Diffusion Rates and Transport Pathways of Fluorescein Isothiocyanate (FITC)-Labeled Model Compounds Through Buccal Epithelium

The aim of this study was to characterize transport of FITC-labeled dextrans of different molecular weights as model compounds for peptides and proteins through buccal mucosa. The penetration of these dextrans through porcine buccal mucosa (a nonkeratinized epithelium, comparable to human buccal mucosa) was investigated by measuring transbuccal fluxes and by analyzing the distribution of the fluorescent probe in the epithelium, using confocal laser scanning microscopy for visualizing permeation pathways. The results revealed that passage of porcine buccal epithelium by hydrophilic compounds such as the FITC-dextrans is restricted to permeants with a molecular weight lower than 20 kDa. The permeabilities of buccal mucosa for the 4- and 10-kDa FITC-dextran (of the order of 10⁻⁸ cm/sec) were not significantly different from each other or from the much smaller compound FITC. The confocal images of the distribution pattern of FITC-dextrans showed that the paracellular route is the major pathway through buccal epithelium.