Nitrative DNA damage in cultured macrophages exposed to indium oxide

Abstract

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.

Inflammation and cancer

“…In a collaboration with Khon Kaen University, Thailand, we firstly reported 8-nitroguanine and 8-oxodG formation in the livers of hamsters treated orally with the liver fluke in an animal model for OV-related cholangiocarcinoma [ 4 ]. In our previous studies based on DNA lesions, we investigated the molecular mechanisms of cancers due to infection (e.g., OV-related cholangiocarcinoma [ 2 , 4 – 6 ], Schistosoma haematobium -associated bladder cancer [ 7 , 8 ], Helicobacter pylori -infected gastric cancer [ 9 ], human papillomavirus-related cervical cancer [ 10 ], Epstein-Barr (EB) virus-infected nasopharyngeal carcinoma [ 11 ]), and pro-inflammatory factors (e.g., asbestos [ 12 , 13 ], nanomaterials [ 14 – 17 ], and inflammatory diseases such as Barrett’s esophagus [ 18 , 19 ], and oral leukoplakia [ 20 ]). In addition, inflammation plays a role in the epigenetic alterations in cancer.…”

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

“…We have previously reported that 8-nitroG was formed at the sites of inflammation-related carcinogenesis in various animal model and clinical specimens 20,40,41 . Our studies using cultured cells have shown that particulate materials, including MWCNT 27,28 , carbon black 29 and In 2 O 3 21 , induced 8-nitroG formation. Because the glycosidic bond between 8-nitroG and deoxyribose is chemically unstable, 8-nitroG can be spontaneously released from DNA, resulting in the formation of apurinic site 42 .…”

“…The objective of this study was to determine the genotoxic effects of indium compounds on lung epithelial cells, and clarify the molecular mechanism. We have recently reported that In 2 O 3 induced 8-nitroG formation in mouse macrophages 21 . In this study, we used In 2 O 3 and ITO nanoparticles as representative indium compounds to examine 8-nitroG formation in human lung epithelial cells.…”

Possibility of lung cancer risk in indium-exposed workers: An 11-year multicenter cohort study

“…5 Mouse macrophages with indium oxide in vitro suggested that endocytosis and NO generation participate in indium-induced 8-nitroguanine (a mutagenic DNA lesion formed during inflammation formation). 15 These results suggest that inhalation of indium compounds, causing pulmonary inflammation associated with oxidative stress, endocytosis, and NO released from indium-exposed inflammatory cells, may induce DNA damage in adjacent lung epithelial cells and contribute to carcinogenesis. However, the development of interstitial fibrotic changes and its relationship with the carcinogenesis needs to be further explored.…”

“…InP inhalation demonstrated the development of oxidative stress, identified by elevated levels of inducible nitric oxide synthase, cyclooxygenase‐2, glutathione‐S‐transferase Pi, and 8‐hydroxydeoxyguanosine, resulting in pulmonary inflammation in progression to atypical hyperplasia and lung cancer . Mouse macrophages with indium oxide in vitro suggested that endocytosis and NO generation participate in indium‐induced 8‐nitroguanine (a mutagenic DNA lesion formed during inflammation formation) . These results suggest that inhalation of indium compounds, causing pulmonary inflammation associated with oxidative stress, endocytosis, and NO released from indium‐exposed inflammatory cells, may induce DNA damage in adjacent lung epithelial cells and contribute to carcinogenesis.…”