Pharmacokinetics, tissue distribution, and excretion of zinc oxide nanoparticles

Miri Baek,^1,* Hae-Eun Chung,^1,* Jin Yu,1_^,* Jung-A Lee,¹ Tae-Hyun Kim,² Jae-Min Oh,² Won-Jae Lee,³ Seung-Min Paek,³ Jong Kwon Lee,⁴ Jayoung Jeong, ⁴ Jin-Ho Choy,⁵ Soo-Jin Choi<sup>1

1</sup>Department of Food Science and Technology, Seoul Women's University, Seoul, ²Department of Chemistry and Medical Chemistry, College of Science and Technology, Yonsei University, Wonju, Gangwondo; ³Department of Chemistry and Green-Nano Materials Research Center, Kyungpook National University, Taegu, ⁴Toxicological Research Division, National Institute of Food and Drug Safety Evaluation, Chungchungbuk-do, ⁵Center for Intelligent Nano-Bio Materials, Department of Bioinspired Science and Department of Chemistry and Nano Science, Ewha Womans University, Seoul, Republic of Korea
^*These authors contributed equally to this work

Background: This study explored the pharmacokinetics, tissue distribution, and excretion profile of zinc oxide (ZnO) nanoparticles with respect to their particle size in rats.
Methods: Two ZnO nanoparticles of different size (20 nm and 70 nm) were orally administered to male and female rats, respectively. The area under the plasma concentration-time curve, tissue distribution, excretion, and the fate of the nanoparticles in organs were analyzed.
Results: The plasma zinc concentration of both sizes of ZnO nanoparticles increased during the 24 hours after administration in a dose-dependent manner. They were mainly distributed to organs such as the liver, lung, and kidney within 72 hours without any significant difference being found according to particle size or rat gender. Elimination kinetics showed that a small amount of ZnO nanoparticles was excreted via the urine, while most of nanoparticles were excreted via the feces. Transmission electron microscopy and x-ray absorption spectroscopy studies in the tissues showed no noticeable ZnO nanoparticles, while new Zn-S bonds were observed in tissues.
Conclusion: ZnO nanoparticles of different size were not easily absorbed into the bloodstream via the gastrointestinal tract after a single oral dose. The liver, lung, and kidney could be possible target organs for accumulation and toxicity of ZnO nanoparticles was independent of particle size or gender. ZnO nanoparticles appear to be absorbed in the organs in an ionic form rather than in a particulate form due to newly formed Zn-S bonds. The nanoparticles were mainly excreted via the feces, and smaller particles were cleared more rapidly than the larger ones. ZnO nanoparticles at a concentration below 300 mg/kg were distributed in tissues and excreted within 24 hours. These findings provide crucial information on possible acute and chronic toxicity of ZnO nanoparticles in potential target organs.

Keywords: ZnO nanoparticles, pharmacokinetics, tissue distribution, excretion, fate