Evidence of increased brain amyloid in severe TBI survivors at 1, 12, and 24 months after injury: report of 2 cases

Improving quantitative susceptibility mapping for the identification of traumatic brain injury neurodegeneration at the individual level

BACKGROUND

Emerging evidence suggests that traumatic brain injury (TBI) is a major risk factor for developing neurodegenerative disease later in life. Quantitative susceptibility mapping (QSM) has been used by an increasing number of studies in investigations of pathophysiological changes in TBI. However, generating artefact-free quantitative susceptibility maps in brains with large focal lesions, as in the case of moderate-to-severe TBI (ms-TBI), is particularly challenging. To address this issue, we utilized a novel two-pass masking technique and reconstruction procedure (two-pass QSM) to generate quantitative susceptibility maps (QSMxT; Stewart et al., 2022, Magn Reson Med.) in combination with the recently developed virtual brain grafting (VBG) procedure for brain repair (Radwan et al., 2021, NeuroImage) to improve automated delineation of brain areas. We used QSMxT and VBG to generate personalised QSM profiles of individual patients with reference to a sample of healthy controls.

METHODS

Chronic ms-TBI patients (N = 8) and healthy controls (N = 12) underwent (multi-echo) GRE, and anatomical MRI (MPRAGE) on a 3T Siemens PRISMA scanner. We reconstructed the magnetic susceptibility maps using two-pass QSM from QSMxT. We then extracted values of magnetic susceptibility in grey matter (GM) regions (following brain repair via VBG) across the whole brain and determined if they deviate from a reference healthy control group [Z-score < -3.43 or > 3.43, relative to the control mean], with the aim of obtaining personalised QSM profiles.

RESULTS

Using two-pass QSM, we achieved susceptibility maps with a substantial increase in quality and reduction in artefacts irrespective of the presence of large focal lesions, compared to single-pass QSM. In addition, VBG minimised the loss of GM regions and exclusion of patients due to failures in the region delineation step. Our findings revealed deviations in magnetic susceptibility measures from the HC group that differed across individual TBI patients. These changes included both increases and decreases in magnetic susceptibility values in multiple GM regions across the brain.

CONCLUSIONS

We illustrate how to obtain magnetic susceptibility values at the individual level and to build personalised QSM profiles in ms-TBI patients. Our approach opens the door for QSM investigations in more severely injured patients. Such profiles are also critical to overcome the inherent heterogeneity of clinical populations, such as ms-TBI, and to characterize the underlying mechanisms of neurodegeneration at the individual level more precisely. Moreover, this new personalised QSM profiling could in the future assist clinicians in assessing recovery and formulating a neuroscience-guided integrative rehabilitation program tailored to individual TBI patients.

Traumatic brain injury and Alzheimer's Disease biomarkers: A systematic review of findings from amyloid and tau positron emission tomography (PET)

Traumatic brain injury (TBI) has been discussed as a risk factor for Alzheimer's disease (AD) due to its association with dementia 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 amyloid-β and/or tau to examine subjects with history of TBI who are at risk for AD due to advanced age. A comprehensive literature search was conducted on January 9, 2023, and 24 resulting citations met inclusion criteria. Common methodological concerns included small samples, limited clinical detail about subjects' TBI, recall bias due to reliance on self-reported TBI, and an inability to establish causation. For both amyloid and tau, results were widespread but inconsistent. The regions which showed the most compelling evidence for increased amyloid deposition were the cingulate gyrus, cuneus/precuneus, and parietal lobe. Evidence for increased tau was strongest in the medial temporal lobe, entorhinal cortex, precuneus, and frontal, temporal, parietal, and occipital lobes. However, conflicting findings across most regions of interest in both amyloid- 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 subjects at risk for AD.

Early Brain Amyloid Accumulation at PET in Military Instructors Exposed to Subconcussive Blast Injuries

Background Traumatic brain injury (TBI) is the leading cause of disability in young adults. Recurrent TBI is associated with a range of neurologic sequelae, but the contributing factors behind the development of such chronic encephalopathy are poorly understood. Purpose To quantify early amyloid β deposition in the brain of otherwise healthy adult men exposed to repeated subconcussive blast injury using amyloid PET. Materials and Methods In this prospective study from January 2020 to December 2021, military instructors who were routinely exposed to repeated blast events were evaluated at two different points: baseline (before blast exposure from breacher or grenade) and approximately 5 months after baseline (after blast exposure). Age-matched healthy control participants not exposed to blasts and without a history of brain injury were evaluated at similar two points. Neurocognitive evaluation was performed with standard neuropsychologic testing in both groups. Analysis of PET data consisted of standardized uptake value measurements in six relevant brain regions and a whole-brain voxel-based statistical approach. Results Participants were men (nine control participants [median age, 33 years; IQR, 32-36 years] and nine blast-exposed participants [median age, 33 years; IQR, 30-34 years]; P = .82). In the blast-exposed participants, four brain regions showed significantly increased amyloid deposition after blast exposure: inferomedial frontal lobe (P = .004), precuneus (P = .02), anterior cingulum (P = .002), and superior parietal lobule (P = .003). No amyloid deposition was observed in the control participants. Discriminant analysis on the basis of regional changes of amyloid accumulation correctly classified the nine healthy control participants as healthy control participants (100%), and seven of the nine blast-exposed participants (78%) were correctly classified as blast exposed. Based on the voxel-based analysis, whole-brain parametric maps of early abnormal early amyloid uptake were obtained. Conclusion Early brain amyloid accumulation was identified and quantified at PET in otherwise healthy adult men exposed to repetitive subconcussive traumatic events. © RSNA, 2023 Supplemental material is available for this article. See also the editorial by Haller in this issue.

Brain Trauma Imaging

Imaging of mild traumatic brain injury (TBI) using conventional techniques such as CT or MRI often results in no specific imaging correlation that would explain cognitive and clinical symptoms. Molecular imaging of mild TBI suggests that secondary events after injury can be detected using PET. However, no single specific pattern emerges that can aid in diagnosing the injury or determining the prognosis of the long-term behavioral profiles, indicating the heterogeneous and diffuse nature of TBI. Chronic traumatic encephalopathy, a primary tauopathy, has been shown to be strongly associated with repetitive TBI. In vivo data on the available tau PET tracers, however, have produced mixed results and overall low retention profiles in athletes with a history of repetitive mild TBI. Here, we emphasize that the lack of a mechanistic understanding of chronic TBI has posed a challenge when interpreting the results of molecular imaging biomarkers. We advocate for better target identification, improved analysis techniques such as machine learning or artificial intelligence, and novel tracer development.

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.

Advances in Brain Amyloid Imaging

Amyloid-β (Aβ) PET imaging has now been available for over 15 years. The ability to detect Aβ in vivo has greatly improved the clinical and research landscape of Alzheimer's disease (AD) and other neurodegenerative conditions. Aβ imaging provides very reliable, accurate, and reproducible measurements of regional and global Aβ burden in the brain. It has proved invaluable in anti-Aβ therapy trials, and is now recognized as a powerful diagnostic tool. The appropriate use of Aβ PET, when combined with comprehensive clinical evaluation by a dementia-trained specialist, can improve the accuracy of a clinical diagnosis of AD and substantially alter management. It can assist in differentiating AD from other neurodegenerative conditions, often by its ability to rule out the presence of Aβ. When combined with tau imaging, further increase in specificity for the diagnosis of AD can be achieved. The integration of Aβ PET, in conjunction with biomarkers of tau, neurodegeneration and neuroinflammation, into large, longitudinal, observational cohort studies continues to increase our understanding of the development of AD. Its incorporation into clinical trials has been pivotal in defining the most effective anti-Aβ biological therapies and optimal dosing so that effective disease modifying therapy now appears imminent. Aβ deposition is a gradual and protracted process, permitting a wide treatment window for anti-Aβ therapies and Aβ PET has made trials in this preclinical AD period feasible. Continuing improvement in Aβ tracer target to background ratio is allowing trials in earlier AD that tailor drug dosage to Aβ level. The quest to standardize quantification and define universally applicable thresholds for all Aβ tracers has produced the Centiloid method. Centiloid values that correlate well with neuropathologic findings and prognosis have been identified. Rapid cloud-based automated individual scan analysis is now possible and does not require MRI. Challenges remain, particularly around cross camera standardized uptake value ratio variation that need to be addressed. This review will compare available Aβ radiotracers, discuss approaches to quantification, as well as the clinical and research applications of Aβ PET.

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.

Reduced Neuron-Specific Enolase Levels in Chronic Severe Traumatic Brain Injury

Growing evidence suggests that pathophysiological mechanisms leading to neurodegeneration and neuronal loss take place during the chronic phase of a severe traumatic brain injury (TBI). In this study we evaluated a well-established marker of brain injury, the neuron-specific enolase (NSE), in the serum of 51 patients with severe TBI (86% males, mean age 33.8 ± 11.1 years). All patients' samples were available from a previous study and the mean time between TBI and blood sample collection was 23.2 ± 31.5 months (28 patients were evaluated within 12 months of TBI and 23 patients were evaluated ≥12 months after TBI). Patients' NSE levels were compared with those obtained from 30 age and sex-matched healthy controls (87% males, 33.7 ± 11.3 years). We found that NSE levels were significantly lower in patients (median 3.2 ng/mL; 25th, 75th percentile 2.5, 5.1) than in healthy controls (median 4.1 ng/mL; 25th, 75th percentile 3.1, 7.5) (p = 0.026). This finding was mainly driven by data from the chronic patients, that is, those who experienced their TBI at least 12 months before the evaluation. Indeed, these patients had significantly lower NSE levels (median 2.6 ng/mL; 25th, 75th percentile 1.9, 4) than healthy controls (p < 0.01). On the other hand, NSE levels evaluated in patients <12 months from TBI (median 3.9 ng/mL; 25th, 75th percentile 2.8, 5.7) did not significantly differ from controls (p = 0.3). These findings possibly reflect a progressive brain atrophy with reduced baseline NSE release in the chronic phase of a severe TBI.

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.

CHIMERA repetitive mild traumatic brain injury induces chronic behavioural and neuropathological phenotypes in wild-type and APP/PS1 mice

Background

The annual incidence of traumatic brain injury (TBI) in the United States is over 2.5 million, with approximately 3–5 million people living with chronic sequelae. Compared with moderate-severe TBI, the long-term effects of mild TBI (mTBI) are less understood but important to address, particularly for contact sport athletes and military personnel who have high mTBI exposure. The purpose of this study was to determine the behavioural and neuropathological phenotypes induced by the Closed-Head Impact Model of Engineered Rotational Acceleration (CHIMERA) model of mTBI in both wild-type (WT) and APP/PS1 mice up to 8 months post-injury.

Methods

Male WT and APP/PS1 littermates were randomized to sham or repetitive mild TBI (rmTBI; 2 × 0.5 J impacts 24 h apart) groups at 5.7 months of age. Animals were assessed up to 8 months post-injury for acute neurological deficits using the loss of righting reflex (LRR) and Neurological Severity Score (NSS) tasks, and chronic behavioural changes using the passive avoidance (PA), Barnes maze (BM), elevated plus maze (EPM) and rotarod (RR) tasks. Neuropathological assessments included white matter damage; grey matter inflammation; and measures of Aβ levels, deposition, and aducanumab binding activity.

Results

The very mild CHIMERA rmTBI conditions used here produced no significant acute neurological or motor deficits in WT and APP/PS1 mice, but they profoundly inhibited extinction of fear memory specifically in APP/PS1 mice over the 8-month assessment period. Spatial learning and memory were affected by both injury and genotype. Anxiety and risk-taking behaviour were affected by injury but not genotype. CHIMERA rmTBI induced chronic white matter microgliosis, axonal injury and astrogliosis independent of genotype in the optic tract but not the corpus callosum, and it altered microgliosis in APP/PS1 amygdala and hippocampus. Finally, rmTBI did not alter long-term tau, Aβ or amyloid levels, but it increased aducanumab binding activity.

Conclusions

CHIMERA is a useful model to investigate the chronic consequences of rmTBI, including behavioural abnormalities consistent with features of post-traumatic stress disorder and inflammation of both white and grey matter. The presence of human Aβ greatly modified extinction of fear memory after rmTBI.

Electronic supplementary material

The online version of this article (10.1186/s13195-018-0461-0) contains supplementary material, which is available to authorized users.

Higher exosomal tau, amyloid-beta 42 and IL-10 are associated with mild TBIs and chronic symptoms in military personnel

OBJECTIVE

Identify biomarkers in peripheral blood that relate to chronic post-concussive and behavioural symptoms following traumatic brain injuries (TBIs) to ultimately improve clinical management.

RESEARCH DESIGN

We compared military personnel with mild TBIs (mTBIs) (n = 42) to those without TBIs (n = 22) in concentrations of tau, amyloid-beta (Aβ42) and cytokines (tumour necrosis factor alpha (TNFα, interleukin (IL)-6 and -10) in neuronal-derived exosomes from the peripheral blood. We utilized nanosight technology coupled with ultra-sensitivity immunoassay methods. We also examined the impact of post-concussive and behavioural symptoms including depression and post-traumatic stress disorder (PTSD) on these neuronal-derived markers.

RESULTS

We report that concentrations of exosomal tau (F_1, 62 = 10.50), Aβ42 (F_1, 61 = 5.32) and IL-10 (F_1, 59 = 4.32) were elevated in the mTBI group compared to the controls. Within the mTBI group, regression models show that post-concussive symptoms were most related to exosomal tau elevations, whereas exosomal IL-10 levels were related to PTSD symptoms.

CONCLUSIONS

These findings suggest that chronic post-concussive symptoms following an mTBI relate to altered exosomal activity, and that greater tau pathology may underlie chronic post-concussive symptoms that develop following mTBIs. It also suggests that central inflammatory activity contributes to PTSD symptoms following an mTBI, providing necessary insights into the role of inflammation in chronic PTSD symptoms.

Structural imaging of mild traumatic brain injury may not be enough: overview of functional and metabolic imaging of mild traumatic brain injury

A majority of patients with traumatic brain injury (TBI) present as mild injury with no findings on conventional clinical imaging methods. Due to this difficulty of imaging assessment on mild TBI patients, there has been much emphasis on the development of diffusion imaging modalities such as diffusion tensor imaging (DTI). However, basic science research in TBI shows that many of the functional and metabolic abnormalities in TBI may be present even in the absence of structural damage. Moreover, structural damage may be present at a microscopic and molecular level that is not detectable by structural imaging modality. The use of functional and metabolic imaging modalities can provide information on pathological changes in mild TBI patients that may not be detected by structural imaging. Although there are various differences in protocols of positron emission tomography (PET), single photon emission computed tomography (SPECT), functional magnetic resonance imaging (fMRI), electroencephalography (EEG), and magnetoencephalography (MEG) methods, these may be important modalities to be used in conjunction with structural imaging in the future in order to detect and understand the pathophysiology of mild TBI. In this review, studies of mild TBI patients using these modalities that detect functional and metabolic state of the brain are discussed. Each modality's advantages and disadvantages are compared, and potential future applications of using combined modalities are explored.

The Neuropsychology of Traumatic Brain Injury: Looking Back, Peering Ahead

The past 50 years have been a period of exciting progress in neuropsychological research on traumatic brain injury (TBI). Neuropsychologists and neuropsychological testing have played a critical role in these advances. This study looks back at three major scientific advances in research on TBI that have been critical in pushing the field forward over the past several decades: The advent of modern neuroimaging; the recognition of the importance of non-injury factors in determining recovery from TBI; and the growth of cognitive rehabilitation. Thanks to these advances, we now have a better understanding of the pathophysiology of TBI and how recovery from the injury is also shaped by pre-injury, comorbid, and contextual factors, and we also have increasing evidence that active interventions, including cognitive rehabilitation, can help to promote better outcomes. The study also peers ahead to discern two important directions that seem destined to influence research on TBI over the next 50 years: the development of large, multi-site observational studies and randomized controlled trials, bolstered by international research consortia and the adoption of common data elements; and attempts to translate research into health care and health policy by the application of rigorous methods drawn from implementation science. Future research shaped by these trends should provide critical evidence regarding the outcomes of TBI and its treatment, and should help to disseminate and implement the knowledge gained from research to the betterment of the quality of life of persons with TBI. (JINS, 2017, 23, 806-817).

The chronic and evolving neurological consequences of traumatic brain injury

Traumatic brain injury (TBI) can have lifelong and dynamic effects on health and wellbeing. Research on the long-term consequences emphasises that, for many patients, TBI should be conceptualised as a chronic health condition. Evidence suggests that functional outcomes after TBI can show improvement or deterioration up to two decades after injury, and rates of all-cause mortality remain elevated for many years. Furthermore, TBI represents a risk factor for a variety of neurological illnesses, including epilepsy, stroke, and neurodegenerative disease. With respect to neurodegeneration after TBI, post-mortem studies on the long-term neuropathology after injury have identified complex persisting and evolving abnormalities best described as polypathology, which includes chronic traumatic encephalopathy. Despite growing awareness of the lifelong consequences of TBI, substantial gaps in research exist. Improvements are therefore needed in understanding chronic pathologies and their implications for survivors of TBI, which could inform long-term health management in this sizeable patient population.

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.

Traumatic Axonal Injury: Mechanisms and Translational Opportunities

Traumatic axonal injury (TAI) is an important pathoanatomical subgroup of traumatic brain injury (TBI) and a major driver of mortality and functional impairment. Experimental models have provided insights into the effects of mechanical deformation on the neuronal cytoskeleton and the subsequent processes that drive axonal injury. There is also increasing recognition that axonal or white matter loss may progress for years post-injury and represent one mechanistic framework for progressive neurodegeneration after TBI. Previous trials of novel therapies have failed to make an impact on clinical outcome, in both TBI in general and TAI in particular. Recent advances in understanding the cellular and molecular mechanisms of injury have the potential to translate into novel therapeutic targets.

Multiple therapeutic targets are emerging that offer the potential to reduce secondary brain injury at a cellular level. These include cytoskeletal and membrane stabilisation, control of calcium flux and calpain activation, optimisation of cellular energetics, and modulation of the inflammatory response.

Wallerian degeneration, as occurs following an axonal injury, is an active, cell-autonomous death pathway that involves failure of axonal transport to deliver key enzymes involved in NAD biosynthesis.

Chronic microglial activation occurs following traumatic brain injury (TBI) and may persist for decades afterwards. This ongoing response has been linked to long-term neurodegeneration, particularly of white matter tracts.

Phagoptosis is the process whereby physiologically stressed but otherwise viable neurons are phagocytosed by microglia in response to a range of eat-me signals induced by tissue injury.