Demonstration of the Clathrin- and Caveolin-Mediated Endocytosis at the Maternal–Fetal Barrier in Mouse Placenta after Intravenous Administration of Gold Nanoparticles

Exposure to nanoparticles during pregnancy is a public concern, because nanoparticles may pass from the mother to the fetus across the placenta. The purpose of this study was to determine the possible translocation pathway of gold nanoparticles across the maternal–fetal barrier as well as the toxicity of intravenously administered gold nanoparticles to the placenta and fetus. Pregnant ICR mice were intravenously injected with 0.01% of 20- and 50-nm gold nanoparticle solutions on the 16th and 17th days of gestation. There was no sign of toxic damage to the placentas as well as maternal and fetal organs of the mice treated with 20- and 50-nm gold nanoparticles. ICP-MS analysis demonstrated significant amounts of gold deposited in the maternal livers and placentas, but no detectable level of gold in the fetal organs. However, electron microscopy demonstrated an increase of endocytic vesicles in the cytoplasm of syncytiotrophoblasts and fetal endothelial cells in the maternal–fetal barrier of mice treated with gold nanoparticles. Clathrin immunohistochemistry and immunoblotting showed increased immunoreactivity of clathrin protein in the placental tissues of mice treated with 20- and 50-nm gold nanoparticles; clathrin immunopositivity was observed in syncytiotrophoblasts and fetal endothelial cells. In contrast, caveolin-1 immunopositivity was observed exclusively in the fetal endothelium. These findings suggested that intravenous administration of gold nanoparticles may upregulate clathrin- and caveolin-mediated endocytosis at the maternal–fetal barrier in mouse placenta.