Imaging blood-brain barrier dysfunction in football players

Restoration of blood brain barrier integrity post neurosurgical resection in drug resistant epilepsy

Surgery for temporal lobe epilepsy (TLE) is a well-recognised therapy for drug resistant seizures which occur in more than 50 % of patients with TLE. Blood-brain barrier (BBB) dysfunction is commonly observed in resected brain tissue from patients with treatment resistant epilepsy however, no studies have documented the recovery of BBB function following surgery. We firstly prospectively performed dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) on seven patients scheduled for temporal lobe resections before and after resection. DCE-MRI revealed BBB dysfunction in frontal and temporal brain regions. At 6-24 months post-resection, there was a reduction in the percentage of brain volume with BBB dysfunction in 5/7 patients. We then retrospectively characterised resected brain tissue from 6 further TLE cases (total n = 13) by q-RT-PCR and immunohistochemistry which revealed region-specific changes in markers of BBB integrity and inflammation with changes in CLDN12 and TJP1/2 in the hippocampus and CSF1R pathway genes in cortical and hippocampal tissue. BBB dysfunction is a key component of the molecular disruption caused by seizures and in longstanding early onset chronic epilepsy that is refractory to treatment. Here, we demonstrate for the first time the rescue of BBB dysfunction by controlling seizures after surgery.

Traumatic Brain Injury and Chronic Traumatic Encephalopathy: Not Only Trigger for Neurodegeneration but Also for Cerebral Amyloid Angiopathy?

Traumatic brain injury (TBI) has been linked to the development of neurodegenerative diseases, particularly Alzheimer's disease (AD) and chronic traumatic encephalopathy (CTE). This review critically assesses the relationship between TBI and cerebral amyloid angiopathy (CAA), highlighting the complexities of diagnosing CAA in the context of prior head trauma. While TBI has been shown to facilitate the accumulation of amyloid plaques and tau pathology, the interplay between neurodegenerative processes and vascular contributions remains underexplored. Epidemiological studies indicate that TBI increases the risk of various dementias, not solely AD, emphasizing the need for a comprehensive understanding of TBI-related neurodegeneration as a polypathological condition. This review further delineates the mechanisms by which TBI can lead to CAA, particularly focusing on the vascular changes that occur post-injury. It discusses the challenges associated with diagnosing CAA after TBI, particularly due to the overlapping symptoms and pathologies that complicate clinical evaluations. Notably, this review includes a clinical case that exemplifies the diagnostic challenges posed by TBI in patients with subsequent cognitive decline and vascular pathology. By synthesizing current research on TBI, CAA, and associated neurodegenerative conditions, this review aims to foster a more nuanced understanding of how these conditions interact and contribute to long-term cognitive outcomes. The findings underscore the importance of developing standardized diagnostic criteria and imaging techniques to better elucidate the relationship between TBI and vascular pathology, which could enhance clinical interventions and inform therapeutic strategies for affected individuals.

Imaging blood-brain barrier dysfunction in drug-resistant epilepsy: A multi-center feasibility study

OBJECTIVE

Blood-brain barrier dysfunction (BBBD) has been linked to various neurological disorders, including epilepsy. This study aims to utilize dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) to identify and compare brain regions with BBBD in patients with epilepsy (PWE) and healthy individuals.

METHODS

We scanned 50 drug-resistant epilepsy (DRE) patients and 58 control participants from four global specialized epilepsy centers using DCE-MRI. The presence and extent of BBBD were analyzed and compared between PWE and healthy controls.

RESULTS

Both greater brain volume and higher number of brain regions with BBBD were significantly present in PWE compared to healthy controls (p < 10-7). No differences in total brain volume with BBBD were observed in patients diagnosed with either focal seizures or generalized epilepsy, despite variations in the affected regions. Overall brain volume with BBBD did not differ in PWE with MRI-visible lesions compared with non-lesional cases. BBBD was observed in brain regions suspected to be related to the onset of seizures in 82% of patients (n = 39) and was typically identified in, adjacent to, and/or in the same hemisphere as the suspected epileptogenic lesion (n = 10).

SIGNIFICANCE

These findings are consistent with pre-clinical studies that highlight the role of BBBD in the development of DRE and identify microvascular stabilization as a potential therapeutic strategy.

The neuropathological basis of elevated serum neurofilament light following experimental concussion

Mild traumatic brain injury (mTBI) or concussion is a substantial health problem globally, with up to 15% of patients experiencing persisting symptoms that can significantly impact quality of life. Currently, the diagnosis of mTBI relies on clinical presentation with ancillary neuroimaging to exclude more severe forms of injury. However, identifying patients at risk for a poor outcome or protracted recovery is challenging, in part due to the lack of early objective tests that reflect the relevant underlying pathology. While the pathophysiology of mTBI is poorly understood, axonal damage caused by rotational forces is now recognized as an important consequence of injury. Moreover, serum measurement of the neurofilament light (NfL) protein has emerged as a potentially promising biomarker of injury. Understanding the pathological processes that determine serum NfL dynamics over time, and the ability of NfL to reflect underlying pathology will be critical for future clinical research aimed at reducing the burden of disability after mild TBI. Using a gyrencephalic model of head rotational acceleration scaled to human concussion, we demonstrate significant elevations in serum NfL, with a peak at 3 days post-injury. Moreover, increased serum NfL was detectable out to 2 weeks post-injury, with some evidence it follows a biphasic course. Subsequent quantitative histological examinations demonstrate that axonal pathology, including in the absence of neuronal somatic degeneration, was the likely source of elevated serum NfL. However, the extent of axonal pathology quantified via multiple markers did not correlate strongly with the extent of serum NfL. Interestingly, the extent of blood-brain barrier (BBB) permeability offered more robust correlations with serum NfL measured at multiple time points, suggesting BBB disruption is an important determinant of serum biomarker dynamics after mTBI. These data provide novel insights to the temporal course and pathological basis of serum NfL measurements that inform its utility as a biomarker in mTBI.

Blood-brain barrier dysfunction and decreased transcription of tight junction proteins in epileptic dogs

BACKGROUND

Epilepsy in dogs and humans is associated with blood-brain barrier (BBB) dysfunction (BBBD), which may involve dysfunction of tight junction (TJ) proteins, matrix metalloproteases, and astrocytes. Imaging techniques to assess BBB integrity, to identify potential treatment strategies, have not yet been evaluated in veterinary medicine.

HYPOTHESIS

Some dogs with idiopathic epilepsy (IE) will exhibit BBBD. Identifying BBBD may improve antiepileptic treatment in the future.

ANIMALS

Twenty-seven dogs with IE and 10 healthy controls.

METHODS

Retrospective, prospective cohort study. Blood-brain barrier permeability (BBBP) scores were calculated for the whole brain and piriform lobe of all dogs by using dynamic contrast enhancement (DCE) magnetic resonance imaging (MRI) and subtraction enhancement analysis (SEA). Matrix metalloproteinase-9 (MMP9) activity in serum and cerebrospinal fluid (CSF) was measured and its expression in the piriform lobe was examined using immunofluorescent staining. Gene expression of TJ proteins and astrocytic transporters was analyzed in the piriform lobe.

RESULTS

The DCE-MRI analysis of the piriform lobe identified higher BBBP score in the IE group when compared with controls (34.5% vs 26.5%; P = .02). Activity and expression of MMP9 were increased in the serum, CSF, and piriform lobe of IE dogs as compared with controls. Gene expression of Kir4.1 and claudin-5 in the piriform lobe of IE dogs was significantly lower than in control dogs.

CONCLUSIONS AND CLINICAL IMPORTANCE

Our findings demonstrate BBBD in dogs with IE and were supported by increased MMP9 activity and downregulation of astrocytic potassium channels and some TJ proteins. Blood brain barrier dysfunction may be a novel antiepileptic therapy target.

From spreading depolarization to blood-brain barrier dysfunction: navigating traumatic brain injury for novel diagnosis and therapy

Considerable strides in medical interventions during the acute phase of traumatic brain injury (TBI) have brought improved overall survival rates. However, following TBI, people often face ongoing, persistent and debilitating long-term complications. Here, we review the recent literature to propose possible mechanisms that lead from TBI to long-term complications, focusing particularly on the involvement of a compromised blood-brain barrier (BBB). We discuss evidence for the role of spreading depolarization as a key pathological mechanism associated with microvascular dysfunction and the transformation of astrocytes to an inflammatory phenotype. Finally, we summarize new predictive and diagnostic biomarkers and explore potential therapeutic targets for treating long-term complications of TBI.

Targeting of nanoparticles to the cerebral vasculature after traumatic brain injury

Traumatic brain injury has faced numerous challenges in drug development, primarily due to the difficulty of effectively delivering drugs to the brain. However, there is a potential solution in targeted drug delivery methods involving antibody-drug conjugates or nanocarriers conjugated with targeting antibodies. Following a TBI, the blood-brain barrier (BBB) becomes permeable, which can last for years and allow the leakage of harmful plasma proteins. Consequently, an appealing approach for TBI treatment involves using drug delivery systems that utilize targeting antibodies and nanocarriers to help restore BBB integrity. In our investigation of this strategy, we examined the efficacy of free antibodies and nanocarriers targeting a specific endothelial surface marker called vascular cell adhesion molecule-1 (VCAM-1), which is known to be upregulated during inflammation. In a mouse model of TBI utilizing central fluid percussion injury, free VCAM-1 antibody did not demonstrate superior targeting when comparing sham vs. TBI brain. However, the administration of VCAM-1-targeted nanocarriers (liposomes) exhibited a 10-fold higher targeting specificity in TBI brain than in sham control. Flow cytometry and confocal microscopy analysis confirmed that VCAM-1 liposomes were primarily taken up by brain endothelial cells post-TBI. Consequently, VCAM-1 liposomes represent a promising platform for the targeted delivery of therapeutics to the brain following traumatic brain injury.

Effect of Repetitive Head Impacts on Saccade Performance in Canadian University Football Players

OBJECTIVE

Investigate the effect of cumulative head impacts on saccade latency and errors, measured across two successive football seasons.

DESIGN

Participants were acquired from a sample of convenience-one Canadian university football team. Head impacts were collected during training camp, practices, eight regular season games, and four playoff games in each season. Saccade measurements were collected at five time points-before and after training camp, at midseason, after regular season, and after playoffs.

SETTING

Two seasons following players from a single USports football team during practices and games.

PARTICIPANTS

Players who completed a baseline saccade measurement and a minimum of one follow-up measurement were included in the study. A total of 127 players were monitored across two competitive seasons, including 61 players who participated in both seasons.

INDEPENDENT VARIABLES

Head impact measurements were collected using helmet-mounted sensors.

MAIN OUTCOME MEASURES

Saccade latency and number of errors were measured using high-speed video or electro-oculography.

RESULTS

On average, each head impact increased prosaccade latency by 5.16 × 10 -3 ms (95% confidence interval [CI], 2.26 × 10 -4 -1.00 × 10 -2 , P = 0.03) and antisaccade latency by 5.74 × 10 -3 ms (95% CI, 7.18 × 10 -4 -1.06 × 10 -2 , P = 0.02). These latency increases did not decrease between the two seasons; in fact, prosaccade latencies were 23.20 ms longer (95% CI, 19.40-27.14, P < 0.001) at the second season's baseline measurement than the first. The number of saccade errors was not affected by cumulative head impacts.

CONCLUSIONS

Repetitive head impacts in Canadian university football result in cumulative declines in brain function as measured by saccade performance.

CLINICAL RELEVANCE

Football organizations should consider implementing policies focused on reducing head impacts to improve player safety.

Blood-brain barrier disruption and sustained systemic inflammation in individuals with long COVID-associated cognitive impairment

Vascular disruption has been implicated in coronavirus disease 2019 (COVID-19) pathogenesis and may predispose to the neurological sequelae associated with long COVID, yet it is unclear how blood-brain barrier (BBB) function is affected in these conditions. Here we show that BBB disruption is evident during acute infection and in patients with long COVID with cognitive impairment, commonly referred to as brain fog. Using dynamic contrast-enhanced magnetic resonance imaging, we show BBB disruption in patients with long COVID-associated brain fog. Transcriptomic analysis of peripheral blood mononuclear cells revealed dysregulation of the coagulation system and a dampened adaptive immune response in individuals with brain fog. Accordingly, peripheral blood mononuclear cells showed increased adhesion to human brain endothelial cells in vitro, while exposure of brain endothelial cells to serum from patients with long COVID induced expression of inflammatory markers. Together, our data suggest that sustained systemic inflammation and persistent localized BBB dysfunction is a key feature of long COVID-associated brain fog.

Blood-Brain Barrier Dysfunction and Exposure to Head Impacts in University Football Players

OBJECTIVE

To investigate the link between dysfunction of the blood-brain barrier (BBB) and exposure to head impacts in concussed football athletes.

DESIGN

This was a prospective, observational pilot study.

SETTING

Canadian university football.

PARTICIPANTS

The study population consisted of 60 university football players, aged 18 to 25. Athletes who sustained a clinically diagnosed concussion over the course of a single football season were invited to undergo an assessment of BBB leakage.

INDEPENDENT VARIABLES

Head impacts detected using impact-sensing helmets were the measured variables.

MAIN OUTCOME MEASURES

Clinical diagnosis of concussion and BBB leakage assessed using dynamic contrast-enhanced MRI (DCE-MRI) within 1 week of concussion were the outcome measures.

RESULTS

Eight athletes were diagnosed with a concussion throughout the season. These athletes sustained a significantly higher number of head impacts than nonconcussed athletes. Athletes playing in the defensive back position were significantly more likely to sustain a concussion than remain concussion free. Five of the concussed athletes underwent an assessment of BBB leakage. Logistic regression analysis indicated that region-specific BBB leakage in these 5 athletes was best predicted by impacts sustained in all games and practices leading up to the concussion-as opposed to the last preconcussion impact or the impacts sustained during the game when concussion occurred.

CONCLUSIONS

These preliminary findings raise the potential for the hypothesis that repeated exposure to head impacts may contribute to the development of BBB pathology. Further research is needed to validate this hypothesis and to test whether BBB pathology plays a role in the sequela of repeated head trauma.

Memantine inhibits cortical spreading depolarization and improves neurovascular function following repetitive traumatic brain injury

Cortical spreading depolarization (CSD) is a promising target for neuroprotective therapy in traumatic brain injury (TBI). We explored the effect of NMDA receptor antagonism on electrically triggered CSDs in healthy and brain-injured animals. Rats received either one moderate or four daily repetitive mild closed head impacts (rmTBI). Ninety-three animals underwent craniectomy with electrocorticographic (ECoG) and local blood flow monitoring. In brain-injured animals, ketamine or memantine inhibited CSDs in 44 to 88% and 50 to 67% of cases, respectively. Near-DC/AC-ECoG amplitude was reduced by 44 to 75% and 52 to 67%, and duration by 39 to 87% and 61 to 78%, respectively. Daily memantine significantly reduced spreading depression and oligemia following CSD. Animals (N = 31) were randomized to either memantine (10 mg/kg) or saline with daily neurobehavioral testing. Memantine-treated animals had higher neurological scores. We demonstrate that memantine improved neurovascular function following CSD in sham and brain-injured animals. Memantine also prevented neurological decline in a blinded, preclinical randomized rmTBI trial.

Neuropathologic and Clinical Findings in Young Contact Sport Athletes Exposed to Repetitive Head Impacts

Importance

Young contact sport athletes may be at risk for long-term neuropathologic disorders, including chronic traumatic encephalopathy (CTE).

Objective

To characterize the neuropathologic and clinical symptoms of young brain donors who were contact sport athletes.

Design, Setting, and Participants

This case series analyzes findings from 152 of 156 brain donors younger than 30 years identified through the Understanding Neurologic Injury and Traumatic Encephalopathy (UNITE) Brain Bank who donated their brains from February 1, 2008, to September 31, 2022. Neuropathologic evaluations, retrospective telephone clinical assessments, and online questionnaires with informants were performed blinded. Data analysis was conducted between August 2021 and June 2023.

Exposures

Repetitive head impacts from contact sports.

Main Outcomes and Measures

Gross and microscopic neuropathologic assessment, including diagnosis of CTE, based on defined diagnostic criteria; and informant-reported athletic history and informant-completed scales that assess cognitive symptoms, mood disturbances, and neurobehavioral dysregulation.

Results

Among the 152 deceased contact sports participants (mean [SD] age, 22.97 [4.31] years; 141 [92.8%] male) included in the study, CTE was diagnosed in 63 (41.4%; median [IQR] age, 26 [24-27] years). Of the 63 brain donors diagnosed with CTE, 60 (95.2%) were diagnosed with mild CTE (stages I or II). Brain donors who had CTE were more likely to be older (mean difference, 3.92 years; 95% CI, 2.74-5.10 years) Of the 63 athletes with CTE, 45 (71.4%) were men who played amateur sports, including American football, ice hockey, soccer, rugby, and wrestling; 1 woman with CTE played collegiate soccer. For those who played football, duration of playing career was significantly longer in those with vs without CTE (mean difference, 2.81 years; 95% CI, 1.15-4.48 years). Athletes with CTE had more ventricular dilatation, cavum septum pellucidum, thalamic notching, and perivascular pigment-laden macrophages in the frontal white matter than those without CTE. Cognitive and neurobehavioral symptoms were frequent among all brain donors. Suicide was the most common cause of death, followed by unintentional overdose; there were no differences in cause of death or clinical symptoms based on CTE status.

Conclusions and Relevance

This case series found that young brain donors exposed to repetitive head impacts were highly symptomatic regardless of CTE status, and the causes of symptoms in this sample are likely multifactorial. Future studies that include young brain donors unexposed to repetitive head impacts are needed to clarify the association among exposure, white matter and microvascular pathologic findings, CTE, and clinical symptoms.

Quantitative analysis of magnetic resonance images for characterization of blood-brain barrier dysfunction in dogs with brain tumors

BACKGROUND

Blood-brain barrier (BBB) permeability can be assessed quantitatively using advanced imaging analysis.

HYPOTHESIS/OBJECTIVES

Quantification and characterization of blood-brain barrier dysfunction (BBBD) patterns in dogs with brain tumors can provide useful information about tumor biology and assist in distinguishing between gliomas and meningiomas.

ANIMALS

Seventy-eight hospitalized dogs with brain tumors and 12 control dogs without brain tumors.

METHODS

In a 2-arm study, images from a prospective dynamic contrast-enhanced (DCE; n = 15) and a retrospective archived magnetic resonance imaging study (n = 63) were analyzed by DCE and subtraction enhancement analysis (SEA) to quantify BBB permeability in affected dogs relative to control dogs (n = 6 in each arm). For the SEA method, 2 ranges of postcontrast intensity differences, that is, high (HR) and low (LR), were evaluated as possible representations of 2 classes of BBB leakage. BBB score was calculated for each dog and was associated with clinical characteristics and tumor location and class. Permeability maps were generated, using the slope values (DCE) or intensity difference (SEA) of each voxel, and analyzed.

RESULTS

Distinctive patterns and distributions of BBBD were identified for intra- and extra-axial tumors. At a cutoff of 0.1, LR/HR BBB score ratio yielded a sensitivity of 80% and specificity of 100% in differentiating gliomas from meningiomas.

CONCLUSIONS AND CLINICAL IMPORTANCE

Blood-brain barrier dysfunction quantification using advanced imaging analyses has the potential to be used for assessment of brain tumor characteristics and behavior and, particularly, to help differentiating gliomas from meningiomas.

Concussion in the UK: a contemporary narrative review

Concussion has been receiving an increasing amount of media exposure following several high-profile professional sports controversies and multimillion-dollar lawsuits. The potential life-changing sequalae of concussion and the rare, but devasting, second impact syndrome have also gained much attention. Despite this, our knowledge of the pathological processes involved is limited and often extrapolated from research into more severe brain injuries. As there is no objective diagnostic test for concussion. Relying on history and examination only, the diagnosis of concussion has become the rate-limiting step in widening research into the disease. Clinical study protocols therefore frequently exclude the most vulnerable groups of patients such as those with existing cognitive impairment, concurrent intoxication, mental health issues or learning difficulties. This up-to-date narrative review aims to summarize our current concussion knowledge and provides an insight into promising avenues for future research.

Blood–brain barrier and brain structural changes in lung cancer patients with non-brain metastases

Purpose

To explore the relationship between blood-brain barrier (BBB) leakage and brain structure in non-brain metastasis lung cancer (LC) by magnetic resonance imaging (MRI) as well as to indicate the possibility of brain metastasis (BM) occurrence.

Patients and methods

MRI were performed in 75 LC patients and 29 counterpart healthy peoples (HCs). We used the Patlak pharmacokinetic model to calculate the average leakage in each brain region according to the automated anatomical labeling (AAL) atlas. The thickness of the cortex and the volumes of subcortical structures were calculated using the FreeSurfer base on Destrieux atlas. We compared the thickness of the cerebral cortex, the volumes of subcortical structures, and the leakage rates of BBB, and evaluated the relationships between these parameters.

Results

Compared with HCs, the leakage rates of seven brain regions were higher in patients with advanced LC (aLC). In contrast to patients with early LC (eLC), the cortical thickness of two regions was decreased in aLCs. The volumes of twelve regions were also reduced in aLCs. Brain regions with increased BBB penetration showed negative correlations with thinner cortices and reduced subcortical structure volumes (P<0.05, R=-0.2 to -0.50). BBB penetration was positively correlated with tumor size and with levels of the tumor marker CYFRA21-1 (P<0.05, R=0.2–0.70).

Conclusion

We found an increase in BBB permeability in non-BM aLCs that corresponded to a thinner cortical thickness and smaller subcortical structure volumes. With progression in LC staging, BBB shows higher permeability and may be more likely to develop into BM.

Dynamic contrast enhanced MRI for characterization of blood-brain-barrier dysfunction after traumatic brain injury

BACKGROUND AND PURPOSE

Dysfunction of the blood-brain-barrier (BBB) is a recognized pathological consequence of traumatic brain injury (TBI) which may play an important role in chronic TBI pathophysiology. We hypothesized that BBB disruption can be detected with dynamic contrast-enhanced (DCE) MRI not only in association with focal traumatic lesions but also in normal-appearing brain tissue of TBI patients, reflecting microscopic microvascular injury. We further hypothesized that BBB integrity would improve but not completely normalize months after TBI.

MATERIALS AND METHODS

DCE MRI was performed in 40 adult patients a median of 23 days after hospitalized TBI and in 21 healthy controls. DCE data was analyzed using Patlak and linear models, and derived metrics of BBB leakage including the volume transfer constant (Ktrans) and the normalized permeability index (NPI) were compared between groups. BBB metrics were compared with focal lesion distribution as well as with contemporaneous measures of symptomatology and cognitive function in TBI patients. Finally, BBB metrics were examined longitudinally among 18 TBI patients who returned for a second MRI a median of 204 days postinjury.

RESULTS

TBI patients exhibited higher mean Ktrans (p = 0.0028) and proportion of suprathreshold NPI voxels (p = 0.001) relative to controls. Tissue-based analysis confirmed greatest TBI-related BBB disruption in association with focal lesions, however elevated Ktrans was also observed in perilesional (p = 0.011) and nonlesional (p = 0.044) regions. BBB disruption showed inverse correlation with quality of life (rho = -0.51, corrected p = 0.016). Among the subset of TBI patients who underwent a second MRI several months after the initial evaluation, metrics of BBB disruption did not differ significantly at the group level, though variable longitudinal changes were observed at the individual subject level.

CONCLUSIONS

This pilot investigation suggests that TBI-related BBB disruption is detectable in the early post-injury period in association with focal and diffuse brain injury.

A companion to the preclinical common data elements and case report forms for in vivo rodent neuroimaging: A report of the TASK3-WG3 Neuroimaging Working Group of the ILAE/AES Joint Translational Task Force

The International League Against Epilepsy/American Epilepsy Society (ILAE/AES) Joint Translational Task Force established the TASK3 working groups to create common data elements (CDEs) for various aspects of preclinical epilepsy research studies, which could help improve the standardization of experimental designs. In this article, we discuss CDEs for neuroimaging data that are collected in rodent models of epilepsy, with a focus on adult rats and mice. We provide detailed CDE tables and case report forms (CRFs), and with this companion manuscript, we discuss the methodologies for several imaging modalities and the parameters that can be collected.

GFAP and S100B: What You Always Wanted to Know and Never Dared to Ask

Traumatic brain injury (TBI) is a major global health issue, with outcomes spanning from intracranial bleeding, debilitating sequelae, and invalidity with consequences for individuals, families, and healthcare systems. Early diagnosis of TBI by testing peripheral fluids such as blood or saliva has been the focus of many research efforts, leading to FDA approval for a bench-top assay for blood GFAP and UCH-L1 and a plasma point-of-care test for GFAP. The biomarker S100B has been included in clinical guidelines for mTBI (mTBI) in Europe. Despite these successes, several unresolved issues have been recognized, including the robustness of prior data, the presence of biomarkers in tissues beyond the central nervous system, and the time course of biomarkers in peripheral body fluids. In this review article, we present some of these issues and provide a viewpoint derived from an analysis of existing literature. We focus on two astrocytic proteins, S100B and GFAP, the most commonly employed biomarkers used in mTBI. We also offer recommendations that may translate into a broader acceptance of these clinical tools.

Detection of blood‐brain barrier dysfunction using advanced imaging methods to predict seizures in dogs with meningoencephalitis of unknown origin

Background

The blood‐brain barrier (BBB), which separates the intravascular and neuropil compartments, characterizes the vascular bed of the brain and is essential for its proper function. Recent advances in imaging techniques have driven the development of methods for quantitative assessment of BBB permeability.

Hypothesis/Objectives

Permeability of the BBB can be assessed quantitatively in dogs with meningoencephalitis of unknown origin (MUO) and its status is associated with the occurrence of seizures.

Animals

Forty dogs with MUO and 12 dogs without MUO.

Methods

Retrospective, prospective cohort study. Both dynamic contrast enhancement (DCE) and subtraction enhancement analysis (SEA) methods were used to evaluate of BBB permeability in affected (DCE, n = 8; SEA, n = 32) and control dogs (DCE, n = 6; SEA, n = 6). Association between BBB dysfunction (BBBD) score and clinical characteristics was examined. In brain regions where BBBD was identified by DCE or SEA magnetic resonance imaging (MRI) analysis, immunofluorescent staining for albumin, glial fibrillary acidic protein, ionized calcium binding adaptor molecule, and phosphorylated mothers against decapentaplegic homolog 2 were performed to detect albumin extravasation, reactive astrocytes, activated microglia, and transforming growth factor beta signaling, respectively.

Results

Dogs with BBBD had significantly higher seizure prevalence (72% vs 19%; P = .01) when compared to MUO dogs with no BBBD. The addition of SEA to routine MRI evaluation increased the identification rate of brain pathology in dogs with MUO from 50% to 72%.

Conclusions and Clinical Importance

Imaging‐based assessment of BBB integrity has the potential to predict risk of seizures in dogs with MUO.

Salivary S100 calcium-binding protein beta (S100B) and neurofilament light (NfL) after acute exposure to repeated head impacts in collegiate water polo players

Blood-based biomarkers of brain injury may be useful for monitoring brain health in athletes at risk for concussions. Two putative biomarkers of sport-related concussion, neurofilament light (NfL), an axonal structural protein, and S100 calcium-binding protein beta (S100B), an astrocyte-derived protein, were measured in saliva, a biofluid which can be sampled in an athletic setting without the risks and burdens associated with blood sampled by venipuncture. Samples were collected from men’s and women’s collegiate water polo players (n = 65) before and after a competitive tournament. Head impacts were measured using sensors previously evaluated for use in water polo, and video recordings were independently reviewed for the purpose of validating impacts recorded by the sensors. Athletes sustained a total of 107 head impacts, all of which were asymptomatic (i.e., no athlete was diagnosed with a concussion or more serious). Post-tournament salivary NfL was directly associated with head impact frequency (RR = 1.151, p = 0.025) and cumulative head impact magnitude (RR = 1.008, p = 0.014), while controlling for baseline salivary NfL. Change in S100B was not associated with head impact exposure (RR < 1.001, p > 0.483). These patterns suggest that repeated head impacts may cause axonal injury, even in asymptomatic athletes.

A preliminary model of football-related neural stress that integrates metabolomics with transcriptomics and virtual reality

Research suggests contact sports affect neurological health. This study used permutation-based mediation statistics to integrate measures of metabolomics, neuroinflammatory miRNAs, and virtual reality (VR)-based motor control to investigate multi-scale relationships across a season of collegiate American football. Fourteen significant mediations (six pre-season, eight across-season) were observed where metabolites always mediated the statistical relationship between miRNAs and VR-based motor control (pSobelperm≤ 0.05; total effect > 50%), suggesting a hypothesis that metabolites sit in the statistical pathway between transcriptome and behavior. Three results further supported a model of chronic neuroinflammation, consistent with mitochondrial dysfunction: (1) Mediating metabolites were consistently medium-to-long chain fatty acids, (2) tricarboxylic acid cycle metabolites decreased across-season, and (3) accumulated head acceleration events statistically moderated pre-season metabolite levels to directionally model post-season metabolite levels. These preliminary findings implicate potential mitochondrial dysfunction and highlight probable peripheral blood biomarkers underlying repetitive head impacts in otherwise healthy collegiate football athletes.

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Permutation-based mediation statistics can be applied to multi-scale biology problems

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Fatty acids were a critical link between elevated miRNAs and motor control

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HAEs interacted with pre-season metabolite levels to model post-season levels

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Together, our observations point to brain-related mitochondrial dysfunction

Concussion susceptibility is mediated by spreading depolarization-induced neurovascular dysfunction

The mechanisms underlying the complications of mild traumatic brain injury, including post-concussion syndrome, post-impact catastrophic death, and delayed neurodegeneration remain poorly understood. This limited pathophysiological understanding has hindered the development of diagnostic and prognostic biomarkers and has prevented the advancement of treatments for the sequelae of mild traumatic brain injury.

We aimed to characterize the early electrophysiological and neurovascular alterations following repetitive mild traumatic brain injury and sought to identify new targets for the diagnosis and treatment of individuals at risk of severe post-impact complications. We combined behavioural, electrophysiological, molecular, and neuroimaging techniques in a rodent model of repetitive mild traumatic brain injury. In humans, we used dynamic contrast-enhanced MRI to quantify blood–brain barrier dysfunction after exposure to sport-related concussive mild traumatic brain injury.

Rats could clearly be classified based on their susceptibility to neurological complications, including life-threatening outcomes, following repetitive injury. Susceptible animals showed greater neurological complications and had higher levels of blood–brain barrier dysfunction, transforming growth factor β (TGFβ) signalling, and neuroinflammation compared to resilient animals. Cortical spreading depolarizations were the most common electrophysiological events immediately following mild traumatic brain injury and were associated with longer recovery from impact. Triggering cortical spreading depolarizations in mild traumatic brain injured rats (but not in controls) induced blood–brain barrier dysfunction. Treatment with a selective TGFβ receptor inhibitor prevented blood–brain barrier opening and reduced injury complications. Consistent with the rodent model, blood–brain barrier dysfunction was found in a subset of human athletes following concussive mild traumatic brain injury.

We provide evidence that cortical spreading depolarization, blood–brain barrier dysfunction, and pro-inflammatory TGFβ signalling are associated with severe, potentially life-threatening outcomes following repetitive mild traumatic brain injury. Diagnostic-coupled targeting of TGFβ signalling may be a novel strategy in treating mild traumatic brain injury.

S100B, GFAP, UCH-L1 and NSE as predictors of abnormalities on CT imaging following mild traumatic brain injury: a systematic review and meta-analysis of diagnostic test accuracy

Biomarkers such as calcium channel binding protein S100 subunit beta (S100B), glial fibrillary acidic protein (GFAP), ubiquitin c-terminal hydrolase L1 (UCH-L1) and neuron-specific enolase (NSE) have been proposed to aid in screening patients presenting with mild traumatic brain injury (mTBI). As such, we aimed to characterise their accuracy at various thresholds. MEDLINE, SCOPUS and EMBASE were searched, and articles reporting the diagnostic performance of included biomarkers were eligible for inclusion. Risk of bias was assessed using the QUADAS-II criteria. A meta-analysis was performed to assess the predictive value of biomarkers for imaging abnormalities on CT. A total of 2939 citations were identified, and 38 studies were included. Thirty-two studies reported data for S100B. At its conventional threshold of 0.1 μg/L, S100B had a pooled sensitivity of 91% (95%CI 87-94) and a specificity of 30% (95%CI 26-34). The optimal threshold for S100B was 0.72 μg/L, with a sensitivity of 61% (95% CI 50-72) and a specificity of 69% (95% CI 64-74). Nine studies reported data for GFAP. The optimal threshold for GFAP was 626 pg/mL, at which the sensitivity was 71% (95%CI 41-91) and specificity was 71% (95%CI 43-90). Sensitivity of GFAP was maximised at a threshold of 22 pg/mL, which had a sensitivity of 93% (95%CI 73-99) and a specificity of 36% (95%CI 12-68%). Three studies reported data for NSE and two studies for UCH-L1, which precluded meta-analysis. There is evidence to support the use of S100B as a screening tool in mild TBI, and potential advantages to the use of GFAP, which requires further investigation.

Quantitative Imaging of Blood-Brain Barrier Permeability Following Repetitive Mild Head Impacts

This was an exploratory study designed to evaluate the feasibility of a recently established imaging modality, quantitative ultrashort time-to-echo contrast enhanced (QUTE-CE), to follow the early pathology and vulnerability of the blood brain barrier in response to single and repetitive mild head impacts. A closed-head, momentum exchange model was used to produce three consecutive mild head impacts aimed at the forebrain separated by 24 h each. Animals were measured at baseline and within 1 h of impact. Anatomical images were collected to assess the extent of structural damage. QUTE-CE biomarkers for BBB permeability were calculated on 420,000 voxels in the brain and were registered to a bilateral 3D brain atlas providing site-specific information on 118 anatomical regions. Blood brain barrier permeability was confirmed by extravasation of labeled dextran. All head impacts occurred in the absence of any structural brain damage. A single mild head impact had measurable effects on blood brain barrier permeability and was more significant after the second and third impacts. Affected regions included the prefrontal ctx, basal ganglia, hippocampus, amygdala, and brainstem. Our findings support the concerns raised by the healthcare community regarding mild head injuries in participants in organized contact sports and military personnel in basic training and combat.

Blood biomarkers for mild traumatic brain injury: a selective review of unresolved issues

Background

The use of blood biomarkers after mild traumatic brain injury (mTBI) has been widely studied. We have identified eight unresolved issues related to the use of five commonly investigated blood biomarkers: neurofilament light chain, ubiquitin carboxy-terminal hydrolase-L1, tau, S100B, and glial acidic fibrillary protein. We conducted a focused literature review of unresolved issues in three areas: mode of entry into and exit from the blood, kinetics of blood biomarkers in the blood, and predictive capacity of the blood biomarkers after mTBI.

Findings

Although a disruption of the blood brain barrier has been demonstrated in mild and severe traumatic brain injury, biomarkers can enter the blood through pathways that do not require a breach in this barrier. A definitive accounting for the pathways that biomarkers follow from the brain to the blood after mTBI has not been performed. Although preliminary investigations of blood biomarkers kinetics after TBI are available, our current knowledge is incomplete and definitive studies are needed. Optimal sampling times for biomarkers after mTBI have not been established. Kinetic models of blood biomarkers can be informative, but more precise estimates of kinetic parameters are needed. Confounding factors for blood biomarker levels have been identified, but corrections for these factors are not routinely made. Little evidence has emerged to date to suggest that blood biomarker levels correlate with clinical measures of mTBI severity. The significance of elevated biomarker levels thirty or more days following mTBI is uncertain. Blood biomarkers have shown a modest but not definitive ability to distinguish concussed from non-concussed subjects, to detect sub-concussive hits to the head, and to predict recovery from mTBI. Blood biomarkers have performed best at distinguishing CT scan positive from CT scan negative subjects after mTBI.

Insulin Resistance and Blood-Brain Barrier Dysfunction Underlie Neuroprogression in Bipolar Disorder

Bipolar disorder (BD) often progresses to a more chronic and treatment resistant (neuroprogressive) course. Identifying which patients are at risk could allow for early intervention and prevention. Bipolar disorder is highly comorbid with metabolic disorders including type II diabetes mellitus (T2DM), hypertension, obesity, and dyslipidemia. Our studies have shown that insulin resistance (IR) is present in over 50% of patients with BD and that IR might underlie the progression of BD. While no confirmed predictors exist for identifying which patients with BD are likely to develop a more chronic course, emerging evidence including our own studies suggest that IR and related inflammatory pathways lead to impairments in blood-brain barrier (BBB) functioning. For the first time in living psychiatric patients, we have shown that the severity of BBB leakage is proportional to BD severity and is associated with IR. In this hypothesis paper we (i) highlight the evidence for a key role of IR in BD, (ii) show how IR in BD relates to shared inflammatory pathways, and (iii) hypothesize that these modulations result in BBB leakage and worse outcomes in BD. We further hypothesize that (iv) reversing IR through lifestyle changes or the actions of insulin sensitizing medications such as metformin, or optimizing BBB function using vascular protective drugs, such as losartan, could provide novel strategies for the prevention or treatment of neuroprogressive BD.

Targeting the Cerebrovascular System: Next-Generation Biomarkers and Treatment for Mild Traumatic Brain Injury

The diagnosis, prognosis, and treatment of mild traumatic brain injuries (mTBIs), such as concussions, are significant unmet medical issues. The kinetic forces that occur in mTBI adversely affect the cerebral vasculature, making cerebrovascular injury (CVI) a pathophysiological hallmark of mTBI. Given the importance of a healthy cerebrovascular system in overall brain function, CVI is likely to contribute to neurological dysfunction after mTBI. As such, CVI and related pathomechanisms may provide objective biomarkers and therapeutic targets to improve the clinical management and outcomes of mTBI. Despite this potential, until recently, few studies have focused on the cerebral vasculature in this context. This article will begin by providing a brief overview of the cerebrovascular system followed by a review of the literature regarding how mTBI can affect the integrity and function of the cerebrovascular system, and how this may ultimately contribute to neurological dysfunction and neurodegenerative conditions. We then discuss promising avenues of research related to mTBI biomarkers and interventions that target CVI, and conclude that a clinical approach that takes CVI into account could result in substantial improvements in the care and outcomes of patients with mTBI.

Permeability of the Blood-Brain Barrier after Traumatic Brain Injury; Radiological Considerations

Traumatic brain injury (TBI) is a leading cause of death and disability, especially in young persons, and constitutes a major socioeconomic burden worldwide. It is regarded as the leading cause of mortality and morbidity in previously healthy young persons. Most of the mechanisms underpinning the development of secondary brain injury are consequences of disruption of the complex relationship between the cells and proteins constituting the neurovascular unit or a direct result of loss of integrity of the tight junctions (TJ) in the blood-brain barrier (BBB). A number of changes have been described in the BBB after TBI, including loss of TJ proteins, pericyte loss and migration, and altered expressions of water channel proteins at astrocyte end-feet processes. There is a growing research interest in identifying optimal biological and radiological biomarkers of severity of BBB dysfunction and its effects on outcomes after TBI. This review explores the microscopic changes occurring at the neurovascular unit, after TBI, and current radiological adjuncts for its evaluation in pre-clinical and clinical practice.

Repetitive mTBI is associated with age-related reductions in cerebral blood flow but not cortical thickness

Mild traumatic brain injury (mTBI) is a risk factor for Alzheimer's disease (AD), and evidence suggests cerebrovascular dysregulation initiates deleterious neurodegenerative cascades. We examined whether mTBI history alters cerebral blood flow (CBF) and cortical thickness in regions vulnerable to early AD-related changes. Seventy-four young to middle-aged Veterans (mean age = 34, range = 23-48) underwent brain scans. Participants were divided into: (1) Veteran Controls (n = 27), (2) 1-2 mTBIs (n = 26), and (2) 3+ mTBIs (n = 21) groups. Resting CBF was measured using MP-PCASL. T1 structural scans were processed with FreeSurfer. CBF and cortical thickness estimates were extracted from nine AD-vulnerable regions. Regression analyses examined whether mTBI moderated the association between age, CBF, and cortical thickness. Regressions adjusting for sex and posttraumatic stress revealed mTBI moderated the association between age and CBF of the precuneus as well as superior and inferior parietal cortices (p's < .05); increasing age was associated with lower CBF in the 3+ mTBIs group, but not in the VCs or 1-2 mTBIs groups. mTBI did not moderate associations between age and cortical thickness (p's >.05). Repetitive mTBI is associated with cerebrovascular dysfunction in AD-vulnerable regions and may accelerate pathological aging trajectories.

Slow blood-to-brain transport underlies enduring barrier dysfunction in American football players

Repetitive mild traumatic brain injury in American football players has garnered increasing public attention following reports of chronic traumatic encephalopathy, a progressive tauopathy. While the mechanisms underlying repetitive mild traumatic brain injury-induced neurodegeneration are unknown and antemortem diagnostic tests are not available, neuropathology studies suggest a pathogenic role for microvascular injury, specifically blood–brain barrier dysfunction. Thus, our main objective was to demonstrate the effectiveness of a modified dynamic contrast-enhanced MRI approach we have developed to detect impairments in brain microvascular function. To this end, we scanned 42 adult male amateur American football players and a control group comprising 27 athletes practicing a non-contact sport and 26 non-athletes. MRI scans were also performed in 51 patients with brain pathologies involving the blood–brain barrier, namely malignant brain tumours, ischaemic stroke and haemorrhagic traumatic contusion. Based on data from prolonged scans, we generated maps that visualized the permeability value for each brain voxel. Our permeability maps revealed an increase in slow blood-to-brain transport in a subset of amateur American football players, but not in sex- and age-matched controls. The increase in permeability was region specific (white matter, midbrain peduncles, red nucleus, temporal cortex) and correlated with changes in white matter, which were confirmed by diffusion tensor imaging. Additionally, increased permeability persisted for months, as seen in players who were scanned both on- and off-season. Examination of patients with brain pathologies revealed that slow tracer accumulation characterizes areas surrounding the core of injury, which frequently shows fast blood-to-brain transport. Next, we verified our method in two rodent models: rats and mice subjected to repeated mild closed-head impact injury, and rats with vascular injury inflicted by photothrombosis. In both models, slow blood-to-brain transport was observed, which correlated with neuropathological changes. Lastly, computational simulations and direct imaging of the transport of Evans blue-albumin complex in brains of rats subjected to recurrent seizures or focal cerebrovascular injury suggest that increased cellular transport underlies the observed slow blood-to-brain transport. Taken together, our findings suggest dynamic contrast-enhanced-MRI can be used to diagnose specific microvascular pathology after traumatic brain injury and other brain pathologies.

Blood-brain barrier leakage in systemic lupus erythematosus is associated with gray matter loss and cognitive impairment

OBJECTIVES

To examine the association between blood-brain barrier (BBB) integrity, brain volume and cognitive dysfunction in adult patients with systemic lupus erythematosus (SLE).

METHODS

A total of 65 ambulatory patients with SLE and 9 healthy controls underwent dynamic contrast-enhanced MRI scanning, for quantitative assessment of BBB permeability. Volumetric data were extracted using the VolBrain pipeline. Global cognitive function was evaluated using a screening battery consisting of tasks falling into five broad cognitive domains, and was compared between patients with normal versus extensive BBB leakage.

RESULTS

Patients with SLE had significantly higher levels of BBB leakage compared with controls (p=0.04). Extensive BBB leakage (affecting over >9% of brain volume) was identified only in patients with SLE (16/65; 24.6%), who also had smaller right and left cerebral grey matter volumes compared with controls (p=0.04). Extensive BBB leakage was associated with lower global cognitive scores (p=0.02), and with the presence of impairment on one or more cognitive tasks (p=0.01).

CONCLUSION

Our findings provide evidence for a link between extensive BBB leakage and changes in both brain structure and cognitive function in patients with SLE. Future studies should investigate the mechanisms underlying BBB-mediated cognitive impairment, validate the diagnostic utility of BBB imaging, and determine the potential of targeting the BBB as a therapeutic strategy in patients with SLE.

Microglia dynamics in adolescent traumatic brain injury

Repetitive, mild traumatic brain injuries (RmTBIs) are increasingly common in adolescents and encompass one of the largest neurological health concerns in the world. Adolescence is a critical period for brain development where RmTBIs can substantially impact neurodevelopmental trajectories and life-long neurological health. Our current understanding of RmTBI pathophysiology suggests key roles for neuroinflammation in negatively regulating neural health and function. Microglia, the brain’s resident immune population, play important roles in brain development by regulating neuronal number, and synapse formation and elimination. In response to injury, microglia activate to inflammatory phenotypes that may detract from these normal homeostatic, physiological, and developmental roles. To date, however, little is known regarding the impact of RmTBIs on microglia function during adolescent brain development. This review details key concepts surrounding RmTBI pathophysiology, adolescent brain development, and microglia dynamics in the developing brain and in response to injury, in an effort to formulate a hypothesis on how the intersection of these processes may modify long-term trajectories.

Evidence of early vasogenic edema following minor head impact that can be reduced with a vasopressin V1a receptor antagonist

BACKGROUND

Does minor head impact without signs of structural brain damage cause short-term changes in vasogenic edema as measured by an increase apparent diffusion coefficient (ADC) using diffusion weighted imaging? If so, could the increase in vasogenic edema be treated with a vasopressin V1a receptor antagonist? We hypothesized that SRX251, a highly selective V1a antagonist, would reduce vasogenic edema in response to a single minor head impact.

METHODS

Lightly anesthetized male rats were subjected to a sham procedure or a single hit to the forehead using a closed skull, momentum exchange model. Animals recovered in five min and were injected with saline vehicle (n = 8) or SRX251 (n = 8) at 15 min post head impact and again 7-8 hrs later. At 2 h, 6 h, and 24 h post injury, rats were anesthetized and scanned for increases in ADC, a neurological measure of vasogenic edema. Sham rats (n = 6) were exposed to anesthesia and scanned at all time points but were not hit or treated. Images were registered to and analyzed using a 3D MRI rat atlas providing site-specific data on 150 different brain areas. These brain areas were parsed into 11 major brain regions.

RESULTS

Untreated rats with brain injury showed a significant increase in global brain vasogenic edema as compared to sham and SRX251 treated rats. Edema peaked at 6 h in injured, untreated rats in three brain regions where changes in ADC were observed, but returned to sham levels by 24 h. There were regional variations in the time course of vasogenic edema and drug efficacy. Edema was significantly reduced in cerebellum and thalamus with SRX251 treatment while the basal ganglia did not show a response to treatment.

CONCLUSION

A single minor impact to the forehead causes regional increases in vasogenic edema that peak at 6 h but return to baseline within a day in a subset of brain regions. Treatment with a selective V1a receptor antagonist can reduce much of the edema.

Vascular contributions to cognitive impairment and dementia (VCID): A report from the 2018 National Heart, Lung, and Blood Institute and National Institute of Neurological Disorders and Stroke Workshop

Vascular contributions to cognitive impairment and dementia (VCID) are characterized by the aging neurovascular unit being confronted with and failing to cope with biological insults due to systemic and cerebral vascular disease, proteinopathy including Alzheimer's biology, metabolic disease, or immune response, resulting in cognitive decline. This report summarizes the discussion and recommendations from a working group convened by the National Heart, Lung, and Blood Institute and the National Institute of Neurological Disorders and Stroke to evaluate the state of the field in VCID research, identify research priorities, and foster collaborations. As discussed in this report, advances in understanding the biological mechanisms of VCID across the wide spectrum of pathologies, chronic systemic comorbidities, and other risk factors may lead to potential prevention and new treatment strategies to decrease the burden of dementia. Better understanding of the social determinants of health that affect risks for both vascular disease and VCID could provide insight into strategies to reduce racial and ethnic disparities in VCID.

Systemic inflammation moderates the association of prior concussion with hippocampal volume and episodic memory in high school and collegiate athletes

BACKGROUND

There is a need to determine why prior concussion has been associated with adverse outcomes in some retired and active athletes. We examined whether serum inflammatory markers moderate the associations of prior concussion with hippocampal volumes and neurobehavioral functioning in active high school and collegiate athletes.

METHODS

Athletes (N = 201) completed pre-season clinical testing and serum collection (C-reactive protein [CRP]; Interleukin-6 [IL]-6; IL-1 receptor antagonist [RA]) and in-season neuroimaging. Linear mixed-effects models examined associations of prior concussion with inflammatory markers, self-reported symptoms, neurocognitive function, and hippocampal volumes. Models examined whether inflammatory markers moderated associations of concussion history and hippocampal volume and/or clinical measures.

RESULTS

Concussion history was significantly associated with higher symptom severity, p = 0.012, but not hippocampal volume or inflammatory markers (ps > 0.05). A significant interaction of prior concussion and CRP was observed for hippocampal volume, p = 0.006. Follow-up analyses showed that at high levels of CRP, athletes with two or more prior concussions had smaller hippocampal volume compared to athletes without prior concussion, p = 0.008. There was a significant interaction between prior concussion and levels of IL-1RA on memory scores, p = 0.044, i.e., at low levels of IL-1RA, athletes with two or more concussions had worse memory performance than those without prior concussion (p = 0.014).

CONCLUSION

Findings suggest that certain markers of systemic inflammation moderate the association between prior concussion and hippocampal volume and episodic memory performance. Current findings highlight potential markers for predicting at-risk individuals and identify therapeutic targets for mitigating the long-term adverse consequences of cumulative concussion.

Effects of sub-concussion on neuropsychological performance and its potential mechanisms: A narrative review

Concussion and mild traumatic brain injury (mTBI) are recognised as serious medical events that are relatively common in contact sports. Recently, the seemingly non-injurious phenomenon of sub-concussion has gained interest among neuroscience researchers and early studies are showing that there may be some acute and chronic effects on brain health and function with repeated sub-concussive events of the type seen in soccer, where players strike the ball with the head, and collision sports like the rugby codes. The aim of this narrative review is to describe sub-concussion and the current understanding of short and long term effects of repeated minor impacts that have been found to occur in human and animal models. Here, potential mechanisms for cognitive dysfunction following sub-concussion and recommend directions for future research are discussed. The Potential mechanisms of injuries resulting from sub-concussion such as changes in blood brain barrier integrity, neuroinflammation, cognitive impairment, and oxidative stress damage, among other changes in central nervous system function vary considerably making understanding of the underlying causative mechanism challenging for researchers. Some evidence suggests a link between impaired cerebrovascular function and cognitive impairment which poses a potential mechanism linking the two. It is hoped that this review helps guide researchers toward a potential direction of investigations.

Paroxysmal slow cortical activity in Alzheimer's disease and epilepsy is associated with blood-brain barrier dysfunction

A growing body of evidence shows that epileptic activity is frequent but often undiagnosed in patients with Alzheimer's disease (AD) and has major therapeutic implications. Here, we analyzed electroencephalogram (EEG) data from patients with AD and found an EEG signature of transient slowing of the cortical network that we termed paroxysmal slow wave events (PSWEs). The occurrence per minute of the PSWEs was correlated with level of cognitive impairment. Interictal (between seizures) PSWEs were also found in patients with epilepsy, localized to cortical regions displaying blood-brain barrier (BBB) dysfunction, and in three rodent models with BBB pathology: aged mice, young 5x familial AD model, and status epilepticus-induced epilepsy in young rats. To investigate the potential causative role of BBB dysfunction in network modifications underlying PSWEs, we infused the serum protein albumin directly into the cerebral ventricles of naïve young rats. Infusion of albumin, but not artificial cerebrospinal fluid control, resulted in high incidence of PSWEs. Our results identify PSWEs as an EEG manifestation of nonconvulsive seizures in patients with AD and suggest BBB pathology as an underlying mechanism and as a promising therapeutic target.

Blood-Brain Barrier Dysfunction in Mild Traumatic Brain Injury: Evidence From Preclinical Murine Models

Mild traumatic brain injury (mTBI) represents more than 80% of total TBI cases and is a robust environmental risk factor for neurodegenerative diseases including Alzheimer’s disease (AD). Besides direct neuronal injury and neuroinflammation, blood–brain barrier (BBB) dysfunction is also a hallmark event of the pathological cascades after mTBI. However, the vascular link between BBB impairment caused by mTBI and subsequent neurodegeneration remains undefined. In this review, we focus on the preclinical evidence from murine models of BBB dysfunction in mTBI and provide potential mechanistic links between BBB disruption and the development of neurodegenerative diseases.

Blood-Brain Barrier Disruption in Mild Traumatic Brain Injury Patients with Post-Concussion Syndrome: Evaluation with Region-Based Quantification of Dynamic Contrast-Enhanced MR Imaging Parameters Using Automatic Whole-Brain Segmentation

Objective

This study aimed to investigate the blood-brain barrier (BBB) disruption in mild traumatic brain injury (mTBI) patients with post-concussion syndrome (PCS) using dynamic contrast-enhanced (DCE) magnetic resonance (MR) imaging and automatic whole brain segmentation.

Materials and Methods

Forty-two consecutive mTBI patients with PCS who had undergone post-traumatic MR imaging, including DCE MR imaging, between October 2016 and April 2018, and 29 controls with DCE MR imaging were included in this retrospective study. After performing three-dimensional T1-based brain segmentation with FreeSurfer software (Laboratory for Computational Neuroimaging), the mean K^trans and v_p from DCE MR imaging (derived using the Patlak model and extended Tofts and Kermode model) were analyzed in the bilateral cerebral/cerebellar cortex, bilateral cerebral/cerebellar white matter (WM), and brainstem. K^trans values of the mTBI patients and controls were calculated using both models to identify the model that better reflected the increased permeability owing to mTBI (tendency toward higher K^trans values in mTBI patients than in controls). The Mann-Whitney U test and Spearman rank correlation test were performed to compare the mean K^trans and v_p between the two groups and correlate K^trans and v_p with neuropsychological tests for mTBI patients.

Results

Increased permeability owing to mTBI was observed in the Patlak model but not in the extended Tofts and Kermode model. In the Patlak model, the mean K^trans in the bilateral cerebral cortex was significantly higher in mTBI patients than in controls (p = 0.042). The mean v_p values in the bilateral cerebellar WM and brainstem were significantly lower in mTBI patients than in controls (p = 0.009 and p = 0.011, respectively). The mean K^trans of the bilateral cerebral cortex was significantly higher in patients with atypical performance in the auditory continuous performance test (commission errors) than in average or good performers (p = 0.041).

Conclusion

BBB disruption, as reflected by the increased K^trans and decreased v_p values from the Patlak model, was observed throughout the bilateral cerebral cortex, bilateral cerebellar WM, and brainstem in mTBI patients with PCS.

Chronic Traumatic Encephalopathy and Neuropathological Comorbidities

With age, the presence of multiple neuropathologies in a single individual becomes increasingly common. Given that traumatic brain injury and the repetitive head impacts (RHIs) that occur in contact sports have been associated with the development of many neurodegenerative diseases, including chronic traumatic encephalopathy (CTE), Alzheimer's disease, Lewy body disease, and amyotrophic lateral sclerosis, it is becoming critical to understand the relationship and interactions between these pathologies. In fact, comorbid pathology is common in CTE and likely influenced by both age and the severity and type of exposure to RHI as well as underlying genetic predisposition. Here, we review the major comorbid pathologies seen with CTE and in former contact sports athletes and discuss what is known about the associations between RHI, age, and the development of neuropathologies. In addition, we examine the distinction between CTE and age-related pathology including primary age-related tauopathy and age-related tau astrogliopathy.

Is Salivary S100B a Biomarker of Traumatic Brain Injury? A Pilot Study

Traumatic brain injury (TBI) results in short and long-term disability neurodegeneration. Mild traumatic brain injury (mTBI) represents up to 85% of head injuries; diagnosis and early management is based on computed tomography (CT) or in-hospital observation, which are time- and cost- intensive. CT involves exposure to potentially harmful ionizing radiation and >90% of the scans are negative. Blood-brain barrier (BBB) damage is suspected pathological event post-TBI contributing to long-term sequelae and a reliable and rapid point-of-care test to screen those who can safely forego acute head CT would be of great help in evaluating patients with an acute mTBI. In this pilot study, 15 adult patients with suspected TBI (mean age = 47 years, range 18–79) and 15 control subjects (mean age = 33 years, range 23–53) were enrolled. We found that the average salivary S100B level was 3.9 fold higher than blood S100B, regardless of the presence of pathology. [S100B]_saliva positively correlated with [S100B]_serum (Pearson' coefficient = 0.79; p < 0.01). Salivary S100B levels were as effective in differentiating TBI patients from control subjects as serum levels (Control vs. TBI: p < 0.01; Serum ROC_AUC = 0.94 and Saliva ROC_AUC = 0.75). I These initial results suggest that measuring salivary S100B could represent an alternative to serum S100B in the diagnosis of TBI. Larger and confirmatory trials are needed to define salivary biomarker kinetics in relation to TBI severity and the possible roles of gender, ethnicity and age in influencing salivary S100B levels.

Unravelling the mechanisms of blood-brain barrier dysfunction in repetitive mild head injury

This scientific commentary refers to ‘Slow blood-to-brain transport underlies enduring barrier dysfunction in American football players’, by Veksler et al. (doi:10.1093/brain/awaa140).

Tau immunophenotypes in chronic traumatic encephalopathy recapitulate those of ageing and Alzheimer's disease

Traumatic brain injury (TBI) is a risk factor for neurodegenerative disease, including chronic traumatic encephalopathy (CTE). Preliminary consensus criteria define the pathognomonic lesion of CTE as patchy tau pathology within neurons and astrocytes at the depths of cortical sulci. However, the specific tau isoform composition and post-translational modifications in CTE remain largely unexplored. Using immunohistochemistry, we performed tau phenotyping of CTE neuropathologies and compared this to a range of tau pathologies, including Alzheimer's disease, primary age-related tauopathy, ageing-related tau astrogliopathy and multiple subtypes of frontotemporal lobar degeneration with tau inclusions. Cases satisfying preliminary consensus diagnostic criteria for CTE neuropathological change (CTE-NC) were identified (athletes, n = 10; long-term survivors of moderate or severe TBI, n = 4) from the Glasgow TBI Archive and Penn Neurodegenerative Disease Brain Bank. In addition, material from a range of autopsy-proven ageing-associated and primary tauopathies in which there was no known history of exposure to TBI was selected as non-injured controls (n = 32). Each case was then stained with a panel of tau antibodies specific for phospho-epitopes (PHF1, CP13, AT100, pS262), microtubule-binding repeat domains (3R, 4R), truncation (Tau-C3) or conformation (GT-7, GT-38) and the extent and distribution of staining assessed. Cell types were confirmed with double immunofluorescent labelling. Results demonstrate that astroglial tau pathology in CTE is composed of 4R-immunoreactive thorn-shaped astrocytes, echoing the morphology and immunophenotype of astrocytes encountered in ageing-related tau astrogliopathy. In contrast, neurofibrillary tangles of CTE contain both 3R and 4R tau, with post-translational modifications and conformations consistent with Alzheimer's disease and primary age-related tauopathy. Our observations establish that the astroglial and neurofibrillary tau pathologies of CTE are phenotypically distinct from each other and recapitulate the tau immunophenotypes encountered in ageing and Alzheimer's disease. As such, the immunohistochemical distinction of CTE neuropathology from other mixed 3R/4R tauopathies of Alzheimer's disease and ageing may rest solely on the pattern and distribution of pathology.

Dynamic Blood-Brain Barrier Regulation in Mild Traumatic Brain Injury

Whereas the diagnosis of moderate and severe traumatic brain injury (TBI) is readily visible on current medical imaging paradigms (magnetic resonance imaging [MRI] and computed tomography [CT] scanning), a far greater challenge is associated with the diagnosis and subsequent management of mild TBI (mTBI), especially concussion which, by definition, is characterized by a normal CT. To investigate whether the integrity of the blood-brain barrier (BBB) is altered in a high-risk population for concussions, we studied professional mixed martial arts (MMA) fighters and adolescent rugby players. Additionally, we performed the linear regression between the BBB disruption defined by increased gadolinium contrast extravasation on dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) on MRI and multiple biomechanical parameters indicating the severity of impacts recorded using instrumented mouthguards in professional MMA fighters. MMA fighters were examined pre-fight for a baseline and again within 120 h post-competitive fight, whereas rugby players were examined pre-season and again post-season or post-match in a subset of cases. DCE-MRI, serological analysis of BBB biomarkers, and an analysis of instrumented mouthguard data, was performed. Here, we provide pilot data that demonstrate disruption of the BBB in both professional MMA fighters and rugby players, dependent on the level of exposure. Our data suggest that biomechanical forces in professional MMA and adolescent rugby can lead to BBB disruption. These changes on imaging may serve as a biomarker of exposure of the brain to repetitive subconcussive forces and mTBI.

Blood-Brain Barrier Leakage: A New Biomarker in Transient Ischemic Attacks

Background and Purpose- The diagnosis of transient ischemic attack is challenging. Evidence of acute ischemia on MRI diffusion-weighted imaging is highly variable and confirmed in only about one-third of patients. This study investigated the significance of blood-brain barrier dysfunction (BBBD) mapping in patients with transient neurological deficits, as a diagnostic and prognostic biomarker required for risk stratification and stroke prevention. Methods- We used dynamic contrast-enhanced MRI to quantitatively map BBBD in a prospective cohort study of 57 patients diagnosed with transient ischemic attack/minor stroke and 50 healthy controls. Results- Brain volume with BBBD was significantly higher in patients compared with controls ( P=0.002). BBBD localization corresponded with the clinical presentation in 41 patients (72%) and was more extensive in patients with acute infarct on diffusion-weighted imaging ( P=0.05). Patients who developed new stroke during follow-up had a significantly greater BBBD at the initial presentation ( P=0.03) with a risk ratio of 5.35 for recurrent stroke. Conclusions- This is the first description of the extent and localization of BBBD in patients with transient ischemic attack/minor stroke. We propose BBBD mapping as a valuable tool for detection of subtle brain ischemia and a promising predictive biomarker required for risk stratification and stroke prevention.

Blood-brain barrier dysfunction in aging induces hyperactivation of TGFβ signaling and chronic yet reversible neural dysfunction

Aging involves a decline in neural function that contributes to cognitive impairment and disease. However, the mechanisms underlying the transition from a young-and-healthy to aged-and-dysfunctional brain are not well understood. Here, we report breakdown of the vascular blood-brain barrier (BBB) in aging humans and rodents, which begins as early as middle age and progresses to the end of the life span. Gain-of-function and loss-of-function manipulations show that this BBB dysfunction triggers hyperactivation of transforming growth factor-β (TGFβ) signaling in astrocytes, which is necessary and sufficient to cause neural dysfunction and age-related pathology in rodents. Specifically, infusion of the serum protein albumin into the young rodent brain (mimicking BBB leakiness) induced astrocytic TGFβ signaling and an aged brain phenotype including aberrant electrocorticographic activity, vulnerability to seizures, and cognitive impairment. Furthermore, conditional genetic knockdown of astrocytic TGFβ receptors or pharmacological inhibition of TGFβ signaling reversed these symptomatic outcomes in aged mice. Last, we found that this same signaling pathway is activated in aging human subjects with BBB dysfunction. Our study identifies dysfunction in the neurovascular unit as one of the earliest triggers of neurological aging and demonstrates that the aging brain may retain considerable latent capacity, which can be revitalized by therapeutic inhibition of TGFβ signaling.

Blood-brain barrier dysfunction in status epileptics: Mechanisms and role in epileptogenesis

The blood-brain barrier (BBB), a unique anatomical and physiological interface between the central nervous system (CNS) and the peripheral circulation, is essential for the function of neural circuits. Interactions between the BBB, cerebral blood vessels, neurons, astrocytes, microglia, and pericytes form a dynamic functional unit known as the neurovascular unit (NVU). The NVU-BBB crosstalk plays a key role in the regulation of blood flow, response to injury, neuronal firing, and synaptic plasticity. Blood-brain barrier dysfunction (BBBD), a hallmark of brain injury, is a prominent finding in status epilepticus. Blood-brain barrier dysfunction is observed within the first hour of status epilepticus, and in epileptogenic brain regions, may last for months. Blood-brain barrier dysfunction was shown to have a role in astroglial dysfunction, neuroinflammation, increasing neural excitability, reduction of seizure threshold, excitatory synaptogenesis, impaired plasticity, and epileptogenesis. A key signaling pathway associated with BBBD-induced neurovascular dysfunction is the transforming growth factor beta (TGF-β) proinflammatory pathway, activated by the extravasation of serum albumin into the brain when BBB functions are compromised. Specific small molecules blocking TGF-β, and the nonspecific, Food and Drug Administration (FDA) approved blocker and angiotensin antagonist losartan, were shown to reduce BBBD and block epileptogenesis. With these encouraging preclinical data, we have developed imaging approach to quantitatively assess BBBD as a diagnostic, predictive, and pharmacodynamic biomarker after brain injury. Clinical trials in the foreseen future are expected to test the feasibility of BBB-targeted diagnostic coupled therapy in status epileptics and seizure disorders. This article is part of the Special Issue "Proceedings of the 7th London-Innsbruck Colloquium on Status Epilepticus and Acute Seizures".

Association of White Matter Rarefaction, Arteriolosclerosis, and Tau With Dementia in Chronic Traumatic Encephalopathy

IMPORTANCE

Chronic traumatic encephalopathy (CTE) is a neurodegenerative disease associated with repetitive head impacts, including those from US football, that presents with cognitive and neuropsychiatric disturbances that can progress to dementia. Pathways to dementia in CTE are unclear and likely involve tau and nontau pathologic conditions.

OBJECTIVE

To investigate the association of white matter rarefaction and cerebrovascular disease with dementia in deceased men older than 40 years who played football and had CTE.

DESIGN, SETTING, AND PARTICIPANTS

This cross-sectional study involves analyses of data from the ongoing Understanding Neurologic Injury and Traumatic Encephalopathy (UNITE) Study, which is conducted via and included brain donors from the Veterans Affairs-Boston University-Concussion Legacy Foundation brain bank between 2008 and 2017. An original sample of 224 men who had played football and were neuropathologically diagnosed with CTE was reduced after exclusion of those younger than 40 years and those missing data.

EXPOSURES

The number of years of football play as a proxy for repetitive head impacts.

MAIN OUTCOMES AND MEASURES

Neuropathological assessment of white matter rarefaction and arteriolosclerosis severity (on a scale of 0-3, where 3 is severe); number of infarcts, microinfarcts, and microbleeds; and phosphorylated tau accumulation determined by CTE stage and semiquantitative rating of dorsolateral frontal cortex (DLFC) neurofibrillary tangles (NFTs) (none or mild vs moderate or severe). Informant-based retrospective clinical interviews determined dementia diagnoses via diagnostic consensus conferences.

RESULTS

A total of 180 men were included. The mean (SD) age of the sample at death was 67.9 (12.7) years. Of 180, 120 [66.7%]) were found to have had dementia prior to death. Moderate to severe white matter rarefaction (84 of 180 [46.6%]) and arteriolosclerosis (85 of 180 [47.2%]) were common; infarcts, microinfarcts, and microbleeds were not. A simultaneous equations regression model controlling for age and race showed that more years of play was associated with more severe white matter rarefaction (β, 0.16 [95% CI, 0.02-0.29]; P = .03) and greater phosphorylated tau accumulation (DLFC NFTs: β, 0.15 [95% CI, 0.004-0.30]; P = .04; CTE stage: β, 0.27 [95% CI, 0.14-0.41]; P < .001). White matter rarefaction (β, 0.16 [95% CI, 0.02-0.29]; P = .03) and DLFC NFTs (β, 0.16 [95% CI, 0.03-0.28]; P = .01) were associated with dementia. Arteriolosclerosis and years of play were not associated, but arteriolosclerosis was independently associated with dementia (β, 0.21 [95% CI, 0.07-0.35]; P = .003).

CONCLUSIONS AND RELEVANCE

Among older men who had played football and had CTE, more years of football play were associated with more severe white matter rarefaction and greater DLFC NFT burden. White matter rarefaction, arteriolosclerosis, and DLFC NFTs were independently associated with dementia. Dementia in CTE is likely a result of neuropathologic changes, including white matter rarefaction and phosphorylated tau, associated with repetitive head impact and pathologic changes not associated with head trauma, such as arteriolosclerosis.

Blood-brain barrier imaging as a potential biomarker for bipolar disorder progression

Bipolar disorder affects approximately 2% of the population and is typically characterized by recurrent episodes of mania and depression. While some patients achieve remission using mood-stabilizing treatments, a significant proportion of patients show progressive changes in symptomatology over time. Bipolar progression is diverse in nature and may include a treatment-resistant increase in the frequency and severity of episodes, worse psychiatric and functional outcomes, and a greater risk of suicide. The mechanisms underlying bipolar disorder progression remain poorly understood and there are currently no biomarkers for identifying patients at risk. The objective of this study was to explore the potential of blood-brain barrier (BBB) imaging as such a biomarker, by acquiring the first imaging data of BBB leakage in bipolar patients, and evaluating the potential association between BBB dysfunction and bipolar symptoms. To this end, a cohort of 36 bipolar patients was recruited through the Mood Disorders Clinic (Nova Scotia Health Authority, Canada). All patients, along with 14 control subjects (matched for sex, age and metabolic status), underwent contrast-enhanced dynamic MRI scanning for quantitative assessment of BBB leakage as well as clinical and psychiatric evaluations. Outlier analysis has identified a group of 10 subjects with significantly higher percentages of brain volume with BBB leakage (labeled the "extensive BBB leakage" group). This group consisted exclusively of bipolar patients, while the "normal BBB leakage" group included the entire control cohort and the remaining 26 bipolar subjects. Among the bipolar cohort, patients with extensive BBB leakage were found to have more severe depression and anxiety, and a more chronic course of illness. Furthermore, all bipolar patients within this group were also found to have co-morbid insulin resistance, suggesting that insulin resistance may increase the risk of BBB dysfunction in bipolar patients. Our findings demonstrate a clear link between BBB leakage and greater psychiatric morbidity in bipolar patients and highlight the potential of BBB imaging as a mechanism-based biomarker for bipolar disorder progression.

Contact sport participation and chronic traumatic encephalopathy are associated with altered severity and distribution of cerebral amyloid angiopathy

Cerebral amyloid angiopathy (CAA) consists of beta-amyloid deposition in the walls of the cerebrovasculature and is commonly associated with Alzheimer's disease (AD). However, the association of CAA with repetitive head impacts (RHI) and with chronic traumatic encephalopathy (CTE) is unknown. We evaluated the relationship between RHI from contact sport participation, CTE, and CAA within a group of deceased contact sport athletes (n = 357), a community-based cohort (n = 209), and an AD cohort from Boston University AD Center (n = 241). Unsupervised hierarchal cluster analysis demonstrated a unique cluster (n = 11) with increased CAA in the leptomeningeal vessels compared to the intracortical vessels (p < 0.001) comprised of participants with significantly greater frequencies of CTE (7/11) and history of RHI. Overall, participants with CTE (n = 251) had more prevalent (p < 0.001) and severe (p = 0.010) CAA within the frontal leptomeningeal vessels compared to intracortical vessels. Compared to those with AD, participants with CTE had more severe CAA in frontal than parietal lobes (p < 0.001) and more severe CAA in leptomeningeal than intracortical vessels (p = 0.002). The overall frequency of CAA in participants with CTE was low, and there was no significant association between contact sport participation and the presence of CAA. However, in those with CAA, a history of contact sports was associated with increased CAA severity in the frontal leptomeningeal vessels (OR = 4.01, 95% CI 2.52-6.38, p < 0.001) adjusting for AD, APOE ε4 status, and age. Participants with CAA had increased levels of sulcal tau pathology and decreased levels of the synaptic marker PSD-95 (p's < 0.05), and CAA was a predictor of dementia (OR = 1.75, 95% CI 1.02-2.99, p = 0.043) adjusting for age, sex, and comorbid pathology. Overall, contact sport participation and CTE were associated with more severe frontal and leptomeningeal CAA, and CAA was independently associated with worse pathological and clinical outcomes.