Intracellular Dissolution of Silver Nanoparticles: Evidence from Double Stable Isotope Tracing

摘要

To track transformations of silver nanoparticles (AgNPs) in vivo, HepG2 and AS49 cells were cocultured with two enriched stable Ag isotopes ((107)AgNPs and (AgNO3)-Ag-109) at nontoxic doses. After enzymatic digestion, (107)AgNPs, ionic Ag-107(+) and Ag-109(+) in exposed cells could be separated and quantified by liquid chromatography combined with ICP-MS. We found that ratios of Ag-107(+) to total Ag-107 and proportions of Ag-107(+)/in cells increased gradually after exposure, proving that the Trojan-horse mechanism occurred, i.e., AgNPs released high contents of Ag+ after internalization. While the presence of Ag-109(+) (5 and 100 mu g/L) has little influence on the uptake of (107)AgNPs (0.1 and 2 mg/L), the presence of (107)AgNPs at a high dose (2 mg/L) dramatically increases the ingestion of Ag-109(+), even though (107)AgNPs at a low dose (100 mu g/L) showed negligible effects on the internalization of Ag-109(+). Cellular homeostasis may be perturbed under sublethal exposure of (107)AgNPs, and thus enhanced uptake of Ag-109(+). Our findings suggest that the widely adopted control experiments in toxicology studies, culturing organisms with AgNO3 at the same concentration of Ag+ in the AgNP exposure medium, may underestimate uptake of Ag+ and thus cannot exclude suspected toxic effects of Ag+ at high AgNP exposure doses.