title: Toxicity assessment of zinc oxide nanoparticles using sub-acute and sub-chronic murine inhalation models.
abstract: BACKGROUND
  Although ZnO nanoparticles (NPs) are used in many commercial products and the potential for human exposure is increasing, few in vivo studies have addressed their possible toxic effects after inhalation. We sought to determine whether ZnO NPs induce pulmonary toxicity in mice following sub-acute or sub-chronic inhalation exposure to realistic exposure doses.
  
  
  METHODS
  Mice (C57Bl/6) were exposed to well-characterized ZnO NPs (3.5 mg/m3, 4 hr/day) for 2 (sub-acute) or 13 (sub-chronic) weeks and necropsied immediately (0 wk) or 3 weeks (3 wks) post exposure. Toxicity was assessed by enumeration of total and differential cells, determination of total protein, lactate dehydrogenase activity and inflammatory cytokines in bronchoalveolar lavage (BAL) fluid as well as measurements of pulmonary mechanics. Generation of reactive oxygen species was assessed in the lungs. Lungs were evaluated for histopathologic changes and Zn content. Zn concentration in blood, liver, kidney, spleen, heart, brain and BAL fluid was measured.
  
  
  RESULTS
  An elevated concentration of Zn2+ was detected in BAL fluid immediately after exposures, but returned to baseline levels 3 wks post exposure. Dissolution studies showed that ZnO NPs readily dissolved in artificial lysosomal fluid (pH 4.5), but formed aggregates and precipitates in artificial interstitial fluid (pH 7.4). Sub-acute exposure to ZnO NPs caused an increase of macrophages in BAL fluid and a moderate increase in IL-12(p40) and MIP-1α, but no other inflammatory or toxic responses were observed. Following both sub-acute and sub-chronic exposures, pulmonary mechanics were no different than sham-exposed animals.
  
  
  CONCLUSIONS
  Our ZnO NP inhalation studies showed minimal pulmonary inflammation, cytotoxicity or lung histopathologic changes. An elevated concentration of Zn in the lung and BAL fluid indicates dissolution of ZnO NPs in the respiratory system after inhalation. Exposure concentration, exposure mode and time post exposure played an important role in the toxicity of ZnO NPs. Exposure for 13 wks with a cumulative dose of 10.9 mg/kg yielded increased lung cellularity, but other markers of toxicity did not differ from sham-exposed animals, leading to the conclusion that ZnO NPs have low sub-chronic toxicity by the inhalation route.
authors.forename: Andrea
authors.initials: A
authors.lastname: Adamcakova-Dodd
authors.forename: Larissa V
authors.initials: LV
authors.lastname: Stebounova
authors.forename: Jong Sung
authors.initials: JS
authors.lastname: Kim
authors.forename: Sabine U
authors.initials: SU
authors.lastname: Vorrink
authors.forename: Andrew P
authors.initials: AP
authors.lastname: Ault
authors.forename: Patrick T
authors.initials: PT
authors.lastname: O'Shaughnessy
authors.forename: Vicki H
authors.initials: VH
authors.lastname: Grassian
authors.affiliation: Department of Occupational and Environmental Health, University of Iowa, Iowa City, IA 52242, USA. peter-thorne@uiowa.edu.
authors.forename: Peter S
authors.initials: PS
authors.lastname: Thorne
mesh_terms: D000280:Administration, Inhalation; D000336:Aerosols; D000818:Animals; D001273:Atmosphere Exposure Chambers; D001822:Body Burden; D001992:Bronchoalveolar Lavage Fluid; D016085:Bronchoconstrictor Agents; D002470:Cell Survival / Q000187:drug effects; D015227:Lipid Peroxidation / Q000187:drug effects; D008171:Lung Diseases / Q000139:chemically induced / Q000473:pathology; D008297:Male; D016210:Methacholine Chloride; D051379:Mice; D008810:Mice, Inbred C57BL; D053758:Nanoparticles / Q000633:toxicity*; D018384:Oxidative Stress / Q000187:drug effects; D011014:Pneumonia / Q000139:chemically induced / Q000473:pathology; D017382:Reactive Oxygen Species / Q000378:metabolism; D015656:Respiratory Mechanics / Q000187:drug effects; D012995:Solubility; D023382:Toxicity Tests, Acute; D036401:Toxicity Tests, Chronic; D015430:Weight Gain / Q000187:drug effects; D015034:Zinc Oxide / Q000633:toxicity*
chemical_list: D000336:Aerosols; D016085:Bronchoconstrictor Agents; D017382:Reactive Oxygen Species; D016210:Methacholine Chloride; D015034:Zinc Oxide