Extracellular vesicles as a biomarkers in traumatic brain injury: a systematic review of animal and clinical studies

Traumatic brain injury (TBI) is one of the leading causes of disability worldwide. Clinical or imaging scales are currently used to stratify severity, but they show a limited correlation with clinical prognosis, which has raised interest in biomarkers. Extracellular vesicles (EV)-based biomarkers may be superior to soluble biomarkers because of their stability, resistance to degradation and unique signature according to tissue of origin. Identification of EV-associated TBI biomarkers remains challenging due to the significant heterogeneity in experimental design, exosome isolation methods and study populations. This systematic review aims to analyze the role of EVs as biomarkers in TBI across both animal and clinical models, with particular focus on their association with prognosis. A systematic review was conducted according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Four electronic databases were searched from inception to December 31st, 2024, using the terms “traumatic brain injury”, “extracellular vesicles” and “biomarkers”. Animal studies and human cohort, case control, and case series studies were included; previous reviews, congress abstracts, and non-peer-reviewed works were excluded. Studies conducted on adult individuals or in experimental models of acute TBI, regardless of the mechanism and severity, and which studied biomarkers within the first week of injury, were included. The primary outcome was the EV-based biomarker identified by each study and its diagnostic accuracy when provided. Secondary outcomes were sample type for EV isolation, origin of EVs and methods for isolation and characterization. A total of 18 animal and 19 human studies were included. miRNAs were the most frequently identified biomarker in animal studies, while proteins were most common in human studies. The most commonly identified proteins in EVs were GFAP, UCH-L1, and Tau, with miRNA-124-3p also being repeatedly found. EVs were most frequently obtained from plasma, followed by brain tissue lysates in animals and cerebrospinal fluid or saliva in humans. Most studies used ultracentrifugation or polymer-based precipitation for EV isolation, with western blotting and electron microscopy for characterization. Few studies provided a measure of accuracy for the studied biomarkers; the highest diagnostic performance has been achieved with neural EV-based miRNA panels. While several studies explored diagnostic applications, only a limited number investigated prognostic utility, with few using scales such as GOS-E or evaluating long-term neurocognitive complications. This review highlights the potential of EV-based biomarkers in TBI, emphasizing their stability and tissue-specific signatures. Standardized protocols for EV isolation and characterization are needed for consistency across studies. While diagnostic applications have been explored, more research is required on the prognostic value of EV biomarkers, particularly for neurological outcomes, with future studies incorporating performance metrics to assess their clinical relevance.