| Summary: | 碩士 === 中山醫學大學 === 醫學分子毒理學研究所 === 93 === Lung cancer is the first and the second leading cause of cancer death among females and males in Taiwan, respectively. Several studies showed that lung cancer is associated with exposure to the environmental carcinogens and mutagens. Epidemiological studies suggested that exposure to cooking oil fumes (COF) increased the risk of female lung cancer in Taiwan. Dienaldehydes are by-products of peroxidation of polyunsaturated lipids and found in many foods and food-products. Trans, trans-2,4-decadienal (tt-DDE or 2,4-De) is a type of dienaldehydes and is abundantly found in heated oils, including COF. The aim of this study was to investigate the biological effects induced by tt-DDE and the possible protective mechanism of antioxidant-vitamin C and N-acetylcysteine (NAC) in immortalized human bronchial epithelial cells BEAS-2B. Cell proliferation was assayed using MTT method. Intracellular reactive oxygen species (ROS) was analyzed by flow cytometry and the genes expression was determined with the real-time RT-PCR method. We found that treatment with 0.1 micromole or 1 micromole tt-DDE for 48 hr or 29 days significantly increased intracellular oxidative stress in lung cells. Furthermore, 5 micromole tt-DDE selectively reduced viable cell numbers in BEAS-2B cells, but not in lung cancer cells. On the other hands, treatment with 0.1 micromole or 1 micromole tt-DDE for 48 hr or 32 days decreased the GSH/GSSG ratio and GSH (reduced form), but increased total GSH (including reduced and oxidized forms) and GSSG (oxidized form). Therefore, these data suggested that tt-DDE induced intracellular oxidative stress might urge the GSH (reduced form) to turn into GSSG, and also increase the total glutathione. Long-term exposure (30-45 days) with sub-lethal doses (0.1 or 1 micromole) of tt-DDE significantly increased cell growth of BEAS-2B cells. On day 45, TNF-alpha and IL-1 beta gene expression and secretion was significantly increased in 1 micromole tt-DDE-treated cells, and also IL-6 mRNA levels were increased. In contrast, co-treatment with vitamin C or N-acetylcysteine, antioxidants, partially pervented tt-DDE induced cell proliferation, decreased pro-inflammatory genes expression. TNF-alpha、IL-1beta and IL-6 are pro-inflammatory cytokines. Several tumor promoters were shown to increase their secretion. On the other hands, we found that p27 mRNA levels reduced by 1 micromole DDE- treated for 45 days in BEAS-2B cells, and this reduction was protected by NAC co-treatment. It has been reported that TNF-alpha and IL-1beta had tumor promotion function, and many tumor promoters increased ROS generation. Therefore, tt-DDE might be a tumor promoter via increasing intracellular ROS in human bronchial epithelium cells.
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