asbestos--crocidolite and Cell-Transformation--Neoplastic

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

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

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.

Topics: Animals; Antigens, Polyomavirus Transforming; Apoptosis; Asbestos, Crocidolite; Blotting, Western; Cell Adhesion; Cell Movement; Cell Proliferation; Cell Transformation, Neoplastic; Cells, Cultured; Cocarcinogenesis; Drug Resistance, Neoplasm; Humans; Immunoenzyme Techniques; Lung Neoplasms; Mesothelioma; Mesothelioma, Malignant; Mice; Mice, Inbred C57BL; Mice, Transgenic; Peritoneum; Real-Time Polymerase Chain Reaction; Reverse Transcriptase Polymerase Chain Reaction; RNA, Messenger

Asbestos was used worldwide in huge quantities in the past century. However, because of the unexpected carcinogenicity to mesothelial cells with an extremely long incubation period, many countries face this long-lasting social problem. Mesothelioma is often diagnosed in an advanced stage, for which no effective therapeutic protocols are yet established. We previously reported on the basis of animal experiments that the major pathology in asbestos-induced mesothelial carcinogenesis is local iron overload. Here, we undertook to find an effective strategy to prevent, delay, or lower the malignant potential of mesothelioma during asbestos-induced carcinogenesis. We used intraperitoneal injections of crocidolite to rats. We carried out a 16-week study to seek the maximal-tolerated intervention for iron reduction via oral deferasirox administration or intensive phlebotomy. Splenic iron deposition was significantly decreased with either method, and we found that Perls' iron staining in spleen is a good indicator for iron reduction. We injected a total of 10 mg crocidolite at the age of six weeks, and the preventive measures were via repeated oral administration of 25 to 50 mg/kg/d deferasirox or weekly to bimonthly phlebotomy of 4 to 10 mL/kg/d. The animals were observed until 110 weeks. Deferasirox administration significantly increased the fraction of less malignant epithelioid subtype. Although we found a slightly prolonged survival in deferasirox-treated female rats, larger sample size and refinement of the current protocol are necessary to deduce the cancer-preventive effects of deferasirox. Still, our results suggest deferasirox serves as a potential preventive strategy in people already exposed to asbestos via iron reduction.

Topics: Animals; Asbestos, Crocidolite; Benzoates; Cell Transformation, Neoplastic; Deferasirox; Epithelial-Mesenchymal Transition; Female; Iron; Iron Chelating Agents; Male; Mesothelioma; Phlebotomy; Rats; Spleen; Triazoles

Malignant mesothelioma is strongly associated with asbestos exposure. Among asbestos fibers, crocidolite is considered the most and chrysotile the least oncogenic. Chrysotile accounts for more than 90% of the asbestos used worldwide, but its capacity to induce malignant mesothelioma is still debated. We found that chrysotile and crocidolite exposures have similar effects on human mesothelial cells. Morphological and molecular alterations suggestive of epithelial-mesenchymal transition, such as E-cadherin down-regulation and β-catenin phosphorylation followed by nuclear translocation, were induced by both chrysotile and crocidolite. Gene expression profiling revealed high-mobility group box-1 protein (HMGB1) as a key regulator of the transcriptional alterations induced by both types of asbestos. Crocidolite and chrysotile induced differential expression of 438 out of 28,869 genes interrogated by oligonucleotide microarrays. Out of these 438 genes, 57 were associated with inflammatory and immune response and cancer, and 14 were HMGB1 targeted genes. Crocidolite-induced gene alterations were sustained, whereas chrysotile-induced gene alterations returned to background levels within 5 weeks. Similarly, HMGB1 release in vivo progressively increased for 10 or more weeks after crocidolite exposure, but returned to background levels within 8 weeks after chrysotile exposure. Continuous administration of chrysotile was required for sustained high serum levels of HMGB1. These data support the hypothesis that differences in biopersistence influence the biological activities of these two asbestos fibers.

Topics: Animals; Asbestos, Crocidolite; Asbestos, Serpentine; beta Catenin; Cadherins; Cell Death; Cell Line; Cell Shape; Cell Transformation, Neoplastic; Epithelium; Gene Expression Profiling; Gene Expression Regulation; Genome, Human; HMGB1 Protein; Humans; Mice; Signal Transduction; Transcription, Genetic; Tumor Necrosis Factor-alpha

Toxicological investigations of carbon nanotubes have shown that they can induce pulmonary toxicity, and similarities with asbestos fibers have been suggested. We previously reported that multiwall carbon nanotubes (MWCNT) induced lung inflammation, granulomas and fibrotic reactions. The same MWCNT also caused mutations in epithelial cells in vitro and in vivo. These inflammatory and genotoxic activities were related to the presence of defects in the structure of the nanotubes. In view of the strong links between inflammation, mutations and cancer, these observations prompted us to explore the carcinogenic potential of these MWCNT in the peritoneal cavity of rats. The incidence of mesothelioma and other tumors was recorded in three groups of 50 male Wistar rats injected intraperitoneally with a single dose of MWCNT with defects (2 or 20 mg/animal) and MWCNT without defects (20 mg/animal). Two additional groups of 26 rats were used as positive (2 mg UICC crocidolite/animal) and vehicle controls. After 24 months, although crocidolite induced a clear carcinogenic response (34.6% animals with mesothelioma vs. 3.8% in vehicle controls), MWCNT with or without structural defects did not induce mesothelioma in this bioassay (4, 0, or 6%, respectively). The incidence of tumors other than mesothelioma was not significantly increased across the groups. The initial hypothesis of a contrasting carcinogenic activity between MWCNT with and without defects could not be verified in this bioassay. We discuss the possible reasons for this absence of carcinogenic response, including the length of the MWCNT tested (< 1 mum on average), the absence of a sustained inflammatory reaction to MWCNT, and the capacity of these MWCNT to quench free radicals.

Topics: Abdominal Neoplasms; Animals; Asbestos, Crocidolite; Biological Assay; Carcinogenicity Tests; Carcinogens; Cell Transformation, Neoplastic; Injections, Intraperitoneal; Male; Mesothelioma; Nanotubes, Carbon; Peritoneal Cavity; Rats; Rats, Wistar; Reference Standards; Risk Assessment; Surface Properties; Time Factors

The calcium-binding protein calretinin has emerged as a useful marker for the identification of mesotheliomas of the epithelioid and mixed types, but its putative role in tumor development has not been addressed previously. Although exposure to asbestos fibers is considered the main cause of mesothelioma, undoubtedly, not all mesothelioma patients have a history of asbestos exposure. The question as to whether the SV40 virus is involved as a possible co-factor is still highly debated. Here we show that increased expression of SV40 early gene products in the mesothelial cell line MeT-5A induces the expression of calretinin and that elevated calretinin levels strongly correlate with increased resistance to asbestos cytotoxicity. Calretinin alone mediates a significant part of this protective effect because cells stably transfected with calretinin cDNA were clearly more resistant to the toxic effects of crocidolite than mock-transfected control cells. Down-regulation of calretinin by antisense methods restored the sensitivity to asbestos toxicity to a large degree. The protective effect observed in clones with higher calretinin expression levels could be eliminated by phosphatidylinositol 3-kinase (PI3K) inhibitors, implying an important role for the PI3K/AKT signaling (survival) pathway in mediating the protective effect. Up-regulation of calretinin, resulting from either asbestos exposure or SV40 oncoproteins, may be a common denominator that leads to increased resistance to asbestos cytotoxicity and thereby contributes to mesothelioma carcinogenesis.

Topics: Antigens, Polyomavirus Transforming; Asbestos, Crocidolite; Blotting, Western; Calbindin 2; Cell Line, Tumor; Cell Transformation, Neoplastic; Gene Expression; Humans; Immunohistochemistry; Mesothelioma; Phosphatidylinositol 3-Kinases; Polyomavirus Infections; Proto-Oncogene Proteins c-akt; Reverse Transcriptase Polymerase Chain Reaction; S100 Calcium Binding Protein G; Signal Transduction; Simian virus 40; Transfection; Tumor Virus Infections; Up-Regulation

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

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

Cell transformation is one of the most common assays used to study morphological changes in the multistep process of carcinogenesis. The present study was initiated to investigate the ability of crocidolite to induce cell transformation in BALB/c-3T3 cells and to analyze the relationship between p53 mutations and crocidolite-induced cell transformation, if any. Cell transformation was carried out according to standard procedures. Exponentially growing cells were exposed to different concentrations (0.2-20 microg/cm(2)) of crocidolite fibers for 72 h. Foci obtained from cell transformation were analyzed for their ability to grow in soft agar (anchorage-independence) and p53 alterations. The results of this study demonstrate that there was an increase in transformation frequency (TF) with an increase in concentration of crocidolite. Also, focal cells were able to grow on soft agar, indicating anchorage-independence. cDNA was prepared from RNA isolated from Type 3 foci and subjected to mutational analysis. Eleven exons of the p53 gene from eight transformed cell lines were analyzed for alterations using polymerase chain reaction single-strand conformation polymorphism (PCR-SSCP). Alterations were found in seven of eight cell lines, two of them were in exons 4-6, and five in exons 9-11. The alterations were randomly scattered among the crocidolite dose groups. These results suggest that crocidolite induces mutations predominantly in exons 9-11 of the p53 gene in a nondose-dependent manner.

Topics: 3T3 Cells; Animals; Asbestos, Crocidolite; Cell Adhesion; Cell Survival; Cell Transformation, Neoplastic; Genes, p53; Mice; Mice, Inbred BALB C; Mutagenesis; Mutagenicity Tests; Polymerase Chain Reaction; Polymorphism, Single-Stranded Conformational; Reverse Transcriptase Polymerase Chain Reaction

This study sought to address the relationship between crocidolite and p53 gene mutation. The mutations of p53 gene in 8 BALB/c 3T3 cell lines transformed by crocidolite were analysed. Altogether 11 exons of the gene from 8 cell lines were detected by PCR-SSCP. 7 alterations were found; 2 of them were located in exon 4-6, and 5 in 9-11. Most of the mutations (5/7) were of one more band than that of wild cell from SSCP, and alterations were randomly scattered among the crocidolite doses groups. The results suggest that the presence of a p53 alteration is not related to the dose of crocidolite used. Besides, p53 mutation may occur in a relatively later period of the growth of the transformed cell lines. The results also showed that the mutations occurred predominantly in exons 9-11. This was different from that seen in human mesothelioma where mutations in the exon 5-8 of p53 gene were more frequently observed.

Topics: 3T3 Cells; Animals; Asbestos, Crocidolite; Cell Line, Transformed; Cell Transformation, Neoplastic; Exons; Genes, p53; Mice; Mice, Inbred BALB C; Mutation; Polymerase Chain Reaction; Polymorphism, Single-Stranded Conformational

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.

Topics: Animals; Antioxidants; Asbestos; Asbestos, Crocidolite; Carcinogens; Cell Line; Cell Transformation, Neoplastic; Gene Expression Regulation; Glycoproteins; Intercellular Signaling Peptides and Proteins; Mice; Mice, Inbred C3H; Prolactin; RNA, Messenger; Tetradecanoylphorbol Acetate

Topics: Animals; Asbestos, Crocidolite; Cell Line; Cell Survival; Cell Transformation, Neoplastic; Cricetinae; Epithelium; Glass; Lung; Mesocricetus; Microscopy, Fluorescence

To investigate the mechanisms of asbestos-induced carcinogenesis, expression of c-fos and c-jun protooncogenes was examined in rat pleural mesothelial cells and hamster tracheal epithelial cells after exposure to crocidolite or chrysotile asbestos. In contrast to phorbol 12-myristate 13-acetate, which induces rapid and transient increases in c-fos and c-jun mRNA, asbestos causes 2- to 5-fold increases in c-fos and c-jun mRNA that persist for at least 24 hr in mesothelial cells. The induction of c-fos and c-jun mRNA by asbestos in mesothelial cells is dose-dependent and is most pronounced with crocidolite, the type of asbestos most pathogenic in the causation of pleural mesothelioma. Induction of c-jun gene expression by asbestos occurs in tracheal epithelial cells but is not accompanied by a corresponding induction of c-fos gene expression. In both cell types, asbestos induces increases in protein factors that bind specifically to the DNA sites that mediate gene expression by the AP-1 family of transcription factors. The persistent induction of AP-1 transcription factors by asbestos suggests a model of asbestos-induced carcinogenesis involving chronic stimulation of cell proliferation through activation of the early response gene pathway that includes c-jun and/or c-fos.

Topics: Animals; Asbestos; Asbestos, Crocidolite; Asbestos, Serpentine; Blotting, Northern; Cell Division; Cell Transformation, Neoplastic; Cells, Cultured; Cricetinae; Dose-Response Relationship, Drug; Epithelial Cells; Epithelium; Gene Expression; Genes, fos; Genes, jun; Kinetics; Models, Biological; Pleura; Proto-Oncogene Proteins c-fos; Proto-Oncogene Proteins c-jun; Rats; Rats, Inbred F344; RNA, Messenger; Trachea

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.

Topics: Animals; Asbestos; Asbestos, Crocidolite; Benzo(a)pyrene; Carcinogens; Cell Transformation, Neoplastic; Cricetinae; Drug Synergism; Embryo, Mammalian; Glass; Mesocricetus; Minerals

An orthogonal design method was used to study the transforming effects of chrysotile and crocidolite asbestos fibres in BALB/3T3 cells. Three experiments, designed by tables L9 (3(4)), L8 (2(7)) and L6 (3(1) x 2(2)) of the orthogonal method respectively, were performed separately. The results indicate exponential reductions in survival of treated cells concomitant with a linear increase in exposure concentrations from 0.1 to 10.0 micrograms/cm2, and that chrysotile was more toxic than crocidolite; the total transformation frequency was significantly increased with both chrysotile and TPA concentrations. There was synergism between chrysotile and TPA in sequential treatment, which suggests that chrysotile is an initiator and has a complete transforming effect at 10.0 micrograms/cm2. Crocidolite only has an initiating-like effect within the dose range of 0.1-10.0 micrograms/cm2, and no synergistic effect when associated with TPA.

Topics: Animals; Asbestos; Asbestos, Crocidolite; Asbestos, Serpentine; Cell Transformation, Neoplastic; Cells, Cultured; Dose-Response Relationship, Drug; Drug Synergism; Mice; Mice, Inbred BALB C; Mutagenicity Tests; Mutagens; Tetradecanoylphorbol Acetate

The in vitro cytotoxicity and oncogenic potential of both native and acid leached asbestos fibres were studied using the C3H 10T1/2 cell model. Both native and leached fibres induced a dose-dependent toxicity. At high fibre concentrations, acid leached fibres were significantly less toxic than their untreated counterparts. While asbestos fibres alone do not induce oncogenic transformation at the concentration examined, it was found that both leached and native fibres substantially enhanced the oncogenicity of gamma-irradiation in a more than additive fashion. Although no significant chromosomal aberrations or sister chromatid exchanges (SCE) were found in asbestos treated cultures, a significantly higher number of SCEs was observed in cells treated with both asbestos and radiation compared to cells receiving radiation alone. The results suggest that the enhancement in radiation induced oncogenicity by asbestos fibres may be attributed to the mere physical presence of the fibres rather than any chemical contaminants the fibres may contain. Furthermore, the carcinogenicity of asbestos may be unrelated to genotoxicity.

Topics: Animals; Asbestos; Asbestos, Amosite; Asbestos, Crocidolite; Cell Survival; Cell Transformation, Neoplastic; Cells, Cultured; Chromosome Aberrations; Fibroblasts; Gamma Rays; Mice; Mice, Inbred C3H; Mitosis; Neoplasms, Radiation-Induced; Sister Chromatid Exchange

The cytogenetic effects of chrysotile asbestos on Syrian hamster embryo cells in vitro were investigated at doses which induced morphological and neoplastic transformation but which failed to induce measurable gene mutations in the cells at two genetic loci. Chrysotile asbestos treatment of the cells significantly induced chromosome changes in a dose-dependent manner. Up to 50% of the cells had chromosome abnormalities in number or structure following treatment with asbestos (2.0 micrograms/sq cm) for 48 hr. Numerical chromosome changes were the most pronounced abnormalities although significant increases in metaphases with other chromosome aberrations (breaks, fragments, exchanges, and/or dicentrics) and cells with binuclei or micronuclei were also observed. A linear relationship was observed between the incidences of cells with tetraploid metaphases and binucleated cells, suggesting that binucleation and tetraploidy are related. Cytogenetic effects of other mineral dusts were also tested 48 hr following treatment at a concentration of 2.0 micrograms/sq cm. Crocidolite asbestos was less potent than chrysotile asbestos in its ability to induce cell transformation and cytogenetic damage. Treatment of the cells with thin glass fibers (Code 100) was also able to induce cell transformation and cytogenetic effects, but thick glass fibers (Code 110) were much less potent for both endpoints. Milling of the thin glass fibers decreased the length of the fibers and abolished their ability to induce cell transformation and cytogenetic effects. Nonfibrous alpha-quartz induced neither cell transformation nor cytogenetic effects at the dose of 2.0 micrograms/sq cm. The results indicate that the physical characteristics of the fibers determine their ability to induce cell transformation and their ability to induce chromosome mutations, suggesting a possible mechanistic relationship.

Topics: Animals; Asbestos; Asbestos, Crocidolite; Asbestos, Serpentine; Benzo(a)pyrene; Cell Survival; Cell Transformation, Neoplastic; Cells, Cultured; Chromosome Aberrations; Cricetinae; Embryo, Mammalian; Kinetics; Mesocricetus; Mutagens; Mutation

The abilities of chrysotile and crocidolite asbestos, glass fibers of differing dimensions, and nonfibrous mineral particulates to induce morphological transformation of Syrian hamster embryo cells in culture were compared. Chrysotile and crocidolite asbestos induced morphologically transformed colonies which were indistinguishable from transformed colonies observed following treatment with known chemical carcinogens. A linear, dose-dependent increase in the frequency of transformed colonies was observed. The slope of the dose-response curve on a log-log scale was approximately 1, which is consistent with a one-hit mechanism for their induction. The transforming potency of chrysotile asbestos was decreased by milling of the fibers but not by extraction with an organic solvent. Chrysotile asbestos was nearly twice as potent in inducing morphological transformation as crocidolite asbestos. Glass fibers were also very active in this assay. Thin glass fibers with an average diameter of 0.1 to 0.2 micrometer were as active as asbestos. In contrast, two nonfibrous particulates, alpha-quartz and Min-U-Sil, were inactive over the same concentration range used for the fibrous dusts; however, both were active at higher doses. The effect of varying fiber dimension on induction of morphological transformation was examined with glass fibers. When compared on a per-weight basis, thick glass fibers [average diameter, 0.8 plus/minus 0.06 micrometer (S.E.)] were 20-fold less potent than thin fibers [average diameter, 0.13 plus/minus 0.005 micrometer] in inducing cell transformation. When the average fiber length of thin glass fibers was reduced from 9.5 to 1.7 micrometer by milling the fibers in a mortar and pestle, a 10-fold decrease in transforming activity resulted. When the average fiber length was reduced to 0.95 micrometer, transforming ability was totally absent. The cytotoxic potencies of the various mineral dusts correlated with their transforming potencies. The varying abilities of the mineral dusts to induce cell transformation in vitro are similar to their abilities to induce mesotheliomas in vivo. Thus, this system provides a unique model for studying the mechanism of mineral fiber tumorigenesis and for comparing the relative risks of mineral dusts.

Topics: Animals; Asbestos; Asbestos, Crocidolite; Asbestos, Serpentine; Cell Transformation, Neoplastic; Cells, Cultured; Cricetinae; Dose-Response Relationship, Drug; Dust; Embryo, Mammalian; Glass; Mesocricetus; Microscopy, Electron; Minerals; Quartz

The cell transforming ability of asbestos dust was investigated using C3H10T 1/2 murine fibroblasts. In a series of experiments both crocidolite and amosite caused no increase in the number of transformed foci over that seen in cultures from untreated cells. The dusts, were, however, capable of augmenting the oncogenic effect of benzo[a]pyrene (BP). This putative synergistic effect was evident when fibres and chemicals were added to cultures as simple mixtures and when BP was adsorbed to the surface of the fibres.

Topics: Animals; Asbestos; Asbestos, Amosite; Asbestos, Crocidolite; Cell Transformation, Neoplastic; Cells, Cultured; Mice

The cell transforming ability of asbestos dusts was investigated using C3H10T1/2 murine fibroblasts. In a series of experiments, crocidolite and amosite caused no increase in the number of transformed colonies over that seen in cultures from untreated cells. The dusts were, however, capable of augmenting the oncogenic effect of benzo(a)pyrene. This synergistic effect was evident when fibers and chemicals were added to cultures as simple mixtures and when benzo(a)pyrene was adsorbed to the surface of fibers. Asbestos dust did not, however, appear to exert its oncogenic enhancing effect by modifying the metabolism of benzo(a)pyrene in C3H10T1/2 cells.

Topics: Animals; Asbestos; Asbestos, Amosite; Asbestos, Crocidolite; Benzo(a)pyrene; Benzopyrenes; Cell Line; Cell Transformation, Neoplastic; DNA; Embryo, Mammalian; Fibroblasts; Mice; Mice, Inbred C3H; Protein Binding