Jeong Eun Ju, Lin Huimin, Hu Ming
Department of Pharmaceutical Sciences, College of Pharmacy, Washington State University, Pullman, Washington 99164-6510, USA.
J Pharmacol Exp Ther. 2004 Jul;310(1):376-85. doi: 10.1124/jpet.103.063925. Epub 2004 Mar 12.
The purpose of this study was to determine the mechanisms responsible for transport of raloxifene and its hydrophilic conjugates. Human intestinal Caco-2 cell culture model and Caco-2 cell lysate were used for the studies. The results indicated that absorptive permeability (PAB) of raloxifene was lower than its secretory permeability (PAB). As the concentration increased, the efflux ratio (PBA/PAB) decreased, but PBA increased. PAB was also increased in the presence of verapamil and cyclosporine A, two P-glycoprotein inhibitors. Raloxifene was extensively metabolized into sulfated and glucuronidated conjugates. The extent of metabolism or clearance was decreased as the concentration increased from 3.4 (96%) to 30 (22%) microM. Multidrug resistance-related protein inhibitors MK-571 (C26H26ClN2O3S2) and leukotriene C4 significantly decreased (maximal 80%) apical efflux of both conjugates. They also significantly decreased (maximal 85%) basolateral efflux of glucuronides but not sulfates. On the other hand, organic anion transporter (OAT) inhibitor estrone sulfate and estrone glucuronide significantly decreased (maximal 50%) the efflux of sulfate from both sides but had variable effects on glucuronide efflux. Inhibition of conjugate efflux with the OAT inhibitor estrone sulfate was concentration dependent, which resulted in increased transport of intact raloxifene (maximal 90%). This increase in raloxifene transport was also observed in the presence of another OAT inhibitor estrone glucuronide (70%). In conclusion, this is the first report that inhibition of an efflux transporter responsible for the transport of metabolites can result in increase in the transport of the intact compound. It also provides additional explanation why raloxifene has low bioavailability but a long half-life.
本研究的目的是确定负责雷洛昔芬及其亲水性共轭物转运的机制。采用人肠道Caco-2细胞培养模型和Caco-2细胞裂解物进行研究。结果表明，雷洛昔芬的吸收渗透率（PAB）低于其分泌渗透率（PAB）。随着浓度增加，外排率（PBA/PAB）降低，但PBA增加。在维拉帕米和环孢素A这两种P-糖蛋白抑制剂存在的情况下，PAB也增加。雷洛昔芬被广泛代谢为硫酸化和葡萄糖醛酸化的共轭物。随着浓度从3.4（96%）增加到30（22%）微摩尔，代谢或清除程度降低。多药耐药相关蛋白抑制剂MK-571（C26H26ClN2O3S2）和白三烯C4显著降低（最大80%）两种共轭物的顶端外排。它们还显著降低（最大85%）葡萄糖醛酸苷的基底外侧外排，但对硫酸盐没有影响。另一方面，有机阴离子转运体（OAT）抑制剂硫酸雌酮和葡萄糖醛酸雌酮显著降低（最大50%）两侧硫酸盐的外排，但对葡萄糖醛酸苷外排的影响各不相同。用OAT抑制剂硫酸雌酮抑制共轭物外排是浓度依赖性的，这导致完整雷洛昔芬的转运增加（最大90%）。在另一种OAT抑制剂葡萄糖醛酸雌酮存在的情况下（70%）也观察到雷洛昔芬转运的这种增加。总之，这是第一份报告，即抑制负责代谢物转运的外排转运体可导致完整化合物转运增加。它还为雷洛昔芬生物利用度低但半衰期长提供了额外解释。
