Effects of two kinds of green tea (Loongjin and screw-shaped green tea) on DNA damage and protection

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Effects of two kinds of green tea (Loongjin and screw-shaped green tea) on DNA damage and protection

 

Author: Han, Kam-chu
Title: Effects of two kinds of green tea (Loongjin and screw-shaped green tea) on DNA damage and protection
Degree: D.H.Sc.
Year: 2010
Subject: Hong Kong Polytechnic University -- Dissertations
Green tea -- Therapeutic use
Active oxygen in the body
DNA repair
Department: Faculty of Health and Social Sciences
Pages: xv, 154 leaves : ill. ; 31 cm.
InnoPac Record: http://library.polyu.edu.hk/record=b2354995
URI: http://theses.lib.polyu.edu.hk/handle/200/5718
Abstract: Due to the aging of our population, healthy aging is an important target for our society. Researchers try to study the cause of age-related diseases so that healthy aging and functional longevity can be promoted. The body structures are continuously exposed to potentially damaging reactive oxygen species (ROS). These ROS are believed to cause oxidative DNA damage leading to mutation cellular aging, dysfunction and cell death within the body. These changes are counteracted by the antioxidant defences. Dietary supplementation with antioxidants and increased intake of antioxidant-rich foods and beverages is the trend, as there is some evidence that this is a possible way to lower risk of age-related disease. Green tea (Camellia sinensis) contains high concentration of polyphenols which are a class of powerful antioxidants that scavenge ROS. There are many kinds of green tea on the market and Loongjin and Screw-shaped Green Tea are two types of green tea commonly consumed by Chinese. In the first part of this study, the in vitro effect of different concentrations of Loongjin and Screw-shaped Green Tea on DNA damage and protection was determined. In the second part of the study, the effects of 4 weeks' supplementation with each of the two green teas on basal DNA damage and protection against standard oxidant stress were investigated in a controlled human (n=18) intervention trial of cross-over design. The effects on human lymphocytic DNA damage and protection against oxidant stress were measured by different forms of the comet assay, a well validated and widely used biomonitoring tool. In vitro test results showed that antioxidant content and DNA protective effects in oxidative stressed cells of the two teas were similar and they do not induce DNA damage at all the concentrations tested. A significant protective effect (P<0.05) was seen following exposure to both types of tea at as low a concentration as 0.005% w/v. However such effect is not seen in unstressed cells. In human intervention trial, supplementation with Loongjin and screw-shaped green tea, as compared to water (control treatment), significantly (P<O.O1) increased the resistance of lymphocytic DNA to oxidative challenge. In addition. result of enzyme-assisted comet assay showed that the basal oxidative DNA damage in lymphocytes was decreased by ~30% (P<0.05) after 4 weeks' supplementation with tea. No significant difference was found between the response to Loongjin and Screw shaped green tea.

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