Investigate cytokines and neurodegenerative proteins in whole plasma and neuron-derived exosomes as biomarkers for traumatic brain injury (TBI).

Blood-circulating exosomes have potential as diagnostic biomarkers for various diseases, such as HIV and certain malignancies. This study investigated the utility of measuring TBI-associated proteins in neuron-derived exosomes as potential biomarkers for TBI.

Blood samples were collected from 17 subjects (10 TBI, 7 control) within 24 hours of injury and assayed for concentrations of 7 TBI-relevant proteins (cytokines-interleukins 6 and 10 (IL-6, IL-10), tumor necrosis factor-alpha (TNF- αalpha); neurodegeneration-associated – neurofilament light chain (NFL), ubiquitin C-terminal hydrolase L1 (UCHL-1), Tau, glial fibrillary acidic protein (GFAP)) using the SIMOA immunoassay (Quanterix, Inc.) The concentration of each protein was measured in whole plasma, total exosomes, and glutamate receptor -2 (GLU-R2)- containing exosomes. These values were analyzed along with the pertinent clinical information to determine their diagnostic and prognostic potential.

Within total plasma, NFL and GFAP levels were significantly increased in TBI subjects as compared to controls (p < 0.05). Differences in protein and cytokine content were observed between whole plasma and exosomes as well. Receiver operator characteristic (ROC) curves were generated from logistic regression models. GluR2-exosome and whole plasma proteins showed modest to excellent predictive power of TBI vs. control subjects (AUC=0.71-0.93). A machine learning algorithm improved the diagnostic model’s AUC above 0.9. When all neurodegenerative proteins were combined in a logistic regression model for prediction of 3-month outcome (‘good recovery’ = GOSE score of 7-8), the GLU-R2 exosome protein content (AUC=0.93) performed better than whole plasma content (AUC=0.86).

This study showed cytokine and neurodegenerative protein concentrations differ within whole plasma, total exosome, and Glu-R2 exosomes. The data also indicate modest to excellent diagnostic and prognostic power for these proteins suggesting potential for Glu-R2 exosome proteins as biomarkers for TBI.