Alterations in CSF Amyloid-β and Tau Biomarkers in Former College and Professional American Football Players: Findings from the DIAGNOSE CTE Research Project

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 <i>postmortem</i>, 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 <i>in vivo</i> 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, <i>n</i> = 100) and college (COL, <i>n</i> = 40) football players at high risk of CTE compared to asymptomatic unexposed controls (UE, <i>n</i> = 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 Aβ₄₀, Aβ₄₂, tTau, and pTau (pTau₁₈₁, pTau₂₁₇, pTau₂₃₁) 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, <i>APOE</i>-ε4 allele status, race, and body mass index. Our analysis revealed that football exposure affected both CSF Aβ₄₀ (<i>p</i> = 0.039) and Aβ₄₂ (<i>p</i> = 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 Aβ₄₀ (<i>p</i> = 0.0041) and Aβ₄₂ (<i>p</i> = 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 Aβ₄₀ (<i>p</i> = 0.011) and Aβ₄₂ (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 <i>postmortem</i> 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.