Preventive Effects of Chlorophyll Derivatives on Induced-type DNA Damage

Autor: Ching-Yun Hsu, 許青雲
Rok vydání: 2008
Druh dokumentu: 學位論文 ; thesis
Popis: 97
Chlorophylls (Chls) are the most abundant natural plant pigments. Four chlorophyll derivatives, including chlorophyllide a and b (Chlide a and b) and pheophorbide a and b (Pho a and b), were investigated for their in vitro antioxidative capacities and anticytotoxicity properties to the cell DNA damage. First, the antioxidative effects of four chlorophyll derivatives on hydrogen peroxide (H2O2)-induced strand breaks and oxidative damage were evaluated in human lymphocyte. Lymphocytes exposed to H2O2 at a concentration of 10 and 50µM revealed an increased frequency of DNA single-strand breaks (ssbs; as measured by the comet assay) and also the level of oxidized nucleoside (as measured by 8-hydroxy-2-deoxyguanosine; 8-OHdG). All Chls reduced the level of DNA ssbs and 8-OHdG within human lymphocytes following exposure to 10µM H2O2. Only Pho a and b were able to decrease DNA ssbs and 8-OHdG following treatment of lymphocytes with 50µM H2O2, in a concentration-dependent fashion. It was demonstrated herein that Pho a and b, were more antioxidative than others. We applied DPPH free-radical scavenge assays in vitro, and also got similar results. Pho a and b were higher ability on scavenging capacities than others. In the second part, the inhibitory effects of four chlorophyll derivatives on aflatoxin B1 (AFB1)-DNA adduct formation, and on the modulation of hepatic glutathione S-transferase (GST) were evaluated in murine hepatoma (Hepa-1) cells. Enzyme-linked immunosorbent assay (ELISA) showed that pretreatment with Chlide or Pho significantly reduced the formation of AFB1-DNA adducts, and that Pho was the most potent inhibitor. However, wash-out prior to adding AFB1 totally eliminated inhibition by Childe and partially eliminated inhibition by Pho, indicating that the inhibitory effect of Chlide, and to some extent Pho, was mediated through direct trapping of AFB1. Furthermore, spectrophotometric analysis showed that Pho treatment could increase GST activity in Hepa-1 cells. These observations indicate that the chlorophyll derivatives studied may attenuate AFB1-induced DNA damage in the Hepa-1 cell by direct trapping of AFB1. Pho provided additional protection not only by direct trapping, but also by increasing GST activity against hepatic AFB1 metabolites. We conclude that water extract Chls are able to enhance cells’ ability to resist H2O2-induced oxidative damage and (AFB1)-DNA adduct formation, especially for Pho a and b.
Databáze: Networked Digital Library of Theses & Dissertations
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