P-glycoprotein-170 inhibition significantly reduces cortisol and ciclosporin efflux from human intestinal epithelial cells and T lymphocytes

Aim: To assess the role of P-glycoprotein-170 (P-gp) in transporting cortisol and ciclosporin from human intestinal epithelium and T lymphocytes. Methods: The effect of P-gp inhibitors (verapamil, 0-100 muM: PSC 833, 0-20 muM) on the intracellular accumulation of H-3-cortisol and H-3-ciclosporin was studied in confluent layers of human Caco-2 cells (n = 6), a P-gp-dependent absorptive intestinal epithelial cell phenotype, and moderately resistant MDRhigh CEM/VBL 100 T cells (n = 6). The transport of H-3-vinblastine, a strong multidrug resistance (MDR) substrate, and H-3-progesterone, a poor MDR substrate, was also studied. Results: Caco-2 cells had a 2.4-, 6.6-, 6.7- and 1.03-fold higher net basal to apical transport (efflux) of H-3-vinblastine and H-3-progesterone-cortisol, H-3-ciclosporin H-3-vinblastine and H-3-progesterone, respectively. PSC 833 (20 muM) reduced cortisol efflux by 69% (0.23 +/- 0.04 to 1 h, P < 0.05) and ciclosporin efflux by 76% (11.1 +/- 1.4 to 2.7 +/- 0.6 pmol/cm(2)/h, P < 0.001). MDRlow CEM T cells had a 1.4-, 1.9-, 3.2- and 1.02-fold higher intracellular accumulation of cortisol, ciclosporin, vinblastine and progesterone than MDRhigh CEM/VBL 100 T cells. Increasing concentrations of PSC 833 (> 0.1 muM) and verapamil (> 1 muM) restored the intracellular level of H-3-cortisol and H-3-ciclosporin in MDRhigh CEM/VBL 100 T cells to that of MDRlow CEM cells with little change in accumulation in the MDRlow parental cell line. Conclusions: P-gp inhibitors significantly increase intracellular cortisol and ciclosporin levels in human intestinal epithelium and T lymphocytes in a dose-dependent manner, demonstrating a potential mechanism for overcoming poor response to immunosuppressant therapy in refractory inflammatory bowel disease.