Pre-exposure to titanium or iron oxide nanoparticles suppresses the subsequent cellular uptake of gold nanoparticles.

Humans are exposed to a wide variety of natural and engineered nanoparticles (NPs) during their lifetime. However, the effects of pre-exposure to NPs on subsequent uptake of other NPs have not been investigated. In the present study, we investigated the effects of pre-exposure to three NPs (TiO, FeO, and SiO NPs) on the subsequent uptake of gold NPs (AuNPs) by hepatocellular carcinoma cells (HepG2). When HepG2 cells were pre-exposed to TiO or FeO NPs, but not SiO NPs for 2 days, their subsequent uptake of AuNPs was inhibited. Such inhibition was also observed in human cervical cancer (HeLa) cells, suggesting that this phenomenon is present in different cell types. The mechanisms underlying the inhibitory effect of NP pre-exposure include altered plasma membrane fluidity due to changes in lipid metabolism and reduced intracellular ATP production due to decreased intracellular oxygen. Despite the inhibitory effects of NP pre-exposure, full recovery was observed after transferring the cells to medium without NPs, even when the pre-exposure time was extended from 2 days to 2 weeks. Overall, the pre-exposure effects observed in the present study should be considered in the biological application and risk evaluation of NPs.