Traumatic brain injury and young onset dementia: a nationwide cohort study

Additive effects of mild head trauma, blast exposure, and aging within white matter tracts: A novel Diffusion Tensor Imaging analysis approach

Existing diffusion tensor imaging (DTI) studies of neurological injury following high-level blast exposure (hlBE) in military personnel have produced widely variable results. This is potentially due to prior studies often not considering the quantity and/or recency of hlBE, as well as co-morbidity with non-blast head trauma (nbHT). Herein, we compare commonly used DTI metrics: fractional anisotropy and mean, axial, and radial diffusivity, in Veterans with and without history of hlBE and/or nbHT. We use both the traditional method of dividing participants into 2 equally weighted groups and an alternative method wherein each participant is weighted by quantity and recency of hlBE and/or nbHT. While no differences were detected using the traditional method, the alternative method revealed diffuse and extensive changes in all DTI metrics. These effects were quantified within 43 anatomically defined white matter tracts, which identified the forceps minor, middle corpus callosum, acoustic and optic radiations, fornix, uncinate, inferior fronto-occipital and inferior longitudinal fasciculi, and cingulum, as the pathways most affected by hlBE and nbHT. Moreover, additive effects of aging were present in many of the same tracts suggesting that these neuroanatomical effects may compound with age.

A case of cognitive impairment in an ex-boxer

Chronic traumatic encephalopathy (CTE) is a neurodegenerative disease related to the long-term consequences of repetitive cranial trauma. However, the CTE clinical phenotype has yet to be clearly defined. A 63-year-old man visited the hospital due to memory impairment. He was a former boxer. He scored 23 points on the Mini-Mental State Examination (MMSE). Magnetic resonance imaging (MRI) of the brain showed mild hippocampal atrophy. Reduced perfusion is identified in the bilateral frontal and parietotemporal lobes in cerebral blood flow on single photon emission computed tomography (SPECT). From detailed history taking, neuropsychological testing and neuroimaging, our case has not only suggestive probable CTE but also comorbid Alzheimer's disease (AD). The diagnosis process of CTE is complex; therefore, detailed longitudinal history taking, neuropsychological testing and imaging were important.

Tentative Causes of Brain and Neuropsychological Alterations in Women Victims of Intimate Partner Violence

Victims of Intimate Partner Violence Against Women (IPVAW) experience neuropsychological and cerebral changes, which have been linked to several tentative causal mechanisms, including elevated cortisol levels, psychopathological disorders, traumatic brain injury (TBI), hypoxic/ischemic brain damage, and medical conditions related to IPVAW. While these mechanisms and their effects on brain function and neuropsychological health are well-documented in other clinical populations, they manifest with unique characteristics in women affected by IPVAW. Specifically, IPVAW is chronic and repeated in nature, and mechanisms are often cumulative and may interact with other comorbid conditions. Thus, in light of existing literature on neuropsychological alterations in other populations, and recognizing the distinct features in women who experience IPVAW, we propose a new theoretical model-the Neuro-IPVAW model. This framework aims to explain the complex interplay between these mechanisms and their impact on cognitive and brain health in IPVAW victims. We anticipate that this theoretical model will be valuable for enhancing our understanding of neuropsychological and brain changes related to intimate partner violence, identifying research gaps in these mechanisms, and guiding future research directions in this area.

Macular, Choroidal, and Peripapillary Perfusion Changes in Mild and Moderate Traumatic Brain Injury Using Optical Coherence Tomography and Angiography

Introduction: To compare the retinal and choroidal architecture and microvasculature between patients with mild or moderate traumatic brain injury (TBI) and controls with normal cognition using optical coherence tomography (OCT) and OCT angiography (OCTA). Methods: Patients with a documented history of TBI, and age-matched and sex-matched controls were recruited. The primary outcome measures were differences between OCT parameters, including the choroidal vascularity index, and between OCTA superficial capillary plexus metrics, including foveal avascular zone (FAZ) circularity, 3.0 mm × 3.0 mm and 6.0 mm × 6.0 mm macular vessel density and perfusion density, and 4.5 mm × 4.5 mm peripapillary capillary perfusion density and capillary flux index. Results: Sixty-seven eyes of 36 patients with TBI and 72 eyes of 36 control patients met the inclusion criteria. Twelve patients (33.3%) had a diagnosis of mild TBI without loss of consciousness (LOC), 21 (58.3%) had mild TBI with LOC, and 3 (8.3%) had moderate TBI. There was a significant reduction in FAZ circularity and in 3.0 mm × 3.0 mm macular OCTA vessel density and perfusion density in patients with TBI. In cases with TBI associated with posttraumatic stress disorder, all macular OCTA parameters were significantly reduced. There was an increase in the choroidal vascularity index across the severity of TBI; however, it was reduced in those with more than 1 TBI (P = .03). Conclusions: There was a reduction in macular perfusion in eyes of patients with mild or moderate TBI. The choroidal vascularity index helps differentiate subtle effects of more severe or mild repeated TBI. Further prospective investigation will evaluate OCT imaging and OCTA imaging as a noninvasive screening modalities to assess changes in retinal and choroidal microvasculature.

Resistance and Resilience to Alzheimer's Disease

Dementia is a significant public health crisis; the most common underlying cause of age-related cognitive decline and dementia is Alzheimer's disease neuropathologic change (ADNC). As such, there is an urgent need to identify novel therapeutic targets for the treatment and prevention of the underlying pathologic processes that contribute to the development of AD dementia. Although age is the top risk factor for dementia in general and AD specifically, these are not inevitable consequences of advanced age. Some individuals are able to live to advanced age without accumulating significant pathology (resistance to ADNC), whereas others are able to maintain cognitive function despite the presence of significant pathology (resilience to ADNC). Understanding mechanisms of resistance and resilience will inform therapeutic strategies to promote these processes to prevent or delay AD dementia. This article will highlight what is currently known about resistance and resilience to AD, including our current understanding of possible underlying mechanisms that may lead to candidate preventive and treatment interventions for this devastating neurodegenerative disease.

Perivascular Space Burden and Cerebrospinal Fluid Biomarkers in US Veterans With Blast-Related Mild Traumatic Brain Injury

Blast-related mild traumatic brain injury (mTBI) is recognized as the "signature injury" of the Iraq and Afghanistan wars. Sleep disruption, mTBI, and neuroinflammation have been individually linked to cerebral perivascular space (PVS) dilatation. Dilated PVSs are putative markers of impaired cerebrospinal fluid (CSF) and interstitial fluid exchange, which plays an important role in removing cerebral waste. The aim of this cross-sectional, retrospective study was to define associations between biomarkers of inflammation and MRI-visible PVS (MV-PVS) burden in Veterans after blast-related mTBI (blast-mTBI) and controls. The CSF and plasma inflammatory biomarker concentrations were compared between blast-mTBI and control groups and correlated with MV-PVS volume and number per white matter cm3. Multiple regression analyses were performed with inflammatory biomarkers as predictors and MV-PVS burden as the outcome. Correction for multiple comparisons was performed using the Banjamini-Hochberg method with a false discovery rate of 0.05. There were no group-wise differences in MV-PVS burden between Veterans with blast-mTBI and controls. Greater MV-PVS burden was significantly associated with higher concentrations of several proinflammatory biomarkers from CSF (i.e., eotaxin, MCP-1, IL-6, IL-8) and plasma (i.e., MCP-4, IL-13) in the blast-mTBI group only. After controlling for sleep time and symptoms of post-traumatic stress disorder, temporal MV-PVS burden remained significantly associated with higher CSF markers of inflammation in the blast-mTBI group only. These data support an association between central, rather than peripheral, neuroinflammation and MV-PVS burden in Veterans with blast-mTBI independent of sleep. Future studies should continue to explore the role of blast-mTBI related central inflammation in MV-PVS development, as well as investigate the impact of subclinical exposures on MV-PVS burden.

CSF β-Amyloid and Tau Biomarker Changes in Veterans With Mild Traumatic Brain Injury

BACKGROUND AND OBJECTIVES

Moderate-to-severe traumatic brain injuries (TBI) have been reported to increase the risk of Alzheimer disease (AD). Whether mild TBI (mTBI) in veterans confers a similar increased risk of AD is less known. This study investigated early AD changes using CSF biomarkers in veterans with blast mTBI.

METHODS

This was a cross-sectional case-control study of veterans with mTBI and non-mTBI veterans and civilians from 2 study sources. Blast-mTBI veterans had at least 1 war zone blast or combined blast/impact mTBI meeting Veterans Affairs (VA) and Department of Defense (DoD) criteria for mTBI. Non-mTBI participants had no lifetime history of TBI. All participants underwent standardized clinical and neuropsychological assessments and lumbar puncture for collection of the CSF. CSF biomarkers were measured using MesoScale Discovery assays for Aβ40 and Aβ42 and INNOTEST ELISAs for phosphorylated tau181 (p-tau181) and total tau (t-tau).

RESULTS

Our sample comprised 51 participants with mTBI and 85 non-mTBI participants with mean (SD) ages 34.0 (10.1) and 33.5 years (8.9), respectively. All participants but 1 (99%) were male. Differences in CSF AD biomarkers between mTBI and non-mTBI groups were age dependent and most pronounced at older ages (omnibus test p ≤ 0.08). At age 50 years, the mTBI group had lower mean [95% CI] CSF Aβ42 and Aβ40 than the non-mTBI group by 154 [-12 to 319] and 1864 [610-3,118] pg/mL, respectively. By contrast, CSF p-tau181 and t-tau mean levels remained relatively constant with age in participants with mTBI, while tending to be higher at older ages for the non-mTBI group. The mTBI group also demonstrated poorer cognitive performance at older ages (omnibus p < 0.08): at age 50 years, the mean TMT-B time was higher by 34 seconds [10-58] and the mean CVLT-II short-delay recall was lower by 4.2 points [1.9-6.6]. Poorer verbal memory and verbal fluency performance were associated with lower CSF Aβ42 (p ≤ 0.05) in older participants.

DISCUSSION

CSF Aβ levels decreased in middle-aged veterans with blast-related mTBI. These data suggest that chronic neuropathologic processes associated with blast mTBI share properties in common with pathogenic processes known to portend AD onset, thus raising concern that veterans with blast-related mTBI may develop a dementing disorder later in life.

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.

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.

p17/C18-ceramide-mediated mitophagy is an endogenous neuroprotective response in preclinical and clinical brain injury

Repeat concussions (or repetitive mild traumatic brain injury [rmTBI]) are complex pathological processes consisting of a primary insult and long-term secondary complications and are also a prerequisite for chronic traumatic encephalopathy (CTE). Recent evidence implies a significant role of autophagy-mediated dysfunctional mitochondrial clearance, mitophagy, in the cascade of secondary deleterious events resulting from TBI. C18-ceramide, a bioactive sphingolipid produced in response to cell stress and damage, and its synthesizing enzyme (CerS1) are precursors to selective stress-mediated mitophagy. A transporter, p17, mediates the trafficking of CerS1, induces C18-ceramide synthesis in the mitochondrial membrane, and acts as an elimination signal in cell survival. Whether p17-mediated mitophagy occurs in the brain and plays a causal role in mitochondrial quality control in secondary disease development after rmTBI are unknown. Using a novel repetitive less-than-mild TBI (rlmTBI) injury paradigm, ablation of mitochondrial p17/C18-ceramide trafficking in p17 knockout (KO) mice results in a loss of C18-ceramide-induced mitophagy, which contributes to susceptibility and recovery from long-term secondary complications associated with rlmTBI. Using a ceramide analog with lipid-selenium conjugate drug, LCL768 restored mitophagy and reduced long-term secondary complications, improving cognitive deficits in rlmTBI-induced p17KO mice. We obtained a significant reduction of p17 expression and a considerable decrease of CerS1 and C18-ceramide levels in cortical mitochondria of CTE human brains compared with age-matched control brains. These data demonstrated that p17/C18-ceramide trafficking is an endogenous neuroprotective mitochondrial stress response following rlmTBI, thus suggesting a novel prospective strategy to interrupt the CTE consequences of concussive TBI.

Changes in decision-making function in patients with subacute mild traumatic brain injury

Although awareness regarding patients with mild traumatic brain injury has increased, they have not received sufficient attention in clinics; hence, many patients still experience only partial recovery. Deficits in decision-making function are frequently experienced by these patients. Accurate identification of impairment in the early stages after brain injury is particularly crucial for timely intervention and the prevention of long-term cognitive consequences. Therefore, we investigated the changes in decision-making ability under tasks of ambiguity and risk in patients with mild traumatic brain injury with a rule-based neuropsychological paradigm. In this study, patients (n = 39) and matched healthy controls (n = 38) completed general neuropsychological background tests and decision-making tasks (Iowa Gambling Task and Game of Dice Task). We found that patients had extensive cognitive impairment in general attention, memory and information processing speed in the subacute phase, and confirmed that patients had different degrees of impairment in decision-making abilities under ambiguity and risk. Furthermore, the decline of memory and executive function may be related to decision-making dysfunction.

Plasma von Willebrand Factor Is Elevated Hyperacutely After Mild Traumatic Brain Injury

Each year in the United States, ∼2.7 million persons seek medical attention for traumatic brain injury (TBI), of which ∼85% are characterized as being mild brain injuries. Many different cell types in the brain are affected in these heterogeneous injuries, including neurons, glia, and the brain vasculature. Efforts to identify biomarkers that reflect the injury of these different cell types have been a focus of ongoing investigation. We hypothesized that von Willebrand factor (vWF) is a sensitive biomarker for acute traumatic vascular injury and correlates with symptom severity post-TBI. To address this, blood was collected from professional boxing athletes (n = 17) before and within 30 min after competition. Plasma levels of vWF and neuron-specific enolase were measured using the Meso Scale Discovery, LLC. (MSD) electrochemiluminescence array-based multi-plex format (MSD, Gaithersburg, MD). Additional symptom and outcome data from boxers and patients, such as the Rivermead symptom scores (Rivermead Post Concussion Symptoms Questionnaire [RPQ-3]), were collected. We found that, subsequent to boxing bouts, there was a 1.8-fold increase in vWF levels within 30 min of injury (p < 0.0009). Moreover, fold-change in vWF correlates moderately (r = 0.51; p = 0.03) with the number of head blows. We also found a positive correlation (r = 0.69; p = 0.002) between fold-change in vWF and self-reported post-concussive symptoms, measured by the RPQ-3. The receiver operating curve analysis of vWF plasma levels and RPQ-3 scoring yielded a sensitivity of 94.12% and a specificity of 76.5% with an area under the curve of 83% for boxers after a fight compared to the pre-bout baseline. This study suggests that vWF is a potential blood biomarker measurable in the hyperacute period after blunt mild TBI. This biomarker may prove to be useful in diagnosing and monitoring traumatic vascular injury.

Repetitive mild traumatic brain injury-induced neurodegeneration and inflammation is attenuated by acetyl-L-carnitine in a preclinical model

Repetitive mild traumatic brain injuries (rmTBI) may contribute to the development of neurodegenerative diseases through secondary injury pathways. Acetyl-L-carnitine (ALC) shows neuroprotection through anti-inflammatory effects and via regulation of neuronal synaptic plasticity by counteracting post-trauma excitotoxicity. This study aimed to investigate mechanisms implicated in the etiology of neurodegeneration in rmTBI mice treated with ALC. Adult male C57BL/6J mice were allocated to sham, rmTBI or ALC + rmTBI groups. 15 rmTBIs were administered across 23 days using a modified weight drop model. Neurological testing and spatial learning and memory assessments via the Morris Water Maze (MWM) were undertaken at 48 h and 3 months. RT-PCR analysis of the cortex and hippocampus was undertaken for MAPT, GFAP, AIF1, GRIA, CCL11, TDP43, and TNF genes. Gene expression in the cortex showed elevated mRNA levels of MAPT, TNF, and GFAP in the rmTBI group that were reduced by ALC treatment. In the hippocampus, mRNA expression was elevated for GRIA1 in the rmTBI group but not the ALC + rmTBI treatment group. ALC treatment showed protective effects against the deficits displayed in neurological testing and MWM assessment observed in the rmTBI group. While brain structures display differential vulnerability to insult as evidenced by location specific postimpact disruption of key genes, this study shows correlative mRNA neurodegeneration and functional impairment that was ameliorated by ALC treatment in several key genes. ALC may mitigate damage inflicted in the various secondary neurodegenerative cascades and contribute to functional protection following rmTBI.

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.

Aβ1-6A2V(D) peptide, effective on Aβ aggregation, inhibits tau misfolding and protects the brain after traumatic brain injury

Alzheimer's disease (AD), the leading cause of dementia in older adults, is a double proteinopathy characterized by amyloid-β (Aβ) and tau pathology. Despite enormous efforts that have been spent in the last decades to find effective therapies, late pharmacological interventions along the course of the disease, inaccurate clinical methodologies in the enrollment of patients, and inadequate biomarkers for evaluating drug efficacy have not allowed the development of an effective therapeutic strategy. The approaches followed so far for developing drugs or antibodies focused solely on targeting Aβ or tau protein. This paper explores the potential therapeutic capacity of an all-D-isomer synthetic peptide limited to the first six amino acids of the N-terminal sequence of the A2V-mutated Aβ, Aβ1-6A2V(D), that was developed following the observation of a clinical case that provided the background for its development. We first performed an in-depth biochemical characterization documenting the capacity of Aβ1-6A2V(D) to interfere with the aggregation and stability of tau protein. To tackle Aβ1-6A2V(D) in vivo effects against a neurological decline in genetically predisposed or acquired high AD risk mice, we tested its effects in triple transgenic animals harboring human PS1(M146 V), APP(SW), and MAPT(P301L) transgenes and aged wild-type mice exposed to experimental traumatic brain injury (TBI), a recognized risk factor for AD. We found that Aβ1-6A2V(D) treatment in TBI mice improved neurological outcomes and reduced blood markers of axonal damage. Exploiting the C. elegans model as a biosensor of amyloidogenic proteins' toxicity, we observed a rescue of locomotor defects in nematodes exposed to the brain homogenates from TBI mice treated with Aβ1-6A2V(D) compared to TBI controls. By this integrated approach, we demonstrate that Aβ1-6A2V(D) not only impedes tau aggregation but also favors its degradation by tissue proteases, confirming that this peptide interferes with both Aβ and tau aggregation propensity and proteotoxicity.

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.

Clinical Updates in Mild Traumatic Brain Injury (Concussion)

Traumatic brain injury (TBI) affects > 3 million people in the United States annually. Although the number of deaths related to severe TBIs has stabalized, mild TBIs, often termed concussions, are increasing. As evidence indicates that a significant proportion of these mild injuries are associated with long-lasting functional deficits that impact work performance, social integration, and may predispose to later cognitive decline, it is important that we (a) recognize these injuries, (b) identify those at highest risk of poor recovery, and (c) initiate appropriate treatments promptly. We discuss the epidemiology of TBI, the most common persistent symptoms, and treatment approaches.

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.

Evans Blue and Fluorescein Isothiocyanate-Dextran Double Labeling Reveals Precise Sequence of Vascular Leakage and Glial Responses after Exposure to Mild-Level Blast-Associated Shock Waves

Abstract Blast-induced shock waves (BSWs) are responsible for several aspects of psychiatric disorders that are collectively termed mild traumatic brain injury (mTBI). The pathophysiology of mTBI includes vascular leakage resulting from blood-brain barrier (BBB) disruption. In this study, the precise sequence of BBB breakdown was examined using an Evans blue and fluorescein isothiocyanate (FITC)-dextran double labeling technique. Evans blue solution was injected into the tail vein of male C57BL6/J mice just before and 4 h, 1 day, 3 days, and 7 days after a single BSW exposure at as low as 25-kPa peak overpressure. In contrast, the FITC-dextran solution was transcardially injected just before perfusion fixation. Differences in the labeling time-point revealed that BBB breakdown was initiated after approximately 3 h, with significant remodeling by 1 day, and continued until 7 days after BSW exposure. BBB breakdown was upregulated in three distinct regions, namely the brain surface and subsurface areas facing the skull, regions closely associated with capillaries, and the circumventricular organ and choroid plexus. These regions showed distinct responses to BSW; moreover, clusters of reactive astrocytes were closely associated with the sites of BBB breakdown. In severe cases, these reactive astrocytes recruited activated microglia. Our findings provide important insights into the pathogenesis underlying mTBI and indicate that even mild BSW exposure affects the whole brain.

Culturally Adapting Evidence on Dementia Prevention for Ethnically Diverse Communities: Lessons Learnt from co-design

OBJECTIVES

40% of dementia cases can be prevented by addressing 12 lifestyle factors. These risk factors have increased presence in ethnic minorities, yet dementia prevention messages have not reached these communities. This article investigates the experience of co-designing a dementia prevention animated film with 9 ethnic groups in Australia.

METHODS

Evidence-based recommendations were adapted through an iterative process involving workshops with a stakeholder advisory committee and nine focus groups with 104 participants from the Arabic-, Hindi-, Tamil-, Cantonese-, Mandarin-, Greek-, Italian-, Spanish-, and Vietnamese-speaking communities. Data were analyzed using the Normalization Process Theory.

RESULTS

Cultural adaptation involves consideration of the mode of delivery, imagery and tone of the resource being developed; ensuring cultural adequacy; anticipating the need of the end-users; and managing linguistic challenges associated with working across multiple languages.

CONCLUSIONS

Learnings from this co-design process offer valuable insights for researchers and program developers who work with ethnic minority groups.

CLINICAL IMPLICATIONS

• Adaptation across cultures and languages is a negotiation not a consensus building exercise• Linguistic adaptation requires consideration of the education levels, and linguistic and intergenerational preferences of community members• Co-designing across multiple languages and cultures risks "flattening out" key aspects of cultural specificity.

Neuroprotective Potential of Bacopa monnieri: Modulation of Inflammatory Signals

BACKGROUND

To date, much evidence has shown the increased interest in natural molecules and traditional herbal medicine as alternative bioactive compounds to fight many inflammatory conditions, both in relation to immunomodulation and in terms of their wound healing potential. Bacopa monnieri is a herb that is used in the Ayurvedic medicine tradition for its anti-inflammatory activity.

OBJECTIVE

In this study, we evaluate the anti-inflammatory and regenerative properties of the Bacopa monnieri extract (BME) in vitro model of neuroinflammation.

METHODS

Neuronal SH-SY5Y cells were stimulated with TNFα and IFNγ and used to evaluate the effect of BME on cell viability, cytotoxicity, cytokine gene expression, and healing rate.

RESULTS

Our results showed that BME protects against the Okadaic acid-induced cytotoxicity in SH-SY5Y cells. Moreover, in TNFα and IFNγ primed cells, BME reduces IL-1β, IL-6, COX-2, and iNOS, mitigates the mechanical trauma injury-induced damage, and accelerates the healing of wounds.

CONCLUSION

This study indicates that BME might become a promising candidate for the treatment of neuroinflammation.

Sex and gender differences in mild traumatic brain injury/concussion

The high incidence of concussions/mild traumatic brain injury and the significant number of people with persisting concussion symptoms as well as the concern for delayed, neurodegenerative effects of concussions makes them a major public health concern. There is much to learn on concussions with respect to pathophysiology as well as vulnerability and resiliency factors. The heterogeneity in outcome after a concussion warrants a more personalized approach to better understand the biological and psychosocial factors that may affect outcome. In this chapter we address biological sex and gender as they impact different aspects of concussion including incidence, risk factors and outcome. As well, this chapter will provide a more fulsome overview of intimate partner violence, an often-overlooked cause of concussion in women. Applying the sex and gender lens to concussion/mild traumatic brain injury is imperative for discovery of its pathophysiology and moving closer to treatments.

Comparison Groups Matter in Traumatic Brain Injury Research: An Example with Dementia

The association between traumatic brain injury (TBI) and risk for Alzheimer's disease and related dementias (ADRD) has been investigated in multiple studies yet reported effect sizes have varied widely. Large differences in comorbid and demographic characteristics between individuals with and without TBI could result in spurious associations between TBI and poor outcomes, even when control for confounding is attempted. Yet, inadvertent control for post-TBI exposures (e.g., psychological and physical trauma) could result in an underestimate of the effect of TBI. Choice of the unexposed or comparison group is critical to estimating total associated risk. The objective of this study was to highlight how selection of the comparison group impacts estimates of the effect of TBI on risk for ADRD. Using data on veterans aged ≥55 years obtained from the Veterans Health Administration (VA) for years 1999-2019, we compared risk of ADRD between veterans with incident TBI (n=9,440) and 1) the general population of veterans who receive care at the VA (All VA)(n=119,003); 2) veterans who received care at a VA emergency department (VA ED)(n=111,342); and 3) veterans who received care at a VA ED for non-TBI trauma (VA ED NTT)(n=65,710). In inverse probability of treatment weighted models, TBI was associated with increased risk of ADRD compared to All VA (HR 1.94; 95% CI 1.84, 2.04), VA ED (HR 1.42; 95% CI 1.35, 1.50), and VA ED NTT (HR 1.12; 95% CI 1.06, 1.18). The estimated effect of TBI on incident ADRD was strongly impacted by choice of the comparison group.

Mild Traumatic Brain Injuries and Future Risk of Developing Alzheimer’s Disease: Systematic Review and Meta-Analysis

Background: Traumatic brain injury (TBI) increases the risk of future dementia and Alzheimer’s disease (AD). However, it is unclear whether this is true for mild TBI (mTBI). Objective: To explore the association between mTBI and subsequent risk of developing AD. Method: We systematically searched four electronic databases from January 1954 to April 2020. We included studies reporting primary data and where mTBI preceded AD by≥5 years. We meta-analyzed included studies for both high quality studies and studies with a follow up of > 10 years. Result: We included 5 of the 10,435 results found. Meta-analysis found a history of mTBI increased risk of AD (pooled relative risk = 1.18, 95% CI 1.11–1.25, N = 3,149,740). The sensitivity analysis including only studies in which mTBI preceded AD by > 10 years, excluded two very large studies and resulted in wider confidence intervals (RR = 2.02, 95% CI 0.66–6.21, N = 2307). Conclusion: There is an increased risk of AD following mTBI. Our findings of increased risk even with mTBI means it cannot be assumed that mild head injuries from sports are harmless. The sensitivity analysis suggests that we cannot exclude reverse causation, and longer follow up times are needed. Implementation of policy to reduce mTBIs, including in children and sportsmen, are urgently needed. Further research is needed on the effect of frequency and age at injury of mTBIs.

Blood Biomarkers Predict Future Cognitive Decline after Military-Related Traumatic Brain Injury

BACKGROUND

Traumatic brain injury (TBI) has been associated with increased likelihood of late-life dementia; however, the mechanisms driving this relationship are elusive. Blood-based biomarkers may provide insight into these mechanisms and serve as useful prognostic indicators of cognitive recovery or decline following a TBI.

OBJECTIVE

The aim of this study was to examine blood biomarkers within one year of TBI and explore their relationship with cognitive decline.

METHODS

Service members and veterans (n=224) without injury (n=77), or with history of bodily injury (n=37), uncomplicated mild TBI (n=55), or more severe TBI (n=55), underwent a blood draw and neuropsychological assessment within one year of their injury as part of a case-control study. A subsample (n=87) completed follow-up cognitive assessment.

RESULTS

In the more severe TBI group, baseline glial fibrillary acidic protein (p=.008) and ubiquitin C-terminal hydrolase-L1 (p=.026) were associated with processing speed at baseline, and baseline ubiquitin C-terminal hydrolase-L1 predicted change in immediate (R2Δ=.244, p=.005) and delayed memory (R2Δ=.390, p=.003) over time. In the mild TBI group, higher baseline tau predicted greater negative change in perceptual reasoning (R2Δ=.188, p=.033) and executive functioning (R2Δ=.298, p=.007); higher baseline neurofilament light predicted greater negative change in perceptual reasoning (R2Δ=.211, p=.012).

CONCLUSION

Baseline ubiquitin C-terminal hydrolase-L1 strongly predicted memory decline in the more severe TBI group, while tau and neurofilament light strongly predicted decline in the mild TBI group. A panel including these biomarkers could be particularly helpful in identifying those at risk for future cognitive decline following TBI.

Cognitive Outcome 1 Year After Mild Traumatic Brain Injury: Results From the TRACK-TBI Study

BACKGROUND AND OBJECTIVES

The objectives of this study were to develop and establish concurrent validity of a clinically relevant definition of poor cognitive outcome 1 year after mild traumatic brain injury (mTBI), to compare baseline characteristics across cognitive outcome groups, and to determine whether poor 1-year cognitive outcome can be predicted by routinely available baseline clinical variables.

METHODS

Prospective cohort study included 656 participants ≥17 years of age presenting to level 1 trauma centers within 24 hours of mTBI (Glasgow Coma Scale score 13-15) and 156 demographically similar healthy controls enrolled in the Transforming Research and Clinical Knowledge in TBI (TRACK-TBI) study. Poor 1-year cognitive outcome was defined as cognitive impairment (below the ninth percentile of normative data on ≥2 cognitive tests), cognitive decline (change score [1-year score minus best 2-week or 6-month score] exceeding the 90% reliable change index on ≥2 cognitive tests), or both. Associations of poor 1-year cognitive outcome with 1-year neurobehavioral outcomes were performed to establish concurrent validity. Baseline characteristics were compared across cognitive outcome groups, and backward elimination logistic regression was used to build a prediction model.

RESULTS

Mean age of participants with mTBI was 40.2 years; 36.6% were female; 76.6% were White. Poor 1-year cognitive outcome was associated with worse 1-year functional outcome, more neurobehavioral symptoms, greater psychological distress, and lower satisfaction with life (all p < 0.05), establishing concurrent validity. At 1 year, 13.5% of participants with mTBI had a poor cognitive outcome vs 4.5% of controls (p = 0.003). In univariable analyses, poor 1-year cognitive outcome was associated with non-White race, lower education, lower income, lack of health insurance, hyperglycemia, preinjury depression, and greater injury severity (all p < 0.05). The final multivariable prediction model included education, health insurance, preinjury depression, hyperglycemia, and Rotterdam CT score ≥3 and achieved an area under the curve of 0.69 (95% CI 0.62-0.75) for the prediction of a poor 1-year cognitive outcome, with each variable associated with >2-fold increased odds of poor 1-year cognitive outcome.

DISCUSSION

Poor 1-year cognitive outcome is common, affecting 13.5% of patients with mTBI vs 4.5% of controls. These results highlight the need for better understanding of mechanisms underlying poor cognitive outcome after mTBI to inform interventions to optimize cognitive recovery.

Differential association of baseline body weight and body-weight loss with neurological deficits, histology, and death after repetitive closed head traumatic brain injury

Clinical observations indicate that body weight (BW) extremes are associated with worse outcome after traumatic brain injury (TBI); yet, it is uncertain whether the baseline BW (bBW) may affect outcome after mouse TBI. We retrospectively analyzed 129 similarly aged (9-12 weeks) male C57BL6/J mice that were subjected to repetitive closed head TBI (rTBI) using an established weight drop paradigm as well as 55 sham injured mice. We sought to determine whether the bBW as well as the post-TBI weight relative to baseline (%BW) were associated with a variety of post-rTBI outcomes, including acute model complications (skull fractures and macroscopic hemorrhage), impact seizures, return of the righting reflex (RR), the neurological severity score (NSS), post-rTBI BW-change, and 28-day mortality. In a subset of rTBI mice, we also assessed for potential associations between the bBW and %BW and performance in the novel object recognition (NOR) task and various histological outcomes at 28 days. We found no association between the bBW with acute model complications, impact seizure burden, RR, NSS, and NOR performance at 28 days, as well as cerebral microbleed burden, presence of hyperphosphorylated tau, and TDP-43 pathology after rTBI. However, a higher bBW was associated with a longer time to first impact seizure, a greater microglial activation, astrocytosis, and neuronal loss in the injured cerebral cortex at 28 days. A greater %BW-loss was associated with a shorter impact seizure-free survival, longer time to return of the righting reflex, greater neurological deficit severity as assessed by the NSS and NOR, and worse mortality. On multiple linear regression there was no independent association of the %BW-loss with neuronal loss and neuroinflammation after adjustment for the bBW. These observations indicate that the bBW and %BW-loss may be important biological variables in certain experimental mouse TBI investigations, depending on the outcome measures of interest.

Traumatic brain injury, cardiovascular disease, and risk of dementia among older US Veterans

OBJECTIVE

Traumatic brain injury (TBI) is associated with elevated rates of cardiovascular disease (CVD), and both CVD and TBI are risk factors for dementia. We investigated whether CVD and its risk factors underlie the association between TBI and dementia.

MATERIALS AND METHODS

Cox proportional hazards models among 195,416 Veterans Health Administration patients age 55+ with TBI and a non-TBI, age/sex/race-matched comparison sample.

RESULTS

Veterans +TBI were more likely to have any CVD diagnosis (24% vs 36% p = <0.001) or risk factor (83 vs. 90% p < .001) compared to -TBI. During follow-up (mean ~7 years), 12.0% of Veterans with TBI only (HR: 2.17 95% CI 2.09-2.25), and 10.3% with CVD only developed dementia (HR 1.21 95% CI 1.15-1.28), compared to 6.5% with neither. There was an additive association between TBI and CVD on dementia risk (HR 2.51, 95% CI 2.41-2.61). Among those +TBI (±CVD), risk was minimally attenuated by adjustment for CVD/CVD risk factors (unadjusted HR: 2.38, 95% CI: 2.31-2.45; adjusted HR: 2.17, 95% CI 2.10-2.23).

CONCLUSIONS

Older veterans TBI have increased prevalence of CVD/CVD risk factors. TBI and CVD had an additive statistical association, with dementia risk increased by ~2.5-fold. However, CVD accounted for little of the association between TBI and dementia. More research is needed to understand mechanisms of TBI-dementia and inform clinical guidelines post-TBI.

Traumatic brain injuries among veterans and the risk of incident dementia: A systematic review & meta-analysis

BACKGROUND

Traumatic brain injuries (TBI) among military veterans are increasingly recognized as important causes of both short and long-term neuropsychological dysfunction. However, the association between TBI and the development of dementia is controversial. This systematic review and meta-analysis sought to quantify the risks of all-cause dementia including Alzheimer's diseases and related dementias (ADRD), and to explore whether the relationships are influenced by the severity and recurrence of head injuries.

METHODS

Database searches of Medline, Embase, Ovid Healthstar, PubMed and PROSPERO were undertaken from inception to December 2020 and supplemented with grey literature searches without language restrictions. Observational cohort studies examining TBI and incident dementia among veterans were analysed using Dersimonian-Laird random-effects models.

RESULTS

Thirteen cohort studies totalling over 7.1 million observations with veterans were included. TBI was associated with an increased risk of all-cause dementia (hazard ratio [HR] = 1.95, 95% confidence interval [CI]: 1.55-2.45), vascular dementia (HR = 2.02, 95% CI: 1.46-2.80), but not Alzheimer's disease (HR = 1.30, 95% CI: 0.88-1.91). Severe and penetrating injuries were associated with a higher risk of all-cause dementia (HR = 3.35, 95% CI: 2.47-4.55) than moderate injuries (HR = 2.82, 95% CI: 1.44-5.52) and mild injuries (HR = 1.91, 95% CI: 1.30-2.80). However, the dose-response relationship was attenuated when additional studies with sufficient data to classify trauma severity were included.

CONCLUSION

TBI is a significant risk factor for incident all-cause dementia and vascular dementia. These results need to be interpreted cautiously in the presence of significant heterogeneity.

Pathogenic cis p-tau levels in CSF reflects severity of traumatic brain injury

Traumatic brain injury (TBI) is the main cause of death and disability among young people. Following TBI, immune system activation and cytokine release induce kinase activity and hyperphosphorylation of tau protein, a structural molecule in axonal microtubules. The cis configuration of phosphorylated tau at Th231 is extremely neurotoxic and is having a prion nature, spreads to brain areas as well as CSF.We examined the cerebrospinal fluid (CSF) cis p-tau levels in 32 TBI patients and 5 non-TBI controls to find out the correlation with TBI severity.   CSF samples were drained 5-7 days after TBI and subjected for ELISA analysis with anti cis p-tau and β-amyloid antibodies.We had no patients with mild TBI, two patients with moderate (6.2%), 23 patients with severe (71.9%), and 7 patients with critical TBI (21.9%). While mean CSF β-amyloid in TBI and control groups did not show a statistically significant difference, the mean CSF cis p-tau level was significantly higher in the TBI group than the control samples. Also, intergroup analysis demonstrated that CSF cis p-tau levels were statistically different according to the head injury severity.Although CSF cis p-tau increased in the TBI patients, β-amyloid did not show a significant difference between patients and controls. Also, we observed an obvious negative correlation between CSF cis p-tau levels and GCS scores. Therefore, future researches on suppression of cis P-tau production or removing previously produced cis P-tau could be a suitable approach in treating TBI in order to prevent tauopathies and future neurodegeneration.

Traumatic Brain Injury and Risk of Alzheimer's Disease and Related Dementias in the Population

BACKGROUND

Epidemiological studies examining associations between traumatic brain injury (TBI) and Alzheimer's disease and related dementias (ADRD) have yielded conflicting results, which may be due to methodological differences.

OBJECTIVE

To examine the relationship between the presence and severity of TBI and risk of ADRD using a population-based cohort with medical record abstraction for confirmation of TBI and ADRD.

METHODS

All TBI events among Olmsted County, Minnesota residents aged > 40 years from 1985-1999 were confirmed by manual review and classified by severity. Each TBI case was randomly matched to two age-, sex-, and non-head injury population-based referents without TBI. For TBI events with non-head trauma, the Trauma Mortality Prediction Model was applied to assign an overall measure of non-head injury severity and corresponding referents were matched on this variable. Medical records were manually abstracted to confirm ADRD diagnosis. Cox proportional hazards models examined the relationship between TBI and severity with risk of ADRD.

RESULTS

A total of 1,418 residents had a confirmed TBI (865 Possible, 450 Probable, and 103 Definite) and were matched to 2,836 referents. When combining all TBI severities, the risk of any ADRD was significantly higher for those with a confirmed TBI compared to referents (HR = 1.32, 95% CI: 1.11, 1.58). Stratifying by TBI severity, Probable (HR = 1.42, 95% CI: 1.05, 1.92) and Possible (HR = 1.29, 95% CI: 1.02-1.62) TBI was associated with an increased risk of ADRD, but not Definite TBI (HR = 1.22, 95% CI: 0.68, 2.18).

CONCLUSION

Our analyses support including TBI as a potential risk factor for developing ADRD.

Post-Traumatic Stress Disorder Symptoms Are Related to Cognition after Complicated Mild and Moderate Traumatic Brain Injury but Not Severe and Penetrating Traumatic Brain Injury

Although post-traumatic stress disorder (PTSD) has been associated with worse cognitive outcomes after mild traumatic brain injury (TBI), its impact has not been evaluated after more severe TBI. This study aimed to determine whether PTSD symptoms are related to cognition after complicated mild, moderate, severe, and penetrating TBI. Service members (n = 137) with a history of complicated mild/moderate TBI (n = 64) or severe/penetrating TBI (n = 73) were prospectively enrolled from United States Military Treatment Facilities. Participants completed a neuropsychological assessment one year or more post-injury. Six neuropsychological composite scores and an overall test battery mean (OTBM) were considered. Participants were excluded if there was evidence of invalid responding. Hierarchical linear regressions were conducted evaluating neuropsychological performance. The interaction between TBI severity and PTSD Checklist-Civilian version total score was significant for processing speed (β = 0.208, p = 0.034) and delayed memory (β = 0.239, p = 0.021) and trended toward significance for immediate memory (β = 0.190, p = 0.057) and the OTBM (β = 0.181, p = 0.063). For each of these composite scores, the relationship between PTSD symptoms and cognition was stronger in the complicated mild/moderate TBI group than the severe/penetrating TBI group. Within the severe/penetrating TBI group, PTSD symptoms were unrelated to cognitive performance. In contrast, within the complicated mild/moderate TBI group, PTSD symptoms were significantly related to processing speed (R²Δ = 0.077, β = -0.280, p = 0.019), immediate memory (R²Δ = 0.197, β = -0.448, p < 0.001), delayed memory (R²Δ = 0.176, β = -0.423, p < 0.001), executive functioning (R²Δ = 0.100, β = -0.317, p = 0.008), and the OTBM (R²Δ = 0.162, β = -0.405, p < 0.001). The potential impact of PTSD symptoms on cognition, over and above the impact of brain injury alone, should be considered with service members and veterans with a history of complicated mild/moderate TBI. In addition, in research comparing cognitive outcomes between patients with histories of complicated-mild, moderate, severe, and/or penetrating TBI, it will be important to account for PTSD symptoms.

Effects of physical impairments on fitness correlates of the white-footed mouse, Peromyscus leucopus

Physical impairments are widely assumed to reduce the viability of individual animals, but their impacts on individuals within natural populations of vertebrates are rarely quantified. By monitoring wild populations of white-footed mice over 26 years, we assessed whether missing or deformed limbs, tail or eyes influenced the survival, body mass, movement and ectoparasite burden of their bearers. Of the 27 244 individuals monitored, 543 (2%) had visible physical impairments. Persistence times (survival) were similar between mice with and without impairments. Mice with eye and tail impairments had 5% and 6% greater mass, respectively, than unimpaired mice. Mice with tail impairments had larger home ranges than did unimpaired mice. Burdens of black-legged ticks (Ixodes scapularis) were higher among mice with tail and limb impairments while burdens of bot fly larvae (Cuterebra) were higher among mice with cataracts compared to mice without impairments. Our findings do not support the presupposition that physical impairments reduce viability in their bearers and are inconsistent with the devaluation of impaired individuals that pervaded early thinking in evolutionary biology.

Mechanical Stretching-Induced Traumatic Brain Injury Is Mediated by the Formation of GSK-3β-Tau Complex to Impair Insulin Signaling Transduction

Traumatic brain injury confers a significant and growing public health burden. It is a major environmental risk factor for dementia. Nonetheless, the mechanism by which primary mechanical injury leads to neurodegeneration and an increased risk of dementia-related diseases is unclear. Thus, we aimed to investigate the effect of stretching on SH-SY5Y neuroblastoma cells that proliferate in vitro. These cells retain the dopamine-β-hydroxylase activity, thus being suitable for neuromechanistic studies. SH-SY5Y cells were cultured on stretchable membranes. The culture conditions contained two groups, namely non-stretched (control) and stretched. They were subjected to cyclic stretching (6 and 24 h) and 25% elongation at 1 Hz. Following stretching at 25% and 1 Hz for 6 h, the mechanical injury changed the mitochondrial membrane potential and triggered oxidative DNA damage at 24 h. Stretching decreased the level of brain-derived neurotrophic factors and increased amyloid-β, thus indicating neuronal stress. Moreover, the mechanical injury downregulated the insulin pathway and upregulated glycogen synthase kinase 3β (GSK-3β)^S9/p-Tau protein levels, which caused a neuronal injury. Following 6 and 24 h of stretching, GSK-3β^S9 was directly bound to p-Tau^S396. In contrast, the neuronal injury was improved using GSK-3β inhibitor TWS119, which downregulated amyloid-β/p-Taus396 phosphorylation by enhancing ERK1/2T202/Y204 and AktS473 phosphorylation. Our findings imply that the neurons were under stress and that the inactivation of the GSK3β could alleviate this defect.

Dementia in military and veteran populations: a review of risk factors-traumatic brain injury, post-traumatic stress disorder, deployment, and sleep

The military population face a unique set of risk factors that may increase the risk of being diagnosed with dementia. Traumatic brain injury (TBI) and post-traumatic stress disorder (PTSD) have a higher prevalence in this group in comparison to the civilian population. By delving into the individual relationships between TBI and dementia, and PTSD and dementia, we are able to better explore dementia in the military and veteran populations. While there are some inconsistencies in results, the TBI-dementia association has become more widely accepted. Moderate-to-severe TBI has been found to increase the risk of being diagnosed with Alzheimer's disease. A correlation between PTSD and dementia has been established, however, whether or not it is a causal relationship remains unclear. Factors such as blast, combat and chemical exposure may occur during a deployment, along with TBI and/or PTSD diagnosis, and can impact the risk of dementia. However, there is a lack of literature exploring the direct effects of deployment on dementia risk. Sleep problems have been observed to occur in those following TBI, PTSD and deployment. Poor sleep has been associated with possible dementia risk. Although limited studies have focused on the link between sleep and dementia in military and veteran populations, sleep is a valuable factor to study due to its association and interconnection with other military/veteran factors. This review aims to inform of various risk factors to the cognitive health of military members and veterans: TBI, PTSD, deployment, and sleep.

Cerebrospinal Fluid MicroRNA Changes in Cognitively Normal Veterans With a History of Deployment-Associated Mild Traumatic Brain Injury

A history of traumatic brain injury (TBI) increases the odds of developing Alzheimer's disease (AD). The long latent period between injury and dementia makes it difficult to study molecular changes initiated by TBI that may increase the risk of developing AD. MicroRNA (miRNA) levels are altered in TBI at acute times post-injury (<4 weeks), and in AD. We hypothesized that miRNA levels in cerebrospinal fluid (CSF) following TBI in veterans may be indicative of increased risk for developing AD. Our population of interest is cognitively normal veterans with a history of one or more mild TBI (mTBI) at a chronic time following TBI. We measured miRNA levels in CSF from three groups of participants: (1) community controls with no lifetime history of TBI (ComC); (2) deployed Iraq/Afghanistan veterans with no lifetime history of TBI (DepC), and (3) deployed Iraq/Afghanistan veterans with a history of repetitive blast mTBI (DepTBI). CSF samples were collected at the baseline visit in a longitudinal, multimodal assessment of Gulf War veterans, and represent a heterogenous group of male veterans and community controls. The average time since the last blast mTBI experienced was 4.7 ± 2.2 years [1.5 - 11.5]. Statistical analysis of TaqMan^TM miRNA array data revealed 18 miRNAs with significant differential expression in the group comparisons: 10 between DepTBI and ComC, 7 between DepC and ComC, and 8 between DepTBI and DepC. We also identified 8 miRNAs with significant differential detection in the group comparisons: 5 in DepTBI vs. ComC, 3 in DepC vs. ComC, and 2 in DepTBI vs. DepC. When we applied our previously developed multivariable dependence analysis, we found 13 miRNAs (6 of which are altered in levels or detection) that show dependencies with participant phenotypes, e.g., ApoE. Target prediction and pathway analysis with miRNAs differentially expressed in DepTBI vs. either DepC or ComC identified canonical pathways highly relevant to TBI including senescence and ephrin receptor signaling, respectively. This study shows that both TBI and deployment result in persistent changes in CSF miRNA levels that are relevant to known miRNA-mediated AD pathology, and which may reflect early events in AD.

Executive dysfunction after multiple concussions is not related to cerebrovascular dysfunction

Objective.We investigated the relation between prior concussion history and working memory (WM), self-reported cognitive symptom burden, and cerebrovascular function in adolescents and young adults (14-21 years old).Approach.We recruited 59 participants, 34 clinically diagnosed with a sports-related concussion and 25 controls. Concussed subjects were studied at baseline (within 28 days of their injury) and eight weeks after, while control subjects only had one assessment. We assessed WM (n-back task up to four-back), and neurovascular coupling (cerebrovascular responses at middle cerebral artery duringn-back tasks) using a transcranial Doppler ultrasonograph.Main results.There was no significant difference in WM between controls and concussed participants (p = 0.402). However, WM capacity was lower in those who had sustained ≥3 concussions (7.1% with WM capacity of four) compared to those with their first ever concussion (33.3%) and controls (28.0%, overallp = 0.025). At the sub-acute point (n = 24), self-reported cognitive symptom burden was mostly resolved in all but two participants. Despite the resolution of symptoms, WM performance was not different eight weeks post injury (p = 0.706). Neurovascular coupling was not different between controls and concussed participants regardless of prior concussion history.Significance. Up to 20% of concussed individuals experience covert sequelae lasting beyond the resolution of self-reported overt symptoms. How a prior history of concussion impacts the potential for sequelae is not well established, and the underlying mechanisms are unknown. Despite no alterations in neurovascular coupling, a history of prior concussion was associated with significant deficits in WM capacity, and lasted beyond self-reported cognitive symptom resolution.

Physical and Functional Impairment Among Older Adults With a History of Traumatic Brain Injury

OBJECTIVES

To examine the association of lifetime history of traumatic brain injury (TBI) with later-life physical impairment (PI) and functional impairment (FI) and to evaluate the impact of neurobehavioral symptoms that frequently co-occur with TBI on these relations.

PARTICIPANTS

A total of 1148 respondents to the 2014 Wave of the Health and Retirement Study, a nationally representative survey of older community-dwelling adults, randomly selected to participate in a TBI exposure survey. They reported no prior TBI (n = 737) or prior TBI (n = 411).

DESIGN

Cross-sectional survey study.

MAIN MEASURES

Physical impairment (self-reported difficulty with ≥1 of 8 physical activities); FI (self-reported difficulty with ≥1 of 11 activities of daily living); self-reported current neurobehavioral symptoms (pain, sleep problems, depression, subjective memory impairment); The Ohio State University TBI Identification Method (OSU-TBI-ID)-short form.

ANALYSES

Stepwise logistic regression models ([1] unadjusted; [2] adjusted for demographics and medical comorbidities; [3] additionally adjusted for neurobehavioral symptoms) compared PI and FI between TBI groups.

RESULTS

Traumatic brain injury-exposed (mean: 33.6 years postinjury) respondents were younger, less likely to be female, and reported more comorbidities and neurobehavioral symptoms. Although TBI was significantly associated with increased odds of PI and FI in unadjusted models and models adjusted for demographics/comorbidities (adjusted odds ratio, 95% confidence interval: PI 1.62, 1.21-2.17; FI 1.60, 1.20-2.14), this association was no longer statistically significant after further adjustment for neurobehavioral symptoms.

CONCLUSION

History of TBI is associated with substantial PI and FI among community-dwelling older adults. Further research is warranted to determine whether aggressive management of neurobehavioral symptoms in this population may mitigate long-term PI and FI in this population.

Association Between Traumatic Brain Injury and Dementia in Veterans: A Rapid Systematic Review

OBJECTIVE

To systematically review the prevalence of dementia in Veterans versus civilians and the association between previous traumatic brain injuries (TBIs) and the risk and timing of dementia onset in Veterans.

DESIGN

We systematically searched MEDLINE, PsycINFO, and Cochrane Central Register of Controlled Trials from database inception to October 2018. One reviewer assessed articles for inclusion, evaluated study quality, graded strength of evidence, and extracted data, with second reviewer checking.

RESULTS

Forty articles were included, among which 10 presented the best evidence. Evidence suggests that dementia rates are likely similar between Veterans and civilians (10.7% vs 8.8%-11.6%, respectively). Dementia prevalence is likely higher in those with TBI (6%-16%) than in those without (3%-10%), with a possible dose-response relationship between the two. There may also be an association between TBI and early-onset dementia, although this evidence has important limitations. No studies evaluated whether dementia prevalence varied on the basis of combat deployment history or era of conflict.

CONCLUSION

Dementia prevalence is likely similar in Veteran and civilian populations, and the risk of dementia is likely increased by TBI. To inform development of screening, prevention, and rehabilitation efforts, research is still needed addressing the mechanism of association and timing of dementia onset.

PROTOCOL

PROSPERO; CRD42018107926.

Head injury and 25-year risk of dementia

INTRODUCTION

Head injury is associated with significant morbidity and mortality. Long-term associations of head injury with dementia in community-based populations are less clear.

METHODS

Prospective cohort study of 14,376 participants (mean age 54 years at baseline, 56% female, 27% Black, 24% with head injury) enrolled in the Atherosclerosis Risk in Communities (ARIC) Study. Head injury was defined using self-report and International Classification of Diseases, Ninth/Tenth Revision (ICD-9/10) codes. Dementia was defined using cognitive assessments, informant interviews, and ICD-9/10 and death certificate codes.

RESULTS

Head injury was associated with risk of dementia (hazard ratio [HR] = 1.44, 95% confidence interval [CI] = 1.3-1.57), with evidence of dose-response (1 head injury: HR = 1.25, 95% CI = 1.13-1.39, 2+ head injuries: HR = 2.14, 95% CI = 1.86-2.46). There was evidence for stronger associations among female participants (HR = 1.69, 95% CI = 1.51-1.90) versus male participants (HR = 1.15, 95% CI = 1.00-1.32), P-for-interaction < .001, and among White participants (HR = 1.55, 95% CI = 1.40-1.72) versus Black participants (HR = 1.22, 95% CI = 1.02-1.45), P-for-interaction = .008.

DISCUSSION

In this community-based cohort with 25-year follow-up, head injury was associated with increased dementia risk in a dose-dependent manner, with stronger associations among female participants and White participants.

The Impact of Age and Severity on Dementia After Traumatic Brain Injury: A Comparison Study

BACKGROUND

Growing evidence associates traumatic brain injury (TBI) with increased risk of dementia, but few studies have evaluated associations in patients younger than 55 yr using non-TBI orthopedic trauma (NTOT) patients as controls to investigate the influence of age and TBI severity, and to identify predictors of dementia after trauma.

OBJECTIVE

To investigate the relationship between TBI and dementia in an institutional group.

METHODS

Retrospective cohort study (2000-2018) of TBI patients aged 45 to 100 yr vs NTOT controls. Primary outcome was dementia after TBI (followed ≤10 yr). Cox proportional hazards models were used to assess risk of dementia; logistic regression models assessed predictors of dementia.

RESULTS

Among 24 846 patients, TBI patients developed dementia (7.5% vs 4.6%) at a younger age (78.6 vs 82.7 yr) and demonstrated higher 10-yr mortality than controls (27% vs 14%; P < .001). Mild TBI patients had higher incidence of dementia (9%) than moderate/severe TBI (5.4%), with lower 10-yr mortality (20% vs 31%; P < .001). Risk of dementia was significant in all mild TBI age groups, even 45 to 54 yr (hazard ratio 4.1, 95% CI 2.7-7.8). A total of 10-yr cumulative incidence was higher in mild TBI (14.4%) than moderate/severe TBI (11.3%) and controls (6.8%) (P < .001). Predictors of dementia include TBI, sex, age, hypertension, hyperlipidemia, stroke, depression, anxiety, and Injury Severity Score.

CONCLUSION

Mild and moderate/severe TBI patients experienced higher incidence of dementia, even in the youngest group (45-54 yr old), than NTOT controls. All TBI patients, especially middle-aged adults with minor injury who are more likely to be overlooked, should be monitored for dementia.

Effects of head trauma and sport participation in young-onset Parkinson's disease

Head trauma (HT) is emerging as an event anticipating onset of neurodegenerative disorders. However, the potential contribution of HT in young-onset cases (YOPD, age at onset < 50) of Parkinson’s disease (PD) has not been examined yet. Here, we systematically assessed HT history in PD patients to estimate the risk associated, especially in terms of age of onset, and define the correlations with the clinical-biochemical profile. The Brain Injury Screening Questionnaire (BISQ) was administered to 94 PD patients (31 with YOPD, known monogenic forms excluded) and 70 controls. HT history was correlated with motor and non-motor scores in all patients, and to CSF biomarkers of neurodegeneration (α-synuclein, amyloid-β42, total and phosporiled-181 tau, lactate, CSF/serum albumin) into a subgroup. HT increased the risk for both PD and YOPD. In PD patients, but not in those with YOPD, the number of HTs directly correlated with CSF total-tau levels. No other correlations resulted between HT and clinical parameters. Sport-related HT was a specific risk factor for YOPD; conversely, the prolonged sporting life represented a protective factor. HTs can favor PD onset, even as YOPD. Sport-related HT resulted a risk factor for YOPD, although the longer sporting practice delayed PD onset, protecting from YOPD. Tauopathy may underlie the overall association between HT and PD. Additional mechanisms could be instead implicated in HT contribution to YOPD onset.

Traumatic brain injury fast-forwards Alzheimer's pathology: evidence from amyloid positron emission tomorgraphy imaging

PURPOSE

Traumatic brain injury (TBI) has been proposed as a risk factor for Alzheimer's disease (AD), although the mechanisms underlying the putative association are poorly understood. We investigated elderly individuals with a remote history of TBI, aiming to understand how this may have influenced amyloidosis, neurodegeneration, and clinical expression along the AD continuum.

METHODS

Total of 241 individual datasets including amyloid beta (Aβ) positron emission tomography ([¹⁸F]-AV45), structural MRI, and neuropsychological measures, were obtained from the Alzheimer's Disease Neuroimaging Initiative. The data were stratified into groups with (TBI +) or without (TBI -) history of head injury, and by clinical dementia rating (CDR) scores, into subgroups with normal cognition (CDR = 0) and those with symptomatic cognitive decline (CDR ≥ 0.5). We contrasted the TBI + and TBI - subgroups with respect to the onset age and extent of cognitive decline, cortical thickness changes, and Aβ standard uptake value (SUVr).

RESULTS

Compared to the TBI -/CDR ≥ 0.5 subgroup, the TBI + /CDR ≥ 0.5 subgroup showed a 3-4 year earlier age of cognitive impairment onset (ACIO, p = 0.005). Among those participants on the AD continuum (Aβ + , as defined by a cortical SUVr ≥ 1.23), irrespective of current CDR, a TBI + history was associated with greater Aβ deposition and more pronounced cortical thinning. When matched for severity of cognitive status, the TBI + /CDR ≥ 0.5 group showed greater Aβ burden, but earlier ACIO as compared to the TBI -/CDR ≥ 0.5, suggesting a more indolent clinical AD progression in those with TBI history.

CONCLUSION

Remote TBI history may alter the AD onset trajectory, with approximately 4 years earlier ACIO, greater amyloid deposition, and cortical thinning.

Poor sleep correlates with biomarkers of neurodegeneration in mild traumatic brain injury patients: a CENC study

STUDY OBJECTIVES

Sleep disorders affect over half of mild traumatic brain injury (mTBI) patients. Despite evidence linking sleep and neurodegeneration, longitudinal TBI-related dementia studies have not considered sleep. We hypothesized that poor sleepers with mTBI would have elevated markers of neurodegeneration and lower cognitive function compared to mTBI good sleepers and controls. Our objective was to compare biomarkers of neurodegeneration and cognitive function with sleep quality in warfighters with chronic mTBI.

METHODS

In an observational warfighters cohort (n = 138 mTBI, 44 controls), the Pittsburgh Sleep Quality Index (PSQI) was compared with plasma biomarkers of neurodegeneration and cognitive scores collected an average of 8 years after injury.

RESULTS

In the mTBI cohort, poor sleepers (PSQI ≥ 10, n = 86) had elevated plasma neurofilament light (NfL, x̅ = 11.86 vs 7.91 pg/mL, p = 0.0007, d = 0.63) and lower executive function scores by the categorical fluency (x̅ = 18.0 vs 21.0, p = 0.0005, d = -0.65) and stop-go tests (x̅ = 30.1 vs 31.1, p = 0.024, d = -0.37). These findings were not observed in controls (n = 44). PSQI predicted NfL (beta = 0.22, p = 0.00002) and tau (beta = 0.14, p = 0.007), but not amyloid β42. Poor sleepers showed higher obstructive sleep apnea (OSA) risk by STOP-BANG scores (x̅ = 3.8 vs 2.7, p = 0.0005), raising the possibility that the PSQI might be partly secondary to OSA.

CONCLUSIONS

Poor sleep is linked to neurodegeneration and select measures of executive function in mTBI patients. This supports implementation of validated sleep measures in longitudinal studies investigating pathobiological mechanisms of TBI related neurodegeneration, which could have therapeutic implications.

Brain-gut axis dysfunction in the pathogenesis of traumatic brain injury

Traumatic brain injury (TBI) is a chronic and progressive disease, and management requires an understanding of both the primary neurological injury and the secondary sequelae that affect peripheral organs, including the gastrointestinal (GI) tract. The brain-gut axis is composed of bidirectional pathways through which TBI-induced neuroinflammation and neurodegeneration impact gut function. The resulting TBI-induced dysautonomia and systemic inflammation contribute to the secondary GI events, including dysmotility and increased mucosal permeability. These effects shape, and are shaped by, changes in microbiota composition and activation of resident and recruited immune cells. Microbial products and immune cell mediators in turn modulate brain-gut activity. Importantly, secondary enteric inflammatory challenges prolong systemic inflammation and worsen TBI-induced neuropathology and neurobehavioral deficits. The importance of brain-gut communication in maintaining GI homeostasis highlights it as a viable therapeutic target for TBI. Currently, treatments directed toward dysautonomia, dysbiosis, and/or systemic inflammation offer the most promise.

SIRT2 inhibition exacerbates p53-mediated ferroptosis in mice following experimental traumatic brain injury

OBJECTIVE

Ferroptosis plays an important role in traumatic brain injury (TBI). The p53 protein is a major mediator of ferroptosis. However, the role of p53-mediated ferroptosis in TBI has not been studied. Sirtuin 2 (SIRT2) exerts a protective effects role in TBI, although the underlying mechanism of this protection remains unclear. In the present study, we tested the hypothesis that that SIRT2 mitigates TBI by regulating p53-mediated ferroptosis.

METHODS AND RESULTS

To model TBI in mice, we used the controlled cortical impact (CCI) injury method. We found that ferroptosis was significantly activated by CCI, and peaked 3 days following CCI, as evidenced by upregulation of GPX4 and SLC7A11, increased content of decreases glutathione, lipid peroxidation, malondialdehyde and ferrous ion. Inhibition of ferroptosis significantly alleviated neurological indications and brain edema. In addition, knockout of p53 significantly blocked ferroptosis following CCI. Furthermore, we found that inhibition of SIRT2 upregulated the acetylation of p53, as well as p53 expression, and exacerbated ferroptosis following CCI. Interestingly, knockout of p53 rescued the SIRT2 inhibition-induced exacerbation of ferroptosis.

CONCLUSIONS

These findings indicate that p53-mediated ferroptosis contributes to the pathogenesis of TBI. Furthermore, we demonstrate that SIRT2 exerts a neuroprotective effect against TBI by suppressing p53-mediated ferroptosis.