Main and interactive effects of vitamin C and green tea supplementation on biomarkers of DNA damage and repair

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Main and interactive effects of vitamin C and green tea supplementation on biomarkers of DNA damage and repair

 

Author: Wong, Tin-che Grace
Title: Main and interactive effects of vitamin C and green tea supplementation on biomarkers of DNA damage and repair
Degree: M.Sc.
Year: 2006
Subject: Hong Kong Polytechnic University -- Dissertations.
Vitamin C -- Health aspects.
Green tea -- Health aspects.
Antioxidants -- Therapeutic use.
DNA.
Biochemical markers.
Department: Dept. of Health Technology and Informatics
Pages: vii, 120 leaves : ill. (some col.) ; 30 cm.
Language: English
InnoPac Record: http://library.polyu.edu.hk/record=b2174239
URI: http://theses.lib.polyu.edu.hk/handle/200/800
Abstract: Background: Prolonged exposure to oxidative stress will increase oxidative damage to biomolecules. Oxidative damage to biomolecules is believed to be an important causative factor in cancer and in a variety of aged-related diseases including cardiovascular disease. Therefore, if the disease risk can be lowered through increasing the protective defense against oxidative damage by a simple strategy of increasing intake of dietary antioxidants, then antioxidant-rich foods including green tea and vitamin C may have important implications in the prevent/delay the onset of aged-related diseases. Delaying the onset of these diseases will greatly increase the quality of life and also lower healthcare cost. Thus, it is of interest to evaluate the antioxidant and other effects of vitamin C and green tea, alone and in combination in healthy subjects in relation to the plasma antioxidant status after ingestion and the effects on DNA integrity and repair. Method: A randomized, single blinded human supplementation trial of 32 apparently healthy, consenting subjects with placebo control and incomplete balanced block design was employed. Fasting venous blood plasma and lymphocytes were collected from subjects before and after four weeks' supplementation with vitamin C, or green tea alone, both in combination or neither (double placebo), with each subject taking two different supplementation regimens in the study. There was a 6 week washout period in between the two supplementation regimens. Total antioxidant capacity of plasma was measured by the Ferric Reducing/ Antioxidant Power (FRAP) assay. The protective and repair effect of supplementation regimens on lymphocytic DNA damage after an in vitro oxidant challenge by different concentrations of H2O2 with or without repair treatment was assessed by the Comet assay. A non-parametric, two tailed unpaired t-test was used to investigate a) pre and post supplementation within each regimen and b) between the four supplementations on stressed lymphocytes with or without repair treatment. Pearson's correlation analysis was used to investigate the interrelationships between FRAP values and DNA damage in stressed lymphocytes. All comparisons that met the 5% significance level (P<0.05) were considered statistically significant. Results: Before supplementation, a similar background oxidative DNA damage was seen in both the supplemented and the control group and the damage caused by H2O2 at each concentration level (0uM, 15uM and 45uM) was also similar. Post vitamin C supplementation statistical significantly showed both a decrease in oxidative DNA damage after repair and no repair treatment. Post green tea did not show any significant decrease in oxidative DNA damage after repair and no repair treatment. Post vitamin C and green tea supplementation, no statistical significantly decrease in oxidative DNA damage after repair and no repair treatment, in fact the effect of vitamin C alone was lost. When plasma antioxidant capacity was correlated to basal and stressed DNA damage, mixed results of both a direct and inverse correlation was seen. Conclusion: Vitamin C alone supplementation conferred a significant protective effect on basal DNA damage and an increased repair capacity in damaged lymphocytes. No synergistic or co-operative interaction effect between vitamin C and green tea on total antioxidant capacity or in oxidative DNA damage with or without repair treatment was seen. Further study is needed to ascertain the benefits of green tea alone supplementation and follow-up study is needed for the adjustment of uric acid in the total antioxidant capacity.

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