The oxidative metabolism of dimemorfan by human cytochrome P450 enzymes.
To characterize the human cytochrome P450 (P450) forms involved in dimemorfan oxidation (DFO), human liver microsomes, and recombinant P450s were investigated. Liquid chromatography-mass spectral analysis suggested that metabolite (M)1 ([M + H](+) m/z at 272.200) and M2 ([M + H](+) m/z at 242.190) were d-3-hydroxymethyl-N-methylmorphinan and d-3-methylmorphinan, respectively. Kinetic analyses of microsomal DFO showed that the substrate concentration showing a half-maximal velocity (S(50)) of M1 formation was less than that of M2. Microsomal M1 and M2 formation activities correlated significantly with the CYP2D6 marker, dextromethorphan O-demethylation activity. The M2 formation activity was also correlated with the CYP3A4 marker, nifedipine oxidation activity. Microsomal M1 and M2 formation was most sensitive to the inhibition by a CYP2D6 inhibitor, paroxetine and a CYP3A4 inhibitor, ketoconazole, respectively. The immunoinhibition-defined P450 contributions indicated the participation of CYP2C9, CYP2C19, and CYP2D6 in the M1 formation and CYP2B6, CYP2C9, CYP2C19, CYP2D6, and CYP3A4 in the M2 formation. Among recombinant P450s, CYP2D6 had the highest intrinsic clearance with a K(m) value of 0.02 mM in forming M1. CYP2B6, CYP2C9, and CYP2C19 had the K(m) or S(50) values smaller than those (1 mM) of CYP2D6 and CYP3A4 in forming M2. These results indicated the participation of multiple P450 forms in DFO.
Chou
Yueh-Ching
YC
Pharmacy Department, Taipei Veterans General Hospital, Taipei, Taiwan, ROC.
Chung
Yu-Ting
YT
Liu
Tsung-Yun
TY
Wang
Szu-Yu
SY
Chau
Gar-Yang
GY
Chi
Chin-Wen
CW
Soucek
Pavel
P
Krausz
Kristopher W
KW
Gelboin
Harry V
HV
Lee
Chen-Hsen
CH
Ueng
Yune-Fang
YF
D000368:Aged; D000369:Aged, 80 and over; D000911:Antibodies, Monoclonal / Q000494:pharmacology; D000996:Antitussive Agents / Q000493:pharmacokinetics*; D002851:Chromatography, High Pressure Liquid; D065607:Cytochrome P-450 Enzyme Inhibitors; D003577:Cytochrome P-450 Enzyme System / Q000235:genetics / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005260:Female; D006801:Humans; D007527:Isoenzymes / Q000235:genetics / Q000378:metabolism; D007700:Kinetics; D008297:Male; D013058:Mass Spectrometry; D008862:Microsomes, Liver / Q000378:metabolism; D008875:Middle Aged; D009019:Morphinans / Q000493:pharmacokinetics*; D010084:Oxidation-Reduction; D010957:Plasmids / Q000235:genetics; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism
D000911:Antibodies, Monoclonal; D000996:Antitussive Agents; D065607:Cytochrome P-450 Enzyme Inhibitors; D004791:Enzyme Inhibitors; D007527:Isoenzymes; D009019:Morphinans; D011994:Recombinant Proteins; C012621:dimemorfan; D003577:Cytochrome P-450 Enzyme System