Traumatic brain injury increases beta-amyloid peptide 1-42 in cerebrospinal fluid

Intraneuronal accumulation of amyloid-β peptides as the pathomechanism linking autism and its co-morbidities: epilepsy and self-injurious behavior - the hypothesis

Autism spectrum disorder (ASD) is associated with enhanced processing of amyloid-β precursor protein (APP) by secretase-α, higher blood levels of sAPPα and intraneuronal accumulation of N-terminally truncated Aβ peptides in the brain cortex - mainly in the GABAergic neurons expressing parvalbumin - and subcortical structures. Brain Aβ accumulation has been also described in epilepsy-the frequent ASD co-morbidity. Furthermore, Aβ peptides have been shown to induce electroconvulsive episodes. Enhanced production and altered processing of APP, as well as accumulation of Aβ in the brain are also frequent consequences of traumatic brain injuries which result from self-injurious behaviors, another ASD co-morbidity. We discuss distinct consequences of accumulation of Aβ in the neurons and synapses depending on the Aβ species, their posttranslational modifications, concentration, level of aggregation and oligomerization, as well as brain structures, cell types and subcellular structures where it occurs. The biological effects of Aβ species which are discussed in the context of the pathomechanisms of ASD, epilepsy, and self-injurious behavior include modulation of transcription-both activation and repression; induction of oxidative stress; activation and alteration of membrane receptors' signaling; formation of calcium channels causing hyper-activation of neurons; reduction of GABAergic signaling - all of which lead to disruption of functions of synapses and neuronal networks. We conclude that ASD, epilepsy, and self-injurious behaviors all contribute to the enhanced production and accumulation of Aβ peptides which in turn cause and enhance dysfunctions of the neuronal networks that manifest as autism clinical symptoms, epilepsy, and self-injurious behaviors.

Temporal proteomics of human cerebrospinal fluid after severe traumatic brain injury

The pathophysiology of traumatic brain injury (TBI) requires further characterization to fully elucidate changes in molecular pathways. Cerebrospinal fluid (CSF) provides a rich repository of brain-associated proteins. In this retrospective observational study, we implemented high-resolution mass spectrometry to evaluate changes to the CSF proteome after severe TBI. 91 CSF samples were analyzed with mass spectrometry, collected from 16 patients with severe TBI (mean 32 yrs; 81% male) on day 0, 1, 2, 4, 7 and/or 10 post-injury (8-16 samples/timepoint) and compared to CSF obtained from 11 non-injured controls. We quantified 1152 proteins with mass spectrometry, of which approximately 80% were associated with CSF. 1083 proteins were differentially regulated after TBI compared to control samples. The most highly-upregulated proteins at each timepoint included neutrophil elastase, myeloperoxidase, cathepsin G, matrix metalloproteinase-8, and S100 calcium-binding proteins A8, A9 and A12-all proteins involved in neutrophil activation, recruitment, and degranulation. Pathway enrichment analysis confirmed the robust upregulation of proteins associated with innate immune responses. Conversely, downregulated pathways included those involved in nervous system development, and several proteins not previously identified after TBI such as testican-1 and latrophilin-1. We also identified 7 proteins (GM2A, Calsyntenin 1, FAT2, GANAB, Lumican, NPTX1, SFRP2) positively associated with an unfavorable outcome at 6 months post-injury. Together, these findings highlight the robust innate immune response that occurs after severe TBI, supporting future studies to target neutrophil-related processes. In addition, the novel proteins we identified to be differentially regulated by severe TBI warrant further investigation as potential biomarkers of brain damage or therapeutic targets.

Physiological Roles of Monomeric Amyloid-β and Implications for Alzheimer's Disease Therapeutics

Alzheimer's disease (AD) progressively inflicts impairment of synaptic functions with notable deposition of amyloid-β (Aβ) as senile plaques within the extracellular space of the brain. Accordingly, therapeutic directions for AD have focused on clearing Aβ plaques or preventing amyloidogenesis based on the amyloid cascade hypothesis. However, the emerging evidence suggests that Aβ serves biological roles, which include suppressing microbial infections, regulating synaptic plasticity, promoting recovery after brain injury, sealing leaks in the blood-brain barrier, and possibly inhibiting the proliferation of cancer cells. More importantly, these functions were found in in vitro and in vivo investigations in a hormetic manner, that is to be neuroprotective at low concentrations and pathological at high concentrations. We herein summarize the physiological roles of monomeric Aβ and current Aβ-directed therapies in clinical trials. Based on the evidence, we propose that novel therapeutics targeting Aβ should selectively target Aβ in neurotoxic forms such as oligomers while retaining monomeric Aβ in order to preserve the physiological functions of Aβ monomers.

Early Aβ42 Exposure Causes Learning Impairment in Later Life

Amyloid cascade hypothesis proposes that amyloid β (Aβ) accumulation is the initiator and major contributor to the development of Alzheimer’s disease (AD). However, this hypothesis has recently been challenged by clinical studies showing that reduction of Aβ accumulation in the brain does not accompany with cognitive improvement, suggesting that therapeutically targeting Aβ in the brain may not be sufficient for restoring cognitive function. Since the molecular mechanism underlying the progressive development of cognitive impairment after Aβ clearance is largely unknown, the reason of why there is no behavioral improvement after Aβ clearance remains elusive. In the current study, we demonstrated that transient Aβ expression caused learning deficit in later life, despite the accumulated Aβ was soon being removed after the expression. Early Aβ exposure decreased the cellular expression of XBP1 and both the antioxidants, catalase, and dPrx5, which made cells more vulnerable to oxidative stress in later life. Early induction of XBP1, catalase, and dPrx5 prevented the overproduction of ROS, improved the learning performance, and preserved the viability of cells in the later life with the early Aβ induction. Treating the early Aβ exposed flies with antioxidants such as vitamin E, melatonin and lipoic acid, after the removal of Aβ also preserved the learning ability in later life. Taken together, we demonstrated that early and transient Aβ exposure can have a profound impact on animal behavior in later life and also revealed the cellular and molecular mechanism underlying the development of learning impairment by the early and transient Aβ exposure.

Alzheimer's disease neuropathology is exacerbated following traumatic brain injury. Neuroprotection by co-administration of nanowired mesenchymal stem cells and cerebrolysin with monoclonal antibodies to amyloid beta peptide

Military personnel are prone to traumatic brain injury (TBI) that is one of the risk factors in developing Alzheimer's disease (AD) at a later stage. TBI induces breakdown of the blood-brain barrier (BBB) to serum proteins into the brain and leads to extravasation of plasma amyloid beta peptide (ΑβP) into the brain fluid compartments causing AD brain pathology. Thus, there is a need to expand our knowledge on the role of TBI in AD. In addition, exploration of the novel roles of nanomedicine in AD and TBI for neuroprotection is the need of the hour. Since stem cells and neurotrophic factors play important roles in TBI and in AD, it is likely that nanodelivery of these agents exert superior neuroprotection in TBI induced exacerbation of AD brain pathology. In this review, these aspects are examined in details based on our own investigations in the light of current scientific literature in the field. Our observations show that TBI exacerbates AD brain pathology and TiO₂ nanowired delivery of mesenchymal stem cells together with cerebrolysin-a balanced composition of several neurotrophic factors and active peptide fragments, and monoclonal antibodies to amyloid beta protein thwarted the development of neuropathology following TBI in AD, not reported earlier.

Association of cerebrospinal fluid protein biomarkers with outcomes in patients with traumatic and non-traumatic acute brain injury: systematic review of the literature

BACKGROUND

Acute brain injuries are associated with high mortality rates and poor long-term functional outcomes. Measurement of cerebrospinal fluid (CSF) biomarkers in patients with acute brain injuries may help elucidate some of the pathophysiological pathways involved in the prognosis of these patients.

METHODS

We performed a systematic search and descriptive review using the MEDLINE database and the PubMed interface from inception up to June 29, 2021, to retrieve observational studies in which the relationship between CSF concentrations of protein biomarkers and neurological outcomes was reported in patients with acute brain injury [traumatic brain injury, subarachnoid hemorrhage, acute ischemic stroke, status epilepticus or post-cardiac arrest]. We classified the studies according to whether or not biomarker concentrations were associated with neurological outcomes. The methodological quality of the studies was evaluated using the Newcastle-Ottawa quality assessment scale.

RESULTS

Of the 39 studies that met our criteria, 30 reported that the biomarker concentration was associated with neurological outcome and 9 reported no association. In TBI, increased extracellular concentrations of biomarkers related to neuronal cytoskeletal disruption, apoptosis and inflammation were associated with the severity of acute brain injury, early mortality and worse long-term functional outcome. Reduced concentrations of protein biomarkers related to impaired redox function were associated with increased risk of neurological deficit. In non-traumatic acute brain injury, concentrations of CSF protein biomarkers related to dysregulated inflammation and apoptosis were associated with a greater risk of vasospasm and a larger volume of brain ischemia. There was a high risk of bias across the studies.

CONCLUSION

In patients with acute brain injury, altered CSF concentrations of protein biomarkers related to cytoskeletal damage, inflammation, apoptosis and oxidative stress may be predictive of worse neurological outcomes.

The Bidirectional Relationship Between Sleep and Inflammation Links Traumatic Brain Injury and Alzheimer's Disease

Traumatic brain injury (TBI) and Alzheimer's disease (AD) are diseases during which the fine-tuned autoregulation of the brain is lost. Despite the stark contrast in their causal mechanisms, both TBI and AD are conditions which elicit a neuroinflammatory response that is coupled with physical, cognitive, and affective symptoms. One commonly reported symptom in both TBI and AD patients is disturbed sleep. Sleep is regulated by circadian and homeostatic processes such that pathological inflammation may disrupt the chemical signaling required to maintain a healthy sleep profile. In this way, immune system activation can influence sleep physiology. Conversely, sleep disturbances can exacerbate symptoms or increase the risk of inflammatory/neurodegenerative diseases. Both TBI and AD are worsened by a chronic pro-inflammatory microenvironment which exacerbates symptoms and worsens clinical outcome. Herein, a positive feedback loop of chronic inflammation and sleep disturbances is initiated. In this review, the bidirectional relationship between sleep disturbances and inflammation is discussed, where chronic inflammation associated with TBI and AD can lead to sleep disturbances and exacerbated neuropathology. The role of microglia and cytokines in sleep disturbances associated with these diseases is highlighted. The proposed sleep and inflammation-mediated link between TBI and AD presents an opportunity for a multifaceted approach to clinical intervention.

Traumatic brain injury triggers APP and Tau cleavage by delta-secretase, mediating Alzheimer's disease pathology

Traumatic brain injury (TBI) is associated in some studies with clinical dementia, and neuropathological features, including amyloid plaque deposition and Tau neurofibrillary degeneration commonly identified in Alzheimer's disease (AD). However, the molecular mechanisms linking TBI to AD remain unclear. Here we show that TBI activates transcription factor CCAAT/Enhancer Binding Protein Beta (C/EBPβ), increasing delta-secretase (AEP) expression. Activated AEP cleaves both APP and Tau at APP N585 and Tau N368 sites, respectively, which mediate AD pathogenesis by promoting Aβ production and Tau hyperphosphorylation and inducing neuroinflammation and neurotoxicity. Knockout of AEP or C/EBPβ diminishes TBI-induced AD-like pathology and cognitive impairment in the 3xTg AD mouse model. Remarkably, viral expression of AEP-resistant Tau N368A in the hippocampus of 3xTg mice also ameliorates the pathological and cognitive consequences of TBI. Finally, clinical TBI activates C/EBPβ and escalates AEP expression, leading to APP N585 and Tau N368 proteolytic cleavage in TBI patient brains. Hence, our findings support a potential role for AEP in linking TBI exposure with AD pathogenesis.

Subchronic Pathobiological Response Following Chronic Repetitive Mild Traumatic Brain Injury in an Aged Preclinical Model of Amyloid Pathogenesis

Repetitive mild traumatic brain injury (r-mTBI) is a risk factor for Alzheimer disease (AD). The precise nature of how r-mTBI leads to, or precipitates, AD pathogenesis remains unclear. In this study, we explore subchronic effects of chronic r-mTBI (12-impacts) administered over 1-month in aged-PS1/APP mice and littermate controls. We investigate specific mechanisms that may elucidate the molecular link between AD and r-mTBI, focusing primarily on amyloid and tau pathology, amyloid processing, glial activation states, and associated clearance mechanisms. Herein, we demonstrate r-mTBI in aged PS1/APP mice does not augment, glial activation, amyloid burden, or tau pathology (with exception of pS202-positive Tau) 1 month after exposure to the last-injury. However, we observed a decrease in brain soluble Aβ42 levels without any appreciable change in peripheral soluble Aβ42 levels. This was accompanied by an increase in brain insoluble to soluble Aβ42 ratio in injured PS1/APP mice compared with sham injury. A parallel reduction in phagocytic receptor, triggering receptor expressed on myeloid cells 2, was also observed. This study demonstrates very subtle subchronic effects of r-mTBI on a preexisting amyloid pathology background, which may be on a continuum toward a slow and worsening neurodegenerative outcome compared with sham injury, and therefore, have many implications, especially in the elderly population exposed to TBI.

Pathological Assessment of Chronic Traumatic Encephalopathy: Review of Concepts and Methodology

Chronic traumatic encephalopathy (CTE) has become a topic of considerable interest in recent years, with wide-ranging implications for athletes, military members, and other groups exposed to frequent concussive or subconcussive head trauma. The condition has been subject to intensive neuropathological characterization by various groups, with assessment methodologies and staging criteria proposed. Clinical characterization of symptoms has also been performed, but has not yet been definitively formalized. While efforts are underway to develop in vivo markers of tauopathies including CTE, these remain experimental at this time, necessitating postmortem analysis for definitive diagnosis. The putative link between development of cognitive and behavioral dysfunction and neuropathological findings of CTE may prompt requests for postmortem assessment in the forensic setting. Here, we review current concepts in CTE research, describe histopathological findings in CTE, and describe methodologies for pathological assessment of CTE which may be useful to the forensic pathologist.

A Unified View of Assessing the Pro-oxidant versus Antioxidant Nature of Amyloid Beta Conformers

Transition-metal-catalyzed oxidative stress is a widespread concern in the pathogenesis of Alzheimer's disease. However, the exact role of amyloid beta oligomers towards oxidative stress is widely debated. Assessing the oxidative nature of the oligomers in vitro is complicated by the different experimental conditions under which they are prepared. We have investigated Cu²⁺ -catalyzed reactive oxygen species (ROS) generation by using oligomers prepared in phosphate-buffered saline (Aβ^O-PBS ) and in cell culture medium (Aβ^O-CCM ), and compared their activities with respect to the monomers and fibrils prepared at neutral and acidic pH. Although both are deca- to dodecamers, the Aβ^O-PBS oligomers have a spherical morphology and are smaller than the Aβ^O-CCM . The Aβ^O-PBS behaved as pro-oxidants; in contrast, Aβ^O-CCM quench OH^. generation attributed to CCM itself. Although the pro-oxidant oligomers showed oxidation, they also partially protect themselves from radical damage and maintain their overall spherical arrangement. The monomers and fibrils manifested antioxidant properties: radical scavenging as opposed to redox silencing. A dual role of Aβ species depending on the stage of the disease is proposed. In the earlier stages, the monomers can act as antioxidants, whereas at the later stages, the oligomers take on a pro-oxidant role. Kaempferol, a natural flavonoid, bound Cu²⁺ in 2:1 ratio and abolished ROS production in all Aβ species. It also distinctly modified the folding landscape of Aβ species into new or altered morphologies.

Profiling biomarkers of traumatic axonal injury: From mouse to man

Traumatic brain injury (TBI) poses a major public health problem on a global scale. Its burden results from high mortality and significant morbidity in survivors. This stems, in part, from an ongoing inadequacy in diagnostic and prognostic indicators despite significant technological advances. Traumatic axonal injury (TAI) is a key driver of the ongoing pathological process following TBI, causing chronic neurological deficits and disability. The science underpinning biomarkers of TAI has been a subject of many reviews in recent literature. However, in this review we provide a comprehensive account of biomarkers from animal models to clinical studies, bridging the gap between experimental science and clinical medicine. We have discussed pathogenesis, temporal kinetics, relationships to neuro-imaging, and, most importantly, clinical applicability in order to provide a holistic perspective of how this could improve TBI diagnosis and predict clinical outcome in a real-life setting. We conclude that early and reliable identification of axonal injury post-TBI with the help of body fluid biomarkers could enhance current care of TBI patients by (i) increasing speed and accuracy of diagnosis, (ii) providing invaluable prognostic information, (iii) allow efficient allocation of rehabilitation services, and (iv) provide potential therapeutic targets. The optimal model for assessing TAI is likely to involve multiple components, including several blood biomarkers and neuro-imaging modalities, at different time points.

Current Opportunities for Clinical Monitoring of Axonal Pathology in Traumatic Brain Injury

Traumatic brain injury (TBI) is a multidimensional and highly complex disease commonly resulting in widespread injury to axons, due to rapid inertial acceleration/deceleration forces transmitted to the brain during impact. Axonal injury leads to brain network dysfunction, significantly contributing to cognitive and functional impairments frequently observed in TBI survivors. Diffuse axonal injury (DAI) is a clinical entity suggested by impaired level of consciousness and coma on clinical examination and characterized by widespread injury to the hemispheric white matter tracts, the corpus callosum and the brain stem. The clinical course of DAI is commonly unpredictable and it remains a challenging entity with limited therapeutic options, to date. Although axonal integrity may be disrupted at impact, the majority of axonal pathology evolves over time, resulting from delayed activation of complex intracellular biochemical cascades. Activation of these secondary biochemical pathways may lead to axonal transection, named secondary axotomy, and be responsible for the clinical decline of DAI patients. Advances in the neurocritical care of TBI patients have been achieved by refinements in multimodality monitoring for prevention and early detection of secondary injury factors, which can be applied also to DAI. There is an emerging role for biomarkers in blood, cerebrospinal fluid, and interstitial fluid using microdialysis in the evaluation of axonal injury in TBI. These biomarker studies have assessed various axonal and neuroglial markers as well as inflammatory mediators, such as cytokines and chemokines. Moreover, modern neuroimaging can detect subtle or overt DAI/white matter changes in diffuse TBI patients across all injury severities using magnetic resonance spectroscopy, diffusion tensor imaging, and positron emission tomography. Importantly, serial neuroimaging studies provide evidence for evolving axonal injury. Since axonal injury may be a key risk factor for neurodegeneration and dementias at long-term following TBI, the secondary injury processes may require prolonged monitoring. The aim of the present review is to summarize the clinical short- and long-term monitoring possibilities of axonal injury in TBI. Increased knowledge of the underlying pathophysiology achieved by advanced clinical monitoring raises hope for the development of novel treatment strategies for axonal injury in TBI.

Traumatic brain injuries

Traumatic brain injuries (TBIs) are clinically grouped by severity: mild, moderate and severe. Mild TBI (the least severe form) is synonymous with concussion and is typically caused by blunt non-penetrating head trauma. The trauma causes stretching and tearing of axons, which leads to diffuse axonal injury - the best-studied pathogenetic mechanism of this disorder. However, mild TBI is defined on clinical grounds and no well-validated imaging or fluid biomarkers to determine the presence of neuronal damage in patients with mild TBI is available. Most patients with mild TBI will recover quickly, but others report persistent symptoms, called post-concussive syndrome, the underlying pathophysiology of which is largely unknown. Repeated concussive and subconcussive head injuries have been linked to the neurodegenerative condition chronic traumatic encephalopathy (CTE), which has been reported post-mortem in contact sports athletes and soldiers exposed to blasts. Insights from severe injuries and CTE plausibly shed light on the underlying cellular and molecular processes involved in mild TBI. MRI techniques and blood tests for axonal proteins to identify and grade axonal injury, in addition to PET for tau pathology, show promise as tools to explore CTE pathophysiology in longitudinal clinical studies, and might be developed into diagnostic tools for CTE. Given that CTE is attributed to repeated head trauma, prevention might be possible through rule changes by sports organizations and legislators.

Traumatic brain injury as a risk factor for Alzheimer's disease: current knowledge and future directions

There is growing concern about the late effects of traumatic brain injury (TBI). This scoping review summarizes clinical research from the past 10 years that evaluates the relationship between TBI and Alzheimer's disease. This review identified five studies that found increased risk for dementia after TBI, two studies that found no increased risk and four studies that found a relationship only under certain conditions or in specified subsamples. Methodological differences across studies preclude direct comparison of results, and discrepant findings elucidate the complex course of post-TBI neurodegeneration. We discuss the factors that influence the strength and direction of the relationship between TBI and Alzheimer's disease, and the implications of this body of research for patient care and future research.

Biomarkers

Biomarkers are key tools and can provide crucial information on the complex cascade of events and molecular mechanisms underlying traumatic brain injury (TBI) pathophysiology. Obtaining a profile of distinct classes of biomarkers reflecting core pathologic mechanisms could enable us to identify and characterize the initial injury and the secondary pathologic cascades. Thus, they represent a logical adjunct to improve diagnosis, track progression and activity, guide molecularly targeted therapy, and monitor therapeutic response in TBI. Accordingly, great effort has been put into the identification of novel biomarkers in the past 25 years. However, the role of brain injury markers in clinical practice has been long debated, due to inconsistent regulatory standards and lack of reliable evidence of analytical validity and clinical utility. We present a comprehensive overview of the markers currently available while characterizing their potential role and applications in diagnosis, monitoring, drug discovery, and clinical trials in TBI. In reviewing these concepts, we discuss the recent inclusion of brain damage biomarkers in the diagnostic guidelines and provide perspectives on the validation of such markers for their use in the clinic.

Axonal Damage in Traumatic Brain Injury

Axonal damage is one of the most common and important pathologic features of traumatic brain injury. Severe diffuse axonal injury, resulting from inertial forces applied to the head, is associated with prolonged unconsciousness and poor outcome. The susceptibility of axons to mechanical injury appears to be due to both their viscoelastic properties and their highly organized structure in white matter tracts. Although axons are supple under normal conditions, they become brittle when exposed to rapid deformations associated with brain trauma. Accordingly, rapid stretch of axons can damage the axonal cytoskeleton, resulting in a loss of elasticity and impairment of axoplasmic transport. Subsequent swelling of the axon occurs in discrete bulb formations or in elongated varicosities that accumulate organelles. Calcium entry into damaged axons is thought to initiate further damage by the activation of proteases and the induction of mitochondrial swelling and dysfunction. Ultimately, swollen axons may become disconnected and contribute to additional neuropathologic changes in brain tissue. However, promising new therapies that reduce proteolytic activity or maintain mitochondrial integrity may attenuate progressive damage of injured axons following experimental brain trauma. Future advancements in the prevention and treatment of traumatic axonal injury will depend on our collective understanding of the relationship between the biomechanics and pathophysiology of various phases of axonal trauma.

Cerebral amyloid-β accumulation and deposition following traumatic brain injury--A narrative review and meta-analysis of animal studies

Traumatic brain injury (TBI) increases the risk of neurodegenerative disorders many years post-injury. However, molecular mechanisms underlying the relationship between TBI and neurodegenerative diseases, such as Alzheimer's disease (AD), remain to be elucidated. Nevertheless, previous studies have demonstrated a link between TBI and increased amyloid-β (Aβ), a protein involved in AD pathogenesis. Here, we review animal studies that measured Aβ levels following TBI. In addition, from a pool of initially identified 1209 published papers, we examined data from 19 eligible animal model studies using a meta-analytic approach. We found an acute increase in cerebral Aβ levels ranging from 24h to one month following TBI (overall log OR=2.97 ± 0.40, p<0.001). These findings may contribute to further understanding the relationship between TBI and future dementia risk. The methodological inconsistencies of the studies discussed in this review suggest the need for improved and more standardised data collection and study design, in order to properly elucidate the role of TBI in the expression and accumulation of Aβ.

Connectivity of Pathology: The Olfactory System as a Model for Network-Driven Mechanisms of Alzheimer's Disease Pathogenesis

The pathogenesis of Alzheimer’s disease (AD) has been postulated to preferentially impact specific neural networks in the brain. The olfactory system is a well-defined network that has been implicated in early stages of the disease, marked by impairment in olfaction and the presence of pathological hallmarks of the disease, even before clinical presentation. Discovering the cellular mechanisms involved in the connectivity of pathology will provide insight into potential targets for treatment. We review evidence from animal studies on sensory alteration through denervation or enrichment, which supports the notion of using the olfactory system to investigate the implications of connectivity and activity in the spread of pathology in AD.

Paradigm shift redefining molecular, metabolic and structural events in Alzheimer's disease involves a proposed contribution by transition metals. Defined lengthy preclinical stage provides new hope to circumvent advancement of disease- and age-related neurodegeneration

It is estimated that 5.5 Million North Americans suffer from varying degrees of Alzheimer's disease (AD) and by the year 2050 it may be one in 85 people globally (100 Million). It will be shown that heavy metal toxicity plays a significant role in sporadic AD. Although current literature speaks to involvement of metal ions (via Fenton reaction), studies and reviewers have yet to link cellular events including known structural changes such as amyloid plaque development to this metal toxicity the way it is proposed here. Contrary to the current AD model which positions BACE1 (β-secretase) as an aberrant or AD-advancing enzyme, it is proposed herein that the neuron's protective counteraction to this metal toxicity is, in fact, a justified increase in BACE1 activity and amyloid precursor protein (APP) processing to yield more secreted APP (sAPP) and β-amyloid peptide in response to metal toxicity. This new perspective which justifies a functional role for APP, BACE1 enzyme activity and the peptide products from this activity may at first appear to be counterintuitive. Compelling evidence, however, is presented and a mechanism is shown herein that validate BACE1 recruitment and the resulting β-amyloid protein as strategic countermeasures serving the cell effectively against neuro-impeding disease. It is proposed that β-amyloid peptide chelates and sequesters free heavy metals in the extracellular medium to aggregate as amyloid plaque while unchelated β-amyloid migrates across the cell membrane to chelate intracellular free divalent metals. The sequestered intracellular metal is subsequently chaperoned as a metallo-peptide to cross the plasma membrane and aggregate as amyloid plaques extracellularly. The BACE1 countermeasure is not genetic or metabolic aberration; and this novel conclusion demonstrates that it must not be inhibited as currently targeted. APP, BACE1, β-amyloid peptide, and sAPP play positive roles against the preclinical oxidative load that predates AD symptoms for as long as 20 years. A healthy neuron may tolerate free metal toxicity, such as iron in the case of injury-induced amyloid, for as long as twenty years due to this very BACE1 activity. In later stages, the uncontrolled metals and ROS are compounded by other factors which together overcome this BACE1/β-amyloid protein countermeasure. This results in a sudden increase in IL-1 leading to Tau's hyperphosphorylation as cited and eventually to Tau dissociation from the microtubule cytoskeleton interrupting cell trafficking. At this later stage of AD the β-amyloid protein which once served as a vehicle to escort toxic metals to the extracellular medium and a trap to form a relatively benign extraneuronal disposal site is no longer translocated due to interruption of trafficking and now accumulates intracellularly facilitating hyper-oxidative ROS levels and contributes to irreversible neuron apoptosis.

A new avenue for lithium: intervention in traumatic brain injury

Traumatic brain injury (TBI) is a leading cause of disability and death from trauma to central nervous system (CNS) tissues. For patients who survive the initial injury, TBI can lead to neurodegeneration as well as cognitive and motor deficits, and is even a risk factor for the future development of neurodegenerative disorders such as Alzheimer's disease. Preclinical studies of multiple neuropathological and neurodegenerative disorders have shown that lithium, which is primarily used to treat bipolar disorder, has considerable neuroprotective effects. Indeed, emerging evidence now suggests that lithium can also mitigate neurological deficits incurred from TBI. Lithium exerts neuroprotective effects and stimulates neurogenesis via multiple signaling pathways; it inhibits glycogen synthase kinase-3 (GSK-3), upregulates neurotrophins and growth factors (e.g., brain-derived neurotrophic factor (BDNF)), modulates inflammatory molecules, upregulates neuroprotective factors (e.g., B-cell lymphoma-2 (Bcl-2), heat shock protein 70 (HSP-70)), and concomitantly downregulates pro-apoptotic factors. In various experimental TBI paradigms, lithium has been shown to reduce neuronal death, microglial activation, cyclooxygenase-2 induction, amyloid-β (Aβ), and hyperphosphorylated tau levels, to preserve blood-brain barrier integrity, to mitigate neurological deficits and psychiatric disturbance, and to improve learning and memory outcome. Given that lithium exerts multiple therapeutic effects across an array of CNS disorders, including promising results in preclinical models of TBI, additional clinical research is clearly warranted to determine its therapeutic attributes for combating TBI. Here, we review lithium's exciting potential in ameliorating physiological as well as cognitive deficits induced by TBI.

Addressing the needs of traumatic brain injury with clinical proteomics

Background

Neurotrauma or injuries to the central nervous system (CNS) are a serious public health problem worldwide. Approximately 75% of all traumatic brain injuries (TBIs) are concussions or other mild TBI (mTBI) forms. Evaluation of concussion injury today is limited to an assessment of behavioral symptoms, often with delay and subject to motivation. Hence, there is an urgent need for an accurate chemical measure in biofluids to serve as a diagnostic tool for invisible brain wounds, to monitor severe patient trajectories, and to predict survival chances. Although a number of neurotrauma marker candidates have been reported, the broad spectrum of TBI limits the significance of small cohort studies. Specificity and sensitivity issues compound the development of a conclusive diagnostic assay, especially for concussion patients. Thus, the neurotrauma field currently has no diagnostic biofluid test in clinical use.

Content

We discuss the challenges of discovering new and validating identified neurotrauma marker candidates using proteomics-based strategies, including targeting, selection strategies and the application of mass spectrometry (MS) technologies and their potential impact to the neurotrauma field.

Summary

Many studies use TBI marker candidates based on literature reports, yet progress in genomics and proteomics have started to provide neurotrauma protein profiles. Choosing meaningful marker candidates from such ‘long lists’ is still pending, as only few can be taken through the process of preclinical verification and large scale translational validation. Quantitative mass spectrometry targeting specific molecules rather than random sampling of the whole proteome, e.g., multiple reaction monitoring (MRM), offers an efficient and effective means to multiplex the measurement of several candidates in patient samples, thereby omitting the need for antibodies prior to clinical assay design. Sample preparation challenges specific to TBI are addressed. A tailored selection strategy combined with a multiplex screening approach is helping to arrive at diagnostically suitable candidates for clinical assay development. A surrogate marker test will be instrumental for critical decisions of TBI patient care and protection of concussion victims from repeated exposures that could result in lasting neurological deficits.

Amyloid-β Peptides and Tau Protein as Biomarkers in Cerebrospinal and Interstitial Fluid Following Traumatic Brain Injury: A Review of Experimental and Clinical Studies

Traumatic brain injury (TBI) survivors frequently suffer from life-long deficits in cognitive functions and a reduced quality of life. Axonal injury, observed in many severe TBI patients, results in accumulation of amyloid precursor protein (APP). Post-injury enzymatic cleavage of APP can generate amyloid-β (Aβ) peptides, a hallmark finding in Alzheimer’s disease (AD). At autopsy, brains of AD and a subset of TBI victims display some similarities including accumulation of Aβ peptides and neurofibrillary tangles of hyperphosphorylated tau proteins. Most epidemiological evidence suggests a link between TBI and AD, implying that TBI has neurodegenerative sequelae. Aβ peptides and tau may be used as biomarkers in interstitial fluid (ISF) using cerebral microdialysis and/or cerebrospinal fluid (CSF) following clinical TBI. In the present review, the available clinical and experimental literature on Aβ peptides and tau as potential biomarkers following TBI is comprehensively analyzed. Elevated CSF and ISF tau protein levels have been observed following severe TBI and suggested to correlate with clinical outcome. Although Aβ peptides are produced by normal neuronal metabolism, high levels of long and/or fibrillary Aβ peptides may be neurotoxic. Increased CSF and/or ISF Aβ levels post-injury may be related to neuronal activity and/or the presence of axonal injury. The heterogeneity of animal models, clinical cohorts, analytical techniques, and the complexity of TBI in the available studies make the clinical value of tau and Aβ as biomarkers uncertain at present. Additionally, the link between early post-injury changes in tau and Aβ peptides and the future risk of developing AD remains unclear. Future studies using methods such as rapid biomarker sampling combined with enhanced analytical techniques and/or novel pharmacological tools could provide additional information on the importance of Aβ peptides and tau protein in both the acute pathophysiology and long-term consequences of TBI.

Biomarkers of mild traumatic brain injury in cerebrospinal fluid and blood

Mild traumatic brain injury (TBI), which is defined as a head trauma resulting in a brief loss of consciousness and/or alteration of mental state, is usually benign, but occasionally causes persistent and sometimes progressive symptoms. Whether a threshold for the amount of brain injury and/or individual vulnerability might contribute to the development of these long-term consequences is unknown. Furthermore, reliable diagnostic methods that can establish whether a blow to the head has affected the brain (and in what way) are lacking. In this Review, we discuss potential biomarkers of injury to different structures and cell types in the CNS that can be detected in body fluids. We present arguments in support of the need for further development and validation of such biomarkers, and for their use in assessing patients with head trauma in whom the brain might have been affected. Specifically, we focus on the need for such biomarkers in the management of sports-related concussion, the most common cause of mild TBI in young individuals, to prevent long-term neurological sequelae due to concussive or subconcussive blows to the head.

New perspectives on central and peripheral immune responses to acute traumatic brain injury

Traumatic injury to the brain (TBI) results in a complex set of responses involving various symptoms and long-term consequences. TBI of any form can cause cognitive, behavioral and immunologic changes in later life, which underscores the problem of underdiagnosis of mild TBI that can cause long-term neurological deficits. TBI disrupts the blood–brain barrier (BBB) leading to infiltration of immune cells into the brain and subsequent inflammation and neurodegeneration. TBI-induced peripheral immune responses can also result in multiorgan damage. Despite worldwide research efforts, the methods of diagnosis, monitoring and treatment for TBI are still relatively ineffective. In this review, we delve into the mechanism of how TBI-induced central and peripheral immune responses affect the disease outcome and discuss recent developments in the continuing effort to combat the consequences of TBI and new ways to enhance repair of the damaged brain.

Lithium reduces BACE1 overexpression, β amyloid accumulation, and spatial learning deficits in mice with traumatic brain injury

Traumatic brain injury (TBI) leads to both acute injury and long-term neurodegeneration, and is a major risk factor for developing Alzheimer's disease (AD). Beta amyloid (Aβ) peptide deposits in the brain are one of the pathological hallmarks of AD. Aβ levels increase after TBI in animal models and in patients with head trauma, and reducing Aβ levels after TBI has beneficial effects. Lithium is known to be neuroprotective in various models of neurodegenerative disease, and can reduce Aβ generation by modulating glycogen synthase kinase-3 (GSK-3) activity. In this study we explored whether lithium would reduce Aβ load after TBI, and improve learning and memory in a mouse TBI model. Lithium chloride (1.5 mEq/kg, IP) was administered 15 min after TBI, and once daily thereafter for up to 3 weeks. At 3 days after injury, lithium attenuated TBI-induced Aβ load increases, amyloid precursor protein (APP) accumulation, and β-APP-cleaving enzyme-1 (BACE1) overexpression in the corpus callosum and hippocampus. Increased Tau protein phosphorylation in the thalamus was also attenuated after lithium treatment following TBI at the same time point. Notably, lithium treatment significantly improved spatial learning and memory in the Y-maze test conducted 10 days after TBI, and in the Morris water maze test performed 17-20 days post-TBI, in association with increased hippocampal preservation. Thus post-insult treatment with lithium appears to alleviate the TBI-induced Aβ load and consequently improves spatial memory. Our findings suggest that lithium is a potentially useful agent for managing memory impairments after TBI or other head trauma.

Clinical Relevance of Biomarkers for Traumatic Brain Injury

Approximately 1.4 million people in the United States sustain a traumatic brain injury (TBI) each year, resulting in more than 235 000 hospitalizations and 50 000 deaths. An estimated 5.3 million Americans have current long-term disabilities as a result of TBI, which results in an estimated $60 billion in healthcare expenditures. Mild TBI (mTBI), which accounts for 80% to 90% of all cases, is the most prevalent form of brain injury in athletes. Many of these traumas still remain undetected, as they are difficult to diagnose. New biomarkers of TBI may allow more rapid diagnosis of TBI, improving early identification and treatment, and could help to predict clinical outcome. The field of TBI biomarkers is rapidly evolving. This chapter will discuss some of the most clinically relevant biomarkers for TBI that have been recently studied in human subjects.

Interactions between amyloid-β and hemoglobin: implications for amyloid plaque formation in Alzheimer's disease

Accumulation of amyloid-β (Aβ) peptides in the brain is one of the central pathogenic events in Alzheimer's disease (AD). However, why and how Aβ aggregates within the brain of AD patients remains elusive. Previously, we demonstrated hemoglobin (Hb) binds to Aβ and co-localizes with the plaque and vascular amyloid deposits in post-mortem AD brains. In this study, we further characterize the interactions between Hb and Aβ in vitro and in vivo and report the following observations: 1) the binding of Hb to Aβ required iron-containing heme; 2) other heme-containing proteins, such as myoglobin and cytochrome C, also bound to Aβ; 3) hemin-induced cytotoxicity was reduced in neuroblastoma cells by low levels of Aβ; 4) Hb was detected in neurons and glial cells of post-mortem AD brains and was up-regulated in aging and APP/PS1 transgenic mice; 5) microinjection of human Hb into the dorsal hippocampi of the APP/PS1 transgenic mice induced the formation of an envelope-like structure composed of Aβ surrounding the Hb droplets. Our results reveal an enhanced endogenous expression of Hb in aging brain cells, probably serving as a compensatory mechanism against hypoxia. In addition, Aβ binds to Hb and other hemoproteins via the iron-containing heme moiety, thereby reducing Hb/heme/iron-induced cytotoxicity. As some of the brain Hb could be derived from the peripheral circulation due to a compromised blood-brain barrier frequently observed in aged and AD brains, our work also suggests the genesis of some plaques may be a consequence of sustained amyloid accretion at sites of vascular injury.

Characterisation of the effect of knockout of the amyloid precursor protein on outcome following mild traumatic brain injury

The amyloid precursor protein (APP) increases following traumatic brain injury (TBI), although the functional significance of this remains unclear largely because the functions of the subsequent APP metabolites are so different: Aβ is neurotoxic whilst sAPPα is neuroprotective. To investigate this further, APP wildtype and knockout mice were subjected to mild diffuse TBI and their outcomes compared. APP knockout mice displayed significantly worse cognitive and motor deficits, as demonstrated by the Barnes Maze and rotarod respectively, than APP wildtype mice. This was associated with a significant increase in hippocampal and cortical cell loss, as well as axonal injury, in APP knockout mice and an impaired neuroreparative response as indicated by diminished GAP-43 immunoreactivity when compared to APP wildtype mice. This study is the first to demonstrate that endogenous APP is beneficial following mild TBI, suggesting that the upregulation of APP observed following injury is an acute protective response.

Is Alzheimer's disease amyloidosis the result of a repair mechanism gone astray?

Here, we synthesize several lines of evidence supporting the hypothesis that at least one function of amyloid-β is to serve as a part of the acute response to brain hemodynamic disturbances intended to seal vascular leakage. Given the resilient and adhesive physicochemical properties of amyloid, an abluminal hemostatic repair system might be highly advantageous, if deployed on a limited and short-term basis, in young individuals. However, in the aged, inevitable cardiovascular dysfunction combined with brain microvascular lesions may yield global chronic hypoperfusion that may lead to continuous amyloid deposition and consequential negative effects on neuronal viability. A large body of experimental evidence supports the hypothesis of an amyloid-β rescue function gone astray. Preventing or inducing the removal of amyloid in Alzheimer's disease (AD) has been simultaneously successful and disappointing. Amyloid deposits clearly play major roles in AD, but they may not represent the preeminent factor in dementia pathogenesis. Successful application of AD preventative approaches may hinge on an accurate and comprehensive view of comorbidities, including cardiovascular disease, diabetes, and head trauma.

Traumatic brain injury and amyloid-β pathology: a link to Alzheimer's disease?

Traumatic brain injury (TBI) has devastating acute effects and in many cases seems to initiate long-term neurodegeneration. Indeed, an epidemiological association between TBI and the development of Alzheimer's disease (AD) later in life has been demonstrated, and it has been shown that amyloid-β (Aβ) plaques — one of the hallmarks of AD — may be found in patients within hours following TBI. Here, we explore the mechanistic underpinnings of the link between TBI and AD, focusing on the hypothesis that rapid Aβ plaque formation may result from the accumulation of amyloid precursor protein in damaged axons and a disturbed balance between Aβ genesis and catabolism following TBI.

Biomarkers associated with diffuse traumatic axonal injury: exploring pathogenesis, early diagnosis, and prognosis

BACKGROUND

Diffuse traumatic axonal injury (dTAI) is a significant pathologic feature of traumatic brain injury and is associated with substantial mortality and morbidity. It is still a challenge for clinicians to make an early diagnosis of dTAI and generate accurate prognosis and direct therapeutic decisions because most patients rapidly progress to coma after trauma and because specific neurologic symptoms and focal lesions detectable with current routine imaging techniques are absent. To address these issues, many investigations have sought to identify biomarkers of dTAI.

METHODS

This article is a review of the pertinent medical literature.

RESULTS

From the perspective of the pathophysiology of dTAI, we reviewed several biomarkers that are associated with structural damage and biochemical cascades in the secondary injury or repair response to traumatic brain injury. Although some biomarkers are not specific to dTAI, they are nevertheless useful in elucidating its pathogenesis, making early diagnosis possible, predicting outcomes, and providing candidate targets for novel therapeutic strategies.

CONCLUSIONS

The availability of biomarker data, clinical case histories, and radiologic information can improve our current ability to diagnose and monitor pathogenic conditions and predict outcomes in patients with dTAI.

Amyloid-β oligomer specificity mediated by the IgM isotype--implications for a specific protective mechanism exerted by endogenous auto-antibodies

BACKGROUND

Alzheimers disease (AD) has been strongly linked to an anomalous self-assembly of the amyloid-β peptide (Aβ). The correlation between clinical symptoms of AD and Aβ depositions is, however, weak. Instead small and soluble Aβ oligomers are suggested to exert the major pathological effects. In strong support of this notion, immunological targeting of Aβ oligomers in AD mice-models shows that memory impairments can be restored without affecting the total burden of Aβ deposits. Consequently a specific immunological targeting of Aβ oligomers is of high therapeutic interest.

METHODOLOGY/PRINCIPAL FINDINGS

Previously the generation of conformational-dependent oligomer specific anti-Aβ antibodies has been described. However, to avoid the difficult task of identifying a molecular architecture only present on oligomers, we have focused on a more general approach based on the hypothesis that all oligomers expose multiple identical epitopes and therefore would have an increased binding to a multivalent receptor. Using the polyvalent IgM immunoglobulin we have developed a monoclonal anti-Aβ antibody (OMAB). OMAB only demonstrates a weak interaction with Aβ monomers and dimers having fast on and off-rate kinetics. However, as an effect of avidity, its interaction with Aβ-oligomers results in a strong complex with an exceptionally slow off-rate. Through this mechanism a selectivity towards Aβ oligomers is acquired and OMAB fully inhibits the cytotoxic effect exerted by Aβ(1-42) at highly substoichiometric ratios. Anti-Aβ auto-antibodies of IgM isotype are frequently present in the sera of humans. Through a screen of endogenous anti-Aβ IgM auto-antibodies from a group of healthy individuals we show that all displays a preference for oligomeric Aβ.

CONCLUSIONS/SIGNIFICANCE

Taken together we provide a simple and general mechanism for targeting of oligomers without the requirement of conformational-dependent epitopes. In addition, our results suggest that IgM anti-Aβ auto-antibodies may exert a more specific protective mechanism in vivo than previously anticipated.

Update on protein biomarkers in traumatic brain injury with emphasis on clinical use in adults and pediatrics

PURPOSE

This review summarizes protein biomarkers in mild and severe traumatic brain injury in adults and children and presents a strategy for conducting rationally designed clinical studies on biomarkers in head trauma.

METHODS

We performed an electronic search of the National Library of Medicine's MEDLINE and Biomedical Library of University of Pennsylvania database in March 2008 using a search heading of traumatic head injury and protein biomarkers. The search was focused especially on protein degradation products (spectrin breakdown product, c-tau, amyloid-beta(1-42)) in the last 10 years, but recent data on "classical" markers (S-100B, neuron-specific enolase, etc.) were also examined.

RESULTS

We identified 85 articles focusing on clinical use of biomarkers; 58 articles were prospective cohort studies with injury and/or outcome assessment.

CONCLUSIONS

We conclude that only S-100B in severe traumatic brain injury has consistently demonstrated the ability to predict injury and outcome in adults. The number of studies with protein degradation products is insufficient especially in the pediatric care. Cohort studies with well-defined end points and further neuroproteomic search for biomarkers in mild injury should be triggered. After critically reviewing the study designs, we found that large homogenous patient populations, consistent injury, and outcome measures prospectively determined cutoff values, and a combined use of different predictors should be considered in future studies.

Monitoring of brain interstitial total tau and beta amyloid proteins by microdialysis in patients with traumatic brain injury

OBJECT

Damage to axons contributes to postinjury disabilities and is commonly observed following traumatic brain injury (TBI). Traumatic brain injury is an important environmental risk factor for the development of Alzheimer disease (AD). In the present feasibility study, the aim was to use intracerebral microdialysis catheters with a high molecular cutoff membrane (100 kD) to harvest interstitial total tau (T-tau) and amyloid beta 1-42 (Abeta42) proteins, which are important biomarkers for axonal injury and for AD, following moderate-to-severe TBI.

METHODS

Eight patients (5 men and 3 women) were included in the study; 5 of the patients had a focal/mixed TBI and 3 had a diffuse axonal injury (DAI). Following the bedside analysis of the routinely measured energy metabolic markers (that is, glucose, lactate/pyruvate ratio, glycerol, and glutamate), the remaining dialysate was pooled and two 12-hour samples per day were used to analyze T-tau and Abeta42 by enzyme-linked immunosorbent assay from Day 1 up to 8 days postinjury.

RESULTS

The results show high levels of interstitial T-tau and Abeta42 postinjury. Patients with a predominantly focal lesion had higher interstitial T-tau levels than in the DAI group from Days 1 to 3 postinjury (p < 0.05). In contrast, patients with DAI had consistently higher Abeta42 levels when compared with patients with focal injury.

CONCLUSIONS

These results suggest that monitoring of interstitial T-tau and Abeta42 by using microdialysis may be an important tool when evaluating the presence and role of axonal injury following TBI.

Amyloid beta-Cu2+ complexes in both monomeric and fibrillar forms do not generate H2O2 catalytically but quench hydroxyl radicals

Oxidative stress plays a key role in Alzheimer's disease (AD). In addition, the abnormally high Cu(2+) ion concentrations present in senile plaques has provoked a substantial interest in the relationship between the amyloid beta peptide (Abeta) found within plaques and redox-active copper ions. There have been a number of studies monitoring reactive oxygen species (ROS) generation by copper and ascorbate that suggest that Abeta acts as a prooxidant producing H2O2. However, others have indicated Abeta acts as an antioxidant, but to date most cell-free studies directly monitoring ROS have not supported this hypothesis. We therefore chose to look again at ROS generation by both monomeric and fibrillar forms of Abeta under aerobic conditions in the presence of Cu(2+) with/without the biological reductant ascorbate in a cell-free system. We used a variety of fluorescence and absorption based assays to monitor the production of ROS, as well as Cu(2+) reduction. In contrast to previous studies, we show here that Abeta does not generate any more ROS than controls of Cu(2+) and ascorbate. Abeta does not silence the redox activity of Cu(2+/+) via chelation, but rather hydroxyl radicals produced as a result of Fenton-Haber Weiss reactions of ascorbate and Cu(2+) rapidly react with Abeta; thus the potentially harmful radicals are quenched. In support of this, chemical modification of the Abeta peptide was examined using (1)H NMR, and specific oxidation sites within the peptide were identified at the histidine and methionine residues. Our studies add significant weight to a modified amyloid cascade hypothesis in which sporadic AD is the result of Abeta being upregulated as a response to oxidative stress. However, our results do not preclude the possibility that Abeta in an oligomeric form may concentrate the redox-active copper at neuronal membranes and so cause lipid peroxidation.

Tauopathy with paired helical filaments in an aged chimpanzee

An enigmatic feature of age-related neurodegenerative diseases is that they seldom, if ever, are fully manifested in nonhuman species under natural conditions. The neurodegenerative tauopathies are typified by the intracellular aggregation of hyperphosphorylated microtubule-associated protein tau (MAPT) and the dysfunction and death of affected neurons. We document the first case of tauopathy with paired helical filaments in an aged chimpanzee (Pan troglodytes). Pathologic forms of tau in neuronal somata, neuropil threads, and plaque-like clusters of neurites were histologically identified throughout the neocortex and, to a lesser degree, in allocortical and subcortical structures. Ultrastructurally, the neurofibrillary tangles consisted of tau-immunoreactive paired helical filaments with a diameter and helical periodicity indistinguishable from those seen in Alzheimer's disease. A moderate degree of Abeta deposition was present in the cerebral vasculature and, less frequently, in senile plaques. Sequencing of the exons and flanking intronic regions in the genomic MAPT locus disclosed no mutations that are associated with the known human hereditary tauopathies, nor any polymorphisms of obvious functional significance. Although the lesion profile in this chimpanzee differed somewhat from that in Alzheimer's disease, the copresence of paired helical filaments and Abeta-amyloidosis indicates that the molecular mechanisms for the pathogenesis of the two canonical Alzheimer lesions--neurofibrillary tangles and senile plaques--are present in aged chimpanzees.

A lack of amyloid beta plaques despite persistent accumulation of amyloid beta in axons of long-term survivors of traumatic brain injury

Traumatic brain injury (TBI) is a risk factor for developing Alzheimer's disease (AD). Additionally, TBI induces AD-like amyloid beta (Abeta) plaque pathology within days of injury potentially resulting from massive accumulation of amyloid precursor protein (APP) in damaged axons. Here, progression of Abeta accumulation was examined using brain tissue from 23 cases with post-TBI survival of up to 3 years. Even years after injury, widespread axonal pathology was consistently observed and was accompanied by intra-axonal co-accumulations of APP with its cleavage enzymes, beta-site APP cleaving enzyme and presenilin-1 and their product, Abeta. However, in marked contrast to the plaque pathology noted in short-term cases post TBI, virtually no Abeta plaques were found in long-term survivors. A potential mechanism for Abeta plaque regression was suggested by the post-injury accumulation of an Abeta degrading enzyme, neprilysin. These findings fail to support the premise that progressive plaque pathology after TBI ultimately results in AD.

Site-specific Effects of Peptide Lipidation on β-Amyloid Aggregation and Cytotoxicity

Beta-amyloid (Abeta) aggregates at low concentrations in vivo, and this may involve covalently modified forms of these peptides. Modification of Abeta by 4-hydroxynonenal (4-HNE) initially increases the hydrophobicity of these peptides and subsequently leads to additional reactions, such as peptide cross-linking. To model these initial events, without confounding effects of subsequent reactions, we modified Abeta at each of its amino groups using a chemically simpler, close analogue of 4-HNE, the octanoyl group: K16-octanoic acid (OA)-Abeta, K28-OA-Abeta, and Nalpha-OA-Abeta. Octanoylation of these sites on Abeta-(1-40) had strikingly different effects on fibril formation. K16-OA-Abeta and K28-OA-Abeta, but not Nalpha-OA-Abeta, had increased propensity to aggregate. The type of aggregate (electron microscopic appearance) differed with the site of modification. The ability of octanoyl-Abeta peptides to cross-seed solutions of Abeta was the inverse of their ability to form fibrils on their own (i.e. Abeta approximately Nalpha-OA-Abeta>>K16-OA-Abeta>>K28-OA-Abeta). By CD spectroscopy, K16-OA-Abeta and K28-OA-Abeta had increased beta-sheet propensity compared with Abeta-(1-40) or Nalpha-OA-Abeta. K16-OA-Abeta and K28-OA-Abeta were more amphiphilic than Abeta-(1-40) or Nalpha-OA-Abeta, as shown by lower "critical micelle concentrations" and higher monolayer collapse pressures. Finally, K16-OA-Abeta and K28-OA-Abeta are much more cytotoxic to N2A cells than Abeta-(1-40) or Nalpha-OA-Abeta. The greater cytotoxicity of K16-OA-Abeta and K28-OA-Abeta may reflect their greater amphiphilicity. We conclude that lipidation can make Abeta more prone to aggregation and more cytotoxic, but these effects are highly site-specific.

Apolipoprotein E receptors and amyloid expression are modulated in an apolipoprotein E-dependent fashion in response to hippocampal deafferentation in rodent

The entorhinal cortex lesion paradigm is a widely accepted and efficient method to provoke reactive synaptogenesis and terminal remodeling in the adult CNS. This approach has been used successfully to contrast the profile of reactivity from various proteins associated with Alzheimer's disease pathophysiology in wild-type and apolipoprotein E (apoE)-deficient (APOE ko) mice. Results indicate that the production of the beta-amyloid 1-40 peptide (A beta 40) is increased in response to neuronal injury, with a timing that is different between wild-type and APOE ko animals. Moreover, we report that baseline levels of the A beta 40 peptide are significantly higher in the APOE ko mice. The expression of the apolipoprotein E receptor type 2 (apoER2) is also modulated by the deafferentation process in the hippocampus, but only in APOE ko mice. These results provide novel insights as to the molecular mechanisms responsible for the poor plastic response reported in apoE4-expressing and apoE deficient mice in response to hippocampal injury.

Amyloid induced suicidal erythrocyte death

Amyloid peptides are known to induce apoptosis in a wide variety of cells. Erythrocytes may similarly undergo suicidal death or eryptosis, which is characterized by scrambling of the cell membrane with subsequent exposure of phosphatidylserine (PS) at the cell surface. Eryptosis is triggered by increase of cytosolic Ca(2+) activity and by activation of acid sphingomyelinase with subsequent formation of ceramide. Triggers of eryptosis include energy depletion and isosmotic cell shrinkage (replacement of extracellular Cl(-) by impermeable gluconate for 24 h). The present study explored whether amyloid peptide Abeta (1-42) could trigger eryptosis and to possibly identify underlying mechanisms. Erythrocytes from healthy volunteers were exposed to amyloid and PS-exposure (annexin V binding), cell volume (forward scatter), cytosolic Ca(2+) activity (Fluo3 fluorescence) and ceramide formation (anti-ceramide antibody) were determined by FACS analysis. Exposure of erythrocytes to the amyloid peptide Abeta (1-42) (> or = 0.5 microM) for 24 h significantly triggered annexin V binding, an effect mimicked to a lesser extent by the amyloid peptide Abeta (1-40) (1 microM). Abeta (1-42) (> or = 1.0 microM) further significantly decreased forward scatter of erythrocytes. The effect of Abeta (1-42) (> or = 0.5 microM) on erythrocyte annexin V binding was paralleled by formation of ceramide but not by significant increase of cytosolic Ca(2+) activity. The presence of Abeta (1-42) further significantly enhanced the eryptosis following Cl(-) depletion but not of glucose depletion for 24 hours. The present observations disclose a novel action of Abeta (1-42), which may well contribute to the pathophysiological effects of amyloid peptides, such as vascular complications in Alzheimer's disease.

Traumatic brain injury and Alzheimer's disease: a review

In an effort to identify the factors that are involved in the pathogenesis of Alzheimer's disease (AD), epidemiological studies have featured prominently in contemporary research. Of those epidemiological factors, accumulating evidence implicates traumatic brain injury (TBI) as a possible predisposing factor in AD development. Exactly how TBI triggers the neurodegenerative cascade of events in AD remains controversial. There has been extensive research directed towards understanding the potential relationship between TBI and AD and the putative influence that apolipoprotein E (APOE) genotype has on this relationship. The aim of the current paper is to provide a critical summary of the experimental and human studies regarding the association between TBI, AD and APOE genotype. It will be shown that despite significant discrepancies in the literature, there still appears to be an increasing trend to support the hypothesis that TBI is a potential risk factor for AD. Furthermore, although it is known that APOE genotype plays an important role in AD, its link to a deleterious outcome following TBI remains inconclusive and ambiguous.

Neuroprotection following Fluid Percussion Brain Trauma: A Pilot Study Using Quercetin

Previously, we were able to demonstrate the neuroprotective effect of quercetin in an animal model of acute traumatic spinal cord injury. The objective of the present study was to determine whether any neuroprotective effect is seen when quercetin is administered in an animal model of traumatic brain injury. Twenty-six adult male Sprague-Dawley rats were submitted to moderate fluid percussion injury in the anterior midline position. Animals were divided into two experimental groups: one group received 25 mumol/kg quercetin starting 1 h after injury, while animals in the second group received saline vehicle (n = 13 per group). Eight animals were used as uninjured healthy controls. Eight animals in each experimental group were sacrificed at 24 h, while five animals per group were allowed to recover for 72 h following injury. Compound action potential amplitudes (CAPAs) were recorded on 400-microm vibrotome sections of the corpus callosum superfused with oxygenated artificial CSF (n = 3 per animal) in 20 experimental animals and five healthy controls. Three brains from animals in each experimental group and healthy controls were used for histological, immunocytochemical and biochemical analysis after sacrifice at 24 h. CAPAs in uninjured animals had a mean of 1.12 mV. This decreased to 0.55 mV in saline vehicle-treated injured animals by 24 h and changed little over the next 3 days. CAPAs were significantly better at 0.82 mV at 24 h and 0.76 mV at 3 days in quercetin-treated injured animals when compared to injured saline vehicle controls. Quercetin significantly prevented decrease of glutathione levels and decreased myeloperoxidase activity. We conclude that this dietary flavonoid has therapeutic potential following brain trauma.

Apolipoprotein Abeta: black sheep in a good family

Amyloid-beta (Abeta) has for a long time been thought to play a central role in the pathogenesis of Alzheimer disease (AD). Analysis of available data indicates that Abeta possesses properties of a metal-binding apolipoprotein influencing lipid transport and metabolism. Protection of lipoproteins from oxidation by transition metals, synaptic activity and role in the acute phase response represent plausible physiological functions of Abeta. However, these important biochemical qualities which may critically influence the development of AD, have been largely ignored by mainstream AD researchers, making Abeta appear to be a "black sheep" in a "good apolipoprotein" family. New studies are needed to shed further light on the physiological role of Abeta in lipid metabolism in the brain.