Mechanisms in the pathogenesis of asbestosis and silicosis

Molecular pathways: connecting fibrosis and solid tumor metastasis

Pathologic organ fibrosis is a condition that can affect all major tissues and is typically ascribed to the excessive accumulation of extracellular matrix components, predominantly collagens. It typically leads to compromise of organ function and subsequent organ failure, and it is estimated that 45% of deaths in the developed world are linked to fibrotic disease. Fibrosis and cancer are known to be inextricably linked; however, we are only just beginning to understand the common and overlapping molecular pathways between the two. Here, we discuss what is known about the intersection of fibrosis and cancer, with a focus on cancer metastasis, and highlight some of the exciting new potential clinical targets that are emerging from analysis of the molecular pathways associated with these two devastating diseases.

Nanoparticle Uptake: The Phagocyte Problem

Phagocytes are key cellular participants determining important aspects of host exposure to nanomaterials, initiating clearance, biodistribution and the tenuous balance between host tolerance and adverse nanotoxicity. Macrophages in particular are believed to be among the first and primary cell types that process nanoparticles, mediating host inflammatory and immunological biological responses. These processes occur ubiquitously throughout tissues where nanomaterials are present, including the host mononuclear phagocytic system (MPS) residents in dedicated host filtration organs (i.e., liver, kidney spleen, and lung). Thus, to understand nanomaterials exposure risks it is critical to understand how nanomaterials are recognized, internalized, trafficked and distributed within diverse types of host macrophages and how possible cell-based reactions resulting from nanomaterial exposures further inflammatory host responses in vivo. This review focuses on describing macrophage-based initiation of downstream hallmark immunological and inflammatory processes resulting from phagocyte exposure to and internalization of nanomaterials.

Roles of microRNA-146a and microRNA-181b in regulating the secretion of tumor necrosis factor-α and interleukin-1β in silicon dioxide-induced NR8383 rat macrophages

Despite increasing evidence to suggest that microRNA (miR)-146a and miR-181b are involved in the regulation of immune responses and tumor progression, their roles in silicosis remain to be fully elucidated. Therefore, the present study examined the roles of miR-146a and miR-181b in inflammatory responses, and their effect on the expression of the tumor necrosis factor-α (TNF-α) and interleukin-1β (IL-1β) inflammatory chemokines in silicon dioxide (SiO₂)-induced NR8383 rat macrophages. Alterations in the expression levels of miR-146a and miR-181b in rats with silicosis have been previously investigated using miRNA arrays. In the present study, the expression levels of miR-146a and miR-181b were assessed using reverse transcription-quantitative polymerase chain reaction (RT-qPCR). The NR8383 cells were transfected with miRNA-146a and miR-181b mimics or inhibitors, and the cells and culture supernatants were collected following SiO₂ treatment for 12 h. The expression levels of TNF-α and IL-1β were detected using western blotting, RT-qPCR and ELISA. Analysis of variance and Student's two-tailed t-test were used to perform statistical analyses. The expression level of miR-146a was significantly increased, while the expression level of miR-181b was significantly decreased in the fibrotic lungs of the rats with silicosis, compared with the levels in the normal rats. It was observed that, following treatment of the NR8383 cells with SiO₂ for 12 h, the levels of TNF-α were significantly increased following miR-181b knockdown and the levels of IL-1β were significantly increased following miR-146a knockdown, compared with the inhibitor-treated controls (P<0.05). By contrast, miR-181b mimic transfection led to a significant reduction in the levels of TNF-α (P<0.05), and miR-146a mimics were responsible for the decrease in IL-1β (P<0.05). The results of the present study provide evidence supporting the roles of miR-146a and miR-181b in the pathogenesis of silicosis, and suggest that they may be candidate therapeutic target in this disease.

Functional Alteration of Natural Killer Cells and Cytotoxic T Lymphocytes upon Asbestos Exposure and in Malignant Mesothelioma Patients

Malignant mesothelioma is caused by exposure to asbestos, which is known to have carcinogenic effects. However, the development of mesothelioma takes a long period and results from a low or intermediate dose of exposure. These findings have motivated us to investigate the immunological effects of asbestos exposure and analyze immune functions of patients with mesothelioma and pleural plaque, a sign of exposure to asbestos. Here, we review our knowledge concerning natural killer (NK) cells and cytotoxic T lymphocytes (CTL). NK cells showed impaired cytotoxicity with altered expression of activating receptors upon exposure to asbestos, while induction of granzyme(+) cells in CD8(+) lymphocytes was suppressed by asbestos exposure. It is interesting that a decrease in NKp46, a representative activating receptor, is common between NK cells in PBMC culture with asbestos and those of mesothelioma patients. Moreover, it was observed that CD8(+) lymphocytes may be stimulated by some kind of "nonself" cells in plaque-positive individuals and in mesothelioma patients, whereas CTL in mesothelioma is impaired by poststimulation maintenance of cytotoxicity. These findings suggest that analysis of immunological parameters might contribute to the evaluation of health conditions of asbestos-exposed individuals and to a greater understanding of the pathology of malignant mesothelioma.

Systemic autoimmune disease in asbestosis rapidly responding to anti-interleukin-1beta antibody canakinumab: a case report

BACKGROUND

Asbestosis is characterized by lung and pleural fibrosis and by immune system dysregulation, with autoantibody production and systemic immune-mediated disease. No specific therapies are available for asbestosis. Recently, the pivotal pathogenic role exerted by interleukin-1beta has been recently reported.

CASE PRESENTATION

We treated with anti-interleukin 1 beta targeted antibody canakinumab a 67 year old man with asbestosis and long lasting systemic autoimmune features. A dramatic improvement in clinical manifestations was observed at 1 week after the first injection, with complete clinical remission at 4 months.

CONCLUSION

This case suggests new perspectives for the treatment of asbestosis and its systemic features.

Inflammatory Cytokines Contribute to Asbestos-Induced Injury of Mesothelial Cells

BACKGROUND

Several diseases have been related to asbestos exposure, including the pleural tumor mesothelioma. The mechanism of pleural injury by asbestos fibers is not yet fully understood. The inflammatory response with release of mediators leading to a dysregulation of apoptosis may play a pivotal role in the pathophysiology of asbestos-induced pleural disease.

OBJECTIVE

To determine whether pro-inflammatory cytokines produced by asbestos-exposed pleural mesothelial cells modify the injury induced by the asbestos.

METHODS

Mouse pleural mesothelial cells (PMC) were exposed to crocidolite or chrysotile asbestos fibers (3.0 μg/cm(2)) for 4, 24, or 48 h and assessed for viability, necrosis and apoptosis, and the production of cytokines IL-1β, IL-6 and macrophage inflammatory protein-2 (MIP-2). Cells exposed to fibers were also treated with antibodies anti-IL-1β, anti-IL-6, anti- IL-1β+anti-IL-6 or anti-MIP-2 or their irrelevant isotypes, and assessed for apoptosis and necrosis. Non-exposed cells and cells treated with wollastonite, an inert particle, were used as controls.

RESULTS

Mesothelial cells exposed to either crocidolite or chrysotile underwent both apoptosis and necrosis and released cytokines IL-1β, IL-6 and MIP-2. In the crocidolite group, apoptosis and the levels of all cytokines were higher than in the chrysotile group, at comparable concentrations. Neutralization of IL-1β andIL-6, but not MIP-2, inhibited apoptosis and necrosis, especially in the cells exposed to crocidolite fibers.

CONCLUSIONS

Both crocidolite and chrysotile asbestos fibers induced apoptosis and produced an acute inflammatory response characterized by elevated levels of IL-1β, IL-6 and MIP-2 in cultured mouse PMC. IL-1β and IL-6, but not MIP-2, were shown to contribute to asbestos-induced injury, especially in the crocidolite group.

Comparing the role of silica particle size with mineral fiber geometry in the release of superoxide from rat alveolar macrophages

Particulate air pollutants and mineral fibers activate inflammatory cells to release oxidants, which contribute to inflammation and injury in the lower respiratory tract. Our aim was to compare the role of silica particle size with mineral fiber length and width in the ability to induce superoxide release from rat alveolar macrophages. We estimated the ability of four types of silica particle samples, with different mode diameter, and three types of mineral fiber samples, with different geometric mean lengths and widths, to induce lucigenin-dependent chemiluminescence (CL) from the cells per number of dust particles (i.e., silica particles and mineral fibers). A close positive correlation was observed between dust size and the ability to induce CL in silica as well as mineral fiber samples. Moreover, the ability of silica samples to induce CL was weaker than that of long mineral fiber sample. This ability increased at a larger rate in small silica particle and thin mineral fiber samples than in large silica particle and thick mineral fiber samples at the initial stage of administration. These results suggest that the kinetics of the induction superoxide release from macrophages is similar between silica particles and mineral fibers; moreover, this depends on silica particle size and mineral fiber geometry. Finally, large silica particles were more active than small ones.

Silica Triggers Inflammation and Ectopic Lymphoid Neogenesis in the Lungs in Parallel with Accelerated Onset of Systemic Autoimmunity and Glomerulonephritis in the Lupus-Prone NZBWF1 Mouse

Genetic predisposition and environmental factors influence the development of human autoimmune disease. Occupational exposure to crystalline silica (cSiO₂) has been etiologically linked to increased incidence of autoimmunity, including systemic lupus erythematosus (SLE), but the underlying mechanisms are poorly understood. The purpose of this study was to test the hypothesis that early repeated short-term cSiO₂ exposure will modulate both latency and severity of autoimmunity in the lupus-prone female NZBWF1 mouse. Weekly intranasal exposure to cSiO₂ (0.25 and 1.0 mg) for 4 wk beginning at 9 wk of age both reduced latency and increased intensity of glomerulonephritis. cSiO₂ elicited robust inflammatory responses in the lungs as evidenced by extensive perivascular and peribronchial lymphoplasmacytic infiltration consisting of IgG-producing plasma cells, and CD45R+ and CD3+ lymphocytes that were highly suggestive of ectopic lymphoid tissue (ELT). In addition, there were elevated concentrations of immunoglobulins and the cytokines MCP-1, TNF-α and IL-6 in bronchoalveolar lavage fluid. cSiO₂-associated kidney and lung effects paralleled dose-dependent elevations of autoantibodies and proinflammatory cytokines in plasma. Taken together, cSiO₂-induced pulmonary inflammation and ectopic lymphoid neogenesis in the NZBWF1 mouse corresponded closely to systemic inflammatory and autoimmune responses as well as the early initiation of pathological outcomes in the kidney. These findings suggest that following airway exposure to crystalline silica, in mice genetically prone to SLE, the lung serves as a platform for triggering systemic autoimmunity and glomerulonephritis.

Annexin A1 mimetic peptide controls the inflammatory and fibrotic effects of silica particles in mice

BACKGROUND AND PURPOSE

Endogenous glucocorticoids are pro-resolving mediators, an example of which is the endogenous glucocorticoid-regulated protein annexin A1 (ANXA1). Because silicosis is an occupational lung disease characterized by unabated inflammation and fibrosis, in this study we tested the therapeutic properties of the N-terminal ANXA1-derived peptide annexin 1-(2-26) (Ac2-26) on experimental silicosis.

EXPERIMENTAL APPROACH

Swiss-Webster mice were administered silica particles intranasally and were subsequently treated with intranasal peptide Ac2-26 (200 μg per mouse) or dexamethasone (25 μg per mouse) for 7 days, starting 6 h post-challenge. Ac2-26 abolished the leukocyte infiltration, collagen deposition, granuloma formation and generation of pro-inflammatory cytokines evoked by silica; these variables were only partially inhibited by dexamethasone.

KEY RESULTS

A clear exacerbation of the silica-induced pathological changes was observed in ANXA1 knockout mice as compared with their wild-type (WT) littermate controls. Incubation of lung fibroblasts from WT mice with Ac2-26 in vitro reduced IL-13 or TGF-β-induced production of CCL2 (MCP-1) and collagen, but this peptide did not affect the production of CCL2 (MCP-1) by stimulated fibroblasts from formyl peptide receptor type 1 (FPR1) knockout mice. Ac2-26 also inhibited the production of CCL2 (MCP-1) from fibroblasts of FPR2 knockout mice.

CONCLUSIONS AND IMPLICATIONS

Collectively, our findings reveal novel protective properties of the ANXA1 derived peptide Ac2-26 on the inflammatory and fibrotic responses induced by silica, and suggest that ANXA1 mimetic agents might be a promising strategy as innovative anti-fibrotic approaches for the treatment of silicosis.

Selenium and exposure to fibrogenic mineral dust: a mini-review

Individuals exposed to fibrogenic mineral dust may exhibit an impaired antioxidant system and produce high levels of reactive oxygen and nitrogen species through immune cells, contributing to the perturbation of immune cell function, inflammation, fibrosis and lung cancer. The lung diseases which are caused by inhalation of fibrogenic mineral dust, known as pneumoconioses, develop progressively and irreversibly over decades. At the moment there is no known cure. The trace element selenium has potent antioxidant and anti-inflammatory properties mediated mainly through selenoproteins. Research has demonstrated that selenium has the ability to protect against cardiovascular diseases; to kill cancer cells in vitro and reduce cancer incidence; and to immunomodulate various cellular signaling pathways. For these reasons, selenium has been proposed as a promising therapeutic agent in oxidative stress associated pathology that in theory would be beneficial for the prevention or treatment of pneumoconioses such as silicosis, asbestosis, and coal worker's pneumoconiosis. However, studies regarding selenium and occupational lung diseases are rare. The purpose of this study is to conduct a mini-review regarding the relationship between selenium and exposure to fibrogenic mineral dust with emphasis on epidemiological studies. We carried out a systematic literature search of English published studies on selenium and exposure to fibrogenic mineral dust. We found four epidemiological studies. Reviewed studies show that selenium is lower in individuals exposed to fibrogenic mineral dust. However, three out of the four reviewed studies could not confirm cause-and-effect relationships between low selenium status and exposure to fibrogenic mineral dust. This mini-review underscores the need for large follow-up and mechanistic studies for selenium to further elucidate its therapeutic effects.

Bone morphogenetic protein 7 attenuates epithelial-mesenchymal transition induced by silica

The epithelial-mesenchymal transition (EMT) is a critical process in the pulmonary fibrosis. It has been reported that bone morphogenetic protein 7 (BMP-7) was able to reverse EMT in proximal tubular cells. Therefore, we test the hypothesis that EMT contributes to silica-induced pulmonary fibrosis and BMP-7 inhibits EMT in silica-induced pulmonary fibrosis. Progressive silica-induced pulmonary fibrosis in the rat was used as a model of silicosis. Epithelial and mesenchymal markers were measured from rat fibrotic lungs. Then the effects of BMP-7 on the EMT were further confirmed in A549 cells. There are increases of vimentin as a mesenchymal marker and decreases of E-cadherin as an epithelial marker in the silica-exposed rat lungs, which is in agreement with the A549 cells data. However, BMP-7 treatment significantly reduced expression of vimentin in the rat pulmonary fibrosis model and in A549 cells. In conclusion, EMT contributes to silica-induced pulmonary fibrosis. Meanwhile, the treatment of BMP-7 can inhibit silica-induced EMT in vitro and in vivo.

Serum autoantibodies in silicosis and non-silicosis cement workers

AIM

To study serum autoantibodies and immunoglobulin levels in cement workers.

METHODS

Blood samples for numerous antibodies were collected from 30 silicosis and 42 non-silicosis cement workers. Spirometry of the silicosis workers was also studied.

RESULTS

Serum IgA mean level showed a significant increase in the silicosis group compared to the non-silicosis group. Elevated titers of serum anti-smooth muscle antibodies (ASMA) and anti-glomerular basement membrane (anti-GBM) were detected only in the silicosis group. The duration of exposure showed a significant positive correlation with serum IgA, ASMA and anti-GBM, and a significant negative correlation with serum IgG. Serum anti-GBM showed a significant positive correlation with IgG while the inverse titer (1/titer) of anti-GBM showed highly significant positive correlations with serum IgA and ASMA. The percent predicted FVC was the ventilatory function most closely associated with immunological parameters in silicosis group.

CONCLUSION

Serum IgA, ASMA, and anti-GBM are the principal immunologic parameters associated with silicosis.

Increased expression of bone morphogenetic protein-7 and its related pathway provides an anti-fibrotic effect on silica induced fibrosis in vitro

BMP-7 exerts an inhibitory effect on silica induced fibrosis in RLE-6TN cells via suppressing TGF-β signaling and activating BMP signaling.

Exposure Characteristics of Nanoparticles as Process By-products for the Semiconductor Manufacturing Industry

This study aims to elucidate the exposure properties of nanoparticles (NPs; <100 nm in diameter) in semiconductor manufacturing processes. The measurements of airborne NPs were mainly performed around process equipment during fabrication processes and during maintenance. The number concentrations of NPs were measured using a water-based condensation particle counter having a size range of 10-3,000 nm. The chemical composition, size, and shape of NPs were determined by scanning electron microscopy and transmission electron microscopy techniques equipped with energy dispersive spectroscopy. The resulting concentrations of NPs ranged from 0.00-11.47 particles/cm(3). The concentration of NPs measured during maintenance showed a tendency to increase, albeit incrementally, compared to that measured during normal conditions (under typical process conditions without maintenance). However, the increment was small. When comparing the mean number concentration and standard deviation (n ± σ) of NPs, the chemical mechanical polishing (CMP) process was the highest (3.45 ± 3.65 particles/cm(3)), and the dry etch (ETCH) process was the lowest (0.11 ± 0.22 particles/cm(3)). The major NPs observed were silica (SiO2) and titania (TiO2) particles, which were mainly spherical agglomerates ranging in size from 25-280 nm. Sampling of semiconductor processes in CMP, chemical vapor deposition, and ETCH reveled NPs were <100 nm in those areas. On the other hand, particle size exceeded 100 nm in diffusion, metallization, ion implantation, and wet cleaning/etching process. The results show that the SiO2 and TiO2 are the major NPs present in semiconductor cleanroom environments.

Comparison of essential oil components and in vitro anticancer activity in wild and cultivated Salvia verbenaca

The objectives of our research were to study the chemical composition and the in vitro anticancer effect of the essential oil of Salvia verbenaca growing in natural sites in comparison with those of cultivated (Sc) plants. The oil from wild (Sw) S. verbenaca presented hexadecanoic acid (23.1%) as the main constituent, while the oil from Sc plants contained high quantities of hexahydrofarnesyl acetone (9.7%), scarce in the natural oil (0.7%). The growth-inhibitory and proapoptotic effects of the essential oils from Sw and Sc S. verbenaca were evaluated in the human melanoma cell line M14, testing cell vitality, cell membrane integrity, genomic DNA fragmentation and caspase-3 activity. Both the essential oils were able to inhibit the growth of the cancer cells examined inducing also apoptotic cell death, but the essential oil from cultivated samples exhibited the major effects.

Current investigations into the genotoxicity of zinc oxide and silica nanoparticles in mammalian models in vitro and in vivo: carcinogenic/genotoxic potential, relevant mechanisms and biomarkers, artifacts, and limitations

Engineered nanoparticles (NPs) are widely used in many sectors, such as food, medicine, military, and sport, but their unique characteristics may cause deleterious health effects. Close attention is being paid to metal NP genotoxicity; however, NP genotoxic/carcinogenic effects and the underlying mechanisms remain to be elucidated. In this review, we address some metal and metal oxide NPs of interest and current genotoxicity tests in vitro and in vivo. Metal NPs can cause DNA damage such as chromosomal aberrations, DNA strand breaks, oxidative DNA damage, and mutations. We also discuss several parameters that may affect genotoxic response, including physicochemical properties, widely used assays/end point tests, and experimental conditions. Although potential biomarkers of nanogenotoxicity or carcinogenicity are suggested, inconsistent findings in the literature render results inconclusive due to a variety of factors. Advantages and limitations related to different methods for investigating genotoxicity are described, and future directions and recommendations for better understanding genotoxic potential are addressed.

The alarmin IL-1α is a master cytokine in acute lung inflammation induced by silica micro- and nanoparticles

Background

Inflammasome-activated IL-1β plays a major role in lung neutrophilic inflammation induced by inhaled silica. However, the exact mechanisms that contribute to the initial production of precursor IL-1β (pro-IL-1β) are still unclear. Here, we assessed the implication of alarmins (IL-1α, IL-33 and HMGB1) in the lung response to silica particles and found that IL-1α is a master cytokine that regulates IL-1β expression.

Methods

Pro- and mature IL-1β as well as alarmins were assessed by ELISA, Western Blot or qRT-PCR in macrophage cultures and in mouse lung following nano- and micrometric silica exposure. Implication of these immune mediators in the establishment of lung inflammatory responses to silica was investigated in knock-out mice or after antibody blockade by evaluating pulmonary neutrophil counts, CXCR2 expression and degree of histological injury.

Results

We found that the early release of IL-1α and IL-33, but not HMGB1 in alveolar space preceded the lung expression of pro-IL-1β and neutrophilic inflammation in silica-treated mice. In vitro, the production of pro-IL-1β by alveolar macrophages was significantly induced by recombinant IL-1α but not by IL-33. Neutralization or deletion of IL-1α reduced IL-1β production and neutrophil accumulation after silica in mice. Finally, IL-1α released by J774 macrophages after in vitro exposure to a range of micro- and nanoparticles of silica was correlated with the degree of lung inflammation induced in vivo by these particles.

Conclusions

We demonstrated that in response to silica exposure, IL-1α is rapidly released from pre-existing stocks in alveolar macrophages and promotes subsequent lung inflammation through the stimulation of IL-1β production. Moreover, we demonstrated that in vitro IL-1α release from macrophages can be used to predict the acute inflammogenic activity of silica micro- and nanoparticles.

Electronic supplementary material

The online version of this article (doi:10.1186/s12989-014-0069-x) contains supplementary material, which is available to authorized users.

Silica-induced NLRP3 inflammasome activation in vitro and in rat lungs

RATIONALE

Mineral particles in the lung cause inflammation and silicosis. In myeloid and bronchial epithelial cells the inflammasome plays a role in responses to crystalline silica. Thioredoxin (TRX) and its inhibitory protein TRX-interacting protein link oxidative stress with inflammasome activation. We investigated inflammasome activation by crystalline silica polymorphs and modulation by TRX in vitro, as well as its localization and the importance of silica surface reactivity in rats.

METHODS

We exposed bronchial epithelial cells and differentiated macrophages to silica polymorphs quartz and cristobalite and measured caspase-1 activity as well as the release of IL-1β, bFGF and HMGB1; including after TRX overexpression or treatment with recombinant TRX. Rats were intratracheally instilled with vehicle control, Dörentruper quartz (DQ12) or DQ12 coated with polyvinylpyridine N-oxide. At days 3, 7, 28, 90, 180 and 360 five animals per treatment group were sacrificed. Hallmarks of silicosis were assessed with Haematoxylin-eosin and Sirius Red stainings. Caspase-1 activity in the bronchoalveolar lavage and caspase-1 and IL-1β localization in lung tissue were determined using Western blot and immunohistochemistry (IHC).

RESULTS

Silica polymorphs triggered secretion of IL-1β, bFGF and HMGB1 in a surface reactivity dependent manner. Inflammasome readouts linked with caspase-1 enzymatic activity were attenuated by TRX overexpression or treatment. At day 3 and 7 increased caspase-1 activity was detected in BALF of the DQ12 group and increased levels of caspase-1 and IL-1β were observed with IHC in the DQ12 group compared to controls. DQ12 exposure revealed silicotic nodules at 180 and 360 days. Particle surface modification markedly attenuated the grade of inflammation and lymphocyte influx and attenuated the level of inflammasome activation, indicating that the development of silicosis and inflammasome activation is determined by crystalline silica surface reactivity.

CONCLUSION

Our novel data indicate the pivotal role of surface reactivity of crystalline silica to activate the inflammasome in cultures of both epithelial cells and macrophages. Inhibitory capacity of the antioxidant TRX to inflammasome activation was evidenced. DQ12 quartz exposure induced acute and chronic functional activation of the inflammasome in the heterogeneous cell populations of the lung in associated with its crystalline surface reactivity.

Indications for distinct pathogenic mechanisms of asbestos and silica through gene expression profiling of the response of lung epithelial cells

Occupational and environmental exposures to airborne asbestos and silica are associated with the development of lung fibrosis in the forms of asbestosis and silicosis, respectively. However, both diseases display distinct pathologic presentations, likely associated with differences in gene expression induced by different mineral structures, composition and bio-persistent properties. We hypothesized that effects of mineral exposure in the airway epithelium may dictate deviating molecular events that may explain the different pathologies of asbestosis versus silicosis. Using robust gene expression-profiling in conjunction with in-depth pathway analysis, we assessed early (24 h) alterations in gene expression associated with crocidolite asbestos or cristobalite silica exposures in primary human bronchial epithelial cells (NHBEs). Observations were confirmed in an immortalized line (BEAS-2B) by QRT-PCR and protein assays. Utilization of overall gene expression, unsupervised hierarchical cluster analysis and integrated pathway analysis revealed gene alterations that were common to both minerals or unique to either mineral. Our findings reveal that both minerals had potent effects on genes governing cell adhesion/migration, inflammation, and cellular stress, key features of fibrosis. Asbestos exposure was most specifically associated with aberrant cell proliferation and carcinogenesis, whereas silica exposure was highly associated with additional inflammatory responses, as well as pattern recognition, and fibrogenesis. These findings illustrate the use of gene-profiling as a means to determine early molecular events that may dictate pathological processes induced by exogenous cellular insults. In addition, it is a useful approach for predicting the pathogenicity of potentially harmful materials.

Silica and double-stranded RNA synergistically induce bronchial epithelial apoptosis and airway inflammation

Silica crystals (silica), which are the main mineral component of volcanic ash and desert dust, can activate the caspase-1-activating inflammasome in phagocytic cells to secrete IL-1β. Although inhalation of silica-containing dust is known to exacerbate chronic respiratory diseases, probably through inflammasome activation, its direct effects on bronchial epithelial cells remain unclear. Here, we show that silica and double-stranded RNA (dsRNA) synergistically induces caspase-9-dependent apoptosis, but not inflammasome activation, of bronchial epithelial cells. Intranasal administration of silica and dsRNA to mice synergistically enhanced neutrophil infiltration in the airway without IL-1β release in the bronchoalveolar lavage fluid. Histopathological analysis revealed that silica or dsRNA alone induced slight airway inflammation, whereas combined administration significantly enhanced airway inflammation and epithelial damage. These novel findings suggest that inhalation of silica-containing dust may cause inflammasome-independent airway inflammation, possibly by damaging the epithelial barrier, especially at the time of viral infection. These responses may also be involved in acute lung injury caused by inhaled silica-containing dust.

Variability and consistency in lung inflammatory responses to particles with a geogenic origin

BACKGROUND AND OBJECTIVE

Particulate matter <10 μm (PM10 ) is well recognized as being an important driver of respiratory health; however, the impact of PM10 of geogenic origin on inflammatory responses in the lung is poorly understood. This study aimed to assess the lung inflammatory response to community sampled geogenic PM10 .

METHODS

This was achieved by collecting earth material from two regional communities in Western Australia (Kalgoorlie-Boulder and Newman), extracting the PM10 fraction and exposing mice by intranasal instillation to these particles. The physicochemical characteristics of the particles were assessed and lung inflammatory responses were compared to control particles. The primary outcomes were cellular influx and cytokine production in the lungs of the exposed mice.

RESULTS

The physical and chemical characteristics of the PM10 from Kalgoorlie and Newman differed with the latter having a higher concentration of Fe and a larger median diameter. Control particles (2.5 μm polystyrene) caused a significant influx of inflammatory cells (neutrophils) with little production of proinflammatory cytokines. In contrast, the geogenic particles induced the production of MIP-2, IL-6 and a significant influx of neutrophils. Qualitatively, the response following exposure to particles from Kalgoorlie and Newman were consistent; however, the magnitude of the response was substantially higher in the mice exposed to particles from Newman.

CONCLUSIONS

The unique physicochemical characteristics of geogenic particles induced a proinflammatory response in the lung. These data suggest that particle composition should be considered when setting community standards for PM exposure, particularly in areas exposed to high geogenic particulate loads.

The zeta potential of mineral fibres

For the first time, the zeta (ξ) potential of pathogenic mineral fibres (chrysotiles, amphiboles and erionite) was systematically investigated to shed light on the relationship between surface reactivity and fibre pathogenicity. A general model explaining the zeta potential of chrysotile, amphiboles and erionite has been postulated. In double distilled water, chrysotiles showed positive values while crocidolite and erionite showed negative values. In contact with organic solutions, all fibres exhibited negative values of zeta potential. The decrease of the surface potential is deemed to be a defensive chemical response of the macrophage cells to minimize hemolytic damage. Negatively charged surfaces favour the binding of collagen and redox activated Fe-rich proteins, to form the so-called asbestos bodies and prompt the formation of HO via the reaction with peroxide (H2O2+e(-)→HO+HO(-)). An additional mechanism accounting for higher carcinogenicity is possibly related to the Ca(2+) sequestration by the fibres with surface negative potential, impairing the mitochondrial apoptotic pathway. It was also found that with a negative zeta potential, the attractive forces prevailed over repulsions and favoured processes such as agglomeration responsible of a tumorigenic chronic inflammation.

The inflammasome in liver injury and non-alcoholic fatty liver disease

The liver possesses a strong inflammatory response, as seen experimentally and clinically with liver inflammation due to toxic and metabolic stress, sepsis and ischemia. Initiation of this inflammatory response requires the interaction of two types of extracellular signals which collectively upregulate and activate a cytosolic molecular complex termed the inflammasome. Signal 1 is via activation of pattern recognition receptors, and signal 2 is delivered by diverse stimuli including particulates and adenosine triphosphate. The common end result of inflammasome activation is the activation of the protease caspase-1 with release of active interleukin-1β. The inflammasome is important in a wide range of conditions including alcoholic and non-alcoholic steatohepatitis. Kupffer cells are known to be important, but the consequences of inflammasome activation in other hepatic immune cells have not been well characterized. The inflammasome pathway is also known to be required for a full fibrotic response, as demonstrated by reduced lung, skin and liver fibrosis in inflammasome-deficient mice. Identification of the inflammasome machinery has opened up novel therapeutic avenues by the use of antagonists for Toll-like receptors as well as the adenosine triphosphate receptor P2X7, and the interleukin-1 receptor. There is now great interest in how inflammasome pathways are regulated. The initial challenge is to understand how an acute inflammatory response is sustained. This is a significant issue as the known stimuli result in an acute response that is self-limited to under 24 h. This suggests that there are significant regulators which allow sustained inflammasome activation in conditions such as non-alcoholic steatohepatitis and alcoholic hepatitis.

AKT/mTOR and c-Jun N-terminal kinase signaling pathways are required for chrysotile asbestos-induced autophagy

Chrysotile asbestos is closely associated with excess mortality from pulmonary diseases such as lung cancer, mesothelioma, and asbestosis. Although multiple mechanisms in which chrysotile asbestos fibers induce pulmonary disease have been identified, the role of autophagy in human lung epithelial cells has not been examined. In this study, we evaluated whether chrysotile asbestos induces autophagy in A549 human lung epithelial cells and then analyzed the possible underlying molecular mechanism. Chrysotile asbestos induced autophagy in A549 cells based on a series of biochemical and microscopic autophagy markers. We observed that asbestos increased expression of A549 cell microtubule-associated protein 1 light chain 3 (LC3-II), an autophagy marker, in conjunction with dephosphorylation of phospho-AKT, phospho-mTOR, and phospho-p70S6K. Notably, AKT1/AKT2 double-knockout murine embryonic fibroblasts (MEFs) had negligible asbestos-induced LC3-II expression, supporting a crucial role for AKT signaling. Chrysotile asbestos also led to the phosphorylation/activation of Jun N-terminal kinase (JNK) and p38 MAPK. Pharmacologic inhibition of JNK, but not p38 MAPK, dramatically inhibited the protein expression of LC3-II. Moreover, JNK2(-/-) MEFs but not JNK1(-/-) MEFs blocked LC3-II levels induced by chrysotile asbestos. In addition, N-acetylcysteine, an antioxidant, attenuated chrysotile asbestos-induced dephosphorylation of P-AKT and completely abolished phosphorylation/activation of JNK. Finally, we demonstrated that chrysotile asbestos-induced apoptosis was not affected by the presence of the autophagy inhibitor 3-methyladenine or autophagy-related gene 5 siRNA, indicating that the chrysotile asbestos-induced autophagy may be adaptive rather than prosurvival. Our findings demonstrate that AKT/mTOR and JNK2 signaling pathways are required for chrysotile asbestos-induced autophagy. These data provide a mechanistic basis for possible future clinical applications targeting these signaling pathways in the management of asbestos-induced lung disease.

Continuous exposure to chrysotile asbestos can cause transformation of human mesothelial cells via HMGB1 and TNF-α signaling

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

The lung may play a role in the pathogenesis of rheumatoid arthritis

Multiple studies have identified strong associations between the lung and rheumatoid arthritis (RA). Such studies identify a high prevalence of lung disease, both airways and parenchymal disease, in subjects with clinically classifiable RA. It has been suggested that lung disease in RA results from targeting of the lung from circulating autoimmunity or other factors such as medications. However, findings that lung disease, specifically inflammatory airways disease, and lung generation of autoimmunity can be present before the onset of joint symptoms suggest that immune reactions in the lung may be involved in the initial development of RA-related autoimmunity. Herein we review these issues in detail, as well as outline a potential research agenda to understand the natural history of lung involvement in RA and its relation to the overall pathogenesis of RA.

Asbestos modulates thioredoxin-thioredoxin interacting protein interaction to regulate inflammasome activation

BACKGROUND

Asbestos exposure is related to various diseases including asbestosis and malignant mesothelioma (MM). Among the pathogenic mechanisms proposed by which asbestos can cause diseases involving epithelial and mesothelial cells, the most widely accepted one is the generation of reactive oxygen species and/or depletion of antioxidants like glutathione. It has also been demonstrated that asbestos can induce inflammation, perhaps due to activation of inflammasomes.

METHODS

The oxidation state of thioredoxin was analyzed by redox Western blot analysis and ROS generation was assessed spectrophotometrically as a read-out of solubilized formazan produced by the reduction of nitrotetrazolium blue (NTB) by superoxide. Quantitative real time PCR was used to assess changes in gene transcription.

RESULTS

Here we demonstrate that crocidolite asbestos fibers oxidize the pool of the antioxidant, Thioredoxin-1 (Trx1), which results in release of Thioredoxin Interacting Protein (TXNIP) and subsequent activation of inflammasomes in human mesothelial cells. Exposure to crocidolite asbestos resulted in the depletion of reduced Trx1 in human peritoneal mesothelial (LP9/hTERT) cells. Pretreatment with the antioxidant dehydroascorbic acid (a reactive oxygen species (ROS) scavenger) reduced the level of crocidolite asbestos-induced Trx1 oxidation as well as the depletion of reduced Trx1. Increasing Trx1 expression levels using a Trx1 over-expression vector, reduced the extent of Trx1 oxidation and generation of ROS by crocidolite asbestos, and increased cell survival. In addition, knockdown of TXNIP expression by siRNA attenuated crocidolite asbestos-induced activation of the inflammasome.

CONCLUSION

Our novel findings suggest that extensive Trx1 oxidation and TXNIP dissociation may be one of the mechanisms by which crocidolite asbestos activates the inflammasome and helps in development of MM.

Outbreak of silicosis in Spanish quartz conglomerate workers

OBJECTIVES

To describe the epidemiological and clinical characteristics of an outbreak of occupational silicosis and the associated working conditions.

METHODS

Cases were defined as men working in the stone cutting, shaping, and finishing industry in the province of Cádiz, diagnosed with silicosis between July 2009 and May 2012, and were identified and diagnosed by the department of pulmonology of the University Hospital of Puerto Real (Cádiz). A census of workplaces using quartz conglomerates was carried out to determine total numbers of potentially exposed workers. A patient telephone survey on occupational exposures and a review of medical records for all participants were conducted.

RESULTS

Silicosis was diagnosed in 46 men with a median age of 33 years and a median of 11 years working in the manufacturing of countertops. Of these cases, 91.3% were diagnosed with simple chronic silicosis, with an abnormal high-resolution computerized tomography (HRCT) scan. One patient died during the study period. Employer non-compliance in prevention and control measures was frequently reported, as were environmental and individual protection failures.

CONCLUSIONS

The use of new construction materials such as quartz conglomerates has increased silicosis incidence due to intensive occupational exposures, in the context of high demand fuelled by the housing boom. This widespread exposure poses a risk if appropriate preventive measures are not undertaken.

The concentration of iron in real-world geogenic PM₁₀ is associated with increased inflammation and deficits in lung function in mice

Background

There are many communities around the world that are exposed to high levels of particulate matter <10 µm (PM₁₀) of geogenic (earth derived) origin. Mineral dusts in the occupational setting are associated with poor lung health, however very little is known about the impact of heterogeneous community derived particles. We have preliminary evidence to suggest that the concentration of iron (Fe) may be associated with the lung inflammatory response to geogenic PM₁₀. We aimed to determine which physico-chemical characteristics of community sampled geogenic PM₁₀ are associated with adverse lung responses.

Methods

We collected geogenic PM₁₀ from four towns in the arid regions of Western Australia. Adult female BALB/c mice were exposed to 100 µg of particles and assessed for inflammatory and lung function responses 6 hours, 24 hours and 7 days post-exposure. We assessed the physico-chemical characteristics of the particles and correlated these with lung outcomes in the mice using principal components analysis and multivariate linear regression.

Results

Geogenic particles induced an acute inflammatory response that peaked 6 hours post-exposure and a deficit in lung mechanics 7 days post-exposure. This deficit in lung mechanics was positively associated with the concentration of Fe and particle size variability and inversely associated with the concentration of Si.

Conclusions

The lung response to geogenic PM₁₀ is complex and highly dependent on the physico-chemical characteristics of the particles. In particular, the concentration of Fe in the particles may be a key indicator of the potential population health consequences for inhaling geogenic PM₁₀.

The role of genotoxicity in asbestos-induced mesothelioma: an explanation for the differences in carcinogenic potential among fiber types

The mechanism(s) underlying asbestos toxicity associated with the pathogenesis of mesothelioma has been a challenge to unravel for more than 60 years. A significant amount of research has focused on the characteristics of different fiber types and their potential to induce mesothelioma. These mechanistic studies of fiber toxicity have proceeded along two lines: those demonstrating biochemical mechanisms by which fibers induce disease and those investigating human susceptibility. Most recent studies focused on in vitro genotoxic effects induced by asbestos as the mechanism responsible for asbestos-induced disease. Although asbestos exerts a genotoxic effect at certain concentrations in vitro, a positive response in these tests does not indicate that the chemical is likely to produce an increased risk of carcinogenesis in exposed human populations. Thus far, findings from studies on the effects of fiber type in mesothelial cells are seriously flawed by a lack of a dose response relationship. The common limitation of these in vitro experiments is the lack of attention paid to the complexities of the human anatomy, biochemistry and physiology, which make the observed effects in these experimental systems difficult to extrapolate to persons in the workplace. Mechanistic differences between carcinogenic and genotoxic processes indicate why tests for genotoxicity do not provide much insight regarding the ability to predict carcinogenic potential in workers exposed to asbestos doses in the post-Occupational Safety and Health Administration era. This review discusses the existing literature on asbestos-induced genotoxicity and explains why these studies may or may not likely help characterize the dose-response curve at low dose.

Oxidative status and acute phase reactants in patients with environmental asbestos exposure and mesothelioma

Background and Objectives. The aim of this study was to investigate inflammatory indicators and oxidative status in patients with asbestos exposure with and without mesothelioma and to compare results with data from healthy subjects. Methods. Eighty people with exposure to environmental asbestos and without any disease, 46 mesothelioma patients, and a control group of 50 people without exposure to environmental asbestos were enrolled in this prospective study. Serum total oxidant level (TOL), total antioxidant capacity (TAC), and oxidative stress index (OSI), CRP, transferrin, ceruloplasmin, α-1 antitrypsin, ferritin, and copper levels were measured. Results. Mesothelioma group exhibited higher TOL, OSI, α1-antitrypsin, ferritin and copper levels as compared to the other groups (P < 0.001, P = 0.007, P < 0.0001, P < 0.001, and P < 0.001, resp.). Transferrin was lower in the mesothelioma group than in the other two groups (P < 0.001). The asbestos group had higher TOL, TAC, α1-antitrypsin, and transferrin levels (P < 0.001, P < 0.001, P < 0.001, and P < 0.001, resp.), as well as lower OSI and ferritin levels as compared to the control group (P < 0.001 and P < 0.001). Conclusions. We believe that elevated acute phase reactants and oxidative stress markers (TOL and OSI) in the mesothelioma group can be used as predictive markers for the development of asbestos-related malignancy.

In vitro determinants of asbestos fiber toxicity: effect on the relative toxicity of Libby amphibole in primary human airway epithelial cells

Background

An abnormally high incidence of lung disease has been observed in the residents of Libby, Montana, which has been attributed to occupational and environmental exposure to fibrous amphiboles originating from a nearby contaminated vermiculite mine. The composition of Libby amphibole (LA) is complex and minimal toxicity data are available. In this study, we conduct a comparative particle toxicity analysis of LA compared with standard reference asbestiform amphibole samples.

Methods

Primary human airway epithelial cells (HAEC) were exposed to two different LA samples as well as standard amphibole reference samples. Analysis of the samples included a complete particle size distribution analysis, calculation of surface area by electron microscopy and by gas adsorption and quantification of surface-conjugated iron and hydroxyl radical production by the fibers. Interleukin-8 mRNA levels were quantified by qRT-PCR to measure relative pro-inflammatory response induced in HAEC in response to amphibole fiber exposure. The relative contribution of key physicochemical determinants on the observed pro-inflammatory response were also evaluated.

Results

The RTI amosite reference sample contained the longest fibers and demonstrated the greatest potency at increasing IL-8 transcript levels when evaluated on an equal mass basis. The two LA samples and the UICC amosite reference sample consisted of similar particle numbers per milligram as well as similar particle size distributions and induced comparable levels of IL-8 mRNA. A strong correlation was observed between the elongated particle (aspect ratio ≥3:1) dose metrics of length and external surface area. Expression of the IL-8 data with respect to either of these metrics eliminated the differential response between the RTI amosite sample and the other samples that was observed when HAEC were exposed on an equal mass basis.

Conclusions

On an equal mass basis, LA is as potent as the UICC amosite reference sample at inducing a pro-inflammatory response in HAEC but is less potent than the RTI amosite sample. The results of this study show that the particle length and particle surface area are highly correlated metrics that contribute significantly to the toxicological potential of these amphibole samples with respect to the inflammogenic response induced in airway epithelial cells.

Immunopathological effects of malaria pigment or hemozoin and other crystals

Blood-stage malaria parasites produce insoluble hemozoin (Hz) crystals that are released in the blood circulation upon schizont rupture. In general, endogenous crystal formation or inhalation of crystalline materials is often associated with pathology. As the immune system responds differently to crystalline particles than to soluble molecules, in this review, the properties, immunological recognition, and pathogenic responses of Hz are discussed, and compared with two other major pathogenic crystals, monosodium urate (MSU) and asbestos. Because of the size and shape of MSU crystals and asbestos fibers, phagolysosomal formation is inefficient and often results in leakage of lysosomal content in the cell cytoplasm and/or in the extracellular environment with subsequent cell damage and cell death. Phagolysosomal formation after Hz ingestion is normal, but Hz remains stored inside these cells for months or even longer without any detectable degradation. Nonetheless, the different types of crystals are recognized by similar immune receptors, involving Toll-like receptors, the inflammasome, antibodies, and/or complement factors, and through similar signaling cascades, they activate both proinflammatory and anti-inflammatory immune responses that contribute to inflammation-associated pathology.

Consideration of Occupational Lung Disease and Pneumoconiosis in Forensic Pathology

Reports of workers stricken with lung disease sustained during the course of their employment date to antiquity. Despite stringent regulations to mitigate all manners of work place hazards, and the emergence of agencies and physicians engaged in the advancement of occupational health, occupational lung disease remains a significant problem within modern society. Inhalation of dusts and fumes sustained in the course of one's occupation may lead to significant morbidity and mortality, and lead to a huge cost to society in terms of lost productivity, medical care for the worker, and litigation. In certain circumstances, the identification of an underlying occupational lung disease may constitute a significant finding in medicolegal death investigation. This article will present an overview of common occupational diseases likely to be encountered in the practice of forensic pathology, based on the particular etiologic agent and occupational means of exposure.

Pulmonary toxicity of carbon nanotubes and asbestos - similarities and differences

Carbon nanotubes are a valuable industrial product but there is potential for human pulmonary exposure during production and their fibrous shape raises the possibility that they may have effects like asbestos, which caused a worldwide pandemic of disease in the20th century that continues into present. CNT may exist as fibres or as more compact particles and the asbestos-type hazard only pertains to the fibrous forms of CNT. Exposure to asbestos causes asbestosis, bronchogenic carcinoma, mesothelioma, pleural fibrosis and pleural plaques indicating that both the lungs and the pleura are targets. The fibre pathogenicity paradigm was developed in the 1970s-80s and has a robust structure/toxicity relationship that enables the prediction of the pathogenicity of fibres depending on their length, thickness and biopersistence. Fibres that are sufficiently long and biopersistent and that deposit in the lungs can cause oxidative stress and inflammation. They may also translocate to the pleura where they can be retained depending on their length, and where they cause inflammation and oxidative stress in the pleural tissues. These pathobiological processes culminate in pathologic change - fibroplasia and neoplasia in the lungs and the pleura. There may also be direct genotoxic effects of fibres on epithelial cells and mesothelium, contributing to neoplasia. CNT show some of the properties of asbestos and other types of fibre in producing these types of effects and more research is needed. In terms of the molecular pathways involved in the interaction of long biopersistent fibres with target tissue the events leading to mesothelioma have been a particular area of interest. A variety of kinase pathways important in proliferation are activated by asbestos leading to pre-malignant states and investigations are under way to determine whether fibrous CNT also affects these molecular pathways. Current research suggests that fibrous CNT can elicit effects similar to asbestos but more research is needed to determine whether they, or other nanofibres, can cause fibrosis and cancer in the long term.

Medicolegal Aspects of Asbestos II — Benign Pleural and Lung Diseases

A variety of benign lesions affecting the pleura and/or lung can result from inhaling asbestos fibers. Establishing the presence or absence of these entities often plays an important role in the evaluation, presentation and ultimate resolution of asbestos disease litigation. Forensic pathologists may become involved in these cases to address issues of diagnosis, exposure and/or disease attribution. This article reviews medicolegal issues pertaining to benign asbestos-induced diseases of the pleura and lung.

Sequestration of mitochondrial iron by silica particle initiates a biological effect

Inhalation of particulate matter has presented a challenge to human health for thousands of years. The underlying mechanism for biological effect following particle exposure is incompletely understood. We tested the postulate that particle sequestration of cell and mitochondrial iron is a pivotal event mediating oxidant generation and biological effect. In vitro exposure of human bronchial epithelial cells to silica reduced intracellular iron, which resulted in increases in both the importer divalent metal transporter 1 expression and metal uptake. Diminished mitochondrial 57Fe concentrations following silica exposure confirmed particle sequestration of cell iron. Preincubation of cells with excess ferric ammonium citrate increased cell, nuclear, and mitochondrial metal concentrations and prevented significant iron loss from mitochondria following silica exposure. Cell and mitochondrial oxidant generation increased after silica incubation, but pretreatment with iron diminished this generation of reactive oxygen species. Silica exposure activated MAP kinases (ERK and p38) and altered the expression of transcription factors (nF-κB and NF-E2-related factor 2), proinflammatory cytokines (interleukin-8 and -6), and apoptotic proteins. All of these changes in indexes of biological effect were either diminished or inhibited by cell pretreatment with iron. Finally, percentage of neutrophils and total protein concentrations in an animal model instilled with silica were decreased by concurrent exposure to iron. We conclude that an initiating event in the response to particulate matter is a sequestration of cell and mitochondrial iron by endocytosed particle. The resultant oxidative stress and biological response after particle exposure are either diminished or inhibited by increasing the cell iron concentration.

New insights into mechanisms controlling the NLRP3 inflammasome and its role in lung disease

Inflammasomes are large macromolecular signaling complexes that control the proteolytic activation of two highly proinflammatory IL-1 family cytokines, IL-1β and IL-18. The NLRP3 inflammasome is of special interest because it can assemble in response to a diverse array of stimuli and because the inflammation it triggers has been implicated in a wide variety of disease pathologies. To avoid aberrant activation, the NLRP3 inflammasome is modulated on multiple levels, ranging from transcriptional control to post-translational protein modifications. Emerging genetic and pharmacological evidence suggests that NLRP3 inflammasome activation may also be involved in acute lung inflammation after viral infection and during progression of several chronic pulmonary diseases, including idiopathic pulmonary fibrosis, chronic obstructive pulmonary disease, and asthma. Here, we review the most recent contributions to our understanding of the regulatory mechanisms controlling activation of the NLRP3 inflammasome and discuss the contribution of the NLRP3 inflammasome to the pathology of lung diseases.