Inhibitory Effects of Fruit Juices on Cytochrome P450 2C9 Activity in Vitro
Muneaki HIDAKA,1;2;3Masashi NAGATA,1;3Yohei KAWANO,3Hiroshi SEKIYA,3Hirofumi KAI,2
Keishi YAMASAKI,3Manabu OKUMURA,3and Kazuhiko ARIMORI3;y
1School of Pharmaceutical Sciences, Kyushu University of Health and Welfare,
1714-1 Yoshinocho, Nobeoka, Miyazaki 882-8508, Japan
2Department of Molecular Medicine, Faculty of Medical and Pharmaceutical Sciences,
Kumamoto University, 5-1 Oe-honmachi, Kumamoto 862-0973, Japan
3Department of Pharmacy, University of Miyazaki Hospital, 5200 Kihara, Kiyotake-cho,
Miyazaki-gun, Miyazaki 889-1692, Japan
Received August 10, 2007; Accepted October 31, 2007; Online Publication, February 7, 2008
There is limited information on the effect of fruits
on human cytochrome P450 (CYP) 2C9 activity. The
objective of this study was to determine the effect of
fruit juice on CYP2C9-mediated drug metabolism. Nine
citrus fruits and eight tropical fruits were chosen.
We investigated effects of the fruits on diclofenac 40-
hydroxylation and tolbutamide hydroxylation by human
liver microsomes. Among the fruits, pineapple juice
showed potent inhibition of CYP2C9 activity. The
addition of 25?l (5.0% v/v) of pineapple juice resulted
in almost complete inhibition. Next we examined the
inhibitory effect of bromelain, a cysteine protease in
pineapple. Bromelain also strongly inhibited CYP2C9
activity. In addition, E-64, a cysteine protease inhibitor,
almost entirely blocked inhibition by pineapple juice
and bromelain. Thus we found that pineapple juice was
a potent inhibitor of CYP2C9, and that the inhibitory
effect might be due to the bromelain contained in
Key words:pineapple; cytochrome P450; cytochrome
P450 2C9 (CYP2C9); bromelain
It has been reported that grapefruit juice interacts with
therapeutic drugs that undergo substantial presystemic
metabolism mediated by cytochrome P450 (CYP) 3A4,1)
and that furanocoumarin derivatives identified in grape-
fruit juice strongly inhibited the catalytic activity of
CYP3A.2)The mechanism of action probably involved
irreversible (mechanism-based) inhibition of CYP3A in
the small intestine,3)which resulted in a decrease in the
first-pass metabolism of orally administered therapeutic
drugs. Furthermore, in recent years, reports have in-
dicated that various kinds of fruits have an inhibitory
effect on CYP3A activities in vitro and/or in vivo.4–7)
The inhibitory effect is assumed to be dependent on the
kind of fruit, and is attributed to the type of chemical
components contained in the fruit.2)
Recent reports indicate that some fruit juices inhibit
CYP2C9 activities and cause food-drug interactions.8,9)
When CYP2C9 substrates such as warfarin and pheny-
toin with low therapeutic margins diminish metabolic
capacity because of drug-food interactions, these drugs
can lead to toxicity even at normal therapeutic doses, but
few reports are available on the inhibition of CYP2C9
activity by fruit juice or extract. Hence it is important to
evaluate the effect of fruit juice on CYP2C9 activity.
In the present study, we investigated to determine
whether fruit juice would inhibit the CYP2C9-mediated
drug metabolism using human liver microsomes. The
fruits that we chose for this study were citrus fruits and
tropical fruits, because people living in all over the
world consume them. Tropical fruits are produced in
areas with warm climates, such as Southwest Asia and
the southern part of Japan. We used diclofenac and
tolbutamide as substrates for CYP2C9, since both drugs
are recommended as probe substrates for in vitro
Materials and Methods
Chemicals. Tolbutamide, 4-hydroxytolbutamide, sul-
faphenazole, E-64, pepstatin A, aprotinin, and bromelain
were purchased from Sigma-Aldrich (St. Louis, MO).
Diclofenac and 40-hydroxydiclofenac were from Daiichi
Pure Chemicals (Tokyo). Pooled human liver micro-
somes were from BD Gentest (Woburn, MA). All
chemicals and solvents were of the highest grade com-
mercially available. All aqueous solutions were prepared
using ultra-pure grade water.
yTo whom correspondence should be addressed. Tel: +81-985-85-1510; Fax: +81-985-85-3362; E-mail: firstname.lastname@example.org
Abbreviation: CYP, cytochrome P450
Biosci. Biotechnol. Biochem., 72 (2), 406–411, 2008
Fruit samples. Citrus fruits, hyuga-natsu, unshu man-
darin, banpeiyu, hirami lemon, valencia orange, pomelo,
grapefruit, lemon, and lime, and tropical fruits, melon,
mango, litchi, pineapple, papaya, mangosteen, passion
fruit, and kiwi fruit, were obtained from local commer-
cial sources. These species and origin information are
shown in Table 1. The fruits were stored at 4?C until
use. Fruit juice was obtained by squeezing the edible
portion of the fruit, and the juice was filtered to remove
the residues. All samples were treated soon after they
were squeezed and filtered.
Analytical procedures for human CYP2C9 activity.
Assay of tolbutamide methyl hydroxylase activity was
performed according to the method of Tang et al.,11)
with minor modifications. Briefly, the incubation mix-
tures (final volume, 0.5ml) consisted of the following:
0.1 M phosphate buffer (pH 7.4), 10mM MgCl2, 1mM
EDTA, 1mM NADPþ, 10mM D-glucose 6-phosphate,
10 units/ml D-glucose 6-phosphate dehydrogenase, and
0.2mg/ml of microsomal protein. The concentration of
tolbutamide was 250mM. The reaction time was prede-
termined based on linearity between the reaction time
versus the metabolite formation rate. Based on the
results obtained, the reaction time was determined to be
75min. The reaction mixture was preincubated at 37?C
for 5min, and the reaction was started by the addition of
substrate, and terminated with 2ml of ice-cold acetoni-
trile. Midazolam (1nM) was added as an internal stand-
ard. Following centrifugation (3,000rpm, 10min), the
organic phase was evaporated at 40?C. The residue was
dissolved in 200ml of HPLC mobile phase, and 100ml of
the resulting mixture was injected into an HPLC.
The HPLC system consisted of an LC-10ADvp pump
(Shimadzu, Kyoto, Japan), a Shimadzu L-4200 UV ab-
sorbance detector, and a Shimadzu SIL-10ADvp auto
injector. The system was equipped with a Cadenza CD-
C18 column (3mm, 4:6 ? 250mm; Intact, Kyoto, Japan)
preceded by a precolumn (5mm, 2 ? 5mm). The mobile
phase consisted of acetonitrile and 0.1% of pH 7.4
phosphate buffer (20:80, v/v; solvent A) and acetonitrile
(solvent B). The initial mobile phase consisted of 5% of
solvent B, which increased linearly to 40% over 8min.
The mobile phase was delivered at a flow rate of 0.7ml/
min at 40?C. Quantification was performed by deter-
mining the UV peak areas monitored at 230nm.
Assay of diclofenac 40-hydroxylase activity was per-
formed according to a previously reported method.9)
Inhibitory effect of fruit and bromelain on CYP2C9
activity. The inhibitory effects of fruits on CYP activity
were investigated according to a previously reported
method,6)with minor modifications. Briefly, an appro-
priate amount of fruit juice was applied to fresh tubes.
The reaction mixture described above (before the ad-
dition of substrate) was added to the tubes and resus-
pended with a mixer. The maximum amount of fruit
juice was 25ml (5.0% v/v), and the pH of the reaction
mixtures was constant under these conditions. After
preincubation of the mixture at 37?C for 5min, the
substrate, diclofenac or tolbutamide, was added. The
reaction was performed as described above. The inhib-
itory effects of a fruit juice on diclofenac 40-hydrox-
ylation and tolbutamide hydroxylation were expressed in
terms of percentage of residual activity as compared
with the control in the absence of the fruit juice.
Similarly, the inhibitory effect of bromelain was also
examined after dissolving bromelain in water. The final
concentration of bromelain was 0.5 to 50mg/ml.
Effect of protease inhibitors on CYP2C9 inhibition
by pineapple juice and bromelain. Pineapple juice (2%
v/v) and bromelain (50mg/ml) were incubated with a
protease inhibitor at 37?C for 5min prior to CYP2C9
inhibition assay. E-64, pepstatin A, and aprotinin, pro-
tease inhibitors, were dissolved in appropriate solvents
and diluted with phosphate buffered saline at 4?C. The
final concentrations of E-64, pepstatin A, and aprotinin
were 100mM, 100mM, and 10mM respectively. After in-
cubation, the effect of these samples on CYP2C9 ac-
tivity was examined according to the method mentioned
Effect of ultrafiltration and heat treatment on
CYP2C9 inhibition by pineapple juice and bromelain.
Low molecular weight fractions were isolated by ultra-
filtration (Ultracent-10; Tosoh, Tokyo) of 1-ml pine-
apple juice and bromelain (50mg/ml) in a centrifuge at
2,200g at 25?C for 15min.
Heat treatment was performed according to the meth-
od of Uesawa et al.12)One ml each of pineapple juice
and bromelain (50mg/ml) was treated at 95?C for 60
min. The effect of these samples on CYP2C9 activity
was examined according to the method described above.
Enzyme assay. The proteolytic activities of pineapple
juice and bromelain were assayed by the procedure of
Ahmad et al.,13)with minor modifications. Briefly, a
denatured casein solution (2%) at pH 7.0 was incubated
for 15min at room temperature with pineapple juice or
bromelain solution. The reaction was stopped by adding
6% trichloroacetic acid, and the undigested casein was
removed by centrifugation or filtration. The amount of
peptide remaining in supernatant was determined spec-
trophotometrically at 275nm against a blank containing
all the reaction mixture except for the activity. Enzyme
activity was expressed in terms of ?A275 of the
supernatant. The absorbance values obtained correlated
with the amounts of product formed.
Data analysis. Data from the experiments are ex-
pressed as mean ? S.D. The concentration of pineapple
juice or bromelain required for 50% inhibition of
CYP2C9 activity (IC50) was calculated by linear
regression analysis of the log inhibitor concentration
versus percentage residual activity plots.
Pineapple Juice Inhibits CYP2C9 Activity407
Inhibition of microsomal human CYP2C9 activity by
To evaluate an inhibitory effect of fruit juice on
CYP2C9 activity, we examined diclofenac 40-hydrox-
ylase and tolbutamide hydroxylase activity with and
without fruit juices using human liver microsomes.
Since we have reported that citrus fruits and tropical
fruits inhibited CYP3A,6,7,14)we chose these fruits for
this study. The results are summarized in Table 1.
Among the various fruit juices evaluated, pineapple
juice showed the strongest inhibition. The addition of
25ml (5.0% v/v) of pineapple juice resulted in almost
complete inhibition of human CYP2C9 activity, and the
inhibition potency was more than a match for that of
sulfaphenazole, a potent inhibitor of CYP2C9.15)In ad-
dition, when we evaluated CYP2C9 activity for pine-
apples from two different sources, reproducibility of the
inhibitory effect was observed. On the other hand, citrus
fruits and other tropical fruits had weak or negligible
CYP2C9 inhibitory capacity. Hence we conducted
further studies of the inhibitory characteristics of pine-
apple juice. After that we used pineapples grown in
Figure 1 shows the effect of pineapple juice on the
diclofenac 40-hydroxylase activity of human CYP2C9.
The degree of inhibition depended on the amount of
pineapple juice added to the reaction mixture. The IC50
value was 0.08% v/v. Next we examined to determine
whether the components of pineapple juice would inhibit
CYP2C9 reversibly or irreversibly. The effect of the
preincubation period on the inhibition of diclofenac 40-
hydroxylase activity by pineapple juice was tested. The
results are shown in Fig. 1. The inhibition potency of
pineapple juice was altered by lengthening of the
preincubation period. The mean residual CYP2C9
activities observed with 0.25ml (0.05% v/v) of pine-
apple juice at preincubation periods of 0, 5, 15, and
30min were 79.4%, 72.4%, 64.9%, and 55.1% respec-
tively. These data suggest that pineapple juice causes
irreversible inhibition of human CYP2C9 activity. Thus,
we discovered that pineapple juice potently inhibited the
CYP2C9-mediated metabolism of diclofenac and tolbu-
tamide in vitro.
Bromelain inhibits CYP2C9 activity
Bromelain is a mixture of cysteine proteases obtained
from pineapple stems, and is also present in pineapple
fruits.16)The mixture of cysteine proteases is different as
between pineapple stems and fruits, but proteolytic
activity is observed in both mixtures.17)Hence we
concluded that bromelain is a candidate for CYP2C9
inhibitor, and we examined the effect of bromelain on
diclofenac 40-hydroxylase activity. The addition of
bromelain resulted in almost complete inhibition of
CYP2C9 activity at a final concentration of 50mg/ml.
The inhibition depended on the concentration of bro-
melain (data not shown), and the IC50 value was cal-
culated to be 1.2mg/ml. The proteolytic activities of
pineapple juice and bromelain were 0.138 ?A275/min/
ml and 0.043 ?A275/min/mg respectively. These data
suggest that bromelain is a potent inhibitor of CYP2C9
and is related to the inhibitory effect of pineapple juice.
Data are presented as mean ? S.D. of triplicate assays. The amount of fruit juice used in assays was 25ml (5.0%, v/v). The control activities of
diclofenac 40-hydroxylation and tolbutamide hydroxylation by human liver microsomes determined in the absence of fruit juice were 972 and
254pmol/min/mg protein respectively.
Effect of Components of Citrus and Tropical Fruits on the CYP2C9 Activity of Human Liver Microsomes
Residual activity (%)
Samples (25ml) SpeciesOrigin
Citrus grandis OSBECK
Bay of Plenty, New Zealand
Chaing Mai, Thailand
54:1 ? 1:4
31:5 ? 1:0
54:1 ? 7:6
98:4 ? 4:9
102:5 ? 2:9
42:8 ? 1:2
57:2 ? 3:5
81:6 ? 2:2
97:4 ? 4:5
91:5 ? 3:0
74:3 ? 7:4
89:2 ? 2:9
44:0 ? 1:1
65:2 ? 3:5
19:4 ? 2:3
113:6 ? 8:8
0:4 ? 0:1
0:3 ? 0:1
38:1 ? 1:1
1:7 ? 0:7
45:3 ? 2:6
49:6 ? 2:2
75:2 ? 3:8
78:2 ? 3:9
97:8 ? 3:6
62:7 ? 5:6
65:3 ? 3:6
72:5 ? 5:2
93:0 ? 8:0
95:8 ? 1:7
65:1 ? 6:3
81:7 ? 4:7
71:0 ? 4:0
79:6 ? 2:1
37:7 ? 2:2
97:0 ? 7:2
1:4 ? 0:3
0:8 ? 0:2
15:9 ? 2:0
1:9 ? 0:3
408 M. HIDAKA et al.
To determine whether bromelain makes a contribution
to the inhibitory effect of pineapple juice on CYP2C9
activity, we used a specific cysteine protease inhibitor,
E-64, to inactivate its protease activity.18)Figure 2
shows the effect of the protease inhibitor on the
CYP2C9 inhibition of pineapple juice and bromelain.
Treatment with E-64 diminished the inhibitory effect of
pineapple juice as well as bromelain did, and it almost
recovered to the control level. In addition, we examined
the effect of other protease inhibitors on the inhibitory
effect of pineapple juice and bromelain. Serine protease
inhibitor, aprotinin, and aspartic protease inhibitor, pep-
statin A, did not affect the inhibitory effect of pineapple
juice or bromelain.
In addition, we investigated whether other compo-
nents of pineapple juice would inhibit CYP2C9 activity
using ultrafiltration with a centrifugal filter and heat
treatment. We confirmed in a preliminary way that the
proteolytic activity of pineapple juice was abolished by
these treatments. A low molecular fraction of pineapple
juice separated by ultrafiltration did not inhibit CYP2C9
activity (Table 2). Heat treatment inactivates proteins
Dose of pineapple juice (% v/v)
Preincubation period (min)
Residual activity (%)
Residual activity (%)
Fig. 1.Inhibition of Human CYP2C9 by Pineapple Juice.
The amounts of fruit juice added to the incubation mixture were 0.05, 0.1, 0.15, 0.2, 0.3, 0.4, 0.6, 1, and 2% v/v. The control activity of
diclofenac 40-hydroxylation by human liver microsomes determined in the absence of fruit juice was 1,019pmol/min/mg. Each point and each
bar represents the mean and S.D. of three independent assays. The inset is the determination of effect of the preincubation period on inhibition.
Pineapple juice (0.05% v/v) was added to the reaction mixture and incubated for the indicated periods before the start of the reaction by the
addition of a substrate. The control activity of diclofenac 40-hydroxylation by human liver microsomes determined in the absence of fruit juice
was 983pmol/min/mg. Each point and each bar represents the mean and S.D. of three independent assays.
Residual activity (%)
(10 µ µl; 2% v/v)
(50 µ µg/ml)
(100 µ µM)
(10 µ µM)
(100 µ µM)
Fig. 2.Effect of Protease Inhibitor on the Inhibition of Diclofenac 40-Hydroxylation by Pineapple Juice and Bromelain.
Pineapple juice (2% v/v) and bromelain (50mg/ml) were incubated with a protease inhibitor or phosphate-buffered saline at 37?C for 5min
prior to the CYP2C9 inhibition assay. After incubation, the samples were added to the reaction mixture and assays were performed. The
proteolytic activities of pineapple juice and bromelain were 0.138 ?A275/min/ml and 0.043 ?A275/min/mg respectively. Each point and each
bar represents the mean and S.D. of three independent assays.
Pineapple Juice Inhibits CYP2C9 Activity409
and some chemicals. Heated pineapple juice also did not
inhibit CYP2C9 activity. These data suggest that
bromelain is a principal ingredient of pineapple juice
that inhibits CYP2C9 activity, and that other compo-
nents in pineapple juice are negligible in CYP2C9
inhibition by the juice.
In this study, we evaluated the effect of various citrus
fruits and tropical fruits on the CYP2C9 activity of
human liver microsomes in vitro. Among the fruits
evaluated, pineapple showed the strongest inhibition of
CYP2C9 activity (Table 1). Pineapple is commonly
grown in the southern part of Japan as well as southern
China, Taiwan, the Philippines, and Hawaii, and it is
consumed in all over the world. It sometimes is taken
concomitantly with various types of drugs, but few data
are available as to whether pineapple influences drug
pharmacokinetics. Hence it is important to assess the
interaction between pineapple and CYP-mediated drugs.
Therefore, we further investigated the inhibitory char-
acteristics of pineapple juice on CYP2C9 activity in
vitro, and discovered that inhibition occurs in a dose-
dependent and mechanism-based manner. It has been
reported that cranberry juice, grape juice, and green tea
all cause significant inhibition of CYP2C9 in vitro, but
there is no evidence of inhibitory activity in vivo.19)
However, since pineapple juice showed very strong
inhibitory activity, we think there is a possibility of
food-drug interactions caused by pineapple juice in vivo.
Next we attempted to elucidate the mechanism of
CYP2C9 inhibition. Since pineapple contains bromelain,
known to be a cysteine protease, we examined the effect
of bromelain on CYP2C9 activity. Bromelain strongly
inhibited CYP2C9 activity. Furthermore, the inhibitory
activities of pineapple juice and bromelain were almost
entirely blocked by E-64, but were not blocked by other
protease inhibitors (Fig. 2). In addition, the inhibitory
effect of pineapple juice decreased with ultrafiltration
and heat treatment (Table 2). Ultrafiltration can remove
the high molecular weight components of pineapple
juice, and this result indicates that the low molecular
weight components of pineapple juice did not inhibit
CYP2C9 activity. Heat treatment under this condition
would inactivate almost all proteins and some chem-
icals. This result indicates that the heat-tolerant compo-
nents of pineapple juice are not involved in the CYP2C9
inhibitory activity. Taken together, these data suggest
that the inhibitory effect of pineapple juice depends on
the proteolytic activity of bromelain, and that other
components are negligible in the inhibitory effect. The
mechanism of inhibition is perhaps that bromelain
degrades CYP2C9 protein and thus decreases CYP2C9
activity. Accordingly, we concluded that bromelain was
the principal component in pineapple juice that inhibited
CYP2C9 activity. Papaya and kiwi fruit include cysteine
protease, papain, and actinidin respectively. In this
study, papaya showed weak inhibition of CYP2C9, and
kiwi fruit did not inhibit CYP2C9 activity. We con-
cluded that bromelain has an especially strong ability to
inhibit CYP2C9 activity, and that the pineapple-drug
interaction should be especially noted.
Furthermore, bromelain itself is taken as a nutritional
supplement, and recently its medical contribution has
been identified.20)It is absorbed from the intestine, and
the plasma concentration reaches as much as 5ng/ml
after oral administration (3g/d), with partial proteolytic
activity.21)Further, Bock et al. investigated the absorp-
tion mechanism of proteolytic enzymes by the Caco-2
monolayer method. They found that bromelain absorp-
tion can occur by self-enhanced paracellular transport,22)
but the obtained IC50 value was 1.2mg/ml, and not
sufficient to inhibit hepatic CYP2C9. Generally, early
after ingestion, the concentrations of orally ingested
chemicals are much greater in the intestine than in the
plasma. Hence there is a possibility that bromelain
makes enteric CYP2C9 inactive even if the uptake of
bromelain into systemic circulation is not sufficient to
inhibit hepatic CYP2C9. CYP2C9 is responsible for the
metabolic clearance of numerous drugs, such as warfarin
and phenytoin, within a narrow range of therapeutic
CYP2C9-metabolized drugs should suffer a disadvant-
age even from small changes in plasma concentrations
caused by food-drug interactions. Therefore, further
investigation in humans is necessary in order to develop
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The inhibitory effects of pineapple juice and bromelain on
diclofenac 40-hydroxylation by human liver microsomes are shown.
Data are presented as mean ? S.D. of triplicate assays. Control activity
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40:8 ? 2:5
94:3 ? 1:5
96:9 ? 4:9
0:5 ? 0:1
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Pineapple Juice Inhibits CYP2C9 Activity411