Silver nano-colloids disrupt medaka embryogenesis through vital gene expressions

Using medaka fish embryo model, toxic effects of silver nanocolloids (SNC, 3.8±1.0nm diameter) on developmental morphology and gene expression profile were investigated. SNC caused morphological changes in embryos including cardiovascular malformations, ischemia, underdeveloped central nervous system and eyes, and kyphosis at exposures of 0.5mg/L and 1.0mg/L.. To determine in vivo distribution of SNC, medaka embryos were exposed to 0.5mg/L for 6 days and subjected to ICP-OES analyses. Silver was detected in medaka embryos and chorion at levels of 16.6±9.3pg and 720±29pg, respectively. TEM analyses showed SNC adhered to the chorion surface and inside the chorion. On investigation of oxidative mechanism, NAC (0.05mM) rescued all embryos by 96-hr post treatment, while 0.5mM GSH did not. NAC blocked lipid peroxidation. Furthermore, medaka oligo DNA microarray and qRT-PCR were used for gene expression profiling in embryos exposed for 48-hr to 0.05mg/L SNC. Six genes relative to embryogenesis and morphogenesis such as ctsL, Tpm1, RBP, mt, atp2a1 and hox6b6 turned out to be affected and their involvement to the above malformations was implied. In conclusion, SNC causes gross malformations in the cardiovascular and central nervous systems in developing medaka embryos through potentially SNC-affected differential expression of a series of genes related to oxidative stress, embryonic cellular proliferation, and morphological development. Three of the stage-21 medaka embryos per sample were exposed in triplicate to 0mg/L (control) and 0.05mg/L SNC for 48 hours. Therefore, for each exposure condition nine of the stage-21 embryos were prepared and used in the SNC exposure test.