Demonstration of an Olfactory Bulb–Brain Translocation Pathway for ZnO Nanoparticles in Rodent Cells In Vitro and In Vivo

Abstract

ZnO nanoparticles (ZnO-NPs) are widely used in the engineering and cosmetic industries, and inhaled airborne particles pose a known hazard to human health; their translocation into humans is a recognized public health concern. The pulmonary-blood pathway for ZnO-NP toxicity is well documented, but whether translocation of these particles can also occur via an olfactory bulb-brain route remains unclear. The potential toxicity of ZnO-NPs for the human central nervous system (CNS) is predicated on the possibility of their translocation. Our study investigated translocation of ZnO-NPs both in vitro using the neuronal cell line PC12 and in vivo in a Sprague-Dawley rat model. Our findings indicate that the zinc-binding dye, Newport-Green DCF, binds ZnO stoichiometrically and that ZnO-NP concentration can therefore be measured by the fluorescence intensity of the bound dye in confocal fluorescence microscopy. Confocal data obtained using Newport-Green DCF-2 K(+)-conjugated ZnO-NPs along with the membrane probe FM1-43 demonstrated endocytosis of ZnO-NPs by PC12 cells. In addition, Fluozin-3 measurement showed elevation of cytosolic Zn(2+) concentration in these cells. Following in vivo nasal exposure of rats to airborne ZnO-NPs, olfactory bulbs and brains that were examined by Newport-Green fluorescence and TEM particle measurement clearly showed the presence of ZnO-NPs in brain. We conclude that an olfactory bulb-brain translocation pathway for airborne ZnO-NPs exists in rats, and that endocytosis is required for interneuron translocation of these particles.

Sub-toxic concentrations of nano-ZnO and nano-TiO₂ suppress neurite outgrowth in differentiated PC12 cells

“…1 and 2). Our results using nano-ZnO are consistent with previous reports describing the toxicity of nano-ZnO to mouse neuro-2A neuroblastoma cells, human-derived SH-SY5 neuronal cells, or PC12 cells (Jeng and Swanson, 2006;Valdiglesias et al, 2013a;Kao et al, 2012b), although the toxic nano-ZnO concentrations reported were slightly different from those determined in this study. Nano-ZnO-induced cytotoxicity would be caused by Zn 2+ ions released from nano-ZnO (Xu et al, 2013).…”

“…Nasal exposure of airborne nano-ZnO or nano-TiO 2 in rodents results in their translocations into the brain (Kao et al, 2012b;Wang et al, 2008), and several groups have reported the effects of these nanomaterials on neuronal viability or neuronal excitability in vitro (Gramowski et al, 2010;Valdiglesias et al, 2013aValdiglesias et al, , 2013bLiu et al, 2010;Long et al, 2007;Jeng and Swanson, 2006). However, it is still unclear whether these nanomaterials affect the differentiation and development of neurons.…”

Zinc oxide nanoparticles induce toxic responses in human neuroblastoma SHSY5Y cells in a size-dependent manner

“…[16][17][18] Moreover, the olfactory brain route has also been reported as a potential route for ZnO NPs transfer into the brain. 19 However, information regarding the neurotoxic effects of ZnO NPs is scarce. Therefore, understanding the effects of nanomaterial exposure, including neurotoxicity, is important for ensuring the safety of nanomaterials, particularly when the particles are used in biomedical applications.…”

Potential Links between Cytoskeletal Disturbances and Electroneurophysiological Dysfunctions Induced in the Central Nervous System by Inorganic Nanoparticles

“…Due to these means of penetrating the BBB, some advanced nanomaterials conjugated with ligands or PEGylated NPs, among others, have been considered meaningful materials for cancer drug delivery and bioimaging applications [4], which is a significant advantage over other conventional medicine, which were incapable of penetrating the BBB. Furthermore, studies have found that these NPs could be translocated into the brain via the olfactory nerve after inhalation or intranasal instillation [15,16], as demonstrated by high NPs concentrations in the olfactory bulbs [17].…”