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.