Repetitive head injuries in German American football players do not change blood-based biomarker candidates for CTE during a single season.

Background: Repetitive traumatic brain injuries in American football players (AFPs) can lead to the neurodegenerative disease chronic traumatic encephalopathy (CTE). Clinical symptoms of CTE range from mood and behavioral changes to cognitive impairment, depression, and suicidality. So far, CTE cannot be diagnosed in vivo and thus specific diagnostic parameters for CTE need to be found, to observe and treat exposed athletes as early as possible. Promising blood-based biomarkers for CTE include total tau (tTau), hyperphosphorylated tau (pTau), neurofilament light protein (NF-L), glial fibrillary acidic protein (GFAP), amyloid-β₄₀ (Aβ₄₀), amyloid-β₄₂ (Aβ₄₂) and calcium-binding protein B (S100-B). Previous studies have found elevated levels of these biomarkers in subjects exposed to TBIs, whereas cerebrospinal fluid (CSF) levels of Aβ₄₀ and Aβ₄₂ were decreased in CTE subjects. Here, we investigated whether young AFPs already exhibit changes of these biomarker candidates during the course of a single active season.

Methods: Blood samples were drawn from n = 18 American Football Players before and after a full season and n = 18 male age-matched control subjects. The plasma titers of tTau, pTau, NF-L, GFAP, Aβ₄₀, Aβ₄₂ and S100-B were determined. Additionally, Apathy, Depression, and Health status as well as the concussion history and medical care were assessed and analyzed for correlations.

Results: Here we show, that the selected biomarker candidates for CTE do not change significantly during the seven-month period of a single active season of American Football in blood samples of AFPs compared to healthy controls. But interestingly, they exhibit generally elevated pTau titers. Furthermore, we found correlations of depression, quality-of-life, career length, training participation and training continuation with headache after concussion with various titers.

Conclusion: Our data indicates, that changes of CTE marker candidates either occur slowly over several active seasons of American Football or are exclusively found in CSF. Nevertheless, our results underline the importance of a long-term assessment of these biomarker candidates, which might be possible through repeated blood biomarker monitoring in exposed athletes in the future.