Research Database

Author: Yoshinori Fujimura and Shuntaro Tsukamoto and Miho Irie and Daisuke Miura and Hiroyuki Miura and Hirofumi Tachibana

 

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Author: Joshua D. Lambert and Ryan J. Elias

Green tea (Camellia sinensis) is rich in catechins, of which (−)-epigallocatechin-3-gallate (EGCG) is the most abundant. Studies in animal models of carcinogenesis have shown that green tea and EGCG can inhibit tumorigenesis during the initiation, promotion and progression stages. Many potential mechanisms have been proposed including both antioxidant and pro-oxidant effects, but questions remain regarding the relevance of these mechanisms to cancer prevention. In the present review, we will discuss the redox chemistry of the tea catechins and the current literature on the antioxidant and pro-oxidative effects of the green tea polyphenols as they relate to cancer prevention. We report that although the catechins are chemical antioxidants which can quench free radical species and chelate transition metals, there is evidence that some of the effects of these compounds may be related to induction of oxidative stress. Such pro-oxidant effects appear to be responsible for the induction of apoptosis in tumor cells. These pro-oxidant effects may also induce endogenous antioxidant systems in normal tissues that offer protection against carcinogenic insult. This review is meant point out understudied areas and stimulate research on the topic with the hope that insights into the mechanisms of cancer preventive activity of tea polyphenols will result.

 

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Author: Tomomi Kinoshita and Satoshi Hirata and Ziyin Yang and Susanne Baldermann and Emiko Kitayama and Shigetaka Matsumoto and Masayuki Suzuki and Peter Fleischmann and Peter Winterhalter and Naoharu Watanabe

Damascenone is well-known for its potent flavour with an extremely low odour threshold. Several glycosidically bound precursors of damascenone have been isolated from several plants, but little is known about their occurrences in green tea infusions. In this work, three major glycosidic precursors of damascenone, 9-O-β-d-glucopyranosyl-megastigma-6,7-dien-3,5,9-triol (1a), 9-O-β-d-glucopyranosyl-3-hydroxy-7,8-didehydro-β-ionol (2a), and 3-O-β-d-glucopyranosyl-3-hydroxy-7,8-didehydro-β-ionol (2b) were isolated and identified in green tea infusions, and the stereochemistries at C-3 and C-9 positions of aglycone parts of the three glycosidic precursors were determined as (3S, 9R)-1a, (3R, 9R)-2a, and (3R, 9R)-2b, respectively. Compounds 1a, 2a, and 2bas well as 3-O-β-d-glucopyranosyl-megastigma-6,7-dien-3,5,9-triol (1b) were hydrolysed to form damascenone in a model system with strong acidic conditions (pH 2.0) and at high temperature (90 °C). In contrast to hydrolysis of 2a and 2b, more damascenone was transformed from 1a and 1b. Furthermore, the β-d-glucosyl moiety at the C-3 position gave a higher dehydration rate from megastigma-6,7-dien-3,5,9-triol to 3-hydroxy-7,8-didehydro-β-ionol than compound 1a carrying the sugar residue at C-9 position. Interestingly, the four glycosidic precursors of damascenone were not hydrolysed to give damascenone under slightly acidic conditions (pH 5.4 and 120 °C for 10 min), but they could be transformed to damascenone in the presence of green tea infusions even under the equal conditions.

 

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Author: Marco Assunção and Maria J. Santos-Marques and Félix Carvalho and José P. Andrade

Author: Martina Bancirova

Tea is a common beverage. The green tea is preferentially recommended for its strong antioxidant properties and also for its antimicrobial activity. The antioxidant capacities of 30 samples (black and green tea) were determined by the chemiluminescent Trolox equivalent antioxidant capacity (TEAC) determination. The average value of TEAC of the non-fermented (green tea) and semi-fermented tea samples was 1.43 mM and the average value of TEAC of the fermented teas (black tea) samples was 1.43 mM. All samples were stored in freezer (−20 °C) and the TEAC determination was repeated after a year. The average values of TEAC of non-fermented and semi-fermented tea samples were twofold lower in comparison to fermented tea samples and only 20% of average value of TEAC of the fresh tea infusion. The parallel determinations of minimal inhibitory concentration (MIC) on gram-positive and gram-negative bacterial strains (Enterococcus faecalis, Staphylococcus aureus, Pseudomonas aeruginosa and Escherichia coli) were done. Also the MIC was possible to determine after a year. The assumed prevailing antioxidant and antimicrobial activities of non-fermented tea infusions were not confirmed as well as the dominant antioxidant and antimicrobial properties of specific type of tea infusion.

 

 

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Author: Yan Xu and Jun-jian Zhang and Li Xiong and Lei Zhang and Dong Sun and Hui Liu

Responses to oxidative stress contribute to damage caused by chronic cerebral hypoperfusion, which is characteristic of certain neurodegenerative diseases. We used a rat model of chronic cerebral hypoperfusion to determine whether green tea polyphenols, which are potent antioxidants and free radical scavengers, can reduce vascular cognitive impairment and to investigate their underlying mechanisms of action. Different doses of green tea polyphenols were administered orally to model rats from 4 to 8 weeks after experimentally induced cerebral hypoperfusion, and spatial learning and memory were assessed using the Morris water maze. Following behavioral testing, oxygen free radical levels and antioxidative capability in the cortex and hippocampus were measured biochemically. The levels of lipid peroxidation and oxidative DNA damage were assessed by immunohistochemical staining for 4-hydroxynonenal and 8-hydroxy-2′-deoxyguanosine, respectively. Rats that received green tea polyphenols 400 mg/kg per day had better spatial learning and memory than saline-treated rats. Green tea polyphenols 400 mg/kg per day were found to scavenge oxygen free radicals, enhance antioxidant potential, decrease lipid peroxide production and reduce oxidative DNA damage. However, green tea polyphenols 100 mg/kg per day had no significant effects, particularly in the cortex. This study suggests that green tea polyphenols 400 mg/kg per day improve spatial cognitive abilities following chronic cerebral hypoperfusion and that these effects may be related to the antioxidant effects of these compounds.

 

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Author: Quansheng Chen and Jiewen Zhao and Zhiming Guo and Xinyu Wang

Taste sensor technique with multivariate calibration was attempted to determine the contents of catechins (EGCG, EGC and ECG) and caffeine in green tea in this work. The system of data acquisitions based on taste sensor was developed in the experiment. Two multivariate calibrations, which were partial least square (PLS) and artificial neural network with principal component analysis (PCA-ANN), were applied to build forecasting models, respectively. Some parameters were optimized by cross-validation in building model. The performance of the final model was evaluated according to root mean square error of prediction (RMSEP) and correlation coefficient (R) in the prediction set. Experimental results showed that the PCA-ANN model is superior to the PLS model, and the results of each optimal model were obtained by PCA-ANN as follows: RMSEP (%) = 0.2399, R = 0.9037 for Caffeine model; RMSEP (%) = 0.3101, R = 0.8204 for ECG model; RMSEP (%) = 0.4113, R = 0.8384 for EGC model; RMSEP (%) = 0.6065, R = 0.9473 for EGCG model. This work demonstrated that taste sensor technique with multivariate calibration can be successfully employed to determine main catechins and caffeine contents in green tea.

 

 

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Author: Xiaobing Fan and Devkumar Mustafi and Marta Zamora and Jonathan N. River and Sean Foxley and Gregory S. Karczmar

The purpose of this research was to test whether dynamic contrast enhanced MRI could assess the effect of green tea on the angiogenic properties of transplanted rodent tumors. Copenhagen rats bearing AT6.1 prostate tumors inoculated in the hind limbs were randomly assigned to cages in which they were allowed to only drink either plain water (control group) or water containing green tea extract (treated group). Assignments were made after a baseline MRI experiment (week 0) was performed on each rat at 4.7 T. All the rats were subsequently imaged at day 7 (week 1) and day 14 (week 2) to follow tumor growth and vascular development. The two-compartment pharmacokinetic model was used to analyze the dynamic contrast Gd-DTPA enhanced MRI data on a pixel-by-pixel basis over the tumor area to obtain the volume transfer constant (Ktrans) and extravascular extracellular space (ve). An identity Chi-squared test showed that the distributions of averaged histograms (n=6) of Ktrans and ve were significantly different from week 0 to both weeks 1 and 2 (p<0.001) in both the control and the treated rats due to increasing areas of tumor necrosis. However, the tumor growth rate was statistically indistinguishable between control and treated rats. There was no significant difference in the distributions of Ktrans and ve between control and treated rats. The results showed that no effects of green tea on tumor micro-vasculature were measurable by dynamic Gd-DTPA enhanced MRI.

 

 

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Author: Lei Li and C.-Y. Oliver Chen and Giancarlo Aldini and Elizabeth J. Johnson and Helen Rasmussen and Yasukazu Yoshida and Etsuo Niki and Jeffrey B. Blumberg and Robert M. Russell and Kyung-Jin Yeum

Epigallocatechin gallate, a major component of green tea polyphenols, protects against the oxidation of fat-soluble antioxidants including lutein. The current study determined the effect of a relatively high but a dietary achievable dose of lutein or lutein plus green tea extract on antioxidant status. Healthy subjects (50–70 years) were randomly assigned to one of two groups (n=20 in each group): (1) a lutein (12 mg/day) supplemented group or (2) a lutein (12 mg/day) plus green tea extract (200 mg/day) supplemented group. After 2 weeks of run-in period consuming less than two servings of lightly colored fruits and vegetables in their diet, each group was treated for 112 days while on their customary regular diets. Plasma carotenoids including lutein, tocopherols, flavanols and ascorbic acid were analyzed by HPLC-UVD and HPLC-electrochemical detector systems; total antioxidant capacity by fluorometry; lipid peroxidation by malondialdehyde using a HPLC system with a fluorescent detector and by total hydroxyoctadecadienoic acids using a GC/MS. Plasma lutein, total carotenoids and ascorbic acid concentrations of subjects in either the lutein group or the lutein plus green tea extract group were significantly increased (P<.05) at 4 weeks and throughout the 16-week study period. However, no significant changes from baseline in any biomarker of overall antioxidant activity or lipid peroxidation of the subjects were seen in either group. Our results indicate that an increase of antioxidant concentrations within a range that could readily be achieved in a healthful diet does not affect in vivo antioxidant status in normal healthy subjects when sufficient amounts of antioxidants already exist.

 

 

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Author: Daniele Del Rio and Luca Calani and Chiara Cordero and Sara Salvatore and Nicoletta Pellegrini and Furio Brighenti

Objective The aim of this study was to investigate green tea flavan-3-ol catabolism and plasma pharmacokinetic and urinary excretion by high-performance liquid chromatography with tandem mass spectrometry to evaluate their absolute bioavailability by taking into account all known and some unknown catabolites deriving from their interaction with the gastrointestinal tract and its host microflora. Methods A feeding study was carried out in 20 healthy human volunteers who ingested 400 mL of a ready-to-drink green tea containing approximately 400 μmol of flavan-3-ols. Urine and plasma were collected for 4 and 24 h, respectively, and 39 relevant catabolites were identified in these biological fluids by tandem mass spectrometry. Results In biological fluids, 39 relevant flavan-3-ol catabolites were identified. In plasma, (−)-epigallocatechin-3-gallate was the only unmetabolized compound and the highest in absolute concentration compared with (−)-epigallocatechin and (−)-epicatechin conjugates. Colonic microflora-derived polyhydroxyphenyl-γ-valerolactones were by far the main urinary catabolites, averaging 10 times greater concentratin than flavan-3-ol conjugates. The calculated bioavailability was equal to 39% and it is interesting to notice the great variability in urinary excretion of colonic metabolites among participants, probably related to differences in their own colonic microflora. Conclusion This study demonstrates that green tea catechins are more bioavailable than previously observed when colonic ring fission metabolites are taken into consideration. Regular consumption of ready-to-drink green tea containing flavan-3-ols allows a non-marginal exposure of the human body to these catabolites, somehow justifying the numerous beneficial actions described as linked to green tea intake.

 

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