Mechanisms of alveolar epithelial translocation of a defined population of nanoparticles

Am J Respir Cell Mol Biol. 2010 May;42(5):604-14. doi: 10.1165/rcmb.2009-0138OC. Epub 2009 Jul 2.


To explore mechanisms of nanoparticle interactions with and trafficking across lung alveolar epithelium, we utilized primary rat alveolar epithelial cell monolayers (RAECMs) and an artificial lipid bilayer on filter model (ALBF). Trafficking rates of fluorescently labeled polystyrene nanoparticles (PNPs; 20 and 100 nm, carboxylate (negatively charged) or amidine (positively charged)-modified) in the apical-to-basolateral direction under various experimental conditions were measured. Using confocal laser scanning microscopy, we investigated PNP colocalization with early endosome antigen-1, caveolin-1, clathrin heavy chain, cholera toxin B, and wheat germ agglutinin. Leakage of 5-carboxyfluorescein diacetate from RAECMs, and trafficking of (22)Na and (14)C-mannitol across ALBF, were measured in the presence and absence of PNPs. Results showed that trafficking of positively charged PNPs was 20-40 times that of negatively charged PNPs across both RAECMs and ALBF, whereas translocation of PNPs across RAECMs was 2-3 times faster than that across ALBF. Trafficking rates of PNPs across RAECMs did not change in the presence of EGTA (which decreased transepithelial electrical resistance to zero) or inhibitors of endocytosis. Confocal laser scanning microscopy revealed no intracellular colocalization of PNPs with early endosome antigen-1, caveolin-1, clathrin heavy chain, cholera toxin B, or wheat germ agglutinin. Leakage of 5-carboxyfluorescein diacetate from alveolar epithelial cells, and sodium ion and mannitol flux across ALBF, were not different in the presence or absence of PNPs. These data indicate that PNPs translocate primarily transcellularly across RAECMs, but not via known major endocytic pathways, and suggest that such translocation may take place by diffusion of PNPs through the lipid bilayer of cell plasma membranes.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Alveolar Epithelial Cells / cytology
  • Alveolar Epithelial Cells / drug effects
  • Alveolar Epithelial Cells / metabolism*
  • Animals
  • Biological Transport / drug effects
  • Cations
  • Egtazic Acid / pharmacology
  • Endocytosis / drug effects
  • Fluoresceins / metabolism
  • Hydrophobic and Hydrophilic Interactions
  • Lipid Bilayers / metabolism
  • Male
  • Mannitol / metabolism
  • Nanoparticles*
  • Peptides / pharmacology
  • Permeability / drug effects
  • Polystyrenes / metabolism
  • Rats
  • Rats, Sprague-Dawley
  • Sodium / metabolism
  • Vesicular Transport Proteins / metabolism
  • Wheat Germ Agglutinins / metabolism


  • Cations
  • Fluoresceins
  • Lipid Bilayers
  • Peptides
  • Polystyrenes
  • Vesicular Transport Proteins
  • Wheat Germ Agglutinins
  • early endosome antigen 1
  • Mannitol
  • Egtazic Acid
  • 5-carboxyfluorescein diacetate
  • Sodium