Role of CYP2C19 in stereoselective hydroxylation of mephobarbital by human liver microsomes.
The 4-hydroxylation of mephobarbital enantiomers was investigated by using human liver microsomes from the extensive metabolizers (EM) and poor metabolizers of CYP2C19. The 4-hydroxylase activity of R-mephobarbital in the EM microsomes was >10 times higher than that of S-mephobarbital. In the poor metabolizer microsomes, the 4-hydroxylase activity of R-mephobarbital was much lower than that in the EM microsomes, and the ratio of 4-hydroxylase activity of R-mephobarbital to that of S-mephobarbital was also lower than that in the EM microsomes. Moreover, the 4-hydroxylase activity of R-mephobarbital showed a high correlation (r = 0.985, p<0.001) with the 4'-hydroxylase activity of S-mephenytoin in a panel of nine human liver microsomes. Anti-CYP2C antibody inhibited R-mephobarbital 4-hydroxylase activity by 85% of the control activity. R-Mephobarbital competitively inhibited S-mephenytoin 4'-hydroxylase activity (K(i) = 34 microM), while S-mephenytoin inhibited R-mephobarbital 4-hydroxylase activity (K(i) = 103 microM). Among the seven cDNA-expressed CYPs studied, only CYP2C19 catalyzed R-mephobarbital 4-hydroxylation. These findings suggest that the 4-hydroxylation of mephobarbital catalyzed by CYP2C19 is preferential for R-enantiomer in human liver microsomes.
Kobayashi
K
K
Department of Clinical Pharmacy, Showa University, Tokyo, Japan. kaoruk@p.chiba-u.ac.jp
Kogo
M
M
Tani
M
M
Shimada
N
N
Ishizaki
T
T
Numazawa
S
S
Yoshida
T
T
Yamamoto
T
T
Kuroiwa
Y
Y
Chiba
K
K
D001189:Aryl Hydrocarbon Hydroxylases; D002851:Chromatography, High Pressure Liquid; D065731:Cytochrome P-450 CYP2C19; D003577:Cytochrome P-450 Enzyme System / Q000235:genetics / Q000378:metabolism*; D018076:DNA, Complementary; D006801:Humans; D006900:Hydroxylation; D066298:In Vitro Techniques; D008618:Mephobarbital / Q000493:pharmacokinetics*; D008862:Microsomes, Liver / Q000201:enzymology / Q000378:metabolism*; D006899:Mixed Function Oxygenases / Q000235:genetics / Q000378:metabolism*; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism
D018076:DNA, Complementary; D011994:Recombinant Proteins; D008618:Mephobarbital; D003577:Cytochrome P-450 Enzyme System; D006899:Mixed Function Oxygenases; D001189:Aryl Hydrocarbon Hydroxylases; C045793:CYP2C19 protein, human; D065731:Cytochrome P-450 CYP2C19