Carcinogenesis

Our medical research library holds 82 studies published in Carcinogenesis (1980–2024). Each entry links to the study's record on PubMed and, where there is one, to the publisher's page and a free full text. 75 have an abstract, the authors' own summary as PubMed records it: open "Abstract" to read it. For 2 studies PubMed has no abstract for, we give the abstract printed in the article or, where there is none, a summary we wrote from it, each labeled as such.

About the journal

• Publisher: Irl Press At Oxford University Press
• Published: 1980 to the present, England
• Language: English
• ISSN: 0143-3334 (print), 1460-2180 (electronic)
• Its record in the NLM Catalog

2020s

• Asbestos burden in lungs of mesothelioma patients with pleural plaques, lung fibrosis and/or ferruginous bodies at histology: a postmortem SEM-EDS study. S.D. Visonà, B. Bertoglio, S. Capella, et al. 2024;45(3):131-139. PubMed · Publisher

  Abstract

  The causal attribution of asbestos-related diseases to past asbestos exposures is of crucial importance in clinical and legal contexts. Often this evaluation is made based on the history of exposure, but this method presents important limitations. To assess past asbestos exposure, pleural plaques (PP), lung fibrosis and histological evidence of ferruginous bodies (FB) can be used in combination with anamnestic data. However, such markers have never been associated with a threshold value of inhaled asbestos. With this study we attempted to shed light on the dose-response relationship of PP, lung fibrosis and FBs, investigating if their prevalence in exposed individuals who died from malignant mesothelioma (MM) is related to the concentration of asbestos in lungs assessed using scanning electron microscopy equipped with energy dispersive spectroscopy. Moreover, we estimated the values of asbestos concentration in lungs associated with PP, lung fibrosis and FB. Lung fibrosis showed a significant positive relationship with asbestos lung content, whereas PP and FB did not. We identified, for the first time, critical lung concentrations of asbestos related to the presence of PP, lung fibrosis and FB at histology (respectively, 19 800, 26 400 and 27 400 fibers per gram of dry weight), that were all well-below the background levels of asbestos identified in our laboratory. Such data suggest that PP, lung fibrosis and FB at histology should be used with caution in the causal attribution of MM to past asbestos exposures, while evaluation of amphibole lung content using analytical electron microscopy should be preferred.

  © The Author(s) 2023. Published by Oxford University Press. All rights reserved. For Permissions, please email: [email protected].

• Inflammation as a chemoprevention target in asbestos-induced malignant mesothelioma. Y. Kadariya, E. Sementino, U. Shrestha, et al. 2022;43(12):1137-1148. PubMed · Publisher · Free full text

  Abstract

  Malignant mesothelioma (MM) is an incurable cancer of the serosal lining that is often caused by exposure to asbestos. Therefore, novel agents for the prevention and treatment of this disease are urgently needed. Asbestos induces the release of pro-inflammatory cytokines such as IL-1β and IL-6, which play a role in MM development. IL-6 is a component of the JAK-STAT3 pathway that contributes to inflammation-associated tumorigenesis. Glycoprotein 130 (gp130), the signal transducer of this signaling axis, is an attractive drug target because of its role in promoting neoplasia via the activation of downstream STAT3 signaling. The anticancer drug, SC144, inhibits the interaction of gp130 with the IL-6 receptor (IL6R), effectively blunting signaling from this inflammatory axis. To test whether the inflammation-related release of IL-6 plays a role in the formation of MM, we evaluated the ability of SC144 to inhibit asbestos-induced carcinogenesis in a mouse model. The ability of sulindac and anakinra, an IL6R antagonist/positive control, to inhibit MM formation in this model was tested in parallel. Asbestos-exposed Nf2+/-;Cdkn2a+/- mice treated with SC144, sulindac or anakinra showed significantly prolonged survival compared to asbestos-exposed vehicle-treated mice. STAT3 activity was markedly decreased in MM specimens from SC144-treated mice. Furthermore, SC144 inhibited STAT3 activation by IL-6 in cultured normal mesothelial cells, and in vitro treatment of MM cells with SC144 markedly decreased the expression of STAT3 target genes. The emerging availability of newer, more potent SC144 analogs showing improved pharmacokinetic properties holds promise for future trials, benefitting individuals at high risk of this disease.

  © The Author(s) 2022. Published by Oxford University Press. All rights reserved. For Permissions, please email: [email protected].

2010s

• Comment on: Malignant mesothelioma diagnosed at a younger age is associated with heavier asbestos exposure. E. Oddone, B. Terracini, D. Mirabelli, et al. 2019;40(3):488-489. Letter · Comment PubMed · Publisher

• Corrigendum: Malignant mesothelioma diagnosed at a younger age is associated with heavier asbestos exposure. T.A. Dragani, F. Colombo, E.N. Pavlisko, et al. 2019;40(3):492. PubMed · Publisher

• Letter to the editor re: Dragani et al. (2018), 'Malignant mesothelioma diagnosed at a younger age is associated with heavier asbestos exposure'. A. Farioli, S. Mattioli, S. Curti, et al. 2019;40(3):487. Letter · Comment PubMed · Publisher

• Response to comments on 'Malignant mesothelioma diagnosed at a younger age is associated with heavier asbestos exposure' by Farioli et al. and Oddone et al. T.A. Dragani, F. Colombo, E.N. Pavlisko, et al. 2019;40(3):490-491. Letter · Comment PubMed · Publisher

• Whole-genome sequencing of human malignant mesothelioma tumours and cell lines. H. Oey, M. Daniels, V. Relan, et al. 2019;40(6):724-734. PubMed · Publisher

  Abstract

  Pleural mesothelioma is a cancer of serosal surfaces caused by environmental exposure to asbestos. Clinical outcome remains poor and while trials of new treatments are ongoing it remains an understudied cancer. Mesothelioma cell lines can readily be grown from primary tumour and from tumour cells shed into pleural effusion with the latter representing a particularly valuable source of DNA in clinical settings, procurable without the need for additional invasive procedures. However, it is not well understood how accurately patient-derived cultured tumour cells represent the molecular characteristics of their primary tumour. We used whole-genome sequencing of primary tumour and matched cultured cells to comprehensively characterize mutations and structural alterations. Most cases had complex rearranged genomes with evidence of chromoanagenesis and rearrangements reminiscent of chromoplexy. Many of the identified driver mutations were structural, indicating that mesothelioma is often caused by structural alterations and catastrophic genomic events, rather than point mutations. Because the majority of genomic changes detected in tumours were also displayed by the genomes of cultured tumour cells, we conclude that low-passage cultured tumour cells are generally suitable for molecular characterization of mesothelioma and may be particularly useful where tissue samples with high tumour cell content are not available. However, the subclonal compositions of the cell lines did not fully recapitulate the subclonal diversity of the primary tumours. Furthermore, longitudinal acquisition of major alterations in subclonal cell populations was observed after long-term passaging. These two factors define limitations of tumour-derived cell lines as genomic substrate for clinical purposes.

  © The Author(s) 2019. Published by Oxford University Press. All rights reserved. For Permissions, please email: [email protected].

• FGF2 and EGF induce epithelial-mesenchymal transition in malignant pleural mesothelioma cells via a MAPKinase/MMP1 signal. K. Schelch, C. Wagner, S. Hager, et al. 2018;39(4):534-545. PubMed · Publisher

  Abstract

  Malignant pleural mesothelioma (MPM), an aggressive malignancy affecting pleural surfaces, occurs in three main histological subtypes. The epithelioid and sarcomatoid subtypes are characterized by cuboid and fibroblastoid cells, respectively. The biphasic subtype contains a mixture of both. The sarcomatoid subtype expresses markers of epithelial-mesenchymal transition (EMT) and confers the worst prognosis, but the signals and pathways controlling EMT in MPM are not well understood. We demonstrate that treatment with FGF2 or EGF induced a fibroblastoid morphology in several cell lines from biphasic MPM, accompanied by scattering, decreased cell adhesion and increased invasiveness. This depended on the MAP-kinase pathway but was independent of TGFβ or PI3-kinase signaling. In addition to changes in known EMT markers, microarray analysis demonstrated differential expression of MMP1, ESM1, ETV4, PDL1 and BDKR2B in response to both growth factors and in epithelioid versus sarcomatoid MPM. Inhibition of MMP1 prevented FGF2-induced scattering and invasiveness. Moreover, in MPM cells with sarcomatoid morphology, inhibition of FGF/MAP-kinase signaling induced a more epithelioid morphology and gene expression pattern. Our findings suggest a critical role of the MAP-kinase axis in the morphological and behavioral plasticity of mesothelioma.

• Malignant mesothelioma diagnosed at a younger age is associated with heavier asbestos exposure. T.A. Dragani, F. Colombo, E.N. Pavlisko, et al. 2018;39(9):1151-1156. PubMed · Publisher

  Abstract

  Asbestos exposure is the main etiology of malignant mesothelioma, but there are conflicting data on whether the intensity of exposure modulates the development of this disease. This study considered 594 patients with malignant mesothelioma for whom count data on asbestos bodies and fibers (per gram of wet lung tissue) were available. The relationships between age at diagnosis (a time-to-event outcome variable) and these two measures of internal asbestos exposure, along with other possible modulating factors (sex, tumor location, histological subtype and childhood exposure), were assessed on multivariable Cox proportional hazard models, stratifying by decade of birth year. For both measures of asbestos in lung tissue, younger age at diagnosis was associated with higher internal measures of exposure to asbestos. Stratified Cox analyses showed that for each doubling in asbestos body count patients were 1.07 times more likely to be diagnosed at a younger age [hazard ratio (HR) = 1.07; 95% confidence interval (CI), 1.04-1.09; P = 2.2 × 10-7] and for each doubling in asbestos fiber count patients were 1.13 times more likely to be diagnosed at a younger age (HR = 1.13; 95% CI, 1.09-1.17; P = 8.6 × 10-11). None of the other variables considered were associated with age at diagnosis. Our finding that tumors become clinically apparent at a younger age in heavily exposed subjects suggests that asbestos is involved not only in the malignant mesothelioma tumor initiation but, somehow, also in the progression of the disease.

• Flaxseed lignans enriched in secoisolariciresinol diglucoside prevent acute asbestos-induced peritoneal inflammation in mice. R.A. Pietrofesa, A. Velalopoulou, E. Arguiri, et al. 2016;37(2):177-87. PubMed · Publisher · Free full text

  Abstract

  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.

  © The Author 2015. Published by Oxford University Press.

• Gene-asbestos interaction in malignant pleural mesothelioma susceptibility. S. Tunesi, D. Ferrante, D. Mirabelli, et al. 2015;36(10):1129-35. PubMed · Publisher

  Abstract

  Asbestos exposure is the main risk factor for malignant pleural mesothelioma (MPM), a rare aggressive tumor. Nevertheless, on average less than 10% of subjects highly exposed to asbestos develop MPM, suggesting the possible involvement of other risk factors. To identify the genetic factors that may modulate the risk of MPM, we conducted a gene-environment interaction analysis including asbestos exposure and 15 single nucleotide polymorphisms (SNPs) previously identified through a genome-wide association study on Italian subjects. In the present study, we assessed gene-asbestos interaction on MPM risk using relative excess risk due to interaction and synergy index for additive interaction and V index for multiplicative interaction. Generalized multifactor dimensionality reduction (GMDR) analyses were also performed. Positive deviation from additivity was found for six SNPs (rs1508805, rs2501618, rs4701085, rs4290865, rs10519201, rs763271), and four of them (rs1508805, rs2501618, rs4701085, rs10519201) deviated also from multiplicative models. However, after Bonferroni correction, deviation from multiplicative model was still significant for rs1508805 and rs4701085 only. GMDR analysis showed a strong MPM risk due to asbestos exposure and suggested a possible synergistic effect between asbestos exposure and rs1508805, rs2501618 and rs5756444. Our results suggested that gene-asbestos interaction may play an additional role on MPM susceptibility, given that asbestos exposure appears as the main risk factor.

  © The Author 2015. Published by Oxford University Press. All rights reserved. For Permissions, please email: [email protected].

• Mesothelioma patients with germline BAP1 mutations have 7-fold improved long-term survival. F. Baumann, E. Flores, A. Napolitano, et al. 2015;36(1):76-81. PubMed · Publisher · Free full text

  Abstract

  BRCA1-associated protein-1 (BAP1) mutations cause a new cancer syndrome, with a high rate of malignant mesothelioma (MM). Here, we tested the hypothesis that MM associated with germline BAP1 mutations has a better prognosis compared with sporadic MM. We compared survival among germline BAP1 mutation MM patients with that of all MM (N = 10 556) recorded in the United States Surveillance, Epidemiology, and End Results (SEER) data from 1973 to 2010. We identified 23 MM patients--11 alive--with germline BAP1 mutations and available data on survival. Ten patients had peritoneal MM, ten pleural MM and three MM in both locations. Thirteen patients had one or more malignancies in addition to MM. Actuarial median survival for the MM patients with germline BAP1 mutations was 5 years, as compared with <1 year for the median survival in the United States SEER MM group. Five-year survival was 47%, 95% confidence interval (24-67%), as compared with 6.7% (6.2-7.3%) in the control SEER group. Analysis of the pooled cohort of germline BAP1 mutation MM showed that patients with peritoneal MM (median survival of 10 years, P = 0.0571), or with a second malignancy in addition to MM (median survival of 10 years, P = 0.0716), survived for a longer time compared with patients who only had pleural MM, or MM patients without a second malignancy, respectively. In conclusion, we found that MM patients with germline BAP1 mutations have an overall 7-fold increased long-term survival, independently of sex and age. Appropriate genetic counseling and clinical management should be considered for MM patients who are also BAP1 mutation carriers.

  © The Author 2014. Published by Oxford University Press. All rights reserved. For Permissions, please email: [email protected].

• Cancer-promoting role of adipocytes in asbestos-induced mesothelial carcinogenesis through dysregulated adipocytokine production. S.H. Chew, Y. Okazaki, H. Nagai, et al. 2014;35(1):164-72. PubMed · Publisher

  Abstract

  Like many other human cancers, the development of malignant mesothelioma is closely associated with a chronic inflammatory condition. Both macrophages and mesothelial cells play crucial roles in the inflammatory response caused by asbestos exposure. Here, we show that adipocytes can also contribute to asbestos-induced inflammation through dysregulated adipocytokine production. 3T3-L1 preadipocytes were differentiated into mature adipocytes prior to use. These cells took up asbestos fibers (chrysotile, crocidolite and amosite) but were more resistant to asbestos-induced injury than macrophages and mesothelial cells. Expression microarray analysis followed by reverse transcription-PCR revealed that adipocytes respond directly to asbestos exposure with an increased production of proinflammatory adipocytokines [e.g. monocyte chemoattractant protein-1 (MCP-1)], whereas the production of anti-inflammatory adipocytokines (e.g. adiponectin) is suppressed. This was confirmed in epididymal fat pad of mice after intraperitoneal injection of asbestos fibers. Such dysregulated adipocytokine production favors the establishment of a proinflammatory environment. Furthermore, MCP-1 marginally promoted the growth of MeT-5A mesothelial cells and significantly enhanced the wound healing of Y-MESO-8A and Y-MESO-8D human mesothelioma cells. Our results suggest that increased levels of adipocytokines, such as MCP-1, can potentially contribute to the promotion of mesothelial carcinogenesis through the enhanced recruitment of inflammatory cells as well as a direct growth and migration stimulatory effect on mesothelial and mesothelioma cells. Taken together, our findings support a potential cancer-promoting role of adipocytes in asbestos-induced mesothelial carcinogenesis.

• Long-term exposure of mesothelial cells to SV40 and asbestos leads to malignant transformation and chemotherapy resistance. A.L. Cleaver, K. Bhamidipaty, B. Wylie, et al. 2014;35(2):407-14. PubMed · Publisher

  Abstract

  Simian virus 40 (SV40) has been implicated in the development of several cancers including malignant mesothelioma. A definitive role for the virus in human mesothelioma has not been unequivocally demonstrated but has been rigorously debated. The virus clearly has oncogenic potential: the TAg is one of the most potent transforming proteins known and acts synergistically with crocidolite asbestos to transform mesothelial cells. In this study, we show that SV40 oncogenes alone can cause malignant transformation and that asbestos-induced DNA damage and apoptosis occurs principally in cycling cells. After long-term exposure (up to 100 days) to both SV40 and asbestos, cells become resistant to stress-induced senescence. Significantly, these cells demonstrate resistance to chemotherapy-induced apoptosis. This finding has implications for the development of effective treatment options for patients with mesothelioma.

• Molecular pathogenesis of malignant mesothelioma. Y. Sekido. 2013;34(7):1413-9. Review PubMed · Publisher

  Abstract

  Malignant mesothelioma (MM) is an aggressive tumor arising primarily from the pleural or peritoneal cavities. It develops by asbestos exposure after a long latency, which is characterized by insidious growth and clinical presentation at an advanced stage of disease. MM is highly refractory to conventional therapies even with a combination of aggressive surgical intervention and multimodality strategies, with cure remaining elusive. Molecular genetic analysis has revealed several key genetic alterations, which are responsible for the development and progression of MM. The cyclin-dependent kinase inhibitor 2A/alternative reading frame (CDKN2A/ARF), neurofibromatosis type 2 (NF2) and BRCA1-associated protein-1 (BAP1) genes are the most frequently mutated tumor suppressor genes detected in MM cells; the alterations of the latter two are relatively characteristic of MM. Merlin, which is encoded by NF2, regulates multiple cell signaling cascades including the Hippo and mammalian target of rapamycin pathways, which regulate cell proliferation and growth. BAP1 is involved in histone modification and its inactivation induces the disturbance of global gene expression profiling. The discovery of a new familial cancer syndrome with germline mutation of BAP1 also indicates the importance of genetic factors in MM susceptibility. Meanwhile, although frequent expression and functional activations of oncogene products such as receptor tyrosine kinases are observed in MM cells, activating mutations of these genes are rare. With further comprehensive genome analyses, new genetic and epigenetic alterations in MM cells are expected to be revealed more precisely, and the new knowledge based on them will be applied for developing new diagnostic tools and new target therapies against MMs.

• Deficiency of Fyn protein is prerequisite for apoptosis induced by Src family kinase inhibitors in human mesothelioma cells. R. Eguchi, S. Kubo, H. Takeda, et al. 2012;33(5):969-75. PubMed · Publisher

  Abstract

  Malignant mesothelioma is an aggressive tumor arising from mesothelial cells of serous membranes. Src family kinases (SFKs) have a pivotal role in cell adhesion, proliferation, survival and apoptosis. Here, we examined the effect of SFK inhibitors in NCI-H2052, ACC-MESO-4 and NCI-H28 cells, mesothelioma cell lines and Met5A, a human non-malignant mesothelial cell line. We found that PP2, a selective SFK inhibitor, inhibited SFK activity and induced apoptosis mediated by caspase-8 in NCI-H28 but not Met5A, NCI-H2052 and ACC-MESO-4 cells. Src, Yes, Fyn and Lyn protein, which are members of the SFK, were expressed in these cell lines, whereas NCI-H28 cells were deficient in Fyn protein. Small interfering RNA (siRNA) targeting Fyn facilitated PP2-induced apoptosis mediated by caspase-8 in NCI-H2052 and ACC-MESO-4 cells. PP2 reduced Lyn protein levels and suppressed SFK activity in all mesothelioma cell lines. Lyn siRNA induced caspase-8 activation and apoptosis in NCI-H28 cells but not in NCI-H2052 and ACC-MESO-4 cells. However, double RNA interference knockdown of Fyn and Lyn induced apoptosis accompanied by caspase-8 activation in NCI-H2052 and ACC-MESO-4 cells. Dasatinib, an inhibitor of multi-tyrosine kinases including SFK, also inhibited SFK activity and induced reduction of Lyn protein levels, caspase-8 activation and apoptosis in NCI-H28 cells but not in other cell lines. Present study suggests that SFK inhibitors induce caspase-8-dependent apoptosis caused by reduction of Lyn protein in Fyn-deficient mesothelioma cells.

• Genome-wide gene-environment interaction analysis for asbestos exposure in lung cancer susceptibility. S. Wei, L.E. Wang, M.K. McHugh, et al. 2012;33(8):1531-7. PubMed · Publisher · Free full text

  Abstract

  Asbestos exposure is a known risk factor for lung cancer. Although recent genome-wide association studies (GWASs) have identified some novel loci for lung cancer risk, few addressed genome-wide gene-environment interactions. To determine gene-asbestos interactions in lung cancer risk, we conducted genome-wide gene-environment interaction analyses at levels of single nucleotide polymorphisms (SNPs), genes and pathways, using our published Texas lung cancer GWAS dataset. This dataset included 317 498 SNPs from 1154 lung cancer cases and 1137 cancer-free controls. The initial SNP-level P-values for interactions between genetic variants and self-reported asbestos exposure were estimated by unconditional logistic regression models with adjustment for age, sex, smoking status and pack-years. The P-value for the most significant SNP rs13383928 was 2.17×10(-6), which did not reach the genome-wide statistical significance. Using a versatile gene-based test approach, we found that the top significant gene was C7orf54, located on 7q32.1 (P = 8.90×10(-5)). Interestingly, most of the other significant genes were located on 11q13. When we used an improved gene-set-enrichment analysis approach, we found that the Fas signaling pathway and the antigen processing and presentation pathway were most significant (nominal P < 0.001; false discovery rate < 0.05) among 250 pathways containing 17 572 genes. We believe that our analysis is a pilot study that first describes the gene-asbestos interaction in lung cancer risk at levels of SNPs, genes and pathways. Our findings suggest that immune function regulation-related pathways may be mechanistically involved in asbestos-associated lung cancer risk.

• Pleural mesothelioma side populations have a precursor phenotype. C. Frei, I. Opitz, A. Soltermann, et al. 2011;32(9):1324-32. PubMed · Publisher

  Abstract

  DyeCycleViolet was used to set up the side population (SP) functional assay aimed at identifying subpopulations of malignant pleural mesothelioma (MPM) tumor cells with chemoresistance phenotype associated with ABCG2 transporter activity. Self-renewal, chemoresistance and tumorigenicity were tested for SP and non-side population (NSP) cells. Tumors were characterized by mesothelin, calretinin, N-cadherin, D2-40 and Wilms tumor 1 (WT1) immunohistochemistry. Surface expression of mesenchymal stem cell markers CD90, CD73 and CD105 was investigated in SP and NSP cells. We identified SP cells with self-renewal properties and increased chemoresistance in MPM cell lines and tumor-derived primary cell cultures. Compared with the non-SP fraction (NSP), the SP fraction led to the development of tumors including cells with mesothelium precursor phenotype characterized by mesenchymal morphology, being WT1 negative but cytoplasmic D2-40 positive and having a tendency of increased tumorigenicity. The same phenotypic shift was observed in patients with relapsing tumors after chemotherapy. Furthermore, the SP cells were enriched in CD105(-)(/low) expressing cells, which were small sized and had increased tumorigenicity compared with CD105(high) cells. Taken together, our results support the hypothesis that MPM CD105(-)(/low), chemoresistant small sized SP cells may constitute the cellular pool out of which recurrence develops. Further characterization of mechanisms of chemoresistance and self-renewal should lead to targets specific for this subpopulation in MPM patients.

• Downregulation of Bcl-xL and Mcl-1 is sufficient to induce cell death in mesothelioma cells highly refractory to conventional chemotherapy. E. Varin, C. Denoyelle, E. Brotin, et al. 2010;31(6):984-93. PubMed · Publisher

  Abstract

  Malignant pleural mesothelioma (MPM) is an aggressive tumor with poor prognosis and limited response to platinum-based chemotherapy. Several lines of evidence support a role for the anti-apoptotic protein Bcl-x(L) in MPM chemoresistance. Since it has been recently suggested that Mcl-1 cooperates with Bcl-x(L) for protection against cell death, we investigated the response of mesothelioma cell lines to the downregulation of Bcl-x(L) (alone or in combination with cisplatin) and the potential interest of its concomitant inhibition with that of Mcl-1. Using RNA interference, we showed that Bcl-x(L) depletion sensitized two highly chemoresistant mesothelioma cell lines to cisplatin and that under this treatment, one cell line, MSTO-211H, displayed an apoptotic type of cell death, whereas the other, NCI-H28, evidenced mainly necrotic-type cell death. Otherwise, the inhibition of Mcl-1 by cisplatin may contribute to this induction of cell death observed after Bcl-x(L) downregulation. Strikingly, we observed that the simultaneous inhibition of Bcl-x(L) and Mcl-1 using small interfering RNA (siRNA) induced a massive cell death in the absence of chemotherapy and was sufficient to avoid escape to treatment in MSTO-211H cells. In NCI-H28, the addition of a low cisplatin concentration allowed to impede the long-term recovery observed after treatment by the siRNA combination. Together, these findings provide a strong molecular basis for the clinical evaluation of therapies targeting both Bcl-x(L) and Mcl-1, alone or in combination with conventional chemotherapy, for the treatment of MPM.

2000s

• Combined inhibition of MET and EGFR suppresses proliferation of malignant mesothelioma cells. K. Kawaguchi, H. Murakami, T. Taniguchi, et al. 2009;30(7):1097-105. PubMed · Publisher

  Abstract

  Malignant pleural mesothelioma (MPM) is an aggressive neoplasm associated with asbestos exposure. Although expression and activation of receptor tyrosine kinases (RTKs), including MET, have been reported in most MPM, specific RTK inhibitors showed less than the expected response in MPM cells. To determine whether the lack of response of MET inhibitors was due to cooperation with other RTKs, we determined activation status of MET and other RTKs, including epidermal growth factor receptor (EGFR) family of 20 MPM cell lines, and tested whether dual RTK inhibition is an effective therapeutic strategy. We detected MET upregulation and phosphorylation (thus indicating activation) in 14 (70%) and 13 (65%) cell lines, but treatment with MET-specific inhibitors showed weak or modest effect of suppression in most of the cell lines. Phospho-RTK array analysis revealed that MET was simultaneously activated with other RTKs, including EGFR, ErbB2, ErbB3 and platelet-derived growth factor receptor-beta. Combination of MET and EGFR inhibitors triggered stronger inhibition on cell proliferation and invasion of MPM cells than that of each in vitro. These results indicated that coactivation of RTKs was essential in mesothelioma cell proliferation and/or survival, thus suggesting that simultaneous inhibition of RTKs may be a more effective strategy for the development of molecular target therapy for MPM.

• 'Environment' in cancer causation and etiological fraction: limitations and ambiguities. D. Mirabelli, E. Merler. 2008;29(5):1083. Comment · Letter PubMed · Publisher

• Aberrations of chromosome 19 in asbestos-associated lung cancer and in asbestos-induced micronuclei of bronchial epithelial cells in vitro. S.T. Ruosaari, P.E. Nymark, M.M. Aavikko, et al. 2008;29(5):913-7. PubMed · Publisher

  Abstract

  Exposure to asbestos is known to induce lung cancer, and our previous studies have suggested that specific chromosomal regions, such as 19p13, are preferentially aberrant in lung tumours of asbestos-exposed patients. Here, we further examined the association between the 19p region and exposure to asbestos using array comparative genomic hybridization and fluorescence in situ hybridization (FISH) in lung tumours and FISH characterization of asbestos-induced micronuclei (MN) in human bronchial epithelial BEAS 2B cells in vitro. We detected an increased number of 19p losses in the tumours of asbestos-exposed patients in comparison with tumours from non-exposed subjects with similar distribution of tumour histology in both groups (13/33; 39% versus 3/25; 12%, P = 0.04). In BEAS 2B cells, a 48 h exposure to crocidolite asbestos (2.0 microg/cm(2)) was found to induce centromere-negative MN-harbouring chromosomal fragments. Furthermore, an increased frequency of rare MN containing a 19p fragment was observed after the crocidolite treatment in comparison with untreated controls (6/6000 versus 1/10 000, P = 0.01). The results suggest that 19p has significance in asbestos-associated carcinogenesis and that asbestos may be capable of inducing specific chromosome aberrations.

• Asbestos exposure predicts cell cycle control gene promoter methylation in pleural mesothelioma. B.C. Christensen, J.J. Godleski, C.J. Marsit, et al. 2008;29(8):1555-9. PubMed · Publisher · Free full text

  Abstract

  Malignant pleural mesothelioma (MPM) is a rapidly fatal tumor with increasing incidence worldwide responsible for many thousands of deaths annually. Although there is a clear link between exposure to asbestos and mesothelioma, and asbestos is known to be both clastogenic and cytotoxic to mesothelial cells, the mechanisms of causation of MPM remain largely unknown. However, there is a rapidly emerging literature that describes inactivation of a diverse array of tumor suppressor genes (TSGs) via promoter DNA CpG methylation in MPM, although the etiology of these alterations remains unclear. We studied the relationships among promoter methylation silencing, asbestos exposure, patient demographics and tumor histology using a directed approach; examining six cell cycle control pathway TSGs in an incident case series of 70 MPMs. Promoter hypermethylation of APC, CCND2, CDKN2A, CDKN2B, HPPBP1 and RASSF1 were assessed. We observed significantly higher lung asbestos body burden if any of these cell cycle genes were methylated (P < 0.02), and there was a significant trend of increasing asbestos body counts as the number of methylated cell cycle pathway genes increased from 0 to 1 to >1 (P < 0.005). This trend of increasing asbestos body count and increasing number of methylated cell cycle pathway genes remained significant (P < 0.05) after controlling for age, gender and tumor histology. These data suggest a novel tumorigenic mechanism of action of asbestos and may contribute to the understanding of precisely how asbestos exposure influences the etiology and clinical course of malignant mesothelioma.

• 'Environment' in cancer causation and etiological fraction: limitations and ambiguities. P. Boffetta, J.K. McLaughlin, C. la Vecchia, et al. 2007;28(5):913-5. Review PubMed · Publisher

  Summary

  In this commentary, the authors examined how the term 'environment' is used in cancer research and the limitations of estimating the fraction of cancers attributable to environmental factors. They noted that 'environment' is used both broadly, for all non-genetic factors, and narrowly, for pollutants of air, water, soil and food. They proposed replacing it with 'non-genetic or modifiable determinants' and 'pollutants'. They contrasted a World Health Organization estimate that 19% of cancers worldwide were attributable to environmental factors, including occupational exposures, with other reviews, excluding occupation, that gave 1–3%. They described several sources of error: combining risk estimates from heavily exposed groups with prevalence data based on looser exposure definitions, residual confounding (for example by smoking), applying risks from past exposures to present conditions, underestimating past exposure levels in dose–response models, and ignoring effect modifiers. Non-occupational asbestos exposure was a main example. A meta-analysis of 10 residential studies gave a relative risk of mesothelioma of 3.5 (95% CI 1.8–7.0). Combined with a 5% exposure estimate for Europe, this gave an attributable fraction of 11%, or 174 cases per year in men and 30 in women in a country like Great Britain, which the authors considered highly probably an overestimate. An earlier nickel example was also discussed. The authors concluded that errors combined in one direction could inflate estimates by an order of magnitude, and they urged caution.

  PubMed has no abstract for this study, and the article doesn't print one. We wrote this summary from the full article with the help of AI. It is not the authors' wording.

• Clinico-pathological features and somatic gene alterations in refractory ceramic fibre-induced murine mesothelioma reveal mineral fibre-induced mesothelioma identities. P. Andujar, C. Lecomte, A. Renier, et al. 2007;28(7):1599-605. PubMed · Publisher · Free full text

  Abstract

  Although human malignant mesothelioma (HMM) is mainly caused by asbestos exposure, refractory ceramic fibres (RCFs) have been classified as possibly carcinogenic to humans on the basis of their biological effects in rodents' lung and pleura and in cultured cells. Hence, further investigations are needed to clarify the mechanism of fibre-induced carcinogenicity and to prevent use of harmful particles. In a previous study, mesotheliomas were found in hemizygous Nf2 (Nf2(+/-)) mice exposed to asbestos fibres, and showed similar alterations in genes at the Ink4 locus and in Trp53 as described in HMM. Here we found that Nf2(+/-) mice developed mesotheliomas after intra-peritoneal inoculation of a RCF sample (RCF1). Clinical features in exposed mice were similar to those observed in HMM, showing association between ascite and mesothelioma. Early passages of 12 mesothelioma cell cultures from ascites developed in RCF1-exposed Nf2(+/-) mice demonstrated frequent inactivation by deletion of genes at the Ink4 locus, and low rate of Trp53 point and insertion mutations. Nf2 gene was inactivated in all cultures. In most cases, co-inactivation of genes at the Ink4 locus and Nf2 was found and, at a lower rate, of Trp53 and Nf2. These results are the first to identify mutations in RCF-induced mesothelioma. They suggest that nf2 mutation is complementary of p15(Ink4b), p16(Ink4a) and p19(Arf) or p53 mutations and show similar profile of gene alterations resulting from exposure to ceramic or asbestos fibres in Nf2(+/-) mice, also consistent with the one found in HMM. These somatic genetic changes define different pathways of mesothelial cell transformation.

• Potential role of ferritin heavy chain in oxidative stress and apoptosis in human mesothelial and mesothelioma cells: implications for asbestos-induced oncogenesis. W. Aung, S. Hasegawa, T. Furukawa, et al. 2007;28(9):2047-52. PubMed · Publisher

  Abstract

  Exposure to asbestos is a known etiological factor in malignant mesothelioma (MM). However, in vitro cell culture studies have provided paradoxical evidence that asbestos exposure to mesothelial cells causes cytotoxicity or apoptosis rather than malignant transformation. Although it has been shown that the iron associated with asbestos participates in the cell toxicity and probably MM pathogenesis via generation of reactive oxygen species (ROS), the molecular mechanisms largely remain unknown. Here, we demonstrate that ferritin heavy chain (FHC), a core subunit of iron-binding protein ferritin, works as an anti-apoptotic protein against toxic asbestos and oxidative stress in human mesothelial cells and MM cells. We found that FHC was induced in asbestos-exposed MeT-5A human mesothelial cells. The mesothelial cell line stably expressing FHC generated less amount of hydrogen peroxide (H2O2), one of the main ROS, after asbestos exposure and was more resistant to apoptosis induced by H2O2 compared with the cells transfected with the empty vector. Next, we investigated biological roles of FHC in human MM cell. We found that NCI-H2052, a human MM cell line, had a higher expression of endogenous FHC than MeT-5A and used the cell to address FHC function in MM. NCI-H2052 showed reduced H2O2 production and an apoptosis-resistant phenotype compared with MeT-5A. Suppression of the over-expressed FHC by using FHC small interfering RNA rendered the MM cells sensitive to apoptosis, suggesting the contribution of FHC to apoptosis resistance of the MM cells. Our findings highlight the potential role of FHC in the pathogenesis of asbestos-induced mesothelioma.

• Alterations of the p16(INK4) locus in human malignant mesothelial tumors. T. Hirao, R. Bueno, C.J. Chen, et al. 2002;23(7):1127-30. PubMed · Publisher

  Abstract

  The INK4 locus has two promoters and encodes two unique proteins that share exons in different reading frames, p16(INK4a) and p14(ARF). The p16(INK4a) protein, by inhibiting cyclin-dependent kinase, down regulates Rb-E2F and leads to cell cycle arrest in the G1 phase. The p14(ARF) protein interacts with the MDM2 protein, neutralizing MDM2-mediated degradation of p53. Since p53/Rb genes are not altered in malignant mesothelioma, additional components of these pathways, such as p16(INK4a) and p14(ARF), are candidates for inactivation. In this study, we have examined p16(INK4a) and p14(ARF) alterations (gene deletion, mutation and promoter methylation) in 45 primary malignant mesothelioma specimens. Fourteen patients (31%) had altered p16; four tumors had a methylated promoter region (8.8%), 10 tumors showed p16 to be deleted (22.2%), and one tumor had a point mutation (2%). We did not find any instances of methylation in the p14(ARF) 5'-CpG island. Patients whose tumors had p16 deletion were significantly younger than those with methylation, and, in the patients whose lungs were studied for the prevalence of asbestos fibers, those with any p16 alteration had lower fiber counts than those with no p16 alteration. Hence, p16 gene alteration is relatively common in malignant mesothelioma, while p14(ARF) is rarely, if ever, methylated. Our data suggest that deletion of p16 occurs in a relatively susceptible subset of the population.

• Inhibitor of apoptosis protein-1 promotes tumor cell survival in mesothelioma. G.J. Gordon, K. Appasani, J.P. Parcells, et al. 2002;23(6):1017-24. PubMed · Publisher

  Abstract

  Malignant pleural mesothelioma (MPM) is a highly lethal pleural neoplasm that is often resistant to chemotherapeutic drugs, including cisplatin, and for which little is known regarding carcinogenic pathways. We used differential display to compare gene expression patterns in mesothelioma, normal pleura and normal lung, in order to better understand MPM pathobiology, and to search for genes that may facilitate drug resistance in this cancer. The human inhibitor of apoptosis protein-1 gene (IAP-1/MIHC/cIAP2) was discovered to be highly expressed in MPM. We confirmed overexpression of IAP-1 mRNA and protein in 39 additional human MPM tumor specimens and 3/5 (60%) MPM cell lines by multiple methods, including real time quantitative reverse transcription-PCR and western blot analysis. Using an antisense targeting approach, we found that attenuation of IAP-1 mRNA levels decreases baseline cell viability and increases the sensitivity of MPM cell lines to cisplatin by nearly 20-fold. Reduced IAP-1 gene expression also results in a concordant increase of the pro-apoptotic cleavage product of caspase 9 and a reduction in the number of viable tumor cells. Our observations strongly suggest that IAP-1 is at least partly responsible for promoting carcinogenesis and mediating resistance to cisplatin in many MPM tumors and that further study of this apoptotic pathway is warranted.

• 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. H.N. Kim, Y. Morimoto, T. Tsuda, et al. 2001;22(2):265-9. PubMed · Publisher

  Abstract

  We examined 8-hydroxyguanine (8-OH-Gua) formation and 8-OH-Gua repair enzyme activity in pulmonary type-II-like epithelial cells to determine whether oxidative stress induced by asbestos plays a role in its carcinogenic mechanism. A549 cells were incubated with crocidolite asbestos at concentrations of 0, 10, 50 and 100 microg/ml over 27 h. We then evaluated 8-OH-Gua formation, 8-OH-Gua repair enzyme activity and gene expression of 8-oxoguanine-DNA glycosylase 1 (hOGG1) and human MUtT homologue (hMTH1). This was done using a high-performance liquid chromatography system equipped with an electrochemical detector, endonuclease nicking assay and reverse transcription polymerase chain reaction, respectively. Crocidolite induced the formation of 8-OH-Gua in DNA at concentrations of 50 and 100 microg/ml. 8-OH-Gua levels increased at 9 h and had declined to near baseline at 27 h, whereas 8-OH-Gua repair enzyme activity peaked at 18 h post-crocidolite exposure. hOGG1 and hMTH1 mRNA levels were also increased by crocidolite exposure. These data suggest that crocidolite asbestos is associated with epithelial cell injury in the process of carcinogenesis through oxidative stress.

• Differentially expressed genes in asbestos-induced tumorigenic human bronchial epithelial cells: implication for mechanism. Y.L. Zhao, C.Q. Piao, L.J. Wu, et al. 2000;21(11):2005-10. PubMed · Publisher

  Abstract

  Although exposure to asbestos fibers is associated with the development of lung cancer, the underlying mechanism(s) remains unclear. Using human papillomavirus-immortalized human bronchial epithelial (BEP2D) cells, we previously showed that UICC chrysotiles can malignantly transform these cells in a stepwise fashion before they become tumorigenic in nude mice. In the present study we used cDNA expression arrays to screen differentially expressed genes among the tumorigenic cells. A total of 15 genes were identified, 11 of which were further confirmed by northern blot. Expression levels of these genes were then determined among transformed BEP2D cells at different stages of the neoplastic process, including non-tumorigenic cells that were resistant to serum-induced terminal differentiation, early and late passage transformed BEP2D cells, five representative tumor cell lines and fused tumorigenic-control cell lines which were no longer tumorigenic. A consistent 2- to 3-fold down-regulation of the DCC (deleted in colon cancer), Ku70 and heat shock protein 27 genes were detected in all the independently generated tumor cell lines while expression levels in early transformants as well as in the fusion cell lines remained normal. In contrast, all the tumor cell lines examined demonstrated 2- to 4-fold overexpression of the insulin receptor and its signal transduction genes. Differential expression of these genes was completely restored in the fusion cell lines examined. No alteration in c-jun or EGF receptor expression was found in any of the cell lines. Our data suggest that activation of the insulin receptor pathway and inactivation of DCC and Ku70 may cooperate in malignant transformation of BEP2D cells induced by asbestos.

• Increased expression of epidermal growth factor receptor in rat pleural mesothelial cells correlates with carcinogenicity of mineral fibres. S.P. Faux, C.E. Houghton, A. Hubbard, et al. 2000;21(12):2275-80. PubMed · Publisher

  Abstract

  Asbestos fibres have been shown to stimulate the mitogen-activated protein kinase signalling cascade in rat pleural mesothelial (RPM) cells after autophosphorylation of the epidermal growth factor receptor (EGFR). We examined if mineral fibres with known carcinogenicity can be discriminated from materials with less or no carcinogenicity by their ability to up-regulate expression of EGFR protein in RPM cells in vitro. Crocidolite and erionite, two fibrous preparations with marked potential to induce mesothelioma, were associated with increases in EGFR protein expression over sham controls, whereas chrysotile asbestos and milled (non-fibrous) crocidolite did not. Intense patterns of EGFR protein expression were linked to RPM cells phagocytosing long fibres. To determine the role of EGFR expression in these cells, we assessed cell proliferation using an antibody against proliferating cell nuclear antigen (PCNA) in combination with an antibody against EGFR. In these co-localization studies, cells showed intense staining for EGFR protein 24 h before being PCNA positive at 48 h. These results suggest that carcinogenic fibres induce EGFR and initiate cell signalling cascades in mesothelial cells, leading to cell proliferation and carcinogenesis.

• mRNA expression patterns in different stages of asbestos-induced carcinogenesis in rats. H. Sandhu, W. Dehnen, M. Roller, et al. 2000;21(5):1023-9. PubMed · Publisher

  Abstract

  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.

1990s

• Asbestos induction of extended lifespan in normal human mesothelial cells: interindividual susceptibility and SV40 T antigen. L. Xu, B.J. Flynn, S. Ungar, et al. 1999;20(5):773-83. PubMed · Publisher

  Abstract

  Normal human mesothelial cells from individual donors were studied for susceptibility to asbestos-induction of apoptosis and generation of an extended lifespan population. Such populations were generated after death of the majority of cells and arose from a subset of mesothelial cultures (4/16) whereas fibroblastic cells (5/5) did not develop extended lifespan populations after asbestos exposure. All mesothelial cultures were examined for the presence of SV40 T antigen to obtain information on (i) the presence of SV40 T antigen expression in normal human mesothelial cells and (ii) the relationship between generation of an extended lifespan population and expression of SV40 T antigen. Immunostaining for SV40 T antigen was positive in 2/38 normal human mesothelial cultures. These cultures also had elevated p53 expression. However, the two isolates expressing SV40 T antigen did not exhibit enhanced proliferative potential or develop an extended lifespan population. Asbestos-generated extended lifespan populations were specifically resistant to asbestos-mediated but not to alpha-Fas-induced apoptosis. Deletion of p16Ink4a was shown in 70% of tumor samples. All mesothelioma cell lines examined showed homozygous deletion of this locus which extended to exon 1beta. Extended lifespan cultures were examined for expression of p16Ink4a to establish whether deletion was an early response to asbestos exposure. During their rapid growth phase, extended lifespan cultures showed decreased expression of p16Ink4a relative to untreated cultures, but methylation was not observed, and p16Ink4a expression became elevated when cells entered culture crisis. These data extend the earlier observation that asbestos can generate extended lifespan populations, providing data on frequency and cell type specificity. In addition, this report shows that generation of such populations does not require expression of SV40 T antigen. Extended lifespan cells could represent a population expressing early changes critical for mesothelioma development. Further study of these populations could identify such changes.

• Environmental factors as regulators and effectors of multistep carcinogenesis. T. Minamoto, M. Mai, Z. Ronai. 1999;20(4):519-27. Review PubMed · Publisher

  Abstract

  This review highlights current knowledge of environmental factors in carcinogenesis and their cellular targets. The hypothesis that environmental factors influence carcinogenesis is widely supported by both epidemiological and experimental studies. The fact that only a small fraction of cancers can be attributed to germline mutations in cancer-related genes further buttresses the importance of environmental factors in carcinogenesis. Furthermore, penetrance of germline mutations may be modified by either environmental or other genetic factors. Examples of environmental factors that have been associated with increased cancer risk in the human population include chemical and physical mutagens (e.g. cigarette smoke, heterocyclic amines, asbestos and UV irradiation), infection by certain viral or bacterial pathogens, and dietary non-genotoxic constituents (e.g. macro- and micronutrients). Among molecular targets of environmental influences on carcinogenesis are somatic mutation (genetic change) and aberrant DNA methylation (epigenetic change) at the genomic level and post-translational modifications at the protein level. At both levels, changes elicited affect either the stability or the activity of key regulatory proteins, including oncoproteins and tumor suppressor proteins. Together, via multiple genetic and epigenetic lesions, environmental factors modulate important changes in the pathway of cellular carcinogenesis.

• Patterns of 8-hydroxydeoxyguanosine formation in DNA and indications of oxidative stress in rat and human pleural mesothelial cells after exposure to crocidolite asbestos. H. Fung, Y.W. Kow, B. Van Houten, et al. 1997;18(4):825-32. PubMed · Publisher

  Abstract

  Oxidative damage is a proposed mechanism of asbestos-induced carcinogenesis, but the detection of oxidative DNA lesions in target cells of asbestos-induced mesothelioma has not been examined. In studies here, DNA was isolated from both rat pleural mesothelial (RPM) cells and a human mesothelial cell line (MET5A) after exposure in vitro to crocidolite asbestos at various concentrations. DNA was then examined for formation of 8-hydroxydeoxyguanosine (8-OHdG) at 24, 48 and 72 h using HPLC with electrochemical detection. In addition, steady-state mRNA levels of manganese-containing superoxide dismutase (MnSOD) were assessed as an indication of oxidative stress. Whereas RPM cells showed dose-dependent and significant increases in 8-OHdG formation in response to crocidolite asbestos or iron-chelated crocidolite fibers (but not after exposure to glass beads), MET5A cells showed decreases in 8-OHdG. Both cell types exhibited elevations in message levels of MnSOD. In comparison with human MET5A cells, RPM cells exhibited increased cytotoxicity and apoptosis in response to asbestos, as documented by cell viability assays and flow cytometry analysis using propidium iodide. Results in RPM cells indicate that asbestos causes oxidative damage that may result in potentially mutagenic lesions in DNA and/or apoptosis, despite compensatory increases in expression of an antioxidant enzyme.

• Asbestos promotes morphological transformation and elevates expression of a gene family invariably induced by tumor promoters in C3H/10T1/2 cells. C.L. Parfett, R. Pilon, A.A. Caldeira. 1996;17(12):2719-26. PubMed · Publisher

  Abstract

  The murine proliferin gene family, which has been shown to respond consistently to tumor promoters and other cellular pro-oxidant agents in C3H/10T1/2 cells, was used to monitor responses after treatment of these cell cultures with toxic, pro-oxidant asbestos fibres. Proliferin mRNA levels were increased by amosite, crocidolite or chrysotile asbestos fibres, especially in the presence of fresh serum and at low cell densities. Promotion of morphological transformation was confirmed in two-stage focus formation assays using crocidolite at a fibre density that induced proliferin expression. Asbestos-induced gene expression was inhibited by millimolar levels of N-acetylcysteine (NAC), supporting a linkage between: (i) induced oxidant stress that was sufficient to promote morphological transformation; (ii) induction of proliferin expression. Other anti-oxidant compounds (dithiothreitol and pyrrolidine dithiocarbamate) or enzymes (superoxide dismutase and catalase) did not inhibit induced expression. Non-fibrous powders (titanium dioxide, quartz or silica gel) were also effective inducers of proliferin mRNA accumulation. Latex beads and activated charcoal were effective at higher particle densities, implying that ubiquitous particle-induced surface membrane effects can lead to an NAC-reversible step necessary for proliferin induction. The results showed that asbestos resembled all other promoters of morphological transformation in C3H/10T1/2 cells in that an antioxidant-sensitive induction of the proliferin gene family occurred following treatment.

• Detection of 8-oxo-2'-deoxyguanosine, a marker of oxidative DNA damage, in culture medium from human mesothelial cells exposed to crocidolite asbestos. Q. Chen, J. Marsh, B. Ames, et al. 1996;17(11):2525-7. PubMed · Publisher

  Abstract

  Crocidolite asbestos is associated with the development of mesothelioma. Although chromosomal changes have been documented in mesothelial cells, the mechanisms of interaction of crocidolite with DNA remain obscure. Since human mesothelial cells are exquisitely sensitive to asbestos, oxidative DNA damage was measured in an asbestos-exposed human mesothelial cell line (MET5A) by assaying oxidized guanine bases [8-oxo-2'-deoxyguanosine (oxo8dG), 8-oxoguanine (oxo8G), and 8-oxoguanosine (oxo8Gua)] excreted into the spent culture medium after DNA repair or turnover. At growth inhibitory, but not cytolytic concentrations, asbestos caused significant elevation of all bases in the spent medium over a 48-h period. In contrast, riebeckite, a chemically similar, nonfibrous analog of crocidolite did not cause increased adduct release. Results show that oxidative RNA and DNA bases are produced in response to asbestos in target cells of asbestos-induced cancers.

• Determination of 8-hydroxydeoxyguanosine in human cells under oxygen-free conditions. M. Nakajima, T. Takeuchi, K. Morimoto. 1996;17(4):787-91. PubMed · Publisher

  Abstract

  To establish an accurate 8-hydroxydeoxyguanosine (8OHdG) determination system, we examined two potential factors causing experimental error in 8OHdG determination. First, we examined the efficiency of the enzymatic digestion of DNA, that could cause misestimation of 8OHdG. Second, since we considered that the oxygen molecules in atmosphere and in reagents were the main factor contributing to the experimental errors, we carried out the 8OHdG determination under oxygen-free conditions and compared the 8OHdG value with that determined by the methods under ambient atmosphere. The calf thymus DNA was sufficiently digested in the condition we used and the yields of dG were constant, even when the DNA was damaged with H2O2 (80 mM) and UV irradiation. By carrying out the DNA extraction manually, instead of using the DNA extractor, we could reduce the additional 8OHdG formation during sample processing. No trend was found in the difference between the 8OHdG values determined under oxygen-free conditions and under ambient atmosphere. However, when the 8OHdG values were compared in samples with asbestos, the value determined under oxygen-free conditions was significantly lower than that determined under ambient atmosphere. These findings suggest that the removal of oxygen molecules was effective in reducing accidental ROS generation by impurities in the sample, which could cause the additional 8OHdG formation, and that the oxygen-free system made the determination of 8OHdG reproducible and more accurate than before. When the oxygen-free system was applied to human leukocytes, the system showed good reproducibility (r = 0.535, P < 0.001), even though the 8OHdG level was low. With the system, we could detect a significant difference between 8OHdG in polymorphonuclear leukocytes (0.241 +/- 0.129) and mononuclear leukocytes (0.188 +/- 0.126, P < 0.01).

• Fibre-induced lipid peroxidation leads to DNA adduct formation in Salmonella typhimurium TA104 and rat lung fibroblasts. P.J. Howden, S.P. Faux. 1996;17(3):413-9. PubMed · Publisher

  Abstract

  Certain end-products of lipid peroxidation bind to DNA forming a fluorescent chromophore. Incubation of both Salmonella typhimurium TA104 and a rat lung fibroblast cell line, RFL-6, with various types of mineral fibre resulted in a time- and dose-dependent increase in DNA fluorescence. The increase in DNA fluorescence was shown to be directly related to the amount of iron that could be mobilized from the fibre surface using in vitro studies in the absence of cells or bacteria. Crocidolite and man-made vitreous fibre-21 (MMVF-21) mobilized significant quantities of iron and were significantly more active than chrysotile and refactory ceramic fibre-1 (RCF-1). Fibre-induced malondialdehyde-DNA adduct formation, the fluorescent product, was increased by incubating cells with buthionine sulfoximine and ameliorated by co-treatment with N-acetylcysteine, indicating a protective role for glutathione. Similarly, vitamin E was also shown to inhibit DNA adduct formation. These results suggest that mineral fibre-induced lipid peroxidation produced genotoxic products which can diffuse into nucleus and interact with cellular DNA. In conclusion, fibre-induced lipid peroxidation may be a possible mechanism in the genotoxic action of fibrous materials.

• Glutathione modulates the formation of 8-hydroxydeoxyguanosine in isolated DNA and mutagenicity in Salmonella typhimurium TA100 induced by mineral fibres. P.J. Howden, S.P. Faux. 1996;17(10):2275-7. PubMed · Publisher

  Abstract

  Treatment of isolated DNA with crocidolite and man-made vitreous fibre-21 (MMVF-21) significantly increased the concentration of 8-hydroxydeoxyguanosine (8-OHdG) in isolated DNA above background levels and co-treatment with glutathione (GSH) eliminated this effect. Crocidolite, MMVF-21 and chrysotile fibres increased the number of revertants in Salmonella typhimurium TA100 and GSH-deficient strains, TA100/NG-54 and TA100/NG-57, over background levels. This increase was small in TA100 but was greater in the GSH-deficient strains. When these bacterial strains were further depleted of GSH by co-culture with buthionine sulfoximine, all fibres tested caused a significant increase in the number of revertants over the parent strains. Pre-treatment with the GSH precursor N-acetyl-L-cysteine reduced the number of revertants to below that of the parent strain. Previous studies have shown a mechanistic role for iron-catalyzed production of oxygen radicals in the mutagenicity of fibres and this study suggests a protective role for GSH against such oxidative damage possibly by acting as a radical scavenger.

• Induction of heme oxygenase in mammalian cells by mineral fibers: distinctive effect of reactive oxygen species. K. Suzuki, T.K. Hei. 1996;17(4):661-7. PubMed · Publisher

  Abstract

  Exponentially growing human-hamster hybrid [AL] cells treated with a 40 micrograms/ml (8 micrograms/cm2) dose of UICC standard reference chrysotile fibers induced heme oxygenase (HO) protein with a maximum expression level at 8 h post-treatment. While the constitutive HO expression was detectable in non-treated AL cells, the protein level was increased approximately 4.5-fold in fiber-treated cells. The induction was dose-dependent at fiber concentration between 2.5 micrograms/ml (0.5 microgram/cm2) and 40 micrograms/ml (8 micrograms/cm2) with the induced HO concentrated mostly in the cytoplasm as shown by immunostaining. Several other types of mineral fibers examined including crocidolites, tremolites, and erionites also induced HO synthesis with varying degree of efficiency. In general, chrysotile and crocidolite were more efficient inducers of HO than tremolite and erionite when compared at fiber doses that resulted in approximately 50% survival (LD50) level. The effects of antioxidant enzymes on HO induction were examined by concurrent treatment of fiber-exposed cultures with SOD and catalase. Although addition of superoxide dismutase (SOD) and catalase inhibited HO induction in a dose-dependent manner, they offered no protection on fiber-mediated clonogenic toxicity in the same population of treated cells. These results suggest that reactive oxygen species (ROS) produced by asbestos fibers play an essential role in the induction of HO and that different mineral fibers, when applied at equitoxic doses, often result in different oxidative stress status as determined by the induction of HO proteins.

• Long crocidolite asbestos fibers cause polyploidy by sterically blocking cytokinesis. C.G. Jensen, L.C. Jensen, C.L. Rieder, et al. 1996;17(9):2013-21. PubMed · Publisher

  Abstract

  Asbestos has been described as a physical carcinogen in that its carcinogenic effects appear to be related primarily to fiber dimensions. It has been hypothesized that long asbestos fibers may interfere with chromosome distribution during cell division, causing genomic changes that lead to cell transformation and neoplastic progression. Using high-resolution time-lapse light microscopy and serial-section electron microscopy, we have followed individual crocidolite asbestos fibers through the later stages of cell division in LLC-MK2 epithelial cells, and have detailed for the first time their effect on cytokinesis. We found that long fibers (15-55 microgram), trapped by the cleavage furrow, sterically blocked cytokinesis, sometimes resulting in the formation of a binucleated cell. The ends of blocking fibers were usually found within invaginations of the newly formed nuclei. Nuclear envelope-fiber attachment was evident when a chromatin strand ran with the fiber into the intercellular bridge. Such strands may break, causing chromosome structural rearrangements. Our data are the first to show that individual crocidolite fibers can cause genomic changes by sterically blocking cytokinesis and that fiber length and affinity for the nuclear envelope are important factors. Such genomic changes may be among the initial events leading to asbestos-induced cancers.

• Detection of surface free radical activity of respirable industrial fibres using supercoiled phi X174 RF1 plasmid DNA. P.S. Gilmour, P.H. Beswick, D.M. Brown, et al. 1995;16(12):2973-9. PubMed · Publisher

  Abstract

  The ability of a number of respirable industrial fibres, amosite and crocidolite asbestos, refractory ceramic fibres (RCFs) and man-made vitreous fibres (MMVFs) to cause free radical injury to plasmid phi X174 RFI DNA was assessed. The oxidative DNA damage was observed as depletion of supercoiled DNA after fibre treatment was quantified by scanning laser densitometry. The mechanism of fibre-mediated damage was determined by the use of the specific hydroxyl radical scavenger mannitol and the iron chelator desferrioxamine-B. The amosite and crocidolite asbestos caused substantial damage to DNA that was dose-related. The free radicals responsible for the asbestos-mediated DNA damage were hydroxyl radicals, as determined by inhibition with mannitol. Asbestos fibre-mediated damage to DNA was completely ameliorated by the chelation of fibre-associated iron with desferrioxamine-B. The amount of Fe(II) and Fe(III) released by equal numbers of the different fibre types at equal fibre number was determined. The fibres released very small amounts of Fe(II) and there were no significant differences between the fibre types. The fibres released substantial amounts of Fe(III); MMVF 21 released significantly more Fe(III) than any of the other fibres and short fibre amosite also released more Fe(III) than three of the MMVFs and two of the RCFs. When ability to release Fe(II) and Fe(III) was compared with ability to cause DNA damage there was not a good correlation, because only the long amosite and crocidolite caused substantial free radical injury to DNA; this contrasts with MMVF 21 and short amosite being the two fibres that released the greatest amounts of iron. The loss of ability to damage DNA in DSF-B-treated asbestos fibres shows that iron at the surface of asbestos fibres definitely has a role in generating hydroxyl radicals. However, it is clear that some fibres, such as short amosite and MMVF 21, release large quantities of iron without causing free radical damage, whilst neither long amosite nor crocidolite released more iron than the other fibres. The exact role of iron in fibre reactivity therefore remains unresolved, but fibre-bound iron not released from the surface of asbestos could be important. Further research is under way to investigate this possibility.

• Effects of antioxidants on fiber mutagenesis. T.K. Hei, Z.Y. He, K. Suzuki. 1995;16(7):1573-8. PubMed · Publisher

  Abstract

  Recent studies from this laboratory have shown that asbestos fibers are mutagenic in cultured mammalian cells when assayed using a system that can detect multilocus deletions. Southern analysis of the induced mutants shows that the majority contain large deletions ranging in size from a few thousand to several million basepairs. In the present study, the effects of free radical scavenging enzymes on the cytotoxic and mutagenic potential of chrysotile fibers were examined using the human-hamster hybrid (AL) cells. Exponentially growing cells were treated with graded doses of fibers for a 24 h period either in the presence or absence of catalase, superoxide dismutase (SOD) or Tempol. Fiber-exposed cells were treated with the various enzymes either concurrently with the fiber or extended through the entire expression period. While the survival of AL cells treated with graded doses of chrysotile fibers with or without a concurrent treatment with SOD and catalase was not significantly different, the mutation yield at the S1 locus was significantly reduced in cells treated with these antioxidant enzymes. Furthermore, cells treated with the enzymes for a prolonged period were not better protected than those treated only during fiber treatment. The SOD mimic nitroxide, Tempol, had no effect on either the survival or mutagenic yield of chrysotile fibers. While SOD and catalase reduced the mutagenic potency of asbestos fibers in AL cells, they did not alter the molecular spectrum of fiber-induced mutagenesis. Our results indicate that antioxidant enzymes can protect cells against the genotoxic damages induced by chrysotile fibers, and are highly suggestive of the roles of oxyradicals in the fibrogenic and carcinogenic mechanisms of asbestos fibers.

• Gender comparisons in human lung cancer: analysis of p53 mutations, anti-p53 serum antibodies and C-erbB-2 expression. D.G. Guinee, W.D. Travis, G.E. Trivers, et al. 1995;16(5):993-1002. PubMed · Publisher

  Abstract

  Little is known about the molecular mechanisms of lung carcinogenesis in women. We initiated an investigation of the role of gender in pulmonary carcinogenesis by analysis of p53 mutations, immunohistochemistry, serum antibodies and c-erbB-2 expression in a series of 63 male and 44 female lung cancer patients whose tumors were resected at the Mayo Clinic between 1991 and 1992. There were 102 smokers and 5 never smoked. Adenocarcinoma was the more frequent histological type in women (62%) than in men (41%). Sequence analysis of exons 5-8 in 42 females and 49 males identified 44 p53 mutations in 42 tumors (46%). Base substitution mutations showed a preponderance of G:C-->T:A transversions, which were more frequent in women than men (40 versus 25%) and in individuals exposed to asbestos. c-erbB-2 immunohistochemical staining was identified more frequently in females (nine cases) than males (two cases). Marked immunohistochemical staining for p53 positively correlated with the presence of missense mutations in exons 5-8 (81%, P < 0.001). Seven missense mutations (four in exon 5, two in exon 6, one in exon 8) were identified in five of nine patients who had serum antibodies recognizing p53; tumors from these patients were also strongly positive for p53 by immunohistochemistry. These and other results indicate gender differences in the genetic and biochemical alterations in lung cancer and generate hypothesis regarding gender differences in lung cancer susceptibility.

• Role of fibre characteristics on cytotoxicity and induction of anaphase/telophase aberrations in rat pleural mesothelial cells in vitro: correlations with in vivo animal findings. M. Yegles, X. Janson, H.Y. Dong, et al. 1995;16(11):2751-8. PubMed · Publisher

  Abstract

  Thirteen samples of natural fibres and five samples of man-made fibres (MMF) were tested to determine their cytotoxicity and ability to produce chromosome missegregation in cultures in rat pleural mesothelial cells (RPMC). The natural samples included attapulgite, two amphiboles (amosite and crocidolite); seven consisted of chrysotile from various origins and three were obtained after chemical treatment of chrysotile. MMF included three refractory ceramic fibres (RCF) and two vitreous fibres (MMVF). All fibre samples were characterized by electron microscopic measurement of the fibre dimensions. Cytotoxicity was assayed on the basis of determination of mitochondrial integrity and chromosome missegregation by light microscopy examination of anaphases/telophases. The carcinogenic potency of 10 natural samples has been previously investigated using intrapleural inoculation in rats. It was therefore possible to establish correlations between in vitro and in vivo data obtained with the same set of samples. The various samples of chrysotile produced different in vitro effects, in agreement with the dispersion of response also observed in vivo. Cytotoxicity appears to be dependent on both fibre length and fibre diameter, as the longest or thickest fibres were the most toxic. The production of abnormal anaphases/telophases appears to depend on the presence of fibres of selected size, such as those previously defined by Stanton et al. (L > 8 micrograms; D < or = 0.25 microns); a threshold values was determined below which no abnormal anaphases/telophases were detected. This non-observable effect level was estimated to be 2.5 x 10(5) 'Stanton' fibres per cm2. There was no correlation between cytotoxicity and mesothelioma induction; in contrast, a correlation was found between the ability of a sample to produce chromosome missegregation in vitro and mesothelioma in vivo.

• The effect of iron binding on the ability of crocidolite asbestos to catalyze DNA single-strand breaks. J.A. Hardy, A.E. Aust. 1995;16(2):319-25. PubMed · Publisher

  Abstract

  Crocidolite or crocidolite pretreated with desferrioxamine-B (DF crocidolite) was exposed to ferrous chloride solutions to determine whether iron could be bound from solution. Native crocidolite was capable of binding up to 57 nmol Fe2+/mg fiber in 60 min, while the DF crocidolite was capable of binding only 5.5 nmol Fe2+/mg fiber. The rate of iron binding for the first 5 min of exposure was independent of the concentration of iron in the solution, suggesting that there was a group of rapidly saturable sites, approximately 1.5 x 10(18) binding sites/m2 crocidolite surface, which were responsible for the immediate binding. This process was followed by a slower binding phase, likely occurring at other sites. Crocidolite and DF crocidolite, with various amounts of iron bound, were assayed for their abilities to catalyze the formation of DNA single-strand breaks (SSBs) in phi X174 RFI DNA. Native crocidolite with additional iron bound did not significantly change in its ability to cause DNA SSBs in 15 or 30 min incubations, even though more iron could be mobilized from the iron-treated crocidolite at 4 or 24 h. DF crocidolite, after the addition of iron, had a significantly increased ability to form DNA SSBs. DF crocidolite with 0, 3.0 or 5.5 mmol Fe2+/mg catalyzed the formation of DNA SSBs in 21, 42 or 51% of the DNA respectively in the presence of EDTA and ascorbate. Fibers were also incubated in tissue culture medium with or without iron salts. The fibers incubated in the iron-containing medium had an increased ability to form DNA SSBs. These results suggest that fibers such as crocidolite may be capable of binding iron from intracellular sources. This additional iron may be as reactive as the intrinsic iron and may increase the reactive lifetime of the fiber.

• Crocidolite asbestos increased 8-hydroxydeoxyguanosine levels in cellular DNA of a human promyelocytic leukemia cell line, HL60. T. Takeuchi, K. Morimoto. 1994;15(4):635-9. PubMed · Publisher

  Abstract

  Crocidolite, one of the most carcinogenic asbestos fibers, induces the release of reactive oxygen species (ROS) from neutrophils and macrophages. Using HPLC combined with electrochemical detection, we determined that 8-hydroxydeoxyguanosine (8OHdG), a molecule typical of mutagenic oxidative DNA damage, was induced in the cellular DNA of a human promyelocytic leukemia cell line, HL60, incubated with crocidolite. Crocidolite increased 8OHdG in the cellular DNA of phorbol myristate acetate (PMA)-differentiated HL60, which phagocytosed crocidolite. PMA-differentiated HL60 released ROS spontaneously, as determined by ESR with 5,5-dimethylpyrrolone-N-oxide as a spin trap. However, the release of ROS from the cell line did not increase after the addition of crocidolite. The addition of superoxide dismutase at a sufficient concentration to scavenge ROS released from the cell did not inhibit the 8OHdG increase induced by crocidolite. Cytochalasin B, which inhibited phagocytosis, did not inhibit the release of ROS. However, it inhibited the crocidolite-induced 8OHdG increase by 48.3%. Contrary to PMA-differentiated HL60, undifferentiated HL60 neither phagocytosed crocidolite nor showed a crocidolite-induced increase in 8OHdG formation. The 8OHdG increase induced by crocidolite was not correlated with ROS release, but with the internalization of crocidolite, suggesting that the increase was not due to an increase in ROS release from the cell but was due to the conversion of relatively inert ROS to highly reactive ROS, such as hydroxyl radicals, by crocidolite that was internalized and close to DNA.

• Expression of cell adhesion molecules and connexins in gap junctional intercellular communication deficient human mesothelioma tumour cell lines and communication competent primary mesothelial cells. K. Pelin, A. Hirvonen, K. Linnainmaa. 1994;15(11):2673-5. PubMed · Publisher

  Abstract

  Gap junctional intercellular communication (GJIC) has been reported to be markedly reduced in human mesothelioma tumour cell lines compared with primary mesothelial cells. Immunofluorescence stainings have shown that the gap junction protein connexin43 (Cx43) is expressed in both malignant and normal mesothelial cells. In this study the mRNA expression of Cx43 and three different connexins--Cx37, Cx40 and Cx45, which are highly expressed in lung tissue--was investigated in eight human mesothelioma cell lines, and in human primary mesothelial cells from several donors. The expression of the intercellular adhesion molecules A-CAM (N-cadherin) and L-CAM (E-cadherin) was studied at the protein level. No mRNA expression of Cx37, Cx40 or Cx45 in either mesothelioma tumour cells or the primary mesothelial cells was detected. Cx43 was expressed at both the mRNA and the protein level, in seven out of eight mesothelioma cell lines, as well as in all the primary mesothelial cell cultures. The well as in all the primary mesothelial cell cultures. The intercellular adhesion molecule A-CAM was expressed at the cell-cell borders in six out of seven mesothelioma cell lines, as well as in normal mesothelial cells. No expression of L-CAM was observed in these cells. The results suggest that Cx43 and A-CAM are the major proteins in gap and adherens junctions respectively in human mesothelial cells. Most mesothelioma tumour cell lines with markedly reduced GJIC still express both Cx43 and A-CAM. Only one of our mesothelioma tumour cell lines severely deficient in GJIC lacks both the gap junction protein Cx43 and the cell adhesion molecule A-CAM.

• In vitro cytotoxicity of asbestos and man-made vitreous fibers: roles of fiber length, diameter and composition. G.A. Hart, L.M. Kathman, T.W. Hesterberg. 1994;15(5):971-7. PubMed · Publisher

  Abstract

  The present study investigated (i) the impact of various fiber parameters on in vitro toxicity to cells and (ii) the validity of an in vitro test system as a toxic screen for fibrous materials. Chinese hamster ovary cells were exposed in vitro to a series of size-selected inorganic test fibers that represented a range of different diameters, lengths and compositions (glass, refractory ceramic, mineral wool, asbestos). Toxic end-points included inhibition of proliferation, induction of micronuclei and polynuclei and viability. For all compositions tested, toxic effects were similar: a concentration-dependent decrease in proliferation and increase in incidence of morphologically abnormal nuclei with minor decreases in viability. Diameter-dependent differences in toxicity were slight or absent for fiber diameters ranging from 0.3-7 microns when concentration was expressed as number of fibers/cm2. Length-dependent differences in toxicity were, however, striking. EC50 values (concentration in fibers/cm2 that reduced cell proliferation to 50% of unexposed control cultures) plotted against fiber length produced a hyperbolic curve, demonstrating that toxicity increases with fiber length up to 20 microns. All fibers tested fell on this hyperbola. These data suggest that: (a) the primary toxic effect of fibers on CHO cells is the induction of nuclear morphologic alterations resulting in cytostasis; (b) fiber diameter has little or no impact on in vitro toxicity when concentration is calculated as fibers/cm2; (c) fiber length is directly proportional to in vitro toxicity; and (d) toxicity of asbestos and vitreous fibers to CHO cells is not affected by composition. The lack of compositional effect in CHO cells does not correlate with findings from recent rodent inhalation studies using the same test fibers. Thus CHO cells may not be an appropriate in vitro model of fiber pathogenesis and would not constitute a valid toxicologic screening system for fibers.

• Inductions of oxidative DNA damage and mesothelioma by crocidolite, with special reference to the presence of iron inside and outside of asbestos fiber. S. Adachi, S. Yoshida, K. Kawamura, et al. 1994;15(4):753-8. PubMed · Publisher

  Abstract

  Inductions of oxidative DNA damage (oh8dG) in vitro and peritoneal mesothelioma in rats (F344, female) were compared between crocidolite (CR) and de-ironized crocidolite [DCR, washed by HCl and ethylenediamine tetraacetic acid (EDTA)] to verify the hypothesis that reactive oxygen species contribute to carcinogenesis, focusing on the role of iron present inside or outside of the CR. The yield of oh8dG was 14.6 oh8dG/10(5)dG in CR and 30.2 in DCR under simple incubation with DNA. In the incubation systems added several chemicals and H2O2, DCR induced higher levels of oh8dG than CR. Especially, the addition of Fe2O3 and H2O2 to DCR increased oh8dG in DNA depending on the Fe2O3 concentration, however, this tendency was not observed in the same system of CR. Surprisingly, 7 out of 10 rats died within 2 days after the injection of 10 mg of Fe2O3 following the DCR injection (5 mg/rat), showing necroses of hepatocytes from the surface of each lobe where CR and Fe2O3 particles had been deposited together. There was no death in other groups of rats. One year after the i.p. injection of CR (5 mg/rat, single injection), mesotheliomas were found in all rats administered DCR and Fe2O3 (2 mg/rat, once a week, for 35 weeks), in 4 rats of DCR alone (n = 10), in 5 rats of CR alone (n = 10) and in none of the rats administered Fe2O3 alone (n = 10). Therefore, present results indicate that the induction of oxidative DNA damage changed even when the same type of asbestos was washed by chemical treatment, and Fe2O3 promoted the development of mesothelioma which was induced by DCR.

• Iron-dependent formation of 8-hydroxydeoxyguanosine in isolated DNA and mutagenicity in Salmonella typhimurium TA102 induced by crocidolite. S.P. Faux, P.J. Howden, L.S. Levy. 1994;15(8):1749-51. PubMed · Publisher

  Abstract

  Treatment of isolated DNA with crocidolite asbestos significantly increased the concentration of 8-hydroxydeoxyguanosine (8-OHdG) above background. Furthermore, incubating DNA with H2O2 and crocidolite potentiated the formation of 8-OHdG above levels observed with crocidolite alone. In the presence of desferrioxamine, desferrioxamine and ferrozine, dimethylsulphoxide (DMSO) or o-phenanthroline, crocidolite-induced DNA oxidation was reduced by 36, 73, 74 and 70% respectively. Crocidolite, but not chrysotile asbestos, enhanced background revertants in Salmonella typhimurium TA102, at sub-cytotoxic concentrations in a dose-dependent manner. The mutagenic effects of crocidolite were quite small and this indicates that crocidolite was a weak mutagen in this study. The number of revertants was reduced to the spontaneous rate for this strain after the fibres had been pretreated with desferrioxamine before assaying for genotoxicity in this oxygen radical-sensitive strain. These results help to explain a mechanistic role for iron in crocidolite-induced DNA oxidation and mutagenicity in TA102.

• Role of oxygen derivatives in the cytotoxicity and DNA damage produced by asbestos on rat pleural mesothelial cells in vitro. H. Dong, A. Buard, A. Renier, et al. 1994;15(6):1251-5. PubMed · Publisher

  Abstract

  The role of reactive oxygen metabolites in the toxic effects of asbestos on pleural mesothelial cells is not well defined. We exposed rat pleural mesothelial cells (RPMC) to chrysotile and crocidolite fibers (0-40 micrograms/cm2) in the presence or absence of catalase and superoxide dismutase (SOD). Cell injury was measured using the colorimetric 3-4 (5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay and DNA damage was evaluated in terms of unscheduled DNA synthesis (UDS). Catalase (100 U/ml) and SOD (250 U/ml) protected RPMC against asbestos-induced cytotoxicity and DNA damage. However, the inactivated enzymes and bovine serum albumin also showed some protection, suggesting that the effect of antioxidant enzymes may be partly related to their protein nature. These results suggest that oxygen derivatives are partly involved in the toxic effects of asbestos on cultures of RPMC. The presence of extracellular proteins may also decrease asbestos-produced toxicity by reducing the degree of RPMC-fiber interaction.

• A reappraisal of the carcinogenicity of surface modified asbestos fibres. P. Carthew, R.E. Edwards, B.M. Dorman, et al. 1993;14(11):2413-4. PubMed · Publisher

  Abstract

  A previous study using intrapleural administration of surface-modified amosite asbestos showed a difference in the number of pleural mesotheliomas induced with C18-hydrocarbon derivatised fibres compared to native amosite asbestos. The study has been repeated with larger groups of animals (30) under specific pathogen free conditions, resulting in an increase in the mean animal survival time for both fibre-treated groups. Under these conditions there was no significant difference between the numbers of pleural mesotheliomas induced by C18 hydrocarbon-modified amosite asbestos and native amosite asbestos. The major difference between the two studies was the mean time to death from tumour of rats exposed to fibres. The C18 amosite treated rats in the first study may not have had a mean survival time long enough to allow mesotheliomas to develop.

• Cytotoxic and cytogenetic effects of asbestos on human bronchial epithelial cells in culture. Y. Kodama, C.J. Boreiko, S.C. Maness, et al. 1993;14(4):691-7. PubMed · Publisher

  Abstract

  Asbestos and other mineral fibers elicit responses in several rodent cell transformation systems. The mechanism of this transformation has been hypothesized to involve specific chromosome alterations, especially changes in chromosome number. However, the cytogenetic effects of asbestos fibers in cultured human respiratory epithelium have not been well characterized. The present study examined the effects of chrysotile and crocidolite asbestos fibers on cultures of human bronchial epithelial (HBE) cells growing in serum-free medium. HBE cells were continuously treated with chrysotile (0-4 micrograms/cm2) or crocidolite (0-300 micrograms/cm2) asbestos and examined after 24, 48, 72 or 96 h for cytotoxic and cytogenetic effects. Both asbestos fiber types induced a concentration-dependent inhibition of cell proliferation and colony-forming efficiency; however, in these assays chrysotile was 100-300 times more toxic than crocidolite. Concentrations of asbestos that inhibited growth had little effect upon trypan blue exclusion or intracellular esterase activity, suggesting that the majority of asbestos-exposed cells were still viable. A 2.7-fold increase in binuclei and a 1.6-fold increase in micronuclei were observed 72 h after treatment with 4 micrograms/cm2 chrysotile. A 1.9-fold increase in binuclei was observed 72 h after treatment with 300 micrograms/cm2 crocidolite, but crocidolite did not increase the incidence of micronuclei. Chrysotile asbestos failed to induce significant numerical chromosome changes in HBE cells and increased structural aberrations only at the 24 h time point. These findings contrast with the relatively high incidences of asbestos-induced chromosome changes previously observed in some rodent cell cultures and suggest the existence of species-specific or cell-type-specific differences in either chromosome stability or mechanism(s) of asbestos-induced toxicity.

• Gap junctional intercellular communication of primary and asbestos-associated malignant human mesothelial cells. K. Linnainmaa, K. Pelin, E. Vanhala, et al. 1993;14(8):1597-602. PubMed · Publisher

  Abstract

  We examined gap junctional intercellular communication (GJIC) of primary human mesothelial cells and cell lines of asbestos-associated human pleural mesotheliomas, and the effect of asbestos and other mineral fibres on these cells. In homologous cultures, the GJIC capacity of six out of seven tumour cell lines was markedly less than for primary mesothelial cells. This defect in GJIC appeared not to be at the expression level of mRNA and protein of the gene encoding the 43 kDa gap junction protein. In heterologous cocultures of tumour cells and primary mesothelial cells, however, 80-90% of the tumour cell/normal cell contacts were functional. Exposure of primary mesothelial cells to TPA, a phorbol ester tumour promoter, resulted in marked inhibition of GJIC, being an action common to numerous tumour promoters. Such an effect though was not observed with the carcinogenic mesothelioma-inducing mineral fibres chrysotile and amosite, neither with glass wool. These results suggest that a permanent defect in GJIC capacity is a common feature of human mesothelioma cells, but how mineral fibres are involved in the process of mesotheliomagenesis is still unclear.

• Radical oxidation reactions of the purine moiety of 2'-deoxyribonucleosides and DNA by iron-containing minerals. M. Berger, M. de Hazen, A. Nejjari, et al. 1993;14(1):41-6. PubMed · Publisher

  Abstract

  The radical oxidation capability of several classes of iron minerals, including biotite, hematite, magnetite, minette, nemalite, pyrite, vivianite and two chrysotiles (asbestos), was investigated by using a double experimental approach. One involved the electron spin resonance spin-trapping measurement of organic radicals obtained by the reaction of activated oxygen species, released upon incubation of the minerals in phosphate buffered solutions with formate used as the target molecule. In addition, the formation of mineral-mediated oxidation purine decomposition products, including 7,8-dihydro-8-oxo-2'-deoxyguanosine and 7,8-dihydro-8-oxo-2'-deoxyadenosine, was searched within nucleosides and DNA by using specific and sensitive HPLC electrochemical assays. Emphasis was placed on the mechanistic aspects of the radical oxidation reactions involved in the formation of the two C(8) hydroxylated purine decomposition products.

• Fiber-induced hydroxyl radical formation: correlation with mesothelioma induction in rats and humans. K.R. Maples, N.F. Johnson. 1992;13(11):2035-9. PubMed · Publisher

  Abstract

  As part of a program to study the effects of inhaled fibers, we characterized the capacity of various fibers to initiate hydroxyl radical (.OH) formation from hydrogen peroxide in a non-cellular system. We studied five natural fibers (erionite, crocidolite, amosite, anthophyllite and chrysotile) and two man-made fibers (JM code 100 glass fibers and glass wool). The fibers were incubated for 5 min at 37 degrees C with hydrogen peroxide and salicylic acid in pH 7.0 aqueous solutions. The salicylate reacted with any .OH formed in these mixtures to produce stable addition products. The amount of .OH addition products formed during the incubations was determined by the salicylate assay which uses HPLC with electrochemical detection. Erionite, JM code 100 and glass wool were the most effective initiators of .OH formation, followed, in order, by crocidolite, amosite and chrysotile. When the capacity of the natural fibers to initiate .OH formation was plotted versus either the values for tumor rates of rats that received pleural inoculations of fibers or the literature values for the human mesothelioma mortality rates, positive correlations (r2 > or = 0.896) were found. Similar correlations with man-made fibers were not found. No positive correlation could be made between .OH formation capacity versus the tumor rates of rats that received peritoneal injections of either type of fibers.

• Human mesothelioma cells and asbestos-exposed mesothelial cells are selectively resistant to amosite toxicity: a possible mechanism for tumor promotion by asbestos. E.W. Gabrielson, A. Van der Meeren, R.R. Reddel, et al. 1992;13(8):1359-63. PubMed · Publisher

  Abstract

  To determine if asbestos exposure could contribute to mesothelial cell carcinogenesis by selection and/or expansion of an initiated cell population, we compared normal human pleural mesothelial cells to either human mesothelioma cell lines or mesothelial cells transfected with cancer-related genes for sensitivity to amosite fibers in vitro. Neither normal nor mesothelioma cells were directly stimulated to replicate or increase DNA synthesis by any of the asbestos exposure conditions tested. The potential selective effect of asbestos exposure was demonstrated by a differential sensitivity of normal mesothelial cells and mesothelioma cells to amosite: for example, up to 20-fold higher concentrations of amosite fibers were required to inhibit replication of mesothelioma cell lines than normal mesothelial cells. In addition, a significant resistance (4-fold) to amosite toxicity was observed for SV40 immortalized mesothelial cell lines that had previously been selected in vitro for resistance to asbestos. SV40 immortalized cells that have become tumorigenic after transfection with either Ha-ras or PDGF A-chain genes were not significantly more resistant to the cytotoxic effects of amosite than primary normal cells, and the primary cells were equally sensitive to amosite as mesothelial cells that were only immortalized by SV40. The sensitivity of normal mesothelial cells to asbestos does not appear to be simply a result of general fragility of the mesothelial cells, since similar levels of hydrogen peroxide and silica were cytotoxic for normal mesothelial cells and mesothelioma cell lines. Because mesothelioma cells have a greater resistance to asbestos cytotoxicity than normal mesothelial cells, we hypothesize that a differential resistance to cell killing by asbestos fibers in vivo may result in a selective expansion of an initiated or transformed cell population and thus contribute to the carcinogenesis process. Since tumorigenicity and asbestos resistance occur independently of one another in genetically altered mesothelial cell lines, genotypic and phenotypic alterations that lead to tumorigenic conversion may not be the same changes that provide resistance to cell killing by asbestos.

• Iron mobilization from crocidolite asbestos greatly enhances crocidolite-dependent formation of DNA single-strand breaks in phi X174 RFI DNA. L.G. Lund, A.E. Aust. 1992;13(4):637-42. PubMed · Publisher

  Abstract

  The ability of the iron associated with asbestos to catalyze damage to phi X174 RFI DNA was determined and compared with iron mobilized from asbestos. Asbestos (1 mg/ml) suspended for 30 min in 50 mM NaCl containing 0.5 micrograms phi X174 RFI DNA, pH 7.5, did not catalyze detectable amounts of DNA single-strand breaks (SSB). However, addition of ascorbate (1 mM) resulted in 19, 26, 7 or 8% DNA with SSB for crocidolite, amosite, chrysotile or tremolite respectively. The percentage of DNA with SSB induced by each form of asbestos was directly related to its iron content. Inclusion of desferrioxamine B, which binds Fe(III) rendering it redox inactive, completely inhibited asbestos-dependent formation of DNA SSB, suggesting that iron was responsible for catalyzing the formation of DNA SSB. Mobilization of Fe(II) from crocidolite by citrate, EDTA or nitrilotriacetate (1 mM) in the absence of ascorbate resulted in 15, 33 or 63% DNA with SSB respectively. This activity was completely inhibited by compounds considered to be .OH scavengers, i.e. mannitol, 5,5-dimethyl-1-pyrroline N-oxide or salicylate (100 mM). Preincubation of crocidolite with citrate (1 mM) for 24 h resulted in mobilization of 52 microM iron and increased ascorbate-dependent induction of DNA SSB compared with crocidolite that was preincubated without citrate. Iron mobilized by citrate was entirely responsible for crocidolite-dependent formation of DNA SSB as evidenced by complete inhibition with desferrioxamine B. Therefore, the results of the present study strongly suggest that iron was responsible for asbestos-dependent generation of oxygen radicals, which resulted in the formation of DNA SSB. Mobilization of iron by chelators, followed by redox cycling, greatly enhanced crocidolite-dependent formation of DNA SSB. Thus, mobilization of iron in vivo by low mol. wt chelators may lead to the increased production of reactive oxygen species resulting in damage to biomolecules, such as DNA.

• Activation of protein kinase C by crocidolite asbestos in hamster tracheal epithelial cells. M. Perderiset, J.P. Marsh, B.T. Mossman. 1991;12(8):1499-502. PubMed · Publisher

  Abstract

  To determine the mechanisms of cell signalling by asbestos in epithelial cells of the respiratory tract, the activity of protein kinase C (PKC) was examined in hamster tracheal epithelial (HTE) cells exposed to mitogenic concentrations of crocidolite asbestos. In the histone phosphorylation assay, asbestos significantly increased activity of PKC associated with the membrane fraction of HTE cells. However, in contrast to 12-O-tetradecanoylphorbol-13-acetate, which caused redistribution of almost all PKC activity from the cytosolic to the membrane fraction, the majority of the PKC activity was associated with the cytosolic fraction at all time periods examined. Asbestos did not inhibit binding of [3H]phorbol-12,13-dibutyrate to intact HTE cells, whereas binding was inhibited by the phorbol compounds phorbol dibutyrate and phorbol dibenzoate. Thus, crocidolite-induced activation of PKC does not appear to be mediated through the same mechanism as classical phorbol ester tumor promoters, compounds which activate PKC by structurally resembling diacylglycerol.

• Platinum-DNA damage in leukocyte DNA of patients receiving carboplatin and cisplatin chemotherapy, measured by atomic absorption spectrometry. R.J. Parker, I. Gill, R. Tarone, et al. 1991;12(7):1253-8. PubMed · Publisher

  Abstract

  Previous studies have shown that platinum-DNA adduct level in leukocyte DNA (measured by antibody methodology) is directly related to disease response in ovarian cancer and testicular cancer. To determine if this principle could be more broadly applied, platinum-DNA damage was studied in a blinded fashion in leukocyte DNA of 21 cancer patients who received carboplatin (day 1) and cisplatin (day 3) in a phase 1 clinical trial. Fifteen different tumor types were included in this cohort. Using atomic absorption spectrometry with Zeeman background correction, DNA-bound platinum was measured during cycles 1 (C1) and 2 (C2) of therapy for most patients. For each of two cycles of therapy, most patients developed measurable levels of adduct after carboplatin, and in most patients adduct levels increased further after cisplatin, often in a supra-additive fashion. Total mg dose levels varied by less than 2-fold, whereas individual patients differed by as much as 10(3) in their adduct measurements after C1 and after C2, and by 29-fold after the very first carboplatin dose. All patients had refractory disease at the initiation of therapy, and 19 patients were evaluable for disease response. Adduct determinations were made 24 h after the first dose of platinum therapy in 17 of these individuals. Mean adduct levels after the first dose of carboplatin were higher in six responders (50 fmol/micrograms DNA +/- 26) than in 11 non-responders (14 fmol/micrograms DNA +/- 10); Wilcoxon two sample test two-sided P = 0.0071. The six responders were patients with pleural mesothelioma (2), breast cancer, buccal mucosa cancer, esophageal cancer and ovarian cancer. Adduct levels were consistently higher in the group of responders on each day that adduct was measured, with a summary two-sided P value of 0.00011. We conclude that analysis of platinum-DNA adduct formation may help determine whether pharmacogenetics are important in cancer drug resistance; and may help to determine the relationship between DNA damage in the peripheral blood compartment and internal organ response to in vivo exposures to DNA-damaging agents.

• Asbestos-related malignant mesothelioma: growth, cytology, tumorigenicity and consistent chromosome findings in cell lines from five patients. K. Pelin-Enlund, K. Husgafvel-Pursiainen, L. Tammilehto, et al. 1990;11(4):673-81. PubMed · Publisher

  Abstract

  Seven mesothelioma cell lines were established from clinical specimens from five patients with asbestos-related malignant pleural mesothelioma. The cells in culture show either epithelial or mixed epithelial/fibrosarcomatous growth with an average doubling time of 30 h. Giant multinucleated cells are common in all the cell lines, as well as long thin microvilli on the cell surfaces. All cell lines were cytokeratin positive and they stained negatively for monocyte-macrophage markers. All seven cell lines and one long-term tissue culture from a sixth mesothelioma patient were characterized cytogenetically. Karyotype analyses revealed complex structural and numerical abnormalities, primarily involving chromosome 1, 4, 5, 6, 7, 8, 9, 11, 12, 13 and 22. An excess of chromosome material of the short arm of chromosome 5 was seen consistently in six cell lines and in the long-term culture. In cell lines from four patients, changes in chromosome 13, mainly monosomy 13, were observed. The marker chromosomes observed in the early passages were conserved and few additional changes appeared in later passages. Six of the cell lines tested for tumorigenicity in athymic nude mice were weakly positive.

• Surface modification can affect the carcinogenicity of asbestos. R.C. Brown, P. Carthew, J.A. Hoskins, et al. 1990;11(10):1883-5. PubMed · Publisher

  Abstract

  A sample of amosite asbestos was modified by effectively adding C8 and C18 hydrocarbon chains to the fibre surfaces. The altered fibres interacted less readily with cells in vitro and were less cytotoxic. In whole animals the number of mesotheliomas produced by the C8 material was the same as that with the parent material but the tumours occurred earlier. The C18 derivatized fibre was markedly less active in the production of tumours. This is the first report demonstrating that similar size fibres with differing surfaces have different pathogenic properties.

1980s

• Apparent synergy between chrysotile asbestos and N-nitrosoheptamethyleneimine in the induction of pulmonary tumours in rats. P.T. Harrison, J.C. Heath. 1988;9(12):2165-71. PubMed · Publisher

  Abstract

  Environmental carcinogenesis in man is widely accepted to be a multifactorial process, and in the causation of lung cancers it is suspected that low levels of systemic carcinogens may act synergistically with inhaled particulates so that some exposed individuals are at increased risk. In the present study the carcinogenic effects of low levels of industrially/environmentally significant particulate materials (chrysotile asbestos and metallic cadmium) and a putative systemic carcinogen, N-nitrosoheptamethyleneimine (NHMI), were investigated in the laboratory rat, using this as a model of potential human exposure. The overall lung tumour incidence rate in the groups of animals receiving chrysotile and NHMI together (8/50) or chrysotile, cadmium and NHMI together (6/44) was substantially higher than in the groups receiving chrysotile alone (1/86) or chrysotile and cadmium (1/94) or NHMI alone (2/48). The results demonstrated apparent synergy between chrysotile and NHMI in the induction of lung tumours. Incidence of pulmonary hyperplastic lesions paralleled the trend in tumour incidence. Cadmium had little or no influence on the incidence of either lung tumours or hyperplastic lesions. This study helps to evaluate further the role of asbestos in the causation of lung cancer. It is suggested that people who are or have been exposed to chrysotile asbestos may show a significantly elevated risk of lung cancer if concomitantly or subsequently exposed to tumour initiating agents.

• Binding of deferoxamine to asbestos fibers in vitro and in vivo. S.A. Weitzman, J.F. Chester, P. Graceffa. 1988;9(9):1643-5. PubMed · Publisher

  Abstract

  We studied the binding of tritium-labeled deferoxamine, a strong iron chelator, to crocidolite asbestos fibers in vitro and in vivo. In aqueous suspension of asbestos, deferoxamine binding was rapid and strong, suggesting specific binding to iron. For the in vivo experiments, diffusion chambers containing native asbestos fibers or deferoxamine-washed asbestos were implanted in the peritoneal cavities of mice. Five days after parenteral injection of tritiated deferoxamine chambers were removed and the asbestos counted. More than twice as much label (2206 +/- 348 c.p.m./100 mg asbestos) was bound to the native asbestos as compared to the deferoxamine-washed asbestos (1080 +/- 201 c.p.m./100 mg asbestos), suggesting specific binding in vivo. Since deferoxamine can inhibit asbestos toxicity in vitro, these experiments suggest the feasibility of testing whether deferoxamine can prevent asbestos-related disease in vivo.

• Morphological transformation of Syrian hamster embryo cells induced by mineral fibres and the alleged enhancement of benzo[a]pyrene. S.O. Mikalsen, E. Rivedal, T. Sanner. 1988;9(6):891-9. PubMed · Publisher

  Abstract

  The ability of different mineral fibres to induce morphological transformation of Syrian hamster embryo cells has been studied. Increased transformation frequencies were obtained in the presence of chrysotile, crocidolite, amosite, anthophyllite and the glass fibres (GF) 100, while no significant increase in transformation frequency was observed with GF 110 and TiO2. Chrysotile was the most potent of the fibres tested. GF 100 was more potent than crocidolite, amosite and anthophyllite. By comparing transformation frequency and toxicity, it could be concluded that induction of transformation is not caused by unspecific cytotoxic effects. In contrast to some earlier studies, no synergistic effect was observed between benzo[a]pyrene (BaP) and asbestos fibres. Adsorption of BaP to crocidolite fibres had no effect on the transformation frequency. Moreover, crocidolite was not able to promote the transformation of cells pre-exposed to BaP. Electron microscopy studies showed that the fibres were rapidly phagocytosed. Blebs were often formed on the cell surface and were most pronounced after crocidolite exposure. The blebs did not seem to be associated with the areas of physical interaction between the cells and the fibres, but were distributed throughout the cell surface.

• Metaphase and anaphase analysis of V79 cells exposed to erionite, UICC chrysotile and UICC crocidolite. L.D. Palekar, J.F. Eyre, B.M. Most, et al. 1987;8(4):553-60. PubMed · Publisher

  Abstract

  The cytogenetic effects of erionite treatment of V79 cells were compared with those of UICC crocidolite and UICC chrysotile treatment. A significant reduction in diploid cells with an accompanying increase in aneuploid and polyploid cells was observed with all three treatments. In the erionite-treated cultures, an increase in aneuploidy was observed at all dose levels ranging from 10 to 100 micrograms/ml, whereas in the crocidolite- and chrysotile-treated cultures, significant increases in aneuploidy were observed at all dose levels except the low dose, 10 micrograms/ml. Chromatid aberrations were observed in cultures treated with crocidolite and chrysotile and were especially pronounced at dose 100 micrograms/ml of chrysotile. The clastogenic effect of erionite was weaker but statistically significant at dose 100 micrograms/ml. An extrapolation of these cytogenetic changes over dose in number of fibers suggests that erionite was more reactive than the other two minerals in producing aneuploidy. The number of fibers required to produce a similar degree of cytogenetic effects was several orders of magnitude higher for chrysotile and crocidolite than erionite. These results correlate with the higher tumorigenic potency of erionite. In general, fewer cells treated with erionite entered anaphase than those treated with the other two minerals. As a result, abnormal anaphases representing chromosomal mis-segregation were observed only in the chrysotile- and crocidolite-treated cultures. To our knowledge, this is the first report on cytogenetic effects of erionite.

• Apparent synergy in lung carcinogenesis: interactions between N-nitrosoheptamethyleneimine, particulate cadmium and crocidolite asbestos fibres in rats. P.T. Harrison, J.C. Heath. 1986;7(11):1903-8. PubMed · Publisher

  Abstract

  Environmental carcinogenesis in man is widely accepted to be a multifactorial process, and in the causation of lung cancers it is suspected that low levels of systemic carcinogens may act synergistically with inhaled particulates so that some exposed individuals are at increased risk. In the present study the carcinogenic effects of low levels of industrially and environmentally significant particulate materials (crocidolite asbestos and metallic cadmium) and a putative systemic carcinogen, N-nitrosoheptamethyleneimine (NHMI), were investigated in the laboratory rat, using this as a model of potential human exposure. The overall lung tumour incidence rate in the group of animals receiving crocidolite, cadmium and NHMI (14/45) was significantly higher than in the groups of animals receiving either crocidolite and cadmium together (2/51) or crocidolite and NHMI together (7/42). The results demonstrated an apparent synergy between cadmium and NHMI in the presence of crocidolite in the causation of lung cancer in rats, a finding which was confirmed statistically. This study helps to further evaluate and define the roles of asbestos and particulate cadmium in the causation of lung cancer. It is suggested that people who are exposed through occupation and/or environment to cadmium and asbestos and to low levels of systemic carcinogens may show a significantly elevated risk of lung cancer.

• Studies on the role of oxygen radicals in asbestos-induced cytopathology of cultured human lung mesothelial cells. E.W. Gabrielson, G.M. Rosen, R.C. Grafstrom, et al. 1986;7(7):1161-4. PubMed · Publisher

  Abstract

  The possible role of oxygen radicals in mediating the cytopathologic effects of asbestos was studied using human mesothelial cells in culture. Electron paramagnetic resonance measurements of intact cells using the spin trap 5,5-dimethyl-1-pyrroline-1-oxide failed to detect any increase in oxygen radicals in mesothelial cells after exposure to amosite asbestos, although oxygen radicals were readily detected in cells exposed to menadione, an uncoupler of oxidation-reduction reactions. Cellular thiol levels were reduced after exposure to menadione, but were not affected by exposure to asbestos. Addition to the culture media of the free radical scavengers superoxide dismutase, reduced glutathione, N-acetylcysteine, or D-alpha-tocopherol had no affect on the dose-dependent cytotoxicity of amosite fibers. Furthermore, exposure of the mesothelial cells to amosite fibers resulted in no significant increase in the level of DNA single-strand breaks. These results all suggest that for cultured human mesothelial cells, oxygen free radicals are not important mediators of the cytopathic effect of asbestos.

• Genotoxicity of dimethylnitrosamine in the presence of chrysotile asbestos UICC B and xonotlite. F. Denizeau, M. Marion, G. Chevalier, et al. 1985;6(12):1815-7. PubMed · Publisher

  Abstract

  Interactions of particulates with chemical genotoxic agents may play an important role in the induction of carcinogenesis. With respect to bronchogenic cancer, the synergism associated with combined exposure to asbestos and tobacco smoke is a well-documented phenomenon. The present work focused on chrysotile asbestos and xonotlite. The latter is a fibrous calcium silicate which is increasingly being used to replace asbestos in various industrial applications. The study was aimed at testing the possible interaction of these materials with dimethylnitrosamine (DMN), a genotoxic component of tobacco smoke. The capacity of fibers to interfere with the genotoxic response elicited by DMN in the UDS/hepatocyte assay system specifically designed for sensitive detection of short-patch DNA repair, was looked for. The properties of the selected fibers with respect to binding affinity towards DMN were also examined.

• In vitro transformation of rat pleural mesothelial cells by chrysotile fibres and/or benzo[a]pyrene. M.J. Paterour, J. Bignon, M.C. Jaurand. 1985;6(4):523-9. PubMed · Publisher

  Abstract

  Rat pleural mesothelial cells (RPMC) were treated, in vitro, in a two-stage model of carcinogenesis. RPMC obtained from passage 12th were treated once with 1 microgram/ml of benzo-[a]pyrene (BP) and from passage 13th to 40th with 0.4 microgram/cm2 of chrysotile fibres (Chr). Transformation was determined by the observation of the colonies formed when the cells were plated at low density. Colonies were classified into four classes according to the level of lack in contact inhibition between cells (0 to III). BP as well as chrysotile fibres were potent in inducing a high proportion of type III colonies which were not observed in control series. In addition, there was no synergistic effect between BP and Chr. These results would indicate that chrysotile fibres do not act as a promoter on rat pleural mesothelial cells in culture, but induce morphologically transformed colonies.

• Induction by asbestos fibers of anaphase abnormalities: mechanism for aneuploidy induction and possibly carcinogenesis. T.W. Hesterberg, J.C. Barrett. 1985;6(3):473-5. PubMed · Publisher

  Abstract

  Syrian hamster embryo cells were treated with crocidolite asbestos at a dose (1 microgram/cm2) which was shown in previous studies to induce cell transformation and aneuploidy in these cells. Treatment of cells with asbestos induced a greater than 20-fold increase in the incidence of cells in anaphase with abnormalities, including lagging chromosomes, bridges, and sticky chromosomes. Asbestos fibers were observed in mitotic cells and appeared, in some cases, to be interacting directly with the chromosomes. From these studies, we propose that the physical interaction of the asbestos fibers with the chromosomes or structural proteins of the spindle apparatus causes missegregation of chromosomes during mitosis resulting in aneuploidy. These findings provide a mechanism, at the chromosomal level, by which asbestos and other mineral fibers might induce cell transformation and cancer.

• Inhalation studies on the effects of tremolite and brucite dust in rats. J.M. Davis, J. Addison, R.E. Bolton, et al. 1985;6(5):667-74. PubMed · Publisher

  Abstract

  Samples of commercially used asbestos, especially chrysotile, are frequently contaminated by small amounts of other fibrous minerals. Among these are tremolite and brucite although pure tremolite is also produced commercially in relatively small quantities. In order to determine how harmful commercially exploited tremolite might be in comparison with other asbestos types and to explore the possibility that small amounts of tremolite and brucite as contaminants could significantly affect the pathogenicity of industrially used chrysotile, long-term animal inhalation and injection studies using rats were undertaken with what were considered to be mineralogically pure samples of these minerals. Rats treated with tremolite developed very high levels of pulmonary fibrosis as well as 16 carcinomas and two mesotheliomas in a group of 39 animals. Tremolite thus proved to be the most dangerous mineral that we have studied. Animals treated with 'brucite' developed moderate levels of pulmonary fibrosis and two carcinomas. Both tremolite and brucite produced mesotheliomas in greater than 90% of animals following i.p. injection. However, it was found that the supposedly pure brucite in fact contained 10% chrysotile, a level of contamination that could well have been responsible for the pathological changes found in both inhalation and intraperitoneal injection studies. The greatest care should be exercised by industry in handling tremolite or materials contaminated with it.

• Pulmonary response of hamsters to fibrous glass: chronic effects of repeated intratracheal instillation with or without benzo[a]pyrene. V.J. Feron, P.M. Scherrenberg, H.R. Immel, et al. 1985;6(10):1495-9. PubMed · Publisher

  Abstract

  Syrian golden hamsters were given intratracheal instillations of glass fibres with or without benzo[a]pyrene suspended in saline, once a fortnight for 52 weeks. The experiment was terminated at week 85. 'Silicotic granulomas' consisting of tightly packed, iron-positive macrophages filled with glass fibres and surrounded by a layer of alveolar epithelial cells were the predominant pulmonary lesion. No mesotheliomas or other tumours of the respiratory tract were observed in hamsters treated with glass fibres alone. There was no indication that glass fibres enhanced the development of respiratory tract tumours induced by benzo[a]pyrene. In hamsters similarly exposed to crocidolite fibres with or without benzo[a]pyrene no mesotheliomas or other respiratory tract tumours were observed either. An explanation for the absence of pulmonary tumours might be that repeated administration of fibres over a period of 52 weeks entails an acute pulmonary reaction after each administration with the implication that the fibres cannot settle down well enough to be able to induce tumours. Another possible explanation is the relatively short duration of the experimental period.

• Asbestos and benzo[a]pyrene act synergistically to induce squamous metaplasia and incorporation of [3H]thymidine in hamster tracheal epithelium. B.T. Mossman, A. Eastman, E. Bresnick. 1984;5(11):1401-4. PubMed · Publisher

  Abstract

  When exposed to either crocidolite asbestos (single 1-h exposure to 0.4 mg/ml medium) or the polycyclic aromatic hydrocarbon, benzo[a]pyrene (BaP) (less than or equal to 2.5 micrograms/ml medium, 1x weekly for 4 weeks), the epithelium of hamster tracheal explants exhibits insignificant amounts of squamous metaplasia, an atypical lesion, in comparison to amounts observed in untreated tissues. Incorporation of [3H]thymidine, an indication of DNA synthesis by epithelial cells, likewise is unchanged. However, the extent of squamous metaplasia and numbers of labeled basal and suprabasal cells are increased substantially when BaP and asbestos are added in combination. These results suggest an important mechanism of co-carcinogenesis involving chemical and physical carcinogens and support epidemiologic observations documenting an increased risk of bronchogenic carcinoma in asbestos workers who smoke.

• Xeroderma pigmentosum fibroblasts are more sensitive to asbestos fibers than are normal human fibroblasts. L.L. Yang, R.E. Kouri, R.D. Curren. 1984;5(2):291-4. PubMed · Publisher

  Abstract

  Xeroderma pigmentosum fibroblasts (XPF) are defective in the repair of certain DNA adducts. We show here that XPF cells are more sensitive to the toxic effects of chrysotile, amosite and crocidolite asbestos than are normal human fibroblasts (NF). XPF cells from different complementation groups have a sensitivity to chrysotile which parallels the degree of their DNA repair deficiency. In addition, the survival of normal cells after chrysotile exposure increases with time if they are kept from replicating, while the survival of XPF cells under the same circumstances does not change.

• Incidence of various types of thoracic malignancy induced in rats by intrapleural injection of 2 mg of various mineral dusts after inhalation of 222Ra. J. Bignon, G. Monchaux, J. Chameaud, et al. 1983;4(5):621-8. PubMed · Publisher

  Abstract

  After inhalation of 222Ra at equilibrium with radon daughters, male Sprague-Dawley rats were inoculated intrapleurally with 2 mg of unleached or acid-leached asbestos fibres or glass fibres or quartz. The additive co-carcinogenic effects of this type of insult were demonstrated by the increased incidence of malignant thoracic tumours. In rats given mineral materials, bronchopulmonary carcinomas and mixed carcinomas were observed, as well as typical mesotheliomas and combined pulmonary pleural tumours, whereas in control rats inhaling radon alone, only bronchopulmonary carcinomas occurred. No significant differences in tumour incidence were observed between the groups of animals given the different types of dusts, but statistically significant differences were noted in survival times, according to the histological type of tumour. The co-carcinogenic effects of an insult of the pleura by mineral dusts following inhalation of radon are discussed in relation to a possible tumour-promoting effect by these agents.

• DNA repair in human bronchial epithelial cells. A.J. Fornace, J.F. Lechner, R.C. Grafstrom, et al. 1982;3(12):1373-7. PubMed · Publisher

  Abstract

  The purpose of this investigation was to compare the response of human cell types (bronchial epithelial cells and fibroblasts and skin fibroblasts) to various DNA damaging agents. Repair of DNA single strand breaks (SSB) induced by 5 krads of X-ray was similar for all cell types; approximately 90% of the DNA SSB were rejoined within one hour. During excision repair of DNA damage from u.v.-radiation, the frequencies of DNA SSB as estimated by the alkaline elution technique, were similar in all cell types. Repair replication as measured by BND cellulose chromatography was also similar in epithelial and fibroblastic cells after u.v.-irradiation. Similar levels of SSB were also observed in epithelial and fibroblastic cells after exposure to chemical carcinogens: 7,12-dimethylbenz[a]anthracene; benzo[a]pyrene diol epoxide (BPDE); or N-methyl-N-nitro-N-nitrosoguanidine. Significant repair replication of BPDE-induced DNA damage was detected in both bronchial epithelial and fibroblastic cells, although the level in fibroblasts was approximately 40% of that in epithelial cells. The pulmonary carcinogen asbestos did not damage DNA. DNA-protein crosslinks induced by formaldehyde were rapidly removed in bronchial cells. Further, epithelial and fibroblastic cells, which were incubated with formaldehyde and the polymerase inhibitor combination of cytosine arabinoside and hydroxyurea, accumulated DNA SSB at approximately equal frequencies. These results should provide a useful background for further investigations of the response of human bronchial cells to various DNA damaging agents.

• The influence of mineral dusts on metabolic co-operation between mammalian cells in tissue culture. M. Chamberlain. 1982;3(3):337-9. PubMed · Publisher

  Abstract

  Carcinogenic UICC amosite asbestos has been tested in V79-4 cultures to determine whether it acts like a tumour promoter, such as TPA, by inhibiting metabolic co-operation. TPA inhibited metabolic co-operation at the non-toxic dose of 0.01 µg/ml but UICC amosite did not inhibit the cell to cell communication even at a toxic dose. Min-U-Sil silica and ball-milled amosite which were included as non-carcinogenic control dusts similarly did not inhibit metabolic co-operation.

  PubMed has no abstract for this study. This is the authors' abstract, copied from the article.

• Mesotheliomas in rats following inoculation with acid-leached chrysotile asbestos and other mineral fibres. G. Monchaux, J. Bignon, M.C. Jaurand, et al. 1981;2(3):229-36. PubMed · Publisher

  Abstract

  The carcinogenicity of untreated UICC chrysotile A, of acid (oxalic and hydrochloric)-leached UICC chrysotile A, of crocidolite and of JM 104 glass fibres has been studied by intrapleural injection into rats. This experiment, carried out on 304 animals, demonstrated that when more than 80% of the Mg had been leached from chrysotile fibres by either hydrochloric or oxalic acid, the proportion of pleural mesotheliomas was either nil or dramatically lower than that obtained with untreated chrysotile. The carcinogenic effect of crocidolite was higher than that of 43.7% oxalic acid-leached chrysotile. The proportion of mesotheliomas observed in animals injected with JM 104 glass fibres was similar to that in animals injected with fibres from which 63.8% had been leached with oxalic acid. These results indicate that with regard to the induction of pleural carcinogenicity by chrysotile fibres, not only size characteristics but also parameters such as chemical composition and physiochemical properties must intervene.

• Studies on the morphological patterns of asbestos induced mesotheliomas in vivo and in vitro. I.P. Gormley, R.E. Bolton, G. Brown, et al. 1980;1(3):219-31. PubMed · Publisher

  Abstract

  Cell lines were established in vitro from five peritoneal mesotheliomas produced in rats by the injection of crocidolite asbestos. These tumours exhibited the previously described diverse range of histological patterns normally associated with mesotheliomas. This diversity of appearance was also evident in culture but cell patterns in vitro did not necessarily correspond to the histology of the original tumour. With increased time in culture most cell lines tended towards a pattern of random orientation associated with the piling up of cells to form discrete masses. Despite this variation in cell pattern in culture, few ultrastructural differences were seen during electron microscope examination. Following varying periods in culture, some cell lines from these tumours were injected into either rats or athymic mice. Only one typical rat mesothelioma was produced but all cell lines produced tumours in athymic mice. The implications of these findings are discussed in relation to the aetiology of asbestos induced mesotheliomas.

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