Silver Nanoparticle Cytotoxicity and Antidote Proteins against Silver Toxicity in Paramecium

35 Introduction Silver has been deeply associated with human life in areas including tableware, accessories and both surgical and dental materials. In the recent advancement of nanotechnology, silver nanoparticles have been used as chemical catalysis, in medical and electronic devices and as antimicrobial agents. On the other hand, the cytotoxicity of silver nanoparticles have been increasingly reported in many organisms [1]; for instance, apoptosis with DNA degradation in human alveolar epithelial cells [2], a decrease in dopamine production in PC-12 (cultured neuronal phenotype) [3], a decrease in mitochondrial functions in a rat liver derived cell [4], an antimicrobial agent against Escherichia coli [5], and bio-concentration in Psudomonas aeroginosa [6]. For the analysis of molecular events associated with silver cytotoxicity, rat alveolar macrophages were selected as a model assay system system and reactive oxygen species (ROS) were found as one of the potent candidates. The production of ROS was nanoparticle-size dependent and oxidative stress was considered as a predominant mechanism of the cytotoxicity [7]. In this study, we used Paramecium, a free-living unicellular eukaryotic organism in fresh water, as a bioassay system for silver cytotoxicity. The Paramecium system (P system) provides several advantages, 1) P system enables us to examine single cell behavior involving excitable membrane and ciliary movement, 2) P system enables us to examine cytotoxicity by application to the inside of a cell, 3) P system has various types of cellular functions giving a stable and sensitive bioassay. In this study, we will demonstrate that silver nanoparticles produce silver ions which associate with the main cause of cytotoxicity and, in addition, the discovery of some proteins which decrease the cytotoxicity of silver ions. Silver Nanoparticle Cytotoxicity and Antidote Proteins against Silver Toxicity in Paramecium