EFFECTS OF BILE-SALTS ON TRANSPORT RATES AND ROUTES OF FITC-LABELED COMPOUNDS ACROSS PORCINE BUCCAL EPITHELIUM IN-VITRO

In this study the penetration enhancing effect of bile salts on the tr ansport of hydrophilic macromolecular compounds across porcine buccal mucosa was investigated in-vitro. Coadministration of 100 mM of the tr ihydroxy bile salts sodium glycocholate (GC) and sodium taurocholate ( TC) and the dihydroxy bile salts sodium glycodeoxycholate (GDC) and so dium taurodeoxycholate (TDC) increased the in-vitro transport of fluor escein isothiocyanate (FITC) by a factor of a hundred or more, without a significant difference between the four bile salts. The concentrati on dependence of the enhancing effect of GDC was studied using FITC-la belled dextrans of increasing molecular weight as permeants (FD4, MW 4 400; FD10, MW 9400; FD20, MW 19 600). The maximal enhancement was obse rved when GDC was coadministered in a concentration of 10 mM, resultin g in an enhancement ratio of about 2000 for FD4. Using confocal laser scanning microscopy the effects of bile salts on the penetration pathw ays of hydrophilic compounds were investigated. The uniform distributi on of FITC throughout the epithelium was changed by coadministration o f 100 mM of bile salt to an increased amount of the fluorescent probe present in the intercellular domains. The intercellular distribution o f both FD4 and FD10 was not changed by a low, but effective, concentra tion of GDC (2 mM, enhancement ratio of 72 for FD4). Increasing the co ncentration of GDC to 10 and 100 mM resulted in uptake of the fluoresc ent probe in the epithelial cells. From these results we conclude that the di- and trihydroxy bile salts studied increase the transport of h ydrophilic compounds across buccal epithelium in vitro, below 10 mM by increasing the intercellular transport and at 10 mM and higher concen trations by opening up a transcellular route.