Molecular Mechanisms of Toxicity of Silver Nanoparticles in Zebrafish Embryos

Silver
nanoparticles cause toxicity in exposed organisms and are
an environmental health concern. The mechanisms of silver nanoparticle
toxicity, however, remain unclear. We examined the effects of exposure
to silver in nano-, bulk-, and ionic forms on zebrafish embryos (Danio rerio) using a Next Generation Sequencing approach
in an Illumina platform (High-Throughput SuperSAGE). Significant alterations
in gene expression were found for all treatments and many of the gene
pathways affected, most notably those associated with oxidative phosphorylation
and protein synthesis, overlapped strongly between the three treatments
indicating similar mechanisms of toxicity for the three forms of silver
studied. Changes in oxidative phosphorylation indicated a down-regulation
of this pathway at 24 h of exposure, but with a recovery at 48 h.
This finding was consistent with a dose-dependent decrease in oxygen
consumption at 24 h, but not at 48 h, following exposure to silver
ions. Overall, our data provide support for the hypothesis that the
toxicity caused by silver nanoparticles is principally associated
with bioavailable silver ions in exposed zebrafish embryos. These
findings are important in the evaluation of the risk that silver particles
may pose to exposed vertebrate organisms.