Brain injury biomarker levels increase as a result of asymptomatic high-acceleration head impacts

Written by Carissa Drake

Serum levels of two biomarkers of traumatic brain injury (TBI) were found to have increased in American varsity football players following high-acceleration head impacts (HHIs), researchers from the University of Michigan (MI, USA) have revealed.
The study, published in the Journal of Neurosurgery, aimed to determine whether injury to the brain occurs in the absence of clinical symptoms.

The nature of American football makes it difficult to detect whether, and to what extent, brain injury has occurred. Helmet-based accelerators were used by the researchers to measure the head impact data of 16 players across the 2016 football season, during both training sessions and matches.

Of the 7756 head impacts recorded, only 11 (0.001%) were considered to be an HHI, which was defined as a head impact involving linear acceleration greater than 95 g and rotational acceleration greater than 3760 rad/second2. Six of the 16 athletes experienced at least one HHI during the season, while five other athletes acted as controls.

The team collected blood samples from the 16 high-school athletes to measure serum levels of a number of TBI biomarkers, including tau and UCH-L1. All 16 players were tested at the beginning of the season and 12 players were tested once the season had ended.

Players were also tested at the end of games in which an HHI occurred (six players), and five players who were used as controls against the six players with an HHI had their blood collected after the final game.

The study revealed significant increases in tau and UCH-L1 serum levels following a single HHI, compared with athletes who did not experience an HHI. In players without symptoms of concussion, levels of both biomarkers were higher post-season compared with levels before the season began. Other TBI biomarkers were tested but no significant increase in serum levels were found.

High serum levels of UCH-L1 and tau indicate neuronal body injury and axonal injury, respectively. The results suggest an association between increasing biomarker levels and HHIs in varsity football, as well as an association between rising biomarker levels and athletes who played throughout the whole season, whether they experienced an HHI or not.

Lead author Jacob Joseph from the University of Michigan concluded: “This study suggests asymptomatic HHIs, which represent only 0.001% of all impacts, may be on the same spectrum as concussion. Whether these elevations in blood biomarkers of TBI are clinically significant is yet to be known.”

“However, we are excited as this potentially provides a new avenue to reduce the risk to young athletes. Specifically, we believe that technological improvements and refinements of game rules may be able to reduce the incidence of HHI.”

Sources: Joseph JR, Swallow JS, Willsey K et al. Elevated markers of brain injury as a result of clinically asymptomatic high-acceleration head impacts in high-school football athletes. J. Neurosurg. doi:10.317/2017.12.JNS172386 (2018) (Epub ahead of print);