Oxidative metabolism of bunitrolol by complementary DNA-expressed human cytochrome P450 isozymes in a human hepatoma cell line (Hep G2) using recombinant vaccinia virus.
We examined the oxidative metabolism of a beta-blocker bunitrolol (BTL) by 10 human cytochromes P450 (CYP) (1A2, 2A6, 2B6, 2C8, 2C9, 2D6, 2E1, 3A3, 3A4 or 3A5), which were individually expressed in Hep G2 cells with a vaccinia virus complementary DNA expression system. Among the 10 isozymes, only CYP2D6 and 1A2 at a substrate concentration of 5 microns, and CYP2C8 and 2C9 in addition to the two isozymes at a BTL concentration of 1 mM, exhibited detectable BTL 4-hydroxylase activities. The activities at 1 mM BTL were on the order of CYP2D6 (100% as relative activity) > CYP1A2 (86%) >> CYP2C8 and 2C9 (7-8%). Enzyme kinetic parameters of CYP2D6 were calculated to be 4.41 microns as a Km value and 0.442 nmol min-1 per nmol CYP as a Vmax value. Kinetic parameters of CYP1A2 were calculated as 295 microns and 0.411 nmol min-1 per nmol CYP for Km and Vm values, respectively. These results suggest that both CYP2D6 and 1A2 primarily catalyse BTL 4-hydroxylation, but that the former is a predominant isozyme responsible for the reaction at a low substrate concentration range of BTL in human liver.
Ono
S
S
Central Laboratory, Amersham K. K., Chiba, Japan.
Tsutsui
M
M
Gonzalez
F J
FJ
Satoh
T
T
Masubuchi
Y
Y
Horie
T
T
Suzuki
T
T
Narimatsu
S
S
D000319:Adrenergic beta-Antagonists / Q000378:metabolism*; D006528:Carcinoma, Hepatocellular; D003577:Cytochrome P-450 Enzyme System / Q000096:biosynthesis / Q000378:metabolism*; D018076:DNA, Complementary; D006801:Humans; D007527:Isoenzymes / Q000096:biosynthesis / Q000378:metabolism*; D007700:Kinetics; D008113:Liver Neoplasms; D011412:Propanolamines / Q000378:metabolism*; D011994:Recombinant Proteins / Q000096:biosynthesis / Q000378:metabolism; D013379:Substrate Specificity; D014162:Transfection; D014407:Tumor Cells, Cultured; D014616:Vaccinia virus
D000319:Adrenergic beta-Antagonists; D018076:DNA, Complementary; D007527:Isoenzymes; D011412:Propanolamines; D011994:Recombinant Proteins; D003577:Cytochrome P-450 Enzyme System; C084811:bunitrolol