Yasumori T, Chen L S, Li Q H, Ueda M, Tsuzuki T, Goldstein J A, Kato R, Yamazoe Y
Department of Pharmacology, School of Medicine, Keio University, Tokyo, Japan.
Biochem Pharmacol. 1999 Jun 1;57(11):1297-303. doi: 10.1016/s0006-2952(99)00034-9.
Regio- and stereoselective hydroxylation of phenytoin was determined in liver microsomes of nine extensive (EM) and three poor metabolizers (PM) of mephenytoin. Hydroxyphenytoins (HPPH) were isolated and quantified after separation into four regio- and stereoisomers. The total rates of microsomal phenytoin 4'- hydroxylation were approximately 3-fold higher than those of 3'-hydroxylation, and not significantly different in EM and PM. Formation of 4'-(R)-HPPH was 4.4-fold higher in EM than in PM, whereas no clear differences between EM and PM were detected in the formation of 4'-(S)-, 3'-(R)-, and 3'-(S)-HPPH. Cytochrome P450 (CYP)2C9, expressed in a fission yeast, Schizosaccharomyces pombe, catalyzed the formation of 4'-(R)- and 4'-(S)-HPPH stereoselectively, as observed with EM, in which predominantly 4'-(S)-HPPH was formed. Recombinant CYP2C19 was more stereoselective for 4'-(R)-HPPH formation. These results, in addition to inhibition experiments with anti-human CYP2C antibody, indicate that phenytoin hydroxylation is mainly catalyzed by CYP2C9. Furthermore, CYP2C19 showed limited contribution to phenytoin 4'-hydroxylation with a different chiral preference from CYP2C9.
在9名美芬妥因的快代谢者（EM）和3名慢代谢者（PM）的肝微粒体中测定了苯妥英的区域和立体选择性羟基化。将羟基苯妥英（HPPH）分离为4种区域和立体异构体后进行分离和定量。微粒体苯妥英4'-羟基化的总速率比3'-羟基化的总速率高约3倍，在EM和PM中无显著差异。4'-(R)-HPPH在EM中的形成比在PM中高4.4倍，而在4'-(S)-、3'-(R)-和3'-(S)-HPPH的形成中，EM和PM之间未检测到明显差异。在粟酒裂殖酵母中表达的细胞色素P450（CYP）2C9催化了4'-(R)-和4'-(S)-HPPH的立体选择性形成，正如在EM中观察到的那样，其中主要形成4'-(S)-HPPH。重组CYP2C19对4'-(R)-HPPH的形成具有更高的立体选择性。这些结果，除了用人抗CYP2C抗体进行的抑制实验外，表明苯妥英羟基化主要由CYP2C9催化。此外，CYP2C19对苯妥英4'-羟基化的贡献有限，其手性偏好与CYP2C9不同。
