Treatment with silver nanoparticles delays repair of X-ray induced DNA damage in HepG2 cells

Nanoparticles (NPs) defined as particles having at least one dimension below 100 nm have been applied in the last decade in industry and medicine. Recently, there is an increased concern about the biohazard aspect of the presence of NP in consumer goods and in the environment. Silver NP (Ag NP) cause oxidative stress in mammalian cells in result of generation of reactive oxygen species (ROS). This results in genotoxicity and mutagenicity, disturbed mitochondrial respiration, slowed proliferation and cell death. Using the alkaline comet assay, we examined the effect of combined treatment with Ag NP 20 nm or 200 nm and X-rays (2 Gy) in HepG2 cells. In addition, combined treat-ment with X-rays and titanium dioxide NP (TiO2 NP) 21 nm was also studied. No effect of NP pre-treatment on X-ray induced initial deoxyribonucleic acid (DNA) damage levels was observed for all three NP. In contrast, Ag NP treatment preceding exposure to X-rays caused a marked decrease in the rate of single strand break rejoining. The effect was particularly strong for Ag NP 20 nm. TiO2 NP pre-treatment had no effect on DNA repair.