A Single Primary Blast-Induced Traumatic Brain Injury in a Rodent Model Causes Cell-Type Dependent Increase in Nicotinamide Adenine Dinucleotide Phosphate Oxidase Isoforms in Vulnerable Brain Regions

MCC950 Attenuates Microglial NLRP3-Mediated Chronic Neuroinflammation and Memory Impairment in a Rat Model of Repeated Low-Level Blast Exposure

Blast-induced traumatic brain injury is typically regarded as a signature medical concern for military personnel who are exposed to explosive devices in active combat zones. However, soldiers as well as law enforcement personnel may be repeatedly exposed to low-level blasts during training sessions with heavy weaponries as part of combat readiness. Service personnel who sustain neurotrauma from repeated low-level blast (rLLB) exposure do not display overt pathological symptoms immediately but rather develop mild symptoms including cognitive impairments, attention deficits, mood changes, irritability, and sleep disturbances over time. Recently, we developed a rat model of rLLB by applying controlled low-level blast pressures (≤ 70 kPa) repeated five times successively to mimic the pressures experienced by service members. Using this model, we assessed anxiety-like symptoms, motor coordination, and short-term memory as a function of time. We also investigated the role of the NLRP3 inflammasome, a complex involved in chronic microglial activation and pro-inflammatory cytokine interleukin (IL)-1β release, in rLLB-induced neuroinflammation. NLRP3 and caspase-1 protein expression, microglial activation, and IL-1β release were examined as factors likely contributing to these neurobehavioral changes. Animals exposed to rLLB displayed acute and chronic short-term memory impairments and chronic anxiety-like symptoms accompanied by increased microglial activation, NLRP3 expression, and IL-1β release. Treatment with MCC950, an NLRP3 inflammasome complex inhibitor, suppressed microglial activation, reduced NLRP3 expression and IL-1β release, and improved short-term memory deficits after rLLB exposure. Collectively, this study demonstrates that rLLB induces chronic neurobehavioral and neuropathological changes by increasing NLRP3 inflammasome protein expression followed by cytokine IL-1β release.

Phylogenetic conservation of the interdependent homeostatic relationship of sleep regulation and redox metabolism

Sleep is an essential and evolutionarily conserved process that affects many biological functions that are also strongly regulated by cellular metabolism. The interdependence between sleep homeostasis and redox metabolism, in particular, is such that sleep deprivation causes redox metabolic imbalances in the form of over-production of ROS. Likewise (and vice versa), accumulation of ROS leads to greater sleep pressure. Thus, it is theorized that one of the functions of sleep is to act as the brain's "antioxidant" at night by clearing oxidation built up from daily stress of the active day phase. In this review, we will highlight evidence linking sleep homeostasis and regulation to redox metabolism by discussing (1) the bipartite role that sleep-wake neuropeptides and hormones have in redox metabolism through comparing cross-species cellular and molecular mechanisms, (2) the evolutionarily metabolic changes that accompanied the development of sleep loss in cavefish, and finally, (3) some of the challenges of uncovering the cellular mechanism underpinning how ROS accumulation builds sleep pressure and cellularly, how this pressure is cleared.

Twenty Years of Blast-Induced Neurotrauma: Current State of Knowledge

Blast-induced neurotrauma (BINT) is an important injury paradigm of neurotrauma research. This short communication summarizes the current knowledge of BINT. We divide the BINT research into several broad categories-blast wave generation in laboratory, biomechanics, pathology, behavioral outcomes, repetitive blast in animal models, and clinical and neuroimaging investigations in humans. Publications from 2000 to 2023 in each subdomain were considered. The analysis of the literature has brought out salient aspects. Primary blast waves can be simulated reasonably in a laboratory using carefully designed shock tubes. Various biomechanics-based theories of BINT have been proposed; each of these theories may contribute to BINT by generating a unique biomechanical signature. The injury thresholds for BINT are in the nascent stages. Thresholds for rodents are reasonably established, but such thresholds (guided by primary blast data) are unavailable in humans. Single blast exposure animal studies suggest dose-dependent neuronal pathologies predominantly initiated by blood-brain barrier permeability and oxidative stress. The pathologies were typically reversible, with dose-dependent recovery times. Behavioral changes in animals include anxiety, auditory and recognition memory deficits, and fear conditioning. The repetitive blast exposure manifests similar pathologies in animals, however, at lower blast overpressures. White matter irregularities and cortical volume and thickness alterations have been observed in neuroimaging investigations of military personnel exposed to blast. Behavioral changes in human cohorts include sleep disorders, poor motor skills, cognitive dysfunction, depression, and anxiety. Overall, this article provides a concise synopsis of current understanding, consensus, controversies, and potential future directions.

Development of the Blast Ordnance and Occupational Exposure Measure for Self-Reported Lifetime Blast Exposures

INTRODUCTION

To address the military gap in the standardized collection of lifetime blast exposures across clinical and research endeavors, researchers at the National Intrepid Center of Excellence (NICoE) completed a quality improvement project that utilized systematic, iterative focus groups that leveraged the input from various stakeholders including subject matter experts, clinical providers, and service members (SMs) to develop a comprehensive, self-report blast exposure inventory that could be completed within 5-10 minutes. This manuscript outlines the process of the development of this inventory.

MATERIALS AND METHODS

This project included three phases of focus groups that occurred at the NICoE between August 2020 and March 2021 to collect feedback and input from relevant military stakeholders. The study team utilized related assessments available in the literature, together with clinical experience with the NICoE patient population, to inform the development of an initial draft inventory. Phase 1 consisted of blast injury research subject matter experts who had extensive experience researching and providing clinical care to SMs exposed to blast. Phase 2 consisted of NICoE clinicians across numerous clinical specialties. Phase 3 included current active duty patients in the NICoE intensive outpatient program.

RESULTS

Following completion of the focus groups, a lifetime blast exposure inventory was developed in the form of a single page table including incoming, outgoing, training, and operational exposures and broken down by levels of weapon systems as well as breaching and explosive ordnance disposal exposures. In addition, select questions related to the first and most recent blast exposures and experience as an instructor for explosive ordnance disposal- and breaching-related training were included.

CONCLUSIONS

Researchers at the NICoE developed a self-report blast exposure inventory through a quality improvement project that included active, ongoing participation and feedback of clinical experts and military SMs. The end result is a brief, single page inventory that can be administered within 5-10 minutes. Although additional research is needed to refine and validate the inventory, the project team believes that the tool begins to address a long-standing gap in the DoD in the standardized collection of lifetime blast exposures.

Temporal Changes in Functional and Structural Neuronal Activities in Auditory System in Non-Severe Blast-Induced Tinnitus

Background and Objectives: Epidemiological data indicate that blast exposure is the most common morbidity responsible for mild TBI among Service Members (SMs) during recent military operations. Blast-induced tinnitus is a comorbidity frequently reported by veterans, and despite its wide prevalence, it is also one of the least understood. Tinnitus arising from blast exposure is usually associated with direct structural damage that results in a conductive and sensorineural impairment in the auditory system. Tinnitus is also believed to be initiated by abnormal neuronal activities and temporal changes in neuroplasticity. Clinically, it is observed that tinnitus is frequently accompanied by sleep disruption as well as increased anxiety. In this study, we elucidated some of the mechanistic aspects of sensorineural injury caused by exposure to both shock waves and impulsive noise. The isolated conductive auditory damage hypothesis was minimized by employing an animal model wherein both ears were protected. Materials and Methods: After the exposure, the animals' hearing circuitry status was evaluated via acoustic startle response (ASR) to distinguish between hearing loss and tinnitus. We also compared the blast-induced tinnitus against the well-established sodium salicylate-induced tinnitus model as the positive control. The state of the sensorineural auditory system was evaluated by auditory brainstem response (ABR), and this test helped examine the neuronal circuits between the cochlea and inferior colliculus. We then further evaluated the role of the excitatory and inhibitory neurotransmitter receptors and neuronal synapses in the auditory cortex (AC) injury after blast exposure. Results: We observed sustained elevated ABR thresholds in animals exposed to blast shock waves, while only transient ABR threshold shifts were observed in the impulsive noise group solely at the acute time point. These changes were in concert with the increased expression of ribbon synapses, which is suggestive of neuroinflammation and cellular energy metabolic disorder. It was also found that the onset of tinnitus was accompanied by anxiety, depression-like symptoms, and altered sleep patterns. By comparing the effects of shock wave exposure and impulsive noise exposure, we unveiled that the shock wave exerted more significant effects on tinnitus induction and sensorineural impairments when compared to impulsive noise. Conclusions: In this study, we systematically studied the auditory system structural and functional changes after blast injury, providing more significant insights into the pathophysiology of blast-induced tinnitus.

Effect of minocycline and its nano-formulation on central auditory system in blast-induced hearing loss rat model

Blast injuries are common among the military service members and veterans. One of the devastating effects of blast wave induced TBI is either temporary or permanent hearing loss. Treating hearing loss using minocycline is restricted by optimal drug concentration, route of administration, and its half-life. Therefore, therapeutic approach using novel therapeutic delivery method is in great need. Among the different delivery methods, nanotechnology-based drug delivery is desirable, which can achieve longer systemic circulation, pass through some biological barriers and specifically targets desired sites. The current study aimed to examine therapeutic effect of minocycline and its nanoparticle formulation in moderate blast induced hearing loss rat model through central auditory system. The I.v. administered nanoparticle at reduced dose and frequency than regularly administered toxic dose. After moderate blast exposure, rats had hearing impairment as determined by ABR at 7- and 30-days post exposure. In chronic condition, free minocycline also showed the significant reduction in ABR threshold. In central auditory system, it is found in this study that minocycline nanoparticles ameliorate excitation in inferior colliculus; and astrocytes and microglia activation after the blast exposure is reduced by minocycline nanoparticles administration. The study demonstrated that in moderate blast induced hearing loss, minocycline and its nanoparticle formulation exhibited the optimal therapeutic effect on the recovery of the ABR impairment and a protective effect through central auditory system. In conclusion, targeted and non-targeted nanoparticle formulation have therapeutic effect on blast induced hearing loss.

The Hidden Notes of Redox Balance in Neurodegenerative Diseases

Reactive oxygen species (ROS) are versatile molecules that, even if produced in the background of many biological processes and responses, possess pleiotropic roles categorized in two interactive yet opposite domains. In particular, ROS can either function as signaling molecules that shape physiological cell functions, or act as deleterious end products of unbalanced redox reactions. Indeed, cellular redox status needs to be tightly regulated to ensure proper cellular functioning, and either excessive ROS accumulation or the dysfunction of antioxidant systems can perturb the redox homeostasis, leading to supraphysiological concentrations of ROS and potentially harmful outcomes. Therefore, whether ROS would act as signaling molecules or as detrimental factors strictly relies on a dynamic equilibrium between free radical production and scavenging resources. Of notice, the mammalian brain is particularly vulnerable to ROS-mediated toxicity, because it possesses relatively poor antioxidant defenses to cope with the redox burden imposed by the elevated oxygen consumption rate and metabolic activity. Many features of neurodegenerative diseases can in fact be traced back to causes of oxidative stress, which may influence both the onset and progression of brain demise. This review focuses on the description of the dual roles of ROS as double-edge sword in both physiological and pathological settings, with reference to Alzheimer's and Parkinson's diseases.

HDAC1 expression is positively correlated with NADPH oxidase 4-mediated oxidative stress in a mouse model of traumatic brain injury

Accumulating evidence has demonstrated that histone deacetylase 1 (HDAC1) expression is statistically correlated with the severity of traumatic brain injury (TBI). However, the specific role of HDAC1 in the occurrence and development of TBI remains unclear. The Lateral Fluid Percussion Injury (LFPI) was used to conduct TBI mouse model in C57BL/6J and C57BL/6J-Hdac1^em1cyagen mice. Western blot and qRT-PCR were performed to estimate the expression of HADC1 and nicotinamide adenine dinucleotide phosphate oxidase 4 (NOX4) in brain tissues. Modified Neurological Severity Score (mNSS) and brain water content were performed to detect the neurological deficit. Malondialdehyde (MDA), superoxide dismutase (SOD) and glutathione (GSH) were used to detect the oxidative stress. Oxidative stresses, HDAC1 and NOX4 expression were upregulated in the lesioned cortices tissues after TBI. HDAC1 protein expression was positively correlated with the NOX4 in TBI mouse. Hdac1 knockout attenuated brain edema and neurological dysfunction caused by TBI in mice. Hdac1 knockout inhibited the expressions of NOX4 induced by TBI and attenuated TBI induced oxidative stress. HDAC1 expression is positively correlated with to NOX4-mediated oxidative stress in a TBI mouse model.

Matrix Inversion and Subset Selection (MISS): A pipeline for mapping of diverse cell types across the murine brain

The advent of increasingly sophisticated imaging platforms has allowed for the visualization of the murine nervous system at single-cell resolution. However, current experimental approaches have not yet produced whole-brain maps of a comprehensive set of neuronal and nonneuronal types that approaches the cellular diversity of the mammalian cortex. Here, we aim to fill in this gap in knowledge with an open-source computational pipeline, Matrix Inversion and Subset Selection (MISS), that can infer quantitatively validated distributions of diverse collections of neural cell types at 200-μm resolution using a combination of single-cell RNA sequencing (RNAseq) and in situ hybridization datasets. We rigorously demonstrate the accuracy of MISS against literature expectations. Importantly, we show that gene subset selection, a procedure by which we filter out low-information genes prior to performing deconvolution, is a critical preprocessing step that distinguishes MISS from its predecessors and facilitates the production of cell-type maps with significantly higher accuracy. We also show that MISS is generalizable by generating high-quality cell-type maps from a second independently curated single-cell RNAseq dataset. Together, our results illustrate the viability of computational approaches for determining the spatial distributions of a wide variety of cell types from genetic data alone.

Animal model of repeated low-level blast traumatic brain injury displays acute and chronic neurobehavioral and neuropathological changes

Blast-induced neurotrauma (BINT) is not only a signature injury to soldiers in combat field and training facilities but may also a growing concern in civilian population due to recent increases in the use of improvised explosives by insurgent groups. Unlike moderate or severe BINT, repeated low-level blast (rLLB) is different in its etiology as well as pathology. Due to the constant use of heavy weaponry as part of combat readiness, rLLB usually occurs in service members undergoing training as part of combat readiness. rLLB does not display overt pathological symptoms; however, earlier studies report chronic neurocognitive changes such as altered mood, irritability, and aggressive behavior, all of which may be caused by subtle neuropathological manifestations. Current animal models of rLLB for investigation of neurobehavioral and neuropathological alterations have not been adequate and do not sufficiently represent rLLB conditions. Here, we developed a rat model of rLLB by applying controlled low-level blast pressures (<10 psi) repeated successively five times to mimic the pressures experienced by service members. Using this model, we assessed anxiety-like symptoms, motor coordination, and short-term memory as a function of time. We also examined levels of superoxide-producing enzyme NADPH oxidase, microglial activation, and reactive astrocytosis as factors likely contributing to these neurobehavioral changes. Animals exposed to rLLB displayed acute and chronic anxiety-like symptoms, motor and short-term memory impairments. These changes were paralleled by increased microglial activation and reactive astrocytosis. Conversely, animals exposed to a single low-level blast did not display significant changes. Collectively, this study demonstrates that, unlike a single low-level blast, rLLB exerts a cumulative impact on different brain regions and produces chronic neuropathological changes in so doing, may be responsible for neurobehavioral alterations.

NADPH Oxidases in the Central Nervous System: Regional and Cellular Localization and the Possible Link to Brain Diseases

Significance: The significant role of reduced nicotinamide adenine dinucleotide phosphate (NADPH) oxidase (Nox) in signal transduction is mediated by the production of reactive oxygen species (ROS), especially in the central nervous system (CNS). The pathogenesis of some neurologic and psychiatric diseases is regulated by ROS, acting as a second messenger or pathogen. Recent Advances: In the CNS, the involvement of Nox-derived ROS has been implicated in the regulation of multiple signals, including cell survival/apoptosis, neuroinflammation, migration, differentiation, proliferation, and synaptic plasticity, as well as the integrity of the blood/brain barrier. In these processes, the intracellular signals mediated by the members of the Nox family vary among different tissues. The present review illuminates the regions and cellular, subcellular localization of Nox isoforms in the brain, the signal transduction, and the role of NOX enzymes in pathophysiology, respectively. Critical Issues: Different signal transduction cascades are coupled to ROS derived from various Nox homologues with varying degrees. Therefore, a critical issue worth noting is the varied role of the homologues of NOX enzymes in different signaling pathways and also they mediate different phenotypes in the diverse pathophysiological condition. This substantiates the effectiveness of selective Nox inhibitors in the CNS. Future Directions: Further investigation to elucidate the role of various homologues of NOX enzymes in acute and chronic brain diseases and signaling mechanisms, and the development of more specific NOX inhibitors for the treatment of CNS disease are urgently needed. Antioxid. Redox Signal. 35, 951-973.

Investigation of the direct and indirect mechanisms of primary blast insult to the brain

The interaction of explosion-induced blast waves with the head (i.e., a direct mechanism) or with the torso (i.e., an indirect mechanism) presumably causes traumatic brain injury. However, the understanding of the potential role of each mechanism in causing this injury is still limited. To address this knowledge gap, we characterized the changes in the brain tissue of rats resulting from the direct and indirect mechanisms at 24 h following blast exposure. To this end, we conducted separate blast-wave exposures on rats in a shock tube at an incident overpressure of 130 kPa, while using whole-body, head-only, and torso-only configurations to delineate each mechanism. Then, we performed histopathological (silver staining) and immunohistochemical (GFAP, Iba-1, and NeuN staining) analyses to evaluate brain-tissue changes resulting from each mechanism. Compared to controls, our results showed no significant changes in torso-only-exposed rats. In contrast, we observed significant changes in whole-body-exposed (GFAP and silver staining) and head-only-exposed rats (silver staining). In addition, our analyses showed that a head-only exposure causes changes similar to those observed for a whole-body exposure, provided the exposure conditions are similar. In conclusion, our results suggest that the direct mechanism is the major contributor to blast-induced changes in brain tissues.

Central and peripheral auditory abnormalities in chinchilla animal model of blast-injury

Exposure to blast overpressure or high-intensity sound can cause injuries to the auditory system, which leads to hearing loss or tinnitus. In this study, we examined the involvement of peripheral auditory system (PAS), and central auditory system (CAS) changes after exposure to blast overpressure (15-25 psi) on Day 1 and additionally during 7 days of post blast time period in chinchillas. Auditory brainstem response (ABR), distortion product otoacoustic emission (DPOAE), and cochlear hair cell changes were measured or identified in post-blast period within 7 days to detect injuries in the PAS. In the CAS, changes in NMDAR1 (excitatory receptor) and GABAA (inhibitory receptor) as well as changes in serotonin (5-HT_2A) and acetylcholine (AChR) receptors were examined in different brain regions: auditory cortex (AC), geniculate body (GB), inferior colliculus (IC) and amygdala by immunofluorescence staining. We observed the PAS abnormalities of increased ABR threshold and decreased DPOAE response in animals after blast exposure with hearing protection devices (e.g., earplug). Blast exposure also caused a reduction in both NMDAR1 and GABA_A receptor levels in acute condition (post-blast or Day 1) in AC and IC, while serotonin and acetylcholine receptor levels displayed a biphasic response at Day 1 and Day 7 post-exposure. Results demonstrate that the earplug can protect the tympanic membrane and middle ear against structural damage, but the hearing level, cochlear outer hair cell, and the central auditory system (levels of excitatory and inhibitory neurotransmitter receptors) were only partially protected at the tested blast overpressure level. The findings in this study indicate that blast exposure can cause both peripheral and central auditory dysfunctions, and the central auditory response is independent of peripheral auditory damage. The CAS dysfunction is likely mediated by direct transmission of shockwaves in all the regions of central nervous system (CNS), including nerves and surrounding tissues along the auditory pathways. Hence, targeting central auditory neurotransmitter abnormalities may have a therapeutic benefit to attenuate blast-induced hearing loss and tinnitus.

Nutraceutical induction and mimicry of heme oxygenase activity as a strategy for controlling excitotoxicity in brain trauma and ischemic stroke: focus on oxidative stress

Introduction: Ischemic stroke and traumatic brain injury are leading causes of acute mortality, and in the longer run, major causes of significant mental and physical impairment. Most of the brain neuronal cell death in the minutes and hours following an ischemic stroke or brain trauma is mediated by the process of excitotoxicity, in which sustained elevations of extracellular glutamate, reflecting a failure of ATP-dependent mechanism which sequester glutamate in neurons and astrocytes, drive excessive activation of NMDA receptors. Areas covered: A literature search was undertaken to clarify the molecular mechanisms whereby excessive NMDA activation leads to excitotoxic neuronal death, and to determine what safe nutraceutical agents might have practical potential for rescuing at-risk neurons by intervening in these mechanisms. Expert opinion: Activation of both NADPH oxidase and neuronal nitric oxide synthase in the microenvironment of activated NMDA receptors drives production of superoxide and highly toxic peroxynitrite. This leads to excessive activation of PARP and p38 MAP kinase, mitochondrial dysfunction, and subsequent neuronal death. Heme oxygenase-1 (HO-1) induction offers protection via inhibition of NADPH oxidase and promotion of cGMP generation. Phase 2-inductive nutraceuticals can induce HO-1, and other nutraceuticals can mimic the effects of its products biliverdin and carbon monoxide.

Protein kinase inhibitors in traumatic brain injury and repair: New roles of nanomedicine

Traumatic brain injury (TBI) causes physical injury to the cell membranes of neurons, glial and axons causing the release of several neurochemicals including glutamate and cytokines altering cell-signaling pathways. Upregulation of mitogen associated protein kinase (MAPK) and extracellular signal-regulated kinase (ERK) occurs that is largely responsible for cell death. The pharmacological blockade of these pathways results in cell survival. In this review role of several protein kinase inhibitors on TBI induced oxidative stress, blood-brain barrier breakdown, brain edema formation, and resulting brain pathology is discussed in the light of current literature.

Glial Activation in the Thalamus Contributes to Vestibulomotor Deficits Following Blast-Induced Neurotrauma

Vestibular impairment has become a frequent consequence following blast-related traumatic brain injury (bTBI) in military personnel and Veterans. Behavioral outcomes such as depression, fear and anxiety are also common comorbidities of bTBI. To accelerate pre-clinical research and therapy developments, there is a need to study the link between behavioral patterns and neuropathology. The transmission of neurosensory information often involves a pathway from the cerebral cortex to the thalamus, and the thalamus serves crucial integrative functions within vestibular processing. Pathways from the thalamus also connect with the amygdala, suggesting thalamic and amygdalar contributions to anxiolytic behavior. Here we used behavioral assays and immunohistochemistry to determine the sub-acute and early chronic effects of repeated blast exposure on the thalamic and amygdala nuclei. Behavioral results indicated vestibulomotor deficits at 1 and 3 weeks following repeated blast events. Anxiety-like behavior assessments depicted trending increases in the blast group. Astrogliosis and microglia activation were observed upon post-mortem pathological examination in the thalamic region, along with a limited glia response in the amygdala at 4 weeks. These findings are consistent with a diffuse glia response associated with bTBI and support the premise that dysfunction within the thalamic nuclei following repeated blast exposures contribute to vestibulomotor impairment.

Chemokine signaling mediated monocyte infiltration affects anxiety-like behavior following blast injury

The activation of resident microglia and infiltrated monocytes are known potent mediators of chronic neuroinflammation following traumatic brain injury (TBI). In this study, we use a mouse model of blast-induced TBI (bTBI) to investigate whether microglia and monocytes contribute to the neuroinflammatory and behavioral consequences of bTBI. Eight-ten week old mice were subject to moderate TBI (180 kPa) in a shock tube. Using double transgenic CCR2^RFP/+: CX3CR1^GFP/+ mice, we were able to note that in addition to resident Cx3CR1+ microglia, infiltrating CCR2+ monocytes also contributed to the expanding macrophage population that was observed after bTBI. The microglia activation and monocyte infiltration occurred as early as 4 h and lasted up to 30d after blast exposure, suggesting chronic inflammation. The infiltration of monocytes may be partly mediated by chemokine CCL2-CCR2 signaling axis and compromised blood brain barrier permeability. Hence, bTBI-induced infiltration of monocytes and production of IL-1β were prevented in mice lacking CCR2 (CCR2 KO). Finally, this study showed that interference of monocyte infiltration using CCR2 KO, ameliorated the chronic effects of bTBI such as anxiety-like behavior and short-term memory decline. Taken together, these data suggest that bTBI leads to activation of both resident microglia and infiltrated monocytes. The infiltration of monocytes was partly mediated by CCL2-CCR2 signaling, which in turn contributes to increased production of IL-1β leading to behavioral deficits after bTBI. Furthermore, bTBI induced behavioral outcomes were reduced by targeting CCL2-CCR2 signaling, highlighting the significance of this signaling axis in bTBI pathology.

The role of NADPH oxidases in neuronal development

Reactive oxygen species (ROS) are critical for maintaining cellular homeostasis and function when produced in physiological ranges. Important sources of cellular ROS include NADPH oxidases (Nox), which are evolutionary conserved multi-subunit transmembrane proteins. Nox-mediated ROS regulate variety of biological processes including hormone synthesis, calcium signaling, cell migration, and immunity. ROS participate in intracellular signaling by introducing post-translational modifications to proteins and thereby altering their functions. The central nervous system (CNS) expresses different Nox isoforms during both development and adulthood. Here, we review the role of Nox-mediated ROS during CNS development. Specifically, we focus on how individual Nox isoforms contribute to signaling in neural stem cell maintenance and neuronal differentiation, as well as neurite outgrowth and guidance. We also discuss how ROS regulates the organization and dynamics of the actin cytoskeleton in the neuronal growth cone. Finally, we review recent evidence that Nox-derived ROS modulate axonal regeneration upon nervous system injury.

Blast exposure predisposes the brain to increased neurological deficits in a model of blast plus blunt traumatic brain injury

Soldiers are often exposed to more than one traumatic brain injury (TBI) over the course of their service. In recent years, more attention has been drawn to the increased risk of neurological deficits caused by the 'blast plus' polytrauma, which typically is a blast trauma combined with other forms of TBI. In this study, we investigated the behavioral and neuronal deficits resulting from a blast plus injury involving a mild-moderate blast followed by a mild blunt trauma using the fluid percussion injury model. We identified that the blast injury predisposed the brain to increased cognitive deficits, chronic ventricular enlargement, increased neurodegeneration at acute time points and chronic neuronal loss. Interestingly, a single blast and single blunt injury differed in their onset and manifestation of cognitive and regional neuronal loss. We also identified the presence of cleaved RIP1 from caspase 8 mediated apoptosis in the blunt injury while the blast injury did not activate immediate apoptosis but led to decreased hilar neuronal survival over time.

Oxidative stress contributes to cerebral metabolomic profile changes in animal model of blast-induced traumatic brain injury

INTRODUCTION

Blast-induced neurotrauma (BINT) has been recognized as the common mode of traumatic brain injury amongst military and civilian personnel due to an increased insurgent activity domestically and abroad. Previous studies from this laboratory have identified three major pathological events following BINT which include blood brain barrier disruption the earliest event, followed by oxidative stress and neuroinflammation as secondary events occurring a few hours following blast.

OBJECTIVES

Our recent studies have also identified an increase in oxidative stress mediated by the activation of superoxide producing enzyme NADPH oxidase (NOX) in different brain regions at varying levels with neurons displaying higher oxidative stress (NOX activation) compared to any other neural cell. Since neurons have higher energy demands in brain and are more prone to oxidative damage, this study evaluated the effect of oxidative stress on blast-blast induced changes in metabolomics profiles in different brain regions.

METHODS

Animals were exposed to mild/moderate blast injury (180 kPa) and examined the metabolites of energy metabolism, amino acid metabolism as well as the profiles of plasma membrane metabolites in different brain regions at different time points (24 h, 3 day and 7 day) after blast using ¹H NMR spectroscopy. Effect of apocynin, an inhibitor of superoxide producing enzyme NADPH oxidase on cerebral metabalomics profiles was also examined.

RESULTS

Several metabolomic profile changes were observed in frontal cortex and hippocampus with concomitant decrease in energy metabolism. In addition, glutamate/glutamine and other amino acid metabolism as well as metabolites involved in plasma membrane integrity were also altered. Hippocampus appears metabolically more vulnerable than the frontal cortex. A post-treatment of animals with apocynin, an inhibitor of NOX activation significantly prevented the changes in metabolite profiles.

CONCLUSION

Together these studies indicate that blast injury reduces both cerebral energy and neurotransmitter amino acid metabolism and that oxidative stress contributes to these processes. Thus, strategies aimed at reducing oxidative stress can have a therapeutic benefit in mitigating metabolic changes following BINT.

Why Does Brain Trauma Research Fail?

Traumatic brain injury (TBI) represents a major health care problem and a significant social and economic issue worldwide. Considering the generalized failure in introducing effective drugs and clinical protocols, there is an urgent need for efficient treatment modalities, able to improve devastating posttraumatic morbidity and mortality. In this work, the status of brain trauma research is analyzed in all its aspects, including basic and translational science and clinical trials. Implicit and explicit challenges to different lines of research are discussed and clinical trial structures and outcomes are scrutinized, along with possible explanations for systematic therapeutic failures and their implications for future development of drug and clinical trials. Despite significant advances in basic and clinical research in recent years, no specific therapeutic protocols for TBI have been shown to be effective. New potential therapeutic targets have been identified, following a better understanding of pathophysiologic mechanisms underlying TBI, although with disappointing results. Several reasons can be pinpointed at different levels, from inaccurate animal models of disease to faulty preclinical and clinical trials, with poor design and subjective outcome measures. Distinct strategies can be delineated to overcome specific shortcomings of research studies. Identifying and contextualizing the failures that have dominated TBI research is mandatory. This review analyzes current approaches and discusses possible strategies for improving outcomes.

Synergistic Role of Oxidative Stress and Blood-Brain Barrier Permeability as Injury Mechanisms in the Acute Pathophysiology of Blast-induced Neurotrauma

Blast-induced traumatic brain injury (bTBI) has been recognized as the common mode of neurotrauma amongst military and civilian personnel due to an increased insurgent activity domestically and abroad. Previous studies from our laboratory have identified enhanced blood-brain barrier (BBB) permeability as a significant, sub-acute (four hours post-blast) pathological change in bTBI. We also found that NADPH oxidase (NOX)-mediated oxidative stress occurs at the same time post-blast when the BBB permeability changes. We therefore hypothesized that oxidative stress is a major causative factor in the BBB breakdown in the sub-acute stages. This work therefore examined the role of NOX1 and its downstream effects on BBB permeability in the frontal cortex (a region previously shown to be the most vulnerable) immediately and four hours post-blast exposure. Rats were injured by primary blast waves in a compressed gas-driven shock tube at 180 kPa and the BBB integrity was assessed by extravasation of Evans blue and changes in tight junction proteins (TJPs) as well as translocation of macromolecules from blood to brain and vice versa. NOX1 abundance was also assessed in neurovascular endothelial cells. Blast injury resulted in increased extravasation and reduced levels of TJPs in tissues consistent with our previous observations. NOX1 levels were significantly increased in endothelial cells followed by increased superoxide production within 4 hours of blast. Blast injury also increased the levels/activation of matrix metalloproteinase 3 and 9. To test the role of oxidative stress, rats were administered apocynin, which is known to inhibit the assembly of NOX subunits and arrests its function. We found apocynin completely inhibited dye extravasation as well as restored TJP levels to that of controls and reduced matrix metalloproteinase activation in the sub-acute stages following blast. Together these data strongly suggest that NOX-mediated oxidative stress contributes to enhanced BBB permeability in bTBI through a pathway involving increased matrix metalloproteinase activation.

Isoliquiritigenin Provides Protection and Attenuates Oxidative Stress-Induced Injuries via the Nrf2-ARE Signaling Pathway After Traumatic Brain Injury

Traumatic brain injury (TBI) is a serious public health and medical problem worldwide. Oxidative stress plays a vital role in the pathogenesis of TBI. Nuclear factor erythroid 2-related factor 2 (Nrf2), an important factor in the cellular defense against oxidative stress, is activated following TBI. In this study, the protective effects of Isoliquiritigenin (ILG), a promising antioxidant stress drug, was evaluated as a protective agent against TBI. In a mouse model of controlled cortical impact Injury, we found that the ILG administration reduced the Garcia neuroscore, injury histopathology, brain water content, cerebral vascular permeability, the expression of cleaved caspase3, aquaporin-4, glial fibrillary acidic protein and the increased the expression of neurofilament light chain protein, indicating the protective effects against TBI in vivo. ILG treatment after TBI also restored the oxidative stress and promoted the Nrf2 protein transfer from the cytoplasm to the nucleus. We then used Nrf2-/- mice to test the protective effect of Nrf2 during ILG treatment of TBI. Our findings indicated that Nrf2-/- mice had greater brain injury and oxidative stress than wild-type (WT) mice and ILG was less effective at inhibiting oxidative stress and repairing the brain injury than in the WT mice. In vitro studies in SY5Y cells under oxygen glucose deprivation/re-oxygenation stimulation yielded results that were consistent with those obtained in vivo showing that ILG promotes Nrf2 protein transfer from the cytoplasm to the nucleus. Taken together, our findings demonstrate that Nrf2 is an important protective factor against TBI-induced injuries, which indicates that the protective effects of ILG are mediated by inhibiting oxidative stress after TBI via a mechanism that involves the promotion of Nrf2 protein transfer from the cytoplasm to the nucleus.

Oxidized phospholipid signaling in traumatic brain injury

Oxidative stress is a major contributor to secondary injury signaling cascades following traumatic brain injury (TBI). The role of lipid peroxidation in the pathophysiology of a traumatic insult to neural tissue is increasingly recognized. As the methods to quantify lipid peroxidation have gradually improved, so has the understanding of mechanistic details of lipid peroxidation and related signaling events in the injury pathogenesis. While free-radical mediated, non-enzymatic lipid peroxidation has long been studied, recent advances in redox lipidomics have demonstrated the significant contribution of enzymatic lipid peroxidation to TBI pathogenesis. Complex interactions between inflammation, phospholipid peroxidation, and hydrolysis define the engagement of different cell death programs and the severity of injury and outcome. This review focuses on enzymatic phospholipid peroxidation after TBI, including the mechanism of production, signaling roles in secondary injury pathology, and temporal course of production with respect to inflammatory response. In light of the newly identified phospholipid oxidation mechanisms, we also discuss possible therapeutic targets to improve neurocognitive outcome after TBI. Finally, we discuss current limitations in identifying oxidized phospholipids and possible methodologic improvements that can offer a deeper insight into the region-specific distribution and subcellular localization of phospholipid oxidation after TBI.