Author: Chugani, Rajeev Ramesh
Title: Are the components of green tea directly responsible for preventing DNA damage?
Degree: M.Sc.
Year: 2012
Subject: Green tea -- Therapeutic use.
Active oxygen in the body.
DNA repair.
Hong Kong Polytechnic University -- Dissertations
Department: Department of Health Technology and Informatics
Pages: xv, 101 leaves : ill. (some col.) ; 30 cm.
Language: English
Abstract: Due to the aging population of our society, many age related diseases are becoming increasingly dominant. These include cardiovascular diseases and cancers. This has led researchers to try and study the causes of age-related diseases as well as potential sources of drugs and natural resources to aid in slowing down the process of aging and increase the longevity of life. The cells within the human body are continuously being repaired and grown through the cell cycle. Ultimately, this would leave room for different factors and components to interact with cells' natural processes, be it to aid or damage them. Included is a group of damaging molecules known as reactive oxygen species (ROS). These ROS are believed to cause oxidative damage to DNA, which lead to mutations, cellular dysfunction and ultimately death. These molecules are normally counteracted with other molecules known as antioxidants. Dietary supplements with antioxidants together with rich antioxidant foods and beverages are thus consumed specifically to aid in possibly lowering the risk of age related diseases. There is some positive evidence that agrees with this. However, antioxidants have also been reported to generate hydrogen peroxide and to damage DNA under certain conditions. Green tea (Camellia sinensis) contains high concentrations of polyphenols. Polyphenols are a class of powerful antioxidants that scavenges ROS. There are many different kinds of tea in the market; however this study focuses on a particular type of green tea known as Loongjin, which is commonly available in China. This study is divided into two parts. In the first part of this study, the in vitro effects of the different concentrations of green tea on DNA damage were determined. The damaging effects were also observed, to see if these were due to hydrogen peroxide produced by the green tea. This was done by removing hydrogen peroxide with the aid of enzymes. The enzymes used were catalase and superoxide dismutase. The least damaging concentration of tea observed in this part was then used in the second part of the study.
In the second part of the study, the concentration of green tea that demonstrated no or minimal damaging effects upon lymphocytes was tested again, however after incubating the cells with green tea, the cells were exposed to a standard oxidant challenge induced by a known amount of hydrogen peroxide. The results observed would demonstrate the protective effects of the green tea upon cells, when compared to the control. The effects on human lymphocytic DNA damage and protection were measured using the comet assay. Eight apparently healthy, non-smokers of ages between 20 to 55 years old were recruited with their informed consent. 20ml of blood was harvested from each individual. Lymphocytes were harvested, pooled and cryopreserved. The first part of the study demonstrated that for all the tested concentrations, the green tea induced some DNA damage. A significant amount of damage (p < 0.05) was seen at concentrations of green tea at 0.01% (w/v) and higher. It was observed that with the addition of catalase and superoxide dismutase the amount of damage seen decreased across all concentrations. There was statistical significance between the amount of damage seen with and without the use of catalase and superoxide dismutase with concentrations of 0.01% (w/v) green tea and higher. As a result, in the second part of the study, the least damaging concentration (0.005% (w/v) green tea) was used, together with a concentration half of that to observe if protection was seen when the cells were further stressed with oxidant challenge after incubating them with green tea first. Interestingly enough, when comparing 0.0025% (w/v) green tea with the control (PBS), there was a statistical significance seen after application of oxidative stress. Additionally, with the addition of catalase and superoxide dismutase, the damage in DNA seen in both concentrations was similar to the control group. This means there was an increase in damage observed, though not statistically significant when compared to cells incubated without catalase and superoxide dismutase, with the concentrations tested. In conclusion, the current study demonstrated that the damage seen in the lymphocytes was due to hydrogen peroxide produced at higher concentrations of green tea. It also demonstrated that at lower concentrations, it was the small amount of hydrogen peroxide that provided cytoprotection when oxidative stress was subsequently applied to the pre-treated cells. Further studies including both testing lower concentrations of green tea and to observe proteins related to cytoprotection and DNA repair are suggested to be carried out to gain a better understanding of the mechanisms of protection seen.
Rights: All rights reserved
Access: restricted access

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