Inhalation of Silver Silicate Nanoparticles Leads to Transient and Differential Microglial Activation in the Rodent Olfactory Bulb
Ho Thi Thuy Huynh, Priya Upadhyay, Cora H. Lopez, Malia K. Miyashiro, Laura S. Van Winkle, Sara M. Thomasy, Kent E. Pinkerton
Abstract
Engineered silver nanoparticles (AgNPs), including silver silicate nanoparticles (Ag-SiO 2 NPs), are used in a wide variety of medical and consumer applications. Inhaled AgNPs have been found to translocate to the olfactory bulb (OB) after inhalation and intranasal instillation. However, the biological effects of Ag-SiO 2 NPs and their potential nose-to-brain transport have not been evaluated. The present study assessed whether inhaled Ag-SiO 2 NPs can elicit microglial activation in the OB. Adult Sprague-Dawley rats inhaled aerosolized Ag-SiO 2 NPs at a concentration of 1 mg/ml for 6 hours. On day 0, 1, 7, and 21 post-exposure, rats were necropsied and OB were harvested. Immunohistochemistry on OB tissues were performed with anti-ionized calcium-binding adapter molecule 1 and heme oxygenase-1 as markers of microglial activation and oxidative stress, respectively. Aerosol characterization indicated Ag-SiO 2 NPs were sufficiently aerosolized with moderate agglomeration and high-efficiency deposition in the nasal cavity and olfactory epithelium. Findings suggested that acute inhalation of Ag-SiO 2 NPs elicited transient and differential microglial activation in the OB without significant microglial recruitment or oxidative stress. The delayed and differential pattern of microglial activation in the OB implied that inhaled Ag-SiO 2 may have translocated to the central nervous system via intra-neuronal pathways.