Saito Konomu, Sakai Noriaki, Kim Hyung-Sub, Ishizuka Mayumi, Kazusaka Akio, Fujita Shoichi
Laboratory of Toxicology, Department of Environmental Veterinary Sciences, Graduate School of Veterinary Medicine, Hokkaido University, N18W9 North Ward, Sapporo 060-0818, Japan.
Drug Metab Dispos. 2004 Sep;32(9):959-65.
Knowledge of strain differences in drug metabolism is important for the selection of animals for pharmacokinetic, pharmacodynamic, and toxicological studies. Hepatic microsomes from Sprague-Dawley (SD) and Brown Norway (BN) rats had 300-fold higher diazepam p-hydroxylation activity than Dark Agouti (DA) and Wistar (W) rats at a low diazepam concentration (3 microM). Kinetic studies indicated that diazepam p-hydroxylation in SD and BN rats proceeded with lower K(m) and higher V(max) values than it did in DA and W rats. However, the expression levels of cytochrome P450 CYP2D1, the reported enzyme for diazepam p-hydroxylation, did not cosegregate with the activity. These results suggest the presence of a new high-affinity diazepam p-hydroxylation enzyme other than CYP2D1 in SD and BN rats. DA rats showed 3- and 2-fold higher diazepam 3-hydroxylation and N-desmethylation activities, respectively, than the other rat strains. In agreement with this, DA rat liver microsomes had a higher expression of CYP3A2, which is responsible for diazepam 3-hydroxylation and partly responsible for N-desmethylation. Values of CL(int) (V(max)/K(m)) indicated that p-hydroxy-diazepam is the major metabolite in SD and BN rats, whereas 3-hydroxy-diazepam is the major metabolite in DA and W rats. The sum of the CL(int) in each strain was in the order of DA > SD = BN >> W. Strain differences in the pharmacodynamics of diazepam between SD and DA rats may be due to these differences in diazepam metabolism. We found that both the rate of elimination of diazepam and the major metabolic pathways in diazepam metabolism differed among the different rat strains due to polymorphic expression of the two enzymes involved in diazepam metabolism.
了解药物代谢中的品系差异对于药代动力学、药效学和毒理学研究中实验动物的选择至关重要。在低地西泮浓度（3 microM）下，来自Sprague-Dawley（SD）大鼠和Brown Norway（BN）大鼠的肝微粒体的地西泮对羟基化活性比Dark Agouti（DA）大鼠和Wistar（W）大鼠高300倍。动力学研究表明，与DA大鼠和W大鼠相比，SD大鼠和BN大鼠的地西泮对羟基化反应的米氏常数（K(m)）较低，最大反应速度（V(max)）较高。然而，据报道负责地西泮对羟基化的细胞色素P450 CYP2D1的表达水平与活性并不共分离。这些结果表明，在SD大鼠和BN大鼠中存在一种不同于CYP2D1的新的高地西泮对羟基化酶。DA大鼠的地西泮3-羟基化和N-去甲基化活性分别比其他大鼠品系高3倍和2倍。与此一致的是，DA大鼠肝微粒体中负责地西泮3-羟基化并部分负责N-去甲基化的CYP3A2表达较高。内在清除率（CL(int)，V(max)/K(m)）值表明，对羟基地西泮是SD大鼠和BN大鼠中的主要代谢产物，而3-羟基地西泮是DA大鼠和W大鼠中的主要代谢产物。各品系的CL(int)总和顺序为DA > SD = BN >> W。SD大鼠和DA大鼠之间地西泮药效学的品系差异可能归因于地西泮代谢的这些差异。我们发现，由于参与地西泮代谢的两种酶的多态性表达，不同大鼠品系在地西泮消除速率和地西泮代谢的主要途径方面均存在差异。
