title: Comparative lung toxicity of engineered nanomaterials utilizing in vitro, ex vivo and in vivo approaches.
abstract: BACKGROUND
  Although engineered nanomaterials (ENM) are currently regulated either in the context of a new chemical, or as a new use of an existing chemical, hazard assessment is still to a large extent reliant on information from historical toxicity studies of the parent compound, and may not take into account special properties related to the small size and high surface area of ENM. While it is important to properly screen and predict the potential toxicity of ENM, there is also concern that current toxicity tests will require even heavier use of experimental animals, and reliable alternatives should be developed and validated. Here we assessed the comparative respiratory toxicity of ENM in three different methods which employed in vivo, in vitro and ex vivo toxicity testing approaches.
  
  
  METHODS
  Toxicity of five ENM (SiO2 (10), CeO2 (23), CeO2 (88), TiO2 (10), and TiO2 (200); parentheses indicate average ENM diameter in nm) were tested in this study. CD-1 mice were exposed to the ENM by oropharyngeal aspiration at a dose of 100 μg. Mouse lung tissue slices and alveolar macrophages were also exposed to the ENM at concentrations of 22-132 and 3.1-100 μg/mL, respectively. Biomarkers of lung injury and inflammation were assessed at 4 and/or 24 hr post-exposure.
  
  
  RESULTS
  Small-sized ENM (SiO2 (10), CeO2 (23), but not TiO2 (10)) significantly elicited pro-inflammatory responses in mice (in vivo), suggesting that the observed toxicity in the lungs was dependent on size and chemical composition. Similarly, SiO2 (10) and/or CeO2 (23) were also more toxic in the lung tissue slices (ex vivo) and alveolar macrophages (in vitro) compared to other ENM. A similar pattern of inflammatory response (e.g., interleukin-6) was observed in both ex vivo and in vitro when a dose metric based on cell surface area (μg/cm(2)), but not culture medium volume (μg/mL) was employed.
  
  
  CONCLUSIONS
  Exposure to ENM induced acute lung inflammatory effects in a size- and chemical composition-dependent manner. The cell culture and lung slice techniques provided similar profiles of effect and help bridge the gap in our understanding of in vivo, ex vivo, and in vitro toxicity outcomes.
authors.affiliation: Curriculum in Toxicology, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA. kim.yongho@epa.gov.
authors.forename: Yong Ho
authors.initials: YH
authors.lastname: Kim
authors.affiliation: Environmental Public Health Division, National Health and Environmental Effects Research Laboratory, United States Environmental Protection Agency, Research Triangle Park, NC, USA. boykin.elizabeth@epa.gov.
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Boykin
authors.affiliation: Research Triangle Park Division, National Center for Environmental Assessment, United States Environmental Protection Agency, Research Triangle Park, NC, USA. stevens.tina@epa.gov.
authors.forename: Tina
authors.initials: T
authors.lastname: Stevens
authors.affiliation: Curriculum in Toxicology, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA. Lavrich.klavrich@email.unc.edu.
authors.forename: Katelyn
authors.initials: K
authors.lastname: Lavrich
authors.affiliation: Environmental Public Health Division, National Health and Environmental Effects Research Laboratory, United States Environmental Protection Agency, Research Triangle Park, NC, USA. gilmour.ian@epa.gov.
authors.forename: M Ian
authors.initials: MI
authors.lastname: Gilmour
mesh_terms: D000818:Animals; D002478:Cells, Cultured; D002563:Cerium / Q000633:toxicity; D016207:Cytokines / Q000378:metabolism; D005260:Female; D066298:In Vitro Techniques; D008168:Lung / Q000187:drug effects* / Q000378:metabolism / Q000473:pathology; D016676:Macrophages, Alveolar / Q000187:drug effects; D008815:Mice, Inbred Strains; D049329:Nanostructures / Q000737:chemistry / Q000633:toxicity*; D010316:Particle Size; D011014:Pneumonia / Q000139:chemically induced / Q000378:metabolism; D012822:Silicon Dioxide / Q000633:toxicity; D014025:Titanium / Q000633:toxicity; D018675:Toxicity Tests / Q000379:methods*
chemical_list: D016207:Cytokines; C009495:titanium dioxide; D002563:Cerium; C030583:ceric oxide; D012822:Silicon Dioxide; D014025:Titanium