Head injury as a risk factor in Alzheimer's disease

Ageing with Traumatic Brain Injury: Long-Term Cognition and Wellbeing

Whether and how traumatic brain injury (TBI) impacts ageing in the decades post-injury remains a matter of debate, partly due to a lack of controlled studies. This study examined the long-term impact of TBI on cognition and wellbeing in middle-aged and older adults and explored the relationship between age, cognition, and wellbeing, compared with a non-TBI control group. Cross-sectional data from 143 participants aged ≥40 with moderate-severe TBI (6-33 years post-injury; mean age 59.64) were compared with 71 non-TBI controls (mean age 62.10) group matched on age, gender, and premorbid IQ. Individuals with significant confounding comorbidities were excluded. A battery of neuropsychological tests and wellbeing measures (emotional distress, sleep, health-related quality of life [HRQoL]) was administered. Older age and TBI were each independently associated with poorer cognition across multiple domains (p < 0.05). The relationship between verbal learning and memory impairment post-TBI differed between age groups: individuals with TBI in their 40s-60s performed significantly worse than same-aged controls on verbal story acquisition (B = 0.09, p = 0.040, 95% confidence interval [CI] [0.004, 0.17]) and recall (B = 0.12, p = 0.009, 95% CI [0.03, 0.21]), and verbal wordlist recall (B = 0.11, p = 0.007, 95% CI [0.03, 0.19]). In comparison, no significant group differences in verbal memory emerged for ages 70-90. The TBI group reported greater emotional distress (B = 3.55, p < 0.001, 95% CI [1.73, 5.37]), poorer sleep quality (B = 1.07, p = 0.016, 95% CI [0.20, 1.94]), and poorer physical HRQoL (B = -4.26, p = 0.003, 95% CI [-7.08, -1.43]) than controls at all ages. Poorer physical HRQoL was related to poorer cognition post-TBI (p < 0.05). Our results challenge the notion that TBI exacerbates ageing. Moderate-severe TBI resulted in significant long-term impairments in cognition and wellbeing, with verbal learning and memory more impaired during middle-adulthood but not older adulthood compared to controls. TBI was not associated with changes to wellbeing with ageing. Intervention for verbal memory deficits in middle-aged adults with TBI is important, along with wider long-term supports for cognition, wellbeing, and activity participation in all individuals with TBI.

A preliminary study on plasma markers across cognitive stages and links to a history of mild traumatic brain injury

Potential implications of a history of mild traumatic brain injury (mTBI) during aging are understudied. Seven plasma markers were measured in matched participants having normal cognition, mild cognitive impairment (MCI) and dementia of the Alzheimer's type (DAT) with and without a history of mTBI. Phosphorylated tau181 showed a moderate effect size for being greater in mTBI + individuals having MCI and DAT, and effect sizes for lower amyloid-β 42/40 and higher neurofilament light were seen for mTBI + DAT individuals. This preliminary report shows a potential role of plasma-derived markers in detecting associations between mTBI history and the development of Alzheimer's disease and related disorders.

Traumatic Brain Injury in Mice Generates Early-Stage Alzheimer's Disease Related Protein Pathology that Correlates with Neurobehavioral Deficits

Traumatic brain injury (TBI) increases the long-term risk of neurodegenerative diseases, including Alzheimer's disease (AD). Here, we demonstrate that protein variant pathology generated in brain tissue of an experimental TBI mouse model is similar to protein variant pathology observed during early stages of AD, and that subacute accumulation of AD associated variants of amyloid beta (Aβ) and tau in the TBI mouse model correlated with behavioral deficits. Male C57BL/6 mice were subjected to midline fluid percussion injury or to sham injury, after which sensorimotor function (rotarod, neurological severity score), cognitive deficit (novel object recognition), and affective deficits (elevated plus maze, forced swim task) were assessed post-injury (DPI). Protein pathology at 7, 14, and 28 DPI was measured in multiple brain regions using an immunostain panel of reagents selectively targeting different neurodegenerative disease-related variants of Aβ, tau, TDP-43, and alpha-synuclein. Overall, TBI resulted in sensorimotor deficits and accumulation of AD-related protein variant pathology near the impact site, both of which returned to sham levels by 14 DPI. Individual mice, however, showed persistent behavioral deficits and/or accumulation of toxic protein variants at 28 DPI. Behavioral outcomes of each mouse were correlated with levels of seven different protein variants in ten brain regions at specific DPI. Out of 21 significant correlations between protein variant levels and behavioral deficits, 18 were with variants of Aβ or tau. Correlations at 28 DPI were all between a single Aβ or tau variant, both of which are strongly associated with human AD cases. These data provide a direct mechanistic link between protein pathology resulting from TBI and the hallmarks of AD.

Antiepileptic Drugs as Potential Dementia Prophylactics Following Traumatic Brain Injury

Seizures and other forms of neurovolatility are emerging as druggable prodromal mechanisms that link traumatic brain injury (TBI) to the progression of later dementias. TBI neurotrauma has both acute and long-term impacts on health, and TBI is a leading risk factor for dementias, including chronic traumatic encephalopathy and Alzheimer's disease. Treatment of TBI already considers acute management of posttraumatic seizures and epilepsy, and impressive efforts have optimized regimens of antiepileptic drugs (AEDs) toward that goal. Here we consider that expanding these management strategies could determine which AED regimens best prevent dementia progression in TBI patients. Challenges with this prophylactic strategy include the potential consequences of prolonged AED treatment and that a large subset of patients are refractory to available AEDs. Addressing these challenges is warranted because the management of seizure activity following TBI offers a rare opportunity to prevent the onset or progression of devastating dementias.

Traumatic brain injury in mice generates early-stage Alzheimer's disease related protein pathology that correlates with neurobehavioral deficits

Traumatic brain injury (TBI) increases the long-term risk of neurodegenerative diseases, including Alzheimer's disease (AD). Here, we demonstrate that protein variant pathology generated in brain tissue of an experimental TBI mouse model is similar to protein variant pathology observed in human ADbrains, and that subacute accumulation of two AD associated variants of amyloid beta (Aβ) and tau in the TBI mouse model correlated with behavioral deficits. Male C57BL/6 mice were subjected to midline fluid percussion injury or to sham injury, after which sensorimotor function (rotarod, neurological severity score), cognitive deficit (novel object recognition), and affective deficits (elevated plus maze, forced swim task) were assessed at different days post-injury (DPI). Protein pathology at 7, 14, and 28 DPI was measured in multiple brain regions using an immunostain panel of reagents selectively targeting different neurodegenerative disease-related variants of Aβ, tau, TDP-43, and alpha-synuclein. Overall, TBI resulted in sensorimotor deficits and accumulation of AD-related protein variant pathology near the impact site, both of which returned to sham levels by 14 DPI. Individual mice, however, showed persistent behavioral deficits and/or accumulation of selected toxic protein variants at 28 DPI. Behavioral outcomes of each mouse were correlated with levels of seven different protein variants in ten brain regions at specific DPI. Out of 21 significant correlations between protein variant levels and behavioral deficits, 18 were with variants of Aβ or tau. Correlations at 28 DPI were all between a single Aβ or tau variant, both of which are strongly associated with human AD cases. These data provide a direct mechanistic link between protein pathology resulting from TBI and the hallmarks of AD.

Phytochemicals: A Promising Alternative for the Prevention of Alzheimer's Disease

Alzheimer's disease (AD) is a neurological condition that worsens with ageing and affects memory and cognitive function. Presently more than 55 million individuals are affected by AD all over the world, and it is a leading cause of death in old age. The main purpose of this paper is to review the phytochemical constituents of different plants that are used for the treatment of AD. A thorough and organized review of the existing literature was conducted, and the data under the different sections were found using a computerized bibliographic search through the use of databases such as PubMed, Web of Science, Google Scholar, Scopus, CAB Abstracts, MEDLINE, EMBASE, INMEDPLAN, NATTS, and numerous other websites. Around 360 papers were screened, and, out of that, 258 papers were selected on the basis of keywords and relevant information that needed to be included in this review. A total of 55 plants belonging to different families have been reported to possess different bioactive compounds (galantamine, curcumin, silymarin, and many more) that play a significant role in the treatment of AD. These plants possess anti-inflammatory, antioxidant, anticholinesterase, and anti-amyloid properties and are safe for consumption. This paper focuses on the taxonomic details of the plants, the mode of action of their phytochemicals, their safety, future prospects, limitations, and sustainability criteria for the effective treatment of AD.

Neuroprotective Effects of Nanowired Delivery of Cerebrolysin with Mesenchymal Stem Cells and Monoclonal Antibodies to Neuronal Nitric Oxide Synthase in Brain Pathology Following Alzheimer's Disease Exacerbated by Concussive Head Injury

Concussive head injury (CHI) is one of the major risk factors in developing Alzheimer's disease (AD) in military personnel at later stages of life. Breakdown of the blood-brain barrier (BBB) in CHI leads to extravasation of plasma amyloid beta protein (ΑβP) into the brain fluid compartments precipitating AD brain pathology. Oxidative stress in CHI or AD is likely to enhance production of nitric oxide indicating a role of its synthesizing enzyme neuronal nitric oxide synthase (NOS) in brain pathology. Thus, exploration of the novel roles of nanomedicine in AD or CHI reducing NOS upregulation for neuroprotection are emerging. Recent research shows that stem cells and neurotrophic factors play key roles in CHI-induced aggravation of AD brain pathologies. Previous studies in our laboratory demonstrated that CHI exacerbates AD brain pathology in model experiments. Accordingly, it is quite likely that nanodelivery of NOS antibodies together with cerebrolysin and mesenchymal stem cells (MSCs) will induce superior neuroprotection in AD associated with CHI. In this review, co-administration of TiO2 nanowired cerebrolysin - a balanced composition of several neurotrophic factors and active peptide fragments, together with MSCs and monoclonal antibodies (mAb) to neuronal NOS is investigated for superior neuroprotection following exacerbation of brain pathology in AD exacerbated by CHI based on our own investigations. Our observations show that nanowired delivery of cerebrolysin, MSCs and neuronal NOS in combination induces superior neuroprotective in brain pathology in AD exacerbated by CHI, not reported earlier.

Chronic Cognitive and Cerebrovascular Function after Mild Traumatic Brain Injury in Rats

Severe traumatic brain injury (TBI) results in cognitive dysfunction in part due to vascular perturbations. In contrast, the long-term vasculo-cognitive pathophysiology of mild TBI (mTBI) remains unknown. We evaluated mTBI effects on chronic cognitive and cerebrovascular function and assessed their interrelationships. Sprague-Dawley rats received midline fluid percussion injury (n = 20) or sham (n = 21). Cognitive function was assessed (3- and 6-month novel object recognition [NOR], novel object location [NOL], and temporal order object recognition [TOR]). Six-month cerebral blood flow (CBF) and cerebral blood volume (CBV) using contrast magnetic resonance imaging (MRI) and ex vivo circle of Willis artery endothelial and smooth muscle-dependent function were measured. mTBI rats showed significantly impaired NOR, with similar trends (non-significant) in NOL/TOR. Regional CBF and CBV were similar in sham and mTBI. NOR correlated with CBF in lateral hippocampus, medial hippocampus, and primary somatosensory barrel cortex, whereas it inversely correlated with arterial smooth muscle-dependent dilation. Six-month baseline endothelial and smooth muscle-dependent arterial function were similar among mTBI and sham, but post-angiotensin 2 stimulation, mTBI showed no change in smooth muscle-dependent dilation from baseline response, unlike the reduction in sham. mTBI led to chronic cognitive dysfunction and altered angiotensin 2-stimulated smooth muscle-dependent vasoreactivity. The findings of persistent pathophysiological consequences of mTBI in this animal model add to the broader understanding of chronic pathophysiological sequelae in human mild TBI.

A multi-expert ensemble system for predicting Alzheimer transition using clinical features

Alzheimer’s disease (AD) diagnosis often requires invasive examinations (e.g., liquor analyses), expensive tools (e.g., brain imaging) and highly specialized personnel. The diagnosis commonly is established when the disorder has already caused severe brain damage, and the clinical signs begin to be apparent. Instead, accessible and low-cost approaches for early identification of subjects at high risk for developing AD years before they show overt symptoms are fundamental to provide a critical time window for more effective clinical management, treatment, and care planning. This article proposes an ensemble-based machine learning algorithm for predicting AD development within 9 years from first overt signs and using just five clinical features that are easily detectable with neuropsychological tests. The validation of the system involved both healthy individuals and mild cognitive impairment (MCI) patients drawn from the ADNI open dataset, at variance with previous studies that considered only MCI. The system shows higher levels of balanced accuracy, negative predictive value, and specificity than other similar solutions. These results represent a further important step to build a preventive fast-screening machine-learning-based tool to be used as a part of routine healthcare screenings.

The road to precision medicine: Eliminating the "One Size Fits All" approach in Alzheimer's disease

The expeditious advancement of Alzheimer's Disease (AD) is a threat to the global healthcare system, that is further supplemented by therapeutic failure. The prevalence of this disorder has been expected to quadrupole by 2050, thereby exerting a tremendous economic pressure on medical sector, worldwide. Thus, there is a dire need of a change in conventional approaches and adopt a novel methodology of disease prevention, treatment and diagnosis. Precision medicine offers a personalized approach to disease management, It is dependent upon genetic, environmental and lifestyle factors associated with the individual, aiding to develop tailored therapeutics. Precision Medicine Initiatives are launched, worldwide, to facilitate the integration of personalized models and clinical medicine. The review aims to provide a comprehensive understanding of the neuroinflammatory processes causing AD, giving a brief overview of the disease interventions. This is further followed by the role of precision medicine in AD, constituting the genetic perspectives, operation of personalized form of medicine and optimization of clinical trials with the 3 R's, showcasing an in-depth understanding of this novel approach in varying aspects of the healthcare industry, to provide an opportunity to the global AD researchers to elucidate suitable therapeutic regimens in clinically and pathologically complex diseases, like AD.

The Delayed Neuropathological Consequences of Traumatic Brain Injury in a Community-Based Sample

The late neuropathological effects of traumatic brain injury have yet to be fully elucidated, particularly with respect to community-based cohorts. To contribute to this critical gap in knowledge, we designed a multimodal neuropathological study, integrating traditional and quantitative approaches to detect pathologic changes in 532 consecutive brain autopsies from participants in the Adult Changes in Thought (ACT) study. Diagnostic evaluation including assessment for chronic traumatic encephalopathy (CTE) and quantitative immunoassay-based methods were deployed to examine levels of pathological (hyperphosphorylated) tau (pTau) and amyloid (A) β in brains from ACT participants with (n = 107) and without (n = 425) history of remote TBI with loss of consciousness (w/LOC). Further neuropathological assessments included immunohistochemistry for α-synuclein and phospho-TDP-43 pathology and astro- (GFAP) and micro- (Iba1) gliosis, mass spectrometry analysis of free radical injury, and gene expression evaluation (RNA sequencing) in a smaller sub-cohort of matched samples (49 cases with TBI and 49 non-exposed matched controls). Out of 532 cases, only 3 (0.6%-none with TBI w/LOC history) showed evidence of the neuropathologic signature of chronic traumatic encephalopathy (CTE). Across the entire cohort, the levels of pTau and Aβ showed expected differences for brain region (higher levels in temporal cortex), neuropathological diagnosis (higher in participants with Alzheimer's disease), and APOE genotype (higher in participants with one or more APOE ε4 allele). However, no differences in PHF-tau or Aβ1-42 were identified by Histelide with respect to the history of TBI w/LOC. In a subset of TBI cases with more carefully matched control samples and more extensive analysis, those with TBI w/LOC history had higher levels of hippocampal pTau but no significant differences in Aβ, α-synuclein, pTDP-43, GFAP, Iba1, or free radical injury. RNA-sequencing also did not reveal significant gene expression associated with any measure of TBI exposure. Combined, these findings suggest long term neuropathological changes associated with TBI w/LOC may be subtle, involve non-traditional pathways of neurotoxicity and neurodegeneration, and/or differ from those in autopsy cohorts specifically selected for neurotrauma exposure.

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

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

Experiences and Perceptions of Hospitalization and Recovery of Older Adults and Their Caregivers Following Traumatic Brain Injury: "Not Knowing"

The purpose of the current study is to describe the experience and perceptions of older adults and their caregivers following hospitalization for mild or moderate traumatic brain injury (TBI). Qualitative analysis of data obtained in individual semi-structured interviews with older adults and their caregivers (N = 11, five dyads and one individual) was performed to capture the perceptions and experiences of the survivor and their caregivers about the acute injury, hospitalization, and recovery. Data were collected over a 2-month period following discharge from the hospital. Open coding and constant comparative analysis generated codes that were revised throughout the analysis and reformulated into thematic descriptions. As a result, seven interrelated themes were identified. These findings can be used to implement interventions focused on recovery, communication, teaching, patient outcomes, and satisfaction. [Res Gerontol Nurs. 2019; 12(5):227-238].

CNS disease-related protein variants as blood-based biomarkers in traumatic brain injury

OBJECTIVE

To utilize a panel of 11 single chain variable fragments (scFvs) that selectively bind disease-related variants of TAR DNA-binding protein (TDP)-43, β-amyloid, tau, and α-synuclein to assess damage following traumatic brain injury (TBI), and determine if the presence of protein variants could account for the increased risk of various neurodegenerative diseases following TBI.

METHODS

We utilized the panel of 11 scFvs in a sensitive ELISA format to analyze sera from 43 older veterans, 25 who had experienced at least 1 TBI incident during their lifetime (∼29.4 years after TBI), and 18 controls who did not incur TBI, in a cross-sectional study.

RESULTS

Each of the 11 scFvs individually could significantly distinguish between TBI and control samples, though they did not detect each TBI sample. Comparing the levels of all 11 variants, all 25 TBI cases displayed higher reactivity compared to the controls and receiver operating characteristic analysis revealed 100% sensitivity and specificity. Higher total protein variants levels correlated with TBI severity and with loss of consciousness. Oligomeric tau levels distinguished between single and multiple TBI incidents. While all TBI cases were readily selected with the panel, the binding pattern varied from patient to patient, suggesting subgroups that are at increased risk for different neurodegenerative diseases.

CONCLUSION

The panel of protein variants-specific scFvs can be used to identify blood-based biomarkers indicative of TBI even 20 years or more after the initial TBI. Being able to identify subgroups of biomarker profiles allows for the possibility of individually targeted treatments.

Traumatic Brain Injury as a Risk Factor for Dementia and Alzheimer Disease: Critical Review of Study Methodologies

Despite much previous research stating that traumatic brain injury (TBI) has been confirmed as a risk factor for dementia and Alzheimer disease (AD), findings from observational studies are mixed and are of low methodological quality. This review aimed to critically evaluate the methodologies used in previous studies. Relevant literature was identified by examining reference lists for previous reviews and primary studies, and searches in MEDLINE, PubMed, Google Scholar, and Research Gate. Sixty-eight identified reports, published between 1982 and August 2018, met inclusion criteria. Common methodological weaknesses included self-reported TBI (62%); poor TBI case definition (55%); low prevalence of TBI in samples (range 0.07-28.7%); reverse causality (86% moderate to high risk of reverse causality); not controlling for important confounding factors. There were also key areas of methodological rigor including use of individual matching for cases and controls (57%); gold standard dementia and AD criteria (53%); symmetrical data collection (65%); large sample sizes (max, 2,794,752); long follow-up periods and controlling of analyses for age (82%). The quality assessment revealed methodological problems with most studies. Overall, only one study was identified as having strong methodological rigor. This critical review identified several key areas of methodological weakness and rigor and should be used as a guideline for improving future research. This can be achieved by using longitudinal prospective cohort designs, with medically confirmed and well characterized TBI sustained sufficient time before the onset of dementia, including appropriate controls and informants, and considering the impacts of known protective and risk factors.

Impact of mild traumatic brain injury on cingulate functions

Mild traumatic brain injury (mTBI) is a condition of normal neuroimaging, because conventional MRI is not sensitive to brain lesions. Neurocognitive deficits persist for years after injury in 15% of patients. Persistent TAI can continue after the trauma and contribute to progressive disability. Neuropathologic studies underestimate the total axonal damage, by failure to identify fine-caliber unmyelinated fiber. Swollen axons represent the "tip of the iceberg" of damage. Progression of molecular changes, including mitochondrial dysfunction, leads to secondary injuries. Primary low-intensity "invisible injury" is solely detectable at ultrastructural levels. Over the long term, mTBI is not a static event but a progressive injury, increasing risk of neurodegenerative diseases. Lack of evidence of brain injury has led to the development of more sensitive methods: morphometric MRI (VBM, DTI) and functional techniques (fMRI, PET, SPECT). By deformation of the surface of gray matter cingulate gyrus and disruption of long-coursing WM of CB structures, striking the falx, mTBI causes alteration of cingulate functions. Postconcussion, blast, and whiplash-associated disorders are the main mechanisms providing behavior and cognitive symptoms after mTBI.

Is traumatic brain injury a risk factor for neurodegeneration? A meta-analysis of population-based studies

Background

To determine the association of prior traumatic brain injury (TBI) with subsequent diagnosis of neurodegeneration disease.

Methods

All studies from 1980 to 2016 reporting TBI as a risk factor for diagnoses of interest were identified by searching PubMed, Embase, study references, and review articles. The data and study design were assessed by 2 investigators independently. A meta-analysis was performed by RevMan 5.3.

Results

There were 18 studies comprising 3,263,207 patients. Meta-analysis revealed a significant association of prior TBI with subsequent dementia. The pooled odds ratio (OR) for TBI on development of dementia, FTD and TDP-43 associated disease were 1.93 (95% CI 1.47–2.55, p < 0.001), 4.44 (95% CI 3.86–5.10, p < 0.001), and 2.97 (95% CI 1.35–6.53, p < 0.001). However, analyses of individual diagnoses found no evidence that the risk of Alzheimer’s disease, and Parkinson’s disease in individuals with previous TBI compared to those without TBI.

Conclusions

History of TBI is not associated with the development of subsequent neurodegeneration disease. Care must be taken in extrapolating from these results because no suitable criteria define post TBI neurodegenerative processes. Therefore, further research in this area is needed to confirm these questions and uncover the link between TBI and neurodegeneration disease.

Traumatic brain injury history is associated with an earlier age of dementia onset in autopsy-confirmed Alzheimer's disease

OBJECTIVE

To evaluate whether a history of traumatic brain injury (TBI) with reported loss of consciousness (LOC) is a risk factor for earlier onset of Alzheimer's disease (AD) in an autopsy-confirmed sample.

METHOD

Data from 2,133 participants with autopsy-confirmed AD (i.e., at least Braak neurofibrillary tangle stages III to VI and CERAD neuritic plaque score moderate to frequent) were obtained from the National Alzheimer's Coordinating Center (NACC). Participants were categorized by presence/absence of self-reported remote (i.e., >1 year prior to their first Alzheimer's Disease Center visit) history of TBI with LOC (TBI+ vs. TBI-). Analyses of Covariance (ANCOVA) controlling for sex, education, and race compared groups on clinician-estimated age of symptom onset and age of diagnosis.

RESULTS

Average age of onset was 2.34 years earlier (p = .01) for the TBI+ group (n = 194) versus the TBI- group (n = 1900). Dementia was diagnosed on average 2.83 years earlier (p = .002) in the TBI+ group (n = 197) versus the TBI- group (n = 1936). Using more stringent neuropathological criteria (i.e., Braak stages V-VI and CERAD frequent), both age of AD onset and diagnosis were 3.6 years earlier in the TBI+ group (both p's < .001).

CONCLUSIONS

History of TBI with reported LOC appears to be a risk factor for earlier AD onset. This is the first study to use autopsy-confirmed cases, supporting previous investigations that used clinical criteria for the diagnosis of AD. Further investigation as to possible underlying mechanisms of association is needed. (PsycINFO Database Record

What is the Relationship of Traumatic Brain Injury to Dementia?

There is a long history linking traumatic brain injury (TBI) with the development of dementia. Despite significant reservations, such as recall bias or concluding causality for TBI, a summary of recent research points to several conclusions on the TBI-dementia relationship. 1) Increasing severity of a single moderate-to-severe TBI increases the risk of subsequent Alzheimer's disease (AD), the most common type of dementia. 2) Repetitive, often subconcussive, mild TBIs increases the risk for chronic traumatic encephalopathy (CTE), a degenerative neuropathology. 3) TBI may be a risk factor for other neurodegenerative disorders that can be associated with dementia. 4) TBI appears to lower the age of onset of TBI-related neurocognitive syndromes, potentially adding "TBI cognitive-behavioral features". The literature further indicates several specific risk factors for TBI-associated dementia: 5) any blast or blunt physical force to the head as long as there is violent head displacement; 6) decreased cognitive and/or neuronal reserve and the related variable of older age at TBI; and 7) the presence of apolipoprotein E ɛ4 alleles, a genetic risk factor for AD. Finally, there are neuropathological features relating TBI with neurocognitive syndromes: 8) acute TBI results in amyloid pathology and other neurodegenerative proteinopathies; 9) CTE shares features with neurodegenerative dementias; and 10) TBI results in white matter tract and neural network disruptions. Although further research is needed, these ten findings suggest that dose-dependent effects of violent head displacement in vulnerable brains predispose to dementia; among several potential mechanisms is the propagation of abnormal proteins along damaged white matter networks.

Head or brain injuries and Alzheimer's disease: A nested case-control register study

INTRODUCTION

Many previous studies have been limited by self- or proxy-reported injury or short follow-up. We investigated whether head or brain injuries are associated with Alzheimer's disease (AD), possible modifying factors and dose-response relationship.

METHODS

Nested register-based case-control study of all community dwellers who received clinically verified AD diagnosis in Finland in 2005 to 2011 (n = 70,719) and one to four matched controls for each case (n of controls = 282,862).

RESULTS

The magnitude of association between hospital-treated head and/or brain injuries was strongly dependent on the lag time between exposure and outcome. With a 5-year lag time, head injury (adjusted odds ratio; 95% confidence interval 1.19; 1.15-1.23) or brain injury (1.23; 1.18-1.29) was associated with higher risk of AD. Dose-response relationship with number and severity of injuries was observed. Associations were stronger in those with earlier onset of AD.

CONCLUSIONS

Stronger associations with shorter lag times indicate that head and/or brain injuries may also reflect the ongoing AD disease process.

Effects of traumatic brain injury and posttraumatic stress disorder on development of Alzheimer's disease in Vietnam Veterans using the Alzheimer's Disease Neuroimaging Initiative: Preliminary Report

INTRODUCTION

Traumatic brain injury (TBI) and posttraumatic stress disorder (PTSD) have previously been reported to be associated with increased risk of Alzheimer's disease (AD). We are using biomarkers to study Vietnam Veterans with/without mild cognitive impairment with a history of at least one TBI and/or ongoing PTSD to determine whether these contribute to the development of AD.

METHODS

Potential subjects identified by Veterans Administration records underwent an initial telephone screen. Consented subjects underwent clinical evaluation, lumbar puncture, structural MRI and amyloid PET scans.

RESULTS

We observed worse cognitive functioning in PTSD and TBI + PTSD groups, worse global cognitive functioning in the PTSD group, lower superior parietal volume in the TBI + PTSD group, and lower amyloid positivity in the PTSD group, but not the TBI group compared to controls without TBI/PTSD. Medial temporal lobe atrophy was not increased in the PTSD and/or TBI groups.

DISCUSSION

Preliminary results do not indicate that TBI or PTSD increase the risk for AD measured by amyloid PET. Additional recruitment, longitudinal follow-up, and tau PET scans will provide more information in the future.

Head Injury as a Risk Factor for Dementia and Alzheimer's Disease: A Systematic Review and Meta-Analysis of 32 Observational Studies

BACKGROUND

Head injury is reported to be associated with increased risks of dementia and Alzheimer's disease (AD) in many but not all the epidemiological studies. We conducted a systematic review and meta-analysis to estimate the relative effect of head injury on dementia and AD risks.

METHODS

Relevant cohort and case-control studies published between Jan 1, 1990, and Mar 31, 2015 were searched in PubMed, Web of Science, Scopus, and ScienceDirect. We used the random-effect model in this meta-analysis to take into account heterogeneity among studies.

RESULTS

Data from 32 studies, representing 2,013,197 individuals, 13,866 dementia events and 8,166 AD events, were included in the analysis. Overall, the pooled relative risk (RR) estimates showed that head injury significantly increased the risks of any dementia (RR = 1.63, 95% CI 1.34-1.99) and AD (RR = 1.51, 95% CI 1.26-1.80), with no evidence of publication bias. However, when considering the status of unconsciousness, head injury with loss of consciousness did not show significant association with dementia (RR = 0.92, 95% CI 0.67-1.27) and AD (RR = 1.49, 95% CI 0.91-2.43). Additionally, this positive association did not reach statistical significance in female participants.

CONCLUSIONS

The findings from this meta-analysis indicate that head injury is associated with increased risks of dementia and AD.

Self-Reported Traumatic Brain Injury and Mild Cognitive Impairment: Increased Risk and Earlier Age of Diagnosis

This study examined whether history of traumatic brain injury (TBI) is associated with increased risk and earlier onset of mild cognitive impairment (MCI). Subjects with MCI (n = 3,187) and normal cognition (n = 3,244) were obtained from the National Alzheimer's Coordinating Center database. TBI was categorized based on lifetime reported TBI with loss of consciousness (LOC) without chronic deficit. Logistic regression was used to examine TBI history as a predictor of MCI, adjusted for demographics, apolipoprotein E-ɛ4 (ApoE4), a composite vascular risk score, and history of psychiatric factors. ANCOVA was used to examine whether age at MCI diagnosis and estimated age of onset differed between those with (TBI+) and without (TBI-) a history of TBI. TBI history was a significant predictor (p <  0.01) and associated with increased odds of MCI diagnosis in unadjusted (OR = 1.25; 95% CI = 1.05-1.49) and adjusted models, accounting for age, education, ApoE4, and a composite vascular score (OR = 1.32; 95% CI = 1.10-1.58). This association, however, was largely attenuated (OR = 1.14; 95% CI = 0.94-1.37; p = 0.18) after adjustment for reported history of depression. MCI was diagnosed a mean of 2.3 years earlier (p <  0.001) in the TBI+ group, and although TBI+ subjects had an estimated mean of decline 1.7 years earlier, clinician-estimated age of onset failed to differ (p = 0.13) when gender and psychiatric factors were controlled. This is the first report of a possible role for TBI as a risk factor in MCI, but its association may be related to other factors such as gender and depression and requires further investigation.

Traumatic brain injury history is associated with earlier age of onset of Alzheimer disease

OBJECTIVE

This study examined whether a history of traumatic brain injury (TBI) is associated with earlier onset of Alzheimer disease (AD), independent of apolipoprotein ε4 status (Apoe4) and gender.

METHOD

Participants with a clinical diagnosis of AD (n = 7625) were obtained from the National Alzheimer's Coordinating Center Uniform Data Set, and categorized based on self-reported lifetime TBI with loss of consciousness (LOC) (TBI+ vs. TBI-) and presence of Apoe4. ANCOVAs, controlling for gender, race, and education were used to examine the association between history of TBI, presence of Apoe4, and an interaction of both risk factors on estimated age of AD onset.

RESULTS

Estimated AD onset differed by TBI history and Apoe4 independently (p's < .001). The TBI+ group had a mean age of onset 2.5 years earlier than the TBI- group. Likewise, Apoe4 carriers had a mean age of onset 2.3 years earlier than non-carriers. While the interaction was non-significant (p = .34), participants having both a history of TBI and Apoe4 had the earliest mean age of onset compared to those with a TBI history or Apoe4 alone (M_Difference = 2.8 and 2.7 years, respectively). These results remained unchanged when stratified by gender.

CONCLUSIONS

History of self-reported TBI can be associated with an earlier onset of AD-related cognitive decline, regardless of Apoe4 status and gender. TBI may be related to an underlying neurodegenerative process in AD, but the implications of age at time of injury, severity, and repetitive injuries remain unclear.

Pumping the Brakes: Neurotrophic Factors for the Prevention of Cognitive Impairment and Dementia after Traumatic Brain Injury

Traumatic brain injury (TBI) is the leading cause of disability and death worldwide, affecting as many as 54,000,000-60,000,000 people annually. TBI is associated with significant impairments in brain function, impacting cognitive, emotional, behavioral, and physical functioning. Although much previous research has focused on the impairment immediately following injury, TBI may have much longer-lasting consequences, including neuropsychiatric disorders and cognitive impairment. TBI, even mild brain injury, has also been recognized as a significant risk factor for the later development of dementia and Alzheimer's disease. Although the link between TBI and dementia is currently unknown, several proposed mechanisms have been put forward, including alterations in glucose metabolism, excitotoxicity, calcium influx, mitochondrial dysfunction, oxidative stress, and neuroinflammation. A treatment for the devastating long-term consequences of TBI is desperately needed. Unfortunately, however, no such treatment is currently available, making this a major area of unmet medical need. Increasing the level of neurotrophic factor expression in key brain areas may be one potential therapeutic strategy. Of the neurotrophic factors, granulocyte-colony stimulating factor (G-CSF) may be particularly effective for preventing the emergence of long-term complications of TBI, including dementia, because of its ability to reduce apoptosis, stimulate neurogenesis, and increase neuroplasticity.

Traumatic brain injury history is associated with earlier age of onset of frontotemporal dementia

OBJECTIVE

We retrospectively examined whether a history of traumatic brain injury (TBI) is associated with an earlier age of symptom onset and diagnosis in a large sample of patients with behavioural variant frontotemporal dementia (bvFTD).

METHODS

Data on patients with bvFTD (n=678) were obtained from the National Alzheimer's Coordinating Center Uniform Data Set. TBI was categorised based on reported lifetime history of TBI with loss of consciousness (LOC) but no chronic deficits occurring more than 1 year prior to diagnosis of bvFTD. Analysis of covariance (ANCOVA) was used to determine if clinician-estimated age of symptom onset and age at diagnosis of bvFTD differed between those who reported a history of TBI with LOC (TBI+) and those who did not (TBI-).

RESULTS

Controlling for sex, the TBI+ bvFTD group had an age of symptom onset and age of diagnosis that was on average 2.8 and 3.2 years earlier (p<0.01) than the TBI- bvFTD group.

CONCLUSIONS

TBI history with LOC occurring more than 1 year prior to diagnosis is associated with an earlier age of symptom onset and diagnosis in patients with bvFTD. TBI may be related to the underlying neurodegenerative processes in bvFTD, but the implications of age at time of injury, severity and repetitive injuries remain unclear.

Toward precision medicine in Alzheimer's disease

In Western societies, Alzheimer's disease (AD) is the most common form of dementia and the sixth leading cause of death. In recent years, the concept of precision medicine, an approach for disease prevention and treatment that is personalized to an individual's specific pattern of genetic variability, environment and lifestyle factors, has emerged. While for some diseases, in particular select cancers and a few monogenetic disorders such as cystic fibrosis, significant advances in precision medicine have been made over the past years, for most other diseases precision medicine is only in its beginning. To advance the application of precision medicine to a wider spectrum of disorders, governments around the world are starting to launch Precision Medicine Initiatives, major efforts to generate the extensive scientific knowledge needed to integrate the model of precision medicine into every day clinical practice. In this article we summarize the state of precision medicine in AD, review major obstacles in its development, and discuss its benefits in this highly prevalent, clinically and pathologically complex disease.

The Neuroprotective Properties of the Amyloid Precursor Protein Following Traumatic Brain Injury

Despite the significant health and economic burden that traumatic brain injury (TBI) places on society, the development of successful therapeutic agents have to date not translated into efficacious therapies in human clinical trials. Injury to the brain is ongoing after TBI, through a complex cascade of primary and secondary injury events, providing a valuable window of opportunity to help limit and prevent some of the severe consequences with a timely treatment. Of note, it has been suggested that novel treatments for TBI should be multifactorial in nature, mimicking the body's own endogenous repair response. Whilst research has historically focused on the role of the amyloid precursor protein (APP) in the pathogenesis of Alzheimer's disease, recent advances in trauma research have demonstrated that APP offers considerable neuroprotective properties following TBI, suggesting that APP is an ideal therapeutic candidate. Its acute upregulation following TBI has been shown to serve a beneficial role following trauma and has lead to significant advances in understanding the neuroprotective and neurotrophic functions of APP and its metabolites. Research has focused predominantly on the APP derivative sAPPα, which has consistently demonstrated neuroprotective and neurotrophic functions both in vitro and in vivo following various traumatic insults. Its neuroprotective activity has been narrowed down to a 15 amino acid sequence, and this region is linked to both heparan binding and growth-factor-like properties. It has been proposed that APP binds to heparan sulfate proteoglycans to exert its neuroprotective action. APP presents us with a novel therapeutic compound that could overcome many of the challenges that have stalled development of efficacious TBI treatments previously.

Association of traumatic brain injury with subsequent neurological and psychiatric disease: a meta-analysis

OBJECTIVE

Mild traumatic brain injury (TBI) has been proposed as a risk factor for the development of Alzheimer's disease, Parkinson's disease, depression, and other illnesses. This study's objective was to determine the association of prior mild TBI with the subsequent diagnosis (that is, at least 1 year postinjury) of neurological or psychiatric disease.

METHODS

All studies from January 1995 to February 2012 reporting TBI as a risk factor for diagnoses of interest were identified by searching PubMed, study references, and review articles. Reviewers abstracted the data and assessed study designs and characteristics.

RESULTS

Fifty-seven studies met the inclusion criteria. A random effects meta-analysis revealed a significant association of prior TBI with subsequent neurological and psychiatric diagnoses. The pooled odds ratio (OR) for the development of any illness subsequent to prior TBI was 1.67 (95% CI 1.44-1.93, p < 0.0001). Prior TBI was independently associated with both neurological (OR 1.55, 95% CI 1.31-1.83, p < 0.0001) and psychiatric (OR 2.00, 95% CI 1.50-2.66, p < 0.0001) outcomes. Analyses of individual diagnoses revealed higher odds of Alzheimer's disease, Parkinson's disease, mild cognitive impairment, depression, mixed affective disorders, and bipolar disorder in individuals with previous TBI as compared to those without TBI. This association was present when examining only studies of mild TBI and when considering the influence of study design and characteristics. Analysis of a subset of studies demonstrated no evidence that multiple TBIs were associated with higher odds of disease than a single TBI.

CONCLUSIONS

History of TBI, including mild TBI, is associated with the development of neurological and psychiatric illness. This finding indicates that either TBI is a risk factor for heterogeneous pathological processes or that TBI may contribute to a common pathological mechanism.

Polypathology and dementia after brain trauma: Does brain injury trigger distinct neurodegenerative diseases, or should they be classified together as traumatic encephalopathy?

Neuropathological studies of human traumatic brain injury (TBI) cases have described amyloid plaques acutely after a single severe TBI, and tau pathology after repeat mild TBI (mTBI). This has helped drive the hypothesis that a single moderate to severe TBI increases the risk of developing late-onset Alzheimer's disease (AD), while repeat mTBI increases the risk of developing chronic traumatic encephalopathy (CTE). In this review we critically assess this position-examining epidemiological and case control human studies, neuropathological evidence, and preclinical data. Epidemiological studies emphasize that TBI is associated with the increased risk of developing multiple types of dementia, not just AD-type dementia, and that TBI can also trigger other neurodegenerative conditions such as Parkinson's disease. Further, human post-mortem studies on both single TBI and repeat mTBI can show combinations of amyloid, tau, TDP-43, and Lewy body pathology indicating that the neuropathology of TBI is best described as a 'polypathology'. Preclinical studies confirm that multiple proteins associated with the development of neurodegenerative disease accumulate in the brain after TBI. The chronic sequelae of both single TBI and repeat mTBI share common neuropathological features and clinical symptoms of classically defined neurodegenerative disorders. However, while the spectrum of chronic cognitive and neurobehavioral disorders that occur following repeat mTBI is viewed as the symptoms of CTE, the spectrum of chronic cognitive and neurobehavioral symptoms that occur after a single TBI is considered to represent distinct neurodegenerative diseases such as AD. These data support the suggestion that the multiple manifestations of TBI-induced neurodegenerative disorders be classified together as traumatic encephalopathy or trauma-induced neurodegeneration, regardless of the nature or frequency of the precipitating TBI.

Cognitive changes and dementia risk after traumatic brain injury: implications for aging military personnel

Traumatic brain injury (TBI) is recognized as an important risk factor for the long-term cognitive health of military personnel, particularly in light of growing evidence that TBI increases risk for Alzheimer's disease and other dementias. In this article, we review the neurocognitive and neuropathologic changes after TBI with particular focus on the potential risk for cognitive decline across the life span in military service members. Implications for monitoring and surveillance of cognition in the aging military population are discussed. Additional studies are needed to clarify the factors that increase risk for later life cognitive decline, define the mechanistic link between these factors and dementia, and provide empirically supported interventions to mitigate the impact of TBI on cognition across the life span.

Evidence of cognitive decline in older adults after remote traumatic brain injury: an exploratory study

Separate bodies of literature indicate that a history of a traumatic brain injury (TBI) and natural aging may result in overlapping cognitive profiles, yet little is known about their combined effect. We predicted that a remote TBI would compound normal age-related cognitive decline, particularly affecting executive function. Neuropsychological task performance was compared between a group of older adults who sustained a TBI in their distant past (N = 9) and a group of older adults with no history of head injury (N = 15). While all participants scored in the normal range on the Mini-Mental State Examination, the TBI group scored lower than the non-TBI group. Also, in line with predictions, the TBI group made more errors on measures of executive functioning compared to the non-TBI group (the Trail Making B test and the incongruent condition of the Stroop Test), but performed similarly on all tasks with little executive requirements. Findings from this exploratory study indicate that a past TBI may put older adults at a higher risk for exacerbated age-related cognitive decline compared to older adults with no history of TBI.

Functionally-detected cognitive impairment in high school football players without clinically-diagnosed concussion

Head trauma and concussion in football players have recently received considerable media attention. Postmortem evidence suggests that accrual of damage to the brain may occur with repeated blows to the head, even when the individual blows fail to produce clinical symptoms. There is an urgent need for improved detection and characterization of head trauma to reduce future injury risk and promote development of new therapies. In this study we examined neurological performance and health in the presence of head collision events in high school football players, using longitudinal measures of collision events (the HIT(™) System), neurocognitive testing (ImPACT(™)), and functional magnetic resonance imaging MRI (fMRI). Longitudinal assessment (including baseline) was conducted in 11 young men (ages 15-19 years) participating on the varsity and junior varsity football teams at a single high school. We expected and observed subjects in two previously described categories: (1) no clinically-diagnosed concussion and no changes in neurological behavior, and (2) clinically-diagnosed concussion with changes in neurological behavior. Additionally, we observed players in a previously undiscovered third category, who exhibited no clinically-observed symptoms associated with concussion, but who demonstrated measurable neurocognitive (primarily visual working memory) and neurophysiological (altered activation in the dorsolateral prefrontal cortex [DLPFC]) impairments. This new category was associated with significantly higher numbers of head collision events to the top-front of the head, directly above the DLPFC. The discovery of this new category suggests that more players are suffering neurological injury than are currently being detected using traditional concussion-assessment tools. These individuals are unlikely to undergo clinical evaluation, and thus may continue to participate in football-related activities, even when changes in brain physiology (and potential brain damage) are present, which will increase the risk of future neurological injury.

Alzheimer disease: epidemiology, diagnostic criteria, risk factors and biomarkers

The global prevalence of dementia is as high as 24 million, and has been predicted to quadruple by the year 2050. In the US alone, Alzheimer disease (AD) - the most frequent cause of dementia characterized by a progressive decline in cognitive function in particular the memory domain - causes estimated health-care costs of $ 172 billion per year. Key neuropathological hallmarks of the AD brain are diffuse and neuritic extracellular amyloid plaques - often surrounded by dystrophic neurites - and intracellular neurofibrillary tangles. These pathological changes are frequently accompanied by reactive microgliosis and loss of neurons, white matter and synapses. The etiological mechanisms underlying these neuropathological changes remain unclear, but are probably caused by both environmental and genetic factors. In this review article, we provide an overview of the epidemiology of AD, review the biomarkers that may be used for risk assessment and in diagnosis, and give suggestions for future research.

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.

Mild Traumatic Brain Injury among the Geriatric Population

Mild traumatic brain injury (TBI) is an unfortunately common occurrence in the elderly. With the growing population of older adults in the United States and globally, strategies that reduce the risk of becoming injured need to be developed, and diagnostic tools and treatments that may benefit this group need to be explored. Particular attention needs to be given to polypharmacy, drug interactions, the use of anticoagulants, safety issues in the living environment, elder abuse, and alcohol consumption. Low-mechanism falls should prompt health care providers to consider the possibility of head injury in elderly patients. Early and tailored management of our seniors following a mild TBI can provide them with the best possible quality of life. This review will discuss the current literature on mild TBI in the older adult, address gaps in research, and discuss the implications for future care of the older TBI patient.

Prevalence of dementia and its correlates among participants in the National Early Dementia Detection Program during 2006-2009

OBJECTIVE

To investigate the prevalence of dementia and its correlates among people with poor socioeconomic status, poor social support systems, and poor performance on the Korean version of the Mini-Mental Status Exam (MMSE-KC).

METHODS

We used 2006-2009 data of the National Early Dementia Detection Program (NEDDP) conducted on Jeju Island. This program included all residents >65 years old who were receiving financial assistance. We examined those who performed poorly (standard deviation from the norm of <-1.5) on the MMSE-KC administered as part of the NEDDP, using age-, gender-, and education-adjusted norms for Korean elders. A total of 1708 people were included in this category.

RESULTS

The prevalence of dementia in this group was 20.5%. Multivariate logistic regression analysis revealed that the following factors were statistically significantly associated with dementia: age of 80 or older, no education, nursing home residence, and depression.

CONCLUSION

The prevalence of dementia is very high among those with lower MMSE-KC scores, and significant correlates include older age, no education, living in a nursing home, and depression. Enhancing lifetime education to improve individuals' cognitive reserves by providing intellectually challenging activities, encouraging living at home rather than in a nursing home, and preventing and treating depression in its early phase could reduce the prevalence of dementia in this population.

sAPPα rescues deficits in amyloid precursor protein knockout mice following focal traumatic brain injury

The amyloid precursor protein (APP) is thought to be neuroprotective following traumatic brain injury (TBI), although definitive evidence at moderate to severe levels of injury is lacking. In the current study, we investigated histological and functional outcomes in APP-/- mice compared with APP+/+ mice following a moderate focal injury, and whether administration of sAPPα restored the outcomes in knockout animals back to the wildtype state. Following moderate controlled cortical impact injury, APP-/- mice demonstrated greater impairment in motor and cognitive outcome as determined by the ledged beam and Barnes Maze tests respectively (p < 0.05). This corresponded with the degree of neuronal damage, with APP-/- mice having significantly greater lesion volume (25.0 ± 1.6 vs. 20.3 ± 1.6%, p < 0.01) and hippocampal damage, with less remaining CA neurons (839 ± 245 vs. 1353 ± 142 and 1401 ± 263). This was also associated with an impaired neuroreparative response, with decreased GAP-43 immunoreactivity within the cortex around the lesion edge compared with APP+/+ mice. The deficits observed in the APP-/- mice related to a lack of sAPPα, as treatment with exogenously added sAPPα post-injury improved APP-/- mice histological and functional outcome to the point that they were no longer significantly different to APP+/+ mice (p < 0.05). This study shows that endogenous APP is potentially protective at moderate levels of TBI, and that this neuroprotective activity is related to the presence of sAPPα. Importantly, it indicates that the mechanism of action of exogenously added sAPPα is independent of the presence of endogenous APP.

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.

Epidemiology of Alzheimer disease

The global prevalence of dementia is estimated to be as high as 24 million, and is predicted to double every 20 years through to 2040, leading to a costly burden of disease. Alzheimer disease (AD) is the leading cause of dementia and is characterized by a progressive decline in cognitive function, which typically begins with deterioration in memory. Before death, individuals with this disorder have usually become dependent on caregivers. The neuropathological hallmarks of the AD brain are diffuse and neuritic extracellular amyloid plaques-which are frequently surrounded by dystrophic neurites-and intracellular neurofibrillary tangles. These hallmark pathologies are often accompanied by the presence of reactive microgliosis and the loss of neurons, white matter and synapses. The etiological mechanisms underlying the neuropathological changes in AD remain unclear, but are probably affected by both environmental and genetic factors. Here, we provide an overview of the criteria used in the diagnosis of AD, highlighting how this disease is related to, but distinct from, normal aging. We also summarize current information relating to AD prevalence, incidence and risk factors, and review the biomarkers that may be used for risk assessment and in diagnosis.

Dendritic alterations after dynamic axonal stretch injury in vitro

Traumatic axonal injury (TAI) is the most common and important pathology of traumatic brain injury (TBI). However, little is known about potential indirect effects of TAI on dendrites. In this study, we used a well-established in vitro model of axonal stretch injury to investigate TAI-induced changes in dendrite morphology. Axons bridging two separated rat cortical neuron populations plated on a deformable substrate were used to create a zone of isolated stretch injury to axons. Following injury, we observed the formation of dendritic alterations or beading along the dendrite shaft. Dendritic beading formed within minutes after stretch then subsided over time. Pharmacological experiments revealed a sodium-dependent mechanism, while removing extracellular calcium exacerbated TAI's effect on dendrites. In addition, blocking ionotropic glutamate receptors with the N-methyl-d-aspartate (NMDA) receptor antagonist MK-801 prevented dendritic beading. These results demonstrate that axon mechanical injury directly affects dendrite morphology, highlighting an important bystander effect of TAI. The data also imply that TAI may alter dendrite structure and plasticity in vivo. An understanding of TAI's effect on dendrites is important since proper dendrite function is crucial for normal brain function and recovery after injury.

ReviewGenetics, lifestyle and the roles of amyloid β and oxidative stress in Alzheimer’s disease

This paper reviews a wide range of recent studies that have linked AD-associated biochemical and physiological changes with oxidative stress and damage. Some of these changes include disruptions in metal ion homeostasis, mitochondrial damage, reduced glucose metabolism, decreased intracellular pH and inflammation. Although the changes mentioned above are associated with oxidative stress, in most cases, a cause and effect relationship is not clearcut, as many changes are interlinked. Increases in the levels of Abeta peptides, the main protein components of the cerebral amyloid deposits of AD, have been demonstrated to occur in inherited early-onset forms of AD, and as a result of certain environmental and genetic risk factors. Abeta peptides have been shown to exhibit superoxide dismutase activity, producing hydrogen peroxide which may be responsible for the neurotoxicity exhibited by this peptide in vitro. This review also discusses the biochemical aspects of oxidative stress, antioxidant defence mechanisms, and possible antioxidant therapeutic measures which may be effective in counteracting increased levels of oxidative stress. In conclusion, this review provides support for the theory that damage caused by free radicals and oxidative stress is a primary cause of the neurodegeneration seen in AD with Abeta postulated as an initiator of this process.

The role of mitochondrial transition pore, and its modulation, in traumatic brain injury and delayed neurodegeneration after TBI

Following severe traumatic brain injury (TBI), a complex interplay of pathomechanism, such as exitotoxicity, oxidative stress, inflammatory events, and mitochondrial dysfunction occurs. This leads to a cascade of neuronal and axonal pathologies, which ultimately lead to axonal failure, neuronal energy metabolic failure, and neuronal death, which in turn determine patient outcome. For mild and moderate TBI, the pathomechanism is similar but much less frequent and ischemic cell death is unusual, except with mass lesions. Involvement of mitochondria in acute post-traumatic neurodegeneration has been extensively studied during the last decade, and there are a number of investigations implicating the activation of the mitochondrial permeability transition pore (mPTP) as a "critical switch" which determines cell survival after TBI. Opening of the mPTP is modulated by several factors occurring after a severe brain injury. Modern neuroprotective strategies for prevention of the neuropathological squeal of traumatic brain injury have now begun to address the issue of mitochondrial dysfunction, and drugs that protect mitochondrial viability and prevent apoptotic cascade induced by mPTP opening are about to begin phase II and III clinical trials. Cyclosporin A, which has been reported to block the opening of mPTP, showed a significant decrease in mitochondrial damage and intra-axonal cytoskeletal destruction thereby protecting the axonal shaft and blunting axotomy. This review addresses an important issue of mPT activation after severe head injury, its role in acute post-traumatic neurodegeneration, and the rationale for targeting the mPTP in experimental and clinical TBI studies.

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.

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.