Figure 5.

Recent studies confirm that exosomes can pass through the blood-brain barrier (BBB)^201–204 in both directions. This means that specific exosomes detected in the cerebrospinal fluid (CSF), or in the blood from the brain can release into the bloodstream and vice versa. Each cell type releases a specific type of exosome(s) that are released and communicates with neighboring cells, acting as the messenger. This characteristic makes exosomes attractive as new sources of biomarkers and therapeutic targets suitable for use in clinical practice, such as liquid biopsy that could replace current invasive diagnostic methods. Exosomes also have a potential role in drug delivery for brain disease models, and their membrane markers can be used to identify their cellular origin.