beta-amyloid (Abeta)42(43), abeta42, abeta40 and apoE immunostaining of plaques in fatal head injury

The Effect of Reduced Fibrinogen on Cerebrovascular Permeability during Traumatic Brain Injury in Fibrinogen Gene Heterozygous Knockout Mice

Vascular contribution to cognitive impairment and dementia (VCID) is a term referring to all types of cerebrovascular and cardiovascular disease-related cognitive decline, spanning many neuroinflammatory diseases including traumatic brain injury (TBI). This becomes particularly important during mild-to-moderate TBI (m-mTBI), which is characterized by short-term memory (STM) decline. Enhanced cerebrovascular permeability for proteins is typically observed during m-mTBI. We have previously shown that an increase in the blood content of fibrinogen (Fg) during m-mTBI results in enhanced cerebrovascular permeability. Primarily extravasated via a transcellular pathway, Fg can deposit into the parenchyma and exacerbate inflammatory reactions that can lead to neurodegeneration, resulting in cognitive impairment. In the current study, we investigated the effect of a chronic reduction in Fg concentration in blood on cerebrovascular permeability and the interactions of extravasated Fg with astrocytes and neurons. Cortical contusion injury (CCI) was used to generate m-mTBI in transgenic mice with a deleted Fg γ chain (Fg γ+/-), resulting in a low blood content of Fg, and in control C57BL/6J wild-type (WT) mice. Cerebrovascular permeability was tested in vivo. Interactions of Fg with astrocytes and neurons and the expression of neuronal nuclear factor-кB (NF-кB) were assessed via immunohistochemistry. The results showed that 14 days after CCI, there was less cerebrovascular permeability, lower extravascular deposition of Fg, less activation of astrocytes, less colocalization of Fg with neurons, and lower expression of neuronal pro-inflammatory NF-кB in Fg γ+/- mice compared to that found in WT mice. Combined, our data provide strong evidence that increased Fg extravasation, and its resultant extravascular deposition, triggers astrocyte activation and leads to potential interactions of Fg with neurons, resulting in the overexpression of neuronal NF-кB. These effects suggest that reduced blood levels of Fg can be beneficial in mitigating the STM reduction seen in m-mTBI.

Chronic traumatic encephalopathy and aging-related tau astrogliopathy in community-dwelling older persons with and without moderate-to-severe traumatic brain injury

This study examined the frequency of chronic traumatic encephalopathy-neuropathologic change (CTE-NC) and aging-related tau astrogliopathy (ARTAG) in community-dwelling older adults and tested the hypothesis that these tau pathologies are associated with a history of moderate-to-severe traumatic brain injury (msTBI), defined as a TBI with loss of consciousness >30 minutes. We evaluated CTE-NC, ARTAG, and Alzheimer disease pathologies in 94 participants with msTBI and 94 participants without TBI matched by age, sex, education, and dementia status TBI from the Rush community-based cohorts. Six (3%) of brains showed the pathognomonic lesion of CTE-NC; only 3 of these had a history of msTBI. In contrast, ARTAG was common in older brains (gray matter ARTAG = 77%; white matter ARTAG = 54%; subpial ARTAG = 51%); there were no differences in severity, type, or distribution of ARTAG pathology with respect to history of msTBI. Furthermore, those with msTBI did not have higher levels of PHF-tau tangles density but had higher levels of amyloid-β load (Estimate = 0.339, SE = 0.164, p = 0.040). These findings suggest that CTE-NC is infrequent while ARTAG is common in the community and that both pathologies are unrelated to msTBI. The association of msTBI with amyloid-β, rather than with tauopathies suggests differential mechanisms of neurodegeneration in msTBI.

Factors influencing recovery from mild traumatic brain injury

PRIMARY OBJECTIVE

This study determined whether initial GCS score, head CT results, cognitive performance on IMPACT testing, or APOE genotype most effectively predicted 1-month functional outcome after mild traumatic brain injury (mTBI). This study tested the hypotheses that participants with poor performance on initial cognitive testing and those with an APOEe4 genotype would exhibit a poorer 1-month recovery after mTBI.

RESEARCH DESIGN

Regression analysis determined which independent variables were most effective in predicting 1-month GOS-E or DRS score. Independent t-test procedures determined whether cognitive recovery varied across APOEe4 carriers.

METHODS AND PROCEDURES

49 participants admitted to the hospital with mTBI received cognitive evaluation within 48 hours after injury and again one month later. DNA analysis provided participant APOE genotype.

MAIN OUTCOMES AND RESULTS

Results showed that no study variables significantly predicted GOS-E or DRS scores, however, differences were identified when APOE groups were compared. Participants who were noncarriers of APOEe4 had significantly slower reaction times compared to APOEe4 carriers. Participants who were homozygous APOEe4 carriers had significantly lower instances of impulsivity than noncarriers.

CONCLUSIONS

Further research is needed to understand how APOE allele status and performance on initial cognitive testing may influence short-term recovery after mTBI.

Brain injury-induced dysfunction of the blood brain barrier as a risk for dementia

The blood-brain barrier (BBB) is a complex and dynamic physiological interface between brain parenchyma and cerebral vasculature. It is composed of closely interacting cells and signaling molecules that regulate movement of solutes, ions, nutrients, macromolecules, and immune cells into the brain and removal of products of normal and abnormal brain cell metabolism. Dysfunction of multiple components of the BBB occurs in aging, inflammatory diseases, traumatic brain injury (TBI, severe or mild repetitive), and in chronic degenerative dementing disorders for which aging, inflammation, and TBI are considered risk factors. BBB permeability changes after TBI result in leakage of serum proteins, influx of immune cells, perivascular inflammation, as well as impairment of efflux transporter systems and accumulation of aggregation-prone molecules involved in hallmark pathologies of neurodegenerative diseases with dementia. In addition, cerebral vascular dysfunction with persistent alterations in cerebral blood flow and neurovascular coupling contribute to brain ischemia, neuronal degeneration, and synaptic dysfunction. While the idea of TBI as a risk factor for dementia is supported by many shared pathological features, it remains a hypothesis that needs further testing in experimental models and in human studies. The current review focusses on pathological mechanisms shared between TBI and neurodegenerative disorders characterized by accumulation of pathological protein aggregates, such as Alzheimer's disease and chronic traumatic encephalopathy. We discuss critical knowledge gaps in the field that need to be explored to clarify the relationship between TBI and risk for dementia and emphasize the need for longitudinal in vivo studies using imaging and biomarkers of BBB dysfunction in people with single or multiple TBI.

No association between head injury with loss of consciousness and Alzheimer disease pathology-Findings from the University of Manchester Longitudinal Study of Cognition in Normal Healthy Old Age

OBJECTIVES

Head injury with loss of consciousness (HI-LOC) is a common occurrence. Some studies have linked such injuries with an increased risk of Alzheimer disease (AD). However, recent large clinicopathologic studies have failed to find a clear relationship between HI-LOC and the pathological changes associated with AD. The present study aims to further investigate the relationship between HI-LOC and AD pathology in the elderly.

METHODS/DESIGN

History of HI-LOC in participants in the University of Manchester Longitudinal Study of Cognition in Normal Healthy Old Age was ascertained. The donated brains of 110 of these individuals were assessed for AD pathology using consensus guidelines. Analyses aimed to elucidate relationships between HI-LOC and AD pathology.

RESULTS

No associations were found between incidence of HI-LOC and regional AD pathology or any of the three established measures of the neuropathology associated with AD: CERAD score, Thal phase, or Braak stage.

CONCLUSIONS

Single incidences of HI-LOC may not be sufficient to cause the pathology associated with late-stage AD. Other routes of damage, such as diffuse axonal injury or Lewy body pathology, may play a greater role in causing cognitive impairment associated with head injury.

Cause and consequence of Aβ - Lipid interactions in Alzheimer disease pathogenesis

Self-templating propagation of protein aggregate conformations is increasingly becoming a significant factor in many neurological diseases. In Alzheimer disease (AD), intrinsically disordered amyloid-β (Aβ) peptides undergo aggregation that is sensitive to environmental conditions. High-molecular weight aggregates of Aβ that form insoluble fibrils are deposited as senile plaques in AD brains. However, low-molecular weight aggregates called soluble oligomers are known to be the primary toxic agents responsible for neuronal dysfunction. The aggregation process is highly stochastic involving both homotypic (Aβ-Aβ) and heterotypic (Aβ with interacting partners) interactions. Two of the important members of interacting partners are membrane lipids and surfactants, to which Aβ shows a perpetual association. Aβ-membrane interactions have been widely investigated for more than two decades, and this research has provided a wealth of information. Although this has greatly enriched our understanding, the objective of this review is to consolidate the information from the literature that collectively showcases the unique phenomenon of lipid-mediated Aβ oligomer generation, which has largely remained inconspicuous. This is especially important because Aβ aggregate "strains" are increasingly becoming relevant in light of the correlations between the structure of aggregates and AD phenotypes. Here, we will focus on aspects of Aβ-lipid interactions specifically from the context of how lipid modulation generates a wide variety of biophysically and biochemically distinct oligomer sub-types. This, we believe, will refocus our thinking on the influence of lipids and open new approaches in delineating the mechanisms of AD pathogenesis. This article is part of a Special Issue entitled: Protein Aggregation and Misfolding at the Cell Membrane Interface edited by Ayyalusamy Ramamoorthy.

Age at injury and genotype modify acute inflammatory and neurofilament-light responses to mild CHIMERA traumatic brain injury in wild-type and APP/PS1 mice

Peak incidence of traumatic brain injury (TBI) occurs in both young and old individuals, and older age at injury is associated with worse outcome and poorer recovery. Moderate-severe TBI is a reported risk factor for dementia, including Alzheimer's disease (AD), but whether mild TBI (mTBI) alters AD pathogenesis is not clear. To delineate how age at injury and predisposition to amyloid formation affect the acute response to mTBI, we used the Closed Head Impact Model of Engineered Rotational Acceleration (CHIMERA) model of TBI to induce two mild injuries in wild-type (WT) and APP/PS1 mice at either 6 or 13months of age and assessed behavioural, histological and biochemical changes up to 14days post-injury. Age at injury did not alter acute behavioural responses to mTBI, including measures of neurological status, motor performance, spatial memory, fear, or anxiety, in either strain. Young APP/PS1 mice showed a subtle and transient increase in diffuse Aβ deposits after injury, whereas old APP/PS1 mice showed decreased amyloid deposits, without significant alterations in total soluble or insoluble Aβ levels at either age. Age at injury and genotype showed complex responses with respect to microglial and cytokine outcomes, where post-injury neuroinflammation is increased in old WT mice but attenuated in old APP/PS1 mice. Intriguingly, silver staining confirmed axonal damage in both strains and ages, yet only young WT and APP/PS1 mice showed neurofilament-positive axonal swellings after mTBI, as this response was almost entirely attenuated in old mice. Plasma neurofilament-light levels were significantly elevated after injury only in young APP/PS1 mice. This study suggests that mild TBI has minimal effects on Aβ metabolism, but that age and genotype can each modify acute outcomes related to white matter injury.

Localized cortical chronic traumatic encephalopathy pathology after single, severe axonal injury in human brain

Chronic traumatic encephalopathy (CTE) is a neurodegenerative disease associated with repetitive mild impact traumatic brain injury from contact sports. Recently, a consensus panel defined the pathognomonic lesion for CTE as accumulations of abnormally hyperphosphorylated tau (p-tau) in neurons (neurofibrillary tangles), astrocytes and cell processes distributed around small blood vessels at sulcal depths in irregular patterns within the cortex. The pathophysiological mechanism for this lesion is unknown. Moreover, a subset of CTE cases harbors cortical β-amyloid plaques. In this study, we analyzed postmortem brain tissues from five institutionalized patients with schizophrenia and history of surgical leucotomy with subsequent survival of at least another 40 years. Because leucotomy involves severing axons bilaterally in prefrontal cortex, this surgical procedure represents a human model of single traumatic brain injury with severe axonal damage and no external impact. We examined cortical tissues at the leucotomy site and at both prefrontal cortex rostral and frontal cortex caudal to the leucotomy site. For comparison, we analyzed brain tissues at equivalent neuroanatomical sites from non-leucotomized patients with schizophrenia, matched in age and gender. All five leucotomy cases revealed severe white matter damage with dense astrogliosis at the axotomy site and also neurofibrillary tangles and p-tau immunoreactive neurites in the overlying gray matter. Four cases displayed p-tau immunoreactivity in neurons, astrocytes and cell processes encompassing blood vessels at cortical sulcal depths in irregular patterns, similar to CTE. The three cases with apolipoprotein E ε4 haplotype showed scattered β-amyloid plaques in the overlying gray matter, but not the two cases with apolipoprotein E ε3/3 genotype. Brain tissue samples from prefrontal cortex rostral and frontal cortex caudal to the leucotomy site, and all cortical samples from the non-leucotomized patients, showed minimal p-tau and β-amyloid pathology. These findings suggest that chronic axonal damage contributes to the unique pathology of CTE over time.

Disordered APP metabolism and neurovasculature in trauma and aging: Combined risks for chronic neurodegenerative disorders

Traumatic brain injury (TBI), advanced age, and cerebral vascular disease are factors conferring increased risk for late onset Alzheimer's disease (AD). These conditions are also related pathologically through multiple interacting mechanisms. The hallmark pathology of AD consists of pathological aggregates of amyloid-β (Aβ) peptides and tau proteins. These molecules are also involved in neuropathology of several other chronic neurodegenerative diseases, and are under intense investigation in the aftermath of TBI as potential contributors to the risk for developing AD and chronic traumatic encephalopathy (CTE). The pathology of TBI is complex and dependent on injury severity, age-at-injury, and length of time between injury and neuropathological evaluation. In addition, the mechanisms influencing pathology and recovery after TBI likely involve genetic/epigenetic factors as well as additional disorders or comorbid states related to age and central and peripheral vascular health. In this regard, dysfunction of the aging neurovascular system could be an important link between TBI and chronic neurodegenerative diseases, either as a precipitating event or related to accumulation of AD-like pathology which is amplified in the context of aging. Thus with advanced age and vascular dysfunction, TBI can trigger self-propagating cycles of neuronal injury, pathological protein aggregation, and synaptic loss resulting in chronic neurodegenerative disease. In this review we discuss evidence supporting TBI and aging as dual, interacting risk factors for AD, and the role of Aβ and cerebral vascular dysfunction in this relationship. Evidence is discussed that Aβ is involved in cyto- and synapto-toxicity after severe TBI, and that its chronic effects are potentiated by aging and impaired cerebral vascular function. From a therapeutic perspective, we emphasize that in the fields of TBI- and aging-related neurodegeneration protective strategies should include preservation of neurovascular function.

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.

Dura mater is a potential source of Aβ seeds

Deposition of amyloid-β (Aβ) in the brain parenchyma and vessels is one of the hallmarks of Alzheimer disease (AD). Recent observations of Aβ deposition in iatrogenic Creutzfeldt-Jakob disease (iCJD) after dural grafting or treatment with pituitary extracts raised concerns whether Aβ is capable of transmitting disease as seen in prion diseases by the disease-associated prion protein. To address this issue, we re-sampled and re-evaluated archival material, including the grafted dura mater of two cases with iCJD (28 and 33-years-old) without mutations in the AβPP, PSEN1 and PSEN2 genes, and carrying ε3/ε3 alleles of the APOE gene. In addition, we evaluated 84 dura mater samples obtained at autopsy (mean age 84.9 ± 0.3) in the community-based VITA study for the presence of Aβ deposition. We show that the dura mater may harbor Aβ deposits (13 %) in the form of cerebral amyloid angiopathy or amorphous aggregates. In both iCJD cases, the grafted dura mater had accumulated Aβ. The morphology and distribution pattern of cerebral Aβ deposition together with the lack of tau pathology distinguishes the Aβ proteinopathy in iCJD from AD, from that seen in young individuals without cognitive decline carrying one or two APOE4 alleles, and from that related to traumatic brain injury. Our novel findings of Aβ deposits in the dura mater, including the grafted dura, and the distinct cerebral Aβ distribution in iCJD support the seeding properties of Aβ. However, in contrast to prion diseases, our study suggests that such Aβ seeding is unable to reproduce the full clinicopathological phenotype of AD.

Neurodegeneration and sport

The recent interest in concussion in sport has resulted in significant media focus about chronic traumatic encephalopathy (CTE), although a direct causative link(s) between concussion and CTE is not established. Typically, sport-related CTE occurs in a retired athlete with or without a history of concussion(s) who presents with a constellation of cognitive, mood, and/or behavioral symptoms and who has postmortem findings of tau deposition within the brain. There are many confounding variables, however, that can account for brain tau deposition, including genetic mutations, drugs, normal aging, environmental factors, postmortem brain processing, and toxins. To understand the roles of such factors in neurodegenerative diseases that may occur in athletes, this article reviews some neurodegenerative diseases that may present with similar findings in nonathletes. The article also reviews pathological changes identified with normal aging, and reviews the pathological findings of CTE in light of all these factors. While many of these athletes have a history of exposure to head impacts as a part of contact sport, there is insufficient evidence to establish causation between sports concussion and CTE. It is likely that many of the cases with neuropathological findings represent the normal aging process, the effects of opiate abuse, or a variant of frontotemporal lobar degeneration. Whether particular genetic causes may place athletes at greater risk of neurodegenerative disease is yet to be determined.

Effects of traumatic brain injury and posttraumatic stress disorder on Alzheimer's disease in veterans, using the Alzheimer's Disease Neuroimaging Initiative

Both traumatic brain injury (TBI) and posttraumatic stress disorder (PTSD) are common problems resulting from military service, and both have been associated with increased risk of cognitive decline and dementia resulting from Alzheimer's disease (AD) or other causes. This study aims to use imaging techniques and biomarker analysis to determine whether traumatic brain injury (TBI) and/or PTSD resulting from combat or other traumas increase the risk for AD and decrease cognitive reserve in Veteran subjects, after accounting for age. Using military and Department of Veterans Affairs records, 65 Vietnam War veterans with a history of moderate or severe TBI with or without PTSD, 65 with ongoing PTSD without TBI, and 65 control subjects are being enrolled in this study at 19 sites. The study aims to select subject groups that are comparable in age, gender, ethnicity, and education. Subjects with mild cognitive impairment (MCI) or dementia are being excluded. However, a new study just beginning, and similar in size, will study subjects with TBI, subjects with PTSD, and control subjects with MCI. Baseline measurements of cognition, function, blood, and cerebrospinal fluid biomarkers; magnetic resonance images (structural, diffusion tensor, and resting state blood-level oxygen dependent (BOLD) functional magnetic resonance imaging); and amyloid positron emission tomographic (PET) images with florbetapir are being obtained. One-year follow-up measurements will be collected for most of the baseline procedures, with the exception of the lumbar puncture, the PET imaging, and apolipoprotein E genotyping. To date, 19 subjects with TBI only, 46 with PTSD only, and 15 with TBI and PTSD have been recruited and referred to 13 clinics to undergo the study protocol. It is expected that cohorts will be fully recruited by October 2014. This study is a first step toward the design and statistical powering of an AD prevention trial using at-risk veterans as subjects, and provides the basis for a larger, more comprehensive study of dementia risk factors in veterans.

Post-traumatic neurodegeneration and chronic traumatic encephalopathy

Traumatic brain injury (TBI) is a leading cause of mortality and morbidity around the world. Concussive and subconcussive forms of closed-head injury due to impact or blast neurotrauma represent the most common types of TBI in civilian and military settings. It is becoming increasingly evident that TBI can lead to persistent, long-term debilitating effects, and in some cases, progressive neurodegeneration and chronic traumatic encephalopathy (CTE). The epidemiological literature suggests that a single moderate-to-severe TBI may be associated with accelerated neurodegeneration and increased risk of Alzheimer's disease, Parkinson's disease, or motor neuron disease. However, the pathologic phenotype of these post-traumatic neurodegenerations is largely unknown and there may be pathobiological differences between post-traumatic disease and the corresponding sporadic disorder. By contrast, the pathology of CTE is increasingly well known and is characterized by a distinctive pattern of progressive brain atrophy and accumulation of hyperphosphorylated tau neurofibrillary and glial tangles, dystrophic neurites, 43 kDa TAR DNA-binding protein (TDP-43) neuronal and glial aggregates, microvasculopathy, myelinated axonopathy, neuroinflammation, and white matter degeneration. Clinically, CTE is associated with behavioral changes, executive dysfunction, memory deficits, and cognitive impairments that begin insidiously and most often progress slowly over decades. Although research on the long-term effects of TBI is advancing quickly, the incidence and prevalence of post-traumatic neurodegeneration and CTE are unknown. Critical knowledge gaps include elucidation of pathogenic mechanisms, identification of genetic risk factors, and clarification of relevant variables-including age at exposure to trauma, history of prior and subsequent head trauma, substance use, gender, stress, and comorbidities-all of which may contribute to risk profiles and the development of post-traumatic neurodegeneration and CTE. This article is part of a Special Issue entitled 'Traumatic Brain Injury'.

The neuropathology of traumatic brain injury

Traumatic brain injury, a leading cause of mortality and morbidity, is divided into three grades of severity: mild, moderate, and severe, based on the Glasgow Coma Scale, the loss of consciousness, and the development of post-traumatic amnesia. Although mild traumatic brain injury, including concussion and subconcussion, is by far the most common, it is also the most difficult to diagnose and the least well understood. Proper recognition, management, and treatment of acute concussion and mild traumatic brain injury are the fundamentals of an emerging clinical discipline. It is also becoming increasingly clear that some mild traumatic brain injuries have persistent, and sometimes progressive, long-term debilitating effects. Evidence indicates that a single traumatic brain injury can precipitate or accelerate multiple age-related neurodegenerations, increase the risk of developing Alzheimer's disease, Parkinson's disease, and motor neuron disease, and that repetitive mild traumatic brain injuries can provoke the development of a tauopathy, chronic traumatic encephalopathy. Clinically, chronic traumatic encephalopathy is associated with behavioral changes, executive dysfunction, memory loss, and cognitive impairments that begin insidiously and progress slowly over decades. Pathologically, chronic traumatic encephalopathy produces atrophy of the frontal and temporal lobes, thalamus, and hypothalamus, septal abnormalities, and abnormal deposits of hyperphosphorylated tau (τ) as neurofibrillary tangles and disordered neurites throughout the brain. The incidence and prevalence of chronic traumatic encephalopathy and the genetic risk factors critical to its development are currently unknown. Chronic traumatic encephalopathy frequently occurs as a sole diagnosis, but may be associated with other neurodegenerative disorders, including Alzheimer's disease, Lewy body disease, and motor neuron disease. Currently, chronic traumatic encephalopathy can be diagnosed only at autopsy; however, promising efforts to develop imaging, spinal fluid, and peripheral blood biomarkers are underway to diagnose and monitor the course of disease in living subjects.

Chronic neurodegeneration after traumatic brain injury: Alzheimer disease, chronic traumatic encephalopathy, or persistent neuroinflammation?

It has long been suggested that prior traumatic brain injury (TBI) increases the subsequent incidence of chronic neurodegenerative disorders, including Alzheimer disease, Parkinson disease, and amyotrophic lateral sclerosis. Among these, the association with Alzheimer disease has the strongest support. There is also a long-recognized association between repeated concussive insults and progressive cognitive decline or other neuropsychiatric abnormalities. The latter was first described in boxers as dementia pugilistica, and has received widespread recent attention in contact sports such as professional American football. The term chronic traumatic encephalopathy was coined to attempt to define a "specific" entity marked by neurobehavioral changes and the extensive deposition of phosphorylated tau protein. Nearly lost in the discussions of post-traumatic neurodegeneration after traumatic brain injury has been the role of sustained neuroinflammation, even though this association has been well established pathologically since the 1950s, and is strongly supported by subsequent preclinical and clinical studies. Manifested by extensive microglial and astroglial activation, such chronic traumatic brain inflammation may be the most important cause of post-traumatic neurodegeneration in terms of prevalence. Critically, emerging preclinical studies indicate that persistent neuroinflammation and associated neurodegeneration may be treatable long after the initiating insult(s).

Amyloid imaging with carbon 11-labeled Pittsburgh compound B for traumatic brain injury

OBJECTIVES

To image amyloid deposition in patients with traumatic brain injury (TBI) using carbon 11-labeled Pittsburgh Compound B ([11C]PiB) positron emission tomography (PET) and to validate these findings using tritium-labeled PiB ([3H]PiB) autoradiography and immunocytochemistry in autopsy-acquired tissue.

DESIGN, SETTING, AND PARTICIPANTS

In vivo PET at tertiary neuroscience referral center and ex vivo immunocytochemistry of autopsy-acquired brain tissue from a neuropathology archive. [11C]PiB PET was used to image amyloid deposition in 11 controls (median [range] age, 35 [24-60] years) and in 15 patients (median [range] age, 33 [21-50] years) between 1 and 361 days after a TBI. [3H]PiB autoradiography and immunocytochemistry for β-amyloid (Aβ) and β-amyloid precursor protein in brain tissue were obtained from separate cohorts of 16 patients (median [range] age, 46 [21-70] years) who died between 3 hours and 56 days after a TBI and 7 controls (median [range] age, 61 [29-71] years) who died of other causes.

MAIN OUTCOMES AND MEASURES

We quantified the [11C]PiB distribution volume ratio and standardized uptake value ratio in PET images. The distribution volume ratio and the standardized uptake value ratio were measured in cortical gray matter, white matter, and multiple cortical and white matter regions of interest, as well as in striatal and thalamic regions of interest. We examined [3H]PiB binding and Aβ and β-amyloid precursor protein immunocytochemistry in autopsy-acquired brain tissue.

RESULTS

Compared with the controls, the patients with TBI showed significantly increased [11C]PiB distribution volume ratios in cortical gray matter and the striatum (corrected P < .05 for both), but not in the thalamus or white matter. Increases in [11C]PiB distribution volume ratios in patients with TBI were seen across most cortical subregions, were replicated using comparisons of standardized uptake value ratios, and could not be accounted for by methodological confounders. Autoradiography revealed [3H]PiB binding in neocortical gray matter, in regions where amyloid deposition was demonstrated by immunocytochemistry; white matter showed Aβ and β-amyloid precursor protein by immunocytochemistry, but no [3H]PiB binding. No plaque-associated amyloid immunoreactivity or [3H]PiB binding was seen in cerebellar gray matter in autopsy-acquired tissue from either controls or patients with TBI, although 1 sample of cerebellar tissue from a patient with TBI showed amyloid angiopathy in meningeal vessels.

CONCLUSIONS AND RELEVANCE

[11C]PiB shows increased binding following TBI. The specificity of this binding is supported by neocortical [3H]PiB binding in regions of amyloid deposition in the postmortem tissue of patients with TBI. [11C]PiB PET could be valuable in imaging amyloid deposition following TBI.

Aging, cortical injury and Alzheimer's disease-like pathology in the guinea pig brain

Alzheimer's disease (AD) is a progressive neurodegenerative disorder characterized histopathologically by the abnormal deposition of the proteins amyloid-beta (Aβ) and tau. A major issue for AD research is the lack of an animal model that accurately replicates the human disease, thus making it difficult to investigate potential risk factors for AD such as head injury. Furthermore, as age remains the strongest risk factor for most of the AD cases, transgenic models in which mutant human genes are expressed throughout the life span of the animal provide only limited insight into age-related factors in disease development. Guinea pigs (Cavia porcellus) are of interest in AD research because they have a similar Aβ sequence to humans and thus may present a useful non-transgenic animal model of AD. Brains from guinea pigs aged 3-48 months were examined to determine the presence of age-associated AD-like pathology. In addition, fluid percussion-induced brain injury was performed to characterize mechanisms underlying the association between AD risk and head injury. No statistically significant changes were detected in the overall response to aging, although we did observe some region-specific changes. Diffuse deposits of Aβ were found in the hippocampal region of the oldest animals and alterations in amyloid precursor protein processing and tau immunoreactivity were observed with age. Brain injury resulted in a strong and sustained increase in amyloid precursor protein and tau immunoreactivity without Aβ deposition, over 7 days. Guinea pigs may therefore provide a useful model for investigating the influence of environmental and non-genetic risk factors on the pathogenesis of AD.

Review: the long-term consequences of microglial activation following acute traumatic brain injury

The brain is vulnerable to a number of acute insults, with traumatic brain injury being among the commonest. Neuroinflammation is a common response to acute injury and microglial activation is a key component of the inflammatory response. In the acute and subacute phase it is likely that this response is protective and forms an important part of the normal tissue reaction. However, there is considerable literature demonstrating an association between acute traumatic brain injury to the brain and subsequent cognitive decline. This article will review the epidemiological literature relating to both single and repetitive head injury. It will focus on the neuropathological features associated with long-term complications of a single blunt force head injury, repetitive head injury and blast head injury, with particular reference to chronic traumatic encephalopathy, including dementia pugilistica. Neuroinflammation has been postulated as a key mechanism linking acute traumatic brain injury with subsequent neurodegenerative disease, and this review will consider the response to injury in the acute phase and how this may be detrimental in the longer term, and discuss potential genetic factors which may influence this cellular response. Finally, this article will consider future directions for research and potential future therapies.

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.

Neurochemical profile of dementia pugilistica

Dementia pugilistica (DP), a suite of neuropathological and cognitive function declines after chronic traumatic brain injury (TBI), is present in approximately 20% of retired boxers. Epidemiological studies indicate TBI is a risk factor for neurodegenerative disorders including Alzheimer disease (AD) and Parkinson disease (PD). Some biochemical alterations observed in AD and PD may be recapitulated in DP and other TBI persons. In this report, we investigate long-term biochemical changes in the brains of former boxers with neuropathologically confirmed DP. Our experiments revealed biochemical and cellular alterations in DP that are complementary to and extend information already provided by histological methods. ELISA and one-dimensional and two dimensional Western blot techniques revealed differential expression of select molecules between three patients with DP and three age-matched non-demented control (NDC) persons without a history of TBI. Structural changes such as disturbances in the expression and processing of glial fibrillary acidic protein, tau, and α-synuclein were evident. The levels of the Aβ-degrading enzyme neprilysin were reduced in the patients with DP. Amyloid-β levels were elevated in the DP participant with the concomitant diagnosis of AD. In addition, the levels of brain-derived neurotrophic factor and the axonal transport proteins kinesin and dynein were substantially decreased in DP relative to NDC participants. Traumatic brain injury is a risk factor for dementia development, and our findings are consistent with permanent structural and functional damage in the cerebral cortex and white matter of boxers. Understanding the precise threshold of damage needed for the induction of pathology in DP and TBI is vital.

Acute and chronic traumatic encephalopathies: pathogenesis and biomarkers

Over the past decade, public awareness of the long-term pathological consequences of traumatic brain injury (TBI) has increased. Such awareness has been stimulated mainly by reports of progressive neurological dysfunction in athletes exposed to repetitive concussions in high-impact sports such as boxing and American football, and by the rising number of TBIs in war veterans who are now more likely to survive explosive blasts owing to improved treatment. Moreover, the entity of chronic traumatic encephalopathy (CTE)--which is marked by prominent neuropsychiatric features including dementia, parkinsonism, depression, agitation, psychosis, and aggression--has become increasingly recognized as a potential late outcome of repetitive TBI. Annually, about 1% of the population in developed countries experiences a clinically relevant TBI. The goal of this Review is to provide an overview of the latest understanding of CTE pathophysiology, and to delineate the key issues that are challenging clinical and research communities, such as accurate quantification of the risk of CTE, and development of reliable biomarkers for single-incident TBI and CTE.

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.

The neuropathology and neurobiology of traumatic brain injury

The acute and long-term consequences of traumatic brain injury (TBI) have received increased attention in recent years. In this Review, we discuss the neuropathology and neural mechanisms associated with TBI, drawing on findings from sports-induced TBI in athletes, in whom acute TBI damages axons and elicits both regenerative and degenerative tissue responses in the brain and in whom repeated concussions may initiate a long-term neurodegenerative process called dementia pugilistica or chronic traumatic encephalopathy (CTE). We also consider how the neuropathology and neurobiology of CTE in many ways resembles other neurodegenerative illnesses such as Alzheimer's disease, particularly with respect to mismetabolism and aggregation of tau, β-amyloid, and TDP-43. Finally, we explore how translational research in animal models of acceleration/deceleration types of injury relevant for concussion together with clinical studies employing imaging and biochemical markers may further elucidate the neurobiology of TBI and CTE.

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.

The association between apolipoprotein E and traumatic brain injury severity and functional outcome in a rehabilitation sample

Traumatic brain injury (TBI) can result in significant disability, but outcome is variable. The impact of known predictors accounts for a limited proportion of the variance in outcomes. Apolipoprotein E (ApoE) genotype has been investigated as an additional source of variability in injury severity and outcome, with mixed findings reflecting variable methodology and generally limited sample sizes. This study aimed to examine whether possession of the ApoE ɛ4 allele was associated with greater acute injury severity and poorer long-term outcome in patients referred for rehabilitation following TBI. ApoE genotype was determined for 648 patients with TBI, who were prospectively followed up a mean of 1.9 years post-injury. Hypotheses that ɛ4 carriers would have lower Glasgow Coma Scale (GCS) scores and longer post-traumatic amnesia (PTA) duration were not supported. Prediction of worse Glasgow Outcome Scale-Extended (GOSE) scores for ɛ4 carriers was supported with greater susceptibility seen in females. These results indicate the ApoE ɛ4 allele may be associated with poorer long-term outcome, but not acute injury severity. Possible mechanisms include differential effects of the ɛ4 allele on inflammatory and cellular repair processes, and/or amyloid deposition.

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.

ABCA1, apoE and apoA-I as potential therapeutic targets for treating Alzheimer’s disease

SUMMARY The association between apoE genotype and risk and age of onset for Alzheimer’s disease (AD) was first discovered in 1993. Innumerable studies since then have defined Aβ-dependent and Aβ-independent roles for apoE in AD pathogenesis. Although therapeutic approaches that specifically target apoE are not yet developed for AD, apoE may have a more fundamental role in brain physiology than previously appreciated. ApoE is the major apolipoprotein in the CNS, coordinating the uptake and delivery of lipids among various cell types in the brain. ApoE receives lipids from the membrane-bound cholesterol and phospholipid transporter ATP-binding cassette transporter A1 (ABCA1). Genetic and pharmacological methods to enhance ABCA1 activity generate lipid-rich apoE particles and provide cognitive and neuropathological benefits in animal models of AD. Recent studies on apoA-I, which is the major lipid acceptor for ABCA1 in peripheral tissues and is also present in the CNS, suggest that increasing apoA-I function may also have neuroprotective effects. In this article, we will discuss the potential of ABCA1, apoE and apoA-I as therapeutic targets for the treatment of AD.

Exploring new routes for neuroprotective drug development in traumatic brain injury

Worldwide, traumatic brain injury (TBI) is a major cause of mortality and morbidity with a substantial predicted increase in incidence. Despite an obvious need, there are no pharmacological treatment options for TBI because translation of neuroprotection from preclinical studies to clinical practice has so far failed. Here, we identify potential causes for this failure. We suggest that the monitoring and investigation tools that are commonly used in patients with TBI may provide an experimental medicine route to facilitate a more rational approach to translational research. This suggestion is underpinned by existing research data on disease biology, drug delivery, and treatment response obtained with these methods.

A megalin polymorphism associated with promoter activity and Alzheimer's disease risk

Elevated cerebral levels of amyloid beta-protein (Abeta) occur in Alzheimer's disease (AD), yet only a few patients show evidence of increased Abeta production. This observation suggests that many, perhaps most, cases of AD are caused by faulty clearance of Abeta. Megalin, which plays an important role in mediating Abeta clearance, is an attractive candidate gene for genetic association with AD. To investigate this hypothesis, we analyzed the megalin gene in a population of 2,183 subjects. Genetic analysis indicated that the rs3755166 (G/A) polymorphism located in the megalin promoter associated with risk for AD, dependently of apolipoprotein E genotype. The rs3755166 AA genotype frequency was significantly greater in AD patients than in control subjects. Furthermore, the luciferase reporter assay indicated that the rs3755166 A variant has 20% less transcriptional activity than the rs3755166 G variant. This study provides strong evidence that this megalin polymorphism confers a greater risk for AD, and supports a biological role for megalin in the neurodegenerative processes involved in AD.

Genetic association studies in patients with traumatic brain injury

Traumatic brain injury (TBI) constitutes a major cause of mortality and disability worldwide, especially among young individuals. It is estimated that despite all the recent advances in the management of TBI, approximately half of the patients suffering head injuries still have unfavorable outcomes, which represents a substantial health care, social, and economic burden to societies.

Considerable variability exists in the clinical outcome after TBI, which is only partially explained by known factors. Accumulating evidence has implicated various genetic elements in the pathophysiology of brain trauma. The extent of brain injury after TBI seems to be modulated to some degree by genetic variants.

The authors' current review focuses on the up-to-date state of knowledge regarding genetic association studies in patients sustaining TBI, with particular emphasis on the mechanisms underlying the implication of genes in the pathophysiology of TBI.

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.

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.

Alzheimer-type neuropathology in a 28 year old patient with iatrogenic Creutzfeldt-Jakob disease after dural grafting

We report the case of a 28 year old man who had received a cadaverous dura mater graft after a traumatic open skull fracture with tearing of the dura at the age of 5 years. A clinical suspicion of Creutzfeldt-Jakob disease (CJD) was confirmed by a brain biopsy 5 months prior to death and by autopsy, thus warranting the diagnosis of iatrogenic CJD (iCJD) according to WHO criteria. Immunohistochemistry showed widespread cortical depositions of disease associated prion protein (PrP(sc)) in a synaptic pattern, and western blot analysis identified PrP(sc) of type 2A according to Parchi et al. Surprisingly, we found Alzheimer-type senile plaques and cerebral amyloid angiopathy in widespread areas of the brain. Plaque-type and vascular amyloid was immunohistochemically identified as deposits of beta-A4 peptide. CERAD criteria for diagnosis of definite Alzheimer's disease (AD) were met in the absence of neurofibrillar tangles or alpha-synuclein immunoreactive inclusions. There was no family history of AD, CJD, or any other neurological disease, and genetic analysis showed no disease specific mutations of the prion protein, presenilin 1 and 2, or amyloid precursor protein genes. This case represents (a) the iCJD case with the longest incubation time after dural grafting reported so far, (b) the youngest documented patient with concomitant CJD and Alzheimer-type neuropathology to date, (c) the first description of Alzheimer-type changes in iCJD, and (d) the second case of iCJD in Austria. Despite the young patient age, the Alzheimer-type changes may be an incidental finding, possibly related to the childhood trauma.

Caspase inhibition therapy abolishes brain trauma-induced increases in Abeta peptide: implications for clinical outcome

The detrimental effects of traumatic brain injury (TBI) on brain tissue integrity involve progressive axonal damage, necrotic cell loss, and both acute and delayed apoptotic neuronal death due to activation of caspases. Post-injury accumulation of amyloid precursor protein (APP) and its toxic metabolite amyloid-beta peptide (Abeta) has been implicated in apoptosis as well as in increasing the risk for developing Alzheimer's disease (AD) after TBI. Activated caspases proteolyze APP and are associated with increased Abeta production after neuronal injury. Conversely, Abeta and related APP/Abeta fragments stimulate caspase activation, creating a potential vicious cycle of secondary injury after TBI. Blockade of caspase activation after brain injury suppresses apoptosis and improves neurological outcome, but it is not known whether such intervention also prevents increases in Abeta levels in vivo. The present study examined the effect of caspase inhibition on post-injury levels of soluble Abeta, APP, activated caspase-3, and caspase-cleaved APP in the hippocampus of nontransgenic mice expressing human Abeta, subjected to controlled cortical injury (CCI). CCI produced brain tissue damage with cell loss and elevated levels of activated caspase-3, Abeta(1-42) and Abeta(1-40), APP, and caspase-cleaved APP fragments in hippocampal neurons and axons. Post-CCI intervention with intracerebroventricular injection of 100 nM Boc-Asp(OMe)-CH(2)F (BAF, a pan-caspase inhibitor) significantly reduced caspase-3 activation and improved histological outcome, suppressed increases in Abeta and caspase-cleaved APP, but showed no significant effect on overall APP levels in the hippocampus after CCI. These data demonstrate that after TBI, caspase inhibition can suppress elevations in Abeta. The extent to which Abeta suppression contributes to improved outcome following inhibition of caspases after TBI is unclear, but such intervention may be a valuable therapeutic strategy for preventing the long-term evolution of Abeta-mediated pathology in TBI patients who are at risk for developing AD later in life.

Alzheimer's pathology in human temporal cortex surgically excised after severe brain injury

Traumatic brain injury (TBI) is a risk factor for the development of Alzheimer's disease (AD). This immunohistochemical study determined the extent of AD-related changes in temporal cortex resected from individuals treated surgically for severe TBI. Antisera generated against Abeta species (total Abeta, Abeta(1-42), and Abeta(1-40)), the C-terminal of the Abeta precursor protein (APP), apolipoprotein E (apoE), and markers of neuron structure and degeneration (tau, ubiquitin, alpha-, beta-, and gamma-synuclein) were used to examine the extent of Abeta plaque deposition and neurodegenerative changes in 18 TBI subjects (ages 18-64 years). Diffuse cortical Abeta deposits were observed in one third of subjects (aged 35-62 years) as early as 2 h after injury, with only one (35-year old) individual exhibiting "mature", dense-cored plaques. Plaque-like deposits, neurons, glia, and axonal changes were also immunostained with APP and apoE antibodies. In plaque-positive cases, the only statistically significant change in cellular immunostaining was increased neuronal APP (P = 0.013). There was no significant correlation between the distribution of Abeta plaques and markers of neuronal degeneration. Diffuse tau immunostaining was localized to neuronal cell soma, axons or glial cells in a larger subset of individuals. Tau-positive, neurofibrillary tangle (NFT)-like changes were detected in only two subjects, both of more advanced age and who were without Abeta deposits. Other neurodegenerative changes, evidenced by ubiquitin- and synuclein-immunoreactive neurons, were abundant in the majority of cases. Our results demonstrate a differential distribution and course of intra- and extra-cellular AD-like changes during the acute phase following severe TBI in humans. Abeta plaques and early evidence of neuronal degenerative changes can develop rapidly after TBI, while fully developed NFTs most likely result from more chronic disease- or injury-related processes. These observations lend further support to the hypothesis that head trauma significantly increases the risk of developing pathological and clinical symptoms of AD, and provide insight into the molecular mechanisms that initiate these pathological cascades very early during severe brain injury.

Long-term accumulation of amyloid-beta, beta-secretase, presenilin-1, and caspase-3 in damaged axons following brain trauma

Plaques composed of amyloid beta (Abeta) have been found within days following brain trauma in humans, similar to the hallmark plaque pathology of Alzheimer's disease (AD). Here, we evaluated the potential source of this Abeta and long-term mechanisms that could lead to its production. Inertial brain injury was induced in pigs via head rotational acceleration of 110 degrees over 20 ms in the coronal plane. Animals were euthanized at 3 hours, 3 days, 7 days, and 6 months post-injury. Immunohistochemistry and Western blot analyses of the brains were performed using antibodies specific for amyloid precursor protein (APP), Abeta peptides, beta-site APP-cleaving enzyme (BACE), presenilin-1 (PS-1), caspase-3, and caspase-mediated cleavage of APP (CCA). Substantial co-accumulation for all of these factors was found in swollen axons at all time points up to 6 months following injury. Western blot analysis of injured brains confirmed a substantial increase in the protein levels of these factors, particularly in the white matter. These data suggest that impaired axonal transport due to trauma induces long-term pathological co-accumulation of APP with BACE, PS-1, and activated caspase. The abnormal concentration of these factors may lead to APP proteolysis and Abeta formation within the axonal membrane compartment.

Cerebrovascular requirement for sealant, anti-coagulant and remodeling molecules that allow for the maintenance of vascular integrity and blood supply

The integrity of the vasculature and the maintenance of the blood supply to the brain are crucial for the survival of higher vertebrates. However, peripheral mechanisms of sealing the vasculature that rely on the clotting of blood and platelet aggregation around the site of a 'leak' would lead to decreased cerebral perfusion and compromise the viability of terminally differentiated and irreplaceable neurons. Therefore, in higher organisms it is likely that a sealant/anti-coagulant system that maintains vascular supply has evolved as a necessity to life. We propose that one such system involves the amyloid-beta precursor protein (AbetaPP) and its cleavage product Abeta since (1) both AbetaPP/Abeta are known to deposit in the media of the cerebrovasculature wall following localized injury, (2) Abeta is generated from AbetaPP, a known acute phase reactant, (3) Abeta's physiochemical properties allow it to span between the extracellular matrix and the (endothelial) cell membrane and under inflammatory conditions aggregate to form an intracranial 'scab', thereby maintaining structural integrity of the blood brain barrier, (4) AbetaPP/Abeta together act as an anti-coagulant, (5) Abeta promotes vascular/neuronal remodeling, and (6) Abeta deposits resolve after injury. These properties are consistent with the acute phase generation and rapid cortical deposition of AbetaPP/Abeta following injury (either sustained by trauma or stresses associated with aging) that would be an important compensatory response aimed at limiting the loss of terminally differentiated neurons. Such a system would allow the maintenance of blood supply to the brain by sealing vascular lesions, preventing hemorrhagic stroke while at the same time inhibiting the coagulation cascade from blocking capillaries. Obviously, strategies to remove Abeta would have serious consequences for the integrity of the blood-brain barrier. Indeed, recent in vivo evidence demonstrates that the removal of deposited Abeta from the vasculature leads to increased cerebral microhemorrhage and strongly support the above mentioned functions of AbetaPP/Abeta. These insights also explain the root cause of the encephalitis and meningitis suffered by individuals in immunotherapy trials as being directly associated with the removal of Abeta from the vasculature, i.e. immunological responses to Abeta vaccination do not discriminate between physiologically purposive deposits of Abeta (vascular deposits) and pathological deposits of Abeta (senile plaques).

Alterations in cerebrospinal fluid apolipoprotein E and amyloid beta-protein after traumatic brain injury

There is evidence that apolipoprotein E (apoE) and amyloid beta-protein (Abeta), which are implicated in the pathology of chronic neurodegenerative disorders, are involved in the response of the brain to acute injury; however, human in vivo evidence is sparse. We conducted a prospective observational study to determine the magnitude and time-course of alterations in cerebrospinal fluid (CSF) apoE and Abeta concentrations after traumatic brain injury (TBI), and the relationship of these changes to severity of injury and clinical outcome. Enzyme linked immunosorbant assay (ELISA) was used to assay apoE, Abeta(1-40) and Abeta(1-42) in serial CSF samples from 13 patients with TBI and 13 controls. CSF S100B and tau were assayed as surrogate markers of brain injury. There was a significant decrease in CSF apoE (p < 0.001) and Abeta (p< 0.001) after TBI contrasting the observed elevation in CSF S100B (p < 0.001) and tau (p < 0.001) concentration. There was significant correlation (r = 0.67, p = 0.01) between injury severity and the decrease in Abeta(1-40) concentration after TBI. In vivo, changes in apoE and Abeta concentration occur after TBI and may be important in the response of the human brain to injury.

Tau immunohistochemistry in acute brain injury

Epidemiological studies have identified a history of head injury as a risk factor for Alzheimer's disease. However, the neuropathological mechanism underlying this relationship is as yet unclear. Neuronal cytoskeletal changes in the form of neurofibrillary tangles and neuropil threads have recently been demonstrated in young men who had sustained repetitive head injury and subsequently died in their 20s. In addition, recent experimental studies have found accumulation of tau within neuronal somata and damaged axons following diffuse brain injury. We hypothesized that tau-immunoreactive tangles may be present in the brains of patients who died after a single acute blunt head injury. A total of 45 cases of fatal head injury were immunostained for tau. They comprised nine groups (n=5 for each group) separated by age (0-19 years, 20-50 years, 50+ years) and survival time (<24 h, 24 h-1 week, 1 week-1 month) and were compared with age-matched controls. Subtle alterations in tau immunoreactivity, for example, in oligodendrocytes, were present in some head injury cases but not controls. However, neurofibrillary tangles did not appear more prevalent after traumatic brain injury (TBI) when compared with age-matched controls. Although alterations in tau immunoreactivity may occur which warrant further study, neurofibrillary tangles were not more prevalent after a single fatal episode of TBI.

Epidemiology of neurodegeneration

Alzheimer's disease, Parkinson's disease, and motor neuron disease share a propensity to occur with increasing age and as either a sporadic or a familial disorder. A number of behavioral and environmental risk factors have been proposed for each disorder, but most associations lack consistency and specificity. Over the last decade the remarkable frequency of these disorders has become apparent, and the identification of mutations in genes has provided the means to understand their pathogenesis. Better and more accurate means to characterize and diagnose these diseases has greatly facilitated analytic epidemiology. The analysis of behavioral and genetic factors that may lower disease risk has led to clinical trials that are either in progress or being planned with the aim of preventing these disorders.

Remodelling of cerebrospinal fluid lipoproteins after subarachnoid hemorrhage

Lipoprotein particles (Lps) in normal human cerebrospinal fluid (CSF) are distinct from those found in plasma and include unique apolipoprotein E (apoE indicates protein; APOE, gene) containing lipoproteins rarely seen in human plasma. Less favourable neurological recovery after subarachnoid hemorrhage (SAH) has been observed in patients who possess the APOE epsilon4 allele raising the possibility that apoE influences neuronal survival after brain injury. We analysed Lps from control and SAH CSF testing the hypotheses that following brain injury CSF Lps undergo remodelling and apoE containing Lps are selectively depleted from brain injury CSF. Lipoproteins were fractionated using CSF from six control pools and six patients with SAH on a sepharose 6HR 10/30 size exclusion column. Fractions were assayed for total cholesterol (TC), free cholesterol (FC), phospholipid, triglyceride (TG), apoE, apolipoprotein B (apoB), and apolipoprotein AI (apoAI). Compared to control CSF there were significant (P<0.05) increases in TC, FC, TG, and apoAI in SAH CSF. Plasma sized apoB-containing lipoproteins and a very small apoAI-containing Lps were identified in the SAH CSF, which were not present in controls. However, despite the release of plasma lipoproteins into the subarachnoid space, there was no significant increase in CSF apoE. These data provide novel indirect evidence suggesting that after SAH CSF Lps undergo remodelling and apoE containing Lps are selectively reduced in brain injury CSF. The remodelling of CSF Lps and selective reduction of apoE containing lipoproteins may reflect an important response of the human brain to injury.

Remodeling of cerebrospinal fluid lipoprotein particles after human traumatic brain injury

The association between possession of the APOE epsilon4 allele and unfavourable outcome after traumatic brain injury (TBI) suggests that the apolipoprotein E protein (apoE) plays a key role in the response of the human brain to injury. ApoE is known to regulate cholesterol metabolism in the periphery through its action as a ligand for receptor mediated uptake of lipoprotein particles (Lps). Greater understanding of cholesterol metabolism in the human central nervous system may identify novel treatment strategies applicable to acute brain injury. We report findings from the analysis of lipoproteins in the cerebrospinal fluid (CSF) of patients with TBI and non-injured controls, testing the hypothesis that remodeling of CSF lipoproteins reflects the response of the brain to TBI. CSF Lps were isolated from the CSF of controls and patients with severe TBI by size exclusion chromatography, and the lipoprotein fractions analysed for cholesterol, phospholipid, apoAI, and apoE. There was a marked decrease in apoE containing Lps in the TBI CSF compared to controls (p=0.002). After TBI there was no significant decrease in apoAI containing CSF Lps (CSF LpAI), but the apoAI resided on smaller sized particles than in control CSF. There was a population of very small sized Lps in TBI CSF, which were associated with the increased cholesterol (p=0.0001) and phospholipid (p=0.040) seen after TBI. The dramatic loss of apoE containing Lps from the CSF, and the substantial increase in CSF cholesterol, support the concept that apoE and cholesterol metabolism are intimately linked in the context of acute brain injury. Treatment strategies targeting CNS lipid transport, required for neuronal sprouting and synaptogenesis, may be applicable to traumatic brain injury.

Cerebrospinal fluid apolipoprotein E concentration decreases after traumatic brain injury

The APOE epsilon4 allele has been associated with unfavorable outcome after several types of acute brain injury, yet the biological mechanisms underlying this observation are poorly understood. Postmortem and experimental brain injury studies suggest the presence of increased amounts of apolipoprotein E (apoE) within the neuropil after acute brain injury. We assayed the concentration of apolipoprotein E in the cerebrospinal fluid (CSF) of non-injured controls and patients with traumatic brain injury (TBI) to determine whether differences exist, and if these differences correlate with injury severity and clinical outcome. CSF apoE and S100B, a marker of injury severity, were measured by enzyme linked immunosorbant assay. CSF was sampled from 27 traumatic brain injury patients (mean age 32, median 25, range 16-65 years) within 3 days of injury, and 28 controls (mean age 40, median 37, range 19-73 years). The TBI patients all had a Glasgow Coma Score (GCS) of less than eight (i.e., severe head injury). Clinical outcome was determined using the Glasgow Outcome Score (GOS). The average concentration of apoE in the CSF of controls was 12.4 mg/L (95% CI: 10.5-14.3 mg/L) and in TBI patients was 3.7 mg/L (95% CI: 2.1-4.1 mg/L; Mann-Whitney: p < 0.0001). In contrast, the concentration of S100B in the CSF of TBI patients was significantly higher than that of controls (Mann-Whitney: p < 0.0001). We speculate that apoE is retained within the parenchyma of the central nervous system in response to injury where in view of previous data, it may have a protective role.