Study of The Effects of Silver Ions and Silver Nanoparticles on Embryonic Development

STUDY OF THE EFFECTS OF SILVER IONS AND SILVER NANOPARTICLES ON EMBRYONIC DEVELOPMENT Martha Sharisha Johnson Old Dominion University, 2019 Director: Dr. Xiao-Hong Nancy Xu This dissertation focuses on the study of the toxicity of metal nanoparticles (NPs) and their ions on the development of zebrafish embryos, aiming to understand unique biological effects of NPs and ions, and design new in vivo assays to characterize the toxicity of these metal NPs and metal ions. Currently, the underlying molecular mechanisms of biological effects of nanomaterials are partially understood. Some studies assume that the toxic effects of NPs can be attributed to the release of their ions. We investigate the effects of silver NPs (Ag NPs) and silver ions (Ag ions) on the embryonic development of zebrafish and compare both of their biocompatibility and toxicity. By statistically comparing the distributions of normal, deformed, and dead embryos, we conclude that the Ag ions cause deformities and death of developing embryos in a concentration dependent manner, where the critical concentration of the Ag ion is 0.20 μM for chronic exposure and varies in a stage-dependent manner in acute exposures during specific developmental stages. Exposure to Ag ions influences specific types of defects in development, which are far less drastic than those caused by the purified Ag NPs with the same amount of Ag atom. Thus, we can conclude that toxicity of Ag NPs on embryonic development is not due to the release of Ag ions, but rather their own unique physicochemical properties. We also synthesized and purified spherical Ag NPs (42 nm in diameter) that are stable (non-aggregated) in egg water media. We examined the biocompatibility and toxicity of single Ag NPs in vivo at specific stages of development and the defects associated with treatment at those specific developmental stages. We then developed new imaging approaches to characterize single Ag NPs as they interact with key brain biomarkers that are significant for neurological development in zebrafish embryos. More specifically, we exposed Tg(pax2a:GFP) zebrafish embryos to various concentrations of the Ag NPs, and studied the effects of Ag NPs on the expression of the pax2a gene during treatment using fluorescent microscopy. Sublethal concentrations of the Ag NPs (0.00, 0.50, 1.00, 2.00, and 5.00 pM) resulted in a phenotypical dependent effect on embryonic development. However, we did not observe a significant decrease in expression of pax2a:GFP when exposing developing embryos to the Ag NPs. We did, however, observe that a higher dose of the Ag NPs led to severe deformities. We have further demonstrated the effects of Ag NPs on cardiac response. We found a decrease in heart-rate of both normal and deformed zebrafish, as the developing embryos were exposed to the Ag NPs. Our study also shows the dose-dependent effects of Ag NPs on eye development, where higher concentrations of Ag NPs leads to microphthalmia in developing embryos. We further studied the accumulation of Ag NPs in treated embryos. We found that each embryo accumulated a significant amount of Ag NPs in a dose dependent manner, which explains why some embryos developed normally, abnormally or resulted in embryonic death during treatment. In summary, this study demonstrates that developing zebrafish embryos can serve as effective in vivo model organism to study biocompatibility and toxicity of nanomaterials and metal ions, and can potentially lead to better design of applications to study developmental biology.