The Role of Green Tea Extract on the Proliferation of Human Ovarian Cancer Cells (in vitro) Study
Faiza A. Mahboub
Faten A. Khorshid
This study investigated the role of green tea extracts as a cytotoxic agent against human ovarian cancer cells in vitro using different concentrations of green tea extracts (20, 50,100 and 250 μg mL-1) for 24 h. In vitro proliferation assays were performed to compare the growth rate of all groups of cells. The numbers of viable cells were counted using Heamocytometer and Trypan blue staining (0.4%). The effect of green tea extracts was also studied for long period (24, 48 and 72 h) using the IC50 = 100 μg mL-1. The results of statistical analysis revealed significant decrease in the number of treated human ovarian cancer cells inversely proportion with increasing the concentration of green tea extracts, this experiments determined that the IC50 = 100 μg mL-1. In long term study, the results approved that there was significant reduction in the number of tumor cells by time in contrast with control none treated one. Morphologically, the images of the fixed and stained human ovarian cancer cells with Coomassie stain revealed that the Green tea extracts causing cells shrinkage, blabbing, chromatin condensation and loss of cell-cell contacts which were known as sign of apoptosis. In conclusion, green tea extract has been shown antiproliferative activity against the growth of HOCC which might be considered in clinical situation.
Cancer is one of the major causes of death worldwide. It is estimated that
12.8% of the world population die due to cancer (WHO, 2004;
Hanachi et al., 2006). The number of new cases
has been increasing every year from the year 1990 to 2000 alone, there has been
increase of 22% in incidence and mortality (Parkin, 2001).
Green tea has shown promise effect in the prevention of several cancers (Lee
et al., 2005). It contains several compounds, including polyphenols
that have been reported as chemoprotective agents (Graham,
1992). Ioannides and Yoxall (2003) reported that
tea intake has been linked to many beneficial effects in human health. There
is ample evidence from in vitro and in vivo studies indicating
that components of tea are associated with decreased risk or progression of
several cancers (Chung et al., 2003), cancer
and cardiovascular disease (McKay and Blumberg, 2002).
Currently, the epidemiologic evidence is strongest with organs of the gastro-
intestinal tract, possibly because of their direct contact with tea constituents
(Setiawan et al., 2001; Su
and Arab, 2002; Sun et al., 2002; Sasazuki
et al., 2004). Evidence has also emerged from human observational
studies on cancer of the skin (Hakim et al., 2000)
prostate, breast (Nakachi et al., 1998; Inoue
et al., 2001; Chung et al., 2003;
Wu et al., 2003; Crespy and
Williamson, 2004) pancreas, esophagus and lung (Nagano
et al., 2001) and from over 80 published studies in animal models
(Matsumoto and Yamana, 2000; Chung
et al., 2003). Green tea components can be distributed to a wide
variety of target organs in rodents after ingestion (Suganuma
et al., 1999). Interestingly, the majority of studies reporting protective
effects were conducted in Asian countries where, green tea is predominantly
consumed (Chung et al., 2003). In studies conducted
in rodents, tea has exhibited strong anticarcinogenic activity against a number
of carcinogens of human relevance including heterocyclic amines and polycyclic
aromatic hydrocarbons that are important food contaminants, being formed during
the normal cooking process (Yang et al., 2002;
Chung et al., 2003). The potent chemopreventive
activity of tea has been observed on a number of target organs and has been
attributed to the fact that it influences favorably all stages of carcinogenesis
process, namely initiation, promotion and progression as well as metastasis
(Fujiki and Suganuma, 2002).Tea can modulate the initiation
stage by preventing the bending of genotoxic carcinogens to DNA to induce mutations,
that is on its antimutagenic activity (Matsumoto and Yamana,
2000; Ioannides and Yoxall, 2003).
Findings from in vitro and in vivo studies need to be supported
by human studies that take into account the absorption and uptake of green tea
compounds in vivo. Many in vitro and animal studies used very
high concentrations of one component of green tea polyphenols called catechins
to demonstrate a protective effect (Chung et al.,
2003; Crespy and Williamson, 2004). However, green
tea polyphenols undergo several processes after ingestion so that the high catechin
concentrations do not reflect the actual levels found in the human body (Chung
et al., 2003). Furthermore, animal studies utilize a variety of preparation
methods for green tea that can influence the content of green tea components
such as catechins, leading to unstable levels (Crespy and
Williamson, 2004). It is thus, difficult to evaluate the relationship between
the amount of green tea ingestion and the biologic effect that can be applied
to humans (Gupta et al., 2001; Crespy
and Williason, 2004; Baliga et al., 2005;
Nihal et al., 2005).
The anticancer properties of green tea and of the bioactive polyphenol, (-)-epigalloctachin-3-gallate
(EGCG), are a result of induction of G1 arrest an apoptosis as well as regulation
of cell cycle-related proteins in cancer cell lines (Huh
et al., 2004).
Yihai and Renhai (1999) reported that, a study by Swedish
researchers, suggested that green teas cancer fighting benefits may be
due to a component of the drink that prevents angiogenesis, the process of blood
vessels growth. Tumors are depended on the continual development of new blood
vessels to grow and multiply, they believed that a EGCG may be active in preventing
the growth of new blood vessels in tumors and could be the green teas
association with lower cancer incidence, they found 70% less blood vessel growth
in mice that were given green tea than in water consuming controls.
There is ample evidence from in vitro and in vivo studies indicating that components of tea are associated with decreased risk or progression of several cancers, relatively few studies have specifically investigated ovarian cancer. This stimulated the present investigation to study the effect of GTEs on the human ovarian cancer, using human ovarian cancer on in vitro study.
MATERIALS AND METHODS
This study was conducted between 2007-2009 in Tissue Culture Unit King Fahd Medical Research Center, King Abdul-Aziz University, Jeddah, Saudi Arabia.
Human ovarian tumor was kindly obtained through the courtesy of Abdul-Jabbar,
Professor of Gynecology, King Abdul-Aziz University Hospital (KAUH), Jeddah.
It was immediately transported in sterilized transporting media to Tissue Culture
Unit, King Fahd Medical Research Center (KFMRC), to prepare the tissue for in
Green Tea Extracts Preparation
Green tea was locally purchased from Green tea center Jeddah-KSA and stored
at 4°C in sealed bag (2.5% w/v). It was prepared by adding boiling water
(100 mL) to the tea (2.5 g) in flask, leaving to stand for 10-15 min inverting
every 30 sec and then filtering through cotton wool, according to the method
of Nicolas et al. (1999).
Human Ovarian Cancer Cells
Human ovarian tumor cells were prepared f or in vitro study in growth
media (MCDB 105+M199 in a 1:1) supplemented with 10% Fetal Calf Serum (FCS)
and 1% penicillin-streptomycin at 37°C under 5% CO2 and 95% air
(Dunfield et al., 2002).The cells were dispensed
in 24 wells plate 1x105 mL in each well.
Assay of Cytotoxic Activity
Part of cells were treated with tea extract for 24 h and IC50
was determined by Trypan blue dye exclusion test according to the method of
Pollard and Walker (1989), Khorshid
et al. (2005) and Khorshid and Moshref (2006).
Other part were treated with concentration equal to IC50 and the
treatment was continued for (24, 48 and 72 h). Third part of the cells was used
For morphological effect of the tea extract, cells of each group were fixed
in 4% formaldehyde for 5 min at room temperature after double washing with 1x
PBS each for 5 min. Cell was then stained with Coomassie blue for 5-10 min.
Followed by repeated washing with tap water (Khorshid and
Moshref, 2006; Khorshid et al., 2005) assays
were performed in duplicate.
Data in the present investigation were given as Mean±SD. The results
were analyzed statistically using One-way Analysis of Variance (ANOVA) and Two-way
ANOVA and Statistical Package for Social Science (SPSS 16.0 for window), at
p-value<0.05 indicating statistical significant difference.
RESULTS AND DISCUSSION
The effect of GTEs at different concentrations was examined on the number of
viable cells of Human Ovarian Cancer Cells (HOCC) by the Trypan blue method
(Pollard and Walker, 1989; Khorshid
and Moshref, 2006; Khorshid et al., 2005).
The results were compared with control (non-treated HOCC), where the cancer
cells were incubated in ordinary media.
Cytotoxic Assays ( IC50 Estimation)
Cytotoxic activity was defined as the number of cells in tea treated group
compared with untreated cells using Trypan blue dye exclusion test revealed
that, the treated groups of HOCC cells incubated in GTEs media in different
concentration exhibited conspicuous and significant decrease in the number of
the cells by several concentrations.
cytotoxic activity of green tea extract on the proliferation of HOCC incubated
for 24 h
represents as (Mean±SD). *Significant at p<0.05
Represent HOCC incubated in ordinary and GTEs medium for 24 h. (x4) Scale
par 50 μm showing: (a) HOCC incubated in ordinary medium as control
showed the crowded and contact between cancer cells. (b-e) HOCC incubated
in 20, 50, 100 and 250 μg of GTEs, respectively, showing reduction
in the number of the cancer cell
At the control (0 concentrations of GTEs) the mean number of the cancer cells
was (1.7x105) and, by incubated in different concentrations of GTEs
(20, 50, 100 and 250% μg mL-1 for 24 h) the mean number of the
cancer cells was (1.1600, 1.0450, 0.6400 and 0.5900x105) as shown
in the Table 1. Whereas, statistical analysis revealed that
the number of treated cells significantly reduced. Table 1
showed that the ideal concentration of GTEs affect the proliferation of cancer
cells was 100 μg mL-1.
On long term exposure of HOCC to green tea extract showed there were about (0.61500, 0.56000, 0.43500 x105 cells) decrease in the number of cells in comparison with control after (24, 48 and 72) h incubation, respectively (Fig. 4).
The images of the fixed and stained HOCC with Coomassie stain revealed that
the cancerous cells appear very crowded in control group, large in its size,
contain no vacuoles, clear distinguished, its nuclei appear very large and pleomorphism
(Fig. 1a-e, 2a and 3a).
Represent HOCC incubated in ordinary and GTEs medium for 24 h (x20), Scale
par 200 μm showing: (a) HOCC incubated in ordinary as control showing
pleomorphism nuclei (n) and large number of cells. (b, c, d and e) Represent
HOCC incubated in 20, 50, 100 and 250 μg GTEs showing chromatin condensation
(C) loose cell-cell contacts (red arrows) shrinkage of cells (green arrows)
signs of apoptosis
Whereas, in the tea treated groups, the cells show a degree of injury and discomfiture.
Moreover, the cells shrinked and started to degenerated at various concentrations
(20, 50, 100 and 250 μg mL-1) up to 24 h (Fig.
1a-e, 2b-e and 3b-e).
This indicates that the examined substrate attacks cancer cells and may causing
loss of cell-cell contacts (Fig. 2b-e and
3b-e), cells shrinkage, blabbing and specific
chromatin condensation (Fig. 2, 3b-e),
which leads to cell death by apoptosis not by necrosis.
The present study proved that the green tea extract inhibited the proliferation rate of human ovarian cancer cells in vitro in a dose dependent manner.
Chemoprevention therapy by the use of green tea or green tea polyphenols has
offered new approaches to block tumor growth and progression. Green tea extract
and especially its major polyphenolic component EGCG, is capable of inhibiting
the growth of a variety of human cancer cells, via induction of apoptosis
in vitro (Masuda et al., 2001, 2003;
Huh et al., 2004; Chan et
al., 2006), our work proved this approach.
Chang et al. (2003) reported that, the role of tea in protection against cancer has been supported by ample evidence from studies in cell culture and animal models.
However, results of epidemiological studies on tea and cancer have been inconsistent,
some of which associated with reduced risk of cancer, whereas others found that
tea lacks protective activity against certain human cancers.
Represent HOCC incubated in ordinary and GTEs medium for 24 (x40), Scale
par 500 μm showing: (a) HOCC incubated in ordinary as control showing
pleomorphism nuclei (n) and large number of cells. (b, c, d and e) Represent
HOCC incubated in 20,50, 100 and 250 μg GTEs showing chromatin condensation
(C), loose cell-cell contacts (red arrows) shrinkage of cells (green arrows)
signs of apoptosis
the difference of proliferation between HOCC cells incubated in IC50
of GTEs and HOCC cells incubated in ordinary medium. Values represents
as (Mean±SD). *Significant at p<0.05
Aucamp et al. (1997) also, has agreeing results
with ours, in cultured human leukemia cells, where EGCG from green tea and theaflavins
gallates from black tea inhibited xanthine oxidase activity.
Frei and Higdon (2003) investigated that, a great deal
of research has evaluated the antioxidant and biological activities of green
and black tea as well as their individual catechins and polyphenols in vitro.
Also, Thangapazham et al. (2007) said that, our
investigation results showing the effect of GTP and EGCG treatment in vivo
in human breast cancer MDA-MB321cells xenograft in nude mice as well as in
vitro cell culture models inhibits proliferation and induce apoptosis of
MDA-MB231 cells in vitro and in vivo, these data sustain our contention
that GTEs have anti-tumor properties.
The anticancer effect of green tea may relate to the phase II detoxification
enzymes that promote the excretion of potentially toxic or carcinogenic chemicals.
Most phase II enzymes contain cis-acting regulatory elements called Antioxidant
Response Elements (ARE). Glutathione S-Transferases (GST) are a family of phase
II enzymes that catalyze the conjugation of glutathione to electrophiles, thereby
reducing their ability to react with and damage nucleic acids and proteins (Parkinson,
1996). Green tea polyphenol extract (Yu et al.,
1997) as well as individual green tea catechins (Chen
et al., 2000) have been found to increase ARE-mediated reporter gene
activity in transected HepG2 cells. Feeding rats green tea leaves significantly
increased liver Glutathion S-Tranferases (GST) activity (Lin
et al., 1998) and providing mice with green tea polyphenols in their
drinking water also significantly increased GST activity in the liver and small
intestine (Khan et al., 1992) thus, may explained
our results in this project.
Epidemiologic studies on tea and ovarian cancer have generated inconsistent
results as a recent research reported a protective effect of green tea on ovarian
cancer risk (Zhang et al., 2002) and survival
rates (Zhang et al., 2004) among Chinese women.
In terms of cancer chemoprevention, tea polyphenols can inhibit several of
these transcription factors, such as activator protein-1 and nuclear factor-êB,
thereby blocking mitotic signaling pathways (Lin, 2002).
Lu et al. (2000) showed that green tea and caffeine
enhance UV-induced apoptosis and P53 p21 wafl-positive skin cells in SK-H1 mice.
Administration of green tea as drinking water induces apoptosis in lung adenomas
that developed in A/J mice after exposure to NNK and prostate cancer cell in
TRAMP mice (Gupta et al., 2001; Liao
et al., 2001).
August et al. (1999) showed that green tea causes
a significant reduction in prostaglandin E synthesis in rectal mucosa of human
volunteers suggesting the active compounds in tea inhibit the cycloxygenases.
The P53 (tumor suppression gene) plays a pivotal role in protecting cells from
various stresses including DNA damage, oncogene stimulation and change in cellular
redoxe potential (Vogelstein et al., 2000). It
regulates cell cycle arrest and apoptosis in response to certain stresses in
its role as tumor suppressor. The EGCG and theaflavins digallate are inhibitors
of cell growth and both agents induce a significant antiproliferative and proapoptic
effect on various cell types including human oral epithelial cells (Ahmad
et al., 1997, 2000; Liang
et al., 1999; Katdare et al., 1998;
Yang et al., 1998, 2000).
Tea polyphenoles increase P53 levels and induction of apoptosis by stresses
such as UVB1, whicsh are known to activate P53, mediated apoptosis (Lu
et al., 2000; Ahmad et al., 1997;
Yang et al., 1998).
Green tea extract and especially its major polyphenolic component EGCG, are
capable of inhibiting the growth of a variety of human cancer cells via induction
of apoptosis in vitro (Masuda et al., 2001,
2003; Huh et al., 2004;
Chan et al., 2006).
Kennedy et al. (1999) found that GTEs exhibits
cytotoxicity to Ehrlich ascietes tumor cells in the cellular thiol-dependent
way. The GTEs caused a significant reduction in the viability of the tumor cells
and further analysis revealed that this effect was attributable to one of GTEs
EGC caused significant reductions in both non-protein sulfhydrals (GSH) and
protein sulfhydral (PSH) levels.
The effect of EGC on the reductions in cellular thiol levels was found to be
both dose and time dependent. The EGCG also had a slight effect on cell viability
but like the other polyphenols, which had no effect on cell viability, did not
have any effect on GSH or PSH reductions. The unique effect of one catechin
over other structurally related catechins is not new in tea polyphenol research.
Several studies have reported differential inhibitory or enhancement effect
of structurally related catechins. Most recently Watanable
et al. (1998) found an IC50 value of acetyle CoA carboxylase
inhibitory activity of EGCG and ECG to be ~ 300 μg mL-1, whereas,
(+) -catechins, EC, EGC and gallic acid had no effect. The inhibitory activity
was attributable to the presences of the 3-0-gallate group of the catechin structure
Green tea polyphenols have been shown to be efficient antioxidants and the concept
that tea components may inhibit carcinogenesis through antioxidative activities
is supported by many findings. The H2 formation induced by 120-tetradecanoylphorbol
13-acetate in HeLA cells was inhibited by EGCH and the oxidation of lard as
evaluated by the active oxygen method was suppressed as well (Matsuzaki
and Hara, 1985; Bhimani and Frenkel, 1991). Activation
of protein tyrosine kinase activity by EGC via decreased cell viability (Kennedy
et al., 1998). Green tea and its individual epicatechin derivatives
inhibited skin tumor promoter-mediated induction of epidermal ornithine decarboxylase
in SENCAR mice.
In conclusion, green tea extract has antiproliferative activity against the growth of HOCC which might be considered in clinical situation.
Authors gratefully acknowledge King Abdulaziz City for Science and Technology for their financial support, Prof. H. Abdul-jabbar professor of Gynecology, KAUH, Jeddah for kindly providing the ovarian tumor, Prof. Abdel-moniem Osman professor of pharmacology for courtesy revising this study and Tissue Culture Unit in King Fahd Medical Research Center especially Mrs. Najwa T. Heffny and Miss. Jehan Al-Amri for their excellent technical assistance. This work was funded by King Abdul-Aziz City for Science and Technology (Saudi Arabia).
Ahmad, N., D.K. Feyes, A.L. Nieminen, R. Agarwal and H. Mukhtar, 1997.
Green tea constituent epigallocatechin-3-gallate and induction of apoptosis and cell cycle arrest in human carcinoma cells. J. Natl. Cancer Inst., 89: 1881-1886.CrossRef | PubMed | Direct Link |
Ahmad, N., P. Cheng and H. Mukhtar, 2000.
Cell cycle dysregulation by green tea polyphenol epigallocatechin-3-gallate. Biochem. Biophys. Res. Commun., 275: 328-334.PubMed |
Aucamp, J., A. Gaspar, Y. Hara and Z. Apostolides, 1997.
Inhibition of xanthine oxidase by catechins from tea (Camellia sinensis
). Anticancer Res., 17: 4381-4385.Direct Link |
August, D.A., J. Landau, D. Caputo, J. Hong, M.J. Lee and C.S. Yang, 1999.
Ingestion of green tea rapidly decreases prostaglandin E2 levels in rectal mucosa in humans. Cancer Epidemiol. Biomarkers Prev., 8: 709-713.PubMed |
Baliga, M.S., S. Meleth and S.K. Katiyar, 2005.
Growth inhibitory and metastatic effect of green tea polyphenols on metastasis-specific mouse mammary carcinoma 4T1 cells in vitro
and in vivo
systems. Clin. Cancer Res., 11: 1918-1927.Direct Link |
Bhimani, R. and K. Frenkel, 1991.
Suppression of H 2
production and oxidative DNA damage in HeLa cells by epigallocagallate (EGCG). Proc. Am. Assoc. Cancer Res., 32: 126-126.
Chan, M.M., K.J. Soprano, K. Weinstein and D. Fong, 2006.
Epigallocatechin-3-gallate delivers hydrogen peroxide to induce death of ovarian cancer cells and enhances their cisplatin susceptibility. J. Cell Physiol., 207: 389-396.PubMed |
Chen, C., R. Yu, E.D. Owuor and A.N. Kong, 2000.
Activation of-antioxidant-response element (ARE), mitogen-activated protein.kinases (MAPKs) and caspases by major green tea polyphenol components during cell survival and death. Arch. Pharm. Res., 23: 605-612.PubMed |
Chung, F.L., J. Schwartz, C.R. Herzog and Y.M. Yang, 2003.
Tea and cancer prevention: Studies in animals and humans. J. Nutr., 133: 3268S-3274S.PubMed | Direct Link |
Crespy, V. and G. Williamson, 2004.
A review of the health effects of green tea catechins in in vivo
animal models. J. Nutr., 134: 3431S-3440S.PubMed | Direct Link |
Dunfield, L.D., T.G. Shepherd and M.W. Nachtigal, 2002.
Primary culture and mRNA analysis of human ovarian cells. Biol. Proced., 4: 55-61.CrossRef |
Frei, B. and J.V. Higdon, 2003.
Antioxidant activity of tea polyphenols in vivo
: Evidence from animal studies. J. Nutr., 133: 3275S-3284S.PubMed | Direct Link |
Fujiki, H. and M. Suganuma, 2002.
Green tea and cancer prevention. Proc. Japan Acad. Ser. B, 78: 263-270.
Graham, H.N., 1992.
Green tea composition and polyphenol chemistry. Prev. Med., 21: 334-350.PubMed | Direct Link |
Gupta, S., K. Hastak, N. Ahmad, J.S. Lewin and H. Mukhtar, 2001.
Inhibition of prostate carcinogenesis in TRAMP mice by oral infusion of green tea polyphenols. Proc. Nat. Acad. Sci. USA., 8: 10350-10355.PubMed |
Hakim, I.A., R.B. Harris and U.M. Weisgerber, 2000.
Tea intake and squamous cell carcinoma of the skin: Influence of type of tea beverages. Cancer Epidemiol. Biomarkers Prev., 9: 727-731.PubMed |
Hanachi, P., S.H. Kua, R. Asmah, G. Motalleb and O. Fauziah, 2006.
Cytotoxic effect of Berberis vulgaris
fruit extract on the proliferation of human liver cancer cell line (HepG2) and its antioxidant properties. Int. J. Cancer Res., 2: 1-9.CrossRef | Direct Link |
Huh, S.W., S.M. Bae, Y.W. Kim, J.M. Lee and S. Eun et al
Anticancer effects of (-)-epigallocatechin-3- gallate on ovarian carcinoma cell lines. Gynecol. Oncol., 94: 760-768.CrossRef |
Inoue, M., K. Tajima, M. Mizutani, H. Iwata and T. Iwase et al
Regular consumption of green tea and the risk of breast cancer recurrence: follow-up study from the Hospital-based Epidemiologic Research Program at Aichi Cancer Center (HERPACC) Japan. Cancer Lett., 167: 175-182.Direct Link |
Ioannides, C. and V. Yoxall, 2003.
Antimutagenic activity of tea: Role of polyphenols. Curr. Opin. Clin. Nutr. Metab. Care., 6: 649-656.PubMed |
Khan, S.G., S.K. Katiyar, R. Agarwal and H. Mukhata, 1992.
Enhancement of antioxidant and phase II enzymes by oral feeding of green tea polyphenols in drinking water to SKH-1 hairless mice: Possible role in cancer prevention. Cancer Res., 52: 4050-4052.Direct Link |
Katdare, M., M.P. Osborne and N.T. Telang, 1998.
Inhibition of aberrant proliferation and induction of apoptosis in pre-neoplastic human mammary epithelial cells by natural phytochemicals Oncol. Rep., 5: 311-315.PubMed | Direct Link |
Kennedy, D.O., S. Nishimura, T. Hasuma, Y. Yano, S. Otani and I. Matsuiyuasa, 1998.
Involvement of protein tyrosine phosphrylation in the effect of green tea polyphenoles on Ehrlich ascietes tumor cells in vitro
. Chem. Biol. Interact., 110: 159-172.
Kennedy, D.O., M. Matsumoto, A. Kojima and I. Matsui, 1999.
Cellular thiols status and cell death in the effect of green tea polyphenol Ehrich ascites tumor cells. Chemico. Biol. Interact., 122: 59-71.PubMed |
Khorshid, F.A., S.S. Mushref and N.T. Heffny, 2005.
An ideal selective anti-cancer agent in vitro
I-tissue culture study of human lung cancer cells A549. J. King Abdulaziz Univ.-Med. Sci., 12: 3-19.CrossRef | Direct Link |
Khorshid, F.A. and S.S. Moshref, 2006. In vitro
anticancer agent, I-tissue culture study of human lung cancer cells A549 II-tissue culture study of mice leukemia cells L1210. Int. J. Cancer Res., 2: 330-344.Direct Link |
Lee, A.H., M.L. Fraser and C.W. Binns, 2005.
Possible role for green tea in ovarian cancer prevention. Future Oncol., 1: 771-777.CrossRef |
Liang, Y.C., S.Y.L. Shiau, C.F. Chen and J.K. Lin, 1999.
Inhibition of cyclin dependent kinases 2 and 4 activities as well as induction of cdk inhibitors p21
during growth arrest of human breast carcinoma cells by EGCG. J. Cell Biochem., 75: 1-12.PubMed |
Liao, J., G.Y. Yang, E.S. Park, X. Meng and K.K.L. Ho et al
Inhibition of angiogenesis and induction of cell apoptosis during lung carcinogenesis by green tea in A/J mice. Proc. Am. Assn. Cancer Res., 42: 575-575.
Lin, Y.L., C.Y. Cheng, Y.P. Lin, Y.W. Lau, I.M. Juan and J.K. Lin, 1998.
Hypolipidemic effect of green tea leaves through induction of antioxidant and phase II enzymes including superoxide dismutase, catalase,and glutathione-S-transferase in rats. J. Agric. Food Chem., 46: 1893-1899.CrossRef | Direct Link |
Lin, J.K., 2002.
Cancer chemoprevention by tea polyphenols through modulating signal transduction pathways. Arch. Pharm. Res., 25: 561-571.Direct Link |
Lu, Y.P., Y.R. Lou, X.H. Li, J.G. Xie, D. Brash, M.T. Huang and A.H. Conney, 2000.
Stimulatory effect of oral administration of green tea or caffeine on ultraviolet light-induced increases in epidermal wildtype, p53, p21(WAF1/CIP1) and apoptotic sunburn cells in SKH-1 mice. Cancer Res., 60: 4785-4791.PubMed |
Masuda, M., M. Suzui and I.B. Weinstein, 2001.
Effects of epigallocatechin-3-gallate on growth, epidermal growth factor receptor signaling pathways, gene expression, an chemosensitivity in human head and neck squamous cell carcinoma cell lines. Clin. Cancer Res., 7: 4220-4229.PubMed |
Masuda, M., M. Suzui, J.T. Lim and I.B. Weinstein, 2003.
Epigallocatechin-3-gallate inhibits activation of HER-2/neu and downstream signaling pathways in human head and neck and breast carcinoma cells. Clin. Cancer Res., 9: 3486-3491.PubMed |
Matsumoto, H. and T. Yamana, 2000.
Green tea and cancer prevention. J. Women Cancer, 2: 152-158.
Matsuzaki, T. and Y. Hara, 1985.
Antioxidative activity of tea leaf catechins. J. Agric. Chem. Soc. Jpn., 59: 129-134.CrossRef | Direct Link |
McKay, D.L. and J.B. Blumberg, 2002.
The role of tea in human health: An update. J. Am. Coll. Nutr., 21: 1-13.PubMed |
Nagano, J., S. Kono, D.L. Preston and K. Mabuchi, 2001.
A prospective study of green tea consumption and cancer incidence, Hiroshima and Nagasaki (Japan). Cancer Causes Control, 12: 501-508.PubMed |
Nakachi, K., K. Suemasu, K. Suga, T. Takeo, K. Imai and Y. Higashi, 1998.
Influence of drinking green tea on breast cancer malignancy among Japanese patients. Jpn. J. Cancer Res., 89: 254-261.Direct Link |
Nicolas, J.M., M.N. Clifford and C. Ionnides, 1999.
Consumption of tea modulates the urinary excretion of mutagens in rat treated with IQ Role of caffeine. Mut. Res., 441: 191-203.PubMed |
Nihal, M., N. Ahmad, H. Mukhtar and G.S. Wood, 2005.
Anti-proliferative and proapoptotic effects of (-)-epigallocatechin-3-gallate on human melanoma: Possible implications for the chemoprevention of melanoma. Int. J. Cancer, 114: 513-521.PubMed |
Parkinson, A., 1996.
Biotransformation of Xenobiotics. In: Casarett and Doull's Toxicology, The Basic Science of Poisons, Klaassen, C.D. (Ed.). McGraw-Hill, New York, pp: 113-186Direct Link |
Parkin, D.M., 2001.
Global cancer statistics in the year 2000. Lancet, 2: 533-543.PubMed | Direct Link |
Pollard, J.W. and J.M. Walker, 1989.
Methods in Molecular Biology, Animal Cell Culture. Vol. 5, Humana Press, Clifton, New Jersey, pp: 2-10
Sasazuki, S., M. Inoue, T. Hanaoka, S. Yamamoto, T. Sobue and S. Tsugane, 2004.
Green tea consumption and subsequent risk of gastric cancer by subsite: The JPHC Study. Cancer Causes Control, 15: 483-491.Direct Link |
Setiawan, V.W., Z.F. Zhang, G.P. Yu, Q.Y. Lu and Y.L. Li et al
Protective effect of green tea on the risks of chronic gastritis and stomach cancer. Int. J. Cancer, 92: 600-604.CrossRef | PubMed | Direct Link |
Su, L.J. and L. Arab, 2002.
Tea consumption and the reduced risk of colon cancer-results from a national prospective cohort study. Public Health Nutr., 5: 419-426.Direct Link |
Suganuma, M., S. Okabe, N. Sueoka, E. Sueoka and S. Matsuyama et al
Green tea and cancer chemoprevention. Mutat. Res., 428: 339-344.PubMed |
Sun, C.L., J.M. Yuan, M.J. Lee, C.S. Yang, Y.T. Gao, R.K. Ross and M.C. Yu, 2002.
Urinary tea polyphenols in relation to gastric and oesophageal cancers: A prospective study of men in Shanghai, China. Carcinogenesis, 23: 1497-1503.Direct Link |
Thangapazham, R.L., A.K. Singh, A. Sharma, J. Warren, J.P. Gaddipati and R.K. Maheshwari, 2007.
Green tea polyphenols and its constituent epigallocatechin gallate inhibits proliferation of human breast cancer cells in vitro
and in vivo
. Cancer Lett., 245: 232-241.PubMed |
Vogelstein, B., D. Lane and A.J. Levine, 2000.
Surfing the p53 network. Nature, 408: 307-310.CrossRef | PubMed | Direct Link |
Watanable, J., J. Kawabata and R. Niki, 1998.
Isolation and identification of acetyl-CoA carboxylase inhibitors from green tea (Camellia sinensis
). Biosci. Biotechnol. Biochem., 62: 532-534.PubMed |
The world health report 2004: Changing history. World Health Organization, Geneva. http://www.who.int/whr/2004/en/.
Wu, A.H., M.C. Yu, C.C. Tseng, J. Hankin and M.C. Pike, 2003.
Green tea and risk of breast cancer in Asian Americans. Int. J. Cancer, 106: 574-579.CrossRef | PubMed | Direct Link |
Yang, G., J. Liao, K. Kim, E. Yurkow and C.S. Yang, 1998.
Inhibition of growth and induction of apoptosis in human cancer cell lines by tea polyphenols. Carcinogenesis, 19: 611-616.PubMed | Direct Link |
Yang, G.Y., J. Liao, C. Li, J. Chung, E.J. Yurkow, C.T. Ho and C.S. Yang, 2000.
Effect of black and green tea polyphenols on c-jun phosphorylation and H2
production in transformed and non- tranformed human bronchial cell lines: Possible mechanisms of cell growth inhibition and apoptosis induction. Carcinogenesis, 21: 2035-2039.PubMed |
Yang, C.S., P. Maliakal and X. Meng, 2002.
Inhibition of carcinogenesis by tea. Ann. Rev. Pharmacol. Toxicol., 42: 25-54.CrossRef | Direct Link |
Yihai, C. and C. Renhai, 1999.
Can green tea minimize cancer risk?. Nature, 398: 381-382.
Yu, R., J.J. Jiao, J.L. Duh, K. Gudehithlu, T.H. Tan and A.N. Kong, 1997.
Activation of mitogen-activated protein kinases by green tea polyphenols: Potential signaling pathways in the regulation of antioxidant-responsive element-mediated phase II enzyme gene expression. Carcinogenesis, 18: 451-456.PubMed |
Zhang, M., C.W. Binns and A.H. Lee, 2002.
Tea consumption and ovarian cancer risk: A case-control study in China. Cancer Epidemiol. Biomarkers Prev., 11: 713-718.PubMed | Direct Link |
Zhang, M., A.H. Lee, C.W. Binns and X. Xie, 2004.
Green tea consumption enhances survival of epithelial ovarian cancer. Int. J. Cancer, 112: 465-469.PubMed |