Silver nanocolloids affects glycosylation in medaka fish to cause embryonic malformation.

We observed silver nanocolloids (SNCs) exposure to medaka embryo induced morphological deformities like shortened body and undeveloped head and eyes, and our gene expression analysis using medaka oligo DNA microarray suggested that glycan/glycosylation genes, such as gns and alg2, might be the targets of SNCs' toxicity. Validation studies of gns and alg2 gene expressions by qPCR showed stage-dependent and altered mRNA expression patterns, and their altered expressions were more severe in earlier stages of embryogenesis. A result from structural analysis of glycan revealed that stage 11 was the most sensitive stage to SNCs exposure, and stress seemed to be imposed upon endplasmic reticulum (ER) by SNCs. In fact, qPCR analysis of ER mannosidase demonstrated that N-glycan synthesis in ER was inhibited by SNCs. Overall, this study revealed that SNCs exposure caused embryonic malformations through disruption of glycan biosynthetic pathway in ER. Silver content of the purified silver nanocolloids which we used in our experiment contained approximately 15-20% ionic silver and 80-85% particle silver. Mean particle diameter of SNCs was about 28.4 ± 8.5 nm. For the DNA microarray gene expression analysis, each of the three sets of fifteen medaka embryos at stage 21 were exposed to 5 mL of 0.05 mg/L SNCs (dissolved in dH2O) solution in embryo-rearing medium at pH7.0 in 6-well plate at 25℃ in the dark for 48 hours (the test solutions were renewed every 24 hours). No-exposure (control) experiment was also carried out in the same way except that the SNCs solution was replaced by 5 mL of dH2O.