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.

Role of metal oxide nanoparticles in histopathological changes observed in the lung of welders.

BACKGROUND: Although major concerns exist regarding the potential consequences of human exposure to nanoparticles (NP), no human toxicological data is currently available. To address this issue, we took welders, who present various adverse respiratory outcomes, as a model population of occupational exposure to NP.The aim of this study was to evaluate if welding fume-issued NP could be responsible, at least partially, in the lung alterations observed in welders. METHODS: A combination of imaging and material science techniques including ((scanning) transmission electron microscopy ((S)TEM), energy dispersive X-ray (EDX), and X-ray microfluorescence (µXRF)), was used to characterize NP content in lung tissue from 21 welders and 21 matched control patients. Representative NP were synthesized, and their effects on macrophage inflammatory secretome and migration were evaluated, together with the effect of this macrophage inflammatory secretome on human lung primary fibroblasts differentiation. RESULTS: Welding-related NP (Fe, Mn, Cr oxides essentially) were identified in lung tissue sections from welders, in macrophages present in the alveolar lumen and in fibrous regions. In vitro macrophage exposure to representative NP (Fe2O3, Fe3O4, MnFe2O4 and CrOOH) induced the production of a pro-inflammatory secretome (increased production of CXCL-8, IL-1ß, TNF-α, CCL-2, -3, -4, and to a lesser extent IL-6, CCL-7 and -22), and all but Fe3O4 NP induce an increased migration of macrophages (Boyden chamber). There was no effect of NP-exposed macrophage secretome on human primary lung fibroblasts differentiation. CONCLUSIONS: Altogether, the data reported here strongly suggest that welding-related NP could be responsible, at least in part, for the pulmonary inflammation observed in welders. These results provide therefore the first evidence of a link between human exposure to NP and long-term pulmonary effects.

Differential mutation profiles and similar intronic TP53 polymorphisms in asbestos-related lung cancer and pleural mesothelioma.

Given the interest in defining biomarkers of asbestos exposure and to provide insights into asbestos-related and cell-specific mechanisms of neoplasia, the identification of gene alterations in asbestos-related cancers can help to a better understanding of exposure risk. To understand the aetiology of asbestos-induced malignancies and to increase our knowledge of mesothelial carcinogenesis, we compared genetic alterations in relevant cancer genes between lung cancer, induced by asbestos and tobacco smoke, and malignant pleural mesothelioma (MPM), a cancer related to asbestos, but not to tobacco smoke. TP53, KRAS, EGFR and NF2 gene alteration analyses were performed in 100 non-small cell lung cancer (NSCLC) patients, 50 asbestos-exposed and 50 unexposed patients, matched for age, gender, histology and smoking habits. Detailed assessment of asbestos exposure was based on both specific questionnaires and asbestos body quantification in lung tissue. Genetic analyses were also performed in 34 MPM patients. TP53, EGFR and KRAS mutations were found in NSCLC with no link with asbestos exposure. NF2 was only altered in MPM. Significant enhancement of TP53 G:C to T:A transversions was found in NSCLC from asbestos-exposed patients when compared with unexposed patients (P = 0.037). Interestingly, TP53 polymorphisms in intron 7 (rs12947788 and rs12951053) were more frequently identified in asbestos-exposed NSCLC (P = 0.046) and MPM patients than in unexposed patients (P < 0.001 and P = 0.012, respectively). These results emphasise distinct genetic alterations between asbestos-related thoracic tumours, but identify common potential susceptibility factors, i.e. single nucleotide polymorphisms in intron 7 of TP53. While genetic changes in NSCLC are dominated by the effects of tobacco smoke, the increase of transversions in TP53 gene is consistent with a synergistic effect of asbestos. These results may help to define cell-dependent mechanisms of action of asbestos and identify susceptibility factors to asbestos.

Pulmonary carcinoid tumors and asbestos exposure.

OBJECTIVES: The hypothesis that asbestos exposure may have more specific associations with particular histological types of lung cancer remains controversial. The aim of this study was to analyze the relationships between asbestos exposure and pulmonary carcinoid tumors. METHODS: A retrospective case-control study was conducted in 28 cases undergoing surgery for pulmonary carcinoid tumors and aged >40 years and in 56 controls with lung cancer of a different histological type, matched for gender and age, from 1994 to 1999, recruited in two hospitals in the region of Paris. Asbestos exposure was assessed via expertise of a standardized occupational questionnaire and mineralogical analysis of lung tissue, with quantification of asbestos bodies (AB). RESULTS: Definite asbestos exposure was identified in 25% of cases and 14% of controls (ns). Cumulative asbestos exposure was significantly higher in cases than in controls (P < 0.05), and results of the quantification of AB tended to be higher in cases than in controls (24 and 9% had >1000 AB per gram dry lung tissue, respectively, P = 0.09). Mean cumulative smoking was lower in cases than in controls (P < 0.05). CONCLUSIONS: This study argues in favor of a relationship between asbestos exposure and certain pulmonary carcinoid tumors.

A comparative transmission electron microscopy study of titanium dioxide and carbon black nanoparticles uptake in human lung epithelial and fibroblast cell lines.

Several studies suggest that the biological responses induced by manufactured nanoparticles (MNPs) may be linked to their accumulation within cells. However, MNP internalisation has not yet been sufficiently characterised. Therefore, the aim of this study was to compare the intracellular uptake of three different MNPs: two made of carbon black (CB) and one made of titanium dioxide (TiO(2)), in 16HBE bronchial epithelial cells and MRC5 fibroblasts. Transmission electron microscopy was used to evaluate the intracellular accumulation. Different parameters were analysed following a time and dose-relationship: localisation of MNPs in cells, percentage of cells having accumulated MNPs, number of aggregated MNPs in cells, and the size of MNP aggregates in cells. The results showed that MNPs were widely and rapidly accumulated in 16HBE cells and MRC5 fibroblasts. Moreover, MNPs accumulated chiefly as aggregates in cytosolic vesicles and were absent from the mitochondria or nuclei. CB and TiO(2) MNPs had similar accumulation patterns. However, TiO(2) aggregates had a higher size than CB aggregates. Intracellular MNP accumulation was dissociated from cytotoxicity. These results suggest that cellular uptake of MNPs is a common phenomenon occurring in various cell types.

p16INK4A inactivation mechanisms in non-small-cell lung cancer patients occupationally exposed to asbestos.

Epidemiological studies have shown that asbestos fibers constitute the major occupational risk factor and that asbestos acts synergistically with tobacco smoking to induce lung cancer. Although some somatic gene alterations in lung cancer have been linked to tobacco smoke, few data are available on the role of asbestos fibers. P16/CDKN2A is an important tumor suppressor gene that is frequently altered in lung cancer via promoter 5'-CpG island hypermethylation and homozygous deletion, and rarely via point mutation. Many studies suggest that tobacco smoking produces P16/CDKN2A promoter hypermethylation in lung cancer, but the status of this gene in relation to asbestos exposure has yet to be determined. The purpose of this study was to investigate the mechanism of P16/CDKN2A alterations in lung cancer in asbestos-exposed patients. P16/CDKN2A gene status was studied in 75 human non-small-cell lung cancer (NSCLC) cases with well-defined smoking habits, and detailed assessment of asbestos exposure, based on occupational questionnaire and determination of asbestos bodies in lung tissue. The results of this study confirm published data on the effect of tobacco smoke on P16/CDKN2A gene alterations, characterized by significantly higher P16/CDKN2A promoter hypermethylation in heavy smokers (more than 40 pack-years (P-Y)) than in smokers of less than 40 P-Y. These results also demonstrate a higher incidence of loss of heterozygosity and homozygous deletion in asbestos-exposed cases, after adjustment for age and cumulative tobacco consumption, than in unexposed cases (P=0.0062). This study suggests that P16/CDKN2A gene inactivation in asbestos-exposed NSCLC cases mainly occurs via deletion, a feature also found in malignant mesothelioma, a tumor independent of tobacco smoking but associated with asbestos exposure, suggesting a possible relationship with an effect of asbestos fibers.

Oxidative stress and proinflammatory effects of carbon black and titanium dioxide nanoparticles: role of particle surface area and internalized amount.

The ubiquitous presence of nanoparticles (NPs) together with increasing evidence linking them to negative health effects points towards the need to develop the understanding of mechanisms by which they exert toxic effects. This study was designed to investigate the role of surface area and oxidative stress in the cellular effects of two chemically distinct NPs, carbon black (CB) and titanium dioxide (TiO(2)), on the bronchial epithelial cell line (16HBE14o-). CB and TiO(2) NPs were taken up by 16HBE cells in a dose-dependent manner and were localized within the endosomes or free in the cytoplasm. Oxidative stress produced inside the cell by NPs was well correlated to the BET surface area and endocytosis of NPs. Contrary to intracellular conditions only CB NPs produced reactive oxygen species (ROS) under abiotic conditions. Exposure of cells to NPs resulted in an increased granulocyte macrophage colony stimulating factor (GM-CSF) mRNA expression and secretion. Inflammatory effects of NPs were dependent on the surface area and were mediated through oxidative stress as they were inhibited by catalase. It can be concluded that NP induced oxidative stress and pro-inflammatory responses are well correlated not only with the BET (Brunauer, Emmett and Teller) surface of the individual NPs but also with the internalized amount of NPs. Differences of even few nanometers in primary particle size lead to significant changes in inflammatory and oxidative stress responses.

Assessment of environmental and domestic exposure to tremolite in New Caledonia.

In this study, the authors characterized exposure to asbestos in the population of New Caledonia, an area where a high mesothelioma incidence was found to be associated with the use of a tremolite-containing whitewash on dwellings. The authors collected airborne samples from various sources. Lung tissue samples or bronchoalveolar lavage fluids were available for 80 subjects, who were interviewed regarding their residential and occupational histories. The authors analyzed all samples by analytical transmission electron microscopy. Results indicated that the use of the tremolite-based whitewash may generate high airborne fiber levels and result in asbestos lung contents comparable with those observed in occupational settings. The highest airborne tremolite concentrations were reached during sweeping in whitewashed houses. Lung concentrations of tremolite fibers were significantly higher in subjects exposed to the whitewash than in unexposed subjects, and the concentrations increased with the duration of exposure.