Sister-chromatid exchange and cell kinetics in CHO-K1 cells, human fibroblasts and lymphoblastoid cells exposed in vitro to asbestos and glass fibre

Possible mutagenic activity of the asbestos dusts crocidolite and chrysotile, and fine and coarse glass, was assessed in CHO-K1 cells, human fibroblasts and human lymphoblastoid cells using the sister-chromatid exchange assay and by examining the effects on cell kinetics. Asbestos caused no dose-related increase in sister-chromatid exchange levels in any of the cell types. However, mitotic delay was induced in CHO-K1 cells and human fibroblasts. The order of magnitude of induced delay in CHO-K1 cells was chrysotile greater than fine glass greater than crocidolite greater than coarse glass. Mitotic inhibition was more pronounced in these cells if they were still in suspension when initially exposed to the dusts compared with 1 h after plating.     

A comparison of asbestos burden in non-urban patients with and without lung cancer

Asbestos is a recognized carcinogen which is widely available for environmental exposure. Since all members of our society are exposed to asbestos containing environments and, indeed, have asbestos fibres in their lungs, the concern exists as to its significance in contributing to the incidence of lung cancer in such populations. The asbestos burden was compared in lung tissue from control and lung cancer patients who had resided in a non-urban environment. There were no significant differences between the asbestos burdens in both age matched groups; however, the proportions of amphiboles to chrysotile were different from those reported in previous urban based studies. This difference was suggested to be attributable to chrysotile exposure in urban air. All patients had appreciable non-asbestos fibres within their lungs. The results indicate that when comparing any dust burden in lungs, it is necessary to have data from regional control populations before attempting to explore causal-disease relationships.     

Bioweathering of chrysotile by fungi isolated in ophiolitic sites

Asbestos minerals are commonly found in serpentine rocks and because of the hazard to human health, research has recently focused on possible detoxification strategies. Some fungal species that inhabit serpentine sites (two disused chrysotile asbestos mines in the Western Alps) have been isolated and characterized in order to obtain data on their biodiversity and bioweathering abilities on chrysotile fibres. The three dominant species (Verticillium leptobactrum, Paecilomyces lilacinus and Aspergillus fumigatus) have proved to be able to actively remove iron from chrysotile fibres, V. leptobactrum being the most efficient. A wide range of serpentinicolous fungi release siderophores, iron-chelating compounds, that could play a role in iron extraction from fibres. Iron removal had been correlated previously with a decrease in the toxic potential of fibres, and a biotechnological application of fungi can be envisaged for asbestos detoxification.     

Malignant mesothelioma: facts, myths, and hypotheses

Malignant mesothelioma (MM) is a neoplasm arising from mesothelial cells lining the pleural, peritoneal, and pericardial cavities. Over 20 million people in the US are at risk of developing MM due to asbestos exposure. MM mortality rates are estimated to increase by 5–10% per year in most industrialized countries until about 2020. The incidence of MM in men has continued to rise during the past 50 years, while the incidence in women appears largely unchanged. It is estimated that about 50–80% of pleural MM in men and 20–30% in women developed in individuals whose history indicates asbestos exposure(s) above that expected from most background settings. While rare for women, about 30% of peritoneal mesothelioma in men has been associated with exposure to asbestos. Erionite is a potent carcinogenic mineral fiber capable of causing both pleural and peritoneal MM. Since erionite is considerably less widespread than asbestos, the number of MM cases associated with erionite exposure is smaller. Asbestos induces DNA alterations mostly by inducing mesothelial cells and reactive macrophages to secrete mutagenic oxygen and nitrogen species. In addition, asbestos carcinogenesis is linked to the chronic inflammatory process caused by the deposition of a sufficient number of asbestos fibers and the consequent release of pro‐inflammatory molecules, especially HMGB‐1, the master switch that starts the inflammatory process, and TNF‐alpha by macrophages and mesothelial cells. Genetic predisposition, radiation exposure and viral infection are co‐factors that can alone or together with asbestos and erionite cause MM. J. Cell. Physiol. 227: 44–58, 2012. © 2011 Wiley Periodicals, Inc.     

Asbestos bodies in rat lung following intratracheal instillation of chrysotile

Asbestos bodies in rat lung have rarely been reported, and just one previous record of their formation from chrysotile fibres in the rat is known. This paper illustrates the production of numerous true asbestos bodies in the lungs of Lister hooded rats after a single small intratracheal dose of lightly milled chrysotile. The demonstration of these bodies is particularly useful because uncoated chrysotile fibres in lung tissue cannot normally be visualized by light microscopy; the detection of asbestos bodies, and therefore of asbestos fibres, provides a means of directly relating asbestos exposure to observed tissue lesions. The asbestos bodies detected in the present study were nearly always associated with small pulmonary fibrotic lesions. The bodies ranged in length from 5 to 80 micron and were up to 5 micron in diameter. Small spheres, rods and bodies the shape of a comma were common; larger beaded structures were somewhat rarer. The bodies were visible in tissue sections stained routinely with modified Azan stain and with haematoxylin and eosin, but their detection and localization was enhanced by the use of Perls' Prussian blue stain in association with a pale eosin counterstain.     

Adsorption of proteins by artificial mineral fibers: in vitro experiments

Since previous studies reported that in vitro some proteins and phospholipids were absorbed by asbestos fibres, namely chrysotile, in this study, man made filamentous glass fibers are been tested in vitro at the presence of proteins. The objective was to obtain evidence to evaluate whether continuous glass fibers have a behaviour similar to asbestos fibres. A sample of chrysotile fibres was used as control. Uptake of bovine serum albumin and horse spleen ferritin on these continuous glass fibres has been observed. However on glass fibres adsorbed less proteins per weight unit (22 mg/g and 12 mg/g respectively for albumin and ferritin) than asbestos chrysotile fibres (42 mg/g and 49 mg/g respectively for albumin and ferritin).     

Man-made mineral (vitreous) fibres: evaluations of cancer hazards by the IARC Monographs Programme

Man-made vitreous (glass-like) fibres are non-crystalline, fibrous inorganic substances (silicates) made primarily from rock, slag, glass or other processed minerals. These materials, also called man-made mineral fibres, include glass fibres (used in glass wool and continuous glass filament), rock or stone wool, slag wool and refractory ceramic fibres. They are widely used for thermal and acoustical insulation and to a lesser extent for other purposes. These products are potentially hazardous to human health because they release airborne respirable fibres during their production, use and removal. Man-made mineral fibres and man-made vitreous fibres have been the subject of reviews by IARC Monographs Working Groups in 1987 and 2001, respectively, which resulted in evaluations of the carcinogenic hazard to humans from exposure to these materials. These reviews and evaluations have been published as Volumes 43 and 81 of the IARC Monographs series [IARC Monographs on the Evaluation of Carcinogenic Risks to Humans, vol. 43, Man-made Mineral Fibres and Radon (1988); IARC Monographs on the Evaluation of Carcinogenic Risks to Humans, vol. 81, Man-made Vitreous Fibres (2002)]. The re-evaluation in 2001 was undertaken because there have been substantial improvements in the quality of the epidemiological information available on the carcinogenicity to humans of glass fibres, continuous glass filament and rock/slag wool. The new evaluations have addressed the limitations of earlier cohort studies, particularly concerning the lack of adjustment with respect to concomitant risk factors such as smoking and other sources of occupational exposure. In addition, the evaluation of the evidence for carcinogenicity of glass fibres to experimental animals has been refined, by making a distinction between insulation glass wool and special-purpose glass fibres. The results of the evaluations in 1987 and 2001 are thus different in several aspects. In this paper, the reviews and evaluations of the carcinogenic hazards of exposure to man-made mineral fibres (MMMF, Monograph volume 43, [1]) and man-made vitreous fibres (MMVF, Monograph volume 81, [2]) are summarised, and the differences explained. In particular, the considerations of the respective IARC Monographs Working Groups (1987, 2001) in reaching their conclusions are discussed in some detail.     

Is there a health hazard for building occupants of airborne mineral fibers exposure?

Summary Asbestos containing material (ACM) inside buildings is an important concern for the health of their occupants. In France, for the assessment of airborne asbestos concentrations inside building, we use the indirect TEM measurement method constantly improved from 1978 on. By contrast, in the U.S.A. and UK the direct method is used. We have carried out a study in order to compare mass and numerical concentration fibres from the same samples, the tendency being now to express the results in fibre/litre. Concerning asbestos fibres released from man made mineral fibres (MMMF), optical microscope is used and results are expressed in numerical concentrations. Epidemiological studies of different occupational cohorts suggest that amphibole fibres present a greater health risk than chrysotile. Concerning indoor pollution by mineral wool, the health hazard seems negligible. The appraisal of this public health problem remains to be done. In France, a multidisciplinary study group has been created to provide advices related to corrective actions. Information on this public health problem is expected from the epidemiologic longitudinal survey, still in progress, of a cohort of workers, exposed to ACM in Paris university buildings.     

Immunomodulatory effects of mineral fibres in occupationally exposed workers

In the context of a large-scale molecular epidemiology study, the possible immunomodulatory effects of mineral fibres, in workers occupationally exposed to asbestos, rockwool and glass fibres, were examined. In each plant, 61, 98 and 80 exposed workers and 21, 43 or 36 control clerical subjects, respectively, were recruited. In the case of the asbestos-exposed subjects, an additional town-control group of 49 people was included. Evidence of pulmonary fibrosis was found in 42% of the asbestos-exposed workers, while evidence of pleural fibrosis was found in 24%. The asbestos-exposed cohort had significantly decreased forced vital capacity of lungs as well as forced expiratory volume per first second. Our findings indicate that exposure to all three types of fibres examined modulates to different degrees the immune response. Suppression of T-cell immunity and to a lesser extent, B-cell immunity was found in the case of workers from a former asbestos cement plant, while stimulation of T-cell response was observed in rockwool workers, and stimulation of T- and B-cell response was seen in glass fibre workers. Depression of the percentage of lymphocyte subpopulation of CD 16+56 (natural killer cells) in peripheral blood was found in glass fibre workers. Statistical analysis showed increased levels of proinflammatory cytokines (IL-6 asbestos; IL-8 all three fibres), expression of adhesion molecule L-selectin on granulocytes and monocytes (asbestos), levels of soluble adhesion molecules (SAMs) in sera (ICAM-1 all three fibres; E-selectin glass fibres), increased levels of immunoglobulin E (asbestos and rockwool) and elevated expression of activation markers on eosinophils (CD66b asbestos, glass fibres; CD69 asbestos). Significant correlations were observed between lymphocyte proliferation and markers of DNA damage and repair. Increased levels of proinflammatory cytokines, SAMs, immunoglobulin E and elevated expression of activation markers on eosinophils was found in people with symptoms of hypersensitivity and an elevated inflammatory status.     

Mutagenesis of Escherichia coli (CSH50) by asbestos

The mutagenic character of richterite asbestos was detected in Escherichia coli strain CSH50, using a modified Ames test. Two sets of experimental plates which contained naturally occurring asbestos were used, to one set of which S-9 rat liver homogenate was added. Control plates contained no asbestos. Mutant colonies appeared in significantly greater frequency in both experimental sets as compared with controls, and experimental plates with rat liver homogenate contained the greatest number of mutant colonies. It is postulated that enzymes contained in rat liver metabolize some unknown mutagen introduced with the natural asbestos sample other than the inert richterite fibers themselves. This finding, together with the unlikelihood that bacterial cell walls could be easily penetrated by asbestos fibers, tends to negate fiber penetration as the mechanism of mutagenesis. The mutagenic mechanism operative in E. coli (CSH50) may be applicable to animal cell systems.     

Mutagenicity,carcinogenicity and teratogenicity of vanadium compounds

The mutagenic, carcinogenic and teratogenic effects of vanadium and its compounds are reviewed. It is concluded that vanadium is not clastogenic and only weakly mutagenic; it has marked mitogenic activity affecting the distribution of chromosomes during mitosis and possibly causing aneuploidy. The few positive data on effects of vanadium during development leave it open whether direct effects on the embryo or fetus or physiological disturbances in the mother are responsible. No data exist indicating that vanadium is carcinogenic in animals or man, but since it interferes with mitosis and chromosome distribution, the possibility that vanadium might be carcinogenic under certain conditions cannot be dismissed offhand.     

Growth of Frankia strains in leaf litter-amended soil and the rhizosphere of a nonactinorhizal plant

Verticillium leptobactrum , a rare fungal species, has repeatedly been isolated from serpentinic rocks in the Western Alps, thus suggesting that it adapts easily to this selective mineral substrate. The rRNA internal transcribed spacer region of several isolates has been sequenced to confirm their identity and taxonomic position within Verticillium , a recently revised polyphyletic entity. Isolates of V. leptobactrum have also been investigated to establish their ability to weather asbestos chrysotile, the most common mineral in the isolation sites. The results of solubilization assays on magnesium and silicon, as well as measurement of the Mg/Si ratio in the asbestos fibres after exposure to fungal mycelia, indicate a high bioweathering activity of V. leptobactrum towards chrysotile. Comparison with data on Fusarium oxysporum shows differences among species, with V. leptobactrum being more active than F. oxysporum in removing structural ions from chrysotile. Asbestos weathering by fungi could be envisaged as a bioremediation strategy for hazardous asbestos-rich soils (e.g. abandoned mines). Fungi that have adapted to live in serpentine sites could be good candidates for this purpose.     

Induction of 8-hydroxydeoxyguanosine by man made vitreous fibres and crocidolite asbestos administered intraperitoneally in rats

Inhaled fibres with certain physico-chemical properties are known to induce mesothelioma in humans. The induction of reactive oxygen (ROS) or nitrogen species (RNS) have been suggested as molecular mechanism of fibre induced carcinogenesis. In earlier studies we were able to demonstrate that crocidolite asbestos in vivo induces mutations in transgenic rats with a specific molecular spectrum that indicates the involvement of 8-hydroxydeoxyguanosine (8-OHdG) as pre-mutagenic adduct. 8-OHdG may be induced by primary (direct) and/or secondary (cellular mediated) mechanisms. Therefore, the induction of 8-OHdG as well as the inflammatory response of animals treated with fibre samples significantly differing in their physico-chemical characteristics was investigated. As appropriate system to study mesothelioma carcinogenesis, intraperitoneal injection in rats was used with samples of UICC crocidolite, crocidolite with reduced iron content, and a vitreous fibre (MMVF 11). Equal numbers of carcinogenic fibres from each sample revealed significant comparable increases in 8-OHdG induction. Parameters of inflammation (percentage of macrophages and TNF-alpha secretion) correlated significantly with the induction of 8-OHdG, 10 weeks after treatment.     

Biological durability and oxidative potential of man-made vitreous fibres as compared to crocidolite asbestos fibres

In this study we investigated relationships between redox properties and biodurability of crocidolite asbestos fibres and three different man-made vitreous fibres (MMVF): traditional stone wool fibres (MMVF 21), glass fibres (MMVF 11) and refractory ceramic fibres (RCF). Each fibre type was incubated up to 22 weeks in four different incubation media: gamble solution (GS) pH 5.0 and pH 7.4, representing blood plasma without proteins, and surfactant-like solution (SLS) pH 5.0 and pH 7.4. During incubation time aliquots of incubation mixtures were removed and analysed in a biochemical model reaction, mimicking activated phagocytes. In addition, changes of fibre morphology and chemical composition were examined using SEM- and EDX-technology. In the presence of crocidolite asbestos fibres and MMVF 21 the formation of OH*-radicals according to the Haber-Weiss sequence could be demonstrated, whereas MMVF 11 and RCF showed no reactivity. Crocidolite asbestos fibres exhibited a significant higher activity compared with the stone wool fibres at the onset of incubation. The oxidative capacities of these fibre types were shown to depend on both specific surface area and iron content. The oxidative potentials of crocidolite asbestos fibres as well as MMVF 21 were not constant during incubation over several weeks in each incubation medium. The reactivities showed sinoidal curves including reactivities much higher than those at the onset of incubation time. These irregular changes of oxidative capacity may be explained by changes of the redox state of fibre surface-complexed iron. Furthermore our results showed clear differences between incubation of fibres in GS and SLS, respectively, indicating that phospholipids play an important part in fibre dissolution behaviour and oxidative reactivity. In conclusion we suggest, that biodurability testing procedures should not exclusively concentrate on dissolution rates of fibres. They should include fibre characteristics concerning known pathogenic mechanisms to evaluate the real toxic potential of the fibre type looking at. Secondly we suggest, that phospholipids should be constituents of incubation liquids used for standardised fibre biodurability test procedures thus representing more realistic incubation conditions.     

Mycotoxins: food contamination, mechanism, carcinogenic potential and preventive measures

Mycotoxins constitute a large number of naturally occurring fungal secondary metabolites with very diversified toxic effects in humans and animals. Among many mycotoxins discovered, aflatoxins, ochratoxin A, sterigmatocystin and several others are identified as carcinogens; several others were found to be mutagenic. Nevertheless, aflatoxin B1 has been found to be one of the most potent carcinogens and contamination of aflatoxins in the food supply is still a major concern. Whereas extensive studies have been made on aflatoxins, little is known about the mode of action of other carcinogenic and mutagenic mycotoxins. Recent progress on research for the carcinogenic and mutagenic mycotoxins is presented in this review with emphasis on their contamination in foods, their carcinogenic potential to humans, and the mode of action as well as possible preventive measures.     

The role of oxidative stress in diseases caused by mineral dusts and fibres: Current status and future of prophylaxis and treatment

Inhalation of silica and asbestos fibres by humans can lead to fibrosis of the lung and cancer. Different mechanistic approaches, including oxidative stress, are used for prophylactic and therapeutic interventions to attenuate the fibrogenic and carcinogenic effects of these particles. Thus far, most of these therapeutic interventions have been only partly successful. A review of the mechanisms which are thought to be involved in mineral particle-induced toxicity and the relevant therapeutic interventions used to date to counteract these mechanisms, will help formulate better prophylactic and treatment intervention strategies in the future.     

Mutagenesis by man-made mineral fibres in the lung of rats

The potential of two asbestos substitute mineral fibres--rock (stone) wool RW1 and glass wool MMVF10--to induce gene mutations, DNA strand breaks, inflammation and oxidative stress has been studied in rats. Male homozygous lamda-lacI transgenic F344 rats were intratracheally instilled with single doses of 1 and 2 mg/animal of fibres or with multiple doses of 2 mg/animal administered weekly on four consecutive weeks (8 mg in total). Exposure to RW1 fibres for 16 weeks significantly increased mutant frequency (MF) in the lung in a dose-dependent manner, while MMVF10 fibres did not exhibit any increase of MF at any dose. RW1 fibres gave a significant increase of MF at a dose of 1 mg. Four weeks after instillation, neither the single nor the multiple doses significantly increased MF for both fibre types. To investigate mechanisms for induction of mutations, other genotoxicity markers and parameters of inflammatory and oxidative damage were determined in relation to MF. A weak correlation of mutagenicity data with other genotoxicity parameters studied was observed. DNA strand breaks as measured by comet assay were increased in alveolar macrophages and lung epithelial cells of RW1 and MMVF10 treated rats. RWl fibres caused more extensive lung inflammation as measured by release of neutrophils into broncho-alveolar lavage fluid than MMVF10 fibres. The effects were observed 16 weeks post-exposure, indicating a persistence of the pathogenic process during the exposure period. Only minor differences in the extent of inflammatory processes were observed between the doses of 2 mg and 4 x 2 mg, suggesting that any threshold for inflammation lies below the dose of 2 mg. With the exception of the highest dose of MMVF10 fibres after 16 weeks of exposure, no significant increase of oxidative damage as measured by levels of malondialdehyde in lung tissue was observed. MMVF10 fibres caused weaker inflammation in the lung of rats and did not exhibit any mutagenic effect. We conclude that a weak but chronic inflammation (more likely than acute inflammation or direct oxidative damage) in the lung tissue of fibre treated rats characterized by moderate influx of inflammatory cells into BAL is probably responsible for the observed mutagenic effect of RW1 fibres.     

Genetic susceptibility to malignant mesothelioma and exposure to asbestos: the influence of the familial factor

BACKGROUND: Asbestos is the principal etiological factor of malignant mesothelioma (MM), accounting for more than 80% of all tumor cases. However, other co-factors, including genetic susceptibility may play a role in the etiology of this disease, possibly modulating the effects of exposure to asbestos and other carcinogenic mineral fibers. The frequent report of familial clustering was the first indication supporting the involvement of genetic factors. Therefore, we performed an extensive literature search to evaluate existing studies reporting familial cases of MM. METHODS: Published reports addressing the issue of familial susceptibility to MM have been searched through PubMed using keywords and free text tools. Eighty-two citations were retrieved and 20 of them actually reported a familial cluster of MM. Three more articles were identified through the references. The probability that the observed familial clusters of mesothelioma could have randomly occurred in exposed families was evaluated with the Family History Score Zi (FHSi). RESULTS: The result of this analysis suggested that clustering of MM cases in families exposed to asbestos may be explained with the additional contribution of other familial factors. The FHSi allowed to reject the hypothesis of random occurrence of these clusters with a probability of a first type error ranging between 1 per cent and 1 per billion. CONCLUSIONS: The evaluation of the published materials supports the hypothesis that - although familial clustering of MM is largely attributable to shared asbestos exposure - the additional contribution of factors dealing with genetic susceptibility may play a role in the etiology of MM.     

Mutagenicities of quinoline and its derivatives.

Quinoline, recently reported to be carcinogenic in rats [12], was mutagenic to Salmonella typhimurium tester strains TA100 and TA98 in the presence of the metabolic activation system S-9 mix. 2-Chloroquinoline, a non-carcinogen [12], was non-mutagenic with or without S-9 mix. 8-Hydroxyquinoline, which is t known to be carcinogenic, was mutagenic with S-9 mix to both bacterial strains. The mutagenicities of 17 other quinoline derivatives that are not known to be carcinogenic were tested, and 12 of these compounds were mutagenic.     

Levels of 8-hydroxy-2'-deoxyguanosine in DNA of white blood cells from workers highly exposed to asbestos in Germany

Asbestos fibers have genotoxic effects and are a potential carcinogenic hazard to occupationally exposed workers. The ability of inhaled asbestos fibers to induce the formation of 8-hydroxy-2'-deoxyguanosine (8-OHdG) in the DNA of white blood cells (WBC) of workers highly exposed at the workplace has been studied. The 8-OHdG adduct level of asbestos-exposed workers was significantly increased (p<0.001) compared to that in the control group in all three years of the study. Asbestos-exposed individuals showed a mean value of 2.61+/-0.91 8-OHdG/10(5) dG (median 2.49, n=496) in 1994-1995, 2.96+/-1.10 8-OHdG/10(5) dG (median 2.76, n=437) in 1995-1996 and 2.55+/-0.56 8-OHdG/10(5) dG (median 2.53, n=447) in 1996-1997. For the control subjects, a mean of 1.52+/-0.39 (median 1.51, n=214) was determined. The results indicate that human DNA samples from exposed individuals contain between 1.7 times and twice the level of oxidative damage relative to that found in control samples in all 3 years of the study. The studies presented here show that asbestos exposure can result in oxidative DNA damage. Our data confirm that oxidative DNA damage occurs in the WBC of workers highly exposed to asbestos fibers, thus supporting the hypothesis that asbestos fibers damage cells through an oxidative mechanism. These in vivo findings underline the importance of oxidative damage in asbestos-induced carcinogenesis and highlight the need for exploring the molecular basis of asbestos-induced diseases, and for more effective diagnosis, prevention and therapy of mesothelioma, lung cancer and pulmonary fibrosis. In addition, preventive and therapeutic approaches using antioxidants may be relevant.