Lampen A, Christians U, Guengerich F P, Watkins P B, Kolars J C, Bader A, Gonschior A K, Dralle H, Hackbarth I, Sewing K F
Institut für Allgemeine Pharmakologie, Medizinische Hochschule Hannover, Germany.
Drug Metab Dispos. 1995 Dec;23(12):1315-24.
The small intestinal metabolism of tacrolimus, which is used as an immunosuppressant in transplantation medicine, was investigated in this study. Tacrolimus was metabolized in vitro by isolated human, pig, and rat small intestinal microsomes. The metabolites generated were identified by HPLC/MS. Tacrolimus and its metabolites were quantified using HPLC or HPLC/MS. The cytochrome P450 (CYP) enzymes responsible for tacrolimus metabolism in small intestine were identified using specific CYP antibodies and inhibitors. For characterization of the interindividual variability, microsomes were isolated from small intestinal samples of patients who had undergone resection for various reasons. In an in vitro model using pig small intestinal microsomes, 32 drugs were analyzed for their interactions with tacrolimus metabolism. After incubation with human, rat, and pig small intestinal microsomes, the metabolites 13-O-demethyl and 13,15-O-demethyl tacrolimus were identified. The metabolism of tacrolimus by human small intestine was inhibited by anti-CYP3A, troleandomycin, and erythromycin, indicating that, as in the liver, CYP3A enzymes are the major enzymes for tacrolimus metabolism in the human small intestine. Metabolism of tacrolimus by small intestinal microsomes isolated from 14 different patients varied between 24 and 110 pmol/13-O-demethyl tacrolimus/min/mg microsomal protein, with a mean +/- SD of 54.2 +/- 29.2 pmol/min/mg. Of 32 drugs tested, 15 were found to inhibit small intestinal tacrolimus metabolism: bromocryptine, corticosterone, cyclosporine, dexamethasone, ergotamine, erythromycin, ethinyl estradiol, josamycin, ketoconazole, nifedipine, omeprazole, progesterone, rapamycin, troleandomycin, and verapamil. All of these drugs inhibited tacrolimus metabolism by human liver microsomes as well. It is concluded that tacrolimus is metabolized by cytochrome CYP3A enzymes in the small intestine. The rate of the CYP3A enzymatic activities varies about 5 times from patient to patient, and drugs that interfere with the in vitro metabolism of tacrolimus in the liver also inhibit its small intestinal metabolism.
本研究对用于移植医学的免疫抑制剂他克莫司的小肠代谢情况进行了调查。他克莫司在体外可被分离出的人、猪和大鼠小肠微粒体代谢。生成的代谢产物通过高效液相色谱/质谱联用仪（HPLC/MS）进行鉴定。他克莫司及其代谢产物使用高效液相色谱（HPLC）或高效液相色谱/质谱联用仪进行定量分析。利用特异性细胞色素P450（CYP）抗体和抑制剂来鉴定负责他克莫司在小肠中代谢的CYP酶。为了表征个体间差异，从小肠样本中分离微粒体，这些样本来自因各种原因接受切除术的患者。在一个使用猪小肠微粒体的体外模型中，分析了32种药物与他克莫司代谢的相互作用。在与人类、大鼠和猪小肠微粒体孵育后，鉴定出了代谢产物13-O-去甲基他克莫司和13,15-O-去甲基他克莫司。人小肠对他克莫司的代谢受到抗CYP3A、三乙酰竹桃霉素和红霉素的抑制，这表明，与在肝脏中一样，CYP3A酶是人类小肠中他克莫司代谢的主要酶。从14名不同患者分离出的小肠微粒体对他克莫司的代谢情况有所不同，范围在24至110皮摩尔/13-O-去甲基他克莫司/分钟/毫克微粒体蛋白之间，平均±标准差为54.2±29.2皮摩尔/分钟/毫克。在测试的32种药物中，发现有15种抑制小肠他克莫司代谢：溴隐亭、皮质酮、环孢素、地塞米松、麦角胺、红霉素、炔雌醇、交沙霉素、酮康唑、硝苯地平、奥美拉唑、孕酮、雷帕霉素、三乙酰竹桃霉素和维拉帕米。所有这些药物也抑制人肝脏微粒体对他克莫司的代谢。得出的结论是，他克莫司在小肠中被细胞色素CYP3A酶代谢。CYP3A酶活性的速率在患者之间相差约5倍，并且干扰他克莫司在肝脏中体外代谢的药物也会抑制其小肠代谢。
