Higher exosomal phosphorylated tau and total tau among veterans with combat-related repetitive chronic mild traumatic brain injury.

OBJECTIVE: The objective of the study is to measure plasma and exosomal levels of tau, phosphorylated tau (p-tau), and amyloid beta (Aβ) in Veterans with historical mild traumatic brain injury (mTBI) and chronic neuropsychological symptoms.

METHODS: Tau, p-tau, Aβ40, and Aβ42 were measured by ultrasensitive immunoassay in plasma and exosomes from 195 Veterans enrolled in the Chronic Effects of Neurotrauma Consortium Multicenter Observational Study. Protein biomarkers were compared among groups with and without mTBI with loss of consciousness (LOC) or post-traumatic amnesia (PTA), and also in those with and without repetitive (≥3) mTBI (rTBI) compared to those with 0 (TBI-neg) and 1-2 mTBI.

RESULTS: There were no differences in measures of plasma and exosomal protein levels among mTBI with LOC or PTA, mTBI with alteration of consciousness only or TBI-neg. Exosomal tau and exosomal p-tau were elevated in rTBI compared to those with 2 or fewer mTBIs and TBI-neg (p < 0.05). Elevations of exosomal tau and p-tau significantly correlated with post-traumatic and post-concussive symptoms, with exosomal tau also relating specifically to cognitive, affective, and somatic post-concussive symptoms (p < 0.05).

CONCLUSION: rTBI is associated with elevations of exosomal p-tau and exosomal tau, suggesting that blood-based exosomes may provide a peripheral source of informative, centrally derived biomarkers in remote mTBI and that rTBI may contribute to chronic neuropsychological symptoms.