Studies to Further Investigate the Inhibition of Human Liver Microsomal CYP2C8 by the Acyl-β-Glucuronide of Gemfibrozil
作者:S. M. Jenkins、T. Zvyaga、S. R. Johnson、J. Hurley、A. Wagner、R. Burrell、W. Turley、J. E. Leet、T. Philip、A. D. Rodrigues
DOI:10.1124/dmd.111.041947
日期:2011.12
In previous studies, gemfibrozil acyl-β-glucuronide, but not gemfibrozil, was found to be a mechanism-based inhibitor of cytochrome P450 2C8. To better understand whether this inhibition is specific for gemfibrozil acyl-β-glucuronide or whether other glucuronide conjugates are potential substrates for inhibition of this enzyme, we evaluated several pharmaceutical compounds (as their acyl glucuronides) as direct-acting and metabolism-dependent inhibitors of CYP2C8 in human liver microsomes. Of 11 compounds that were evaluated as their acyl glucuronide conjugates, only gemfibrozil acyl-β-glucuronide exhibited mechanism-based inhibition, indicating that CYP2C8 mechanism-based inhibition is very specific to certain glucuronide conjugates. Structural analogs of gemfibrozil were synthesized, and their glucuronide conjugates were prepared to further examine the mechanism of inhibition. When the aromatic methyl groups on the gemfibrozil moiety were substituted with trifluoromethyls, the resulting glucuronide conjugate was a weaker inhibitor of CYP2C8 and mechanism-based inhibition was abolished. However, the glucuronide conjugates of monomethyl gemfibrozil analogs were mechanism-based inhibitors of CYP2C8, although not as potent as gemfibrozil acyl-β-glucuronide itself. The ortho -monomethyl analog was a more potent inhibitor than the meta -monomethyl analog, indicating that CYP2C8 favors the ortho position for oxidation and potential inhibition. Molecular modeling of gemfibrozil acyl-β-glucuronide in the CYP2C8 active site is consistent with the ortho -methyl position being the favored site of covalent attachment to the heme. Moreover, hydrogen bonding to four residues (Ser100, Ser103, Gln214, and Asn217) is implicated.
在以前的研究中,发现吉非罗齐酰基-β-葡萄糖醛酸苷,而不是吉非罗齐,是细胞色素 P450 2C8 的一种基于机制的抑制剂。为了更好地了解这种抑制作用是否是对吉非罗齐酰基-β-葡萄糖醛酸的特异性抑制,或者其他葡萄糖醛酸结合物是否是抑制这种酶的潜在底物,我们评估了几种药物化合物(作为其酰基葡萄糖醛酸)作为 CYP2C8 在人肝微粒体中的直接作用和代谢依赖性抑制剂。在以酰基葡萄糖醛酸苷共轭物形式进行评估的 11 种化合物中,只有吉非罗齐酰基-β-葡萄糖醛酸苷表现出基于机理的抑制作用,这表明基于机理的 CYP2C8 抑制作用对某些葡萄糖醛酸苷共轭物具有很强的特异性。为了进一步研究吉非罗齐的抑制机制,我们合成了吉非罗齐的结构类似物,并制备了它们的葡萄糖醛酸苷共轭物。当吉非罗齐分子上的芳香甲基被三氟甲基取代时,得到的葡萄糖醛酸苷共轭物对 CYP2C8 的抑制作用较弱,基于机制的抑制作用被取消。然而,单甲基吉非罗齐类似物的葡萄糖醛酸苷结合物是基于机制的 CYP2C8 抑制剂,尽管其效力不如吉非罗齐酰基-β-葡萄糖醛酸苷本身。正-单甲基类似物是比偏-单甲基类似物更有效的抑制剂,这表明 CYP2C8 更倾向于正位氧化和潜在抑制。吉非罗齐酰基-β-葡萄糖醛酸在 CYP2C8 活性位点的分子模型与正-甲基位点是与血红素共价连接的有利位点相一致。此外,与四个残基(Ser100、Ser103、Gln214 和 Asn217)的氢键也有关联。