Mesothelioma in rats following intrapleural injection of chrysotile and phosphorylated chrysotile (chrysophosphate)

Multiwalled Carbon Nanotubes Induce Fibrosis and Telomere Length Alterations

Telomere shortening can result in cellular senescence and in increased level of genome instability, which are key events in numerous of cancer types. Despite this, few studies have focused on the effect of nanomaterial exposure on telomere length as a possible mechanism involved in nanomaterial-induced carcinogenesis. In this study, effects of exposure to multiwalled carbon nanotubes (MWCNT) on telomere length were investigated in mice exposed by intrapleural injection, as well as in human lung epithelial and mesothelial cell lines. In addition, cell cycle, apoptosis, and regulation of genes involved in DNA damage repair were assessed. Exposure to MWCNT led to severe fibrosis, infiltration of inflammatory cells in pleura, and mesothelial cell hyperplasia. These histological alterations were accompanied by deregulation of genes involved in fibrosis and immune cell recruitment, as well as a significant shortening of telomeres in the pleura and the lung. Assessment of key carcinogenic mechanisms in vitro confirmed that long-term exposure to the long MWCNT led to a prominent telomere shortening in epithelial cells, which coincided with G1-phase arrest and enhanced apoptosis. Altogether, our data show that telomere shortening resulting in cell cycle arrest and apoptosis may be an important mechanism in long MWCNT-induced inflammation and fibrosis.

Chrysotile and chrysophosphate chemical modification of the chrysotile surface and its effect on biological behavior

Chrysotile asbestos was reacted with phosphorus oxychloride (POC) gas to produce a chemically modified fiber referred to as chrysophosphate. The presence of phosphorus and chlorine on the fiber surface and in small fiber bundles was verified by means of energy dispersive x-ray spectrometry and laser mass spectrometry. The altered fiber exhibits different physical-chemical properties when compared with the unaltered precursor material. In addition to marked surface changes, fibrils of the reacted material appear to be cross-linked increasing the size of particulates, fiber bundles and increasing their mechanical stability. The reacted specimens exhibit fewer fibrils reducing their surface area. In vitro testing using the human erythrocyte model showed the membranolytic activity of the reacted fiber to be substantially reduced to the background level measured for mechanical membrane breakage during manipulation. Membranolytic activity of unreacted chrysotile displayed values reported previously in the literature. These data support the observation made in other studies that fiber surface modification by means of an industrial process may be a method for reducing the biological potential of mineral particles. The membrane model is considered a useful and preliminary examination. These materials will require further testing in more complex in vivo systems. Some in vivo assays were performed on chrysophosphate with results that appeared to differ from our membrane tests. These differences are described and the variation of batch chemistry, stability of the reacted surface, and the resulting surface chemistry, are discussed.

Quantification of short and long asbestos fibers to assess asbestos exposure: a review of fiber size toxicity

The fibrogenicity and carcinogenicity of asbestos fibers are dependent on several fiber parameters including fiber dimensions. Based on the WHO (World Health Organization) definition, the current regulations focalise on long asbestos fibers (LAF) (Length: L ≥ 5 μm, Diameter: D < 3 μm and L/D ratio > 3). However air samples contain short asbestos fibers (SAF) (L < 5 μm). In a recent study we found that several air samples collected in buildings with asbestos containing materials (ACM) were composed only of SAF, sometimes in a concentration of ≥10 fibers.L-1. This exhaustive review focuses on available information from peer-review publications on the size-dependent pathogenetic effects of asbestos fibers reported in experimental in vivo and in vitro studies. In the literature, the findings that SAF are less pathogenic than LAF are based on experiments where a cut-off of 5 μm was generally made to differentiate short from long asbestos fibers. Nevertheless, the value of 5 μm as the limit for length is not based on scientific evidence, but is a limit for comparative analyses. From this review, it is clear that the pathogenicity of SAF cannot be completely ruled out, especially in high exposure situations. Therefore, the presence of SAF in air samples appears as an indicator of the degradation of ACM and inclusion of their systematic search should be considered in the regulation. Measurement of these fibers in air samples will then make it possible to identify pollution and anticipate health risk.

Factors that impact susceptibility to fiber-induced health effects

Asbestos and related fibers are associated with a number of adverse health effects, including malignant mesothelioma (MM), an aggressive cancer that generally develops in the surface serosal cells of the pleural, pericardial, and peritoneal cavities. Although approximately 80% of individuals with MM are exposed to asbestos, fewer than 5% of asbestos workers develop MM. In addition to asbestos, other mineralogical, environmental, genetic, and possibly viral factors might contribute to MM susceptibility. Given this complex etiology of MM, understanding susceptibility to MM needs to be a priority for investigators in order to reduce exposure of those most at risk to known environmental carcinogens. In this review, the current body of literature related to fiber-associated disease susceptibility including age, sex, nutrition, genetics, asbestos, and other mineral exposure is addressed with a focus on MM, and critical areas for further study are recommended.

An update on the detoxification processes for silica particles and asbestos fibers: successess and limitations

Inhalation of asbestos fibers and crystalline silica produces a number of diseases including fibrosis and cancer. Investigations into the mechanisms involved in mineral particle-induced toxicity indicated the importance of their surfaces in the pathological consequences. Masking of the surface sites has therefore featured prominently in a number of detoxification processes that have been investigated. The majority of the detoxification processes were, however, conducted to elucidate the involvement of a particular surface site in the toxicity of a specific mineral. Others were investigated with the aim of large industrial applications to be applied during mining, handling, processing, transporting, and disposing of minerals. It can be concluded that, to date, there is no single detoxification process that could be applied universally to all different types of mineral particles. Those that have shown some success could not completely abolish all adverse effects. Further elucidation of mechanisms of particle-induced toxicity may open new possibilities for detoxification processes.

Mesothelioma pathogenesis, facts and expectations

It is the merit of Dr J.C. Wagner and his co-workers to have triggered the research on mesothelioma, going back to 1960 when they published data demonstrating a relationship between mesothelioma occurrence and exposure to asbestos fibres in the Cape Province, in South Africa. From that time, epidemiological and toxicological investigations were performed in order to better define the occupational and environmental background of this pathology, to identify the fibre parameters accounting for the toxic effects, and to understand their mechanisms of action. Improvements in our knowledge in these areas benefited to health issues, by preventing risks associated with exposure to mineral fibres and by recognising the disease. Due to the actual progresses in the fields of biology and biotechnologies, the research on mesothelioma presently focuses on study of the mechanisms of mesothelial cell transformation, and on development of strategies to kill tumour cells. While mesothelioma benefited to fibre toxicology and allowed to improve the management health related issue, it would be a just return if the present advances in different scientific areas will permit a rapid eradication of the disease.

Induction of metaphase and anaphase/telophase abnormalities by asbestos fibers in rat pleural mesothelial cells in vitro

The cytogenetic effects of asbestos fibers on rat pleural mesothelial cells were studied in vitro. Crocidolite UICC significantly enhanced aneuploidy and produced few structural chromosome aberrations, whereas anatase, an isomorphic particle, induced no numerical or structural changes. Mitomycin C (300 nM) produced a tenfold increase in abnormal anaphases compared with controls. Asbestos produced anaphase/telophase abnormalities in a concentration-dependent manner. The majority of the abnormalities involved lagging chromosomes. Crocidolite UICC induced abnormalities at a dose of 7.0 micrograms/cm2, whereas Canadian chrysotile did so at 1.0 to 2.0 micrograms/cm2. When the response was assessed by the number of long and thin fibers per cm2 (length > 8 microns; diameter < or = 0.25 microns), crocidolite UICC produced more abnormalities than Canadian chrysotile at all concentrations. On a per-weight basis, these findings differ from those obtained after intrapleural inoculation, as crocidolite induced more mesotheliomas than chrysotile; however, on a per-fiber basis, the in vitro and in vivo effects were similar. These results show that anaphase/telophase analysis is sensitive and complementary to metaphase analysis, and suggest that asbestos might produce cell transformation by inducing chromosome missegregation and aneuploidy.

Use of mesothelial cell cultures to assess the carcinogenic potency of mineral or man made fibers

Natural mineral fibers may produce pulmonary cancers and mesothelioma. In contrast with lung cancer, the incidence of fiber-induced mesothelioma is not enhanced in smokers compared to non smokers. It is therefore of special interest to use mesothelial cells to study the toxicity of natural or man made mineral fibers. Several years ago, we have developed a method to culture rat pleural mesothelial cells (RPMC). We have first studied the effects of asbestos fibers by the application of in vitro tests formerly developed to determine the genotoxicity and transforming potency of soluble xenobiotics. Moreover, we have determined whether RPMC expressed cytochromes P450 known to metabolize polycyclic aromatic hydrocarbons. This paper reviews the results obtained so far. It has been found that asbestos fibers produced a cell transformation and a genotoxicity characterized by the formation of aneuploid cells, abnormal anaphases, chromosomal aberrations and DNA repair (UDS). In addition, RPMC expressed different forms of cytochromes P450. It is nowadays suggested that the tumorigenic potency of asbestos fibers may be related to the fiber dimensions, to their surface properties and in vivo biopersistence; this term involves the fiber solubility in biological medium and the fiber epuration from the lung by clearance mechanisms. Experiments are now in progress to determine whether the in vitro effects are dependent on the fiber parameters suggested as playing a role in the carcinogenic potency.