Mechanisms in the pathogenesis of asbestosis and silicosis

Fractional exhaled nitric oxide concentration is increased in asbestosis and pleural plaques

OBJECTIVE AND BACKGROUND

Asbestos exposure induces generation of reactive oxygen and nitrogen species. Nitric oxide is involved in asbestos-related lung toxicity in vitro and can be measured non-invasively in humans in exhaled breath. The authors hypothesized that fractional exhaled nitric oxide concentration (FENO) would be increased in subjects with asbestos-related lung disorders.

METHODS

FENO was measured in 56 subjects with asbestos-related disorders (asbestosis: 12; pleural plaques: 32; asbestos-related diffuse pleural thickening: 12) and in 35 normal subjects. The authors also measured exhaled carbon monoxide, another marker of lung inflammation.

RESULTS

Median (25-75 percentile) FENO was increased in subjects with asbestosis (7.9 (6.6-15.7) p.p.b.; P=0.001) and pleural plaques (6.3 (5.3-9) p.p.b.; P=0.03) compared with normal controls (4.6 (3.5-6) p.p.b.). Subjects with DPT had a median FENO of 5.6 p.p.b., similar to controls. No significant differences in exhaled carbon monoxide were observed between controls (1.0+/-0.3 p.p.m.) and subjects with asbestosis (1.3+/-0.3 p.p.m.), pleural plaques (1.2+/-0.3 p.p.m.) or diffuse pleural thickening (1.1+/-0.3 p.p.m.).

CONCLUSIONS

FENO is raised in asbestosis consistent with lung inflammation, and also in pleural plaques.

Cysteine cathepsins and caspases in silicosis

Silicosis is an occupational pneumoconiosis caused by inhalation of crystalline silica. It leads to the formation of fibrohyalin nodes that result in progressive fibrosis. Alternatively, emphysema may occur, with abnormal destruction of collagen fibres in the advanced stages. Although the pathophysiological mechanisms remain unclear, it has been established that the lung responds to silica by massive enrollment of alveolar macrophages, triggering an inflammatory cascade of reactions. An imbalance in the expression of lung proteases and their inhibitors is implicated in extracellular matrix remodelling and basement membrane disruption. Moreover, exposure to silica can initiate apoptotic cell death of macrophages. This review summarises the current knowledge on cysteine cathepsins that have been ignored so far during silicosis and outlines the recent progress on cellular pathways leading to silica-induced caspase activation, which have been partly delineated.

Apoptosis and extracellular matrix remodelling in human silicosis

AIMS

Silicosis is a chronic occupational disease caused by the inhalation of free crystalline silica particles which produce inflammation and tissue destruction followed by remodelling of the extracellular matrix. Apoptosis has been implicated in the development of the initial inflammation that triggers the remodelling process. Our aim was to elucidate the importance of Fas-ligand (Fas-L) in this disorder and to study the relationship between Fas-L and several other inflammatory and fibrotic remodelling markers.

METHODS AND RESULTS

We analysed 23 lung biopsies from silicotic patients and five controls, quantifying Fas-L and Bcl-2 expression by inflammatory cells as well as mast cells and collagen and elastic fibres. We used immunohistochemistry and morphometry to evaluate the amount of Fas-L and Bcl-2. Our analysis revealed that the silicotic lung stage was significantly related to Fas-L, mast cell and extracellular matrix remodelling. Fas-L expression was inversely associated with mast cells, collagen/elastic deposition and the silicotic lung.

CONCLUSION

Fas-L, mast cell staining and collagen/elastic fibre quantities in silicotic lungs are strongly related to silicosis progression.

Cellular and molecular parameters of mesothelioma

Malignant mesotheliomas (MM) are neoplasms arising from mesothelial cells that line the body cavities, most commonly the pleural and peritoneal cavities. Although traditionally recognized as associated with occupational asbestos exposures, MMs can appear in individuals with no documented exposures to asbestos fibers, and emerging data suggest that genetic susceptibility and simian virus 40 (SV40) infections also facilitate the development of MMs. Both asbestos exposure and transfection of human mesothelial cells with SV40 large and small antigens (Tag, tag) cause genetic modifications and cell signaling events, most notably the induction of cell survival pathways and activation of receptors, and other proteins that favor the growth and establishment of MMs as well as their resistance to chemotherapy. Recent advances in high-throughput technologies documenting gene and protein expression in patients and animal models of MMs can now be validated in human MM tissue arrays. These have revealed expression profiles that allow more accurate diagnosis and prognosis of MMs. More importantly, serum proteomics has revealed two new candidates (osteopontin and serum mesothelin-related protein or SMRP) potentially useful in screening individuals for MMs. These mechanistic approaches offer new hope for early detection and treatment of these devastating tumors.

Direct and indirect effects of single walled carbon nanotubes on RAW 264.7 macrophages: Role of iron

Single-walled carbon nanotubes (SWCNT), nano-cylinders with an extremely small diameter (1-2 nm) and high aspect ratio, have unique physico-chemical, electronic and mechanical properties and may exhibit unusual interactions with cells and tissues, thus necessitating studies of their toxicity and health effects. Manufactured SWCNT usually contain significant amounts of iron that may act as a catalyst of oxidative stress. Because macrophages are the primary responders to different particles that initiate and propagate inflammatory reactions and oxidative stress, we utilized two types of SWCNT: (1) iron-rich (non-purified) SWCNT (26 wt.% of iron) and (2) iron-stripped (purified) SWCNT (0.23 wt.% of iron) to study their interactions with RAW 264.7 macrophages. Ultrasonication resulted in predominantly well-dispersed and separated SWCNT strands as evidenced by scanning electron microscopy. Neither purified nor non-purified SWCNT were able to generate intracellular production of superoxide radicals or nitric oxide in RAW 264.7 macrophages as documented by flow-cytometry and fluorescence microscopy. SWCNT with different iron content displayed different redox activity in a cell-free model system as revealed by EPR-detectable formation of ascorbate radicals resulting from ascorbate oxidation. In the presence of zymosan-stimulated RAW 264.7 macrophages, non-purified iron-rich SWCNT were more effective in generating hydroxyl radicals (documented by EPR spin-trapping with 5,5-dimethyl-1-pyrroline-N-oxide, DMPO) than purified SWCNT. Similarly, EPR spin-trapping experiments in the presence of zymosan-stimulated RAW 264.7 macrophages showed that non-purified SWCNT more effectively converted superoxide radicals generated by xanthine oxidase/xanthine into hydroxyl radicals as compared to purified SWCNT. Iron-rich SWCNT caused significant loss of intracellular low molecular weight thiols (GSH) and accumulation of lipid hydroperoxides in both zymosan-and PMA-stimulated RAW 264.7 macrophages. Catalase was able to partially protect macrophages against SWCNT induced elevation of biomarkers of oxidative stress (enhancement of lipid peroxidation and GSH depletion). Thus, the presence of iron in SWCNT may be important in determining redox-dependent responses of macrophages.

Identification of specific gene copy number changes in asbestos-related lung cancer

Asbestos is a well-known lung cancer-causing mineral fiber. In vitro and in vivo experiments have shown that asbestos can cause chromosomal damage and aberrations. Lung tumors, in general, have several recurrently amplified and deleted chromosomal regions. To investigate whether a distinct chromosomal aberration profile could be detected in the lung tumors of heavily asbestos-exposed patients, we analyzed the copy number profiles of 14 lung tumors from highly asbestos-exposed patients and 14 matched tumors from nonexposed patients using classic comparative genomic hybridization (CGH). A specific profile could lead to identification of the underlying genes that may act as mediators of tumor formation and progression. In addition, array CGH analyses on cDNA microarrays (13,000 clones) were carried out on 20 of the same patients. Classic CGH showed, on average, more aberrations in asbestos-exposed than in nonexposed patients, and an altered region in chromosome 2 seemed to occur more frequently in the asbestos-exposed patients. Array CGH revealed aberrations in 18 regions that were significantly associated with either of the two groups. The most significant regions were 2p21-p16.3, 5q35.3, 9q33.3-q34.11, 9q34.13-q34.3, 11p15.5, 14q11.2, and 19p13.1-p13.3 (P < 0.005). Furthermore, 11 fragile sites coincided with the 18 asbestos-associated regions (P = 0.08), which may imply preferentially caused DNA damage at these sites. Our findings are the first evidence, indicating that asbestos exposure may produce a specific DNA damage profile.

Silica-induced apoptosis in alveolar macrophages: evidence of in vivo thiol depletion and the activation of mitochondrial pathway

Studies have shown that silica induces apoptosis through mechanisms that also regulate the inflammatory responses of lung cells to silica exposure. Although implicated in cell culture studies, the major in vivo pathway through which silica induces apoptosis has not been characterized. The present study is to study the role of mitochondria in silica-induced oxidative stress and apoptosis in vivo. Rats were intratracheally instilled with saline or silica (20 mg/kg) and sacrificed at 3 days post-exposure unless otherwise specified. Alveolar macrophages (AM) were harvested by bronchoalveolar lavage and measured for apoptosis and secretion of inflammatory mediators in the presence or absence of appropriate inhibitors. Concurrent studies were carried out to determine the presence of intracellular reactive oxygen species (ROS) via confocal microscopy, mitochondrial trans-membrane potential by flow cytometry, mitochondrial release of cytochrome c, and the activation of caspase activities in AM by Western blot analysis. Silica was shown to induce elevated levels of intracellular ROS, resulting in a marked decrease in intracellular glutathione (GSH) and cysteine and a sustained presence of apoptotic AM in silica-exposed rats up to two weeks post-exposure. The apoptotic AM were characterized by decreased mitochondrial trans-membrane potential, increased mitochondrial release of cytochrome c, activated caspase 9 (but not caspase 8) and caspase 3 activities, and PARP degradation, comparing to cells from the saline control. Silica induced AM production of IL-1 and TNF-alpha, which may be inhibited by ex vivo treatment of cells with N-acetylcysteine (NAC) or microtubule modifiers such as tetrandrine and taxol. NAC was shown to prevent intracellular GSH depletion and silica-induced production of IL-1beta and TNF-alpha but not apoptosis in AM from silica-exposed rats. These results show that silica-induced apoptosis is mediated through the mitochondrial pathway but not through cellular production of inflammatory cytokines, ROS generation, however, induces both apoptosis and cellular secretion of inflammatory mediators.

TNF-alpha inhibits asbestos-induced cytotoxicity via a NF-kappaB-dependent pathway, a possible mechanism for asbestos-induced oncogenesis

Asbestos is the main cause of human malignant mesothelioma (MM). In vivo, macrophages phagocytize asbestos and, in response, release TNF-alpha and other cytokines that contribute to carcinogenesis through unknown mechanisms. In vitro, asbestos does not induce transformation of primary human mesothelial cells (HM); instead, asbestos is very cytotoxic to HM, causing extensive cell death. This finding raised an apparent paradox: How can asbestos cause MM if HM exposed to asbestos die? We found that asbestos induced the secretion of TNF-alpha and the expression of TNF-alpha receptor I in HM. Treatment of HM with TNF-alpha significantly reduced asbestos cytotoxicity. Through numerous technical approaches, including chemical inhibitors and small interfering RNA strategies, we demonstrate that, in HM, TNF-alpha activates NF-kappaB and that NF-kappaB activation leads to HM survival and resistance to the cytotoxic effects of asbestos. Our data show a critical role for TNF-alpha and NF-kappaB signaling in mediating HM responses to asbestos. TNF-alpha signaling through NF-kappaB-dependent mechanisms increases the percent of HM that survives asbestos exposure, thus increasing the pool of asbestos-damaged HM that are susceptible to malignant transformation. Cytogenetics supported this hypothesis, showing only rare, aberrant metaphases in HM exposed to asbestos and an increased mitotic rate with fewer irregular metaphases in HM exposed to both TNF-alpha and asbestos. Our findings provide a mechanistic rationale for the paradoxical inability of asbestos to transform HM in vitro, elucidate and underscore the role of TNF-alpha in asbestos pathogenesis in humans, and identify potential molecular targets for anti-MM prevention and therapy.

Câncer pleuropulmonar ocupacional

O objetivo deste trabalho é revisar os riscos ocupacionais relacionados ao câncer de pulmão. Inicialmente, situa-se a importância desse câncer na população brasileira. Discute-se a seguir a associação de alguns agentes físicos e químicos, presentes em diferentes processos industriais relevantes, na gênese desse tipo de neoplasia. Na parte final é salientado o diagnóstico clínico e a importância da prevenção primária para seu controle.

Reactivity of carbon nanotubes: free radical generation or scavenging activity?

Carbon nanotubes (CNTs) currently attract intense research efforts because of their unique properties which make them suitable for many industrial applications. When inhaled, CNTs constitute a possible hazard to human health. Several studies have shown that when instilled in the lung of experimental animals, CNTs induced an inflammatory and fibrotic response similar to that caused by other toxic particles which might be the result of oxidative stress caused by particle- and/or cell-derived free radicals. There is, however, no direct experimental evidence of a capacity of carbon nanotubes to generate directly free radicals. Here we report that multiwall carbon nanotubes (MWCNT) in aqueous suspension do not generate oxygen or carbon-centered free radicals in the presence of H2O2 or formate, respectively, as detected with the spin-trapping technique. Conversely, we observed that, when in contact with an external source of hydroxyl or superoxide radicals, MWCNT exhibit a remarkable radical scavenging capacity. It is therefore possible that the inflammatory reaction reported in vivo must be ascribed to MWCNT features other than particle-derived free radical generation.

Matrix metalloproteinases promote inflammation and fibrosis in asbestos-induced lung injury in mice

Inhalation of asbestos fibers causes pulmonary inflammation and eventual pulmonary fibrosis (asbestosis). Although the underlying molecular events are poorly understood, protease/antiprotease and oxidant/antioxidant imbalances are believed to contribute to the disease. Implicated in other forms of pulmonary fibrosis, the matrix metalloproteinases (MMPs) have not been examined in asbestosis. We therefore hypothesized that MMPs play a pathogenic role in asbestosis development. Wild-type C57BL/6 mice were intratracheally instilled with 0.1 mg crocidolite asbestos, causing an inflammatory response at 1 d and a developing fibrotic response at 7, 14, and 28 d. Gelatin zymography demonstrated an increase in MMP-9 (gelatinase B) during the inflammatory phase, while MMP-2 (gelatinase A) was profoundly increased in the fibrotic phase. Immunohistochemistry revealed MMP-9 in and around bronchiolar and airspace neutrophils that were often associated with visible asbestos fibers. MMP-2 was found in fibrotic regions at 7, 14, and 28 d. No increases in RNA levels of MMP-2, MMP-9, or MMP-8 were found, but levels of MMP-7, MMP-12, and MMP-13 RNA did increase at 14 d. The MMP inhibitors, TIMP-1 and TIMP-2, were also increased at 7-28 d after asbestos exposure. To confirm the importance of MMP activity in disease progression, mice exposed to asbestos were given daily injections of the MMP inhibitor, GM6001. MMP inhibition reduced inflammation and fibrosis in asbestos-treated mice. Collectively, these data suggest that MMPs contribute to the pathogenesis of asbestosis through effects on inflammation and fibrosis development.

Transcriptional up‐regulation of MMPs 12 and 13 by asbestos occurs via a PKCδ‐dependent pathway in murine lung

Asbestos is a known inflammatory, carcinogenic, and fibrotic agent, but the mechanisms leading to asbestos-induced lung diseases are unclear. Using a murine inhalation model of fibrogenesis, we show that asbestos causes significant increases in mRNA levels of lung matrix metalloproteinases (MMPs 12 and 13) and tissue inhibitor of metalloproteinases (TIMP1), as well as increased activities of MMP 2, 9, and 12 in bronchoalveolar lavage fluids (BALF). Asbestos-exposed PKCdelta knockout (PKCdelta-/-) mice exhibited decreased expression of lung MMP12 and MMP13 compared with asbestos-exposed wild-type mice. Studies using small molecule inhibitors in murine alveolar epithelial type II cells (C10) and primary lung fibroblasts confirmed that asbestos transcriptionally up-regulates MMPs via an EGFR (or other growth factor receptors)/PI3K/PKCdelta/ERK1/2 pathway. Moreover, use of a broad-spectrum MMP inhibitor showed that MMPs play an important role in further enhancing asbestos-induced signaling events by activating EGFR. These data reveal a potentially important link between asbestos signaling and integrity of the extracellular matrix (ECM) that likely contributes to asbestos-induced lung remodeling and diseases.

Detecting cryptic epitopes created by nanoparticles

As potential applications of nanotechnology and nanoparticles increase, so too does the likelihood of human exposure to nanoparticles. Because of their small size, nanoparticles are easily taken up into cells (by receptor-mediated endocytosis), whereupon they have essentially free access to all cellular compartments. Similarly to macroscopic biomaterial surfaces (that is, implants), nanoparticles become coated with a layer of adsorbed proteins immediately upon contact with physiological solutions (unless special efforts are taken to prevent this). The process of adsorption often results in conformational changes of the adsorbed protein, which may be affected by the larger curvature of nanoparticles compared with implant surfaces. Protein adsorption may result in the exposure at the surface of amino acid residues that are normally buried in the core of the native protein, which are recognized by the cells as "cryptic epitopes." These cryptic epitopes may trigger inappropriate cellular signaling events (as opposed to being rejected by the cells as foreign bodies). However, identification of such surface-exposed epitopes is nontrivial, and the molecular nature of the adsorbed proteins should be investigated using biological and physical science methods in parallel with systems biology studies of the induced alterations in cell signaling.

Surface Modification of Silica Core−Shell Nanocapsules: Biomedical Implications

In this article we present the synthesis of oil core silica shell nanocapsules with different shell thicknesses. The surface of the nanocapsules was modified with polyethyleoxide (PEO) and succinic anhydride. Two biomedical tests were then used to study the biocompatibility properties of these nanocapsules with different surface treatments, hemolysis and thromboelastography (TEG). PEO surface modification greatly reduced the damaging interactions of nanocapsules with red blood cells (RBCs) and platelets and attenuated particle size effects. It was found that the blood toxicity of charged particles increased with the acid strength on the surface. Experiments toward the assessment of detoxification of these nanocapsules in model drug overdose concentrations are currently underway.

Interaction of Bovine Serum Albumin with Chrysotile: Spectroscopic and Morphological Studies

The biodurability of chrysotile fibers, which is related to their cytotoxicity and mutagenic responses, is strongly affected by the surface chemical adsorption of biological molecules. Natural chrysotile is a heterogeneous material in both structure and composition. The availability of synthetic stoichiometric chrysotile of constant structure and uniform morphology has allowed us to investigate its interaction with bovine serum albumin (BSA). By using transmission electron microscopy (TEM) and atomic force microscopy (AFM), we have obtained the first morphological evidence of albumin adsorption onto chrysotile nanocrystals. FTIR spectroscopy was used to quantify modifications of BSA secondary structure that were induced by the surface interaction. The protein transition to beta-turns allows a stronger interaction between the protein hydrophilic side-chains and the charged asbestos surface, which is consistent with hydrogen bonds involving the superficial OH groups. Synthetic stoichiometric chrysotile nanocrystals were shown to be an ideal reference standard with which to study the interaction of asbestos fibers with biological systems, in order to elucidate the chemical mechanisms of asbestos toxicity.

Carbon nanotubes: a review of their properties in relation to pulmonary toxicology and workplace safety

Carbon nanotubes (CNT) are an important new class of technological materials that have numerous novel and useful properties. The forecast increase in manufacture makes it likely that increasing human exposure will occur, and as a result, CNT are beginning to come under toxicological scrutiny. This review seeks to set out the toxicological paradigms applicable to the toxicity of inhaled CNT, building on the toxicological database on nanoparticles (NP) and fibers. Relevant workplace regulation regarding exposure is also considered in the light of our knowledge of CNT. CNT could have features of both NP and conventional fibers, and so the current paradigm for fiber toxicology, which is based on mineral fibers and synthetic vitreous fibers, is discussed. The NP toxicology paradigm is also discussed in relation to CNT. The available peer-reviewed literature suggests that CNT may have unusual toxicity properties. In particular, CNT seem to have a special ability to stimulate mesenchymal cell growth and to cause granuloma formation and fibrogenesis. In several studies, CNT have more adverse effects than the same mass of NP carbon and quartz, the latter a commonly used benchmark of particle toxicity. There is, however, no definitive inhalation study available that would avoid the potential for artifactual effects due to large mats and aggregates forming during instillation exposure procedures. Studies also show that CNT may exhibit some of their effects through oxidative stress and inflammation. CNT represent a group of particles that are growing in production and use, and therefore, research into their toxicology and safe use is warranted.

Molecular biology of malignant mesothelioma: a review

Malignant mesothelioma (MM) is an uncommon tumor with high mortality and morbidity rates. It arises from mesothelial cells that line the pleural, pericardial, peritoneal, and testicular cavities. This is a disease with an indolent course because tumors arise 20 to 40 years after exposure to an inciting agent. Extensive research has shown that mesothelial cells are transformed into MM cells through various chromosomal and cellular pathway defects. These changes alter the normal cells' ability to survive, proliferate, and metastasize. This article discusses the alterations that occur in transforming normal mesothelial cells into MM. It also details some of the signal transduction pathways that seem to be important in MM with the potential for novel targeted therapeutics.

Gene expression profiles reveal increased mClca3 (Gob5) expression and mucin production in a murine model of asbestos-induced fibrogenesis

To elucidate genes important in development or repair of asbestos-induced lung diseases, gene expression was examined in mice after inhalation of chrysotile asbestos for 3, 9, and 40 days. We identified changes in the expression of genes linked to proliferation (cyclin B2, CDC20, and CDC28 protein kinase regulatory subunit 2), inflammation (CCL9, CCL6, complement component 1, chitinase3-like 3, TNF superfamily member 10, and IL-1B), and matrix remodeling (MMP12, MMP3, integrin alphaX, and cathepsins K, Z, B, and S). The most highly induced gene at all time points was mclca3 (gob5), a putative calcium-activated chloride channel involved in the regulation of mucus production and/or secretion. Using histochemistry, we demonstrated accumulation of mucus and increased mClca3 protein in the bronchiolar epithelium of asbestos-exposed mice at all time points but peaking at 9 days. Cytokine levels (interleukin-1beta, interleukin-4, interleukin-6) in bronchoalveolar lavage fluid also increased at 9 days, suggesting Th2-mediated immunity may play a role in asbestos-induced mucus production. In contrast, levels of cathepsin K, a potent elastase, increased between 3 and 40 days at both the mRNA and protein levels, localizing primarily in CD45-positive leukocytes and interstitial cells. Identification of genes involved in lung injury and remodeling after asbestos exposure could aid in defining mechanisms of airborne particulate-induced disease and in developing therapeutic strategies.

Diffuse malignant mesothelioma of the peritoneum: a clinicopathological study of 35 patients treated locoregionally at a single institution

BACKGROUND

In the current study, the authors report the clinicopathologic features of patients with peritoneal diffuse malignant mesothelioma (DMM) who were treated in a uniform fashion at a single institution to assess prognostic factors.

METHODS

Thirty-five patients were treated with cytoreductive surgery (CRS) and intraperitoneal hyperthermic perfusion (IPHP). The tumors were classified into epithelial, sarcomatoid, and biphasic types. Immunohistochemistry stains were performed for calretinin, WT-1, pCEA, Ber-EP4, epidermal growth factor receptor (EGFR), p16, matrix metalloprotease-2 (MMP-2), and MMP-9. Statistical correlation was evaluated for age, gender, completeness of cytoreduction (CC), tumor histotype, mitotic count (MC), necrosis, nuclear grade (NG), and biologic markers with regard to overall survival (OS) and progression-free survival (PFS).

RESULTS

The patient group was comprised of 15 men and 20 women with a median age of 52 years (range, 24-73 yrs). Twenty-five patients underwent optimal cytoreduction. There were 32 epithelial tumors and 3 biphasic tumors, and 3 patients had an NG of 1, 19 had an NG of 2, and 13 had an NG of 3. The mean MC was 14.1 (range, 0-160 per 50 high-power fields). Necrosis was present in 11 cases. All the tumors were found to be positive for calretinin and WT-1 and were negative for pCEA and Ber-EP4. The NG and MC were found to be significantly associated with OS (P = 0.02 and P = 0.01, respectively) whereas CC was found to be associated with both OS (P = 0.05) and PFS (P = 0.03). No biologic markers were found to be of prognostic significance.

CONCLUSIONS

The results of the current study indicate that NG, MC, and CC may be useful prognostic factors in patients treated with CRS and IPHP. The expression of EGFR, MMP-2, and MMP-9 and absent and/or reduced expression of p16 in DMMs confirms the results of previous studies suggesting their role in tumor pathogenesis and kinetics.

Interleukin-12 is not essential for silicosis in mice

BACKGROUND

Silicosis features foci of inflammation where macrophages and lymphocytes precede and accompany fibroblast proliferation, alveolar epithelial hyperplasia, and increased deposition of connective tissue matrix material. In the mouse following silica inhalation there is recruitment of natural killer-, B-, and CD4+ and CD8+ lymphocytes to the alveolar spaces, enlargement of bronchial-associated lymphoid tissues (BALT), and aggregation of lymphocytes surrounding small airways and blood vessels. A substantial fraction of the recruited lung lymphocytes produce interferon-gamma (IFN-gamma), and IFN-gamma gene-deleted mice develop less silicosis than wild-type mice. Interleukin-12 (IL-12) is an important pathway for driving the adaptive immune response towards a TH1-like phenotype. We hypothesized that IL-12 might stimulate lymphocyte activation and the up-regulation of IFN-gamma, and consequently be an essential mediator for silicosis.

RESULTS

C57Bl/6 wild-type (WT) and IL-12 deficient (IL-12 KO) mice were exposed to sham-air or crystobalite silica (61 mg/m3) by inhalation for 5 hours/day for 12 days and then studied from 1 to 112 days after exposure. Mice exposed to sham-air had normal lung histology at all time points. WT mice exposed to titanium dioxide (72 mg/m3) showed pulmonary macrophage recruitment but no increase in lung collagen. Both WT and IL-12 KO mice exposed to silica showed similar progressive lung pathology, increased wet lung weight and increased total lung collagen (hydroxyproline). IL-12 p35 mRNA was not increased in either strain after silica exposure; IL-12 p40 mRNA was up-regulated after silica in WT mice and constitutively absent in the IL-12 KO mice. IL-18 mRNA was not increased after silica exposure. The expression of IL-15 (an important driver for innate immunity, Natural Killer cell activation, and IFN-gamma production) was abundant in air-exposed mice and was increased slightly in the lungs of mice with silicosis.

CONCLUSION

The axis of IL-12 driving IFN-gamma production is not essential for the full manifestations of silicosis in mice exposed to a crystobalite silica aerosol.

Asbestos-induced lung inflammation and epithelial cell proliferation are altered in myeloperoxidase-null mice

Asbestos fibers are carcinogens causing oxidative stress and inflammation, but the sources and ramifications of oxidant production by asbestos are poorly understood. Here, we show that inhaled chrysotile asbestos fibers cause increased myeloperoxidase activity in bronchoalveolar lavage fluids (BALF) and myeloperoxidase immunoreactivity in epithelial cells lining distal bronchioles and alveolar ducts, sites of initial lung deposition of asbestos fibers. In comparison with sham mice, asbestos-exposed myeloperoxidase-null (MPO-/-) and normal (MPO+/+) mice exhibited comparable increases in polymorphonuclear leukocytes, predominately neutrophils, in BALF after 9 days of asbestos inhalation. Differential cell counts on BALF revealed decreased proportions of macrophages and increased lymphocytes in all mice exposed to asbestos, but numbers were decreased overall in asbestos-exposed myeloperoxidase-null versus normal mice. Asbestos-associated lung inflammation in myeloperoxidase-null mice was reduced (P < or = 0.05) in comparison with normal asbestos-exposed mice at 9 days. Decreased lung inflammation in asbestos-exposed myeloperoxidase-null mice at 9 days was accompanied by increases (P < or = 0.05) in Ki-67- and cyclin D1-positive immunoreactive cells, markers of cell cycle reentry, in the distal bronchiolar epithelium. Asbestos-induced epithelial cell proliferation in myeloperoxidase-null mice at 30 days was comparable to that found at 9 days. In contrast, inflammation and epithelial cell proliferation in asbestos-exposed normal mice increased over time. These results support the hypothesis that myeloperoxidase status modulates early asbestos-induced oxidative stress, epithelial cell proliferation, and inflammation.

P53 mediates amosite asbestos-induced alveolar epithelial cell mitochondria-regulated apoptosis

Asbestos causes pulmonary toxicity in part by generating reactive oxygen species that cause DNA damage. We previously showed that the mitochondria-regulated (intrinsic) death pathway mediates alveolar epithelial cell (AEC) DNA damage and apoptosis. Because p53 regulates the DNA damage response in part by inducing intrinsic cell death, we determined whether p53-dependent transcriptional activity mediates asbestos-induced AEC mitochondrial dysfunction and apoptosis. We show that inhibitors of p53-dependent transcriptional activation (pifithrin and type 16-E6 protein) block asbestos-induced AEC mitochondrial membrane potential change (DeltaPsim), caspase 9 activation, and apoptosis. We demonstrate that asbestos activates p53 promoter activity, mRNA levels, protein expression, and Bax and p53 mitochondrial translocation. Further, pifithrin, E6, phytic acid, or rho(0)-A549 cells (cells incapable of mitochondrial reactive oxygen species production) block asbestos-induced p53 activation. Finally, we show that asbestos augments p53 expression in cells at the bronchoalveolar duct junctions of rat lungs and that phytic acid prevents this. These data suggest that p53-dependent transcription pathways mediate asbestos-induced AEC mitochondria-regulated apoptosis. This suggests an important interactive effect between p53 and the mitochondria in the pathogenesis of asbestos-induced pulmonary toxicity that may have broader implications for our understanding of pulmonary fibrosis and lung cancer.

The central role of Fas-ligand cell signaling in inflammatory lung diseases

Following inflammation and injury in the lung, loss of epithelial cell precursors could determine the balance between tissue regeneration and fibrosis. This review discusses evidence that proapoptotic Fas‐Fas ligand (FasL) signaling plays a central role in pulmonary inflammation, injury and fibrosis. FasL signaling induces inflammatory apoptosis in epithelial cells and alveolar macrophages, with concomitant IL‐1β and chemokine release, leading to neutrophil infiltration. FasL signaling plays a critical role in models of acute lung injury, idiopathic pulmonary fibrosis and silicosis; blockade of Fas‐FasL interactions either prevents or attenuates pulmonary inflammation and fibrosis. Serologic and immunohistochemical studies in patients support a major pathogenic role of Fas and FasL molecules in inflammatory lung diseases. Identification of the pathogenic role of FasL could facilitate the discovery of more effective treatments for currently untreatable inflammatory lung diseases.

Cysteine cathepsins in human silicotic bronchoalveolar lavage fluids

Mature, active cysteine cathepsins (CPs) were identified in human inflammatory bronchoalveolar lavage fluid (BALF) supernatants from patients suffering from silicosis by both western blot and surface plasmon resonance analyses. BALFs are not a reservoir of activatable proforms, since no autocatalytic maturation at acidic pH occurs. Cathepsin H is the most profuse among studied CPs (median value: 36.5 nM), while cathepsins B and L are the two most abundant thiol-dependent endoproteases. The overall concentration of active cathepsins B, H, K, L, and S is approximately 10-fold lower than their concentration in BALF supernatants from patients suffering from inflammatory acute lung injuries (962+/-347 nM).The cathepsins (approximately 70 nM)/cystatin-like inhibitors (approximately 9 nM) ratio is unbalanced in favor of enzymes ( approximately 8-fold). This presence of uncontrolled CPs suggests that they may contribute, in addition to matrix metalloproteases, to the lung tissue breakdown/remodeling occurring during silicosis, although their exact contribution to interstitial inflammation remains to be evaluated.

Oxidant-mediated cAMP response element binding protein activation: calcium regulation and role in apoptosis of lung epithelial cells

Oxidant stress-mediated regulation of extracellular signal-regulated kinases (ERK1/2) is linked to pathologic outcomes in lung epithelium, yet a role for Ca2+ and Ca2+/cAMP-response element binding protein (CREB) in ERK1/2 signaling has not been defined. In this study, we tested the hypotheses that oxidants induce Ca2+-mediated phosphorylation of ERK and CREB, and that CREB is required for oxidant-induced proliferation and apoptosis. H2O2 initiated an influx of extracellular Ca2+ that was required for phosphorylation of both ERK and CREB in C10 lung epithelial cells. H2O2-mediated CREB phosphorylation was sensitive to MEK inhibition, suggesting that crosstalk between Ca2+, ERK, and CREB signaling pathways contributes to the oxidant-induced response. Reduction of CREB activity, using a dominant-negative CREB construct, inhibited c-fos steady-state mRNA levels, but unexpectedly enhanced bcl-2 steady-state mRNA levels after H2O2 exposure. Whereas inhibition of CREB activity had no detectable effect on H2O2 stimulation of cell cycle, loss of CREB activity significantly reduced the number of cells undergoing apoptosis. These data support a novel communication between Ca2+-ERK1/2 and CREB elicited by H2O2, and further provide evidence that CREB is an important regulator of apoptosis in oxidant-mediated responses of lung epithelial cells.

Amorphous silica particles promote inflammatory gene expression through the redox sensitive transcription factor, AP-1, in alveolar epithelial cells

Ultrafine particulate (UFP) matter, from environmental or industrial exposure, can induce expression of inflammatory mediators and promote production of reactive oxygen species. Previous studies showed various cellular stresses activate signaling pathways operating through specific transcription factors (TFs), activator protein (AP)-1 and nuclear factor (NF)-kappaB, known to regulate inflammatory gene expression. Exposing MLE15 cells to inflammatory, or UFP, stimuli increased macrophage inflammatory protein (MIP)-2 protein, in the absence of the NF = kappaB inhibitor IkappaBc degradation, synergistically increasing in the presence of proteosomal inhibition. Although thiol antioxidants attenuate MIP-2 induction, mitogen-activated protein kinase (MAPK) inhibitors significantly inhibit MIP-2 protein production. This suggests UFP promote inflammatory gene expression through the redox responsive TF AP-1.

Relevância do lavado broncoalveolar na quantificação de partículas inaladas nas diversas formas de silicose

Silicosis is a disease caused by inhalation and deposition of crystalline silica that produces a fibrous tissue reaction. Bronchoalveolar lavage is a noninvasive technique that allows identifying particles, thus characterizing exposure to mineral dust. The aim of this work was to study bronchoalveolar lavage as a mean of estimating the amount of alveolar particles in different forms of silicosis. Bronchoalveolar lavage was carried out in 27 silicotic patients with simple (n = 12), complicated (n = 13), and acute (n = 2) forms of the disease and 7 healthy individuals as a control group. Macrophages were scored enumerating the percentage of cells with particles by polarizing light microscopy. Silicotic patients showed a marked increase in BAL cell particles compared to control population, however, relating simple to complicated silicosis, no significant difference was observed. In acute silicotic patients with massive silica dust exposure, more than 70% of BAL alveolar macrophages contained dust particles. When duration of exposure and retirement from work were evaluated, an inverse correlation between duration of exposure and the amount of alveolar dust, and a tendency to a smaller involvement on macrophages with the greater period of retirement from work were observed. These results suggest that particle analysis in BAL may be important in order to establish the nature and intensity of exposure.

Lung cancer and mesothelioma in towns with environmental exposure to asbestos in Eastern Anatolia

OBJECTIVE

Our previous study demonstrated the presence of environmental tremolite and chrysotile asbestos fiber exposure in Hekimhan town in Malatya located in eastern Turkey. The aim of this study was to investigate whether environmental asbestos exposure increases the incidence of lung cancer and mesothelioma.

METHOD

One hundred and forty-nine patients with mesothelioma and lung cancer living in the center or in the towns of Malatya were retrospectively analyzed. The Incidences of lung cancer and mesothelioma were calculated.

RESULTS

The incidences of lung cancer and mesothelioma were 3.39/100,000 and 0.21/100,000, respectively, for the whole population of Malatya; while they were 8.23/100,000 and 1.45/100,000 in Hekimhan. The incidences were strikingly high (22.39/100,000 for lung cancer and 7.46/100,000 for mesothelioma) in Arguvan, another town in Malatya where an analysis for asbestos could not be performed. The overall incidence in Turkey was reported as 5.9/100,000 by the Health Ministry in 1994. The incidences of lung cancer were nearly 1.3-fold higher in Hekimhan and fourfold higher in Arguvan then in the general population of Turkey.

CONCLUSION

The incidences of mesothelioma and lung carcinoma in Hekimhan were higher than those of the general population in Turkey, suggesting a role of environmental asbestos exposure in lung cancer and mesothelioma.

Effects of airborne fine particulate matter on antioxidant capacity and lipid peroxidation in multiple organs of rats

The purpose of this research was to determine whether airborne fine particulate matter (PM(2.5)) could increase levels of lipid peroxidation and alter intracellular redox status in multiple organs of rats. Thirty-two male Wistar rats were randomly divided into the treated groups using PM(2.5) at different dosages (1.5, 7.5, 37.5 mg/kg) and with a control group using saline. Rats were sacrificed 24 h after one-time intratracheal instillation. Then we investigated the activities of Cu, Zn-superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), and the levels of glutathione (GSH) and thiobarbituric acid-reactive substances (TBARS) in hearts, livers, spleens, lungs, kidneys, brains, and testicles. It was found that PM(2.5) at dosages of 7.5 and 37.5 mg/kg significantly increased lipid peroxidation levels in the hearts, livers, lungs, and testicles, decreased SOD, CAT, and GPx activities in the lungs, livers, kidneys, and brains, and depleted GSH levels in all the measured organs compared to the control. There were also differences in the changes of antioxidative enzymes activities and lipid peroxidation levels in seven organs. These results led to a conclusion that airborne PM(2.5) was a systemic toxic agent, not only to respiratory and cardiovascular systems. Its toxic effects might be attributed to oxidative damage mediated by prooxidant/antioxidant imbalance or excess free radicals. Further work is required to explain the toxicity role of PM(2.5) on multiple organs of mammals.

Poly(ADP-ribosyl)ation in asthma and other lung diseases

Inhibition of poly(ADP-ribosyl)ation in oxidative stress-related pathologies has recently emerged as a very effective anti-inflammatory intervention in animal models of arthritis, colitis, diabetes and shock. Recent data from three laboratories also support the role of poly(ADP-ribose) polymerase-1 (PARP-1) activation in asthma. Similarly to other inflammatory conditions, the protective effects of PARP inhibition and the PARP-1 knock out phenotype in asthma models have been attributed to inhibition of inflammatory signal transduction (mainly via NF-kappaB) and of oxidative stress-induced cell dysfunction and tissue injury. Here I discuss the complex role of poly(ADP-ribosyl)ation in the regulation of inflammatory cell migration, chemokine and cytokine production and expression of other inflammatory mediators (inducible nitric oxide synthase, matrix metalloproteinases) in asthma. The role of PARP-1 in other oxidative stress-related lung diseases such as asbestosis, silicosis, acute respiratory distress syndrome and ischemia-reperfusion injury is also reviewed.

Basic pathogenetic mechanisms in silicosis: current understanding

PURPOSE OF REVIEW

Silicosis continues to be a common cause of chronic lung diseases, despite evidence that these diseases can be prevented by environmental dust control. Silicosis has been studied extensively by basic and clinical scientists, yet little is known about the crucial cellular and molecular mechanisms that initiate and propagate the process of inflammation and scarring.

RECENT FINDINGS

Recent in vivo, in vitro, and human studies have focused on several main areas of investigation into the causes and processes of the development of silicosis. These areas of investigation include the variability of pathogenic potential of different varieties of silica; the role of activated alveolar macrophages products in the development and progression of silicosis; and the direct role played by the silica particle surface in triggering adverse biologic reactions, such as generating ROS and RNS. The generation of oxidants by silica particles and by silica-activated cells results in cell and lung damage; increased expression of inflammatory cytokines, including TNF-alpha, IL 1 beta, and TGF-beta; activation of cell signaling pathways, including the MAP kinase pathways; and phosphorylation and activation of specific transcription factors (e.g., NFkB). The ROS, RNS, and NO generated by the silica particles also induce apoptosis in macrophages and other cells.

SUMMARY

Further research on the molecular mechanisms involved in the inflammatory processes important for progression to fibrotic diseases is needed for the development of effective treatment of silicosis. Potential therapeutic strategies include inhibition of cytokines such as IL-1, TNF alpha, the use of anti-oxidants, and the inhibition of apoptosis.

Roles of plasma proteins in the formation of silicotic nodules in rats

The contribution of plasma protein(s) to the stabilization of fibroids formed in rat lungs exposed to acute silica dust inhalation was examined. Antibodies against component proteins of the nodules remaining insoluble in 2% SDS, 10M urea and 40 mM sulfhydryl reagents under prolonged boiling conditions were raised in rabbits and used to capture plasma proteins, which were identified by 2D-gel electrophoresis and MALDI-TOF analysis. The silica particles were encapsulated with extracellular protein composites whose amino acid compositions showed high levels of alanine, i.e., above those of glycine and proline, a building block of collagen. Antibody-captured plasma proteins showed the dominant presences of fibrinogen, albumin, and prealbumin (transthyretin), and other minor proteins, which included alpha-1-protease inhibitor, contraspin-like protease inhibitor, cathepsin B, etc. The presence of the N(epsilon)-(gamma-glutamyl) lysine isopeptide bond in the nodules was evidenced by direct chemical methods and by immunoreactivity for anti-isopeptide bonds. Immunostaining of affected lung tissue and of the fibroid regions showed elevated levels of transglutaminase (TGase) E and plasma factor XIII (F-XIII), but showed no reactivity towards other TGases. These findings suggest that the silica encapsulated nodules are a mixture of extracellular proteins that include collagen type I, fibrin and transthyretin, which is stabilized by TGase catalyzed crosslinking between plasma and extracellular proteins during fibrosis to eventually form insoluble nodules.

Chemo-enzymatic synthesis and cell-growth inhibition activity of resveratrol analogues

The stilbenoid resveratrol (1) was subjected to regioselective acetylation catalysed by Candida antarctica lipase (CAL) to obtain 4'-acetylresveratrol (2). CAL biocatalysed regioselective alcoholysis of 3,5,4'-triacetylresveratrol (3), 3,5,4'-tributanoylresveratrol (6), and 3, 4, 5'-trioctanoylresveratrol (9) afforded derivatives 4, 5, 7, 8, 10, and 11. Further resveratrol analogues (12-18) were obtained through methylation and hydrogenation reactions, whereas the 3,4,4'-trimethoxystilbene (19) was obtained by complete synthesis. Resveratrol and its lipophylic analogues were subjected to cell-growth inhibition bioassays towards DU-145 human prostate cancer cells. Compounds 2-19 showed cell-growth inhibition activity comparable to or higher than resveratrol (GI(50)=24.09 microM), displaying low or very low toxicity against non-tumorigenic human fibroblast cells. Comparison of the trimethoxy stilbenes 12 (GI(50)=2.92 microM) and 19 (GI(50)=25.39 microM) indicates that the position of the substituents is important for the activity. The marked activity of methyl ethers 12, 13, and 18 in comparison with that of the corresponding esters suggests that the different chemical reactivity, rather than steric factors, strongly influences the activity.

Scavenger receptor class A type I/II (CD204) null mice fail to develop fibrosis following silica exposure

Alveolar macrophages express the class A scavenger receptor (CD204) (Babaev VR, Gleaves LA, Carter KJ, Suzuki H, Kodama T, Fazio S, and Linton MF. Arterioscler Thromb Vasc Biol 20: 2593-2599, 2000); yet its role in vivo in lung defense against environmental particles has not been clearly defined. In the current study, CD204 null mice (129Sv background) were used to investigate the link between CD204 and downstream events of inflammation and fibrosis following silica exposure in vivo. CD204-/- macrophages were shown to recognize and uptake silica in vitro, although this response was attenuated compared with 129Sv wild-type mice. The production of tumor necrosis factor-alpha in lavage fluid was significantly enhanced in CD204 null mice compared with wild-type mice following silica exposure. Moreover, after exposure to environmental particles, CD204-/- macrophages exhibited improved cell viability in a dose-dependent manner compared with wild-type macrophages. Finally, histopathology from a murine model of chronic silicosis in 129Sv wild-type mice displayed typical focal lesions, interstitial thickening with increased connective tissue matrix, and cellular infiltrate into air space. In contrast, CD204-/- mice exhibited little to no deposition of collagen, yet they demonstrated enhanced accumulation of inflammatory cells largely composed of neutrophils. Our findings point to an important role of CD204 in mounting an efficient and appropriately regulated immune response against inhaled particles. Furthermore, these results indicate that the functions of CD204 are critical to the development of fibrosis and the resolution of inflammation.

Cytotoxicity assessment of some carbon nanotubes and related carbon nanoparticle aggregates and the implications for anthropogenic carbon nanotube aggregates in the environment

Nanotechnology and nanomaterials have become the new frontier world-wide over the past few years and prospects for the production and novel uses of large quantities of carbon nanotubes in particular are becoming an increasing reality. Correspondingly, the potential health risks for these and other nanoparticulate materials have been of considerable concern. Toxicological studies, while sparse, have been concerned with virtually uncharacterized, single wall carbon nanotubes, and the conclusions have been conflicting and uncertain. In this research we performed viability assays on a murine lung macrophage cell line to assess the comparative cytotoxicity of commercial, single wall carbon nanotubes (ropes) and two different multiwall carbon nanotube samples; utilizing chrysotile asbestos nanotubes and black carbon nanoaggregates as toxicity standards. These nanotube materials were completely characterized by transmission electron microscopy and observed to be aggregates ranging from 1 to 2 microm in mean diameter, with closed ends. The cytotoxicity data indicated a strong concentration relationship and toxicity for all the carbon nanotube materials relative to the asbestos nanotubes and black carbon. A commercial multiwall carbon nanotube aggregate exhibiting this significant cell response was observed to be identical in structure to multiwall carbon nanotube aggregates demonstrated to be ubiquitous in the environment, and especially in indoor environments, where natural gas or propane cooking stoves exist. Correspondingly, preliminary epidemiological data, although sparse, indicate a correlation between asthma incidence or classification, and exposure to gas stoves. These results suggest a number of novel epidemiological and etiological avenues for asthma triggers and related respiratory or other environmental health effects, especially since indoor number concentrations for multiwall carbon nanotube aggregates is at least 10 times the outdoor concentration, and virtually all gas combustion processes are variously effective sources. These results also raise concerns for manufactured carbon nanotube aggregates, and related fullerene nanoparticles.

Fibroblast Growth Factor-10 Prevents Asbestos-Induced Alveolar Epithelial Cell Apoptosis by a Mitogen-Activated Protein Kinase–Dependent Mechanism

Asbestos induces alveolar epithelial cell (AEC) DNA damage and apoptosis by the mitochondria-regulated death pathway and oxidative stress. Fibroblast growth factor-10 (FGF-10), an alveolar epithelial type II cell mitogen that is required for the lung development, prevents H(2)O(2)-induced AEC DNA damage by a mitogen activated protein kinase (MAPK)/extracellular signal-regulated kinase (ERK)-dependent mechanism. In this study, we show that FGF-10 attenuates asbestos-induced AEC DNA strand break formation and apoptosis. MAPK/ERK kinase (MEK) inhibitors, U0126 or PD98059, each blocked the protective effect of FGF-10 against asbestos-induced DNA damage and apoptosis, whereas a p38-MAPK inhibitor had a negligible effect, suggesting a crucial role for MEK/ERK activation in mediating the protective effects of FGF-10. Further, we show that FGF-10 attenuates asbestos-induced change in AEC mitochondrial membrane potential and caspase 9 activation, both of which are blocked by U0126. We conclude that FGF-10 decreases asbestos-induced AEC DNA damage and apoptosis in part by mechanisms involving MEK/ERK-dependent signaling that affects the mitochondria-regulated death pathway.

Asbestos induces tissue factor in Beas-2B human lung bronchial epithelial cells in vitro

Asbestos has been implicated in the pathogenesis of interstitial lung diseases including asbestosis. Tissue factor (TF) initiates blood coagulation in vivo contributing to inflammation and tissue remodeling via extravascular fibrin deposition and signaling for profibrogenic mediators. We hypothesized that asbestos could induce TF expression by lung epithelial cells. We found that TF mRNA and TF-dependent procoagulant activity were induced in asbestos-treated Beas-2B human airway epithelial cells, which we used as a model system. The effect was increased by crocidolite and chrysotile versus control particulates, including titanium dioxide (TiO2) and Wollastonite (W). Transcription factors that bind the TF gene promoter, including NF-kappaB, AP1 and Sp1, were induced by asbestos while TF mRNA was unstable. TF mRNA was inhibited by mithramycin in asbestos-treated as well as control cells suggesting that Sp1 contributes to TF maintenance in Beas-2B cells. Sp1 knockdown with specific siRNA decreased TF antigen, which is consistent with Sp1-mediated control of TF in Beas-2B cells. The results demonstrate that asbestos induces TF expression in lung epithelial cells in vitro, representing a newly recognized potential mechanism by which asbestos may modulate epithelial cell responses germane to lung remodeling. The mechanism involves alterations in steady-state TF mRNA that do not involve posttranscriptional regulation, implicating control of TF gene expression at the transcriptional level through Sp1 or other transcription factors.

Evaluation of cellular toxicity of TAFMAG, a natural substitute for asbestos from China

Asbestos is a very important material for industrial use. However, the need for a substitute for asbestos fiber is currently on the rise due to its high disease causing potential. This study evaluated the potential bio-hazardous effects of TAFMAG, a natural fibrous silicate produced in China, in comparison with chrysotile, a typical toxic asbestos. The physicochemical properties of TAFMAG were very similar to those of chrysotile when it was examined by a scanning electron microscope (SEM) and X-ray diffraction (XRD) analyses. Both of TAFMAG and chrysotile showed high content of magnetite and Fenton activity when compared with wollastonite, a non-asbestos fiber with a known low toxicity. When their cellular toxicity was assessed, TAFMAG showed no or less comparable to that of chrysotile in the hemolysis and lipid peroxidation of erythrocytes, and also on a MTT assay in RLE-6TN, a rat alveolar epithelial cell line. Pre-treatment of fibers with desferrioxamine, an iron chelator, showed that iron content of TAFMAG and chrysotile might be important in their cellular toxicity. These results suggest that TAFMAG is potentially toxic when inhaled into the lung and appropriate laws and regulations should be established for its use.

Potential toxicity of nonregulated asbestiform minerals: balangeroite from the western Alps. Part 1: Identification and characterization

In the Italian western Alps, asbestos mineralization (both chrysotile and tremolite amphibole) takes place from serpentinites, together with other less common asbestiform minerals not regulated by the current legislation. In the context of a study on the evaluation of the asbestos risk in this area, the possible role played by the associated asbestiform minerals in the overall toxicity of the airborne fraction has been examined. The first mineral investigated was balangeroite [(Mg,Fe2+,Fe3+,Mn2+)42Si16O54(OH)36], an iron-rich asbestiform contaminant of chrysotile from the Balangero mine (Piedmont), which crystallizes as rigid and brittle fibers. In order to prepare a sample in a form appropriate for chemical and cellular tests, the fibers were separated from the rock and comminuted without damage to their crystalline structure and surface state (as confirmed by X-ray diffraction [XRD] and ultraviolet-visible [UV-Vis] spectroscopy). The first properties examined were durability in simulated body fluids (Gamble's solution) and toxicity to epithelial cells. When compared to UICC crocidolite (the amphibole blue asbestos, regarded as the most pathogenic form), balangeroite appears even more durable than crocidolite. Balangeroite and UICC crocidolite showed a similar in vitro cytotoxic effect on a human epithelial cell line, as evidenced by leakage of intracellular lactate dehydrogenase (LDH) activity, which, observed after a 24-h incubation, was dose dependent and maximal at 12 microg/cm2 for each fiber type. Data show that chemical composition, form, durability, and cell toxicity indicate balangeroite as a potentially harmful fibrous mineral that needs to be examined by further chemical and cellular tests.

Matrix metalloproteinase/epidermal growth factor receptor/mitogen-activated protein kinase signaling regulate fra-1 induction by cigarette smoke in lung epithelial cells

Exposure to cigarette smoke (CS) can lead to the development of lung cancer, but the molecular mechanisms underlying this process remain unclear. Given that activator protein 1 (AP-1) regulates genes involved in both physiologic and pathophysiologic processes, we have investigated the effects of CS on Jun and Fos family member expression and regulation using a nonmalignant human bronchial epithelial cell line, 1HAEo. Exposure to CS caused a marked upregulation of c-Jun, c-Fos, and Fra-1, but not of Fra-2, Jun-B, and Jun-D expression. Because Fra-1 is overexpressed in various tumors and upregulates genes associated with tumor progression, we further elucidated the mechanisms that control CS-stimulated fra-1 induction. CS stimulated fra-1 induction primarily at the transcriptional level. However, epidermal growth factor receptor (EGFR)-specific inhibitor, AG1478, completely suppressed CS-stimulated fra-1 expression. Similarly, the specific inhibitors of extracellular signal-regulated kinase (ERK), c-Jun NH2 terminal kinase (JNK), and p38 kinase signaling markedly suppressed fra-1 induction. Consistent with this finding, AG1478 blocked CS-stimulated ERK, JNK, and p38 phosphorylation. These results suggest that EGFR-activated multiple kinase signaling is essential for fra-1 induction. Furthermore, treatment of cells with GM6001, which inhibits matrix metalloproteinase activity, significantly suppressed CS-stimulated EGF shedding, EGFR and ERK kinase phosphorylation, and subsequent fra-1 induction. Collectively, our findings indicate an obligatory role for metalloproteinase-EGFR-mediated mitogen-activated protein kinase signaling in controlling CS-induced fra-1 expression.

A case report of anthracosilicotic spindle-cell pseudotumor of mediastinal lymph node: Cytologic diagnosis by endoscopic ultrasound-guided fine-needle aspiration

Pigmented spindle-cell tumors of the lymph nodes have a broad differential diagnosis, including both benign and malignant neoplasms. Here, we report a case of a pigmented spindle-cell lesion in a mediastinal lymph node mimicking a spindle-cell melanoma on fine-needle aspiration cytology. Smears showed atypical polygonal and spindle cells with bland nuclear features and abundant cytoplasmic anthracotic pigment. Immunohistochemistry was negative for melanoma markers, but showed positivity for histiocyte markers. Polarization microscopy revealed minute birefringent intracellular crystals consistent with silica. Electron microscopy was confirmatory and a diagnosis of anthracosilicotic spindle-cell pseudotumor was made. To the best of our knowledge, fine-needle aspiration cytology findings of this lesion have not been reported.

The γ-Glutamylcysteine Synthetase and Glutathione Regulate Asbestos-induced Expression of Activator Protein-1 Family Members and Activity

Asbestos fibers cause persistent increases in activator protein-1 (AP-1) family member proto-oncogenes in lung epithelial and mesothelial cells that are linked to proliferation and cell transformation. Using lung epithelial cells, the progenitor cells of lung cancers, we report that crocidolite asbestos initially depletes intracellular glutathione followed by up-regulation of both catalytic and modifier subunits of gamma-glutamylcysteine synthetase. In vivo asbestos inhalation experiments confirm increased protein levels of gamma-glutamylcysteine synthetase in mouse lungs. We also show that asbestos-induced mRNA levels of fos/jun proto-oncogenes, fra-1 transactivation, and AP-1 to DNA binding activity are glutathione-dependent. Epidermal growth factor receptor activity by asbestos is blocked by N-acetyl-l-cysteine, suggesting that it is an initial redox-activated event leading to downstream AP-1 proto-oncogene up-regulation. The overexpression of subunits of gamma-glutamylcysteine synthetase in combination completely blocked asbestos-induced up-regulation of AP-1 proto-oncogene expression. However, when overexpressed individually, the modifier subunit had more dramatic effects than the catalytic subunit. Our work shows that the glutathione-controlled redox status of the epithelial cell plays a pivotal role in asbestos-induced epidermal growth factor receptor and proto-oncogene activation as well as AP-1 activity.

Lung oxidative response after acute coal dust exposure

Coal dust exposure can induce an acute alveolar and interstitial inflammation that can lead to chronic pulmonary diseases. The objective of this study was to describe the acute and later effects of acute coal dust exposure in lung parenchyma and the involvement of reactive oxygen species in coal dust effects. Forty-eight male Wistar rats (200-250 mg) were separated into four groups: 48 h, 7 days, 30 days, and 60 days after coal dust instillation. Gross mineral coal dust (3 mg/0.5 mL saline) was administered directly in the lungs of the treatment group by intratracheal instillation. Control animals received only saline solution (0.5 mL). Lipid peroxidation was determined by the quantity of thiobarbituric acid-reactive species (TBARS), oxidative damage to protein was obtained by the determination of carbonyl groups, the total radical-trapping antioxidant parameter (TRAP) was estimated by luminol chemoluminescence emission, catalase activity was measured by the rate of decrease in hydrogen peroxide, and superoxide dismutase activity was assayed by the inhibition of adrenaline autooxidation. Histological evaluation of coal dust-treated rats demonstrated an inflammatory infiltration after 48 h of the exposure. Initially, this was a cellular infiltration suggestive of lymphocyte infiltration with lymphoid hyperplasia that remained until 7 days after induction. This initial response was followed by a chronic inflammatory infiltration characterized by aggregates of macrophages 30 days after induction. This inflammatory response tended to resolve 60 days after induction, being similar to that of control animals. During both the acute and chronic phases of lung inflammation we observed a decrease in the TRAP in the lung of coal dust-exposed animals compared to that in control animals. We also observed an activation of superoxide dismutase 60 days after coal dust exposition. TBARS were increased 60 days after coal dust exposure and protein carbonyl groups increased at all times after coal dust exposure (48 h, 7 days, 30 days, and 60 days). These data suggested a biphasic inflammatory response and the involvement of oxidative damage in coal dust-induced lung damage.

Behaviour of the new asbestos amphibole fluor-edenite in different lung cell systems

The aim of the present research was to determine whether the recently identified and characterized new fibrous amphibole fluoro-edenite may induce a cytopathic response in cultured cells. The final goal was to gain suggestions on the potentiality of fluoro-edenite to be harmful to human beings. Epidemiological studies, in fact, have shown an excess of developing mesothelioma among residents in Biancavilla, a town in eastern Sicily located in the Etna volcanic area. Therefore, we treated human lung fibroblasts, human lung alveolar epithelial cancer cell line A549 and monocyte-macrophage cell line J774 with fluoro-edenite or crocidolite; the latter used as a highly toxic amphibole asbestos reference. Our results show that fluoro-edenite may induce functional modifications and affects some biochemical parameters in tested cell cultures in a concentration and time dependent manner. However, the observed functional modifications induced by fluoro-edenite are generally less dramatic than those induced by crocidolite and more evident on human lung alveolar epithelial cancer cell line A549 with respect to those obtained on human lung fibroblasts or monocyte-macrophage cell line J774. The sequence of the damage is hypothesised to be as follows: at increasing fluoro-edenite concentrations, and/or treatment times, the increase in reactive oxygen species (ROS) production could trigger significant DNA damage in cell cultures, concomitantly with drop in cell metabolism and increase in lactic dehydrogenase release. In conclusion, according to our data, fluoro-edenite appears as a probable carcinogenic agent, responsible for the high incidence of malignant pleural mesothelioma in Biancavilla.

Production of nitric oxide elevates nitrosothiol formation resulting in decreased glutathione in macrophages exposed to asbestos or asbestos substitutes

The purpose of this study was to investigate the effects of pneumoconiogenic particles, such as asbestos, on nitrosothiol formation in macrophages. In addition, the effects of man-made mineral fibers (MMMFs) were also evaluated, because they have come into heavy use as substitutes for asbestos. RAW264.7 cells and J774 cells of murine macrophage cell lines were cultured with chrysotile B (CH) asbestos, crocidolite (CR) asbestos, or MMMFs comprised of glass wool (GW), rock wool (RW), or ceramic (RF1). All of these fibers significantly increased nitric oxide (NO) production in the culture with macrophages. Chrysotile B, CR, and GW significantly decreased the level of reduced glutathione (GSH) in RAW264.7 cells. S-nitrosothiol (RS-NO) formation was increased by both types of cells on exposure to every fiber. A large portion of this increased RS-NO may be in the form of S-nitrosoglutathione (GS-NO), because GSH is the most abundant thiol substance in the cell. Both CH and GW significantly increased superoxide anion in the media cultured of RAW264.7 cells. These results indicate that macrophages exposed to asbestos or MMMFs are subject to oxidative stress, not only through the generation of reactive oxygen and nitrogen species, but also through decreases in the level of the cellular antioxidant, GSH, by GS-NO formation. The increase of RS-NO in macrophages exposed to asbestos or MMMFs may deserve more attention as the indicator of continuous oxidative stress by NO on cells and tissues, which causes inflammation and involves the development of asbestos-induced diseases.