Accumulation of nanoparticles after acute traumatic brain injury is particle size dependent

摘要

Introduction: Traumatic brain injury (TBI) is a major cause of death and permanent neurological disability, an estimated of 1.7 million TBI occur annually and account for over 50,000 deaths in the U.S. TBI is initiated by a mechanical insult that leads to a host of cellular and molecular alterations, including transient blood-brain-barrier (BBB) breakdown. Nanoparticles (NP) have played an important role as diagnostic and therapeutic (theranostic) agents in various diseases, but, limited permeability across BBB is a major obstacle for NP-based approaches for neural disease/injury. Previous studies with pre-clinical TBI models demonstrated permeability of large molecules such as Evans blue or horseradish peroxidase (～5nm) post-injury. There is a critical gap in understanding the behavior of theranostic sized (＞10nm) NP delivery after TBI. Therefore, the objective of this study was to investigate the effect of NP's size on extravasation after TBI. Materials and Methods: Specifically, carboxylated polystyrene NPs of 20,40,100, and 500nm with unique fluorescent spectra were pegylated to both increase circulation time and neutralize the surface charge of the nanoparticles. Pegylated-NP cocktail were intravenously injected in mice (n=4 retro-orbital injection) immediately, 2h, 12h and 23h post-injury (controlled cortical impact) and allowed to circulate for 1 h prior to sacrifice and perfusion. The brains were frozen, sectioned, and imaged (8 sections per animal, four animals per cohort) using confocal microscopy. Images were analyzed using ImageJ and the total number of positive pixels was quantified for each NP over the time course. Results and Discussion: Pegylation of NPs led to modest increases in hydrodynamic diameter (～5-7nm above baseline diameter) and reduced zeta-potential (range: -9mV to -29mV). Histological analysis demonstrated the presence of pegylated-NPs exclusively within the injury penumbra, indicating BBB breakdown and accumulation post injury. Results showed maximum accumulation occurred at 1h post injury for all the NPs compared to their respective contralateral region. The accumulation of each NP was reduced over the time course from 1h to 24h, compared to the contralateral region. Accumulation of 40nm particles was highest compared to 20nm, 100nm and 500nm at each time point. NPs accumulate at the injury site due to leaky vasculature, leading to enhanced permeability and retention effect. Conclusion: We have demonstrated the potential for NP accumulation up to 24h post injury, with 40nm particles having highest accumulation. Thus, the short-lived BBB permeability post-injury can be effectively utilized to deliver NP-based theranostics for TBI. Further characterization of NP accumulation using injury models such as fluid-percussion, will provide insights as to the full utility of NP-based theranostics agents for TBI.