THE USE OF SURFACTANTS TO ENHANCE THE PERMEABILITY OF PEPTIDES THROUGH CACO-2 CELLS BY INHIBITION OF AN APICALLY POLARIZED EFFLUX SYSTEM

Purpose. It has recently been reported that the permeability of peptid es across Caco-2 cells, an in vitro model of the intestinal mucosa, wa s limited by an apically polarized efflux mechanism. Since surfactants (e.g. Cremophor EL, Polysorbate 80) have been reported to inhibit sim ilar efflux systems in tumor cells, we determined whether they could e nhance the permeability of peptides across monolayers of Caco-2 cells. Methods. The transport studies of [H-3]-mannitol and [C-14]-model pep tides were carried out across the Caco-2 cell monolayers. TEER values were determined using Voltohmmeter with STX-2 electrode and the equili brium dialysis studies were conducted using side-by-side dialysis appa ratus with cellulose ester membranes. Results. Initially, [H-3]-mannit ol flux studies were conducted to find concentrations of the surfactan ts that did not cause damage to the cell monolayer. Based on these stu dies, Polysorbate 80 and Cremophor EL were selected for further study. The fluxes of [C-14]-AcfNH(2) (a nonsubstrate for this efflux system) and [C-14]-Acf(N-Mef)(2)NH2 (a substrate for this efflux system) were then measured in the absence and presence of the two surfactants. The permeability of [C-14]-AcfNH(2) was not affected by the surfactants, while that of [C-14]-Acf(N-Mef)(2)NH2 increased with increasing concen trations of surfactants and then decreased. For example, the P-e value s for [C-14]-Acf(N-Mef)(2)NH2 were 3.75 x 10(-6), 8.58 x 10(-6), 10.29 x 10(-6), 7.48 x 10(-6), and 1.46 x 10(-6) cm/sec with Cremophor EL c oncentrations of 0, 0.01, 0.1, 1 and 10% w/v, respectively. This bimod al effect of surfactants on the Caco-2 cell permeability of this pepti de was shown to be due to the interactions between the peptide and mic elles at higher concentrations of surfactants, which were demonstrated by the equilibrium dialysis experiments. Conclusions. These results s uggest that surfactants, which are commonly added to pharmaceutical fo rmulations, may enhance the intestinal absorption of some drugs by inh ibiting this apically polarized efflux system.