Weiss Johanna, Sawa Evelyn, Riedel Klaus-Dieter, Haefeli Walter Emil, Mikus Gerd
Department of Internal Medicine VI, Clinical Pharmacology and Pharmacoepidemiology, University of Heidelberg, Heidelberg, Germany.
Naunyn Schmiedebergs Arch Pharmacol. 2008 Sep;378(3):275-82. doi: 10.1007/s00210-008-0294-7. Epub 2008 May 31.
Tilidine is one of the most widely used narcotics in Germany and Belgium. The compound's active metabolite nortilidine easily penetrates the blood-brain barrier and activates the mu-opioid receptor. Thus far, the enzymes involved in tilidine metabolism are unknown. Therefore, the aim of our study was to identify the cytochrome P450 isozymes (CYPs) involved in N-demethylation of tilidine in vitro. We used human liver microsomes as well as recombinant CYPs to investigate the demethylation of tilidine to nortilidine and quantified nortilidine by liquid chromatography-tandem mass spectrometry. Inhibition of CYPs was quantified with commercial kits. Moreover, inhibition of ABCB1 and ABCG2 was investigated. Our results demonstrated that N-demethylation of tilidine to nortilidine followed a Michaelis-Menten kinetic with a K(m) value of 36 +/- 13 microM and a v(max) value of 85 +/- 18 nmol/mg/h. This metabolic step was inhibited by CYP3A4 and CYP2C19 inhibitors. Investigations with recombinant CYP3A4 and CYP2C19 confirmed that the demethylation of tilidine occurs via these two CYPs. Inhibition assays demonstrated that tilidine and nortilidine can also inhibit CYP3A4, CYP2C19, CYP2D6, ABCB1, but not ABCG2, whereas inhibition of CYP2D6 and possibly also of CYP3A4 might be clinically relevant. By calculating the metabolic clearance based on the in vitro and published in vivo data, CYP3A4 and CYP2C19 were identified as the main elimination routes of tilidine. In vivo, drug-drug interactions of tilidine with CYP3A4 or CYP2C19 inhibitors are to be anticipated, whereas substrates of CYP2C19, ABCB1, or ABCG2 will presumably not be influenced by tilidine or nortilidine.
替利定是德国和比利时使用最广泛的麻醉药品之一。该化合物的活性代谢产物去甲替利定很容易穿透血脑屏障并激活μ-阿片受体。到目前为止，参与替利定代谢的酶尚不清楚。因此，我们研究的目的是在体外鉴定参与替利定N-去甲基化的细胞色素P450同工酶（CYPs）。我们使用人肝微粒体以及重组CYPs来研究替利定向去甲替利定的去甲基化反应，并通过液相色谱-串联质谱法定量去甲替利定。使用商业试剂盒对CYPs的抑制作用进行定量。此外，还研究了ABCB1和ABCG2的抑制作用。我们的结果表明，替利定向去甲替利定的N-去甲基化反应遵循米氏动力学，K(m)值为36±13微摩尔，v(max)值为85±18纳摩尔/毫克/小时。这一代谢步骤受到CYP3A4和CYP2C19抑制剂的抑制。对重组CYP3A4和CYP2C19的研究证实，替利定的去甲基化反应是通过这两种CYPs发生的。抑制试验表明，替利定和去甲替利定也可以抑制CYP3A4、CYP2C19、CYP2D6、ABCB1，但不抑制ABCG2，而对CYP2D6以及可能对CYP3A4的抑制在临床上可能具有相关性。通过根据体外和已发表的体内数据计算代谢清除率，确定CYP3A4和CYP2C19是替利定的主要消除途径。在体内，可以预期替利定会与CYP3A4或CYP2C19抑制剂发生药物相互作用，而CYP2C19、ABCB1或ABCG2的底物可能不会受到替利定或去甲替利定的影响。
