Changes in DNA 8-hydroxyguanine levels, 8-hydroxyguanine repair activity, and hOGG1 and hMTH1 mRNA expression in human lung alveolar epithelial cells induced by crocidolite asbestos

Genetic and epigenetic modulations in toxicity: The two-sided roles of heavy metals and polycyclic aromatic hydrocarbons from the environment

This study emphasizes the importance of considering the metabolic and toxicity mechanisms of environmental concern chemicals in real-life exposure scenarios. Furthermore, environmental chemicals may require metabolic activation to become toxic, and competition for binding sites on receptors can affect the severity of toxicity. The multicomplex process of chemical toxicity is reflected in the activation of multiple pathways during toxicity of which AhR activation is major. Real-life exposure to a mixture of concern chemicals is common, and the composition of these chemicals determines the severity of toxicity. Nutritional essential elements can mitigate the toxicity of toxic heavy metals, while the types and ratio of composition of PAH can either increase or decrease toxicity. The epigenetic mechanisms of heavy metals and PAH toxicity involves either down-regulation or up-regulation of some non-coding RNAs (ncRNAs) whereas specific small RNAs (sRNAs) may have dual role depending on the tissue and circumstance of expression. Similarly, decrease DNA methylation and histone modification are major players in heavy metals and PAH mediated toxicity and FLT1 hypermethylation is a major process in PAH induced carcinogenesis. Overall, this review provides the understanding of the metabolism of environmental concern chemicals, emphasizing the importance of considering mixed compositions and real-life exposure scenarios in assessing their potential effects on human health and diseases development as well as the dual mechanism of toxicity via genetic or epigenetic axis.

Mitotic MTH1 Inhibitors in Treatment of Cancer

The DNA damage response (DDR) protein MTH1 is sanitising the oxidized dNTP pool and preventing incorporation of oxidative damage into DNA and has an emerging role in mitosis. It is a stress-induced protein and often found to be overexpressed in cancer. Mitotic MTH1 inhibitors arrest cells in mitosis and result in incorporation of oxidative damage into DNA and selective killing of cancer cells. Here, I discuss the leading mitotic MTH1 inhibitor TH1579 (OXC-101, karonudib), now being evaluated in clinical trials, and describe its dual effect on mitosis and incorporation of oxidative DNA damage in cancer cells. I describe why MTH1 inhibitors that solely inhibits the enzyme activity fail to kill cancer cells and discuss if MTH1 is a valid target for cancer treatment. I discuss emerging roles of MTH1 in regulating tubulin polymerisation and mitosis and the necessity of developing the basic science insights along with translational efforts. I also give a perspective on how edgetic perturbation is making target validation difficult in the DDR field.

Targeting the DNA damage response and repair in cancer through nucleotide metabolism

The exploitation of the DNA damage response and DNA repair proficiency of cancer cells is an important anticancer strategy. The replication and repair of DNA are dependent upon the supply of deoxynucleoside triphosphate (dNTP) building blocks, which are produced and maintained by nucleotide metabolic pathways. Enzymes within these pathways can be promising targets to selectively induce toxic DNA lesions in cancer cells. These same pathways also activate antimetabolites, an important group of chemotherapies that disrupt both nucleotide and DNA metabolism to induce DNA damage in cancer cells. Thus, dNTP metabolic enzymes can also be targeted to refine the use of these chemotherapeutics, many of which remain standard of care in common cancers. In this review article, we will discuss both these approaches exemplified by the enzymes MTH1, MTHFD2 and SAMHD1. © 2022 The Authors. Molecular Oncology published by John Wiley & Sons Ltd on behalf of Federation of European Biochemical Societies.

Formation and repair of oxidatively generated damage in cellular DNA

In this review article, emphasis is placed on the critical survey of available data concerning modified nucleobase and 2-deoxyribose products that have been identified in cellular DNA following exposure to a wide variety of oxidizing species and agents including, hydroxyl radical, one-electron oxidants, singlet oxygen, hypochlorous acid and ten-eleven translocation enzymes. In addition, information is provided about the generation of secondary oxidation products of 8-oxo-7,8-dihydroguanine and nucleobase addition products with reactive aldehydes arising from the decomposition of lipid peroxides. It is worth noting that the different classes of oxidatively generated DNA damage that consist of single lesions, intra- and interstrand cross-links were unambiguously assigned and quantitatively detected on the basis of accurate measurements involving in most cases high performance liquid chromatography coupled to electrospray ionization tandem mass spectrometry. The reported data clearly show that the frequency of DNA lesions generated upon severe oxidizing conditions, including exposure to ionizing radiation is low, at best a few modifications per 106 normal bases. Application of accurate analytical measurement methods has also allowed the determination of repair kinetics of several well-defined lesions in cellular DNA that however concerns so far only a restricted number of cases.

Does the crystal habit modulate the genotoxic potential of silica particles? A cytogenetic evaluation in human and murine cell lines

Crystalline silica inhaled from occupational sources has been classified by IARC as carcinogenic to humans; in contrast, for amorphous silica, epidemiological and experimental evidence remains insufficient. The genotoxicity of crystalline silica is still debated because of the inconsistency of experimental results ("variability of silica hazard"), often related to the features of the particle surfaces. We have assessed the role of crystal habit in the genotoxicity of silica powders. Pure quartz (crystalline) and vitreous silica (amorphous), sharing the same surface features, were used in an in vitro study with human pulmonary epithelial (A549) and murine macrophage (RAW264.7) cell lines, representative of occupational and environmental exposures. Genotoxicity was evaluated by the comet and micronucleus assays, and cytotoxicity by the trypan blue method. Cells were treated with silica powders for 4 and 24h. Quartz but not vitreous silica caused cell death and DNA damage in RAW264.7 cells. A549 cells were relatively resistant to both powders. Our results support the view that crystal habit per se plays a pivotal role in modulating the biological responses to silica particles.

Effects of silver nanoparticles on oxidative DNA damage-repair as a function of p38 MAPK status: a comparative approach using human Jurkat T cells and the nematode Caenorhabditis elegans

The large-scale use of silver nanoparticles (AgNPs) has raised concerns over potential impacts on the environment and human health. We previously reported that AgNP exposure causes an increase in reactive oxygen species, DNA damage, and induction of p38 MAPK and PMK-1 in Jurkat T cells and in Caenorhabditis elegans. To elucidate the underlying mechanisms of AgNP toxicity, here we evaluate the effects of AgNPs on oxidative DNA damage-repair (in human and C. elegans DNA glycosylases hOGG1, hNTH1, NTH-1, and 8-oxo-GTPases-hMTH1, NDX-4) and explore the role of p38 MAPK and PMK-1 in this process. Our comparative approach examined viability, gene expression, and enzyme activities in wild type (WT) and p38 MAPK knock-down (KD) Jurkat T cells (in vitro) and in WT and pmk-1 loss-of-function mutant strains of C. elegans (in vivo). The results suggest that p38 MAPK/PMK-1 plays protective role against AgNP-mediated toxicity, reduced viability and greater accumulation of 8OHdG was observed in AgNP-treated KD cells, and in pmk-1 mutant worms compared with their WT counterparts, respectively. Furthermore, dose-dependent alterations in hOGG1, hMTH1, and NDX-4 expression and enzyme activity, and survival in ndx-4 mutant worms occurred following AgNP exposure. Interestingly, the absence or depletion of p38 MAPK/PMK-1 caused impaired and additive effects in AgNP-induced ndx-4(ok1003); pmk-1(RNAi) mutant survival, and hOGG1 and NDX-4 expression and enzyme activity, which may lead to higher accumulation of 8OHdG. Together, the results indicate that p38 MAPK/PMK-1 plays an important protective role in AgNP-induced oxidative DNA damage-repair which is conserved from C. elegans to humans.

Lipid peroxidation-induced DNA adducts in human gastric mucosa

DNA adducts are a major cause of DNA mutation and DNA mutation-related diseases, but the simultaneous identification of multiple DNA adducts has been a challenge for a decade. An adductome approach using consecutive liquid chromatography and double mass spectrometry after micrococcal nuclease treatment has paved the way to demonstrations of numerous DNA adducts in a single experiment and is expected to contribute to the comprehensive understanding of overall environmental and endogenous exposures to possible mutagens in individuals. In this report, we applied an adductome approach to gastric mucosa samples taken at the time of a gastrectomy for gastric cancer in Lujiang, China, and in Hamamatsu, Japan. Seven lipid peroxidation-related DNA adducts [1,N6-etheno-2'-deoxyadenosine, butanone-etheno-2'-deoxycytidine (BεdC), butanone-etheno-2'-deoxy-5-methylcytidine, butanone-etheno-2'-deoxyadenosine (BεdA), heptanone-etheno-2'-deoxycytidine, heptanone-etheno-2'-deoxyadenosine (HεdA) and heptanone-etheno- 2'-deoxyguanosine] were identified in a total of 22 gastric mucosa samples. The levels of these adducts ranged from 0 to 30,000 per 10(9) bases. Although the presence of Helicobacter pylori DNA in the mucosa was not related to these adducts level, the levels of BεdC, BεdA and HεdA were higher in the Japanese gastric mucosa samples. The profiles of these 7 adduct levels among the 21 cases were capable of discriminating between the possible origins (China or Japan) of the gastric mucosa samples. Our report is the first demonstration of lipid peroxidation-related DNA adducts in the human stomach, and these observations warrant further investigation in the context of the significance of DNA adducts in human gastric carcinogenesis.

Regulation of DNA glycosylases and their role in limiting disease

This review will present a current understanding of mechanisms for the initiation of base excision repair (BER) of oxidatively-induced DNA damage and the biological consequences of deficiencies in these enzymes in mouse model systems and human populations.

[DNA damage in human pleural mesothelial cells induced by exposure to carbon nanotubes]

OBJECTIVES

Nanomaterials are currently used in electronics, industrial materials, cosmetics, and medicine because they have useful physicochemical properties, such as strength, conductivity, durability, and chemical stability. As these materials have become widespread, many questions have arisen regarding their effects on health and the environment. In particular, recent studies have demonstrated that carbon nanotubes (CNTs) cause significant inflammation and mesothelioma in vivo. In this study, we investigated the potential risk posed by singlewalled carbon nanotube (SWCNT) and multiwalled carbon nanotube (MWCNT) exposure in human pleural mesothelial cells.

METHODS

CNT cytotoxicity was determined by a trypan blue exclusion assay, and DNA damage was detected by an alkaline comet assay. The concentration of 8-oxodeoxyguanosine (8-OHdG) in DNA was measured by high perhormance liquid chromatography with electrochemical detection. The expression of base excision repair enzymes in the cell was estimated by immunoblot analysis.

RESULTS

We observed inhibitory effects on cell proliferation and the induction of DNA damage following exposure of cells to purified CNTs that were suspended in dispersion medium. However, accumulation of 8-OHdG in DNA was not found. In addition, the expression levels of base excision enzymes that are involved in hOGG1, hMTH1, and MYH in MeT-5A cells remained unchanged for 24 h after carbon nanotube exposure.

CONCLUSIONS

CNTs significantly inhibit cell proliferation and decrease DNA damage in human pleural mesothelial cells. Our results indicate that the mechanism of CNT-induced genotoxicity is different from that following exposure to reactive oxygen species, which causes oxidative DNA modifications and 8-OHdG production. Further investigation is required to characterize the specific DNA mutations that occur following CNT exposure.

Regulation of base excision repair in eukaryotes by dynamic localization strategies

This chapter discusses base excision repair (BER) and the known mechanisms defined thus far regulating BER in eukaryotes. Unlike the situation with nucleotide excision repair and double-strand break repair, little is known about how BER is regulated to allow for efficient and accurate repair of many types of DNA base damage in both nuclear and mitochondrial genomes. Regulation of BER has been proposed to occur at multiple, different levels including transcription, posttranslational modification, protein-protein interactions, and protein localization; however, none of these regulatory mechanisms characterized thus far affect a large spectrum of BER proteins. This chapter discusses a recently discovered mode of BER regulation defined in budding yeast cells that involves mobilization of DNA repair proteins to DNA-containing organelles in response to genotoxic stress.

Obesity and hepatosteatosis in mice with enhanced oxidative DNA damage processing in mitochondria

Mitochondria play critical roles in oxidative phosphorylation and energy metabolism. Increasing evidence supports that mitochondrial DNA (mtDNA) damage and dysfunction play vital roles in the development of many mitochondria-related diseases, such as obesity, diabetes mellitus, infertility, neurodegenerative disorders, and malignant tumors in humans. Human 8-oxoguanine-DNA glycosylase 1 (hOGG1) transgenic (TG) mice were produced by nuclear microinjection. Transgene integration was analyzed by PCR. Transgene expression was measured by RT-PCR and Western blot analysis. Mitochondrial DNA damage was analyzed by mutational analyses and measurement of mtDNA copy number. Total fat content was measured by a whole-body scan using dual-energy X-ray absorptiometry. The hOGG1 overexpression in mitochondria increased the abundance of intracellular free radicals and major deletions in mtDNA. Obesity in hOGG1 TG mice resulted from increased fat content in tissues, produced by hyperphagia. The molecular mechanisms of obesity involved overexpression of genes in the central orexigenic (appetite-stimulating) pathway, peripheral lipogenesis, down-regulation of genes in the central anorexigenic (appetite-suppressing) pathway, peripheral adaptive thermogenesis, and fatty acid oxidation. Diffuse hepatosteatosis, female infertility, and increased frequency of malignant lymphoma were also seen in these hOGG1 TG mice. High levels of hOGG1 expression in mitochondria, resulting in enhanced oxidative DNA damage processing, may be an important factor in human metabolic syndrome, infertility, and malignancy.

Role of mutagenicity in asbestos fiber-induced carcinogenicity and other diseases

The cellular and molecular mechanisms of how asbestos fibers induce cancers and other diseases are not well understood. Both serpentine and amphibole asbestos fibers have been shown to induce oxidative stress, inflammatory responses, cellular toxicity and tissue injuries, genetic changes, and epigenetic alterations in target cells in vitro and tissues in vivo. Most of these mechanisms are believe to be shared by both fiber-induced cancers and noncancerous diseases. This article summarizes the findings from existing literature with a focus on genetic changes, specifically, mutagenicity of asbestos fibers. Thus far, experimental evidence suggesting the involvement of mutagenesis in asbestos carcinogenicity is more convincing than asbestos-induced fibrotic diseases. The potential contributions of mutagenicity to asbestos-induced diseases, with an emphasis on carcinogenicity, are reviewed from five aspects: (1) whether there is a mutagenic mode of action (MOA) in fiber-induced carcinogenesis; (2) mutagenicity/carcinogenicity at low dose; (3) biological activities that contribute to mutagenicity and impact of target tissue/cell type; (4) health endpoints with or without mutagenicity as a key event; and finally, (5) determinant factors of toxicity in mutagenicity. At the end of this review, a consensus statement of what is known, what is believed to be factual but requires confirmation, and existing data gaps, as well as future research needs and directions, is provided.

Hydrogen sulfide induces oxidative damage to RNA and DNA in a sulfide-tolerant marine invertebrate

Hydrogen sulfide acts as an environmental toxin across a range of concentrations and as a cellular signaling molecule at very low concentrations. Despite its toxicity, many animals, including the mudflat polychaete Glycera dibranchiata, are periodically or continuously exposed to sulfide in their environment. We tested the hypothesis that a broad range of ecologically relevant sulfide concentrations induces oxidative stress and oxidative damage to RNA and DNA in G. dibranchiata. Coelomocytes exposed in vitro to sulfide (0-3 mmol L(-1) for 1 h) showed dose-dependent increases in oxidative stress (as 2',7'-dichlorofluorescein fluorescence) and superoxide production (as dihydroethidine fluorescence). Coelomocytes exposed in vitro to sulfide (up to 0.73 mmol L(-1) for 2 h) also acquired increased oxidative damage to RNA (detected as 8-oxo-7,8-dihydroguanosine) and DNA (detected as 8-oxo-7,8-dihydro-2'-deoxyguanosine). Worms exposed in vivo to sulfide (0-10 mmol L(-1) for 24 h) acquired elevated oxidative damage to RNA and DNA in both coelomocytes and body wall tissue. While the consequences of RNA and DNA oxidative damage are poorly understood, oxidatively damaged deoxyguanosine bases preferentially bind thymine, causing G-T transversions and potentially causing heritable point mutations. This suggests that sulfide can be an environmental mutagen in sulfide-tolerant invertebrates.

Potassium bromate enhances N-ethyl-N-hydroxyethylnitrosamine-induced kidney carcinogenesis only at high doses in Wistar rats: indication of the existence of an enhancement threshold

As susceptibility to carcinogens varies considerably among different strains of experimental animals, evaluation of dose-response relationships for genotoxic carcinogen in different strains is indispensable for risk assessment. Potassium bromate (KBrO(3)) is a genotoxic carcinogen inducing kidney cancers at high doses in male F344 rats, but little is known about its carcinogenic effects in other strains of rats. The purpose of the present study was to determine dose-response relationships for carcinogenic effects of KBrO(3) on N-ethyl-N-hydroxyethylnitrosamine (EHEN)-induced kidney carcinogenesis in male Wistar rats. We found that KBrO(3) showed significant enhancement effects on EHEN-induced kidney carcinogenesis at above 250 ppm but not at doses of 125 ppm and below when evaluated in terms of induction of either preneoplastic lesions or tumors in male Wistar rats. Furthermore, KBrO(3) significantly increased the formation of oxidative DNA damage at doses of 125 and above but not at doses of 30 ppm and below in kidneys. These results demonstrated that low doses of KBrO(3) exert no effects on development of EHEN-initiated kidney lesions and induction of oxidative DNA damage. Taking account of previous similar findings in male F344 rats, it is strongly suggested that a threshold dose exists for enhancement effects of KBrO(3) on kidney carcinogenesis in rats.

Up-regulation of 8-oxo-dGTPase activity of MTH1 protein in the brain, testes and kidneys of mice exposed to (137)Cs gamma radiation

Abstract Mammalian MTH1 protein is an antimutagenic (2'-deoxy)ribonucleoside 5'-triphosphate pyrophosphohydrolase that prevents the incorporation of oxidatively modified nucleotides into nucleic acids. It decomposes most specifically the miscoding products of oxidative damage to purine nucleic acid precursors (e.g. 8-oxo-dGTP, 2-oxo-dATP, 2-oxo-ATP, 8-oxo-GTP) that may cause point mutations or transcription errors when incorporated into DNA and RNA, respectively. The increased expression of MTH1 mRNA and MTH1 protein was previously proposed as a molecular marker of oxidative stress. Therefore, we hypothesized that increased 8-oxo-dGTPase activity of MTH1 protein in mouse organs could serve as a dose-dependent marker of exposure to ionizing radiation, which is known to induce oxidative stress. To test our hypothesis, we measured 8-oxo-dGTPase activity in six organs of male BL6 mice after exposure to 0, 10, 25 and 50 cGy and 1 Gy of (137)Cs gamma radiation given as a single whole-body dose (1 Gy/min). The mice were killed 4, 8 and 24 h after irradiation. A statistically significant induction of 8-oxo-dGTPase was found in brains, testes and kidneys but not in lungs, hearts or livers. Brains, which demonstrated the highest (4.3-fold) increase of 8-oxo-dGTPase activity, were shown to express approximately 50% higher levels of MTH1 protein. However, due to the lack of a simple positive correlation between the dose and the observed 8-oxo-dGTPase activity in brain, testes and kidneys, we conclude that measurements of 8-oxo-dGTPase activity in these organs may serve as a rough indicator rather than a quantifiable marker of radiation-induced oxidative stress.

Role of mitochondrial hOGG1 and aconitase in oxidant-induced lung epithelial cell apoptosis

8-Oxoguanine DNA glycosylase (Ogg1) repairs 8-oxo-7,8-dihydroxyguanine (8-oxoG), one of the most abundant DNA adducts caused by oxidative stress. In the mitochondria, Ogg1 is thought to prevent activation of the intrinsic apoptotic pathway in response to oxidative stress by augmenting DNA repair. However, the predominance of the beta-Ogg1 isoform, which lacks 8-oxoG DNA glycosylase activity, suggests that mitochondrial Ogg1 functions in a role independent of DNA repair. We report here that overexpression of mitochondria-targeted human alpha-hOgg1 (mt-hOgg1) in human lung adenocarcinoma cells with some alveolar epithelial cell characteristics (A549 cells) prevents oxidant-induced mitochondrial dysfunction and apoptosis by preserving mitochondrial aconitase. Importantly, mitochondrial alpha-hOgg1 mutants lacking 8-oxoG DNA repair activity were as effective as wild-type mt-hOgg1 in preventing oxidant-induced caspase-9 activation, reductions in mitochondrial aconitase, and apoptosis, suggesting that the protective effects of mt-hOgg1 occur independent of DNA repair. Notably, wild-type and mutant mt-hOgg1 coprecipitate with mitochondrial aconitase. Furthermore, overexpression of mitochondrial aconitase abolishes oxidant-induced apoptosis whereas hOgg1 silencing using shRNA reduces mitochondrial aconitase and augments apoptosis. These findings suggest a novel mechanism that mt-hOgg1 acts as a mitochondrial aconitase chaperone protein to prevent oxidant-mediated mitochondrial dysfunction and apoptosis that might be important in the molecular events underlying oxidant-induced toxicity.

Quercetin inhibits hydrogen peroxide-induced DNA damage and enhances DNA repair in Caco-2 cells

Flavonoids are known to have antioxidant activity that may limit DNA damage and help prevent degenerative diseases, including cancer. However, our knowledge of flavonoids' role in DNA protection/repair mechanism(s) is limited. This study investigated the effects of quercetin on DNA oxidation and DNA repair in Caco-2 cells with or without oxidant (H2O2) challenge. Quercetin (1, 100 microM) significantly reduced oxidative DNA damage, as measured by the number of single-strand breaks identified by single cell gel electrophoresis. Quercetin treatment also caused a measurable increase in the mRNA expression of human 8-oxoguanine DNA glycosylase (hOGG1) at 0 and 4h after H2O2 treatment (measured using RT-PCR). In addition, the highest level of quercetin tested (100 microM) maintained hOGG1 expression at basal levels or higher for up to 12h after H2O2 treatment, while oxidant treatment alone resulted in significant reduction of hOGG1 at 8h. Our study indicates that quercetin could protect DNA both by reducing oxidative DNA damage and by enhancing DNA repair through modulation of DNA repair enzyme expression.

Effects of an acute exposure to toluene on the DNA repair activity of the human 8-oxoguanine DNA glycosylase 1 (hOGG1) in healthy subjects

The structure and previous studies on the biotransformation of toluene lead to the suspicion that metabolites may be formed which preferentially react with strongly nucleophilic partners such as sulfhydryl groups of cysteines in proteins. Human 8-oxoguanine DNA glycosylase 1 removes the major oxidative DNA damage and possesses eight cysteines. Its potential inactivation may lead to accumulation of DNA damage by reactive oxygen species formed by exogenous agents or by ubiquitous endogenous processes. The goal of the present investigation was to study the in vivo effect in humans of an acute toluene exposure on hOGG1 activity. Twenty healthy, non-smoking males were exposed to 50 ppm toluene and to filtered air in an exposure chamber for 270 min, using a cross-over design. Before and 30 min after the end of exposure, blood samples were taken and toluene concentrations and the hOGG1 activity were measured. hOGG1 activity was determined in peripheral mononuclear blood cells. Thirty minutes after exposure to toluene, we found a median blood concentration of 0.25 mg toluene/l. Compared with the activity before exposure, upon exposure to toluene a statistically insignificant median increase of hOGG1 activity by +0.4% and upon exposure to air by +2.3% was determined. Thus, no reduction of the hOGG1 repair activity after acute exposure to 50 ppm toluene was observed.

Negative Effect of Long-Term Inhalation of Toner on Formation of 8-Hydroxydeoxyguanosine in DNA in the Lungs of Rats In Vivo

We assessed the effects of long-term inhalation of toner on the pathological changes and formation of 8-hydroxydeoxyguanosine (8-OH-Gua) in DNA in a rat model. Female Wistar rats (10 wk old) were divided evenly into a high concentration exposure group (H: 15.2 mg/m(3)), a low concentration exposure group (L: 5.5 mg/m(3)), and a control group. The mass median aerodynamic diameter of the toner was 4.5 microm. The rats were sacrificed at the termination of a 1-yr or 2-yr inhalation period. Pathological examination was performed on the left lung, and the level of 8-OH-Gua in DNA from the right lung was measured using a high-performance liquid chromatography (HPLC) column. The pathological findings showed that lung cancer was not observed in any of the exposed or control groups, though pleural thickening and small foci of collagen were observed in toner-exposed rat lungs. Inhalation of the toner for 1 and even 2 yr did not induce the formation of 8-OH-Gua in DNA in rat lungs. These data suggest that long-term inhalation of toner may not induce lung tumors.

Combustion products of 1,3-butadiene inhibit catalase activity and induce expression of oxidative DNA damage repair enzymes in human bronchial epithelial cells

1,3-Butadiene, an important petrochemical, is commonly burned off when excess amounts need to be destroyed. This combustion process produces butadiene soot (BDS), which is composed of a complex mixture of polycyclic aromatic hydrocarbons in particulates ranging in size from <1 microm to 1 mm. An organic extract of BDS is both cytotoxic and genotoxic to normal human bronchial epithelial (NHBE) cells. Based on the oxidizing potential of BDS, we hypothesized that an organic extract of this particulate matter would (1) cause enzyme inactivation due to protein amino acid oxidation and (2) induce oxidative DNA damage in NHBE cells. Thus, our aims were to determine the effect of butadiene soot ethanol extract (BSEE) on both enzyme activity and the expression of proteins involved in the repair of oxidative DNA damage. Catalase was found to be sensitive to BDS as catalase activity was potently diminished in the presence of BSEE. Using Western analysis, both the alpha isoform of human 8-oxoguanine DNA glycosylase (alpha-hOGG1) and human apurinic/apyrimidinic endonuclease (APE-1) were shown to be significantly overexpressed as compared to untreated controls after exposure of NHBE cells to BSEE. Our results indicate that BSEE is capable of effectively inactivating the antioxidant enzyme catalase, presumably via oxidation of protein amino acids. The presence of oxidized biomolecules may partially explain the extranuclear fluorescence that is detected when NHBE cells are treated with an organic extract of BDS. Overexpression of both alpha-hOGG1 and APE-1 proteins following treatment of NHBE cells with BSEE suggests that this mixture causes oxidative DNA damage.

AtNUDX1, an 8-oxo-7,8-dihydro-2'-deoxyguanosine 5'-triphosphate pyrophosphohydrolase, is responsible for eliminating oxidized nucleotides in Arabidopsis

Cellular DNA, RNA and their precursor nucleotides are at high risk of being oxidized by reactive oxygen species. An oxidized base, 8-oxo-7,8-dihydro-2'-(deoxy)guanosine, can pair with both adenine and cytosine, and thus would cause both replicational and translational errors. Previously, we have reported that an Arabidopsis Nudix hydrolase, AtNUDX1, acts to hydrolyze an oxidized deoxyribonucleotide, 8-oxo-7,8-dihydro-2'-deoxyguanosine 5'-triphosphate (8-oxo-dGTP). Here we showed that 8-oxo-dGTP pyrophosphohydrolase activity is not exhibited by any other Arabidopsis Nudix hydrolase. AtNUDX1 acted on an oxidized ribonucleotide, 8-oxo-GTP, with high affinity (K(m) 28.1 microM). In a transcriptional mutational analysis using the lacZ reporter gene, the phenotypic suppression of the lacZ amber mutation in a mutT-deficient Escherichia coli strain caused by the misincorporation of 8-oxo-GTP into the mRNA was significantly diminished by expression of AtNUDX1. These findings suggest that AtNUDX1 prevents transcriptional errors in vivo. A confocal microscopic analysis using a green fluorescent protein (GFP) fusion protein demonstrated that AtNUDX1 is distributed in the cytosol, where the main pool of nucleotides in the cells exists. The level of 8-oxo-guanosine in genomic DNA was significantly increased in knockout nudx1 plants compared with wild-type plants under normal and oxidative stress (3 microM paraquat) conditions. The results obtained here indicate that AtNUDX1 functions in cellular defense against oxidative DNA and RNA damage through the sanitization of their precursor pools in the cytosol in Arabidopsis cells.

DNA damage in rats after a single oral exposure to diesel exhaust particles

The gastrointestinal route of exposure to particulate matter is important because particles are ingested via contaminated foods and inhaled particles are swallowed when removed from the airways by the mucociliary clearance system. We investigated the effect of an intragastric administration by oral gavage of diesel exhaust particles (DEP) in terms of DNA damage, oxidative stress and DNA repair in colon epithelial cells, liver, and lung of rats. Eight rats per group were exposed to Standard Reference Material 2975 at 0.064 or 0.64 mg/kg bodyweight for 6 and 24 h. Increased levels of 8-oxo-7,8-dihydro-2'-deoxyguanosine lesions were observed at the highest dose after 6 and 24 h in all three organs. 8-Oxo-7,8-dihydro-2'-deoxyguanosine is repaired by oxoguanine DNA glycosylase 1 (OGG1); upregulation of this repair system was observed as elevated pulmonary OGG1 mRNA levels after 24 h at both doses of DEP, but not in the colon and liver. A general response of the antioxidant defence system is further indicated by elevated levels of heme oxygenase 1 mRNA in the liver and lung 24 h after administration. The level of bulky DNA adducts was increased in liver and lung at both doses after 6 and 24h (DNA adducts in colon epithelium were not investigated). In summary, DEP administered via the gastrointestinal tract at low doses relative to ambient exposure generates DNA damage and increase the expression of defence mechanisms in organs such as the lung and liver. The oral exposure route should be taken into account in risk assessment of particulate matter.

Base excision repair modulation as a risk factor for human cancers

Oxidative DNA damage and DNA repair mediate the development of several human pathologies, including cancer. The major pathway for oxidative DNA damage repair is base excision repair (BER). Functional assays performed in blood leukocytes of cancer patients and matched controls show that specific BER pathways are decreased in cancer patients, and may be risk factors. These include 8-oxoguanine (8-oxoG) repair in lung and head and neck cancer patients and repair of lipid peroxidation (LPO) induced 1,N(6)-ethenoadenine (epsilonA) in lung cancer patients. Decrease of excision of LPO-induced DNA damage, epsilonA and 3,N(4)-ethenocytosine (epsilonC) was observed in blood leukocytes of patients developing lung adenocarcinoma, specific histological type of cancer related to inflammation and healing of scars. BER proteins activity depends on gene polymorphism, interactions between BER system partners and post-translational modifications. Polymorphisms of DNA glycosylases may change their enzymatic activities, and some polymorphisms increase the risk of inflammation-related cancers, colorectal, lung and other types. Polymorphisms of BER platform protein, XRCC1 are connected with increased risk of tobacco-related cancers. BER efficiency may also be changed by reactive oxygen species and some diet components, which induce transcription of several glycosylases as well as a major human AP-endonuclease, APE1. BER is also changed in tumors in comparison to unaffected surrounding tissues, and this change may be due to transcription stimulation, post-translational modification of BER enzymes as well as protein-protein interactions. Modulation of BER enzymes activities may be, then, an important factor determining the risk of cancer and also may participate in cancer development.

Cytotoxicity and DNA-damage in human lung epithelial cells exposed to respirable α-quartz

Occupational exposure to respirable crystalline silica is associated with the development of silicosis, lung cancer and airways diseases. In order to assess cytotoxic effects and direct-oxidative DNA damage induced by short-term exposure to different doses of respirable alpha-quartz (NIST SRM1878a), we conducted a study using A549 cells. The cells were exposed to alpha-quartz at 25, 50, 100 microg/ml for 4 h and analysed by scanning electron microscope (SEM) and LDH release assay for cytotoxic effect evaluation. Cells were also exposed to 10, 25, 50, 100 microg/ml of alpha-quartz for 2 h and 4 h and analysed by Fpg comet test to evaluate direct and oxidative DNA damage. SEM observations of treated cells showed bleb development at lower doses and alterations of microvilli morphology at the highest dose. A slight LDH release was found only at 100 microg/ml. Fpg comet test showed a dose-related oxidative DNA damage in cells exposed for 2 h to quartz. Cells exposed for 4h at the same concentrations showed a dose-related direct DNA damage and the presence of oxidative DNA damage at lower doses. The bleb induction on cell surface evidenced by SEM at lower doses correlates with the presence of oxidative DNA damage at 4 h. The cell surface modifications observed by SEM at 100 microg/ml indicate that high doses of quartz induce more evident cytotoxic effects confirmed by LDH analysis and correlate with the genotoxicity showed by comet assay.

Site-directed photoproteolysis of 8-oxoguanine DNA glycosylase 1 (OGG1) by specific porphyrin-protein probe conjugates: a strategy to improve the effectiveness of photodynamic therapy for cancer

The specific light-induced, non-enzymatic photolysis of mOGG1 by porphyrin-conjugated or rose bengal-conjugated streptavidin and porphyrin-conjugated or rose bengal-conjugated first specific or secondary anti-IgG antibodies is reported. The porphyrin chlorin e6 and rose bengal were conjugated to either streptavidin, rabbit anti-mOGG1 primary specific antibody fractions or goat anti-rabbit IgG secondary antibody fractions. Under our experimental conditions, visible light of wavelengths greater than 600 nm induced the non-enzymatic degradation of mOGG1 when this DNA repair enzyme either directly formed a complex with chlorin e6-conjugated anti-mOGG1 primary specific antibodies or indirectly formed complexes with either streptavidin-chlorin e6 conjugates and biotinylated first specific anti-mOGG1 antibodies or first specific anti-mOGG1 antibodies and chlorin e6-conjugated anti-rabbit IgG secondary antibodies. Similar results were obtained when rose bengal was used as photosensitizer instead of chlorin e6. The rate of the photochemical reaction of mOGG1 site-directed by all three chlorin e6 antibody complexes was not affected by the presence of the singlet oxygen scavenger sodium azide. Site-directed photoactivatable probes having the capacity to generate reactive oxygen species (ROS) while destroying the DNA repair system in malignant cells and tumors may represent a powerful strategy to boost selectivity, penetration and efficacy of current photodynamic (PDT) therapy methodologies.

Increased mRNA expression levels of ERCC1, OGG1 and RAI in colorectal adenomas and carcinomas

BACKGROUND

The majority of colorectal cancer (CRC) cases develop through the adenoma-carcinoma pathway. If an increase in DNA repair expression is detected in both early adenomas and carcinomas it may indicate that low repair capacity in the normal mucosa is a risk factor for adenoma formation.

METHODS

We have examined mRNA expression of two DNA repair genes, ERCC1 and OGG1 as well as the putative apoptosis controlling gene RAI, in normal tissues and lesions from 36 cases with adenomas (mild/moderat n = 21 and severe n = 15, dysplasia) and 9 with carcinomas.

RESULTS

Comparing expression levels of ERCC1, OGG1 and RAI between normal tissue and all lesions combined yielded higher expression levels in lesions, 3.3-fold higher (P = 0.005), 5.6-fold higher (P < 3.10-5) and 7.7-fold higher (P = 0.0005), respectively. The levels of ERCC1, OGG1 and RAI expressions when comparing lesions, did not differ between adenomas and CRC cases, P = 0.836, P = 0.341 and P = 0.909, respectively. When comparing expression levels in normal tissue, the levels for OGG1 and RAI from CRC cases were significantly lower compared to the cases with adenomas, P = 0.012 and P = 0.011, respectively.

CONCLUSION

Our results suggest that increased expression of defense genes is an early event in the progression of colorectal adenomas to carcinomas.

Effects of low-dose gamma radiation on DNA damage, chromosomal aberration and expression of repair genes in human blood cells

Exposure to low-dose gamma radiation is common in certain occupations but the biological and health effects from such exposure remain to be determined. The aim of this study was to investigate the effects of low-dose gamma radiation on DNA damage, chromosomal aberration and DNA repair gene expressions in whole blood and peripheral lymphocytes. The study revealed a dose-dependent effect of gamma radiation on DNA damage. Significant increases in DNA strand breaks and oxidative base damage, determined as formamidopyrimidine-DNA-glycosylase (FPG)-sensitive sites, were observed at absorbed doses of 5 and 10cGy, respectively. However, gamma radiation at doses up to 500cGy did not significantly increase the level of 8-oxo-7, 8-dihydro-2'-deoxyguanosine (8-oxodG) determined by HPLC with electrochemical detection (HPLC-ECD). Gamma radiation as low as 5cGy caused chromosomal aberrations determined as dicentric and deletion frequencies. This finding is significant since the genotoxic effects of gamma radiation can be observed even at a low dose of 5cGy. Furthermore, gamma radiation decreased the mRNA expression of both hOGG1 and XRCC1 repair genes determined by reverse transcriptase-polymerase chain reaction (RT-PCR), with a significant decrease of expression being observed at 20cGy. The expression levels of hOGG1 and XRCC1 mRNA were inversely correlated with the levels of FPG-sensitive sites and DNA strand breaks. The finding of decreased expression levels for hOGG1 and XRCC1 in gamma-irradiated lymphocytes has not been reported elsewhere. Our observations suggest that the genotoxic effects of gamma radiation may be due to a combination of DNA-damaging effects and reduced DNA repair capacity, and may explain the significant increase in health risk from high doses of ionizing radiation.

In vivo mutagenicity and initiation following oxidative DNA lesion in the kidneys of rats given potassium bromate

To clarify the role of 8-OHdG formation as a starting point for carcinogenesis, we examined the dose-dependence and time-course of changes of OGG1 mRNA expression, 8-OHdG levels and in vivo mutations in the kidneys of gpt delta rats given KBrO3 in their drinking water for 13 weeks. There were no remarkable changes in OGG1 mRNA in spite of some increments being statistically significant. Increases of 8-OHdG occurred after 1 week at 500 p.p.m. and after 13 weeks at 250 p.p.m. Elevation of Spi- mutant frequency, suggestive of deletion mutations, occurred after 9 weeks at 500 p.p.m. In a two-stage experiment, F344 rats were given KBrO3 for 13 weeks then, after a 2-week recovery, treated with 1% NTA in the diet for 39 weeks. The incidence and multiplicity of renal preneoplastic lesions in rats given KBrO3 at 500 p.p.m. followed by NTA treatment were significantly higher than in rats treated with NTA alone. Results suggest that a certain period of time might be required for 8-OHdG to cause permanent mutations. The two-step experiment shows that cells exposed to the alteration of the intranuclear status by oxidative stress including 8-OHdG formation might be able to form tumors with appropriate promotion.

2- and 4-Aminobiphenyls induce oxidative DNA damage in human hepatoma (Hep G2) cells via different mechanisms

4-Aminobiphenyl (4-ABP) and its analogue, 2-aminobiphenyl (2-ABP), were examined for their ability to induce oxidative DNA damage in Hep G2 cells. Using the alkaline comet assay, we showed that 2-ABP and 4-ABP (25-200 microM) were able to induce the DNA damage in Hep G2 cells. With both compounds, formation of intracellular reactive oxygen species (ROS) was detected using flow cytometry analysis. Post-treatment of 2-ABP and 4-ABP-treated cells by endonuclease III (Endo III) or formamidopyrimidine-DNA glycosylase (Fpg) to determine the formation of oxidized pyrimidines or oxidized purines showed a significant increase of the extent of DNA migration. This indicated that oxidative DNA damage occurs in Hep G2 cells after exposure to 2-ABP and 4-ABP. This assumption was further substantiated by the fact that the spin traps, 5,5-dimethyl-pyrroline-N-oxide (DMPO) and N-tert-butyl-alpha-phenylnitrone (PBN), decreased DNA damage significantly. Furthermore, addition of the catalase (100 U/ml) caused a decrease in the DNA damage induced by 2-ABP or 4-ABP, indicating that H(2)O(2) is involved in ABP-induced DNA damage. Pre-incubation of the cells with the iron chelator desferrioxamine (DFO) (1mM) and with the copper chelator neocupronine (NC) (100 microM) also decreased DNA damage in cells treated with 200 microM 2-ABP or 200 microM 4-ABP, while the calcium chelator {1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid acetoxymethyl ester}(BAPTA/AM) (10 microM) decreased only DNA strand breaks in cells exposed to 4-ABP. This suggested that ions are involved in the formation of DNA strand breaks. Using RT-PCR and Western blotting, lower inhibition of the expression of the OGG1 gene and of the OGG1 protein was observed in cells treated with 4-ABP, and 2-ABP-treated cells showed a marked reduction in the expression of OGG1 gene and OGG1 protein. Taken together, our finding indicated the mechanisms of induced oxidative DNA damage in Hep G2 cell by 2-ABP and 4-ABP are different, although both tested compounds are isomers.

ROS-mediated genotoxicity of asbestos-cement in mammalian lung cells in vitro

Asbestos is a known carcinogen and co-carcinogen. It is a persisting risk in our daily life due to its use in building material as asbestos-cement powder. The present study done on V79-cells (Chinese hamster lung cells) demonstrates the cytotoxic and genotoxic potential of asbestos-cement powder (ACP) in comparison with chrysotile asbestos. A co-exposure of chrysotile and ACP was tested using the cell viability test and the micronucleus assay. The kinetochore analysis had been used to analyse the pathway causing such genotoxic effects. Thiobarbituric acid-reactive substances were determined as evidence for the production of reactive oxygen species. Both, asbestos cement as well as chrysotile formed micronuclei and induced loss of cell viability in a concentration- and time-dependent way. Results of TBARS analysis and iron chelator experiments showed induction of free radicals in ACP- and chrysotile exposed cultures. CaSO4 appeared to be a negligible entity in enhancing the toxic potential of ACP. The co-exposure of both, ACP and chrysotile, showed an additive effect in enhancing the toxicity. The overall study suggests that asbestos-cement is cytotoxic as well as genotoxic in vitro. In comparison to chrysotile the magnitude of the toxicity was less, but co-exposure increased the toxicity of both.

Cadmium Down-regulates Human OGG1 through Suppression of Sp1 Activity

Cadmium is a well known human and animal carcinogen and is a ubiquitous contaminant in the environment. Although the carcinogenic mechanism of cadmium is a multifactorial process, oxidative DNA damage is believed to be of prime importance. In particular, cadmium suppresses the capacity of cells to repair oxidative DNA damage. In this study, cadmium treatment led to a significant increase in gamma-ray-induced 8-oxoguanine (8-oxoG) formation. Western blotting and semiquantitative reverse transcription-PCR revealed that cadmium treatment caused a decrease in the expression level of human OGG1 (8-oxoguanine-DNA glycosylase-1; hOGG1) in human fibroblast GM00637 and HeLa S3 cells. In addition, the cadmium-mediated decrease in hOGG1 transcription was the result of decreased binding of the transcription factor Sp1 to the hOGG1 promoter. Finally, we show that an increase in the functional hOGG1 expression level could inhibit the cadmium-mediated increase in gamma-ray-induced 8-oxoG accumulation as well as in gamma-radiation-induced mutation frequency at the HPRT (hypoxanthine-guanine phosphoribosyltransferase) gene locus. These results suggest that cadmium attenuates removal of gamma-ray-induced 8-oxoG adducts, which in turn increases the mutation frequency, and that this effect might, at least in part, result from suppression of hOGG1 transcription via inactivation of Sp1 as a result of cadmium treatment.

Lung cancer in smoking patients inversely alters the activity of hOGG1 and hNTH1

N-Glycosylases excise the damaged adducts from DNA. 7,8-Dihydro-8-oxoguanine in human cells is repaired by OGG1 and hNTH1. The activities of hOGG1 and hNTH1 were measured, using modified and 32P labelled oligonucleotides, in bronchial biopsy samples of smoking patients with non-small cell lung carcinoma. The activity of hOOG1 was significantly higher in biopsies from tumour tissues compared with intra-individual control samples. On the contrary, the activity of endonuclease III homologue, hNTH1, was lower in tumours compared to controls. These opposing alterations in DNA repair enzymes may affect cancer growth due to the increased formation of AP sites.

Cell-specific oxidative DNA damage induced by estrogen in rat testicular cells in vitro

17 alpha-Ethinylestradiol (EE) can induce oxidative DNA damage in terms of 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG) in rat testicular cells by an apparent estrogen receptor-mediated mechanism. We investigated differential susceptibility to EE in cell sub-populations from rat testes and the role of rat 8-oxo-guanine DNA glycosylase (rOGG1). Isolated rat testicular cells were incubated with EE concentrations ranging from 0.1 to 1000 nM. Single strand DNA breaks and oxidised purines as fapyguanine glycosylase (FPG) sensitive sites were assessed by the comet assay. In the total cell population and in round haploid cells, oxidised purines showed a bell-shaped concentration-response relationship with a maximally increased levels at 10 nM EE, whereas, no significant effects were seen in diploid, S-phase or tetraploid cells. The mRNA level of rOGG1 in testes cells was unaffected by EE, whereas, baseline levels were higher than in liver tissue and similar to colon tissue.

Contribution of hMTH1 to the maintenance of 8-oxoguanine levels in lung DNA of non-small-cell lung cancer patients

BACKGROUND

The level of 8-oxoguanine (8-oxoG), a general marker of oxidative DNA damage, in DNA is the result of both an equilibrium between the rates of its formation and removal from DNA by DNA repair enzymes and the removal of 8-oxodGTP from the cellular nucleotide pool by hydrolysis to 8-oxodGMP, preventing its incorporation into DNA. To determine the contribution of each component to the level of 8-oxoG in DNA, we compared 8-oxoG-excising activity (encoded by hOGG1), 8-oxodGTPase activity (encoded by hMTH1), and 8-oxoG levels in DNA from tumors and surrounding normal lung tissues from non-small-cell lung cancer patients.

METHODS

We measured the level of 8-oxoG in DNA of 47 patients by high-performance liquid chromatography/electrochemical detection (HPLC/ECD), hOGG1 activity in tissue extracts of 56 patients by the nicking assay using an oligodeoxynucleotide containing a single 8-oxoG, and hMTH1 activity in tissue extracts of 33 patients by HPLC/UV detection. All statistical tests were two-sided.

RESULTS

The 8-oxoG level was lower in tumor DNA than in DNA from normal lung tissue (geometric mean: 5.81 versus 10.18 8-oxoG/10(6) G, geometric mean of difference = 1.75; P<.001). The hOGG1 activity was also lower in tumor than in normal lung tissue (geometric mean: 8.76 versus 20.91 pmol/h/mg protein, geometric mean of difference = 2.39; P<.001), whereas the hMTH1 activity was higher in tumor than in normal lung tissue (geometric mean: 28.79 versus 8.94 nmol/h/mg protein, geometric mean of difference = 0.31; P<.001). The activity of hMTH1 was three orders of magnitude higher than that of hOGG1 (nanomoles versus picomoles per hour per milligram of protein, respectively).

CONCLUSIONS

Several different components contribute to the maintenance of 8-oxoG levels in human DNA, with the greatest contributor being the removal of 8-oxodGTP from the cellular nucleotide pool by hMTH1.

The murine DNA glycosylase NEIL2 (mNEIL2) and human DNA polymerase beta bind microtubules in situ and in vitro

8-oxoguanine DNA glycosylase (OGG1), a major DNA repair enzyme in mammalian cells and a component of the base excision repair (BER) pathway, was recently shown to be associated with the microtubule network and the centriole at interphase and the spindle assembly at mitosis. In this study, we determined whether other participants in the BER pathway also bind microtubules in situ and in vitro. Purified recombinant human DNA polymerase beta (DNA Pol beta) and purified recombinant mNEIL2 were chemically conjugated to fluorochromes and photosensitive dyes and used in in situ localization and binding experiments. Results from in situ localization, microtubule co-precipitation and site-directed photochemical experiments showed that recombinant human DNA Pol beta and recombinant mNEIL2 associated with microtubules in situ and in vitro in a manner similar to that shown earlier for another BER pathway component, OGG1. Observations reported in this study suggest that these BER pathway components are microtubule-associated proteins (MAPs) themselves or utilize yet to be identified MAPs to bind microtubules in order to regulate their intracellular trafficking and activities during the cell cycle.

Contribution of mitochondrial DNA repair to cell resistance from oxidative stress

Numerous studies have revealed that a part of the cellular response to chronic oxidative stress involves increased antioxidant capacity. However, another defense mechanism that has received less attention is DNA repair. Because of the important homeostatic role of mitochondria and the exquisite sensitivity of mitochondrial DNA (mtDNA) to oxidative damage, we hypothesized that mtDNA repair plays an important role in the protection against oxidative stress. To test this hypothesis mtDNA damage and repair was evaluated in normal HA1 Chinese hamster fibroblasts and oxidative stress-resistant variants isolated following chronic exposure to H2O2 or 95% O2. Reactive oxygen species were generated enzymatically using xanthine oxidase and hypoxanthine. When treated with xanthine oxidase reduced levels of initial mtDNA damage and enhanced mtDNA repair were observed in the cells from the oxidative stress-resistant variants, relative to the parental cell line. This enhanced mtDNA repair correlated with an increase in mitochondrial apurinic/apyrimidinic endonuclease activity in both H2O2- and O2-resistant HA1 variants. This is the first report showing enhanced mtDNA repair in the cellular response to chronic oxidative stress. These results provide further evidence for the crucial role that mtDNA repair pathways play in protecting cells against the deleterious effects of reactive oxygen species.

Cell cycle regulation of the murine 8-oxoguanine DNA glycosylase (mOGG1): mOGG1 associates with microtubules during interphase and mitosis

8-Oxoguanine DNA glycosylase (OGG1) is a major DNA repair enzyme in mammalian cells. OGG1 participates in the repair of 8-oxoG, the most abundant known DNA lesion induced by endogenous reactive oxygen species in aerobic organisms. In this study, antibodies directed against purified recombinant human OGG1 (hOGG1) or murine (mOGG1) protein were chemically conjugated to either the photosensitizer Rose Bengal or the fluorescent dye Texas red. These dye-protein conjugates, in combination with binding assays, were used to identify associations between mOGG1 and the cytoskeleton of NIH3T3 fibroblasts. Results from these binding studies showed that mOGG1 associates with the cytoskeleton by specifically binding to the centriole and microtubules radiating from the centrosome at interphase and the spindle assembly at mitosis. Similar results were obtained with hOGG1. Together results reported in this study suggest that OGG1 is a microtubule-associated protein itself or that OGG1 utilizes yet to be identified motor proteins to ride on microtubules as tracks facilitating the movement and redistribution of cytoplasmic OGG1 pools during interphase and mitosis and in response to oxidative DNA damage.

Cellular 8-oxo-7,8-dihydro-2'-deoxyguanosine 5'-triphosphate pyrophosphohydrolase activity of human and mouse MTH1 proteins does not depend on the proliferation rate

Mammalian MTH1 proteins, homologs of Escherichia coli MutT, are enzymes decomposing 8-oxo-7,8-dihydro-2'-deoxyguanosine 5'-triphosphate (8-oxo-dGTP) to 8-oxo-7,8-dihydro-2'-deoxyguanosine 5'-monophosphate and inorganic pyrophosphate. They play an antimutagenic role by preventing the incorporation of promutagenic 8-oxo-dGTP into DNA. MTH1 gene expression is higher in some physiological types of mammalian cells and in numerous cancer cells, but the mechanism of that upregulation still remains unclear. It has been hypothesized that MTH1 expression might be associated with a proliferation rate of the cells. Therefore, we tested this hypothesis by comparing the functional levels of MTH1 gene expression measured as the 8-oxo-dGTPase activity of its protein products in normal mouse livers and hepatectomized regenerating livers. Although the proliferation rate of the hepatocytes in the regenerating livers was much higher than that in control livers, as confirmed by immunohistochemical assay of proliferating cell nuclear antigen, the 8-oxo-dGTPase activity was not different. In a second approach, we used 57 lines of human cancer cells in which 8-oxo-dGTPase activity was measured and confronted with cell population doubling time. No significant correlations between 8-oxo-dGTPase activity and proliferation rate were observed within groups of six leukemia, eight melanoma, nine lung, seven colon, six central nervous system, six ovarian, eight renal, and seven breast cancer cell lines. Thus, we conclude that the MTH1 expression manifested as the 8-oxo-dGTPase activity of its protein products in mammalian cells is not associated with proliferation rate. Our results will help in further testing of the hypothesis that MTH1 overexpression may be a specific marker of carcinogenesis and/or oxidative stress.

Protection of pulmonary epithelial cells from oxidative stress by hMYH adenine glycosylase

Background

Oxygen toxicity is a major cause of lung injury. The base excision repair pathway is one of the most important cellular protection mechanisms that responds to oxidative DNA damage. Lesion-specific DNA repair enzymes include hOgg1, hMYH, hNTH and hMTH.

Methods

The above lesion-specific DNA repair enzymes were expressed in human alveolar epithelial cells (A549) using the pSF91.1 retroviral vector. Cells were exposed to a 95% oxygen environment, ionizing radiation (IR), or H₂O₂. Cell growth analysis was performed under non-toxic conditions. Western blot analysis was performed to verify over-expression and assess endogenous expression under toxic and non-toxic conditions. Statistical analysis was performed using the paired Student's t test with significance being accepted for p < 0.05.

Results

Cell killing assays demonstrated cells over-expressing hMYH had improved survival to both increased oxygen and IR. Cell growth analysis of A549 cells under non-toxic conditions revealed cells over-expressing hMYH also grow at a slower rate. Western blot analysis demonstrated over-expression of each individual gene and did not result in altered endogenous expression of the others. However, it was observed that O₂ toxicity did lead to a reduced endogenous expression of hNTH in A549 cells.

Conclusion

Increased expression of the DNA glycosylase repair enzyme hMYH in A549 cells exposed to O₂ and IR leads to improvements in cell survival. DNA repair through the base excision repair pathway may provide an alternative way to offset the damaging effects of O₂ and its metabolites.

Genotoxic effects of asbestos in humans

Risks of carcinogenic and non-carcinogenic effects from asbestos continue owing to the persistence of the fibres in building materials and other products. For this reason, epidemiological and mechanistic research on the toxic effects of asbestos and mineral fibres is still needed. The present molecular epidemiological study was conducted in a former asbestos cement plant in Slovakia. Altogether 82 subjects were investigated, 61 exposed subjects (24 smokers and 37 non-smokers), and 21 factory controls (8 smokers and 13 non-smokers). Workers were exposed to asbestos for between 5 and 40 years. Though the exposure to asbestos during past 40 years was relatively high, at the time of sampling the concentrations of asbestos in the production hall exceeded the Slovak occupational limit (0.001 fibre/cm3) by a factor of only 3-5. The office area levels were below this limit. Biomarkers of exposure, effect and individual susceptibility were measured, including DNA damage (strand breaks [SBs], base oxidation and alkylation, using the comet assay); cytogenetic parameters; and individual DNA repair capacity (incision at 8-oxoguanine measured using a modified comet assay). Oxidised pyrimidines were significantly higher in exposed men compared with non-exposed (P = 0.04). There was also a positive association between SBs (P = 0.04) and age, and alkylation damage to DNA (P = 0.04) and age. Moreover, oxidised pyrimidines (P = 0.01) and alkylated bases (P = 0.001) strongly correlated with years of occupational exposure. Micronucleus frequency did not differ between exposed and control subjects. Repair capacity overall did not show any effect of exposure, though female controls had higher incision rates than did female exposed subjects. However, exposed asbestos workers had significantly higher numbers of chromosomal aberrations (P = 0.01) compared with control group. This finding is consistent with the known association of chromosome aberrations with cancer-risk.

Oxidative DNA damage and disease: induction, repair and significance

The generation of reactive oxygen species may be both beneficial to cells, performing a function in inter- and intracellular signalling, and detrimental, modifying cellular biomolecules, accumulation of which has been associated with numerous diseases. Of the molecules subject to oxidative modification, DNA has received the greatest attention, with biomarkers of exposure and effect closest to validation. Despite nearly a quarter of a century of study, and a large number of base- and sugar-derived DNA lesions having been identified, the majority of studies have focussed upon the guanine modification, 7,8-dihydro-8-oxo-2'-deoxyguanosine (8-OH-dG). For the most part, the biological significance of other lesions has not, as yet, been investigated. In contrast, the description and characterisation of enzyme systems responsible for repairing oxidative DNA base damage is growing rapidly, being the subject of intense study. However, there remain notable gaps in our knowledge of which repair proteins remove which lesions, plus, as more lesions identified, new processes/substrates need to be determined. There are many reports describing elevated levels of oxidatively modified DNA lesions, in various biological matrices, in a plethora of diseases; however, for the majority of these the association could merely be coincidental, and more detailed studies are required. Nevertheless, even based simply upon reports of studies investigating the potential role of 8-OH-dG in disease, the weight of evidence strongly suggests a link between such damage and the pathogenesis of disease. However, exact roles remain to be elucidated.

Effects of asbestos on initiation of DNA damage, induction of DNA-strand breaks, P53-expression and apoptosis in primary, SV40-transformed and malignant human mesothelial cells

Human mesothelial cells (HMC), the progenitor cells of asbestos-induced mesothelioma, are particularly sensitive to the genotoxic effects of asbestos, although the molecular mechanisms by which asbestos induces injury in HMC are not well known. The high susceptibility of HMC to simian virus 40 (SV40)-mediated transformation is assumed to play a causative role in the pathogenesis of mesothelioma. The aim of this study was to investigate the asbestos-induced DNA damage in cultured HMC and SV40-transformed HMC (MeT-5A) compared with their malignant counterparts, i.e. human mesothelioma cells (MSTO). The time-dependent initiation of DNA-strand breaks as well as the induction of oxidative DNA base modifications were key factors for investigation. HMC, MeT-5A and MSTO cells were exposed to chrysotile and crocidolite asbestos (3 microg/cm2) during different time periods (1-72 h). DNA damage was investigated by use of the Comet assay and alkaline unwinding, the latter in combination with the Fpg protein. The P53 level was analyzed by immunofluorescence, and measurement of apoptosis was conducted by flow cytometry. We found a significant induction of DNA damage in asbestos-treated HMC already after an exposure time of 1.5 h. This effect could not be observed in treated MeT-5A and MSTO cells. Also, a time-dependent significant increase in DNA-strand breaks was observed by alkaline unwinding in asbestos-treated HMC, but not in treated MeT-5A and MSTO cells. In none of the three cell lines we could detect oxidative DNA damage recognized by the Fpg protein (e.g. 8-oxo-guanine), up to 24 h after exposure to asbestos. In contrast to what was found in HMC, P53 was over-expressed in untreated MeT-5A and MSTO. The induction of apoptosis by asbestos fibers was suppressed in MeT-5A and MSTO cells. Crocidolite fibers induced the higher genotoxic effects and chrysotile the more pronounced apoptotic effects. We conclude that asbestos induces DNA damage in HMC already after a very short exposure time in the absence of 8-oxo-guanine formation. The presence of SV40-Tag in MeT-5A and MSTO cells results in an increased expression of P53, but not in additive genotoxic effects after exposure to asbestos. The deregulation of the apoptotic pathway may lead to proliferation of genomically damaged cells and finally to the development of mesothelioma.

Protective effect of vitamin C on 8-hydroxy-2′-deoxyguanosine level in peripheral blood lymphocytes of chronic hemodialysis patients

BACKGROUND

This study focused on the effect of vitamin C on the 8-hydroxy-2'-deoxyguanosine (8-OHdG) level of cellular DNA, as well as 8-oxoguanine-DNA glycosylase 1 (hOGG1) and human MutT homologue (hMTH1) gene expression in peripheral blood lymphocytes of chronic hemodialysis patients.

METHODS

Sixty chronic hemodialysis patients (35 men and 25 women) were recruited to participate in a randomized, placebo-controlled study. Treatment order is block-randomized with intravenous sodium ascorbate (vitamin C, 300 mg) or placebo (0.9% saline), administered postdialysis three times a week. We evaluated 8-OHdG level, intracellular reactive oxygen species (ROS) production, and gene expression of hOGG1 and hMTH1 in peripheral blood lymphocytes by using high-performance liquid chromatography (HPLC) electrochemical detection method, flow cytometric analysis, and reverse transcription-polymerase chain reaction (RT-PCR), respectively.

RESULTS

A total of 51 patients completed the study (26 in placebo group and 25 in vitamin C group). Mean 8-OHdG levels significantly decreased in total subjects following 8 weeks of vitamin C supplementation (22.9 vs. 18.8/10(6) dG, P < 0.01). The decrease in 8-OHdG levels after vitamin C supplementation was also noted in the patients with ferritin <500 or > or =500 microg/L and transferrin saturation (TSAT) <50 or > or =50% (P < 0.05). But 8-OHdG levels had no significant changes in total patients or in the four subgroups of patients treated with placebo as compared to their baselines. Intracellular ROS production by lymphocytes from the four subgroups of patients, either spontaneous (P < 0.05) or phorbol-12-myristate-13-acetate (PMA)-stimulated (P < 0.001), was significantly reduced after 8 weeks vitamin C supplementation. Steady-state hOGG1 mRNA levels were significantly up-regulated at 24 hours after vitamin C administration (P < 0.05), but hMTH1 mRNA levels were not. The changes in the spontaneous and PMA-stimulated ROS production, and an up-regulation of hOGG1 mRNA expression were not observed in patients treated with placebo as compared to their baselines.

CONCLUSION

Vitamin C supplementation in chronic hemodialysis patients can reduce the lymphocyte 8-OHdG levels and intracellular ROS production, as well as up-regulate hOGG1 gene expression for repair. There is no compelling evidence for an in vivo pro-oxidant effect of vitamin C on lymphocyte DNA base oxidation, even in the status of increased iron stores.

Immunofluorescent localization of the murine 8-oxoguanine DNA glycosylase (mOGG1) in cells growing under normal and nutrient deprivation conditions

OGG1 is a major DNA glycosylase in mammalian cells, participating in the repair of 7,8-dihydro-8-oxoguanine (8-oxoguanine, 8-oxoG), the most abundant known DNA lesion induced by endogenous reactive oxygen species in aerobic organisms. 8-oxoG is therefore often used as a marker for oxidative DNA damage. In this study, polyclonal and monoclonal antibodies were raised against the purified wild-type recombinant murine 8-oxoG DNA glycosylase (mOGG1) protein and their specificity against the native enzyme and the SDS-denatured mOGG1 polypeptide were characterized. Specific antibodies directed against the purified wild-type recombinant mOGG1 were used to localize in situ this DNA repair enzyme in established cell lines (HeLa cells, NIH3T3 fibroblasts) as well as in primary culture mouse embryo fibroblasts growing under either normal or oxidative stress conditions. Results from these studies showed that mOGG1 is localized to the nucleus and the cytoplasm of mammalian cells in culture. However, mOGG1 levels increase and primarily redistribute to the nucleus and its peripheral cytoplasm in cells exposed to oxidative stress conditions. Immunofluorescent localization results reported in this study suggest that susceptibility to oxidative DNA damage varies among mammalian tissue culture cells and that mOGG1 appears to redistribute once mOGG1 cell copy number increases in response to oxidative DNA damage.

Expression of the oxidative base excision repair enzymes is not induced in TK6 human lymphoblastoid cells after low doses of ionizing radiation

Most of the DNA damage produced by ionizing radiation is repaired by the base excision repair (BER) pathway. To determine whether the BER genes were up-regulated by low doses of ionizing radiation, we investigated their expression in TK6 human lymphoblastoid cells by measuring mRNA levels using real-time quantitative PCR. No induction at the transcriptional level of any of the base excision repair genes, NTH1 (NTHL1), OGG1, NEIL1, NEIL2, NEIL3, APE1, POLB, or accessory protein genes, LIG3, XRCC1 or XPG, was found at gamma-radiation doses ranging from 1 cGy to 2 Gy in a 24-h period. As has been measured in other cell lines, a dose-dependent induction of CDKN1A (WAF1) mRNA levels was observed in TK6 cells in the dose range of 0.5 to 2.0 Gy. We also examined BER enzyme activity on 8-oxoguanine-, dihydrouracil- and furan-containing oligonucleotide substrates and found no increase in extracts of TK6 cells after gamma-ray doses of 0.5-2.0 Gy. These data were corroborated by Western blot analysis of APE1 and NTH1, suggesting that the BER enzymes are also not up-regulated at the post-transcriptional level after ionizing radiation exposure.

Inhaled particles and lung cancer. Part A: Mechanisms

Both occupational and environmental exposure to particles is associated with an increased risk of lung cancer. Particles are thought to impact on genotoxicity as well as on cell proliferation via their ability to generate oxidants such as reactive oxygen species (ROS) and reactive nitrogen species (RNS). For mechanistic purposes, one should discriminate between a) the oxidant-generating properties of particles themselves (i.e., acellular), which are mostly determined by the physicochemical characteristics of the particle surface, and b) the ability of particles to stimulate cellular oxidant generation. Cellular ROS/RNS can be generated by various mechanisms, including particle-related mitochondrial activation or NAD(P)H-oxidase enzymes. In addition, since particles can induce an inflammatory response, a further subdivision needs to be made between primary (i.e., particle-driven) and secondary (i.e., inflammation-driven) formation of oxidants. Particles may also affect genotoxicity by their ability to carry surface-adsorbed carcinogenic components into the lung. Each of these pathways can impact on genotoxicity and proliferation, as well as on feedback mechanisms involving DNA repair or apoptosis. Although abundant evidence suggests that ROS/RNS mediate particle-induced genotoxicity and mutagenesis, little information is available towards the subsequent steps leading to neoplastic changes. Additionally, since most of the proposed molecular mechanisms underlying particle-related carcinogenesis have been derived from in vitro studies, there is a need for future studies that evaluate the implication of these mechanisms for in vivo lung cancer development. In this respect, transgenic and gene knockout animal models may provide a useful tool. Such studies should also include further assessment of the relative contributions of primary (inflammation-independent) and secondary (inflammation-driven) pathways.

Transcription Factors NF-YA Regulate the Induction of Human OGG1 Following DNA-alkylating Agent Methylmethane Sulfonate (MMS) Treatment

A human 8-oxoguanine-DNA glycosylase (hOGG1) is the main enzyme that repairs 8-oxoG, which is a critical mutagenic lesion. There is a great deal of interest in the up- or down-regulation of OGG1 expression after DNA damage. In this study, we investigated the effect of a DNA-alkylating agent, methylmethane sulfonate (MMS), on hOGG1 expression level and found that MMS treatment resulted in an increase in the functional hOGG1 expression in HCT116 cells. A region between -121 and -61 of the hOGG1 promoter was found to be crucial for this induction by MMS. Site-directed mutations of the two inverted CCAAT motifs substantially abrogated the induction of the hOGG1 promoter as a result of MMS treatment. In addition, the NF-YA protein (binding to the inverted CCAAT box) was induced after exposing cells to MMS. Moreover, gel shift and supershift analyses with the nuclear extracts prepared from HCT116 cells identified NF-YA as the transcription factor interacting with the inverted CCAAT box. Mutations of the inverted CCAAT box either prevented the binding of this factor or abolished its activation as a result of MMS treatment. Finally, this study showed that hOGG1-expressing HCT116 cells exhibited increased hOGG1 repair activity and resistance to MMS. Overall, these results demonstrate that MMS can up-regulate hOGG1 expression through the induction of the transcription factor, NF-YA, and increased transcription level of the hOGG1 gene correlates with an increase in enzyme activity providing functional protection from MMS.