asbestos--crocidolite and Precancerous-Conditions

Malignant mesothelioma (MM), linked to asbestos exposure, is a highly lethal form of thoracic cancer with a long latency period, high mortality and poor treatment options. Chronic inflammation and oxidative tissue damage caused by asbestos fibers are linked to MM development. Flaxseed lignans, enriched in secoisolariciresinol diglucoside (SDG), have antioxidant, anti-inflammatory and cancer chemopreventive properties. As a prelude to chronic chemoprevention studies for MM development, we tested the ability of flaxseed lignan component (FLC) to prevent acute asbestos-induced inflammation in MM-prone Nf2(+/mu) mice. Mice (n = 16-17 per group) were placed on control (CTL) or FLC-supplemented diets initiated 7 days prior to a single intraperitoneal bolus of 400 µg of crocidolite asbestos. Three days post asbestos exposure, mice were evaluated for abdominal inflammation, proinflammatory/profibrogenic cytokine release, WBC gene expression changes and oxidative and nitrosative stress in peritoneal lavage fluid (PLF). Asbestos-exposed mice fed CTL diet developed acute inflammation, with significant (P < 0.0001) elevations in WBCs and proinflammatory/profibrogenic cytokines (IL-1ß, IL-6, TNFα, HMGB1 and active TGFß1) relative to baseline (BL) levels. Alternatively, asbestos-exposed FLC-fed mice had a significant (P < 0.0001) decrease in PLF WBCs and proinflammatory/profibrogenic cytokine levels relative to CTL-fed mice. Importantly, PLF WBC gene expression of cytokines (IL-1ß, IL-6, TNFα, HMGB1 and TGFß1) and cytokine receptors (TNFαR1 and TGFßR1) were also downregulated by FLC. FLC also significantly (P < 0.0001) blunted asbestos-induced nitrosative and oxidative stress. FLC reduces acute asbestos-induced peritoneal inflammation, nitrosative and oxidative stress and may thus prove to be a promising agent in the chemoprevention of MM.

Topics: Animals; Antioxidants; Asbestos, Crocidolite; Butylene Glycols; Chromatography, Liquid; Diet; Dietary Supplements; Disease Models, Animal; Enzyme-Linked Immunosorbent Assay; Flax; Glucosides; Inflammation; Lignans; Mesothelioma; Mice; Mice, Mutant Strains; Oxidative Stress; Peritoneal Lavage; Peritoneum; Precancerous Conditions; Reverse Transcriptase Polymerase Chain Reaction; Seeds; Tandem Mass Spectrometry; Transcriptome

Malignant mesothelioma (MM) is one of the worst cancers in terms of clinical outcome, urging the need to establish and characterize new preclinical tools for investigation of the tumorigenic process, improvement of early diagnosis and evaluation of new therapeutic strategies. For these purposes, we characterized a collection of 27 cell lines established from F344 rats, after 136 to 415 days of induction with crocidolite asbestos administered intraperitoneally. Four mesotheliomas were distinguished from 23 preneoplastic mesothelial cell lines (PN) according to their propensity to generate tumors after orthotopic transplantation into syngeneic rats, their growth pattern, and the expression profile of three genes. PN cell lines were further discriminated into groups / subgroups according to morphology in culture and the expression profiles of 14 additional genes. This approach was completed by analysis of positive and negative immunohistochemical MM markers in the four tumors, of karyotype alterations in the most aggressive MM cell line in comparison with a PN epithelioid cell line, and of human normal mesothelial and mesothelioma cells and a tissue array. Our results showed that both the rat and human MM cell lines shared in common a dramatic decrease in the relative expression of Cdkn2a and of epigenetic regulators, in comparison with PN and normal human mesothelial cells, respectively. In particular, we identified the involvement of the relative expression of the Ten-Eleven Translocation (TET) family of dioxygenases and Dnmt3a in relation to the 5-hydroxymethylcytosine level in malignant transformation and the acquisition of metastatic potential.

Topics: 5-Methylcytosine; Animals; Asbestos, Crocidolite; Biomarkers, Tumor; Cell Line, Tumor; Cell Movement; Cell Proliferation; Cell Transformation, Neoplastic; Cyclin-Dependent Kinase Inhibitor p16; Cyclin-Dependent Kinase Inhibitor p18; DNA (Cytosine-5-)-Methyltransferases; DNA Methyltransferase 3A; Epithelial Cells; Epithelium; Humans; Karyotype; Lung Neoplasms; Mesothelioma; Mesothelioma, Malignant; Mixed Function Oxygenases; Precancerous Conditions; Proto-Oncogene Proteins; Rats; Rats, Inbred F344

Human malignant mesotheliomas are induced almost exclusively by fibrous dusts. The nature of interactions between fibers and target cells, and the molecular mechanisms leading to tumorigenesis, are not yet understood. Here, the mRNA expression patterns at different stages of asbestos-induced carcinogenesis in rats were monitored by suppression subtractive hybridization (SSH) and array assay. Several genes were upregulated in pretumorous tissues from asbestos-treated rats, in asbestos-induced tumors and in cells treated with asbestos in vitro. The upregulation of the proto-oncogene c-myc, fra-1 and egfr in fiber-induced carcinogenesis was demonstrated at different stages of carcinogenesis. A possible role of Fra-1 as one of the dimeric proteins generating the AP-1 transcription factor was substantiated by its dose-dependent expression in mesothelial cells treated with asbestos in vitro. The upregulation of osteopontin (an extracellular matrix protein) and of zyxin and integrin-linked kinase (intracellular proteins associated with the focal adhesion contact), indicate that fibers may affect integrin-linked signal transduction and extracellular matrix proteins.

Topics: Animals; Asbestos, Crocidolite; Base Sequence; Carcinogens; Cell Transformation, Neoplastic; DNA Primers; ErbB Receptors; Genes, myc; Mesothelioma; Precancerous Conditions; Proto-Oncogene Mas; Proto-Oncogene Proteins c-fos; Rats; Rats, Wistar; Reverse Transcriptase Polymerase Chain Reaction; RNA, Messenger; Up-Regulation

The carcinogenicity of asbestos to the gut is controversial. The aberrant crypt focus (ACF) assay is proposed as a test for colon carcinogens. We have scored ACF in the colon of rats and mice, one month after per os gavages with suspensions of asbestos fibers. Crocidolite asbestos induced ACF in the colon of rats in two independent experiments (P = 0.02 and P < 0.01 compared to controls given water), and was ten times less effective than the carcinogen azoxymethane. Chrysotile asbestos also induced ACF in rats. Neither crocidolite nor chrysotile induced ACF in mice. The data suggest that ingested asbestos may be carcinogenic to the colon.

Topics: Animals; Asbestos, Crocidolite; Asbestos, Serpentine; Azoxymethane; Carcinogenicity Tests; Colonic Neoplasms; Female; Mice; Precancerous Conditions; Rats; Rats, Inbred F344

90 Wistar strain rats were used in this experiment, 56 rats (Group A) were injected intrapleurally with crocidolite fibers suspended in physiological (NaCl) solution. Another 34 rats (Group B), serving as controls, were injected with the same volume of mere NaCl solution. The rats were killed 1, 3, 6, 9, 12, 14 and 16 months respectively after injection. The results showed that the rats of Group B only exhibited reactive proliferation of mesothelial cells caused by inflammation. In Group A, there appeared 9 cases of mesothelioma. The tumorigenic stages of mesothelioma include three processes: (1). reactive proliferation: the mesothelial cells became cuboid. (2). precancerous changes: the atypical proliferation of stratified, nodular or papillary mesothelial cells and of the cell elements around asbestos granulomas. (3). the occurrence of mesothelioma. Ultrastructural observation revealed that in mesothelioma tissue mesenchymal cells directly or indirectly (via transitional cells) differentiated cinto epithelioid cells. The mesenchymal cells may also become fibroblastoid cells. These findings suggest that mesothelioma originates from mesenchymal cells.

Topics: Animals; Asbestos; Asbestos, Crocidolite; Female; Injections; Male; Mesothelioma; Pleura; Pleural Neoplasms; Precancerous Conditions; Rats; Rats, Inbred Strains

Topics: Abdominal Neoplasms; Aerosols; Animals; Asbestos; Asbestos, Crocidolite; Asbestos, Serpentine; Carcinogens; Female; Glass; Injections, Intraperitoneal; Lung Neoplasms; Precancerous Conditions; Rats; Rats, Inbred Strains