Superparamagnetic\nIron Oxide Nanoparticle-Labeled\nExtracellular Vesicles for Magnetic Resonance Imaging of Ischemic\nStroke

Stroke is a leading cause of death and disability worldwide.\nExtracellular\nvesicles (EVs) derived from human mesenchymal stem cells (hMSCs) offer\na unique and promising alternative to direct cell injection as part\nof a cell-based therapy for stroke treatment. The development of labeling\nstrategies is essential to identifying the initial biodistribution\nand clearance of EV-based therapeutics. In this study, hMSC-EVs were\nlabeled with ultrasmall superparamagnetic iron oxide (USPIO) nanoparticles\nfor magnetic resonance imaging (MRI). Two methods of preparation were\nevaluated after EVs were sonicated in the presence of USPIO nanoparticles.\nThe labeled EVs were purified by (1) ultracentrifugation only or (2)\nan extension of a harvesting approach that employs poly(ethylene glycol)\n(PEG) to enrich EVs. Following in vitro assessment, labeled EVs were\napplied to an ischemic stroke model and imaged both immediately and\nlongitudinally using MRI. In vitro assessment showed the EV characteristics\nafter USPIO nanoparticle labeling. The PEG method exhibited a 3.6-fold\nenhancement in contrast by using an equivalent USPIO concentration\nof 0.5 mg/mL and equivalent acquisition parameters (TE = 3.5 ms, TR\n= 5 s) when the dilution factor is considered. Sufficient USPIO nanoparticle\nlabeling was achieved to visualize the initial biodistribution and\nassess the initial therapeutic potential. Taken together, simultaneous\nUSPIO nanoparticle labeling and EV enrichment with PEG enhanced MRI\ncontrast and improved outcomes with respect to delivery and ischemic\nstroke recovery.