cancer-prevention

Author: Phing Chian Chai and Lee Hua Long and Barry Halliwell

Green tea and red wine are claimed to have health benefits because of their high content of polyphenolic compounds, but they have also been reported as mutagenic in some test systems. In this paper, we show that a commonly used cell culture medium, Dulbecco’s modified Eagle’s medium (DMEM), catalyses oxidation of green tea and red wines to generate H2O2. The level of H2O2produced from green tea accounted for all of the cytotoxic effects of this beverage on PCl2 cells. By contrast, H2O2 was only responsible for part of the cytotoxicity of the red wines examined. Our data illustrate the danger of extrapolating from cell culture studies to predict the effects of complex beverages in vivo.

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Author: Richard Béliveau and Denis Gingras

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Author: H. Osman and R. Nasarudin and S.L. Lee

Cocoa shoot (CS), young leaves (CL) and tea leaves (GT) were processed according to green tea processing procedures. Polyphenol components was extracted and analysed using high pressure liquid chromatography. The total polyphenol of CS, CL and GT were 19.0, 28.4 and 17.3 mg/100 mg, respectively. The main catechin-polyphenols in extracts were epicatechin (EC), epigallocatechin gallate (EGCG), epigallocatechin (EGC), gallic acid (GA) and epicatechin gallate (ECG). The concentrations of caffeine for CS, CL and GT were 2.24, 1.33 and 3.34 mg/100 mg, respectively. The concentrations of EGCG, in both cocoa leaves, were lower than commercial green tea. However, the concentrations of EC in CS (5.93 mg/100 mg) and in CL (2.82 mg/100 mg) were significantly higher that those found in green tea (0.65 mg/100 mg). The antioxidation properties of the polyphenol extracts were tested, using ferric chloride reduction, and compared against a synthetic antioxidant (BHA). The polyphenol extracts (CS and CL) showed similar antioxidation powers to GT and BHA throughout the entire concentration range (100–2000 ppm). In the oil-based test medium; the antioxidative performance of polyphenol extracts were better than BHA at 50 ppm. At 200 ppm, the performance is quite similar to BHA. At higher concentration (400 ppm) the antioxidant activities are much better than BHA. In the presence of Cu2+ prooxidant (20 ppm), BHA (200 ppm) and all the extracts (200 pmm) showed similar performances. Since the oxidation test was conducted at 65 °C, the 8 days of stability provided by 200 ppm addition of CL and CS extracts, can be equated to 8 months of room temperature (25 °C) stability. Hence, the cocoa leaves extracts have the potential to complement or replace synthetic antioxidants in aqueous and oil-based food applications.

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Author: Deborah J Kuhn and Audrey C Burns and Aslamuzzaman Kazi and Q Ping Dou

Green tea has been shown to lower plasma cholesterol, associated with up-regulation of the low-density lipoprotein receptor (LDLR) although the responsible molecular mechanism is unknown. Previously, we reported that ester bond-containing green tea polyphenols (GTPs), such as (−)-epigallocatechin-3-gallate [(−)-EGCG], potently inhibit the tumor cellular proteasome activity, which may contribute to the cancer-preventative effect of green tea. In the current study, we hypothesize that the proteasome is a heart disease-associated molecular target of GTPs. We have shown that ester bond-containing GTPs, including (−)-EGCG, potently inhibit the proteasomal activity in intact hepatocellular carcinoma HepG2 and cervical carcinoma HeLa cells, as evident by accumulation of ubiquitinated proteins and three natural proteasome targets (p27, IκB-α and Bax). (−)-EGCG selectively inhibits the chymotrypsin-like, but not trypsin-like, activity of the proteasome. Associated with proteasome inhibition by ester bond-containing GTPs, there was a significant, time- and concentration-dependent increase in levels of the cleaved, activated, but not the precursor, form of sterol regulatory element-binding protein 2 (SREBP-2), an essential factor for LDLR transcription. Subsequently, LDL receptor expression was increased dramatically in HepG2 and HeLa cells treated with (−)-EGCG. Our results suggest that ester bond-containing GTPs inhibit ubiquitin/proteasome-mediated degradation of the active SREBP-2, resulting in up-regulation of LDLR. This identified molecular mechanism may be related to the previously reported cholesterol-lowering and heart disease-preventative effects of green tea.

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Author: S. Coimbra and P. Rocha-Pereira and I. Rebelo and S. Rocha and A. Santos-Silva and E.M.B. Castro

Several studies suggest a protective effect of green tea prepared with leafs of Camellia sinensis for CVD. The interest of the green tea is due to its high content in catechins. Our aim was to evaluate the effect of green tea on some risk factors for CVD. A sample of 34 Portuguese individuals was used. We evaluated the total cholesterol, HDLc, LDLc, triglycerides, lipoprotein (a), apolipoprotein A-I and B, total antioxidant status, lipid peroxidation products, oxidative changes in erythrocyte membrane and the P-selectin levels. The analyses were performed at the beginning, after 3 weeks drinking 1 liter of water daily, and after 4 weeks drinking 1 liter of green tea daily. The tea was prepared everyday in the same conditions. We found no dilution effect on the analyzed parameters. After ingestion of green tea, we found a significant reduction in total cholesterol, LDLc, and apolipoprotein B; an increase in HDLc and apolipoprotein A-I; a decrease in lipid peroxidation and a significant reduction in the oxidative stress within the erythrocyte. We found also an increase in the antioxidant capacity and a decrease in P-selectin levels. Our resuts suggest that green tea has a beneficial effect, protecting for CVD, by improving the lipid profile and the oxidative stress. 

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Author: Dorota Majchrzak and Sabine Mitter and Ibrahim Elmadfa

The beneficial effects of green and black tea are generally attributed to the antioxidant activity of their phenolic compounds. Tea is commonly used with milk or lemon. Milk proteins might complex with tea polyphenols and reduce their antioxidant activity. Lemon contains vitamin C (ascorbic acid) which has antioxidative properties and can positively influence the antioxidant potential of tea. The present study aimed to compare, in vitro, the antioxidant activities of different commercially available types of tea, prepared by commonly used domestic methods and to evaluate the possible effects of different doses (5–40 mg/100 ml) of vitamin C (ascorbic acid) on the total antioxidant capacity (TAC) of tea. The antioxidant activity of tea extracts was determined by the photometric method, according to Rice-Evans and Miller [Methods Enzymol. 234 (1994) 279], measuring the formation of the radical cation ABTS. The values of antioxidant activity of teas prepared in the same way as when consumed were in similar ranges, from 13.3 to 21.6 mmol TE (TE = Trolox equivalents) in green tea and 10.4–17.6 mmol TE in black tea. The experiment in which ascorbic acid was added to teas showed that TAC in black tea extracts increased in a linear manner between 5 and 20 mg ascorbic acid/100 ml tea solution (r=0.984; p<0.01) and in green tea extracts up to 30 mg ascorbic acid/100 ml tea solution (r=0.959; p<0.01).

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Author: Periasamy Srinivasan and Kuruvimalai Ekambaram Sabitha and Chennam Srinivasulu Shyamaladevi

In cancer, a high flux of oxidants not only depletes the cellular thiols, but damages the whole cell as well. Epidemiological studies suggest green tea may mitigate cancers in human and animal models for which several mechanisms have been proposed. In the present investigation, the levels of cellular thiols such as reduced glutathione (GSH), oxidised glutathione (GSSG), protein thiols (PSH), total thiols, lipid peroxidation product conjugated dienes and the activity of gamma glutamyl transferase (GGT) were assessed in tongue and oral cavity. In 4-Nitroquinoline 1-oxide- (4-NQO) induced rats, there was a decrease in the levels of GSH, PSH and total thiols and an increase in the levels of GSSG, conjugated dienes and the activity of GGT. On supplementation of green tea polyphenols (GTP) for 30 days (200 mg/kg) for the oral cancer-induced rats, there was a moderate increase in the levels of GSH, PSH and total thiols and a decrease in the levels of GSSG, conjugated dienes and the activity of GGT. Thus, GTP reduces the oxidant production thereby maintains the endogenous low molecular weight cellular thiols in oral cancer-induced rats. From the results, it can be concluded that GTP supplementation enhances the cellular thiol status thereby mitigate oral cancer.

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Author: Kalyan Sundar Ghosh and Tushar Kanti Maiti and Swagata Dasgupta

Ribonucleases (RNases), which are essential for cleavage of RNA, may be cytotoxic due to undesired cleavage of RNA in the cell. The quest for small molecule inhibitors of members of the ribonuclease superfamily has become indispensable with a growing number exhibiting unusual biological properties. Thus, inhibitors of RNases may serve as potential drug candidates. Green tea catechins (GTC), particularly its major constituent (−)-epigallocatechin-3-gallate (EGCG), have reported potential against cell proliferation and angiogenesis induced by several growth factors including angiogenin, a member of the RNase superfamily. This study reports the inhibition of bovine pancreatic ribonuclease A (RNase A) by EGCG and GTC. This has been checked qualitatively by an agarose gel based assay. Enzyme kinetic studies with cytidine 2′,3′ cyclic monophosphate as the substrate have also been conducted. Results indicate substantial inhibitory activity of a noncompetitive nature with an inhibition constant of ∼80 μM for EGCG and ∼100 μM for GTC measured in gallic acid equivalents.

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Author: Thiraviam Geetha and Amita Garg and Kanwaljit Chopra and Indu Pal Kaur

Tea is consumed worldwide as second largest to water in popularity as a beverage. It has been reported that tea extracts have antibacterial, antiviral, antioxidative, antitumor and antimutagenic activities. The protective effect of green tea has been assumed to be due to the powerful scavenging and antioxidative property of high concentrations of unpolymerised catechins and their gallates. In the present proposal green tea extract (GT), (+)-catechin (C) and (−)-epicatechin (EC) were investigated for their antioxidant activity by different in vitro methods like (i) DPPH assay (ii) superoxide anion scavenging and (iii) hydrogen peroxide scavenging activity. Further these agents were also tested against mutagenesis using the well-standardized Ames microsomal test system. The Ames tester strain Salmonella typhimurium TA102, which readily responds to reactive oxygen species, was used and the antimutagenic activity was evaluated against oxidative mutagens tertiary butyl hydroperoxide (ID50-24.41, 29.63 and 113.23 μg for EC, C and GT, respectively) and hydrogen peroxide (ID50-17.3, 18.4 and 88.1 μg for EC, C and GT, respectively). Ascorbic acid was used as a standard antioxidant in all the experiments. Results indicate that all the three agents possess excellent DPPH free radical scavenging activity (IC50-1.5 μg for EC, 3.45 μg for C and 3.8 μg for GT), good hydrogen peroxide (IC50-11.18 μg for EC, 13.5 μg for C and 11.78 μg for GT) and superoxide anion scavenging (IC50-1.64 μg for EC, 1.74 μg for C and 3.52 μg for GT) activities. Further, they also show antimutagenic activity in the above-mentioned test systems establishing their antioxidant nature to be responsible for such activity. The in vitro antioxidant activity correlates well with the antimutagenic action. (−)-Epicatechin is indicated to be a better agent in comparison to the other two agents (ID50-1.2 times more than C and 5 times more than GT in antimutagenicity studies against t-BOOH and hydrogen peroxide induced mutagenesis). Ascorbic acid however showed a much less activity (ID50-12.1 mg against t-BOOH and 7.2 mg with hydrogen peroxide induced mutagenesis).

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Author: Marcel W.L. Koo and Chi H. Cho

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.

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