title: Genotoxic responses to titanium dioxide nanoparticles and fullerene in gpt delta transgenic MEF cells.
abstract: BACKGROUND
  Titanium dioxide (TiO2) nanoparticles and fullerene (C60) are two attractive manufactured nanoparticles with great promise in industrial and medical applications. However, little is known about the genotoxic response of TiO2 nanoparticles and C60 in mammalian cells. In the present study, we determined the mutation fractions induced by either TiO2 nanoparticles or C60 in gpt delta transgenic mouse primary embryo fibroblasts (MEF) and identified peroxynitrite anions (ONOO-) as an essential mediator involved in such process.
  
  
  RESULTS
  Both TiO2 nanoparticles and C60 dramatically increased the mutation yield, which could be abrogated by concurrent treatment with the endocytosis inhibitor, Nystatin. Under confocal scanning microscopy together with the radical probe dihydrorhodamine 123 (DHR 123), we found that there was a dose-dependent formation of ONOO- in live MEF cells exposed to either TiO2 nanoparticles or C60, and the protective effects of antioxidants were demonstrated by the nitric oxide synthase (NOS) inhibitor, NG-methyl-L-arginine (L-NMMA). Furthermore, suppression of cyclooxygenase-2 (COX-2) activity by using the chemical inhibitor NS-398 significantly reduced mutation frequency of both TiO2 nanoparticles and C60.
  
  
  CONCLUSIONS
  Our results provided novel information that both TiO2 nanoparticles and C60 were taken up by cells and induced kilo-base pair deletion mutations in a transgenic mouse mutation system. The induction of ONOO- may be a critical signaling event for nanoparticle genotoxicity.
authors.affiliation: Center for Radiological Research, College of Physicians & Surgeons, Columbia University, New York, New York, USA. tkh1@columbia.edu.
authors.forename: An
authors.initials: A
authors.lastname: Xu
authors.forename: Yunfei
authors.initials: Y
authors.lastname: Chai
authors.forename: Takehiko
authors.initials: T
authors.lastname: Nohmi
authors.forename: Tom K
authors.initials: TK
authors.lastname: Hei