Tissue distribution of intravenously administrated hydroxyapatite nanoparticles labeled with 125I

Hydroxyapatite nanoparticles (HANPs) have been developed for biomedical use due to its extraordinary properties. However, the side effects of HANPs on human body have also been concerned, especially in vivo. Now it is still unknown how about the distribution and biobehavior of HANPs in vivo is, though it's very important for application in biosystem. This study was to establish a new method of 125I radiolabeling on HANPs at 80 nm, investigate the long-term tissue distribution of HANPs quantitatively after intravenously administrated HANPs labeled with 125I and the subcellular distribution in liver and spleen by TEM. The results indicated the labeled HANPs had high stability in vitro, and could accumulate mainly in the liver and spleen and decrease in time dependent manner, but still retain in body for more than 28 days. This stagnation most probably attribute to the endocytosis by macrophages in these tissues. The results implied the radioactive iodine labeling was an effective and sensitive method for tracing and analyzing the distribution of NPs in vivo. Liver and spleen should be the main target organ reached when HANPs were injected into circulation system. Because HANPs could stay in vivo for over one month, the biosafety shouldn't be neglected.