Optical imaging of absorption and distribution of RITC-SiO₂ nanoparticles after oral administration

Chang-Moon Lee,¹ Tai Kyoung Lee,^2–5 Dae-Ik Kim,^1,6 Yu-Ri Kim,⁷ Meyoung-Kon Kim,⁷ Hwan-Jeong Jeong,^2–5 Myung-Hee Sohn,^2–5 Seok Tae Lim<sup>2–5

1</sup>Department of Biomedical Engineering, Chonnam National University, Yeosu, Jeollanam-Do, Republic of Korea; ²Department of Nuclear Medicine, Chonbuk National University Medical School and Hospital, Jeonju, Jeollabuk-Do, Republic of Korea; ³Cyclotron Research Center, Chonbuk National University Medical School and Hospital, Jeonju, Jeollabuk-Do, Republic of Korea; ⁴Biomedical Research Institute, Chonbuk National University Medical School and Hospital, Jeonju, Jeollabuk-Do, Republic of Korea; ⁵Molecular Imaging and Therapeutic Medicine Research Center, Chonbuk National University Medical School and Hospital, Jeonju, Jeollabuk-Do, Republic of Korea; ⁶School of Electrical, Electronic Communication, and Computer Engineering, Chonnam National University, Yeosu, Jeollanam-Do, Republic of Korea; ⁷Department of Biochemistry and Molecular Biology, Korea University Medical School and College, Seounbuk-Gu, Seoul, Republic of Korea


Purpose: In this study, we investigated the absorption and distribution of rhodamine B isothiocyanate (RITC)-incorporated silica oxide nanoparticles(SiNPs) (RITC-SiNPs) after oral exposure, by conducting optical imaging, with a focus on tracking the movement of RITC-SiNPs of different particle size and surface charge.
Methods: RITC-SiNPs (20 or 100 nm; positively or negatively charged) were used to avoid the dissociation of a fluorescent dye from nanoparticles via spontaneous or enzyme-catalyzed reactions in vivo. The changes in the nanoparticle sizes and shapes were investigated in an HCl solution for 6 hours. RITC-SiNPs were orally administered to healthy nude mice at a dose of 100 mg/kg. Optical imaging studies were performed at 2, 4, and 6 hours after oral administration. The mice were sacrificed at 2, 4, 6, and 10 hours post-administration, and ex vivo imaging studies were performed.
Results: The RITC-SiNPs were stable in the HCl solution for 6 hours, without dissociation of RITC from the nanoparticles and without changes in size and shape. RITC-SiNPs flowed into the small intestine from the stomach and gradually moved along the gut during the experiment. In the ex vivo imaging studies, optical signals were observed mostly in the lungs, liver, pancreas, and kidneys. The orally administered RITC-SiNPs, which were absorbed in the systemic circulation, were eliminated from the body into the urine. The 20 nm RITC-SiNPs showed higher uptake in the lungs than the 100 nm RITC-SiNPs. The distribution of the 100 nm RITC-SiNPs in the liver was higher than that of the 20 nm RITC-SiNPs, but the differences in the surface charge behavior were imperceptible.
Conclusion: We demonstrated that the movement of RITC-SiNPs after oral exposure could be traced by optical imaging. Optical imaging has the potential to provide valuable information that will help in understanding the behavior of SiNPs in the body following exposure.

Keywords: silica nanoparticles, oral exposure, rhodamine B isothiocyanate, RITC-SiNP

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