Olivia Osborne, Sijie Lin, Shuo Lin, and André Nel
The goal of this project is to delineate size dependent differences of AgNPs (20nm and 110nm) vs ionic control in two known target organs for Ag in fish, the gills and intestines, with the following aims: 1) to explore the toxicity of the particles 2) to explore the mechanism behind the toxicity observed in the target organs. We know from past literature that silver toxicity affects gills and the intestines and therefore wanted to compare this with silver nanoparticles.
In Aim 1 we developed a subchronic exposure platform for adult zebrafish with the intention to use this approach to study toxicokinetics and obtain histopathological analysis of critical target organs. The study demonstrated different toxicokinetic profiles for different particle sizes. The gills showed a significantly higher Ag content for the 20nm than the 110nm particles. While both particulates were retained after a depuration period, there was striking size-dependent differences upon histopathology analysis, with the 20 nm particles demonstrating the loss of distinguishable primary and secondary filaments, as a result of fusion of the secondary filaments. Silver staining of the gills and intestines confirmed prominent silver deposition in the basolateral membranes for the 20nm but not for the 110nm particles. To further analyze the mechanism of toxicity observed in the target organs we also explored an already known target for Ag in fish: the Na+/K+ ATPAse pump in the gill.
Therefore, Aim 2 set out to link the deleterious consequences on the target organs to a possible impact on this pump. We performed immunohistochemical analysis on the α subunit of the Na+/K+ ion channel which is localized in the basolateral membrane, the same site where we observed silver localization. Use of an ATPase assay demonstrated that 20nm particles caused more inhibition and reduction in ATPase activity than the 110nm particles or an ionic control. In summary, we achieved the goal of our project by demonstrating size dependent differences across different Ag treatment groups that included different size AgNPs and an ionic control. The results were published in ACS Nano. In the next year of study, we propose to use the adult platform as well new assays to asses the hazard potential of III-V materials present in CMP slurries.