title: Low-solubility particles and a Trojan-horse type mechanism of toxicity: the case of cobalt oxide on human lung cells.
abstract: BACKGROUND
  The mechanisms of toxicity of metal oxide particles towards lung cells are far from being understood. In particular, the relative contribution of intracellular particulate versus solubilized fractions is rarely considered as it is very challenging to assess, especially for low-solubility particles such as cobalt oxide (Co3O4).
  
  
  METHODS
  This study was possible owing to two highly sensitive, independent, analytical techniques, based on single-cell analysis, using ion beam microanalysis, and on bulk analysis of cell lysates, using mass spectrometry.
  
  
  RESULTS
  Our study shows that cobalt oxide particles, of very low solubility in the culture medium, are readily incorporated by BEAS-2B human lung cells through endocytosis via the clathrin-dependent pathway. They are partially solubilized at low pH within lysosomes, leading to cobalt ions release. Solubilized cobalt was detected within the cytoplasm and the nucleus. As expected from these low-solubility particles, the intracellular solubilized cobalt content is small compared with the intracellular particulate cobalt content, in the parts-per-thousand range or below. However, we were able to demonstrate that this minute fraction of intracellular solubilized cobalt is responsible for the overall toxicity.
  
  
  CONCLUSIONS
  Cobalt oxide particles are readily internalized by pulmonary cells via the endo-lysosomal pathway and can lead, through a Trojan-horse mechanism, to intracellular release of toxic metal ions over long periods of time, involving specific toxicity.
authors.affiliation: Univ, Bordeaux, CENBG, UMR 5797, Gradignan F-33170, France. ortega@cenbg.in2p3.fr.
authors.forename: Richard
authors.initials: R
authors.lastname: Ortega
authors.forename: Carole
authors.initials: C
authors.lastname: Bresson
authors.forename: Carine
authors.initials: C
authors.lastname: Darolles
authors.forename: Céline
authors.initials: C
authors.lastname: Gautier
authors.forename: Stéphane
authors.initials: S
authors.lastname: Roudeau
authors.forename: Laura
authors.initials: L
authors.lastname: Perrin
authors.forename: Myriam
authors.initials: M
authors.lastname: Janin
authors.forename: Magali
authors.initials: M
authors.lastname: Floriani
authors.forename: Valérie
authors.initials: V
authors.lastname: Aloin
authors.forename: Asuncion
authors.initials: A
authors.lastname: Carmona
authors.forename: Véronique
authors.initials: V
authors.lastname: Malard
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D002460:Cell Line; D002467:Cell Nucleus / Q000378:metabolism; D002470:Cell Survival / Q000187:drug effects; D003035:Cobalt / Q000378:metabolism / Q000633:toxicity*; D003593:Cytoplasm / Q000378:metabolism; D006801:Humans; D007202:Indicators and Reagents; D008168:Lung / Q000166:cytology / Q000187:drug effects / Q000473:pathology*; D008247:Lysosomes / Q000378:metabolism; D018613:Microscopy, Confocal; D046529:Microscopy, Electron, Transmission; D053758:Nanoparticles / Q000378:metabolism / Q000633:toxicity*; D010087:Oxides / Q000378:metabolism / Q000633:toxicity*; D010316:Particle Size; D013347:Subcellular Fractions / Q000378:metabolism; D015032:Zinc / Q000378:metabolism
chemical_list: D007202:Indicators and Reagents; D010087:Oxides; D003035:Cobalt; D000255:Adenosine Triphosphate; D015032:Zinc; C060728:cobalt oxide