Satoh T, Hosokawa M, Atsumi R, Suzuki W, Hakusui H, Nagai E
Laboratory of Biochemical Pharmacology and Biotoxicology, Faculty of Pharmaceutical Sciences, Chiba University, Japan.
Biol Pharm Bull. 1994 May;17(5):662-4. doi: 10.1248/bpb.17.662.
We measured the plasma concentrations of 7-ethyl-10-[4-(1-piperidino)-1- piperidine]carbonyloxycamptothecin (CPT-11) and the active metabolite 7-ethyl-10-hydroxycamptothecin (SN-38), after treatment with CPT-11 to rats pretreated with bis-p-nitrophenylphosphate (BNPP) which is a specific inhibitor of carboxylesterase, and non-pretreated rats. The plasma level of SN-38 was decreased in the BNPP-pretreated group compared with these of non-pretreated group, indicating that the esterase involved in CPT-11 metabolism is a carboxylesterase. We also characterized the molecular species of carboxylesterase involved in CPT-11 metabolism using enzyme preparations purified from liver microsomes. Thirteen carboxylesterase isozyme activities towards CPT-11 were compared and guinea pig GLP1 was found to have the highest activity, while human HU1 isozyme had relatively lower activity than those of animal species. In studies on the kinetic parameters of the hydrolysis of CPT-11 by the purified carboxylesterase isozymes the highest Vmax value of the isozymes was found in human HU1 and the smallest was seen in rat RL1. The Vmax/Km for RL1 showed the largest value of 21.7 nmol/mg protein/mM.
我们测定了用7-乙基-10-[4-(1-哌啶基)-1-哌啶]羰基氧喜树碱（CPT-11）处理经双对硝基苯基磷酸酯（BNPP，一种羧酸酯酶特异性抑制剂）预处理的大鼠和未预处理大鼠后，血浆中CPT-11及其活性代谢物7-乙基-10-羟基喜树碱（SN-38）的浓度。与未预处理组相比，BNPP预处理组中SN-38的血浆水平降低，表明参与CPT-11代谢的酯酶是羧酸酯酶。我们还使用从肝微粒体中纯化的酶制剂对参与CPT-11代谢的羧酸酯酶的分子种类进行了表征。比较了13种羧酸酯酶同工酶对CPT-11的活性，发现豚鼠GLP1活性最高，而人HU1同工酶的活性相对低于动物物种。在对纯化的羧酸酯酶同工酶水解CPT-11的动力学参数研究中，发现同工酶的最大反应速度（Vmax）值在人HU1中最高，在大鼠RL1中最低。RL1的Vmax/Km显示出21.7 nmol/mg蛋白质/毫摩尔的最大值。
