Extracellular Vesicles Tracking and Quantification Using CT and Optical Imaging in Rats.

Exosomes, a subtype of extracellular vesicles, are nanovesicles of endocytic origin. Exosomes contain a plethora of proteins, lipids, and genetic materials of parent cells to facilitate intercellular communications. Tracking exosomes in vivo is fundamentally important to understand their biodistribution pattern and the mechanism of biological actions in experimental models. Until now, a number of tracking protocols have been developed, including fluorescence labeling, bioluminescence imaging, magnetic resonance imaging, and computed tomography (CT) tracking of exosomes. Recently, we have shown the tracking and quantification of exosomes in a spinal cord injury model, by using two tracking approaches. More specifically, following intranasal administration of gold nanoparticle-encapsulated exosomes to rats bearing complete spinal cord injury, exosomes in the whole central nervous system were tracked by using microCT, and quantified by using inductively coupled plasma and flame atomic absorption spectroscopy. In addition, optical imaging of fluorescently labeled exosomes was performed to understand the abundance of migrating exosomes in the spinal cord lesion, as compared to the healthy controls, and to further examine their affinity to different cell types in the lesion. Thus, the protocol presented here aids in the study of exosome biodistribution at both cellular and organ levels, in the context of spinal cord injury. This protocol will also enable researchers to better elucidate the fate of administered exosomes in other models of interest.