Imaging and Tracking of Exosomes within the Brain Using Gold Nanoparticles

Exosomes are emerging as effective therapeutic tools for various pathologies. These extracellular vesicles can bypass biological barriers, including the blood- brain barrier, and can serve as powerful drug and gene therapy transporters. However, the progress of therapy development is impeded by several challenges, including insufficient data on exosome trafficking and biodistribution and the difficulty to image deep brain structures in vivo. Herein, we established a method for noninvasive in vivo neuroimaging and tracking of exosomes, based on glucose-coated gold nanoparticle (GNP) labeling and computed tomography imaging. Labeling of exosomes with the GNPs was achieved directly, as opposed to the typical and less efficient indirect labeling mode through parent cells. On the mechanistic level, we found that the glucose-coated GNPs were uptaken into MSC-derived exosomes via an active, energy-dependent mechanism that is mediated by the glucose transporter GLUT-1 and involves endocytic proteins. Next, we determined optimal parameters of size and administration route; we demonstrated that 5 nm GNPs enabled improved exosome labeling and that intranasal, compared to intravenous, administration led to superior brain accumulation and thus enhanced in vivo neuroimaging. Furthermore, we used this technique to track the migration and homing patterns of intranasally administrated exosomes derived from mesenchymal stem cells (MSC-exo) in different brain pathologies, including stroke, autism, Parkinson`s disease and Alzheimer`s disease. We found that MSC-exo specifically targeted and accumulated in pathologically-relevant brains regions up to 96 hrs post administration. Thus, this exosome labeling technique can serve as a powerful diagnostic tool for various brain disorders and could potentially enhance exosome-based treatments for neuronal recovery.