title: Translocation of gold nanoparticles across the lung epithelial tissue barrier: Combining in vitro and in silico methods to substitute in vivo experiments.
abstract: BACKGROUND
  The lung epithelial tissue barrier represents the main portal for entry of inhaled nanoparticles (NPs) into the systemic circulation. Thus great efforts are currently being made to determine adverse health effects associated with inhalation of NPs. However, to date very little is known about factors that determine the pulmonary translocation of NPs and their subsequent distribution to secondary organs.
  
  
  METHODS
  A novel two-step approach to assess the biokinetics of inhaled NPs is presented. In a first step, alveolar epithelial cellular monolayers (CMLs) at the air-liquid interface (ALI) were exposed to aerosolized NPs to determine their translocation kinetics across the epithelial tissue barrier. Then, in a second step, the distribution to secondary organs was predicted with a physiologically based pharmacokinetic (PBPK) model. Monodisperse, spherical, well-characterized, negatively charged gold nanoparticles (AuNP) were used as model NPs. Furthermore, to obtain a comprehensive picture of the translocation kinetics in different species, human (A549) and mouse (MLE-12) alveolar epithelial CMLs were exposed to ionic gold and to various doses (i.e., 25, 50, 100, 150, 200 ng/cm(2)) and sizes (i.e., 2, 7, 18, 46, 80 nm) of AuNP, and incubated post-exposure for different time periods (i.e., 0, 2, 8, 24, 48, 72 h).
  
  
  RESULTS
  The translocation kinetics of the AuNP across A549 and MLE-12 CMLs was similar. The translocated fraction was (1) inversely proportional to the particle size, and (2) independent of the applied dose (up to 100 ng/cm(2)). Furthermore, supplementing the A549 CML with two immune cells, i.e., macrophages and dendritic cells, did not significantly change the amount of translocated AuNP. Comparison of the measured translocation kinetics and modeled biodistribution with in vivo data from literature showed that the combination of in vitro and in silico methods can accurately predict the in vivo biokinetics of inhaled/instilled AuNP.
  
  
  CONCLUSIONS
  Our approach to combine in vitro and in silico methods for assessing the pulmonary translocation and biodistribution of NPs has the potential to replace short-term animal studies which aim to assess the pulmonary absorption and biodistribution of NPs, and to serve as a screening tool to identify NPs of special concern.
authors.affiliation: ETH Zürich, Institute for Chemical and Bioengineering, 8093, Zürich, Switzerland. gerald.bachler@chem.ethz.ch.|University of Fribourg, Adolphe Merkle Institute, 1700, Fribourg, Switzerland. gerald.bachler@chem.ethz.ch.
authors.forename: Gerald
authors.initials: G
authors.lastname: Bachler
authors.affiliation: ETH Zürich, Institute for Chemical and Bioengineering, 8093, Zürich, Switzerland. sabrina.losert@empa.ch.|EMPA, Swiss Federal Laboratories for Material Science and Technology, 8600, Dübendorf, Switzerland. sabrina.losert@empa.ch.
authors.forename: Sabrina
authors.initials: S
authors.lastname: Losert
authors.affiliation: University of Fribourg, Adolphe Merkle Institute, 1700, Fribourg, Switzerland. yuki.umehara@unifr.ch.
authors.forename: Yuki
authors.initials: Y
authors.lastname: Umehara
authors.affiliation: ETH Zürich, Institute for Chemical and Bioengineering, 8093, Zürich, Switzerland. natalie.von.goetz@chem.ethz.ch.
authors.forename: Natalie
authors.initials: N
authors.lastname: von Goetz
authors.affiliation: University of Fribourg, Adolphe Merkle Institute, 1700, Fribourg, Switzerland. laura.rodriguez-lorenzo@unifr.ch.
authors.forename: Laura
authors.initials: L
authors.lastname: Rodriguez-Lorenzo
authors.affiliation: University of Fribourg, Adolphe Merkle Institute, 1700, Fribourg, Switzerland. alke.fink@unifr.ch.
authors.forename: Alke
authors.initials: A
authors.lastname: Petri-Fink
authors.affiliation: University of Fribourg, Adolphe Merkle Institute, 1700, Fribourg, Switzerland. barbara.rothen@unifr.ch.
authors.forename: Barbara
authors.initials: B
authors.lastname: Rothen-Rutishauser
authors.affiliation: ETH Zürich, Institute for Chemical and Bioengineering, 8093, Zürich, Switzerland. konrad.hungerbuehler@chem.ethz.ch.
authors.forename: Konrad
authors.initials: K
authors.lastname: Hungerbuehler
mesh_terms: D000280:Administration, Inhalation; D000336:Aerosols; D000818:Animals; D001692:Biological Transport; D045744:Cell Line, Tumor; D003198:Computer Simulation; D004847:Epithelial Cells / Q000378:metabolism*; D017612:Gold Compounds / Q000008:administration & dosage / Q000097:blood / Q000493:pharmacokinetics*; D006801:Humans; D053768:Metal Nanoparticles; D051379:Mice; D008954:Models, Biological; D010316:Particle Size; D020545:Respiratory Mucosa / Q000378:metabolism*; D014018:Tissue Distribution
chemical_list: D000336:Aerosols; D017612:Gold Compounds