Effects of metabolic activation and altered gene expression on the induction of oxidative stress, DNA damage, and cell toxicity in human breast cancer cells by polychlorinated biphenyls (PCBs)

• Main Authors: Ching-Lung Huang, 黃景隆
• Other Authors: Po-Hsiung Lin
• Format: Others
• Language: zh-TW
• Published: 2005
• Online Access: http://ndltd.ncl.edu.tw/handle/34040164716643403534

碩士 === 國立中興大學 === 環境工程學系 === 93 === The objective of this research is to examine the effects of metabolic activation and altered gene expression on the induction of oxidative stress, DNA damage, and cell toxicity by polychlorinated biphenyls (PCBs), including PCB52 and PCB77, in human ERα(++)/MCF-7, ERα(+)/T47D and ERα(-)/MDA-MB-231 breast cancer cells. Results indicated that both PCB52 and PCB77 induced concentration- and time-dependent increases in cytotoxic response in MCF-7, T47D, and MDA-MB-231 cells. The extent of cytotoxic response induced by these two PCB congeners in human breast cancer cells was greater for PCB52 than for PCB77. Additionally, the reduction in the number of viable cells exposed to PCBs was primarily mediated by apoptosis. Further, α-naphthoflavone, resveratrol, and metyrapone blocked the PCB52-induced cell toxicity in T47D and MDA-MB-231 cells, but not in MCF-7 cells. The data also showed that PCB52 and PCB77 induced significant increases in intracellular levels of reactive oxygen species (ROS) in MCF-7, T47D, and MDA-MB-231 cells, particularly in MDA-MB-231 cells. In addition, when cells were exposed to PCBs at non-cytotoxic concentration, we observed that PCB52 (1 mM) and PCB77 (10 mM) alone or mixture did not induce decreases in intracellular NAD(P)H in MCF-7 cells. In contrast, both PCB52 and PCB77 induced decreases in intracellular NAD(P)H and NAD＋ through formation of DNA strand breaks and poly(ADP-ribose)polymerase-1 activation in T47D and MDA-MB-231 cells. Antagonism was detected in T47D and MDA-MB-231 cells exposed to PCB52/PCB77 mixture. Further, results from semi-quantitative reverse-transcription polymerase chain reaction (semi-quantitative RT-PCR) analyses indicated that exposure to PCB77 (10 mM) induced increases in the expression of CYP1A1, hAPE, and XRCC1 whereas PCB52 (1 mM) alone induced increases in the expression of hOGG1, hAPE, and XRCC1. Similar observation was also detected in MCF-7 cells exposed to PCB52/PCB77 mixture. On the other hand, both PCB52 (10 mM) and PCB77 (10 mM) induced increases in the expression of CYP1A1 and XRCC1 genes whereas PCB52/PCB77 mixture induced increases in the expression of CYP1A1 in MDA-MB-231 cells. Overall, this evidence indicates that both PCB52 and PCB77 may induce ROS formation and imbalances in the expression of genes responsible for the DNA repair process and apoptosis in MCF-7 cells. In contrast, PCB52 and PCB77 are likely to mediate the induction of ROS formation, DNA strand breaks, and cell toxicity through futile cycling and/or redox cycling in MDA-MB-231 cells. The data also suggests that the status of estrogen receptor a may play a role in modulating the PCB-induced DNA damage and cytotoxic response in human breast cancer cells.