title: Transfer of lipophilic markers from PLGA and polystyrene nanoparticles to caco-2 monolayers mimics particle uptake.
abstract: OBJECTIVE
  The objective of this study was to evaluate nanoparticle uptake by the Caco-2 monolayer model in vitro. Special emphasis was placed on the localization and the quantification of the uptake of fluorescently labeled polystyrene and poly(lactic-co-glycolic acid) (PLGA) nanoparticles.
  
  
  METHODS
  Intracellular fluorescence was localized by fluorescence and confocal laser scanning microscopy. Particle uptake was quantified either directly, by counting internalized nanoparticles after separation from the Caco-2 monolayers, or indirectly, by extraction of the lipophilic fluorescence marker. In vitro release studies of lipophilic markers from nanoparticles were performed in standard buffer systems and buffer systems supplemented with liposomes.
  
  
  RESULTS
  Instead of uptake of polystyrene and PLGA nanoparticles by Caco-2 monolayers an efficient transfer of lipophilic fluorescence markers from nanoparticles into Caco-2 cells with subsequent staining of intracellular lipophilic compartments was observed. Whereas in standard buffer no release of fluorescent marker from polystyrene and PLGA nanoparticles was observed, the release studies using liposome dispersions as receiver revealed an efficient transfer of fluorescent marker into the liposome dispersion.
  
  
  CONCLUSIONS
  The results suggest that the deceptive particle uptake is caused by a collision-induced process facilitating the transfer of lipophilic fluorescent marker by formation of a complex between the nanoparticles and the biomembranes. Diffusion of the marker within this complex into lipophilic compartments of the cell strongly affects quantitative evaluation of particle uptake.
authors.affiliation: Institute of Pharmaceutical Sciences, ETH Zurich.
authors.forename: Peter
authors.initials: P
authors.lastname: Pietzonka
authors.forename: Barbara
authors.initials: B
authors.lastname: Rothen-Rutishauser
authors.forename: Peter
authors.initials: P
authors.lastname: Langguth
authors.forename: Heidi
authors.initials: H
authors.lastname: Wunderli-Allenspach
authors.forename: Elke
authors.initials: E
authors.lastname: Walter
authors.forename: Hans P
authors.initials: HP
authors.lastname: Merkle
mesh_terms: D001692:Biological Transport; D018938:Caco-2 Cells; D004058:Diffusion; D005456:Fluorescent Dyes / Q000378:metabolism*; D006801:Humans; D066298:In Vitro Techniques; D019344:Lactic Acid; D008855:Microscopy, Electron, Scanning; D036103:Nanotechnology; D010316:Particle Size; D010539:Permeability; D011100:Polyglycolic Acid; D000077182:Polylactic Acid-Polyglycolic Acid Copolymer; D011108:Polymers; D011137:Polystyrenes
chemical_list: D005456:Fluorescent Dyes; D011108:Polymers; D011137:Polystyrenes; D000077182:Polylactic Acid-Polyglycolic Acid Copolymer; D011100:Polyglycolic Acid; D019344:Lactic Acid