title: Alveolar epithelial cell injury due to zinc oxide nanoparticle exposure.
abstract: BACKGROUND
  Although inhalation of zinc oxide (ZnO) nanoparticles (NPs) is known to cause systemic disease (i.e., metal fume fever), little is known about mechanisms underlying injury to alveolar epithelium.
  
  
  OBJECTIVE
  Investigate ZnO NP-induced injury to alveolar epithelium by exposing primary cultured rat alveolar epithelial cell monolayers (RAECMs) to ZnO NPs.
  
  
  METHODS
  RAECMs were exposed apically to ZnO NPs or, in some experiments, to culture fluid containing ZnCl₂ or free Zn released from ZnO NPs. Transepithelial electrical resistance (R(T)) and equivalent short-circuit current (I(EQ)) were assessed as functions of concentration and time. Morphologic changes, lactate dehydrogenase release, cell membrane integrity, intracellular reactive oxygen species (ROS), and mitochondrial activity were measured.
  
  
  RESULTS
  Apical exposure to 176 μg/ml ZnO NPs decreased R(T) and I(EQ) of RAECMs by 100% over 24 hours, whereas exposure to 11 μg/ml ZnO NPs had little effect. Changes in R(T) and I(EQ) caused by 176 μg/ml ZnO NPs were irreversible. ZnO NP effects on R(T) yielded half-maximal concentrations of approximately 20 μg/ml. Apical exposure for 24 hours to 176 μg/ml ZnO NPs induced decreases in mitochondrial activity and increases in lactate dehydrogenase release, permeability to fluorescein sulfonic acid, increased intracellular ROS, and translocation of ZnO NPs from apical to basolateral fluid (most likely across injured cells and/or damaged paracellular pathways).
  
  
  CONCLUSIONS
  ZnO NPs cause severe injury to RAECMs in a dose- and time-dependent manner, mediated, at least in part, by free Zn released from ZnO NPs, mitochondrial dysfunction, and increased intracellular ROS.
authors.affiliation: Will Rogers Institute Pulmonary Research Center, University of Southern California, Los Angeles, California, USA.
authors.forename: Yong Ho
authors.initials: YH
authors.lastname: Kim
authors.forename: Farnoosh
authors.initials: F
authors.lastname: Fazlollahi
authors.forename: Ian M
authors.initials: IM
authors.lastname: Kennedy
authors.forename: Nazanin R
authors.initials: NR
authors.lastname: Yacobi
authors.forename: Sarah F
authors.initials: SF
authors.lastname: Hamm-Alvarez
authors.forename: Zea
authors.initials: Z
authors.lastname: Borok
authors.forename: Kwang-Jin
authors.initials: KJ
authors.lastname: Kim
authors.forename: Edward D
authors.initials: ED
authors.lastname: Crandall
mesh_terms: D000818:Animals; D018929:Cell Culture Techniques; D004195:Disease Models, Animal; D004305:Dose-Response Relationship, Drug; D017097:Electric Impedance; D004847:Epithelial Cells / Q000187:drug effects* / Q000378:metabolism; D007770:L-Lactate Dehydrogenase / Q000187:drug effects / Q000378:metabolism; D008297:Male; D018613:Microscopy, Confocal; D008928:Mitochondria / Q000187:drug effects / Q000378:metabolism; D053758:Nanoparticles / Q000633:toxicity*; D011650:Pulmonary Alveoli / Q000187:drug effects* / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D017382:Reactive Oxygen Species / Q000378:metabolism; D013997:Time Factors; D015034:Zinc Oxide / Q000378:metabolism / Q000633:toxicity*
chemical_list: D017382:Reactive Oxygen Species; D007770:L-Lactate Dehydrogenase; D015034:Zinc Oxide