Repetitive head impacts (RHI) have been linked to multiple neuropathologies, including increased burden of hyper-phosphorylated tau (p-tau) proteins, neuroinflammation, and white matter degeneration. Biomarkers of RHI-related pathologies have traditionally been examined with neuroimaging. Blood-based biomarkers offer a clinically-promising cost-effective and scalable solution. We evaluated the usefulness of plasma biomarkers in individuals with RHI exposure to collect inferential observations regarding underlying neuropathologies.

The sample included 180 former American football players (120 former professional football players, 60 former college football players), and 60 asymptomatic men without RHI exposure (i.e., controls); all males, aged 45-74 years. Participants completed the Montreal Cognitive Assessment (MoCA) and a blood draw. Plasma assays were conducted for biomarkers of amyloid (Aβ40, Aβ42), neurodegeneration (total tau), axonal degeneration (NfL) and neuroinflammation (GFAP) using the Simoa 4-plex assay (Quanterix commercial). Plasma assays for p-tau proteins (p-tau181, p-tau231) were done using Simoa. Plasma IL-6 was analyzed using the V-PLEX Proinflammatory Panel 1 (Meso Scale Diagnostics. Due to skewed distribution, some plasma biomarkers were log-transformed by ln. Analysis of covariance compared former football players and controls on each plasma biomarker. Among football players, multivariable linear regressions tested the association between metrics of RHI (i.e., total years of football play, age of first exposure to football) and plasma biomarkers, in separate models. Models controlled for age, body mass index (BMI), revised Framingham stroke risk profile and Alcohol Use Disorders Identification Test (AUDIT) score; age of first exposure models controlled for total years of football play. P-values were adjusted for multiple comparisons using false discovery rate methods; p-values were corrected by the number of analyses per biomarker domain.

Of the sample, 87 (36.3%) were Black and 64 (26.7%) were AP0E e4 carriers; e4 status was not associated with any plasma biomarkers. On average, former football players had higher concentrations of log-p-tau181 (est. marginal mean difference = 0.193, p=0.027) and log-ptau-231 (est. marginal mean difference = 0.185, p=0.027) compared to controls. There were no group differences for Aβ40 (est. marginal mean difference = 5.478, p-value = 0.258), Aβ42 (est. marginal mean difference = 0.282, p-value = .258), log-t-tau (est. marginal mean difference = 0.077, p-value = 0.597), log-NfL (est. marginal mean difference = 0.075, p-value =0.287), log-GFAP (est. marginal mean difference = 0.002, p-value = 0.974) or log-IL6 (est. marginal mean difference = 0.239, p-value = 0.178). Total years of football play was not significantly associated with any of the plasma biomarkers. However, younger age of first exposure was associated with increased log-NfL (unstandardized β=-0.029, 95% CI [-0.053, -0.004], p-value=0.021) and log-GFAP (unstandardized β=-0.025, 95% CI [-0.044, 0-0.006], p-value = 0.024). Higher concentrations of log-GFAP were associated with lower raw MoCA scores (unstandardized β=-1.295, 95% CI [-2.576, -0.013], p-value=0.02).

We found higher levels of plasma biomarkers of p-tau181 and p-tau231 in football players compared to asymptomatic unexposed men, as well as significant associations between age of first exposure and biomarkers of axonal degeneration and neuroinflammation. Additional analyses will examine the association between the plasma biomarkers and diagnostic status and comprehensive neuropsychological testing and neuropsychiatric measures.