Ogilvie Brian W, Zhang Donglu, Li Wenying, Rodrigues A David, Gipson Amy E, Holsapple Jeff, Toren Paul, Parkinson Andrew
XenoTech, LLC, 16825 West 116 Street, Lenexa, KS 66219, USA.
Drug Metab Dispos. 2006 Jan;34(1):191-7. doi: 10.1124/dmd.105.007633. Epub 2005 Nov 18.
Gemfibrozil more potently inhibits CYP2C9 than CYP2C8 in vitro, and yet the opposite inhibitory potency is observed in the clinic. To investigate this apparent paradox, we evaluated both gemfibrozil and its major metabolite, an acyl-glucuronide (gemfibrozil 1-O-beta-glucuronide) as direct-acting and metabolism-dependent inhibitors of the major drug-metabolizing cytochrome P450 enzymes (CYP1A2, 2B6, 2C8, 2C9, 2C19, 2D6, and 3A4) in human liver microsomes. Gemfibrozil most potently inhibited CYP2C9 (IC50 of 30 microM), whereas gemfibrozil glucuronide most potently inhibited CYP2C8 (IC50 of 24 microM). Unexpectedly, gemfibrozil glucuronide, but not gemfibrozil, was found to be a metabolism-dependent inhibitor of CYP2C8 only. The IC50 for inhibition of CYP2C8 by gemfibrozil glucuronide decreased from 24 microM to 1.8 microM after a 30-min incubation with human liver microsomes and NADPH. Inactivation of CYP2C8 by gemfibrozil glucuronide required NADPH, and proceeded with a K(I) (inhibitor concentration that supports half the maximal rate of enzyme inactivation) of 20 to 52 microM and a k(inact) (maximal rate of inactivation) of 0.21 min(-1). Potent inhibition of CYP2C8 was also achieved by first incubating gemfibrozil with alamethicin-activated human liver microsomes and UDP-glucuronic acid (to form gemfibrozil glucuronide), followed by a second incubation with NADPH. Liquid chromatography-tandem mass spectrometry analysis established that human liver microsomes and recombinant CYP2C8 both convert gemfibrozil glucuronide to a hydroxylated metabolite, with oxidative metabolism occurring on the dimethylphenoxy moiety (the group furthest from the glucuronide moiety). The results described have important implications for the mechanism of the clinical interaction reported between gemfibrozil and CYP2C8 substrates such as cerivastatin, repaglinide, rosiglitazone, and pioglitazone.
在体外，吉非贝齐对CYP2C9的抑制作用比对CYP2C8更强，然而在临床中却观察到相反的抑制效力。为了探究这一明显的矛盾，我们评估了吉非贝齐及其主要代谢产物酰基葡萄糖醛酸（吉非贝齐1-O-β-葡萄糖醛酸）作为人肝微粒体中主要药物代谢细胞色素P450酶（CYP1A2、2B6、2C8、2C9、2C19、2D6和3A4）的直接作用和代谢依赖性抑制剂的情况。吉非贝齐对CYP2C9的抑制作用最强（IC50为30微摩尔），而吉非贝齐葡萄糖醛酸对CYP2C8的抑制作用最强（IC50为24微摩尔）。出乎意料的是，仅发现吉非贝齐葡萄糖醛酸是CYP2C8的代谢依赖性抑制剂，而吉非贝齐不是。在与人肝微粒体和NADPH孵育30分钟后，吉非贝齐葡萄糖醛酸对CYP2C8抑制的IC50从24微摩尔降至1.8微摩尔。吉非贝齐葡萄糖醛酸使CYP2C8失活需要NADPH，其K（I）（支持酶失活最大速率一半的抑制剂浓度）为20至52微摩尔，k（inact）（最大失活速率）为0.21分钟（-1）。通过先将吉非贝齐与阿拉霉素激活的人肝微粒体和UDP-葡萄糖醛酸孵育（以形成吉非贝齐葡萄糖醛酸），然后再与NADPH进行第二次孵育，也实现了对CYP2C8的强效抑制。液相色谱-串联质谱分析表明，人肝微粒体和重组CYP2C8均将吉非贝齐葡萄糖醛酸转化为一种羟基化代谢产物，氧化代谢发生在二甲基苯氧基部分（离葡萄糖醛酸部分最远的基团）。所述结果对于吉非贝齐与CYP2C8底物（如西立伐他汀、瑞格列奈、罗格列酮和吡格列酮）之间临床相互作用的机制具有重要意义。
