title: Nasal epithelial permeation of thymotrinan (TP3) versus thymocartin (TP4): competitive metabolism and self-enhancement.
abstract: OBJECTIVE
  To investigate concentration dependent permeabilities and metabolism kinetics of thymotrinan (TP3) versus thymocartin (TP4) in nasal epithelium in vitro.
  
  
  METHODS
  Excised bovine nasal mucosa was used as an in vitro model. Permeabilities were studied in a diffusion chamber, metabolism kinetics in a reflection kinetics set-up. Studies were performed at various TP3 and TP4 concentrations. The 3H-mannitol flux was measured to monitor junctional permeability. Potential Ca(2+)-complexation was investigated using a Ca(2+)-selective electrode.
  
  
  RESULTS
  Permeability of TP3 was negligible at 0.1 and 0.2 mM and increased drastically above 0.4 mM up to -2 X 10(-5) cm s(-1). In the presence of 2 mM TP4 the TP3 permeabilites were significantly above (approximately 4 x 10(-5) cm s(-1)) the level of TP3 without TP4, and TP3 metabolism was totally inhibited. TP3 and TP4 showed a significant concentration dependent effect on the permeability of 3H-mannitol. A hyperosmolarity effect of the peptide solutions was excluded. Transepithelial electrical resistance (TEER; approximately 30 ohms cm2) was unchanged by either TP3 or TP4. At 1 mM TP3 the mucosal-to-serosal permeability was four times higher than serosal-to-mucosal, indicating enzyme polarization. In reflection kinetics studies, TP3 degradation was slightly higher on the mucosal than on the serosal side. TP3 and TP4 followed the same non-linear metabolism kinetics.
  
  
  CONCLUSIONS
  Increase in permeability at high TP concentrations involves competitive enzyme saturation combined with self-enhanced paracellular permeation.
authors.affiliation: Department of Applied BioSciences, Swiss Federal Institute of Technology Zurich (ETH), Switzerland.
authors.forename: M C
authors.initials: MC
authors.lastname: Schmidt
authors.forename: W
authors.initials: W
authors.lastname: Rubas
authors.forename: H P
authors.initials: HP
authors.lastname: Merkle
mesh_terms: D000276:Adjuvants, Immunologic / Q000493:pharmacokinetics*; D000626:Aminopeptidases / Q000378:metabolism; D000818:Animals; D001667:Binding, Competitive; D002118:Calcium / Q000493:pharmacokinetics; D002417:Cattle; D002463:Cell Membrane Permeability / Q000187:drug effects; D017097:Electric Impedance; D004734:Energy Metabolism / Q000187:drug effects; D004847:Epithelial Cells / Q000201:enzymology*; D066298:In Vitro Techniques; D008353:Mannitol / Q000493:pharmacokinetics; D009297:Nasal Mucosa / Q000166:cytology* / Q000201:enzymology; D009842:Oligopeptides / Q000493:pharmacokinetics*; D010446:Peptide Fragments / Q000493:pharmacokinetics*; D013379:Substrate Specificity; D013946:Thymopoietins / Q000493:pharmacokinetics*; D014316:Tritium
chemical_list: D000276:Adjuvants, Immunologic; D009842:Oligopeptides; D010446:Peptide Fragments; D013946:Thymopoietins; D014316:Tritium; D008353:Mannitol; C045801:RGH 0205; D000626:Aminopeptidases; C045802:thymocartin; D002118:Calcium