title: Silica nanoparticles are less toxic to human lung cells when deposited at the air-liquid interface compared to conventional submerged exposure.
abstract: BACKGROUND
  Investigations on adverse biological effects of nanoparticles (NPs) in the lung by in vitro studies are usually performed under submerged conditions where NPs are suspended in cell culture media. However, the behaviour of nanoparticles such as agglomeration and sedimentation in such complex suspensions is difficult to control and hence the deposited cellular dose often remains unknown. Moreover, the cellular responses to NPs under submerged culture conditions might differ from those observed at physiological settings at the air-liquid interface.
  
  
  RESULTS
  In order to avoid problems because of an altered behaviour of the nanoparticles in cell culture medium and to mimic a more realistic situation relevant for inhalation, human A549 lung epithelial cells were exposed to aerosols at the air-liquid interphase (ALI) by using the ALI deposition apparatus (ALIDA). The application of an electrostatic field allowed for particle deposition efficiencies that were higher by a factor of more than 20 compared to the unmodified VITROCELL deposition system. We studied two different amorphous silica nanoparticles (particles produced by flame synthesis and particles produced in suspension by the Stöber method). Aerosols with well-defined particle sizes and concentrations were generated by using a commercial electrospray generator or an atomizer. Only the electrospray method allowed for the generation of an aerosol containing monodisperse NPs. However, the deposited mass and surface dose of the particles was too low to induce cellular responses. Therefore, we generated the aerosol with an atomizer which supplied agglomerates and thus allowed a particle deposition with a three orders of magnitude higher mass and of surface doses on lung cells that induced significant biological effects. The deposited dose was estimated and independently validated by measurements using either transmission electron microscopy or, in case of labelled NPs, by fluorescence analyses. Surprisingly, cells exposed at the ALI were less sensitive to silica NPs as evidenced by reduced cytotoxicity and inflammatory responses.
  
  
  CONCLUSIONS
  Amorphous silica NPs induced qualitatively similar cellular responses under submerged conditions and at the ALI. However, submerged exposure to NPs triggers stronger effects at much lower cellular doses. Hence, more studies are warranted to decipher whether cells at the ALI are in general less vulnerable to NPs or specific NPs show different activities dependent on the exposure method.
authors.affiliation: Institute of Toxicology and Genetics, Karlsruhe Institute of Technology, Campus North, Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, Germany.
authors.forename: Alicja
authors.initials: A
authors.lastname: Panas
authors.affiliation: Institute for Meteorology and Climate Research, Karlsruhe Institute of Technology, Campus North, Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, Germany.
authors.forename: Andreas
authors.initials: A
authors.lastname: Comouth
authors.affiliation: Institute for Meteorology and Climate Research, Karlsruhe Institute of Technology, Campus North, Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, Germany.
authors.forename: Harald
authors.initials: H
authors.lastname: Saathoff
authors.affiliation: Institute for Meteorology and Climate Research, Karlsruhe Institute of Technology, Campus North, Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, Germany.
authors.forename: Thomas
authors.initials: T
authors.lastname: Leisner
authors.affiliation: Institute of Toxicology and Genetics, Karlsruhe Institute of Technology, Campus North, Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, Germany.
authors.forename: Marco
authors.initials: M
authors.lastname: Al-Rawi
authors.affiliation: Institute of Biomedical Engineering, Karlsruhe Institute of Technology, Campus South, Kaiserstraße 12, 76128 Karlsruhe, Germany.
authors.forename: Michael
authors.initials: M
authors.lastname: Simon
authors.affiliation: Institute of Biomedical Engineering, Karlsruhe Institute of Technology, Campus South, Kaiserstraße 12, 76128 Karlsruhe, Germany.
authors.forename: Gunnar
authors.initials: G
authors.lastname: Seemann
authors.affiliation: Institute of Biomedical Engineering, Karlsruhe Institute of Technology, Campus South, Kaiserstraße 12, 76128 Karlsruhe, Germany.
authors.forename: Olaf
authors.initials: O
authors.lastname: Dössel
authors.affiliation: Institute for Technical Chemistry, Karlsruhe Institute of Technology, Campus North, Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, Germany.
authors.forename: Sonja
authors.initials: S
authors.lastname: Mülhopt
authors.affiliation: Institute for Technical Chemistry, Karlsruhe Institute of Technology, Campus North, Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, Germany.
authors.forename: Hanns-Rudolf
authors.initials: HR
authors.lastname: Paur
authors.affiliation: Institute of Toxicology and Genetics, Karlsruhe Institute of Technology, Campus North, Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, Germany.
authors.forename: Susanne
authors.initials: S
authors.lastname: Fritsch-Decker
authors.affiliation: Institute of Toxicology and Genetics, Karlsruhe Institute of Technology, Campus North, Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, Germany.
authors.forename: Carsten
authors.initials: C
authors.lastname: Weiss
authors.affiliation: Institute of Toxicology and Genetics, Karlsruhe Institute of Technology, Campus North, Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, Germany.
authors.forename: Silvia
authors.initials: S
authors.lastname: Diabaté
keywords: aerosol; air–liquid interface; dose; silica nanoparticles; toxicity