PERMEABILITY CHARACTERISTICS OF TETRAGASTRINS ACROSS INTESTINAL MEMBRANES USING THE CACO-2 MONOLAYER SYSTEM - COMPARISON BETWEEN ACYLATION AND APPLICATION OF PROTEASE INHIBITORS

Purpose. Three types of acyl tetragastrin (TG), acetyl-TG (C-2-TG), bu tyryl-TG (C-4-TG) and caproyl-TG (C-6-TG) were synthesized and their i n vitro intestinal permeability characteristics were examined using Ca co-2 monolayers. Methods. The disappearance of acyl-TGs from the apica l side of Caco-2 monolayers was estimated by analyzing degradation and permeation processes in terms of clearance. Results. The amount of na tive TG transported to the basolateral side was very low due to its la rge degradation clearance (CLd) on the apical side. Degradation of TG was reduced by chemical modification with fatty acids, which resulted in an increase in the transport of TG across Caco-2 monolayers. In add ition, the permeation clearance (CLp) value of carboxyfluorescein (CF) , a paracellular transport and undegradable marker, was increased in t he presence of acyl-TGs. Furthermore, we investigated the effects of t he protease inhibitors bacitracin and gabexate on the transport of TG across Caco-2 monolayers. In the presence of a low concentration (0.1 mM) of protease inhibitor, the CLd value of TG was reduced, but they d id not affect its CLp value. However, a higher concentration (1.0 mM) of bacitracin significantly reduced TG degradation on the apical side, and further increased its CLp value. Conclusions. We demonstrated tha t acylation of TG made it resistant to intestinal proteases and caused it to enhance absorption of drugs, including itself, across Caco-2 mo nolayers. Further, bacitracin acted as both a protease inhibitor and a n absorption enhancer.