| Summary: | 碩士 === 國立中興大學 === 食品科學系 === 88 === Abstract
The objectives of this study were to investigate the antioxidant properties of the extracts from various tea extracts (green tea, GTE; oolong tea, OTE; and black tea, BTE), and five tea polyphenols (epicatechin, EC; epicatechin gallate, ECG; epigallocatechin, EGC; epigallocatechin gallate, EGCG; and theaflavins, THFs) using TEAC (trolox equivalent antioxidant capacity) method. The effects of those tea extracts and polyphenols on H2O2 and B[a]P-induced DNA damage in human blood lymphocytes and Chang liver cells were also evaluated using comet assay.
According to TEAC assay results, total antioxidant activity (expressed as trolox equivalent) of those three tea extracts was in the order of GTE (3.6) > OTE (3.3) > BTE (2.3), and the tea polyphenols was in the order of ECG (4.9) > EGCG (4.0) > THFs (3.6) > EGC (3.1) > EC (2.5). The results indicated that catechins with binding gallate group on C ring have higher antioxidant activity than those without binding. The total polyphenolic contents in GTE, OTE and BTE were 32, 28.1 and 22.8%, and the total catechins contents was 25.8, 21.2 and 8.7%, respectively. Total polyphenolics and catechins content and antioxidant activity of tea extracts were correlated to their fermentation degree.
Tea extracts did not affect the cell viability of human blood lymphocytes and Chang liver cells. In the same test conditions, tea extracts also did not cause the DNA damage in these cells.
The H2O2-induced DNA damage in lymphocytes was significantly inhibited by those three tea extracts at a concentration of 10 mg/ml (P<0.05). At a concentration of 100 mg/ml, the % tail DNA was reduced from 41.17% (H2O2 treated only) to 11.20, 7.74, 15.73%, by GTE, OTE and BTE. The inhibition percentage for those three tea extracts was 72.8, 81.2, and 61.8%, respectively. The results also indicated that GTE, OTE and BTE showed 56, 60, and 52%, respectively, scavenging effects on H2O2 at a concentration of 100 mg/ml. Therefore, the inhibitory effect of tea extracts on H2O2 —induced DNA damage in lymphocytes was due to the scavenging effects on H2O2.
The B[a]P-induced DNA damage in Chang liver cells was also significantly (P<0.05) inhibited by GTE and OTE at a concentration of 10 mg/ml and BTE at 25 mg/ml. At a concentration of 100 mg/ml, the % tail DNA was reduced from 33.40% (only B[a]P treated) to 9.82, 8.69, 12.8% by GTE, OTE and BTE. The inhibition percentage for those three tea extracts was 70.6, 74, and 61.5%, respectively. The activity of glutathion S-transferase in Chang liver cells was significantly (P<0.05) enhanced by incubating with tea extracts at a concentration of 100 mg/ml.
Tea polyphenols, EC, ECG, EGC, EGCG and theaflavins at a concentration of 10-200 mM did not affect the cell viability of lymphocytes and Chang liver cells. EC and ECG did not cause DNA damage in these two cells using comet assay; however, EGC, EGCG and theaflavins caused DNA damage in cells at a concentration of 100-200 mM. The results indicated that EC and ECG showed protective effects against H2O2 and B[a]P-induced DNA damage in cells at a concentration of 100-200 mM. Although EGC, EGCG and theaflavins caused DNA damage at a high concentrations, but they showed protective effects against H2O2 and B[a]P-induced DNA damage in cells at low concentration of 10-50 mM.
The results also showed that DNA damage induced by EGC, EGCG and theaflavins was due to generation of superoxide during incubated with cells at high concentration of 200 mM.
Based on the results of this study, these tea extracts could inhibit H2O2 and B[a]P-induced DNA damage in lymphocytes and Chang liver cells by scavenging hydrogen peroxide and enhanced activity of glutathione S-transferase. Although EGC, EGC and THFs might cause DNA damage in cells by generation of superoxide at a high concentration, EC, ECG, EGC, EGCG and THFs also could inhibite DNA damage in cells induced by H2O2 or B[a]P at low concentration (10-50 mM). Therefore, tea catechins and theaflavins contribute an important factors in tea extracts to inhibit DNA damage in human blood lymphocytes and Chang liver cells.
Key word: tea, tea polyphenols, catechin, theaflavins, TEAC, comet assay, DNA damage, lymphocytes, Chang liver cell.
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