An investigation of the potential for silver nanoparticles to cause toxicity to human cells in vitro

Abstract

Engineered nanoparticles are defined as having at least one dimension between 1 to 100 nm, which are intentionally produced because of specific properties based on shape, size and surface chemistry. The small size of nanomaterials gives them specific and/or enhanced physicochemical properties compared with the same materials at the macroscale, making them of great interest for development of “new” products. Silver nanoparticles (AgNPs) are being increasingly used in consumer products such as ‘stay fresh’ clothing, water purification and household cleaning agents. They are released into the environment in increasing amounts and concerns have been raised about the risk of harmful impact on both the environment and human health. This research used human cells in culture as a model system to investigate the potential toxicity of AgNPs. Early experiments used the MTT assay to define the concentrations of AgNPs and AgNO3 and incubation times that caused an acceptable loss of cell viability (≤ 20% loss). Using these conditions, the Comet method and phosphorylation of gH2AX determined DNA damage by the AgNPs in comparison to AgNO3 on the basis of weight (μg/ml). Epigenetic changes in response to AgNPs and AgNO3 were indicated by measurement of methylation of LINE-1 using pyrosequencing. The effect on oxidative stress was evaluated using a qPCR array platform followed by functional analysis of SOD1. A novel dialysis method was then developed to quantify release of Ag+ ions from the AgNPs that were available to the cells and TEM determined cellular localisation of the AgNPs. In conclusion, this research showed that both AgNPs and AgNO3 caused DNA damage in time and dose response manners by oxidative stress mechanisms, involving inhibition of SOD1. TEM imaging of cells exposed to AgNPs indicated that they were not internalized, but bound to the cell membrane, and from here released Ag+ ions into the cell.