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Comparison of in vitro metabolism of ticlopidine by human cytochrome P450 2B6 and rabbit cytochrome P450 2B4.
- Source :
-
Drug metabolism and disposition: the biological fate of chemicals [Drug Metab Dispos] 2011 Mar; Vol. 39 (3), pp. 539-50. Date of Electronic Publication: 2010 Dec 14. - Publication Year :
- 2011
-
Abstract
- A recent X-ray crystal structure of a rabbit cytochrome P450 2B4 (CYP2B4)-ticlopidine complex indicated that the compound could be modeled with either the thiophene or chlorophenyl group oriented toward the heme prosthetic group. Subsequent NMR relaxation and molecular docking studies suggested that orientation with the chlorophenyl ring closer to the heme was the preferred one. To evaluate the predictive value of these findings, the oxidation of ticlopidine by reconstituted CYP2B4 was studied and compared with CYP2B6, in which the thiophene portion of the molecule likely orients toward the heme. In vitro incubation of ticlopidine with both enzymes yielded the same set of metabolites: 7-hydroxyticlopidine (M1), 2-oxoticlopidine (M2), 5-(2-chlorobenzyl)thieno[3,2-c]pyridin-5-ium metabolite (M3), 5-(2-chlorobenzyl)thieno[3,2-c]pyridin-5-ium metabolite (M4), ticlopidine N-oxide (M5), and ticlopidine S-oxide dimer, a dimerization product of ticlopidine S-oxide (M6). The rates of metabolite formation deviated markedly from linearity with time, consistent with the known inactivation of CYP2B6 by ticlopidine. Fitting to a first-order equation yielded similar rate constants (k(obs)) for both enzymes. However, the amplitude (R(max)) of M1 and M6 formation was 4 to 5 times higher for CYP2B6 than CYP2B4, indicating a greater residence time of ticlopidine with its thiophene ring closer to heme in CYP2B6. In contrast, CYP2B4 formed M4 and M5 in more abundance than CYP2B6, indicating an alternate orientation. Overall, the results suggest that the preferential orientation of ticlopidine in the active site of CYP2B4 predicted by X-ray crystallography and NMR studies is unproductive and that ticlopidine likely reorients within CYP2B4 to a more productive mode.
- Subjects :
- Animals
Aryl Hydrocarbon Hydroxylases antagonists & inhibitors
Aryl Hydrocarbon Hydroxylases genetics
Aryl Hydrocarbon Hydroxylases isolation & purification
Biocatalysis
Bupropion metabolism
Chromatography, High Pressure Liquid
Coumarins metabolism
Cytochrome P-450 CYP2B6
Cytochrome P-450 Enzyme Inhibitors
Cytochrome P-450 Enzyme System genetics
Cytochrome P-450 Enzyme System isolation & purification
Cytochrome P450 Family 2
Enzyme Inhibitors chemistry
Enzyme Inhibitors metabolism
Enzyme Inhibitors pharmacology
Humans
Kinetics
Models, Molecular
Molecular Structure
Oxidation-Reduction
Platelet Aggregation Inhibitors chemistry
Platelet Aggregation Inhibitors pharmacology
Rabbits
Recombinant Proteins metabolism
Spectrometry, Mass, Electrospray Ionization
Tandem Mass Spectrometry
Ticlopidine analogs & derivatives
Ticlopidine chemistry
Ticlopidine pharmacology
Aryl Hydrocarbon Hydroxylases metabolism
Cytochrome P-450 Enzyme System metabolism
Platelet Aggregation Inhibitors metabolism
Ticlopidine metabolism
Subjects
Details
- Language :
- English
- ISSN :
- 1521-009X
- Volume :
- 39
- Issue :
- 3
- Database :
- MEDLINE
- Journal :
- Drug metabolism and disposition: the biological fate of chemicals
- Publication Type :
- Academic Journal
- Accession number :
- 21156812
- Full Text :
- https://doi.org/10.1124/dmd.110.037101