Koyama E, Chiba K, Tani M, Ishizaki T
Department of Clinical Pharmacology, International Medical Center of Japan, Tokyo, Japan.
J Pharmacol Exp Ther. 1996 Jul;278(1):21-30.
To identify cytochrome P450 (CYP) isoform(s) involved in the major metabolic pathways of mianserin (MS) enantiomers in humans, we examined the metabolites formed from S-(+)- and R-(-)-MS using human liver microsomes and eight recombinant human CYP isoforms (i.e., CYP1A2, 2A6, 2B6, 2C9, 2C19, 2D6, 2E1 and 3A4). The mean V(max)/K(m) values of the 8-hydroxylation and N-oxidation were greater for S-(+)- than for R-(-)-MS, whereas that of the N-demethylation gave the opposite observation. When relationships were evaluated in microsomes from 10 human livers between the metabolism of substrates toward the respective CYP isoforms and stereoselective metabolism of MS at a low (5 microM) and at a high (200 microM) MS concentration, significant correlations existed in: 2-hydroxylation of desipramine vs. 8-hydroxylation of S-(+)-MS (r = 0.94, P < .01), O-deethylation of phenacetin vs. N-demethylation of S-(+)-MS (r = 0.85, P < .01) and R-(-)-MS (r = 0.69, P < .05) or N-oxidation of S-(+)-MS (r = 0.94, P < .01) at the low concentration; and 6 beta-hydroxylation of testosterone vs. three metabolic reactions of both MS enantiomers at the high concentration (r = 0.68-0.93, P < .05-.01). Quinidine inhibited the 8-hydroxylation of both enantiomers by < 40% of the respective control values. Furafylline and alpha-naphthoflavone showed a potent inhibitory effect on the N-demethylation and N-oxidation of S-(+)-MS (by up to < 50% of the respective control activities). In addition, troleandomycin inhibited the N-demethylation and N-oxidation of R-(-)-MS by < 50% of the respective control activities. Among the recombinant human CYP isoforms, CYP2D6, 2B6, 3A4 and 1A2 catalyzed the 8-hydroxylation, and CYP1A2 and 3A4 were involved exclusively in the N-oxidation, whereas CYP2B6, 2C19, 1A2, 3A4 and 2D6 showed a catalytic activity for the N-demethylation, for either or both of MS enantiomers. Taken together, the 8-hydroxylation for both MS enantiomers is mediated mainly via CYP2D6, whereas the N-demethylation for both the enantiomers and N-oxidation for S-(+)-MS are catalyzed mainly via CYP1A2. The two in vitro experiments suggested that CYP3A is involved to a certain extent in each of the stereoselective MS metabolic pathways.
为了确定参与米安色林（MS）对映体在人体内主要代谢途径的细胞色素P450（CYP）同工酶，我们使用人肝微粒体和8种重组人CYP同工酶（即CYP1A2、2A6、2B6、2C9、2C19、2D6、2E1和3A4）研究了S-(+)-和R-(-)-MS形成的代谢产物。S-(+)-MS的8-羟基化和N-氧化的平均V(max)/K(m)值高于R-(-)-MS，而N-去甲基化的情况则相反。当评估10个人肝脏微粒体中底物对各自CYP同工酶的代谢与低浓度（5 microM）和高浓度（200 microM）MS时MS的立体选择性代谢之间的关系时，存在显著相关性：地昔帕明的2-羟基化与S-(+)-MS的8-羟基化（r = 0.94，P <.01）、非那西丁的O-去乙基化与S-(+)-MS的N-去甲基化（r = 0.85，P <.01）以及R-(-)-MS的N-去甲基化（r = 0.69，P <.05）或低浓度下S-(+)-MS的N-氧化（r = 0.94，P <.01）；以及睾酮的6β-羟基化与高浓度下两种MS对映体的三种代谢反应（r = 0.68 - 0.93，P <.05 -.01）。奎尼丁抑制两种对映体的8-羟基化，抑制率均低于各自对照值的40%。呋拉茶碱和α-萘黄酮对S-(+)-MS的N-去甲基化和N-氧化显示出强效抑制作用（分别高达各自对照活性的<50%）。此外，三乙酰竹桃霉素抑制R-(-)-MS的N-去甲基化和N-氧化，抑制率均低于各自对照活性的50%。在重组人CYP同工酶中，CYP2D6、2B6、3A4和1A2催化8-羟基化，CYP1A2和3A4仅参与N-氧化，而CYP2B6、2C19、1A2、3A4和2D6对MS两种对映体中的一种或两种显示出N-去甲基化的催化活性。综上所述，两种MS对映体的8-羟基化主要通过CYP2D6介导，而两种对映体的N-去甲基化和S-(+)-MS的N-氧化主要由CYP1A2催化。这两项体外实验表明，CYP3A在MS的每种立体选择性代谢途径中都有一定程度的参与。
