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Vol. 283, Issue 2, 434-442, 1997
Osaka Prefectural Institute of Public Health, 3-69 Nakamichi 1-chome, Higashinari-ku, Osaka 537, Japan (H.Y., K.I., T.S.); PanVera Corporation, 545 Sciences Drive, Madison, Wisconsin (P.M.S., W.J.C.); and Department of Biochemistry and Center in Molecular Toxicology, Vanderbilt University School of Medicine, Nashville, Tennessee (F.P.G.)
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Abstract |
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 Top
Abstract
Introduction
Materials & Methods
Results
Discussion
References
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Omeprazole 5-hydroxylation and sulfoxidation activities were determined
in liver microsomes of different humans whose levels of individual
forms of cytochrome P450 (P450 or CYP) varied. Correlation coefficients
between omeprazole 5-hydroxylation activities (when determined at a
substrate concentration of 10 µM) and S-mephenytoin 4
-hydroxylation and testosterone 6
-hydroxylation activities were
found to be 0.64 and 0.67, respectively, in liver microsomes of 84 human samples examined. Omeprazole sulfoxidation activities in these
human samples were correlated with testosterone 6-hydroxylation activities (r = 0.86). Omeprazole 5-hydroxylation
by liver microsomes of a human sample that contained relatively high
levels of CYP3A4 and low levels of CYP2C19 were inhibited very
significantly by ketoconazole and anti-CYP3A4 antibodies, although a
human sample having high in CYP2C19 and low in CYP3A4 was found to be
sensitive toward fluvoxamine and anti-CYP2C9 antibodies. Sulfaphenazole (at 100 µM) did not affect the omeprazole 5-hydroxylation and sulfoxidation catalyzed by human liver microsomes. Both recombinant human CYP2C19 and CYP3A4 enzymes had activities for omeprazole 5-hydroxylation, with low Km and high
Vmax values for the former enzyme and high
Km and low Vmax
values for the CYP3A4. These results suggest that contributions of
CYP2C19 and CYP3A4 in the omeprazole 5-hydroxylation depend upon the
ratio of these two P450 levels in human liver microsomes. Omeprazole
5-hydroxylation activities of different human samples were found to be
related to predicted values calculated from the kinetic parameters of
recombinant enzymes and the levels of liver microsomal CYP2C19 and
CYP3A4 enzymes. Finally, when recombinant human CYP2C19 and CYP3A4 were
mixed at levels found in different human samples, relatively similar profiles of omeprazole oxidation by the recombinant and microsomal enzyme systems were determined by analysis of high-performance liquid
chromatography. These results suggest that both CYP2C19 and CYP3A4 are
involved in the 5-oxidation of omeprazole (at a substrate concentration
of 10 µM) in human liver microsomes and that contributions of these
P450 enzymes depend on the compositions of CYP2C19 and CYP3A4 in liver.
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Introduction |
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Top
Abstract
Introduction
Materials & Methods
Results
Discussion
References
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P450
or CYP comprises a superfamily of the enzymes that catalyze oxidation
of xenobiotic chemicals such as drugs, toxic chemicals and carcinogens
and endobiotic chemicals such as steroids, fatty acids, prostaglandins
and vitamins (Nelson et al., 1996
; Gonzalez, 1989;
Guengerich, 1991) and individual P450 enzymes have considerable but
overlapping, substrate specificities (Ryan and Levin, 1990). Liver
microsomes contain the highest levels and multiple forms of P450
enzymes that detoxicate, and in some instances activate, a number of
xenobiotic chemicals. CYP2C and 3A subfamily enzymes are the major P450
forms in human liver microsomes and contribute significantly to the
oxidation of clinically used drugs and other xenobiotic chemicals
(Guengerich and Shimada, 1991; Shimada et al., 1994).
Both CYP2C9 and CYP2C19 proteins have been reported to be polymorphic
enzymes. The molecular bases of the genetic polymorphisms of the CYP2C9
and CYP2C19 genes have been identified, and there are ethnic-related
differences in the incidence in poor metabolizer phenotypes (in
vivo) (de Morais et al., 1994; Sullivan-Klose et al., 1996; Chang et al., 1995a). CYP2C9 catalyzes the
oxidation of a number of clinically-used drugs (e.g.,
tolbutamide, S-warfarin, phenytoin, piroxicam, tienilic acid
and torsemide) and CYP2C19 has been shown to be involved in the
oxidation of a limited number of drugs including
S-mephenytoin, citalopram, proguanil and omeprazole (Goldstein et al., 1994; Goldstein and de Morais, 1994; Jean
et al., 1996).
Omeprazole is a substituted benzimidazole derivative and a potent
long-acting inhibitor of gastric acid secretion by irreversible binding
to the proton pump (H+,K+)
ATPase in the gastric parietal cell. This drug has been shown to be
oxidized by several forms of P450 in human liver microsomes in
vitro and in vivo (Marinac et al., 1996;
Chang et al., 1995a; Ieiri et al., 1996; Ibeanu
et al., 1996; Ishizaki et al., 1994). CYP2C19 is
suggested to be a major form involved in the 5-hydroxylation, while
CYP3A4 catalyzes sulfoxidation of omeprazole in humans (Chiba et
al., 1993; Chang et al., 1995b; Karam et
al., 1996). However, several lines of evidence have suggested that
CYP3A4 is also active in catalyzing formation of 5-hydroxyomeprazole as
well as of omeprazole sulfone (Andersson et al., 1993;
Vandenbranden et al., 1996; Karam et al., 1996;
Rost and Roots, 1996). Because the levels of CYP3A4 have been shown to
be more than 20-fold higher than those of CYP2C19 in human liver
microsomes (Inoue et al., 1997), it is suggested that CYP3A4
may be an important enzyme in the oxidation of omeprazole in human
liver microsomes, as well as CYP2C19.
In this study, we examined the roles of CYP2C19 and CYP3A4 in the oxidation of omeprazole by human liver microsomes and several types of recombinant human P450 enzymes. Different human samples who were genotyped for CYP2C19 gene were used for the analysis. The results presented in this study collectively indicate that both CYP2C19 and CYP3A4 are involved in the 5-hydroxylation of omeprazole (at a substrate concentration of 10 µM) by liver microsomes, depending on the contents of these P450 forms in the different human samples.
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Materials and Methods |
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Top
Abstract
Introduction
Materials & Methods
Results
Discussion
References
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Chemicals.
S-Mephenytoin was purchased from
Ultrafine Chemicals Co. (Manchester, UK). Omeprazole and its
metabolites were kindly donated by Dr. T. Ishizaki of International
Medical Center of Japan. Other drug substrates, their oxidation
products, and reagents used in this study were obtained from sources as
described previously or of highest qualities commercially available
(Shimada et al., 1989; Shimada et al., 1994;
Mimura et al., 1993; Yamazaki et al., 1994a).
Enzyme preparation.
Human liver samples were obtained from
organ donors or patients undergoing liver resection as described
previously (Shimada et al., 1994; Mimura et al.,
1993). Liver microsomes were prepared as described and suspended in 10 mM Tris-Cl buffer (pH 7.4) containing 1.0 mM EDTA and 20% glycerol
(v/v) (Guengerich, 1994).
), with the resulting ratio of
reductase: P450 = ~8. The infected cells were harvested by centrifugation and microsomes prepared using a procedure described elsewhere (Penman et al., 1993).
Rabbit anti-P450 antibodies raised against human CYP2C9 and CYP3A4 were
prepared and the IgG fractions were obtained as described (Shimada
et al., 1986; Guengerich et al., 1986).
Enzyme assays.
Omeprazole 5-hydroxylation and sulfoxidation
activities were determined as described elsewhere, with slight
modification (Birkett et al., 1996; Karam et al.,
1996). The standard incubation mixture consisted of microsomal protein
(0.5 mg/ml) in a final volume of 0.25 ml of 50 mM potassium phosphate
buffer (pH 7.4) containing an NADPH-generating system and omeprazole
(10 or 400 µM). Incubations were carried out at 37°C for 15 min and
terminated by adding 6 vol. of
CH2Cl2 and 0.3 M NaCl.
Product formation was determined by HPLC with a reverse-phase Nucleosil
C8 (5 µm) column (4.6 × 150 mm, Chemco
Scientific, Osaka, Japan) in a mobile phase consisting of a mixture of
CH3OH/CH3CN/H2O
(40:8:52, v/v) with a flow rate of 1.2 ml/min. Detection was by UV
absorbance at 302 nm.
-hydroxylation and testosterone
6-hydroxylation were determined using HPLC as described (Yamazaki
et al., 1994b; Shimada et al., 1985; Shimada
et al., 1994).
P450 contents were estimated spectrally by the original method (Omura
and Sato, 1964). The contents of human P450 proteins in liver
microsomes were estimated by coupled sodium dodecyl
sulfate-polyacrylamide gel electrophoresis/immunochemical development
("Western-blotting") (Guengerich et al., 1982). The
intensities of the immunoblots were measured with an Epson GT-8000
Scanner equipped with NIH Image/Gel Analysis Program adapted for
Macintosh computers. Protein concentrations were estimated by the
method of Lowry et al. (1951).
Statistical analysis.
Kinetic parameters for the omeprazole
oxidation by human P450 enzymes were estimated using a computer program
(KaleidaGraph program from Synergy Software, Reading, PA) designed for
nonlinear regression analysis. The correlations between activities of
S-mephenytoin 4-hydroxylation, testosterone
6-hydroxylation and omeprazole 5-hydroxylation and omeprazole
sulfoxidation in different human liver microsomal preparations were
analyzed using a linear regression analysis program (InStat program
from GraphPad Software, San Diego, CA). Statistical analysis was
analyzed by Student's t test.
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Results |
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Top
Abstract
Introduction
Materials & Methods
Results
Discussion
References
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Oxidation of omeprazole by liver microsomes of different human
samples.
Omeprazole (10 µM concentration) was incubated in
vitro with liver microsomes of 84 human samples and the levels of
5-hydroxyomeprazole and omeprazole sulfone thus formed were compared
with activities of S-mephenytoin 4-hydroxylation and
testosterone 6-hydroxylation, two prototypic reactions catalyzed by
CYP2C19 and CYP3A4, respectively (fig. 1)
(Goldstein and de Morais, 1994; Guengerich and Shimada, 1991;
Guengerich et al., 1986). Correlation coefficients between activities of omeprazole 5-hydroxylation and S-mephenytoin
4-hydroxylation and of omeprazole 5-hydroxylation and testosterone
6-hydroxylation in these human samples were found to be 0.64 and
0.67, respectively, suggesting that CYP2C19 and 3A4 enzymes may play
important roles for the omeprazole 5-hydroxylation reaction. There was
good correlation between omeprazole sulfoxidation and testosterone
6-hydroxylation activities in these human samples (r = 0.86).
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-hydroxylation, and
CYP3A4-rich samples HL-C6 and HL-C19 showed high activities for
testosterone 6-hydroxylation in liver microsomes (table 1). These
three samples also had relatively high omeprazole 5-hydroxylation and
sulfoxidation activities, although the ratio of activities at substrate
concentrations of 10 and 400 µM differed somewhat, depending on the
samples used. For example, the ratio of activities of omeprazole
5-hydroxylation between 10 and 400 µM omeprazole was high in liver
microsomes of HL-C15, indicating that different P450 enzymes contribute
to the oxidation of omeprazole in human liver microsomes, depending on
the substrate concentrations determined.
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Effects of fluvoxamine, ketoconazole and sulfaphenazole on
oxidations of S-mephenytoin, testosterone, and omeprazole
by human liver microsomes.
The effects of fluvoxamine,
ketoconazole, and sulfaphenazole, known inhibitors of CYP2C19, CYP3A4
and CYP2C9 (fig. 2) (Guengerich and
Shimada, 1991; Xu et al., 1996; Yamazaki et al.,
1996b; Brian et al., 1989), respectively, were examined
towards oxidation of S-mephenytoin (fig. 2A), testosterone
(fig. 2D), and omeprazole in liver microsomal samples HL-C15 and HL-C6.
Fluvoxamine was found to be inhibitory towards omeprazole
5-hydroxylation catalyzed by liver microsomes of human sample HL-C15
(fig. 2B), although it very weakly inhibited the omeprazole
5-hydroxylation by those of human sample HL-C6 (fig. 2C).
5-Hydroxylation of omeprazole by human sample HL-C6 was significantly
inhibited by ketoconazole (fig. 2C). Omeprazole sulfoxidation
activities were inhibited very significantly by ketoconazole in both
human samples (figs. 2E and F). None of the activities were inhibited
by sulfaphenazole at concentration of 100 µM.
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Effects of anti-CYP2C9 and anti-CYP3A4 on omeprazole
5-hydroxylation and sulfoxidation by human liver microsomes.
Effects of anti-CYP2C9 and anti-CYP3A4 on oxidation of omeprazole by
human liver microsomes were studied in samples HL-C15 and HL-C6 (fig.
3). Anti-CYP2C9 antibodies have already
been characterized and shown to inhibit CYP2C19-dependent
S-mephenytoin 4-hydroxylation activities as well as
CYP2C9-dependent tolbutamide methyl hydroxylation and
S-warfarin 7-hydroxylation activities in human liver
microsomes (Shimada et al., 1986; Brian et al.,
1989). Anti-CYP2C9 was found to significantly inhibit omeprazole
5-hydroxylation catalyzed by liver microsomes of a human sample HL-C15
(fig. 3A), but not of HL-C6 (fig. 3B). This antibody failed to inhibit
omeprazole sulfoxidation activities in both samples. However,
anti-CYP3A4 inhibited omeprazole sulfoxidation activities of both human
samples (figs. 3C and D) and completely inhibited omeprazole
5-hydroxylation catalyzed by a human sample HL-C6 (fig. 3D), although
the inhibition of omeprazole 5-hydroxylation by anti-CYP3A4 in sample
HL-C15 was only 50% (fig. 3C).
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Omeprazole hydroxylation activities by recombinant human CYP2C19
and CYP3A4 expressed in different chimeras.
To define the roles of
CYP2C19 and CYP3A4 more clearly, we examined the omeprazole
hydroxylation activities by recombinant human P450 enzymes (fig.
4). The recombinant P450 enzymes used were obtained from three different sources, e.g., microsomes
of human lymphoblastoid cells (Gonzalez et al., 1991; Crespi
et al., 1990), yeast microsomes (Imaoka et al.,
1996), and baculovirus microsomes (P. M. Shaw, N. A. Hosea,
D. V. Thompson, J. M. Lenius and F. P. Guengerich,
submitted for publication). HPLC analysis showed that recombinant
CYP2C19 produced 5-hydroxylated product of omeprazole (peak a in the
chromatograms), although turnover numbers varied with source of enzymes
used (fig. 4 A-C). Insect microsomes showed the highest turnover
numbers for the formation of the 5-hydroxy product and also the
unidentified metabolite (peak c; possibly 5-O-desmethylomeprazole)
(Birkett et al., 1996). Recombinant CYP3A4 also produced
formation of 5-hydroxyomeprazole as well as of omeprazole sulfone (fig.
4D to F), although the turnover numbers for 5-hydroxylation activities
were lower than those catalyzed by CYP2C19. Of the three CYP3A4 enzyme
systems examined, the baculovirus sample showed the highest turnover
numbers for omeprazole 5-hydroxylation and sulfoxidation and formation of the unidentified metabolite (peak b; possibly 3-hydroxyomeprazole) (Birkett et al., 1996).
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Prediction of omeprazole hydroxylation by human liver microsomes
based on kinetic parameters of recombinant P450 enzymes.
To define
the potential contributions of CYP2C19 and CYP3A4 in the omeprazole
5-hydroxylation by three human samples (HL-C6, C15 and C19), we
calculated the predicted activities of human liver microsomal
omeprazole 5-hydroxylation activities based on the kinetic parameters
of CYP2C19 and CYP3A4 and estimated contents of these P450 proteins by
immunoblotting. The equation used for the prediction of expected
activities was from the previous method (Iwatsubo et al.,
1997b):
![v<IT>=</IT>A<IT> · </IT>[<IT>V</IT><SUB>max1</SUB><IT> · </IT>S/(<IT>K</IT><SUB>m1</SUB><IT>+</IT>S)]<IT>+</IT>B<IT> · </IT>[<IT>V</IT><SUB>max2</SUB><IT> · </IT>S/(<IT>K</IT><SUB>m2</SUB><IT>+</IT>S)]](/content/vol283/issue2/fulltext/434/img001.gif)
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Omeprazole 5-hydroxylation activities by recombinant CYP2C19 and
CYP3A4 when these two P450 enzymes were mixed at ratio similar to those
in human liver microsomes.
Because both CYP2C19 and CYP3A4 are
suggested to be involved in the 5-hydroxylation of omeprazole in human
liver microsomes, we determined the omeprazole oxidation by recombinant
P450 enzymes mixed at ratio similar to those estimated in liver
microsomal samples HL-C6, HL-C15 and HL-C19 (fig.
8). The HPLC profiles of omeprazole
oxidation formed by recombinant CYP2C19 and CYP3A4 mixtures were found
to be resemble those in human liver microsomes.
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Discussion |
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Top
Abstract
Introduction
Materials & Methods
Results
Discussion
References
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Our results supported the view that both CYP3A4 and CYP2C19 are
involved in the 5-hydroxylation of omeprazole (when determined at a
substrate concentration of 10 µM) in human liver microsomes, on the
basis of the following lines of evidence. First, there were some
correlations between omeprazole 5-hydroxylation activities and
S-mephenytoin 4-hydroxylation (r = 0.64)
and testosterone 6-hydroxylation (r = 0.67) in liver
microsomes of 84 human samples. Second, both fluvoxamine and
ketoconazole, known inhibitors of CYP2C19 and CYP3A4, respectively (Xu
et al., 1996; Yamazaki et al., 1996b; Guengerich
and Shimada, 1991), inhibited the formation of 5-hydroxyomeprazole,
depending on which P450 enzymes are more abundant in liver microsomes
of different human samples examined. Third, a similar tendency was also
noted when specific antibodies raised against CYP2C9, which inhibit
both CYP2C9 and 2C19 activities (Shimada et al., 1986; Brian
et al., 1989), and CYP3A4 antibodies were used for the
effects on omeprazole 5-hydroxylation activities by human liver
microsomes. The role of CYP2C9 in the oxidation of omeprazole by human
liver microsomes was ruled out, because sulfaphenazole, a selective
inhibitor of CYP2C9, did not inhibit the activities by liver
microsomes. Finally, both recombinant human CYP2C19 and CYP3A4 had
omeprazole 5-hydroxylation activity (at low substrate concentrations);
the former enzyme was an enzyme with low Km
and high Vmax and the CYP3A4 gave high
Km and low Vmax
values.
Average levels of CYP2C19 and CYP3A4 in liver microsomes have been
determined to be about 1 and 30%, respectively, of total P450 in
different human samples examined (Inoue et al., 1997; Shimada et al., 1994). Although the
Km value of recombinant CYP2C19 for
omeprazole 5-hydroxylation in baculosomes was about one-tenth that of
CYP3A4, the contribution of these P450 enzymes in the catalytic
activities may be affected by the levels of these two P450 forms in
human liver microsomes. In fact, when the recombinant CYP2C19 and
CYP3A4 were mixed at ratio similar to those found in liver microsomes
of different humans, HPLC profiles of oxidation of omeprazole were
found to be resemble to those in intact microsomal incubations. These
results suggest that CYP3A4 as well as CYP2C19 is involved in the
oxidation of omeprazole, depending on the human samples examined.
It has been reported that contributions of several P450 forms toward
oxidations of xenobiotics in vitro are affected by the substrate concentrations determined (Yamazaki et al., 1994a,
1996a; Kato and Yamazoe, 1994; Iwatsubo et al., 1997a). In
this study, we observed that at a 10 µM substrate concentration,
5-hydroxyomeprazole formation was found to be decreased and omeprazole
sulfone formation was increased with the increasing the ratio of levels
of recombinant CYP3A4 and CYP2C19 in the incubation mixture (fig. 9).
However, at a 400 µM substrate concentration, both omeprazole
5-hydroxylation and sulfoxidation activities were determined largely by
the presence of CYP3A4, but not CYP2C19. These results suggest that at
higher substrate concentrations, both 5-hydroxylation and sulfoxidation of omeprazole are catalyzed principally by CYP3A4 in human liver microsomes.
Extrapolation from in vitro data to intrinsic metabolism of
clinically used drugs in humans has been a subject of interest in many
laboratories, because of the potential usefulness in predicting pharmacological actions and safety of these drugs in vivo
(Iwatsubo et al., 1997a, 1997b; Crespi, 1995). Kinetic
parameters obtained from recombinant human P450 enzymes toward
oxidation of drugs are generally used for the calculation, because
kinetic parameters of the drug oxidation activities by structurally
defined P450s can be determined (Iwatsubo et al., 1997a;
Crespi, 1995). However, it must be assumed that all of the recombinant
P450 enzymes obtained from different chimeric organisms give the same
kinetic parameters, i.e., Km and
Vmax values (Crespi, 1995), to use this
approach in a valid manner. In fact, our results show that recombinant CYP2C19 and CYP3A4 expressed in three different chimeras such as human
lymphoblastoid cells, yeast and baculosomes have different turnover
numbers for the oxidation of omeprazole. Using kinetic parameters from
baculovirus-expressed CYP2C19 and CYP3A4 and levels of human liver P450
proteins determined immunochemically, however, we obtained good
correlations between predicted and experimental values of omeprazole
5-hydroxylation by liver microsomes; the calculation was based on a
suggested procedure reported recently (Iwatsubo et al.,
1997a, 1997b). These results again support the view that both CYP2C19
and CYP3A4 are involved in omeprazole 5-hydroxylation by human liver
microsomes, and that predictions can be made if kinetic parameters for
the oxidation of drugs by recombinant P450 enzymes and levels of
individual P450 forms in human liver microsomes have already been
determined. However, estimation of the modeling to the in
vivo situation is yet another step, and other assumptions must be
considered.
In this study, we used the P450 inhibitors ketoconazole and fluvoxamine
for studies of inhibition of CYP3A4- and CYP2C19-dependent oxidations
of omeprazole in human liver microsomes. It is well known that
ketoconazole is a potent and selective inhibitor of CYP3A enzymes in
humans and experimental animals both in vitro and in
vivo (Xu et al., 1996; Yamazaki et al.,
1996b; Guengerich and Shimada, 1991). However, detailed studies are
lacking regarding which chemicals are selective and potent inhibitors
of CYP2C19 in humans, although sulfaphenazole has been determined to be
a potent and relatively selective inhibitor of another CYP2C member, CYP2C9 (Brian et al., 1989). Recent studies have shown that
fluvoxamine, a potent inhibitor of CYP1A2 (Br
sen et al.,
1993; Gjerving et al., 1995; Jeppesen et al.,
1996b), is also an inhibitor of CYP2C19 in vivo in humans
(Jeppesen et al., 1996a; Xu et al., 1996). In this work, fluvoxamine was found to inhibit CYP2C19-dependent S-mephenytoin 4-hydroxylation activities by human liver
microsomes. Inhibition of omeprazole 5-hydroxylation activities by
fluvoxamine and anti-CYP2C9 in liver microsomes of a human sample
HL-C15, a sample having a high level of CYP2C19 in the liver, supported the view that omeprazole 5-hydroxylation is catalyzed mainly by CYP2C19
in this subject. However, omeprazole 5-hydroxylation by liver
microsomes of a human sample HL-C6 (which had a high level of CYP3A4)
was inhibited weakly by fluvoxamine and anti-CYP2C19, but very strongly
by ketoconazole and anti-CYP3A4, suggesting that CYP3A4 is a major form
involved in the 5-hydroxylation of omeprazole in this human sample.
Our studies have been done in liver microsomes, which contain both
CYP2C19 and CYP3A4. However, the in vivo situation may also
be influenced by the extent of omeprazole oxidation that occurs in the
small intestine. CYP3A4 is known to be highly abundant in the small
intestine (Kolars et al., 1994; Watkins et al.,
1987) but the concentration of CYP2C19 in small intestine has not been measured, to our knowledge.
In conclusion, our results supported the view that CYP3A4 as well as CYP2C19 is involved in the 5-hydroxylation of omeprazole in human liver microsomes. The contribution of these two P450 forms in the omeprazole 5-hydroxylation reaction may be determined by the levels and ratio of CYP2C19 and CYP3A4 in liver microsomes of different human samples. Using kinetic parameters from recombinant CYP2C19 and CYP3A4 and levels of liver microsomal CYP2C19 and CYP3A4 determined immunochemically, predicted values for the 5-hydroxylation of omeprazole were roughly related to the activities of intact liver microsomes of different human samples.
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Acknowledgments |
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The authors thank Dr. T. Ishizaki of International Medical Center of Japan for supplying omeprazole and its metabolites and Dr. Y. Sugiyama of University of Tokyo for preprint of a paper submitted.
| |
Footnotes |
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Accepted for publication July 25, 1997.
Received for publication April 21, 1997.
1 This work was supported in part by Grants from the Ministry of Education, Science, and Culture of Japan, the Ministry of Health and Welfare of Japan, and the Developmental and Creative Studies from Osaka Prefectural Government, and by United States Public Health Service Grants R35 CA44353 and P30 ES00267.
Send reprint requests to: Dr. T. Shimada, Osaka Prefectural Institute of Public Health, 3-69 Nakamichi 1-chome, Higashinari-ku, Osaka 537, Japan.
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Abbreviations |
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P450 or CYP, cytochrome P450; IgG, immunoglobulin G; HPLC, high-performance liquid chromatography.
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References |
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Top
Abstract
Introduction
Materials & Methods
Results
Discussion
References
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sen, K.,
Skjelbo, E.,
Rasmussen, B. B.,
Poulsen, H. E. and
Loft, S.:
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48: 1524-1527, 1994b.This article has been cited by other articles:
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R. Yuan, S. Madani, X.-X. Wei, K. Reynolds, and S.-M. Huang Evaluation of Cytochrome P450 Probe Substrates Commonly Used by the Pharmaceutical Industry to Study in Vitro Drug Interactions Drug Metab. Dispos., December 1, 2002; 30(12): 1311 - 1319. [Abstract] [Full Text] [PDF]
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W. Zhang, Y. Ramamoorthy, T. Kilicarslan, H. Nolte, R. F. Tyndale, and E. M. Sellers Inhibition of Cytochromes P450 by Antifungal Imidazole Derivatives Drug Metab. Dispos., March 1, 2002; 30(3): 314 - 318. [Abstract] [Full Text] [PDF]
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T. Komatsu, H. Yamazaki, N. Shimada, M. Nakajima, and T. Yokoi Roles of Cytochromes P450 1A2, 2A6, and 2C8 in 5-Fluorouracil Formation from Tegafur, an Anticancer Prodrug, in Human Liver Microsomes Drug Metab. Dispos., April 13, 2001; 28(12): 1457 - 1463. [Abstract] [Full Text]
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K. Venkatakrishnan, L. L. von Moltke, M. H. Court, J. S. Harmatz, C. L. Crespi, and D. J. Greenblatt Comparison between Cytochrome P450 (CYP) Content and Relative Activity Approaches to Scaling from cDNA-Expressed CYPs to Human Liver Microsomes: Ratios of Accessory Proteins as Sources of Discrepancies between the Approaches Drug Metab. Dispos., April 13, 2001; 28(12): 1493 - 1504. [Abstract] [Full Text]
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 K. Venkatakrishnan, L. L. von Moltke, and D. J. Greenblatt Application of the Relative Activity Factor Approach in Scaling from Heterologously Expressed Cytochromes P450 to Human Liver Microsomes: Studies on Amitriptyline as a Model Substrate J. Pharmacol. Exp. Ther., April 1, 2001; 297(1): 326 - 337. [Abstract] [Full Text]
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D. F. McGinnity, A. J. Parker, M. Soars, and R. J. Riley Automated Definition of the Enzymology of Drug Oxidation by the Major Human Drug Metabolizing Cytochrome P450s Drug Metab. Dispos., November 1, 2000; 28(11): 1327 - 1334. [Abstract] [Full Text]
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T. Komatsu, H. Yamazaki, S. Asahi, E. M. J. Gillam, F. P. Guengerich, M. Nakajima, and T. Yokoi Formation of A Dihydroxy Metabolite of Phenytoin in Human Liver Microsomes/cytosol: Roles of Cytochromes P450 2c9, 2c19, and 3a4 Drug Metab. Dispos., November 1, 2000; 28(11): 1361 - 1368. [Abstract] [Full Text]
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Y. Shu, L.-S. Wang, Z.-H. Xu, N. He, W.-M. Xiao, W. Wang, S.-L. Huang, and H.-H. Zhou 5-Hydroxylation of Omeprazole by Human Liver Microsomal Fractions from Chinese Populations Related to CYP2C19 Gene Dose and Individual Ethnicity J. Pharmacol. Exp. Ther., November 1, 2000; 295(2): 844 - 851. [Abstract] [Full Text]
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J.-S. Wang, J. T. Backman, P. Taavitsainen, P. J. Neuvonen, and K. T. Kivistö Involvement of CYP1A2 and CYP3A4 in Lidocaine N-Deethylation and 3-Hydroxylation in Humans Drug Metab. Dispos., August 1, 2000; 28(8): 959 - 965. [Abstract] [Full Text]
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A. Äbelö, T. B. Andersson, M. Antonsson, A. K. Naudot, I. Skånberg, and L. Weidolf |
) and sulfoxidation (
)
catalyzed by liver microsomes of HL-C15 (A and C) and HL-C6 (B and D).
Preimmune IgG did not inhibit the microsomal catalytic activities
determined (data not shown). Oxidation of omeprazole was determined at
a substrate concentration of 10 µM.
). Different
concentrations of omeprazole were used for the determinations of
omeprazole 5-hydroxylation activities. Symbols, measured activities;
lines, predicted values.
