GLUCURONIDES OF TEA CATECHINS: ENZYMOLOGY OF BIOSYNTHESIS AND
BIOLOGICAL ACTIVITIES
HONG LU, XIAOFENG MENG, CHUAN LI, SHENGMIN SANG, CHRISTOPHER PATTEN, SHUQUN SHENG, JUNGIL HONG,
NAISHENG BAI, BOZENA WINNIK, CHI-TANG HO, AND CHUNG S. YANG
Department of Chemical Biology, Ernest Mario School of Pharmacy (H.L., X.M., C.L., J.H., C.S.Y.); Department of Food Science and Center for
Advanced Food Technology (S.Sa., N.B., C-T.H); Department of Chemistry, Rutgers, the State University of New Jersey, Piscataway, New
Jersey (S.Sh.); Shanghai Institute of Materia Medica, Chinese Academy of Sciences, Shanghai, China (C.L.); BD Biosciences, Woburn,
Massachusetts (C.P.); and Environmental and Occupational Health Sciences Institute, Piscataway, New Jersey (B.W., C.S.Y.)
(Received October 15, 2002; accepted January 3, 2002)
This article is available online at http://dmd.aspetjournals.org
ABSTRACT:
()-Epigallocatechin gallate (EGCG) and ()-epigallocatechin
(EGC) are major green tea catechins with antioxidant and antican-
cer activities. In this study, we characterized the glucuronidation of
EGCG and EGC in human, mouse, and rat microsomes and by nine
different human UGT 1A and 2B isozymes expressed in insect cells.
Six EGCG and EGC glucuronides were biosynthesized, and their
structures were identified for the first time. ()-EGCG-4-O-gluc-
uronide was the major EGCG glucuronide formed in all incuba-
tions. The catalytic efficiency (V
max
/K
m
) for ()-EGCG-4-O-gluc-
uronide formation followed the order: mouse intestine > mouse
liver > human liver > rat liver rat small intestine. The UGT-
catalyzed glucuronidation of EGC was much lower than that of
EGCG. The V
max
/K
m
for ()-EGC-3-O-glucuronide followed the
following order: mouse liver > human liver > rat liver > rat and
mouse small intestine. Human UGT1A1, 1A8, and 1A9 had high
activities with EGCG. UGT1A8, an intestine-specific UGT, had the
highest V
max
/K
m
for EGCG but low activity with EGC. Mice ap-
peared to be more similar to humans than rats to humans in the
glucuronidation of EGCG and EGC. Some of these catechin glucu-
ronides retained the activities of their parent compounds in radical
scavenging and in inhibiting the release of arachidonic acid from
HT-29 human colon cancer cells. These results provide founda-
tions for understanding the biotransformation and biological ac-
tivities of tea catechins.
Green tea has been suggested to have activities in the prevention of
cancer and cardiovascular disease (Yang and Landau, 2000; Yang et
al., 2002). (-)-Epigallocatechin gallate (EGCG
1
) and (-)-epigallo-
catechin (EGC) are major green tea polyphenols (catechins) with
significant antioxidative and biological activities. The blood, tissue,
and urine levels of EGCG, EGC, and other tea catechin derivatives
have been studied in animals and humans (Chen et al., 1997; Chow et
al., 2001), but the biotransformation of EGCG and EGC is not well
understood. After oral absorption, EGC and (-)-epicatechin undergo
extensive methylation, glucuronidation, and sulfation (Li et al., 2001;
Meng et al., 2001). Using liquid chromatography/electrospray ioniza-
tion-mass spectrometry, we identified several EGC-O-monoglucu-
ronides in human and mouse urine after ingestion of green tea (Li et
al., 2001). We also detected significant urinary excretion of EGCG
conjugates in mice (Meng et al., 2002). After oral ingestion of green
tea catechins, most of the EGCG existed in the free form, but most of
the EGC was in conjugate form in the human plasma (Chow et al.,
2001). EGCG metabolites were predominantly excreted through bile,
but large amounts of EGC metabolites were found in urine (Chen et
al., 1997; Kida et al., 2000; Kim et al., 2000; Chow et al., 2001; Li et
al., 2001). After oral administration of 100 mg of EGCG to rats,
sulfates/glucuronides were the predominant forms (97.4%) of EGCG
secreted into the bile (Kida et al., 2000). These data suggest that
EGCG and EGC differ significantly in their metabolism and elimina-
tion; first-pass metabolism of EGCG may play an important role in
determining the bioavailability of EGCG. Further studies on the
metabolism of catechins and the biological activities of the metabo-
lites are vital for understanding the biological activities of catechins.
UDP-glucuronosyltransferase (UGT)-catalyzed glucuronidation is
a major pathway in Phase II metabolism. At present, 15 human UGTs
have been cloned. UGT1A1 catalyzes the glucuronidation of bilirubin,
phenols, flavonoids, anthraquinones, and certain estrogens (King et
al., 1996). UGT1A3 glucuronidates certain estrogens, flavonoids,
coumarins, amines, and anthraquinones (Green et al., 1998). UGT1A6
catalyzes the glucuronidation of planar phenols, whereas UGT1A9
glucuronidates bulky phenols, flavonoids, anthraquinones, and many
This work was supported by National Institutes of Health Grants CA56673 and
CA88961.
1
Abbreviations used are: EGCG, (-)-epigallocatechin gallate; EGC, (-)-epi-
gallocatechin; EGCG-7-Gluc, (-)-EGCG-7-O-glucuronide (and similar abbrevia-
tions for other glucuronides); 4'-MeEGC, 4'-O-methyl-(-)-epigallocatechin; 4-
MeEGCG, 4-O-methyl-EGCG; 4',4-DiMeEGCG, 4',4-di-O-methyl-EGCG;
DPPH, 1,1-diphenyl-2-picrylhydrazyl; UGT, UDP-glucuronosyltransferase; UD-
PGA, uridine 5'-diphosphoglucuronic acid; G-7896, Escherichia coli -D-glucu-
ronidase; HLM, human liver microsomes; MLM, mouse liver microsomes; RLM,
rat liver microsomes; LC/MS/MS, liquid chromatography mass spectrometry;
HPLC, high performance liquid chromatography.
Address correspondence to: Dr. Chung S. Yang, Department of Chemical
Biology, Ernest Mario School of Pharmacy, Rutgers, The State University of
New Jersey, 164 Frelinghuysen Road, Piscataway, NJ 08854. E-mail:
csyang@rci.rutgers.edu
0090-9556/03/3104-452–461$7.00
DRUG METABOLISM AND DISPOSITION Vol. 31, No. 4
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