WANG ET AL EFFECTS OF ST. JOHN’S WORT ON THE ACTIVITY OF CYP2C19 PHARMACOGENETICS
The Influence of St. John’s Wort on
CYP2C19 Activity with Respect to Genotype
Lian-Sheng Wang, MD, Bing Zhu, PhD, A. M. Abd El-Aty, PhD, Gan Zhou, MD,
Zhi Li, MD, Jun Wu, PhD, Guo-Lin Chen, MD, Jie Liu, MD, Zhi Rong Tang, MD,
Wang An, MD, Qing Li, MD, Dan Wang, BS, and Hong-Hao Zhou, MD
medicine for more than 2000 years.1In Europe and the
United States, St. John’s wort products are available as
over-the-counter and self-medications to treat depres-
sion, anxiety, sleep disorders, and other diseases, with
111 million daily doses of hypericum extracts taken in
in Europe in 1998.2
t. John’s wort, an extract of the medicinal plant
As a natural product, it has been viewed as a safe
treatment for a long time; however, recent reports
indicate that St. John’s wort interacts with a number of
different medicines, which could result in potentially
serious adverse reactions. Since 1998, seven spontane-
ous cases of a reduced anticoagulant effect of warfarin
(i.e., a decreased international normalized ratio [INR])
associated with the concomitant use of St. John’s wort
tablets have been published. The decrease in INR was
thought to be clinically significant.3During St. John’s
wort treatment, another 4 patients who received trans-
plantation suffered graft rejection with decreased
blood concentrations of cyclosporine.4-7Unplanned
pregnancies occurred in 9 women taking oral contra-
ceptives and St. John’s wort tablets as well.7In addi-
tion, theophylline, HIV protease inhibitors, and some
other kinds of drugs are also likely to interact with St.
Serious cases of clinical drug interactions of St.
John’s wort sparked rigorous scientific investigations.
Progresses in this direction identified that St. John’s
wort is a potent agonist of the orphan nuclear receptor
J Clin Pharmacol 2004;44:577-581
investigated, but its effect on CYP2C19 is lacking. Thus, the
wort on CYP2C19activity using CYP1A2as acontrol. Twelve
healthy adult men—6 extensive metabolizers of CYP2C19
(2C19*1/2C19*1) and 6 poor metabolizers (4 2C19*2/
2C19*2 and 2 2C19*2/2C19*3)—were enrolled in a two-
phase, randomized, crossover manner. All subjects took a
14 days, and then the activities of CYP2C19 and CYP1A2
were measured using mephenytoin and caffeine. It was
found that St. John’s wort treatment significantly increased
CYP2C19 activity in CYP2C19 wild-genotype subjects, with
urinary 4 -hydroxymephenytoin excretion raised by 151.5% ±
served for CYP2C19 poor metabolizers. Repeated St. John’s
wort administration did not affect the CYP1A2 phenotypic
ratio for both CYP2C19 genotype subjects. In conclusion, St.
John’s wort is an inducer to the human CYP2C19, and clini-
cians should pay great attention when St. John’s wort is
added to or withdrawn from an existing drug regimen con-
taining substrates for such enzymes.
Keywords: St. John’s wort; rifampicin; CYP2C19; drug
interactions; poor metabolizers; extensive
Journal of Clinical Pharmacology, 2004;44:577-581
©2004 the American College of Clinical Pharmacology
From the Pharmacogenetics Research Institute, Institute of Clinical Phar-
macology, Central South University, Changsha, Hunan, China (Dr. L.-S.
Dr. An, Dr. Q. Li, Mr. D. Wang, Dr. H.-H. Zhou) and Department of
Cardiovasology, First Affiliated Hospital, Guangzhou Medical College,
Guangzhou, China (Dr. Wu). This work was supported by the National
Natural Science Foundation of China grants F30130210, C30000211,
and C30200346 and the China Medical Board of New York grants 99-
697 and 01-755. Submitted for publication April 17, 2003; revised ver-
sion accepted March 21, 2004. Address for reprints: Professor Hong-Hao
Zhou, Pharmacogenetics Research Institute, Institute of Clinical Pharma-
cology, Central South University, Changsha, Hunan 410078, China.
pregnane X receptor.2,10In addition, repeated St.
John’s wort treatment increases the expressions of
cytochrome P450 (CYP) 3A4 and P-glycoprotein,11
thereby promoting the in vivo elimination of a number
other P450 isoforms, such as 1A2, 2C9, 2D6, are also
subjected to be involved in the clinical interactions of
St. John’s wort treatment. Wang and his coworkers12
found that long-term administration of St. John’s wort
resulted in a significant and selective induction of
CYP3A activity in vivo, but the activities of 2C9, 1A2,
or 2D6 did not alter. To date, the in vivo effect of St.
extract of St. John’s wort contains potent inhibitors of
CYP2C19 in vitro.
CYP2C19 is a clinically important isoform that is
responsible for the biotransformation of diazepam,
omeprazole, certain barbiturates, chloroguanide (INN
proguanil), and many other clinically used drugs.13
CYP2C19 is almost exclusively responsible for S-
mephenytoin 4-hydroxylation, and S-mephenytoin
has been established to be an ideal probe to measure
the activity of such enzymes in vivo14,15by measuring
of CYP2C19 have resulted in poor or extensive
metabolizers. Two defective alleles, CYP2C19*2 (m1:
681 G → A) and CYP2C19*3 (m2: 636 G → A), have
been characterized as the main genetic factor for
CYP2C19 poor metabolizers.17This study was de-
signed to observe the effect of long-term use of St.
John’s wort on CYP2C19 activity, using the activity of
CYP1A2 as a control.
MATERIALS AND METHODS
6.7 kg (mean ± SD), were recruited for this study.
Twelve of them were recruited from a total of 101
individuals were homozygous for the wild-type allele
(CYP 2C19*1/*1), 4 were homozygous of the allele
with a 681 G → A m1 mutation (CYP 2C19*2/*2), and
the other 2 were heterozygous of allele m1 and the al-
Board of Central South University, Hunan, China, all
subjects gave written informed consent to participate
in our study. They all finished the entire protocol of
this study. All participants were required to be from
smokers, and to have a standard body mass index
between 18 and 30 kg/m2. The participants also must
have been in good health, with no clinically relevant
condition identified from physical examination, elec-
trocardiogram, and medical records. Participants re-
ceiving over-the-counter medications, St. John’s wort,
or other herbal medicines within the past month; in-
gesting alcohol within 2 weeks before admission; re-
ceiving an investigational remedy within 2 months of
enrollment; or having a previous history of alcohol or
drug abuse and an allergy to St. John’s wort, caffeine,
and mephenytoin were excluded from completion of
design with a 5-week interval between phases. In each
phase, 12 volunteers (6 2C19*1/2C19*1, 4 2C19*2/
2C19*2, and 2 2C19*2/2C19*3) received placebo or an
oral St. John’s wort tablet containing 0.3% hypericin
research grade, 300 mg per tablet, Hypericum Buyers
Club, CA) three times daily for 14 days. On the 15th
day, after voiding their bladders, all subjects were
given a single oral dose of 100 mg mephenytoin and
300 mg caffeine at the same time. Aliquot samples of
stored at –20°C until analyzed. Venous blood samples
(5 mL) were collected into heparinized tubes from the
antecubital vein 6 hours after administration. Blood
samples were centrifuged at 3500g for 10 min, and the
plasma was harvested and stored at –20°C pending as-
say. No medications, including alcohol, were permit-
subjects were monitored for the development of ad-
caffeine, and mephenytoin (such as dry mouth and
trimethylxanthine, 137X) and paraxanthine (1,7-
dimethylxanthine, 17X) were quantified by Hewlett-
Packard 1050 series high-performance liquid chroma-
tography (HPLC) with ultraviolet detection at a wave-
length of 282 nm according to the method described
previously with minor modifications.19Briefly, a mix-
ture of a 200-µL aliquot of plasma and 100 µL of β-
hydroxyethyltheophylline (Sigma Chemical Co., St.
concentrationsof caffeine (1,3,7-
578 • J Clin Pharmacol 2004;44:577-581
WANG ET AL
Louis, MO) as an internal standard were treated with
400 mg ammonium sulfate and extracted with 5 mL
chloroform and isopropanol (9:1 [vol/vol]). The resi-
due was reconstituted with 100 µL mobile phase,
acetonitrile. A portion of 20 µL was injected onto a
Zorbax eclipse XDB-C8 column (particle size, 5 µm;
4.6 × 150 mm; Agilent, Palo Alto, CA). The validated
limit of quantification (LOQ) was 0.6 µmol/L and 0.5
(interday) coefficients of variation for 137X were
13.2%, 6.6%, and 11.7% at 0.7, 2, and 10 µmol/L, re-
variation at the corresponding concentrations were
11.2%, 9.5%, and 12.5%. For 17X, at 0.8, 2, and 5
µmol/L, the within-day coefficients of variation were
9.8%, 7.2%, and 12.3%, and the day-to-day coeffi-
cients of variation were 10.7%, 8.4%, and 11.7%,
The assay for 4-hydroxymephenytoin excreted in
the urine was modified as described previously.20
Briefly, the HPLC system was also composed of a
Hewlett-Packard 1050 series with ultraviolet detec-
tion. Urine 4′-hydroymephenytoin and internal stan-
dard phenobarbital were extracted with absolute di-
remaining after evaporation was dissolved in 50 µL of
eluate, and 20-µL preparations were measured by
HPLC with a Zorbax eclipse XDB-C8 column (4.6 mm,
24% acetonitrile and 76% water. The flow rate was 1
mL/min,and the column eluteswere monitored at 204
nm. The intra- and interday variations were less than
12% and 14%, respectively.
fidence intervals (CIs). The treatment effect was ana-
lyzed by the rank sum test. Differences were regarded
as statistically significant when p < 0.05.
Two subjects felt a little dizzy when they used the St.
John’s wort in the study. Overall, the treatments in the
EFFECTS OF ST. JOHN’S WORT ON THE ACTIVITY OF CYP2C19
Average Caffeine Metabolic Ratio 17X/137X and Urine Recovery of 4′-Hydroxymephenytoin in CYP
2C19*1/*1 and CYP 2C19*2/*2 and *3 Subjects after a 14-Day Treatment of Placebo or St. John’s Wort
Urine Recovery of
4′-OH-mephenytoin (µmol) 17X/137X Ratio
PlaceboSt. John’s WortPlacebo St. John’s Wort
2C19*2/*2 and *3
0.49 ± 0.18
0.36 ± 0.08
0.43 ± 0.13
0.36 ± 0.09
36.3 ± 9.3
26.5 ± 13.3
92.4 ± 45.4a
28.0 ± 17.1
a. p = 0.0156.
placebo st john's wort
urine recovery of 4-OH mephenytoin
in 12 subjects after a 14-day treatment of placebo or St. John’s wort
The 0- to 8-hour urine recovery of 4-hydroxymephenytoin
Placebo St John's wort
Ratio of 17X/137X
14-day treatment of placebo or St. John’s wort.
Caffeine metabolic ratio 17X/137X in 12 subjects after a
completed the whole fixed-order protocol. No serious
adverse events were recorded.
Inthis study, we
hydroxymephenytoin as an index for CYP2C19 activ-
hydroxymephenytoin in urine increased from 64.0%
of 4′-hydroxymephenytoin in CYP 2C19*2/*2 and *3
individuals exhibited two-way alterations following
treatment phases. The distributions of 17X/137X, a
phenotypic ratio of CYP1A2, are displayed in Figure 2
and Table I. Following 14-day treatments with placebo
and/or St. John’s wort, two-way alteration was ob-
served in the two subject groups.
phase of this study, we found that the 2C19 activity
somewhat overlapped between the extensive
metabolizers and the poor metabolizers, but in the St.
John’s wort phase, the activity in the wild 2C19
genotype was significantly higher than in poor
tutive androstane receptor (CAR) binding site in the
CYP2C19 promoter; this androstane-responsive ele-
receptor (PXR).21This study suggests that CYP2C19
may be induced by the corresponding receptor
agonists. Our earlier study had shown that rifampin, a
fect is genotype dependent.22,23Johne and his cowork-
ers24have even supposed that CYP2C19 might be in-
volved in the interactions between the PXR agonist in
St. John’s wort and amitriptyline. However, the rela-
clear. At the same time, St. John’s wort was reported to
contain potent inhibiting constituents for the activity
of P450 enzymes in vitro, including CYP2C19.25Thus,
it seems that St. John’s wort has the potential to cause
effect on the CYP2C19 isoform.In thisstudy,we found
that the activity of 2C19 markedly increased in *1/*1
subjects,incontrast to *2/*2and*2/*3individuals,af-
ter intake of St. John’s wort tablets for 14 days. Our
study demonstrated that St. John’s wort is a potent in-
ducer of CYP2C19. To our knowledge, this is the first
report about the inductive potential of St. John’s wort
on CYP2C19 in vivo.
In clinical situations, the addition or withdrawal of
St. John’s wort from an existing drug regimen contain-
ing CYP2C19 substrates, such as omeprazole, diaze-
appropriate monitoring of therapeutic efficacy and ad-
verse events since well-documented interactions have
substrates cyclosporine and oral contraceptives.7
Clinical observations suggest a potential metabolic
in vitro study, found that the expression of CYP1A2 in
the LS180 intestinal cells was greatly increased by St.
P450 target enzyme of St. John’s wort. However, at the
entire body level, the short-term coadministration of
St. John’s wort did not alter the plasma theophylline
concentrations and the 1A2-mediated metabolic ra-
tio.12,27Prolonged St. John’s wort exposure, however,
may augment the minor contribution of CYP3A4 and
CYP2E1 pathways involved in theophylline bio-
differences in the activity of 1A2 after 2 weeks of St.
John’s wort administration.
As currently known, rifampin and St. John’s wort
belong to the same type of inducer. They both interact
with other drugs in clinical situations by activating
PXR.10,29Similar to St. John’s wort, rifampin has also
been well documented clinically to interact with the
tives, cyclosporine, theophylline, and so on.30How-
ever, these two agents seems to have various effects on
potent inducer to this enzyme,31our study and others
have found that St. John’s wort does not affect 1A2 ac-
tivity.12,27Since the pregnane X receptor activated by
St. John’s wort does not enhance the activity of
such an enzyme. Therefore, the inducing effect of
rifampin on CYP1A2 must be through a mechanism
other than PXR.
In summary, our study demonstrated that the inges-
tion of St. John’s wort does not change the activity of
CYP1A2 but substantially increases the activity of
CYP2C19. Clinicians should pay great attention when
580 • J Clin Pharmacol 2004;44:577-581
WANG ET AL
St. John’s wort is added to or withdrawn from an exist-
ing drug regimen containing a substrate of CYP2C19.
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EFFECTS OF ST. JOHN’S WORT ON THE ACTIVITY OF CYP2C19