Polymorphism in stereoselective hydroxylations of mephenytoin and hexobarbital by Japanese liver samples in relation to cytochrome P-450 human-2 (IIC9).
1. Stereoselective 4'-hydroxylations of R-(--)-mephenytoin and S-(+)-mephenytoin were determined in liver microsomes of 19 Japanese subjects. 2. The content of P-450 human-2 assessed by Western-blots correlated with microsomal S-(+)-mephenytoin 4'-hydroxylation. Antibody raised against P-450 human-2 effectively inhibited microsomal S-(+)-mephenytoin 4'-hydroxylation, but was less efficient for inhibition of R-(--)-mephenytoin 4'-hydroxylation in extensive metabolizers, and 4'-hydroxylation of both mephenytoin enantiomers in poor metabolizers. 3. Similar results were observed on the stereoselective hydroxylations of R-(--)- and S-(+)-hexobarbital. Clear correlations were observed for the content of P-450 human-2 and microsomal R-(--)-hexobarbital 3'alpha-hydroxylation and S-(+)-hexobarbital 3'beta-hydroxylation. 4. Moreover, yeast microsomes expressing P-450 human-2 cDNA showed high stereoselectivities for hydroxylations of mephenytoin and hexobarbital similar to those observed in human liver. 5. Two other cytochromes P-450(IIC 9/10) expressed in yeast, whose cDNA were synthesized by site-directed mutagenesis from human-2 cDNA, showed no stereoselectivity for the hydroxylations of mephenytoin and hexobarbital, in spite of the modification of only two amino acid substitutions or deletions in the whole sequence. 6. Only a cytochrome derived from P-450 human cDNA corresponding to P-450 human-2 was expressed in human livers, the two cytochromes of the three related IIC9/10 forms were not expressed. 7. These findings indicate that P-450 human-2 is the major cytochrome P-450 responsible for the polymorphisms in stereoselective hydroxylations of mephenytoin and hexobarbital.
Kato
R
R
Department of Pharmacology, School of Medicine, Keio University, Tokyo, Japan.
Yamazoe
Y
Y
Yasumori
T
T
D003577:Cytochrome P-450 Enzyme System / Q000235:genetics* / Q000378:metabolism; D004247:DNA / Q000235:genetics; D006591:Hexobarbital / Q000378:metabolism*; D006801:Humans; D006900:Hydroxylation; D008099:Liver / Q000201:enzymology* / Q000378:metabolism; D008617:Mephenytoin / Q000378:metabolism*; D006899:Mixed Function Oxygenases / Q000235:genetics* / Q000378:metabolism; D011110:Polymorphism, Genetic / Q000235:genetics*; D013237:Stereoisomerism
D004247:DNA; D003577:Cytochrome P-450 Enzyme System; D006591:Hexobarbital; D006899:Mixed Function Oxygenases; D008617:Mephenytoin