Increase of circulating cell free mitochondrial DNA in amateur boxers after sparring matches

Objectives: To determine if circulating mitochondrial deoxyribonucleic acid levels increase after sport activity involving blows to the head, such as boxing, and if it could play a role in inflammatory cascade regulation in response to trauma. Design: Observational, longitudinal. Methods: We measured mitochondrial deoxyribonucleic acid levels and integrity in ten non-professional male boxers before and after three weekly sparring matches. We set up a protocol to separate three different plasma fractions enriched in mitochondria-containing vesicles, mitochondrial deoxyribonucleic acid bound to proteins and naked mitochondrial deoxyribonucleic acid. We quantified the levels of the main cytokines involved in inflammatory response and the levels of neurofilament light, a well-known marker of brain damage. Results: Circulating mitochondrial deoxyribonucleic acid levels increased after each match. In the second fraction, we also observed an increase over the weeks. Mitochondrial deoxyribonucleic acid is less intact after each match if compared with pre-match integrity, especially the naked form which is not protected within vesicles or mitochondria. Circulating levels of interleukin-6, interleukin-1beta and interleukin-10 increased after each match linking traumatic brain injuries to inflammatory state. Neurofilament light chain showed a similar trend to mitochondrial deoxyribonucleic acid. Conclusions: As mitochondrial deoxyribonucleic acid displays an inflammatory effect and neurofilament light chain is more specific for brain injury, we concluded that the simultaneous analysis of these two parameters could be helpful to monitor the effects of traumatic brain injury in contact sports, and that mitochondrial deoxyribonucleic acid is a promising candidate biomarker to study the inflammatory state of patients who suffered repeated traumatic brain injuries.