QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Abstract Full Text (PDF) Submit a response Alert me when this article is cited Alert me when eLetters are posted Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Ma, B. Articles by Tang, C. Search for Related Content PubMed PubMed Citation Articles by Ma, B. Articles by Tang, C.

SHORT COMMUNICATION

CYTOCHROME P450 2C8 (CYP2C8)-MEDIATED HYDROXYLATION OF AN ENDOTHELIN ET_A RECEPTOR ANTAGONIST IN HUMAN LIVER MICROSOMES

Department of Drug Metabolism, Merck Research Laboratories, West Point, Pennsylvania (B.M., R.S., M.L.S., C.T.); and Bristol-Myers Squibb, Princeton, New Jersey (A.D.R.)

(Received January 9, 2004; accepted February 13, 2004)

	Abstract

Top Abstract Materials and Methods Results and Discussion References

 
In vitro studies were performed to identify the human cytochrome P450 enzyme(s) involved in the hydroxylation (isopropyl moiety) of a previously reported endothelin ET_A receptor antagonist, compound A [(+)-(5S,6R,7R)-2-isopropylamino-7-{4-methoxy-2-[(2R)-3-methoxy-2-methylpropyl]}-5-(3,4-methylenedioxyphenyl)cyclopenteno(1,2-b) pyridine 6-carboxylic acid]. Several lines of evidence indicated that the reaction was mainly catalyzed by CYP2C8. Of the 10 recombinant cytochrome P450 isoforms tested, only CYP2C8 exhibited hydroxylase activity. In agreement, inhibitory antibodies selective for CYP2C8 attenuated (>95%) the hydroxylase activity in human liver microsomes, whereas antibodies and chemical inhibitors selective for other cytochrome P450 isoforms had a minor or no effect on the reaction. In addition, the formation of the hydroxy metabolite correlated well with CYP2C8-selective paclitaxel 6-hydroxylation (r² 0.92; p < 0.0001) and amodiaquine N-de-ethylation (r² 0.91; p < 0.0001) in a bank of human liver microsomes (n = 15 organ donors). Finally, compound A hydroxylase activity conformed to Michaelis-Menten kinetics, and the K_m (Michaelis constant) in human liver microsomes was similar to that of CYP2C8 (10 µM). It is concluded that the hydroxylation of compound A is mainly catalyzed by CYP2C8, and thus the reaction can possibly serve as an alternative marker assay for CYP2C8 in human liver microsomes.

In recent years, there has been a growing interest in the involvement of CYP2C8 in drug metabolism. CYP2C8 has been reported to play a role in the biotransformation of paclitaxel, cerivastatin, rosiglitazone, troglitazone, verapamil, amodiaquine, amiodarone, and zopiclone (Baldwin et al., 1999; Becquemont et al., 1999; Tracy et al., 1999; Yamazaki et al., 1999; Ohyama et al., 2000; Li et al., 2002; Wang et al., 2002). In the case of cerivastatin, a hydroxymethylglutaryl coenzyme A reductase inhibitor withdrawn from the market in 2001, patients were shown to have elevated cerivastatin levels in plasma when gemfibrozil was coadministered (Backman et al., 2002). The inhibition of cerivastatin metabolism by gemfibrozil was, in part, mediated by CYP2C8 (Prueksaritanont et al., 2002; Wang et al., 2002). It is therefore of interest to prospectively evaluate drug candidates as inhibitors of CYP2C8. Toward this end, paclitaxel 6-hydroxylation has been used as a marker assay for CYP2C8 (Rahman et al., 1994), and, more recently, amodiaquine N-de-ethylation has been proposed (Li et al., 2002).

In the present study, the oxidative metabolism of compound A, a potent endothelin ET_A receptor antagonist (Okada et al., 2000), was studied after incubation with human liver microsomes. Preliminary data indicated that the hydroxylation on the isopropyl moiety (Fig. 1) was catalyzed almost exclusively by CYP2C8. Therefore, we sought to determine the P450s involved in the reaction using inhibitory antibodies, chemical inhibitors, correlation analysis, and recombinant human P450 proteins.

View larger version (22K): [in this window] [in a new window]   FIG. 1. Structures of compound A and its oxidative metabolites.

	Materials and Methods

Top Abstract Materials and Methods Results and Discussion References

 
Chemicals and Biologicals. Compound A and (-)-N-3-benzyl-phenobarbital were synthesized at Banyu Pharmaceutical Co. (Ibaraki, Japan) and in-house (Merck Research Laboratories, West Point, PA), respectively. NADPH, verapamil, amodiaquine, paclitaxel, bactin III, sulfaphenazole, quinidine, troleandomycin, and furafylline were obtained from Sigma-Aldrich (St. Louis, MO). 6-Hydroxypaclitaxel was purchased from BD Biosciences Discovery Labware (Bedford, MA). Human liver microsomes prepared from individual or pooled (n = 20) subjects were purchased from BD Biosciences Discovery Labware, Tissue Transformation Technologies (Edison, NJ), Xeno-Tech, LLC (Lenexa, KA), and In Vitro Technologies, Inc. (Baltimore, MD). Microsomes prepared from insect cells infected with baculovirus expressing human P450 isoforms (CYP1A2, 2A6, 2B6, 2C8, 2C9, 2C19, 2D6, 2E1, 3A4, and 3A5) were obtained in-house. Inhibitory mouse anti-human P450 antibodies selective for CYP2A6, CYP2C, CYP2D6, and CYP3A were prepared in-house (Mei et al., 1999, 2002), and anti-human CYP1A2, CYP2B6, CYP2C8, and CYP2E1 antibodies were purchased from BD Biosciences Discovery Labware. Other reagents were of analytical grade or higher.

Incubations with Human Liver Microsomes and Recombinant Human P450 Isoforms. Incubation mixtures (0.5 ml) contained 50 mM potassium phosphate (pH 7.4), 1 mM magnesium chloride, 0.1 mg/ml pooled human liver microsomal protein or 10 pmol/ml recombinant human P450, 1 mM NADPH, and 0.1 to 100 µM compound A dissolved in acetonitrile [1% (v/v) final concentration]. The reaction was started by the addition of compound A after a 2-min preincubation at 37°C in a shaking water bath. Acetonitrile (1 ml) was added after 3 min to terminate the reaction. A 50-µl aliquot of a 20 nM stock solution of verapamil was added to the reaction mixture as internal standard. After centrifugation at 2000g for 10 min, supernatant fractions were transferred to clean tubes and dried under nitrogen in a TurboVap evaporator (Zymark Corp., Hopkinton, MA). Dried samples were reconstituted in 0.25 ml of 5% (v/v) acetonitrile in water containing 0.1% (v/v) formic acid for LC-MS analysis. Under these conditions, the formation rate of all four metabolites of compound A was linear with respect to protein and P450 concentrations as well as time of incubation.

Immunoinhibition Studies. Pooled human liver microsomes (0.05 mg protein) were preincubated on ice (10–15 min) with the anti-P450 antibody preparation (2 µl) or control sera prepared from mouse ascites. The ratio of microsomal protein-to-antibody volume was chosen to give a maximal inhibitory effect. After the preincubation with antibody, the sample was diluted with potassium phosphate buffer and the other assay components as described above. Immunoinhibition was evaluated at two concentrations of compound A (2 and 50 µM).

Chemical Inhibition Experiments. Known P450 isoform-selective chemical inhibitors for CYP1A2 (furafylline), CYP2C9 (sulfaphenazole), CYP2C19 [(-)-N-3-benzyl-phenobarbital], CYP2D6 (quinidine), and CYP3A (troleandomycin) were used to perform inhibition experiments. Concentrations of furafylline (50 µM), sulfaphenazole (10 µM), (-)-N-3-benzyl-phenobarbital (5 µM), quinidine (5 µM), and troleandomycin (25 µM) were chosen to give maximal inhibitory effect, based on previously reported results (Newton et al., 1995; Suzuki et al., 2002). Stock solutions of chemical inhibitors were prepared in 50% acetonitrile/water (v/v). The final concentration of acetonitrile in the incubation mixture was 1.5% (v/v). Control incubations contained the same volume of acetonitrile but no inhibitor. In the experiments with furafylline and troleandomycin, inhibitors were preincubated with liver microsomes and NADPH for 30 min at 37°C before adding the substrate. All other inhibitors were coincubated with the substrate. Chemical inhibition experiments were performed at the substrate concentrations of 2 and 50 µM and were determined using pooled human liver microsomes.

LC-MS Analysis. Chromatographic separation of compound A and its metabolites was carried out on an Agilent 1100 LC system (Agilent Technologies, Palo Alto, CA) using a Phenomenex Synergi Hydro-RP column (2.0 x 150 mm, 4 µm; Phenomenex, Torrance, CA). Solvent A consisted of 25 mM ammonium formate, pH 7.0, and solvent B of acetonitrile, and was delivered at a constant flow rate of 0.25 ml/min. The initial mobile phase consisted of 30% of solvent B, which was linearly increased to 50% over 10 min, held for 3 min, then increased to 80% in another 5 min. The column was then equilibrated under initial conditions for 8 min.

Mass spectrometric analysis was performed on a Thermo Finnigan TSQ Quantum triple quadruple mass spectrometer using an electrospray ionization probe (Thermo Finnigan, San Jose, CA). Electrospray ionization was operated in a positive mode, with a spray voltage of 5.0 kV, a sheath gas flow of 40, an auxiliary gas flow of 18, and a capillary temperature of 350°C. To perform collision-induced dissociation, the mass isolation window, the collision energy, and the collision gas flow were set at 1 m/z unit, 34 V, and 1.5 mtorr, respectively. For quantitation, selected reaction monitoring experiments were performed to detect ion pairs at m/z 533/339 (compound A), 549/355 (hydroxy metabolite), and 455/165 (verapamil; internal standard).

NMR Analysis. Proton NMR studies were carried out on metabolite I (hydroxy metabolite) isolated from a human liver microsomal incubate. Isolated metabolite was dissolved in 160 µl of CD₃OD and transferred to a 3-mm NMR tube. All NMR data were acquired at 25°C on an Inova spectrometer operating at a nominal proton frequency of 500 MHz (Varian, Inc., Palo Alto, CA) equipped with a cryogenically cooled 5-mm HCN triple-resonance probe (Varian, Inc.). In a cryogenically cooled probe, the radio frequency detection coil is maintained at 25 K, thereby reducing the thermal noise contribution, which in turn raises the signal-to-noise ratio of an NMR peak. In our setup, for a given sample in a 3-mm tube, a signal-to-noise ratio gain of approximately 3.3 is seen from a cryogenically cooled probe compared with the one-dimensional spectrum acquired in a 3-mm conventional HCN triple-resonance probe.

Measurement of CYP2C8 Activities. Paclitaxel (30 µM) and amodiaquine (10 µM) were used as probe substrates for CYP2C8 in human liver microsomes. Assays for paclitaxel 6-hydroxylation and amodiaquine N-de-ethylation were performed as described by Rahman et al. (1994) and Li et al. (2002), respectively. For each assay, the final substrate concentration was 5 times the reported K_m value. The rates of compound A hydroxylation (2 and 50 µM) determined across a panel of 15 individual human liver microsomes were correlated with both paclitaxel 6-hydroxylase and amodiaquine N-de-ethylase activities. In each case, the correlation coefficient (r²) was determined graphically using SigmaPlot (SPSS Inc., Chicago, IL).

Kinetic Analysis. The apparent K_m and V_max values were estimated by fitting the untransformed data to the Michaelis-Menten model, using SigmaPlot. The data were also analyzed by linear transformation (Eadie-Hofstee plot) to confirm a single K_m system.

	Results and Discussion

Top Abstract Materials and Methods Results and Discussion References

 
After incubation of compound A with NADPH-fortified human liver microsomes, LC-MS analysis revealed the formation of an isopropyl hydroxy metabolite (I) and three other major metabolites (Fig. 1). At a compound A concentration of 2 µM, the formation rates of metabolites I, II, III, and IV were determined to be 6.7, 14.8, 29.0, and 24.5 pmol/min/mg protein, respectively. Additional characterization of metabolites II, III, and IV is not within the scope of this article and will not be described further. Under positive ion electrospray ionization, the molecular ions (MH⁺) of compound A and metabolite I were determined to be at m/z 533 and 549, respectively. Upon tandem mass spectrometry fragmentation, metabolite I with MH⁺ at m/z 549 gave rise to fragments at m/z 253, 279, 297, and 355, indicating that the hydroxylation had occurred at the isopropyl moiety (Fig. 2). Proton NMR data confirmed the structure of metabolite I, and the following correlated resonances, arising from hydroxylation of a methyl group in the isopropyl moiety, were observed: 3.81 ppm [m,–CHCH₃(CH₂OH) proton], 3.38, 3.46 [AB multiplet,–CHCH₃(CH₂OH), and 1.14 (d, 6.8 Hz,–CHCH₃(CH₂OH)] ppm, whereas for the parent compound, the two methyls and the methine resonances of the isopropyl moiety appeared at 1.11 (d, 6.5 Hz), 1.15 (d, 6.5 Hz), and 3.78 (m) ppm. It is interesting to note that the tertiary carbon of the isopropyl group of the compound A is a prochiral center. Because the hydroxylation at the terminal carbon introduces an additional chiral center, the formation of the metabolite I may be a stereoselective process. At the time of writing, authentic standards of the enantiomerically pure isomers were not available.

View larger version (20K): [in this window] [in a new window]   FIG. 2. Tandem mass spectrometry spectrum of the isopropyl hydroxy metabolite of compound A generated in pooled human liver microsomes.

The kinetics of compound A isopropyl hydroxylation in pooled human liver microsomes were evaluated and conformed to the Michaelis-Menten model (Fig. 3A). These data suggested that one or more enzymes with similar K_m values were responsible for the reaction. The apparent K_m, V_max, and V_max/K_m values were estimated to be 6.6 µM, 28 pmol/min/mg protein, and 4.3 µl/min/mg protein, respectively. Subsequent kinetic study showed that the apparent K_m value determined in CYP2C8 (11.8 µM; Fig. 3B) was similar to that obtained in human liver microsomes. It was previously reported that compound A also underwent sugar conjugation in human liver microsomes (Tang et al., 2003). The intrinsic clearance (V_max/K_m) of glucuronidation (42 µl/min/mg protein) and glucosidation (18 µl/min/mg protein) was higher than that of the hydroxylation, consistent with the observation that sugar conjugates were more abundant than the hydroxy metabolite (I) in human hepatocytes (data not shown).

View larger version (21K): [in this window] [in a new window]   FIG. 3. Rate of compound A hydroxylation (metabolite I formation) in the presence of pooled human liver microsomes (A) and recombinant CYP2C8 (B). Insets, Eadie-Hofstee plots. Each data point represents the mean of duplicates.

The formation of metabolite I was monitored in a panel of 10 recombinant human P450 isoforms (CYPs 1A2, 2A6, 2B6, 2C8, 2C9, 2C19, 2D6, 2E1, 3A4, and 3A5). Compound A hydroxylation was only detected in CYP2C8-containing incubation mixtures. To confirm the observation that only CYP2C8 exhibited compound A isopropyl hydroxylase activity, pooled human liver microsomes were preincubated with inhibitory monoclonal antibody preparations raised against human P450 isoform(s). At a compound A concentration of 2 µM, preincubation with anti-CYP2C8 and anti-CYP2C monoclonal antibodies completely abolished the formation of metabolite I (Fig. 4). However, inhibitory antibodies selective for other P450 isoforms had no significant effect, indicating that metabolite I formation is catalyzed exclusively by CYP2C8. A similar inhibition study was conducted using previously characterized P450 isoform-selective inhibitors, furafylline (CYP1A2), sulfaphenazole (CYP2C9), (-)-N-3-benzyl-phenobarbital (CYP2C19), quinidine (CYP2D6), ketoconazole (CYP3A), and troleandomycin (CYP3A). As shown in Fig. 4, the majority of the inhibitors had a minimal effect on metabolite I formation. The 20 to 30% inhibition by ketoconazole and quinidine was consistent with, and possibly caused by, nonselective inhibition of CYP2C8 (Ong et al., 2000; Sai et al., 2000; Dierks et al., 2001; Li et al., 2002).

View larger version (40K): [in this window] [in a new window]   FIG. 4. Inhibition of compound A hydroxylase activity in human liver microsomes by isoform-selective antibodies and chemical inhibitors. P450 isoform-selective antibody or chemical inhibitor was incubated with pooled human liver microsomes containing 2 µM compound A. Chemical inhibitors selective for CYP1A2 [furafylline (FUR)], CYP2C9 [sulfaphenazole (SUL)], CYP2C19 [(-)-N-3-benzyl-phenobarbital (BPB)], CYP2D6 [quinidine (QND)], and CYP3A [troleandomycin (TAO) and ketoconazole (KTZ)] were used. Each data point represents the mean ± standard deviation of triplicates.

The correlation between the hydroxylase activity of compound A and the activities of two marker substrates of CYP2C8 was determined using a panel of 15 human liver microsomes (Fig. 5). Compound A (2 µM) hydroxylation correlated well with paclitaxel 6-hydroxylation (r² 0.92; p < 0.0001) and amodiaquine N-deethylation (r² 0.91; p < 0.0001).

View larger version (16K): [in this window] [in a new window]   FIG. 5. Correlations of compound A hydroxylation with paclitaxel 6-hydroxylation (A) and amodiaquine N-de-ethylation (B) in a bank of human liver microsomes. The correlation coefficient (r2) was calculated by the least-squares regression method. Compound A, paclitaxel, and amodiaquine were used at the concentrations of 2, 30, and 10 µM, respectively.

Interestingly, the hydroxylation of compound A was nonlinear after a short (5 min) incubation, at relatively low microsomal protein content (0.1 mg/ml; data not shown), suggesting that significant product inhibition may occur during the biotransformation of compound A. It is well documented that N-dealkylation and methylenedioxyphenyl oxidation (and subsequent catechol formation) may result in the formation of a metabolite-P450 complex, which leads to quasi-reversible inhibition of P450 activity (Murray and Reidy, 1990; Ma et al., 2000; Chatterjee and Franklin, 2003). Since CYP2C8, along with other P450s, catalyzes both N-dealkylation and methylenedioxyphenyl oxidation to form metabolites II and III, respectively (data not shown), product inhibition may result from metabolite-P450 complex formation through either or both mechanisms mentioned above.

Based on the in vitro data described, it is concluded that CYP2C8 is the major P450 isoform that catalyzes the formation of the hydroxy metabolite (I) in human liver microsomes. The kinetics of compound A hydroxylation performed using human liver microsomes and recombinant CYP2C8 conform to the Michaelis-Menten model, with apparent K_m values of 10 µM. Results obtained from the inhibition studies and correlation studies performed at the substrate concentration of 2 µM were essentially the same as those determined at 50 µM, indicating CYP2C8 was the predominant P450 isoform involved in the isopropyl hydroxylation of compound A over that concentration range.

For nearly a decade, paclitaxel 6-hydroxylation has been used as a marker for CYP2C8 (Rahman et al., 1994). Recently, amodiaquine was proposed as an alternative CYP2C8 probe substrate because of its high affinity and high turnover rate (Li et al., 2002). The hydroxylation of compound A correlated well with both paclitaxel 6-hydroxylation and amodiaquine N-de-ethylation (r² >0.90; Fig. 5), suggesting that the hydroxylation of compound A can be used as an alternative marker assay for CYP2C8 activity in human liver microsomes. The assay described herein requires a short incubation period (3 min) and a relatively low protein concentration (0.1 mg/ml). Also, the LC-MS/MS assay was more sensitive and less prone to interference by other compounds. Even though the limited availability of the compound A makes it less desirable, the current assay offers a quick and sensitive method to assess CYP2C8 activity in human liver microsomes.

	Acknowledgments

 
We thank Dr. Magang Shou for providing expressed human P450 preparations and P450 isoform-selective inhibitory monoclonal antibodies. We thank Drs. Takashi Hayama and Tomoharu Iino (Banyu Pharmaceutical Co., Ibaraki, Japan) for the synthesis of compound A.

	Footnotes

 
¹ Abbreviations used are: P450, cytochrome P450; LC-MS, liquid chromatography/mass spectrometry; Compound A, (+)-(5S,6R,7R)-2-isopropylamino-7-{4-methoxy-2-[(2R)-3-methoxy-2-methylpropyl]-5-(3,4-methylenedioxyphenyl)cyclopenteno(1,2-b) pyridine 6-carboxylic acid.

Address correspondence to: Bennett Ma, Department of Drug Metabolism, WP 75A-203, Merck Research Laboratories, West Point, PA 19486. E-mail: bennett_ma{at}merck.com

	References

Top Abstract Materials and Methods Results and Discussion References

 


Backman JT, Kyrklund C, Neuvonen M, and Neuvonen PJ (2002) Gemfibrozil greatly increases plasma concentrations of cerivastatin. Clin Pharmacol Ther 72: 685-691.[CrossRef][Medline]

Baldwin SJ, Clarke SE, and Chenery RJ (1999) Characterization of the cytochrome P450 enzymes involved in the in vitro metabolism of rosiglitazone. Br J Clin Pharmacol 48: 424-432.[CrossRef][Medline]

Becquemont L, Mouajjah S, Escaffre O, Beaune P, Funck-Brentano C, and Jaillon P (1999) Cytochrome P-450 3A4 and 2C8 are involved in zopiclone metabolism. Drug Metab Dispos 27: 1068-1073.[Abstract/Free Full Text]

Chatterjee P and Franklin MR (2003) Human cytochrome P450 inhibition and metabolic-intermediate complex formation by goldenseal extract and its methylenedioxyphenyl components. Drug Metab Dispos 31: 1391-1397.[Abstract/Free Full Text]

Dierks EA, Stams KR, Lim H-K, Cornelius G, Zhang H, and Ball SE (2001) A method for the simultaneous evaluation of the activities of several major human drug-metabolizing cytochrome P450s using an in vitro cocktail of probe substrates and fast gradient liquid chromatography tandem mass spectrometry. Drug Metab Dispos 29: 23-29.[Abstract/Free Full Text]

Klose TS, Blaisdell JA, and Goldstein JA (1999) Gene structure of CYP2C8 and extrahepatic distribution of the human CYP2Cs. J Biochem Mol Toxiocol 13: 289-295.

Li X-Q, Björkman A, Andersson TB, Ridderström M, and Masimirembwa CM (2002) Amodiaquine clearance and its metabolism to N-desethylamodiaquine is mediated by CYP2C8: a new high affinity and turnover enzyme-specific probe substrate. J Pharmacol Exp Ther 300: 399-407.[Abstract/Free Full Text]

Ma B, Prueksaritanont T, and Lin JH (2000) Drug interactions with calcium channel blockers: possible involvement of metabolite-intermediate complexation with CYP3A. Drug Metab Dispos 28: 125-130.[Abstract/Free Full Text]

Mei Q, Tang C, Assang C, Lin Y, Slaughter D, Rodrigues AD, Baillie TA, Rushmore TH, and Shou M (1999) Role of a potent inhibitory monoclonal antibody to cytochrome P-450 3A4 in assessment of human drug metabolism. J Pharmacol Exp Ther 291: 749-759.[Abstract/Free Full Text]

Mei Q, Tang C, Lin Y, Rushmore TH, and Shou M (2002) Inhibition kinetics of monoclonal antibodies against cytochrome P450. Drug Metab Dispos 30: 701-708.[Abstract/Free Full Text]

Murray M and Reidy GF (1990) Selectivity in the inhibition of mammalian cytochromes P-450 by chemical agents. Pharmacol Rev 42: 85-101.[Medline]

Newton DJ, Wang RW, and Lu AYH (1995) Evaluation of specificities in the in vitro metabolism of therapeutic agents by human liver microsomes. Drug Metab Dispos 23: 154-158.[Abstract]

Ohyama K, Nakajima M, Nakamura S, Shimada N, Yamazaki H, and Yokoi T (2000) A significant role of human cytochrome P450 2C8 in amiodarone N-deethylation: an approach to predict the contribution with relative activity factor. Drug Metab Dispos 28: 1303-1310.[Abstract/Free Full Text]

Okada M, Nishino M, Saito M, Ikeda T, Uehara S, Okada H, Niiyama K, Ohtake N, Hayama T, and Nishikibe M (2000) Marked reduction of mortality in salt-loaded Dahl salt-sensitive rats by the new, selective endothelin ET_A receptor antagonist, J-105859. J Hypertension 18: 1815-1823.[CrossRef][Medline]

Ong C-E, Coulter S, Birkett DJ, Bhasker CR, and Miners JO (2000) The xenobiotic inhibitor profile of cytochrome P4502C8. Br J Clin Pharmacol 50: 573-580.[CrossRef][Medline]

Prueksaritanont T, Zhao JJ, Ma B, Roadcap BA, Tang C, Qiu Y, Liu L, Lin JH, Pearson PG, and Baillie TA (2002) Mechanistic studies on metabolic interactions between gemfibrozil and statins. J Pharmacol Exp Ther 301: 1042-1051.[Abstract/Free Full Text]

Rahman A, Korzekwa KR, Grogan J, Gonzalez FJ, and Harris JW (1994) Selective biotransformation of taxol to 6-hydroxytaxol by human cytochrome P450 2C8. Cancer Res 54: 5543-5556.[Abstract/Free Full Text]

Rendic S (2002) Summary of information on human CYP enzymes: human P450 metabolism data. Drug Metab Rev 34: 83-448.[CrossRef][Medline]

Rodrigues AD and Rushmore TH (2002) Cytochrome P450 pharmacogenetics in drug development: in vitro studies and clinical consequences. Curr Drug Metab 3: 289-309. [Erratum in: Curr Drug Metab 3:559.][CrossRef][Medline]

Sai Y, Dai R, Yant TJ, Krausz KW, Gonzalez FJ, Gelboin HV, and Shou M (2000) Assessment of specificity of eight chemical inhibitors using cDNA-expressed cytochromes P450. Xenobiotica 30: 327-343.[CrossRef][Medline]

Suzuki H, Kneller MB, Haining RL, Trager WF, and Rettie AE (2002) (+)-N-3-Benzyl-nirvanol and (-)-N-3-benzyl-phenobarbital: new potent and selective in vitro inhibitors of CYP2C19. Drug Metab Dispos 30: 235-239.[Abstract/Free Full Text]

Tang C, Hochman JH, Ma B, Subramanian R, and Vyas KP (2003) Acyl glucuronidation and glucosidation of a new and selective endothelin ET_A receptor antagonist in human liver microsomes. Drug Metab Dispos 31: 37-45.[Abstract/Free Full Text]

Tracy TS, Korzekwa KR, Gonzalez FJ, and Wainer IW (1999) Cytochrome P450 isoforms involved in metabolism of the enantiomers of verapamil and norverapamil. Br J Clin Pharmacol 47: 545-552.[CrossRef][Medline]

Wang J-S, Neuvonen M, Wen X, Backman JT, and Neuvonen PJ (2002) Gemfibrozil inhibits CYP2C8-mediated cerivastatin metabolism in human liver microsomes. Drug Metab Dispos 30: 1352-1356.[Abstract/Free Full Text]

Yamazaki H, Shibata A, Suzuki M, Nakajima M, Shimada N, Guengerich FP, and Yokoi T (1999) Oxidation of troglitazone to a quinone-type metabolite catalyzed by cytochrome P-450 2C8 and P-450 3A4 in human liver microsomes. Drug Metab Dispos 27: 1260-1266.[Abstract/Free Full Text]

This article has been cited by other articles:

				B. Ma, S. L. Polsky-Fisher, S. Vickers, D. Cui, and A. D. Rodrigues Cytochrome P450 3A-Dependent Metabolism of a Potent and Selective {gamma}-Aminobutyric AcidA{alpha}2/3 Receptor Agonist in Vitro: Involvement of Cytochrome P450 3A5 Displaying Biphasic Kinetics Drug Metab. Dispos., August 1, 2007; 35(8): 1301 - 1307. [Abstract] [Full Text] [PDF]

This Article Abstract Full Text (PDF) Submit a response Alert me when this article is cited Alert me when eLetters are posted Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Ma, B. Articles by Tang, C. Search for Related Content PubMed PubMed Citation Articles by Ma, B. Articles by Tang, C.