Detection of brain amyloid β deposition in patients with neuropsychological impairment after traumatic brain injury: PET evaluation using Pittsburgh Compound-B

Traumatic Brain Injury and Alzheimer's Disease Biomarkers: A Systematic Review of Findings from Amyloid and Tau Positron Emission Tomography

Traumatic brain injury (TBI) has been discussed as a risk factor for Alzheimer's disease (AD) due to its association with AD risk and earlier cognitive symptom onset. However, the mechanisms behind this relationship are unclear. Some studies have suggested TBI may increase pathological protein deposition in an AD-like pattern; others have failed to find such associations. This review covers literature that uses positron emission tomography (PET) of β-amyloid (Aβ) and/or tau to examine individuals with a history of TBI who are at increased risk for AD due to age. A comprehensive literature search was conducted on January 9, 2023, and 26 resulting citations met inclusion criteria. Common methodological concerns included small samples, limited clinical detail about participants' TBI, recall bias due to reliance on self-reported TBI, and an inability to establish causation. For both Aβ and tau, results were widespread but inconsistent. The regions that showed the most compelling evidence for increased Aβ deposition were the cingulate gyrus and cuneus/precuneus. Evidence for elevated tau was strongest in the medial temporal lobe, entorhinal cortex, precuneus, and frontal, temporal, parietal, and occipital lobes. However, conflicting findings across most regions in both Aβ- and tau-PET studies indicate the critical need for future work in expanded samples and with greater clinical detail to offer a clearer picture of the relationship between TBI and protein deposition in older individuals at risk for AD.

Trajectories of blood-based protein biomarkers in chronic traumatic brain injury

Blood-based protein biomarkers may provide important insights into the long-term neuropathology of traumatic brain injury (TBI). This is urgently required to identify mechanistic processes underlying post-traumatic neurodegeneration (PTND); a progressive post-recovery clinical decline experienced by a portion of TBI survivors. The aim of this study was to examine change over time in protein levels in a chronic TBI cohort. We selected six markers (Aβ 42 /Aβ 40 , GFAP, NfL, BD-tau, p-tau231, and p-tau181) with known importance in acute TBI and/or other neurodegenerative conditions. We used a longitudinal design with two time points approximately 3.5 years apart on average (SD 1.34). Proteins were measured in plasma using the ultrasensitive Single molecule array technology for 63 participants with mild to severe chronic TBI (sustained ≥ 1 year ago; M 28 years; SD 16.3 since their first blow to the head) from the Late Effects of TBI study (48% female; current age M 52 years; SD 13.4). Multivariate linear mixed effect models with adjustments for multiple comparisons were performed to examine trajectories in proteins over time with age and age squared as covariates. A series of sensitivity analyses were conducted to account for outliers and to explore effects of key covariates: sex, APOE ε4 carrier status, medical comorbidities, age at first blow to the head, time since first blow to the head, and injury severity. Over an average of 3.5 years, there were significant reductions in plasma Aβ 42 /Aβ 40 (β = -0.004, SE = 0.001, t = -3.75, q = .001) and significant increases in plasma GFAP (β = 12.96, SE = 4.41, t = 2.94, q = .01). There were no significant changes in NFL, BD-tau, p-tau231, or p-tau181. Both plasma Aβ 42 /Aβ 40 and GFAP have been associated with brain amyloidosis, suggesting a role for Aβ mis-metabolism and aggregation in the long-term neuropathological consequences of TBI. These findings are hypothesis generating for future studies exploring the diverse biological mechanisms of PTND.

CT, MRI, and PET Imaging in Patients with Traumatic Brain Injury

Traumatic brain injury (TBI) is a major health concern in the United States and worldwide. Neuroimaging is a critical element in the clinical evaluation of TBIs, as computed tomography (CT) and MR imaging are commonly used to identify structural changes that may aid in treatment decision-making and long-term patient monitoring. This article reviews the utility of CT and MR imaging while focusing on the emerging applications of PET in TBI. Pertinent research findings in the molecular imaging of cerebral metabolism, tau and β-amyloid, neurotransmitters, and neuroinflammation are discussed.

Cognitive impairment following traumatic brain injury in Uganda: Prevalence and associated factors

BACKGROUND

As the burden of dementia continues to rise in sub-Saharan Africa, it is crucial to develop an evidence base for potentially modifiable risk factors such as Traumatic Brain Injury (TBI). Cognitive impairment may result from TBI and since it is an established prodromal form of dementia, we investigated the burden of cognitive impairment and associated factors in persons with a history of TBI in southwestern Uganda.

METHODS

This was a community-based quantitative study with a cross-sectional design among 189 persons with a history of TBI in southwestern Uganda. Data were collected by the research team in March and June 2022 and entered into Kobo Toolbox before being transferred to RStudio version 4.1.0 for cleaning and analysis. Data were analyzed at a 5% level of significance.

RESULTS

Most study participants had some form of cognitive impairment (56.1%), with 43.1% of the participants having mild cognitive impairment (MCI). Cognitive impairment was associated with older age (p-value<0.001); loss of consciousness following the TBI (p-value = 0.019) and a history of tobacco use (p-value = 0.003). As a measure of severity of the TBI, loss of consciousness (aOR = 4.09; CI = 1.57-11.76; p<0.01) and older age (aOR = 1.04; CI = 1.01-1.07; p<0.01) were identified as risk factors for cognitive impairment.

CONCLUSION

There is a high burden of cognitive impairment among individuals with a history of TBI in southwestern Uganda, and most associated risk factors are potentially modifiable. Long-term follow-up of TBI patients would enable early identification of some risks. Patients with TBI could benefit from behavioural modifications such as restriction of alcohol intake and tobacco use to slow down the progression into dementia.

Co-administration of Nanowired Oxiracetam and Neprilysin with Monoclonal Antibodies to Amyloid Beta Peptide and p-Tau Thwarted Exacerbation of Brain Pathology in Concussive Head Injury at Hot Environment

Environmental temperature adversely affects the outcome of concussive head injury (CHI)-induced brain pathology. Studies from our laboratory showed that animals reared at either cold environment or at hot environment exacerbate brain pathology following CHI. Our previous experiments showed that nanowired delivery of oxiracetam significantly attenuated CHI-induced brain pathology and associated neurovascular changes. Military personnel are the most susceptible to CHI caused by explosion, blasts, missile or blunt head trauma leading to lifetime functional and cognitive impairments affecting the quality of life. Severe CHI leads to instant death and/or lifetime paralysis. Military personnel engaged in combat operations are often subjected to extreme high or low environmental temperature zones across the globe. Thus, further exploration of novel therapeutic agents at cold or hot ambient temperatures following CHI are the need of the hour. CHI is also a major risk factor for developing Alzheimer's disease by enhancing amyloid beta peptide deposits in the brain. In this review, effect of hot environment on CHI-induced brain pathology is discussed. In addition, whether nanodelivery of oxiracetam together with neprilysin and monoclonal antibodies (mAb) to amyloid beta peptide and p-tau could lead to superior neuroprotection in CHI is explored. Our results show that co-administration of oxiracetam with neprilysin and mAb to AβP and p-tau significantly induced superior neuroprotection following CHI in hot environment, not reported earlier.

Posttraumatic Stress and Traumatic Brain Injury: Cognition, Behavior, and Neuroimaging Markers in Vietnam Veterans

BACKGROUND

Posttraumatic stress disorder (PTSD) and traumatic brain injury (TBI) are common in Veterans and linked to behavioral disturbances, increased risk of cognitive decline, and Alzheimer's disease.

OBJECTIVE

We studied the synergistic effects of PTSD and TBI on behavioral, cognitive, and neuroimaging measures in Vietnam war Veterans.

METHODS

Data were acquired at baseline and after about one-year from male Veterans categorized into: PTSD, TBI, PTSD+TBI, and Veteran controls without PTSD or TBI. We applied manual tractography to examine white matter microstructure of three fiber tracts: uncinate fasciculus (N = 91), cingulum (N = 87), and inferior longitudinal fasciculus (N = 95). ANCOVAs were used to compare Veterans' baseline behavioral and cognitive functioning (N = 285), white matter microstructure, amyloid-β (N = 230), and tau PET (N = 120). Additional ANCOVAs examined scores' differences from baseline to follow-up.

RESULTS

Veterans with PTSD and PTSD+TBI, but not Veterans with TBI only, exhibited poorer behavioral and cognitive functioning at baseline than controls. The groups did not differ in baseline white matter, amyloid-β, or tau, nor in behavioral and cognitive functioning, and tau accumulation change. Progression of white matter abnormalities of the uncinate fasciculus in Veterans with PTSD compared to controls was observed; analyses in TBI and PTSD+TBI were not run due to insufficient sample size.

CONCLUSIONS

PTSD and PTSD+TBI negatively affect behavioral and cognitive functioning, while TBI does not contribute independently. Whether progressive decline in uncinate fasciculus microstructure in Veterans with PTSD might account for cognitive decline should be further studied. Findings did not support an association between PTSD, TBI, and Alzheimer's disease pathology based on amyloid and tau PET.

Amyloid- and Tau Imaging in Chronic Traumatic Brain Injury: A Cross-sectional Study

BACKGROUND AND OBJECTIVES

Traumatic brain injury (TBI) has been promoted as a risk factor for Alzheimer's disease. There is evidence of elevated amyloid-β and tau, the pathological hallmarks of Alzheimer's disease, immediately following TBI. It is not clear whether amyloid-β and tau remain elevated in the chronic period. To address this issue, we assessed amyloid-β and tau burden in long-term TBI survivors and healthy controls using PET imaging.

METHODS

Using a cross-sectional design, we recruited individuals following a single moderate to severe TBI at least 10 years previously from an inpatient rehabilitation program. A demographically similar healthy control group was recruited from the community. PET data were acquired using ¹⁸F-NAV4694 (amyloid-β) and ¹⁸F-MK6240 (tau) tracers. Amyloid-β deposition was quantified using the Centiloid scale. Tau deposition was quantified using the standardized uptake value ratio (SUVR) in four regions of interest (ROI). As a secondary measure, PET scans were also visually read as positive or negative. We examined PET data in relation to time since injury and age at injury. PET data were analysed in a series of regression analyses.

RESULTS

The sample comprised 87 individuals with TBI (71.3% male; 28.7% female; M = 57.53 years, SD = 11.53) and 59 controls (59.3% male; 40.7% female; M = 60.34 years, SD = 11.97). Individuals with TBI did not have significantly higher ¹⁸F-NAV4694 Centiloid values (p = 0.067) or ¹⁸F-MK6240 tau SUVRs in any ROI (p = ≤ 0.001; SUVR greater for controls). Visual assessment was consistent with the quantification; individuals with TBI were not more likely than controls to have a positive amyloid-β (p = 0.505) or tau scan (p = 0.221). No associations were identified for amyloid-β or tau burden with time since injury (p = 0.057 to 0.332) or age at injury.

DISCUSSION

A single moderate to severe TBI was not associated with higher burden of amyloid-β or tau pathologies in the chronic period relative to healthy controls. Amyloid-β and tau burden did not show a significant increase with years since injury, and burden did not appear to be greater for those who were older at the time of injury.

Chaperone-Mediated Autophagy in Neurodegenerative Diseases and Acute Neurological Insults in the Central Nervous System

Autophagy is an important function that mediates the degradation of intracellular proteins and organelles. Chaperone-mediated autophagy (CMA) degrades selected proteins and has a crucial role in cellular proteostasis under various physiological and pathological conditions. CMA dysfunction leads to the accumulation of toxic protein aggregates in the central nervous system (CNS) and is involved in the pathogenic process of neurodegenerative diseases, including Parkinson’s disease and Alzheimer’s disease. Previous studies have suggested that the activation of CMA to degrade aberrant proteins can provide a neuroprotective effect in the CNS. Recent studies have shown that CMA activity is upregulated in damaged neural tissue following acute neurological insults, such as cerebral infarction, traumatic brain injury, and spinal cord injury. It has been also suggested that various protein degradation mechanisms are important for removing toxic aberrant proteins associated with secondary damage after acute neurological insults in the CNS. Therefore, enhancing the CMA pathway may induce neuroprotective effects not only in neurogenerative diseases but also in acute neurological insults. We herein review current knowledge concerning the biological mechanisms involved in CMA and highlight the role of CMA in neurodegenerative diseases and acute neurological insults. We also discuss the possibility of developing CMA-targeted therapeutic strategies for effective treatments.

Positron emission tomography imaging for the assessment of mild traumatic brain injury and chronic traumatic encephalopathy: recent advances in radiotracers

A chronic phase following repetitive mild traumatic brain injury can present as chronic traumatic encephalopathy in some cases, which requires a neuropathological examination to make a definitive diagnosis. Positron emission tomography (PET) is a molecular imaging modality that has high sensitivity for detecting even very small molecular changes, and can be used to quantitatively measure a range of molecular biological processes in the brain using different radioactive tracers. Functional changes have also been reported in patients with different forms of traumatic brain injury, especially mild traumatic brain injury and subsequent chronic traumatic encephalopathy. Thus, PET provides a novel approach for the further evaluation of mild traumatic brain injury at molecular levels. In this review, we discuss the recent advances in PET imaging with different radiotracers, including radioligands for PET imaging of glucose metabolism, tau, amyloid-beta, γ-aminobutyric acid type A receptors, and neuroinflammation, in the identification of altered neurological function. These novel radiolabeled ligands are likely to have widespread clinical application, and may be helpful for the treatment of mild traumatic brain injury. Moreover, PET functional imaging with different ligands can be used in the future to perform large-scale and sequential studies exploring the time-dependent changes that occur in mild traumatic brain injury.

Association of remote mild traumatic brain injury with cortical amyloid burden in clinically normal older adults

We investigated whether clinically normal older adults with remote, mild traumatic brain injury (mTBI) show evidence of higher cortical Aβ burden. Our study included 134 clinically normal older adults (age 74.1 ± 6.8 years, 59.7% female, 85.8% white) who underwent Aβ positron emission tomography (Aβ-PET) and who completed the Ohio State University Traumatic Brain Injury Identification questionnaire. We limited participants to those reporting injuries classified as mTBI. A subset (N = 30) underwent a second Aβ-PET scan (mean 2.7 years later). We examined the effect of remote mTBI on Aβ-PET burden, interactions between remote mTBI and age, sex, and APOE status, longitudinal Aβ accumulation, and the interaction between remote mTBI and Aβ burden on memory and executive functioning. Of 134 participants, 48 (36%) reported remote mTBI (0, N = 86; 1, N = 31, 2+, N = 17; mean 37 ± 23 years since last mTBI). Effect size estimates were small to negligible for the association of remote mTBI with Aβ burden (p = .94, η2 < 0.01), and for all interaction analyses. Longitudinally, we found a non-statistically significant association of those with remote mTBI (N = 11) having a faster rate of Aβ accumulation (B = 0.01, p = .08) than those without (N = 19). There was no significant interaction between remote mTBI and Aβ burden on cognition. In clinically normal older adults, history of mTBI is not associated with greater cortical Aβ burden and does not interact with Aβ burden to impact cognition. Longitudinal analyses suggest remote mTBI may be associated with more rapid cortical Aβ accumulation. This finding warrants further study in larger and more diverse samples with well-characterized lifelong head trauma exposure.

Is Cerebral Amyloid-β Deposition Related to Post-stroke Cognitive Impairment?

Approximately two-thirds of ischemic stroke patients suffer from different levels of post-stroke cognitive impairment (PSCI), but the underlying mechanisms of PSCI remain unclear. Cerebral amyloid-β (Aβ) deposition, a pathological hallmark of Alzheimer's disease, has been discovered in the brains of stroke patients in some autopsy studies. However, less is known about the role of Aβ pathology in the development of PSCI. It is hypothesized that cerebral ischemic injury may lead to neurotoxic Aβ accumulation in the brain, which further induces secondary neurodegeneration and progressive cognitive decline after stroke onset. In this review, we summarized available evidence from pre-clinical and clinical studies relevant to the aforementioned hypothesis. We found inconsistency in the results obtained from studies in rodents, nonhuman primates, and stroke patients. Moreover, the causal relationship between post-stroke cerebral Aβ deposition and PSCI has been uncertain and controversial. Taken together, evidence supporting the hypothesis that brain ischemia induces cerebral Aβ deposition has been insufficient so far. And, there is still no consensus regarding the contribution of cerebral amyloid pathology to PSCI. Other non-amyloid neurodegenerative mechanisms might be involved and remain to be fully elucidated.

Quantitative multimodal imaging in traumatic brain injuries producing impaired cognition

PURPOSE OF REVIEW

Cognitive impairments are a devastating long-term consequence following traumatic brain injury (TBI). This review provides an update on the quantitative mutimodal neuroimaging studies that attempt to elucidate the mechanism(s) underlying cognitive impairments and their recovery following TBI.

RECENT FINDINGS

Recent studies have linked individual specific behavioural impairments and their changes over time to physiological activity and structural changes using EEG, PET and MRI. Multimodal studies that combine measures of physiological activity with knowledge of neuroanatomical and connectivity damage have also illuminated the multifactorial function-structure relationships that underlie impairment and recovery following TBI.

SUMMARY

The combined use of multiple neuroimaging modalities, with focus on individual longitudinal studies, has the potential to accurately classify impairments, enhance sensitivity of prognoses, inform targets for interventions and precisely track spontaneous and intervention-driven recovery.

Does cognitive decline occur decades after moderate to severe traumatic brain injury? A prospective controlled study

This prospective controlled study examined long-term trajectories of neuropsychological performance in individuals with traumatic brain injury (TBI) compared to healthy controls, and the impact of IQ, age at injury, time since injury, and injury severity on change over time. Fifty-three individuals with moderate to severe TBI (60.37% male; M = 59.77 yrs, SD = 14.03), and 26 controls (46.15% male; M = 63.96 yrs, SD = 14.42) were studied prospectively (M = 12.72 yrs between assessments). Participants completed measures of premorbid IQ (Weschler Test of Adult Reading), processing speed (Digit Symbol Coding Test), working memory (Digit Span Backwards), memory (Rey Auditory Verbal Learning Test) and executive function (Trail Making Test Part B; Hayling Errors), at a mean of 10.62 yrs (Initial) and 23.91 yrs (Follow-Up) post injury. Individuals with TBI did not show a significantly greater decline in neuropsychological performance over time compared with demographically similar controls. There was no association between change over time with IQ, time since injury or injury severity. Being older at injury had a greater adverse impact on executive function at follow-up. In this small sample, a single moderate to severe TBI was not associated with ongoing cognitive decline up to three decades post injury. Changes in cognitive function were similar between the groups and likely reflect healthy aging.

Spatial Patterns of Amyloid Deposition in Patients with Chronic Focal or Diffuse Traumatic Brain Injury Using 18F-FPYBF-2 PET

AIM

Amyloid-β (Aβ) accumulation, accelerated by traumatic brain injury (TBI), may play a crucial role in neurodegeneration in chronic-stage TBI. The injury type could influence Aβ dynamics because of TBI's complex, heterogeneous nature. We, therefore, investigated spatial patterns of amyloid deposition according to injury type after TBI using 5-(5-(2-(2-(2-[F]-fluoroethoxy)ethoxy)ethoxy)benzofuran-2-yl)-N-methylpyridin-2-amine (¹⁸F-FPYBF-2) positron emission tomography (PET).

METHODS

Altogether, 20 patients with chronic TBI [12 with focal injury, 8 with diffuse axonal injury (DAI)] underwent ¹⁸F-FPYBF-2 PET, structural magnetic resonance imaging (MRI), and neuropsychological examination. Additionally, 50 healthy controls underwent either ¹⁸F-FPYBF-2 PET (n=30) or structural MRI (n=20).

RESULTS

Standardized uptake value ratio (SUVR) on PET images and regional brain volumes were measured in four cortical (frontal, parietal, occipital, temporal) and subcortical (combined caudate, putamen, pallidum, thalamus) regions. Patients with DAI showed significantly increased (compared with controls) SUVR in occipital and temporal cortices and decreased brain volume in occipital cortex (corrected p < 0.05). Although patients with focal injury showed decreased SUVR in all regions except occipital cortex, there were no significant differences (compared with controls) in the SUVR in any regions. There were no significant correlations between increased SUVR and neuropsychological impairments in patients with DAI.

CONCLUSION

Varying spatial patterns of amyloid deposition suggest amyloid pathology diversity depending on the injury type in chronic-TBI patients.

Association of Head Injury with Brain Amyloid Deposition: The ARIC-PET Study

Our objective was to examine associations of head injury with total and regional brain amyloid deposition. We performed cross-sectional analyses of 329 non-demented participants (81 with prior head injury) in the Atherosclerosis Risk in Communities-Positron Emission Tomography (ARIC-PET) Study who underwent 18-florbetapir PET imaging in 2012-2014. A history of head injury was defined by self-report or emergency department/hospitalization International Classification of Diseases, Ninth Revision codes. Generalized linear regression models adjusted for demographic, socioeconomic, and dementia/cardiovascular risk factors were used to estimate prevalence ratios (PRs; 95% confidence intervals [CIs]) for elevated (> 1.2) global and regional standard uptake value ratios (SUVRs). Mean age of participants was 76 years, 57% were women, and 43% were black. Head injury was associated with increased prevalence of elevated SUVR >1.2 globally (PR: 1.31; 95% CI: 1.19-1.57), as well as in the orbitofrontal cortex (PR: 1.23); (95% CI: 1.04-1.46), prefrontal cortex (PR: 1.18; 95% CI: 1.00-1.39), superior frontal cortex (PR: 1.24; 95% CI: 1.05-1.48), and posterior cingulate (PR: 1.26; 95% CI: 1.04-1.52). There also was evidence for a dose-response relationship, whereby a history of ≥1 head injury was associated with elevated SUVR >1.2 in the prefrontal cortex and superior frontal cortex compared with persons with a history of one head injury (all, p < 0.05). In conclusion, head injury was associated with increased amyloid deposition globally and in the frontal cortex and posterior cingulate, with suggestion of a dose-response association of head injuries with beta-amyloid deposition. Further work is needed to determine if increased amyloid deposition contributes to dementia in this population.

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.

Detection of brain amyloid-β deposits due to the repetitive head trauma in a former karate player

Head trauma is a well-established epidemiological risk factor for Alzheimer's disease, but a study of early detection of its pathology has not yet been performed in human patients in vivo. To address this issue, we performed ¹¹ C-labelled Pittsburgh compound B-positron emission tomography on a right-handed 30-year-old man with cognitive deterioration after repetitive head trauma during karate matches. Structural magnetic resonance imaging was also performed on this patient. The same positron emission tomography analysis was performed on elderly healthy controls (15 men, mean age: 70.7 ± 6.2 years). To analyze grey matter volume, structural magnetic resonance imaging was performed on age-matched healthy controls (15 men, mean age: 28.5 ± 3.6 years). The cognitive deterioration in our patient was fixed and partially improved in the 10 years after the repetitive head trauma. However, Pittsburgh compound B-non-displaceable binding potential was significantly elevated in the patient. Volume reduction was shown in the medial temporal region, cerebellum, and the basal frontal cortex, while amyloid-β increase was shown in the bilateral prefrontal cortex. This is the first study to show an early degenerative process due to head trauma in the prefrontal cortex, where structural damage is not yet visible. Early recognition of the degenerative pathology due to repetitive head trauma by amyloid and possibly tau imaging would help clinicians determine how to treat those with early symptoms.

Traumatic Brain Injury by Weight-Drop Method Causes Transient Amyloid-β Deposition and Acute Cognitive Deficits in Mice

There has been growing awareness of the correlation between an episode of traumatic brain injury (TBI) and the development of Alzheimer's disease (AD) later in life. It has been reported that TBI accelerated amyloid-β (Aβ) pathology and cognitive decline in the several lines of AD model mice. However, the short-term and long-term effects of TBI by the weight-drop method on amyloid-β pathology and cognitive performance are unclear in wild-type (WT) mice. Hence, we examined AD-related histopathological changes and cognitive impairment after TBI in wild-type C57BL6J mice. Five- to seven-month-old WT mice were subjected to either TBI by the weight-drop method or a sham treatment. Seven days after TBI, the WT mice exhibited significantly lower spatial learning than the sham-treated WT mice. However, 28 days after TBI, the cognitive impairment in the TBI-treated WT mice recovered. Correspondingly, while significant amyloid-β (Aβ) plaques and amyloid precursor protein (APP) accumulation were observed in the TBI-treated mouse hippocampus 7 days after TBI, the Aβ deposition was no longer apparent 28 days after TBI. Thus, TBI induced transient amyloid-β deposition and acute cognitive impairments in the WT mice. The present study suggests that the TBI could be a risk factor for acute cognitive impairment even when genetic and hereditary predispositions are not involved. The system might be useful for evaluating and developing a pharmacological treatment for the acute cognitive deficits.

Association of late effects of single, severe traumatic brain injury with Alzheimer's disease using amyloid PET

Traumatic brain injury (TBI) is suggested to be a risk factor for the onset of Alzheimer's disease (AD); however, the data remain controversial. This is the first report on cognitive decline in patients with TBI over 30 years post-injury. The medical significance/key learning points of this report are that (1) Functional Independence Measure (FIM) is useful in clinical settings, such as for higher brain dysfunction and dementia; (2) amyloid PET findings represent an essential biomarker for follow-up after TBI; and (3) cognitive decline can occur in patients with TBI more than 30 years post-injury.

Military Blast Injury and Chronic Neurodegeneration: Research Presentations from the 2015 International State-of-the-Science Meeting

Blast-related traumatic brain injury (TBI) is a signature injury of recent military conflicts, leading to increased Department of Defense (DoD) interest in its potential long-term effects, such as chronic traumatic encephalopathy (CTE). The DoD Blast Injury Research Program Coordinating Office convened the 2015 International State-of-the-Science Meeting to discuss the existing evidence regarding a causal relationship between TBI and CTE. Over the course of the meeting, experts across government, academia, and the sports community presented cutting edge research on the unique pathological characteristics of blast-related TBI, blast-related neurodegenerative mechanisms, risk factors for CTE, potential biomarkers for CTE, and treatment strategies for chronic neurodegeneration. The current paper summarizes these presentations. Although many advances have been made to address these topics, more research is needed to establish the existence of links between the long-term effects of single or multiple blast-related TBI and CTE.

The aggressiveness of neurotrauma practitioners and the influence of the IMPACT prognostic calculator

Published guidelines have helped to standardize the care of patients with traumatic brain injury; however, there remains substantial variation in the decision to pursue or withhold aggressive care. The International Mission for Prognosis and Analysis of Clinical Trials in TBI (IMPACT) prognostic calculator offers the opportunity to study and decrease variability in physician aggressiveness. The authors wish to understand how IMPACT’s prognostic calculations currently influence patient care and to better understand physician aggressiveness. The authors conducted an anonymous international, multidisciplinary survey of practitioners who provide care to patients with traumatic brain injury. Questions were designed to determine current use rates of the IMPACT prognostic calculator and thresholds of age and risk for death or poor outcome that might cause practitioners to consider withholding aggressive care. Correlations between physician aggressiveness, putative predictors of aggressiveness, and demographics were examined. One hundred fifty-four responses were received, half of which were from physicians who were familiar with the IMPACT calculator. The most frequent use of the calculator was to improve communication with patients and their families. On average, respondents indicated that in patients older than 76 years or those with a >85% chance of death or poor outcome it might be reasonable to pursue non-aggressive care. These thresholds were robust and were not influenced by provider or institutional characteristics. This study demonstrates the need to educate physicians about the IMPACT prognostic calculator. The consensus values for age and prognosis identified in our study may be explored in future studies aimed at reducing variability in physician aggressiveness and should not serve as a basis for withdrawing care.

Self-reported traumatic brain injury and in vivo measure of AD-vulnerable cortical thickness and AD-related biomarkers in the ADNI cohort

In this study, we aimed to investigate whether self-reported mild traumatic brain injury (mTBI) was associated with decreased AD-vulnerable cortical thickness, and to assess the relationship between AD-vulnerable cortical thickness and AD-related biomarker in the Alzheimer's Disease Neuroimaging Initiative subjects. We identified 45 self-reported mTBI subjects, who had structural MRI, 18F-AV45 PET, and cerebrospinal fluid (CSF) data. Of them, eight subjects were normal; ten were preclinical AD; seventeen were MCI due to AD; ten were AD. Additional demographics-controlled 45 subjects were included. Cortical thickness of eight AD-vulnerable regions, mean AD-vulnerable cortical thickness, 18F-AV45 PET mean amyloid SUVR, CSF Aβ42, CSF total tau (T-tau), and CSF phosphorylated tau (P-tau) were compared between mTBI and non-TBI groups. Correlational analysis was done to investigate the relationship between mean AD-vulnerable cortical thickness and mean amyloid SUVR, CSF Aβ42, CSF T-Tau, CSF P-Tau. Our study revealed that preclinical AD subjects with self-reported mTBI had smaller cortical thickness in mean and three AD-vulnerable cortical regions than non-TBI subjects (P<0.05). The mean AD-vulnerable cortical thickness was correlated with CSF T-tau (r=-0.81, P=0.001). There was no statistical difference in the comparison of normal, MCI due to AD, and AD groups. Our study indicated that among individuals with preclinical AD, but not normal, MCI due to AD and AD subjects, self-reported mTBI was associated with more decreased AD-vulnerable cortical thickness which was related to CSF tau pathology, suggesting the possible early involvement of tau pathology in the decreased AD-vulnerable cortical thickness of self-reported TBI subjects.

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

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

Advanced neuroimaging applied to veterans and service personnel with traumatic brain injury: state of the art and potential benefits

Traumatic brain injury (TBI) remains one of the most prevalent forms of morbidity among Veterans and Service Members, particularly for those engaged in the conflicts in Iraq and Afghanistan. Neuroimaging has been considered a potentially useful diagnostic and prognostic tool across the spectrum of TBI generally, but may have particular importance in military populations where the diagnosis of mild TBI is particularly challenging, given the frequent lack of documentation on the nature of the injuries and mixed etiologies, and highly comorbid with other disorders such as post-traumatic stress disorder, depression, and substance misuse. Imaging has also been employed in attempts to understand better the potential late effects of trauma and to evaluate the effects of promising therapeutic interventions. This review surveys the use of structural and functional neuroimaging techniques utilized in military studies published to date, including the utilization of quantitative fluid attenuated inversion recovery (FLAIR), susceptibility weighted imaging (SWI), volumetric analysis, diffusion tensor imaging (DTI), magnetization transfer imaging (MTI), positron emission tomography (PET), magnetoencephalography (MEG), task-based and resting state functional MRI (fMRI), arterial spin labeling (ASL), and magnetic resonance spectroscopy (MRS). The importance of quality assurance testing in current and future research is also highlighted. Current challenges and limitations of each technique are outlined, and future directions are discussed.

Update on fluid biomarkers for concussion

Concussions are difficult to diagnose and symptoms may not appear immediately. As an accurate initial diagnosis has profound implications for the clinical management, there is an unmet need for better diagnostic tools. Fluid biomarkers for CNS injury may represent such tools. These markers are often proteins, peptides or other molecules with selective or high expression in the brain, which can be measured in the cerebrospinal fluid or blood as they leak out or get secreted into the biofluid in response to the injury. Here, we review the literature on fluid markers of neuronal, axonal and astroglial injury and response mechanisms to diagnose CNS injury upon head impact and to determine when the injurious process has resolved.

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

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

A Review of the Effectiveness of Neuroimaging Modalities for the Detection of Traumatic Brain Injury

The incidence of traumatic brain injury (TBI) in the United States was 3.5 million cases in 2009, according to the Centers for Disease Control and Prevention. It is a contributing factor in 30.5% of injury-related deaths among civilians. Additionally, since 2000, more than 260,000 service members were diagnosed with TBI, with the vast majority classified as mild or concussive (76%). The objective assessment of TBI via imaging is a critical research gap, both in the military and civilian communities. In 2011, the Department of Defense (DoD) prepared a congressional report summarizing the effectiveness of seven neuroimaging modalities (computed tomography [CT], magnetic resonance imaging [MRI], transcranial Doppler [TCD], positron emission tomography, single photon emission computed tomography, electrophysiologic techniques [magnetoencephalography and electroencephalography], and functional near-infrared spectroscopy) to assess the spectrum of TBI from concussion to coma. For this report, neuroimaging experts identified the most relevant peer-reviewed publications and assessed the quality of the literature for each of these imaging technique in the clinical and research settings. Although CT, MRI, and TCD were determined to be the most useful modalities in the clinical setting, no single imaging modality proved sufficient for all patients due to the heterogeneity of TBI. All imaging modalities reviewed demonstrated the potential to emerge as part of future clinical care. This paper describes and updates the results of the DoD report and also expands on the use of angiography in patients with TBI.

Chaperone-Mediated Autophagy after Traumatic Brain Injury

Chaperone-mediated autophagy (CMA) and the ubiquitin-proteasomal system (UPS) are two major protein degradation systems responsible for maintaining cellular homeostasis, but how these two systems are regulated after traumatic brain injury (TBI) remains unknown. TBI produces primary mechanical damage that must be repaired to maintain neuronal homeostasis. The level of lysosomal-associated membrane protein type 2A (LAMP2A) is the hallmark of CMA activity. The level of polyubiquitinated proteins (ubi-proteins) reflects UPS activity. This study utilized a moderate fluid percussion injury model in rats to investigate the changes in CMA and the UPS after TBI. Induction of CMA was manifested by significant upregulation of LAMP2A and secondary lysosomes during the periods of 1-15 days of recovery after TBI. In comparison, the levels of ubi-proteins were increased only moderately after TBI. The increases in the levels of LAMP2A and 70 kDa heat-shock protein for CMA after TBI were seen mainly in the secondary lysosome-containing fractions. Confocal and electron microscopy further showed that increased LAMP2A or lysosomes were found mainly in neurons and proliferated microglia. Because CMA and the UPS are two major routes for elimination of different types of cellular aberrant proteins, the consecutive activation of these two pathways may serve as a protective mechanism for maintaining cellular homeostasis after TBI.

Recent imaging advances in neurology

Over the recent years, the application of neuroimaging techniques such as magnetic resonance imaging (MRI) and positron emission tomography (PET) has considerably advanced the understanding of complex neurological disorders. PET is a powerful molecular imaging tool, which investigates the distribution and binding of radiochemicals attached to biologically relevant molecules; as such, this technique is able to give information on biochemistry and metabolism of the brain in health and disease. MRI uses high intensity magnetic fields and radiofrequency pulses to provide structural and functional information on tissues and organs in intact or diseased individuals, including the evaluation of white matter integrity, grey matter thickness and brain perfusion. The aim of this article is to review the most recent advances in neuroimaging research in common neurological disorders such as movement disorders, dementia, epilepsy, traumatic brain injury and multiple sclerosis, and to evaluate their contribution in the diagnosis and management of patients.

Chronic traumatic encephalopathy in contact sports: a systematic review of all reported pathological cases

Chronic traumatic encephalopathy (CTE) is a neurodegenerative disease associated with head trauma. Although initially believed to affect only boxers, the at-risk population has expanded to encompass a much wider demographic, including American football players, hockey players, wrestlers, and military veterans. This expansion has garnered considerable media attention and public concern for the potential neurodegenerative effects of head trauma. The main aim of this systematic review is to give a complete overview of the common findings and risk factors for CTE as well as the status quo regarding the incidence and prevalence of CTE. This systematic review was performed using PubMed and MEDLINE and includes all neuropathologically confirmed cases of CTE in the medical literature to date, from the first published case in 1954 to August 1, 2013 (n = 153). The demographics, including the primary source of mTBI (mild Traumatic Brain Injury), age and cause of death, ApoE genotype, and history of substance abuse, when listed, were obtained from each case report. The demographics of American football players found to have CTE are also presented separately in order to highlight the most prevalent group of CTE cases reported in recent years. These 153 case reports of CTE represent the largest collection to date. We found that a history of mTBI was the only risk factor consistently associated with CTE. In addition, we found no relationships between CTE and age of death or abnormal ApoE allele. Suicide and the presence of premorbid dementia was not strongly associated with CTE. We conclude that the incidence of CTE remains unknown due to the lack of large, longitudinal studies. Furthermore, the neuropathological and clinical findings related to CTE overlap with many common neurodegenerative diseases. Our review reveals significant limitations of the current CTE case reporting and questions the widespread existence of CTE in contact sports.

Amyloid PET imaging: applications beyond Alzheimer's disease

As a biomarker of beta-amyloid, positron emission tomography (PET) amyloid imaging offers a unique opportunity to detect the presence of this protein in the human body during life. Besides Alzheimer's disease (AD), deposits of beta-amyloid in the brain are also present in other neurodegenerative diseases associated to dementia, such as Parkinson's disease and dementia with Lewy bodies, as well as in other processes affecting brain function, such as cerebral amyloid angiopathy, brain trauma, Down's syndrome and meningiomas, as shown by post-mortem pathology studies. Furthermore, in systemic amyloidosis other organs besides the brain are affected, and amyloid PET imaging may be suitable for the identification of these extra-cerebral amyloid depositions. Finally, the potential use of amyloid PET tracer accumulation in cerebral white matter (WM) as a marker of myelin is being investigated, leading to some promising results in patients with WM lesions and multiple sclerosis. In this article, a review of the ongoing research pointing to a broader application of amyloid PET imaging in clinical practice beyond AD is provided.

Traumatic brain injury and cognition

Traumatic brain injury (TBI) is a major cause of death and disability, and therefore an important health and socioeconomic problem for our society. Individuals surviving from a moderate to severe TBI frequently suffer from long-lasting cognitive deficits. Such deficits include different aspects of cognition such as memory, attention, executive functions, and awareness of their deficits. This chapter presents a review of the main neuropsychological and neuroimaging studies of patients with TBI. These studies found that patients evolve differently according to the severity of the injury, the mechanism causing the injury, and the lesion location. Further research is necessary to develop rehabilitation methods that enhance brain plasticity and recovery after TBI. In this chapter, we summarize current knowledge and controversies, focusing on cognitive sequelae after TBI. Recommendations from the Common Data Elements are provided, with an emphasis on diagnosis, outcome measures, and studies organization to make data more comparable across studies. Final considerations on neuroimaging advances, rehabilitation approaches, and genetics are described in the final section of the chapter.

A case of Alzheimer's disease following mild traumatic brain injury

OBJECTIVE

To report a case of Alzheimer's disease (AD) following mild traumatic brain injury (TBI).

METHOD

Case report.

RESULTS

We report the time course of AD following mild TBI with evidence of AD pathology. A patient complained of minor memory disturbance 6 months after TBI and was diagnosed with mild cognitive impairment 1.5 years after TBI, and she was finally diagnosed as probable AD 4 years after TBI. Amyloid PET revealed brain accumulation of beta-amyloid at a pathological AD level.

CONCLUSION

Our case well illustrated how TBI can accelerate the AD process. Clinicians should carefully follow up patients with persistent cognitive impairment after TBI.

Accumulation of amyloid in cognitive impairment after mild traumatic brain injury

Recent epidemiology studies have indicated that traumatic brain injury (TBI) can increase the risk of developing neurodegenerative diseases such as Alzheimer's disease (AD). Amyloid-β (Aβ) plaques and neurofibrillary tangles are pathological indicators of AD. The accumulation of Aβ is considered the first step of AD pathophysiology. Compelling studies have supported the hypothesis that TBI accelerates the formation and accumulation of Aβ. These findings could link TBI with AD, although the research that reported these findings had limitations, particularly regarding mild TBI (mTBI) patients. The effects of mTBI on Aβ accumulation remain uncertain because of a lack of mTBI pathology data. Using amyloid-positron emission tomography (amyloid-PET), researchers can help to determine whether mTBI increases the accumulation of Aβ, which might be involved in the pathophysiological mechanisms of mTBI in AD, and could be a target for the treatment of neurodegenerative diseases associated with TBI. In this study, we recruited 27 mTBI patients with mTBI in mean 6years before this study (21 mTBI patients without cognitive impairment, 6 mTBI patients with cognitive impairment,) and 10 controls. All of them underwent mini-mental state examination, apolipoprotein E (APOE) genotyping, and amyloid-PET. The results show an increase of amyloid accumulation and allele frequency of APOE4 in the mTBI patients with cognitive impairment. These findings indicate that amyloid accumulation is an important indicator of cognitive impairment, and amyloid-PET should be a safe and useful tool for diagnosing amyloid-related cognitive impairment. APOE allele might play a role in the occurrence of cognitive impairment after mTBI. The contribution of mTBI to the amyloid accumulation requires further study, and mTBI patients should be recruited for longitudinal research with repeated amyloid-PET studies.

Head trauma in sport and neurodegenerative disease: an issue whose time has come?

A number of small studies and anecdotal reports have been suggested that sports involving repeated head trauma may have long-term risks of neurodegenerative disease. There are now plausible mechanisms for these effects, and a recognition that these problems do not just occur in former boxers, but in a variety of sports involving repeated concussions, and possibly also in sports in which low-level head trauma is common. These neurodegenerative effects potentially include increased risks of impaired cognitive function and dementia, Parkinson's disease, and amyotrophic lateral sclerosis. Many would argue for taking a precautionary approach and immediately banning or restricting sports such as boxing. However, there are important public health issues in terms of how wide the net should be cast in terms of other sports, and what remedial measures could be taken? This in turn requires a major research effort involving both clinical and basic research to understand the underlying mechanisms, leading from head trauma to neurodegenerative disease and epidemiologic studies to assess the long-term consequences.

Chronic traumatic encephalopathy: clinical-biomarker correlations and current concepts in pathogenesis

Background

Chronic traumatic encephalopathy (CTE) is a recently revived term used to describe a neurodegenerative process that occurs as a long term complication of repetitive mild traumatic brain injury (TBI). Corsellis provided one of the classic descriptions of CTE in boxers under the name “dementia pugilistica” (DP). Much recent attention has been drawn to the apparent association of CTE with contact sports (football, soccer, hockey) and with frequent battlefield exposure to blast waves generated by improvised explosive devices (IEDs). Recently, a promising serum biomarker has been identified by measurement of serum levels of the neuronal microtubule associated protein tau. New positron emission tomography (PET) ligands (e.g., [¹⁸ F] T807) that identify brain tauopathy have been successfully deployed for the in vitro and in vivo detection of presumptive tauopathy in the brains of subjects with clinically probable CTE.

Methods

Major academic and lay publications on DP/CTE were reviewed beginning with the 1928 paper describing the initial use of the term CTE by Martland.

Results

The major current concepts in the neurological, psychiatric, neuropsychological, neuroimaging, and body fluid biomarker science of DP/CTE have been summarized. Newer achievements, such as serum tau and [¹⁸ F] T807 tauopathy imaging, are also introduced and their significance has been explained.

Conclusion

Recent advances in the science of DP/CTE hold promise for elucidating a long sought accurate determination of the true prevalence of CTE. This information holds potentially important public health implications for estimating the risk of contact sports in inflicting permanent and/or progressive brain damage on children, adolescents, and adults.