title: Zinc oxide nanoparticles exhibit cytotoxicity and genotoxicity through oxidative stress responses in human lung fibroblasts andDrosophila melanogaster.
abstract: BACKGROUND
  Although zinc oxide nanoparticles (ZnO NPs) have been widely used, there has been an increasing number of reports on the toxicity of ZnO NPs. However, study on the underlying mechanisms under in vivo conditions is insufficient.
  
  
  METHODS
  In this study, we investigated the toxicological profiles of ZnO NPs in MRC5 human lung fibroblasts in vitro and in an in vivo model using the fruit flyDrosophila melanogaster. A comprehensive study was conducted to evaluate the uptake, cytotoxicity, reactive oxygen species (ROS) formation, gene expression profiling and genotoxicity induced by ZnO NPs.
  
  
  RESULTS
  For in vitro toxicity, the results showed that there was a significant release of extracellular lactate dehydrogenase and decreased cell viability in ZnO NP-treated MRC5 lung cells, indicating cellular damage and cytotoxicity. Generation of ROS was observed to be related to significant expression of DNA Damage Inducible Transcript (DDIT3) and endoplasmic reticulum (ER) to nucleus signaling 1 (ERN1) genes, which are ER stress-related genes. Oxidative stress induced DNA damage was further verified by a significant release of DNA oxidation product, 8-hydroxydeoxyguanosine (8-OHdG), as well as by the Comet assay. For the in vivo study using the fruit flyD. melanogasteras a model, significant toxicity was observed in F1 progenies upon ingestion of ZnO NPs. ZnO NPs induced significant decrease in the egg-to-adult viability of the flies. We further showed that the decreased viability is closely associated with ROS induction by ZnO NPs. Removal of one copy of theD. melanogaster Nrf2alleles further decreased the ZnO NPs-induced lethality due to increased production of ROS, indicating that nuclear factor E2-related factor 2 (Nrf2) plays important role in ZnO NPs-mediated ROS production.
  
  
  CONCLUSIONS
  The present study suggests that ZnO NPs induced significant oxidative stress-related cytotoxicity and genotoxicity in human lung fibroblasts in vitro and inD. melanogasterin vivo. More extensive studies would be needed to verify the safety issues related to increased usage of ZnO NPs by consumers.
authors.affiliation: Department of Anatomy, Yong Loo Lin School of Medicine, National University of Singapore, Singapore; Environmental Research Institute, National University of Singapore, Singapore.
authors.forename: Cheng Teng
authors.initials: CT
authors.lastname: Ng
authors.affiliation: Department of Anatomy, Yong Loo Lin School of Medicine, National University of Singapore, Singapore.
authors.forename: Liang Qing
authors.initials: LQ
authors.lastname: Yong
authors.affiliation: Department of Physiology, Yong Loo Lin School of Medicine.
authors.forename: Manoor Prakash
authors.initials: MP
authors.lastname: Hande
authors.affiliation: Environmental Research Institute, National University of Singapore, Singapore.
authors.forename: Choon Nam
authors.initials: CN
authors.lastname: Ong
authors.affiliation: Department of Civil and Environmental Engineering, National University of Singapore, Singapore, Singapore.
authors.forename: Liya E
authors.initials: LE
authors.lastname: Yu
authors.affiliation: Department of Anatomy, Yong Loo Lin School of Medicine, National University of Singapore, Singapore.
authors.forename: Boon Huat
authors.initials: BH
authors.lastname: Bay
authors.affiliation: Department of Anatomy, Yong Loo Lin School of Medicine, National University of Singapore, Singapore.
authors.forename: Gyeong Hun
authors.initials: GH
authors.lastname: Baeg
mesh_terms: D000818:Animals; D002460:Cell Line; D049109:Cell Proliferation / Q000187:drug effects; D048430:Cell Shape / Q000187:drug effects; D002470:Cell Survival / Q000187:drug effects; D004249:DNA Damage; D004331:Drosophila melanogaster / Q000166:cytology* / Q000187:drug effects*; D005347:Fibroblasts / Q000187:drug effects / Q000473:pathology*; D006801:Humans; D007814:Larva / Q000187:drug effects; D008168:Lung / Q000473:pathology*; D051267:NF-E2-Related Factor 2 / Q000378:metabolism; D053758:Nanoparticles / Q000633:toxicity* / Q000648:ultrastructure; D018384:Oxidative Stress / Q000187:drug effects*; D017382:Reactive Oxygen Species / Q000378:metabolism; D015034:Zinc Oxide / Q000633:toxicity*
chemical_list: D051267:NF-E2-Related Factor 2; D017382:Reactive Oxygen Species; D015034:Zinc Oxide
keywords: Drosophila; MRC5 cells; ROS; oxidative stress; zinc oxide nanoparticles