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Functional Foods R&D Laboratories, Meiji Seika Kaisha, Ltd., Sakado 350-0289, Japan and the
Department of Nutrition, School of Medicine, The University of Tokushima, Tokushima 770, Japan
*
1To whom correspondence should be addressed. E-mail: seigo_baba{at}meiji.co.jp
ABSTRACT
We compared levels of (+)-catechin, (-)-epicatechin, and their metabolites in rat plasma and urine after oral administration. Rats were divided into four groups and given (+)-catechin (CA group), (-)-epicatechin (EC group), a mixture of the two (MIX group) or deionized water. Blood samples were collected before administration and at designated time intervals thereafter. Urine samples were collected 0–24 h postadministration. (+)-Catechin, (-)-epicatechin and their metabolites in plasma and urine were analyzed by HPLC-mass spectrometry after treatment with ß-glucuronidase and/or sulfatase. After administration, absorbed (+)-catechin and (-)-epicatechin were mainly present in plasma as metabolites, such as nonmethylated or 3'-O-methylated conjugates. In the CA and MIX groups, the primary metabolite of (+)-catechin in plasma was glucuronide in the nonmethylated form. In the EC and MIX groups, in contrast, the primary metabolites of (-)-epicatechin in plasma were glucuronide and sulfoglucuronide in nonmethylated forms, and sulfate in the 3'-O-methylated forms. Urinary excretion of the total amount of (-)-epicatechin metabolites in the EC group was significantly higher than the amount of (+)-catechin metabolites in the CA group. The sum of (+)-catechin metabolites in the urine was significantly lower in the MIX group than in the CA group, and the sum of (-)-epicatechin metabolites in the MIX group was also significantly lower than in the EC group. These results suggest that the bioavailability of (-)-epicatechin is higher than that of (+)-catechin in rats, and that, in combination, (+)-catechin and (-)-epicatechin might be absorbed competitively in the gastrointestinal tract of rats.
KEY WORDS: • rats • (+)-catechin • (-)-epicatechin • absorption • excretion
According to epidemiological data, there is a negative correlation
between plant polyphenol consumption and the incidence of coronary
heart disease (1
, 2
). Flavonoids that have several hydroxyl
groups are widely distributed in fruits and vegetables and are consumed
frequently in our daily diet (3
). In previous reports, the
daily intake of flavonoids from food was estimated to range between 23
mg in The Netherlands and 1 g in the United States
(1
, 4
). Recently, it was reported that daily
catechin intake was 50 mg/d in the Dutch population
(5
). This report indicated that tea was the
primary source of catechins for all ages and that chocolate was an
important source of catechins in children (5
). These
reports suggest that daily intake of catechins from food may confer
health benefits in humans.
(+)-Catechin and (-)-epicatechin are flavonoids that are both found in
green tea, black tea, wine and other plant foods, such as fruits and
cacao products (6
). Catechins, such as (+)-catechin and
(-)-epicatechin, are reported to have various physiological effects in
terms of their antioxidative ability. In an in vitro study, the
addition of catechins such as (+)-catechin and (-)-epicatechin delayed
lipid oxidation and 
-tocopherol and ß-carotene depletion in human
oxidized plasma induced by a radical generator (7
). In an
ex vivo study, consumption of green tea prevented oxidation of low
density lipoproteins in humans (8
). Moreover, in an in
vivo study, Miura et al. (9
) showed that tea catechins
attenuated the development of atherosclerosis in apolipoprotein
E-deficient mice. Recently, Schroeter et al. (10
)
reported a possible role for (-)-epicatechin in reducing
neurodegenerative disorders such as Parkinson’s disease and
Alzheimer’s disease.
Previous reports have indicated that orally ingested (+)-catechin and
(-)-epicatechin are absorbed from the intestinal tract and metabolized
to a conjugated and/or methylated form found in plasma
(11
–14
). We also previously reported that
(-)-epicatechin from cocoa powder is absorbed, metabolized to various
conjugated and/or methylated forms and excreted in urine in rats and
humans (15
, 16
). It was found that (+)-catechin was present
in a conjugated and/or methylated form in human plasma after
consumption of red wine (17
). (-)-Epicatechin was
detected in the plasma of rats and humans after ingestion of green tea
(18
, 19
). Taken together, these reports suggest that foods
containing (+)-catechin and (-)-epicatechin may promote health
benefits.
It has been reported that conjugation and methylation of phenolic
hydrogen result in a decrease in antioxidative activity at the point of
scavenging chain-initiating oxygen radicals or chelating transition
metal ions (20
). Harada et al. (21
) showed
that conjugates of (+)-catechin and (-)-epicatechin
(5-O-ß-glucuronide form) maintained antioxidative activity
compared with 3'-O-methylated glucuronide conjugates. Nanjo
et al. (22
) reported that partial modification of
(+)-catechin and (-)-epicatechin had an influence on their scavenging
abilities. Moreover, Silva et al. (14
) demonstrated that
in rat plasma, administration of (-)-epicatechin enhanced
antioxidative activity. These results suggest that certain kinds of
metabolites of (+)-catechin and (-)-epicatechin have potent
antioxidative activity. We also recently reported that daily intake of
cocoa powder, which is rich in polyphenols such as (+)-catechin and
(-)-epicatechin, decreased the susceptibility of low density
lipoproteins in humans (23
).
The purpose of this study was to compare the absorption, metabolism and urinary excretion of (+)-catechin and (-)-epicatechin metabolites after oral administration of (+)-catechin, (-)-epicatechin or their mixture.
MATERIALS AND METHODS
This study was approved by the Animal Committee of Meiji Seika Functional Foods R&D Laboratories. All animals received humane care under institutional guidelines.
Chemicals.
(+)-Catechin, (-)-epicatechin, D-saccharic acid
1,4-lactone, ß-glucuronidase type VII-A, sulfatase type VIII and
sulfatase type H-5 were purchased from Sigma (St. Louis, MO). All other
chemicals were analytical or HPLC grade. Figure 1
shows the structures of (+)-catechin and (-)-epicatechin and their
3'-O-methylated forms.
|
Sprague-Dawley male rats (n = 10) were obtained at 10 wk of age from Clea Japan (Tokyo, Japan). They were deprived of food for 12 h before administration and were operated on for collection of urine. A plastic tube was attached to the penis of each animal. Rats were divided into two groups of five and (+)-catechin or (-)-epicatechin, each suspended in deionized water (172 µmol/L), was administered orally to the animals at a dose of 1.72 mmol/kg of body. All urine samples excreted from 0 to 24 h postadministration were collected. Twenty milliliters of urine was extracted three times with ethyl acetate. The ethyl acetate phase was concentrated to dryness in vacuo and then dissolved in 3 mL of 70% methanol. One microliter of solution was injected into a reversed-phase semipreparative HPLC column (Deverosil ODS-HG-5, 5 µm, 250 x 20 mm; Nomura Chemical, Aichi, Japan). The column was eluted at room temperature with a linear gradient of solvent A starting from 10% methanol containing 8.32 mmol/L acetic acid to 45% methanol containing 8.32 mmol/L acetic acid in 30 min at a flow rate of 15 mL/min. The eluted compounds were monitored at a wavelength of 220 nm. Each fraction of methylated (+)-catechin and methylated (-)-epicatechin was collected and used as a sample for HPLC-mass spectrometry (LC-MS)2 and nuclear magnetic resonance (NMR) analyses.
LC-MS analyses of methylated (+)-catechin and methylated
(-)-epicatechin were performed using an HP1100 series HPLC according
to previous reports (15
). NMR spectra were obtained by a
JEOL JNM-JSX 400 spectrometer, using CD3OD as a
solvent. As the internal chemical shift standard, the proton and carbon
peaks of deuterated methanol were set at 3.35 and 49 ppm, respectively.
Measurement of metabolites of (+)-catechin and (-)-epicatechin in plasma and urine.
Sprague-Dawley male rats (n = 20) were obtained at 9 wk of age from Clea Japan. They were kept at 23°C and 55% relative humidity under a 12-h dark/light cycle with free access to pelleted food (Oriental Yeast Ltd., Tokyo, Japan) and deionized water for 1 wk. Rats were deprived of food for 12 h before administration and were operated on under anesthesia with diethyl ether inhalation for collection of blood and urine. A polyethylene tube was implanted into the femoral artery and sutured, and a plastic tube was attached to the penis of each animal. Thereafter, animals were placed in restraining cages (Natsume Seisakusho Ltd., Tokyo, Japan) with free access to deionized water. Rats were divided into four groups of five according to body weight (range: 250–300 g). (+)-Catechin (17.2 mmol/L), (-)-epicatechin (17.2 mmol/L) or a mixture of the two [(17.2 mmol of (+)-catechin + 17.2 mmol of (-)-epicatechin)/L] was suspended in deionized water. Each suspension was administered orally to the animals, with one group receiving (+)-catechin at a dose of 172 µmol/kg of body (CA group), the second group receiving (-)-epicatechin at a dose of 172 µmol/kg of body (EC group) and the third group receiving the mixture at a dose of 345 µmol/kg of body (MIX group). Deionized water was administered orally to the rats in the fourth group at a dose of 10 mL/kg of body (DW group). Blood samples were collected from the cannulated femoral artery into heparinized tubes before and at 30, 60, 120, 180 and 300 min postadministration. All urine samples excreted from 0 to 24 h postadministration were collected under chilled conditions using an ice bath and the volume was measured. Plasma was isolated by centrifugation at 1400 x g for 10 min at 4°C. Plasma and urine samples were stored at -80°C with nitrogen gas until required for analysis.
(+)-Catechin, (-)-epicatechin and their metabolites in rat plasma were
determined by LC-MS according to Piskula and Terao
(13
) and Baba et al. (15
). Glucuronide,
sulfate or sulfoglucuronide (a mixture of glucuronide and sulfate)
conjugates of nonmethylated or 3'-O-methylated forms
were hydrolyzed to the nonconjugated form by ß-glucuronidase type
VII-A, sulfatase type VIII or sulfatase type H-5. The amount of
each metabolite (glucuronide, sulfate or sulfoglucuronide conjugates of
nonmethylated or 3'-O-methylated forms) in the samples
was calculated as the amount after enzymatic hydrolysis minus the
amount before hydrolysis in nonmethylated or
3'-O-methylated forms (13
). Urine samples
were filtered and diluted optimally with saline for analysis and
analyzed as described above.
LC-MS analyses of (+)-catechin and (-)-epicatechin in plasma and urine
extracts were performed using an HP 1100 Series HPLC (Hewlett Packard,
Palo Alto, CA) according to previous reports (15
).
Calculations and statistics.
All data were presented as means with standard errors. The plasma area under the curve (AUC) from the baseline was calculated by WinNonlin, Version 3.1 software (Scientific Consulting, Cary, NC) with a noncompartment model. Data were analyzed by Tukey’s test after one-way ANOVA. When variances were unequal, data were log-transformed before ANOVA and reanalyzed. Significance was recognized at P < 0.05. All statistical analyses were performed using SPSS for Windows, Version 7.5.1 software (SPSS Japan, Tokyo, Japan).
RESULTS
Purification of 3'-O-methyl-(+)-catechin and 3'-O-methyl-(-)-epicatechin from urine as a standard.
MS data for methylated (+)-catechin and methylated (-)-epicatechin
showed a prominent [M-H]- product ion at m/z 303, which
was assigned to the molecular ion. Each methylated (+)-catechin
and methylated (-)-epicatechin was identified as
3'-O-methyl-(+)-catechin and
3'-O-methyl-(-)-epicatechin by NMR analyses similarly to
previous reports (12
, 21
). These compounds were used as
standards for LC-MS analysis.
Identification of nonmethylated and 3'-O-methylated forms by HPLC-mass spectrometry.
Typical LC-MS chromatograms of rat plasma hydrolyzed by sulfatase
type H-5 at 60 min after administration are shown in Figure 2
. At m/z 289 in the LC-MS analysis, a peak was detected at 8 min in
the CA group (Fig. 2E)
, at 11 min in the EC group (Fig. 2G)
and at 8
and 11 min in the MIX group (Fig. 2I)
. No peak was detected in the DW
group (Fig. 2C)
. The peak detected at 8 min showed the same retention
time as the (+)-catechin standard (Fig. 2A)
; thus, it was identified as
(+)-catechin. The peak eluted at 11 min showed the same retention time
as the (-)-epicatechin standard (Fig. 2A)
; thus, it was identified as
(-)-epicatechin. At m/z 303 in the LC-MS analysis, a peak was
detected at 12 min in the CA group (Fig. 2F)
, at 14 min in the EC group
(Fig. 2H)
and at 12 and 14 min in the MIX group (Fig. 2J)
. No peak was
detected in the DW group (Fig. 2D)
. The peak detected at 12 min showed
the same retention time as the 3'-O-methyl-(+)-catechin
standard (Fig. 2B)
; thus, it was identified as
3'-O-methyl-(+)-catechin. The peak eluted at 14 min showed
the same retention time as the 3'-O-methyl-(-)-epicatechin
standard (Fig. 2B)
; thus, it was identified as
3'-O-methyl-(-)-epicatechin.
|
Metabolites of (+)-catechin and (-)-epicatechin were not detectable in
plasma in the DW group (data not shown). By using enzymatic treatment
of plasma in the CA, EC and MIX groups, metabolites such as
glucuronide, sulfate and sulfoglucuronide conjugates were distinguished
as nonmethylated or 3'-O-methylated forms (Table 1
and Figs. 3
and
4). Based on the AUC, the main metabolite of (+)-catechin in the CA and
MIX groups was glucuronide in the nonmethylated form (Table 1)
. In
contrast, in the EC and MIX groups, the main metabolites of
(-)-epicatechin were glucuronide and sulfoglucuronide in nonmethylated
forms and sulfate in the 3'-O-methylated forms (Table 1)
.
|
|
No metabolites of (+)-catechin or (-)-epicatechin were detectable in
urine in the DW group (data not shown). By using the enzymatic
treatment of urine in the CA, EC and MIX groups, metabolites such as
glucuronide, sulfate and sulfoglucuronide conjugates were distinguished
as nonmethylated or 3'-O-methylated forms (Table 2
). Moreover, nonconjugates of nonmethylated and
3'-O-methylated forms were also detected in the CA, EC and
MIX groups (Table 2)
. The total amount of nonmethylated
(-)-epicatechin metabolites in the EC group was significantly greater
than that of nonmethylated (+)-catechin metabolites in the CA group or
that of nonmethylated (-)-epicatechin metabolites in the MIX group
(Table 2)
. The sum of 3'-O-methylated (-)-epicatechin
metabolites in the EC group was also significantly greater than that of
3'-O-methylated (+)-catechin metabolites in the CA group or
3'-O-methylated (-)-epicatechin metabolites in the MIX
group (Table 2)
. Urinary excretion recovery of total (+)-catechin and
(-)-epicatechin metabolites (nonmethylated +
3'-O-methylated forms) compared with the oral dose are shown
in Figure 5
. Urinary excretion of total (-)-epicatechin metabolites compared with
the oral dose in the EC group was significantly greater than that of
total (+)-catechin metabolites in the CA group or that of total
(-)-epicatechin metabolites in the MIX group (Fig. 5)
. Urinary
excretion of total (+)-catechin metabolites compared with the oral dose
in the CA group was significantly greater than that of total
(+)-catechin metabolites in the MIX group (Fig. 5)
.
|
|
DISCUSSION
In this study, we compared the absorption, metabolism and urinary excretion of (+)-catechin and (-)-epicatechin metabolites after administration of (+)-catechin, (-)-epicatechin and their mixture.
There are many reports regarding the levels of (+)-catechin and
(-)-epicatechin in plasma. After red wine consumption, (+)-catechin
was detected in human plasma and reached maximum plasma levels 
1.5 h
postingestion (24
). Yang et al. (19
) reported
that plasma levels of (-)-epicatechin reached a peak between 1.4 and
2.4 h after ingestion of green tea. Rein et al. (25
)
also showed that (-)-epicatechin from chocolate could be found in
human plasma and reached a peak at 2 h after intake. In a study
with rats, (-)-epicatechin in the plasma reached maximum concentration
1–2 h after administration (13
). In our previous study,
total (-)-epicatechin levels in plasma showed a maximum concentration
at 1 h in rats and at 2 h in humans after ingestion of cocoa
powder (15
, 16
). In this study, total levels (the sum of
the nonconjugated forms and glucuronide, sulfate and sulfoglucuronide
of nonmethylated and 3'-O-methylated forms) reached a peak
at 30–60 min postadministration in the CA, EC and MIX groups (Figs. 3
and 4)
. Results of the present study are in accordance with previous
reports and suggest that (+)-catechin and (-)-epicatechin might be
rapidly absorbed from the upper portion of the digestive tract and
distributed in the plasma.
|
and Fig. 5
). In the CA group, the
total amount of (+)-catechin metabolites in urine excreted within
24 h postadministration was greater than that of the total
amount of (+)-catechin metabolites in the MIX group (Fig. 5)
. Harada et
al. (21
) reported that after oral administration of
(+)-catechin or (-)-epicatechin, glucuronide of (-)-epicatechin was
at a higher level compared with (+)-catechin in plasma and urine. These
results suggest that absorption of (-)-epicatechin from the digestive
tract might be more efficient than that of (+)-catechin and that
(+)-catechin and (-)-epicatechin might be competitively absorbed in
the gastrointestinal tract of rats when taken in combination. The
solubility, lipophilicity and excretion of each component might have
had an effect on the results in the present study. Further study is
needed to clarify the absorption mechanisms, including the interaction
of (+)-catechin and (-)-epicatechin.
Piskula and Terao (13
) reported that the highest activity
of uridine 5'-diphosphate glucuronosyltransferase was found in the
intestinal mucosa, that activity of phenolsulfotransferase was found
only in the liver and that catechol-O-methyltransferase
showed high activity in both the liver and kidneys of rats. Moreover,
they proposed that when (-)-epicatechin is absorbed from the digestive
tract, it is conjugated with glucuronic acid by uridine 5'-diphosphate
glucuronosyltransferase and that the glucuronide form is sulfated by
phenolsulfotransferase in the liver and the conjugated form is
methylated by catechol-O-methyltransferase in the liver and
kidney. In the present study, several related metabolites, such as
glucuronide, sulfate and sulfoglucuronide in nonmethylated and
3'-O-methylated forms, were detected in the plasma of the
CA, EC and MIX groups (Table 1)
. Nonconjugates of nonmethylated and
3'-O-methylated forms were at low levels compared with
conjugates of nonmethylated and 3'-O-methylated forms in the
plasma of the CA, EC and MIX groups (Table 1)
. These results suggest
that (+)-catechin and (-)-epicatechin were absorbed from the digestive
tract, rapidly conjugated and present as metabolites in plasma. This
confirms the proposition by Piskula and Terao (13
).
In this study, differences were found in the major metabolites of
(+)-catechin and (-)-epicatechin in the plasma of the CA, EC and MIX
groups. As shown in the results of the AUC, the major metabolites of
(+)-catechin in plasma in the CA and MIX groups were glucuronide in the
nonmethylated form (Table 1)
. In contrast, major metabolites of
(-)-epicatechin in the EC and MIX groups were sulfoglucuronide and
glucuronide in the nonmethylated forms and sulfate in the
3'-O-methylated forms (Table 1)
. Moreover, the AUC of the
total 3'-O-methylated (+)-catechin metabolites in the CA
group was significantly lower than that of 3'-O-methylated
(-)-epicatechin metabolites in the EC group (Table 1)
. Manach et al.
(11
) reported that plasma metabolites of (+)-catechin fed
in the diet differed from that of quercetin fed in the diet. They
reasoned that this difference might be due to the solubility of
metabolites in biological fluid and the route of excretion (i.e.,
biliary or urinary elimination) and that the methylation rate of
(+)-catechin was lower than that of quercetin in an in vitro study. In
the present study, the difference in metabolite profiles in the plasma
between these test groups might be due to the affinity of individual
chemicals to metabolic enzymes, such as uridine 5'-diphosphate
glucuronosyltransferase, phenolsulfotransferase and
catechol-O-methyltransferase. Further study is needed to
elucidate the affinity of catechins to the enzymes that mediate
conjugation and methylation.
As shown in Table 2
, nonconjugated forms, glucuronide, sulfate and
sulfoglucuronide nonmethylated or 3'-O-methylated forms were
detectable in the urine of the CA, EC and MIX groups. Nonconjugates of
nonmethylated or 3'-O-methylated forms in the CA, EC and MIX
groups were minor components in the plasma, especially the free
3'-O-methylated forms. In contrast, in urine excreted within
24 h postadministration, nonconjugates of nonmethylated
(+)-catechin in the CA and MIX groups were 12.8% ± 4.5% and 14.6%
± 5.5% of the sum of nonmethylated (+)-catechin metabolites,
respectively. Nonconjugates of 3'-O-methylated (+)-catechin
in the CA and MIX groups were 17.8% ± 6.3% and 28.9% ± 9.1% of
the sum of 3'-O-methylated (+)-catechin metabolites,
respectively. Nonconjugates of nonmethylated (-)-epicatechin in the EC
and MIX groups were 31.5% ± 9.8% and 58.7% ± 12.5% of the sum of
nonmethylated (-)-epicatechin metabolites, respectively. Nonconjugates
of 3'-O-methylated (-)-epicatechin in the EC and MIX groups
were 26.0% ± 8.1% and 58.8% ± 11.1% of the sum of
3'-O-methylated (-)-epicatechin metabolites, respectively.
Okushio et al. (12
) reported that nonconjugates of
nonmethylated and 3'-O-methylated-(-)-epicatechin were
present in rat urine after administration of (-)-epicatechin. We also
previously reported that the nonconjugate of nonmethylated and
methylated (-)-epicatechin was present in human urine after ingestion
of chocolate and cocoa, which are rich in (-)-epicatechin
(16
). The results in the present study suggest that
deconjugation of conjugated (+)-catechin and (-)-epicatechin
metabolites may occur in the rat kidney and the metabolites excreted in
urine; however, the physiological significance of this deconjugation
remains unclear.
Okushio et al. (12
) detected several
(-)-epicatechin-related compounds, such as 3' or
4'-O-methyl-(-)-epicatechin,
(-)-epicatechin-5-O-ß-glucuronide, and
3'-O-methyl-(-)-epicatechin-5-O-ß-glucuronide,
in the urine after administration of (-)-epicatechin. Harada et
al. (21
) also isolated
(+)-catechin-5-O-ß-glucuronide,
(-)-epicatechin-5-O-ß-glucuronide,3'-O-methyl-(+)-catechin-O-ß-glucuronide
and
3'-O-methyl-(-)-epicatechin-5-O-ß-glucuronide
in rat urine after administration of (+)-catechin and (-)-epicatechin.
They reported that the superoxide anion radical scavenging activity of
(+)-catechin and (-)-epicatechin was similar to that of
(+)-catechin-5-O-ß-glucuronide and
(-)-epicatechin-5-O-ß-glucuronide, whereas the superoxide
anion radical scavenging activity of
3'-O-methyl-(+)-catechin-5-O-ß-glucuronide and
3'-O-methyl-(-)-epicatechin-5-O-ß-glucuronide
was drastically lower than that of (+)-catechin and (-)-epicatechin
(21
). In the present study, (+)-catechin or
(-)-epicatechin were mostly present as a conjugation of nonmethylated
or 3'-O-methylated forms in the plasma (Tables 1
and Figs. 3
and 4
). Silva et al. (14
) reported that oral
administration of (-)-epicatechin enhanced the level of antioxidative
activity in rat plasma. Nevertheless, absorbed (-)-epicatechin was
present mainly as metabolites such as conjugates and/or methylated
forms (14
). These results suggest that certain kinds of
(+)-catechin- and (-)-epicatechin-related metabolites in plasma,
especially conjugates of nonmethylated forms, may have potent
antioxidative activity.
The administration level of (-)-epicatechin or (+)-catechin in this
study corresponds to 3.0–6.0 g in humans (at a body weight of 60
kg). In previous reports, the estimated average level of daily intake
of flavonoids from food ranged from 25 mg to 1 g in humans
(1
, 4
). The administration level in this study corresponds
to 3–240 times the daily flavonoid intake in humans. Most studies of
bioavailability of flavonoids in rats have been conducted at a higher
dose compared with the estimated average level of daily intake of
flavonoids. Further study will be needed to investigate a more
practical dose in the future.
Ingested (+)-catechin and (-)-epicatechin were absorbed from the
digestive tract and were primarily present in plasma as metabolites
such as conjugated and/or methylated forms. Recently, there have been
reports regarding the physiological function of metabolites of
(+)-catechin and (-)-epicatechin. Koga and Meydani (26
)
showed that plasma metabolites of (+)-catechin have an inhibitory
effect on monocyte adhesion to IL-1ß-stimulated human aortic
endothelial cells. Spencer et al. (27
) reported that
3'-O-methyl-epicatechin inhibits cell death induced by
hydrogen peroxide and activation of caspase-3. However, the biological
ability of metabolites of (+)-catechin and (-)-epicatechin remains
largely unknown. To clarify this point, further study is needed on the
chemical structures and biological functions of these components.
ACKNOWLEDGMENTS
We thank M. Ohyama (Meiji Seika Kaisha, LTD., Pharmaceutical Research Center, Yokohama, Japan) for the 1H- and 13C-NMR analysis and for helpful suggestions concerning this study. We also thank K. Aizawa and T. Nawa (Meiji Seika Kaisha, Ltd., Pharmaceutical Research Center, Yokohama, Japan) for the AUC analysis using WinNonlin, Version 3.1 (Scientific Consulting, Cary, NC).
FOOTNOTES
2 Abbreviations used: AUC, area under the curve;
LC-MS, HPLC-mass spectrometry; NMR, nuclear magnetic
resonance. 
Manuscript received 12 June 2001. Initial review completed 22 June 2001. Revision accepted 26 July 2001.
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