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Importance In vivo biomarkers for detecting neuropathologies from repetitive head impacts (RHI), including chronic traumatic encephalopathy (CTE), are needed. Objective To evaluate the utility of plasma phosphorylated tau 217 (p-tau217), assess its performance as a beta-amyloid (Aβ) biomarker in participants with RHI exposure at risk for CTE, and explore concordance with CTE neuropathology in a postmortem subsample. Design, Setting, and Participants This longitudinal, multicenter, case-control study used data from the Diagnostics, Imaging, and Genetics Network for the Objective Study and Evaluation of CTE (DIAGNOSE CTE) Research Project, collected from September 2016 to October 2023. Participants were former American football players (case participants) and asymptomatic men unexposed to RHI (control participants). A subsample had available neuropathologic data. Exposures RHI, traumatic encephalopathy syndrome (TES) diagnoses, and levels of CTE certainty. Main Outcomes and Measures Plasma p-tau217 (classified as positive [≥0.63 pg/mL], intermediate [0.40-0.62 pg/mL], and negative [<0.40 pg/mL]), Aβ–positron emission tomography (PET; 18 F-florbetapir; with Aβ-positive defined as a standardized uptake value ratio [SUVR] ≥1.10), and tau-PET ( 18 F-flortaucipir). TES diagnoses were assigned by multidisciplinary consensus conference. Analyses of postmortem brains controlled for age, race, and APOE ε4 status. Results Among 231 participants (mean [SD] age, 57.75 [8.25] years), 177 were former football players (117 professional and 60 college) and 54 were unexposed participants. Former football players had higher baseline mean (SD) p-tau217 concentrations than unexposed participants (0.35 [0.26] pg/mL vs 0.27 [0.14] pg/mL; P = .008), although this was driven by a higher proportion of Aβ-PET–positive participants among former players. Plasma p-tau217 increased over time across the sample (B = 0.207 [95% CI, 0.117-0.298]; P < .001), with no significant time × exposure group interactions. Among football players, p-tau217 showed no time × group interactions with TES diagnosis, TES-CTE certainty, or RHI metrics. Higher p-tau217 concentration correlated with higher global Aβ-PET SUVR (B = 0.058 [95% CI, 0.053-3.501; P = .01), with a few discordant cases (5 participants were p-tau217–negative and Aβ-PET–positive; 7 participants were p-tau217–positive and Aβ-PET–negative). P-tau217 had similar areas under the curve for projecting Aβ-PET positivity as cerebrospinal fluid (CSF) p-tau181/Aβ42 and CSF Aβ40/42 measures (p-tau217: AUC, 0.88 [95% CI, 0.80-0.96]; CSF p-tau181/Aβ42: AUC, 0.89 [95% CI, 0.79-1.00]; CSF Aβ40/42: AUC, 0.85 [95% CI, 0.72-0.98]). Among 9 brain donors, 6 had CTE (stages II-IV; none with Alzheimer disease). Seven had negative or intermediate p-tau217, concordant with Aβ-PET. Two p-tau217 outliers with stage III CTE had normal concentrations upon additional testing. Conclusions and Relevance The findings of this study suggest that plasma p-tau217 concentration is unlikely to be useful for the detection of CTE, but it does show utility for ruling out Aβ pathology in participants at risk for CTE.

Dynamic fluid and solute transportation across the arachnoid barrier in the meninges of healthy participants was measured by tracking intravenous gadolinium-based contrast agent entering cerebrospinal fluid from dural blood vessels using dynamic dual-spin-echo perfusion MRI.

Chronic traumatic encephalopathy (CTE) is a neurodegenerative disease associated with exposure to repetitive head impacts (RHIs), characterized by tau tangles around small blood vessels at the depths of the sulci. Currently, CTE can be diagnosed only postmortem , but can present with an array of cognitive, behavioral, mood, and motor symptoms. However, traumatic brain injury is also associated with increased risk of Alzheimer’s disease (AD) and may lead to comorbid neuropathology. Characterization of the in vivo biomarkers of CTE is a necessary next step to facilitate accurate diagnoses. We examined the profile of cerebrospinal fluid (CSF) biomarkers of amyloid-β, total tau (tTau), and phospho-tau (pTau) in a cohort of former professional (PRO, n = 100) and college (COL, n = 40) football players at high risk of CTE compared to asymptomatic unexposed controls (UE, n = 43). CSF was collected under controlled conditions using collection, processing, and cryostorage kits provided by the DIAGNOSE CTE Research Project Biomarker Core, and concentrations of Aβ 40 , Aβ 42 , tTau, and pTau (pTau 181 , pTau 217 , pTau 231 ) were measured at the University of Gothenburg, Sweden, using immunoassays. Associations between CSF biomarker levels with football history, and diagnosis of traumatic encephalopathy syndrome (TES) were examined using linear regression, and corrected for age, education, APOE -ε4 allele status, race, and body mass index. Our analysis revealed that football exposure affected both CSF Aβ 40 ( p = 0.039) and Aβ 42 ( p = 0.038), particularly among those under 60 years of age in the PRO compared to the UE exposure group. Among former football players, estimates of RHI exposure were not generally associated with CSF Aβ, tTau, and pTau biomarker levels. CSF Aβ 40 ( p = 0.0041) and Aβ 42 ( p = 0.011) were lower in former football players with TES diagnosis compared to unexposed participants, although CSF Aβ, tTau, and pTau biomarker levels did not differ between former players with and without a TES diagnosis. Among former football players, reduced CSF Aβ 40 ( p = 0.011) and Aβ 42 (p = 6e-04) were observed in those with cognitive impairment compared to those with neurobehavioral dysregulation. The findings of significant associations of reduced CSF Aβ levels with RHI in elite football players are in line with recent postmortem studies; however, the lack of relationship with CSF tTau and pTau species observed to be altered in the setting of AD suggests that the pathological features of CTE reflected in fluid biomarkers are complex and require further study. The overlapping comorbid age-dependent features of neurodegeneration that occur in those at risk for CTE suggest that tau pathology in CTE is not reliably reflected by currently available fluid biomarkers and that the use of multiple biomarkers related to the compound characteristics of CTE may be required for early detection.

ImportanceExposure to repetitive head impacts (RHI) is associated with increased risk for neurodegeneration. Accumulation of toxic proteins due to impaired brain clearance is suspected to play a role.ObjectiveTo investigate whether perivascular space (PVS) volume is associated with lifetime exposure to RHI in individuals at risk for RHI-associated neurodegeneration.Design, Setting, and ParticipantsThis cross-sectional study was part of the Diagnostics, Imaging, and Genetics Network for the Objective Study and Evaluation of Chronic Traumatic Encephalopathy (DIAGNOSE CTE) Research Project, a 7-year multicenter study consisting of 4 US study sites. Data were collected from September 2016 to February 2020 and analyses were performed between May 2021 and October 2023. After controlling for magnetic resonance image (MRI) and processing quality, former American football players and unexposed asymptomatic control participants were included in analyses.ExposurePrior exposure to RHI while participating in American football was estimated using the 3 cumulative head impact indices (CHII-G, linear acceleration; CHII-R, rotational acceleration; and CHII, number of head impacts).Main Outcomes and MeasuresIndividual PVS volume was calculated in the white matter of structural MRI. Cognitive impairment was based on neuropsychological assessment. Linear regression models were used to assess associations of PVS volume with neuropsychological assessments in former American football players. All analyses were adjusted for confounders associated with PVS volume.ResultsAnalyses included 224 participants (median [IQR] age, 57 [51-65] years), with 170 male former football players (114 former professional athletes, 56 former collegiate athletes) and 54 male unexposed control participants. Former football players had larger PVS volume compared with the unexposed group (mean difference, 0.28 [95% CI, 0.00-0.56]; P = .05). Within the football group, PVS volume was associated with higher CHII-R (β = 2.71 × 10−8 [95% CI, 0.50 × 10−8 to 4.93 × 10−8]; P = .03) and CHII-G (β = 2.24 × 10−6 [95% CI, 0.35 × 10−6 to 4.13 × 10−6]; P = .03). Larger PVS volume was also associated with worse performance on cognitive functioning in former American football players (β = −0.74 [95% CI, −1.35 to −0.13]; P = .04).Conclusions and RelevanceThese findings suggest that impaired perivascular brain clearance, as indicated by larger PVS volume, may contribute to the association observed between RHI exposure and neurodegeneration.

AbstractBackgroundThe NINDS criteria define Traumatic Encephalopathy Syndrome (TES) as the clinical manifestation of the neuropathologically diagnosed chronic traumatic encephalopathy (CTE). The core clinical features of TES include both cognitive and neuropsychiatric symptoms, the latter termed neurobehavioral dysregulation (NBD). We explored potential biological correlates of NBD by investigating fluid biomarkers of neuronal damage, astrogliosis, phosphorylated tau (pTau), neuroinflammation, and catecholamines in former American football players.MethodOur cohort consisted of former professional (PRO) and college (COL) American football players from the DIAGNOSE CTE Research Project. NBD was measured by four subscales (i.e., explosivity, emotional dyscontrol, impulsivity, affective lability) and a total NBD score, derived by factor analysis of multiple self‐report neuropsychiatric measures. Plasma neurofilament light (NfL) and glial fibrillary acidic protein (GFAP), CSF total tau and pTau181/231/217, as well as CSF biomarkers related to neuroinflammation (IL‐6, CRP, TNF‐α, VEGF‐A), were measured with various well‐validated immunoassay methods. Catecholamines in CSF (dopamine, 3,4‐dihydroxyphenylacetic acid, 3,4‐dihydroxyphenylalanine, noradrenaline, 3,4‐dihydroxyphenylglycol) were measured with HPLC. Multivariate linear regression models assessed the relationships between biomarkers and NBD scales, adjusted for age, BMI, race, and APOE e4, including stratification by exposure group, i.e., PRO, COL.ResultDemographics and biomarker levels are displayed in Table 1. High levels of IL‐6 were significantly associated with higher scores of all NBD subscales, independent of exposure group. Other significant relationships included plasma NfL with emotional dyscontrol and impulsivity. Within the college group, CSF pTau181 was significantly associated with emotional dyscontrol and CSF noradrenaline with explosivity, emotional dyscontrol, impulsivity, and total NBD score. (Table 2 & Figure 1). IL‐6 models were repeated with measures of cognitive dysfunction (another core feature of TES) added as covariates; these analyses again found significant relationships between IL‐6 and NBD, irrespective of cognitive functioning.ConclusionWe observed specific fluid biomarkers related to NBD in former American football players. Of note were the associations between IL‐6 and all NBD subscales (and not with cognitive functioning), suggesting that neuroinflammation may be a specific component in the expression of NBD symptoms. Future studies will investigate how these neuroinflammatory processes are related to other biomarkers, level of RHI exposure, and neuropathology.