Demonstration of an Olfactory Bulb–Brain Translocation Pathway for ZnO Nanoparticles in Rodent Cells In Vitro and In Vivo
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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 Zn2+ 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.
KeywordsZinc oxide nanoparticles Zn2+ PC12 cells Olfactory bulb–brain pathway
Zinc oxide nanoparticles
Cytosolic Zn2+ concentration
NPG salt form
Central nervous system
We thank all members of the ZnO-NP team, supported by the National Science Council, especially Miss Jung-Yen Liu, Meng Ho, and Miao-Chuan Yu for expert assistance with animal care and dissection. We also deeply appreciate Ms Suzanne Hosier’s critical editing of the English text. This work was supported by grants from the National Science Council, Taiwan, R.O.C. (NSC-96-2621-Z-031-001, NSC-97-2320-B-031-001 and NSC-97-2320-B-031-001) and Institute of Occupational Safety and Health, Taiwan, ROC (IOSH101-M326).
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