Inhibitory effects of tea extracts and (-)-epigallocatechin gallate on DNA synthesis and proliferation of hepatoma and erythroleukemia cells

Metabolic improvements of novel microbial fermentation on black tea by Eurotium cristatum

Due to its traditional fermentation, there are obvious limits on the quality improvements in black tea. However, microbial fermentation can provide an abundance of metabolites and improve the flavor of tea. The "golden flower" fungi are widely used in the microbial fermentation of tea and has unique uses in healthcare. To further explore the improvements in black tea quality achieved via microbial fermentation, we used widely targeted metabolomics and metagenomics analyses to investigate the changes in and effects of metabolites and other microorganisms during the interaction between the "golden flower" fungi and black tea. Five key flavor metabolites were detected, the levels of catechin, epigallocatechin gallate, (-)-epicatechin gallate were decreased by different degrees after the inoculation of the "golden flower" fungus, whereas the levels of caffeine and (+)-gallocatechin increased. Botryosphaeriaceae, Botryosphaeriales, Dothideomycetes, Aspergillaceae, Trichocomaceae, and Lecanoromycetes play a positive role in the black tea fermentation process after inoculation with the "golden flower" fungi. D-Ribose can prevent hypoxia-induced apoptosis in cardiac cells, and it shows a strong correlation with Botryosphaeriaceae and Botryosphaeriales. The interaction between microorganisms and metabolites is manifested in tryptophan metabolism, starch and sucrose metabolism, and amino sugar and nucleotide sugar metabolism. In conclusion, the changes in metabolites observed during the fermentation of black tea by "golden flower" fungi are beneficial to human health. This conclusion extends the knowledge of the interaction between the "golden flower" fungi and black tea, and it provides important information for improving the quality of black tea.

Epigallocatechin-3-gallate enhances differentiation of acute promyelocytic leukemia cells via inhibition of PML-RARα and HDAC1

The use of all-trans retinoic acid (ATRA) has dramatically improved the treatment and survival rate of patients with acute promyelocytic leukemia (APL). However, toxicity and resistance to this drug are major problems in the treatment of APL with ATRA. Earlier studies have suggested that the green tea polyphenol epigallocatechin gallate (EGCG) induces cell death in hematopoietic neoplasms without adversely affecting normal cells. In the present study, the potential therapeutic effect of EGCG in APL and the underlying molecular mechanisms were investigated. EGCG (100 μM) significantly inhibited proliferation and induced apoptosis in HL-60 and NB4 cells. This effect was associated with decreased expressions of multidrug resistance proteins ABCB1, and ABCC1, whereas the expressions of pro-apoptotic genes CASP3, CASP8, p21, and Bax/Bcl-2 ratio were significantly increased. EGCG, at 25 μM concentration, induced differentiation of leukemic cells towards granulocytic pattern in a similar manner to that observed for ATRA (1 μM). Furthermore, EGCG suppressed the expression of clinical marker PML/RARα in NB4 cells and reduced the expression of HDAC1 in leukemic cells. In conclusion, the results suggested that EGCG can be considered as a potential treatment for APL.

Small-Molecule and Peptide Inhibitors of the Pro-Survival Protein Mcl-1

The ability of protein-protein interactions to regulate cellular processes in both beneficial and detrimental ways has made them obvious drug targets. The Bcl-2 family of proteins undergo a series of protein-protein interactions which regulate the intrinsic cell-death pathway. The pro-survival members of the Bcl-2 family, including Bcl-2, Bcl-xL , and Mcl-1, are commonly overexpressed in a number of human cancers. Effective modulators of members of the Bcl-2 family have been developed and are undergoing clinical trials, but the efficient modulation of Mcl-1 is still not represented in the clinic. In addition, Mcl-1 is a major cause of resistance to radio- and chemotherapies, including inhibitors that target other Bcl-2 family members. Subsequently, the inhibition of Mcl-1 has become of significant interest to the scientific community. This review covers the progress made to date in modulating the activity of Mcl-1, by both stapled peptides and small molecules. The development of peptides as drug candidates, and the advancement of experimental and computational techniques used to discover small molecules are also highlighted.

A thought on the biological activities of black tea

Tea is the most widely used ancient beverage in the world and black tea possesses many biological effects on the organisms. It acts as an effective antioxidant because of its free radical-scavenging and metal-chelating ability. Due to this, it is active against inflammation, clastogenesis, and several types of cancer. Tea reduces DNA damage and mutagenesis due to oxidative stress or the presence of pro-mutagens through antioxidant function, blocking activation pathways of mutagens, suppressing transcription of enzymes involved etc. Inhibition of low-density lipoprotein (LDL) peroxidation, suppression of fatty acid synthase etc., suggest that tea may have a role in preventing cardiovascular diseases. Some epidemiological studies support the protective role of black tea against cardiovascular diseases but some do not. Besides, black tea has beneficial effects on the gastrointestinal tract; it affects motility, absorption, microflora etc., by influencing the hormonal balance and antioxidant function black tea improves bone mineral density. It is also antiviral due to its enzyme-inhibiting and receptor-blocking properties. Although its role in cancers of the gastrointestinal tract, liver, and prostate is confirmed, its effect against urinary tract cancer is uncertain and further studies are required. Apart from these, excess consumption may lead to the formation of a stained pellicle layer on teeth, which is difficult to eliminate, inhibits trypsin, influences mineral absorption, causes convulsions etc. Excess caffeine intake may have adverse effects on selected organs as reported in studies on some organisms. These reports indicate that there is a wide scope of further research for the efficient use of black tea active conserves/isolates to reap health benefits.

Phytochemicals as potential chemopreventive and chemotherapeutic agents in hepatocarcinogenesis

Hepatocellular carcinoma (HCC) is the fifth commonest malignancy worldwide and the incidence is rising. Surgery, including transplantation resection, is currently the most effective treatment for HCC; however, recurrence rates are high and long-term survival is poor. Identifying novel chemopreventive and chemotherapeutic agents and targeting them to patients at high risk of developing HCC or following curative treatment may go some way towards improving prognosis. This review examines current knowledge regarding the chemopreventive and chemotherapeutic potential of phytochemicals in heptocarcinogenesis. Both in-vitro and animal studies demonstrate that several phytochemicals, including curcumin, resveratrol, green tea catechins, oltipraz and silibinin, possess promising chemopreventive and chemotherapeutic properties. Despite this, very few clinical trials have been performed. Problems regarding validation of biomarkers, agent delivery, side effects and patient selection are barriers that need to be overcome to determine the potential of such agents in clinical practice.

Effects of low dose quercetin: cancer cell-specific inhibition of cell cycle progression

Quercetin is a flavonoid present in many vegetables, fruits, and beverages. Due to its anti-oxidant, anti-tumor, and anti-inflammatory activity, quercetin has been studied extensively as a chemoprevention agent in several cancer models. Since most of these studies used higher doses of quercetin than clinically achievable, we focused on the effectiveness of physiologically relevant doses of quercetin. A low dose of quercetin exerted cancer cell-specific inhibition of proliferation and this inhibition resulted from cell cycle arrest at the G(1) phase. Quercetin induced p21 CDK inhibitor with a concomitant decrease of phosphorylation of pRb, which inhibits the G(1)/S cell cycle progression by trapping E2F1. A low dose of quercetin induced mild DNA damage and Chk2 activation, which is the main regulator of p21 expression by quercetin. In addition, quercetin down-regulated the cyclin B1 and CDK1, essential components of G(2)/M cell cycle progression. Inhibition of the recruitment of key transcription factor NF-Y to cyclin B1 gene promoter by quercetin led to transcriptional inhibition. This study proved that the chemo-preventive efficacy of a physiologically relevant dose of quercetin can be achievable through the inhibition of cell cycle progression.

Inhibition of mammalian thioredoxin reductase by black tea and its constituents: implications for anticancer actions

Black tea is recently reported to have anti-carcinogenic effects through pro-oxidant property, but the underlying mechanisms remain unclear. Mammalian cytosolic thioredoxin reductase (TrxR1) is well -known for its anti-oxidation activity. In this study, we found that black tea extract (BTE) and theaflavins (TFs), the major black tea polyphenols, inhibited the purified TrxR1 with IC(50) 44 microg/ml and 21+/-1 microg/ml, respectively. Kinetics of TFs exhibited a mixed type of competitive and non-competitive inhibition, with K(is) 4+/-1 microg/ml and K(ii) 26+/-5 microg/ml against coenzyme NADPH, and with K(is) 12+/-3 microg/ml and K(ii) 27+/-5 microg/ml against substrate DTNB. In addition, TFs inhibited TrxR1 in a time-dependent manner. In an equilibrium step, a reversible TrxR1-TFs complex (E*I) forms, which is followed by a slow irreversible first-order inactivation step. Rate constant of the inactivation was 0.7 min(-1), and dissociation constant of E*I was 51.9 microg/ml. Treatment of NADPH-reduced TrxR1 with TFs decreased 5-(Iodoacetamido) fluorescein incorporation, a fluorescent thiol-reactive reagent, suggesting that Sec/Cys residue(s) in the active site may be involved in the binding of TFs. The inhibitory capacity of TFs depends on their structure. Among the TFs tested, gallated forms had strong inhibitory effects. The interactions between TFs and TrxR1 were investigated by molecular docking, which revealed important features of the binding mechanism of theaflavins. An inhibitory effect of BTE on viability of HeLa cells was observed with IC(50) 29 microg/ml. At 33 microg/ml of BTE, TrxR1 activity in HeLa cells was decreased by 73% at 22 h after BTE treatment. TFs inhibited cell viability with IC(50) 10+/-4 microg/ml for HeLa cells and with IC(50) 20+/-5 microg/ml for EAhy926 cells. The cell susceptibility to TFs was inversely correlated to cellular levels of TrxR1. The inhibitory actions of TFs on TrxR1 may be an important mechanism of their anti-cancer properties.

Designed polar cosolvent-modified supercritical CO2 removing caffeine from and retaining catechins in green tea powder using response surface methodology

This study examines cosolvent-modified supercritical carbon dioxide (SC-CO2) to remove caffeine from and to retain catechins in green tea powder. The response surface method was adopted to determine the optimal operation conditions in terms of the extraction efficiencies and concentration factors of caffeine and catechins during the extractions. When SC-CO2 was used at 333 K and 300 bar, 91.5% of the caffeine was removed and 80.8% of catechins were retained in the tea: 3600 g of carbon dioxide was used in the extraction of 4 g of tea soaked with 1 g of water. Under the same extraction conditions, 10 g of water was added to <800 g of carbon dioxide in an extraction that completely removed caffeine (that is, the caffeine extraction efficiency was 100%). The optimal result as predicted by three-factor response surface methodology and supported by experimental data was that in 1.5 h of extraction, 640 g of carbon dioxide at 323 K and 275 bar with the addition of 6 g of water extracted 71.9% of the caffeine while leaving 67.8% of the catechins in 8 g of tea. Experimental data indicated that supercritical carbon dioxide decaffeination increased the concentrations of caffeine in the SC-CO2 extracts at 353 K.

Myeloperoxidase Is a Key Regulator of Oxidative Stress–Mediated Apoptosis in Myeloid Leukemic Cells

PURPOSE

We reported previously that reactive oxygen species (ROS) are key mediators of apoptosis induced by a polyphenol, (-)-epigallocatechin-3-gallate (EGCG), in myeloid leukemic cells. This study aimed to further examine the mechanism of ROS-mediated apoptosis induced by EGCG and its relationship to the heme enzyme myeloperoxidase (MPO).

EXPERIMENTAL DESIGN

We established stably transfected K562 cells expressing wild-type and mutant MPO. Then, sensitivity against EGCG and other ROS-inducing agent was examined and further investigated the detailed molecular mechanism of ROS-inducing apoptosis in MPO-positive leukemic cells.

RESULTS

EGCG rapidly induced apoptosis in MPO-positive leukemia cells. Preincubation of myeloid leukemic cells with the MPO-specific inhibitor, 4-aminobenzoic acid hydrazide, and the heme biosynthesis inhibitor, succinylacetone, resulted in inhibition of the intracellular MPO activity, ROS production, and induction of apoptosis following addition of EGCG. Overexpression of MPO sensitized EGCG-resistant K562 cells to apoptosis induced by EGCG. In contrast, an enzymatically inactive MPO mutant-expressing K562 cell could not respond to EGCG, suggesting that MPO is important for determining the sensitivity to EGCG-induced oxidative stress. Hypochlorous acid scavengers and the hydroxyl radical (.OH) scavenger inhibited EGCG-induced apoptosis in myeloid leukemic cells. The fluorescence intensity of both aminophenyl fluorescein- and hydroxyphenyl fluorescein-loaded myeloid leukemic cells significantly increased on stimulation with EGCG, indicating that EGCG generated highly toxic ROS in myeloid leukemic cells.

CONCLUSIONS

These results indicated that highly toxic ROS such as .OH generated via the hydrogen peroxide/MPO/halide system induce apoptosis and that ROS may be the direct mediators of EGCG-induced apoptosis in MPO-positive leukemic cells.

Isolation, purification and identification of ellagic acid derivatives, catechins, and procyanidins from the root bark of Anisophyllea dichostyla R. Br

The root bark of Anisophyllea dichostyla R. Br. is traditionally used in the Democratic Republic Congo for the treatment of several conditions such as anorexia, fatigue and intestinal infections. We have identified and quantitated several polyphenol antioxidants in the methanol extract of the root bark (120g). The polyphenol content (3.32g/kg) was predominantly ellagitannins (25%) and polyhydroxyflavan-3-ols (catechins and procyanidins, 75%) with 3'-O-methyl-3,4-methylenedioxo ellagic acid 4'-O-beta-d-glucopyranoside and (-)-epicatechin as the major species in each class. These two compounds and the following species were identified unequivocally by NMR spectroscopy: (+)-catechin, (-)-epicatechin 3-O-gallate, 3-O-methyl ellagic acid, 3,3'-di-O-methyl ellagic acid, 3'-O-methyl-3,4-methylenedioxo ellagic acid, 3'-O-methyl-3,4-methylenedioxo ellagic acid 4'-O-beta-d-glucopyranoside, and 3'-O-methyl ellagic acid 4-O-beta-d-xylopyranoside. The following additional compounds were purified by semi-preparative HPLC and tentatively identified on the basis of UV spectra, HPLC-ESI-MS and nano-ESI-MS-MS: (+)-catechin-3-O-beta-d-glucopyranoside, epicatechin-(4beta-->8)-catechin (procyanidin B(1)), epicatechin-(4beta-->8)-epicatechin (procyanidin B(2)), an (epi)catechin trimer, 3-O-methyl ellagic acid 4-O-beta-d-glucopyranoside, (-)-epicatechin 3-O-vanillate, 3,4-methylenedioxo ellagic acid 4'-O- beta-d-glucopyranoside, and 3,3'-di-O-methyl ellagic acid 4-O-beta-d-xylopyranoside. Fractionation of the raw extract by column chromatography on silicic acid yielded 10 fractions. In the hypoxanthine/xanthine oxidase antioxidant assay system, CC-9 which contained a range of polyphenols dominated by (-)-epicatechin-O-gallate proved to be the most potent antioxidant fraction (IC(50)=52 micro g/mL) in terms of ROS scavenging. In terms of XO inhibition CC-8, dominated by (epi)catechin trimer and which also contained appreciable amounts of 3'-O-methyl ellagic acid 4'-O-beta-d-xylopyranoside, as well as the catechins (+)-catechin-3-O-beta-d-glucopyranoside, epicatechin-(4beta-->8)-catechin (procyanidin B(1)), and (-)-epicatechin 3-O-gallate, proved to be the most potent (IC(50)=36 micro g/mL).

Induction of cell apoptosis in 3T3-L1 pre-adipocytes by flavonoids is associated with their antioxidant activity

Obesity is biologically characterized at the cellular level by an increase in the number and size of adipocytes differentiated from fibroblastic pre-adipocytes in adipose tissue. In this study, we focused on the relationship between the influence of flavonoids on cell population growth and their antioxidant activity. The results showed that the inhibition of flavonoids (naringenin, rutin, hesperidin, resveratrol, naringin and quercetin) on 3T3-L1 pre-adipocytes was 28.3, 8.1, 11.1, 33.2, 5.6 and 71.5%, respectively. In oxygen radical absorbance capacity (ORAC) assay, quercetin had the highest ORAC(ROO) value among the six flavonoids tested. Apoptosis assays showed that quercetin increased apoptotic cells in time- and dose-dependent manner. Treatment of cells with quercetin decreased the mitochondrial membrane potential in the courses of time and dose. The cell apoptosis/necrosis assay showed that quercetin increased the number of apoptotic cells, but not necrotic cells. Quercetin treatment of cells caused a significant time- and dose-dependent increase in the caspase-3 activity. Western analysis indicated that treatment of quercetin markedly down-regulated PARP and Bcl-2 proteins, and activated caspase-3, Bax, and Bak proteins. These results indicate that quercetin efficiently inhibits cell population growth and induction of apoptosis in 3T3-L1 pre-adipocytes.

Cytotoxic and apoptotic effects of prenylflavonoid artonin B in human acute lymphoblastic leukemia cells

AIM

To investigate the anticancer effects and molecular mechanism of artonin B on the human acute lymphoblastic leukemia CCRF-CEM cells compared with other prenylflavonoid compounds.

METHODS

The effects of four prenylflavonoids on the growth of CCRF-CEM and HaCa cells were studied by 3-(4,5)-2,5-diphenyl-tetrazolium bromide (MTT) assay. Apoptosis were detected through Hoechst 33258 staining. The effect of artonin B on the cell cycle of CCRF-CEM cells were studied by propidium iodide method. The change in mitochondrial membrane potential was detected by rohdamine 123 staining. The cytochrome c release and caspase 3 activity were checked by immunoassay kits, respectively. The expression of Bcl-2 family proteins was detected by Western blot.

RESULTS

Our data revealed that artonin B strongly induced human CCRF-CEM leukemia cell death in a dose- and time-dependent manner by MTT assay, but not on normal epithelia cells (HaCa cells). Artonin B-induced cell death was considered to be apoptotic by observing the typical apoptotic morphological change by Hoechst 33258 staining. The induction of human CCRF-CEM leukemia cancer cell death was caused by an induction of apoptosis through mitochondrial membrane potential change, cytochrome c release, sub-G1 proportion increase, downregulation of Bcl-2 expression, upregulation of Bax and Bak expression and activation of caspase 3 pathways.

CONCLUSION

These results clearly demonstrated that artonin B is able to inhibit proliferation by induction of hypoploid cells and cell apoptosis. Moreover, the anticancer effects of artonin B were related to mitochondrial pathway and caspase 3 activation in human CCRF-CEM leukemia cells.

A review of the effects and mechanisms of polyphenolics in cancer

This paper is a comprehensive review of the effects of bioactive polyphenolic compounds commonly found in many fruits and vegetables on cancer. These include the pheniolic acids, anthocyanins, catechins, stilbenes and several other flavonoids. We have attempted to compile information from most of the major studies in this area into one source. The review encompasses the occurrence and bioavailability of the polyphenolics, the in vitro and in vivo evidence for their effects on cancer, both positive and negative, and the various mechanisms by which the chemicals may exert their effects. Although most of the work done to date indicates a chemopreventative activity of these compounds, there are some studies that show cancer-inducing or no effects. There are several common mechanisms by which these chemicals exert their effects that could be conducive to additive, synergistic, or antagonistic interactions. These include effects on cellular differentiation, proliferation, and apoptosis, effects on proteins and enzymes that are involved in these processes at a molecular level, and other various effects through altered immune function and chemical metabolism.

New Therapeutic Approach for Myeloid Leukemia: Induction of Apoptosis via Modulation of Reactive Oxygen Species Production by Natural Compounds

The therapeutic approach to acute myeloid leukemia is based on chemotherapy, but the side effects of the drugs used and various complications, including infections and bleedings, are sometimes fatal. Recently, imatinib mesylate has shown remarkable efficacy and less toxicity as a molecularly targeted therapy in patients with chronic myeloid leukemia. Natural products appear to be safer than the current chemotherapeutic drugs, and we have therefore sought out new potential agents from various natural compounds with the ability to induce the apoptosis of myeloid leukemic cells.

Cellular and in vivo hepatotoxicity caused by green tea phenolic acids and catechins

Tea phenolic acids and catechins containing gallic acid moieties are most abundant in green tea, and various medical benefits have been proposed from their consumption. In the following, the cytotoxicities of these major tea phenolics toward isolated rat hepatocytes have been ranked and the mechanisms of cytotoxicity evaluated. The order of cytotoxic effectiveness found was epigallocatechin-3-gallate>propyl gallate>epicatechin-3-gallate>gallic acid, epigallocatechin>epicatechin. Using gallic acid as a model tea phenolic and comparing it with the tea catechins and gallic acid-derivative food supplements, the major cytotoxic mechanism found with hepatocytes was mitochondrial membrane potential collapse and ROS formation. Epigallocatechin-3-gallate was also the most effective at collapsing the mitochondrial membrane potential and inducing ROS formation. Liver injury was also observed in vivo when these tea phenolics were administered ip to mice, as plasma alanine aminotransferase levels were significantly increased. In contrast, GSH conjugation, methylation, metabolism by NAD(P)H:quinone oxidoreductase 1, and formation of an iron complex were important in detoxifying the gallic acid. In addition, for the first time, the GSH conjugates of gallic acid and epigallocatechin-3-gallate have been identified using mass spectrometry. These results add insight into the cytotoxic and cytoprotective mechanisms of the simple tea phenolic acids and the more complex tea catechins.

Pharmacological effects of green tea on the gastrointestinal system

Green tea is rich in polyphenolic compounds, with catechins as its major component. Studies have shown that catechins possess diverse pharmacological properties that include anti-oxidative, anti-inflammatory, anti-carcinogenic, anti-arteriosclerotic and anti-bacterial effects. In the gastrointestinal tract, green tea was found to activate intracellular antioxidants, inhibit procarcinogen formation, suppress angiogenesis and cancer cell proliferation. Studies on the preventive effect of green tea in esophageal cancer have produced inconsistent results; however, inverse relationships of tea consumption with cancers of the stomach and colon have been widely reported. Green tea is effective to prevent dental caries and reduce cholesterols and lipids absorption in the gastrointestinal tract, thus benefits subjects with cardiovascular disorders. As tea catechins are well absorbed in the gastrointestinal tract and they interact synergistically in their disease-modifying actions, thus drinking unfractionated green tea is the most simple and beneficial way to prevent gastrointestinal disorders.

Pycnogenol induces differentiation and apoptosis in human promyeloid leukemia HL-60 cells

Pycnogenol, rich of many phytochemicals of medical value, is a commercialized nutrient supplement extracted from the bark of European coastal pine. In this study, we investigated the anti-tumor effects of Pycnogenol on HL-60, U937 and K562 human leukemia cell lines. We found that Pycnogenol inhibited cell proliferation dose- and time-dependently, and the IC(50)s of Pycnogenol on HL-60, U937 and K562 cells were 150, 40 and 100 microg/ml, respectively. When HL-60 cells were incubated with low concentrations of Pycnogenol (50, 100 and 125 microg/ml) for 24 h, a prominent G0/G1 arrest was observed, followed by gradual accumulation of sub-G0/G1 nuclei. At 48 h of treatment, 50-70% of HL-60 cells differentiated, as evidenced by morphological changes, NBT reduction, induction of NSE activity, and increases of cell surface expression of CD11b. However, results from Annexin V/PI staining, DAPI staining and DNA fragmentation assay indicated that Pycnogenol induced HL-60, U937 and K562 cell apoptosis at their respective IC(50)s after 24 h of treatments. Pretreatment of z-DEVD-fmk, a caspase-3 specific inhibitor, not only decreased caspase-3 activity but also reduced the percentage of apoptotic cells induced by Pycnogenol. This indicated that caspase-3 activation was involved in Pycnogenol induced-apoptosis. In conclusion, Pycnogenol induced differentiation and apoptosis in leukemia cells. Our data suggest that Pycnogenol could serve as a potent cancer chemopreventive or chemotherapeutic agent for human leukemia.

The intermediate filament protein vimentin is a new target for epigallocatechin gallate

Epigallocatechin gallate (EGCG) is the major active polyphenol in green tea. Protein interaction with EGCG is a critical step in the effects of EGCG on the regulation of various key proteins involved in signal transduction. We have identified a novel molecular target of EGCG using affinity chromatography, two-dimensional electrophoresis, and mass spectrometry for protein identification. Spots of interest were identified as the intermediate filament, vimentin. The identification was confirmed by Western blot analysis using an anti-vimentin antibody. Experiments using a pull-down assay with [3H]EGCG demonstrate binding of EGCG to vimentin with a Kd of 3.3 nm. EGCG inhibited phosphorylation of vimentin at serines 50 and 55 and phosphorylation of vimentin by cyclin-dependent kinase 2 and cAMP-dependent protein kinase. EGCG specifically inhibits cell proliferation by binding to vimentin. Because vimentin is important for maintaining cellular functions and is essential in maintaining the structure and mechanical integration of the cellular space, the inhibitory effect of EGCG on vimentin may further explain its anti-tumor-promoting effect.

Survivin and p53 modulate quercetin-induced cell growth inhibition and apoptosis in human lung carcinoma cells

Quercetin, a ubiquitous bioactive plant flavonoid, has been shown to inhibit the proliferation of cancer cells. However, the regulation of survivin and p53 on the quercetin-induced cell growth inhibition and apoptosis in cancer cells remains unclear. In this study, we investigated the roles of survivin and p53 in the quercetin-treated human lung carcinoma cells. Quercetin (20-80 mum for 24 h) induced the cytotoxicity and apoptosis in both A549 and H1299 lung carcinoma cells in a concentration-dependent manner. Additionally, quercetin inhibited the cell growth, increased the fractions of G(2)/M phase, and raised the levels of cyclin B1 and phospho-cdc2 (threonine 161) proteins. Moreover, quercetin induced abnormal chromosome segregation in H1299 cells. The survivin proteins were highly expressed in mitotic phase and were located on the midbody of cytokinesis; however, the survivin proteins were increased and concentrated on the nuclei following quercetin treatment in the lung carcinoma cells. Transfection of a survivin antisense oligodeoxynucleotide enhanced the quercetin-induced cell growth inhibition and cytotoxicity. Subsequently, quercetin increased the levels of total p53 (DO-1), phospho-p53 (serine 15), and p21 proteins, which were translocated to the nuclei in A549 cells. Treatment with a specific p53 inhibitor, pifithrin-alpha, or transfection of a p53 antisense oligodeoxynucleotide enhanced the cytotoxicity of the quercetin-treated cells. Furthermore, transfection of a small interfering RNA of p21 enhanced the quercetin-induced cell death in A549 cells. Together, our results suggest that survivin can reduce the cell growth inhibition and apoptosis, and p53 elevates the p21 level, which may attenuate the cell death in the quercetin-treated human lung carcinoma cells.

Potential toxicity of flavonoids and other dietary phenolics: significance for their chemopreventive and anticancer properties

Flavonoids, including isoflavones, are natural components in our diet and, with the burgeoning interest in alternative medicine, are increasingly being ingested by the general population. Plant phenolics, which form moieties on flavonoid rings, such as gallic acid, are also widely consumed. Several beneficial properties have been attributed to these dietary compounds, including antioxidant, anti-inflammatory, and anticarcinogenic effects. Flavonoid preparations are marketed as herbal medicines or dietary supplements for a variety of alleged nontoxic therapeutic effects. However, they have yet to pass controlled clinical trials for efficacy, and their potential for toxicity is an understudied field of research. This review summarizes the current knowledge regarding potential dietary flavonoid/phenolic-induced toxicity concerns, including their pro-oxidant activity, mitochondrial toxicity (potential apoptosis-inducing properties), and interactions with drug-metabolizing enzymes. Their chemopreventive activity in animal in vivo experiments may result from their ability to inhibit phase I and induce phase II carcinogen metabolizing enzymes that initiate carcinogenesis. They also inhibit the promotion stage of carcinogenesis by inhibiting oxygen radical-forming enzymes or enzymes that contribute to DNA synthesis or act as ATP mimics and inhibit protein kinases that contribute to proliferative signal transduction. Finally, they may prevent tumor development by inducing tumor cell apoptosis by inhibiting DNA topoisomerase II and p53 downregulation or by causing mitochondrial toxicity, which initiates mitochondrial apoptosis. While most flavonoids/phenolics are considered safe, flavonoid/phenolic therapy or chemopreventive use needs to be assessed as there have been reports of toxic flavonoid-drug interactions, liver failure, contact dermatitis, hemolytic anemia, and estrogenic-related concerns such as male reproductive health and breast cancer associated with dietary flavonoid/phenolic consumption or exposures.

Determination of catechins in matcha green tea by micellar electrokinetic chromatography

Catechins in green tea are known to have many beneficial health properties. Recently, it has been suggested that matcha has greater potential health benefits than other green teas. Matcha is a special powdered green tea used in the Japanese tea ceremony. However, there has been no investigation to quantitate the catechin intake from matcha compared to common green teas. We have developed a rapid method of analysis of five catechins and caffeine in matcha using micellar electrokinetic chromatography. Results are presented for water and methanol extractions of matcha compared with water extraction of a popular green tea. Using a mg catechin/g of dry leaf comparison, results indicate that the concentration of epigallocatechin gallate (EGCG) available from drinking matcha is 137 times greater than the amount of EGCG available from China Green Tips green tea, and at least three times higher than the largest literature value for other green teas.

Tannins elevate the level of poly(ADP-ribose) in HeLa cell extracts

Phenolic phytochemicals such as tannins, which are natural constituents of green tea, red wine, and other plant products, are considered to have cancer-preventive properties. An important endogenous mediator of tumorigenesis is the nuclear enzyme poly(ADP-ribose) polymerase 1 (PARP-1). PARP-1 synthesizes polymers of ADP-ribose (PAR), which, in turn, are degraded by the catabolic enzyme poly(ADP-ribose) glycohydrolase (PARG). In the present study, we investigated the effects of tannins on the level of PAR in HeLa nuclear extracts. The addition of tannins to nuclear extracts led to a 40-fold elevation of PAR-levels. The observed increased PAR-levels resulted from inhibition of the catalytic activity of PARG. Additionally, the human PARG cDNA was cloned and the recombinant enzyme was overexpressed and isolated. Recombinant PARG was immobilized using an affinity column composed of tannins covalently linked to Sepharose beads. Finally, an interaction between immobilized PARG and endogenous PARP-1 from HeLa cell extracts is demonstrated.

A regulatory role for p38 delta MAPK in keratinocyte differentiation. Evidence for p38 delta-ERK1/2 complex formation

p38 MAPK isoforms are important in the regulation of a variety of cellular processes. Among the four described p38 isoforms, p38 alpha, beta, and delta are expressed in keratinocytes (Dashti, S. R., Efimova, T., and Eckert, R. L. (2001) J. Biol. Chem. 276, 8059-8063). However, very little is known about how individual p38 isoforms regulate keratinocyte function. In the present study, we use okadaic acid (OA) as a tool to study the role of p38 MAPKs as regulators of keratinocyte differentiation. We demonstrate that OA activates p38 delta but not other p38 isoforms. p38 delta activation is increased as early as 0.5 h after OA addition, and activity is maximal at 8 and 24 h. ERK1 and ERK2 activity are reduced on an identical time course. We show that p38 delta forms a complex with ERK1/2, and overexpression of p38 delta inhibits ERK1/2 activity without reducing ERK1/2 level. Thus, p38 delta may directly suppress ERK1/2 activity. Additional studies show that p38 delta is expressed in the epidermis, suggesting a role for p38 delta in regulating differentiation. To evaluate its function, we show that increased p38 delta activity is associated with increased levels of AP1 and CAATT enhancer binding protein factors, increased binding of these factors to the involucrin (hINV) promoter, and increased expression. Moreover, these responses are maintained in the presence of SB203580, an agent that inhibits p38 alpha and beta, further suggesting a central role for the p38 delta isoform. Dominant-negative p38 also inhibits these responses. These unique observations suggest that p38 delta is the major p38 isoform driving suprabasal hINV gene expression and that p38 delta directly regulates ERK1/2 activity via formation of a p38 delta-ERK1/2 complex.

Effects of black tea theafulvins on aflatoxin B(1) mutagenesis in the Ames test

Black tea theafulvins, a fraction of thearubigins isolated from black tea aqueous infusions, potentiated the mutagenic activity of the mycotoxin aflatoxin B(1) in the Ames test, in the presence of a hepatic S9 activation system derived from Aroclor 1254-treated rats. In contrast, when the S9 activation system was replaced with isolated microsomes, theafulvins suppressed the mutagenicity of the mycotoxin. When microsomal metabolism was terminated after metabolic activation of the mycotoxin, incorporation of the theafulvins into the activation system reduced the mutagenic activity, whereas if it was added before termination of microsomal activity a potentiation of mutagenic response was observed. In in vitro studies, theafulvins inhibited epoxide hydrolase and glutathione S-transferase activities in a concentration-dependent manner. Finally, the mutagenicity of aflatoxin B(1) was much more pronounced in bacteria that were pre-exposed to theafulvins but from which they were subsequently washed off. It may be inferred from the above studies that the genotoxic synergy between aflatoxin B(1) and black tea theafulvins does not occur during the bioactivation of the carcinogen, but may partly be due to decreased deactivation of the reactive intermediate, aflatoxin B(1) 8,9-oxide, by conjugation with glutathione.

Green tea polyphenol blocks h(2)o(2)-induced interleukin-8 production from human alveolar epithelial cells

Reactive oxygen species (ROS) play crucial roles in ischemia-reperfusion (IR) injury of lung transplants. Reactive oxygen species may stimulate the production of neutrophil chemotactic factors such as interleukin-8 (IL-8), from alveolar epithelial cells, causing recruitment and activation of neutrophils in the reperfused tissue. Green tea polyphenol has potent anti-oxidative activities and anti-inflammatory effects by decreasing cytokine production. In the present study, we found that green tea polyphenol significantly inhibited IL-8 production induced by hydrogen peroxide (H(2)O(2)) in human lung alveolar epithelial cells (A549 line). It has been shown that mitogen activated protein kinases, such as Jun N-terminal kinase (JNK), p38 and p44/42, could mediate IL-8 production from a variety of cell types. We further investigated the effect of green tea polyphenol on these protein kinases, and demonstrated that H(2)O(2)-induced phosphorylation of JNK and p38 but not p44/42 was inhibited by green tea polyphenol in A549 cells. We speculate that green tea polyphenol may inhibit H(2)O(2)-induced IL-8 production from A549 cells through inactivation of JNK and p38.

Synergistic effects of (-)-epigallocatechin gallate with sulindac against colon carcinogenesis of rats treated with azoxymethane

(-)-Epigallocatechin gallate (EGCG), a major constituent of green tea, has been shown to exhibit anti-cancer activity. Sulindac is also well known as a cancer-preventive agent against colon cancer, but its usage is restricted because of its adverse effects, as exemplified by gastrointestinal bleeding. In the present study, we examined whether a combination of EGCG and sulindac shows synergistic effects for cancer-preventive activity for rat colon carcinogenesis induced by azoxymethane (AOM); we examined the number of aberrant crypt foci (ACF) representing preneoplastic lesions, the argyrophilic nucleolar organizer region (AgNOR) as an indicator of cell proliferation, and the incidence of apoptosis. The AOM treatment induced an average of 46.2+/-4.9 ACF/colon, and sulindac and EGCG significantly reduced the incidence of ACF/colon to 21.4+/-3.4 and 19.5+/-5.8, respectively (P<0.01). The co-treatment with EGCG and sulindac resulted in significantly reduced ACF formation (10.0+/-3.2; P<0.01). The results of the AgNOR analysis indicated that the treatment with EGCG and/or sulindac suppressed AOM-induced cell proliferation. The present results also revealed that the combination of EGCG and sulindac synergistically enhanced apoptosis significantly (P<0.01). Thus, our findings suggest that EGCG with sulindac synergistically suppresses ACF formation by enhancing apoptosis and, therefore, that EGCG is a suitable candidate for use in combination with cancer-preventive agents, such as sulindac, to reduce their adverse effects.

Chemoprevention of aflatoxin B1-initiated and carbon tetrachloride-promoted hepatocarcinogenesis in the rat by green tea

Chemoprevention of hepatocarcinogenesis by green tea (GT) has been examined in young male Fischer rats fed AIN-76A diet with aflatoxin B1 (AFB1) and CCl4 as the initiator and promoter, respectively. Animals were administered AFB1 (0.25 mg/kg body wt ip) twice a week for 2 weeks, and 2 weeks later, CCl4 was injected (0.8 ml/kg body wt ip) once per week for 11 weeks. Rats given 0.5% GT in their drinking water before and during initiation (0-4 wk) or during promotion (6-16 wk) or throughout the experimental period were sacrificed 24 hours after the last dose of CCl4. Bromodeoxyuridine incorporation as a measure of cell proliferation and glutathione S-transferase placentalform- and gamma-glutamyl transpeptidase-positive hepatic foci were analyzed by histochemical methods. Feeding of GT during initiation or promotion inhibited the number of glutathione S-transferase placental form- and gamma-glutamyl transpeptidase-positive hepatic foci by 30-40% and the area and volume by 50%. GT treatment throughout the period inhibited the number of both types of hepatic foci by 60% and the area and volume by 75-80%. Cell proliferation was inhibited 35% by GT given during promotion, whereas inhibition was 65% when GT was given during initiation or throughout the period. These results indicate that GT feeding inhibits initiation and promotion steps of AFB1 hepatocarcinogenesis and that the inhibition of cell proliferation is responsible for the inhibition of promotion.

Membrane-rigidifying effects of anti-cancer dietary factors

Since several anti-cancer drugs interact with cell membrane lipids, the effects of anti-cancer dietary factors on liposomal membranes with different lipid composition were comparatively studied by measuring fluorescence polarization. Fluidity was imparted on both hydrophobic and hydrophilic regions of lipid bilayers by decreasing cholesterol and increasing unsaturated phosphatidylcholine in membranes. At 0.625-10 microM, (-)-epigallocatechin gallate, genistein, apigenin, resveratrol and a reference anti-cancer drug, doxorubicin, rigidified the tumor cell model membranes consisting of 20 mol% cholesterol and 80 mol% phosphatidylcholine with the acyl chain 18:1/16:0 ratio of 1.0, but not daidzein. They were more effective on the membrane core than the membrane surface. Quercetin showed a biphasic effect on the hydrophobic regions of membrane lipid bilayers to rigidify above 5 microM and fluidize below 2.5 microM. In contrast, anti-cancer dietary factors and doxorubicin were not or much less effective in rigidifying the normal cell model membranes consisting of 40 mol% cholesterol and 60 mol% phosphatidylcholine with the acyl chain 18:1/16:0 ratio of 0.5. The membrane-rigidifying effects were greater depending on a decrease of the cholesterol/phosphatidylcholine ratio and an increase of the phosphatidylcholine unsaturation degree. Membrane-active dietary factors and doxorubicin inhibited the growth of mouse myeloma cells at 10-100 microM, while the growth inhibition by membrane-inactive daidzein was relatively weak. Anti-cancer dietary factors appear to act on more fluid membranes like tumor cells as well as doxorubicin to induce rigidification, especially in the hydrocarbon core of membrane lipids, which is determined by the composition of cholesterol and unsaturated phospholipids.

Prevention of carcinogenesis by tea polyphenols

Tea, an extract of the leaves of the plant Camellia sinensis, has been considered a medicine and healthful beverage for ages. The beneficial effects of tea are thought to be due to its polyphenolic components. Herein, we discuss the present status of tea as a possible cancer chemopreventive agent, covering basic chemistry and biochemical activity of tea, pharmacokinetics of major tea components, studies in animal and cell lines, epidemiological investigations, and future challenges. Tea is one of the few chemopreventive agents known to have protective effects at different stages of the carcinogenic process. Tea constituents may inhibit this process by modulating signal transduction pathways leading to the inhibition of cell proliferation and transformation and enhancement of apoptosis. These activities may or may not be due to the antioxidative activity of tea polyphenols. The bioavailability and tissue levels of tea polyphenols is a key topic to be studied in order to understand the mechanisms of action of tea and its possible protection against cancer in humans.

Specific induction of glutathione S-transferase GSTM2 subunit expression by epigallocatechin gallate in rat liver

The antitumor effect of green tea polyphenols has been well characterized in numerous papers. However, the mechanism of their action is still poorly defined. In this study, epigallocatechin gallate (EGCG), the main ingredient of green tea extract, was studied for its effect on the expression of glutathione S-transferases (GSTs) in rat liver to examine the mechanism of action. Liver samples were collected from Sprague-Dawley rats treated with EGCG in H(2)O by portal vein perfusion and examined for total GST activity and GST expression. The results showed that the induction of GST activity by EGCG was dose- and time-dependent. GST activity was increased about 28-fold at 12 hr after treatment. Three GST subunits (GSTA1/2, GSTM1, and GSTM2) were examined by Western blot for changes in protein level affected by EGCG (1 mg/kg weight). Only GSTM2 revealed a significant time-dependent increase, with a maximal induction of approximately 2.0-fold. The differential effect of EGCG on GST subunit expression was also verified by immunocytochemical examination and showed strong induction of the GSTM2 (but not the GSTA1/2 and GSTM1) level in liver section. This induction occurred as early as 3 hr after treatment and extended gradually outward from the hepatic veins as treatment time increased. The change in the GSTM2 protein level was accompanied by a corresponding alteration in mRNA quantity ( approximately 2.0-fold of control). Our report is the first to demonstrate a specific induction of the GSTM2 subunit by a chemopreventor and suggests a primary influence of EGCG on GSTM2 gene expression.

Growth factor-dependent induction of p21(CIP1) by the green tea polyphenol, epigallocatechin gallate

Tea polyphenols inhibit tumorigenesis and cell proliferation in rodent models, but their effects on cell signaling and cell cycle control pathways are undefined. Here, we show that the major polyphenol in green tea, epigallocatechin gallate (EGCG), inhibits S phase entry in epidermal growth factor (EGF) - stimulated MCF10A breast epithelial cells when provided in G0 or mid G1, but not when provided after the late G1 restriction point. EGCG induced p21(CIP1/WAF1/SDI1), inhibited cyclin D1-associated pRB kinase activity, and impaired pRB phosphorylation. The ability of EGCG to induce p21 depended upon the addition of EGF, indicating that EGCG synergizes with growth factor-dependent signals to induce p21 and impair cell cycle progression.

Comparative analysis of tea catechins and theaflavins by high-performance liquid chromatography and capillary electrophoresis

This paper describes the simultaneous determination of catechins and theaflavins in green and black teas, using reversed-phase high-performance liquid chromatography (HPLC) and capillary electrophoresis (CE). The tea polyphenols analyzed included (+)-catechin, catechin gallate, (-)-epicatechin, epicatechin-3-gallate, epigallocatechin, epigallocatechin-3-gallate, theaflavin, theaflavin-3-monogallate, theaflavin-3'-monogallate and theaflavin-3,3'-gallate. These polyphenols together with six other tea ingredients such as caffeine, adenine, theophylline, quercetin, gallic acid and caffeic acid were separated within 27 min by HPLC and in less than 10 min by CE. The optimal analytical conditions of both chromatographic methods were investigated for the convenience and reliability for routine analysis. Both HPLC and CE were found to be reliable and compatible. The reproducibility of the within-day assay using both methods was generally >90%. The day-to-day variation of retention time was <5% for HPLC, while the variation of migration time for CE was <2%. The analysis time of CE was three-times faster, however it is five-times less sensitive than HPLC, which has detection limits of 0.05 microg/ml and 0.5 microg/ml for catechins and theaflavins, respectively.

Growth inhibition, cell-cycle dysregulation, and induction of apoptosis by green tea constituent (-)-epigallocatechin-3-gallate in androgen-sensitive and androgen-insensitive human prostate carcinoma cells

Prostate cancer (PCA) is the most prevalent cancer diagnosed and the second leading cause of cancer-related deaths among men in the United States. Descriptive epidemiological data suggest that androgens and environmental exposures play a key role in prostatic carcinogenesis. Since androgen action is intimately associated with proliferation and differentiation, at the time of clinical diagnosis in humans most PCA represent themselves as a mixture of androgen-sensitive and androgen-insensitive cells. Androgen-sensitive cells undergo rapid apoptosis upon androgen withdrawal. On the other hand, the androgen-insensitive cells do not undergo apoptosis upon androgen blocking, but maintain the molecular machinery of apoptosis. Thus, agents capable of inhibiting growth and/or inducing apoptosis in both androgen-sensitive and androgen-insensitive cells will be useful for the management of PCA. In the present study, we show that (-)-epigallocatechin-3-gallate (EGCG), the major polyphenolic constituent present in green tea, imparts antiproliferative effects against both androgen-sensitive and androgen-insensitive human PCA cells, and this effect is mediated by deregulation in cell cycle and induction of apoptosis. EGCG treatment was found to result in a dose-dependent inhibition of cell growth in both androgen-insensitive DU145 and androgen-sensitive LNCaP cells. In both the cell types, EGCG treatment also resulted in a dose-dependent G(0)/G(1)-phase arrest of the cell cycle as observed by DNA cell-cycle analysis. As evident by DNA ladder assay, confocal microscopy, and flow cytometry, the treatment of both DU145 and LNCaP cells with EGCG resulted in a dose-dependent apoptosis. Western blot analysis revealed that EGCG treatment resulted in (i) a dose-dependent increase of p53 in LNCaP cells (carrying wild-type p53), but not in DU145 cells (carrying mutant p53), and (ii) induction of cyclin kinase inhibitor WAF1/p21 in both cell types. These results suggest that EGCG negatively modulates PCA cell growth, by affecting mitogenesis as well as inducing apoptosis, in cell-type-specific manner which may be mediated by WAF1/p21-caused G(0)/G(1)-phase cell-cycle arrest, irrespective of the androgen association or p53 status of the cells.

Supplementation of Jurkat T cells with green tea extract decreases oxidative damage due to iron treatment

Regular tea consumption has been associated with a reduced risk of cancer. As demonstrated in vitro, green tea contains catechins with antioxidant properties. We evaluated the effect of the supplementation of the Jurkat T-cell line with green tea extract on oxidative damage. Cells grown in medium with or without green tea extract (10 mg/L) were treated with Fe(2+) (100 micromol/L) as an oxidative stimulus for 2 h. Cell membrane lipid peroxidation was evaluated by fatty acids pattern analysis and malondialdehyde production in alpha-linolenic acid-loaded cells. Furthermore, oxidative DNA damage (single strand breaks) was detected in cells by the Comet assay and quantified as relative tail moment (RTM). Supplementation with green tea extract significantly decreased malondialdehyde production (1.6 +/- 0.3 vs. 0.6 +/- 0.1 nmol/mg protein, P < 0.05) and DNA damage (0.32 +/- 0.07 vs. 0.12 +/- 0.04 RTM, P < 0.05) after Fe(2+) oxidative treatment. In control cells, there was no effect on membrane distribution of (n-3) fatty acids due to Fe(2+) treatment. Cell enrichment with alpha-linolenic acid increased total membrane (n-3) fatty acids. However, the oxidative treatment did not modify the distribution of polyunsaturated fatty acids. It is likely that the observed protective effects can be attributed to epigallocatechin gallate, which is present mainly (670 g/kg) in green tea extract; however, we cannot exclude contributions by other catechins. These data support a protective effect of green tea against oxidative damage.

Induction of apoptosis by penta-O-galloyl-beta-D-glucose through activation of caspase-3 in human leukemia HL-60 cells

Penta-O-galloyl-beta-D-glucose is structurally related to (-)-epigallocatechin gallate and is isolated from hydrolyzed tannin. Penta-O-galloyl-beta-D-glucose can inhibit tumor promotion by teleocidin. We investigated the effects of penta-O-galloyl-beta-D-glucose and various tea polyphenols on cell viability in human leukemia HL-60 cells. In this study, we demonstrated that penta-O-galloyl-beta-D-glucose was able to induce apoptosis in a concentration- and time-dependent manner; however, other polyphenols were less effective. We further investigated the molecular mechanisms of penta-O-galloyl-beta-D-glucose-induced apoptosis. Treatment with penta-O-galloyl-beta-D-glucose caused induction of caspase-3/CPP32 activity in dose- and time-dependent manner, but not caspase-1 activity, and induced the degradation of poly-(ADP-ribose) polymerase. Pretreatment with acetyl-Asp-Glu-Val-Asp-aldehyde (Ac-DEVD-CHO) and Z-Val-Ala-Asp-fluoromethyl-ketone (Z-VAD-FMK) inhibited penta-O-galloyl-beta-D-glucose-induced DNA fragmentation. Furthermore, treatment with penta-O-galloyl-beta-D-glucose (50 microM) caused a rapid loss of mitochondrial transmembrane potential, release of mitochondrial cytochrome c into cytosol, and subsequent induction of procaspase-9 processing. Our results indicate that penta-O-galloyl-beta-D-glucose allows caspase-activated deoxyribonuclease to enter the nucleus and degrade chromosomal DNA, and induces DFF-45 (DNA fragmentation factor) degradation. These results lead to a working hypothesis that penta-O-galloyl-beta-D-glucose-induced apoptosis is triggered by the release of cytochrome c into the cytosol, procaspase-9 processing, activation of caspase-3, degradation of poly-(ADP-ribose) polymerase, and DNA fragmentation caused by the caspase-activated deoxyribonuclease through the digestion of DFF-45. The induction of apoptosis by penta-O-galloyl-beta-D-glucose may provide a pivotal mechanism for its cancer chemopreventive action.

Cancer chemoprevention by tea polyphenols through mitotic signal transduction blockade

Tea is a popular beverage. The consumption of green tea is associated with a lower risk of several types of cancer, including stomach, esophagus, and lung. The cancer chemopreventive effect of tea has been attributed to its major phytopolyphenols. The tea polyphenols comprise about one-third of the weight of the dried leaf, and they show profound biochemical and pharmacological activities including antioxidant activities, modulation of carcinogen metabolism, inhibition of cell proliferation, induction of cell apoptosis, and cell cycle arrest. They intervene in the biochemical and molecular processes of multistep carcinogenesis, comprising tumor initiation, promotion, and progression. Several studies demonstrate that most tea polyphenols exert their scavenging effects against reactive oxygen species (ROS); excessive production of ROS has been implicated for the development of cardiovascular diseases, neurodegenerative disorders, and cancer. Recently, we have found that the major tea polyphenol (-)-epigallocatechin-3-gallate (EGCG) suppresses extracellular signals and cell proliferation through epidermal growth factor receptor binding in human A431 epidermoid carcinoma cells; EGCG also blocks the induction of nitric oxide synthase by down-regulating lipopolysaccharide-induced activity of the transcription factor NFKB in macrophages. Furthermore, EGCG blocks the cell cycle at the G1 phase in MCF-7 cells. We have demonstrated that EGCG inhibits the activities of cyclin-dependent kinases 2 and 4; meanwhile, EGCG induces the expression of the Cdk inhibitors p21 and p27. These results suggest that tumor promotion can be enhanced by ROS and oxidative mitotic signal transduction, and this enhancement can be suppressed by EGCG or other tea polyphenols.

Health-promoting properties of common herbs

Herbs have been used as food and for medicinal purposes for centuries. Research interest has focused on various herbs that possess hypolipidemic, antiplatelet, antitumor, or immune-stimulating properties that may be useful adjuncts in helping reduce the risk of cardiovascular disease and cancer. In different herbs, a wide variety of active phytochemicals, including the flavonoids, terpenoids, lignans, sulfides, polyphenolics, carotenoids, coumarins, saponins, plant sterols, curcumins, and phthalides have been identified. Several of these phytochemicals either inhibit nitrosation or the formation of DNA adducts or stimulate the activity of protective enzymes such as the Phase II enzyme glutathione transferase (EC 2.5.1.18). Research has centered around the biochemical activity of the Allium sp. and the Labiatae, Umbelliferae, and Zingiberaceae families, as well as flaxseed, licorice root, and green tea. Many of these herbs contain potent antioxidant compounds that provide significant protection against chronic diseases. These compounds may protect LDL cholesterol from oxidation, inhibit cyclooxygenase and lipoxygenase enzymes, inhibit lipid peroxidation, or have antiviral or antitumor activity. The volatile essential oils of commonly used culinary herbs, spices, and herbal teas inhibit mevalonate synthesis and thereby suppress cholesterol synthesis and tumor growth.

Flavonoids: old and new aspects of a class of natural therapeutic drugs

Flavonoids are natural products widely distributed in the vegetable kingdom and currently consumed in large amounts in the daily diet. Flavonoids are capable of modulating the activity of enzymes and affect the behaviour of many cell systems, suggesting that the compounds may possess significant antihepatotoxic, antiallergic, anti-inflammatory, antiosteoporotic and even antitumor activities. This review summarizes available data on these beneficial effects of flavonoids.

Molecular mechanisms of chemopreventive effects of selected dietary and medicinal phenolic substances

Recently, considerable attention has been focused on identifying naturally occurring chemopreventive substances capable of inhibiting, retarding, or reversing the multi-stage carcinogenesis. A wide array of phenolic substances, particularly those present in dietary and medicinal plants, have been reported to possess substantial anticarcinogenic and antimutagenic activities. The majority of these naturally occurring phenolics retain antioxidative and anti-inflammatory properties which appear to contribute to their chemopreventive or chemoprotective activity. Capsaicin (trans-8-methyl-N-vanillyl-6-nonenamide), a pungent ingredient of hot chili pepper, protects against experimentally-induced mutagenesis and tumorigenesis. It also induces apoptosis in various immortalized or malignant cell lines. Plants of ginger family (Zingiberaceae) have been frequently and widely used as spices and also, in traditional oriental medicine. Curcumin, a yellow ingredient from turmeric (Curcuma longa L., Zingiberaceae), has been extensively investigated for its cancer chemopreventive potential. Yakuchinone A [1-(4'-hydroxy-3'-methoxyphenyl)-7-phenyl-3-heptanone] and yakuchinone B [1-(4'-hydroxy-3'-methoxyphenyl)-7-phenylhept-1-en-3-one] present in Alpinia oxyphylla Miquel (Zingiberaceae) have inhibitory effects on phorbol ester-induced inflammation and skin carcinogenesis in mice, and oxidative stress in vitro. These diarylheptanoids suppress phorbol ester-induced activation of ornithine decarboxylase and production of tumor necrosis factor-alpha or interleukin-1alpha and their mRNA expression. They also nullified the phorbol ester-stimulated induction of activator protein 1 (AP-1) in cultured human promyelocytic leukemia (HL-60) cells. In addition, both yakuchinone A and B induced apoptotic death in HL-60 cells. Ginger (Zingiber officinale Roscoe, Zingiberaceae) contains such pungent ingredients as [6]-gingerol and [6]-paradol, which also have anti-tumor promotional and antiproliferative effects. Resveratrol (3, 5,4'-trihydroxy-trans-stilbene), a phytoalexin found in grapes and other dietary and medicinal plants, and (-)-epigallocatechin gallate, a major antioxidative green tea polyphenol, exert striking inhibitory effects on diverse cellular events associated with multi-stage carcinogenesis. In addition, these compounds have ability to suppress proliferation of human cancer cells via induction of apoptosis.

Consumption of tea modulates the urinary excretion of mutagens in rats treated with IQ. Role of caffeine

The present study was undertaken to investigate whether the consumption of green tea and black tea influences the excretion of mutagens and promutagens in rats treated orally with the food carcinogen 2-amino-3-methylimidazo[4,5-f]quinoline (IQ). Rats were maintained on aqueous extracts (2.5%, w/v) of green tea, black tea or decaffeinated black tea as their sole drinking liquid. After 4 weeks, the animals received, by gastric intubation, a single dose of IQ (5 mg/kg), and urine was collected for 48 h. Direct and indirect mutagenicity, in the presence of an activation system derived from Aroclor 1254-treated rats, was determined in the urine samples using the Ames mutagenicity assay. Consumption of green tea and black tea, but not of decaffeinated black tea, markedly decreased the urinary excretion of mutagens and promutagens. In a further study, supplementation of decaffeinated black tea with caffeine suppressed the excretion of mutagens and promutagens in the urine of rats pretreated with IQ. It is concluded that both green tea and black tea modulate the bioactivation and metabolism of IQ, and that caffeine is largely responsible for this effect.

Suppression of extracellular signals and cell proliferation by the black tea polyphenol, theaflavin-3,3'-digallate

Previous studies in our laboratory have shown that the major green tea polyphenol, (-)-epigallocatechin-3-gallate (EGCG), suppressed autophosphorylation of epidermal growth factor (EGF) receptor induced by EGF in human A431 epidermoid carcinoma cells. In this study, we examined the inhibitory effects of black tea polyphenols, including theaflavin (TF-1), a mixture (TF-2) of theaflavin-3-gallate (TF-2a) and theaflavin-3'-gallate (TF-2b), theaflavin-3,3'-digallate (TF-3) and the thearubigin fraction on the autophosphorylation of the EGF and PDGF receptors in A431 cells and mouse NIH3T3 fibroblast cells, respectively. First, we examined the effects of these polyphenols on the proliferation of A431 and NIH3T3 cells. Both EGCG and TF-3 strongly inhibited the proliferation of A431 and NIH3T3 cells more than the other theaflavins did. In cultured cells with pre-treatment of tea polyphenol, TF-3 was stronger than EGCG on the reduction of EGF receptor and PDGF receptor autophosphorylation induced by EGF and PDGF, respectively. Other theaflavins slightly reduced the autophosphorylation of the EGF and PDGF receptors; furthermore, TF-3 could reduce autophosphorylation of the EGF receptor (or PDGF receptor) even with co-treatment with EGF (or PDGF) and TF-3, but EGCG was inactive under these conditions. In addition, TF-3 was stronger than EGCG in blocking EGF binding to its receptor. These results suggest that not only the green tea polyphenol, EGCG, but also the black tea polyphenol, TF-3, have an antiproliferative activity on tumor cells, and the molecular mechanisms of antiproliferation may block the growth factor binding to its receptor and thus suppress mitogenic signal transduction.

Green tea epigallocatechin gallate shows a pronounced growth inhibitory effect on cancerous cells but not on their normal counterparts

(-)-Epigallocatechin gallate (EGCG), a catechin polyphenol compound, represents the main ingredient of green tea extract. Although EGCG has been shown to be growth inhibitory in a number of tumor cell lines, it is not clear whether the effect is cancer-specific. In this study we compared the effect of EGCG on the growth of SV40 virally transformed WI38 human fibroblasts (WI38VA) with that of normal WI38 cells. The IC50 value of EGCG was estimated to be 120 and 10 microM for WI38 and WI38VA cells, respectively. Thus, EGCG at 40 microM completely inhibited the growth of WI38VA cells, but had little or no inhibitory effect on the growth of WI38 cells. Similar differential growth inhibition was also observed between a human colorectal cancer cell line (Caco-2), a breast cancer cell line (Hs578T) and their respective normal counterparts. EGCG at a concentration range of 40-200 microM induced a significant amount of apoptosis in WI38VA cultures, but not in WI38 cultures, as determined by terminal deoxynucleotidyl transferase assay. After exposure to EGCG at 200 microM for 8 h, more than 50% of WI38VA cells in a confluent culture became apoptotic. In contrast, less than 1% of WI38 cells displayed apoptotic labeling under the same condition. EGCG did not affect the serum-induced expression of c-fos and c-myc genes in normal WI38 cells. However, it significantly enhanced their expression in transformed W138VA cells. It is possible that differential modulation of certain genes, such as c-fos and c-myc, may cause differential effects of EGCG on the growth and death of cancer cells.

Tea and tea polyphenols inhibit cell hyperproliferation, lung tumorigenesis, and tumor progression

Both green and black tea have been shown to inhibit lung tumorigenesis in laboratory animal experiments. Green tea inhibited N-nitrosodiethylamine-induced lung tumor incidence and multiplicity in female A/J mice when tea was given either during the carcinogen treatment period or during the post-carcinogen treatment period. In a separate tumorigenesis model, both decaffeinated black tea and decaffeinated green tea inhibited 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK)-induced lung tumor formation. Studies in which tea was administered during different time periods in relation to the NNK suggest that tea can inhibit lung tumorigenesis at both the initiation and promotion stages. The antiproliferative effects of tea may be responsible for these anti-carcinogenic actions. Black tea polyphenol preparations decreased NNK-induced hyperproliferation. Black tea also inhibited the progression of pulmonary adenomas to adenocarcinomas and the formation of spontaneous lung tumors in A/J mice. Growth inhibition by various tea polyphenols has been demonstrated in human lung H661 and H1299 cells. Although inhibition of cell growth and signal transduction pathways by tea components have been demonstrated, the concentrations required to produce the effect are higher than achievable in tissues in vivo. More research is necessary to translate these laboratory results to applications in human chemoprevention.

Suppression of extracellular signals and cell proliferation through EGF receptor binding by (-)-epigallocatechin gallate in human A431 epidermoid carcinoma cells

Tea polyphenols are known to inhibit a wide variety of enzymatic activities associated with cell proliferation and tumor progression. The molecular mechanisms of antiproliferation are remained to be elucidated. In this study, we investigated the effects of the major tea polyphenol (-)-epigallocatechin gallate (EGCG) on the proliferation of human epidermoid carcinoma cell line, A431. Using a [3H]thymidine incorporation assay, EGCG could significantly inhibit the DNA synthesis of A431 cells. In vitro assay, EGCG strongly inhibited the protein tyrosine kinase (PTK) activities of EGF-R, PDGF-R, and FGF-R, and exhibited an IC50 value of 0.5-1 microgram/ml. But EGCG scarcely inhibited the protein kinase activities of pp60v-src, PKC, and PKA (IC50 > 10 micrograms/ml). In an in vivo assay, EGCG could reduce the autophosphorylation level of EGF-R by EGF. Phosphoamino acid analysis of the EGF-R revealed that EGCG inhibited the EGF-stimulated increase in phosphotyrosine level in A431 cells. In addition, we showed that EGCG blocked EGF binding to its receptor. The results of further studies suggested that the inhibition of proliferation and suppression of the EGF signaling by EGCG might mainly mediate dose-dependent blocking of ligand binding to its receptor, and subsequently through inhibition of EGF-R kinase activity.