(T1130-04-22) The Effect and Distribution of Amorphous Nanosilica Particle in the Brain and Microglial Cells

Purpose: Among several types of development in drug carriers, drug delivery by nanoparticles (NP) has been extensively studied. Because of the small size of NPs which are less than 100 nm, they exhibit numerous advantages including penetration of natural barriers in the human body and a much greater surface area to volume ratio that is useful for chemical coating. In addition to the drug carrier, an effective and minimally invasive drug delivery route has been studied. Among several types of drug delivery paths, such as oral administration or intramuscular administration, there is increasing attention to intranasal administration for the following reasons: By intranasal drug delivery, bioavailability is increased, drug metabolism is slower, and drugs could pass the blood-brain barrier. Despite the positive aspects of nanoparticle and intranasal administration in the drug delivery system, the precise drug delivery routes and safety information are not fully understood. To develop a safe and effective drug delivery system with NPs via intranasal routes to cure brain disease, further experiments are needed to comprehend the behavior of NPs in the brain and their distribution. Here, we tried to collect kinetics information using microglial cells in vitro, and distribution after intranasal administration in vivo using silica nanoparticles (nSP) as a model NP.

Methods: In this study, we utilized the mouse microglial cell line MG6 and employed fluorescent amorphous silica nanoparticles with a diameter of 10 nm (nSP10). The uptake of these nanoparticles was analyzed using a confocal high-content imaging system and flow cytometry. Furthermore, intranasal administration of nSP was performed, and sagittal sections of heads were observed using microscopy.

Results: Firstly, we attempted to evaluate the behavior of nSP10 in terms of cellular uptake using microglial cells that act as the main role in immune defense in the central nervous system. MG6 cells were treated with nSP10 and cellular uptake of nSP10 was evaluated by flow cytometry. As a results, nSP10 was incorporated into MG6 cells concentration dependent manner, indicating that silica nanoparticle with a diameter of 10 nm was taken up to microglial cells. Since mammalian cells have several way of uptake nanoparticle from outside of the cell such as endocytosis and phagocytosis, we further validate the key pathway to be involved in the uptake of nSP10. As a result of flow cytometry, cellular uptake of nSP10 was decreased when MG6 cells were treated with nSP10 along with endocytosis inhibitor. These in vitro data suggest that microglial cells have a capacity to uptake nanoparticle via endocytosis pathway. Next, to examine the distribution of nSP10 after intranasal administration in mice, we intranasally administrated nSP10 to Balb/c mice and sagittal sections of heads including brain region was observed. As a result, fluorescence of nSP10 was detected in olfactory bulb, olfactory epithelium, and respiratory epithelium, suggesting that intranasal administrated nSP10 could reach the brain.

Conclusion: In conclusion, the present study illustrated that amorphous silica nanoparticle with a diameter of 10 nm were incorporated into microglial cells. Moreover, intranasally administrated nSP10 was detected in the part of the brain in mice. These findings provide new insights into the potential hazard of nSP and the development of more safe nanoparticle as a drug carrier. We are currently working on omics analysis to clarify the biological dynamics in the brain when it is administrated by intranasal routes in mice.

Acknowledgements: This study was supported by a Health Labor Sciences Research Grant from the Ministry of Health, Labor, and Welfare of Japan.