Repeated blows to the head can cause lasting damage to the delicate blood-brain barrier, a finding that scientists believe may be a significant factor in the development of chronic traumatic encephalopathy (CTE). This neurodegenerative condition affects individuals who have engaged in contact sports such as football, rugby, and boxing. The current understanding is that CTE can only be definitively identified post-mortem. However, this new research offers the possibility of developing novel methods for diagnosis, prevention, and treatment.
Matthew Campbell of Trinity College Dublin in Ireland noted the ongoing development of medications aimed at restoring the blood-brain barrier for various neurological disorders. He expressed optimism about the future prospects should some of these treatments gain approval.
Investigating Blood-Brain Barrier Integrity in Athletes
Campbell and his research team conducted brain scans on 47 former athletes from contact sports, who had retired an average of 12 years prior to the study. The study also included retired athletes from non-contact sports, such as rowing, and individuals with no history of athletic participation, all of whom underwent similar brain scans. Participants were administered a magnetic resonance imaging (MRI) contrast agent.
This agent was designed to enter brain tissue only if the blood-brain barrier was compromised, enabling substances to move from blood vessels into the brain. For 17 of the former contact sport athletes, MRI scans revealed the contrast agent had permeated numerous areas of their brains, indicating significant damage to their blood-brain barriers. In contrast, among individuals who had not participated in contact sports, the contrast agent was barely detectable.
Correlation Between Barrier Damage and Cognitive Decline
Furthermore, retired athletes exhibiting more extensive blood-brain barrier damage also demonstrated poorer performance on cognitive and memory assessments. This correlation suggests that damage to this protective barrier may be an early contributor to CTE. The condition is characterized by difficulties with thinking and memory, alongside symptoms of depression and emotional instability.
Michael Buckland from the University of Sydney in Australia commented that while previous evidence had linked blood-brain barrier disruption to CTE, this study substantially reinforces that association.
The Biomechanical Impact of Head Trauma
Team member Chris Greene at the Royal College of Surgeons in Ireland explained that the mechanical forces resulting from repeated collisions and whiplash movements in sports are responsible for damaging the blood-brain barrier. He described the barrier not as a static wall, but rather as a dynamic, living system composed of tightly-packed cells lining the brain’s small blood vessels. Impact forces, he stated, loosen the cellular connections within this barrier, increasing its permeability.
Inflammation and Protein Misfolding Mechanisms
This increased permeability allows proteins, immune cells, and inflammatory substances from the bloodstream to enter the brain, initiating inflammation and cellular damage. The research team also examined the brains of deceased individuals diagnosed with CTE, identifying signs of immune cell and blood protein infiltration in affected regions. CTE shares notable similarities with Alzheimer’s disease, a condition some researchers theorize is also linked to age-related weakening of the blood-brain barrier and subsequent entry of immune cells and other substances into brain tissue.
Similar to Alzheimer’s, CTE is associated with an abnormal accumulation of tau protein in the brain. While tau serves a normal structural function in neurons in healthy brains, head trauma can cause it to misfold and become disorganized. Greene suggested that when head injuries concurrently disrupt the blood-brain barrier, blood proteins and inflammatory factors can enter the brain, exacerbating tau misfolding and aggregation. This process, he believes, ultimately leads to the cognitive changes observed in CTE. Buckland and his colleagues had previously identified gene signatures related to blood-brain barrier compromise in the brains of individuals with CTE, providing further support for these latest findings.
Potential for Early Diagnosis and Therapeutic Intervention
Currently, a definitive CTE diagnosis relies on post-mortem examination of the brain for abnormal tau buildup. However, Campbell and Greene suggest that their MRI technique could potentially be utilized to aid in the diagnosis of living individuals exhibiting symptoms like cognitive and mood alterations. They also propose that this imaging method might, with further research, be employed to monitor CTE risk in active athletes. Such studies are necessary to validate this potential application.
Greene elaborated on the potential for interventions if blood-brain barrier disruption is indeed an early driver of CTE. He indicated that drugs could be repurposed or developed to strengthen or repair the barrier, thereby preventing or slowing the progression of the condition. For instance, bevacizumab, a drug known to reduce blood vessel leakage, might warrant investigation. Other medications that reduce brain inflammation, such as minocycline, are also garnering interest, with additional drugs in development.
“Instead of waiting until tau pathology is entrenched, we may be able to intervene earlier by protecting the vasculature, reducing harmful blood-derived signals and calming the inflammatory cascade before it becomes self-sustaining,” Greene stated.
Journal reference: Science Translational Medicine DOI: 10.1126/scitranslmed.adu6037