Exosomes: A new frontier in the treatment of neurological diseases.

Exosomes (Exos) are an essential class of extracellular vesicles enriched with a wide range of biologically active molecules, which gives them a unique advantage in participating in intercellular signaling and communication and serving as carriers for drug delivery. Exo-based diagnostic and therapeutic strategies are currently hot topics in disease research. Owing to their naturally low immunogenicity, good biocompatibility, ability to penetrate the blood‒brain barrier (BBB), and engineered modifications, exos have significant advantages and possible applications in the treatment of nervous system diseases. Due to the serious harm of neurological diseases to human health, they have been widely studied by researchers. Exos can be administered in a variety of ways, including intranasal administration, intracranial administration, local stereotactic injection, and encapsulation in biomaterials, each of which has its own advantages and disadvantages. However, several requirements need to be met before exo-based therapies can be implemented, such as the standardization of isolation and purification techniques, an in-depth understanding of the mechanism of action, and safety assessments and regulation for clinical translation. The aim of this review is to provide a comprehensive overview of the biogenesis, molecular composition, function, and delivery modes of exos and their therapeutic roles and mechanisms in neurological diseases (e.g., multiple sclerosis (MS), Alzheimer's disease (AD), Parkinson's disease (PD), and stroke) and to discuss the current challenges and future perspectives to support ongoing research and clinical applications.