Documented head injury in early adulthood and risk of Alzheimer's disease and other dementias

Detecting and Predicting Cognitive Decline in Individuals with Traumatic Brain Injury: A Longitudinal Telephone-Based Study

Traumatic brain injuries (TBIs) can lead to long-lasting cognitive impairments, and some survivors experience cognitive decline post-recovery. Early detection of decline is important for care planning, and understanding risk factors for decline can elucidate targets for prevention. While neuropsychological testing is the gold standard approach to characterizing cognitive function, there is a need for brief, scalable tools that are capable of detecting clinically significant changes in post-TBI cognition. This study examines whether clinically significant change can be detected using the Brief Test of Adult Cognition by Telephone (BTACT) in a sample of individuals with chronic TBI and investigates whether potentially modifiable factors are associated with cognitive decline. Ninety participants aged 40 or older with complicated mild to severe TBI participated in two telephone-based study visits approximately one year apart. Demographic, head trauma exposure, comorbid medical conditions, physical and psychosocial functioning data were collected via self-report. The BTACT, a brief measure of global cognitive function, was used to assess cognitive performance across six domains. A Reliable Change Index (RCI) for quantifying clinically significant changes in BTACT performance was calculated. Results revealed cognitive decline in 10% to 27% of participants across various cognitive domains. More specifically, only depressive symptoms, including depressed affect and anhedonia, were significantly associated with cognitive decline after correcting for multiple comparisons using FDR. Other factors such as the number of blows to the head, male gender, dyspnea, increased anxiety symptoms, seizures, illicit drug use, and fewer cardiovascular comorbidities should be considered hypothesis-generating. Importantly, age was not a significant predictor of cognitive decline, which challenges the assumption that cognitive decline is solely related to the natural aging process. It suggests that there are unique factors associated with TBI that impact cognitive function, and these factors can affect individuals across the lifespan. The BTACT is a brief and sensitive tool for identifying clinically meaningful changes in cognitive function over a relatively brief period (i.e., one year) in a sample of individuals in the chronic stages of TBI (i.e., x̅=6.7 years post-TBI). Thus, the BTACT may be useful in surveillance efforts aimed at understanding and detecting decline, particularly in situations where in-person cognitive screening is impractical or unfeasible. We also identified potentially modifiable targets for the prevention of post-TBI cognitive decline. These findings can offer insights into treatment goals and preventive strategies for individuals at risk for cognitive decline, as well as help to facilitate early identification efforts.

Cerebrospinal fluid biomarkers and cognitive trajectories in patients with Alzheimer's disease and a history of traumatic brain injury

Traumatic brain injury (TBI) and Alzheimer's disease (AD) have overlapping mechanisms but it remains unknown if pathophysiological characteristics and cognitive trajectories in AD patients are influenced by TBI history. Here, we studied AD patients (stage MCI or dementia) with TBI history (ADTBI+, n=110), or without (ADTBI-, n=110) and compared baseline CSF concentrations of amyloid beta 1-42 (Aβ42), phosphorylated tau181 (pTau181), total tau, neurofilament light chain (NfL), synaptosomal associated protein-25kDa (SNAP25), neurogranin (Ng), neuronal pentraxin-2 (NPTX2) and glutamate receptor-4 (GluR4), as well as differences in cognitive trajectories using linear mixed models. Explorative, analyses were repeated within stratified TBI groups by TBI characteristics (timing, severity, number). We found no differences in baseline CSF biomarker concentrations nor in cognitive trajectories between ADTBI+ and ADTBI- patients. TBI >5 years ago was associated with higher NPTX2 and a tendency for higher SNAP25 concentrations compared to TBI ≤ 5 years ago, suggesting that TBI may be associated with long-term synaptic dysfunction only when occurring before onset or in a pre-clinical disease stage of AD.

2024 Alzheimer's disease facts and figures

This article describes the public health impact of Alzheimer's disease (AD), including prevalence and incidence, mortality and morbidity, use and costs of care and the ramifications of AD for family caregivers, the dementia workforce and society. The Special Report discusses the larger health care system for older adults with cognitive issues, focusing on the role of caregivers and non-physician health care professionals. An estimated 6.9 million Americans age 65 and older are living with Alzheimer's dementia today. This number could grow to 13.8 million by 2060, barring the development of medical breakthroughs to prevent or cure AD. Official AD death certificates recorded 119,399 deaths from AD in 2021. In 2020 and 2021, when COVID-19 entered the ranks of the top ten causes of death, Alzheimer's was the seventh-leading cause of death in the United States. Official counts for more recent years are still being compiled. Alzheimer's remains the fifth-leading cause of death among Americans age 65 and older. Between 2000 and 2021, deaths from stroke, heart disease and HIV decreased, whereas reported deaths from AD increased more than 140%. More than 11 million family members and other unpaid caregivers provided an estimated 18.4 billion hours of care to people with Alzheimer's or other dementias in 2023. These figures reflect a decline in the number of caregivers compared with a decade earlier, as well as an increase in the amount of care provided by each remaining caregiver. Unpaid dementia caregiving was valued at $346.6 billion in 2023. Its costs, however, extend to unpaid caregivers' increased risk for emotional distress and negative mental and physical health outcomes. Members of the paid health care and broader community-based workforce are involved in diagnosing, treating and caring for people with dementia. However, the United States faces growing shortages across different segments of the dementia care workforce due to a combination of factors, including the absolute increase in the number of people living with dementia. Therefore, targeted programs and care delivery models will be needed to attract, better train and effectively deploy health care and community-based workers to provide dementia care. Average per-person Medicare payments for services to beneficiaries age 65 and older with AD or other dementias are almost three times as great as payments for beneficiaries without these conditions, and Medicaid payments are more than 22 times as great. Total payments in 2024 for health care, long-term care and hospice services for people age 65 and older with dementia are estimated to be $360 billion. The Special Report investigates how caregivers of older adults with cognitive issues interact with the health care system and examines the role non-physician health care professionals play in facilitating clinical care and access to community-based services and supports. It includes surveys of caregivers and health care workers, focusing on their experiences, challenges, awareness and perceptions of dementia care navigation.

KCNJ2 inhibition mitigates mechanical injury in a human brain organoid model of traumatic brain injury

Traumatic brain injury (TBI) strongly correlates with neurodegenerative disease. However, it remains unclear which neurodegenerative mechanisms are intrinsic to the brain and which strategies most potently mitigate these processes. We developed a high-intensity ultrasound platform to inflict mechanical injury to induced pluripotent stem cell (iPSC)-derived cortical organoids. Mechanically injured organoids elicit classic hallmarks of TBI, including neuronal death, tau phosphorylation, and TDP-43 nuclear egress. We found that deep-layer neurons were particularly vulnerable to injury and that TDP-43 proteinopathy promotes cell death. Injured organoids derived from C9ORF72 amyotrophic lateral sclerosis/frontotemporal dementia (ALS/FTD) patients displayed exacerbated TDP-43 dysfunction. Using genome-wide CRISPR interference screening, we identified a mechanosensory channel, KCNJ2, whose inhibition potently mitigated neurodegenerative processes in vitro and in vivo, including in C9ORF72 ALS/FTD organoids. Thus, targeting KCNJ2 may reduce acute neuronal death after brain injury, and we present a scalable, genetically flexible cerebral organoid model that may enable the identification of additional modifiers of mechanical stress.

Impact of dementia and socioeconomic disadvantage on days at home after traumatic brain injury among older Medicare beneficiaries: A cohort study

INTRODUCTION

Time spent at home may aid in understanding recovery following traumatic brain injury (TBI) among older adults, including those with Alzheimer's disease and related dementias (ADRD). We examined the impact of ADRD on recovery following TBI and determined whether socioeconomic disadvantages moderated the impact of ADRD.

METHODS

We analyzed Medicare beneficiaries aged ≥65 years diagnosed with TBI in 2010-2018. Home time was calculated by subtracting days spent in a care environment or deceased from total follow-up, and dual eligibility for Medicaid was a proxy for socioeconomic disadvantage.

RESULTS

A total of 2463 of 20,350 participants (12.1%) had both a diagnosis of ADRD and were Medicaid dual-eligible. Beneficiaries with ADRD and Medicaid spent markedly fewer days at home following TBI compared to beneficiaries without either condition (rate ratio 0.66; 95% confidence interval [CI] 0.64, 0.69).

DISCUSSION

TBI resulted in a significant loss of home time over the year following injury among older adults with ADRD, particularly for those who were economically vulnerable.

HIGHLIGHTS

Remaining at home after serious injuries such as fall-related traumatic brain injury (TBI) is an important goal for older adults. No prior research has evaluated how ADRD impacts time spent at home after TBI. Older TBI survivors with ADRD may be especially vulnerable to loss of home time if socioeconomically disadvantaged. We assessed the impact of ADRD and poverty on a novel DAH measure after TBI. ADRD-related disparities in DAH were significantly magnified among those living with socioeconomic disadvantage, suggesting a need for more tailored care approaches.

INviting Veterans InTo Enrollment in Alzheimer's Disease Research Centers (INVITE-ADRC): An NIA and VA-sponsored initiative to increase veteran participation in aging and dementia research

INTRODUCTION

Older military veterans often present with unique and complex risk factors for Alzheimer's disease (AD) and related dementias. Increasing veteran participation in research studies offers one avenue to advance the field and improve health outcomes.

METHODS

To this end, the National Institute on Aging (NIA) and Department of Veterans Affairs (VA) partnered to build infrastructure, improve collaboration, and intensify targeted recruitment of veterans. This initiative, INviting Veterans InTo Enrollment in Alzheimer's Disease Research Centers (INVITE-ADRC), provided funding for five sites and cross-site organizing structure. Diverse and innovative recruitment strategies were used.

RESULTS

Across five sites, 172 veterans entered registries, and 99 were enrolled into ADRC studies. Of the enrolled, 39 were veterans from historically underrepresented racial and ethnic groups.

CONCLUSIONS

This initiative laid the groundwork to establish sustainable relationships between the VA and ADRCs. The partnership between both federal agencies demonstrates how mutual interests can accelerate progress. In turn, efforts can help our aging veterans.

Association between mammillary body atrophy and memory impairment in retired athletes with a history of repetitive mild traumatic brain injury

Cognitive dysfunction, especially memory impairment, is a typical clinical feature of long-term symptoms caused by repetitive mild traumatic brain injury (rmTBI). The current study aims to investigate the relationship between regional brain atrophy and cognitive impairments in retired athletes with a long history of rmTBI. Overall, 27 retired athletes with a history of rmTBI (18 boxers, 3 kickboxers, 2 wrestlers, and 4 others; rmTBI group) and 23 age/sex-matched healthy participants (control group) were enrolled. MPRAGE on 3 T MRI was acquired and segmented. The TBV and TBV-adjusted regional brain volumes were compared between groups, and the relationship between the neuropsychological test scores and the regional brain volumes were evaluated. Total brain volume (TBV) and regional brain volumes of the mammillary bodies (MBs), hippocampi, amygdalae, thalami, caudate nuclei, and corpus callosum (CC) were estimated using the SPM12 and ITK-SNAP tools. In the rmTBI group, the regional brain volume/TBV ratio (rmTBI vs. control group, Mann-Whitney U test, p < 0.05) underwent partial correlation analysis, adjusting for age and sex, to assess its connection with neuropsychological test results. Compared with the control group, the rmTBI group showed significantly lower the MBs volume/TBV ratio (0.13 ± 0.05 vs. 0.19 ± 0.03 × 10-3, p < 0.001). The MBs volume/TBV ratio correlated with visual memory, as assessed, respectively, by the Rey-Osterrieth Complex Figure test delayed recall (ρ = 0.62, p < 0.001). In conclusion, retired athletes with rmTBI have MB atrophy, potentially contributing to memory impairment linked to the Papez circuit disconnection.

Sex-Biased Expression and Response of microRNAs in Neurological Diseases and Neurotrauma

Neurological diseases and neurotrauma manifest significant sex differences in prevalence, progression, outcome, and therapeutic responses. Genetic predisposition, sex hormones, inflammation, and environmental exposures are among many physiological and pathological factors that impact the sex disparity in neurological diseases. MicroRNAs (miRNAs) are a powerful class of gene expression regulator that are extensively involved in mediating biological pathways. Emerging evidence demonstrates that miRNAs play a crucial role in the sex dimorphism observed in various human diseases, including neurological diseases. Understanding the sex differences in miRNA expression and response is believed to have important implications for assessing the risk of neurological disease, defining therapeutic intervention strategies, and advancing both basic research and clinical investigations. However, there is limited research exploring the extent to which miRNAs contribute to the sex disparities observed in various neurological diseases. Here, we review the current state of knowledge related to the sexual dimorphism in miRNAs in neurological diseases and neurotrauma research. We also discuss how sex chromosomes may contribute to the miRNA sexual dimorphism phenomenon. We attempt to emphasize the significance of sexual dimorphism in miRNA biology in human diseases and to advocate a gender/sex-balanced science.

Glial cells react to closed head injury in a distinct and spatiotemporally orchestrated manner

Traumatic brain injury (TBI) is a leading cause of mortality and disability worldwide. Acute neuroinflammation is a prominent reaction after TBI and is mostly initiated by brain-resident glial cells such as microglia, NG2-glia and astrocytes. The magnitude of this reaction paves the way for long-lasting consequences such as chronic neurological pathologies, for which therapeutic options remain limited. The neuroinflammatory response to TBI is mostly studied with craniotomy-based animal models that are very robust but also rather artificial. Here, we aimed to analyze the reaction of glial cells in a highly translational but variable closed head injury (CHI) model and were able to correlate the severity of the trauma to the degree of glial response. Furthermore, we could show that the different glial cell types react in a temporally and spatially orchestrated manner in terms of morphological changes, proliferation, and cell numbers in the first 15 days after the lesion. Interestingly, NG2-glia, the only proliferating cells in the healthy brain parenchyma, divided at a rate that was correlated with the size of the injury. Our findings describe the previously uncharacterized posttraumatic response of the major brain glial cell types in CHI in order to gain a detailed understanding of the course of neuroinflammatory events; such knowledge may open novel avenues for future therapeutic approaches in TBI.

Antiepileptic Drugs as Potential Dementia Prophylactics Following Traumatic Brain Injury

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

Investigation of Potential Drug Targets Involved in Inflammation Contributing to Alzheimer's Disease Progression

Alzheimer's disease has become a major public health issue. While extensive research has been conducted in the last few decades, few drugs have been approved by the FDA to treat Alzheimer's disease. There is still an urgent need for understanding the disease pathogenesis, as well as identifying new drug targets for further drug discovery. Alzheimer's disease is known to arise from a build-up of amyloid beta (Aβ) plaques as well as tangles of tau proteins. Along similar lines to Alzheimer's disease, inflammation in the brain is known to stem from the degeneration of tissue and build-up of insoluble materials. A minireview was conducted in this work assessing the genes, proteins, reactions, and pathways that link brain inflammation and Alzheimer's disease. Existing tools in Systems Biology were implemented to build protein interaction networks, mainly for the classical complement pathway and G protein-coupled receptors (GPCRs), to rank the protein targets according to their interactions. The top 10 protein targets were mainly from the classical complement pathway. With the consideration of existing clinical trials and crystal structures, proteins C5AR1 and GARBG1 were identified as the best targets for further drug discovery, through computational approaches like ligand-protein docking techniques.

Broadening horizons: ferroptosis as a new target for traumatic brain injury

Traumatic brain injury (TBI) is a leading cause of death and disability worldwide, with ~50 million people experiencing TBI each year. Ferroptosis, a form of regulated cell death triggered by iron ion-catalyzed and reactive oxygen species-induced lipid peroxidation, has been identified as a potential contributor to traumatic central nervous system conditions, suggesting its involvement in the pathogenesis of TBI. Alterations in iron metabolism play a crucial role in secondary injury following TBI. This study aimed to explore the role of ferroptosis in TBI, focusing on iron metabolism disorders, lipid metabolism disorders and the regulatory axis of system Xc-/glutathione/glutathione peroxidase 4 in TBI. Additionally, we examined the involvement of ferroptosis in the chronic TBI stage. Based on these findings, we discuss potential therapeutic interventions targeting ferroptosis after TBI. In conclusion, this review provides novel insights into the pathology of TBI and proposes potential therapeutic targets.

Traumatic Brain Injury and Post-Traumatic Stress Disorder and Their Influence on Development and Pattern of Alzheimer's Disease Pathology in Later Life

Background

Traumatic brain injury (TBI) and posttraumatic stress disorder (PTSD) are potential risk factors for the development of dementia including Alzheimer's disease (AD) in later life. The findings of studies investigating this question are inconsistent though.

Objective

To investigate if these inconsistencies are caused by the existence of subgroups with different vulnerability for AD pathology and if these subgroups are characterized by atypical tau load/atrophy pattern.

Methods

The MRI and PET data of 89 subjects with or without previous TBI and/or PTSD from the DoD ADNI database were used to calculate an age-corrected gray matter tau mismatch metric (ageN-T mismatch-score and matrix) for each subject. This metric provides a measure to what degree regional tau accumulation drives regional gray matter atrophy (matrix) and can be used to calculate a summary score (score) reflecting the severity of AD pathology in an individual.

Results

The ageN-T mismatch summary score was positively correlated with whole brain beta-amyloid load and general cognitive function but not with PTSD or TBI severity. Hierarchical cluster analysis identified five different spatial patterns of tau-gray matter interactions. These clusters reflected the different stages of the typical AD tau progression pattern. None was exclusively associated with PTSD and/or TBI.

Conclusions

These findings suggest that a) although subsets of patients with PTSD and/or TBI develop AD-pathology, a history of TBI or PTSD alone or both is not associated with a significantly higher risk to develop AD pathology in later life. b) remote TBI or PTSD do not modify the typical AD pathology distribution pattern.

[Traumatic brain injury as risk factor of Alzheimer's disease and possibilities of pathogenetic therapy]

The article examines the potential role of brain mechanical damage as a trigger for the development of neurodegenerative changes. Attention is paid to dysfunction of the neurovascular unit, and disruption of the functional and compensatory capabilities of blood flow. The importance of microhemorrhages that occur in the acute period of injury and the formation of first focal and then diffuse neuroinflammation is emphasized. The importance of mitochondrial dysfunction was separately determined as a significant factor in increasing the risk of developing Alzheimer's disease (AD) in patients after traumatic brain injury (TBI). In TBI, there is a decrease in the expression of tight junction (TC) proteins of endothelial cells, such as occludin, claudin, JP, which leads to increased permeability of the blood-brain barrier. TBI, provoking endothelial dysfunction, contributes to the development of metabolic disorders of β-amyloid and tau protein, which in turn leads to worsening vascular damage, resulting in a vicious circle that can ultimately lead to the development of AD and dementia. Age-related changes in cerebral arteries, which impair perivascular transport of interstitial fluid, are currently considered as an important part of the «amyloid cascade», especially against the background of genetically mediated disorders of glial membranes associated with defective aquaporin-4 (encoded by the APOE4). Studies in animal models of TBI have revealed an increase in tau protein immunoreactivity and its phosphorylation, which correlates with the severity of injury. A comprehensive analysis of research results shows that the cascade of reactions triggered by TBI includes all the main elements of the pathogenesis of AD: disorders of energy metabolism, microcirculation and clearance of cerebral metabolic products. This leads to a disruption in the metabolism of amyloid protein and its accumulation in brain tissue with the subsequent development of tauopathy. Cerebrolysin, by modulating the permeability of the blood-brain barrier, blocks the development of neuroinflammation, reduces the accumulation of pathological forms of proteins and may be slow down the progression of neurodegeneration.

Low-dose ionizing radiation promotes motor recovery and brain rewiring by resolving inflammatory response after brain injury and stroke

Traumatic brain injury (TBI) and stroke share a common pathophysiology that worsens over time due to secondary tissue injury caused by sustained inflammatory response. However, studies on pharmacological interventions targeting the complex secondary injury cascade have failed to show efficacy. Here, we demonstrated that low-dose ionizing radiation (LDIR) reduced lesion size and reversed motor deficits after TBI and photothrombotic stroke. Magnetic resonance imaging demonstrated significant reduction of infarct volume in LDIR-treated mice after stroke. Systems-level transcriptomic analysis showed that genes upregulated in LDIR-treated stoke mice were enriched in pathways associated with inflammatory and immune response involving microglia. LDIR induced upregulation of anti-inflammatory- and phagocytosis-related genes, and downregulation of key pro-inflammatory cytokine production. These findings were validated by live-cell assays, in which microglia exhibited higher chemotactic and phagocytic capacities after LDIR. We observed substantial microglial clustering at the injury site, glial scar clearance and reversal of motor deficits after stroke. Cortical microglia/macrophages depletion completely abolished the beneficial effect of LDIR on motor function recovery in stroke mice. LDIR promoted axonal projections (brain rewiring) in motor cortex and recovery of brain activity detected by electroencephalography recordings months after stroke. LDIR treatment delayed by 8 h post-injury still maintained full therapeutic effects on motor recovery, indicating that LDIR is a promising therapeutic strategy for TBI and stroke.

Thirty Risk Factors for Alzheimer's Disease Unified by a Common Neuroimmune-Neuroinflammation Mechanism

One of the major obstacles confronting the formulation of a mechanistic understanding for Alzheimer's disease (AD) is its immense complexity-a complexity that traverses the full structural and phenomenological spectrum, including molecular, macromolecular, cellular, neurological and behavioural processes. This complexity is reflected by the equally complex diversity of risk factors associated with AD. However, more than merely mirroring disease complexity, risk factors also provide fundamental insights into the aetiology and pathogenesis of AD as a neurodegenerative disorder since they are central to disease initiation and subsequent propagation. Based on a systematic literature assessment, this review identified 30 risk factors for AD and then extended the analysis to further identify neuroinflammation as a unifying mechanism present in all 30 risk factors. Although other mechanisms (e.g., vasculopathy, proteopathy) were present in multiple risk factors, dysfunction of the neuroimmune-neuroinflammation axis was uniquely central to all 30 identified risk factors. Though the nature of the neuroinflammatory involvement varied, the activation of microglia and the release of pro-inflammatory cytokines were a common pathway shared by all risk factors. This observation provides further evidence for the importance of immunopathic mechanisms in the aetiopathogenesis of AD.

Differences in Risk of Alzheimer's Disease Following Later-Life Traumatic Brain Injury in Veteran and Civilian Populations

OBJECTIVE

To directly compare the effect of incident age 68+ traumatic brain injury (TBI) on the risk of diagnosis of clinical Alzheimer's disease (AD) in the general population of older adults, and between male veterans and nonveterans; to assess how this effect changes with time since TBI.

SETTING AND PARTICIPANTS

Community-dwelling traditional Medicare beneficiaries 68 years or older from the Health and Retirement Study (HRS).

DESIGN

Fine-Gray models combined with inverse-probability weighting were used to identify associations between incident TBI, post-TBI duration, and TBI treatment intensity, with a diagnosis of clinical AD dementia. The study included 16 829 older adults followed over the 1991-2015 period. For analyses of veteran-specific risks, 4281 veteran males and 3093 nonveteran males were identified. Analysis of veteran females was unfeasible due to the age structure of the population. Information on occurrence(s) of TBI, and onset of AD and risk-related comorbidities was constructed from individual-level HRS-linked Medicare claim records while demographic and socioeconomic risk factors were based on the survey data.

RESULTS

Later-life TBI was strongly associated with increased clinical AD risk in the full sample (pseudo-hazard ratio [HR]: 3.22; 95% confidence interval [CI]: 2.57-4.05) and in veteran/nonveteran males (HR: 5.31; CI: 3.42-7.94), especially those requiring high-intensity/duration care (HR: 1.58; CI: 1.29-1.91). Effect magnitude decreased with time following TBI (HR: 0.72: CI: 0.68-0.80).

CONCLUSION

Later-life TBI was strongly associated with increased AD risk, especially in those requiring high-intensity/duration care. Effect magnitude decreased with time following TBI. Univariate analysis showed no differences in AD risk between veterans and nonveterans, while the protective effect associated with veteran status in Fine-Gray models was largely due to differences in demographics, socioeconomics, and morbidity. Future longitudinal studies incorporating diagnostic procedures and documentation quantifying lifetime TBI events are necessary to uncover pathophysiological mediating and/or moderating mechanisms between TBI and AD.

Associations Between Traumatic Brain Injury and Cognitive Decline Among Older Male Veterans: A Twin Study

BACKGROUND AND OBJECTIVES

Traumatic brain injuries (TBIs) are associated with increased risk of dementia, but whether lifetime TBI influences cognitive trajectories in later life is less clear. Cognitive interventions after TBI may improve cognitive trajectories and delay dementia. Because twins share many genes and environmental factors, we capitalize on the twin study design to examine the association between lifetime TBI and cognitive decline.

METHODS

Participants were members of the National Academy of Sciences-National Research Council's Twin Registry of male veterans of World War II with self or proxy-reported history of TBI and with up to 4 observations over 12 years of the modified Telephone Interview for Cognitive Status (TICS-m). We used linear random-effects mixed models to analyze the association between TBI and TICS-m in the full sample and among co-twins discordant for TBI. Additional TBI predictor variables included number of TBIs, severity (loss of consciousness [LOC]), and age of first TBI (age <25 vs 25+ years [older age TBI]). Models were adjusted for age (centered at 70 years), age-squared, education, wave, twin pair, lifestyle behaviors, and medical conditions.

RESULTS

Of 8,662 participants, 25% reported TBI. History of any TBI (β = -0.56, 95% CI -0.73 to -0.39), TBI with LOC (β = -0.51, 95% CI -0.71 to -0.31), and older age TBI (β = -0.66, 95% CI -0.90 to -0.42) were associated with lower TICS-m scores at 70 years. TBI with LOC (β = -0.03, 95% CI -0.05 to -0.001), more than one TBI (β = -0.05, 95% CI -0.09 to -0.002,), and older age TBI (β = -0.06, 95% CI -0.09 to -0.03) were associated with faster cognitive decline. Among monozygotic pairs discordant for TBI (589 pairs), history of any TBI (β = -0.55, 95% CI -0.91 to -0.19) and older age TBI (β = -0.74, 95% CI -1.22 to -0.26) were associated with lower TICS-m scores at 70 years. Those with more than one TBI (β = -0.13, 95% CI -0.23 to -0.03) and older age TBI (β = -0.07, 95% CI -0.13 to -0.002) showed greater cognitive decline compared with their co-twin without TBI.

DISCUSSION

These findings support an association of the effect of TBI on cognitive score and the rapidity of cognitive decline in later life. The results in monozygotic pairs, who share all genes and many exposures, particularly in early life, provide additional evidence of a causal relationship between TBI and poorer late-life cognitive outcomes.

Investigation into the vascular contributors to dementia and the associated treatments

As the average lifespan has increased, memory disorders have become a more pressing public health concern. However, dementia in the elderly population is often neglected in light of other health priorities. Therefore, expanding the knowledge surrounding the pathology of dementia will allow more informed decision-making regarding treatment within elderly and older adult populations. An important emerging avenue in dementia research is understanding the vascular contributors to dementia. This review summarizes potential causes of vascular cognitive impairment like stroke, microinfarction, hypertension, atherosclerosis, blood-brain-barrier dysfunction, and cerebral amyloid angiopathy. Also, this review address treatments that target these vascular impairments that also show promising results in reducing patient's risk for and experience of dementia.

HMG-CoA Reductase Inhibitors for Traumatic Brain Injury

Traumatic brain injuries (TBIs) are associated with high morbidity and mortality due to both the original insult as well as the destructive biological response that follows. Medical management aims to slow or even halt secondary neurological injury while simultaneously laying the groundwork for recovery. Statins are one class of medications that is showing increased promise in the management of TBI. Used extensively in cardiovascular disease, these drugs were originally developed as competitive inhibitors within the cholesterol production pipeline. They are now used in diverse disease states due to their pleiotropic effects on other biological processes such as inflammation and angiogenesis. Preclinical studies, retrospective reviews, and randomized clinical trials have shown a variety of benefits in the management of TBI, but to date, no large-scale randomized clinical trial has been performed. Despite this limitation, statins' early promise and well-tolerated side effect profile make them a promising new tool in the management of TBIs. More bench and clinical studies are needed to delineate proper treatment regimens as well as understand their true potential.

Co-administration of dl-3-n-butylphthalide and neprilysin is neuroprotective in Alzheimer disease associated with mild traumatic brain injury

dl-3-n-Butylphthalide is a potent synthetic Chinese celery extract that is highly efficient in inducing neuroprotection in concussive head injury (CHI), Parkinson's disease, Alzheimer's disease, stroke as well as depression, dementia, anxiety and other neurological diseases. Thus, there are reasons to believe that dl-3-n-butylphthalide could effectively prevent Alzheimer's disease brain pathology. Military personnel during combat operation or veterans are often the victims of brain injury that is a major risk factor for developing Alzheimer's disease in their later lives. In our laboratory we have shown that CHI exacerbates Alzheimer's disease brain pathology and reduces the amyloid beta peptide (AβP) inactivating enzyme neprilysin. We have used TiO2 nanowired-dl-3-n-butylphthalide in attenuating Parkinson's disease brain pathology exacerbated by CHI. Nanodelivery of dl-3-n-butylphthalide appears to be more potent as compared to the conventional delivery of the compound. Thus, it would be interesting to examine the effects of nanowired dl-3-n-butylphthalide together with nanowired delivery of neprilysin in Alzheimer's disease model on brain pathology. In this investigation we found that nanowired delivery of dl-3-n-butylphthalide together with nanowired neprilysin significantly attenuated brain pathology in Alzheimer's disease model with CHI, not reported earlier. The possible mechanism and clinical significance is discussed based on the current literature.

Traumatic brain injury-associated epigenetic changes and the risk for neurodegenerative diseases

Epidemiological studies have shown that traumatic brain injury (TBI) increases the risk for developing neurodegenerative diseases (NDs). However, molecular mechanisms that underlie this risk are largely unidentified. TBI triggers widespread epigenetic modifications. Similarly, NDs such as Alzheimer's or Parkinson's are associated with numerous epigenetic changes. Although epigenetic changes can persist after TBI, it is unresolved if these modifications increase the risk of later ND development and/or dementia. We briefly review TBI-related epigenetic changes, and point out putative feedback loops that might contribute to long-term persistence of some modifications. We then focus on evidence suggesting persistent TBI-associated epigenetic changes may contribute to pathological processes (e.g., neuroinflammation) which may facilitate the development of specific NDs - Alzheimer's disease, Parkinson's disease, or chronic traumatic encephalopathy. Finally, we discuss possible directions for TBI therapies that may help prevent or delay development of NDs.

Single Versus Repetitive Traumatic Brain Injury: Current Knowledge on the Chronic Outcomes, Neuropathology and the Role of TDP-43 Proteinopathy

Traumatic brain injury (TBI) is one of the most important causes of death and disability in adults and thus an important public health problem. Following TBI, secondary pathophysiological processes develop over time and condition the development of different neurodegenerative entities. Previous studies suggest that neurobehavioral changes occurring after a single TBI are the basis for the development of Alzheimer's disease, while repetitive TBI is considered to be a contributing factor for chronic traumatic encephalopathy development. However, pathophysiological processes that determine the evolvement of a particular chronic entity are still unclear. Human post-mortem studies have found combinations of amyloid, tau, Lewi bodies, and TAR DNA-binding protein 43 (TDP-43) pathologies after both single and repetitive TBI. This review focuses on the pathological changes of TDP-43 after single and repetitive brain traumas. Numerous studies have shown that TDP-43 proteinopathy noticeably occurs after repetitive head trauma. A relatively small number of available preclinical research on single brain injury are not in complete agreement with the results from the human samples, which makes it difficult to draw specific conclusions. Also, as TBI is considered a heterogeneous type of injury, different experimental trauma models and injury intensities may cause differences in the cascade of secondary injury, which should be considered in future studies. Experimental and post-mortem studies of TDP-43 pathobiology should be carried out, preferably in the same laboratories, to determine its involvement in the development of neurodegenerative conditions after one and repetitive TBI, especially in the context of the development of new therapeutic options.

Preliminary Observations of Personalized Repetitive Magnetic Stimulation (PrTMS) Guided by EEG Spectra for Concussion

There are no FDA-approved treatments for the chronic sequelae of concussion. Repetitive magnetic transcranial stimulation (rTMS) has been explored as a therapy but outcomes have been inconsistent. To address this we developed a personalized rTMS (PrTMS) protocol involving continual rTMS stimulus frequency adjustment and progressive activation of multiple cortical sites, guided by spectral electroencephalogram (EEG)-based analyses and psychological questionnaires. We acquired pilot clinical data for 185 symptomatic brain concussion patients who underwent the PrTMS protocol over an approximate 6 week period. The PrTMS protocol used a proprietary EEG spectral frequency algorithm to define an initial stimulation frequency based on an anteriorly graded projection of the measured occipital alpha center peak, which was then used to interpolate and adjust regional stimulation frequency according to weekly EEG spectral acquisitions. PrTMS improved concussion indices and normalized the cortical alpha band center frequency and peak EEG amplitude. This potentially reflected changed neurotransmitter, cognitive, and perceptual status. PrTMS may be a promising treatment choice for patients with persistent concussion symptoms. This clinical observational study was limited in that there was no control group and a number of variables were not recorded, such as time since injury and levels of depression. While the present observations are indeed preliminary and cursory, they may suggest further prospective research on PrTMS in concussion, and exploration of the spectral EEG as a concussion biomarker, with the ultimate goals of confirmation and determining optimal PrTMS treatment parameters.

An exhaustive analysis of post-traumatic brain injury dementia using bibliometric methodologies

Background

It is widely accepted that traumatic brain injury (TBI) increases the risk of developing long-term dementia, although some controversies surrounding this topic exist. Annually, approximately 69 million individuals suffer from TBI all around the world. Such a large population of TBI patients could lead to a future surge in the number of dementia patients. Due to the potentially severe consequences of TBI, various research projects on post-TBI dementia have emerged worldwide. Therefore, it is essential to comprehend the current status and development of post-TBI dementia for future research.

Objective

The purpose of the study was to provide an overview of the field and identify hotspots, research frontiers, and future research trends for post-TBI dementia.

Methods

Articles related to post-TBI dementia were retrieved from the Web of Science Core Collection for the period between 2007 and 2022, and analyzing them based on factors such as citations, authors, institutions, countries, journals, keywords, and references. Data analysis and visualization were conducted using VOSviewer, CiteSpace, and an online bibliometric platform (https://bibliometric.com).

Results

From 2007 to 2022, we obtained a total of 727 articles from 3,780 authors and 1,126 institutions across 52 countries, published in 262 journals. These articles received a total of 29,353 citations, citing 25,713 references from 3,921 journals. Over the last 15 years, there has been a significant upward trend in both publications and citations. The most productive country was the United States, the most productive institution was Boston University, and the most productive author was McKee AC. Journal of Neurotrauma has been identified as the periodical with the greatest number of publications. Three clusters were identified through cluster analysis of keywords. A burst in the use of the term "outcome" in 2019 is indicative of a future research hotspot. The timeline view of references showed 14 clusters, of which the first 4 clusters collected the majority of papers. The first 4 clusters were "chronic traumatic encephalopathy," "age of onset," "tauopathy," and "cognitive decline," respectively, suggesting some areas of interest in the field.

Conclusion

The subject of post-TBI dementia has raised much interest from scientists. Notably, America is at the forefront of research in this area. Further collaborative research between different countries is imperative. Two topical issues in this field are "The association between TBI and dementia-related alterations" and "chronic traumatic encephalopathy (CTE)." Studies on clinical manifestation, therapy, pathology, and pathogenic mechanisms are also popular in the field.

Potential Biomarkers in Experimental Animal Models for Traumatic Brain Injury

Traumatic brain injury (TBI) is a complex and multifaceted disorder that has become a significant public health concern worldwide due to its contribution to mortality and morbidity. This condition encompasses a spectrum of injuries, including axonal damage, contusions, edema, and hemorrhage. Unfortunately, specific effective therapeutic interventions to improve patient outcomes following TBI are currently lacking. Various experimental animal models have been developed to mimic TBI and evaluate potential therapeutic agents to address this issue. These models are designed to recapitulate different biomarkers and mechanisms involved in TBI. However, due to the heterogeneous nature of clinical TBI, no single experimental animal model can effectively mimic all aspects of human TBI. Accurate emulation of clinical TBI mechanisms is also tricky due to ethical considerations. Therefore, the continued study of TBI mechanisms and biomarkers, of the duration and severity of brain injury, treatment strategies, and animal model optimization is necessary. This review focuses on the pathophysiology of TBI, available experimental TBI animal models, and the range of biomarkers and detection methods for TBI. Overall, this review highlights the need for further research to improve patient outcomes and reduce the global burden of TBI.

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.

Tau, β-Amyloid, and Glucose Metabolism Following Service-Related Traumatic Brain Injury in Vietnam War Veterans: The Australian Imaging Biomarkers and Lifestyle Study of Aging-Veterans Study (AIBL-VETS)

Traumatic brain injury (TBI) is common among military veterans and has been associated with an increased risk of dementia. It is unclear if this is due to increased risk for Alzheimer's disease (AD) or other mechanisms. This case control study sought evidence for AD, as defined by the 2018 National Institute on Aging - Alzheimer's Association (NIA-AA) research framework, by measuring tau, β-amyloid, and glucose metabolism using positron emission tomography (PET) in veterans with service-related TBI. Seventy male Vietnam war veterans-40 with TBI (age 68.0 ± 2.5 years) and 30 controls (age 70.1 ± 5.3 years)-with no prior diagnosis of dementia or mild cognitive impairment underwent β-amyloid (18F-Florbetaben), tau (18F-Flortaucipir), and fluorodeoxyglucose (18F-FDG) PET. The TBI cohort included 15 participants with mild, 16 with moderate, and nine with severe injury. β-Amyloid level was calculated using the Centiloid (CL) method and tau was measured by standardized uptake value ratios (SUVRs) using the cerebellar cortex as reference region. Analyses were adjusted for age and APOE-e4. The findings were validated in an independent cohort from the Department of Defense-Alzheimer's Disease Neuroimaging Initiative (DOD ADNI) study. There were no significant nor trending differences in β-amyloid or tau levels or 18F-FDG uptake between the TBI and control groups before and after controlling for covariates. The β-amyloid and tau findings were replicated in the DOD ADNI validation cohort and persisted when the Australian Imaging Biomarkers and Lifestyle study of aging-Veterans study (AIBL-VETS) and DOD ADNI cohorts were combined (114 TBI vs. 87 controls in total). In conclusion, no increase in the later life accumulation of the neuropathological markers of AD in veterans with a remote history of TBI was identified.

Modelling Microglial Innate Immune Memory In Vitro: Understanding the Role of Aerobic Glycolysis in Innate Immune Memory

Microglia, the resident macrophages of the central nervous system, play important roles in maintaining brain homeostasis and facilitating the brain's innate immune responses. Following immune challenges microglia also retain immune memories, which can alter responses to secondary inflammatory challenges. Microglia have two main memory states, training and tolerance, which are associated with increased and attenuated expression of inflammatory cytokines, respectively. However, the mechanisms differentiating these two distinct states are not well understood. We investigated mechanisms underlying training versus tolerance memory paradigms in vitro in BV2 cells using B-cell-activating factor (BAFF) or bacterial lipopolysaccharide (LPS) as a priming stimulus followed by LPS as a second stimulus. BAFF followed by LPS showed enhanced responses indicative of priming, whereas LPS followed by LPS as the second stimulus caused reduced responses suggestive of tolerance. The main difference between the BAFF versus the LPS stimulus was the induction of aerobic glycolysis by LPS. Inhibiting aerobic glycolysis during the priming stimulus using sodium oxamate prevented the establishment of the tolerized memory state. In addition, tolerized microglia were unable to induce aerobic glycolysis upon LPS restimulus. Therefore, we conclude that aerobic glycolysis triggered by the first LPS stimulus was a critical step in the induction of innate immune tolerance.

Effects and mechanisms of extremely cold environment on body response after trauma

With the outbreak of the Ukrainian crisis, extremely cold environment warfare has once again become the focus of international attention. People exposed to extremely cold environments may suffer from cold damage, further aggravate trauma, trigger high disability and mortality rates, and even cause serious sequelae. To declare the effects and mechanisms of the extremely cold environment on the body after trauma, this paper reviews, firstly, physiological reaction of human body in an extremely cold environment. Then, the post-traumatic body response in an extremely cold environment was introduced, and finally, the sequelae of trauma in extremely cold environment was further summarized in the paper. The results indicated that extremely cold environment can cause a series of damage to the body, especially the body after trauma. The extremely cold factor is a double-edged sword, showing a favorable and unfavorable side in different aspects. Moreover, in addition to the trauma suffered by the body, the subsequent sequelae such as cognitive dysfunction, anxiety, depression and even post-traumatic stress disorder may also be induced. The paper summarizes the human body's physiological response in an extremely cold environment, and declares the effects and mechanisms of the extremely cold environment on the body after trauma, which may provide a theoretical basis for effectively improving the level of combat trauma treatment in extremely cold regions.

Inflammaging, cellular senescence, and cognitive aging after traumatic brain injury

Traumatic brain injury (TBI) is associated with mortality and morbidity worldwide. Accumulating pre-clinical and clinical data suggests TBI is the leading extrinsic cause of progressive neurodegeneration. Neurological deterioration after either a single moderate-severe TBI or repetitive mild TBI often resembles dementia in aged populations; however, no currently approved therapies adequately mitigate neurodegeneration. Inflammation correlates with neurodegenerative changes and cognitive dysfunction for years post-TBI, suggesting a potential association between immune activation and both age- and TBI-induced cognitive decline. Inflammaging, a chronic, low-grade sterile inflammation associated with natural aging, promotes cognitive decline. Cellular senescence and the subsequent development of a senescence associated secretory phenotype (SASP) promotes inflammaging and cognitive aging, although the functional association between senescent cells and neurodegeneration is poorly defined after TBI. In this mini-review, we provide an overview of the pre-clinical and clinical evidence linking cellular senescence with poor TBI outcomes. We also discuss the current knowledge and future potential for senotherapeutics, including senolytics and senomorphics, which kill and/or modulate senescent cells, as potential therapeutics after TBI.

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

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

Exogenous interleukin 33 enhances the brain's lymphatic drainage and toxic protein clearance in acute traumatic brain injury mice

The persistent dysregulation and accumulation of poisonous proteins from destructive neural tissues and cells activate pathological mechanisms after traumatic brain injury (TBI). The lymphatic drainage system of the brain, composed of the glymphatic system and meningeal lymphatic vessels (MLVs), plays an essential role in the clearance of toxic waste after brain injury. The neuroprotective effect of interleukin 33 (IL-33) in TBI mice has been demonstrated; however, its impact on brain lymphatic drainage is unclear. Here, we established a fluid percussion injury model to examine the IL-33 administration effects on neurological function and lymphatic drainage in the acute brain of TBI mice. We verified that exogenous IL-33 could improve the motor and memory skills of TBI mice and demonstrated that in the acute phase, it increased the exchange of cerebrospinal and interstitial fluid, reversed the dysregulation and depolarization of aquaporin-4 in the cortex and hippocampus, improved the drainage of MLVs to deep cervical lymph nodes, and reduced tau accumulation and glial activation. We speculate that the protective effect of exogenous IL-33 on TBI mice's motor and cognitive functions is related to the enhancement of brain lymphatic drainage and toxic metabolite clearance from the cortex and hippocampus in the acute stage. These data further support the notion that IL-33 therapy may be an effective treatment strategy for alleviating acute brain injury after TBI.

Systematic Review, Meta-Analysis, and Population Attributable Risk of Dementia Associated with Traumatic Brain Injury in Civilians and Veterans

Traumatic brain injury (TBI) is an established risk factor for dementia. However, the magnitude of risk is highly variable across studies. Identification of sub-populations at highest risk, with careful consideration of potential sources of bias, is urgently needed to guide public health policy and research into mechanisms and treatments. We conducted a systematic review and meta-analysis of risk of all-cause dementia after all-severity TBI. We assessed for effect of participant age and sex, veteran status, research methods, and region. The search window covered January 1990 to January 2019. We followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) reporting guidelines. Thirty-two studies met inclusion criteria. Data were pooled using random effects models. Population attributable risk (PAR) of dementia due to TBI in the U.S. was calculated by sex and veteran status. Pooled risk ratio (RR) for dementia after TBI was 1.66 (95% confidence interval 1.42-1.93). Younger age, male sex, and studies from Asia were associated with significantly higher risk; veteran status was not. Risk of dementia associated with "head injury/trauma" was not significantly different from that associated with "TBI" diagnosis specifically. PAR of dementia due to TBI among U.S. veterans was twice that of the general U.S. population, largely due to the high prevalence of TBI exposure in the majority male veteran population. This meta-analysis found that TBI is associated with nearly 70% increased risk of dementia. Risk may be highest among younger adults, men, and cohorts in Asia. Efforts to prevent TBI and also to prevent post-TBI dementia are of high importance. Additionally, improved methods for diagnosing and tracking TBI on a public health level, such as national registries, may improve the quality and generalizability of future epidemiological studies investigating the association between TBI and dementia.

Traumatic MicroRNAs: Deconvolving the Signal After Severe Traumatic Brain Injury

History of traumatic brain injury (TBI) represents a significant risk factor for development of dementia and neurodegenerative disorders in later life. While histopathological sequelae and neurological diagnostics of TBI are well defined, the molecular events linking the post-TBI signaling and neurodegenerative cascades remain unknown. It is not only due to the brain's inaccessibility to direct molecular analysis but also due to the lack of well-defined and highly informative peripheral biomarkers. MicroRNAs (miRNAs) in blood are promising candidates to address this gap. Using integrative bioinformatics pipeline including miRNA:target identification, pathway enrichment, and protein-protein interactions analysis we identified set of genes, interacting proteins, and pathways that are connected to previously reported peripheral miRNAs, deregulated following severe traumatic brain injury (sTBI) in humans. This meta-analysis revealed a spectrum of genes closely related to critical biological processes, such as neuroregeneration including axon guidance and neurite outgrowth, neurotransmission, inflammation, proliferation, apoptosis, cell adhesion, and response to DNA damage. More importantly, we have identified molecular pathways associated with neurodegenerative conditions, including Alzheimer's and Parkinson's diseases, based on purely peripheral markers. The pathway signature after acute sTBI is similar to the one observed in chronic neurodegenerative conditions, which implicates a link between the post-sTBI signaling and neurodegeneration. Identified key hub interacting proteins represent a group of novel candidates for potential therapeutic targets or biomarkers.

2023 Alzheimer's disease facts and figures

This article describes the public health impact of Alzheimer's disease, including prevalence and incidence, mortality and morbidity, use and costs of care, and the overall impact on family caregivers, the dementia workforce and society. The Special Report examines the patient journey from awareness of cognitive changes to potential treatment with drugs that change the underlying biology of Alzheimer's. An estimated 6.7 million Americans age 65 and older are living with Alzheimer's dementia today. This number could grow to 13.8 million by 2060 barring the development of medical breakthroughs to prevent, slow or cure AD. Official death certificates recorded 121,499 deaths from AD in 2019, and Alzheimer's disease was officially listed as the sixth-leading cause of death in the United States. In 2020 and 2021, when COVID-19 entered the ranks of the top ten causes of death, Alzheimer's was the seventh-leading cause of death. Alzheimer's remains the fifth-leading cause of death among Americans age 65 and older. Between 2000 and 2019, deaths from stroke, heart disease and HIV decreased, whereas reported deaths from AD increased more than 145%. This trajectory of deaths from AD was likely exacerbated by the COVID-19 pandemic in 2020 and 2021. More than 11 million family members and other unpaid caregivers provided an estimated 18 billion hours of care to people with Alzheimer's or other dementias in 2022. These figures reflect a decline in the number of caregivers compared with a decade earlier, as well as an increase in the amount of care provided by each remaining caregiver. Unpaid dementia caregiving was valued at $339.5 billion in 2022. Its costs, however, extend to family caregivers' increased risk for emotional distress and negative mental and physical health outcomes - costs that have been aggravated by COVID-19. Members of the paid health care workforce are involved in diagnosing, treating and caring for people with dementia. In recent years, however, a shortage of such workers has developed in the United States. This shortage - brought about, in part, by COVID-19 - has occurred at a time when more members of the dementia care workforce are needed. Therefore, programs will be needed to attract workers and better train health care teams. Average per-person Medicare payments for services to beneficiaries age 65 and older with AD or other dementias are almost three times as great as payments for beneficiaries without these conditions, and Medicaid payments are more than 22 times as great. Total payments in 2023 for health care, long-term care and hospice services for people age 65 and older with dementia are estimated to be $345 billion. The Special Report examines whether there will be sufficient numbers of physician specialists to provide Alzheimer's care and treatment now that two drugs are available that change the underlying biology of Alzheimer's disease.

Cdk5 mediates rotational force-induced brain injury

Millions of traumatic brain injuries (TBIs) occur annually. TBIs commonly result from falls, traffic accidents, and sports-related injuries, all of which involve rotational acceleration/deceleration of the brain. During these injuries, the brain endures a multitude of primary insults including compression of brain tissue, damaged vasculature, and diffuse axonal injury. All of these deleterious effects can contribute to secondary brain ischemia, cellular death, and neuroinflammation that progress for weeks, months, and lifetime after injury. While the linear effects of head trauma have been extensively modeled, less is known about how rotational injuries mediate neuronal damage following injury. Here, we developed a new model of repetitive rotational head trauma in rodents and demonstrated acute and prolonged pathological, behavioral, and electrophysiological effects of rotational TBI (rTBI). We identify aberrant Cyclin-dependent kinase 5 (Cdk5) activity as a principal mediator of rTBI. We utilized Cdk5-enriched phosphoproteomics to uncover potential downstream mediators of rTBI and show pharmacological inhibition of Cdk5 reduces the cognitive and pathological consequences of injury. These studies contribute meaningfully to our understanding of the mechanisms of rTBI and how they may be effectively treated.

Is dementia more likely following traumatic brain injury? A systematic review

BACKGROUND

The association between traumatic brain injury (TBI) and dementia is controversial, and of growing importance considering the ageing demography of TBI.

OBJECTIVE

To review the scope and quality of the existing literature investigating the relationship between TBI and dementia.

METHODS

We conducted a systematic review following PRISMA guidelines. Studies that compared TBI exposure and dementia risk were included. Studies were formally assessed for quality with a validated quality-assessment tool.

RESULTS

44 studies were included in the final analysis. 75% (n = 33) were cohort studies and data collection was predominantly retrospective (n = 30, 66.7%). 25 studies (56.8%) found a positive relationship between TBI and dementia. Clearly defined and valid measures of assessing TBI history were lacking (case-control studies-88.9%, cohort studies-52.9%). Most studies failed to justify a sample size (case-control studies-77.8%, cohort studies-91.2%), blind assessors to exposure (case-control-66.7%) or blind assessors to exposure status (cohort-3.00%). Studies that identified a relationship between TBI and dementia had a longer median follow-up time (120 months vs 48 months, p = 0.022) and were more likely to use validated TBI definitions (p = 0.01). Studies which clearly defined TBI exposure (p = 0.013) and accounted for TBI severity (p = 0.036) were also more likely to identify an association between TBI and dementia. There was no consensus method by which studies diagnosed dementia and neuropathological confirmation was only available in 15.5% of studies.

CONCLUSIONS

Our review suggests a relationship between TBI and dementia, but we are unable to predict the risk of dementia for an individual following TBI. Our conclusions are limited by heterogeneity in both exposure and outcome reporting and by poor study quality. Future studies should; (a) use validated methods to define TBI, accounting for TBI severity; (b) follow consensus agreement on criteria for dementia diagnosis; and (c) undertake follow-up that is both longitudinal, to determine if there is a progressive neurodegenerative change or static post-traumatic deficit, and of sufficient duration.

Traumatic Brain Injury Associates with an Earlier Onset in Sporadic Frontotemporal Dementia

BACKGROUND

Currently, there are few studies considering possible modifiable risk factors of frontotemporal dementia (FTD).

OBJECTIVE

In this retrospective case-control study, we evaluated whether a history of traumatic brain injury (TBI) associates with a diagnosis of FTD or modulates the clinical phenotype or onset age in FTD patients.

METHODS

We compared the prevalence of prior TBI between individuals with FTD (N = 218) and age and sex-matched AD patients (N = 214) or healthy controls (HC; N = 100). Based on the patient records, an individual was categorized to the TBI+ group if they were reported to have suffered from TBI during lifetime. The possible associations of TBI with age of onset and disease duration were also evaluated in the whole FTD patient group or separately in the sporadic and genetic FTD groups.

RESULTS

The prevalence of previous TBI was the highest in the FTD group (19.3%) when compared to the AD group (13.1%, p = 0.050) or HC group (12%, p = 0.108, not significant). Preceding TBI was more often associated with the sporadic FTD cases than the C9orf72 repeat expansion-carrying FTD cases (p = 0.003). Furthermore, comparison of the TBI+ and TBI- FTD groups indicated that previous TBI was associated with an earlier onset age in the FTD patients (B = 3.066, p = 0.010).

CONCLUSION

A preceding TBI associates especially with sporadic FTD and with earlier onset of symptoms. The results of this study suggest that TBI may be a triggering factor for the neurodegenerative processes in FTD. However, understanding the precise underlying mechanisms still needs further studies.

How Traumatic Brain Injury History Relates to Brain Health MRI Markers and Dementia Risk: Findings from the 3C Dijon Cohort

BACKGROUND

The long-term effects of traumatic brain injury (TBI) with loss of consciousness (LOC) on magnetic resonance imaging (MRI) markers of brain health and on dementia risk are still debated.

OBJECTIVE

To investigate the associations of history of TBI with LOC with incident dementia and neuroimaging markers of brain structure and small vessel disease lesions.

METHODS

The analytical sample consisted in 4,144 participants aged 65 and older who were dementia-free at baseline from the Three City -Dijon study. History of TBI with LOC was self-reported at baseline. Clinical Dementia was assessed every two to three years, up to 12 years of follow-up. A subsample of 1,675 participants <80 years old underwent a brain MRI at baseline. We investigated the associations between history of TBI with LOC and 1) incident all cause and Alzheimer's disease (AD) dementia using illness-death models, and 2) neuroimaging markers at baseline.

RESULTS

At baseline, 8.3% of the participants reported a history of TBI with LOC. In fully-adjusted models, participants with a history of TBI with LOC had no statistically significant differences in dementia risk (HR = 0.90, 95% CI = 0.60-1.36) or AD risk (HR = 1.03, 95% CI = 0.69-1.52), compared to participants without TBI history. History of TBI with LOC was associated with lower white matter volume (β= -4.58, p = 0.048), but not with other brain volumes, white matter hyperintensities volume, nor covert brain infarct.

CONCLUSION

This study did not find evidence of an association between history of TBI with LOC and dementia or AD dementia risks over 12-year follow-up, brain atrophy, or markers of small vessel disease.

Overview of the meningeal lymphatic vessels in aging and central nervous system disorders

In the aging process and central nervous system (CNS) diseases, the functions of the meningeal lymphatic vessels (MLVs) are impaired. Alterations in MLVs have been observed in aging-related neurodegenerative diseases, brain tumors, and even cerebrovascular disease. These findings reveal a new perspective on aging and CNS disorders and provide a promising therapeutic target. Additionally, recent neuropathological studies have shown that MLVs exchange soluble components between the cerebrospinal fluid (CSF) and interstitial fluid (ISF) and drain metabolites, cellular debris, misfolded proteins, and immune cells from the CSF into the deep cervical lymph nodes (dCLNs), directly connecting the brain with the peripheral circulation. Impairment and dysfunction of meningeal lymphatics can lead to the accumulation of toxic proteins in the brain, exacerbating the progression of neurological disorders. However, for many CNS diseases, the causal relationship between MLVs and neuropathological changes is not fully clear. Here, after a brief historical retrospection, we review recent discoveries about the hallmarks of MLVs and their roles in the aging and CNS diseases, as well as potential therapeutic targets for the treatment of neurologic diseases.

Consideration of sex and gender in Alzheimer's disease and related disorders from a global perspective

Sex or gender differences in the risk of Alzheimer's disease and related dementias (ADRD) differ by world region, suggesting that there are potentially modifiable risk factors for intervention. However, few epidemiological or clinical ADRD studies examine sex differences; even fewer evaluate gender in the context of ADRD risk. The goals of this perspective are to: (1) provide definitions of gender, biologic sex, and sexual orientation. and the limitations of examining these as binary variables; (2) provide an overview of what is known with regard to sex and gender differences in the risk, prevention, and diagnosis of ADRD; and (3) discuss these sex and gender differences from a global, worldwide perspective. Identifying drivers of sex and gender differences in ADRD throughout the world is a first step in developing interventions unique to each geographical and sociocultural area to reduce these inequities and to ultimately reduce global ADRD risk. HIGHLIGHTS: The burden of dementia is unevenly distributed geographically and by sex and gender. Scientific advances in genetics and biomarkers challenge beliefs that sex is binary. Discrimination against women and sex and gender minority (SGM) populations contributes to cognitive decline. Sociocultural factors lead to gender inequities in Alzheimer's disease and related dementias (ADRD) worldwide.

Linking the Amyloid, Tau, and Mitochondrial Hypotheses of Alzheimer's Disease and Identifying Promising Drug Targets

Damage or loss of brain cells and impaired neurochemistry, neurogenesis, and synaptic and nonsynaptic plasticity of the brain lead to dementia in neurodegenerative diseases, such as Alzheimer's disease (AD). Injury to synapses and neurons and accumulation of extracellular amyloid plaques and intracellular neurofibrillary tangles are considered the main morphological and neuropathological features of AD. Age, genetic and epigenetic factors, environmental stressors, and lifestyle contribute to the risk of AD onset and progression. These risk factors are associated with structural and functional changes in the brain, leading to cognitive decline. Biomarkers of AD reflect or cause specific changes in brain function, especially changes in pathways associated with neurotransmission, neuroinflammation, bioenergetics, apoptosis, and oxidative and nitrosative stress. Even in the initial stages, AD is associated with Aβ neurotoxicity, mitochondrial dysfunction, and tau neurotoxicity. The integrative amyloid-tau-mitochondrial hypothesis assumes that the primary cause of AD is the neurotoxicity of Aβ oligomers and tau oligomers, mitochondrial dysfunction, and their mutual synergy. For the development of new efficient AD drugs, targeting the elimination of neurotoxicity, mutual potentiation of effects, and unwanted protein interactions of risk factors and biomarkers (mainly Aβ oligomers, tau oligomers, and mitochondrial dysfunction) in the early stage of the disease seems promising.

Traumatic brain injury and dementia risk in male veteran older twins-Controlling for genetic and early life non-genetic factors

INTRODUCTION

This study leveraged the twin study design, which controls for shared genetic and early life exposures, to investigate the association between traumatic brain injury (TBI) and dementia.

METHODS

Members of the National Academy of Sciences-National Research Council's Twins Registry of World War II male veterans were assigned a cognitive outcome based on a multi-step assessment protocol. History of TBI was obtained via interviews.

RESULTS

Among 8302 individuals, risk of non-Alzheimer's disease (non-AD) dementia was higher in those with TBI (hazard ratio [HR] = 2.00, 95% confidence interval [CI], 0.97-4.12), than for AD (HR = 1.23, 95% CI, 0.76-2.00). To add more control of genetic and shared environmental factors, we analyzed 100 twin pairs discordant for both TBI and dementia onset, and found TBI-associated risk for non-AD dementia increased further (McNemar odds ratio = 2.70; 95% CI, 1.27-6.25).

DISCUSSION

These findings suggest that non-AD mechanisms may underlie the association between TBI and dementia, potentially providing insight into inconsistent results from prior studies.

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

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

Unraveling axonal mechanisms of traumatic brain injury

Axonal swellings (AS) are one of the neuropathological hallmark of axonal injury in several disorders from trauma to neurodegeneration. Current evidence proposes a role of perturbed Ca²⁺ homeostasis in AS formation, involving impaired axonal transport and focal distension of the axons. Mechanisms of AS formation, in particular moments following injury, however, remain unknown. Here we show that AS form independently from intra-axonal Ca²⁺ changes, which are required primarily for the persistence of AS in time. We further show that the majority of axonal proteins undergoing de/phosphorylation immediately following injury belong to the cytoskeleton. This correlates with an increase in the distance of the actin/spectrin periodic rings and with microtubule tracks remodeling within AS. Observed cytoskeletal rearrangements support axonal transport without major interruptions. Our results demonstrate that the earliest axonal response to injury consists in physiological adaptations of axonal structure to preserve function rather than in immediate pathological events signaling axonal destruction.

Neuroinflammation represents a common theme amongst genetic and environmental risk factors for Alzheimer and Parkinson diseases

Multifactorial diseases are characterized by inter-individual variation in etiology, age of onset, and penetrance. These diseases tend to be relatively common and arise from the combined action of genetic and environmental factors; however, parsing the convoluted mechanisms underlying these gene-by-environment interactions presents a significant challenge to their study and management. For neurodegenerative disorders, resolving this challenge is imperative, given the enormous health and societal burdens they impose. The mechanisms by which genetic and environmental effects may act in concert to destabilize homeostasis and elevate risk has become a major research focus in the study of common disease. Emphasis is further being placed on determining the extent to which a unifying biological principle may account for the progressively diminishing capacity of a system to buffer disease phenotypes, as risk for disease increases. Data emerging from studies of common, neurodegenerative diseases are providing insights to pragmatically connect mechanisms of genetic and environmental risk that previously seemed disparate. In this review, we discuss evidence positing inflammation as a unifying biological principle of homeostatic destabilization affecting the risk, onset, and progression of neurodegenerative diseases. Specifically, we discuss how genetic variation associated with Alzheimer disease and Parkinson disease may contribute to pro-inflammatory responses, how such underlying predisposition may be exacerbated by environmental insults, and how this common theme is being leveraged in the ongoing search for effective therapeutic interventions.

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

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

Fluid biomarkers and risk of neurodegenerative disease in retired athletes with multiple concussions: results from the International Concussion and Head Injury Research Foundation Brain health in Retired athletes Study of Ageing and Impact-Related Neurodegenerative Disease (ICHIRF-BRAIN study)

Objectives

To investigate the association and utility of blood plasma markers of neurodegeneration in a population of retired athletes self-reporting multiple concussions throughout a sporting career. It is hypothesised that this type of athletic history would cause an increased prevalence of neurodegenerative disease, as detected by biomarkers for neurodegenerative disease processes.

Methods

One hundred and fifty-nine participants were recruited (90 males, 69 females, mean age 61.3±9.13 years), including 121 participants who had retired from playing professional or semiprofessional sports and self-reported ≥1 concussion during their careers (range 1–74; mean concussions=10.7). The control group included 38 age-matched and sex-matched controls, with no history of concussion. We measured neurofilament light (NfL) and tau (neurodegeneration markers), glial fibrillar acidic protein (GFAP) (astrocytic activation marker) and 40 and 42 amino acid-long amyloid beta (Aβ40 and Aβ42) (Alzheimer-associated amyloid pathology markers) concentrations using ultrasensitive single molecule array technology.

Results

We found retired athletes reporting one or more concussions throughout an athletic career showed no significant changes in NfL, tau, GFAP and Aβ40 and Aβ42 concentrations in comparison to a control group. No correlations were found between biomarkers and number of concussions (mean=10.7). A moderate correlation was found between NfL concentration and age.

Conclusion

No difference in blood concentrations of neurodegeneration markers NfL, tau, GFAP and Aβ40 and Aβ42 was found in retired athletes with a history of concussion compared with controls. An increased prevalence of neurodegenerative diseases is not detected by biomarkers in a population self-reporting multiple concussions.

Trial registration number

ISRCTN 11312093

Alcohol Consumption and Mild Cognitive Impairment: A Mendelian Randomization Study from Rural China

Alcohol consumption has been associated with the risk of mild cognitive impairment (MCI) in observational studies. The result is inconsistent and whether the association is causal remains unknown. To examine the causal effect of alcohol consumption on MCI in rural China, this study used a cross-sectional dataset that included 1966 observations collected in rural China, of which 235 observations’ genotyping were collected. All participants accepted the MCI evaluation using Mini-Cog and were asked about the participants’ alcohol consumption behavior. The causal effect of alcohol consumption on MCI was investigated by Mendelian randomization (MR) of genetic variation in the aldehyde dehydrogenase 2 (ALDH2 rs671) gene. The risk of MCI in Chinese rural areas was 43%. Alcohol consumption was causally associated with a higher risk of MCI under MR design. Parameter estimates of drinking or not (b = 0.271, p = 0.007, 95% CI = 0.073 to 0.469), drinking frequency during the past 30 days (b = 0.016, p = 0.003, 95% CI = 0.005 to 0.027), and the weekly ethanol consumption (b = 0.132, p = 0.004, 95% CI = 0.042 to 0.223) were all positive and statistically significant at the 5% level. In conclusion, there was a high risk of MCI in rural China, and alcohol consumption was causally associated with a higher risk of MCI.