title: Evaluation of the Caco-2 monolayer as a model epithelium for iontophoretic transport.
abstract: OBJECTIVE
  To assess the Caco-2 monolayer as a model for iontophoresis of drugs across a model epithelium.
  
  
  METHODS
  The apparent permeability co-efficient (Papp) of mannitol, thyrotrophin releasing hormone (TRH), dexamethasone and a range of sizes of fluorescein isothiocyanate (FITC) dextrans across Caco-2 monolayers was measured under passive and electrically stimulated conditions. Trans-epithelial electrical resistance (TEER) was determined throughout. Transmission electron micrographs (TEM) of the monolayers were taken. Confocal laser scanning microscopy (CLSM) was used to visualize the iontophoretic transport route of FITC-Dextran (MW = 20 kDa) across a Caco-2 monolayer.
  
  
  RESULTS
  Application of 14.3 micro-Eq x cm(-2) across the monolayer evoked a transient drop in TEER. The drop in TEER was accompanied by statistically significant increases in fluxes of all the agents in the mucosal to serosal direction except for FD-70. TEM of test samples exhibited tight junction dilatation, in addition to intracellular vacuolisation. The iontophoresis of FD-20 was visualised with confocal laser scanning microscopy and was localised in paracellular spaces of the monolayer.
  
  
  CONCLUSIONS
  The fluxes of mannitol, TRH, dexamethasone, FD-4, FD-10 and FD-20 across the Caco-2 monolayer were significantly enhanced when electric field was applied. The iontophoretic effect appeared to be directly upon tight junctions
authors.affiliation: Elan Biotechnology Research, Trinity College, Dublin, Ireland.
authors.forename: M
authors.initials: M
authors.lastname: Leonard
authors.forename: E
authors.initials: E
authors.lastname: Creed
authors.forename: D
authors.initials: D
authors.lastname: Brayden
authors.forename: A W
authors.initials: AW
authors.lastname: Baird
mesh_terms: D001692:Biological Transport; D018938:Caco-2 Cells / Q000378:metabolism* / Q000502:physiology; D002463:Cell Membrane Permeability / Q000502:physiology; D003907:Dexamethasone / Q000493:pharmacokinetics; D003911:Dextrans / Q000493:pharmacokinetics; D017097:Electric Impedance; D004848:Epithelium / Q000378:metabolism / Q000502:physiology; D016650:Fluorescein-5-isothiocyanate / Q000031:analogs & derivatives* / Q000493:pharmacokinetics; D006801:Humans; D007408:Intestinal Absorption / Q000502:physiology; D007478:Iontophoresis / Q000379:methods*; D008353:Mannitol / Q000493:pharmacokinetics; D008564:Membrane Potentials / Q000502:physiology; D018613:Microscopy, Confocal; D008854:Microscopy, Electron; D013973:Thyrotropin-Releasing Hormone / Q000493:pharmacokinetics
chemical_list: D003911:Dextrans; C015219:fluorescein isothiocyanate dextran; D008353:Mannitol; D013973:Thyrotropin-Releasing Hormone; D003907:Dexamethasone; D016650:Fluorescein-5-isothiocyanate