TRANSEPITHELIAL TRANSPORT-PROPERTIES OF PEPTIDOMIMETIC THROMBIN INHIBITORS IN MONOLAYERS OF A HUMAN INTESTINAL-CELL LINE (CACO-2) AND THEIRCORRELATION TO IN-VIVO DATA

Peptidomimetic thrombin inhibitors (TI), derived from L-Asp-D-Phe were examined in confluent monolayers of a human colon carcinoma cell line (Caco-2) to elucidate their transepithelial transport properties. Eff ect availabilities, based on activated partial thromboplastin time (aP TT) measurements in rats, after peroral administration of five TI corr elated reasonably well with permeability coefficients obtained from in vitro transport studies in Caco-2 monolayers, whereas physicochemical properties, such as molecular mass, solubilities, pK(a) and octanol-b uffer partition coefficients failed to yield meaningful relationships. Substitution of the beta-carboxylic group of L-Asp leads to analogues which are mainly transported by passive diffusion, while an unsubstit uted carboxylic group favours carrier-mediated active transport. The e ffects of concentration, temperature, competitive inhibitors and direc tion dependence on in vitro transport were investigated. The results o btained are compatible with a saturable carrier-mediated transport, op erating parallel to a passive paracellular route. The Michaelis-Menten parameters for the active transport component (K-m = 1.67 mM, V-max = 26.5 pmol min(-1) mg protein(-1)) indicate an involvement of the inte stinal di/tripeptide transport system for one of the TI. The Caco-2 tr ansport model may be helpful for the design of perorally active peptid omimetics.