Diameters of cerebral arterioles were assessed using two-photon microscopy. Neurovascular coupling and astrocytic endfoot Ca²⁺ were measured in brain slices using two-photon and infrared-differential interference contrast microscopy. Vessels of sham-operated mice dilated normally to CO₂ and forepaw stimulation. Three hours after subarachnoid hemorrhage, CO₂ reactivity was completely lost in both pial and parenchymal arterioles, while neurovascular coupling was not affected. Brain slices studies also showed normal neurovascular coupling and a normal increase in astrocytic endfoot Ca²⁺ acutely after subarachnoid hemorrhage. These findings suggest that communication between neurons, astrocytes, and parenchymal arterioles is not affected in the first few hours after subarachnoid hemorrhage, while CO₂ reactivity, which is dependent on NO signaling, is completely lost.

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.

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.

Dynamic Profiling: Modeling the Dynamics of Inflammation and Predicting Outcomes in Traumatic Brain Injury Patients

Inflammation induced by traumatic brain injury (TBI) is complex, individual-specific, and associated with morbidity and mortality. We sought to develop dynamic, data-driven, predictive computational models of TBI-induced inflammation based on cerebrospinal fluid (CSF) biomarkers. Thirteen inflammatory mediators were determined in serial CSF samples from 27 severe TBI patients. The Glasgow Coma Scale (GCS) score quantifies the initial severity of the neurological status of the patient on a numerical scale from 3 to 15. The 6-month Glasgow Outcome Scale (GOS) score, the outcome variable, was taken as the variable to express and predict as a function of the other input variables. Data on each subject consisting of ten clinical (one-dimensional) variables, such as age, gender, and presence of infection, along with inflammatory biomarker time series were used to generate both multinomial logistic as well as probit models that predict low (poor outcome) or high (favorable outcome) levels of the GOS score. To determine if CSF inflammation biomarkers could predict TBI outcome, a logistic model for low (≤3; poor neurological outcome) or high levels (≥4; favorable neurological outcome) of the GOS score involving a full effect of the pro-inflammatory cytokine tumor necrosis factor-α and both linear and quadratic effects of the anti-inflammatory cytokine interleukin-10 was obtained. To better stratify patients as their pathology progresses over time, a technique called “Dynamic Profiling” was developed in which patients were clustered, using the spectral Laplacian and Hartigan’s k-means method, into disjoint groups at different stages. Initial clustering was based on GCS score; subsequent clustering was performed based on clinical and demographic information and then further, sequential clustering based on the levels of individual inflammatory mediators over time. These clusters assess the risk of mortality of a new patient after each inflammatory mediator reading, based on the existing information in the previous data in the cluster to which the new patient belongs at the time, in essence acting as a “virtual clinician.” Using the Dynamic Profiling method, we show examples that suggest that severe TBI patient neurological outcomes could be predicted as a function of time post-TBI using CSF inflammatory mediators.

Early Inflammatory Response following Traumatic Brain Injury in Rabbits Using USPIO- and Gd-Enhanced MRI

Purpose. To monitor the inflammatory response (IR) following traumatic brain injury (TBI) before and after the rehabilitation of the blood-brain barrier (BBB) in rabbits using USPIO- and Gd-enhanced MRI. Materials and Methods. Twenty white big-eared rabbits with mild TBI (mTBI) were randomly and equally divided into four groups. Rabbits were sacrificed for the brain specimens immediately after the last MRI-monitoring. Sequences were tse-T1WI, tse-T2WI, Gd-T1WI, and USPIO-T1WI. Dynamical MRI presentations were evaluated and compared with pathological findings for each group. Results. Twenty-four hours after injury, all rabbits displayed high signal foci on T2WI, while only 55% lesions could be found on Gd-T1WI and none on USPIO-T1WI. The lesions were enhanced on Gd-T1WI in 100% subjects after 48 h and the enhancement sizes augmented to the largest after 72 h. At the time point of 72 h after TBI, 90% lesions were enhanced by USPIO. Five days after injury, 19 lesions showed decreased Gd-enhancement and one disappeared; however, USPIO-enhancement became larger than before. Pathological findings showed microglias slightly appeared in dense leukocytes at 48 h, but became the dominant inflammatory cells after five days. Conclusions. Dynamic IR following injury could be monitored by combination of Gd- and USPIO-MRI in mTBI rabbits.

Does enoxaparin interfere with HMGB1 signaling after TBI? A potential mechanism for reduced cerebral edema and neurologic recovery

BACKGROUND

Enoxaparin (ENX) has been shown to reduce cerebral edema and improve neurologic recovery after traumatic brain injury (TBI), through blunting of cerebral leukocyte (LEU) recruitment. High mobility group box 1 (HMGB1) protein may induce inflammation through LEU activation. We hypothesized that ENX after TBI reduces LEU-mediated edema through blockade of HMGB1 signaling.

METHODS

Twenty-three CD1 mice underwent severe TBI by controlled cortical impact and were randomized to one of four groups receiving either monoclonal antibody against HMGB1 (MAb) or isotype (Iso) and either ENX (1 mg/kg) or normal saline (NS): NS + Iso (n = 5), NS + MAb (n = 6), ENX + Iso (n = 6), ENX + MAb (n = 6). ENX or NS was administered 2, 8, 14, 23 and 32 hours after TBI. MAb or Iso (25 μg) was administered 2 hours after TBI. At 48 hours, cerebral intravital microscopy served to visualize live LEU interacting with endothelium and microvascular fluorescein isothiocyanate-albumin leakage. The Neurological Severity Score (NSS) graded neurologic recovery; wet-to-dry ratios determined cerebral/lung edema. Analysis of variance with Bonferroni correction was used for statistical analyses.

RESULTS

ENX and MAb similarly reduced in vivo pial LEU rolling without demonstrating additive effect. In vivo albumin leakage was greatest in vehicle-treated animals but decreased by 25% with either MAb or ENX but by 50% when both were combined. Controlled cortical impact-induced cerebral wet-to-dry ratios were reduced by MAb or ENX without additive effect. Postinjury lung water was reduced by ENX but not by MAb. Neurologic recovery at 24 hours and 48 hours was similarly improved with ENX, MAb, or both treatments combined.

CONCLUSION

Mirroring ENX, HMGB1 signaling blockade reduces LEU recruitment, cerebrovascular permeability, and cerebral edema following TBI. ENX further reduced lung edema indicating a multifaceted effect beyond HMGB1 blockade. Further study is needed to determine how ENX may play a role in blunting HMGB1 signaling in brain injury patients.

Nuclear Factor Erythroid 2-Related Factor 2 (Nrf2) Mediates Neuroprotection in Traumatic Brain Injury at Least in Part by Inactivating Microglia

Background

Microglial activation has been reported to be involved in traumatic brain injury (TBI). Nuclear factor erythroid 2-related factor 2 (Nrf2) plays a significant role in protecting against TBI-induced secondary brain injury. However, the exact mechanism is not clearly understood. The present study aimed to explore whether Nrf2 protects against TBI partly by regulating microglia function.

Material/Methods

Microglia cells were isolated from C57BL/6 mouse brains (postnatal day 1–3). The expression of Nrf2 was suppressed by transfection with Nrf2-specific small interfering RNA (siRNA), and overexpressed by transfections with pcDNA3.1-Nrf2. The expression of Nrf2 was confirmed by real-time PCR and Western blotting. After transfection, cell viability, phagocytic ability, and the expression of pro-inflammatory cytokines (tumor necrosis factor (TNF)-α and interleukin (IL)-6) were determined by 3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide (MTT) colorimetric assay, phagocytosis assay, and enzyme-linked immunosorbent assay (ELISA), respectively.

Results

mRNA and protein expression levels of Nrf2 were significantly reduced by transfection with Nrf2-specific siRNA (both P<0.05) but were elevated by transfection with pcDNA3.1-Nrf2 (both P<0.01). The cell viability, phagocytic ability, and the expression of TNF-α and IL-6 were all significantly reduced by overexpression of Nrf2 but were significantly increased by silencing of Nrf2 compared with the control group.

Conclusions

Our results suggest that Nrf2 protects against TBI, at least part by regulating microglia function.

Protein profile changes in the frontotemporal lobes in human severe traumatic brain injury

Severe traumatic brain injury (sTBI) is a serious public health issue with high morbidity and mortality rates. Previous proteomic studies on sTBI have mainly focused on human cerebrospinal fluid and serum, as well as on brain protein changes in murine models. However, human proteomic data in sTBI brain is still scarce. We used proteomic and bioinformatic strategies to investigate variations in protein expression levels in human brains after sTBI, using samples from the Department of Neurosurgery, Affiliated Hospital of Hebei University (Hebei, China). Our proteomic data identified 4031 proteins, of which 160 proteins were overexpressed and 5 proteins were downregulated. Bioinformatics analysis showed significant changes in biological pathways including glial cell differentiation, complement activation and apolipoprotein catalysis in the statin pathway. Western blot verification of protein changes in a subset of the available tissue samples showed results that were consistent with the proteomic data. This study is one of the first to investigate the whole proteome of human sTBI brains, and provide a characteristic signature and overall landscape of the sTBI brain proteome.

Sodium butyrate exerts neuroprotective effects by restoring the blood-brain barrier in traumatic brain injury mice

Sodium butyrate (SB) has been widely used to treat cerebral diseases. The aim of the present study is to examine the neuroprotective effects of SB on early TBI in mice and to explore the underlying mechanisms of these effects. TBI was induced using a modified weight-drop method. Neurological deficits were evaluated according to the neurological severity score (NSS), brain oedema was measured by brain water content, and blood-brain barrier (BBB) permeability was evaluated by Evans blue (EB) dye extravasation. Neuronal injury was assessed by hematoxylin and eosin (H&E) staining and Fluoro-Jade C staining. The expression of tight junction-associated proteins, such as occludin and zonula occludens-1 (ZO-1), was analysed by western blotting and immunofluorescence. Our results showed that mice subjected to TBI exhibited worsened NSS, brain oedema, neuronal damage and BBB permeability. However, these were all attenuated by SB. Moreover, SB reversed the decrease in occludin and ZO-1 expression induced by TBI. These findings suggest that SB might attenuate neurological deficits, brain oedema, neuronal change and BBB damage, as well as increase occludin and ZO-1 expression in the brain to protect against TBI. The protective effect of SB may be correlated with restoring the BBB following its impairment.

Changes in Binding of [(123)I]CLINDE, a High-Affinity Translocator Protein 18 kDa (TSPO) Selective Radioligand in a Rat Model of Traumatic Brain Injury

After traumatic brain injury (TBI), secondary injuries develop, including neuroinflammatory processes that contribute to long-lasting impairments. These secondary injuries represent potential targets for treatment and diagnostics. The translocator protein 18 kDa (TSPO) is expressed in activated microglia cells and upregulated in response to brain injury and therefore a potential biomarker of the neuroinflammatory processes. Second-generation radioligands of TSPO, such as [(123)I]CLINDE, have a higher signal-to-noise ratio as the prototype ligand PK11195. [(123)I]CLINDE has been employed in human studies using single-photon emission computed tomography to image the neuroinflammatory response after stroke. In this study, we used the same tracer in a rat model of TBI to determine changes in TSPO expression. Adult Sprague-Dawley rats were subjected to moderate controlled cortical impact injury and sacrificed at 6, 24, 72 h and 28 days post surgery. TSPO expression was assessed in brain sections employing [(123)I]CLINDE in vitro autoradiography. From 24 h to 28 days post surgery, injured animals exhibited a marked and time-dependent increase in [(123)I]CLINDE binding in the ipsilateral motor, somatosensory and parietal cortex, as well as in the hippocampus and thalamus. Interestingly, binding was also significantly elevated in the contralateral M1 motor cortex following TBI. Craniotomy without TBI caused a less marked increase in [(123)I]CLINDE binding, restricted to the ipsilateral hemisphere. Radioligand binding was consistent with an increase in TSPO mRNA expression and CD11b immunoreactivity at the contusion site. This study demonstrates the applicability of [(123)I]CLINDE for detailed regional and quantitative assessment of glial activity in experimental models of TBI.

Dietary Docosahexaenoic Acid Improves Cognitive Function, Tissue Sparing, and Magnetic Resonance Imaging Indices of Edema and White Matter Injury in the Immature Rat after Traumatic Brain Injury

Traumatic brain injury (TBI) is the leading cause of acquired neurologic disability in children. Specific therapies to treat acute TBI are lacking. Cognitive impairment from TBI may be blunted by decreasing inflammation and oxidative damage after injury. Docosahexaenoic acid (DHA) decreases cognitive impairment, oxidative stress, and white matter injury in adult rats after TBI. Effects of DHA on cognitive outcome, oxidative stress, and white matter injury in the developing rat after experimental TBI are unknown. We hypothesized that DHA would decrease early inflammatory markers and oxidative stress, and improve cognitive, imaging and histologic outcomes in rat pups after controlled cortical impact (CCI). CCI or sham surgery was delivered to 17 d old male rat pups exposed to DHA or standard diet for the duration of the experiments. DHA was introduced into the dam diet the day before CCI to allow timely DHA delivery to the pre-weanling pups. Inflammatory cytokines and nitrates/nitrites were measured in the injured brains at post-injury Day (PID) 1 and PID2. Morris water maze (MWM) testing was performed at PID41-PID47. T2-weighted and diffusion tensor imaging studies were obtained at PID12 and PID28. Tissue sparing was calculated histologically at PID3 and PID50. DHA did not adversely affect rat survival or weight gain. DHA acutely decreased oxidative stress and increased anti-inflammatory interleukin 10 in CCI brains. DHA improved MWM performance and lesion volume late after injury. At PID12, DHA decreased T2-imaging measures of cerebral edema and decreased radial diffusivity, an index of white matter injury. DHA improved short- and long-term neurologic outcomes after CCI in the rat pup. Given its favorable safety profile, DHA is a promising candidate therapy for pediatric TBI. Further studies are needed to explore neuroprotective mechanisms of DHA after developmental TBI.

Neural stem/progenitor cells differentiate into oligodendrocytes, reduce inflammation, and ameliorate learning deficits after transplantation in a mouse model of traumatic brain injury

The central nervous system has limited capacity for regeneration after traumatic injury. Transplantation of neural stem/progenitor cells (NPCs) has been proposed as a potential therapeutic approach while insulin-like growth factor I (IGF-I) has neuroprotective properties following various experimental insults to the nervous system. We have previously shown that NPCs transduced with a lentiviral vector for IGF-I overexpression have an enhanced ability to give rise to neurons in vitro but also in vivo, upon transplantation in a mouse model of temporal lobe epilepsy. Here we studied the regenerative potential of NPCs, IGF-I-transduced or not, in a mouse model of hippocampal mechanical injury. NPC transplantation, with or without IGF-I transduction, rescued the injury-induced spatial learning deficits as revealed in the Morris Water Maze. Moreover, it had beneficial effects on the host tissue by reducing astroglial activation and microglial/macrophage accumulation while enhancing generation of endogenous oligodendrocyte precursor cells. One or two months after transplantation the grafted NPCs had migrated towards the lesion site and in the neighboring myelin-rich regions. Transplanted cells differentiated toward the oligodendroglial, but not the neuronal or astrocytic lineages, expressing the early and late oligodendrocyte markers NG2, Olig2, and CNPase. The newly generated oligodendrocytes reached maturity and formed myelin internodes. Our current and previous observations illustrate the high plasticity of transplanted NPCs which can acquire injury-dependent phenotypes within the host CNS, supporting the fact that reciprocal interactions between transplanted cells and the host tissue are an important factor to be considered when designing prospective cell-based therapies for CNS degenerative conditions.

Apolipoprotein E knockout induced inflammatory responses related to microglia in neonatal mice brain via astrocytes

More and more evidences suggestted that ApoE plays an important role in modulating the systemic and central nervous inflammatory responses. However, there is a lack of exacted mechanism of ApoE. In this study, we aimed to investigate whether apolipoprotein E (ApoE) induced inflammatory responses and apoptosis in neonatal mice brain from ApoE deficient (ApoE(-/-)) and wildtype (WT). Compared to control group, the microglia cell from ApoE(-/-) mice showed more severe inflammation and cell death such as iNOS and IL-1β. Furthermore, anti-inflammatory such as TGF-β, IL-10 from microglia and astrocytes in ApoE(-/-) mice were decreased. On the other way, TGF-β from astrocytes can inhibit inflammation factors secretion from microglia. Our findings suggested that the anti- inflammation factor such as IL-10 mainly from microglia and TGF-β mainly from astrocyte is significant decreased after Loss of ApoE function in ApoE(-/-) mice which induced severe inflammation. Furthrtmore, anti- inflammation factor such as IL-10 and TGF-β Therefore, we conclude that apolipoprotein E knockout induced inflammatory responses related to microglia in neonatal mice brain via astrocytes.