Formation of the nitrative DNA lesion 8-nitroguanine is associated with asbestos contents in human lung tissues: a pilot study

Cancer Development and Progression Through a Vicious Cycle of DNA Damage and Inflammation

Infections and chronic inflammation play a crucial role in the development of cancer. During inflammatory processes, reactive oxygen and nitrogen species are generated by both inflammatory and epithelial cells, leading to the induction of oxidative and nitrative DNA damage, such as the formation of 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG) and 8-nitroguanine (8-nitroG). These DNA alterations can trigger mutations, which are believed to contribute to cancer formation driven by inflammation. The authors observed the generation of 8-nitroG through iNOS expression in human and animal tissues under inflammatory conditions, where cancer is likely to develop. 8-NitroG serves as a predictive and prognostic indicator for cancers linked to inflammation. Inflammation causes DNA damage, and the subsequent DNA damage response can create an inflammatory environment marked by hypoxia, with HMGB1 being a key factor. The interplay between HIF-1α, NF-ĸB, and HMGB1 sustains DNA damage and the accumulation of mutations, driving cancer progression and worsening prognosis. 8-NitroG is involved not only in the onset and advancement of cancer but also in its progression and conversion. Herein, the authors propose a vicious cycle of DNA damage and inflammation in cancer development (initiation and promotion) and progression, including conversion, via HMGB1.

Oxidative and nitrative DNA damage induced by industrial chemicals in relation to carcinogenesis

OBJECTIVES

Many chemicals have been used for industrial purposes, and some of them are carcinogenic to humans. However, the molecular mechanisms of their carcinogenetic effects have not been well understood. Reactive oxygen species are generated from industrial chemicals and contribute to carcinogenesis. Particles and fibers are accumulated in respiratory systems by inhalation exposure and cause chronic inflammation. Under inflammatory conditions, reactive nitrogen species are generated from inflammatory and epithelial cells. These species cause oxidative and nitrative DNA damage, leading to carcinogenesis. We carried out experiments on DNA damage induced by various industrial chemicals and investigated their molecular mechanisms.

METHODS

We examined oxidative DNA damage induced by industrial chemicals using DNA fragments derived from human cancer-relevant genes by polyacrylamide gel electrophoresis. Using immunohistochemistry and immunocytochemistry we also examined the formation of 8-nitroguanine (8-nitroG), a DNA lesion formed under inflammatory conditions, in lung tissues and cultured cells exposed to industrial chemicals.

RESULTS

Benzene and o-toluidine metabolites caused oxidative damage to DNA fragments in the presence of Cu(II). H2O2 and Cu(I) were generated during oxidation of these chemicals and involved in DNA damage. 8-NitroG formation was observed in lung tissues of asbestos-exposed mice and humans. Carbon nanomaterials and indium compounds induced 8-nitroG formation in human lung epithelial cells via the release of damage-associated molecular patterns from exposed cells.

CONCLUSIONS

Various industrial chemicals are considered to induce carcinogenesis by causing oxidative and nitrative DNA damage. These findings provide an insight into risk assessment of industrial chemicals and prevention of carcinogenesis in workplaces.

Microarray analysis of gene expression in lung tissues of indium-exposed rats: possible roles of S100 proteins in lung diseases

Indium compounds are used in manufacturing displays of mobile phones and televisions. These compounds cause interstitial pneumonia in workers and lung cancer in animals, but their precise mechanisms are unclear. In this study, we performed microarray analysis of gene expression in lung tissues of indium-exposed rats. Male Wistar rats (8-week-old) were exposed to indium oxide (In2O3, mean particle diameter 0.14 μm) and indium-tin oxide (ITO, mean particle diameter 0.95 μm) by intratracheal instillation (10 mg indium/kg body weight/instillation) twice a week and five times in total. These rats were sacrificed immediately, 3 weeks and 12 weeks after the last instillation. Hematoxylin and eosin and Masson's trichrome staining showed that indium compounds induced infiltration of neutrophils and macrophages into alveolar space, and fibrosis around bronchial epithelium and in alveolar wall. Microarray analysis revealed that In2O3 and ITO significantly upregulated 233 and 676 genes at 12 weeks, respectively (> twofold, p < 0.05 by ANOVA + Tukey's test). In2O3 and ITO largely upregulated Lcn2 (lipocalin-2) (49.4- and 91.8-fold), S100a9 (30.2- and 46.5-fold) and S100a8 (11.5- and 22.0-fold), respectively. Metascape database predicted that these genes participate in immunomodulatory and inflammatory responses. Real-time PCR confirmed that these genes were upregulated by indium compounds throughout the experiments. In Western blotting, S100A9 expression was significantly increased by indium exposure, whereas LCN2 expression was only slightly increased. Fluorescent immunohistochemistry revealed that S100A9 and S100A8 were expressed in alveolar epithelial cells and neutrophils in indium-exposed rats. These results suggest that S100 proteins contribute to indium-induced lung diseases via neutrophil-mediated inflammatory responses.

Reactive Oxygen Species Bridge the Gap between Chronic Inflammation and Tumor Development

According to numerous animal studies, adverse environmental stimuli, including physical, chemical, and biological factors, can cause low-grade chronic inflammation and subsequent tumor development. Human epidemiological evidence has confirmed the close relationship between chronic inflammation and tumorigenesis. However, the mechanisms driving the development of persistent inflammation toward tumorigenesis remain unclear. In this study, we assess the potential role of reactive oxygen species (ROS) and associated mechanisms in modulating inflammation-induced tumorigenesis. Recent reports have emphasized the cross-talk between oxidative stress and inflammation in many pathological processes. Exposure to carcinogenic environmental hazards may lead to oxidative damage, which further stimulates the infiltration of various types of inflammatory cells. In turn, increased cytokine and chemokine release from inflammatory cells promotes ROS production in chronic lesions, even in the absence of hazardous stimuli. Moreover, ROS not only cause DNA damage but also participate in cell proliferation, differentiation, and apoptosis by modulating several transcription factors and signaling pathways. We summarize how changes in the redox state can trigger the development of chronic inflammatory lesions into tumors. Generally, cancer cells require an appropriate inflammatory microenvironment to support their growth, spread, and metastasis, and ROS may provide the necessary catalyst for inflammation-driven cancer. In conclusion, ROS bridge the gap between chronic inflammation and tumor development; therefore, targeting ROS and inflammation represents a new avenue for the prevention and treatment of cancer.

Role of PARP1 on DNA damage induced by mineral silicate chrysotile in bronchial epithelial and pleural mesothelial cells

To investigate whether poly (ADP ribose) polymerase-1 (PARP1) is involved in chrysotile-induced DNA damage in pleural mesothelial cells (MeT-5A) and bronchial epithelial cells (BEAS-2B), two PARP1-deficient cell lines were established. Efficiencies of RNA interference on PARP1 were detected by western blot and qPCR. Here, normal cells and PARP1-deficient cells were exposed to chrysotile, and DNA damage and DNA repair were detected by alkaline comet assay. All cells were treated with chrysotile at the indicated concentrations (5, 10, 20, and 40 μg/cm²) for 24 h and then the DNA repair capacity was observed for 12 and 24 h, respectively. The results showed that chrysotile caused DNA damage at an obvious dose-dependent manner in MeT-5A and BEAS-2B cells. In addition, MeT-5A cells had more persistent DNA damage than BEAS-2B. Compared to normal cells, the PARP1-deficient cells were more sensitive to DNA damage caused by chrysotile. In DNA repair experiments, all cell lines recovered from the damage over time. The results of relative repair percentage (RRP) of MeT-5A and BEAS-2B were higher than those of MeT-5A shPARP1 and BEAS-2B shPARP1 cells at all experimental concentrations (except 5 μg/cm²) at 12-h repair. However, RRP of BEAS-2B and BEAS-2B shPARP1 tended to be closer, and RRP of MeT-5A shPARP1 was still lower than that of MeT-5A at 24-h repair. All results suggest that PARP1 plays an important role in early repair of DNA damage in BEAS-2B and MeT-5A cells exposed to chrysotile.

MicroRNA expression in lung tissues of asbestos-exposed mice: Upregulation of miR-21 and downregulation of tumor suppressor genes Pdcd4 and Reck

OBJECTIVES

Asbestos causes lung cancer and malignant mesothelioma in humans, but the precise mechanism has not been well understood. MicroRNA (miRNA) is a short non-coding RNA that suppresses gene expression and participates in human diseases including cancer. In this study, we examined the expression levels of miRNA and potential target genes in lung tissues of asbestos-exposed mice by microarray analysis.

METHODS

We intratracheally administered asbestos (chrysotile and crocidolite, 0.05 or 0.2 mg/instillation) to 6-week-old ICR male mice four times weekly. We extracted total RNA from lung tissues and performed microarray analysis for miRNA and gene expression. We also carried out real-time polymerase chain reaction (PCR), Western blotting, and immunohistochemistry to confirm the results of microarray analysis.

RESULTS

Microarray analysis revealed that the expression levels of 14 miRNAs were significantly changed by chrysotile and/or crocidolite (>2-fold, P < .05). Especially, miR-21, an oncogenic miRNA, was significantly upregulated by both chrysotile and crocidolite. In database analysis, miR-21 was predicted to target tumor suppressor genes programmed cell death 4 (Pdcd4) and reversion-inducing-cysteine-rich protein with kazal motifs (Reck). Although real-time PCR showed that Pdcd4 was not significantly downregulated by asbestos exposure, Western blotting and immunohistochemistry revealed that PDCD4 expression was reduced especially by chrysotile. Reck was significantly downregulated by chrysotile in real-time PCR and immunohistochemistry.

CONCLUSIONS

This is the first study demonstrating that miR-21 was upregulated and corresponding tumor suppressor genes were downregulated in lung tissues of asbestos-exposed animals. These molecular events are considered to be an early response to asbestos exposure and may contribute to pulmonary toxicity and carcinogenesis.

Nitrative DNA damage in lung epithelial cells exposed to indium nanoparticles and indium ions

Indium compounds have been widely used in manufacturing displays of mobile phones, computers and televisions. However, inhalation exposure to indium compounds causes interstitial pneumonia in exposed workers and lung cancer in experimental animals. 8-Nitroguanine (8-nitroG) is a mutagenic DNA lesion formed under inflammatory conditions and may participate in indium-induced carcinogenesis. In this study, we examined 8-nitroG formation in A549 cultured human lung epithelial cells treated with indium compounds, including nanoparticles of indium oxide (In₂O₃) and indium-tin oxide (ITO), and indium chloride (InCl₃). We performed fluorescent immunocytochemistry to examine 8-nitroG formation in indium-exposed A549 cells. All indium compounds significantly increased 8-nitroG formation in A549 cells at 5 ng/ml after 4 h incubation. 8-NitroG formation was largely reduced by 1400 W, methyl-β-cyclodextrin (MBCD) and monodansylcadaverine (MDC), suggesting the involvement of nitric oxide synthase and endocytosis. 8-NitroG formation in A549 cells was also largely suppressed by small interfering RNA (siRNA) for high-mobility group box-1 (HMGB1), receptor for advanced glycation and end products (AGER, RAGE) and Toll-like receptor 9 (TLR9). These results suggest that indium compounds induce inflammation-mediated DNA damage in lung epithelial cells via the HMGB1-RAGE-TLR9 pathway. This mechanism may contribute to indium-induced genotoxicity in the respiratory system.

Inflammation and cancer

Infection and inflammation account for approximately 25% of cancer-causing factors. Inflammation-related cancers are characterized by mutagenic DNA lesions, such as 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG) and 8-nitroguanine. Our previous studies demonstrated the formation of 8-oxodG and 8-nitroguanine in the tissues of cancer and precancerous lesions due to infection (e.g., Opisthorchis viverrini-related cholangiocarcinoma, Schistosoma haematobium-associated bladder cancer, Helicobacter pylori-infected gastric cancer, human papillomavirus-related cervical cancer, Epstein-Barr virus-infected nasopharyngeal carcinoma) and pro-inflammatory factors (e.g., asbestos, nanomaterials, and inflammatory diseases such as Barrett's esophagus and oral leukoplakia). Interestingly, several of our studies suggested that inflammation-associated DNA damage in cancer stem-like cells leads to cancer development with aggressive clinical features. Reactive oxygen/nitrogen species from inflammation damage not only DNA but also other biomacromolecules, such as proteins and lipids, resulting in their dysfunction. We identified oxidatively damaged proteins in cancer tissues by 2D Oxyblot followed by MALDI-TOF/TOF. As an example, oxidatively damaged transferrin released iron ion, which may mediate Fenton reactions and generate additional reactive oxygen species. Dysfunction of anti-oxidative proteins due to this damage might increase oxidative stress. Such damage in biomacromolecules may form a vicious cycle of oxidative stress, leading to cancer development. Epigenetic alterations such as DNA methylation and microRNA dysregulation play vital roles in carcinogenesis, especially in inflammation-related cancers. We examined epigenetic alterations, DNA methylation and microRNA dysregulation, in Epstein-Barr virus-related nasopharyngeal carcinoma in the endemic area of Southern China and found several differentially methylated tumor suppressor gene candidates by using a next-generation sequencer. Among these candidates, we revealed higher methylation rates of RAS-like estrogen-regulated growth inhibitor (RERG) in biopsy specimens of nasopharyngeal carcinoma more conveniently by using restriction enzyme-based real-time PCR. This result may help to improve cancer screening strategies. We profiled microRNAs of nasopharyngeal carcinoma tissues using microarrays. Quantitative RT-PCR analysis confirmed the concordant downregulation of miR-497 in cancer tissues and plasma, suggesting that plasma miR-497 could be used as a diagnostic biomarker for nasopharyngeal carcinoma. Chronic inflammation promotes genetic and epigenetic aberrations, with various pathogeneses. These changes may be useful biomarkers in liquid biopsy for early detection and prevention of cancer.

Inflammation and cancer

Infection and inflammation account for approximately 25% of cancer-causing factors. Inflammation-related cancers are characterized by mutagenic DNA lesions, such as 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG) and 8-nitroguanine. Our previous studies demonstrated the formation of 8-oxodG and 8-nitroguanine in the tissues of cancer and precancerous lesions due to infection (e.g., Opisthorchis viverrini-related cholangiocarcinoma, Schistosoma haematobium-associated bladder cancer, Helicobacter pylori-infected gastric cancer, human papillomavirus-related cervical cancer, Epstein-Barr virus-infected nasopharyngeal carcinoma) and pro-inflammatory factors (e.g., asbestos, nanomaterials, and inflammatory diseases such as Barrett's esophagus and oral leukoplakia). Interestingly, several of our studies suggested that inflammation-associated DNA damage in cancer stem-like cells leads to cancer development with aggressive clinical features. Reactive oxygen/nitrogen species from inflammation damage not only DNA but also other biomacromolecules, such as proteins and lipids, resulting in their dysfunction. We identified oxidatively damaged proteins in cancer tissues by 2D Oxyblot followed by MALDI-TOF/TOF. As an example, oxidatively damaged transferrin released iron ion, which may mediate Fenton reactions and generate additional reactive oxygen species. Dysfunction of anti-oxidative proteins due to this damage might increase oxidative stress. Such damage in biomacromolecules may form a vicious cycle of oxidative stress, leading to cancer development. Epigenetic alterations such as DNA methylation and microRNA dysregulation play vital roles in carcinogenesis, especially in inflammation-related cancers. We examined epigenetic alterations, DNA methylation and microRNA dysregulation, in Epstein-Barr virus-related nasopharyngeal carcinoma in the endemic area of Southern China and found several differentially methylated tumor suppressor gene candidates by using a next-generation sequencer. Among these candidates, we revealed higher methylation rates of RAS-like estrogen-regulated growth inhibitor (RERG) in biopsy specimens of nasopharyngeal carcinoma more conveniently by using restriction enzyme-based real-time PCR. This result may help to improve cancer screening strategies. We profiled microRNAs of nasopharyngeal carcinoma tissues using microarrays. Quantitative RT-PCR analysis confirmed the concordant downregulation of miR-497 in cancer tissues and plasma, suggesting that plasma miR-497 could be used as a diagnostic biomarker for nasopharyngeal carcinoma. Chronic inflammation promotes genetic and epigenetic aberrations, with various pathogeneses. These changes may be useful biomarkers in liquid biopsy for early detection and prevention of cancer.

Sensitive Detection of 8-Nitroguanine in DNA by Chemical Derivatization Coupled with Online Solid-Phase Extraction LC-MS/MS

8-Nitroguanine (8-nitroG) is a major mutagenic nucleobase lesion generated by peroxynitrite during inflammation and has been used as a potential biomarker to evaluate inflammation-related carcinogenesis. Here, we present an online solid-phase extraction (SPE) LC-MS/MS method with 6-methoxy-2-naphthyl glyoxal hydrate (MTNG) derivatization for a sensitive and precise measurement of 8-nitroG in DNA. Derivatization optimization revealed that an excess of MTNG is required to achieve complete derivatization in DNA hydrolysates (MTNG: 8-nitroG molar ratio of 3740:1). The use of online SPE effectively avoided ion-source contamination from derivatization reagent by washing away all unreacted MTNG before column chromatography and the ionization process in mass spectrometry. With the use of isotope-labeled internal standard, the detection limit was as low as 0.015 nM. Inter- and intraday imprecision was <5.0%. This method was compared to a previous direct LC-MS/MS method without derivatization. The comparison showed an excellent fit and consistency, suggesting that the present method has satisfactory effectiveness and reliability for 8-nitroG analysis. This method was further applied to determine the 8-nitroG in human urine. 8-NitroG was not detectable using LC-MS/MS with derivatization, whereas a significant false-positive signal was detected without derivatization. It highlights the use of MTNG derivatization in 8-nitroG analysis for increasing the method specificity.

Chemistry of the 8-Nitroguanine DNA Lesion: Reactivity, Labelling and Repair

The 8-nitroguanine lesion in DNA is increasingly associated with inflammation-related carcinogenesis, whereas the same modification on guanosine 3',5'-cyclic monophosphate generates a second messenger in NO-mediated signal transduction. Very little is known about the chemistry of 8-nitroguanine nucleotides, despite the fact that their biological effects are closely linked to their chemical properties. To this end, a selection of chemical reactions have been performed on 8-nitroguanine nucleosides and oligodeoxynucleotides. Reactions with alkylating reagents reveal how the 8-nitro substituent affects the reactivity of the purine ring, by significantly decreasing the reactivity of the N2 position, whilst the relative reactivity at N1 appears to be enhanced. Interestingly, the displacement of the nitro group with thiols results in an efficient and specific method of labelling this lesion and is demonstrated in oligodeoxynucleotides. Additionally, the repair of this lesion is also shown to be a chemically feasible reaction through a reductive denitration with a hydride source.

Nitrative DNA damage in cultured macrophages exposed to indium oxide

Objectives:

Indium compounds are used in manufacturing displays of mobile phones and televisions. However, these materials cause interstitial pneumonia in exposed workers. Animal experiments demonstrated that indium compounds caused lung cancer. Chronic inflammation is considered to play a role in lung carcinogenesis and fibrosis induced by particulate matters. 8-Nitroguanine (8-nitroG) is a mutagenic DNA lesion formed during inflammation and may participate in carcinogenesis. To clarify the mechanism of carcinogenesis, we examined 8-nitroG formation in indium-exposed cultured cells.

Methods:

We treated RAW 264.7 mouse macrophages with indium oxide (In₂O₃) nanoparticles (primary diameter: 30-50 nm), and performed fluorescent immunocytochemistry to detect 8-nitroG. The extent of 8-nitroG formation was evaluated by quantitative image analysis. We measured the amount of nitric oxide (NO) in the culture supernatant of In₂O₃-treated cells by the Griess method. We also examined the effects of inhibitors of inducible NO synthase (iNOS) and endocytosis on In₂O₃-induced 8-nitroG formation.

Results:

In₂O₃ significantly increased the intensity of 8-nitroG formation in RAW 264.7 cells in a dose-dependent manner. In₂O₃-induced 8-nitroG formation was observed at 2 h and further increased at 4 h, and the amount of NO released from In₂O₃-exposed cells was significantly increased at 2-4 h compared with the control. 8-NitroG formation was suppressed by 1400W (an iNOS inhibitor), methyl-β-cyclodextrin and monodansylcadaverine (inhibitors of caveolae- and clathrin-mediated endocytosis, respectively).

Conclusions:

These results suggest that endocytosis and NO generation participate in indium-induced 8-nitroG formation. NO released from indium-exposed inflammatory cells may induce DNA damage in adjacent lung epithelial cells and contribute to carcinogenesis.

Crosstalk between DNA Damage and Inflammation in the Multiple Steps of Carcinogenesis

Inflammation can be induced by chronic infection, inflammatory diseases and physicochemical factors. Chronic inflammation is estimated to contribute to approximately 25% of human cancers. Under inflammatory conditions, inflammatory and epithelial cells release reactive oxygen (ROS) and nitrogen species (RNS), which are capable of causing DNA damage, including the formation of 8-oxo-7,8-dihydro-2'-deoxyguanosine and 8-nitroguanine. We reported that 8-nitroguanine was clearly formed at the sites of cancer induced by infectious agents including Helicobacter pylori, inflammatory diseases including Barrett's esophagus, and physicochemical factors including asbestos. DNA damage can lead to mutations and genomic instability if not properly repaired. Moreover, DNA damage response can also induce high mobility group box 1-generating inflammatory microenvironment, which is characterized by hypoxia. Hypoxia induces hypoxia-inducible factor and inducible nitric oxide synthase (iNOS), which increases the levels of intracellular RNS and ROS, resulting DNA damage in progression with poor prognosis. Furthermore, tumor-producing inflammation can induce nuclear factor-κB, resulting in iNOS-dependent DNA damage. Therefore, crosstalk between DNA damage and inflammation may play important roles in cancer development. A proposed mechanism for the crosstalk may explain why aspirin decreases the long-term risk of cancer mortality.

Nitrative DNA damage induced by carbon-black nanoparticles in macrophages and lung epithelial cells

Carbon black (CB) is a nanomaterial used mainly in rubber products. Exposure to CB by inhalation causes malignant lung tumors in experimental animals. CB inhalation may cause chronic inflammation in the respiratory system, leading to carcinogenesis, but the mechanism remains unclear. Reactive oxygen and nitrogen species are generated from inflammatory and epithelial cells under inflammatory conditions, and resulting DNA damage may contribute to carcinogenesis. In this study, we performed immunocytochemistry to determine whether CB exposure induces formation of 8-nitroguanine (8-nitroG), a nitrative DNA lesion formed under inflammatory conditions, in RAW 264.7 macrophage and A549 lung epithelial cells. We compared the DNA-damaging effects of CB particles with primary diameter 56nm (CB56) and 95nm (CB95). Both types of CB induced 8-nitroG formation, mainly in the nucleus of RAW 264.7 and A549 cells, and CB95 tended to induce more 8-nitroG formation than did CB56. Flow cytometry revealed that CB95 generated larger amount of reactive oxygen species than did CB56 in RAW 264.7 cells. The Griess method showed that CB95 produced significantly larger amount of nitric oxide (NO) than did CB56. Flow cytometry showed that CB95 was more efficiently internalized into the cells than was CB56. The cellular uptake of CB and 8-nitroG formation in RAW 264.7 cells were reduced by monodansylcadaverine, an inhibitor of clathrin-mediated endocytosis, and by siRNA for Ctlc (clathrin heavy chain) gene. CB induces nitrative DNA damage in cultured cells, and clathrin-mediated endocytosis is involved, at least in part.

Risk of occupational exposure to asbestos, silicon and arsenic on pulmonary disorders: Understanding the genetic-epigenetic interplay and future prospects

BACKGROUND

Epidemiological studies suggest strong association of lung disorders with occupational exposure to asbestos, silicon and arsenic. The chronic occupational exposure primarily through inhalation results in adverse outcome on the respiratory tract which may also be fatal. Although several mechanisms have attributed towards these diseases; the molecular pathogenesis is still unknown.

OBJECTIVE

In this review, we investigated the plausible molecular mechanism based on current research that may identify the genetic and epigenetic susceptibility of respiratory disorders upon such occupational exposures in humans.

METHODS

We considered genetic variants and epigenetic alterations associated with pulmonary exposure hazards leading to asbestosis, silicosis and arsenicosis. Our review is stringently based on the literatures available through peer-reviewed articles mostly published in the last 10 years. Relevant search were conducted using keywords like "occupational lung disorders" along with "asbestos", "silicon" and "arsenic".

RESULTS

Till September 2015, pubmed search yielded approximately 780 articles relating to asbestos exposure; 240 articles for silicon exposure and 60 articles for arsenic exposure. Extensive screening for genetic and epigenetic factors identified certain genes and related pathways that are important to determine the susceptibility of an individual towards such occupational exposure.

CONCLUSION

The link between genotype and phenotype and its association with disease susceptibility is very complex in nature due to several factors like person's environment, lifestyle and nutritional status. The epigenome is dynamic as well as reversible and can be reshaped further by certain dietary components throughout its life. In the present review, we have addressed the role of molecular pathogenesis of occupational lung diseases based on the genetic variability and epigenetic alterations and also attempted to highlight the promising aspect of dietary interventions to counter toxic outcomes upon occupational exposure to asbestos, silicon or arsenic.

Multi-walled carbon nanotube induces nitrative DNA damage in human lung epithelial cells via HMGB1-RAGE interaction and Toll-like receptor 9 activation

Background

Carbon nanotube (CNT) is used for various industrial purposes, but exhibits carcinogenic effects in experimental animals. Chronic inflammation in the respiratory system may participate in CNT-induced carcinogenesis. 8-Nitroguanine (8-nitroG) is a mutagenic DNA lesion formed during inflammation. We have previously reported that multi-walled CNT (MWCNT) induced 8-nitroG formation in lung epithelial cells and this process involved endocytosis. To clarify the mechanism of CNT-induced carcinogenesis, we examined the role of Toll-like receptor (TLR) 9, which resides in endosomes and lysosomes, in 8-nitroG formation in human lung epithelial cell lines.

Methods

We performed immunocytochemistry to examine 8-nitroG formation in A549 and HBEpC cells treated with MWCNT with a length of 1-2 μm (CNT-S) or 5-15 μm (CNT-L) and a diameter of 20-40 nm. We examined inhibitory effects of endocytosis inhibitors, small interfering RNA (siRNA) for TLR9, and antibodies against high-mobility group box-1 (HMGB1) and receptor for advanced glycation end-products (RAGE) on 8-nitroG formation. The release of HMGB1 and double-stranded DNA (dsDNA) into the culture supernatant from MWCNT-treated cells was examined by ELISA and fluorometric analysis, respectively. The association of these molecules was examined by double immunofluorescent staining and co-immunoprecipitation.

Results

CNT-L significantly increased 8-nitroG formation at 0.05 μg/ml in A549 cells and its intensity reached a maximum at 1 μg/ml. CNT-L tended to induce stronger cytotoxicity and 8-nitroG formation than CNT-S. Endocytosis inhibitors, TLR9 siRNA and antibodies against HMGB1 and RAGE largely reduced MWCNT-induced 8-nitroG formation. MWCNT increased the release of HMGB1 and dsDNA from A549 cells into culture supernatant. The culture supernatant of MWCNT-exposed cells induced 8-nitroG formation in fresh A549 cells. Double immunofluorescent staining and co-immunoprecipitation showed that TLR9 was associated with HMGB1 and RAGE in lysosomes of MWCNT-treated cells.

Conclusions

MWCNT induces injury or necrosis of lung epithelial cells, which release HMGB1 and DNA into the extracellular space. The HMGB1-DNA complex binds to RAGE on neighboring cells and then CpG DNA is recognized by TLR9 in lysosomes, leading to generation of nitric oxide and 8-nitroG formation. This is the first study demonstrating that TLR9 and related molecules participate in MWCNT-induced genotoxicity and may contribute to carcinogenesis.

Electronic supplementary material

The online version of this article (doi:10.1186/s12989-016-0127-7) contains supplementary material, which is available to authorized users.

Oxidative stress and its significant roles in neurodegenerative diseases and cancer

Reactive oxygen and nitrogen species have been implicated in diverse pathophysiological conditions, including inflammation, neurodegenerative diseases and cancer. Accumulating evidence indicates that oxidative damage to biomolecules including lipids, proteins and DNA, contributes to these diseases. Previous studies suggest roles of lipid peroxidation and oxysterols in the development of neurodegenerative diseases and inflammation-related cancer. Our recent studies identifying and characterizing carbonylated proteins reveal oxidative damage to heat shock proteins in neurodegenerative disease models and inflammation-related cancer, suggesting dysfunction in their antioxidative properties. In neurodegenerative diseases, DNA damage may not only play a role in the induction of apoptosis, but also may inhibit cellular division via telomere shortening. Immunohistochemical analyses showed co-localization of oxidative/nitrative DNA lesions and stemness markers in the cells of inflammation-related cancers. Here, we review oxidative stress and its significant roles in neurodegenerative diseases and cancer.