Silver nanoparticles in vitro toxicity study

The size and physical characteristics of NPs make endocytotic entry into the epithelia possible. As silver NPs are widely used and commercially available, it is important to study their potential toxicity. The project NANOTRAFFIC performed such a toxicity study.

Team members developed a polarised intestinal-hepatic cell line, RTgutGC, from rainbow trout. This intestinal-hepatic cell culture system enabled evaluation of the transport across the intestinal epithelia, and measurement of the effects on the liver cells growing underneath. The chosen model allowed scientists to differentiate between the apical and basolateral membranes' uptake of the NPs in vitro.

NANOTRAFFIC used citrate-coated ion-producing silver NPs (19 nm) and non-dissolving titanium oxide NPs (21 and 25 nm). Cell viability was evaluated through metabolic activity and membrane and lysosome integrity. The cytotoxicity of both silver NPs and ions increased greatly in the media without amino acids and proteins. The NPs mostly affected lysosome integrity. NPs entered lysosomes directly, as visualised by scanning electron microscopy. While exposure to 1 micrometre of silver NPs for 24 hours was non-toxic to the RTgutGC cells, exposure to 10 micrometres resulted in a 15 % reduction in viability. On the contrary, while the cells internalised titanium oxide NPs, these were accumulated in the endosomes and without measurable toxicity.

The intracellular concentration of essential metals (copper, zinc and iron) was measured along with concentrations of exposure to metal (silver). Intracellular concentrations of essential metals characterised transcriptional and post-translational changes elicited in cells upon exposure to metal NPs. While silver ions are known to be transported by copper transporter proteins, the project showed that silver NPs did not alter copper homeostasis. The knowledge generated in this project supports environmental risk assessment with regard to metal NP exposure.