Tyndale R F, Sunahara R, Inaba T, Kalow W, Gonzalez F J, Niznik H B
Department of Pharmacology, University of Toronto, Ontario, Canada.
Mol Pharmacol. 1991 Jul;40(1):63-8.
Catalytic, pharmacological, and molecular criteria have been used to identify cytochrome P450IID1 in mammalian brain (enzyme, P450IID; gene, CYP2D). Sparteine metabolism in canine striatal membranes was shown to be inhibited in a concentration-dependent and stereoselective manner by quinidine (Ki, approximately 51 nM), quinine (Ki, approximately 5.9 microM), and various other known substrates and inhibitors of hepatic P450IID1 activity. In addition, canine striatal P450IID1 was inhibited with high affinity by dopamine uptake blockers, such as (-)-cocaine (Ki, approximately 74 nM), d-amphetamine (Ki, approximately 4.5 microM), and methylphenidate (Ki, approximately 15 microM). Inhibitory constants (Ki) of numerous compounds for inhibition of sparteine metabolism in canine striatal membranes correlated well with (a) Ki values observed in human liver microsomes (r = 0.95), (b) [3H]GBR-12935 binding to P450IID1 in canine striatal membranes (r = 0.85), and (c) the inhibition (IC50) of sparteine metabolism in HepG2 cells expressing human CYP2D6 cDNA (r = 0.93). Moreover, antibodies raised against rat hepatic enzyme inhibited, in a concentration-dependent manner, sparteine metabolism in canine striatal membranes. Enzymatic activity was unevenly distributed throughout the canine brain and ranged from 0.5 to 21 pmol/mg of protein/hr in cerebellum and supraorbital cortex, respectively, with the striatum displaying moderate levels of activity (8 pmol/mg of protein/hr). The polymerase chain reaction was used to amplify cDNA from a human caudate lambda gt11 library encoding exons 6-9 of the human CYP2D6 gene, which revealed, upon sequencing, 100% nucleic acid sequence identity. These data indicate that P450IID1 is expressed centrally and is similar, at the functional and molecular levels, to the human hepatic P450IID1 enzyme. Because the debrisoquine/sparteine mono-oxygenase is a polymorphic enzyme, in which 5-10% of caucasians are deficient in metabolism of various drugs, a genetic difference in human brain metabolism of P450IID1 substrates may possibly lead to differences in drug response and toxicity.
催化、药理学和分子标准已被用于在哺乳动物大脑中鉴定细胞色素P450IID1（酶，P450IID；基因，CYP2D）。奎尼丁（Ki，约51 nM）、奎宁（Ki，约5.9 μM）以及其他各种已知的肝P450IID1活性底物和抑制剂，均以浓度依赖性和立体选择性方式抑制犬纹状体膜中的司巴丁代谢。此外，多巴胺摄取阻滞剂，如（-）-可卡因（Ki，约74 nM）、d-苯丙胺（Ki，约4.5 μM）和哌甲酯（Ki，约15 μM），对犬纹状体P450IID1具有高亲和力抑制作用。许多化合物对犬纹状体膜中司巴丁代谢的抑制常数（Ki）与以下各项具有良好的相关性：（a）在人肝微粒体中观察到的Ki值（r = 0.95）；（b）[3H]GBR-12935与犬纹状体膜中P450IID1的结合（r = 0.85）；以及（c）在表达人CYP2D6 cDNA的HepG2细胞中司巴丁代谢的抑制（IC50）（r = 0.93）。此外，针对大鼠肝酶产生的抗体以浓度依赖性方式抑制犬纹状体膜中的司巴丁代谢。酶活性在整个犬脑中分布不均，小脑和眶上皮质中分别为0.5至21 pmol/mg蛋白质/小时，纹状体显示出中等水平的活性（8 pmol/mg蛋白质/小时）。聚合酶链反应用于从人尾状核λgt11文库中扩增编码人CYP2D6基因外显子6 - 9的cDNA，测序后显示核酸序列同一性为100%。这些数据表明P450IID1在中枢表达，并且在功能和分子水平上与人肝P450IID1酶相似。由于异喹胍/司巴丁单加氧酶是一种多态性酶，其中5 - 10%的高加索人对各种药物的代谢存在缺陷，P450IID1底物在人脑中的代谢遗传差异可能导致药物反应和毒性的差异。
