The sequestration of metal nanoparticles in the liver: A trade-off between density and degradability

The widespread use and casual disposal of nanoproducts increase human exposure to nanoparticles (NPs), posing potential health risks. When coming into contact with biofluid, NPs passively move in the bloodstream and reach target organs and cells. The nano-bio interactions, distribution, and fate of NPs are highly dependent on their physicochemical properties after direct exposure into the systemic circulation. In this study, silver nanoparticles (AgNPs) and gold nanoparticles (AuNPs) with the same size, shape, surface chemistry, and particle number but different densities were co-exposed to mice to explore their blood circulation and liver accumulation. The co-exposure avoids the individual differences in a single-material exposure model. Post-exposure, Au remained longer in the bloodstream than Ag, while 92.2 % of the injected dose (%ID) of Ag accumulated in the liver compared to 78.0 % for Au. Over a span of 3 to 72 h, Ag content in bloodstream increased while Au was undetectable. In the liver, the %ID of Ag sharply decreased to 9.4 %, while the %ID of Au remained nearly unchanged. We proved the gradual dissociation of AgNPs into Ag ions using a fluorescent probe. Therefore, density-dependent dynamics of NPs in the blood caused greater liver accumulation of low-density Ag. However, the gradual degradation of AgNPs contributes to a high degree of distribution of Ag in the body while the AuNPs remain sequestered in the liver. This study implies that the dynamic transformation of NPs complicates their density-dependent retention, which are plausible to determine the accumulation and biological effects to the organisms.