Development of silica-coated silver iodide nanoparticles and their biodistribution.

Nanomaterials have great potential in the field of medicine and have been studied extensively. In a previous study, we addressed the potential of silver iodide (AgI) as X-ray contrast media, because it possessed high imaging ability in the measurement by X-ray computed tomography (X-CT) in vitro, and its surface can be modified with many functional groups. We developed the method of silica coating to make AgI nanoparticles more stable and uniform in size. However, the safety and metabolism of nanoparticles in vivo remains to be determined. The objective of the present study was to evaluate the in vivo biodistribution of silica-coated AgI nanoparticles (SAgINPs). X-CT, transmission electron microscopy (TEM), and inductively coupled plasma atomic emission spectrometry (ICP-AES) were performed prior to and at intervals following the intravenous administration of SAgINPs to rats and rabbits. ICP-AES is a spectral technique that can determine the presence and concentrations of metal samples. The X-CT study showed long-period enhancement in the liver and spleen, but not in the bladder of rats. The TEM study demonstrated that SAgINPs were found in hepatocytes. Using ICP-AES, Ag was detected in the bile juice of rabbits, but not found in the urine of these animals, suggesting that SAgINPs are excreted via the liver. This study shows the quantitative biodistribution of silica-coated nanoparticles for the first time, indicating that our silica coating technique is useful for development of nanoparticles with hepatic excretion. In conclusion, the SAgINPs may provide X-ray contrast media with high imaging ability and biocompatibility.