DNA damage and alterations in expression of DNA damage responsive genes induced by TiO₂ nanoparticles in human hepatoma HepG2 cells

Abstract

We investigated the genotoxic responses to two types of TiO₂ nanoparticles (<25 nm anatase: TiO₂-An, and <100 nm rutile: TiO₂-Ru) in human hepatoma HepG2 cells. Under the applied exposure conditions the particles were agglomerated or aggregated with the size of agglomerates and aggregates in the micrometer range, and were not cytotoxic. TiO₂-An, but not TiO₂-Ru, caused a persistent increase in DNA strand breaks (comet assay) and oxidized purines (Fpg-comet). TiO₂-An was a stronger inducer of intracellular reactive oxygen species (ROS) than TiO₂-Ru. Both types of TiO₂ nanoparticles transiently upregulated mRNA expression of p53 and its downstream regulated DNA damage responsive genes (mdm2, gadd45α, p21), providing additional evidence that TiO₂ nanoparticles are genotoxic. The observed differences in responses of HepG2 cells to exposure to anatase and rutile TiO₂ nanoparticles support the evidence that the toxic potential of TiO₂ nanoparticles varies not only with particle size but also with crystalline structure.

Keywords::

• TiO₂ nanoparticles
• genotoxic
• oxidative DNA damage
• gene expression
• HepG2 cells

Acknowledgments

This study was supported by Slovenian Research Agency: Program P1-0245 and young researcher grant to JP. We also thank Dr Zoran Samardžija for FEG-SEM examination of the powders. We thank Anja Pucer for her valuable advice in technical support. We thank Professor Roger Pain for critical reading of the manuscript.

Declaration of interest: The authors report no conflict of interest. The authors alone are responsible for the content and writing of the paper.