title: Confocal laser scanning microscopic visualization of the transport of dextrans after nasal administration to rats: effects of absorption enhancers.
abstract: OBJECTIVE
  To visualize the transport pathway(s) of high molecular weight model compounds across rat nasal epithelium in vivo using confocal laser scanning microscopy. Furthermore, the influence of nasal absorption enhancers (randomly methylated beta-cyclodextrin and sodium taurodihydrofusidate) on this transport was studied.
  
  
  METHODS
  Fluorescein isothiocyanate (FITC)-labelled dextrans with a molecular weight of 3,000 or 10,000 Da were administered intranasally to rats. Fifteen minutes after administration the tissue was fixed with Bouin. The nasal septum was surgically removed and stained with Evans Blue protein stain or DiIC18(5) lipid stain prior to visualization with the confocal laser scanning microscope.
  
  
  RESULTS
  Transport of FITC-dextran 3,000 across nasal epithelium occurred via the paracellular pathway. Endocytosis of FITC-dextran 3,000 was also shown. In the presence of randomly methylated beta-cyclodextrin 2% (w/v) similar transport pathways for FITC-dextran 3,000 were observed. With sodium taurodihydrofusidate 1% (w/v) the transport route was also paracellular with endocytosis, but cells were swollen and mucus was extruded into the nasal cavity. For FITC-dextran 10,000 hardly any transport was observed without enhancer, or after co-administration with randomly methylated beta-cyclodextrin 2% (w/v). Co-administration with sodium taurodihydrofusidate 1% (w/v) resulted in paracellular transport of FITC-dextran 10,000, but morphological changes, i.e. swelling of cells and mucus extrusion, were observed.
  
  
  CONCLUSIONS
  Confocal laser scanning microscopy is a suitable approach to visualize the transport pathways of high molecular weight hydrophilic compounds across nasal epithelium, and to study the effects of absorption enhancers on drug transport and cell morphology.
authors.affiliation: Division of Pharmaceutical Technology and Biopharmaceutics, Leiden/Amsterdam Center for Drug Research, Leiden University, The Netherlands.
authors.forename: E
authors.initials: E
authors.lastname: Marttin
authors.forename: J C
authors.initials: JC
authors.lastname: Verhoef
authors.forename: C
authors.initials: C
authors.lastname: Cullander
authors.forename: S G
authors.initials: SG
authors.lastname: Romeijn
authors.forename: J F
authors.initials: JF
authors.lastname: Nagelkerke
authors.forename: F W
authors.initials: FW
authors.lastname: Merkus
mesh_terms: D000042:Absorption; D000277:Adjuvants, Pharmaceutic; D000281:Administration, Intranasal; D000818:Animals; D001693:Biological Transport, Active; D003911:Dextrans / Q000008:administration & dosage / Q000493:pharmacokinetics* / Q000494:pharmacology*; D004848:Epithelium / Q000378:metabolism; D005404:Fixatives; D016650:Fluorescein-5-isothiocyanate; D005672:Fusidic Acid / Q000031:analogs & derivatives; D008297:Male; D018613:Microscopy, Confocal; D008970:Molecular Weight; D009297:Nasal Mucosa / Q000187:drug effects / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D013268:Stimulation, Chemical
chemical_list: D000277:Adjuvants, Pharmaceutic; D003911:Dextrans; D005404:Fixatives; D005672:Fusidic Acid; C053824:tauro-24,25-dihydrofusidate; D016650:Fluorescein-5-isothiocyanate