From the Cover: Zinc oxide Nanoparticles-Induced Reactive Oxygen Species Promotes Multimodal Cyto- and Epigenetic Toxicity

Toxicol Sci. 2017 Mar 1;156(1):261-274. doi: 10.1093/toxsci/kfw252.


In this study we evaluated and correlated the cytotoxic effects of zinc oxide nanoparticles (ZnO-NPs) to the epigenetic modifications, using human embryonic kidney (HEK-293) cells as a model system. Imaging of singlet and total reactive oxygen species (ROS) in ZnO-NPs-treated live cells was performed followed by the evaluation of its effects on cytoskeletal, mitochondrial, and nuclear integrity, and on the expression of ROS responsive genes. Next, we determined the global and locus-specific changes in DNA-methylation at the 3 global genomic repeat sequences namely LINE-1, subtelomeric D4Z4 and pericentromeric NBL2, and at the promoter of selected ROS responsive genes (AOX1, HMOX1, NCF2, SOD3). Our studies revealed severe actin depolymerization, increased release of mitochondrial cytochrome C, and nuclear enlargement in ZnO-NPs-treated cells. At the epigenetic level, we observed global reduction in 5-methylcytosine and increase in 5-hydroxymethylcytosine content. Additionally, we observed significant increase in the expression of Ten-Eleven Translocation (TET)-methylcytosine dioxygenase genes but not in the expression of DNA-methyltransferases (DNMTs). Based on our findings, we suggest that ZnO-NPs induce abundant increase in ROS to promote multimodal structural and functional anomalies in cells. Most importantly, ZnO-NP-induced ROS may promote global hypomethylation in cells by triggering the expression of TET-enzymes, avoiding DNMT interferences. Global DNA demethylation is considered to be the hallmark of the majority of cancers and once acquired this could be propagated to future progenies. The present study, hence, can be used as a platform for the assessment of epigenomic toxicity of ZnO-NPs in humans in the light of its use in commercial products.

Keywords: DNA-methylation.; ZnO-nanoparticles; cytotoxicity; epigenetics.

Publication types

  • Research Support, U.S. Gov't, Non-P.H.S.
  • Research Support, Non-U.S. Gov't

MeSH terms

  • 5-Methylcytosine / analogs & derivatives
  • 5-Methylcytosine / metabolism
  • Actin Cytoskeleton / drug effects
  • Carcinogens, Environmental / chemistry
  • Carcinogens, Environmental / toxicity
  • Cell Membrane / drug effects
  • Cell Membrane / metabolism
  • Cell Membrane / ultrastructure
  • Cell Nucleus Size / drug effects
  • Cell Survival / drug effects
  • DNA Demethylation / drug effects*
  • Epigenesis, Genetic / drug effects*
  • Gene Expression Regulation, Enzymologic / drug effects
  • HEK293 Cells
  • Hepatocytes / drug effects*
  • Hepatocytes / metabolism
  • Hepatocytes / ultrastructure
  • Humans
  • Metal Nanoparticles / toxicity*
  • Metal Nanoparticles / ultrastructure
  • Microscopy, Electron, Scanning
  • Microscopy, Electron, Transmission
  • Oxidative Stress / drug effects*
  • Oxidoreductases / genetics
  • Oxidoreductases / metabolism
  • Promoter Regions, Genetic / drug effects
  • Reactive Oxygen Species / agonists*
  • Reactive Oxygen Species / metabolism
  • Repetitive Sequences, Nucleic Acid / drug effects
  • Zinc Oxide / chemistry
  • Zinc Oxide / toxicity*


  • Carcinogens, Environmental
  • Reactive Oxygen Species
  • 5-hydroxymethylcytosine
  • 5-Methylcytosine
  • Oxidoreductases
  • Zinc Oxide