| Author: | Tse, Ying-kit |
| Title: | An in vitro study on the effect of green tea on oxidative DNA damage anda comparison of basal DNA damage and antioxidant enzymes in normal human white blood cells (lymphocytes) and malignant human white blood cells (HL 60 cells) |
| Degree: | M.Sc. |
| Year: | 2005 |
| Subject: | Hong Kong Polytechnic University -- Dissertations Green tea -- Analysis |
| Department: | School of Nursing |
| Pages: | viii, 84 leaves : ill. (some col.) ; 30 cm |
| Language: | English |
| Abstract: | An in vitro study was undertaken to investigate the genotoxic and genoprotective effects of green tea on normal human white blood cells (lymphocytes) and malignant human white blood cells (HL60 cells). Single cell gel electrophoresis (comet assay) was performed to measure DNA damage in treated, untreated, challenged and unchallenged cells in parallel, oxidant challenge being induced by hydrogen peroxide. In addition to possible differences in DNA damage scores in the two types of cells, baseline activities of the antioxidant enzymes - glutathione reductase (GR), glutathione peroxide (GPX) and superoxide dismutase (SOD) of both types of cells were compared. GPX and SOD were measured by commercial kit methods and GR was relatively measured by in-house protocol. Green tea showed no cytotoxicity to normal lymphocytes and HL 60 cells at the tested concentration 0.0001% - 0.01% (w/v). However, DNA damage was induced by 0.002% (w/v) and higher concentrations of green tea. The highest non-damaging concentration of green tea in normal lymphocytes and HL 60 cells was the same (0.001% w/v). There were no significant differences in basal DNA damage between the two types of cells. Incubation in PBS, DNA damage (Mean tail DNA content % +- SD) in normal lymphocytes was 7.74 +- 0.57 and HL 60 cells was 7.23 +- 0.53. In addition, incubation in 0.001% w/v green tea significantly decreased DNA damage (Mean tail DNA content % +- SD) in normal lymphocytes (12.93 +- 2.67 vs 9.14 +- 0.97, P < 0.05) and HL60 cells (12.80 +- 1.06 vs 8.09 +- 1.07, P<0.05)after subsequent exposure to a standard oxidant challenge (15 uM H2O2). These data indicate that tea has the same effect on both types of cells studied in relation to damage and genoprotection in both types of cells. Furthermore, the pro-oxidant effect of high concentration of green tea in both types of cells was mediated by generation of H2O2, as demonstrated by the removing the damaging effect by adding catalase to the incubation mixture. Our results demonstrated that low concentration of green tea caused no DNA damage and had the protective effect of oxidative challenge in normal lymphocytes and HL6O cells. Results imply that some of the health benefits of green tea in relation to lower risk of heart disease and cancer may be mediated by generation of small amounts of H2O2 which stimulates the cells to upregulate the antioxidant enzymes or other defenses against oxidant challenge under the concept of 'hormesis' theory. Baseline enzyme activities of both types of cells were low and different. Normal lymphocytes had more GR and GPX than HL 60 cells. However, HL 60 cells had more SOD than normal lymphocytes. The differences may be due to different types of cells used; HL 60 cells are myeloid cells and lymphocytes are lymphoid cells. Baseline enzymes activities did not show any significant relationship to basal DNA damage. Data will support further investigation on the effect of green tea on enzyme levels of cells and their role in genoprotection. |
| Rights: | All rights reserved |
| Access: | restricted access |
Files in This Item:
| File | Description | Size | Format | |
|---|---|---|---|---|
| b18181338.pdf | For All Users (off-campus access for PolyU Staff & Students only) | 3.58 MB | Adobe PDF | View/Open |
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