Critical role of NADPH oxidase in neuronal oxidative damage and microglia activation following traumatic brain injury

Oxidative Stress and Redox Imbalance: Common Mechanisms in Cancer Stem Cells and Neurodegenerative Diseases

Oxidative stress (OS) is an established hallmark of cancer and neurodegenerative disorders (NDDs), which contributes to genomic instability and neuronal loss. This review explores the contrasting role of OS in cancer stem cells (CSCs) and NDDs. Elevated levels of reactive oxygen species (ROS) contribute to genomic instability and promote tumor initiation and progression in CSCs, while in NDDs such as Alzheimer's and Parkinson's disease, OS accelerates neuronal death and impairs cellular repair mechanisms. Both scenarios involve disruption of the delicate balance between pro-oxidant and antioxidant systems, which leads to chronic oxidative stress. Notably, CSCs and neurons display alterations in redox-sensitive signaling pathways, including Nrf2 and NF-κB, which influence cell survival, proliferation, and differentiation. Mitochondrial dynamics further illustrate these differences: enhanced function in CSCs supports adaptability and survival, whereas impairments in neurons heighten vulnerability. Understanding these common mechanisms of OS-induced redox imbalance may provide insights for developing interventions, addressing aging hallmarks, and potentially mitigating or preventing both cancer and NDDs.

Oxidative Stress Promotes Axonal Atrophy through Alterations in Microtubules and EB1 Function

Axons are crucial for transmitting neurochemical signals. As organisms age, the ability of neurons to maintain their axons declines; hence, aged axons are more susceptible to damage or dysfunction. Understanding how aging causes axonal vulnerability is crucial for developing strategies to enhance overall resilience of neurons and prevent neuronal deterioration during aging and in age-related neurodegenerative diseases. Increasing levels of reactive oxygen species (ROS) causes oxidative stress - a hallmark of aging and age-related diseases. Despite this association, a causal relationship between oxidative stress and neuronal aging remains unclear, particularly in how subcellular physiology may be affected by ROS. By using Drosophila-derived primary neuronal cultures and a recently developed in vivo neuronal model of aging, which involves the visualisation of Drosophila medulla neurons, we investigated the interplay between oxidative stress, neuronal aging and the microtubule cytoskeleton. Our results showed that oxidative stress is a key driver of axonal and synaptic decay, as shown by an enhanced appearance of axonal swellings, microtubule alterations (in both axons and synapses) and morphological transformation of axonal terminals during aging. We demonstrated that increasing the levels of ROS sensitises microtubule plus end-binding protein 1 (EB1), leading to microtubule defects that effect neuronal integrity. Furthermore, manipulating EB1 proved to be a valuable therapeutic strategy to prevent aging hallmarks enhanced in conditions of elevated ROS. In summary, we demonstrate a mechanistic pathway linking cellular oxidative stress with changes in the microtubule cytoskeleton leading to axonal deterioration during aging and provide evidence of the therapeutic potential of enhancing microtubule plus-end physiology to improve the resilience of axons.

Immunometabolism In Brain Aging and Neurodegeneration: Bridging Metabolic Pathways and Immune Responses

The complex set of interactions between the immune system and metabolism, known as immunometabolism, has emerged as a critical regulator of disease outcomes in the central nervous system. Numerous studies have linked metabolic disturbances to impaired immune responses in brain aging, neurodegenerative disorders, and brain injury. In this review, we will discuss how disruptions in brain immunometabolism balance contribute to the pathophysiology of brain dysfunction. The first part of the review summarizes the contributions of critical immune cell populations such as microglia, astrocytes, and infiltrating immune cells in mediating inflammation and metabolism in CNS disorders. The remainder of the review addresses the impact of metabolic changes on immune cell activation and disease progression in brain aging, Alzheimer's disease, Parkinson's disease, multiple sclerosis, stroke, spinal cord injury, and traumatic brain injury. Furthermore, we also address the therapeutic potential of targeting immunometabolic pathways to reduce neuroinflammation and slow disease progression. By focusing on the interactions among brain immune cells and the metabolic mechanisms they recruit in disease, we present a comprehensive overview of brain immunometabolism in human health and disease.

NHE1 Protein in Repetitive Mild TBI-Mediated Neuroinflammation and Neurological Function Impairment

Mild traumatic brain injuries (mTBIs) are highly prevalent and can lead to chronic behavioral and cognitive deficits often associated with the development of neurodegenerative diseases. Oxidative stress and formation of reactive oxygen species (ROS) have been implicated in mTBI-mediated axonal injury and pathogenesis. However, the underlying mechanisms and contributing factors are not completely understood. In this study, we explore these pathogenic mechanisms utilizing a murine model of repetitive mTBI (r-mTBI) involving five closed-skull concussions in young adult C57BL/6J mice. We observed a significant elevation of Na+/H+ exchanger protein (NHE1) expression in GFAP+ reactive astrocytes, IBA1+ microglia, and OLIG2+ oligodendrocytes across various brain regions (including the cerebral cortex, corpus callosum, and hippocampus) after r-mTBI. This elevation was accompanied by astrogliosis, microgliosis, and the accumulation of amyloid precursor protein (APP). Mice subjected to r-mTBI displayed impaired motor learning and spatial memory. However, post-r-mTBI administration of a potent NHE1 inhibitor, HOE642, attenuated locomotor and cognitive functional deficits as well as pathological signatures of gliosis, oxidative stress, axonal damage, and white matter damage. These findings indicate NHE1 upregulation plays a role in r-mTBI-induced oxidative stress, axonal damage, and gliosis, suggesting NHE1 may be a promising therapeutic target to alleviate mTBI-induced injuries and restore neurological function.

Concussion May Result in New-Onset Bipolar Disorder: A Case Report

Emotional dysregulation following a concussion is well established. New onset of major psychiatric diseases such as bipolar disorder (BPD) post-concussion has not been investigated. BPD typically presents with an initial depressive episode followed by mania and concurrent depressive and manic states. Multiple theories explaining the etiology of BPD exist, including the diathesis-stress model (DiSM), though an accepted theory is not established. In this case study, medical records of a 50-year-old ambidextrous male with co-morbid attention deficit hyperactivity disorder (ADHD) inattentive type, obsessive-compulsive disorder (OCD), and a family history of BPD suffered a motor vehicle collision (MVC) resulting in a grade II concussion. New onset BPD was diagnosed one-year after a concussion following an involuntary admission and led to the patient self-terminating his medications and suffering a hypertensive crisis and aortic dissection, and stroke. One year later, the patient was again involuntarily admitted for a suicide attempt. Bipolar disorder persisted unchanged indefinitely. This case study may serve as a real-world example of the DiSM in the etiology of BPD post-concussion. We aim to highlight the importance of early identification of risk factors for progression to psychiatric conditions following concussion.

Stretch-Induced Injury Affects Cortical Neuronal Networks in a Time- and Severity-Dependent Manner

Traumatic brain injury (TBI) is the leading cause of accident-related death and disability in the world and can lead to long-term neuropsychiatric symptoms, such as a decline in cognitive function and neurodegeneration. TBI includes primary and secondary injury, with head trauma and deformation of the brain caused by the physical force of the impact as primary injury, and cellular and molecular cascades that lead to cell death as secondary injury. Currently, there is no treatment for TBI-induced cell damage and neural circuit dysfunction in the brain, and thus, it is important to understand the underlying cellular mechanisms that lead to cell damage. In the current study, we use stretchable microelectrode arrays (sMEAs) to model the primary injury of TBI to study the electrophysiological effects of physically injuring cortical cells. We recorded electrophysiological activity before injury and then stretched the flexible membrane of the sMEAs to injure the cells to varying degrees. At 1, 24, and 72 h post-stretch, we recorded activity to analyze differences in spike rate, Fano factor, burstlet rate, burstlet width, synchrony of firing, local network efficiency, and Q statistic. Our results demonstrate that mechanical injury changes the firing properties of cortical neuron networks in culture in a time- and severity-dependent manner. Our results suggest that changes to electrophysiological properties after stretch are dependent on the strength of synchronization between neurons prior to injury.

The Neurovascular Unit as a Locus of Injury in Low-Level Blast-Induced Neurotrauma

Blast-induced neurotrauma has received much attention over the past decade. Vascular injury occurs early following blast exposure. Indeed, in animal models that approximate human mild traumatic brain injury or subclinical blast exposure, vascular pathology can occur in the presence of a normal neuropil, suggesting that the vasculature is particularly vulnerable. Brain endothelial cells and their supporting glial and neuronal elements constitute a neurovascular unit (NVU). Blast injury disrupts gliovascular and neurovascular connections in addition to damaging endothelial cells, basal laminae, smooth muscle cells, and pericytes as well as causing extracellular matrix reorganization. Perivascular pathology becomes associated with phospho-tau accumulation and chronic perivascular inflammation. Disruption of the NVU should impact activity-dependent regulation of cerebral blood flow, blood-brain barrier permeability, and glymphatic flow. Here, we review work in an animal model of low-level blast injury that we have been studying for over a decade. We review work supporting the NVU as a locus of low-level blast injury. We integrate our findings with those from other laboratories studying similar models that collectively suggest that damage to astrocytes and other perivascular cells as well as chronic immune activation play a role in the persistent neurobehavioral changes that follow blast injury.

Pomalidomide Improves Motor Behavioral Deficits and Protects Cerebral Cortex and Striatum Against Neurodegeneration Through a Reduction of Oxidative/Nitrosative Damages and Neuroinflammation After Traumatic Brain Injury

Neuronal damage resulting from traumatic brain injury (TBI) causes disruption of neuronal projections and neurotransmission that contribute to behavioral deficits. Cellular generation of reactive oxygen species (ROS) and reactive nitrogen species (RNS) is an early event following TBI. ROS often damage DNA, lipids, proteins, and carbohydrates while RNS attack proteins. The products of lipid peroxidation 4-hydroxynonenal (4-HNE) and protein nitration 3-nitrotyrosine (3-NT) are often used as indicators of oxidative and nitrosative damages, respectively. Increasing evidence has shown that striatum is vulnerable to damage from TBI with a disturbed dopamine neurotransmission. TBI results in neurodegeneration, oxidative stress, neuroinflammation, neuronal apoptosis, and autophagy in the striatum and contribute to motor or behavioral deficits. Pomalidomide (Pom) is a Food and Drug Administration (FDA)-approved immunomodulatory drug clinically used in treating multiple myeloma. We previously showed that Pom reduces neuroinflammation and neuronal death induced by TBI in rat cerebral cortex. Here, we further compared the effects of Pom in cortex and striatum focusing on neurodegeneration, oxidative and nitrosative damages, as well as neuroinflammation following TBI. Sprague-Dawley rats subjected to a controlled cortical impact were used as the animal model of TBI. Systemic administration of Pom (0.5 mg/kg, intravenous [i.v.]) at 5 h post-injury alleviated motor behavioral deficits, contusion volume at 24 h after TBI. Pom alleviated TBI-induced neurodegeneration stained by Fluoro-Jade C in both cortex and striatum. Notably, Pom treatment reduces oxidative and nitrosative damages in cortex and striatum and is more efficacious in striatum (93% reduction in 4-HNE-positive and 84% reduction in 3-NT-positive neurons) than in cerebral cortex (42% reduction in 4-HNE-positive and 55% reduction in 3-NT-positive neurons). In addition, Pom attenuated microgliosis, astrogliosis, and elevations of proinflammatory cytokines in cortical and striatal tissue. We conclude that Pom may contribute to improved motor behavioral outcomes after TBI through targeting oxidative/nitrosative damages and neuroinflammation.

Revisiting Transcranial Light Stimulation as a Stroke Therapeutic-Hurdles and Opportunities

Near-infrared laser therapy, a special form of transcranial light therapy, has been tested as an acute stroke therapy in three large clinical trials. While the NEST trials failed to show the efficacy of light therapy in human stroke patients, there are many lingering questions and lessons that can be learned. In this review, we summarize the putative mechanism of light stimulation in the setting of stroke, highlight barriers, and challenges during the translational process, and evaluate light stimulation parameters, dosages and safety issues, choice of outcomes, effect size, and patient selection criteria. In the end, we propose potential future opportunities with transcranial light stimulation as a cerebroprotective or restorative tool for future stroke treatment.

Senolytic therapy is neuroprotective and improves functional outcome long-term after traumatic brain injury in mice

Introduction

Chronic neuroinflammation can exist for months to years following traumatic brain injury (TBI), although the underlying mechanisms remain poorly understood.

Methods

In the current study, we used a controlled cortical impact mouse model of TBI to examine whether proinflammatory senescent cells are present in the brain long-term (months) after TBI and whether ablation of these cells via administration of senolytic drugs can improve long-term functional outcome after TBI. The results revealed that astrocytes and microglia in the cerebral cortex, hippocampus, corpus callosum and lateral posterior thalamus colocalized the senescent cell markers, p16Ink4a or p21Cip1/Waf1 at 5 weeks post injury (5wpi) and 4 months post injury (4mpi) in a controlled cortical impact (CCI) model. Intermittent administration of the senolytic drugs, dasatinib and quercetin (D + Q) beginning 1-month after TBI for 13 weeks significantly ablated p16Ink4a-positive- and p21Cip1/Waf1-positive-cells in the brain of TBI animals, and significantly reduced expression of the major senescence-associated secretory phenotype (SASP) pro-inflammatory factors, interleukin-1β and interleukin-6. Senolytic treatment also significantly attenuated neurodegeneration and enhanced neuron number at 18 weeks after TBI in the ipsilateral cortex, hippocampus, and lateral posterior thalamus. Behavioral testing at 18 weeks after TBI further revealed that senolytic therapy significantly rescued defects in spatial reference memory and recognition memory, as well as depression-like behavior in TBI mice.

Discussion

Taken as a whole, these findings indicate there is robust and widespread induction of senescent cells in the brain long-term after TBI, and that senolytic drug treatment begun 1-month after TBI can efficiently ablate the senescent cells, reduce expression of proinflammatory SASP factors, reduce neurodegeneration, and rescue defects in reference memory, recognition memory, and depressive behavior.

An Activity-Based Nanosensor for Minimally-Invasive Measurement of Protease Activity in Traumatic Brain Injury

Current screening and diagnostic tools for traumatic brain injury (TBI) have limitations in sensitivity and prognostication. Aberrant protease activity is a central process that drives disease progression in TBI and is associated with worsened prognosis; thus direct measurements of protease activity could provide more diagnostic information. In this study, a nanosensor is engineered to release a measurable signal into the blood and urine in response to activity from the TBI-associated protease calpain. Readouts from the nanosensor were designed to be compatible with ELISA and lateral flow assays, clinically-relevant assay modalities. In a mouse model of TBI, the nanosensor sensitivity is enhanced when ligands that target hyaluronic acid are added. In evaluation of mice with mild or severe injuries, the nanosensor identifies mild TBI with a higher sensitivity than the biomarker GFAP. This nanosensor technology allows for measurement of TBI-associated proteases without the need to directly access brain tissue, and has the potential to complement existing TBI diagnostic tools.

Effects of apocynin on sciatic nerve injury in rabbits

We investigated the effects of apocynin (APO) on experimental sciatic nerve compression injury in rabbits. We used 21 male rabbits divided randomly into three groups of seven. The control group was subjected to sciatic nerve compression with no further intervention. The APO treated group was subjected to compression injury and 20 mg/kg APO was administered daily for 21 days by intraperitoneal injection beginning the day after the injury. The sham group was treated with APO without injury. The control group exhibited shrinkage of axons, disruption of myelin sheaths and loss of nerve fibers. The damage for the control group was significantly greater than for the sham group. The severity of histopathology was decreased in the APO treated group compared to the control group, as was the oxidative stress index. Our findings suggest that APO treatment may contribute to healing of sciatic nerve damage.

Traumatic brain injury: Mechanisms, manifestations, and visual sequelae

Traumatic brain injury (TBI) results when external physical forces impact the head with sufficient intensity to cause damage to the brain. TBI can be mild, moderate, or severe and may have long-term consequences including visual difficulties, cognitive deficits, headache, pain, sleep disturbances, and post-traumatic epilepsy. Disruption of the normal functioning of the brain leads to a cascade of effects with molecular and anatomical changes, persistent neuronal hyperexcitation, neuroinflammation, and neuronal loss. Destructive processes that occur at the cellular and molecular level lead to inflammation, oxidative stress, calcium dysregulation, and apoptosis. Vascular damage, ischemia and loss of blood brain barrier integrity contribute to destruction of brain tissue. This review focuses on the cellular damage incited during TBI and the frequently life-altering lasting effects of this destruction on vision, cognition, balance, and sleep. The wide range of visual complaints associated with TBI are addressed and repair processes where there is potential for intervention and neuronal preservation are highlighted.

Elevated Serum NOX2 Levels Contribute to Delayed Cerebral Ischemia and a Poor Prognosis After Aneurysmal Subarachnoid Hemorrhage: A Prospective Cohort Study

Background

NADPH oxidase 2 (NOX2) is highly expressed in injured brain tissues. We determined serum NOX2 levels of aneurysmal subarachnoid hemorrhage (aSAH) patients and further investigated correlation of serum NOX2 levels with disease severity, delayed cerebral ischemia (DCI) plus prognosis after aSAH.

Methods

Serum NOX2 levels were measured in 123 aSAH patients and 123 healthy controls. World Federation of Neurological Surgeons scale (WFNS) score and modified Fisher (mFisher) score were utilized to assess disease severity. Modified Rankin scale (mRS) score was used to evaluate the clinical prognosis at 90 days after aSAH. Relations of serum NOX2 levels to DCI and 90-day poor prognosis (mRS score of 3-6) were analyzed using multivariate analysis. Receiver operating characteristic curve (ROC) was built to evaluate the prognostic predictive capability.

Results

Serum NOX2 levels in aSAH patients, compared with healthy controls, were significantly increased, and were independently correlated with WFNS score, mFisher score and post-stroke 90-day mRS score. Patients with poor prognosis or DCI had significantly higher serum NOX2 levels than other remainders, and serum NOX2 levels independently predicted 90-day poor prognosis and DCI. Serum NOX2 had high prognosis and DCI predictive abilities, and their areas under ROC curve were similar to those of WFNS score and mFisher score.

Conclusion

Serum NOX2 levels are significantly associated with hemorrhage severity, poor 90-day prognosis and DCI in aSAH patients. Hence, complement NOX2 may serve as a potential prognostic biomarker after aSAH.

Therapeutic targeting of microglia mediated oxidative stress after neurotrauma

Inflammation is a primary component of the central nervous system injury response. Traumatic brain and spinal cord injury are characterized by a pronounced microglial response to damage, including alterations in microglial morphology and increased production of reactive oxygen species (ROS). The acute activity of microglia may be beneficial to recovery, but continued inflammation and ROS production is deleterious to the health and function of other cells. Microglial nicotinamide adenine dinucleotide phosphate (NADPH) oxidase (NOX), mitochondria, and changes in iron levels are three of the most common sources of ROS. All three play a significant role in post-traumatic brain and spinal cord injury ROS production and the resultant oxidative stress. This review will evaluate the current state of therapeutics used to target these avenues of microglia-mediated oxidative stress after injury and suggest avenues for future research.

Blood-Brain Barrier Mechanisms in Stroke and Trauma

The brain microenvironment is tightly regulated. The blood-brain barrier (BBB), which is composed of cerebral endothelial cells, astrocytes, and pericytes, plays an important role in maintaining the brain homeostasis by regulating the transport of both beneficial and detrimental substances between circulating blood and brain parenchyma. After brain injury and disease, BBB tightness becomes dysregulated, thus leading to inflammation and secondary brain damage. In this chapter, we overview the fundamental mechanisms of BBB damage and repair after stroke and traumatic brain injury (TBI). Understanding these mechanisms may lead to therapeutic opportunities for brain injury.

Antioxidant therapies in traumatic brain injury

Oxidative stress plays a crucial role in traumatic brain injury (TBI) pathogenesis. Reactive oxygen species (ROS) and reactive nitrogen species (RNS) formed in excess after TBI synergistically contribute to secondary brain damage together with lipid peroxidation products (reactive aldehydes) and inflammatory mediators. Furthermore, oxidative stress, endoplasmic reticulum stress and inflammation potentiate each other. Following TBI, excessive oxidative stress overloads the endogenous cellular antioxidant system leading to cell death. To combat oxidative stress, several antioxidant therapies were tested in preclinical animal models of TBI. These include free radical scavengers, activators of antioxidant systems, Inhibitors of free radical generating enzymes and antioxidant enzymes. Many of these therapies showed promising outcomes including reduced edema, blood-brain barrier (BBB) protection, smaller contusion volume, and less inflammation. In addition, many antioxidant therapies also promoted better sensory, motor, and cognitive functional recovery after TBI. Overall, preventing oxidative stress is a viable therapeutic option to minimize the secondary damage and to improve the quality of life after TBI.

ROS-Scavenging Therapeutic Hydrogels for Modulation of the Inflammatory Response

Although reactive oxygen species (ROS) are essential for cellular processes, excessive ROS could be a major cause of various inflammatory diseases because of the oxidation of proteins, DNA, and membrane lipids. It has recently been suggested that the amount of ROS could thus be regulated to treat such physiological disorders. A ROS-scavenging hydrogel is a promising candidate for therapeutic applications because of its high biocompatibility, 3D matrix, and ability to be modified. Approaches to conferring antioxidant properties to normal hydrogels include embedding ROS-scavenging catalytic nanoparticles, modifying hydrogel polymer chains with ROS-adsorbing organic moieties, and incorporating ROS-labile linkers in polymer backbones. Such therapeutic hydrogels can be used for wound healing, cardiovascular diseases, bone repair, ocular diseases, and neurodegenerative disorders. ROS-scavenging hydrogels could eliminate oxidative stress, accelerate the regeneration process, and show synergetic effects with other drugs or therapeutic molecules. In this review, the mechanisms by which ROS are generated and scavenged in the body are outlined, and the effects of high levels of ROS and the resulting oxidative stress on inflammatory diseases are described. Next, the mechanism of ROS scavenging by hydrogels is explained depending on the ROS-scavenging agents embedded within the hydrogel. Lastly, the recent achievements in the development of ROS-scavenging hydrogels to treat various inflammation-associated diseases are presented.

Regulation of Phosphorylated State of NMDA Receptor by STEP61 Phosphatase after Mild-Traumatic Brain Injury: Role of Oxidative Stress

Traumatic Brain Injury (TBI) mediates neuronal death through several events involving many molecular pathways, including the glutamate-mediated excitotoxicity for excessive stimulation of N-methyl-D-aspartate receptors (NMDARs), producing activation of death signaling pathways. However, the contribution of NMDARs (distribution and signaling-associated to the distribution) remains incompletely understood. We propose a critical role of STEP₆₁ (Striatal-Enriched protein tyrosine phosphatase) in TBI; this phosphatase regulates the dephosphorylated state of the GluN2B subunit through two pathways: by direct dephosphorylation of tyrosine-1472 and indirectly via dephosphorylation and inactivation of Fyn kinase. We previously demonstrated oxidative stress’s contribution to NMDAR signaling and distribution using SOD2^+/− mice such a model. We performed TBI protocol using a controlled frontal impact device using C57BL/6 mice and SOD2^+/− animals. After TBI, we found alterations in cognitive performance, NMDAR-dependent synaptic function (decreased synaptic form of NMDARs and decreased synaptic current NMDAR-dependent), and increased STEP₆₁ activity. These changes are reduced partially with the STEP₆₁-inhibitor TC-2153 treatment in mice subjected to TBI protocol. This study contributes with evidence about the role of STEP₆₁ in the neuropathological progression after TBI and also the alteration in their activity, such as an early biomarker of synaptic damage in traumatic lesions.

Repetitive low-level blast exposure improves behavioral deficits and chronically lowers Aβ42 in an Alzheimer's disease transgenic mouse model

Public awareness of traumatic brain injury (TBI) in the military increased recently because of the conflicts in Iraq and Afghanistan where blast injury was the most common mechanism of injury. Besides overt injuries, concerns also exist over the potential adverse consequences of subclinical blast exposures, which are common for many service members. TBI is a risk factor for the later development of neurodegenerative diseases, including Alzheimer's disease (AD)-like disorders. Studies of acute TBI in humans and animals have suggested that increased processing of the amyloid precursor protein (APP) towards the amyloid beta protein (Aβ) may explain the epidemiological associations with AD. However, in a prior study we found in both rat and mouse models of blast overpressure exposure (BOP), that rather than increasing, rodent brain Aβ42 levels were decreased following acute blast exposure. Here we subjected APP/presenilin 1 transgenic mice (APP/PS1 Tg) to an extended sequence of repetitive low-level blast exposures (34.5 kPa) administered three times per week over 8 weeks. If initiated at 20 weeks of age, these repetitive exposures, which were designed to mimic human subclinical blast exposures, reduced anxiety and improved cognition as well as social interactions in APP/PS1 Tg mice, returning many behavioral parameters in APP/PS1 Tg mice to levels of non-transgenic wild type mice. Repetitive low-level blast exposure was less effective at improving behavioral deficits in APP/PS1 Tg mice when begun at 36 weeks of age. While amyloid plaque loads were unchanged, Aβ42 levels and Aβ oligomers were reduced in brain of mice exposed to repetitive low-level blast exposures initiated at 20 weeks of age, although levels did not directly correlate with behavioral parameters in individual animals. These results have implications for understanding the nature of blast effects on the brain and their relationship to human neurodegenerative diseases.

CCL5 via GPX1 activation protects hippocampal memory function after mild traumatic brain injury

Traumatic brain injury (TBI) is a prevalent head injury worldwide which increases the risk of neurodegenerative diseases. Increased reactive oxygen species (ROS) and inflammatory chemokines after TBI induces secondary effects which damage neurons. Targeting NADPH oxidase or increasing redox systems are ways to reduce ROS and damage. Earlier studies show that C–C motif chemokine ligand 5 (CCL5) has neurotrophic functions such as promoting neurite outgrowth as well as reducing apoptosis. Although CCL5 levels in blood are associated with severity in TBI patients, the function of CCL5 after brain injury is unclear. In the current study, we induced mild brain injury in C57BL/6 (wildtype, WT) mice and CCL5 knockout (CCL5-KO) mice using a weight-drop model. Cognitive and memory functions in mice were analyzed by Novel-object-recognition and Barnes Maze tests. The memory performance of both WT and KO mice were impaired after mild injury. Cognition and memory function in WT mice quickly recovered after 7 days but recovery took more than 14 days in CCL5-KO mice. FJC, NeuN and Hypoxyprobe staining revealed large numbers of neurons damaged by oxidative stress in CCL5-KO mice after mTBI. NADPH oxidase activity show increased ROS generation together with reduced glutathione peroxidase-1 (GPX1) and glutathione (GSH) activity in CCL5-KO mice; this was opposite to that seen in WT mice. CCL5 increased GPX1 expression and reduced intracellular ROS levels which subsequently increased cell survival both in primary neuron cultures and in an overexpression model using SHSY5Y cell. Memory impairment in CCL5-KO mice induced by TBI could be rescued by i.p. injection of the GSH precursor – N-acetylcysteine (NAC) or intranasal delivery of recombinant CCL5 into mice after injury. We conclude that CCL5 is an important molecule for GPX1 antioxidant activation during post-injury day 1–3, and protects hippocampal neurons from ROS as well as improves memory function after trauma.

Rice bran, an off-shoot to newer therapeutics in neurological disorders

Normal brain functioning involves the interaction of interconnected molecular and cellular activities, which appear to alter normal to abnormal brain functioning when worsened, contributing to the emergence of neurological disorders. There are currently millions of people who are living with brain disorders globally and this will rise if suitable prevention strategies are not explored. Nutraceutical intended to treat numerous health goals with little adverse effect possible together can be more beneficial than pharmaceutical monotherapy for fostering balanced brain functioning. Nutraceutical provides a specific composition of effective macronutrients and micronutrients that are difficult to synthesize in the laboratory. Numerous elements of rice fibers in rice bran are characterized as natural anti-oxidant and having potential anti-inflammatory activity. The rice bran captures interest among the researchers as it is widespread, affordable, and rich in nutrients including protein, fat, carbohydrates, bioactive components, and dietary fiber. This review covers the neuroprotective multiplicity of rice bran and its constituents to deter pathological conditions of the brain and to facilitate balanced brain functioning at the same time.

Microglia as therapeutic targets after neurological injury: strategy for cell therapy

INTRODUCTION

Microglia is the resident tissue macrophages of the central nervous system. Prolonged microglial activation often occurs after traumatic brain injury and is associated with deteriorating neurocognitive outcomes. Resolution of microglial activation is associated with limited tissue loss and improved neurocognitive outcomes. Limiting the prolonged pro-inflammatory response and the associated secondary tissue injury provides the rationale and scientific premise for considering microglia as a therapeutic target.

AREAS COVERED

In this review, we discuss markers of microglial activation, such as immunophenotype and microglial response to injury, including cytokine/chemokine release, free radical formation, morphology, phagocytosis, and metabolic shifts. We compare the origin and role in neuroinflammation of microglia and monocytes/macrophages. We review potential therapeutic targets to shift microglial polarization. Finally, we review the effect of cell therapy on microglia.

EXPERT OPINION

Dysregulated microglial activation after neurologic injury, such as traumatic brain injury, can worsen tissue damage and functional outcomes. There are potential targets in microglia to attenuate this activation, such as proteins and molecules that regulate microglia polarization. Cellular therapeutics that limit, but do not eliminate, the inflammatory response have improved outcomes in animal models by reducing pro-inflammatory microglial activation via secondary signaling. These findings have been replicated in early phase clinical trials.

The Role of NADPH Oxidase in Neuronal Death and Neurogenesis after Acute Neurological Disorders

Oxidative stress is a well-known common pathological process involved in mediating acute neurological injuries, such as stroke, traumatic brain injury, epilepsy, and hypoglycemia-related neuronal injury. However, effective therapeutic measures aimed at scavenging free reactive oxygen species have shown little success in clinical trials. Recent studies have revealed that NADPH oxidase, a membrane-bound enzyme complex that catalyzes the production of a superoxide free radical, is one of the major sources of cellular reactive oxygen species in acute neurological disorders. Furthermore, several studies, including our previous ones, have shown that the inhibition of NADPH oxidase can reduce subsequent neuronal injury in neurological disease. Moreover, maintaining appropriate levels of NADPH oxidase has also been shown to be associated with proper neurogenesis after neuronal injury. This review aims to present a comprehensive overview of the role of NADPH oxidase in neuronal death and neurogenesis in multiple acute neurological disorders and to explore potential pharmacological strategies targeting the NADPH-related oxidative stress pathways.

The second phase of brain trauma can be controlled by nutraceuticals that suppress DAMP-mediated microglial activation

INTRODUCTION

A delayed second wave of brain trauma is mediated in large part by microglia that are activated to a pro-inflammatory M1 phenotype by DAMP proteins released by dying neurons. These microglia can promote apoptosis or necrosis in neighboring neurons by producing a range of pro-inflammatory cytokines and the deadly oxidant peroxynitrite. This second wave could therefore be mitigated with agents that blunt the post-traumatic M1 activation of microglia and that preferentially promote a pro-healing M2 phenotype.

AREAS COVERED

The literature on nutraceuticals that might have clinical potential in this regard.

EXPERT OPINION

The chief signaling pathway whereby DAMPs promote M1 microglial activation involves activation of toll-like receptor 4 (TLR4), NADPH oxidase, NF-kappaB, and the stress activated kinases JNK and p38. The green tea catechin EGCG can suppress TLR4 expression. Phycocyanobilin can inhibit NOX2-dependent NADPH oxidase, ferulate and melatonin can oppose pro-inflammatory signal modulation by NADPH oxidase-derived oxidants. Long-chain omega-3 fatty acids, the soy isoflavone genistein, the AMPK activator berberine, glucosamine, and ketone bodies can down-regulate NF-kappaB activation. Vitamin D activity can oppose JNK/p38 activation. A sophisticated program of nutraceutical supplementation may have important potential for mitigating the second phase of neuronal death and aiding subsequent healing.

Oxidative stress in phenylketonuria-evidence from human studies and animal models, and possible implications for redox signaling

Phenylketonuria (PKU) is one of the commonest inborn error of amino acid metabolism. Before mass neonatal screening was possible, and the success of introducing diet therapy right after birth, the typical clinical finds in patients ranged from intellectual disability, epilepsy, motor deficits to behavioral disturbances and other neurological and psychiatric symptoms. Since early diagnosis and treatment became widespread, usually only those patients who do not strictly follow the diet present psychiatric, less severe symptoms such as anxiety, depression, sleep pattern disturbance, and concentration and memory problems. Despite the success of low protein intake in preventing otherwise severe outcomes, PKU's underlying neuropathophysiology remains to be better elucidated. Oxidative stress has gained acceptance as a disturbance implicated in the pathogenesis of PKU. The conception of oxidative stress has evolved to comprehend how it could interfere and ultimately modulate metabolic pathways regulating cell function. We summarize the evidence of oxidative damage, as well as compromised antioxidant defenses, from patients, animal models of PKU, and in vitro experiments, discussing the possible clinical significance of these findings. There are many studies on oxidative stress and PKU, but only a few went further than showing macromolecular damage and disturbance of antioxidant defenses. In this review, we argue that these few studies may point that oxidative stress may also disturb redox signaling in PKU, an aspect few authors have explored so far. The reported effect of phenylalanine on the expression or activity of enzymes participating in metabolic pathways known to be responsive to redox signaling might be mediated through oxidative stress.

The NLRP3 inflammasome: a potential therapeutic target for traumatic brain injury

Although the precise mechanisms contributing to secondary brain injury following traumatic brain injury are complex and obscure, a number of studies have demonstrated that inflammatory responses are an obvious and early feature in the pathogenesis of traumatic brain injury. Inflammasomes are multiprotein complexes that prompt the stimulation of caspase-1 and subsequently induce the maturation and secretion of proinflammatory cytokines, such as interleukin-1β and interleukin-18. These cytokines play a pivotal role in facilitating innate immune responses and inflammation. Among various inflammasome complexes, the NOD-like receptor family pyrin domain-containing 3 (NLRP3) inflammasome is the best characterized, a crucial role for NLRP3 has been demonstrated in various brain diseases, including traumatic brain injury. Several recent studies have revealed the contribution of NLRP3 inflammasome in identifying cellular damage and stimulating inflammatory responses to aseptic tissue injury after traumatic brain injury. Even more important, blocking or inhibiting the activation of the NLRP3 inflammasome may have substantial potential to salvage tissue damage during traumatic brain injury. In this review, we summarize recently described mechanisms that are involved in the activation and regulation of the NLRP3 inflammasome. Moreover, we review the recent investigations on the contribution of the NLRP3 inflammasome in the pathophysiology of TBI, and current advances and challenges in potential NLRP3-targeted therapies. A significant contribution of NLRP3 inflammasome activation to traumatic brain injury implies that therapeutic approaches focused on targeting specific inflammasome components could significantly improve the traumatic brain injury outcomes.

Traumatic brain injury and the misuse of alcohol, opioids, and cannabis

Traumatic brain injury (TBI), most often classified as concussion, is caused by biomechanical forces to the brain resulting in short- or long-term impairment in brain function. TBI resulting from military combat, sports, violence, falls, and vehicular accidents is a major cause of long-term physical, cognitive, and psychiatric dysfunction. Psychiatric disorders associated with TBI include depression, anxiety, and substance use disorder, all having significant implications for post-TBI recovery and rehabilitation. This chapter reviews the current preclinical and clinical literature describing the bidirectional relationship between TBI and misuse of three commonly abused drugs: alcohol, opioids, and cannabis. We highlight the influence of each of these drugs on the incidence of TBI, as well as trends in their use after TBI. Furthermore, we discuss factors that may underlie post-injury substance use. Understanding the complex relationship between TBI and substance misuse will enhance the clinical treatment of individuals suffering from these two highly comorbid conditions.

Traumatic Brain Injury: Oxidative Stress and Novel Anti-Oxidants Such as Mitoquinone and Edaravone

Traumatic brain injury (TBI) is a major health concern worldwide and is classified based on severity into mild, moderate, and severe. The mechanical injury in TBI leads to a metabolic and ionic imbalance, which eventually leads to excessive production of reactive oxygen species (ROS) and a state of oxidative stress. To date, no drug has been approved by the food and drug administration (FDA) for the treatment of TBI. Nevertheless, it is thought that targeting the pathology mechanisms would alleviate the consequences of TBI. For that purpose, antioxidants have been considered as treatment options in TBI and were shown to have a neuroprotective effect. In this review, we will discuss oxidative stress in TBI, the history of antioxidant utilization in the treatment of TBI, and we will focus on two novel antioxidants, mitoquinone (MitoQ) and edaravone. MitoQ can cross the blood brain barrier and cellular membranes to accumulate in the mitochondria and is thought to activate the Nrf2/ARE pathway leading to an increase in the expression of antioxidant enzymes. Edaravone is a free radical scavenger that leads to the mitigation of damage resulting from oxidative stress with a possible association to the activation of the Nrf2/ARE pathway as well.

The Role of NLRP3 Inflammasome in the Pathogenesis of Traumatic Brain Injury

Traumatic brain injury (TBI) represents an important problem of global health. The damage related to TBI is first due to the direct injury and then to a secondary phase in which neuroinflammation plays a key role. NLRP3 inflammasome is a component of the innate immune response and different diseases, such as neurodegenerative diseases, are characterized by NLRP3 activation. This review aims to describe NLRP3 inflammasome and the consequences related to its activation following TBI. NLRP3, caspase-1, IL-1β, and IL-18 are significantly upregulated after TBI, therefore, the use of nonspecific, but mostly specific NLRP3 inhibitors is useful to ameliorate the damage post-TBI characterized by neuroinflammation. Moreover, NLRP3 and the molecules associated with its activation may be considered as biomarkers and predictive factors for other neurodegenerative diseases consequent to TBI. Complications such as continuous stimuli or viral infections, such as the SARS-CoV-2 infection, may worsen the prognosis of TBI, altering the immune response and increasing the neuroinflammatory processes related to NLRP3, whose activation occurs both in TBI and in SARS-CoV-2 infection. This review points out the role of NLRP3 in TBI and highlights the hypothesis that NLRP3 may be considered as a potential therapeutic target for the management of neuroinflammation in TBI.

Modulating neuroinflammation and oxidative stress to prevent epilepsy and improve outcomes after traumatic brain injury

Traumatic brain injury (TBI) is a leading cause of death and disability in young adults worldwide. TBI survival is associated with persistent neuropsychiatric and neurological impairments, including posttraumatic epilepsy (PTE). To date, no pharmaceutical treatment has been found to prevent PTE or ameliorate neurological/neuropsychiatric deficits after TBI. Brain trauma results in immediate mechanical damage to brain cells and blood vessels that may never be fully restored given the limited regenerative capacity of brain tissue. This primary insult unleashes cascades of events, prominently including neuroinflammation and massive oxidative stress that evolve over time, expanding the brain injury, but also clearing cellular debris and establishing homeostasis in the region of damage. Accumulating evidence suggests that oxidative stress and neuroinflammatory sequelae of TBI contribute to posttraumatic epileptogenesis. This review will focus on possible roles of reactive oxygen species (ROS), their interactions with neuroinflammation in posttraumatic epileptogenesis, and emerging therapeutic strategies after TBI. We propose that inhibitors of the professional ROS-generating enzymes, the NADPH oxygenases and myeloperoxidase alone, or combined with selective inhibition of cyclooxygenase mediated signaling may have promise for the treatment or prevention of PTE and other sequelae of TBI. This article is part of the special issue entitled 'New Epilepsy Therapies for the 21st Century - From Antiseizure Drugs to Prevention, Modification and Cure of Epilepsy'.

Glia Maturation Factor (GMF) Regulates Microglial Expression Phenotypes and the Associated Neurological Deficits in a Mouse Model of Traumatic Brain Injury

Traumatic brain injury (TBI) induces inflammatory responses through microglial activation and polarization towards a more inflammatory state that contributes to the deleterious secondary brain injury. Glia maturation factor (GMF) is a pro-inflammatory protein that is responsible for neuroinflammation following insult to the brain, such as in TBI. We hypothesized that the absence of GMF in GMF-knockout (GMF-KO) mice would regulate microglial activation state and the M1/M2 phenotypes following TBI. We used the weight drop model of TBI in C57BL/6 mice wild-type (WT) and GMF-KO mice. Immunofluorescence staining, Western blot, and ELISA assays were performed to confirm TBI-induced histopathological and neuroinflammatory changes. Behavioral analysis was done to check motor coordination ability and cognitive function. We demonstrated that the deletion of GMF in GMF-KO mice significantly limited lesion volume, attenuated neuronal loss, inhibited gliosis, and activated microglia adopted predominantly anti-inflammatory (M2) phenotypes. Using an ELISA method, we found a gradual decrease in pro-inflammatory cytokines (TNF-α and IL-6) and upregulation of anti-inflammatory cytokines (IL-4 and IL-10) in GMF-KO mice compared with WT mice, thus, promoting the transition of microglia towards a more predominantly anti-inflammatory (M2) phenotype. GMF-KO mice showed significant improvement in motor ability, memory, and cognition. Overall, our results demonstrate that GMF deficiency regulates microglial polarization, which ameliorates neuronal injury and behavioral impairments following TBI in mice and concludes that GMF is a regulator of neuroinflammation and an ideal therapeutic target for the treatment of TBI.

Sodium butyrate inhibits high cholesterol-induced neuronal amyloidogenesis by modulating NRF2 stabilization-mediated ROS levels: involvement of NOX2 and SOD1

The gut-brain axis is currently being studied as a therapeutic strategy for neurological diseases, especially Alzheimer's disease (AD). Obesity results in the gut microbiota dysbiosis, which includes butyrate-producing bacteria are reduced. Although sodium butyrate (NaB) has emerged as the potential therapeutic substance in AD, there is a lack of detailed results into what signaling pathways affect amyloidogenesis in AD induced by obesity. Thus, we investigated the regulatory role of NaB on amyloidogenesis in neuronal cells under high cholesterol. In our results, we verified that increased amyloid β peptide (Aβ) accumulation in the brain of obese mice and a reduction in butyrate-producing bacteria due to the gut microbiota dysbiosis induced by obesity. We showed that NaB decreased the expression levels of beta-site amyloid precursor protein cleaving enzyme 1 (BACE1) and Aβ accumulation induced by high cholesterol in SK-N-MC cells. We demonstrated that NaB was absorbed in cells through sodium-coupled monocarboxylate transporter 1 (SMCT1) and then inhibited high cholesterol-induced Aβ accumulation. Subsequently, we also observed that reactive oxygen species (ROS) were overproduced because of increased NADPH oxidase 2 (NOX2) expression under high cholesterol. Meanwhile, NaB decreased NOX2 levels through a reduction of NF-κB activity, which ultimately inhibited Aβ accumulation caused by high cholesterol. We demonstrated that NaB increased the expression levels of p21 under high cholesterol, contributing to p21/NRF2 (Nuclear factor erythroid 2-related factor 2) colocalization, which leads to NRF2 stabilization. NRF2 stabilization causes NF-κB inactivation, followed by NOX2 suppression and superoxide dismutase 1 (SOD1) upregulation. Thus, NaB with SOD1 silencing under high cholesterol did not eliminate excessive ROS, and eventually resulted in Aβ accumulation. In conclusion, we demonstrated that NaB prevents excessive ROS through NOX2 suppression and SOD1 upregulation by p21/NRF2 pathway, which is critical for inhibiting BACE1-dependent amyloidogenesis in neuronal cells exposed to high cholesterol environment.

Mechanisms of Blood-Brain Barrier Dysfunction in Traumatic Brain Injury

Traumatic brain injuries (TBIs) account for the majority of injury-related deaths in the United States with roughly two million TBIs occurring annually. Due to the spectrum of severity and heterogeneity in TBIs, investigation into the secondary injury is necessary in order to formulate an effective treatment. A mechanical consequence of trauma involves dysregulation of the blood–brain barrier (BBB) which contributes to secondary injury and exposure of peripheral components to the brain parenchyma. Recent studies have shed light on the mechanisms of BBB breakdown in TBI including novel intracellular signaling and cell–cell interactions within the BBB niche. The current review provides an overview of the BBB, novel detection methods for disruption, and the cellular and molecular mechanisms implicated in regulating its stability following TBI.

Antioxidant status of uric acid, bilirubin, albumin and creatinine during the acute phase after traumatic brain injury: sex-specific features

BACKGROUND

It is known that the alteration of antioxidants can been seen in early phase after traumatic brain injury (TBI) in order to block oxidative damage, but little is known about the influence of sex on antioxidant system in patients with TBI. This study investigates whether there are sex differences in these endogenous antioxidant agents during the acute phase after TBI and their association with the disease.

METHODS

Serum levels of uric acid (UA), bilirubin, albumin and creatinine were measured in 421 individuals included 157 female TBI patients, 156 male TBI patients and 108 age- and sex-matched controls.

RESULTS

The statistically significant changes were found in UA, bilirubin, albumin and creatinine for both sexes with TBI, but the trend of changes in bilirubin and creatinine was opposite for gender groups. Serum levels of UA, bilirubin, albumin and creatinine were associated with the severity of TBI patients for both sexes. Male patient subgroups with elevated UA, albumin and creatinine had higher frequency of regaining consciousness in a month. Moreover, addition of UA and creatinine to the established clinical model had significantly improved the predictive performance over using clinical model alone in male patients with TBI. However, no similar findings were observed on female TBI patients.

CONCLUSION

Our results suggest sex-based differences in the serum endogenous antioxidant response to TBI. Use of serum UA and creatinine could help in the outcome prediction of male patients with TBI in combination with other prognostic factors.

Neuroinflammation Mediated by Glia Maturation Factor Exacerbates Neuronal Injury in an in vitro Model of Traumatic Brain Injury

Traumatic brain injury (TBI) is the primary cause of death and disability affecting over 10 million people in the industrialized world. TBI causes a wide spectrum of secondary molecular and cellular complications in the brain. However, the pathological events are still not yet fully understood. Previously, we have shown that the glia maturation factor (GMF) is a mediator of neuroinflammation in neurodegenerative diseases. To identify the potential molecular pathways accompanying TBI, we used an in vitro cell culture model of TBI. A standardized injury was induced by scalpel cut through a mixed primary cell culture of astrocytes, microglia and neurons obtained from both wild type (WT) and GMF-deficient (GMF-KO) mice. Cell culture medium and whole-cell lysates were collected at 24, 48, and 72 h after the scalpel cuts injury and probed for oxidative stress using immunofluorescence analysis. Results showed that oxidative stress markers such as glutathione and glutathione peroxidase were significantly reduced, while release of cytosolic enzyme lactate dehydrogenase along with nitric oxide and prostaglandin E2 were significantly increased in injured WT cells compared with injured GMF-KO cells. In addition, injured WT cells showed increased levels of oxidation product 4-hydroxynonenal and 8-oxo-2'-deoxyguanosine compared with injured GMF-KO cells. Further, we found that injured WT cells showed a significantly increased expression of glial fibrillary acidic protein, ionized calcium binding adaptor molecule 1, and phosphorylated ezrin/radixin/moesin proteins, and reduced microtubule associated protein expression compared with injured GMF-KO cells after injury. Collectively, our results demonstrate that GMF exacerbates the oxidative stress-mediated neuroinflammation that could be brought about by TBI-induced astroglial activation.

Microglia and macrophage metabolism in CNS injury and disease: The role of immunometabolism in neurodegeneration and neurotrauma

Innate immune responses, particularly activation of macrophages and microglia, are increasingly implicated in CNS disorders. It is now appreciated that the heterogeneity of functions adopted by these cells dictates neuropathophysiology. Research efforts to characterize the range of pro-inflammatory and anti-inflammatory phenotypes and functions adopted by microglia and macrophages are fueled by the potential for inflammatory cells to both exacerbate neurodegeneration and promote repair/disease resolution. The stimulation-based, M1/M2 classification system has emerged over the last decade as a common language to discuss macrophage and microglia heterogeneity across different fields. However, discontinuities between phenotypic markers and function create potential hurdles for the utility of the M1/M2 system in the development of effective immunomodulatory therapeutics for neuroinflammation. A framework to approach macrophage and microglia heterogeneity from a function-based phenotypic approach comes from rapidly emerging evidence that metabolic processes regulate immune cell activation. This concept of immunometabolism, however, is only beginning to unfold in the study of neurodegeneration and has yet to receive much focus in the context of neurotrauma. In this review, we first discuss the current views of macrophage and microglia heterogeneity and limitations of the M1/M2 classification system for neuropathological studies. We then review and discuss the current literature supporting metabolism as a regulator of microglia function in vitro. Lastly, we evaluate the evidence that metabolism regulates microglia and macrophage phenotype in vivo in models of Alzheimer's disease (AD), stroke, traumatic brain injury (TBI) and spinal cord injury (SCI).

Deterioration of cognitive function after transient cerebral ischemia with amyloid-β infusion-possible amelioration of cognitive function by AT2 receptor activation

Background

To promote understanding of the pathogenesis of cognitive impairment or dementia, we explored the potential interaction between transient cerebral ischemia and amyloid-β (Aβ) infusion in mediating cognitive decline and examined the possible ameliorative effect of angiotensin II type 2 (AT₂) receptor activation in vascular smooth muscle cells (VSMC) on this cognitive deficit.

Methods

Adult male wild-type mice (WT) and mice with VSMC-specific AT₂ receptor overexpression (smAT₂) were subjected to intracerebroventricular (ICV) injection of Aβ1-40. Transient cerebral ischemia was induced by 15 min of bilateral common carotid artery occlusion (BCCAO) 24 h after Aβ injection.

Results

Aβ injection in WT induced a cognitive decline, whereas BCCAO did not cause a significant cognitive deficit. In contrast, WT with BCCAO following Aβ injection exhibited more marked cognitive decline compared to Aβ injection alone, in concert with increases in superoxide anion production, nicotinamide adenine dinucleotide phosphate (NADPH) oxidase activity, and expression of p22phox, p40phox, monocyte chemoattractant protein (MCP)-1 and interleukin (IL)-1β in the hippocampus, and upregulation of RAGE (receptor for advanced glycation end product), an Aβ transporter. BCCAO following Aβ injection further enhanced neuronal pyknosis in the hippocampus, compared with BCCAO or Aβ injection alone. In contrast, smAT₂ did not show a cognitive decline, increase in oxidative stress, inflammation, and RAGE level or neuronal pyknosis, which were induced by BCCAO with/without Aβ injection in WT.

Conclusions

Transient cerebral ischemia might worsen Aβ infusion-mediated cognitive decline and vice versa, with possible involvement of amplified oxidative stress and inflammation and impairment of the RAGE-mediated Aβ clearance system, contributing to exaggerated neuronal degeneration. AT₂ receptor activation in VSMC could play an inhibitory role in this cognitive deficit.

Cationic Arginine-Rich Peptides (CARPs): A Novel Class of Neuroprotective Agents With a Multimodal Mechanism of Action

There are virtually no clinically available neuroprotective drugs for the treatment of acute and chronic neurological disorders, hence there is an urgent need for the development of new neuroprotective molecules. Cationic arginine-rich peptides (CARPs) are an expanding and relatively novel class of compounds, which possess intrinsic neuroprotective properties. Intriguingly, CARPs possess a combination of biological properties unprecedented for a neuroprotective agent including the ability to traverse cell membranes and enter the CNS, antagonize calcium influx, target mitochondria, stabilize proteins, inhibit proteolytic enzymes, induce pro-survival signaling, scavenge toxic molecules, and reduce oxidative stress as well as, having a range of anti-inflammatory, analgesic, anti-microbial, and anti-cancer actions. CARPs have also been used as carrier molecules for the delivery of other putative neuroprotective agents across the blood-brain barrier and blood-spinal cord barrier. However, there is increasing evidence that the neuroprotective efficacy of many, if not all these other agents delivered using a cationic arginine-rich cell-penetrating peptide (CCPPs) carrier (e.g., TAT) may actually be mediated largely by the properties of the carrier molecule, with overall efficacy further enhanced according to the amino acid composition of the cargo peptide, in particular its arginine content. Therefore, in reviewing the neuroprotective mechanisms of action of CARPs we also consider studies using CCPPs fused to a putative neuroprotective peptide. We review the history of CARPs in neuroprotection and discuss in detail the intrinsic biological properties that may contribute to their cytoprotective effects and their usefulness as a broad-acting class of neuroprotective drugs.

An Effective NADPH Oxidase 2 Inhibitor Provides Neuroprotection and Improves Functional Outcomes in Animal Model of Traumatic Brain Injury

Traumatic brain injury (TBI) has become a leading cause of death and disability all over the world. Pharmacological suppression of nicotinamide adenine dinucleotide phosphate (NADPH) oxidase 2 (NOX2) can inhibit oxidative stress which is implicated in the pathology of TBI. GSK2795039 was reported to target NOX2 to inhibit [Formula: see text] and ROS production. The present study aimed to investigate the effect of GSK2795039 on NOX2 activity and neurological deficits in a TBI mouse model. TBI mouse model was established by a weight-drop to mouse skull. GSK2795039 at a dose of 100 mg/kg was administrated to mice 30 min before TBI. NOX2 expression and activity were detected by Western blot and biochemical method. Neurological damage and apoptosis were detected by behavioral test and terminal deoxynucleotidyl transferase dUTP nick end labeling staining. GSK2795039 significantly inhibited NOX2 expression and activity in the TBI mouse model. It also attenuated TBI-induced neurological deficits, apoptosis, and neurological recovery. The results indicate that GSK2795039 can be used as a potential drug for TBI treatment.

Interferon-β Plays a Detrimental Role in Experimental Traumatic Brain Injury by Enhancing Neuroinflammation That Drives Chronic Neurodegeneration

DNA damage and type I interferons (IFNs) contribute to inflammatory responses after traumatic brain injury (TBI). TBI-induced activation of microglia and peripherally-derived inflammatory macrophages may lead to tissue damage and neurological deficits. Here, we investigated the role of IFN-β in secondary injury after TBI using a controlled cortical impact model in adult male IFN-β-deficient (IFN-β^-/-) mice and assessed post-traumatic neuroinflammatory responses, neuropathology, and long-term functional recovery. TBI increased expression of DNA sensors cyclic GMP-AMP synthase and stimulator of interferon genes in wild-type (WT) mice. IFN-β and other IFN-related and neuroinflammatory genes were also upregulated early and persistently after TBI. TBI increased expression of proinflammatory mediators in the cortex and hippocampus of WT mice, whereas levels were mitigated in IFN-β^-/- mice. Moreover, long-term microglia activation, motor, and cognitive function impairments were decreased in IFN-β^-/- TBI mice compared with their injured WT counterparts; improved neurological recovery was associated with reduced lesion volume and hippocampal neurodegeneration in IFN-β^-/- mice. Continuous central administration of a neutralizing antibody to the IFN-α/β receptor (IFNAR) for 3 d, beginning 30 min post-injury, reversed early cognitive impairments in TBI mice and led to transient improvements in motor function. However, anti-IFNAR treatment did not improve long-term functional recovery or decrease TBI neuropathology at 28 d post-injury. In summary, TBI induces a robust neuroinflammatory response that is associated with increased expression of IFN-β and other IFN-related genes. Inhibition of IFN-β reduces post-traumatic neuroinflammation and neurodegeneration, resulting in improved neurological recovery. Thus, IFN-β may be a potential therapeutic target for TBI.SIGNIFICANCE STATEMENT TBI frequently causes long-term neurological and psychiatric changes in head injury patients. TBI-induced secondary injury processes including persistent neuroinflammation evolve over time and can contribute to chronic neurological impairments. The present study demonstrates that TBI is followed by robust activation of type I IFN pathways, which have been implicated in microglial-associated neuroinflammation and chronic neurodegeneration. We examined the effects of genetic or pharmacological inhibition of IFN-β, a key component of type I IFN mechanisms to address its role in TBI pathophysiology. Inhibition of IFN-β signaling resulted in reduced neuroinflammation, attenuated neurobehavioral deficits, and limited tissue loss long after TBI. These preclinical findings suggest that IFN-β may be a potential therapeutic target for TBI.

Photobiomodulation therapy for repeated closed head injury in rats

Repeated traumatic brain injury, leads to cumulative neuronal injury and neurological impairments. There are currently no effective treatments to prevent these consequences. Growing interest is building in the use of transcranial photobiomodulation (PBM) therapy to treat traumatic brain injury. Here, we examined PBM in a repeated closed head injury (rCHI) rat model. Rats were administered a total of three closed head injuries, with each injury separated by 5 days. PBM treatment was initiated 2 hours after the first injury and administered daily for a total of 15 days. We found that PBM-treated rCHI rats had a significant reduction in motor ability, anxiety and cognitive deficits compared to CHI group. PBM group showed an increase of synaptic proteins and surviving neurons, along with a reduction in reactive gliosis and neuronal injury. These findings highlight the complexity of gliosis and neuronal injury following rCHI and suggest that PBM may be a viable treatment option to mitigate these effects and their detrimental consequences.

New Insights into Oxidative Damage and Iron Associated Impairment in Traumatic Brain Injury

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Traumatic Brain Injury is considered one of the most prevalent causes of death around the world; more than seventy millions of individuals sustain the condition per year. The consequences of traumatic brain injury on brain tissue are complex and multifactorial, hence, the current palliative treatments are limited to improve patients’ quality of life. The subsequent hemorrhage caused by trauma and the ongoing oxidative process generated by biochemical disturbances in the in the brain tissue may increase iron levels and reactive oxygen species. The relationship between oxidative damage and the traumatic brain injury is well known, for that reason, diminishing factors that potentiate the production of reactive oxygen species have a promissory therapeutic use. Iron chelators are molecules capable of scavenging the oxidative damage from the brain tissue and are currently in use for ironoverload- derived diseases.

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Here, we show an updated overview of the underlying mechanisms of the oxidative damage after traumatic brain injury. Later, we introduced the potential use of iron chelators as neuroprotective compounds for traumatic brain injury, highlighting the action mechanisms of iron chelators and their current clinical applications.

Inhibition of NOX2 signaling limits pain-related behavior and improves motor function in male mice after spinal cord injury: Participation of IL-10/miR-155 pathways

NADPH oxidase (NOX2) is an enzyme that induces reactive oxygen species (ROS) and serves as a switch between the pro-inflammatory and neurorestorative microglial/macrophage phenotypes; such changes play an important role in neuropathic pain and motor dysfunction. Increased NOX2 expression after spinal cord injury (SCI) has been reported, and inhibition of NOX2 improves motor function. However, the underlying mechanisms of NOX2 in post-traumatic pain and motor deficit remain unexplored. In the present study, we report that depletion of NOX2 (NOX2^-/-) or inhibition of NOX2 using NOX2ds-tat significantly reduced mechanical/thermal cutaneous hypersensitivity and motor dysfunction after moderate contusion SCI at T10 in male mice. Western blot (WB, 3 mm lesion area) and immunohistochemistry (IHC) showed that SCI elevates NOX2 expression predominantly in microglia/macrophages up to 8 weeks post-injury. Deletion of NOX2 significantly reduced CD11b⁺/CD45^hiF4/80⁺ macrophage infiltration at 24 h post-injury detected by flow cytometry and 8-OHG⁺ ROS production at 8 weeks post-injury by IHC in both lesion area and lumbar enlargement. NOX2 deficiency also altered microglial/macrophage pro-inflammatory and anti-inflammatory balance towards the neurorestorative response. WB analysis showed robust increase of Arginase-1 and YM1 proteins in NOX2^-/- mice. Furthermore, qPCR analysis showed significant up-regulation of anti-inflammatory cytokine IL-10 levels in NOX2^-/- mice, associated with reduced microRNA-155 expression. These findings were confirmed in CD11b⁺ microglia/macrophages isolated from spinal cord at 3 days post-injury. Taken together, our data suggest an important role for IL-10/miR-155 pathway in regulating NOX2-mediated SCI-dysfunction. Thus, specific targeting of NOX2 may provide an effective strategy for treating neurological dysfunction in SCI patients.

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.

Inula L. Secondary Metabolites against Oxidative Stress-Related Human Diseases

An imbalance in the production of reactive oxygen species in the body can cause an increase of oxidative stress that leads to oxidative damage to cells and tissues, which culminates in the development or aggravation of some chronic diseases, such as inflammation, diabetes mellitus, cancer, cardiovascular disease, and obesity. Secondary metabolites from Inula species can play an important role in the prevention and treatment of the oxidative stress-related diseases mentioned above. The databases Scopus, PubMed, and Web of Science and the combining terms Inula, antioxidant and secondary metabolites were used in the research for this review. More than 120 articles are reviewed, highlighting the most active compounds with special emphasis on the elucidation of their antioxidative-stress mechanism of action, which increases the knowledge about their potential in the fight against inflammation, cancer, neurodegeneration, and diabetes. Alantolactone is the most polyvalent compound, reporting interesting EC50 values for several bioactivities, while 1-O-acetylbritannilactone can be pointed out as a promising lead compound for the development of analogues with interesting properties. The Inula genus is a good bet as source of structurally diverse compounds with antioxidant activity that can act via different mechanisms to fight several oxidative stress-related human diseases, being useful for development of new drugs.

Incretin Mimetics as Rational Candidates for the Treatment of Traumatic Brain Injury

Traumatic brain injury (TBI) is becoming an increasing public health issue. With an annually estimated 1.7 million TBIs in the United States (U.S) and nearly 70 million worldwide, the injury, isolated or compounded with others, is a major cause of short- and long-term disability and mortality. This, along with no specific treatment, has made exploration of TBI therapies a priority of the health system. Age and sex differences create a spectrum of vulnerability to TBI, with highest prevalence among younger and older populations. Increased public interest in the long-term effects and prevention of TBI have recently reached peaks, with media attention bringing heightened awareness to sport and war related head injuries. Along with short-term issues, TBI can increase the likelihood for development of long-term neurodegenerative disorders. A growing body of literature supports the use of glucagon-like peptide-1 (GLP-1), glucose-dependent insulinotropic peptide (GIP), and glucagon (Gcg) receptor (R) agonists, along with unimolecular combinations of these therapies, for their potent neurotrophic/neuroprotective activities across a variety of cellular and animal models of chronic neurodegenerative diseases (Alzheimer's and Parkinson's diseases) and acute cerebrovascular disorders (stroke). Mild or moderate TBI shares many of the hallmarks of these conditions; recent work provides evidence that use of these compounds is an effective strategy for its treatment. Safety and efficacy of many incretin-based therapies (GLP-1 and GIP) have been demonstrated in humans for the treatment of type 2 diabetes mellitus (T2DM), making these compounds ideal for rapid evaluation in clinical trials of mild and moderate TBI.

Quantitative changes in perineuronal nets in development and posttraumatic condition

Perineuronal net (PNN) is a highly structured portion of the CNS extracellular matrix (ECM) regulating synaptic plasticity and a range of pathologic conditions including posttraumatic regeneration and epilepsy. Here we studied Wisteria floribunda agglutinin-stained histological sections to quantify the PNN size and enrichment of chondroitin sulfates in mouse brain and spinal cord. Somatosensory cortex sections were examined during the period of PNN establishment at postnatal days 14, 21 and 28. The single cell PNN size and the chondroitin sulfate intensity were quantified for all cortex layers and specifically for the cortical layer IV which has the highest density of PNN-positive neurons. We demonstrate that the chondroitin sulfate proteoglycan staining intensity is increased between P14 and P28 while the PNN size remains unchanged. We then addressed posttraumatic changes of the PNN expression in laminae 6 and 7 of cervical spinal cord following hemisection injury. We demonstrate increase of the chondroitin sulfate content at 1.6-1.8 mm rostrally from the injury site and increase of the density of PNN-bearing cells at 0.4-1.2 mm caudally from the injury site. We further demonstrate decrease of the single cell PNN area at 0.2 mm caudally from the injury site suggesting that the PNN ECM takes part in the posttraumatic tissue rearrangement in the spinal cord. Our results demonstrate new insights on the PNN structure dynamics in the developing and posttraumatic CNS.

Iron accentuated reactive oxygen species release by NADPH oxidase in activated microglia contributes to oxidative stress in vitro

BACKGROUND

Excessive iron contributes to oxidative stress after central nervous system injury. NADPH oxidase (NOX) enzymes are upregulated in microglia after pro-inflammatory activation and contribute to oxidative stress. The relationship between iron, microglia, NOX, and oxidative stress is currently unclear.

METHODS

We evaluated the effects of iron on lipopolysaccharide (LPS)-activated microglia and its secondary effect within neuronal co-cultures. Further, NOX2 and four specific inhibitors were tested to evaluate the relationship with the reactive oxygen species (ROS)-producing enzymes.

RESULTS

An iron dose-dependent increase in ROS production among microglia treated with LPS was identified. Interestingly, despite this increase in ROS, inflammatory polarization alterations were not detected among the microglia after exposure to iron and LPS. Co-culture experimentation between primary neurons and exposed microglia (iron and LPS) significantly reduced neuronal cell number at 24 h, suggesting a profound neurotoxic effect despite the lack of a change in polarization phenotype. NOX2 and NOX4 inhibition significantly reduced ROS production among microglia exposed to iron and LPS and reduced neuronal damage and death in response to microglial co-culture.

CONCLUSIONS

In conclusion, iron significantly increased ROS production and neurotoxicity without exacerbating LP-activated microglia phenotype in vitro, suggesting that iron contributes to microglia-related oxidative stress, and this may be a viable therapeutic target for injury or neurodegeneration. Further, this study highlights both NOX2 and NOX4 as potential therapeutic targets in the treatment of iron-induced microglia-related inflammation and neurotoxicity.

Reducing age-dependent monocyte-derived macrophage activation contributes to the therapeutic efficacy of NADPH oxidase inhibition in spinal cord injury

OBJECTIVE

The average age at the time of spinal cord injury (SCI) has increased to 43 years old. Middle-aged mice (14 months old, MO) exhibit impaired recovery after SCI with age-dependent increases in reactive oxygen species (ROS) production through NADPH oxidase (NOX) along with pro-inflammatory macrophage activation. Despite these aging differences, clinical therapies are being examined in individuals regardless of age based upon preclinical data generated primarily using young animals (∼4 MO). Our objective is to test the extent to which age affects SCI treatment efficacy. Specifically, we hypothesize that the effectiveness of apocynin, a NOX inhibitor, is age-dependent in SCI.

METHODS

Apocynin treatment (5 mg/kg) or vehicle was administered 1 and 6 h after moderate T9 contusion SCI (50kdyn IH) and then daily for 1 week to 4 and 14 MO mice. Locomotor and anatomical recovery was evaluated for 28 days. Monocyte-derived macrophage (MDM) and microglial activation and ROS production were evaluated at 3 and 28 days post-injury.

RESULTS

Apocynin improved functional and anatomical recovery in 14 but not 4 MO SCI mice. Apocynin-mediated recovery was coincident with significant reductions in MDM infiltration and MDM-ROS production in 14 MO SCI mice. Importantly, microglial activation was unaffected by treatment.

CONCLUSION

These results indicate that apocynin exhibits age-dependent neuroprotective effects by blocking excessive neuroinflammation through NOX-mediated ROS production in MDMs. Further, these data identify age as a critical regulator for SCI treatment efficacy and indicate that pharmacologically reduced macrophage, but not microglia, activation and ROS production reverses age-associated neurological impairments.