The formation of
reactive oxygen species (ROS) plays a critical role in
2,3,7,8-tetrachlorodibenzo-p-dioxin (
TCDD)-induced toxicities in mammalian cells since it promotes cell proliferation, growth arrest, and apoptosis. In this study, we investigated whether
TCDD induces oxidative stress and DNA damage in human
ERalpha(+)/MCF-7 and
ERalpha(-)/MDA-MB-231
breast cancer cells and whether this is accompanied by the initiation of DNA repair events. Results indicated that viability of MCF-7 and MDA-MB-231 cells was concentration- and time-dependently reduced by
TCDD. Further, we observed significant increases in ROS formation and decreases in intracellular
glutathione (GSH) in these two cell lines after
TCDD treatment. Overall, the extent of cell death was greater in MCF-7 cells than in MDA-MB-231 cells whereas the magnitude of ROS formation and GSH depletion was greater in MDA-MB-231 cells than in MCF-7 cells. In addition, we observed that at non-cytotoxic concentration (1nM for 5h),
TCDD induced decreases in intracellular
NAD(P)H and
NAD(+) in MCF-7 and MDA-MB-231 cells. These decreases were completely blocked by three types of
poly(ADP-ribose) polymerase-1 (PARP-1) inhibitors. The catalytic activation of PARP-1 in cells treated with
TCDD was confirmed by detection of the presence of
polymers of
ADP-ribose-modified PARP-1 using Western blotting. Moreover, we demonstrated increases in the number of
DNA strand breaks in MCF-7 and MDA-MB-231 cells exposed to
TCDD as measured by the single-cell gel electrophoresis (Comet) assay. Overall, this evidence confirms that
TCDD induces decreases in intracellular
NAD(P)H and
NAD(+) through PARP-1 activation mediated by formation of
DNA strand breaks. In addition, we demonstrated that the extent of oxidative stress and DNA damage was greater in MDA-MB-231 cells than in MCF-7 cells, with a strong correlation to
estrogen receptor (ER) status. In conclusions, our findings add further support to the theme that ROS formation is a significant determinant factor in mediating the induction of oxidative DNA damage and repair in human
breast cancer cells exposed to
TCDD and that the
TCDD-induced oxidative stress and DNA damage may, in part, contribute to
TCDD-induced
carcinogenesis.