Search

Aim: To quantitatively evaluate the inhibition of human DNA repair proteins APE1 and MTH1 by dextran-coated γ-Fe2O3 ultrasmall superparamagnetic iron oxide nanoparticles (dUSPIONs). Materials & methods: Liquid chromatography–tandem mass spectrometry with isotope-dilution was used to measure the expression levels of APE1 and MTH1 in MCL-5 cells exposed to increasing doses of dUSPIONs. The expression levels of APE1 and MTH1 were measured in cytoplasmic and nuclear fractions of cell extracts. Results: APE1 and MTH1 expression was significantly inhibited in both cell fractions at the highest dUSPION dose. The expression of MTH1 was linearly inhibited across the full dUSPION dose range in both fractions. Conclusion: These findings warrant further studies to characterize the capacity of dUSPIONs to inhibit other DNA repair proteins in vitro and in vivo. Inhibitors of DNA repair proteins are increasingly being utilized as potential anticancer agents to supplement traditional chemotherapy and radiation-based approaches. The present study was focused on investigating the use of iron oxide nanoparticles to inhibit the expression of relevant human DNA repair proteins in a cellular model (MCL-5 cells). The authors utilized liquid chromatography–tandem mass spectrometry with isotope dilution to measure the expression levels of two different DNA repair proteins (MTH1 and APE1) in cells after the cells were exposed to increasing levels of the iron oxide nanoparticles. The authors observed significant decreases in DNA repair protein levels that were associated with increasing doses of the iron oxide nanoparticles. The authors' findings warrant more comprehensive studies using other cellular models and suitable animal models. [ABSTRACT FROM AUTHOR]

A study was conducted to investigate the cellular repair of several oxidatively induced DNA lesions in lymphoblasts in women with no detectable breast cancer 1 (BRCA1) deficiency. The results reveal that failure of cells with BRCA1 mutations to repair 8, 5'-cyclopurine-2'-deoxynucleosides indicate the involvement of BRCA1 in nucleotide-excision repair of oxidative DNA damage.

The substrate specificity and excision kinetics of mNEIL1 using high-molecular weight DNA with multiple lesions is investigated. It is concluded that NEIL1 possesses specificity, with similar efficiency of excision, for two purine-derived formamidopyrimidines that are formed in DNA by hydroxyl radical attack or by UV radiation.

Research describes the identification and quantification of 8,5'-cyclo-2'-deoxyguanosine in mammalian DNA by liquid chromatography/isotope dilution- and gas chromatography/isotope dilution mass spectrometry techniques. Data indicate that the levels of (5'R)-8,5'-cdGuo and (5'S)-8,5'-cdGuo are about 2 and 10 lesions per one million DNA molecules, respectively.

BACKGROUND: Exposure to bisphenol A (BPA) has been reported to alter global gene expression, induce epigenetic modifications, and interfere with complex regulatory networks of cells. In addition to these reprogramming events, we have demonstrated that BPA exposure generates reactive oxygen species and promotes cellular survival when co-exposed with the oxidizing agent potassium bromate (KBr[O.sub.3]). OBJECTIVES: We determined the cellular microenvironment changes induced by co-exposure of BPA and KBr[O.sub.3] versus either agent alone. METHODS: Ku70-deficient cells were exposed to 150 µM BPA, 20 mM KBr[O.sub.3], or co-exposed to both agents. Four and 24 hr post-damage initiation by KBr[O.sub.3], with BPA-only samples timed to coincide with these designated time points, we performed whole-genome microarray analysis and evaluated chromatin structure, DNA lesion load, glutathione content, and intracellular pH. RESULTS: We found that 4 hr post-damage initiation, BPA exposure and co-exposure transiently condensed chromatin compared with untreated and KBr[O.sub.3]-only treated cells; the transcription of DNA repair proteins was also reduced. At this time point, BPA exposure and co-exposure also reduced the change in intracellular pH observed after treatment with KBr[O.sub.3] alone. Twenty-four hours post-damage initiation, BPA-exposed cells showed less condensed chromatin than cells treated with KBr[O.sub.3] alone; the intracellular pH of the co-exposed cells was significantly reduced compared with untreated and KBr[O.sub.3]-treated cells; and significant up-regulation of DNA repair proteins was observed after co-exposure. CONCLUSION: These results support the induction of an adaptive response by BPA co-exposure that alters the microcellular environment and modulates DNA repair. Further work is required to determine whether BPA induces similar DNA lesions in vivo at environmentally relevant doses; however, in the Ku70-deficient mouse embryonic fibroblasts, exposure to a high dose of BPA was associated with changes in the cellular microenvironment that may promote survival. http://dx.doi.org/10.1289/EHP237, Introduction World-wide production of bisphenol A (BPA) has increased exponentially as the demand for this chemical in consumer products, from food and beverage containers to epoxies, has grown (Vandenberg et [...]

Abstract Background Breast cancer is the second leading cause of cancer deaths in women in the United States. Although the causes of this disease are incompletely understood, oxidative DNA damage is presumed to play a critical role in breast carcinogenesis. A common oxidatively induced DNA lesion is 8-hydroxyguanine (8-OH-Gua), which has been implicated in carcinogenesis. The aim of this study was to investigate the ability of HCC1937 and MCF-7 breast cancer cell lines to repair 8-OH-Gua relative to a nonmalignant human mammary epithelial cell line, AG11134. Methods We used oligonucleotide incision assay to analyze the ability of the two breast cancer cell lines to incise 8-OH-Gua relative to the control cell line. Liquid chromatography/mass spectrometry (LC/MS) was used to measure the levels of 8-OH-Gua as its nucleoside, 8-OH-dG in the cell lines after exposure to H2O2 followed by 30 min repair period. Protein expression levels were determined by Western blot analysis, while the hOGG1 mRNA levels were analyzed by RT-PCR. Complementation of hOGG1 activity in HCC1937 cells was assessed by addition of the purified protein in the incision assay, and in vivo by transfection of pFlagCMV-4-hOGG1. Clonogenic survival assay was used to determine sensitivity after H2O2-mediated oxidative stress. Results We show that the HCC1937 breast cancer cells have diminished ability to incise 8-OH-Gua and they accumulate higher levels of 8-OH-dG in the nuclear genome after H2O2 treatment despite a 30 min repair period when compared to the nonmalignant mammary cells. The defective incision of 8-OH-Gua was consistent with expression of undetectable amounts of hOGG1 in HCC1937 cells. The reduced incision activity was significantly stimulated by addition of purified hOGG1. Furthermore, transfection of pFlagCMV-4-hOGG1 in HCC1937 cells resulted in enhanced incision of 8-OH-Gua. HCC1937 cells are more sensitive to high levels of H2O2 and have up-regulated SOD1 and SOD2. Conclusion This study provides evidence for inefficient repair of 8-OH-Gua in HCC1937 breast cancer cell line and directly implicates hOGG1 in this defect.

The significant accumulation of (5'R)-8,5'-cyclo-2'-deoxyadenosine (R-cdA) and (5'S)-8,5'-cyclo-2'-deoxyadenosine (S-cdA) in liver DNA of [neil1.sup.-/-] mice which were not exposed to exogenous oxidative stress and which did not accumulation of these lesions in liver DNA from control or [ogg1.sup.-/-] mice, is reported. The accumulation of R-cdA and S-cdA in [neil1.sup.-/-] mice which strongly pointed to the failure of their repair suggested the involvement of NEIL1 in NER of R-cdA and S-cdA and called for further studies on the mechanism of action of NEIL1 in NER.

Rabbits were treated subcutaneously with buthionine sulfoximine (BSO), an effective GSH-depleting compound to study the oxidatively induced damage to DNA by Glutathione (GSH) depletion in different organs of rabbits in vivo. The findings might be used as guidelines to better understand the pathologies associated with DNA damage, oxidative stress, and/or defective antioxidant responses and also provide insight on the effect of BSO in increasing the efficacy of anticancer therapeutics.

Gas chromatography/mass spectrometry and liquid chromatography/mass spectrometry is used for examining the characterization of tirapazamine-mediated damage to the genetic information stored in the heterocyclic base residues of double-stranded DNA. DNA transcription and replication is blocked by a set of poorly repaired, potentially cytotoxic DNA base lesions generated by tirapazamine.

Results show that Arabidopsis thaliana Ogg1 enzyme exhibits substrate specificity for 8-hydroxyguanine and 2,6-diamino-4-hydroxy-5-formamidopyrimidine during the DNA excision reaction containing multiple pyrimidine- and purin-derived lesions. A comparative analysis of the Ogg1 activity across the eukaryotic systems reveals that DNA excision kinetics differ, indicating differences in the active sites.

Summary: Background: Ragweed pollen extract (RWPE) induces TLR4‐NFκB‐CXCL‐dependent recruitment of ROS‐generating neutrophils to the airway and OGG1 DNA glycosylase‐dependent excision of oxidatively induced 8‐OH‐Gua DNA base lesions from the airway epithelial cell genome. Administration of free 8‐OH‐Gua base stimulates RWPE‐induced allergic lung inflammation. These studies suggest that stimulation of innate receptors and their adaptor by allergenic extracts initiates excision of a set of DNA base lesions that facilitate innate/allergic lung inflammation. Objective: To test the hypothesis that stimulation of a conserved innate receptor/adaptor pathway by allergenic extracts induces excision of a set of pro‐inflammatory oxidatively induced DNA base lesions from the lung genome that stimulate allergic airway inflammation. Methods: Wild‐type (WT), Tlr4KO, Tlr2KO, Myd88KO, and TrifKO mice were intranasally challenged once or repeatedly with cat dander extract (CDE), and innate or allergic inflammation and gene expression were quantified. We utilized GC‐MS/MS to quantify a set of oxidatively induced DNA base lesions after challenge of naïve mice with CDE. Results: A single CDE challenge stimulated innate neutrophil recruitment that was partially dependent on TLR4 and TLR2, and completely on Myd88, but not TRIF. A single CDE challenge stimulated MyD88‐dependent excision of DNA base lesions 5‐OH‐Cyt, FapyAde, and FapyGua from the lung genome. A single challenge of naïve WT mice with 5‐OH‐Cyt stimulated neutrophilic lung inflammation. Multiple CDE instillations stimulated MyD88‐dependent allergic airway inflammation. Multiple administrations of 5‐OH‐Cyt with CDE stimulated allergic sensitization and allergic airway inflammation. Conclusions and Clinical Relevance: We show for the first time that CDE challenge stimulates MyD88‐dependent excision of DNA base lesions. Our data suggest that the resultant‐free base(s) contribute to CDE‐induced innate/allergic lung inflammation. We suggest that blocking the MyD88 pathway in the airways with specific inhibitors may be a novel targeted strategy of inhibiting amplification of innate and adaptive immune inflammation in allergic diseases by oxidatively induced DNA base lesions. [ABSTRACT FROM AUTHOR]

Activities of fast growing human population are altering freshwater ecosystems, endangering their inhabitants and public health. Organic and trace compounds have a high potential for adverse impacts on aquatic organisms in some Great Lakes tributaries. Toxic compounds in tissues of organisms living in contaminated environments change their metabolism and alter cellular components. We measured oxidatively induced DNA damage in the soft tissues of dreissenid mussels to check on the possible contaminant-induced impact on their DNA. The animals were obtained from archived samples of the National Oceanic and Atmospheric Administration (NOAA) Mussel Watch Program. Mussels were collected from the harbor of Ashtabula River in Ohio, and a reference area located at the Lake Erie shore. Using gas chromatography-tandem mass spectrometry with isotope dilution, we identified and quantified numerous oxidatively modified DNA bases and 8,5′-cyclopurine-2′-deoxynucleosides. We found significant differences in the concentrations of these potentially mutagenic and/or lethal lesions in the DNA of mussels from the harbor as compared to the animals collected at the reference site. These results align NOAA's data showing that elevated concentrations of polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), and heavy metals were found in mussels within the harbor as compared to mussels collected in the reference site. The measured DNA lesions can be used as biomarkers for identifying DNA damage in mussels from polluted and reference sites. Such biomarkers are needed to identify the bioeffects of contaminants in affected organisms, as well as whether remedial actions have proven successful in reducing observed toxic effects. [ABSTRACT FROM AUTHOR]

Some engineered nanomaterials (ENMs) may have the potential to cause damage to the genetic material in living systems. The mechanistic machinery functioning at the cellular/molecular level, in the form of DNA repair processes, has evolved to help circumvent DNA damage caused by exposure to a variety of foreign substances. Recent studies have contributed to our understanding of the various DNA damage repair pathways involved in the processing of DNA damage. However, the vast array of ENMs may present a relatively new challenge to the integrity of the human genome; therefore, the potential hazard posed by some ENMs necessitates the evaluation and understanding of ENM-induced DNA damage repair pathways. This review focuses on recent studies highlighting the differential regulation of DNA repair pathways, in response to a variety of ENMs, and discusses the various factors that dictate aberrant repair processes, including intracellular signalling, spatial interactions and ENM-specific responses. [ABSTRACT FROM AUTHOR]

BACKGROUND: Exposure to bisphenol A (BPA) has been reported to alter global gene expression, induce epigenetic modifications, and interfere with complex regulatory networks of cells. In addition to these reprogramming events, we have demonstrated that BPA exposure generates reactive oxygen species and promotes cellular survival when co-exposed with the oxidizing agent potassium bromate (KBrO3). OBJECTIVES: We determined the cellular microenvironment changes induced by co-exposure of BPA and KBrO3 versus either agent alone. METHODS: Ku70-deficient cells were exposed to 150 µM BPA, 20 mM KBrO3, or co-exposed to both agents. Four and 24 hr post-damage initiation by KBrO3, with BPA-only samples timed to coincide with these designated time points, we performed whole-genome microarray analysis and evaluated chromatin structure, DNA lesion load, glutathione content, and intracellular pH. RESULTS: We found that 4 hr post-damage initiation, BPA exposure and co-exposure transiently condensed chromatin compared with untreated and KBrO3-only treated cells; the transcription of DNA repair proteins was also reduced. At this time point, BPA exposure and co-exposure also reduced the change in intracellular pH observed after treatment with KBrO3 alone. Twenty-four hours post-damage initiation, BPA-exposed cells showed less condensed chromatin than cells treated with KBrO3 alone; the intracellular pH of the co-exposed cells was significantly reduced compared with untreated and KBrO3-treated cells; and significant up-regulation of DNA repair proteins was observed after co-exposure. CONCLUSION: These results support the induction of an adaptive response by BPA co-exposure that alters the microcellular environment and modulates DNA repair. Further work is required to determine whether BPA induces similar DNA lesions in vivo at environmentally relevant doses; however, in the Ku70-deficient mouse embryonic fibroblasts, exposure to a high dose of BPA was associated with changes in the cellular microenvironment that may promote survival. [ABSTRACT FROM AUTHOR]

Apurinic/apyrimidinic endonuclease 1 (APE1) is a DNA repair protein and plays other important roles. Increased levels of APE1 in cancer have been reported. However, available methods for measuring APE1 levels are indirect and not quantitative. We previously developed an approach using liquid chromatography and tandem mass spectrometry with isotope dilution to accurately measure APE1 levels. Here, we applied this methodology to measure APE1 levels in normal and cancerous human breast tissues. Extreme expression of APE1 in malignant tumors was observed, suggesting that breast cancer cells may require APE1 for survival. Accurate measurement of APE1 may be essential for the development of novel treatment strategies and APE1 inhibitors as anticancer drugs. [ABSTRACT FROM AUTHOR]

MTH1 protein sanitizes the nucleotide pool so that oxidized 2′-deoxynucleoside triphosphates (dNTPs) cannot be used in DNA replication. Cancer cells require MTH1 to avoid incorporation of oxidized dNTPs into DNA that results in mutations and cell death. Inhibition of MTH1 eradicates cancer, validating MTH1 as an anticancer target. By overexpressing MTH1, cancer cells may mediate cancer growth and resist therapy. To date, there is unreliable evidence suggesting that MTH1 is increased in cancer cells, and available methods to measure MTH1 levels are indirect and semi-quantitative. Accurate measurement of MTH1 in disease-free tissues and malignant tumors of patients may be essential for determining if the protein is truly upregulated in cancers, and for the development and use of MTH1 inhibitors in cancer therapy. Here, we present a novel approach involving liquid chromatography–isotope-dilution tandem mass spectrometry to positively identify and accurately quantify MTH1 in human tissues. We produced full length 15 N-labeled MTH1 and used it as an internal standard for the measurements. Following trypsin digestion, seven tryptic peptides of both MTH1 and 15 N-MTH1 were identified by their full scan and product ion spectra. These peptides provided a statistically significant protein score that would unequivocally identify MTH1. Next, we identified and quantified MTH1 in human disease-free breast tissues and malignant breast tumors, and in four human cultured cell lines, three of which were cancer cells. Extreme expression of MTH1 in malignant breast tumors was observed, suggesting that cancer cells are addicted to MTH1 for their survival. The approach described is expected to be applicable to the measurement of MTH1 levels in malignant tumors vs. surrounding disease-free tissues in cancer patients. This attribute may help develop novel treatment strategies and MTH1 inhibitors as potential drugs, and guide therapies. [ABSTRACT FROM AUTHOR]

Bisphenol A (BPA) is a biologically active industrial chemical used in production of consumer products. BPA has become a target of intense public scrutiny following concerns about its association with human diseases such as obesity, diabetes, reproductive disorders, and cancer. Recent studies link BPA with the generation of reactive oxygen species, and base excision repair (BER) is responsible for removing oxidatively induced DNA lesions. Yet, the relationship between BPA and BER has yet to be examined. Further, the ubiquitous nature of BPA allows continuous exposure of the human genome concurrent with the normal endogenous and exogenous insults to the genome, and this co-exposure may impact the DNA damage response and repair. To determine the effect of BPA exposure on base excision repair of oxidatively induced DNA damage, cells compromised in double-strand break repair were treated with BPA alone or co-exposed with either potassium bromate (KBrO3) or laser irradiation as oxidative damaging agents. In experiments with KBrO3, co-treatment with BPA partially reversed the KBrO3-induced cytotoxicity observed in these cells, and this was coincident with an increase in guanine base lesions in genomic DNA. The improvement in cell survival and the increase in oxidatively induced DNA base lesions were reminiscent of previous results with alkyl adenine DNA glycosylase-deficient cells, suggesting that BPA may prevent initiation of repair of oxidized base lesions. With laser irradiation-induced DNA damage, treatment with BPA suppressed DNA repair as revealed by several indicators. These results are consistent with the hypothesis that BPA can induce a suppression of oxidized base lesion DNA repair by the base excision repair pathway. [ABSTRACT FROM AUTHOR]

Following the formation of oxidatively-induced DNA damage, several DNA glycosylases are required to initiate repair of the base lesions that are formed. Recently, NEIL1 and other DNA glycosylases, including OGG1 and NTH1 were identified as potential targets in combination chemotherapeutic strategies. The potential therapeutic benefit for the inhibition of DNA glycosylases was validated by demonstrating synthetic lethality with drugs that are commonly used to limit DNA replication through dNTP pool depletion via inhibition of thymidylate synthetase and dihydrofolate reductase. Additionally, NEIL1-associated synthetic lethality has been achieved in combination with Fanconi anemia, group G. As a prelude to the development of strategies to exploit the potential benefits of DNA glycosylase inhibition, it was necessary to develop a reliable high-throughput screening protocol for this class of enzymes. Using NEIL1 as the proof-of-principle glycosylase, a fluorescence-based assay was developed that utilizes incision of site-specifically modified oligodeoxynucleotides to detect enzymatic activity. This assay was miniaturized to a 1536-well format and used to screen small molecule libraries for inhibitors of the combined glycosylase/AP lyase activities. Among the top hits of these screens were several purine analogs, whose postulated presence in the active site of NEIL1 was consistent with the paradigm of NEIL1 recognition and excision of damaged purines. Although a subset of these small molecules could inhibit other DNA glycosylases that excise oxidatively-induced DNA adducts, they could not inhibit a pyrimidine dimer-specific glycosylase. [ABSTRACT FROM AUTHOR]