Formation Of DNA Strand Breaks Research Articles

Protective role of estrogen receptor-alpha on lower chlorinated PCB congener-induced DNA damage and repair in human tumoral breast cells

Polychlorinated biphenyls (PCBs) are ubiquitous environmental contaminants. Much of the research has focused on the carcinogenic potential of higher chlorinated PCBs, but accumulative evidence has shown that lower chlorinated PCB congeners have initiating and promoting activities. The goal of this study was to examine the potential of lower chlorinated PCBs, including 2,2',5,5'-tetrachlorobiphenyl (PCB52) and 3,3',4,4'-tetrachlorobiphenyl (PCB77), to induce DNA damage and apoptosis in human MDA-MB-231 (MDA) and MCF-7 breast cancer cells. Results confirmed that treatment of cells with PCB52 and PCB77 resulted in oxidative stress and caspase-dependent apoptosis in both MDA and MCF-7 cells. We noticed that at non-cytotoxic concentrations PCB52 and PCB77-induced decreases in intracellular NAD(P)H in MDA cells but not in MCF-7 cells. Further investigation confirmed that decreases in intracellular NAD(P)H in PCB-treated MDA cells are primarily due to reduction in intracellular NAD(+) pool mediated by poly(ADP-ribose)polymerase-1 activation through formation of DNA strand breaks. Antagonism was observed between PCB52 and PCB77 for the effect on induction of DNA strand breaks in MDA cells. Overall, this evidence demonstrates that at non-cytotoxic concentrations, lower chlorinated PCB congeners are capable of inducing oxidative DNA lesions in ERalpha(-)/MDA cells but not in ERalpha(+)/MCF-7 cells and that functional ERalpha plays a protective role in modulating the PCB-induced DNA damage in human breast cancer cells.

Bioreduction of Idarubicin and Formation of ROS Responsible for DNA Cleavage by NADPH-Cytochrome P450 Reductase and its Potential Role in the Antitumor Effect

Idarubicin is a clinically effective synthetic anthracycline analog used in the treatment of several human neoplasms. Anthracyclines have the potential to undergo bioactivation by flavoenzymes to free radicals and thus exert their cytotoxic actions. In this study, our main objective was to investigate the possible involvement of NADPH-cytochrome P450 reductase in the bioreductive activation of idarubicin to DNA-damaging species. A pBR322 plasmid DNA damage assay was used as a sensitive method for detecting strand breaks in DNA exposed to idarubicin in the presence of P450 reductase and cofactor NADPH under various incubation conditions. In addition, the rates of idarubicin reduction by P450 reductases purified from phenobarbital-treated rabbit liver, beef liver and sheep lung microsomes were determined by measuring NADPH oxidation at 340 nm. The plasmid DNA experiments demonstrated that idarubicin could undergo bioreduction by P450 reductase with the resulting formation of DNA strand breaks. The antioxidant enzymes SOD and catalase, and hydroxyl radical scavengers, DMSO and thiourea, afforded significant levels of protection against idarubicin-induced DNA strand breaks. These findings suggested that DNA damage by idarubicin occurs through a mechanism which involves its redox cycling with P450 reductase to generate reactive oxygen species (ROS). The extent of DNA damage by idarubicin was found to increase with increasing concentrations of drug or enzyme as well as with increasing incubation time. The capacity of idarubicin to induce DNA damage under above incubation conditions was compared with that of a model compound, mitomycin C. Finally, enzyme assays carried out with purified P450 reductases revealed that idarubicin exhibited about two-fold higher rate of reduction than mitomycin C. Our findings implicated bioreduction of idarubicin by P450 reductase and subsequent redox cycling under aerobic conditions as being one mode of idarubicin action potentially contributing to its antitumor effect.

Alpha-lipoic acid potently inhibits peroxynitrite-mediated DNA strand breakage and hydroxyl radical formation: implications for the neuroprotective effects of alpha-lipoic acid

Alpha-lipoic acid (LA) has recently been reported to afford protection against neurodegenerative disorders in humans and experimental animals. However, the mechanisms underlying LA-mediated neuroprotection remain an enigma. Because peroxynitrite has been extensively implicated in the pathogenesis of various forms of neurodegenerative disorders, this study was undertaken to investigate the effects of LA in peroxynitrite-induced DNA strand breaks, a critical event leading to peroxynitrite-elicited cytotoxicity. Incubation of phi X-174 plasmid DNA with the 3-morpholinosydnonimine (SIN-1), a peroxynitrite generator, led to the formation of both single- and double-stranded DNA breaks in a concentration- and time-dependent fashion. The presence of LA at 100-1,600 microM was found to significantly inhibit SIN-1-induced DNA strand breaks in a concentration-dependent manner. The consumption of oxygen induced by 250 microM SIN-1 was found to be decreased in the presence of high concentrations of LA (400-1,600 microM), indicating that LA at these concentrations may affect the generation of peroxynitrite from auto-oxidation of SIN-1. It is observed that incubation of the plasmid DNA with authentic peroxynitrite resulted in a significant formation of DNA strand breaks, which could also be dramatically inhibited by the presence of LA (100-1,600 microM). EPR spectroscopy in combination with spin-trapping experiments, using 5,5-dimethylpyrroline-N-oxide (DMPO) as spin trap, resulted in the formation of DMPO-hydroxyl radical adduct (DMPO-OH) from authentic peroxynitrite and LA at 50-1,600 microM inhibited the adduct signal. Taken together, these studies demonstrate for the first time that LA can potently inhibit peroxynitrite-mediated DNA strand breakage and hydroxyl radical formation. In view of the critical involvement of peroxynitrite in the pathogenesis of various neurodegenerative diseases, the inhibition of peroxynitrite-mediated DNA damage by LA may be responsible, at least partially, for its neuroprotective activities.

Alloantigeneic Reactions after Human Hematopoietic Cell Transplantation Induce Genomic Alterations in Epithelium: A Confirmation in Vivo and in Vitro Study and Implications to Secondary Neoplasia

We previously demonstrated frequent genomic alterations measured by microsatellite instability (MSI) in non-neoplastic epithelial tissues of pts who underwent allogeneic Hematopoietic Cell Transplantation (HCT) but not after autologous transplantation (Blood 2006; 107:3389–3396). Confirmation in a larger and independent patient cohort and demonstration in an in vitro system was needed. In total 176 buccal samples obtained from 71 unselected patients who underwent allogeneic HCT were analyzed for MSI with standard PCR for microsatellite markers (THO-1, SEE33, D14S120 and D1S80) and analysis by capillary electrophoresis. MSI was observed in 37 (52%) allo-transplanted pts but never in the 31 controls (16 healthy and 15 pts after auto-HCT, 47 samples). MSI+ pts were significantly older than MSI-pts (median age 60y vs 48y, p<0.05). Other clinical features were not significantly different between MSI+ and MSI− pts: gender, myeloid vs lymphoid disease, sibling vs unrelated HCT, myeloablative vs reduced intensity conditioning, sex mismatched transplantation, bone marrow vs mobilized peripheral blood graft, T-cell depletion of the graft, use of methotrexate for GvHD prophylaxis, number of CD3+ cells/kg b.w. infused, occurrence and grade of mucositis during neutropenia, CMV reactivation, median ferritin levels post-transplant and occurrence of GvHD vs no GvHD. When GVHD was analyzed according to its severity we found that there was a trend for increasing risk of MSI for pts who experienced severe GvHD (RR=1.8) as compared to pts with no GvHD (RR=1). Secondary malignancy (5 skin-, 1 adeno-Ca) was diagnosed in 5 (14%) of the MSI+ pts and only in 1 (3%) MSI− pts. In an in vitro model of mutation analysis we tested the hypothesis that an alloantigenic stimulus is substantially involved in the mutation process. Briefly, keratinocyte DNA-repair proficient HaCaT cells were transfected with a reporter plasmid and genomic instability (GI) was detected and measured as hygromycin resistant clones. Treatment of HaCaT cells with H2O2 resulted in a time and dose dependent GI induction (1.9–5.7 fold). Cytokines abundant in alloreactions such as IFN-γ, TNF-α, TGF-β didn't result in any GI in various concentrations and incubation times. Also, treatment with supernatants from different MHC non-matched Mixed Lymphocyte Cultures (MLC-SN) or with MLC separated from HaCaT cells with a semipermeable membrane didn't induce any significant GI. In contrast, exposure of HaCaT cells to the whole MLC which includes activated cellular components (measured as BrdU+) resulted in significant induction of GI in 6 out of 8 different cases (mean 2.4-fold). GI was also evaluated in terms of DNA strand break formation by using the neutral comet assay. Treatment of HaCaT cells with whole MLC resulted in significant increase of DNA strand breaks as compared to HaCaT cells exposed to MLC-SN (p=0.039) or untreated controls (p=0.048). Western blot analysis revealed no significant alterations in the levels of MMR proteins upon treatment with MLC or MLC-SN. Exposure of HaCaT cells to MLC or MLC-SN resulted in increase of intracellular ROS levels as compared to untreated cells. The MLC treatment caused significantly higher increase of ROS levels than MLC-SN. The results of the present study confirm that GI of epithelial cells is a frequent phenomenon in patients after allogeneic HCT and give in vivo and in vitro support that alloantigeneic processes can be the cause of such a phenomenon. Progress in understanding DNA damage and repair after allogeneic HCT can potentially provide molecular biomarkers and therapeutic targets.

Caspase‐3 Activation and DNA Damage in Pig Skin Organ Culture After Solar Irradiation

In the present study, a convenient and easy-to-handle skin organ culture was developed from domestic pig ears using polycarbonate Transwell culture inserts in 12-well plate. This alternative model was then tested for its suitability in analyzing the short-term effects of a single solar radiation dose (from 55 to 275 kJ.m(-2)). Differentiation of the pig skin was maintained for up to 48 h in culture, and its morphology was similar to that of fresh human skin. Solar irradiation induced a significant release of the cytosolic enzymes lactate dehydrogenase and extracellular signal-related kinase 2 protein in the culture medium 24 h after exposure. These photocytotoxic effects were associated with the formation of sunburn cells, thymine dimers and DNA strand breaks in both the epidermis and dermis. Interestingly, cell death was dose dependent and associated with p53 protein upregulation and strong caspase-3 activation in the basal epidermis. None of these cellular responses was observed in non-irradiated skin. Finally, topical application of a broad-spectrum UVB + A sunfilter formulation afforded efficient photoprotection in irradiated explants. Thus, the ex vivo pig ear skin culture may be a useful tool in the assessment of solar radiation-induced DNA damage and apoptosis, and for evaluating the efficacy of sunscreen formulations.

Selenite induces topoisomerase I and II‐DNA complexes in K562 leukemia cells

The essential trace element selenium is one of the most promising cancer chemopreventive agents. Data from preclinical studies have revealed that selenite, an inorganic form of selenium, may also be useful in cancer chemotherapy. DNA topoisomerases (topos) are the target of several useful anticancer drugs. These drugs induce DNA complexes with either topo I or topo II; then cellular processing coverts these topo-DNA complexes into permanent DNA strand breaks that ultimately lead to cell death. Previous reports have revealed that selenite can induce apoptosis in cancer cells selectively and that selenite-induced apoptosis is preceded by the formation of DNA strand breaks. In vitro experiments have shown that selenite induces topo II-DNA complexes, which seem to be involved in selenite-induced apoptosis. Using the cell-based assay TARDIS, here we show that selenite induces topo II-DNA complexes (topo IIalpha and topo IIbeta) in K562 leukemia cells; these complexes appeared in a time-dependent manner and correlated with the induction of apoptosis. Cells lacking topo IIbeta were resistant to selenite-induced cell growth inhibition, suggesting that this isoenzyme is a target for selenite. We report for the first time that selenite induces topo I-DNA complexes in K562 cells; the levels of these complexes were high at short exposure times and seem to appear before the induction of apoptosis. Overall, our results show that selenite induces topo-DNA complexes in cells with both topo I and II, and support previous data that suggest that this agent has potential for the treatment of cancer.

The effects of 1,4-benzoquinone on c-Myb and topoisomerase II in K-562 cells

Exposure to benzene, a ubiquitous environmental pollutant, has been linked to leukemia, although the mechanism of benzene-initiated leukemogenesis remains unclear. Benzene can be bioactivated to toxic metabolites such as 1,4 benzoquinone (BQ), which can alter signaling pathways and affect chromosomal integrity. BQ has been shown to increase the activity of c-Myb, which is an important transcription factor involved in hematopoiesis, cell proliferation, and cell differentiation. The c-Myb protein has also been shown to increase topoisomerase IIα (Topo IIα) promoter activity specifically in cell lines with hematopoietic origin. Topo IIα is a critical nuclear enzyme that removes torsional strain by cleaving, untangling and religating double-stranded DNA. Since Topo IIα mediates DNA strand breaks, aberrant Topo IIα activity or increased protein levels may increase the formation of DNA strand breaks, leaving the cell susceptible to mutational events. We hypothesized that BQ can increase c-Myb activity, which in turn increases Topo IIα promoter activity resulting in increased DNA strand breaks. Using luciferase reporter assays in K-562 cells we demonstrated that BQ (25 and 37 μM) exposure caused an increase in c-Myb activity after 24 h. Contradictory to previous findings, overexpression of exogenous c-Myb or a polypeptide consisting of c-Myb’s DNA binding domain (DBD), which competitively inhibits the binding of endogenous c-Myb to DNA, did not affect Topo IIα promoter activity. However, BQ (37 μM for 24 h) exposure caused a significant increase in Topo IIα promoter activity, which could be blocked by the overexpression of the DBD polypeptide, suggesting that BQ exposure increases Topo IIα promoter activity through the c-Myb signaling pathway.

2,3,7,8-Tetrachlorodibenzo-p-Dioxin Modulates the Induction of DNA Strand Breaks and Poly(ADP-ribose) Polymerase-1 Activation by 17β-Estradiol in Human Breast Carcinoma Cells Through Alteration of CYP1A1 and CYP1B1 Expression

The primary purpose of this research is to investigate the effects of 2,3,7,8-tetrachlorodibenzo- p-dioxin (TCDD) pretreatment and estrogen receptors-alpha (ER alpha) status on the induction of DNA damage by 17beta-estradiol (E 2) in human ER alpha(+)/MCF-7 and ER alpha(-)/MDA-MB-231 breast cancer cells. Results indicated that E 2 (0.1-100 nM) alone induced significant increases in cytotoxic response, reactive oxygen species (ROS) generation, and glutathione depletion in MDA-MB-231 cells but not in MCF-7 cells. At noncytotoxic concentrations, E 2 induced dose-related reduction in intracellular NAD(P)H in MDA-MB-231 cells through decreases in intracellular NAD (+) mediated by poly(ADP-ribose) polymerase-1 (PARP-1) activation as determined by detection of the presence of polymers of ADP-ribose-modified PARP-1 using Western blotting. Further investigation using the single-cell gel electrophoresis (Comet) assay confirmed that the PARP-1 activation induced by estrogen in MDA-MB-231 was due to increases in the number of DNA strand breaks. This evidence indicates that E 2 induces decreases in intracellular NAD(P)H and NAD (+) in MDA-MB-231 cells through PARP-1 activation mediated by the formation of DNA strand breaks. Further investigation indicated that the cytotoxic and DNA-damaging effects induced by E 2 in MDA-MB-231 cells were completely blocked by pretreatment of TCDD (10 nM for 72 h). In contrast, with TCDD pretreatment, significant increases in cytotoxic response, ROS generation, glutathione (GSH) depletion, DNA strand breaks, and PARP-1 activation were detected in MCF-7 cells exposed to E 2. We demonstrated that TCDD modulated the differential induction of DNA damage by estrogen in MDA-MB-231 and MCF-7 cells primarily through the inducibility of cytochrome P450 1A1 and 1B1 expression. Overall, this evidence suggests that TCDD is capable of inducing imbalances in the expression of enzymes responsible for the bioactivation of estrogen leading to the subsequent accumulation of DNA damage and initiation of DNA repair in MDA-MB-231 and MCF-7 cells. Furthermore, we confirmed that ER alpha plays a protective role in modulating the induction of DNA damage by E 2 in human breast cancer cells.

The Role of πσ* Excited States in Electron-Induced DNA Strand Break Formation: A Time-Dependent Density Functional Theory Study

Mechanisms of low-energy electron attachment to the DNA and subsequent single-strand break (SSB) formation are of crucial importance to understand the DNA damage. In the present study, we used time-dependent density functional theory (TD-BH&HLYP/6-31G*) to explore the mechanism of SSB, in detail, by calculating the lowest excited states of 5‘-dTMPH radical anion considered as a model of DNA. The C5‘−O5‘ bond dissociation of 5‘-dTMPH radical anion was considered as the reaction coordinate along the potential energy surface of 5‘-dTMPH. The dissociative σ* state, mainly localized on the phosphate of the 5‘-dTMPH radical anion, is considered responsible for the SSB formation in DNA. Our work predicts that in this DNA model system there are available π* and σ* excited states, near 2 eV, which can couple vibronically and lead to a DNA single strand break via the dissociative σ* surface.

Electrochemical Sensing of Chromium‐Induced DNA Damage: DNA Strand Breakage by Intermediates of Chromium(VI) Electrochemical Reduction

AbstractDNA damage by CrV and/or CrIV intermediates of CrVI electrochemical reduction was detected using a supercoiled DNA‐modified mercury electrode. A signal sensitive to formation of DNA strand breaks, AC voltammetric DNA peak 3, increased due to incubation of the DNA‐modified electrode in micromolar solutions of CrVI at potentials sufficiently negative for CrVI reduction. Damage to DNA in solutions containing CrVI and a chemical reductant (ascorbic acid, AA) was observed only at relatively high chromium concentrations (hundreds of μM). To eliminate interferences of excess CrVI in measurements of guanine electrochemical signals, a magnetoseparation double surface electrochemical technique was introduced. Using this approach, DNA damage in solution was detected for 50–250 μM CrVI upon addition of 1 mM AA. Our results suggest a more efficient DNA damage at the electrode surface due to continuous production of the reactive chromium species, compared to DNA exposure to chromium being reduced chemically in solution.

ATM Phosphorylation Kinetics as a Biological Reporter of Cellular Radiosensitivity

AIM: Exposure to ionizing radiation (IR) causes DNA strand break formation, resulting in the rapid activation and autophosphorylation of ATM on Ser-1981. We hypothesize that quantitative analysis of ATM autophosphorylation may serve as a reporter of DNA damage induction and repair after IR in two ATM wild-type prostate cancer cell lines PC-3 and DU-145 and two oral squamous cell carcinoma cell lines SCC25 and SQ-20B. METHODS: Immunocytochemistry was performed on glass coverslips using polyclonal anti-phospho-H2AX or monoclonal anti-phospho-ATM phospho-specific antibodies. Cells were treated with 0 to 4 Gy of IR, incubated, fixed, and stained. Stained cells were analyzed using epifluorescence microscopy and discrete foci of brightness in each nucleus were counted. In vitro clonogenic assays were performed to determine the relative radiosensitivity of PC-3, DU-145, SCC25, and SQ-20B cells. RESULTS: Within 10 min after IR, discrete foci of ATM autophosphorylation appeared at putative sites of DNA strand breaks. The number and relative brightness of γ-H2AX and ATM autophosphorylation foci increased linearly with dose at 30 min after clinically relevant IR doses in these cell lines. The relatively radiosensitive PC-3 and SCC-25 cells retained a greater percentage of ATM autophosphorylation and γ-H2AX foci, which was most evident at 30 min after IR. CONCLUSION: Our preliminary data suggest that persistence of ATM autophosphorylation is a promising reporter of in vitro radiosensitivity. Further research is necessary to validate this finding and to develop additional applications for ATM autophosphorylation in radiation research.

Pterocarpans phaseollin and neorautenol isolated from Erythrina addisoniae induce apoptotic cell death accompanied by inhibition of ERK phosphorylation

The genus Erythrina ( Leguminosae), consisting of over 100 different species, is distributed in tropical regions. In traditional medicine, Erythrina species are used to treat cancer, but little is known about the anticancer mechanisms. From the stem bark of Erythrina addisoniae Hutch. & Dalziel, six prenylated pterocarpans were isolated and analysed for pharmacological activity: While calopocarpin, cristacarpin, orientanol c, and isoneorautenol showed only a weak or moderate toxicity in H4IIE hepatoma cells (EC 50-value > 25 μM), the toxicity of neorautenol and phaseollin was in the low micromolar range (EC 50-value: 1 and 1.5 μM, respectively). We further focused on these two substances showing that both increased caspase 3/7 activity and nuclear fragmentation as markers for apoptotic cell death. Neorautenol (10 μM, 2 h), but not phaseollin induced the formation of DNA strand breaks (comet assay). Both substances showed no effect on NF-κB signalling (SEAP assay: basal activity and stimulation with TNF-α), on the other hand both pterocarpans (10 μM, 2 h) decreased the activation of the ERK kinase (p44/p42), an mitogen activated protein kinase which is associated with cell proliferation. We conclude that the pterocarpans phaseollin and neorautenol may be responsible for the anticarcinogenic actions of the plant extract reported in the literature. Further analysis of these substances may lead to new pharmacons to be used in cancer therapy.

Effects of mixing metal ions on oxidative DNA damage mediated by a Fenton-type reduction

The formation of 8-hydroxy-deoxyguanosine (8-OHdG) and strand breaks in DNA by Fenton-type reactions by mixtures of two of five metal ions, iron (II), cadmium (II), nickel (II), chromium (III) or copper (II), has been investigated and compared to their formation by each single metal ion. Salmon sperm DNA and pBluescript K+ plasmid were each incubated with hydrogen peroxide and metal ions. The formation of 8-OHdG declined in the Fe (II) or Cu (II) Fenton reaction upon addition of Cd (II) or Ni (II) ion. In contrast, the Fe (II) reaction upon addition of Cr (III) ion showed an additive influence on the formation of 8-OHdG. Furthermore, the Cu (II) plus Cr (III) reaction showed a synergistic effect. These influences relate to the interaction of metal ions with DNA, the potentials of the metal ions to generate activated oxygen and electron transfer between metal ions. The formation of DNA strand breaks was investigated in plasmid DNA by agarose gel electrophoresis and subsequent densitometry. The formation of DNA strand breaks in the Fe (II) or Cu (II) Fenton reaction decreased upon the addition of Ni (II) ion, as with the formation of 8-OHdG mediated by these metal ions. On the other hand, the formation of DNA strand breaks in the Fe (II) reaction decreased upon addition of Cr (III) ion, and the Cu (II) plus Cr (III) reaction did not show the synergistic influence on DNA strand breaks. These results suggest that interactions between two metal ions can influence the generation of 8-OHdG and the formation of DNA strand breaks and demonstrate that these lesions can arise by different mechanisms.

Toxicological potential of 2-alkylcyclobutanones – specific radiolytic products in irradiated fat-containing food – in bacteria and human cell lines

Food irradiation has been considered as a safe processing technology to improve food safety and preservation, eliminating efficiently bacterial pathogens, parasites and insects. This study aims to characterize the toxicological potential of 2-alkylcyclobutanones (2-ACBs), radiolytic derivatives of triglycerides, formed uniquely upon irradiation of fat-containing food. In irradiated food they are generated proportionally to fat content and absorbed radiation dose. The cyto- and genotoxic potentials of various highly pure synthetic 2-ACBs were studied in bacteria and human cell lines. While pronounced cytotoxicity was evident in bacteria, no mutagenic activity has been revealed by the Ames test in Salmonella strains TA 97, TA 98 and TA 100. In mammalian cells genotoxicity was demonstrated mainly by the induction of DNA base lesions recognized by the Fpg protein as determined by both the Comet Assay and the Alkaline Unwinding procedure. Formation of DNA strand breaks was observed by the Alkaline Unwinding procedure but not by the Comet Assay. The extent of cytotoxicity and genotoxicity were dependent on chain length and degree of unsaturation of the fatty acid chain. Further studies will have to clarify mechanisms of action and potential relevance for human exposure situation.

2,3,7,8-Tetrachlorodibenzo- p-dioxin (TCDD) induces oxidative stress, DNA strand breaks, and poly(ADP-ribose) polymerase-1 activation in human breast carcinoma cell lines

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 ERα(+)/MCF-7 and ERα(−)/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 (1 nM for 5 h), 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.

Induction of apoptosis by plumbagin through reactive oxygen species-mediated inhibition of topoisomerase II

Reactive oxygen species (ROS) have been recognized as key molecules, which can selectively modify proteins and therefore regulate cellular signalling including apoptosis. Plumbagin, a naphthoquinone exhibiting antitumor activity, is known to generate ROS and has been found to inhibit the activity of topoisomerase II (Topo II) through the stabilization of the Topo II–DNA cleavable complex. The objective of this research was to clarify the role of ROS and Topo II inhibition in the induction of apoptosis mediated by plumbagin. As determined by the comet assay, plumbagin induced DNA cleavage in HL-60 cells, whereas in a cell line with reduced Topo II activity—HL-60/MX2, the level of DNA damage was significantly decreased. The onset of DNA strand break formation in HL-60 cells was delayed in comparison with the generation of intracellular ROS. In HL-60/MX2 cells, ROS were generated at a similar rate, whereas a significant reduction in the level of DNA damage was detected. The pretreatment of cells with N-acetylcysteine (NAC) attenuated plumbagin-induced DNA damage, pointing out to the involvement of ROS generation in cleavable complex formation. These results suggest that plumbagin-induced ROS does not directly damage DNA but requires the involvement of Topo II. Furthermore, experiments carried out using light spectroscopy indicated no direct interactions between plumbagin and DNA. The induction of apoptosis was significantly delayed in HL-60/MX2 cells indicating the involvement of Topo II inhibition in plumbagin-mediated apoptosis. Thus, these findings strongly suggest ROS-mediated inhibition of Topo II as an important mechanism contributing to the apoptosis-inducing properties of plumbagin.

Anti-tumor 12-deoxyphorbol esters from Euphorbia cornigera

Nine ( 1– 8 and 10) new and two ( 9 and 11) known compounds have been isolated from roots of Euphorbia cornigera Boiss. Their structure and relative stereochemistry were acquired through NMR ( 1H, 13C, COSY-45, HOHAHA, HMQC, HMBC, NOE and HMBC) spectroscopic measurements. Compounds 1– 10 were identified as diesters of 13,20- O-diacyl and 11 as 13- O-acetyl of 12-deoxyphorbol. Cytotoxic activity of the compounds was investigated on human KB cells by reduction of MTT. Compounds 8– 10 displayed IC 50 of 0.8, 0.5, and 1.0 μg mL −1, respectively, whereas the activity of rest of the compounds ( 1– 7) was either very low or ( 11) zero even up to 1000 μg mL −1. The inhibition of DNA synthesis through Trypan blue exclusion and Brd-U assay was investigation to figure out the role of compounds 8– 10 and concluded that these were responsible for the death of KB cells. Significant correlation has been found between the cytotoxicity and DNA cross-link and DNA strand-break formation.

Induction of DNA strand breaks and oxidative stress in HeLa cells by ethanol is dependent on CYP2E1 expression

Induction of cytochrome P4502E1 (CYP2E1) is considered to be an important mechanism by which ethanol can cause toxicity related to oxidative stress both in vivo and in vitro. In the current study, we used HeLa cells with doxycycline-regulated CYP2E1 expression to test the hypothesis that induction of CYP2E1 could lead to secondary DNA oxidation that could potentially contribute to the carcinogenicity of ethanol in vivo. Overexpression of CYP2E1 protein was not associated with oxidative stress per se as assessed by markers of lipid peroxidation (cis-parinaric acid oxidation), glutathione depletion and elevation of intracellular reactive oxygen species (dichlorofluoroscin oxidation) in the presence or absence of ethanol substrate (10 mM, 24 h). Furthermore, there was no evidence of elevation of frequency of DNA strand breaks as assessed by the comet assay. In contrast, however, after pre-incubation of cells with L-buthionine-(S,R)-sulphoximine (BSO, 10 microM) which caused a 75% reduction in intracellular reduced glutathione (GSH) levels, CYP2E1 expression resulted in oxidative stress as assessed by all of these markers and DNA strand breaks but only in the presence of ethanol (10 mM). No effect was observed under these conditions in control cells not expressing CYP2E1. Furthermore, these effects could be attenuated by co-incubation with 1-aminobenzotriazole (0.5 mM), a suicide inhibitor of P450 activity. In conclusion, in this in vitro model CYP2E1-mediated interaction with ethanol results in the intracellular oxidative stress and the formation of DNA strand breaks which are detectable in cells pre-sensitized by depletion of intracellular levels of GSH.

Protective effect of caffeic acid phenethyl ester (CAPE) on fluoride-induced oxidative stress and apoptosis in rat endometrium

High fluoride intake may affect biological systems by increasing free radicals, which may enhance lipid peroxidation levels of the tissues, thus leading to oxidative damage. Caffeic acid phenethyl ester (CAPE), a component of honeybee propolis, protects tissues from reactive oxygen species mediated oxidative stress in ischemia–reperfusion and toxic injuries. Several studies suggest that supplementation with anti-oxidant can influence fluoride induced tissue damage. The aims of this study was to investigate the possible role of malondialdehyde (MDA) levels and activity of superoxide dismutase (SOD) and catalase (CAT), in the pathogenesis of fluoride-induced endometrial damage and to demonstrate the effect of CAPE, the potent antioxidant, in decreasing the toxicity. Twenty-four adult female rats were randomly divided into three experimental groups, as follows: control group, fluoride-treated group (F), and fluoride plus CAPE-treated group (F + CAPE). Fluoride was given orally as 30 mg/L NaF solution in spring water daily for 45 days. CAPE was co-administered intraperitoneally (i.p.) with a dose of 10 μM/(kg day) for 46 days. Extensive formation of DNA strand breaks, the typical biochemical feature of apoptosis, was detected with the use of the terminal deoxynucleotidyl transferase (TdT)-mediated d UTP-biotin nick and labeling (TUNEL) method. The activities of antioxidant enzymes such as SOD and CAT as well as the concentration of MDA, as an indicator of lipid peroxidation, were measured to evaluate oxidative stress in homogenates of the endometrium. Fluoride administration increased MDA levels ( p < 0.05), decreased SOD ( p < 0.05) and CAT ( p < 0.05) activities. CAPE co-administration with fluoride treatments caused significantly decreased MDA levels ( p < 0.05), increased SOD ( p < 0.05) and CAT ( p < 0.05) activities in endometrial tissue when compared with F alone. Diffuse apoptosis in glandular epithelium and stromal cells was found by TUNEL method in endometrial tissues of rats treated with fluoride. The severity of these lesions was reduced by administration of CAPE. In conclusion, our study demonstrated that MDA may play an important role in the pathogenesis of fluoride-induced oxidative endometrial damage. CAPE may have protective aspects in this process by its antioxidant and anti-inflammatory effect.

Induction of apoptosis through reactive oxygen species mediated inhibition of topoisomerase II by plumbagin from Drosera

Reactive oxygen species (ROS) have been recognized as key molecules, which can selectively modify proteins and therefore regulate cellular signalling including apoptosis. Plumbagin, a naphthoquinone present in the Drosera genus, is known to generate ROS and has been found to inhibit the activity of topoisomerase II (Topo II) through the stabilization of the Topo II-DNA cleavable complex. The objective of this research was to clarify the role of ROS and Topo II inhibition in the induction of apoptosis mediated by plumbagin. As determined by the comet assay, plumbagin induced DNA cleavage in HL-60 cells, whereas in a cell line with reduced Topo II activity (HL-60/MX2), the level of DNA damage was significantly decreased. The onset of DNA strand break formation in HL-60 cells was delayed in comparison with the generation of intracellular ROS. In HL-60/MX2 cells, ROS were generated at a similar rate, whereas a significant reduction in the level of DNA damage was detected. The pretreatment of cells with N-acetylcysteine (NAC) attenuated plumbagin-induced DNA damage, pointing out to the involvement of ROS generation in cleavable complex formation. The induction of apoptosis was significantly delayed in HL-60/MX2 cells indicating the involvement of Topo II inhibition in plumbagin-mediated apoptosis. Direct interactions between plumbagin and DNA were excluded based on spectroscopic analysis. Thus, these results suggest that ROS generated by plumbagin at low concentrations (3µM) act as signalling molecules mediating apoptosis through Topo II inactivation rather than through direct DNA damage.