Overpressure Exposure From .50-Caliber Rifle Training Is Associated With Increased Amyloid Beta Peptides in Serum

Background: Overpressure (OP) is an increase in air pressure above normal atmospheric levels. Military personnel are repeatedly exposed to low levels of OP caused by various weapon systems. OP exposure is associated with acute Breacher’s brain symptomology inclusive of headaches, dizziness, and tinnitus similar to mild traumatic brain injury (mTBI) or concussion. Repeated OP may increase risk of neurological disease or psychological disorder diagnoses. Yet, a means to detect early-phase effects that may be relevant to trauma remain elusive. Therefore, development of quantitative and objective OP-mediated effects during acute time-frames would vastly augment point-of-care or field-based decisions. This study evaluated the amplitude of traumatic brain injury (TBI)-associated biomarkers in serum as a consequence of repeated OP exposure from .50 caliber rifle use over multiple days during training. Objective: To determine the acute temporal profile of TBI-associated serum biomarkers and their association with neurocognitive decrements or self-reported symptoms among participants exposed to low level, repeated OP from weapons used in a training environment. Methods: Study participants were enrolled in .50 caliber sniper rifle training and exposed to mild OP (peak pressure 3.8-4.5 psi, impulse 19.27-42.22 psi-ms per day) for three consecutive days (D1-D3). Defense Automated Neurobehavioral Assessment (DANA) neurocognitive testing, symptom reporting, and blood were collected 2-3 h before (pre-) and 0.45-3h after (post-) OP exposure. The TBI-associated serum biomarkers, glial fibrillary acidic protein (GFAP), Ubiquitin C-terminal hydrolase-L1 (UCH-L1), Neurofilament light (Nf-L), Tau, amyloid beta peptides (Aβ-40 and Aβ-42) were measured using digital ELISAs. Results: Serum GFAP decreased on D1 and D3, but not D2 after OP exposure. Nf-L was suppressed on D3 alone. Aβ-40 and Aβ-42 were elevated each day after OP exposure. Suppression of GFAP and elevation of Aβ-42 correlated to OP-mediated impulse levels measured on D3. Conclusions: Acute measurement of Aβ-peptides may have utility as biomarkers of subconcussive OP caused by rifle-fire. Fluctuation of GFAP, Nf-L, and, in particular, Aβ peptide levels may have utility as acute, systemic responders of subconcussive OP exposure caused by rifle-fire, even in the absence of extreme operational deficits or clinically defined concussion.