P-glycoprotein attenuating effect of human intestinal fluid

Purpose. To evaluate the effect of human intestinal fluid (HIF) on P-glycoprotein (P-gp)-mediated efflux. Methods. HIF was obtained from eight healthy volunteers by duodenal aspiration. HIF was applied at different concentrations (0-75%) to the apical compartment of the Caco-2 system. Cyclosporin A (CsA) was used as a model compound for P-gp mediated efflux. Results. When the bidirectional transport of CsA across Caco-2 monolayers was assessed, a significant polarity in transport could be observed, the absorptive transport being much lower than the secretory transport. Inclusion of HIF resulted in a moderate increase of the absorptive transport, as well as a significant concentration dependent decrease of the secretory transport, without compromising the integrity of the monolayer. Interestingly, a possible gender difference could be detected as inclusion of HIF obtained from female subjects resulted in a decreased absorptive transport of CsA, whereas inclusion of HIF obtained from male subjects resulted in an increased absorptive transport. The P-gp modulating effect of HIF is not caused by a lack of glucose as an energy source for the efflux mechanism when high concentrations of HIF were present in the buffer used. Conclusions. The results of this study indicate that the contribution of P-gp efflux carriers may be overestimated when using salt buffer solutions as transport media. Additionally, it can be concluded that ( presently unidentified) components of HIF may attenuate the P-gp mediated intestinal efflux. The clinical significance of this modulating effect remains to be investigated.