Inhibition of P-Glycoprotein Mediated Efflux in Caco-2 Cells by Phytic Acid.

Phytic acid (IP6) is a natural phosphorylated inositol, which is abundantly present in most cereal grains and seeds. This study investigated the effects of IP6 regulation on P-glycoprotein (P-gp) and its potential mechanisms using in situ and in vitro models. The effective permeability of the typical P-gp substrate rhodamine 123 (R123) in colon was significantly increased from (1.69 ± 0.22) × 10-5 cm/s in the control group to (3.39 ± 0.417) × 10-5 cm/s (p < 0.01) in the 3.5 mM IP6 group. Additionally, IP6 can concentration-dependently decrease the R123 efflux ratio in both Caco-2 and MDCK II-MDR1 cell monolayers and increase intracellular R123 accumulation in Caco-2 cells. Furthermore, IP6 noncompetitively inhibited P-gp by impacting R123 efflux kinetics. The noncompetitive inhibition of P-gp by IP6 was likely due to decreases in P-gp ATPase activity and P-gp molecular conformational changes induced by IP6. In summary, IP6 is a promising P-gp inhibitor candidate.