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.