Neuroimaging in the Diagnosis of Chronic Traumatic Encephalopathy: A Systematic Review

Evolving significance of kinase inhibitors in the management of Alzheimer's disease

Alzheimer's disease is a neurodegenerative problem with progressive loss of memory and other cognitive function disorders resulting in the imbalance of neurotransmitter activity and signaling progression, which poses the need of the potential therapeutic target to improve the intracellular signaling cascade brought by kinases. Protein kinase plays a significant and multifaceted role in the treatment of Alzheimer's disease, by targeting pathological mechanisms like tau hyperphosphorylation, neuroinflammation, amyloid-beta production and synaptic dysfunction. In this review, we thoroughly explore the essential protein kinases involved in Alzheimer's disease, detailing their physiological roles, regulatory impacts, and the newest inhibitors and compounds that are progressing into clinical trials. All the findings of studies exhibited the promising role of kinase inhibitors in the management of Alzheimer's disease. However, it still poses the need of addressing current challenges and opportunities involved with this disorder for the future perspective of kinase inhibitors in the management of Alzheimer's disease. Further study includes the development of biomarkers, combination therapy, and next-generation kinase inhibitors with increased potency and selectivity for its future prospects.

Return to Play Following Concussion: Role for Imaging?

This review surveys concussion management, focusing on the use of neuroimaging techniques in return to play (RTP) decisions. Clinical assessments traditionally were the foundation of concussion diagnoses. However, their subjective nature prompted an exploration of neuroimaging modalities to enhance diagnosis and management. Magnetic resonance spectroscopy provides information about metabolic changes and alterations in the absence of structural abnormalities. Diffusion tensor imaging uncovers microstructural changes in white matter. Functional magnetic resonance imaging assesses neuronal activity to reveal changes in cognitive and sensorimotor functions. Positron emission tomography can assess metabolic disturbances using radiotracers, offering insight into the long-term effects of concussions. Vestibulo-ocular dysfunction screening and eye tracking assess vestibular and oculomotor function. Although these neuroimaging techniques demonstrate promise, continued research and standardization are needed before they can be integrated into the clinical setting. This review emphasizes the potential for neuroimaging in enhancing the accuracy of concussion diagnosis and guiding RTP decisions.

Molecular mechanisms involved in the destabilization of two types of R3-R4 tau fibrils associated with chronic traumatic encephalopathy by Fisetin

Chronic traumatic encephalopathy is a neurodegenerative tauopathy pathologically characterized by fibrillary tau aggregates in the depth of sulci. Clearing fibrous tau aggregates is considered a promising strategy in the treatment of CTE. Fisetin (FS), a natural polyphenolic small molecule, was confirmed to disassociate the tau filaments in vitro. However, the molecular mechanisms of FS in destabilizing the CTE-related R3-R4 tau fibrils remain largely unknown. In this study, we compared the atomic-level structural differences of the two types of CTE-related R3-R4 tau fibrils and explored the influence and molecular mechanisms of FS on the two types of fibrils by conducting multiple molecular dynamics (MD) simulations. The results reveal that the type 1 fibril displays higher structural stability than the type 2 fibril, with a lower root-mean-square-fluctuation value and higher β-sheet structure probability. FS can destabilize both types of fibrils by decreasing the β-sheet structure content, interrupting the mainchain H-bond network, and increasing the solvent accessible surface area and β7-β8 angle of the fibrils. H-bonding, π-π stacking and cation-π are the common interactions driving FS molecules binding on the two types of fibrils, while the hydrophobic interaction occurs only in the type 2 fibril. Due to the relatively short simulation time, our study captures the early molecular mechanisms. However, it does provide beneficial information for the design of drugs to prevent or treat CTE.

A Molecular Toolbox of Positron Emission Tomography Tracers for General Anesthesia Mechanism Research

With appropriate radiotracers, positron emission tomography (PET) allows direct or indirect monitoring of the spatial and temporal distribution of anesthetics, neurotransmitters, and biomarkers, making it an indispensable tool for studying the general anesthesia mechanism. In this Perspective, PET tracers that have been recruited in general anesthesia research are introduced in the following order: 1) ¹¹C/¹⁸F-labeled anesthetics, i.e., PET tracers made from inhaled and intravenous anesthetics; 2) PET tracers targeting anesthesia-related receptors, e.g., neurotransmitters and voltage-gated ion channels; and 3) PET tracers for studying anesthesia-related neurophysiological effects and neurotoxicity. The radiosynthesis, pharmacodynamics, and pharmacokinetics of the above PET tracers are mainly discussed to provide a practical molecular toolbox for radiochemists, anesthesiologists, and those who are interested in general anesthesia.

Molecular Mechanism in the Disruption of Chronic Traumatic Encephalopathy-Related R3-R4 Tau Protofibril by Quercetin and Gallic Acid: Similarities and Differences

Chronic traumatic encephalopathy (CTE) is a unique progressive neurodegenerative tauopathy pathologically related to the aggregation of the tau protein to neurofibrillary tangles. Disrupting tau oligomers (protofibril) is a promising strategy to prevent CTE. Quercetin (QE) and gallic acid (GA), two polyphenol small molecules abundant in natural crops, were proved to inhibit recombinant tau and the R3 fragment of human full-length tau in vitro. However, their disruptive effect on CTE-related protofibril and the underlying molecular mechanism remain elusive. Cryo-electron microscopy resolution reveals that the R3-R4 fragment of tau forms the core of the CTE-related tau protofibril. In this study, we conducted extensive all-atom molecular dynamics simulations on CTE-related R3-R4 tau protofibril with and without QE/GA molecules. The results disclose that both QE and GA can disrupt the global structure of the protofibril, while GA shows a relatively strong effect. The binding sites, exact binding patterns, and disruptive modes for the two molecules show similarities and differences. Strikingly, both QE and GA can insert into the hydrophobic cavity of the protofibril, indicating they have the potential to compete for the space in the cavity with aggregation cofactors unique to CTE-related protofibril and thus impede the further aggregation of the tau protein. Due to relatively short time scale, our study captures the early disruptive mechanism of CTE-related R3-R4 tau protofibril by QE/GA. However, our research does provide valuable knowledge for the design of supplements or drugs to prevent or delay the development of CTE.

Systematic Review of the Long-Term Neuroimaging Correlates of Mild Traumatic Brain Injury and Repetitive Head Injuries

Objective: To systematically review the literature on the long-term neuroimaging findings (≥10 years from exposure) for exposure in adulthood to mild traumatic brain injury (mTBI) and repetitive head impacts (RHIs) using neuroimaging across all available populations. Data sources: Four electronic databases: MEDLINE, SPORTDiscus, PsycINFO, and EMBASE. Study selection: All articles were original research and published in English. Studies examined adults with remote exposure to mTBI and/or RHIs from ten or more years ago in addition to any associated neuroimaging findings. Data extraction: Parameters mainly included participants' population, age, years since head injury, race, sex, education level, and any neuroimaging findings. Scores for the level of evidence and risk of bias were calculated independently by two authors. Results: 5,521 studies were reviewed, of which 34 met inclusion criteria and were included in this study. The majority of adults in these studies showed positive neuroimaging findings one or more decades following mTBI/RHI exposure. This was consistent across study populations (i.e., veterans, athletes, and the general population). There was evidence for altered protein deposition patterns, micro- and macro-structural, functional, neurochemical, and blood flow-related differences in the brain for those with remote mTBI/RHI exposure. Conclusion: Findings from these studies suggest that past mTBI/RHI exposure may be associated with neuroimaging findings. However, given the methodological constraints related to relatively small sample sizes and the heterogeneity in injury types/exposure and imaging techniques used, conclusions drawn from this review are limited. Well-designed longitudinal studies with multimodal imaging and in-depth health and demographic information will be required to better understand the potential for having positive neuroimaging findings following remote mTBI/RHI.

Identifying degenerative effects of repetitive head trauma with neuroimaging: a clinically-oriented review

BACKGROUND AND SCOPE OF REVIEW

Varying severities and frequencies of head trauma may result in dynamic acute and chronic pathophysiologic responses in the brain. Heightened attention to long-term effects of head trauma, particularly repetitive head trauma, has sparked recent efforts to identify neuroimaging biomarkers of underlying disease processes. Imaging modalities like structural magnetic resonance imaging (MRI) and positron emission tomography (PET) are the most clinically applicable given their use in neurodegenerative disease diagnosis and differentiation. In recent years, researchers have targeted repetitive head trauma cohorts in hopes of identifying in vivo biomarkers for underlying biologic changes that might ultimately improve diagnosis of chronic traumatic encephalopathy (CTE) in living persons. These populations most often include collision sport athletes (e.g., American football, boxing) and military veterans with repetitive low-level blast exposure. We provide a clinically-oriented review of neuroimaging data from repetitive head trauma cohorts based on structural MRI, FDG-PET, Aβ-PET, and tau-PET. We supplement the review with two patient reports of neuropathology-confirmed, clinically impaired adults with prior repetitive head trauma who underwent structural MRI, FDG-PET, Aβ-PET, and tau-PET in addition to comprehensive clinical examinations before death.

REVIEW CONCLUSIONS

Group-level comparisons to controls without known head trauma have revealed inconsistent regional volume differences, with possible propensity for medial temporal, limbic, and subcortical (thalamus, corpus callosum) structures. Greater frequency and severity (i.e., length) of cavum septum pellucidum (CSP) is observed in repetitive head trauma cohorts compared to unexposed controls. It remains unclear whether CSP predicts a particular neurodegenerative process, but CSP presence should increase suspicion that clinical impairment is at least partly attributable to the individual's head trauma exposure (regardless of underlying disease). PET imaging similarly has not revealed a prototypical metabolic or molecular pattern associated with repetitive head trauma or predictive of CTE based on the most widely studied radiotracers. Given the range of clinical syndromes and neurodegenerative pathologies observed in a subset of adults with prior repetitive head trauma, structural MRI and PET imaging may still be useful for differential diagnosis (e.g., assessing suspected Alzheimer's disease).

Chronic traumatic encephalopathy-a blueprint for the bridge between neurological and psychiatric disorders

Chronic traumatic encephalopathy (CTE) is a perplexing condition characterized by a broad and diverse range of neuropathology and psychopathology. While there are no agreed upon or validated clinical criteria for CTE, case series of CTE have described a wide range of neuropsychiatric symptoms that have been attributed to repetitive traumatic brain injuries (rTBI). However, the direct links between the psychopathology of psychiatric and neurological conditions from rTBI to CTE remains poorly understood. Prior studies suggest that repetitive cerebral injuries are associated with damage to neural circuitry involved in emotional and memory processes, but these studies do not offer longitudinal assessments that prove causation. More recent studies on novel targets, such as transmission of misfolded proteins, as well as newly advanced non-invasive imaging techniques may offer more direct evidence of the pathogenesis of CTE by tracing the progression of pathology and display of related behavioral impairments. Understanding this interface in the context of rTBI can play an important role in future approaches to the definition, assessment, prevention, and treatment of CTE and mental illnesses.

Screening of tau protein kinase inhibitors in a tauopathy-relevant cell-based model of tau hyperphosphorylation and oligomerization

Tauopathies are a class of neurodegenerative disorders characterized by abnormal deposition of post-translationally modified tau protein in the human brain. Tauopathies are associated with Alzheimer's disease (AD), chronic traumatic encephalopathy (CTE), and other diseases. Hyperphosphorylation increases tau tendency to aggregate and form neurofibrillary tangles (NFT), a pathological hallmark of AD. In this study, okadaic acid (OA, 100 nM), a protein phosphatase 1/2A inhibitor, was treated for 24h in mouse neuroblastoma (N2a) and differentiated rat primary neuronal cortical cell cultures (CTX) to induce tau-hyperphosphorylation and oligomerization as a cell-based tauopathy model. Following the treatments, the effectiveness of different kinase inhibitors was assessed using the tauopathy-relevant tau antibodies through tau-immunoblotting, including the sites: pSer202/pThr205 (AT8), pThr181 (AT270), pSer202 (CP13), pSer396/pSer404 (PHF-1), and pThr231 (RZ3). OA-treated samples induced tau phosphorylation and oligomerization at all tested epitopes, forming a monomeric band (46-67 kDa) and oligomeric bands (170 kDa and 240 kDa). We found that TBB (a casein kinase II inhibitor), AR and LiCl (GSK-3 inhibitors), cyclosporin A (calcineurin inhibitor), and Saracatinib (Fyn kinase inhibitor) caused robust inhibition of OA-induced monomeric and oligomeric p-tau in both N2a and CTX culture. Additionally, a cyclin-dependent kinase 5 inhibitor (Roscovitine) and a calcium chelator (EGTA) showed contrasting results between the two neuronal cultures. This study provides a comprehensive view of potential drug candidates (TBB, CsA, AR, and Saracatinib), and their efficacy against tau hyperphosphorylation and oligomerization processes. These findings warrant further experimentation, possibly including animal models of tauopathies, which may provide a putative Neurotherapy for AD, CTE, and other forms of tauopathy-induced neurodegenerative diseases.

Emerging advances of in vivo detection of chronic traumatic encephalopathy and traumatic brain injury

Chronic traumatic encephalopathy (CTE) is a neurodegenerative disorder that is of epidemic proportions in contact sports athletes and is linked to subconcussive and concussive repetitive head impacts (RHI). Although postmortem analysis is currently the only confirmatory method to diagnose CTE, there has been progress in early detection techniques of fluid biomarkers as well as in advanced neuroimaging techniques. Specifically, promising new methods of diffusion MRI and radionucleotide PET scans could aid in the early detection of CTE.The authors examine early detection methods focusing on various neuroimaging techniques. Advances in structural and diffusion MRI have demonstrated the ability to measure volumetric and white matter abnormalities associated with CTE. Recent studies using radionucleotides such as flortaucipir and 18F-FDDNP have shown binding patterns that are consistent with the four stages of neurofibrillary tangle (NFT) distribution postmortem. Additional research undertakings focusing on fMRI, MR spectroscopy, susceptibility-weighted imaging, and singlephoton emission CT are also discussed as are advanced MRI methods such as diffusiontensor imaging and arterial spin labeled. Neuroimaging is fast becoming a key instrument in early detection and could prove essential for CTE quantification. This review explores a global approach to in vivo early detection.Limited data of in vivo CTE biomarkers with postmortem confirmation are available. While some data exist, they are limited by selection bias. It is unlikely that a single test will be sufficient to properly diagnosis and distinguish CTE from other neurodegenerative diseases such as Alzheimer disease or Frontotemporal Dementia. However, with a combination of fluid biomarkers, neuroimaging, and genetic testing, early detection may become possible.

Pathological Assessment of Chronic Traumatic Encephalopathy: Review of Concepts and Methodology

Chronic traumatic encephalopathy (CTE) has become a topic of considerable interest in recent years, with wide-ranging implications for athletes, military members, and other groups exposed to frequent concussive or subconcussive head trauma. The condition has been subject to intensive neuropathological characterization by various groups, with assessment methodologies and staging criteria proposed. Clinical characterization of symptoms has also been performed, but has not yet been definitively formalized. While efforts are underway to develop in vivo markers of tauopathies including CTE, these remain experimental at this time, necessitating postmortem analysis for definitive diagnosis. The putative link between development of cognitive and behavioral dysfunction and neuropathological findings of CTE may prompt requests for postmortem assessment in the forensic setting. Here, we review current concepts in CTE research, describe histopathological findings in CTE, and describe methodologies for pathological assessment of CTE which may be useful to the forensic pathologist.

Limbic system structure volumes and associated neurocognitive functioning in former NFL players

Chronic traumatic encephalopathy (CTE) is a neurodegenerative disease associated with exposure to repetitive head impacts. CTE has been linked to disruptions in cognition, mood, and behavior. Unfortunately, the diagnosis of CTE can only be made post-mortem. Neuropathological evidence suggests limbic structures may provide an opportunity to characterize CTE in the living. Using 3 T magnetic resonance imaging, we compared select limbic brain regional volumes - the amygdala, hippocampus, and cingulate gyrus - between symptomatic former National Football League (NFL) players (n = 86) and controls (n = 22). Moreover, within the group of former NFL players, we examined the relationship between those limbic structures and neurobehavioral functioning (n = 75). The former NFL group comprised eighty-six men (mean age = 55.2 ± 8.0 years) with at least 12 years of organized football experience, at least 2 years of active participation in the NFL, and self-reported declines in cognition, mood, and behavior within the last 6 months. The control group consisted of men (mean age = 57.0 ± 6.6 years) with no history of contact-sport involvement or traumatic brain injury. All control participants provided neurobehavioral data. Compared to controls, former NFL players exhibited reduced volumes of the amygdala, hippocampus, and cingulate gyrus. Within the NFL group, reduced bilateral cingulate gyrus volume was associated with worse attention and psychomotor speed (r = 0.4 (right), r = 0.42 (left); both p < 0.001), while decreased right hippocampal volume was associated with worse visual memory (r = 0.25, p = 0.027). Reduced volumes of limbic system structures in former NFL players are associated with neurocognitive features of CTE. Volume reductions in the amygdala, hippocampus, and cingulate gyrus may be potential biomarkers of neurodegeneration in those at risk for CTE.

Emotional Lability as a Unique Presenting Sign of Suspected Chronic Traumatic Encephalopathy

Chronic traumatic encephalopathy (CTE) is a neurodegenerative disease caused by head trauma. Diagnosis of this disease is difficult as reliable biomarkers have not been established and often this clinical entity is underappreciated with poor recognition of its clinical presentations (Lenihan and Jordan, 2015). The definitive diagnosis of CTE is determined by identification of neurofibrillary tangles in the perivascular space around the sulci in postmortem tissue (McKee et al., 2015). However, performing brain biopsies searching for neurofibrillary tangles is not a feasible option for early diagnosis. Thus, diagnosis of suspected CTE in the living has been based on clinical suspicion using proposed research criteria of clinical presentations. In addition, neuroimaging techniques have shown some promise in assisting diagnosis. Clinically, CTE is more commonly known to be associated with memory impairment and executive function disorder (Stern et al., 2013). However, here, we present two unique cases of prior professional football players where behavioral changes were the first identifying factors in clinical presentation and discuss possible neuroimaging options to help with CTE diagnosis. Because behavioral changes can be mistaken for other neuropsychological diseases, recognizing differing clinical constellations is critical to early diagnosis, early intervention, and improving patient care in suspected CTE.