Traumatic brain injury as a risk factor for Alzheimer's disease: a review

Environmental factors in the development and progression of late-onset Alzheimer's disease

Late-onset Alzheimer's disease (LOAD) is an age-related neurodegenerative disorder characterized by gradual loss of synapses and neurons, but its pathogenesis remains to be clarified. Neurons live in an environment constituted by neurons themselves and glial cells. In this review, we propose that the neuronal degeneration in the AD brain is partially caused by diverse environmental factors. We first discuss various environmental stresses and the corresponding responses at different levels. Then we propose some mechanisms underlying the specific pathological changes, in particular, hypothalamic-pituitary adrenal axis dysfunction at the systemic level; cerebrovascular dysfunction, metal toxicity, glial activation, and Aβ toxicity at the intercellular level; and kinase-phosphatase imbalance and epigenetic modification at the intracellular level. Finally, we discuss the possibility of developing new strategies for the prevention and treatment of LOAD from the perspective of environmental stress. We conclude that environmental factors play a significant role in the development of LOAD through multiple pathological mechanisms.

Long-term cognitive correlates of traumatic brain injury across adulthood and interactions with APOE genotype, sex, and age cohorts

There is continuing debate about long-term effects of brain injury. We examined a range of traumatic brain injury (TBI) variables (TBI history, severity, frequency, and age of injury) as predictors of cognitive outcome over 8 years in an adult population, and interactions with apolipoprotein E (APOE) genotype, sex, and age cohorts. Three randomly sampled age cohorts (20-24, 40-44, 60-64 years at baseline; N = 6333) were each evaluated three times over 8 years. TBI variables, based on self-report, were separately modeled as predictors of cognitive performance using linear mixed effects models. TBI predicted longitudinal cognitive decline in all three age groups. APOE ε4 + genotypes in the young and middle-aged groups predicted lower baseline cognitive performance in the context of TBI. Baseline cognitive performance was better for young females than males but this pattern reversed in middle age and old age. The findings suggest TBI history is associated with long-term cognitive impairment and decline across the adult lifespan. A role for APOE genotype was apparent in the younger cohorts but there was no evidence that it is associated with impairment in early old age. The effect of sex and TBI on cognition varied with age cohort, consistent with a proposed neuroprotective role for estrogen.

Network dysfunction after traumatic brain injury

Diffuse axonal injury after traumatic brain injury (TBI) produces neurological impairment by disconnecting brain networks. This structural damage can be mapped using diffusion MRI, and its functional effects can be investigated in large-scale intrinsic connectivity networks (ICNs). Here, we review evidence that TBI substantially disrupts ICN function, and that this disruption predicts cognitive impairment. We focus on two ICNs--the salience network and the default mode network. The activity of these ICNs is normally tightly coupled, which is important for attentional control. Damage to the structural connectivity of these networks produces predictable abnormalities of network function and cognitive control. For example, the brain normally shows a 'small-world architecture' that is optimized for information processing, but TBI shifts network function away from this organization. The effects of TBI on network function are likely to be complex, and we discuss how advanced approaches to modelling brain dynamics can provide insights into the network dysfunction. We highlight how structural network damage caused by axonal injury might interact with neuroinflammation and neurodegeneration in the pathogenesis of Alzheimer disease and chronic traumatic encephalopathy, which are late complications of TBI. Finally, we discuss how network-level diagnostics could inform diagnosis, prognosis and treatment development following TBI.

Hypothèses étiopathogéniques de la schizophrénie au décours d’un traumatisme crânien : revue de la littérature

Introduction

La schizophrénie et le traumatisme crânien (TC) sont deux problèmes majeurs de la santé publique. Parmi les complications neuropsychologiques et psychiatriques secondaires au traumatisme crânien, les psychoses post-traumatiques interrogent plusieurs cadres nosographiques. Cependant, les liens épidémiologiques entre TC et schizophrénie sont difficiles à établir [2].

Objectif

L’objectif de notre travail est de détailler les différentes hypothèses étiopahogéniques avancées dans la littérature à propos de la schizophrénie se développant au décours d’un TC.

Résultats

Cette entité clinique interroge les théories physiopathologiques de la schizophrénie dans une approche étiologique. Les modèles neurodégénératifs, de dysrégulation dopaminergique et neurodéveloppemental sont souvent utiles pour expliciter les troubles psychotiques post-traumatiques.

Hypothèse dégénérative

Le TC peut entraîner une baisse des capacités de réserve cérébrale par une accumulation de peptide amyloïde bêta pourvoyeuse de déficits cognitifs. Le modèle interactif gène environnement entre le TC qui éprouve une vulnérabilité allélique de l’apolipoprotéine E et décrit dans la physiopathologie de la maladie d’Alzheimer. Le même modèle est transposable à la schizophrénie post-traumatique [1].

Hypothèse neurodéveloppementale

Les lésions cérébrales microscopiques secondaires à un TC peuvent entraîner un remodelage neuronal induisant le développement d’un trouble schizophrénique chez un sujet vulnérable et prédisposé. La latence entre le TC et l’apparition des premiers symptômes cliniques correspond aux remaniements neuronaux [3].

Hypothèse dopaminergique

La présence de symptômes psychotiques secondaires à un TC peut résulter d’une interaction entre la blessure cérébrale et une prédisposition neurobiologique anté-traumatique à la schizophrénie. L’efficacité des antipsychotiques sur les symptômes psychotiques post-traumatiques ou schizophréniques est un argument indirect suggérant le rôle d’une dysrégulation dopaminergiques dans ces pathologies.

Conclusion

Les avancées techniques de neuro-imagerie et de neurobiologie offrent des perspectives nouvelles pour la compréhension physiopathologique des troubles psychotiques post-traumatiques ainsi que son lien avec la schizophrénie primaire.

Older adults with acquired brain injury: a population based study

Background

Acquired brain injury (ABI), which includes traumatic (TBI) and non-traumatic brain injury (nTBI), is a leading cause of death and disability worldwide. The objective of this study was to examine the trends, characteristics, cause of brain injury, and discharge destination of hospitalized older adults aged 65 years and older with an ABI diagnosis in a population with universal access to hospital care. The profile of characteristics of patients with TBI and nTBI causes of injury was also compared.

Methods

A population based retrospective cohort study design with healthcare administrative databases was used. Data on acute care admissions were obtained from the Discharge Abstract Database and patients were identified using the International Classification of Diseases – Version 10 codes for Ontario, Canada from April 1, 2003 to March 31, 2010. Older adults were examined in three age groups – 65 to 74, 75 to 84, and 85+ years.

Results

From 2003/04 to 2009/10, there were 14,518 episodes of acute care associated with a TBI code and 51, 233 episodes with a nTBI code. Overall, the rate of hospitalized TBI and nTBI episodes increased with older age groups. From 2007/08 to 2009/10, the percentage of patients that stayed in acute care for 12 days or more and the percentage of patients with delayed discharge from acute care increased with age. The most common cause of TBI was falls while the most common type of nTBI was brain tumours. The percentage of patients discharged to long term care and complex continuing care increased with age and the percentage discharged home decreased with age. In-hospital mortality also increased with age. Older adults with TBI and nTBI differed significantly in demographic and clinical characteristics and discharge destination from acute care.

Conclusions

This study showed an increased rate of acute care admissions for both TBI and nTBI with age. It also provided additional support for falls prevention strategies to prevent injury leading to cognitive disability with costly human and economic consequences. Implications for increased numbers of people with ABI are discussed.

The pathophysiology of traumatic brain injury at a glance

Traumatic brain injury (TBI) is defined as an impact, penetration or rapid movement of the brain within the skull that results in altered mental state. TBI occurs more than any other disease, including breast cancer, AIDS, Parkinson's disease and multiple sclerosis, and affects all age groups and both genders. In the US and Europe, the magnitude of this epidemic has drawn national attention owing to the publicity received by injured athletes and military personnel. This increased public awareness has uncovered a number of unanswered questions concerning TBI, and we are increasingly aware of the lack of treatment options for a crisis that affects millions. Although each case of TBI is unique and affected individuals display different degrees of injury, different regional patterns of injury and different recovery profiles, this review and accompanying poster aim to illustrate some of the common underlying neurochemical and metabolic responses to TBI. Recognition of these recurrent features could allow elucidation of potential therapeutic targets for early intervention.

The impact of traumatic brain injury on pituitary function

It is paramount that clinicians who care for patients with traumatic brain injury (TBI) at any point in time, including neurosurgeons, rehabilitation physicians, internists, neurologists, and endocrinologists, are aware of the prevalence of posttraumatic hypopituitarism and its impacts on acute and long-term recovery. This article reviews the natural history, pathophysiology, and presenting features of hypopituitarism occurring after TBI. Proposed methodologies for screening, diagnosis, and initiation of treatment are discussed, as well as the effect of hormone replacement therapy on clinical outcomes.

The impact of alcohol on Alzheimer's disease: a systematic review

Currently, there is discrepancy regarding alcohol's impact on Alzheimer's disease (AD). Consequently, the purpose of this systematic review was to determine whether alcohol serves as a protective agent against the development of AD, as well as whether protective effects are influenced by quantity and/or frequency of drinking. Adapted versions of the Matrix Method and PRISMA guidelines were used in order to identify, organize, and synthesize relevant research. Overall, there is no consensus regarding alcohol's impact on AD. Specifically, seven articles suggested drinking alcohol decreases the risk of AD, three studies found drinking led to an increased risk of AD, and yet another nine reported alcohol had no impact on AD. Validity and consistency of both alcohol and AD measures across studies represents a severe limitation. Prior to the development of standards and/or clinical recommendations, more investigations into the association between alcohol and AD are necessary. Considering the current evidence base, alcohol should not be used as a means to decrease risk of developing AD.

Cognitive reserve components as expressed in traumatic brain injury

Traumatic brain injury (TBI) is the most common cause of brain damage, resulting in long-term disability. The "reserve" construct has been proposed to account for the reported mismatch between brain damage and its clinical expression. Although numerous studies have used various measures thought to reflect this construct, few studies have examined its underlying structure in clinical populations, and no studies have systematically studied this construct in TBI. In the present study, structural equation modeling technique was used to evaluate several models hypothesized to represent cognitive reserve (CR) in TBI. A broad range of data typically reported in the literature as representing CR was collected from 89 individuals who sustained moderate-to-severe TBI. Analyses revealed a best fitting model that consisted of three separate factors representing premorbid intelligence, socioeconomic status and leisure activity, with distinct pattern of associations among the three factors. Findings provide empirical support for the notion of a multi-factorial CR and suggest a coherent framework for further investigation.

Reactive oxygen species-activated nanoprodrug of Ibuprofen for targeting traumatic brain injury in mice

Traumatic brain injury (TBI) is an enormous public health problem, with 1.7 million new cases of TBI recorded annually by the Centers for Disease Control. However, TBI has proven to be an extremely challenging condition to treat. Here, we apply a nanoprodrug strategy in a mouse model of TBI. The novel nanoprodrug contains a derivative of the nonsteroidal anti-inflammatory drug (NSAID) ibuprofen in an emulsion with the antioxidant α-tocopherol. The ibuprofen derivative, Ibu2TEG, contains a tetra ethylene glycol (TEG) spacer consisting of biodegradable ester bonds. The biodegradable ester bonds ensure that the prodrug molecules break down hydrolytically or enzymatically. The drug is labeled with the fluorescent reporter Cy5.5 using nonbiodegradable bonds to 1-octadecanethiol, allowing us to reliably track its accumulation in the brain after TBI. We delivered a moderate injury using a highly reproducible mouse model of closed-skull controlled cortical impact to the parietal region of the cortex, followed by an injection of the nanoprodrug at a dose of 0.2 mg per mouse. The blood brain barrier is known to exhibit increased permeability at the site of injury. We tested for accumulation of the fluorescent drug particles at the site of injury using confocal and bioluminescence imaging of whole brains and brain slices 36 hours after administration. We demonstrated that the drug does accumulate preferentially in the region of injured tissue, likely due to an enhanced permeability and retention (EPR) phenomenon. The use of a nanoprodrug approach to deliver therapeutics in TBI represents a promising potential therapeutic modality.

Chronic neuropathologies of single and repetitive TBI: substrates of dementia?

Traumatic brain injury (TBI) has long been recognized to be a risk factor for dementia. This association has, however, only recently gained widespread attention through the increased awareness of 'chronic traumatic encephalopathy' (CTE) in athletes exposed to repetitive head injury. Originally termed 'dementia pugilistica' and linked to a career in boxing, descriptions of the neuropathological features of CTE include brain atrophy, cavum septum pellucidum, and amyloid-β, tau and TDP-43 pathologies, many of which might contribute to clinical syndromes of cognitive impairment. Similar chronic pathologies are also commonly found years after just a single moderate to severe TBI. However, little consensus currently exists on specific features of these post-TBI syndromes that might permit their confident clinical and/or pathological diagnosis. Moreover, the mechanisms contributing to neurodegeneration following TBI largely remain unknown. Here, we review the current literature and controversies in the study of chronic neuropathological changes after TBI.

Combination of Aβ clearance and neurotrophic factors as a potential treatment for Alzheimer's disease

There is no effective drug to treat Alzheimer's disease (AD), a neurodegenerative disease affecting an estimated 30 million people around the world. Strongly supported by preclinical and clinical studies, amyloid-beta (Aβ) may be a target for developing drugs against AD. Meanwhile, the fact that localized neuronal death/loss and synaptic impairment occur in AD should also be considered. Neuronal regeneration, which does not occur normally in the mammalian central nervous system, can be promoted by neurotrophic factors (NTFs). Evidence from clinical trials has shown that both Aβ clearance and NTFs are potentially effective in treating AD, thus a new approach combining Aβ clearance and administration of NTFs may be an effective therapeutic strategy.

Risk for late-life re-injury, dementia and death among individuals with traumatic brain injury: a population-based study

OBJECTIVES

To determine the association of self-reported traumatic brain injury (TBI) with loss of consciousness (LOC) with late-life re-injury, dementia diagnosis and mortality.

DESIGN

Ongoing longitudinal population-based prospective cohort study.

SETTING

Seattle-area integrated health system.

PARTICIPANTS

4225 dementia-free individuals age 65 and older were randomly selected and enrolled between 1994 and 2010. Participants were seen every 2 years, with mean (range) follow-up of 7.4 (0-16) years. 606 (14%) participants reported a lifetime history of TBI with LOC at enrolment. 3466 participants provided information regarding lifetime history of TBI and completed at least one follow-up visit.

MAIN OUTCOME MEASURES

Self-reported TBI with LOC after study entry, incident all-cause dementia and Alzheimer's disease (AD), and all-cause mortality.

RESULTS

There were 25 567 person-years of follow-up. History of TBI with LOC reported at study enrolment was associated with increased risk for TBI with LOC during follow-up, with adjusted HRs ranging from 2.54 (95% CI 1.42 to 4.52) for those reporting first injury before age 25 to 3.79 (95% CI 1.89 to 7.61) for those with first injury after age 55. History of TBI with LOC was not associated with elevated risk for developing dementia or AD. There was no association between baseline history of TBI with LOC and mortality, though TBI with LOC since the previous study visit ('recent TBI') was associated with increased mortality (HR 2.12, 95% CI 1.62 to 2.78).

CONCLUSIONS

Individuals aged 65 or older who reported a history of TBI with LOC at any time in their lives were at elevated risk of subsequent re-injury. Recent TBI with LOC sustained in older adulthood was associated with increased risk for mortality. Findings support the need for close clinical monitoring of older adults who sustain a TBI with LOC.

Cognitive decline in older adults with a history of traumatic brain injury

Traumatic brain injury (TBI) is an important public health problem with potentially serious long-term neurobehavioural sequelae. There is evidence to suggest that a history of TBI can increase a person's risk of developing Alzheimer's disease. However, individuals with dementia do not usually have a history of TBI, and survivors of TBI do not invariably acquire dementia later in life. Instead, a history of traumatic brain injury, combined with brain changes associated with normal ageing, might lead to exacerbated cognitive decline in older adults. Strategies to increase or maintain cognitive reserve might help to prevent exacerbated decline after TBI. Systematic clinical assessment could help to differentiate between exacerbated cognitive decline and mild cognitive impairment, a precursor of Alzheimer's disease, with important implications for patients and their families.

Metabolic reserve as a determinant of cognitive aging

Mild cognitive impairment (MCI) and Alzheimer's disease (AD) represent points on a continuum of cognitive performance in aged populations. Cognition may be impaired or preserved in the context of brain aging. One theory to account for memory maintenance in the context of extensive pathology involves 'cognitive reserve', or the ability to compensate for neuropathology through greater recruitment of remaining neurons. In this review, we propose a complementary hypothesis of 'metabolic reserve', where a brain with high metabolic reserve is characterized by the presence of neuronal circuits that respond adaptively to perturbations in cellular and somatic energy metabolism and thereby protects against declining cognition. Lifestyle determinants of metabolic reserve, such as exercise, reduced caloric intake, and intake of specific dietary components can promote neuroprotection, while pathological states arising from sedentary lifestyles and excessive caloric intake contribute to neuronal endangerment. This bidirectional relationship between metabolism and cognition may be mediated by alterations in central insulin and neurotrophic factor signaling and glucose metabolism, with downstream consequences for accumulation of amyloid-β and hyperphosphorylated tau. The metabolic reserve hypothesis is supported by epidemiological findings and the spectrum of individual cognitive trajectories during aging, with additional data from animal models identifying potential mechanisms for this relationship. Identification of biomarkers for metabolic reserve could assist in generating a predictive model for the likelihood of cognitive decline with aging.

2012 Alzheimer's disease facts and figures

This report provides information to increase understanding of the public health impact of Alzheimer's disease (AD). Topics addressed include incidence, prevalence, mortality rates, health expenditures and costs of care, and effect on caregivers and society. The report also explores issues that arise when people with AD and other dementias live alone. The characteristics, risks, and unmet needs of this population are described. An estimated 5.4 million Americans have AD, including approximately 200,000 age <65 years who comprise the younger-onset AD population. Over the coming decades, the aging of the baby boom generation is projected to result in an additional 10 million people with AD. Today, someone in America develops AD every 68 seconds. By 2050, there is expected to be one new case of AD every 33 seconds, or nearly a million new cases per year, and AD prevalence is projected to be 11 million to 16 million. Dramatic increases in the number of "oldest-old" (those age ≥85 years) across all racial and ethnic groups are expected to contribute to the increased prevalence of AD. AD is the sixth leading cause of death in the United States and the fifth leading cause of death in Americans age ≥65 years. Although the proportions of deaths due to other major causes of death have decreased in the last several years, the proportion due to AD has risen significantly. Between 2000 and 2008, the proportion of deaths due to heart disease, stroke, and prostate cancer decreased by 13%, 20%, and 8%, respectively, whereas the proportion due to AD increased by 66%. In 2011, more than 15 million family members and other unpaid caregivers provided an estimated 17.4 billion hours of care to people with AD and other dementias, a contribution valued at more than $210 billion. Medicare payments for services to beneficiaries age ≥65 years with AD and other dementias are three times as great as payments for beneficiaries without these conditions, and Medicaid payments are 19 times as great. In 2012, payments for health care, long-term care, and hospice services for people age ≥65 years with AD and other dementias are expected to be $200 billion (not including the contributions of unpaid caregivers). An estimated 800,000 people with AD (one in seven) live alone, and up to half of them do not have an identifiable caregiver. People with dementia who live alone are exposed to risks that exceed the risks encountered by people with dementia who live with others, including inadequate self-care, malnutrition, untreated medical conditions, falls, wandering from home unattended, and accidental deaths.

The immunology of traumatic brain injury: a prime target for Alzheimer's disease prevention

A global health problem, traumatic brain injury (TBI) is especially prevalent in the current era of ongoing world military conflicts. Its pathological hallmark is one or more primary injury foci, followed by a spread to initially normal brain areas via cascades of inflammatory cytokines and chemokines resulting in an amplification of the original tissue injury by microglia and other central nervous system immune cells. In some cases this may predispose individuals to later development of Alzheimer’s disease (AD). The inflammatory-based progression of TBI has been shown to be active in humans for up to 17 years post TBI. Unfortunately, all neuroprotective drug trials have failed, and specific treatments remain less than efficacious. These poor results might be explained by too much of a scientific focus on neurons without addressing the functions of microglia in the brain, which are at the center of proinflammatory cytokine generation. To address this issue, we provide a survey of the TBI-related brain immunological mechanisms that may promote progression to AD. We discuss these immune and microglia-based inflammatory mechanisms involved in the progression of post-trauma brain damage to AD. Flavonoid-based strategies to oppose the antigen-presenting cell-like inflammatory phenotype of microglia will also be reviewed. The goal is to provide a rationale for investigations of inflammatory response following TBI which may represent a pathological link to AD. In the end, a better understanding of neuroinflammation could open therapeutic avenues for abrogation of secondary cell death and behavioral symptoms that may mediate the progression of TBI to later AD.

Do traditional executive measures tell us anything about daily-life functioning after traumatic brain injury in Spanish-speaking individuals?

PRIMARY OBJECTIVE

To examine the relationship between traditional executive function measures and everyday competence in Spanish-speaking individuals with moderate-to-severe traumatic brain injury (TBI).

METHODS AND PROCEDURES

Thirty-two TBI patients (24 men, eight women) with an age range of 17-59 years (mean age = 30.73 years; SD = 13.34) were administered a battery of performance-based executive function measures. Such measures included the Trail Making Test part B, Wisconsin Card Sorting Test, Stroop Colour Word Interference Test, Controlled Oral Word Association Test and Letter-Number Sequencing. Behavioural manifestations of executive deficits were assessed by the Behaviour Rating Inventory of Executive Function-Adult version (BRIEF-A). Patient's everyday functioning was examined with the Patient Competency Rating Scale (PCRS).

MAIN OUTCOMES AND RESULTS

Traditional performance-based executive measures correlated significantly, although moderately, with the PCRS; this relationship was more significant in the Controlled Oral Word Association Test and Trail Making Test part B. A significant correlation was obtained between the BRIEF-A clinical scales and patient's everyday competence as measured by the PCRS.

CONCLUSIONS

The current findings suggest that traditional performance-based executive measures reveal some degree of ecological validity or real-world relevance, providing relevant information for predicting everyday competence after moderate-to-severe TBI.

Role of pro-inflammatory cytokines released from microglia in neurodegenerative diseases

Microglia are activated in response to a number of different pathological states within the CNS including injury, ischemia, and infection. Microglial activation results in their production of pro-inflammatory cytokines such as IL-1, IL-6, and TNF-α. While release of these factors is typically intended to prevent further damage to CNS tissue, they may also be toxic to neurons and other glial cells. Mounting evidence indicates that chronic microglial activation may also contribute to the development and progression of neurodegenerative disorders. Unfortunately, determining the role of pro-inflammatory cytokines in these disorders has been complicated by their dual roles in neuroprotection and neurodegeneration. The purpose of this review is to summarize current understanding of the involvement of cytokines in neurodegenerative disorders and their potential signaling mechanisms in this context. Taken together, recent findings suggest that microglial activation and pro-inflammatory cytokines merit interest as targets in the treatment of neurodegenerative disorders.

[Medicolegal assessment of cerebral ischemia and hemorrhage]

Cerebral ischemia and hemorrhage are the most frequent cause of invalidity and disability in the elderly, corresponding to the significance of these diseases for social law and expert opinion. The sequelae of media infarcts and extended hemorrhage are obvious and offer little reason for litigation. Conflicts occur in cases of minor deficits and less obvious neuropsychological or psychiatric symptoms, including mental, cognitive, mnestic and executive functions.

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.

2011 Alzheimer's disease facts and figures

Alzheimer's disease (AD) is the sixth leading cause of all deaths in the United States and is the fifth leading cause of death in Americans aged ≥65 years. Although other major causes of death have been on the decrease, deaths because of AD have been rising dramatically. Between 2000 and 2008 (preliminary data), heart disease deaths decreased by 13%, stroke deaths by 20%, and prostate cancer-related deaths by 8%, whereas deaths because of AD increased by 66%. An estimated 5.4 million Americans have AD; approximately 200,000 people aged <65 years with AD comprise the younger-onset AD population. Every 69 seconds, someone in America develops AD; by 2050, the time is expected to accelerate to every 33 seconds. Over the coming decades, the baby boom population is projected to add 10 million people to these numbers. In 2050, the incidence of AD is expected to approach nearly a million people per year, with a total estimated prevalence of 11 to 16 million people. Dramatic increases in the numbers of "oldest-old" (those aged ≥85 years) across all racial and ethnic groups will also significantly affect the numbers of people living with AD. In 2010, nearly 15 million family and other unpaid caregivers provided an estimated 17 billion hours of care to people with AD and other dementias, a contribution valued at more than $202 billion. Medicare payments for services to beneficiaries aged ≥65 years with AD and other dementias are almost 3 times higher than for beneficiaries without these conditions. Total payments in 2011 for health care, long-term care, and hospice services for people aged ≥65years with AD and other dementias are expected to be $183 billion (not including the contributions of unpaid caregivers). This report provides information to increase understanding of the public health effect of AD, including incidence and prevalence, mortality, health expenditures and costs of care, and effect on caregivers and society in general. The report also examines the current state of AD detection and diagnosis, focusing on the benefits of early detection and the factors that present challenges to accurate diagnosis.

Incremental contribution of reported previous head injury to the prediction of diagnosis and cognitive functioning in older adults

BACKGROUND

Severe brain injuries may be a risk factor for the development of dementia in later life. Less severe incidents with relatively short or even no loss of consciousness may not carry the same prognosis.

OBJECTIVES

This study used data from the first two waves of the Canadian Study of Health and Ageing (CSHA-1 and CSHA-2) to investigate two questions. (1) Does a history of head injury improve the prediction of the diagnosis of dementia? This analysis was based on the 921 elderly individuals who underwent a clinical assessment in CSHA-2 and, 5 years earlier, had reported whether or not they had had a head injury. (2) Does adding information about a history of head injury improve the prediction of neuropsychological test scores? This second analysis included 585 elderly people who underwent neuropsychological assessment in both waves and who also reported whether or not they had had a history of mild or moderate-to-severe head injury.

RESULTS

RESULTS showed that the inclusion of head injury information did not improve the prediction of diagnostic outcome of dementia. Age and overall cognitive status were associated with most neuropsychological test scores, more so than the more limited influence of chronic health problems, which was associated with about half of the neuropsychological measures.

Histone deacetylase inhibitors as therapeutic agents for acute central nervous system injuries

Histone deacetylase (HDAC) inhibitors are emerging as a novel class of potentially therapeutic agents for treating acute injuries of the central nervous system (CNS). In this review, we summarize data regarding the effects of HDAC inhibitor administration in models of acute CNS injury and discuss issues warranting clinical trials. We have previously shown that the pan-HDAC inhibitor ITF2357, a compound shown to be safe and effective in humans, improves functional recovery and attenuates tissue damage when administered as late as 24 h after injury. Using a well-characterized, clinically relevant mouse model of closed head injury, we demonstrated that a single dose of ITF2357 administered 24 h after injury improves neurobehavioral recovery and reduces tissue damage. ITF2357-induced functional improvement was found to be sustained up to 14 d after trauma and was associated with augmented histone acetylation. Single postinjury administration of ITF2357 also attenuated injury-induced inflammatory responses, as indicated by reduced glial accumulation and activation as well as enhanced caspase-3 expression within microglia/macrophages after treatment. Because no specific therapeutic intervention is currently available for treating brain trauma patients, the ability to affect functional outcome by postinjury administration of HDAC inhibitors within a clinically feasible timeframe may be of great importance. Furthermore, a growing body of evidence indicates that HDAC inhibitors are beneficial for treating various forms of acute CNS injury including ischemic and hemorrhagic stroke. Because HDAC inhibitors are currently approved for other use, they represent a promising new avenue of treatment, and their use in the setting of CNS injury warrants clinical evaluation.

Traumatic brain injury: a disease process, not an event

Traumatic brain injury (TBI) is seen by the insurance industry and many health care providers as an "event." Once treated and provided with a brief period of rehabilitation, the perception exists that patients with a TBI require little further treatment and face no lasting effects on the central nervous system or other organ systems. In fact, TBI is a chronic disease process, one that fits the World Health Organization definition as having one or more of the following characteristics: it is permanent, caused by non-reversible pathological alterations, requires special training of the patient for rehabilitation, and/or may require a long period of observation, supervision, or care. TBI increases long-term mortality and reduces life expectancy. It is associated with increased incidences of seizures, sleep disorders, neurodegenerative diseases, neuroendocrine dysregulation, and psychiatric diseases, as well as non-neurological disorders such as sexual dysfunction, bladder and bowel incontinence, and systemic metabolic dysregulation that may arise and/or persist for months to years post-injury. The purpose of this article is to encourage the classification of TBI as the beginning of an ongoing, perhaps lifelong process, that impacts multiple organ systems and may be disease causative and accelerative. Our intent is not to discourage patients with TBI or their families and caregivers, but rather to emphasize that TBI should be managed as a chronic disease and defined as such by health care and insurance providers. Furthermore, if the chronic nature of TBI is recognized by government and private funding agencies, research can be directed at discovering therapies that may interrupt the disease processes months or even years after the initiating event.

CD38 facilitates recovery from traumatic brain injury

Traumatic brain injury (TBI) is a major cause of death and disability worldwide. It causes progressive tissue atrophy and consequent neurological dysfunctions. TBI is accompanied by neuroinflammation, a process mediated largely by microglia. CD38 is an ectoenzyme that promotes transmembrane signaling via the synthesis of potent calcium mobilizing agents or via its receptor activity. CD38 is expressed in the brain in various cell types including microglia. In previous studies, we showed that CD38 regulates microglial activation and response to chemokines. In view of the important role of neuroinflammation in TBI and the effects of CD38 on microglial responses, the present study examines the role of CD38 in the recovery of mice from closed head injury (CHI), a model of focal TBI. For this purpose, CD38-deficient and wild-type (WT) mice were subjected to a similar severity of CHI and the effect of the injury on neurobehavioral and cognitive functions was assessed by the Neurological Severity Score (NSS) and the Object Recognition Test, at various time points post-injury. The results show that recovery after CHI (as indicated by the NSS) was significantly lower in CD38-deficient mice than in WT mice and that the object recognition performance after injury was significantly impaired in injured CD38-deficient mice than in WT mice. In addition, we also observed that the amount of activated microglia/macrophages at the injury site was significantly lower in CD38-deficient mice compared with WT mice. Taken together, our findings indicate that CD38 plays a beneficial role in the recovery of mice from CHI and that this effect is mediated, at least in part, via the effect of CD38 on microglia responses.

Neurocognitive fitness in the sub-acute stage after mild TBI: The effect of age

OBJECTIVE

Age is assumed to be a negative prognostic factor in recovery from moderate-to-severe traumatic brain injury (TBI). Little is known on cognitive performance after mild TBI in relation to age in the sub-acute stage after injury.

METHOD

Ninety-nine mild TBI subjects (age 15-75) were compared with 91 healthy control subjects (age 14-74) in a case-control design. Patients were matched on age, sex and level of education, with control subjects. Mean interval between injury and cognitive assessment was 13 days. Neurocognitive test battery contained tests of verbal memory, selective attention, general speed of information processing and verbal fluency.

RESULTS

An overall effect was found of a single mild TBI on neurocognitive performance in the sub-acute stage after injury. Age did not add significantly to the effect of mild TBI on cognitive functioning.

CONCLUSION

Patients suffering from mild TBI are characterized by subtle neurocognitive deficits in the weeks directly following the trauma. The notion that elderly subjects have a worse outcome in the sub-acute period after mild TBI is at least not in line with the results of this study.

Unusually rapid and severe cognitive deterioration after mild traumatic brain injury

A 56-year-old man (AB) presented with dramatic cognitive deterioration following a mild traumatic brain injury. There was no indication of severe brain injury or significant anoxic encephalopathy. Detailed history indicated no significant pre-morbid cognitive deficits. His pre-injury psychosocial and occupational functioning was intact. Cognition functioning was impaired immediately post-injury and remained impaired. Neuropsychological examination at 8 months post-injury showed severe cognitive deficits. The cognitive profile was consistent with Alzheimer's disease. MRI at 1-year post-injury showed minor ischaemic changes not consistent with hypoxic injury and insufficient to explain his cognitive problems. Early SPECT was consistent with a diagnosis of Alzheimer's disease and a repeat SPECT showed a significant deterioration in an Alzheimer pattern. AB was seen for detailed serial neuropsychological examination over a 3-year period, which revealed clear evidence of cognitive deterioration consistent with Alzheimer's disease. AB is presented as an unusual case of rapid progressive AD following a mild head injury.

Modifiable Midlife Risk Factors for Late-Life Cognitive Impairment and Dementia

The baby boom generation is approaching the age of greatest risk for cognitive impairment and dementia. There is growing interest in strategies to modify the environment in midlife to increase the probability of maintaining cognitive health in late life. Several potentially modifiable risk factors have been studied in relation to cognitive impairment and dementia in late life, but methodological limitations of observational research have resulted in some inconsistencies across studies. The most promising strategies are maintaining cardiovascular health, engagement in mental, physical, and social activities, using alcohol in moderation, abstaining from tobacco use, and following a heart-healthy diet. Other factors that may influence cognitive health are occupational attainment, depression, personality, exposure to general anesthesia, head injury, postmenopausal hormone therapy, non-steroidal anti-inflammatory medications, and nutritional supplements such as antioxidants. Some long-term observational studies initiated in midlife or earlier, and some randomized controlled trials, have examined the effects of specific cognitive health promotion behaviors in midlife on the risk of cognitive impairment in late life. Overall, these studies provide limited support for risk reduction at this time. Recommendations and challenges for developing effective strategies to reduce the burden of cognitive impairment and dementia in the future are discussed.

Dicyclomine, an M1 muscarinic antagonist, reduces biomarker levels, but not neuronal degeneration, in fluid percussion brain injury

Recent studies indicate that alphaII-spectrin breakdown products (SBDPs) have utility as biological markers of traumatic brain injury (TBI). However, the utility of SBDP biomarkers for detecting effects of therapeutic interventions has not been explored. Acetylcholine plays a role in pathological neuronal excitation and TBI-induced muscarinic cholinergic receptor activation may contribute to excitotoxic processes. In experiment I, regional and temporal changes in calpain-mediated alpha-spectrin degradation were evaluated at 3, 12, 24, and 48 h using immunostaining for 145-kDa SBDP. Immunostaining of SBDP-145 was only evident in the hemisphere ipsilateral to TBI and was generally limited to the cortex except at 24 h when immunostaining was also prominent in the dentate gyrus and striatum. In Experiment II, cerebral spinal fluid (CSF) samples were analyzed for various SBDPs 24 h after moderate lateral fluid percussion TBI. Rats were administered either dicyclomine (5 mg/kg i.p.) or saline vehicle (n = 8 per group) 5 min prior to injury. Injury produced significant increases (p < 0.001) of 300%, 230%, and >1000% in SBDP-150, -145, and -120, respectively in vehicle-treated rats compared to sham. Dicyclomine treatment produced decreases of 38% (p = 0.077), 37% (p = 0.028), and 63% (p = 0.051) in SBDP-150, -145, and -120, respectively, compared to vehicle-treated injury. Following CSF extraction, coronal brain sections were processed for detecting degenerating neurons using Fluoro-Jade histofluorescence. Stereological techniques were used to quantify neuronal degeneration in the dorsal hippocampus CA2/3 region and in the parietal cortex. No significant differences were detected in numbers of degenerating neurons in the dorsal CA2/3 hippocampus or the parietal cortex between saline and dicyclomine treatment groups. The percent weight loss following TBI was significantly reduced by dicyclomine treatment. These data provide additional evidence that, as TBI biomarkers, SBDPs are able to detect a therapeutic intervention even in the absence of changes in neuronal cell degeneration measured by Fluoro-jade.

Increased expression of the gamma-secretase components presenilin-1 and nicastrin in activated astrocytes and microglia following traumatic brain injury

Gamma-secretase is an aspartyl protease composed of four proteins: presenilin (PS), nicastrin (Nct), APH1, and PEN2. These proteins assemble into a membrane complex that cleaves a variety of substrates within the transmembrane domain. The gamma-secretase cleavage products play an important role in various biological processes such as embryonic development and Alzheimer's disease (AD). The major role of gamma-secretase in brain pathology has been linked to AD and to the production of the amyloid beta-peptide. However, little is known about the possible role of gamma-secretase following acute brain insult. Here we examined by immunostaining the expression patterns of two gamma-secretase components, PS1 and Nct, in three paradigms of brain insult in mice: closed head injury, intracerebroventricular injection of LPS, and brain stabbing. Our results show that in naïve and sham-injured brains expression of PS1 and Nct is restricted mainly to neurons. However, following insult, the expression of both proteins is also observed in nonneuronal cells, consisting of activated astrocytes and microglia. Furthermore, the proteins are coexpressed within the same astrocytes and microglia, implying that these cells exhibit an enhanced gamma-secretase activity following brain damage. In view of the important role played by astrocytes and microglia in brain disorders, our findings suggest that gamma-secretase may participate in brain damage and repair processes by regulating astrocyte and microglia activation and/or function.

Impact of age on long-term recovery from traumatic brain injury

OBJECTIVE

To determine whether older persons are at increased risk for progressive functional decline after traumatic brain injury (TBI).

DESIGN

Longitudinal cohort study.

SETTING

Traumatic Brain Injury Model Systems (TBIMS) rehabilitation centers.

PARTICIPANTS

Subjects enrolled in the TBIMS national dataset.

INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASURES

Disability Rating Scale (DRS), FIM instrument cognitive items, and the Glasgow Outcome Scale-Extended.

RESULTS

Participants were separated into 3 age tertiles: youngest (16-26y), intermediate (27-39y), and oldest (> or =40y). DRS scores were comparable across age groups at admission to a rehabilitation center. The oldest group was slightly more disabled at discharge from rehabilitation despite having less severe acute injury severity than the younger groups. Although DRS scores for the 2 younger groups improved significantly from year 1 to year 5, the greatest magnitude of improvement in disability was seen among the youngest group. In addition, after dividing patients into groups according to whether their DRS scores improved (13%), declined (10%), or remained stable (77%) over time, the likelihood of decline was found to be greater for the 2 older groups than for the youngest group. A multiple regression model showed that age has a significant negative influence on DRS score 5 years post-TBI after accounting for the effects of covariates.

CONCLUSIONS

This study supported our primary hypothesis that older patients show greater decline over the first 5 years after TBI than younger patients. In addition, the greatest amount of improvement in disability was observed among the youngest group of survivors. These results suggest that TBI survivors, especially older patients, may be candidates for neuroprotective therapies after TBI.

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.

Alterations of acetylcholinesterase activity after traumatic brain injury in rats

OBJECTIVE

The cholinergic system is highly vulnerable to traumatic brain injury (TBI). However, limited information is available to what extent the degrading enzyme acetylcholinesterase (AChE) is involved. The present study addresses this question.

METHOD

Thirty-six anaesthetized Sprague-Dawley rats were subjected to sham operation or to TBI using controlled cortical impact (CCI). The AChE activity was histochemically determined in frozen brain slices at 2, 24 and 72 hours after TBI.

RESULTS

High enzyme activity was observed in regions rich in cholinergic innervation such as the olfactory tubercle, basal forebrain, putamen and superior colliculi. Low activity was found in the cortex, cerebellum and particularly in the white matter. A decrease of AchE activity (20-35%) was found in the hippocampus and hypothalamus already at 2 hours after TBI. An increase of approximately 30% was found in the basal forebrain at 2 and 24 hours. No changes occurred at 72 hours.

CONCLUSION

The findings are consistent with impairment of the cholinergic neurotransmission after TBI and suggest the involvement of the AChE in short-term regulatory mechanisms.

Multiple proteins implicated in neurodegenerative diseases accumulate in axons after brain trauma in humans

Studies in animal models have shown that traumatic brain injury (TBI) induces the rapid accumulation of many of the same key proteins that form pathologic aggregates in neurodegenerative diseases. Here, we examined whether this rapid process also occurs in humans after TBI. Brain tissue from 18 cases who died after TBI and from 6 control cases was examined using immunohistochemistry. Following TBI, widespread axonal injury was persistently identified by the accumulation of neurofilament protein and amyloid precursor protein (APP) in axonal bulbs and varicosities. Axonal APP was found to co-accumulate with its cleavage enzymes, beta-site APP cleaving enzyme (BACE), presenilin-1 (PS1) and their product, amyloid-beta (Abeta). In addition, extensive accumulation of alpha-synuclein (alpha-syn) was found in swollen axons and tau protein was found to accumulate in both axons and neuronal cell bodies. These data show rapid axonal accumulation of proteins implicated in neurodegenerative diseases including Alzheimer's disease and the synucleinopathies. The cause of axonal pathology can be attributed to disruption of axons due to trauma, or as a secondary effect of raised intracranial pressure or hypoxia. Such axonal pathology in humans may provide a unique environment whereby co-accumulation of APP, BACE, and PS1 leads to intra-axonal production of Abeta as well as accumulation of alpha-syn and tau. This process may have important implications for survivors of TBI who have been shown to be at greater risk of developing neurodegenerative diseases.

Improving dementia assessment by reducing sample heterogeneity

Outcome assessment for clinical dementia trials could be enhanced by using the Mini-mental State Examination (MMSE) and the Hopkins Verbal Learning Test (HVLT), in addition to imaging and genetic screening. The statistical power of trials could be increased if heterogeneity of the sample were reduced by the administration of a risk factor inventory which could be used for subject selection or selection of drug responders.

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.

Traumatic brain injury in the elderly: diagnostic and treatment challenges

The purpose of this review is to introduce geriatric practitioners to issues and challenges presented in the elderly after onset of traumatic brain injury (TBI). Issues discussed include the magnitude of TBI in the elderly, mechanisms of onset, issues specific to both acute and rehabilitation care for the elderly with TBI, and specific physical and behavioral manifestations of TBI that may need to be addressed on an inpatient or outpatient basis. General guidelines are provided for the diagnosis and treatment of older individuals who have TBI, with specific clinical scenarios illustrating key points.

Outcome after traumatic brain injury sustained in older adulthood: a one-year longitudinal study

OBJECTIVE

The objective of this study was to explore the effects of traumatic brain injury (TBI) on cognition and functioning in older adults in a one-year longitudinal study.

METHODS

Participants with mild-to-moderate TBI were compared with an age-, gender-, and education-matched healthy comparison group on aspects of cognition. Neuropsychologic tests were administered at one year. Self-reported measures of functioning were completed at baseline, six months, and one year. Informants rated instrumental functioning at one year.

RESULTS

Sixty-nine subjects aged 50 years and over (mean: 67 years; standard deviation: 7.9) and a comparison group of 79 participants were assessed. Patients with TBI had poorer processing speed, verbal memory, language, and executive function; they self-reported more psychologic distress, psychosocial dysfunction, and postconcussive symptoms; and they were rated as more impaired in functioning than the comparison group. TBI of moderate severity accounted for most of the between-group differences.

CONCLUSION

TBI, particularly of moderate severity, led to poorer cognitive and psychosocial functioning one year postinjury among older adults. The clinical significance of this may become more evident with time in this vulnerable population.

MRI findings and Axis I and II psychiatric disorders after traumatic brain injury: a 30-year retrospective follow-up study

We studied the association between psychiatric disorders and the presence and location of traumatic lesions on magnetic resonance imaging (MRI) in 58 patients, on average, 30 years after traumatic brain injury. Axis I psychiatric disorders that had begun after the injury were assessed with the Schedules for Clinical Assessment in Neuropsychiatry (version 2.1), and Axis II disorders with the Structured Clinical Interview for DSM-III-R Personality Disorders. A 1.5-Tesla MRI scanner was used. One-third of the subjects had traumatic lesions visible on MRI. Only three psychiatric disorders, that is, delusional disorder, dementia, and the disinhibited type of organic personality syndrome, were significantly more common in subjects with contusions. Concerning the location of contusions, organic personality syndrome and its disinhibited subtype were associated with frontal lesions, and major depression was, surprisingly, inversely associated with temporal lesions. These results, which should be interpreted with caution due to the limited size of the study group, suggest that the majority of psychiatric disorders after traumatic brain injury are not closely related to the specific location or even the presence of contusions detectable with post-acute MRI.

Diffusion tensor imaging in chronic head injury survivors: correlations with learning and memory indices

Diffusion tensor imaging (DTI) provides a unique insight into the cellular integrity of the brain. While conventional magnetic resonance imaging underestimates the extent of pathology following closed head injury, diffusion-weighted imaging has been shown to more accurately delineate the extent of cerebral damage. There have only been a few case studies of DTI in chronic head injury survivors. This study used DTI to investigate changes in anisotropy and diffusivity in survivors of head injury at least 6 months after their injury. The relationship between cognition and diffusion abnormality was also investigated. The voxel-based analysis revealed significant bilateral decreases in anisotropy, in major white matter tracts and association fibers in the temporal, frontal, parietal and occipital lobes. Statistically significant increases in diffusivity were also found in widespread areas of the cortex. A significant positive correlation was found between diffusivity and impairment of learning and memory in the left posterior cingulate, left hippocampal formation and left temporal, frontal and occipital cortex. The common pattern of abnormality despite heterogeneous injury mechanism and lesion location in the group suggests that these cellular changes reflect secondary insults. The importance of diffusion abnormalities in head injury outcome is emphasized by the significant correlation between a learning and memory index and diffusivity in areas known to subserve this cognitive function.